Unconformable event and its tectonic significance at Middle-Late Mesozoic of Qiangtang terrane, Tibet

Abstract

Uncomfortable event is significant to continent collision.Collision timing of Qiangtang-Lhasa terrane has always been controversial, because of the different definition of collision time.There are two definitions of collision time in terms of timing of uncomfortable event.One is connection with regional angular unconformity of collision suture zone at late Early Cretaceous(100 Ma), and the other is connection with angular unconformity in the basin edge with disappeared oceanic crust and initial touch of crust between continents at late Middle Jurassic(166 Ma).Focusing on the issue, this study researched unconformity of two difference definitions in Qiangtang Basin and they are Daoban 114 unconformity in Anduo area and southwest Beileicuo unconformity.U-Pb age of anshanite magmatic zircon is 77 Ma, combined with the collision timing of Qiangtang-Lhasa terrane research result, and we think strong interaction time between Qiangtang and Lhasa terrane was at late Early Cretaceous(100 Ma), continuous range 100-75 Ma.The maximum depositional age of continental stratum in Beileicuo area is 94 Ma.Synthesizing sedimentology, geochronology and attitude stratum, we think the strata deposited after 94 Ma and it was not late Middle Jurassic Biluocuo Formation but Cenozoic Kangtuo Formation.And then, initial touch of crust between Qiangtang-Lhasa terrane was not 166Ma but before 100 Ma.

Keywords

• qiangtang basin, tibet
• unconformable event
• mesozoic
• stratigraphic age
• tectonic significance