攀西地区早白垩世以来地壳抬升运动的裂变径迹年龄研究

The Elevation History of Crustal Blocks in Panzhihua-Xichang Region (Western Yangtze Craton) since Early Cretaceous Time—— Constraints from Fission Track Dating of Granulites

通过对扬子板块西缘攀枝花一西昌地区麻粒岩中锆石和磷灰石的裂变径迹(FT)年龄测定,首次研究和报道了该区中一新生代地壳的低温热历史和抬升运动过程,分析显示,锆石FT年龄为143.8～68.4Ma;磷灰石FT年龄为24.1～12.8Ma.磷灰石FT平均长度的变化范围在10.54～13.20μm.研究表明,攀西地区从早白垩世到白垩纪末期地壳抬升是十分缓慢的,抬升速率仅为46～51m/Ma;但从第三纪开始地壳抬升运动明显加快,抬升速率达208～391m/Ma.这可能是印度板块与欧亚板块碰撞效应.

This paper reports the fission track(FT)dating results of zircons and apatites from granulites, in order to trace the lowtemperature thermal history and uplift evolution of crustal rocks in PanzhihuaXichang southnorth geologic structure belt, western margin of Yangtze craton. The FT ages of zircons range from 143.8 Ma to 68.4 Ma; and the FT ages of apatites from 24.1 Ma to 12.8 Ma.The average lengths of FT in apatites change from 10.54 μm to 13.20 μm. The results indicate that crustal blocks in PanzhihuaXichang region were exhumed slowly in the Late Mesozoic (from Early Cretaceous to the end of Cretaceous). The speeds of uplift movement of crustal rocks were from about 46 m/Ma to 51 m/Ma only. But later the uplift speeds of the rocks were accelerated from 208 m/Ma to 391 m/Ma in Cenozoic time. This is likely attributed to the elevation of the Tibetan plateau due to the Indo_Asian collision since early Cenozoic time.