| 东秦岭造山带南缘北大巴山构造反转及其动力学 |
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| 引用本文： | 何建坤,卢华复.东秦岭造山带南缘北大巴山构造反转及其动力学[J].地质科学,1999,34(2):139-153. |
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| 作者姓名： | 何建坤 卢华复 |
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| 作者单位： | 1. 中国科学院地球物理研究所 北京 100101;2. 南京大学地球科学系 南京 210093 |
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| 摘 要： | 自元古代以来,北大巴山经历了构造伸展(∈-D2)、构造反转(T2)和构造冲断作用(T2-J1).伸展构造主要由极性相同、北倾的大型犁式正断层构成,它控制了早古生代地层的强烈差异沉积。其成因可能受控于扬子板块北缘早古生代幔源裂谷作用所引起的大陆边缘岩石圈拉伸、减簿的动力学机制。之后,因华北和扬子两板块的对接和碰撞,扬子板块北缘发生内硅铝层A型俯冲。使北大巴山构造作用由早期的伸展向大规模的冲断转变,形成中三叠世区域性构造反转作用。经构造反转后,北大巴山构造变形以强烈的深层次韧性滑脱和浅层次脆性冲断为特征。深层滑脱由发育在10-35km的韧性台阶状逆断层冲断叠置而成、浅层滑脱则主要由脆性台阶状断层构成的盖层冲断岩席,双重推覆体和冲起构造等构成。由此北大巴山区地层缩短率平均至少达35.5%-44.2%,并造成绿片岩相的活化盖层。
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| 关 键 词： | 北大巴山 伸展构造 构造反转 冲断-推覆构造 |
| 收稿时间： | 1998-03-25 |
| 修稿时间： | 1998-03-25; |
THE TECTONIC INVERSION AND ITS GEODYNAMIC PROCESSES IN NORTHERN DABA MOUNTAINS OF EASTERN QINLING OROGENIC BELT |
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| He Jiankun Lu Huafu Zhu Bin Institute of Geophysics,Chinese Academy of Sciences,Beij ing\.THE TECTONIC INVERSION AND ITS GEODYNAMIC PROCESSES IN NORTHERN DABA MOUNTAINS OF EASTERN QINLING OROGENIC BELT[J].Chinese Journal of Geology,1999,34(2):139-153. |
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| Authors: | He Jiankun Lu Huafu Zhu Bin Institute of Geophysics Chinese Academy of Sciences Beij ing\ |
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| Institution: | 1. Institute of Geophysics, Chinese Academy of Sciences, Beijing 100101;2. Department of Earth Sciences, Nanjing University, Nanjing, 210093 |
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| Abstract: | Daba mountains locate between the Qinling collisional orogenic belt and northea st ern border of the Sichuan cratonic basin. On the plate tectonic affinity, it sho uld be ascribed to the marginal tectonic regime of Yangtz plate. Tectonically, the mountain ranges can be divided into two tectono-stratigraphic units by the large-scaled Zhengping Chengkou-Zhongbao thrust (ZCZT), namely the northern block of Da ba mountains (NDM) and the southern block of Daba mountains (SDM). Since the late Proterozoic, the northern block of Daba mountains had underwent the geological p rocesses of tectonic extension from early Cambrian to middle Devonian (∈D2), tectonic inversion in the middle Triassic (T2) and at last in the period from middle Triassic to early Jurassic the tectonic thrusting (T2 J1). The deformation styles caused by the tectonic extension are mainly in the forms of large-scaled syn s edimentary listric normal fault system with the north dipping structural polarities. It had controlled the differential deposition of lower Paleozoic strata bet ween different fault-bounded blocks. Based on the researches of basic and ultra b asic rocks emplaced in these Palaeozoic strata on the isotopic chronology, the compositions of major elements, REE and trace elements, It has been proved that the geodynamics to form the tectonic extension was resultted from the tensile thi nning of continental crust which was dominantly caused by the upper mantle doming due to the mantle derived lithospheric rifting developped in the northern mar g in of Yangtze plate in the Palaeozoic. Later with the occurrence of Qinling coll isional orogen, the A-type subduction was initiated within the sialic crust in t he northern Daba and southern Qinling belt. Thus the tectonic inversion was take n place in the period of middle Triassic. The deformation styles formed by tectonic inversion are of the deep-seated ductile stepped detachement along the early formed normal listric faults that had caused the crustal superimposition at the depth of 10km to 35km and of the shallow brittle stepped thrusting along the in competent strata that had formed the thrusting silices, the duplex and the pup u p in the cover strata. By making the balanced cross section, The crustal shortening rate is calculated at least about 35.5-44.2% and the crust had been shorten e d about 220km with the annual shortening rate of 0.81cm. Furthermore, owing to the crustal superimposition, the cover strata were underthrusted to a great depth. As the result, the cover mobilization was formed with the greenschist faces ch aracteristed by the bearing disthene, grossularite and muscovite. |
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| Keywords: | Extensional tectonics Tectonic inversion Thrust tecto nics Northern Daba mountains |
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