Zircon U-Pb age, geochemical data: Constraints on the origin and tectonic evolution of the metamafic rocks from Longmuco-Shuanghu-Lancang suture zone, Tibet

Abstract

Bulk-rock major and trace elements and zircon U-Pb data are reported for Permian metamafic rocks from Guoganjianan, in the western part of Longmuco-Shuanghu-Lancang suture zone. These results offer new insights into mantle source characteristics and geodynamic setting of Permian ophiolitic fragments. U-Pb isotopic dating using SHRIMP II method reveals that the metamafic rocks were formed at 274.7±3.9 and 279.8±3.6 Ma. The metamafic rocks mostly show N-MORB-typed rare earth element patterns and are enrichment in large-ion lithophile elements, indicating that they are probably derived from partial melting of a depleted mantle in a back-arc basin. Our new data, together with recent studied results on Paleozoic ophiolitic fragments suggest the Paleo-Tethys Ocean in Central Qiangtang opened at Cambrian and widened between Ordovician and Devonian. Northward subduction started in the Late Devonian-Early Carboniferous and a back-arc basin developed during Permian.

Keywords

Tibet / Longmuco-Shuanghu-Lancang suture zone / metamafic rock / zircon SHRIMP U-Pb dating / geochemistry

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