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

miocene andalusite leucogranite in central east himalaya everest masang kang area low pressure melting during heating abstract the studied miocene andalusite bearing leucogranites intrude the upper part of the high himalayan crystallines hhc and the north himalayan domes and outcrop in an area stretching from mt everest to the kula khangri massif bhutan towards the east the leucogranites constitute both dykes as well as sills and parts of larger andalusite free leucogranite plutons e g makalu they represent mainly of two mica muscovite biotite tourmaline cordierite andalusite sillimanite dumortierite leucogranite and tourmaline muscovite tourmaline biotite andalusite sillimanite garnet kyanite spinel corundum leucogranites microstructures reveal several generations of andalusite from residual peritectic early magmatic to cotectic late magmatic even in the same sample the occurrence of residual and or peritectic andalusite together with inclusions of sillimanite biotite in cordierite indicates that melts formed by dehydration melting of biotite at t 660 700 c during prograde heating at low pressure conditions p according to current models leucogranites are produced by dehydration melting of muscovite and or biotite during exhumation of the hhc in this case micas are consumed in the sillimanite stability field as a consequence these models cannot explain the occurrence of residual and or peritectic magmatic andalusite conditions for anatexis in the andalusite field may have been achieved by heat transfer within the exhuming extruding hhc from structurally lower and hotter rocks towards upper and colder fertile lithologies

crustal architecture of the himalayan metamorphic front in eastern nepal abstract the himalayan metamorphic front consists of two basinal sequences deposited on the indian passive margin the mesoproterozoic lesser himalayan sequence and the neoproterozoic cambrian greater himalayan sequence the current paradigm is that the unconformity between these two basinal sequences coincides with a crustal scale thrust that has been called the main central thrust and that this acted as the fundamental structure that controlled the architecture of the himalayan metamorphic front geological mapping of eastern nepal and eight detailed stratigraphic kinematic strain and metamorphic profiles through the himalayan metamorphic front define the crustal architecture in eastern nepal the unconformity does not coincide with a discrete structural or metamorphic discontinuity and is not a discrete high strain zone in recognition of this we introduce the term himalayan unconformity to distinguish it from high strain zones in the himalayan metamorphic front the fundamental structure that controls orogen architecture in eastern nepal occurs at higher structural levels within the greater himalayan sequence and we suggest the name high himal thrust this 100 400 m thick mylonite zone marks a sharp deformation discontinuity associated with a steep metamorphic transition and separates the upper plate from the lower plate in the himalayan metamorphic front the high t moderate p metamorphism at 20 24 ma in the upper plate reflects extrusion of material between the high himal thrust and the south tibet detachment system at the top of the section the lower plate is a broad schistose zone of inverted diachronous moderate t high p metamorphic rocks formed between 18 and 6 ma the high himal thrust is laterally continuous into sikkim and bhutan where it also occurs at higher structural levels than the himalayan unconformity and main central thrust as originally defined to the west in central nepal the upper plate lower plate boundary has been placed at lower structural levels coinciding with the himalayan unconformity and has been named the main central thrust above the originally defined main central thrust or ramgarh thrust

tibetan tectonic evolution inferred from spatial and temporal variations in post collisional magmatism cenozoic magmatism on the tibetan plateau shows systematic variations in space and time that must be considered in models concerning tibetan tectonic evolution after the india asia collision which started in the early tertiary and terminated the gangdese arc magmatism in the lhasa terrane made of the southern tibetan plateau widespread potassium rich lavas and subordinate sodium rich basalts were generated from f50 to 30 ma in the qiangtang terrane of northern tibet subsequent post collisional magmatism migrated southwards producing ultrapotassic and adakitic lavas coevally between f26 and 10 ma in the lhasa terrane then potassic volcanism was renewed to the north and has become extensive and semicontinuous since f13 ma in the western qiangtang and songpan ganze terranes such spatial temporal variations enable us to elaborate a geodynamic evolution model which depicts when and how the indian continental lithospheric mantle started thrusting under asia by involving rollback and breakoff of the subducted neo tethyan slab followed by removal of the thickened lhasa lithospheric root we propose that only after the lithospheric removal which occurred at f26 ma could the indian mantle lithosphere have commenced its northward underthrusting and henceforth served as a pivotal control to the himalayan tibetan orogenesis consequently the tibetan plateau is suggested to have risen diachronously from south to north whereas the southern part of the plateau may have been created and maintained since the late oligocene the northern plateau would have not attained its present day elevation and size until the mid miocene when the lower part of the western qiangtang and songpan ganze lithospheres began to founder owing to the push of the underthrust indian mantle lithosphere d 2004 elsevier b v all rights reserved

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

himalayan metamorphism and its tectonic implications the himalayan range exposes a spectacular assemblage of metamorphic rocks from the mid and deep crust that have fostered numerous models of how the crust responds to continental collisions recent petrogenetically based petrologic and geochronologic studies elucidate processes with unprecedented resolution and critically test models that range from continuum processes to one time events the pronounced metamorphic inversion across the main central thrust reflects continuum thrusting between ca 15 and 20 ma whereas exposure of ultrahigh pressure rocks in northwestern massifs and syntaxis granulites reflects singular early 45 ma and late 10 ma exhumation events multiple mechanisms including wedge collapse and flow of melt weakened midcrust are debated to explain pressure temperature trajectories patterns of thinning and thermal overprinting a geochronologic revolution is under way in which spatially resolved compositions and ages of accessory minerals are combined in a petrogenetically valid co

tectonics of the himalaya an introduction soumyajit mukherjee1 rodolfo carosi2 peter van der beek3 barun kumar mukherjee4 delores m robinson5 department of earth sciences indian institute of technology bombay powai mumbai 400 076 maharashtra india dipartimento di scienze della terra v valperga caluso 35 10125 torino italy universite grenoble alpes institut des sciences de la terre 38041 grenoble france petrology and geochemistry group wadia institute of himalayan geology 33 gms road dehra dun 248001 india department of geological sciences university of alabama 201 7th ave room 2003 bevill building tuscaloosa al 35487 usa

crustal lithospheric structure and continental extrusion of tibet crustal shortening and thickening to c 70 85 km in the tibetan plateau occurred both before and mainly after the c 50 ma india asia collision potassic ultrapotassic shoshonitic and adakitic lavas erupted across the qiangtang c 50 29 ma and lhasa blocks c 30 10 ma indicate a hot mantle thick crust and eclogitic root during that period the progressive northward underthrusting of cold indian mantle lithosphere since collision shut off the source in the lhasa block at c 10 ma late miocene pleistocene shoshonitic volcanic rocks in northern tibet require hot mantle we review the major tectonic processes proposed for tibet including rigid block continuum and crustal flow as well as the geological history of the major strike slip faults we examine controversies concerning the cumulative geological offsets and the discrepancies between geological quaternary and geodetic slip rates low present day slip rates measured from global positioning system and insar along the karakoram and altyn tagh faults in addition to slow long term geological rates can only account for limited eastward extrusion of tibet since mid miocene time we conclude that despite being prominent geomorphological features sometimes with wide mylonite zones the faults cut earlier formed metamorphic and igneous rocks and show limited offsets concentrated strain at the surface is dissipated deeper into wide ductile shear zones

rongbuk re visited geochronology of leucogranites in the footwall of the south tibetan detachment system everest region southern tibet abstract the hermit s gorge area adjacent to the rongbuk glacier on the north side of mount everest is a critical location to establish the timing and duration of movement along the ductile strand of the south tibetan detachment system stds a low angle north dipping normal fault that bounds the upper part of the greater himalayan sequence monazite from four leucogranite samples in the hermit s gorge that bracket the timing of ductile fabric development has been dated using both u th pb id tims and la mc icpms results suggest that the earliest 16 4 ma leucogranite sills have been folded and deformed along with the host sillimanite gneisses and calc silicates whereas structurally higher sills and dykes that post date fabric development are slightly younger all within uncertainty of one another at 15 6 to 15 4 ma field relations combined with age data constrain ductile fabric formation associated with movement along this strand of the stds as being on going at 16 4 ma but had ceased prior to 15 6 ma while brittle faulting along the stds is younger than 15 4 ma combined with data from the everest massif and surrounding region ages of granite crystallization and ductile shearing propagated up structural section and northward with time

anatomy age and evolution of a collisional mountain belt the baltoro granite batholith and karakoram metamorphic complex pakistani karakoram abstract geological mapping and u th pb geochronology from the karakoram metamorphic complex and baltoro granite batholith has resulted in more detailed timing constraints on tectonic evolution of asian crust during and following collision and accretion of the kohistan arc and the indian plate to the southern margin of asia crustal thickening along the karakoram resulted in polyphase deformation metamorphism and melting u pb zircon and monazite ages show that kyanite and sillimanite grade metamorphism in the baltoro region peaked during oligocene early miocene c 28 22 ma times at structurally deeper levels sillimanite grade migmatites of the dassu dome have pliocene c 5 4 3 5 ma ages new u pb ages from crustal melt biotite muscovite garnet leucogranites from the trango towers cathedral peak and paiyu peak across the baltoro batholith range from 19 8 0 5 ma to perhaps as young as 14 ma using data from both the hunza and baltoro regions we suggest that regional high grade metamorphism was diachronous in space and time and could have lasted continuously for at least 37 ma c 50 13 ma or as much as 50 ma c 63 13 ma along the southern margin of the asian plate in the karakoram crustal melting along the baltoro granite batholith spanned at least 13 ma 26 4 13 ma supplementary material analytical methods and description of u th pb data of samples are available at http www geolsoc org uk sup18382

himalayan megathrust geometry and relation to topography revealed by the gorkha earthquake the himalayan mountain range has been the locus of some of the largest continental earthquakes including the 2015 magnitude 7 8 gorkha earthquake competing hypotheses suggest that himalayan topography is sustained and plate convergence is accommodated either predominantly on the main plate boundary fault or more broadly across multiple smaller thrust faults here we use geodetic measurements of surface displacement to show that the gorkha earthquake ruptured the main himalayan thrust fault the earthquake generated about 1 m of uplift in the kathmandu basin yet caused the high himalaya farther north to subside by about 0 6 m we use the geodetic data combined with geologic geomorphological and geophysical analyses to constrain the geometry of the main himalayan thrust in the kathmandu area structural analyses together with interseismic and coseismic displacements are best explained by a steep shallow thrust fault flattening at depth between 5 and 15 km and connecting to a mid crustal steeper thrust we suggest that present day convergence across the himalaya is mostly accommodated by this fault no significant motion on smaller thrust faults is required furthermore given that the gorkha earthquake caused the high himalayan mountains to subside and that our fault geometry explains measured interseismic displacements we propose that growth of himalayan topography may largely occur during the ongoing post seismic phase

trans hudson orogen of north america and himalaya karakoram tibetan orogen of asia structural and thermal characteristics of the lower and upper plates 1 the trans hudson orogen tho of north america and the himalaya karakoram tibetan orogen hkto of asia preserve a paleoproterozoic and cenozoic record respectively of continent continent collision that is notably similar in scale duration and character in tho the tectonothermal evolution of the lower plate involves 1 early thin skinned thrusting and barrovian metamorphism 2 out of sequence thrusting and high t metamorphism and 3 fluid localized reequilibration anatexis and leucogranite formation the crustal evolution of the indian lower plate in hkto involves 1 early subduction of continental crust to ultrahigh pressure uhp eclogite depths 2 regional barrovian metamorphism and 3 widespread high t metamorphism anatexis and leucogranite formation the shallow depths of the high t metamorphism in hkto are consistent with early to mid miocene ductile flow of an indian lower plate midcrustal channel from beneath the southern tibetan plateau to the greater himalaya melt weakening of the lower plate in tho is not observed at a similar scale probably due to the paucity of pelitic lithologies tectonothermal events in the upper plate of both orogens include precollisional accretion of crustal blocks emplacement of andean type plutonic suites and high t metamorphism syncollisional to postcollisional events include emplacement of garnet biotite muscovite leucogranites anatectic granites and sporadic metamorphism up to 90 myr following the onset of collision in tho comparing the type and duration of tectonothermal events for tho and hkto supports the notion of tectonic uniformitarianism for at least the later half of dated earth history and highlights the complementary nature of the rock record in an older exhumed orogen compared to one undergoing present day orogenesis

cretaceous tertiary carbonate platform evolution and the age of the india asia collision along the ladakh himalaya northwest india abstract the india asia collision resulted in the formation and uplift of the himalaya and the enhanced uplift of the tibetan plateau the transition from marine to continental facies within the indus yarlung tsangpo suture zone and along the northern margin of the indian plate provides the most accurate method of dating the closure of the tethys ocean separating the indian and asian plates other indirect methods of dating the collision such as paleomagnetism dating the uhp metamorphism along the north margin of india dating the youngest subduction related granites along the southern margin of asia and dating the postorogenic indus molasse group deposits within the suture zone cannot provide such a precise or reliable age of collision ophiolite obduction onto the indian passive margin occurred during the latest cretaceous and predated initial collision of the two continental plates unconformities occur beneath the late maastrichtian marpo formation and beneath the danian stumpata formation on the

effects of soil structure on the shear behaviour of an unsaturated loess at different suctions and temperatures previous studies of shear behaviour at different suctions and temperatures focused mainly on recompacted soils limited attention has been paid to intact soil in this paper the shear behaviour of

thermal model for the zanskar himalaya abstract crustal thickening along the northern margin of the indian plate following the 50 ma collision along the indus suture zone in ladakh caused widespread high temperature medium pressure barrovian facies series metamorphism and anatexis in the zanskar himalaya metamorphic isograds are inverted and structurally telescoped along the main central thrust mct zone at the base of the high himalayan slab along the zanskar valley at the top of the slab isograds are the right way up and are also telescoped along northeast dipping normal faults of the zanskar shear zone zsz which are related to culmination collapse behind the miocene himalayan thrust front between the mct and the zsz a metamorphic anatectic core within sillimanite grade rocks contains abundant leucogranite granite crustal melts of probable himalayan age a thermal model based on a crustal scale cross section across the zanskar himalaya suggests that m1 isograds developed during early himalayan barrovian metamorphism were overprinted during high grade mct related anatexis and folded around a large scale recumbent fold developed in the hanging wall of the mct

tectonic evolution of the himalayas and tibet shackleton r m dewey j f and windley b f editors 1988 philosophical transactions of the royal society of london series a 325 pp price 65

defining the himalayan main central thrust in nepal an inverted metamorphic field gradient associated with a crustal scale south vergent thrust fault the main central thrust has been recognized along the himalaya for over 100 years a major problem in himalayan structural geology is that recent workers have mapped the main central thrust within the greater himalayan sequence high grade metamorphic sequence along several different structural levels some workers map the main central thrust as coinciding with a lithological contact others as coincident with the kyanite isograd up to 1 3 km structurally up section into the tertiary metamorphic sequence without supporting structural data some workers recognize a main central thrust zone of high ductile strain up to 2 3 km thick bounded by an upper thrust mct 2 vaikrita thrust and a lower thrust mct 1 munsiari thrust some workers define an upper lesser himalaya thrust sheet that shows similar p t conditions to the greater himalayan sequence others define the main central thrust either on isotopic nd sr differences differences in detrital zircon ages or as being coincident with a zone of young

greater india basin hypothesis and a two stage cenozoic collision between india and asia cenozoic convergence between the indian and asian plates pro duced the archetypical continental collision zone comprising the himalaya mountain belt and the tibetan plateau how and where india asia convergence was accommodated after collision at or be fore 52 ma remains a long standing controversy since 52 ma the two plates have converged up to 3 600 35 km yet the upper crustal shortening documented from the geological record of asia and the himalaya is up to approximately 2 350 km less here we show that the discrepancy between the convergence and the shortening can be explained by subduction of highly extended continental and oceanic indian lithosphere within the himalaya be tween approximately 50 and 25 ma paleomagnetic data show that this extended continental and oceanic greater india promontory resulted from 2 675 700 km of north south extension between 120 and 70 ma accommodated between the tibetan himalaya and cratonic india we suggest that the approximately 50 ma india asia collision was a collision of a tibetan himalayan microconti nent with asia followed by subduction of the largely oceanic greater india basin along a subduction zone at the location of the greater himalaya the hard india asia collision with thicker and contiguous indian continental lithosphere occurred around 25 20 ma this hard collision is coincident with far field deforma tion in central asia and rapid exhumation of greater himalaya crys talline rocks and may be linked to intensification of the asian monsoon system this two stage collision between india and asia is also reflected in the deep mantle remnants of subduction imaged with seismic tomography

secondary migration of petroleum along syncline axes a case study of the southern kuqa foreland basin tracing petroleum migration pathways for petroleum exploration in a sedimentary basin is challenging paleo uplifts are generally considered to represent the primary migration directions of petroleum here we propose a model for the kuqa foreland basin in which petroleum migrates along the axes of synclines between paleo uplifts based on an integrated analysis of seismic geochemical and production data interpretation of detailed seismic data indicates that petroleum is unlikely to migrate to the paleo uplifts because of their relatively low positions fault disruptions or a lack of mesozoic reservoirs geochemical parameters including the ratios of alkyl dibenzothiophenes and the gas wetness parameter show that petroleum maturity gradually decreases along the axes of synclines between paleo uplifts from northeast to southwest petroleum production data and gas oil ratios also show decreasing trends from northeast to southwest this evidence suggests that petroleum is likely to migrate along the ax

structural and geochronological evidence for the leading edge of the greater himalayan crystalline complex in the central nepal himalaya abstract the himalaya is commonly described as a three layer two fault stack namely a high grade crystalline core featuring an inverted metamorphic field gradient the greater himalayan crystalline complex ghc is separated from units above and below by shear zones the lesser himalayan sequence lhs underlies the ghc below the main central thrust and the tethyan himalayan sequence ths overlies it along the south tibet detachment however the southern main central thrust hanging wall consists of a lower unit dominated by a right way up metamorphic sequence of biotite garnet schists bhimphedi group and an upper unit with only anchizone metamorphism pulchauki group the bhimphedi group is commonly equated to the ghc while the pulchauki group is well correlated to the ths however no shear zone separates these units we present new structural and geochronological data along the boundary between the ghc and the bhimphedi group in the kathmandu region these data reveal an 200 m thick early middle miocene top north northeast shear zone that we term the galchi shear zone we correlate this shear zone to the south tibet detachment on the basis of lithological metamorphic structural and chronological criteria the galchi shear zone merges with the main central thrust to the south bounding the leading edge of the ghc this result combined with recent work in the western himalaya suggests that the locally preserved leading edge of the ghc is sub parallel to the arc of the orogen and the southern main central thrust hanging wall is dominated by ths rocks this orogenic architecture rules out wedge extrusion and channel flow focused denudation kinematic models for the himalayan orogen but is accommodated by tectonic wedging kinematic models including channel tunneling models with modified timing

age constraints on ductile deformation and long term slip rates along the karakoram fault zone ladakh the dextral karakoram fault zone that bounds the southwestern margin of tibet is widely regarded as one of the major strike slip faults that accommodates the eastward extrusion of the thickened crust of tibet in northern ladakh the karakoram fault bounds the pangong transpressional zone with the active fault trace following the eastern margin of the range exhumation within this zone reveals mylonites that have absorbed much of the deformation along the fault two sets of dikes are evident within the main fault strand that bounds the transpressional zone whilst one dike set is concordant with the dominant foliation and shows mylonitic fabric the youngest dike set are less deformed and cross cut the shear zone fabric using u pb id tims data from five shear zone samples deformed by differing degrees we infer that fault initiation occurred between 15 68f0 52 and 13 73f0 28 ma since absolute offset is difficult to determine we couple these age constraints with suggested minimum and maximum offsets of the baltoro type granites the offset range of 40 150 km reveals that the karakoram fault has a longterm average slip rate in the range 2 7 10 2 mm year the lower rate being compatible with gps insar and cosmogenic data for the fault the small range of offset and low slip rates do not support rapid large scale extrusion of tibet along lithosphericscale faults and strengthens the argument that tibet does not behave in a rigid plate like manner d 2004 elsevier b v all rights reserved