Resistivity Structure of the Central Indian Tectonic Zone (CITZ) from Multiple Magnetotelluric (MT) Profiles and Tectonic Implications     

K. K. Abdul Azeez  Martyn J. Unsworth  Prasanta K. Patro  T. Harinarayana  R. S. Sastry 《Pure and Applied Geophysics》2013,170(12):2231-2256

The Central Indian Tectonic Zone (CITZ) is a major tectonic feature extending across the Indian subcontinent. It was formed in the Paleoproterozoic when the Bastar Craton and the Bundelkhand Craton were sutured together. This region is recognized in the geological record as a persistent zone of weakness with many tectonothermal events occurring over geologic time. The weakness of this region may have caused the late Cretaceous/early Tertiary Deccan volcanism to have been localized in the CITZ. The zone is still tectonically active, as evidenced by sustained levels of seismic activity. This paper presents the first systematic investigation of the resistivity structure of the CITZ using multiple magnetotelluric (MT) transects. Two-dimensional (2D) resistivity models were generated for five north–south profiles that cross the CITZ and encompass an area of ~60,000 km². The models were based on the joint inversion of transverse electric (TE), transverse magnetic (TM) and tipper (Hz) data. All the profiles showed a low resistive (10–80 Ωm) middle to lower crust beneath the CITZ with a crustal conductance of 300–800 S. The presence of an interconnected fluid phase and/or hydrous/metallic minerals appears to be the most likely explanation for the elevated conductivity that is observed beneath the CITZ. The presence of fluids is significant because it may indicate the cause of persistent weakness at crustal depths. A northward dip of both the crustal conductive layer and coincident seismic reflections favor a northward polarity of the subduction process associated with the formation of the CITZ.  相似文献   

Use of daily precipitation uncertainties in streamflow simulation and forecast   总被引：3，自引：2，他引：1  

Yeonsang Hwang  Martyn P. Clark  Balaji Rajagopalan 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(7):957-972

Among other sources of uncertainties in hydrologic modeling, input uncertainty due to a sparse station network was tested. The authors tested impact of uncertainty in daily precipitation on streamflow forecasts. In order to test the impact, a distributed hydrologic model (PRMS, Precipitation Runoff Modeling System) was used in two hydrologically different basins (Animas basin at Durango, Colorado and Alapaha basin at Statenville, Georgia) to generate ensemble streamflows. The uncertainty in model inputs was characterized using ensembles of daily precipitation, which were designed to preserve spatial and temporal correlations in the precipitation observations. Generated ensemble flows in the two test basins clearly showed fundamental differences in the impact of input uncertainty. The flow ensemble showed wider range in Alapaha basin than the Animas basin. The wider range of streamflow ensembles in Alapaha basin was caused by both greater spatial variance in precipitation and shorter time lags between rainfall and runoff in this rainfall dominated basin. This ensemble streamflow generation framework was also applied to demonstrate example forecasts that could improve traditional ESP (Ensemble Streamflow Prediction) method.  相似文献   

Deep Structure Beneath the Southwestern Section of the Longmenshan Faults and Lushan Ms7.0 Earthquake on 20 April 2013     

ZHAN Yan  ZHAO Guoze  Martyn Unsworth  WANG Lifeng  CHEN Xiaobin  LI Tao  QIAO Qibin  WANG Jijun  TANG Ji  CAI Juntao  WANG Yuanzhao 《《地质学报》英文版》2013,87(Z1):421-424

  相似文献   

班公—怒江构造带的电性结构特征——大地电磁探测结果   总被引：8，自引：4，他引：4       下载免费PDF全文

金胜  魏文博  叶高峰  邓明  谭捍东  Martyn Unsworth 《地球物理学报》2009,52(10):2666-2675

对青藏高原过班公—怒江构造带的三条大地电磁剖面进行探测,获得班公—怒江构造带及其邻区的电性结构模型,研究了班公—怒江构造带的深部结构与构造特征.研究结果表明：构造带及其两侧上地壳内广泛分布不连续高阻体,反映了岩浆岩的空间分布特征,表明构造带南北两侧岩浆的活动规律可能存在较大差别.研究区内的冈底斯及羌塘地体的中、下地壳普遍发育高导层,反映了印度大陆碰撞、俯冲过程的效应与痕迹,而高导层之下的高阻块体则可能是向北俯冲、冷的、刚性的印度大陆地壳.羌塘地体的电性结构模型可以分为南北两个区段,南羌塘块体的壳内高导层与班公—怒江构造带对印度板块俯冲的阻挡作用有关;而北羌塘块体壳内高导层与亚洲大陆对印度板块向北俯冲的“阻挡”与向南“对冲”有关.印度板块向北的俯冲与挤入,受到班公—怒江构造带及亚洲板块的阻挡,可能没有越过班公—怒江构造带,并在班公—怒江构造带附近向下插入软流圈,导致幔源物质上涌,形成壳、幔热交换与物质交换的通道和规模巨大、延伸至上地幔的高导体.班公—怒江构造带的电性结构证明了该构造带是一组产状陡立、巨型的超壳深断裂带.  相似文献   

藏北高原地壳及上地幔导电性结构——超宽频带大地电磁测深研究结果   总被引：27，自引：14，他引：13       下载免费PDF全文

魏文博  金胜  叶高峰  邓明  谭捍东  Martyn Unsworth  Alan G.Jones  John Booker  Shenghui Li 《地球物理学报》2006,49(4):1215-1225

为了研究西藏中、北部壳、幔导电性结构,讨论高原中、北部岩石圈热状态,1998年和1999年（INDEPTH（Ⅲ） MT）在西藏中、北部完成了德庆—龙尾错（500线）和那曲—格尔木（600线）超宽频带大地电磁深探测剖面的研究.研究结果表明,西藏中、北部以昆仑山断裂为界,其南北壳、幔电性结构有很大差异.昆仑山断裂以北地壳和上地幔为高阻区.而昆仑山以南,地壳和上地幔的导电性有明显的分层结构：地壳上部以不连续的高阻体为主,夹有局部低阻异常体,沿南北方向上地壳的电性结构复杂,具有不连续、分块的特点;但中、下地壳为大范围的高导异常区,区内发育有大规模、不相连续、产状各异的高导体,其电阻率均小于4Ωm;在班公—怒江和金沙江缝合带之下,壳内高导体都具有向上地幔延伸的趋势,存在连通壳、幔的低阻通道.根据西藏高原中、北部壳、幔电性结构的研究推断：如同藏南一样,这里也普遍存在部分熔融体和热流体,它们的成因主要与班公—怒江和金沙江缝合带的壳-幔热交换、热活动有关,这是两期形成的壳-幔热交换通道.其中,班公—怒江缝合带的壳-幔热交换通道形成时间比金沙江缝合带早.因此,研究区壳、幔的热活动是从南边和西边开始,向北、向东扩展,导致现今西藏中、北部地壳和上地幔的热流分布由西向东、由南向北增大.  相似文献   

Seismic‐stratigraphic constraints on the age of the Faroe Islands Basalt Group,Faroe–Shetland region,Northeast Atlantic Ocean     

Jana lavsdttir  Martyn S. Stoker  Lars O. Boldreel  Morten Sparre Andersen   luva R. Eidesgaard 《Basin Research》2019,31(5):841-865

Lower Palaeogene extrusive igneous rocks of the Faroe Islands Basalt Group (FIBG) dominate the Faroese continental margin, with flood basalts created at the time of breakup and separation from East Greenland extending eastwards into the Faroe‐Shetland Basin. This volcanic succession was emplaced in connection with the opening of the NE Atlantic; however, consensus on the age and duration of volcanism remains lacking. On the Faroe Islands, the FIBG comprises four main basaltic formations (the pre‐breakup Lopra and Beinisvørð formations, and the syn‐breakup Malinstindur and Enni formations) locally separated by thin intrabasaltic sedimentary and/or volcaniclastic units. Offshore, the distribution of these formations remains ambiguous. We examine the stratigraphic framework of these rocks on the Faroese continental margin combining onshore (published) outcrop information with offshore seismic‐reflection and well data. Our results indicate that on seismic‐reflection profiles, the FIBG can be informally divided into lower and upper seismic‐stratigraphic packages separated by the strongly reflective A‐horizon. The Lower FIBG comprises the Lopra and Beinisvørð formations; the upper FIBG includes the Malinstindur and Enni formations. The strongly reflecting A‐horizon is a consequence of the contrast in properties of the overlying Malinstindur and underlying Beinisvørð formations. Onshore, the A‐horizon is an erosional surface, locally cutting down into the Beinisvørð Formation; offshore, we have correlated the A‐horizon with the Flett unconformity, a highly incised, subaerial unconformity, within the juxtaposed and interbedded sedimentary fill of the Faroe‐Shetland Basin. We refer to this key regional boundary as the A‐horizon/Flett unconformity. The formation of this unconformity represents the transition from the pre‐breakup to the syn‐breakup phase of ocean margin development in the Faroe–Shetland region. We examine the wider implications of this correlation considering existing stratigraphic models for the FIBG, discussing potential sources of uncertainty in the correlation of the lower Palaeogene succession across the Faroe–Shetland region, and implications for the age and duration of the volcanism.  相似文献   

The Othris Ophiolite, Greece: A snapshot of subduction initiation at a mid-ocean ridge     

Matthias G. Barth  Paul R.D. Mason  Gareth R. Davies  Martyn R. Drury 《Lithos》2008,100(1-4):234-254

The mantle section of the Tethyan-type Othris Ophiolite, Greece, records tectono-magmatic processes characteristic of both mid-ocean ridges and supra-subduction zones. The Othris Ophiolite is a remnant of the Jurassic Neotethys Ocean, which existed between Eurasia and Gondwanaland. Othris peridotites range from fertile plagioclase lherzolites to depleted harzburgites. Abundances of Al₂O₃ and CaO show well-defined inverse linear correlations with MgO, suggesting that the Othris peridotites formed as residua from variable degrees of partial melting.

Peridotites from the Fournos Kaïtsa and western Katáchloron sub-massifs are similar to abyssal peridotites and can be explained by a multistage model with some melting in the garnet stability field followed by moderate degrees of anhydrous near-fractional melting in the spinel stability field. In contrast, the peridotites from the Metalleio, Eretria, and eastern Katáchloron sub-massifs, and the Vourinos ophiolite are highly depleted and have extremely low concentrations of Al₂O₃ and heavy rare earth elements. These peridotites have enriched light REE contents compared to the middle REE. These residua are best modelled by hydrous melting due to a flux of slab-derived fluid to the mantle wedge during melting.

The occurrence of both styles of melting regimes within close spatial and temporal association in the same ophiolite is explained by intra-oceanic thrusting and forced subduction initiation at (or near) a mid-ocean ridge. Thus, the Othris Ophiolite, and probably Tethyan-type ophiolites in general, represent a transient phase of plate tectonic reorganisation rather than quasi-steady state plate tectonics.  相似文献   

Neogene stratigraphy and the sedimentary and oceanographic development of the NW European Atlantic margin     

Martyn S. Stoker  Daniel Praeg  Berit Oline Hjelstuen  Jan Sverre Laberg  Tove Nielsen  Pat M. Shannon 《Marine and Petroleum Geology》2005,22(9-10):977

A regional correlation of Neogene stratigraphy has been attempted along and across the NW European Atlantic continental margin, between Mid-Norway and SW Ireland. Two unconformity-bounded successions are recognised. These are referred to as the lower and upper Neogene successions, and have been dated as Miocene–early Pliocene and early Pliocene–Holocene, respectively, in age. Their development is interpreted to reflect plate-wide, tectonically driven changes in the sedimentary, oceanographic and latterly climatic evolution of the NE Atlantic region. The lower Neogene succession mainly preserves a record of deep-water sedimentation that indicates an expansion of contourite sediment drifts above submarine unconformities, within this succession, on both sides of the eastern Greenland–Scotland Ridge from the mid-Miocene. This is interpreted to record enhanced deep-water exchange through the Faroe Conduit (deepest part of the Southern Gateway), and can be linked to compressive inversion of the Wyville–Thomson Ridge Complex. Thus, a pervasive, interconnected Arctic–North Atlantic deep-water circulation system is a Neogene phenomenon. The upper Neogene succession records a regional change, at about 4 Ma, in the patterns of contourite sedimentation (submarine erosion, new depocentres) coeval with the onset of rapid seaward-progradation of the continental margin by up to 100 km. This build-out of the shelf and slope is inferred to record a marked increase in sediment supply in response to uplift and tilting of the continental margin. Associated changes in deep-water circulation may be part of an Atlantic-wide reorganisation of ocean bottom currents. Glacial sediments form a major component of the prograding shelf margin (shelf-slope) sediment wedges, but stratigraphic data indicate that the onset of progradation pre-dates significant high-latitude glaciation by at least 1 Ma, and expansive Northern Hemisphere glaciation by at least 3 Ma.  相似文献   

Cenozoic alongslope processes and sedimentation on the NW European Atlantic margin     

Jan Sverre Laberg  Martyn S. Stoker  K.I. Torbjrn Dahlgren  Henk de Haas  Haflidi Haflidason  Berit O. Hjelstuen  Tove Nielsen  Pat M. Shannon  Tore O. Vorren  Tjeerd C.E. van Weering  Silvia Ceramicola 《Marine and Petroleum Geology》2005,22(9-10):1069

Based on studies of sediment accumulations deposited from-and erode by-alongslope flowing ocean currents on the European continental margin from Porcupine (Ireland) to Lofoten (Norway), the evolution of the Cenozoic paleocirculation was reconstructed as part of the STRATAGEM project. There is evidence of ocean current-controlled erosion and deposition in the Rockall Trough, in the Faeroe-Shetland Channel and on the Vøring Plateau since the late Eocene, although the circulation pattern remains ambiguous. The late Palaeogene flow in the Rockall Trough was almost probably driven by southerly-derived Tethyan Outflow Water. The extent and strength of any northerly-derived flow is uncertain. From the early Neogene (early-mid-Miocene), there was a massive regional expansion of contourite drift development both in the North Atlantic and in the Norwegian-Greenland Sea. This was most probably related to the development of the Faroe Conduit, the opening of the Fram Strait and the general subsidence of the Greenland-Scotland Ridge. These may have combined to cause a considerable acceleration in the exchange and overflow of deep waters between the Arctic and Atlantic Oceans. An early late Neogene (late early Pliocene) regional erosional event has been ascribed to a vigorous pulse of bottom-current activity, most probably the result of a global reorganisation of ocean currents associated with the closure of the Central American Seaway. During the late Neogene, contourites and sediment drifts developed in deep-water basins, between units of glacigenic sediments as well as infill of several paleo-slide scars. These sediments were derived from areas of bottom-current erosion as well as from the development of Plio-Pleistocene prograding sediment wedges, incorporating the extensive sediment supply derived from shelf-wide ice sheets. Presently a profound winnowing prevails along the shelf and upper slope due to the inflowing currents of Atlantic water. Depocentres of sediments derived from the winnowing are located (locally) in lower slope embayments and in slide scars.  相似文献   

Hydration-induced climb dissociation of dislocations in naturally deformed mantle olivine     

Martyn R. Drury 《Physics and Chemistry of Minerals》1991,18(2):106-116

Widely dissociated dislocations have been observed in mantle olivine from the Erro-Tobbio peridotite in N.W. Italy. Analysis of diffraction contrast in transmission electron microscopy (TEM) indicates that the dissociation reaction involves the climb dissociation on (001) and {021} planes of b=[001] unit dislocations into partial dislocations with Burgers vectors approximately equal to 1/x 011. In the most extreme case a unit dislocation dissociates into four partials which bound three planar defects. The unusually wide dissociation and the greater extent of dissociation in olivine from amphibole-bearing rocks suggests that the dissociation is related to hydration. The occurrence of fluid inclusions along the dislocations confirms that the partials and planar defects are saturated with volatiles. Analysis of possible planar defect structures in Fo₉₀ shows that; (i) the most likely partial Burgers vectors are b=0 3/11 1/4; (ii) two of the planar defects are cation-deficient and can be stabilised by segregation of H⁺ to produce (Mg, Fe) (OH)₂ layers which are iso-structural with the OH-rich interlayer of the humite group minerals; (iii) the central planar defect is formed by removing a stoichiometric olivine (002) layer so does not produce any local chemical changes. The climb dissociation provides a possible mechanism for the transformation of olivine to a humite group mineral. OH-rich interlayers may nucleate on dislocations and extend into the crystal by climb resulting in a gradual increase of (Mg, Fe) (OH)₂ content. The only addition of material required is hydrogen which can rapidly diffuse into olivine. If the dissociation is stable and occurs at high temperatures and pressures it may significantly influence the nature and kinetics of deformation mechanisms and the olivine — spinel shear transformation mechanism in hydrated olivine.  相似文献