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1.
A Bouguer gravity anomaly map is presented of the North Sea and adjacent land areas in Norway and Denmark, covering an area situated between 56° and 62°N, 1°W and 10°E. The gravity data from the UK sector of the North Sea, the land and offshore areas of Denmark, and the land areas of Norway have been published before. However, the gravity data from the Norwegian sector of the North Sea are new. A large number (about 60) of individual gravity features can be defined in the mapped area. Most of those situated in the UK sector of the North Sea and on land in Norway have been discussed earlier; however, most of the anomalies found elsewhere which are qualitatively interpreted here have not been discussed before. An interpreted Bouguer anomaly map is presented which identifies all these features. The majority of the gravity anomalies encountered in the mapped area can be shown to be associated with one of the following geological features: (i) basement highs, (ii) large bodies of heavy basic or ultrabasic rock in the crystalline basement, (iii) large igneous intrusions within the sedimentary column and thick accumulations of volcanic rocks or their associated eruption centers, (iv) major basement faults. Large-scale geological structures such as the Central, Viking and Sogn Grabens and the East Shetland, Stord, Forth Approaches and Norwegian-Danish Basins are essentially in isostatic equilibrium and are only locally marked by relatively weak gravity minima. A residual gravity anomaly map has been produced by subtracting from the observed Bouguer anomalies the estimated gravity effect of an assumed thinned crust. This residual gravity anomaly map shows a number of features of the Bouguer anomaly field with greater clarity. 相似文献
2.
The goal of this study was to determine the main factors that controlled the kinematic evolution and the structural architecture developed during the Late Triassic to Early Jurassic rifting that led to the opening of the Neuquén basin in the southwestern sector of Gondwana. We carried out a series of analog models to simulate an extensional system with a bent geometry similar to the northeastern border of the basin. In different experiments, we varied the extension direction between NNE (N10°E) and NE (N45°E) orientations, inducing rift systems with different degrees of obliquity in each sector of the extended area. We compared the kinematic evolution and the final structural architecture observed in the experiments with data from two selected representative areas of the basin: (1) the Atuel depocenter, situated in the northern Andean sector, and (2) the Entre Lomas area, situated in the northeastern Neuquén Embayment. In both cases, the good match between the field and subsurface data and the results of the analog models supports a NNE orientation of the regional extension (N30°E–N20°E) during the synrift stage. Our experimental results suggest that lithospheric weakness zones of NNW to NW trend could have controlled and localized the extension in the Neuquén basin. These previous anisotropies were linked to the sutures and rheological contrasts generated during the collision of terranes against the southwestern margin of Gondwana during the Paleozoic, as well as further modifications of the thermo-mechanical state of the lithosphere during the Late Paleozoic to Early Mesozoic evolution. 相似文献
3.
4.
南海深部构造对研究南海构造演化和油气勘探具有重要意义.本文对南海地区的自由空气重力异常进行布格校正、海水层校正和沉积层校正,得到布格重力异常,再对布格重力异常进行区域异常和局部异常分离,利用位场界面反演方法对区域布格异常进行反演计算得到研究区域的莫霍面深度分布;采用全变倾角化极方法对研究区域的卫星磁异常数据进行化极处理,并进一步对化极磁异常作向上延拓,得到延拓后化极磁异常结果.分析布格重力异常、莫霍面深度及化极磁异常特征,结合天然地震层析成像的证据,得到以下结论：推测南海北部陆缘的古俯冲带位置是从118.5°E,24°N沿北东向延伸至109°E,15°N;红河断裂入海后经过莺歌海盆地在海南岛南部转为南北向与越东断裂相接并延伸至万安盆地;推测中特提斯洋的部分闭合位置是从110°E,2°N到101°E,21°N. 相似文献
5.
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. 相似文献
6.
A. S. N. Murty Kalachand Sain B. Rajendra Prasad 《Pure and Applied Geophysics》2008,165(9-10):1733-1750
The 2-D shallow velocity structure along the north-south Palashi-Kandi profile in the West Bengal sedimentary basin has been updated by travel-time inversion of seismic refraction, wide-angle reflection and gravity data. A six-layer shallow model up to a depth of about 7 km has been derived. The first layer, which has an average velocity of 2.0 kms?1, represents the alluvium deposit, which rests over the shale formation with average velocity of 3.0 kms?1. The thin (200 m) Sylhet limestone, observed at a nearby Palashi well, remains hidden in the present data set. Hence a 200-m thin layer with a velocity of 3.7 kms?1, corresponding to the Sylhet limestone, has been assumed to be present throughout the profile. The fourth layer with a velocity of 4.5–4.7 kms?1 at a depth of 1.7–2.4 km represents the Rajmahal traps. The ‘skip’ phenomenon and rapid amplitude decay of first arrivals indicate a low-velocity zone (LVZ) in the study area. Using the ‘skip’ phenomena and wide-angle reflection data, identified on seismograms, the LVZ with a velocity of 4.0 kms?1, indicating the Gondwana sediments, has been delineated below the Rajmahal traps. The next layer with a velocity 5.4–5.6 kms?1 overlying the crystalline basement (5.8–6.25 kms?1) may be associated with the Singhbhum group of meta volcanic rock that has been exposed in the western part of the basin. The basement lies at a variable depth of 4.9 to 6.8 km. The overall uncertainties of various velocity and boundary nodes are ± 0.15 kms?1 and ± 0.5 km, respectively. The elevated basement feature in the north might have acted as a structural barrier for the deposition of Sylhet limestone during the Eocene epoch. The seismically derived shallow structure correctly explains the observed Bouguer gravity anomaly along the profile. The addition of reflections in the present analysis provides a stronger control on the depths and velocities of basement and overlying sedimentary formations, compared to the earlier model derived mainly by the first arrival seismic data. 相似文献
7.
《Physics of the Earth and Planetary Interiors》2005,148(2-4):215-232
The Narmada–Son Lineament (NSL) Zone is the second most important tectonic feature after Himalayas, in the Indian geology. Magnetotelluric (MT) studies were carried out in the NSL zone along a 130 km long NNE-SSW trending profile. The area of investigation extends from Edlabad (20°46′16″; 75°59′05″) in the South to Khandwa (21°53′51″; 76°18′05″) in the North. The data shows in general the validity of a two-dimensional (2D) approach. Besides providing details on the shallow crustal section, the 2D modeling results resolved four high conductive zones extending from the middle to deep crust, spatially coinciding with the major structural features in the area namely the Gavligarh, Tapti, Barwani-Sukta and Narmada South faults. The model for the shallow section has brought out a moderately resistive layer (30–150 Ω m) representing the exposed Deccan trap layer, overlying a conductive layer (10–30 Ω m) inferred to be the subtrappean Gondwana sediments, the latter resting on a high resistive basement/upper crust. The Deccan trap thickness varies from around a few hundred meters to as much as 1.5 km along the traverse. A subtrappean sedimentary basin like feature is delineated in the northern half of the traverse where a sudden thickening of subtrappean sediments amounting to as much as 2 km is noticed. The high resistive upper crust is relatively thick towards the southern end and tends to become thinner towards the middle and northern part of the traverse. The lower crustal segment is conductive over a major part of the profile. Considering the generally enhanced heat flow values in the NSL region, coupled with characteristic gravity highs and enhanced seismic velocities coinciding with the mid to lower crustal conductors delineated from MT, presence of zones of high density mafic bodies/intrusives with fluids, presumably associated with magmatic underplating of the crust in the zone of major tectonic faults in NSL region are inferred. 相似文献
8.
在云南省西部,跨越中、缅两国交界的横断山系地区（97°E~102°E,24°N~30°N）有近一半的面积尚没有重力测点、即重力数据空白区和重力测点稀少的普查级测区.以前的有关文献、图集中所给出对此地区的重力场都是十分模糊的结果与图件.因此应用这些资料无法详细地研究该地区重力场特征与深部地壳结构（构造）.本文应用卫星重力异常资料作为“近似空间重力异常”,经中间层改正后给出的“计算布格重力异常”,其分布特征与该地区的地形高程呈很好的镜像相关.对相应山脉、河谷以及断裂构造都有所反映.特别是在横断山系地区该布格重力异常呈现为近南北的走向.为此,据该“计算布格重力异常”,并选定对该区有代表性的一条重力异常剖面作正反演计算,以得到其地壳深部结构剖面.结果表明,在横断山脉地区的地壳厚度在51~56 km间起伏变化;滇西北云岭山系以及玉龙山区的地壳厚度约在60 km以上. 最后,对所得结果与图件进行了讨论,并提出了几点认识和纠正的建议. 相似文献
9.
Parabolic density function in sedimentary basin modelling 总被引：1，自引：0，他引：1
For modelling sedimentary basins of large thickness from their gravity anomalies, the concept of parabolic density function which explains the variation of true density contrast of the sediments with depth in such basins is introduced inBott's (1960) procedure. The analytical expression the gravity anomaly of a two-dimensional vertical prism with parabolic density contrast needed to estimate the gravity effect of the basin in modelling procedure is derived in a closed form. Two profiles of gravity anomalies, one across San Jacinto Graben, California and the other across Tucson basin, Arizona where the density of sediments is found to vary with depth are interpreted. 相似文献
10.
用热退磁辅以交变退磁方法对采自塔里木盆地阿克苏地区四石厂剖面47个采样点518块标本进行了逐步磁清洗和测试。由本征剩磁方向统计得到塔里木地台晚古生代的古地磁极位置(晚泥盆世φ=10.5°S、λ=151.2°E;晚石炭世φ=52.2°N、λ=179.5°E;早二叠世φ=56.5°N,λ=190.1°E)。古地磁结果表明:塔里木地台在晚古生代是北方大陆的块体之一。从晚石炭世至早二叠世塔里木地台已和北方的哈萨克斯坦板块、西伯利亚地台、俄罗斯地台等连成一片,并且从中生代以来它们之间的相对位置没有发生过大规模的变动 相似文献
11.
P. S. Martyshko I. V. Ladovskii A. G. Tsidaev 《Izvestiya Physics of the Solid Earth》2010,46(11):931-942
The technique of solving the inverse structural gravity problem based on the joint interpretation of gravity and seismic data
is described in this paper. The method of solving is based on the method of local corrections, but involves some modifications
described in the paper. An area of the northeastern part of the Urals and West Siberia (60°-65°N, 54°-72°E) was studied with
the use of this technology and the spatial position of the boundaries of the crystalline crust of the Earth (its roof K0 and base M) were determined from seismic and gravity data. 相似文献
12.
利用南海海盆及周边最新的重力,经过海底地形、沉积层的重力效应改正,并采用岩石圈减薄模型的温度场公式,校正了从张裂边缘到扩张海盆的热扰动重力效应.通过研究区的地震剖面和少量声呐数据得到的莫霍面深度点作为约束,采用基于"起伏界面初始模型"的深度修正量反演迭代公式,反演、计算了研究区的莫霍面深度及地壳厚度.结果表明,海盆区莫霍面深度在8~14 km之间,地壳厚度在3~9 km之间;东部海盆和西南海盆残留扩张中心沿NNE向展布向西南延伸至112°E,莫霍面深度超过12 km,地壳厚度在6 km以上,而西北海盆没有明显的增厚扩张中心;在西南海盆北缘的中沙地块南侧,存在一个近EW向地壳减薄带,地壳厚度在9~10 km;莫霍面深度14 km的等深线和地壳厚度9 km的等值线可指示洋陆边界位置. 相似文献
13.
I. B. P. Rao P. R. K. Murthy P. Koteswara Rao A. S. N. Murty N. Madhava Rao K. L. Kaila 《Pure and Applied Geophysics》1999,156(4):701-718
--The crustal structure in the West Bengal basin, India has been investigated by means of wide-angle reflection data recorded along (i) Bishnupur-Palashi-Kandi, 227-km long profile in the north-south direction and (ii) Taki-Arambagh, 120-km long profile in the east-west direction. The data were acquired using multichannel digital seismic instruments with close station spacing. The crustal model, initially derived by 1-D forward modeling of the wide-angle reflection data, has been iteratively refined by 2-D ray tracing and modeling of travel-time observations and the corresponding synthetic seismograms computation. The structural contour map of the Moho prepared from the present data set, indicates the crustal thickness of about 37 km in the western margin of the basin, thinning to about 28 km in the east with an upwarp in the Moho boundary. The upwarp in the Moho and the inferred structural features may be indicative of crustal rifting. The well-known gravity anomaly in the West Bengal basin, 'Calcutta gravity high,' appears to have resulted from the Moho upwarp in combination with the huge thickness of sediments deposited east of the steep flexure of the crystalline basement representing the 'Hinze zone.' 相似文献
14.
普里兹湾位于南极洲东部大陆边缘,其深部地壳结构特征对认识白垩纪冈瓦纳古陆裂解和新生代大陆边缘形成具有重要意义.本文利用重磁、多道反射地震、声纳浮标折射地震和ODP钻井数据对普里兹湾海域的深部地壳结构进行了研究.研究结果显示,普里兹凹陷表现为典型的盆地负重力异常特征,其沉积基底较深,而在四夫人浅滩为高幅重力正异常,其沉积基底普遍抬升.在大陆架中部存在SW-NE向条带状基底的抬升,且呈朝NE向逐渐变深的趋势.在中大陆架外侧,均衡残余重力异常呈V字形负异常条带状分布,其两翼分别与四夫人浅滩和弗拉姆浅滩外的大陆坡相连.该异常带在大陆架中部向陆的偏移可能是由于古大陆架边缘的地形影响,推测其与普里兹冲积扇同属于洋陆过渡带向陆的部分,在重力模拟剖面表现为地壳向海逐渐减薄.普里兹冲积扇的地壳厚度较薄,平均为6 km,最薄处可达4.6 km,并且根据洋陆过渡带向海端的位置,推测可能属于接近洋壳厚度的过渡壳.重力异常分区的走向与兰伯特地堑在普里兹湾的构造走向基本一致,可能主要反映了二叠纪-三叠纪超级地幔柱对普里兹湾的裂谷作用的影响.该区域的自由空间重力异常和均衡残余异常均表现为超过100×10-5m/s2的高幅正异常特征,可能由位于大陆架边缘的巨厚沉积体负载在高强度岩石圈之上的区域挠曲均衡作用所导致,可能与该区域第二期裂谷期之后的沉积间断以及快速进积加厚的演化过程有关.普里兹湾磁力异常的走向与重力异常明显不同,大致可分为东北高幅正异常区和西南低幅异常区.重磁异常在走向上的差异反映高磁异常主要来源于岩浆作用形成的铁镁质火成岩的影响,并且岩浆作用的时代不同于基底隆升的时代,而可能形成于前寒武纪或者南极洲和印度板块裂谷期间(白垩纪). 相似文献
15.
The subsurface information gathered during exploration for oil and gas in the Cambay basin shows it as a deep graben with 5 km or more of Tertiary and Quaternary sediments resting on the Deccan Trap floor. The Trap floor of this graben extends from Lat. 24° N to about Lat. 19° N and possibly further south. The basin is divisible into separate morphotectonic blocks as a result of block differentiation in the Trap basement, reflected in the structural attitudes of the overlying sediments. This differentiation is believed to have originated in the Paleocene. The dominant structural grain of the area to south of the Narmada river is ENE-WSW with block faulting in the Traps along the older Satpura trend. North of the Narmada river, the trend is longitudinal upto the Meshwa river while further north the trends veer to a NNW-SSE alignment. These latter trends, in the greater part of the Cambay basin, were impressed early during its subsidence and are the result of reactivation along the old Dharwarian trends in post-Delhi times. Maximum thickness of the Traps penetrated so far is near Mechsana and Cambay where more than 1000 meters thickness has been drilled through. The drilling and gravity-magnetic evidence shows the thickness of Deccan Traps in this trough to be of the order of 2.5 km and points to the possibility of active subsidence of Cambay basin, concomitant with the outpouring of the basaltic lavas. The age of the Traps in the Cambay basin, as evidenced by the available data, is Upper Crealaceous. The influence of the structural grain of the basaltic floor on the overlying sedimentary sequence is evidenced during all the stages in the evolution of the Cambay Tertiary basin. Conglomerates, wackes and reddish brown clays of exclusive Trap derivation predominate in the sedimentary section in the initial stage of the basin evolution during Paleocene. General absence of well developed terrigenous reservoirs on a regional scale in the Paleogene section is due to predominance of Trap terrain as the provenance of clastic detritus, contributing essentially argillaceous matter. 相似文献
16.
A statistical analysis is made for the eastern part of Turkey in the beginning of 2009 by studying the phenomenon of seismic quiescence as a potential precursor of the main shocks. The results produced four areas having seismic quiescence in the beginning of 2009. These areas are observed to be centered at 39.96°N–40.69°E (around A?kale, Erzurum), 39.36°N–39.74°E (around Ovac?k, Tunceli), 39.02°N–40.52°E (including Elaz?? and Bingöl), and 38.45°N–42.94°E (Van Lake). Based on the recent results showing 5 ± 1.5 years quiescence before the occurrence of an earthquake in this region, the future earthquake would be expected between 2009.5 and 2010.5. The future earthquake occurrence may reach 2012 if we consider the standard deviation of average seismic quiescence as ±1.5 years. We have found that the M W = 6.0 Elaz?? earthquake on 8 March 2010, followed a seismic quiescence starting about 5 years before the main shock. Thus, special interest should be given to the other regions where the seismic quiescence is observed. 相似文献
17.
Geological structure of the yellow sea area from regional gravity and magnetic interpretation 总被引：7，自引：0，他引：7
Regional gravity and aeromagnetic data covering the area of 32°- 38° N, 118°-127° E at the scale of 1：1,000,000 are coordinated and integrated in a synthetic study of the South China Yellow Sea and adjacent areas. Depth to magnetic crystalline basement and its structure are determined by magnetic anomaly inversion. Depth to and thickness of the Paleozoic rock are also revealed by gravity anomaly inversion with constrains of the basement and known seismic information from several profiles. Structure units, main faults, basin boundaries, and sub-suppressions are outlined on the basis of gravity data interpretation. 相似文献
18.
青藏高原内部除大规模的东西向走滑断裂以外,另一个显著的地质特征就是在藏南及高原腹地广泛发育东西向的伸展构造,形成走向近南北的断裂构造,如亚东一谷露裂谷带及双湖断裂.伸展构造已经成为青藏高原地质研究的一个焦点问题.在羌塘地块89°E附近存在明显的低重力、负磁、深度达300 km的低速异常及连通壳幔的高导异常,且地表伴生大规模的新生代火山岩,这些特殊的地质及地球物理场特征的发生位置与地表双湖断裂的位置基本对应.本文通过卫星重力数据的多尺度小波分析结果发现,双湖断裂之下,存在一明显由上地壳一直向下延伸至地幔深部的低重力异常,说明双湖断裂向下延伸深度大,且上下连通性好.结合已有的地质和地球物理资料,认为由于双湖断裂的存在,使得深部幔源岩浆沿断裂构造薄弱带上涌,从而导致羌塘地块之下壳幔温度的升高及大规模部分熔融的发生. 相似文献
19.
R.E. Chvez E.L. Flores J.O. Campos M. Ladrn de Guevara M.C. Fernndez‐Puga J. Herrera 《Geophysical Prospecting》2000,48(5):835-870
A comprehensive reinterpretation of the available gravity, magnetic, geothermal, geological and borehole information has been made of the Laguna Salada Basin to establish a 3D model of the basement and sedimentary infill. According to statistical spectral analysis, the residual gravity anomaly is due to sources with a mean regional depth of 2.8 km. The topography of the basement was obtained from a three‐dimensional inversion carried out in the wavenumber domain using an iterative scheme. The maximum density contrast of ?300 kg/m3 estimated from previous studies and the mean depth of 2.5 km finally constrained this inversion. The resulting model indicated that the sedimentary infill is up to 4.2 km thick at its deepest point. According to the gravity‐derived basement topography, the basin presents an asymmetry (i.e. it is of the half‐graben type). It is deeper to the east, where it is delimited from the Sierra Cucapah by a step fault. By contrast, the limit with the Sierra de Juarez is a gently sloping fault (i.e. a listric fault). The basement is not even, but it comprises a series of structural highs and lows. N–S to NW–SE and E–W to NE–SW faults delimit these structural units. The magnetic modelling was constrained by (i) the gravity‐derived basement topography; (ii) a Curie isotherm assumed to be between 7 km and 10 km; (iii) assuming induced magnetization only; (iv) the available geological and borehole information. The magnetic anomalies were interpreted successfully using the gravity‐derived basement/sedimentary interface as the top of the magnetic bodies (i.e. the magnetic modelling supports the gravity basement topography). An elongated N–S to NW–SE trending highly magnetized body running from south to north along the basin is observed to the west of the basin. This magnetic anomaly has no gravity signature. Such a feature can be interpreted as an intrusive body emplaced along a fault running through the Laguna Salada Basin. Treatment of the gravity and magnetic information (and of their horizontal gradients) with satellite image processing techniques highlighted lineaments on the basement gravity topography correlating with mapped faults. Based on all this information, we derived detailed geological models along four selected profiles to simulate numerically the heat and fluid flow in the basin. We used a finite‐difference scheme to solve the coupled Darcy and Fourier differential equations. According to our results, we have fluid flow in the sedimentary layers and a redistribution of heat flow from the basin axis toward its rims (Sierra de Juárez and Sierra Cucapah). Our model temperatures agree within an error of 4% with the observed temperature profiles measured at boreholes. Our heat‐flow determinations agree within an error of ±15% with extrapolated observations. The numerical and chemical analyses support the hypothesis of fluid circulation between the clay–lutite layer and the fractured granitic basement. Thermal modelling shows low heat‐flow values along the Laguna Salada Basin. Deep fluid circulation patterns were observed that redistribute such flow at depth. Two patterns were distinguished. One displays the heat flow increasing from the basin axis towards its borders (temperature increase of 20°C). The second pattern shows an increasing heat flow from south to north of the basin. Such behaviour is confirmed by the temperature measurements in the thermometric boreholes. 相似文献
20.
D.C. Mishra 《Earth and Planetary Science Letters》1977,36(2):301-308
Geophysical data contiguous with the Narmada-Son lineament suggests its possible extension westward into the Arabian Sea and eastward up to the Shillong Plateau. The airborne magnetic anomaly map of the north Arabian Sea delineates a linear trend of magnetic anomalies in line with the Narmada-Son lineament. This group of magnetic anomalies, spreading over 20°N to 22°N, starts near the west coast of India at 21°N, 69°30′E and extends to the Murray Ridge. The tectonic feature represented by this group of magnetic anomalies is buried by a thick layer of sediments. This westward extension of the lineament is also reflected in the average Bouguer gravity anomaly map of the Indian Ocean. Towards the east, the gravity and magnetic data delineate a subsurface linear tectonic feature which extends in line with this lineament to the eastern syntaxial bend. These various geophysical signatures further suggest the lineament to be a typical rift-like structure. The tectonic implications of the lineament, which extends from the western to the eastern margins of the Indian plate, is discussed. 相似文献