Provenance Analysis of the Middle-Lower Jurassic Clastic Rocks in the Southern Margin of the Yili Basin and Their Insight into the Evolution of Southern Tianshan Orogenic Belt

Key words: 
• provenance /
• middle-lower Jurassic /
• southern margin of the Yili Basin /
• South Tianshan Orogenic Belt /
• zircon U-Pb chronology

Abstract: The provenance features of the middle and lower Jurassic clastic rocks in southern margin of the Yili Basin can provide important information for insights into the evolution of southern Tianshan Orogenic Belt. Detrital zircon age of the Badaowan Formation sandstone of lower Jurassic in southern margin of the Yili Basin demonstrates a prominent age population at 290-260 Ma, whereas the Sangonghe Formation of lower Jurassic shows two prominent age populations at 350-290 Ma and 460-390 Ma, respectively. The Xishanyao Formation of middle Jurassic has two prominent detrital zircon age populations at 370-320 Ma and 450-390 Ma. All study samples have little zircon age record of Precambrian period. These features indicate that Mesozoic detrital sediments in southern margin of the Yili Basin predominantly might be derived from the south part of the Yili-Central Tianshan Block. The late Permian to middle Triassic zircons are nearly absent, consistenting with magmatic record in the South Tianshan Orogenic Belt and probably indicating no strong magmatic activities associated with collision or post-collision occurred in South Tianshan Block during late Permian-middle Triassic periods, which does not support the idea that the collision between the Tarim Craton and Yili-CTS Block occurred in the late Permian-middle Triassic periods. Combined with previously published data of tectonic exhumation of high to ultrahigh pressure metamorphic rocks and stratigraphic records, these data support the idea that the collision between the Tarim Craton and Yili-CTS Block occurred in the late Carboniferous period. The youngest detrital zircon ages of the studied samples are increasing from the middle-late Triassic to early Jurassic periods to middle Jurassic period, indicating a feature of unroofing and sedimentation. Integration of the provenance data of Mesozoic strata in the southern Yili Basin with the time equivalent of the South Tianshan Belt, provides an integrated record of the tectonic subsidence and planation in the early-middle Jurassic period.