藏北改则康托盆地逆冲推覆构造磷灰石裂变径迹年代学制约
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摘要
对采自羌塘地块南部改则地区康托盆地的碎屑岩及火山岩进行磷灰石裂变径迹年代学测试及AFT热历史模拟,获得77±6Ma、62±5Ma、44±3Ma、35±2Ma四组磷灰石裂变径迹年龄,平均径迹长度介于11.6±2.0~13.3±1.9μm之间。AFT热历史模拟结果指示,研究区自晚白垩世至现今主要历经了3次构造抬升冷却过程:晚白垩世(100~65Ma)快速隆升剥蚀阶段,其降温速率和隆升速率分别为1.46~4.26℃/Ma、0.05~0.14mm/a,该事件为新特提斯洋洋壳沿雅鲁藏布江俯冲作用的响应;始新世中期(50~35Ma)快速隆升剥蚀阶段,该阶段降温幅度相对以第一次较小,该构造事件与印度大陆的向北俯冲具有成因联系;20Ma至现今的快速抬升冷却阶段为青藏高原整体拉张走滑构造环境所影响,其隆升速率和降温速率分别为3.25~6.0℃/Ma、0.03~0.2mm/a。
Four rock samples collected from the Kangtuo Basin in northern Tibetan Plateau were used to determine the apatite fission track ages. Results of all the samples show that the individual grains belong to a single population with a single mean age and have central ages of 77±6 Ma, 62±5 Ma, 44±3 Ma and 35±2 Ma. Their mean track lengths are 11.6±2.0 ~13.3±1.9μm with a single peak.The authors used thermal history simulation software AFTSolve to simulate the thermal history of the samples and the results show three important stages of tectonic movement in Kangtuo Basin since Late Mesozoic. From 100 Ma to 65 Ma,the cooling and denudation rates were 1.46~4.26℃/Ma and 0.05~0.14 mm/a respectively. Combined with field condition and study results,some conclusions have been reached: The Cretaceous tectonic uplift event was influenced by the subduction of the Yarlung Zangbo River. The second tectonic movement took place between 50 Ma and 35 Ma and its intensity was weaker than that of the first one. The Paleogene tectonic uplift event was related to Indo-Eurasian collision. Since 20 Ma, the cooling and denudation rates have been 3.25~6.0℃/Maand 0.03~0.2 mm/a respectively,and this tectonic movement has been influenced by the Cenozoic whole uplifting and the stretching strike-slip environment in Tibet.
Four rock samples collected from the Kangtuo Basin in northern Tibetan Plateau were used to determine the apatite fission track ages. Results of all the samples show that the individual grains belong to a single population with a single mean age and have central ages of 77±6 Ma, 62±5 Ma, 44±3 Ma and 35±2 Ma. Their mean track lengths are 11.6±2.0 ~13.3±1.9μm with a single peak.The authors used thermal history simulation software AFTSolve to simulate the thermal history of the samples and the results show three important stages of tectonic movement in Kangtuo Basin since Late Mesozoic. From 100 Ma to 65 Ma,the cooling and denudation rates were 1.46~4.26℃/Ma and 0.05~0.14 mm/a respectively. Combined with field condition and study results,some conclusions have been reached: The Cretaceous tectonic uplift event was influenced by the subduction of the Yarlung Zangbo River. The second tectonic movement took place between 50 Ma and 35 Ma and its intensity was weaker than that of the first one. The Paleogene tectonic uplift event was related to Indo-Eurasian collision. Since 20 Ma, the cooling and denudation rates have been 3.25~6.0℃/Maand 0.03~0.2 mm/a respectively,and this tectonic movement has been influenced by the Cenozoic whole uplifting and the stretching strike-slip environment in Tibet.
引文
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