Fluid-present and fluid-absent melting of muscovite in migmatites in the Himalayan orogen: Constraints from major and trace element zoning and phase equilibrium relationships

Lithos ◽  
2021 ◽  
pp. 106071
Author(s):  
Zi-Yue Meng ◽  
Xiao-Ying Gao ◽  
Ren-Xu Chen ◽  
Yong-Fei Zheng ◽  
Qiang-Qiang Zhang ◽  
...  
Keyword(s):  
Phase Equilibrium ◽  
Trace Element ◽  
Himalayan Orogen ◽  
Equilibrium Relationships

The Origin of Garnets in Anatectic Rocks from the Eastern Himalayan Syntaxis, Southeastern Tibet: Constraints from Major and Trace Element Zoning and Phase Equilibrium Relationships

2019 ◽  
Vol 60 (11) ◽  
pp. 2241-2280 ◽  
Author(s):  
Qiong-Xia Xia ◽  
Peng Gao ◽  
Guang Yang ◽  
Yong-Fei Zheng ◽  
Zi-Fu Zhao ◽  
...  
Keyword(s):  
Phase Equilibrium ◽  
Trace Element ◽  
Granulite Facies ◽  
Major And Trace Elements ◽  
Dehydration Melting ◽  
Biotite Gneiss ◽  
Mineral Inclusions ◽  
Equilibrium Relationships ◽  
Eastern Himalayan Syntaxis ◽  
Southeastern Tibet

Abstract Amphibolite- and granulite-facies metamorphic rocks are common in the eastern Himalayan syntaxis of southeastern Tibet. These rocks are composed mainly of gneiss, amphibolite and schist that underwent various degrees of migmatization to produce leucogranites, pegmatites and felsic veins. Zircon U–Pb dating of biotite gneiss, leucocratic vein and vein granite from the syntaxis yields consistent ages of ∼49 Ma, indicating crustal anatexis during continental collision between India and Asia. Garnets in these rocks are categorized into peritecitc and anatectic varieties based on their mode of occurrence, mineral inclusions and major- and trace-element zoning. The peritectic garnets mainly occur in the biotite gneiss (mesosome layer) and leucocratic veins. They are anhedral and contain abundant mineral inclusions such as high-Ti biotites and quartz, and show almost homogeneous major-element compositions (except Ca) and decreasing HREE contents from core to rim, indicating growth during the P- and T-increasing anatexis. Peak anatectic conditions at 760–800°C and 9–10·5 kbar are well constrained by phase equilibrium calculations, mineral assemblages, and garnet isopleths. In contrast, anatectic garnets only occur in the vein granite. They are round or subhedral, contain quartz inclusions, and exhibit increasing spessartine and trace-element contents from core to rim. The garnet–biotite geothermometry and the garnet–biotite–plagioclase–quartz geobarometry suggest that the anatectic garnets crystallized at ∼620–650°C and 4–5 kbar. Some garnet grains show two-stage zoning in major and trace elements, with the core similar to the peritectic garnet but the rim similar to the anatectic garnet. Mineralogy, whole-rock major- and trace-element compositions and zircon O isotopes indicate that the two types of leucosomes were produced by hydration (water-present) melting and dehydration (water-absent) melting, respectively. The leucocratic veins contain peritectic garnet but no K-feldspar, have lower whole-rock K2O contents and Rb/Sr ratios, higher whole-rock CaO contents and Sr/Ba ratios, and show homogeneous δ18O values that are lower than those of relict zircons, indicating that such veins were produced by the hydration melting. In contrast, the vein granite contains peritectic garnet and K-feldspar, has higher whole-rock K2O contents and Rb/Sr ratios, lower whole-rock CaO contents and Sr/Ba ratios, and shows comparable δ18O values with those of relict zircons, suggesting that this granite were generated by the dehydration melting. Accordingly, both hydration and dehydration melting mechanisms have occurred in the eastern Himalayan syntaxis.

Phase Relationships of Al2O3-ZrO2-SiO2 System with Microwave Heating

2010 ◽  
Vol 434-435 ◽  
pp. 856-859
Author(s):  
Ying Na Zhao ◽  
Peng Yu Zhang ◽  
Hai Xu ◽  
Qi Hui Jia ◽  
Jia Chen Liu
Keyword(s):  
Phase Diagram ◽  
Phase Equilibrium ◽  
Microwave Heating ◽  
Thermodynamic Equilibrium ◽  
Tetragonal Zirconia ◽  
Heating Time ◽  
Sio2 System ◽  
Equilibrium Relationships ◽  
Phase Relationships

Based on the Al2O3-ZrO2-SiO2 system, the conventional pre-sintering samples were reheated by microwave to investigate the influence of microwave to the thermodynamic equilibrium and phase equilibrium relationships. It was found that microwave can accelerate transitions to thermodynamic equilibrium. The phase equilibrium of the samples prepared by microwave heating was identical with the traditional phase diagram. In addition, the amount of tetragonal zirconia in the prepared samples remained constant as the microwave heating time prolonging. All of the observed phenomenon can be explained by microwave nonthermal effects.

scholarly journals Phase Equilibrium Relationships in the System Al2O3-ZrO2-SiO2: An Update

1991 ◽  
Vol 53-55 ◽  
pp. 58-63 ◽  
Author(s):  
M. Conceição Greca ◽  
J.V. Emiliano ◽  
Ana M. Segadães
Keyword(s):  
Phase Equilibrium ◽  
Equilibrium Relationships

The effects of source mixing and fractional crystallization on the composition of Eocene granites in the Himalayan orogen

2021 ◽  
Author(s):  
Peng Gao ◽  
Yong-Fei Zheng ◽  
Chris Yakymchuk ◽  
Zi-Fu Zhao ◽  
Zi-Yue Meng
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Fractional Crystallization ◽  
Melt Inclusions ◽  
Thermal Anomaly ◽  
Continental Collision ◽  
Plate Boundaries ◽  
Crustal Anatexis ◽  
Himalayan Orogen ◽  
Heavy Rare Earth Elements

Abstract Granites are generally the final products of crustal anatexis. The composition of the initial melts may be changed by fractional crystallization during magma evolution. Thus, it is crucial to retrieve the temperatures and pressures conditions of crustal anatexis on the basis of the composition of the initial melts rather than the evolved melts. Here we use a suite of ∼46–41 Ma granites from the Himalayan orogen to address this issue. These rocks can be divided into two groups in terms of their petrological and geochemical features. One group has high maficity (MgO + FeOt = 2–4 wt%) and mainly consists of two-mica granites, and is characterized by apparent adakite geochemical signatures, including high Sr concentrations, Sr/Y and La/Yb ratios; and low concentrations of HREE (heavy rare earth elements) and Y. The other group has low maficity (MgO + FeOt <1 wt%) and consists of subvolcanic porphyritic granites and garnet/tourmaline-bearing leucogranites. This group does not possess apparent adakite signatures. The low maficity group (LMG) has lower MgO + FeOt contents and the high maficity group (HMG) has higher Mg# compared with initial anatectic melts determined by experiment petrology and melt inclusions study. Petrological observations indicate that the HMG and the LMG can be explained as a crystal-rich cumulate and its fractionated melt, respectively, such that the initial anatectic melt is best represented by an intermediate composition. Such a cogenetic relationship is supported by the comparable Sr–Nd isotopic compositions of the two coeval groups. However, these compositions are also highly variable, pointing to a mixed source that was composed of amphibolite and metapelite with contrasting isotope compositions. We model the major and trace element compositions of anatectic melts generated by partial melting of the mixed source at four apparent thermobaric ratios of 600, 800, 1000 and 1200 °C/GPa. Modeling results indicate that melt produced at 1000 °C/GPa best matches the major and trace element compositions of the inferred initial melt compositions. In particular, a binary mixture generated from 10 vol% partial melting of amphibolite and 30 vol% melting of metapelite at 850 ± 50 °C and 8.5 ± 0.5 kbar gives the best match. Therefore, this study highlights that high thermobaric ratios and subsequent fractional crystallization are responsible for the generation of the apparent adakitic geochemical signatures, rather than melting at the base of the thickened crust as previously proposed. The thermal anomaly responsible for the Eocene magmatism in the Himalayan orogen was probably related to asthenosphere upwelling in response to rollback of the subducting Neo-Tethyan oceanic slab at the terminal stage of continental collision between India and Asia. As such, a transition in dynamic regime from compression to extension is necessary for the generation of high thermobaric ratios in the continental collision zone. Therefore, on the basis of evaluating the potential role of fractional crystallization in altering the composition of the initial melt, granite geochemistry coupled with thermodynamic modeling can better elucidate the petrogenesis of granites and the geodynamic mechanisms associated with anatexis at convergent plate boundaries.

PHASE EQUILIBRIUM RELATIONSHIPS IN THE BINARY SYSTEM METHYL ETHYL KETONE–WATER

1960 ◽  
Vol 38 (10) ◽  
pp. 2015-2023 ◽  
Author(s):  
Irwin Siegelman ◽  
C. H. Sorum
Keyword(s):  
Phase Equilibrium ◽  
Binary System ◽  
Methyl Ethyl Ketone ◽  
Freezing Point ◽  
Miscibility Gap ◽  
Methyl Ethyl ◽  
Partially Miscible ◽  
Binary Eutectic ◽  
Equilibrium Relationships ◽  
Solid Liquid

A complete investigation of the phase equilibrium relationships in the binary system of the partially miscible liquid pair methyl ethyl ketone–water is presented. The system shows a minimum azeotrope at 73.35 ± 0.05 °C with a composition of 88.45 ± 0.15 wt.% ketone. The azeotrope falls outside of the miscibility gap for this system. The liquid–vapor curves intersect the miscibility gap at the temperature of 73.60 ± 0.05 °C at which two conjugate solutions of compositions 18.10 ± 0.10 and 87.78 ± 0.15 wt.% ketone, respectively, are in equilibrium with a vapor phase of composition 88.00 ± 0.15 wt.% ketone. The partially miscible liquid pair shows an upper consolute temperature of 139 ± 0.5 °C at a composition of 44.9 ± 0.2 wt.% ketone. The liquid–liquid curves intersect the solid–liquid curves at a temperature of −6.0 ± 0.5° C at which two conjugate solutions of composition 40.0 ± 0.2 and 78.0 ± 0.2 wt.% ketone, respectively, are in equilibrium with ice. A binary eutectic exists at a temperature of −89.0 ± 0.5 °C with composition of the eutectic solid equal to 99.4 ± 0.4 wt.% ketone. The freezing point of pure, dry methyl ethyl ketone is determined to be −83.5 ± 0.5 °C.

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