The Dongcaohe ophiolite from the North Qilian Moun-tains: A fossil oceanic crust of the Paleo-Qilian ocean

查看全文 作　　者：Chien-Yuan [1]TSENG;Huai-Jen [1]YANG;Houng-Yi [1]YANG;LIU [2]DunYi;Ching-Lang [1]TSAI;WU [3]HanQuan;ZUO [4]GuoChao

机构地区：[1]Department of Earth Sciences, Cheng Kung University, Tainan 701, Taiwan, China;[2]Beijing SHRIMP Centre, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;[3]Xi'an institute of Geology and Mineral Resources, Xi'an 710054, China;[4]Gansu Bureau of Geology and Mineral Resources, Lanzhou 730000, China

出　　处：《Chinese Science Bulletin》索引2007年第52卷第17期,共12页

摘　　要：The Dongcaohe ophiolite, located at the south of the North Qilian subduction complexes, is a tectonic block with an exposed area of about 3 km×6 km. It consists of an intrusive section overlain by an ex- trusive section. The lower part of the intrusive section consists of cyclic layers of cumulate dunites, troctolites, anorthosites, anorthositic gabbros, and gabbros with small discordant dunite and troctolite bodies. This layered sequence grades upward to isotropic gabbros and gabbronorites, which are overlain by the extrusive sequence of diabasic sheeted dikes and basaltic lavas. The overall mineral crystallization sequence was olivine±Cr-spinel, plagioclase, clinopyroxene, orthopyroxene, and Fe-Ti oxides. The Cr-spinel (Mg#: 42-66, Cr#: 41-57) in these layered cumulates and present-day abyssal peridotites have similar compositions. Also, the compositional variations of the plagioclase and cli- nopyroxene in the intrusive section reflect crystallization from melts compositionally similar to the present-day ocean basalts. Moreover, the rare earth element (REE) and multi-element distribution pat- terns of the intrusive and extrusive lithologies in the Dongcaohe ophiolite are consistent with crystal- lization of mid-ocean ridge basalts. The zircon grains separated from the gabbronorite have an SHRIMP average 206Pb/238U weighted age of 497 ± 7 Ma, which is considered as the tectonic emplacement age of the Dongcaohe ophiolite. The field occurrence, mineral and whole-rock compositions indicate that the Dongcaohe ophiolite represents a well-persevered oceanic crustal fragment composed of a complete oceanic crustal section of layered cumulates at bottom upgrading through isotropic cumulates to sheeted dikes and lava flows. 关键词：蛇绿岩祁连山海洋底壳化石

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The Dongcaohe ophiolite from the North Qilian Moun-tains: A fossil oceanic crust of the Paleo-Qilian ocean

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