Geochronology And Geochemistry Of The Yazidaban Ophiolitic Melange In Qimantagh: Constraints On The Early Paleozoic Backarc Basin Of The East Kunlun Orogen, Northern Tibetan Plateau

The East Kunlun Orogenic Belt of the northern Tibetan Plateau can be divided by the Qimantagh-Xiangride, Aqikekulehu-Kunzhong and Murtagh-Buqingshan sutures into, from north to south, the Northern Qimantagh, Central Kunlun and Southern Kunlun belts. The Yazidaban ophiolitic melange, located in the westernmost region of the Qimantagh-Xiangride suture between the Northern Qimantagh and Central Kunlun belts, consists predominantly of serpentinite, basalt, diabase and andesite. The serpentinites are characterized by low total rare earth element (Sigma REE) concentrations and depletion of mid-Sigma EEs, showing an ophiolitic ultramafic affinity. The basalts have low Sigma REE concentrations, a slight enrichment in light Sigma EEs, depletion of large ion lithophile elements and insignificant fractionation of high field strength elements, which are attributed to an incompatible element-enriched mid-ocean ridge basalt. Both diabases and ande sites are characterized by high Sigma REE, strong enrichment in light REEs, depletion of Nb, Ta, P and Ti, and significant fractionation of high field strength elements. These geochemical characteristics indicate that the diabase and andesite were mostly generated in a subduction-related setting. Igneous zircons from the diabase yielded a Pb-206 /U-238 age of 421.5 +/- 2.2 Ma (MSWD = 0.44), representing the formation time of the subduction-related rocks. Together with the regional geology, these constraints on the ultramafic rock, basalt, andesite and diabase suggest that the Yazidaban ophiolitic melange represents the remnants of oceanic crust from a back-arc basin and the associated subduction-related magmatic rocks.