库车盆地-南天山逆冲褶皱带构造热演化及隆升剥蚀的低温热年代学约束

The geologists have paid close attention to the thrust-fold zones of the Kuqa-South Tianshan because of the special tectonic location and rich resources of oil and gas. The Tianshan orogenic belt thrust towards the Kuqa Depression resulting in folding, rapid uplift and denudation of South Tianshan and the northern part of the Kuqa Depression during the Cenozoic and a series of Cenozoic thrust-fold zones developed (e.g. thrust-fold zones of South Tianshan, northern monocline belt, Kelasue-Yiqikelike structural belt and Qiulitag structural belt). In this work, the fission track, (U-Th)/He and vitrinite reflectance technology will be applied in studying tectonic thermal history and uplift/exhumation history in the Kuqa-South Tianshan area. Samples will be systematically collected from different thrust-fold zones according to detailed field geology investigation and seismic observation. Cenozoic tectonothermal histories of the thrust-fold zones will be greater precision reconstructed using the thermal indicators of (U-Th)/He, apatite fission track (AFT) and vitrinite reflectance (Ro) data. Cenozoic uplift/exhumation histories of these thrust-fold zones will be quantitatively analyzed. Then, it will be further studied on differential uplift/exhumation and the forming mechanism of these thrust-fold zones. This work promotes further understanding tectonic evolution mechanism for the Tianshan orogenic belt and Kuqa foreland. It also provides the basis for the research on oil and gas accumulation and resource assessment, and has the important significance of reducing exploration risk by focusing on more prospective areas.

库车盆地-南天山逆冲褶皱带由于其独特的构造位置及蕴藏着丰富的矿产资源，备受地质学家关注。新生代天山造山带向库车盆地大规模逆冲推覆，在库车-南天山地区形成一系列逆冲褶皱带，如天山南缘冲断带、山前单斜带、克依构造带及秋里塔格构造带等，这些褶皱带新生代遭受了强烈的隆升剥蚀及变形。本项目在详细的野外地质考察和室内地震剖面观测基础上，对库车前陆不同逆冲褶皱带展开系统取样，通过对裂变径迹、(U-Th)/He及镜质体反射率热信息的识别、提取及计算模拟，恢复库车-南天山构造热演化史，精细限定库车盆地北缘逆冲褶皱带新生代隆升剥蚀时间、速率及剥蚀量等，揭示库车-南天山逆冲褶皱带新生代隆升剥蚀的时空分布差异性及其形成机制等。该研究有助于进一步认识天山造山带和库车盆地构造演化机制，同时也为研究库车盆地油气成藏及油气资源评价提供依据，对更加有效的油气勘探和降低勘探风险有重要的意义。

新生代天山造山带向库车盆地大规模逆冲推覆，在库车-南天山地区形成一系列逆冲褶皱带，这些褶皱带蕴藏着丰富的油气资源，项目开展了该地区构造热演化及隆升剥蚀史研究，不仅对认识中亚造山带构造变形过程与机制具有重要的意义，而且对更加有效的油气勘探和降低勘探风险有重要的意义。本项目利用低温热年代学技术研究南天山-库车盆地构造热演化及隆升剥蚀史，取得的主要认识包括：（1）开展锆石(U-Th)/He定年实验研究，测试FCT锆石标样(U-Th)/He年龄与国内外实验室测试年龄结果一致，表明了锆石(U-Th)/He定年实验流程可靠；基于热活化扩散过程原理进行了 FCT锆石分步加热实验，结果显示锆石He扩散活化能分布在144～184 kJ/mol，平均值169±12kJ/mol，(U-Th)/He封闭温度介于144～216°C（冷却速率为10°C/Ma），平均值为176±18°C，上述研究为锆石(U-Th)/He定年应用在天山-库车盆地隆升剥蚀研究提供基础。（2）库车盆地白垩系砂岩中白云母进行了电子探针及40Ar/39Ar定年结果表明在白垩纪西南天山低温高压变质岩带已抬升至地表遭受剥蚀，为库车盆地提供大量的物质，也表明了在白垩纪西南天山低温高压变质岩带高度（海拔）高于其南部的哈尔克山，而现今天山地貌形态显示低温高压变质岩海拔低于哈尔克山，这可能是由于新生代天山地区差异隆升剥蚀引起的；（3）(U-Th)/He年龄模拟表明中天山南缘科克苏河地区至少存在晚白垩世、早中新世、晚中新世3期快速隆升剥蚀事件，晚中新世快速隆升剥蚀起始时间为~5 Ma，隆升剥蚀厚度为~2300 m，剥蚀速率为~0.47 mm/yr；（4）库车盆地低温热年代学数据研究表明新生代经历了晚始新世、晚渐新世、早中新世末期及晚中新世-上新世等构造挤压隆升剥蚀事件，新生代逆冲褶皱带存在差异隆升剥蚀现象，起始隆升剥蚀时间从盆地边缘（始新世）到盆地内部（晚中新世）逐渐的变年轻，剥蚀幅度逐渐减小；平行造山带方向上（东西向），同一逆冲褶皱带隆升剥蚀或变形时间也存在差异这，表明造山运动在某一构造带上存在阶段性和空间不均匀性。