structure of the north indian continental margin in the ladakh zanskar himalayas implications for the timing of obduction of the spontang ophiolite india asia collision and deformation events in the himalaya the collision of india and asia can be defined as a process that started with the closing of the tethyan ocean that during mesozoic and early tertiary times separated the two continental plates following initial contact of indian and asian continental crust the indian plate continued its northward drift into asia a process which continues to this day in the ladakh zanskar himalaya the youngest marine sediments both in the indus suture zone and along the northern continental margin of india are lowermost eocene nummulitic limestones dated at similar 54 ma along the north indian shelf margin southwest facing folded palaeocene lower eocene shallow marine limestones unconformably overlie highly deformed mesozoic shelf carbonates and allochthonous upper cretaceous shales indicating an initial deformation event during the latest cretaceous early palaeocene corresponding with the timing of obduction of the spontang ophiolite onto the indian margin it is suggested here that all the ophiolites from oman along western pakistan bela muslim bagh zhob and waziristan to the spontang and amlang la ophiolites in the himalaya were obducted during the late cretaceous and earliest palaeocene prior to the closing of tethys

synsedimentary tectonic soft sediment deformation and volcanism in the rifted tethyan margin from the upper triassic middle jurassic deep water carbonates in central sicily abstract the pizzo lupo section sicanian mts central sicily is an upper triassic lower jurassic condensed deep water succession where the relationships among synsedimentary tectonic soft sediment deformations volcanism and lithological changes reflect the evolution of a rift basin the morphostructural setting of the studied basin appears as a gently dipping slope where a fault delimited area graben to halfgraben was developed the instability of the sea floor related to the seismic shocks was the cause of the gravity driven deformational sedimentary structures slumping breccia channelized bodies the partly stratified basaltic rocks with disorganized and chaotic stratification suggest the occurrence of a volcanic complex located in neighbouring areas a regional comparison with the tectono sedimentary evolution of the pelagic drowning platform succession i e trapanese domain auct outcropping in adjacent areas suggests that these different domains were close to each other during the studied period forming a stepped margin platform to basin system the environmental changes synsedimentary tectonic activity and gravity driven phenomena were the result of repeated events occurred during a long time interval spanning from late triassic to early jurassic

sedimentology and tectonic implications of the lamayuru complex deep water facies of the indian passive margin indus suture zone ladakh himalaya

mesozoic deep water slope rise sedimentation and volcanism along the north indian passive margin evidence from the karamba complex indus suture zone western ladakh himalaya abstract mesozoic deep water sedimentary and basic volcanogenic rocks defined as the karamba complex are exposed within the indus suture zone of western ladakh n india the karamba complex originated as part of the north indian passive margin in its entirety and does not include exotic melange or accreted oceanic units as recently suggested the complex preserves younger more distal equivalents relative to more proximal deep water slope lamayuru complex and shelf zanskar successions of the north indian passive margin the karamba complex is mainly inverted youngs to the nnw and includes many outcrop scale folds that face nnw the complex was initially emplaced onto the zanskar shelf as three main thrust slices probably in the latest cretaceous and later inverted faulted and sheared during mid late tertiary nw backthrusting that accompanied uplift of the high himalaya sedimentation in the karamba complex began in the mid late triassic with mainly siliciclastic turbidites derived from the indian basement together with redeposited limestones and minor basic volcanics mixed radiolarian sediments siliciclastic turbidites and redeposited shelf derived calciturbidites accumulated in early mid jurassic accompanied by eruption of alkaline volcanic rocks mainly in the mid jurassic the probable cause of the jurassic volcanism was a pulse of crustal extension along the continent ocean transition zone triggered by late stage rifting of india from gondwana as a precursor to its northward drift quartzose sandstone turbidites accumulated on the upper slope in the early cretaceous whereas sedimentation on the lower slope rise was pelagic marked by depositional hiatuses and sediment redeposition during the late cretaceous a switch to mainly calcareous pelagic deposition took place interspersed with radiolarian accumulation on the lower slope rise initial thrust emplacement onto the zanskar shelf in the latest cretaceous is suggested by the absence of post upper cretaceous sediments within the karamba complex

a biogeographically mixed late guadalupian late middle permian brachiopod fauna from an exotic limestone block at xiukang in lhaze county tibet a total of 17 brachiopod species belonging to 15 genera are recorded from a limestone block of about 3 4 km2 in the indus tsangbo suture zone at xiukang in lhaze county of tibet the brachiopod fauna generally indicates a late guadalupian age late wordian capitanian late middle permian based on its association with the timorites bearing ammonoid fauna and the presence of the brachiopod urushtenoidea crenulata palaeobiogeographically the fauna exhibits transitional mixed characters between the warm water cathaysian and cold to temperate gondwanan faunas and may have developed on a carbonate build up or seamount on the oceanic crust

composition and origin of hydrothermal ironstones from central pacific seamounts abstract ironstones recovered from five late cretaceous seamounts in the central pacific region probably formed during late stage edifice building volcanism ironstones are dense and compact with the appearance of brown chert the ironstones are characterized by a goethite mineralogy with feooh contents up to 88 extreme fractionation of fe and mn low trace element and rare earth element abundances low co zn ratios and isotopic equilibration temperatures of about 20 45 c these characteristics indicate that the ironstones formed from hydrothermal fluids ironstones probably formed below the seawater seafloor interface as indicated by their occurrence as a proximal hydrothermal deposit presence of primary goethite cement pervasive replacement of rocks by goethite and absence of interbedded pyro clastic beds

the dras arc complex lithofacies and reconstruction of a late cretaceous oceanic volcanic arc in the indus suture zone ladakh himalaya abstract the purpose of this paper is to give an integrated description and interpretation of mainly volcaniclastic sediments related to excellently exposed oceanic volcanic arc successions in the ladakh himalayas the mainly late cretaceous aptian paleocene dras arc complex in the indus suture zone n india is reconstructed as an oceanic arc passing southwards into a proximal to distal forearc apron the arc complex comprises three structural units from west to east these are the suru unit the naktul unit and the nindam formation the suru unit and the naktul unit are unconformably underlain by dissected late jurassic oceanic crust and mantle the suru unit preserves the interior of the arc and is divided into dras 1 and dras 2 sub units the dras 1 sub unit of mid late cretaceous age was intruded by arc plutonics deformed then unconformably overlain by the poorly dated dras 2 sub unit lower tertiary the dras 1 sub unit comprises arc extrusives volcaniclastic and tuffaceous sedimentary rocks and mainly redeposited shallow water limestones the dras 2 sub unit is dominated by coarse volcaniclastics and lava flows passing up into rhythmically layered acidic extrusives with interbedded turbiditic siltstones and siliceous pelagic limestones further east the naktul unit is mainly clastic with large volumes of massive volcaniclastic talus thick bedded debris flows volcaniclastic turbidites and reworked shallow water carbonates pillowed extrusives and ribbon radiolarites are present mainly low in the succession in some areas while pelagic carbonates are abundant near the top the naktul unit is interpreted as a proximal forearc apron the nindam formation in the east is dominated by deep water volcaniclastic turbidites tuffaceous sediments and pelagic carbonates with subordinate debris flows and is interpreted as a distal deep water forearc succession cyclical alternations of mainly volcaniclastics and pelagic carbonates in the nindam formation are thought to reflect relative sea level changes of tectono magmatic and or global eustatic origin the oceanic dras arc complex formed within neotethys in the mid late cretaceous above an assumed northward dipping subduction zone around 79 ma campanian the oceanic arc underwent collisional deformation possibly related to accretion to the trans himalaya ladakh block and or the southern margin of eurasia to form an andean type active continental margin the suru unit in the west dras 1 sub unit was deformed then overlain by the mainly acidic dras 2 sub unit however there is no direct evidence that the nindam formation in the east was deformed until the early eocene when final collision of india and eurasia took place with southward thrusting of the dras arc complex this was followed by partial erosion during deposition of the indus molasse and then back thrusting and folding related to uplift of the high himalayas in the later tertiary

constraints to the timing of india eurasia collision a re evaluation of evidence from the indus basin sedimentary rocks of the indus tsangpo suture zone ladakh india deposited within the indus tsangpo suture zone the cenozoic indus basin sedimentary rocks have been interpreted to hold evidence that may constrain the timing of india eurasia collision a conclusion challenged by data presented here the eurasian derived 50 8 51 ma chogdo formation was previously considered to overlie indian plate marine sedimentary rocks in sedimentary contact thus constraining the timing of collision as having occurred by this time using isotopic analysis u pb dating on detrital zircons ar ar dating on detrital white mica sm nd analyses on detrital apatite sandstone and conglomerate petrography mudstone geochemistry facies analysis and geological mapping to characterize and correlate the formations of the indus basin sedimentary rocks we review the nature of these contacts and the identification and correlation of the formations our results reveal that previously interpreted stratigraphic contacts identifying chogdo formation unconformably overlying indian plate sedimentary rocks are incorrect rather we suggest that the inaccuracy of previous interpretations is most likely a result of formation misidentification and thus cannot be used to constrain the timing of india asia collision

plastic deformation of garnets systematics and implications for the rheology of the mantle transition zone abstract plastic properties of materials with garnet structure have been studied under wide temperature conditions ranging from room temperature to 95 of the melting temperatures using uniaxial compression and hot microhardness tests garnets studied include single crystals of oxide garnets y 3 al 5 o 12 gd 3 ga 5 o 12 and y 3 fe 5 o 12 and silicate garnets various solid solutions including grossular almandine andradite pyrope spessartine and uvarovite both uniaxial compression and hot hardness tests indicate that there is a general trend in the plasticity of garnets when the data are compared at normalized conditions t t m and and that the resistance to plastic deformation in garnets is significantly higher than most of the other minerals in the earth s mantle based on both stress dip tests and microstructural observations it is proposed that the creep strength of garnet is largely controlled by the resistance to dislocation glide rather than by recovery processes this conclusion is consistent with the high peierls stress inferred from the hot hardness tests the high peierls stress in garnets is presumably due to the large unit cell i e long burgers vectors and or the bcc packing which are common to all garnets we postulate therefore that the present results can be applied to the strength of high pressure garnet majorite and suggest that garnet rich layers in the earth such as subducted oceanic crust in the transition zone or a possibly garnet rich bottom part of the transition zone will be considerably stronger than surrounding regions

tectonic evolution of the qiangtang block northern tibet during the late cisuralian late early permian evidence from fusuline fossil records abstract the tectonic evolution of the qiangtang block in the qinghai tibetan plateau has been a controversial subject for a long time in this paper the discovery of new stratigraphic and fusuline fossil evidence from the permian sequences qudi and lugu formations of the qiangtang block is reported and the palaeogeographical position and tectonic history of this block during the late cisuralian late early permian are discussed the qudi formation is typified by thick turbidite deposits and contains artinskian fusulines such as pseudofusulina and chalaroschwagerina the fusulines were deposited as grains involved in debris flow deposits suggesting a synchronicity with the depositional time of the turbidites the subsequent lugu formation is dominated by seamount type carbonates with an irregular basalt base fusulines cancellina pseudodoliolina and parafusulina in the base of the carbonates confirm its age as middle kungurian the transition from the turbidite qudi formation to the seamount lugu formation is here interpreted to be a continuous depositional process recording the qiangtang block s separation from the indian plate this separation signaled the opening of the neotethys ocean between the qiangtang block and the indian plate palaeogeographically the qiangtang block s separation is comparable with the baoshan block s separation in the east and central pamir s separation in the west by contrast the ultimate opening of the neotethys ocean by the separation of india pakistan and northern oman is apparently much later than this event recorded in the qiangtang block consequently it is interpreted that the opening of the neotethys ocean in the whole northern gondwanan margin is a diachronous series of events

rheological modelling and deformation instability of lithosphere under extension summary continental break up which precedes oceanic accretion probably results from an unstable extension of the lithosphere analogous to necking of metals when they are submitted to tension by reason of complexity of the rheology no conclusion about lithospheric extension stability may be reached by an a priori analysis we thus examine directly the evolution when the lithosphere is stretched of lateral inhomogeneities represented in our example by small scale variations of thickness the rheological model is derived from the hypotheses of brace kohlstedt 1980 and is consistent with the results of rock mechanics the lithosphere consists of three or four layers of varying thicknesses and mechanical properties the brittle upper crust and eventually the brittle part of the mantle are assimilated to perfectly plastic media and are described in a state of uniform extension by a constant viscosity in the lower crust and ductile mantle lithosphere the effective viscosity is supposed to be exponential the mechanical model relies on a perturbation method developed by fletcher hallet 1983 among others contrary to previous published results no unstable behaviour of the lithosphere is observed unless the latter is more dense than the asthenosphere in which case a gravitational instability may develop this discrepancy can be explained by differences in assumptions concerning the variation of strength in the lithosphere as yet poorly constrained by the data we observe a great sensitivity of the results to the strength stratification and to the artificial discontinuities of density or viscosity implied by the models

what drives orogeny in the andes the andes the world9s second highest orogenic belt were generated by the cenozoic tectonic shortening of the south american plate margin overriding the subducting nazca plate we use a coupled thermomechanical numerical modeling technique to identify factors controlling the intensity of the tectonic shortening from the modeling we infer that the most important factor was accelerated westward drift of the south american plate changes in the subduction rate were less important other important factors are crustal structure of the overriding plate and shear coupling at the plates9 interface the model with a thick 40 45 km at 30 ma south american crust and relatively high friction coefficient 0 05 at the nazca south american interface generates 300 km of tectonic shortening during 30 35 m y and replicates the crustal structure and evolution of the high central andes the model with an initially thinner

a simple global model of plate dynamics and mantle convection cooling and thickening of lithospheric plates with age and subduction result in large scale horizontal density contrasts tending to drive plate motions and mantle flow we quantify the driving forces associated with these density contrasts to determine if they can drive the observed plate motions first two dimensional models are computed to evaluate the effects of assumed rheologies and boundary conditions we are unable to obtain platelike behavior in viscous models with traction free boundary conditions the piecewise uniform velocities distinctive of plate motion can be imposed as boundary conditions and the dynamic consistency of the models evaluated by determining if the net force on each vanishes if the lithosphere has a newtonian viscous rheology the net force on any plate is a strong function of the effective grid spacing used leading to ambiguities in interpretation incorporating a rigid plastic lithosphere which fails at a critical yield stress into the otherwise viscous model removes these ambiguities the model is extended to the actual three dimensional spherical plate geometry the observed velocities of rigid plastic plates are matched to the solution of the viscous stokes equation at the lithosphere asthenosphere boundary body forces from the seismically observed slabs from the thickening of the lithosphere obtained from the actual lithospheric ages and from the differences in structure between continents and oceans are included interior density contrasts such as those resulting from upwellings from a hot bottom boundary layer are assumed to occur on a scale small compared to plate dimensions and are not included the driving forces from the density contrasts within the plates are calculated and compared to resisting forces resulting from viscous drag computed from the three dimensional global return flow and resistance to deformation at converging boundaries the rms residual torque is 30 of the driving torque the density contrasts within the plates themselves can reasonably account for plate motions body forces from convection in the interior may provide only a small net force on the plates at converging boundaries the lithosphere has a yield stress of 100 bars drag at the base of the plates is 5 bars and resists plate motion the net driving forces from subducting slabs and collisional resistance are localized and approximately balance driving forces from lithospheric thickening are distributed over the areas of the plates as is viscous drag the approximate balance of these two forces predicts plate velocities uncorrelated with plate area as observed the model represents a specific case of boundary layer convection the dynamical results are consistent with either upper mantle or mantle wide convection

fluid evolution of indus basin ladakh north west himalaya india constraint from fluid inclusion and oxygen isotope thermometry fluid inclusions and oxygen isotope thermometry were carried out on quartz calcite veins of the indus basin in indus suture zone isz of northwest ladakh himalaya to constrain fluid evolution history of the basin three types of veins are identified as fault fill network and sigmoidal in the study area the fault fill veins microstructures of calcite and quartz suggest the deformation temperature of veins between 250 and 400 c and oxygen isotope thermometry provide the range between 192 and 359 c the network type veins microstructures of calcite revel deformation temperature in the range of 170 250 c and oxygen isotope thermometry indicate vein temperature range between 144 and 276 c stable isotopic values of sigmoidal and network type veins suggest the magmatic source of fluid the fault fill veins display magmatic to the marine fluid signature microstructures and isotope data set advocate the formation of veins from the wall rocks by leaching processes fluid inclusion microthermometric dataset indicates that veins were formed at a maximum depth of 20 km at 700 c the co2 fluids were trapped below 6 2 kbar at 700 c ch4 fluid was trapped at a shallower depth between 4 2 kbar 650 c and 2 3 kbar 381 c the primary aqueous fluids were trapped below 3 0 kbar up to 2 3 kbar at 594 to 382 c and secondary aqueous fluids were trapped between 2 9 and 1 5 kbar at 359 to 197 c the p t path for the entrapment defines an initial isothermal decompression itd itd is also supported by decrepitated and stretched inclusions texture as well as c shaped or hook like fluid inclusions morphology which collectively points towards fast basin uplift

terrestrial planet evolution in the stagnant lid regime size effects and the formation of self destabilizing crust the ongoing discovery of terrestrial exoplanets accentuates the importance of studying planetary evolution for a wide range of initial conditions we perform thermal evolution simulations for generic terrestrial planets with masses ranging from that of mars to 10m in the stagnant lid regime the most natural mode of convection with strongly temperature dependent viscosity given considerable uncertainty surrounding the dependency of mantle rheology on pressure we choose to focus on the end member case of pressure independent potential viscosity where viscosity does not change with depth along an adiabatic temperature gradient we employ principal component analysis and linear regression to capture the first order systematics of possible evolutionary scenarios from a large number of simulation runs with increased planetary mass crustal thickness and the degree of mantle processing are both predicted to decrease and such size effects can also be derived with simple scaling analyses the likelihood of plate tectonics is quantified using a mantle rheology that takes into account both ductile and brittle deformation mechanisms confirming earlier scaling analyses the effects of lithosphere hydration dominate the effects of planetary mass the possibility of basalt eclogite phase transition in the planetary crust is found to increase with planetary mass and we suggest that massive terrestrial planets may escape the stagnant lid regime through the formation of a self destabilizing dense eclogite layer

influence of water fugacity and activation volume on the flow properties of fine grained anorthite aggregates 1 to specify quantitatively the effect of pressure and water weakening on the flow strength of feldspar we performed triaxial creep experiments in a gas deformation apparatus at temperatures of 1000 1150 c confining pressures of 100 450 mpa and axial stresses of 10 400 mpa resulting in strain rates of 6 10 7 to 3 10 3 s 1 dense samples with a grain size of 3 m were prepared by hot isostatic pressing of anorthite glass powder hydrous samples contain about 0 33 0 14 wt h2o and dry specimens 0 0005 0 02 wt h2o the estimated residual glass content of wet samples is 2 vol samples deformed by grain boundary diffusion controlled creep at low stresses and dislocation creep at stresses 150 mpa we estimate an activation volume of v 24 cm3mol 1 for anhydrous samples deforming in diffusion creep for wet samples deformed in hydrous conditions with varying buffers fixing oxygen fugacity the activation volume is about 38 cm3 mol 1 creep rate of hydrous anorthite aggregates depends on water fugacity raised to a power of r 1 0 0 3 suggesting hydrolysis of oxygen bonds considering the effect of activation volume and water fugacity on extrapolation of constitutive laws to conditions prevailing in the continental lower crust viscosities of hydrous feldspar aggregates increase by a factor of 3

numerical simulation of rayleigh taylor instability for single and multiple salt diapirs abstract the diapiric ascent of light rocks through a denser oberburden is simulated using a new numerical method based in part on finite differences rocks are modelled as viscous newtonian liquids and the internal interfaces are located with the help of passive markers these markers are relocated using a new algorithm equivalent to a cellular automaton rule this allows the markers to be redistributed very rapidly this new method appears to be well adapted to quickly resolving geological problems simulations of the growth of a single dome are performed under various viscosity ratios for the salt and the overburden the effect of asymmetrical initial deformations of the salt layer is to produce diapiric structures that slowly return to symmetry as the diapir matures and rises in an isotropic medium simulations involving continuous sedimentation of the overburden are also performed an initial geometry on a basin margin in which multiple diapirs eventually develop is studied diapirs grow relatively rapidly near the centre while on the margins the salt layer flows upward following the basement simulations with salt that is more viscous than sediments show the development of previously unnoticed asymmetrical structures

rift related sedimentation and volcanism of the north indian margin inferred from a permian triassic exotic block at lamayuru indus suture zone ladakh himalaya and regional comparisons abstract stratigraphical petrographical and geochemical work on an important limestone exotic within the indus suture zone near lamayuru reveals the following history of events i late permian deposition on a shallow water carbonate platform open to the neotethys ocean ii late permian early triassic break up tilting fissuring and subsidence iii early triassic mantling by ammonite bearing pink pelagic carbonate and chlorite rich volcaniclastic sediment iv deposition of fe mn and or mn rich oxide sediments as crusts and fissure fills the metal rich oxides were precipitated from hydrothermal solutions related to nearby volcanism v late triassic eruption of pillowed and massive basalts of within plate type on an irregular seafloor taking account of evidence from similar exotic units associated with upper cretaceous melange beneath the spontang ophiolite further south in the zanskar mountains e g photoskar unit the lamayuru exotic is interpreted as part of a small carbonate platform formed somewhere between the zanskar lamayuru passive continental margin and a permian triassic neotethyan spreading axis to the north the carbonates probably capped a volcanic seamount that later collapsed and was covered by pelagic sediments and basic extrusives the lamayuru exotic was later detached from its igneous basement and tectonically emplaced probably in the latest cretaceous and was also influenced by early tertiary suturing of neotethys and mid late tertiary backthrusting

crustal evolution and mantle dynamics through earth history resolving the modes of mantle convection through earth history i e when plate tectonics started and what kind of mantle dynamics reigned before is essential to the understanding of the evolution

oman exotics oceanic carbonate build ups associated with the early stages of continental rifting the so called oman exotic limestones form isolated masses from boulder size to 1 000 m thick of middle to upper permian and upper triassic fossiliferous limestones and crop out within imbricated thrust slices beneath the semail ophiolite in the oman mountains permian exotics are of dominantly reef and forereef facies whereas triassic exotics are more typically of back reef and lagoonal facies they are commonly associated with a substrate of alkalic and transitional tholeiitic basalts and are interpreted as a series of reef associated carbonate buildups deposited in part on oceanic islands or seamounts close to the site of initial rifting of the oman continental margin

radiolarian evidence for the stratigraphy and palaeo oceanography of the deep water passive margin of the indian plate karamba formation indus suture zone ladakh himalaya abstract new radiolarian biostratigraphical information sheds light on the mesozoic sedimentary tectonic and palaeoceanographic evolution of a south tethyan margin in northern india radiolarian cherts studied here form part of deformed deep water successions within the indus suture zone ladakh himalaya these are defined as the karamba formation and interpreted as the stratigraphically higher and palaeogeographically more distal parts of a passive margin lamayuru group this formation includes radiolarites pelagic carbonates redeposited limestones ferruginous shales sandstones and abundant mafic extrusive rocks radiolarian assemblages of early and late middle jurassic mid cretaceous mid albian to cenomanian and late cretaceous santonian age were obtained from four measured sequences results indicate i long intact jurassic cretaceous successions rather than disrupted melange are present in the karamba formation ii extensive basic volcanism took place during the middle jurassic and can be correlated with an extensional phase affecting the nw indian continental margin iii non calcareous radiolarian rich sediments accumulated during the middle jurassic reflecting the influence either of a broad jurassic equatorial upwelling zone or a more localised coastal upwelling system after drowning of the zanskar clastic shelf in the late albian sedimentation on the distal shelf and upper slope was restricted by bottom current activity late albian cenomanian radiolarites of the karamba formation are contemporaneous with stratigraphie gaps and glauconite phosphorite deposition on the zanskar shelf a well developed eastward boundary current off the northern margin of india may have persisted until near the end of the late cretaceous during the late albian cenomanian current activity and coastal upwelling were probably strong and radiolarian rich sediments accumulated on the distal margin beneath the ccd pelagic limestones accumulated during the turanian over the entire margin possibly related to eustatic sea level rise and consequent reduction in bottom current activity intense oceanic circulation apparently was renewed during the coniacian santonian as indicated by sedimentary hiatuses in the zanskar shelf succession and accumulation of carbonate free radiolarian ooze in the karamba formation