eocene north south trending dikes in central tibet new constraints on the timing of east west extension with implications for early plateau uplift east west extension has been a prominent feature of cenozoic tectonics in central southern tibet and the onset of this extension has been interpreted as indicating the surface uplift of the tibetan plateau to a critical level previous studies suggested that extension started in the neogene between 18 13 ma and 8 ma based on dating results from north south trending normal faults grabens or rifts and dikes we report here the discovery of widespread north south trending diabase and andesitic porphyry dikes in and around the shuang hu graben central tibet where crustal extension has previously been argued to start from 13 5 ma based on mineral ages from graben bounding faults our results show that dikes in this area were mainly formed in the eocene 47 38 ma geochemical and nd sr isotopic data suggest that the diabase dikes originated from partial melting of an enriched lithospheric mantle source metasomatized by melts from subducted continental crust and the andesitic porphyry dikes were probably derived from interactions between the subducted continental crust derived melts and the mantle given that north south trending eocene dikes are found widely dispersed in central tibet we argue that the onset of east west extension and likely regional uplift of the tibetan plateau began much earlier than previously thought our study implies that a large part of the tibetan plateau had already attained near maximum elevation in the eocene and is consistent with recent investigations regarding the middle late eocene 47 34 ma initiation of aridification in asia evidence from contemporary global oceanic o sr isotope curves and temperatures and the carbon cycle 2010 elsevier b v

trace element modelling of pelite derived granites the presence or absence of a vapour phase during incongruent melt reactions of muscovite and biotite together with the composition of the protolith determines the trace element characteristics of the resulting melt provided that equilibrium melting occurs for those phases that host the tracc elements of interest for granitic melts rb sr and ba provide critical constraints on the conditions that prevailed during melting whereas ree are primarily controlled by accessory phase behaviour mass balance constraints for eutectic granites that are formed by the incongruent melting of muscovite in pelites indicate that melting in the presence of a vapour phase will result in a large melt fraction and deplete the restite in feldspar hence the melt will be characterized by low rb sr and high sr ba ratios in contrast vapour absent melting will result in a smaller melt fraction and an increase in the restitic feldspar consequently high rb sr and low sr ba ratios are predicted vapour absent melting will also enhance the negative eu anomaly in the melt granites that result from the incongruent melting of biotite in the source will be characterized by higher rb concentrations than those that result from the incongruent melting of muscovite the himalayan leucogranites provide an example of unfractionated crustally derived eutectic melts that are enriched in rb but depleted in sr and ba relative to their metasedimentary protoliths these compositions may be generated by the incongruent melting of muscovite as a low melt fraction f 0 1 from a pelitic source under vapour absent conditions

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

kinematic evolution of the ama drime detachment insights into orogen parallel extension and exhumation of the ama drime massif tibet nepal abstract the ama drime massif is a north south trending antiformal structure located on the southern margin of the tibetan plateau that is bound by the ama drime and nyonno ri detachments on the western and eastern sides respectively detailed kinematic and vorticity analyses were combined with deformation temperature estimates on rocks from the ama drime detachment to document spatial and temporal patterns of deformation deformation temperatures estimated from quartz and feldspar microstructures quartz c axis fabrics and two feldspar geothermometry of asymmetric strain induced myrmekite range between 400 and 650 c micro and macro kinematic indicators suggest west directed displacement dominated over this temperature range mean kinematic vorticity estimates record early pure shear dominated flow 49 66 pure shear overprinted by later simple shear 1 57 pure shear high strain 36 50 shortening and 57 99 down dip extension dominated flow during the later increments of ductile deformation exhumation of the massif was accommodated by at least 21 42 km of displacement on the ama drime detachment samples from the nyonno ri detachment were exhumed from similar depths we propose that exhumation on the nyonno ri detachment during initiation of orogen parallel extension 11 13 ma resulted in a west dipping structural weakness in the footwall that reactivated as the ama drime detachment

boron isotope fractionation between tourmaline and fluid an experimental re investigation the fractionation of boron isotopes between synthetic dravitic tourmaline and fluid was determined by hydrothermal experiments between 400 and 700 c at 200 mpa and at 500 c 500 mpa tourmaline was crystallized from an oxide mix in presence of water that contained boron in excess in one series of experiments b fluid b tour was 9 after the run in another series it was 0 1 all experiments produced tourmaline as the sole boron bearing solid along with traces of quartz and talc powder xrd and rietveld refinements revealed no significant amounts of tetrahedrally coordinated boron in tourmaline 11b always preferentially fractionated into the fluid for experiments where b fluid b tour was 9 a consistent temperature dependent boron isotope fractionation curve resulted approximated by 11b tour fluid 4 20 1 000 t k 3 52 r2 0 77 and valid from 400 to 700 c no pressure dependence was observed the fractionation 2 7 0 5 at 400 c and 0 8 0 5 at 700 c is much lower than that previously presented by palmer et al 1992 experiments where b fluid b tour was 0 1 showed a significant larger apparent fractionation of up to 4 7 in one of these runs the isotopic composition of handpicked tourmaline crystals of different size varied by 1 3 this is interpreted as resulting from fractional crystallization of boron isotopes during tourmaline growth due to the small boron reservoir of the fluid relative to tourmaline thus indicating larger fractionation than observed at equilibrium the effect is eliminated or minimized in experiments with very high boron excess in the fluid we therefore suggest that values given by the above relation represent the true equilibrium fractionations

evidence for tibetan plateau uplift before 14 myr ago from a new minimum age for east west extension important changes in south asian climate occurred in the late miocene epoch 8 myr ago 1 2 and these have been attributed by some researchers to uplift of the tibetan plateau at about the same time3 5 unfortunately this link has been difficult to test because the timing of plateau uplift remains poorly constrained by independent evidence one way to determine the minimum age of uplift is to establish the initiation age of the north striking normal fault systems in southern tibet that are widely regarded6 10 as being related to gravitational collapse of the tibetan plateau here we report an40ar 39ar age of 14 myr for hydrothermal mica from an extensional fracture belonging to such a fault system in north central nepal this age implies that east west extension began before 14 myr ago in at least some parts of the tibetan plateau suggesting that the plateau attained its high mean elevation well before late miocene time

evolution of the melt source during protracted crustal anatexis an example from the bhutan himalaya the chemical compositions of magmatic zircon growth zones provide powerful insight into evolving magma compositions due to their ability to record both time and the local chemical environment in situ u pb and hf isotope analyses of zircon rims from oligocene miocene leucogranites of the bhutan himalaya reveal for the first time an evolution in melt composition between 32 and 12 ma the data indicate a uniform melt source from 32 ma to 17 ma and the progressive addition of an older source component to the melt from at least ca 17 ma age corrected ehf ratios decrease from between 10 and 15 down to values as low as 23 by 12 ma complementary whole rock nd isotope data corroborate the hf data with a progressive decrease in end t from ca 18 to 12 ma published zircon and whole rock nd data from different lithotectonic units in the himalaya suggest a chemical distinction between the younger greater himalayan series ghs and the older lesser himalayan series lhs the time dependent isotopic evolution shown in the leucogranites demonstrates a progressive increase in melt contribution from older lithologies suggestive of increasing lhs involvement in himalayan melting over time the time resolved data are consistent with lhs material being progressively accreted to the base of the ghs from ca 17 ma facilitated by deformation along the main central thrust from 17 ma decompression which had triggered anatexis in the ghs since the paleogene enabled melting in older sources from the accreted lhs now forming the lowermost hanging wall of the thrust

petrogenesis of the ramba leucogranite in the tethyan himalaya and constraints on the channel flow model abstract the himalayan leucogranites are critical for understanding the geodynamic process of himalayan orogenesis in this article we present petrological geochronological and geochemical results of the ramba leucogranites that crop out in the center of the ramba dome within the tethyan himalaya u th pb dating of zircon monazite and xenotime revealed three episodes of leucogranitic magmatism in the ramba dome at ca 44 ma ca 28 ma and ca 8 ma respectively the ca 44 ma and ca 28 ma magmatisms are both represented by strongly deformed porphyritic two mica granite gneiss dykes that intruded into the margin of the dome these granite gneisses have high cao and sr contents relatively high na k sr y and low rb sr ratios and much lower initial 87sr 86sr ratios but higher end t and ehf t values than the ancient indian crustal material these results indicate that the granite gneisses were not derived from metasedimentary rocks of the high himalayan sequence but most likely were derived from partial melting of mafic rocks at a thickened crustal condition the ca 8 ma leucogranites consist of a two mica granite pluton in the core of the dome and garnet bearing granite dykes in the margin of the dome major and trace element compositions indicate that these miocene leucogranites are typical s type granites and were most likely derived from muscovite and or biotite dehydration melting of metapelites the relatively lower tio2 tfeo mgo and cao contents higher rb concentration and rb sr ratio and more strongly negative eu anomaly of the garnet bearing granite indicate that it was more evolved than the coeval two mica granite the non charac charge and radius controlled trace element behavior and the tetrad effect of the ree distribution of the garnet bearing granite further suggest that it is a highly fractionated granite besides our study detected some asian like materials in the ramba leucogranites such as mesozoic aged inherited zircons and the relatively depleted sr nd hf isotopic compositions of some leucogranite samples these features of leucogranites in the tethyan himalaya have been previously considered as direct geological evidence for the channel flow model however detailed geochronological and geochemical studies of the country rocks suggest that these asian like materials are most likely sourced from the country rock rather than the asian lithosphere thus they may not be used as solid evidence for the channel flow model

structure and geochronology of the southern xainza dinggye rift and its relationship to the south tibetan detachment system abstract the xainza dinggye rift is one of several north south trending rifts in central and southern tibet created by cenozoic east west extension during indo asian convergence the southern part of the rift cuts through the tethyan and high himalayas in the tethyan himalaya this rift consists of an early domal structure and a late normal fault developed during the progressive deformation the dome is cored by leucogranitic plutons that intruded during extension muscovite 40ar 39ar ages of the mylonitic leucogranite indicate that extension in the tethyan himalaya began at 8 ma or before in the high himalaya the rift is controlled by a normal fault dipping to the southeast this fault has a structural constitution similar to a detachment fault its lower block is made up of mylonitic high himalayan gneiss intruded by early mylonitic leucogranite sills and late less deformed biotite bearing leucogranite dikes mica 40ar 39ar ages of these leucogranites and the retrograded metamorphosed gneiss of the lower block range from 13 to 10 ma in the study area the south tibetan detachment system stds is a ductile shear zone composed of mylonitic leucogranite that is intruded by less deformed leucogranite and overlain by low grade metamorphic rocks mica 40ar 39ar ages of leucogranites in the shear zone and schist from the detachment hanging wall indicate a protracted deformation history of the stds from 19 to 13 ma the xainza dinggye rift is younger than the stds because it offsets the stds this north south trending rift belongs to a different tectonic system from the east west striking stds and may be caused by geological process related to india asia convergence this temporal and spatial relationship of the stds to the rift may indicate an important change in tectonic regime at 13 ma in the building of the plateau

contrasting geochemical signatures of fluid absent versus fluid fluxed melting of muscovite in metasedimentary sources the himalayan leucogranites most of the himalayan cenozoic leucogranites are products of partial melting of metapelite sources in the malashan gyirong area southern tibet the geochemical compositions of leucogranites define two groups with distinct whole rock major elements large ion lithophile elements rare earth elements high field strength elements and sr and hf isotope ratios based on published experimental results that define generalized melting reactions of metapelitic sources we infer that these leucogranites are the products of two different types of crustal anatexis fluid fluxed melting and fluid absent melting of muscovite in metasedimentary sources as compared to the leucogranites derived from fluid absent melting those from fluid fluxed melting have relatively higher ca sr ba zr hf th and light rare earth element concentrations and zr hf eu eu and nd nd but lower rb nb ta and u concentrations rb sr and 87 sr 86 sr ratios and e hf t the geochemical differences can be explained by melting behaviors of major muscovite feldspar and accessory minerals zircon and monazite during different modes of crustal anatexis the systematic elemental and isotopic signatures of different types of crustal anatexis and in particular the coupling of major and trace elements that results from common influences on rock forming and accessory mineral behaviors provide tools with which to refine our understanding of the nature of crustal anatexis

structure and evolution of the himalaya tibet orogenic belt the 1981 french chinese expedition to tibet focused on the lhasa block extending earlier coverage 400 km north of the tsangpo suture the lhasa block stood between 10 and 15 n latitude over most of the upper cretaceous and eocene and if gondwanian in origin had detached from gondwana by early permian seismic profiles reveal a complex moho topography resulting both from multiple continental thrusting and large scale strike slip faulting subduction related granitoids representing mixtures of mantle and crustal components and anatectic granitoids have been analysed and dated this study emphasizes the role of smaller blocks in the accretion of the continental mosaic

age and composition of dikes in southern tibet new constraints on the timing of east west extension and its relationship to postcollisional volcanism controversy exists over whether east west extension in southern tibet is related to plateau uplift or to the accommodation of plate boundary forces relationships between the onset of extension plateau uplift and the thermal state of the lithosphere are critical to this debate we present new data on postcollisional north south trending dikes in southern tibet their ages range from 18 3 2 7 ma to 13 3 0 8 ma and define the onset of regional east west extension in southern tibet dikes are compositionally indistinguishable from postcollisional lavas in southern tibet being either ultrapotassic having a source in the subcontinental lithospheric mantle or calc alkaline with a dominantly crustal origin the ultrapotassic dikes demonstrate that east west extension and subcontinental lithospheric mantle derived magmatism were temporally and spatially linked supporting models that relate the latest phase of plateau uplift to subcontinental lithospheric mantle thinning thus the onset of extension by 18 3 2 7 ma represents the time at which the potential energy of the plateau exceeded convergent boundary forces this places a new age limitation on the attainment of high elevation in southern tibet with implications for models that relate cenozoic monsoon intensification to plateau uplift

the stability of ground ice in the equatorial region of mars consideration of the partial pressure of h2o in the martian atmosphere and the range of mean annual temperatures at the martian surface suggests that the occurrence of ground ice in equilibrium with the atmosphere is restricted to latitudes poleward of 40 however there is a growing body of morphologic evidence that indicates that substantial quantities of ground ice may have been present in the equatorial regolith throughout martian geologic time the accepted explanation for this apparent contradiction has been that the h2o found near the equator is a relic emplaced very early in martian geologic history 3 5 b y ago and under substantially different climatic conditions it is generally believed that this fossil ground ice layer has been preserved to the present day by the diffusion limiting properties of a relatively shallow layer 10 m of fine grained regolith to evaluate this hypothesis the lifetime of a 200 m layer of ground ice buried below 100 m of ice free regolith has been examined for the latitudes between 30 on mars twelve model pore size distributions representative of silt and clay type soils found on earth were selected to simulate the pore structure of the martian regolith the parallel pore model of gaseous diffusion was then used to calculate the flux of escaping h2o molecules from the buried ground ice layer the potential effects of such factors as depth of burial the martian geothermal gradient regolith porosity adsorption surface diffusion and climatic change were also considered based on our analysis the most important factors affecting the stability of equatorial ground ice appear to be 1 soil structure 2 the magnitude of the geothermal gradient and 3 the climatic desorption of co2 from the regolith we conclude that while the conditions necessary for the long term survival of ground ice may exist in isolated regions within the equatorial regolith on the global scale it appears unlikely that a fossil ground ice layer has been preserved throughout martian geologic history if massive ground ice does presently exist in the equatorial regolith then its presence may imply the existence of some continuous or periodic process of replenishment

fluxed melting of metapelite and the formation of miocene high cao two mica granites in the malashan gneiss dome southern tibet identifying the timing of formation and geochemical nature of the cenozoic granites along the himalayan orogen is essential to test or formulate models that link crustal anatexis with tectonic transition during the evolution of large scale collisional orogenic belts the malashan gneiss dome one of the prominent domes within the tethyan himalaya experienced barrovian type metamorphism and partial melting of pelitic rocks at relatively deep levels during the collision between india and eurasia new la mc icp ms zircon u pb analyses yielded that the malashan two mica granites formed at a time span of 17 6 0 1 to 16 9 0 1 ma the malashan two mica granites are characterized by 1 high sio2 71 3 wt al2o3 14 8 wt and relatively high cao 1 3 wt 2 relatively high sr 146 ppm but low rb sr ratios 1 3 which are nearly constant relative to large variations in ba concentrations 3 enrichment in lree depletion in hree and no or weak negative eu anomalies eu eu 0 7 0 9 4 as compared to granites in the other northern himalayan gneiss domes and high himalayan belt relatively lower initial 87sr 86sr ratios 0 7391 0 7484 and similar unradiogenic nd isotope compositions end t 13 7 to 14 4 these characteristics imply that the two mica granites were derived from fluid fluxing melting of metapelite possibly triggered by the e w extension our new data in combination with literature data indicate that there are three types of granites with diverse geochemical characteristics and distinct formation mechanisms along the himalayan orogen since the cenozoic india eurasia continental collision conceivably our new results will provide new insights on how the partial melting behavior of relatively deeper crustal rocks evolved as the tectonic evolution of large orogenic belts

causes and consequences of protracted melting of the mid crust exposed in the north himalayan antiform gneiss domes exposed by the north himalayan antiform in southern tibet provide evidence for protracted melting of the mid crust during convergent tectonics anatexis was initiated during underthrusting and recurred during the southwards extrusion of a low viscosity crustal sheet sr nd isotope systematics establish that the cores of the domes dominated by cambrian gneiss form a window of the high himalayan crystalline series hhcs indian plate combined trace element and isotopic analyses from 4 two mica granites that intrude both core and the metasedimentary mantle of the domes indicate an origin from melting of the high himalayan crystalline series by the incongruent breakdown of muscovite and to a lesser extent biotite at temperatures from 680 to 760 c u pb dating of accessory phases extends the known period of granite magmatism from the late oligocene to mid miocene a ca rich garnet bearing leucogranite of oligocene age 27 5 ma provides a rare insight into the pre miocene history of the underthrust indian plate reflecting prograde melting at greater depths during a period of crustal thickening the origin of the miocene granites 15 10 ma can be modeled from the exhumation of an extruding channel at a rate of ca 1 mm year constrained by ar isotope data melting over a protracted time scale along the leading edge of the indian plate less than 50 km from the suture accelerated horizontal shortening within the collision zone and provided a positive feedback mechanism between magmagenesis and deformation

long term control mechanisms of stream piracy processes in southeast spain the guadix basin developed as an endorheic depression during the upper miocene upper pleistocene its principal palaeogeographical characteristics are a large lake in the eastern sector an axial fluvial system and two fluvial systems transverse to it in the western sector the uplift of a central sector of the betic cordillera during the upper pleistocene affected the study area causing northward tilting from the internal zone of the cordillera sierra nevada and sierra de baza step faulting of the plio pleistocene infill of the ancient basin leaving more northern sectors in a lower topographical position alteration of fluvial current profiles and displacement of the ancient axial system to a position very close to the divide between the ancient endorheic guadix basin and the guadalquivir basin this facilitated capture of the endorheic basin by the headward erosion of a tributary of the guadalquivir river the region then began to be rapidly eroded as the new base level was now some 500 m lower than that of the ancient basin the present drainage network is similar to that of the ancient endorheic basin as regards the location of the main streams and the distribution of drainage patterns and fluvial styles although flow reversal is found in some stretches and a barbed drainage pattern appears locally as a result of the inheritance of drainage from the ancient basin fluvial superimposition is found in some stretches of the main streams 1997 by john wiley sons ltd

evolution of north himalayan gneiss domes structural and metamorphic studies in mabja dome southern tibet field structural and metamorphic petrology investigations of mabja gneiss dome southern tibet suggest that contractional extensional and diapiric processes contributed to the structural evolution and formation of the domal geometry the dome is cored by migmatites overlain by sillimanite zone metasedimentary rocks and orthogneiss metamorphic grade diminishes upsection and is defined by a series of concentric isograds evidence for three major deformational events two older penetrative contractional and extensional events and a younger doming event is preserved metamorphism migmitization and emplacement of a leucocratic dike swarm were syntectonic with the extensional event at mid crustal levels metamorphic temperatures and pressures range from 500 8c and 150 450 mpa in chloritoid zone rocks to 705 65 8c and 820 100 mpa in sillimanite zone rocks we suggest that adiabatic decompression during extensional collapse contributed to development of migmatites diapiric rise of low density migmatites was the driving force at least in part for the development of the domal geometry the structural and metamorphic histories documented in mabja dome are similar to kangmar dome suggesting widespread occurrence of these events throughout southern tibet q 2004 elsevier ltd all rights reserved

the kinematic evolution of the nepalese himalaya interpreted from nd isotopes neodymium nd isotopes from the himalayan fold thrust belt and its associated foreland basin deposits are useful for distinguishing between himalayan tectonostratigraphic zones and revealing the erosional unroofing history as controlled by the kinematic development of the orogen neodymium isotopic data from the himalayan fold thrust belt in nepal n 35 reveal that the lesser himalayan zone consistently has a more negative nd 0 value than the greater and tibetan himalayan zones our data show the average nd 0 value in the lesser himalayan zone is 21 5 whereas the greater and tibetan himalayan zones have an average nd 0 value of 16 these consistently distinct values throughout nepal enable the use of nd isotopes as a technique for distinguishing between lesser himalayan zone and greater himalayan zone rock the less negative nd 0 values of the greater himalayan rocks support the idea that the greater himalayan zone is not indian basement but rather a terrane that accreted onto india during early paleozoic time neodymium isotopic data from eocene through pliocene foreland basin deposits n 34 show that sediment provenance has been dominated by greater and tibetan himalayan detritus across nepal the nd t values in the synorogenic rocks in western and central nepal generally show an up section shift toward more negative values and record the progressive unroofing of the different tectonostratigraphic zones at 10 ma in khutia khola and 11 ma in surai khola a shift in nd t values from 16 to 18 marks the erosional breaching of a large duplex in the northern part of the lesser himalayan zone this shift is not seen in eastern nepal where the nd t values remain close to 16 throughout miocene time because there has been less erosional unroofing in this region

isotopic characteristics of the gurla mandhata metamorphic core complex implications for the architecture of the himalayan orogen isotopic data from the gurla mandhata metamorphic core complex provide insight on the character of rocks exposed within it and permit possible correlations of these rocks to those exposed in the himalayan thrust belt whole rock sr and nd isotopic analyses show that rock units in the metamorphic core have isotopic signatures that correlate to those of greater and lesser himalayan rocks exposed in the foreland these data are the first to document lesser himalayan rocks north of the higher himalayan physiographic zone when combined with previously published structural reconstructions of the himalayan orogen these data reveal a crustal architecture that requires significant uplift of lesser himalayan rocks in the hinterland with respect to their position in the foreland a greater amount of underthrusting of the lesser himalayan rocks and more shortening in the hinterland within the tethyan himalaya physiographic zone than currently estimated

crustal generation of the himalayan leucogranites abstract detailed studies of the himalayan two mica leucogranites such as the manaslu pluton indicate that they have very uniform mineralogical petrological and structural characteristics one can relate their occurrence to the thickest zones of the underlying tibetan slab in these zones migmatization attains its greatest development and vertical extension the granite is emplaced at first along the main disharmonic plane above the main central thrust mct at the top of the tibetan slab infrastructure ductile deformation of the granite is variable the granite being syn to late kinematic with regard to the functioning of the mct major elements are very homogeneous except for na and k implying that p t conditions of melting were relatively uniform the melted material was of a similar composition over a vast volume and the percentage of melting was small 10 15 trace elements are highly variable some are characteristic for very evolved material ta rb cs u or show the link with the tibetan slab ba sr whilst others are problematic th ree ree and th abundances being much less in the granite than in the tibetan slab imply that they have been extracted during one of the main stages of formation possibly by monazite radiogenic pb sr nd and stable o isotopes are consistent with the origin of the granite from the tibetan slab however the heterogeneous sr isotopic ratios make age dating difficult and imply poor mixing or little fluid interaction during its evolution h isotope data indicate that magmatic compositions of the main body of the manaslu granite have been preserved late or post magmatic alterations are extremely local in the main pluton to the north another belt of two mica granites occurs whose characteristics are very similar to the high himalaya belt they were probably generated in a similar way during this recent intracontinental evolution

when did the roof collapse late miocene north south extension in the high himalaya revealed by th pb monazite dating of the khula kangri granite th pb ion microprobe measurements made on 12 monazite grains from the khula kangri granite tibet bhutan frontier are interpreted to indicate that crystallization occurred at 12 5 0 4 ma the leucogranite is cut by the gonto la detachment part of the southern tibet detachment system that has allowed upper level north directed extension of the himalayan orogen significant orogen normal extension in southern tibet appears to have continued 8 10 m y later than previously recognized this is the first reported crystallization age for a leucogranite east of the yadong cross structure an apparent 70 km offset of the high himalaya and southern tibet detachment west of the yadong cross structure reliable ages for high himalaya events major main central thrust slip granite generation and emplacement attainment of critical topography and major detachment extension group between ca 24 and 19 ma we interpret the west to east change across the yadong cross structure to be due to either 1 an abrupt 10 m y younging of principal high himalayan events or 2 a deeper thus younger exposed part of the footwall of the southern tibet detachment near khula kangri the southern tibet detachment is cut by the highly oblique yadong gulu rift a manifestation of tibet plateau east west extension integrated estimates of magnitude and rate of detachment displacement suggest that the observed postcrystallization north directed extension lasted for 1 3 m y after which time the yadong gulu rift formed this interpretation is consistent with initiation of east west extension of tibet at ca 8 ma

geochemical constraints on the bimodal origin of high himalayan leucogranites major and trace element and rb sr isotope systematics of the manaslu leucogranite central nepal have been examined to constrain the role of mineral fractionation and fluids in peraluminous granite petrogenesis biotite and tourmaline are for the most part mutually exclusive with a predominance of two mica leucogranites over tourmaline leucogranites the 87sr86sr initial isotopic ratios sri indicate that leucogranitic melts were derived from two different sources the two mica leucogranites having a metagreywacke origin with sri 0 752 nd 15 such a bimodal nature of the source zone does not directly influence the magmatic evolution except that probably the higher initial boron content in the metapelitic rocks may increase the na2ok2o ratio in contrast the amount of water present during melting principally controls in part anatectic processes and element behaviour water saturated conditions probably occured during melting of metagreywackeous rocks and favoured crystallization of two mica leucogranites whereas water absent conditions prevailed during melting of metapelitic layers and favoured biotite plagioclase and monazite fractionation in the source zone and tourmaline crystallization in the leucogranite

oligocene crustal anatexis in the tethyan himalaya southern tibet abstract recent studies in the xiaru and malashan gneiss dome of the tethyan himalaya southern tibet identify that xiaru and paiku tourmaline bearing leucogranite dike formed at 28 29 ma together with 28 ma kuday garnet bearing leucogranites it is demonstrated that the himalayan orogenic belt experienced a major episode of crustal melting in the mid oligocene geochemical data indicate that three suites of leucogranite are characterized by large variations in the major and trace element compositions as well as sr nd isotope systematics which could be explained by combined fractional crystallization and relative contributions of micas and accessory phases dissolved into a crustal melt during decompressional melting of metapelitic rocks documentation of oligocene partial melting of crustal rocks could indicate that the exhumation of deep crustal rocks in the himalayan orogenic belt could have started as early as oligocene

secular boron isotope variations in the continental crust an ion microprobe study abstract tourmalines of various chemical compositions hosted in magmatic rocks with ages ranging from 3 8 ga to the present were analysed for 11 b by ion microprobe a large range of 11 b values from 2 to 30 1 5 was observed the 11 b values are correlated with the chemical composition of the tourmalines the li rich tourmalines being enriched in 11 b compared to fe and or mg rich tourmalines this may reflect mixing in the continental crust between a marine reservoir characterized by high li contents and 11 b values and a continental reservoir characterized by low li contents and 11 b values no relationship between the age and the 11 b values is observed for the fe or for the mg rich tourmalines in contrast the 11 b values of the li rich tourmalines show a tendency to regularly decrease with increasing age this pattern is consistent with a simple model of constant boron isotopic fractionation between seawater and the continental crust during the progressive extraction of the continents a variation in the mean 11 b value of the continental crust from 20 ga ago to 7 at present is predicted by the model the largest variation occurred during the first 2 5 ga

late cenozoic right lateral strike slip faulting in southern tibet field observations collected during the sino french himalaya tibet cooperation project 1980 1982 show that right lateral faulting between southern and northern tibet roughly along the chord joining the eastern and western syntaxes of the himalayan arc is a major component of the active tectonics north of the himalayas just north of the well developed rifts of southern tibet we studied three right lateral 100 200 km long strike slip faults forming an en echelon array along that chord evidence for earthquake surface breaks was found on each of these faults for the m 8 beng co or damxung strike slip earthquake of november 18 1951 rupture parameters could be constrained to be 8 2 m and l 90 km offset glacial and postglacial morphological markers 105 years and 104 years b p imply displacement rates of the order of 1 2 cm yr on the three faults the en echelon fault zone appears to extend westward 2000 km across the plateau to the karakorum fault and is thus referred to as the karakorum jiali fault zone kjfz fast rates of slip on it and on faults along the northern rim of tibet appear to contrast with the slower rates of deformations in the interior of the plateau our estimates of slip rates on the strike slip and normal faults of southeastern tibet suggest that eastward extrusion of north tibet between the right lateral kjfz and the left lateral altyn tagh and kun lun faults absorbs at least 30 of the present convergence between india and asia we propose an instantaneous velocity model of the active tectonics of asia compatible with such faulting rates and geometries evidence for tertiary right lateral strike slip movements in southern tibet and around the eastern syntaxis of the himalayas is also found in the structural record offsets of various large scale geological features imply that these movements have been large

tectonics of the northern himalaya since the india asia collision abstract the india asia collision resulted in the construction of the vast himalayan orogen the northern himalayan domain began to experience extensional tectonics since eocene oligocene transition eot when the himalayan orogeny was still in progress major structures generated by the extension in the northern himalaya include the south tibet detachment system stds the north himalayan gneiss domes nhgd and the north south trending rifts nstr the earliest emplacement of syn deformational leucogranite at 36 32 ma along the stds marks the initial transformation from thickening to thinning in the northern himalayan domain at eot the thickening before eot caused crustal partial melting which formed the weak root of the thickened orogen or the so called channel flow this channel flow triggered the collapse of the orogen extrusion of the greater himalayan crystalline complex ghc and the onset of extensional tectonics of the stds the similarities in tectono thermal history and geochemistry of rocks between the stds and nhgd suggest that the formation of the nhgd has a direct relationship to the activity of the stds the extension of stds and the resultant thinning caused further partial melting of the crust leading to the larger scale emplacement of leucogranite during miocene 27 13 ma diapirism of these plutons shaped the domes in nhgd exposing the ghc and the shear zones of the stds in the northern himalaya in gyirong another tectonic transform from extension to shortening occurred after 18 7 ma in dinggye region the stds was offset by the nstr culminating the deformation at 13 ma when the nstr began to be active this indicates another tectonic transform in the northern himalaya at 13 ma when the n s extension of the stds ceased and gave way to e w extension of the nstr marking the end of the peak granitic magmatism in northern himalaya multiple episodes of deformation in the major structures such as the stds mct and nstr and superposition of different structures indicate a multiphase orogenic process in the himalayas in which mountain building and collapse occurred alternately with the formation of nstr and conjugate shear zones in tibet this tectonic scenario was possibly controlled by the india asia convergent rate we propose that the extension was an integral part of the orogenic process rather than a simple marker of the culmination of the orogeny

evidence for early 44 ma himalayan crustal thickening tethyan himalaya southeastern tibet abstract comprehensive understanding of himalayan orogenesis is limited in part by a poor knowledge of the eohimalayan episode a phase of tectonic activity predating the better understood neohimalayan crustal thickening associated with coaxial deformation along the main central thrust the cambo ordovician to tertiary metasedimentary sequences outcropping within the tethyan himalaya are the structurally highest units of the himalayan fold and thrust belt they and are inferred to have been the first to have accreted to asia a compilation of data from transects along the length of the main himalayan arc shows that the tethyan sequences have experienced at least five deformation events although the timing of these episodes is poorly constrained emplacement of a series of undeformed granitoid bodies following the second of these events which accounts for the majority of crustal thickening in the tethyan himalayan units is constrained by u pb zircon dating to be older than 44 1 1 2 ma thus significant crustal thickening had occurred along the length of the proto himalayan arc by the mid eocene or within 10 to 20 myr of the initiation of himalayan orogenesis

fluid enhanced melting during prograde metamorphism anatexis is a commonly recognized feature of high grade metamorphism but segregated melts are generally ascribed to anatexis during peak metamorphic conditions and little is known about melting along the prograde path a suite of small volume deformed two mica leucogranites has been recognized within the high himalayan crystalline series of the garhwal himalaya these granites are consistently more siliceous than minimum melt granite compositions and are characterized by low rb sr ratios high ba low abundances of hfs elements and positive eu anomalies such trace element characteristics contrast strongly with the geochemistry of the well studied early miocene leucogranites of the high himalaya derived from fluid absent melting sm nd garnet dating of one deformed granite indicates a crystallization age of 39 3 ma c 15 ma before the emplacement of the more voluminous high himalayan leucogranites whilst some entrainment of restitic phases cannot be excluded trace element signatures suggest a low temperature 2 o activity positive eu anomalies and unusually low rb sr ratios are indicative of rapid disequilibrium melting fluid enhanced melting may be a common feature of prograde upper amphibolite facies metamorphism of orogenic belts predating peak metamorphism by at least 15 ma these melts will only crystallize within this period if they segregate from their protoliths subsequent dating of long lived melts would indicate erroneously young ages for the prograde melting events however melts formed in this way may be recognized by their distinctive trace element chemistry the persistence of early formed melts within an orogen provides insights into the prograde heating path and may be critical in controlling the rheology of the middle crust and hence its deformational history

nd isotopic data reveal the material and tectonic nature of the main central thrust zone in nepal himalaya abstract the main central thrust mct is a tectono metamorphic boundary between the higher himalayan crystallines hhc and lesser himalayan metasediments lhs reactivated in the tertiary but which had already formed as a collisional boundary in the early paleozoic to investigate the nature of the mct we analyzed whole rock nd isotopic ratios of rocks from the mct and surrounding zones in the taplejung ilam area of far eastern nepal annapurna galyang area of central nepal and maikot barekot area of western nepal we define the mct zone as a ductile brittle shear zone between the upper mct umct and lower mct lmct the protoliths of the mct zone may provide critical constraints on the tectonic evolution of the himalaya the lhs is lithostratigraphically divided into the upper and lower units in the taplejung ilam area different lithologic units and their e nd 0 values are as follows hhc 10 0 to 18 1 mct zone 18 5 to 26 2 upper lhs unit 17 2 and lower lhs unit 22 0 to 26 9 there is a distinct gap in the e nd 0 values across the umct except for the southern frontal edge of the ilam nappe in the annapurna galyang and maikot barekot areas different lithologic units and their e nd 0 values are as follows hhc 13 9 to 17 7 mct zone 23 8 to 26 2 except for an outlier of 12 4 upper lhs unit 15 6 to 26 8 and lower lhs unit 24 9 to 26 8 these isotopic data clearly distinguish the lower lhs unit from the hhc combining these data with the previously published data the lowest e nd 0 value in the hhc is 19 9 we regard rocks with e nd 0 values below 20 0 as the lhs in contrast rocks with those above 19 9 are not always the hhc and some parts of them may belong to the lhs due to the overlapping nd isotopic ratio between the hhc and lhs most rocks of the mct zone have nd isotopic ratios similar to those of the lhs but very different from those of the hhc the spatial patterns in the distribution of e nd 0 value around the umct suggest no substantial structural mixing of the hhc and lhs during the umct activities in the tertiary a discontinuity in the spatial distribution of e nd 0 values is laterally continuous along the umct throughout the himalayas these facts support the theory that the umct was originally a material boundary between the hhc and lhs suggesting the mct zone was mainly developed with undertaking a role of sliding planes during overthrusting of the hhc in the tertiary

isotopic study of the manaslu granite himalaya nepal inferences on the age and source of himalayan leucogranites a detailed isotopic study of the manaslu leucogranite was carried out a u pb age of 25 ma and a whole rock rb sr age isochron of 18 ma were obtained suggesting that the magmatic activity lasted at least 7 ma initial sr isotopic ratios are very high 0 740 to 0 760 and initial nd isotopic ratios are low nd in 13 to 16 and they show the existence of large isotopic variations even at the metre scale these are not the result of perturbations by fluids but rather they reflect the initial isotopic heterogeneity of the source material which has not been obliterated by magmatic processes e g fusion mixing by convection these results also support the crustal origin of this leucogranite the tibetan slab paragneisses whose sr and nd isotopic ratios are very similar to those of the granite at an age of 20 ma are the most probable parental material nd model ages for both the leucogranite and the gneisses are in the range 1 5 2 ga a model of formation of the manaslu granite by coalescence of different batches of magma is in agreement with the present data

orogen parallel extension and exhumation enhanced by denudation in the trans himalayan arun river gorge ama drime massif tibet nepal focused denudation and mid crustal flow are coupled in many active tectonic settings including the himalaya where exhumation of mid crustal rocks accommodated by thrust faults and low angle detachment systems during crustal shortening is well documented new structural and u th he apatite data from the mount everest region demonstrate that the trans himalayan ama drime massif has been exhumed at a minimum rate of 1 mm yr between 1 5 and 3 0 ma during orogen parallel extension the ama drime massif offsets the south tibetan detachment system and therefore the south tibetan detachment system is no longer capable of accommodating south directed mid crustal flow or coupling it with focused denudation previous investigations interpreted the nne ssw striking shear zone on the west side of the ama drime massif as the main central thrust zone however our data show that the ama drime massif is bounded on either side by 100 300 m thick normal sense shear zone and detachment systems that are kinematically linked to young brittle faults that offset quaternary deposits and record active orogen parallel extension when combined with existing data these results suggest that the ama drime massif was exhumed during orogen parallel extension that was enhanced by or potentially coupled with denudation in the trans himalayan arun river gorge this model provides important insights into the mechanisms that exhumed trans himalayan antiformal structures during orogen parallel extension along the southern margin of the tibetan plateau

mid eocene high sr y granites in the northern himalayan gneiss domes melting thickened lower continental crust abstract within the himalayan collisional belt granotoids occur along two sub parallel belts the northern himalayan gneiss domes nhgd and the high himalayan crystalline series hhcs in the yardoi area of nhgd two mica granite a new type granite occurs in the core of the yardoi gneiss dome ygd dala and quedang from north to south and extends at least 50 km long these granites have similar mineral composition elemental and radiogenic isotope geochemistry and age of formation shrimp zircon u pb dating indicates that the yardoi and the quedang two mica granites formed at 42 6 1 1 ma and 42 8 0 6 ma respectively similar to the dala pluton these two mica granites have 1 high sio2 68 wt al2o3 15 wt and a cnk 1 0 2 relatively high sr and lree but low y 40 and up to 250 and la yb 30 4 very weak or no eu anomalies and 5 as compared with those in the himalayan leucogranites low initial sr 87sr 86sr i

the geochemical cycle of boron constraints from boron isotope partitioning experiments between mica and fluid abstract the fractionation of boron isotopes between synthetic boromuscovite and fluid was experimentally determined at 3 0 gpa 500 c and 3 0 gpa 700 c for near neutral fluids 11b mica fluid 11b mica 11b fluid is 10 9 1 3 at 500 c and 6 5 0 4 at 700 c this supports earlier assumptions that the main fractionation effect is due to the change from trigonal coordination of boron in neutral fluids to tetrahedrally coordinated boron in micas clays and melts the t dependence of this effect is approximated by the equation 11b mica clay melt neutral fluid 10 69 1000 t k 3 88 r2 0 992 valid from 25 c for fluid clay up to about 1000 c for fluid silicate melt experiments at 0 4 gpa that used strongly basic fluids produced significantly lower fractionations with 11b mica fluid of 7 4 1 0 at 400 c and 4 8 1 0 at 500 c showing the reduced fractionation effect when large amounts of boron in basic fluids are tetrahedrally coordinated field studies have shown that boron concentrations and 11b 10b ratios in volcanic arcs systematically decrease across the arc with increasing distance from the trench thus reflecting the thermal structure of the subducting slab our experiments show that the boron isotopic signature in volcanic arcs probably results from continuous dehydration of micas along a distinct p t range continuous slab dehydration and boron transport via fluid into the mantle wedge is responsible for the boron isotopic signature in volcanic arcs

chemical and boron isotopic composition of tourmaline from the conadong leucogranite pegmatite system in south tibet abstract tourmalines occur widely within leucogranites and pegmatites that intrude the leucogranites in the south tibetan plateau morphological and geochemical elemental and boron isotopic studies on these tourmalines are very limited furthermore the tourmaline genetic correlation between the leucogranite and the pegmatite is also unknown in this contribution two types of tourmaline occurrences have been identified in the conadong area south tibet including randomly disseminated tourmaline in leucogranite gt type and radial dendritic or massive tourmaline aggregates in pegmatite dikes that intrude the leucogranite pt type we performed major element and boron isotopic analyses of tourmaline using electron microprobe empa and laser ablation multi collector inductively coupled plasma mass spectrometry respectively the two types of tourmalines are enriched in fe na and al but relatively depleted in ca and mg elements with compositions close to alkali group tourmaline and schorl all the tourmalines are likely the products of equilibrium crystallization and their dominance of na was controlled by the magmatic compositions of their host rocks the gt type tourmalines show a narrow range of 11b values between 9 78 0 81 and 8 53 0 68 with a mean of 8 91 0 18 whereas the pt type tourmalines have significantly lower 11b values than the gt type ranging from 14 02 0 85 to 11 83 0 57 with a mean of 13 31 0 49 these data together with their morphology and petrography indicate that the conadong granitic tourmalines were derived by the melts at the early magmatic stage whereas the pegmatitic tourmalines precipitated from magmatic hydrothermal fluids at the late magmatic stage the variation in boron isotopic compositions 11b 4 4 between the pt and the gt type tourmalines is most likely correlated with their different melt fluid source regions that had distinct sr nd b isotopic compositions

dielectric signatures of adsorbed and salty liquid water at the phoenix landing site mars 1 the real part of the dielectric permittivity of the martian regolith was measured by the thermal and electrical conductivity probe tecp on the phoenix lander we interpret these data using laboratory measurements of permittivity as a function of h2o and salt content soil type and temperature due to variability in sensor coupling we focus on data taken at one locality vestri three separate times spanning multiple sols a daytime increase in permittivity suggests progressive melting of a heterogeneous disconnected salty ice with a eutectic temperature of 239 k which is close to the eutectic temperatures of naclo4 or mgcl2 we found no evidence for mg clo4 2 naclo4 and mgcl2 are consistent with precipitation by freezing following a prior epoch of high obliquity the evaporation of diurnal briny meltwater is inhibited by surface tension in small pores an increase in permittivity occurred on the night of sol 70 that coincided with surface frost and measurement of a decrease in atmospheric water vapor the permittivity jump can be matched by an increase in adsorbed h2o from 1 monolayer to 3 monolayers in an analog soil with a viking like specific surface area 17 m2 g however the amount of adsorbed h2o is an order of magnitude larger than that inferred to have precipitated during the night we suggest that the electrical signature of adsorbed water on mars is stronger than we measured in the laboratory possibly due to radiation damage of the regolith

high pressure melting of metapelite and the formation of ca rich granitic melts in the namche barwa massif southern tibet abstract a detailed geochemical and geochronological study of anatectic migmatites from the namche barwa massif nbm southern tibet has been carried out to place important constraints on the thermal and tectonic evolution of the eastern himalayan syntaxis shrimp zircon u pb dating indicates that the granulite facies metapelite underwent metamorphism at 21 8 0 7 ma and 24 5 0 7 ma respectively the latter is similar to the timing of partial melting and the formation of ca rich leucosomes at 24 25 ma these leucosomes are characterized by 1 high cao na 2 o and na k ratios 2 radiogenic sr 87 sr 86 sr t 0 7407 0 7904 but unradiogenic nd e nd t 7 0 to 21 2 isotope compositions 3 depleted hfse and 3 variable but depleted hree relative to their host pelites some of the leucosomes show large degrees of nd isotopic disequilibrium up to 10 epsilon units with respect to their hosts these high cao and na 2 o leucosomes were derived from fluxing melting of metapelite at high pressures a similar process could have operated during the formation of the himalayan leucogranites and contributes to the heterogeneities in such granites

beryllium and boron in subduction zone minerals an ion microprobe study secondary ion mass spectrometry was used to measure the distribution of be b rb sr y nb ba and ce among minerals in rocks from the franciscan complex and catalina schist paleosubduction zone terranes the rocks examined represent a wide range of metamorphic pressure temperature conditions 6 15 kb 300 750 c and include metasomatized and migmatitic samples white mica is the primary host of be 2 5 ppm and b 107 ppm in the rocks examined average concentrations amphibole be 0 7 b 15 ppm lawsonite be 0 9 b 37 ppm and biotite be 0 9 b 25 ppm may also contain significant amounts of both be and b omphacite may host be 4 1 ppm in veins 0 7 ppm groundmass and chlorite is a minor host of b 22 ppm minerals in these subduction zone metamorphic rocks that lack measurable be or b include albite apatite calcite clinozoisite epidote garnet ilmenite sphene stilpnomelane plagioclase quartz rutile and zoisite white mica biotite and stilpnomelane are the major mineral hosts of rb 90 300 and 30 ppm respectively and ba 2100 1000 and 4700 ppm epidote and lawsonite are the major host minerals of sr 600 and 300 ppm and ce 12 and 15 ppm garnet epidote lawsonite and sphene host y 100 30 40 and 60 ppm respectively sphene 77 ppm 1 analysis ilmenite and rutile host nb evidence of veining and metasomatism is strongly correlated with be and or b enrichment of white mica omphacite amphibole and lawsonite at the p t conditions examined both be and b appear to be transported in aqueous fluids at depths of 20 50 km in subduction zones the transfer of be b and other elements from the subducted slab into the mantle wedge can be accomplished by aqueous fluids transfer of the elements hosted by white mica could result directly from the breakdown of white mica through pressure dependent dehydration reactions or alternatively the be and b in white mica could be partitioned into infiltrating fluids produced at deeper levels in the slab and subsequently transported into the region of are magma genesis

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

tourmaline as a recorder of contrasting boron source and potential tin mineralization in the mopanshan pluton from inner mongolia northeastern china abstract abundant tourmaline occurs in the mopanshan pluton in inner mongolia of ne china and can be classified by its occurrence into four types nodular tourmalines nd type pegmatite pocket tourmalines pp type stockwork tourmalines sw type and vein tourmalines vt type all these tourmalines belong to the alkali group and are dravite schorl petrography and major elements data suggest that the nd and pp type tourmalines crystallized during the transition from late magmatic to early hydrothermal evolution of granite with all the components derived from the magma petrography and trace elements especially sr v cr ni ti data suggest that the sw and vt type tourmalines may form by the mixing of magmatic and country rocks components in the post magmatic hydrothermal environment due to the similar 11b of the sw type with the nd and pp type tourmalines variation

correction to stability of perchlorate hydrates and their liquid solutions at the phoenix landing site mars 1 in the paper stability of perchlorate hydrates and their liquid solutions at the phoenix landing site mars by vincent f chevrier et al geophysical research letters 36 l10202 doi 10 1029 2009gl037497 2009 there is an error in figure 3b of the published paper the curve describing the gcm global circulation model results for humidity at the phoenix landing site is wrong the new figure gives the right humidity variations from the gcm the legend is the same as for the original figure 3b this error does not affect subsequent calculations and all the conclusions of the paper remain valid since they were based on the measured humidity data by the phoenix thermal and electrical conductivity prove tecp instrument rather than on the gcm model results 2 the description of the gcm results in the paper page 5 end of the first paragraph should be modified accordingly the gcm results on water vapor pressure show a similar trend than the tecp data with high daytime values up to 7 pa and low nighttime value down to 3 5 10 3 pa however the amplitude of pressure variations calculated form the gcm is higher than the tecp data which range from 2 10 3 to 2 pa this suggests some form of interaction of water vapor with the regolith compared to pure atmospheric processes

seasonal ice cycle at the mars phoenix landing site 2 postlanding crism and ground observations 1 the combination of ground observations from the mars phoenix lander and orbital data from the compact reconnaissance imaging spectrometer for mars crism provided a detailed view of the formation of late summer surface water ice at the landing site and surrounding regions crism observations of the landing site during and immediately after phoenix operations were analyzed to track the seasonal and diurnal ice cycles during the late spring to late summer and a nonlinear mixing model was used to estimate grain sizes and relative abundances of water ice and dust the surface around the phoenix landing site was ice free from late spring through midsummer although transient patches of mobile ices were observed in an 85 m diameter crater to the northeast of the landing site at the 10 km diameter heimdal crater located 10 km east of the landing site permanent patches of water ice were observed to brighten during the late spring and darken during the summer possibly as fine grained water ice that was cold trapped onto the ice during late spring sintered into larger grains or finally sublimated exposing larger grained ice crism spectra first show evidence of widespread ice during the night at solar longitude ls 109 9 sols before phoenix s surface stereo imager detected it crism spectra first show evidence of afternoon surface ice and water ice clouds after ls 155 after phoenix operations ended

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

diverse magma sources for the himalayan leucogranites evidence from b sr nd isotopes abstract the himalayan orogen is featured by widespread s type leucogranites ca 45 to 9 ma formed primarily from the partial melting of metapelites 800 480 ma and minor from the partial melting of amphibolite with subordinate metapelites the ama drime gneiss and mabja leucogranite pluton are both located at the footwall of the ns trending xainza dinggye normal fault in the central part of the himalayan orogen with published end t values of 21 0 to 19 6 and 19 3 to 18 3 and 87sr 86sr t values of 0 90954 0 92574 and 0 84853 0 85474 respectively in this study we presented new shrimp zircon u pb ages and laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms tourmaline boron isotope data on the metamorphic rocks and leucogranites of the himalayan orogen the weighted mean 207pb 206pb age of the zircon cores of the ama drime gneiss t0446 2 3 is 1854 4 ma the tourmaline 11b values of the ama drime gneiss t0446 1 6 are 17 6 to 14 3 similar to those of the mabja leucogranite t0436 4 18 9 to 17 4 in contrast the tourmaline 11b values of the quedang metapelite t0389 18 and its partial melting product malashan leucogranite t0659 12a 3 are substantially higher i e 15 3 to 12 5 and 16 2 to 8 0 respectively the tourmaline 11b values of the yadoi leucogranite t0321 4 derived from partial melting of amphibolite range from 8 4 to 5 4 therefore the tourmaline b isotopes and sr nd isotopes results are consistent and may have reflected an e w extension along the southern tibetan rift system indicating a late miocene anatexis in the north himalaya region the melts derived from the partial melting of metapelites and mature crustal materials e g paleoproterozoic ama drime gneiss ascended along the n s trending xainza dinggye normal fault and were subsequently emplaced in the tethyan himalaya sequence

the himalayan leucogranites constraints on the nature of their crustal source region and geodynamic setting article i nfo late oligocene miocene leucogranites within southern tibet form part of an extensive intrusive igneous province within the himalayan orogen the main rock types are tourmaline leucogranites tg and two mica leucogranites 2 mg they have high sio2 70 56 75 32 wt al2o3 13 55 15 67 wt and 87 sr 86 sr i 0 724001 0 797297 and low mgo 0 02 0 46 wt and 143 nd 144 nd i 0 511693 0 511906 chondri te normalized rare earth element ree patterns display strong negative eu anomalies whole rock major and trace element and sr nd isotope data for the leucogranites suggest that their source region was a two component mixture between a fluid derived from the lesser himalayan lh crustal sequence and the bulk crust of the higher himalayan hh sequence trace element and sr nd isotope modeling indicate that the proportion of fluid derived from the lh sequence varied from 2 to 19 and the resulting metasomatised source experienced 7 16 melting the amount of fluid derived from the lh sequence increases from north to south northward underthrusting of the indian continent resulted in infiltration of the lh derived fluid into the overlying hh sequence subsequent decompression melting of this metasomatised crust mostly during the miocene 25 9 ma generated the leucogranites this may be linked to steepening of the subducted slab of indian lithosphere beneath the orogenic belt