oxygen and hydrogen isotope ratios in tree rings how well do models predict observed values we have measured annual oxygen and hydrogen isotope ratios in the cellulose of the latewood of oak quercus robur l growing on well drained ground in norfolk uk we compare the observed values of isotope ratios with those calculated using equations that allow for isotopic fractionation during the transfer of oxygen and hydrogen from source water taken by the tree to cellulose laid down in the cambium the equations constitute a model in which isotopic fractionation occurs during evaporative enrichment within the leaf and during isotopic change between carbohydrates and water in the trunk during cellulose synthesis from the relationship between isotope ratios in precipitation and cellulose we deduce that the source water used by the tree comprises a constant mixture of groundwater and precipitation chiefly from the months of may june and july of the growth year by selection of isotopic fractionation factors and the degree of isotope exchange within the trunk we are able to model the observed annual values of oxygen isotope ratios of cellulose to a significant level r 0 77 p 0 01 when we apply the same model to hydrogen isotope ratios however we find that although we can predict the average value over the time series we can no longer predict the year to year variation we suggest that this loss of environmental signal in the hydrogen isotopes is caused by differences in the kinetic isotope effects of the biochemical reactions involved in the fixation of hydrogen in different positions of the glucose molecule owing to these effects the hydrogen isotope ratios of cellulose can vary in a way not anticipated in current models and hence may induce non climatic noise in the hydrogen isotope time series

oligocene slow and miocene quaternary rapid deformation and uplift of the yumu shan and north qilian shan evidence from high resolution magnetostratigraphy and tectonosedimentology

model evaluation for reconstructing the oxygen isotopic composition in precipitation from tree ring cellulose over the last century the oxygen isotope composition of tree rings is controlled by many factors including temperature amount of precipitation and changes in relative humidity in this study we present a modified leaf water model from dongmann et al radiation and environmental biophysics 11 1974 41 that can be used to calculate the isotopic composition of the source water and thus of precipitation that a tree used during the growing season the calibration of the model was accomplished by comparing a previously measured oxygen isotope tree ring chronology from central switzerland with the swiss network for isotopes in the hydrologic cycle station at bern from 1971 to 1995 and integrating temperature relative humidity data and ring width in particular our efforts focused on understanding the significance of the dampening factor f which we relate to changes in humidity and its variability over both the calibration period 1971 to 1995 and the study period 1913 to 1995 our results indicate that f ranging between 0 27 to 0 49 is variable based on correlation with relative humidity average daily temperature and ring width index using this model we have constructed a record of the oxygen isotope composition of precipitation during the growing season may through september for the last century in central western europe this approach can be potentially used in other locations where isotopic and meteorological data are available to extend records of the isotopic composition of precipitation back in time beyond observational records

influence of changing atmospheric circulation on precipitation δ18o temperature relations in canada during the holocene postglacial precipitation 18o history has been reconstructed for two regions of canada long term shifts in the oxygen isotope composition of annual precipitation 18op in southern ontario appear to have occurred with a consistent isotope temperature relation throughout the past 11 50014c yr the modern isotope temperature relation in central canada near present boreal treeline evidently became established between 5000 and 4000 years ago although the relation during the last glacial maximum and deglaciation may also have been similar to present in the early holocene however unusually high 18opapparently persisted in spite of low temperature locally probably associated with high zonal index a rudimentary sensitivity analysis suggests that a small reduction in distillation of moisture in pacific air masses traversing the western cordillera perhaps accompanied by a higher summer winter precipitation ratio could have been responsible for the observed effect equivalent isotope temperature anomalies apparently occurred elsewhere in western north america in response to changing early holocene atmospheric circulation patterns suggesting that a time slice map of 18opfor north america during this period might provide a useful target for testing and validation of atmospheric general circulation model simulations using isotopic water tracers

neotectonics of the thakkhola graben and implications for recent activity on the south tibetan fault system in the central nepal himalaya the thakkhola graben is one of many north trending rifts that define the neogene structural pattern of the southern tibetan plateau lying at the southern margin of the plateau and extending to the crest of the himalaya the graben provides an opportunity to evaluate the kinematic relationships between east west extensional strain in southern tibet and north south extensional strain in the himalaya neotectonic and structural mapping of the dangardzong fault along the western margin of the graben reveals a southward decreasing component of normal slip coupled with a southward increasing component of right lateral slip that affects pleistocene basin fill sediments we present 14c ages for river terraces in the thakkhola graben that provide a ca 17 2 ka minimum age on the latest stage of dangardzong fault movement near the southern termination of the graben the dangardzong fault apparently offsets the annapurna detachment an early miocene strand of the east striking south tibetan fault system however the dangardzong fault itself terminates against a young i e younger than ca 17 2 ka strand of the south tibetan fault system the dhumpu detachment structural relationships among the dangardzong annapurna and dhumpu faults suggest that the dangardzong structure is a tear fault in the south tibetan allochthon that accommodates differential amounts and rates of displacement along the south tibetan fault system thus although the south tibetan fault system first developed as part of the structural architecture of the himalaya in miocene time at least some strands have been active as recently as the pleistocene in a regional context the south tibetan fault system serves to accommodate the strain gradient between extension in tibet and shortening in the himalaya

metallogenesis in tibetan collisional orogenic belt i mineralization in main collisional orogenic setting metallogenesis of continents is an important research frontier in the present regional metallogeny and its theoretic framework might be built up by deepening the understanding of metallogenesis in the collisional orogenic belt however metallogenesis in the collisional orogenic belt is rather poorly understood in comparison with metallogenesis in the plate tectonic setting the himalayan tibetan orogenic belt which is characterized by the existence of large scale intense and young mineralizations as well as various kinds of large size and weakly reformed deposits is regarded as an ideal field for understanding the ore forming processes in the collisional orogenic belt based on three years systematical work on metallogeny in the tibetan collisional orogenic belt the authors have summarized the main ore forming events and their temporal spatial distribution analyzed four important metallogenic belts and representative deposits as well as their plutonic processes and tectonic control factors and on such a basis set up a metallogenic model in the main collisional orogenic setting the main collisional event lasted about 25 ma from 65 ma to 41 ma resulting in the formation of the principal part of the tibetan plateau orogenic belt characterized by the south tibet foreland thrust belt the gangdese main collisional tectonic magmatic belt and the north tibet fold thrust belt in company with the collisional orogenic event many important magmatic events were developed as evidenced by the existence of the crust derived muscovite granite potassic calc alkaline granite assemblage 66 50 ma the positive e nd granite gabbro assemblage 52 47 ma and the mantle derived basaltic subvolcanics diabase assemblage as well as widespread and thick linzizong volcanics 64 43 ma the development of above magmatic activities suggests that the deep part of tibetan plateau experienced in turn continental collision 65 52 ma breakoff of continental plate 52 42 ma and low angle underthrust of continental plate 40 ma at least four important ore forming events occurred during the main collisional orogenic epoch which included the sn and rare metal event related to crust derived granite forming the tengchong sn and rare metal ore concentration area in east tibetan plateau the copper gold molybdenum event related to crust mantle derived granite forming a cu au ore belt 100 km long in south gangdese the shear zone gold event related to collisional orogeny forming the potential au belt along the yarlung zangbo suture zone and the copper gold event related to crust uplift forming porphyry epithermal transitional type cu au deposits represented by the xiongcun cu au deposit

velocity density systematics mean atomic weight and the interior of the moon abstract mean atomic weight profiles for the lunar mantle have been calculated from velocity density systematic relations using lunar density and seismic velocity models despite large variability among the models the calculation including poisson s ratio yields a range of mean atomic weight values between 22 and 23 g mol 1 below 150 km a similar calculation for the earth s mantle produces a mean atomic weight of 21 1 0 4 g mol 1 this suggests that the moon cannot be derived directly from the earth s mantle or that it has had a differentiation history different from the earth s the lunar m s require an fe mole fraction between 0 25 and 0 33 for a pure olivine mantle or between 0 33 and 0 45 for pure pyroxene the present profiles are 0 5 3 0 g mol 1 higher than those calculated from lunar compositional models based on lunar rock compositions and petrology and assumed lunar histories indicating inadequacies in either the seismic or compositional models or in both the mean atomic weight approach provides a method of comparing the consistency of seismic and compositional models of planetary interiors

oxygen and hydrogen isotopes in the hydrologic cycle changes of the isotopic composition of water within the water cycle provide a recognizable signature relating such water to the different phases of the cycle the isotope fractionations that accompany the evaporation from the ocean and other surface waters and the reverse process of rain formation account for the most notable changes as a result meteoric waters are depleted in the heavy isotopic species of h and o relative to ocean waters whereas waters in evaporative systems such as lakes plants and soilwaters are relatively enriched during the passage through the aquifers the isotope composition of water is essentially a conservative property at ambient temperatures but at elevated temperatures interaction with the rock matrix may perturb the isotope composition these changes of the isotope composition in atmospheric waters surface water soil and groundwaters as well as in the biosphere are applied in the characterization of hydrological system as well as indicators of paleo climatological conditions in proxy materials in climatic archives such as ice lake sediments or organic materials

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

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

mode of cenozoic east west extension in tibet suggesting a common origin of rifts in asia during the indo asian collision cenozoic rifts in tibet were traditionally interpreted as a result of topographic collapse of the tibetan plateau reaching the maximum elevation that can be supported by its mechanical strength recent studies have emphasized possible similarities between rifting in tibet and extension in the basin and range of the western united states however when examined in detail one finds that spacing of long 100 km rifts in tibet 100 300 km is significantly greater than that in the basin and range 20 40 km from south to north rift spacing decreases systematically from 191 67 km in the himalaya south of the indus yalu suture to 146 34 km in south tibet between the indus yalu and bangong nujiang sutures and farther north to 101 31 km in central tibet between the bangong nujiang and jinsha sutures instability analysis suggests that the mantle lithosphere must have been involved in east west tibetan extension specifically the widely spaced rifts in the himalaya and tibet may have been related to the presence of a relatively light crust density 2 90 g cm 3 and a strong mantle lithosphere 40 km thick and a factor of 5 stronger than the upper crust the observed systematic decrease in rift spacing can be explained by the known decrease in the crustal thickness in tibet from 70 80 km in the himalaya in the south to 50 55 km in central tibet in the north a regional comparison of rifts in east asia suggests that both the involvement of the mantle lithosphere and the age of rift initiation are similar for tibetan rifts the baikal rift and the shanxi graben this implies that topographic collapse or a convective event in the mantle cannot be the sole cause for the development of the tibetan rifts a regional boundary condition applied throughout east asia must be required

multiproxy record of late pleistocene holocene climate and vegetation changes from a peat bog in patagonia abstract pollen assemblage changes and stable hydrogen isotope analysis of mosses sphagnum magellanicum and drepanocladus s l from a bog in tierra del fuego argentina provided independent proxies for reconstructing changes in effective moisture and temperature over the past 16 000 cal yr b p a deterministic model was used to reconstruct the stable hydrogen isotope composition of meteoric water from the d h ratios of bog mosses over the last 16 000 years abrupt changes in temperature as recorded in d h ratios of moss cellulose were accompanied by synchronous changes in vegetation composition during the late pleistocene and early and middle holocene when moisture levels were lower than today in contrast temperature variability during the late holocene was not accompanied by comparable vegetation changes in particular grass pollen poaceae increased during periodic cold spells between 15 000 and 11 000 cal yr b p but a cold spell of similar magnitude ca 2000 cal yr b p did not appear to affect vegetation during the late pleistocene the isotopic record from the peat core shows variations similar to the d h ratios in the antarctic taylor dome ice core however the timing of the changes in the harberton record is more in line with the timing of other southern hemisphere records

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

fault plane solutions of earthquakes and active tectonics of the tibetan plateau and its margins summary fault plane solutions of earthquakes within and on the margins of the tibetan plateau show diverse styles of faulting and deformation with thrust faulting and crustal shortening normal to the margins of the plateau and with normal and strike slip faulting resulting in roughly east west crustal extension within the plateau the direction of overthrusting of the himalaya onto the indian shield is radially outward varying from southwest in the western himalaya to south southeast in the east assuming that the indian shield behaves rigidly this requires a west northwest divergence of western tibet from southeastern tibet at a rate of 18 9 mm yr 1 comparable with the rate of convergence at the himalaya fault plane solutions of earthquakes in the southern portion of the tibet plateau consistently show large components of normal faulting on roughly north striking planes and corroborate such extension within the high plateau where elevations exceed 5000 m normal and strike slip faulting occur so that an overall east southeast west northwest extension of the region at about 10 mm yr 1 is partitioned into roughly equal parts of crustal thinning and north northeast south southwest crustal shortening about 5 mm yr 1 in general strike slip faulting characterizes solutions for earthquakes within eastern tibet where mean elevations drop below 4500 5000 m but the orientations of the strike slip faults vary across the region in central tibet left lateral slip occurs on planes trending roughly northeast but for earthquakes farther east the orientations of that plane become progressively east west and then southeast this variation in orientation implies a rotation of material along curved left lateral shear zones thus the eastward extrusion of tibet appears to be facilitated not only by rapid left lateral shear but also by large clockwise rotations of the material in eastern tibet the rate of eastward extrusion of material in eastern tibet relative to the tarim basin to its north is roughly 30 40 mm yr 1 fault plane solutions of earthquakes in the northern and eastern margins of tibet show large components of thrust faulting with the p axes oriented radially outward from the plateau and approximately perpendicular to the regional topographic contours of the plateau the orientation of this crustal shortening is northeast southwest on the northeastern margin east west on the eastern margin and northwest southeast in the longmenshan on the southeastern margin thus at least some of the extrusion of eastern tibet out of india s northward path into asia is absorbed by crustal shortening on the margins of the plateau the variation from normal faulting in the high tibetan plateau where elevations exceed 5000 m to dominantly strike slip faulting farther east where elevations are lower and then to thrust faulting on the margins of the plateau where elevations drop below 3000 m surely results at least in part from a decrease in the value of the vertical stress the magnitude of the east west compressive stress need not vary across the plateau

deciphering relationships between the nicobar and bengal submarine fans indian ocean abstract the nicobar fan and bengal fans can be considered as the eastern and western parts respectively of the largest submarine fan system in the world this study presents the integrated results of petrographic and provenance studies from the nicobar fan and evaluates these in the context of controls on sedimentation both fans were predominantly supplied by himalaya derived material from the main tectono stratigraphic sequences as well as the gangdese arc a lack of volcanic material in the nicobar fan rules out sources from the sumatra magmatic arc overall the petrographic data shows a progressive decrease in sedimentary detritus and corresponding increase of higher grade metamorphic detritus up section changes in sediment provenance and exhumation rates in the himalaya are seen to track changes in sediment accumulation rates high sediment accumulation rates in the bengal fan occurred at 13 5 8 3 ma and in the nicobar fan from 9 5 5 ma both fans show peak accumulation rates at 9 5 8 3 ma but with the nicobar fan being about twice as high and both record a sharp drop from 5 5 5 2 ma that coincided with a change in river drainage associated with the brahmaputra river diverting west of the uplifting shillong plateau at 5 ma the nicobar fan was supplied by an eastern drainage route that finally closed at 2 ma when sediment accumulation rates in the nicobar fan significantly decreased sediment provenance record these changes in routing whereby bengal fan deposits include granitoid sources from the namche barwa massif in the eastern syntaxis that are not seen in the nicobar fan likely due to a more localised eastern drainage that included material from the indo burman wedge prior to 3 ma source exhumation rates were rapid and constant and the short lag time rules out significant intermediate storage and mixing in terms of climate versus tectonic controls tectonically driven changes in the river network have had most influence on fan sedimentation

late cenozoic tectonic activity of the altyn tagh range constraints from sedimentary records from the western qaidam basin ne tibetan plateau the altyn tagh range atr is the northern geological boundary of the tibetan plateau and plays a key role in accommodating its cenozoic lithospheric deformation however knowledge of the structural style and age of uplift of the atr is limited and controversial the qaidam basin in the southeast side of the atr provides an outstanding field laboratory for understanding the history and mechanisms of atr growth this study presents a detailed sedimentological analysis of a 1040 m thick late cenozoic similar to 17 5 0 ma sedimentary sequence from the western qaidam basin together with the analysis of sedimentological data from nearby boreholes and sections our aims were to determine the spatiotemporal evolution of the sedimentary sequences in the study area and to explore their response to late cenozoic tectonic activity in the atr the results show three major intervals of the sedimentary characteristics in the study area similar to 17 16 ma 10 ma and 17 16 ma similar to 16 10 ma and similar to 10 ma during which the atr respectively experienced tectonic uplift fast strike slip motion and intense uplift

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

cenozoic tectonic evolution of the elashan range and its surroundings northern tibetan plateau as constrained by paleomagnetism and apatite fission track analyses abstract magnetostratigraphic studies of sediments in the western gonghe and eastern qaidam basins together with apatite fission track aft analyses in the elashan range suggest that the elashan range and its surroundings experienced a two stage evolution a protracted uplift from the cretaceous to the early tertiary which explains the absence of the paleogene strata in the region and an accelerated growth of the elashan range since the latest oligocene caused by extensively distributed thrust faults in the region this later phase of uplift resulted in the subsequent thick sediments within the both easternmost qaidam and gonghe basins basal ages of 21 22 ma in the wulan section of 20 ma in the southern gonghe section and of l2 ma in the chaka section the two phases of thrust motion and range growth mean that the qaidam and gonghe basins were never united during cenozoic times the strike slip is likely to have occurred at l0 ma as shown by the paleomagnetic declination data which show a rapid transition in rotation sense from counterclockwise to clockwise at that time this time is also similar to the 9 ma age of initiation of the wenquan fault determined by backward calculation based on its late quaternary slip rate eventually the qinghai nan shan thrust belt began to develop at 6 ma

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

miocene sn polymetallic mineralization in the tethyan himalaya southeastern tibet a case study of the cuonadong deposit abstract the cuonadong deposit is located in the cuonadong gneiss dome of the eastern tethyan himalaya and is characterized as a large to superlarge scale sn polymetallic deposit in the himalaya orogen the mineralization pattern includes skarn w sn mineralization in the strong shear zone of the dome mantle hydrothermal sn w veins controlled by north south trending rifts nstrs and be rb mineralization in pegmatitic leucogranite the results of this study show that the zircon u pb age of undeformed postkinematic leucogranites is 15 5 0 1 ma n 28 mswd 1 4 the cassiterite u pb age of the vein type sn w orebody is 14 3 0 5 ma n 40 mswd 3 2 and the muscovite ar ar age of beryl bearing pegmatitic leucogranite is 15 2 0 2 ma mswd 1 5 the isotopic dating results demonstrate that the cuonadong sn w be rb mineralization has a close genetic relationship with the miocene ca 16 14 ma leucogranite magmatic hydrothermal activity in the cuonadong dome the deformed synkinematic two mica granite 18 ma was cut by the sn w ore veins 14 ma faulted by nstrs indicating that the e w trending extension of the nstrs initiated at ca 18 14 ma the himalaya leucogranite belongs to a highly fractionated granite with high sn content 15 ppm in conclusion the himalaya leucogranite is considered to be tin granite in this study and therefore the himalaya presents high potential for sn polymetallic mineralization prospecting

a deglacial and holocene record of climate variability in south central alaska from stable oxygen isotopes and plant macrofossils in peat we used stable oxygen isotopes derived from bulk peat d 18 otom in conjunction with plant macrofossils and previously published carbon accumulation records in a w14 500 cal yr bp peat core ht fen from the kenai lowlands in south central alaska to reconstruct the climate history of the area we find that patterns are broadly consistent with those from lacustrine records across the region and agree with the interpretation that major shifts in d 18 otom values indicate changes in strength and position of the aleutian low al a semi permanent low pressure cell that delivers winter moisture to the region we find decreased strength or a more westerly position of the al relatively higher d 18 otom values during the bolling allerod holocene thermal maximum htm and late holocene which also correspond to warmer climate regimes these intervals coincide with greater peat preservation and enhanced carbon c accumulation rates at the ht fen and with peatland expansion across alaska the htm in particular may have experienced greater summer precipitation as a result of an enhanced pacific subtropical high a pattern consistent with modern d 18 o values for summer precipitation the combined warm summer temperatures and greater summer precipitation helped promote the observed rapid peat accumulation a strengthened al relatively lower d 18 otom values is most evident during the younger dryas neoglaciation and the little ice age consistent with lower peat preservation and c accumulation at the ht fen suggesting less precipitation reaches the leeward side of the kenai mountains during periods of enhanced al strength the peatlands on the kenai peninsula thrive when the al is weak and the contribution of summer precipitation is higher highlighting the importance of precipitation seasonality in promoting peat accumulation this study demonstrates that d 18 otom values in peat can be applied

field evidence for active normal faulting in tibet crustal thickening does not now occur in southern tibet field observations made during the chinese french expedition of 1980 support an earlier hypothesis based on a combined analysis of satellite images and fault plane solutions of earthquakes immediately north of the highest peaks of the himalayas the tectonic regime is dominated by east west extension we have mapped a large number of north south normal faults which sharply cut the glacial and post glacial morphology and followed several recent earthquake breaks along faults detected on satellite and aerial photographs microtectonic measurements in the quaternary suggest that the maximum principal stress is vertical

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

mesozoic and cenozoic volcanic rocks from central and southern tibet 39ar 40ar dating petrological characteristics and geodynamical significance field relations radiometric ages and mineralogical and chemical characteristics of the orogenic volcanic rocks from the lhasa block tibet are studied volcanic activity started before the deposition of the albian aptian sedimentary units takena formation and xigaze group volcanism is volumetrically limited in the northern part of the lhasa block basalts andesites and dacites are present while ignimbrites are scarce radiometric ages of these rocks range between 110 and 80 ma conversely in the southern part of the lhasa block volcanism is largely developed gangdese belt there paroxysmal activity occurred later than in the north between 60 and 50 ma lingzizong formation this volcanism is mainly represented by andesites and ignimbrites a younger episode at about 15 10 ma took place in this southern region the mineralogical and geochemical characteristics indicate that as a whole the volcanic rocks from the lhasa block belong to a calc alkaline continental margin series enriched in k20 and other incompatible elements subordinate potassic alkaline lavas are present in the northern margin of the gangdese belt some basalts exhibit a tholeiitic affinity daquin area southern region the geodynamic significance of these cenozoic volcanic rocks lies in the relative motion of india and the lhasa block after accretion of the latter to the northern qantang block a geodynamic model based on changes of the type of subduction of the indian oceanic crust beneath the lhasa block for the period 120 40 ma is proposed to account for the abundance age and magmatic affinity of the volcanic products

new paleomagnetic constraints on syntectonic growth strata in the western qaidam basin ne tibetan plateau abstract accompanied by crustal shortening and mountain uplift caused by the large magnitude south north directed shortening under the collision between india and eurasia syntectonic growth strata in the western qaidam basin document important information about intense intracontinental deformation of the ne tibetan plateau to better address the development of the qaidam basin and the propagation of the growth strata associated with multiple tectonic uplifts of the tibetan plateau we conducted a detailed paleomagnetic study on the late neogene fluvio lacustrine sedimentary sequence exposed at two outcrop sections and a drill core in the western qaidam basin and integrated the results with previous magnetostratigraphic studies based on well determined ages of the centers and limbs of the two anticlines we found an episodic late cenozoic crustal shortening in the center of the western qaidam basin as evidenced by syntectonic offlap growth strata deposited beginning at 3 2 ma combined with data from sedimentary facies and seismic profiles we suggest that offlap growth strata progressively became younger from southwest to northeast in the center of the western qaidam basin due to strong basinward propagation of the eastern kunlun fault and quick short lived pulses of multiple tectonic uplifts of the ne tibetan plateau

u th pb systematics and ages of himalayan leucogranites south tibet abstract the age and origin of five leucogranites from the high and tethys himalaya and two country rock gneisses were investigated by u pb dating of zircon fractions and single grains and fractions of monazite additionally th u concentrations in whole rock powders and isotopic compositions of pb in leached k feldspars were determined monazites yield ages of 16 8 0 6 m y for the nialam migmatite granite 15 1 0 5 m y for the lhagoi kangri granite 14 3 0 6 m y for a granite from mt everest and 9 8 0 7 m y and 9 2 0 9 m y for two varieties of the maja granite these data together with monazite ages of 21 9 0 2 and 24 0 0 4 m y determined earlier on the makalu granite 1 substantiate a period of intracontinental granite emplacements from 24 to 9 m y ago i e from uppermost oligocene to late miocene times such a period of plutonic activity is consistent with the view that all these granites result from intracrustal melting following the collision of india with eurasia furthermore the individual ages together with structural relationships between granites and country rocks suggest that granite formation and tectono metamorphism occurred as alternating and strongly related processes with a periodicity of 7 to 9 m y inherited lead components present in all granite zircons point to large proportions of precambrian material in the magma source regions up to 2200 m y old th u systematics between monazite and country rocks indicate that u has been leached from most of the granites after crystallisation of monazite zircon dating of the kangmar granite gneiss which occurs in a window through the tethys himalayan sediments shows that this pluton transformed to a gneiss during the alpine orogeny crystallised in lowermost palaeozoic times 562 4 m y ago

fission track evidence for quaternary uplift of the nanga parbat region pakistan the north striking nanga parbat haramosh massif protrudes into the northwestern himalaya along the axis of a great syntaxis1 2 fig 1 where the hindu kush karakorum and himalayan ranges converge as the indus suture zone3 enters this region from the east it bifurcates into two branches encircling what may be a docked island arc terrane4 the southern branch the main mantle thrust crops out on both flanks of the nanga parbat massif forming a tight structural loop5 this massif and the adjacent terrane contain some of the highest peaks in the himalaya nanga parbat and the indus river located just 20km away define the world s greatest continental relief 6 930 m we report here the discovery of unexpectedly young sphene zircon and apatite fission track dates from the nanga parbat haramosh massif these dates as low as 1 3 myr for zircon and 0 4 myr for apatite imply that during the pleistocene the nanga parbat region was uplifted and eroded at nearly 1 cm yr 1

metallogenesis in tibetan collisional orogenic belt iii mineralization in post collisional extension setting as a significant and late stage process in the collisional orogeny characterized by a variety of geological features indicating tectonic evolution and large scale high intense mineralization post collision has aroused much interest among geologists however numerous geological issues such as post collisional structural features and tectonic evolution magmatic sequences and tectonic magmatic associations and metallogensis and mineralization systems in the post collisional settings have not yet been fully understood this paper studied and summarized the major features of post collisional orogeny and related metallogensis and proposed a tectonic model for metallogensis in the post collisional setting in tibet the available data indicate that there have been at least two stages of tectonic evolution since miocene in the tibetan plateau which is now tectonically in a post collisional stage the low crustal flow and upper crustal shortening took place in an early post collisional stage 18 ma which led to the southward extrusion of the low crustal materials producing the ew tending south tibet an detachment system d and the high himalayan block to the south and the ew striking thrust faulting systems and the thrust nappe structures along the gangdese range in the lhasa terrane respectively the crust extension and rifting occurring in the late post collisional stage 18 ma formed a series of ns striking normal faults and associated rifting basins 13 5 ma across the tibetan plateau the post collsional magmatism in tibet is characterized by the mid miocene ultra potassic and potassic volcanic rocks adakitic intrusives and calc alkaline granites developed along the gangdese batholiths and the south tibetan lecuogranites related to d mineralization during the post collisional periods produced a variety of significant mid miocene deposits including the porphyry cu deposits and the associated skarn ag pb zn deposits along the gangdese batholiths the epithermal sb au deposits in southern tibet the hydrothermal vein type and skarn type ag pb zn deposits to the north of the gangdese porphyry cu belt and modern cs au deposits related to hot spring activity in tibetan plateau the porphyry cu deposits occurring in the post collisional setting are associated with felsic stocks that show geochemical affinity with adakites which are regarded as products of partial melting of newly formed underplated basaltic lower crustal source beneath the tibet the sb au vein deposits tectonically located in the ds and controlled by the metamorphic nuclear complexes thermal domes and ns striking normal faults are related to the epithermal systems driven by the mid miocene leucogranitic bodies the vein type ag pb zn deposits occur within a thrusting nappe structural zone in the lhasa terrane and are related to the fluid flows discharged and moved along a northward gently dipping detachment fault zone related to upper crust shortening in general three kinds of structural systems in the upper crust level i e the ns striking normal faulting system and associated rifting basins the ew tending thrusting faults and associated nappe structures and the ew tending ds constrained the metallogensis during the post collisional periods nevertheless the flow and extrusion of the mid lower crust and the breaking off of the subducted indian continental slab are considered to be the principal deep dynamic processes leading to the formation of these distinct deposits in the post collisional setting in tibet

quaternary extension in southern tibet field observations and tectonic implications we summarize evidence for quaternary and active faulting collected in the field during three sino french expeditions to southeastern tibet 1980 1982 detailed mapping of quaternary and active faults as well as microtectonic measurements indicate that normal faulting has been the dominant tectonic regime north of the himalayas in the last 2 0 5 m y the maximum horizontal principal stress in south tibet appears to be only the intermediate principal stress 2 1 being vertical south of the chord joining the eastern and western syntaxes of the himalayan arc extensional strains are principally localized within seven regularly spaced rift zones three of which have been studied in some detail the extension direction is determined to be n96 e 7 mainly from statistical averaging of strikes of newly formed normal faults throw rates on normal faults are evaluated for different time spans 2 0 5 m y 60 40 kyr and 10 2 kyr b p using structural and topographic reliefs as well as synglacial and postglacial vertical offsets the rate of quaternary extension is about 1 m y 1 along an 1100 km long ese traverse across south tibet this corresponds to a spreading rate of 1 0 6 cm yr this rate and the divergent horizontal projections of slip vectors of earthquakes along the himalayan front constrain the rate at which rigid india underthrusts southern tibet to be 2 1 cm yr although most of the normal faults appear to be independent of and nearly orthogonal to the e w mesozoic tertiary tectonic fabric the yadong gulu rift appears to be guided for over 130 km by the older oblique ne sw nyainqentanglha range and fault zones along it this reactivated zone is the most prominent left lateral strike slip fault system in se tibet excepting this zone and the vicinity of the se extremity of the karakorum fault quaternary strike slip faulting is rare in south tibet i e south of the chord between the syntaxes of the himalayan arc north of the chord the tectonic style is different there minor conjugate strike slip faulting is widespread and appears to control quaternary normal faulting which is more diffuse and subdued than in south tibet along the chord the presence of a major zone of active right lateral en echelon strike slip faults karakorum jiali fault zone probably reflects the greater facility of eastward extrusion in north central tibet in response to the northward push of india the eastern himalayan syntaxis may be an obstacle to such extrusion movements south of the chord

paleohydrology of lake victoria east africa inferred from 18o 16o ratios in sediment cellulose delta 18 o values of aquatic cellulose preserved in a 7 6 m sediment core from near the center of lake victoria east africa record a 13 000 yr hydrological history of the basin relative to the present value 3 4 highly elevated lake water 18 o values of 8 2 from 13 200 to 7250 14 c yr b p indicate closed basin conditions and precipitation evaporation ratios much smaller than at present an abrupt drop in the lake water 18 o to 0 1 marks the rapid transition to an open basin between 7250 and 7150 14 c yr b p from 7140 to 5400 14 c yr b p increasing lake water 18 o values from 0 1 to 5 1 5 are proposed to reflect outlet downcutting and a likely decrease in relative humidity these data have unexpectedly shifted our view of the timing of changes in the lake victoria water balance and imply a period of at least 10 000 years 17 000 to 7000 14 c yr b p when the lake victoria basin did not contribute waters to the main nile river

estimates of arctic land surface temperatures during the early pliocene from two novel proxies during the pliocene 2 6 to 5 ma ago atmospheric co 2 levels have been estimated as similar to or slightly above present levels tripati et al 2009 pagani et al 2010 and yet earth s climate was considerably different recent evidence suggests that although global temperatures were 2 3 c warmer than pre industrial arctic warming may have been amplified during the pliocene thus precise temperature records of this interval are required to assess the sensitivity of earth s climate to persistent levels of co 2 between 365 and 415 ppm we present records of two independent proxies for terrestrial growing season temperatures at the early pliocene beaver pond site on ellesmere island 18 o values of cellulose from well preserved peat constrain the 18 o values of meteoric water to 20 7 0 3 which we combined with 18 ovalues of aragonitic freshwater molluscs found within the peat in order to calculate mollusc growth temperatures this approach results in an average growing season temperature of 14 2 1 3 c temperatures were independently derived by applying carbonate clumped isotope thermometry to mollusc shells from the same site indicating an average growing season temperature of 10 2 1 4 c a one way anova indicates that the differences between the two techniques are not significant as the difference in mean temperatures between both methods is no different than the difference between individual shells using a single technique both techniques indicate temperatures 11 16 c warmer than present may sept temperature 1 6 1 3 c and represent the first thermodynamic proxy results for early pliocene ellesmere island

middle to late miocene extremely rapid exhumation and thermal reequilibration in the kung co rift southern tibet 1 the kung co rift is an approximately nnw striking wsw dipping normal fault exposed in southern tibet and is part of an extensive network of active approximately ns striking normal faults exposed across the tibetan plateau detailed new and published u th he zircon and apatite thermochronometric data from the footwall of the early miocene kung co granite provide constraints on the middle miocene to present day exhumation history of the footwall to the kung co fault inverse modeling of thermochronometric data yield age patterns that are interpreted as indicating 1 initiation of normal fault slip at 12 13 ma and rapid exhumation of the footwall between 13 and 10 ma 2 acceleration of normal fault slip at rates of 21 9 6 9 mm yr at 10 ma 3 rapid thermal reequilibration between 10 and 9 ma and 4 slow exhumation and or quiescence from 9 ma to the present day hanging glacial valleys in the footwall and fault scarps that cut late quaternary till and moraine deposits indicate that fault slip continues today middle to late miocene initiation of extension across the kung co rift is broadly the same as the documented initiation of ew extension across the south central tibetan plateau eastward flow of middle or lower crust from beneath tibet accommodated by northward underthrusting of indian crust beneath tibet provides a plausible explanation for the onset of ew extension across the tibetan plateau

erosion and tectonics at the margins of continental plateaus the topography across the eastern margin of the central andean plateau north of 18 s beni region bears a strong resemblance to the topography of the southern margin of the tibetan plateau nepal himalaya with both regions featuring a steep frontal slope and high peaks at the plateau edge in contrast the topography of the eastern margin of the central andean plateau south of 18 s pilcomayo region tapers toward the foreland more gently and has no line of high peaks at the margin both the himalayan and the beni regions have been the sites for large amounts of denudation and in both regions geologic evidence suggests that erosion has been sufficiently vigorous for the physiographic plateau margin to have retreated toward the plateau interior during the neogene we hypothesize that the steep frontal slope and high peaks of the beni region and himalayan front largely reflect the high orographic precipitation and high erosion rates occurring in these regions and that the more gentle topography of the semiarid pilcomayo region reflects a tectonic landform only slightly modified by erosion we propose that orographic precipitation impinging on a plateau margin will generally tend to drop moisture low on the slope eroding back the plateau while enhancing or maintaining the steep long wavelength slope a numerical model coupling orographic precipitation erosion and tectonic uplift demonstrates the plausibility of this hypothesis the erosional efflux in both the beni and nepal himalaya have been considerable and simple mass balance calculations for the himalaya suggest that during the neogene the erosional mass efflux has generally outpaced the tectonic mass influx this contrasts with the apparent prior domination of tectonic influx and may reflect a decrease in the rate of tectonic addition during the same period and or increased late cenozoic erosion rates

new paleomagnetic constraints on rift basin evolution in the northern himalaya mountains abstract the late cenozoic sediments in the rift basins in the northern himalaya mountains document important information about the uplift and deformation of the most active tectonic region in the tibetan plateau however these sediments have not been precisely dated hindering our ability to address the basin development and termination associated with a series of uplifts in the southern tibetan plateau here we report a detailed magnetostratigraphic study on the fluvio lacustrine sedimentary sequence of the dati formation bearing abundant hipparion forstenae fossils in the dati basin in the northern frontal region of the himalaya mountains the 195 m thick section yielded six normal and seven reversed polarity zones that correlate well with chrons c3an 1r to c4r 2r of the geomagnetic polarity time scale constraining the section age to 8 6 6 2 ma together with the magnetostratigraphic results from other rift basins in the region these results indicate that the horizons bearing the hipparion fossils were deposited during the age interval of 7 1 6 5 ma in the northern himalaya mountains the regional tectonic activity and comprehensive magnetostratigraphic and sedimentologic comparisons suggest that the evolution of the rift basins in the northern himalaya mountains has involved three major stages since the late cenozoic i e 1 10 0 8 0 ma onset of the basins with fan delta facies 2 8 0 3 0 ma expansion of the basins with mainly lacustrine facies 3 3 0 1 7 ma shrinking and termination of the basins with alluvial fans the basin evolutionary history indicates an accelerated tectonic uplift of the himalaya mountains at 10 0 ma and two deformational events at 3 0 ma and at 1 7 ma

oxygen isotopes in cellulose from modern and quaternary intertropical peatbogs implications for palaeohydrology abstract cellulose 18o values were measured in modern peatbog plants in recent peats and in mountain peatbog cores from burundi in a study of the hydrologic control of the frsol 18o 16o ratio in intertropical peat cellulose modern plants and waters were collected under various altitudes 800 2500 m a s l with mean annual relative humidity ranging from 0 72 to 0 82 the water 18o values i vary between 4 and 2 5 the cellulose water enrichment is of 25 3 0 5 for aquatic plants of 24 6 emergent plant species the scatter in the cellulose 18o values in vary between 4 and 2 5 the cellulose water enrichment is cellulose 18o values of emergent plantss tend to decrease with increasing elevation 0 6 to 0 07 per 100 m and relative humidity 0 5 to 0 1 per mean emergent plant 18o values are approximated within 0 6 by available cellulose 18o models relating cellulose 18o to the relative humidity h and the environmental water 18o except in a large swampy system peats were subsampled in core ka 2 kashiru burundi 3 28 s 29 34 e 890 cm long 2240 m a s l altitude and for control in the topmost 50 cm of core ku 2 kuruyangwe 3 35 s 29 41 e 2020 m a s l altitude similar 18o vaues 26 to 28 5 were found in the topmost 50 cm of both cores they compare well with the mean 18o for modern emergent plants at kashiru ams 14c dating showed that core ka 2 spans the last 30 ka celluloses are mainly derived from emergent plants and yield 18o values ranging from 19 to 29 with the highest values between 2 1 and 0 ka and the lowest values 19 to 23 5 between 6 and 4 5 ka for the period between 6 and 4 5 ka the models yield a decrease in in of 4 to 2 5 relative to present for an h increase of 6 to 11 before 11 7 ka the models yield a in value close to the present value for an h increase of 6

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

argon 39 argon 40 dating of metamorphic and plutonic events in the north and high himalaya belts southern tibet china new 39ar 40ar radiometric data are presented they concern the metasedimentary series and the orthogneiss pluton of kangmar ages as young as 13 ma are found which may be related either to the metamorphism or to the resetting of the minerals during the emplacement of the numerous intrusive bodies into the north himalaya belt inherited excess argon is found in micas from the orthogneiss previously dated at 562 ma these bodies are constituted by leucogranitic magmas the biotites and the muscovites of which the granites intrude lhagoi kangri massif same range of ages is found in the high himalaya belt for micas from leucogranites ages as young as 4 ma are found on micas from the southern part of the cross section between nyalam and zham the recent uplifts and or the movement of recent normal faults may be related to these young ages

paleoclimatic implications of the relationship between oxygen isotope ratios of moss cellulose and source water in wetlands of lake superior abstract groundwater dominated wetlands contain abundant peat deposits but few studies have addressed the potential of using the oxygen isotopic composition 18 o of fen peat cellulose to evaluate past changes in climate here we investigated the relationship between 18 o values of pond water and those of moss cellulose from species inhabiting different micro environments in three different swales near lake superior united states isotope results over two growing seasons indicate a negligible effect of evaporation on the studied fens and the strong control of groundwater on the isotopic composition of swale water isotopic values for groundwater show a small seasonal variability and their low values suggest the influence of snowmelt our results show a consistent offset of 27 1 between average swale water 18 o and cellulose 18 o values for hollow sphagnum species reflecting the fractionation associated with cellulose biosynthesis when sphagnum species from hummocks are included the offset shows a larger variability 27 3 pointing to evaporative effects affecting hummock species this evaporative effect is more pronounced in emerged mosses which show the largest difference 30 relative to their source water the smaller variability associated with hollow species points to the possibility of performing species specific analyses from peat cellulose for improved paleoclimatic reconstructions

metallogenesis in tibetan collisional orogenic belt ii mineralization in late collisional transformation setting the collisional processes established many paleo mountain belts are commonly divided by many geologists into two simple but distinct stages i e syn collisional and post collisional periods as the transition from late to post collisional is not clear and the definition of post and late collisions also is blurring however the tectonic evolution of the tibetan orogen underwent a complicate history which is divided into 1 syn collisional 65 41 ma 2 late collisional 40 26 ma and 3 post collisional 25 0 ma periods the orogeny during the late collisional period generally happened in a compressional regime resulted from successional convergence between indian and asian continents and is characterized by intra continental subduction underthrust crustal shortening large scale thrusting and strike slip faulting systems developed in the margins of the tibetan plateau which resulted in the development of potassic porphyry stocks and carbonatite alkalic complexes in the eastern tibet and potassic ultrapotassic volcanic rocks in the northern tibet at least four significant metallogenic events associated with the late collsional orogeny have been recognized in the eastern margin of the tibetan plateau a tectonic transformation belt they are 1 the porphyry cu mo au mineralization related to large scale strike slip faults system which controlled the localization of the yulong porphyry cu belt 40 36 ma in east tibet 2 the ree mineralization associated with carbonatite alkalic complexes formed the mianning dechang ree belt 40 27 ma in the western sichuan 3 the pb zn ag mineralization controlled by thrust faulting systems formed at least two large sized pb zn ag deposits 40 30 ma in the lanping strike slip pull apart basin western yunnan and 4 the au mineralization related to large scale shearing which produced the ailaoshan au belts composed of numerous shear type or orogenic type au deposits in the western sichuan and yunnan these data indicate that the late collisional metallogensis in the tibetan orogen were mainly developed in an intra continental transformation orogenic sdetting characterized by a series of large scale strike slip faulting thrusting and shearing systems developed in the late collisional period available data suggest that the metallogensis is probably controlled by a shared deep lithospheric process most likely related to upwelling of the asthenosphere triggered by face to face subduction of the yangtze and lhasa blocks continental slabs in the eastern margin of the tibetan plateau during the late collisional period

sequential late cenozoic structural disruption of the northern himalayan foredeep chronologies for the siwalik molasse and intermontane basins along the southern margin of the himalaya and hindu kush ranges constrain the timing and pattern of facies migration and structural disruption of the indo gangetic foredeep this synthesis indicates that quiescent intervals are punctuated by pulses of rapid deformation as thrusting migrates in a stepwise fashion across the foredeep

composition of the upper mantle geophysical tests of two petrological models the elastic properties of candidate mantle phases are used to test the viability of olivine rich pyrolitic and cao al 2o 3 rich eclogitic assemblages for the mantle high temperature adiabats for each phase of interest are constructed and compared to mantle seismic properties both pyrolitic and eclogitic assemblages satisfy the seismic properties between 200 and 400 km between 400 and 670 km depth an eclogitic assemblage yields a superior match to velocities and velocity gradients the 400 km seismic discontinuity may represent a chemical boundary between pyrolite and picritic eclogite piclogite or phase transformations in the olivine orthopyroxene components of a piclogitic assemblage containing about 16 olivine high velocity gradients in the transition zone may be explained by the transformation of ca rich cpx to majorite garnet seismic properties at the top of the lower mantle are consistent with pyrolite piclogite or perovskite implying that the 670 km discontinuity may be a chemical boundary

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

characterizing carbon isotopic variability in sphagnum to understand more fully the nature of isotopic fractionation in mosses and to explore the potential of stable isotope analyses of selected peat constituents for palaeoenvironmental research we present results from a study of inter and intra plant 13c variability in sphagnum spp subdivisions of stem pendant and horizontal branch elements of modern sphagnum capillifolium plants revealed consistent and statistically significant differences in their isotopic composition sequential downstem analysis of a further cohort of four modern sphagnum capillifolium plants also reveals evidence of common forcing on the isotopic composition of sequentially formed stem and branch increments this relationship was tested further by analysis of a series of branch and stem samples manually recovered from sphagnum fuscum preserved within a late holocene ad 2003 1970 peat monolith from a european mire the high degree of isotopic coherence observed between plants supports the analysis of sphagnum in palaeoecological

variations of 18o 16o in plants from temperate peat bogs switzerland implications for paleoclimatic studies despite the great potential of peat bogs as climatic archives to date only few studies have focused on the climatic controls on cellulose isotopic composition in modern bog plants this study attempts to calibrate plant climate relationships by sampling a set of modern plant species both vascular plants and mosses and bog surface waters along an altitude transect in switzerland isotopic analyses of water samples show that the 18o values of surface bog waters follow the trend of precipitation despite significant scatter in the data set detailed sampling of surface waters within one bog shows that 18o values vary widely and are closely related to the micro topography of the bog surface more enriched 18o 16o ratios in water samples collected from small raised hummocks than the ones collected from hollows are documented in both horizontal and vertical profiles a 18o d plot indicates that the process leading to the isotopic enrichment of the uppermost surface waters is evaporation greater above sphagnum covered hummocks than above open pools to investigate the implications of such high variability of source water for plant cellulose 18o values a detailed study of both surface water and cellulose 18o values within one site is conducted the large 18o variability observed in surface waters is found to be considerably smoothed in cellulose by a factor of 5 10 depending on the plant species this indicates that the water used by plant photosynthetic processes reflects the isotopic composition of the average annual precipitation this points to a source water level for plants of a few decimeters where the variations are smaller than at the air water interface the response of the cellulose 18o to the environmental gradient along the altitude transect varies considerably from species to species for most of the species studied the 18o values decrease with altitude following the trends of 18o values in precipitation and in surface water samples some species the cotton sedge eriophorum vaginatum and the moss sphagnum capillifolium show statistically significant 18o relationships to an altitude of 1 8 km and 2 9 km respectively however some other plant species calluna vulgaris vaccinium uliginosum andromeda poliflora carex pauciflora sphagnum cuspidatum and sphagnum magellanicum do not or only partially reflect changes in climatic parameters associated with an altitude increase furthermore changes in relative humidity which are not correlated with altitude are found to explain a large part of the variability in 18o values for the sedge carex pauciflora and the moss sphagnum cuspidatum therefore this study confirms the importance of species specific studies when interpreting 18o 16o ratios of macrofossils along a fossil peat sequence as a record of past climate changes our study allows to extend the mechanistic model that isotopically links source water and cellulose to the physiological specificities of sedges and mosses a comparison of the modeled and calculated net biological fractionation factors for eriophorum vaginatum and sphagnum capillifolium reveals that these two species appear to have a more homogeneous leaf reservoir than trees

paleoclimatic significance of the temperature dependent susceptibility of holocene loess along a nw se transect in the chinese loess plateau we have conducted mineral magnetic investigations of samples of modern dune sand pristine loess and present day loess along a nw se transect from the northern to the central loess plateau in china the methods used include the temperature dependence of susceptibility tds before and after citrate bicarbonate dithionite cbd treatment as well as x ray diffraction xrd analysis the xrd analyses demonstrate that magnetite and hematite both exist in the chinese loess paleosol sequence and its modem source area but the tds measurements show that magnetite is the predominant contributor to magnetic susceptibility maghemite is present in the pristine loess and the present day loess due to pedogenesis the pedogenic processes that produce the maghemite are closely linked to paleoclimate and for this transect precipitation appears to be the most important climatic variable we suggest that tds can be used as a useful method for the analysis of pedogenesis and climatic change

climatic correlations in the stable isotope records of silver fir abies pindrow trees from kashmir india a high degree of coherence in the annual stable isotopic records along different radial directions of a silver fir tree and between two members of this species from the kashmir valley has recently been reported by us since such a common pattern of isotopic variability is most likely due to the climatic fluctuations in the site we have compared the mean d 13c and 18o records of these trees with instrumentally measured climatic parameters recorded in a nearby weather station to identify the climatic parameters predominantly influencing the isotopic record a multiple regression analysis of the two records for the period 1903 1932 yields the following 1 d is most sensitive to the amount of growing season precipitation followed by mean maximum temperature tree cellulose shows an amount effect analogous to precipitation samples the temperature coefficient for d is in good agreement with earlier estimates based on spatial correlations 2 13c is significantly related to humidity and cloud amount the signs of the regression coefficients are consistent with the recent model of francey and farquhar for13c 12c fractionation in c3 plants 3 18o of cellulose appears to be controlled significantly by relative humidity 18o shows less overall correlation with climatic parameters than d and 13c 4 d of carbon bound hydrogen and 18o of tree cellulose are linearly related with a slope of7 9 0 3 suggesting evaporative enrichment in leaf water

activation of the nyainqentanghla shear zone implications for uplift of the southern tibetan plateau neogene extension of the tibetan plateau is manifested as a series of north south trending graben the most prominent of which is the yadong gulu rift the nyainqen tanghla shan a ne sw trending mountain range 100 km nw of lhasa bounds the western margin of the yangbajian graben the central segment of the yadong gulu rift the eastern edge of the nyainqentanghla massif is marked by a low angle 25 o detachment fault shear zone of amphibolite grade mylonites the noar 3 ar thermal history results from samples collected along two deeply incised valleys within the massif reveal that a rapid cooling event propagated from 8 ma in the core of the range to 4 ma within the high strain zone at the eastern boundary assuming that faulting initiated at high angle 60o thermal histories were fit to a numerical simulation of slip on a normal fault to yield estimates of both the age of fault initiation and the slip rate history the form of the isotopically derived thermal histories are similar to general form predicted by the thermal model and suggests that significant movement began at 8 1 ma in the southern valley goring la and proceeded at an average slip rate of 3 mm yr between 8 and 3 ma a more complex history is required to fit the data from the northern valley balum chun but the timing of initiation and average slip rate are similar to the goring la result numerical simulations in which the fault angle is varied indicate that the isotopically derived temperature histories are inconsistent with slip occurring at low angle 40o because the extension direction of the yangbajian graben is representative of most rifts on the southern tibetan plateau our data suggest that crustal thickness and elevation reached close to their present values by 8 1 ma a carbon isotopic shift in pedogenic carbonates from the siwalik formation at about 7 5 ma appears to reflect intensification of the asian monsoon and by inference that the plateau had attained an important threshold elevation by that time formation of a diffuse plate boundary in the indian oceanic lithosphere beginning at 7 5 8 0 ma is also consistent with this history we suggest that the plateau had attained a threshold area and elevation by 8 1 ma sufficient to trigger these three independent manifestations

cenozoic volcanism in tibet evidence for a transition from oceanic to continental subduction geochronological k ar or ar ar major and trace element sr nd pb isotopic and mineral chemical data are presented for newly discovered cenozoic volcanic rocks in the western qiangtang and central lhasa terranes of tibet alkali basalts of 65 45ma occur in the western qiangtang terrane and represent primitive mantle melts as indicated by high mgnumbers 100 mg mg fe 54 65 cr 204 839 ppm and ni 94 218 ppm contents and relatively low ratios of sr sr 0 7046 0 7061 pb pb 18 21 18 89 pb pb 15 49 15 61 and pb pb 38 42 38 89 and high ratios of nd nd 0 5124 0 5127 in contrast younger volcanic rocks in the western qiangtang terrane 30ma and the central lhasa terrane 23 13 and 8ma are potassic to ultrapotassic and interpreted to have been derived from an enriched mantle source they are characterized by very high contents of incompatible trace elements negative ta nb and ti anomalies and radiogenic pb isotopic compositions pb pb 18 43 19 10 pb pb 15 64 15 83 pb pb 39 14 39 67 sr sr 0 7088 0 7092 and nd nd 0 5122 ratios of the western qiangtang terrane potassic lavas are similar to those of 45 29ma potassic volcanic rocks in the north central qiangtang terrane whereas sr sr 0 7167 0 7243 and nd nd 0 5119 ratios of central lhasa terrane lavas are similar to those of 25 16ma ultrapotassic volcanic rocks in the western lhasa terrane the 65 45ma alkali basalts in the western qiangtang terrane along with widespread calc alkaline volcanic rocks of this age in the lhasa terrane may be related to roll back of a previously shallow north dipping slab of tethyan oceanic lithosphere beneath tibet subduction as opposed to convective thinning of continental lithosphere is favored to explain potassic volcanism in tibet because of its occurrence in distinct east west trending belts 45 29ma in the qiangtang terrane 25 17ma in the northern lhasa terrane 16 8ma in the southern lhasa terrane and temporal and spatial relationships with major thrust systems

tertiary structural evolution of the gangdese thrust system southeastern tibet structural and thermochronological investigations of southern tibet xizang suggest that intracontinental thrusting has been the dominant cause for formation of thickened crust in the southernmost tibetan plateau since late oligocene two thrust systems are documented in this study the north dipping gangdese system gts and the younger south dipping renbu zedong system rzt west of lhasa the gangdese thrust juxtaposes the late cretaceous forearc basin deposits of the lhasa block the xigaze group over the tethyan sedimentary rocks of the indian plate whereas east of lhasa the fault juxtaposes the late cretaceous eocene andean type arc the gangdese batholith over tethyan sedimentary rocks near zedong 150 km southeast of lhasa the gangdese thrust is marked by a 200 m thick mylonitic shear zone that consists of deformed granite and metasedimentary rocks a major south dipping backthrust in the hanging wall of the gangdese thrust puts the xigaze group over tertiary conglomerates and the gangdese plutonics north of xigaze and west of lhasa a lower age bound for the gangdese thrust of 18 3 0 5 ma is given by crosscutting relationships the timing of slip on the gangdese thrust is estimated to be 27 23 ma from 40 ar 39 ar thermochronology and a displacement of at least 46 9 km is indicated near zedong the age of the gangdese thrust gt is consistent with an upper age limit of 24 ma for the initiation of movement on the main central thrust in places the younger renbu zedong fault is thrust over the trace of the gt obscuring its exposure the rzt appears to have been active at circa 18 ma but had ceased movement by 8 1 ma the suture between india and asia has been complexly modified by development of the gts rzt and locally strike slip and normal fault systems

formation and re orientation of the suerkuli basin within the altyn tagh in northeastern tibetan plateau since late miocene abstract the altyn tagh fault atf had formed in eocene time however the temporal evolution of slip along the fault remains elusive despite its important role in governing growth of the tibetan plateau tp and evaluating models of continental lithosphere deformation here we perform a high resolution magnetostratigraphic study on neogene sediments from the suerkuli basin a small basin located between two active strands of the atf results show that both depositional environment and the sedimentation rate changed at about 5 4 and 6 ma respectively lithofacies shift from conglomerates and sandstones with parallel and cross beddings to mudstones with horizontal bedding suggesting a sedimentary fluvial to lacustrine depositional environment shift even aridification increased over northern china from the tarim basin to the qaidam basin during late miocene to early pliocene times lacustrine deposition had started in the suerkuli basin still we argue that an increase in slip rate along the atf triggered concurrently forming of the intermontane basin the inferred timing of increased slip rate on the atf coincides with a variation in movement of the indian plate relative to eurasian plate since late miocene early pliocene time our work suggests that a re orientation of crustal shortening and deformation in the northern tp began since late miocene and supports the idea that the modern boundary of the tp orogen had rejuvenated to adjust deformation in plate boundary conditions

paleomagnetic chronology fluvial processes and tectonic implications of the siwalik deposits near chinji village pakistan a 2800 m section of siwalik strata containing the stratotypes for both the chinji and nagri formations has been dated by magnetic polarity stratigraphy and the observed polarity zonation has securely been correlated with the chron 17 7 segment of the time scale the base of the section is the base of the kamlial formation which occurs near the top of chron 17 18 3 m y the kamlial chinji formation boundary occurs in the middle of chron 15 14 3 m y the chinji nagri boundary near the bottom of chron 10 10 8 m y and the nagri dhok pathan boundary at the chron 8 9 boundary 8 5 m y the siwalik deposits near chinji village consist of four distinct classes of fluvial cycles each with a characteristic periodicity a first order of 10 7 years a second order of 10 6 years a third order of 10 4 10 5 years and a fourth order of 10 0 10 4 years the river system responsible for siwalik sedimentation flowed from west to east and had properties much like the modern ganges river syste

the late miocene through present paleoelevation history of southwestern tibet recent research using stable isotopes of carbon and oxygen from carbonates and fossil teeth seems to support both a pre and post mid miocene uplift of the southern tibetan plateau we examined this issue by analysis of well preserved fossil mollusks and plant remains from the zhada basin in southwestern tibet which ranges in age from 9 2 to paleoenvironmental modeling and physical evidence shows that the climate in zhada basin was cold and arid indistinguishable from modern the 13cpm values of well preserved vascular plant material increase from 23 4 to 26 8 permil at the base of the zhada formation to as high as 8 4 permil above 250 to 300 m this shift denotes the expansion of c4 biomass in this high arid watershed at 7 ma and thus corresponds to the c3 c4 transition observed in neogene deposits of the northern indian sub continent

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

intermontane basin development in the past 4 myr in the north west himalaya the through the combined use of magnetic polarity stratigraphy with fission track dating of volcanic ashes a new chronology spanning 4 myr has been developed for the intermontane basin of kashmir in the northwestern himalaya

reflection properties of phase transition and compositional change models of the 670 km discontinuity seismic observations of the amplitude ratio amplitude p 670p amplitude p p suggest a reflection coefficient r 7 13 for reflections from the underside of the 670 km discontinuity this can be compared with calculated reflection coefficients to constrain the nature of the mantle transition region velocity and density profiles through the transition region were calculated for olivine pyroxene garnet and olivine garnet model mineral assemblages for models with identical upper and lower mantle compositions the computed reflection coefficients from the phase transitions pertinent to the 670 km discontinuity are less than 0 5 these phase transitions produce their maximum r if they are effectively discontinuous which gives r 2 3 except for the garnet to perovskite transformation which gives r 8 in general given realistic impedance contrasts across a phase transition the change in material properties must occur over a region less than 3 km thick for r to be of the order of 5 a discontinuous change in chemical composition at 670 km depth coupled with a change in phase can also produce a reflection coefficient of the observed magnitude r 2 3 for a first order change in phase at 670 km with different iron concentrations on each side of the discontinuity and r 4 6 for cases with a discontinuous increase in silica content based on our analysis the thermal and chemical boundary layers which would occur across such a chemical discontinuity would probably have negligible effects on the reflection coefficient thus although limited by considerable uncertainties the mineralogical and seismic data suggest a two layered model of the mantle with a discontinuous change in both phase and composition at 670 km

pliocene uplift of the northern tibetan plateau neogene redbeds passing upward into upward coarsening conglomerate and debris flow deposits at the foot of the kunlun mountains record the change in paleoslope related to uplift of the surface of the northern tibetan plateau detailed magnetostratigraphy of a 4 5 km section near yecheng in the western kunlun mountains shows that the change from deposition on distal alluvial plains to proximal alluvial fans occurred during the gilbert reversed chron 4 5 3 5 ma the change in depositional facies was accompanied by an increase in sedimentation rate from an average 0 15 mm yr between the earliest oligocene and the earliest pliocene to 1 4 mm yr in the gauss normal chron 3 6 2 6 ma we interpret the change in depositional facies and increase in sedimentation rate as indicating that the main uplift of the northwestern tibetan plateau began ca 4 5 ma

sedimentology sedimentary petrology and paleoecology of the monsoon driven fluvio lacustrine zhada basin sw tibet abstract in this paper we present sedimentologic petrographic and paleoecologic data from a 810 m thick section of late neogene ca 9 7 to 1 ma fluvio lacustrine deposits in the high elevation zhada basin of sw tibet the tectonic evolution of the zhada basin region located between the himalayan mountains in the s and the transhimalayan mountains in the n is poorly understood but sediment accumulation was probably initiated in response to the middle late miocene uplift of the gurla mandhata and leo pargil domes in the e and w respectively the sedimentary record can be subdivided into five stratigraphic units with distinctly different lithofacies associations la these are from bottom to top a bedload dominated fluvial la unit 1 0 90 m a nearshore lacustrine deltaic la unit 2 90 220 m an offshore lacustrine la unit 3 220 500 m a nearshore lacustrine fan delta la unit 4 500 600 m and a fan delta alluvial fan la unit 5 600 810 m clast and heavy mineral compositions revealed sediment supply from two different provenance areas one from the south and one from the north east based on catchment geology of the himalaya and transhimalaya ostracode faunal assemblages are largely comparable to those of modern tibetan lakes and allow the reconstruction of paleo lake environments including lake level changes and salinity the sedimentary pattern shows strong cyclicity at various scales m 10 s m and 100 m small scale cycles are interpreted as intrinsically controlled depositional processes of deltas lobe switching whereas medium and large scale cycles are most likely forced by climate fluctuations the overall evolution of the sedimentologic record includes a strong and rapid increase in fluvial discharge in the uppermost portion of unit 1 a transition from fluvial to lacustrine deposition during deposition of unit 2 rhythmic variations in the style of lacustrine sedimentation during deposition of unit 3 an increase in the supply of coarse clastics starting with deposition of unit 4 and a transition from lacustrine to alluvial sedimentation during deposition of unit 5 we speculate that the increase in discharge and presumably precipitation leading to the establishment of lacustrine conditions in the lower part of the section unit 2 is largely due to regional summer monsoon intensification during the late miocene and that the transition from lacustrine to alluvial sedimentation in the uppper part of the section reflects the onset of northern hemisphere glaciation and winter monsoon strengthening at 2 6 ma

ancient diets indicate significant uplift of southern tibet after ca 7 ma the uplift of the tibetan plateau plays a critical role in controlling global climate yet the history of the tibetan uplift is still a contentious issue in particular the elevation of the plateau during the neogene a crucial period in the development of the asian monsoons and c4 ecosystems remains uncertain here we present carbon isotopic evidence preserved in tooth enamel from 7 m y old horses and rhinos from the high himalayas which indicates that unlike modern herbivores in the area these ancient mammals ate substantial amounts of c4 grasses the presence of significant amounts of c4 grasses in the diets of these ancient mammals indicates that the climate in the area was much warmer and the elevation was much lower in the late miocene than today the carbon isotope data from the high himalayas after accounting for late cenozoic global cooling and paleoatmospheric co2 levels indicate that this part of southern tibet was less than 2900 3400 m above sea level in the latest miocene this implies that the present elevation of the area must have been attained after 7 ma much later than generally believed

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

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

tectonic and climate controls on neogene environmental change in the zhada basin southwestern tibetan plateau evidence for a long lived high elevation plateau contradicts the hypothesis that uplift of the southern tibetan plateau was a driver of late miocene pliocene changes in ecology and monsoon strength we illuminate the mechanisms underlying late miocene pliocene environmental changes using a multi proxy record from the zhada basin southwestern tibetan plateau between ca 9 2 and 2 3 ma an increase in mean carbonate 18oc and 13cc values decrease in grain size and onset of lacustrine deposition at 6 0 ma is attributed to local tectonic damming and transition from a through flowing fluvial system to a terminal lake this is followed at 3 5 ma by a decrease in lake size indicated by synchronous increase in grain size progradation of lake margin depositional systems increase in 18oc values at lake central locations and divergence in 18oc values between inflowing and lake water we attribute lake shrinking to decreasing indian summer monsoon precipitation due to the combined effects of decreased southern tibetan plateau elevations and cooler indian ocean temperatures we attribute increased grain size and 18oc value variability to changes in fluvial discharge due to increased sensitivity to orbital forcing itself possibly coupled with onset of glacial conditions at high elevations these mechanisms link regional tectonic events to pliocene changes in climate and environmental conditions including erosion granularity sediment accumulation rates and potentially biological turnover on and around the tibetan plateau

holocene paleohydrology and paleoclimate at treeline north central russia inferred from oxygen isotope records in lake sediment cellulose lake water oxygen isotope histories for three lakes in northern russia derived from the cellulose oxygen isotope stratigraphies of sediment cores provide the basis for preliminary reconstruction of holocene paleohydrology in two regions along the boreal treeline deconvolution of shifting precipitation 18o from secondary evaporative isotopic enrichment is aided by knowledge of the distribution of isotopes in modern precipitation the isotopic composition of paleo waters preserved in frozen peat deposits as well as other supporting paleoclimatic information these data indicate that during the early holocene when the boreal treeline advanced to the current arctic coastline conditions in the lower yenisey river region were moist compared to the present whereas greater aridity prevailed to the east near the lower lena river this longitudinal moisture gradient is consistent with the suggestion that oceanic forcing increased sea surface temperatures in the nordic seas and reduced sea ice cover was a major contributor to the development of a more maritime climate in western eurasia in addition to increased summer insolation east of the taimyr peninsula large tracts of the continental shelf exposed by glacial sea level drawdown may have suppressed maritime climatic influence in what are now coastal areas in contrast during the late holocene the two regions have apparently experienced coherent shifts in effective moisture the similarity of the records may primarily reflect reduced north atlantic influence in the nordic seas and southward retreat of coastline in eastern siberia coupled with declining summer insolation

international geomagnetic reference field the eleventh generation the eleventh generation of the international geomagnetic reference field igrf was adopted in december 2009 by the international association of geomagnetism and aeronomy working group v mod it updates the previous igrf generation with a definitive main field model for epoch 2005 0 a main field model for epoch 2010 0 and a linear predictive secular variation model for 2010 0 2015 0 in this note the equations defining the igrf model are provided along with the spherical harmonic coefficients for the eleventh generation maps of the magnetic declination inclination and total intensity for epoch 2010 0 and their predicted rates of change for 2010 0 2015 0 are presented the recent evolution of the south atlantic anomaly and magnetic pole positions are also examined