lithospheric uplift in eastern gondwana evidence for a long lived mantle plume system recent work has demonstrated that modern drainage systems on rifted continental margins may be the product of ancient lithospheric doming in areas of flood basalt magmatism this uplift is thought to reflect the existence of widespread mafic underplating and excess melt generation at rift zones here i show that uplift due to the initiation of a thermal anomaly plume head in the asthenosphere may be evidenced by the formation of discrete rift structures and persistent paleodrainage sediment dispersal patterns for up to 150 m y prior to the commencement of igneous activity and final continental breakup volcanism thus occurs as a comparatively late stage geochemical response to the long term residence of hot plume material beneath continental mantle lithosphere

india madagascar paleo fit based on flexural isostasy of their rifted margins the present study contributes new constraints on and definitions of the reconstructed plate margins of india and madagascar based on flexural isostasy along the western continental margin of india wcmi and the eastern continental margin of madagascar ecmm we have estimated the nature of isostasy and crustal geometry along the two margins and have examined their possible conjugate structure here we utilize elastic thickness te and moho depth data as the primary basis for the correlation of these passive margins we employ the flexure inversion technique that operates in spatial domain in order to estimate the spatial variation of effective elastic thickness gravity inversion and flexure inversion techniques are used to estimate the configuration of the moho crust mantle interface that reveals regional correlations with the elastic thickness variations these results correlate well with the continental and oceanic segments of the indian and african plates the present study has found a linear zone of anomalously low te 1 5 km along the wcmi similar to 1680 km which correlates well with the low te patterns obtained all along the ecmm we suggest that the low te zones along the wcmi and ecmm represent paleo rift inception points of lithosphere thermally and mechanically weakened by the combined effects of the marion hotspot and lithospheric extension due to rifting we have produced an india madagascar paleo fit representing the initial phase of separation based on the te estimates of the rifted conjugate margins which is confirmed by a close fit correlation of moho geometry and bathymetry of the shelf margins the matching of tectonic lineaments lithologies and geochronological belts between india and madagascar provide an additional support for the present plate reconstruction c 2014 international association for gondwana research published by elsevier b v all rights reserved

evolution of the passive continental margins of india a geophysical appraisal abstract the passive continental margins of india have evolved as india broke and drifted away from east antarctica madagascar and seychelles at various geological times in this study we have attempted to collate and re examine gravity and topographic bathymetry data over india and the adjoining oceans to understand the structure and tectonic evolution of these margins including processes such as crustal lithosphere extension subsidence due to sedimentation magmatic underplating and so on the eastern continental margin of india ecmi seems to have evolved in a complex rift and shear tectonic settings in its northern and southern segments respectively and bears similarities with its conjugate in east antarctica crustal extension rates are uniform along the stretch of the ecmi in spite of the presence or absence of crustal underplated material variability in lithospheric strength and tectonic style of evolution ranging from rifting to shearing the krishna godavari basin is underlain by a strong 30 km elastic lithosphere while the cauvery basin is underlain by a thin elastic lithosphere 3 km the coupling between the ocean and continent lithosphere along the rifted segment of the ecmi is across a stretched continental crust while it is direct beneath the cauvery basin the western continental margin of india wcmi seems to have developed in an oblique rift setting with a strike slip component unlike the ecmi the wcmi is in striking contrast with its conjugate in the eastern margin of madagascar in respect of sedimentation processes and alignment of magnetic lineations and fracture zones the break up between eastern india and east antarctica seems to have been accommodated along a proterozoic mobile belt while that between western india and madagascar is along a combination of both mobile belt and cratonic blocks

transient regional uplift in the early tertiary of the northern north sea and the development of the iceland plume abstract forward and reverse 2d flexural modelling of syn rift and post rift stratigraphy has been used to investigate departures from mckenzie post rift subsidence for the cretaceous tertiary following late jurassic rifting in the northern north sea basin the analysis shows uplift in the palaeocene of 375 525 m relative to calibrated mckenzie subsidence curves followed by a rapid decrease in uplift in the early eocene of 160 310 m both palaeocene uplift and eocene subsidence increase northwards the timing distribution and magnitude of regional palaeocene uplift is consistent with an origin relating to the development of a mantle plume between 65 and 55 ma transient regional palaeocene uplift in the northern north sea basin was produced by long wavelength dynamic uplift generated by the flow field of a mantle plume heating of the asthenosphere or lithosphere beneath the north sea by hot plume material or magmatic underplating are not believed to have contributed to palaeocene uplift in the northern north sea basin rapid early eocene subsidence was generated by a decrease in dynamic uplift caused by a reduction in plume activity the plume responsible for north sea palaeocene uplift may have been the early iceland plume or a distinct british tertiary igneous province plume related to the same mantle convection event

rifting between india and madagascar mechanism and isostasy abstract the nature of isostasy along the western continental margin of india wcmi and the eastern continental margin of madagascar ecmm and their conjugate nature are examined the first part of the study deals with the estimation of effective elastic thickness te of the lithosphere for the two margins through cross spectral analysis of gravity and bathymetry data the results bring out comparable te values of 8 15 km for the wcmi and 10 13 km for the ecmm despite the wcmi having been traversed along strike by a hotspot trace we have also compared topographic profiles across the two margins extending inland to examine the rift flank uplift experienced by the two landmasses abutting the margins which bear a striking similarity these results establish the symmetrical rifting mechanism resulting in the formation of the two margins and indicate that despite the presence of a hotspot trace along one margin i e the wcmi the two margins have comparable isostatic compensation mechanisms with low te values in the second part of the study we have examined the possible mechanism for the rift flank uplifts using a process oriented approach of backstripping the sediments along a traverse across the wcmi and reconstructing the original rift flank topography by flexurally backstacking the amount of eroded material on the present day topography of the western ghats the backstack load configuration is taken from the amount of erosion that took place over the western ghats obtained from afta apatite fission track analysis studies the reconstructed rift time topography and bathymetry are used to get the moho configuration which was used to calculate the gravity anomaly and is compared with the observed anomaly to derive a possible evolution model for the region we have tried to examine the observed gravity anomaly through two different processes in the first process a te 15 km for backstripping and backstacking and a compensated underplating for the topography give a best fit model to the observed gravity in the second process a necking model with a deep level of necking 20 km with te 15 km and without any underplating explains the topography as well as the observed gravity the nature and amount of the western ghat topography and cratonic age archaen of the pre rifted crust of western india and eastern madagascar are more in favor of the rifting mechanism necking model rather than due to the passage of the reunion hotspot underplating model this is evidenced by the observed increase in topography away from the influence of the reunion hotspot trace as well as the presence of a similar topography in madagascar

paleogene igneous underplating and subsidence anomalies in the rockall faeroe shetland area abstract crustal thickening caused by igneous underplating related to continental break up in the northeast atlantic has been invoked as the cause of the apparent lack of thermal subsidence seen in many mesozoic basins in the northwest european area in this study we examine a set of commercial wells in the rockall faeroe shetland region and calculate tectonic subsidence histories the rate of post rift basement subsidence during the cretaceous cenozoic determined from backstripping calculations always implies a higher degree of extension than the total basement subsidence assuming uniform extension furthermore the size of this discrepancy increases northward along the rockall trough and westwards in the northern north sea towards scotland we interpret this depth anomaly to reflect the effect of igneous underplating rethickening the crust following mesozoic and cenozoic extension late paleocene extension is identified in subsidence reconstructions throughout the west of britain area and is greatest in the rockall trough assuming that the underplating is gabbroic in composition the subsidence depth anomalies indicate a regional pattern of 2 3 km underplated between the erris trough and porcupine basin increasing to 4 5 km in the west lewis basin and hebrides shelf area in the faeroe shetland basin underplating is 1 0 1 5 km in the east and increases to 4 5 km in the west the data support the hypothesis of a major asthenospheric thermal anomaly centered under the faeroes in the paleocene dynamic uplift of the region is often difficult to identify but is locally seen to develop rapidly around 63 ma implying rapid emplacement of the mantle anomaly the intrusion of gabbroic bodies to the base of the crust in the late paleocene may have had an impact on the thermal maturation of petroleum source rocks in the region however thermal maturity indicators show smaller peak heatflows than predicted from simple thermal models suggesting that underplating was a gradual process achieved through the accretion of several small rapidly cooled bodies

structure and isostatic compensation of the comorin ridge north central indian ocean summary bathymetry gravity and magnetic data about 9200 lkm of the comorin ridge north central indian ocean were investigated using the transfer function and forward model techniques to understand the mode of isostatic compensation and origin of the ridge the ridge extends for about 500 km in nnw sse direction and associates with low amplitude gravity anomalies ranging from 25 to 30 mgal compared to the ridge relief suggesting that the anomalies are compensated at deeper depths from admittance analysis an airy model or local compensation with an elastic plate thickness t e of about 3 km and crust thickness t of 15 20 km are suggested for the southern part of the comorin ridge south of 5 n whereas for the northern part a flexural plate model with an elastic thickness of about 15 km is obtained admittance analysis together with the results from gravity forward modelling reveal that the south part was emplaced on relatively weak oceanic crust with both surface and subsurface loading while the north part was emplaced on the continental crust based on present studies and published plate kinematic models we interpret that the comorin ridge was evolved at about 90 ma during the rift stage of madagascar from the southwest of india we have also demarcated the continent ocean boundary cob west of sri lanka and southern tip of india which runs across the strike of the ridge placing the northern part of the ridge on continent and southern part on oceanic crust on the southern part of the ridge eastern flank is steep faulted up to 0 6 km and is controlled by the 79 e fz and then by cob

crustal structure and nature of emplacement of the 85 e ridge in the mahanadi offshore based on constrained potential field modeling implications for intraplate plume emplaced volcanism abstract an integrated interpretation of multi channel seismic reflection gravity and magnetic datasets belonging to northern most part of the 85 e ridge in the mahanadi offshore is carried out to study the crustal structure and mode of its emplacement the basement structure map of the ridge reveals that it is 130 150 km wide and is composed of an eastern high which appears as a continuous broad and smooth topographyand the western high characterized by several steep isolated highs the seismic velocities reported for the first time over the ridge indicate several sedimentary sequences ranging in velocities between 1 6 and 4 0 km s above the acoustic basement top the salient aspects of the sedimentary velocities are a low velocity layer 2 6 3 2 km s within the cretaceous sequence in the intervening depressions encompassing the flank region and a regionally widespread higher velocity layer 3 5 3 8 km s belonging to the eocene oligocene section overlying the ridge a layer having a velocity of 4 2 4 7 km s probably made of volcanoclastic rocks is observed immediately below the acoustic basement the sediment isopach maps presented here for three major horizons are used to compute the 3 d sediment gravity effect to obtain a crustal bouguer anomaly map of the region detailed analysis of the gravity and magnetic anomaly maps clearly demonstrates the continuity of ridge up to the mahanadi coast at chilka lake seismically constrained gravity and magnetic models indicate that the ridge is composed of volcanic material that was emplaced on continental crust in the shelf slope areas and over the oceanic crust in the deep offshore areas the modeled crustal structure below the ridge further indicates volcanic emplacement of the ridge on a relatively younger lithosphere we propose two alternative models for the emplacement of the ridge

subsidence and isostasy along a sheared margin cauvery basin eastern continental margin of india we have applied a process oriented method to a seismo geological section across cauvery basin a sedimentary basin along the southern part of the eastern continental margin of india ecmi to examine the isostatic mechanism operating beneath the margin the evolution of the ecmi appears to be within a shear rift tectonic setting mainly driven by the difference in the relative motions of india and east antarctica and the subsequent direction of spreading and the cauvery basin seems to have formed in this pull apart tectonic setting shearing along the southern ecmi is modeled with gravity anomalies and the resultant crustal configuration through various models of isostasy backstripping analysis suggests a very low te of 3 km beneath the basin the shelf edge gravity anomaly reflects a strong contrast across a wrench fault parallel to the coast inferred from gravity forward modeling denoting coast parallel transform motion in the initial stages of continental separation prior to rotation and spreading

effect of thermal non equilibrium seafloor topography and fluid advection on bsr derived geothermal gradient abstract the seafloor and bottom simulating reflectors bsrs are interpreted from the 3d seismic data acquired in krishna godavari kg offshore basin in the vicinity of sites drilled cored during national gas hydrate program nghp expedition 01 the shallow structures such as inner toe thrust fault system regional and local linear fault systems and mass transport deposits are inferred from attributes of seafloor time structure as well as from the seismic profiles the geothermal gradient is estimated from the depths and temperatures of the seafloor and the bsr the temperature at the bsr depth is estimated from the methane hydrate and seawater salinity phase boundary assuming that the bsr represents the base of the gas hydrate stability zone the spatial variations in geothermal gradient gtg show a strong correlation with seafloor topography in the kg basin the gtg decreases by 13 30 over the topographic mounds formed due to inner toe thrust faults and recent mass transport deposits the gtg decreases by only 5 10 over the mounds likely due to defocusing of heat flux based on one dimensional topographic modeling hence the gtg perturbation due to topography alone cannot explain the observed gtg anomaly the temperature profile beneath these mounds may not be in equilibrium with the surroundings either due to the recent upliftment of sediments along the inner toe thrust faults or rapid deposition of sediments due to slumping sliding in contrast an increase in gtg by 10 15 is observed in the vicinity of major fault systems we presume that the likely mechanism for the increase in gtg is fluid advection from a deeper part of the basin a detailed thermal modeling involving the effect of surface topography high sedimentation rates fluid advection and sediment thickening due to tectonics is required to understand the thermal profile in kg offshore basin

marine geophysical study of the comorin ridge north central indian basin marine geophysical data are used to interpret the continental margin structure south of india and west of sri lanka in the northern central indian basin free air and isostatic anomaly maps are presented they show the prominent indian ocean gravity low with values more negative than 100 mgal south west of sri lanka a steep gradient in the free air and isostatic anomaly forms a nnw sse trending line extending south and striking parallel to the southwest coast of india this line marks the eastern boundary of a topographic and basement high here named the comorin ridge which is also clearly seen on a sediment isopach map the ridge seems to act as a barrier to the passage of ganges cone sediments to the west a comparison of the eastern landward edge of the comorin ridge with similar structures of other passive continental margins such as those off southern south africa agulhas fracture zone off the falkland plateau and off western norway is made it is suggested that the eastern edge of the comorin ridge may mark a significant structural crustal boundary

repeat ridge jumps and microcontinent separation insights from ne arabian sea abstract microcontinents separate due to ridge jumps associate either asymmetric sea floor spreading or plume ridge interactions india separated from seychelles at 64 ma by asymmetric sea floor spreading initially when the spreading centre in the mascarene basin jumped towards the indian sub continent between magnetic chrons c29 and c28 the subsequent tectonics is difficult to comprehend since laxmi ridge another microcontinent formed during the later phase most of the studies considered the laxmi ridge as a sliver others considered it to be oceanic crust high resolution deep 25 km seismic data reveals that i the ridge possesses 15 km deep sea ward dipping reflector sdr packages ii normal faulted rift valleys devoid of syn rift sedimentary packages and iii axial magma chambers 5 7 km beneath the ridge top additionally from 2d forward gravity models we deduce that the ridge most possibly comprises of high density oceanic crust we conclude the laxmi ridge to be indeed composed of oceanic crust and a fossil spreading centre we thus identified the ridge jumps and their relation to the seychelles microcontinent separation previous numerical models suggest that the time required for a ridge jump is controlled by magmatic heating spreading rate at the ridge and plate ages for repeated ridge jumps the additional factor is the dynamic relation between the plume and lithosphere in terms of melt transfer and heating we find that the medium spreading rates and high magmatic heating due to the reunion plume and young plates favoured rapid and repeated ridge jumps towards the plume

origin of the rajmahal traps and the 85 e ridge preliminary reconstructions of the trace of the crozet hotspot the 85 e ridge is a buried aseismic ridge approximately parallel to and west of the ninetyeast ridge in the northeastern indian ocean it was previously shown to be of probable volcanic origin emplaced on very young oceanic crust but no satisfactory model of emplacement of the rocks was offered we propose a model of origin of the rajmahal traps of northeastern india the 85 e ridge and afanasy nikitin seamount as the trace of the hotspot that now lies beneath the crozet islands in the southern indian ocean this reconstruction places the kerguelen hotspot which formed the ninetyeast ridge at the triple junction between greater india australia and antarctica before the breakup of eastern gondwana

upper plate magma poor rifted margins stratigraphic architecture and structural evolution abstract although it is generally accepted that many distal magma poor rifted margins are asymmetric and can be divided into lower and upper plate margins little is known about the details of how and when this asymmetry evolves and how upper and lower plate margins can be distinguished this is due to the fact that most papers focused on the so called lower plate margins while the upper plate margins remained less well understood mainly due to the lack of public accessible drill hole data the aim of this paper is to provide a first order description of the global architecture and stratigraphic evolution of an upper plate magma poor rifted margin in order to provide such a template we focused on 2 seismic sections the ion 1000 line east indian margin and the screech 2 line newfoundland margin and describe key km scale outcrops from the fossil european margin exposed in the western central alps all of which document classical upper plate margins based on these data we show that upper plate magma poor rifted margins can be characterized by a staircase type architecture with terraces t 1 t 2 t 3 and ramps r 1 r 2 that result as a consequence of an evolution through a coupling exhumation and breakup stage we also defined key stratigraphic levels that we try to link with the evolution of the margin which enables us to link the tectonic evolution with the creation of accommodation space and formation of the staircase architecture that characterizes the upper plate margin from these observations we develop a conceptual model for the evolution of upper plate margins and discuss the applicability of this model for different strain rates rates of subsidence and sedimentation rates

regional tectonic interpretation of image enhanced gravity and magnetic data covering the mid norwegian shelf and adjacent mainland abstract gravity and magnetic field data covering mid norway and the norwegian sea were processed in order to enhance tectonic features on various scales the local features were subjected to an unconventional processing technique involving a non linear adaptive wallis filter designed to enhance the smallest wave lengths when compared with recent structural information derived from seismic data the processed gravity and magnetic maps show the main structural trends major fault zones and basin boundaries thus proving their worth for regional tectonic mapping previously undetected nw se trending offshore crustal lineaments are revealed a landward prolongation of the bivrost lineament appears to continue subparallel towards proterozoic shear zones below the caledonian nappes in the rana area either along the western margin of the transscandinavian granite porphyry belt or the nw se trending mala skelleftea tectonic zone a large lineament is also observed as a landward prolongation of the surt lineament indicating a relationship with the storsjon edsbyn deformation zone a major deep crustal shear zone in the precambrian of sweden a slightly increased seismic activity which is possibly related to the present ridge push force is observed along parts of the previously unknown transfer zones combined gravity and magnetic modelling indicates a low crustal thickness in the northwesternmost part of the voring basin between the surt and the jan mayen lineaments the lack of correlation between the gravity and the magnetic patterns observed on the residual field maps suggests the presence of a shallow curie isotherm situated above or within the uppermost basement

crustal evolution and sedimentation history of the bay of bengal since the cretaceous multichannel seismic reflection gravity magnetic and bathymetric investigations were made along five latitudinal profiles from the eastern shelf of india to the andaman shelf and four nw se profiles in the western basin off madras seismics on three latitudinal profiles in the bay of bengal the trend of the fracture zones the locations of the magnetic chron 34 and the cretaceous magnetic quiet zone suggest that greater india separated from antarctica after a period of transform motion in the early cretaceous that is about polarity chron m0 120 ma and drifted northwestward negative gravity anomalies are associated with basement rises including the 85 e ridge between the continental margin of india and the ninetyeast ridge magnetic reversals and northward trend of the 85 e ridge support a hotspot origin of the ridge and its emplacement most likely after the cretaceous quiet period juxtaposition of high amplitude hyperbolic reflections down faulted continental blocks buried under thick sediments and associated gravity and magnetic anomalies mark the boundary between continental and oceanic rocks at the foot of continental slope about 80 km seaward of the present continental shelf edge eight seismic sequences as thick as 8 5 km overlie the early cretaceous oceanic basement and include four unconformities lower eocene upper oligocene upper miocene and upper pleistocene which have been correlated to the major geologic tectonic events we also interpret the late cretaceous early tertiary features on the eastern flank of the buried 85 e ridge as carbonate reefs the observation of steep subduction of older cold indian plate beneath the burmese plate near the andaman islands suggests the sunda arc in this region as low to intermediate stress subduction zone

antarctic marine gravity field from high density satellite altimetry summary closely spaced satellite altimeter profiles 5 km collected during the geosat geodetic mission geosat gm and those planned for the extended ers 1 mission are easily converted to grids of vertical gravity gradient and gravity anomaly as profile spacing decreases it becomes increasingly difficult to perform a crossover adjustment on the original geoid height profiles without introducing large cross track gradients if one is only interested in the horizontal and vertical derivatives of the gravitational potential however adjustment of the profile is unnecessary the long wavelength radial orbit error is suppressed well below the noise level of the altimeter by simply taking the along track derivative of each profile ascending and descending slope profiles are then interpolated onto separate uniform grids these two grids are summed and differenced to form comparable grids of east and north vertical deflection using laplace s equation the vertical gravity gradient is calculated directly from the vertical deflection grids fourier analysis is required to construct gravity anomalies from the two vertical deflection grids these techniques are applied to high density 2 km profile spacing geosat gm profiles in antarctic waters 60 s to 72 s gridding and interpolation are performed using the method of projection onto convex sets where the smoothness criteria corresponds to upward continuation through 4 km of ocean the resultant gravity grids have resolution and accuracy comparable to shipboard gravity profiles after adjustment of a dc shift in the shipboard gravity profiles 5 mgal the rms difference between the ship and satellite gravity is 5 5 mgal many interesting and previously uncharted features are apparent in these new gravity maps including a propagating rift wake and a large leaky transform along the pacific antarctic rise

near n s paleo extension in the western deccan region india does it link strike slip tectonics with india seychelles rifting this is the first detailed report and analyses of deformation from the w part of the deccan large igneous province dlip maharashtra india this deformation related to the india seychelles rifting during late cretaceous early paleocene was studied and the paleostress tensors were deduced near n s trending shear zones lineaments and faults were already reported without significant detail an e w extension was envisaged by the previous workers to explain the india seychelles rift at 64 ma the direction of extension however does not match with their n s brittle shear zones and also those faults sub vertical ne sw nw se and few n s we report and emphasize in this work slickenside bearing fault planes brittle shear zones and extension fractures in meso scale enabled us to estimate the paleostress tensors directions and relative magnitudes the field study was complemented by remote sensing lineament analyses to map dykes and shear zones dykes emplaced along pre existing n s to ne sw nw se shears fractures this information was used to derive regional paleostress trends a nw se ne sw minimum compressive stress in the oldest kalsubai subgroup and a n s direction for the younger lonavala wai and salsette subgroups were deciphered thus a nw ne to n s extension is put forward that refutes the popular view of e w india seychelles extension paleostress analyses indicate that this is an oblique rifted margin field criteria suggest only ne sw and nw se with some n s strike slip faults brittle shear zones we refer this deformation zone as the western deccan strike slip zone wdsz the observed deformation was matched with offshore tectonics deciphered mainly from faults interpreted on seismic profiles and from magnetic seafloor spreading anomalies these geophysical findings too indicate oblique rifting in this part of the w indian passive margin we argue that the seychelles microcontinent separated from india only after much of the dlip erupted further studies of magma rich passive margins with respect to timing and architecture of deformation and emplacement of volcanics are required

the karnataka late cretaceous dykes as products of the marion hot spot at the madagascar india breakup event evidence from 40ar 39ar geochronology and geochemistry two late cretaceous mafic dykes with an ene strike that is orthogonal to the west coast of india and located nearly 200 km inland around huliyardurga karnataka state yield 40ar 39ar plateau ages of 90 0 1 0 and 87 5 0 9 ma these fe ti enriched tholeiites are essentially co eval with at least four other igneous suites widely scattered in southern india namely the south and north kerala dykes the agali anaikatti dykes of central kerala tamil nadu and lavas of st mary islands off the west coast of india the karnataka cretaceous dykes are also co eval and compositionally very similar to the fe ti enriched tholeiitic lavas and dykes around mananjary a major phase of late cretaceous magmatism along the eastern rifted margin of madagascar which are believed to be products of the marion hot spot that extruded at 88 ma synchronous with the india madagascar break up event the age and compositional similarities between these late cretaceous magmatic rocks from india and madagascar constitute a clear evidence for extension of the thermal manifestations deep into the indian peninsula

break up of australia india madagascar block opening of the indian ocean and continental accretion in southeast asia with special reference to the characteristics of the peri indian collision zones abstract linear belts of gondwana basins developed in the indian continent since late palaeozoic along favoured sites of precambrian weak zones like cratonic sutures and reactivated mobile belts the tibetan and sibumasu west yunnan continental blocks that were located adjacent to proto himalayan part of the indian continent rifted and drifted from the northern margin of the east gondwanic indo australian continent during late palaeozoic when the said northern margin was under glacial or cool climatic condition and rift drift tectonic setting the indo burma andaman iba sikule lolotoi blocks were also rifted and drifted from the same northern margin during late jurassic this was followed by the break up of the australia india madagascar continental block during the cretaceous the activity was associated with hot spot related volcanism and opening up of the indian ocean the late cretaceous and tertiary phases of opening of the arabian sea succeeded the early cretaceous phase of opening of the bay of bengal part of the indian ocean the palaeo and neo tethyan sutures in tibet yunnan laos thailand and vietnam reveal the complex opening and closing history of the tethys the iba block rotated clockwise from its initial e w orientation because of 90 e and adjacent dextral transcurrent fault movements caused due to faster northward movement of the indian plate relative to that of australia the india tibet terminal collision during early middle eocene initiated himalayan orogenesis and contemporaneously there was foreland basin development that was accompanied with sporadic but laterally extensive continental flood basalt cfb type and related volcanism the paleogene rocks of the himalayan foreland basin are involved in tectonism and are mostly concealed under older rocks the mesozoic early eocene ophiolite terrane on iba does not represent the eastern suture of the indian plate but occurs as klippe on iba caused due to oblique collision between sibumasu and iba during late oligocene post collisional indentation of y shaped indian continent into the asian collage produced himalayan syntaxes clockwise rotation of the sibumasu block which was then sutured to the tibetan and se asian blocks and tectonic extrusion of the indochina block along the ailao shan red river asrr shear zone highly potassic magmatic rocks were emplaced during late palaeogene at the oroclinally flexed marginal parts of the south china continental lithosphere these magmatic bodies were dislocated by the asrr left lateral shear zone soon afterwards petrogenetic and tectonic processes that generated the eocene cfb volcanics at the himalayan foreland basin may have also produced late palaeogene magmatism from outer parts of the namche barwa syntaxis their site specific location and time sequence suggest them to be genetically related to the india asia collision process and indian continent s indentation induced syntaxial buckling deep mantle reaching fractures were apparently produced during india asia terminal collision at the strongly flexed leading brittle edge of the indian continental lithosphere and possibly later in time at the outer oroclinally bent marginal parts of the rigid south china continental lithosphere generating typical magma the subduction zone that developed along the western margin of iba due to oblique convergence between the iba and the indian plate is still active the northern end of iba ultimately collided with the ne prolongation of the indian continent and was accreted to it during mio pliocene the shillong massif was uplifted and overthrust over the bengal basin located over its passive margin to the south whereas the eocene distal shelf sediments of iba were overthrust over the tertiary shelf of the indian continent

structure and evolution of the afanasy nikitin seamount buried hills and 85 e ridge in the northeastern indian ocean abstract geophysical data of the afanasy nikitin seamount ans partly buried hills and 85 e ridge in the northeastern indian ocean were studied together with published seismic refraction results to understand genesis and evolution of the structures the ans joins the 85 e ridge through isolated buried hills and intervening subsurface structures and together they form a linear ridge system the gravity signature of the ridge system changes from negative to positive towards south of 5 n which seems to coincide with termination thinning of pre collision continental sediments in the bay of bengal thick pile of bengal fan sediments had great impact on underneath pre collision sediments as well as on basement rocks the process resulted in attaining higher velocities up to 6 6 and 7 1 km s respectively gravity model studies suggest that structures of the ridge system are compensated in different modes the ans is underlain by an 8 km thick deep crustal body of magmatic rocks while beneath other structures oceanic crust is down flexed up to 2 5 km the presence of metasediments more dense than volcanic rocks and flexure of the lithosphere would explain the negative gravity anomaly over the 85 e ridge whereas lack of metasediments and magmatic rocks at depth would explain the compensated positive anomaly over the ans the width of the 85 e ridge the wavelength 190 km and amplitude 2 5 km of the flexed oceanic crust and the intersection of the ridge with the mesozoic fracture zones suggest that the ridge was formed in intraplate position when the lithosphere underneath was approximately 35 myr old initial emplacement of the ans was coeval with the formation of oceanic lithosphere at 80 73 ma the hotspot forming the 85 e ridge had reactivated the ans during the paleocene and brought it to the sea surface then it underwent erosion and subsidence processes the deformation activity had converged the north and south parts of the ans at late miocene and again at late pleistocene and northward buried hills at early pliocene

deep sub crustal features in the bengal basin seismic signatures for plume activity the basaltic rajmahal traps 117 ma india are believed to be due to a mantle plume the plausible plume path on the continental side has not been traced probably because of the thick sedimentary cover these traps are located close to the bengal basin therefore a re examination of the deep seismic velocity structure should help in tracing the plume path on the continental side and its possible relationship to plume activity data obtained along four seismic profiles in the bengal basin were re examined which helped in identifying and modeling strong reflections from lower crust and moho the results indicate a 7 5 km s velocity zone as an underplated mantle material injected by the mantle plume or hotspot at the base of the continental crust the study also indicates the probable trace of plume in the continental region a nnw sse trending path east of 87 e with an up warp in moho

geochemical evolution of the tertiary succession of the nw shelf bengal basin bangladesh implications for provenance paleoweathering and himalayan erosion abstract whole rock major trace and rare earth element ree compositions of paleogene to neogene sedimentary rocks of the nw shelf succession province 1 of bangladesh contain a record of interaction of the india and asian plates himalayan tectonism and climatic development analyses of 66 sandstones and mudrocks from the tertiary succession of bangladesh were made to examine provenance source weathering and the influence of paleoclimate and tectonism the sediments display linear geochemical trends due to quartz dilution and varying quartz clay ratios produced by hydrodynamic sorting chondrite normalized ree patterns for both sandstones and mudrocks from different groups are similar to upper continental crust with moderate to high lree enrichment lithotypes within formations average lan ybn 5 31 11 41 and marked negative eu anomalies eu eu 0 51 0 69 based on geochemical criteria the succession can be divided into three parts jaintia barail surma and dupi tila very high silica contents in jaintia tura sandstones and high chemical index of alteration cia indices in kopili mudrocks fe shales suggest derivation from a deeply weathered and stable cratonic source india the tura sandstones are interpreted as first cycle quartz arenites produced while the indian plate drifted across equatorial regions during the paleocene eocene thermal maximum petm the barail surma and dupi tila sediments were derived from a felsic orogen the himalaya the barail surma sediments were mainly derived from the trans himalayan batholith and associated granitoids with significant contribution from the lesser himalaya mafic input is also evident probably from intraoceanic arc material within the himalaya barail mudrocks have uniformly high cia values 92 95 suggesting intense steady state weathering of their proto himalayan source and warm and humid climate in contrast cia values of surma mudrocks range from 66 to 93 average 84 suggesting non steady state weathering related to active uplift in the himalaya the dupi tila sediments were derived from a more felsic lesser himalaya source with significant contribution from the trans himalaya and very little or no ophiolitic or arc material dupi tila mudrocks have cia ratios of 62 99 average 72 also indicating non steady state weathering in the rising himalayan source geochemical compositions of the nw shelf sediments are comparable to coeval successions in the surma basin province 2 of bangladesh and the siwaliks india indicating similar source evolution of the indian monsoon and associated high precipitation caused intense chemical weathering of the surma and dupi tila source despite rapid uplift the surma group thus bears the signature of evolution of the asian monsoon in the bengal basin at 21 ma simultaneous with the development of the east asian monsoon this supports proposals that both monsoon systems developed at the same time

seafloor spreading magnetic anomalies in the enderby basin east antarctica abstract the timing of the early separation of india from the contiguous antarctica australia is still an unresolved problem although it is well established that antarctica and india formed a single indo antarctic platform prior to the fragmentation of eastern gondwanaland inadequate age information either in the form of magnetic anomaly isochrons or dating of oceanic rocks from the conjugate margins of antarctica and india perhaps led several authors to propose incomplete plate reconstruction models particularly for the early separation of india from antarctica analysis of magnetic and satellite derived gravity data in the enderby basin east antarctica reveals the presence of seafloor spreading type linear magnetic anomalies and eight new fracture zones the observed magnetic anomalies can be interpreted as the younger sequence of mesozoic anomalies m11 m0 half spreading rates range from 6 5 to 2 8 cm yr and are comparable with those measured in the bay of bengal these similarities in the mesozoic magnetic anomaly sequence and in the spreading rates provide evidence that these two basins are conjugate and contemporary a consistent plate reconstruction model can be derived from the identified conjugate patterns of mesozoic magnetic anomalies and fracture zones the occurrence of the oldest magnetic anomaly m11 close to the coasts in these two offshore basins unequivocally suggests that the break up of india from antarctica occurred before 134 ma

mesozoic anomalies in the bay of bengal abstract the analysis of 8200 line km of total magnetic intensity data in the bay of bengal northeastern indian ocean revealed the presence of approximately n30 e trending seafloor spreading type magnetic anomalies these anomalies resemble the mesozoic anomaly series m11 m0 reported elsewhere the oldest anomaly m11 132 5 ma identified close to the east coast of india is followed by the younger series of mesozoic anomalies towards the offshore some of the anomalies are offset by 60 80 km the configuration of the offsets of the isochrons allowed us to propose approximately n120 e trending oceanic fracture zones the mesozoic crust of 132 5 118 ma is estimated to evolve with an average half spreading rate of 3 5 cm yr except for the ocean floor between the m9 and m4 magnetic isochrons this part of the crust appears to be affected by the buried subsurface 85 e ridge

seismicity and geodynamics of the low to high grade transition zone of peninsular india abstract a new seismogenetic belt has been identified in the well known transition zone of peninsular india lat 12 14 n and long 74 80 e based on a critical analysis of historical and recent seismic data the diffused and weak seismicity in the area could be attributed to the reactivation of adjoining shear zones a seismic energy release map has been prepared for southern peninsular india which depicts the long term seismicity in this region temporal variations in seismic activity in space indicate migration of seismic activity from east to west within the transition zone this phenomenon is discussed in relation to the mobility of shear belts adjacent to the dharwar craton further the maximum horizontal principal compressive stress directions on the indian continent are also briefly discussed these stresses may be mainly responsible for the mobility of the major shear zones adjacent to the dharwar craton the analysis of the seismic data in space and time thus suggests two possible geodynamic models viz 1 a stick slip model and 2 a crustal shortening model

nature of the crust in the laxmi basin 14 20 n western continental margin of india 1 the nature of the crust in the laxmi basin western margin of india is an uncertain issue more importantly this has implications on paleogeographic reconstructions of the western indian ocean we have analyzed three geophysical data sets and modeled gravity and magnetic anomalies for determining nature of the crust basement of the laxmi basin includes numerous highs which make the basement uneven and shallower compared to the western basin the laxmi basin is characterized by a broad gravity high and a narrower prominent gravity low within it while within the basin the broad anomaly gradually increases toward north the panikkar ridge is associated with the gravity low which is comparable at least in sign to known negative gravity anomaly of the laxmi ridge intrusive structures mapped in the laxmi basin coincide with significant magnetic anomalies which were earlier interpreted as seafloor spreading anomalies model studies reveal that the laxmi basin consists of 14 km thick stretched continental crust in which magmatic bodies have been emplaced whereas the panikkar ridge remains less altered stretched continental crust the crust of the laxmi basin is mostly thinner than crust under the laxmi ridge and continental margin in addition to the rift drift related stretching of the continental margin the laxmi basin possibly has undergone extra stretching in e w direction during the pre tertiary period at 68 ma deccan volcanism on western india may have disrupted the initial conditions that were leading to onset of spreading in the basin subsequently the reunion hot spot had emplaced the volcanic material within the stretched thinned continental crust we interpret the laxmi basin as a failed rift undergone stretching following intraplate kinematics prior to deccan volcanism

provenance and paleo weathering of tertiary accretionary prism forearc sedimentary deposits of the andaman archipelago india abstract in order to understand the provenance and tectono sedimentary processes occurring in the andaman subduction zone asz the late cretaceous to oligocene sedimentary records from the andaman islands have been studied these sedimentary records are considered to have preserved the history of the india asia collision evolution of the himalayas climatic development and palaeo drainage reorganizations on the indian and asian plates about 47 sandstones and mudstones shales and siltstones samples were analyzed for whole rock major trace and rare earth element compositions the geochemical results suggest mixing of sediments derived from the mafic igneous sources comprising local ophiolites and volcanic arc of the asz and an older archean to proterozoic age felsic cratonic source with compositions similar to average granodiorite or upper continental crustal sources the compositions were dominated by sources of the mafic arc during deposition of the mithakhari group whereas they were controlled by continental sources during deposition of the andaman flysch group the hope town conglomerate unit of the mithakhari group was mainly derived from weathering and erosion of the subaerially exposed local ophiolite thrust sheets whereas its namunagarh unit contains significant detritus from volcanic arcs the andaman flysch turbidites were deposited with a greater supply of sediments from first cycle active continental margin sources probably located in the tibetan and eastern myanmar region and recycled quartzose sedimentary sources within the nascent himalayas the sediments supplied to both the mithakhari and the andaman flysch groups were characterized by varying values of cia pia and w these variable values were either due to non steady state weathering conditions in the sources or the changing climatic conditions owing to the motion of indian plate with reference to the equator the uniformly high cia and w values in the andaman flysch rocks can be related to high precipitation and strong chemical weathering associated with the initiation of the indian monsoon

pre breakup continental extension in east gondwanaland and the early opening of the eastern indian ocean abstract extension of continental crust by up to 360 km on a north northeast azimuth in the great australian bight occurred prior to the middle cretaceous 96 ma onset of seafloor spreading between australia and antarctica this large amount of continental extension is constrained to the late jurassic 160 ma middle cretaceous interval about a pole estimated to lie about 40 southeastward of southeastern australia using bathymetric data combined with seismic and magnetic determinations of the continent ocean boundaries off australia india and antarctica we determine a revised fit of east gondwanaland prior to continental extension and at various stages thereafter in the first stage from 160 to 132 5 ma m11 india australia rotated from antarctica with continental crustal extension between australia and antarctica and largely transform motion between the coromandel coast margin of india and the kron prins olav kyst margin of antarctica in the second stage from 132 5 to 96 ma india rotated northwestward away from australia antarctica producing m10 and younger magnetic anomalies along the western margin of australia continental extension was greatest between australia and antarctica during this stage the newly determined 132 5 96 ma rotation between india and australia provides an improved fit between the orientation of observed m10 m0 magnetic anomalies and the southward decrease in spreading rate off the western australian margin together with bathymetry the new rotation parameters lead to identification of the abandoned 96 ma spreading ridge along the lost dutchmen and dirck hartog ridges the naturaliste fracture zone is found to lie nearly parallel to the early cretaceous transform direction between india and antarctica suggesting that slow seafloor spreading required between australia and antarctica to accommodate the continental extension further east occurred between naturaliste fracture zone and the m4 m0 anomalies adjacent to the naturaliste plateau the revised fit of india in east gondwanaland reduces the eastward extent of greater india to 95 e but does not change its extent as far north as the cape range fracture zone the new pole determined for the early cretaceous rotation between india and australia antarctica lies within 15 of the southern tip of india significantly closer than in previous determinations thereby reducing the amount of seafloor spreading generated between africa and antarctica by the india antarctica rotation and thus offering a possible solution to the perceived spreading rate problems between m11 and m0 in the somali mozambique and antarctic basins

admittance signatures of rifted and transform margins examples from eastern canada examination of the gravity and bathymetry data across the rifted scotian margin and the sheared grand banks margin off the canadian east coast using a spectral analysis or admittance approach yielded different results the admittance for the scotian margin best fitted a regional compensation model in contrast a local compensation mechanism reproduced the transfer function for the grand banks margin the results for the longer wavelengths were verified using satellite altimetry data the effect of a hidden or subsurface load was investigated for both margins and this was also found to differ the differences in the compensation mechanism between rifted and sheared margins was attributed to their formation mechanisms

thin oceanic crust below bay of bengal inferred from 3 d gravity interpretation abstract the bay of bengal bob lithosphere evolved due to rifting between india and antarctica and subsequent seafloor spreading process since the early cretaceous is known for the presence of thick bengal fan sediments covering the entire bob with maximum sediment accumulation of 22 km in the offshore bangladesh three dimensional crustal structure of the bob is investigated by integrating the sediment isopach map seismic reflection refraction and wide angle reflection data with the 3 d gravity modelling large amount of sediment seismic velocities have been used to construct depth varying density contrast with respect to the underlying crustal layer due to deeper burial effect by a quadratic density function 3 d gravity effect of the sedimentary layer computed for the derived density distribution shows large variations ranging from 5 mgal over the ninetyeast ridge near the equator to as low as 210 mgal at the apex of bengal fan in the bangladesh shelf region the residual crustal bouguer anomaly map obtained after subtracting the effect of water and sediment layers and normalised for 6 km uniform crust display crustal thickness variations with depth to moho in the bob region varying from 11 km in the south to as much as 35 km in the bangladesh shelf with moho depressed locally below both 85 e and ninetyeast ridges the total crust map obtained after subtracting the water and sediment layers from the moho depth map shows an unusually thin oceanic crust of 2 4 km in the deep basinal areas of bob and 10 12 km of thick crust below 85 e and ninetyeast ridges due to the widespread nature of observed thin crust as well as the presence of plume traces that have emplaced 85 e and ninetyeast ridges we infer its formation during plume spreading interactions in the eastern indian ocean further higher flexural rigidity of lithosphere and cold mantle in the bob region indicates that huge amount of bengal fan sediments were emplaced over the unusually thin oceanic crust and a strong mantle similar to that observed in the amazon fan

acidification buffering and salt effects in the unsaturated zone of a sandy aquifer klosterhede denmark acidification of groundwater in a noncalcareous sandy aquifer at klosterhede denmark is the result of acid rain deposition in the 4 to 5 m thick unsaturated zone the ph ranges from 4 2 to 4 9 with al concentrations of up to 0 8 mmol l sup minus 1 the groundwater at the top of the saturated zone still has a ph below 5 deposition of sea salt affects the solute profiles and its importance varies both spatially from the forest margin to the inner part of the forest and temporally through seasonal variations in infiltration and dry deposition as a result pulses of high solute concentrations travel downward through the unsaturated zone the cation exchange capacity cec of the sediments ranges between 0 2 and 1 meq 100 g sup minus 1 and in the acidified zone base saturation is around 17 the pore waters are close to equilibrium with gibbsite supersaturated for kaolinite and strongly undersaturated for other silicate minerals mass balance calculations on increases in dissolved silica over depth suggest that the buffering effect of silicate weathering is small buffering processes and solute transport were modeled with the code phreeqm simulation of pre acid rain weathering indicates that this process operates on a timescale of thousands of years more yielding minimum ph values near 5 2 and a base saturation of greater than 70 the present leaching of al sup 3 rich acid water from the soil yields acidification rates of 7 and 10 cm yr sup minus 1 for weathering of a naturally weathered and a pristine profile respectively simulation of infiltration of sea salt pulses indicates that the cation distribution quickly becomes attenuated by the exchanger composition however due to coupling of gibbsite equilibrium with ion exchange processes downward traveling pulses with high solute concentrations will cause ph variations throughout the unsaturated zone by precipitation and dissolution of gibbsite 67 refs 16 figs 3 tabs less

evolution of the cauvery basin india from subsidence modelling backstripping and sediment unloading have been carried out on stratigraphic data from wells in the various sub basins of cauvery basin to obtain tectonic subsidence curves analysis of the tectonic subsidence curves reveals that cessation of rifting extension occurred earlier on the western side and rifting persisted for a longer time on the eastern side subsidence was more or less continuous through most of cretaceous time a non uniform or two layer extension model is used to determine extension parameters from the tectonic subsidence curves the values of the crustal and subcrustal stretching parameters obtained in the various sub basins show the trends of evolution of the different sub basins the analysis suggests that the tectonic subsidence curves conform more to those in an intracratonic basin than those on a passive margin geological evidence corroborating this hypothesis are presented necessitating the classification of cauvery basin as an intracratonic failed rift basin as opposed to the earlier classification as a pericratonic basin

crustal architecture and moho topography beneath the eastern indian and bangladesh margins new insights on rift evolution and the continent ocean boundary the thick sedimentary cover 18 km along the eastern continental margin of india ecmi and over the bay of bengal has hindered understanding of the mechanisms of rifting that operated on the eastern indian and bangladesh margins analysis of multichannel seismic reflection data together with 3d gravity inversion and 2d gravity forward modelling illuminates basement configuration crustal thickness and moho topography thereby revealing the modes of rift evolution and the location of the continent ocean boundary cob along these margins the basement particularly in the shelf and slope regions of eastern peninsular india is traversed by nearly coast perpendicular graben and their seaward continuity is delineated up to 125 km from the coastline three different types of continental margin are present along the ecmi 1 sheared rift on the southern segment of the ecmi up to 14 n latitude offshore the southern granulite terrain 2 hyper extended rift in the central segment between 14 n and 17 n offshore the dharwar craton and 3 hypo extended rift on the northern segment between 17 n and 20 n offshore the eastern ghats mobile belt the graben terminations crustal thickness and moho topography of both the ecmi and offshore bengal basin clearly suggest that the cob runs nearly parallel to the coastline of peninsular india but takes an orthogonal turn offshore in the bengal basin and connects the palaeo continental shelf and the rajmahal sylhet line onshore in the bengal basin crustal thickness 8 10 km and depth to the moho discontinuity 28 km beneath the bangladesh margin are unusual because the crustal thickness increased through interaction of the kerguelen plume with the existing oceanic lithosphere the moho deepened largely due to the load of the bengal fan sediments the absence of rifted crustal blocks on the bangladesh margin and the continuity of the cob into the onshore bengal basin together imply that the present bangladesh region was under marine conditions at least until the beginning of bengal fan sedimentation i e no less than 23 ma

kimberlite from rajmahal magmatic province sr nd pb isotopic evidence for kerguelen plume derived magmas 1 previous studies showed that the rajmahal sylhet bengal rsb flood basalt province 117 2 ma in eastern india was spatially close to the active kerguelen hotspot about 118 ma ago yet it could not be unequivocally correlated to this hotspot due to wide variation in isotopic compositions of both the rsb and kerguelen plateau basalts however we report sr nd pb isotopic compositions 87sr 86sri 0 70535 to 0 70561 end t 2 6 to 3 2 206pb 204pbi 17 88 to 18 07 of a co eval 116 2 ma group ii kimberlite from this flood basalt province that is identical to recently identified pristine kerguelen plume basalts from the kerguelen plateau archipelago and broken ridge this suggests that the kerguelen hotspot could indeed be responsible for the 117 ma magmatic activity in eastern india

seabed morphology and gas venting features in the continental slope region of krishna godavari basin bay of bengal implications in gas hydrate exploration abstract increased oil and gas exploration activity has led to a detailed investigation of the continental shelf and adjacent slope regions of mahanadi krishna godavari kg and cauvery basins which are promising petroliferous basins along the eastern continental margin of india in this paper we analyze the high resolution sparker subbottom profiler and multibeam data in kg offshore basin to understand the shallow structures and shallow deposits for gas hydrate exploration we identified and mapped prominent positive topographic features in the bathymetry data these mounds show fluid gas migration features such as acoustic voids acoustic chimneys and acoustic turbid layers it is interesting to note that drilling coring onboard joides in the vicinity of the mounds show the presence of thick accumulation of subsurface gas hydrate further geological and geochemical study of long sediment cores collected onboard marion dufresne in the vicinity of the mounds and sedimentary ridges shows the imprints of paleo expulsion of methane and sulfidic fluid from the seafloor to understand the origin of the mounds and their relationship with gas hydrate cold seep formation we analyzed the multi channel seismic reflection mcs data close to the mounds the mcs data show that the subsurface layers beneath the mounds are folded below the folded overburden we observe zones of no coherent reflections probably originating from miocene sequence since the study area is located in shale tectonics regime where miocene sequences are known to be overpressured we interpret the zones of no coherent reflections as miocene shale diapirs the upward movement of shale diapirs has folded the overburden layer and resulted in the formation of numerous faults fractures these faults act as permeable pathways for fluid gas movement facilitating the formation of gas hydrate and cold seeps close to shale diapiric mound

seismicity and tectonics of the bay of bengal evidence for intraplate deformation of the northern indian plate abstract seismicity and fault plane solutions of several earthquakes in the bay of bengal have been studied to focus attention on the nature of intraplate deformation in the northern indian plate a widely dispersed diffuse seismicity provides evidence that the intraplate region of the entire bay of bengal and peninsular india of the indian plate are seismically active of which the gangetic delta and the eastern flank of the ninety east ridge show somewhat higher seismicity in comparison to the thickly populated epicenters at the eastern plate boundary predominance of thrust faulting earthquake mechanisms with consistent north dipping fault planes and more or less n s pressure axes imply that n s compression is more prevalent in the intraplate region of the bay of bengal which is analogous to the himalayan arc this intraplate seismicity and n s compressive deformation is presumed to be the result of collisional resistance to the north moving indian plate with the eurasian plate at the himalayas where subduction of the indian lithosphere in mantle has stopped recently as a result to compensate the horizontal compressive force by ridge push at the carlsberg ridge the intraplate region of the northern indian plate in continuation to the central indian ocean basin no longer remains passive due to a strong repulsive force at the collisonal plate boundary himalaya that causes stress transmission towards south and makes the intraplate region seismically active

gravity anomalies sediment loading and lithospheric flexure associated with the krishna godavari basin eastern continental margin of india abstract gravity anomalies constrained by seismic data have been used to examine the long term mechanical properties of the lithosphere beneath the krishna godavari basin a deltaic sedimentary basin on the eastern continental margin of india the gravity effect of the rift crust sedimentary loading and erosional unloading have been computed and the sum effect of these when compared with the observed gravity anomalies gives a best fitting te of 30 km at the margin the results suggest that the lithosphere which was weak during the early rifting stage has gained strength during sedimentation the onshore dipping doublet gravity anomaly at the margin reflects a weak rifted continental lithosphere abutting a strong oceanic lithosphere comparison with the results of similar investigations for the bengal basin in the north and cauvery basin in the south suggests increasing strength for the lithosphere from north to south

seismic evidence of free gas migration through the gas hydrate stability zone ghsz and active methane seep in krishna godavari offshore basin abstract seismic amplitude versus offset avo analysis was performed on the multichannel seismic data in the vicinity of site nghp 01 10 where thick fracture filled gas hydrate is reported to understand the fluid migration in fracture dominated gas hydrate system amplitude preserved common image gathers cig are used in extracting the seismic amplitude with offset for seafloor bottom simulating reflectors bsr and different horizons within the gas hydrate stability zone ghsz the extracted amplitudes are fitted with three term shuey s avo approximation to estimate the intercept and gradient values based on the intercept and gradient values two distinct classes of seismic avo responses are observed class iv avo decreasing negative amplitudes with increasing offsets and class iii avo increasing negative amplitudes with increasing offsets for the bsr and other horizons above the bsr the large negative intercept and gradient values which indicate class iii avo ranges from 0 2 to 1 8 for the inline seismic profile and from 0 01 to 0 3 for the crossline profile the presence of class iii avo anomaly within the gas hydrate stability zone ghsz provides evidence of existence of free gas which may be migrating along the fault system some of the active faults are exposed on the surface and show gas venting signatures such as gas flares and pockmarks in the multibeam data

crustal structure of the northern part of the voring basin mid norway margin from wide angle seismic and gravity data abstract three regional ocean bottom seismograph obs profiles with a total of fifteen recovered obss were acquired in the northern part of the voring basin mid norway margin in 1996 the data have been modelled by inversion and forward modelling of the obs vertical components p waves the velocity is found to increase downwards within the sedimentary layers due to increasing depth of burial confining pressure within the two deepest sedimentary layers there seems to be an increase of 0 5 1 km s in velocity northwestwards this increase is most likely caused by high velocity sill intrusions in the sedimentary rocks emplaced during the rift episode leading to early eocene opening of the ne atlantic the presence of significant amounts of sills seems to terminate close to the nyk high along profile 5 dip profile and close to a dome northwest of the shelf edge along profile 6 dip profile the velocity in the top of this dome is anomalously high 3 4 km s at only 1 km depth beneath the seafloor suggesting that the high consists of volcanic rocks or heavily intruded sedimentary rocks the relatively low velocities derived from within the upper crystalline crust 5 9 6 2 km s confirms that the crust is of continental origin within the lower crust there seems to be a clear increase in velocity northwestwards from about 7 0 km s to about 7 4 km s suggesting that the amount of high velocity intrusions underplating in the lower crust decreases landwards the modelling of the strike profile profile 7 suggests that the transition from a lower crust dominated by magmatic intrusions to a more undisturbed continental lower crust is located approximately beneath this profile the model for profile 7 ties closely southwestwards to the models derived from obs data acquired in 1992 and northeastwards to lofoten obs data acquired in 1988 the models indicate that the thick magmatic intrusions in the sedimentary rocks and lower crust extend further landwards in the area of the 1992 survey and that the transition zone is related to the surt lineament the distribution of magmatic rocks thus seems to correlate strongly with pre breakup structures in addition to the p wave modelling gravity modelling has been performed along all profiles the gravity modelling confirmed all main aspects of the obs models and provided constraints on the crustal structures towards the ends of the profiles

structure and tectonics of the southwestern continental margin of india abstract a nnw sse trending graben in the inner shelf 40 60 m isobaths a mid shelf basement ridge 60 150 m isobaths a shelf margin basin 150 1000 m isobaths and the prathap ridge complex in the slope 1000 2000 m isobaths extend as linear features along the southwestern continental margin of india between 12 20 n and 15 00 n the basic structural framework of the margin seems to be influenced by the pre existing precambrian structural fabric of the continent the mid shelf basement ridge and the prathap ridge complex are interpreted as manifestation of the rift phase volcanism when india separated from madagascar around 84 ma

shoulder uplift of the western ghats passive margin india a denudational model the paper presents a denudational rift flank uplift model of the western ghats of karnataka india the cenozoic denudation of the deccan plateau was constrained by relative dating of regional planation surface levels in combination with preliminary apatite fission track results the denudational history of the western ghats escarpment coastal foreland was constrained both by onshore fission track and offshore sediment data methods are briefly described results were used as reference data to elaborate a computer simulation model of both flexural rift flank upwarp and escarpment retreat from the k t boundary to the present depending on the assumptions concerning the attributes of the thin elastic lithospheric sheet infinite or semi infinite the shape and elevation of the initial deccan topography flat lying or affected by lithospheric updoming due to the reunion mantle plume and the position of the continental divide upon rifting the flexural response to denudational unloading is shown to yield either a concave up flexure of the dharwar craton or a convex monoclinal downwarp of the margin the relative merits of each model are discussed in the light of auxiliary field evidence particularly from the neighbouring deccan traps however the diverse assumptions on boundary conditions fail to entirely avoid geomorphological equifinality 1998 john wiley sons ltd

composition and origin of authigenic carbonates in the krishna godavari and mahanadi basins eastern continental margin of india abstract the mineralogical and stable isotopic composition of authigenic carbonates from the krishna godavari kg and mahanadi basin provide a deeper insight into the processes inducing carbonate formation in the sediments of the eastern continental margin of india in the bay of bengal authigenic carbonate cements micro nodules bioturbation casts and tubes from 12 core locations drilled during the indian national gas hydrate program nghp expedition 01 were investigated for this study three main processes responsible for authigenic carbonate precipitation are identified organoclastic sulfate reduction anaerobic oxidation of methane and methanogenesis evidence of vigorous methane seepage is indicated in carbonates recovered at sites 7 10 12 kg basin and 19 mahanadi basin these methane derived carbonates display typical paragenetic carbonate mineralogies aragonite high mg calcite with 15 mol mgco 3 ca rich dolomite two separate horizons of methane derived carbonates are correlated between 4 drill holes up to 16 km apart the upper horizon has been dated with 14 c 40 100 51 600 a bp 1950 and clearly indicates that methane seepage has been much more vigorous in the past possibly due to the effect of lower sea level on the gas hydrate stability zone across the margin

structure and early evolution of the arabian sea and east somali basin summary the laxmi ridge is a large scale basement high buried beneath the sediments of the indus fan the location of the ocean continent transition oct on this margin has previously been proposed at either the southern edge of the laxmi ridge or beyond it towards the india pakistan shelf the former explains the margin parallel laxmi basin as thinned continental crust the latter as a failed rift of earlier seafloor spreading to examine the structure of this margin a reassessment of marine magnetic data has detailed seafloor spreading magnetic anomalies prior to anomaly 24 in both the arabian and east somali basins the previously identified anomaly 28 is not interpreted as a seafloor spreading anomaly but as a magnetized basement feature adjacent to and merging with the ridge the laxmi spur new gravity models across the laxmi ridge and adjacent margin using ship and satellite data corroborate the existence of underplated crust beneath the laxmi ridge and basin and the location of the oct at the southern edge of the ridge the results are not compatible with the existence of a pre anomaly 28 phase of seafloor spreading although large scale intrusions may be the origin of some of the basement features in the laxmi basin the models also identify the laxmi spur as a low density feature with a natural remanent magnetization nrm compatible with serpentinization the laxmi ridge is mapped to the southeast where it appears to terminate at a point coinciding with the appearance of e w magnetic lineations and gravity anomalies at 15 5 n thereafter it becomes indistinct this is interpreted as necessary in the reconstruction to the mascarene plateau to avoid continental overlap

wide and narrow margins of the brazilian south atlantic two contrasting end members of passive continental margins here referred to as wide and narrow margins are present in the south atlantic although some margin segments are intermediate between these two styles narrow margins are characterized by a large bounding fault 4 km throw near the shelf edge a sharp transition zone 10 20 km wide from normal thickness to substantially thinned continental crust or oceanic crust where the total width of extended continental crust is usually less than 100 km wide continental margins are characterized by a broad continental shelf and a wide zone 50 600 km of thinned crust with an even distribution of faults wide margins usually have a more gentle continental shelf and slope narrow narrow wide wide and wide narrow conjugate margin pairs exist in the south atlantic and are suggested to be controlled mainly by the opening kinematics and the thermal structure of the lithosphere during rifting basement structure and strain rate appear to have exerted little control on the style of margin extension although basement architecture appears to control the trend of the initial rifts the positions of fracture zones which separate narrow and wide segments and the rate of lateral rift propagation

the erosional and uplift history of ne atlantic passive margins constraints on a passing plume new apatite fission track analyses from nw britain indicate that a maximum of 2 5 km of erosion has occurred there during the cenozoic similar to values for se greenland and the east greenland coast north of scoresby sund the erosion may have been facilitated by magmatic underplating during break up however at kangerdlugssuaq east greenland 4 6 km of erosion is measured since 45 ma lower mid eocene marine sedimentary rocks overlying the lavas on the blosseville coast indicate that magmatic underplating on the central greenland coast substantially post dated flood volcanism and break up behaviour not predicted by simple plume rift models subsidence reconstructions of the hebrides shelf and the east and west greenland coasts show that rapid dynamic uplift was effectively synchronous at 63 ma and preceded volcanism by c 400 m is compatible with a mantle temperature anomaly of c 100 c these data suggest very rapid lateral flow of the impacting iceland plume head the predicted crossing of the plume by the east greenland coast in the mid late eocene would account for post rift magmatic underplating and dynamic support on the greenland but not the european side of the north atlantic basin

occurrences of large magnitude earthquakes in the kachchh region gujarat western india tectonic implications abstract moderate to large damaging earthquakes in the peninsular part of the indian plate do not support the long standing belief of the seismic stability of this region the historical record shows that about 15 damaging earthquakes with magnitudes from 5 5 to 8 0 occurred in the indian peninsula most of these events were associated with the old rift systems our analysis of the 2001 bhuj earthquake and its 12 year aftershock sequence indicates a seismic zone bound by two linear trends nnw and nne that intersect an e w trending graben the bouguer gravity values near the epicentre of the bhuj earthquake are relatively low 2 mgal the gravity anomaly maps the distribution of earthquake epicentres and the crustal strain rate patterns indicate that the 2001 bhuj earthquake occurred along a fault within strain hardened mid crustal rocks the collision resistance between the indian plate and the eurasian plate along the himalayas and anticlockwise rotation of the indian plate provide the far field stresses that concentrate within a fault bounded block close to the western margin of the indian plate and is periodically released during earthquakes such as the 2001 m w 7 7 bhuj earthquake we propose that the moderate to large magnitude earthquakes in the deeper crust in this area occur along faults associated with old rift systems that are reactivated in a strain hardened environment

juxtaposition of india and madagascar a perspective abstract proterozoic terrains in south india and madagascar provide important clues in understanding the gondwanaland tectonics especially the assembly of this mega continent during the pan african period the archaean terrains in both madagascar and india are characterized by n s trending greenstone belts occurring within gneissose granitic rocks in the northern part extensive development of k rich granitic rocks of ca 2 5 ga is also characteristic in both areas such a broad age zonation of younger dharwar ca 2 6 3 0 ga in the north and the older sargur ca 3 0 3 4 ga in the south as in south india remains to be identified in future studies from madagascar the occurrence of greenschist facies rocks in the northeastern part and higher grade rocks in most of other parts in the north central terrain of madagascar is comparable with the general tendency of increasing metamorphic grade from northwestern to southern areas ranging from greenschist to granulite facies in south india the proterozoic crystalline rocks in both continents show pronounced lithological similarity with the wide occurrence of graphite bearing khondalite in association with charnockitic rocks while the archaean proterozoic boundary is well defined in southern india by the palghat cauvery or the kkpt shear zones as recently identified this boundary is ill defined in madagascar due to extensive pan african overprinting as well as the development of the proterozoic cover sequence the itremo group there is also a possible general correlation between the mesoproterozoic cover sequences in madagascar and india such as between the itremo group of west central madagascar and the kaladgi and cuddapah sequences of south india the pan african granulite facies metamorphism of ca 0 5 ga extensively developed in both india and madagascar is generally comparable in intensity and extent p t conditions and p t t paths also appear comparable with the general range of ca 700 1000 c and 6 9 kb and near isothermal decompressional paths a type granite plutons and alkaline rocks including anorthosites and mafic plutonic rocks of ca 500 800 ma develop in both terrains provide strong basis for the correlation of both terrains and define a pan african igneous province within east gondwanaland major shear zones in both continents are expected to play a critical role in the correlation albeit are still poorly constrained detailed elucidation of the tectonic history of the shear zones and the timing of various events along the shear zones would provide important constraints on the correlation of the two continental fragments

understanding the thermal evolution of deep water continental margins areas of exploration for new hydrocarbons are changing as the hydrocarbon industry seeks new resources for economic and political reasons attention has turned from easily accessible onshore regions such as the middle east to offshore continental shelves over the past ten years there has been a marked shift towards deep water continental margins 500 2 500 m below sea level in these more hostile regions the risk and cost of exploration is higher but the prize is potentially enormous the key to these endeavours is a quantitative understanding of the structure and evolution of the thinned crust and lithosphere that underlie these margins

tectonics of the bay of bengal new insights from satellite gravity and ship borne geophysical data abstract recently released satellite derived free air gravity anomalies and the existing ship board geophysical data provide new insights into the tectonics of the bay of bengal with respect to the structure and regional extension of the buried 85 e ridge and the tectonics of the eastern continental margin of india ecmi the 85 e ridge can be visualized extending inland via the mahanadi basin volcanics to the rajmahal traps a large volcanic province in eastern india encompassing the rajmahal and sylhet traps and volcanics in the bengal and mahanadi basins almost on the scale of the deccan volcanic province along the west coast can be envisaged taking into account the occurrences of intrusive and extrusive rocks around the age of 117 ma the 85 e ridge represents the deep ocean volcanic trace of this magmatic activity towards the south the ridge continues in an arcuate manner to the afanasy nikitin seamount at equatorial latitudes in the central indian ocean gravity models of the ridge are indicative of hotspot related crustal underplating processes beneath the ridge the ecmi can be divided into a southern transform and northern rifted segments on the basis of gravity and bathymetry data which bear similarities with the conjugate east antarctica margin

morphotectonic architecture of an india madagascar breakup related anomalous submarine terrace complex on the southwest continental margin of india abstract an anomalous lateral bathymetric protrusion alleppey trivandrum terrace complex attc in the form of two contiguous terrace like features exists in the mid continental slope off southwest coast of india this bathymetric protrusion and a bathymetric notch in the northern madagascar ridge nmr have been postulated as conjugate features related to india madagascar separation in late cretaceous however geoscientific studies aimed to understand the crustal structure and genesis of the attc or its postulated conjugate region are meagre and ambiguous in this context the present study based on recently acquired as well existing bathymetry gravity magnetic and multi channel seismic reflection data was carried out to understand the morphotectonic architecture of the attc the bathymetric data suggest an escarpment chain kairali escarpment cke to demarcate the westward limit of the attc and another escarpment quilon escarpment qe to demarcate the boundary between the southerly larger trivandrum terrace tt and northerly smaller alleppey terrace at the multichannel seismic reflection data suggests a block faulted basement and presence of a nearly n s trending wide basement high in the central part of the trivandrum terrace forward modelling of gravity data constrained by seismic reflection information suggests that the crustal structure of the attc region is comparable to thinned continental crust forward modelling of prominent high amplitude magnetic anomalies suggest that the thinned continental crust of the attc region also contains volcanic bodies as intrusives extrusives the cke is inferred to be a sheared continental margin segment along which the se coast of madagascar glided past india and the volcanic emplacements in the attc region perhaps relates to the marion hotspot volcanism

analyses of multichannel seismic reflection gravity and magnetic data along a regional profile across the central western continental margin of india abstract analyses of multichannel seismic reflection gravity magnetic and bathymetry data along a regional profile across the central western continental margin of india have revealed the depositional pattern of sediments crustal structure and tectonics the four most distinct and varied crustal regions of the margin are palaeo shelf edges shelf margin basin prathap and laccadive ridges and the arabian basin the shelf margin basin is carpeted by 4 5 km maximum thick aggraded and prograded paleocene to holocene sediments six major seismic sequences of the sediments of the margin are identified and their ages are assigned on correlation with drill well results development of the sequence boundaries is attributed to the events of rifting of western india eustatic sea level changes indian and eurasian plate collision and himalayan orogeny tilted fault blocks half grabens located almost equi distance from the igneous construct of the prathap ridge in the shelf margin basin suggest a failed rift associated with stretched continental crust of the basin 2 d model studies of gravity and magnetic anomalies constrained by the seismic results have revealed 6 to 27 km thick crust across the margin the laccadive ridge crust limited by two volcanic intrusives and a steep scarp at its western end is 16 km thick it gradually thins towards offshore and juxtaposed with early tertiary normal oceanic crust 6 km thick of the arabian basin the crustal thickness and velocity and density structure of the ridge are comparable to that of the laxmi ridge a continental sliver the inferences and abrupt change in magnetic and gravity anomaly signatures across the western end of the laccadive ridge mark the zone of transition from continental to oceanic crust

effective elastic thickness along the conjugate passive margins of india madagascar and antarctica a re evaluation using the hermite multitaper bouguer coherence application abstract gondwana correlation studies had rationally positioned the western continental margin of india wcmi against the eastern continental margin of madagascar ecmm and the eastern continental margin of india ecmi against the eastern antarctica continental margin eacm this contribution computes the effective elastic thickness te of the lithospheres of these once conjugated continental margins using the multitaper bouguer coherence method the results reveal significantly low strength values te 2 km in the central segment of the wcmi that correlate with consistently low te values 2 3 km obtained throughout the entire marginal length of the ecmm this result is consistent with the previous te estimates of these margins and confirms the idea that the low te segments in the central part of the wcmi and along the ecmm represents paleo rift inception points of the lithospheric margins that was thermally and mechanically weakened by the combined action of the marion hotspot and lithospheric extension during the rifting the uniformly low te value 2 km along the eacm indicates a mechanically weak lithospheric margin probably due to considerable stretching of the lithosphere considering the fact that this margin remained almost stationary throughout its rift history in contrast the ecmi has comparatively high te variations 5 11 km that lack any correlation with the regional tectonic setting using gravity forward and inversion applications we find a leading order of influence of sediment load on the flexural properties of this marginal lithosphere the study concludes that the thick pile of the bengal fan sediments in the ecmi masks and has erased the signal of the original load induced topography and its gravity effect has biased the long wavelength part of the observed gravity signal the hence uncorrelated flat topography and deep lithospheric flexure together contribute a bias in the flexure modeling which likely accounts a relatively high te estimate

southern granulite terrain south of the palghat cauvery shear zone implications for india madagascar connection abstract the present paper correlates the southern madgascar terrain south of the ranotsara shear with the granulite terrain of southern india occurring south of the palghat cauvery p c shear zone both the terrains have witnessed high temperature to ultra high temperature granulite metamorphism at 550 ma and are traversed by shear zones and deep crustal faults the 550 ma old granulite terrains of madagascar and southern india have similar lithologies in particular sapphirine bearing pelitic assemblages graphite deposits and gem occurrences are common to both these terrains the 550 ma old southern granulite terrain of southern india comprises of different blocks the madurai and the kerala khondalite belt but all the blocks have similar lithologies with pelite calc silicate rocks inter banded with two pyroxene granulite bodies these lithologies occur amidst an essentially charnockitic terrain the protolith ages of the southern granulite terrain south of the p c shear zone ranges between 2400 2100 ma the terrain as a whole has witnessed the 550 ma old granulite event the granulite metamorphism took place under temperatures of 800 1000 c and at pressures of 9 5 to 5 kbar the source of heat for the high temperature granulite event of the southern madagascar terrain has been linked to advective heat transfer along mantle deep faults the source for the high temperature granulite metamorphism for the southern granulite terrain may be attributed to high temperature carbonatite and alkaline intrusives in an extensional setting which followed an initial crustal thickening many workers have linked madagascar to southern india by connecting the ranotsara shear either to the p c shear zone or to the achankovil shear zone further south the important factor is the lithologies of the madagascar terrain south of ranotsara shear zone and the 550 ma old southern indian granulite terrain are similar in many aspects it will be more appropriate to link the ranotsara shear to the curvilinear lineament bounding the anaimalai kodaikanal ranges and which merges with the southern margin of the p c shear zone however north of the ranotsara shear fault the northern madagascar terrain comprises of a dominant itremo sequence

evidence for multiphase folding of the central indian ocean lithosphere long wavelength 100 300 km folding in the central indian ocean associated with the diffuse plate boundary separating the indian australian and capricorn plates is earth s most convincing example of organized large scale lithospheric deformation to test the timing and mechanics of this deformation as implied by plate kinematic and deformation models we present a new analysis of the seismic stratigraphy of the bengal fan sediments this analysis shows that the folding of the oceanic lithosphere was multiphase with major events occurring in the miocene 8 0 7 5 ma pliocene 5 0 4 0 ma and pleistocene 0 8 ma the miocene phase was the most intense and involved deformation of an area south of 1 s whereas in the pliocene the activity shifted northward in the final phase pleistocene the activity was focused in the equatorial region no evidence was found for deformation prior to 8 0 7 5 ma the spatial extent of the pleistocene folding event overlaps the pliocene and or miocene folding events and coincides with both the area of most active faulting and the zone of greatest historical seismicity the seismic data show that the timing of reverse faulting and thus more significant shortening of the lithosphere generally coincided with the phases of folding but there are examples of folding of the oceanic lithosphere without associated reverse faulting

feature modeling approach to simulating loop current frontal eddies abstract loop current frontal eddies lcfe in the gulf of mexico are simulated with a regional configuration of the princeton ocean model using a feature oriented initialization technique the initialization procedure is based on a prior investigation of stability characteristics of the loop current lc zonal channel experiments conducted with a multi layer intermediate equations model allowed to identify conditions necessary for formation and growth of frontal eddies the simulations were able to reproduce key features of lcfe topography interaction in the desoto canyon region observed during the eddy intrusion study

structural lineaments from the magnetic anomaly maps of the eastern continental margin of india ecmi and nw bengal fan abstract three major structural lineaments are inferred from the magnetic and bathymetry data collected over the eastern continental margin of india ecmi and nw bengal fan covering the area between 10 55 n to 20 15 n and 80 e to 88 e analysis of magnetic data associated with these trends suggests that 1 trend i located at the foot of the continental slope around 3000 m water depth represents the ocean continent boundary ocb of ecmi 2 trend ii represents the northern extension of 85 e ridge abutting the continental shelf off chilka lake and 3 trend iii located over the continental shelf slope between visakhapatnam and paradip represents a folded ridges and depressions nature of the continental basement the study also reveals the occurrence of dyke intrusions within the continental crust landward of ocb which might be related to the rift phase volcanism along the ecmi

evidence of underplating from seismic and gravity studies in the mahanadi delta of eastern india and its tectonic significance 1 we have imaged the crustal configuration of the mahanadi delta of eastern india by modeling both wide angle seismic and bouguer gravity data this delta has undergone several stages of rifting subsidence sedimentation and uplift it is one of the important gondwana sedimentary basins of india where widespread volcanic activity occurred during the early cretaceous along the rift zones this volcanic activity corresponds to the breakup of greater india from east gondwana e g present antarctica and australia we have derived a five layer crustal model with velocities of 6 0 6 5 6 0 7 0 and 7 5 km s having estimated densities of 2 7 2 8 2 65 2 9 and 3 05 g cm3 respectively the velocity density relation along with heat flux and other geological geochronological information indicates typical rift related evolution of the delta with a midcrustal low velocity 6 0 km s and low density 2 65 g cm3 zone and a 10 km thick high velocity 7 5 km s and high density 3 05 g cm3 layer at the base of the crust presumably due to underplating the moho upwarping or crustal thinning in the rift zone and emplacement of thick high velocity material at the base of the crust strongly suggests basaltic underplating probably due to the kerguelen hot spot activity these activities are synchronous with 117 ma rajmahal volcanism in northeast india and the lambert graben in east antarctica and are closely associated with the gondwana breakup in the india antarctica sector the rifting stages are closely correlated with the sedimentation phases of the lower and upper gondwana deposits in the mahanadi delta which evolved parallel to the lambert graben in east antarctica