Structure and evolution of the eastern Gulf of Aden conjugate margins from seismic reflection data   总被引：2，自引：0，他引：2  

Elia d'Acremont  Sylvie Leroy  Marie-Odile Beslier  Nicolas Bellahsen  Marc Fournier  Cécile Robin  Marcia Maia  Pascal Gente 《Geophysical Journal International》2005,160(3):869-890

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V_p/V_s ratio along the Vøring Margin, NE Atlantic, derived from OBS data: implications on lithology and stress field     

R. Mjelde  T. Raum  P. Digranes  H. Shimamura  H. Shiobara  S. Kodaira   《Tectonophysics》2003,369(3-4):175-197

A total of 13 regional Ocean Bottom Seismograph (OBS) profiles with an accumulated length of 2207 km acquired on the Vøring Margin, NE Atlantic have been travel time modelled with regards to S-waves. The V_p/V_s ratios are found to decrease with depth through the Tertiary layers, which is attributed to increased compaction and consolidation of the rocks. The V_p/V_s ratio in the intra-Campanian to mid-Campanian layer (1.75–1.8) in the central Vøring Basin is significantly lower than for the layers above and beneath, suggesting higher sand/shale ratio. This layer was confirmed by drilling to represent a layer of sandstone. This mid-Cretaceous ‘anomaly’ is also present in the northern Vøring Basin, as well as on the southern Lofoten Margin further north. The V_p/V_s ratio in the extrusive rocks on the Vøring Plateau is estimated to be 1.85, conformable with mafic (basaltic) rocks. Landward of the continent/ocean transition (COT), the V_p/V_s ratio in the layer beneath the volcanics is estimated to be 1.67–1.75. These low values suggest that this layer represents sedimentary rocks, and that the sand/shale ratio might be relatively high here. The V_p/V_s ratio in the crystalline basement is estimated to be 1.67–1.75 in the basin and on the landward part of the Vøring Plateau, indicating the presence of granitic/granodioritic continental crust. In the lower crust, the V_p/V_s ratio in the basin decreases uniformly from southwest to northeast, from 1.85–1.9 to 1.68–1.73, suggesting a gradual change from mafic (gabbroic) to felsic (granodioritic) lower crust. Significant (3–5%) azimuthal S-wave anisotropy is observed for several sedimentary layers, as well as in the lower crust. All these observations can be explained by invoking the presence of liquid-filled microcracks aligned vertically along the direction of the present day maximum compressive stress (NW–SE).  相似文献   

The nature and distribution of bottom simulating reflectors at the Costa Rican convergent margin   总被引：5，自引：0，他引：5  

Ingo A. Pecher  Cesar R. Ranero  Roland von Huene  Timothy A. Minshull  & Satish C. Singh 《Geophysical Journal International》1998,133(2):219-229

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Passive and active margin history of the northern Tatricum (Western Carpathians,Slovakia)     

D. Plašienka 《International Journal of Earth Sciences》1995,84(4):748-760

The Tatricum, an upper crustal thrust sheet of the Central Western Carpathians, comprises pre-Alpine crystalline basement and a Late Paleozoic-Mesozoic sedimentary cover. The sedimentary record indicates gradual subsidence during the Triassic, Early Jurassic initial rifting, a Jurassic-Early Cretaceous extensional tectonic regime with episodic rifting events and thermal subsidence periods, and Middle Cretaceous overall flexural subsidence in front of the orogenic wedge prograding from the hinterland. Passive rifting led to the separation of the Central Carpathian realm from the North European Platform. A passive margin, rimmed by peripheral half-graben, was formed along the northern Tatric edge, facing the Vahic (South Penninic) oceanic domain. The passive versus active margin inversion occurred during the Senonian, when the Vahic ocean began to be consumed southwards below the Tatricum. It is argued that passive to active margin conversion is an integral part of the general shortening polarity of the Western Carpathians during the Mesozoic that lacks features of an independent Wilson cycle. An attempt is presented to explain all the crustal deformation by one principal driving force - the south-eastward slab pull generated by the subduction of the Meliatic (Triassic-Jurassic Tethys) oceanic lithosphere followed by the subcrustal subduction of the continental mantle lithosphere.  相似文献   

武当山地区中上元古界及成岩构造环境的地球化学论证   总被引：1，自引：0，他引：1  

汪东波 《大地构造与成矿学》1991,15(3):255-264

通过对分布于武当山地区的中上元古界武当山群,耀岭河群的变火山岩、变沉积岩的岩石学、岩石化学,微量元素地球化学和稀土元素地球化学及有关图解的综合研究和应用,笔者认为武当山群的成岩环境为古岛弧,而耀岭河群的成岩环境为古陆缘裂谷。中晚元古代期间,武当山地区构造演化经历了从古岛弧向古陆缘裂谷转化的历程。  相似文献   

Denudation,isostasy and landscape evolution     

A. R. Gilchrist  M. A. Summerfield 《地球表面变化过程与地形》1991,16(6):555-562

The idea that the isostatic response to progressive denudational unloading can be episodic over cyclic timescales is widely cited in the geomorphological literature. We demonstrate, however, that this notion, which has been regarded as a possible mechanism of widespread landscape rejuvenation, is based on a fundamental misunderstanding of the principles of flexural isostasy. Rather than a discontinuous response, in cases where the half-width of the applied load is greater than a few tens of kilometres the lithosphere experiences a continuous compensation which is dependent upon the wavelength of the applied load rather than upon a lateral, or vertical, threshold of unloading which has to be exceeded before isostatic recovery is initiated. Although a flexural isostatic response cannot account for episodic uplift during a denudational cycle, it can explain the growth and persistence of significant marginal upwarps along passive margins across which there is a marked contrast in denudation rates. Such marginal upwarps, in turn, probably play a critical role in the long-term evolution of drainage systems and landscapes in adjacent continental hinterlands.  相似文献   

Palaeomagnetic confirmation of Palaeozoic clockwise rotation of the Famatina Ranges (NW Argentina): implications for the evolution of the SW margin of Gondwana     

C. M. Spagnuolo  A. E. Rapalini  R. A. Astini 《Geophysical Journal International》2008,173(1):63-78

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Demerara Plateau – the structure and evolution of a transform passive margin     

C. J. Greenroyd  C. Peirce  M. Rodger  A. B. Watts  R. W. Hobbs 《Geophysical Journal International》2008,172(2):549-564

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Three-dimensional gravity inversion for Moho depth at rifted continental margins incorporating a lithosphere thermal gravity anomaly correction   总被引：1，自引：0，他引：1  

A. R. Chappell  N. J. Kusznir 《Geophysical Journal International》2008,174(1):1-13

This paper describes a method for determining Moho depth, lithosphere thinning factor (γ= 1 − 1/β) and the location of the ocean–continent transition at rifted continental margins using 3-D gravity inversion which includes a correction for the large negative lithosphere thermal gravity anomaly within continental margin lithosphere. The lateral density changes caused by the elevated geotherm in thinned continental margin and adjacent ocean basin lithosphere produce a significant lithosphere thermal gravity anomaly which may be in excess of −100 mGal, and for which a correction must be made in order to determine Moho depth accurately from gravity inversion. We describe a method of iteratively calculating the lithosphere thermal gravity anomaly using a lithosphere thermal model to give the present-day temperature field from which we calculate the lithosphere thermal density and gravity anomalies. For continental margin lithosphere, the lithosphere thermal perturbation is calculated from the lithosphere thinning factor (γ= 1 − 1/β) obtained from crustal thinning determined by gravity inversion and breakup age for thermal re-equilibration time. For oceanic lithosphere, the lithosphere thermal model used to predict the lithosphere thermal gravity anomaly may be conditioned using ocean isochrons from plate reconstruction models to provide the age and location of oceanic lithosphere. A correction is made for crustal melt addition due to decompression melting during continental breakup and seafloor spreading. We investigate the sensitivity of the lithosphere thermal gravity anomaly and the predicted Moho depth from gravity inversion at continental rifted margins to the methods used to calculate and condition the lithosphere thermal model using both synthetic models and examples from the North Atlantic.  相似文献   

两种不同类型的活动大陆边缘及其动力学机制          下载免费PDF全文

胡桂明 《地质找矿论丛》2000,15(1):24-29

东、西太平洋存在压性和张性两种不同类型的活动大陆边缘。它们产出的地质特征表明,岩石圈相对地幔对流体,持续或幕式地向西滑移。其滑移机制,可从（地球）旋转体不同圈层之间存在不同的（旋转）动量矩得到解释。  相似文献