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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

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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, {2. 10002., china 2. Department of Earth and Space Science, University of Science and Technology of china, Hefei 2.002., 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)×1. 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.

Cryptomelane(KxMn(8-x)O(1.)) Natural active octahedral molecular sieve(OMS-2.

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Chinese Science Bulletin 2003年第9期48卷 920-923页

作者： LU Anhuai, GAO Xiang, QIN Shan & wang ChangqiuDepartment of {1., Peking University, {2. 1.0871. china correspondence should be addressed to Lu Anhuai (e-mail: ahlu@ ***) 1. Department of geology Peking University Beijing 100871 China

The Xiangtan manganese deposit (XTM) used to be considered a supergene oxide manganese ore in South china. We reported a new identification of the naturally outcropping cryptomelane by examining the physical, chemical and structural features of the XTM supergene oxide manganese ore. The MnO2.content was over 90%, K2. more than 3%, and water from 2.2.-3.1% which is similar to one in zeolite. The cell parameters of the cryptomelane were given as a0 = 0.9974 nm, b0 = 0.2.63 nm, c0 = 0.9693 nm and β91.47(. There was a larger pseduotetragonal tunnel in the natural cryptomelane that was formed by [MnO6] octahedral double chains with aperture of 0.462.0.466 nm2. filled with K cations resulting in some Mn3+ substituting for Mn4+ to balance the negative charges of structure. The finding is important not only for prospecting manganese resources in South china, but also in application of octahedral molecular sieve of natural cryptomelane as that developed in the tetragonal molecular sieve of natural zeolite over the past century. The XTM cryptomelane (OMS-2. may be the real mineral of the active octahedral molecular sieve in nature.

关键词：隐钾锰矿天然活性分子筛 OMS-2 湘潭锰沉积物浅生矿床氧化物

Ultramafic xenoliths in Mesozoic diorite in west Shandong Province

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Science china Earth Sciences 2004年第6期47卷 489-499页

作者： CHEN Lihui1,2.& ZHOU Xinhua2.1.The Key Laboratory of Orogenic Belts and Crustal Evolution,Ministry of Education,china and School of Earth and Space Sciences,Peking University,beijing 100871,china 2.Institute of geology and Geophysics,Chinese Academy of Sciences,beijing 10002.,china correspondence should be addressed to Chen Lihui(email: lihui_chen@***) 1. The Key Laboratory of Orogenic Belts and Crustal Evolution Ministry of Education China and School of Earth and Space Science Peking University 100871 Beijing China 2. Institute of {1. and Geophysics Chinese Academy of Sciences 100029 Beijing China

Ultramafic xenoliths are common in Tietonggou intrusion, Laiwu, Shandong Prov-ince. Peridotite xenoliths develop two-stage metasomatism popularly: (i) The early metasoma-tism is characterized by intergranular clinopyroxene and phlogopite; (ii) The later metasomatism is characterized by orthopyroxene veins with a few plagioclases and amphiboles. These ul-tramafic xenoliths are thought to be mostly from the crust-mantle transitional zone on the basis of their combination, mineral chemistry, equilibrium temperature, and metasomatic characteristics. Major elements, rare earth elements, and Sr-Nd isotopic composition of the ultramafic xenoliths indicate that there is a petrogenetic relationship between the silica-enriched xenoliths and their host diorites. We propose that such silica enrichment might be an indicator of melt-rock interac-tions in the Mesozoic lithosphere beneath western Shandong.

关键词： ultramafic xenoliths, crust-mantle transitional zone,metasomatism, Tietonggou intrusion, Laiwu.

Zircon SHRIMP U-Pb dating for the Cangshuipu volcanic rocks and its implications for the lower boundary age of the Nanhua strata in South china

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Science Bulletin 2003年第16期48卷 1663-1669页

作者： wang Jian1, LI Xianhua2. DUAN Taizhong3, LIU Dunyi4, SONG Biao4, LI Zhongxiong1 & GAO Yonghua5 1. Chengdu Institute of geology and {2. resources, china Geologi-cal Survey, Chengdu 610082. china 2. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, china 3. Colorado School of Mines, Golden, CO 80401-1887, USA (Present address: Marathon Oil Company, Houston, TX 77056-2.2., USA) 4. Institute of geology, Chinese Academy of Geological Sciences, Bei-jing 100037, china 5. Graduate School of the Chinese Academy of Geological Sciences, beijing 100037, china correspondence {12. be addressed to wang Jian (e-mail: jianwang@ ***) Chengdu Institute of geology and {1. {2. China Geological Survey Chengdu 610082 China Guangzhou Institute of Geochemistry Chinese Academy of Sciences Guangzhou 510640 China Colorado School of Mines Golden CO 80401-1887 USA Institute of geology Chinese Academy of Geological Sciences Beijing 100037 China Graduate School of the Chinese Academy of Geological Sciences Beijing 100037 China

The continental volcanic rocks and volcaniclas-tic sedimentary conglomerates of the Cangshuipu Formation occur well in Yiyang of Hunan Province, consisting of a wedge-shaped succession of Neoproterozoic strata that over-lie with high-angle unconformity the flysch turbidites of the Lengjiaxi Group in the Upper Mesoproterozoic Eonothem. SHRIMP zircon U-Pb dating gives a weighted mean age of 81. 1.0}Ma for the dacitic volcanic agglomerates from the lowest part of the volcanic rocks in the Cangshuipu Forma-tion. This age is younger than previously reported values of 92.—933 Ma for the volcanic rocks from the Cangshuipu Formation. Our new dating represents the lower boundary age of the Neoproterozoic System in the studied area. The younger age for the Cangshuipu volcanic rocks is supported by the following observations: （1. Lower Neoproterozoic strata （81.—1.00 Ma） are missing in the studied area; （2. the Nanhua rift system was initiated at about 82. Ma; and （3） an age of82. Ma may be taken as the lower boundary tim-ing of the Nanhua System （even Neoproterozoic） in South china.

关键词： Zicon U-Pb dating Neoproterozoic volcanics rift basin Nanhua System.

A 2.8 Ma record of environmental evolution and tectoni events inferred from the Cuoe core in the middle of Tibetan Plateau

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Science china Earth Sciences 2004年第11期47卷 1025-1034页

作者： SHEN Ji1,Lü Houyuan2.wang Sumin1,CHEN Shiyue1,YANG Xiangdong1,WU Yanhong1 & ZHU Zhaoyu3 1.Nanjing Institute of Geography and Limnology,Chinese Academy of Sciences,Nanjing 2.0008,china 2.Institute of {2. and Geophysics,Chinese Academy of Sciences,beijing 10002.,china 3.Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,china correspondence should be addressed to Shen Ji(email: jishen@***)

Based on a multi-proxy investigation into the deep core of the Cuoe Lake in the middle of Tibetan Plateau, a 2.8 Ma paleoclimatic and paleoenvironmental evolution is recon- structed. The result of magnetic stratum indicates that the lake basin was formed at about 2.8 MaBP, while the multi-proxy analyses of lithology, grain size, magnetic susceptibility and geo- chemical elements reveal that there have been three major environmental evolution stages and at least two intensive uplifts of the Tibetan Plateau in the lake basin area, i.e. during 2.8—2.5 MaBP, the lake basin came into being as a result of the disaggregation of the planation surface and rapid rising of the Tibetan Plateau. During 2.5—0.8 MaBP, with gradual uplift of the Tibetan Plateau, the environment of this area was more effectively controlled by the climatic cycle of the alternative glacial-interglacial stages. After 0.8 MaBP, the middle part of the Plateau accelerated its uplift and entered cryoshere.

关键词： Tibetan Plateau, 2.8 MaBP, environmental evolution, tectonic events, Cuoe Lake.