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1.
The Galilee study area, northern Israel, is at present an uplifted, steep continental margin that formed mainly during the Jurassic and has a large positive isostatic anomaly. Since the Jurassic, it was modified by several tectonomagmatic events, which this study attempts to define and classify by updating, reprocessing and reinterpreting gravity, aeromagnetic and geological data. The prominent Rehovot-Carmel N–S positive reduced-to-pole (RTP) magnetic anomaly caused by the Gevim Volcanics, as well as the coexisting Helez-Gaash high Bouguer gravity and the Pleshet low Bouguer gravity, represent the deep (>5 km) Permo-Triassic dominant horst and graben structure of Israel. The Jonah Ridge and Beirut high SW–NE RTP magnetic anomalies in the Levant basin delineate the Levant continental edge that is marked by a deeply buried horst covered by a Late Cretaceous volcanic complex. The Asher and Devora Jurassic volcanics appear to be responcible for the Atlit and Galilee negative magnetic anomalies and for significant negative gravity anomalies which became clear after removing gravity effect of the upper (post-Turonian) light density sediments from the observed gravity. The volcanics extend along a SW–NE belt parallel to the strike of the Moho. It is suggested here that the Carmel-Gilboa fault propagated during the Late Cretaceous from the Levant basin across the Galilee area southeastward to form the Azraq-Sirhan graben in Jordan. As such, it forms a right-step, en echelon, dextral strike-slip fault with associated tectonic basins of various shapes. During the Oligocene and before formation of the Dead Sea transform (DST), the reactivation of the Azraq-Sirhan graben was accompanied by tectonic driven rift propagation in the opposite direction, from Azraq-Sirhan to northwest. It dispersed into many faults and terminated ∼10 km west of the present DST. During the Miocene it propagated in the same direction and includes internal volcanic activity. The numerous Miocene-Pliocene volcanic centers on the margins of the DST indicate that the preferred pathway for magmas at that time was not within the deep basins of the DST. 相似文献
2.
Characteristics of gravity anomalies and prediction of volcanosedimentary boron deposit distribution in the Xiongba area,Tibet 总被引：1，自引：0，他引：1
Volcanosedimentary boron deposits are present within Tertiary lacustrine sediments and volcanic rocks in Xiongba, Tibet. Boron deposits are characterized by low density relative to country rocks; thus, it is possible to locate them by gravity measurements. We conducted a 1:50000 high-precision gravity survey in the Xiongba area, Tibet, and obtained the Bouguer and residual gravity anomalies. We analyzed fault systems and the distribution of sedimentary and volcanic rocks and their relation to the volcanosedimentary boron deposits. The processing of the gravity data revealed local gravity variations and fault structures. We applied preferential downward continuation and wavelet transform to the gravity data, and in conjunction with geological data, we predicted the distribution of volcanosedimentary boron deposits. 相似文献
3.
From our interpretation of the Bouguer gravity and aeromagnetic anomalies in south-east Scotland, we conclude that a massive granite batholith underlies the greater part of the eastern Southern Uplands. The granite model which we computed earlier from gravity anomalies in the Tweeddale area fits the observed magnetic anomalies closely, if a normal magnetization of 0.095 A m–1 is assigned, similar to values found for exposed local granites. Further gravity modelling shows that, apart from the Tweeddale boss, the granite shallows to less than 1 km near Lammer Law in East Lothian and extends north of the Lammermuir Fault. A model for the East Lothian volcanics was computed from their aeromagnetic anomalies, then their gravitational effect was combined with that estimated for the Devonian and Carboniferous sediments and the result stripped off the observed gravity field. The residual gravity anomalies were used to generate a two-dimensional model for the granite north of the Lammermuir Fault. The expected tectonic consequences of a massive granite batholith in the eastern Southern Uplands are compared with the known development of faults and sedimentary basins around its margins. 相似文献
4.
A land gravity survey of the Aeolian volcanic arc, including 235 measurament points, has shown the occurrence of Bouguer gravity lows related to each island, except Panarea. As Bouguer anomalies of the southern Tyrrhenian sea are only slightly disturbed by the Aeolian arc, the anomalies found in the present survey are generally due to shallow causes. These lows can be ascribed to the effect of low density superficial volcanics thickening in correspondence of each volcano. For Vulcano-Lipari and Stromboli the occurrence of a shallow magmatic reservoir can be a concomitant cause. The Bouguer high related to Panarea and associated islets indicates shallow high density masses, probably solidified within a magmatic pipe. 相似文献
5.
A useful tool to elucidate past tectonic environments is the geochemistry of volcanic and sedimentary rocks when used together.The regional structural setting of the Oman Mountains indicates that deep-water sediments and volcanic rocks formed adjacent to the rifted Arabian margin in the Late Triassic near the axis of a narrow ocean basin of Red Sea-type. Tholeiitic to trachytic extrusives formed seamounts associated with Late Triassic reefal build-ups. “Immobile” trace element compositions point to a within-plate origin. The interbedded and overlying Late Triassic deep-sea sedimentary cover comprises ribbon radiolarites and both distal siliclastic and calcareous turbidites that accumulated on an abyssal plain at least ca. 180 km northeast of the Arabian continent. Associated ferromanganiferous oxide-sediments are interpreted as chemical precipitates derived from high-temperature vents in the spreading axis of the young ocean basin. Pervasive regional subsidence took place during end Triassic/Early Jurassic time.Later, in the Cretaceous, oceanic crust was consumed in a northeast-dipping subduction zone. MORB-type crust was subducted while Late Triassic volcanic edifices and sedimentary cover were accreted. During eventual trench-margin collision the Semail ophiolite split into blocks allowing sub-ophiolite melange rocks to be expelled upwards through corridors, creating the Batinah Melange. As the ophiolite nappe ploughed inboard over already thrust-assembled abyssal plain sediments (Hawasina Complex), some duplexes were uplifted, oversteepened, overturned and then slid backwards onto the ophiolite to form the Batinah Sheets. 相似文献
6.
Lei SHAO Chuanlian LIU and Karl STATTEGGER Laboratory of Marine Geology Tongji University Shanghai China E-mail: lshaok@online.sh.cn Institute of Geoscience University of Kiel Germany 《国际泥沙研究》2001,16(4)
1 INTRODUCnONThe comPonents of terrigenous sedimenop rocks indicate not only provenance information, but alsotoctOnic evolution of basin. The chdrical composition of the soure rOCks is probaby the major conttDon the chendstry of sedimentny rocks although this can be greaily modified by subsequent Processes(Rollinson l993). Thus, through exndning Petrological and chendcal comPosihons of tenigenoussedlinmp rocks, the comPonentS of the provenance or somee rOCks - which are conunnly a fun… 相似文献
7.
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
8.
Remelting of subducted continental lithosphere: Petrogenesis of Mesozoic magmatic rocks in the Dabie-Sulu orogenic belt 总被引：7，自引：0，他引：7
The Dabie-Sulu orogenic belt was formed by the Triassic continental collision between the South China Block and the North China Block. There is a large area of Mesozoic magmatic rocks along this orogenic belt, with emplacement ages mainly at Late Triassic, Late Jurassic and Early Cretaceous. The Late Triassic alkaline rocks and the Late Jurassic granitoids only crop out in the eastern part of the Sulu orogen, whereas the Early Cretaceous magmatic rocks occur as massive granitoids, sporadic intermedi- ate-ma... 相似文献
9.
基于EGM2008重力场模型计算获得了渭河盆地及邻区布格重力异常。采用小波多尺度分解方法对布格重力异常进行了4阶小波逼近和小波细节分解,同时基于平均径向对数功率谱方法定量化地计算出1~4阶小波细节和小波逼近所对应的场源平均埋深。结合区域地质和地震资料,对获得的重力场结果进行分析,得到如下结论:①鄂尔多斯地块、渭河盆地、秦岭造山带3个一级构造单元的布格重力异常之间存在明显差异;构造区内部重力异常也存在横向的显著差异。布格重力异常的走向、规模、分布特征与二级构造区及主要的断裂具有一定的对应关系。②渭河盆地及邻区布格重力异常1~4阶细节对应4~23 km不同深度的场源信息,鄂尔多斯地块南缘东、西部的地壳结构存在明显的差异;渭河盆地凹陷、凸起构造区边界清晰,断裂边界与重力异常边界具有较好的一致性;秦岭造山带重力异常连贯性不好,东、西部重力异常变化特征表现出明显的差异。③渭河盆地及邻区布格重力异常分布与莫霍面埋深具有非常明显的镜像关系。渭河盆地及邻区地震主要分布在六盘山—陇县—宝鸡断裂带、渭河断裂与渭南塬前断裂交汇处、韩城断裂与双泉—临猗断裂交汇处。渭河盆地及邻区重力异常主要由中上地壳剩余密度体所影响,这可能是该区地震以浅源地震为主的主要原因。 相似文献
10.
《Journal of Geodynamics》2003,35(1-2):209-220
The occurrence of swarm earthquakes in the Vogtland/NW-Bohemia area results probably from the physical interactions of fluids, the stress field and the geometry of the geological units. Therefore the present study aims at the development of a 3-D density model of the region with a vertical range of 35 km. A new Bouguer anomaly map is presented containing about 17 000 gravity data points. Prominent Bouguer anomalies are produced by the granites of Eibenstock and Karlovy Vary (low with −75 mGal), the metabasites near Mariánzké Lázně (high with 5 mGal) and the Münchberg Gneiss Massif (gravity high of Hof with 10 mGal). The geometry of the internal model structures correspond to geological units and, thus, the modelled gravity fits well the observed Bouguer anomaly. The 3-D gravimetric modellings indicate detailed geometries of the geological settings. With regard to the periodic occurrence of swarm earthquakes in the Vogtland region the existence of an upwelling mantle or a magmatic body is investigated. Precise information only can be given, if the vertical extension of the near surface bodies is known. 相似文献
11.
Pedro Del Río Antonio Casas Juan J. Villalaín Tania Mochales Ruth Soto Belén Oliva-Urcia 《Studia Geophysica et Geodaetica》2013,57(3):442-459
Outstanding potential field anomalies (gravimetric and magnetic) in the Cameros Basin (N Spain) follow a WNW-ESE trend, parallel to the geological structures resulting from Mesozoic extension and Tertiary basin inversion. The positive Bouguer gravity anomaly (15 mGal) is interpreted as the result of a strong contrast between the density of Tertiary rocks of the foreland basin and the Paleozoic and Mesozoic rocks, combined with crustal thickening in the Iberian Chain with respect to the Ebro Basin. The dipolar magnetic anomaly, slightly shifted to the south with respect to the relative maximum of the Bouguer anomaly, can be interpreted as related to volcanic rocks within the basement, which are linked to Triassic rifting as witnessed by outcrops of basalts along the basin margins. An exhaustive analysis of rock properties (density, magnetic susceptibility and remanence) and basin geometry from other sources (seismic reflection profiles) allow to constrain variations in crustal thickness and the location of large-scale basement faults. 相似文献
12.
火山沉积型硼矿形成于新近纪特定的火山+湖相沉积环境条件下,含硼地层具有含硼湖相沉积岩与凝灰岩、安山岩等火山岩互层的多旋回二元沉积结构的特点.由于硼酸盐矿物的沉积发生多在沉积后期,通常与凝灰岩、粘土、灰岩等互层沉积,因此形成的硼矿层具有低密度、低电阻率的特征.针对硼矿层的这种特征,采用综合地球物理技术进行探测.在西藏雄巴地区,首先进行了1:5万高精度重力勘探,获得了研究区的布格重力异常,通过对重力资料的处理分析,获取了研究区的断裂构造发育和重力异常变化,推断了地下地层岩性空间变化特点并圈定出火山沉积型硼矿的发育有利区;在此基础上对有利区域进行了1:5000音频大地电磁测深,获得了研究区地下地层电性结构特征.通过对研究区电法数据的震电拟合及重力和大地电磁资料联合反演并与研究区地质资料相结合,进一步分析了该区地层构造、断裂体系、沉积单元与火山沉积型硼矿的形成关系,并对该区火山沉积型硼矿的分布进行了预测,最终钻探验证结果与预测结果基本一致. 相似文献
13.
南海位于太平洋板块、印澳板块和欧亚板块交汇处,自晚中生代以来历经张裂作用、海底扩张以及印藏碰撞、菲律宾海板块西向运动等构造事件的叠加改造,不仅形成了复杂多样的构造格局,而且堆积了厚薄不均的沉积层.为了考察沉积层密度改正对利用重力资料分析南海不同尺度构造特征的影响,本文利用南海各区域不同深度沉积层的地震波速度及钻孔密度等数据,建立了沉积层与沉积基底密度差随深度变化的二次函数关系式,并基于该关系式,计算了南海沉积层相对基底密度低而产生的重力异常值.结果显示,南海沉积层的重力异常值在海盆区介于-40~-60 mGal,而在堆积巨厚沉积物的莺歌海盆地可达到-135 mGal;相对于空间重力异常、布格重力异常,经沉积层重力异常改正后的地壳布格重力异常更能突出深部不同尺度的密度结构和莫霍面的起伏特征,其总水平导数模更突显了南海西北部红河断裂带的海上延伸;利用谱分析技术估算岩石圈强度时,经沉积层重力异常改正的地壳布格重力异常数据获得的岩石圈有效弹性厚度值更为符合地质实际,特别是在长条形的巨厚沉积区如莺歌海盆地和马来盆地.分析表明,重力异常的沉积层密度改正对揭示南海构造特征具有重要的意义. 相似文献
14.
通过对东海陆架盆地西部地震和重磁资料的综合地球物理解释,对雁荡低凸起展布形态进行了细致刻画,凸起呈NE方向不连续展布于瓯江凹陷和闽江凹陷之间,长约170 km、宽约15~50 km.地震资料揭示雁荡低凸起上广泛发育了侏罗纪与白垩纪地层,厚度约为500~1500 m,展布面积约5000 km2,局部缺失中生界地层.凸起两侧中生代盆地结构差异明显,西侧瓯江凹陷为典型的断陷盆地,东断西超、断裂发育,半地堑、掀斜断块等中生界构造样式发育;东侧闽江凹陷为坳陷型盆地,断裂、火成岩不发育,挤压背斜、断背斜、反转构造等中生界构造样式发育.自由空间重力异常图与剩余重力异常图上,凸起表现为一系列NE向团块状重力高值区,而磁力异常ΔT图上则表现为深部磁场强度低的特征,火成岩影响部位可见磁力高值异常.综合凸起及邻域重磁震、莫霍面深度等地质地球物理资料,认为雁荡低凸起为一元古界组成的古隆起,区别于东部的台北低凸起.同时,结合区域构造演化及沉积特征,推测侏罗纪时期雁荡低凸起与浙闽隆起区可能连为一体,晚白垩世近东西向伸展作用下浙闽隆起发生裂陷进而形成了雁荡低凸起. 相似文献
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16.
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
17.
Deformation of the Circum-Rhodope Belt Mesozoic (Middle Triassic to earliest Lower Cretaceous) low-grade schists underneath an arc-related ophiolitic magmatic suite and associated sedimentary successions in the eastern Rhodope-Thrace region occurred as a two-episode tectonic process: (i) Late Jurassic deformation of arc to margin units resulting from the eastern Rhodope-Evros arc–Rhodope terrane continental margin collision and accretion to that margin, and (ii) Middle Eocene deformation related to the Tertiary crustal extension and final collision resulting in the closure of the Vardar ocean south of the Rhodope terrane. The first deformational event D1 is expressed by Late Jurassic NW-N vergent fold generations and the main and subsidiary planar-linear structures. Although overprinting, these structural elements depict uniform bulk north-directed thrust kinematics and are geometrically compatible with the increments of progressive deformation that develops in same greenschist-facies metamorphic grade. It followed the Early-Middle Jurassic magmatic evolution of the eastern Rhodope-Evros arc established on the upper plate of the southward subducting Maliac-Meliata oceanic lithosphere that established the Vardar Ocean in a supra-subduction back-arc setting. This first event resulted in the thrust-related tectonic emplacement of the Mesozoic schists in a supra-crustal level onto the Rhodope continental margin. This Late Jurassic-Early Cretaceous tectonic event related to N-vergent Balkan orogeny is well-constrained by geochronological data and traced at a regional-scale within distinct units of the Carpatho-Balkan Belt. Following subduction reversal towards the north whereby the Vardar Ocean was subducted beneath the Rhodope margin by latest Cretaceous times, the low-grade schists aquired a new position in the upper plate, and hence, the Mesozoic schists are lacking the Cretaceous S-directed tectono-metamorphic episode whose effects are widespread in the underlying high-grade basement. The subduction of the remnant Vardar Ocean located behind the colliding arc since the middle Cretaceous was responsible for its ultimate closure, Early Tertiary collision with the Pelagonian block and extension in the region caused the extensional collapse related to the second deformational event D2. This extensional episode was experienced passively by the Mesozoic schists located in the hanging wall of the extensional detachments in Eocene times. It resulted in NE-SW oriented open folds representing corrugation antiforms of the extensional detachment surfaces, brittle faulting and burial history beneath thick Eocene sediments as indicated by 42.1–39.7 Ma 40Ar/39Ar mica plateau ages obtained in the study. The results provide structural constraints for the involvement components of Jurassic paleo-subduction zone in a Late Jurassic arc-continental margin collisional history that contributed to accretion-related crustal growth of the Rhodope terrane. 相似文献
18.
Hakim Gabtni Chokri Jallouli Kevin Mickus Hédi Zouari Mohamed Moncef Turki 《Pure and Applied Geophysics》2005,162(11):2051-2069
Gravity data, integrated with seismic refraction/reflection data, well data and geological investigations, were used to determine the location of the paleogeographic boundary between the Precambrian Saharan domain and the younger Tunisian Atlas domain. This boundary (North Saharan Flexure or NSF) has not been as clearly defined as it has been to the west in Algeria and Morocco. The gravity data analysis, which included the construction of complete Bouguer and residual gravity anomaly maps, revealed that the Atlasic domain is characterized by relative negative gravity anomalies and numerous linear gravity trends implying a thick and deformed sediment cover. The Saharan domain is characterized by relatively positive gravity anomalies with few gravity trends implying a thin and relatively undeformed sediment cover. An edge-enhancement analysis of the residual gravity anomalies revealed that the NSF is characterized by a series of discontinuous east- and northwest-trending linear anomalies south of 34°N that are not related to the well-known faults within the Gafsa and Accident de Medenine regions. Based on the continuity of the amplitudes of seismic reflection data and the trends of the residual gravity anomalies, the NSF is not an abrupt discontinuity but a series of step faults dipping toward the Atlasic domain. To obtain a more quantitative representation of the southern edge of Tunisian Atlas, a regional gravity model constrained by two wells and seismic reflection/refraction data was constructed along a north-south trending profile which confirms the presence of thicker sediments north of the NSF. Our analysis shows that the NSF has controlled the depositional environment of the sedimentary rocks within the region since at least Triassic time and has acted as a barrier to Atlasic deformation south of the NSF. The NSF is considered an important tectonic feature that has controlled the paleogeographic evolution of the southern margin of the Tethys Ocean, and it continues to be active today based on seismicity hazard studies. 相似文献
19.
长期以来,对内蒙古贺根山缝合带中的镁铁-超镁铁岩,有着"蛇绿岩"、"岩浆岩"、"幔源熔-流体"等不同认识.近年来在铬铁矿中发现了金刚石等深部地幔矿物,如何认识携带这些物质的幔源熔-流体的上涌?缝合带在镁铁-超镁铁岩的形成过程中起到什么作用?解决问题的关键之一是弄清镁铁-超镁铁岩的深部产状,这需要来自地球物理观测数据的依据.本文基于航磁和重力数据的研究表明,贺根山地区的蛇绿岩块均呈现高磁异常特征,其中贺根山岩块埋深明显大于其他岩块,表现为高磁异常与低重力异常,与地表出露的蛇纹石化的镁铁-超镁铁岩带对应.对航磁化极异常与布格重力异常数据做了向上延拓处理,进行了磁源形态及底界深度的估算,并利用基于相异度算子的边缘增强方法辅助识别断裂.结果表明,贺根山岩块贯穿地壳,且附近存在超壳断裂.地表至中地壳主要由蛇纹石化的镁铁-超镁铁岩组成,下地壳主要为超镁铁质岩组成,它们充填在一组宽约30km的NEE向断裂带中,大地电磁测深剖面揭示的壳-幔电性结构进一步证实控制缝合带的是岩石圈断裂,贺根山缝合带具有明显的根部.由此推测,在地幔底辟上涌的背景下,幔源熔-流体沿着岩石圈断裂持续上升到达浅表,暗示该区板块的拼合可能是通过深部幔源物质的侵入而成的. 相似文献
20.
Two volcanic cycles can be distinguished, in the Pontid magmatic arc. They comprise an Upper Cretaceous, Lower Volcanic Cycle of which only the waning stage contains abundant pyroclastic rocks. The latter show spatial association to the fault pattern and are closely related to mineralisation. The overlying, early Tertiary, Upper Volcanic Cycle shows evidence of explosive vulcanicity in the Upper Basic Series. Dacites and rhyodacites are only locally developed and again show spatial association with the faulting.Comparison of the major and minor element chemistries of the two cycles demonstrates the clear separation into a lower tholeiitic and an upper calc-alkaline cycle. The rocks show similar chemistry to volcanic suites from island arcs in other areas.The origin of the tholeiitic magma is ascribed to melting of “dry” amphibolite during early subduction of Tethyan ocean floor beneath “Pontian Land”. This resulted in low K abundances and K/Rb ratios, and some Fe enrichment in the tholeiitic basalts.The calc-alkaline magma is thought to be derived from a later stage in the subduction process when melting of amphibole was joined by melting of biotite or phlogopite. The Upper Volcanic Cycle is thus enriched in K and shows no Fe enrichment due to a probable higher water content. The higher Cr and Ni contents of the Upper Volcanic Cycle, together with K, may imply some melting of lherzolite overlying the subducted slab. 相似文献