variations in the discharge and organic matter content of stalagmite drip waters in lower cave bristol six drip waters which were actively depositing stalagmites in lower cave bristol were analysed both for discharge and luminescence properties drip discharges were determined for two different years and show a complex response to surface precipitation variations inter annual variability in drip discharge is demonstrated to be significantly higher than intra annual variability and discharge was demonstrated both to increase and decrease non linearly with increased precipitation drip waters demonstrate a correlation between their luminescence intensity and drip discharge with increased luminescence in winter as more organic matter is flushed through the aquifer the strength of the relationship between luminescence intensity and discharge increases with increased discharge the results presented here have implications for the palaeoenvironmental interpretation of annual growth laminae and the growth rates of stalagmite samples 1997 john wiley sons ltd

controls on cave drip water temperature and implications for speleothem based paleoclimate reconstructions while several studies explore cave climate and thermal regimes little is known about the controls on cave drip water temperature yet water temperature significantly influences biogeochemical processes associated with cave drips to identify the processes that control the cave drip water temperature we measured the temperatures at multiple locations along a speleothem flow path and drip sources stalactites concurrently with the drip rates in cathedral cave wellington australia we monitored long term drip water temperature drip rates surface and cave climate and in cave evaporation rates and conducted 3 infiltration experiments with different flow temperature and isotopic conditions our results show that the drip water temperature is controlled by multiple superimposed heat transport mechanisms that act upon the infiltrating water in the epikarst the water film after it enters the cave and before it becomes a drip the two main heat sources sinks for drip water are the cave air and the surrounding rock the subsurface temperature is coupled to the surface temperature by conduction through the soil and rock mass but the cave climate is also coupled to the surface climate by venting on a regional scale drip temperatures are mainly driven by the annual ground surface temperature signal but damped with depth and shifted in time compared to the surface on a local scale the drip water temperature can differ significantly from cave air and speleothem temperature due to the latent heat exchange of evaporation and localised water film convection the main controls are ground surface temperature subsurface depth air density induced ventilation distance from entry and drip rate we present a conceptual model that explains drip water temperature signals and provide signal driven guidance on best type and location for speleothem sampling we anticipate that our results will significantly improve the understanding of temperature dependent paleoclimate signals from speleothem archives

a 9000 year carbon isotopic record of acid soluble organic matter in a stalagmite from heshang cave central china paleoclimate implications abstract organic matter preserved in speleothems has the potential to reflect the changes of the overlying vegetation and soil ecosystem here we report the first near 50 yr resolution acid soluble organic matter asom carbon isotope 13 c asom sequence derived from a laminated stalagmite hs 4 spanning the last 9 ky in heshang cave central china the 13 c asom values vary between 25 8 and 22 0 with lower values from 9 to 4 ka bp and less negative values from 4 to 0 ka bp we postulate that the 13 c asom sequence is mainly controlled by temperature and water balance temperature could affect both vegetation physiology and microbial degradation in soil horizons the influence of temperature on the 13 c asom is supported by the negative correlation r 0 48 p 13 c asom record and the paleotemperature record in the nearby dajiuhu peatland the water balance can affect the retention time of organic matter in soils under drier conditions the soil organic matter will be retained longer and is more likely to be biologically degraded resulting in more negative 13 c asom values our results reveal that 13 c asom in speleothems has the potential to reflect the response of vegetation and or soil processes to paleoclimate changes

tectonometamorphic evolution of the himalayan metamorphic core between the annapurna and dhaulagiri central nepal the metamorphic core of the himalaya in the kali gandaki valley of central nepal corresponds to a 5 km thick sequence of upper amphibolite facies metasedimentary rocks this greater himalayan sequence ghs thrusts over the greenschist to lower amphibolite facies lesser himalayan sequence lhs along the lower miocene main central thrust mct and it is separated from the overlying low grade tethyan zone tz by the annapurna detachment structural petrographic geothermobaro metric and thermochronological data demonstrate that two major tectonometamorphic events charac terize the evolution of the ghs the first eohimalayan episode included prograde kyanite grade metamorphism during which the ghs was buried at depths greater than c 35 km a nappe structure in the lowermost tz suggests that the eohimalayan phase was associated with underthrusting of the ghs below the tz a c 37 ma 40ar 39ar hornblende date indicates a late eocene age for this phase the second neohimalayan event corresponded to a retrograde phase of kyanite grade recrystallization related to thrust emplacement of the ghs on the lhs prograde mineral assemblages in the mct zone equilibrated at average t 880 k 610 c and p 940 mpa 35 km probably close to peak of meta morphic conditions slightly higher in the ghs final equilibration of retrograde assemblages occurred at average t 810 k 540 c and p 650 mpa 24 km indicating re equilibration during exhumation controlled by thrusting along the mct and extension along the annapurna detachment these results suggest an earlier equilibration in the mct zone compared with higher levels as a consequence of a higher cooling rate in the basal part of the ghs during its thrusting on the colder lhs the annapurna detachment is considered to be a neohimalayan synmetamorphic structure representing extensional reactivation of the eohimalayan thrust along which the ghs initially underthrust the tz within the upper ghs a metamorphic discontinuity across a mylonitic shear zone testifies to significant late to post metamorphic out of sequence thrusting the entire ghs cooled homogeneously below 600 700 k 330 430 c between 15 and 13 ma middle miocene suggesting a rapid tectonic exhumation by movement on late extensional structures at higher structural levels

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

spatially correlated anomalous 40ar 39ar age variations in biotites about a lithologic contact near simplon pass switzerland a mechanistic explanation for excess ar forty four biotite samples collected about a lithologic contact between pelite and amphibolite were analyzed for 40ar 39ar and demonstrate the importance of bulk ar diffusivity and system geometry factors not usually considered in the interpretation and collection of 40ar 39ar age data the resulting 40ar 39ar apparent ages range from 11 30 0 05 ma to 17 90 0 10 ma the ages and excess argon contents are spatially and lithologically correlated the pelite samples all yield ages clustering around 12 ma the age expected for cooling through biotite closure 360 c in this region of the alps ages in the amphibolite biotites are older showing a smooth trend between 15 ma at the contact with the pelite to 18 ma 34 cm from the contact this data shows that characterization of the ar closure age for biotite in a given system should not rest on a single sample as otherwise irresolvable differences in age between samples within the same outcrop can exist a generalized mechanistic model for excess argon is presented the presence or absence of excess ar depends on an intrinsic system parameter t the transmissive timescale which is the characteristic time for 40ar to escape through the local intergranular transporting medium itm to some sink for argon to prevent buildup of geochronologically significant excess 40ar t must be very short relative to the true closure age of the mineral a fortran code including radiogenic ar production diffusive loss of ar from biotite and bulk ar diffusion through the itm has been developed application of numerical modeling suggests that the time averaged effective bulk diffusivity deffar in the biotite amphibolite rock during early retrograde cooling is 2 2 1 0 10 8 m2 yr assuming steady state conditions the first such measurement available numerical modeling also provides information about the transmissivity and geologic history specific to the field site including a drop in deffar at 15 5 1 0 ma the timing of this drop is related to coincident rheological changes and the onset of rapid exhumation of the nappe stack

an irrigation experiment to compare soil water and speleothem tetraether membrane lipid distributions measurement of glycerol dialkyl glycerol tetraethers gdgts preserved in speleothems offers a potential proxy for past temperature but in general their origin is unknown to understand the source of speleothem gdgts we undertook an irrigation experiment to activate drip sites within a hydrogeochemically well characterised cave the cave drip water was analysed for gdgts inorganic elements major ions and trace elements stable isotopes and dissolved organic matter concentration and character published speleothem gdgt records from the site have been observed to be dominated by isoprenoid gdgts and interpreted as deriving from in situ microbial communities within the cave or vadose zone the drip water in our irrigation experiment had a gdgt distribution distinct from that of soil and speleothem samples providing direct evidence that the distinctive gdgt signature in speleothems is derived from a subsurface source analysis of gdgts in this context allowed further elucidation of their source and transport in cave systems enhancing our understanding of how they might be used as a temperature proxy

extension in compressional orogenic belts the eastern alps extension in the eastern alps encompasses the following 1 extension accompanying simple shear crustal stacking subhorizontal stretching occurs along flat lying foliations and regionally consistent stretching lineations with associated high strains on a local scale stretching results from extrusion of ductile sediments squeezed between rigid basement blocks basement blocks during thrust sheet imbrication the overall geometric effect is crustal thickening 2 classical extensional tectonics extension first occurs as a consequence of accretion and underthrusting of continental and oceanic material and represents gravitational adjustment of an unstable orogenic wedge extension then occurs as a consequence of terminal continental collision and is accommodated by lateral extrusion of crustal of crustal blocks the overall geometric effect is crustal thinning extension is generally oriented subparallel to the strike of the orogen

possible thermal buffering by crustal anatexis in collisional orogens thermobarometric evidence from the nepalese himalaya one dimensional thermal models suggest that large thrust faults may exert first order control on the thermal structure of collisional orogenic belts and an increasing body of petrologic data may be interpreted as consistent with these models we present new thermobarometric data from the central nepalese himalaya which imply that large sections of the himalayan orogen may have been at roughly uniform temperatures during active thrusting a phenomenon that is not predicted by existing models we attribute this phenomenon to thermal buffering as a consequence of widespread in situ anatexis if this process is common in the intermediate and lower crust of active orogens and if it is localized spatially one dimensional thermal models may produce an extremely oversimplified picture of heat transfer processes during collisional orogenesis

structural and thermal constraints on the initiation angle of detachment faulting in the southern basin and range the chemehuevi mountains case study the cenozoic normal fault system exposed in the chemehuevi mountains of the southern cordillera provides constraints on the initiation angle and geometry of an extensional fault system that has accommodated extreme crustal stretching there three stacked brittle low angle normal faults that formed at depths as great as 10 12 km cut gently down section northeastward through deformed proterozoic and mesozoic crystalline basement hanging wall blocks are displaced relatively northeastward the upper crust above the chemehuevi detachment fault was pulled apart along high angle normal faults that rotated to more gentle dips through time in contrast rocks of originally mid crustal affinity in the footwall were only gently rotated and accommodated minor extension application of 40 ar 39 ar and fission track thermochronology to rocks in the footwall of the chemehuevi detachment fault system provides further constraints on the timing and initiation angle of regional detachment faulting at the onset of extension between 22 and 24 ma granitic rocks exposed in the southwestern and northeastern portions of the footwall were at 200 c and 350 400 c respectively separated by a distance of some 23 km down the known slip direction this gradual increase in temperature with original depth is attributed to the gentle southwest tilting of broadly planar pre extension isothermal surfaces and constrains the exposed part of the chemehuevi detachment fault to have had a regional dip initially of about 15 to 30 the fault system apparently cut gently down through the upper crust to a minimum depth of 10 12 km the deepest exposed parts of the system today and was domed from midcrustal depths and locally denuded during continued slip together the structural and thermochronologic data confirm the suggestion that faults accommodating large magnitude slip can be initiated and move within the seismogenic regime at moderate to low angles that is 30

synconvergence spreading of the higher himalaya crystalline in ladakh in ladakh suru valley nw himalaya regional fabrics of the higher himalaya crystalline result from a major deformation event that 1 is restricted to the indian crust above the main central thrust mct 2 postdates piling up of units above the mct 3 ended while thrusting was still continuing on the mct 4 developed under high temperature conditions following thickening 5 resulted in an asymmetric gneiss dome and 6 is associated with ene wsw to ew regional extension we suggest that extension was accommodated by spreading of the hot basement accompanied and followed by its uplift within the overlying cover along a major detachment zone the onset of the process appears closely related to strong thermal softening of the higher himalaya crystalline and is broadly synchronous with the formation of the himalayan leucogranites around 25 ma the regional pattern suggests that the mct zone could have acted as a decoupling zone between a thickening lower part and a thinning upper part of the indian crust during miocene times the extension direction is consistent with bulk himalayan kinematics involving nw se dextral wrenching along the western syntax and eastward extrusion of tibet we suggest that exhumation of gneissic ridges which characterize indian units above the mct all along the himalayan belt could reflect large scale crustal instability developed from thermally anomalous layers whose spreading ability can favor synconvergence extension

contrasting distributions of glycerol dialkyl glycerol tetraethers gdgts in speleothems and associated soils glycerol dialkyl glycerol tetraethers gdgts preserved in speleothems can form useful records of terrestrial palaeotemperature however understanding of the sources of these compounds in caves is limited particularly whether or not they should be considered as an in situ signal derived from microbial communities in the cave or vadose zone a transported soil signal or a mixture of the two we have analysed speleothem samples and related soils from five cave sites and demonstrate that clear differences were apparent between soils and speleothems in gdgt distributions speleothems were primarily but not uniformly dominated by crenarchaeol reflected in the branched and isoprenoid tetraether bit index values and had a lower relative abundance of the crenarchaeol regioisomer than soils the most distinct differences were in the bacterially derived branched gdgts where no relationship was seen between speleothems and soils for the cyclisation of branched tetraethers cbt index with speleothems in four out of five caves showing a greater degree of cyclisation in gdgt structures than could be explained by measured ph values differences in speleothem gdgt composition between sites were also seen we suggest that the speleothem gdgt record is distinct from the gdgt distribution produced in soils and is primarily derived from in situ microbial communities within the cave or vadose zone variation within these communities or in the cave microenvironment also acts to produce site specific differences

sr isotope evolution of seawater the role of tectonics we use a high resolution seawater sr isotopic evolution curve for the last 100 m y in conjunction with modern riverine sr flux measurements and also geologic tectonic and geochronological data to make the case for a close relationship between seawater sr isotopic composition and the india asia continental collision using a simple seawater sr budget model we begin by showing that the sr flux associated with alteration of seafloor basalts is too small and does not have the right time evolution to account for much of the seawater sr isotopic curve of the last 100 m y the flux of dissolved sr carried by rivers originating in the himalaya tibet region on the other hand is presently a significant fraction of the global sr budget we calculate how this riverine flux would have had to change with time in order to match the observed seawater sr isotopic curve and find that the riverine flux remains relatively constant prior to the collision of india with asia but then increases very significantly after collision we note that the period of most rapid change in seawater sr isotopic ratio from 20 ma to 15 ma is also a period of exceptionally high erosion in parts of the himalayas and the tibetan plateau as further evidence that sr derived from the collision of india with asia plays a major role in the sr isotopic evolution of seawater we show that the total amount erosion of the himalaya tibetan plateau since collision which we calculate separately represents a total amount of sr that is very nearly the same as the cumulative amount required by the sr isotopic change of seawater since collision the relationship between erosion and riverine sr flux allows us to use the sr isotopic evolution of seawater to reconstruct a history of erosion since collision and we find that the erosion rate accelerates with time since collision with the present having the largest rate when we apply the sr budget model to the entire phanerozoic using a new compilation of deformed continental area versus time we find that we can account for the large scale structure of the seawater sr isotopic curve but fail to reproduce several local maxima and minima especially in the period 100 300 ma the present high s7sr s6sr of seawater and similar highs in the devonian and cambrian do correlate with extensive deformation on the continents

organic compounds preserved in a 2 9 million year old stalagmite from the nullarbor plain australia a 2 9 ma stalagmite from the nullarbor plain south australia was analysed for organic components in contrast to previously analysed stalagmites no significant lipid record was recovered however qualitative tmah thermochemolysis of the residual organic matter recovered a range of compounds including a number of phenols previously associated with lignin comparison of this sample with a range of modern stalagmite samples from different environments indicated that the phenolic record in stalagmites can reflect the overlying vegetation regime and has potential in investigating palaeoenvironmental change in this climatically important region

holocene temperature and hydrological changes reconstructed by bacterial 3 hydroxy fatty acids in a stalagmite from central china abstract to achieve a sufficient understanding of the spatial dynamics of terrestrial climate variability new proxies and networks of data that cover thousands of years and run up to the present day are needed here we show the first gram negative bacterial 3 hydroxy fatty acid 3 oh fa based temperature and hydrological records from any paleoclimate archive globally the data covering the last 9 ka before present bp are generated from an individual stalagmite collected from heshang cave located on a tributary of the yangtze river central china 30 27 n 110 25 e 294 m our results indicate a clear early to middle holocene climatic optimum 8 0 6 0 ka bp followed by a long term monotonic cooling and increasing variability over the last 0 9 ka bp the hydrological record shows two relatively long wet periods 8 8 5 9 ka bp and 3 0 0 ka bp and one relatively dry period 5 9 3 0 ka bp in central china we show that 3 oh fa biomarkers hold promise as independent tools for paleoclimate reconstruction with the potential to deconvolve temperature and hydrological signals from an individual stalagmite

limits on the tectonic significance of rapid cooling events in extensional settings insights from the bitterroot metamorphic core complex idaho montana rapid cooling events deduced from thermochronologic data are often interpreted to be coincident with the age of extensional denudation in metamorphic core complexes 40 ar 39 ar data for mylonitic and nonmylonitic footwall rocks from the bitterroot core complex idaho montana united states challenge this view previous work brackets the age of the principal detachment in this area the bitterroot mylonite zone between 48 1 and 46 4 0 8 ma newly obtained hornblende 40 ar 39 ar cooling ages for samples collected from the mylonite zone are within this age range consistent with mylonitization at amphibolite facies conditions however muscovite biotite and potassium feldspar 40 ar 39 ar ages of 45 40 ma for rocks from the same area define a rapid cooling event that is significantly younger than the bitterroot mylonite zone if the 45 40 ma event is related to tectonic denudation by movement on the detachment then we can infer a time lag of 1 3 m y between the age of unroofing and the time of thermal reequilibration these data suggest caution in the use of 40 ar 39 ar data from the footwalls of metamorphic core complexes to suggest the precise age of tectonic denudation

molecular organic matter in speleothems and its potential as an environmental proxy abstract organic matter preserved in speleothems has considerable potential to record changes in the surrounding environment particularly in the overlying vegetation here we review three types of organic matter analysis relevant to speleothems organic fluorescence lipid biomarker analysis and amino acid racemisation organic matter luminescence provides a useful non destructive and rapid method for assessing dissolved organic matter quantity and quality while biomarker analysis amino acids and lipids has the potential to provide a more detailed signal related to specific parts of the surrounding ecosystem such as the dominant vegetation regime and bacterial activity amino acid analysis has yet to prove demonstrably useful in stalagmites due to the inability to characterise the sources of proteinaceous matter however the small but increasing body of work on lipid biomarker analysis in stalagmites has shown that a wide variety of recognisable biomarkers are preserved over long periods of time 100 ka can be recovered at temporal resolutions of

an empirical evaluation of the argon diffusion geometry in muscovite the temperature time significance of 40ar 39ar muscovite ages is difficult to evaluate quantitatively because of ambiguities in the choice of an appropriate model diffusion geometry the effective diffusion dimension and large uncertainties in experimentally determined diffusion parameters laser 40ar 39ar studies of natural 40ar concentration gradients suggest that argon loss in muscovite occurs primarily via cylindrical volume diffusion commonly with an effective diffusion dimension equal to the crystal diameter the present study tests the cylinder model geometry and the control of physical grain size on the effective diffusion dimension by measuring the anisotropy of a natural40ar diffusion gradient parallel and perpendicular to 001 in a single euhedral muscovite phenocryst the new data combined with previous studies clearly indicate loss of 40ar via cylindrical volume diffusion and strongly suggest that loss of 40ar across the 001 sheets slab diffusion geometry is minimal in undeformed crystals

a microstructural and argon laserprobe study of shear zone development at the western margin of the nanga parbat haramosh massif western himalaya a sample of banded amphibolite from the western margin of the nanga parbat haramosh massif as sassi has been studied using microstructural and 40ar 39ar laserprobe techniques to investigate the relationship between deformation and argon isotope variations in a natural system amphibolite grade deformation occurred during south directed overthrusting of the kohistan arc over india along the main mantle thrust and was overprinted by extensional reactivation of the earlier fabric and the formation of biotite rich shear zones subsequent deformation along discrete fine grained fault zones was characterised by the formation of scapolite chlorite and k feldspar early plastic deformation and later cataclasis different minerals developed during this history show a wide range in apparent 40ar 39ar ages biotite chlorite and scapolite exhibit much lower concentrations of excess argon indicating their equilibration in a fluid relatively poor in excess argon a true age of ca 8 ma from biotite represents a minimum age for deformation associated with formation of the nanga parbat syntaxis and also precludes pliocene metamorphism in this area of the syntaxis both high and low closure temperature minerals amphiboles and feldspars record apparent ages which are associated with the incorporation of excess argon within the mineral lattice although differential thermal resetting of minerals at different closure temperatures is important variations in the inherited 40ar 36ar ratio throughout the sample is dominated by deformation and fluid infiltration consequently it appears that within deforming metamorphic rocks areas with significantly different argon isotope compositions may be present and need not be homogenised by diffusion

ages of deformation from k ar and 40ar 39ar dating of white micas a structural and isotopic dating study of white micas from mylonites in the ruby gap duplex off central australia shows that mylonitic deformation occurred during the paleozoic alice springs orogeny deformation of the white micas took place under greenschist facies conditions in the approximate temperature range 250 350 c two distinct populations of white mica have been found 1 porphyroclasts of original muscovite and 2 neocrystallized phengites that define the fabric associated with deformation 40ar 39ar age spectra of neocrystallized phengites yield plateau like spectra of paleozoic age in contrast 40ar 39ar age spectra of muscovite porphyroclasts exhibit proterozoic apparent ages indicating that white micas were not open to significant argon diffusion during formation of the ruby gap duplex we conclude that the ages measured on neocrystallized phengites record the cessation of ductile deformation and migration of tectonic activity toward the internal zones of the thrust system

deep seismic reflection evidence for continental underthrusting beneath southern tibet the himalaya and adjacent tibetan plateau constituting earth s largest region of elevated topography and anomalously thick crust formed as a consequence of cenozoic collision between india and asia itself considered the archetypal continent continent collision1 3 here we report the first results from an attempt to image the structure of the crust beneath this region using deep seismic reflection profiling our 100 km long profile acquired in the tethyan himalaya shows a mid crustal reflection that prob ably marks the active thrust fault along which the indian plate is underthrusting southern tibet upper crustal reflections with geo metries suggestive of large scale structural imbrication of the upper crust and moho reflections from the base of the double normal thickness crust underlying the region these results lend substantial support to the view that crustal thickening beneath southernmost tibet was accomplished by wholesale underthrusting of indian continental crust beneath the structurally imbricated upper crust comprising the tethyan himalaya

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

north south extension within the convergent himalayan region recent work by burg et al 1984 indicates the presence of east west striking gently north dipping normal faults in the higher himalayas and southern tibet that formed during postcollisional convergence of india and tibet these faults extend for at least 800 km along strike we interpret these normal faults as probable late miocene extensional features with perhaps several tens of kilometres of down to the north displacement a simple elastic model suggests that these normal faults may have formed during gravitational collapse of the miocene topographic front between india and tibet in this interpretation gravitational collapse occurred by southward motion relative to india and tibet of a wedge of crustal rocks bounded above by gently north dipping normal faults and below by thrust faults that probably dip north north south extension produced in this way is probably confined to upper crustal levels only and does not reflect regional extension of the entire lithosphere

platform sedimentation and collapse in a carbonate dominated margin of a foreland basin jaca basin eocene southern pyrenees the eocene jaca basin is a foreland basin with well exposed carbonate platforms in the distal margin this margin underwent alternating periods of stable platform growth and platform drowning periods of drowning were accompanied by large scale collapses with generation of shelf edge truncations and resedimentation of carbonate megabreccias into a terrigenous turbiditic trough these features caused a stepped retreat of the platforms and are related to episodic variations of tectonic loading in the hinterland and correlative flexural bending of the distal basin

age of crustal melting and leucogranite formation from u pb zircon and monazite dating in the western himalaya zanskar india new u pb data from leucogranites in the high himalayan slab in the western himalaya of zanskar reveal that crustal melting occurred at 21 19 5 ma and that anatexis occurred along the himalaya at least from kashmir zanskar to eastern nepal at approx 24 19 5 ma high u monazites from leucogranitic melt pods in migmatites within the 35 km wide sillimanite k feldspar zone at the deepest structural levels exposed umasi la have u pb ages of 20 6 19 5 ma higher level migmatitic melt pods from shafat in the suru valley also contain magmatic monazites with u pb ages of 20 8 0 3 ma zircons from the leucogranites contain an approx 460 ma inherited component as do some umasi la monazites showing that the protoliths were at least ordovician in age

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

a 2000 year lipid biomarker record preserved in a stalagmite from north west scotland previous studies on lipid biomarkers preserved in chinese stalagmites have indicated that ratios of low molecular weight lmw to high molecular weight hmw n alkanes n alkan 2 ones n alkanols and n alkanoic acids can be used as an index of vegetation versus microbial organic matter input to the system and by extension a marker of climatic changes with increases in the proportion of lmw compounds coinciding with colder periods here we test whether this hypothesis is equally applicable to a different geographical region north west scotland by examining a stalagmite record of the past 200 years and a wider range of lipid markers we also test the applicability of other lipid proxies in this context including the use of n alkane ratios to interpret vegetation changes and unsaturated alkanoic acid ratios as climatic indicators the results show that lipid proxies preserved in stalagmites and especially those related to vegetation are potentially extremely useful in palaeoenvironmental research of particular value is the use of c27 c31n alkane ratios as a proxy for vegetation change clearly indicating variations between herbaceous and arboreal cover this proxy has now been successfully applied to samples from diverse environments and can be considered sufficiently robust to be of use in analysing future stalagmite records it will be of particular value in areas where reliable pollen records are not available as is often the case with deeper cave deposits however the division between lmw and hmw aliphatic compounds is not a clear cut case of microbial versus plant activity with the changes in lmw compounds relating more closely to those in their hmw analogues than in specific bacterial biomarkers the use of unsaturated alkanoic acid ratios here gives conflicting results with the observed variation through time depending on the isomer measured the discrepancies between the findings of this study and previous work are likely to be due to the varying controls on the lipids original organic matter input and compound degradation which in turn will be affected by whether the main climatic limiting factor on the soil is temperature or precipitation this suggests that lipid proxies preserved in stalagmites must be interpreted with care particularly in the case of bacterial compounds which may be derived from within the cave or from the soil however many of these issues can be resolved by the use of multi proxy studies copyright 2011 john wiley sons ltd

zanskar shear zone northeast southwest extension within the higher himalayas ladakh india a complete geologic section through the northwestern himalayas is well exposed in ladakh india the collision between the indian shield and the tibetan platform caused large scale intracrustal thrusting and piling up of the himalayan nappes this compressional event was accompanied by prograde regional metamorphism the metamorphism ranges from low grade anchimetamorphism in the indus suture zone in the northeast to upper amphibolite grade in the higher himalaya tectonic unit in the southwest in the zanskar area a well exposed and morphologically prominent shear zone 2 25 to 6 75 km wide can be followed from the northwest to the southeast for at least 80 km in contrast to the main compressional tectonics this shear zone indicates an extensional event within the higher himalaya tectonic unit the zanskar shear zone involves granitic rocks leucogranites of miocene age and various metasediments and in general separates the late precambrian early cambrian sedimentary sequence phe formation from the underlying crystalline basement zanskar crystalline unit a normal sense of shear has been determined by using asymmetric macroscopic and microscopic structures such as pegmatite boudins feldspar augen and crystallographic fabrics the metamorphic isograds are very close within this shear zone as a result of shear deformation a gradual transition from upper amphibolite to lower greenschist facies occurs within 200 m movement in this zone occurred late in the metamorphic history under greenschist or lower metamorphic conditions the minimum horizontal extension and vertical displacement are on the order of 16 and 19 km respectively

timing of prograde metamorphism in the zanskar himalaya the timing of the prograde metamorphism of continental crust buried during the collision of india and eurasia is of importance to our understanding of the mechanics of mountain building and crustal metamorphism our knowledge of the himalaya indicates that continental collision at 55 50 ma culminated in crustal melting and leucogranitic magmatism at 24 18 ma however the timing of events in the intervening 30 m y is poorly understood here we present sm nd isotope analyses of garnets from the zanskar himalaya that also preserve information on crustal and orogenic evolution during that period the prograde p t t paths indicate that heating and burial from 6 to 10 kbar continued until at least 25 30 ma and imply peak temperatures 700 c close to those necessary to cause the crustal melting in the himalaya at ca 20 ma without a requirement for additional heat sources such as shear heating on major crustal shear zones the persistence of high temperatures as late as 20 ma in the himalaya may be related to postcollisional thrusting south of the suture zone and within the indian plate at 40 35 ma

detrital zircon fission track ages from the lower cenozoic sediments nw himalayan foreland basin clues for exhumation and denudation of the himalaya during the india asia collision detrital zircon fission track ft ages from the lower cenozoic sub himalayan foreland basin reflect the progressive effects of crustal thickening and exhumation on the himalayan source rocks as a consequence of the india asia collision the oldest stratum the transgressive marine paleocene eocene subathu formation 57 41 5 ma contains ca 50 ma detrital zircon p1 peak which was derived from the indus tsangpo suture zone and the ladakh batholith of the asian plate a dominant 302 4 21 9 ma peak with a few 520 ma grains in this formation has been derived by erosion of the zircon partial annealing zone zpaz of 240 180 c as the first imprint of the collision this zone affected the himalayan proterozoic basement and its tethyan sedimentary cover since the detritus in the subathu has been derived both from the indian and asian plates the possible suturing of these plates took place during the subathu sedimentation a sudden change in the provenance is recorded in the detrital zircon ft cooling ages in the oligo miocene dagshai and kasauli formations which have dominant 30 and 25 ma p1 peaks respectively we interpret a distinct unconformity spanning 10 m y between the subathu and dagshai formations since ca 30 ma molassic sedimentation coincides with shifting of the source rocks to the himalayan metamorphic belt this belt has sequentially undergone three distinct cooling and exhumation pulses after the ultrahigh pressure high pressure uhp hp metamorphism 53 50 ma in the extreme north and two widespread m1 and m2 metamorphisms 40 30 and 25 15 ma in the middle parts these events appear to be largely responsible for the deposition of the ca 30 ma zircon himalayan peak and ca 25 and 15 ma young himalayan peaks respectively the latter appears within the lower siwalik subgroup 13 11 ma during the lower siwalik deposition pre himalayan peaks gradually decrease with the intensification of the himalayan events in source rocks in spite of uninterrupted fluvial sedimentation in the dagshai kasauli lower siwalik sequences since 30 ma breaks of 5 7 m y in the zircon ft ages reveal pulsative cooling and exhumation in the well identified source areas although cooling and exhumation of the himalayan source rocks remained almost uniform during the eocene source heterogeneity is reflected in fluvial sedimentation since 37 ma from pakistan to nepal in response to the india asia collision

a new approach to detecting vegetation and land use change using high resolution lipid biomarker records in stalagmites a hundred year stalagmite lipid biomarker record from mechara southeastern ethiopia is presented the record has been recovered at a 10 yr temporal resolution marking the first time this has been achieved in stalagmite biomarker work and providing the first opportunity to investigate the relationship between stalagmite lipid records and hydrological transport lags a vital issue in interpreting palaeoenvironmental signals preserved plant derived n alkanes and n alkanols show clear changes in composition over time relating to known land use changes in the area particularly the expansion of agriculture in the early twentieth century the level of environmental detail provided by this technique combined with the long term chronological framework offered by stalagmites holds significant promise for the investigation of early human environments and their associated climatic and anthropogenic controls

simultaneous miocene extension and shortening in the himalayan orogen the south tibetan detachment system separates the high grade metamorphic core of the himalayan orogen from its weakly metamorphosed suprastructure it is thought to have developed in response to differences in gravitational potential energy produced by crustal thickening across the mountain front geochronologic data from the rongbuk valley north of qomolangma mount everest in southern tibet demonstrate that at least one segment of the detachment system was active between 19 and 22 million years ago an interval characterized by large scale crustal thickening at lower structural levels these data suggest that decoupling between an extending upper crust and a converging lower crust was an important aspect of himalayan tectonics in miocene time

isotopic preservation of himalayan tibetan uplift denudation and climatic histories of two molasse deposits two distinctive molasse deposits within the indo asian collision zone have been investigated to help understand the post oligocene evolution of the himalaya and southern tibetan plateau the siwalik group predominantly fluvial sandstones and siltstones is widespread throughout the foothills of the himalaya from pakistan to eastern india paleomagnetic analysis of a measured section in the bakiya khola southeastern nepal constrains depositional ages t dep to between 10 8 and 4 9 ma the average accumulation rate during this interval was 0 4 0 5 mm yr 40 ar 39 ar dating of 126 detrital k feldspars from nine horizons in the bakiya khola section t dep 8 25 to 2 2 ma provide snapshots in time of the cooling ages exposed at the earth s surface in this drainage basin the minimum age in the spectra from seven of the nine horizons averages only 3 m y older than t dep indicating exceptionally rapid unroofing in the himalaya throughout that interval half of the grains fro

detection of inherited monazite in the manaslu leucogranite by 208pb232th ion microprobe dating crystallization age and tectonic implications abstract although leucogranites are among the least petrologically variable of all igneous rocks ironically they are among the most difficult to reliably date the high himalayan leucogranites have been the subject of numerous geochronological investigations because of their interrelationship with the most significant tectonic features of that mountain belt for a variety of reasons linked to the minimum melt composition of these leucogranites these dating studies have not been entirely successful we report results of a new ion microprobe dating method based on the decay of 232 th to 208 pb in monazite that has directly revealed the presence of inherited pb in monazite from the manalsu granite casting doubt on its previously accepted age monazite ages obtained from this leucogranite yield two distinct populations a large number of ages with a normal distribution and mean age of 22 4 0 5 ma 2 s e that we interpret to be the crystallization age and a smaller inherited fraction with an age of ca 600 ma because formation of the granite is thought to be related to slip on the main central thrust both this date and a second less precise result from a structurally similar pluton near mt everest indicate that the main central thrust was active in the interval 24 22 ma but do not constrain its initiation together with crosscutting relationships these data require that movement on the north himalayan fault occurred prior to 22 ma at both locations

bedrock incision rock uplift and threshold hillslopes in the northwestern himalayas the topography of tectonically active mountain ranges reflects a poorly understood competition between bedrock uplift and erosion dating of abandoned river cut surfaces in the northwestern himalayas reveals that the indus river incises through the bedrock at extremely high rates 2 12 mm yr 1 in the surrounding mountains the average angles of hillslopes are steep and essentially independent of erosion rate suggesting control by a common threshold process in this rapidly deforming region an equilibrium is maintained between bedrock uplift and river incision with landsliding allowing hillslopes to adjust efficiently to rapid river down cutting

magmatism and metamorphism in the ladakh himalayas the indus tsangpo suture zone abstract ladakh india provides a complete geological section through the northwestern part of the himalayas from kashmir to tibet within this section the magmatic metamorphic and geotectonic evolution of the northern himalayan orogeny has been studied using petrographic geochemical and isotope analytical techniques the beginning of the himalayan cycle was marked by large basaltic extrusions panjal trap of permian to lower triassic age at the northern margin of the gondwana continent indian shield these continental type tholeiitic basalts were followed by a more alkaline volcanism within the triassic to jurassic lamayuru unit of the gondwana continental margin lower jurassic to cretaceous oceanic crust and sediments ophiolitic melange s s accompany the triassic to cretaceous flysch deposits within the indus tsangpo suture zone the major structural divide between the indian shield high himalaya and the tibetan platform so far no relic of paleozoic oceanic crust has been found subduction of the tethyan oceanic crust during upper jurassic and cretaceous time produced an island arc represented by tholeiitic and calc alkaline volcanic rock series dras volcanics and related intrusives accompanied by volcaniclastic flysch deposits towards the tibetan continental margin subsequent to the subduction of oceanic crust large volumes of calc alkaline plutons trans himalayan or kangdese plutons intruded the tibetan continental margin over a distance of 2000 km and partly the dras island arc in the ladakh region the collision of the indian shield and tibetan platform started during the middle to upper eocene and caused large scale still active intracrustal thrusting as well as the piling up of the himalayan nappes the tectonically highest of these nappes is built up of oceanic crust and huge slices of peridotitic oceanic mantle spongtang klippe in the high himalayas the tectonic activity was accompanied and outlasted by a barrovian type metamorphism that affected triassic sediments of the kashmir nun kun synclinorium up to kyanite staurolite grade and the deeper seated units up to sillimanite grade cooling ages of micas are around 20 m y muscovite and 13 m y biotite towards the indus tsangpo suture zone metamorphism decreases with no obvious discontinuity through greenschist prehnite pumpellyite to zeolite grade remnants of possibly an eo himalayan blueschist metamorphism have been found within thrust zones accompanying ophiolitic melange in the suture zone

a new perspective on the δ13c signal preserved in speleothems using lc irms analysis of bulk organic matter and compound specific stable isotope analysis abstract the analysis of 13 c in speleothem calcite is established as a palaeoenvironmental proxy but records can often be complex to interpret due to multiple controls on the signal here we present a novel palaeoenvironmental application of non purgeable organic carbon npoc 13 c analysis and compound specific isotope analysis csia to speleothems and compare the resultant signals to a conventional calcite 13 c record by accessing the carbon pool held in molecular organic matter we are able for the first time to produce stable isotope records complementary to the co 2 derived signal from the speleothem calcite and begin to identify separate ecological and climatic controls in this sample from north west scotland the calcite 13 c record and the npoc 13 c both show fluctuations at a period of increasing wetness and change from birch woodland to more open peatland the npoc signal having a strong correlation with biomarkers for vegetation change we interpret an inverse correlation between the npoc and co 2 13 c signals as primarily driven by changes in soil conditions impacting upon microbial activity with decreased activity leading to a reduction in 13 c enrichment of the residual organic matter the npoc fraction and an increase in 13 c in the co 2 pool calcite due to a decrease in respired 12 c this opens the way for the application of parallel analyses to distinguish between soil conditions and vegetation parameters as the primary control on a record and highlights the advantage of combining both inorganic and organic geochemical techniques in the palaeoenvironmental interpretation of stable carbon isotopic records

organic proxies in speleothems new developments advantages and limitations abstract research into organic matter in speleothems has progressed recently to encompass new analytical approaches and applications which offer increased potential in areas such as palaeo temperature reconstruction and high resolution palaeo environmental records from the quaternary here we review three major areas of relevance for future work in the field the origin transport and transformation of the organic matter which is ultimately preserved in speleothems the types of proxies currently available for use or in development and their advantages and issues and the recently developed prospect of high resolution organic matter records derived from the analysis of organic trace elements complexes the continuing extension of work in these research areas offers excellent potential for organic speleothem proxies to grow as a valuable tool in palaeoenvironmental research

sources of glycerol dialkyl glycerol tetraethers gdgts in catchment soils water column and sediments of lake rotsee switzerland implications for the application of gdgt based proxies for lakes abstract we analysed glycerol dialkyl glycerol tetraether gdgt distributions in the water column sediment and catchment soils of the swiss lake rotsee to determine the sources of gdgts in the lake sediment and to determine the implications for gdgt based palaeoclimate proxies the branched gdgt brgdgt distribution in the soils surrounding the lake showed significant heterogeneity which may be partly explained by vegetation cover and soil moisture one group of soils seems to provide the largest contribution of soil derived gdgts to the lake or the distribution of gdgts in these soils is affected by the relatively high soil moisture availability creating lake like conditions and gdgt distributions comparison of gdgt distributions in soils water column and sediments indicated that brgdgts and crenarchaeol in the sediment are partly soil derived but that in situ production in the water column and or sediment also takes place eutrophication seems to affect the distributions of brgdgts by dilution of the supply of soil derived brgdgts to the lake and by changing the degree of in situ production of brgdgts in the water column furthermore the eutrophic conditions in the lake promote methanogenic activity and subsequently cause a contribution of isoprenoid gdgts isogdgts of methanogenic origin to the sediments the aquatic production of gdgts has implications for the reliability of gdgt based proxy results in particular the application of the bit and tex86 indices is hampered by the mixed sources of the gdgts in the lake in contrast global lake specific brgdgt based temperature calibrations resulted in temperature estimates that resemble measured mean annual and summer air temperatures cbt derived ph values agreed well with measured soil and water column values our results demonstrate that understanding the source of gdgts in lake sediments is important for the robust interpretation of palaeoclimate records obtained from downcore proxy applications

deformation of leucogranites of the crystalline main central sheet in southern tibet china abstract towards the top of the main central sheet in southern tibet china leucogranites intrude metamorphic rocks related to rocks of the main central thrust in the himalayas our study shows that the leucogranites suffered a northward shear deformation the significance of this event is discussed in terms of gravity driven decollement of the 10 000 m thick tethyan sedimentary pile over its crystalline basement

composition and sources of lipid compounds in speleothem calcite from southwestern oregon and their paleoenvironmental implications we analyzed speleothem calcite from the oregon caves national monument southwestern oregon to determine the preservation distribution concentrations and sources of aliphatic lipid compounds preserved in the calcite maximum speleothem growth rate occurs during interglaciations and minimum during glacial intervals concentrations of the total lipid compounds range from 0 5 to 12 9 g g 1 they increase at times of low speleothem growth rate suggesting dilution whereas the apparent accumulation rate of lipid compounds tends to be highest during times of fastest speleothem growth rate such increased accumulation generally corresponds to times of warm interglacial climate suggesting either a greater source of organic materials during interglacial times and or greater efficiency of compound capture during more rapid calcite growth aliphatic lipid compounds include homologous n alkanoic acids n alkanols and methyl n alkanoates and sterols with concentrations ranging from 0 3 to 7 8 g g 1 0 4 to 1 1 g g 1 0 5 to 9 6 g g 1 and 0 1 to 2 7 g g 1 respectively minor amounts of branched methyl n alkanoates and dimethyl n alkanedioates are also present the high concentrations of methyl n alkanoates are the result of esterification reactions of free fatty acids in alkaline solutions with high ph values associated with the dripping cave waters the distribution patterns and geochemical parameters and indices indicate that the major sources of the aliphatic lipids involved leaching from higher plants and microbial residues derived from the soil zone above the cave system the estimated percentage of microbial inputs ranged from 42 to 90 of the total lipids and also showed an increase in accumulation during warm climates these well preserved lipid compounds in speleothem calcite could be used as biomarkers for paleoenvironmental study

branched and isoprenoid glycerol dialkyl glycerol tetraethers in soils and lake river sediments in lake biwa basin and implications for mbt cbt proxies abstract we investigated glycerol dialkyl glycerol tetraether gdgt distributions in soils and river lake sediments in the lake biwa basin of central japan in order to understand their source and fate in a terrigenous environment gdgts in 16 soil profiles exhibited significant depth variation at each site branched br gdgts were generally most abundant in the surface litter layer o layer and decreased with depth while the maximum concentration of crenarcheol appeared in the upper soil layer a layer above the maximum concentration of the other isoprenoid iso gdgts the finding is consistent with different microbial communities contributing to the gdgt pools of the subsurface soil sequences the relationship between methylation index of br tetraethers cyclization ratio of br tetraethers mbt cbt and ph mean annual air temperature maat for lake biwa basin soils was consistent with that found in global soil samples the gdgt distributions in surface sediments from the lake differed from those in soils and river sediments in the watershed suggesting that the gdgts were produced in the lake water rather than supplied from the land the cbt for lake sediments from different water depths corresponded to water ph values we thus infer that the cbt for lake sediments may serve as proxy for lake water ph and can be applied to paleoenvironmental reconstruction

40ar 39ar age constraints on deformation and metamorphism in the main central thrust zone and tibetan slab eastern nepal himalaya in eastern nepal structural and petrologic observations suggest that movement on the main central thrust mct the development of an inverted metamorphic sequence and leucogranite plutonism were genetically related samples from across the mct zone and its hanging wall the tibetan slab were collected from four locations in the everest region for 40ar 39ar studies 1 the mct zone 2 the lower tibetan slab 3 the upper tibetan slab away from intrusive rocks and 4 the upper tibetan slab adjacent to and including leucogranitic material within the mct zone muscovite and hornblende yield cooling ages of 12 0 0 2 ma and 20 9 0 2 ma respectively k feldspar gives a minimum age of 8 0 0 2 ma closure temperature tc 220 15 c in the lower tibetan slab a sample from a sheared pegmatite yields muscovite and biotite isochron ages of 7 7 0 4 ma and 7 5 0 6 ma and a k feldspar minimum age of 6 4 0 8 ma tc 225 20 c an adjacent gneiss yields a 9 1 0 2 ma biotite isochron and a k feldspar minimum age of 3 6 0 2 ma tc 210 50 c in the upper tibetan slab samples collected 200 m from visible intrusives yield a biotite isochron age of 20 2 0 2 ma and a complex hornblende age spectrum suggestive of excess argon at the fourth location an augen gneiss a pegmatite and a tourmaline bearing leucogranite all in mutual contact yield indistinguishable mineral ages the average biotite and muscovite isochron ages for these samples are 17 0 1 4 and 16 6 0 2 ma respectively the minimum age for k feldspar from the leucogranite is 15 5 1 8 ma as thermobarometric data from the mct zone in this area suggest synmetamorphic deformation at temperatures of 500 550 c the mct hornblende tc 500 c dates this event at 21 ma diffusion experiments on hornblendes from the mct zone provide data which support a maximum duration of peak metamorphic temperatures of 2 ma biotite ages as old as 20 ma from the upper tibetan slab near leucogranites indicate that leucogranite intrusion was essentially coeval with deformation and metamorphism in the mct zone very young ages in a ductile shear zone in the lower tibetan slab suggest that there has been deformation within the tibetan slab that postdates major movement on the mct

the thermal response of a metamorphic belt to extension constraints from laser ar data on metamorphic micas abstract metamorphic rocks may be exhumed to the surface either by isostatic rebound uplift and erosion or tectonically via thrusting or extension the latter mechanism is particularly important in the himalayas where a large extensional detachment system appears to be responsible for very fast unroofing at 20 ma here we present the results of a laser argon study of micas and quartz aimed at investigating the thermal response of an orogenic belt to such extension the data when combined with existing constraints on the prograde evolution lead to a uniquely complete thermal history for a metamorphic belt laser argon data are reported for quartz and micas from semi pelitic metamorphic rocks from the zanskar himalayas nw india the samples derive from three traverses extending from low grade rocks near the detachment to high grade rocks in the core of the belt most samples demonstrably contain no excess component and the ages of muscovite and biotite show a correlation with distance from the extensional detachment the ages themselves as well as the difference between the muscovite and biotite ages both increase as the detachment is approached muscovite and biotite ages from within the shear zone date deformation associated with extension at 20 25 ma the remaining data are most readily interpreted in terms of early slow cooling of the lower grade rocks near the detachment in response to erosional denudation before the detachment became active rocks in the core of the orogen were still heating at this time later fast cooling of the high grade rocks in the core of the belt ensued when the extensional regime became active simple heat transfer calculations based on the distance of the high grade rocks from the fault and the argon ages of their micas provide further constraints on the timing of extension and suggest that the fault first moved 23 25 ma ago and that it abruptly terminated metamorphism in the core of the metamorphic belt our analysis of the thermal history suggests that cooling and exhumation rates determined from metamorphic belts beneath extensional detachments will often be minima

drip water isotopes in semi arid karst implications for speleothem paleoclimatology abstract we report the results of the first multi year monitoring and modelling study of the isotopic composition of drip waters in a semi arid karst terrane high temporal resolution drip rate monitoring combined with monthly isotope drip water and rainfall sampling at cathedral cave australia demonstrates that drip water discharge to the cave occurs irregularly and only after occasional long duration and high volume rainfall events where the soil moisture deficit and evapotranspiration is overcome all drip waters have a water isotopic composition that is heavier than the weighted mean annual precipitation some fall along the local meteoric water line others trend towards an evaporation water line it is hypothesised that in addition to the initial rainfall composition evaporation of unsaturated zone water as well as the time between infiltration events are the dominant processes that determine infiltration water isotopic composition we test this hypothesis using a soil moisture balance and isotope model our research reports for the first time the potential role of sub surface evaporation in altering drip water isotopic composition and its implications for the interpretation of speleothem o 18 records from arid and semi arid regions

pressure temperature and time constraints on himalayan metamorphism from eastern kashmir and western zanskar himalayan metamorphism in the kashmir and zanskar sector of the high himalaya resulted from thrust and fold related crustal thickening within the indian plate following the collision of india and asia at c 50 ma interbanded metapelites marbles calcareous schists amphibolites and quartzites represent metamorphosed equivalents of the palaeozoic lower mesozoic continental margin rocks granitic rocks include pre collision k feldspar megacrystic and biotite granites and post collision two mica garnet tourmaline granites average pressure temperature conditions of equilibration using the self consistent thermodynamic data set of holland powell 1990 are presented across a 45 km traverse of the eastern kashmir western zanskar high himalaya kyanite is the stable aluminosilicate phase across 35 km outcrop width in the middle of the slab complex microstructures indicate that prograde metamorphism up to kyanite grade and fabric development in the upper structural nappes is early and unrelated to the main central thrust diachronous metamorphism propagated southwards with the overall structural evolution early isograds and thrust fold structures were carried passively in the hanging wall of the main central thrust peak metamorphism based on 40 ar 39 ar hornblende ages occurred pre 30 7 2 0 ma at the top of the slab and in the middle of the slab was pre 22 1 0 ma probably 25 28 ma the lower structural levels in zanskar record peak metamorphic conditions around 700 750 c and 8 kbar reflecting depths of burial of 28 30 km a new younger schistosity which is not present in the higher structural levels was developed under kyanite grade conditions the regional distribution of high temperatures recorded by thermo barometry does not support the concept of additional heat being supplied by frictional heating along the main central thrust or magmatic heat resulting from anatexis exhumation of the himalayan metamorphic rocks was achieved by three major processes erosion as a result of crustal thickening uplift of the rocks along the hangingwall of the main central thrust above a major frontal ramp in the kishtwar window area and extensional unroofing along the footwall of a large scale ne dipping normal fault at upper crustal levels probably synchronous with compression at depth

calibrating the glycerol dialkyl glycerol tetraether temperature signal in speleothems palaeotemperature proxies based on glycerol dialkyl glycerol tetraethers gdgts lipids have been established for marine and lacustrine environments but there has been relatively little study of their application in speleothems in this study we analyse the gdgt content of 33 speleothem samples from 16 different sites around the globe and test whether proxies based on isoprenoid tetraethers tex86 or branched tetraethers mbt cbt are correlated with measured surface and cave mean annual air temperature mat the results show that the tex86 has a strong relationship with measured temperature r2 0 78 standard error of the estimate 2 3 c when calibrated with surface mat furthermore the mbt cbt also showed a significant relationship with temperature r2 0 73 standard error of the estimate 2 7 c when calibrated with surface mat some issues remain requiring future work in particular the development of a larger calibration sample set with measured cave temperature data and the investigation of controls other than temperature on gdgt distribution but overall the results indicate that gdgt based proxies derived from speleothems may be highly viable new methods for reconstructing continental palaeotemperatures

a 40ar 39ar laser probe study of micas from the sesia zone italian alps implications for metamorphic and deformation histories two samples from the eclogite micaschist complex emc and the seconda zona diorito kinzigitica iidk of the sesia zone have been studied using a high spatial resolution laser probe 40ar 39ar technique with the aim of investigating the complexities of argon behaviour in metamorphic rocks and comparing their thermal histories data from a single large phengite grain from the emc show a range of ages from mid jurassic to upper cretaceous these apparent age variations are spatially related to both location within the grain and to intragrain microstructure modelling of the data shows that the profile formed by the diffusion of an excess argon component into the grain parallel to the mica cleavage profile asymmetry is explained by temporal variations in microstructural development enabling excess argon to enter the grain at different times in different places the temperatures of the initiation of deformation and the possible time scales for the deformation can be calculated as a function of cooling rate all estimates suggest deformation at greenschist facies in accord with the observed retrograde mineral assemblage absolute temperature estimates for deformation vary by less than 22 c for different cooling rates of 10 and 30 c ma 1 but vary by 80 c with different estimates of diffusion parameters the duration of deformation was for at least 2 ma at 10 c ma 1 or 0 7 ma at 30 c ma 1 biotites from the iidk sample record a permian to upper cretaceous age range that correlates with grain size the smallest grain sizes yielding the youngest ages this relationship is best explained by a partial resetting of biotites during an alpine thermal event initiated not more than 70 ma ago modelling of these data suggest that the sample never exceeded 300 c during the alpine the profoundly different thermal histories of the two units the emc recrystallized at 550 c whilst the iidk remained below 300 c suggests that they may not have been juxtaposed until much later than the eclogite facies metamorphism

structural evolution and sequence of thrusting in the high himalayan tibetan tethys and indus suture zones of zanskar and ladakh western himalaya reply abstract the timing of motion on major thrusts in the western himalaya shows an extremely complex sequence that spans approximately 70 ma from the latest cretaceous throughout the tertiary three major phases of thrusting can be distinguished the earliest phase t1 is associated with emplacement of tethyan basin thrust sheets lamayuru sediments and spontang ophiolite south and south westwards onto the submerged northern passive margin of india 75 60 ma collision between india and asia occurred at 50 36 ma and was followed immediately by the major phase t2 of crustal shortening involving large scale south and south westward directed thrusting of the complete palaeozoic mesozoic and late tertiary tibetan tethys zone rocks preliminary balanced cross sections show a minimum shortening of 126 km of these rocks across the zanskar range the late collision phase t3 involved re thrusting of the previously stacked pile breaching or leap frog thrusting reversing the earlier stacking order in places and widespread steepening overturning and backthrusting along the whole northern margin of the tibetan tethys zone and throughout the indus suture zone

lipid distribution in a subtropical southern china stalagmite as a record of soil ecosystem response to paleoclimate change abstract lipid extracts from a 61 7 cm long subtropical stalagmite in southern china spanning the period of ca 10 000 21 000 yr ago as constrained by u th dating were analyzed using gas chromatography mass spectrometry the higher plants and microorganisms in the overlying soils contribute a proportion of n alkanes identified in the stalagmite the occurrence of lmw lower molecular weight n alkanols and n alkan 2 ones in the stalagmite was mainly related to the soil microorganisms we suggest that hmw higher molecular weight n alkanols and n alkan 2 ones identified in the stalagmite originate from soil organics and reflect input from contemporary vegetation shifts in the ratio of lmw to hmw n alkanols or n alkan 2 ones indicative of the variation of soil ecosystems e g microbial degradation of organic matter and or the relative abundance of soil microorganisms to higher plants are comparable with the subtropical alkenone sst sea surface temperature record of the same period the similar trends seen in the 13c data and the lipid parameters in this stalagmite imply that the overlying soil ecosystem response to climate might be responsible for the variation of 13c values

occurrence of tetraether lipids in stalagmites implications for sources and gdgt based proxies lipid biomarkers in stalagmites have potential in palaeoenvironmental reconstruction but glycerol dialkyl glycerol tetraethers gdgts in stalagmites have rarely been investigated we report the occurrence of archaeal isoprenoid gdgts and bacterial branched gdgts in heshang cave stalagmites in central china the archaeal component crenarchaeol dominated bacterial branched gdgts in the stalagmites and on the weathered parent rock surface collected inside the cave in contrast the distribution of gdgts in the overlying soil shows that branched gdgts dominated archaeal gdgts hence the majority of archaeal gdgts in stalagmites may be produced by crenarchaeota inhabiting the cave rather than being inherited from the overlying soil bacterial branched gdgt distributions expressed as mbt and cbt indices showed remarkable differences between stalagmite and soil samples implying that most branched gdgts may also be produced in situ in the cave the tex86 or tex86 values were found to increase with more depleted 18o values representing much stronger monsoon and therefore usually higher temperatures in the study region however the mbt cbt index in stalagmites may be influenced by a variety of factors besides palaeotemperature

pressure temperature paths from p t pseudosections and zoned garnets potential limitations and examples from the zanskar himalaya nw india the extraction of p t histories from metamorphic rocks provides a valuable dataset for the elucidation of the tectonic mechanisms for orogeny while continued re equilibration frequently obliterates early information garnet zonation and inclusion assemblages can often surmount this problem the task is more difficult in high variance assemblages or if inclusions are not preserved but one approach is to use pseudosections that are specific to the bulk composition of a given rock in the latter case the compositions and abundances of all the minerals are fixed at a given p t point such that if the effective bulk composition is known the garnet composition alone can be used to reconstruct the history here we explore this approach using examples from the zanskar himalaya nw india pseudosections have been calculated for four pelitic to semipelitic rocks from the zanskar himalaya and have been contoured for garnet composition the calculations adequately model the mineral assemblages in the rocks and predict the presence of chlorite in the early assemblage where chlorite is found as inclusions within garnet moreover the pseudosections successfully model the garnet core compositions with all three independent compositional contours overlapping at a single pressure and temperature this occurs at 550 c and at pressures varying from 3 7 kbar for the four rocks studied we have been less successful however at modelling garnet compositions beyond the cores because fractionation of the effective bulk composition is caused by garnet growth itself however in this case a combination of the pseudosection and conventional thermobarometry using fe ti inclusions and matrix phases allows us to reconstruct the entire p t history the resulting p t paths record burial of 3 5 kbar without significant temperature increase followed by isobaric heating of 50 100 c this evolution is consistent with himalayan collision in the early tertiary but a combination of the p t data presented here and published geochronological data suggests renewed thrusting south of the suture zone in the oligocene in addition the data demonstrate that no extra heat source is required to cause melting of the himalayan crust in the miocene while melting could have occurred both by dehydration during decompression or in the presence of a fluid the lack of garnet resorption does suggest decompression was rapid and followed quickly by cooling this scenario favours melting by decompression

s cl and f degassing as an indicator of volcanic dynamics the 2001 eruption of mount etna 1 the recent eruption of mount etna july 2001 offered the opportunity to analyze magma derived volatiles emitted during pre and syn eruptive phases and to verify whether their composition is affected by changes in volcanic dynamics this paper presents the results of analyses of f cl and s in the volcanic plume collected by filter packs and interprets variations in the composition based on contrasting solubility in magmas a rayleigh type degassing mechanism was used to fit the acquired data and to estimate henry s solubility constant ratios in etnean basalt this model provided insights into the dynamics of the volcano abundances of sulfur and halogens in eruptive plumes may help predict the temporal evolution of an ongoing effusive eruption

dynamics of orogenic wedges and the uplift of high pressure metamorphic rocks subduction accretion complexes can be approximated as wedge shaped continua with a rigid buttress behind and a subducting litho spheric slab beneath thick wedges undergoing prograde metamorphism have a negligible long term yield strength and are likely to exhibit a complex nonlinear viscous rheology such a wedge will tend to deform internally until it reaches a stable configuration in which the gravitational forces generated by the wedge geometry balance the traction exerted on its underside by the subducting slab accretion of material at the wedge front will lengthen the wedge and cause it to shorten internally to regain the stable geometry this shortening will be expressed as late out of sequence thrusting backthrusting and folding conversely underplating of sediment or crustal slices will thicken the wedge which may need to extend internally to regain stability extension will cause listric normal faults that may merge downward into zones of ductile extension continued underplating at depth and compensating extension above provides a mechanism for bringing high p low t metamorphic rocks to upper levels in the rear of the wedge where they are commonly observed many major tectonic boundaries in convergent orogens such as the coast range thrust in the franciscan complex major nappe contacts in the alps and the contact between the nevado filabride and higher betic nappe complexes in the betic cordillera show abrupt increases in metamorphic grade downward across them this is consistent with their origin or reactivation as uplift related extensional structures

new constraints on the age of the manaslu leucogranite evidence for episodic tectonic denudation in the central himalayas the manaslu leucogranite of central nepal transacts one segment of the south tibetan detachment system a major extensional feature that helped to moderate large topographic gradients in the himalayan orogen in middle tertiary time 40 ar 39 ar ages for hornblendes from the northeastern contact aureole of the pluton indicate that intrusion occurred prior to 22 23 ma providing a minimum age for formation of the detachment system in the manaslu region that is at least 2 m y older than previous estimates from other parts of the orogen 40 ar 39 ar mica ages from the aureole similar to previously published mica ages from the upper part of the leucogranite indicate an episode of rapid cooling at 19 16 ma we attribute this cooling event to tectonic denudation of the pluton by movement on structurally higher exten sional faults and we suggest that gravitational collapse of the orogenic front occurred episodically over the late oligocene early miocene interval in the manaslu area

dripwater organic matter and trace element geochemistry in a semi arid karst environment implications for speleothem paleoclimatology a series of four short term infiltration experiments which revealed hydrochemical responses relevant to semi arid karst environments were carried out above cathedral cave wellington new south wales nsw australia dripwater samples were collected at two sites for trace element and organic matter analysis organic matter was characterised using fluorescence and interpreted using a parafac model three components were isolated that represented unprocessed soil derived humic like and fulvic like material processed humic fulvic like material and tryptophan like fluorescence principal component analysis pca performed on the entire dataset comprising trace element concentrations and parafac scores revealed two dominant components that were identified as soil and limestone bedrock the soil component was assigned based on significant contributions from the parafac scores and additionally included ba cu ni and mg the bedrock component included the expected elements of ca mg and sr as well as si the same elemental behaviour was observed in recent stalagmite growth collected from the site our experiments demonstrate that existing paleoclimate interpretations of speleothem mg and sr developed in regions of positive water balance are not readily applicable to water limited environments we provide a new interpretation of trace element signatures unique to speleothems from water limited karst environments

semi arid zone caves evaporation and hydrological controls on δ18o drip water composition and implications for speleothem paleoclimate reconstructions oxygen isotope ratios in speleothems may be affected by external processes that are independent of climate such as karst hydrology and kinetic fractionation consequently there has been a shift towards characterising and understanding these processes through cave monitoring studies particularly focussing on temperate zones where precipitation exceeds evapotranspiration here we investigate oxygen isotope systematics at wellington caves in semi arid se australia where evapotranspiration exceeds precipitation we use a novel d2o isotopic tracer in a series of artificial irrigations supplemented by pre irrigation data comprised four years of drip monitoring and three years of stable isotope analysis of both drip waters and rainfall this study reveals that 1 evaporative processes in the unsaturated zone dominate the isotopic composition of drip waters 2 significant soil zone wetting up is required to overcome soil moisture deficits in order to achieve infiltration which is highly dependent on antecedent hydro climatic conditions 3 lateral flow preferential flow and sorption in the soil zone are important in redistributing subsurface zone water 4 isotopic breakthrough curves suggest clear evidence of piston flow at some drip sites where an older front of water discharged prior to artificial irrigation water and 5 water residence times in a shallow vadose zone 2 m are highly variable and can exceed six months oxygen isotope speleothem records from semi arid regions are therefore more likely to contain archives of alternating paleo aridity and paleo recharge rather than paleo rainfall e g the amount effect or mean annual speleothem forming drip waters will be dominated by evaporative enrichment up to 3 in the context of this study relative to precipitation weighted mean annual rainfall the oxygen isotope variability of such coeval records may further be influenced by flow path and storage in the unsaturated zone that is not only drip specific but also influenced by internal cave climatic conditions which may vary spatially in the cave

evidence for extension in the western alpine orogen the contact between the oceanic piemonte and overlying continental sesia units abstract in the alps and other orogens major tectonic contacts must have been established during convergence and overthrusting what is less clear is how strongly these contacts were modified as the orogen evolved during alpine collision continental crust of the overriding plate the sesia unit is inferred to have been thrust northwest over oceanic material of the piemonte unit both units preserve in parts eclogite facies metamorphism however all structures along this contact in our study area indicate that final movement was southeast directed with no clear evidence of the kinematics of earlier movement these structures include se verging folds se directed shear bands and larger normal faults downthrowing to the southeast it is inferred that there was a se directed shear regime below the contact which although locally buckling and shortening earlier lithological contacts was dominantly extensional with respect to pre existing tectonic layering the lower limit of this shear regime has not been identified although se directed shear is common throughout the upper greenschist facies part of the piemonte unit we show that this shear passes beneath the sesia zone and does not re emerge it is therefore a shear which was net extensional relative both to the modern surface and to the palaeosurface it may have contributed to the unroofing of eclogite facies rocks in the lower part of the piemonte unit although additional timing data are required to clarify this nearby se directed shears buckle and imbricate earlier layering within the piemonte unit these are normally identified as backthrusts yet they do not appear to breach the base of the sesia unit and might merge with the extensional shear even though these structures shorten layering they too could have been extensional relative to the earth s surface the significance of alpine backthrusts should be reappraised in this context this study indicates that hinterland directed extension could have been an important phenomenon during alpine evolution

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

molecular signatures of dissolved organic matter in a tropical karst system karst areas are widespread landforms present on all continents formed by the dissolution of carbonate or evaporite host rock little is known about the composition and nature of dissolved organic matter dom as it moves through karst systems although karst dom has been recognized as important for a range of natural processes microbial communities living in karst systems are some of the most diverse and intriguing on the planet and their metabolism and life cycle can give clues related to the development of a host of different life forms karst areas are also of interest due to their mostly subterranean hydrology and the repercussions of these processes on local carbon cycles we illustrate some of the processes acting on dom in karst waters through the analysis of soil drip and cave pool waters at the tropical site of yok balum cave in southern belize water samples were analyzed using ultra high resolution electrospray ionization fourier transform ion cyclotron resonance mass spectrometry esi ft icr ms a technique that enables the resolution of single molecular formulae within a dom spectrum we perform multivariate statistics to detect trends in the data and identify provenance of detected molecular components in addition to karst waters four aliquots of a powdered stalagmite sample from the same cave system are analyzed our results show a clear gradient between the soil and the cave system we hypothesize that both sorption on mineral surfaces and microbial reworking are responsible for the observed trend in dom composition the stalagmite extracts show an anomalous dom pattern which may be due to a variety of factors including microbial activity on the stalagmite surface and different affinities of compounds to incorporation in the carbonate the goal of this study was to follow the molecular transformations of dom on its journey from the surface to the cave and to provide a molecular basis for the establishment of stalagmite dom proxies in karst systems

australian dust deposits modern processes and the quaternary record abstract dust raising and transport are common and important processes in australia today the aridity of the australian continent and high climatic variability result in widespread dust raising in the arid and semi arid areas and transport to the humid margins and surrounding oceans the supply of erodible particles appears to be the greatest limitation on total flux of transported dust dust raising is greatest in the lake eyre basin including the simpson desert and murray darling basin where internal drainage renews supplies of fine particles to the arid zone in the west and northwest dust entrainment is low despite considerable aridity the marine record of dust flux shows at least a threefold increase in dust flux compared with the holocene in the last glacial maximum in both tropical and temperate australia driven by weakened australian monsoon rains and drier westerly circulation respectively despite the widespread confirmation of aeolian dust deposits in southeastern and southwestern australia dated or quantified records are extremely rare the dominant model of australian dust deposits the clay rich parna is shown to be poorly substantiated while modern and ancient dust deposits examined in detail are shown to bear a strong similarity to conventional definitions of loess