西天山白垩纪隆升-剥露的裂变径迹证据

摘要

白垩纪的隆升-剥露事件在新疆不同构造单元广泛发育.本文主要是通过磷灰石裂变径迹测年技术,结合温度-时间热模拟反演的研究,探讨西天山北段和中段白垩纪的隆升-剥露过程.17个样品分别采自西天山北段的博罗科鲁山、依连哈比尔尕山以及西天山中段的独库公路附近的花岗岩体.裂变径迹测试结果显示,样品的径迹年龄介于45.4±3.2～81.6±4.9 Ma,平均径迹长度介于12.62±0.17～13.53±0.14μm之间.进一步根据温度-时间的模拟结果推断,西天山北段和中段在晚白垩世都经历了快速隆升-剥露过程.在时间上,西天山北段样品记录的快速隆升的时间主要集中在50～70 Ma之间,西天山中段样品记录的快速隆升时间集中在70～90Ma之间.结合相应的地质证据,认为从晚白垩世开始,西天山地区开始出现差异性的隆升剥露过程,伊犁盆地从早中白垩世隆升剥蚀状态转变为晚白垩世接受沉积,其两侧山脉继续处于快速隆升剥蚀的状态.导致这种隆升-剥露事件的动力学机制是受多因素综合控制的,印亚碰撞的远程效应可能是该期事件的主要动力来源,但天山不同地段的热-流变性质的差异性及不同块体之间的相互作用是导致差异性隆升-剥蚀的主要因素.%Cretaceous uplifting-exhumation events occurred widely in different tectonic units in Xinjiang.Apatite fission tract dating and thermal history modeling were carried out on 17 granite samples collected from the Boluokelu mountain,Yilianhabierga mountain and Duku road to investigate the uplifting-exhumation processes of mountains.The studying areas include the northern part and middle part of West Tianshan.Fission-track ages for these samples range from (81.6 ± 4.9) to (45.4± 3.2) Ma with mean track lengths varying from (12.62±0.17) to (13.53±0.14) μm.Temperature-Time modeling of apatite was completed based on date measurements of the fission track length and age.Analyses results reveal that the north part and middle part of West Tianshan has probably experienced rapid cooling events in late Cretaceous.The time for rapid cooling events in the northern part of West Tianshan mainly concentrates during 50～70 Ma,and the time for middle part of West Tianshan mainly concentrates during 70～90 Ma.In combination with other geological evidence,it can be suggested that West Tianshan started to experience differential uplift and exhumation process in late Cretaceous,and Yil basin changed from early-to mid Cretaceous uplift and exhumation to late Cretaceous deposition,with both flanks still experiencing rapid uplifting.The reason for that is attributed to multiple factors which controlled dynamic mechanism for uplift and exhumation events.The distant effect of the India-Asia collision likely provided such dynamical source,but differentiation of thermal-rheological structures and interaction of different structural boundaries should be the main control factor for different uplift and exhumation.