Tectonic Framework of Late Paleozoic Intrusions in Xingxingxia: Implications for Final Closure of South Tianshan Ocean in East Tianshan

Abstract

AbstractThis work carried out systematic geological field investigation, petrography observation, zircon geochronology and whole rock geochemistry on Late Paleozoic intrusions in the Xingxingxia region near the Xinjiang‐Gansu provincial boundary, western China, aiming to constrain the Late Paleozoic tectonic framework of the Xingxingxia region and the final closure time of South Tianshan Ocean in the East Tianshan. The Xingxingxia area is located in the east part of the Tianshan orogen, and adjacent to the north of the Tarim Basin. The Late Paleozoic magma activities in the Xingxingxia region can be mainly divided into three stages. The first stage includes intrusive magma activities under a collision setting between Late Ordovician to the Late Devonian. The second stage is intrusive magma activities under a subduction setting during (304±3)–(278±3) Ma, and the third stage involves intrusive magma activities under a collision and post‐collision setting during (268±5)–(259.9±2.6) Ma. The final suture zone of South Tianshan Ocean should be between the Central Tianshan Block and South Tianshan accretionary complex. Based on previous work, both the first stage magma activities (i.e., intrusive magmatic activities between the Late Ordovician to Late Devonian) and the Hongliuhe ophiolitic complex indicate a close event between Central Tianshan Block and South Tianshan Accretionary Complex. The 304±3 Ma dioritic metamorphic gneiss of the XingXingxia complex and the 278±3 Ma diorite are all island arc calc‐alkaline rocks, the 289±3 Ma gabbro is island arc tholeiitic gabbro formed by magma from metasomatic enrichment mantle. All these results indicate that the second stage of magmatic activities is under a subduction setting. The third stage magma activities i.e. the granitic magma activities of (268±5)–(259.9±2.6) Ma occurred at a transitional setting from compressional to post‐collision extensional tectonic setting. Thus, around (268±5)–(260±3) Ma, the final closure of the South Tianshan Ocean occurred and the Tianshan orogen shifted into the intracontinental evolution stage. During and after the closure process, a wide range of metamorphism and large dextral strike‐slip faults developed.