柴达木盆地北缘30Ma左右的去顶剥蚀作用——^(40)Ar/^(39)Ar热年代学定量制约

The Cooling Event Around 30*!Ma in Northern Edge of Qaidam Basin—Constrains from 40Ar/ 39Ar and Fission Track Thermochronology

通过对柴达木盆地北缘两个花岗质岩体的钾长石进行的氩多重扩散域理论 (MDD)模拟及年龄测定 ,得到了这些岩体的冷却历史。结果表明 ,30Ma左右这里曾发生过一次快速冷却事件 (7.5～ 9.4°C Ma) ,表示该地区此时曾发生去顶剥蚀作用 ,是该地区的抬升作用的结果。这可能和阿尔金断裂的走滑活动有关。

A 40Ar/ 39Ar thermochronological study has been carried out on two suites of granitoid collected along the northern edge of Qaidam basin to better constrain the mechanisms accommodating the India-Asia collision around the Qaidam basin (northern Tibet), which is essential to understand the evolution of the entire deformations area. Biotite and K-feldspar have been analyzed and the cooling histories of the latter have been modelled. The cooling histories based upon K-feldspar modelling show that samples recorded simultaneously an important cooling event (7～10℃/Ma) around 30Ma, which is thought to reflect an increasing rate of denudation related to the tectonic activity in this area associated with uplift, suggesting that it experience an important crustal thickening period at 30Ma ago in this area. This crustal thickening event is suggested to be related to the great Asian strike-slip faults in a way which remains problematic but possibly associated to the Cenozoic propagation of the Altyn-Tagh fault.