eocene tibetan plateau remnants preserved in the northwest himalaya in the northwest himalaya deeply incised mountain ranges contrast with high elevation low relief areas such as the deosai plateau in northern pakistan thermochronology data from the deosai plateau together with thermal history modelling suggest that this plateau along with other morphologically similar surfaces is a remnant of an eocene southwestern tibetan plateau

structural evolution of the yushu nangqian region and its relationship to syncollisional igneous activity east central tibet field mapping geochronological analyses and cross section construction reveal a protracted deformation history and a minimum of 61 km of cenozoic ne sw shortening in present coordinates across the yushu nangqian thrust belt in northern tibet cenozoic contraction started prior to 51 ma and was followed first by northwest striking right slip faulting and later by northwest striking left slip faulting renewed ne sw contraction is expressed by folding of neogene strata and thrusting which again was followed by northwest striking left slip faults late neogene deformation is expressed by local north striking normal faults shortening across the yushu nangqian belt appears to be accommodated by thin skinned thrusting which raises the question of how the deformation was accommodated in the lower crustal levels to resolve this problem we perform geochemical analysis of igneous rocks dated as 51 49 and 38 37 ma the rocks exhibit geochemical signatures characteristic of subduction which implies that coeval crustal thickening in northeastern tibet was most likely induced by continental subduction

indian punch rifts tibet the strikes of late cenozoic normal faults in tibet fan systematically from a northwesterly to northeasterly direction from west to east they exhibit an axis of symmetry that bisects the himalayan arc and trends subparallel to india asia motion the two dimensional stress field inferred from the spatial pattern of normal fault orientations can be explained solely by collisional stresses localized along a southern part of the himalayan arc continued insertion of indian crust into tibet can explain the persistence of extension and may be increasing plateau crustal thickness and elevation coeval with rifting

timing of tibetan uplift constrained by analysis of volcanic rocks the tibetan plateau has had a central role in the development of recent models for the mechanics of mountain belts1 2 and cenozoic global climate change3 the present elevation and extensional deformation of the plateau probably result from uplift owing to convective thinning of the underlying lithospheric mantle1 2 an age for the uplift would provide a valuable constraint on these models but because recently proposed indicators of uplift are all climate dependent they are equivocal possibly reflecting global cooling rather than regional uplift4 here we present new geochemical data on post mid miocene lavas from the plateau which show that the lavas were derived from the lithospheric mantle simple thermal arguments indicate that the generation of such magmas also necessitates thinning of the lithospheric mantle thus volcanism is coincident with uplift providing a climate independent means of dating the onset of uplift dating by the laser 40ar 39ar technique places the beginning of this volcanism and therefore the time of uplift of the tibetan plateau at 13 myr ago

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

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

exhumation history of the gangdese batholith southern tibetan plateau evidence from apatite and zircon u th he thermochronology abstractto test previously suggested exhumation histories of the gangdese batholith in the central part of the transhimalayan plutonic belt we conducted paired apatite and zircon u th he thermochronological investigations of the yarlung zangbo gorge in the central part of the batholith age elevation relationships and multisystem thermochronometers showed three periods of accelerated exhumation 46 48 22 18 and 11 8 ma combining these data with previously published thermochronological ages and synthesizing these ages with regional geological events provides an entire exhumation history the cretaceous early paleogene exhumation of the gangdese batholith was probably caused by both the northward subduction of the neo tethys and the collision between the lhasa and qiangtang blocks the early miocene rapid exhumation might be a response to shortening caused by the gangdese thrust or erosion driven by dynamic uplift following lithospheric delamination in contrast the late miocene exhumation is coi

how flat is tibet high resolution digital topography three arc second grid for most of tibet provides new information to characterize the relief of the highest and largest plateau on earth the arid to semiarid central and northern part of the plateau interior has low relief average slopes of over 250 m windows and a mean elevation of 5023 m above sea level at moderate wavelengths of m relief is or less for most of tibet as opposed to the much higher relief of up to 6 km on the plateau edges where glacial and fluvial dissection is greater because of higher levels of precipitation the only faults manifesting significant topographic relief are the relatively small scale generally north trending graben systems primarily in southern tibet and several large scale fault systems near the edges of tibet the flatness of tibet implies that 1 there has been little deformation especially shortening of the uppermost crust north of the graben systems during the late cenozoic and 2 shallow crustal isostatic compensation has been acting to level the surface of the plateau

development of east asian summer monsoon environments in the late miocene radiolarian evidence from site 1143 of odp leg 184 abundant radiolarians are preserved in the relatively complete upper miocene section of odp site 1143 three radiolarian zones rn6 rn7 and rn8 are recognized on the basis of diartus petterssoni total range in rn6 6 7 ma variations in the abundance of radiolarians especially pyloniid forms radiolarian flux and species diversity are good proxies of upwelling which similar to today s was likely driven by summer monsoons these radiolarian paleomonsoon proxies indicate that the east asian summer monsoon first initiated close to the middle late miocene boundary at similar to 12 11 ma and reached a maximum strength at similar to 8 24 ma therefore the initiation of the east asian summer monsoon was likely earlier than the first indian monsoon which appeared similar to 8 myr ago c 2003 elsevier b v all rights reserved

insights into the early tibetan plateau from u th he thermochronology the central songpan ganzi belt located on the eastern margin of the tibetan plateau has a similar high elevation and low relief to parts of central tibet thermochronological studies from the central tibetan plateau reveal a history of slow exhumation rates 1 since 45ma however the exhumation history of the central songpan ganzi belt is unknown to address this we conducted an apatite and zircon u th he thermochronology study of bedrock samples collected across the central songpan ganzi belt and into central parts of the tibetan plateau zircon u th he ages range from 54 2 7 5 to 146 5 10 0ma and the majority of apatite u th he ages fall between 74 7 19 0 and 35 7 9 4ma thermal history models of these data show rapid cooling in the late mesozoic and much slower cooling diagnostic of low rates of erosion throughout most of the cenozoic the late mesozoic rapid cooling is consistent with the existence of significant topography and relief at least in some parts of the songpan ganzi belt at that time we find no evidence for a regional miocene acceleration in erosion although three samples from the headwaters of the salween and mekong rivers gave younger ahe ages between 15 and 16ma that reflect an acceleration in river incision supplementary material laser ablation inductively coupled plasma mass spectrometry zircon u pb data from central and eastern tibet are available at www geolsoc org uk sup18647

magmatic hydrothermal albite actinolite apatite rich rocks from the cloncurry district nw queensland australia abstract albite quartz actinolite apatite rich rocks with accessory titanite form a carapace that caps a small dome like intrusion of roxmere pluton and provide evidence of the accumulation and release of magmatic fluids that may have contributed to regionally extensive na ca alteration in the proterozoic cloncurry district australia the roxmere pluton was emplaced after the peak amphibolite facies metamorphism and into psammitic metasedimentary rocks that are stratigraphically younger and overlie the calc silicate rich mary kathleen group na ca hydrothermal assemblages closely spatially related to the roxmere pluton suggest that na ca alteration in this case is inconsistent with excepted up temperature metamorphic fluid circulation models the carapace rocks comprise two variants aplite and pegmatite both of which were affected by alteration and brecciation aplitic material predominates and the carapace has a brecciated top and a distinct textural zonation from an aplite rich pegmatite poor base to a relatively aplite poor pegmatite rich top this zonation is interpreted to represent the progressive accumulation of volatile phases toward the top of the carapace which culminated in fluid overpressuring and brecciation of the granitoid stock the convoluted and ptygmatic habit of the aplitic and pegmatitic material within the carapace is similar in nature to the comb quartz unidirectional solidification textures that are developed in the roof zones of some porphyry stocks these complex textures are interpreted to have formed from a single phase of fluid saturation the roxmere pluton or a deeper equivalent has a na mg and ca rich composition and a clinopyroxene amphibole rich mineralogy that is consistent with the formation of the contained albite actinolite apatite rich phases however the source of the rocks within the carapace is equivocal given that their contact relationships are obscured the 18 o composition of minerals within the carapace has the following ranges albite 7 1 8 7 actinolite 8 0 8 5 and quartz 8 9 11 4 albite and quartz 18 o equilibria suggest that these minerals in the pegmatitic and aplitic components formed at temperatures of 510 c to 540 c the calculated 18 o composition of a fluid in equilibrium with these minerals 6 0 to 8 0 at temperatures between 450 c and 550 c is consistent with a magmatic origin these estimated temperatures and 18 o fluid composition are comparable to estimates for regional na ca alteration in contrast d analysis of actinolite 136 to 150 within the carapace demonstrates that these fluids have a significantly lower d signature compared to na ca alteration assemblages associated with regional alteration 70 to 90 the low values in the carapace could either be interpreted as being produced from meteoric fluids or from degassed magmatic fluids although a meteoric fluid model is deemed improbable as meteoric fluids in the district have a documented d composition of ca 0 0 as a consequence an open system degassed magmatic hydrothermal fluid origin is considered to be the most plausible explanation for the low isotopic signatures and is also consistent with the complex textural relationships described within the carapace

late cenozoic uplift of southeastern tibet the age of surface uplift in southeastern tibet is currently unknown but the initiation of major river incision can be used as a proxy for the timing of initial uplift the topographically high eastern plateau and gently dipping southeastern plateau margin are mantled by an elevated low relief relict landscape that formed at a time of slow erosion at low elevation and low tectonic uplift rates prior to uplift of the eastern tibetan plateau thermochronology from deep river gorges that are cut into the relict landscape shows slow cooling between ca 100 and ca 10 20 ma and a change to rapid cooling after ca 13 ma with initiation of rapid river incision at 0 25 0 5 mm yr between 9 and 13 ma a rapid increase in mean elevation of eastern tibet beginning at this time supports tectonic climate models that correlate the lateral eastern expansion of high topography in tibet with the late miocene intensification of the indian and east asian monsoons

late mesozoic tectonic evolution and growth of the tibetan plateau prior to the indo asian collision abstract the elevation of the tibetan plateau is a revolutionary event in the earth history which resulted in change not only of cenozoic regional and global climate but also of monsoon intensity a critical aspect for the development of the tibetan plateau that remains open to intense debate is whether the collision among the tibetan continental blocks or the subduction of the tethys prior to the indo asian collision in the cenozoic contributed to the plateau growth we propose here that an andean type orogen could have been present in southern tibet from the jurassic to early cretaceous but collapsed during the middle cretaceous based on a synthesis of existing structural sedimentary geochronological and geochemical data the orogeny is marked by north verging jurassic early cretaceous thrusting in the lhasa block a result of flat subduction of the yarlung zangpo neo tethys that is recorded by a narrow belt of 205 174 ma adakitic rocks along the southernmost margin of the lhasa block denudation of the orogen produced a thick up to 15 km sequence of jurassic turbidites and molasse type sediments on the northern lhasa block widespread middle cretaceous 135 100 ma postorogenic strongly peraluminous to calc alkaline magmatism and extensional deformation in the lhasa block and an extensive marine transgression in tibet indicate that the orogen broke down due to extension resulting from lithosphere delamination and asthenosphere upwelling meanwhile the north dipping subduction of the bangong meso tethys produced a wide jurassic middle cretaceous magmatic arc along the southern margin of the qiangtang block findings of 132 108 ma aged ophiolites rich with middle cretaceous radiolarians in central tibet indicate that the bangong meso tethys did not close until the late cretaceous repeated flat slab subduction of the yarlung zangpo neo tethys occurred during the late cretaceous 90 78 ma as indicated by the adakites in the southernmost lhasa block which together with the ongoing qiangtang lhasa collision could have contributed to the growth of the tibetan plateau

did the indo asian collision alone create the tibetan plateau it is widely believed that the tibetan plateau is a late cenozoic feature produced by the indo asian collision however because tibet was the locus of continental accretion and subduction throughout the mesozoic crustal thickening during that time may also have contributed to growth of the plateau this portion of the geologic history was investigated in a traverse through the central lhasa block southern tibet together with earlier studies our mapping and geochronological results show that the lhasa block underwent little north south shortening during the cenozoic rather our mapping shows that 60 crustal shortening perhaps due to the collision between the lhasa and qiangtang blocks occurred during the early cretaceous this observation implies that a significant portion of southern tibet was raised to perhaps 3 4 km elevation prior to the indo asian collision

early cenozoic faulting of the northern tibetan plateau margin from apatite u th he ages models to explain the distributed nature of continental deformation predict the propagation of strain and high topography away from the plate boundary yet a growing body of evidence in the tibetan orogen suggests that deformation occurred at the far northern extent of the modern plateau early in the orogen s history and thus our current mechanical understanding of orogenic plateau development is incomplete new apatite u th he ages from four elevation transects document periods of rapid exhumation related to erosion pulses in hanging wall rocks of major thrust structures accelerated erosion is used as a proxy of fault timing and is interpreted in a larger context of structural data and sediment accumulation in adjacent foreland basins helium results are synthesized with published geologic thermochronometric and sedimentologic data from which a growing picture of regional compressional deformation in middle to late eocene time in northern tibet emerges we relate the early cenozoic period of deformation to the initiation of collision between india and eurasia despite the fact that the plate boundary was located 3000 km to the south regardless of whether or not high topography was built simultaneously as a result of this deformation early cenozoic strain signifies that the modern limit of the orogen has been relatively stationary since continental collision began and that deformation has not significantly propagated farther away from the plate boundary in time

implications of shortening in the himalayan fold thrust belt for uplift of the tibetan plateau 1 recent research in the himalayan fold thrust belt provides two new sets of observations that are crucial to understanding the evolution of the himalayan tibetan orogenic system first u pb zircon ages and sm nd isotopic studies demonstrate that 1 greater himalayan medium to high grade metasedimentary rocks are much younger than true indian cratonic basement and 2 these rocks were tectonically mobilized and consolidated with the northern margin of gondwana during early paleozoic orogenic activity these observations require that greater himalayan rocks be treated as supracrustal material in restorations of the himalayan fold thrust belt rather than as indian cratonic basement in turn this implies the existence of greater himalayan lower crust that is not exposed anywhere in the fold thrust belt second a regional compilation of shortening estimates along the himalayan arc from pakistan to sikkim reveals that 1 total minimum shortening in the fold thrust belt is up to 670 km 2 total shortening is greatest in western nepal and northern india near the apex of the himalayan salient and 3 the amount of himalayan shortening is equal to the present width of the tibetan plateau measured in an arc normal direction north of the indus yalu suture zone this information suggests that a slab of greater indian lower crust composed of both indian cratonic lower crust and greater himalayan lower crust with a north south length of 700 km may have been inserted beneath the tibetan crust during the cenozoic orogeny we present a modified version of the crustal underthrusting model for himalayan tibetan orogenesis that integrates surface geological data recent results of mantle tomographic studies and broadband seismic studies of the crust and upper mantle beneath the tibetan plateau previous studies have shown that incremental mesozoic and early cenozoic shortening had probably thickened tibetan crust to 45 55 km before the onset of the main cenozoic orogenic event thus the insertion of a slab of greater indian lower crust with maximum thickness of 20 km tapering northward could explain the cenozoic uplift of the tibetan plateau the need for tibetan crust to stretch laterally as the greater indian lower crust was inserted may explain the widespread east west extension in the southern half of the plateau our reconstruction of the himalayan fold thrust belt suggests that indian cratonic lower crust of presumed mafic composition and high strength should extend approximately halfway across the tibetan plateau to the banggong suture from there northward we predict that the tibetan plateau is underlain by more felsic and therefore weaker lower crust of greater himalayan affinity two slab break off events are predicted by the model the first involved neotethyan oceanic lithosphere that foundered 45 35 ma and the second consisted of greater indian lithosphere most likely composed of greater himalayan material that delaminated and foundered 20 10 ma asthenospheric upwelling associated with the break off events may explain patterns of cenozoic volcanism on the tibetan plateau although the model predicts a northward migrating topographic front due solely to insertion of greater indian lower crust the actual uplift history of the plateau was complicated by early middle tertiary shortening of tibetan crust

petrologic case for eocene slab breakoff during the indo asian collision the greater himalayan sequence is the metamorphic core of the himalaya and has been a focus of considerable study yet its petrologic evolution remains controversial pre oligocene metamorphism was nearly obliterated by miocene metamorphism and melting which many workers ascribe to shear heating unusually high concentrations of radioactive elements accompanying burial and or several kilometers of miocene exhumation due to extensional faulting sparse oligocene to eocene ages are often assigned to a tectonically unspecified event an alternative slab breakoff model subduction of greater himalayan rocks to 100 km depth in the eocene followed by buoyant extrusion due to decoupling of the oceanic lithosphere has also been proposed based on rare eocene eclogites but without explanation of miocene melting or metamorphic petrogenesis we argue that slab breakoff readily explains the eocene eclogites miocene partial melts and late eocene k rich magmas in southeastern tibet and that metamorphic and plutonic ages help define the timing and rates of breakoff and extrusion this model implies that 1 much of the greater himalayan sequence was subducted to depths greater than commonly considered 2 fluid absent decompression melting at 30 35 km depth was the consequence of as much as 100 km of extrusion rather than radioactive heating or a smaller crustal level extensional or erosional event and 3 eruption of eocene k rich tibetan plateau lavas has no implication for topography of the tibetan plateau

normal faulting in central tibet since at least 13 5 myr ago tectonic models for the evolution of the tibetan plateau interpret observed east west thinning of the upper crust to be the result of either increased potential energy of elevated crust1 or geodynamic processes that may be unrelated to plateau formation2 3 4 5 6 a key piece of information needed to evaluate these models is the timing of deformation within the plateau the onset of normal faulting has been estimated to have commenced in southern tibet between about 14 myr ago7 and about 8 myr ago8 and in central tibet about 4 myr ago9 here however we report a minimum age of approximately 13 5 myr for the onset of graben formation in central tibet based on mineralization ages determined with rb sr and 40ar 39ar data that post date a major graben bounding normal fault these data along with evidence for prolonged activity of normal faulting in this and other tibetan grabens support models that relate normal faulting to processes occurring beneath the plateau thinning of the upper crust is most plausibly the result of potential energy increases resulting from spatially and temporally heterogeneous changes in thermal structure and density distribution within the crust and upper mantle beneath tibet this is supported by recent geophysical and geological data10 11 12 13 14 15 16 17 which indicate that spatial heterogeneity exists in both the tibetan crust and lithospheric mantle

constraints on the early uplift history of the tibetan plateau the surface uplift history of the tibetan plateau and himalaya is among the most interesting topics in geosciences because of its effect on regional and global climate during cenozoic time its influence on monsoon intensity and its reflection of the dynamics of continental plateaus models of plateau growth vary in time from pre india asia collision e g 100 ma ago to gradual uplift after the india asia collision e g 55 ma ago and to more recent abrupt uplift 7 ma ago and vary in space from northward stepwise growth of topography to simultaneous surface uplift across the plateau here we improve that understanding by presenting geologic and geophysical data from north central tibet including magnetostratigraphy sedimentology paleocurrent measurements and 40ar 39ar and fission track studies to show that the central plateau was elevated by 40 ma ago regions south and north of the central plateau gained elevation significantly later during eocene time the northern boundary of the protoplateau was in the region of the tanggula shan elevation gain started in pre eocene time in the lhasa and qiangtang terranes and expanded throughout the neogene toward its present southern and northern margins in the himalaya and qilian shan

the origin and pre cenozoic evolution of the tibetan plateau different hypotheses have been proposed for the origin and pre cenozoic evolution of the tibetan plateau as a result of several collision events between a series of gondwana derived terranes e g qiangtang lhasa and india and asian continent since the early paleozoic this paper reviews and reevaluates these hypotheses in light of new data from tibet including 1 the distribution of major tectonic boundaries and suture zones 2 basement rocks and their sedimentary covers 3 magmatic suites and 4 detrital zircon constraints from paleozoic metasedimentary rocks the western qiangtang amdo and tethyan himalaya terranes have the indian gondwana origin whereas the lhasa terrane shows an australian gondwana affinity the cambrian magmatic record in the lhasa terrane resulted from the subduction of the proto tethyan ocean lithosphere beneath the australian gondwana the newly identified late devonian granitoids in the southern margin of the lhasa terrane may represent an extensional magmatic event associated with its rifting which ultimately resulted in the opening of the songdo tethyan ocean the lhasa northern australia collision at similar to 263 ma was likely responsible for the initiation of a southward dipping subduction of the bangong nujiang tethyan oceanic lithosphere the yarlung zangbo tethyan ocean opened as a back arc basin in the late triassic leading to the separation of the lhasa terrane from northern australia the subsequent northward subduction of the yarlung zangbo tethyan ocean lithosphere beneath the lhasa terrane may have been triggered by the qiangtang lhasa collision in the earliest cretaceous the mafic dike swarms ca 284 ma in the western qiangtang originated from the panjal plume activity that resulted in continental rifting and its separation from the northern indian continent the subsequent collision of the western qiangtang with the eastern qiangtang in the middle triassic was followed by slab breakoff that led to the exhumation of the qiangtang metamorphic rocks this collision may have caused the northward subduction initiation of the bangong nujiang ocean lithosphere beneath the western qiangtang collision related coeval igneous rocks occurring on both sides of the suture zone and the within plate basalt affinity of associated mafic lithologies suggest slab breakoff induced magmatism in a continent continent collision zone this zone may be the site of net continental crust growth as exemplified by the tibetan plateau c 2012 international association for gondwana research published by elsevier b v all rights reserved