CONTACT METAMORPHISM OF THE LUCERNE PLUTON HANCOCK CO. , MAINE
by
Steven W. Novak
Thesis submitted to the Graduate Faculty of the
Virginia Polytechnic Institute and State University
in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE
in
Geological Sciences
APPROVED:
D. R. Wones, Chairman
M. C. Gilbert D. A. Hewitt
March~ 1979
Blacksburg, Virginia
ACKNOWLEDGMENTS
It is an honor to acknowledge the help and support of my
advisor, David R. Wones, whose detailed mapping of this area
formed the basis of this study. Critical reviews by my advisory
committee, D. A. Hewitt and M. C. Gilbert, have also greatly
improved the manuscript. Fellow students and
provided help with a critical review and many
informal discussions. Thanks to
on the microprobe and especially to
and
for instruction
for drafting
for photo-figures. The help of
graphy and for typing is also appreciated. Last
but not least, I thank my wife
standing during this study.
for her support and under-
Financial support was provided by a grant from the research
divisi.on of VPI & SU and N.S.F. Grant EAR 78-03655 to David R.
Wanes.
i
TABLE OF CONTENTS
INTRODUCTION AND PURPOSE OF STUDY.
GEOLOGIC SETTING • • • • • • • • •
PETROGRAPHY OF LOW GRADE BUCKSPORT FORMATION
MINERAL CHANGES IN THE BUCKSPORT FORMATION •
MINERAL CHANGES IN THE PENOBSCOT FORMATION •
MINERAL CHEMISTRY. • • • • • • • • • • •
INTENSIVE VARIABLES DURING METAMORPHISM.
Pressure During Metamorphism. • •
Temperatures During Metamorphism.
FLUID COMPOSITIONS DURING METAMORPHISM
MINERAL ZONING IN THE BUCKSPORT FORMATION ••
CONCLUSIONS. •
REFERENCES .
APPENDIX I .
APPENDIX II.
APPENDIX.III .
VITA ••••
Page
1
2
. . . . . . . . . • • . 21
23
31
35
. ..
• • • • • 56
56
65
• • • • 6 7
• • • • •· 74
• • • • 79
81
86
91
92
• 109
INTRODUCTION AND PURPOSE OF STUDY
The Lucerne pluton is a coarse, seriate biotite.-bearing p1uton
located in Hancock County, Maine. It intrudes several structurally
distinct, fault-bounded blocks containing lower paleozoic metamorphic
rocks. The pluton is located on the northeast limit of regional
biotite grade metamorphism in Maine and probably represents a
transitional area between the deeper erosional levels of central
Maine and the shallower low grade,terranes of northeastern Maine (Doyle
and Hussey, 1967; Thompson and Norton, 1968). This study char-
acterizes the mineral assemblages of the Silurian-Devonian?
Bucksport formation and the Ordovician-Silurian? Penobscot formation
within the Lucerne's contact aureole in order to determine the
conditions of emplacement of the pluton. The Bucksport formation,
which is thought by Wbnes (1976) to be equivalent to the Vassalboro
formation is a calcareous turbidite. The study area is similar to that
investigated by Ferry (1976a,b) of the metamorphic aureole in the
Vassalboro formation in contact with the Togus plutons. However, the
area of the Lucerne pluton is not affected by the higher grade regional
metamorphism of central Maine, nor is late stage hydrothermal alteration
and important aspect of the Lucerne pluton. Petrographic observations
combined with microprobe analyses of minerals from the contact aureole
allow an estimate of pressure during intrusion and a temperature gradient
within the aureole. This information provides an initial estimate of
the evolution of H2o-co2 fluids in the Bucksport formation and H2o rich
fluids in the Penobscot formation during contact metamorphism.
1
GEOLOGIC SETTING
Recent ideas on the geologic evolution of central and eastern
Maine are given by Osberg (1974) and Pankiwskyj and others (1976).
Stewart and Wanes (1976) review the geology of the Penobscot bay
area that includes the Lucerne pluton. The study area (fig. 1)
includes the Coastal Volcanic Belt of eastern Maine and the south-
east limb of the Marrimack synclinorium (Pankiwskyj and others, 1976).
The Lucerne intrudes three and possibly four structural blocks,
each with its own stratigraphic section (fig. 1). From north to
south respectively, these are: the Waterville-Vassalboro block,
the Passagassawakeag-Bucksport block, the Penobscot block, and.
the Castine-Ellsworth or Coastal Volcanic block. Each block is
separated from adjacent blocks by faults or unconf ormities and each
has its own characteristic sequence of formations (Wones, 1976).
1he Waterville-Vassalboro block lies north of the Lucerne and contains
the area of Buchan metamorphism studied by Osberg (1968, 1971, 1974)
and Ferry (1976a,b, 1978). Chlorite grade Vassalboro formation
found in this block is separated from biotite grade Vassalboro of
the adjacent Passagassawakeag-Bucksport block by the Norumbega fault.
This major strike-slip fault may extend to New Brunswick and truncates
the north end of the Lucerne pluton (Wones and Stewart, 1976).
If Wanes (1976) is correct, the Waterville-Vassalboro and Passagassa-
wakeag-Bucksport blocks are equivalent so the Norumbega fault is
confined within one large structural block. Since the Noru.mbega fault
cuts the Lucerne, the pluton probably intruded both the Waterville-
Vassalboro and Passagassawakeag blocks, however, the Lucerne has not
2
3
Figure 1. Geologic map of the Lucerne pluton and surroundings. Sampling of the aureole was from the Vassalboro (Bucksport) and Penobscot formations.
N
M\20t ~ 6i:l'35 '
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44°55' -
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I
\ GEOLOGY OF
THE LUCERNE PLUTON HANCOCK COUNTY, MAINE
DAVID R. WONE S 1979
)~ CONGLOMERATE S , Pt) $ T M IO - u E. 110NIAN
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D WALLAMATOGUS PL U T(J N
D WAL LA MATOGLJ S PLU T\J N ' PORPHYRIT IC FA CI E "
D BLU E HILL PLUTON
~ SOUTH PENOBSCO T PLUTON
D PARK S PONi) MONZ GN I T E
D VASSALBORO t B u ci-: s Po RT l r o RMAT 10 N
D H'!' BRI OIZEO Z0 NE . PENOB SCO T PL US GRAN I T IC DI KES
~ PENOBSC O T FOR '1A T 10N
t<~~-j ELL S WORTH FORMAT ION
~ COPELA ND FORMATI ON , ~ RIDER B L UFF MEMBER
D CO PELAND FOR M AT IO "
IO M.les ~ PAS SAGASSAWAKEA G GNE I SS, 1--~-1.~~_...~~-"-~~.._~_. ~ MIXER PONC MEMBE R
~ PA SSAGA SSA WA KEA G GNE I SS
5
Figure la. Locations of samples of the Bucksport formation from the Orono quadrangle. All samples preceded by prefix OND.
7
\
Figure lb. Locations of samples of the Bucksport formation from the northwest.corner of the Orland quadrangle. All samples preceded by the prefix ORB. Samples 101-1 through 101-13 collected by D. R. Wones, all others collected by S. Novak.
9
Figure le. Locations of samples of the Bucksport formation from the southwest corner of the Orland quadrangle. All sample numbers preceded by the prefix ORC.
11
Figure ld. Locations of samples of the Penobscot formation from the Ellsworth quadrangle. All sample numbers have the prefix ELA. Sample ELA 13b is 5 km north of Greenwood cemetery along Route 180.
13
been identified north of the fault. South of the Norumbega fa.ult is
the Passagassawakeag-Bucksport block which extends to the contact of
the Vassalboro (Bucksport) with the Penobscot formation. This block
contains rocks ranging from pre-Cambrian to Devonian age and also
contains the portion of the ~ucksport (=Vassalboro). formation that
has been thermally metamorphosed by the Lucerne pluton. To the
south of the Passagassawakeag-Bucksport block, the Lucerne has also
intruded the Penobscot block that extends from the Bucksport (=Vassal-
boro)-Penobscot contact to the Turtle Head fault. This block contains
the Ordovician-Silurian? Pen.obscot formation that has also been
metamorphosed by the Lucerne pluton. The Bucksport-Penobscot contact
has been interpreted by Wanes (1976) as an unconformity but may be a
fault since chlorite-biotite grade rocks of the Bucksport formation
are in contact with andalusite-cordierite rocks of the Penobscot
formation. Ludman (1978) has demonstrated that this contact is a
reverse fault to the Northeast of the Lucerne, but Ruitenberg and
Ludman (1978) interpret it as an unconformity in New Brunswick. South
of the Penobscot block is the Castine-Ellsworth or Coastal Volcanic
block. The boundary between these two blocks is the Turtle Head fault
zone which places andalusite-cordierite grade Penobscot formation against
biotite grade Ellsworth formation.
The number of faults in the area indicates a complex structural
history with faulting occurring at several different times. The Turtle
Head fault zone extends southwest from the southern end of the Lucerne
pluton and was active from upper Silurian-lower Devonian through middle
Devonian time (Wanes, 1976). This fault zone is a major northeast
14
trending strike slip zone and may have been utilized as a zone .,of weak-
ness intruded by the Lucerne and other major plutons found to the east
(Wones, 1976). The northeast trending Norumbega fault zone is also
a major strike slip fault, and as it truncates the Lucerne it must .be
younger than the Turtle Head fault zone. The Norumbega has been traced I
from Winterport to the Grartd Lake area northeast of the Lucerne, with
a minimum of 25 km of right-lateral displacement (Wones and Stewart,
1976). Similar strike slip faults have been mapped on strike in
eastern Maine and western New Brunswick (Larrabee, 1965; Van de Poll,
1973; Ludman, 1978)~ If these faults are the northeast extension of
the Norumbega, 25 km of right-lateral ·motion is also suggested in
Mississippian rocks near Fredricton, New Brunswick. A smaller post
intrusional fault which may be equivalent to the Sunnyside fault in
the Belfas.t area (Bickel, 1976) cuts the Lucerne within the Passagassa-
wakeag-Bucksport structural block. It is a vertical fault with both
vertical and horizontal displacements. Thrust faults have been
mapped to the southwest of the Lucerne in the Rockland area (Osberg
and Guidotti, 1974). This faulting has affected rocks that appear
to be correlative with the Penobscot formation near the Lucerne
(Ordovician-Silurian?). No available evidence indicates thrust
faulting of the Penobscot formation near the Lucerne, but this
cannot be ruled out. However, the present distribution of later
sediments (Bucksport = Vassalboro) and the structural blocks surround-
ing the Lucerne appear to be due to the action of strike~slip
faulting along the Turtle Head and Norumbega fault zones (Wones
and Stewart, 1976).
15
Recumbent folding and thrust faulting figure prominently ina
plate tectonic model proposed for eastern central Maine by Osberg
(1975, 1978). In this model, collision of continental plates in
early Devonian time caused abduction of a Siluro-Devonian turbidite
sequence with the formation of large nappes and east dipping thrust
faults. Continued compression caused thickening of the crust in this
vicinity and produced plutonism and regional metamorphism during the
middle Devonian. The model is proposed to explain the large recumbent
folds and thrust faults in central and western New England. However,
no firm evidence for major recumbent folding or thrusting involving
the Vassalboro has been found in the vicinity of the Lucerne pluton.
There is a long history of deformation in the rocks surrounding
the Lucerne pluton. The Passagassawakeag gneiss was deformed during
the pre-Cambrian (Stewart and Wones, 1974; Bickel, 1976). Cambrian
and Ordovician sediments of the Copeland, Ellsworth, and Penobscot
formations that uncomf ormably overlie the Passagassawakeag were
deformed prior to the deposition of the Buckspo_rt formation. Refolded
folds found in these formations are not observed in the Bucksport.
A later large-scale fold, the Liberty-Orrington anticline, is responsi-
ble for· the map pattern of pre-Cambrian and Cambre-Ordovician rocks
in the Penobscot block. The plunging nose of this fold is exposed
to the west of the Lucerne pluton. This major northeast trending
anticline is one of several mapped in east-central Maine and was
probably produced during the lower Devonian. A later post Lucerne
folding has produced small scale open folds in the Bucksport
(=Vassalboro). These folds strike Nl5E to N25E and· their axial
16
parallel to the intrusive contact of the Lucerne. Most of the
foliation observed in the pluton also is subparallel to this strike.
In the calcareous rocks of the Bucksport formation, com.-
positional layering may reflect original bedding. However, most of
the observed layering was formed by calcareous material transposed
from bedding. The transposed layers are nearly vertical and parallel
to the axial planes of the small scale folds striking N25E (see fig.
17). Compositional bands in the calc-silicate gneiss of the contact
aureole also have this strike and dip. Similar transposition of
bedding has been reported from the calcareous rocks of ,the Flume
Ridge formation, though to be correlative with the Bucksport forma-
tion, to the northeast of the Lucerne (Ludman, 1978). Near the contact
of the Lucerne, whitish veins of zoisite are found at the center of
some of the calc-silicate layers. These veins may be beds that were
originally calcite rich due to transposition of calcareous material.
Thermal metamorphism has produced the abundant zoisite. Alternatively,
these veins could be equivalent to quartz-calcite veins found outside
the thermal aureole. Where deformation of low grade rocks has taken
place, e.g., near the Norumbega fault zone, these veins are stretched
and boudinaged into thin discontinous layers. These small characteris-
tics are found in the whitish veins within the thermal aureole of
the Lucerne.
Several metamorphic events have been noted in the rocks surround-
ing the Lucerne pluton. The earliest is metamorphism of the pre-Cambrian
Passagassawakeag gneiss. This formation was metamorphosed to silli-
manite grade prior to deposition of the Cambrian Copeland formation.
17
Figure 17. Sketch of outcrop showing transposed bedding in the Bucksport formation. Original bedding is shown by theisoclinly folded layer angling from upper right to lower left across the page. Transposed layering is shown by the nearly straight layers running from upper left to lower right. These layers parallel the axial planes of folds in original bedding. Width of outcrop perpendicular to trans ... posed layering is approximately 2 meters. Outcrop is located along Route 1 approximately 900 meters northwest of East Holden.
I I
'! I /JI / ; 1J I / 11
'111111 I I I
J J
18
OUTCROP SKETCH SHOWING TRANSPOSED BEDDING
LOCATED 900 M NW OF EAST HOLDEN
19
A later metamorphism affected the Ellsworth formation, in the coastal
Volcanic block to the southeast of the study area. Metamorphosed
fragments of the Ellsworth formation (Cambra-Ordovician) are found
at the unconformity within the Castine volcanics (Silurian). This
dates the metamorphism at Cambre-Ordovician to mid-Silurian (Stewart
and Wanes, 1974). Metamorphism of the Penobscot formation to c.ordi-
erite-andalusite grade could have taken place at any time between
the Ordovician and early to mid-Devonian. The metamorphic event
that produced the chlorite-biotite grade rocks in the Vassalboro
formation must be post-Silurian (Wanes, 1976). The Parks Pond
Monzonite metamorphosed the Bucksport formation prior to the in-
trusion of the Lucerne pluton. Sampling of the Lucerne aureole was
more than 3 km from the exposed monzonite so that superposed meta-
morphism should not have affected the samples. However, the position
of the Parks Pond prior to the intrusion of the Lucerne is unknown.
The hybridized zone southeast of the Lucerne contains inclusions of
material similar to the Parks Pond Monzonite. This indicates the
monzonite contact could have been close to the western edge of the
Lucerne, so may have affected the Bucksport formation in this area.
Textural evidence in the Bucksport indicates only one metamorphic
event, however. No reaction rims, overgrowths, psedumorphs or other
signs of multiple metamorphism were observed in any of the Bucksport
samples.
A series of granitic plutons intrude the various structural blocks
surrounding the Lucerne pluton. Isotopic ages for most of the plutons
are 375 ± 25 my in age (Brookins, 1976) and at present the concordance
20
and precision of these ages cannot be used to establish an intrusion
sequence. However, geologic evidence can be used to construct an in-
trusive history. The oldest dated intrusive is the Stricklen Ridge
pluton, a pegmatitic body within a pre-Devonian migmatite terrane.
The next older appear to be the Wallamatogus and South Penobscot
plutons to the south of the Lucerne. Both are cut by the Lucerne.
The Wallamatogus pluton contains garnet, sillimanite and muscovite and
appears to have crystallized at a somewhat deeper level than the
surrounding plutons. The Mt. Waldo pluton to the west of the Lucerne
is inferred to be younger than the Wallamatogus since it intrudes
and metamorphoses the Siluro-Devonian Bucksport (=Vassalboro)
formation while the Wallamatogus is confined to the older rocks of
the Penobscot block. On the northwest, the Lucerne also intrudes
the dike-like Parks Pond Monzonite. The relationship of this body
to the other surrounding plutons is unknown, however, it intrudes
and metamorphoses the Bucksport formation. Thus the Lucerne pluton
appears to be the youngest intrusive body in this area, except for a
single basaltic dike observed on the western edge of the pluton.
The Lucerne pluton is a large (20 x 60 km), biotite-bearing,
granitic pluton (Wones, 1976). It consists of coarse, tabular
potassium feldspar phenocrysts, some with viborgitic texture, in a
seriate groundmass of plagioclase, alkali feldspar, and quartz.
Biotite is the predominate maf ic phase and ilmenite is the common
oxide. A few grains of tourmaline have been observed. These mafic
minerals make up about 8% of the rock. The white alkali feldspar
and plagioclase give the rock its very light color. All of the
21
observed contacts except for the Norumbega fault are intrusive
and quite sharp. Geophysical studies indicate sharp, essentially
vertical contacts for the pluton (Sweeney, 1972). At the north end
of the pluton, a porphyritic f acies is developed in the core of the
pluton. It consists of coarse alkali feldspar, plagioclase, quartz,
and medium-grained biotite in a groundmass of mediumigrained quartz,
plagioclase, alkali feldspar, and fine-grained biotite. Miarolitic
cavities are found in this facies. A few small aplitic dikes intrude
the pluton and the country rock.
PETROGRAPHY OF LOW GRADE BUCKSPORT FORMATION
The Bucksport formation is a calcareous, quartzofeldspathic
. pelite interbedded with a highly phyllitic, rusty weathering pelite.
This formation is uniform over large areas in the sense that these
two rock types are present in roughly the same proportions and
appearance. The pelite is generally less than 30% of any given out-
crop. The Bucksport in the vicinity of the Lucerne pluton is thought
to be correlative with the Vassalboro, Kellyland, and Flume Ridge
formations found at various locations in eastern Maine, but may not
be correlative with the Bucksport as mapped by Bickel in the Belfast
area (Osberg, 1968, Larrabee, 1965; Ludman, 1978; Bickel, 1976; Wanes,
1976).
Outside of the contact metamorphic aureole, 70-80% of the
Bucksport consists of a massive, grey to green schist composed mainly
of quartz, calcite, and albite with smaller amounts of muscovite,
biotite, and chlorite. Tourmaline, apatite, and ilmenite occur as
accessory minerals. Randomly spaced laminations .5 -2mm in width are
22
common and are caused by higher concentrations of calcite and lesser
amounts of phyllosilicates. These layers weather to a lighter
greenish brown color giving the rock a distinctive striped appearance
in weathered outcrops. The calcite rich layers apparently represent
original bedding features and have been folded into small scale open
folds with the axial planes striking N25E. Grain sizes in these rocks
is uniform and quite fine (<.l-.3mm). Isolated larger grains of
muscovite are found scattered through the rock and are probably
detrital, although muscovite is also present in elongate stringers
interleaved with chlorite. Some of the detrital muscovite grains are
kinked. Biotite is found in varying amounts and may be absent from
samples of thin section size. 'It is always associated with muscovite
and chlorite. A moderately well defined schistosity is formed by
intergranular stringers of muscovite, chlorite and ~iotite with the
long axes of quartz grains parallel as well.
Approximately 20-30% of the Bucksport formation consists of finely
laminated beds composed primarily of muscovite with some quartz,
plagioclase, and pyrite. Beds of calcareous material may be several
meters thick while the pelite beds are less than a meter thick. The
grain size is extremely fine (<.Olmm) and the rocks have a highly
crinkled and well developed schistosity. The quartz and feldspar are
generally found in layers that parallel the schistosity and are
probably the result of metamorphic segregationrather than original
bedding. In hand specimen these rocks are shiny greenish grey to
black with a very irregular surface due to breakage along the
schistosity. These beds are rusty weathering because of the presence
23
of pyrite.
MINERAL CHANGES IN THE BUCKSPORT FORMATION
Near the contact of the Lucerne pluton, a distinctive series
of mineral changes is observed within the rocks of the Bucksport
formation. In the field, the massive grey calcareous schists and
phyllites are recrystallized to banded calc-silicate gneiss with
pelitic interbeds. The calc-silicate layers assume a grey to greenish
grey cast due to the presence of actinolite and diopside while the
pelitic material appears purplish due to the larger amounts of biotite.
Concurrently, the amount of calcite in the rocks decreases markedly
as shown by the lack of reaction with HCl. Bedding in the low grade
metamorphics (strike N25E) gives way to thicker compositional banding
that dips 80-90 degrees and strikes N30E, subparallel to the igneous
contact. These layers, while related to original bedding, are mainly
the result of metamorphic differentiation.
The lowest grade assemblage observed in the Bucksport formation
is: quartz + calcite + albite + chlorite +muscovite + biotite +
ilmenite + tourmaline. With increasing grade, muscovite and chlorite
disappear, biotite increases and the plagioclase changes composition
to about An30. In thin section, biotite occurs between chlorite
and muscovite in the presence of calcite, albite, and quartz. This
·type of assemblage may be the result of a reaction such as:
Muscovite + Calcite + Quartz + Chlorite = Biotite + Anorthite + H20 + co2 (1)
5KA13si3o10 (OH) + 8Caco3 + 7Si02 + 3Mg5Al2si3o10 (0H) 8 = 5KMg3Alsi3o10 (OH) 2 + 8CaA12si2o8 + 12H20
24
(Crawford, 1966; Chatterjee, 1971; Ferry, 1976a). The modal
percentages of muscovite and chorite are not equal and it is
probable that muscovite is consumed first. In two samples a.t this
grade, coexisting plagioclases of different composition were observed.
In the lower grade sample, ,the plagioclase compositions (An0-1 vs
An30-33) are consistent with those proposed for the peristerite
solvus as observed in metamorphic rocks (Crawford, 1966; Jones, 1972).
In the higher grade sample that contains actinolite without diopside,
plagioclase near An40 coexists with albite. This is indicative of
disequilibrium as large detrital albites persist to this grade. No
coexisting plagioclases were observed at higher grade.
With increasing grade, calcic amphibole forms along with a very
small amount of potassium feldspar. Textural existence indicates the
amphibole forms at the expense of biotite by the reaction:
Biotite + Calcite + Quartz =
Ca Amphibole + K"<"·feldspar + H2o + co2 (2)
5KMg3AlSi3o10 (0H) 2 + 6CaC03 + 24Si0 2 =
3Ca2Mg5Si8022(0H)2 + 5KA1Si308 + 6C02 + 2H20
(Hewitt, 1975). Compositions of coexisting biotite, calcic amphibole,
and potassium feldspar plotted on a diagram with coordinates FeO,
MgO, and K20 (fig. 2) show three phase triangles shifted as a result
of differing conditions of formation. Very little potassium feldspar
was found associated with the products of this reaction and most of
that was identified during microprobe examination. The potassium
feldspar that was present occurs as extremely fine intergrowths with
plagioclase. This lack of feldspar may be due to the relative mobility
25
Figure 2. Compositions of coexisting actinolites (open figures) biotites (closed figures) and alkali feldspar co-existing with calcite and quartz. All samples from the Bucksport formation. Each point was plotted on the basis of FeO + MgO + K4o.= 100%. The approximate order of increasing grade is: OND lllb, ORA 24, ORC 27, ORC 23, ORA 2la. Increasing Fe in the biotite and actinolite indicates an Fe-Mg exchange reaction.
26
LU ~
w :i 0
~ ~ ~ ~ 0 0 iii cl
ORA 210 • 0 ORA 24 • 0
ORC 27 • A
ONO lllb • 0 ORC 23 • 0
BIOTITES
MgO
27
of K2o in the metamorphic fluid. Vidale (1969) shows that potassium
feldspar from calc-silicate bands in regionally metamorphosed lime-
stones is concentrated in associated pelite beds. Large concentrations
of feldspar were not observed in the pelitic layers of the Bucksport
formation. The potassium feldspar may have reacted with chlorite
in the pelitic layers to produce the abundant biotite found throughout
the aureole. In addition, circulating fluids could have carried some
feldspar components out of the system. Some amphibole may have been
produced by reaction of excess chlorite with calcite in the calcareous
beds (Ferry, 1976a). This could not be verified texturally in the
Bucksport formation.
Above the grade at which amphibole is formed, zoisite is stable
in all calc-silicate assemblages. The zoisite coexists with plagio-
clase, calcite, or both, so it appears to be the result of the reaction:
Anorthite + Ca~cite + H20 = Zoisite + C02
3CaAlzSi208 + CaC03 + HzO = 2Ca2Al3Si3012(0H) + co2
(3)
Most frequently the zoisite is found in an extremely fine grained
mixture of calcite plus quartz. In some samples, whitish veins are
at the center of calc-silicate bands that consist of larger grains
of diopside, quartz, and sphene in a groundmass of fine zoisite. The
textural relationship suggest that the zoisite has replaced the
plagioclase of the groundmass outside the vein. Varying amounts of
calcite may remain in these veins. The whitish veins probably
represent thin calcite and plagioclase rich layers originally formed
during transposition of bedding. With higher temperature conditions,
calcite has reacted with the anorthite rich plagioclase to form
28
zoisite. Zoisite can also form as a product of the reaction of
amphibole to diopside since aluminum present in the amphibole is
not found in the pyroxene (Hewitt, 1973a).
At the highest grade within the aureole, the greenish calc-
silicate bands consist of small rounded diopside grains associated
with plagioclase (An90), quartz, sphene, zoisite, and calcite. Some
of these grains retain the elongate habit of the repalced amphibole
and, in transitional zones on the edges of calc-silicate bands, clearly
replace amphibole. The production of diopside is probably the result
of the commonly deduced reaction:
Ca Amphibole + Calcite + Quartz =
Diopside (+ Zoisite) + H20 + co2 (4)
Ca2Mg5si8o22 (0H) 2 + 3Caco3 + 2Si02 = 5CaMgSi2o6 + H20 + 3C02
(Skippen, 1974, Slaughter, Kerrick and Wall, 1975). A diagram with
coordinates FeO, MgO, and Al2o3 (fig. 3) shows the compositions of
coexisting actinolite, diopside, and zoisite. The amphibole in this
area is slightly aluminous actinolite (Leake, 1978). Upon reaction
of the amphibole to diopside, the aluminium probably reacts to form
the small isolated zoisite grains frequently associated with diopside,
or anorthite component, depending on the composition of the metamorphic
fluid present. Some of the larger diopside grains show well developed
lamellae that may be due to exsolution or twinning. Small isolated
zoisite grains are usually associated with rounded and well crystalized
hematite, suggesting a moderately oxidizing environment.
29
Figure 3. Compositions of coexisting diopsides (triangles), actinolites (squares) and zoisites (circles) from two samples in the Bucksport formation. Each point plotted on the basis of FeO + MgO + Al 2o3 = 100%. The variation in zoisite composition is actually due to Fe2o3.
.)0
Al 20 3 ~
ZOISITES ~~
•
ZOISITE ACTIHOLITE OIOPSIOE ONO 2e • • • ORA 210 ° 0 6
Co.I ACTINOLITES
• .c. .t. •
A~--= .. ::.....:~~~'--~--Y-~~-¥-~~--~---MgO FeOL----lL----...¥.-------~
31
The purple biotite schists that occur interbedded with the calc-
silicates uniformly consist of biotite + plagioclase + quartz + pyrite
in varying proportions, with apatite a common accessory. Immediately
at the granite contact, one sc;i.mple contains small rounded grains of
corundum in a biotite-plagioclase schist and probably represents a
muscovite-rich quartz-poor bed. Corundum was probably produced from
the dehydration of muscovite through the reaction:
Muscovite = Corundum + K-feldspar + H2o
KA13Si3o10(0H) 2 + A12o3 + KA1Si3o8 + 2H20
MINERAL CHANGES IN THE PENOBSCOT FORMATION
(5)
Mineralogical changes in the Penobscot formation within the
thermal aureole of the Lucerne are less obvious than in the Bucksport
formation. The extensive reconstitution visible in the Bucksport is
not as well developed. Layering on the scale of l-5cm may be bedding
and is mainly due to variation in the proportions of micas to quartz
and feldspar. This layering, while not as strongly affected by the
Lucerne as in the Bucksport formation, is strongly folded in some areas.
The lowest grade assemblage observed is biotite + muscovite +
quartz + plagioclase + andalusite + cordierite + pyrrhotite. This
assemblage was formed during earlier (regional) metamorphism of the
~Penobscot formation and may be related to the intrusion of the
Wallamatogus pluton. Andalusite is the stable aluminosilicate through-
out the formation. Cordierite is fauna both with and without anda-
lusite in rocks of suitable bulk composition throughout the aureole.
Compositions of coexisting cordierite, biotite, and andalusite are
plotted in figure 4. Near the contact, symplectites of muscovite +
32
Figure 4. Compositions of coexisting cordierite (filled symbols) and biotite (open symbols) in equilibrium with anda-lusite, muscovite, and quartz. This diagram is a projection through muscovite.
34
quartz become more and more connnon until nearly all of the muscovite
has been consumed. Andalusite is commonly found as small rounded
grains within the mixture indicating the reaction:
Muscovite + Quartz = Andalusite + K-f eldspar + H2o (6)
KA13s13o10 (0H) 2 + Al 2Si05 + KA1Si308
Potassium feldspar is very common in rocks at higher grade. At the
contact, one thin bed shows rounded and embayed grains of corundum
with rims of muscovite in a matrix of biotite and plagioclase. This
bed lacks potassium feldspar and quartz and there is a thin zone in
the adjacent bed where potassium feldspar is depleted. The texture
suggests the muscovite is forming from the retrograde reaction:
Corundum + K-feldspar + H2o = Muscovite
Both of the samples from the Bucksport and Penobscot formations
that contain corundum occur directly at the contact with the Lucerne.
The restricted occurrence indicates that corundum formed as a prograde
mineral due to thermal effects of the intrusion. The beds that formed
corundum were probably phyllitic with a very high percentage of
muscovite and very little quartz. For this reason, muscovite survived
to high enough grade to react:
Muscovite = Corundum + K-feldspar + H2o (5)
In the Penobscot sample enough K-feldspar was present to allow the
retrograde reaction to occur producing the muscovite rims. In
contrast, insufficient K-feldspar remained in the Bucksport sample
to produce the retrograde reaction.
Pyrrhotite is the dominant sulfide in the high grade Penobscot
formation and is abundant in some samples. Graphite is also present
35
in both high and low grade samples. Reaction of pyrite to form
pyrrhotite in the presence of graphite probably involves Fe-Mg
silicates through such reactions as:
Chlorite + Pyrite + Graphite =
Pyrrhotite + Aluminosilicate + Quartz + co2 + H20
or
Biot'ite + Pyrite + Graphite =
(7)
K-feldspar + Pyrrhotite + Quartz + C02 + H20 (8)
Garnet is notably absent from the Penobscot formation. This is
apparently due to reactions such as the above causing an effective
change in bulk composition of the silicate assemblages. Iron in-
corporated by the pyrrhotite might shift the bulk composition to the
Mg-rich side of the biotite-aluminosilicate tie line, thus giving
the assemblage biotite + cordierite + aluminosilicate (fig. 4).
Textural evidence for this reaction occurs in sample ELA8 where
embayed pyrite grains are rimmed by pyrrhotite. It is also possible
that the original bulk composition of the Penobscot formation may
have been too magnesian for the formation of garnet.
MINERAL CHEMISTRY
Maximum information about the intensive variables during meta-
morphism requires determination of the chemical compositions of the
coexisting minerals. Microprobe analyses are used to explore the
variations for a given mineral group as well as variations between
groups. Mineral analyses were performed on an automated ARL-SEMQ
microprobe with an accelerating voltage of 15kv and beam current of
36
lOua. Nine major element analyses were made with a 10 sec. count
time using natural silicate and sulfide mineral standards. Data
reduction followed the method of Bence and Albee (1968) with correction
factors from Albee and Ray (1970). Mineral analyses were recalculated
by computer using the programs of Rucklidge (1972) and Goff and
Czamanske (1972) for amphiboles. Each reported mineral analysis
represents single analyses with totals of 100+2 weight percent that
best fulfill the stoichometry.
A plot of Fe vs. Mg per formula unit (fig. 5) for the ferro-
magnesian minerals of the Bucksport formation shows a generally
similar Fe/Mg ratio for biotite, diopside, and some chlorites. This
is evidently due to the fact that the Fe/Mg ratio of the precursor
minerals exerts some control on the Fe/Mg ratio in the higher grade
minerals. The overall Fe/Mg ratio probably reflects accurately the
original bulk composition of the sediment that formed the Bucksport
formation. While some of the amphlboles have similar Fe/Mg, there is
clearly a greater variation than in any of the other minerals.
Amphiboles coexisting with diopside have Fe/Mg similar to other minerals
while those coexisting with biotite and chlorite have wide Fe/Mg
variation. At least some of the Fe/Mg variation in the amphiboles
of the Bucksport formation can be attributed to Fe/Mg variation in
chlorite. In addition, an amphibole forming reaction apparently
proceeds at somewhat higher grade than the biotite forming reaction.
That is, once muscovite is consumed by the formation of biotite,
excess chlorite reacts with calcite to form amphibole. This is
consistent with observations by Ferry (1976a) although textural
37
Figure 5. Plots of total Fe per formula unit against total Mg per formula unit for minerals in the Bucksport and Penobscot formations. All diopsides, chlorites and actinolites are from the Bucksport formation. All cordierites are from the Penobscot formation. Patterned areas repre-sent different samples and show variation within individual samples. The line drawn through the mineral groupings show the similarity in Fe/Mg for the minerals and probably reflects the bulk Fe/Mg of the Bucksport forma-tion. This line is for reference only and is not a re-gression line.
3 I '
I I
SLOPE =
0.795 ~
/ +
-·-c :::> c 3
2 E '-
00 ~
M
'-Q)
a. Q
) LL -0 +
-
~
0 I
2 3
4
Total Mg per Form
ula Unit
39
evidence in the Bucksport formation is lacking. Formation of biotites
with the restricted Fe/Mg observed would tend to leave Mg enriched
chlorites. These chlorites would then react with calcite to form
amphiboles higher in Mg than those formed froinbiotite. Chlorites
coexisting with.amphibole are more magnesian than those without
amphibole. For comparison, cordierites and biotites of the Penobscot
formation are also plotted in fig. 5. Both of these show a much more
limited Mg c.ontent than the Bucksport minerals and there is also a
less well developed correlation of sympathetic Fe-Mg variation.
The chemical variation of the amphiboles as a group was investi-
gated to see what, if any, substitutions were occurring that might
affect the variation of Fe/Mg. Site assignments for the amphiboles
were calculated with the program of Goff and Czamanske (1972) with
the Fe+3 estimated using the method of Ferry (1976b). Amphiboles
from the Bucksport formation are actinolites (Leake, 1978). Coupled
substitutions possible in amphiboles have been outlined by Robinson
and others (1971) and Czamanske and Wones (1973). Czamanske and
Wones point out that calculated site assignments are sensitive to
assigned Fe+3 , but that the trends shown by site substitutions
would not be significantly affected by errors here.
A plot of AlIV vs FeVI (fig. 6) shows that changes in Fe
content take place without affecting Al1v. A plot of Mg+ Si vs Al IV
+ AlVI (fig. 7) shows an excellent linear correlation suggesting that
the tschermakite substitution is causing variation in tetrahedral
Al. The edenite substitution is also causing . . . Al IV variation in
shown by a IV total A site occupancy (fig. 8). content as plot of Al vs
40
Figure 6. Plot of tetrahedral Al vs octahedral Fe for amphiboles in the Bucksport formation. Open circles represent sample ORC 27. Changes in oct. Fe occur without affecting octahedral Fe.
-<t
1.0 0
0.8
0.6 •
0.4
0.2 • • •
41
0
• • •
• •
• •
0-----------------'-------------------1.0 1.2 1.4 1.6 1.8 2.0 Fen
42
Figure 7. Plot of octahedral plus tetrahedral Al vs octahedral Mg plus tetrahedral Si for Bucksport amphiboles. Open circles represent sample ORC 27.
43
1.0
0 0.8
N 0.6 0
·~ -<.t 0 + 0.4 • P1 •• '· <( ••
0.2 • • •
0 ---""----..L..----1 5.0 5.5
Mg·:iI.+ S iN/ 2
44
Figure 8. Plot of tetrahedral Al vs total A site occupancy for Bucksport amphiholes. Open circles represent sample ORC 27. The line is drawn for reference only to show a 1:1 slope.
46
The 1:1 slope of this line indicates that there is little coupling
of other substitutions that would affect tetrahedral Al content.
The intercept near .2 AlIV indicates that some other substitution
IV i.e. tschermakite, is operating producing an excess of Al •
There is a slight excess of total Al over AlIV as shown by the
AlIV vs total Al plot (fig. 9). This indicates the major tschermakite
substitution is:
Fe(III)IV + AlVI =Mg + Si
but there is also a slight amount of the substitution:
AlIV + AlVI =Mg+ Si.
This coupling identifies these amphiboles as hastingsitic (Czamanske
and Wones, 1973).
Biotite is another commonly occurring mineral in both the Bucksport
and Penobscot formations. As the Fe/Mg plot (fig. 5) shows, there is
much less variation of biotite composition than for amphiboles. The
Penobscot biotites show a higher Fe/Mg probably reflecting differing
bulk compositions between the two formations. The major variations
in chemistry expected in the biotites is substitution of AlIV + AlVI
for R +2 + Si. A plot of Al IV vs Fe (fig. 10) shows that biotites from
the Bucksport formation lie along a line with a slope of one
indicating that this substitution is producing variation in aluminum
content. Since Fe+3 was not determined the effect of this omission is
not known. Biotites from the Penobscot formation also show a
relationship between AlIV and Fe, but the slope for this line
indicates 4Fe = lAl. Charge balance would have to be made up by
additional substitutions possibly involving Fe(III) or Ti, however,
4.7
Figure 9. Plot of tetrahedral Al vs total Al for Bucksport amphiboles. Open circles represent sample ORC 27. The line is drawn for references only to show a 1:1 slope.
-I 0
0
0 .. I\)
0 . ~
0 c,,
i! ,.. 9 CD
l> -· . 0
. I\)
. en
0
48
Al :m: 0 0 0 0 . . . . . I\) 0
0
0
49
Figure 10. Plot of tetrahedral Al vs octahedral Fe for biotites in the Bucksport and Penobscot formations. Closed circles are Bucksport biotites and open circles are Penobscot biotites. The Bucksport biotites lie along a line with a 1/1 slope indicating a coupled sub-stitution between octahedral and tetrahedral sites. The Penobscot biotites lie along a line with a slope of 1/4.
o'r 11"1
3.0
I I
I I
I I
I I
I I
I I
I I
I I 0
o PE
NO
BS
CO
T 0
2.8
L •B
UC
KS
PO
RT
•
0 •
0 •
2.6
L 0
• <1 0
0 •
0
I •
• • • •
• • ~ 2.4 ~
• ••
• •
• •
• • <t 2.2 ~
. ' r--
•
2.0 I I
I I
I I
I e
e .I
I ,w
x:d I
' '
' I
1.8 2.0
2.2 2.4
Fe JI 2.6
2.8 3.0
3.2 3,4
51
the lack of Fe(III) determination precludes a solution. No correla-
tion of Ti with any other element was observed.
Analyses of pyroxene for higher grade Bucksport samples show
compositions midway between diopside and hedenbergite. Again, the
Fe/Mg ratio (fig. 5) probably reflects bulk compositional influence.
The main deviation from quadrilateral components is Al which is present
in amounts up to 2.4 wt%. This is due to MgAl-CATS substitution IV (Papike and Cameron, 1976) as shown by a plot of Mg vs Al (fig. 11).
No correlations of AlIV were found with any other major cation and
all other non-quadrilateral components are present in very small
amounts.
Zoisite is commonly found in rocks of the Bucksport formation
that also contain diopside. The compositions range from nearly
pure zoisite up to the beginning of the clinozoisite range of composi-• tion.s (30 mole% epidote component).· Most fall in the compositional
range 0-25 mole% epidote component. A plot of Fe (assumed Fe+3) vs
Al (fig. 12) shows that Fe+3 substitutes directly +3 for Al • Although
no optical zoning was noted in the zoisites, compositions vary somewhat
within grains. One exception to this sample ORB 15, an albite..;..
chlorite-zoisite rock in which small rounded zoisite grains contain
concentric optical zones around a distinctly different core. Energy
dispersive analysis shows that the cores contain cerium while the
outer zones do not. No compositional differences were found between
the optically distinct zones. These grains may represent altered
allanite grains from a highly deformed igneous dike. No compositional
break was observed in the zoisites which agrees with the epidote
52
Figure 11. Plot of tetrahedral Alvs octahedral Mg for pyroxenes from the Bucksport formation. The line has a slope of 1/2. The linear relationship shows substitution of Al in cpx is due to the MgAl-Calcium Tschermakite substitution. The line is for reference only.
54
Figurel2. Plot of octahedral Al vs Fe+3 in zoisites ff_~m the Bucksport formation. All Fe ~~s assumed Fe • The 1:1 relationship indicates Fe substituted directly for Al in zoisites. The line drawn is for reference only.
55
3.0 ~-------_,..... ______ _..,.
2.9
f;:1 2.8
<( 2.7
2.6 1: 1
2.5 ____________________________ --.l
0 0.1 0.3 0~4
56
miscibility gap existing at higher molar epidote compositions
(50-75 mole%; Raith, 1976).
INTENSIVE VARIABLES DURING METAMORPHISM
Pressure During Metamorphism
One of the most important pieces of information about the
geologic history of an intrusion is the depth of crystallization.
The mineralogical data compiled on the assemblages of the contact
aureole allow an estimate of the depth of the present erosional level
during contact metamorphism. Several pieces of information suggest
a relatively low lithostatic pressure during intrusion.
Andalusite is the stable aluminosilicate in the aureole and it
occurs within 15 m of the contact. Therefore, if the temperature
at the contact is known, an upper limit can be placed on the litho-
static pressure. Figure 13 shows the position of the andalusite=
sillimanite curve as determined by Holdaway (1971) with the dashed
curve giving the position determined by Richardson, Gilbert, and Bell
(1968). Recent measurements of the enthalpy of solution for anda-
lusite by Anderson, Newton, and Kleppa (1977) show that the slope for
the andalusite=sillimanite curve is most accurately predicted by
Holdaway. In addition, they point out that the amount of Al-Si
disorder observed in natural sillimanites was accurately predicted
by Holdaway based on his experimental data. ·For these reasons the
lower pressure triple point of Holdaway is preferred, although neither
curve can be positively favored at this time.
The maximum temperature of the contact was the temperature at
which the Lucerne magma was intruded. The solidus temperature is
57
Figure 13. Pressure-Temperature diagram showing some reactions con-sidered in the Bucksport and Penobscot formations. All are plotted for PH20 = Ptotal' Data sources are: Holdaway, 1971; Chatterjee and Johannes, 1974; Hewitt, 1975; Holdaway and Lee, 1977, Richardson, Gilbert and Bell, 1968.
) .'·
-I fT1 3:: -0 rr1 :a ):> -I c ::0 f'Tl .
. --0 (') .......
~ 0 0
(J1 0 0
O') 0 0
-.J 0 0
N
58
P( kb) PH20 = ProT c.,.i . CJ1 O')
59
.·' 0 a minimum of 725 C from two feldspar geothermometry (D.R. Wanes,
personal communication, · 19 78 ):. ; however, the temperature of the
country rock at the contact was probably somewhat less. Cal~
culations by Jaeger (1957, 1959) suggest that the contact temperatures·
are near l00°C less than intrusion temperatures. Therefore, the
occurrence of andalusite restricts the pressure to less than 2000
bars using the Holdaway curve and less than 5000 bars using that of
Richardson, Gilbert, and Bell. Since contact temperatures may be
greater than 600°C, these are maximum pressures.
The occurrence of corundum at the contact in both the Bucksport
and Penobscot formations was probably the result of the reaction:
Muscovite = Corundum + Sanidine + H2o To have andalusite stable with the production of corundum requires
pressures less than 1.4 kb (3.3 using RGB) if P = P H2o total (Chatterjee and Johannes, 1974). However, the presence of pyrite in
the Bucksport formation and pyrrhotite + graphite in the Penobscot
formation indicates PH20 was probably less than Ptotal i.e. ~20 in the fluid was less than one. Calculations by Ohmoto and Kerrick
(1977) show that the maximum ~ 0 in fluids in equilibrium with 2
pyrrhotite + pyrite + graphite is .8 for temperatures near those
asstimed for the contact F0 = QFM). Since sulfur fugadties are 2
small compared to H20 and co2 , the absence of pyrite does not change
the amount of diluting species significantly. If the fluid did have
~ 0 = .7, the production of corundum with andalusite stable would 2
require pressures less than 1.9 kb (4.5 using RGB). Since~ 0 could 2
have been less than .7, the presenc~. of corundum does not limit the
60
possible lithostatic pressure more than the presence of andalusite.
An additional calculation of lithostatic pressure was attempted
using the method and data of Ferry (1976b) and microprobe analyses of
minerals from the Bucksport formation. This method is based on
linear combinations of mineral equilibria modified 'for solid solution
of the phases. The calculati~n yielded a value somewhat les\ than
3kb. Hotvever, the present accuracy of this type of calculation com ...
bined with the inaccurate temperature estimate for the sample gives
this value questionable significance. Ferry (1976b) estimates that
even with accurate temperatures, the method is accurate only to
+900 bars. The calculation does indicate a lithostaticpressure
consistent with the stability of andalusite and corundUm. when referred·
to the aluminosilicate diagram. of Holdaway (1971).
Independent evidence of lithostatic pressure during crystalli ...
zation comes from the porphyritic f acies of the Lucerne. This
rock contains miarolitic cavities indicating water saturation during
crystallization. In addition, the open cavities indicate PH 0 = . 2
P total during late stage crystallization. The temperature during
crystallization of this facies is a minimum of 675-700°c from two
feldspar geothermometry (D.R. Wones, personal communication, 1978).
Using the water saturated granite minimum of Tuttle and Bowen (1958),
these temperatures indicate pH20 during crystallization was 1500 ...
2500 bars. The few aplite dikes that cut the Lucerne were probably
also water saturated during crystallization. Comparison of the
normative data for the aplites (D.R. Wones, personal communication,
·1978) with the water saturated minimum of the Ab ... Or - Qtz system
61
indicates pressures of 500-1000 bars (Tuttle and Bowen, 1958). The
reason for this discrepancy could be alkali exchange of the feldspars
which would give a lower apparent pressure.
The assemblage muscovite + corrierite + biotite + quartz + alumina-
silicate (andalusite) present in the Penobscot formation has been
shown to be a good geobarometer if metamorphic temperatures are known
(Haase and Rutherford, 1975; Holdaway and Lee, 1977). The experimental
data of Haase and Rutherford and Holdaway and Lee along with data
provided by M. Rutherford (personal communication, 1978) are combined
in figure 15. Phase relations in this assemblage are greatly affected
by PH 0 and the diagram is plotted to show the effects of reduced 2
PH 0 • Thus, given that andalusite is stable and that the sample con-2
taining cordierite of composition XFe= .50 is at lower temperature than
the muscovite + quartz reaction temperature, the pressure would be a
maximum of 2.8 kb. If PH 0 is .5 Ptotal' the pressure would be 2.5 kb., 2
and further reductions of PH 0 would give still lower pressure 2
estimates. The pressure estimates apply to the Lucerne only if the
biotite and cordierite equilibrated within the contact aureole. No
cordierite was found nearer to the contact than SOOm and in one sample
nearer than this the cordierite was completely pseudomorphed by a fine
grained mixture of muscovite and chlorite. The calculated temperature
gradient for the Lucerne aureole indicates the samples lie within the
thermal aureole, although at a lower temperature than that indicated
by the biotite-cordierite pairs. The Kd values for the mineral pairs
are systematically related to the contact. Sample ELA 7 has a Kd
of 1. 39 while ELA 8 and ELA 13b has Kd' s of 1. 77 and 1.79 respectively.
62
Figure 15. Pressure-Temperature diagram showing a portion of Figure 13 with equilibria relevant to the Penobscot formation. The andalusite-sillimanite boundary is from Holdaway, 1971. All other curves from Holdaway and Lee, 1977. The shaded areas shows the stability field for Penobscot cordierites.
4
a..
2
63
>>>>: LIMITING CONDITIONS FOR THE ASSEMBLAGE -:·:-:-:-:-:-:-:· MUS+ 810 + AND+ CORO(XFe • .50) + QTZ IN
THE PENOBSCOT FORMATION ~
""
550 600 650
64
The samples closer to the contact have a lower Kd, although the XFe
of cordierites are less well correlated with distance. This dis-
turbance of Kd indicates the compositions of cordierite·-biotite pairs
re-equilibrated within the thermal aureole to reflect the conditions
of crystallization of the Lucerne. Variations in XFe are probably
due to bulk compositional variation or differences in PH 0 • 2
Available evidence of lithostatic pressure during intrusion
of the Lucerne pluton indicates values near 2000 bars with probable
maximum limits of 1000 bars. These values are compatible with both
aluminosilicate curves. Pressures near 3000 bars are unlikely if the
Holdaway diagram accurately represents the stability of andalusite.~
In addition, because feldspar temperatures may represent minimums for
the plutons, the Richardson, Gilbert and Bell diagram also limits
pressures below 3000 bars. If the lower contact temperatures near
625°C are assumed, the Richardson, Gilbert and Bell curve restricts
pressures only to less than 4500 bars.
Those values are lower than the 3-4 kb proposed for regional
metamorphism in central Maine (Osberg, 1968; Ferry, 1976b; Guidotti,
1970). Abbott (1977, 1978) has investigated the petrology of the
Red Beach granite near Calais, Maine and estimated conditions for its
formation. On the basis of a biotite + K-feldspar + magnetite
assemblage, a lithostatic pressure of 270-490 bars was calculated for
the intrusion of this pluton. Associated volcanics thought to be
petrogenetically related to the granite also give support for a very
shallow depth of intrusion. The Lucerne then appears to represent an
intermediate depth between the shallow plutons to the northeast and
65
the deeper intrusions of western and central Maine. This is supported
as well by the regional grade of metamorphism decreasing to the
northeast.
Temperatures During Metamorphism
Given that the lithostatic pressure during intrusion of the
Lucerne was between 1000 and 3000 bars, temperatures reached within
the contact aureole can be estimated. The pressure was probably
constant over the size of the study area although fluid pressures
may not have been equal to total pressure. Again the reactions
referred to are compiled in figure 13. The andalusite = sillimanite
transition provides a temperature maximum if a pressure is assumed.
Thus, given that andalusite is stable, the maximum temperature in
the aureole could be 700°C if a pressure of 1000 bars is assumed but
only 550°C if a pressure of 3000 bars is assumed, using the data
of Holdaway. These values would be 800°C and 720°C respectively
using the Richardson, Gilbert, and Bell curve. Both temperatures
determined by the Holdaway curve are consistent with feldspar
temperatures for the pluton although the lower temperature value
is unlikely. The preferred pressure of 2000 bars gives a temperature
maximum of 625°C which is in good agreement with the idealized values
for contact temperatures calculated by Jaeger (1957, 1959). Given
the possible pressure variation, the temperature range could be +75°C.
For the narrow range of crystallization temperatures indicated by the
Lucerne feldspars (700-750°C, D. R. Wanes, personal connnunication, 0 1978), Jaeger calculated a contact temperature of 512 C based on
66
assumptions of ideal conduction of heat away from an :igneous contact.
Since the rocks of the Bucksport formation were at biotite grade
prior to intrusion, the rocks were already at an elevated temperature.
Preheating of the country r~ck was ~ot taken into account in the
calculations by Jaeger and the additional. amount of heating brings
his calculated value within the estimated temperatures for the
Lucerne aureole.
The occurrence of corundum at the contact due to the reaction of
muscovite also gives an indication of contact temperature. To produce
corundum with andalusite stable requires a temperature of 660°C if
P = P If the value of 2000 bars is assumed for total pressure, H2o total"
production of corundum requires a temperature of 625°C with PH 0 = .77. 2
This agrees well with the assumption of reduced ~ 0 due to the presence 2
pyrrhotite + graphite. Corundum could be produced at lower temperatures
if ~ 0 is reduced still further. This would also be the case if the 2
total pressure was higher.
Approximately 136m (450 ft.) from the contact, muscovite+ quartz
is unstable due to the.reaction: Muscovite + Quartz = Andalusite + K-feldspar + H2o·
The temperature of this reaction is .also highly dependent on fluid
pressure or ~20 • However, both the theoretical calculations and
production of corundum at 2000 bars indicate ~ 0 was less than or 2
equal to .8 in the Penobscot formation. This restricts this reaction
to less than 574°C (Chatterjee and Johanees, 1974). Again, the lower
temperature limit for this reaction would depend on further reduction
of PH 0 or ~ 0 , or a higher total pressure. 2 2
67
The lowest grade Bucksport samples have a temperature maximum
imposed by the assemblage muscovite+ calcite+ quartz (Hewitt, 1973).
This reaction reaches a thermal maximum at XCO = .5. For a total 2
0 pressure of 2000 bars, this .reaction occurs at 475 C or less depending
on fluid composition. The low grade muscovites in the Bucksport for~
mation have a significant celadonite component. This reduces the
activity of muscovite in the mica and would cause the reaction to
occur at still lower temperatures. In addition, Ferry (1976b)
indicates that the reaction:
Muscovite + Chlorite + Calcite + Quartz =
Biotite + Anorthite + H2o + co2
occurs at lower temperature than the muscovite + calcite + quartz
reaction. This also indicates the low temperature estimate is
(1)
probably too high. The curves of Jaeger lie within the error brackets
of temperatures estimated for the Lucerne aureole. The curve for the
Lucerne actually lies at somewhat lower temperatures than those cal-
culated by Jaeger at larger distances from the contact. This is
probably due to endothermic reaction occurring within the aureole.
This additional source of heat loss was not taken into account in
the calculations by Jaeger.
FLUID COMPOSITIONS DURING METAMORPHISM
A metamorphic fluid phase was present in both the Penobscot and
Bucksport formations during production of the thermal aureole around
the Lucerne pluton. Abundant evidence of fluids is found throughout
the Bucksport formation where numerous veins containing quartz,
plagioclase, zoisite, and actinolite cut the rocks. Such prominent
68
Figure 16. Estimated temperature gradient for the Lucerne aureole. The solid circles give position of estimated tempera-tures at 2 kb with error brackets estimated. Both the muse + qtz = and + K-feldspar and muse + cc + qtz points are maximum temperatures as indicated by arrows. The two upper curves are calculated gradients from Jaeger (1957).
O'I
\C
650 u
r MUSC = CO
RUNDUM t K
FELDSPAR
~
600 w
0:: ::> ~
550-a:
MU
SC
I
+ Q =A
ND
w
CL ::;?:
500 L + KFE
LDS
PA
R
~· w
I-l
450
Tc = 62
5
18 km thick
Tc = 625 10 km thick
LUC
ER
NE
M
UStC
C+Q
-,
40
0 ....__ _
__
.._---.-&
-__
__
__
_ ...._
_-&
__
_.._ __
__
__
_ _
0 1000
2000 3000
4000
DIS
TAN
CE
FR
OM
C
ON
TAC
T (F
EE
T)
70
veining is not seen in the Penobscot formation, however, dehydration
reactions occurring in the aureole liberate H20 so some form of fluid
must have been present.
The metamorphic fluid present in the calcareous Bucksport
formation is assumed to have been a mixture of H20 and co2 since
prograde reactions give off H2o and co2 in various proportions. In
addition, H2o could be supplied by the Lucerne. ·The fluid composition
of rocks of the Bucksport formation outside the contact aureole could
not be determined. Ferry (1976b) suggests that low grade calcareous
rocks of the Vassalboro formation approximately 100 km west of the
Lucerne have co2 enriched fluids due to reactions at low grade that
produce co2 • However, the amount of dilution by H2o will depend upon
the amount of interbedded pelite reacting to give off H2o alone
(Hewitt, 1973a). Within a larger part of the aureole, the fluid
is clearly H2o rich as indicated by the presence of zoisite (see
figure 14). The zoisite commonly occurs in whitish veins within
calc-silicate bands, however, it is also found as isolate.d grains
throughout some of the high grade calc-silicates. Thus, it is not
limited to obviously H2o rich areas such as quartz veins. While the
exact position of the zoisite curve is in dispute, there is agreement
that H2o rich fluids (ZN rf:-.90) are necessary for its formation 2
(Storee and Nitsch, 1972; Kerrick, 1974). The source of this H2o rich
fluid could be the interbedded pelitic material undergoing dehydration
within the aureole or H2o being released during intrusion of the Lucerne.
During the production of prograde minerals within the aureole,
fluid compositions probably varied greatly between the highly calcareous
71
Figure 14. T-X diagram showing mineral reactions relevant to the Bucksport formation. The diagram is plotted for pfluid = 2000 bars. Data sources: Kerrick, 1977; Greenwood, 1967; Hewitt, 1973b, 1975; Kerrick, 1974.
N
........
-u 0
-700
w 600
0:: :::> ~ er: w
a..
500 ~
w
I-
400 (izo + co2
0 (\J :I: + u u
0
P = 2000 bars
~ /./l?O
•Co~ ·.
Mo~+c~
0.2 0.4
0.6 0.8
1.0
Xco2
73
beds and pelite beds. The calcareous beds had a higher co/H20
than the surrounding pelites because of decarbonation reactions.
The comm.on occurrence of isobaric "univariant" assemblages, such as
biotite + calcite + quartz + actinolite + K-feldspar, indicates
fluids in the calcareous beds were buffered by the calc-silicate
assemblages. In the Bucksport formation, these assemblages are not
truly univariant because of varying Fe/Mg and excess Al, however,
they do buffer the fluid composition. Fluids rich in co2 would explain
why calcite plus quartz survives in the calcareous layers at high
grade. 0 For a contact temperature of 625 C at 2 kb, the fluid would
have to have XCO >.3 (Greenwood, 1967). At some point, H20 rich 2
fluids must have been introduced to produce the abundant zoisite.
Zoisites have lower Fe contents approaching the Lucerne. Kerrick
(1977) shows that increasing Fe in zoisite increases :its stability
in more co2 rich fluids. Thus, it appears that H2o rich fluids
were associated with the intrusion of the Lucerne. These fluids
were released during late stage crystallization of the porphyritic
facies of the Lucerne where there is definite evidence of H2o satu-
ration. Introduction of fluids also produced the abundant veins
found at low grade. This must have occurred after peak metamorphism
at temperatures below the intersection of the Calcite + Quartz =
Wollastonite curve with the Anorthite + Calcite = Zoisite curve
(475°c in the pure system (fig. 13). The late stage deformation
seen in the Lucerne could have been responsible for fracturing of
the rocks, thus allowing access of H20 rich fluids. Abundant
zoisite bearing veins in the Bucksport formation fit with H2o rich
74
fluid circulation during production of the contact aureole. Cal-
culations by Ferry (1976b) indicates that co2 and H20 are by far
the most common fluid species in calcareous pelites at moderate
grade.
Pelitic rocks of the Penobscot formation were also coexisting
with a fluid phase during metamorphism, but of a different nature
than that of the calcareous Bucksport formation. Prograde reactions
in the Penobscot formation produce only H2o; however, the presence of
abundant pyrrhotite and graphite indicate fluid species were of the
C-0-H-S system. Calculations of fluid compositions coexisting with
graphite + pyrrhotite + pyrite at typical metamorphic conditions
show that H2o, co2, and CH4 are the main constituents of the fluid.
The difference between graphite + pyrrhotite + pyrite and graphite +
pyrrhotite is small because of the extremely low fugacities of sulfur
species in the fluid (Ohmoto and Kerrick, 1977). Due to the presence
of co2 and CH4 in the fluid, the maximum XH 0 of the fluid will be 2
.85-.75 at estimated conditions within the aureole (QFM Buffer). This
is essentially the same fluid composition required for the decomposition
of muscovite in the presence of andalusite at 2 kb (~ 0 = .77) 2
(Chatterjee and Johannes, 1974). The amount of dilution of H2o and co2
and CH4 is controlled by oxygen fugacity and shifts of less than one
log unit of oxygen fugacity could produce a change to XH 0= .5. 2
MINERAL ZONING IN THE BUCKSPORT FORMATION
Recrystallization of the Bucksport formation to the banded calc-
silicate gneiss within the contact aureole has probably been the result
75
Figure 18. Tracing of a photo of mineral layers developed in sample OND 2e. Pelite layer is on the left, calcareous layer is on the right. Tracing covers approximately 3 millimeters. Graph below the tracing shows plagio-clase compositions through the layer at the locations given by small spots in the tracing. The dashed vertical lines show the separate zones. The bottom, approximate modes are given for each layer. These are visual estimates only. Potassium feldspar was determined by microprobe.
-z ~ 80 ~ z 0 ... -en 60 0 A. 2 0 u
... en ~ 40 ..J u 0 ~ • ~ 20 t
TRACING
Qtz - 35 Bio - 30 Plag - 19 Op - 1
I
I
76
OF SAMPLE
t t
APPROXIMATE
Qtz - 50 Act - 37 Plag - 10 Ksp - Tr Sph - 2 Op - 1
ONO 2e
t1 t
MODES
63x
t t
Qtz - 34 Plag - 30 Dio - 30 Ksp - Tr Sph - 3 Zo - 2 Cal - Tr Op . - 1
t
( . . '
77
of both mechanical movement of material which produced the calcareous
and non-calcareous beds and thermal metamorphism. Wherever calcareous
layer$ are in contact with pelite layers, a distinct mineral zone is
developed between the two .layers. It consists of coarser actinolite
in a groundmass of quartz and plagioclase with traces of potassium
feldspar and sphene. The actinolites in this zone are coarser than
either the biotite or diopside in the adjacent layers. Layering is
on a very fine scale with the transition occurring over several milli-
meters or less. Figure 18 diagrams a mineral zone in sample OND 2e
for which microprobe data were obtained. The e2ttreme1y fine scale
of layering precludes accurate modes and the given modes represent
visual·estimates only. This zoning is found throughout the
Bucksport formation in rocks that contain diopside. The presence of
An25 plagioclase and lack of muscovite and chlorite in the pelite
indicates reaction 1 has gone to completion. The appearance of
actinolite coincides with a sharp increase in the artorthite content
of plagioclase probably because of excess aluminum released during
reaction of biotite to actinolite. The slight drop in anorthite
content of plagioclase in the diopside bearing zone is probably
due to the presence of zoisite as the result of reaction 3.
The sequence of minerl:lls developed could be caused by an
initial gradient in bulk .composition, with the amount of calcite
decre~ing as the pelite layer is approached. However, the thick-
ness of the zoning is generally constant from sample to sample and
is symmetrically developed on either side of calcareous layers. These
facts suggest compositional control is unlikely although an initial
78
compositional gradient must have been present. Two alternative
methods of producing this type of zoning at pelite-limestone boundar-
ies have been described by Vidale and Hewitt (1973). The first is
that the zones are produced by a co2/H2o gradient between the layers.
Each new mineral zone is produced by crossing an isobaric univariant
curve in T-x space at constant temperature. The zoning developed in
the Bucksport formation is consistent with this model only if the
calcareous layers have a relatively high CO/H2o (.::_. 75).
A second method of producing mineral zones is cation diffusion
(Vidale, 1969, Thompson, 1975). In this case, the mineral zones are
formed by diffusion of calcium out of the calcareous layers and
reciprocal diffusion of other elements into the calcareous layer.
This produces an effective change in bulk composition in the zones
which is responsible for the different assemblages. The sequence
of assemblages in the Bucksport formation is also consistent with
this model. Unfortunately, the scale of layering is so small that
the accurate modes needed to prove changes in bulk composition
cannot be obtained.
CONCLUSIONS
The Lucerne pluton has intruded a series of lower Paleozoic
rocks producing a contact metamorphic aureole about one kilometer
in width. In the Bucksport (=Vassalboro) formation, prograde
minerals are biotite, slightly aluminous actinolite, diopside,
and zoisite. Contact metamorphism also produced andalusite and
corundum. in both the Bucksport and Penobscot formations. The
minerals present in the aureole indicate crystallization of the
pluton at a pressure between 1000 and 3000 bars, equivalent to
3.5 - llkm depth. Crystallization 6f the pluton took place near
750-700°c while temperatures in the aureole ranged from near
600-6S0°c to less than 475°C. Contact metamorphism of the Bucksport
records a complicated history. Initial effects of the intrusion
or pre-intrusion faulting produced vertical calc-silicate banding
in the aureole by shearing and flattening these isoclinally folded
rocks. Calcareous material was transposed parallel to fold axes
forming alternating calcareous and pelite layers. Thermal meta-
morphism produced prograde minerals with the calcareous layers
remaining co2 rich because of fluid buffering by calc~silicate
assemblages. A late stage tectonic event, possibly associated with·.·
the Turtle Head fault zone, produced deformation and foliation
in the Lucerne and surrounding sediments. The rocks of the
aureole were fractured allowing circulation of H20 rich fluids,- .
possibly associated with late stage crystallization of the.porphyritic
facies of the Lucerne. These HzO rich fluids produced· the._ ~wiSite. ·
found near the pluton by reaction of calcite and anorthite~ ·
79
80
The present distribution of structural blocks surrounding the
Lucerne pluton appear to have been the result of strike-slip faulting
along the Turtle Head and Norumbega fault zones. However, thrust
faulting has also been proposed as a means of explaining the structure
of eastern Maine. The areas of western Maine that have unquestionably
been thrust faulted appear to show a somewhat higher pressure meta-
morphism than that estimated for the Lucerne (Ferry, 1976a,b,
Guidotti, 1970). In addition, detailed mapping northeast of the
Lucerne has not revealed major thrusts (Ludman, 1978, Ruitenberg and
Ludman, 1978). The low pressure of intrusion for the Lucerne is
consistent with a model of strike-slip faulting for the region
surrounding the Lucerne. This implies that either the thrust faulting
and recumbent folding observed to the southwest and west of the
Lucerne occurred before deposition of the Vassalboro (=Bucksport)
formation, or that the Vassalboro was involved in thrusting and
was extensively eroded prior to the intrusion of the Lucerne.
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82
Doyle, R. G., and Hussey, A. M. (compilers), 1967, Preliminary geologic map of Maine: Maine Geol. Survey, Augusta, Maine.
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83
Jaeger, J. C., 1957, The temperature in the neighborhood of a cool-ing intrusive sheet: Amer. Jour. Sci. , v.. 255, p. 306-318.
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-----, 1978, A plate tectonic model based on the geology of east-central Maine: Abstracts with programs, Geol. Soc. Am., v. 10, p. 79.
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Stewart, D. B., and Wones, D. R., 1974, Bedrock geology of the Penobscot Bay region: In Osberg, P. H., ed., Geology of east-central and north-central Maine: Univ. of Maine, Orono, p. 223-239.
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---'----, and Stewart, D. B.; 1976, Middle paleozoic regional right lateral. strike slip faults in central coastal Maine: Abstracts with programs, Geol. Soc. Amer., v. 8, p. 304.
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APPENDIX I OBSERVED MINERAL ASSEMBLAGES
Abbreviations Used In Assemblage Table
Act - Actinolite
And - Andalusite
Bio - Biotite
Cal - Calcite
Chl - Chlorite
Cord - Cordierite
Dio - Diopside
Kspar - Potassium feldspar
Mus - Muscovite
Op - Opaques
Flag - Plagioclase
Po - Pyrrhotite
Sph - Sphene
Zo - Zoisite
86
87
Mineral Assemblages in Samples of the Penobscot Formation
Sample II ~ Muse Bio Cord And Kspar Plag Po Chl
ELA 2a A re M A M s EI.f\ 2b A Ac Ms A M M r ELA 2c A Ms M s M Mr ELA 2d A Mc M M M M M ELA 2e A Mc M M M s M ELA 2f A Mc Ms M M A ELA 2g ELA 2h A Mc s s s d ELA 3 M M M Aa M A ELA 4 A M A M A ELA 5 t A M M M s M
ELA 6 s A M Mp M s A ELA 7 M A M Ap M s A ELA 8 g M A M Ap Mp s Mb
ELA 13b g M A A Ap s M
Approximate Limits
A - Abundant 20% M - Moderate 5-20% s - Sparse 5%
a - pseudomorphed b - rims pyrite c - sytnplectitic d - contains chlorit.e + sphene veins e - sparse corundum with muscovite rims g - contains trace graphite p - porphyroblastic r - retrograde $ - sagenitic biotite t - contains trace tourmaline
88
Mtneral Assemblages in Sam:eles from the Bucksport Fomation Orono Quadrangle - MaE la
(
Sample fl gg_ Bio Cal Act Dio Zo Plag Ksp Sph Op Other
OND 2a A A M x Chl-x,t OND 2b A A M Mp Chl-r OND 2c A A x M x. Chl-x OND 2d A A m,n,t OND 2e, 1 A A M A M A s s Si Chl-r,a OND 2£ A A x M s Chl-r OND 2g, 1 A A M s s ? So Si Chl-Sr,a OND 2h A s M A Ax A ? So Si OND 2i, b A A Sx Sx s Sp OND 2j' 1 M M M M M M M Tr Sp OND 2k OND 4, l.A A M x M ? x Sp OND 5, d A A M Mp t,a OND 6 OND 7, b A s s Mp
A - Abundant M - Moderate s = Sparse
a - trace apatite b - coarse quartz veins c - zoisite in whitish veins, concordant d - contains bed of extremely fine grained muscovite + biotite i - ilmenite 1 - layered or zoned calc-silicate bands m - abundant muscovite n - moderate andalusite 0 -· rims ilmenite p - pyrite r· - retrograde Tr - trace t - trace tourmaline x - in crosscutting veins
89
Mineral Assemblages in Samples from the Bucksport Formation Orland Quadrangle - Map lb Sample fl Qtz Bio Cal Act Dio Zo Plag Ksp Sph Op Other -- --ORB 21 A A M Sp ORB 2la, 1 A s s A Mc A s So Si ORB 101-1 A A s M Sp 101-2 A Mx Mx M s Si t,a 101-3, d A A M Mus-Ms, t 101-4 A A M Sp Chl-r,t 101-5 A A M Sp Chl-r,t 101-6 A A M Sp Mus-Ss,t 101-7 A s s M Sr Sp Chl-Mr 101-8 101-9, 1 A A s s s s M Tr s Sp,i a 101-10 M s s M M M s s Si 101-11 A A M Sp Chl-r,t 101-12 A M M M Tr s Si,p a 101-13,1 M A s Sp Mus-M llla, d A s Mp Mus-M lllb A M s M Tr Si,p Chl-Tr ORB 24 A M M M M Tr Si t ORB 22 A M A M Si ORB 9a A s M M Si Chl-M
Mus-S ORB 9b M s Sp Mus-A ORB 1 A M M Si Chl-S A - abundant a - trace apatite M - moderate c - zoisite in whitish veins, concordant s - sparse d - cut by numerous quartz veins
i - ilmenite 1 - layered or zoned calc-silicate bands 0 - rims ilmenite p - pyrite r - retrograde Tr - trace s - symplectite t - trace tourmaline x - in cross cutting veins
90
Mineral Assemblages in Samples from the Bucksport.Formation Orland Quadrangle .~- Map le
Sample II Qtz Bio Cal Act Dia Zo Plag Ksp Sph Op Other
ORC 20, b A s M M s M s So Si,p ORC 20-2 A M M ? Si,p t ORC 20-3 A M s M M s Si t ORC 23 A M s M M ? Sp ORC 24 ORC 25 A s M M Si Mus-S ORC 27 A M M M M s Si t ORC 28 ORC 29 Ad s M M ? So Si,p Chl-r,t ORC 30 A M M M Si,p a ORC 31 Ad A M Si,p Mus-S,t ORC 32 A M s M Si,p t
A - abundant M - moderate s - sparse
a - trace. apatite b cut by veins of qtz + plag + calcite + ?prehnite d - cut by numerous quartz veins i - ilmenite 0 - riws ilmenite p - pyrite r - retrograde t - trace tourmaline
APP
END
IX II
MO
DAL
ANAL
YSIS
OF
BUCK
SPOR
T FO
RMAT
ION
(100
0 PT
S).
ORB
SN
ORA
~2
ORA
2lb
ORA
24
ONC
113b
O
RA
9a
OR
B 10
1-·1
0 ----
----
Qua
rtz
20. 7
1 19
.2
21.3
32
.9
29.2
22
.4
9.6
Pla
gio
clas
e .
29. 5
21
.4
31. 9
15
.3
12.0
1
9.l
36
.5
Cal
cite
34
.3
41.9
5.
0 10
.0
24.9
23
.0
1.6
Ch
lori
te
8.5
7.4
6.5
Mus
covi
te
5.8
5.1
25.7
B
ioti
te
16.5
21
. 8
19.5
2.
0 T
r A
ctin
oli
te
19.6
3L
f. 3
Dio
p sid
e 35
.0
14 ..
1
Sphe
ne
1. 7
3.
4 \D
!-
-' E
pido
te
4.8
Opa
ques
1
.1
0.9
0.2
0.
Lt 1
.8
1.1
0.
3 A
pati
te
Tr
Tou
rmal
ine
0.1
0.
3 K
-fel
df?p
ar
Tr
Tr
?
APPENDIX III ANALYSES OF MINERALS BIOTITES
Si02 Al203 Na20 cao :<:o Ti02 !'!nO FeO MgO H20 SUM
:i<;LA 2a
36 .. 09 21 .. 07
.. 23 ,. 0 5
9.42 2- 26
19 .. 56 7 .. 24 3. 99
100 .. 34
s i 5 .. 42 Al .2 .. 59 Sum Tet 8.00
Al :e '.'L; Mn 'I' i t11-M2
Ca Na K sum .~
1. 1 ~ 2.45 1 .. 6 2
• 06 • 26
5.52
• 01 • 07
1.. 8(} 1,. 38
Penobscot Formation
ELA 13b
35.68 21 .. 86
• 23 .. 12
7.20 2 .. 27
• 19 2 4 .. 14
5,.29 3 .. 99
100 .. 97
5 .. 35 2 .. 65 8 .. 00
1. 22 3. 0 3 1 .• 12 "02 .. 2E
5 .. 71
.02
.. 07 1 .. 38 1 .. 46
ELA 8
33.84 20.55
.. 13 .. 02
8 .. 05 1. 77
• 04 22 .. 90
8. 64 3"" 92
99.86
92
5 .. 17 2 .. 83 8. 0 I)
" 8 7
1.97 • c 1 .. 20
5 .. 97
.JO .04
1. 57 1. 61
ELA 7
34.05 22.66
• 2 1 .os
8. 19 2 .. 28
• 1 0 23 .. 20
7 .. 92 4 .. .J4
102.70
2 .. 9 s 8 ... -JI)
1. 0 1 2 .. 3 8 1.. 75
.. J 1
.25 5 • 9 ('
.. 0 1
.06 1 .. s 5 1 .. 6 2
Si02 Al203 Na20 cao K20 Ti02 t1nO FeO :'!gO H20 Su in
Si Al Su~ Tet
Al :F'e Mg Mn 'i'. ~ ].
:i1~:--:2
Ca ~id
ORA 21a
3g_ 67 16. 41
.. 96 .. 76
8 ... 35 3.92
.. 09 18. 94 8. 18 4. 07
101,. 35
5.84 2. 16 8. 00
"5g 2 .. 33 1.80
• 01 .43
5. 26
.. 12 • 27
1. 57 1. 96
93
BIOTITES
Bucksport Formation
ORC 13
36 .. 64 19 .. 04
• 14 .03
9 .. 18 1. 18
• 15 16. 96 11. 81 3.99
99 .. 12
5.50 2 .. 50 8 .. 00
.86 2 .. 13 2.64
.. 02 • 13
5. 78
.01
.04 1. 7 6 1 .. 80
ORA 21
38 .. 72 15" 21
• 21 .08
9.26 2. 38
.20 17 .. 24 12.70 4.02
10 o .. 0 2
5.77 2.23 8.00
• :.+4 2 .. 15 2 .. 82 .03 .27
s .. 70
• 01 .C6
1 .. 7 6 1 .. 83
OBC 27
37.16 17 .. 82
.. 12
.. 08 8 .. 69 2. 11 .02
17"' 33 12.26
4 .. J 2 99 .. 61
5 ... 54 2 .. 46 8.JO
.67 2'" 16 2.73
.. \) 0 • 2 4
:: •• 3 0
• J 1 .. ·J4
1 .. 6 5 1 .. 7 0
Si02 Al20 3 Na20 cao K20 Ti02 MnO FeO L1g0 H20 Sum
Si Al Sum Tet
Al Fe Mg Mn 'l' . J. 1. M:1-M2
Ca Na K Sum A
ORA 24
36. 78 16. 9 2
... 05 • 06
9. 25 2.00
• 11 18 .. 11 12. 65
3 .. 99 99.92
5. 52 2.48 8.00
• 51 2 .. 27 2.83
a 01 • 23
5.85
• 01 • 02
1. 77 1. 80
94
EIOTITES
Bucksport Formation
OND 111b CRC 23
37.35 17.42
.07 • l 1
8.72 3. 18 .17
17.61 11. 4 2 4.03
100.08
5.56 2. 46 8" ()I)
• 6 1 2. 19 2 ... 53
.. 02
.36 5. 71
.02 .02
1. 6 5 l. 6 9
37.23 , 8. 43
• (15 .20
8'9 52 2.07 .12
17. 52 11,,, 8 4
U,.04 no. 02
5. 52 2 .. 48 8. 00
"'75 2. 17 2. 62 .02 .• 2.3
5.79
.03
.. 0 1 1 .. 6 1 1. 6 6
ORC 20- 3
37. 27 17.69
.05 .06
9.34 1. 77
.. 14 16.99 12 .. 09 4.00
99 .. 40
s .. 5 8 2 .. 4 2 8 ... 00
.70 2 .. 13 2.70
.20 5 .. 75
• J 1 .02
1 .. 7 8 1 .. 81
95
DIO!?SIDES
OND 2e OND 2e ORA 21a 0 F: A 21a ORA 21b 1 2 1 2 2
Si02 51 .. 31 51.42 51. 19 51.74 . 52. 07 Al203 • 41 .62 1 .. 29 1.65 .. 19 Na20 • 11 .13 .. 22 • 1 3 .. 13 Cao 23 .. 28 23 .. 97 22.79 21. 28 23.91 K2C • 03 .02 • 02 .. 05 • 00 Ti02 • 11 .13 .37 • 06 .07 MnO • 57 .so ""'61 .. 57 • 76 FeO 1 ~- 78 13.70 13.25 14.76 14. 67 MgO 9. 37 9.61 9.96 10. 08 8. 54 Sum 99 ... 97 100 .. 10 99.70 100. 32 100. 31+
c: • ~l. 1. 98 1. 9 8 1. 97 1.97 2.00 Al • 02 .02 .03 .03 • 00 Sum :'et 2. 00 2.00 2. 00 2 .. 00 2.JJ
Ca 0'" • J 0 .. 99 .. 94 .37 • 99
Na .01 .. o 1 .02 .. J 1 • 0 1 K • 00 .oo .. 00 .oo ·• 00 Mn • 02. .02 .02 • i) 2 .03 Sum :12 .. 99 1. 02 .. 98 • '3 0 1 .. 0 3
Al .. 00 .. 00 '"02 .. •JS • 0 1 Fe • 48 .• 44 .43 .47 .. 47 ~g • 54 .55 .57 • 57 • 49 Sum M1 1 .. 02 .99 1.02 1. 09 .. 97
96
CORDIEFITES
ELA 13b ELA 8 ELA 7
Si02 47 .. 85 49.29 4 7.10 A 1203 33 .. 02 33 ... 31 34 .. 59 Na20 • 39 • 35 .58 cao • 02 .01 .. 00 K20 ,. 00 .oo .. 00 Ti02 .03 .. 0 3 .04 ~lnO • 61 .. 08 .. 06 FeO 12.74 10 .. 59 11.30 MgO 5 .. 15 6. 46 5. 88 Sum 99.81 100.12 99 .. 55
Si 4.97 5 .. 03 4 .. 87 Al 3 .. 03 2 .. 97 3. 13 Sum I'et .3 .. 00 8.00 8.00
Al 1. 01 1. 0 3 1. c 8 Fe 1. 11 .. 90 .98 Mg • 80 .98 • 9 1 Mn • 05 .01 • 01 ~~a • 08 .07 •• 12 Sum 3.05 3. ') 0 3. oe
Si02 Al203 Na20 cao K20 Ti02 MnO Fe203 .MgO H20 sum
Si Al Sum ~et
Al F e-.+-.J Sum
an Ti Na Ca K 11 q S nm
ORA 2 la
39 .. 12 31. 31
.02 23. 97
.02
.. 03
.. 02 2.75
• 10 1. 9 5
99. 29
3" 0 1 • co
3.01
2. 84 - 16
3 .. 00
.. 00 • 00 • 00
1 .. 97 • 00 • 01
1. 99
ORC 13
38. 93 29.20
.01 23. 67
.03 • 15 .20
4 .. 95 "'15
1 .. 9 3 99 .. 22
3. 02 .00
3 .. 02
2. 67 .29
2. 83
• 0 1 • 0 1 .oo
1 .. 97 .oo .02
2. 0 l
97
ZOISITES
OF.A 211:
37. 77 31 .. 95
.02 23.94
.01
.. 05 • 10
1. 69 •• 07
1.92 97. 52
2.95 • 05
3 .. 00
2 .. 90 "'10
3,. 0 0
.01
.oo - 00
2.01 • 0 !) • 0 1
2 .. 03
OND 2e 1
39.53 31.99
• 28 23 .• 6 8
.06
.01 .• (} 5
2.24 .. 11
1.97 99 .. 92
J.01 11 00
3.01
2 .. 87 .. 13
3.00
.. 00
.oo
.04 1 .. 9 3
• J 1
OND 2e 2
39. 04 30.92
.03 23. 58
• 37 • 02 • 12
4. 27 • 09
1. 9 6 100.40
2. 99 .. 01
3 .. 00
2. 78 • 25
3.03
• 0 1 ~ 00 "00
L 93 .. 04 ... 0 1
1. g9
Si02 Al203 FeO MgO ti no Ti02 cao Na20 K20 Sum
Si Al Sum Tet
Fe Mg N1+M3
Al 'T' • . l. Fe..,+-..J 11 g Fe..,+-, 2 M2
Fe-,+ .,2 Mn Ca M4
Ca Na K Sum A
ORA 210 2
so .. 97 2. 54
18.06 11.92
• 1+0 n 20
12 .. 10 • 33 • 12
95. 6:+
7. 65 • 35
8. Q,J
1. 23 l. 77 3. 00
.. 10 • 02 • 37 .. 83 • 6 2
2.00
.. 05 • 05
1. 9 !J 2.00
• 05 • 10 • 02 • 17
98
AM PHI BOLES
OEA 21b 3
50.54 4. 69
19.20 11. 0 6
.. 43 • 18
11. 66 • 34 .16
98 .. 26
7. 48 .52
8 ... 00
1 .. 21 1 .. 79 3. i) 0
• 29 402 .. 59 .65 .44
2. 00
.. 13
.05 1 .. 8 2 2. 00
.03 • 10 .03 • 16
ORC 27 1
50 .. 7 3 4 .. 98
13. 8 1 14. ~6
.. 29 .26
11 .. 97 .. 53 .. 05
97.0S
7 .. 41 .. 59
8. 00
"fi 8 2. 3 2 3 .. 00
.27 .• 03 .. 63 .83
2.00
.. 14
.04 1. 8 3 2 .. 00
.05
.. 15
.01 • 21
ORC 20-3 ORA 24 2 1
53.06 3 .. 44
12.91 14.91
.. 29 .. 23
11 • 7 9 .. 28 .. 13
97 .. 04
7 .. 6 9 • 31
8.00
.77 2. 23 3 .. 00
• 27 • "0 3 .. 38 .99 .. 34
2.0J
.. 08
.. () 4 1. 3 3 2.00
.oc • () 2 .02 .. 04
52. 10 3.£2
16. 61 13.38
"2 9 • 31
12. 16 • 27 • 09
98 .. 83
7 .. 56 .44
8 .. 00
• g 8 2 .. 02 3.00
• 18 "' I) 3 , 48 • 8 8 "'43
2.00
• 12 .04
1. 3 4 2.00
.. 05
.. 08
.• 0 2 u 15
99
AMP HI BOLES
ORA 24 OND 111 b OND 111 b OBA 21a ORC 23 2 1 2 1
SiC2 53 .. 21 55. 04 54. 96 SC.84 51 .. 46 Al203 3. 44 2. 67 3. 01 4 .. 04 7 .. 25 FeO 12. 51 10.86 1l • .36 17.61 13. 31 MgO 15. 58 16. 71 16. 47 12. 20 13 .. 0 1 ~no • 26 - 49 .. 49 .36 .. 19 Ti02 • 07 .. 23 .26 • 29 • 43 cao 12 .. 19 12.32 11. 91 12.<+4 11. 99 Na20 .. 33 .. 25 .. 28 "36 .. 50 K20 .. 16 • 06 • Cl 6 .24 • 18 Sum 97.75 98 .. 63 98.80 98.38 98.32
Si 7. 65 . 7 .. 76 7. 7 5 7 .. 48 7. 37 ;..1 .35 .;. 24 .. 25 .52 .. 63 Sum 'Tet 8.00 8 .. 00 R.OQ 8.00 8.00
Fe-,+..,2 - 76 .71 .63 1 • 13 .89 Mg 2 .. 24 2. 29 2. 3 7 1.37 2. 11 ~1+[13 3. 00 3 .. 00 3.00 3 .. 00 3. 00
.~l .. 23 .21 .22 • 18 • 60 m' L 1. .. 01 .02 ~03 • 03 ~ 05 Fe..,+-.3 • 2'3 • 16 • 35 .25 - 40 Mg 1. 10 1.23 1.09 .81 .. 6 7 Fe..,+-.2 • 38 .38 a29 .49 • 28 Sur:i 1'12 2 .. 00 2.00 2.00 2 .. 00 2.00
Fe-.+...,2 • 08 .03 .07 .06 .02 Mn • 03 .06 .06 .. J4 • 0:: Ca 1. 88 1. 8 6 1... 80 1. 90 1, 34 Sum M4 2.00 2 .. 00 2. 0 0 2. :)0 2. OJ
Ca • 00 .oo .. 00 .OS .. 00 Na • 08 O" .. ~ • 0 1 .. 10 • 02 K .03 • 0 1 • 0 1 • 05 .03 Sum A • 11 .. 03 •· .02 • 15 .05
100
AM'.?HIBOLES
ORC 23 ORC 23 OND 2e OND 2e 2 1 1 2
Si02 l'1. 80 52 .. 25 51.. 74 50 .. 32 Al203 9 .. 99 5.24 3. f. 7 3.78 :'eO 14 .. 66 13 .. 05 16 .. 24 15.17 ~go 11.75 14 .. 04 12. 38 12 .. 89 11n0 .. 25 • 26 .34 .. 29 Ti02 .53 • 34 .39 • 36 cao 11. 8 5 11. 9 3 11. 8 2 11 ... 76 Na20 • 96 .29 .. 52 .47 K20 ' 17 • 13 .• 33 "'28 Sum 97 .. 96 97.53 97.43 9F ... 32
Si 6. q1 7,. 53 7 .. 62 7 .. 51 Al 1- OJ • 4 7 .. 38 .. 49 Sum ::",~·
~ - L. 8 .. 00 8,. r)O 8.JO 3,.:)0
Fe-.+-.2 • 88 .92 1. 16 .99 ~g 2. 12 2 .. 08 1 .. 84 2.01 111+1'13 3. 00 3 .. 00 3 .. 00 3.00
Al .. 6.3 .43 .25 • l8 Ti • 06 .04 .. 04 .04 Fe,+-.3 ,._65 • 18 .27 '• 50 ~g 0 43 .. 94 .88 • 8 f. .Fe-.+-.2 .. 18 .. 4 2 - 56 4 ": . ... Sum ~12 2. 00 2.00 2 .. 00 2.00
Na .04 .07 .08 .. J 0 fe-.+-.2 • 08 .05 .01 • 10 Mn .. () 3 .03 .. o.:+ .04 Ca 1. 8 5 1. 8 4 1.86 1. 8 (i Su rn "14 2.00 2. 00 2 .. 0 0 2.00
Ca • 00 • 00 .. OG .02 Na '"24 .. 01 .07 • 14 :\ .. 0 3 • 02 • 06 oc " ~
Sum A. .. 27 .03 .13 • 21
101
PLAGIOCLASES Bucksport :rorr.iation
ORB 1 OF:A 22 ORA 22 ORA 24 ORA 24
Si02 68.65 59.24 6 7. 23 SE.69 68.14 Al203 19 .. 76 25. 72 2 o. 11 26 .. 99 19. 48 Na20 11 .. 74 7.77 1o.99 6 .. 27 12.01 cao .09 6. 98 .79 9.29 .• 07 K20 ,. 02 .05 • 04 .25 - 05 Ti02 • 00 .. 00 "00 .. 04 • 01 M. no .oo .. 05 .05 .. 00 • 00 FeO • 04 • 10 .04 .19 • 17 MgO .03 .03 .. 02 • 08 .. 05 Sum 100.33 99 .. 94 S9.27 99 .. 80 99.98
An • 42 33 .. 17 3 .. 82 Ll 5 .. 12 .. 32 Ab 99.58 66.83 96 .. 18 54 ... 98 99. 68 Or • 11 .. 28 .23 1 .. 4 2 • 27
ONQ 2e OND 2E> ODA 21b OPC 27 ORA 21 i\
Si02 57. 1 u 45 .. 59 43.80 62 .. 45 56.75 Al203 26. AU 3 4 .. 32 37 .. 44 24.28 28. 13 ~a20 6. 61 1.09 .75 f.47 6. 15 Ca~O 8 .. 51 18 ... 0 8 18 .. 35 6 .. 50 9.53 i\20 1 ,-• • :J .. 03 .. 02 .. '.)8 - 19 Ti02 .02 .02 .. 0 4 .. )0 , 01 '.1n0 • 0 1 "'00 .. 00 • 01 .03 FeO • 06 .os " 10 • ·)0 .05 £1 go • 0 3 .. 05 .05 • ·')6 • 10 Sum 99.37 99.23 100.55 99.35 100.94
An 41. 57 9 o. 16 9 J,. 11 35.7C 46. 13 Ab 58. 43 9. 84 6. 89 64 .. 30 53.87 Cr • 86 .. 23 " 12 .. 5 2 1. 08
Si02 Al203 Na20 cao K20 Ti02 MnO FeO MgO Sum
An Ab 0 :r
Si02 .~ 1203 Na20 cao K20 7i02 MnO FeO MgO Sum
An Ab Or
ORC 13
SA .. 76 27 .. 92
6 .. 74 8.62
,. 1 t) • 04 .. 04 • 16 .09
·102 .. 1n
'~1 .. 41 58. 59
• 57
ELA 8
69. 02 2tJ. 0 1 7.83 2 .. 40 1. 27
• 02 .oo • 18 • 12
99. 79
14.43 85.52
8.63
102
PLAGIOCL;.SES Bucksport Formation
OBA 21
60.23 25.53
7 .. 1+ 7 6. 60 .07 .oo .00 .02 ,. 0 3
99.95
3 2. 81 67. 19
.41
OB3 101a
5 6 .. 7 4 28.25
6 .. 35 9. 6 2
.. 12
.02
.oo • 08 .. 07
101.25
4 5. 26 5 4,. 07
.67
PLAGIOCLASES Penobscot Formation
ELA 13b
65.13 22. 89 12.10
• 59 .03 ... 01 .. c 0 .. 13 .oo
101 .. 94
2. 6 2 97.22
Q 16
Si02 :\1201 Na20 CaO K20 Ti02 MnO FeO MgC H20 Sum
Si Al Sum '!'et
Fe Mg Sum
Ca Na K Sum A
ELA 2a
43.98 38. 82
.68
.02 10.06
• 51 • 01 • 88 • 88
4 .. 53 100 .. 37
s .. 81 2 .. 19 d .. 00
3. 8 5 • 05 .. 1 '.) .. 17
4 .. 18
• 17 1. 7 0 1. 87
103
MUSCOVITES
Penobscot Formation
EL& 7
4f.46 38.95
.59
.. 00 9. 62
.. 49
.oo
.65
.67 4. 65
102.08
5. 99. 2.01 8.00
3 .. 90 .. 0 5 .07 .. 13
4. 14
• 15 1. 58 1.73
ELA 13b
49.13 36.70
1. 26 • 28
7. 5 2 .45 .oo • 91 .. 28
4. 6 7 101.20
6 .. 31 1.69 8.00
3 .. 86 • 0 Ll • 10 .05
4.06
.04 • 31
1. 2 3 1 .. 58
104
MUSCOVITES
Buckspol:'t Formation
ORB 1 ORB 1 ORC 109a ORC 109a ORC 109a 2 3 1 2 3
Si02 45.76 49 .. 63 46.61 48 .. 73 \ 47. 34 Al203 34. 25 28 .. 15 35.93 31..82 32. 63 Na20 .45 .28 .44 .19 • 26 cao .. 05 .03 .. 01 Q'J .. - .. 0 3 K20 9.32 9. 85 9 .. 43 1o .. 27 1 o .. 15 Ti02 • 81 .. 54 • 91 .• 4 1 1. 17 :'lnO • 00 ,02 - 0 lt .• 0 3 .OS FeO 2:so 4 .. 16 1. 15 1.76 2. 36 !'1g0 2.20 J .. 55 .ES 2. 18 1,. 2 8 H20 4. 51 4.50 4.54 4 .. 52 4. 49 Sum 100. 41 100.71 J 9 .. 71 99. 93 99.76
Si 6. 08 6.61 6.16 f.46 f .. 32 Al 1.92 1. 39 1 .. 84 1 .. 5 4 1.68 Sum 'let 8.00 8.00 8.00 8.JO 8.00
Jl. l 3 .. 45 3 .. 03 J .. 75 3 .. 44 3. !~5 'Ii • 08 .OS .09 .. J Li • 12 Mn .. 01 FP. • 29 .46 .. 13 .• 20 .26 Mg .44 .71 • 1 3 .. ~ 3 ,., ,.
-· .:...0 Sun 4. 24 4. 25 u .. 10 4. 11 4.C9
Ca • 0 1 N"' . ~ .. 12 .. 07 .. 11 .. 05 .. 07 :-\ 1.67 1. 6 7 1.59 1.. 7 4 1. 7 3 Sum A 1. 79 1 .. 75 1. 70 1 .. 79 1. 80
10,5
CHLORITES
OND 111b OND 111 b OFA 24 0£.C 27
Si02 26 .. 89 23. 15 28 .. 15 29 .. 2 5 Al203 22.20 27 .. 40 18. 30 20.92 Na20 .• 00 "0 3 .07 • 21 cao .05 • 18 .20 • 11 t\20 • 05 ' .07 .48 • 26 Ti02 .06 • 11 .17 .18 MnO .. 43 .. 27 .21 .13 FeO 19 .. 64 28 .. 21 21.40 22.55 MgO 18. 50 8.98 16.01 17.21 H20 1l.77 11. 33 11.31 12.06 Sum 99. 59 99 .. 7 3 96 .. 66 102~38
Si s.~7 4.90 E.04 5 .. s 1 Al 2 .• 53 3. 10 1. 9 6 2.19 Sum ret 8. 00 8.00 8.00 8 •• JO
Al 2.80 3.73 2 .. 61 2. 7 1 Fe 3. 34 4. 99 3. 79 "=! ., a:::
-· .• .I
Mg 5 .. 61 2. 83 5.06 5.10 "'. • 0 l .02 .03 0., J. 1. .. J
"!n • 07 .OS .04 .02 Na .01 .03 • 08 Ca .• 01 .04 .05 .. 0 2 K • c 1 0"' . ... • 1 J .07 Snr.l 11.85 11 .. 6 y 11.73 1L78
106
CHLO RITES
ORC 109a ORC 109a OFB 1 , 2
Si02 25.92 27. 01 2E.20 Al20J 21. 17 19 .. 48 23.84 Na20 .. 05 .05 .39 cao • 00 .19 .07 r.:20 "'00 .oo .,.33 Ti02 .oo .oo • 1 1 MnO .oo .oo .. 19 F'eO 24 .. 99 23.98 21.58 MgO 16 .. f), 16 .. 38 15 .. 7 4 H20 11. 55 11.46 11. 73 Sum 100 .• 20 99.05 100. 1f,
Si 5. 38 5. 65 5.35 Al 2.62 2.35 2. 65 Sum Tet 8. co 8. 00 8. 00
Al ' 2.55 2.45 3 .. oq Fe 4 .. 34 4.1S 3. 69 Mg s. 14 5.26 4. 79 Ti -"""\ 11 02 ~n .. 0 3 Na .02 .. 02 • 15 Ca .04 .02 K • 09 Snm 12. 0 :.+ 11 .. 9 t 11 .. 8 8
107
PYFRHOTITES Penobscot Fonna t:ion
ELA 7 ELA 8 ELA .13b Fe 61. 03 61. 10 60. 69 Ni • 19 • 16 • 14 s 38 .. 78 38. 66 38. 6.6 Sum 100. 00 99. 92 99.49
Xpo • 95 .95 .. qs
IL~1ENI~E SP HE NE ORC 1J ELA 7 ORA 21b
Si02 • 12 .08 28 .. 91 Al20 3 • 42 .. 19 4 ~ 18 Na20 s 13 .08 .04 cao • 37 .08 27. 2 5 K20 • 05 .. 08 Qt:; ... '
Ti02 54. 48 52. 84 36.05 r1n0 ~- 20 .72 .. 04 FPO 40.70 47.60 .. 45 MgO • 39 • 28 .. 2-J Sum 100 .. 86 101.95 97.25
108
CALCITES Bucksport .Formation
ORA 22 ORC 27 () p. B 1
Si02 1 '' • 4 .oo • 0 1 Al203 .. 03 .oo - 01 \ Na20 - 02 .07 .. 20 cao so. 56 53.15 53. 56 K20 .02 .oo .03 Ti02 • 00 .01 .03 r-!nO • 59 • 26 .39 FeO l. 14 .46 • 88 MgO • 92 .. 77 .75 C02 44. 00 4U.- 00 4 4 .. 00 Sum 9T.43 98.72 99.87
Ca - 95 • 97 .; 96 r1g .02 .02 .• 02 Fe .02 .01 • 01 Mn • a 1 .01
l?OT ASSI Ur' FELDSPAR
.Eli\ 2a ORA 21a
Si02 65.46 65. 11 Al203 17. 82 18. 52 Na20 • 61 • 61 cao • 00 .. 03 K20 16. 02 15. 99 Ti02 .oo .05 '.1nO • 00 .. 00 FeO • 00 .oo MgO • 02 .06 Sum 99 .. 93 100 .. 37
An 0'" ... v .. 15 Ab 5 .. 47 5. 47 Or 94 .. 53 94 .. 38
CONTACT METAMORPHISM OF THE LUCERNE PLUTON, HANCOCK COUNTY, MAINE
by
Steven W. Novak
(ABSTRACT)
The Lucerne pluton intrudes rocks of the Penobscot formation
Ordovician-Silurian (?)), a quartz-rich sulfidic pelite that contains
muscovite, biotite, cordierite, andalusite, plagioclase, pyrrhotite
and graphite outside the thermal aureole; and the Bucksport for-
mation (=Vassalboro, Silvian-Devonian (?)), a calcareous, quartzo-
feldspathic pelite that contains chlorite, biotite, celadonitic
muscovite, albite, and ilmenite outside the Lucerne aureole. Within
the aureole, the Penobscot formation contains K-feldspar plus
andalusite as the result of muscovite reaction with quartz. Corundum
occurs at the immediate contact of the granite from the. reaction of
the remaining muscovite. The Bucksport formation is recrystallized
within the aureole to a purple and green gneiss. The gneissic
banding is not present in the low grade calcareous rocks, and
represents the segregation of biotite-rich and calc-silicate.-rich
bands. Vertical or sleepy dipping, the banding parallels both
the regional strike and the intrusive contact, and is probably
the result of both mechanical and chemical effects. The following
sequence of assemblages (+ quartz) is found in the calcareous portions
of the Bucksport formation as the Lucerne contact is approached:
a) chl + bio +muse+ cc+ albite; b) bio +cc+ plag (An25 _33);
c) actinolite +cc+ K-feldspar + plag (An40); d) diopside +
zoisite + sphene +cc+ plag (An85_90). Interbedded pelites contain
· biotite + quartz + plagioclase + pyrite with corundum occurring at
the igneous contact in quartz free beds. The mineral assemblages
in the Lucerne aureole indicate a lithostatic pressure between 1000
and 3000 bars during metamorphism with temperatures between 700°C
and 450°C. Isobaric univariant assemblages in the calc-silicate
beds indicate buffering of H2o/co2 fluids produced by prograde
reactions. H2o rich fluids that produced zoisite were probably
associated with late stage crystallization of the Lucerne.
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