The thermo-tectonic history of the Song-Kul plateau, Kyrgyz Tien Shan: Constraints by apatite and titanite thermochronometry and zircon U/Pb dating

摘要

The Song-Kul Basin sits on a plateau at the Northern and Middle Kyrgyz Tien Shan junction. It is a lacustrine basin, occupied by Lake Song-Kul and predominantly developed on igneous basement. This basement was targeted for a multi-method chronological study to identify the different magmatic episodes responsible for basement formation and to constrain the timing of the development of its present-day morphology. Zircon U/Pb dating by LA-ICP-MS revealed four different magmatic episodes: a Late Cambrian (~. 500. Ma) island arc system, a Late Ordovician (~. 450. Ma) subduction related intrusion, an Early Permian (~. 290. Ma) collisional stage, and a Middle to Late Permian (~. 260. Ma) post-collisional magmatic pulse. Middle to Late Triassic (~. 200-230. Ma) titanite fission-track ages and Late Triassic - Early Jurassic (~. 180-210. Ma) apatite fission-track ages and thermal history modeling indicate the Song-Kul basement was already emplaced in the shallow crust at that time. An exhumed fossil apatite fission-track partial annealing zone is recognized in the bordering Song-Kul mountain ranges. The area experienced only minor post-Early Mesozoic denudation. The igneous basement was slowly brought to apatite (U-Th)/He retention temperatures in the Late Cretaceous-Palaeogene. Miocene to present reactivation of the Tien Shan does not manifestly affect this part of the orogen.