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David M. Jenkins - One of the best experts on this subject based on the ideXlab platform.
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experimental study along the magnesio hornblende Glaucophane join
American Mineralogist, 2015Co-Authors: Jie Lei, David M. Jenkins, Kiyotaka IshidaAbstract:Amphiboles have played a leading role in metamorphic petrology, from helping to define several metamorphic facies to forming the basis of geothermobarometry, if their thermodynamic mixing properties can be calibrated to the temperature and pressure of formation. Compositional variations of sodium- and sodium-calcium-amphiboles may reveal important information about paleo-subduction zones but have not been studied as much as the more common calcium-amphiboles. In this study we investigate the mixing properties of amphibole solid solutions between magnesio-hornblende and Glaucophane [ B Ca 2 C (Mg 4 Al) T (AlSi 7 )O 22 (OH) 2 – B Na 2 C (Mg 3 Al 2 ) T (Si 8 )O 22 (OH) 2 ] as a binary sub-join within the ternary amphibole system tremolite–Glaucophane–tschermakite where the principal substitutions are Ca for Na at the B, Al for Mg at the C, and Al for Si at the T crystallographic sites. Amphiboles were made from mixtures of reagent oxides at 10 mol% increments between magnesio-hornblende and Glaucophane, formed in a piston-cylinder press at 735–860 °C and 1.3–2.5 GPa for 72–216 h giving good yields (92–100 wt%). A positive deviation is present in the volume-composition plot, even after correcting volumes for non-binary components, supporting the presence of a positive deviation in the enthalpy of mixing (Δ H mix ) along this join. Fourier transform infrared spectra (FTIR) were obtained in the range of 350–4000 cm −1 for the mid-infrared spectra (MIR) for the purpose of estimating the extent of short-range ordering and for autocorrelation analysis, and, in the 650–50 cm −1 , for far-infrared spectra (FIR) for autocorrelation analysis. Autocorrelation analysis gave δΔ Corr values, which further support a positive deviation in the Δ H mix along the magnsio-hornblende–Glaucophane join, although the δΔ Corr maximum did not occur at the calcium-poor (i.e., Glaucophane-rich) portion of the join as expected. Synthetic end-member Glaucophane and magnesio-hornblende were mixed in a molar ratio of 1:1 and allowed to equilibrate by homogenization for variable durations in the range of 600–800 °C at 2.0 GPa to determine the maximum-width of the miscibility gap. These compositional re-equilibration experiments suggested the presence of an asymmetric miscibility gap (steeper toward Glaucophane) with a critical-point below 700 °C. Combining the results of this study with previously published results on the tremolite–Glaucophane join allowed refinement of several asymmetric formalism mixing parameters (i.e., W Gl,Ts = 20 kJ, α Ts = 1.2) and modeling of the miscibility gap within the tremolite–Glaucophane–tschermakite ternary system. The results showed that the composition of the critical point is very close to the maximum in the autocorrelation parameter δΔ Corr , as one would predict. An important implication of this study is that low-temperature immiscibility between calcium- and sodium-rich amphiboles may be more important than the role of pressure, as proposed by Brown (1977), in accounting for the change in B-site Na contents of metamorphic amphiboles.
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Experimental study along the magnesio-hornblende–Glaucophane join
American Mineralogist, 2015Co-Authors: Jie Lei, David M. Jenkins, Kiyotaka IshidaAbstract:Amphiboles have played a leading role in metamorphic petrology, from helping to define several metamorphic facies to forming the basis of geothermobarometry, if their thermodynamic mixing properties can be calibrated to the temperature and pressure of formation. Compositional variations of sodium- and sodium-calcium-amphiboles may reveal important information about paleo-subduction zones but have not been studied as much as the more common calcium-amphiboles. In this study we investigate the mixing properties of amphibole solid solutions between magnesio-hornblende and Glaucophane [ B Ca 2 C (Mg 4 Al) T (AlSi 7 )O 22 (OH) 2 – B Na 2 C (Mg 3 Al 2 ) T (Si 8 )O 22 (OH) 2 ] as a binary sub-join within the ternary amphibole system tremolite–Glaucophane–tschermakite where the principal substitutions are Ca for Na at the B, Al for Mg at the C, and Al for Si at the T crystallographic sites. Amphiboles were made from mixtures of reagent oxides at 10 mol% increments between magnesio-hornblende and Glaucophane, formed in a piston-cylinder press at 735–860 °C and 1.3–2.5 GPa for 72–216 h giving good yields (92–100 wt%). A positive deviation is present in the volume-composition plot, even after correcting volumes for non-binary components, supporting the presence of a positive deviation in the enthalpy of mixing (Δ H mix ) along this join. Fourier transform infrared spectra (FTIR) were obtained in the range of 350–4000 cm −1 for the mid-infrared spectra (MIR) for the purpose of estimating the extent of short-range ordering and for autocorrelation analysis, and, in the 650–50 cm −1 , for far-infrared spectra (FIR) for autocorrelation analysis. Autocorrelation analysis gave δΔ Corr values, which further support a positive deviation in the Δ H mix along the magnsio-hornblende–Glaucophane join, although the δΔ Corr maximum did not occur at the calcium-poor (i.e., Glaucophane-rich) portion of the join as expected. Synthetic end-member Glaucophane and magnesio-hornblende were mixed in a molar ratio of 1:1 and allowed to equilibrate by homogenization for variable durations in the range of 600–800 °C at 2.0 GPa to determine the maximum-width of the miscibility gap. These compositional re-equilibration experiments suggested the presence of an asymmetric miscibility gap (steeper toward Glaucophane) with a critical-point below 700 °C. Combining the results of this study with previously published results on the tremolite–Glaucophane join allowed refinement of several asymmetric formalism mixing parameters (i.e., W Gl,Ts = 20 kJ, α Ts = 1.2) and modeling of the miscibility gap within the tremolite–Glaucophane–tschermakite ternary system. The results showed that the composition of the critical point is very close to the maximum in the autocorrelation parameter δΔ Corr , as one would predict. An important implication of this study is that low-temperature immiscibility between calcium- and sodium-rich amphiboles may be more important than the role of pressure, as proposed by Brown (1977), in accounting for the change in B-site Na contents of metamorphic amphiboles.
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Constraints on the upper pressure stability of blueschist facies metamorphism along the reaction: Glaucophane = talc + 2 jadeite in the Na2O-MgO-Al2O3-SiO2-H2O system
American Journal of Science, 2013Co-Authors: Juan Carlos Corona, David M. Jenkins, Tim HollandAbstract:Blueschist-facies metamorphism, which is associated with high pressure and low temperature subduction zone metamorphism, is usually recognized by the presence of the sodic-amphibole Glaucophane. Determining the upper- and lower-pressure stability of end-member Glaucophane places important constraints on the conditions of blueschist metamorphism. An experimental investigation into the upper-pressure stability of Glaucophane has been done in the system Na2O-MgO-Al2O3-SiO2-H2O over the range of 600 to 750 °C and 2.5 to 4.5 GPa. Mixtures of synthetic Glaucophane, jadeite, and talc were used to determine the location of the reaction boundary Glaucophane = 2 jadeite + talc by reversing the sense of reaction direction. The upper-pressure stability of Glaucophane is located over a pressure interval (0.2-0.3 GPa in width) whose midpoints lie at 2.6 GPa at 600 °C and at 3.1 GPa at 700 °C, across which the proportion of Glaucophane decreases to zero as talc and jadeite increase. This band has a positive dP/dT slope of around 0.005 GPa/°C. Glaucophane showed the largest change in composition, consistent with the incorporation of significant amounts of the nyboite (17-34 mol%) and cummingtonite (10-18 mol%) components. Talc showed minor, but definite incorporation of Na (0.08 atoms per formula unit, apfu) and Al (0.15 apfu) consistent with incorporation of the components aspidolite and tschermak-talc. Jadeite displayed no clear change from its ideal composition. The results from this study were combined with the lower-pressure stability of Glaucophane + quartz reported earlier by Corona and Jenkins (2007) to refine the thermodynamic values for Glaucophane (ΔfH° = −11,956.36 kJ/mol), report an initial set of values for the amphibole nyboite (ΔfH° = −12,165.85 kJ/mol) and phyllosilicate aspidolite (ΔfH° = −6163.86 kJ/mol), and to develop activity-composition relationships for both the amphibole and talc in this chemical system. The results of this study place an upper-pressure limit to a key index mineral of the blueschist-facies at about 3.2 GPa at 700 °C, which is just above the quartz-coesite transition, allowing nearly end-member Glaucophane to remain stable up to the conditions of ultra-high-pressure metamorphism.
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constraints on the upper pressure stability of blueschist facies metamorphism along the reaction Glaucophane talc 2 jadeite in the na2o mgo al2o3 sio2 h2o system
American Journal of Science, 2013Co-Authors: Juan Carlos Corona, David M. Jenkins, T J B HollandAbstract:Blueschist-facies metamorphism, which is associated with high pressure and low temperature subduction zone metamorphism, is usually recognized by the presence of the sodic-amphibole Glaucophane. Determining the upper- and lower-pressure stability of end-member Glaucophane places important constraints on the conditions of blueschist metamorphism. An experimental investigation into the upper-pressure stability of Glaucophane has been done in the system Na2O-MgO-Al2O3-SiO2-H2O over the range of 600 to 750 °C and 2.5 to 4.5 GPa. Mixtures of synthetic Glaucophane, jadeite, and talc were used to determine the location of the reaction boundary Glaucophane = 2 jadeite + talc by reversing the sense of reaction direction. The upper-pressure stability of Glaucophane is located over a pressure interval (0.2-0.3 GPa in width) whose midpoints lie at 2.6 GPa at 600 °C and at 3.1 GPa at 700 °C, across which the proportion of Glaucophane decreases to zero as talc and jadeite increase. This band has a positive dP/dT slope of around 0.005 GPa/°C. Glaucophane showed the largest change in composition, consistent with the incorporation of significant amounts of the nyboite (17-34 mol%) and cummingtonite (10-18 mol%) components. Talc showed minor, but definite incorporation of Na (0.08 atoms per formula unit, apfu) and Al (0.15 apfu) consistent with incorporation of the components aspidolite and tschermak-talc. Jadeite displayed no clear change from its ideal composition. The results from this study were combined with the lower-pressure stability of Glaucophane + quartz reported earlier by Corona and Jenkins (2007) to refine the thermodynamic values for Glaucophane (ΔfH° = −11,956.36 kJ/mol), report an initial set of values for the amphibole nyboite (ΔfH° = −12,165.85 kJ/mol) and phyllosilicate aspidolite (ΔfH° = −6163.86 kJ/mol), and to develop activity-composition relationships for both the amphibole and talc in this chemical system. The results of this study place an upper-pressure limit to a key index mineral of the blueschist-facies at about 3.2 GPa at 700 °C, which is just above the quartz-coesite transition, allowing nearly end-member Glaucophane to remain stable up to the conditions of ultra-high-pressure metamorphism.
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Synthesis and characterization of amphiboles along the tremolite-Glaucophane join
American Mineralogist, 2013Co-Authors: David M. Jenkins, Giancarlo Della Ventura, Roberta Oberti, Krassimir N. BozhilovAbstract:Actinolite and Glaucophane are the principal amphiboles in greenschist- and blueschist-facies metamafic rocks, respectively, and constitute an important mineral pair for deducing the conditions of medium- and high-pressure metamorphism. Here we present the crystal-chemical properties of amphiboles synthesized along the tremolite–Glaucophane join as an important starting point for the more chemically complex samples occurring in nature. Amphiboles were synthesized in 10 mol% increments at conditions ranging from 840 °C and 0.6 GPa for tremolite-rich to 750 °C and 2.5 GPa for Glaucophane-rich amphiboles. The amphibole yields were generally high (~95 wt%), though minor quartz, pyroxene, and amorphous material (either glass or quenched solute) were often present. Electron microprobe analysis of the amphibole showed that deviations from the nominal or intended compositions occurred, with the observed compositions showing solid solution primarily toward the katophorite component and reaching a maximum near the middle of the join. Unit-cell dimensions showed a pronounced positive deviation from ideality, even after (linear) correction for the non-join components, suggesting a strong tendency toward exsolution. Single-crystal refinements of a couple of selected amphiboles confirmed the deviation from nominal composition and confirmed the presence of ANa, TAl, and CAl, the latter disordered between the M (2) and M (3) sites. Infrared spectra in the OH-stretching region were measured on samples that were heated to 250–350 °C to remove absorbed moisture. The spectra consist of a main band centered in the 3675–3660 cm−1 region and two minor absorptions on both sides of the dominant central peak, which are centered at 3720 and 3640 cm−1 and can be attributed to OH next to ANa and CAl, respectively. The main band is evidently composed of several overlapping components due to local arrangements of B cations typical of tremolite, CaCa, Glaucophane, NaNa, and cummingtonite, MgMg. Examination of several intermediate amphiboles by both single-crystal XRD and by high-resolution TEM analysis could not identify evidence of reflections or ordered domains that would violate the C 2 /m symmetry of the end-member amphiboles. Comparing the compositions of the synthetic amphiboles from this study with winchite-rich amphiboles in nature shows that deviations from the tremolite–Glaucophane join are common. The inability to make pure winchite or even winchite-rich amphiboles on the tremolite–Glaucophane join suggests that this structure is unstable.
Chunjing Wei - One of the best experts on this subject based on the ideXlab platform.
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Calculated phase equilibria for MORB compositions: a reappraisal of the metamorphic evolution of lawsonite eclogite
Journal of Metamorphic Geology, 2011Co-Authors: Chunjing Wei, Geoffrey L. ClarkeAbstract:Pseudosections calculated with thermocalc predict that lawsonite-bearing assemblages, including lawsonite eclogite, will be common for subducted oceanic crust that experiences cool, fluid-saturated conditions. For Glaucophane–lawsonite eclogite facies conditions (500–600 °C and 18–28 kbar), MORB compositions are predicted in the NCKMnFMASHO system to contain Glaucophane, garnet, omphacite, lawsonite, phengite and quartz, with chlorite at lower temperature and talc at higher temperature. In these assemblages, the pyrope content in garnet is mostly controlled by variations in temperature, and grossular content is strongly controlled by pressure. The silica content in phengite increases linearly with pressure. As the P–T conditions for these given isopleths are only subtly affected by common variations in bulk-rock compositions, the P–T pseudosections potentially present a robust geothermobarometric method for natural Glaucophane-bearing eclogites. Thermobarometric results recovered both by isopleth and conventional approaches indicate that most natural Glaucophane–lawsonite eclogites (Type-L) and Glaucophane–epidote eclogites (Type-E) record similar peak P–T conditions within the lawsonite stability field. Decompression from conditions appropriate for lawsonite stability should result in epidote-bearing assemblages through dehydration reactions controlled by lawsonite + omphacite = Glaucophane + epidote + H2O. Lawsonite and omphacite breakdown will be accompanied by the release of a large amount of bound fluid, such that eclogite assemblages are variably recrystallized to Glaucophane-rich blueschist. Calculated pseudosections indicate that eclogite assemblages form most readily in Ca-rich rocks and blueschist assemblages most readily in Ca-poor rocks. This distinction in bulk-rock composition can account for the co-existence of low-T eclogite and blueschist in high-pressure terranes.
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phase equilibria and metamorphic evolution of Glaucophane bearing uhp eclogites from the western dabieshan terrane central china
Journal of Metamorphic Geology, 2010Co-Authors: Chunjing Wei, Jing ZhangAbstract:Glaucophane-bearing ultrahigh pressure (UHP) eclogites from the western Dabieshan terrane consist of garnet, omphacite, Glaucophane, kyanite, epidote, phengite, quartz/coesite and rutile with or without talc and paragonite. Some garnet porphyroblasts exhibit a core–mantle zoning profile with slight increase in pyrope content and minor or slight decrease in grossular and a mantle–rim zoning profile characterized by a pronounced increase in pyrope and rapid decrease in grossular. Omphacite is usually zoned with a core–rim decrease in j(o) [=Na/(Ca + Na)]. Glaucophane occurs as porphyroblasts in some samples and contains inclusions of garnet, omphacite and epidote. Pseudosections calculated in the NCKMnFMASHO system for five representative samples, combined with petrographic observations suggest that the UHP eclogites record four stages of metamorphism. (i) The prograde stage, on the basis of modelling of garnet zoning and inclusions in garnet, involves P–T vectors dominated by heating with a slight increase in pressure, suggesting an early slow subduction process, and P–T vectors dominated by a pronounced increase in pressure and slight heating, pointing to a late fast subduction process. The prograde metamorphism is predominated by dehydration of Glaucophane and, to a lesser extent, chlorite, epidote and paragonite, releasing ∼27 wt% water that was bound in the hydrous minerals. (ii) The peak stage is represented by garnet rim compositions with maximum pyrope and minimum grossular contents, and P–T conditions of 28.2–31.8 kbar and 605–613 °C, with the modelled peak-stage mineral assemblage mostly involving garnet + omphacite + lawsonite + talc + phengite + coesite ± Glaucophane ± kyanite. (iii) The early decompression stage is characterized by dehydration of lawsonite, releasing ∼70–90 wt% water bound in the peak mineral assemblages, which results in the growth of Glaucophane, j(o) decrease in omphacite and formation of epidote. And, (iv) The late retrograde stage is characterized by the mineral assemblage of hornblendic amphibole + epidote + albite/oligoclase + quartz developed in the margins or strongly foliated domains of eclogite blocks due to fluid infiltration at P–T conditions of 5–10 kbar and 500–580 °C. The proposed metamorphic stages for the UHP eclogites are consistent with the petrological observations, but considerably different from those presented in the previous studies.
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Phase equilibria and metamorphic evolution of Glaucophane‐bearing UHP eclogites from the Western Dabieshan Terrane, Central China
Journal of Metamorphic Geology, 2010Co-Authors: Chunjing Wei, Jing ZhangAbstract:Glaucophane-bearing ultrahigh pressure (UHP) eclogites from the western Dabieshan terrane consist of garnet, omphacite, Glaucophane, kyanite, epidote, phengite, quartz/coesite and rutile with or without talc and paragonite. Some garnet porphyroblasts exhibit a core–mantle zoning profile with slight increase in pyrope content and minor or slight decrease in grossular and a mantle–rim zoning profile characterized by a pronounced increase in pyrope and rapid decrease in grossular. Omphacite is usually zoned with a core–rim decrease in j(o) [=Na/(Ca + Na)]. Glaucophane occurs as porphyroblasts in some samples and contains inclusions of garnet, omphacite and epidote. Pseudosections calculated in the NCKMnFMASHO system for five representative samples, combined with petrographic observations suggest that the UHP eclogites record four stages of metamorphism. (i) The prograde stage, on the basis of modelling of garnet zoning and inclusions in garnet, involves P–T vectors dominated by heating with a slight increase in pressure, suggesting an early slow subduction process, and P–T vectors dominated by a pronounced increase in pressure and slight heating, pointing to a late fast subduction process. The prograde metamorphism is predominated by dehydration of Glaucophane and, to a lesser extent, chlorite, epidote and paragonite, releasing ∼27 wt% water that was bound in the hydrous minerals. (ii) The peak stage is represented by garnet rim compositions with maximum pyrope and minimum grossular contents, and P–T conditions of 28.2–31.8 kbar and 605–613 °C, with the modelled peak-stage mineral assemblage mostly involving garnet + omphacite + lawsonite + talc + phengite + coesite ± Glaucophane ± kyanite. (iii) The early decompression stage is characterized by dehydration of lawsonite, releasing ∼70–90 wt% water bound in the peak mineral assemblages, which results in the growth of Glaucophane, j(o) decrease in omphacite and formation of epidote. And, (iv) The late retrograde stage is characterized by the mineral assemblage of hornblendic amphibole + epidote + albite/oligoclase + quartz developed in the margins or strongly foliated domains of eclogite blocks due to fluid infiltration at P–T conditions of 5–10 kbar and 500–580 °C. The proposed metamorphic stages for the UHP eclogites are consistent with the petrological observations, but considerably different from those presented in the previous studies.
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chloritoid Glaucophane schist in the north qilian orogen nw china phase equilibria and p t path from garnet zonation
Journal of Metamorphic Geology, 2008Co-Authors: Chunjing Wei, Shuguang SongAbstract:Chloritoid–Glaucophane-bearing rocks are widespread in the high-pressure belt of the north Qilian orogen, NW China. They are interbedded and cofacial with felsic schists originated from greywackes, mafic garnet blueschists and low-T eclogites. Two representative chloritoid–Glaucophane-bearing assemblages are chloritoid + Glaucophane + garnet + talc + quartz (sample Q5-49) and chloritoid + Glaucophane + garnet + phengite + epidote + quartz (sample Q5-12). Garnet in sample Q5-49 is coarse-, medium- and fine-grained and shows two types of zonation patterns. In pattern I, Xgrs is constant as Xpy rises, and in pattern II Xgrs decreases as Xpy rises. Phase equilibrium modelling in the NC(K)MnFMASH system with Thermocalc 3.25 indicates that pattern I can be formed during progressive metamorphism in lawsonite-stable assemblages, while pattern II zonation can be formed with further heating after lawsonite has been consumed. Garnet growth in Q5-49 is consistent with a continuous progressive metamorphic process from ∼14.5 kbar at 470 °C to ∼22.5 kbar at 560 °C. Garnet in sample Q5-12 develops with pattern I zonation, which is consistent with a progressive metamorphic process from ∼21 kbar at 540 °C to ∼23.5 kbar at 580 °C with lawsonite present in the whole garnet growth. The latter sample shows the highest P–T conditions of the reported chloritoid–Glaucophane-bearing assemblages. Phase equilibrium calculation in the NCKFMASH system with a recent mixing model of amphibole indicates that chloritoid + Glaucophane paragenesis does not have a low-pressure limit of 18–19 kbar as previously suggested, but has a much larger pressure range from 7–8 to 27–30 kbar, with the low-pressure part being within the stability field of albite.
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Chloritoid–Glaucophane schist in the north Qilian orogen, NW China: phase equilibria and P–T path from garnet zonation
Journal of Metamorphic Geology, 2008Co-Authors: Chunjing Wei, Shuguang SongAbstract:Chloritoid–Glaucophane-bearing rocks are widespread in the high-pressure belt of the north Qilian orogen, NW China. They are interbedded and cofacial with felsic schists originated from greywackes, mafic garnet blueschists and low-T eclogites. Two representative chloritoid–Glaucophane-bearing assemblages are chloritoid + Glaucophane + garnet + talc + quartz (sample Q5-49) and chloritoid + Glaucophane + garnet + phengite + epidote + quartz (sample Q5-12). Garnet in sample Q5-49 is coarse-, medium- and fine-grained and shows two types of zonation patterns. In pattern I, Xgrs is constant as Xpy rises, and in pattern II Xgrs decreases as Xpy rises. Phase equilibrium modelling in the NC(K)MnFMASH system with Thermocalc 3.25 indicates that pattern I can be formed during progressive metamorphism in lawsonite-stable assemblages, while pattern II zonation can be formed with further heating after lawsonite has been consumed. Garnet growth in Q5-49 is consistent with a continuous progressive metamorphic process from ∼14.5 kbar at 470 °C to ∼22.5 kbar at 560 °C. Garnet in sample Q5-12 develops with pattern I zonation, which is consistent with a progressive metamorphic process from ∼21 kbar at 540 °C to ∼23.5 kbar at 580 °C with lawsonite present in the whole garnet growth. The latter sample shows the highest P–T conditions of the reported chloritoid–Glaucophane-bearing assemblages. Phase equilibrium calculation in the NCKFMASH system with a recent mixing model of amphibole indicates that chloritoid + Glaucophane paragenesis does not have a low-pressure limit of 18–19 kbar as previously suggested, but has a much larger pressure range from 7–8 to 27–30 kbar, with the low-pressure part being within the stability field of albite.
W G Ernst - One of the best experts on this subject based on the ideXlab platform.
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new p t constraints on the tamayen Glaucophane bearing rocks eastern taiwan perple_x modelling results and geodynamic implications
Journal of Metamorphic Geology, 2017Co-Authors: Ioannis Baziotis, Chinho Tsai, W G Ernst, Bor-ming Jahn, Yoshiyuki IizukaAbstract:New pseudosection modeling was applied to better constrain the P-T conditions and evolution of Glaucophane-bearing rocks in the Tamayen block of the Yuli belt, recognized as the world's youngest known blueschist complex. Based on the predominant clinoamphibole, textural relationships, and mineral compositions, these Glaucophane-bearing high-pressure rocks can be divided into four types. We focused on the three containing garnet. The chief phase assemblages are (in decreasing mode): amphibole + quartz + epidote + garnet + chlorite + rutile/titanite (Type-I), phengite + amphibole + quartz + garnet + chlorite + epidote + titanite + biotite + magnetite (Type-II), and amphibole + quartz + albite + epidote + garnet + rutile + hematite + titanite (Type-III). Amphibole exhibits compositional zoning from core to rim as follows: Glaucophane → pargasitic amphibole → actinolite (Type-I), barroisite → Mg-katophorite/taramite → Fe-Glaucophane (Type-II), Glaucophane → winchite (Type-III). Using petrographic data, mineral compositions, and Perple_X modeling (pseudosections and superimposed isopleths), peak P-T conditions were determined as 13 ± 1 kbar and 550 ± 40 °C for Type-I, 10.5 ± 0.5 kbar and 560 ± 30 °C for Type-II (thermal peak), and 11 ± 1 kbar and 530 ± 30 °C for Type-III. The calculations yield higher pressures and temperatures than previously thought; the difference is about 1-6 kbar and 50-200 °C. The three rock types record similar P-T retrograde paths with clockwise trajectories; all rocks followed trajectories with substantial pressure decrease under near-isothermal conditions (Type-I and Type-III), with the probable exception of Type-II where decompression followed colder geotherms. The P-T paths suggest a tectonic environment in which the rocks were exhumed from maximum depths of ~45 km within a subduction channel along a relative cold geothermal gradient of ~11-14 ˚C km-1. This article is protected by copyright. All rights reserved.
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New P‐T constraints on the Tamayen Glaucophane‐bearing rocks, eastern Taiwan: Perple_X modelling results and geodynamic implications
Journal of Metamorphic Geology, 2016Co-Authors: Ioannis Baziotis, Chinho Tsai, W G Ernst, Bor-ming Jahn, Yoshiyuki IizukaAbstract:New pseudosection modeling was applied to better constrain the P-T conditions and evolution of Glaucophane-bearing rocks in the Tamayen block of the Yuli belt, recognized as the world's youngest known blueschist complex. Based on the predominant clinoamphibole, textural relationships, and mineral compositions, these Glaucophane-bearing high-pressure rocks can be divided into four types. We focused on the three containing garnet. The chief phase assemblages are (in decreasing mode): amphibole + quartz + epidote + garnet + chlorite + rutile/titanite (Type-I), phengite + amphibole + quartz + garnet + chlorite + epidote + titanite + biotite + magnetite (Type-II), and amphibole + quartz + albite + epidote + garnet + rutile + hematite + titanite (Type-III). Amphibole exhibits compositional zoning from core to rim as follows: Glaucophane → pargasitic amphibole → actinolite (Type-I), barroisite → Mg-katophorite/taramite → Fe-Glaucophane (Type-II), Glaucophane → winchite (Type-III). Using petrographic data, mineral compositions, and Perple_X modeling (pseudosections and superimposed isopleths), peak P-T conditions were determined as 13 ± 1 kbar and 550 ± 40 °C for Type-I, 10.5 ± 0.5 kbar and 560 ± 30 °C for Type-II (thermal peak), and 11 ± 1 kbar and 530 ± 30 °C for Type-III. The calculations yield higher pressures and temperatures than previously thought; the difference is about 1-6 kbar and 50-200 °C. The three rock types record similar P-T retrograde paths with clockwise trajectories; all rocks followed trajectories with substantial pressure decrease under near-isothermal conditions (Type-I and Type-III), with the probable exception of Type-II where decompression followed colder geotherms. The P-T paths suggest a tectonic environment in which the rocks were exhumed from maximum depths of ~45 km within a subduction channel along a relative cold geothermal gradient of ~11-14 ˚C km-1. This article is protected by copyright. All rights reserved.
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diverse mineral compositions textures and metamorphic p t conditions of the Glaucophane bearing rocks in the tamayen melange yuli belt eastern taiwan
Journal of Asian Earth Sciences, 2013Co-Authors: Chinho Tsai, Yoshiyuki Iizuka, W G ErnstAbstract:Abstract This paper presents new petrologic data for high-pressure, low-temperature (HP–LT) metamorphic rocks at Juisui. We reinterpret the so-called “Tamayen block” ( Yang and Wang, 1985 ) or “Juisui block” ( Liou, 1981; Beyssac et al., 2008 ) as a tectonic melange. It is not a coherent sheet but rather a mixture dominated by greenschist and pelitic schist with pods of serpentinite, epidote amphibolite, and rare blueschist. Four types of Glaucophane-bearing rocks are newly recognized in this melange. Type I is in contact with greenschist lacking Glaucophane and garnet. Glaucophane is present only as rare inclusions within pargasite. This type records metamorphic evolution from epidote blueschists-, epidote amphibolite-, to greenschist-facies. Type II contains characteristic zoned amphiboles from barroisite core to Mg-katophorite mantle and Glaucophane rim, implying an epidote amphibolite-facies stage overprinted by an epidote blueschists-facies one. Type III includes winchite and indicates P – T conditions of about 6–8 kbar, approaching 400 °C. Type IV contains paragonite but lacks garnet; amphibole shows a Na–Ca core surrounded by a Glaucophane rim. This type shows a high-pressure (?) epidote amphibolite-facies stage overprinted by an epidote blueschists-facies one. Amphibole zoning trends and mineral assemblages imply contradictory P – T paths for the four types of Glaucophane-bearing rocks—consistent with the nature of a tectonic melange. The new P – T constraints and petrologic findings differ from previous studies ( Liou et al., 1975; Beyssac et al., 2008 ).
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Diverse mineral compositions, textures, and metamorphic P–T conditions of the Glaucophane-bearing rocks in the Tamayen mélange, Yuli belt, eastern Taiwan
Journal of Asian Earth Sciences, 2013Co-Authors: Chinho Tsai, Yoshiyuki Iizuka, W G ErnstAbstract:Abstract This paper presents new petrologic data for high-pressure, low-temperature (HP–LT) metamorphic rocks at Juisui. We reinterpret the so-called “Tamayen block” ( Yang and Wang, 1985 ) or “Juisui block” ( Liou, 1981; Beyssac et al., 2008 ) as a tectonic melange. It is not a coherent sheet but rather a mixture dominated by greenschist and pelitic schist with pods of serpentinite, epidote amphibolite, and rare blueschist. Four types of Glaucophane-bearing rocks are newly recognized in this melange. Type I is in contact with greenschist lacking Glaucophane and garnet. Glaucophane is present only as rare inclusions within pargasite. This type records metamorphic evolution from epidote blueschists-, epidote amphibolite-, to greenschist-facies. Type II contains characteristic zoned amphiboles from barroisite core to Mg-katophorite mantle and Glaucophane rim, implying an epidote amphibolite-facies stage overprinted by an epidote blueschists-facies one. Type III includes winchite and indicates P – T conditions of about 6–8 kbar, approaching 400 °C. Type IV contains paragonite but lacks garnet; amphibole shows a Na–Ca core surrounded by a Glaucophane rim. This type shows a high-pressure (?) epidote amphibolite-facies stage overprinted by an epidote blueschists-facies one. Amphibole zoning trends and mineral assemblages imply contradictory P – T paths for the four types of Glaucophane-bearing rocks—consistent with the nature of a tectonic melange. The new P – T constraints and petrologic findings differ from previous studies ( Liou et al., 1975; Beyssac et al., 2008 ).
Aral I. Okay - One of the best experts on this subject based on the ideXlab platform.
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jadeite chloritoid Glaucophane lawsonite blueschists in north west turkey unusually high p t ratios in continental crust
Journal of Metamorphic Geology, 2002Co-Authors: Aral I. OkayAbstract:Sodic metapelites with jadeite, chloritoid, Glaucophane and lawsonite form a coherent regional metamorphic sequence, several tens of square kilometres in size, and over a kilometre thick, in the Orhaneli region of northwest Turkey. The low-variance mineral assemblage in the sodic metapelites is quartz +phengite +jadeite +Glaucophane +chloritoid +lawsonite. The associated metabasites are characterized by sodic amphibole +lawsonite ± garnet paragenesis. The stable coexistence of jadeite +chloritoid +Glaucophane +lawsonite, not reported before, indicates metamorphic pres- sures of 24 ± 3 kbar and temperatures of 430 ± 30 � C for the peak blueschist facies conditions. These P-T conditions correspond to a geotherm of 5 � Ck m )1 , one of the lowest recorded in continental crustal rocks. The low geotherm, and the known rate of convergence during the Cretaceous subduction suggest low shear stresses at the top of the downgoing continental slab.
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Jadeite–chloritoid–Glaucophane–lawsonite blueschists in north-west Turkey: unusually high P/T ratios in continental crust
Journal of Metamorphic Geology, 2002Co-Authors: Aral I. OkayAbstract:Sodic metapelites with jadeite, chloritoid, Glaucophane and lawsonite form a coherent regional metamorphic sequence, several tens of square kilometres in size, and over a kilometre thick, in the Orhaneli region of northwest Turkey. The low-variance mineral assemblage in the sodic metapelites is quartz +phengite +jadeite +Glaucophane +chloritoid +lawsonite. The associated metabasites are characterized by sodic amphibole +lawsonite ± garnet paragenesis. The stable coexistence of jadeite +chloritoid +Glaucophane +lawsonite, not reported before, indicates metamorphic pres- sures of 24 ± 3 kbar and temperatures of 430 ± 30 � C for the peak blueschist facies conditions. These P-T conditions correspond to a geotherm of 5 � Ck m )1 , one of the lowest recorded in continental crustal rocks. The low geotherm, and the known rate of convergence during the Cretaceous subduction suggest low shear stresses at the top of the downgoing continental slab.
Xu Chu - One of the best experts on this subject based on the ideXlab platform.
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lawsonite bearing chloritoid Glaucophane schist from sw tianshan china phase equilibria and p t path
Journal of Asian Earth Sciences, 2011Co-Authors: Lifei Zhang, Xu ChuAbstract:Abstract Lawsonite-bearing chloritoid–Glaucophane schist has been discovered firstly in the high to ultra-high pressure (HP–UHP) metamorphic belt in Southwestern Tianshan, China. It is characterized by the mineral assemblage of lawsonite + chloritoid + Glaucophane + phengite + paragonite + epidote/allanite + chlorite + quartz + dolomite/calcite + rutile + tourmaline. Lawsonite and chloritoid exclusively occur as micro-inclusions in the cores and mantles of porphyroblastic Glaucophane. The Glaucophane is coarse-grained (about 1–20 mm long), and forms euhedral to subhedral crystals with distinct growth zonation. The X (gln) [=Fe2 + /(Fe 2+ + Mg)] increases outwards from 0.40 to 0.63, indicating growth under decreasing temperature and pressure. Phase equilibrium modeling in the system of NCKFMASHO (Na 2 O–CaO–K 2 O–FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O–O) by THERMOCALC 3.30 reveals that Glaucophane was formed during retrograde metamorphism. Based on the compositional zonation of Glaucophane and its mineral inclusions, the peak P – T conditions were 23.2–25.3 kbar and 499–519 °C, 17–20 kbar and 430–530 °C for the first retrograde stage (A) and 15–17 kbar and 470–530 °C for the second retrograde stage (B). The obtained retrograde P – T path indicates a rapid uplift involving an early isothermal decompressional stage similar to that of Alpine-type blueschists.
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Lawsonite-bearing chloritoid–Glaucophane schist from SW Tianshan, China: Phase equilibria and P–T path
Journal of Asian Earth Sciences, 2011Co-Authors: Lifei Zhang, Xu ChuAbstract:Abstract Lawsonite-bearing chloritoid–Glaucophane schist has been discovered firstly in the high to ultra-high pressure (HP–UHP) metamorphic belt in Southwestern Tianshan, China. It is characterized by the mineral assemblage of lawsonite + chloritoid + Glaucophane + phengite + paragonite + epidote/allanite + chlorite + quartz + dolomite/calcite + rutile + tourmaline. Lawsonite and chloritoid exclusively occur as micro-inclusions in the cores and mantles of porphyroblastic Glaucophane. The Glaucophane is coarse-grained (about 1–20 mm long), and forms euhedral to subhedral crystals with distinct growth zonation. The X (gln) [=Fe2 + /(Fe 2+ + Mg)] increases outwards from 0.40 to 0.63, indicating growth under decreasing temperature and pressure. Phase equilibrium modeling in the system of NCKFMASHO (Na 2 O–CaO–K 2 O–FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O–O) by THERMOCALC 3.30 reveals that Glaucophane was formed during retrograde metamorphism. Based on the compositional zonation of Glaucophane and its mineral inclusions, the peak P – T conditions were 23.2–25.3 kbar and 499–519 °C, 17–20 kbar and 430–530 °C for the first retrograde stage (A) and 15–17 kbar and 470–530 °C for the second retrograde stage (B). The obtained retrograde P – T path indicates a rapid uplift involving an early isothermal decompressional stage similar to that of Alpine-type blueschists.