首页|Short-lived intra-oceanic arc-trench system in the North Qaidam belt(NW China)reveals complex evolution of the Proto-Tethyan Ocean
Short-lived intra-oceanic arc-trench system in the North Qaidam belt(NW China)reveals complex evolution of the Proto-Tethyan Ocean
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Recognition of any intra-oceanic arc-trench system(IOAS)could provide invaluable information on the tectonic framework and geodynamic evolution of the vanished ocean basin.The Tanjianshan Complex and mafic-ultramafic rocks along the North Qaidam ultra-high pressure metamorphic belt in NW China record the subduction process of the Proto-Tethyan Ocean.Four lithotec-tonic units,including island arc,ophiolite,forearc basin,and accretionary complex,are recognized based on detailed field investigation.They rest on the northern margin of the Qaidam block and occur as alloch-thons in fault contact with underlying high-grade metamorphic rocks.The ophiolite unit mainly consists of ultramafic rocks,527-506 Ma gabbro,515-506 Ma plagiogranite,dolerite,and massive lava.High-Cr spinels in serpentinite,dolerite with forearc basalt affinity,and boninitic lava collectively indicate a forearc setting.The accretionary complex,exposed to the south of the ophiolite complex and island arc,is highly disrupted and contains repeated slices of basalt,495-486 Ma tuff,chert,limestone,and melange.luffs with positive zircon e^t)values indicate derivation from a nearby juvenile island arc.These lithotectonic units,as well as the back-arc basin,are interpreted to constitute a Cambrian IOAS that formed during the northward subduction of the Proto-Tethyan Ocean.Combined with regional geology,we propose a new geodynamic model involving short-lived Mariana-type subduction and prolonged Andean-type subduction to account for the complex evolution of the Proto-Tethyan Ocean.The reconstruction of a relatively complete IOAS from the North Qaidam belt not only reveals a systematic evolution of intra-oceanic subduction but also advances our understanding of the subduction and accretion history of the Proto-Tethyan Ocean.;
Changlei Fu、Zhen Yan、Jonathan C.Aitchison
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Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China
School of Earth and Environmental Sciences,University of Queensland,Brisbane 4072,Australia
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