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Acta Geologica Sinica(English Edition) 1998年第2期72卷 131-141,242页

作者： SONG Shuguang SU Li Xi'an Institute of Geology and Mineral Resources CAGS166 East Youyi Rd.Xi'anShaanxi 710054

Abstract: This paper discusses in detail the deformation textures, glide system, petrofabrics and olivine dislocation microstructures of mantle peridotites at Yushigou in the north qilian mountains, northwestern China. The peridotites have undergone high-pressure, high-temperature and low-strain rate plastic flow deformation. According to the dynamic recrystallized-grain size of olivine and the average spacing between the dislocation walls as well as the chemical composition of enstatite, the authors calculated the rheological parameters of the ancient upper mantle in the study area as follows: temperatures 1025–1093°C; pressures 3043–4278 MPa; depths 95–132 km; deviatoric stress 28–32 MPa; strain rates 0.2×10?14-2.13×10?14s?1 and equivalent viscosities 0.45×1020-4.65×1020 Pa ? s. These parameters suggest that the position where plastic flow took place was correspondent to the lowvelocity zone beneath the oceanic lithosphere and that oceanization characterized by middle-velocity (1–3 cm/a) sea-floor spreading took place in the north qilian mountains during the Early Palaeozoic.

关键词： oceanic mantle rocks rheology sea-floor spreading north qilian mountains

Geochronology and Geochemistry of the Middle Proterozoic Aoyougou Ophiolite in the north qilian mountains,northwestern China

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Acta Geologica Sinica(English Edition) 2001年第1期75卷 41-50页

作者： ZHANG Zhaochong MAO Jingwen ZUO Guochao YANG Jianmin Paul T.ROBINSON Institute of Geology Chinese Academy of Geological SciencesBaiwanzhuang Road 26Beijing 100037China Institute of Mineral Deposits Chinese Academy of Geological SciencesBaiwanzhuang Road 26Beijing 100037China Institute of Geology Gansu Bureau of Geology and Mineral ResourcesLanzhou 730000China Centre For Marine Geology Dalhousie UniversityHalifaxNova ScotiaB3H 3J5Canada

The Aoyougou ophiolite lies in an early Palaeozoic orogenic belt of the western north qilian mountains, near the Aoyougou valley in Gansu Province, northwestern China. It consists of serpentinite, a cumulate sequence of gabbro and diorite, pillow and massive lavas, diabase and chert. Ages of 1840±2 Ma, 1783±2 Ma and 1784±2 Ma on three zircons from diabase, indicate an early Middle Proterozoic age. The diabases and basalts show light rare-earth element enrichment and have relatively high TiO2 contents, characteristic of ocean island basalts. All of the lavas have low MgO, Cr, Ni contents and Mg numbers indicating a more evolved character. They are believed to have been derived from a more mafic parental magma by fractionation of olivine, Cr-spinel and minor plagioclase. Based on the lava geochemistry and regional geology, the Aoyougou ophiolite was probably believed to have formed at a spreading centre in a small marginal basin. Subduction of the newly formed oceanic lithosphere in the Middle Proterozoic produced a trench-arc-basin system, which is preserved in the north qilian mountains.

关键词： Proterozoic ophiolite geochronology geochemistry north qilian mountains

Geochemical Characteristics and Tectonic Setting of the Laohushan Basalts, north qilian mountains

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Acta Geologica Sinica(English Edition) 2001年第4期75卷 452-457页

作者： QIAN Qing and ZHANG Qi Institute of Geology and Geophysics, CAS, P. O. Box 9825, Beijing 100029 CAS Inst Geol & Geophys Beijing 100029 Peoples R China

The Ordovician Laohushan ophiolite, located in the eastern part of the north qilian mountains, is mainly composed of meta-peridotites, gabbros and basalts alternating with sediments. The sediments are mainly turbidites, including sandstones, siltstones, cherts etc. Major elements show that the basalts are subalkaline tholeiites and may be analogous to ocean-floor basalts. Except a few N-MORBs, most of the basalts are E-MORBs as indicated by incompatible element ratios such as (La/Ce)N, La/Sm, Ce/Zr, Zr/Y and Zr/Nb. Negative Nb anomaly is common but negative Zr, Hf and Ti anomalies are quite rare. Based on the geochemical characteristics, it is suggested that the Laohushan basalts were formed in a back-arc basin. ENd (t) of the basalts ranges between +3.0 and +8.9 and (87Sr/86Sr), ranges between 0.7030 and 0.7060, indicating a depleted mantle source which was mixed with more or less enriched mantle components. Furthermore, the petrography of the sandstones and geochemistry of the cherts suggest that the sediments were deposited near a continental margin.

关键词： north qilian mountains Laohushan basalts sediments geochemistry

U-Pb Zircon Dating of the Yeniutan Granitic Intrusion in the Western Sector of the north qilian mountains

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Acta Geologica Sinica(English Edition) 2000年第4期74卷 781-785页

作者： MAO Jingwen ZHANG Zuoheng JIAN Ping WANG Zhiliang YANG Jianmin ZHANG Zhaochong Institute of Mineral Resources Chinese Academy of Geological Sciences Beijing 100037 Institute of Geology Chinese Academy of Geological Sciences Beijing 100037

Zircons from granodiorite and biotite granite in the Yeniutan granitic intrusion in the western north qilian mountains yielded a weighted mean 206Pb/238U apparent age of 460±3 Ma, suggesting that the intrusion originated during the late stage of plate subduction. Its related Ta'ergou and Xiaoliugou deposits are two of the few large tungsten deposits formed in the plate subduction environment in the world. The U-Pb dating of the zircons from the biotite granite gave a discordant lower intercept age of 183±4 Ma, which implies that the Yanshanian event was probably superimposed on the north qilian region.

关键词： U-Pb dating granodiorite biotite granite tungsten deposit north qilian mountains

From Flysch to Molasse—Sedimentary and Tectonic Evolution of Late Caledonian -Early Hercynian Foreland Basin in north qilian mountains

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Journal of China University of Geosciences 2003年第1期14卷 1-7页

作者： DuYuansheng WangJiasheng HanXin ShiGR FacultyofEarthSciences ChinaUniversityofGeosciencesWuhan430074 SchoolofEcologyandEnvironment DeakinUniversityMelbourneAustralia

The Late Caledonian to Early Hercynian north qilian orogenic belt in no rthwestern China is an elongate tectonic unit situated between the north China p late in the north and the Qaidam plate in the south. north qilian started in the latest Proterozoic to Cambrian as a rift basin on the southern margin of north China, and evolved later to an archipelagic ocean and active continental margin during the Ordovician and a foreland basin from Silurian to the Early and Middle Devonian. The Early Silurian flysch and submarine alluvial fan, the Middle to L ate Silurian shallow marine to tidal flat deposits and the Early and Middle Devo nian terrestrial molasse are developed along the corridor Nanshan. The shallowin g upward succession from subabyssal flysch, shallow marine, tidal flat to terre strial molasse and its gradually narrowed regional distribution demonstrate that the foreland basin experienced the transition from flysch stage to molasse stag e during the Silurian and Devonian time.

关键词： north qilian mountains Silurian Devonian flysch molasse foreland basin.

Geochemical Characteristics and Tectonic Setting of the Laohushan Basalts,north qilian mountains

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Geochemical Characteristics and Tectonic Setting of the Laoh...