unexposed archean components and complex post archean accretion reworking processes beneath the southern yangtze block revealed by zircon xenocrysts from the paleozoic lamproites south china abstract integrated u pb dating and hf isotope analysis of zircon xenocrysts from the baifen lamproites of the zhenyuan area in the southeastern guizhou province offer a unique glimpse into the evolution of the deep continental crust beneath the southern part of the yangtze block south china a total of 148 zircons with 90 110 concordance yield u pb ages varying from 3458 9 ma to 252 2 ma they generally have high th u ratios 0 3 indicating a magmatic origin the two youngest magmatic zircons give a weighted mean 206pb 238u age of 253 0 2 8 ma which is interpreted as the emplacement age of the host baifen lamproites most zircons with pre eruption ages are xenocrysts derived from the deeper crust of the southern yangtze block they define two major paleoproterozoic age populations at 2 17 ga and 1 8 ga with similar hf model ages tcrust of 2 4 2 8 ga peak at 2 64 ga the oldest zircon has a 207pb 206pb age of 3458 9 ma with ehf t 1 47 and tcrust 3 7 ga this demonstrates the presence of archean crustal components or remnants as old as 3 7 ga beneath the southern yangtze block magmatic events involving significant addition of juvenile mantle derived materials mainly occurred at 2 2 2 1 ga and 2 0 1 8 ga but the latter event also involved reworking of the neoarchean crust and might represent the cratonization of the yangtze continent during the middle paleoproterozoic which could be correlated to the assembly of the columbia supercontinent this segment of the yangtze block became tectonically quiescent until 1 2 ga implying that the crustal stabilization lasted for ca 600 million years a few late mesoproterozoic zircon xenocrysts within the age range 1 3 1 0 ga suggest the occurrence of grenville aged events these neoproterozoic zircon xenocrysts 992 547 ma have a wide range of ehf t values 8 47 to 22 07 consistent with the zircon hf isotopic compositions of widespread coeval igneous rocks in the yangtze block the data show that the yangtze block has undergone important crustal growth and reworking during the neoproterozoic in response to the breakup of the rodinia supercontinent the early middle paleozoic zircon xenocrysts 513 357 ma have negative ehf t values 2 97 to 12 69 and tcrust hf model ages of 1 59 2 27 ga indicating reworking of the precambrian crustal basement without juvenile contributions during the caledonian orogeny the positive ehf t values 13 79 to 0 22 of twelve late paleozoic zircons 284 264 ma with a major age peak at ca 275 ma suggest that the precambrian basement beneath the southern yangtze block experienced an episode of strong rejuvenation during the permian we propose a possible linkage between the baifen lamproite magmatism 284 252 ma and the emeishan flood basalt volcanism

direct determination of the timing of sea level change during termination ii an outcrop within the last interglacial terrace on barbados contains corals that grew during the penultimate deglaciation or termination ii we used combined 230th and231pa dating to determine that they grew 135 8 0 8 thousand years ago indicating that sea level was 18 3 meters below present sea level at the time this suggests that sea level had risen to within 20 of its peak last interglacial value by 136 thousand years ago in conflict with milankovitch theory predictions orbital forcing may have played a role in the deglaciation as may have isostatic adjustments due to large ice sheets other corals in the same outcrop grew during oxygen isotope 18o substage 6e indicating that sea level was 38 5 meters below present sea level about 168 0 thousand years ago when compared to the 18o signal in the benthic v19 30 v19 28 record at that time the coral data extend to the previous glacial cycle the conclusion that deep water temperatures were colder during glacial periods

tentative correlation of pollen records of the last interglacial at grande pile and ribains with marine isotope stages eemian lake deposits in grande pile and ribains france correlate with marine isotope substages mis 5e and 5d as delimited in two pollen bearing deep sea cores off portugal the eemian forests in france lasted for approximately 20 millennia from at least 126 000 to ca 107 000 yr b p oscillatory climate deteriorations began about 115 000 yr ago an intense cold spell affected the region approximately 110 000 yr ago

late pleistocene sea level change in the bahamas from mass spectrometric u series dating of submerged speleothem abstract the dating of sea level events by a method independent of orbital tuning techniques and the marine foraminiferal isotopic record provides a test of both the dating of the marine record and the strength and nature of the relationship between climatic change sea level change and milankovitch cycles dating of fossil corals and submerged speleothem provides such independent information results of thermal ionization mass spectrometric u series dating on layers of flowstone speleothem from lucayan caverns grand bahama island indicate that multiple sea level events have passed through a depth of 10 to 15 m below modern sea level during the last 300 000 years these data are used to constrain the magnitude and timing of sea level fluctuations during the late pleistocene the new sea level curve constructed from these data correlates closely with the marine isotopic record sea level peaks occurred at around 233 215 125 and 100 ka bp there is no evidence at the depth from which this speleothem was retrieved of any high sea stands at 195 or 80 ka corresponding to the foraminiferal 7a and 5a oxygen isotope peaks there is also no evidence of a double rise around the 125 ka 5e peak although such an oscillation could have occurred above 10 m leaving no record in the lucayan caverns speleothem

the vegetation and climate history of the last glacial cycle in a new pollen record from lake fimon southern alpine foreland n italy abstract the sediments of lake fimon n italy contain the first continuous archive of the late pleistocene environmental and climate history of the southern alpine foreland we present here the detailed palynological record of the interval between termination ii and the last glacial maximum the age depth model is obtained by radiocarbon dating in the uppermost part of the record downward we correlated major forest expansion and contraction events to isotopic events in the greenland ice core records via a stepping stone approach involving intermediate correlation to isotopic events dated by tims u th in alpine and apennine stalagmites and to pollen records from marine cores of the iberian margin modelled ages obtained by bayesian analysis of deposition are thoroughly consistent with actual ages with maximum offset of 1700 years sharp expansion of broad leaved temperate forest and of sudden water table rise mark the onset of the last interglacial after a treeless steppe phase at the end of penultimate glaciation this event is actually a two step process which matches the two step rise observed in the isotopic record of the nearby antro del corchia stalagmite respectively dated to 132 5 2 5 and 129 1 5 ka at the interglacial decline mixed oak forests were replaced by oceanic mixed forests the latter persisting further for 7 ka till the end of the eemian succession warm temperate woody species are still abundant at the eemian end corroborating a steep gradient between central europe and the alpine divide at the inception of the last glacial after a stadial phase marked by moderate forest decline a new expansion of warm broad leaved forests interrupted by minor events and followed by mixed oceanic forests can be identified with the north alpine saint germain i the spread of beech during the oceanic phase is a valuable circumalpine marker the subsequent stadial interstadial succession lacking the telocratic oceanic phase is also consistent with the evidence at the north alpine foreland the middle wurmian full glacial is marked by persistence of mixed forests dominated by conifers but with significant lime and other broad leaved species a major arboreal pollen decrease is observed at modelled age of 38 7 0 5 ka larch expansion and last occurrence of lime which has been related to heinrich event 4 the evidence of afforestation persisting south of the alps throughout most of mis 3 contrasts with a boreal and continental landscape known for the northern alpine foreland pointing to a sharp rainfall boundary at the alpine divide and to southern air circulation this is in agreement with the alpine paleoglaciological record and is supported by the pressure and rainfall patterns designed by mesoscale paleoclimate simulations strenghtening the continental high pressure during the full glacial triggered cyclogenesis in the middle latitude eastern europe and orographic rainfall in the eastern alps and the balkanic mountains thus allowing forests development at current sea level altitudes

evidence from u th dating against northern hemisphere forcing of the penultimate deglaciation milankovitch proposed that summer insolation at mid latitudes in the northern hemisphere directly causes the ice age climate cycles1 this would imply that times of ice sheet collapse should correspond to peaks in northern hemisphere june insolation but the penultimate deglaciation has proved controversial because june insolation peaks 127 kyr ago whereas several records of past climate suggest that change may have occurred up to 15 kyr earlier2 3 4 5 6 7 8 there is a clear signature of the penultimate deglaciation in marine oxygen isotope records but dating this event which is significantly before the 14c age range has not been possible here we date the penultimate deglaciation in a record from the bahamas using a new u th isochron technique after the necessary corrections for recoil mobility of 234u and 230th and a small age correction for sediment mixing the midpoint age for the penultimate deglaciation is determined to be 135 2 5 kyr ago this age is consistent with some coral based sea level estimates but it is difficult to reconcile with june northern hemisphere insolation as the trigger for the ice age cycles potential alternative driving mechanisms for the ice age cycles that are consistent with such an early date for the penultimate deglaciation are either the variability of the tropical ocean atmosphere system or changes in atmospheric co2 concentration controlled by a process in the southern hemisphere

open system coral ages reveal persistent suborbital sea level cycles sea level is a sensitive index of global climate that has been linked to earth s orbital variations with a minimum periodicity of about 21 000 years although there is ample evidence for climate oscillations that are too frequent to be explained by orbital forcing suborbital frequency sea level change has been difficult to resolve primarily because of problems with uranium thorium coral dating here we use a new approach that corrects coral ages for the frequently observed open system behavior of uranium series nuclides substantially improving the resolution of sea level reconstruction this curve reveals persistent sea level oscillations that are too frequent to be explained exclusively by orbital forcing

destruction of ancient lower crust through magma underplating beneath jiaodong peninsula north china craton u pb and hf isotopic evidence from granulite xenoliths abstract zircons from granulite xenoliths entrained in a late cretaceous mafic dike in the jiaodong peninsula north china craton ncc show three distinct u pb age populations part of the old zircon grains yield discordant data that project to ages of about 2 4 to 2 5 ga a few grains indicate growth at about 2 0 ga and a third group yield cretaceous ages with peaks at 120 and 90 ma the oldest zircons give hf t dm model ages of 2 6 2 8 ga these results demonstrate the existence of original archean lower crust in the jiaodong region zircons of 2 0 ga have similar hf t dm model ages as the neoarchean paleoproterozoic grains suggesting that these zircons were products of metamorphic recrystallization due to thermal event without juvenile input early cretaceous zircons yield ehf t values of 21 to 12 and late cretaceous zircons large variable ehf t from 4 to 50 these data suggest that magmatic underplating occurred in the neoarchean to earliest proterozoic lower crust of the ncc both in the early and late cretaceous it is suggested that the mesozoic magma underplating which also provided the heat source for the voluminous mesozoic magmatism in the ncc significantly modified the composition of the archean to paleoproterozoic lower crust of the ncc

initial hf isotope compositions in magmatic zircon from early proterozoic rocks from the gawler craton australia a test for zircon model ages abstract we evaluate the validity of age information obtained from two stage hf model ages in zircon multiple isotope investigations of minerals from the kiana granite of the archean sleafordian complex from the southern gawler craton australia reveal a complex geologic evolution of the suite rubidium sr mineral ages define a tectono thermal event at 1673 4 4 2 ma associated with the kimban orogeny id tims u pb ages from single zircons yield an upper concordia intercept at 2348 21 ma which marks the time of magmatic emplacement whole rock nd model ages yield crustal residence ages of 2 8 ga for each single zircon grain the lu hf isotope systematic was determined by solution mc icpms two stage hf model ages for the magmatic zircons vary by as much as 500 myrs depending on the choice of lu hf for the source of the host rock putting further emphasis on the need to constrain the source lu hf of a rock used for model age calculations an average lu hf for mafic crust was assumed for the source reservoir of the rocks to calculate its hf isotope evolution through time which yields zircon model ages of 3 5 ga that coincide with the initial growth episode postulated for the gondwana supercontinent it is demonstrated that two stage zircon model ages deduced from initial hf isotopes can provide important age information for the source of igneous rocks and consequently on important crustal formation events even when conventional geochronologic investigations fail e g due to thermo tectonic overprints or mixing

delamination of eclogitized lower crust control on the crust mantle boundary in the central fennoscandian shield abstract the crustal structure of the central part of the fennoscandian shield is dominated by a high velocity lower crust hvlc vp 7 3 7 5 km s at the depth of 40 63 km in an area of ca 400 km 600 km formed in the palaeoproterozoic svecofennian orogen at 1 91 1 87 ga in the area of the hvlc the moho is deeper than 50 km and attains depths of up to 63 km in eastern finland at the archaean proterozoic boundary zone we suggest that the present moho dates back to late svecofennian time and was determined by delamination of high density eclogitized lower crust after tectonic collisional thickening of crust densities deduced from seismic and gravity data suggest a very small or completely lacking density contrast between lower crust and uppermost mantle new geological evidence from kimberlite hosted garnet xenocrysts supports the presence of a garnet population with compositions in agreement with crustal eclogitic garnets in addition small clinopyroxene garnet mineral aggregates microxenoliths show omphacitic clinopyroxene compositions therefore the presence of eclogites in the high velocity lower crust is implied although the eclogite proportion as estimated from seismic velocity data is only a few percent in the present hvlc with results on near incidence and wide angle seismic studies and geological and geochemical data on heat producing elements we modeled the svecofennian collision and the thermal evolution of the crust to provide temperature constraints for the delamination model the constructed thermal model simulates the genesis of svecofennian synkinematic at 1 89 1 88 ga and postkinematic 1 88 1 87 ga granitoids as well as the general metamorphic grade of the surface rocks and lower crustal xenoliths moreover the narrow distribution of the ages of the svecofennian mafic ultramafic magmatism ca 1 89 1 87 ga dispersed around the hvlc area is explained by the homogeneous warming of the lithosphere the conditions of lower crustal delamination were estimated with a rayleigh taylor convective instability model constrained with lower crustal and upper mantle rheological data delamination of a lower crustal eclogite layer 5 30 km thick takes place in about 7 50 ma if the rock dynamic viscosity is 1 1021 pa s it requires temperatures of 1000 c in the lower crust and upper mantle in the svecofennian crust such temperatures were attained at about 1860 1850 ma i e after the orogenic peak we conclude that the moho of the hvlc area was controlled by delamination of a ca 5 10 km thick layer of high density lowermost crust into the mantle such a density controlled process may have controlled the moho depth also in other proterozoic shield areas

a terrestrial u th dated stable isotope record of the penultimate interglacial abstract here we present the first u series dated stable oxygen isotope record in continental europe that covers the entire tripartite penultimate interglacial i e marine isotope stages 7 5 to 7 1 this record was obtained from a u rich stalagmite from spannagel cave in the austrian alps which is largely devoid of kinetic isotope fractionation effects which comprised previously studied flowstone from this site composed of dense columnar calcite this speleothem apparently grew without significant interruption for ca 50 ka albeit at a very slow rate the age model was established based on 23 individual u th tims dates using a combination of a bayesian approach which includes additional information using stratigraphic constraints and the mixed effect regression model the resulting record shows three prominent maxima in 18 o mis 7 5 7 3 and 7 1 separated by a long earlier and a shorter later cold period mis 7 4 and 7 2 respectively the mid points of the transitions into the three warm phases occurred at 240 3 215 2 and 200 3 ka and the mis 7 6 transition was dated to 190 3 ka the timing of these climate transitions is supported by other samples from the same cave and agrees within analytical uncertainties with u th dated evidence from corals marine aragonitic sediments and submerged stalagmites as well as with orbitally tuned deep sea records good agreement was also found with new speleothem data from china as far as mis 7 1 and 7 5 are concerned whereas mis 7 3 apparently started earlier and mis 7 2 lasted longer than in the alps comparing the european speleothem data with antarctic ice cores reveals obvious differences in age the latter suggesting an earlier start and a generally shorter duration of the three warm episodes in essence this study underscores the great potential of speleothems as accurate and precise chronometers of pleistocene climate change and emphasizes the need for similar studies in other continents including submerged caves in order to improve the imperfect chronological framework of mis 7

quaternary environmental evolution in the south carpathians reconstructed from glaciokarst geomorphology and sedimentary archives abstract the carpathian island type glaciokarst has a great potential of preserving signals of past environments archived in cave deposits like speleothems and clastic infills we present here the geomorphology and structural control of several relict alpine caves and the surrounding glaciated marble karst in the f g ra mountains four truncated and partially unroofed caves remained on the ridge top of mu eteica mountain above the glacial cirque while a ponor cave that developed on the cirque bottom could be related to the last glacial period structural measurements and cave morphology showed that the conduits formed at the intersection of foliation planes and tectonic fractures on the ne sw and nw se directions cave development reflects three speleogenetic stages 1 texture and fabric controlled dissolution and distension 2 structurally controlled breakdown and 3 truncation unroofing and cave infilling with sediments slow diffuse dissolution was typical for the ridge top caves whereas m1 cave developed by pressure flow further we report the first u th speleothem ages related to the evolution of alpine caves and island glaciokarst in the south carpathians during the middle and late pleistocene dating results show a minimum estimated age of 560 ka for the ridge top caves and that speleothem deposition met optimal conditions only during warmer periods largely corresponding to interglacials stable carbon isotope values in speleothems range between 9 96 and 4 11 indicating the presence of plant and soil organic activity at the time of deposition in total five speleothem growth phases were distinguished during the last 560 ka we excavated the sediment infill of a ridge top doline down to a 2 m depth radiocarbon dating revealed that it was deposited during the late holocene and preliminary pollen analysis identified a plant assemblage dominated by grasses using the relationships between karst development glaciation and cave sedimentary archives we present a time slice chronology of alpine landscape evolution at 560 ka 400 ka 330 ka the last glacial period 70 12 ka and the late holocene our geomorphological isotopic and geochronological results also support the existing hypothesis that the south carpathians may have experienced at least two glacial phases during the pleistocene glacial erosion rate during the last glacial period and most likely during the penultimate glaciation averages around 0 6 mm yr 1

u pb and hf isotope analysis of zircons in mafic xenoliths from fuxian kimberlites evolution of the lower crust beneath the north china craton mafic xenoliths from the paleozoic fuxian kimberlites in the north china craton include garnet granulite and minor pyroxene amphibolite metagabbro anorthosite and pyroxenite the formation conditions of the amphibolites are estimated at 745 820 c and 7 6 8 8 kb 25 30 km the granulites probably are derived from greater depths in the lower crust lam icpms u pb dating of zircons from four granulites reveals multiple age populations recording episodes of magmatic intrusion and metamorphic recrystallisation concordant ages and upper intercept ages interpreted as minimum estimates for the time of magmatic crystallisation range from 2 620 to 2 430 ma in three granulites two amphibolites and two metagabbros lower intercept ages represented by near concordant zircons are interpreted as reflecting metamorphic recrystallisation and range from 1 927 to 1 852 ma one granulite contains two metamorphic zircon populations dated at 1 927 55 ma and 600 700 ma separated minerals from one granulite and one amphibolite yield sm nd isochron ages of 1 619 48 ma 143nd 144nd i 0 51078 and 1 716 120 ma 143nd 144nd i 0 51006 respectively these ages are interpreted as recording cooling following metamorphic resetting model ages for both samples are in the range 2 40 2 66 ga lam mc icpms analyses of zircon show a range in 176hf 177hf from 0 28116 to 0 28214 corresponding to a range of ehf from 34 to 12 the relationships between 207pb 206pb age and ehf show that 1 the granulites amphibolites and metagabbro were derived from a depleted mantle source at 2 6 2 75 ga 2 zircons in most samples underwent recrystallisation and pb loss for 100 200 ma after magmatic crystallisation consistent with a residence in the lower crust 3 metamorphic zircons in several samples represent new zircon growth incorporating hf liberated from breakdown of silicates with high lu hf 4 in other samples metamorphic and magmatic zircons have identical 176hf 177hf and the younger ages reflect complete resetting of u pb systems in older zircons the fuxian mafic xenoliths are interpreted as the products of basaltic underplating derived from a depleted mantle source in neoarchean time an important period of continental growth in the north china craton paleoproterozoic metamorphic ages indicate an important tectonic thermal event in the lower crust at 1 8 1 9 ga corresponding to the timing of collision between the eastern and western blocks that led to the final assembly of the north china craton the growth of metamorphic zircon at 600 700 ma may record an asthenospheric upwelling in neoproterozoic time related to uplift and a regional disconformity in the north china craton

modern aragonite formation at near freezing conditions in an alpine cave carnic alps austria abstract aragonite is a common mineral in caves hosted in dolomitic bedrock and in particular in those from warm climate regions it is much less common in cold caves such as in the alps where the vast majority of speleothems consist of low mg calcite here we report the occurrence of modern aragonite at very low temperatures the first of its kind from an alpine cave in the interior part of obstanser eishohle a high alpine cave containing perennial ice in its near entrance zone aragonite forms stalactites and flowstones which coexist with calcite and locally also hydromagnesite precipitation of aragonite occurs at saturation indices between 0 4 and 0 6 at 1 0 0 4 c modern 230th dates of the youngest aragonite deposits demonstrate that aragonite formation is an ongoing process 13c values are high and overlap with those of the host rock a comparison between 18o values of aragonite and drip water showed that modern aragonite formation does not occur at isotopic equilibrium surprisingly no radiocarbon bomb peak was detected in these speleothems despite their young age in addition these samples are characterized by extremely high reservoir ages between 8800 and 10 100 yr the highest ever reported for a speleothem worldwide these data are best reconciled with a model of karst dissolution largely decoupled from the soil zone oxidation of disseminated pyrite in the dark gray host rock gives rise to acidic solutions driving carbonate dissolution the dolomitic nature of the bedrock prior calcite precipitation and ventilation enhanced degassing leads to high mg ca ratios in the drip water favoring aragonite formation these in situ observations confirm previous findings that temperature is not the dominant control on calcite versus aragonite formation in caves they also suggest that ancient aragonite speleothems should be examined carefully and ideally be compared to coeval calcite samples prior to interpreting their stable isotope data in terms of environmental climatic changes

start of the last interglacial period at 135 ka evidence from a high alpine speleothem a detailed study of growth periods of a flowstone from spannagel cave in the zillertal alps austria at 2500 m above sea level a site highly sensitive to climate changes offers unprecedented new insights into pleistocene climate change in central europe flowstone sample spa 52 has a high u content to 116 ppm analyses of this sample reveal that episodes of calcite deposition started at 204 3 ka 135 1 2 ka and 122 ka suggesting that at these times the mean air temperature at this high alpine site was within 1 5 c of the present day condition the beginning of growth at 135 ka corresponds to the ending of the last glaciation and is concordant with a midpoint age for the penultimate deglaciation at 135 2 5 ka as deduced from the absolutely dated oxygen isotope curve in sediments from the bahamas as well as with recent coral evidence from barbados indicating a high sea level already by 135 8 0 8 ka this set of data supports evidence against northern hemisphere forcing of termination ii because the insolation maximum is at 127 ka

climate and vegetation changes 180 000 to 345 000 years ago recorded in a deep sea core off portugal a new high resolution combined marine proxy pollen sequence from the portuguese margin md01 2443 enables direct comparison of ocean and ice volume changes with vegetation development in south west iberia during marine isotope stages mis 7 8 and 9 changes in sea surface conditions on both orbital and millennial time scales are closely mirrored by forest extent indicating a coherence of climate variability between the north atlantic and south west iberia deglacial warming at the start of mis 7 and 9 was interrupted by incursions of subpolar water masses at the site accompanied by reversals in tree population expansion during mis 7e and 9e the close relationship in timing and amplitude between vegetation and offshore conditions broke down early forest collapse points to pronounced cooling and aridification on land which although not accompanied by a change in water masses at the portuguese margin appears to have coincided with abrupt decreases in atmospheric methane concentration recorded in antarctic ice cores the most extreme glacial conditions of mis 8 occurred during the early part followed by an interval of warmer conditions and tree population expansion similar to 263 ka this has sometimes been considered as indicating an early deglaciation but the data presented here show that it was distinct from termination iii which occurred later in line with milankovitch forcing a sub orbital oscillation in both isotopic and pollen records is observed at the end of mis 7 ca 184 ka which appears to be coeval with a recently identified sea level high stand c 2006 elsevier b v all rights reserved

evidence of warm and humid interstadials in central europe during early mis 3 revealed by a multi proxy speleothem record abstract marine isotope stage 3 mis 3 57 27 ka was characterised by numerous rapid climate oscillations i e dansgaard oeschger d o events which are reflected in various climate archives so far mis 3 speleothem records from central europe have mainly been restricted to caves located beneath temperate alpine glaciers or close to the atlantic ocean thus mis 3 seemed to be too cold and dry to enable speleothem growth north of the alps in central europe here we present a new speleothem record from bunker cave germany which shows two distinct growth phases from 52 0 0 8 0 5 to 50 9 0 6 1 3 ka and 47 3 1 0 0 6 to 42 8 0 9 ka rejecting this hypothesis these two growth phases potentially correspond to the two warmest and most humid phases in central europe during mis 3 which is confirmed by pollen data from the nearby eifel the hiatus separating the two phases is associated with heinrich stadial 5 hs 5 although the growth stop precedes the onset of hs 5 the first growth phase is characterised by a fast growth rate and mg concentrations and sr isotope data suggest high infiltration and the presence of soil cover above the cave the second growth phase was characterised by drier but still favourable conditions for speleothem growth during this phase the 13c values show a significant decrease associated with d o event 12 the timing of this shift is in agreement with other mis 3 speleothem data from europe and greenland ice core data

stalagmite evidence for the onset of the last interglacial in southern europe at 129 1 ka multi proxy data from an italian stalagmite constrain the commencement of full last interglacial conditions in southern europe at 129 1 ka consistent with absolutely dated records currently available from both hemispheres the post glacial transition towards warmer and wetter conditions commenced at 134 2 ka oxygen isotope evidence suggests this was interrupted briefly at 130 2 ka an event probably related to the termination ii pause associated with heinrich event 11 for most of the stalagmite the pattern of delta 18 o variation mimics the air temperature record from the vostok ice core especially through marine isotope stage 5 there is no obvious evidence for substantial early interglacial warming

pre eruption history of phyric basalts from dsdp legs 45 and 46 evidence from morphology and zoning patterns in plagioclase phyric basalts recovered from dsdp legs 45 and 46 contain abundant plagioclase phenocrysts which occur as either discrete single grains megacrysts or aggregates glomerocrysts and which are too abundant and too anorthitic to have crystallized from a liquid with the observed bulk rock composition almost all the plagioclase crystals are complexly zoned in most cases two abrupt and relatively large compositional changes associated with continuous internal morphologic boundaries divide the plagioclase crystals into three parts core mantle and rim the cores exhibit two major types of morphology tabular with a euhedral to slightly rounded outline or a skeletal inner core wrapped by a slightly rounded homogeneous outer core the mantle region is characterized by a zoning pattern composed of one to several spikes plateaus superimposed on a gently zoned base line with one large plateau always at the outside of the mantle and by in most cases a rounded internal morphology the inner rim is typically oscillatory zoned the width of the outer rim can be correlated with the position of the individual crystal in the basalt pillow the presence of a skeletal inner core and the concentration of glass inclusions in low an zones in the mantle region suggest that the liquid in which these parts of the crystals were growing was undercooled some amount the resorption features at the outer margins of low an zones indicate superheating of the liquid with respect to the crystal

sea level during the penultimate interglacial period based on a submerged stalagmite from argentarola cave italy accurate constraints are presented for the absolute age duration and sea level for the highstand corresponding to marine isotope stage mis 7 1 our work is based on a stalagmite collected in a currently submerged cave from italy argentarola cave flooding of this coastal cave is clearly marked within the stalagmite by a thick marine overgrowth of serpulid worms precise uranium thorium u th ages measured by thermal ionization mass spectrometry suggest that the stalagmite growth varied in phase with climate during mis 7 2 and mis 6 the penultimate glacial period in addition the period of marine transgression is bracketed between 202 and 190 kyr bp defining a mis 7 1 duration of 11 2 kyr comparison with previous studies provides a new constraint on the sea level during mis 7 1 that has approximately remained between 318 and 39 m relative to present sea level the timing of the mis 7 1 highstand is in full agreement with the specmap chronology which contrasts with the growing body of evidence showing a significant phase difference for mis 5 5 a tempting conclusion is that second order sea level highstands such as mis 7 1 may be purely driven by astronomical changes in contrast with major terminations such as termination ii atmospheric co2 levels may partly explain this contrast since the two sea level transitions mis 7 2 7 1 and mis 6 5 5 are characterized by very different co2 rises 20 vs 100 ppm fl 2002 elsevier science b v all rights reserved

multi stage modification of paleoarchean crust beneath the anabar tectonic province siberian craton abstract according to present views the crustal terranes of the anabar province of the siberian craton were initially independent blocks separated from the convecting mantle at 3 1 daldyn terrane 2 9 magan terrane and 2 5 ga markha terrane rosen 2003 2004 rosen et al 1994 2005 2009 previous studies of zircons in a suite of crustal xenoliths from kimberlite pipes of the markha terrane concluded that the evolution of the crust of the markha terrane is very similar to that of the daldyn terrane to test this conclusion we present results of u pb and hf isotope studies on zircons in crustal xenoliths from the zapolyarnaya kimberlite pipe upper muna kimberlite field located within the daldyn terrane and the botuobinskaya pipe nakyn kimberlite field in the center of the markha terrane the data on xenoliths from the botuobinskaya kimberlite pipe record tectonothermal events at 2 94 2 8 2 7 and 2 ga the event at 2 ga caused pb loss in zircons from a mafic granulite u pb dating of zircons from the zapolyarnaya pipe gives an age of 2 7 ga all zircons from the studied crustal xenoliths have archean hf model ages ranging from 3 65 to 3 11 ga this relatively narrow range suggests that reworking of the ancient crust beneath the nakyn and upper muna kimberlite fields was minor compared with the daldyn and alakit markha fields shatsky et al 2016 this study when combined with dating of detrital zircons implies that tectonic thermal events at 2 9 2 85 2 75 2 7 and 2 0 1 95 ga occurred everywhere on the anabar tectonic province and could reflect the upwelling of superplumes at 2 9 2 7 and 2 ga the presence of the same tectonic thermal events in the daldyn and markha terranes rosen et al 2006a b supports the conclusion that the identification of the markha terrane as a separate unit is not valid

mass spectrometric 230th 234u 238u dating of the devils hole calcite vein the devils hole calcite vein contains a long term climatic record but requires accurate chronologic control for its interpretation mass spectrometric u series ages for samples from core dh 11 yielded 230 th ages with precisions ranging from less than 1 000 years 2 for samples younger than 140 ka thousands of years ago to less than 50 000 years for the oldest samples 566 ka the 234 u 238 u ages could be determined to a precision of 20 000 years for all ages calcite accumulated continuously from 566 ka until 60 ka at an average rate of 0 7 millimeter per 10 3 years the precise agreement between replicte analyses and the concordance of the 230 th 238 u 234 u 238 u ages for the oldest samples indicate that the dh 11 samples were closed systems and validate the dating technique in general

warm period growth of travertine during the last interglaciation in southern germany abstract late quaternary travertine at two sites near stuttgart formed entirely during interglacial periods the travertine contains structures from growth induced by bacteria and such structures have been dated by 230th u mass spectrometry the resulting ages from both sites imply growth episodes of short duration with growth rates up to 5 mm yr 1 at 99 800 1300 yr b p 2 n 8 and 105 900 1300 yr b p 2 n 7 these episodes were likely part of marine isotope stage mis 5 3 deposition of silt interrupted travertine growth at one of the sites 105 000 yr b p likely correlatives of this silt are the st germain i b stade recorded in the grand pile peat bog and a cold episode 1000 yr long recorded by 18o values in the grip ice core travertine also formed during stage 5 5 115 000 yr and during the early holocene we found no evidence for travertine accumulation in stages 2 3 4 and 5 1 at both sites the sr u ratio and the initial 234u 238u activity ratio resemble those of modern spring water however the sites differ in the chemical composition of spring water and in stratigraphic sequence of travertine accumulation

speleothems from the earliest quaternary snapshots of paleoclimate and landscape evolution at the northern rim of the alps abstract ancient cave systems in the northern calcareous alps today located well above the timberline at altitudes of 2400 2500 m host u rich speleothems that preserved growth layers on the microscopic scale of presumably annual origin two flowstone samples were dated to 2 019 0 037 0 069 ma and 1 730 0 032 0 068 ma respectively using u pb isochron techniques these ages are corroborated by the late pliocene to early pleistocene pollen spectrum extracted from one of the samples we use a multiproxy approach and exploit laminated speleothem sequences to tie high resolution stable isotope data to a floating lamina counted chronology o isotope values of growth intervals when calcite deposition was close to isotopic equilibrium are low compared to modern and holocene speleothems from other alpine caves and are inconsistent with the current altitudinal setting of the caves a vegetated but geomorphologically stable alpine catchment i e 2000 m asl no peri glacial processes combined with a deep seated cave the thickness of the vadose zone might have exceeded 1000 m is required in order to reconcile the isotopic data with the pollen record and the petrographic evidence furthermore the data can be used to constrain the rate for quaternary rock uplift to 0 8 mm annum for this frontal part of the european alps collectively the data suggest that these speleothems formed both during interglacials mis 59 or 61 and interglacial glacial transitions mis 75 74 or 77 76 but the seasonal precipitation pattern was arguably markedly different from today s provided that the highly regular microscopic laminae are indeed annual lamina counts suggest a minimum length of ca 6 ka for interglacials during the earliest pleistocene

polyphase zircon in ultrahigh temperature granulites rogaland sw norway constraints for pb diffusion in zircon shrimp u pb ages have been obtained for zircon in granitic gneisses from the aureole of the rogaland anorthosite norite intrusive complex both from the ultrahigh temperature uht 900 c pigeonite in zone and from outside the hypersthene in isograd magmatic and metamorphic segments of composite zircon were characterised on the basis of electron backscattered electron and cathodoluminescence images plus trace element analysis a sample from outside the uht zone has magmatic cores with an age of 1034 7 ma 2 n 8 and 1052 5 ma 1 n 1 overgrown by m1 metamorphic rims giving ages between 1020 7 and 1007 5 ma in contrast samples from the uht zone exhibit four major age groups 1 magmatic cores yielding ages over 1500 ma 2 magmatic cores giving ages of 1034 13 ma 2 n 4 and 1056 10 ma 1 n 1 3 metamorphic overgrowths ranging in age between 1017 6 ma and 992 7 ma 1 corresponding to the regional m1 sveconorwegian granulite facies metamorphism and 4 overgrowths corresponding to m2 uht contact metamorphism giving values of 922 14 ma 2 n 6 recrystallized areas in zircon from both areas define a further age group at 974 13 ma 2 n 4 this study presents the first evidence from rogaland for new growth of zircon resulting from uht contact metamorphism more importantly it shows the survival of magmatic and regional metamorphic zircon relics in rocks that experienced a thermal overprint of c 950 c for at least 1 myr magmatic and different metamorphic zones in the same zircon are sharply bounded and preserve original crystallization age information a result inconsistent with some experimental data on pb diffusion in zircon which predict measurable pb diffusion under such conditions the implication is that resetting of zircon ages by diffusion during m2 was negligible in these dry granulite facies rocks imaging and th u y systematics indicate that the main processes affecting zircon were dissolution reprecipitation in a closed system and solid state recrystallization during and soon after m1

effective precipitation in southern spain 266 to 46 ka based on a speleothem stable carbon isotope record abstract we present the longest duration directly dated terrestrial palaeoclimate record from the western mediterranean region a flowstone speleothem from gitana cave southeast spain the main phase of growth was 274 to 58 ka dated by multi collector inductively coupled plasma mass spectrometry mc icpms u series methods effective precipitation which we consider primarily responsible for flowstone calcite 13 c variations measured at 300 m resolution was higher during interglacials associated with marine oxygen isotope stages mis 7 and 5 and lower during glacial mis 6 there is a close correspondence between speleothem 13 c and sea surface temperature sst estimates from adjacent atlantic ocean cores during mis 6 which implies that oceanic conditions are critical in controlling the western mediterranean terrestrial moisture balance during glacial periods other features of our record such as the sequence of termination ii warming moistening between approximately 133 and 127 ka including a pause around 130 128 ka and the lagged termination of mis 5 warm intervals 5e 5c and 5a are similar to other terrestrial records within the mediterranean basin indicating climate synchroneity along the northern mediterranean coast the gitana cave region also may have been a refugium for temperate species during short lived cold arid periods during mis 5

the crust mantle boundary beneath cratons and craton margins a transect across the south west margin of the kaapvaal craton lower crustal suite xenoliths occur in on craton and off craton kimberlites located across the south western margin of the kaapvaal craton southern africa rock types include mafic granulite plagioclase bearing assemblages eclogite plagioclase absent assemblages with omphacitic clinopyroxene and garnet pyroxenite orthopyroxene bearing eclogite the mafic granulites are subdivided into three groups garnet granulites cpx grt plag qtz two pyroxene garnet granulites cpx opx grt plag kyanite granulites cpx grt ky plag qtz reaction microstructures preserved in many of the granulite xenoliths involve the breakdown of plagioclase by a combination of reactions 1 cpx plag grt qtz 2 plag grt ky qtz 3 plag cpx jd rich qtz compositional zoning in minerals associated with these reactions records the continuous transition from granulite facies mineral assemblages and pressure p temperature t conditions to those of eclogite facies two distinct p t arrays are produced 1 off craton granulites away from the craton margin define a trend from 680 c 7 5 kbar to 850 c 12 kbar 2 granulite xenoliths from kimberlites near the craton margin and on craton granulites produce a trend with similar geothermal gradient but displaced to lower t by 100 c both p t fields define higher geothermal gradients than the model steady state conductive continental geotherm 40 mwm2 and are not consistent with the paleogeotherm constructed from mantle derived garnet peridotite xenoliths a model involving intrusion of basic magmas around the crust mantle boundary followed by isobaric cooling is proposed to explain the thermal history of the lower crust beneath the craton margin the model is consistent with the thermal evolution of the exposed namaqua natal mobile belt low pressure granulites and the addition of material from the mantle during the namaqua thermal event c 1150 ma the xenolith p t arrays are not interpreted as representing paleogeotherms at the time of entrainment in the host kimberlite they most likely record p t conditions frozen in during various stages of the tectonic juxtaposition of the namaqua mobile belt with the kaapvaal craton

the siberian lithosphere traverse mantle terranes and the assembly of the siberian craton abstract the kimberlite fields scattered across the ne part of the siberian craton have been used to map the subcontinental lithospheric mantle sclm as it existed during devonian to late jurassic time along a 1000 km traverse ne sw across the archean magan and anabar provinces and into the proterozoic olenek province 4100 garnets and 260 chromites from 65 kimberlites have been analysed by electron probe major elements and proton microprobe trace elements these data and radiometric ages on the kimberlites have been used to estimate the position of the local paleo geotherm and the thickness of the lithosphere and to map the detailed distribution of specific rock types and mantle processes in space and time a low geotherm corresponding approximately to the 35 mw m2 conductive model of pollack and chapman tectonophysics 38 279 296 1977 characterised the devonian lithosphere beneath the magan and anabar crustal provinces the devonian geotherm beneath the northern part of the area was higher rising to near a 40 mw m2 conductive model areas intruded by mesozoic kimberlites are generally characterised by this higher but still cratonic geotherm lithosphere thickness at the time of kimberlite intrusion varied from ca 190 to ca 240 km beneath the archean magan and anabar provinces but was less 150 180 km beneath the proterozoic olenek province already in devonian time thinner devonian lithosphere 140 km in parts of this area may be related to riphean rifting near the northern end of the traverse differences in geotherm lithosphere thickness and composition between the devonian toluopka area and the nearby mesozoic kimberlite fields suggest thinning of the lithosphere by ca 50 60 km related to devonian rifting and triassic magmatism a major conclusion of this study is that the crustal terrane boundaries defined by geological mapping and geophysical data extended from outcrops in the anabar shield represent major lithospheric sutures which continue through the upper mantle and juxtapose lithospheric domains that differ significantly in composition and rock type distribution between 100 and 250 km depth the presence of significant proportions of harzburgitic and depleted lherzolitic garnets beneath the magan and anabar provinces is concordant with their archean surface geology the lack of harzburgitic garnets and the chemistry of the lherzolitic garnets beneath most of the other fields are consistent with the proterozoic surface rocks mantle sections for different terranes within the archean portion of the craton show pronounced differences in bulk composition rock type distribution metasomatic overprint and lithospheric thickness these observations suggest that individual crustal terranes of both archean and proterozoic age had developed their own lithospheric roots and that these differences were preserved during the proterozoic assembly of the craton data from kimberlite fields near the main archean proterozoic suture the billyakh shear zone suggest that reworking and mixing of archean and proterozoic mantle was limited to a zone less than 100 km wide

a possible mechanism for growth of calcite speleothems without participation of biogenic carbon dioxide abstract using plummer et al s 11 rate equations on the dissolution and deposition of caco3 in h2o co2 systems we have calculated deposition rates of caco3 to stalagmites in caves which are covered by glaciers or bare karst in this case no biogenic co2 from vegetated soil is available and the deposition of caco3 involves only atmospheric co2 the mechanism of deposition proceeds by a temperature effect cold melting waters of about 0 c dissolve caco3 under open system conditions at the surface of the rock when this solution saturated with respect to caco3 flows through the limestone rock its temperature increases by several degrees therefore it becomes supersaturated and caco3 is deposited under open system conditions in the warmer cave maximal growth rates of about 10 3 cm year are possible from the kinetics of the deposition of caco3 from the thin water films present at the surface of stalagmites we are able to estimate the isotopic composition of carbon in the caco3 deposited on the stalagmites to be approximately 13c 8 which is close to some observed values from our data we conclude that substantial growth of stalagmites is possible during glacial periods as well as in areas of bare karst a question which was not resolved up to now

speleothem evidence from oman for continental pluvial events during interglacial periods growth periods and stable isotope analyses of speleothems from hoti cave in northern oman provide a record of continental pluvial periods extending back over the past four of earth s glacial interglacial cycles rapid speleothem growth occurred during the early to middle holocene 6 10 5 ka b p 78 82 ka b p 120 135 ka b p 180 200 ka b p and 300 325 ka b p the speleothem calcite deposited during each of these episodes is highly depleted in 18 o compared to modern speleothems the d 18 o values for calcite deposited within pluvial periods generally fall in the range of 24 to 28 relative to the vienna peedee belemnite standard whereas modern speleothems range from 21 to 23 the growth and isotopic records indicate that during peak interglacial periods the limit of the monsoon rainfall was shifted far north of its present location and each pluvial period was coincident with an interglacial stage of the marine oxygen isotope record the association of continental pluvial periods with peak interglacial conditions suggests that glacial boundary conditions and not changes in solar radiation are the primary control on continental wetness on glacial interglacial time scales

dated paleontological cave sites of central europe from late middle pleistocene to early upper pleistocene ois 5 to ois 8 abstract caves are terrestrial depositories that preserve a large variety of organic and inorganic remains these may contain important quaternary climatic and ecological information most of the faunal remains however cannot be linked to any interglacial or glacial period exclusively reliable dating of such remains is therefore required experience has however shown that esr dating of speleothems or 230 th u dating of bones are of disputable value only tims 230 th u dating of speleothems appears to yield reliable ages dating the bottom and top of speleothem layers permit assigning pleistocene faunal remains to the ois chronology if the deposition of the speleothems and the faunal remains are clearly correlated care must be taken to consider the depositional situation of each site before interpreting any age dates in this paper we present an overview of all numerically dated paleontological cave sites in central europe between ois 5 and ois 8 a total of 25 strata were dated from 13 sites most of them deposited during ois 5 the rest belonging to ois 6 and 7 numerically dated paleontological sites older than ois 8 are not known

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

fe mg interdiffusion rates in clinopyroxene experimental data and implications for fe mg exchange geothermometers chemical interdiffusion of fe mg along the c axis 001 in natural diopside crystals x di 0 93 was experimentally studied at ambient pressure at temperatures ranging from 800 to 1 200 c and oxygen fugacities from 10 11 to 10 17 bar diffusion couples were prepared by ablating an olivine x fo 0 3 target to deposit a thin film 20 100 nm onto a polished surface of a natural oriented diopside crystal using the pulsed laser deposition technique after diffusion anneals compositional depth profiles at the near surface region 400 nm were measured using rutherford backscattering spectroscopy in the experimental temperature and compositional range no strong dependence of d fe mg on composition of clinopyroxene fe mg ratio between di93 di65 or oxygen fugacity could be detected within the resolution of the study the lack of fo2 dependence may be related to the relatively high al content of the crystals used in this study diffusion coefficients d fe mg can be described by a single arrhenius relation with d text fe text mg 2 7 7 pm 4 2 7 times 10 7 text exp 3 20 7 pm 1 6 0 text kj text mol text rt m 2 text s d fe mg in clinopyroxene appears to be faster than diffusion involving ca species e g d ca mg while it is slower than d fe mg in other common mafic minerals spinel olivine garnet and orthopyroxene as a consequence diffusion in clinopyroxene may be the rate limiting process for the freezing of many geothermometers and compositional zoning in clinopyroxene may preserve records of a higher compared to that preserved in other coexisting mafic minerals temperature segment of the thermal history of a rock in the absence of pervasive recrystallization clinopyroxene grains will retain compositions from peak temperatures at their cores in most geological and planetary settings where peak temperatures did not exceed 1 100 c e g resetting may be expected in slowly cooled mantle rocks many plutonic mafic rocks or ultra high temperature metamorphic rocks

multi stage origin of the lower crust of the karelian craton from 3 5 to 1 7ga based on isotopic ages of kimberlite derived mafic granulite xenoliths abstract mafic garnet granulite xenoliths recovered from 500 to 600 ma old eastern finland kimberlites provide direct information on the petrology and physical properties of the lower cust below the archean karelian craton mineral thermobarometry together with isotopic petrological and seismic velocity constraints imply that the xenolith suite is derived from a geophysically determined dense high velocity layer at the base of the crust 40 58 km depth single grain zircon u pb dates and nd model ages t dm imply that this is a hybrid layer consisting of both archean and proterozoic mafic granulites zircon ages of up to 3 5 ga and nd t dm model ages 3 7 ga of the xenoliths are equivalent to those of the oldest upper crustal assemblages during the proterozoic transient heating of these archean granulites by voluminous basic magmatic intrusions resulted in multiple younger zircon generations within individual xenoliths the most important post archean lower crust growth took place during 1 9 ga accretion of the svecofennian arc complex to the craton margin when underplating proterozoic basaltic magmas became mingled with pre existing archean mafic granulites later post orogenic 1 80 1 73 ga transient heating of the lower crust occurred as a response to magmas ponded at the uppermost lithospheric mantle in conclusion karelian lower crust records the geological evolution of the craton margin environment through a period of nearly 4 billion years our data add a new piece to the emerging picture that emphasises the global importance of the 3 5 ga crustal growth episode we suggest that it represents a major mantle plume event more widespread than previously recognized when a significant fraction of paleoarchean continental crust was formed

stable isotope stratigraphy of a late last interglacial speleothem from rana northern norway abstract a stalagmite from rana northern norway dated by the tims uranium series technique yields records of stable oxygen and carbon isotopes covering the period from late marine oxygen isotope substages mis 5e to 5a that is 123 350 to 73 300 yr ago rapid growth 46 m yr between 123 350 and 119 500 yr ago reflects climatic conditions favorable for speleothem growth this period is characterized by century to millennial scale oscillations in both stable isotope records where both the absolute values and the isotope ranges are similar to holocene and older samples from the region from 119 500 to 107 700 yr ago speleothem growth was slow 0 7 m yr and between 107 700 and 73 300 yr ago growth is barely noticeable 0 07 m yr during the period of slow growth the stable isotope records show an overall enrichment trend the transition between rapid and slow growth rate occurring sometime between 119 500 and 107 700 yr ago is believed to reflect the termination of interglacial climate in this region the absence of detritus and corrosion features in the slowly deposited calcite suggests that the valley outside the cave remained sufficiently ice free for speleothem growth to occur until at least 73 300 yr ago

reply to comment to short communication ʽcomment hf isotope heterogeneity in zircon 91500 by w l griffin n j pearson e a belousova and a saeed chemical geology 233 2006 358 363 by f corfu

trace element and age characteristics of zircons in granulite xenoliths from the udachnaya kimberlite pipe siberia trace element and shrimp u pb geochronological data are presented for zircons from granulite xenoliths from the devonian udachnaya kimberlite pipe situated in the central part of the siberian craton 66 05 n 110 45 e the xenoliths include three two pyroxene garnet granulites one garnet granulite lacking orthopyroxene three felsic garnet granulites one kinzigite and one amphibolized garnet granulite most of them are clearly distinct from the local upper crustal lithologies and have pressure and temperature estimates indicative of derivation from the lower crust zircons from these granulites show a record of several magmatic and metamorphic events with different domains revealed by cl imaging and variations in ree content and th u ratios the first event is shown by magmatic zircon in the cores of some grains that yield discordant archaean to proterozoic ages all other domains of the studied zircons have textures typical for metamorphic zircons they have proterozoic ages and were formed by subsolidus growth or as a result of solid state recrystallization of pre existing zircon they give a range of concordant ages from 1 94 to 1 81 ga in which several distinct episodes can be distinguished that relate to the collision of terranes during the accretion of the siberian craton accompanied by formation of granite melts during these events the xenolith protoliths were metamorphosed under granulite facies conditions at pressures corresponding to lower crustal depths except for the kinzigite that is probably derived from shallower depths

the demise of the last interglacial recorded in isotopically dated speleothems from the alps abstract the transition from interglacial to glacial climate has attracted much attention in paleoclimatic research partly because orbital forcing dictates that such a return to a new ice age is inescapable albeit in the distant future only the detailed series of steps that leads to glacial inceptions remains poorly understood however and studies of past glacial inceptions are often compromised by incomplete records imprecise chronological control and or uncertainties associated with proxy transfer functions here we present results from u th dated speleothems from a cave in the austrian alps entrische kirche cave which grew continuously between ca 127 and 114 ka and intermittently also during subsequent stadials and interstadials the alpine setting of this cave is prone to periglacial and glacial processes as well as temperature and precipitation changes which are recorded in these cave deposits we use high resolution stable isotope data to constrain paleoenvironmental changes associated with the demise of the last interglacial unprecedented in detail for central europe peak interglacial conditions are characterized by high 18 o values and high growth rates from ca 127 to 124 ka a major drop in 18 o by 3 occurred at ca 118 ka which coincided with cold event c26 in the north atlantic this isotopic shift which occurred at or close to isotopic equilibrium cannot be explained by simple uniform cooling modelling suggests that enhanced seasonality dominated by significant changes in winter precipitation are required to reconcile the isotope data with the fact that calcite deposition continued across the mis 5e d transition i e no cave freezing this period of enhanced seasonality lasted for several millennia during which the catchment area of the cave remained geomorphologically stable and ice free eventually speleothem growth terminated at ca 114 ka which is in line with widespread ice rafting in the north atlantic cold event c24 and the onset of fully stadial conditions during mis 5d

tectonothermal evolution of the continental crust beneath the yakutian diamondiferous province siberian craton u pb and hf isotopic evidence on zircons from crustal xenoliths of kimberlite pipes abstract u pb age and hf isotope data were collected on zircons from crustal xenoliths from the late devonian kimberlite pipes of markha terrane the xenoliths include mafic garnet granulites gt pl cpx opx amp bt scp and garnet biotite gneisses grt bt pl kfs qtz scp the data from this study demonstrate that the crust of the markha terrane experienced several tectonothermal events zircons with archean hf model ages tdm 3 13 2 5 ga are predominant in all xenoliths with one exception these data imply that most of the lower and middle crust beneath the markha terrane was produced in the archean time later this paleoarchean crust was significantly reworked in several tectonothermal events including a neoarchean stage 2 9 2 5 ga and several paleoproterozoic metamorphic stages 1 98 1 9 and 1 8 ga there is very little evidence for generation of juvenile crust associated with these metamorphic events importantly crustal xenoliths from kimberlite pipes of the markha terrane record all the same events that occurred in the adjacent daldyn and magan terranes

metamorphic growth and recrystallization of zircon distinction by simultaneous in situ analyses of trace elements u th pb and lu hf isotopes in zircons from eclogite facies rocks in the sulu orogen simultaneous in situ analyses of trace elements u th pb and lu hf isotopes were carried out on distinct domains of zircons in ultrahigh pressure uhp eclogite facies metamorphic rocks from the main hole of the chinese continental scientific drilling ccsd in the sulu orogen for the first time trace elements are directly linked to lu hf isotopes in metamorphic zircons with reference to their u pb dates this enables methodological integration to distinguish four types of metamorphic zircon solid state replacement and dissolution recrystallizations of protolith zircons and new growth from the aqueous fluid metamorphically grown zircons are characterized by concordant u pb ages for the metamorphism flat hree patterns typical of the garnet effect low contents of ree especially hree y nb ta and th u high contents of hf low lu gd n lu hf and th u 0 1 ratios and elevated 176hf 177hf ratios relative to solid state recrystallized zircons this suggests the effects of both garnet and fluid on the growth of metamorphic zircons in contrast metamorphic recrystallization has reset the u th pb isotope system of protolith zircons to different extents depending on the extents of fluid action during metamorphism solid state recrystallized zircons exhibit the lowest degrees of resetting and thus almost inherit all geochemical features from the protolith zircons which are characterized by discordant u pb ages close to or below the protolith age steep mree hree patterns typical of magmatic origin high contents of trace elements and their ratios and low 176hf 177hf ratios on the other hand dissolution recrystallized zircons show the highest degrees of reworking and thus have concordant or nearly concordant u pb ages for the metamorphism steep mree hree patterns lowered contents of trace elements such as ree th u y nb ta and ti relative to the protolith zircons and almost unchanged hf isotope ratios replacement recrystallized zircons display intermediate degrees of reworking and thus have their many features of elements and isotopes in between while the metamorphic growth in the presence of both garnet and fluid is characterized by both depletion of hree with flat pattern and the low contents of trace elements the metamorphic recrystallization in the presence of aqueous fluid is indicated by gradual decreases of mree to hree without the flat hree pattern therefore the simultaneous in situ analyses of metamorphic zircons have the advantage over single term analyses in making distinction between the new growth and the different types of recrystallization

age and composition of granulite and pyroxenite xenoliths in hannuoba basalts reflect paleogene underplating beneath the north china craton abstract in situ u pb and hf isotope systematics of zircons mineral chemistry of silicates and whole rock major element trace element and platinum group element pge data are reported for five mafic xenoliths granulites and pyroxenite in the hannuoba cenozoic basalts north china temperature estimates of 859 886 c suggest that these xenoliths are derived from the lower crust the whole rock compositions of the xenoliths show weakly negative eu anomalies eu 0 67 0 95 high sio 2 al 2 o 3 5 80 13 8 low ir 0 10 0 29 ppb and wide ranges of ni 4 5 235 ppm and la nb 1 70 7 64 most zircons in these samples are structureless and give paleogene 44 5 47 3 ma u pb ages minor populations have early mesozoic 210 220 ma late mesozoic 90 ma and neogene 14 ma ages the fractionation of pyroxene and plagioclase controlled the petrogenesis of the xenoliths which are interpreted as the products of basaltic underplating and fractionation cumulates in paleogene time 45 47 ma with assimilation of some older intermediate crustal components the paleogene underplating corresponds in time to lithosphere scale extension in the north china craton leading to the widespread formation of sedimentary basins most paleogene zircons have positive e hf up to 13 2 with uniform t dm 0 46 0 50 ga whereas most mesozoic zircons have negative e hf this evolution suggests a temporal decrease in the degree of crustal assimilation during the extension of the lithosphere in addition to complex modification in early and late mesozoic times the thermal event related to the eruption of the host magmas ca 14 ma also reheated the lower crust beneath the north china craton

the classic marine isotope substage 5e since its identi cation nearly fty years ago marine iso tope stage 5 mis 5 has been placed onto absolute time scaleson the basis of three independent approaches cesare emiliani who set up the isotope stages emiliani 1955 depended onuranium series dating of the sediments a method that today isregarded as not generally capable of yielding useful precisionor accuracy broecker and van donk 1970 pioneered the ap proach of correlating to radiometrically dated marine coral ter races thishasbeenmuchaidedinrecentyearsbyimprovementsin the precision and accuracy of these age determinations thathave owed from the development of thermal ionization massspectrometry tims for uranium series dating edwards

u th dating of marine isotope stage 7 in bahamas slope sediments in order to understand the driving forces for pleistocene climate change more fully we need to compare the timing of climate events with their possible forcing in contrast to the last interglacial marine isotope stage mis 5 the timing of the penultimate interglacial mis 7 is poorly constrained this study constrains its timing and structure by precise u th dating of high resolution n 18 o records from aragonite rich bahamian slope sediments of odp leg 166 sites 1008 and 1009 the major glacial interglacial cycles in n 18 o are distinct within these cores and some mis 7 substages can be identified these sediments are well suited for u th dating because they have uranium concentrations of up to 12 ppm and very low initial 230 th contributions with most samples showing 230 th 232 th activity ratio of s 75 u and th concentrations and isotope ratios were measured by thermal ionisation mass spectrometry and multiple collector inductively coupled plasma mass spectrometry with the latter providing dramatically better precision twenty nine of the 41 samples measured have a n 234 u value close to modern seawater suggesting that they have experienced little diagenesis ages from 27 of the 41 samples were deemed reliable on the basis of both their u and their th isotope ratios ages generally increase with depth although we see a repeated section of stratigraphy in one core extrapolation of constant sedimentation rate through each substage suggests that the peak of mis 7e lasted from v237 to 228 ka and that 7c began at 215 ka this timing is consistent with existing low precision radiometric dates from speleothem deposits the beginning of both these substages appears to be slightly later than in orbitally tuned timescales the end of mis 7 is complex but also appears to be somewhat later than is suggested by orbitally tuned timescales although this event is not particularly well defined in these cores fl 2002 elsevier science b v all rights reserved

sea surface temperature variability in the north atlantic during the last two glacial interglacial cycles comparison of faunal oxygen isotopic and mg ca derived records climate variability in the northeast atlantic was investigated on glacial interglacial and millennial time scales during the last 200 000 years using sea surface temperature sst records derived from planktonic foraminiferal diversities and from mg ca measurements on globigerina bulloides paleoceanographical interpretations are supported by species composition analyses benthic and planktonic isotopic data as well as records of iceberg rafted debris ird differences of climate development are recognized for both interglacial and glacial periods temperature estimates indicate slightly warmer conditions up to 2 c during marine oxygen isotope stage mis 5e than during the holocene in contrast to the last glaciation when the sst minimum coincided with a minimum in solar insolation immediately before termination i during the penultimate glaciation a long sst minimum occurred at times of intermediate solar insolation well preceding the onset of termination ii this discrepancy between two glacial terminations may be explained by an inherently different orbital configuration characteristic for each glacial interval despite these differences between the two glacial trends the superimposed shorter lived climatic events reveal the same order of principal steps implying their common causal nature a direct comparison of faunal ssts with those retrieved from mg ca analysis shows that mg ca derived temperatures follow the general glacial interglacial trend however the latter appear to be largely overestimated supported by 18o data in g bulloides which show little response to millennial scale variability there seems to be a need for species dependent calibration experiments that also consider the different oceanographic settings this particular species can live in

increasing vegetation and climate gradient in western europe over the last glacial inception 122 110 ka data model comparison high resolution terrestrial pollen and marine planktic and benthic isotopes coarse fraction and n pachyderma s analyses have been performed in the marine isotope stage mis 5 interval of images core md99 2331 retrieved in the northwestern iberian margin this study shows the occurrence of a zeifen interstadial stadial succession on land and in the ocean during the first part of mis 5e in northwestern iberia the eemian is marked from 126 to 122 ka by the development of deciduous quercus forest at the same time as mediterranean forest colonised southern iberia and deciduous quercus corylus forest occupied northernmost european regions from 121 to 115 ka carpinus betulus forest developed in nw iberia indicating a winter cooling by 2degreesc on land and an increase in annual precipitation by 100 200 min along with a sea surface temperature sst decreasing trend off iberia a similar cooling has been documented at the same time in northern germany 52degreesn by the replacement of deciduous forest by coniferous abies picea formations implying a southward displacement of the deciduous tree line between similar to60degreesn and 50degreesn as early as 120 ka the southward migration of the tree line between 72degreesn and 58degreesn simulated by the earth model of intermediate complexity mobidic from 122 and 120 ka and considered as a major process to initiate the last glaciation is therefore compatible with data between 115 and 110 ka the substantial ice accumulation in northern high latitudes mis 5e 5d transition was synchronous with successive drops c26 and c25 in northeastern atlantic sst in northwestern iberia abies pinus trees developed at the expense of quercus carpinus forest a tundra like environment occupied northern germany marking the end of the interglacial in northwestern europe at 115 ka and boreal forest likely colonised northeastern france the first displacement of the vegetation belts at 121 ka was enhanced at 115 ka indicating an amplification of the vegetation and climate gradients in northeastern atlantic and european borderlands probably related with the well developed ice caps at that time the comparison between the general trend in the estimated and simulated mobidic winter and summer temperatures for latitudes between 35 and 45degreesn shows that both follow quite straightforwardly the precession signal although the simulated and reconstructed temperatures agree better in the south than north of 40degreesn annual precipitation is exhibiting opposite trend in the data and in the model this contradiction is likely the fact that the zonal climate simulated by the model may not accurately represent the regional climate features as reconstructed from the pollen c 2004 elsevier b v all rights reserved

duration and structure of the past four interglaciations reanalysis and additional dating of the devils hole 18o paleotemperature record confirm that the last interglaciation in the great basin the continental analog of marine isotopic substage 5e lasted 22 000 yr consistent with the vostok paleotemperature record which suggests a duration of 19 000 yr for this event in antarctica the three preceding interglaciations in the devils hole record analogs of marine isotopic substages 7e 9c and 11c range from 20 000 to 26 000 yr in duration a 20 000 yr duration for the last interglaciation is consistent with tims uranium series dated sea level high stands thus the widely held view that interglaciations were of 11 000 to 13 000 yr duration and constituted only about 10 of mid to late pleistocene climatic cycles needs reexamination the warmest portion of each interglaciation in the devils hole time series is marked by a 18o plateau signifying apparent climatic stability for periods of 10 000 to 15 000 yr duration

archaean to proterozoic crustal evolution in the central zone of the limpopo belt south africa botswana constraints from combined u pb and lu hf isotope analyses of zircon a combined set of u pb and lu hf in situ laser ablation icp mc ms zircon analyses were obtained from orthogneisses and granitoids in the central zone of the limpopo belt which comprises the beit bridge and mahalapye complexes the results indicate that by combining the two isotope systems primary magmatic zircon domains can be distinguished from those formed during later metamorphic events even if the distinct zircon domains underwent multiple pb loss and the texture age relationships as obtained by cathodoluminescence images and u pb analyses are ambiguous furthermore the applied technique allows distinction of zircon grains formed in juvenile magmas from those generated by melting of older continental crust or affected by substantial crustal contamination the combined u pb and lu hf data reveal that the sand river gneiss suite of the beit bridge complex was emplaced at 3283 8ma and formed from melting of an older archaean crust which was derived from a depleted mantle source at around 3 65 ga the hafnium model age tdm is significantly older than those obtained from zircons from numerous neoarchaean granitoids of the beit bridge complex comprising the singelele gneiss 2647 12ma the bulai granite 2612 7ma the regina gneiss 2649 9ma and two samples of the zanzibar gneiss 2613 6ma these granitoids show initial ehf t values between 0 5 and 7 1 which correspond to initialtdm between 3 46 and 3 01ga these variable tdminitial and ehf t initial values are interpreted to be the result of different mixtures of reworked 3 65 ga palaeoarchaean crust with juvenile magmas extracted from the depleted mantle during the neoarchaean at 2 65 ga this conclusion is supported by results obtained from the mahalapye complex which was affected by migmatization and granite intrusions during the palaeoproterozoic at 2 02 2 06 ga the mokgware granite 2019 9ma contains zircon xenocrysts with pb pb ages of 2 52 2 65 ga and 2 93 ga and hafnium model ages of 3 0 3 4 ga indicating that this granite is derived from remelting of archaean crust in contrast uniformtdm hf initial ages of 2 61 2 67 ga obtained from a diorite gneiss 2061 6ma of the mahalapye complex indicate that its protolith may have been formed from remelting of a neoarchaean juvenile crust variable ehf t initial values from 3 7 to 6 3 of zircon cores 2711 11ma in an adjacent leucosome also support a model of mixing of juvenile mantle derived matter with older crust in the neoarchaean

two new geobarometers for garnet amphibolites with applications to southeastern vermont two new geobarometers for the assemblage garnet hornblende plagioclase quartz have been calibrated on the basis of the equilibrium 6 anorthite 3 tremolite 2 grossular 1 pyrope 3 tschermakite 6 quartz and its fe end member equivalent data representing 37 natural samples that equilibrated at conditions of 2 5 to 13 kbar and 500 to 800 c were fitted to the general equation rt in keq a bt p i c by using a weighted least squares method multiple correlation coefficients are high 0 98 and 0 97 lines of constant keqhave extremely shallow slopes in p t space 2 to 8 bars per degree suggesting that pressures may be deduced precisely even where temperatures are only poorly constrained typical analytical errors and temperature imprecisions propagate to very small errors in pressure about 500 bars caution is advised in applying the barometers outside the range of calibrant mineral compositions application of the calibrations to samples from southeastern vermont near the strafford chester and athens domes documents relatively high pressure metamorphism 7 to 10 kbar for these structures

reconstructing palaeoprecipitation from an active cave flowstone several drill cores were obtained from a laminated actively forming flowstone from a shallow cave in austria highly resolved petrographic and geochemical analyses combined with multi annual cave monitoring reveal a distinct sensitivity of flowstone growth and composition to late holocene meteoric precipitation the regular sub millimetre scale lamination consists of thicker translucent laminae and thinner organic inclusion rich laminae there is also a macroscopic millimetre scale banding of darker and lighter bands comprising several laminae stable isotope analyses of drill cores and modern calcite precipitates show a pronounced positive covariation of 13c and 18o values indicative of kinetic isotope effects comparing the isotope values with petrography shows gradual changes across several of the annual laminae i e changes of several per mille on a multi annual to decadal timescale the stable isotope and trace element composition as well as the flowstone petrography are mainly controlled by the variable drip water discharge controlling the water film thickness and water residence time on the flowstone surface and consequently the intensity of co2 degassing kinetic isotope enrichment and concomitant calcite precipitation drill core pfu6 provides an isotope record of the last ca 3000 years at near annual resolution a distinct phase of low c and o isotope values interpreted as increased discharge and hence higher meteoric precipitation occurred from ca 300 to 140 a b2k second half of the little ice age and another wet interval occurred around 700 a corresponding to reported medieval glacier advances the roman warm period was also dominated by relatively wet conditions although significant decadal variability prevailed increased precipitation further characterized the intervals from ca 2480 to 2430 and 2950 to 2770 a dry conditions persisted during the medieval climate anomaly although this trend towards reduced precipitation started earlier the highest c isotope values of the last 2 ka are recorded around 750 a and another dry phase is centred at 1480 a this new record shows that inter annual to decadal oscillations are a dominant mode of variation during the last 3 ka in the alps copyright 2011 john wiley sons ltd

age provenance and precambrian evolution of the anabar shield from u pb and lu hf isotope data on detrital zircons and the history of the northern and central siberian craton the anabar shield in northern siberia is one of the world s least studied precambrian areas and provides a window into the crustal basement of the central and northern siberian craton we report u pb and hf isotope data for detrital zircons sampled in a profile across its major structural units they define a u pb age range from 1 8 to 3 4 ga with three main periods 1 8 2 0 ga 2 4 2 8 ga and 3 0 3 4 ga the oldest zircons yield super chondritic ehf t implying that the parental magmas of their source rocks were juvenile i e formed from depleted mantle dm thus the crustal basement of the anabar shield and probably the whole central and northern siberian craton started to form in the mid paleoarchean and included no recycled crust zircons with 2 5 2 7 ga ages define two ehf t intervals one is super chondritic 2 to 7 implying juvenile sources the other is sub chondritic 3 to 12 indicative of recycled crust probably formed at 3 2 3 4 ga in magma sources nearly all 1 8 2 0 ga zircons have sub chondritic ehf t 2 to 29 implying derivation from sources dominated by recycled crust formed at 2 6 ga and 3 4 ga and little or no juvenile addition these events accompanied amalgamation of the entire craton by welding of archean domains the bekelekh unit of the daldyn series has the highest proportion of 2 6 ga zircons and may be the oldest nucleus of the anabar shield whereas the kilegur unit of the same series is essentially proterozoic 1 95 ga the largest amount of 3 1 3 4 ga zircons as well as common 2 6 2 7 ga zircons occur in the ambardakh unit of the upper anabar series our data suggest alternation of areas with dominant ages of 1 95 ga and 2 6 ga with the younger zircons coming from granites and granulites and the older ones from gneisses they show no evidence for significant ages differences for the anabar and olenek provinces the final amalgamation of the entire siberian craton by welding of archean blocks may have taken place at around 1954 6 ma

u th age constraints on the absence of ice in the central inn valley eastern alps austria during marine isotope stages 5c to 5a abstract calcitic flowstones are present in fractures of a pleistocene breccia near innsbruck austria and record periods of carbonate precipitation in the unsaturated zone between 101 500 1500 and 70 300 1800 yr constrained by u series disequilibrium dates the occurrence of these speleothems their low carbon isotopic composition and the lack of infiltrated siliciclastic material demonstrate that the central inn valley which harbored one of the most extensive valley glaciers during the last glacial maximum was ice free during marine isotope stages 5c to 5a climatically warm periods are separated by distinct drops in the oxygen isotopic composition of the speleothem calcite attributed to strong and possibly seasonally biased atmospheric cooling during these intervening stadials which mirror those identified in the greenland ice cores and marine sea surface temperature records calcite deposition apparently came to a halt but the inn valley remained ice free the youngest calcite layer formed between 74 000 and 70 000 yr and places a maximum age limit on the likely expansion of alpine glaciers during the marine isotope stage 5 4 transition consistent with other speleothem records

reconstruction of temperature in the central alps during the past 2000 yr from a δ18o stalagmite record the precisely dated isotopic composition of a stalagmite from spannagel cave in the central alps is translated into a highly resolved record of temperature at high elevation during the past 2000 yr temperature maxima during the medieval warm period between 800 and 1300 ad are in average about 1 7 8c higher than the minima in the little ice age and similar to present day values the high correlation of this record to d 14 c suggests that solar variability was a major driver of climate in central europe during the past 2 millennia d 2005 elsevier b v all rights reserved

rock varnish microlamination dating of late quaternary geomorphic features in the drylands of western usa abstract varnish microlamination vml dating is a correlative age determination technique that can be used to date and correlate various geomorphic features in deserts in this study we establish a generalized late quaternary i e 0 300 ka varnish layering sequence for the drylands of western usa and tentatively correlate it with the specmap oxygen isotope record we then use this climatically correlated varnish layering sequence as a correlative dating tool to determine surface exposure ages for late quaternary geomorphic features in the study region vml dating of alluvial fan deposits in death valley of eastern california indicates that during the mid to late pleistocene 5 15 ky long aggradation events occurred during either wet or dry climatic periods and that major climate shifts between glacial and interglacial conditions may be the pacemaker for alteration of major episodes of fan aggradation during the holocene interglacial time however 0 5 1 ky long brief episodes of fan deposition may be linked to short periods of relatively wet climate vml dating of alluvial desert pavements in death valley and the mojave desert reveals that pavements can be developed rapidly

direct u th dating of marine sediments from the two most recent interglacial periods a knowledge of the age of marine sediments is necessary to determine the timing of events and rates of processes in the marine realm and the relationships among marine and other climatically sensitive records the establishment of an accurate chronology for pleistocene marine sediments beyond the range of radiocarbon dating approximately the past 45 kyr has therefore been a goal of palaeoceanographers for decades early attempts1 2 based on measurements of the radionuclides 230th and 231pa were beset with problems and subsequent studies focused on tying fluctuations in marine sediment oxygen isotope records to events such as the formation of coral reef terraces and changes in the earth s magnetic polarity3 4 and tuning the resultant chronologies to the earth s orbitally driven insolation variations5 8 but these chronologies especially the age and duration of the last interglacial period have been challenged by several studies9 12 raising questions about the fundamental cause of pleistocene climate fluctuations here we report the direct u th dating of aragonite rich marine sediments from the bahamas and present an accurately dated marine oxygen isotope record for the last two interglacials we obtain dates of 120 127 kyr bp for the last interglacial and 189 190 kyr bp for the late stage 7 interglacial these dates are in accord with the general theory of orbitally forced climate fluctuations and demonstrate the potential of our direct dating approach for developing an absolute chronology for the pleistocene marine oxygen isotope record

timing and progression of the last interglacial derived from a high alpine stalagmite 1 u th dating and oxygen isotope analysis of a stalagmite from spannagel cave in the austrian alps provides information about the timing and progression of the last interglacial climate we determined two distinct growth intervals warm climate from 130 7 thousand years ka before the present to 130 0 ka and from 125 7 ka to 118 2 ka the latter containing two periods of ceased stalagmite growth colder climate at around 123 8 ka and 120 5 ka high resolution 18o analysis of stalagmite spa 50 reveals a clear regular cyclic pattern with periods of 197 109 and 21 years which are likely to be related to the suess gleissberg and hale cycles respectively indicating that eemian climate in the alps was forced by the sun

rapid fluctuations in sea level recorded at huon peninsula during the penultimate deglaciation about 140 000 years ago the breakup of large continental ice sheets initiated the last interglacial period sea level rose and peaked around 135 000 years ago about 14 meters below present levels a record of last interglacial sea levels between 116 000 years to 136 000 years ago is preserved at reef vii of the uplifted coral terraces of huon peninsula in papua new guinea however corals from a cave situated about 90 meters below the crest of reef vii are 130 000 2000 years old and appear to have grown in conditions that were 6 c cooler than those at present these observations imply a drop in sea level of 60 to 80 meters after 130 000 years sea level began rising again in response to the major insolation maximum at 126 000 to 128 000 years ago the early about 140 000 years ago start of the penultimate deglaciation well before the peak in insolation is consistent with the devils hole chronology

collapse of the california current during glacial maxima linked to climate change on land time series of alkenone unsaturation indices gathered along the california margin reveal large 4 to 8 c glacial interglacial changes in sea surface temperature sst over the past 550 000 years interglacial times with ssts equal to or exceeding that of the holocene contain peak abundances in the pollen of redwood the distinctive component of the temperate rainforest of the northwest coast of california in the region now dominated by the california current ssts warmed 10 000 to 15 000 years in advance of deglaciation at each of the past five glacial maxima ssts did not rise in advance of deglaciation south of the modern california current front glacial warming along the california margin therefore is a regional signal of the weakening of the california current during times when large ice sheets reorganized wind systems over the north pacific both the timing and magnitude of the sst estimates suggest that the devils hole nevada calcite record represents regional but not global paleotemperatures and hence does not pose a fundamental challenge to the orbital milankovitch theory of the ice ages

the timing of high sea levels over the past 200 000 years the 230 th ages and 234 u 238 u ratios were determined for barbados corals that grew during periods of high sea level within the last 200 000 years the similarity of the initial 234 u 238 u ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine 234 u 238 u ratio 83 000 and 200 000 years ago was within 2 per mil of the modern value the accuracies of the 230 th ages are evaluated on the basis of the 234 u 238 u values and a model of the behavior of uranium and thorium isotopes during diagenesis for the last three interglacial and two intervening interstadial periods sea level peaked at or after peaks in summer insolation in the northern hemisphere this overall pattern supports the idea that glacial interglacial cycles are caused by changes in earth9s orbital geometry the sea level drop at the end of the penultimate interglacial the last interglacial and a subsequent interstadial period lagged behind the decrease in insolation by 5 000 to 10 000 years

a precisely dated climate record for the last 9 kyr from three high alpine stalagmites spannagel cave austria 1 here we use the 18o time series of three stalagmites from the high alpine spannagel cave austria which grew in small distance from each other to construct a precisely dated continuous 18o curve for the last 9 kyr comnispa this speleothem record is not influenced by effects of kinetic isotope fractionation due to the low temperatures in the cave thus the variations in 18o can be interpreted in terms of past climate change comnispa exhibits several oscillations within the holocene and their timing and duration is in agreement with that documented by other alpine archives

moored observations of deep low frequency motions in the central pacific ocean vertical structure and interpretation as equatorial waves abstract two year time series of current and temperature collected in the deep equatorial central pacific 0cean as part of the pacific equatorial ocean dynamics pequod project indicate that motions with vertical scales comparable to those of low baroclinic modes dominate motions from annual to fortnightly frequencies properties of equatorial waves are consistent with many aspects of the observed spectra and coherences in particular the hypothesis of a spectrum of long rossby and kelvin waves at periods longer than about 40 days and rossby mixed rossby gravity and kelvin waves at periods between about 14 and 40 days is consistent with the observations neither vertically propagating rays nor randomly phased baroclinic modes can explain coherence phases uniformly but forced phase locked baroclinic modes provide a possible explanation sea level in the central pacific is coherent with deep motions at periods of months or shorter in particular the quasi annual sea level signal associated with the 19

u pb shrimp ii lu hf isotope and trace element geochemistry of zircons from high grade metamorphic rocks of the irkut terrane sharyzhalgay uplift implications for the neoarchaean evolution of the siberian craton abstract this paper presents new data on the bulk rock composition petrogenesis and u pb zircon ages of high grade metamorphic rocks and granitoids of the irkut terrane which is part of the sharyzhalgay basement uplift located at the southwestern margin of the siberian craton our results allowed us to reliably constrain the neoarchaean evolution of the southwestern siberian craton the high grade rocks under study are two pyroxene amphibole mafic granulites and orthopyroxene bearing intermediate felsic granulites both types of granulite are enriched in ba th and lree and both show clear nb depletion characteristics that are typical of subduction related volcanic rocks the mafic and felsic granulites contain magmatic zircons of 2698 9 ma and 2662 16 ma respectively indicating that most of the protoliths of the high grade rocks formed in the neoarchaean the variable values of end 4 8 to 1 2 whole rock and ehf 1 6 to 2 4 zircons suggest contribution of older crust in the genesis of intermediate felsic granulites the relicts of ca 3 4 ga older rocks have recently been recognized within the irkut high grade metamorphic complex the petrological geochemical and isotopic features of high grade rocks are indicative of their protolith formation in a subduction related setting at the margin of an older continental block the metamorphic zircons in the high grade rocks with ages of 2567 6 and 2540 10 ma and the zircons in the gneissic granitoids with an age of 2540 11 ma probably record neoarchaean collisional events in the irkut terrane the coeval metamorphism ca 2 6 ga and granitoid magmatism ca 2 54 ga in the irkut and kitoy high grade terranes of the sharyzhalgay uplift suggest their neoarchean collision which resulted in the assembly of the sharyzhalgay superterrane similarly amalgamation of the ancient core of the siberian craton which consisted of the west aldan daldyn terranes and the two high grade terranes of the sharyzhalgay uplift probably began in the neoarchaean and was completed by 2 0 to 1 85 ga

rejuvenation vs recycling of archean crust in the gawler craton south australia evidence from u pb and hf isotopes in detrital zircon abstract zircon grains from modern and ancient drainages of the gawler craton south australia have been analysed to define the relative contributions of juvenile sources and recycled crust to magmatic activity as a function of time and to constrain the role of mantle inputs during the proterozoic rejuvenation of the archean gawler craton the integration of hf isotope data with u pb age spectra shows that the crustal evolution was dominated by long periods of crustal reworking and that crust generated in the paleoarchean 3 2 3 5 ga was largely reworked during proterozoic time four periods of juvenile mantle input can be recognised at ca 2540 ma 1853 ma 1595 ma and 1169 ma the 1169 ma event is not previously recognised in the gawler craton but the absence of other important age peaks argues against the transport of these zircons from the musgrave block only minor proportions of the magmatic zircons with paleoproterozoic to mesoproterozoic ages have strongly juvenile signatures e hf 4 indicating that crustal reworking was the dominant process with relatively minor mantle input comparison of the crustal evolution with that of nearby australian terranes suggests that although the gawler craton shows some similarities with the mount isa block and the georgetown inlier in neoarchean paleoproterozoic time it evolved independently between ca 1800 and 1550 ma

mass spectrometric dating of flowstones from stump cross caverns and lancaster hole yorkshire palaeoclimate implications a terrestrial flowstone sequence 97 cm thick from stump cross caverns yorkshire has been dated by both mass spectrometric and alpha spectrometric 238u 234u 230th dating and is demonstrated to have been deposited predominantly during interstadial periods over the last 170 ka with no growth in periods of glaciation or within the oxygen isotope stage 5 interglacial growth also occurs within oxygen isotope stages 4 and 6 the former possibly correlating with interstadials recognised in high resolution ice and ocean core records comparison with the timing of growth of a mass spectrometrically dated lancaster hole flowstone also from the same region demonstrates only limited agreement these differences are due to two factors limiting deposition at stump cross flooding of the cave passage in warm periods and the development of continuous permafrost or glacier cover in periods of severe climatic deterioration deposition at lancaster hole was controlled by limitations in ground water supply rather than flooding of the cave passage the results presented here demonstrate that in addition to regional palaeoclimate factors local site conditions may limit speleothem growth we conclude that in future palaeoclimate studies the growth record from several coeval speleothem samples must be considered before a regional palaeoclimate interpretation can be made

archaean re os age for siberian eclogites and constraints on archaean tectonics considerable uncertainty surrounds the nature and evolution of the earth s mantle in archaean times 2 5 gyr ago mantle derived eclogite xenoliths erupted by kimberlites provide important clues in this regard because their basaltic composition suggests that they may be remnants of an early 4 gyr magma ocean1 2 subducted archaean oceanic crust3 5 or crystallized high pressure mantle melts6 9 better constraints on the age and origin of mantle eclogites are thus important for our understanding of early earth processes here we present rhenium osmium isotope data for diamond bearing eclogites from the udachnaya kimberlite pipe in siberia which indicate formation in the archaean 2 9 0 4 gyr this age is too young for the eclogites to be remnants of early earth differentiation but overlaps the age range for crust generation and craton stabilization on both the aldan and anabar shields of the siberian craton 2 85 3 2 gyr 10 11 these data together with 3 1 gyr re os model ages for diamond bearing udachnaya peridotites12 show that the siberian craton lithosphere was at least 150 km thick the minimum required for diamond stability by the mid archaean

micromill and in situ laser ablation sampling techniques for high spatial resolution mc icpms u th dating of carbonates abstract procedures for accurate determinations of 230th 234u 238u isotope ratios using in situ laser ablation la and micromill techniques for carbonates such as speleothems and corals are presented for la analyses we use a new wave research up193he laser and a new multiple ion counting detector system available for the thermofinnigan neptune mc icpms multiple ion counting increases the efficiency of low level ion beam collection by allowing simultaneous collection of all ion beams and also circumvents problems associated with unstable transient beams we present results of la u series measurements on a u rich 10 168 g g speleothem from spannagel cave austria and of small sub samples from the same speleothem section prepared using a new wave research micromill and processed through separation and purification solution chemistry using a secular equilibrium speleothem with u concentration of 0 25 g g we demonstrate that la measurements yield accurate results on speleothem samples with less than 0 5 g g u for la results we currently obtain 230th 238u results with precisions of 2 95 confidence limit for single isotope ratio measurements on a u rich sample on the low u 0 25 g g u sample we achieve a precision between 10 and 20 for single 230th 238u measurements precisions of 1 and 5 2 m can be achieved for high and low u concentration samples respectively using 10 15 measurements on coeval sub samples 0 4 mg micromill sub samples of the low u concentration sample yield 230th 238u isotope ratios with precisions of 2 accuracy of la and micromill measurements is assessed by comparison with mc icpms and tims measurements on larger sub samples key advantages of our la technique are for example high spatial resolution analyses and the possibility of rapid determination of numerous coeval sub samples the results on micromill samples are more precise but this sample preparation technique is time consuming and larger sample sizes than used for la are needed for individual measurements

calculation and application of clinopyroxene garnet plagioclase quartz geobarometers recently published thermodynamic and experimental data in a variety of chemical systems have been evaluated to derive gibbs free energies for hedenbergite and pyrope these were used to calculate the geobarometric equilibria

u th pb and lu hf systematics of zircon from ttg s leucosomes meta anorthosites and quartzites of the limpopo belt south africa constraints for the formation recycling and metamorphism of palaeoarchaean crust abstract results of more than 400 in situ u th pb and lu hf zircon isotope analyses combined with cathodoluminescence images and field relationships reveal that the oldest magmatic rocks of the limpopo belt musina area formed during the palaeoarchaean between 3 40 and 3 27 ga experienced a first anatexis at 3 24 3 07 ga m1 and were overlain by sediments mainly between 3 24 and 3 0 ga subsequently the infra and supracrustal rocks together underwent two high grade metamorphic overprints a first during the neoarchaean at 2 65 ga m2 and a second at 2 025 ga m3 hafnium isotope data additionally reveal that the palaeoarchaean magmatic rocks result from substantial recycling of much older crust this is well reflected by nearly chondritic hf int obtained from primary magmatic zircon domains of four sand river ttg gneiss samples hf 3 27 3 28 ga 1 3 to 1 8 from leucosomes within the sand river gneisses hf 3 40 ga 2 0 hf 3 28 ga 1 5 and from two meta anorthosite samples of the messina layered intrusion hf 3 35 ga 0 1 1 4 crustal recycling is also supported by hafnium isotope data of detrital zircon grains from two quartzite samples these data reflect a general increase of the hf int between 3 65 and 3 2 ga from ca 4 0 to 0 0 indicating that an eo to palaeoarchaean crust was mixed with juvenile mantel material in the hinterland of the limpopo belt the present study also demonstrates that hf isotope data provide a powerful tool which makes it possible to distinguish zircon domains formed during distinct magmatic or metamorphic events from such affected by a pseudomorphic alteration even if the investigated zircon grain underwent multiple alteration processes

rapid sea level fall and deep ocean temperature change since the last interglacial period we have dated huon peninsula papua new guinea and barbados corals that formed at times since the last interglacial period applying both 230 th and 231 pa dating techniques as a test of age accuracy we show that marine isotope stage mis 5e ended prior to 113 1 8 0 7 kyr when sea level was 319 m during mis 5b sea level was 357 m at 92 6 8 0 5 kyr having dropped about 40 m in approximately 10 kyr during the mis 5c 5b transition sea level then rose more than 40 m during the mis 5b 5a transition also in about 10 kyr mis 5a lasted until at least 76 2 8 0 4 kyr at a level of 324 m at that time combined with earlier data that places mis 4 sea level at 381 m at 70 8 kyr our late mis 5a data indicate that sea level fell almost 60 m in less than 6 kyr 10 6 m kyr during the mis 5 4 transition the magnitude of the drop is half that of the glacial interglacial amplitude and approximatelyequivalent to the volume of the present dayantarctic ice sheet during this interval the minimum average rate of net continental ice accumulation was 18 cm yr likely facilitated by efficient moisture transport from lower latitudes at three specific times 60 6 8 0 3 50 8 8 0 3 and 36 8 0 2 kyr during mis 3 sea level was between 385 and 374 m sea level then dropped to 3107 m at 23 7 8 0 1 kyr early in mis 2 before dropping further to last glacial maximum lgm values and then rising to present values during the last deglaciation times of rapid sea level drop correspond to times of high winter insolation at low northern latitudes and high winter latitudinal gradients in northern hemisphere insolation supporting the idea that these factors mayhave resulted in high water vapor pressure in moisture sources and efficient moisture transport to high latitude glaciers therebycontributing to glacial buildup we combined our sea level results with deep sea n 18 o records as a means of estimating the temperature and ice volume components in the marine n 18 o record this analysis confirms large deep ocean temperature shifts following mis 5e and during termination i deep ocean temperatures changed bymuch smaller amounts between mis 5c and 2 maximum temperature shift in the deep pacific is about 2 whereas the shift at a site in the atlantic is 4 under glacial conditions temperatures at both sites are near the freezing point the shift in the atlantic is likelycaused bya combination of changing proportions of northern and southern source waters as well as changing temperature at the sites where these deep waters form

stalagmite from the austrian alps reveals dansgaard oeschger events during isotope stage 3 implications for the absolute chronology of greenland ice cores a mass spectrometric uranium series dated stalagmite from the central alps of austria provides unprecedented new insights into high altitude climate change during the peak of isotope stage 3 the stalagmite formed continuously between 57 and 46 kyr before present a series of hendy tests demonstrates that the outer parts of the sample show a progressive increase of both stable c and o isotope values no such covariant increase was detected within the axial zone this in conjunction with other observations suggests that the continuous stable oxygen isotope profile obtained from the axial zone of the stalagmite largely reflects the unaltered isotopic composition of the cave drip water the n 18 o record shows events of high n 18 o values that correlate remarkably with interstadials 15 a and b 14 and 12 identified in the greenland ice cores interstadial 15b started rapidly at 55 6 kyr and lasted v300 yr only interstadial 15a peaked 54 9 kyr ago and was even of shorter duration v100 yr and interstadial 14 commenced 54 2 kyr ago and lasted v3000 yr this stalagmite thus represents one of the first terrestrial archives outside the high latitudes which record precisely dated dansgaard oeschger d o events during isotope stage 3 provided that rapid d o warmings occurred synchronously in greenland and the european alps the new data provide an independent tool to improve the grip and gisp2 chronologies 2002 elsevier science b v all rights reserved

assembly of the siberian craton constraints from paleoproterozoic granitoids abstract the paper presents a synthesis of geochronological geochemical and isotopic data on paleoproterozoic granitoids in the siberian craton and in some cases on volcanics related to these granitoids different evolution stages of the craton including its assembly are recorded in several major events in the history of paleoproterozoic granitic magmatism they are 2 52 2 40 ga and 2 15 2 04 ga granitoids of different tectonic settings 2 06 2 00 ga subduction related granitoids 2 00 1 87 ga collisional granitoids 1 88 1 84 postcollisional granitoids and 1 76 1 71 ga within plate anorogenic varieties granitoids with ages of 2 5 2 4 ga and 2 15 2 04 ga are distributed locally in separate blocks and terranes which later entered the craton structure these rocks are of different types and represent different tectonic settings of the respective blocks and terranes i e the siberian craton did not exist yet as a single unit at that time the 2 06 2 00 ga subduction related granitoids and volcanics are found in the southern and southeastern craton parts magmatism of that time interval probably was associated with subduction beneath the archean olekma aldan and anabar continental microplates and with the formation of their active margins granitoids of the 2 00 1 87 ga age interval represent a collisional stage of the craton evolution collisional granitoids that intruded between 2 00 and 1 95 ga record the first large scale stage of craton assembly with collisions of terranes that had built the core of the anabar aldan and olenek superterranes the intrusions of 1 95 1 90 ga granitoids mark the consolidation of the southeastern craton part collisional granitoids with the 1 90 1 87 ga ages which are especially abundant in the south and southwest of the craton but almost lack from the north led to general assembly of the craton the granitoid and volcanic magmatic activity of 1 88 1 84 ga in the craton south produced the south siberian postcollisional magmatic belt that had completed the assembly of the craton which in its turn may have been part of the paleoproterozoic supercontinent of columbia granitic intrusions at 1 76 1 71 ga are limited to the southwestern and southeastern craton parts and correspond to a setting of continental extension which never led to the breakup of the craton

high precision constraints on timing of alpine warm periods during the middle to late pleistocene using speleothem growth periods a long standing problem in the reconstruction of warm climate periods during the late quaternary is the difficulty of determining absolute ages for undisturbed terrestrial climate archives speleothems offer an important source of information about the timing and duration of middle and late pleistocene warm phases a flowstone from the high elevation spannagel cave zillertal alps austria provides a new absolutely dated climate record which includes the most prominent warm phases between 260 and 50 ka before present new data from the penultimate interglacial improve our knowledge about the timing and progression of warm periods in the alps corresponding to marine isotope stages 7 and 8 speleothem growth phases were identified from 261 to 249 from 236 to 229 and from 200 to 192 ka an early onset of the last interglacial is corroborated by a growth phase commencing at 136 7f2 8 ka and the youngest section of the flowstone provides further evidence for an alpine climate during time intervals corresponding to marine isotope stages 5a and 3 sufficiently warm to allow speleothems to grow the high resolution stable isotope profile taken along the growth axis of the flowstone provides information about the hydrological conditions during the growth phases d 2005 elsevier b v all rights reserved

chronology and paleoenvironment of marine isotope stage 3 from two high elevation speleothems austrian alps abstract a new high resolution stable isotope record from the alpine kleegruben cave 2165 m central alps is presented this record largely duplicates a previously reported speleothem record from this site high precision u series thermal ionization mass spectrometry dates constrain the growth history of this new sample 56 48 ka to the marine isotope stage mis 3 both stalagmites reveal highly similar variations in o isotopes that can be directly compared to o isotope variability associated with dansgaard oeschger interstadials recorded in the greenland ice cores greenland interstadials gis based on the new record we refine our previous age assignments of the gis during this time interval i e gis 15b at 55 7 ka gis 15a at 55 3 ka onset mid point of the prominent gis 14 at 54 5 yr and onset of gis 12 at 48 ka the overall uncertainties associated with these ages are 0 1 0 3 ka the timing of these dansgaard oeschger interstadials is within 0 2 ka of the newly proposed grip sfcp04 timescale the age data for both kleegruben stalagmites demonstrate that liquid water was at least seasonally present in the shallow sub surface allowing calcite precipitation to continue even during stadials of mis 3 given the present day low temperature 2 4 c we propose that these unusual speleothems formed in a karst system overlain by a warm based glacier

hypogene speleogenesis in dolomite host rock by co2 rich fluids kozak cave southern austria a growing number of studies suggest that cave formation by deep seated groundwater hypogene is a more common process of subsurface water rock interaction than previously thought fossil hypogene caves are identified by a characteristic suite of morphological features on different spatial scales in addition mineral deposits speleothems may provide clues about the chemical composition of the paleowater which range from co2 rich to sulfuric acid bearing waters this is one of the first studies to examine hypogene cave formation in dolomite kozak cave is a fossil cave near the periadriatic lineament an area known for its abundance of co2 rich springs the cave displays a number of macro meso and micromorphological elements found also in other hypogene caves hosted in limestone marble or gypsum including cupolas cusps laughohle type chambers and notches the existance of cupolas and cusps suggests a thermal gradient capable of sustaining free convection during a first phase of speleogenesis while triangular cross sections laughohle morphology indicate subsequent density driven convection close to the paleowater table notches mark the final emergence of the cave due to continued rock uplift and valley incision very narrow shafts near the end of the cave may be part of the initial feeder system but an epigene vadose overprint cannot be ruled out vadose speleothems indicate that the phreatic phase ended at least about half a million years ago drill cores show no evidence of carbon or oxygen isotope alteration of the wall rock this is in contrast to similar studies in limestone caves and highlights the need for further wall rock studies of caves hosted in limestone and dolomite

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr