U/Pb Zircon Ages of Plutons from the Central Appalachians and GIS-Based assessment

of Plutons with Comments on Their Regional Tectonic Significance

John R. Wilson

Virginia Polytechnic Institute and State University

Master of Science in Geological Sciences

Committee:

A. K. Sinha (Chair)

Bill Henika

James Beard

September 28, 2001

Blacksburg, Virginia

Key Words: U/Pb Ages, GIS, Databases, Plutons, Central Appalachians

Copyright 2001, John R. Wilson

U/Pb Zircon Ages of Plutons from the Central Appalachians and GIS-Based assessment

of Plutons with Comments on Their Regional Tectonic Significance

John R. Wilson

(ABSTRACT)

The rocks of the Appalachian orogen are world-class examples of collisional and

extensional tectonics, where multiple episodes of mountain building and rifting from the

pre-Cambrian to the present are preserved in the geologic record. These orogenic events

produced plutonic rocks, which can be used as probes of the thermal state of the source

region. SIMS (secondary ion mass spectrometry) U/Pb ages of zircons were obtained for

ten plutons (Leatherwood, Rich Acres, Melrose, Buckingham, Diana Mills, Columbia,

Poore Creek, Green Springs, Lahore and Ellisville) within Virginia. These plutons are

distinct chemically, isotopically, and show an age distribution where felsic rocks are

approximately 440 Ma, and Mafic rocks are approximately 430 Ma. Initial strontium

isotopic ratios and bulk geochemical analyses were also performed. These analyses show

the bimodal nature of magmatism within this region.

In order to facilitate management of geologic data, including radiometric ages,

strontium isotope initial ratios and major element geochemistry, a GIS based approach

has been developed. Geospatially references sample locations, and associated attribute

data allow for analysis of the data, and an assessment of the accuracy of field locations of

plutons at both regional and local scales. The GIS based assessment of plutons also

allows for the incorporation of other multidisciplinary databases to enhance analysis of

regional and local geologic processes. Extending such coverage to the central

Appalachians (distribution of lithotectonic belts, plutons, and their ages and

compositions) will enable a rapid assessment of tectonic models.

Acknowledgements

I would like to express my thanks to all of those who have been involved in my research

here at Virginia Tech. My sincere appreciation goes to my advisor A. K. Sinha for his

guidance and for the opportunities that he made available to me. His knowledge and

patience allowed me to expand my geologic background and apply it to a great research

opportunity. I also wish to thank the rest of my committee, James Beard, and Bill

Henika. Their background in igneous petrogenesis and regional geology was invaluable.

I thoroughly enjoyed working with them and discussing geologic topics of both small and

large scale processes. I also wish to thank the research staff at the UCLA Ion Microprobe

Facility for teaching me the value of SIMS ages, and the operation of the ion probe itself.

I would also like to express my thanks to the Virginia Division of Mineral

Resources, especially David Spears and Rick Berquist. They provided large amounts of

information to me, both geologic, and GIS related. Their assistance is greatly

appreciated.

Funding for research came from National Science Foundation (NSF Grant EAR

9303694), and from a research grant (Graduate Research Development Program) from

the Graduate Student Assembly of Virginia Tech. I also wish to thank the Faculty, staff

and fellow graduate students for the many discussion opportunities they provided.

Special thanks go to Hal Pendrak for his support in the laboratory, providing me with

information to run the Mass Spectrometer, and various other computer programs, and to

James Jerden, for his company in the PITLAB, and his assistance with the lab facilities.

Additional thanks are extended to Mr. Bill Armstrong for taking me to the

Geology Merit Badge course at summer camp.

Lastly I wish to thank my family for their love and support. They introduced me

to the outdoors and all the wonders of the natural world. Their support through my youth

allowed me to purse my interests and attend the University of New Hampshire for my

undergraduate degree in Geology. Thank you for always encouraging me to go one step

further.

iii

Table of Contents:

Title Page…………………………………………………………………..i

Abstract…………………………………………………………………....ii

Acknowledgements………………………………………………………..iii

Table of Contents………………………………………………………….iv

Geologic Setting of Selected Plutons in the western Piedmont

and Blue Ridge Provinces of Virginia……………………………………..1

U-Pb Ages of Zircons from Selected Plutons…………………………..…6

Ages and Geochemistry of Plutons……………………………………..…9

Major Element and Strontium Isotope Geochemistry…………………..…9

New U/Pb SIMS Ages……………………………………………………17

An Overview of GIS and its Application to Data in the Geosciences……20

Integration of Data and Plutons…………………………………………..25

GIS and Geosciences……………………………………………………..25

Development of a GIS Pluton Database………………………………….26

GIS, Mapping and Accuracy……………………………………………..39

Geologic Discussion…………………………………………………...…45

Figure 1………………………………………………………………….…2

Figure 2…………………………………………………………………….4

Figure 3…………………………………………………………………….7

Figure 4……………………………………………………………………15

Figure 5…………………………………………………………………....18

Figure 6…………………………………………………………………....23

Figure 7…………………………………………………………………....28

Figure 8……………………………………………………………...…….30

Figure 9……………………………………………………………...…….32

iv

Figure 10…………………………………………………………………..37

Figure 11…………………………………………………………………..41

Figure 12…………………………………………………………………..43

Figure 13…………………………………………………………………..47

Table 1: …………………………………………………………………..10

Table 2: …………………………………………………………………..13

Table 3: …………………………………………………………………..20

Table 4: …………………………………………………………………..60

Table 5: …………………………………………………………………..62

Table 6:…………………………………………………………………...64

Appendix A……………………………………………………………....56

Appendix B……………………………………………………………….70

Appendix C……………………………………………………………….77

Appendix D……………………………………………………………….80

Appendix E………………………………………………………………..84

Appendix F………………………………………………………………..96

Appendix G…………………………………………………………..…102

References………………………………………………………………..49

Vita………………………………………………………………………108

v

Geologic Setting of Selected Plutons in the western Piedmont and Blue Ridge Provinces

of Virginia

The rocks of the Appalachian orogen are world-class examples of collisional and

extensional tectonics, where multiple episodes of mountain building and rifting from the

pre-Cambrian to the present are preserved in the geologic record. These plate driven

processes in the Appalachian region produced the Grenvillian, Avalonian, Penobscotian,

Taconic, Acadian, and Alleghenian compressional events (Hatcher, 1989). The Central

and southern Appalachians are composed of numerous lithotectonic belts (Hatcher et al.,

1990; Williams, 1978), which are the result of the accretion associated with orogenic

events. These lithotectonic belts, also interpreted as terranes (Horton and Zullo, 1991;

Coler et al., 2000; Hibbard, 2001; Rankin et al., 1989), are characterized by their

distinctive metamorphic, deformational and igneous events (figure 1a). The igneous

events (plutons) can be useful as probes into the thermal state of a region during

mountain building. This study focuses on the Taconic (middle Ordovician) orogenic

event (Drake et al., 1989), especially plutonic rocks generated in pre-, syn-, and post

tectonic environments.

The relationship between generation of thermal anomalies resulting in magmatism

and terrane accretion can be identified through spatial and temporal distributions of

igneous rocks (Zen, 1992). Igneous rocks are more readily interpreted with regard to age

and tectonic setting and thus provide a powerful means in which the tectonic-thermal-

kinematic history of a complex orogen can be probed (Sinha et al., 1989). The western

Piedmont and Central Virginia Volcanic and Plutonic Belt of Virginia host a number of

plutons, which are the focus of this study. These plutons include (figure 2) the

Leatherwood, Rich Acres, Melrose, Columbia, Carysbrook, Buckingham, Diana Mills,

Poore Creek, Green Springs, Ellisville and Lahore plutons of Virginia.

1

Figure 1: a) Figure adapted from Hatcher (1990). HFZ = Hayesville Fault Zone, BFZ =

Brevard Fault Zone, IP = Inner Piedmont, PM = Pine Mountain Window, CPS = Central

Piedmont Suture, CSB = Carolina Slate Belt, RB = Raleigh Belt, G = Goochland Terrane.

b) Enlarged version of figure 1a, showing distribution of plutons within central and

southern Appalachians. Shaded region contains plutons discussed in this study.

2

Figure 1:

3

Figure 2: Map showing plutons in Virginia, Maryland, Delaware and Pennsylvania,

within lithotectonic belts.

4

Figure 2

5

U-Pb Ages of Zircon from Selected Plutons

The mineral zircon (ZrSiO4) is an ideal geochronometer (Rollinson, 1993). During

crystallization, zircon takes uranium into its crystal structure, which naturally decays to

form its daughter product, lead, thus leading to the measurement of U/Pb ages. Zircons

can have a complex history in the rock cycle, going from igneous to sedimentary to

metamorphic, and back to igneous again. This complex history can lead to complex age

structures within a single grain (e.g., an older core surrounded by new zircon growth)

(Schuhmacher et al, 1994). Such small-scale heterogeneities in lead and uranium within

a zircon crystal are best revealed by in-situ isotopic measurements (Schuhmacher et al.,

1994).

Uranium and lead may be measured in situ, through the use of secondary ion mass

spectrometry (SIMS). This technique uses a beam of ions (oxygen) to strike the zircon

crystal (~30 micron spots), producing an ion bean that can yield uranium and lead

isotopic ratios. The use of SIMS allows for complex ages to be resolved spatially, and

for ages of the separate events that affected the zircon crystal to be obtained (figure 3).

Many of the plutons previously had been dated through Rb/Sr whole rock, and

U/Pb TIMS methods (e.g. Pavlides et al., 1994, Sinha et al., 1989, Mose and Nagel, 1982;

Hund, 1987; and others). These data are beneficial in providing time constraints for the

crystallization ages of the plutons, but do not provide high-resolution ages of plutons, due

to the heterogeneity within individual zircons, and zircon populations. This study

employed the use of SIMS U/Pb mass spectrometry of zircons to obtain high precision

ages for the plutons. A discussion of analytical techniques used in this study, as well as

discussion of data analysis can be found in Appendix A.

6

Figure 3: Backscatter SEM image of a zircon grain from the Ellicott City pluton,

Maryland. Small semi-circular pits are points where SIMS analyses were taken. Image

of zircon grain displays zoning, and when paired with the age data from SIMS analyses

shows complex age patterns that may occur in single zircon crystals. This study uses

SIMS analysis of zircons in order to resolve core/overgrowth relationships.

7

Figure 3:

8

Ages and Geochemistry of Plutons

The ages and geochemistry of the plutons provide us with data for creating a

temporal and spatial framework related to the genesis of these rocks. All of the bulk rock

geochemical data used in this study is given in table 1, and initial strontium ratios and

SIMS ages can be seen in table 2. Detailed pluton descriptions can be seen in Appendix

B. The ages, gathered on the UCLA Ion Microprobe (see Appendix A for description of

analytical techniques), and the bulk rock geochemistry measured by Activation

Laboratories (see Appendix D for an example of metadata associated with

measurements), are described in Appendix C in more detail. Images of zircons used in

this study can be seen in Appendix E.

Major Element and Strontium Isotope Geochemistry

The plutons within this study vary greatly in composition, initial Sr isotopic

ratios, and ages. K2O vs SiO2 (figure 4a) highlight the bimodal nature of the plutons in

the study area. Mafic plutons such as the Rich Acres, and the Green Springs show a

range in silica values (~45 to ~58 Wt. %), with values in K2O which is comparable to

those from the felsic plutons. The Lahore pluton shows the highest values of K2O

(average 5 Wt. %) for the mafic rocks, and is comparable to the values exhibited in the

felsic Leatherwood Pluton. Felsic plutons also display a range in K2O, from 1 to 6 Wt.

%. 87Sr/86Sr initial vs SiO2 (figure 4b) show the variability of Sr isotopes for the plutons.

Utilizing the average 87Sr/86Sr initial ratio for each pluton the contrast between mafic and

felsic magmas is easily recognized. The mafic rocks have a range in isotopic values from

0.7034 to 0.7051 (average 0.7045), while the felsic rocks have a range from 0.7059 to

0.7074 (average 0.7066). These values reflect different source regions for the mafic and

felsic rocks. The 87Sr/86Sr initial ratio shows no correlation to the presence or absence of

inheritance in the ages of zircons (see next section for inheritance).

9

Table 1: Table of major element geochemical data from plutons in study.

10

Table 1:

Pluton Name Buckingham Buckingham Buckingham Carysbrook Carysbrook Columbia Sample ID JRW00B6 JRW00B11 JRW00B2 JRW 00 CB5 JRW 00 CB3 JRW99COL1

SiO2 63.01 51.61 62.79 67.43 67.52 73.26

TiO2 0.35 0.70 0.42 0.47 0.43 0.15

Al2O3 15.91 9.34 16.07 15.61 15.39 13.69

Fe2O3 4.22 9.65 4.77 3.57 3.40 2.94 MnO 0.08 0.19 0.09 0.06 0.07 0.07 MgO 2.87 12.22 3.30 1.87 1.63 0.68 CaO 4.73 13.44 5.22 2.94 2.72 3.50

Na2O 3.52 0.75 3.68 3.84 3.86 3.45

K2O 3.10 0.39 2.88 2.37 3.70 1.88

P2O5 0.13 0.10 0.14 0.17 0.17 0.05 LOI 1.57 1.71 1.03 1.79 1.48 0.46

Total 99.49 100.10 100.39 100.12 100.37 100.13

Pluton Name Diana Mills Diana Mills Ellisville Green Springs Leatherwood Leatherwood Sample ID JRW00DM1 JRW00DM3 JRW00E1 JRW00GS1 JRW00LRW11 JRW00LRW6

SiO2 49.74 47.39 70.08 58.75 63.12 70.54

TiO2 0.54 0.72 0.33 0.58 0.92 0.50

Al2O3 19.30 14.82 15.29 13.99 16.20 15.22

Fe2O3 7.33 9.43 2.87 6.38 5.43 1.63 MnO 0.11 0.15 0.04 0.11 0.09 0.03 MgO 5.44 11.36 0.88 4.91 2.01 0.53 CaO 9.87 10.00 3.24 6.50 4.12 1.90

Na2O 3.57 2.26 3.63 2.84 3.88 3.59

K2O 1.31 1.15 3.23 3.72 2.80 5.59

P2O5 0.42 0.18 0.13 0.36 0.29 0.11 LOI 2.47 2.70 0.52 1.51 0.99 0.38

Total 100.11 100.15 100.24 99.65 99.84 100.01

11

Table 1 (continued):

Pluton Name Leatherwood Melrose Poore Creek Rich Acres Rich Acres Sample ID JRW99LRW1 JRW00MEL2 JRW00PC2 JRW00LRW5 JRW00LRW4

SiO2 71.53 60.88 66.53 50.21 51.71 TiO2 0.39 0.86 0.22 1.31 1.03

Al2O3 14.01 18.14 16.82 16.07 17.25 Fe2O3 2.62 4.47 2.08 9.88 7.53 MnO 0.03 0.09 0.03 0.17 0.12 MgO 0.66 1.34 1.44 7.78 7.00 CaO 2.00 2.94 2.23 6.96 10.20

Na2O 3.40 4.62 4.27 3.84 3.01 K2O 4.39 4.61 4.72 2.41 0.95

P2O5 0.14 0.26 0.07 0.43 0.37 LOI 1.01 1.58 1.36 1.12 1.09

Total 100.18 99.79 99.77 100.18 100.26

12

Table 2: Table showing Rb and Sr (ppm), measured value of 87Sr/86Sr, 87Sr/86Sr initial

ratios and U/Pb SIMS age used in calculating 87Sr/86Sr initial ratio. Initial strontium

ratio from Carysbrook calculated assuming an age of 457 Ma, based on field relations

seen by Goodman et al., 2001.

13

Table 2:

Pluton Name Sample ID Rb (ppm) Sr (ppm) Measured 87Sr/86Sr Initial 87Sr/86Sr SIMS U/Pb Agevalue (Age of Crystallization)

Diana Mills JRW-00-DM3 23 858 Not Measured 436 (+/-) 5 MaDiana Mills JRW-00-DM1 33 1280 0.70558 +/- 0.000028 0.70511 436 (+/-) 5 Ma

Green Springs JRW-00-GS1 89 1260 0.70635 +/- 0.000045 0.70504 448 (+/-) 3 MaPoore Creek JRW-00-PC2 129 1040 0.70844 +/- 0.000179 0.70614 448 (+/-) 3 MaCarysbrook JRW-00-CB3 126 409 0.71240 +/- 0.000116 0.70659 Assumed age of 457 MaCarysbrook JRW-00-CB5 81 427 0.71019 +/- 0.000036 0.70651 Assumed age of 457 Ma

Columbia JRW-99-COL1 57 77 Not Measured 457 (+/-) 7 MaBuckingham JRW-00-B11 5 237 0.70917 +/- 0.000035 0.70879 429 (+/-) 5 MaBuckingham JRW-00-B6 77 843 0.7051 +/- 0.000198 0.70348 429 (+/-) 5 MaBuckingham JRW-00-B2 86 913 0.70739 +/- 0.000070 0.70572 429 (+/-) 5 Ma

Melrose JRW-00-MEL2 87 524 0.71021 +/- 0.000067 0.70718 442 (+/-) 8 MaEllisville JRW-00-E1 107 396 Not Measured 444 (+/-) 6 Ma

Rich Acres JRW-00-LRW5 67 636 0.70649 +/- 0.000029 0.70462 430 (+/-) 7 MaRich Acres JRW-00-LRW4 19 783 Not Measured 430 (+/-) 7 Ma

Leatherwood (Gretna) JRW-00-LRW11 98 328 0.71285 +/- 0.000034 0.70743 442 (+/-) 8 MaLeatherwood (Martinsville) JRW-00-LRW6 119 255 0.71482 +/- 0.000039 0.70630 444 (+/-) 9 MaLeatherwood (Martinsville) JRW-99-LRW1 78 273 Not Measured 444 (+/-) 9 Ma

14

Figure 4: a) Plot showing K2O vs SiO2. Plutons with large ranges of values are circled.

Many plutons (Rich Acres, Lahore, Green Springs, Leatherwood, and Ellisville) show

enrichment in K2O. b) Plot showing 87Sr/86Sr initial ratio vs SiO2. Those plutons with

multiple analyses, are shown here with an average value.

15

Figure 4:

16

New U/Pb SIMS Ages

The ages of the plutons (analytical techniques can be seen in Appendix A) are

given in figure 5, Table 2 and in Appendix F, figures a-j. The analyses from the SIMS

gave data showing both ages of crystallization, and ages of inheritance. The calculated

ages (table 2) represent the best estimate for the age of crystallization of the pluton.

Plutons which displayed inheritance were given an age of crystallization by removing

those data points that showed clear evidence of older ages on both concordia and

weighted average plots. Inherited ages were found in some of the plutons, e.g.,

Columbia, Diana Mills, Gretna body of Leatherwood, Melrose, Poore Creek and Green

Springs (Appendix G, figures a-e). . Inherited ages ranged in age from 900 Ma to 1400

Ma. The Columbia pluton showed inheritance of 900 to 1000 Ma, the Diana Mills pluton

showed inheritance of 1000 Ma, the Gretna body of the Leatherwood pluton showed

1200 and 1400 Ma inheritance, the Melrose pluton showed 1100 Ma inheritance, and the

Poore Creek and Green Springs plutons showed 1200 and 1400 Ma inheritance. The

inheritance seen in the plutons seems to have no association with lithotectonic belts

(figure 5). The crystallization ages of the plutons range in age from 457 Ma to 429 Ma.

When the ages are compared to the composition of the rock, a distinct trend is visible.

The felsic rocks are predominantly older, ranging from 457 Ma to 441 Ma, while the

mafic rocks are predominantly younger, ranging from 436 Ma to 429 Ma.

Geochemical and U/Pb SIMS analyses obtained for this study have large amounts

of data associated with them. These data are essential to understanding the thermal

processes occurring during the tectonic history of the central Appalachians. Therefore,

making such data sets accessible on a regional scale is essential for further analysis and

assessment of the geologic history of the region.

17

Figure 5: Map showing plutons in this study and their U/Pb SIMS ages. Ages in brackets

are ages of inheritance found during analysis.

18

Figure 5:

19

An Overview of GIS and its application to data in the geosciences

Geographic information systems are designed to store and manipulate data related

to spatially referenced locations. To achieve this objective, the GIS can be separated into

five essential components (see Figure 6, and Table 3 for acronyms). They are 1) data

acquisition, 2) preprocessing, 3) data management, 4) manipulation and analysis, and 5)

product generation (Star and Estes, 1990). Data acquisition is the process of identifying

and acquiring the data necessary for the project of interest. Preprocessing takes the data

gathered in the first step, and puts it into a form where it can be easily entered into the

GIS. Data-management is essential to the proper functioning of a GIS, as it allows for

the creation of, and access to the data. Manipulation and analysis are often the focus of

attention for a user, as it is here where data can be analyzed and queried to create new

data and information. From this new data and information, products can be generated to

present the results from the project of interest. These products can range from tables of

data, to maps depicting the data, as well as other graphics of interest.

Table 3:

Acronyms and their associated terms GIS Geographic Information System UTM Universal Transverse Mercator NAD North American Datum DLG Digital Line Graph DEM Digital Elevation Model DOQ Digital Orthophoto Quads GPS Global Positioning System DbaseIII Database program

Data is commonly found as four types of variables. They are nominal, ordinal,

interval, and ratio. Nominal data are described by name, with no specific order.

Geologic examples of nominal data would be a list of rock types: limestone, granite, and

shale. Ordinal data are lists of discrete classes with an inherent order. Stream

classifications (1st order, 2nd order, etc.) are a good example of ordinal data as they

20

indicate order, but there is no value for the levels. Interval data have a natural sequence,

but in addition, the distances between the values have meaning. An example of interval

data would include temperature data for Ar39/Ar40 step heating. The temperatures are

values in a natural sequence and the values between temperatures have meaning. Ratio

data have the same characteristics as interval data, but in addition, they have a natural

zero, or starting point. Ratio data in the geological sciences can include values of bulk

geochemical analyses.

In addition to these four types of data, there are two different classes of data found

in most geographic information systems. They are spatial and non-spatial data. Spatial

data refers to geographic space, i.e. mapable data that can be located in space. Non-

spatial data, or attribute data, is data that is logically connected to the spatial data (Star

and Estes, 1990). An attribute is a description of a feature. Examples of non-spatial data

include the name of the spatially referenced feature, a classification, or color, or a

numerical value for the feature. It is the relationships between these two types of data,

which make a geographic information system the powerful tool that it is. The

combination of these two data types is called a relational database. GIS’s accept data

from multiple sources, which can be in a variety of formats (Davis, 1996). Data types

that GIS’s can include are maps, images (pictures and digital data from aircraft and

satellites), digital products (data already stored digitally from other media), GPS data

(highly accurate locational data), text data (reports and text dealing with spatial subjects),

and tabular data (lists of numeric or text data) (Davis, 1996).

The data used in a GIS has information pertaining to it. This metadata includes

identification information, data quality information, spatial data organization information,

entity and attribute information, and additional references. These items label geospatial

datasets, with information pertaining to the method of data collection, errors involved,

spatial resolution, and definitions. This additional information allows the users of a GIS

to decide if the data is acceptable for use in their project. See Appendix D for an

example of metadata, following the metadata outline recommended by the USGS

(National Geospatial Data Clearinghouse, http://clearinghouse1.fgdc.gov/).

21

All maps are two-dimensional representations of an area on a three dimensional

earth (elevation on the surface, and curvature of the earth). These items need to be

accounted for when map data is placed into a GIS. When a map is digitized into a GIS, it

is described as a digital coverage. This coverage is the digital representation of the items

on the original map. The original map is first georeferenced, which is registering, or

fixing data to a standard coordinate system (the coordinate system of the map being

digitized). The data on the original map, is then digitized into the GIS, and becomes a

digital coverage. This coverage is now available to be reprojected. The coverage can be

projected either in the coordinate system in which it was digitized, or in another

coordinate system. Re-projecting allows for the manipulation and integration of multiple

coverages of different original coordinate systems. An example would be taking a map

that was produced in NAD27, zone 17 UTM, and projecting it into NAD83, zone 17

UTM. Reprojecting older maps is often beneficial, because it removes some of the

coordinate errors, which have since been removed from newer maps with the advent of

newer and more accurate surveying methods. See the metadata from the spatial data files

of the 1993 Geologic Map of Virginia (VDMR, 1993; Berquist et al., 2000), for an

example of map manipulation and digitizing. Materials digitized during this study

underwent reprojections, to convert coordinate systems from decimal degrees, (e.g.

Pavlides et al., 1994, and others) to a UTM 1983 projection for the state of Virginia.

22

Figure 6: The Five Elements of a geologic GIS. (modified from Star and Estes, 1990)

Items seen within five elements ae typical examples of the processes and steps involved

in developing a pluton database.

23

Figure 6:

24

Integration of data and plutons

The availability of geospatially referenced geologic maps and their associated

databases are likely to accelerate the development of more integrated models for a better

assessment of geologic processes. Geographic information systems (GIS) allow for

geologic analysis of regions by increasing the speed and efficiency with which answers

can be obtained.

Over the past decade, numerous institutions and agencies are utilizing GIS for

management, manipulation, analysis, and distribution of their data. Examples include the

USGS (Alhadeff et al., 1999), the Georgia Geologic Survey (Cocker, 1999), the British

Geological Survey (Giles et al., 1997; Bain and Giles, 1997; Allen, 1997), the Geological

Survey of Canada (Colman-Sadd et al., 1997), the University of Western Australia

(Knox-Robinson and Gardoll, 1998) and Colorado State University (Molnar and Julien,

1998). Current GIS users in the geological sciences are creating digital geologic maps,

spatial models of erosion in basins, programs for 3-D visualization of geologic data, and

field based GIS mapping software (Doellner and Hinrichs, 2000; Cocker, 1999; Molnar

and Julien, 1998). It is clear that in all instances the availability of databases associated

with geologic maps or models must be error free as possible, and be tagged with

abundant metadata files.

GIS and Geosciences

The use of a GIS as a tool in geology has the potential of changing the way

geologic maps are made, and the way data is collected and analyzed. Geographical

information systems are already in use by numerous geoscience professions. The USGS

has developed the national cooperative geologic mapping program, whose goal is to

collect, process, analyze, translate and disseminate earth-science information through

geologic maps (The National Cooperative Geologic Mapping Program’s web site has

more information pertaining to their goals, at http://ncgmp.usgs.org). Data generated by

this program is to be provided in digital formats that can be used by the public at all

levels, to assist in analysis and decision-making. The British Geological survey has also

25

created a digital mapping program (Digital Map Production System), which creates and

disseminates geologic data (Nickless and Jackson, 1994). These organizations, along

with other federal, state, and academic institutions have used GIS and geologic databases

to bring geologic mapping and analysis to a new level.

The earth science community can benefit greatly from the use of GIS, and related

information technologies. The development of geoinformatics, a program with emphasis

on ease of access and use of the large amounts of data generated by earth scientists,

provides an opportunity for individuals and groups to use the vast databases for

integration into their research. The ultimate goal of the geoinformatics program would be

to create a fully integrated data system populated with high quality, freely available data

as well as a robust set of software to analyze and interpret the data. This study fits into

the ultimate vision of geoinformatics, with the integration of data from plutons, and

geographic information. See the geoinformatics program website at

www.geoinformaticsnetwork.org, for more information.

Development of a GIS Pluton Database

The central and southern Appalachians were part of a series of continental scale

collisions during the Precambrian to Paleozoic (Rankin et al., 1989; Drake et al., 1989,

Osberg et al., 1989, Hatcher et al., 1989). The geology seen on the surface today can be

divided into distinct lithotectonic belts (Hatcher, 1990; Williams, 1978). Within these

belts are plutons, which reflect the thermal instability of the crust during these orogenies

(Drake et al., 1989). As there are numerous plutons within the central and southern

Appalachians (figure 1b), this GIS based study focuses on plutons of varying ages,

compositions, and source regions within the western Piedmont of Virginia (figure 7).

Following the structures developed by others, a GIS (ArcView 3.2) was used to

develop a project to analyze plutonism associated with collisional tectonics within the

western Piedmont Province of Virginia, and demonstrate its usefulness by extending it to

the four states (Virginia, Maryland, Delaware and Pennsylvania, Figure 8) within the

26

central Appalachians. This project is utilizing GIS as a tool to analyze information from

plutons as probes to the processes involved in continental collisions.

The data acquisition phase for the project was initiated by gathering statewide

data from TIGER (Topologically Integrated Geographic Encoding and Referencing)

census files (http://www.geographynetwork.com/data/tiger/2000,

http://www.census.gov). These data include county and water polygons, and lines of

streams, rivers and roads. Digital geologic map coverages from state or federal agencies

were gathered next. In this case, Virginia, Maryland and Pennsylvania had coverages of

their most recent state geologic maps available, at the scale of 1:500,000. These maps are

digital replicas of the paper publication, with very little or no changes included from

newer mapping. The digital maps were added as themes in the GIS. These regional

geologic maps provide the framework for the lithotectonic belts. From these large-scale

maps, a theme of plutons was added as well. This theme allows the regional spatial

distribution of the plutons to be seen, within their respective lithotectonic belts. Paper

copies of geologic maps for Delaware were obtained for digitizing as coverages for the

purposes of the project.

For more detailed spatial data of plutons, geologically sensitive quadrangles were

gathered for digitization. These maps were at the 7.5-minute quadrangle scale

(1:24,000), and included the study plutons (e.g., Henika et al., 1996; Rossman, 1991).

These maps of the plutons were digitized as themes into the GIS, allowing for greater

positional accuracy of the plutons. These maps came from the USGS, state geological

surveys, and from maps created at VPI&SU. At the same time the maps were being

digitized, a theme for sample localities was being created. In this theme sample localities

were placed as a geographic point. These points contain an attributes table, which is

where data such as bulk geochemical data, modal data from thin sections, isotopic data,

and ages, are stored. This data is referenced to the sample locality, which is referenced to

the pluton polygon, such that when queries are made, results can be seen in table form,

and as highlighted polygons, illustrating their spatial distribution. Other data that was

acquired for this GIS included notes from fieldwork, and pictures of outcrop and hand

samples (See Figure 9 for an example of the database architecture).

27

Figure 7: Map of Lithotectonic belts and plutons within Virginia. Boxes are used to

highlight the Martinsville Igneous Complex, and the Ellisville and Lahore Plutons, which

are shown in detail in figures 11 and 12.

28

Figure 7:

29

Figure 8: Lithotectonic map with study area plutons within four state region used in the

GIS. Digital geologic map of Maryland not available during creation of GIS based

pluton database. Delaware geology digitized at VPI&SU, positional accuracy within 30

feet, from maps by Woodruff and Thompson (1972, 1975). Virginia map from spatial

data files (Berquist et al., 2000), and Pennsylvania map from spatial data files of

Pennsylvania Bureau of Topographic and Geologic Survey (2001).

30

Figure 8:

31

Figure 9: Broad outline example of GIS based pluton database architecture developed at

VPI&SU (refer to http://gs6151.geol.vt.edu). The three fields represent the major areas

of data for plutons. Each field has an example of the type of attribute which it contains.

32

Figure 9:

33

Step two involved the preprocessing of the above data. The data that was

acquired came in many forms; digital coverages, paper maps, field notes, numerical and

text data tables, as well as digital and non-digital images. The digital coverages were

added to the GIS, after being converted to the same coordinate system. Paper maps, were

digitized in their printed coordinate system, and then reprojected to the coordinate system

of our GIS. Field notes, numerical and text data, and the images were then placed into

appropriate databases and file formats for the GIS to readily access them (typically

dbaseIII). Strike and dip data from field notes was placed in databases formats that were

readily available to common stereonet programs. Geochemical and isotopic data were

also placed in databases that were in formats for common geochemical, petrologic, and

isotopic software to read. Bitmap (.bmp) images were linked to the sample localities, so

that field pictures could be viewed.

Data management is essential in the creation and implementation of a GIS. The

amounts of data gathered for the project were cumbersome before they were incorporated

into the GIS. To be able to incorporate the data into our four state GIS, a database

architecture for plutons was developed. This involved determining what items were

essential to the understanding of the age, origin and distribution of plutonic rocks, and

how to properly express them in a database. The results of this process are expressed in

the database architecture seen in figure 9. The data essential for creating a pluton

database can be broken down into three scales. They are the field/outcrop scale, the

whole rock (hand sample) scale, and the mineral scale.

Examples of attributes at the field/outcrop scale (kilometers to meters) include the

sample location (latitude and longitude), fabrics and textures seen, its appearance (color

and weathering state), distribution of inclusion or xenoliths, and images taken in the field.

These field scale attributes are essential to be displayed in a pluton database, because

they provide accurate descriptions of the plutons, as well as provide information on the

magmatic and post-magmatic history of the plutons. For example at the surface

sample/core database attribute, and the fabrics database attribute (figure 9), an accurate

elevation of that sample is important. The elevation can then be used in uplift/erosion

models when it is analyzed with techniques such as U-Th-He Fission Track dating ages,

34

and it can be used to show depth and temperature of emplacement when analyzed with

amphibole thermobarometry measurements (Hammarstrom and Zen, 1986). The fabric

of a pluton when seen in the field needs to be accurately measured and assessed in order

to determine if the fabric is magmatic, or metamorphic (Wager and Brown, 1967). This

data allows assessment of emplacement and post emplacement histories of the pluton

(e.g. Becker, 1996, Pavlides et al., 1994). Both the elevation of the sample, and the fabric

of the rock have metadata pertaining to it. Pertinent metadata for the elevation of the

sample may include how it was obtained (directly from plotting on a map, or GPS

satellite), and the error (±) in the elevation measurement. Metadata for the fabric might

include information about the device used to measure the strike and dip, and the error (±)

in the measurement, as well as the minerals involved in the definition of the fabric.

The whole rock scale attributes (centimeters) include petrographic analyses,

modal abundances, crystallization sequences, bulk rock geochemistry, and images.

Analyses at the rock scale allow for chemical modeling, mineral histories, and source

region discrimination. Major and trace element composition of the rock can be used as

chemical indicators of tectonic environments (e.g. Pearce, 1967; Pearce and Cann, 1971,

1973; McCulloch and Chappell, 1982), and whole rock Rb/Sr isotope ratios provide

information for determining source regions of the plutons (e.g. Faure and Hurley, 1963;

Jung et al., 2001). These database attributes provide more examples for metadata within

the pluton database. Important items to be displayed in the metadata include where the

analyses were performed, what process was used for measurement, what standards were

used in analyses, what errors and detection limits are involved, and what processing has

been done to the data. See Appendix D for an example of metadata related to whole rock

geochemical analyses used in this project.

Mineral scale attributes (centimeter to micron scale) include measurements of

isotopic ratios, (Ion Probe data, Mass Spectrometer data, Micro Probe Data) melt and

fluid inclusion data, and micron scale elemental and isotopic analyses. These items are

important parts of the pluton database, as they provide information on processes

occurring during both the melting and the cooling histories. Isotope measurements of

minerals can provide ages and then be used with other data in the pluton database to

35

analyze the spatial and temporal aspects of the pluton. Metadata in the mineral scale is

similar to that of the rock scale.

Placing the pluton data in this architecture allows for ease of access, increased

speed of access (reduced searching through theses and publications for data points), and

access to databases from other disciplines. The benefit of a GIS is the ability to

manipulate and analyze data in new ways, to answer old questions, create new data, and

pose a new level of scientific questioning (see figure 10). The data in the GIS is available

to be queried at the users discretion. Thus, the user can manipulate data in the GIS to

create new coverages, link different data files, and see spatial distributions of the data.

An example might be to query the pluton database for all plutons in the study region that

have silica values above 70%, and 87Sr/86Sr isotopic ratios that are greater than 0.7050,

and that are greater than 10 square kilometers. The GIS will search the databases

available to it, and return samples that meet the criteria, resulting in a rapid assessment of

the distribution of I or S-Type granitoids in the region, e.g. Chappell and White, 1974;

McCulloch and Chappell, 1982. At the same time, it will highlight them on the main

coverage, allowing a spatial relation between the queried samples to be seen. The

querying capability of a GIS could also be beneficial in identifying mineral deposits,

water sources, and other items of economic and social importance.

With the multiple ways of querying, and manipulating the data, new products can

be generated for further analysis, or for display of spatial data (see figure 10). The data

when queried and manipulated can be used to create a new coverage, or can make a map

to display data of interest. The use of the GIS will also allow the ability to link to other

databases in related disciplines. The user of the GIS can use what they have manipulated

and analyzed, to create new geologic models, and pose questions for further research.

The development of a four state GIS has enabled a better understanding of the

spatial, temporal, and chemical trends, that were not as readily seen before being placed

into the GIS.

36

Figure 10: An example of manipulation and analysis used in this project, and possible

new products that can be developed.

37

Figure 10:

38

GIS, Mapping, and Accuracy

The Martinsville Igneous Complex, and the Lahore and Ellisville plutons provide

unique opportunities for testing the accuracy methods in geospatially locating the plutons

in our GIS. These plutons (figures 11A and 12A) are taken from the VDMR spatial data

files of the 1993 Geologic Map of Virginia, showing 1:500,000 scale geologic map

features (VDMR, 1993; Berquist et al., 2000). The same 1:500,000-scale background is

used in figure 11B and 12B, with the 1:500,000 scale plutons removed. In place of the

1:500,000 scale plutons from the VDMR digital map are plutons polygons that were

digitized at VPI&SU at scales of 1:50,000 (Henika et al., 1996), and 1:100,000 (Pavlides

et al., 1994) respectively. The original field mapping of these plutons for the publications

was done at a scale of 1:24,000.

The number of scale expressed above shows the importance of scales and

accuracy within a GIS. In samples 10B and 11B, there are obvious gaps between the

surrounding polygons (shape files from 1:500,000 digital map, Berquist et al., 2000) and

the polygons that were digitized at VPI&SU. These gaps range in distance from 30 to

1000 feet and are attributed to the scales at which the material is digitized. The metadata

for the VDMR digital map, states that the material is accurate only for the 1:500,000

scale, the scale at which it was digitized. The material that was digitized at VPI&SU was

digitized at a smaller scale, and is accurate to that scale. The cross sections, and sample

localities were digitized with the pluton polygons, and are also accurate to the scale of the

original paper map.

Geologic mapping typically takes place at scales of 1:62,500, or larger. Mapping

at these larger scales (smaller areas), provides better positional accuracy for the geology.

When mapping on a 1:24,000 topographic map, geologic contacts and samples can be

accurately plotted within 10 to 30 feet. This positional accuracy is needed for GIS based

pluton database program. All scales of mapping are important to creating a GIS based

pluton study, because this provides both large area information, and enhanced resolution

and detailed attributes for the plutons under consideration. The East Coast of the United

39

States provides excellent accessibility at all scales, and makes it a prime location for

implementation of a large project of this nature.

40

Figure 11: a) Map of Martinsville Igneous Complex in Henry County, VA. All features

are from 1:500,000 scale VDMR digital representation of 1993 geologic map of Virginia.

White regions represent lakes and reservoirs. b) Map showing same lithotectonic belts

around Martinsville Igneous Complex, with 1:500,000 scale pluton polygons removed.

Shape files of Martinsville Igneous complex digitized at a scale of 1:50,000 at VPI&SU

(from map of Henika et al., 1996). Gaps between plutons and blue Smith River

Allocthon region range from 30-1000 feet. These gaps represent the error of the

1:500,000 features, when viewed at a larger scale. Large white regions within Henry

County outline that are not lakes and reservoirs from 10a are places where no pluton is

shown on the map that was digitized. This shows the greater accuracy of large scale

maps compared to the regional 1:500,000 scale. Sample localities and cross section are

digitized from same map as pluton shape files. Within GIS, the sample localities and

cross section can be selected to show the inage that corresponds with it. Sample localities

also have an associated geochemical database.

41

Figure 11:

42

Figure 12: a) Map of Ellisville and Lahore plutons, Orange, Louisa, and Spotsylvania

Counties, VA. All features are from 1:500,000 scale VDMR digital representation of

1993 geologic map of Virginia. White regions represent lakes and reservoirs. b) Map

showing same lithotectonic belts around Ellisville and Lahore plutons, with 1:500,000

scale pluton polygons removed. Shape files of Ellisville and Lahhore plutons digitized at

a scale of 1:100,000 at VPI&SU (from map of Pavlides et al., 1994). Gaps between

plutons and blue melange complexes region range from 30-1000 feet. These gaps

represent the error of the 1:500,000 features, when viewed at a larger scale. Large white

regions within Louisa County outline that are not lakes and reservoirs from 11a are places

where plutons were in previous picture. This shows the greater accuracy of large scale

maps compared to the regional 1:500,000 scale. Sample localities and cross section are

digitized from same map as pluton shape files. Within GIS, the sample localities can be

selected to show the inage that corresponds with it. Sample localities also have an

associated geochemical database.

43

Figure 12:

44

Geologic Discussion

The inter-relationship between magmatism and tectonic processes, especially in

collision zones, provides a window into the thermo-tectonic evolution of orogenic belts.

In the Appalachian orogen (Maine to Alabama) the spatial and temporal distribution of

igneous rocks has provided compelling evidence for both collisional and extensional

kinematics of plate reorganization (e.g. Rankin, 1972; Ashwal et al., 1979; Miller et al.,

1997). Although many distinct magmatic cycles have been recognized (late Precambrian

to Carboniferous), the most enigmatic episode belongs to the Siluro-Devonian (Acadian

orogeny). The magmatic record of this event in the northern Appalachians has been

attributed to both collisional and plume related tectonic processes (Osberg et al., 1989).

In contrast to the voluminous Acadian age igneous activity present in the northern

Appalachians, the more modest record of magmatism in the southern region provides a

continuum of ages and complex geochemical signatures ranging from the middle

Ordovician (Taconic orogeny) through the Devonian.

Although traditional two stage collisional processes (similar to the northern

segment) have been proposed, the data suggest a model that more uniquely explains the

enigmatic record of the igneous activity. Ages of plutons measured in this study range

from approximately 460 Ma to 430 Ma. When plutons ages are compared to their

composition, a striking trend appears. The older magmatism is predominantly felsic, and

occurs around 440 Ma, while younger magmatism, occurring around 430 Ma, is

dominantly mafic.

Further north along the strike of the study area (figure 5), a broader range in ages

of plutons (464-357 Ma) have been identified (Srogi and Lutz, 1997, Sinha et al., 1989,

Drake and Froelich, 1997). In order to assess this regional age distribution it has been

suggested (Sinha et al., 2001) that those regions (embayments) with abundant fertile

lithologies are capable of yielding younger magmas through crustal anatexis and delayed

decompressional melting.

Along the late Precambrian- Cambrian margin of southern Laurentia, the

distribution and thickness of synrift sedimentary and volcanic rocks correspond

systematically to the outline of promontories and embayments of the continental margin

45

(Thomas, 1977, 1991). Embayments host thick successions of synrift sedimentary and

volcanic rocks, as well as thicker passive margin shelf successions, whereas promontories

are essentially devoid of synrift deposits and have a thin blanket of passive margin

sediments. The plutons within this study lie within a promontory environment, and

transition to an embayment environment (figure 13). The approximately 460 Ma

magmas are pre-tectonic, possibly representing arc stage magmatism. The 440 Ma

magmas are syn- to post- tectonic, produced by melting available lithologies within the

promontory. The mafic plutonism at approximately 430 Ma may be explained by a

period of extension. These mafic magmas were able to intrude into the promontory

environment, due to the thinness of syn-rift and passive margin sediments above. Mafic

magmatism of this age is as yet unrecognized in neighboring embayments. The high

precision SIMS U/Pb dates of the plutons allows for the separation of two age groups as

they are related to possible tectonic settings. The bimodal nature of the magmatism is

suggested to be related to syn-tectonic felsic magmatism, and extensional related mafic

magmatism.

The data suggest that collisional tectonics superimposed on these contrasting

sedimentary environments has resulted in a magmatic record that images the availability

of fertile lithologies required for generating melts in overthrust regions. Accordingly, the

"pseudo- Acadian" plutons of the southern Appalachian reflect a time-depth variation in

melting conditions within the embayment environments following middle Ordovician

collisional processes.

46

Figure 13: Distribution of Plutons within Lithotectonic belts of Virginia Promontory to

Pennsylvania Embayment. Hachured area represents extent of maximum sediment

thickness within embayment region. Major Transform faults separate the Virginia

Promontory from its southern neighbor, the Tennessee Embayment, and the Pennsylvania

Embayment from the New York Promontory. Between the Virginia Promontory and

Pennsylvania Embayment is a transition zone, as no large transform has been described

here. This transition zone has a large effect on the attributes of the plutons. Plutons

within the embayment are generally higher in 87Sr/86Sr initial ratios, and no known mafic

plutons of younger ages are present.

47

Figure 13:

48

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55

Appendix A

Analytical Techniques

Bulk samples of rock were processed for zircons. Sample localities are presented

in Table 4. These samples were processed by first jaw crushing the samples in to small

chips, (a portion of the chips were taken aside for processing for bulk chemical analyses),

then running the chips through a roller mill, to make the material small enough to pass

through a #40 mesh screen. The material that passed through the screen was then

separated into heavy and light fractions using the Wilfley Table. The heavy mineral

separate from the Wilfley Table was then taken to a heavy liquid phase. The materials

were separated by density, using Bromoform as the dense liquid medium. The heavy

mineral separate was then processed through a Frantz Isodynamic separator, removing

the magnetic heavy minerals, leaving a clean mineral separate of mostly zircon. The non-

magnetic, heavy mineral fraction was then analyzed optically, to determine and describe

the morphology of the zircon populations. Description of the zircon populations was

done on the basis of size, color, and optical properties (see table 5). From these

descriptions, representative samples of each population were mounted in an epoxy bead

for analysis.

SIMS Ages

The ring mount was polished to expose the zircon crystals using a 1200-grit

polishing sheet. The mount was carbon coated for imaging on the SEM, then cleaned,

and gold coated for analyses on the ion probe. The Secondary Ion Mass Spectrometry

(SIMS) U/Pb ages of Zircons were gathered at the UCLA Ion Microprobe Facility. The

ion probe gathered data in static collection mode, cycling between 94ZrO2, 204Pb, 206Pb, 207Pb, 208Pb, Th, U, and UO. The data collected was then processed using the Zips

Program of Coath (2000, Personal Communication). Processing within the ZIPS

program took into account standards of a known and well-defined age. These standards

allowed a regression to be made on a plot of UO/U vs. Pb/U RSF (Relative Sensitivity

56

Factor). Relative sensitivity factor is described in Gill (1997) as the sensitivity of an

analyte as a ratio of the sensitivity of another element, or the same element under

different conditions. In this case, it is the sensitivity of lead in the standard, as compared

to the sensitivity of the uranium in the standard. Multiple regressions were made due to

data being gathered on four separate occasions. The slopes of the regressions for the four

data gathering occasions are 0.481 ± 0.019, 0.512 ± 0.018, 0.366 ± 0.027, and 0.398 ±

0.044 respectively. All errors are at 1 sigma. Once the regression was calculated

(MSWD of 1 - 2.3), unknowns were then processed in the ZIPS program with the

regression of standards in place, to account for machine error, and drift. The ages of

plutons in this study were measured with regressions two and three. Regression two

contains the Melrose Pluton, Leatherwood pluton, and Columbia pluton, and regression

three contains the Buckingham, Poore Creek, Green Springs, Leatherwood, Lahore,

Melrose, Columbia, Ellisville, Diana Mills, Rich Acres, and Leatherwood Gretna.

The processed data was then imported into Microsoft Excel, for use with the

Isoplot/EX software of Ludwig (1999). Here, the processed data was reviewed to remove

anomalous data points. Anomalous data points typically included machine errors in

measuring 207Pb, and data points that indicated reverse discordance, inheritance, or lead

loss. The data values that showed inheritance and lead loss were compared to the SEM

images of their respective spot. This was done to study the images for the proximity of

the analysis spot to cracks, discontinuities, cores/rims, and places where an anomalous

age could be obtained. The anomalous data points were not used in the interpretation of

plutonic ages. Data points that showed inheritance were set aside for later use in

understanding the history of the zircon crystal.

After the data had been reviewed, it was plotted on an U/Pb Concordia diagram to

gather an approximation of its age (Appendix F, figure a-j). If additional anomalous data

points were found, they were studied for what caused the anomaly. When all anomalous

data were removed, the data was plotted on a weighted average diagram (inset, Appendix

F, figure a-j). A weighted average MSWD value of 1 or less was the acceptance level for

ages, and all three ages (206Pb/238U, 207Pb/235U, and 207Pb/206Pb) were within 2 sigma

errors of each other. The 206Pb/238U ages (inset, Appendix F, figure a-j) are the ones

being reported in this study. The plutons measured in this study with the SIMS method

57

show some similarity to older ages, but are more precise, and help to show which plutons

have inherited ages. The ages of the plutons, and the processed SIMS data are given in

Appendix F, figure a-j, and table 6 respectively.

Rb/Sr Isotopic Ratios

Whole Rock Rb-Sr isotopic analysis was performed at Virginia Polytechnic

Institute and State University under the supervision of Dr. A. K. Sinha using the VG

Sector 54 mass spectrometer. The NBS E&A standard was used during analysis. All

processing and lab work was performed in the Petrogenesis, Isotope Geology and

Tectonics Laboratory at Virginia Polytechnic Institute and State University. Chemical

work was performed under laminar flow hoods in an ultra-clean environment, and

distilled acids and water was used al all times.

Samples were initially processed in a manner similar to the samples for zircon

collection. Chips of sample were taken from the jaw-crushed portion, and crushed

further in a shatter box. The initial shatterbox crushing was used to reduce the chips to

sand sized particles, which were then coned and quartered, to ensure a heterogeneous

whole rock sample. Approximately 150 grams of material was then returned to the

shatterbox for a final crushing, reducing the material to a fine powder. 50 to 100

milligrams of sample were then placed in savilex containers, and 1.0 ml of HF was

added. Then 1.0 ml of HNO3 was added, and the containers were tightly capped and

placed on a hot plate (~90°c) for 4 days. Dissolved samples were then evaporated

overnight, and when dry, approximately 1.0 ml of 6N HCl was added, and then

evaporated. When this was dry, 1.0 ml of 2.5 N HCl was added to the savilex container,

and the sample was ready for column chemistry.

Rb/Sr Column Chemistry

1. The columns were cleaned with 15.0 ml of 6 N Quartz distilled HCl.

2. 5.0 ml of 6 N Teflon HCl was added to the columns.

3. Columns were resettled with 2.5 N Teflon HCl.

4. The 1.0 ml sample was added to the columns.

58

5. Rinse 1.0 ml of 2.5 N HCl.

6. Rinse 5.0 ml of 2.5 N HCl.

7. Rinse 3.0 ml of 2.5 N HCl.

8. Rinse 7.5 ml of 2.5 N HCl.

9. Rinse 4.0 ml of 2.5 N HCl, collect Sr.

10. The samples were collected in labeled PMP beakers which were cleaned in a bath

of approximately 20% HNO3 at 80c for a week, rinsed with Teflon distilled water,

and cleaned further on a hot plate for 3 hours containing approximately 3ml of 6

N HCl. The beakers were rinsed again and ready for collection.

11. The samples were evaporated on a hot plate, covered with parafilm and stored in

airtight boxes until loading onto the filaments for analysis.

59

Table 4: List of sample localities for samples used in SIMS and geochemical analyses.

60

Table 4:

Pluton Name Sample ID Quadrangle Descriptor

Diana Mills JRW-00-DM3 Diana Mills Along Rt. 611, 100 yards north of Sharps Creek Diana Mills JRW-00-DM1 Diana Mills NW corner of intersection of Rt. 611 and 671

Green Springs JRW-00-GS1 Boswells Tavern Along northeast side of South Anna River, south east of bridge on Rt. 613 Poore Creek JRW-00-PC2 Mineral 100 Feet North of Poore Creek along Rt. 636, Right side of road Carysbrook JRW-00-CB3 Columbia East side of Rivanna River, Under Bridge Carysbrook JRW-00-CB5 Columbia Carys Creek Wayside, Rt. 15

Columbia JRW-99-COL1 Columbia Cowherd Quarry, Along Rt. 6, just east of town of Columbia Buckingham JRW-00-B11 Buckingham Along flood plain of North River, approx. 1 mile due west of Dentons Corner Buckingham JRW-00-B6 Buckingham In field area on South side of Horsepen Creek, along Rt. 638 Buckingham JRW-00-B2 Saint Joy In Stream Bed of Intermittent stream north of Rt. 691

Melrose JRW-00-MEL2 Long Island Along Buffalo Creek, in Logging Area, west of Rt. 639 Ellisville JRW-00-E1 Mineral In quarry along Rt. 624

Rich Acres JRW-00-LRW5 Martinsville East West of intersection of Rt. 220 and 986 (along quadrangle edge) Rich Acres JRW-00-LRW4 Martinsville East Along Rt. 650, 100 yds. south of Mullberry Creek

Leatherwood Gretna Body JRW-00-LRW11 Gretna Pavement outcrop along Stinking Creek, north of bridge along Rt. 808 Leatherwood Martinsville Body JRW-00-LRW6 Price Old quarry along North side of Rt. 58 {Filled in} Leatherwood Martinsville Body JRW-99-LRW1 Martinsville East Behind Winn Dixie, at intersection of Rt. 57 and 58

61

Table 5: Descriptions of zircons used in U/Pb SIMS analyses. Images of Zircons can be

seen in Appendix 5.

62

Table 5:

Zircon Populations Color L/W ratio Long Axis (microns) Crystal Shape

Lahore P-81-12 1 Clear 3 to 1 400 Euhedral 2 Pale Brown 3 to 1 200 Subhedral

Ellisville P-80-36 1 Clear 2 to 1 400 Euhedral 2 Light Brown 3 to 1 400 Euhedral 3 Light Brown 3 to 1 200 Euhedral

Green Springs JRW-00-GS1 1 Clear 3 to 1 300 Euhedral 2 Light Brown 4 to 1 500 Euhedral 3 Light Brown 2-3 to 1 300 Euhedral

Poore Creek JRW-00-PC1 1 Pink/Brown 2 to 1 200 Subhedral 2 Pink 7 to 1 400 Euhedral 3 Light Brown 4 to 1 200 Euhedral

Diana Mills JRW-00-DM1 1 Pale Brown 2 to 1 200 Euhedral 2 Pale Brown 2 to 1 400 Euhedral

Buckingham JRW-00-B2 Felsic 1 Brown 2-3 to 1 500 Euhedral

2 Brown 2-3 to 1 300 Subhedral 3 Pink/Clear 3 to 1 200 Euhedral

Buckingham JRW-00-B11 Mafic 1 Brown 3 to 1 600 Euhedral

2 Clear 2 to 1 400 Subhedral Melrose JRW-00-MEL2

1 Clear/Pale Pink 2 to 1 200 Euhedral 2 Light Brown 2-3 to 1 400 Euhedral

Leatherwood JRW-00-LRW11 Gretna 1 Clear/Pale Pink 3 to 1 400 Subhedral

2 Pale Brown 2-3 to 1 300 Euhedral Leatherwood JRW-99-LRW1 Martinsville 1 Clear 3 to 1 400 Euhedral

2 Pale Pink 2-3 to 1 300 Euhedral Rich Acres JRW-00-LRW5

1 Clear 3 to 1 200 Euhedral 2 Pink/Brown 2-3 to 1 400 Subhedral 3 Grey/Clear 2-3 to 1 400 Subhedral

63

Table 6: Table of U/Pb SIMS analyses for plutons in this study. Highlighted data points

are those which show lead loss and inheritance, and were not used in the determination of

the age of the pluton.

64

Table 6:

Correlation Age (Ma) Age (Ma) Age (Ma) Age (Ma) Age (Ma) Age (Ma) % Radiogenic Name207Pb*/ 207Pb*/ 206Pb*/ 206Pb*/ of Concordia 206Pb/ 206Pb/ 207Pb/ 207Pb/ 207Pb/ 207Pb/ 206Pb

235U 235U 238U 238U Ellipses 238U 238U 235U 235U 206Pb 206Pberror error error error error

Buckingham 0.5303 0.02214 0.0689 0.0007464 0.495 429.5 4.502 432 14.69 445.5 83.54 99.29 2001-01-09Jan\ b1c1r6g1s109.ais0.5099 0.01579 0.06807 0.001142 0.7476 424.5 6.895 418.4 10.62 384.8 48.38 99.4 Block 20.531 0.01812 0.0694 0.001025 0.5924 432.5 6.179 432.4 12.02 432 62.45 99.12 2001-01-09Jan\ b1c1r6g6s109.ais

0.5167 0.01838 0.06906 0.001395 0.8078 430.5 8.411 422.9 12.31 381.8 50.91 99.51 Block 20.5187 0.02886 0.06951 0.001485 0.5807 433.2 8.953 424.3 19.3 376.1 104.8 99.2 2001-01-09Jan\ b1c1r6g15s109.ais0.5163 0.02232 0.06846 0.002103 0.7712 426.9 12.69 422.7 14.95 399.7 61.95 99.24 Block 20.5215 0.09333 0.06751 0.002531 0.6179 421.1 15.28 426.2 62.28 453.6 352 97.48 2001-01-10Jan\ b1c1r7g1s110.ais0.5208 0.05515 0.06924 0.00345 0.4907 431.6 20.8 425.7 36.82 393.8 207 99.07 Block 20.3678 0.02635 0.04809 0.0007563 0.4048 302.8 4.652 318 19.56 431.4 148.9 94.87 2001-01-09Jan\ b1c1r6g2s109.ais0.4055 0.02551 0.04956 0.0009887 0.552 311.8 6.072 345.6 18.43 579.9 118.4 96.01 Block 20.4668 0.06066 0.05908 0.001488 0.4777 370 9.06 389 41.99 503.5 264 78.98 2001-01-09Jan\ b1c1r6g2s209.ais0.387 0.04677 0.05585 0.001275 0.4646 350.3 7.784 332.2 34.24 207.1 259.9 79 Block 2

0.4349 0.03668 0.05779 0.001417 0.4663 362.2 8.635 366.6 25.96 394.8 170.6 87.53 2001-01-09Jan\ b1c1r6g3s109.ais0.5296 0.03814 0.07322 0.002315 0.5103 455.5 13.9 431.5 25.32 305.5 141.6 98.66 2001-01-10Jan\ b1c1r7g11s110.ais0.5761 0.01456 0.0718 0.002363 0.6304 447 14.21 461.9 9.381 536.7 56.78 99.97 Block 2

PC + GS 0.5 0.1237 0.07105 0.004146 0.3155 442.5 24.95 411.7 83.75 242.4 543 96.93 2001-01-08Jan\ b1c1r4g1s1.ais0.547 0.1044 0.07098 0.002424 0.5107 442 14.59 443 68.54 448.2 390.9 97.35 2001-01-08Jan\ b1c1r4g1s2.ais

0.4815 0.02539 0.06973 0.00118 0.4854 434.5 7.113 399.1 17.4 198.8 109 96.16 2001-01-08Jan\ b1c1r5g1s1.ais0.5506 0.02422 0.07235 0.001409 0.6124 450.3 8.472 445.4 15.86 420.2 79.41 98.09 2001-01-08Jan\ b1c1r5g6s1.ais0.5552 0.02586 0.07125 0.0009319 0.49 443.7 5.608 448.4 16.88 473 92.37 98.34 Block 20.5435 0.01236 0.0728 0.0005485 0.4638 453 3.296 440.7 8.13 377 45.82 99.17 2001-01-09Jan\ b1c1r5g11s109.ais0.5316 0.01349 0.07141 0.0006688 0.1299 444.7 4.024 432.9 8.944 370.6 58.3 99.24 Block 20.5525 0.02086 0.07372 0.001591 0.7574 458.5 9.553 446.6 13.65 386 57.57 98.47 2001-01-09Jan\ b1c1r5g11s209.ais0.5416 0.01925 0.07323 0.001838 0.731 455.6 11.04 439.4 12.68 355.8 54.8 98.3 Block 20.5648 0.02022 0.07366 0.001443 0.4281 458.2 8.667 454.6 13.12 436.7 72.67 96.99 2001-01-09Jan\ b1c1r5g17s109.ais0.537 0.02218 0.07164 0.001478 0.6568 446 8.892 436.4 14.65 385.9 71.47 96.93 Block 2

0.6262 0.07953 0.07193 0.002174 0.1669 447.8 13.08 493.8 49.66 713.1 266.8 97.91 2001-01-10Jan\ b1c1r4g21s110.ais0.6112 0.02379 0.07114 0.001747 0.7189 443 10.51 484.3 14.99 685.1 58.22 100 Block 20.6329 0.06066 0.0712 0.001638 0.2599 443.4 9.855 497.9 37.72 757.1 195.3 98.85 2001-01-10Jan\ b1c1r4g201s110.ais2.056 0.1328 0.2007 0.00615 0.6551 1179 33.02 1134 44.12 1049 101.1 91.72 2001-01-09Jan\ b1c1r5g22s109.ais2.156 0.1574 0.2019 0.01021 0.7102 1185 54.75 1167 50.65 1133 102.4 91.8 Block 23.232 0.1804 0.2546 0.01002 0.823 1462 51.49 1465 43.29 1469 61.49 98.82 2001-01-09Jan\ b1c1r5g16s109.ais3.114 0.1391 0.2449 0.007996 0.5605 1412 41.4 1436 34.32 1472 71.66 98.95 Block 2

0.5945 0.01453 0.07824 0.001175 0.6637 485.6 7.027 473.7 9.253 416.5 40.93 98.36 2001-01-09Jan\ b1c1r5g14s109.ais0.5845 0.01309 0.07609 0.001159 0.7497 472.8 6.945 467.3 8.388 440.9 33.15 98.52 Block 20.5145 0.04729 0.06659 0.001975 0.2488 415.6 11.94 421.5 31.71 453.7 198.2 99 Block 20.5836 0.09849 0.06839 0.002165 0.4838 426.5 13.07 466.8 63.15 670.4 333.6 93.72 Block 20.5719 0.0409 0.07508 0.003917 0.7694 466.7 23.48 459.2 26.42 422.2 102.2 99.56 Block 2

65

Table 6 (continued):

Correlation Age (Ma) Age (Ma) Age (Ma) Age (Ma) Age (Ma) Age (Ma) % Radiogenic Name207Pb*/ 207Pb*/ 206Pb*/ 206Pb*/ of Concordia 206Pb/ 206Pb/ 207Pb/ 207Pb/ 207Pb/ 207Pb/ 206Pb

235U 235U 238U 238U Ellipses 238U 238U 235U 235U 206Pb 206Pberror error error error error

Melrose 0.5734 0.05974 0.07003 0.001599 0.5699 436.4 9.634 460.2 38.55 581.3 202.1 98.46 Block 20.5687 0.217 0.07108 0.003401 0.5618 442.7 20.47 457.1 140.5 530.6 782 93.22 98-09-17Sept\ melg5s1.ais0.6976 0.0771 0.07444 0.002281 0.5759 462.8 13.69 537.4 46.12 867.6 199.4 97.7 98-09-17Sept\ melg6s2.ais0.5261 0.07007 0.07092 0.003857 0.3563 441.7 23.22 429.2 46.62 362.7 281.1 97.63 Block 20.5312 0.01939 0.0708 0.002192 0.6663 441 13.19 432.6 12.86 388.5 62.89 99.21 98-09-17Sept\ melg9s1.ais0.545 0.01795 0.07005 0.0018 0.7462 436.4 10.84 441.7 11.79 469.5 48.59 99.48 Block 2

0.5457 0.09278 0.07112 0.001484 0.567 442.9 8.934 442.2 60.95 438.5 354.1 96.98 98-09-17Sept\ melg9s2.ais0.5567 0.04617 0.07379 0.003729 0.6198 459 22.39 449.4 30.11 400.6 145.8 98.86 Block 20.7206 0.07671 0.0774 0.005243 0.4498 480.6 31.37 551 45.27 853.9 201.8 97.72 Block 22.107 0.1352 0.1928 0.008706 0.6918 1137 47.05 1151 44.17 1178 91.61 98.73 98-09-17Sept\ melg6s1.ais2.031 0.08471 0.1928 0.006149 0.7332 1137 33.23 1126 28.38 1106 56.76 99.13 Block 20.516 0.05929 0.06702 0.002154 0.4931 418.2 13.02 422.5 39.71 445.9 228.8 96.79 98-09-17Sept\ melg1s1.ais

0.5621 0.1201 0.06778 0.00246 0.5037 422.7 14.85 452.9 78.06 608.9 427.8 97.09 2001-01-10Jan\ b1c2r3g12s110.ais0.5587 0.05692 0.067 0.003452 0.6211 418.1 20.85 450.7 37.08 620.5 174.1 99 Block 20.4716 0.07211 0.06796 0.00224 0.4004 423.8 13.52 392.3 49.76 210.4 331.3 97.1 2001-01-10Jan\ b1c2r3g11s110.ais0.4954 0.03018 0.06652 0.002544 0.553 415.2 15.38 408.6 20.49 371.5 114.7 99.5 Block 21.672 0.2468 0.1853 0.009498 0.516 1096 51.66 998.1 93.77 789.2 270.4 97.41 2001-01-10Jan\ b1c2r3g3s110.ais2.104 0.1551 0.1993 0.01333 0.9201 1171 71.65 1150 50.72 1110 57.69 99.55 Block 2

Leatherwood 0.5422 0.1478 0.07231 0.002266 0.3918 450 13.62 439.8 97.34 386.9 588.4 92.92 98-09-17Sept\ lg1s2.ais0.5752 0.1029 0.07472 0.003874 0.6154 464.5 23.24 461.4 66.31 445.9 339 95.75 98-09-17Sept\ lg2s1.ais0.553 0.05661 0.07133 0.003862 0.4543 444.2 23.24 447 37.02 461.4 202.9 98.36 Block 2

0.4826 0.135 0.0677 0.00214 0.5691 422.3 12.92 399.8 92.47 272.1 603 94.81 98-09-17Sept\ lg3s2.ais0.5389 0.1328 0.07191 0.00261 0.5634 447.6 15.7 437.7 87.6 385.9 511.9 96.45 98-09-17Sept\ lg6s1.ais0.5869 0.05449 0.07344 0.004806 0.6981 456.9 28.86 468.9 34.86 528.2 145.7 98.85 Block 20.5855 0.1051 0.07362 0.002988 0.2971 457.9 17.94 468 67.3 517.6 377.3 96.8 98-09-17Sept\ lg7s1.ais0.5654 0.03463 0.0726 0.001895 0.5037 451.8 11.39 455 22.46 471.4 117.6 98.84 Block 20.4745 0.1137 0.07158 0.00291 0.4854 445.7 17.5 394.3 78.28 103.1 526.5 95.3 2001-01-10Jan\ c2r2g4s110.ais0.5219 0.06853 0.072 0.004449 0.5313 448.2 26.75 426.4 45.72 310.6 253.9 98.44 Block 20.6164 0.1501 0.07254 0.004633 0.5548 451.5 27.84 487.6 94.29 661.1 460.3 95.7 2001-01-10Jan\ c2r2g9s110.ais0.4904 0.08039 0.07006 0.001794 0.3648 436.5 10.81 405.2 54.77 229.9 361.3 98.26 2001-01-10Jan\ c2r2g13s110.ais0.5249 0.04264 0.06788 0.003541 0.8514 423.4 21.38 428.4 28.39 455.8 101.8 99.6 Block 20.6356 0.08056 0.07142 0.003435 0.5057 444.7 20.67 499.6 50.01 759.4 233.1 97.3 Block 20.4795 0.09643 0.07101 0.006435 0.532 442.2 38.74 397.7 66.18 146.7 401.2 96.17 Block 20.5734 0.05203 0.0669 0.002547 0.645 417.5 15.39 460.2 33.57 679.7 154.4 98.46 Block 20.6063 0.1089 0.07185 0.01032 0.8678 447.3 62.09 481.2 68.86 646.4 193.6 99.17 Block 2

66

Table 6 (continued):

Correlation Age (Ma) Age (Ma) Age (Ma) Age (Ma) Age (Ma) Age (Ma) % Radiogenic Name207Pb*/ 207Pb*/ 206Pb*/ 206Pb*/ of Concordia 206Pb/ 206Pb/ 207Pb/ 207Pb/ 207Pb/ 207Pb/ 206Pb

235U 235U 238U 238U Ellipses 238U 238U 235U 235U 206Pb 206Pberror error error error error

Lahore 0.5295 0.01862 0.07051 0.001637 0.8433 439.2 9.855 431.5 12.36 390.5 44.81 99.44 2001-01-08Jan\ b1c1r3g2s1.ais0.5395 0.01796 0.07021 0.001995 0.9013 437.4 12.02 438.1 11.84 441.5 32.27 99.79 Block 20.5592 0.05918 0.07294 0.002321 0.4654 453.8 13.95 451 38.54 436.8 212.1 98.79 2001-01-08Jan\ b1c1r3g6s1.ais0.5518 0.03753 0.07064 0.002237 0.2707 440 13.47 446.2 24.55 478.2 147.6 99.46 Block 20.5615 0.02252 0.07356 0.002525 0.8295 457.6 15.16 452.5 14.64 426.7 50.01 99.79 Block 20.5839 0.03452 0.07572 0.004492 0.897 470.5 26.92 467 22.13 449.6 59.71 99.64 2001-01-08Jan\ b1c1r3g8s1.ais0.5497 0.03007 0.07144 0.002596 0.9101 444.8 15.62 444.8 19.7 444.8 58.58 99.77 Block 20.5728 0.02104 0.07492 0.001509 0.6651 465.7 9.052 459.8 13.58 430.5 61.87 99.43 2001-01-08Jan\ b1c1r3g11s1.ais0.5609 0.01441 0.07306 0.001368 0.7961 454.6 8.221 452.1 9.371 439.4 34.8 99.71 Block 20.4923 0.04657 0.06782 0.002385 0.385 423 14.4 406.5 31.68 313.3 198.7 98.07 2001-01-08Jan\ b1c1r3g9s1.ais0.5649 0.01627 0.07545 0.001137 0.5837 468.9 6.815 454.7 10.56 383.5 52.69 99.5 2001-01-08Jan\ b1c1r3g7s1.ais0.5208 0.06601 0.06967 0.004614 0.4868 434.2 27.81 425.7 44.07 379.9 249.2 99.18 Block 20.6054 0.07657 0.0732 0.003754 0.582 455.4 22.55 480.6 48.43 603 227.8 98.29 2001-01-08Jan\ b1c1r3g6s2.ais0.523 0.04971 0.0738 0.002041 0.4793 459 12.25 427.1 33.15 258.7 196.1 98.5 2001-01-08Jan\ b1c1r3g4s1@1.ais0.544 0.02863 0.06661 0.002796 0.753 415.7 16.9 441 18.83 575.7 75.45 99.83 Block 2

Leather Gretna 0.5521 0.04433 0.07235 0.001365 0.4258 450.3 8.206 446.4 29 426.3 165.6 98.55 2001-01-09Jan\ b1c1r12g3s109.ais0.5072 0.03183 0.06846 0.002157 0.5994 426.9 13.01 416.6 21.44 359.8 114.2 99.04 Block 20.5656 0.03721 0.07235 0.00221 0.6155 450.3 13.28 455.2 24.13 479.8 116.7 99.03 2001-01-09Jan\ b1c1r12g14s109.ais0.6109 0.05851 0.07326 0.004979 0.945 455.8 29.91 484.1 36.88 620.6 83.26 99.79 Block 20.5458 0.02593 0.07173 0.00207 0.4388 446.6 12.45 442.2 17.03 419.8 96.99 99.65 2001-01-09Jan\ b1c1r12g5s109.ais0.5382 0.01286 0.06947 0.0008897 0.6582 432.9 5.363 437.2 8.491 459.9 40.42 99.94 Block 20.557 0.02244 0.07302 0.001129 0.8366 454.3 6.781 449.6 14.63 425.6 63.88 99.56 2001-01-09Jan\ b1c1r12g7s109.ais0.5443 0.01617 0.06968 0.001367 0.8277 434.2 8.237 441.3 10.63 478.1 38.47 99.76 Block 23.183 0.2426 0.256 0.01749 0.784 1470 89.74 1453 58.89 1429 91.78 99.16 2001-01-09Jan\ b1c1r12g15s109.ais2.994 0.2081 0.2325 0.01501 0.9277 1347 78.5 1406 52.92 1496 49.11 100 Block 22.281 0.1659 0.2049 0.007298 0.7152 1202 39.05 1207 51.33 1215 105 98.93 2001-01-09Jan\ b1c1r12g4s109.ais2.332 0.0999 0.2113 0.006936 0.6701 1236 36.91 1222 30.44 1198 63.24 99.81 Block 2

Ellisville 0.5188 0.01451 0.06954 0.001541 0.7474 433.4 9.29 424.4 9.697 375.7 41.89 99.66 2001-01-08Jan\ b1c1r2g3s1.ais0.5549 0.01676 0.07062 0.001333 0.7061 439.9 8.026 448.2 10.95 491.1 47.49 99.81 2001-01-08Jan\ b1c1r2g3s2.ais0.5291 0.01419 0.06896 0.001274 0.7947 429.9 7.684 431.2 9.424 438.5 36.78 99.85 Block 20.5362 0.01678 0.07258 0.001534 0.6613 451.7 9.219 435.9 11.09 353.4 53.05 99.52 2001-01-08Jan\ b1c1r2g4s1.ais0.5401 0.01185 0.06972 0.001087 0.5254 434.5 6.55 438.5 7.81 459.6 42.35 99.87 Block 20.5484 0.01853 0.0725 0.001382 0.5996 451.2 8.307 443.9 12.15 406.3 60.6 98.75 Block 20.5442 0.01694 0.07169 0.001257 0.5438 446.3 7.561 441.2 11.14 414.3 58.42 99.64 2001-01-08Jan\ b1c1r2g6s1.ais0.5387 0.01063 0.07084 0.001488 0.7364 441.2 8.956 437.5 7.012 418.1 33.13 99.89 Block 20.5544 0.01845 0.07051 0.00183 0.7965 439.2 11.02 447.9 12.05 492.6 44.38 99.7 Block 20.5851 0.01557 0.07392 0.001449 0.6039 459.7 8.701 467.7 9.975 507.1 47.3 99.68 2001-01-08Jan\ b1c1r2g13s1.ais0.5283 0.01742 0.07113 0.001976 0.7806 443 11.9 430.7 11.58 365.5 46.69 99.63 Block 20.5667 0.009049 0.0738 0.00115 0.45 459 6.905 455.9 5.864 440.2 36.82 99.88 Block 2

67

Table 6 (continued):

Correlation Age (Ma) Age (Ma) Age (Ma) Age (Ma) Age (Ma) Age (Ma) % Radiogenic Name207Pb*/ 207Pb*/ 206Pb*/ 206Pb*/ of Concordia 206Pb/ 206Pb/ 207Pb/ 207Pb/ 207Pb/ 207Pb/ 206Pb

235U 235U 238U 238U Ellipses 238U 238U 235U 235U 206Pb 206Pberror error error error error

Ellisville 0.4948 0.02361 0.06751 0.002085 0.7559 421.1 12.59 408.2 16.04 335.6 71.76 99.25 2001-01-08Jan\ b1c1r2g1s1.ais0.4955 0.01314 0.06538 0.001071 0.687 408.3 6.478 408.7 8.918 410.9 43.27 99.82 Block 20.4983 0.02062 0.06879 0.0008899 0.6443 428.9 5.367 410.6 13.97 309 78.51 99.21 2001-01-08Jan\ b1c1r2g2s1.ais0.5056 0.01388 0.0674 0.001745 0.764 420.5 10.54 415.5 9.358 387.9 41.27 99.62 Block 20.5533 0.02439 0.07529 0.001408 0.5913 468 8.44 447.2 15.94 341.7 82.18 99.23 2001-01-08Jan\ b1c1r2g12s1.ais0.5238 0.01635 0.06934 0.001919 0.8806 432.2 11.57 427.7 10.9 403.4 33.13 99.84 Block 20.5699 0.01358 0.07596 0.0009808 0.6989 472 5.876 458 8.78 388.1 39.16 99.64 2001-01-08Jan\ b1c1r2g8s1.ais

Diana Mills 0.5452 0.01349 0.07081 0.0009362 0.5898 441 5.636 441.8 8.864 445.9 44.51 99.76 2001-01-10Jan\ b1c1r8g4s110.ais0.5333 0.01263 0.0696 0.0009332 0.7288 433.7 5.624 434 8.362 435.4 37.11 99.86 Block 20.5355 0.01938 0.07101 0.001371 0.621 442.2 8.25 435.5 12.81 399.9 63.94 99.42 2001-01-10Jan\ b1c1r8g5s110.ais0.5403 0.01174 0.06993 0.001279 0.827 435.7 7.708 438.6 7.736 453.9 27.11 99.86 Block 20.5415 0.02588 0.07141 0.00167 0.7742 444.6 10.05 439.4 17.05 412.2 74.17 99.59 2001-01-10Jan\ b1c1r8g10s110.ais0.5316 0.01003 0.06897 0.001102 0.8875 429.9 6.644 432.8 6.652 448.4 19.41 99.98 Block 20.5655 0.01711 0.07552 0.0008275 0.5325 469.3 4.96 455.1 11.1 383.8 58.71 99.54 2001-01-10Jan\ b1c1r8g2s110.ais0.5662 0.007516 0.07336 0.0007236 0.6848 456.4 4.346 455.6 4.872 451.4 21.55 99.88 Block 21.729 0.05686 0.1742 0.004137 0.7762 1035 22.71 1020 21.15 986.2 42.34 99.29 2001-01-10Jan\ b1c1r8g9s110.ais1.691 0.0788 0.1704 0.008167 0.9112 1014 44.98 1005 29.73 985.7 40.64 99.65 Block 20.566 0.01117 0.0747 0.0008542 0.6317 464.4 5.124 455.4 7.24 410.1 34.28 99.72 2001-01-10Jan\ b1c1r8g21s110.ais0.5752 0.007251 0.07421 0.0008302 0.7245 461.4 4.982 461.4 4.674 460.9 19.79 99.97 Block 20.5599 0.008516 0.07419 0.001168 0.7362 461.3 7.007 451.5 5.543 401.5 25.2 99.77 2001-01-10Jan\ b1c1r8g22s110.ais0.5634 0.006751 0.07315 0.0009292 0.8311 455.1 5.582 453.8 4.384 446.9 16.02 99.92 Block 20.6581 0.01824 0.0815 0.001436 0.4764 505.1 8.56 513.4 11.17 550.8 54.06 99.48 2001-01-10Jan\ b1c1r8g22s210.ais0.6679 0.01504 0.07656 0.00164 0.8634 475.6 9.82 519.4 9.158 717.3 24.49 99.91 Block 20.5858 0.01992 0.07735 0.001788 0.6989 480.3 10.7 468.2 12.75 409.3 54.41 99.54 2001-01-10Jan\ b1c1r8g23s110.ais0.5434 0.0149 0.07409 0.00149 0.822 460.8 8.942 440.7 9.804 337.1 35.81 99.66 Block 2

Columbia 0.552 0.04268 0.07256 0.003012 0.7812 451.6 18.11 446.3 27.92 419.5 115.7 99.38 2001-01-09Jan\ b1c1r20g23s109.ais0.5249 0.02374 0.0703 0.001494 0.6102 438 9.001 428.4 15.81 377.3 81.85 99.77 Block 20.6185 0.02715 0.07743 0.003024 0.7736 480.7 18.09 488.9 17.03 527.2 61.99 99.85 2001-01-09Jan\ b1c1r20g24s109.ais0.5926 0.01971 0.07578 0.00196 0.7297 470.9 11.74 472.6 12.57 480.6 50.36 99.97 Block 20.5536 0.03272 0.07516 0.001664 0.486 467.2 9.974 447.3 21.39 346.6 117.8 99.11 2001-01-09Jan\ b1c1r20g3s109.ais0.5544 0.02628 0.07165 0.003238 0.8433 446.1 19.48 447.9 17.17 457.1 57.68 99.76 Block 20.5911 0.02541 0.07503 0.001795 0.8499 466.4 10.76 471.6 16.22 497.1 57.12 99.73 Block 20.5635 0.05561 0.07275 0.001752 0.3855 452.7 10.53 453.8 36.11 459.3 204.3 94.22 2001-01-09Jan\ b1c1r20g16s109.ais0.5528 0.04069 0.07275 0.002515 0.414 452.7 15.12 446.8 26.61 416.6 150 98.8 2001-01-09Jan\ b1c1r20g12s209.ais0.5217 0.04177 0.07062 0.005159 0.8062 439.9 31.06 426.3 27.87 353.5 108.7 99.69 Block 20.5543 0.1088 0.07452 0.002345 0.5461 463.4 14.07 447.8 71.09 368.6 408 92.15 Block 2

1.66 0.1817 0.1691 0.007133 0.6591 1007 39.33 993.3 69.37 962.4 179 97.56 98-09-18Sept\ cog1s1.ais1.545 0.1301 0.1582 0.01058 0.8196 946.7 58.87 948.4 51.89 952.2 98.79 98.66 Block 21.772 0.07811 0.1731 0.002935 0.2113 1029 16.13 1035 28.61 1048 88.23 98.74 98-09-18Sept\ cog1s2.ais1.706 0.08799 0.1689 0.008753 0.8706 1006 48.28 1011 33.02 1021 53.26 99.3 Block 2

68

Table 6 (continued):

Correlation Age (Ma) Age (Ma) Age (Ma) Age (Ma) Age (Ma) Age (Ma) % Radiogenic Name207Pb*/ 207Pb*/ 206Pb*/ 206Pb*/ of Concordia 206Pb/ 206Pb/ 207Pb/ 207Pb/ 207Pb/ 207Pb/ 206Pb

235U 235U 238U 238U Ellipses 238U 238U 235U 235U 206Pb 206Pberror error error error error

Columbia 1.638 0.1489 0.1713 0.007439 0.3685 1019 40.94 985 57.31 909.7 175.2 97.17 98-09-18Sept\ cog5s1.ais1.699 0.1228 0.1692 0.01032 0.8861 1008 56.89 1008 46.21 1010 68.23 98.93 Block 21.608 0.05524 0.1607 0.003034 0.5651 960.9 16.85 973.5 21.5 1002 57.54 99.17 98-09-18Sept\ cog7s1.ais1.649 0.0375 0.163 0.002701 0.7981 973.7 14.97 989.2 14.37 1024 27.91 99.79 Block 21.393 0.1952 0.1486 0.007699 0.4457 893.3 43.21 886 82.83 867.7 261 96.43 98-09-18Sept\ cog7s2.ais1.457 0.1609 0.1479 0.0132 0.8749 889 74.12 912.7 66.48 970.4 110.1 98.99 Block 20.6354 0.02048 0.08371 0.001844 0.8435 518.2 10.97 499.4 12.71 414.2 40.37 99.71 2001-01-09Jan\ b1c1r20g25s109.ais0.6116 0.01505 0.08037 0.001512 0.9078 498.3 9.023 484.6 9.482 419.9 24.35 99.96 Block 20.6268 0.06425 0.08416 0.002938 0.3025 520.9 17.47 494.1 40.1 371.6 220.2 98.67 2001-01-09Jan\ b1c1r20g12s109.ais0.6179 0.03042 0.08025 0.002053 0.5136 497.6 12.25 488.5 19.09 446.1 93.91 99.44 2001-01-09Jan\ b1c1r20g10s109.ais

Rich Acres 0.5226 0.03007 0.07054 0.002363 0.6107 439.4 14.23 426.9 20.05 359.7 102.9 98.86 2001-01-10Jan\ b1c1r10g1s110.ais0.5339 0.02585 0.06757 0.002617 0.8169 421.5 15.8 434.4 17.11 503.5 61.48 99.69 Block 20.519 0.03846 0.06888 0.00287 0.6105 429.4 17.31 424.5 25.71 397.7 131.8 98.81 2001-01-10Jan\ b1c1r10g1s210.ais0.5416 0.02156 0.07094 0.002321 0.687 441.8 13.97 439.5 14.2 427.3 65.6 99.63 Block 20.5264 0.04053 0.06897 0.001798 0.4927 429.9 10.84 429.4 26.96 426.7 151.7 98.97 2001-01-10Jan\ b1c1r10g4s110.ais0.5248 0.02424 0.06879 0.002064 0.8028 428.8 12.45 428.4 16.14 425.9 63.42 99.66 Block 20.5437 0.0362 0.06871 0.001628 0.5863 428.4 9.822 440.8 23.81 506.4 123.4 99.27 Block 20.4993 0.03413 0.06426 0.002615 0.7881 401.5 15.84 411.2 23.12 466.3 97.68 99.66 Block 20.5302 0.03449 0.07049 0.002546 0.6021 439.1 15.33 432 22.89 393.9 116.7 99.05 Block 20.4632 0.04158 0.05734 0.001579 0.317 359.4 9.628 386.5 28.86 551.8 185.9 98.02 2001-01-10Jan\ b1c1r10g5s310.ais0.4236 0.03545 0.05664 0.002508 0.667 355.2 15.3 358.6 25.28 380.9 142.6 99 Block 20.5745 0.05221 0.07229 0.001503 0.4473 450 9.038 460.9 33.67 515.9 183.7 98.71 2001-01-10Jan\ b1c1r10g1s310.ais0.483 0.05934 0.06813 0.0013 0.513 424.9 7.844 400.1 40.63 259.4 262.5 97.79 2001-01-10Jan\ b1c1r10g2s110.ais

69

Appendix B

Pluton Descriptions

Leatherwood Granite

The Leatherwood Granite occurs as dikes, sill-like bodies, and irregularly shaped plutons,

the major part of which occurs as thin sheets on top of the large plutons of Rich Acres

Gabbro (Henika et al., 1996). The Leatherwood Granite (Jonas, 1927; Pegeau, 1932;

Conley, 1985) is a medium-grained to coarse-porphyritic light gray granite that generally

shows rapakivi texture. The rock contains quartz, potassium feldspar, plagioclase,

biotite, muscovite, epidote, apatite, titanite zircon and magnetite. Conley and Henika

(1973) and Ragland et al. (1997), describe the Leatherwood Granite as being composed

of 20 to 42 percent quartz, 5 to 52 percent potassium feldspar, 10 to 30 percent

plagioclase (An10-An30), 5 to 26 percent biotite, and trace to 15 percent muscovite.

Minerals in amounts less than 2 percent are epidote, clinozoisite, apatite, sphene, zircon,

and opaques.

Field relations (Conley and Henika, 1973; Henika, 1996) show the Leatherwood

Granite cross cutting the Rich Acres Gabbro (See description of Rich Acres for similar

and contrasting descriptions). The Leatherwood Granite also cuts the surrounding

country rocks, the Bassett Formation and the Fork Mountain Formation.

The Leatherwood Granite has a large areal extent, as seen on the 1993 Geologic

Map (VDMR, 1993). A body near Gretna, Virginia is included in this study. This body

has similar mineralogy to the bodies of Leatherwood near Martinsville. The rock is gray,

medium- to coarse grained, porphyritic and flow banded.

Rich Acres Formation

The Rich Acres formation makes up the major part of the Martinsville Igneous Complex.

It generally occurs in concordant to slightly discordant plutons, as well as irregular

70

shaped masses and possibly as dikes (Henika et al., 1996). The Rich Acres formation,

originally the Rich Acres Norite (Conley and Toewe, 1968), is composed of norite,

gabbros, and diorite much of which has been metamorphosed to amphibolite grade. The

Gabbro is medium to fine grained, equigranular, and medium gray in color. The rock is

composed of 30 to 70 percent plagioclase (bytownite-labradorite), 5 to 15 percent

orthopyroxene, 5 to 20 percent clinopyroxene (augite), 6 to 20 percent biotite, 7 to 40

percent hornblende, 2 to 9 percent magnetite, and traces of epidote, sphene, ilmenite,

pyrite, quartz, carbonate, apatite, zircon, sericite, actinolite, and sphene (Conley and

Henika, 1973).

The diorite is medium to coarse grained, generally porphyritic, and medium

grayish-green. The rock is composed of 40 to 70 percent plagioclase (andesine to

oligoclase), 50 to 30 percent hornblende, 5 to 15 percent biotite, and 1 to 15 percent

quartz. Accessory minerals include chlorite, ilmenite-magnetite, pyrite, carbonate,

epidote, apatite, zircon, sphene, tourmaline, muscovite and rutile (Conley and Henika,

1973).

The norite is dark gray to almost black and medium to coarse grained. Textures

range from granular to ophitic although most specimens are sub-ophitic and some are

porphyritic. The norite is composed of 30 to 60 percent plagioclase (bytownite-

labradorite), 10 to 38 percent orthopyroxene, (predominantly hypersthene) 5 to 15

percent augite, 10 to 20 percent amphibole, and less than 1 to 10 percent biotite. Olivine

is not always present, but can comprise as much as 20 percent of the rock. Accessory

minerals are opaques (magnetite, with some ilmenite and pyrite), spinel, carbonate,

apatite, and zircon (Conley and Henika, 1973).

Field relations of the Rich Acres Formation are complex. All three units cut the

Bassett Formation and the Fork Mountain Formation. The noritic unit has been observed

cutting the Leatherwood granite, as well as the Gabbro cutting the Leatherwood Granite

(Conley and Toewe, 1968). In places, the dioritic unit contains inclusions of both the

gabbro and the granite (Conley and Henika, 1973).

Ellisville Pluton

71

The Ellisville pluton is a mesocratic, coarse- to medium- grained, equigranular to

porphyritic, massive to strongly foliated granodiorite. The rock is composed of quartz,

plagioclase, potassium feldspar, and biotite; accessories include epidote, allanite, titanite,

apatite and zircon (Rader and Evans, 1993). Pavlides et al., (1994) reports that the

Ellisville is composed almost exclusively of granodiorite under the Streckeisen (1976)

modal classification system, as well as the chemical classification system of De La Roche

and others (1980).

The modal make-up of the Ellisville Pluton is 14.8 to 30.8 percent quartz, 31.1 to

54.3 percent plagioclase, 4.9 to 29.3 percent potassium feldspar, and 2.2 to 15.7 percent

biotite. The Ellisville granodiorite is intrusive into the deformed metavolcanic rocks of

the Chopawamsic Formation as well as into greenschist-facies metasedimentary rocks of

the Mine Run Complex (Pavlides et al., 1994).

Lahore Pluton

The Lahore Complex is composed of three units, an amphibole monzonite, a pyroxene

monzonite, and a mafic/ultramafic unit. The amphibole monzonite is a mesocratic,

medium grained, amphibole monzonite, and amphibole quartz monzonite. Mineralogy

includes microcline or orthoclase, intermediate composition plagioclase, and quartz.

Mafic minerals are amphibole ranging from common hornblende to edenite, locally

rimming pyroxene, subordinate biotite, and magnetite. Epidote, titanite, apatite and

allanite are also present. The pyroxene monzonite is dark gray to black, fine to medium

grained, and massive to indistinctly foliated. It consists of large, locally twinned augite,

poikilitic in part, enclosing apatite, opaque oxide, biotite and plagioclase. The

mafic/ultramafic unit is a composite mass that consists of partially serpentinized

pyroxenite containing diopside rimmed by antigorite or by tremolite (Rader and Evans,

1993).

The Lahore complex, similar to the Ellisville pluton, intrudes into deformed

metavolcanics of the Chopawamsic Formation as well as into greenschist facies

metasedimentary rocks of the Mine Run Complex. The Lahore Complex is intruded by

felsic dikes thought to have been derived from the Ellisville pluton (Pavlides et al., 1994).

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Green Springs Intrusive Complex

The Green Springs Intrusive complex is composed of two to six lithologies based on

texture, color, and composition (Rossman, 1991; Hopkins, 1960). The complex is

divided into two plutonic units, a diorite + hornblendite unit, and a quartz diorite +

granite unit, the Green Springs, and Poore Creek Plutons, respectively. The Green

springs pluton is a light to dark gray, fine to coarse-grained diorite (Rader and Evans,

1993). It is composed of hornblende and plagioclase (An 30-An70), with accessory

minerals including apatite, titanite, zircon, garnet, pyrite and magnetite. Augite, diopside,

quartz, and potassium feldspar are locally present. The more felsic Poore Creek Pluton is

a light gray, medium to coarse grained, massive to indistinctly foliated quartz diorite and

granite. It is composed of quartz, plagioclase, potassium feldspar, biotite, and muscovite

(Rader and Evans, 1993). Field relations show that the quartz diorite-granite phase

surround and intrude the diorite phase as dikes and small apophyses. Both units are

intrusive into metasediments of the Mine Run Complex (Rossman, 1991).

Buckingham Complex

The Buckingham Complex is a series of well differentiated, intensely deformed and

metamorphosed sills inter-layered with meta-sedimentary rocks (Ern, 1968). The

complex is composed of three units, an ultramafic unit, a differentiated meta-gabbro unit,

and a quartz diorite unit. Rocks of the ultramafic unit occur both as individual sills up to

several hundred feet in outcrop width, surrounded by rocks of the differentiated

metagabbro unit and as thin basal layers within rhythmically layered meta gabbro

sequences. The least altered of these rocks contains 35 percent hornblende, 42 percent

augite, and 20 percent hypersthene; weathering products include epidote and chlorite.

Accessory minerals include apatite, zircon, sphene, and magnetite (Henika, 1969).

The differentiated meta-gabbro unit is the most common rock type in the

complex. The metagabbro occurs in differentiated sills which grade stratigraphically

from metapyroxenite at the base through leucocratic, medium to coarse-grained meta-

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gabbros. This unit is composed of hornblende, clinopyroxene, orthopyroxene, biotite,

plagioclase, and magnetite. Common secondary minerals include biotite, chlorite,

epidote, muscovite, quartz, and garnet. Accessory minerals include apatite, zircon, and

ilmenite (Henika, 1969).

The third unit is a light gray, medium to coarse-grained biotite-quartz diorite

(Henika, 1969). The rock is composed of quartz, plagioclase, potassium feldspar, and

biotite. The biotite is often altered to chlorite, and the plagioclase is often sericitized.

Common accessory minerals include epidote, clinozoisite, allanite, apatite, zircon and

magnetite. The coarse-grained biotite rich diorite occurs as synkinematically injected

sills and dikes, which cut across all other meta-igneous and metasedimentary units in the

complex (Henika, 1969).

Diana Mills Pluton

The Diana Mills Pluton is principally a hornblende meta-diorite and hornblende-

quartz meta-diorite, but also includes hornblendite, amphibolite, meta-peridotite,

orbicular serpentinite, pegmatite and aplite (Rader and Evans, 1993). Graham, (1975)

divided the Diana Mills Pluton into three distinct groups. Group three is composed of

hornblendites and ultramafics, group two of hornblende pegmatites, fine-grained

ultramafic rocks, and distinctive mafic diorites, and group one of Hornblende or biotite

diorites. Graham also stated that the pluton is generally non-foliated, and is concordant

with the foliations in the enclosing meta-graywackes.

Group one is commonly a dark green to gray, medium grained, often porphyritic

quartz diorite. It is composed of, in order of abundance, plagioclase, hornblende, biotite,

epidote, clinozoisite, chlorite, quartz, and serecite. Accessory minerals include

muscovite, apatite, sphene, zircon, and magnetite. Group two contains mafic diorites and

hornblendes that are composed almost entirely (60-70 percent) of hornblende, and altered

plagioclase. Some of the hornblende is secondary after pyroxene. Apatite is present with

small amounts of secondary quartz, and magnetite and sphene are common accessory

minerals. Group three contains large plagioclase crystals in a matrix (50 to 60 percent) of

small hornblendes. The pegmatites often contain hornblende blades up to 6cm long

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(Graham, 1975). Group three contains interesting orbicular serpentinites, which are

described in detail by Garry (1999). The Diana Mills Pluton is intrusive into the meta-

graywackes of the Hardware Anticline (Brown, 1969).

Melrose Pluton

The Melrose pluton is a coarse grained, greenish, slightly metamorphosed,

hypidiomorphic granular, biotite quartz monzonite to quartz diorite. The rock is

composed of oligoclase, and lesser amounts of highly perthitic microcline, quartz, biotite

and titanite. Accessory minerals include zircon, apatite, magnetite, secondary epidote,

hematite, calcite, and muscovite (Gates, 1981).

Columbia Pluton

The Columbia Pluton is a light gray, medium to coarse grained, foliated biotite-muscovite

granite to tonalite (Rader and Evans, 1993). The Columbia meta-granite is typically an

inequigranular mosaic of quartz, plagioclase and microcline. The texture is

predominantly granoblastic. Biotite is commonly altered to muscovite, and epidote is

often found in biotite-muscovite clumps. Pyrite, magnetite, zircon and apatite are

common accessory minerals (Bourland, 1976). Recent mapping by Goodman (Personal

Communication), has divided the Columbia pluton into three distinct units, one that is

massive and equigranular, a second that is porphyritic, and a third that is fine grained and

foliated. This mapping has also shown that the Columbia is not separated from the

Carysbrook pluton by the septum of metasediments that is shown on the 1993 Virginia

Division of Mineral Resources State Geologic Map (Goodman et al., 2001). The

Columbia pluton is intrusive into the Chopawamsic volcanics (Bourland and Glover,

1979).

Carysbrook Pluton

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The Carysbrook pluton is a light gray, medium to coarse grained massive to indistinctly

foliated biotite granite. Mineralogically it is composed of quartz, potassium feldspar,

plagioclase, biotite, chlorite, muscovite and epidote (Rader and Evans, 1993).

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Appendix C

Pluton Ages, Isotope and Bulk Geochemistry

The Buckingham pluton, description in Appendix B, has a 206Pb/238U age of 429 ±

5 Ma (Appendix F, figure a). This age is from U/Pb measurements of zircons from both

the mafic and felsic phases of the pluton. The geochemistry of the Buckingham pluton is

distinct for the two phases. The mafic samples are enriched in Fe, Mg, Mn and Ti, while

the felsic samples are enriched in K, Ca, Na, Al. All samples plot in the sub-alkaline

field on an alkalies vs. SiO2 plot. Initial strontium isotopic ratios calculated at VPI&SU,

range between .7034 and .7083, corresponding to the mafic and felsic units respectively.

The Columbia pluton, description in Appendix B, has a 206Pb/238U age of 457 ± 7

Ma (Appendix F, figure b). The Columbia pluton also contains inherited components of

approximately 1000 Ma within the zircon grains (see Appendix G, figure a, and table 6

for inheritance data). The Columbia pluton contains approximately 70% SiO2, low

percentages of mafic elements, Fe, Mg, Mn, and increased amounts of Na, Ca, K, and Al.

The calculated initial strontium ratio for the Columbia pluton is .7098 (Mose and Nagel,

1982).

The Diana Mills pluton, description in Appendix B, has a 206Pb/238U age of 436 ±

5 Ma (Appendix F, figure c). Zircons from the pluton also contained inherited

components of 1000 Ma (Appendix G, figure b, and table 6). Samples from the pluton

contain approximately 50% SiO2, and are enriched in Ca, Fe, and Mg. The measured

initial strontium ratio for the Diana Mills Pluton is approximately .7051.

The Ellisville pluton, description in Appendix B, has a 206Pb/238U age of 444 ± 6

Ma (Appendix F, figure d), which is in agreement with the 441 ± 8 Ma whole rock Rb/Sr

age of Pavlides et al. (1982). No inherited component was discovered during analysis.

Chemical analyses from the Ellisville pluton done by Pavlides (1994), along with one

sample from this study, are all tightly constrained on the chemical plots. Silica values

range between 66 and 72%, and other elements are within few percent of each other.

Strontium ratios gathered by Pavlides (1994), provide an initial 87Sr/86Sr ratio of .7067.

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The Lahore pluton, description in Appendix B, has a 206Pb/238U age of 451 ± 7 Ma

(Appendix F, figure f), which is in agreement with the 450 ± 8 Ma U/Pb TIMS zircon age

of Pavlides et al. (1994). No inherited component was found during analysis. Samples

from the Lahore pluton contain between 50 and 60% silica. Major elements such as

TiO2, P2O5, MgO, FeO, and CaO, generally decrease with increasing silica, while

elements such as Na2O and K2O generally increase with increasing silica. Initial

strontium isotopic values measured by Pavlides (1994), range from .7045 to .7048.

The Gretna, VA body of the Leatherwood pluton, description in Appendix B, has

a 206Pb/238U age of 441 ± 8 Ma (Appendix F, figure e). The error ellipse marked with an

x on figure 6e may reflect inheritance in the pluton, but inclusion of the data point does

not change the 206Pb/238U age of the pluton. Inherited components were discovered

during analysis, and ranged from 1200 to 1400 Ma (Appendix G, figure c). The sample

analyzed from this body contains 63% SiO2, which is less than the average value for the

Leatherwood samples from the Martinsville, VA area. Values of all other major

elements, except K2O, are consistently higher than the Martinsville area samples. Initial

strontium isotopic values for the sample from the Gretna, VA body range from 0.7067 to

0.7074, with an average of 0.7070

The Leatherwood pluton, sampled in Martinsville, VA, description in Appendix

B, has a 206Pb/238U age of 444 ± 9 Ma (Appendix F, figure g), which is younger than the

values obtained by Sinha et al. (1989) of 516 Ma by U/Pb TIMS method of zircon, and

that of 462 ± 28 by whole rock Rb/Sr dating by Kish (1997). Samples from the

Leatherwood of the Martinsville, VA area, range in SiO2 values from approximately 68

to nearly 80 percent. Overall, the major elements, except K2O, show a general decrease

with increasing SiO2. Initial Strontium isotopic values for the Leatherwood range from

.7058 (Kish, 1997) to .7062 (Allison et al., 1984) to .7070 measured during this study.

The Melrose pluton, description in Appendix B, has a 206Pb/238U age of 442 ± 8

Ma (Appendix F, figure h), which is younger than the U/Pb TIMS age of 515 Ma given

by Sinha et al. (1989). The 515 Ma age may be a mixed age representing multigrain

homogenization of the magmatic age of 442 Ma, and ages of inheritance (~1100Ma)

found during this study (see Appendix G, figure d). The chemical analysis of the

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Melrose pluton can be seen in table 1. The initial strontium isotopic value measured

during this study for the Melrose pluton is .7071.

The Poore Creek and Green Spring plutons, description in Appendix B, have a

combined 206Pb/238U age of 448 ± 3 Ma (Appendix F, figure i). Zircon populations used

from both plutons give us this age. More analyses need to be done to see if there is any

difference in ages between the mafic and felsic units. Zircons from the felsic Poore

Creek pluton showed inherited components of approximately 1200 and 1400 Ma (see

Appendix G, figure e). Samples from the Green Springs pluton show a general decrease

in percentages of major elements with an increase of silica. Exceptions to this are K2O

and Na2O. The Poore Creek pluton shows a general increase in major elements with an

increase in silica. Initial strontium isotopic ratios performed during this study yield

values of .7050 for the Green Springs pluton, and .7061 for the Poore Creek pluton.

The Rich Acres pluton, description in Appendix B, have a combined 206Pb/238U

age of 430 ± 7 Ma (Appendix F, figure j). Samples from the Rich Acres show a decrease

in FeO, MgO, MnO, and CaO, and an increase in K2O, TiO2, Na2O and P2O5, with

increasing Silica. Measured values of the Rich Acres pluton range from .7045 to .7065

(Kish, 1997), and are in agreement with values measured during this study of .7050.

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Appendix D: The following (from USGS “Tools for creation of formal metadata,” http://geology.usgs.gov/tools/metadata/tools/doc/ctc/) is a general approach to creating metadata. Data in Italics are metadata relating to a bulk rock geochemical analysis from sample JRW-00-E1.

1. What does the data set describe? a. What is the title of the data set?

Bulk rock geochemical analysis of sample JRW-00-E1 b. What geographic area does the data set cover?

Latitude: 38°04’21” N, Longitude: 77°55’37”W c. Does the data set describe conditions during a particular time period?

Sample collected April 15, 2000 d. Is this a digital map or remote-sensing image, or something different like

tabular data? Tabular data

e. How does the data set represent geographic features? 1. How are geographic features stored in the data set?

Geographic features are stored as points in Sample localities theme

2. What coordinate system is used to represent geographic features? Decimal Degrees

f. How does the data set describe geographic features? 1. What are the types of features present?

Features present include bulk geochemical analysis from sample

2. For each feature, what attributes of these features are described? Attributes described as elements

3. What sort of values does each attribute hold? Concentration of element

4. For measured attributes, what are the units of measure, resolution of the measurements, frequency of the measurements in time, and estimated accuracy of the measurements?

Concentration of element in % or ppm 2. Who produced the data set?

a. Who created the data set? 1. Formal authors of the published work

John R. Wilson 2. Compilers and editors who converted the work to digital form

John R. Wilson 3. Technical specialists who did some of the processing but aren't

listed as formal authors Adrienne I. Rittau, ICP Technical Manager, Activation Laboratories

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4. Cooperators, collaborators, funding agencies, and other contributors who deserve mention

A.K. Sinha: Funding VPI&SU Graduate Student Assembly: Funding

b. To whom should users address questions about the data? John R. Wilson

3. Why was the data set created? a. What were the objectives of the research that resulted in this data set?

Describing the geochemistry of plutons within the western Piedmont and Blue Ridge Provinces of Virginia

b. What objectives are served by presenting the data in digital form? Quick access, easy use in geochemical modeling programs (such as Geochemists Workbench, and Igpet, and ability to query as spatial data

c. How do you recommend that the data be used? Data for use with geospatially referenced sample location, to analyze Ellisville pluton

d. Are you concerned that nonspecialists might misinterpret the data? If so, of what aspects of the data set should they be especially wary?

Error analysis 4. How was the data set created?

a. From what previous works were the data drawn? 1. Are the source data original observations made by the authors and

their cooperators? Yes

2. Were parts of the data previously packaged in a publication or distributed informally?

No 3. Were the source data published?

No 4. Were the source data compiled at a particular scale?

Bulk rock scale 5. What time period do the source data represent?

1999-2001 6. What information was obtained from each data source?

Geochemistry b. How were the data generated, processed, and modified?

1. How were the data collected, handled, or processed? Data collected by ICP and ICPMS at Activation Laboratories, Ancaster, Ontario Canada

2. For this activity did you use data from some other source? Additional data sources include standard values data, and detection limit values (see list at end of this table)from Activation Laboratories

3. Did this activity generate an intermediate data product that stands on its own?

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No 4. When did this processing occur?

March 27, 2001 5. Did someone other than the formal authors do the data processing?

Yes, Adrienne I. Rittau, and D. D’Anna, Activation Laboratories

c. What similar or related data should the user be aware of? Data from additional samples not collected by John Wilson

5. How reliable are the data; what problems remain in the data set? a. What can you say about the accuracy of the observations?

Data accuracy checked by randomized multiple analysis b. How accurately are the geographic locations known?

Accuracy within NMAS limits (±) 50 feet c. If data vary in depth or height, how accurately is vertical position known?

Vertical position not measured d. Where are the gaps in the data? What is missing there?

None e. Do the observations mean the same thing throughout the data set?

No, some in values in %, and some in ppm 6. How can someone get a copy of the data set?

a. Are there legal restrictions on access or use of the data? None

b. Who distributes the data? VPI&SU

c. What is the distributor's name or number for this data set? John R. Wilson, PITLAB, Department of Geological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

d. As a distributor, what legal disclaimers do you want users to read? Proper Citation: Wilson, John R., 2001, U/Pb Zircon Ages of Plutons from the Central Appalachians and GIS-Based assessment of Plutons with Comments on Regional Tectonic Significance, MS. Thesis, Virginia Polytechnic Institute and State University, Blacksburg, VA.

e. How can people download or order the data? 1. In what formats are the data available?

Available through PITLAB GIS data-server 2. Can users download the data from the network?

Yes 3. Can users get the data on disk or tape?

No 4. Is there a fee to get the data?

No 5. How long will it take to get the data?

Available, 2002 f. What hardware or software do people need in order to use the data set?

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Geochemical plotting software and GIS application of their choice g. Will these data be available for only a limited time?

No 7. Who wrote the metadata?

a. When were the metadata last modified? September 01, 2001

b. Has this metadata record been reviewed or will it be reviewed in the future?

Review occurred September 01, 2001 c. Who wrote the metadata?

John R. Wilson d. To what standard are the metadata intended to conform?

USGS Federal Geographic Data Committee standards

e. If you specified any clock times in the metadata, did you use local time, GMT, or something else?

N/A f. Are there legal restrictions on who can get or use the metadata?

No List showing detection limits for Elements at Activation Laboratories.

Element Detection Limit

SiO2 0.01% TiO2 0.001% Al2O3 0.01% Fe2O3 0.01% MnO 0.001% MgO 0.01% CaO 0.01% Na2O 0.01% K2O 0.01% P2O5 0.01% LOI 0.01%

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Appendix E, Figures A-K: Bacskatter SEM images of zircons used in U/Pb SIMS

analyses. Scale bars are present on individual photos. Zircons of interest are in center of

image. Parts of zircons seen on edges of images are from other plutons.

84

Appendix E:

A: Zircons From Buckingham Pluton (Felsic Unit)

85

B: Zircons from Buckingham Pluton (Mafic)

86

C: Zircons from Diana Mills Pluton

87

D: Zircons from Ellisville Pluton

88

E: Zircons from Leatherwood Pluton (Gretna)

89

F: Zircons from Green Springs Pluton

90

G: Zircons from Lahore Pluton

91

H: Zircons from Leatherwood Pluton (Martinsville)

92

I: Zircons from Melrose Pluton

93

J: Zircons from Poore Creek Pluton

94

K: Zircons from Rich Acres Pluton

95

Appendix F Figures a-j: 206Pb/238U vs 207Pb/235U Concordia plots for ages of plutons.

Insets are weighted averages of 206Pb/238U age. Ages calculated using Isoplot EX, of

Ludwig, 1999.

96

97

98

99

100

101

Appendix G, Figures A-E: 206Pb/238U vs 207Pb/235U Concordia plots showing inheritance

seen in plutons.

102

Figure A:

103

Figure B:

104

Figure C:

105

Figure D:

106

Figure E:

107

John Robert Wilson DOB: August 16, 1977

Laboratory Coordinator 434 McCartney Street, Apt. 2F Department of Geology and Environmental Geosciences Easton, PA 18042 Lafayette College (610) 438-3086 (Home) 116 Van Wickle Hall wilsonj@lafayette.edu Easton, PA 18042 (610) 330-5197 (Work)

Education: 1999-Present M.S. Geology

Thesis Title: GIS-Based Assessment of Plutons and their Attributes with Comments on Their Regional Tectonic Significance

Virginia Polytechnic Institute and State University Advisor: Dr. A. K. Sinha 1999 Iowa State University Geological Field Camp Big Horn Basin, Shell, Wyoming 1995-1999 B.S. Geology

University of New Hampshire Advisors: Dr. Jo Laird, Dr. Wallace Bothner

Employment: 2001-Present Laboratory Coordinator, Department of Geology, Lafayette College 1999-2001 Laboratory Instructor (Physical Geology) VPI&SU 1999 Laboratory Instructor (Environmental Geology) UNH 1996-1999 Wilderness Instructor, (Sea Kayaking and Winter Backpacking) BSA

Achievements, Awards, Scholarships: 2000 Virginia Tech Graduate Research Development Program (VT) 2000 Department of Geological Sciences Teaching Excellence (VT) 1999 Capitol Mineral Club Field Camp Scholarship (UNH) 1999 Tech Alumni Achievement Award (UNH) 1998-1999 Robert Carroll Kimball Scholarship (UNH) 1998 Movers and Shakers Award (UNH) 1997-1999 Who’s Who Among American Universities and Colleges (UNH) 1994 Eagle Scout Award, Daniel Webster Council, Boy Scouts of America Summary of M.S. Research: Research program integrating field and laboratory analysis of plutons within Virginia. A Geographic Information System is being utilized to geospatially record information on mineralogic, geochemical, isotopic and structural data. Data from the research area will become useful for studies of crustal scale orogenesis. Analytical Skills: Field mapping, surveying, sample description, collection and processing skills. Material characterization by hand sample description, as well as optical

108

microscopy, and secondary electron microscopy, thermal ionization and secondary ion mass spectrometry. Geochemical analysis and interpretation of materials. Database analysis and interpretation through Geographic Information Systems (GIS). Publications: Wilson, John R., and Sinha, A. K., 2001, A petrologic and Geochronologic Database of

Plutons for Studying the 4-D evolution of Continents: A GIS Based Geoinformatics Program, Geological Society of America National Meeting, Boston, Massachusetts.

Sinha, A. K., Wilson, J. R., and Jerden, J. L. Jr., 2001, Collisional Tectonics: Correlation

Between Nature and Duration of Magmatism and Pre-Collisional Geometry of the Continental Margin, Geological Society of America Northeastern Meeting, Burlington, Vermont, A-68, 139.

Wilson, John R., Sinha, A. K., and Jerden, J. L. Jr., 2000, A digital map of the central

and southern Appalachians: spatial and temporal distributions of plutons associated with collisional tectonics and their geochemical signatures, Geological Society of America, Abstracts with Programs (Southeast Section Meeting), v. 32, no. 2, p. A-84.

Henika, William S., Beard, James, Tracy, Robert, and Wilson, John R., 2000, Structure

and tectonics and field trip to the eastern Blue Ridge and western Piedmont near Martinsville, Virginia, Virginia Minerals, v. 46, n. 3. pp. 31.

Professional Society Memberships: Geological Society of America National Eagle Scout Association

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