| 摘要: |
| 活动大陆造山带大多以活跃的断裂错断及褶皱发育为特征，这些过程同时改变区域高程与地势，进而影响气候变化的进程。位于我国西北部的天山山脉南北两侧均发育有明显的三列褶皱-断裂系统。根据褶皱地层中前生长地层和生长地层均可计算区域地层的隆起高度。东天山北侧近平行分布着齐古、玛纳斯和独山子褶皱-逆冲带，根据前生长地层能够开展区域隆升过程分析和天山生长历史恢复。本文通过三列褶皱-断裂体系地层组成分析及地层变形特征测量，获得天山平均高程在中新世早期约1800米，在中新世晚期约2600米，而晚上新世与现在高度接近。结合前人对中新世以前区域高程的恢复数据，天山北侧褶皱和断裂活动是区域生长的主要构造形式，也造成了区域阶段性隆升。 |
| 关键词: 中国天山 新生代沉积 生长地层 前生长地层 构造隆起 缩短率 逆冲断裂 |
| DOI：10.7515/JEE182038 |
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| 基金项目:国家自然科学基金项目（41420104008，41572166）；中国科学院项目（QYZDY-SSW-DQC001，XDB26000000） |
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| Cenozoic tectonic deformations of the north Chinese Tian Shan and its implications for the building of the mountain range |
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CHANG Hong, TU Hongzhi, CUI Jianxin, LI Leyi
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1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
2. University of the Chinese Academy of Sciences, Beijing 100049, China
3. Institute for Historical environment and Socio-Economic Development in Northwest China, Shaanxi Normal University, Xi’an 710062, China
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| Abstract: |
| Background, aim, and scope Active continental orogenic movements are generally characterized by animate faulting and folding which can alter elevation and relief and then the process of climate change. Geomorphological variation could also trigger climate change because it can influence the atmospheric circulation pattern and its position which will control the energy distribution in troposphere from the equatorial to the polar. Here we report a method to calculate the uplift amplitude according to the attitude of sediments, if they had deposited and kept parallel to the level before the tectonic movement and deformed with it in an orogenic system. There are three lines of the fold-thrust systems in the northern and southern margins of the Tian Shan Mountains. Several episodes of tectonic movement have tilted the Mesozoic and Cenozoic strata and developed the anticlines on the north side of the East Tian Shan. It is the intriguing natural lab to check this method and suitable areas to reconstruct mountain range growth evolution. Materials and methods The Tian Shan is the quintessential intracontinental range, with its uplift controlled by the tectonic movement of thrusts and strike-slip faults. We have determined the relationship of the Late Cenozoic faults and the anticlines along the NWW—SEE-trending active faults on the northern flank of the East Chinese Tian Shan, they are Qigu, Manas and Dushanzi anticline (fold-thrust system) from the south (mountain) to the north (basin). Data of strikes, dips and depth for Cenozoic sedimentary beds were measured in the field. Onset of the growth strata started since the Early Miocene Taxihe Formation in Qugu anticline, the late Miocene Dushanzi Formation in the Manas anticline, and the middle Pliocene upper Xiyu Formation in Dushanzi anticline. Results The ages of the thrusts are gradually younger from the Tian Shan range to the Junggar basin. The sediments are divided to pre-growth and growth strata in every fold-thrust system, on the base of attitude data of stratum gained in the field. The age of the growth strata constrains to the beginning of the deformation. According to the dip angles and the thicknesses of the pre-growth strata, we estimate that the Eastern Tian Shan has been growth about 1400 m since 4 Ma (Pliocene), ~2200 m since 10 — 8 Ma, and ~3000 m since 25—20 Ma. Discussion Previous study suggested that the average elevation of the Tian Shan was about 1100 m in the very early of the Miocene. Our observation indicates that stepwise growth of the fold-thrust systems from the mountain to the basin has developed the mountain ranges. The average elevation of the East Tian Shan may be about 1000 m in the Late Oligocene, 1800 m in most of the Miocene, 2600 m in the Late Middle Miocene and present peak in the Late Pliocene on our data. The subtle growth of the Tian Shan during the Late Oligocene to Late Miocene perhaps shows that the most of the tectonic movement attributed to India-Asia collision had been accommodated by the deformation in and around the Tibetan Plateau in that time. And rapid uplift of the Tian Shan as well as Qilian Shan and other areas around the Tibetan Plateau during the Late Pliocene reveals that outward growth is the most important role to form the huge plateau since that time. Rapidly and quickly growth around the Tibetan Plateau and new basin development in the plateau since the Late Pliocene infer that marginal uplift has been the vital tectonic movement to absorption energy of the collision in the very distant places. If the Altyh Tagh-Kunlun Mountains — Pamir Plateau was the northern margin of the Tibetan orogenic system since the Eocene as suggested by previous studies, the northern margin of the system should be the Tian Shan since the Late Pliocene because it has contributed to deformation in whole Tibetan orogenic system. Conclusions The relief of the Tian Shan is the result of phased growth in response to pulses of nappe thrusting toward the Junggar Basin and erosion during the long-time scales. The Tian Shan expansions outward and upward occurred three stages, they had occurred during Late Oligocene to Early Miocene, Late Miocene and Late Pliocene. Our data infer that the growth of episodes of the north flank of the East Chinese Tian Shan since the Late Cenozoic are characterized by the thrusting and folding which were propagated from collision between Indian-Asian Plates. Recommendations and perspectives Tectonic modeling and more geological evidence are needed to confirm that growth of the marginal zones of the Tibetan Plateau accommodated substantial energy from the collision between India and Asian plates, even a few phenomena suggests this probability. The method to calculate the amplitude of growth around the Tibetan Plateau in different geological period is a tentative way to add dataset in order to establish a reasonable explanation to evolution of the Tibetan Plateau and its climatic effects. To combine the low-temperature thermochronological data which can be employed to marker of the tectonic movement and its age, the evolution of the orogenic belt and its dynamics may be more reasonable and understandable. |
| Key words: Chinese Tian Shan Cenozoic deposit growth strata pre-growth strata tectonic uplift shortening rate thrust |
