The youngest Permian Ocean in Central Asian Orogenic Belt: Evidence from Geochronology and Geochemistry of Bingdaban Ophiolitic Melange in Central Tianshan, northwestern China

The Tianshan Belt, which lies in the southwest part of Central Asian Orogenic Belt (CAOB), is characterized by abundant ophiolites or ophiolitic melanges, which are indicators of the existence of oceanic basin can be used for tracking the tectonic evolutionary history of the orogen. The Bindaban (BD) ophiolitic melange is located in the Central Tianshan Belt, northwest China, which comprises mainly gabbros, diabases, basalts, basaltic lavas (greenschist), and cherts. This paper presents new zircon geochronology, whole-rock major and trace elements, and Sr, Nd isotope data for mafic rocks in the BD ophiolitic melanges. In the eastern part of BD ophiolitic melanges, one normal (N)-MORB-type basalt has a U-Pb zircon age of 265.2 +/- 1.8 Ma, and one enriched-MORB-type dolorite in the western part of BD ophiolitic melanges has an age of 425.4 +/- 3.9 Ma, respectively, indicating either an existing ocean basin from continental rifting to normal oceanic spreading with a long time span from late Silurian to Permain, or two separate ocean basins that formed in late Permian and late Silurian during the Paleo-Tianshan Ocean evolution. In particular, the 265.2 +/- 1.8 Ma age of N-MORB-type basalt from BD ophiolitic melange suggests the youngest oceanic basin (late Permian) existed in southwest CAOB, which reveals that Paleo-Asian Ocean might last to late Permian, therefore finally closed in or after the late Permian in the North Tianshan area.