喜玛拉雅“东构造结”地区特异重力场的探讨
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摘要
跨越中、印、缅三国交界的青藏高原东南的喜玛拉雅“东构造结”地区(92°E~97°E,26°N~30°N)一半以上的面积尚没有重力测点,是重力数据空白区,故无法直接研究其重力场特征与深部地壳结构(构造).本文分析了卫星重力异常的特性,提出应用卫星重力异常作为近似空间重力异常,并作布格改正后,得到的布格重力异常具有与该地区地形高程呈镜像相关的特征,可用以研究深部地壳结构.据三条重力剖面计算得到该地区三个地壳深部结构剖面的结果,给出青藏高原地壳厚度>70 km;喜马拉雅造山带为55 km左右;布拉马普特拉河谷盆地为33~35 km;那加山山脉地区为40~45 km,显示出三者为三个不同的构造单元.同时给出布拉马普特拉构造单元为相对高密度的刚性物质构成,随着印度洋板块向北运移,在碰撞、挤压下,插入青藏高原东南缘一带.导致该地带的强烈构造运动,和频发大、小地震.最后提出了几点认识和建议.
More than half of the 'Himalayas east structural knot' area(92°E~97°E,26°N~30°N) that stretch cross boundaries of China,India and Burma has no ground gravity measuring point yet.Here it is hard to research directly the gravity field characteristic and the deep crustal structure.In this paper,the satellite gravity anomaly data are employed as pseudo free air gravity anomaly to calculate Bouguer gravity anomaly.The calculated Bouguer gravity anomaly exhibits well mirror correlation with the topography altitude of this district.It can be used to research the deep crustal structure.Three profiles of deep crust structure according to three Bouguer gravity anomaly profiles are obtained.In Tibetan plateau the crust thickness is more than 70 km,in orogenic belt of Himalayan mountains it is about 55 km of,in Brahmaputra basin valley it is 33 to 35 km,and in Naga mountain it is 40 to 45 km.Three tectonic units are displayed.The Brahmaputra tectonic unit in 'east structural knot' is composed of high-density matter,moves northward after collision and extrusion by Indian Ocean plate,and then inserts into east margin of Tibetan plateau.This dynamic process results in violent tectonic movement of southeast and northeast edges of Tibetan plateau,induces a series of earthquakes frequently.At last,some conclusions are advanced.
More than half of the 'Himalayas east structural knot' area(92°E~97°E,26°N~30°N) that stretch cross boundaries of China,India and Burma has no ground gravity measuring point yet.Here it is hard to research directly the gravity field characteristic and the deep crustal structure.In this paper,the satellite gravity anomaly data are employed as pseudo free air gravity anomaly to calculate Bouguer gravity anomaly.The calculated Bouguer gravity anomaly exhibits well mirror correlation with the topography altitude of this district.It can be used to research the deep crustal structure.Three profiles of deep crust structure according to three Bouguer gravity anomaly profiles are obtained.In Tibetan plateau the crust thickness is more than 70 km,in orogenic belt of Himalayan mountains it is about 55 km of,in Brahmaputra basin valley it is 33 to 35 km,and in Naga mountain it is 40 to 45 km.Three tectonic units are displayed.The Brahmaputra tectonic unit in 'east structural knot' is composed of high-density matter,moves northward after collision and extrusion by Indian Ocean plate,and then inserts into east margin of Tibetan plateau.This dynamic process results in violent tectonic movement of southeast and northeast edges of Tibetan plateau,induces a series of earthquakes frequently.At last,some conclusions are advanced.
引文
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[2]王二七,Barchfiel B C,季建清.喜马拉雅构造结区新生代地壳缩短量的估算及其地质依据[J].中国科学(D辑),2001,31(1):1~9.
[3]钟大赉,丁林.青藏高原隆起过程及其机制探讨[J].中国科学(D辑),1996,26(3):289~295.
[4]Bai D H,Maxwell M J.Deep structure of the Longling-Ruilifault underneath Kuili Basin near the eastern Himalayan Syn-tax insight from Magnetotelluric imaging[J].Tectonophysics,2003,364:131~146.
[5]Holt W E,Ni J F,Wallace T C,et al.The active tectonics ofthe eastern Himalayan Syntaxis and surrounding Regions[J].J.Geophys,Res.1991,96:14596~14632.
[6]周国藩,陈建国,张健.青藏高原卫星重力场及所反映的壳幔结构和深部构造特征[J].地球科学—中国地质大学学报,1996,21(2):191~197.
[7]袁学诚主编,中国地球物理图集[M].北京:地质出版社,1996,22~42.
[8]马杏垣主编,中国岩石圈动力学地图集[M].北京:中国地图出版社,1989,8~10.
[9]许厚泽,张赤军,蒋福珍,等.青藏高原的大地测量学研究[M].湖北:湖北科学技术出版社,2001,37~44.
[10]王谦身,张赤军,安玉林,等.重力学[M].北京,地震出版社,2003,33~36.
[11]Bowin C.Depth of principal mass anomalies contributing tothe earth’s geoidal undulations and gravity anomalies[J].Marine Geodesy,1983,7:61~100.
[12]王谦身,武传真,江为为,刘洪臣.青藏高原重力场与地壳构造研究,《青藏高原岩石圈结构、演化和动力学》[M].广州:广东科技出版社,1998,36~63.
[13]孔祥儒,王谦身,熊绍栢.青藏高原西部综合地球物理与岩石圈结构研究[J].中国科学(D辑),1996,26(4):308~315.
[14]孔祥儒,王谦身,熊绍栢.青藏高原西部综合地球物理剖面和岩石圈结构与动力学[J].科学通报,1999,44(12):1257~1265.
[15]王谦身,武传真,魏英.亚洲大陆地壳厚度分布轮廓与地壳构造特征[J].地震地质,1982,4(3):1~12.
[16]王谦身,武传真,江为为.青藏高原西部吉隆—鲁谷地区重力场与地壳构造[J].科学通报,1997,42(8):858~862.
[17]王谦身,安玉林.青藏高原东部玛多—沙马地区的重力场与深部构造[J].地球物理学进展,2001,16(4):4~11.
[18]滕吉文,王谦身,王光杰,徐亚,张雪梅.青藏高原“东构造结”地区的特异重力场与深部地壳结构[J].地球物理学报,2006,49(4):1045~1052.