| 天山东段推覆构造研究 |
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| 引用本文： | 舒良树,孙家齐.天山东段推覆构造研究[J].地质科学,1997,32(3):337-350. |
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| 作者姓名： | 舒良树 孙家齐 |
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| 作者单位： | 1. 南京大学地球科学系, 南京210093;2. 南京建筑工程学院地质系, 南京210009 |
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| 摘 要： | 本文概括性总结了天山东段大型推覆构造的基本特征。根据地质证据和同位素年龄,东天山存在早古生代末,晚古生代晚期和新生代三期推覆构造;根据推覆构造分布规律及构造背景,在平面上划分为五大推覆带、9个大型韧剪带;根据出露岩石的矿物变形相将东天山推覆构造划分为深、中深和浅三个深度层次;通过韧剪变形组构的观察分析,确定了多期韧性变形性质与运动方向。糜棱岩中超微构造、古应力及小构造变形缩短率测量统计,证明东天山推覆变形具有显著的地壳缩短增厚作用。新生代板块碰撞导致本区中新生代盆地基底向造山带A型俯冲,造山带向盆地推覆,其结果就构成了今日看到的镶嵌状盆地-山脉构造地貌景观。
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| 关 键 词： | 东天山 造山带 推覆构造 韧性剪切作用 古生代 新生代 |
| 收稿时间： | 1996-09-09 |
| 修稿时间： | 1996-09-09; |
RESEARCH ON THE THRUST TECTONICS OF THE EASTERN TIANSHAN BELT, XINJIANG |
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| Shu Liangshu,Ma Ruishi,Guo Lingzhi,Sun Jiaqi.RESEARCH ON THE THRUST TECTONICS OF THE EASTERN TIANSHAN BELT, XINJIANG[J].Chinese Journal of Geology,1997,32(3):337-350. |
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| Authors: | Shu Liangshu Ma Ruishi Guo Lingzhi Sun Jiaqi |
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| Institution: | 1. Department of Earth Sciences, Nanjing University, Nanjing 210093;2. Nanjing Institute of Architectural and Civil Engineering, 210009 |
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| Abstract: | A large scale ductile thrust tectonics occurs in the Paleozoic eastern Tianshan belt Xinjiang, that is a 300-400km width and extends more than 700km along a sub-latitudinal direction. In the past decade, the authors investigated and researched this tectonic belt; some basic features in geometry and kinematics were understood. On the basis of several typical deformed minerals and microstructures: ductile deformed feldspar and quartz, deformed quartz and feldspar subgrains, rotated and sheared pyroxene and non-coaxial shear indicators, we divided the eastern Tianshan deformed layer into three sub-layers in depth direction as follows. (1)The lower ductile shear layer equal to a crustal depth of 20-30km that is characterised by basic rock type granulite and mafic-ultramafic allochthonous blocks in which asymmetric pyroxene porphyroclastic system and deformed newborn pyroxene subgrains around large pyroxene grains develop well; the outcrop-scale rocks of the lower ductile shear layer are mainly scattered along the Kumishi-Hongliuhe ductile shear zone and the northern margin of the central Tianshan belt. (2)The intermadiate ductile shear layer corresponding to a crustal depth of 10-20km that is marked by feldspar-quartz mylonitic rocks; this ductile deformed layer exposes widespreadly at the surface in a large extent. (3)The shallow brittle shear layer equal to an upper crustal depth less than lOkm in which only brittle fracturing, faulting and fault-folding develop commonly in the rocks, not ductile deformation; this brittle shear layer is distributed along the margins of Mesozoic-Cxnozoic basin near the orogenic belt and in the weakly denuuded orogenic belt. The geological evidence and radioisotopic data suggest that the eastern Tianshan thrust tectonics was resulted from polyphase tectonism; three stages of thrusting are proposed in this text The first phase ductile thrusting took place during the interval from late Silurian to Devonian, about 420-380Ma; most ductile deformed structures and mylonited rocks in the central-southern Tianshan belt were formed in this stage; the deformed structures and rocks came from both the lower layer for a part and the intermadiate layer for most parts. The second-phase ductile thrusing developed in the time of the late Carboniferous-early Permian, dated at 290-260Ma and occurs in the northern Tianshan belt including the Aqishan-Yamansu volcanic arc; in which several ductile shear zones of the intermadiate layer are exposed. The third-phase thrusting is a Cenozoic intracontinental brittle deformation, this phase tectonism affected and reformed the whole Tianshan belt We propose that the first phase thrusing was caused by the Tu-Ha(Turpan-Hami)continental temane collided with the central Tianshan‘along the Aqikekuduge-Weiya zone, accompanmg by a northward retreating of subduction; the second-phase thrusing was resulted from a large scale collision of late Carboniferous age between the Tarim and the Dzungar-Siberia continental plates along the Kelameili suture zone; the third-phase brittle deformation was affected by the Himalaya collisional event to the south. The five large scale ductile thrust zones are divided in the paper, we name them the southern Tianshan Kumishi-Hongliuhe zone, the central Tianshan zone, the Yamansu-Kangguer zone, the Haerkike-Bogeda zone and the Kelameili zone, respectively. Sheared foliation, stretching lineation and non-coaxial asymmetric macro-microscopic shear criteria are common in the deformed rocks of the above-mentioned five zones. The detailed kinematic analyses for the eastern Tianshan thrust tectonics reveal a deformationary evolution from northward thrusting to dextral strike-slip shearing, accompaning by local extension. The above mentioned five zones are characterised by northward thrust movement, but their boundaries were superimposed by strike-slip ductile shear structures. The Aqikekuduge-Weiya ductile shear zone is a striking dextral strike slip one, in which ophiolitic melange and HP/LT bleuschist blocks are involved. The observation of TEM ultra-mictostructures of deformed quartz grins and the calculation of dislocation density, subgrain size and recrystallized grin size as well as the statistics of shortened radio (39%-62%) for fold structures indicate that an obvious crustal thickening and shortening took place in the studied area. The klippe bodies, that distribute in the southern Tianshan and have a clear northward sense of shear, come from the Tarim continental block; the displacement of klippes is 50km at least. The Cenozoic Himalaya collision resulted in the re-uplift of the eastern Tiahshan belt and the A-type subduction of a basin toward an orogenic belt. The age data of 0.255±0.02Ma and 0.262±0.021 Ma dated at faulted mud samples verify this tectonic affect The Cenozoic tectonics is marked by (1)large-scale brittle nappe of klippe, pre-Mesozoic rock slabs thrust on the Mesozoic-Cenozoic subhorizontal continent derived rocks along a gentle fault plane, only developing near margins of mountains or basins; (2)brittle fracture; (3)brittle extensional faulting trending sublongitude, accompaning by quartz veins and porphyry dikes; (4)Altyn Tag type strike slip brittle faulting N70°E trending, that cut the pre-Mesozoic rocks; (5)Cenozoic basin tectonics characterised by stepped thrusting faults. Present-day Xinjiang-type mosaic basin-range geomorphologic landscape was setted. |
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| Keywords: | The eastern Tianshan Orogenic belt Thrust tectonics Ductile shear Paleozoic Cenozoic |
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