Ordovician to Early Permian accretionary tectonics of Eastern Tianshan: Insights from Kawabulak ophiolitic melange, granitoid, and granitic gneiss

摘要

There is a broad consensus that the final closure of the Paleo-Asian Ocean lead to the formation of the southern segment of the Central Asian Orogenic Belt. However, the final closure of the Paleo-Asian Ocean remains controversial. To address this issue, a systematical study of geochemical and zircon U-Pb on the Kawabulak ophiolite in the southern Eastern Tianshan was carried out. The Kawabulak ophiolite is an accretionary prism that consists of different lithological tectonic slices and marks the suture zone that welded the Central Tianshan composite arc and the northern passive margin of the Tarim Craton. Zircon U-Pb data show that gabbro blocks of the Kawabulak ophiolite formed at 360.9 +/- 3.3 Ma in the northern part and 326.0 +/- 3.3 Ma in the southern part, respectively. The geochemistry features of basalts and gabbros show OIB-type, arc/subduction-related affinities, indicating different tectonic setting origins. A granitic gneiss with an arc-related geochemical feature yielded a zircon U-Pb age of 477.2 Ma, indicating the earliest subduction event. The youngest deformed arc-related granitic intrusion (295 Ma) in the Kawabulak prism indicates that the final closure timing of the Paleo-Asian Ocean in Eastern Tianshan is after the Early Permian. The results of our study shed light to the temporal and spatial evolution of the southern Central Asian Orogenic Belt.