constraints from 40ar 39ar geochronology on the tectonothermal history of the kapuskasing uplift in the canadian superior province the kapuskasing uplift ku in the superior province of the canadian shield has been interpreted as an oblique cross section through the archean mid crust however the time of juxtaposition of the granulites of the ku against the lower grade rocks of the abitibi greenstone belt agb along the ivanhoe lake fault zone is problematic to constrain the postmetamorphic tectonothermal history of the ku we have conducted 57 40ar 39ar step heating analyses on mineral and rock samples collected in a transect across the southern ku and adjacent agb the age spectra record a complex thermal history amphiboles from the agb in the footwall of the ivanhoe lake fault zone have ca 2 66 ga dates similar to closure ages for amphiboles from farther east in the agb amphibole dates of 2 46 2 52 ga from the deepest structural levels of the ku place an upper limit on the time of major uplift of the granulites and their juxtaposition with the agb biotite and muscovite dates from the transect cluster into three age groups

remagnetization in keweenawan rocks part i conglomerates conglomerate tests are used to show that late precambrian keweenawan conglomerates on the keweenaw peninsula michigan and at mamainse point ontario have suffered a partial chemical remagnetization that predated tectonic tilting at mamainse point the overprint was acquired during the final normal polarity stage of keweenawan volcanism whereas on the keweenaw peninsula it occurred after cessation of volcanism and has a maximum late freda sandstone age the extent of overprinting on the keweenaw peninsula increases westwards along a 40 km strike length in the copper harbor conglomerate and may at least in part be related to secondary mineral zonation including native copper in the underlying portage lake volcanics it is shown that neither of the two overprinting episodes can be responsible for the reversal asymmetry observed in keweenawan igneous rocks

evidence from aeromagnetics on the configuration of matachewan dykes and the tectonic evolution of the kapuskasing structural zone ontario canada by digital image processing of federal provincial aeromagnetic survey data for the south central superior province we have obtained an improved picture of the distribution of dykes in the huge matachewan mafic dyke swarm 2454 ma we deduce from it a picture of post emplacement deformation in the vicinity of the uplifted granulite gneisses of the kapuskasing structural zone ksz matachewan dykes are emplaced in three subswarms the two easterly subswarms are clearly truncated by the ksz s eastern boundary faults the western subswarm shows an open z bend as it crosses the ksz but it does not reveal any major fault offset on the plausible assumption supported by paleomagnetic data that the subswarms were originally intruded radially the horizontal strain suffered by the ksz since emplacement of the dykes is mainly a northeast southwest trending band of dextral transcurrent deformation which in the northeast is discontinuous and concentrated in a fault horizontal offset 60 80 km and in the south

a 110 000 year history of change in continental biogenic emissions and related atmospheric circulation inferred from the greenland ice sheet project ice core the 110 000 year record of ammonium concentrations from the greenland ice sheet project 2 gisp2 ice core provides the basis for an analysis of terrestrial biological production and atmospheric circulation patterns involved in the transport of biologically produced ammonium to the greenland atmosphere the directly measured concentration series was selected for analysis rather than that of estimated ammonium flux after a detailed analysis of the relationship among ice core glaciochemical concentrations and a high resolution simultaneous record of snow accumulation from the gisp2 core analysis of the ammonium concentration series shows that maxima in background levels of ammonium in the greenland atmosphere are strongly related to and synchronous with summer forcing associated with the precessional cycle of insolation minima in background levels on the other hand are delayed relative to minima in summer insolation at those times when ice volume is significant the duration of these delays are similar in magnitude 6000 years to other paleoclimatic responses to changes in ice volume decadal and centennial scale variation about background levels of ammonium concentration exhibit two modes of behavior when compared to a record of polar atmospheric circulation intensity during warmer periods ammonium transport to greenland is similar to present patterns under coldest conditions the low levels of ammonium transported to greenland are the result of extreme southerly excursions of the predominantly zonal polar circulation the rapid transitions 200 years between these two climatic conditions appear to be associated with a critical volume or extent of the continental ice sheets

231pa and 230th contamination at zero age a possible limitation on u th series dating of speleothem material abstract analysis of 67 new zealand speleothem specimens for both 230 th 234 u and 231 pa 235 u by alpha spectrometry showed that in most cases the age concordance between them was excellent however analysis of two growing speleothems less than 100 years old showed apparent near concordant ages of 2 and 3 ka both 230 th and 231 pa had been added to the speleothem contrary to a basic assumption of the dating method in other cases of discordance there was additional evidence that 230 th and sometimes 231 pa had been added to the growing speleothem and probably originated from erosion of old limestone by carbonate rich waters calculation shows that typical 230 th and 232 th contents in carbonate rich waters could easily be deposited in sufficient quantity in growing speleothems in realistic time intervals to produce the amounts found in the straw stalactites the u contents of these speleothem samples were unusually low 42 contained less than 0 1 mg kg 1 but aragonitic samples contained 100 as much u

effect of wind scouring on climatic records from ice core oxygen isotope profiles removal of winter snow by wind explains why the annual mean oxygen isotope ratio at an ice divide is 2 5 less negative than it is 1 2 km downslope cores from two sites on an ice cap ellesmere island canada show past variations in the difference depending on where the ice originated relative to the scoured zone some ice core climatic records may need correction for scouring

the evolution and environmental significance of glaciochemistry during the ablation period in the north of tibetan plateau china in order to explore the glaciochemistry of shiyi glacier in the central qilian mountains a total of 142 samples have been collected for fresh snow surface snow snowpit and meltwater from july 2012 to november 2013 the results indicated cations dominated the glaciochemistry especially the high ca2 concentration relatively high cl and na concentrations were mainly contributed by desert dust aerosols and the atmospheric aerosols from warm water bodies such as the black caspian and aral seas the analysis also confirmed the chemical ions in fresh snow are mainly contributed by atmospheric wet deposition surface snow is mainly influenced by dry deposition and snowpits are influenced by both atmospheric deposition and leaching process while meltwater is influenced by water rock interactions the profile of ionic concentration in the snowpit became more smoothed during ablation period owing to the influence of leaching the elution sequence of the snowpit in the shiyi glacier was so42 k ca2 mg2 na cl no3 the chemical concentrations for meltwater are mainly influenced by water dilution and soil thawing the ions in snow in the central qilian mountains showed relatively lower concentrations than in the western qilian mountains tianshan mountains and altai mountains it was closer to balance than in glaciers in the central tibetan plateau but was higher than in the southern tibetan plateau different ionic sources and dissolution process had caused the differences of chemical composition for fresh snow surface snow snowpit and meltwater and these chemical compositions reflected the atmospheric background values in the northern tibetan plateau c 2014 elsevier ltd and inqua all rights reserved

indian monsoon and north atlantic oscillation signals reflected by cl and na in a shallow ice core from dasuopu glacier xixabangma himalaya

abrupt and moderate climate changes in the mid latitudes of asia during the holocene a multiple parameter dating technique was used to establish a depth age scale for a 171 3 m 145 87 m w e surface to bedrock ice core bl2003 recovered from the cold recrystallization accumulation zone of the western belukha plateau 4115 m a s l in the siberian altai mountains the ice core record presented visible layering of annual accumulation and of delta o 18 delta d stable isotopes and a clear tritium reference horizon a steady state glacier flow model for layer thinning was calibrated and applied to establish a depth age scale four radiocarbon c 14 measurements of particulate organic carbon contained in ice core samples revealed dates for the bottom part of bl2003 from 9075 1221 cal a bc at 145 2 0 1 m w e 0 665 m w e from the bedrock to 790 93 ad at 121 1 m w e depth sulfate peaks coincident with volcanic eruptions the tunguska meteorite event and the 1842 dust storm were used to verify dating analysis of the bl2003 ice core reveals that the modern altai glaciers were formed during the younger dryas yd similar to 10 950 to similar to 7500 cal a bc and that they survived the holocene climate optimum hco similar to 6500 to similar to 3600 cal a bc and the medieval warm period mwp similar to 640 to similar to 1100 ad a decrease in air temperature at the beginning and an abrupt increase at the end of the yd were identified intensification of winds and dust loading related to asian desert expansion also characterized the yd during the yd major ion concentrations increased significantly up to 50 times for na background up to 45 times for ca2 and mg2 and up to 20 times for so42 relative to the recent warm period from 1993 to 2003 a warm period lasted for about three centuries following the yd signaling onset of the hco a significant and prolonged decrease in air temperature from similar to 2000 to similar to 600 cal a bc was associated with a severe centennial drought scd a sharp increase in air temperatures after the scd was coincident with the mwp after the mwp a cooling was followed gradually with further onset of the little ice age during the modern warm period 1973 2003 an increase in air temperature is noted which nearly reaches the average of hco and mwp air temperature values

soluble ionic and oxygen isotopic compositions of a shallow firn profile baishui glacier no 1 southeastern tibetan plateau in the summer of 2004 a firn profile 18 3m long extending down to glacier ice was recovered in the accumulation area of the largest glacier baishui no 1 on yulong mountain the southernmost glacier covered area in mainland eurasia multivariate empirical orthogonal function eof and statistical correlation analyses of major ion data from the profile demonstrate that three distinct types of ionic material contribute to the chemical characteristics of firn in this monsoonal region material of marine origin which is transported by the indian southwest monsoon crustal materials which come from local sources and anthropogenic pollutants which are produced by industrial and agricultural activities in south asia although the influence of post depositional processes on the seasonal isotopic and soluble ionic compositions is significant dust layers in the firn profile are clearly visible due to the effects of meltwater percolation the dust layers generally coincide with latesummer snow surfaces we therefore use the dust layers combined with the seasonal variations of electrical conductivity ec ca and mg to establish a depth age scale for the firn profile the reconstructed net accumulation has a significant negative correlation with the temperature at lijiang whereas the correlation between the net accumulation and the precipitation amount at lijiang is weak although the do time series of the firn profile was modified significantly by meltwater percolation the correlation between annual mean do values and the indian southwest monsoon index wsi1 is significant this result suggests that do records from monsoon influenced temperate glaciers can provide a valuable record of past variations of the indian southwest monsoon

multi speleothem record reveals tightly coupled climate between central europe and greenland during marine isotope stage 3 the last glacial period was punctuated by abrupt millennial scale climate changes that contain useful information about the rate at which the climate can change from one state to another improvement in our knowledge of the temporal and spatial character of these rapid climate changes is important for understanding their causes and effects and provides essential observational information for modeling studies here we expand the coverage of terrestrial climate records during the last glacial period and present a series of high resolution stalagmite records from a cave in the northern alps central europe covering parts of the period 65 35 ka before a d 1950 the climatic pattern revealed by the stalagmite temperature controlled d 18 o profiles strongly resembles that of greenland ice cores on millennial scales and also corresponds to the detail of decadal scale cooling events within interstadials this demonstrates for the first time a strong climatic similarity and or coupling between the two regions during marine isotope stage 3 mis 3 furthermore an overall long term agreement between the northern european alps stalagmite chronology nalps presented here and the greenland ice core chronology 2005 modelext gicc05modelext suggests that the central value of the greenland chronology may be slightly too young possibly as a result of an undercounting of layers in a younger section of the core and that the uncertainty on the greenland chronology may be overestimated the synchronicity displayed here between greenland and central europe especially during the period 65 49 ka is crucial for our understanding of climate system teleconnections that existed during the last glacial period and will be important for developing mechanisms of abrupt climate events

the tectonic relationship of two early proterozoic dyke swarms to the kapuskasing structural zone a paleomagnetic and petrographic study a tea coloured cloudiness in groundmass feldspars characterizes dykes of two early proterozoic swarms 2 45 ga matachewan 2 04 ga kapuskasing that intrude amphibolite to granulite host rocks with

stable isotopic composition of precipitation over the northern slope of the central himalaya stable water isotope data 6d and 18 o from three groups of samples fresh snow and snow pit samples collected on qomolangma mount everest and xixabangma during field seasons 1997 1998 and 2001 and precipitation samples collected at tingri station during summer 2000 are presented and used to survey the isotopic composition of precipitation over the northern slope of the central himalaya multi year snow pit samples on qomolangma have a local meteoric water line slope 8 close to the global value deuterium excess d d 8 18 o values at tingri are much lower than those in fresh snow from qomolangma probably due to differences in moisture source and air mass trajectories as well as local weather conditions there is no obvious seasonal trend for d values in the qomolangma region a negative relationship exists between 18 o and d values in both fresh snow on qomolangma and precipitation at tingri fresh snow samples collected from different altitudes on xixabangma allow us to investigate the altitude effect on 18 o values in snow of four storm events only one has an obvious altitude effect on 18 o variation and a very low gradient of 0 1 per 100 m elevation

paleomagnetism of the red lake greenstone belt northwestern ontario possible evidence for the timing of gold mineralization we report paleomagnetic results from 1 largely unaltered batholiths and 2 sheared and altered units in the archean red lake greenstone belt a major gold producing region in the uchi subprovince of northwestern ontario group 1 includes the hammell lake killala baird trout lake and little vermilion lake batholiths which were intruded between 2730 and 2700 ma ago u pb zircon group 2 includes the howey diorite the dome stock and dikes and andesites from the dickenson mine these units from the mineralized deformation zones dzs between the batholiths were sheared and hydrothermally altered in the same event that caused gold mineralization in supracrustal units the batholiths carry a stable reversed remanence rlr withd 159 i 74 k 20 95 16 n 4 units 14 sites rlr has high coercivities unblocking temperatures and remanence intensities and appears to be a primary thermal remanence dating from 2700 ma the altered units from the gold bearing dzs carry a different remanence rlg withd 180 i 57 k 23 95 3 n 3 units 6 sites rlg also has relatively high coercivities and unblocking temperatures but its magnetization intensities are 1 2 orders of magnitude lower than those of rlr opaque minerals and silicates observed in thin section are highly altered rlg is therefore believed to be a chemical or thermochemical remanence acquired 2580 ma ago during the late stages of cooling and gold mineralization seeing as rlg characterizes the shear zone rocks but is absent from unaltered rocks outside the dzs it could be used as a rapid prospecting tool in delineating areas of alteration and possible mineralization the paleopoles for rlr 2700 ma and rlg 2580 ma link with those of the shelley lake granite 2580 ma 40ar 39ar hornblende and biotite and the matachewan hearst dikes 2450 ma u pb zircon and baddeleyite the sense of motion on the late archean early proterozoic apparent polar wander path for laurentia as defined by this sequence of paleopoles is opposite to that previously accepted

a review of central asian glaciochemical data the glaciers of central asia provide suitable locations from which to recover continuous high resolution glaciochemical records on a continental scale although the glaciochemical investigations undertaken to date in central asia are few in number and limited in terms of spatial coverage and length of record some preliminary observations can be made concerning regional and seasonal trends in snow chemistry in this region the sodium chloride ratio for most snow samples collected in central asia approaches the ratio found in sea water 0 86 in leq kg i reflecting a marine source for these constituents sodium and chloride concentrations are on average 3 10 times higher in the himalayas than in the karakoram demonstrating the greater influence of monsoonal sources of moisture in the himalayas very high sodium concentrations from khel khod glacier probably reflect a local crustal source from surrounding ice free areas low nitrate concentrations were found in snow collected from the southern margin of the himalayas and high concentrations in snow deposited on the north margin of the himalayas this strong regional trend in the spatial distribution of nitrate suggests the influx of continental aerosols rich in nitrate originating from the arid regions of central asia high calcium concentrations measured in snow from mount everest and the north west corner of china are also indicative of dust derived from the arid regions of central asia very high sulfate concentrations found in snow from the tien shan and the bogda shan most likely reflect local anthropogenic sources the altitude effect on isotopic composition is not apparent from snow samples collected in central asia understanding the processes which control the chemical content of snow the local to regiona l scale complexities

a scanning electron microscope technique for identifying the mineralogy of dust in ice cores dust particles in an ice core from east rongbuk glacier on the northern slope of qomolangma mount everest 28 01 n 86 58 e 6518 m a s l central himalaya have been identified as mica using a combination of scanning electron microscope based techniques and energy dispersive x ray spectroscopy to identify the elements present and electron backscatter diffraction to identify the crystal type this technique for identifying individual crystalline dust particles in samples of glacial ice could be especially useful in the future for identifying water soluble crystals in ice for studying the strain history glaciotectonics of basal ice or in studies of ice mica composites used as analogs of quartz mica rocks

abundant climatic information in water stable isotope record from a maritime glacier on southeastern tibetan plateau climatic significance of ice core stable isotope record in the himalayas and southern tibetan plateau tp where the climate is alternately influenced by indian summer monsoon and mid latitude westerlies is still debated a newly drilled zuoqiupu ice core from a temperate maritime glacier on the southeastern tp covering 1942 2011 is investigated in terms of the relationships between 18o and climate parameters distinct seasonal variation of 18o is observed due to high precipitation amount in this area thus the monsoon june to september and non monsoon october to may 18o records are reconstructed respectively the temperature effect is identified in the annual 18o record which is predominantly contributed by temperature control on the non monsoon precipitation 18o record conversely the negative correlation between annual 18o record and precipitation amount over part of northeast india is mostly contributed by the monsoon precipitation 18o record the variation of monsoon 18o record is greatly impacted by the indian summer monsoon strength while that of non monsoon 18o record is potentially associated with the mid latitude westerly activity the relationship between zuoqiupu 18o record and sea surface temperature sst is found to be inconsistent before and after the climate shift of 1976 1977 in summer monsoon season the role of sst in the monsoon 18o record is more important in eastern equatorial pacific ocean and tropical indian ocean before and after the shift respectively in non monsoon season however the atlantic multidecadal oscillation has a negative impact before but positive impact after the climate shift on the non monsoon 18o record

a 1000 year climate ice core record from the guliya ice cap china its relationship to global climate variability in 1992 an american chinese expedition successfully recovered three ice cores 308 6 93 2 and 34 5m from the guliya ice cap summit 6710 m a s l in the far western kunlun on the qinghai tibetan plateau china guliya resembles a polar icecap with 10 m 200 m and basal temperatures of 15 6 5 9 and 2 1 c respectively the 308 6 m core to bedrock is the longest ice core retrieved from an elevation greater than 4000 m a s l and provides the first ice core history from the western side of the qinghai plateau the plateau experiences a pronounced annual precipitation cycle during which 70 80 of annual total precipitation falls in the summer monsoon season this leads to a marked visible stratigraphy in the glaciers which allows accurate dating of the ice cores and reconstruction of the net mass accumulation this paper presents 1 the results of the geophysical program to determine ice thickness ice flow and surface topography 2 an assessment of net accumulation from stake measurements snow pits and shallow core samples and 3 the analyses of the upper 100 m of the 308 6 m core which provide a 1000 year history including the little ice age which is compared with chinese historical records extended periods of positive accumulation on guliya are closely contemporaneous with dry periods in eastern china a trans pacific teleconnection is suggested by the strong temporal coherence between extended wet and dry phases on guliya and on the quelccaya ice cap peru

anthropogenic sulfate and asian dust signals in snow from tien shan northwest china snow samples were collected from a 0 5 m snowpack at glacier no i and near bogda feng eastern tien shan northwest china samples that were melted in the field were analyzed for chloride nitrate sulfate sodium potassium magnesium calcium and microparticles eight samples were returned frozen and were analyzed for the above ions plus ammonium acetate formate methylsulfonate and hydrogen peroxide there was no significant difference in measured major ion concentrations between the melted and frozen samples measured cations in both sets of samples were two to three times greater than measured anions calcium and sodium are the dominant cations while sulfate is the dominant measured anion high ion burdens are associated with dusty layers in the snowpack indicating that dust from the vast arid regions of central asia is the dominant source for major ions in tien shan snow the significant increase in sulfate and decrease in the cation anion ratio in bogda eng snow relative to glacier no i snow suggest that anthropogenic emissions from urtimqi are an important source of sulfate to precipitation downwind from the city

interpretation of the chemical and physical time series retrieved from sentik glacier ladakh himalaya india analyse a partir de mesures de la radioactivite d analyses chimiques chlorures sodium fer silicates phosphates ammonium d 18 o et ph et de donnees physiques des variations cycliques temporelles des glaciers application aux paleoclimats

rb sr and u pb ages of volcanism and granite emplacement in the michipicoten belt wawa ontario the michipicoten greenstone belt at wawa ontario is typical of archean volcanic belts in the superior province the supracrustal rocks are divisible into lower middle and upper metavolcanic sequences which are separated by iron formation and clastic metasedimentary rocks these are intruded by granitic stocks and embayed by granitic batholiths this study reports whole rock rb sr and zircon u pb ages for the lower and upper metavolcanics for the granitic rocks that are physically within the greenstone belt internal granites and for the granitic rocks that embay the greenstone belt external granites the apparent rb sr ages for the lower metavolcanics are 2530 90 2285 70 and 2680 490 ma the u pb ages are 2749 2 and 2744 10 ma the internal granites give an rb sr age of 2560 270 ma and a u pb age of 2737 6 ma the external granite at hawk lake indicates an rb sr age of 2550 175 ma and a u pb age of 2747 7 ma it is possible that this unit contains elements older than 2812 ma as

monsoon and dust signals recorded in dasuopu glacier tibetan plateau during summer 1997 a 15 m firn core was recovered from dasuopu glacier 28 23 n 85 44 e 7000 m a s l on the northwest margin of xixabarngma feng in the central himalaya oxygen isotope values and concentrations of ca 2 mg 2 nh 4 so 4 2 and no 3 were measured over the 10 years of snow accumulation captured in the firn core the seasonal variations of 18 o values and major ion concentrations in the dasuopu core indicate that summer monsoon and dust signals are clearly recorded in dasuopu glacier annual variations in 18 o values are controlled by the amount effect with more negative i e lighter 18 o values representing summer monsoon precipitation characteristic of tropical regions higher concentrations of ca 2 mg 2 and so 4 2 reflect the influx of mineral aerosols from the vast arid and semi arid desert regions to the north and west during the spring dust storm period high spring concentrations of nh 4 and no 3 appear to reflect changes in regional biogenic source strength

calibration of the speleothem delta function an absolute temperature record for the holocene in northern norway the speleothem delta function sdf provides a new transfer function between the d18o signal of speleothem calcite and surface ground temperature the function is based on physical principles relating d18o of the calcite to thermodynamic fractionation and to the dripwater function which in turn relates d18o of dripwaters to that of the local precipitation and thus to the modification of source water in relationship to the geographical position of the site the sdf must be calibrated against at least two reliable and well dated palaeotemperature points the end product is a reconstruction of absolute cave and surface temperatures the technique is tested using a holocene speleothem from north norway sg93 dated by 12 tims u th dates the reconstructed temperature curve is presented and compared with the gisp2 ice core record and with the historic record in both cases the correlation with sg93 is impressive indicating the validity of the technique

geochemistry of the mamainse point volcanics ontario and implications for the keweenawan paleomagnetic record the keweenawan 1100 ma mamainse point volcanics located along the eastern shore of lake superior in ontario formed in the midcontinent rift of north america they are a 5250 m thick sequence of over 350 predominantly basaltic lava flows the mamainse point section is the most continuous keweenawan volcanic sequence and spans nearly the entire igneous history of the rift the lower part of the section consists of high mgo picrites and basalts but the upper part of the section is composed of olivine tholeiites intercalated with numerous conglomerate layers major and trace element data reveal that the section consists of numerous stratigraphically constrained geochemically distinct groups of lava flows the comprehensive geochemical data on the entire sequence indicate that the section has no repetition due to faulting as has been suggested by other workers on the basis of paleomagnetic studies evidently the three paleomagnetic reversals previously found in the mamainse point section are real and

synopsis of paleomagnetic studies in the kapuskasing structural zone this paper summarizes results from paleomagnetic studies sponsored by lithoprobe on the kapuskasing structural zone ksz data from archean rocks outside the ksz indicate that the wawa subprovince has not been significantly rotated or translated 5 relative to the abitibi subprovince results from the granulites and amphibolites indicate that the ksz underwent several kilometres of uplift at ca 2 51 ga and then 10 5 west northwest tilt with several kilometres of further uplift between 2 04 and 1 88 ga from thrust faulting on the ivanhoe lake fault zone localized chemical remagnetization occurred at 1 1 ga along the west side of the shawmere anorthosite paleomagnetic data from the 2 45 ga matachewan diabase dike swarm indicate that it was emplaced within one reversed to normal polarity interval of less than 5 ma their polarity pattern indicates major north trending faults with several kilometres of dip slip displacement their remanence confirms that the superior province was deformed around th

archean crust as revealed in the kapuskasing uplift superior province canada in the central superior province of the canadian shield a 120 km wide transition from the low grade michipicoten greenstone belt to the high grade kapuskasing structural zone represents an oblique section through some 20 km of archean crust uplifted along a northwest dipping thrust fault the restored vertical section through the upper and middle crust consists of three megalayers with undulating boundaries 1 0 to 25 km a high grade heterogeneous gneissic assemblage in part older than the upper supracrustal succession

constraints on the nature of the kapuskasing structural zone from the study of proterozoic dyke swarms petrochemical paleomagnetic and structural studies on early proterozoic dyke swarms show that the rocks of the kapuskasing structural zone ksz central superior province were upthrust about 10 15 km along the ivanhoe lake fault after intrusion of 2 04 ga kapuskasing dykes this uplift was part of a more widespread deformation in flanking terranes that involved sinistral motion along north north northwest trending faults dextral displacement along east northeast northeast trending faults and a distortion of the 2 45 ga matachewan swarm to the west and northwest of the ivanhoe lake fault the most spectacular demonstration that the ksz is largely a product of proterozoic deformation is that matachewan dykes change their magnetic polarity on crossing the zone a consequence of remanence acquisition at deep crustal levels being delayed until after a reversal of the earth s magnetic field and prior to uplift of the dykes matachewan and kapuskasing dykes within the amphibolite to granulite grade rocks o

reevaluation of the reconstruction of summer temperatures from melt features in belukha ice cores siberian altai 1 in a previous study past summer temperatures were reconstructed from melt features in the belukha ice core siberian altai we evaluated the climatic representativeness of net accumulation and melt features by comparing two belukha ice cores retrieved at neighboring sites by different institutions and dated by different methods melt features in both cores showed a significant correlation but the trends of net accumulation were different between the cores melt features corresponded to the retreat rate of a glacier terminus in a neighboring mountain range these findings demonstrate the spatial representativeness of melt features in the ice cores we reevaluated an equation formulated for reconstructions of summer temperature as used in a previous study and found that it underestimates temperature we propose an alternative equation to obtain more reliable summer temperatures from melt features and net accumulation records for the period from 1914 to 2003

broad scale proterozoic deformation of the central superior province revealed by paleomagnetism of the 2 45 ga matachewan dyke swarm an extensive paleomagnetic study of the 2 45 ga matachewan dyke swarm of the north american superior province suggests that the interior of an archean shield can undergo broad scale distortion as a result of later proterozoic orogenic activity around the craton margins data collected from over 300 sites of which 137 are reported here for the first time reveal that the dykes contain a dual polarity primary remanence that varies across the swarm in both inclination and declination these regional variations are statistically significant at the 95 confidence level and cannot be attributed to remagnetization or to magnetic anisotropy inclination variation is probably due to real or apparent polar wander during the emplacement of the swarm and may in part explain the declination variation as well however for dykes within and northwest of the kapuskasing structural zone ksz a positive correlation is found between regionally averaged values of declination and dyke trend here the dykes appear to hav

late precambrian keweenawan asymmetric reversals palaeopoles from the keweenawan 1 200 1 000 myr rocks of the lake superior region form the western and eastern arms of the great logan palaeomagnetic loop 1 5 fig 1a this is defined by both normal n and reversed r poles which are the consequence of at least two geomagnetic reversals4 6 7 the younger one r n has been detected throughout the lake superior region from various rock types 1 6 the older reversal n r is only recorded in the lowermost keweenawan lavas in the southern part of the lake 8 wherever found the reversals depart from the 180 symmetry fig 1a 2 6 due to these asymmetries the logan loop has large segments that are devoid of data and thus the geophysical interpretations of the loop or hairpin critically depend on the cause of the reversal asymmetry 4 four models11 secondary component6 apparent polar wander1 5 wilson s dipole offset5 7 9 and non dipole field configuration1 3 10 have been put forward to explain the asymmetries here we demonstrate that the two dipole field configuration model can explain the reversal asymmetries and discuss the global effects of this model in the light of worldwide late precambrian palaeomagnetic data

paleomagnetism of the clay howells carbonatite complex constraints on proterozoic motion in the kapuskasing structural zone superior province canada abstract the clay howells complex is located approximately 130 km east of hearst ontario at 49 50 n 82 05 w near the north end of the kapuskasing structural zone ksz of the superior province in the canadian shield the pluton is a large oviform pluton of about 16 km2 that is composed dominantly of syenite with minor carbonatite it was emplaced into an archean gneissic terrain of amphibolite to granulite facies with middle precambrian diabase dikes the complex is unmetamorphosed and late precambrian in age rb sr 1075 15 ma multistep alternating field af and thermal demagnetization was carried out on 194 specimens from 18 sites in the intrusion and three sites in the host rock dikes and gneisses the 18 syenite sites give a unit mean direction of 294 2 27 1 n 18 k 26 95 7 0 which yields a pole position of 178 8 e 26 5 n p 4 1 m 7 6 for the clay howells complex a crude contact test using the three host rock sites proved inconclusive the pole for the intrusion is concordant falling at about 1080 10 ma on the keweenawan apparent polar wander path which agrees with the rb sr age thus the complex has an untilted primary remanence that indicates that there has been no significant uplift

rb sr biotite and whole rock data from the kapuskasing uplift and their bearing on the cooling and exhumation history rb sr isotopic ratios were measured on biotite and whole rocks from a suite of 21 granitoid rocks from the southern kapuskasing uplift results of 18 of the whole rock analyses fall on an isochron with an age of 2 677 0 057 ga and sri 0 70080 biotite model ages range from 2 50 to 1 93 ga in a general spatial relationship of decreasing age with depth in the structural section as calibrated with the igneous hornblende barometer for tonalitic rocks and garnet pyroxene barometers for granulites near the michipicoten belt in the west biotite ages of 2 ga reflect disturbances also recorded by paleomagnetic and whole rock rb sr systems to the east in a 70 km long northwest southeast transect toward the ivanhoe lake fault zone ages decrease from 2 50 to 1 95 ga in a southern transect ages are in the range 2 30 2 38 ga to within 15 km of the fault reflecting consistent erosion levels corresponding to 0 53 mpa but decrease to 1 93 ga to the east in concert with paleopressures in the 0 7 1 0 gpa ra

tropical climate instability the last glacial cycle from a qinghai tibetan ice core an ice core record from the guliya ice cap on the qinghai tibetan plateau provides evidence of regional climatic conditions over the last glacial cycle 36 cl data suggest that the deepest 20 meters of the core may be more than 500 000 years old the 18 o change across termination i is 5 4 per mil similar to that in the huascaran peru and polar ice cores three guliya interstadials stages 3 5a and 5c are marked by increases in 18 o values similar to that of the holocene and eemian 124 000 years ago the similarity of this pattern to that of ch 4 records from polar ice cores indicates that global ch 4 levels and the tropical hydrological cycle are linked the late glacial stage record contains numerous 200 year oscillations in 18 o values and in dust nh 4 and no 3 levels

uranium thorium protactinium dating systematics abstract with precise 234u 230th and 231pa data available 230th and 231pa ages can now be tested rigorously for concordancy if the material is not concordant the isotopic characteristics of this material may be examined in some detail here models similar to those used to describe the u pb system are evaluated for use in u th pa studies for the case in which initial 230th and 231pa concentrations are effectively zero the systematics of concordia plots in relation to models of variation in 234u episodic u loss or gain continuous u loss or gain and continuous 234u 230th and 231pa gain or loss are considered for the case in which initial u concentration is significant for example in many carbonate deposits we also examine linear u uptake models for the case in which initial u concentration is effectively zero for example in teeth and bones such models should prove useful in interpreting data from materials that have behaved as open systems in particular these models may help constrain the nature of diagenetic processes and in some situations it may be possible to determine or constrain true ages with materials that have behaved as open systems

cross dating th u 14c of calcite covering prehistoric paintings in borneo abstract we present the first application of cross dating th u measured by thermo ionization mass spectrometry tims and 14c measured by accelerator mass spectrometry ams of calcite covering prehistoric paintings th u age estimates of cave drapery range from 9800 to 27 300 yr b p while conventional 14c age is estimated between 9900 and 7610 yr b p depending on the dead carbon correction the age discrepancy is attributed to a disturbance of th u and or 14c geochemical systems showing the limits of the geochronological approach applied to this kind of material for the th u system the poor consistency of u data u content 234u 238u activity ratios and apparent ages argue for open system conditions for 14c system variation of the dead carbon fraction dcf and a possible mixing of successive generations of calcite could account for age discrepancy nevertheless one sample shows concordant ages for the two methods compatible ages through corrections for open system conditions are assumed for other samples then the cross dating suggests 9900 yr as the minimum age of the piece of drapery the underlying painting must be older this study of rock art demonstrates the presence of a pleistocene population before 9900 yr in the southeast of borneo whereas previously the only population in evidence in this area was of austronesian type from 5000 to 6000 yrs ago

uranium series dating rock art in east timor at many sites throughout the world rock art paintings have been covered by naturally deposited calcite laminations which we demonstrate can be individually dated by recently improved uranium series methods here we report the application of multi collector inductively coupled plasma mass spectrometry to measure the ages for carbonate coatings that bracket red pigment at lene hara cave east timor which could be evidence of human painting these analyses establish the feasibility of dating milligram samples of finely layered calcite deposits associated with archaeological evidence of human occupation in addition to confirming an age of less then 6300 years for the visible red paintings on the carbonate surface we also report a substantially older age of 24 000 to 29 300 years for a similar older red pigment lamination providing possible evidence for an earlier painting episode

the matachewan dyke swarm canada an early proterozoic magnetic field reversal abstract consistent age relationships between oppositely magnetized dykes of the 2 45 ga matachewan dyke swarm suggest that only a single magnetic field reversal occurred during the period of igneous activity the magnetic field throughout most of this time was characterized by a ssw declination and shallow negative inclination but reversed toward the waning stages of magmatism the new paleomagnetic data provide the oldest known magnetic reversal for which the relative reversal sense is known

elemental fingerprinting of kenya rift valley ochre deposits for provenance studies of rock art and archaeological pigments abstract the kenya rift valley contains many ochre sources that are currently used by indigenous peoples for adornment rituals and art ochre pigments occur in rock art and archaeological sites spanning over 250 000 years chemical analysis for provenience of geological sources is the first step in the process of reconstructing provenance of archaeological artifacts for cultural heritage archaeological and paleoanthropological research development of an ochre source chemical composition database can facilitate reconstruction of social interaction networks and cultural heritage conservation efforts in this region techniques such as laser ablation inductively coupled plasma mass spectrometry la icpms and instrumental neutron activation analysis inaa are often used for compositional analysis and sourcing of ferruginous mineral pigments sourcing has proven challenging due to the diverse range of rocks and minerals that are classified as red and yellow ochres and the diverse processes that induce variation in composition including modes of formation sedimentary transport of parent materials and diagenesis attribution of samples to specific sources is possible only when variation within sources is less than differences between sources the provenience postulate here we present the results of a study using la icpms to determine inter and intra source geochemical variations for ten ochre sources associated with three large volcanic centers in the central rift valley of kenya our results show that differences in chemical composition among sources are greater than variation within sources both at the scale of large volcanic centers and of individual ochre outcrops within these centers clear differentiation of source chemical fingerprints at local and regional scales satisfies the provenience postulate and suggests that provenance studies of ochre artifacts residues and rock art in kenya will be feasible

the large scale circulation and heat sources over the tibetan plateau and surrounding areas during the early summer of 1979 part i precipitation and kinematic analyses abstract the time evolution of the large scale precipitation low level 850 mb wind moisture and vertical motion fields over the tibetan plateau and surrounding areas during a 40 day period from late may to early july 1979 is studied based on the objectively analyzed fgge level ii b data set during this period the general circulation over east asia undergoes a distinct change characterizing the onset of the summer monsoon circulation the tibetan plateau exerts profound orographic and thermal influences upon the low level wind field the inflow towards the eastern part of the plateau with a marked diurnal change in its intensity is the most prominent feature of the low level wind field the areas of organized precipitation are well related to synoptic systems seen in the 850 mb flow the quasi stationary burma india trough the disturbances forming on the trough the mei yu baiu front and the transverse trough extending eastward from the plateau there is a sharp contrast between the western an

proterozoic magnetic overprinting of archaean rocks in the canadian superior province we have measured the various components of natural remanent magnetization nrm exhibited by mafic extrusive and intrusive rocks from the abitibi subprovince of the canadian precambrian shield in addition to providing what seems to be a primary archaean pole for the region the results testify to three episodes of magnetic overprinting at approximately 2 600 2 100 and 1 800 myr respectively the two earlier episodes coincide with the intrusion of matachewan and abitibi diabase dyke swarms here and elsewhere in the superior province magnetic overprinting in these cases extends far beyond areas of surficial dyke exposure the third episode postdates magmatic activity in the abitibi region but coincides in age with the 1 900 1 700 myr hudsonian orogeny in the churchill and bear provinces and the penokean orogeny in the southern province although magnetic overprints presumed to be of this age were known previously from abitibi dykes1 and nipissing sills2 4 our data are the first evidence of a 1 800 myr magnetic overprinting on a regional scale in the superior province

chemistry of snow deposited during the summer monsoon and in the winter season at baishui glacier no 1 yulong mountain china the glaciers on yulong mountain 5596 m a s l china are the southernmost in mainland eurasia the largest is baishui glacier no 1 up to 90 of the annual precipitation there falls in summer when warm moisture rich air masses associated with the southwest monsoon reach the area from the indian ocean the winter climate is influenced by air masses with a continental origin and by the southern branch of the westerlies the snow that accumulates on baishui glacier no 1 includes marine aerosols associated with the summer monsoon and dust brought in winter from central west asia africa or the thar desert area studies in may 2006 at two sites one in the accumulation area 4900 m and one in the ablation area 4750 m revealed differences between the ionic composition of the snow that had accumulated in the 2005 06 winter and that of the snow which had been deposited during the preceding summer monsoon differences in the chemistry of the summer accumulated snow at the two sites probably reflected local differences in ablation and elution rates rather than differences in ion supplies differences in the chemistry of the winter accumulated snow may reflect the influence of up valley winds which bring more crustal material to the lower site

quantitative estimates of emplacement level of postmetamorphic mafic dykes and subsequent erosion magnitude in the southern kapuskasing uplift the early proterozoic matachewan 2 454 ga and kapuskasing 2 04 ga dyke swarms of the central superior province have similar petrographic features including zoned igneous plagioclase and clinopyroxene and interstitial amphibole and quartz dyke crystallization conditions can be estimated using equilibria involving amphibole by assuming that igneous mineral rims reached equilibrium with the interstitial phases twq software using 33 amphibole bearing equilibria yields temperatures ranging from 552 to 811 c with an average of 680 c the average of two calibrated pressure sensitive equilibria 2 diopside 2 quartz tschermakite tremolite 2 anorthite and diopside 5 quartz pargasite tremolite anorthite albite ranges from 0 32 to 0 70 gpa for matachewan dykes and from 0 30 to 0 57 gpa for kapuskasing dykes because dyke pressures are lower than metamorphic pressures in the amphibolite and granulite facies archean country rocks the values represent feasible emplacement pressures the regi

paleomagnetism of alkaline complexes and remagnetization in the kapuskasing structural zone ontario canada the shenango and nemegosenda alkaline complexes of the southern kapuskasing structural zone ksz an uplifted crustal block in northern ontario preserve primary thermoremanent magnetizations with mean directions d 112 i 46 k 13 95 13 n 9 sites and d 304 i 51 k 31 95 10 n 7 sites for shenango and d 124 i 57 k 13 9520 n 4 sites and d 312 i 54 k 17 95 13 n 7 sites for nemegosenda their average paleomagnetic pole is 45 n 189 e dp 6 dm 8 falling on the keweenawan track of the north american apparent polar wander path apwp between 1098 1107 ma reverse polarity r and 1087 1098 ma normal polarity n poles of lake superior lavas and dikes unlike the keweenawan paleopoles which have a reversal asymmetry of 30 the shenango and nemegosenda r and n poles are almost 180 reversed which was found also by lewchuk and symons 1990b this symmetry of r and n poles casts doubt on the previously accepted predominance of asymmetric reversals of the earth s field in keweenawan time the archean shawmere anorthosite is overprinted by a b magnetization with mean direction d 97 i 68 k 12 95 10 n 18 sites the shawmere b paleopole at 38 n 226 e dp 13 dm l6 falls between the carbonatite poles and 1850 ma cratonic poles and the b magnetization seems to be a composite of middle and late proterozoic overprints sites in the western part of the shawmere body close to the carbonatite line of faults linking the various alkaline complexes are severely altered with an abundance of secondary magnetite and hematite virtual geomagnetic poles for these sites fall close to the keweenawan track and have an average pole of 189 53 n dp 15 dm 20 suggesting that the b nrm at these sites is an 1100 ma thermochemical overprint caused by hydrothermal fluids at the time of carbonatite intrusion more easterly sites are less altered their vgps resemble 1850 ma cratonic poles and average to 235 e 30 n dp 15 dm 17 these b natural remanent magnetizations are probably thermochemical remanent magnetizations impressed by middle proterozoic hydrothermal activity associated with intrusion of early alkaline bodies fault movement on the ivanhoe lake fault zone or late stage uplift of the ksz

thirty year history of glacier melting in the nepal himalayas 1 two net balance records of neighboring glaciers under different conditions are analyzed to extract temporal variations in glacier melting in the himalayas significant melt was observed every year at one site wet site whereas no melt occurred at the second site because of its high elevation dry site accumulation at the wet site of a glacier is estimated from the dry site neighboring another glacier through a measured precipitation record for a short time period the difference between the estimated accumulation and the net balances at the wet site is obtained as the melt index which represents the glacier melting conditions the melt index with an interannual timescale is significant as a climatic proxy at high elevation since no relationship between stable isotopes and temperature is established and few long term temperature records are available at high elevations in the himalayas the melt index showed a decadal fluctuation with a major amplitude never reported in previous studies with respect to temperature and ice cores analyses in the himalayas ice cores from a site where significant melt occurs every year have not been considered available in reconstructing past climates since climatic signals in ice were disturbed by meltwater infiltration however we suggest a new approach to glean temperature information by a combination of wet and dry cores not obtainable from a good quality ice core alone

preliminary results from the chemical records of an 80 4 m ice core recovered from east rongbuk glacier qomolangma mount everest himalaya high resolution chemical records from an 80 4m ice core from the central himalaya demonstrate climatic and environmental changes since 1844 the chronological net accumulation series shows a sharp decrease from the mid 1950s which is coincident with the widely observed glacier retreat a negative correlation is found between the ice core 18o record and the monsoon precipitation for indian region 7 the temporal variation of the terrestrial ions ca2 and mg2 is controlled by both the monsoon precipitation for indian regions 3 7 and 8 located directly south and west of the himalaya and the dust storm duration and frequency in the northern arid regions such as the taklimakan desert china the nh4 profile is fairly flat until the 1940s then substantially increases until the end of the 1980s with a slight decrease during the 1990s which may reflect new agricultural practices the so4 2 and no3 profiles show an apparent increasing trend especially during the period 1940s 80s moreover so4 2 concentrations for the east rongbuk glacier core are roughly double that of the nearby dasuopu core at xixabangma himalaya due to local human activity including that of climbing teams who use gasoline for cooking energy and transport

spatial and seasonal variation of major ions in himalayan snow and ice a source consideration abstract the spatial and temporal variation of major ions ca2 mg2 na k nh 4 so 4 2 no 3 and cl in himalayan snow and ice is investigated by using two snow pits from the east rongbuk glacier 28 01 n 86 58 e 6500 m a s l one snow pit from the nangpai gosum glacier 28 03 n 86 39 e 5700 m a s l one snow pit from the gyabrag glacier 28 11 n 86 38 e 6303 m a s l and three ice cores from the sentik 35 59 n 75 58 e 4908 m a s l dasuopu 28 33 n 85 44 e 7000 m a s l and east rongbuk 27 59 n 86 55 e 6450 m a s l glaciers respectively in general the major ions show a significant seasonal variation with high concentrations during the non monsoon pre monsoon and post monsoon season and relatively low concentrations during the monsoon season monsoon precipitation with high local regional dust loading related to summer circulation is possibly responsible for the high concentrations occurring sporadically during the monsoon season the crest of the himalayas is an effective barrier to the spatial distribution of na cl and nh 4 concentrations but not to the major ions associated with dust influx e g ca2 and mg2 atmospheric backward trajectories from the hysplit 4 model used in identifying chemical species sourcing suggest that the major ions in the himalayan snow and ice come mainly from the thar desert located in the north india as well as west asia or even the distant sahara desert in the north africa during the winter and spring seasons this is different from the conventionally assumed arid and semi arid regions of the central asia factors such as different vapor sources due to atmospheric circulation patterns and geographical features e g altitude topography may contribute to the differences in major ionic concentrations between the western and eastern himalayas

climatic and atmospheric circulation pattern variability from ice core isotope geochemistry records altai tien shan and tibet several firn ice cores were recovered from the siberian altai belukha plateau central tien shan inilchek glacier and the tibetan plateau zuoqiupu glacier bomi from 1998 to 2003 the comparison analyses of stable isotope geochemistry records obtained from these firn ice cores identified the physical links controlling the climate related signals at the seasonal scale variability the core data related to physical stratigraphy meteorology and synoptic atmospheric dynamics were the basis for calibration validation and clustering of the relationships between the firn ice core isotope geochemistry and snow accumulation air temperature and precipitation origin the mean annual accumulation in water equivalent was 106 g cm 2 a 1 at inilchek glacier 69 g cm 2 a 1 at belukha and 196 gc m 2 a 1 at zuoqiupu the slopes in regression lines between the d 18 o ice core records and air temperature were found to be positive for the tien shan and altai glaciers and negative for southeastern tibet where heavy amounts of isotopically depleted precipitation occur during summer monsoons the technique of coupling synoptic climatology and meteorological data with d 18 o and d excess in firn core records was developed to determine climate related signals and to identify the origin of moisture in altai two thirds of accumulation from 1984 to 2001 was formed from oceanic precipitation and the rest of the precipitation was recycled over aral caspian sources in the tien shan 87 of snow accumulation forms by precipitation originating from the aral caspian closed basin the eastern mediterranean and black seas and 13 from the north atlantic

uranium thorium dating method and palaeolithic rock art abstract dramatic progress was seen in 14c dating with the introduction of accelerator mass spectroscopy ams which made possible the direct dating of prehistoric artworks painted or drawn with charcoal however in the case of engravings and red paintings only indirect methods can be used that allow us to date deposits that have covered the works over time tl u th oxalates etc the uranium thorium dating method gives reliable and relatively precise results in the case of massive speleothems because the sampling is carried out at the heart of the material where the hypothesis of a closed system that is no exchange with the outside environment is justified in most cases unfortunately the situation is quite different in the case of thin layers of calcite that overlie palaeolithic cave drawings the conditions under which calcite forms depend largely on the hydrologic activity which has greatly varied over the course of the upper palaeolithic and holocene in many cases we can see that the growth of speleothems stopped during much of the upper palaeolithic consequently the ages obtained are minimum ages terminus ante quem which are frequently much younger than the real ages of the underlying artworks moreover a much more serious but rarely considered source of error contradicts the assumption of a closed system in thin layers of carbonate deposits and in damp media the uranium incorporated into the calcite during its crystallization may be partially eliminated because of its solubility in water uranium leaching causes an artificial increase of the age that may reach considerable proportions e g a negative hand in a cave in borneo was dated to 27 000 years by u th whereas its 14c age was only 8 10 000 cal bp plagnes et al 2003 due to these two contradictory sources of error the dates given by the u th method may prove to be younger or older with deviations that are much larger than the standard deviations given by laboratories as a result it is nearly impossible and very dangerous to base archaeological reasoning on u th ages of palaeolithic artworks so long as the dates are not confirmed by an independent method dating the carbonates in the same samples by 14c being the best means of detecting anomalies the application of the u th method for the dating of prehistoric rock art is still experimental technical improvements for less damageable sampling and fundamental research on the causes of errors are needed

changes on ionic concentrations and delta o 18 in the snowpack of zhadang glacier nyainqentanglha mountain southern tibetan plateau to investigate the effects of depositional and post depositional processes on chemical records in the snowpack seven monthly snow pits were sampled at the same site on the pass of zhadang zd glacier 30828 079 0 n 90839 032 0 e 5800 m a s l nyainqentanglha mountain southern tibetan plateau between april and october 2006 meteorological data from an automatic weather station at the sampling site showed that the annual mean air temperature was 5 68c on the pass and that monthly air temperature was above 08c from june to august indicating that snowmelt could occur in this high elevation region during the summer an analysis of d 18 o and major ion variability in snow pits suggests that glaciochemical records were influenced by both meltwater percolation in mid summer july and august and seasonal deposition less negative d 18 o values and high concentrations of major ions occurred during the spring the trends of d 18 o variations in the zd snow pits were consistent with those in precipitation sampled at the nearby nam co station for all months except for july and august suggesting that climate signals are well preserved in the snow pit d 18 o records during the non summer months however these climate signals were destroyed by strong percolation of meltwater during mid summer

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

holocene late pleistocene climatic ice core records from qinghai tibetan plateau three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau of china provide a detailed record of holocene and wisconsin wurm late glacial stage lgs climate changes in the subtropics the records reveal that lgs conditions were apparently colder wetter and dustier than holocene conditions the lgs part of the cores is characterized by more negative 18 o ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes than the holocene part these changes occurred rapidly 10 000 years ago in addition the last 60 years were apparently one of the warmest periods in the entire record equalling levels of the holocene maximum between 6000 and 8000 years ago

u pb zircon ages and the evolution of the michipicoten plutonic volcanic terrane of the superior province ontario the archean michipicoten greenstone belt of the superior province in ontario is made up of supracrustal rocks divided into lower middle and upper metavolcanic rocks with associated metasedimentary rocks the belt has been intruded by granitic rocks and is also surrounded by granitic terranes based on u pb zircon geochronology it appears that volcanism in the area extended from at least 2749 to 2696 ma and plutonism and tectonic activity extended from at least 2888 to 2615 ma the various granitic and also one gabbroic plutons both internal and external to the greenstone belt were emplaced concomitantly with the three volcanic cycles as well as before and after the formation of the volcanic rocks zircon ages reported here together with previously published ages show that the area evolved in six major volcanic and plutonic events i 2888 ma plutonism ii 2743 ma volcanism and plutonism iii 2717 ma volcanism and plutonism iv 2696 ma volcanism and plutonism v 2668 ma plutonism and vi

statistical extraction of volcanic sulphate from nonpolar ice cores 1 ice cores from outside the greenland and antarctic ice sheets are difficult to date because of seasonal melting and multiple sources terrestrial marine biogenic and anthropogenic of sulfates deposited onto the ice here we present a method of volcanic sulfate extraction that relies on fitting sulfate profiles to other ion species measured along the cores in moving windows in log space we verify the method with a well dated section of the belukha ice core from central eurasia there are excellent matches to volcanoes in the preindustrial and clear extraction of volcanic peaks in the post 1940 period when a simple method based on calcium as a proxy for terrestrial sulfate fails due to anthropogenic sulfate deposition we then attempt to use the same statistical scheme to locate volcanic sulfate horizons within three ice cores from svalbard and a core from mount everest volcanic sulfate is 5 of the sulfate budget in every core and differences in eruption signals extracted reflect the large differences in environment between western northern and central regions of svalbard the lomonosovfonna and vestfonna cores span about the last 1000 years with good extraction of volcanic signals while holtedahlfonna which extends to about ad1700 appears to lack a clear record the mount everest core allows clean volcanic signal extraction and the core extends back to about ad700 slightly older than a previous flow model has suggested the method may thus be used to extract historical volcanic records from a more diverse geographical range than hitherto

late pleistocene aeolian activity in the cold desert of ladakh a record from sand ramps abstract ladakh northwest india lies in the rain shadow zone of the indian summer monsoon ism where sand ramps provide a good record of past aeolian activity here we present an archive from five sand ramps that is based on their sedimentological structure and optically stimulated luminescence osl chronology sedimentary architecture indicates that the sand ramps are composite records of aeolian hill slope erosion and fluvio lacustrine activity the osl chronology suggests that aridity and aeolian activity was dominant during 25 17 ka and

dating palaeolithic cave art why u th is the way to go the chronology of european upper palaeolithic cave art is poorly known three chronometric techniques are commonly applicable ams 14c tl and u th and in recent years the efficacy of each has been the subject of considerable debate we review here the use of the u th technique to date the formation of calcites that can be shown to have stratigraphic relationships to cave art we focus particularly on two recent critiques of the method by using specific examples from our own work using this method in spain we demonstrate how these critiques are highly flawed and hence misleading and we argue that the u th dating of calcites is currently the most reliable of available chronometric techniques for dating cave art

seasonal precipitation timing and ice core records this is a commentary on global circulation model experiments of moisture source changes in greenland urging caution in how they are applied because they have important implications for paleoclimate reconstruction from ice cores the work comes from preliminary find is of a ice core gisp2 of the authors the authors conclude that at present anomalies in greenland ice core records should not be interpreted solely in terms of source region variations the combined use of oxygen 18 d and ionic species in the new summit greenland cores should make it possible to answer empirically some of the questions raised by the gcm experiments as to the interpretation of oxygen 18 records in terms of temperature 4 refs 1 fig

paleomagnetism of the hearst dike swarm and implications for the tectonic history of the kapuskasing structural zone northern ontario prominent north to northwest trending dikes herein termed the hearst swarm west of the kapuskasing structural zone ksz in northern ontario yield a paleomagnetic pole position of 48 6 n 69 0 e dm 6 9 dp 3 6 60 samples from 12 dikes using paleomagnetic petrographic and structural criteria the hearst swarm is correlated with the 2 6 ga matachewan swarm east of the ksz a positive correlation is observed between the trend and paleomagnetic declination of hearst matachewan dikes and may result from an 15 post 2 6 ga rotation of terranes across the ksz paleomagnetic and structural data from the hearst dikes are consistent with the regional westward tilting of the crust near the southern ksz as first proposed in 1983 by percival and card

the effects of wind on δ 18o and accumulation give an inferred record of seasonal δ amplitude from the agassiz ice cap ellesmere island canada

a 1000 year history of atmospheric sulfate concentrations in southern asia as recorded by a himalayan ice core 1 a sulfate record covering the period a d 1000 1997 from the dasuopu glacier in the himalayas reveals that this site is sensitive to anthropogenic activity originating in southern asia prior to 1870 atmospheric sulfate concentrations were relatively low and constant but thereafter concentrations have increased and since 1930 the rate of increase has accelerated rapidly this accelerating trend in sulfate deposition is paralleled by growing so2 emissions over southern asia resulting from the increased energy demand the concentration of sulfate deposited in the last 50 years exceeds that for any prior 50 year period in the last millennium unlike the greenland ice core derived sulfate concentrations that have declined since the 1970s sulfate concentrations deposited on the himalayan ice fields continue to increase having nearly doubled since 1970 this reflects regional differences between europe and asia in source strength and transport pathways for atmospheric sulfate as well as differing degrees of environmental regulation

deep crustal structure and tectonic history of the northern kapuskasing uplift of ontario an integrated petrological geophysical study the northeast trending kapuskasing uplift transects the east west belts of the central superior province over a distance of some 500 km granulite to upper amphibolite facies rocks of the uplift form three distinct geological geophysical entities from south to north the chapleau groundhog river and fraserdale moosonee blocks uplift of the granulites along a moderately northwest dipping crustal scale thrust fault is attributed to an early proterozoic compressional event major northeast striking faults that bound the kapuskasing zone on the west were examined by modelling of geophysical anomalies to determine dip and by geobarometry of garnet orthopyroxene plagioclase quartz assemblages to determine vertical displacement granulites in the kapuskasing zone have 7 to 9 kbar signatures whereas those in the quetico belt to the west indicate metamorphic pressure of 4 6 kbar individual calibrations of the barometer yield consistent pressure differences of 2 3 kbar suggesting 7 10 km of west side down movement on the faults modelling of gravity and aeromagnetic gradients indicates westerly dips of 60 65 with west side down offset of up to 14 km these major normal faults probably formed as collapse structures in response to crustal thickening which occurred during the preceding compressional uplift stage differences in the configuration of individual blocks of the kapuskasing zone can be related to variable fault slip and intersection angles between normal and reverse faults thus the groundhog river and southern fraserdale moosonee blocks are perched thrust tips analogous to the sangre de cristo range of the laramide uplift province whereas the southern chapleau block is a tilted slab with similar configuration to the laramide wind river range pop up geometry deduced for the northern fraserdale moosonee block resembles the structure of the laramide uinta mountains a normal fault crosses the surface trace of the basal thrust fault between the groundhog river and fraserdale moosonee blocks and causes a 65 km gap without granulites this article contains supplementary material