死海（约旦）里散半岛的重磁勘查     

A. Batayneh A.Al-Zoubi M.Hassouneh 《吉林大学学报(地球科学版)》1996,(1)

里散半岛位于非洲板块和阿拉伯板块支接处的死海盆地中。该盆地面积大，构造简单且有下沉运动，说明它是一位张型盆地。由重力异常数据发现死海盆地可划分成沿南北延伸各约３０ｋｍ长的几个块体，里散半岛是其一最深的一个。一生代沉积厚度约６ｋｍ，更新世沉积厚度为９ｋｍ。死海盆地的拉张距离为２０ｋｍ，表明死海盆地的年龄约３．３Ｍａ。里散半岛下部的前寒武纪结晶基底磁化率较高，这与区内延续的构造活动性有关。  相似文献   

Mantle Bouguer Anomaly Along an Ultra Slow-Spreading Ridge: Implications for Accretionary Processes and Comparison with Results from Central Mid-Atlantic Ridge     

Rommevaux-Jestin  Céline  Deplus  Christine  Patriat  Philippe 《Marine Geophysical Researches》1997,19(6):481-503

A three-dimensional analysis of gravity andbathymetry data has been achieved along the Southwest Indian Ridge (SWIR)between the Rodriguez Triple Junction (RTJ) and the Atlantis II transform,in order to define the morphological and geophysical expression ofsecond-order segmentation along an ultra slow-spreading ridge(spreading rate of 8 mm/yr), and to compare it with awell-studied section along a slow-spreading ridge (spreadingrate of 12.5 mm/yr): the Mid-Atlantic Ridge (MAR) between 28°and 31°30 N.Between the Atlantis II transform and theRTJ, the SWIR axis exhibits a deep axial valley with an 30°oblique trend relative to the north–south spreading direction. Onlythree transform faults offset the axis, so the obliquity has to beaccommodated by the second-order segmentation. Alongslow-spreading ridges such as the MAR, second-order segmentshave been defined as linear features perpendicular to the spreadingdirection, with a shallow axial valley floor at the segment midpoint,deepening to the segment ends, and are associated with Mantle BouguerAnomaly (MBA) lows. Along the SWIR, our gravity study reveals the presenceof circular MBA lows, but they are spaced further apart than expected. Thesegravity lows are systematically centred over narrow bathymetric highs, andinterpreted as the centres of spreading cells. However, along some obliquesections of the axis, the valley floor displays small topographicundulations, which can be interpreted as small accretionary segments frommorphological analysis, but as large discontinuity domains from thegeophysical data. Therefore, both bathymetry and MBA variations have to beused to define the second-order segmentation of an ultraslow-spreading ridge. This segmentation appears to be characterisedby short segments and large oblique discontinuity domains. Analysis of alongaxis bathymetric and gravimetric profiles exhibits three different sectionsthat can be related to the thermal structure of the lithosphere beneath theSWIR axis.The comparison between characteristics of segmentationalong the SWIR and the MAR reveals two major differences: first, the poorcorrelation between MBA and bathymetry variations and second, the largerspacing and amplitude of MBA lows along the SWIR compared to the MAR. Theseobservations seem to be correlated with the spreading rate and the thermalstructure of the ridge. Therefore, the gravity signature of the segmentationand thus the accretionary processes appear to be very different: there areno distinct MBA lows on fast-spreading ridges, adjacent ones on slowspreading ridges and finally separate ones on ultra slow-spreadingridges. The main result of this study is to point out that 2nd ordersegmentation of an ultra slow-spreading ridge is characterised bywide discontinuity domains with very short accretionary segments, suggestingvery focused mantle upwelling, with a limited magma supply through a cold,thick lithosphere. We also emphasise the stronger influence of themechanical lithosphere on accretionary processes along an ultra slow-spreading ridge.  相似文献   

Precollisional tectonics and terrain amalgamation offshore southern Taiwan:Characterizations from reflection seismic and potential field data   总被引：1，自引：0，他引：1  

LI ChunFeng  ZHOU ZuYi  LI JiaBiao  CHEN HuanJiang  GENG JianHua & LI Hui State Key Laboratory of Marine Geology  Tongji University  Shanghai  China  The Second Institute of Oceanography  State Oceanic Administration  Hangzhou  China 《中国科学D辑(英文版)》2007,50(6):897-908

Sponsored by the Chinese National Fundamental Research and Development Program in 2001,Guang-zhou Marine Geological Survey launched out a long geophysical survey from the northeastern part of the South China Sea (SCS),through the Luzon Arc,to the Huatung Basin and the Gagua Ridge. Based on high-resolution seismic data from this survey,combined with gravimetric and magnetic modeling,a systematic effort is made to the study of the regional geodynamics offshore southern Taiwan. By focusing particularly on precollisional tectonic interactions between adjacent geological units and their tectonic affiliations,this study can help reveal early arc-continent collisional processes that formed the Taiwan orogen. The construction of the Manila accretionary prism and its eastward progressive deformation indicate that the subduction of SCS have experienced multiple phases of increased activity. Active precollisional crustal shortening within the Northern Luzon Trough resulted in tilting of sedimentary layers at angles between 6° and 13°. But the shortening induced by tilting accounts for only a tiny part of regional total crustal compression. The eastern flank of the Luzon Arc appears to be more active than the rest,evidenced by active faulting and folding in the intra-arc basins on the eastern flank. Magnetic modeling/inversion shows that the Luzon Arc may have experienced multiple phases of magmatic activities,causing lateral magnetic inhomogeneity. Bouguer gravity anomalies and gravity modeling indicate that the Huatung Basin has anomalously higher crustal and upper mantle densities than those of SCS and the Luzon Arc. In addition,there is a large bathymetric difference between the Huatung Basin and the northeastern part of SCS basin. These observations argue against early hypothesis that the Huatung Basin and the northeastern part of SCS basin may once have belonged to one single oceanic crust,in part or in whole. The Gagua Ridge,as a sliver of uplifted oceanic crust,may be related to a transient northwestward subduction of the western Philippine plate. All evidences point to the argument that the region offshore southern Taiwan is experiencing multiple terrain amalgamation,which is a classical model for continental growth.  相似文献   

Inversion of gravity and topography data for the crust thickness of China and its adjacent region   总被引：1，自引：0，他引：1  

黄建平  傅容珊  许萍  黄建华  郑勇 《地震学报(英文版)》2006,19(3):264-272

Introduction Since the middle of the century, gravitational isostasy has been a fundamental hypothesis for inverting the gravity data to find the crust thickness. Geophysicists have done a lot of researches on using gravity data to investigate the depth of Moho discontinuity. Since 1980, the International Lithosphere Program emphasized the importance of investigating the Moho depth variation. Thereafter a lot of results have been published in the world (Braitenberg et al, 2000; Kaban et al,…  相似文献   

夏季中高纬500 hPa高度和海表温度异常特征及其相关分析   总被引：6，自引：2，他引：4  

吴国雄  王敬方 《气象学报》1998,56(1):46-54

用旋转主分量（ＲＰＣ）方法,对１９４９～１９８８年４０个夏季的中高纬５００ｈＰａ高度场以及北太平洋和北大西洋海表温度异常（ＳＳＴＡ）的主要时空分布特征作分析,然后通过交叉相关讨论夏季海气相互作用的特征。结果表明,夏季中高纬５００ｈＰａ高度场最明显的异常型为副热带型（ＳＴ）,极地北美型（ＰＡ）,４波型（ＦＷ）,以及３波型（ＴＷ）。夏季北太平洋ＳＳＴ的主要异常型为赤道东太平洋型（ＥＥＰ）,阿拉斯加湾型（ＢＡＬ）,热带中太平洋（ＣＴＰ）,以及北部北太平洋型（ＮＮＰ）。而夏季北大西洋ＳＳＴ的主要异常型为赤道大西洋型（ＥＡＬ）,加勒比海型（ＣＡＲ）,东部北大西洋型（ＥＮＡ）和中部北大西洋型（ＣＮＡ）。夏季中高纬海气之间的最强相关出现在海气异常对应的空间位置上。这种区域性或邻域性的海气相关呈正相关的特征。但海气之间的相关耦合不及冬季紧密,赤道ＳＳＴＡ与中高纬５００ｈＰａ高度异常的相关不显著。太平洋ＳＳＴＡ所对应的５００ｈＰａ高度场的相关中心多为局地性,而大西洋ＳＳＴＡ所对应的５００ｈＰａ高度场的相关中心呈现更有组织性的,甚至是波状的形态。  相似文献   

Shallow crustal structure of Chicxulub impact crater imaged with seismic, gravity and magnetotelluric data: inferences about the central uplift     

J. O. Campos-Enríquez  F. J. Chávez-García  H. Cruz  J. G. Acosta-Chang  T. Matsui  J. A. Arzate  M. J. Unsworth  J. Ramos-López 《Geophysical Journal International》2004,157(2):515-525

  相似文献   

江淮地区布格重力异常与中强地震发生的构造环境分析   总被引：5，自引：0，他引：5  

韩竹军  邬伦  于贵华  叶燕林 《中国地震》2002,18(3):230-238

通过对布格重力异常等值线的离散化、梯度计算和粗化处理，生成江淮地区布格重力异常梯度分级图。布格重力异常高梯度区与中强地震的空间分布有很好的一致性，与低梯度分布区的弱地震活动性形成鲜明的对比。同时，布格重力异常高梯度区的分布具有线性展布特点，可以划分出两组布格重力异常梯级带，一组走向北东，另一组走向北西西。同方向的条带具有相互平行、间距近似相等的特点，不同方向的构造带相互交切，形成一幅网络状图象。沿着这些梯级带存在断裂构造，它们在晚第三纪至第四纪早期有过构造运动，但晚更新世以来活动不明显。在江淮地区，布格重力异常梯级带、晚第三纪至早第四纪活动断裂和中强地震在空间有比较明显的对应关系。因此，在现今构造活动不太强烈的地区，布格重力异常梯级带可以认为是划分中强地震潜在震源区的一个重要标志。  相似文献   

南极重力场特征及界面的计算与解释          下载免费PDF全文

张赤军  蒋福珍  方剑  陆洋 《极地研究》1996,8(2):62-67

本文根据ＯＳＵ９１Ａ地球重力场模型和地形资料，计算了南极洲的空间重力异常和布格重力异常，分析了空间重力异常变化剧烈的原因及其与高程的相关性，同时根据布格重力异常用两层界面的反演方法计算了冰盖厚度和地壳厚度，冰盖厚度较大的地区位于极区的东南部，而极区周围和西南部地区厚度较小。地壳较厚的地区位于极区的东南部，最大达５６ｋｍ，西南部地区地壳较薄，最小值为８ｋｍ。  相似文献   

Three-dimensional SeaMARC II,gravity, and magnetics study of large-offset rift propagation at the Pito Rift,Easter microplate   总被引：1，自引：0，他引：1  

Fernando Martinez  David F. Naar  Thomas B. Reed IV  Richard N. Hey 《Marine Geophysical Researches》1991,13(4):255-285

We present results from a SeaMARC II bathymetry, gravity, and magnetics survey of the northern end of the large-offset propagating East Rift of the Easter microplate. The East Rift is offset by more than 300 km from the East Pacific Rise and its northern end has rifted into approximately 3 Ma lithosphere of the Nazca Plate forming a broad (70–100 km) zone of high (up to 4 km) relief referred to as the Pito Rift. This region appears to have undergone distributed and asymmetric extension that has been primarily accommodated tectonically, by block faulting and tilting, and to a lesser degree by seafloor spreading on a more recently developed magmatic accretionary axis. The larger fault blocks have dimensions of 10–15 km and have up to several km of throw between adjacent blocks suggesting that isostatic adjustments occur on the scale of the individual blocks. Three-dimensional terrain corrected Bouguer anomalies, a three-dimensional magnetic inversion, and SeaMARC II backscatter data locate the recently developed magmatic axis in an asymmetric position in the western part of the rift. The zone of magmatic accretion is characterized by an axis of negative Bouguer gravity anomalies, a band of positive magnetizations, and a high amplitude magnetization zone locating its tip approximately 10 km south of the Pito Deep, the deepest point in the rift area. Positive Bouguer gravity anomalies and negative magnetizations characterize the faulted area to the east of the spreading axis supporting the interpretation that this area consists primarily of pre-existing Nazca plate that has been block faulted and stretched, and that no substantial new accretion has occurred there. The wide zone of deformation in the Pito Rift area and the changing trend of the fault blocks from nearly N-S in the east to NW-SE in the west may be a result of the rapidly changing kinematics of the Easter microplate and/or may result from ridge-transform like shear stresses developed at the termination of the East Rift against the Nazca plate. The broad zone of deformation developed at the Pito Rift and its apparent continuation some distance south along the East Rift has important implications for microplate mechanics and kinematic reconstructions since it suggests that initial microplate boundaries may consist in part of broad zones of deformation characterized by the formation of lithospheric scale fault blocks, and that what appear to be pseudofaults may actually be the outer boundaries of tectonized zones enclosing significant amounts of stretched pre-existing lithosphere.  相似文献   

利用大陆均衡理论研究河西地区地壳的稳定性   总被引：1，自引：1，他引：0  

郭树松  祝意青  刘芳 《大地测量与地球动力学》2011,31(3):38-41

根据大陆均衡理论,对由艾里（Airy）大陆均衡模型计算的理论均衡地壳厚度（D）和实际布格重力异常反演得到的地壳厚度（M）进行比较,探讨北祁连河西地区的地壳均衡状态。结果表明,该地区理论大陆均衡地壳厚度均大于实际地壳厚度,地壳处于不均衡状态。  相似文献