Late Paleozoic tectonic evolution of the Southeast Tianshan Ocean: Implications for the Accretionary orogenesis of the Tianshan Orogenic Belt

The South Tianshan Orogenic Belt (STOB) mainly extends along the southern margin of the Central Asian Orogenic Belt (CAOB), and the late Paleozoic ultramafic and mafic rocks records closure and collision processes of the South Tianshan Ocean. However, there are still controversies regarding the timing of the final closure of the South Tianshan Ocean. Here, we presents geochemistry, zircon U-Pb chronology data for the Halabulake basalts, and geochemistry for the cherts in the west of the STB to better constrained the South Tianshan Ocean closure and follwing collisional processess. In addition, We carried out zircon dating and geochemical analysis of the Wushibei basaltic andesites in the Wushi area of the STOB.The results shows that: (1) the age of the Halabulake basaltes is 283.7±1.7 Ma, mainly early Permain period. The geochemical characteristics indicated that they are formed in the intraplate tectonic background, and belongs to the alkaline asalt and basalt series. Zircons from the Wushi basaltic andesites yield crystallization ages of 286 to 288.4 Ma. The Wushibei basaltic andesites have continental arc magmatism-like geochemical affinities and are slightly enriched in light rare earth elements with high (La/Yb)_N ratios. The Kangkelin Formation is dominated by shallow-marine carbonate rocks deposited in the Wushi sag, which are intercalated with clastic rocks. The cherts in wushi area belongs to the biogenetic siliceous rock series, which has the continental margin characteristics. Our study show that the STOB entered the post-collisional tectonic setting (281~283 Ma) in the early Permian, and the South Tianshan Ocean final closed before the early Permian..Our results provide new insights into the tectonic evolution of the South Tianshan.