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John M Ferry - One of the best experts on this subject based on the ideXlab platform.
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Formation of Wollastonite by Chemically Reactive Fluid Flow During Contact Metamorphism, Mt. Morrison Pendant, Sierra Nevada, California, USA
Journal of Petrology, 2020Co-Authors: John M Ferry, Boswell A Wing, Douglas RumbleAbstract:Quartz–calcite sandstones experienced the reaction calcite + INTRODUCTION quartz = wollastonite + CO2 during prograde Contact metaFlow of chemically reactive fluid may control the minmorphism at P = 1500 bars and T = 560°C. Rocks were in eralogy, stable isotope composition, and trace element equilibrium during reaction with a CO2–H2O fluid with XCO2 = chemistry of rocks during Contact Metamorphism (e.g. 0·14. The transition from calcite-bearing, wollastonite-free to Labotka et al., 1988; Jamtveit et al., 1992a, 1992b; Nabelek wollastonite-bearing, calcite-free rocks across the wollastonite isograd & Labotka, 1993; Bowman et al., 1994; Roselle et al., is only several millimeters wide. The wollastonite-forming reaction 1999). A number of aspects of metamorphic fluid flow, was driven by infiltration of quartz–calcite sandstone by chemically however, remain the subject of debate, including the reactive H2O-rich fluids, and the distribution of wollastonite directly direction of flow (Labotka et al., 1988; Ferry & Dipple, images the flow paths of reactive fluids during Metamorphism. The 1992; Ferry, 1995a; Hanson, 1995a), whether numerical mapped distribution of wollastonite and modeling of an O-isotope models that assume uniform rock properties adequately profile across a lithologic Contact indicate that the principal direction predict the geometry of fluid flow in aureoles that contain of flow was layer-parallel, directed upward, with any cross-layer a variety of anisotropic structural features (Hanson, 1992, component of flow
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formation of forsterite by silicification of dolomite during Contact Metamorphism
Journal of Petrology, 2011Co-Authors: John M Ferry, Takayuki Ushikubo, John W ValleyAbstract:Four samples that experienced the infiltration-driven reaction 2 dolomiteþ SiO2(aq)1⁄4 forsteriteþ 2 calciteþ 2 CO2 exhibit correlations among forsterite crystal morphology, size, number density (number of Fo crystals per cm Fo), and oxygen isotope ratio (dO).The dO of coexisting forsterite, calcite, and dolomite were determined by in situ ion microprobe analysis with a spatial resolution of 15 mm. Sample KP1L from the Twin Lakes pendant, Sierra Nevada, California, contains blocky forsterite with the largest average crystal size and the lowest crystal number density. Forsterite and calcite are uniform in dO with the measured fractionation consistent with equilibrium at the temperature inferred for the reaction (5958C). Sample B4L from the Beinn an Dubhaich aureole, Scotland, contains tabular forsterite with intermediate average size and number density. Forsterite and calcite are uniform in dO but the measured fractionation is smaller than the equilibrium value at the temperature inferred for the reaction (6808C). Samples B1W and B43A from the Beinn an Dubhaich aureole contain rounded forsterite with the smallest average size and largest number density. Forsterite has variable dO differing among grains by up to 7·4o in single samples and by up to 3·1o within a single grain, precluding isotope equilibrium with calcite and dolomite. Crystal morphology, size, number density, dO(Fo), and O(Cal^Fo) can be understood in terms of the interplay between reaction affinity (A) and Peclet Number (Pe) during formation of forsterite (KP1L: low A, high Pe; B4L: intermediate A and low Pe; B43A: high A, low Pe; B1W: high A, increasing Pe). Differences in A were controlled by variations in XCO2 in the infiltrating fluid. Differences in Pe were controlled by variations in fluid flux and/or width of the reaction zone. If the infiltrating fluid is initially quartz-saturated, phase equilibria require that development of forsterite and periclase from dolomite during Contact Metamorphism must be preceded by reactions that produce diopside, wollastonite, and/or other skarn minerals upstream.
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the direction of fluid flow during Contact Metamorphism of siliceous carbonate rocks new data for the monzoni and predazzo aureoles northern italy and a global review
Contributions to Mineralogy and Petrology, 2002Co-Authors: John M Ferry, Boswell A Wing, Sarah C Pennistondorland, Douglas RumbleAbstract:Periclase formed in siliceous dolomitic marbles during Contact Metamorphism in the Monzoni and Predazzo aureoles, the Dolomites, northern Italy, by infiltration of the carbonate rocks by chemically reactive, H2O-rich fluids at 500 bar and 565–710 °C. The spatial distribution of periclase and oxygen isotope compositions is consistent with reactive fluid flow that was primarily vertical and upward in both aureoles with time-integrated flux ~5,000 and ~300 mol fluid/cm2 rock in the Monzoni and Predazzo aureoles, respectively. The new results for Monzoni and Predazzo are considered along with published studies of 13 other aureoles to draw general conclusions about the direction, amount, and controls on the geometry of reactive fluid flow during Contact Metamorphism of siliceous carbonate rocks. Flow in 12 aureoles was primarily vertically upward with and without a horizontal component directed away from the pluton. Fluid flow in two of the other three was primarily horizontal, directed from the pluton into the aureole. The direction of flow in the remaining aureole is uncertain. Earlier suggestions that fluid flow is often horizontal, directed toward the pluton, are likely explained by an erroneous assumption that widespread coexisting mineral reactants and products represent arrested prograde decarbonation reactions. With the exception of three samples from one aureole, time-integrated fluid flux was in the range 102–104 mol/cm2. Both the amount and direction of fluid flow are consistent with hydrodynamic models of Contact Metamorphism. The orientation of bedding and lithologic Contacts appears to be the principal control over whether fluid flow was either primarily vertical or horizontal. Other pre-metamorphic structures, including dikes, faults, fold hinges, and fracture zones, served to channel fluid flow as well.
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formation of wollastonite by chemically reactive fluid flow during Contact Metamorphism mt morrison pendant sierra nevada california usa
Journal of Petrology, 2001Co-Authors: John M Ferry, Boswell A Wing, Douglas RumbleAbstract:Quartz–calcite sandstones experienced the reaction calcite + INTRODUCTION quartz = wollastonite + CO2 during prograde Contact metaFlow of chemically reactive fluid may control the minmorphism at P = 1500 bars and T = 560°C. Rocks were in eralogy, stable isotope composition, and trace element equilibrium during reaction with a CO2–H2O fluid with XCO2 = chemistry of rocks during Contact Metamorphism (e.g. 0·14. The transition from calcite-bearing, wollastonite-free to Labotka et al., 1988; Jamtveit et al., 1992a, 1992b; Nabelek wollastonite-bearing, calcite-free rocks across the wollastonite isograd & Labotka, 1993; Bowman et al., 1994; Roselle et al., is only several millimeters wide. The wollastonite-forming reaction 1999). A number of aspects of metamorphic fluid flow, was driven by infiltration of quartz–calcite sandstone by chemically however, remain the subject of debate, including the reactive H2O-rich fluids, and the distribution of wollastonite directly direction of flow (Labotka et al., 1988; Ferry & Dipple, images the flow paths of reactive fluids during Metamorphism. The 1992; Ferry, 1995a; Hanson, 1995a), whether numerical mapped distribution of wollastonite and modeling of an O-isotope models that assume uniform rock properties adequately profile across a lithologic Contact indicate that the principal direction predict the geometry of fluid flow in aureoles that contain of flow was layer-parallel, directed upward, with any cross-layer a variety of anisotropic structural features (Hanson, 1992, component of flow <0·1% of the layer-parallel component. Fluid 1995b; Cook et al., 1997), and the degree to which local flow was channeled at a scale of 1–100 m by pre-metamorphic mineral–fluid equilibrium is attained (Lasaga & Rye, dikes, thrust and strike-slip faults, fold hinges, bedding, and 1993; Bolton et al., 1999; Lasaga et al., 2000). These and stratigraphic Contacts. Limits on the amount of fluid, based on related questions were addressed in an investigation of minimum and maximum estimates for the displacement of the Contact Metamorphism in the Mt. Morrison pendant, wollastonite reaction front from the fluid source, are (0·7–1·9) × eastern Sierra Nevada, California. The location is an 10 cm fluid/cm rock. The sharpness of the wollastonite isograd, exceptional site for the study of metamorphic fluid flow the consistency of mineral thermobarometry, the uniform measured for several reasons. First, the Mt. Morrison Sandstone, O–O fractionations between quartz and calcite, and model the focus of this study, is ideal for application of concalculations all argue for a close approach to local mineral–fluid tinuum models of coupled fluid flow and reaction because equilibrium during the wollastonite-forming reaction. it is unusually homogeneous in mineralogy and texture.
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Structurally controlled fluid flow during Contact Metamorphism in the Ritter Range pendant, California, USA
Contributions to Mineralogy and Petrology, 1998Co-Authors: John M Ferry, Sorena S. Sorensen, Douglas RumbleAbstract:The mineralogy and O-isotope geochemistry of siliceous limestones from the Ritter Range pendant constrain the geometry and amount of fluid flow during Contact Metamorphism associated with emplacement of a pluton of the Sierra Nevada Batholith. Wollastonite (Wo) replaces calcite (Cal) + quartz (Qtz) on a layer-by-layer basis in homoclinal beds that strike NW and dip almost vertically. At the peak of Metamorphism (P≈ 1500 bars, T≈ 600 °C) fluid in equilibrium with Cal, Qtz, and Wo has composition XCO2=0.28, requiring that the Wo-forming reaction was driven by infiltration of reactive H2O-rich fluid. The spatial distribution of Wo and Cal + Qtz records that peak metamorphic fluid flow was layer-parallel, upward. Bounds on the prograde time-integrated fluid flux associated with formation of Wo are set by: (1) the overlap in O-isotope composition between Wo-bearing and Wo-free rocks (>245 mol fluid/cm2 rock); (2) the amount of fluid that would drive the Wo-reaction front upward to the present level of exposure from a point at depth where Cal, Qtz, and Wo would be in equilibrium with pure CO2 (
Douglas Rumble - One of the best experts on this subject based on the ideXlab platform.
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Formation of Wollastonite by Chemically Reactive Fluid Flow During Contact Metamorphism, Mt. Morrison Pendant, Sierra Nevada, California, USA
Journal of Petrology, 2020Co-Authors: John M Ferry, Boswell A Wing, Douglas RumbleAbstract:Quartz–calcite sandstones experienced the reaction calcite + INTRODUCTION quartz = wollastonite + CO2 during prograde Contact metaFlow of chemically reactive fluid may control the minmorphism at P = 1500 bars and T = 560°C. Rocks were in eralogy, stable isotope composition, and trace element equilibrium during reaction with a CO2–H2O fluid with XCO2 = chemistry of rocks during Contact Metamorphism (e.g. 0·14. The transition from calcite-bearing, wollastonite-free to Labotka et al., 1988; Jamtveit et al., 1992a, 1992b; Nabelek wollastonite-bearing, calcite-free rocks across the wollastonite isograd & Labotka, 1993; Bowman et al., 1994; Roselle et al., is only several millimeters wide. The wollastonite-forming reaction 1999). A number of aspects of metamorphic fluid flow, was driven by infiltration of quartz–calcite sandstone by chemically however, remain the subject of debate, including the reactive H2O-rich fluids, and the distribution of wollastonite directly direction of flow (Labotka et al., 1988; Ferry & Dipple, images the flow paths of reactive fluids during Metamorphism. The 1992; Ferry, 1995a; Hanson, 1995a), whether numerical mapped distribution of wollastonite and modeling of an O-isotope models that assume uniform rock properties adequately profile across a lithologic Contact indicate that the principal direction predict the geometry of fluid flow in aureoles that contain of flow was layer-parallel, directed upward, with any cross-layer a variety of anisotropic structural features (Hanson, 1992, component of flow
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the direction of fluid flow during Contact Metamorphism of siliceous carbonate rocks new data for the monzoni and predazzo aureoles northern italy and a global review
Contributions to Mineralogy and Petrology, 2002Co-Authors: John M Ferry, Boswell A Wing, Sarah C Pennistondorland, Douglas RumbleAbstract:Periclase formed in siliceous dolomitic marbles during Contact Metamorphism in the Monzoni and Predazzo aureoles, the Dolomites, northern Italy, by infiltration of the carbonate rocks by chemically reactive, H2O-rich fluids at 500 bar and 565–710 °C. The spatial distribution of periclase and oxygen isotope compositions is consistent with reactive fluid flow that was primarily vertical and upward in both aureoles with time-integrated flux ~5,000 and ~300 mol fluid/cm2 rock in the Monzoni and Predazzo aureoles, respectively. The new results for Monzoni and Predazzo are considered along with published studies of 13 other aureoles to draw general conclusions about the direction, amount, and controls on the geometry of reactive fluid flow during Contact Metamorphism of siliceous carbonate rocks. Flow in 12 aureoles was primarily vertically upward with and without a horizontal component directed away from the pluton. Fluid flow in two of the other three was primarily horizontal, directed from the pluton into the aureole. The direction of flow in the remaining aureole is uncertain. Earlier suggestions that fluid flow is often horizontal, directed toward the pluton, are likely explained by an erroneous assumption that widespread coexisting mineral reactants and products represent arrested prograde decarbonation reactions. With the exception of three samples from one aureole, time-integrated fluid flux was in the range 102–104 mol/cm2. Both the amount and direction of fluid flow are consistent with hydrodynamic models of Contact Metamorphism. The orientation of bedding and lithologic Contacts appears to be the principal control over whether fluid flow was either primarily vertical or horizontal. Other pre-metamorphic structures, including dikes, faults, fold hinges, and fracture zones, served to channel fluid flow as well.
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formation of wollastonite by chemically reactive fluid flow during Contact Metamorphism mt morrison pendant sierra nevada california usa
Journal of Petrology, 2001Co-Authors: John M Ferry, Boswell A Wing, Douglas RumbleAbstract:Quartz–calcite sandstones experienced the reaction calcite + INTRODUCTION quartz = wollastonite + CO2 during prograde Contact metaFlow of chemically reactive fluid may control the minmorphism at P = 1500 bars and T = 560°C. Rocks were in eralogy, stable isotope composition, and trace element equilibrium during reaction with a CO2–H2O fluid with XCO2 = chemistry of rocks during Contact Metamorphism (e.g. 0·14. The transition from calcite-bearing, wollastonite-free to Labotka et al., 1988; Jamtveit et al., 1992a, 1992b; Nabelek wollastonite-bearing, calcite-free rocks across the wollastonite isograd & Labotka, 1993; Bowman et al., 1994; Roselle et al., is only several millimeters wide. The wollastonite-forming reaction 1999). A number of aspects of metamorphic fluid flow, was driven by infiltration of quartz–calcite sandstone by chemically however, remain the subject of debate, including the reactive H2O-rich fluids, and the distribution of wollastonite directly direction of flow (Labotka et al., 1988; Ferry & Dipple, images the flow paths of reactive fluids during Metamorphism. The 1992; Ferry, 1995a; Hanson, 1995a), whether numerical mapped distribution of wollastonite and modeling of an O-isotope models that assume uniform rock properties adequately profile across a lithologic Contact indicate that the principal direction predict the geometry of fluid flow in aureoles that contain of flow was layer-parallel, directed upward, with any cross-layer a variety of anisotropic structural features (Hanson, 1992, component of flow <0·1% of the layer-parallel component. Fluid 1995b; Cook et al., 1997), and the degree to which local flow was channeled at a scale of 1–100 m by pre-metamorphic mineral–fluid equilibrium is attained (Lasaga & Rye, dikes, thrust and strike-slip faults, fold hinges, bedding, and 1993; Bolton et al., 1999; Lasaga et al., 2000). These and stratigraphic Contacts. Limits on the amount of fluid, based on related questions were addressed in an investigation of minimum and maximum estimates for the displacement of the Contact Metamorphism in the Mt. Morrison pendant, wollastonite reaction front from the fluid source, are (0·7–1·9) × eastern Sierra Nevada, California. The location is an 10 cm fluid/cm rock. The sharpness of the wollastonite isograd, exceptional site for the study of metamorphic fluid flow the consistency of mineral thermobarometry, the uniform measured for several reasons. First, the Mt. Morrison Sandstone, O–O fractionations between quartz and calcite, and model the focus of this study, is ideal for application of concalculations all argue for a close approach to local mineral–fluid tinuum models of coupled fluid flow and reaction because equilibrium during the wollastonite-forming reaction. it is unusually homogeneous in mineralogy and texture.
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Structurally controlled fluid flow during Contact Metamorphism in the Ritter Range pendant, California, USA
Contributions to Mineralogy and Petrology, 1998Co-Authors: John M Ferry, Sorena S. Sorensen, Douglas RumbleAbstract:The mineralogy and O-isotope geochemistry of siliceous limestones from the Ritter Range pendant constrain the geometry and amount of fluid flow during Contact Metamorphism associated with emplacement of a pluton of the Sierra Nevada Batholith. Wollastonite (Wo) replaces calcite (Cal) + quartz (Qtz) on a layer-by-layer basis in homoclinal beds that strike NW and dip almost vertically. At the peak of Metamorphism (P≈ 1500 bars, T≈ 600 °C) fluid in equilibrium with Cal, Qtz, and Wo has composition XCO2=0.28, requiring that the Wo-forming reaction was driven by infiltration of reactive H2O-rich fluid. The spatial distribution of Wo and Cal + Qtz records that peak metamorphic fluid flow was layer-parallel, upward. Bounds on the prograde time-integrated fluid flux associated with formation of Wo are set by: (1) the overlap in O-isotope composition between Wo-bearing and Wo-free rocks (>245 mol fluid/cm2 rock); (2) the amount of fluid that would drive the Wo-reaction front upward to the present level of exposure from a point at depth where Cal, Qtz, and Wo would be in equilibrium with pure CO2 (
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structurally controlled fluid flow during Contact Metamorphism in the ritter range pendant california usa
Contributions to Mineralogy and Petrology, 1998Co-Authors: John M Ferry, Sorena S. Sorensen, Douglas RumbleAbstract:The mineralogy and O-isotope geochemistry of siliceous limestones from the Ritter Range pendant constrain the geometry and amount of fluid flow during Contact Metamorphism associated with emplacement of a pluton of the Sierra Nevada Batholith. Wollastonite (Wo) replaces calcite (Cal) + quartz (Qtz) on a layer-by-layer basis in homoclinal beds that strike NW and dip almost vertically. At the peak of Metamorphism (P≈ 1500 bars, T≈ 600 °C) fluid in equilibrium with Cal, Qtz, and Wo has composition XCO2=0.28, requiring that the Wo-forming reaction was driven by infiltration of reactive H2O-rich fluid. The spatial distribution of Wo and Cal + Qtz records that peak metamorphic fluid flow was layer-parallel, upward. Bounds on the prograde time-integrated fluid flux associated with formation of Wo are set by: (1) the overlap in O-isotope composition between Wo-bearing and Wo-free rocks (>245 mol fluid/cm2 rock); (2) the amount of fluid that would drive the Wo-reaction front upward to the present level of exposure from a point at depth where Cal, Qtz, and Wo would be in equilibrium with pure CO2 (<1615 mol/cm2). Back-reaction of Wo to Cal + Qtz records an additional time-integrated retrograde fluid flux of ≈ 200–1000 mol/cm2. The direction and amount of flow inferred from mineralogical and isotopic data agree with the results of the hydrologic model for metamorphic fluid flow in the area of Hanson et al. (1993). Fingers of Wo-bearing rock that extend farthest from the fluid source along Contacts between limestone and more siliceous rocks point to strong control of flow geometry at the 0.1–100 m scale exerted by premetamorphic structures. Studies that neglect structural control at this scale may fail to predict correctly fundamental aspects of Contact metamorphic fluid flow.
John R Bowman - One of the best experts on this subject based on the ideXlab platform.
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mineralogical evidence for fluid rock interaction accompanying prograde Contact Metamorphism of siliceous dolomites alta stock aureole utah usa
Journal of Petrology, 2000Co-Authors: Stephen J Cook, John R BowmanAbstract:Contact Metamorphism of siliceous dolomite in the southern part of agrees well with the q m TIFF (3·4 × 10 7 mol/m 2 ) determined by the metamorphic aureole of the Alta stock (Utah, USA) produced numerical simulation of the temperature and 18 O depletion profiles the prograde isograd sequence: talc (Tc), tremolite (Tr), forsterite preserved in the southern aureole. The estimates of q m TIFF for the (Fo), and periclase (Per). Calcite (Cc)–dolomite (Do) ge- forsterite and tremolite zones have much greater uncertainty, but othermometry and phase equilibria define a general prograde T– may indicate that fluid flux was considerably lower in these zones X(CO2) path of decreasing X(CO2) with rising temperature for than in the periclase zone. Given the outward (down-temperature), the dolomite. High-variance assemblages typify the aureole. Per + subhorizontal flow geometry indicated by a variety of petrologic, Cc and Fo + Cc + Do characterize the inner aureole (Per and geochemical, and geothermometry evidence presented here and elseFo zones), and Tr + Do + Cc and Tc + Do + Cc are where, this decrease implies that fluid has leaked from the flow widespread in the outer aureole (Tr and Tc zones). Low-variance system between the periclase and tremolite zones. assemblages are rare and the thickness of reaction zones (coexisting reactant and product minerals) at the isogradic reaction fronts are narrow (tens of metres or less). The mineral assemblages, calculated progress of isograd reactions, and the prograde T–X(CO2) path all KEY WORDS: Alta; fluid flow; infiltration; marble; mineralogical indicate that massive dolomite was infiltrated by significant fluxes of water-rich fluids during prograde Metamorphism, and that the fluid flow was down-temperature and laterally away from the igneous Contact. Fluid infiltration continued through at least the initial retrograde cooling of the periclase zone. Down-T fluid flow INTRODUCTION is also consistent with the results of Cc–Do geothermometry and Both mineral assemblages and stable isotopes have been patterns of 18 O depletion in this area. The close spatial association
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Mineralogical Evidence for Fluid–Rock Interaction Accompanying Prograde Contact Metamorphism of Siliceous Dolomites: Alta Stock Aureole, Utah, USA
Journal of Petrology, 2000Co-Authors: Stephen J Cook, John R BowmanAbstract:Contact Metamorphism of siliceous dolomite in the southern part of agrees well with the q m TIFF (3·4 × 10 7 mol/m 2 ) determined by the metamorphic aureole of the Alta stock (Utah, USA) produced numerical simulation of the temperature and 18 O depletion profiles the prograde isograd sequence: talc (Tc), tremolite (Tr), forsterite preserved in the southern aureole. The estimates of q m TIFF for the (Fo), and periclase (Per). Calcite (Cc)–dolomite (Do) ge- forsterite and tremolite zones have much greater uncertainty, but othermometry and phase equilibria define a general prograde T– may indicate that fluid flux was considerably lower in these zones X(CO2) path of decreasing X(CO2) with rising temperature for than in the periclase zone. Given the outward (down-temperature), the dolomite. High-variance assemblages typify the aureole. Per + subhorizontal flow geometry indicated by a variety of petrologic, Cc and Fo + Cc + Do characterize the inner aureole (Per and geochemical, and geothermometry evidence presented here and elseFo zones), and Tr + Do + Cc and Tc + Do + Cc are where, this decrease implies that fluid has leaked from the flow widespread in the outer aureole (Tr and Tc zones). Low-variance system between the periclase and tremolite zones. assemblages are rare and the thickness of reaction zones (coexisting reactant and product minerals) at the isogradic reaction fronts are narrow (tens of metres or less). The mineral assemblages, calculated progress of isograd reactions, and the prograde T–X(CO2) path all KEY WORDS: Alta; fluid flow; infiltration; marble; mineralogical indicate that massive dolomite was infiltrated by significant fluxes of water-rich fluids during prograde Metamorphism, and that the fluid flow was down-temperature and laterally away from the igneous Contact. Fluid infiltration continued through at least the initial retrograde cooling of the periclase zone. Down-T fluid flow INTRODUCTION is also consistent with the results of Cc–Do geothermometry and Both mineral assemblages and stable isotopes have been patterns of 18 O depletion in this area. The close spatial association
B Ryan - One of the best experts on this subject based on the ideXlab platform.
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high to ultrahigh temperature Contact Metamorphism and dry partial melting of the tasiuyak paragneiss northern labrador
Journal of Metamorphic Geology, 2014Co-Authors: R K Mitchell, Aphrodite Indares, B RyanAbstract:Contact aureoles of the anorthositic to granitic plutons of the Mesoproterozoic Nain Plutonic Suite (NPS), Labrador, are particularly well developed in the Palaeoproterozoic granulite facies, metasedimentary, Tasiuyak gneiss. Granulite facies regional Metamorphism (MR), c. 1860 Ma, led to biotite dehydration melting of the paragneiss and melt migration, leaving behind biotite-poor, garnet–sillimanite-bearing quartzofeldspathic rocks. Subsequently, Tasiuyak gneiss within a c. 1320 Ma Contact aureole of the NPS was statically subjected to lower pressure, but higher temperature conditions (MC), leading to a second partial melting event, and the generation of complex mineral assemblages and microstructures, which were controlled to a large extent by the textures of the MR assemblage. This control is clearly seen in scanning electron microscopic images of thin sections and is further supported by phase equilibria modelling. Samples collected within the Contact aureole near Anaktalik Brook, west of Nain, Labrador, mainly consist of spinel–cordierite and orthopyroxene–cordierite (or plagioclase) pseudomorphs after MR sillimanite and garnet, respectively, within a quartzofeldspathic matrix. In addition, some samples contain fine-grained intergrowths of K-feldspar–quartz–cordierite–orthopyroxene inferred to be pseudomorphs after osumulite. Microstructural evidence of the former melt includes (i) coarse-grained K-feldspar–quartz–cordierite–orthopyroxene domains that locally cut the rock fabric and are inferred to represent neosome; (ii) very fine- to medium-grained cordierite–quartz intergrowths interpreted to have formed by a reaction involving dissolution of biotite and feldspar in melt; and (iii) fine-scale interstitial pools or micro-cracks filled by feldspar interpreted to have crystallized from melt. Ultrahigh temperature (UHT) conditions during Contact Metamorphism are supported by (i) solidus temperatures >900 °C estimated for all samples, coupled with extensive textural evidence for Contact-related partial melting; (ii) the inferred (former) presence of osumilite; and (iii) titanium-in-quartz thermometry indicating temperatures within error of 900 °C. The UHT environment in which these unusual textures and minerals were developed was likely a consequence of the superposition of more than one Contact metamorphic event upon the already relatively anhydrous Tasiuyak gneiss.
P S Kozlov - One of the best experts on this subject based on the ideXlab platform.
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Contact Metamorphism of fe and al rich graphitic metapelites in the transangarian region of the yenisei ridge eastern siberia russia
Lithos, 2001Co-Authors: I I Likhanov, V. V. Reverdatto, V S Sheplev, A E Verschinin, P S KozlovAbstract:Abstract Prograde evolution of minerals in Fe- and Al-rich graphitic metapelites in the Ayakhtinsk aureole, Siberia, produced the unusual Contact metamorphic mineral assemblages: chloritoid+biotite, chloritoid+biotite+andalusite and cordierite+garnet+muscovite. Field-petrologic observations show that: (1) the grade of Contact Metamorphism ranges from chloritoid to sillimanite–alkali feldspar zone; (2) chloritoid+biotite assemblages have a restricted temperature interval and give way up-grade to garnet+chlorite assemblages; and (3) garnet+chlorite assemblages have a wide temperature interval and give way to cordierite+biotite parageneses with increasing grade. Geothermobarometry and thermodynamic analysis of mineral equilibria give estimates of the P – T – X H 2 O conditions of the Contact Metamorphism: the temperatures increase toward the intrusive Contact from 430 to 640 °C at P =3.2±0.3 kbar, X H 2 O for the metamorphic fluid decreases toward the intrusive Contact from 0.89–0.85 at T =450 °C to 0.49–0.36 at T =640 °C, assuming ideal and non-ideal mixing, respectively, of H 2 O–CO 2 in the fluid phase. The stability of the rare mineral assemblages chloritoid+biotite and chloritoid+biotite+andalusite within the Contact aureole can be explained by the unusual combination of pressure (>3 kbar) and Fe- and Al-rich bulk-rock compositions. The local occurrence of the cordierite+garnet+muscovite mineral assemblage is controlled by Mn in the garnet composition and Fe- and Al-rich bulk-rock composition than P – T conditions. Our data are compatible with the KFMASH grid of Spear and Cheney [Contrib. Mineral. Petrol. 101 (1989) 149.].