滇西石鼓杂岩南部早白垩世以来剥露隆升的锆石和磷灰石裂变径迹证据
The exhumation and uplift of the southern Shigu complex since Early Cretaceous evidenced by zircon and apatite fission track
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摘要: 石鼓杂岩位于青藏高原东南缘经历了多期变质变形作用叠加。为了揭示杂岩体的低温热演化与浅部剥露历史,采集了石鼓杂岩南段石鼓镇-拉巴支村剖面变质岩中的锆石和磷灰石,开展裂变径迹分析。结果表明,石鼓杂岩从早白垩世(133~145Ma)到渐新世(31Ma)经历了一次缓慢的剥露(1.08℃/Ma),而从渐新世开始,其南部经历了较快速的剥露过程(3.23℃/Ma)。磷灰石热史模拟也反映出第二阶段较为快速的冷却过程。结合区域构造分析认为,拉萨与羌塘板块碰撞的远程效应影响早白垩世以来藏东地区地壳结构的调整,导致石鼓杂岩南部出现了第一阶段的剥露作用;而印度与欧亚板块碰撞与后碰撞过程对于石鼓杂岩的新生代剥露具有重要影响。Abstract: The Shigu complex lies on the southeastern margin of the Tibetan Plateau,and is mainly distributed in Shigu and Zhongdian areas. The complex has experienced polyphase superposition of metamorphism and deformation. In order to reveal the low temperature thermal evolution and exhumation history at the shallow crustal level of the complex and correctly understand the exhumation and tectonic evolution of the metamorphic dome in eastern Tibet,the authors collected zircon and apatite fission track samples for the fission track analysis along the Shigu Town-Labazhi section. The analytical results show that the Shigu complex firstly experienced a slow cooling and exhumation from Early Cretaceous (133~145Ma) to Oligocene (31Ma),and a relatively rapid cooling process started from Oligocene. Time-temperature history simulated by inverse modeling of apatite fission track also reflects a relatively rapid cooling process at the second stage. From regional structural analysis,it is suggested that the far-field effects of the collision between the Lhasa and Qiangtang plates may have strongly affected the Early Cretaceous exhumation of the complex. Furthermore,the Indian-Eurasian collision and post-collisional effects had profound effects on the Cenozoic exhumation of the complex.