early jurassic late pliensbachian co2 concentrations based on stomatal analysis of fossil conifer leaves from eastern australia the stomatal index a measure of stomatal density of an extinct australian early jurassic araucariacean conifer species allocladus helgei jansson is used to reconstruct the atmospheric carbon dioxide concentration pco 2 in the early jurassic the fossil leaves are preserved in a single bed palynologically dated to late pliensbachian similar to 185 183 mya atmospheric pco 2 is estimated from the ratios between the stomatal index of a helgei and the stomatal indices of three modern analogs nearest living equivalent plants co2 concentration in the range of similar to 750 975 ppm was calibrated from the fossil material with a best estimated mean of similar to 900 ppm the new average pco 2 determined for the late pliensbachian is thus similar to although similar to 10 lower than previously inferred minimum concentrations of similar to 1000 based on data from the northern hemisphere but may help constrain pco 2 during this period our results are the first pco 2 estimates produced using jurassic leaves from the southern hemisphere and show that i paleo atmospheric pco 2 estimates are consistent at a global scale though more investigations of southern hemisphere material are required and ii the stomatal proxy method can now be used without the context of relative change in pco 2 when applying the correct methodology c 2014 the authors published by elsevier b v on behalf of international association for gondwana research less

the dynamics of the suture between the kohistan island arc and the indian plate in the himalaya of pakistan abstract the pressure temperature and temperature time paths derived for rocks in the kohistan arc and adjacent nanga parbat haramosh massif record the dynamics of the collision between the island arc and the indian plate studies of p t t paths show that the kohistan arc was thrust over the nanga parbat haramosh massif at least 25 ma ago but not more than 30 35 ma ago rocks in the kohistan arc followed decreasing pressure paths with the early metamorphism beginning at high pressures 9 5 kbar and later metamorphism occurring at 8 0 kbar in contrast rocks in the nanga parbat haramosh massif indian plate experienced increasing pressure and temperature paths prior to thrusting the massif was at low pressures 4 0 kbar and low temperatures 450 c later the pressure and temperature increased to 8 kbar and 580 c the authors interpret the convergence to approximately the same pressure and temperature of the p t paths in the two terranes as being the result of thrusting and thermal equilibration between the thrust sheets 40ar 39ar cooling ages of hornblendes and other geochronological data suggest that the time of peak metamorphism and hence the completion of thickening was approximately 30 35 ma ago temperature time paths show that after thrusting during the period 25 10 ma the kohistan arc and nanga parbat haramosh massif were uplifted at similar rates 0 5 km ma however in the past 10 ma the nanga parbat haramosh massif has been uplifted more rapidly than the adjacent kohistan arc rapid uplift has been accommodated by late faults along the edge of the massif

the posidonia shale lower toarcian of sw germany an oxygen depleted ecosystem controlled by sea level and palaeoclimate abstract the lower toarcian posidonia shale is famous for its excellently preserved fossils and its high amount of organic matter up to 16 both quality of preservation and accumulation of organic matter have been explained by permanent anoxic bottom water conditions high resolution geochemical sedimentological and palaeoecological investigations of various sections of the posidonia shale in sw germany however indicate that oxygen availability was variable and ranged from short oxygenated periods to longer term anoxia the benthic macrofauna consists of nine fossil communities and was used in combination with geochemical data to reconstruct a time averaged oxygen curve anoxic conditions prevailed during the deposition of the toarcian black shales they were however punctuated by various short periods weeks to years with oxygenated bottom water conditions sedimentological e g distinctiveness of microlamination siliciclastic content and geochemical parameters e g organic matter content isotopic signatures 18o and 13c molecular redox parameters pristane phytane ratio arylisoprenoids exhibit a remarkable covariation and seem to be controlled by sea level fluctuations maximum oxygen depletion and an extreme negative shift of 13corg values 34 occurred during the early falciferum zone this is explained by the recycling of 12c enriched carbon derived from remineralization of organic matter on and within the substrate during low sea level stand and a highly elevated redox boundary including photic zone anoxia the subsequent transgression permitted enhanced water exchange with the tethyan ocean and caused improvement of living conditions at the end of the falciferum zone other important factors controlling the depositional environment are the overall palaeogeographic situation and climate the early jurassic is the latest period before break up of pangaea and probably was ruled by a strong meridional atmospheric circulation system with pronounced seasonal changes of prevailing trade and monsoon wind systems an estuarine circulation with a positive water balance and surface water with slightly reduced salinity in the summer alternated with an anti estuarine circulation and a negative water balance in the winter during the summer months a stratified water column with anoxic conditions below the halocline developed 18o data indicate low salinity in the surface water during the monsoon influenced summer high productivity was then located in the photic zone and the corresponding isotopically light 18o signal was fixed in the calcareous nannoplankton during the winter months a saline circulation system brought oxygen to the benthic environment favouring temporary benthic colonization especially during times of relative sea level high stand

exhumation across the indus suture zone a record of back sliding of the hanging wall the kohistan arc complex is an integral part of the nw himalayan collision system and is bounded by two major suture zones the indus suture zone isz and the northern suture in the south and north respectively fission track analyses on samples collected along the indus river across the arcuated isz in the besham region are presented here the footwall yields zircon and apatite fission track ft ages of 23 ma and 3 7 ma respectively the hanging wall ages range from 24 to 42 ma for zircon and 10 ma for apatite thus the change in isz kinematics from thrusting to normal faulting was not later than oligocene and normal faulting on this isz segment was still active at least into early pliocene times at this time normal faulting had already ended at other isz segments but it was still or again active across the isz in the besham region most likely as a local phenomenon caused by the growth of the indus syntaxis a transverse antiform parallel to the nanga parbat syntaxis

zircon hf isotopic constraints on the sources of the indus molasse ladakh himalaya india 1 india asia collision has resulted in the largest orogenic event on earth since at least 500 ma and this has had a profound influence on the drainage patterns of asia on the asian monsoon climate on global oceanography as well as on faunal extinctions despite this importance understanding of the paleogene evolution of this system is limited u pb and lu hf isotopic analyses of detrital zircons from the clastic sedimentary rocks of the indus molasse located within the indus suture of the ladakh himalaya india show that most have mesozoic cenozoic ages and juvenile hf isotopic compositions this suggests that the main source of these sediments is the transhimalayan batholith with minor flux from the lhasa karakoram terrane and indian plate the lower indus molasse chogdo formation is inferred to have been deposited at 60 49 ma whereas the upper choksti formation was deposited later than 45 41 ma and contains a greater contribution from the lhasa terrane the transhimalayan batholith was eroded throughout indus molasse sedimentation but increasing exhumation of lhasa karakoram terrane indicates its progressive uplift after initial collision and requires formation of apaleo indus river shortly after collision

stable carbon isotope signatures preserved in authigenic gibbsite from a forested granitic regolith panola mt georgia usa six samples selected from a weathering profile developed on a granite in the panola mountain research watershed in the georgia piedmont were studied for their stable carbon isotopic properties the purpose was to understand the relationship between the stable carbon isotopic composition of the organic matter pool and the preservation of carbon in the authigenic soil minerals the method for yielding carbon from authigenic phases is based on that of yapp and

groundwater dolocretes from the upper triassic of the paris basin france a case study of an arid continental diagenetic facies thick dolomite cemented horizons dolocretes occur within a fluvial sandstone mudstone sequence of late triassic age in the western part of the paris basin france two types of dolomites can be distinguished a nodular dolomitic beds less than a few metres thick which formed within mottled overbank siltstones and mudstones and b massive dolomite up to 16 m thick which occurs in coarse grained channel sandstones and conglomerates the majority of the dolomite consists of a finely crystalline groundmass of dolomicrospar and less commonly dolomicrite glaebules irregular spar filled cracks spheroidal dolomite silicification and vuggy porosity are locally abundant in the massive dolomite in contrast biologically induced micromorphological features such as rhizocretions and alveolar septal fabrics were observed in the thin nodular dolomite beds the dolomite is near stoichiometric well ordered and non ferroan 18o values range from 7 7 to 0 4 o pdb and 18o values range from 5 1 to 1 8 0 pdb and no obvious difference in the stable isotopic composition between both types of dolomites was observed sr isotope ratios range from 0 7101 to 0 7126 and are invariably higher than the contemporary triassic sea water a vadose pedogenic origin for the thin dolocrete layers is indicated by the occurrence of rhizocretions and other biological structures several features however argue against a pedogenic origin for the massive carbonates most notably the absence of biologically induced structures the occurrence in coarse grained channel and not overbank deposits and the great thickness these units are thus interpreted as groundwater in origin phreatic calcretes of quaternary age widespread in inland australia are regarded as a modern analogue for the triassic paris basin dolocretes petrographic observations argue in favour of primary proto dolomite precipitation although early diagenetic replacement of calcite by proto dolomite cannot be ruled out strontium and carbon isotope data of early diagenetic dolocrete cements and oxygen isotope data of early diagenetic silica indicate an entirely non marine continental origin for the groundwaters the poorly ordered and non stoichiometric protodolomite probably underwent stabilization upon further burial resulting in a near stoichiometric well ordered dolomite that clearly lacks evidence for pervasive recrystallization

estimating paleoatmospheric pco2 during the early eocene climatic optimum from stomatal frequency of ginkgo okanagan highlands british columbia canada abstract estimates of p co 2 for the early paleogene vary widely from near modern day levels to an order of magnitude greater based on various proxy measures resolving the relationship between climate and p co 2 during this globally warm period is a key task in understanding climate dynamics in a warmer world here we use the stomatal frequency of fossil ginkgo adiantoides from the okanagan highlands of british columbia canada to estimate p co 2 during the early eocene climatic optimum eeco the interval of peak warmth in the cenozoic we also examine a dataset of modern ginkgo biloba leaves to critically assess the accuracy and precision of stomatal frequency as a proxy indicator of p co 2 early eocene fossil g adiantoides has significantly lower stomatal frequency than modern g biloba suggesting p co 2 levels 2 modern pre industrial values this result is in contrast to earlier studies using stomatal frequency of ginkgo that indicated near modern day levels of p co 2 in the early paleogene though not including samples from the eeco we also find that levels of p co 2 as indicated by stomatal frequency are correlated with trends in climate mean annual temperature over time at the falkland fossil locality suggesting that climate and p co 2 were coupled during the eeco hyperthermal

a paleoclimate interpretation derived from pedogenic clay minerals from the piedmont province virginia abstract oxygen isotope ratios of pedogenic kaolinites were measured to estimate the ambient climate conditions during the formation of a saprolite in the piedmont province woodbridge va kaolinite is the predominant pedogenic clay mineral in this saprolite it is formed mostly from weathering of muscovite and to a lesser extent from weathering of microcline a dioctahedral smectite vermiculite phase formed by weathering muscovite is present in minor amounts the 18o 16o ratios indicate that most if not all the kaolinite formed in a cooler climatic regime in which meteoric waters were more depleted in 18o than most present meteoric waters it is possible that the pedogenic kaolinite formed shortly after or during the pleistocene glacial stage in north america this interpretation is consistent with the age of this saprolite derived from 10be dating methods the oxygen isotopic signatures of these kaolinites are not consistent with an older middle or early miocene age for this saprolite

miocene north vergent extensional displacements along the main mantle thrust nw himalaya pakistan structural data from n pakistan show that early tertiary s vergent structures within the upper part of the indian plate and the himalayan suture zone were overprinted by regionally developed n vergent extensional structures such extension has been suggested but not previously described from the nw himalaya cooling histories suggest extension was miocene in age extension was most likely the result of isostatic rebound resultant from crustal or lithospheric thickening and or delamination

ecological distribution of cenomanian terrestrial plants based on 13c 12c ratios the cenomanian lagoonal member of the argiles du baugeois anjou france yielded a rich and exceptionally well preserved fossil leaf flora stable carbon isotope ratios of fossil plants were measured in order to investigate the presence of a palaeoenvironmental signal the small intraspecies variations of 13c values observed for most of the fossil leaves suggested that the isotopic signal had not been significantly altered hence an isotopic approach was used as an attempt to assist in reconstructing the ecological distribution of the flora the 13c enrichment of the fossil leaves suggested that the plants underwent water or salt stress the occurrence of the conifer frenelopsis suggested at least locally a saline environment such as a lagoon according to their decreasing 13c values all the plants collected could have been distributed along a decreasing salinity transect from the lagoon to a flood plain the predominant species eretmophyllum andegavense a fossil ginkgo exhibited a wide range of 13c values this could indicate that this taxon grew in a wide range of habitats with varying salinities the origin of the organic matter appeared to be terrestrial with a major contribution from water stressed plants such as frenelopsis as suggested by the similarity between 13c values of the conifer and the sedimentary organic matter 13c values of the sediment indicated stable palaeoenvironmental conditions during the deposition of the argiles du baugeois member hence while detailed palaeovegetation reconstructions are generally limited to the few deposits which present in situ palaeoflora the contribution of isotope geochemistry could allow reconstructions for a wider range of fossil plant deposits

palustrine lacustrine and alluvial facies of the norian owl rock formation chinle group four corners region southwestern u s a implications for late triassic paleoclimate abstract the upper triassic norian owl rock formation was deposited in a low gradient floodbasin at a subtropical paleolatitude the lower part of the formation consists predominantly of fine grained siliciclastic lithofacies deposited by sheetflood and sinuous streams on a muddy floodplain during a period of continuous basin aggradation nodular calcretes are increasingly mature higher in the formation suggesting increasingly episodic depositional conditions the upper part of the formation consists mostly of interbedded fine grained siliciclastic facies and laterally continuous ledges of limestone and sandstone the predominant limestone facies has brecciated to peloidal fabrics spar filled circumgranular cracks and root channeling the subordinate limestone facies displays wavy to irregular argillaceous lamination desiccation cracks and oscillation ripples and is vertically and laterally gradational with the brecciated facies the upper owl rock formation records deposition of aggrading sequences of alluvial sediments deposited during base level rise capped by highstand carbonates deposited in small perennial and ephemeral carbonate lakes and ponds base level lowstand in an overall semiarid climate resulted in extensive pedogenesis of the limestone and laterally equivalent alluvial facies basin wide variations in base level are interpreted as resulting from climatic fluctuations this depositional model is consistent with an interpreted trend towards aridification on the colorado plateau during the late triassic as pangea drifted northward from one climate zone to another

zircon geochronology and ca 400 ma exhumation of norwegian ultrahigh pressure rocks an ion microprobe and chemical abrasion study understanding the formation and exhumation of the remarkable ultrahigh pressure uhp rocks of the western gneiss region norway hinges on precise determination of the time of eclogite recrystallization we conducted detailed thermal ionization mass spectrometry chemical abrasion analysis and sensitive high resolution ion microprobe analysis of zircons from four ultrahigh and high pressure hp rocks ion microprobe analyses from the flatraket eclogite yielded a broad range of apparently concordant caledonian ages suggesting long term growth in contrast higher precision thermal ionization mass spectrometry analysis of zircon subject to combined thermal annealing and multi step chemical abrasion yielded moderate pb loss from the first lowest temperature abrasion step possible minor pb loss or minor growth at 400 ma from the second step and a 407 404 ma cluster of slightly discordant 206pb 238u ages most likely free from pb loss from the remaining abrasion steps we interpret the latter to reflect zircon crystallization at 405 400 ma with minor discordance from inherited cores zircon crystallization occurred at eclogite facies possibly post peak conditions based on compositions of garnet inclusions in zircon as well as nearly flat hree profiles and lack of eu anomalies in zircon fractions subjected to chemical abrasion these ages are significantly younger than the 425 ma age often cited for western norway eclogite recrystallization implying faster rates of exhumation 2 5 8 5 km myr and coeval formation of eclogites across the uhp portion of the western gneiss region

paleoatmospheric pco2 fluctuations across the cretaceous tertiary boundary recorded from paleosol carbonates in ne china abstract a dramatic change in atmospheric composition has been postulated because of global carbon cycle disruption during the cretaceous k tertiary t transition following the chicxulub impact and deccan trap eruptions here pedogenic carbonates were collected from drill core of a borehole sk 1 n straddling the late cretaceous and early paleocene strata in the songliao basin northeast china to reconstruct atmospheric co 2 concentrations using a paleosol paleobarometer our estimates for atmospheric pco 2 from paleosol carbonates range between 277 115 ppmv and 837 164 ppmv between 67 8 ma and 63 1 ma one large 66 65 5 ma and several small co 2 spikes 64 7 64 2 ma during the latest maastrichtian to earliest danian are reported here and incorporated with previously published pco 2 estimates also estimated from paleosol carbonates these co 2 spikes are attributed to one million year long emplacement of the large deccan flood basalts along with the extraterrestrial impact at the k t boundary

application of the osl dating for stratigraphic correlation of late weichselian and holocene sediments in the lithuanian maritime region abstract the lithuanian maritime region of the baltic sea is notable for widely spread sandy sediments of different stages of baltic sea development from post glacial late weichselian to recently settled marine sediments the osl dating of about 70 sandy sediments was performed during the large scale 1 50 000 geological mapping of this region for some boreholes radiocarbon 14 c dating and palaeobotanical studies were also carried out a good agreement of the osl ages with 14 c dating results and palaeobotanical data has been revealed for marine lacustrine and aeolian sediments the overestimation of osl ages for baltic ice lake sediments is caused by a very rapid sedimentation and the resultant insufficient bleaching

applicability of unmanned aerial vehicles in research on aeolian processes surface dynamics and instabilities are characteristic of aeolian formation the method of surface comparison is regarded as the most appropriate one for evaluation of the intensity of aeolian processes and the amount of transported sand the data for surface comparison can be collected by topographic survey measurements and using unmanned aerial vehicles time cost for relief microform fixation and measurement executing topographic survey are very high the method of unmanned aircraft aerial photographs fixation also encounters difficulties because there are no stable clear objects and contours that enable to link aerial photographs to determine the boundaries of captured territory and to ensure the accuracy of surface measurements creation of stationary anchor points is irrational due to intense sand accumulation and deflation in different climate seasons in september 2015 and in april 2016 the combined methodology was applied for evaluation of intensity of aeolian processes in the curonian spit temporary signs marks were installed on the surface coordinates of the marks were fixed using gps and then flight of unmanned aircraft was conducted the fixed coordinates of marks ensure the accuracy of measuring aerial imagery and the ability to calculate the possible corrections this method was used to track and measure very small micro rank relief forms 5 10 cm height and 10 20 cm length using this method morphometric indicators of micro terraces caused by sand dunes pressure to gytia layer were measured in a non contact way an additional advantage of the method is the ability to accurately link the repeated measurements the comparison of 3d terrain models showed sand deflation and accumulation areas and quantitative changes in the terrain very clearly

timing of normal faulting along the indus suture in pakistan himalaya and a case of major 231 pa 235 u initial disequilibrium in zircon we report age data by tims u pb la icp ms and 39ar 40ar techniques for main magmatic events in the lower swat region of pakistan in order to constrain the tectonic evolution of the northwestern himalaya the pre himalayan history of the indian continent is documented by single zircon u pb results from the peraluminous choga granite gneiss which yielded a 468 5 ma lower concordia intercept interpreted to approximate the time of magmatic emplacement the presence of a well defined 870 7 ma inherited component upper intercept suggests a plutonic or volcanic protolith residing at unexposed levels of the indian crust zircon data for the swat granite gneiss from the northern part of the loe sar dome give an emplacement age of 267 6 3 ma which is at variance with earlier correlations favoring an early paleozoic origin subsequent to metamorphic overprint by the himalayan orogeny the swat granite was intruded by late kinematic alkali granite dykes single zircons from one of these dykes show reproducible 206pb 238u data giving a precise mean age of 29 26 0 12 ma whereas the 207pb 235u ages scatter between 34 and 81 ma pointing to huge and variable enrichment in 207pb the unsupported 207pb can be explained by incorporation of 231pa an intermediate long lived daughter nuclide in the 235u decay chain in excess of the secular equilibrium ratio la icp ms measurements confirm the presence of unsupported 207pb but do not show any correlation between the latter and other selected trace element concentrations in these zircons a concordant ar ar muscovite age of 28 4 1 1 ma obtained for the same dyke postdates regional mica cooling ages and indicates a lack of younger regional events capable of resetting the k ar system in muscovite because the dyke is pre to synkinematic relative to normal faulting and related north vergent folds its emplacement age provides a maximum age for this event or reflects already ongoing local extension a lower limit of 15 ma has previously been established by apatite fission track analysis the 29 15 ma age bracket for normal faulting is coeval with extension along the south tibetan detachment system stds on the north side of the high himalaya this suggests that the indus suture in pakistan has acted as a western continuation of the stds and that related faulting was roughly contemporaneous over most of the himalaya

dissecting complex magmatic processes an in depth u pb study of the pavia pluton ossa morena zone portugal the build up of large magmatic complexes can proceed piecemeal over periods of several million years through sequences of complex processes of magma production differentiation assimilation final crystallization and subsequent metasomatic modification all these stages can produce or modify minerals used as geochronometers such as zircon monazite and titanite the present study exemplifies such complex relationships also demonstrating how a systematic approach with comprehensive sampling and careful high resolution u pb analyses can yield a coherent picture of the entire magmatic process the study was conducted on the pavia pluton an elongated variscan intrusion in the ossa morena zone of portugal the geochronological data show that the pavia pluton was emplaced by the amalgamation of multiple magma pulses into the crust over a period of c 11 myr an early event at 340 ma revealed by xenocrystic zircon preceded the magmatic activity at the exposed level of the pluton but is recognized as the main magmatic event elsewhere in the ossa morena zone a second event at 328 ma formed tonalite trondhjemite and granodiorite and subordinate differentiates in the central domains of the pluton units i and ii a third event at c 324 ma emplaced granodiorite in the flanking domains iii v and the contemporaneous and widespread two mica granite in domainvi together with late rhyodacite porphyries microgranodiorites aplite pegmatite and pegmatite dikes a fourth event at 319 317 ma was characterized by the emplacement of some microgranites and pegmatite dikes these two last magmatic events also had an effect on the previously emplaced rocks causing local overgrowths and isotopic resetting of minerals the occurrence of a fifth magmatic event at depth at 313 ma is the inferred cause of the hydrothermal activity responsible for local zircon monazite and titanite resorption and or recrystallization and for some of the textures exhibited by the main rock forming minerals the magmatic episodes were interspersed with periods of quiescence this cyclicity presumably reflects an external control by the transtensional tectonic regime of the ossa morena zone

high precision zircon u pb geochronology of astronomically dated volcanic ash beds from the mediterranean miocene several orbitally tuned miocene sedimentary sequences around the mediterranean contain abundant intercalated volcanic ash beds these sequences provide the rare opportunity to directly compare radioisotopic dating methods with independent and accurate deposition ages derived from astrochronology we present a large data set n 16n 16 n 166n 166 of zircon u pb dates obtained by chemical abrasion isotope dilution thermal ionization mass spectrometry ca id tims techniques for ash beds from an almost continuous orbitally tuned messinian to langhian 6 2 15 4 ma sedimentary sequence exposed along the adriatic coast south of ancona italy we use this unique data set to evaluate 1 the accuracy of zircon u pb dates 2 the significance of initial intermediate daughter product disequilibria for zircon u pb geochronology of young rocks 3 the effect of prolonged pre eruption zircon crystallization and zircon recycling on u pb derived ash bed deposition ages and 4 discuss the implications for the intercalibration of radioisotope geochronometers and the calibration of the geologic time scale

cenozoic kinematic history of the kohistan fault in the pakistan himalaya detailed mapping suggests a new scenario for the kinematic history of the late cretaceous kohistan arc complex and for the cause of cenozoic metamorphism and exhumation along the indian continental margin in pakistan the earliest deformational phases resulted in early cenozoic amphibolite facies metamorphism superposed tight to isoclinal f1 f2 folds and development of strong penetrative rock fabric within the indian plate in response to southwestward and then southeastward overthrusting of ophi olitic melange in the indus suture zone and west pakistan fold belt respectively this deformation included the development of the banna and malakand thrust faults prograde metamorphism ended following this deformational phase and the early structures were deformed along n trending open upright f3 folds and domes this was followed by ese to e directed thrusting of the kohistan arc complex onto the indian continent along the dominantly brittle kohistan fault thrusting ended in the late oligocene early miocene when the kohistan arc assumed its present position along the northern margin of india south verging structures began to form on the indian plate for the first time in the late oligocene early miocene deformation had expanded to the foreland by the middle to late miocene with development of the panjal khairabad thrust neogene structures in the metamorphic zone include n trending east side up high angle fault zones that deform or reactivate the kohistan fault and nw trending east side up reverse faults both of which are seismically active in the tectonic scenario outlined here shortening along the kohistan fault occurred subsequent to metamorphism and was directed toward the ese e throughout its history the southern termination of the fault is considered to be a right slip sidewall ramp such that the kohistan arc never advanced much father south on the indian plate than its present position broad flexure folding and erosion in front of and south of the actively advancing kohistan arc complex contributed to exhumation of the indian plate this differs from interpretations that state that kohistan was thrust in a southward direction that underthrusting beneath kohistan was the primary cause of early cenozoic metamorphism on the indian plate and that top side north extensional reactivation of the kohistan fault contributed to exhumation

tectonics of nanga parbat western himalaya synkinematic plutonism within the doubly vergent shear zones of a crustal scale pop up structure detailed mapping and geochronologic investigations from the eastern southern and western nanga parbat haramosh massif reveal two thrust displacement shear zones that have a spatial and temporal link with granite plutonism from ca 10 to 1 ma the shear zones define a crustal scale antiformal pop up structure with dominant west northwest vergent and subordinate east southeast vergent thrusting this is substantially different than the surrounding area where the main exposed himalayan structures are oriented parallel to the orogenic trend and are early to middle miocene or older structures mapped throughout nanga parbat demonstrate that its rapid and young exhumation is not due to orogen scale structural unroofing and that sustained high erosion rates are required the observed west northwest directed shortening is proposed to be a result of differential arc parallel motion accommodated at the syntaxial bend of the northwest himalaya

luminescence chronology of late pleistocene glacial deposits in north westland new zealand abstract the chronology of the late pleistocene glacial history of north westland south island of new zealand is refined by luminescence dating of sediments it is demonstrated by two case studies that ages determined by different luminescence techniques agree well with the results of radiocarbon dating luminescence ages determined for sediments from two key sites of the loopline formation confirm the previous correlation of this unit with marine isotope stage mis 4 this indicates that late pleistocene glaciers reached their last maximum extent in north westland during the early part of the otira last glaciation furthermore initial dating evidence on coarse alluvial deposits in the lowlands indicates their formation during mis 5b and mis 5d it is probable that these coarse gravel deposits are outwash related to glacial advances if so both advances were probably much less extensive than the glaciations during mis 4 and mis 2

early to middle jurassic vegetation and climatic events in the qaidam basin northwest china abstract jurassic deposits are well exposed in the qaidam basin qinghai province northwest china and are regarded as one of the most completely developed early middle jurassic plant bearing sequences in northern china the early to middle jurassic palynoflora in this basin shows a high diversity of spores and pollen grains which are characterized by four palynological assemblage zones corresponding to the pliensbachian toarcian aalenian bajocian and bathonian in age vegetation reconstruction demonstrates four vegetation types upland coniferous forest in the pliensbachian coastal cheirolepidiacean forest in the toarcian lowland fern forest in the aalenian bajocian and a mixed forest in the bathonian nearest living relative analysis of the major plant groups shows that the early to middle jurassic vegetation in the qaidam basin not only consists of plants with tropical subtropical climate requirements but also those indicating temperate climatic conditions in addition bryophytes and fungi as well as cheirolepidiaceae which are generally considered to indicate warmer and or drier conditions are also documented in the palynofloras it is suggested that a temperate to subtropical climate generally prevailed during the early to middle jurassic in this basin however the vegetation features and the sedimentary data signify that an overall humid to semi humid phase was punctuated by warmer and locally dry and or arid episodes the two higher temperature and aridity events occurred in the toarcian and bathonian callovian periods in the qaidam basin these climatic events can be inferred by increase of relative abundance of classopollis pollen some tropical subtropical fern spores and the occurrences of variegated red beds and evaporite rocks these events may either be associated in some way with a transient global warming phenomenon due to an enhanced greenhouse effect or be linked with intensification of a potential monsoonal circulation such events finally caused a weakening and even arrested coal accumulation in the qaidam basin during the toarcian and the bathonian callovian intervals

biogeochemical constraints on the triassic jurassic boundary carbon cycle event 1 the end triassic mass extinctions represent one of the five most severe biotic crises in earth history yet remain one of the most enigmatic ongoing debate concerns the environmental effects of the central atlantic magmatic province camp eruptions and their linkage with the mass extinction event across the triassic jurassic boundary there is conflicting paleo evidence for changes in atmospheric pco2 during the extrusion of the camp basalts studies on sediments from european and pacific localities have however identified a substantial negative isotopic anomaly up to 3 5 across the tr j boundary providing an important indicator of changes in the operation of the ancient global carbon cycle we sought to explain the paleo evidence by utilizing a carbon cycle model for the hothouse world of the end triassic that emphasizes the chemical weathering of silicate and carbonate rocks and the ocean carbonate chemistry we find that volcanic co2 outgassing fails to fully account for either a sufficient rise in atmospheric pco2 indicated by the stomata of fossil leaves or the sedimentary isotopic fingerprint instead the scenario that best fits all of the geologic evidence is a positive feedback loop in which warming due to a buildup of volcanically derived co2 triggers destabilization of seafloor methane hydrates and the catastrophic release of ch4 palfy et al 2001 we calculate that this carbon cycle perturbation was huge involving the release of 8000 9000 gt c as co2 during the camp basaltic eruptions and 5000 gt c as ch4 in the model the initial isotopic excursion is assumed to take place over 70 kyr while complete reequilibration of the ocean atmosphere system with respect to co2 is accomplished over 700 1000 kyr our results thus provide a preliminary theoretical explanation for the bioevents estimated pco2 changes and isotopic excursions observed in marine and continental sediments at this time

combined high precision chronometry and geochemical tracing using accessory minerals applied to the central alpine bergell intrusion central europe abstract the behaviour of nd u th and pb isotopes in granitic rocks is usually controlled by accessory minerals in this study an approach is adopted which uses the initial 143 nd 144 nd as a geochemical tracer together with high precision u th pb geochronology for accessory phases and their respective whole rock this combination of techniques is applied to zircon allanite sphene apatite and thorite from both a tonalite and a granodiorite from the tertiary alpine bergell intrusion inherited isotopic signatures have been identified in bulk zircon fractions by inverse discordance in the u pb system in the case of the granodiorite the initial nd in the zircon is 1 77 units lower than the bulk rock this result indicates that nd isotopes in zircon may serve as a useful tool for tracing crustal precursors in silicic rocks all other accessories yield an initial nd equal to their respective whole rock and u th pb ages equal to or lower than the respective intrusion ages this indicates either the absence of inherited cores or that such cores have exchanged their nd and pb in the case of apatite also sr by diffusion where available experimental mineral melt equilibria and diffusion models are consistent with this behaviour u pb geochronology of carefully selected core free zircons yields a precise intrusion age of 31 88 0 09 ma for the tonalite in contrast granodioritic zircons are partially reset due to radiation damage caused by high u concentrations however an alternative means of dating young intrusions is to use 232th 208pb ages of allanite in the case of allanite the presence of a large excess of 206pb derived from 230th indicates that no total pb loss has occurred since crystallization and the nd isotopes indicate the absence of inheritance using both the allanite age and a 238u 206pb age for sphene an intrusion age of 30 13 0 17 ma is indicated for the granodiorite taken together with an allanite th pb age for the tonalite these results strongly support the high closure temperatures for the allanites studied here 700 800 c at high post magmatic cooling rates all other accessory mineral ages are reset to values similar to hornblende 39ar 40ar ages and reflect the effect of post magmatic cooling superimposed on post metamorphic cooling

tectonics or climate what drove the miocene global expansion of c4 grasslands investigations into the most plausible causes which triggered the late miocene global expansion of c4 grasslands have reached no consensus and are still being debated the global decline in co2 levels in the late miocene has been thought to be the most common driver although c4 grassland expansion was largely confined to the late miocene their first appearance varied significantly in different parts of the old and new world and therefore emphasizes role of local and or regional factors may or may not be in combination with one or more global factors the dynamic himalayan orogen constitutes a significant global tectonic event that is believed to have affected global climate hence a study of the himalayan foreland basin sediments could help in gleaning out possible causes behind this major paleoecologic event which could perhaps be directly or indirectly related stable carbon isotope analyses of a total of 141 pedogenic carbonates in the mio pleistocene siwalik paleosols of the ramnagar sub basin are coherent providing a better insight into paleovegetational changes across the sub basin on temporal and spatial scales furthermore paleovegetational history during oligocene is reconstructed from dagshai paleosols exposed in the subathu sub basin the isotopic results show dominance of c3 vegetation pre 7 ma and dominance of c4 vegetation post 5 ma percentage abundance of c4 vegetation was less than 20 pre 7 ma but increased to more than 40 post 5 ma reaching up to 100 in the youngest analyzed sediments there is exclusive dominance of c3 vegetation during oligocene these results conform to the pattern of change in vegetation documented in other parts of the himalayan belt the global expansion of c4 grasslands largely during late miocene have long been linked with then climate changes particularly brought by declining atmospheric co2 level large scale fires intensification of monsoon seasonality and aridity as demonstrated by various researchers these major hypotheses explaining expansion of c4 grasslands during late miocene are not very convincing due to significant shortcomings associated with them for example expansion of c4 grasslands in non monsoonal regions put serious constraints on the monsoonal intensification hypothesis likewise aridity as being the primary driver of c4 grassland expansion seems hard to support since there is no substantial evidence that could suggest global onset of arid conditions at about same geologic time and some most arid periods like the triassic show no evidence of c4 plants we suggest that the initial lowering of co2 below 450 ppmv created an environment for the beginning of c4 vegetation but the persistence of this threshold value for a considerable time during late miocene appears to be the probable cause of the late miocene global expansion of c4 grasslands irrespective of their time of first appearance it has been deduced through the correlation of himalayan tectonic events with atmospheric co2 levels and paleovegetational changes since upper miocene times that it was indeed the late miocene continuous intense tectonic instability of the himalayas that significantly decreased atmospheric co2 levels and which perhaps played a key role in changing the nature of photosynthetic pathways

co2 drawdown and cooling at the onset of the great oxidation event recorded in 2 45 ga paleoweathering crust abstract the archean atmosphere is thought to have been devoid of oxygen but instead containing high concentrations of greenhouse gases such as co2 and possibly ch4 that were required to keep the earth surface environments warm enough for maintenance of liquid water under faint young sun conditions earlier studies have suggested that the co2 concentrations must have been as high as over 1000 times present atmospheric levels pal to overcome the effects of weaker solar luminosity however more recent studies of precambrian paleosols imply existence of at least tenfold lower but still high pco2 levels the appearance of minute amounts of atmospheric o2 at the transition of archean and proterozoic is well documented however the bulk composition of the atmosphere and its dynamics at this crucial time is still widely debated different paleoclimate proxies of the 2 45 ga kuksha paleoweathering crust suggest its formation in a cool temperate climate paleoatmospheric pco2 estimates by geochemical and isotopic mass balance models suggest remarkably low paleoatmospheric co2 levels with the best guess estimates of atmospheric co2 between 1 and 10 pal we speculate that the kuksha paleoweathering crust either predates or partly overlaps with the onset of huronian glaciation and corresponds to a time interval of low co2 level during the first recorded large glaciation in earth history

transition from arid to hyper arid environment in the southern levant deserts as recorded by early pleistocene cummulic aridisols abstract the time at which deserts established their current arid or hyper arid conditions remains a fundamental question regarding the history of earth cosmogenic isotope exposure ages of desert pavement and welded calcic gypsic salic reg soils that developed on relatively flat alluvial surfaces 2 ma ago in the negev desert indicate long geomorphic stability under extremely dry conditions over a short interval during their initial stage of development between 1 2 ma these cumulative soils are characterized by calcic soils reaching maximum stage iii of carbonate morphology this interval is the only period when calcic soil horizons formed on stable abandoned alluvial surfaces in the southern negev desert since 1 ma pedogenesis changed toward more arid soil environment and the formation of gypsic salic soil horizons that were later followed by dust accumulation the dichotomy of only moderately developed calcic soil stages ii iii during a relatively long time interval 105 106 years indicates an arid environment that does not support continuous development but only occasional calcic soil formation the very low 18o and relatively high 13c values of these early pedogenic carbonates support soil formation under arid climatic conditions such an environment was probably characterized by rare and relatively longer duration rainstorms which occasionally allowed deeper infiltration of rainwater and longer retention of soil moisture this in turn enabled the growth of sparse vegetation that enhanced deposition of pedogenic carbonate at 1 ma these rare events of slightly wetter conditions ceased and less atmospheric moisture reached the southern negev desert leading to deposition of soluble salts and dust deposited in the soils the combination of long term hyperaridity scarcity of vegetation and lack of bioturbation salts cementation dust accumulation and tight desert pavement cover has protected the surfaces from erosion forming one of the most remarkably stable landscapes on earth a landscape that essentially has not eroded but accumulated salt and dust for more than 106 yr

the four plutonic belts of the transhimalaya himalaya a chemical mineralogical isotopic and chronological synthesis along a tibet nepal section

holocene relative sea level change and deglaciation on alexander island antarctic peninsula from elevated lake deltas abstract field data constraining the rate and spatial pattern of deglaciation and relative sea level rsl change on the antarctic peninsula ap are relatively sparse but are needed to improve regional ice sheet and rsl change models and contribute to better model predictions of future sea level rise we investigated the geomorphology sedimentology and quartz fraction single aliquot regeneration optically stimulated luminescence sar osl geochronology of elevated deltas around two epishelf lakes ablation lake al and moutonnee lake ml alexander island antarctic peninsula al and ml are dammed by george vi ice shelf and maintain a direct hydraulic connection to the sea hence their water levels are controlled by changes in rsl our aim was to provide new terrestrial constraints on rsl and deglaciation for the southern ap by comparing the formation processes age and altitude of the al and ml deltas with 1 existing rsl curves for the ap 2 isostatically coupled ap ice sheet models and 3 existing ap deglaciation history and sar osl ages from elevated deltas around the nearby inland hodgson lake hl although there was insufficient quartz in the ml samples for sar osl dating the 4 6 0 4 ka sar osl age of the elevated delta at al represents the last time active deltas were forming higher than present day lake level and implies 1 a fall in rsl of up to 14 4 m since the mid holocene in this part of alexander island which is consistent with existing field based rsl chronologies for the ap 2 relatively smaller ice masses than suggested by some but not all isostatically coupled ice sheet models since the mid holocene and 3 significant mid holocene thinning of the ap ice sheets which is consistent with regional sediment core data and cosmogenic exposure ages and the 4 4 0 7 ka sar osl age of the lowermost hl delta

ore petrography using megapixel x ray imaging rapid insights into element distribution and mobilization in complex pt and u ge cu ores geologic samples are extremely diverse and share a tendency for both heterogeneity and complexity this is especially true for ores which commonly result from a complex interplay of processes in highly dynamic environments in recent years a number of tools allowing the chemical mapping of major e g mineral liberation analysis mla minor e g electron microprobe epma and trace e g laser ablation inductively coupled plasma mass spectrometry la icp ms elements in geologic samples at 1 to 50 m resolution and over mm2 areas have seen rapid development and have become readily available to date the application of synchrotron based x ray fluorescence sxrf mapping has been limited to addressing key questions because of low availability and high cost this paper demonstrates how recent advances in x ray fluorescence detector technology are bringing new possibilities to ore petrology millisecond dwell times allow collection of thin section size maps at resolutions of a few m in hours while improvements in data analysis software simplify the production of quantitative elemental maps based on the imaging of six samples representative of different commodities pt u cu ge and different geologic contexts pge deposit sandstone hosted u deposit vein type polymetallic hydrothermal deposit iron oxide copper gold iocg deposit we demonstrate that megapixel sxrf msxrf can efficiently provide the information necessary to understand metal speciation in the context of thin section scale textural complexity image analysis revealed a number of new results for the studied deposits for example 1 the distribution of micrometer sized pt rich grains and ti mobility during the formation of schistosity at the fifield point prospect new south wales australia 2 the presence of ge contained in organic matter and of hg minerals associated within quartzite clasts in the lake frome u ores south australia 3 confirmation of the two stage ge enrichment in the barrigao deposit with demonstration of the presence of ge in solid solution in the early chalcopyrite portuguese iberian pyrite belt and 4 the enrichment of u during late dissolution reprecipitation reactions in the bornite ores of the moonta and wallaroo iocg deposits south australia these results illustrate that msxrf is a powerful technique for locating nano to microparticles of precious metals pt and trace contaminants e g hg that form distinct micro minerals in addition it is a powerful tool for understanding commodities with relatively low ore grades and complex distribution 100 1 000 ppm e g u ge

water mass circulation on demerara rise during the late cretaceous based on nd isotopes abstract circulation in the north atlantic during the late cretaceous has implications for poleward heat transport and nutrient distribution during an extreme greenhouse interval with episodes of ocean anoxia nd isotopes of fossil fish teeth and debris represent one of the few water mass tracers that can be used to reconstruct deep ocean circulation we present nd isotopic data interpreted as bottom water values for 290 samples from three ocean drilling program sites on demerara rise sites 1258 1260 and 1261 along with 102 analyses from four other north atlantic sites cape verde goban spur bermuda rise and blake nose that provide additional geographic and bathymetric control our results confirm the presence of a water mass with low end values 14 to 17 that are believed to be influenced by continental material during local water mass formation at low latitudes this demerara bottom water dbw is the primary water mass in the region from the cenomanian to coniacian and from the late campanian through early maastrichtian following a hiatus of 10 my a positive 8 end unit excursion occurs during ocean anoxic event 2 oae2 that cannot be explained by changes in weathering inputs diagenesis or magmatic sources of nd instead it appears to represent an influx of bottom waters sourced from the tethys or north atlantic this replacement of dbw during oae2 argues for decreased production of dbw or enhanced production of tethys north atlantic waters during peak greenhouse conditions from the late campanian through early maastrichtian dbw becomes the only water mass recorded at demerara rise and it appears to expand to abyssal depths at cape verde in the campanian this water mass is ultimately replaced by waters that appear to be sourced from the north atlantic starting in the late maastrichtian observed variations in circulation in the tropical north atlantic during the late cretaceous can account for extensive deposition of black shales in the region prior to the hiatus as well as local warming during a global cooling event in the maastrichtian

holocene evolution of the danube delta an integral reconstruction and a revised chronology abstract the danube delta is one of the few large deltas in the world the evolution of which has involved numerous and varied episodes within a complex framework of interactivity between river sediment supply allochthonous sediments supplied by longshore currents marine dispersing forces vertical movements neotectonics sediment compaction and sea level the resulting complex morphology comprises diversified landscapes varying from labyrinthic net of channels and lakes fluvial delta to massive tracts of monotonous reed marshes large lagoons divided by barriers or beach ridge plains accommodating large transgressive dunefields maritime delta whilst previous studies have focused on various sectors of the danube delta the current paper proposes for the first time an integral reconstruction of delta evolution based on existing and new sedimentological and morphological analyses and absolute ages ams 14 c and osl enabling a comprehensive synthesis in terms of both evolutionary phases and growth patterns a chronological framework was established for all the deltaic lobes and beach ridge plains highlighting the relationship between formation timespan growth rates and the resultant morphology this work unveils the early stage of delta formation including the reconstruction of delta front advancement into danube bay old danube lobe prior to 7 5 5 5 ka and initial spit barrier development 6 7 6 5 5 8 ka inception of the bayhead delta started 1000 yr before the relative stabilization of sea level and of the initial spit formation the original fluvial delta plain topography is now buried at a depth of 4 6 m depth below the present topography representing the current stage of fluvial aggradation as a result of subsidence and sea level rise regarding the maritime delta six large open coast lobes developed in the last six millennia of which four were formed by the sf gheorghe branch attesting the long uninterrupted activity of this branch whereas the other two were created respectively by the sulina and the chilia branches the evolution of each lobe is derived from successive chronological shoreline positions and discussed in relation with changes in danube discharge special attention has been paid to their growth stages and progradation rates for the southern delta we bring in new arguments for an active southern distributary the dunav derived from the sf gheorghe branch that formed successive open coast lobes between 2 6 and 1 3 ka additionally we discuss the effects of modern anthropogenically driven fluvial sediment reduction on the morphology and morphodynamics of the active lobes of the danube

a 40ar 39ar and u pb isotopic study of the ilimaussaq complex south greenland implications for the 40k decay constant and for the duration of magmatic activity in a peralkaline complex abstract magmatism in the gardar province south greenland is related to two main rifting events at 1280 ma and 1180 to 1140 ma little is known about the duration of the magmatic activity in a specific complex the ilimaussaq intrusion belongs to the second period of rifting and comprises an extraordinary diversity of granitic and syenitic rock types which intruded and fractionated in three successive magmatic events as the intrusion contains some of the most evolved incompatible element rich rocks on earth it was chosen for a detailed geochronological study to quantify the duration of melt production intrusion fractionation and cooling amphiboles which are abundant in all rock types including pegmatites and late magmatic veins were dated using the 40 ar 39 ar technique since the solidus temperature of the most evolved melts is below the closure temperature of amphibole and no later heating event occurred the 40 ar 39 ar ages reflect the magmatic crystallisation and can be used to determine the duration of igneous differentiation the 40 ar 39 ar plateau ages range between 1142 6 2 2 ma and 1152 3 3 7 ma using the steiger and jager steiger r h and jager e 1977 subcommision on geochronology convention on the use of decay constants in geo and cosmochronology earth planet sci lett 36 359 362 40 k decay constant these ages are younger than an u pb age of 1160 5 ma on baddeleyite from the first magma batch our results indicate that the 40 k decay constant of steiger and jager may be too high a lambda similar to that proposed by kwon et al kwon j min k bickel p and renne p r 2002 statistical methods for jointly estimating decay constant of 40 k and age of a dating standard math geol 34 457 474 is required to make the 40 ar 39 ar match the u pb age

post glacial stratigraphy and palaeoenvironment of the northern part of the curonian spit western lithuania a complex study including palynological and diatom analysis palaeontological investigation of molluscan fauna carbonates analyses and radiocarbon dating was performed in the northern part of the curonian spit western lithuania environmental changes were reconstructed during the late glacial and holocene cold and dry climate unstable soils open habitats of tundra vegetation spread in the surroundings of the northern part of the curonian spit during the younger dryas birch was dominant the relatively deep baltic ice lake with a freshwater planktonic diatom complex existed during the preboreal and the beginning of boreal forest birch and pine was not dense and wetland development occurred in coastal areas forest spread rapidly in response to significant warming during boreal time a shallow freshwater ancylus lake nearshore environment existed in the area of the northern part of the present curonian spit the surrounding forest was dominated by broad leaved species especially elm lime and oak during the atlantic alder and hazel occurred everywhere pine forest was still widely represented in the area on sandy soils subsequently the shallow litorina sea basin existed around the area spruce forest spread in the early subboreal climate was warm and relatively dry and intensive soil formation took place shallow brackish postlitorina sea lagoonal environmental conditions existed in the first half of subboreal aeolian sand with buried soil formation started to accumulate at the end of subboreal and the northern part of the curonian spit became land

stable isotope geochemistry of vertisols formed on marine limestone and implications for deep time paleoenvironmental reconstructions abstract carbon and oxygen isotope compositions of pedogenic carbonate preserved in paleosols have been used extensively to reconstruct ancient environmental conditions one concern is that pedogenic carbonate precipitated in association with a limestone parent material may include a contribution from inherited detrital lithogenic marine calcite thus compromising interpretations of stable isotope compositions to investigate the impact of lithogenic calcite on environmental interpretations using paleosols we measured stable isotope ratios in pedogenic carbonates and coexisting soil organic matter som in modern vertisols fine smectitic thermic udic haplusterts from riesel texas heiden series and zabcikville texas houston black series forming on cretaceous chalk deposits the pedogenic and lithogenic components in the heiden series soil at riesel were identified using micromorphology and cathodoluminescence cl which showed incorporation of luminescent marine allochems i e foraminifera mollusks into hard nodules and soft powdery pedogenic masses additionally micromorphology showed evidence of meteoric recrystallization of the allochems despite the presence of these inherited carbonates into hard nodules and soft powdery masses the stable isotope compositions recorded a partial pedogenic signal recrystallization of the marine allochems resulted in overprinting of primary marine isotope ratios with ratios that are more similar to those expected for pedogenic carbonates in these soils this study demonstrates that incorporation of parent material into pedogenic carbonates does not necessarily compromise the pedogenic signal that is useful for paleoenvironmental reconstructions however overprinting of marine allochems if present can be important and needs to be identified using micromorphology and cathodoluminescence before using stable isotope ratios of pedogenic carbonates for paleoenvironmental reconstructions

paleomagnetism and u pb geochronology of the 2 17 ga biscotasing dyke swarm ontario canada evidence for vertical axis crustal rotation across the kapuskasing zone u pb dates on baddeleyite yield ages of 2167 8 2 2 and 2171 6 1 2 ma on two northeast trending dykes west of the kapuskasing zone in ontario canada these ages identify the dykes as belonging to the biscotasing dyke swarm east of the kapuskasing zone which was previously dated at 2166 7 1 4 ma by u pb on baddeleyite and zircon the new dates show that the biscotasing swarm was emplaced over an area of at least 300 000 km2 much larger than hitherto suspected and in a geologically short period of time of about 5 million years a comparison of paleomagnetic data from biscotasing and 2 45 ga matachewan dykes on either side of the kapuskasing zone suggests that the western half of the superior province has rotated about 10 20 counterclockwise relative to the eastern half across the kapuskasing zone this movement may have been accompanied by rifting farther north which ultimately led to the paleoproterozoic embayment underlying hudson bay that gives the superior province its characteristic butter

the effect of the instability of muscovite during in vacuo heating on 40ar 39ar step heating spectra abstract the goal of this study was to ascertain the nature of the ar release mechanism s for a single well characterized muscovite heated incrementally in vacuo 1 at temperatures and time intervals typical of 40ar 39ar step heating experiments and 2 isothermally at 500 c and 700 c for time intervals much longer than typical 40ar 39ar experiments the rate of delamination was monitored by sem and the rate of dehydroxylation was determined by xrd analyses the rate of in vacuo ar loss was compared to that for muscovite heated at 700 c and 2 kbar h2o pressure for all experiments the rate of ar loss was found to be consistent with the rates of dehydroxylation and delamination at 500 c ar loss behavior for a 3000 m diameter muscovite grain was approximated by volume diffusion but the ar release pattern became increasingly non fickian with decreasing grain size we propose that the cause of the non fickian behavior is delamination the portions of the isothermal runs exhibiting diffusion like profiles also yielded discordant 40ar 39ar ages and low atmospheric ar contamination we attribute this phenomenon to the preferential concentration of atmospheric ar in interlayer extended defects and of 40ar in interlayer vacancies whereas 39ar is uniformly distributed throughout the muscovite structure by recoil the 40ar 39ar age spectrum of the muscovite heated under hydrothermal conditions has a staircase shape comparable to that usually interpreted as due to 40ar diffusive loss whereas 40ar 39ar laser spot analyses did not allow this interpretation the in vacuo ar release rate for this sample however indicates that it had been altered during the experiment therefore we propose that this 40ar 39ar age spectrum reflects the differential release of ar from the alteration phases vs muscovite for our sample dehydroxylation and delamination control the in vacuo ar release at temperatures less than 900 c whereas ar diffusion from thin dehydroxylated slabs may dominate the ar release mechanism for temperatures greater than 900 c this model would predict that the recovery of fossil 40ar concentration gradients from muscovite by typical incremental heating schedules is not possible the rates of delamination in vacuo and the rate of ar diffusion for muscovite in nature however both depend upon its the chemical composition structural integrity and grain size consequently for samples with either a naturally occurring broad range of grain sizes such as detrital muscovite and authigenic clay from sedimentary rocks or a compositionally or structurally heterogeneous population of grains such as muscovite from shear zones 40ar 39ar incremental heating may be able to detect intergranular variations in the k ar age

mesozoic cenozoic geological evolution of the himalayan tibetan orogen and working tectonic hypotheses the himalayan tibetan orogen culminated during the cenozoic india asia collision but its geological framework and initial growth were fundamentally the result of multiple previous ocean closure and intercontinental suturing events as such the himalayan tibetan orogen provides an ideal laboratory to investigate geological signatures of the suturing process in general and how the earth9s highest and largest orogenic feature formed in specific this paper synthesizes the triassic through cenozoic geology of the central himalayan tibetan orogen and presents our tectonic interpretations in a time series of schematic lithosphere scale cross sections and paleogeographic maps we suggest that north dipping subducting slabs beneath asian continental terranes associated with closure of the paleo meso and neo tethys oceans experienced phases of southward trench retreat prior to intercontinental suturing these trench retreat events created ophiolites in forearc extensional settings and or a backarc oceanic basins between rifted segments of upper plate continental margin arcs this process may have occurred at least three times along the southern asian margin during northward subduction of neo tethys oceanic lithosphere from 174 to 156 ma 132 to 120 ma and 90 to 70 ma at most other times the tibetan terranes underwent cordilleran style or collisional contractional deformation geological records indicate that most of northern and central tibet the hoh xil and qiangtang terranes respectively were uplifted above sea level by jurassic time and southern tibet the lhasa terrane north of its forearc region has been above sea level since 100 ma stratigraphic evidence indicates that the northern himalayan margin of india collided with an asian affinity subduction complex forearc arc system beginning at 60 ma both the himalaya composed of indian crust and tibet show continuous geological records of orogenesis since 60 ma as no evidence exists in the rock record for a younger suture the simplest interpretation of the geology is that india asia collision initiated at 60 ma plate circuit paleomagnetic and structural reconstructions however suggest that the southern margin of asia was too far north of india to have collided with it at that time seismic tomographic images are also suggestive of a second more southerly neo tethyan oceanic slab in the lower mantle where the northernmost margin of india may have been located at 60 ma the geology of tibet and the india asia suture zone permits an alternative collision scenario in which the continental margin arc along southern asia the gangdese arc was split by extension beginning at 90 ma and along with its forearc to the south the xigaze forearc rifted southward and opened a backarc ocean basin the rifted arc collided with india at 60 ma whereas the hypothetical backarc ocean basin may not have been consumed until 45 ma a compilation of igneous age data from tibet shows that the most recent phase of gangdese arc magmatism in the southern lhasa terrane initiated at 70 ma peaked at 51 ma and terminated at 38 ma cenozoic potassic adakitic magmatism initiated at 45 ma within a 200 km wide elliptical area within the northern qiangtang terrane after which it swept westward and southward with time across central tibet until 26 ma at 26 to 23 ma potassic adakitic magmatism swept southward across the lhasa terrane a narrow 20 km width orogen parallel basin developed at low elevation along the axis of the india asia suture zone the kailas basin and greater himalayan sequence rocks began extruding southward between the south tibetan detachment and main central thrust the kailas basin was then uplifted to 4 km elevation by 20 ma after which parts of the india asia suture zone and gangdese arc experienced 6 km of exhumation between 20 and 16 ma between 16 and 12 ma slip along the south tibetan detachment terminated and east west extension initiated in the northern himalaya and tibet potassic adakitic magmatism in the lhasa terrane shows a northward younging trend in the age of its termination beginning at 20 to 18 ma until volcanism ended at 8 ma we interpret the post 45 ma geological evolution in the context of the subduction dynamics of indian continental lithosphere and its interplay with delamination of asian mantle lithosphere

calcretes from a palaeosinkhole in jurassic palaeokarst subbetic southern spain abstract calcretes have been recognized in the bottom of a palaeokarstic sinkhole etched into early jurassic carbonates from the subbetic southern spain these are 3 to 10 cm thick and they show an internal structure in which three units can be distinguished the lower unit is composed of alternate irregular bands of unfossiliferous micrite and sparry calcite in the micrite several features point out the activity of endolithic microorganisms as fungi and bacteria the middle unit which has a laminated structure with palisade calcite spar and some vadose silt is interpreted as a speleothem and finally the upper unit shows calcrete pisoids and rhizocretions the isotope ratio analysis gives results in which 13 c ranges from 10 1 to 10 9 and 18 o ranges from 5 7 to 7 0 these values are very similar to those from palaeosols of other ages and localities which is an important argument favouring emersion stages with continental deposition in an island with an arid or semi arid climate nevertheless these calcretes outcrop in association with a palaeokarstic relief reflecting wet climate before the calcrete formation

stability of atmospheric co2 levels across the triassic jurassic boundary the triassic jurassic boundary 208 million years ago is associated with widespread extinctions in both the marine and terrestrial biota the cause of these extinctions has been widely attributed to the eruption of flood basalts of the central atlantic magmatic province this volcanic event is thought to have released significant amounts of co2 into the atmosphere which could have led to catastrophic greenhouse warming but the evidence for co2 induced extinction remains equivocal here we present the carbon isotope compositions of pedogenic calcite from palaeosol formations spanning a 20 myr period across the triassic jurassic boundary using a standard diffusion model we interpret these isotopic data to represent a rise in atmospheric co2 concentrations of about 250 p p m across the boundary as compared with previous estimates of a 2 000 4 000 p p m increase the relative stability of atmospheric co2 across this boundary suggests that environmental degradation and extinctions during the early jurassic were not caused by volcanic outgassing of co2 other volcanic effects such as the release of atmospheric aerosols or tectonically driven sea level change may have been responsible for this event

uranium series accessory crystal dating of magmatic processes complex and protracted crystallization histories over geologic timescales are recorded in accessory minerals e g zircon allanite although magmatic crystallization was traditionally assumed to occur essentially instantaneously for the purposes of interpreting mineral geochronometers with low absolute time resolution for ancient samples it emerged relatively recently that magmatic crystallization can occur over extended durations this discovery arose from applying high spatial resolution accessory mineral dating techniques for uranium series isotopes to young volcanic and cognate plutonic rocks the emerging pattern from these studies is that individual crystals and crystal populations record crystallization episodes lasting from 1 000 to many hundreds of thousands of years accessory mineral dating of volcanic rocks and cognate plutonic xenoliths opens new research avenues for crystal age fingerprinting that correlates pyroclastic deposits lavas and plutonic rocks by using characteristic age dis

climate change on tectonic time scales abstract observational and modeling studies relevant to climate change on tectonic time scales are reviewed probably the most significant climate result from this time scale involves inferences about nearly ice free conditions for some intervals of earth history some additional results suggest relatively rapid transitions between climate states modeling studies indicate that although tectonic changes significantly modify the atmosphere and ocean circulation in most cases such modifications do not appear to be sufficient to explain ice free climates increased atmospheric co2 levels 5 10 presentvalues may be needed to completely reconcile models and data although the co2 paradigm has received widespread attention in the last few years the results summarized herein indicate that co2 is only one of several important factors influencing climate i believe the time is appropriate for contemplating climate change on tectonic time scales in terms of a post co2 synthesis in which direct tectonic factors are approximately equal in importance to co2 fluctuations in the last few years modeling studies have progressed from a state of virtually no work on the topic to one where the models are in some respect ahead of the observations in the sense that data have not been compiled to test even some of the most basic model predictions in particular information is needed on past atmospheric co2 levels tropical sea surface temperatures seasonality of continental interiors and locations and production rates of deep waters initial steps are being taken to integrate observational and modeling activities on tectonic time scales and some of these shortcomings may be rectified over the next few years

cooling history of the nw himalaya pakistan fission track and 40ar 39ar cooling ages indicate that the late tertiary cooling history of the himalayan ranges of northern pakistan is largely a function of uplift and erosion interpretation of cooling ages which range from under 0 5 ma to over 80 ma suggests that during the late tertiary long term uplift rates at least doubled from under 0 2 mm yr to in some cases well over 0 5 mm yr uplift rates show strong and systematic regional variations as well which reflect the greater uplift of eastern and northern regions the association of very rapid uplift and erosion with the nanga parbat haramosh massif can be explained by a locally vigorous collision of india with eurasia near a promontory of indian crust the resultant rapid uplift of the nanga parbat haramosh massif reactivated the main mantle thrust melange zone with a reversed sense of motion discontinuities in the coolingage distribution along the main mantle thrust in the southern swat hazara region may be the result of the thermal effects of overthrusting

ages of alpine tectonometamorphic events in the northwestern himalaya northern pakistan by 39ar 40ar method the main tectonometamorphic alpine events which occurred in the western part of the western himalayan virgation at south of the main suture in northern pakistan are dated by the 39ar 40ar method these events are as follows 1 the blueschist metamorphism 80 5 ma present in tectonic ophiolititic melanges along the suture this event occurred during an early subduction or obduction stage 2 the alpine barrovian metamorphism 50 30 ma developed in the sedimentary cover and orthogneisses of the indian plate during the postcollisional northward underthrusting of this plate below asia and 3 the emplacement of postmetamorphic leucogranites 23 ma resulting from the melting of the indian crust during the climax of the alpine metamorphism

seawater ph and isotopic paleotemperatures of cretaceous oceans abstract stable oxygen isotope ratios 18 o of foraminifera are widely used to reconstruct the climatic history of earth it is well known that temperature reconstructions based on 18 o are complicated by factors such as the unknown isotopic composition of the ocean in addition recent experimental and theoretical work has shown that the seawater ph has a marked effect on the 18 o of foraminifera here i employ this effect to demonstrate that reconstructions based on 18 o of foraminifera may underestimate sea surface temperatures in the geological past ocean surface temperatures for the mid cretaceous are estimated to have been 2 3 5 c higher than previously thought

the coupled δ13c radiocarbon systematics of three late glacial early holocene speleothems insights into soil and cave processes at climatic transitions abstract the coupled 13 c radiocarbon systematics of three european stalagmites deposited during the late glacial and early holocene were investigated to understand better how the carbon isotope systematics of speleothems respond to climate transitions the emphasis is on understanding how speleothems may record climate driven changes in the proportions of biogenic soil carbon and limestone bedrock derived carbon at two of the three sites the combined 13 c and 14 c data argue against greater inputs of limestone carbon as the sole cause of the observed shift to higher 13 c during the cold younger dryas in these stalagmites gar 01 from la garma cave n spain and so 1 from sofular cave turkey the combined changes in 13 c and initial 14 c activities suggest enhanced decomposition of old stored more recalcitrant soil carbon at the onset of the warmer early holocene alternative explanations involving gradual temporal changes between open and closed system behaviour during the late glacial are difficult to reconcile with observed changes in speleothem 13 c and the growth rates in contrast a stalagmite from pindal cave n spain indicates an abrupt change in carbon inputs linked to local hydrological and disequilibrium isotope fractionation effects rather than climate change for the first time it is shown that while the initial 14 c activities of all three stalagmites broadly follow the contemporaneous atmospheric 14 c trends the younger dryas atmospheric 14 c anomaly can be clearly discerned subtle changes in speleothem initial 14 c activities are linked to climate driven changes in soil carbon turnover at a climate transition

unroofing history of the jambil and jawar carbonatite complexes from nw pakistan constraints from fission track dating of apatite abstract the peshawar plain alkaline igneous province paip is exposed north of the peshawar plain in nw pakistan it stretches from tarbela in the east up to loe shilman near the pakistan afghanistan border in the west within the paip carbonatites are found at loe shilman sillai patti jambil koga and tarbela small isolated sill like bodies and plugs of carbonatites are exposed in the jambil area about 10 km se of mingora in lower swat small isolated bodies of carbonatites have also recently been discovered at the locality of jawar about 4 km north west of the sillai patti carbonatite fission track dating studies on the apatite yielded ages of 15 7 0 4 and 25 2 1 0 ma for the jambil and jawar carbonatites respectively uplift induced denudation and cooling rates of 0 19 0 04 mm y 1 and 5 73 1 15 c ma 1 for jambil carbonatite 0 12 0 03 mm y 1 and 3 57 0 73 c ma 1 for jawar carbonatite and 0 13 0 03 mm y 1 and 3 97 0 82 c ma 1 for sillai patti carbonatite respectively were estimated comparison of the data indicates that all three carbonatite complexes have experienced similar uplift induced denudation and cooling rates during the past 25 15 ma

evidence for initial excess 231pa in mid ocean ridge zircons abstract a limiting factor in the accuracy and precision of u pb zircon dates is accurate correction for initial disequilibrium in the 238u and 235u decay chains the longest lived and therefore most abundant intermediate daughter product in the 235u isotopic decay chain is 231pa t1 2 32 71 ka and the partitioning behavior of pa in zircon is not well constrained here we report high precision thermal ionization mass spectrometry tims u pb zircon data from two samples from ocean drilling program odp hole 735b which show evidence for incorporation of excess 231pa during zircon crystallization the most precise analyses from the two samples have consistent th corrected 206pb 238u dates with weighted means of 11 9325 0 0039 ma n 9 and 11 920 0 011 ma n 4 but distinctly older 207pb 235u dates that vary from 12 330 0 048 ma to 12 140 0 044 ma and 12 03 0 24 to 12 40 0 27 ma respectively if the excess 207pb is due to variable initial excess 231pa calculated initial 231pa 235u activity ratios for the two samples range from 5 6 1 0 to 9 6 1 1 and 3 5 5 2 to 11 4 5 8 the data from the more precisely dated sample yields estimated dpazircon duzircon from 2 2 3 8 and 5 6 9 6 assuming 231pa 235u of the melt equal to the global average of recently erupted mid ocean ridge basaltic glasses or secular equilibrium respectively high precision id tims analyses from nine additional samples from hole 735b and nearby hole 1105a suggest similar partitioning the lower range of dpazircon duzircon is consistent with ion microprobe measurements of 231pa in zircons from holocene and pleistocene rhyolitic eruptions schmitt 2007 schmitt 2011 the data suggest that 231pa is preferentially incorporated during zircon crystallization over a range of magmatic compositions and excess initial 231pa may be more common in zircons than acknowledged the degree of initial disequilibrium in the 235u decay chain suggested by the data from this study and other recent high precision datasets leads to resolvable discordance in high precision dates of cenozoic to mesozoic zircons minor discordance in zircons of this age may therefore reflect initial excess 231pa and does not require either inheritance or pb loss

new constraints on using paleosols to reconstruct atmospheric pco2 ecosystem and climatic changes due to anthro po genic emissions of co 2 are of increasing importance to society one way to predict these changes in the future is to study warming events in the geologic past the main control of earth s temperature over geologic time is the concentration of atmospheric co 2 however the precise relationship between co 2 and temperature is not fully understood therefore it is essential to be able to quantify atmospheric co 2 concentrations in the geologic past especially at times of rapid climate change analogous to current atmospheric changes one widely applied proxy relates the carbon isotopic composition of pedogenic carbonates to atmospheric pco 2 but one of the key variables soil respired co 2 s z is not well constrained this study presents a new proxy where soil respired co 2 is related to mean annual precipitation map by the following equation s z 5 67 map 269 9 r 2 0 59 se 681 ppm this proxy validated for modern atmospheric pco 2 levels constrains the primary source of uncertainty in the soil carbonate paleobarometer we apply this proxy to make atmospheric pco 2 reconstructions for examples from the cenozoic mesozoic and paleozoic and calculate co 2 estimates that are in better agreement with estimates from other independent proxies and model results than previous pedogenic carbonate reconstructions the implications of the uncertainties attributed to pedogenic carbonate paleobarometry as well as guidelines for using this method are discussed by making individual measurements rather than assumptions for each isotopic value and combining those analyses with an s z estimate for each paleosol considered using our new proxy described herein we can obtain increased precision for atmospheric pco 2 reconstructions

k ar and ar ar geochronology of the himalayan collision in nw pakistan constraints on the timing of suturing deformation metamorphism and uplift mica and hornblende k ar and ar ar data are presented from each of the three crustal components of the himalayan collision zone in north pakistan the asian plate the kohistan island arc and the indian plate together with u pb and rb sr data published elsewhere these new data 1 date the age of suturing along the northern suture which separates kohistan from asia at 102 85 ma 2 establish that the basic magmatism in kohistan which postdates collision along the northern suture predates 60 ma and that the later granite magmatism spanned a range of 60 25 ma 3 show that uplift amounts within kohistan are greater toward the nanga parbat syntaxis than away from it and that rate of uplift near the syntaxis increased over the last 20 ma to a current figure of about 5 5 mm a year 4 show that much of southern kohistan had cooled to below 500 c by 80 ma and that the major deformation which imbricated kohistan probably predated 80 ma and certainly predated 60 ma and was related to the kohistan asia collision rather than the kohistan india one 5 imply that uplift along the hunza shear in the asian plate together with imbrication of the metamorphics in its hanging wall took place at about 10 ma and was associated with breakback thrusting in the hanging wall of the main mantle thrust 6 suggest that the indian plate has a lengthy pre himalayan history with an early metamorphism at about 1900 ma major magmatism at 500 550 ma and early jurassic lithospheric extension or inversion and 7 show that the indian plate rocks were metamorphosed shortly after the collision within kohistan which occurred at circa 50 ma and subsequently cooled back through 500 c at circa 38 ma and 300 c at 30 35 ma with ages of cooling through 200 and 100 c as determined by fission track data locally controlled by nanga parbat related uplift tectonics

structural evidence for back sliding of the kohistan arc in the collisional system of northwest pakistan in the naran region of the pakistan himalayas a regionally distributed second generation of folds results from northward directed shear deformation these folds are collapse structures associated with back sliding of the hanging wall namely the kohistan paleo island arc they are explained by a geometrical model that combines coeval vertical and horizontal shortening accordingly they are synconvergence collapse features that indicate at least 5 km of vertical shortening of the imbricate thrust slices derived from the indian continent in the northwest himalayas

petrogenetic and tectonic significance of young leucogranites from the northwestern himalaya pakistan in the himalaya of northwestern pakistan small discordant bodies of leucogranite intrude metamorphosed basement of the indian crust as the first step in assessing the tectonic significance of these granites we have used the shrimp ion microprobe to obtain u pb dates on zircon zircons of igneous appearance are scarce in the leucogranites and with one exception are associated with xenocrystic components which occur as discrete grains and as cores rimmed by young zircon zircons of igneous appearance are high in u 5000 to 40 000 ppm low in th u 0 01 to 0 05 and frequently colored a distinct blue xenocrystic components give a range of proterozoic ages consistent with ages previously reported for indian crust in sharp contrast zircons of igneous appearance yield clusters of concordant tertiary ages two leucogranite dikes from southern localities yield rather old emplacement ages of about 35 ma swat and about 50 ma naran together with previously determined 40ar 39ar and fission track cooling ages these ages document immediate and rapid metamorphism and denudation following eocene collision three leucogranite dikes from northern localities within the nanga parbat haramosh massif are very young having emplacement ages of about 2 3 ma 5 ma and 7 ma the formation and emplacement of these leucogranites during the rapid late tertiary denudation of the nanga parbat region suggests to us that decompression melting may be a viable mechanism for leucogranite genesis

stratigraphy and structure of the indus suture in the lower swat pakistan nw himalaya abstract we present a geological map detailed structural description and new subdivisions of the indus suture zone lithologies in northeast pakistan lower swat region the indus suture zone is a dominantly fore arc related assemblage obducted onto the indian plate initial southward thrusting was followed by the reactivation of the indus suture as a ductile brittle normal fault significant strike slip faulting may have taken place at this stage later brittle reverse faults demonstrate that shortening outlasted normal faulting the comparison of the structural evolution of the indus suture zone and the indian plate shows that both terrains were sharing the deformational history possibly since the earliest stage of collision the lower swat area records a full orogenic cycle from early rifting through continent arc collision to orogenic collapse we present a geodynamic model that integrates all these elements

ion microprobe analysis of 231pa 235u and an appraisal of protactinium partitioning in igneous zircon ion microprobe u pa measurements in zircon crystals from a holocene rhyolite salton buttes california are utilized to assess the partitioning of pa and u between zircon and melt the relative sensitivity factor rsf for ion microprobe u pa zircon analysis was calibrated on a natural high u secular equilibrium zircon from buff peak nevada zircon crystals from salton buttes rhyolite show evidence for excess 231 pa with a weighted average 231 pa 235 u activity ratio of 1 9 from this ratio model zircon melt partition coefficient ratios d pa d u 0 9 2 2 are obtained assuming plausible limits for 231 pa 235 u melt and correcting for the age of zircon crystallization 15 ka these values roughly fit lattice strain models for tetravalent cations but are more than one order of magnitude lower than predictions for pentavalent pa based on this appraisal of pa partitioning initial 231 pa disequilibrium caused by zircon melt fractionation alone can produce minor discordance or excess 207 pb in late cenozoic zircon but is insignificant for older u pb zircon ages

quasi static eocene oligocene climate in patagonia promotes slow faunal evolution and mid cenozoic global cooling abstract new local regional climatic data were compared with floral and faunal records from central patagonia to investigate how faunas evolve in the context of local and global climates oxygen isotope compositions of mammal fossils between c 43 and 21 ma suggest a nearly constant mean annual temperature of 16 3 c consistent with leaf physiognomic and sea surface studies that imply temperatures of 16 18 c carbon isotopes in tooth enamel track atmospheric 13 c but with a positive deviation at 27 2 ma and a strong negative deviation at 21 ma combined with paleosol characteristics and reconstructed leaf area indices rlais these trends suggest aridification from 45 ma c 1200 mm yr to 43 ma c 450 mm yr quasi constant map until at least 31 ma and an increase to 800 mm yr by 21 ma comparable map through most of the sequence is consistent with relatively constant floral compositions rlai and leaf physiognomy abundance of palms reflects relatively dry adapted lineages and greater drought tolerance under higher p co2 pedogenic carbonate isotopes imply low p co2 430 300 ppmv at the initiation of the eocene oligocene climatic transition arid conditions in patagonia during the late eocene through oligocene provided dust to the southern ocean enhancing productivity of silicifiers drawdown of atmospheric co 2 and protracted global cooling as the antarctic circumpolar current formed and earth cooled wind speeds increased across patagonia providing more dust in a positive climate feedback high tooth crowns hypsodonty and ever growing teeth hypselodonty in notoungulates evolved slowly and progressively over 20 ma after initiation of relatively dry environments through natural selection in response to dust ingestion a ratchet evolutionary model may explain protracted evolution of hypsodonty in which small variations in climate or dust delivery in an otherwise static environment drive small morphological shifts that accumulate slowly over geologic time

early permian granitic dykes of alkaline affinity in the indian high himalaya of upper lahul and se zanskar geochemical characterization and geotectonic implications

stable isotope record in mollusca and pedogenic carbonate from late pliocene soils of central italy abstract the late pliocene younger than 2 5 ma alluvial fan succession of toppetti quarry near todi umbria central italy includes many palaeosols pedogenic carbonate concretions and mollusc remains were separated from 73 palaeosols collected along 150 m of exposure and analysed for their oxygen and carbon stable isotope content 13c and 18o of the pedogenic carbonate and land snail shells suggest that no dramatic change in local climate took place values of the pedogenic carbonates are similar to other data reported for the mediterranean region 18o data suggest a mean annual temperature and or 18o similar to modern climatic conditions carbon isotope data from both land snails and pedogenic carbonate are consistent with a prevailing type c3 vegetation a mixture of forest and c3 grassland sustained by a mean annual precipitation between 300 and 1000 mm mainly in the cool periods of the year seems to be the most likely scenario the limited variation shown by the isotope composition of the biogenic and inorganically precipitated carbonate indicates that the environmental variations are referable mainly to change of humidity rather than temperature

regional sediment sources versus the indus river system the plio pleistocene of the peshawar basin nw pakistan abstract sedimentary archives within the peshawar basin in northwest pakistan preserve a record of siliciclastic supply patterns during the plio pleistocene epoch the basin fill consists of fluvial floodplain clays overlain by thick lacustrine glaciofluvial rhythmites with deposits of multiple alluvial fans in the southern parts of the basin and topped by loess deposits in ideal vertical successions framework mineralogical composition and bulk sediment geochemical proxies of these sediments indicate detritus derivation from dominantly acidic igneous sources with contribution from medium grade metamorphic rocks there appears to be no significant contribution from ultramafic mafic or very high grade metamorphic sources in addition sediments from the southern part of the basin support supply from low grade metamorphic rocks and carbonate sediments overall sedimentation occurred in an active continental margin setting under conditions of insignificant chemical weathering the uplift of the attock cherat range during the late pliocene 2 8 ma restricted the indus river from shedding its detritus into the basin therefore the sediments of the peshawar basin do not reflect signatures of the indus river siliciclastics and thus lack the basic igneous geochemical signal which is otherwise typical for the himalayas hinterland on the contrary the geochemical signatures of these sediments favour predominant detritus flux from the acidic rocks of the peshawar plain alkaline igneous complex ppaic and associated metasediments therefore the kabul swat river and other local tributaries of this smaller river system that originated within the ppaic and associated mountains are considered the major transporting agents which contributed siliciclastics into the peshawar basin during the plio pleistocene additionally in the southern part of the basin the uplifting attock cherat range appeared to have contributed detritus in the form of alluvial fluvial fan deposits

late ordovician glaciation initiated by early land plant evolution and punctuated by greenhouse mass extinctions abstractlate ordovician hirnantian glaciation indicated by periglacial paleosols tillites and glacial pavements in saharan africa has been attributed to advances in weathering and carbon sequestration due to evolution of early land plants in the same way that devonian permian glaciation has been attributed to evolution of forests and quaternary glaciations to evolution of grasslands two problems for carbon cycle explanations of this glaciation are an hirnantian co2 greenhouse estimated at 4035 ppmv from mass balance models and possibly related hirnantian mass extinctions this estimate of high co2 is a 10 m yr average here evaluated against high resolution sequences of paleosols that give estimates not only of co2 but also of paleoclimate and vegetation through the late ordovician katian paleosols of the eastern united states show increases in depth and in degree of carbon consumption and storage comparable with those preceding glaciation of the devonian permian and quaternary early thalloid l

u th pb and 230th 238u disequilibrium isotope systematics precise accessory mineral chronology and melt evolution tracing in the alpine bergell intrusion in order to investigate the potential of combined th u pb isotope and 230th 238u disequilibrium systematics for tracing magmatic crystallization and melt evolution conventional high resolution single crystal tims techniques have been applied to zircon titanite and fragments of geochemically characterized growth zones of allanite these minerals were extracted from a single tonalite specimen collected from the feeder zone of the tertiary bergell pluton southern steep belt s switzerland n italy the isotopic results document an extended history of crystallization and melt evolution of at least 5 ma with well resolved zircon ages defining an early interval of 33 0 to 32 0 ma followed by crystallization of zoned allanite from 32 0 to 28 0 ma and formation of magmatic epidote possibly as late as 26 ma trace and major element patterns in zoned allanite closely mirror melt evolution characterized by increase of u concentration and sharp decrease of th and lree reflecting early crystallization of phases low in u and in particular the dominating control by allanite precipitation preservation of substantial quantities of excess 206pb derived from initial excess 230th in all analyzed allanite grains indicates that their isotopic systems have not been reset by loss of radiogenic pb during prolonged residence at magmatic conditions and regional metamorphic cooling and that the measured sequence of 208pb 232th dates translates into a real age sequence major loss of radiogenic pb from compositionally zoned allanite by volume diffusion would have resulted in a data pattern grossly different from the observed one as demonstrated by numerical modeling of 232th 208pb 238u 230th 206pb isotopic evolution the results therefore suggest closure temperatures 700 c for magmatic allanite quantification of 230th 238u disequilibrium relationships reveals a smooth initially steep decrease of th u in the magma from values of 2 9 at 32 0 ma to 0 1 at 28 0 ma in equilibrium with sequential allanite zoning comparison of calculated th u magma with measured total rock th u 0 79 requires fractional crystallization of allanite at an early stage this process of removal of allanite and thus th from the melt was operative at least until 31 5 ma providing an upper limit for the time of emplacement of the studied magma batch the fact that bulk zircon and a large part of allanite crystallization predate emplacement cautions against equating ages determined on refractory minerals from deep seated plutons with intrusion ages the persistence of magmatic conditions over a period of 5 ma concentrated in a narrow collision zone between the european and the african plate has been a major controlling factor for the oligocene evolution of the adjacent insubric fault the main tectonic lineament of the alps being active from late cretaceous to miocene times

u th pb systematics of morphologically characterized zircon and allanite a high resolution isotopic study of the alpine rensen pluton northern italy abstract the rensen pluton is a typical member of the tertiary calc alkaline plutonic suite structurally connected to the periadriatic lineament it intrudes the austroalpine polymetamorphic basement of the eastern alps southwest of the tauern window northern italy zircons and allanites from tonalitic quartz dioritic and monzogranitic lithologies were studied systematically on the basis of refined grain by grain microanalytical techniques high resolution isotope analyses show that morphology and u pb systematics of zircon are highly correlated with magma evolution zircons from the main tonalitic part of the intrusion display a gradual increase of u content from early stage s type morphology to late stage g1 type morphology most of the zircon crystals include premagmatic seeds derived from old crustal sources unevolved s type zircons contain inherited components of late proterozoic early paleozoic apparent age whereas late stage g1 type zircons show inheritance of early proterozoic apparent age both types of inherited components are present in zircons from a fine grained tonalitic domain located at the center of the pluton which shows restitic structures the crustal affinity of this rock is corroborated by its relatively low e nd value 6 0 as compared to values obtained for the main tonalite 3 9 and the quartz diorite 3 5 the accuracy of cainozoic zircon ages is affected by initial radioactive disequilibrium in the u pb decay chains particularly uncertain is the fractionation behavior of protactinium which could be enriched in zircon due to the high stability of the pa 5 oxidation state because the th pb system is devoid of long lived intermediate radioactive nuclides the best approximation to the emplacement age of the rensen pluton is given by allanite th pb ages of 31 70 0 25ma 95 c l for the main tonalite and by a slightly younger age of 31 09 0 32ma for quartz diorite

structural evolution of the footwall of the indus suture in malakand n pakistan during the himalayan collision abstract we report new data on the geometry and kinematics of structures in the rocks of the indian plate below the indus suture in the area of malakand n pakistan the study area forms part of the exposed northwestern promontory of the indian plate indenting eurasia to form the himalayan orogenic belt earlier widespread structures i e regional foliation and lineation are consistent with an approximate n s convergence direction in coincidence with the movement direction of the indian plate younger structures such as nne trending open folds that laterally become syntaxes i e besham or nanga parbat and relatively minor e w dextral strike slip shear zones are related to a regional tectonic shortening direction subparallel to the trend of the suture these folds are radial to the northwestern corner of the indian plate and contemporaneous with the general bulk n s convergence it is only very recently in the structural record that the irregular outline of the indian plate played a role in determining the orientation of new structures during its indentation the structural pattern presents similarities to arcuate megastructures in ancient collisional orogens such as the ibero armorican arc of the variscan belt in europe where indentation tectonics as well as post orogenic oroclinal folding are invoked to explain the present curvature

thermochronology of the modern indus river bedload new insight into the controls on the marine stratigraphic record 1 the indus river is the only major drainage in the western himalaya and delivers a long geological record of continental erosion to the arabian sea which may be deciphered and used to reconstruct orogenic growth if the modern bedload can be related to the mountains in this study we collected thermochronologic data from river sediment collected near the modern delta u pb ages of zircons spanning 3 gyr show that only 5 of the eroding crust has been generated since india asia collision the greater himalaya are the major source of zircons with additional contributions from the karakoram and lesser himalaya the 39ar 40ar dating of muscovites gives ages that cluster between 10 and 25 ma differing from those recorded in the bengal fan biotite ages are generally younger ranging 0 15 ma modern average exhumation rates are estimated at 0 6 km m y or less and have slowed progressively since the early miocene 20 ma although fission track ft dating of apatites may indicate a recent moderate acceleration in rates since the pliocene 1 0 km m y driven by climate change the 39ar 40ar and ft techniques emphasize the dominance of high topography in controlling the erosional flux to the ocean localized regions of tectonically driven very rapid exhumation e g nanga parbat s karakoram metamorphic domes do not dominate the erosional record

timing and duration of himalayan metamorphism within the indian plate northwest himalaya pakistan in indian plate rocks defining the footwall of the indo asian suture in the upper kaghan valley ukv of northern pakistan we resolve four phases in a continuum of himalayan metamorphism and deformation with peak metamorphic pressures of 7 2 0 7 kbar and a minimum estimate for peak temperature of approximately 540 c to attach an absolute age to himalayan metamorphism we used the shrimp ion microprobe to obtain u pb ages on the rims of zircons from granites metamorphosed during the earliest phase of himalayan orogeny four granite samples give a mean u pb age of 47 3 ma zircons from the malakand granite of the swat region 200 km west of the ukv have rims that also give a mean u pb age of 47 3 ma cores of these zircons yield u pb ages of 254 291 ma which approach the previously published rb sr isochron age of 297 4 ma for the peshawar plain igneous province suggesting an expanded areal extent of this carboniferous igneous suite the metamorphic ages of 47 3 ma document that the thermal cu

exhumation of early tertiary coesite bearing eclogites from the pakistan himalaya early tertiary coesite bearing eclogites crop out in the internal zones of the indian plate in the kaghan valley of north pakistan field and geochronological data suggest that uhp metamorphism at c 46 ma accompanied subduction of the leading edge of continental india beneath kohistan a new u pb rutile age of 44 1 1 1 ma can be interpreted as either a growth or a cooling age given the uncertainty of the closure temperature of rutile for pb but clearly documents a very short lived metamorphic peak with cooling occurring between 44 and 40 ma eclogitic assemblages are preserved in permo triassic mafic rocks in both cover and basement sequences with the best preserved eclogites hosted in the anhydrous basement the eclogite facies rocks lie on the hanging wall of a major south directed ductile thrust zone which placed basement rocks that contain coesite eclogites southward onto lower pressure cover metasediments shear criteria show that those sequences that contain eclogite facies rocks are flanked above by a zone of pervasive north directed extensional shearing mineral assemblages contained within both the thrust and extensional shear zones are consistent with them both having operated synchronously during the amphibolite to greenschist facies transition amphibole ar ar cooling history data suggest that this was at c 40 42 ma as in the alps this implies exhumation from the metamorphic peak to greenschist facies conditions within a few million years this short time scale has important implications as it is likely that both the thrust and extensional shear zones represent the late stage of a deformation continuum that commenced at uhp and brought the uhp rocks back to mid crustal levels this late eocene extensional shearing and associated exhumation of hp or uhp rocks has not previously been recorded in the pakistan himalaya the thrusts and shears were later folded by major east trending folds themselves cut by miocene aged north vergent extensional faults that currently separate the indian plate from the structurally overlying kohistan island arc

u pb systematics of the mcclure mountain syenite thermochronological constraints on the age of the 40 ar 39 ar standard mmhb recent advances in u pb geochronology allow unprecedented levels of precision in the determination of geological ages however increased precision has also illuminated the importance of understanding subtle sources of open system behavior such as pb loss inheritance intermediate daughter product disequilibria and the accuracy of the model assumptions for initial pb deconvolution of these effects allows a much richer understanding of the power and limitations of u pb geochronology and thermochronology in this study we report high precision id tims u pb data from zircon baddelleyite titanite and apatite from the mcclure mountain syenite from which the 40 ar 39 ar hornblende standard mmhb is derived we find that excess 206 pb in zircon due to inclusions of high th minerals and ele vated th u in titanite and apatite jeopardize the utility of the 238 u 206 pb system in this rock strongly air abraded zircons give dates that are younger than chemical abraded zircons which yield a statistically robust 207 pb 235 u date of 523 98 0 12 ma that is interpreted as the crystallization age we explore the best method of pbc correction in titanite and apatite by analyzing the u pb isotopes of k feldspar and using 2 d and 3 d regression methods the latter of which yields the best results in each case however the calcu lated compositions of pbc for titanite apatite and k feldspar are different implying that using a single pbc correction for multiple u pb thermochronometers may be inaccurate the u pb thermochronological results are used to predict a closure time for ar in hornblende of 522 98 1 00 ma widely cited k ar and 40 ar 39 ar dates overlap with the u pb date and relatively large errors make it impossible to verify whether u pb dates are systematically 1 older than k ar and 40 ar 39 ar dates

timing of an extensional detachment during convergent orogeny new rb sr geochronological data from the zanskar shear zone northwestern himalaya the zanskar shear zone of northwest india forms the western segment of the south tibetan detachment system a north dipping normal fault and shear zone that unroofed high grade metamorphic rocks during contraction of the himalayan orogen new rb sr mineral ages from the shear zone and its footwall show that ductile deformation was ongoing at 26 ma and continued to 16 ma in some sections the nature of the deformation varies along strike displacement at 25 ma or earlier in the western section did not result in a large thermal offset by contrast the sections to the east display substantial ductile thinning at midcrustal levels that was superseded by brittle detachments as the system continued to exhume rocks of the high himalayan crystalline sequence the implication is that the zanskar shear zone may have had a smaller offset in the west and cut down section to the east the time of the bulk of the deformation of this structure is determined to be similar to that of the equivalent structure in most of the eastern and central himalaya

unroofing history of a suture zone in the himalaya of pakistan by means of fission track annealing ages abstract the uplift history of the swat valley and hazara region of northwestern pakistan has been established using 22 fission track dates on apatite zircon and sphene a major fault the main mantle thrust mmt strikes east west across the swat valley separates regions of markedly differing fission track age regimesm and may be a suture zone separating an extinct island arc terrane on the north from the indian plate to the south fission track ages ranging from about 55 to 58 m y for sphene 18 to 53 m y for zircon and 9 to 17 m y for apatite were obtained from the region north of the mmt to the south the fission track age ranges are 20 to 25 m y for sphene 17 to 26 m y for zircon and 16 to 23 m y for apatite disparate zircon and sphene ages on each side of the mmt imply different cooling histories for each side of the fault prior to 15 m y similar apatite ages on both sides of the fault imply similar cooling histories during the past 15 m y this may indicate that faulting ceased by 15 m y mean uplift rates have been derived from the fission track data using mainly the mineral pair method uplift rates in the region north of the mmt increased from 0 07 to 0 20 mm yr during the period 55 to 15 m y south of the fault uplift rates averaged in excess of 0 70 mm yr for the period 25 to 15 m y during the past 15 m y uplift across the mmt in the swat valley showsno discontinuities ranging from 0 16 mm yr in the south to 0 39 mm yr in the north a plausible interpretation for the fission track uplift data has the mmt verging to the south with overthrusting taking place at a depth between 3 5 and 6 0 km juxtaposing two terranes that were originally separated by a substantial but unknown distance in this model regional uplift followed cessation of faulting just prior to 15 m y

tectonostratigraphic subdivisions of the himalaya a view from the west 1 indian plate rocks in the central himalaya have traditionally been divided into orogen parallel fault bound tectonostratigraphic zones a straightforward westward extrapolation of these zones has proved problematic in part because of a lack of consensus on the existence or significance of major faults within the metamorphic zone of the indian plate in pakistan where more than 10 locations for the main central thrust mct have been proposed we address this ambiguity by systematically tracing established central himalayan tectonostratigraphy around the western himalayan syntaxis and across pakistan this exercise reveals the following stratigraphic and structural relationships 1 there is a westward decrease in neogene shortening across the himalayan fold and thrust belt such that there is no age equivalent thrust in pakistan with displacement and metamorphic juxtaposition equivalent to the central himalayan mct 2 shortening across the fold and thrust belt in western pakistan is concentrated in the unmetamorphosed foreland as opposed to the metamorphic zone in the central himalaya 3 lesser himalayan higher himalayan and tethyan rocks are in stratigraphic order within the metamorphic zone of pakistan which appears to be the metamorphic equivalent of kashmir tethyan stratigraphy 4 the combination of early paleozoic and late paleozoic tectonism in pakistan has locally eliminated upper proterozoic higher himalayan rock and lower to middle paleozoic tethyan rock from the metamorphic zone of pakistan 5 late cretaceous and or early paleocene proto himalayan deformation in the pakistan foreland telescoped and eroded stratigraphy prior to the main phase of himalayan orogeny 6 tectonostratigraphic zones are offset in eastern pakistan by the transverse jhelum balakot fault 7 there is no evidence within the indian plate of pakistan for a large scale normal fault system comparable to the south tibetan detachment system 8 stratigraphy as well as the age and tectonic setting of deformation and metamorphism must be taken into account when drawing tectonostratigraphic zones

the paleozoic to mesozoic carbon cycle revisited the carbon isotopic composition of terrestrial organic matter 1 two thousand one hundred forty eight carbon isotope values for terrestrial organic matter plant fossils coal bulk terrestrial organic matter provide a proxy record for temporal changes in the global carbon cycle 13ctom 13ccarb and 13cco2 allow a full evaluation of carbon transfer in the atmosphere ocean system as well as between the marine and the terrestrial realm the temporal evolution of 13ctom parallels respective data sets from marine carbonate carbon thus reflecting the linkage between both reservoirs via atmospheric carbon dioxide on the basis of a comparison between measured and predicted isotope records for 13ctom changes in the carbon isotopic fractionation associated with plant metabolism are discernible this contradicts the notion of an invariable carbon isotopic fractionation associated with c3 plant metabolism in light of results from current plant growth experiments these changes are viewed as dependent on the atmospheric o2 co2 hence 13ctom might serve as a proxy signal for atmospheric composition

metamorphism of an obducted island arc example of the kohistan sequence pakistan in the himalayan collided range in northern pakistan the extraordinary 40 km thick kohistan sequence of metamorphosed mafic ultramafic and calc alkaline layered plutonic and volcanic mainly andesitic to rhyodacitic rocks has been recently reinterpreted as the only complete vertical section of an intra oceanic island arc presently exposed anywhere in the world plate scale models have been suggested to explain the origin and the tectonic evolution of this arc in the himalayan collision range despite some noticeable differences in the models there is general agreement that the kohistan sequence represents the crust of an arc obducted onto the northern edge of the indian plate before the oligocene collision of india against asia new data on the tectonometamorphic evolution of the kohistan sequence have led to the conclusion that a first major d 1 event developed with increasing metamorphic grades oriented downward the kohistan pile but also toward ensandwiched basic ultrabasic granulitic rocks rare geochronological data and petrological evidence indicate that the latter granulites pyriclasites and various plagiopyrigarnites pyrigarnites metatroctolites metawebsterites metadunites etc were parts of enormous lower to middle cretaceous layered calc alkaline plutons emplaced during the arc building stages as the d 1 metamorphic event is correlated with the upper cretaceous obduction process of the kohistan onto india it is proposed that the d 1 thermal structure was strongly controlled by remnant magmatic heat source s within the obducted arc this interpretation fits nicely with recent theoretical thermal models since the obduction of the arc was probably shortly after 10 20 ma the emplacement of the former plutonic arc rocks a blueschist tectonic melange underlying the obducted arc was possibly synchronous to the obduction and not clearly linked to the older subductive process the oligocene collision of india against asia was associated with a barrovian overprinting metamorphism in the kohistan arc during this second event the dynamo thermal structure was much more classical and not controlled by the occurrence of the cretaceous metaplutonic rocks a tentative model of the thermal structures during the major events which affected the kohistan arc is proposed