检索结果-南通市图书馆

Journal of Earth Science 2011年第6期22卷 677-687页

作者：刘强吴耀章军锋 Faculty of Earth Sciences China University of Geosciences State Key Laboratory of Geological Processes and Mineral Resources China University of Geosciences

The ultrahigh-pressure（UHP） eclogite and gneiss from the Dabie（大别）-Sulu（苏鲁） oro-gen experienced variable degrees of partial melting during exhumation.We report here dehydration partial melting experiments of biotite gneiss and phengite-bearing eclogite at 2 GPa and 800-950 ℃.Our results show that the partial melting of gneiss is associated with the breakdown of biotite into almandine-rich garnet starting at 900 ℃.About 10% granitic melt can be produced at 950 ℃.In con-trast,the partial melting of phengite-bearing eclogite exists at slightly lower temperatures（800-850 ℃）.The melt fraction is in general more in biotite gneiss than in phengite-bearing eclogite under similar pressure and temperature conditions.Both melts are rich in silica and alkali,but poor in FeO,MgO and CaO.These results suggest that low-degree partial melting of gneiss and eclogite is often associated with dehydration of hydrous mineral,such as micas.The dehydration temperature and melt composi-tion can place important constraints on the partial melting phenomena（granitic leucosome and multi-phase mineral inclusions） recorded in UHP rocks.

关键词： gneiss eclogite partial melting dehydration phengite biotite.

Ammonium Impacts on Vibrations of Hydroxyl and Lattice of phengite at High Temperature and High Pressure

在线全文

学校读者我要写书评

暂无评论

Journal of Earth Science 2021年第5期32卷 1278-1286页

作者： Weihua Huang Yan Yang Zeming Qi Wendi Liu Zhongping Wang Yan Liu Qunke Xia School of Earth Sciences Zhejiang UniversityHangzhou 310027China National Synchrotron Radiation Laboratory University of Science and Technology of ChinaHefei 230026China Department of Physics University of Science and Technology of ChinaHefei 230026China

Dehydration in hydrous phases of the downgoing slab controls water release processes in subduction zones. Interplay between volatiles in hydrous minerals has complicated the previous knowledge of their dehydration. phengite is an essential mineral carrying both hydrogen and nitrogen to the deep Earth. To further understand the link between nitrogen and dehydration process of phengite at an atomic level, we here carry out high temperature and high pressure vibrational spectroscopic investigations on hydroxyl and lattice of ammonium-bearing and ammonium-free phengites. The results show that heating to 800 oC hardly influences hydroxyl bonding strength, whereas pressure induces strengthening of hydrogen bonding until 10 GPa. Moreover, hydrogen transits between the sites with increasing temperature and pressure. The lattice modes soften with increasing temperature and stiffen under compression. Ammonium has no effect on hydroxyl bonding strength, but hinders hydrogen transition at high temperatures and high pressures. Ammonium does not influence the lattice at high pressures either, but delays softening of the lattice at high temperatures. These data unveil behavior of hydroxyl and lattice in phengite at high temperature and high pressure, and also evaluate ammonium impacts, shedding new lights on dehydration processes of phengite during subduction.

关键词： hydroxyl lattice ammonium phengite high temperature high pressure

Micro-area Chemical Composition and Preserved P-T Evolution Trace of phengite in Albite Gneiss from the Donghai Ultrahigh-Pressure Metamorphic Area,East China

在线全文

学校读者我要写书评

暂无评论

Acta Geologica Sinica(English Edition) 2000年第2期74卷 183-189页

作者： LIU Fulai ZHANG Zeming XU Zhiqin YANG Jingsui XU Huifen Institute of Geology Chinese Academy of Geological SciencesBeijing 100037China

Study of micro-area chemical compositions indicates that phengite in albite gneiss from hole ZK2304 of the Donghai region has evident compositional zoning. SiO2 and tetrahedrally coordinated Si contents decrease, and Al2O3, AlIVand AlVIcontents increase gradually from core to rim. However, K2O, MgO and FeO contents basically remain unchanged from core to rim. According to P-T estimates obtained from geothermometers and barometers, combined with previous experimental data, the core belt (micro-area I) of phengite was formed at T=637–672°C and P=1.55–1.73 GPa, and the transitional belt (micro-area II) of the phengite were formed at T=594–654°C and P=1.35–1.45 GPa. Towards the rim belt (micro-area III), the temperature decreased slightly, but the pressure decreased rapidly with T=542–630°C and P=1.12–1.19 GPa. The P-T evolution path recorded by the compositional zoning of phengite is characterized by significant near-isothermal decompression, revealing that the gneiss has undergone high-pressure-ultrahigh-pressure metamorphism. The compositional zoning of the phengite in the albite gneiss may have formed in the geodynamic process of rapid exhumation in the Sulu ultrahigh-pressure metamorphic belt.

关键词： phengite compositional zoning gneiss genetic mechanism Donghai drill hole

Thermodynamic modelling of the phengite geobarometry

在线全文

学校读者我要写书评

暂无评论

Science China Earth Sciences 2007年第7期50卷 1033-1039页

作者： ZHU WenPing WEI ChunJing The MOE Laboratory of Orogenic Belts and Crustal Evolution School of Earth and Space Sciences Peking University Beijing 100871 China

Using the updated models of activity-composition relations for solid solutions,P-T pseudosections and Si isopleths of phengite in the system KFMASH (K2O-FeO-MgO-Al2O3-SiO2-H2O) are calculated with the software THERMOCALC 323 for three bulk compositions of the average,Al-rich and K-rich metapelites. The Si isopleths of phengite in the calculated pseudosections are highly dependent on mineral as-semblages. In the chlorite-and biotite-bearing di-and trivariant fields,and in the garnet + kyanite-bearing trivariant fields,the phengite can be used as a good geobarometer. But in the carpho-lite-present and chlorite-absent fields,the Si contents of phengite mainly indicate variance of tem-perature. For a given Si value,the phengite in kyanite-bearing assemblages shows higher pressures than in the K-feldspar-bearing assemblages. Addition of Na2O into the KFMASH leads to reduction of stability of the AFM phases. The Si isopleths of phengite in the mineral assemblages containing only one Na-phase are similar to those in the corresponding KFMASH assemblages. But in the assemblages with two or more Na-phases,the phengite Si isopleths differ remarkably from those in the KFMASH.

关键词： P-T pseudosection phengite geobarometry

Genesis of excess argon in phengite and significance of ^(40)Ar-^(39)Ar age spectra for omphacite:A case study on UHP eclogite of South Dabie Terrain,China

在线全文

学校读者我要写书评

暂无评论

Chinese Science Bulletin 2000年第15期45卷 1345-1351页

作者： WANG Songshan, GE Ningjie, SANG Haiqing & QIU Ji1. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China 2. Department of Earth and Space Science, University of Science and Technology of China, Hefei 230026, China Correspondence should be addressed to Wang Songshan Institute of Geology and Geophysics Chinese Academy of Sciences Beijing China Department of Earth and Space Science University of Science and Technology of China Hefei China

The Ar-Ar dating of phengite and omphacite in ultrahigh-pressure (UHP) eclogite of Bixiling and Hengchong in the South Dabie Terrain shows that the content range of excess argon is as high as (0.4-1.3)×10 8 mol· g 1. The genesis of the excess argon is discussed. The Ar-Ar age spectra of omphacite could not support the opinion that the UHP metamorphism occurred in Caledon epoch and pre-Caledon epoch.

关键词： South Dabie Terrain ultrahigh-pressure metamorphics phengite omphacite excess argon.

Excess and Radiogenic Argon in High-Pressure Mylonites of the Tan-Lu Fault Zone, Eastern China

在线全文

学校读者我要写书评

暂无评论

Acta Geologica Sinica(English Edition) 2008年第1期82卷 84-98页

作者： XIE Chenglong ZHU Guang WANG Yongshen HU Zhaoqi School of Resource and Environment Engineering Hefei University of Technology Hefei Anhui 230009

Bulk separates of porphyroclastic phengite, neoformed phengite and their mixtures from the Tan-Lu HP mylonites overprinted on the Sulu UHP rocks were analyzed with the 40Ar/39Ar step heating method. Two samples of the neoformed phengite from ultramylonite give 40Ar/39Ar plateau ages of 209.9±1.8 Ma and 214.3±1.8 Ma, which are interpreted as representing cooling times of the TanLu sinistral faulting, and provide geochronological evidence for the syn-orogenic faulting of the Tan-Lu fault zone. The results show that the phengite formed during the retrograde eclogite-facies mylonitization was not contaminated with excess argon and can be used for dating the deformation. Argon closure in previous K-bearing minerals with excess argon under a retrograde HP dry condition is considered to be the reason for lack of excess argon incorporation in the neoformed phengite. Five porphyroclastic phengite samples yield 40Ar/39Ar plateau ages ranging from 666±12 Ma to 307.1±3.3 Ma, which are interpreted as being contaminated with excess argon. Two mixture samples with plateau ages of 239.4±2.1 Ma and 239.3±2.0 Ma show upward-convex age spectra caused by the mixture of older porphyroclastic phengite with excess argon incorporation and younger neoformed phengite without excess argon incorporation. It is demonstrated that excess argon introduced from the previous UHP metamorphism is still preserved in the pre-existing phengite after the Tan-Lu eclogite-facies mylonitization. The intense deformation under HT and HP conditions cannot erase excess argon in the previous phengite totally due to restricted fluid activities. These porphyroclastic phengite previously contaminated with excess argon cannot be used for dating the later HP deformation. This indicates that deformation under a HP dry condition does not play an important role in removing previous 40Are in phengite.

关键词： excess argon phengite mylonite Tan-Lu fault zone 40Ar/39Ar dating