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Implications for the lithospheric structure of Cambay rift zone,western India:Inferences from a magnetotelluric study

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Geoscience Frontiers 2020年第5期11卷 1743-1754页

作者： Nagarjuna Danda C.K.Rao Amit Kumar P.Rama Rao P.B.V.Subba Rao Dr.K.S.Krishnan Geomagnetic Research Laboratory IIGAllahabad221505India Indian Institute of Geomagnetism New PanvelNavi Mumbai410218India Department of Geophysics Andhra UniversityVisakhapatnam530003India

Broad-band and long-period magnetotelluric(MT)data were acquired along an east-west trending traverse of nearly 200 km across the Kachchh,Cambay rift basins,and Aravalli-Delhi fold belt(ADFB),western *** regional strike analysis of MT data indicated an approximate N59°E geoelectric strike direction under the traverse and it is in fair agreement with the predominant geological strike in the study *** decomposed transverse electric(TE)-and transverse magnetic(TM)-data modes were inverted using a nonlinear conjugate gradient algorithm to image the electrical lithospheric structure across the Cambay rift basin and its surrounding *** studies show a thick(~1-5 km)layer of conductive Tertiary-Mesozoic sediments beneath the Kachchh and Cambay rift *** resistive blocks indicate presence of basic/ultrabasic volcanic intrusives,depleted mantle lithosphere,and different Precambrian structural *** crustal conductor delineated within the ADFB indicates the presence of fluids within the fault zones,sulfide mineralization within polyphase metamorphic rocks,and/or Aravalli-Delhi sediments/*** observed conductive anomalies beneath the Cambay rift basin indicate the presence of basaltic underplating,volatile(CO2,H2 O)enriched melts and channelization of melt fractions/fluids into crustal depths that occurred due to plume-lithosphere *** variations in electrical resistivity observed across the profile indicate that the impact of Reunion plume on lithospheric structures of the Cambay rift basin is more dominant at western continental margin of India(WCMI)and thus support the hypothesis proposed by Campbell&Griffiths about the plume-lithosphere interactions.

关键词： Cambay rift Deccan basalts Magnetotellurics partial melt Reunion plume

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melt fractions and medium connectivity in the Himalaya-Tibetan crust

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Earthquake Research Advances 2021年第S1期1卷 13-15页

作者： Hui Liu Xiaoping Wu School of Earth and Space sciences University of Science and Technology of ChinaHefei230026China

Seismic and magnetotelluric field campaigns carried out across the Himalaya and the Qinghai-Tibetan Plateau show mid-crustal low resistivity and low-velocity *** these anomalies indicate that there are molten zones present in the Tibet crust is a focus of geophysical and petrological *** interpretations of MT data to infer melt fractions are often based on presumed electrical conductivity values of partial ***,pressure,especially water content in the melt influences the melt conductivity and affects the inferred melt fractions in areas of *** accurate constraints are *** addition,a variety of equations have been proposed to model the conductivity of partially molten rocks in Tibetan ***,different rock electrical models relate to different lithological parameters of *** we need to find an appropriate rock electrical model that can apply to Tibet *** this study,we use a general electrical conductivity model developed by the global fitting of experimental data in previous study and set up a range of temperature,pressure,and water content for five regions in ***’s more,using three widely used rock electrical models to figure out corresponding melt fractions in areas of *** find the most applicable rock electrical model in this region and know better about the distribution and morphology of medium in Tibetan crust.

关键词： partial melt Electrical conductivity model melt fraction Qinghai-Tibetan

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Deep structure of the Longling-Ruili fault underneath Ruili basin near the eastern Himalayan syntaxis:insights from magnetotelluric imaging

Deep structure of the Longling-Ruili fault underneath Ruili ...

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中国科学院地质与地球物理研究所2003学术年会

作者： Maxwell A.Meju Department of Environmental Science Lancaster UniversityLancaster LA1 4YWUK

Magnetotelluric(MT) geophysical profiling has been applied to the determination of the deep structure of the Longling-Ruili fault(LRF),part of a convergent strike-slip fault system,underneath thick Caenozoic cover in Ruili basin in southwestern Yunnan,*** recorded MT data have been inverted using a two-dimensional(2-D) nonlinear conjugate gradients scheme with a variety of smooth starting models,and the resulting models show common subsurface conductivity structures that are deemed geological *** models show the presence of a conductive(5-60Ωm) cover sequence mat is thickest(1 - 1.5 km) in the centre of the basin and rapidly pinches out towards the margins.A half-graben structure is interpreted for the Ruili *** is underlain by about 7-10 km thick upper crustal layer of high resistivity(>200-4000Ωm) that is dissected by steep faults,which we interpret to flatten at depth and root into an underlying mid-crustal conductive layer at about 10 km *** mid-crustal layer does not appear to have been severely affected by faulting;we interpret it as a zone of partial melt or intracrustal detachment The MT models suggest SE directed thrusting of basement rocks in the *** Longling-Ruili fault is interpreted as a NW-dipping feature bounding one of the identified upper crustal fragments underneath Ruili *** suggest that MT imaging is a potent tool for deep subsurface mapping in this terrain.

关键词： Strike-slip fault Seismic hazards Ramp basin Structure Magnetotelluric imaging partial melt

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