青藏高原均衡重力异常研究

根据重力异常图等有关资料，研究了青藏高原均衡重力异常的分布特征与地质构造、地壳新构造运动间的关系，结果表明：（１）高原内各块体的均衡状态并不均一，而且异常幅值大小与地壳的相对隆起或沉降程度相关；（２）高原均衡异常同强地震分布有较密切的联系     

天山地区均衡剩余地形特征及其地质意义

新生代印度板块持续碰撞和俯冲欧亚大陆的远端效应,波及整个天山地区,强烈改造了天山及相邻块体的岩石圈结构。为了更好地研究天山地区的岩石圈演化和形变过程,本文首先采用联合重力和地震数据反演方法,获得研究区岩石圈密度异常结构,然后考虑有效弹性厚度的横向变化计算研究区均衡剩余地形。结果表明,均衡剩余地形幅值在-1.6～0.9 km之间,且与各构造单元具有良好的对应性。天山各段的均衡剩余地形呈现不同的分布特征,中部为较高幅值的负值,指示剧烈增厚的下地壳;西部为较低幅值的负值,可能与软流圈上涌有关;东部为较低幅值的正值,表明岩石圈形变以地表抬升为主。     

苍梧M_S5.4地震孕震环境的多尺度重力场分析及动力学意义

基于EGM2008研究苍梧震源区及华南块体不同尺度重力场的横向和纵向分布特征,探讨深部物质密度变化及可能的动力学意义,为该区地震孕育环境研究提供深部依据。扬子克拉通重力异常横向变化相对较小,显示出其相对稳定的克拉通结构特征;华夏地块上地幔存在与西太平洋板块俯冲角度较为一致的重力正异常和相间分布的重力负异常,其高低密度体分布可能与中生代以来西太平洋板块俯冲作用下岩石圈拆沉和软流圈物质上涌有关;扬子克拉通和华夏地块过渡带呈现显著的重力异常高梯度带和东西差异性特征,揭示了深部复杂构造变形的过渡带特征。本文研究区多尺度布格重力异常横向的复杂性和非均一性及在地壳和上地幔深浅差异性的重力异常特征,反映了研究区深浅物质结构和动力学不平衡的差异相互运动的动力学过程,可能是地震孕育的深部动力学环境。苍梧地震位于重力正负异常的过渡带,与深部物质扰动和密度分布的不均匀密切相关。     

西藏：地球之巅上的“圣域天堂”

260多万年前,印度板块与欧亚板块“激情”碰撞．气势雄伟的青藏高原从远古的海洋中拔地而起,沧海桑田中逐渐抬升为地球上海拨最高、年龄却最小的高原,这就是地质学上最为有名的“喜马拉雅运动”。     

青藏高原及周缘深部结构的重力异常解释与尼泊尔Ms8.1地震

利用离散小波变换获得青藏高原布格重力异常不同尺度的总水平梯度(HGM)和横向、纵向、对角分量平方和的平方根(HVDM)图像。结果表明:1)4、5阶小波细节之和的HGM高值区域存在于尼泊尔喜马拉雅地区、喜马拉雅东构造结和阿尔金断裂带中段,即青藏高原周缘较为活跃的构造带;2)尼泊尔喜马拉雅地区和阿尔金断裂带西段存在5阶小波逼近高值HGM,较高值HGM带呈现环青藏高原形态,反映了青藏高原与周缘构造块体地壳深度变化和岩石圈地幔顶部物质性质的差异性变化特征;3)HVDM高值带分布于喜马拉雅地区、喜马拉雅东构造结地区、阿尔金断裂带和龙门山断裂带,体现了青藏高原周缘构造带形态特征;4)2015尼泊尔Ms8.1地震发生在地壳深部的HGM高-低-高分布形态的低值区和HVDM高值带的边界,是印度板块和欧亚板块持续汇聚及周缘大型走滑断裂带的调节作用、累积能量释放的结果。     

汶川Ms8.0地震前的区域垂直形变背景

根据1951年以来的水准观测资料和1999—2007年的GPS观测资料计算得到的地壳垂直形变速率,研究了青藏块体和华南块体不同时间段的垂直形变特征,以及形变与汶川8.0级地震孕育发生的关系。结果显示,汶川8.0级地震发生在垂直形变强烈上升区的形变速率梯度带上;大震孕育过程的应变能积累与印度板块-欧亚板块相互碰撞有关;与位于两个板块碰撞前缘的青藏块体在南北向强烈挤压,形成垂直方向隆升,物质向东和东南迁移过程相联系。     

均衡异常与喜马拉雅隆起

利用重力测量资料，分析了喜马拉雅地区的均衡异常和板块水平挤压的重力效应，结果表明：沿喜马拉雅山脊存在一条正的均衡异常带；板块水平挤压的均衡效应不明显。基于热异常地幔的观点，讨论了异常的场源，并估算了喜马拉雅的相对上升高度和速率，指出：场源深度在莫氏面以下；推测该场源为一高温异常地幔体，其形状似一水平圆柱；相对上升高度为２．５ｋｍ，上升速率为５．２ｍｍ／ａ。     

类乌齐-玉树-玛多剖面重力异常研究

青海玉树Ms7.1地震发生在巴彦喀拉块体的甘孜-玉树断裂带上。对跨断裂带的重力剖面测线进行了相对重力联测,对观测结果作了大气改正、极移改正、漂移改正,经平差计算后,获取了该剖面的自由空气异常;结合该区1″×１″的ASTER GDEM(2009)地形数字模型,对自由空气异常作了曲率改正、平板改正及高精度的地形改正,得到该探测剖面的完全布格重力异常。分析结果表明：从布格异常的陡变区可初步推断出与地质研究结果一致的断裂构造的位置;在玉树附近沿剖面往东北向出现地壳基底抬升现象,并在清水河附近幅度达到最大,初步推断为印度地壳的俯冲下插对青藏高原东缘的抬升作用的结果。     

汾渭断陷带均衡重力异常研究

本文研究了汾渭断陷带均衡重力异常分布特征与地壳表、浅层结构，新构造运动和现代构造运动，以及均衡重力异常与地震活动性之间的关系。结果表明：局部均衡重力异常分布特征与出露地表的岩石密度和地质构造特征存在明显对应关系，区域均衡重力异常特征反映了本区新构造运动和现代构造运动不是朝着地壳趋于均衡方向发展，而具有反均衡力的特征；不同方向异常带交汇的地方，现今构造运动最强烈，是强震多发区。     

基于现代大地测量手段的青藏高原南缘地壳形变分析

基于2003~2013年GRACE卫星重力、GPS和绝对重力数据对青藏高原南缘地壳形变进行探讨分析。结果表明,拉萨测站1999~2015年垂向隆升速率为1.5 mm/a,显示出拉萨测站持续隆升的特点。结合南加州综合网络构建的远程连续GPS参考站,另外选择TPLJ、CHLM、JMSM测站数据进行分析。GPS结果表明,4个测站2003~2013年平均隆升速率为2.3±0.11 mm/a,GRACE垂向位移时间序列显示4个测站2003~2013年除季节性变化外也具有轻微上升趋势,平均速率为0.35 mm/a。联合绝对重力资料在考虑诸多因素(地壳隆升、侵蚀、GIA等)后得到拉萨测站近年重力变化约为-0.97 μGal/a,青藏高原拉萨测站地下地壳底部增厚速率约为4.4 cm/a,揭示了青藏高原南部地区的地壳形变特征--地壳隆升与底部增厚。     

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Abrupt uplift of Tibetan Plateau a t the end of early Pleistocene and Australasian impact event

The latest sharp uplift of the Tibetan Plateau and adjacent mountains occurred at the end of the early Pleistocene. The uplift of the Plateau resulted from Late Mesozoic－Cenozoic comp ressional structure due to the subduction of the Indian Plate beneath the Asian continent. This event definitively effected the formation of basin-mountain relief, Cenozoic basin deformation, large scale aridity and desertification of western China. The Australasian meteorites impact event happened ca. 0.8 Ma ago, located in the triangle area of the Indian Ocean ridge (20°S/67°E) . The impact may have resulted in an acceleration of speeding of the Indian Ocean ridge pushing the Indian Plate to subduct rapidly northward. Thus, the impact event can give reasonable explanation for the dynamic background of the latest rapid uplift of the Tibetan Plateau and the continental deformation of western China and even of the Middle Asia.     

Abrupt uplift of Tibetan Plateau at the end of early Pleistocene and Australasian impact event

The latest sharp uplift of the Tibetan Plateau and adjacent mountains occurred at the end of the early Pleistocene. The uplift of the Plateau resulted from Late Mesozoic-Cenozoic compressional structure due to the subduction of the Indian Plate beneath the Asian continent. This event definitively effected the formation of basin-mountain relief, Cenozoic basin deformation, large scale aridity and desertification of western China. The Australasian meteorites impact event happened ca. 0.8 Ma ago, located in the triangle area of the Indian Ocean ridge （20°S/67°E）. The impact may have resulted in an acceleration of speeding of the Indian Ocean ridge pushing the Indian Plate to subduct rapidly northward. Thus, the impact event can give reasonable explanation for the dynamic background of the latest rapid uplift of the Tibetan Plateau and the continental deformation of western China and even of the Middle Asia.     

大陆岩石圈的增厚及对流剥离对青藏高原隆升的影响

伴随着印度板块对欧亚板块南缘的碰撞、挤压,青藏高原地壳及下伏地幔岩石圈的厚度增加了１倍。增厚岩石圈热结构的变化可导致高原海拨下降约１５００ｍ。其对流剥离并被较热的软流圈物质替代可用以解释青藏高原自８百万年或３百万年前开始的快速隆升。大陆岩石圈的增厚及热结构变化和对流剥离可能是青藏高原自９百万年前开始的夷平—快速隆升过程的主导控制因素。     

Episodic orogeny deduced from coeval sedimentary sequences in the foreland basin and its implication for uplift process of Longmen Mountain, China

Longmen Mountain located at the boundary between the Sichuan Basin and Tibetan Plateau,representing the steepest gradient of any edges of the plateau.Three endmember models of uplift process and mechanism have been proposed,including crustal thickening,crustal flow,and crustal isostatic rebound.Here we use coeval sedimentary sequences in the foreland basin to restraint uplift process and mechanism in the Longmen Mountain.The more than 10,000 m thick Late TriassicQuaternary strata filled in this foreland basin and can be divided into six megasequences that are distinguished as two distinct types.The first type is the wedge-shaped megasequences which are sedimentary response of strong active thrust loading events,characterized by a high rate of subsidence and sediment accumulation,coarsening-upward succession and a dual-sourced sediment supply.This type includes Late Triassic,Late Jurassic to Early Cretaceous and Late Cretaceous to Paleogene megasequences.The second type is the tabular megasequences,characterized by the low rate of subsidence and sediment accumulation,finingupward succession,and a single-sourced sediment supply,which is sedimentary response of isostatic rebound and erosion unloading.This type includes the Early to Middle Jurassic,Middle Cretaceous and Neogene to Quaternary megasequences.Basing on sedimentary,active tectonic,geomorphic evidence,we infer that the direction has been reversed from SSWdirected sinistral strike-slip to NNE-directed dextral strike-slip during 40-3.6 Ma,and since 3.6 Ma,the Longmen Mountain thrust belt belong to times of isostatic rebound and erosional unloading with NNEdirected dextral strike-slip.This suggests that crustal isostatic rebound is a primary driver for uplift and topography of the present Longmen Mountain.The Wenchuan(Ms8.0) earthquake,which ruptured a large thrust fault with NNE-directed dextral strikeslip along the range front,is an active manifestation of this crustal isostatic rebound process with dextral strike-slipping and shortening.This process may be the cause for the Wenchuan Earthquake and the apparent paradox of high relief,little shortening,the relative dearth of historical seismicity in the region.     

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利用GRACE、GPS和水准数据研究西秦岭地区现今地壳垂直运动特征

利用GRACE卫星数据改正GPS连续站垂向位移时间序列中的周期变化,用主成分分析方法消除区域共模噪声误差,计算获取西秦岭地区GPS连续站的垂直运动速率,并将其作为速率参考基准,联合水准观测资料基于线性动态平差模型,处理得到西秦岭地区现今地壳垂直运动速度场。结果显示,西秦岭整体处于差异性的快速隆升,主要是由青藏高原东北缘的地壳缩短作用所致。六盘山和天水南侧均以3 mm/a速率抬升,是本区上升最快的地方;其次是陇西地块和鄂尔多斯地块南部,分别以2 mm/a和1 mm/a的速率上升;秦岭造山带和渭河盆地的西部表现为下沉,但渭河盆地下沉最快。西秦岭现今地壳垂直运动可能暗示青藏高原东北缘的现今横向逃逸运动通道已从早期的西秦岭-秦岭地块向北转移到六盘山构造带、鄂尔多斯地块南部。     

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