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

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  • Geology
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Chinese Science Bulletin

Abstract

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 extrusive 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 clinopyroxene 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 patterns of the intrusive and extrusive lithologies in the Dongcaohe ophiolite are consistent with crystallization 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.

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Authors and Affiliations

  1. Department of Earth Sciences, Cheng Kung University, Tainan, 701, Taiwan, China

    Chien-Yuan Tseng, Huai-Jen Yang, Houng-Yi Yang & Ching-Lang Tsai

  2. Beijing SHRIMP Centre, Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, China

    Liu DunYi

  3. Xi’an Institute of Geology and Mineral Resources, Xi’an, 710054, China

    Wu HanQuan

  4. Gansu Bureau of Geology and Mineral Resources, Lanzhou, 730000, China

    Zuo GuoChao

Authors
  1. Chien-Yuan Tseng
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  2. Huai-Jen Yang
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  3. Houng-Yi Yang
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  4. Liu DunYi
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  5. Ching-Lang Tsai
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  6. Wu HanQuan
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  7. Zuo GuoChao
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Correspondence to Huai-Jen Yang.

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Tseng, CY., Yang, HJ., Yang, HY. et al. The Dongcaohe ophiolite from the North Qilian Mountains: A fossil oceanic crust of the Paleo-Qilian ocean. CHINESE SCI BULL 52, 2390–2401 (2007). https://doi.org/10.1007/s11434-007-0300-3

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  • DOI: https://doi.org/10.1007/s11434-007-0300-3

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