Petrology and Geochemistry of the Volcanic Rocks Dredged from the Geophysicist Seamount in the Kurile Basin: Evidence for the Existence of Thinned Continental Crust     

Igor A. Tararin  Eugeniy P. Lelikov  Reinhard Werner 《Gondwana Research》2003,6(4):757-765

Dredged samples from the Geophysicist seamount volcano in the northeastern part of the Kurile Basin include volcanic and volcanoclastic rocks ranging from basalt to andesite. The rocks have geochemical features typical of high-K island-arc calc-alkaline volcanism. They are enriched in LILE and depleted in Zr, Ti, Nb, Ta and Y. The chondrite-normalized REE patterns are characterized by enrichment of LREE similar to those of island-arc lava from the submarine volcanoes of rear-arc zone of the Kurile Island Arc. The volcanic rocks have a wide range of ⁸⁷Sr/⁸⁶Sr ratios (0.70287-0.70652), varying ¹⁴³Nd/¹⁴⁴Nd and Pb isotopic ratios. Their trace-element compositions and Sr-Nd-Pb isotope signatures may be explained by a small addition of crustal continental component to mantle-derived magmas that suggest the existence of thinned continental basement under the eastern part of the Kurile Basin.  相似文献   

Flexure of the Indian plate and intraplate earthquakes   总被引：2，自引：0，他引：2  

Roger Bilham  Rebecca Bendick  Kali Wallace 《Journal of Earth System Science》2003,112(3):315-329

The flexural bulge in central India resulting from India's collision with Tibet has a wavelength of approximately 670 km. It is manifest topographically and in the free-air gravity anomaly and the geoid. Calculations of the stress distribution within a flexed Indian plate reveal spatial variations throughout the depth of the plate and also a function of distance from the Himalaya. The wavelength (and therefore local gradient) of stress variation is a function of the effective elastic thickness of the plate, estimates of which have been proposed to lie in the range 40–120 km. The imposition of this stress field on the northward moving Indian plate appears fundamental to explaining the current distribution of intraplate earthquakes and their mechanisms. The current study highlights an outer trough south of the flexural bulge in central India where surface stresses are double the contiguous compressional stresses to the north and south. The Bhuj, Latur and Koyna earthquakes and numerous other recent reverse faulting events occurred in this compressional setting. The N/S spatial gradient of stress exceeds 2 bars/km near the flexural bulge. The overall flexural stress distribution provides a physical basis for earthquake hazard mapping and suggests that areas of central India where no historic earthquakes are recorded may yet be the locus of future damaging events.  相似文献   

中国大陆地震构造研究回顾          下载免费PDF全文

王椿镛  刘琼林 《地震学报》2003,25(5):503-511

简要回顾了近4年来(1999～2002年)我国在地震构造方面研究的进展，重点介绍了在地壳上地幔结构、活动断裂和大地震构造背景、地壳形变和数值模拟方面的工作．在我国境内发生的绝大多数地震都属于大陆地震的范畴，因此,中国地震学家把研究的重点放在大陆地震上．中国在九五期间完成的中国数字地震观测系统和中国地壳运动观测网络重大科学工程为地震构造的研究提供了大量的基础资料．因此，４年来的地震构造研究取得了相当大的进展．   相似文献   

华北地台北缘西段铜多金属矿床的热水沉积成因   总被引：3，自引：0，他引：3  

金章东  李英 《西北地质科学》1997,18(2):54-62

早元古代后狼山成矿区和于陆缘拉张拗陷阶段，一直延续至晚元古代末期。狼山群食矿岩系中存在的限层变基性火山岩，热水沉积岩和条纹条带状构造，胶状构造均显示狼山成矿区在１８００－９５０Ｍａ期间处于高地热异常的被动大陆边缘。  相似文献   

The Origin of the Early Proterozoic Kuandian Complex: Evidence from Geochemistry   总被引：3，自引：0，他引：3  

Zhang Lifei  Sun Min  Wu Jiahong Department of Geology  Peking University  Beijing Department of Earth Sciences  University of Hong Kong  Hong Kong Shenyang Institute of Geology  Mineral Resources  CAGS  Shenyang Liaoning Liu Xinzhu 《《地质学报》英文版》1997,71(1):15-32

The Kuandian Complex is scarcely preserved Early Proterozoic volcanic suite, formed2.3-2.4 Ga ago. It is located in an Early Proterozoic mobile belt bounded by the ArchaeanRangrim and Ryonggang Blocks of the northeastern Sino-Korean Craton. The Complex ismainly made up of amphibolites, gneisses, leucoleptite, leptite and layered granite. Petrologicaland geochemical studies show that the protoliths of the Complex are mainly assoctations ofbimodal volcanics and anorogenic granites. The Kuandian amphibolites are depleted in Nb, Ta,P and Ti, and enriched in LILE, e.g. K, Rb and Cs, with pronounced depletion of Sr relative toNd and Pb; La/Nb ratios are higher than 1(1.75 to 5.18). The trace element patterns of theamphibolites are similar to continental flood basalts formed by the Gondwana break-up, suchas those in South Karoo and Tasmania, which shows continental contamination. ε_(Nd) valuesranging from 0.70 to 1.94 of the Kuandian amphibolites and the relationships between Nb/Yband La/Yb suggest that contamination of basaltic magma happened in the mantle, rather thanalong the conduit. Isotope ratios of ~(208)Pb/~(204)Pb, ~(207)Pb/ ~(204)Pb, ~(206)Pb/~(204)Pb, ~(143)Nd/~(144)Ndand ~(87)Sr/~(86)Sr indicate that the magma was derived from a contaminated mantle source likeDMM or a mixture of DMM and EM2. The Kuandian Complex has Dupal anomaly, as is thecase with some continental basalts in the south hemisphere, e.g. in South Karoo and Tasmania.Petrochemical modelling proposes that the Kuandian gneiss, granite, and amphibolite camefrom the same parental magma, being products of strong fractional crystallization. Protoliths ofthe Kuandian Complex were formed in extensional tectonic setting during the transition fromcontinental crust to oceanic crust. The formation of the Kuandian Complex indicates that 2.3or 2.4 Ga ago tectonic evolution of the Sino-Korean craton was different from that of otherwell-studied Precambrian cratons, e.g. the North American shield, European platform andAustralian continent in that strong volcanic eruption resulted in its accretion. Besides, the con-taminated magma source with a Dupal anomaly for the Complex indicates that crust-mantleconvection whose scale was similar to that of the present plate tectonics had occurred at leastbefore the formation of the Kuandian Complex (2.3-2.4 Ga B.P).  相似文献   

中国北方超大型热水沉积硫化物矿床成矿模式   总被引：4，自引：0，他引：4  

李英  祁思敬 《矿物岩石地球化学通报》1997,(3)

中国北方超大型热水沉积硫化物矿床成矿模式李英祁思敬（西安地质学院，西安７１００５４）关键词超大型矿床热水沉积作用大陆边缘盆地热旋回中国北方超大型热水沉积硫化物矿床（ＳＥＤＥＸ）集中产出于华北地台北缘西段与扬子地台北缘西段，即秦岭与狼山两区。可确定的矿...  相似文献   

秦岭造山带基本组成与结构及其构造演化   总被引：51，自引：7，他引：51  

张国伟  董云鹏  姚安平 《陕西地质》1997,(2)

秦岭造山带主要由三大套构造岩石地层单元组成，经历了三个主要演化阶段：1．前寒武纪古老基底形成演化阶段，2．主造山期（Pt3—T2）板块构造演化阶段，3．中新生代陆内构造演化阶段。在早中元古代以扩张构造体制占主导，形成裂谷与小洋盆兼杂并存的基本构造格局，经10—8亿年晋宁期从扩张垂向加积增生构造体制为主向以侧向增生为主的板块构造体制的过渡，于晚元古代中晚期开始进入板块构造演化阶段。在晚古生代早期由于东古特提斯洋的形成，扬子板块北缘沿秦岭南部扩张打开，形成华北板块、扬子板块及其间的秦岭微板块，沿商丹和勉略二缝合带自南向北俯冲消减碰撞，于中三叠世最后全面陆陆碰撞造山，而后又发生了强烈陆内造山作用，终成今日之秦岭山脉面貌。现今的秦岭造山带岩石圈结构是一正在调整演化中的具流变学分层的“立交桥式”三维结构，上部地壳呈多层逆冲推覆迭置的不对称扇形几何学模式，岩石圈中部则是成水平状流变层，而深部地幔则是最新调整的近南北向的地球物理异常状态与结构，形成从下到上构造方向近乎正交的圈层非耦合关系。  相似文献   

The effects of the spinel—garnet phase transition on the formation of rifted sedimentary basins     

Tadashi Yamasaki  Masao Nakada 《Geophysical Journal International》1997,130(3):681-692

We have examined the effects of the spinel-garnet phase transition on subsidence of extensional sedimentary basins. For a constant positive Clapeyron slope ( dP/dT ), the phase boundary moves downwards in the syn-rift and upwards in the post-rift phase. For a non-linear Clapeyron curve ( dP/dT > 0 above 900°C and dP/dT < 0 below 900°C), theory predicts for the reaction of the spinel-garnet phase transition, the direction of phase boundary movement is dependent on the stretching factor, the position of the Clapeyron curve and the lithospheric thickness. A smaller syn-rift and larger post-rift subsidence are predicted for a deeper phase boundary and a thicker lithosphere. The model with a non-linear Clapeyron curve is applied to the subsidence histories of a young extensional basin (Gulf of Lion) and an old continental margin (eastern Canada). The observed syn-rift uplift and the larger post-rift subsidence can be reasonably explained by this model, where the optimum depth of the phase boundary for eastern Canada (˜90 km) is consistent with the estimate from seismic observations and is larger than that for the Gulf of Lion (˜ 50 km). The depth of the spinel-garnet phase boundary is sensitive to the composition of mantle rocks and increases with the extraction of basaltic components from the lithosphere, compatible with our result that the phase boundary is deeper for an older and thicker lithosphere. Thus the surface movement associated with the rifting for these areas may reflect the chemical evolution of the continental lithosphere.  相似文献   

Ccte d'Ivoire-Ghana margin: seismic imaging of passive rifted crust adjacent to a transform continental margin     

C. Peirce  R. B. Whitmarsh  R. A. Scrutton  B. Pontoise  F. Sage  J. Mascle 《Geophysical Journal International》1996,125(3):781-795

During May 1990 and January-February 1991, an extensive geophysical data set was collected over the Côte d'Ivoire-Ghana continental margin, located along the equatorial coast of West Africa. The Ghana margin is a transform continental margin running subparallel to the Romanche Fracture Zone and its associated marginal ridge—the Côte d'Ivoire-Ghana Ridge. From this data set, an explosive refraction line running ∼ 150 km, ENE-WSW between 3°55'N, 3°21'W and 4°23'N, 2°4'W, has been modelled together with wide-angle airgun profiles, and seismic reflection and gravity data. This study is centred on the Côte d'Ivoire Basin located just to the north of the Côte d'Ivoire-Ghana Ridge, where bathymetric data suggest that a component of normal rifting occurred, rather than the transform motion observed along the majority of the equatorial West African margin.
Traveltime and amplitude modelling of the ocean-bottom seismometer data shows that the continental Moho beneath the margin rises in an oceanward direction, from ∼ 24 km below sea level to ∼ 17 km. In the centre of the line where the crust thins most rapidly, there exists a region of anomalously high velocity at the base of the crust, reaching some 8 km in thickness. This higher-velocity region is thought to represent an area of localized underplating related to rifting. Modelling of marine gravity data, collected coincident with the seismic line, has been used to test the best-fitting seismic model. This modelling has shown that the observed free-air anomaly is dominated by the effects of crustal thickness, and that a region of higher density is required at the base of the crust to fit the observed data. This higher-density region is consistent in size and location with the high velocities required to fit the seismic data.  相似文献   

The S reflector west of Galicia: the seismic signature of a detachment fault     

T. J. Reston 《Geophysical Journal International》1996,127(1):230-244

The so-called S reflector is a group of bright, continuous reflections underlying the landward-tilted fault blocks of the west Galicia rifted margin, S has been interpreted as the brittle-ductile transition, the lop of an intrusion, a detachment fault, and the crust-mantle boundary. To constrain the internal structure of the reflector, we have carried out detailed analyses of these reflections. We compare the waveforms of the seafloor reflection and its first multiple, both to determine the amplitude of the seafloor reflection and to show (hat the seafloor is in effect a spike in the reflectivity series so that the seafloor reflection can be used as the far-field wavelet, including both source and receiver ghosts. We compare (he waveform of the seafloor and 5 and show that, within the resolution of our data, S is a reflection from a step increase in acoustic impedance. This result is confirmed through complex trace analysis, and in particular the determination of the apparent polarity of S, and the examination of the instantaneous frequency function: S is consistently positive polarity, and shows no significant frequency anomaly. Simple modelling shows that S is very unlikely to be a reflection from a thin layer. We thus conclude that S is probably a single steplike interface. From the varying frequency content of the data, we determine a value for the effective Q between S and the seafloor, and use this to assess the amplitude loss due to attenuation and scattering. We use a comparison between the seafloor and the S reflection to constrain the amplitude of S, and estimate a reflection coefficient for S of at least 0.2 in places, decreasing landwards. By analogy with structures developed in the highly extended regions of the western United States, we consider that the most likely interpretation of S is as a sharp west-dipping detachment fault separating a 'granitic' upper plate from a higher-velocity lower plate, locally probably serpentinized mantle.  相似文献