a 4500 year proxy climate record from peatlands in the north of ireland the identification of widespread summer drought phases abstract mid to late holocene high resolution testate amoebae derived water table reconstructions from two peatlands in the north of ireland are presented the proxy climate records are dated and correlated using a combination of ams 14 c dating spheroidal carbonaceous particles and tephrochronology the reconstructions start prior to the hekla 4 tephra isochron 2395 2279 bc and thus span the last 4500 years the records are compiled by the process of tuning within chronological errors standardisation and stacking comparisons are made to existing palaeoclimate records from peatlands in northern britain and ireland and the compiled lake level record for mid latitude europe four coherent dry phases are identified in the records at ca 1150 800 bc 320 bc ad 150 ad 250 470 and ad 1850 2000 recent research has shown that peat derived water table reconstructions reflect summer water deficit and therefore the dry phases are interpreted as periods with a higher frequency and or greater magnitudes of summer drought these drought phases occur during periods of relatively low 14 c production which may add support to the hypothesis of persistent solar forcing of climate change during the holocene any relationship with the north atlantic stacked drift ice record is less clear

growth and deformation of the ladakh batholith northwest himalayas implications for timing of continental collision and origin of calc alkaline batholiths abstract the calc alkaline ladakh batholith nw himalayas was dated to constrain the timing of continental collision and subsequent deformation batholith growth ended when collision disrupted subduction of the tethyan oceanic lithosphere and thus the youngest magmatic pulse indirectly dates the collision both u pb ages on zircons from three samples of the ladakh batholith and k ar from one subvolcanic dike sample were determined magmatic activity near leh the capital of ladakh occurred between 70 and 50 ma with the last major magmatic pulse crystallizing at ca documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand tex

structure of the north indian continental margin in the ladakh zanskar himalayas implications for the timing of obduction of the spontang ophiolite india asia collision and deformation events in the himalaya the collision of india and asia can be defined as a process that started with the closing of the tethyan ocean that during mesozoic and early tertiary times separated the two continental plates following initial contact of indian and asian continental crust the indian plate continued its northward drift into asia a process which continues to this day in the ladakh zanskar himalaya the youngest marine sediments both in the indus suture zone and along the northern continental margin of india are lowermost eocene nummulitic limestones dated at similar 54 ma along the north indian shelf margin southwest facing folded palaeocene lower eocene shallow marine limestones unconformably overlie highly deformed mesozoic shelf carbonates and allochthonous upper cretaceous shales indicating an initial deformation event during the latest cretaceous early palaeocene corresponding with the timing of obduction of the spontang ophiolite onto the indian margin it is suggested here that all the ophiolites from oman along western pakistan bela muslim bagh zhob and waziristan to the spontang and amlang la ophiolites in the himalaya were obducted during the late cretaceous and earliest palaeocene prior to the closing of tethys

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

miocene burial and exhumation of the india asia collision zone in southern tibet response to slab dynamics and erosion the india asia collision zone in southern tibet preserves a record of geodynamic and erosional processes following intercontinental collision apatite fission track and zircon and apatite u th he data from the oligocene miocene kailas formation within the india asia collision zone show a synchronous cooling signal at 17 1 ma which is younger than the ca 26 21 ma depositional age of the kailas formation constrained by u pb and 40 ar 39 ar geochronology and requires heating burial after ca 21 ma and subsequent rapid exhumation data from the gangdese batholith underlying the kailas formation also indicate miocene exhumation the thermal history of the kailas formation is consistent with rapid subsidence during a short lived phase of early miocene extension followed by uplift and exhumation driven by rollback and northward underthrusting of the indian plate respectively significant removal of material from the india asia collision zone was likely facilitated by efficient incision of the paleo indus river and paleo yarlung river in response to drainage reorganization and or intensification of the asian monsoon

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

sedimentology petrography and tectonic significance of the shelf flysch and molasse clastic deposits across the indus suture zone ladakh nw india abstract in the ladakh area of india a passive triassic to lower cretaceous continental margin is indicated by indian shield derived clastics on the shelf and atlantic type turbidites off the continental margin mid cretaceous initiation of ocean closing is reflected in pacific type flysch and associated island are volcanics which were initially emplaced over the northern indian continental margin in late cretaceous times resulting in the formation of a fore deep in which flysch and minor continental molasse accumulated briefly during the late cretaceous these transient uplifts were however rapidly destroyed for by the latest cretaceous to latest palaeocene uniform carbonate sediments were being laid down over the area with the early eocene the development of a second fore deep this time filled with very thick flysch and molasse sediment indicates a major uplift of the northern indian margin which we attribute to the development of an andean type magmatic arc on the northern edge of the indian plate uplift and molasse sedimentation in this fore deep continued through the oligocene and miocene when the collision of india and asia caused extensive deformation of all the sequences and the shift of molasse sedimentation southwards to the himalaya foothills and indo gangetic plain

new holocene tephras and a proxy climate record from a blanket mire in northern skye scotland four holocene tephras of icelandic origin have been identified and geochemically characterised from a water shedding blanket peat sequence on the trotternish ridge isle of skye scotland geochemical characterisation of the shards propose the glen garry tephra to be present a tephra layer of hekla origin incorporating shards from hekla 4 as well as two new tephras dated by interpolation from a radiocarbon based chronology to ca 830 cal yr bp and ca 2340 cal yr bp the new historic tephra has an ambiguous geochemistry and therefore has not been correlated with other known icelandic historic tephras the new prehistoric tephra is suggested as originating from the snaefellsj okull volcano in northwest iceland and forms an important stratigraphical marker in this holocene sequence a proxy climate record has been derived from humification analyses of the peat which compares well with other regional palaeoclimatic reconstructions as well as enabling correlations based on tephra geochemical linkages between sites and climatic records at precise times in the past

a multiproxy approach to reconstructing surface wetness changes and prehistoric bog bursts in a raised mire system at derryville bog co tipperary ireland multiproxy analyses comprising peat stratigraphy testate amoebae pollen and humification analyses from four profiles across a complex raised mire system at derryville bog co tipperary ireland are used to demonstrate the surface wetness changes covering the period cal bc 1500 to cal ad 1000 with special reference to a series of bog bursts identified within the stratigraphic record comparison of the proxies reveals varying levels and forms of response to the bursts depending on the size of the burst and the relative location of the site and reinforces the necessity for such detailed studies in reconstructing the full palaeohydrological history of large and complex sites because of the heavily cut over nature of the bog the availability of extensive sections from which peat stratigraphic data can be obtained also reinforces the inherent weakness in relying on coring data when trying to understand the complex structure of such large systems

environmental indifference a critique of environmentally deterministic theories of peatland archaeological site construction in ireland abstract climate change whether gradual or sudden has frequently been invoked as a causal factor to explain many aspects of cultural change during the prehistoric and early historic periods critiquing such theories has often proven difficult not least because of the imprecise dating of many aspects of the palaeoclimate or archaeological records and the difficulties of merging the two strands of research here we consider one example of the archaeological record peatland site construction in ireland which has previously been interpreted in terms of social response to climate change and examine whether close scrutiny of the archaeological and palaeoenvironmental records upholds the climatically deterministic hypotheses we evaluate evidence for phasing in the temporal distribution of trackways and related sites in irish peatlands of which more than 3500 examples have been recorded through the examination of 350 dendrochronological and 14 c dates from these structures the role of climate change in influencing when such sites were constructed is assessed by comparing visually and statistically the frequency of sites over the last 4500 years with well dated multiproxy climate reconstructions from irish peatlands we demonstrate that national patterns of peatland activity exist that indicate that the construction of sites in bogs was neither a constant nor random phenomenon phases of activity i e periods in which the number of structures increased as well as the lulls that separate them show no consistent correlation with periods of wetter or drier conditions on the bogs suggesting that the impetus for the start or cessation of such activity was not climatically determined we propose that trigger s for peatland site construction in ireland must instead also be sought within the wider contemporary social background perhaps not surprisingly a comparison with archaeological and palynological evidence shows that peatland activity tends to occur at times of more expansive settlement and land use suggesting that the bogs were used when the landscape was being more widely occupied interestingly the lulls in peatland site construction coincide with transitional points between nominal archaeological phases typically defined on the basis of their material culture implying that there may indeed have been a cultural discontinuity at these times

unroofing the ladakh batholith constraints from autochthonous molasse of the indus basin nw himalaya the indus molasse records orogenic sedimentation associated with uplift and erosion of the southern margin of asia in the course of ongoing india eurasia collision detailed field investigation clarifies the nature and extent of the depositional contact between this molasse and the underlying basement units we report the first dataset on detrital zircon u pb ages hf isotopes and apatite u pb ages for the autochthonous molasse in the indus suture zone a latest oligocene depositional age is proposed on the basis of the youngest detrital zircon u pb age peak and is consistent with published biostratigraphic data multiple provenance indicators suggest exclusively northerly derivation with no input from india in the lowermost parts of the section the results provide constraints on the uplift and erosion history of the ladakh range following the initial india asia collision supplementary material method description sample locations figures s1 and s2 and tables s1 to s3 are available at https doi org 10 6084 m9 figshare c 4858848

cenozoic low temperature cooling history of the northern tethyan himalaya in zedang se tibet and its implications abstract major structures and climatic change during the cenozoic especially miocene interacted to shape the giant tibetan plateau whose formation was triggered by convergence of indian and asian plates in this work we report a low temperature thermochronology data set from the northern tethyan himalaya and indus yarlung suture zone in the zedang area where structures are defined by two parallel thrusts the zhongba gyantse thrust to the south and great counter thrust to the north eighteen samples from the region constrain their low temperature cooling and exhumation histories and further elucidate the evolution of the southern tibetan plateau thermal history modelling reveals eocene and miocene cooling episodes based on the temporal and spatial patterns eocene cooling is probably linked to crustal thickening resulting in the eocene anatexis in the northern tethyan himalaya the rapid pronounced cooling episode between ca 20 ma and 15 ma in the luobusha area reflects the activity of the great counter thrust gct the ca 14 10 ma cooling event of the yardoi dome can probably be linked to rapid erosional denudation during that period and pronounced cooling commencing in the middle miocene was probably caused by incision of branches of the yarlung zangbo river a further cooling episode commencing in late miocene time ca 5 ma in luobusha area and yardoi dome may reflect initial activity of the cona graben cutting through the region

origin of indus ophiolite hosted ophicarbonate veins isotopic evidence of mixing between seawater and continental crust derived fluid during neo tethys closure abstract ophicarbonates are found in ophiolite associated peridotites and bear signature of fluid rock interaction either on ocean floor or during ophiolite emplacement the occurrence of ophicarbonate veins hosted by ultramafic rocks of the indus ophiolite nidar valley ladakh himalaya is interpreted within the context of serpentinization of the allochthonous cretaceous upper mantle section during uplift of the himalaya orogen mixed dolomite calcite obtained from two veins show carbon isotope ratios consistent with an origin from bicarbonate dominated fluid and inconsistent with incorporation of atmospheric carbon dioxide in subaerial contact with high ph waters of serpentinization strontium isotope ratio of 0 711452 0 712041 are consistent with serpentinization subsequently to emplacement of the ophiolite and by interaction with cretaceous seawater mixed with continental crust derived fluid during neo tethys closure the predominance of lizardite and chrysotile in ophicarbonate veins as documented by raman spectra also supports a low temperature serpentinization during ophiolite emplacement the presence of hydrocarbon peaks in fluid inclusions in serpentinized olivine suggests that some of the dissolved inorganic carbon reacted with hydrogen released through oxidation of iron the ophicarbonates and serpentines in peridotite of indus ophiolite bear signature of a paleo environment for fischer tropsch reactions during the last phase of neo tethys closure

frictional strength and wear rate of carbonate faults during high velocity steady state sliding article history we ran an extensive series of shear experiments to test the effect of shear velocity and normal stress on wear rate and frictional strength the experiments were conducted on three types of carbonate samples with a rotary shear apparatus on solid ring shaped rock samples that slipped for displacements up to tens of meters at slip velocity of v 0 002 0 96 m s and normal stress n 0 25 6 9m pa the analysis reveals that during steady state stage the values of wear rate and frictional strength depend on both slip velocity and normal stress the wear rates at low slip velocity show linear relations to the normal stress archard s model however at high velocity v 0 5m s the wear rates are independent of the normal stress and may vanish at the highest velocity and normal stress of the present experiments the steady state friction coefficient correlates best with the experimental power density shear stress slip velocity we recognized three friction regimes high 0 8a t low power density low 0 3 at high power density and a transition regime of fast drop of friction coefficient as the power density increases from 0 03 to 0 3 mw m 2 runs of low power density high friction displayed fault surfaces covered with fine grained gouge whereas runs of high power density low friction displayed shiny smooth fault surfaces we interpret the observed intensity variations of wear rate and frictional strength as indicating a brittle to ductile transition associated with frictional heating

replicated proxy climate signals over the last 2000 yr from two distant uk peat bogs new evidence for regional palaeoclimate teleconnections ombrotrophic peat is an established source of proxy climate data but previous records have been produced by different methods and have been difficult to compare high resolution plant macrofossil analysis has been applied to a lowland raised bog at fallahogy northern ireland and a montane blanket bog moine mhor in the cairngorms scotland although the bogs are 300 km apart and differ floristically the results demonstrate parallel responses to climatic forcing especially that of the little ice age this approach provides a powerful tool for reconstructing proxy climate records wherever suitable peat deposits exist in contrast to the ocean and ice core records these proxies are from a terrestrial source and related to climate changes on land over most of the holocene

geological evidence against large scale pre holocene offsets along the karakoram fault implications for the limited extrusion of the tibetan plateau two end member models proposed to accommodate the convergence between india and asia north of the himalaya are 1 homogeneous crustal thickening of the tibetan plateau and 2 continental escape or extrusion of tibet and southeast asia away from the indenting indian plate foremost among the arguments supporting the latter would be large scale 1000 km offsets and high present day slip rates along the major strike slip faults bounding the postulated extruding crust notably the altyn tagh fault along the northern margin of tibet and the karakoram fault along the sw margin satellite photographic interpretation and field mapping in the karakoram mountains in pakistan the nubra siachen area of north ladakh and the pamirs in xinjiang show that although the karakoram fault is extremely active today geological offsets along the right lateral fault are probably less than 120 km the 21 0 5 ma baltoro monzogranite leucogranite batholith has been rotated clockwise about a vertical axis 35 40 into nw se alignment parallel with the karakoram fault east of the siachen glacier with a maximum offset of 90 km across the fault the bangong shyok suture zone similarly has a dextral offset of 85 km the course of the indus river which was antecedent to the rise of the ladakh karakoram and himalayan ranges has been offset dextrally by 120 km south of pangong lake if present day slip rates approximately 32 mm yr avouac and tapponnier 1993 are correct only 4 ma are required to obtain a 120 km offset there is no geological evidence for any larger scale pre holocene offsets and it is suggested that the karakoram fault cannot have accommodated major eastward lateral motion of tibetan crust the fault has also exerted little or no influence on surface topographic uplift cutting obliquely across the highest peaks of the karakoram dextral motion along the central part of the karakoram fault has been transferred in the north to the rangkul murghab and karasu transpressional faults in the central pamir north of tashkurgan the karakoram fault shows mainly normal motion around the kongur and mustagh ata gneiss domes metamorphic core complexes and the extensional muji graben minor dextral displacement has occurred along the shiquanhe fault but this motion cannot be linked to the jiale fault of east tibet the southern end of the karakoram fault merges with the indus yarlung suture zone near mount kailas and does not cut across the himalaya the lack of large scale geological offsets along the karakoram fault together with its very recent initiation 5 or 4 ma suggests that it is related to the pliocene quaternary northward indentation of the pamir and not to any long term extrusion of tibetan crust following the indian collision

the climate of scotland over the last 5000 years inferred from multiproxy peatland records inter site correlations and regional variability the mid to late holocene climates of most of scotland have been reconstructed from seven peat bogs located across north south and east west geographical and climatological gradients the main techniques used for palaeoclimatic reconstruction were plant macrofossil colorimetric humification and testate amoebae analyses which were supported by a radiocarbon based chronology aided by markers such as tephra isochrons and recent rises in pine pollen and in spheroidal carbonaceous particles scps field stratigraphy was undertaken at each site in order to show that the changes detected within the peat profiles were replicable proxy climate records were reconstructed using detrended correspondence analysis dca of the plant macrofossil data and a mean water table depth transfer function on the testate amoebae data these reconstructions coupled with the humification data were standardised for each site and used to produce a composite record of bog surface wetness bsw from each site the results show coherent wet and dry phases over the last 5000 years and suggest regional differences in climate across scotland specifically between northern and southern scotland distinct climatic cycles are identified all of which record a millennial scale periodicity which can be correlated with previously identified marine and ice core holocene cycles the key role of the macrofossil remains of sphagnum imbricatum a taxon now extinct on many sites is discussed in relation to the identified climatic shifts

a 5500 year proxy climate and vegetation record from blanket mire at talla moss borders scotland a monolith of peat taken from an upland blanket mire at talla moss southern scotland was sub jected to peat humification and pollen analyses to produce both a proxy climate record and a vegetational history covering the last 5500 years while the peat showed little visible stratigraphy with no intimation of major peat humification changes colorimetric data indicate a markedly oscillatory climate record which is apparently largely independent of or out of phase with major vegetational changes the raw data imply particular wet shifts in climate at c 3455 bp c 2600 bp c 1930 bp c 1095 bp with a markedly wet or cool and wet episode commencing at c 540 bp these are central age estimates and should not be regarded as precise dates for the inferred climate shifts other wet shifts apparently date from c 3070 bp c 2265 bp and c 1700 bp although the first of these corresponds with pollen evidence for significant prehistoric human activity in the locality spectral analysis of the peat h

spatial variability of tephra and carbon accumulation in a holocene peatland abstract microscopic tephra layers cryptotephras represent important age equivalent stratigraphic markers utilised in many palaeoenvironmental reconstructions when used in conjunction with proximal records of volcanic activity they can also provide information about volcanic ash cloud fallout and frequency however the spatial distributions of tephra layers can be discontinuous even within the same region understanding the deposition and post depositional redistribution of tephra is vital if we are to use cryptotephras as records of ash cloud occurrence and chronostratigraphic markers the discrete nature of tephra layers also allows for detailed study into processes of deposition and reworking which affect many palaeoenvironmental proxy records we undertook a multi core study in order to examine the historical tephrostratigraphy of a raised peatland in northern ireland three tephra layers originating from iceland hekla 1947 hekla 1845 and hekla 1510 are present in 14 of the 15 cores analysed this suggests that in areas not influenced by snowfall or anthropogenic disturbance at the time of tephra delivery the presence or absence of a tephra layer is generally consistent across a peatland of this type however tephra shard counts per unit area vary by an order of magnitude between cores these intra site differences may confound the interpretation of shard counts from single cores as records of regional ash cloud mass density bootstrap resampling analysis suggests that total shard counts from multiple cores are required in order to make a reliable estimate of median shard counts for a site the presence of three historical tephras in 14 cores enables a spatio temporal analysis of the long term apparent rate of carbon accumulation larca in the peatland substantial spatial and temporal variations in larca are identified over the last 450 years this high variability needs to be taken into account when designing studies of peatland carbon accumulation

mesozoic deep water slope rise sedimentation and volcanism along the north indian passive margin evidence from the karamba complex indus suture zone western ladakh himalaya abstract mesozoic deep water sedimentary and basic volcanogenic rocks defined as the karamba complex are exposed within the indus suture zone of western ladakh n india the karamba complex originated as part of the north indian passive margin in its entirety and does not include exotic melange or accreted oceanic units as recently suggested the complex preserves younger more distal equivalents relative to more proximal deep water slope lamayuru complex and shelf zanskar successions of the north indian passive margin the karamba complex is mainly inverted youngs to the nnw and includes many outcrop scale folds that face nnw the complex was initially emplaced onto the zanskar shelf as three main thrust slices probably in the latest cretaceous and later inverted faulted and sheared during mid late tertiary nw backthrusting that accompanied uplift of the high himalaya sedimentation in the karamba complex began in the mid late triassic with mainly siliciclastic turbidites derived from the indian basement together with redeposited limestones and minor basic volcanics mixed radiolarian sediments siliciclastic turbidites and redeposited shelf derived calciturbidites accumulated in early mid jurassic accompanied by eruption of alkaline volcanic rocks mainly in the mid jurassic the probable cause of the jurassic volcanism was a pulse of crustal extension along the continent ocean transition zone triggered by late stage rifting of india from gondwana as a precursor to its northward drift quartzose sandstone turbidites accumulated on the upper slope in the early cretaceous whereas sedimentation on the lower slope rise was pelagic marked by depositional hiatuses and sediment redeposition during the late cretaceous a switch to mainly calcareous pelagic deposition took place interspersed with radiolarian accumulation on the lower slope rise initial thrust emplacement onto the zanskar shelf in the latest cretaceous is suggested by the absence of post upper cretaceous sediments within the karamba complex

solar forcing of climatic change during the mid holocene indications from raised bogs in the netherlands two cores of mid holocene raised bog deposits from the netherlands were 14 c wiggle match dated 14 c as a proxy for changes in solar activity is validated this paper adds to the increasing body of evidence that solar variability forced climatic changes during the holocene 14 c wiggle match dating mid holocene wet shifts

centennial scale climate change in ireland during the holocene we examine mid to late holocene centennial scale climate variability in ireland using proxy data from peatlands lakes and a speleothem a high degree of between record variability is apparent in the proxy data and significant chronological uncertainties are present however tephra layers provide a robust tool for correlation and improve the chronological precision of the records although we can find no statistically significant coherence in the dataset as a whole a selection of high quality peatland water table reconstructions co vary more than would be expected by chance alone a locally weighted regression model with bootstrapping can be used to construct a best estimate palaeoclimatic reconstruction from these datasets visual comparison and cross wavelet analysis of peatland water table compilations from ireland and northern britain show that there are some periods of coherence between these records some terrestrial palaeoclimatic changes in ireland appear to coincide with changes in the north atlantic thermohaline circulation and solar activity however these relationships are inconsistent and may be obscured by chronological uncertainties we conclude by suggesting an agenda for future holocene climate research in ireland

a delayed climatic response to solar forcing at 2800 cal bp multiproxy evidence from three irish peatlands multiproxy palaeohydrological records from three raised bogs in northern ireland indicate that a major shift to wetter cooler climatic conditions postdated the rapid decrease in solar activity at 2800 cal bp by 100 years this event is bracketed by two wiggle match radiocarbon dated cryptotephra layers in each profile enabling a high degree of chronological precision these replicated data corroborate previous findings based on irish peat humification profiles and may indicate spatial complexity in the climatic response to solar activity between oceanic and continental areas

frictional melt and seismic slip 1 frictional melt is implied in a variety of processes such as seismic slip ice skating and meteorite combustion a steady state can be reached when melt is continuously produced and extruded from the sliding interface as shown recently in a number of laboratory rock friction experiments a thin low viscosity high temperature melt layer is formed resulting in low shear resistance a theoretical solution describing the coupling of shear heating thermal diffusion and extrusion is obtained without imposing a priori the melt thickness the steady state shear traction can be approximated at high slip rates by the theoretical form ss n1 4 a under a normal stress n slip rate v radius of contact area r a is a dimensional normalizing factor and w is a characteristic rate although the model offers a rather simplified view of a complex process the predictions are compatible with experimental observations in particular we consider laboratory simulations of seismic slip on earthquake faults a series of high velocity rotary shear experiments on rocks performed for n in the range 1 20 mpa and slip rates in the range 0 5 2 m s 1 is confronted to the theoretical model the behavior is reasonably well reproduced though the effect of radiation loss taking place in the experiment somewhat alters the data the scaling of friction with n r and v in the presence of melt suggests that extrapolation of laboratory measures to real earth is a highly nonlinear nontrivial exercise

mire development pathways and palaeoclimatic records from a full holocene peat archive at walton moss cumbria england plant macrofossil data have been used to identify the successive mire communities occupying both central and marginal locations in the walton moss peatland complex during the last 10 500 years the reconstructed pathways of mire development indicate that early holocene fen and fen carr communities were succeeded by species indicative of deep mire water tables and oligotrophic conditions the character of the fen bog transition fbt is compared with similar records of peatland development from britain and scandinavia and with independent climate data for the early holocene the pseudohochmoor of central europe is suggested as an approximate modern analogue for the dry pioneer oligotrophic mire type and alternative explanations for its presence are explored the first major increase in ombrotrophic sphagna occurred at c 7800 cal bp overlying sphagnum peats provide a continuous record of climate change inferred from fluctuations in raised mire surface wetness the proxy palaeoclimate record reconstr

exhumation history of the nw indian himalaya revealed by fission track and 40ar 39ar ages new fission track and ar ar geochronological data provide time constraints on the exhumation history of the himalayan nappes in the mandi beas valley tso morari transect of the nw indian himalaya results from this and previous studies suggest that the sw directed north himalayan nappes were emplaced by detachment from the underthrusted upper indian crust by 55 ma and metamorphosed by ca 48 40 ma the nappe stack was subsequently exhumed to shallow upper crustal depths 10 km by 40 30 ma in the tso morari dome northern section of the transect and by 30 20 ma close to frontal thrusts in the baralacha la region from the oligocene to the present exhumation continued slowly metamorphism started in the high himalayan nappe prior to the late oligocene high temperatures and anatexis of the subducting upper indian crust engendered the buoyancy driven ductile detachment and extrusion of the high himalayan nappe in the zone of continental collision late extrusion of the high himalayan nappe started about 26 ma ago accompanied by ductile extensional shearing in the zanskar shear zone in its roof between 22 and 19 ma concomitant with thrusting along the basal main central thrust to the south the northern part of the nappe was then rapidly exhumed to shallow depth 10 km between 20 and 6 ma while its southern front reached this depth at 10 5 ma

cenozoic thermo tectonic evolution of the gangdese batholith constrained by low temperature thermochronology abstract gangdese batholith in the southern lhasa block is a key location for exploring the tibetan plateau uplift and exhumation history we present the new low temperature thermochronological data from two north south traverses in the central gangdese batholith to reveal their cooling histories and corresponding controls zircon fission track ages show prominent clusters ranging from 23 7 to 51 6 ma apatite fission track ages from 9 4 to 36 9 ma apatite u th he ages between 9 5 and 12 3 ma and one zircon u th he age around 77 8 ma these new data and thermal modeling in combination with the regional geological data suggest that the distinct parts of gangdese batholith underwent different cooling histories resulted from various dynamic mechanisms the late eocene early oligocene exhumation of northern gangdese batholith coeval with the magmatic gap might be triggered by crust thickening followed by the breakoff of neotethyan slab while this stage of exhumation in southern gangdese batholith cannot be clearly elucidated probably because the most of plutonic rocks with the information of this cooling event were eroded away since then the northern gangdese batholith experienced a slow and stable exhumation while the southern gangdese batholith underwent two more stages of exhumation the late oligocene early miocene rapid cooling might be a response to denudation caused by the gangdese thrust or related to the regional uplift and exhumation in extensional background by the early miocene the rapid exhumation was associated with localized river incision or intensification of asian monsoon or north south normal fault

the detrital record of orogenesis a review of approaches and techniques used in the himalayan sedimentary basins the sediment archive of material eroded from an active tectonic region and stored in adjacent basins can provide a valuable record of hinterland tectonism especially when information in the source region itself is obscured by later metamorphism or removed by tectonism or erosion using the sediment record to document tectonism is a well established approach but more recently there has been a burgeoning of the number of isotopic techniques which can be applied to detrital material in particular single grain analyses thus the scope for application of detrital studies to a number of different tectonic problems has widened considerably in this review the example of sediments eroded from the himalayan orogen and preserved in the suture zone basin foreland basin remnant ocean basins and deep sea fans is used to illustrate the approach techniques as diverse as petrography heavy mineral xrf and sr nd studies single grain dating by ar ar u pb and fission track methodologies and single grain sm nd and pb isotopic analyses are described the paper documents how the sediment record can be used to determine the thermal and tectonic evolution of the orogen constrain mechanisms of continental deformation exhumation rates and palaeodrainage

preslip and cascade processes initiating laboratory stick slip recent modeling studies have explored whether earthquakes begin with a large aseismic nucleation process or initiate dynamically from the rapid growth of a smaller instability in a cascade up process to explore such a case in the laboratory we study the initiation of dynamic rupture stick slip of a smooth saw cut fault in a 76 mm diameter cylindrical granite laboratory sample at 40 120 mpa confining pressure we use a high dynamic range recording system to directly compare the seismic waves radiated during the stick slip event to those radiated from tiny m 6 discrete seismic events commonly known as acoustic emissions aes that occur in the seconds prior to each large stick slip the seismic moments focal mechanisms locations and timing of the aes all contribute to our understanding of their mechanics and provide us with information about the stick slip nucleation process in a sequence of 10 stick slips the first few microseconds of the signals recorded from stick slip instabilities are nearly indistinguishable from those of premonitory aes in this sense it appears that each stick slip begins as an ae event that rapidly 20 s grows about 2 orders of magnitude in linear dimension and ruptures the entire 150 mm length of the simulated fault we also measure accelerating fault slip in the final seconds before stick slip we estimate that this slip is at least 98 aseismic and that it both weakens the fault and produces aes that will eventually cascade up to initiate the larger dynamic rupture

strong velocity weakening and powder lubrication of simulated carbonate faults at seismic slip rates 1 high velocity friction tests were conducted on solid and hollow cylinders of carrara calcite marble dolomite marble silicate bearing calcite marble and calcite gouge to investigate the strength of carbonate faults during seismic slip the experiments performed at normal stresses of 0 6 14 7 mpa slip rates of 0 03 1 60 m s and room temperature in a rotary shear friction testing machine yielded an extraordinarily low steady state friction coefficient 0 1 at slip rates of 1 1 1 2 m s the slip weakening distance of 4 28 m became shorter at higher normal stress or frictional work rate strong velocity weakening was observed not only in steady state but also in nonsteady state friction while the slip rate was changing thus slip deceleration was accompanied by fault strength recovery large rapid temperature rises in narrow shear localization zones less than a few micrometers induced carbonate decomposition such as the breakdown of calcite into aggregates of cao nanograins and co2 in carrara marble scanning electron microscope observation revealed that the shear localization zone in the highly porous decomposition product was a layer of scattered small grains mostly 1 m in diameter these microstructures and the measured high permeability 10 14 m2 of the decomposed marble indicate that the dominant weakening mechanism in our experiments was possibly powder lubrication powder rheology at high slip rates is not yet well understood but the frictional behavior of nanograins appears to be strongly velocity dependent if decarbonation occurs during seismic slip in natural carbonate faults powder lubrication may make the faults slippery even under fluid drained conditions

constraints to the timing of india eurasia collision a re evaluation of evidence from the indus basin sedimentary rocks of the indus tsangpo suture zone ladakh india deposited within the indus tsangpo suture zone the cenozoic indus basin sedimentary rocks have been interpreted to hold evidence that may constrain the timing of india eurasia collision a conclusion challenged by data presented here the eurasian derived 50 8 51 ma chogdo formation was previously considered to overlie indian plate marine sedimentary rocks in sedimentary contact thus constraining the timing of collision as having occurred by this time using isotopic analysis u pb dating on detrital zircons ar ar dating on detrital white mica sm nd analyses on detrital apatite sandstone and conglomerate petrography mudstone geochemistry facies analysis and geological mapping to characterize and correlate the formations of the indus basin sedimentary rocks we review the nature of these contacts and the identification and correlation of the formations our results reveal that previously interpreted stratigraphic contacts identifying chogdo formation unconformably overlying indian plate sedimentary rocks are incorrect rather we suggest that the inaccuracy of previous interpretations is most likely a result of formation misidentification and thus cannot be used to constrain the timing of india asia collision

exhumation history of eastern ladakh revealed by 40ar 39ar and fission track ages the indus river tso morari transect nw himalaya fission track and 40 ar 39 ar ages place time constraints on the exhumation of the north himalayan nappe stack the indus suture zone and molasse and the transhimalayan batholith in eastern ladakh nw india results from this and previous studies on a north south transect passing near tso morari lake suggest that the sw directed north himalayan nappe stack comprising the mata tetraogal and tso morari nappes was emplaced and metamorphosed by c 50 45 ma and exhumed to moderately shallow depths c 10 km by c 45 40 ma from the mid eocene to the present exhumation continued at a steady and slow rate except for the root zone of the tso morari nappe which cooled faster than the rest of the nappe stack rapid cooling occurred at c 20 ma and is linked to brittle deformation along the normal ribil zildat fault concomitant with extrusion of the crystalline nappe in the south data from the indus molasse suggest that sediments were still being deposited during the miocene

the performance of single and multi proxy transfer functions testate amoebae bryophytes vascular plants for reconstructing mire surface wetness and ph peatlands are widely exploited archives of paleoenvironmental change we developed and compared multiple transfer functions to infer peatland depth to the water table dwt and ph based on testate amoeba percentages or presence absence bryophyte presence absence and vascular plant presence absence data from sub alpine peatlands in the se swiss alps in order to 1 compare the performance of single proxy vs multi proxy models and 2 assess the performance of presence absence models bootstrapping cross validation showing the best performing single proxy transfer functions for both dwt and ph were those based on bryophytes the best performing transfer functions overall for dwt were those based on combined testate amoebae percentages bryophytes and vascular plants and for ph those based on testate amoebae and bryophytes the comparison of dwt and ph inferred from testate amoeba percentages and presence absence data showed similar general patterns but differences in the magnitude and timing of some shifts these results show new directions for paleoenvironmental research 1 suggesting that it is possible to build good performing transfer functions using presence absence data although with some loss of accuracy and 2 supporting the idea that multi proxy inference models may improve paleoecological reconstruction the performance of multi proxy and single proxy transfer functions should be further compared in paleoecological data

gangdese culmination model oligocene miocene duplexing along the india asia suture zone lazi region southern tibet u s national science foundation continental dynamics program ear 1008527 u s national science foundation instrumentation and facilities program ear 1338583 to the arizona laserchron center china national science foundation 41490610 geological society of america student research grant

changes in solar activity and holocene climatic shifts derived from 14c wiggle match dated peat deposits closely spaced sequences of accelerator mass spectrometer ams 14 c dates of peat deposits display century scale wiggles which can be e tted to the radiocarbon calibration curve by wiggle matching such sequences high precision calendar age chronologiescan be generated which show that changes in mire surface wetness during the bronze age iron age transition c 850 cal bc and the little ice age wolf sporer maunder and dalton minima occurred during periods of suddenly increasing atmospheric concentration of 14 c replicate evidence from peat based proxy climate indicators in northwest europe suggest these changes in climate may have been driven by temporary declines of solar activity carbon accumulation rates of two raised peat bogs in the uk and denmark record low values during the little ice age which ree ects reduced primary productivity of the peat forming vegetation during these periods of climatic deterioration

cretaceous tertiary carbonate platform evolution and the age of the india asia collision along the ladakh himalaya northwest india abstract the india asia collision resulted in the formation and uplift of the himalaya and the enhanced uplift of the tibetan plateau the transition from marine to continental facies within the indus yarlung tsangpo suture zone and along the northern margin of the indian plate provides the most accurate method of dating the closure of the tethys ocean separating the indian and asian plates other indirect methods of dating the collision such as paleomagnetism dating the uhp metamorphism along the north margin of india dating the youngest subduction related granites along the southern margin of asia and dating the postorogenic indus molasse group deposits within the suture zone cannot provide such a precise or reliable age of collision ophiolite obduction onto the indian passive margin occurred during the latest cretaceous and predated initial collision of the two continental plates unconformities occur beneath the late maastrichtian marpo formation and beneath the danian stumpata formation on the

the indus clastics forearc basin sedimentation in the ladakh himalaya india abstract the mid cretaceous to early tertiary clastic sediments of the indus group represent the forearc basin succession of the transhimalayan arc trench system in the late albian to early eocene a shallowing upward megasequence tar turbidites to nummulitic limestones and alluvial to deltaic sediments basgo and temesgam formations were deposited respectively on the southern and northern flanks of the basin clastic petrography points to provenance from the largely undissected volcanic cover of the massif with more important plutonic detritus recorded in the northern alluvial units after collision with the indian passive margin in the early eocene sedimentation in the whole basin was characterized by huge alluvial fans nurla formation and then by lacustrine deposits formed in an intermontane depression nimu formation a rapid change in petrographic and geochemical composition is recorded in post early eocene units with sharp increase in plutonic detritus and trace elements typically associated with ophiolites testifying to the uplift of both arc massif and subduction complex sources after collision with the indian passive margin the petrography of the indus basin clastics and the evolution of detrital modes compare well with volcano plutonic suites deposited in modern and ancient forearc basins the composition of sandstone units contained within the accretionary prism instead suggests provenance from an undissected magmatic arc and deposition in abyssal plain and trench settings nindam volcaniclastic turbidites reworking of arc derived sandstones took place in small basins perched on the accretionary trench slope the asian continental margin of the neotethys ocean was thus an active pacific type arc trench system until the eocene when it collided with india underwent polyphase fold thrust deformation and was finally uplifted several kilometers to form the indus suture zone of the himalayas

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

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

constraints on the collision and the pre collision tectonic configuration between india and asia from detrital geochronology thermochronology and geochemistry studies in the lower indus basin pakistan abstract knowledge of the timing of india asia collision is a fundamental prerequisite for understanding the evolution of the himalayan tibetan orogen and its role in global climate oceanic chemistry and ecological evolution despite much active research the basic pre collision tectonic configuration and the timing of terminal india asia suturing remain debated for example debates regarding when and how the intervening kohistan ladakh arc was sutured with india and asia still remain elusive some models propose the arc collided with asia at about 100 ma with india asia collision at ca 55 ma whilst a newer model proposed the arc s collision with india at 50 ma and subsequently with asia at 40 ma another example is the recent proposition that an oceanic greater india basin separated the tethyan himalaya microcontinent from the remaining indian plate until 20 25 ma with the consumption of this oceanic basin marking the final collision at this time these controversies relate to whether the commonly documented 50 ma contact represents the terminal india asia suturing or the amalgamation between various arcs or microcontinents with india or asia here we present an integrated provenance study of geochronology thermochronology and geochemistry on the late cretaceous pleistocene sediments from the lower indus basin on the indian plate the detrital zircon u pb and fission track data show a reversal in sediment source from a pure indian signature to increasing inputs from the suture zone and the asian plate between the middle paleocene and early oligocene the nd and sr isotopes narrow down this change to 50 ma by revealing input of asian detritus and the establishment of a nd sr isotopic pattern similar to the present day indus fan by 50 ma with no significant variations up section contrary to what might be expected if later major collisions had occurred our isotopic data indicate that greater india was occupied by a fluvial deltaic system analogous to the present day indus and named as the paleo indus which has been transporting asian detritus southward across the suture zone and kohistan ladakh arc since 50 ma suggesting no other ocean basins intervened between india and asia after this time in this region our data require that in the west the india asia collision were accomplished by 50 ma

paleohydrological records from peat profiles and speleothems in sutherland northwest scotland abstract paleohydrological changes during the late holocene are inferred from humification testate amoebae and pollen evidence from three blanket peat profiles in northwest scotland replicate peat humification records from the traligill basin share the same patterns of change for a 600 yr period of overlap between 1800 and 2400 cal yr b p the shared patterns inferred from samples with a resolution of 5 13 yr represent basinwide hydrological changes in a nearby but hydrologically separate area with caves beneath peat the luminescence emission wavelength measured in two speleothem samples correlated with the humification record in the overlying peat this correlation implies that speleothem luminescence emission wavelength depends primarily on decay rates in the soils from which drip waters are derived as long as there is no major change in soil or vegetation the peat and speleothem records from the cave site further correlate with the peat records from the traligill basin taken together the records thus represent a regional climatic signal peaks in surface wetness replicated in two or more records occur at ca 2300 2090 2030 1820 1600 and 1440 cal yr b p further peaks occur at 800 570 and 115 cal yr b p in the humification and stalagmite records that extend to the present day correlative changes have been observed not only in other peat records from scotland but also in ice accumulation at gisp2 these further correlations imply that precipitation regimes in scotland and greenland were in phase during the late holocene

a sensitive high resolution record of late holocene climatic change from a raised bog in northern england proxy climatic data in the form of plant macrofossils have been analysed from a 5 m core from bolton fell moss cumbria uk detailed analysis of peat from the upper 50 cm of this core is used to demonstrate a strong correlation between changes in the relative proportion of taxa and known climatic changes over the last 1000 years the record of changes in bog vegetation contained within the peat profile is used to reconstruct changes in bog surface wetness for the latter half of the holocene as bog surface wetness is directly controlled by the prevailing climatic conditions this reconstruction can be viewed as a proxy climate record twelve radiocarbon age estimates on the 5m core suggest that between 50 and 500 cm peat accumulated at a relatively constant rate of 12 4 yr cm 1 the regular sampling intervals thus provide a time series of past bog surface wetness spectral analyses of this series indicates that wetness changes are cyclic with a ca 800 year periodicity

geochemical and isotopic constraints on the age and origin of the nidar ophiolitic complex ladakh india implications for the neo tethyan subduction along the indus suture zone abstract the nidar ophiolite complex is exposed within the indus suture zone in eastern ladakh india the suture zone is considered to represent remnant neo tethyan ocean that closed via subduction as the indian plate moved northward with respect to the asian plate the two plates ultimately collided during the middle eocene the nidar ophiolite complex comprises a sequence of ultra mafic rocks at the base gabbroic rocks in the middle and volcano sedimentary assemblage on the top earlier studies considered the nidar ophiolite complex to represent an oceanic floor sequence based on lithological assemblage however present study based on new mineral and whole rock geochemical and isotopic data on bulk rocks and mineral separates indicate their generation and emplacement in an intra oceanic subduction environment the plutonic and volcanic rocks have nearly flat to slightly depleted rare earth element ree patterns the gabbroic rocks in particular show strong positive sr and eu anomalies in their ree and spidergram patterns probably indicating plagioclase accumulation depletion in high field strength elements hfse in the spidergram patterns may be related to stabilization of phases retaining the hfse in the subducting slab and or fractional crystallization of titano magnetite phases the high radiogenic nd and low radiogenic sr isotopic ratios for these rocks exclude any influence of continental material in their genesis implying an intra oceanic environment nine point mineral whole rock sm nd isochron corresponds to an age of 140 32 ma with an initial 143nd 144nd of 0 513835 0 000053 end t 7 4 this age is consistent with the precise early cretaceous age of hauterivian 132 2 to 127 1 6 ma to aptian 121 1 4 to 112 1 1 ma for the overlying volcano sedimentary radiolarian bearing chert sequences based on well preserved radiolarian fossils kojima s ahmad t tanaka t bagati t n mishra m kumar r islam r khanna p p 2001 early cretaceous radiolarians from the indus suture zone ladakh northern india in news of osaka micropaleontologists nom spec vol 12 257 270 and cooling ages of 110 130 ma based on 39ar 40ar for nidar spontang ophiolitic rocks maheo g berttrand h guillot s villa i m keller f capiez p 2004 the south ladakh ophiolites nw himalaya india an intra oceanic tholeiitic arc origin with implications for the closure of the neo tethys chem geol 203 273 303 as these gabbroic and volcanic rocks are interpreted to be arc related the new sm nd age data may indicate that intra ocean subduction in the neo tethyan ocean may have started much before 140 32 ma as this date is interpreted as the age of crystallization of the arc magma present and published age data on the arc magmatic rocks from the indus suture zone may collectively indicate episodic magmatism with increasing maturity of the arc from more basic during 140 32 ma when the arc was immature through intermediate andesitic granodioritic at 100 ma to more felsic rhyolitic dioritic magmatism at 50 45 ma when the indian and the asian plates collided

extended nucleation of the 1999 mw 7 6 izmit earthquake laboratory and theoretical studies suggest that earthquakes are preceded by a phase of developing slip instability in which the fault slips slowly before accelerating to dynamic rupture we report here that one of the best recorded large earthquakes to date the 1999 moment magnitude mw 7 6 izmit turkey earthquake was preceded by a seismic signal of long duration that originated from the hypocenter the signal consisted of a succession of repetitive seismic bursts accelerating with time and increased low frequency seismic noise these observations show that the earthquake was preceded for 44 minutes by a phase of slow slip occurring at the base of the brittle crust this slip accelerated slowly initially and then rapidly accelerated in the 2 minutes preceding the earthquake

replicability and variability of the recent macrofossil and proxy climate record from raised bogs field stratigraphy and macrofossil data from bolton fell moss and walton moss cumbria england replication of results is a basic tenet of science but in palaeoecology this is very time consuming and the signal is subject to noise the derivation of proxy climate signals from ombrotrophic peat was carried out originally using samples from open peat faces where the stratigraphic relationships could be easily observed now that such sections are rare and often degraded there is a need to demonstrate that data can be replicated from core profiles ten short cores taken from two adjacent bogs have been analysed for macrofossils and show a coherent series of changes which are also similar to previous profiles from the same sites it is concluded that variation between profiles is slight and less than observations of present vegetation mosaics might suggest recommendations for a standard approach to fieldwork on raised bogs that emphasises the utility of subfossil pool layers are proposed and the need for a secure chronology is stressed 1998 john wiley sons ltd

india asia convergence insights from burial and exhumation of the xigaze fore arc basin south tibet the composite fore arc syncollisional xigaze basin in south tibet preserves a key record of india asia collision new apatite fission track and zircon u th he data from an n s transect across the preserved fore arc basin sequence near xigaze show a consistent northward late cretaceous to middle miocene younging trend while coexisting apatite u th sm he ages are all miocene corresponding detrital zircon u pb data are also reported for constraining the cretaceous depositional ages of the xigaze basin sequence in the region thermal history modeling indicates that the basin experienced northward propagating episodic exhumation along with a northward migration of the depocenter and a pre existing cenozoic syncollisional basin sequence which had been removed in the southern part fore arc exhumation commenced in the late cretaceous 89 2 ma following transition to a syncollisional basin in the paleocene sedimentation in the central and northern xigaze basin continued until the latest eocene 34 4 ma ongoing folding and thrusting e g great counter thrusts caused by progressive plate convergence during late oligocene early miocene time resulted in regional uplift and considerable basin denudation which fed two fluvial basins along its northern and southern flanks and exposed the basement ophiolite subsequent incision of the yarlung river resulted in miocene cooling in the region different episodes in the exhumation history of the xigaze basin caused by thrusting of an accretionary wedge and ophiolitic basement can be linked to changes in india asia convergence rates and the changing subduction pattern of the indian and neo tethyan slabs

synorogenic morphotectonic evolution of the gangdese batholith south tibet insights from low temperature thermochronology the uplift history of the tibetan plateau remains one of most intriguing and controversial issues in the cenozoic history of our planet and has a significant impact on regional and global climate here we report new low temperature thermochronology apatite and zircon data from the gangdese batholith in southern tibet thermal history modeling of the data show that the batholith experienced a phase of rapid early cenozoic cooling probably associated with exhumation resulting from the initial india asia s collision but possibly also due to postarc volcanic activity in the region the batholith then transitioned to low erosion rates 0 05 mm yr between the middle eocene and early miocene followed by a renewed episode of cooling commencing in the early miocene our results indicate that the gangdese belt as the southern margin of eocene tibetan plateau became plateau like by 45 ma the later cooling episode from early miocene onward can probably be attributed to incision of the ancestral yarlung river system cutting through the gangdese belt by 22 ma at the latest

low temperature thermochronology of the indus basin in central ladakh northwest india implications of miocene pliocene cooling in the india asia collision zone the india asia collision zone in ladakh northwest india records a sequence of tectono thermal events in the interior of the himalayan orogen following the intercontinental collision between india and asia in early cenozoic time we present zircon fission track and zircon and apatite u th he thermochronometric data from the indus basin sedimentary rocks that are exposed along the strike of the collision zone in central ladakh these data reveal a postdepositional miocene pliocene 22 4 ma cooling signal along the india asia collision zone in northwest india our zircon fission track cooling ages indicate that maximum basin temperatures exceeded 200 c but stayed below 280 300 c in the stratigraphically deeper marine and continental strata thermal modeling of zircon and apatite u th he cooling ages suggests postdepositional basin cooling initiated in early miocene time by 22 20 ma occurred throughout the basin across zircon u th he partial retention temperatures from 20 10 ma and continued in the pliocene time until at least 4 ma we attribute the burial of the indus basin to sedimentation and movement along the regional great counter thrust the ensuing miocene pliocene cooling resulted from erosion by the indus river that transects the basin an approximately coeval cooling signal is well documented east of the study area along the collision zone in south tibet our new data provide a regional framework upon which future studies can explore the possible interrelationships between tectonic geodynamic and geomorphologic factors contributing to miocene pliocene cooling along the india asia collision zone from nw india to south tibet

geology of the cenozoic indus basin sedimentary rocks paleoenvironmental interpretation of sedimentation from the western himalaya during the early phases of india eurasia collision this study reassesses the stratigraphy sedimentology and provenance of the indus basin sedimentary rocks deposited within the indus tsangpo suture zone itsz during the early phases of india eurasia collision using field observations biostratigraphy and petrographic and isotopic analyses we create a paleodepositional reconstruction within the paleotectonic setting of the early phases of india eurasia collision we then re examine existing constraints to the timing of india eurasia collision previously interpreted from the earliest occurrence of mixed indian and eurasian derived detritus in the succession from mid cretaceous to early paleocene times the jurutze and sumda formations were deposited within an arc bounded marine basin between the dras and kohistan ladakh island arcs the 51 ma aged deltaic chogdo formation then filled the basin until deposition of the 50 8 49 4 ma aged nummulitic limestone during a marine incursion before continental facies developed in an evolving intermountain basin with the deposition of the paleogene indus group within these systems sediment was sourced from the eurasian margin to the north and was transported southward into the suture zone in this section we see no unequivocal evidence of indian plate input to the sedimentary succession and thus no evidence of mixed indian eurasian derived detritus indicative of india asia collision until the upper stratigraphic horizons of the indus group when facies are representative of an axial northwesterly flowing river system we suggest that the paleo indus river was initiated within the itsz during late oligocene early miocene times sedimentation of the indus group continued until the late miocene

determining the sun s influence on lateglacial and holocene climates a focus on climate response to centennial scale solar forcing at 2800 cal bp abstract the influence of solar variability on the climate of the lateglacial and holocene periods has been the subject of increasing discussion during the last decade in the mid holocene several studies have identified cold wet events that occur at ca 2800 cal bp and a link with a reduction in solar activity inferred from the 14c record has been postulated we present results from a multi proxy study of peat humification plant macrofossils and testate amoebae from a raised bog at glen west northwest ireland that indicate that dry bog surface conditions were experienced in the north of ireland at the time of the solar anomaly starting at 2800 cal bp with the aid of 14c wiggle matching and tephrochronology an abrupt shift to wetter conditions is dated to ca 2700 cal bp coinciding with a 14c maximum but clearly post dating the 2800 cal bp event identified elsewhere in europe we explore the significance of this apparent lag in the irish record considering the possible role of the ocean in generating spatial and temporal complexities in the climate patterns of the north atlantic region we conclude that these complexities are likely to give rise to time transgressive climate responses around the north atlantic that will only be recognised by more critical chronological approaches

multiproxy late holocene peat records from ireland towards a regional palaeoclimate curve two new peat based climate records from ireland covering the late holocene are presented the sequences are dated by a strong chronological framework formed by ams radiocarbon dates and scps three proxy indicators testate amoebae macrofossils and humification have been determined allowing the limitations and strengths of each to be identified and utilised to provide a bog surface wetness bsw record for both sites age depth models take into account the potential for accumulation rates to vary with bog vegetation the records from each site have been used to derive a combined bsw record that displays changes to a wetter cooler climate from ca ad 30 1920 bp ca ad 310 1640 bp ca ad 805 1145 bp ca ad 1040 910 bp and ca ad 1300 650 bp changes follow closely those identified in a northern britain composite bsw record and largely correspond with lake level data in central france suggesting the main changes in water balance were coherent over a large region correspondence with increases in ird and slower iceland scotland overflow water isow suggests that these changes were related to oceanic forcing influencing the track of dominant westerly air flow over ireland copyright 2007 john wiley sons ltd

bog burst in the eastern netherlands triggered by the 2 8 kyr bp climate event the nature and cause of the so called 2 8 kyr bp event have been a subject of much debate peat sequences have provided much of the evidence for this event but the process link between climate and peatland response is not well understood multiproxy high resolution analysis of a core from bargerveen in the eastern netherlands based on pollen non pollen palynomorphs testate amoebae and geochemistry identified an abrupt shift from relatively dry to extremely wet conditions radiocarbon based wiggle match dating wmd and biostratigraphy based on the pollen record show that this shift in local hydrology occurred around 2800 cal yr bp we interpret an erosional hiatus lasting up to 950 years immediately prior to this as the effect of a bog burst after excessive rainfall this phenomenon was not limited to our sampling location but occurred over a large part of the former bargerveen peat at the hiatus contains microfossils that reflect temporary eutrophication as a consequence of local fires and secondary decomposition because of increased drainage after the erosion event our data show how detailed multiproxy analyses can elucidate the past response of peatlands to changing climate and suggest that the climatic change in northwest europe at this time caused major non linear disruption to these ecosystems

high velocity frictional properties of gabbro high velocity friction experiments have been performed on a pair of hollow cylindrical specimens of gabbro initially at room temperature at slip rates from 7 5 mm s to 1 8 m s with total circumferential displacements of 125 to 174 m and at normal stresses to 5 mpa using a rotary shear high speed friction testing machine steady state friction increases slightly with increasing slip rate at slip rates to about 100 mm s velocity strengthening and it decreases markedly with increasing slip rate at higher velocities velocity weakening steady state friction in the velocity weakening regime is lower for the non melting case than the frictional melting case due perhaps to severe thermal fracturing a very large peak friction is always recognized upon the initiation of visible frictional melting presumably owing to the welding of fault surfaces upon the solidification of melt patches frictional properties thus change dramatically with increasing displacement at high velocities and such a non linear effect must be incorporated into the analysis of earthquake initiation processes

erosion in southern tibet shut down at 10 ma due to enhanced rock uplift within the himalaya exhumation of the southern tibetan plateau margin reflects interplay between surface and lithospheric dynamics within the himalaya tibet orogen we report thermochronometric data from a 1 2 km elevation transect within granitoids of the eastern lhasa terrane southern tibet which indicate rapid exhumation exceeding 1 km ma from 17 16 to 12 11 ma followed by very slow exhumation to the present we hypothesize that these changes in exhumation occurred in response to changes in the loci and rate of rock uplift and the resulting southward shift of the main topographic and drainage divides from within the lhasa terrane to their current positions within the himalaya at 17 ma steep erosive drainage networks would have flowed across the himalaya and greater amounts of moisture would have advected into the lhasa terrane to drive large scale erosional exhumation as convergence thickened and widened the himalaya the orographic barrier to precipitation in southern tibet terrane would have strengthened previously documented midcrustal duplexing around 10 ma generated a zone of high rock uplift within the himalaya we use numerical simulations as a conceptual tool to highlight how a zone of high rock uplift could have defeated transverse drainage networks resulting in substantial drainage reorganization when combined with a strengthening orographic barrier to precipitation this drainage reorganization would have driven the sharp reduction in exhumation rate we observe in southern tibet

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

scale dependence of rock friction at high work rate in metre sized rock specimens rock friction starts to decrease at a much smaller work rate than in centimetre sized rock specimens thus demonstrating that rock friction is scale dependent frictional sliding at faults controls the rupture of earthquakes and much effort has gone into the study of the frictional properties of rocks in laboratory experiments this study shows that previously used scaling of results obtained in lab studies investigating the earth s crust didn t accurately take into account the effect of sample size futoshi yamashita et al used metre sized rock specimens not the centimetre sized samples commonly used and demonstrate that friction in the metre size range starts to decrease at a work rate that is an order of magnitude smaller than that of the smaller specimens the authors propose that stress concentrated areas exist in which more gouge materials are produced due to frictional slip resulting in further stress concentrations at these areas as such heterogeneity is common in nature the authors conclude that a natural fault could lose its strength faster than that expected from the properties estimated from small rock samples determination of the frictional properties of rocks is crucial for an understanding of earthquake mechanics because most earthquakes are caused by frictional sliding along faults prior studies using rotary shear apparatus1 2 3 4 5 6 7 8 9 10 11 12 13 revealed a marked decrease in frictional strength which can cause a large stress drop and strong shaking with increasing slip rate and increasing work rate the mechanical work rate per unit area equals the product of the shear stress and the slip rate however those important findings were obtained in experiments using rock specimens with dimensions of only several centimetres which are much smaller than the dimensions of a natural fault of the order of 1 000 metres here we use a large scale biaxial friction apparatus with metre sized rock specimens to investigate scale dependent rock friction the experiments show that rock friction in metre sized rock specimens starts to decrease at a work rate that is one order of magnitude smaller than that in centimetre sized rock specimens mechanical visual and material observations suggest that slip evolved stress heterogeneity on the fault accounts for the difference on the basis of these observations we propose that stress concentrated areas exist in which frictional slip produces more wear materials gouge than in areas outside resulting in further stress concentrations at these areas shear stress on the fault is primarily sustained by stress concentrated areas that undergo a high work rate so those areas should weaken rapidly and cause the macroscopic frictional strength to decrease abruptly to verify this idea we conducted numerical simulations assuming that local friction follows the frictional properties observed on centimetre sized rock specimens the simulations reproduced the macroscopic frictional properties observed on the metre sized rock specimens given that localized stress concentrations commonly occur naturally our results suggest that a natural fault may lose its strength faster than would be expected from the properties estimated from centimetre sized rock samples

a proxy record of late holocene climate change from may moss northeast england quantitative reconstruction of changes in mire surface wetness has been used to reconstruct proxy climate from an upland ombrotrophic blanket mire on the north york moors in northeast england may moss testate amoebae plant macrofossil and humification analyses were carried out for six peat profiles transfer functions are used to generate estimates of water table levels from the testate amoebae stratigraphy which complement the semi quantitative indications of changing surface wetness provided by plant macrofossil and humification analysis 14c dates provide the chronology for the stratigraphy differences were encountered between ams 14c dates on pure sphagnum remains and radiometric dates on bulk peat from the same horizon which perhaps arise from the heterogeneity of peat replicate palaeoecological analysis of adjacent cores identifies consistency within testate amoebae and plant macrofossil stratigraphies and reveals a strong agreement between the water table level proxies the record of hydrological changes at sites across may moss are in synchrony and so climate change is the most likely cause of the moisture fluctuations changes to a wetter or cooler climate were identified cal ad 260 540 ca ad 550 650 cal ad 670 980 ca ad 1350 1450 cal ad 1400 1620 and ca ad 1700 1800 periods with a drier or warmer climate precede all of these wet shifts with particularly dry periods between cal ad 650 860 and 690 980 and between cal ad 1290 1410 and 1400 1620 copyright 2001 john wiley sons ltd

restoration and evolution of the intermontane indus molasse basin ladakh himalaya india abstract collision of the indian plate with the karakorum plate lhasa block during the eocene ca 55 50 ma created predominantly a s or sw verging thrust culmination across the himalaya during the late tertiary two molasse basins existed the siwalik bain formed in the late miocene to present on the indian foreland south of the himalaya and the mid eocene to late miocene indus basin along the indus suture zone north of the high himalaya the indus basin is approximately 2000 km long extending eastwards from ladakh across south tibet a balanced cross section along the zanskar river shows a minimum 36 km shortening in the eocene late miocene molasse and suggests that the minimum basin width was approximately 60 km in ladakh more than 2000 m of post eocene alluvial fan fluvial and fluvio lacustrine sediments accumulated in the ladakh sector with petrographies suggesting derivation mainly from the deeply dissected and uplifted northern granodioritic ladakh batholith aptian eocene with only minor amounts of debris derived from the deformed southern tethyan passive margin palaeocurrents show predominant e w axis parallel sediment transport with subordinate lateral input paths being preserved the indus molasse basin is deformed by numerous post eocene n directed backthrusts many of which cut the entire stratigraphy and therefore were active at least into late tertiary times

melt welt mechanism of extreme weakening of gabbro at seismic slip rates a laboratory study of the frictional properties of the igneous rock gabbro at seismically relevant slip rates suggests that the initial weakening of a fault surface during earthquake rupture may be associated with hotspots and macroscopic streaks of melt which partially unload the rest of the slip interface

the burial and exhumation history of the liuqu conglomerate in the yarlung zangbo suture zone southern tibet insights from clumped isotope thermometry abstract the liuqu conglomerate exposed along the yarlung zangbo suture zone yzsz in southern tibet archives not only the process of the india asia collision but also the exhumation history of the india asia collision zone the burial and exhumation history of the liuqu conglomerate thus could potentially provide clues to the india asia collision and orogeny low temperature thermochronometric data indicate that maximum burial temperatures of the liuqu conglomerate ranged from 80 to 110 c however the exact burial history is not well constrained here we examine the burial conditions of the liuqu conglomerate by applying clumped isotope thermometry to paleosol carbonates extensive microcrystalline recrystallization indicates that the samples have been diagenetically altered during burial moreover the clumped isotope temperatures ranging from 48 to 97 c are clearly above earth surface conditions indicating the original climatic information was overwritten by alteration at higher burial temperatures nevertheless the calculated diagenetic water 18o values represent maximum meteoric water values that can be used to broadly constrain the paleoelevation the highest clumped isotope temperature implies that the maximum burial temperature of the liuqu conglomerate was at least 97 c we conclude that the liuqu conglomerate was buried as deeply as 3 7 4 3 km during the latest paleocene to eocene and then exhumed during the miocene 10 12 ma incision of the paleo yarlung river was likely responsible for erosion and exhumation of the liuqu conglomerate which suggests that the drainage system of paleo yarlung river was similar to that of today and supports the model of outward growth of the tibetan plateau

cenozoic unroofing history of the ladakh batholith western himalaya constrained by thermochronology and numerical modelling abstract the ladakh batholith is part of the transhimalayan plutonic belt which crops out north of the indus suture zone we propose that the exhumation history of the ladakh batholith is linked to the tectonic magmatic and erosion history of the karakoram terrane and sw tibet we present new multiple low temperature thermochronometry data zircon u th he apatite fission track and apatite u th he to gain insight into the cooling history of the ladakh batholith and recognize key periods in the evolution of the region from the indus valley northwards the ages decrease across the batholith for all three thermochronometers applied a model is proposed in which magmatism in the ladakh batholith ceased in the late eocene and initial denudation was driven by topographic uplift caused by collision southward tilting of the batholith occurred in the late palaeogene this tilting resulted in an asymmetric topography with increasing elevation to the north strong erosion occurred in this northern region whereas the southern margin was affected by northwards thrusting of the indus molasse for the first time clear temporal and spatial variations in exhumation rate are identified in this region highlighting why sampling strategy is critical in documenting exhumation changes in active tectonic settings supplementary material sample co ordinates from the ladakh batholith sample preparation and fission track age measurements of apatite grains and grain size dimensions are available at http www geolsoc org uk sup18350

archaeological applications of testate amoebae analyses a case study from derryville co tipperary ireland the value of testate amoebae in the reconstruction of changes in surface wetness from ombrotrophic mires is well known but the potential value of such records in specifically archaeological investigations has not yet been investigated this note describes the analysis of testate amoebae for a sediment sequence from the multi period wetland archaeological site of derryville co tipperary ireland the reconstructed watertable is presented and plotted against the range of dates from excavated archaeological features in the wetland area the data demonstrate a clear association between periods of low watertable and increased anthropogenic activity as reflected by site construction the value of testate amoebae in future integrated archaeological investigations of wetland systems is discussed

rapid early miocene exhumation of the ladakh batholith western himalaya zircon apatite u th he and apatite fission track age data record a rapid cooling event in the ladakh batholith of northwest india ca 22 ma a combination of inverse and forward modeling of the data confirms this qualitative interpretation combining the thermochronometric data with structural evidence we propose that exhumation was due to south directed thrusting of the batholith along a north dipping structure coupled with erosion to bring the rocks to the surface the rapid exhumation recorded in ladakh is contemporaneous with exhumation of the high himalaya this focused surface denudation and structural shortening north of the indus suture zone in early miocene time implies that the actively deforming and eroding himalayan thrust wedge extended farther north than channel flow models currently predict

foreshocks during the nucleation of stick slip instability 1 we report on laboratory experiments which investigate interactions between aseismic slip stress changes and seismicity on a critically stressed fault during the nucleation of stick slip instability we monitor quasi static and dynamic changes in local shear stress and fault slip with arrays of gages deployed along a simulated strike slip fault 2 m long and 0 4 m deep in a saw cut sample of sierra white granite with 14 piezoelectric sensors we simultaneously monitor seismic signals produced during the nucleation phase and subsequent dynamic rupture we observe localized aseismic fault slip in an approximately meter sized zone in the center of the fault while the ends of the fault remain locked clusters of high frequency foreshocks mw 6 5 to 5 0 can occur in this slowly slipping zone 5 50 ms prior to the initiation of dynamic rupture their occurrence appears to be dependent on the rate at which local shear stress is applied to the fault the meter sized nucleation zone is generally consistent with theoretical estimates but source radii of the foreshocks 2 to 70 mm are 1 to 2 orders of magnitude smaller than the theoretical minimum length scale over which earthquake nucleation can occur we propose that frictional stability and the transition between seismic and aseismic slip are modulated by local stressing rate and that fault sections which would typically slip aseismically may radiate seismic waves if they are rapidly stressed fault behavior of this type may provide physical insight into the mechanics of foreshocks tremor repeating earthquake sequences and a minimum earthquake source dimension

the spongtang massif in ladakh nw himalaya an early cretaceous record of spontaneous intra oceanic subduction initiation in the neotethys abstract the spongtang massif is a remnant of neotethyan ocean crust emplaced onto the indian passive margin along the indus yarlung tsangpo suture in the nw himalayan region of ladakh the age tectonic evolution and timing of ophiolite obduction are critical to our understanding of the mechanisms via which entire oceans are formed consumed and partly preserved before the onset of terminal continent continent collisions geochemistry of the gabbro and basaltic units suggest the presence of both morb type and primitive arc related mafic rocks zircons extracted from the spongtang massif gabbros yield u pb shrimp ages of 136 133 ma with initial ehf values of 14 to 16 indicating early cretaceous juvenile depleted mantle sources devoid of contamination by older continental crust previously middle jurassic 177 ma zircon ages were obtained from gabbro and we suggest these represent morb type neotethyan oceanic crust through which a younger intra oceanic island arc spong arc developed in response to subduction initiation during the early cretaceous 136 ma our zircon ages are consistent with early cretaceous ages obtained for radiolarian cherts within the spong arc complex subduction beneath the spong arc continued until its collision with the northern indian continental margin during the early eocene we suggest that the spongtang massif is equivalent to the nearby dras island arc terrane intra oceanic subduction beneath this system was possibly initiated along nne ssw trending transform faults in the neotethyan ocean along which different ages of ocean crust was juxtaposed thereby development of the early cretaceous spong arc is superimposed on the older jurassic spongtang n morb crust the juvenile hf signature indicates the subduction system that spawned the spong island arc was not related to the coeval trans himalayan ladakh gangdese arc that developed along the southern margin of eurasia the age composition and nature of geological relationships with the underlying indian rocks indicate the spong arc was a juvenile intra oceanic terrane that first collided with india before the onset of final continent continent collision therefore final late eocene neotethys closure was between the kohistan ladakh eurasian continental arc and the already inactive indian spongtang margin

granular nanoparticles lubricate faults during seismic slip nanoparticles are known to form in narrow slip zones in natural and experimental fault zones but their possible role in dynamic weakening of faults during seismic slip remains almost unexplored we conducted friction experiments on periclase mgo nanoparticles 50 nm in average size at rates as high as 1 3 m s 1 a typical speed of seismic slip the nanoparticles were used as the initial gouge to avoid complexities arising from comminution and fluid release the dynamic friction decreased with increasing slip rate and the steady state frictional coefficient reduced to as low as 0 1 at a slip rate of 1 3 m s 1 flash heating is not effective for nanoparticles and we propose that development of slickensides and dominant operation of nanoparticle rolling cause such a weakening nanoparticle lubrication appears to be as effective as melt lubrication and thermal pressurization and the formation of nanoparticles in slip zones may be an important fault lubrication process

a high resolution record of mire development and climatic change spanning the late glacial holocene boundary at church moss davenham cheshire england excavations of deposits filling a closed basin within glacial drift at church moss davenham near northwich cheshire england revealed a sequence of late glacial and early holocene sediments analyses of pollen and plant and invertebrate macrofossils were undertaken together with loss on ignition analyses and a programme of ams radiocarbon dating to provide a record of changing biostratigraphy and climatic and ecological regimes the infilling of features identified as frost cracks in the till flooring the basin gave remains that reflected conditions of extreme cold towards the end of the devensian the pollen record from a 3 5 m sequence of peat towards the deepest part of the basin supported by radiocarbon dates shows that organic deposition was initiated during the late glacial interstadial and continued into the early part of the holocene there was some evidence for a cool episode during the interstadial with amelioration prior to the rapid onset of the tundra conditions of the loch lomond stadial following the stadial amelioration was rapid there was evidence from both central and marginal sequences for a mosaic of fen dominated by sedges and often also mosses with short lived small pools through much of the succession change to terrestrial conditions proceeded intermittently probably as a result of subsidence caused by solution of underlying salt bearing strata

evidence for climatic deteriorations associated with the decline of sphagnum imbricatum hornsch ex russ in six ombrotrophic mires from northern england and the scottish borders the decline of sphagnum imbricatum from the peat stratigraphy of six ombrotrophic mires bolton fell moss and walton moss raeburn flow and bell s flow and coom rigg moss and felecia moss has been investigated using colorimetric humification quantitative plant macrofossil and testate amoebae analyses the chronology of each peat profile was determined by radiocarbon assay and pollen land use correlations palaeoclimate reconstructions have been made by linking known documentary historical changes in climate and other proxy climate records to those inferred from the sites investigated in the study region in two of the ombrotrophic mires examined there are wet shifts associated with the decline and local extinction of s imbricatum which are dated to cal ad 1160 1400 raeburn flow and bell s flow in coom rigg moss and felecia moss wet shifts are also associated with the decline and local extinction of s imbricatum between cal ad 1395 1485 the decline of s imbricatum from two other ombrotro

sedimentology of the indus group ladakh northern india implications for the timing of initiation of the palaeo indus river the upper reaches of the indus river form a longitudinal network that drains a large portion of the western himalaya it plays an important role as a sediment routing system feeding the indus delta and submarine fan and has played a controlling role in the denudational history of the western himalaya given the rivers long term significance its timing of initiation remains poorly constrained the facies palaeocurrents and provenance of the post early eocene indus group preserved along the upper reaches of the modern indus reveal a history of fluvial deltaic and deep water sedimentation in an intermontane basin dominated by internal drainage hence the indus group is not considered to represent the deposits of a palaeo indus river as previously thought illite crystallinity values and apatite fission track dating of the indus group suggest that the succession was buried to temperatures of 155 280 c and that unroofing started in early miocene times and proceeded at 0 1 0 4 mm a 1 to the present the youngest sedimentary rocks preserved along the indus basin are early miocene in age from the tectonostratigraphically equivalent deposits around kargil to the west of the study area the transition from sediment accumulation to erosional unroofing in early miocene times coincides with accelerated regional unroofing of the high himalayas to the south and the initiation of the indus delta submarine fan to the west differential uplift between the northward thrusting of the zanskar and indus sedimentary succession against the undeformed ladakh batholith provides a mechanism for post early miocene initiation of a major longitudinal river hence early miocene times is believed to represent the earliest possible age of initiation of the palaeo indus river following this course

a multiproxy climate record from a raised bog in county fermanagh northern ireland a critical examination of the link between bog surface wetness and solar variability a proxy climate record from a raised bog in county fermanagh northern ireland is presented the record spans the interval between 2850 cal yr bc and cal yr ad 1000 and chronological control is achieved through the use of tephrochronology and 14c dating including a wiggle match on one section of the record palaeoclimatic inferences are based on a combination of a testate amoebae derived water table reconstruction peat humification and plant macrofossil analyses this multiproxy approach enables proxy specific effects to be identified major wet shifts are registered in the proxies at ca 1510 cal yr bc 750 cal yr bc and cal yr ad 470 smaller magnitude shifts to wetter conditions are also recorded at ca 380 cal yr bc 150 cal yr bc cal yr ad 180 and cal yr ad 690 it is hypothesised that the wet shifts are not merely local events as they appear to be linked to wider climate deteriorations in northwest europe harmonic analysis of the proxies illustrates statistically significant periodicities of 580 423 373 307 and 265 years that may be related to wider holocene climate cycles this paper illustrates how the timing of climate changes registered in peat profiles records can be precisely constrained using tephrochronology to examine possible climatic responses to solar forcing relying on interpolated chronologies with considerable dating uncertainty must be avoided if the climatic responses to forcing mechanisms are to be fully understood copyright 2007 john wiley sons ltd

multiproxy surface wetness records from replicate cores on an ombrotrophic mire implications for holocene palaeoclimate records ombrotrophic mires can provide records of palaeoclimate over the mid to late holocene in several areas of the world their potential is currently partly limited by difficulties with scaling indices based on plant macrofossils and humification and the need to account for the internal variability of the mire system this paper explores the use of testate amoebae analysis as a third technique and assesses the minimum within site variability by comparing results from two closely spaced cores reconstruction of surface wetness changes was carried out on cores from the centre of an intermediate raised blanket mire coom rigg moss northumberland by analysis of testate amoebae plant macrofossils and humification surface wetness changes were expressed as mean annual water table changes inferred from testate amoebae assemblages two separate indices based on plant macrofossils and percentage transmission of humification extracts comparisons between the proxies suggest good agreement of general trends in sphagnum peats but some differences in monocot and ericaceous peats the magnitude of surface wetness changes also differs within sphagnum peats the records from the separate cores converge over time and replicability between cores is best in the last 1000 yr changes over this period are similar to those shown by estimates based on documentary sources good agreement is obtained between a normalised plant macrofossil index and normalised reconstructed water table values and it is suggested that this approach could form the basis for improved composite multiproxy records from peatlands copyright 1999 john wiley sons ltd