volcano sedimentary processes operating on a marginal continental arc the archean raquette lake formation slave province canada abstract the 200 m thick volcano sedimentary raquette lake formation located in the south central archean slave province represents a remnant arc segment floored by continental crust the formation overlies the gneissic sleepy dragon complex unconformably is laterally interstratified with subaqueous mafic basalts of the cameron river volcanic belt and is considered the proximal equivalent of the turbidite dominated burwash formation a continuum of events associated with volcanism and sedimentation and controlled by extensional tectonics is advocated a complex stratigraphy with three volcanic and three sedimentary lithofacies constitute the volcano sedimentary succession the volcanic lithofacies include 1 a mafic volcanic lithofacies composed of subaqueous pillow pillow breccia and subaerial massive to blocky flows 2 a felsic volcanic lithofacies representing felsic flows that were deposited in a subaerial environment and 3 a felsic volcanic sandstone lithofacies interpreted as shallow water wave and storm reworked pyroclastic debris derived from explosive eruptions the sedimentary lithofacies are represented by 1 a conglomerate sandstone lithofacies consistent with unconfined debris flow hyperconcentrated flood flow and talus scree deposits as well as minor high energy stream flow conglomerates that formed coalescing steep sloped coarse clastic fan deltas 2 a sandstone lithofacies interpreted as hyperconcentrated flood flow deposits that accumulated at the subaerial subaqueous interface and 3 a mudstone lithofacies consistent with suspension sedimentation in a small restricted lagoon type setting the raquette lake formation is interpreted as a fringing continental arc that displays both high energy clastic sedimentation and contemporaneous effusive and explosive mafic and felsic volcanism modern analogues that develop along active plate margins in which continental crust plays a significant role include japan and the baja california peninsula

relative sea level change along the slave craton coastline characteristics of archean continental rifting abstract the 2 8 ga siliciclastic dominated craton cover succession with subordinate mafic volcanic rocks at beniah lake in the slave craton has been informally referred to as the bell lake group the beniah lake succession up to 1 km thick is composed of 7 120 m thick coarsening upward cu sequences arranged with the following lithofacies architecture 1a argillite sandstone 1b mafic volcanic lithofacies 2 sandstone argillite 3a quartz arenite and 3b conglomerate lithofacies a pan slave unconformity indicating an autochthonous 2 8 to 4 013 ga basement cover relationship is present and locally well exposed the lithofacies and their arrangement are consistent with a tide influenced coastal setting whereby the change from argillite sandstone to quartz arenite lithofacies represents an initial estuary system defining transgression with a maximum flooding surface evolving into a fan delta defining progradation with a maximum regressive surface the mafic volcaniclastic lithofacies and associated pillowed flow units suggesting drowning of the siliciclastic succession coincide with a change from rift to drift tectonics as crustal attenuation facilitated magma ascent the slave wide unconformities and lithofacies contacts permit a sequence stratigraphic approach with the major slave basement quartz arenite unconformity suggestive of a 1st order sea level change coinciding with the proposed super continent break up or rifting the consistent stacking of cu sequences with capping subaqueous volcaniclastic volcanic units are considered the expression of 2nd order sea level cycles probably caused by changes of spreading rates at oceanic ridges the cu sequences and their thicknesses constitute 3rd order sea level changes and reflect the immediate response to crustal thinning time constraints for all these orders remain elusive but the hierarchy is consistent with sequence stratigraphic events the observed relative sea level change is attributed primarily to tectono eustasy where mantle dynamics caused rifting basin subsidence and mafic volcanism the latter occurred as the crust was sufficiently attenuated

linking the 8 2 ka event and its freshwater forcing in the labrador sea 1 the 8 2 ka event was the last deglacial abrupt climate event a reduction in the atlantic meridional overturning circulation amoc attributed to the drainage of glacial lake agassiz may have caused the event but the freshwater signature of lake agassiz discharge has yet to be identified in 18o of foraminiferal calcite records from the labrador sea calling into question the connection between freshwater discharge to the north atlantic and amoc strength using mg ca paleothermometry we demonstrate that 3 c of near surface ocean cooling masked an 1 0 decrease in western labrador sea 18o of seawater concurrent with lake agassiz drainage comparison with north atlantic 18o of seawater records shows that the freshwater discharge was transported to regions of deep water formation where it could perturb amoc and force the 8 2 ka event

signature of the gold cove event 10 2 ka in the labrador sea abstract one of the least known catastrophic meltwater and sediment release events of the laurentide ice sheet during the early holocene is the so called gold cove proglacial lake outbursts a drainage event through the hudson strait this event may have disturbed circulation in the labrador sea by releasing freshwater here we report data from four sediment cores and re analysis of six published records spatially covering 2000 km from the mouth of hudson strait to the northeastern sohm abyssal plain abundant detrital carbonate dc and less positive 18o values in neogloboquadrina pachyderma sinistral suggest a short lived meltwater event in the hudson strait region this discharge transported detrital carbonate rich sediment and shallow water benthic forams southward along the labrador margin mixing with the north atlantic current near the grand banks sediments associated with this event were guided through the deep labrador sea from the mouth of hudson strait and the northwest atlantic mid ocean channel namoc to the sohm abyssal plain furthermore we report less positive 13c values in the epibenthic foram cibicidoides wuellerstorfi from the southern labrador sea during this event our twenty one 14c ams dates in addition to earlier published radiocarbon dates from the labrador margin suggest that this dc event was coeval with the gold cove proglacial lake outbursts related to re advance of the laurentide ice sheet

deposition and imbrication of a 2670 2629 ma supracrustal sequence in the indin lake area southwestern slave province canada new u pb age data from the southwestern slave province demonstrate that units of the indin lake supracrustal belt form an imbricated structural stack the oldest rocks of the belt are undated mafic volcanic flows of the hewitt lake group that are crosscut by a 2670 ma felsic sill itself coeval with mafic through felsic volcanic rocks of the 2668 2671 ma leta arm group the youngest rocks of the belt are 2647 2629 ma turbidites and felsic volcanic rocks of the unconformably overlying chalco lake group tonalite orthogneiss of the adjacent cotterill gneiss complex is 2680 ma suggesting that it does not represent in situ basement to the supracrustal belt intercalation of the older hewitt lake and leta arm groups with the younger chalco lake group is interpreted to result from d1 imbrication and folding between 2629 and 2609 ma the age of a crosscutting tonalite intrusion subsequent d2 folding and regional low pressure metamorphism occurred between 2609 ma and ca 2590 ma d3 normal faulting between the

detrital carbonate peaks on the labrador shelf a 13 7 ka template for freshwater forcing from the hudson strait outlet of the laurentide ice sheet into the subpolar gyre abstract the laurentide ice sheet lis was a large dynamic ice sheet in the early holocene the glacial events through hudson strait leading to its eventual demise are recorded in the well dated labrador shelf core md99 2236 from the cartwright saddle we develop a detailed history of the timing of ice sheet discharge events from the hudson strait outlet of the lis during the holocene using high resolution detrital carbonate ice rafted detritus ird 18o and sediment color data eight detrital carbonate peaks dcps associated with ird peaks and light oxygen isotope events punctuate the md99 2236 record between 11 5 and 8 0 ka we use the stratigraphy of the dcps developed from md99 2236 to select the appropriate r to calibrate the ages of recorded glacial events in hudson bay and hudson strait such that they match the dcps in md99 2236 we associate the eight dcps with h0 gold cove advance noble inlet advance initial retreat of the hudson strait ice stream hsis from hudson strait opening of the tyrrell sea and drainage of glacial lakes agassiz and ojibway the opening of foxe channel and retreat of glacial ice from foxe basin are represented by a shoulder in the carbonate data r of 350 years applied to the radiocarbon ages constraining glacial events h0 through the opening of the tyrell sea provided the best match with the md99 2236 dcps r values and ages from the literature are used for the younger events a very close age match was achieved between the 8 2 ka cold event in the greenland ice cores dcp7 8 15 ka bp and the drainage of glacial lakes agassiz and ojibway our stratigraphic comparison between the dcps in md99 2236 and the calibrated ages of hudson strait bay deglacial events shows that the retreat of the hsis the opening of the tyrell sea and the catastrophic drainage of glacial lakes agassiz and ojibway at 8 2 ka are separate events that have been combined in previous estimates of the timing of the 8 2 ka event from marine records sw iceland shelf core md99 2256 documents freshwater entrainment into the subpolar gyre from the hudson strait outlet via the labrador north atlantic and irminger currents the timing of freshwater release from the lis hudson strait outlet in md99 2236 matches evidence for freshwater forcing and lis icebergs carrying foreign minerals to the sw iceland shelf between 11 5 and 8 2 ka the congruency of these records supports the conclusion of the entrainment of freshwater from the retreat of the lis through hudson strait into the subpolar gyre and provides specific time periods when pulses of lis freshwater were present to influence climate

variations in the provenance of sediment from ice sheets surrounding baffin bay during mis 2 and 3 and export to the labrador shelf sea site hu2008029 0008 davis strait based on quantitative x ray diffraction mineralogical analysis of cores hu2008029 0006 0008 857 m water depth located south of the davis strait sill we seek answers to two questions i the temporal correlation of nw labrador shelf sea heinrich h and baffin bay detrital carbonate bbdc events and ii the provenance of the sediments a sediment unmixing model sedunmix is used to determine provenance variations although 12 radiocarbon dates were obtained there were many age reversals and we favour a depth age model for hu2008029 0008pc based on correlations to well dated neighbouring cores north and south of davis strait we find no correlation between h and bbdc events except for h 0 which appears to be a broadly synchronous event along the ne canadian margin and is correlative with an episode of major moraine building along this flank of the laurentide ice sheet unmixing of the sediment composition based on six potential glacial source regions indicates that the bulk of the sediment in 0008pc is derived from glacial erosion of west greenland but is punctuated by intervals when dolomite rich sediments derived from outcrops north of baffin bay dominate the composition estimated dates on these bbdc events are 13 25 and 30 38 cal ka bp copyright 2013 john wiley sons ltd

precambrian ophiolites and related rocks developments in precambrian geology 13 t m kusky editor pp 800 elsevier 2004 isbn 0 444 50923 2 price 198 the purpose of this collection of papers is to address the still controversial question as to the continuity of modern plate tectonic processes back through earth s early geologic history by cataloguing worldwide precambrian ophiolite sequences for the economic geologist and explorationist this volume provides an opportunity to acquaint themselves with geological and geochemical characteristics of precambrian ophiolite assemblages and of phanerozoic analogues this in turn will allow them to recognize this distinctive type of sea floor assemblage in the field and from geochemical study as well as the implications of its presence within certain precambrian volcano sedimentary terranes the editors organized the series of 22 papers into four sections proterozoic ophiolites and related rocks archean ophiolites and related rocks models for the evolution of oceanic crust with time and analogies to precambrian ophiolites the editor s introduction to these sections is somewhat lengthy and repetitious but at the same time it is a good summary of the different ophiolite settings and their characteristics and also serves as a volume synopsis

origin of the northern atlantic s heinrich events as first noted by heinrich 1988 glacial age sediments in the eastern part of the northern atlantic contain layers with unusually high ratios of ice rafted lithic fragments to foraminifera shells he estimated that these layers are spaced at intervals of roughly 10 000 years in this paper we present detailed information documenting the existence of the upper five of these layers in odp core 609 from 50 n and 24 w their ages are respectively 15 000 radiocarbon years 20 000 radiocarbon years 27 000 radiocarbon years about 40 000 years and about 50 000 years we also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers although we are not of one mind regarding the origin of these layers we lean toward an explanation that the heinrich layers are debris released during the melting of massive influxes of icebergs into the northern atlantic these sudden inputs may be the result of surges along the eastern margin of the laurentide ice sheet

the central slave basement complex part ii age and tectonic significance of high strain zones along the basement cover contact the basement cover high strain zone enveloping parts of the sleepy dragon complex northeast of yellowknife slave province canada has been reinvestigated integrated stratigraphic structural and geochronological data show that the high strain zone is of regional extent and is best interpreted as a decollement between crystalline ca 2 9 3 3 ga rocks of the central slave basement complex and pre 2687 ma cover rocks three temporally distinct mafic dyke swarms occur within the high strain zone the two oldest of these constrain the timing of the high strain event to between 2734 2 and 2687 1 ma at the time of decollement development the cover stratigraphy consisted of i the central slave cover group a thin pre 2734 ma succession of mafic and ultramafic volcanic rocks conglomerates fuchsitic quartzites minor rhyolites and banded iron formation and ii an overlying sequence of tholeiitic pillow basalts the central slave cover group is considered to be autochthonous whereas a variety of

isotope stratigraphy sedimentation rates deep circulation and carbonate events in the labrador sea during the last 200 ka high resolution stable isotope and accelerator mass spectrometry 14c measurements in 25 box and piston cores from the labrador sea allow the reconstruction of major paleoceanographical changes during the last 200 ka in this basin and also document the links between the interior of the laurentide ice sheet and the north atlantic ocean during this interval two deep circulation regimes are indicated by contrasting sedimentation rates on the slopes i the modern situation is characterized by a gyre of the north atlantic deep water nadw components into the basin which is responsible for the high energy western boundary undercurrent this regime also prevailed during the former true interglacials and possibly during shorter warm intervals e g bolling allerod ii a more frequent nadw free situation during glacial and interstadial intervals is marked by the presence of a vertically homogeneous water mass in the basin sedimentological records also indicate that carbonate events i e pulses of

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

u pb zircon geochronology of the yellowknife volcanic belt nwt canada new constraints on the timing and duration of greenstone belt magmatism volcanic and sedimentary rocks in the slave province collectively termed the yellowknife supergroup have long been considered to represent laterally continuous and correlative stratigraphically coherent homoclinal sequences correlation based on the lithologic analysis of certain distinctive units has been most intensely applied to the yellowknife volcanic belt in the southern slave province u pb zircon data for seven samples collected from within the belt are reported here the distinctiveness of the townsite formation a term applied to three lenticles of rhyodacitic to dacitic tuffs breccias and pillowed flows in comparison to the overlying and underlying tholeiitic basalts kam group has led to its use as a key marker unit for stratigraphic correlations and palinspastic restorations of offsets on proterozoic faults in the area a sample from each of the three segments was collected for u pb zircon geochronology in addition numerous thinner tuffaceous beds from the kam group were also dated

u pb geochronology of the hope bay elu inlet area bathurst block northeastern slave structural province northwest territories u pb ages for six felsic samples from the dominantly mafic hope bay and elu inlet metavolcanic belts of the bathurst block provide the first constraints on the timing of felsic volcanism 2685 2677 ma and plutonism 2672 2608 ma in the northeastern corner of the slave structural province gold veins that cut a pluton in the eastern hope bay belt are younger than 2672 ma early proterozoic magmatic activity is recorded in a pegmatite dyke that crosscuts metavolcanic rocks of the northern hope bay belt initial nd and sr isotopic ratios from the hope bay and elu inlet belts indicate a juvenile source for the magmas

tectonic and thermal history of the anialik river area northwestern slave province canada the anialik river area in the northwestern slave province comprises two geological domains of different age and origin that were tectonically juxtaposed at ca 2650 ma the older domain the kangguyak gneiss belt comprises ca 3300 2700 ma orthogneisses and paragneisses interpreted as the remnants of a mesoarchean continental margin the younger domain the anialik river greenstone belt consists of ca 2680 ma mafic to felsic volcanic rocks interpreted to have formed in an ensimatic island arc setting structural and geochronological evidence suggest collision of the two domains began around 2650 ma in a transpressive regime that involved oblique sinistral subduction of the greenstone belt beneath the kangguyak domain along the tokhokatak shear zone displacement continued until at least ca 2600 ma when late two mica granites intruded along and were deformed in the shear zone following ca 2600 ma rocks in both domains and along the fault cooled rapidly to about 350 c strongly overprinted musco

heinrich 0 on the east canadian margin source distribution and timing the last deglaciation was marked by intervals of rapid climatic fluctuations accompanied by glacial advances and retreats along the eastern margin of the laurentide ice sheet one of these climatic events the younger dryas cold reversal was accompanied by a detrital carbonate event referred to as heinrich event 0 h0 that deposited ice rafted debris and especially detrital carbonate rich dc sediment layers in the western and southern labrador sea the precise age duration source and geographical distribution of the h0 dc event however are not entirely clear a high sedimentation rate sequence cored off southern newfoundland yielded an age of 11 5 11 3 calibrated kyr b p for this layer thus pointing to its deposition directly following the younger dryas termination likely associated with rapid ice retreat and warming at the onset of the holocene at the study site the h0 layer contains increased concentrations of detrital carbonates calcite dolomite ratio 2 5 1 and a mature biomarker composition similar to that found in heinrich layers 1 2 4 and 5 which together suggest an origin from hudson strait grain size analysis indicates that the h0 sediments were transported to the study site mostly through shallow plumes along the labrador shelf with some hyperpycnal dispersal deeper along the slope and rise our data thus point to a large meltwater release caused by retreat of the ice margin in the hudson strait area the relvatively short duration of the h0 layer and its timing right after a major climatic transition combined with its ubiquitous regional occurrence makes it valuable for correlating different sediment records from the western labrador sea

influence of tectonism and climate on lithofacies distribution and sandstone and conglomerate composition in the archean beaulieu rapids formation northwest territories canada abstract the 0 2 1 km thick archean beaulieu rapids formation is a late orogenic tectonically controlled sedimentary sequence overlying the beaulieu river volcanic belt unconformably on the west and bordering the major n trending beniah lake fault on the east local porphyry stocks characteristic of late orogenic successions were emplaced along strike of the fault four lithofacies comprise the beaulieu rapids formation 1 the 20 320 m thick conglomerate i 2 the 10 305 m thick siltstone sandstone 3 the 20 120 m thick conglomerate ii and 4 the 40 320 m thick quartz rich sandstone lithofacies stacking displays two distinct large scale fining upward sequences represented by the 300 375 m thick conglomerate i and sandstone siltstone sequence a and the 300 400 m thick conglomerate ii and quartz rich sandstone sequence b fining upward sequences a bounding unconformity and the beniah lake fault are compelling indicators of tectonic influence on sedimentation conglomerate i was deposited by debris flows traction currents and sheetfloods on the proximal medial and distal portions of alluvial fans or fan deltas respectively the overlying siltstone sandstone contains two distinct lithological units a sandstone dominated unit formed from fluvial dune migration and overbank deposition in a sandy braidplain setting with scattered ponds whereas sedimentary structures in the siltstone dominated unit are consistent with lacustrine deposition a second phase of tectonic uplift produced sequence b conglomerate ii was deposited in a proximal braided stream setting characterized by abundant longitudinal gravel bars the quartz rich sandstone developed from dune migration on a sandy braidplain mineralogy and textures reflect high sediment influx limited transport distance local sources and climatic influence clast populations in conglomerate indicate a prevalent mafic volcanic source whereas sandstones contain prominent quartz av 76 with subordinate feldspar 13 and lithic fragments 11 the disparity between clast and sandstone composition is a function of chemical weathering typical of a humid climate source areas are restricted to the mafic dominated beaulieu river volcanic belt the 2 8 ga gneisso plutonic sleepy dragon complex and fault related porphyry stocks the humid weathering aggressive archean climate was responsible for destroying labile minerals and lithic fragments in proximal source rocks rich in plagioclase accounting for the high quartz component in the sandstones the beaulieu rapids formation is similar to modern strike slip basins that form along major fault zones in terms of basin geometry faulted and unconformable contacts lithological units and sedimentary facies stacking and organization fault controlled basins of this nature commonly develop during the last stage of terrane accretion on archean cratons

impact of melting of the laurentide ice sheet on sediments from the upper continental slope off southeastern canada evidence from sm nd isotopesthis article is one of a series of papers published in this special issue on the theme polar climate stability network we present new sm nd isotope data for sediments from a core located on the continental slope of the st pierre bank of canada s east coast the nd analyses indicate that the sediments were derived from two principal sources the north american shield that yields an average early proterozoic isotopic signature and a younger proterozoic signature attributed to appalachian crustal sources the appalachian sourced sediments predominated during the last glacial maximum lgm and were associated with low sedimentation rates 30 cm ka with the exception of a strong north american shield signature present in a detrital carbonate layer that corresponds to heinrich layer 1 h1 the dominance of the appalachian signature decreased subsequent to h1 the appalachian signatures closely follow the distribution of sediments interpreted as locally derived glacial tills while the north american shield signatures follow the distribution of hemipelagic mud that was likely deposited by the labrador current the nd data a

lake agassiz outburst age and routing by labrador current and the 8 2 cal ka cold event abstract catastrophic drainage of glacial lake agassiz impounded by the laurentide ice sheet lis into hudson bay and strait is widely thought to have caused the 8 2 cal ka cold event though the path of its drainage in the north atlantic is poorly known analysis and compilation of 10 sediment cores from 8 sites distributed on the eastern canadian continental shelf and upper slope south of hudson strait revealed distinct beds with elevated detrital carbonate dc concentrations known by their distinct composition to originate from erosion of carbonate bedrock and carbonate rich glacial sediments in the hudson bay hudson strait region at all but one site radiocarbon ages bracketing and within the thickest and most widespread of these beds are coeval with the age constraints for the agassiz floods in hudson strait and southeastern hudson bay the dc distribution and concentration of this bed are consistent with southward transport in the labrador current transfer function analysis of dinoflagellate assemblage data from cores on the central labrador shelf in hudson bay and on the northeast newfoundland shelf reveal that early holocene seasonal ice cover was 5 6 months longer than at present requiring the application of a 200 year reduction to the radiocarbon age constraints on the lake agassiz outburst floods the age of the floods is reduced to about 8 33 cal ka 7 5 14 c ka from the previous determination of 8 47 cal ka 7 7 14 c ka with a similar reduction in their error ranges to 8 04 8 49 cal ka from 8 16 8 74 cal ka based on present current routing the agassiz floodwaters and icebergs are inferred to have travelled south in the labrador current and to have possibly become incorporated into the north atlantic current and transported to the nordic seas there the freshwater additions would have lessened deepwater production with a concomitant reduction in northward heat transport in the upper limb of the atlantic meridional overturning circulation thereby contributing to the 8 2 cal ka cold event variation in the calcite and dolomite content of the agassiz dc bed two salinity reductions during agassiz bed deposition and low level shorelines of lakes agassiz and ojibway suggest that more than one outburst was delivered during the final agassiz drainage the 8 2 cal ka cold event registered in greenland was coeval with a second or later flood which possibly accompanied the final collapse of the lis in hudson bay

sea surface temperatures did not control the first occurrence of hudson strait heinrich events during mis 16 1 hudson strait hs heinrich events ice rafting events in the north atlantic originating from the laurentide ice sheet lis are among the most dramatic examples of millennial scale climate variability and have a large influence on global climate however it is debated as to whether the occurrence of hs heinrich events in the eastern north atlantic in the geological record depends on greater ice discharge or simply from the longer survival of icebergs in cold waters using sediments from integrated ocean drilling program iodp site u1313 in the north atlantic spanning the period between 960 and 320 ka we show that sea surface temperatures ssts did not control the first occurrence of hs heinrich like events in the sedimentary record using mineralogy and organic geochemistry to determine the characteristics of ice rafting debris ird we detect the first hs heinrich like event in our record around 643 ka marine isotope stage mis 16 which is similar as previously reported for site u1308 however the accompanying high resolution alkenone based sst record demonstrates that the first hs heinrich like event did not coincide with low ssts thus the hs heinrich like events do indicate enhanced ice discharge from the lis at the end of the mid pleistocene transition not simply the survivability of icebergs due to cold conditions in the north atlantic

itrax description and evaluation of a new multi function x ray core scanner a new automated multi function core scanning instrument named itrax has been developed that records optical radiographic and elemental variations from sediment half cores up to 1 8 m long at a resolution as fine as 200 m an intense micro x ray beam focused through a flat capillary waveguide is used to irradiate samples to enable both x radiography and x ray fluorescence xrf analysis data are acquired incrementally by advancing a split core via a programmable stepped motor drive through the flat rectangular section x ray beam traditional xrf determination of element composition in sediments provides high quality data but it takes a considerable time and normally consumes gram quantities of material that is often only available in limited quantities the itrax core scanner non destructively collects optical and x radiographic images and provides high resolution elemental profiles that are invaluable for guiding sample selection for further destructive detailed sampling this paper presents a description of the construction characteristics and capabilities of the itrax system high resolution itrax data obtained from sediment cores are also presented and compared with results from traditional wavelength dispersive xrf analysis at lower resolution finally some recent technical developments linked to the second generation itrax are presented

electric lithosphere of the slave craton the archean slave craton in northwestern canada is an ideal natural laboratory for investigating lithosphere formation and evolution and has become an international focus of broad geoscientific investigation following the discovery of economic diamondiferous kimberlite pipes three deep probing magnetotelluric surveys have recently been carried out on the craton using novel acquisition procedures the magnetotelluric responses reveal an unexpected and remarkable anomaly in electrical conductivity collocated with the kimberlite field that is modeled as a spatially confined upper mantle region of low resistivity 30 m at depths of 80 100 km and is interpreted to be due to dissolved hydrogen or carbon in graphite form this geophysically anomalous upper mantle region is also spatially coincident with a geochemically defined ultradepleted harzburgitic layer the tectonic processes that emplaced this structure are possibly related to the lithospheric subduction and trapping of overlying oceanic mantle at 2630 2620 ma

biomarker determination as a provenance tool for detrital carbonate events heinrich events fingerprinting quaternary glacial sources into baffin bay sedimentary deposits associated with heinrich events are anomalously rich in detrital carbonate off hudson strait the dominant carbonate is calcite whereas at distal sites in the north atlantic dolomite is dominant more diagnostic a significant source for dolomite is its outcrop at the northern end of baffin bay where major ice streams from the laurentide innuitian and greenland ice sheets converged the provenance of samples containing detrital carbonate mainly dolomite from a core in baffin bay has been confirmed using organic geochemistry to distinguish between alternative sources based upon the thermal maturity of organic matter in carbonates of the source region the core contained five distinct carbonate units dating between 14 and 51 cal ka bp and indicates significant ice stream instability associated with iceberg calving and significant volumes of meltwater the exact temporal relationship to heinrich events is not yet clear a long mid wisconsin interval 38 to 22 cal ka bp devoid of detrital carbonate suggests a major reduction in ice extent at high northern latitudes the core samples yield thermally sensitive biomarker ratios comparable to those from laurentian carbonates in the canadian arctic islands but unlike those from north greenland identifying the former region as their provenance however a late holocene sample from off newfoundland shows a stronger affinity with greenland 2007 elsevier b v all rights reserved

geology and u pb geochronology of the neoarchean snare river terrane tracking evolving tectonic regimes and crustal growth mechanisms u pb zircon crystallization ages determined by isotope dilution thermal ionization mass spectrometry id tims and laser ablation microprobe inductively coupled plasma mass spectrometry lam icp ms for 13 intrusive units in the neoarchean snare river terrane srt provide tight constraints on the timing of crust formation and orogenic evolution seven metaluminous plutons were emplaced over 80 ma from ca 2674 to 2589 ma whereas six peraluminous bodies were emplaced in a 15 ma interval from ca 2598 to 2585 ma a detrital zircon study yielded an age spectrum with peaks correlative with known magmatic events in the slave province with the ca 2635 ma age of the youngest detrital zircon population providing a maximum estimate for the onset of sedimentation this age contrasts with evidence for pre 2635 ma sedimentation elsewhere in the srt indicating that sedimentation was protracted and diachronous evolution of the srt can be subdivided into four stages i 2674 2635 ma formation of a metal

the slave province a distinct archean craton the slave province is a relatively small late archean craton that exhibits distinctive rock associations and structures by comparison with the much larger superior province differences are evident in i the abundance of sedimentary versus volcanic rocks and of felsic versus mafic volcanic rocks ii the greater evidence for sialic basement iii the higher proportion of more evolved potassium rich granite iv the type setting and timing of gold and base metal mineralization and v a regional zonation of gold deposits that seems to be a unique feature of the slave province contrasts in structure are also significant the large scale linear belts and boundaries sutures that characterize the superior province have no obvious counterpart in the slave province despite some similarities with other archean cratons the distinct features of the slave province are important for they imply that no single archean craton should be used to develop a universal paradigm for the genesis and tectonic evol

a 750 kyr detrital layer stratigraphy for the north atlantic iodp sites u1302 u1303 orphan knoll labrador sea abstract integrated ocean drilling program iodp sites u1302 u1303 drilled on the se flank of orphan knoll labrador sea preserve a record of detrital layers and other proxies of hydrographic change that extend the record of ice sheet ocean interactions through most of the brunhes chron the age model is built by tandem matching of relative paleointensity rpi and oxygen isotope data 18o from neogloboquadrina pachyderma sin to reference records indicating a mean brunhes sedimentation rate of 14 cm kyr sedimentation back to marine isotope stage mis 18 is characterized by detrital layers that are detected by higher than background gamma ray attenuation gra density peaks in x ray fluorescence xrf indicators for detrital carbonate ca sr and detrital silicate si sr and an ice rafted debris ird proxy wt 106 m the age model enables correlation of site u1302 03 to iodp site u1308 in the heart of the central atlantic ird belt where an age model and a similar set of detrital layer proxies have already been derived ages of heinrich h layers h1 h2 h4 h5 and h6 are within 2 kyr at the two sites h0 h3 and h5a are not observed at site u1308 and agree with previous work at orphan knoll within 3 kyr at site u1308 brunhes detrital layers are restricted to peak glacials and glacial terminations back to marine isotope stage mis 16 and have near synchronous analogs at site u1302 03 detrital layers at site u1302 03 are distributed throughout the record in both glacial and most interglacial stages we distinguish heinrich like layers associated with ird from detrital layers marked by multiple detrital layer proxies including ca sr but usually not associated with ird that may be attributed to lofted sediment derived from drainage and debris flow events funneled down the nearby northwest atlantic mid ocean channel namoc the prominent detrital layers at sites u1302 03 and u1308 can be correlated to millennial scale features in the chinese speleothem monsoon record over the last 400 kyr implying a link between monsoon precipitation and laurentide ice sheet lis instability the detrital layer stratigraphy at site u1302 03 provides a long record of lis dynamics against which other terrestrial and marine records can be compared

oceanographic regimes in the northwest labrador sea since marine isotope stage 3 based on dinocyst and stable isotope proxy records abstract sea surface temperature sst salinity and density gradients in the upper water column of the northwest labrador sea have been reconstructed based on high resolution analysis of a core hu2008 029 004pc spanning the last 36 ka raised off hudson strait the modern analogue technique was applied to dinocyst assemblages and combined with stable isotope data from neogloboquadrina pachyderma left coiled npl for this purpose three oceanographic regimes were identified broadly corresponding to the glacial deglacial and postglacial intervals the site remained under the direct influence of the laurentide ice sheet lis margin until the postglacial and did not record the bolling allerod warming and weakly recorded the younger dryas event the glacial regime lasted until 12 2 cal ka bp it was characterized by generally low concentrations of dinocysts within an assemblage indicative of quasi perennial sea ice the deglacial regime ca 12 2 8 3 cal ka bp was marked by increased biogenic fluxes and more diversified dinocyst assemblages and possibly an enhanced subsurface inflow of north east atlantic deep water warm summer 11 c but low winter 0 c sea surface temperatures sea ice cover during about 3 months per year and low summer salinity 28 suggest strong stratification in the upper water layer in relation to meltwater supply from the lis following the final drainage of glacial lake agassiz through hudson strait which is dated here at 8 3 cal ka bp and the subsequent lis collapse increased summer salinity up to 35 was accompanied by a reduced seasonal gradient of sea surface temperature from winter 3 8 c to summer 8 6 c suggesting enhanced penetration of north atlantic water weakened stratification of the surface water layer then allowed for winter convection and labrador sea water formation which is consistent with increased npl 13c values in response to higher ventilation of the subsurface water layer

millennial scale ice rafting events and hudson strait heinrich like events during the late pliocene and pleistocene a review abstract various types of abrupt millennial scale climate variability such as dansgaard oeschger and heinrich events characterized the last glacial period over the last decade a number of studies demonstrated that such millennial scale climate variability was not limited to the last glacial but inherent to quaternary climate here we review the occurrence and origin of millennial ice rafting events in the north atlantic during the late pliocene and pleistocene last 3 4 ma with a special focus on north atlantic hudson strait hs heinrich like events we show that heinrich layers 5 4 2 and 1 in marine sediment cores from across the north atlantic all bear the organic geochemical fingerprint of the hudson area using this framework and combining previously published results detailed investigations into the organic and inorganic chemistry of ice rafted debris ird found across the north atlantic demonstrate that prior to mis 16 650 ka ird in the north atlantic did not originate from the hudson area of northern canada the signature of this early ird is distinctly different compared to that of hs heinrich layers rather ice rafting events during the late pliocene and early pleistocene predominantly emanated from the calving of the greenland and fennoscandian ice sheets and possibly minor contributions from local ice streams from the north american and british ice sheets compared to north atlantic hs heinrich events these early pleistocene ird events had a limited impact on surface water characteristics in the north atlantic north atlantic hs heinrich like events first occurred during mis 16 at the same time the dominant frequency in silicate rich ird accumulation shifted from the obliquity 41 ka to a 100 ka frequency across the north atlantic iceberg survivability or a change in iceberg trajectory likely did not control this change in ird regime these results lend further support for the existing hypothesis that an increase in size thickness of the laurentide ice sheet controls the occurrence of north atlantic hs heinrich events favoring an internal dynamic mechanism for their occurrence

stable isotope clue to episodic sea ice formation in the glacial north atlantic sea ice is a determinant parameter of the climate system which acts as amplifier through positive ice albedo feedbacks and induces deep water formation through brine production it is also one of the most elusive parameters in the paleoclimate record most proxies of sea ice provide information on its presence and extent of e g diatoms or dinocysts but do not permit assessment on its rate of formation however seemingly off equilibrium low 18o values in mesopelagic planktic foraminifer species as observed today in the arctic ocean are thought to relate to the production of isotopically light brines during sea ice formation and might thus provide a clue on the rate of sea ice growth with reference to the isotopic properties of modern planktic foraminifers in the arctic ocean and using multi proxy data sets from the last glacial stage in the northwest north atlantic we re examined some of the current interpretations of planktic isotope records in the glacial nw north atlantic the large amplitude light isotopic excursions recorded in neogloboquadrina pachyderma left coiling during heinrich events 1 for example correspond to extensive sea ice cover as reconstructed from dinocysts and do not seem unequivocally linked to low salinity pulses such light isotopic excursion more likely responded to enhanced rates of sea ice formation resulting in the production and sinking of isotopically light brines on the contrary the isotopically heavy planktic foraminifers of the last glacial maximum lgm interval stricto sensu would rather suggest relatively low rates of brine production thus low sea ice growth rates in the area this would imply that the lgm distribution of sea ice in the north atlantic was primarily linked to spreading and drifting from marginal and nordic source areas and not from enhanced in situ production at the scale of glacial interglacial cycles isotopic distillation processes relating to sea ice production at high latitudes could be one of the factors controlling the 18o salinity relationship in deep ocean water masses that might deserve closer examination as it would be independent of continental ice volume changes

mesoarchean continental breakup evolution and inferences from the 2 8 ga slave craton cover succession canada abstract the 20 to 1000 m thick 2 8 ga bell lake group is a siliciclastic dominated succession in the slave craton that contains features consistent with continental rifting the archean succession is composed of four principal lithofacies 1 conglomerate 2 quartz arenite 3 sandstone argillite and 4 argillite sandstone an unconformity with 2 8 4 0 ga basement indicates an autochthonous craton cover relationship and pillowed flows in depositional contact with the argillite sandstone lithofacies reflect contemporaneous sedimentation and volcanism the basement composed of layered intrusions granitic plutons and gneissic rocks served as the source for the quartz arenite with detrital chromite mesoarchean slave stratigraphic sections contain fining upward fu and coarsening upward cu sequences with the former predominant at craton cover contacts the cu sequences are considered to be the results of rifting that produced a coastline featuring estuaries and embayments affected by tides a

a new look at the stratigraphy of the yellowknife supergroup at yellowknife n w t implications for the age of gold bearing shear zones and archean basin evolution based on recent detailed mapping a revised stratigraphic column is proposed for the rocks of the archean yellowknife supergroup in the yellowknife greenstone belt the mafic volcanic rocks of the kam formation previously thought to represent the oldest supracrustal rocks of the belt overlap remnants of an earlier volcanic sedimentary sequence here referred to as the octopus formation as its enormous thickness makes it too unwieldy to be described as a single formation the kam formation is raised to group status and subdivided into four formations it is proposed that the kam group should replace the beaulieu group in the yellowknife area the chan formation at the base of the kam group consists of multiple gabbroic intrusions that were emplaced into a carapace of pillowed flows the intrusions locally resemble sheeted mafic dyke complexes in phanerozoic ophiolites thought to represent evidence for sea floor spreading the crestaurum formation which overlies the chan formation is characterized b

products of 2 65 2 58 ga orogenesis in the slave province correlated with slave northern cordillera lithospheric evolution snorcle seismic reflection patterns reflection patterns along lithoprobe slave northern cordillera lithospheric evolution snorcle seismic reflection line 1 in the southwestern slave province are interpreted as products of tectonic wedging during late archean lithospheric convergence the interpretation is aided by application of new seismic imaging techniques by correlation of upper crustal reflection patterns to known geology and by a comparison of lithospheric reflection patterns to similar convergent zones elsewhere in the yellowknife area reflection patterns consist of 1 east dipping reflections at 12 14 s that project into the upper mantle 2 a wedge shaped body in the lower crust with an east dipping reflection fabric that is truncated on the west by 3 a series of west dipping reflections that outline thrust and fold structures in the upper crust the similarity of these reflection patterns to those of the proterozoic fort simpson hottah collision zone 300 km to the west provides support for the interpretation that reflection patterns beneath the slave province are also products of collisional tectonics rocks within the slave province preserve evidence of a 2 65 2 58 ga pan slave orogenic event in which the 2 9 ga central slave basement collided with the 2 7 ga juvenile eastern slave province their suture is interpreted to be a west dipping surface at 4 5 s 12 15 km beneath yellowknife and to project to the surface east of the profile in the lower crust and upper mantle east dipping reflections are interpreted to delineate a coeval subduction zone and accretionary wedge the upper crustal thrust and fold structures are likely linked to gold bearing shear zones at yellowknife these results provide tantalizing evidence that processes similar to those of modern convergent zones were operational at 2 65 2 58 ga

timing of plutonism deformation and metamorphism in the yellowknife domain slave province canada u pb zircon titanite and monazite ages for plutonic rocks are used to constrain the timing of post 2660 ma deformational and metamorphic events in the yellowknife domain southern slave province diorite and tonalite plutons of the defeat suite yield ages of 2628 3 and 2624 3 ma older than previous less precise estimates for this suite of ca 2618 2620 ma the defeat suite plutons crosscut and postdate upright f1 folds in turbidites of the ca 2680 2660 ma burwash formation d1 deformation is therefore bracketed between 2660 and 2630 ma the d1 event significantly predates deposition of polymict conglomerates of the jackson lake formation a second folding event f2 represented by northwest to north trending steeply plunging folds of bedding and d1 structures affected the area after intrusion of the hidden lake pluton at 2606 2 ma and synchronously with intrusion of the 2596 2 ma sparrow lake pluton a member of the two mica granite prosperous suite the time of initiation and the duratio

sedimentology of archean greenstone belts signatures of tectonic evolution abstract stratigraphic styles in archean greenstone belts are compared to those of modern and phanerozoic depositional basins in order to test the conformity of tectonic style through time six lithological associations in greenstone belts are recognized 1 mafic ultramafic volcanic 2 calc alkaline volcanic 3 bimodal volcanic 4 quartz arenite iron formation or carbonate 5 conglomerate wacke and 6 conglomerate arenite examples of the associations are described from the kaapvaal superior and zimbabwe provinces and the pilbara block each association differs only slightly between the four regions thereby emphasizing a common tectonostratigraphic theme sedimentary rocks are a minor component of the mafic ultramafic volcanic association they were deposited in two types of volcanic basin environments one similar to barred lagoons and bays around oceanic volcanic islands and the other similar to sediment starved platforms adjacent to coalesced volcanoes in inter arc intra arc and back are basins in contrast sedimentary rocks in the calc alkaline volcanic association comprise thick wedges of epiclastic and volcaniclastic detritus deposited in elongate sedimentary basins and thick wedges of pyroclastic and volcaniclastic detritus deposited adjacent to volcanic centers sedimentary facies were identical to those of forearc trench and marine volcanoplutonic arc settings chemogenic lithofacies in both volcanic associations were deposited in shallow to deep marine waters although shallow water profiles were selectively preserved in some terrains sedimentary rocks of the bimodal volcanic association are thick wedges of siliciclastic and volcaniclastic deposits interbedded with subaerial to submarine erupted flows of komatiite basalt and rhyolite depositional environments ranged from braid plain and braid delta to coastal marine and submarine fan starved basin deposits include banded iron formation and sulfidic black shale the association is identical to that of cratonic extensional basins in arc continent and intracontinental rifts sedimentary rocks of the quartz arenite iron formation or carbonate association onlap weathered basement or bimodal volcanic association rocks depositional environments were either transitional from fluvial to siliciclastic and carbonate marginal marine to offshore pelagic hemipelagic or from inshore intrabasinal clastic and volcaniclastic to offshore pelagic hemipelagic siliciclastic deposits are supermature two tectonic sites are represented those with siliciclastic facies represent continent adjacent syn to post rift stable shelves and those dominated by banded iron formation with volcaniclastic deposits represent arc adjacent post rift stable shelves sedimentary rocks of the conglomerate wacke association are represented by thick wedges of siliciclastic or volcaniclastic sandstone with minor volcanic components these were deposited in braid plain braid delta and submarine fan environments within elongate sedimentary basins coastal plain and pelagic basin facies are also present siliciclastic detritus was derived from syndepositional magmatic and metasedimentary thrust belts two stratigraphic styles are preserved one that records a flysch like stage of deep to marginal marine environments and the other that records a molasse like stage of marginal marine to fluvial environments the association is identical to that of compressional foreland basins of arc continent collisional and compressional arc tectonic affinities the conglomerate arenite association is preserved in elongate structural basins that transgress crustal components and all other supracrustal units it is dominated by thick wedges of siliciclastic sandstone although bimodal volcanic and volcaniclastic rocks can also be present depositional environments ranged from talus and alluvial fan and braid plain to either lacustrine or coastal marine local basin margins often show lateral offsets from source terrains and vertically skewed facies patterns longitudinal facies geometries are typical the association is similar to that of strike slip collisional graben in hinterland tectonic escape and terrane accretion orogens the examples show that despite all the ramifications of secular geophysical geothermal and geochemical global change the stratigraphic style of sedimentary rocks in archean greenstone belts can be matched with modern tectonic analogues thereby emphasizing the conformity of stratigraphic style through time the inseparable link between stratigraphic and tectonic styles implies that the tectonic style of greenstone belts was not temporally unique major differences exist with regards to the chemical composition of certain magmatic and sedimentary products but these are compensated for by their constant stratigraphic function in terms of depositional processes depositional environments and tectonic sites

neodymium isotopic evidence for the tectonic assembly of late archean crust in the slave province northwest canada the ca 2 7 2 5 ga slave province is a granitegreenstone terrane comprising deformed sedimentary and subordinate volcanic belts extensively intruded by granitoid rocks the nd isotopic data are reported for 58 samples of supracrustal and granitoid rocks exposed along a 400 km east west transect at 65 n across the structural grain of the province initial nd values reveal distinctly different crustal sources in the eastern compared to the western parts of the province as expected from tectonic assembly of the province through accretion of juvenile crust to older continental crust supracrustal sequences ca 2 71 2 65 ga from the central and eastern parts of the province have positive nd 1 values 0 3 to 3 6 consistent with juvenile sources and formation remote from significantly older crust syn to late deformation ca 2 63 2 60 ga mantle derived diorites and related tonalites type i from the central and eastern parts of the province have similar initial nd values 0 1 to 2 7 in contrast samples from the westernmost plutons which intrude exposed pre 3 1 ga crust have much lower nd 1 values 1 0 to4 6 suggesting contamination of these magmas by older crust the nd 1 values of post deformation granites s s type ii also vary systematically across the province values for granites west of longitude 110 30 w range from 0 2 to 5 3 those to the east range from 0 6 to 3 7 these data suggest mixed crustal sources dominated by mid to early archean material nd 2 6 to 17 at 2 6 ga for the western granitoid rocks and juvenile sources for the eastern granites the nd isotopic data are consistent with the geology of the province in that exposures of mid to early archean crustal rocks predating the principal 2 7 2 5 ga orogenic event are restricted to the western part of the province the asymmetric pattern defined by the nd isotopic data indicates the presence of distinct crustal rocks beneath the slave province similar isotopic variations observed across phanerozoic collisional orogens have been interpreted to reflect tectonic assembly of crust by accretion of juvenile crustal terranes to an older continental margin this process may also have been an important mechanism in the cratonization of the slave province

the timing of the gold cove glacial event a comment on signature of the gold cove event 10 2 ka in the labrador sea abstract the recent paper in quaternary international rashid et al 2014 signature of the gold cove event 10 2 ka in the labrador sea attributes sediment layers rich in detrital carbonate dc in several marine sediment cores in the labrador sea to the so called gold cove gc glacial advance of the early holocene the age estimate for the gc event as well as the correlations between sediment cores in this study are based on radiocarbon dates mostly from previously published studies although this work provides a good overview of an apparently widespread dc layer in the early holocene the reported age of 10 2 cal ka bp for the actual gold cove event is too young due to a mistake made during re calibration of the original radiocarbon dates used to describe the event the 14c dates have been corrected to compensate for the marine reservoir effect two times leading to an unrealistically large total reservoir age of more than thousand years by applying such a large marine reservoir offset the final calibrated age becomes too young originally the gc event was described to consist of an advance and retreat phase in total spanning several centuries the gold cove event should therefore more accurately be reported as an age range and it occurred most likely ca 500 years earlier than 10 2 ka bp the age reported by rashid et al 2014

field relations u pb geochronology and sm nd isotope geochemistry of the point lake greenstone belt and adjacent gneisses central slave craton n w t canada data from the point lake area central slave craton suggest an intimate tectonic and paleogeographic association between volcano sedimentary supracrustal rocks and adjacent gneisses granite plutons and orthogneisses yield u pb zircon crystallization ages ranging from ca 3230 to 2818 ma numerous mafic dykes cut the gneisses and two have been dated by u pb zircon geochronometry at 2673 3 and 2690 3 ma ages similar to those of volcanic rocks in the point lake greenstone belt although high strain zones form the greenstone gneiss in most places a structural repetition of granite about 4 km east of keskarrah bay is cut by numerous mafic dykes and apparently overlain depositionally by pillow basalt mafic volcanic and plutonic rocks from point lake have initial 2 7 ga end values ranging from about 2 2 to 6 3 significantly lower than the depleted mantle at that time the nd data suggest either derivation from a more isotopically evolved reservoir or assimilation of crust similar to the granit

evolution of an archean basement complex and its autochthonous cover southern slave province canada abstract the sleepy dragon complex sdc is one of several antiformal exposures of a 4 0 2 85 ga basement block underlying the west central region of the archean slave province northwestern canada this basement block the central slave basement complex csbc is overlain by an autochthonous to locally parautochthonous dominantly quartz rich clastic sequence the 2 85 2 80 ga central slave cover group together these units comprised a fundamental building block during neoarchean growth and assembly of the slave craton the well exposed patterson lake morose lake area represents a type locality for study of the csbc central slave cover group and overlying rocks of the yellowknife supergroup field mapping and u pb geochronology employing both thermal ionisation mass spectrometry tims and sensitive high resolution ion microprobe shrimp document a prolonged crustal history oldest intact basement units consist of foliated to gneissic tonalite dated in two places at 2955 12 ma and 2944 9 ma indirect evidence for a ca 3150 ma basement component is obtained both from xenocrystic zircon in tonalite and detrital zircons from the overlying central slave cover group which here consists of the patterson lake formation a granite boulder from this formation is dated at 2934 3 ma and may be locally derived a sheared mafic volcanic unit along the basement cover contact contains 2942 3 ma metamorphic titanite which provides a minimum deposition age this volcanic unit is therefore also a part of the basement complex younger events in the sdc mainly reflect tonalite trondhjemite granodiorite plutonism during construction of the overlying cameron river and beaulieu river greenstone belts of the yellowknife supergroup a unit of k feldspar megacrystic granodiorite is dated at 2726 3 ma and tonalite and granodiorite bodies located toward the centre of the sdc have primary crystallization ages of 2683 3 2 ma 2677 2 ma and 2672 7 6 ma the core of the southern sdc is occupied by a late tectonic to post tectonic granite pluton previously dated at 2586 2 ma an intravolcanic unconformity along the southern margin of the sdc developed in part on 2 7 ga granodiorite is constrained by existing u pb data to have formed sometime between ca 2685 2660 ma an abundance of synvolcanic plutons of similar age and the presence of a 3 km thick mafic volcanic sequence overlying a less dense magmatically active felsic crust suggest that gravitational instability and magmatic diapirism may have played important roles in doming and uplift of the sdc prior to regional d 1 deformation the younger toward centre zonation of plutonic rocks in the sdc is documented in other domal granite gneiss complexes of archean age e g pilbara craton western australia where it is attributed to upward and outward displacement of older crust during repeated magma channeling into a growing mid crustal dome in the west central slave craton such a process might account for the regional presence of local unconformities of apparently similar age the domal basement plutonic complexes would have been further amplified after 2660 ma during the development of regional f 1 and f 2 fold belts

late quaternary chronostratigraphic framework of deep baffin bay glaciomarine sediments from high resolution paleomagnetic data 1 the late quaternary baffin bay sediments provide exclusive records of greenland innuitian and laurentide ice sheet margin activities as well as information about the arctic and northern atlantic ocean linkages through the canadian arctic archipelago because of specific oceanographic conditions foraminiferal 18o stratigraphies and radiocarbon ages fail to provide reliable chronologies here we propose an original chronostratigraphy spanning the last glacial cycle based on high resolution paleomagnetic investigations on a 741 cm long core hu2008 029 016pc raised from the deep central baffin bay near odp site 645 two major difficulties were encountered 1 the high frequency occurrence of rapidly deposited layers related to short ice sheet margin events e g ice surges and 2 the magnetic grain size variability physical and magnetic mineralogical properties were used to screen out unreliable magnetic sediment layers the obtained relative paleointensity rpi proxy matches reference paleomagnetic stacks and regional records moreover the resulting record depicts two major excursions which were assigned to the laschamp and the norwegian greenland sea events it has thus been possible to derive a robust 115 ka chronology for the cored sequence we concluded that even under such a dynamic sedimentary regime magnetic properties of the sediments can provide a reliable chronostratigraphy together with information on sedimentary processes

the magnetic signature of rapidly deposited detrital layers from the deep labrador sea relationship to north atlantic heinrich layers rock magnetic parameters from deep labrador sea piston core p 094 are useful for recognizing rapidly deposited detrital layers some of which correlate with north atlantic heinrich layers variations in magnetic properties and lithology distinguish two classes of rapidly deposited detrital layers during the last ice age 1 seven detrital carbonate dc layers have high carbonate content and mean magnetite grain diameters about 4 times greater than the background sediments 2 six low detrital carbonate ldc layers have very similar magnetic properties to dc layers but low carbonate content similar to the background sediments the magnetite associated with dc and ldc layers is well sorted and relatively uniform within and between layers ice rafted detritus ird recognized by increased percentage of the 125 micron grain size fraction and by high magnetic susceptibility is associated with most dc and ldc layers but is not the dominant detrital constituent the correspondence of dc and ldc layers with increased grain size of well sorted magnetite but not with coarse fraction content precludes ice rafting as the primary depositional mechanism dc and ldc layers may have been deposited from suspended sediment derived from turbidite activity in the nearby northwest atlantic mid ocean channel namoc this interpretation is supported by a piston core p 013 from a greenland rise site largely but not completely outside the influence of the namoc the association of dc layers with ird and the apparent age correlation of dc layers to north atlantic heinrich layers suggest that the ice advances which produced the ird in p 094 and in correlative north atlantic heinrich layers also triggered turbiditic flows down the namoc several dc and ldc layers however do not correlate with recognized heinrich layers but appear to be coeval with recently discovered high frequency ird rich layers in the north atlantic

depositional facies of late pleistocene heinrich events in the labrador sea late pleistocene heinrich ice rafting events produced layers rich in ice rafted debris in major parts of the north atlantic north of 40 n a high detrital carbonate content points to the hudson strait outlet of the laurentide ice sheet as a dominant source of the icebergs heinrich events were coupled with short term climate fluctuations during the last and penultimate glaciations and provide evidence for cryosphere hydrosphere atmosphere interaction in pleistocene climate change an unsolved problem with heinrich layers has been their high concentration of fine grained detrital carbonate 80 of the total detrital carbonate which cannot have been delivered by icebergs alone we propose combinations of different processes that deposited four sedimentologically different types of heinrich layers ice rafting alone for the coarser sand to gravel sized fractions and the fine fractions in distal regions type iv heinrich layers whereas nepheloid flows deposited the bulk of the fine sediment in regions proximal to the hudson strait type i heinrich layers on the labrador slope turbidity currents spilling over from canyons were also involved in transporting the fine grained carbonate rich material causing an alternation of mud turbidites and thin laminae of ice rafted debris in type ii heinrich layers on the levees of the northwest atlantic mid ocean channel the thickness relationship is reversed mud turbidites deposited by occasional spillover of currents from the channel are thin and alternate with thicker laminae of ice rafted debris type iii heinrich layers

late orogenic basins in the archaean superior province canada characteristics and inferences abstract the late orogenic archaean duparquet kirkland and stormy basins of the canadian superior province are characterized by bounding crustal scale faults and abundant porphyry stock emplacement lava flows and pyroclastic deposits are restricted to the kirkland and stormy basins and coarse clastic detritus characterizes the duparquet basin seven distinct lithofacies are identified 1 mafic volcanic 2 felsic volcanic 3 pyroclastic 4 volcaniclastic 5 conglomerate sandstone 6 sandstone argillite conglomerate and 7 argillite sandstone tuffaceous sandstone the mafic and felsic volcanic lithofacies represent effusive lava flows the pyroclastic lithofacies is formed of subaerial surge and airfall deposits and the volcaniclastic lithofacies is composed of reworked volcanic debris the conglomerate sandstone lithofacies is interpreted as alluvial fan fan delta or proximal braided stream deposits whereas the sandstone argillite lithofacies is consistent with sandy dominated flood or braidplain deposits a dominantly shallow water lacustrine setting is inferred for the argillite sandstone lithofacies these different lithofacies record the basin history and can be used to identify basin forming processes lithofacies stacking and rapid lateral changes of lithological units in conjunction with interformational unconformities and basin margin faults suggest tectonically induced sedimentation volcanism can also influence basin evolution and the delicate balance between erosion sedimentation and prevalent transport processes is affected by volcanic input catastrophic influx of pyroclastic material facilitated mass wasting processes and formation of non confined hyperconcentrated flood flow deposits account for local congestion of alluvial or fluvial dispersal patterns confined stream flow processes govern sedimentation during intravolcanic phases or prominent tectonic uplift in addition climate which controls the weathering processes and vegetation which stabilizes unconsolidated material affects the transport and depositional process a co 2 rich aggressive weathering humid archaean atmosphere favours traction current deposits and an absence of vegetation promotes rapid denudation although tectonism is the prevalent long term controlling factor in restricted basins the effects of volcanism climate and lack of vegetation can also be detected

geochemistry of the archean kam group yellowknife greenstone belt slave province canada abstract the geochemistry and isotope systematics of archean greenstone belts provide important constraints on the origin of the volcanic rocks and tectonic models for the evolution of archean cratons the kam group is a 10 km thick pile of submarine tholeiitic mafic and subordinate felsic volcanic rocks erupted between 2712 and 2701 ma that forms the bulk of the yellowknife greenstone belt in the dominantly granite metasedimentary slave province mafic rocks range from normal mid ocean range basalt like basalts to slightly light rare earth element enriched lree enriched but nb depleted basaltic andesites and andesites whereas dacitic to rhyodacitic felsic rocks are strongly lree enriched and highly depleted in nb the documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcomma

deep sea records from the southeast labrador sea ocean circulation changes and ice rafting events during the last 160 000 years 1 results from two deep sea cores from northeast of newfoundland at 1251 and 2527 m water depth respectively indicate that during the time period from 160 000 to 10 000 years bp ice rafting events in the labrador sea were accompanied by rapid variations in deep and surface water circulation twelve ice rafting events occurred each coinciding with high concentrations of detrital carbonate and oxygen isotopic depletion of both surface and bottom waters eleven of these can be correlated with the north atlantic heinrich events h1 h11 the remaining very conspicuous ice rafting event took place early in mis substage 5e at a time when the planktic faunal assemblage suggests marked warming of the sea surface in the shallower core benthic delta 13 c values rise from a minimum during the deglaciation to peak substage 5e values following the last ice rafting event indicating that the ventilation of intermediate depths was renewed after the deglaciation was complete and continued throughout substage 5e the benthic foraminifera suggest that this well ventilated water mass was comparable to the modern labrador sea water lsw the benthic faunas suggest that a relatively warm intermediate water mass entered the se labrador sea during heinrich events generally low benthic delta 13 c values indicate that this water mass was poorly ventilated and rich in inorganic nutrients isotope data and benthic faunal distributions indicate that north atlantic deep water nadw formed in the norwegian greenland sea reached the se labrador sea between the heinrich events

glacial interglacial circulation changes inferred from 231pa 230th sedimentary record in the north atlantic region 1 studies from the subtropical western and eastern atlantic ocean using the 231pa 230th ratio as a kinematic proxy for deep water circulation provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation moc over the last deglaciation in this study we present a compilation of existing and new sedimentary 231pa 230th records from north atlantic cores between 1710 and 4550 m water depth comparing sedimentary 231pa 230th from different depths provides new insights into the evolution of the geometry and rate of deep water formation in the north atlantic during the last 20 000 years the 231pa 230th ratio measured in upper holocene sediments indicates slow water renewal above 2500 m and rapid flushing below consistent with our understanding of modern circulation in contrast during the last glacial maximum lgm glacial north atlantic intermediate water gnaiw drove a rapid overturning circulation to a depth of at least 3000 m depth below 4000 m water renewal was much slower than today at the onset of heinrich event 1 transport by the overturning circulation declined at all depths gnaiw shoaled above 3000 m and significantly weakened but did not totally shut down during the bolling allerod ba that followed water renewal rates further decreased above 2000 m but increased below our results suggest for the first time that ocean circulation during that period was quite distinct from the modern circulation mode with a comparatively higher renewal rate above 3000 m and a lower renewal rate below in a pattern similar to the lgm but less accentuated moc during the younger dryas appears very similar to ba down to 2000 m and slightly slower below

the archean deep marine environment turbidite architecture of the burwash formation slave province northwest territories the slave province is an archean craton that contains an unusually large proportion of preserved sedimentary rock including thick turbidite successions the burwash formation is exposed in the southern slave province between the anton and sleepy dragon basement massifs at the base of the succession volcanics and clastic metasedimentary rocks of the raquette lake formation record initiation of the basin in a rifted arc environment these are overlain by thin black slates representing a transgression followed by well over 5 km of burwash formation metamorphosed turbiditic sandstones and slates interspersed with thin felsic tuff layers lateral correlation within the formation is possible using airphotos and recognizable tuff units burwash formation sandstones include thinly bedded units displaying bouma sequences and thicker bedded units with scour and fill structures and stratification bands characteristic of dense sediment gravity flows the sedimentary rocks are organized in architectural elements that include channel fill sandstones and conglomerates muddy levees interchannel sandstones resembling high amplitude reflection packages harps described from modern fans and possible depositional lobes the overall sedimentary architecture was probably controlled by events in the tectonically active source area or areas the archean turbidites resemble their phanerozoic and modern analogues although they show less voluminous levees and are generally less organized than large modern passive margin fans which probably have no equivalents in the archean

geophysical detection of relict metasomatism from an archean 3 5 ga subduction zone when plate tectonics started on earth has been uncertain and its role in the assembly of early continents is not well understood by synthesizing coincident seismic and electrical profiles we show that subduction processes formed the archean slave craton in canada the spatial overlap between a seismic discontinuity and a conductive anomaly at approximately 100 kilometers depth in conjunction with the occurrence of mantle xenoliths rich in secondary minerals representative of a metasomatic front supports cratonic assembly by subduction and accretion of lithospheric fragments although evidence of cratonic assembly is rarely preserved these results suggest that plate tectonics was operating as early as paleoarchean times approximately 3 5 billion years ago ga

development of an ancient back arc basin overlying continental crust the archean peltier formation northwest territories canada abstract the 2 67 2 69 ga peltier formation of the point lake volcanic belt central slave province canada is a mafic dominated succession that erupted in a back arc basin overlying sialic crust the formation overlies the 3 22 ga augustus granite is interstratified with the 2 65 ga turbiditic contwoyto formation and is associated with 2 68 ga felsic and intermediate volcaniclastic rocks of the samandre and beauparlant formations mafic rocks in the peltier formation range from n morb mid ocean ridge basalt with flat to slightly lree light rare earth element enriched patterns to tholeiitic lree enriched e morb with nb and ti depletions and finally to strongly lree enriched calc alkaline compositions with marked nb and ti depletions the nd values are between 2 94 and 3 06 and increase with decreasing la yb n ratios insulation of the conduit walls during ascent of early magmas may have limited the effects of crustal contamination over time a possible tectonic model for the point lake belt

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

temporal distribution of granitoid plutonic rocks in the archean slave province northwest canadian shield granitoid rocks in the slave province consist of 4 0 2 8 ga granitoid gneisses that predate the 2 71 2 65 ga volcanic and turbiditic rocks of the yellowknife supergroup and 2 70 2 58 ga granitoid plutons that intrude the yellowknife supergroup u pb zircon ages and nd and pb isotopic data indicate that the older granitoids are restricted to the western part of the slave province granitoid gneisses in the eastern slave province previously suspected to predate the yellowknife supergroup are similar in age to the volcanic rocks in this paper the results of a detailed geochronological study of plutonic rocks of the contwoyto lake nose lake area of the northcentral slave province are reviewed and integrated with the available age data base for plutonic rocks elsewhere in the slave province the data indicate that the timing of the later 2 7 ga plutonism is bimodal consisting of two distinct magmatic periods separated by approximately 20 ma of apparent magmatic quiescence the first period was synvolc

detecting the source of heinrich layers an organic geochemical study 1 there are controversies regarding the origin of heinrich layer 3 h3 the massive ice rafting and meltwater event in the north atlantic during the last glacial cycle spanning a time window between 29 and 30 kyr b p some argue in favor of a laurentide ice sheet source similar to other heinrich layers while a contending view argues for the european ice sheet source existing geochemical proxies such as 40ar 39ar 206pb 204pb or nd etc could not be used to distinguish among various sources of ice rafted debris in h3 because of their low abundances suggesting a background glacial sediment signal in order to circumvent this problem a biomarker based approach is used to characterize the provenance of h layers 2 3 and 4 and other non heinrich layers the presence of hopanes and steranes and their aromatic counterparts in the h layers is incompatible with recent sediments and is attributed to the transportation of organic matter because of the glacial erosion of source rocks the most diagnostic and useful signatures of this ancient organic matter in the h layers are the dominance of c34 hopanoids over c33 and the occurrence of isorenieratane along with palaerenieratane biomarkers signatures in h layers 2 and 3 of the labrador sea suggest no difference in their source hydrocarbon distributions suggest that these sediments were derived from the middle to late ordovician and silurian source rocks of the hudson bay of eastern canada biomarker data of the h layer 4 from the northwest atlantic reveal that the sediments of this layer have a similar source to the h layers in the labrador sea

megaflutes in a continental shelf setting placentia bay newfoundland abstract megaflutes erosional scours normally found in deep water on continental slopes were identified in 1978 on sidescan sonograms and seismic reflection profiles from placentia bay on the south coast of newfoundland canada data from recent extensive multibeam sonar surveys provide an opportunity to describe the morphology and distribution of the megaflutes in detail and to consider the formative processes they occur on the east side of the outer bay at a depth of 200 m in a 2 3 km wide swath that continues to the south into halibut channel over a total distance of 100 km the megaflutes have been formed by removal of a layer of postglacial mud exposing underlying glaciomarine sediments and releasing a volume of 4 5 km3 they occur in a range of forms including single multiple and coalescent types and in some areas at least their inception was related to pre existing pockmarks radiocarbon dates from piston cores are used to demonstrate that megaflute formation post dated ca 9 ka megaflute formation in placentia bay has been attributed to a reverse flow from the tsunami generated by the 1929 grand banks earthquake and this is still the accepted hypothesis we argue that the return flow from a tsunami did not generate the megaflutes and suggest instead that they could be formed during south flowing density currents generated when volumes of cold saline water stored in the deep 250 m basins at the head of placentia bay are intermittently displaced and spilled south in a shallow channel at the east side of the bay after intense coastal surface dense water formation events perhaps during very cold winters

quantitative mineralogy of the yukon river system changes with reach and season and determining sediment provenance the mineralogy of yukon river basin sediment has been studied by quantitative x ray diffraction bed beach bar and suspended sediments were analyzed using the rockjock computer program the bed sediments were collected from the main stem and from selected tributaries during a single trip down river from whitehorse to the yukon river delta during the summer of 2001 beach and bar sediments were collected from the confluence region of the tanana and yukon rivers during the summer of 2003 suspended sediments were collected at three stations on the yukon river and from a single station on the tanana river at various times during the summers of 2001 through 2003 with the most complete set of samples collected during the summer of 2002 changes in mineralogy of yukon river bed sediments are related to sediment dilution or concentration effects from tributary sediment and to chemical weathering during transport carbonate minerals compose about 2 wt of the bed sediments near whitehorse but increase to 14 wt with the entry of the white river tributary above dawson thereafter the proportion of carbonate minerals decreases downstream to values of about 1 to 7 wt near the mouth of the yukon river quartz and feldspar contents of bed sediments vary greatly with the introduction of pelly river and white river sediments but thereafter either increase irregularly quartz from 20 to about 50 wt or remain relatively constant feldspar at about 35 wt with distance downstream clay mineral content increases irregularly downstream from about 15 to about 30 wt the chief clay mineral is chlorite followed by illite smectite there is little to no kaolinite the total organic carbon content of the bed sediments remains relatively constant with distance for the main stem generally 1 to 2 wt with one exception but fluctuates for the tributaries 1 to 6 wt the mineralogies of the suspended sediments and sediment flow data were used to calculate the amount of mineral dissolution during transport between eagle and pilot station a distance of over 2000 km we estimate that approximately 3 wt of the quartz 15 wt of the feldspar 1 wt of the alkali and 25 wt of the plagioclase and 26 wt of the carbonates 31 wt of the calcite and 15 wt of the dolomite carried by the river dissolve in this reach the mineralogies of the suspended sediments change with the season for example during the summer of 2002 the quartz content varied by 20 wt with a minimum in mid summer the calcite content varied by a similar amount and had a maximum corresponding to the quartz minimum these modes are related to the relative amount of sediment flowing from the white river system which is relatively poor in quartz but rich in carbonate minerals suspended total clay minerals varied by as much as 25 wt with maxima in mid july and suspended feldspar varied up to 10 wt suspended sediment data from the summers of 2001 and 2003 support the 2002 trends a calculation technique was developed to determine the proportion of various sediment sources in a mixed sediment by unmixing its quantitative mineralogy results from this method indicate that at least three sediment sources can be identified quantitatively with good accuracy with this technique sediment mineralogies can be used to calculate the relative flux of sediment from different tributaries thereby identifying sediment provenance

the influence of meltwater on the labrador current in heinrich event 1 and the younger dryas abstract the labrador current transports freshwater from the arctic regions to the northern atlantic and the freshwater flux can influence the meridional overturning circulation the response of the labrador current to meltwater processes is unclear during the deglaciation of the ice sheets around the northwest atlantic this study utilized cores from flemish pass to monitor variations in the strength of the labrador current by using the sortable silt proxy the carbonate content the amount of ice rafted detritus and xrf chemical data were measured to identify the main meltwater events during the last deglaciation this study observed a clear enhancement of the flow strength of the labrador current in heinrich event 1 and the younger dryas with the greatest flow strength during the younger dryas event the onset of the current enhancement was dated at ca 13 cal ka bp which preceded the enhanced ice rafted deposition in hudson strait by about one thousand years the current enhancement in flemish pass during the younger dryas event corresponds to the freshening of the surface water thus meltwater preceding significant iceberg supply has an important effect on the labrador current in heinrich events on the laurentide ice sheet margin

accretion of the archean slave province continental rift models have long been applied to the archean slave province of northwestern canada a reassessment of these models shows them to be incompatible with observed geological relations and suggests that contractional tectonic models may be more appropriate than extensional ones regions composed of different rock suites e g orthogneisses vs mafic volcanics are separated by high strain zones recording large displacements it is proposed that the high strain zones separate four distinct terranes that have been juxtaposed during collisional orogenesis from west to east these include the anton terrane interpreted as an archean microcontinent the sleepy dragon terrane possibly an exhumed more eastern part of the anton terrane the contwoyto terrane a westward verging fold and thrust belt containing tectonic slivers of greenstone volcanics and the hackett river volcanic terrane interpreted as an archean island arc the contwoyto and hackett river terranes represent a paired accretionary prism and island arc system that formed above an east dipping subduction zone these collided with the anton microcontinent producing a basement nappe expressed as the sleepy dragon terrane during the main accretion event within the slave province the whole tectonic assemblage was intruded by late kinematic to postkinematic granitoids

climatic and tectonic influences on fan deltas and wave to tide controlled shoreface deposits evidence from the archaean keskarrah formation slave province canada the 2 6 ga keskarrah formation located in the central slave province northwest territories canada is a late orogenic tectonically controlled sedimentary sequence that developed under unusual climatic and depositional conditions the formation is adjacent to the crustal scale north trending beniah lake fault and overlies the 3 15 ga augustus granite the 2 69 2 7 ga mafic volcanic peltier formation and the turbiditic contwoyto formation unconformably principal lithofacies in the keskarrah formation include conglomerate sandstone and siltstone sandstone the conglomerate lithofacies represents coalescing gravelly streamflow dominated fan deltas adjacent to topographic highs up section quartz rich arenites and quartz arenites of the sandstone lithofacies are interpreted to be shallow water shoreface deposits influenced by wave action and tides the overlying feldspathic litharenites of the siltstone sandstone lithofacies are consistent with a lower shoreface to proximal offshore environment dominated by wave and tide interaction tidal influence in both sandstone dominated lithofacies is inferred from the presence of mudstone laminae between bedforms and on foresets of cross beds as well as from abundant reactivation surfaces with local mudstone drapes intense chemical weathering during the archaean resulting from elevated atmospheric co2 levels higher temperatures and moist climatic conditions played an important role in the development of quartz rich arenites that appear to be first cycle deposits few lithic fragments and feldspar grains are preserved due to in situ host rock weathering chemical weathering during transport and wave and tide action hydraulic sorting and abrasion in the shoreface environment contributed to the continued breakdown and transport of labile minerals increased proportions of lithic fragments in sandstone beds of the conglomerate lithofacies are the result of shorter transport distances from source areas to the depositional environment abundant conglomerate with up to 4 m large granitic boulders derived from the adjacent augustus granite and mafic clasts from the peltier formation indicate high relief and fault related uplift and subsidence the intimate association of fan deltas and wave and tide influenced shallow marine deposits in association with quartz rich sandstones forming in a high relief area make the keskarrah formation remarkable in the rock record

fine grained sediment lofting from meltwater generated turbidity currents during heinrich events turbidity currents generated from sediment carrying freshwater discharges into the sea contain a fluid that is less dense than ambient seawater from experiments it is known that such currents will eventually lift from their substrate either in part or as a whole through buoyancy reversal this ascent will happen when their density is lowered below that of seawater through settling of suspended sediment from the top or deposition from the bottom of the flows evidence for large scale lofting of suspended sediment from the top of giant sand and gravel carrying turbidity currents in the labrador sea comes from two independent lines of observations 1 the first is a distinct sedimentary facies consisting of stacked centimeter thick graded mud layers that contain grains of ice rafted debris ird supported by the mud deposition of these unusual layers requires a gradedlayer forming process that is slow enough to allow the incorporation of ird this is not possible with normal mud carrying turbidity currents 2 the second observation is the presence of a huge abyssal sand and gravel plain in the central labrador sea that received its sediment from bed load rich meltwater discharges from the hudson strait outlet of the pleistocene laurentide ice sheet these discharges turned into turbidity currents that released rising columns of freshwater that carried fine grained suspended sediment and spread out at a water level where their density equaled that of ambient seawater deposition from these slow turbid interflows would allow the incorporation of ird in the accumulating graded mud deposits the ird spiked graded mud facies is restricted to heinrich layers within 300 km radius of the hudson strait ice stream terminus tying the sand carrying turbidity currents via fine grained sediment lofting to heinrich events estimated total discharge volumes of individual currents are on the order of 10 3 km 3 supporting the notion that heinrich ice rafting events were times of maximum meltwater generation

lake agassiz final drainage event in the northwest north atlantic 1 the 8 2 ka climate event recorded in greenland ice cores is subject of debates with respect to causal linkage with a collapse of the atlantic meridional overturning due to the drainage of the late glacial lake agassiz here we present records from the nw north atlantic down current the flood discharge route showing that the 9 5 8 ka interval was marked by a succession of events the drainage itself corresponds to a twin layer of carbonate rich turbidites deposited within the calibrated 8 35 8 5 ka interval proxies of sea surface and deep current conditions do not indicate significant concomitant changes in the nw north atlantic the dataset however supports the concept that the 8 2 ka climate event may represent one of the manifestations of climate instability during an interval with major changes of land drainage in ne america due to the collapse of the laurentide ice sheet subsequent fast sea level rise and large scale reorganization of the north atlantic thermohaline circulation pattern

crust mantle coupling revisited the archean slave craton nwt canada abstract lithospheric domains in the slave province inferred from regional variations in chemistry of mantle derived garnets are parallel with northeasterly structural trends in neoarchean surface rocks and were used previously to infer late neoarchean crust mantle coupling and argue against the presence of diamondiferous mesoarchean lithosphere under the western slave craton prior to its late neoarchean orogenic climax a review of more recent evidence does not support this view but concludes that a mesoarchean lithospheric root was coupled to mesoarchean crust of the central slave superterrane csst prior to accretion of adjacent juvenile neoarchean terranes a significant part of this root survived the neoarchean break up of the csst neoarchean terrane accretion and a complex sequence of post accretion deformation granitoid plutonism and metamorphism it was least modified in the ultra depleted harzburgitic layer udl under the central part of the contwoyto terrane where it is trapped above the deepest part of an underplated paleoproterozoic slab which stabilized the remnants of the archean root and caused downward younging of the lithosphere upper mantle domains recognized on the basis of the distribution of peridotitic garnets are not primary neoarchean features but were either inherited from the original mesoarchean root or resulted from neoarchean and paleoproterozoic tectonic erosion and or metasomatism of this root the slave province resembles other diamondiferous cratons in that its diamond endowment consists of both mesoarchean and paleoproterozoic stones

petrochemistry of the yellowknife volcanic suite at yellowknife n w t the petrochemistry of the yellowknife volcanic belt at yellowknife kam duck and banting formations shows the suite to be more chemically complex than previously thought the kam formation 65 basalt 27 basaltic andesite 17 andesite and 2 dactite has a strong tholeiitic trend involving pyroxene fractionation which shows iron enrichment to feo feo mgo 0 75 after altered samples are removed from consideration it can be shown that the kam is chemically analogous to modern ocean floor or ocean rise tholeiites the andesitic members of the kam were partially melted from a hornblendic region presumably former oceanic crust possibly with a slight sialic component the duck formation 11 basalt 21 basaltic andesite 59 andesite and 9 dacite shows considerable evidence of alkali mobility with varied carbonate content it is thought to have been largely derived as partial melts from former oceanic crust via hornblende fractionation the banting formation 14 basalt 7 basaltic andesi

aftershock stress release along active fault planes of the 1984 round valley california earthquake sequence applying a time domain stress drop method abstract the 23 november 1984 m l 5 8 round valley earthquake is one in a series of moderate m l 6 earthquakes to have occurred in the bishop mammoth lakes california area since 1978 this earthquake and its aftershock sequence occurred within a dense seismic network and hypocentral location quality is excellent in a previous study we determined that the round valley sequence involved faulting on a conjugate set of fault planes one a near vertical plane striking n30 e the mainshock fault plane showing principally left lateral strike slip motion and another subperpendicular to the mainshock fault plane striking n40 w and dipping 55 ne exhibiting dominantly right lateral strike slip this conjugate fault plane conforms to a postulated extension of the hilton creek fault and is the only significant activity on this structure in the 12 year bishop mammoth lakes earthquake sequence source dimensions and stress drops for 87 aftershocks m l 2 8 to 4 2 of the round valley sequence have been determined using an adaptation of the initial p wave pulse width time domain deconvolution technique of frankel and kanamori 1983 the aftershock sequence is confined to a limited volume of crust we have shown that site and instrument effects and not whole path attenuation control the minimum pulse widths for this limited region the determination of a site minimum pulse width rather than a minimum pulse width for each source receiver pair as in the frankel and kanamori study makes the deconvolution procedure practical for processing the large numbers of events in an aftershock sequence with the large data set available for the round valley aftershock sequence patterns of the stress drop along the active fault planes can be seen in detail source radii systematically increase with magnitude from about 100 m for events near magnitude 3 0 to 500 m for events near magnitude 4 0 static stress drops range from 10 to 200 bars and are not strongly correlated with magnitude or depth the stress release pattern reveals a broad stress drop low 10 bars for aftershocks within the mainshock fault plane that is consistent with other evidence of the rupture surface of the round valley mainshock higher stress release occurs above and below the mainshock rupture surface and on the shallower conjugate fault plane further distant from the rupture surface of the mainshock stress drops decrease to average values on the conjugate fault surface stress drops are seen to be high in areas that may be interpreted as off fault clusters with respect to the mainshock rupture surface

the bell lake group and anton complex a basement cover sequence beneath the archean yellowknife greenstone belt revealed and implicated in greenstone belt formation u pb zircon and monazite geochronology indicates the presence of a 2 93 ga basement anton complex and 2 8 ga cover sequence bell lake group beneath the 2 70 to 2 72 ga kam group of the yellowknife greenstone belt in the southern slave province the bell lake group comprises remnants of a quartzite rhyolite banded iron formation succession the ages of detrital zircons from the quartzite unit constrain its deposition to be younger than 2 92 and range up to 3 7 ga u pb ages for gneisses beneath the bell lake group are in excess of 2 93 ga and they are locally overlain by the quartzite the contact between the tholeiitic to calc alkaline kam group and the bell lake group is poorly exposed and equivocal approximately 6 km higher in the section the ranney chert a felsic volcaniclastic layer separates 2 70 2 72 ga tholeiitic to calc alkaline upper kam group rocks from a lower tholeiitic section containing sheeted dike complexes zircons from the ranney chert yield pb pb ages ranging from 2 72

late holocene radiocarbon variability in northwest atlantic slope waters abstract deep sea gorgonian corals secrete a 2 part skeleton of calcite derived from dissolved inorganic carbon at depth and gorgonin derived from recently fixed and exported particulate organic matter radiocarbon contents of the calcite and gorgonin provide direct measures of seawater radiocarbon at depth and in the overlying surface waters respectively using specimens collected from northwest atlantic slope waters we generated radiocarbon records for surface and upper intermediate water layers spanning the pre and post bomb 14 c eras in labrador slope water lsw convective mixing homogenizes the pre bomb 14 c signature 67 4 to at least 1000 m depth surface water bomb 14 c signals were lagged and damped peaking at 45 in the early 1980s relative to other regions of the northwest atlantic and intermediate water signals were damped further off southwest nova scotia the vertical gradient in 14 c is much stronger in surface water pre bomb 14 c averaged 75 5 at 250 475 m depth pre bomb 14 c oscillated quasi decadally between 80 and 100 likely reflecting interannual variability in the presence of labrador slope water vs warm slope water wsw finally subfossil corals reveal no systematic changes in vertical 14 c gradients over the last 1200 yr

archaean sedimentary sequences of the slave craton abstract the slave craton is composed of five archaean terranes that accreted during the neoarchean the central slave superterrane is the only tectonic block containing evidence of four major sedimentary successions including 1 a quartz arenite dominated succession deposited on an extensive tide influenced coastline along a rifted continental margin 2 a turbidite dominated succession that developed as submarine fans in a fore arc or intra arc basin 3 a second turbidite succession representing deep water deposition in a back arc basin and 4 late conglomerate dominated successions representing fluvial alluvial fan and shallow water depositional settings in strike slip basins deposition of the sedimentary rocks took place between ca 3 1 ga and 2 6 ga indicating a complex tectonic history an unconformity between the gneissic basement and the overlying quartz arenite succession marks a marine flooding surface consistent with a first order sea level change a major hiatus lies between the quartz arenite successions and arc backarc related volcanic deposits with interstratified and conformably overlying turbidite strata late conglomerate successions are exposed along north trending lineaments and overlie all sedimentary and volcanic rock units unconformably this depositional hiatus represents a fundamental change from compression and uplift to transcurrent motion during the final stages of craton stabilization between ca 2630 and 2580 ma the slave province experienced considerable pluton emplacement which disaggregated much of the once continuous stratigraphy a wheeler diagram illustrates the major tectonic events that occurred during formation of the central slave superterrane however remaining uncertainties concerning the evolution of the entire slave craton reflect the need for additional detailed field investigations

evidence for archean ocean opening and closing in the southern slave province archean mafic volcanic and plutonic rocks of the cameron and beaulieu river greenstone belts outcrop in the southern slave structural province of the canadian shield lower portions of the greenstone belts have ophiolitic characteristics but young felsic units may represent superimposed arc magmatism the greenstone belts are separated from older circa 2 7 3 2 ga quartzo feldspathic gneisses of the sleepy dragon complex by a regional decollement zone patterson lake structural complex consisting of deformed mafic volcanic rocks thin slivers of gneiss ultramafic rocks and banded iron formation mixed in a highly deformed phyllonitic and phacoidally cleaved metapelitic matrix high synmetamorphic strains are indicated by abundant intrafolial folds transposed layering rare sheath folds and by the parallelism of elongated primary features and metamorphic mineral lineations the patterson lake structural complex is similar to melanges of phanerozoic mountain belts adjacent quartzo feldspathic gneisses are strongly mylonitized the melange and deeper mylonites formed when the greenstone belts were emplaced as thrust sheets wildflysch shed from tips of emergent thrusts was in part incorporated into the basal melange as the allochthon overrode its own detritus continued compression involved the basement in the deformation uplifting the sleepy dragon complex in a structural culmination mantled by the imbricated greenstone stack late granodioritic to granitic intrusions formed regional thermal aureoles which overprint earlier metamorphic fabrics

structural patterns and tectonic evolution of supracrustal domains in the archean slave province canada a new plate tectonic model accounts for lithological relations and regional structural patterns in late archean supracrustal domains of the slave province multiple dykes and pillowed mafic flows most common in the western part of the province suggest sea floor spreading the mafic volcanics lying in narrow homoclinal belts stratigraphically below more extensive turbidites are viewed as megaxenolithic remnants of oceanic crust preserved on the periphery of granitoid plutons and blocks of sialic crust closure of an oceanic basin was marked by emplacement of the granitoid plutons and coeval felsic volcanics the latter predominating over mafic volcanics in northeastern domains the felsic calc alkaline magmas may have risen from a shallow dipping subduction zone westerly verging folds westerly convex fold arcs and inclinations of later foliations particularly in lower level rocks of higher metamorphic grade are in accord with underthrusting to the east the zone of underthrusting shifted progressi

holocene variations in mineral and grain size composition along the east greenland glaciated margin ca 67 70 n local versus long distance sediment transport quantitative x ray diffraction qxrd analysis of the 2 mm sediment fraction from surface sea floor samples and marine sediment cores that span the last 10 12 cal ka bp are used to describe spatial and temporal variations in non clay mineral compositions for an area between kangerlussuaq trough and scoresby sund 67 70 n east greenland bedrock consists primarily of an early tertiary alkaline complex with high weight of pyroxene and plagioclase farther inland and to the north the bedrock is dominantly felsic with a high fraction of quartz and potassium feldspars principal component pc analysis of the non clay sediment compositions indicates the importance of quartz and pyroxene as compositional end members with an abrupt shift from quartz and k feldspar dominated sediments north of scoresby sund to sediments rich in pyroxene and plagioclase feldspars offshore from the early tertiary basaltic outcrop coarse 2 mm or 1 mm ice rafted sediments are largely absent from the trough sediments between 8 and 5 cal ka bp but then increase in the last 4 cal ka bp compositional unmixing of the sediments in grivel basin and kangerlussuaq trough indicate the dominance of local over long distance sediment sources with pulses of sediment from tidewater glaciers in kangerlussuaq and nansen fjords reaching the inner shelf during the neoglaciation the change in ird is more dramatic in the sediment grain size proxies than in the quartz wt forty to seventy percent of the variance in the quartz records from either side of denmark strait is explained by low frequency trends but the data from the grivel basin east greenland are distinctly different with an approximate 2500 yr periodicity

evidence for an additional heinrich event between h5 and h6 in the labrador sea 1 an additional heinrich ice rafting event is identified between heinrich events 5 and 6 in eight cores from the labrador sea and the northwest atlantic ocean it is characterized by sediment rich in detrital carbonate 40 caco3 with high concentration of floating dropstones high coarse fraction 150 m content and has a sharp contact with the underlying but grades into the overlying hemipelagic sediment it also shows lighter 18onpl values indicating freshening due to iceberg rafting and or meltwater discharge this event is correlated with dansgaard oeschger event 14 and interpreted as an additional heinrich event h5a the thickness of h5a in the labrador sea reaches up to 220 cm this additional heinrich event has also been reported in cores ps2644 and so82 5 from the northern north atlantic with the recognition of h5a the temporal spacing between heinrich events 1 to 6 becomes more uniform 7 ka

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

a laurentide outburst flooding event during the last interglacial period episodes of ice sheet disintegration and meltwater release over glacial interglacial cycles are recorded by discrete layers of detrital sediment in the labrador sea1 2 the most prominent layers reflect the release of iceberg armadas associated with cold heinrich events3 but the detrital sediment carried by glacial outburst floods from the melting laurentide ice sheet is also preserved4 here we report an extensive layer of red detrital material in the labrador sea that was deposited during the early last interglacial period we trace the layer through sediment cores collected along the labrador and greenland margins of the labrador sea biomarker data ca sr ratios and 18o measurements link the carbonate contained in the red layer to the palaeozoic bedrock of the hudson bay we conclude that the debris was carried to the labrador sea during a glacial outburst flood through the hudson strait analogous to the final lake agassiz outburst flood about 8 400 years ago probably around the time of a last interglacial cold event in the north atlantic5 we suggest that outburst floods associated with the final collapse of the laurentide ice sheet may have been pervasive features during the early stages of late quaternary interglacial periods

palaeoproterozoic thermal events recorded in the 4 0 ga acasta gneiss canada evidence from shrimp u pb dating of apatite and zircon u pb isotopes of apatites and zircons extracted from a sample of the acasta gneisses that occurs along the western margin of the slave craton in northwest territories of canada have been measured using a shrimp ii ion microprobe eleven apatite analyses 30 m spot give 238u 204pb 206pb 204pb and 204pb 206pb 207pb 206pb isochron ages of 1905 86 ma 2 and 1936 28 ma 2 respectively analyses 20 m spot on the partly recrystallised central portions of fourteen zircons mostly define a mixing array on a 238u 206pb 207pb 206pb concordia plot with concordia intercepts at 4014 25 ma 2 and 1967 93 ma 2 the former agrees with 3 96 4 02 ga protolith ages obtained on the oldest components of the acasta gneisses by other workers the lower concordia intercept for the zircon data is consistent with the u pb age of apatites and may be related to a 500 c thermal event perhaps early in the palaeoproterozoic wopmay orogeny

geology and geochemistry of an archean mafic dike complex in the chan formation basis for a revised plate tectonic model of the yellowknife greenstone belt an archean mafic dike complex in the chan formation at the base of the mafic volcanic section of the yellowknife greenstone belt consists of multiple metagabbro dikes and sills separated by screens of pillowed mafic volcanic rocks which are cut by a younger postvolcanic metadiabase dike swarm field relationships and geochemical characteristics are compatible with a comagmatic origin for the metagabbro and metavolcanic rocks that were fed through and deposited on an older rift related supracrustal sequence of the dwyer group the synvolcanic metagabbro dikes have extended the strike length of the volcanic section by at least 100 the mafic rocks of the chan formation are geochemically similar to mid ocean ridge basalt possibly with a minor subduction zone component preliminary end values for metagabbroic rocks are consistent with the derivation of magmas predominantly from a normal depleted mantle source the chan formation is interpreted to have formed in a marginal basin like setting adjacent to

time transgressive archean unconformities underlying molasse basin fill successions of dissected oceanic arcs superior province canada abstract late archean diachronous unconformities underlying tectonically controlled coarse clastic successions are located throughout the superior province of canada examples studied in detail include hiatuses at the base of the timmins and kirkland basins in the abitibi greenstone belt and the crowduck and stormy basins in the wabigoon subprovince the timmins molasse basin fill succession overlies a high angle subaerial unconformity separating deepwater turbiditic deposits from fluvial conglomerates a subaerial erosional unconformity defines the contact between mafic flows and overlying felsic volcaniclastic deposits and fluvial conglomerates of the kirkland basin the crowduck and stormy successions are characterized by shallow water and subaerial unconformities between quartz feldspar porphyry stocks and clastic deposits the pronounced characteristics of the molasse basins which include 1 basal unconformities with older sedimentary volcanic or plutonic rocks 2 bounding fault systems 3 ba

evolution of the slave craton greenstone belts in the slave craton represent the episodic accumulation of volcanic and sedimentary rocks over as much as 200 m y in the western craton volcanic and sedimentary rocks were deposited between 2 81 and 2 60 ga on 2 9 3 1 ga sialic basement not tectonically juxtaposed with it deposition of 2 6 ga turbidite and conglomerate sequences across the entire slave craton was synchronous with or followed by the main phase of regional deformation and metamorphism at 2 6 2 58 ga and final stabilization of the craton

a multi proxy reconstruction of oceanographic conditions around the younger dryas holocene transition in placentia bay newfoundland abstract a marine sediment core from placentia bay off the south coast of newfoundland was studied to reconstruct past oceanographic conditions based on a multiproxy approach including diatoms benthic foraminifera grain size analysis ip25 x ray fluorescence calcium carbonate and total organic carbon content based on 6 radiocarbon dates the 513 5 cm long core spans the age interval from ca 13 to 10 cal kyrs bp and thus captures the transition from the younger dryas stadial into the holocene at sub decadal resolution the younger dryas was characterized by cold arctic water taxa of diatoms and benthic foraminifera and a stratified water column with high sea ice cover and low productivity due to strong influence of the labrador current during the second half of the younger dryas after ca 12 2 cal kyrs bp the influence of the labrador current gradually decreased and sea ice conditions became more variable the transition towards the holocene is characterized by a sequence of events starting with turnovers in the biogenic proxies followed by an abrupt retreat of sea ice and a rise in productivity these events are believed to be related to a northward migration of the gulf stream labrador current oceanic front the younger dryas termination is directly followed by a detrital carbonate layer associated with the final phase of the heinrich 0 event linked to laurentide ice sheet dynamics during the early holocene productivity remained high with minimal sea ice cover reduced stratification and stronger influence of warmer gulf stream derived waters

the central slave basement complex part i its structural topology and autochthonous cover new field and geochronological data are used to define the distribution of mesoarchean basement rocks in the south central slave province this distribution reflects a single contiguous basement terrane that we propose to call the central slave basement complex it shows a structural topology that is internally consistent and compatible with known regional folding and faulting events a sample of a proposed basement gneiss below the courageous lake greenstone belt central slave province has been dated by u pb methods and yields an age of 3325 8 ma consistent with the new basement distribution this sample also contains 2723 3 ma metamorphic zircon and ca 2680 ma titanite the central slave basement complex is overlain by a thin discontinuous but distinctive cover sequence that includes minor volcanic rocks clastic sedimentary rocks and banded iron formation all previously known and some new occurrences of this distinctive cover sequence occur in the immediate stratigraphic hanging wall of the