| 维西—贵阳剖面重力异常与地壳密度结构特征 |
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| 引用本文： | 申重阳,杨光亮,谈洪波,玄松柏,吴桂桔,汪健.维西—贵阳剖面重力异常与地壳密度结构特征[J].地球物理学报,2015,58(11):3952-3964. |
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| 作者姓名： | 申重阳 杨光亮 谈洪波 玄松柏 吴桂桔 汪健 |
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| 作者单位： | 1. 中国地震局地震研究所(地震大地测量重点实验室), 武汉 430071;2. 中国地震局地壳应力所武汉创新基地, 武汉 430071 |
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| 基金项目： | 中国地震局重大行业专项(中国地震科学台阵探测201008001),国家重点基础研究发展计划(973)项目(2013CB733304)和国家自然科学基金重点项目(41431069)资助. |
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| 摘 要： | 维西—贵阳剖面位于青藏高原东南缘,为青藏高原物质往东南逃逸、东构造结侧向挤压及华南地块北西西向推挤作用的重要地段.利用剖面观测的重力与GPS定位数据,结合区域背景重力场、地质构造及深部地球物理成果,反演研究剖面较为细化的地壳密度结构特征.观测研究表明:剖面布格重力异常总幅差变化达190×10-5 m·s-2,具"斜N"分段变化特征,从西往东呈上升(维西至攀枝花,水平梯变大)—下降(攀枝花至会泽,水平梯变较大)—上升(会泽至贵阳,水平梯变较小)态势;高程与布格重力异常比值的趋势性转折部位为康滇地轴核心和小江断裂带东侧,可能与先存构造或新生构造发育有关;剖面地壳密度结构可分上、中和下三层结构,各层底界面平均埋深分别约20km、35km和51km,金沙江—红河断裂带和鲜水河—小江断裂带为地壳结构相对简单与复杂的过渡带;地壳厚度西深东浅,可能是东构造结的侧向挤压所致;下地壳厚度变化相对较大,可能对地壳增厚起主要作用;华坪—攀枝花附近的Moho面隆起和上地壳高密度体的存在暗示上地幔往上底侵作用,对青藏高原物质向南东逃逸和东构造结的侧向挤压均起到一定阻挡作用;中地壳下伏有限低密度薄层有利于其上物质的南东逃逸和顺时针旋转,有利于其下物质受喜马拉雅东构造结作用下往东向运移.
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| 关 键 词： | 青藏东南缘 重力剖面 布格重力异常 地壳密度结构 动力学环境 |
| 收稿时间： | 2015-01-12 |
Gravity anomalies and crustal density structure characteristics of profile Weixi-Guiyang |
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| SHEN Chong-Yang,YANG Guang-Liang,TAN Hong-Bo,XUAN Song-Bai,WU Gui-Ju,WANG Jian.Gravity anomalies and crustal density structure characteristics of profile Weixi-Guiyang[J].Chinese Journal of Geophysics,2015,58(11):3952-3964. |
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| Authors: | SHEN Chong-Yang YANG Guang-Liang TAN Hong-Bo XUAN Song-Bai WU Gui-Ju WANG Jian |
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| Institution: | 1. Institute of Seismology, Key Laboratory of Earthquake Geodesy, China Earthquake Administration, Wuhan 430071, China;2. Wuhan Base for Institute of Crustal Dynamics, CEA, Wuhan 430071, China |
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| Abstract: | Weixi-Guiyang profile is located in the key area of southeastern margin of the Tibetan Plateau. The profile cuts through the Sichuan, Yunnan and Guizhou tectonic region about 27°N; its western end is adjacent to the eastern Himalayan tectonic syntaxis, the east extends into the Southern China block. The southeastern margin of the Tibetan Plateau is the tectonic transition zone of the Tibetan Plateau and Yangtze Platform, and where the substance escapes to south-eastward, it is caused by the India-Asia continent collision or converging. The geological evolution is very complex in the area, and the tectonic deformation is very developed and strong. The terrains what clamp among large strike-slip faults form a huge lateral extrusion terrains group. Shear strike-slip and nappe tectonics are developed and block hyperplasia alternating with extrusion. At the same time, the earthquake activity is frequent in this area. It is one of the strongest earthquake activity areas in China, known as the southern South-North earthquake belt. The study on the regional crust structure of southeastern margin of the Tibetan Plateau has great significant to understand the characteristics of intracontinental deformation, dynamics caused by the India-Eurasia collision, and the regional earthquake gestation and occurrence regularity.#br#From west to east, the Weixi-Guiyang profile passes by Weixi, Lijiang, Yongsheng, Panzhihua, Huidong, Huize, Weining, Liupanshui, Zhijin and Guiyang. The number of observation points of the profile are 420, the average station spacing is about 2 km, and the length is about 800 km. In this research, the relative gravity surveying method and GNSS (Global Navigation Satellite System) are used, which are applied to obtain gravity observation value and the 3D coordinate(Longitude, latitude, altitude) respectively. Then we got the free air gravity anomaly, the Bouguer gravity anomaly and the ratio of the elevation and Bouguer gravity anomaly along the profile. Finally, combining with regional background gravity field, geologic survey and deep geophysical achievements, we obtained the results of density stratification structures of the profile with Paker-Oldenberg method and Human-computer interaction method of choice.#br#The range of Bouguer gravity anomaly is -345~-159×10-5m·s-2 (mGal) on the profile, and the difference between the amplitudes is about 190 mGal. The segmentation shape of the Bouguer gravity anomaly curve looks like "oblique N" from west to east. From Weixi to Panzhihua the Bouguer gravity anomaly is rising, and the horizontal ladder is about +1.05 mGal·km-1; from Panzhihua to Huize the Bouguer gravity anomaly is decreasing, its horizontal ladder is about -0.46 mGal·km-1; from Huize to Guiyang the Bouguer gravity anomaly is rising, and its horizontal ladder is about +0.35 mGal·km-1. The trend turning parts of the ratio of the elevation and Bouguer gravity anomaly are at the core "axis", and the eastern side of Xiaojiang fault, where may be related to the development of pre-existing or newborn structure.#br#The profile crustal density structure can be divided into upper, middle and lower three layers, the average bottom depth of each layer is about 20 km, 35 km and 51 km, and the average density of each layer is about 2.72 g·cm-3, 2.86 g·cm-3 and 2.94 g·cm-3 respectively, the density of the upper mantle is about 3.30 g·cm-3. Jinshajiang-Red River fault zone and Xianshuihe-Xiaojiang fault are the transition zone of the relatively simple and complex crustal structure. The crustal thickness is deep in west and shallow in east, it may be due to laterally squeezed of eastern tectonic syntaxis. The thickness variation of lower crust is relatively large, it may play a major role for crustal thickening. The Moho surface uplift is near to Huaping-Panzhihua, and there is a high density body in the upper crust, which plays a role in blocking for the south east escaping of Tibet Plateau substance and lateral squeeze of eastern tectonic syntaxis. The addition high density layer on the Moho surface uplift position may be associated with the bottom invasion effect of mantle plume. Between Jinshajiang-Red River fault zone and Xianshuihe-Xiaojiang fault zone there is a limited low-density thin layer in the middle crust. On the effect of the eastern tectonic syntaxis, It is beneficial to Sichuan-Yunnan block upper substance escapes to south-eastward and clockwise rotation, and also beneficial to the eastward migration of its lower substance. |
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| Keywords: | Southeast margin of the Tibetan Gravity profile Bouguer gravity anomaly Structure of the crustal density Dynamics environment |
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