American Mineralogist, Volume 93, pages 7–21, 2008
Element mobility and scale of mass transport in the formation of quartz veins during
regional metamorphism of the Waits River Formation, east-central Vermont
Sarah C. Penniston-Dorland1,* and John M. Ferry2
1
Department of Geology, University of Maryland, College Park, Maryland, 20742, U.S.A.
Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218, U.S.A.
2
Abstract
Veins and adjacent alteration selvages in the Waits River Formation were investigated to determine
whether associated mass transfer was due primarily to large-scale advection or small-scale diffusion.
Samples of the vein, selvage, and adjacent wall rock were collected from the earliest and most numerous generation of veins in pelite and carbonate hosts from outcrops in the chlorite and the kyanite
zones. Bulk compositions of selvages and unaltered wall rocks were compared using a reference frame
defined by a combination of Zr, Ti, REEs, and U. Selvages from both outcrops typically exhibit losses
of Si, K, Ba, and Rb relative to unaltered wall rock. Kyanite zone selvages show losses in Mg and Cs
in addition. Differences in K, Ba, Rb, Cs, and Mg between the vein-selvage system as a whole and
adjacent unaltered wall rock are possibly accounted for by development of micas in veins. The addition of Si and Ca to veins is not balanced by removal of Si and Ca from the selvages. Vein-selvage
systems contain more Si than wall rock, with an overall addition of ≈40 mg Si/cm3 to the chlorite zone
and ≈55 mg Si/cm3 to the kyanite zone. Mass balance of Si at the outcrop scale requires that >90%
of the Si in quartz veins was derived externally. Quartz veins studied formed primarily by fluid flow
and large-scale advective mass transfer with a relatively minor component of local mass transport
by diffusion. The estimated time-integrated fluid flux necessary to produce the observed amount of
quartz in veins in an entire outcrop is ≈2–6·106 cm3 fluid/cm2 rock. Mineral inclusions in garnet and
fracturing of garnets adjacent to veins indicate that formation of selvages and veins initiated prior to
formation of garnet and continued after the end of garnet growth.
Keywords: Mass transfer, regional metamorphism, veins, fluid flow
Introduction
samples far removed from veins. Shaw (1954, 1956) found no
evidence for change in the concentrations of oxides (aside from
H2O and CO2) in average pelitic rock of the Littleton Formation,
New Hampshire, during metamorphism. Subsequent analysis
of Shaw’s data using new statistical methods (Ague 1991)
concluded that SiO2, FeO, MgO, K2O, CaO, and Na2O could all
have been mobile during metamorphism. A study of the pelitic
rocks of the Wepawaug Schist, Connecticut showed that a range
of elements can be mobile during metamorphism, including Si,
P, Na, Mn, Zn, K, and Ba (Ague 1994a). Other studies of pelitic
rocks, however, have concluded that there is no positive evidence
for significant mass transfer of components other than H2O and
CO2 during metamorphism (e.g., Ferry 1982; Moss et al. 1995,
1996; Symmes and Ferry 1995). Ague (1997b) pointed out that
there may be problems due to lithologic heterogeneity in the studies of Moss et al. (1995, 1996). The question of mass transfer in
regionally metamorphosed impure carbonate rocks is clearer but
still incomplete. Calc-silicate and argillaceous carbonate rocks
can be depleted in K and Na during metamorphism (Tanner and
Miller 1980; Ferry 1983).
A significant, and sometimes insurmountable, problem
in determining whether mass transfer has occurred during
metamorphism is the lithologic heterogeneity in rocks prior to
Quartz veins are a common feature in regionally metamorphosed rocks. Their abundance in outcrops of regionally
metamorphosed rocks can be 20–30% by volume (Ague 1994b;
Ferry 1994). The large volume of silica in veins raises the question of whether they represent fossilized paths of large-scale
fluid flow and mass transfer through the metamorphic terrain
(Walther and Orville 1982; Yardley 1986; Walther 1990; Ferry
and Dipple 1991; Ferry 1992; Ague 1994b; Breeding and Ague
2002; Masters and Ague 2005), segregations produced by local
Si transport (Yardley 1975; Yardley and Bottrell 1992), or some
combination of both.
The problem of vein formation has further implications for a
more general understanding of fluid flow and element transport
during regional metamorphism. Investigations of fluid inclusions,
veins, volatile contents of rocks, phase equilibria, reaction progress, and stable isotopic data all indicate that the volatile species
H2O and CO2 are mobile during metamorphism, but there is still
uncertainty about other elements. Several studies have examined
regional-scale mass transfer using bulk rock compositions of
* E-mail: [email protected]
0003-004X/08/0001–007$05.00/DOI: 10.2138/am.2008.2461
7
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Penniston-Dorland and Ferry: Element mobility and scale of mass transport
metamorphism. At the outcrop scale, differences in composition
due to pre-metamorphic heterogeneity are often much larger
than changes in composition that develop from metamorphic
processes. Study of metamorphic veins and their associated
alteration selvages is an alternative approach to investigating
element mobility during metamorphism in which the problem
of pre-metamorphic rock composition is much better constrained
by analysis of unaltered wall rock taken from the same lithologic
layer as the selvage (e.g., Ague 1994b). Compositions of veins
and associated selvages from the Wepawaug Schist, for example,
indicate regional-scale mobility of Si, Na, and K that promoted
the preferential growth of index minerals like garnet, staurolite,
and kyanite in the altered selvages (Ague 1994b) and veins and
selvages from the Dalradian metasediments in Stonehaven, Scotland, indicate regional-scale mobility of Si, Na, Ca, Sr, K, Rb, and
Ba (Masters and Ague 2005). Analysis of the latest generation of
veins and associated selvages from pelites hosting the Kanmantoo
Copper Deposit in the Adelaide Fold Belt of southern Australia
indicates large-scale mobility of Na, Ca, and Sr and local mobility
of Si, Rb, K, and Ba (Oliver et al. 1998). In contrast, the compositions of selvages adjacent to veins hosted by pelitic schists from
West Beach, Australia, indicate little or no mass transfer during
metamorphism (Oliver and Bons 2001).
In spite of the great promise of examining vein-selvage
systems to evaluate the nature, amount, and spatial scale of element mobility during metamorphism, there have been too few
studies to draw firm, general conclusions. The purpose of this
study is to contribute to a better understanding of vein formation
and element mobility during regional metamorphism through a
study of veins and associated selvages in pelites and micaceous
carbonate rocks from the Waits River Formation, east-central
Vermont (Fig. 1). Specific questions addressed include: (1) is
quartz in the veins mostly locally or externally derived; (2) was
there significant mass transfer of elements other than Si in the
formation of veins and selvages; (3) if so, is the mass transfer
of these elements local or larger-scale; and (4) when did mass
transfer occur in the metamorphic history of the rocks?
Geologic background
The Waits River Formation (Fig. 2) typically consists of micaceous carbonates and pelites interlayered on a scale of 1–10 m
and lies stratigraphically below the Gile Mountain Formation
(Fisher and Karabinos 1980). Hueber et al. (1990) concluded
that the stratigraphic age of the two formations ranges from
Silurian through Devonian based on the presence of plant fossils that date part of the Gile Mountain Formation as late Early
Devonian and a Silurian U-Pb zircon age of 423 ± 4 Ma from a
dike that cross-cuts the Standing Pond Volcanics member of the
Waits River Formation.
The Waits River Formation was deformed and regionally
metamorphosed during the Acadian orogeny (Thompson et
al. 1968; Thompson and Norton 1968; Osberg et al. 1989).
Deformation involved the formation of west-verging nappes
and subsequent doming (Woodland 1977). Isograds have been
mapped in the pelites corresponding to the appearance of biotite,
garnet, and kyanite (Fig. 2) and in the carbonates corresponding
to the appearance of oligoclase, biotite, and amphibole (Lyons
1955; Doll et al. 1961; Ferry 1992, 1994). Final prograde mineral
reaction during metamorphism was synchronous with the dome
stage of deformation (Barnett and Chamberlain 1991; Menard
and Spear 1994). The formation of monazite neoblasts at pressure
and temperature conditions recorded by mineral equilibria in the
kyanite zone of pelitic schists has been radiometrically dated at
353 ± 8 Ma (Wing et al. 2003). Mineral equilibria record P ≈ 8
kbar for the area and T from ≈475 °C in the biotite zone to ≈550
°C in the kyanite zone (Ferry 1994). Metamorphic fluids were
composed primarily of H2O and CO2 with minor H2S, CH4, CO,
H2, and dissolved chlorides. Mineral-fluid equilibria record XCO2
from <0.03 to ≈0.2 (Ferry 1992, 1994; Penniston-Dorland and
Ferry 2006).
F igure 1. Representative
V1 vein and adjacent selvage
in kyanite zone pelitic schist.
Selvage is ~1 cm thick. Waits
River Formation, location S35-1.
Penniston-Dorland and Ferry: Element mobility and scale of mass transport
Two outcrops were selected for this study: one in the chlorite
zone and one in the kyanite zone (Figs. 2 and 3). Three distinct
generations of originally planar veins are recognized. Criteria for
identification of the different generations include vein structures
and cross-cutting relationships with other veins and structural
features (Table 1). The oldest veins (V1) are the most numerous
and usually comprise the largest volume of veins within a given
outcrop. The V1 veins are generally highly deformed (dismembered and folded), and they appear as pods and stringers parallel
to layering and schistosity. The second generation (V2) usually is composed of relatively large, branching, and commonly
discontinuous veins that cross-cut lithologic layers, folding,
and schistosity. They are not numerous in a given outcrop, but
because of their large size, their volume is close to or exceeds
that of the V1 veins in some outcrops. The third generation of
veins (V3) is the least deformed and hence youngest, and is
generally composed of small and volumetrically minor veins
(<0.1% of a given outcrop).
Figure 2. Geologic sketch map of the study area in east-central
Vermont (after Lyons 1955; Doll et al. 1961; Ferry 1994). SDwr =
Siluro-Devonian Waits River Formation; SDgm = Siluro-Devonian Gile
Mountain Formation; pre-S = pre-Silurian units, undifferentiated.
9
Methods of investigation
Field aspects of veins, associated selvages, and wall rock were recorded and
measured in kyanite zone outcrop S35-1 and chlorite zone outcrop S40-1 (outcrops
21-2 and 27-11, respectively, of Ferry 1994). Vein selvages were identified in
outcrop and hand sample by a higher concentration of aluminous minerals, such
as garnets or micas, immediately adjacent to the vein and/or by a change in the
color of the rock adjacent to the vein. Specifically, along traverses perpendicular
to layering: (1) the generation of each vein (V1, V2, or V3) and its mineralogy
were recorded; (2) the width of each vein and its associated selvage (if present)
was measured with a steel measuring tape; and (3) the kind of wall rock between
adjacent veins (pelite or carbonate) was noted and its thickness measured.
Three samples of V1 veins were selected from outcrop S40-1 in the chlorite
zone for detailed investigation [two hosted in carbonate rock (A, R) and one in
pelite (D)], and three samples of V1 veins were selected from outcrop S35-1 in
Figure 3. Waits River Formation outcrops. (a) Chlorite-zone outcrop
(S40-1) with single boudinaged vein visible. (b) Kyanite-zone outcrop
(S35-1) with multiple folded and boudinaged veins visible.
10
Penniston-Dorland and Ferry: Element mobility and scale of mass transport
Table 1. Vein descriptions
V1
V2
V3
Thickness up to ~20 cm
up to ~150 cm
up to ~1.5 cm
Mineralogy* Qtz ± Cal ± Ms ± Bt ± Po
Qtz ± Cal ± Fsp ± Ky
Cal or Qtz
Selvages
Up to ~40% of veins in an Up to 75% of veins in an No selvages observed
outcrop have selvages
outcrop have selvages
Cross-cutting Usually conformable, at low Cross-cut V1 veins, schistosity, Cross-cut schistosity, lithologic layers
relationships
grades may cross-cut lithologic layers
schistosity or layering
Structure
Boudinaged, folded
May display slight boudinage, Planar, no deformation
generally irregular in shape
* Abbreviations follow Kretz (1983): Qtz = quartz, Cal = calcite, Ms = muscovite, Bt = biotite, Po = pyrrhotite, Fsp = feldspar, Ky = kyanite.
Table 2. Vein and selvage percentages of outcrop
Traverse
S40-1
S35-1
Metamorphic zone (pelites)
chlorite
kyanite
Total length of traverse
3119 cm
3782 cm
the kyanite zone [one in carbonate rock (X) and two in pelite (G, S)]. As was the
case for all quartz veins hosted by pelite in the chlorite zone outcrop, the vein in
sample S40-1D did not have a selvage visible in hand sample. This sample was
used to test whether there were any significant mineralogical or chemical changes
adjacent to veins where no selvage is visible and to characterize the degree of
chemical heterogeneity in rocks unaffected by formation of veins at the scale of
hand specimens. The V2 and V3 veins were not analyzed in detail because either
their selvages compose a much smaller volume of outcrop than do V1 selvages or
they have no visible selvages at all (Table 2).
Thin sections were made that included part of the vein, the entire selvage,
and part of adjacent unaltered wall rock for each sample (Fig. 1). Wall rock and
selvage for each sample were taken from the same lithologic layer. Layers appear
internally homogenous in hand specimen. Mineral assemblages were determined
in thin section with optical petrography and back-scattered electron (BSE) imaging using the JEOL JXA-8600 electron microprobe at Johns Hopkins University.
Compositions of minerals were determined by electron microprobe analysis using
wavelength-dispersive spectrometry, natural and synthetic mineral standards, and
a ZAF correction scheme (Armstrong 1988). Mineral modes for selvages and wall
rocks were measured by counting >2000 points in thin section using BSE imaging.
Any uncertainty in the identification of a particular point was resolved by obtaining
an energy-dispersive X-ray spectrum (EDS). Modal abundances of minerals were
converted to molar abundances using mineral compositions and molar volumes of
mineral components from Holland and Powell (1998). Graphs of the percentage
of quartz with distance from the selvage-wall rock contact were created for the
five selvage-bearing samples by point counting at intervals of <0.5 mm away from
the vein across the selvage-wall rock contact with an average of 100 points for
each interval. Maps that visually illustrate the mineralogical differences between
selvage and wall rock were made from point counting results across the selvagewall rock contact. Modes of mineral inclusions in garnet from sample S35-1G
were determined in a similar fashion by counting ~300 inclusions in garnet from
both selvage (two garnets examined) and wall rock (one garnet examined) in thin
section using BSE imaging and qualitative EDS analysis.
A portion of each sample was separated into selvage and adjacent wall rock (or
portions proximal to and distal from the vein in sample S40-1D) using a rock saw
and rotating grinding lap. The mass and volume of portions of selvage and wall
rock were measured and rock density was calculated from these measurements. The
pairs for each sample were then crushed into a fine powder in a tungsten carbide
container. The size of most samples of selvage was limited by the relatively narrow
width of the selvage and the size of the sample collected. The amount of sample
pulverized for selvages ranged from 7.8 g (S35-1S) to 67.6 g (S40-1R). The amount
of sample pulverized for wall-rock analyses ranged from 24.4 g (S40-1D) to 50.2
g (S35-1G). Bulk-chemical analyses of major and trace elements using X-ray
fluorescence (XRF) and inductively coupled plasma-mass spectrometry (ICPMS) were obtained commercially from SGS Minerals Services. The accuracy and
long-term reproducibility of analyses from this laboratory (formerly X-ray Assay
Laboratories) have been assessed by Ferry (1988) and Ague (1994a).
Estimates of whole-rock major-element composition were also made for one
sample (S40-1D) from mineral modes and mineral compositions determined with
the electron microprobe combined with published molar volumes of minerals.
Results agree within error of measurement for most elements with those obtained
by XRF analysis (see below). Uncertainties in the microprobe data, however, are
V1 veins
4.5%
6.2%
V2 veins
0%
6.0%
V1 selvage
0.4%
0.3%
V2 selvage
0%
0.1%
larger than for XRF analyses because of the accumulated errors from both point
counting and mineral analysis. For this reason and because XRF analysis samples
a larger volume of rock, estimates of whole-rock composition were not made from
modal and microprobe data for the other samples, and only XRF data were used
for all calculations of mass transfer of the major elements.
Results
Abundances of veins and selvages in outcrop
Vein and selvage abundances are listed in Table 2. In the chlorite-zone outcrop, all veins are V1 veins, and they comprise 4.5%
of the traverse. No V2 or V3 veins were observed. Vein selvages
comprise 0.4% of the length of the traverse. In the kyanite-zone
outcrop, both V1 and V2 veins occur in roughly equal volumes
along the traverse (6.2% and 6.0%, respectively). The V1 vein
selvages account for 0.3% of the traverse, about the same as in
the chlorite-zone outcrop. The total volume of selvages adjacent
to V2 veins along the kyanite-zone traverse (0.1%) is less than
the total volume of selvages adjacent to V1 veins.
Mineral assemblages and modes of V1 veins and vein selvages
The V1 veins are composed of quartz ± calcite ± minor muscovite, biotite, and/or pyrrhotite. Approximate visual estimates
of mineral abundances in veins from both chlorite- and kyanitezone outcrops were determined using a petrographic microscope
for 19 vein samples. Quartz typically comprises 60–100% of
the vein and calcite comprises <5–40% of the vein. Muscovite
is present in small amounts (<1%) in most veins. Biotite and
pyrrhotite are not common and, where present, also occur in
small amounts (<1%).
Selvages typically range in thickness from <5 mm to 2.5 cm.
The boundary between the selvage and the wall rock is usually
<5 mm wide. The mineral assemblages and modes for the distal
and proximal portions of sample S40-1D and for each of the five
selvage-wall rock pairs are listed in Table 3. The designation of
epidote/allanite is used for epidote-group minerals that have cores
that appear bright in BSE imaging. These cores are enriched in
one or more elements of high atomic number found in allanite,
such as Ce, La, Nd, Y, Th, and U. Pelite sample S40-1D contains
~1% small garnets that were likely stabilized at the conditions of
the chlorite zone by their high Mn content (Table 4).
In sample S40-1D, which has no visible selvage, there is no
statistically significant difference in mineral modes between rock
Penniston-Dorland and Ferry: Element mobility and scale of mass transport
11
Table 3. Mineral assemblages and modes (volume percent)
Sample
S40-1A
Rock type*
Carbonate
Wr
Sel
Quartz
42.87
0.20
Plagioclase
1.16
3.25
Muscovite
3.93
3.01
Chlorite
0
0
Biotite
0
0
Calcite
45.05
76.30
Ankerite
6.23
16.03
Garnet
0
0
Ilmenite
0
0
Rutile
0.10
0.15
Apatite
0.47
0.52
Epidote/Allanite 0
0
Tourmaline
0.10
0.33
Paragonite
0
0
Pyrrhotite
0.10
0.22
Zircon
0
0
Amphibole
0
0
* Wr = wall rock, Sel = Selvage.
S40-1R
Carbonate
Wr
Sel
26.54
13.70
0.33
0.17
8.17
5.76
0
0
0
0
55.38
72.15
7.84
6.65
0
0
0
0
0.16
0.08
0.23
0.38
0
0
0.36
0.45
0.95
0.65
0.03
0
0
0.01
0
0
S40-1D
Pelite
Distal
Proximal
30.67
29.99
9.79
10.08
35.81
36.96
19.26
18.21
0
0
0
0
1.23
1.98
1.39
1.01
0.81
1.00
0
0
0.32
0.47
0
0
0.39
0.22
0
0
0.13
0.26
0
0
0
0
immediately adjacent to the vein and rock further away, confirming that there is no selvage on the basis of either macroscopic or
petrographic examination. On the other hand, there are significant
differences in modes between selvage and wall rock in the other
five samples having selvages visible in hand specimen. The mineralogical differences between selvage and wall rock are primarily
in mineral abundance rather than in mineral assemblage. Modal
quartz is less in the selvages than in adjacent wall rock, and in
most cases, near zero through much of the selvage. This depletion in quartz is visible in the point-counting maps (Fig. 4) and
point-counting traverses performed across selvages into wall rock
(Fig. 5). In contrast, compared to wall rock, selvages contain more
modal apatite and tourmaline, more calcite (in carbonate hosts),
and more ilmenite + rutile (in kyanite-zone samples). Qualitatively,
the differences in modes between selvage and adjacent wall rock
require a bulk-chemical difference as well.
Timing of vein selvage formation
Garnets in sample S35-1G contain evidence that vein and
selvage formation for a single V1 vein spanned a wide range in
conditions of metamorphism and hence time. The assemblage and
modes of mineral inclusions in garnets from the selvage are very
different from those in garnet from adjacent wall rock (Fig. 6).
The total volume of inclusions is 16.0% of the wall-rock garnet
whereas the total volume of inclusions is 3.4% of the selvage
garnets. Mineral inclusions in garnets from unaltered wall rock
are primarily quartz with minor ilmenite, epidote/allanite, zircon,
pyrrhotite, and calcite (Fig. 6a; Table 5). Inclusions in garnets
from the adjacent alteration selvage are mostly ilmenite and
epidote/allanite with minor zircon, quartz, apatite, pyrrhotite,
tourmaline, plagioclase, calcite, and rutile. (Fig. 6b; Table 5).
The paucity of quartz inclusions and abundance of plagioclase
inclusions in garnet from the selvage compared to garnet from
the wall rock mirrors the difference in the relative abundance
of quartz and plagioclase between the matrices of the selvage
and wall rock themselves (Tables 3 and 5). This correlation indicates that some and probably most of the alteration involved
in formation of the selvages occurred at a relatively low grade
of metamorphism before the garnets grew.
S35-1X
Carbonate
Wr
Sel
13.33
0.56
15.02
15.10
0
0
0.24
0.96
5.10
21.12
29.90
44.42
8.05
12.85
0
0
0.05
0.04
0.08
0.12
0.40
0.56
0
0.80
0
0.32
0
0
0
0.12
0.08
0
27.76
3.01
S35-1G
Pelite
Wr
52.03
26.76
0.18
1.62
8.36
0.18
2.06
7.47
0.20
0.24
0.15
0.20
0.09
0
0.04
0.04
0.39
Sel
1.96
48.57
3.30
6.50
2.96
1.72
1.96
26.96
1.24
0.24
0.48
1.05
0.10
0.14
0.38
0.14
2.29
S35-1S
Pelite
Wr
18.21
23.81
15.80
0.72
14.21
0
0
24.86
0.51
0.12
1.20
0.03
0.39
0
0.12
0
0
Sel
1.32
17.70
50.47
0.29
1.28
0
0
19.91
1.03
0.39
5.84
0.05
1.42
0
0
0.15
0.15
Garnets in selvages from the same sample, S35-1G, have
been fractured and altered adjacent to the vein, with one fracture
running through the middle of a garnet (Fig. 7). This observation suggests that at least some V1 veins or parts of V1 veins
formed when garnets were already present, at a higher grade
of metamorphism, and that the fracturing and alteration may
have been caused by the vein-forming event. The evidence for
selvage and vein formation within a single vein at two distinctly
different grades of metamorphism suggests that alteration and
concomitant fluid flow occurred over a long duration during
metamorphism.
Mineral compositions
Representative mineral compositions are reported in Table 4.
Mineral compositions in the selvage and wall rock for a given
sample are similar, as are those in the distal and proximal portions of sample S40-1D. Plagioclase from the kyanite zone is
irregularly zoned. Approximately 20 grains of plagioclase were
selected and analyzed in each of the high-grade samples. The
selection method was designed to minimize preferential analysis
of either cores or rims. A grid of regularly spaced points was set
up, and the grain or part of a grain nearest each point on the grid
was analyzed. The average plagioclase composition as well as the
range of plagioclase compositions is reported for each sample.
Whole-rock geochemistry
Bulk-rock XRF and ICP-MS data are reported in Table 6. Detection limits and uncertainties of analysis are listed in Appendix
11. Results for several elements represent probable contamination
from the tungsten carbide container used for crushing samples.
Deposit item AM-08-014, Appendix 1 (detection limits and
uncertainties of analysis). Deposit items are available two ways:
For a paper copy contact the Business Office of the Mineralogical
Society of America (see inside front cover of recent issue) for
price information. For an electronic copy visit the MSA web site
at http://www.minsocam.org, go to the American Mineralogist
Contents, find the table of contents for the specific volume/issue
wanted, and then click on the deposit link there.
1
12
Penniston-Dorland and Ferry: Element mobility and scale of mass transport
Table 4a. Representative mineral compositions: Calcite
Table 4f. Representative mineral compositions: Biotite
Sample
S40-1R
S35-1X
S35-1G
Wr
Sel
Wr
Sel
Wr
Sel
Ca
0.923
0.924
0.927
0.926
0.947
0.927
Mg
0.034
0.035
0.041
0.042
0.024
0.034
Fe
0.039
0.037
0.025
0.025
0.025
0.033
Mn
0.004
0.004
0.007
0.007
0.004
0.006
Oxide sum
55.95
56.46
56.37
56.28
55.62
56.13
No. analyses
6
6
7
7
12
9
Notes: Analyses of calcite, ankerite, muscovite, biotite, and chlorite are averages
of 4–22 “spot” analyses of grains in thin section. Analyses of plagioclase feldspars
are averages of random “spot” analyses of 13–22 grains per thin section; range of
% An is taken from these analyses. Mineral formulae for muscovite, paragonite,
and biotite are cations per 11 O atoms (less H2O); for chlorite, cations per 14 O
atoms (less H2O); for amphibole, cations per 23 O atoms (less H2O); for tourmaline,
cations per 31 O atoms (less H2O); for calcite, cations per oxygen atom (less CO2);
for ankerite, cations per 2 O atoms (less CO2). Oxide sum refers to the average
sum of oxide wt%, excluding B2O3, CO2 and H2O, and with all Fe as FeO. Dist =
distal, Prox = proximal, Wr = wall rock, Sel = selvage.
Sample S35-1X
S35-1G
Wr
Sel
Wr
Sel
K
0.885
0.891
0.860
0.833
Na
0.023
0.021
0.009
0.017
Fe
0.897
0.911
1.032
1.041
Mg
1.501
1.483
1.313
1.322
Mn
0.004
0.003
0.002
0.003
Ti
0.085
0.076
0.097
0.094
AlVI
0.386
0.402
0.419
0.419
AlIV
1.212
1.224
1.213
1.236
Si
2.788
2.776
2.787
2.764
Oxide sum
95.65
95.49
95.53
95.62
No. analyses
6
10
8
5
Table 4b. Representative mineral compositions: Ankerite
Sample
Ca
Mg
Fe
Mn
Oxide sum
No. analyses
S40-1R
Wr
Sel
1.025
1.028
0.685
0.693
0.281
0.269
0.010
0.009
54.77
54.84
8
8
S40-1D
Dist
Prox
1.042
1.052
0.538
0.527
0.411
0.411
0.009
0.010
55.59
55.76
8
8
S35-1X
Wr
Sel
1.021
1.023
0.745
0.730
0.214
0.231
0.020
0.016
54.15
54.22
8
10
Table 4c. Representative mineral compositions: Plagioclase
Sample
S40-1A
S40-1D
S35-1X
S35-1S
Wr
Sel
Dist Prox
Wr
Sel
Wr
Sel
Ave Xan
0.022 0.017 0.008 0.011 0.848 0.886 0.270 0.248
Ave Xab
0.983 0.984 0.991 0.989 0.150 0.114 0.727 0.745
Ave Xor
0.001 0.001 0.003 0.002 0.001 0.001 0.003 0.003
Oxide sum 99.76 100.05 100.34 100.27 99.90 100.26 100.16 100.28
No. analyses 13
20
21
19
20
18
22
22
Range %An 1–5
1–3
0–4
0–3 72–94 55–97 23–33 20–30
Table 4d. Representative mineral compositions: Muscovite
Sample S40-1A
S40-1R
S35-1G
Wr
Sel
Wr
Sel
Wr
Sel
K
0.741
0.765
0.763
0.779
0.797
0.790
Na
0.131
0.110
0.121
0.123
0.108
0.126
Fe
0.031
0.035
0.073
0.073
0.059
0.050
Mg
0.145
0.146
0.120
0.118
0.057
0.049
Mn
0.000
0.000
0.000
0.000
0.002
0.001
Ti
0.020
0.016
0.020
0.019
0.009
0.011
AlVI
1.834
1.831
1.820
1.818
1.902
1.908
AlIV
0.827
0.848
0.825
0.838
0.891
0.917
Si
3.173
3.152
3.175
3.162
3.109
3.083
Oxide sum
94.82
95.11
95.99
95.37
95.20
94.60
No. analyses
10
4
6
7
6
10
Table 4e. Representative mineral compositions: Paragonite
Sample Wr
K
0.105
Na
0.755
Fe
0.027
Mg
0.009
Mn
0.000
Ti
0.005
VI
Al
2.011
IV
Al
1.059
Si
2.941
Oxide sum
96.72
No. analyses
6
S40-1R
Sel
0.106
0.761
0.014
0.006
0.000
0.005
2.017
1.063
2.937
96.58
7
Table 4g. Representative mineral compositions: Amphibole
Sample Na
Ca
Fe
Mg
Mn
Ti
Al
Si
Oxide sum
No. analyses
S35-1X
Wr
0.292
1.810
1.492
2.692
0.026
0.062
1.990
6.852
97.17
8
S35-1G
Sel
0.387
1.796
1.622
2.327
0.015
0.051
2.736
6.406
97.45
4
Sel
0.303
1.833
1.580
2.499
0.017
0.060
2.285
6.670
97.25
4
Table 4h. Representative mineral compositions: Tourmaline
Sample Na
Ca
Fe
Mg
Mn
Ti
Al
Si
Oxide sum
No. analyses
S40-1R
Wr
0.940
0.130
1.182
2.048
0.000
0.130
7.800
7.651
85.58
6
S35-1S
Sel
0.896
0.149
1.181
2.203
0.001
0.107
7.648
7.665
85.18
8
Wr
0.888
0.155
1.132
2.326
0.002
0.106
7.597
7.666
84.67
12
Sel
0.874
0.194
1.235
2.297
0.004
0.130
7.541
7.629
85.20
12
Table 4i. Representative mineral compositions: Garnet
Sample S40-1D
Dist
Prox
Ca
0.561
0.554
Fe
1.911
1.955
Mg
0.115
0.123
Mn
0.381
0.288
Ti
0.005
0.005
Al
1.979
1.994
Si
3.025
3.040
Oxide sum 100.22
99.54
No. analyses 5
6
S35-1X
Wr
Sel
0.673
0.681
1.870
1.893
0.301
0.281
0.141
0.130
0.006
0.005
1.982
1.993
3.014
3.007
100.35
100.39
5
8
S35-1G
Wr
Sel
0.683
0.689
1.972
2.024
0.238
0.224
0.105
0.054
0.005
0.005
1.956
1.959
3.028
3.029
100.11
100.37
8
4
Table 4j. Representative mineral compositions: Chlorite
Sample Fe
Mg
Mn
Ti
Al
Si
Oxide sum
No. analyses
S40-1D
Dist
Prox
2.603
2.620
1.730
1.746
0.019
0.019
0.006
0.006
2.984
2.975
2.578
2.569
88.06
88.02
5
4
S35-1X
Wr
Sel
1.539
1.557
3.002
3.003
0.008
0.007
0.007
0.006
2.729
2.731
2.664
2.659
87.94
88.17
6
8
S35-1G
Wr
Sel
1.840
1.941
2.648
2.556
0.006
0.006
0.008
0.007
2.790
2.803
2.652
2.632
87.48
88.38
10
4
Penniston-Dorland and Ferry: Element mobility and scale of mass transport
13
Table 5. Modes of mineral inclusions in garnet, sample S35-1G
Wall rock (n = 378)
Selvage (n = 299)
Quartz
93%
5%
Ilmenite
3%
41%
Epidote/Allanite
1%
33%
Zircon
1%
5%
Apatite
0%
4%
Pyrrhotite
1%
3%
Tourmaline
0%
3%
Plagioclase
0%
2%
Calcite
1%
1%
Rutile
0%
1%
Note: Inclusions counted within one garnet for wall rock determination and within two garnets for selvage determination. n is the number of points counted.
The container is composed primarily of W, C, and Co with lesser
amounts of Ta, Ti, and Nb. Measured concentrations of Co, Ta,
Ti, and Nb were plotted against that of W, and there are linear
correlations of both Co and Ta with W. None of these elements
would be expected to have large concentrations in typical pelitic
and carbonate rocks, and thus the measured concentrations of Co,
Ta, and W are likely primarily due to contamination. Cobalt, Ta,
and W therefore are not included in Table 6. Because measured
concentrations of Ti and Nb do not show any correlation with
W, they are not considered to reflect significant contamination
from the crusher, and are reported in Table 6. Detailed discussion
of the whole-rock geochemistry follows.
Mass transfer during selvage formation
A geochemical reference frame
Figure 4. Mineral maps of selvages and wall rocks created by point
counting minerals at 0.25 mm intervals. (a) Mineral map of chlorite-zone
metacarbonate rock (S40-1D) without visible selvage. Quartz (dark
blue) at top of map defines the vein. There is no detectable depletion
of quartz in wall rock adjacent to the vein. (b) Mineral map of chloritezone metacarbonate rock (S40-1A). The vein is off the top of the map.
Region with almost no quartz (mostly pink calcite) at top of map is
selvage, region below is wall rock. The transition from selvage with
almost no quartz to wall rock with abundant quartz is sharp (<5 mm
wide). (c) Mineral map of kyanite-zone pelitic rock (S35-1G). The vein
is off the top of the map. Region with almost no quartz (mostly yellow
plagioclase and red garnet) at top of map is selvage. The transition from
selvage with almost no quartz to wall rock with abundant quartz is also
sharp (<5 mm wide).
To quantitatively assess gains and losses of elements during
formation of the veins and selvages, an element or group of elements first must be chosen that is believed to have been immobile
or almost so during alteration (e.g., Gresens 1966; Grant 1986)
to avoid the “closure” problem (Ague and van Haren 1996). The
ratio of the concentration of element i in the altered rock to the
concentration of the element i in the unaltered wall rock, Ci'/C°i
(hereafter referred to as the concentration ratio), for an immobile
element can be used to adjust the concentrations of the other
elements in the altered rock to avoid the problem of closure.
Selection of such an immobile reference frame also circumvents
the effects of volume change during alteration.
Elements that appear in vein minerals were eliminated from
the list of possible immobile elements, including Si and Al (some
V2 veins in the Waits River Formation contain kyanite). Elements
for which there is evidence for mobility or for which analytical
uncertainties are large were further eliminated (Ague and van
Haren 1996). Specifically, mobility of several elements during
metamorphism, including K, Na, Ca, Fe, Mg, Mn, Al, P, Rb,
Ba, Sr, Zn, Ni, and/or Y, have been documented by Shaw (1954,
1956), Tanner and Miller (1980), Ferry (1983), and Ague (1994a,
2003). Elements with excessively large analytical uncertainties
include Cr, Li, Sc, Ga, Ge, V, Cs, Eu, Nb, Tb, Hf, Lu, Tm, and
Ti (when TiO2 or Ti <0.2 wt%). The method of Baumgartner and
Olsen (1995) was then followed, in which several elements with
overlapping concentration ratios were used to define a reference
frame. Elements used to define the immobile reference frame
include Ti (when TiO2 or Ti >0.2 wt%), Zr, La, Ce, Pr, Nd, Sm,
Gd, Dy, Ho, Er, Yb, and U. There is documented mobility of
Ti in some geologic settings (e.g., Ague 2003). However, in
14
Penniston-Dorland and Ferry: Element mobility and scale of mass transport
Table 6. XRF and ICP-MS whole rock data
Sample Method
Units
S40-1A
S40-1R
S40-1D
S35-1X
S35-1G
S35-1S
Wr
Sel
Wr
Sel
Dist
Prox
Wr
Sel
Wr
Sel
Wr
Sel
SiO2
XRF
wt%
43.07
12.17
29.42
13.06
62.35
59.84
38.52
30.07
74.54
46.16
48.98
50.05
Al2O3
XRF
wt%
2.12
2.23
3.86
2.51
14.97
17.10
8.84
10.98
9.65
22.73
24.91
20.94
CaO
XRF
wt%
27.17
41.88
31.72
41.95
1.22
1.41
21.52
26.96
4.70
9.48
2.99
4.81
MgO
XRF
wt%
2.00
3.30
2.07
1.83
2.54
2.40
4.53
3.68
1.32
1.70
2.65
1.72
Na2O
XRF
wt%
0.16
0.48
0.17
0.08
1.31
1.44
0.20
0.37
1.06
2.00
2.50
2.02
K2O
XRF
wt%
0.45
0.28
0.80
0.47
2.11
2.78
1.92
1.28
0.66
0.65
4.85
2.90
Fe2O3
XRF
wt%
1.41
1.93
3.42
3.40
8.65
8.36
5.38
5.22
5.33
14.24
8.19
12.17
MnO
XRF
wt%
0.07
0.12
0.23
0.28
0.15
0.11
0.29
0.31
0.14
0.40
0.13
0.29
TiO2
XRF
wt%
0.14
0.15
0.22
0.14
0.82
0.98
0.53
0.49
0.63
1.51
1.40
1.58
P2O5
XRF
wt%
0.12
0.18
0.16
0.19
0.18
0.16
0.08
0.09
0.10
0.19
0.23
0.80
Cr2O3
XRF
wt%
<0.01
<0.01
<0.01
<0.01
0.01
0.02
0.01
0.01
0.01
0.03
0.03
0.03
LOI
XRF
wt%
23.50
36.85
28.55
34.80
5.90
4.45
18.25
20.55
2.00
0.75
3.10
1.55
Sum
XRF
wt% 100.4
100.0
100.8
98.91
100.3
99.58
100.2
100.2
100.2
99.98
100.2
99.04
Rb XRF
ppm
23
12
32
22
99
131
55
36
31
36
209
110
Sr
XRF
ppm 1440
2180
1100
1450
127
166
535
743
221
505
402
353
Y
XRF
ppm
4
8
14
18
24
30
43
71
26
50
30
46
Zr
XRF
ppm
80
126
89
99
144
156
110
142
242
453
218
469
Nb
XRF
ppm
2
<2
2
<2
10
15
13
10
19
42
50
149
Ba
XRF
ppm
61
49
139
70
308
416
286
245
124
191
936
484
Al ICP-MS
wt%
1.12
1.02
1.88
1.12
7.56
8.74
4.51
5.44
4.88
12.10
12.56
10.95
Ba ICP-MS
ppm
76.3
40.9
113.9
63.8
305.9
389.6
298
244.2
114.4
188.5
892.4
513.8
Ca ICP-MS
wt%
18.98
27.68
21.86
29.05
0.77
0.86
14.62
18.14
3.03
6.25
1.90
3.16
Cr ICP-MS
ppm
11
24
24
14
93
92
58
65
80
195
158
174
Fe ICP-MS
wt%
1.01
1.29
2.31
2.30
6.33
6.04
3.79
3.45
3.86
10.08
5.56
8.72
K
ICP-MS
wt%
0.38
0.22
0.61
0.36
1.57
2.06
1.44
1.00
0.49
0.52
3.74
2.25
Li ICP-MS
ppm <10
<10
<10
<10
98
82
64
50
34
48
74
47
Mg ICP-MS
wt%
1.29
1.84
1.26
1.13
1.56
1.45
2.70
2.14
0.80
1.07
1.57
1.07
Mn ICP-MS
ppm 465
705
1500
1780
1120
1270
2030
2110
1020
3060
963
2190
Ni
ICP-MS
ppm
17
9
22
11
91
75
20
42
40
49
57
53
P
ICP-MS
wt%
0.05
0.07
0.06
0.07
0.08
0.06
0.03
0.03
0.04
0.08
0.09
0.32
Sc ICP-MS
ppm
<5
<5
<5
<5
13
18
8
9
10
24
21
25
Sr ICP-MS
ppm 1543.7
2251.7
1171.7
1524.6
127.4
159.1
549
784.5
224
546.9
402.4
341.6
Ti ICP-MS
wt%
0.07
0.07
0.12
0.07
0.46
0.56
0.29
0.26
0.36
0.92
0.81
0.93
V
ICP-MS
ppm
18
16
34
19
113
134
79
92
66
190
190
144
Zn ICP-MS
ppm
19
27
41
32
166
127
61
40
41
69
115
79
Zr ICP-MS
ppm
24.6
82.4
61.4
69.5
133.7
148.7
102.7
137.8
207.1
467.3
202.6
393.5
Bi
ICP-MS
ppm
<0.1
<0.1
0.1
<0.1
<0.1
<0.1
0.4
0.8
0.3
0.6
0.2
0.2
Cd
ICP-MS
ppm
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
0.2
0.4
<0.2
0.2
Ce ICP-MS
ppm
13.1
16.7
21.5
19.3
50
77
51.7
50.3
46.6
116
128.3
112.7
Cs ICP-MS
ppm
1.2
0.6
1.9
1.1
4.5
5.8
2.8
2
2.6
3.8
13
6.4
Dy ICP-MS
ppm
1.2
1.4
2.28
2.67
4.45
5.75
5.06
6.76
4.96
11
7.69
9.91
Er ICP-MS
ppm
0.74
0.91
1.39
1.57
2.98
3.74
3.99
6.11
3
7.06
3.87
6.58
Eu ICP-MS
ppm
0.38
0.57
0.88
0.96
1
1.53
1.19
1.31
1.18
2.58
2.32
2.3
Ga ICP-MS
ppm
2
2
4
2
15
18
12
13
8
22
26
17
Gd ICP-MS
ppm
1.34
1.73
2.53
2.56
4.75
6.82
4.98
5.04
5.53
12.9
10
11.3
Ge
ICP-MS
ppm
<1
<1
<1
<1
2
2
1
1
2
7
3
5
Hf
ICP-MS
ppm
<1
2
2
1
4
4
3
4
6
14
6
10
Ho ICP-MS
ppm
0.24
0.29
0.45
0.52
0.9
1.18
1.2
1.74
1.01
2.26
1.37
2.05
La ICP-MS
ppm
7.9
10.5
11.9
10.7
24
41.4
27.3
26.4
21.3
49.9
61.6
55.3
Lu
ICP-MS
ppm
0.08
0.12
0.16
0.16
0.49
0.51
0.42
0.70
0.41
0.80
0.44
0.95
Mo
ICP-MS
ppm
<2
<2
<2
<2
<2
<2
<2
3
6
6
<2
<2
Nb ICP-MS
ppm
4
3
4
4
13
13
15
12
25
48
59
144
Nd ICP-MS
ppm
7.2
9
10.9
9.9
23.5
36
25.6
25.1
23.6
57.9
56.7
54.9
Pb
ICP-MS
ppm
6
12
24
31
16
18
20
30
16
24
29
23
Pr ICP-MS
ppm
1.87
2.37
2.82
2.58
6.18
9.71
6.77
6.59
5.91
14.5
15.4
14.3
Rb ICP-MS
ppm
22.2
11.8
36
21.6
99.8
130.8
63.1
41.5
32.3
45
213.9
113.2
Sm ICP-MS
ppm
1.5
1.8
2.5
2.3
5.3
7.6
5.5
5.3
6.3
15.1
10.8
12.4
Sn
ICP-MS
ppm
<1
<1
<1
<1
2
3
3
3
2
4
6
4
Tb ICP-MS
ppm
0.2
0.26
0.4
0.45
0.78
1.06
0.79
0.91
0.86
1.96
1.49
1.79
Th ICP-MS
ppm
1.6
2.3
3.2
2.3
8.9
11.4
7.2
7.4
7.2
19.9
20.9
17.2
Tl
ICP-MS
ppm
<0.5
<0.5
<0.5
<0.5
0.6
0.8
<0.5
<0.5
<0.5
<0.5
1.3
0.6
Tm
ICP-MS
ppm
0.09
0.12
0.17
0.21
0.45
0.53
0.54
0.85
0.4
0.93
0.50
0.95
U
ICP-MS
ppm
0.85
1.05
1.04
0.86
2.6
3.31
2.21
2.49
2.17
5.21
3.78
3.46
Y
ICP-MS
ppm
7.3
9.7
14
17.2
21.1
27
32.5
47.3
22.6
52
30.7
47.2
Yb ICP-MS
ppm
0.7
0.8
1.2
1.3
3.4
3.8
3.6
6
3
6.5
3.3
7.2
Notes: Wr = wall rock, Sel = selvage, Dist = distal, Prox = proximal. Concentrations for Be, Cu, ag, As, and In were below the detection limit. Concentrations for W,
Co, and Ta not reported. Italics are measurements that are below 20 times the detection limit.
this study the concentration ratio for Ti in each sample falls in
line with the other immobile elements used. For each sample, a
range of values was defined for the immobile reference frame
with upper and lower bounds based on the smallest interval in
Ci'/C°i that included all of the elements considered immobile. In
addition, a minimum value for the range of Ci'/C°i = 0.6 was set
by the range of the XRF and ICP-MS data for rock adjacent to
and distal from the vein in chlorite-zone sample S40-1D (Fig.
Penniston-Dorland and Ferry: Element mobility and scale of mass transport
15
Figure 5. Modal percentage of quartz along traverses perpendicular to the selvage-wall rock contact in five samples studied in detail. Quartz is
depleted in selvages relative to wall rock in all samples, and in most samples large portions of the selvage do not have any quartz. Different scales in
each panel. The outer boundary of the selvage was determined for most samples by the location at which the abundance of quartz increased above
~0%. The inner boundary of the wall rock was defined as the location beyond which the abundance of quartz remained relatively constant (keeping
in mind the inherent heterogeneity of the rock). The transition zone was the region between the outer boundary of the selvage and the inner boundary
of the wall rock. Sample S40-1R was an exception to this characterization, since the selvage exhibited a gradational increase in quartz over a greater
distance than the other samples and there was only a very small (<1 mm) region in which quartz was ~0%. For S40-1R, the inner boundary of the
wall rock was defined similarly to the other samples, and that boundary was also defined as the outer boundary of the selvage.
8a) that shows no visual, petrographic, or chemical evidence for
development of an alteration selvage. The range in Ci'/C°i = 0.6
therefore is believed to be a representative minimum estimate
of uncertainties introduced both by the heterogeneity in the premetamorphic bulk composition of individual hand specimens and
by the analytical errors associated with measured concentrations
of the collection of immobile elements.
Plots of the concentration ratio for the distal and proximal
portions of sample S40-1D and for the five wall rock-selvage
pairs in the other samples are shown in Figure 8 along with lines
showing the upper and lower bounds on the range of values for
the immobile reference frame.
Geochemical, volume, and mineralogical changes during
selvage formation
Geochemical changes. If the concentration ratio for a particular element or species falls above the immobile reference
frame (black symbols, Fig. 8), then the element was added during alteration, and if it falls below the immobile reference frame
(open symbols, Fig. 8), then it was lost during alteration. If the
16
Penniston-Dorland and Ferry: Element mobility and scale of mass transport
concentration ratio of a given element falls within the immobile
reference frame (gray symbols, Fig. 8) then there is no conclusive
evidence for either loss or gain.
The quantitative change in mass for element i (ΔCi/C°i) can
be calculated following Ague (1994a):
∆Ci
C
Figure 6. Photomicrographs of garnets in sample S35-1G under
crossed polars. (a) Garnets in unaltered wall rock have a large abundance
of inclusions most of which are quartz. (b) Garnets in adjacent altered
selvage have fewer inclusions most of which are ilmenite and epidote/
allanite.
Figure 7. Photomicrograph of garnet adjacent to V1 quartz-calcite
vein (right-hand side of image) in sample S35-1G under crossed polars.
Garnet is fractured and altered to chlorite adjacent to vein.

i
=

Cref
C
'
ref
*
Ci'
Ci
−1 (1)
using the concentration ratios at the upper and lower bounds of
the immobile reference frame for each sample as the limiting
values for C'ref/C°ref.
Chlorite-zone samples. Measured XRF, ICP-MS,
and electron microprobe data for portions of pelite sample S401D that are adjacent to and distal from the quartz vein fall near
a concentration ratio of 1, which is the value expected for no
mass change [log(C'/C°) = 0, dashed horizontal line in Fig. 8a].
Accordingly, there is no conclusive evidence for gain or loss
of mass of any analyzed element. Not only is there no visual
or modal evidence for development of an alteration selvage
adjacent to the vein in sample S40-1D, but also there is no
conclusive geochemical evidence for the development of an
alteration selvage.
Concentration ratios for numerous elements are illustrated
in Figures 8b and 8c for the two chlorite-zone selvage-wall
rock pairs (carbonate rocks S40-1A and S40-1R). In both cases,
errors on the concentration ratios for Na and Ti are large (Figs.
8b and 8c) because of large analytical errors in XRF analyses
of elements in low concentration. The concentration ratio for Zr
based on ICP-MS analysis for sample S40-1A is anomalously
large compared to the ratio based on XRF analysis (Fig. 8b).
The result is contrary to expectation because Zr is traditionally
used as a reliable immobile reference frame (e.g., Breeding and
Ague 2002; Ague 2003; Masters and Ague 2005). The high Zr
concentration ratio from ICP-MS analysis is likely the result
of a “nugget” effect, an accidental incorporation of slightly
more zircon in the aliquot of selvage sample S40-1A used for
ICP-MS analysis. This datum was therefore not included in
the determination of the immobile reference frame. Even if the
higher Zr analysis is accepted as part of the immobile reference
frame, however, conclusions are not changed. For both samples
S40-1A and S40-1R Si, K, and Ba fall below the immobile reference frame (Figs. 8b and 8c). The datum for Rb falls below the
immobile reference frame in sample S40-1A but within error of
the immobile reference frame in sample S40-1R. No element in
either sample plots significantly above the immobile reference
frame. During formation of alteration selvages around veins
hosted by carbonate rocks in the chlorite zone, therefore, Si, K,
and Ba were consistently lost from the protolith, Rb was lost
from one but not both samples, and no elements were added.
The relative magnitudes of Si, K, Rb, and Ba loss were 34–82,
13–61, 11–66, and 17–66%, respectively (Table 7). A range of
values results both from uncertainty in the immobile reference
frame and from a possible difference in the process of alteration
between the samples.
Kyanite-zone samples. Concentration ratios are illustrated in Figures 8d–8f for the three kyanite-zone selvage-wall
rock pairs (pelite samples S35-1G and S35-1S and carbonate
sample S35-1X). As for carbonate samples from the chlorite
Penniston-Dorland and Ferry: Element mobility and scale of mass transport
17
Figure 8. Concentration ratios (log scale) for major, minor, and trace elements for analyzed material adjacent to and distal from the vein in
sample S40-1D and for the five analyzed selvage-wall rock pairs. Triangles, data from modal and electron microprobe analyses; diamonds, XRF
data; squares, ICP-MS data. Error bars are ±2σ. When error bars are not shown, they are smaller than the size of the symbol. Dashed horizontal line
indicates concentration ratio for no mass transfer. Solid horizontal lines show range of the immobile reference frame. Gray symbols are elements
that fall within the immobile reference frame (indicating no conclusive evidence for gain or loss during alteration), elements with black symbols
fall above (indicating gain during alteration), and elements with unfilled symbols fall below (indicating loss during alteration). Black x indicates
an element that was used to define the immobile reference frame.
zone, the concentration ratio for Na is large for sample S35-1X
(Fig. 8d) because of large analytical errors in XRF analyses of
elements in low concentration. In sample S35-1X, the concentration ratios for Si, K, and Rb fall below the immobile reference
frame, similar to selvages in carbonate rocks in the chlorite zone.
In addition, concentration ratios for Mg and Cs fall below the
reference frame (Fig. 8d).
The concentration ratios for immobile elements in sample
S35-1S span a larger range of values than for any other. This is
likely the geochemical expression of a larger degree of lithologic
heterogeneity visible in the hand specimen of the rock. Furthermore, the distinctive pattern of concentration ratios of REEs in
Figure 8f suggests a second example of a “nugget” effect, in this
case caused by an accidental incorporation of excess garnet into
the aliquot of selvage sample S35-1S and/or of too little garnet
in the aliquot of wall rock used for ICP-MS analysis. Even if the
REE data for sample S35-1S in Figure 8f are ignored, however,
conclusions are not changed. Concentration ratios for Mg, K,
Rb, Cs, and Ba in both of the kyanite-zone pelites plot below the
immobile reference frame (Figs. 8e and 8f). The concentration
ratio for Si for sample S35-1G also plots significantly below the
immobile reference frame while that for sample S35-1S falls at
the lower end of the immobile reference frame. For sample S351S, concentration ratios for Al, Na, Sr, V, and Th additionally
plot below the immobile reference frame, and the concentration
ratio for P plots above the immobile reference frame.
During formation of alteration selvages in the kyanite zone,
therefore, Si, K, Rb, Cs, and Mg were consistently lost from both
protoliths (with the possible exception of Si in sample S35-1S);
Ba was lost from both pelite samples S35-1G and S35-1S; and
Al, Na, Sr, Th, and V were lost from and P added to sample
S35-1S. The magnitudes of Si, K, Rb, and Ba loss were 0–76,
24–63, 25–67, and 7–65%, respectively (Table 7). As in the
chlorite zone, a range of values results both from uncertainty in
the immobile reference frame and from a possible difference in
the process of alteration between the samples.
Penniston-Dorland and Ferry: Element mobility and scale of mass transport
18
Table 7. Calculated range of % mass change during formation of the selvages (ΔCi/C°)·100
i
Sample
S40-1D
S40-1A
S40-1R
S35-1G
S35-1S
S35-1X
Si –35.2%
–82.1%
–65.2%
–76.4%
–37.2%
–47.3%
K
+ 9.9%
–71.1%
–34.3%
–69.5%
–0.5%
–11.4%
–11.0%
–60.6%
–53.9%
–62.5%
–63.2%
–55.0%
Overview of geochemical changes. Regardless of grade or
type of host rock, formation of selvages around metamorphic
veins in the Waits River Formation typically involved significant
depletions in K, Rb, Ba, and Si. There was significant loss of K
from all five analyzed selvages and significant loss of Rb, Ba,
and Si from all but one. In samples from the kyanite zone, there
is additional systematic depletion of both pelite and carbonate
wall rocks in Mg and Cs during formation of selvages. Regardless
of the details of the immobile reference frame, the amount of
element loss and gain was quite variable from sample to sample.
The qualitative similarity among samples is further evidence that
much of the chemical change in the selvages during formation
of veins occurred at a very early stage of metamorphism (conditions of the chlorite zone or at lower grade). The behavior of
Mg and Cs, however, indicate important differences in element
mobility related to grade.
Volume changes. The change in volume during alteration
(referenced to the original volume of wall rock) can be determined from the concentration ratio for the immobile reference
frame for the sample. If a sample experienced no volume change,
the concentration ratio of the immobile reference frame is 1. If
volume decreased during alteration, the concentration ratio of
the immobile reference frame generally is >1 (the exceptions
are isochemical volume removal, e.g., dissolution of calcite in
a pure calcite limestone and polymorphic phase change accompanied by a density change, e.g., conversion of calcite in a pure
calcite limestone to aragonite), and if volume increased during
alteration, it is <1. The fractional volume change (∆V/V°) can be
calculated using values of the concentration ratio of immobile
elements along with values of rock density for the selvage (ρ')
and wall rock (ρ°):
∆V ρ C 
= ⋅ −1 ρ' C '
V
Rb (ICP-MS) –11.5%
+50.1%
–66.3%
–45.7%
–53.0%
–11.2%
–47.0%
–31.3%
–67.5%
–48.5%
–55.6%
–25.4%
+50.9%
–36.4%
–13.1%
–51.4%
–41.8%
–24.3%
(2)
Results for each sample are presented in Table 8, with a range
of volume loss/gain calculated using the upper and lower bounds
of C'/C° for the immobile reference frame. As expected, application of the analysis to portions of selvage-free sample S40-1D
that are adjacent to and distal from the vein indicates no volume
change within error of measurement. Two of the five selvages
experienced a significant decrease in volume during alteration
of 4–67%, including both kyanite-zone pelite samples. For the
other three samples with selvages (chlorite- and kyanite-zone
carbonate samples S40-1A, S40-1R, and S35-1X), the evidence
for a change in volume is inconclusive because of uncertainty in
the choice of the immobile reference frame.
Mineralogical differences. The amount of quartz is systematically less in selvages than in adjacent unaltered wall rock
(Table 3; Fig. 5). The depletion in quartz is the mineralogical
expression of whole-rock depletion in Si during formation of the
Ba (ICP-MS)
–14.0%
+45.8%
–66.0%
–45.2%
–56.1%
–17.1%
–37.3%
–18.8%
–64.6%
–43.9%
–44.7%
–7.0%
Table 8. Calculated volume change during formation of the selvages
Sample
S40-1D
S40-1A
S40-1R
S35-1G
S35-1S
S35-1X
Rock type
pelite
carbonate
carbonate
pelite
pelite
carbonate
Upper C‘/Cº
1.5
1.6
1.3
2.6
1.6
1.5
Lower
C‘/Cº
0.9
1.0
0.7
2.0
1.0
0.9
Bounds on % Volume
change (∆V/Vº)·100
–32.9%
+13.8%
–37.8%
+ 0.3%
–22.1%
+47.1%
–67.5%
–57.9%
–39.4%
–3.9%
–33.2%
+12.3%
selvages (Table 7). Uncertainty in the immobile reference frame
unfortunately prohibits formulation of mineral-fluid reactions
that would relate in detail the changes in whole-rock chemistry
during development of the alteration selvages to corresponding
mineralogical changes.
Discussion
Mass transfer at the vein scale
The question whether there was an overall gain or loss of
elements in the formation of a given vein-selvage system as a
whole is addressed by a comparison between the mass of elements removed from the selvage and mass added to the vein. For
this calculation, the thickness of both selvages and veins must be
known. In the kyanite-zone outcrop, most veins were highly deformed, and accurate determination of the original proportion of
vein and selvage widths for a single vein is not possible (Fig. 3b).
In the chlorite-zone outcrop, however, the veins are boudinaged
but much less deformed (Fig. 3a). A meaningful determination
of the average widths of vein and selvage prior to deformation
was obtained by measuring both along 23 m of a single vein at
15 cm intervals (a distance much less than that between boudins).
Measured widths for each were then averaged.
If there was no mass transfer of element i into or out of
the vein-selvage system as a whole, the mass of i per volume
removed from the selvage times the average thickness of the selvage zone prior to selvage formation must equal the mass added
per volume to the vein times the average thickness of the vein:
∆Ci,sel · ρsel · xsel = ∆Ci,vein · ρvein · xvein (3)
where xsel and xvein are the average thickness of selvage prior to
selvage formation and vein respectively (the thicknesses of selvage on both sides of the vein were added together). Values for
∆Ci,sel for each element in each sample were determined from the
range of ΔCi'/C°i calculated from equation 1 using the upper and
lower bounds on the immobile reference frame along with measured values for C°i (wall-rock concentrations of each element).
Values for ∆Ci,vein were determined from estimated modes of
minerals (quartz, calcite) assuming ideal mineral compositions.
The density of the selvage material prior to selvage formation
(ρsel) was determined from measurements of sample mass and
volume of the wall rock.
Penniston-Dorland and Ferry: Element mobility and scale of mass transport
For Si in the chlorite-zone sample S40-1A, ∆Ci,sel = –14%
to –17%, ρsel = 2.71 g/cm3, ∆Ci,vein ~ 40% (from 85 vol% of
quartz in the vein), ρvein ~2.66 g/cm3 (density of 85% quartz
+ 15% calcite), requiring the thickness of the selvage to be
approximately 2.4–2.7× greater than the vein if Si was conserved in the vein-selvage system (i.e., if the source of Si
in the vein was local). For the chlorite-zone sample S40-1R
(∆Ci,sel = –6% to –9%, ρsel = 2.71 g/cm3, ∆Ci,vein ~ 30%, ρvein
~ 2.67 g/cm3), the selvage would have to be approximately
3.3–6.4× thicker than the vein if Si was conserved in the
vein-selvage system. The average observed ratio of selvage
width to vein width, calculated from direct measurements
of the thickness of selvages and veins in the chlorite zone,
is 0.4. When the selvage/vein ratio is corrected for the range
of calculated volume changes for chlorite-zone selvages (see
Table 8), the range becomes 0.27 to 0.64. These values are well
below the predicted value for conservation of Si in any veinselvage system. Much of the Si must have been transported
on a scale larger than a single vein and its associated selvage.
Similar analysis for veins in the kyanite zone, applying the vein
and selvage thickness measurements from the chlorite zone,
requires ratios of selvage width to vein width of 0.9–1.0 (S351G), 4.6–19.0 (S35-1X), and 4.5–340 (S35-1S) for derivation
of Si in vein from selvage. At the minimum, local derivation
of the amount of quartz in veins would require a selvage 1.5×
as thick as is observed (sample S35-1G), and in other cases
selvages that are at least ~4–10× thicker than observed.
There is no chemical evidence for loss (or gain) of Ca in any of
the selvages. Most of the veins, however, contain calcite, requiring addition of Ca to the vein-selvage system. For sample S40-1A
~6 wt% Ca was added (~15 vol% calcite) and for sample S40-1R
~14 wt% Ca was added (~34% calcite). For the kyanite-zone
samples the amount of Ca added were 0 wt% (sample S35-1S,
no calcite in vein), ~4 wt% (S35-1X, 10% calcite in vein), and
~18 wt% Ca (S35-1G, ~44% calcite in vein). Calcium, as well
as Si, must have been transported on a scale larger than a single
vein-selvage system.
Potassium in both the veins and the selvages is sited primarily in muscovite and biotite. The observed abundance of micas
in veins is small, <1%. Potassium is the one element removed
from all selvages. If the amount of K in the veins balances the
amount of K removed from the selvages, the veins would have
to contain ~0.1% muscovite + biotite, which is consistent with
the observation that micas constitute <1% of the veins. Barium,
Rb, and Cs are also generally removed from wall rock during
selvage formation and sited primarily in micas. Like K, the
amount lost from selvages may be balanced by that occurring
in micas in the veins.
Overall, both Si and Ca were added to the vein-selvage
system during alteration of selvages and formation of the veins.
The behavior of K, Ba, Rb, and Cs is inconclusive, and these
elements may or may not have been conserved during alteration
in the vein-selvage system as a whole.
The observed depletion of quartz in the selvages (Fig. 5)
contains further information about the mechanism by which
selvages formed. Fluid in both the vein and the wall rock must
have been saturated with respect to quartz because both contain abundant quartz. The absence of quartz in most selvages,
19
however, indicates that fluid in the selvages was undersaturated
with respect to quartz. The apparent paradox is resolved if a
concentration gradient in aqueous SiO2 existed in fluid between
vein (lower) and wall rock (higher). The gradient could have
arisen in one of two ways (or both). First, fluid in the vein
could have had lower XH2O than fluid in wall rock (for example,
if the vein fluid was more saline or had a higher XCO2). Second,
a P gradient between wall rock and adjacent open fracture in
which the vein formed (Walther and Orville 1982) would result
in lower SiO2 solubility in the vein than in the wall rock even
if fluids were otherwise chemically identical in vein and wall
rock. In either case, considering Fick’s first law, the gradient in
dissolved silica between vein and wall rock would drive silica
diffusion from wall rock to vein and hence promote dissolution
of quartz in wall rock adjacent to the vein (now selvage). The
systematic increase in quartz content in the transition zone with
increasing distance from the vein (Fig. 5) and the displacement
of the transition zone away from the vein would have developed
from a negative curvature of the profile in silica concentration
with increasing distance from the vein and/or by progressive
penetration of the composition profile into the wall rock over
the lifetime of the vein.
Mass transfer at the outcrop scale
A comparison of the amount of Si lost from wall rock during
selvage formation and the amount gained through its addition
to veins can be calculated for an entire outcrop by combining
the chemical data for the vein selvages and wall rock, vein
mineralogy, and total vein and selvage abundances at each
outcrop. The original volume of rock before selvage formation
was first calculated by adjusting the current volume of selvage
to its original volume using Equation 2. The average change in
an element for a whole outcrop due to selvage formation can be
calculated from:
∆Ci,TOT(g) = ∆Ci,sel · ρsel · Vsel
(4)
where Vsel is the volume fraction of selvage in an outcrop determined from the total amount of selvage measured along the
traverse (assuming the traverse is representative of the outcrop
as a whole), a range of values for ∆Ci,sel is determined using
Equation 1, and ρsel is the calculated density of the selvage. For
the chlorite zone traverse, the mass of Si removed from wall rock
due to selvage formation is 0.3–2.6 mg/cm3. The amount of Si
added to the same traverse during vein formation (calculated in
the same fashion, assuming an average of 75% quartz in each
vein) is 41.8–42.0 mg/cm3. For the kyanite-zone traverse, the
total amount of Si removed during selvage formation is 0.1–6.0
mg/cm3, and the Si added to V1 veins is 57.3–57.6 mg/cm3. At
the outcrop scale, then, there was an overall addition of ~39–42
mg/cm3 Si in the chlorite zone and of ~51–57 mg/cm3 in the
kyanite zone. The amount of Si lost during selvage formation is
only ~0.4–10.4% of the amount added during vein formation. As
a corollary, ~90% or more of the Si in the V1 veins was derived
from a source further away than the dimensions of the outcrops
investigated. Furthermore, because Si was added to vein-selvage
systems in both pelites and carbonates from both the chlorite and
kyanite zones, the distance of Si transport during vein formation
20
Penniston-Dorland and Ferry: Element mobility and scale of mass transport
was probably similar to or larger than the dimensions of the
study area in Figure 1.
Fluid flow and formation of veins
Potential fluid sources for the fluids that were involved in
the mass transfer recorded in these veins include magmatic
fluids and metamorphic fluids derived from devolatilization
of deeper siliciclastic rocks. The data collected in this study
does not allow for discrimination among these potential fluid
sources.
Regardless of its source, the amount of fluid required for
precipitation of quartz in veins can be calculated using Equation
3 of Ferry and Dipple (1991). The value of reaction progress
was calculated assuming veins are 75% quartz and using the
molar volume of quartz (Holland and Powell 1998). The stoichiometric coefficient for the only fluid species involved in the
precipitation of quartz (H4SiO4) is 1. Values of (∂XSiO2/∂T)P and
(∂XSiO2/∂P)T were calculated at chlorite-zone conditions (400
°C and 7.8 kbar) and kyanite-zone conditions (550 °C and 7.8
kbar) using the solubility of quartz in H2O from Fournier and
Potter (1982) and the density of H2O from Burnham et al. (1969).
Vertical flow down a temperature gradient of –25 °C/km and a
lithostatic pressure gradient of –270 bar/km was assumed. The
range in calculated time-integrated fluid flux for V1 veins is
4–9·107 cm3 fluid/cm2 vein. The range corresponds to the limits of
vein formation under conditions of the chlorite and kyanite zones,
respectively. The time-integrated fluid flux during formation
of V1 veins, averaged for an entire outcrop, is the above result
multiplied by the fraction of the outcrop that is quartz veins; in
the chlorite zone it is 2·106 cm3/cm2 outcrop, and in the kyanite
zone it is 6·106 cm3/cm2 outcrop. The outcrop-scale value for
the kyanite zone is about one order of magnitude greater than
estimates for the time-integrated fluid flux required to account
for the observed progress of prograde biotite- and garnet-forming
reactions in kyanite-zone rocks of the Waits River Formation
(Ferry 1994; Wing and Ferry 2007). These results imply a large
component of fracture-controlled fluid flow during vein formation that had little or no chemical communication with wall rocks
outside the narrow alteration selvages.
Comparison to other geologic settings
The calculated time-integrated fluid flux through individual
veins of the Waits River Formation (4–9·107 cm3/cm2) is similar
to that calculated for veins in a variety of other metamorphic
settings, including amphibolite-facies veins of the Wepawaug
Schist (3·107 cm3/cm2, Ague 1994b), greenschist-facies (350–450
°C, 6–8 kbar) veins of the Otago Schist, New Zealand (5·108
cm3/cm2, Breeding and Ague 2002), and veins in Barrow’s
garnet zone, northeast Scotland (~3·106 cm3/cm2, Ague 1997a).
The calculated time-integrated fluid flux due to fracture flow
over the scale of an entire outcrop in the Waits River Formation
(~2–6·106 cm3/cm2) is also similar to outcrop-scale estimates of
fracture flow in other veined metamorphic systems, including
the Wepawaug Schist (~6·106 cm3/cm2, Ague 1994b) and the
Otago Schist (~106–107 cm3/cm2, Breeding and Ague 2002).
Permeability at the outcrop scale is controlled by fractures.
Transient periods of large permeability during times of fracturing
and fluid flow are suggested by the calculated large volumes of
fluids traveling through fractures and the evidence suggesting
multiple stages of vein formation. Such large volumes of fluid
mobilize and transport several elements. The specific details of
mass transfer are essential for understanding the distribution of
elements in the crust.
The veins that are the subject of this study are just one part
of a larger system of fluid flow and mass transfer during the
Acadian orogeny in eastern Vermont. This study has focused
on one of three generations of veins in one of the two major
formations in the region, the Waits River Formation. The overlying Gile Mountain Formation contains multiple generations
of veins. Nevertheless, patterns are emerging of large-scale
mass transfer through fractures with individual veins recording
multiple stages of fluid flow, during which Si and Ca are added
at the present level of exposure. These results can be placed in
the context of other studies of veins and associated alteration
selvages during metamorphism. The pattern of silica addition
in the Waits River Formation is consistent with studies of
vein formation in the Wepawaug Schist of Connecticut (Ague
1994b). The Waits River Formation and Wepawaug Schist are
believed to have the same depositional age (Fritts 1962; Hueber
et al. 1990), and both were metamorphosed during the Acadian
orogeny (Thompson et al. 1968; Thompson and Norton 1968;
Osberg et al. 1989; Lanzirotti and Hanson 1996). Metamorphic
grade in each terrain ranges from chlorite grade up to kyanite
grade. The ranges of calculated pressures and temperatures are
similar (~400–650 °C in the chlorite through kyanite zones of
the Wepawaug Schist and ~475–550 °C in the biotite through
kyanite zones of the Waits River Formation; 7–9 kbar in the
Wepawaug Schist and ~7–8 kbar in the Waits River Formation).
The two terrains differ in the observed patterns of Na and Ca
alteration. The Waits River records addition of Ca to veins,
and the Wepawaug records depletion of Na in selvages. These
differences may be due to mineralogical differences between
the two formations. Carbonate minerals occur in only minor
abundances at low grades in the wall rock and veins of the
Wepawaug Schist (Ague 1994a). The Waits River contains
abundant carbonate minerals in many of the samples, and the
samples with large abundance of carbonate have very low
concentrations of Na. Indeed, the one Waits River sample that
contains no carbonate minerals (S35-1S) is the only sample
in this study that clearly shows depletion of Na, similar to the
Wepawaug samples. The abundance of carbonate minerals
may account for the addition of Ca to the veins in the Waits
River that is not observed in the Wepawaug. The patterns of
mass transfer through fractures in the continental collisional
settings of the Waits River Formation and Wepawaug Schist are
distinctly different from the patterns observed in accretionary
wedge settings, in which both Na and Ca addition to selvages
is observed (Masters and Ague 2005) and again different from
the Kanmantoo copper deposit in which large-scale depletion
in both Ca and Na is documented (Oliver et al. 1998). The
nature of mass transfer during metamorphism will likely vary
depending on a variety of factors, including geologic setting,
rock type, potential fluid sources, and temperature. Although
the results from different locations differ in details, all of them
show that fluid flow through fractures during metamorphism
changes the bulk composition of the crust. Fluid flow associated
Penniston-Dorland and Ferry: Element mobility and scale of mass transport
with veins is a potent agent for redistributing elements in the
crust at the kilometer to tens of kilometers scale.
Acknowledgments
We thank Michael Zieg, Lizet Christiansen, Sarah Frost, Sarah Carmichael,
and Boswell Wing for assistance with fieldwork. We appreciate the constructive
reviews by Jay Ague and Robert Wintsch. Research supported by NSF grant
EAR-0229267 to J.M.F.
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Manuscript received September 25, 2006
Manuscript accepted September 17, 2007
Manuscript handled by Edward Ghent