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Sven Morgan - One of the best experts on this subject based on the ideXlab platform.
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properties of fluids attending variable recrystallization of quartzite during contact metamorphism in the white inyo range california
Journal of Metamorphic Geology, 2017Co-Authors: Peter I Nabelek, Sven Morgan, S K Stephenson, James J StudentAbstract:Fluid inclusions in the metamorphic Aureole of the Eureka Valley-Joshua Flat-Beer Creek (EJB) pluton in the White-Inyo Range, California, reveal the compositions and origin of fluids that were present during variable recrystallization of quartzite with sedimentary grain shapes to metaquartzite with granoblastic texture. Metamorphosed sedimentary formations, including quartzites, marbles, calc-silicates and schists, became ductile and strongly attenuated in the Aureole during growth of the magma chamber. The microstructures of quartzites have an unusual distribution in that within ~250 m from the pluton, where temperatures exceeded 650 °C, they exhibit relict sedimentary grain shapes, only small amount of grain boundary migration (GBM), and crystallographic preferred orientations (CPO's) dominated by slip. At distances >250 m, quartzites were completely recrystallized by GBM and CPO's are indicative of prism [c] slip, characteristics that are typically associated with H2O-assisted, high-temperature recrystallization. The lack of extensive GBM in the inner Aureole can be attributed to rapid replacement of H2O by CO2 produced by reaction of quartz grains with calcite cement that also produced interstitial wollastonite. Fluid inclusions in the inner-Aureole generally occur in margins of quartz grains and are either wholly aqueous (Type 1) or also contain H2S, CO2 and CH4 (Type 2). Type 2 inclusions occur only in some stratigraphic layers. In both inclusion types, NaCl and CaCl2, in variable proportions, dominate the solutes in the aqueous phase, whereas FeCl2 and KCl are less abundant solutes. The solutes indicate attainment of a degree of equilibrium with carbonates and schists that are interbedded with the quartzites. Some Types 1 and 2 inclusions in the inner Aureole show evidence of decrepitation due to high amounts of strain and/or heating suffered by the host rocks, which suggests that they represent pore fluids that existed in the rocks prior to contact metamorphism. In addition to Type 1 inclusions, outer-Aureole quartzites also contain inclusions that contain CO2 vapour bubbles in addition to aqueous phase (Type 3). These inclusions only occur in interiors of granoblastic quartz that was produced by large amounts of GBM. The aqueous phase has identical ranges of first melting and final ice melting temperatures as Type 1 inclusions, suggesting that they have the same solute compositions. These inclusions are thought to represent the interstitial pore H2O that promoted recrystallization of quartz and reacted with graphite to produce CO2. Absence of significant amounts of CH4 in Type 3 inclusions is attributed to elevated fO2 that was buffered by mineral assemblages in interbedded schists. As opposed to the large amount of CO2 that was produced by the wollastonite-forming reaction in the inner Aureole to inhibit GBM, the amount of CO2 produced in the outer Aureole by reaction between H2O and graphite was apparently insufficient to inhibit recrystallization of quartz. This article is protected by copyright. All rights reserved.
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fluid controlled grain boundary migration and switch in slip systems in a high strain high temperature contact Aureole california usa
Tectonophysics, 2016Co-Authors: Sven Morgan, Peter I Nabelek, James J Student, Joseph F SadorskiAbstract:Abstract Within the highly strained Aureole surrounding the Eureka Valley–Joshua Flat–Beer Creek (EJB) composite pluton of eastern California, an inversion in microstructures and crystallographic preferred orientations (CPOs) exists with distance from the contact. An inner Aureole ( slip in quartz. Within the outer Aureole (250 m to 1500 m from the contact), quartzites are interbedded with pelitic schist and are completely recrystallized and microstructures are indicative of extensive GBM. CPOs are indicative of prism [c] slip. Oxygen isotope ratios in the inner Aureole are only slightly shifted from their original values. Oxygen isotopes from the outer Aureole are shifted more, which is consistent with equilibration with locally derived fluids. We suggest that recrystallization in the outer Aureole was aided by pore water, water derived from fluid inclusions, and water generated by prograde reactions in the schists. The pore fluids in the inner Aureole were also probably initially water-rich. However, during prograde reactions in the intervening calc-silicate rocks, and perhaps more importantly, between calcite cement and quartz in the quartzites, the pore fluid composition in the inner Aureole changed to become dominated by CO 2 , which acted as a non-wetting phase and decreased the fugacity of water slowing grain boundary mobility. Low water fugacity also suppressed the activity of prism [c] slip. Therefore, we propose that dry conditions or a grain boundary fluid with a significant non-wetting component (CO 2 ) can result in apparent temperatures of deformation that are more than 100 °C lower than the real temperatures of deformation.
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unusual transition in quartzite dislocation creep regimes and crystal slip systems in the Aureole of the eureka valley joshua flat beer creek pluton california a case for anhydrous conditions created by decarbonation reactions
Tectonophysics, 2004Co-Authors: Sven Morgan, Richard D LawAbstract:Abstract Microstructures and quartz c -axis fabrics were analyzed in five quartzite samples collected across the eastern Aureole of the Eureka Valley–Joshua Flat–Beer Creek composite pluton. Temperatures of deformation are estimated to be 740±50 °C based on a modified c -axis opening angle thermometer of Kruhl (J. Metamorph. Geol. 16 (1998) 142). In quartzite layers located closest (140 m) to the pluton-wall rock contact, flattened detrital grains are plastically deformed and partially recrystallized. The dominant recrystallization process is subgrain rotation (dislocation creep regime 2 of Hirth and Tullis (J. Struct. Geol. 14 (1992) 145)), although grain boundary migration (dislocation creep regime 3) is also evident. Complete recrystallization occurs in quartzite layers located at a distance of ∼240 m from the contact, and coincides with recrystallization taking place dominantly through grain boundary migration (regime 3). Within the quartzites, strain is calculated to be lowest in the layers closest to the pluton margin based on the aspect ratios of flattened detrital grains. The c -axis fabrics indicate that 〈 a 〉 slip operated within the quartzites closest to the pluton-wall rock contact and that with distance from the contact the operative slip systems gradually switch to prism [ c ] slip. The spatial inversion in microstructures and slip systems (apparent “high temperature” deformation and recrystallization further from the pluton-contact and apparent “low temperature” deformation and recrystallization closer to the pluton-contact) coincides with a change in minor phase mineral content of quartzite samples and also in composition of the surrounding rock units. Marble and calc-silicate assemblages dominate close to the pluton-wall rock contact, whereas mixed quartzite and pelite assemblages are dominant further from the contact. We suggest that a thick marble unit located between the pluton and the quartzite layers acted as a barrier to fluids emanating from the pluton. Decarbonation reactions in marble layers interbedded with the inner Aureole quartzites and calc-silicate assemblages in the inner Aureole quartzites may have produced high X CO 2 (water absent) fluids during deformation. The presence of high X CO 2 fluid is inferred from the prograde assemblage of quartz+calcite (and not wollastonite)+diopside±K-feldspar in the inner Aureole quartzites. We suggest that it was these “dry” conditions that suppressed prism [ c ] slip and regime 3 recrystallization in the inner Aureole and resulted in 〈 a 〉 slip and regime 2 recrystallization, which would normally be associated with lower deformation temperatures. In contrast, the prograde assemblage in the pelite-dominated outer part of the Aureole is biotite+K-feldspar. These “wet” pelitic assemblages indicate fluids dominated by water in the outer part of the Aureole and promoted prism [ c ] slip and regime 3 recrystallization. Because other variables could also have caused the spatial inversion of c -axis fabrics and recrystallization mechanisms, we briefly review those variables known to cause a transition in slip systems and dislocation creep regimes in quartz. Our conclusions are based on a small number of samples, and therefore, the unusual development of crystal fabrics and microstructures in the Aureole to the EJB pluton suggests that further study is needed on the effect of fluid composition on crystal slip system activity and recrystallization mechanisms in naturally deformed rocks.
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Unusual transition in quartzite dislocation creep regimes and crystal slip systems in the Aureole of the Eureka Valley–Joshua Flat–Beer Creek pluton, California: a case for anhydrous conditions created by decarbonation reactions
Tectonophysics, 2004Co-Authors: Sven Morgan, Richard D LawAbstract:Abstract Microstructures and quartz c -axis fabrics were analyzed in five quartzite samples collected across the eastern Aureole of the Eureka Valley–Joshua Flat–Beer Creek composite pluton. Temperatures of deformation are estimated to be 740±50 °C based on a modified c -axis opening angle thermometer of Kruhl (J. Metamorph. Geol. 16 (1998) 142). In quartzite layers located closest (140 m) to the pluton-wall rock contact, flattened detrital grains are plastically deformed and partially recrystallized. The dominant recrystallization process is subgrain rotation (dislocation creep regime 2 of Hirth and Tullis (J. Struct. Geol. 14 (1992) 145)), although grain boundary migration (dislocation creep regime 3) is also evident. Complete recrystallization occurs in quartzite layers located at a distance of ∼240 m from the contact, and coincides with recrystallization taking place dominantly through grain boundary migration (regime 3). Within the quartzites, strain is calculated to be lowest in the layers closest to the pluton margin based on the aspect ratios of flattened detrital grains. The c -axis fabrics indicate that 〈 a 〉 slip operated within the quartzites closest to the pluton-wall rock contact and that with distance from the contact the operative slip systems gradually switch to prism [ c ] slip. The spatial inversion in microstructures and slip systems (apparent “high temperature” deformation and recrystallization further from the pluton-contact and apparent “low temperature” deformation and recrystallization closer to the pluton-contact) coincides with a change in minor phase mineral content of quartzite samples and also in composition of the surrounding rock units. Marble and calc-silicate assemblages dominate close to the pluton-wall rock contact, whereas mixed quartzite and pelite assemblages are dominant further from the contact. We suggest that a thick marble unit located between the pluton and the quartzite layers acted as a barrier to fluids emanating from the pluton. Decarbonation reactions in marble layers interbedded with the inner Aureole quartzites and calc-silicate assemblages in the inner Aureole quartzites may have produced high X CO 2 (water absent) fluids during deformation. The presence of high X CO 2 fluid is inferred from the prograde assemblage of quartz+calcite (and not wollastonite)+diopside±K-feldspar in the inner Aureole quartzites. We suggest that it was these “dry” conditions that suppressed prism [ c ] slip and regime 3 recrystallization in the inner Aureole and resulted in 〈 a 〉 slip and regime 2 recrystallization, which would normally be associated with lower deformation temperatures. In contrast, the prograde assemblage in the pelite-dominated outer part of the Aureole is biotite+K-feldspar. These “wet” pelitic assemblages indicate fluids dominated by water in the outer part of the Aureole and promoted prism [ c ] slip and regime 3 recrystallization. Because other variables could also have caused the spatial inversion of c -axis fabrics and recrystallization mechanisms, we briefly review those variables known to cause a transition in slip systems and dislocation creep regimes in quartz. Our conclusions are based on a small number of samples, and therefore, the unusual development of crystal fabrics and microstructures in the Aureole to the EJB pluton suggests that further study is needed on the effect of fluid composition on crystal slip system activity and recrystallization mechanisms in naturally deformed rocks.
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Laccolith-like emplacement model for the Papoose Flat pluton based on porphyroblast-matrix analysis
Geological Society of America Bulletin, 1998Co-Authors: Sven Morgan, Richard D Law, Matthew W. NymanAbstract:Detailed porphyroblast-matrix analysis within the concordant metasedimentary Aureole rocks surrounding the Papoose Flat pluton of eastern California indicates that inclusion trails within porphyroblasts can be used as strain markers to restore the Aureole rocks to their prepluton emplacement position. Using porphyroblast-matrix relationships in combination with measurement of stratigraphic sections and whole-rock geochemical analyses, we have determined the kinematics of rotation, the change in thickness and volume, and the amount of translation of the metasedimentary formations within the Aureole. These data are consistent with initial emplacement of the magma as an inclined sill and subsequent inflation into a pluton or laccolith. The combination of structural and porphyroblast-matrix analysis leads to a three-dimensional kinematic history of the wall rocks wherein vertical upward translation represents a significant part of the pluton emplacement-related strain history.
Annesophie Bouvier - One of the best experts on this subject based on the ideXlab platform.
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significance of oh f and cl content in biotite during metamorphism of the western adamello contact Aureole
Contributions to Mineralogy and Petrology, 2018Co-Authors: Guillaume Siron, Lukas P Baumgartner, Annesophie BouvierAbstract:The hydroxyl (O(4)) site composition of biotite can in principle be used to retrieve information about fluid composition during fluid–rock interaction; however, due to low F and Cl content, as well as difficulties involved with analyzing the H2O content using in situ techniques, measuring these species in biotite has remained an elusive goal. Here we present high-precision secondary ion mass spectrometry (SIMS) OH–F–Cl measurements from biotite within metapelites from the Western Adamello Tonalite (WAT) contact Aureole, Northern Italy. Fluorine, chlorine and hydrogen are analyzed on the SIMS sequentially by peak-hopping at the same biotite spot; H2O, F and Cl content were measured with a precision (1σ) οφ 0.06 ωτ%, 50 ανδ 5 ππµ, ρeσπeχτιϖeλψ. The compositions of isolated biotite crystals in andalusite are compared with that of biotite in the matrix, documenting that halogens and H2O behave refractory in biotite during the time scale of contact metamorphism. The H2O and halogen contents of biotite are mostly locked in during the prograde to peak formation of biotite, and are not reset during further heating or cooling, unless significant biotite recrystallization occurs. It also appears that both Ti content and XMg of the biotite from the Western Adamello contact Aureole were not significantly reset during cooling. The concentration of F and Cl does not vary systematically with metamorphic grade, which indicates that these species reflect initial compositions. No significant Rayleigh fractionation behavior was observed for these elements. H2O variations in the biotite from samples throughout the Western Adamello contact Aureole suggest that Al-oxy substitution partially controls the variations in OH content through charge balance of the type R2+,VI + OH− = Al3+,VI + O2− + H2, while the Ti-oxy substitution does not seem to influence the O(4) site occupation. The main titanium substitution appears to be the Ti-vacancy ( $${\text{2}}{{\text{R}}^{{\text{2}}+}}~=~{\text{T}}{{\text{i}}^{{\text{4}}+}}~+\,{\square ^{{\text{VI}}}}$$ ) exchange. Variations in H2O and halogen concentrations in biotite define sub mm-scale areas of localized equilibration, even for biotite recrystallized during dehydration reactions that produced large amounts of fluid (chlorite or muscovite breakdown). Similar systematics were observed for Ti4+ and Al3+. These findings further support the increasing number of observations that kinetics control much of the mineralogical reactions occurring in contact Aureoles, and hence care is advised in using equilibrium thermodynamics in this environment.
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Significance of OH, F and Cl content in biotite during metamorphism of the Western Adamello contact Aureole
Contributions to Mineralogy and Petrology, 2018Co-Authors: Guillaume Siron, Lukas Baumgartner, Annesophie BouvierAbstract:The hydroxyl (O(4)) site composition of biotite can in principle be used to retrieve information about fluid composition during fluid–rock interaction; however, due to low F and Cl content, as well as difficulties involved with analyzing the H_2O content using in situ techniques, measuring these species in biotite has remained an elusive goal. Here we present high-precision secondary ion mass spectrometry (SIMS) OH–F–Cl measurements from biotite within metapelites from the Western Adamello Tonalite (WAT) contact Aureole, Northern Italy. Fluorine, chlorine and hydrogen are analyzed on the SIMS sequentially by peak-hopping at the same biotite spot; H_2O, F and Cl content were measured with a precision (1 σ ) οφ 0.06 ωτ%, 50 ανδ 5 ππµ, ρεσπεχτιϖελψ. The compositions of isolated biotite crystals in andalusite are compared with that of biotite in the matrix, documenting that halogens and H_2O behave refractory in biotite during the time scale of contact metamorphism. The H_2O and halogen contents of biotite are mostly locked in during the prograde to peak formation of biotite, and are not reset during further heating or cooling, unless significant biotite recrystallization occurs. It also appears that both Ti content and X _Mg of the biotite from the Western Adamello contact Aureole were not significantly reset during cooling. The concentration of F and Cl does not vary systematically with metamorphic grade, which indicates that these species reflect initial compositions. No significant Rayleigh fractionation behavior was observed for these elements. H_2O variations in the biotite from samples throughout the Western Adamello contact Aureole suggest that Al-oxy substitution partially controls the variations in OH content through charge balance of the type R ^2+,VI + OH^− = Al^3+,VI + O^2− + H_2, while the Ti-oxy substitution does not seem to influence the O(4) site occupation. The main titanium substitution appears to be the Ti-vacancy ( $${\text{2}}{{\text{R}}^{{\text{2}}+}}~=~{\text{T}}{{\text{i}}^{{\text{4}}+}}~+\,{\square ^{{\text{VI}}}}$$ 2 R 2 + = T i 4 + + □ VI ) exchange. Variations in H_2O and halogen concentrations in biotite define sub mm-scale areas of localized equilibration, even for biotite recrystallized during dehydration reactions that produced large amounts of fluid (chlorite or muscovite breakdown). Similar systematics were observed for Ti^4+ and Al^3+. These findings further support the increasing number of observations that kinetics control much of the mineralogical reactions occurring in contact Aureoles, and hence care is advised in using equilibrium thermodynamics in this environment.
Richard D Law - One of the best experts on this subject based on the ideXlab platform.
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unusual transition in quartzite dislocation creep regimes and crystal slip systems in the Aureole of the eureka valley joshua flat beer creek pluton california a case for anhydrous conditions created by decarbonation reactions
Tectonophysics, 2004Co-Authors: Sven Morgan, Richard D LawAbstract:Abstract Microstructures and quartz c -axis fabrics were analyzed in five quartzite samples collected across the eastern Aureole of the Eureka Valley–Joshua Flat–Beer Creek composite pluton. Temperatures of deformation are estimated to be 740±50 °C based on a modified c -axis opening angle thermometer of Kruhl (J. Metamorph. Geol. 16 (1998) 142). In quartzite layers located closest (140 m) to the pluton-wall rock contact, flattened detrital grains are plastically deformed and partially recrystallized. The dominant recrystallization process is subgrain rotation (dislocation creep regime 2 of Hirth and Tullis (J. Struct. Geol. 14 (1992) 145)), although grain boundary migration (dislocation creep regime 3) is also evident. Complete recrystallization occurs in quartzite layers located at a distance of ∼240 m from the contact, and coincides with recrystallization taking place dominantly through grain boundary migration (regime 3). Within the quartzites, strain is calculated to be lowest in the layers closest to the pluton margin based on the aspect ratios of flattened detrital grains. The c -axis fabrics indicate that 〈 a 〉 slip operated within the quartzites closest to the pluton-wall rock contact and that with distance from the contact the operative slip systems gradually switch to prism [ c ] slip. The spatial inversion in microstructures and slip systems (apparent “high temperature” deformation and recrystallization further from the pluton-contact and apparent “low temperature” deformation and recrystallization closer to the pluton-contact) coincides with a change in minor phase mineral content of quartzite samples and also in composition of the surrounding rock units. Marble and calc-silicate assemblages dominate close to the pluton-wall rock contact, whereas mixed quartzite and pelite assemblages are dominant further from the contact. We suggest that a thick marble unit located between the pluton and the quartzite layers acted as a barrier to fluids emanating from the pluton. Decarbonation reactions in marble layers interbedded with the inner Aureole quartzites and calc-silicate assemblages in the inner Aureole quartzites may have produced high X CO 2 (water absent) fluids during deformation. The presence of high X CO 2 fluid is inferred from the prograde assemblage of quartz+calcite (and not wollastonite)+diopside±K-feldspar in the inner Aureole quartzites. We suggest that it was these “dry” conditions that suppressed prism [ c ] slip and regime 3 recrystallization in the inner Aureole and resulted in 〈 a 〉 slip and regime 2 recrystallization, which would normally be associated with lower deformation temperatures. In contrast, the prograde assemblage in the pelite-dominated outer part of the Aureole is biotite+K-feldspar. These “wet” pelitic assemblages indicate fluids dominated by water in the outer part of the Aureole and promoted prism [ c ] slip and regime 3 recrystallization. Because other variables could also have caused the spatial inversion of c -axis fabrics and recrystallization mechanisms, we briefly review those variables known to cause a transition in slip systems and dislocation creep regimes in quartz. Our conclusions are based on a small number of samples, and therefore, the unusual development of crystal fabrics and microstructures in the Aureole to the EJB pluton suggests that further study is needed on the effect of fluid composition on crystal slip system activity and recrystallization mechanisms in naturally deformed rocks.
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Unusual transition in quartzite dislocation creep regimes and crystal slip systems in the Aureole of the Eureka Valley–Joshua Flat–Beer Creek pluton, California: a case for anhydrous conditions created by decarbonation reactions
Tectonophysics, 2004Co-Authors: Sven Morgan, Richard D LawAbstract:Abstract Microstructures and quartz c -axis fabrics were analyzed in five quartzite samples collected across the eastern Aureole of the Eureka Valley–Joshua Flat–Beer Creek composite pluton. Temperatures of deformation are estimated to be 740±50 °C based on a modified c -axis opening angle thermometer of Kruhl (J. Metamorph. Geol. 16 (1998) 142). In quartzite layers located closest (140 m) to the pluton-wall rock contact, flattened detrital grains are plastically deformed and partially recrystallized. The dominant recrystallization process is subgrain rotation (dislocation creep regime 2 of Hirth and Tullis (J. Struct. Geol. 14 (1992) 145)), although grain boundary migration (dislocation creep regime 3) is also evident. Complete recrystallization occurs in quartzite layers located at a distance of ∼240 m from the contact, and coincides with recrystallization taking place dominantly through grain boundary migration (regime 3). Within the quartzites, strain is calculated to be lowest in the layers closest to the pluton margin based on the aspect ratios of flattened detrital grains. The c -axis fabrics indicate that 〈 a 〉 slip operated within the quartzites closest to the pluton-wall rock contact and that with distance from the contact the operative slip systems gradually switch to prism [ c ] slip. The spatial inversion in microstructures and slip systems (apparent “high temperature” deformation and recrystallization further from the pluton-contact and apparent “low temperature” deformation and recrystallization closer to the pluton-contact) coincides with a change in minor phase mineral content of quartzite samples and also in composition of the surrounding rock units. Marble and calc-silicate assemblages dominate close to the pluton-wall rock contact, whereas mixed quartzite and pelite assemblages are dominant further from the contact. We suggest that a thick marble unit located between the pluton and the quartzite layers acted as a barrier to fluids emanating from the pluton. Decarbonation reactions in marble layers interbedded with the inner Aureole quartzites and calc-silicate assemblages in the inner Aureole quartzites may have produced high X CO 2 (water absent) fluids during deformation. The presence of high X CO 2 fluid is inferred from the prograde assemblage of quartz+calcite (and not wollastonite)+diopside±K-feldspar in the inner Aureole quartzites. We suggest that it was these “dry” conditions that suppressed prism [ c ] slip and regime 3 recrystallization in the inner Aureole and resulted in 〈 a 〉 slip and regime 2 recrystallization, which would normally be associated with lower deformation temperatures. In contrast, the prograde assemblage in the pelite-dominated outer part of the Aureole is biotite+K-feldspar. These “wet” pelitic assemblages indicate fluids dominated by water in the outer part of the Aureole and promoted prism [ c ] slip and regime 3 recrystallization. Because other variables could also have caused the spatial inversion of c -axis fabrics and recrystallization mechanisms, we briefly review those variables known to cause a transition in slip systems and dislocation creep regimes in quartz. Our conclusions are based on a small number of samples, and therefore, the unusual development of crystal fabrics and microstructures in the Aureole to the EJB pluton suggests that further study is needed on the effect of fluid composition on crystal slip system activity and recrystallization mechanisms in naturally deformed rocks.
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Laccolith-like emplacement model for the Papoose Flat pluton based on porphyroblast-matrix analysis
Geological Society of America Bulletin, 1998Co-Authors: Sven Morgan, Richard D Law, Matthew W. NymanAbstract:Detailed porphyroblast-matrix analysis within the concordant metasedimentary Aureole rocks surrounding the Papoose Flat pluton of eastern California indicates that inclusion trails within porphyroblasts can be used as strain markers to restore the Aureole rocks to their prepluton emplacement position. Using porphyroblast-matrix relationships in combination with measurement of stratigraphic sections and whole-rock geochemical analyses, we have determined the kinematics of rotation, the change in thickness and volume, and the amount of translation of the metasedimentary formations within the Aureole. These data are consistent with initial emplacement of the magma as an inclined sill and subsequent inflation into a pluton or laccolith. The combination of structural and porphyroblast-matrix analysis leads to a three-dimensional kinematic history of the wall rocks wherein vertical upward translation represents a significant part of the pluton emplacement-related strain history.
Peter I Nabelek - One of the best experts on this subject based on the ideXlab platform.
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properties of fluids attending variable recrystallization of quartzite during contact metamorphism in the white inyo range california
Journal of Metamorphic Geology, 2017Co-Authors: Peter I Nabelek, Sven Morgan, S K Stephenson, James J StudentAbstract:Fluid inclusions in the metamorphic Aureole of the Eureka Valley-Joshua Flat-Beer Creek (EJB) pluton in the White-Inyo Range, California, reveal the compositions and origin of fluids that were present during variable recrystallization of quartzite with sedimentary grain shapes to metaquartzite with granoblastic texture. Metamorphosed sedimentary formations, including quartzites, marbles, calc-silicates and schists, became ductile and strongly attenuated in the Aureole during growth of the magma chamber. The microstructures of quartzites have an unusual distribution in that within ~250 m from the pluton, where temperatures exceeded 650 °C, they exhibit relict sedimentary grain shapes, only small amount of grain boundary migration (GBM), and crystallographic preferred orientations (CPO's) dominated by slip. At distances >250 m, quartzites were completely recrystallized by GBM and CPO's are indicative of prism [c] slip, characteristics that are typically associated with H2O-assisted, high-temperature recrystallization. The lack of extensive GBM in the inner Aureole can be attributed to rapid replacement of H2O by CO2 produced by reaction of quartz grains with calcite cement that also produced interstitial wollastonite. Fluid inclusions in the inner-Aureole generally occur in margins of quartz grains and are either wholly aqueous (Type 1) or also contain H2S, CO2 and CH4 (Type 2). Type 2 inclusions occur only in some stratigraphic layers. In both inclusion types, NaCl and CaCl2, in variable proportions, dominate the solutes in the aqueous phase, whereas FeCl2 and KCl are less abundant solutes. The solutes indicate attainment of a degree of equilibrium with carbonates and schists that are interbedded with the quartzites. Some Types 1 and 2 inclusions in the inner Aureole show evidence of decrepitation due to high amounts of strain and/or heating suffered by the host rocks, which suggests that they represent pore fluids that existed in the rocks prior to contact metamorphism. In addition to Type 1 inclusions, outer-Aureole quartzites also contain inclusions that contain CO2 vapour bubbles in addition to aqueous phase (Type 3). These inclusions only occur in interiors of granoblastic quartz that was produced by large amounts of GBM. The aqueous phase has identical ranges of first melting and final ice melting temperatures as Type 1 inclusions, suggesting that they have the same solute compositions. These inclusions are thought to represent the interstitial pore H2O that promoted recrystallization of quartz and reacted with graphite to produce CO2. Absence of significant amounts of CH4 in Type 3 inclusions is attributed to elevated fO2 that was buffered by mineral assemblages in interbedded schists. As opposed to the large amount of CO2 that was produced by the wollastonite-forming reaction in the inner Aureole to inhibit GBM, the amount of CO2 produced in the outer Aureole by reaction between H2O and graphite was apparently insufficient to inhibit recrystallization of quartz. This article is protected by copyright. All rights reserved.
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fluid controlled grain boundary migration and switch in slip systems in a high strain high temperature contact Aureole california usa
Tectonophysics, 2016Co-Authors: Sven Morgan, Peter I Nabelek, James J Student, Joseph F SadorskiAbstract:Abstract Within the highly strained Aureole surrounding the Eureka Valley–Joshua Flat–Beer Creek (EJB) composite pluton of eastern California, an inversion in microstructures and crystallographic preferred orientations (CPOs) exists with distance from the contact. An inner Aureole ( slip in quartz. Within the outer Aureole (250 m to 1500 m from the contact), quartzites are interbedded with pelitic schist and are completely recrystallized and microstructures are indicative of extensive GBM. CPOs are indicative of prism [c] slip. Oxygen isotope ratios in the inner Aureole are only slightly shifted from their original values. Oxygen isotopes from the outer Aureole are shifted more, which is consistent with equilibration with locally derived fluids. We suggest that recrystallization in the outer Aureole was aided by pore water, water derived from fluid inclusions, and water generated by prograde reactions in the schists. The pore fluids in the inner Aureole were also probably initially water-rich. However, during prograde reactions in the intervening calc-silicate rocks, and perhaps more importantly, between calcite cement and quartz in the quartzites, the pore fluid composition in the inner Aureole changed to become dominated by CO 2 , which acted as a non-wetting phase and decreased the fugacity of water slowing grain boundary mobility. Low water fugacity also suppressed the activity of prism [c] slip. Therefore, we propose that dry conditions or a grain boundary fluid with a significant non-wetting component (CO 2 ) can result in apparent temperatures of deformation that are more than 100 °C lower than the real temperatures of deformation.
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Numerical constraints on degassing of metamorphic CO2 during the Neoproterozoic Franklin large igneous event, Arctic Canada
Geological Society of America Bulletin, 2014Co-Authors: Peter I Nabelek, Jean H. Bédard, Robert H. RainbirdAbstract:Gabbroic sills of the widespread, ca. 720 Ma Franklin large igneous event intruded sedimentary strata of the Neoproterozoic Shaler Supergroup exposed in the Minto Inlier on Victoria Island in the western Arctic. The mafic magmatism occurred during breakup of the supercontinent Rodinia and preceded Sturtian glaciation. Calc-silicate metamorphic reactions produced CO 2 from decameter-scale contact Aureoles in carbonate rocks containing variable amounts of silicates. Numerical modeling of the reactions and fluid flow was done for host-rock permeabilities ( k ) ranging from 10 −18 to 10 −14 m 2 . Metamorphic assemblages and Aureoles widths are best reproduced with k between 10 −18 and 10 −17 m 2 ; however, the lower k produces much broader fracture zones next to the sills than those observed in the field. When k ≥ 10 −16 m 2 , the contribution of advective heat transport produces Aureoles that are too thick. With k = 10 −17 m 2 , the contribution of CO 2 to the atmosphere from the Aureole of one 50-m-thick sill with an area of 50,000 km 2 would have been only 8 ppm (by weight) during the 600 yr metamorphic episode. The sedimentary basin would have to have been more permeable for a higher flux of metamorphic CO 2 to the atmosphere. The results demonstrate that host-rock permeability must be considered before changes in the budgets of atmospheric carbonic gases can be attributed to metamorphic degassing from sedimentary basins.
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heat and fluid flow in contact metamorphic Aureoles with layered and transient permeability with application to the notch peak Aureole utah
Journal of Geophysical Research, 2001Co-Authors: Xiaojun Cui, Peter I Nabelek, Mian LiuAbstract:We have investigated the control of layered and transient permeability structures on fluid flow and thermal evolution in contact metamorphic Aureoles using two-dimensional numerical modeling with petrological and geochemical constraints from the Notch Peak Aureole, Utah. The model includes interbedded aquitard and aquifer lithologies on the scale of formations and transient enhancement of permeability due to devolatilization reactions. The results show that a layered permeability structure causes focusing of fluids into aquifer layers, resulting in flow pattern that is strongly time-dependent and significantly different from the predicted simple convection cells in Aureoles with homogeneous permeability. The model predicts temporal development of three distinctive flow regimes: (1) early radial down-temperature flow due to release of magmatic fluid, (2) small flat convection cells near the pluton-aquifer contacts during peak metamorphism, (3) late unidirectional down-temperature flow in the upper Aureole and up-temperature flow in the middle to lower Aureole. When the bulk permeability of host rocks is >10−16 m2, heat advection by flowing fluids is significant. At lower bulk permeability, heat conduction dominates, and the effects of detailed permeability structure on the thermal field become negligible. Metamorphic reactions enhance permeability within the inner Aureole, localizing fluid convection and increasing fluid flux. The observed spatial distribution of mineral assemblages and oxygen isotopic shifts in the upper part of the Notch Peak Aureole is consistent with the predicted time-integrated fluid flux, which over duration of metamorphism is dominated by the down-temperature flow of a large amount of water from the pluton into the wall rocks.
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properties of fluids attending variable recrystallization of quartzite during contact metamorphism in the white inyo range california
Journal of Metamorphic Geology, 2017Co-Authors: Peter I Nabelek, Sven Morgan, S K Stephenson, James J StudentAbstract:Fluid inclusions in the metamorphic Aureole of the Eureka Valley-Joshua Flat-Beer Creek (EJB) pluton in the White-Inyo Range, California, reveal the compositions and origin of fluids that were present during variable recrystallization of quartzite with sedimentary grain shapes to metaquartzite with granoblastic texture. Metamorphosed sedimentary formations, including quartzites, marbles, calc-silicates and schists, became ductile and strongly attenuated in the Aureole during growth of the magma chamber. The microstructures of quartzites have an unusual distribution in that within ~250 m from the pluton, where temperatures exceeded 650 °C, they exhibit relict sedimentary grain shapes, only small amount of grain boundary migration (GBM), and crystallographic preferred orientations (CPO's) dominated by slip. At distances >250 m, quartzites were completely recrystallized by GBM and CPO's are indicative of prism [c] slip, characteristics that are typically associated with H2O-assisted, high-temperature recrystallization. The lack of extensive GBM in the inner Aureole can be attributed to rapid replacement of H2O by CO2 produced by reaction of quartz grains with calcite cement that also produced interstitial wollastonite. Fluid inclusions in the inner-Aureole generally occur in margins of quartz grains and are either wholly aqueous (Type 1) or also contain H2S, CO2 and CH4 (Type 2). Type 2 inclusions occur only in some stratigraphic layers. In both inclusion types, NaCl and CaCl2, in variable proportions, dominate the solutes in the aqueous phase, whereas FeCl2 and KCl are less abundant solutes. The solutes indicate attainment of a degree of equilibrium with carbonates and schists that are interbedded with the quartzites. Some Types 1 and 2 inclusions in the inner Aureole show evidence of decrepitation due to high amounts of strain and/or heating suffered by the host rocks, which suggests that they represent pore fluids that existed in the rocks prior to contact metamorphism. In addition to Type 1 inclusions, outer-Aureole quartzites also contain inclusions that contain CO2 vapour bubbles in addition to aqueous phase (Type 3). These inclusions only occur in interiors of granoblastic quartz that was produced by large amounts of GBM. The aqueous phase has identical ranges of first melting and final ice melting temperatures as Type 1 inclusions, suggesting that they have the same solute compositions. These inclusions are thought to represent the interstitial pore H2O that promoted recrystallization of quartz and reacted with graphite to produce CO2. Absence of significant amounts of CH4 in Type 3 inclusions is attributed to elevated fO2 that was buffered by mineral assemblages in interbedded schists. As opposed to the large amount of CO2 that was produced by the wollastonite-forming reaction in the inner Aureole to inhibit GBM, the amount of CO2 produced in the outer Aureole by reaction between H2O and graphite was apparently insufficient to inhibit recrystallization of quartz. This article is protected by copyright. All rights reserved.
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fluid controlled grain boundary migration and switch in slip systems in a high strain high temperature contact Aureole california usa
Tectonophysics, 2016Co-Authors: Sven Morgan, Peter I Nabelek, James J Student, Joseph F SadorskiAbstract:Abstract Within the highly strained Aureole surrounding the Eureka Valley–Joshua Flat–Beer Creek (EJB) composite pluton of eastern California, an inversion in microstructures and crystallographic preferred orientations (CPOs) exists with distance from the contact. An inner Aureole ( slip in quartz. Within the outer Aureole (250 m to 1500 m from the contact), quartzites are interbedded with pelitic schist and are completely recrystallized and microstructures are indicative of extensive GBM. CPOs are indicative of prism [c] slip. Oxygen isotope ratios in the inner Aureole are only slightly shifted from their original values. Oxygen isotopes from the outer Aureole are shifted more, which is consistent with equilibration with locally derived fluids. We suggest that recrystallization in the outer Aureole was aided by pore water, water derived from fluid inclusions, and water generated by prograde reactions in the schists. The pore fluids in the inner Aureole were also probably initially water-rich. However, during prograde reactions in the intervening calc-silicate rocks, and perhaps more importantly, between calcite cement and quartz in the quartzites, the pore fluid composition in the inner Aureole changed to become dominated by CO 2 , which acted as a non-wetting phase and decreased the fugacity of water slowing grain boundary mobility. Low water fugacity also suppressed the activity of prism [c] slip. Therefore, we propose that dry conditions or a grain boundary fluid with a significant non-wetting component (CO 2 ) can result in apparent temperatures of deformation that are more than 100 °C lower than the real temperatures of deformation.
