By Robert O. Castle , J. Christopher Hepburn , and Joseph ... · PDF fileDSd DSp Jrd Ong Ons...
Transcript of By Robert O. Castle , J. Christopher Hepburn , and Joseph ... · PDF fileDSd DSp Jrd Ong Ons...
?
?
?
?
?
?
?
?
?
?
?
A
A'
SOmb
Sap
Sabg
Sam
SOmb
SOmba
DSd
Ong
SOmba
Sag
Pcm(?)
Otb
Ons
Sag
Sab
Sab
Ssbh
Ssb
Ons
Ons
Ong
Sap
Ons
Ssbh
Ong
Ong
Ong
Ssd
Ons
Ons
Jrd
DSp
Ong
DSp
0
75
7070
85
75
5960
80
31
25
10
84
15
82
80
7085
8570
64
70
75
85
68
7075
78
75
85
30
6050
65
7080
8544
82
7050
82
75
80
40
35
71
68
62
4048
72
38
32
45
34
45
7035
62
1540
4733
15
45
25
65
65
32
25
68
55
50
19
25
25
20
4536
38
45
3030
52
25
17
5665
75
75
70
42
64
70
75
70
SOmb
Sam
Sabg
Sap
Sap
SOmb
CLINTON - NEWBURY FAULT ZONE
DRAFT IN REVIEW
Zone of sheared rocks (? denotes uncertainty as to degree of shearing in Sap)
Location approximate
Lithologic Contacts
Bedrock Exposure
Individual Outcrop Areas of abundant outcrops or shallow bedrock
(within 10 ft (3 m) of surface)
Faults
Contact, location generally approximate
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50
Structural Symbols
Strike and dip of dominant foliation / vertical foliation (includes mylonitic foliation). Compositional layering generally parallels foliation in stratified rocks
Planar Features
Linear Features
Strike and dip of axial plane of minor fold
Strike and dip of cleavage
Trend and plunge of mineral lineation
Antiformal axis, location inferred
Synformal axis, location inferred
EXPLANATION OF MAP SYMBOLS
Only faults traceable at map-scale and on surface are shown
Strike and dip of bedding
Strike and dip of overturned bedding
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Approximate strike and dip of heavily deformedfoliation / vertical deformed foliation
Mine or bedrock quarry
A'500 ft
-500
-1000
-1500
-2000
sea level
CLIN
TON
- NEW
BURY
FAU
LT
ZONE
MER
RIM
AC
K B
ELT
NA
SHO
BA
TER
RA
NE
Sha
wsh
een
Riv
er
Mar
ricm
ac R
iver
Law
renc
eA
ndov
er
Spi
cket
t Riv
er
Spickett River
Met
huen
Law
renc
e
New
Ham
pshi
reM
assa
chus
etts
A200 m
-200
-400
-600
sea level
SOmb
SOmbSOmba
SOmba
Pcm(?)
SamSap
Sab
Ons
EXPLANATION OF LITHOLOGIC UNITS
MERRIMACK BELT
Metasedimentary Rocks
Coal Mine Brook Formation (?)
Dark blue-gray, prominently foliated, highly contorted, very fine-grained, graphite-bearing carbonaceous phyllite. Existence uncertain as exposure has been covered or destroyed.
Merrimack Group (Silurian or Ordovician following Lyons and others, 1997)
Berwick Formation
Light-gray to purplish-gray beds from cms. to 1 meter thick of calcareous metasiltstone, biotite-feldspar-quartz granofels, impure quartzite and metasiltstone interbedded with lesser amounts of thin-bedded dark-gray micaceous phyllite, schist and impure quartzite.
Berwick Fm., Actinolitic granofels
Light-gray to light-greenish-gray, massive, actinolite-bearing calcareous granofels and quartzite; commonly more calcareous than SOmb.
Igneous Rocks
Dracut Diorite
Medium- to coarse-grained, generally massive, black to light-gray, greenish to brown weathering, sulfide-bearing, hornblende-pyroxene-plagioclase diorite and gabbro. More foliated tonalitic varieties exist near the contact with the Berwick Fm. Sulfides are scattered throughout the mapped area and locally concentrated at Nickel Mine Hill. Locally intensely sheared and altered.
Pegmatite
Areas north of the Merrimack River where coarse-grained, white to light-gray muscovite-quartz-alkali-feldspar pegmatite is common.
NASHOBA TERRANE
Metasedimentary and Metavolcanic Rocks
Tadmuck Brook Schist
South of the Clinton-Newbury Fault. Well foliated, rusty weathering, dark-gray to silvery-gray mica schist, phyllite and phyllonite (?). Locally contains amphibolite interlayers.
Nashoba Formation
Nashoba Fm., Biotite gneiss
Gray to dark-gray, medium-grained paragneiss. Biotite-quartz-feldspar gneiss predominates with lesser amounts of interlayered biotite-rich schist, amphibolite, calc-silicate granofels, gray sillimanite-bearing mica schist and quartzo-feldspathic granofels or gneiss. Interlayering takes place on all scales from a few cm. to tens of meters. Included within the mapped Nashoba Fm. are small bodies, lenses and sheets of pegmatite and granite. Migmatitic granite veins and lenses are locally abundant.
Nashoba Fm., Schist
Fine- to medium-grained, well foliated, commonly rusty-brown weathering, gray to silvery-gray quartz-mica schist that may contain biotite, garnet and/or sillimanite.
Igneous Rocks
Diabase
Fine-grained, massive, dark-gray to black diabase composed chiefly of plagioclase and pyroxene and their alteration products.
Andover Granite
Andover Granite, pegmatite facies
Medium to extreamly coarse-grained, massive, white to light-gray pegmatite and monzogranite. Composed mainly of microcline, plagioclase, quartz and muscovite. Biotite occurs locally and garnet is a common accessory. Broad areas underlain entirely by pegmatite.
Andover Granite, binary granite facies
Medium-grained, massive to weakly foliated, white to light-gray monzogranite composed mainly of plagioclase, quartz, muscovite and biotite with accessory garnet. Pegmatites too small to map separately are locally prominent.
Andover Granite, fine-grained granite-gneiss facies
Fine- to medium-grained, generally prominently foliated, light-gray to white monzogranite-gneiss.
Andover Granite, biotite granite-gneiss facies
Chiefly coarse-grained, weakly foliated, light-gray monzogranite-gneiss composed mainly of microcline, plagioclase, quartz, biotite and muscovite with accessory garnet. Cross-cut locally by pegmatite and diabase dikes.
Andover Granite, muscovite granite-gneiss facies
Chiefly coarse-grained, faintly to prominently foliated, white monzogranite-gneiss composed chiefly of microcline, plagioclase, quartz and muscovite. Biotite and garnet are accessory. Cross-cut locally by pegmatite and diabase dikes.
Sharpners Pond Tonalite
Sharpners Pond Tonalite, hornblende diorite facies
Medium- to coarse-grained, massive, medium-gray to black hornblende diorite and tonalite composed mainly of plagioclase and hornblende with variable by small amounts of quartz. Biotite only locally composes as much as 10% of the rock. Principal accessories include magnetite, sphene and apatite.
Sharpners Pond Tonalite, biotite-hornblende tonalite facies
Medium-grained, massive to weakly foliated, medium to dark-gray biotite tonalite composed mainly of plagioclase, hornblende, quartz and biotite.
DSd
DSp
Jrd
Ong
Ons
Otb
Pcm
Sab
Sabg
Sag
Sam
Sap
SOmb
SOmba
Ssbh
Ssd
Folded pegmatite veins in the actinolite facies of the Berwick Formation (Smba)
Strongly foliated Andover muscovite-granite gneiss immediatelysouth of the Clinton-Newbury Fault Zone
Jurassic diabase (Jrd) cross-cutting Andover muscovite-granite gneiss
Fine- to medium-grained binary Andover granite (Sab)
Sill of pegmatitic Andover granite (Sap) intruding biotite-hornblende tonalite facies of Sharpners Pond tonalite.
OFFICE OF THE MASSACHUSETTS STATE GEOLOGISTUNIVERSITY OF MASSACHUSETTS
1:25,000 scale topographic base scanned from U.S. Geological Survey, 1966 (photorevised 1979)Polyconic projection. 1927 North American DatumDigitally reprojected to 1983 North American Datum, 1:24,000 scale10,000 foot grid ticks based on Massachusetts state plane coordinate system, mainland zone
Bedrock geology by R.O. Castle (1951-1952, 1992).Updated and revised by J.C. Hepburn and J.P. Kopera (2004). Digitized by J.P. Kopera (2005).
Prepared in cooperation with the COMMONWEALTH OF MASSACHUSETTS
STATE GEOLOGISTBEDROCK GEOLOGIC MAP
LAWRENCE QUADRANGLE, MASSACHUSETTSv. 1.0
Stratigraphic correlation chart accompanies map
This manuscript is submitted for publication with the understanding that the United States Government is authorized to reproduce and distribute reprints for government use.
This research was supported by U.S. Geological Survey, National Cooperative Geologic Mapping Program, under assistance Award No. 04HQAG0028. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.
Citation:Castle, R.O, Hepburn, J.C., and Kopera, J.P., Bedrock geologic map of the Lawrence quadrangle, Massachusetts, v 1.0, Massachusetts Geologic Survey (4th), (in review, April 2005)
Note: This manuscript is currently undergoing peer review, and is not a final version.
Affiliations:
1United States Geological Survey Menlo Park, CA2Department of Geology and Geophysics Boston College Chestnut Hill, MA, 02467
3Corresponding Author: Office of the Massachusetts State Geologist Department of Geosciences University of Massachusetts, Amherst, MA 01003 [email protected]
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QUADRANGLE LOCATION
BEDROCK GEOLOGIC MAP OF THE LAWRENCE QUADRANGLE, MASSACHUSETTSBy
Robert O. Castle1, J. Christopher Hepburn2, and Joseph P. Kopera3
2005 (in review)