structural history and granite emplacement in the rottenstone domain during closure of the trans hudson orogen davin lake northern saskatchewan the rottenstone domain at davin lake northern saskatchewan exhibits structural and granite emplacement evidence for crustal thickening and possible himalayan style extrusion overprinted by transpressional strain increasing toward the contact with the wathaman batholith three discrete rottenstone subdomains parallel the regional strike of the trans hudson orogen i the southeast rottenstone subdomain sersd with gently northwest dipping migmatitic straight gneiss s1 and white granitoid rocks with pinch and swell structures parallel to the straight gneissosity ii the central rottenstone subdomain crsd which partly preserves the same nw dipping fabric s1 but is overprinted at its margins by tight upright f2 folds and includes a stockwork of pink monzogranitic aplites and pegmatites and iii the northwest rottenstone subdomain nwrsd in which the f2 folds are generally tighter and penetrative and its network of narrow white granitoid rocks is deformed and transposed by the f2 folds but in

a special issue on volcanogenic massive sulfide deposits of the trans hudson orogen preface paleoproterozoic volcanogenic massive sulfide vms deposits are hosted in greenstone belts that formed during assembly of earth s first supercontinent nuna at 2 1 to 1 7 ga these deposits account for a significant component of the world s vms tonnage and thus are an important global exploration target among these paleoproterozoic belts the 1 92 to 1 80 ga trans hudson orogen of canada is the largest and best endowed in laurentia with over 29 deposits totaling 320 mt of cu zn au ag pb ore study of its deposits districts and tectonostratigraphic evolution enables greater understanding of metallogenic and geodynamic processes during the paleoproterozoic we briefly overview the trans hudson orogen its vms deposits and their exploration history and illustrate that various distinct types of volcanogenic massive sulfide deposits form in predictive tectonostratigraphic sequences associated with both pre and postaccretion volcanism we present results from a four year program to investigate the deposits and evolution of the trans hudson orogen highlighting various approaches at district and belt scales to improve exploration models for other structurally complex and covered precambrian terranes

coherence between solar activity and the east asian winter monsoon variability in the past 8000 years from yangtze river derived mud in the east china sea ams 14 c dating and grain size analysis for core pc 6 located in the middle of a mud area on the inner shelf of the east china sea ecs were used to rebuild the holocene history of the east asian winter monsoon eawm the 7 5 m core recorded the history of environmental changes during the postglacial transgression the core s mud section the upper 450 cm has been formed mainly by suspended sediment delivered from the yangtze river mouth by the ecs winter coastal current ecswcc since 7 6 kyr bp using a mathematical method called grain size vs standard deviatiow we can divide the core pc 6 s grain size distribution into two populations at about 28 mu m the fine population 28 mu m is considered to be transported by the ecswcc as suspended loads content of the fine population changes little and represents a stable sedimentary environment in accord with the present situation thus variation of mean grain size from the fine population would reflect the strength of ecswcc which is mainly controlled by the east asian winter monsoon abrupt increasing mean grain size in the mud section is inferred to be transported by sudden strengthened ecswcc which was caused by the strengthened eawm thus the high resolution mean grain size variation might serve as a proxy for reconstruction of the eawm a good correlation between sunspot change and the mean grain size of suspended fine population suggests that one of the primary controls on centennial to decadal scale changes of the eawm in the past 8 ka is the variations of sun irradiance i e the eawm will increase in intensity when the number of sunspots decreases spectral analyses of the mean grain size time series of core pc 6 show statistically significant periodicities centering on 2463 1368 128 106 100 88 91 7678 and 70 72 years the eawm and the east asian summer monsoon easm agree with each other well on these cycles and the east asian monsoon eam and the indian monsoon also share in concurrent cycles in holocene which are in accord with the changes of the sun irradiance c 2005 elsevier b v all rights reserved

attenuation of seismic waves in methane gas hydrate bearing sand compressional wave p wave and shear wave s wave velocities vp and vs respectively from remote seismic methods have been used to infer the distribution and volume of gas hydrate within marine sediments recent advances in seismic methods now allow compressional and shear wave attenuations q1p and q1s respectively to be measured however the interpretation of these data is problematic due to our limited understanding of the effects of gas hydrate on physical properties therefore a laboratory gas hydrate resonant column was developed to simulate pressure and temperature conditions suitable for methane gas hydrate formation in sand specimens and the subsequent measurement of both q1p and q1s at frequencies and strains relevant to marine seismic surveys 13 dry gas saturated sand specimens were investigated with different amounts of methane gas hydrate evenly dispersed throughout each specimen the results show that for these dry specimens both q1p and q1s are highly sensitive to hydrate saturation with unexpected peaks observed between 3 and 5 per cent hydrate saturation it is thought that viscous squirt flow of absorbed water or free gas within the pore space is enhanced by hydrate cement at grain contacts and by the nanoporosity of the hydrate itself these results show for the first time the dramatic effect methane gas hydrate can have on seismic wave attenuation in sand and provide insight into wave propagation mechanisms these results will aid the interpretation of elastic wave attenuation data obtained using marine seismic prospecting methods

compressional and shear wave velocities as a function of confining stress in dry sandstones a laboratory study was carried out to investigate the influence of confining stress on compressional and shear wave velocities for a set of rock samples from gas producing sandstone reservoirs in the cooper basin south australia the suite of samples consists of 22 consolidated sublitharenites with helium porosity ranging from 2 6 to 16 6 we used a pulse echo technique to measure compressional and shear wave velocities on dry samples cylindrical 4 6 2 cm at room temperature and at elevated confining stress 60 mpa compressional and shear wave velocities in samples increase non linearly with confining stress a regression equation of the form v a be dp gives a good fit to the measured velocities with improved prediction of velocities at high confining stresses compared with equations suggested by other studies the predicted microcrack closure stresses of the samples show values ranging from 70 mpa to 95 mpa and insignificant correlation with porosity permeability or clay content there is a positive correlation between change in velocity with core porosity and permeability but this association is weak and diminishes with increasing confining stress experimental results show that pore geometry grain contact type and distribution and location of clay particles may be more significant than total porosity and clay content in describing the stress sensitivity of sandstones at in situ reservoir effective stress the stress dependence of cooper basin sandstones is very large compared with data from other studies the implication of our study for hydrocarbon exploration is that where the in situ reservoir effective stress is much less than the microcrack closure stress of the reservoir rocks the variation of reservoir effective stress could cause significant changes in velocity of the reservoir rocks the velocity changes induced by effective stress in highly stress sensitive rocks can be detected at sonic log and probably surface seismic frequencies

variation of zr rb ratios in the chinese loess deposits during the past 1 8 myr and its implication for the change of east asian monsoon intensity most of our knowledge concerning the evolution of the east asian monsoon eam comes from the chinese loess paleosol sequence variations in the eam as recorded in loess are highly correlated to the marine 18o record and show a strong 100 kyr cyclicity during the past 800 kyr this conclusion is based on both weathering and pedogenesis intensity changes as well as grain size variation in loess paleosol sequences which usually serves as a proxy for winter monsoon variation however grain size distributions are subject to modification by pedogenic processes in this paper we used the zr rb ratio from the lingtai section on the loess plateau in central china to trace variations in the east asian winter monsoon for the past 1 8 myr long term zr rb variations in the lingtai section exhibit a similar amplitude and frequency to those of mean grain size in bulk samples over the past 1 8 myr comparing the zr rb record and mean grain size record between l1 and l9 shows that a good linear relationship exists in the glacial age loess samples whereas paleosol samples usually deviate from the linear relationship because of intense pedogenesis during the relatively warm and humid interglacial intervals our results indicate that the zr rb ratio reflects the original eolian grain size and may serve as a proxy for the strength of the east asian winter monsoon in the lingtai section over the past 1 8 myr the zr rb ratio record displays a very strong 41 kyr obliquity periodicity from 1 8 1 2 myr b p implying that variations of the winter monsoon during this interval are controlled by high latitude climate however during the past 0 8 myr the zr rb ratio exhibits a stronger precession cycle influence suggesting a possible low latitude control on the east asian monsoon regime during this interval

tectonic framework of a paleoproterozoic arc continent to continent continent collisional zone trans hudson orogen from geological and seismic reflection studies vertical incidence seismic data were collected along a 300 km long profile across the northwestern flank of the trans hudson orogen in saskatchewan line s2b the present study integrates the seismic data with previously published geological maps and recent results from the la ronge lynn lake bridge project that provide new constraints on the lithological structural and tectonic framework of this collisional zone an interpretative section based on the seismic reflectivity and surface geological constraints is presented the integrated data suggest the following key elements 1 although an early foreland vergent accretion history is suggested by surficial geological constraints the predominant fabric is reflected by penetrative hinterlandward vergence 2 a zone of more reflective lower crust with hinterland verging fabric may represent fossil reflectors from a pre collisional accretionary phase 3 the archean to paleoproterozoic sask craton may extend in the lower middle crust to at least

northern europe climate variations during late holocene evidence from marine skagerrak abstract granulometric and stable oxygen isotope analyses of four sediment cores from two high accumulation areas in the skagerrak ne north sea were carried out in order to reconstruct climate fluctuations and to evaluate climate impact during the upper holocene extremely high sedimentation rates especially in the eastern skagerrak are explained by increased current activity which is responsible for the transport and deposition of high quantities of suspension load during periods of stormy zonal atmospheric circulation patterns these were most frequent during colder periods while warmer phases are characterized by calmer meridional to zonal atmospheric circulation patterns while the subatlantic climate deterioration and the subboreal climate optimum left only indistinct traces in the sediments the roman climate optimum and a colder period between ca 400 and 700 ad are well documented the following medieval warm period is characterized by a clear temperature increase of the waterbody in connection with less frequent advances of atlantic water masses into the skagerak deep and a decrease in bottom current strength a mode of sedimentation prevails similar to that of recent summer conditions suggesting short and mild winters during that period the onset of the little ice age around 1350 ad however shows an intensified bottom current circulation most probably due to amplifying westerly winds and a decrease in water temperatures in connection with more frequent advances of higher saline atlantic waters the little ice age can be divided into 3 phases a stormy zonal onset a calm meridional maximum and a stormy zonal end the stormy phases are characterized by a sedimentation mode similar to that of recent winter conditions while the little ice age maximum shows conditions comparable to exceptional cold modern winters from 1900 ad at the onset of the modern climate optimum the winter type sedimentation decreases and conditions change again to a level comparable to the medieval warm period

a 13 000 year climate record from western tibet although the tibetan plateau is important in influencing the atmospheric circulation of the northern hemisphere1 3 there are only a few continuous palaeoclimate records available and these are limited to the plateau s northeastern margin4 6 here we present a 13 000 yr record from sumxi co western tibet constructed from both lake core and shoreline studies which shows that conditions in the early middle holocene were warmer and wetter than at present these results confirm model predictions of an intensified monsoon over the region at 9 000 yr bp owing to an orbitally induced increase in summer insolation7 8 we also find evidence for warm humid pulses at 12 500 and 10 000 yr bp in phase with the steps of the last deglaciation and for a return to cold dry conditions at 11 10 000 yr bp none of which can be explained by orbital variations the existence of the cold episode confirms that the cooling associated with the younger dry as event occurred in continental china6 9 and provides further evidence of the global nature of this event10

structure of a paleoproterozoic continent continent collision zone a lithoprobe seismic reflection profile across the trans hudson orogen canada abstract an 800 km reflection seismic profile across the trans hudson orogen northern saskatchewan and manitoba images crustal scale tectonic imbrication in an unprecedented picture of paleoproterozoic crustal accretion and continent continent collisional tectonism the profile is crudely symmetric about a crustal scale culmination in the western part of an accreted juvenile collage reindeer zone geologic and isotopic data suggest that this culmination is cored by microcontinental archean basement west of the culmination highly reflective juvenile crustal elements dip westward into the lower crust beneath the wathaman batholith and archean continental crust of hearne craton to the east strong reflections in the juvenile reindeer zone crust and reworked archean foreland of the thompson belt have eastward dips persisting into the middle crust and extending beneath the superior craton a continuous reflection moho well defined for 500 km in the western part of the profile shows marked relief 12 15 s including a prominent root below the crustal culmination these imaged structures give evidence of substantial crustal shortening and thickening via large scale imbrication consistent with collisional orogeny w dipping structures below the wathaman batholith and reworked hearne craton may reflect subduction polarity in this part of the orogen however geological evidence suggests that e dipping structures below superior craton are largely related to late post collisional deformation rather than to prior oceanic subduction polarity

comparison of paleoclimatic change from zr rb ratios in chinese loess with marine isotope records over the 2 6 1 2 ma bp interval 1 the loess paleosol sequences in north china act as a key archive in the study of continental paleoclimatic change over the last 2 6 ma however the correlation between the continental loess records and the marine sediments over the 2 6 1 2 ma bp interval is poorly studied in this paper zr and rb concentrations were measured on samples taken at 20 cm intervals from the lingtai section over the interval from 2 6 1 2 ma bp because zr is enriched in coarse grain fractions whereas rb is enriched in the fine fractions which are retained during loess pedogenesis the zr rb in loess can reflect the original grain size variation and serve as a proxy for winter monsoon strength our zr rb ratios over the interval from 2 6 1 2 ma bp generally match the marine 18o record especially during the 1 9 1 2 ma bp interval strong 400 ka periodicity cycles found in the loess zr rb ratio record are similar to the marine 13c record suggesting a possible low latitude influence on the paleoclimatic regime during this interval

late holocene forcing of the asian winter and summer monsoon as evidenced by proxy records from the northern qinghai tibetan plateau abstract little is known about decadal to centennial scale climate variability and its associated forcing mechanisms on the qinghai tibetan plateau a decadal resolution record of total organic carbon toc and grainsize retrieved from a composite piston core from kusai lake nw china provides solid evidence for decadal to centennial scale asian monsoon variability for the northern qinghai tibetan plateau during the last 3770 yr intensified winter and summer monsoons are well correlated with respective reductions and increases in solar irradiance a number of intensified asian winter monsoon phases are potentially correlated with north atlantic climatic variations including bond events 0 to 2 and more recent subtle climate changes from the medieval warm period to the little ice age our findings indicate that asian monsoon changes during the late holocene are forced by changes in both solar output and oceanic atmospheric circulation patterns our results demonstrate that these forcing mechanisms operate not only in low latitudes but also in mid latitude regions the northern qinghai tibetan plateau

cyclic rapid warming on centennial scale revealed by a 2650 year stalagmite record of warm season temperature 1 a 2650 year bc665 ad1985 warm season mjja may june july august temperature reconstruction is derived from a correlation between thickness variations in annual layers of a stalagmite from shihua cave beijing china and instrumental meteorological records observations of soil co2 and drip water suggest that the temperature signal is amplified by the soil organism co2 system and recorded by the annual layer series our reconstruction reveals that centennial scale rapid warming occurred repeatedly following multicentenial cooling trends during the last millennia these results correlate with different records from the northern hemisphere indicating that the periodic alternation between cool and warm periods on a sub millennial scale had a sub hemispherical influence

a 6000 year record of changes in drought and precipitation in northeastern china based on a δ13c time series from peat cellulose we report a new peat delta c 13 proxy record for humidity or precipitation based on c3 plants from northeastern china the record reveals two times of significant climate shift and eight severe drought periods during the past 6000 years all of which have the nature of widespread global occurrence the variability of precipitation shows periodicities of around 70 80 90 107 110 123 134 141 162 198 205 249 278 324 389 467 584 834 and 1060 years the occurrence and persistent times of drought and periodicities of precipitation show good correspondence with solar variability the remarkable correlations between peat delta c 13 peat delta o 18 and atmospheric delta c 14 suggest that on timescales of decades to centuries the changes in drought and precipitation are likely caused by variations of atmospheric circulation and atmosphere ocean interactions in large scale patterns that seem to be related to solar variability c 2001 elsevier science b v all rights reserved

geology u pb zircon geochronology and geochemistry of pge bearing neoarchean and paleoproterozoic gabbroic rocks of the peter lake domain southern hearne craton canada the peter lake domain a component of the hearne craton in saskatchewan includes several intrusive complexes ranging in age from 2 70 to 1 83 ga two gabbroic complexes swan river and porter bay together represent one of the largest accumulations of precambrian mafic intrusion both metamorphosed at amphibolite facies sulfide poor pge occurrences are found in both complexes and share many textural and lithological characteristics with magmatic contact type pge ni cu deposits such as the chaotic lac des iles pluton and with layered stratiform deposits of large layered intrusions such as bushveld or stillwater lithologically both complexes are dominated by leucocratic gabbronorite and gabbro locally characterized by cumulate layering cross bedding brecciated and pegmatitic textures u pb zircon crystallization ages between 2562 and 2560 ma were obtained for the swan river complex sulfide formation is interpreted to be of magmatic origin rather than remobilized as had been speculated by explora

geochemical characteristics of the eden lake complex evidence for anorogenic magmatism in the trans hudson orogen the eden lake complex intrudes granitic rocks located between the lynn lake and leaf rapids tectonic domains in the reindeer zone of the trans hudson orogenic terrane in northern manitoba it consists of a number of magmatic phases of particular interest are aegirine bearing monzonites and late rare earth element ree and fluorine enriched pegmatites the aegirine monzonite ranges in sio2 content from 51 to 76 wt showing a continuous fractionation trend from low to high silica the cao fe2o3t and mgo contents are low about 1 6 wt tio2 contents range from 0 8 to about 0 1 wt and total alkalis range from about 11 to 13 wt the early evolution of the complex was influenced by pyroxene fractionation during the later stages k feldspar fractionation had an increasing effect on the bulk composition of the magma accumulation of k feldspar has obscured the tectonic signature of the complex but elevated ree high field strength element and fluorine contents are consistent with an a type grani

the effect of pressure on ultrasonic velocity and attenuation in near surface sedimentary rocks accurate laboratory ultrasonic measurements of velocity and attenuation were made on water saturated samples of limestone sandstone and siltstone as a function of effective pressure 5 60 mpa using the pulse echo method core samples were taken from carboniferous sediments at the whitchester shallow borehole test site they were cut perpendicular to the horizontal bedding planes the compressional and shear wave velocities and quality factors of the limestones generally showed negligible increases with pressure while those of the siltstones and sandstones showed intermediate and significant increases with pressure respectively at 60 mpa the sandstone samples generally showed a range of quality factors attributed to their differing porosities and differing proportions of rigid skeletal minerals quartz grains and compliant matrix materials clay kerogenic organic matter at 5 mpa they generally showed similar quality factors attributed to the presence of microcracks which occur predominantly at grain contacts the results show that kerogenic organic matter behaves in a similar way to other compliant matrix minerals in causing high attenuation at ultrasonic frequencies and that caution must be exercised when applying high pressure geostatistical relationships to reservoir rocks at low effective pressures the results indicate the presence of two types of squirt flow loss mechanisms clay squirt flowmore dominates at high pressures while microcrack squirt flow dominates at low pressures clean sandstones and limestones can be distinguished from those with significant amounts of compliant minerals and sandstones with cracks can be distinguished from those without cracks less

re examining the potential of using sensitive grain size of coastal muddy sediments as proxy of winter monsoon strength sensitive components of grain size in coastal muddy sediments of china have been widely used for reconstruction of the east asian winter monsoon strength however trends of the winter monsoon strength profiles reconstructed for the past 2000 years from different sediment cores tend to be inconsistent and even contradictory in the present study the grain size variation sequence of the sensitive components in a sediment core collected from the middle of the min zhe coastal mud with a time span of 2700 years is determined the striking correspondence between the reconstructed mean grain size of the sensitive component with northern hemisphere temperature in particular the medieval warm period and the little ice age showed that coastal muddy sediments of china can be used to reconstruct a high resolution profile of east asian winter monsoon strength the inconsistencies in the winter monsoon proxy sequences from different studies are most likely caused by low resolution of grain size standard deviation data and direct influence of the river input materials in some studies c 2013 elsevier ltd and inqua all rights reserved

variation of rb sr ratios in the loess paleosol sequences of central china during the last 130 000 years and their implications for monsoon paleoclimatology abstract rb sr and magnetic susceptibility have been measured in the last interglacial glacial loess profiles at luochuan and huanxian central china a high degree of similarity between the parameters in both profiles suggests that variations of rb sr ratios in the sequence can be regarded as an indicator of east asian summer monsoon strength matching the rb sr record with the specmap 18o curve suggests that the rb sr ratio responds sensitively to changes of the east asian monsoon induced by global ice volume variation

structural controls on hypozonal orogenic gold mineralization in the la ronge domain trans hudson orogen saskatchewan the la ronge domain is a granite greenstone belt in the saskatchewan segment of the ca 1 9 1 8 ga trans hudson orogen the la ronge volcanic arc was accreted to the archean hearne craton from ca 1 87 to 1 86 ga subduction of oceanic lithosphere beneath the accreted la ronge hearne margin produced a voluminous suite of continental arc intrusions in the waddy lake area the 1852 6 1 5 ma corner lake stock and 1859 4 ma and 1861 2 ma feldspar porphyry dykes crystallized from magmas generated from melting of the subducted oceanic slab during the ca 1 83 1 80 trans hudson collision of the hearne craton with the archean sask and superior cratons a penetrative regional foliation and a steeply plunging lineation formed within the la ronge domain during further contraction across the domain the deformation became localized in dextral and oblique slip shear zones that generally follow contacts between more competent and less competent rock units orogenic gold mineralization is associated with quar

astronomical forcing of the east asian monsoon mirrored by the composition of pliocene south china sea sediments abstract high precision major and minor element records of pliocene core intervals from ocean drilling program odp site 1145 located in the northern part of the south china sea were generated at a 5 cm approximately 2 kyr resolution from the geochemical data distinct proxies those indicating changes in detrital matter provenance as well as those indicating productivity variations could be derived both the terrigenous input to the northern south china sea k si and variations in productivity ba al show a response to insolation forced monsoon variability while the fluvial input k si responds to changes in the summer monsoon productivity increases as documented by ba enrichments seem to reflect variations in winter monsoon intensity a stronger winter monsoon may have increased nutrient availability via dust input and or upwelling phenomena according to our geochemical proxy records summer and winter monsoons are approximately 180 out of phase this may imply forcing of the winter monsoon through southern hemisphere summer insolation maxima the k si ratio shows a linear correlation with the la90 1 0 5 northern hemisphere summer insolation record and has therefore been used to create an astronomical timescale for the investigated sediments of odp site 1145 carbonate contents and corresponding color reflectances display 41 and 100 kyr cycles we propose that these do not reflect glacial cycles but are rather the result of an interference signal of dilution by fluvial and eolian terrigenous material and carbonate production burial flux a sudden onset of gradual changes in sediment composition occurs after 3 0 ma this is also documented by an increase in sedimentation rates and may be caused by enhanced fluvial input from the pearl river due to intensified weathering rates on the asian continent this may be linked to tectonic processes around the himalayan tibetan complex and its consequences regarding land sea heating and atmospheric circulation

rubidium strontium ages of archean and proterozoic rocks in the nejanilini and great island domains churchill province northern manitoba canada rubidium strontium whole rock ages are reported from the nejanilini great island area in northeastern manitoba this area is part of an extensive zone of archean basement that was metamorphosed and intruded by granitic magma during the proterozoic it extends into saskatchewan and southern district of keewatin northwest tertitories an age of 2577 42 ma 1 error for the extensive nejanilini granulite massif nejanilini domain considered one of the oldest rock units in the area is interpreted as a minimum age for late archean granulite facies metamorphism a minimum age of 2052 41 ma initial ratio 0 7150 for quartz feldspar porphyry that intrudes the seal river volcanic suite constrains the age of these volcanics and could represent a partially reset archean age early proterozoic quartzite and metagreywacke of the great island group unconformably overlies the quartz feldspar porphyry these metasedimentary rocks which are probably correlative with the daly lake group saskatchewan or the h

reconstruction of winter monsoon strength by elemental ratio of sediments in the east china sea abstract the east asian winter monsoon eawm transports cold air from the high northern latitudes to the mid and low latitudes thus investigations on its variation pattern and mechanism are essential for acquiring further knowledge on the interplay across the high and low latitudes proxies such as grain size and foraminiferal 18o in marine sediments and elemental ratios in the chinese loess have been used for the reconstruction of eawm strength however more high resolution reconstructions for eawm are required for further understanding the mechanism of climate systems and predicting climate change in this study we present a high resolution time series of the late holocene eawm strength reconstructed by element method comparisons of element concentrations elemental ratios and mean grain size mgs of environment sensitive components in a sediment core from the shelf of the east china sea indicate that k ti ratio is an appropriate proxy for the reconstruction of the eawm strength k ti ratio exhibits similar trends with proxies of sea surface temperature and eawm strength in different regions influenced by the eawm warm and cold periods such as the roman warm period medieval warm period and little ice age are identified in the reconstructed results total solar irradiance anomaly tsi and k ti ratios exhibit comparable tendencies in the last two millennia and frequency spectrum analysis exhibits similar periodicities in the time series of tsi and k ti which confirm that solar irradiance has a significant impact on the easm on centennial time scale

flux and fate of yangtze river sediment delivered to the east china sea numerous cores and dating show the yangtze river has accumulated about 1 16 x 10 12 t sediment in its delta plain and proximal subaqueous delta during holocene high resolution seismic profiling and coring in the southern east china sea during 2003 and 2004 cruises has revealed an elongated similar to 800 km distal subaqueous mud wedge extending from the yangtze river mouth southward off the zhejiang and fujian coasts into the taiwan strait overlying what appears to be a transgressive sand layer this distal clinoform thins offshore from similar to 40 in thickness between the 20 and 30 m water depth to 1 2 in between 60 and 90 m water depth corresponding to an across shelf distance of less than 100 km total volume of this distal mud wedge is about 4 5 x 10 11 m 3 equivalent to similar to 5 4 x 10 11 t of sediment most of the sediment in this mud wedge comes from the yangtze river with some input presumably coming from local smaller rivers thus the total yangtze derived sediments accumulated in its deltaic system and east china sea inner shelf have amounted to about 1 7 x 10 12 t preliminary analyses suggest this longshore and across shelf transported clinoform mainly formed in the past 7000 yrs after postglacial sea level reached its mid holocene highstand and after re intensification of the chinese longshore current system sedimentation accumulation apparently increased around 2000 yrs bp reflecting the evolution of the yangtze estuary and increased land erosion due to human activities such as fanning and deforestation the southward flowing china coastal current the northward flowing taiwan warm current and the kuroshio current appear to have played critical roles in transporting and trapping most of yangtze derived materials in the inner shelf and hence preventing the sediment escape into the deep ocean c 2006 elsevier b v all rights reserved

holocene thinning of the greenland ice sheet the nature of the response of the greenland ice sheet gis to climate change is a fundamental question in climate science but the details remain unclear during the holocene climate optimum 6 000 to 9 000 years ago for example many locations in the northern hemisphere showed unusual warmth yet changes in greenland appeared inconsistent vinther et al now standardize the previously disparate seeming ice core records of climate history on the gis during the holocene and find consistent evidence for a stronger climate optimum than was previously recognized together with elevation reduction and marginal ice sheet thinning the response of the greenland ice sheet gis to changes in climate remains uncertain during the holocene climatic optimum an unusually warm period from about 9 000 to 6 000 years ago changes in greenland appear inconsistent with the rest of the northern hemisphere here the greenland holocene temperature history and the evolution of gis surface elevation are extracted from four gis locations the results may resolve this disparity on entering an era of global warming the stability of the greenland ice sheet gis is an important concern1 especially in the light of new evidence of rapidly changing flow and melt conditions at the gis margins2 studying the response of the gis to past climatic change may help to advance our understanding of gis dynamics the previous interpretation of evidence from stable isotopes 18o in water from gis ice cores was that holocene climate variability on the gis differed spatially3 and that a consistent holocene climate optimum the unusually warm period from about 9 000 to 6 000 years ago found in many northern latitude palaeoclimate records4 did not exist here we extract both the greenland holocene temperature history and the evolution of gis surface elevation at four gis locations we achieve this by comparing 18o from gis ice cores3 5 with 18o from ice cores from small marginal icecaps contrary to the earlier interpretation of 18o evidence from ice cores3 6 our new temperature history reveals a pronounced holocene climatic optimum in greenland coinciding with maximum thinning near the gis margins our 18o based results are corroborated by the air content of ice cores a proxy for surface elevation7 state of the art ice sheet models are generally found to be underestimating the extent and changes in gis elevation and area our findings may help to improve the ability of models to reproduce the gis response to holocene climate

seismic study of the low permeability volume in southern france karst systems locating groundwater in deep seated karst aquifers is inherently difficult with seismic methods we studied the upper epikarst and the underneath low permeability volume lpv of several karst systems located in the southern quercy and larzac regions of france and found that refraction tomography was effective only in the epikarst and not in the lpv we evaluated a 3d case study using a combination of surface records and downhole receivers to overcome this limitation this 3d approach unveiled a set of elongated furrows at the base of the epikarst and identified heterogeneities deep inside the lpv that may represent high permeability preferred pathways for water inside the karst to achieve the same result when no borehole was available we studied seismic amplitudes of the wavefield recognizing that wave induced fluid flow in low permeability carbonates is a driving mechanism of seismic attenuation we developed a workflow describing the heterogeneity of the lpv with spectral attributes derived from surface consistent decomposition principles and we validated its effectiveness at benchmark locations we applied this workflow to the 3d study and found a low amplitude signal area at depth we interpreted this anomaly as a water saturated body perched above the aquifer

continental arc magmatism along the southeast hearne craton margin in saskatchewan canada comparison of the 1 92 1 91ga porter bay complex and the 1 86 1 85ga wathaman batholith abstract detailed mapping coupled with geochronological and geochemical investigations has revealed the presence of a 1917 1913 ma gabbro monzodiorite monzonite suite along the southeast margin of the hearne craton in northern saskatchewan canada the predominantly plutonic suite is also characterised by 1915 ma old trachyandesitic subvolcanic and volcaniclastic inclusions the rocks are hornblende epidote titanite augite bearing and collectively termed the porter bay complex the plutonic rocks cut the 2569 ma lueaza river granitoid suite a component of the hearne craton and are themselves intruded by 1859 ma pegmatitic diorite 1856 ma layered gabbro anorthosite and 1853 ma quartz diorite belonging to the wathaman batholith one of the world s largest paleoproterozoic andean type continental arcs wholerock major element geochemistry characterises the porter bay complex as calc alkalic to alkali calcic metaluminous and variable from ferroan to magnesian trace element concentrations are characterised by negative high field strength element anomalies suggesting emplacement along a destructive plate margin the geochemical signatures of the wathaman batholith and the porter bay complex are largely identical the geographic location map relationships and geochronological geochemical and petrographic constraints are consistent with the porter bay complex having formed in a subduction related continental arc setting the southeastern margin of the hearne craton was therefore a long lived active continental margin with two separate periods of continental arc magmatism between 1 92 1 91 ga and 1 86 1 85 ga

metavolcanic rocks of the la ronge domain in the churchill province saskatchewan geochemical evidence for a volcanic arc origin the la ronge domain in the churchill province of the canadian shield is a volcanic sedimentary plutonic belt of early proterozoic age geochemical data supported by geological evidence strongly suggest that the la ronge metavolcanics were emplaced in an island arc setting the metavolcanic rocks range from basalt through andesite to dacite and rhyolite calcalkaline and tholeiitic types are dominant with minor alkaline varieties classification based on the major elements produces ambiguous results because of mobility of these elements during metamorphism however relatively immobile minor and trace elements provide reliable characterization of the basalts in particular the latter display distinctive trace element properties and morb normalized geochemical patterns similar to those of recent volcanic arc basalts being enriched in incompatible elements of low ionic potential and depleted in those of high ionic potential the calcalkaline basalts are in addition enriched in th p ce and sm a minor within plate component is also displayed by some metabasalts suggesting that magma genesis in parts of the la ronge arc involved sub continental lithosphere rare earth element patterns show enrichment in the lree with little or no eu anomaly interpretation by means of trace element discrimination diagrams incorporating elements such as ti y nb zr cr th yb and ce provides clear evidence for emplacement in a volcanic arc tectonic setting

solar forcing of centennial scale east asian winter monsoon variability in the mid to late holocene abstract centennial scale variability of the east asian winter monsoon during the holocene is poorly understood because suitable archives and proxies are lacking here we present a high resolution 30 yr spacing planktonic foraminiferal o 18 record of neogloboquadrina incompta dextral form which reflects sea surface temperature during the winter season for the last 6000 yrs from marine sediments in the western north pacific stronger winter monsoons indicated by cooler winter ssts correspond to weaker summer monsoons indicated by the cave oxygen isotopes in centennial scale variability the variability also shows good correlation with o 18 records in lake sediments and ice cores from the yukon territory canada spanning the last 4500 yrs suggesting east west climate coupling across the north pacific furthermore the climate changes across the north pacific co vary over widespread regions such as the eastern tropical pacific and the northern red sea and the reconstructed solar activity the cross spectral and wavelet analyses show that the east asian winter monsoon shares some cyclicity with the solar variability our results suggest that the solar activity is a fundamental forcing producing the centennial scale eawm variability mediated by the large scale climate linkages

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

slow post orogenic cooling in a deeply eroded orogen reindeer zone trans hudson orogen saskatchewan we present 40ar 39ar hornblende and muscovite data from a 200 km transect across the northern flank of the paleoproterozoic trans hudson orogen tho exposed along reindeer lake in saskatchewan canada the transect crosses a series of distinct lithotectonic domains that experienced pressure temperature p t conditions of 600 730 c at 4 5 6 0 kbar 1 kbar 100 mpa during d2 peak metamorphism at 1820 1790 ma the distribution of 40ar 39ar hornblende ages shows that most of the transect cooled through approximately 500 c by ca 1765 ma with two significant exceptions at the north end of the transect older ages in the peter lake domain up to 2200 ma suggest that this region did not experience high grade metamorphism that affected the rest of the transect and may indicate a structural break between these archean rocks and the cree lake zone to the north in the south central part of the transect u pb monazite titanite and 40ar 39ar hornblende muscovite ages indicate that rocks in the vicinity

the development of late holocene coastal cooling in the northern south china sea abstract paired high resolution sea surface temperature sst records based on the long chain alkenone unsaturation index u 37 k were reconstructed to decipher the sst evolution over the past 8000 years and its possible driving mechanisms at the hong kong coastal region the two sst records derived from a sediment core in the pearl river estuary and an offshore core in the northern south china sea scs show different patterns of sst changes the coastal record shows relatively stable warm temperatures during the mid holocene 7 4 2 6 ka and substantial cooling 2 c thereafter the cooling was most pronounced in the past 0 6 ka likely associated with the little ice age lia the offshore record generally reveals a warming trend from 8 ka to 3 5 ka and relatively warm temperatures since then as a result the sst difference sst between the two sites increased over time suggesting that the sst gradient gradually developed in the northern scs the declining coastal sst with the increasing sst likely indicates and results from the intensified east asian winter monsoon since 7 ka especially during the late holocene consistent with previous terrestrial records revealing winter monsoon variability and modern observations sst between coastal and offshore sites could thus be used as an indicator of winter monsoon variability

le batholite de de pas nouveau quebec infrastructure composite d arc magmatique proterozoique the de pas batholith in new quebec is a mass of granitoids elongated in a n s direction covering 7000 km2 in the southeastern part of the archean rae province it is located between the paleopro

seasonal temperature variability of the neoglacial 3300 2500 bp and roman warm period 2500 1600 bp reconstructed from oxygen isotope ratios of limpet shells patella vulgata northwest scotland abstract seasonal sea surface temperature variability for the neoglacial 3300 2500 bp and roman warm period rwp 2500 1600 bp which correspond to the bronze and iron ages respectively was estimated using oxygen isotope ratios obtained from high resolution samples micromilled from radiocarbon dated archaeological limpet patella vulgata shells the coldest winter months recorded in neoglacial shells averaged 6 6 0 3 c and the warmest summer months averaged 14 7 0 4 c one neoglacial shell captured a year without a summer which may have resulted from a dust veil from a volcanic eruption in the katla volcanic system in iceland rwp shells record average winter and summer monthly temperatures of 6 3 0 1 c and 13 3 0 3 c respectively these results capture a cooling transition from the neoglacial to rwp which is further supported by earlier studies of pine history in scotland pollen type analyses in northeast scotland and european glacial events the cooling transition observed at the boundary between the neoglacial and rwp in our study also agrees with the abrupt climate deterioration at 2800 2700 bp also referred to as the subboreal subatlantic transition and therefore may have been driven by decreased solar radiation and weakened north atlantic oscillation conditions

the wathaman batholith largest known precambrian pluton the early proterozoic wathaman batholith in northern saskatchewan and manitoba is a 900 km long megacrystic granite granodiorite intrusion that straddles the junction between ensialic miogeoclinal and probably ensimatic eugeoclinal island arc terranes of the trans hudson orogen of the western churchill province although the largest precambrian batholith known it is apart from marginal complexities remarkably homogeneous throughout and unlike comparably sized and situated phanerozoic batholiths shows no evidence of multiple intrusion nor does it have comagmatic early mafic phases however it may be considered as just one phase of a larger batholithic belt that also includes numerous smaller plutons taken as a whole the composite batholithic belt is similar in many aspects to mesozoic pacific rim batholithic belts and like them probably was emplaced during plate collision the batholith is affected by pervasive internal deformation is bounded on the northwest by major blastomylonite zones a

influence of the intertropical convergence zone on the east asian monsoon a palaeoclimate record spanning the past 16 000 years with nearly annual time resolution has been obtained from lake huguang maar in china the magnetic properties and titanium content of the lake sediments are thought to reflect changes in the east asian winter monsoon strength thus providing a complement to palaeoclimate archives that record the strength of the rain bearing summer monsoon the records point to an anti correlation between winter and summer monsoon strength best explained by migration of the intertropical convergence zone itcz a belt of low pressure air at the equator interestingly the decline of china s tang dynasty and the mayan civilization broadly coincide with drought periods recorded in lake huguang maar and cariaco basin sediments respectively did major shifts in the position of the itcz catalyse simultaneous events in civilizations on opposite sides of the pacific ocean the asian australian monsoon is an important component of the earth s climate system that influences the societal and economic activity of roughly half the world s population the past strength of the rain bearing east asian summer monsoon can be reconstructed with archives such as cave deposits1 2 3 but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct here we present high resolution records of the magnetic properties and the titanium content of the sediments of lake huguang maar in coastal southeast china over the past 16 000 years which we use as proxies for the strength of the winter monsoon winds we find evidence for stronger winter monsoon winds before the bolling allerod warming during the younger dryas episode and during the middle and late holocene when cave stalagmites suggest weaker summer monsoons1 2 3 we conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone similar migrations of the intertropical convergence zone have been observed in central america for the period ad 700 to 900 refs 4 6 suggesting global climatic changes at that time from the coincidence in timing we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the tang dynasty in china and the classic maya in central america

sedimentary basin controls on orogenic gold deposits new constraints from u pb detrital zircon and re os sulphide geochronology lynn lake greenstone belt canada abstract sedimentary basins that open and close during the last stages of mountain building represent an important exploration criterion for orogenic gold deposits however the genetic and or preservation controls of these synorogenic or timiskaming type sedimentary basins and their controlling fault systems on orogenic gold deposits remain unclear herein we address that knowledge gap and report new u pb detrital zircon and re os sulphide arsenopyrite and pyrite geochronology and sulphide pb isotope results for the paleoproterozoic lynn lake greenstone belt llgb manitoba canada the youngest detrital zircon from all six meta conglomerate and psammite samples of the synorogenic sickle group and previously reported u pb zircon ages for post sickle group intrusions are used to constrain its depositional timing from 1836 15 to 1831 4 ma replicate analyses of one highly radiogenic arsenopyrite sample from an auriferous vein at the maclellan gold deposit yield a weighted average re os model age of 1824 12 ma which is identical to previously published in situ u pb xenotime ages at the same deposit 1827 8 ma each of these hydrothermal ages demonstrate that early stage auriferous veins immediately post date deposition of the sickle group and most likely occurred prior to peak metamorphism 1814 1801 ma this sequence of events is very similar to the abitibi greenstone belt suggesting that a synorogenic phase of extension and rapid burial of auriferous veins by timiskaming type sickle group sediments may have played an important genetic and or preservation control on early stage gold mineralization in the llgb however unlike the abitibi greenstone belt none of the known gold deposits within the llgb are hosted within the sickle group younger re os model arsenopyrite ages at 1782 16 ma from the maclellan gold deposit also post date synorogenic sedimentary basins by ca 50 myr these late stage auriferous veins are unrelated to the synorogenic extensional phase and more likely reflect repeated fluid focusing along reactivated structures during a post peak metamorphic phase of hydrothermal activity the multi stage hydrothermal history of orogenic gold deposits in the llgb also provides a possible explanation for the mixture of depleted mantle like and highly radiogenic fluid components that are inferred from age corrected sulphide pb isotope compositions 1 8 ga 8 9 10 6 reworked cratonic margins and their associated greenstone belts thus represent favourable depositional settings for auriferous fluids at multiple stages throughout the lifespan of an orogen

hydrography and climate of the last 4400 years in a sw greenland fjord implications for labrador sea palaeoceanography a multiproxy record including benthic foraminifera diatoms and xrf data of a marine sedi ment core from a sw greenland fjord provides a detailed reconstruction of the oceanographic and cli matic variations of the region during the last 4400 cal years the lower part of our record represents the final termination of the holocene thermal maximum after the onset of the neoglaciation at approxi mately 3 2 ka cal bp the fjord system was subject to a number of marked hydrographical changes that were closely linked to the general climatic and oceanographic development of the labrador sea and the north atlantic region our data show that increased advection of atlantic water irminger sea water from the west greenland current into the labrador sea was a typical feature of northeast atlantic cool ing episodes such as the little ice age and the european dark ages while the advection of irminger sea water decreased significantly during warm episodes such as the mediaeval warm period and the roman warm period whereas the mediaeval warm period was characterized by relatively cool climate as suggested by low meltwater production the preceding dark ages display higher meltwater runoff and consequently warmer climate when compared with european climate these regional climate anomalies indicate persisting patterns of advection of colder respectively warmer air masses in the study region dur ing these periods and thus a long term seesaw climate pattern between west greenland and europe

variability of monsoon climate in east asia at the end of the last glaciation abstract high resolution paleomonsoon proxy records from peat and eolian sand paleosol sequences at the desert loess transition zone in china denote a rapid oscillation from cold dry conditions 11 200 10 60014c yr b p to cool humid conditions 10 600 10 20014c yr b p followed by a return to cold dry climate 10 200 10 00014c yr b p variations in precipitation proxies suggest that significant climatic variability occurred in monsoonal eastern asia during the younger dryas interval late glacial climate in the chinese desert loess belt that lies downwind from europe was strongly influenced by cold air from high latitudes and from the north atlantic via the westerlies the inferred precipitation variations were likely caused by variations in the strength of the siberian high which influenced the pressure gradient between land and ocean and therefore influenced the position of the east asian monsoon front

seasonally specific responses of the east asian monsoon to deglacial climate changes the deglacial meltwater pulse in the north atlantic that induced the younger dryas event also prompted climate cooling in east asian monsoon regions such as japan and coastal mid latitude china however very little is understood about the mechanism that can transmit changes in the north atlantic to the far east here we show that the shutdown of the north atlantic thermohaline circulation brought about significantly lower temperatures and higher precipitation in the japanese winter whereas the change in the japanese summer climate was considerably smaller the cooling of the siberian air mass seems to have caused an increased pressure gradient between siberia and the west pacific in winter intensifying the winter monsoon the mongolian high pressure system and the westerly jet stream played an important role in the teleconnection in contrast the warming at the onset of the late glacial interstadial gi 1 bolling allerod in the west pacific did not have season specific features implying that the principal driving mechanism of this warming event may lie in a pan hemispheric or global factor such as insolation changes

geochemical characterization of the luochuan loess paleosol sequence china and paleoclimatic implications abstract chemical major and trace element and isotopic sr nd analyses of the luochuan loess paleosol sequence in china were performed in order to examine the following problems 1 potential source heterogeneity 2 element behavior during pedogenesis 3 paleoclimatic implications and 4 the use of loess data to determine the average composition of the upper continental crust new results clearly indicate that rb sr u and ce abundances are severely depleted in paleosols relative to their parental loess the behavior of these elements is strongly controlled by the breakdown of primary minerals such as carbonate sr or by alteration processes in highly oxidizing environments ce and u the pattern of element variations through the upper section of the luochuan sequence mimics the magnetic susceptibility signal both in position and in intensity thus reinforcing the pedogenesic origin of the enhanced magnetic susceptibility in paleosols all loess samples display highly uniform ree patterns except for ce characterized by the upper continental crust ucc ratios la yb n 10 and eu eu 0 66 the paleosol ree patterns are similar to those of the loess with the same lree hree fractionation but they also show distinct and variable negative ce anomalies nd and sr isotopic compositions are rather uniform in both loess and paleosols and do not vary with stratigraphic position nd 10 5 to 9 2 87 sr 86 sr 0 715 to 0 719 the isotopic homogeneity in the luochuan sequence strongly suggests a uniform source region during the entire period of deposition since 800 ka ago to the present several conclusions may be drawn from the present study 1 1 no geochemical distinction can be made between loess layers l1 to l7 the sources and the dust storm trajectories must have been essendally the same for the last 800 ka 2 2 some elements e g ca rb sr u ce are strongly fractionated by pedogenesis between loess and paleosols ce mobility in soils is clearly demonstrated but the process responsible for this leaching is still poorly understood 3 3 systematic variations of element abundances and ratios between loess and paleosols can be used as chemical indicators for pedogenesic intensity and so for paleoclimatic change these chemical indicators serve a function similar to that of oxygen isotopes in deep sea sediments pelagic foraminifera or that of magnetic susceptibility in loess sequences they are different recorders of paleoclimatic change 4 4 the striking uniformity of ree patterns and la th ratios in the luochuan loess and paleosols as well as in loess worldwide is an excellent starting point for estimating the average composition of the upper continental crust

the history and variability of the east asian paleomonsoon climate abstract changes in the east asian paleomonsoon reflect interactions between the global atmosphere ocean land and ice systems and are also an expression of their combined effect within the boundary conditions imposed by the east asian continent and solar radiation the history of the east asian monsoon is an alternation between dominance by the dry cold winter and warm humid summer monsoons high resolution eolian sequences preserved in the chinese loess plateau reveal that the east asian monsoon may have commenced at least 7 2 ma ago they also provide evidence indicating that the pulsed uplift of the tibetan plateau at about 3 4 and 7 2 ma may have played an important role in inducing climate change the palaeoclimatic records of the last glacial cycle show high frequency variability on time scales of 1000 year or even shorter and instability of the east asian paleomonsoon system the high frequency variability could be due to a non linear response to orbital forcing or a result of the coupling processes between different components of the global system cold air activity in northern high latitudes the trans equatorial air streams from the southern hemisphere and possibly enso may have played an important role in east asian monsoon variability the synchroneity of all the palaeoclimatic events along the polar equator polar pep transect is still an open question correlation of limited palaeoclimatic records for the last 30 kyr obtained from east asia and australia suggests that the trans equatorial air streams driven by the monsoon and trade winds may have had an influence on opposite hemispheres

geochronological constraints on the trans hudsonian tectono metamorphic evolution of the pre athabasca basement within the wollaston mudjatik transition zone saskatchewan the hudsonian pressure temperature deformation time p t d t evolution of the pre athabasca crystalline basement 1700 ma of the wollaston mudjatik transition zone wmtz highlights two major tectono metamorphic events m1 d1 and m2 d2 the ages of these two event have been obtained by in situ la icpms u th pb dating of monazite from grt crd bearing pelitic gneiss and u pb analyses performed on zircons from pegmatites using both exposed basement and drill cores from the wolly mcclean exploration drilling project the m1 d1 event interpreted as the burial of the thinned hearne margin via southward thrusting to pressures varying from 10 to 6 kbar occurred between ca 1840 and 1813 ma the m2 d2 event producing the northeast structural trend of the wmtz was formed in a sinistral transpressional tectonic regime during the late stage of the hudsonian oblique collision between ca 1813 and 1770 ma thermobarometric estimates on the m2 d2 assemblages show that the entire studied area was reequilibrated at about 5 kbar and 750 825 c trans hudsonian pegmatites are viewed as the main proto ore of the uranium rich athabasca unconformity type deposits formation transfer and differenciation of these trans hudsonian pegmatites are replaced in this p t d t evolution during the 1840 1813 ma m1 d1 partial melting event the first batches of melt produced in the deep crust are the most likely enriched in uranium then these melts were transferred upwards to the upper crustal levels owing to the development of crustal scale steeply dipping d2 shear zones and finally were differentiated to form uranium enriched pegmatites between 1813 and 1770 ma some monazite and zircon grains within retrogressed migmatites recorded a later event at ca 1720 ma interpreted as the terminal cooling event down to 300 400 c responsible for partial retrogression of metamorphic assemblages this age provides new insights into the timing of the onset of the athabasca sedimentation that should therefore be at least 1710 ma old or younger

evidence for solar forcing on the indian monsoon during the last millennium abstract solar influence on the intensity of the indian monsoon is demonstrated using a sediment core from the eastern arabian sea dating back to 1200 yr through pattern matching as well as spectral analysis of proxy records of monsoon and solar activity the intensity of the indian monsoon is found to have decreased during periods of solar minima during the last millennium periodicities of 200 20 105 15 and 60 10 yr are observed in the proxy records coinciding with those known for solar cycles the 60 yr periodicity observed in the instrumental rainfall data appears to be of solar origin and supports the hypothesis of solar control on the indian monsoon on a multi decadal time scale evidence for the presence of a coupled atmospheric forcing for the indian and east african monsoons on a centennial time scale is also seen

climatically sensitive eolian and hemipelagic deposition in the cariaco basin venezuela over the past 578 000 years results from al ti and k al al ti and k al ratios in bulk sediment are used to interpret wind blown and hemipelagic sources of deposition to a 578 kyr record in the cariaco basin venezuela ocean drilling program site 1002 graphical and cross spectral analyses indicate that these ratios vary extremely closely with planktonic foraminiferal 18o with both ratios being significantly higher during interglacials and lower during glacials k al indicates that during glacials the lower sea level that results in relative basin isolation increases the relative proportion of kaolinite derived from local rivers draining the relatively humid venezuelan margin al ti decreases during glacials suggesting greater proportions of eolian rutile sourced from the northern sahara due to increased wind strength and or aridity this interpretation is consistent with previous studies of the chemistry and mineralogy of saharan derived eolian matter in the caribbean and with a mass balance determining the effect of changes in eolian rutile accumulation on the bulk sedimentary al ti ratio

a cordilleran type batholitic belt in the churchill province in northern saskatchewan abstract the rottenstone and western la ronge domains of the south central churchill province in saskatchewan consist mostly of hudsonian batholithic complexes spatially and structurally related to an aphebian hudsonian volcanic arc the batholithic belt is of comparable dimensions and compositional variation to cordilleran type phanerozoic batholiths and appears to be emplaced in close proximity to a prior late archean early aphebian continental crustal margin a quartz diorite line separating dominant quartz diorite tonalite granodiorite plutonic rocks from dominant granodiorite quartz monzonite granite intrusives can be defined these general characteristics as well as more detailed features of aphebian deposition and hudsonian thermotectonism within and on either side of the rottenstone domain suggest a continental margin rather than an intracontinental location for evolution of the hudsonian orogenic belt of the south central churchill province and provide some insights into the possible development of this part of the canadian shield as part of a hudsonian wilson cycle

the pelican thrust zone basal detachment between the archean sask craton and paleoproterozoic flin flon glennie complex western trans hudson orogen the pelican thrust zone is a 3 7 km wide recrystallized mylonite zone along which paleoproterozoic arc volcano plutonic and derived sedimentary rocks of the flin flon glennie complex were thrust over an archean package jan lake complex consisting of ca 3 1 ga calc alkaline orthogneisses pelitic migmatites and a ca 2 45 ga tholeiitic charnockite norite intrusive suite a regional northeast plunging stretching lineation and a variety of kinematic indicators imply southwesterly transport matching that of other coeval shallower crustal level structures observed throughout the northern flin flon domain and southern flank of the kisseynew domain e g sturgeon weir and annabel lake shear zones subsequent east side up displacement on the tabbernor fault together with domal fold interference has exposed the pelican window and mantling mylonite zone where it has been seismically profiled along lithoprobe transects tectonic windows also expose archean rocks in the glennie domain to the west where similar southwest verging recrystallized mylonite zones have been documented together these zones record collision and underplating of the flin flon glennie complex by the archean sask craton during prolonged protocontinent continent collision over a minimum 1826 1805 ma interval resume la zone de chevauchement pelican est une zone de mylonite recristallisee d une largeur de 3 7 km le long de laquelle des roches volcano plutoniques d un arc datant du paleoproterozoique et des roches sedimentaires derivees du complexe de flin flon glennie ont ete chevauchees par dessus un ensemble archeen le complexe de jan lake qui est compose d orthogneiss calco alcalins et de migmatites pelitiques gees d environ 3 1 ga ainsi que d une suite intrusive charnockite norite tholeiitique gee d environ 2 45 ga une lineation regionale d etirement a pendage nord est et divers indicateurs cinematiques correspondent a un transport vers le sud ouest rejoignant celui d autres structures contemporaines de niveaux crustaux moins profonds observees a travers tout le domaine de flin flon nord et le flanc sud du domaine kisseynew p ex les zones de cisaillement de sturgeon weir et d annabel lake un deplacement subsequent le cote est vers le haut le long de la faille de tabbernor avec une interference de plis de dome a fait affleurer la fenetre pelican et la zone mylonitique qui la recouvre elle a ete determinee par des profils sismiques le long des transects lithoprobe des fenetres tectoniques permettent aussi l affleurement de roches archeennes du do maine de glennie vers l ouest la ou ont ete documentees des zones semblables de mylonites recristallisees a pendage sud ouest ensemble ces zones enregistrent la collision et le sous placage du complexe de flin flon glennie par le craton archeen sask au cours d une collision prolongee entre le protocontinent et le continent au cours d un intervalle d au moins 1826 a 1805 ma

grain size of quartz as an indicator of winter monsoon strength on the loess plateau of central china during the last 130 000 yr the chinese loess paleosol sequence constitutes an important record of variations in asian monsoon climate over the past 2 4 myr magnetic susceptibility of loess and paleosols has been used as a proxy for summer monsoon intensity while median grain size has been regarded as a measure of the strength of winter monsoon winds that were responsible for most of the dust transport however median grain size is only an approximate index of winter monsoon strength because both paleosols and loess have been modified to various degrees by weathering processes that have produced pedogenic clay the quartz component of loess and paleosols is largely unaffected by weathering processes and therefore constitutes a more reliable proxy index of monsoon wind strength median grain size qmd and maximum grain size qmax values of monomineralic quartz isolated from the loess paleosol section at luochuan in the central loess plateau are characterized by two main intervals during the last ca 130 000 yr when these parameters were significantly greater than 9 and 85 m respectively and three main intervals when they were lower the data imply that the winter monsoon weakened during the intervals with low qmd and qmax values which coincide with marine oxygen isotope stages 5 3 and 1 and was strongest ca 67 000 and 20 000 yr ago during isotope stages 4 and 2 however both quartz grainsize records display second order high frequency high amplitude variations which are lacking in the magnetic susceptibility record that imply rapid and significant changes in atmospheric conditions that affect dust transport and deposition

composition age and origin of granitoid rocks in the davin lake area rottenstone domain trans hudson orogen northern saskatchewan the rottenstone domain of the trans hudson orogen is a 25 km wide granitic migmatitic belt lying between the la ronge volcanic plutonic island arc 1890 1830 ma to the southeast and the ensialic wathaman batholith 1855 ma to the northwest the rottenstone domain consists of three lithotectonic belts parallel to the orogen i southeast gently folded migmatized quartzo feldspathic metasedimentary and mafic metavolcanic rocks intruded by small concordant and discordant white tonalite monzogranite bodies ii central intensely folded and migmatized metasedimentary rocks and minor metavolcanic rocks intruded by largely discordant xenolith rich pink aplite pegmatite monzogranite bodies and iii northwest steeply folded migmatized metasedimentary rocks cut by subvertical white tonalite monzogranite sheets emplacement of granitoid rocks consists predominantly of contiguous orogen parallel steeply dipping syntectonic and post tectonic sheets with prominent magmatic schlieren bands overprinted by parallel solid state deformation features the white granitoid rocks have a cnk mol al2o3 mol cao na2 o k 2o 1 14 1 22 k rb 500 ree sum of rare earth elements 1 87 sr 86 sri 0 7032 and endi 2 the pink monzogranites have a cnk 1 11 1 16 k rb 500 ree 90 ppm eu eu 1 87 sr 86 sri 0 7031 and endi 2 the white granitoid rocks show a wider compositional range and more compositional scatter than the pink monzogranites reflecting some combination of smaller volume melts less homogenization and less control by crystal melt equilibria all metavolcanic metasedimentary and granitic rocks in the rottenstone domain have the distinctive geochemical signatures of an arc environment new sensitive high resolution ion microprobe shrimp u pb geochronology on the rottenstone granitoid rocks reveals complex growth histories for monazite and zircon variably controlled by inheritance magmatism and high grade meta morphism monazite ages for the granitoid bodies and migmatites cluster at 1834 and 1814 ma whereas zircon ages range from 2480 ma rare cores to 1900 1830 ma cores and mantles but also 1818 1814 ma for low th u recrystallized rims overgrowths and rare discrete euhedral prisms these results demonstrate that at least some source material for the granitic magmas included earliest paleoproterozoic crust sask craton or its derived sediments and that rottenstone granitic magmatism postdated plutonism in the bounding la ronge arc and wathaman batholith we estimate the age of terminal metamorphism in the davin lake area to be 1815 ma petrogenetically the rottenstone migmatites and granitoid rocks appear for the most part locally derived from their metasedimentary and metavolcanic host rocks shed from the la ronge arc sask craton and possibly the hearne craton the rottenstone domain was the least competent member in the overthrust stack and probably underwent a combination of fluid present melting and fluid absent decompression melting resulting in largely syntectonic granitoid magmatism 1835 1815 ma analogous to granite production in the high himalayan gneiss belt

summer monsoon variations over the last 1 2 ma from the weathering of loess soil sequences in china the loess soil sequence in northern china contains a near continuous record of quaternary paleoclimate magnetic susceptibility and grain size have so far been the only proxies available to address the long term changes of the east asian paleomonsoon extending back to more than one million years in this study the ratio of cbd citrate bicarbonate dithionite extractable free fe2o3 fed a measure of iron liberated by chemical weathering versus the total fe2o3 available fet was measured on samples at 10 cm intervals taken from two loess sections deposited over the last 1 2 ma variations of this index are highly consistent with other pedological indicators but in addition provide a quantitative measurement of the degree of pedogenesis in the loess plateau since chemical weathering in the region mainly depends upon summer precipitation and temperature weathering intensity primarily reflects changes in the east asian summer monsoon the new proxy has been used to document a series of summer monsoon changes of global significance which are not necessarily recorded by magnetic susceptibility

regional setting and kinematic features of the needle falls shear zone trans hudson orogen needle falls shear zone is the southern part of a major northeast trending ductile shear system within the paleoproterozoic trans hudson orogen in saskatchewan throughout its exposed length of 400 km the shear zone separates reworked archean continental crust and infolded paleoproterozoic supracrustals of the cree lake zone to the northwest from mainly juvenile paleoproterozoic arc terrains and granitoid plutons of the reindeer zone to the southeast it also defines the northwest margin of the ca 1855 ma wathaman batholith which forms the main protolith to shear zone mylonites although not precisely dated available age constraints suggest that the shear zone formed between ca 1855 and 1800 ma toward the end of peak thermotectonism in this part of the orogen in the needle falls study area shear zone mylonites exhibit varied sequentially developed ductile to brittle fabric features including c s fabrics winged porphyroclasts especially delta type small scale compressional and extensional

crustal structure and evolution of the trans hudson orogen results from seismic reflection profiling a 400 km long deep seismic reflection transect across northeastern montana and northern north dakota reveals the crustal scale structural fabric of the early proterozoic trans hudson orogen beneath the williston basin comparison with deep seismic reflection data across the canadian portion of the same orogen 700 km to the north reveals first order similarities in crustal architecture but documents significant along strike variation in orogenic evolution both transects display a broad crustal scale antiform axial to the orogen in the north geologic data suggest that this antiform is cored by an archean microcontinent in the south west dipping reflections on the western flank of the antiform extend from the upper crust to the uppermost mantle and truncate prominent subhorizontal lower crustal reflections of the archean wyoming craton within the wyoming craton the eastern limit of east dipping midcrustal reflections coincides with the subsurface age boundary between the craton and the early proterozoic trans hudson orogen as interpreted from potential field and drill core data on the basis of subsurface geochronologic data from the crystalline basement and by analogy with the glennie domain within the exposed trans hudson orogen in canada we suggest that the southern antiform is cored by an archean crustal fragment that was caught up in the terminal collision of the wyoming and superior cratons during hudsonian orogeny the eastern side of the trans hudson orogen is characterized on both seismic transects by predominantly east dipping crustal penetrating reflections we interpret the easterly dip of these reflections as evidence that the superior province was thrust westward over the interludes of the orogen during terminal collision although juvenile early proterozoic terranes characterize the exposed segment of the trans hudson orogen in canada limited drill core information within the dakota segment of the orogen shows a predominance of granulitic archean age crust this difference in basement lithologies along strike within the orogen may indicate the following either juvenile crust comparable to that exposed in the northern trans hudson was never present in the south or it was removed by progressive over thickening erosion and or faulting postorogenic extensional collapse may be responsible for preservation of juvenile terranes in the north

chinese loess and the paleomonsoon abstract this paper presents a general review of the recent research advances of the east asian paleomonsoon based mainly on studies of the loess soil sequences in the chinese loess plateau in the last 2 6 million years the paleomonsoonal history may be divided into about 166 events on a time scale of the earth s orbital variations during the last glacial period millenial scale oscillations of the monsoon system were prominent which can be fairly well correlated with the dansgaard oeschger cycles recognized in the greenland ice cores the monsoonal rainfall belt has experienced a wide repeated advance retreat change during the glacial interglacial cycles of the pleistocene both temporal and spatial changes of the monsoon system in the quaternary could have been linked closely to global ice volume variations

zr rb ratio in the chinese loess sequences and its implication for changes in the east asian winter monsoon strength abstract the long term dust accumulation sequences on the chinese loess plateau clp provide a valuable opportunity to study the evolution of east asian winter monsoon strength grain size of bulk samples of loess deposits though widely used is a modified measure of the strength of winter monsoon wind due to modification by post depositional weathering and pedogenesis this study proposes a new and reliable geochemical climate proxy that records the variability of the east asian winter monsoon on the clp six loess paleosol sections on the plateau were selected for measuring concentrations of the trace elements zr and rb as well as grain size variations of the zr rb ratio in all the sections encompassing the last 130 ka display a generally similar pattern to that of mean grain size of bulk samples mgsb though a positive correlation exists between the zr rb ratio and mgsb the correlation coefficient decreases in southern and eastern sections where intense pedogenesis occurred in the relatively warm and humid climates long term zr rb variation in the lingtai section exhibits amplitudes and frequencies similar to those in mgsb and the mean grain size of quartz particles mgsq accepted as a more reliable proxy than mgsb in the upper loess paleosol sequence over the past 2 6 ma however for the underlying red clay formation in the interval from about 7 2 6 ma b p the mgsb record is relatively stable whereas both the zr rb ratio and mgsq show distinct variability and display amplitudes similar to those observed in the overlying loess paleosol sequence these results demonstrate that the zr rb ratio reflects original eolian grain size and may serve as a reliable index of the strength of east asian winter monsoon winds

significance of pre 1860 ma granitoid magmatism for crustal evolution and exploration targeting in the flin flon assemblage trans hudson orogen canada granitoid plutonism a significant contributor to orogenic evolution is a commonly overlooked vector in exploration targeting using the flin flon glennie complex of the trans hudson orogen as a template we show that the geochemistry of granitoid rocks can be a useful parameter in differentiating prospective and nonprospective areas for volcanic hosted massive sulfide vhms deposits the flin flon glennie complex includes 1910 to 1860 ma plutonic rocks that can be subdivided into three suites 1 juvenile arc related rocks of ferroan and magnesian subtypes 2 contaminated arc related rocks and 3 successor arc related rocks of both low and high sr y ratio petrogenesis of ferroan juvenile and low sr y successor arc plutons indicates they formed in regions of thinner crust and hence would have been associated with higher heat flow and arc rifting conditions that favor vhms endowment regions of the orogen with both ferroan and low sr y plutonic subtypes were long lived zones of thin crust and preserve vhms mineralization related to both juvenile and successor arc magmatism in contrast volcanic belts dominated by contaminated arc or high sr y successor arc plutons formed on thicker substrates with contaminated arc rocks built on archean paleoproterozoic pericratonic slivers and high sr y successor arc rocks associated with submarine to subaerial arc systems these regions of thicker crust demonstrably lack vhms deposits and were also the locus for late unroofing our results suggest that pluton geochemistry regionally correlates with mineral occurrence and could represent a useful regional exploration tool in buried or poorly exposed parts of the flin flon glennie complex and other paleoproterozoic orogens

thermal evolution of the kisseynew sedimentary gneiss belt manitoba metamorphism at an early proterozoic accretionary margin

a laboratory study of seismic velocity and attenuation anisotropy in near surface sedimentary rocks the laboratory ultrasonic pulse echo method was used to collect accurate p and s wave velocity 0 3 and attenuation 10 data at differential pressures of 5 50 mpa on water saturated core samples of sandstone limestone and siltstone that were cut parallel and perpendicular to the vertical borehole axis the results when expressed in terms of the p and s wave velocity and attenuation anisotropy parameters for weakly transversely isotropic media q q show complex variations with pressure and lithology in general attenuation anisotropy is stronger and more sensitive to pressure changes than velocity anisotropy regardless of lithology anisotropy is greatest over 20 for velocity over 70 for attenuation in rocks with visible clay organic matter laminations in hand specimens pressure sensitivities are attributed to the opening of microcracks with decreasing pressure changes in magnitude of velocity and attenuation anisotropy with effective pressure show similar trends although they can show different signs positive or negative values of q q we conclude that attenuation anisotropy in particular could prove useful to seismic monitoring of reservoir pressure changes if frequency dependent effects can be quantified and modelled

a 225 kyr record of dust supply paleoproductivity and the oxygen minimum zone from the murray ridge northern arabian sea abstract analysis of a 15 m long sediment core recovered from the murray ridge northern arabian sea reveals a 225 000 year record of climate induced variations in surface water productivity mid water ventilation and dust input in the northern arabian sea productivity and dust input records closely resemble those from the owen ridge and oman margin also the phase lag of 10 kyr between maximum productivity and precession minimum is in phase with the summer monsoon upwelling record from the owen ridge and the oman margin this implies that the productivity variations in the northern arabian sea during the last 225 kyr are primarily controlled by changes in the indian ocean summer monsoon the winter monsoon obviously played a minor role in the productivity history of the northern arabian sea another result from this study is that the mg al record from the murray ridge nicely documents the post glacial flooding of the persian gulf which is the main glacial source for dolomite dust in this region finally it is concluded that the intensity of the omz co varies with surface water productivity being weak during periods of reduced summer monsoon especially during glacial periods

petrophysics studies of sedimentary rocks from a cross hole seismic test site in order to provide a site for studying in detail seismic wave propagation over a large range of frequencies through layered sedimentary rocks four vertical boreholes of approximately 260 m depth and maximum distance apart of 95 m have been drilled through five cyclical sequences of shallow dipping sandstone mudrock and limestone formations in the carboniferous limestone series in northern england two of the boreholes were fully cored and a number of core samples from these were carefully preserved at 1 m intervals in the first and at selected intervals in the second bulk density porosity and p and s wave velocities and attenuation in the vertical and horizontal directions have been made on a total of 180 specimens from the preserved core samples permeability and electrical properties have been measured for the sandstone samples multiple linear regression equations have been derived relating the p and s wave velocities to porosity and clay content these equations indicate the relative importance of increases in porosity and in clay content on decreases in all velocities and the relative insensitivity to changes in clay content of ph and sh wave velocities for the samples tested the average anisotropy observed under in situ stress conditions is approximately 0 5 for limestones porosities to 12 and 5 for sandstones porosities in the range 2 to 18 for mudrocks porosities in the range 2 to 15 the average anisotropy is 21 for p waves and 27 for s waves the results have been used to confirm the magnitudes of anisotropy observed in cross hole seismic tomography at the site in modelling the seismic response of sedimentary rocks with an appreciable clay content and in modelling velocity dispersion and attenuation for rocks at the site over a wide range of frequencies

general characteristics of temperature variation in china during the last two millennia three alternate china wide temperature composites covering the last 2000 years were established by combining multiple paleoclimate proxy records obtained from ice cores tree rings lake sediments and historical documents five periods of temperature variation can be identified a warm stage in ad 0 240 a cold interval between ad 240 and 800 a return to warm conditions from ad 800 1400 including the medieval warm period between ad 800 1100 the cool little ice age period between 1400 1920 and the present warm stage since 1920 regional temperature variation is found during ad 800 1100 when warm conditions occurred in eastern china and in the northeastern tibetan plateau and in ad 1150 1380 when the southern tibetan plateau experienced a warm interval in contrast evidence for cool conditions during the lia is more consistent among the proxy records the temperature reconstructions for china and the northern hemisphere show good agreement over the past millennium

centennial scale winter monsoon variability in the northern east china sea during the holocene the east china sea ecs responds to changes in the strength of the kuroshio and east asian monsoon activity multidecadal resolution records of the palaeotemperature indices and from core ky07 04 pc 1 show that the hydrology of the ecs responded to variability in the east asian winter monsoon unlike mg ca derived sea surface temperatures which show neither warming nor cooling trends during the holocene the record showed a general warming trend at a rate of 0 2 c ka 1 this warming was attributable to shrinkage of the yellow sea central cold water and or weaker winter cooling of the surface water the record indicated a centennial scale variability with an 1 c amplitude superimposed on the warming trend that reflected changes in the east asian winter monsoon and or the kuroshio temperature minima appeared at ca 3 0 4 7 6 2 7 9 and 9 0 ka and spectral analysis of the last 7 ka revealed significant peaks with periodicities of approximately 210 250 and 440 years that were close to those observed in solar radiation the reconstructed winter monsoon variability is consistent with chinese documentary records for the last two millennia copyright 2012 john wiley sons ltd

major and trace element variations of the sediments at odp site 1144 south china sea during the last 230 ka and their paleoclimate implications abstract we present here the major and trace element data of the sediments at odp site 1144 of the last 230 ka with time resolution about 1 5 kyr to investigate their relations to the climate changes estimated from tio2 and cao contents over 70 in weight of the sediments are terrestrial materials and caco3 abundance ranges between 7 and 19 the variation patterns of some of the major elements such as al fe k mg and mn and some of the trace elements such as the alkali elements such as rb and cs the alkali earth elements such as ba and most transition metals such as sc v co cr zn well match that of the oxygen isotopes of the planktonic foraminifer after normalized with ti with higher values during interglacial periods and lower values during glacial periods whilst the na abundance exhibits inverse variation patterns with lower values during interglacial periods and higher values during glacial periods however most refractory elements such as y zr nb hf ta rees th and u do not show such patterns these agree well with the behaviors of these elements during chemical weathering therefore the changes of chemical weathering intensity in south china the source area of these sediments may account for such variation patterns during interglacials wet and warm climate might occur at south china which resulted in stronger chemical weathering and dry climate might occur during glacials which resulted in weaker chemical weathering such paleoclimate interpretation agrees with those from other paleoclimate proxies such as pollen records indicating that change of the east asian monsoon especially change of the winter monsoon is the key for such paleoclimate variation patterns

planktonic foraminiferal records of east asia monsoon changes in the southern south china sea during the last 40 000 years planktonic foraminiferal assemblages and benthic foraminiferal oxygen isotopes were obtained in a gravity core n507 25 6 degrees 39 945 n 113 degrees 32 9361 e water depth 2006 m collected from the southern south china sea scs to investigate east asia monsoon changes during the last 40 000 years four cold events identified from four peaks of the relative abundance of neogloboquadrina pachyderma dex and globigerina quinqueloba correlate well with those in the hulu monsoon record within age uncertainty and can be linked to heinrich events in the northern atlantic high latitudes we suggest that the relative abundance of n pachyderma dex and g quinqueloba in the southern scs can be used as a direct proxy for east asia winter monsoon eawm changes during glacial periods in contrast to its low abundance in the northern scs and okinawa trough the relative abundance of pulleniatina obliquiloculata shows high values during the last glacial in the southern scs caused likely by the combined impact of optimum winter sea surface temperature sst and stronger mixing enhanced upwelling at that time a p obliquiloculata minimum event pme found in the okinawa trough and the northern and southern scs during the h1 period was possibly related to a large drop in winter sst due to the intensified eawm we propose that this pme can be also used as a reliable regional stratigraphic marker as the holocene one a 9 cm sandy silt layer deposit in core ns07 25 during the hi period probably related to the enhanced current that was caused by the especially strengthened eawm at that time the last deglacial warming recorded in the relative abundance of warm and cold species of planktonic foraminifer reveals that changes between the easm and eawm were not in phase but alternating between a winter monsoon dominated northern hemisphere influence and a summer monsoon dominated influence of the tropical dynamics and or southern hemisphere climate changes c 2009 elsevier b v all rights reserved

proterozoic collisional tectonism in the trans hudson orogen saskatchewan isotopic and structural data from the juvenile reindeer zone of the trans hudson orogen northern saskatchewan indicate a pre 1 85 ga thermotectonic event possibly reflecting arc continent collision followed by a more extensive nappe forming ca 1 83 1 80 ga thermotectonism during terminal continent continent collision preliminary data from the adjacent ensialic cree lake zone suggest high grade reworking of archean crust by the pre 1 85 ga event in the rae province to the west high grade metamorphism and reworking of archean crust occurred about 2 0 ga and may be related to the formation of the coeval taltson magmatic zone

thermochronological history of the northern canadian shield abstract the northern canadian shield is comprised of multiple archean cratons that were sutured by the late paleoproterozoic to form the canadian component of supercontinent nuna more than 2000 combined k ar and 40ar 39ar cooling ages from across the region reveal a stark contrast in upper and lower plate thermal responses to nuna forming events with the churchill province in particular revealing near complete thermal reworking during the late paleoproterozoic we review the detailed cooling history for five regions that span the churchill province and trans hudson orogen tho thelon tectonic zone south rae reindeer zone south hall peninsula and the cape smith belt the cooling patterns across churchill province are revealed in two 1500 km transects at the plate scale churchill s cooling history is dominated by tho accretionary and collisional events during which it formed the upper plate cooling ages generally young from west to east across both southern and central churchill and latest cooling in the tho is 50 myr older in southernmost churchill reindeer zone compared to eastern churchill hall peninsula indicating diachronous thermal equilibration across 2000 km strike length of the tho churchill exhibits relatively high post terminal tho cooling rates of 4 c myr which support other geological evidence for widespread rapid exhumation of the tho upper plate following terminal collision potentially in response to lithospheric delamination

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

asian monsoon oscillations in the northeastern qinghai tibet plateau since the late glacial as interpreted from visible reflectance of qinghai lake sediments abstract qinghai lake is a large saline lake on the qinghai tibetan plateau of central asia that is effected by both the indian and asian monsoons we used reflectance spectroscopy to characterize the sediments in a 795 cm long core taken from the southeastern part of the lake sediment redness which is related to iron oxide content seems to monitor paleoclimatic changes in the core iron oxides appear to be eroded from nearby red beds or loess deposits and are transported by fluvial means into the lake thus redness increases at times of increased precipitation that is as monsoon strength increases our redness monsoon proxy shows climate changes on several times scales on a millennial scale it records humid conditions during the early and mid holocene from about 4200 to 2300 yr bp low redness values suggest a two millennial long dry period which in the late holocene is followed by a more humid period on a centennial scale the redness proxy records not only the little ice age but also the medieval warm period the dark ages cool period and the roman warm period time series analysis of the redness record indicates a 200 yr frequency which corresponds to the de vries solar cycle suggesting that in addition to insolation changes resulting from orbital variations solar forcing also results from cyclic changes in the sun s luminosity

geochronology at the namew lake ni cu orebody flin flon area manitoba canada thermal history of a metamorphic terrane intermediate composition orthogneisses of the southward extension of the flin flon greenstone belt surround the ultramafic host rock of the namew lake ni cu deposit in northern manitoba the gneiss

records of late holocene east asian winter monsoon in the east china sea key grain size component of quartz versus bulk sediments abstract quartz isolated from bulk sediments taken from a core obtained from the distal mud area in the outer shelf of the east china sea was used as a proxy in order to determine the strength of the east asian winter monsoon eawm this data was compared with the grain size of bulk sediment from the same core it was found that the content of the key quartz based indicator fraction 15 2 65 6 m correlated well with the eawm strength with reference to current conditions high content of quartz in the selected fraction reflected strong eawm and vice versa the core record spanned 2100 years and three periods of change in eawm strength were identified a period of increased eawm strength prior to 1520 cal bp was followed by a period of weakened eawm strength from 1520 to 720 cal bp which is consistent with the sui tang warm period and the medieval warm period this is followed by a period of slightly increased eawm between 720 and 220 cal bp which corresponds to what is called the little ice age the history of eawm revealed by the quartz based proxy is in striking agreement with results from a previous study on bulk sediment based proxy however the quartz based proxy showed much higher sensitivity and resolution to the eawm strength and displayed much more distinct and sharper boundaries of transition across the three intervals of eawm change compared to the bulk sediment records eleven short eawm strengthening periods were found compared with four by the bulk sediment based proxy therefore this suggests that the quartz grain size proxy is a superior indicator of the winter monsoon strength in the study area

evolution and variability of the asian monsoon system state of the art and outstanding issues the asian monsoon is comprised of the indian and east asian subsystems these two components are linked to one another in varying degrees by regions of strong sensible heating indo asian landmass and strong latent heat export the western pacific warm pool and the southern subtropical indian ocean variability within the indian and east asian subsystems interactions among them and the extent to which they interact with other climate phenomena e g enso are current topics of modern and paleoclimate research this work provides an overview of past and current paleomonsoon research on tectonic to interannual time scales with a primary focus on marine sediment records while past and current work has contributed greatly to our understanding of paleomonsoon variability at all time scales additional efforts are required to make further progress in two critical areas 1 additional efforts are needed in terms of proxy development and evaluation requiring concerted efforts at long term sediment trap deployments in key monsoon influenced regions as well as development of adequate and widely available core top databases these are necessary to assess the impact of modern oceanographic and seafloor processes on potential monsoon proxies 2 additional effort is also needed in acquiring a sufficient geographic distribution of downcore records to assess linkages among the subsystems and their role in the context of extratropical climate change these records should have high sedimentation rates including varved sections this requires substantial survey support to identify the most appropriate coring and drilling targets c 2004 elsevier ltd all rights reserved

u pb geochronology in the trans hudson orogen northern saskatchewan canada we have obtained u pb ages on zircons from volcanic and plutonic units in several lithotectonic domains of the southern trans hudson orogen in northern saskatchewan these data constrain the timing of early proterozoic orogenic events in the region and enhance our understanding of both the relationships among local domains and the relationship of the trans hudson orogen to other early proterozoic orogens in north america with one exception all units studied so far yield zircon ages of 1890 1835 ma most of which are systematically earlier than previously reported rb sr isochron ages on the same or similar units suggesting open system behavior in the rb sr systems five metarhyolites from volcanic sequences in the la ronge domain glennie domain and hanson lake block give ages ranging from 1888 to 1876 ma most of the plutons we dated ranging from gneissic syntectonic tonalites and granodiorites to less deformed late intrusions such as the wathaman batholith and other smaller bodies yield ages of 18