塔里木柯坪塔格地区构造抬升的新证据——来自(U-Th)/He年龄的约束

摘要

柯坪塔格地区位于西南天山与塔里木盆地之间,是塔里木地台的一部分,其构造隆升与天山和塔里木盆地的演化密切相关.本文首次将(U-Th)/He热定年技术应用于该地区构造抬升的研究,对该区震旦系露头样品的磷灰石和锆石的(U-Th)/He进行了年龄测定和热史模拟,结果表明柯坪塔格地区主要经历了4期构造抬升事件,导致震旦系抬升至地表,其中磷灰石(U-Th)/He年龄揭示了晚白垩世和中新世两期的构造抬升事件.在早石炭世,震旦系温度达到最大,介于133～150℃之间,结合沉积埋藏史得到当时的最大埋深是3400～3900 m.在渐新世一中新世,受印度一欧亚板块碰撞远程效应的影响,柯坪塔格地区沿柯坪塔格-沙井子断裂向巴楚隆起上逆冲,地层快速抬升遭受剥蚀.在15～10 Ma时,柯坪塔格地区震旦系已抬升至地表.自早石炭世至今,柯坪塔格地区总剥蚀量达6170 m.柯坪塔格地区自中生代以来的构造-热演化史与塔里木盆地北缘是一致的,但与天山及处于塔里木盆地内部的巴楚隆起的构造抬升过程存在差异.中新世以后,受喜山运动远程效应影响,柯坪塔格和天山才同处于抬升状态;而巴楚隆起在古近纪早期仍处于抬升剥蚀状态,与柯坪塔格地区接受沉积相反.本文利用(U-Th)/He热定年技术成功地揭示了柯坪塔格地区自震旦纪以来的构造-热演化史,这些结果有利于人们对这一地区构造抬升的正确认识.同时,本研究对塔里木盆地的油气勘探及天山地区的构造研究具有指导意义.%As part of Tarim platform. Kepingtage area lies between southwest Tienshan and Tarim basin, and its tectonic-uplift evolution is closely correlated with Tienshan and Tarim basin. The (U-Th)/He thermochronometry is used as a new technique to study the tectonic uplift of Kepingtage area in the paper. Based on the measured apatite/zircon ( U-Th)/He ages of Sinian outcrop samples in the region and the thermal modeling, the results reveal four phases of tectonic-uplift events appeared in Kepingtage area. which made the Sinian formation uplift to surface. The apatite (U-Th)/He ages reveal two phases of uplift events at Late Cretaceous and Miocene. During Early Carboniferous. the Sinian formation temperature reached a maximum of 133～150℃. Combined with the burial history of the sample, the maximum depth can be derived to be 3400 ～ 3900 m. Due to the ciistant effect from the collision of the Indian and Eurasian plates, Kepingtage area thrust over Bachu uplift along Kepingtage-Shajingzi fault during the Oligocene-Miocene. The strata were rapidly uplifted and eroded. During 15～10 Ma, the Sinian formation in Kepingtage area had been uplifted to the surface. The total exhumation amount is up to 6170 m since Early Carboniferous. While the tectono-thermal evolution history of the Kepingtage area is consistent with the northern margin of Tarim basin in Mesozoic to Cenozoic, it is inconsistent with Tienshan and the Bachu uplift inside Tarim basin. Since Miocene, Kepingtage area and Tienshan was in the same state of uplifting by the distant effect of the Himalayan movement. During Early Eocene, Bachu uplift area was still uplifted and eroded, while Kepingtage area received deposits. This paper successfully reveals the tectono-thermal evolution history of Kepingtage area since Sinian using the (U-Th)/He thermochronometry, which is useful for understanding the tectonic uplift in the region correctly. Furthermore, the study can support the hydrocarbon exploration of Tarim basin and the tectonic study of Tarim basin and Tienshan.