evidence for increased latent heat transport during the cretaceous albian greenhouse warming quantitative estimates of increased heat transfer by atmospheric h2o vapor during the albian greenhouse warming suggest that the intensified hydrologic cycle played a greater role in warming high latitudes than at present and thus represents a viable alternative to oceanic heat transport sphaerosiderite d 18 o values in paleosols of the north american cretaceous western interior basin are a proxy for meteoric d 18 o values and massbalance modeling results suggest that albian precipitation rates exceeded modern rates at both mid and high latitudes comparison of modeled albian and modern precipitation minus evaporation values suggests amplification of the albian moisture deficit in the tropics and moisture surplus in the mid to high latitudes the tropical moisture deficit represents an average heat loss of 75 w m 2 at 108n paleolatitude at present 21 w m 2 the increased precipitation at higher latitudes implies an average heat gain of 83 w m 2 at 458n at present 23 w m 2 and of 19 w m 2 at 758n at present 4 w m 2 these estimates of increased poleward heat transfer by h2o vapor during the albian may help to explain the reduced equator to pole temperature gradients

meteoric sphaerosiderite lines and their use for paleohydrology and paleoclimatology sphaerosiderite a morphologically distinct millimeter scale spherulitic siderite feco 3 forms predominantly in wetland soils and sediments and is common in the geologic record ancient sphaerosiderites are found in paleosol horizons within coal bearing stratigraphic intervals and like their modern counterparts are interpreted as having formed in water saturated environments here we report on sphaerosiderites from four different stratigraphic units each of which has highly variable 13 c and relatively stable 18 o compositions the unique isotopic trends are analogous to well documented meteoric calcite lines which we define here as meteoric sphaerosiderite lines meteoric sphaerosiderite lines provide a new means of constraining ground water 18 o and thus allow evaluation of paleohydrology and paleoclimate in humid

geology and tectonic setting of paleoproterozoic granitoid suites in the island harbour bay area makkovik province labrador paleoproterozoic granitoid rocks in the island harbour bay area kaipokok domain makkovik province labrador are divided into four separate suites on the basis of field relations petrology and age the redefined island harbour bay plutonic suite consists of ca 1895 1870 ma dioritic to granitic mainly granodioritic and granitic units the rocks are variably foliated as a result of emplacement under amphibolite facies conditions in a dextral transpressive regime during andean type subduction the dominant mafic mineral is biotite and accessory epidote allanite and titanite are abundant the suite is calc alkalic but with rare earth element patterns similar to those of archean tonalitic trondhjemitic granodioritic suites it is interpreted to have formed deep in an andean type magmatic arc at the margin of the nain continent in contrast the younger hares islands and drunken harbour granites emplaced at ca 1805 and 1790 ma respectively were part of widespread late orogenic magmatic activity i

short wave infrared spectral and geochemical characteristics of hydrothermal alteration at the archean izok lake zn cu pb ag volcanogenic massive sulfide deposit nunavut canada application in exploration target vectoring short wave infrared swir field and laboratory spectra were used to identify and characterize hydrothermal alteration mineral chemical variability in host rocks proximal to the izok lake zn cu pb ag volcanogenic massive sulfide vms deposit in nunavut canada the deposit is hosted within a sequence of predominantly felsic pyroclastic rocks of archean age that are regionally metamorphosed to amphibolite facies these rocks are characterized by the muscovite biotite sillimanite and chlorite biotite cordierite mineral suite proximal to the deposit white micas are al rich to potassic muscovite and the biotite and chlorite are mg rich in areas that are immediately outboard of the proximal alteration zones rocks are altered to al poor muscovite and intermediate to fe rich biotite and chlorite outboard of this distal areas are characterized by potassic muscovite and mg rich biotite and chlorite the white micas and biotite chlorite group minerals display considerable variation in their al oh and fe oh absorption feature wavelength positions the variations in muscovite and biotite chlorite compositions as determined by the al oh and fe oh absorption feature wavelength positions broadly correlate with changes in hydrothermal alteration intensity as measured by the ishikawa and chlorite carbonate pyrite alteration indices our findings suggest that the large scale alteration intensity trends of the izok lake study area can be elucidated using the spectral properties of the hydrothermal alteration minerals

episodic early proterozoic granitoid plutonism in the makkovik province labrador u pb geochronological data and geological implications episodic granitoid plutonism in the early proterozoic makkovik province of the easternmost canadian shield is revealed by high precision u pb zircon studies of a range of intrusive rock types the

integrated climate model oxygen isotope evidence for a north american monsoon during the late cretaceous abstract during the late cretaceous western north america was characterized by a close geographic association between the sevier highlands and the western interior seaway in this paper an atmospheric general circulation model agcm is used to simulate the impact of this geographic association on surface pressure wind direction and precipitation and it is predicted that seasonal changes in these variables resulted in a strong monsoon along the eastern flank of the sevier highlands confirmation that these model simulations are accurate is provided by isotopic data from foreland basin sediments in particular oxygen isotope records from different environments large rivers small streams and ponds and proxies unionid bivalve shells and paleosol carbonates indicate that foreland basin streams were recharged by local precipitation with high oxygen isotope ratios while large trunk rivers were recharged by high elevation precipitation this hydrologic pattern is observed from alberta to utah and is consistent with east to west monsoonal air mass movements and associated seasonal rainfall recognition of a highland driven monsoon has implication in regard to studies of fossil taphonomy of water vapor transport and of links between climate and mountain uplift and exhumation in this region

constraints on palaeoenvironments in the lower cretaceous wealden of southern england from the geochemistry of sphaerosiderites abstract sphaerosiderites are millimetre scale concretions of feco 3 that form predominantly in waterlogged environments and are of use in palaeoenvironmental and palaeohydrological studies we present petrographic elemental and stable isotopic 13 c 18 o data from sphaerosiderites collected from the lower cretaceous wealden sediments of southern england the sphaerosiderites are composed of very pure feco 3 with only small amounts of ca mg and mn present suggesting that they are well preserved and were precipitated from fresh groundwater 13 c values display a relatively large range from about 5 to 30 vpdb in contrast 18 o values are relatively invariant 1 0 83 with an average of 3 01 vpdb the relationship between carbon and oxygen suggests that the sphaerosiderites faithfully record palaeo groundwater 18 o likely 18 o values for groundwater were calculated using a published experimentally derived siderite water fractionation equation and plausible assumed values for palaeotemperature the average estimate was 4 9 smow the wealden sphaerosiderite oxygen isotope values are comparable with other early cretaceous data from similar palaeolatitudes but lower than estimated holocene values for equivalent latitudes this observation may indicate greater rainfall at 30 n during the cretaceous relative to the holocene and also suggests relative stability of palaeoclimatic conditions during the early cretaceous at this palaeolatitude

nd and pb isotope mapping of crustal domains within the makkovik province labrador the makkovik province of eastern labrador represents part of an accretionary orogen active during an early stage in the development of the palaeoproterozoic southern laurentian continental margin new nd isotope data for the eastern makkovik province suggest that accreted juvenile makkovik crust was generated in the cape harrison domain during a single crust forming event at c 2 0 ga pb isotope data support this model and show a strong similarity to radiogenic crustal signatures in the juvenile palaeoproterozoic crust of the ketilidian mobile belt of southern greenland as previously proposed an arc accretion event at c 1 9 ga triggered subduction zone reversal and the development of an ensialic arc on the composite margin after the subduction flip a temporary release of compressive stress at c 1 87 ga led to the development of a retro arc foreland basin on the downloaded archean continental edge forming the aillik group unlike previous models a second arc is not envisaged instead a compressive regime at c 1 82 ga is attributed to continued ensialic arc plutonism on the existing margin the tectonic model for the makkovikian orogeny proposed here is similar to that for the ketilidian orogeny major and trace element analyses suggest that much of the magmatism in the makkovik orogen results from post accretionary ensialic arc activity and that few vestiges remain of the original accreted volcanic arc this pattern of arc accretion and intense post accretion reworking is common to many accretionary orogens such as the south american andes and north american cordillera

no extreme bipolar glaciation during the main eocene calcite compensation shift major ice sheets were permanently established on antarctica approximately 34 million years ago1 2 3 close to the eocene oligocene boundary at the same time as a permanent deepening of the calcite compensation depth in the world s oceans4 until recently it was thought that northern hemisphere glaciation began much later between 11 and 5 million years ago1 2 3 5 this view has been challenged however by records of ice rafting at high northern latitudes during the eocene epoch6 7 and by estimates of global ice volume that exceed the storage capacity of antarctica8 at the same time as a temporary deepening of the calcite compensation depth 41 6 million years ago9 here we test the hypothesis that large ice sheets were present in both hemispheres 41 6 million years ago using marine sediment records of oxygen and carbon isotope values and of calcium carbonate content from the equatorial atlantic ocean these records allow at most an ice budget that can easily be accommodated on antarctica indicating that large ice sheets were not present in the northern hemisphere the records also reveal a brief interval shortly before the temporary deepening of the calcite compensation depth during which the calcite compensation depth shoaled ocean temperatures increased and carbon isotope values decreased in the equatorial atlantic the nature of these changes around 41 6 million years ago implies common links in terms of carbon cycling with events at the eocene oligocene boundary4 and with the hyperthermals of the early eocene climate optimum3 10 11 our findings help to resolve the apparent discrepancy between the geological records of northern hemisphere glaciation6 7 8 and model results12 13 that indicate that the threshold for continental glaciation was crossed earlier in the southern hemisphere than in the northern hemisphere

u pb geochronologic constraints on paleoproterozoic orogenesis in the northwestern makkovik province labrador canada a 45 km wide shear zone bounded segment of the northwestern makkovik province labrador is underlain by archean gneisses derived from the adjacent nain craton this lithotectonic block kaipokok domain was reworked at high metamorphic grade overthrust by supracrustal sequences lower aillik and moran lake groups and intruded by granitoid plutons during the paleoproterozoic initial amphibolite facies reworking of the kaipokok domain at 1896 6 ma is indicated by u pb ages of metamorphic zircon from a foliated kikkertavak metadiabase dyke this is one of the oldest paleoproterozoic tectonic events dated thus far in northeast laurentia and may be linked with ca 1890 ma plutonism documented elsewhere in the kaipokok domain intrusion of granitoid plutons at 1877 5 and in the kaipokok bay area postdates early thick and thin skinned thrusting possibly east to northeast directed that involved lower aillik group strata u pb titanite ages of 1866 1847 ma in part record a metamorphic event that fo

burwell domain of the palaeoproterozoic torngat orogen northeastern canada tilted cross section of a magmatic are caught between a rock and a hard place

the mid cretaceous water bearer isotope mass balance quantification of the albian hydrologic cycle a latitudinal gradient in meteoric n 18 o compositions compiled from paleosol sphaerosiderites throughout the cretaceous western interior basin kwib 34 75 n paleolatitude exhibits a steeper more depleted trend than modern predicted values 3 0x 34 n latitude to 9 7x 75 n lighter furthermore the sphaerosiderite meteoric n 18 o latitudinal gradient is significantly steeper and more depleted 5 8x 34 n to 13 8x 75 n lighter than a predicted gradient for the warm mid cretaceous using modern empirical temperature n 18 o precipitation relationships we have suggested that the steeper and more depleted relative to the modern theoretical gradient meteoric sphaerosiderite n 18 o latitudinal gradient resulted from increased air mass rainout effects in coastal areas of the kwib during the mid cretaceous the sphaerosiderite isotopic data have been used to constrain a mass balance model of the hydrologic cycle in the northern hemisphere and to quantify precipitation rates of the equable greenhouse albian stage in the kwib the mass balance model tracks the evolving isotopic composition of an air mass and its precipitation and is driven by latitudinal temperature gradients our simulations indicate that significant increases in albian precipitation 34 52 and evaporation fluxes 76 96 are required to reproduce the difference between modern and albian meteoric siderite n 18 o latitudinal gradients calculations of precipitation rates from model outputs suggest mid high latitude precipitation rates greatly exceeded modern rates 156 220 greater in mid latitudes 2600 3300 mm yr 99 greater at high latitudes 550 mm yr the calculated precipitation rates are significantly different from the precipitation rates predicted by some recent general circulation models gcms for the warm cretaceous particularly in the mid to high latitudes our mass balance model by no means replaces gcms however it is a simple and effective means of obtaining quantitative data regarding the mid cretaceous hydrologic cycle in the kwib our goal is to encourage the incorporation of isotopic tracers into gcm simulations of the midcretaceous and to show how our empirical data and mass balance model estimates help constrain the boundary conditions

18o 16o and d h ratios of pedogenic kaolinite in a north american cenomanian laterite paleoclimatic implications abstract kaolinite gibbsite and quartz are the dominant minerals in samples collected from two outcrops of a cenomanian 95 ma laterite in southwestern minnesota a combination of measured yields and isotope ratios permitted mass balance calculations of the d and 18 o values of the kaolinite in these samples these calculations yielded kaolinite d values of about 73 and 18 o values of about 18 7 the d and 18 o values appear to preserve information on the ancient weathering system if formed in hydrogen and oxygen isotope equilibrium with water characterized by the global meteoric water line gmwl the kaolinite d and 18 o values indicate a crystallization temperature of 22 5 c a nominal paleotemperature of 22 c implies a 18 o value for the corresponding water of 6 3 the combination of temperature and meteoric water 18 o values is consistent with relatively intense rainfall at that mid paleolatitude location 40 n on the eastern shore of the north american western interior seaway the inferred cenomanian paleosol temperature of 22 c is in general accord with published mid cretaceous continental mean annual temperatures mat estimated from leaf margin analyses of fossil plants when compared with results from a published gcm based cenomanian climate simulation which specifies a latitudinal sea surface temperature sst gradient that was either near modern or smaller than modern the kaolinite paleotemperature of 22 c is closer to the gcm predicted mat for a smaller equator to pole temperature difference in the mid cretaceous moreover the warm kaolinite derived mid paleolatitude temperature of 22 c is associated with proxy estimates of high concentrations of atmospheric co 2 in the cenomanian the overall similarity of proxy and model results suggests that the general features of cenomanian continental climate in that north american locale are probably being revealed

baddeleyite zircon relationships in coronitic metagabbro grenville province ontario implications for geochronology in the high grade gneiss terranes of the grenville province in ontario metagabbro with silicate coronas around primary olivine and fe ti oxide contains trace amounts of both baddeleyite and zircon single baddeleyite crystals with radiating columnar coronas of polycrystalline zircon in places with outer rims of garnet are analogous to the coronas around olivine and ilmenite single crystals of zircon and baddeleyite without zircon coronas also occur in the same rocks both zirconium minerals have been isotopically dated at three widely separated localities in each case baddeleyite records an igneous crystallization age of ca 1170 ma 125 ma older than the ca 1045 ma age of the zircons interpreted to be the age of metamorphism these data agree well with u pb ages obtained from other rocks in the same region and refute the alternative interpretation that silicate coronas in these metagabbros formed during cooling following magmatic crystallization the age does not support direct correlation with diabase dykes of either the sudbury or abitibi swarms northwest of the grenville front

u pb ages for late magmatism and regional deformation in the shebandowan belt superior province canada five precise u pb zircon and titanite ages from different lithologic units of the shebandowan greenstone belt in the western wawa subprovince of the superior province put tight constraints on the time of late archean magmatism and of two major deformation events a porphyry sill from the older supracrustal sequence has an age of 2733 3 ma another porphyritic rock a trondhjemite occurring as a clast in a conglomerate of the unconformably overlying timiskaming type supracrustal sequence formed 2704 2 ma ago and defines a maximum age for the deposition of the timiskaming type sequence an alkalic volcanic rock from this sequence has been directly dated at in accord with the above constraint and with another probable maximum age of deposition given by the date of 2696 2 ma for the shebandowan lake pluton a first deformation event d1 was related to a predominantly vertical tectonic regime and occurred during or before intrusion of the shebandowan lake pluton at 2696 2 ma the second deformatio

a multiple proxy and model study of cretaceous upper ocean temperatures and atmospheric co2 concentrations foraminiferal d 18 o and mg ca suggests that the ratio of magnesium to calcium in the turonian coniacian ocean may have been lower than in the albian cenomanian ocean perhaps coincident with an ocean 87 sr 86 sr minimum the carbon isotopic compositions of distinct marine algal biomarkers were measured in the same sediment samples the d 13 c values of phytane combined with foraminiferal d 13 c and inferred temperatures were used to estimate atmospheric carbon dioxide concentrations through this interval estimates of atmospheric co2 concentrations range between 600 and 2400 ppmv within the uncertainty in the various proxies there is only a weak overall correspondence between higher lower tropical temperatures and more less atmospheric co2 the genesis climate model underpredicts tropical atlantic temperatures inferred from odp leg 207 foraminiferal d 18 o and mg ca when we specify approximate co2 concentrations estimated from the biomarker isotopes in the same samples possible errors in the temperature and co2 estimates and possible deficiencies in the model are discussed the potential for and effects of substantially higher atmospheric methane during cretaceous anoxic events perhaps derived from high fluxes from the oxygen minimum zone are considered in light of recent work that shows a quadratic relation between increased methane flux and atmospheric ch4 concentrations with 50 ppm ch4 genesis sea surface temperatures approximate the minimum upper ocean temperatures inferred from proxy data when co2 concentrations specified to the model are near those inferred using the phytane d 13 c proxy however atmospheric co2 concentrations of 3500 ppm or more are still required in the model in order to reproduce inferred maximum temperatures

simulating the biogeochemical effects of volcanic co2 degassing on the oxygen state of the deep ocean during the cenomanian turonian anoxic event oae2 cretaceous anoxic events may have been triggered by massive volcanic co2 degassing as large igneous provinces lips were emplaced on the seafloor here we present a comprehensive modeling study to decipher the marine biogeochemical consequences of enhanced volcanic co2 emissions a biogeochemical box model has been developed for transient model runs with time dependent volcanic co2 forcing the box model considers continental weathering processes marine export production degradation processes in the water column the rain of particles to the seafloor benthic fluxes of dissolved species across the seabed and burial of particulates in marine sediments the ocean is represented by twenty seven boxes to estimate horizontal and vertical fluxes between boxes a coupled ocean atmosphere general circulation model aogcm is run to derive the circulation patterns of the global ocean under late cretaceous boundary conditions the aogcm modeling predicts a strong thermohaline circulation and intense ventilation in the late cretaceous oceans under high pco2 values with an appropriate choice of parameter values such as the continental input of phosphorus the model produces ocean anoxia at low to mid latitudes and changes in marine 13c that are consistent with geological data such as the well established 13c curve the spread of anoxia is supported by an increase in riverine phosphorus fluxes under high pco2 and a decrease in phosphorus burial efficiency in marine sediments under low oxygen conditions in ambient bottom waters here we suggest that an additional mechanism might contribute to anoxia an increase in the c p ratio of marine plankton which is induced by high pco2 values according to our aogcm model results an intensively ventilated cretaceous ocean turns anoxic only if the c p ratio of marine organic particles exported into the deep ocean is allowed to increase under high pco2 conditions being aware of the uncertainties such as diagenesis this modeling study implies that potential changes in redfield ratios might be a strong feedback mechanism to attain ocean anoxia via enhanced co2 emissions the formation of c enriched marine organic matter may also explain the frequent occurrence of global anoxia during other geological periods characterized by high pco2 values

u pb geochronology of a paleoproterozoic continental magmatic arc on the western margin of the archean nain craton northern labrador canada the paleoproterozoic torngat orogen in northernmost labrador and northeastern quebec records the collision between the western margin of the nain province and the eastern margin of the rae province six samples from a suite of calc alkaline plutonic rocks that intrude the nain craton have been dated using the u pb method at 1895 2 1888 2 1885 2 two samples and 1859 ma and support the interpretation that east dipping subduction occurred below the nain craton during this interval a granitic dyke that truncates the sinistral shear fabric in the abloviak shear zone is 1824 2 ma placing a younger limit on the timing of this deformation in the area a second granitic dyke emplaced synchronously with dextral deformation in the bend in the abloviak shear zone is 1798 3 ma a model is proposed in which subduction occurred beneath the nain craton along its entire exposed length from 1 91 to 1 86 ga and collision occurred between 1 86 and 1 84 ga followed by oblique uplift of the southern

dating ductile deformation using u pb geochronology examples from the gilbert river belt grenville province labrador canada the gilbert river belt in the grenville province in southeastern labrador is a distinctive west northwest trending zone of locally intense deformation and voluminous granitoid plutonism up to 30 km in width in an attempt to directly quantify the timing of deformation in ductile shear zones within the belt rocks interpreted as having been intruded synchronously with ongoing deformation were sampled for u pb isotopic analysis three of these samples are 2 m wide granitic veins that have sharp intrusive contacts that truncate ductile deformation fabrics but are themselves deformed at metamorphic conditions similar to their host rocks and are therefore interpreted as having intruded after the initiation of deformation and fabric development but prior to cessation of this deformation the first vein is syntectonic with respect to amphibolite facies deformation and yielded a zircon age of the second vein intruded synchronously with the development of a zone of amphibolite facies straight gneisses wh

co2 forced climate thresholds during the phanerozoic abstract the correspondence between atmospheric co2 concentrations and globally averaged surface temperatures in the recent past suggests that this coupling may be of great antiquity here i compare 490 published proxy records of co2 spanning the ordovician to neogene with records of global cool events to evaluate the strength of co2 temperature coupling over the phanerozoic last 542 my for periods with sufficient co2 coverage all cool events are associated with co2 levels below 1000 ppm a co2 threshold of below 500 ppm is suggested for the initiation of widespread continental glaciations although this threshold was likely higher during the paleozoic due to a lower solar luminosity at that time also based on data from the jurassic and cretaceous a co2 threshold of below 1000 ppm is proposed for the initiation of cool non glacial conditions a pervasive tight correlation between co2 and temperature is found both at coarse 10 my timescales and fine resolutions up to the temporal limits of the data set million year timescales indicating that co2 operating in combination with many other factors such as solar luminosity and paleogeography has imparted strong control over global temperatures for much of the phanerozoic

structural evolution of the makkovik province labrador canada tectonic processes during 200 myr at a paleoproterozoic active margin in the makkovik province the structures and plutonic rocks of the reworked southern edge of the archean nain craton parautochthon and an adjacent juvenile domain form a spatially concentrated record of 200 ma at a paleoproterozoic active margin d1 thin and thick skinned structures formed during terrane collision before ca 1896 ma were nearly erased by d2 transpressive structures present across the entire parautochthon that had been thermally softened by emplacement of arc plutons at ca 1895 1870 ma d3 transpressive inversion of a back arc rift and d4 strike slip shearing formed structures at the oceanward margin of the parautochthon and were responses to events in the active arc that was now widely separated from the parautochthon by accreted terranes the tectonic isolation of the parautochthon ended by the time of d5 ca 1740 1710 ma and d6 with the reappearance there of granite and low grade shear zones structural and plutonic style varied at each stage primarily controlled by the crustal level attained

anatomy and orogenic history of a paleoproterozoic accretionary belt the makkovik province labrador canada the makkovik province is a segment of a paleoproterozoic accretionary belt the makkovik ketilidian orogen that developed on the southern margin of laurentia at 1 9 1 7 ga in contrast to coeval laurentian orogenic belts that mainly resulted from collision of archean plates makkovikian ketilidian orogenesis was dominated by active margin processes including continental margin arc plutonism and juvenile terrane accretion both of which were accompanied by regional transpression in the makkovik province earliest deformation and amphibolite facies metamorphism of paleoproterozoic rift drift assemblages post hill and moran lake groups and the archean foreland nain province occurred at 1 9 ga in response to accretion of a paleoproterozoic island arc following this collision cratonward dipping subduction was established resulting in the formation of the 1895 1870 ma island harbour bay plutonic suite a calc alkaline magmatic arc built on reworked archean crust crust formation continued between ca 1

middle late cretaceous climate of the southern high latitudes stable isotopic evidence for minimal equator to pole thermal gradients a detailed 18 o and 13 c stratigraphy has been generated from analysis of well preserved albian early maastrichtian foraminifera from deep sea drilling project dsdp sites 511 and 327 falkland plateau 58 s 62 s paleolatitude in the southern south atlantic and cenomanian and coniacian santonian foraminifera from dsdp site 258 naturaliste plateau 58 s paleolatitude in the southern indian ocean these results when combined with previously published maastrichtian stable isotope data from ocean drilling program odp site 690 weddell sea 65 s paleolatitude provide new insight into the climatic and oceanographic history of the southern high latitudes during middle late cretaceous time the planktonic foraminifer 18 o curves reveal a gradual warming of surface waters from the albian through the cenomanian followed by extremely warm surface waters from the turonian through the early campanian long term cooling of surface waters began in the late early campanian and continued through the end of the maastrichtian the benthic foraminifer 18 o record generally parallels changes in the oxygen isotopic curves defined by shallow dwelling planktonic foraminifera the vertical oxygen and carbon isotopic gradients were relatively low during the albian cenomanian high from the turonian early campanian and then low during the late campanian and maastrichtian foraminiferal oxygen isotopic data from published sources and this study are averaged for each site corrected for latitudinal changes in salinity based on modern day surface water values and plotted versus paleolatitude for the late albian coniacian santonian and late maastrichtian differences between lowand high latitude surface water paleotemperatures are estimated at 14 c during the late albian and late maastrichtian but the coniacian santonian reconstruction reveals only a 0 4 c latitudinal temperature gradient uncertainty regarding cretaceous salinity gradients and possible diagenetic alteration of 18 o values introduce error into our estimates of paleolatitudinal thermal gradients however apparent low equator to pole temperature differences could indicate much higher poleward heat transport than at present

upb geochronology of the northern torngat orogen labrador canada a record of palaeoproterozoic magmatism and deformation abstract the palaeoproterozoic torngat orogen located in northeastern quebec and northern labrador canada records the sinistral transpressional collision of the western margin of the archaean nain province and the eastern margin of the rae province u pb age determinations are presented for twelve samples from the northern part of the orogen and used to evaluate models for its tectonic evolution voluminous granitoid plutonic rocks which in part intrude gneisses interpreted as the northern extension of the nain province and are possibly related to subduction below it have zircon ages of 1910 2 ma 1895 3 ma 1891 2 ma 1890 2 ma 1869 3 2 ma and 1864 2 ma suggesting at least 45 m y of convergence between the rae and nain provinces granulite facies conditions may have existed in the northern part of the area at 1 84 ga these plutonic rocks as well as tonalitic gneisses of the nain province were reworked at amphibolite facies conditions within a north south corridor referred to as the komaktorvik zone zircon age determinations of two granitic veins which were intruded synchronously with ongoing deformation in the komaktorvik zone are 1789 2 ma and 1719 2 ma suggesting that deformation within the zone may have lasted for up to 70 m y metamorphic titanite from samples within the komaktorvik zone have ages of 1776 4 ma 1774 4 ma 1767 4 ma 1710 4 ma and 1632 4 ma and support the interpretation of long lived deformation in the komaktorvik zone palaeoproterozoic subduction beneath the nain province has not been widely recognized in southern parts of the orogen suggesting that a distinct tectonic regime existed in the study area

geochemistry and age of the aillik group and associated plutonic rocks makkovik bay area labrador implications for tectonic development of the makkovik province the aillik domain of the makkovik province is dominated by deformed and metamorphosed sedimentary and bimodal volcanic rocks of the redefined aillik group and abundant unfoliated late to post orog

tectonic and metamorphic events in the westernmost grenville province central ontario new results from high precision u pb zircon geochronology the u pb isotopic ages of metamorphic zircons from deformed amphibolitized metadiabase dykes and associated unstrained anatectic pegmatites have been determined to constrain the times of postdyke ductile flow related recrystallization and deformation samples from the central gneiss belt of the grenville province in the southern georgian bay region provide a means of linking areas formed during common episodes of ductile flow three zircon fractions from one attenuated dyke in the moon river domain gave identical concordant ages of 1062 1065 and 1064 2 ma while those from another gave identical concordant ages of 1052 1051 and 1050 2 ma for the time of metamorphism zircons from a folded dyke from the go home domain gave identical concordant ages of 1049 1047 and 1046 2 ma while a single overgrowth fragment from an unstrained anatectic pegmatite in the fold hinge gave a concordant age of 1047 2 ma as if folding metamorphic zircon growth and postfolding pegmatite are part of the same proc

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

temperature and salinity of the late cretaceous western interior seaway the western interior seaway wis was a shallow and expansive body of water that covered the central united states during the late cretaceous attempts to reconstruct temperatures in the seaway using the oxygen isotopic composition of biogenic carbonates have suffered from uncertainty in the oxygen isotopic composition of seawater 18 o w in the semi restricted basin we present new reconstructed temperature and 18 o w data from marine and estuarine environments in the wis and freshwater environments in wis source rivers derived from clumped isotope analyses of bivalve and gastropod shells we find temperatures of 5 21 c 18 o w values below contemporaneous gulf of mexico marine sites and a strong correlation between 18 o w and environmental setting we propose that decreasing 18 o w values reflect decreasing salinity driven by an increasing contribution of continental runoff using a two end member salinity 18 o w mixing model we estimate salinities of 29 35 psu practical salinity units for the deep marine 20 32 psu for the shallow marine and 11 26 psu for the estuarine environments of the wis new climate model simulations agree with reconstructed temperatures and salinities and suggest the presence of salinity driven stratification within the seaway

nd isotope evidence for crust mantle interaction in the generation of a type granitoid suites in labrador canada early proterozoic a type granite suites in labrador northeastern canada have initial nd isotopic compositions that lie between those of a depleted mantle reservoir and the local basement rocks one of these a type granite suites consists of a linear array of discrete plutons that crosses the boundary between an archean craton and an adjoining early proterozoic crustal block the nd of these granites at formation t 1720 ma changes from 8 to 4 across this boundary reflecting changes in the nature and antiquity of the continental crust however in both domains the granites cannot be derived entirely by anatexis of the local basement rocks and apparently require significant amounts of juvenile mantle derived material a type granites have been widely interpreted as anatectic derivatives of lower crustal rocks that were depleted by previous melt extraction the nd isotopic data suggest that these labrador examples were instead mixtures of mantle derived magmas and overlying lower crustal rocks and that new material may have been the volumetrically dominant component 50 90 in most cases as an alternative to the prevalent residual source model it is proposed that the distinctive geochemical characteristics of these a type granites are a function of the high liquidus temperatures and primitive mg rich character of subcrustal magma fluxes in post orogenic and anorogenic environments where such magmas are emplaced into stabilized continental crust further nd isotope studies of other a type granite suites are required to ascertain if models invoking crust mantle interaction are more widely applicable

u pb ages of granitoid rocks in the northwestern makkovik province labrador evidence for 175 million years of episodic synorogenic and postorogenic plutonism new u pb zircon titanite and monazite ages reported here along with existing age data demonstrate that granitoid bodies in the northwestern segment of the paleoproterozoic makkovik province labrador are of three distinct ages the redefined island harbour bay plutonic suite consists of varied dioritic to granitic units that were syntectonically emplaced into archean crust of the kaipokok domain between ca 1895 ma and 1870 2 ma this plutonism occurred during the early stages of the makkovikian orogeny in an obliquely convergent andean continental margin setting the hares islands and drunken harbour granites form smaller discrete plutons that were emplaced in or adjacent to the island harbour bay plutonic suite at 1805 5 ma and 1791 2 ma respectively during dextral strike slip deformation that accompanied accretion of an outboard juvenile terrane magmatic activity during this period was preferentially sited along active structural zones but also occurred outside of these zones the undeformed blacklers bight a type granite was emplaced in the kaipokok domain at 1716 1 ma late in the development of the orogen a type granites of this age form a significant component of the southeastern makkovik province and their generation is linked to mafic underplating and heterogeneous regional extension the new age data support the conclusion of earlier workers that crustal growth via synorogenic and postorogenic plutonism was episodic and allow along with field and geochemical data inferences to be made regarding the tectonic setting of individual plutonic events

wall rock alteration and metamorphism of a volcanogenic massive sulfide deposit at que river tasmania petrology and mineralogy the rocks in the alteration halo surrounding the polymetallic massive sulfide deposit at que river preserve primary hydrothermal mineral textures and assemblages despite the imprint of later prehnite pumpellyite facies regional metamorphism their textural preservation is attributed to the mechanical strength of many of the hydrothermal minerals such as pyrite carbonates except calcite and quartz the competency of some of the host rocks and the low strain that has affected many rocks at the margin of the halo assemblages include quartz white mica carbonates albitized plagioclase pyrite and chlorite closer to the ore as intensity of alteration increases albite disappears pyrite apatite rutile and anatase become more common white mica quartz carbonates and chlorite vary in abundance and are distributed irregularly these minerals also occur in hydrothermal veins throughout the stockwork zone several generations of veins are commonly developed with each generation having its own distinctive hydrothermal assemblage both hydrothermal and metamorphic phases are compositionally variable despite some overlap there appear to be systematic differences in composition x ray diffraction and microprobe analyses show that the hydrothermal white micas are variable in composition ranging from illites or muscovites to fuchsites their metamorphic counterparts contain less pyrophyllite and more celadonite the hydrothermal carbonates are most commonly ferroan dolomite magnesian siderite and ferroan magnesite the latter two are more abundant than dolomite where alteration is intense calcite and ferroan dolomite formed during metamorphism and the composition of the hydrothermal and metamorphic carbonates may be different in individual specimens both hydrothermal and metamorphic chlorites are ferro clinochlores and magnesio chamosites metamorphic chlorites outside the halo are more fe rich and more al vi deficient than those within the hydrothermal chlorites exhibit fe mg and al iv al vi si iv mg fe vi tschermakite substitutions and contain al iv contents suggesting temperatures of crystallization of 290 degrees to 320 degrees c similar to the temperature of 280 degrees c inferred from fluid inclusions the chemistry of the hydrothermal phases varies throughout the halo overall fe and mg do not show a systematic trend toward mineralization however fe enrichment of hydrothermal phases in the ore is apparent as is mg enrichment of locally developed chlorite carbonate rocks na and celadonite in white micas and ca in carbonates on the other hand decrease with increasing alteration mg only became an important component in the fluid when seawater infiltrated into the hydrothermal system the heterogeneous distribution of the hydrothermal phases is attributed to successive influxes of hydrothermal fluids of varying composition into the alteration pipe variable water rock ratios and seawater entrainment

alteration of felsic volcanics hosting the thalanga massive sulfide deposit northern queensland australia and geochemical proximity indicators to ore thalanga is an early ordovician stratiform zn pb cu ag rich massive sulfide deposit in northern queensland australia with a total resource of 6 6 mt of ore the host rock succession consists of variably altered rhyolite in the footwall and a dacite dominated volcano sedimentary sequence in the hanging wall the sulfide deposit and the enclosing volcanic sequence were metamorphosed under upper greenschist conditions a laterally continuous footwall alteration zone extends beneath the entire deposit 3 000 m and to a stratigraphic depth of at least 300 m below the ore lenses the bulk of this zone is occupied by feldspar destructive muscovite biotite chlorite rich mottled alteration facies with disseminated pyrite representing the metamorphic equivalent of phyllosilicate dominated hydrothermal alteration discordant zones of intense quartz pyrite alteration represent the principal fluid pathways during mineralizing hydrothermal activity locally quartz k feldspar alteration facies exist on the fringes of the system and calcareous alteration and chlorite pyrite alteration facies exist in the upper part of footwall rhyolite proximal to sulfide lenses quartz feldspar porphyritic rhyolite laterally surrounding the footwall alteration zone and feldspar porphyritic dacite in the hanging wall are unaltered or weakly altered the compositional diversity of altered footwall rhyolite implies that hydrothermal alteration at thalanga was a complex processes this paper presents a model for the evolution of the footwall alteration zone calcareous alteration probably represents the initial phase of hydrothermal activity this was followed by diffuse upwelling of acidic seawater dominated fluids causing destruction of primary feldspar precipitation of pyrite and formation of hydrothermal sericite chlorite and clay minerals subsequent intense quartz pyrite alteration was directly associated with mineralization the thalanga footwall alteration zone has several geochemical characteristics that show systematic changes with increasing proximity to ore these include na depletion and elevated mg s alteration index ai chlorite carbonate pyrite index ccpi mo bi and as furthermore the x mg of chlorite and biotite increases systematically from values of 0 45 to 0 5 in least altered rhyolite to values 0 9 immediately below ore these geochemical features can be used in exploration for massive sulfide deposits as vectors to ore at the prospect scale and in discrimination of prospective hydrothermal from unprospective diagenetic alteration systems at the regional scale

time span of plutonism fabric development and cooling in a neoproterozoic magmatic arc segment u pb age constraints from syn tectonic plutons sark channel islands uk abstract new u pb zircon and titanite dates from syn tectonic plutons on the british channel island of sark constrain the time span of plutonism fabric development and cooling in this part of the neoproterozoic cadomian magmatic arc the tintageu leucogneiss is a mylonitic unit that was dated previously at 615 6 4 2 2 3 ma the port du moulin quartz diorite which intruded the tintageu unit contains a high strain solid state deformation fabric that is less intense than but parallel to fabrics in the leucogneiss and yields a u pb zircon date of 613 5 2 3 1 5 ma the little sark quartz diorite also displays solid state deformation fabrics in addition to relict magmatic textures and yields a u pb zircon date of 611 4 2 1 1 3 ma the north sark granodiorite is largely penetratively undeformed exhibits mainly magmatic fabrics and textures and has a u pb zircon date of 608 7 1 1 1 0 ma two fractions of titanite from each intrusion are essentially concordant and are identical within error with mean dates of 606 5 0 4 ma port du moulin quartz diorite 606 2 0 6 ma little sark quartz diorite 606 4 0 6 ma north sark granodiorite the new u pb data in combination with previous u pb and 40 ar 39 ar data and previous field studies confirm the syn tectonic nature of the sark plutons and quantify the time span ca 7 m y required for intrusion and sufficient crystallization of each body to record incremental strain during waning deformation titanite u pb and hornblende 40 ar 39 ar dates mark final cooling about 2 m y after intrusion of the last pluton

high temperatures in the late cretaceous arctic ocean to understand the climate dynamics of the warm equable greenhouse world of the late cretaceous period it is important to determine polar palaeotemperatures the early palaeoceanographic history of the arctic ocean has however remained largely unknown because the sea floor and underlying deposits are usually inaccessible beneath a cover of floating ice a shallow piston core taken from a drifting ice island in 1970 fortuitously retrieved unconsolidated upper cretaceous organic rich sediment from alpha ridge a submarine elevated feature of probable oceanic origin a lack of carbonate in the sediments from this core has prevented the use of traditional oxygen isotope palaeothermometry here we determine arctic palaeotemperatures from these upper cretaceous deposits using tex86 a new palaeothermometer that is based on the composition of membrane lipids derived from a ubiquitous component of marine plankton crenarchaeota from these analyses we infer an average sea surface temperature of approximately 15 degrees c for the arctic ocean about 70 million years ago this calibration point implies an equator to pole gradient in sea surface temperatures of approximately 15 degrees c during this interval and by extrapolation we suggest that polar waters were generally warmer than 20 degrees c during the middle cretaceous approximately 90 million years ago

u pb age and hf isotope geochemistry of zircon from felsic volcanic rocks of the paleoproterozoic aillik group makkovik province labrador abstract u pb zircon shrimp geochronology and lu hf zircon la mc icpms isotope geochemistry are used to constrain the ages of paleoproterozoic felsic magmatism and their crustal sources in the aillik group makkovik province of labrador this information is important for understanding the extent of crustal reworking vs juvenile crustal growth in subduction related magmatism during the paleoproterozoic and improves framework knowledge for uranium exploration in the central mineral belt of labrador u pb shrimp zircon geochronology from four felsic tuff samples collected from two different areas of the aillik group yield magmatic 207pb 206pb ages of 1852 7 ma 2 1854 7 ma 2 1861 7 ma 2 and 1862 7 ma 2 the ages fall within the range of previous u pb zircon dates reported for felsic volcanic rocks of the aillik group altogether these dates indicate that felsic volcanism spanned at least 30 m y and was perhaps most intense during the last 10 m y of that interval a foliated syn deformational monzogranite in the aillik group cross lake granite yields a 207pb 206pb zircon date of 1805 6 ma 2 which indicates that development of a pervasive planar fabric associated with northwestward thrusting of the aillik group continued after this time initial e h f s t values for magmatic zircons from the four felsic tuffs 4 8 to 1 9 1 7 to 2 2 11 8 to 3 8 9 0 to 4 6 and monzogranite 4 8 to 1 5 exhibit significant variability which indicates heterogeneous sources most of the zircon grains have negative initial e h f s t values and calculated crust formation hf isotope tdm model ages point to substantial contributions from melts of ancient crust ranging in age from ca 2200 to 2900 m y and clustering at ca 2500 m y inherited zircon grains in the felsic tuffs and monzogranite mainly have u pb ages of ca 1880 1920 ma though others are older up to ca 2743 ma hf isotope tdm model ages for the inherited zircons are similar to those of the magmatic zircons the hf isotope results indicate that subduction related felsic magmatism in the makkovik orogen involved significant crustal reworking 80 during formation of the aillik group

general circulation model simulation of the δ18o content of continental precipitation in the middle cretaceous a model proxy comparison we use the genesis atmospheric general circulation model gcm with water isotopic transport and fractionation capabilities to quantify the influence of atmospheric co 2 sea level and elevation of the western cordillera on the 18 o of middle cretaceous precipitation the model predicts a systematic increase of nearly 3 in the 18 o of north american precipitation due to warming associated with an increase in co 2 from 2 to 12 times pre industrial levels in contrast the specification of lowstand conditions and a high ancestral western cordillera reduces the 18 o of north american precipitation locally by as much as 6 and 8 we compare the simulated 18 o of precipitation with the 18 o of paleosol siderite spherules and find good agreement only when the model includes lowstand conditions and a high ancestral western cordillera our results imply either that cretaceous high latitude paleosol 18 o was influenced by orographic precipitation and the western interior seaway or that the gcm9s hydrological cycle is deficient at high p co 2 additional paleosol data are needed to resolve this issue

depositional and tectonic setting of the paleoproterozoic lower aillik group makkovik province canada evolution of a passive margin foredeep sequence based on petrochemistry and u pb tims and lam icp ms geochronology abstract the paleoproterozoic lower aillik group is a deformed metasedimentary metavolcanic succession located in the makkovik province of labrador eastern canada the group is situated near the boundary between reworked archaean gneiss of the nain north atlantic craton and juvenile paleoproterozoic crust that was both tectonically accreted and formed on or adjacent to this craton during the ca 1 9 1 78 ma makkovikian orogeny the lower aillik group is structurally underlain by archaean gneiss and structurally overlain by ca 1860 1807 ma bimodal dominantly felsic volcanic and volcaniclastic rocks of the upper aillik group we present geochemical data from metavolcanic rocks and u pb geochronological data from several units of the lower aillik group in order to address the depositional and tectonic history of this group u pb data were obtained using both thermal ionization mass spectrometry tims and laser ablation microprobe inductively coupled plasma mass spectrometry lam icp ms two quartzite units near the structural base of the lower aillik group contain detrital zircons only of archaean age and are interpreted to have been deposited on the nain craton during post 2235 ma rifting and initiation of a passive continental margin overlying mafic metavolcanic rocks contain thin horizons of intermediate tuff one of which is dated at 2178 4 ma this relatively old age and an inferred stratigraphic relationship with underlying sedimentary units suggest that the volcanic rocks represent transitional oceanic crust consistent with their geochemical similarity to tholeiitic rifted margin sequences of mesozoic age in eastern north america a package of interlayered psammitic and semipelitic metasedimentary rocks that appears to stratigraphically overlie the mafic volcanic unit is dominated by paleoproterozoic detrital zircons but also contains archaean grains this package was deposited after 2013 ma the age of the youngest concordant zircon the u pb data imply a minimum 165 m y time gap between mafic volcanism and sedimentation and are consistent with deposition of the psammite semipelite unit in an evolving foredeep that heralded the approach of a paleoproterozoic arc terrane accretion of this terrane to the nain cratonic margin at ca 1 9 ga initiated the makkovikian orogeny although the lower aillik group is highly deformed and may contain internal tectonic boundaries or be incomplete the u pb and geochemical data allow quantitative assessment of a prolonged rift drift basin closure cycle that characterized the early paleoproterozoic evolution of the southern nain cratonic margin

augmented and reassessed u pb geochronological data from the labradorian grenvillian front in the smokey archipelago eastern labrador four u pb dating sites straddling the grenville front on the labrador coast were investigated sites 1 and 2 exhibit complex intrusive deformational and metamorphic histories and were studied in detail whereas two simpler outcrops sites 3 and 4 were examined only at a reconnaissance level at site 1 south of the grenville front a 1799 3 2 ma granodioritic gneiss is intruded by two phases of mafic dykes then by a 1647 7 5 ma aplite and a ca 1647 1500 ma pegmatite and lastly by the michael gabbro the pegmatite was metamorphosed at 1030 10 ma site 2 is on the cut throat island thrust which defines the grenville front in the area early mylonitization occurred at 1790 2 ma followed by 1730 2 ma pegmatite emplacement and then cooling at 1703 15 ma a post deformational melt pod gave a titanite age of 1662 10 ma in the mylonitic host based on positive correlation between pb loss and degree of granularization in monazite grenvillian deformation was very short lived sites 3 and 4 nort

amphibole and mica 40ar 39ar ages from the kaipokok and aillik domains makkovik province labrador towards a characterization of back arc processes in the paleoproterozoic we report amphibole and mica 40ar 39ar ages from the makkovik province amphibole ages from metamorphic rocks decrease towards the interior of the province indicating a first order pattern of monotonic cooling with progressive migration of the province into a more distal back arc location the amphibole data in combination with muscovite ages reveal a second order pattern consisting of four stages corresponding to changing spatial and temporal configurations of plutonism and deformation 1 the western kaipokok domain cooled through muscovite closure by 1810 ma long after the cessation of arc magmatism 2 the kaipokok bay shear zone bounding the kaipokok and aillik domains cooled through amphibole closure during 1805 1780 ma synchronous with emplacement of syn tectonic granitoid plutons 3 between 1740 and 1700 ma greenschist facies shearing occurred along the boundary between the kaipokok domain and nain province synchronous with a type plutonism and localized shearing in the western kaipoko

thrust loads and foreland basin evolution cretaceous western united states two dimensional modeling of loading during the formation of the idaho wyoming thrust belt shows that regional isostatic compensation by flexure of an elastic lithosphere is sufficient to control the formation of a foreland basin the flexural rigidity of the lithosphere is inferred to have been approximately 1023 nm 1030 dyne cm on the basis of palinspastic comparison of predicted downwarping due to the thrust plate loads to the shape of the sedimentary wedge on the west side of the cretaceous western interior seaway erosion of part of the uplifted thrust plates redistributed the load depositing it farther to the east thereby causing subsidence over a much wider area than could have been accomplished only by the loading by thrust plates paleotopography after major cretaceous thrust events was calculated the resulting mountainous terrain gentle alluvial plain and flat sea floor correspond well with the topography of the modern foreland thrust belt and basin system in the andes of south america and to paleogeographic reconstructions in the western united states thrust belt topography is controlled by the subsurface geometry of the thrust faults particularly the positions of ramp zones and by isostatic subsidence

proterozoic orogens of the northeastern canadian shield new information from the lithoprobe ecsoot crustal reflection seismic survey as part of the eastern canadian shield onshore offshore transect ecsoot lithoprobe acquired 1250 km of deep seismic reflection data along the coast of labrador and across ungava bay to image evidence of proterozoic crustal accretion to the archean nuclei of the nain and superior provinces of the canadian shield the relatively pristine archean crust of the nain province has low reflectivity and generally lacks systematic reflector orientations reworking of archean crust on the margins of the makkovik province has little effect on this weak signature in contrast the archean crust in the eastern churchill rae province appears to have been overprinted by a strongly developed whole crustal easterly dipping reflection fabric interpreted to result from proterozoic collision of the nain and superior provinces in the paired new quebec and torngat orogens juvenile proterozoic crust in the makkovik and grenville provinces also shows strong whole crustal dipping reflection fabrics interpretable as outw

the late cretaceous continental interior of siberia a challenge for climate models geological evidence from the late cretaceous continental interior of the vilui basin siberia suggests a far wetter warmer and more equable annual climate than general circulation models gcms can reproduce the disparity cannot be bridged by the uncertainties inherent in either the models or the geological climate proxies this implies the mismatch is genuine and that either 1 we have systematic errors in the interpretation calibration of the climate proxies and or 2 lack of full knowledge of the boundary conditions needed for gcm models simulations of this period and or 3 an insufficient understanding of the nature of the coupled atmosphere ocean biosphere system and its representation within climate models during warm climate epochs if it is the third explanation this would have important implications for the prediction of future climates and would suggest that we may currently be underestimating future climate change in such regions

episodic paleoproterozoic crustal growth preserved in the aillik domain makkovik province labrador abstract the convergent margin of southeastern laurentia consists of reworked continental crust as well as accretion of continental ribbons and juvenile arc terranes forming part of the great proterozoic accretionary orogen the makkovik orogen in labrador preserves evidence of the timing duration and complexities of these accretionary events during the interval 1 88 1 78 ma new regional bedrock geological mapping combined with new u pb zircon shrimp ages constrain the paleoproterozoic felsic magmatism in the aillik group of the makkovik orogen nine samples from the aillik group yield magmatic 207pb 206pb ages between 1883 7 ma and 1858 3 ma the ages extend the previously documented ages of felsic volcanism providing evidence for periodic volcanism spanning 35 m y with the most prolific volcanic activity occurring ca 1860 ma combined with previous studies the aillik group is now constrained between 1883 7 and 1848 2 7 ma development of a pervasive planar fabric associated with the northwestward thrusting of the aillik group d3 occurred after 1848 ma lithotectonic evolution in the makkovik province comprised significant crustal reworking magmatism and minor preserved juvenile crustal growth between ca 1883 and 1848 ma the revised model for formation of the aillik group proposed herein suggests that the aillik group formed in a continental back arc setting these new ages further refine the timing of the accretionary events as well as characterizing the age of the crustal root of the arc which could be a juvenile substrate neoarchean paleoproterozoic or reworked archean crust possibly the 2 3 2 6 ma mistinibi raude crust of the southeast churchill province

mineral and whole rock compositions of seawater dominated hydrothermal alteration at the arctic volcanogenic massive sulfide prospect alaska the arctic volcanogenic massive sulfide prospect located in the ambler mineral district of northwestern alaska includes three types of hydrothermally altered rocks overlying underlying and interlayered with semimassive sulfide mineralization hydrothermal alteration of wall rocks and deposition of sulfide and gangue minerals were contemporaneous with late devonian or early mississippian basalt rhyolite volcanism whole rock analyses of altered rocks surrounding the prospect indicate that strong chemical gradients exist in major and minor oxides and volatiles these were not homogenized or overprinted by late jurassic to middle cretaceous greenschist to glaucophane schist facies metamorphism very low alkali contents and moderate to very high contents of ba f and mg are the major chemical characteristics of the pervasively altered rocks the strong mg metasomatism high ba contents and limited extent of altered rocks suggest a rapid influx of relatively cold seawater into a hot hydrothermal vent system alteration developed asymmetrically around a linear fissure suggesting fracture control of ore fluids rather than a point source micro probe analyses of phyllosilicates from the arctic area indicate two discrete mineral populations magnesian chlorite barian white mica and barian fiuorphlogopite in hydrothermally altered rocks have compositions distinct from similar minerals chlorite phengite biotite developed during high pressure metamorphism in metapelitic and metavolcanic lithologies these differences in mineral chemistry are the result of differences in protolith composition caused by hydrothermal alteration metasomatism without mineral composition data the contacts between some alteration assemblages and relatively unaltered metavolcanic and metasedimentary rocks with similar mineralogy cannot be determined

new insights into the appalachian orogen from geology and geochronology along the cape ray fault zone southwest newfoundland reverse oblique overthrusting of high grade port aux basques gneiss over the lower grade supracrustal windsor point group along the cape ray fault zone occurred during late silurian to early devonian time and is attributed to major oblique collision between gondwanan and laurentian continental blocks new u pb zircon 40 ar 39 ar and k ar data limit the timing of this orogenic event the megacrystic granitic phase of the cape ray igneous complex and the cape ray tonalite have been dated at 488 3 ma and 469 2 ma respectively a black rhyolite from the windsor point group yielded an ordovician age 453 5 4 ma a pretectonic gabbro sill within the windsor point group dated at 424 4 3 ma is cut by the windowglass hill granite dated at 424 2 ma synkinematic hornblende and biotite from the grand bay complex mylonites of the port aux basques gneiss have 40 ar 39 ar ages of 407 4 ma and 403 4 ma respectively which is indicative of a late silurian early devonian age for the amphibolite grade deformation these ages are compatible with a previously determined 415 ma monazite age interpreted as the time of peak metamorphism in the port aux basques gneiss and suggests rapid exhumation the east west flexure of the cape ray fault zone represents a tear fault accommodating differential shortening between the cape ray fault zone and the correlative fault system in central newfoundland mid devonian granites 386 3 384 2 ma intervene between the thrusting events and a younger sinistral transcurrent movement this deformation and magmatic history can be correlated throughout the northern appalachians along other major fault boundaries

kanairiktok shear zone the boundary between the paleoproterozoic makkovik province and the archean nain province labrador canada the polyphase kanairiktok shear zone knsz separates gneissic rocks of the archean nain craton from their reworked equivalents in the paleoproterozoic kaipokok domain of the makkovik province in its early stages the knsz bounded the kaipokok domain as it was thermally softened by 1895 1870 ma andean type magmatism accompanied by dextral oblique convergence and resultant penetrative deformation the amphibolite facies tectonite that developed in this stage was widely overprinted by greenschist facies mylonite laserprobe and spectral 40ar 39ar ages of recrystallized and porphyroclastic muscovite from the greenschist facies mylonite and from muscovite in a syntectonic quartz vein bracket the age of deformation between 1740 and 1710 ma with the best estimate at 1715 ma these ages are similar to those of a type granites within the makkovik province and amphibole cooling ages from the province interior together with the petrological similarity of the greenschist facies mylonite to localized low grade s

u pb geochronology of deformation and metamorphism across a central transect of the early proterozoic torngat orogen north river map area labrador1 the early proterozoic torngat orogen resulted from the oblique collision of the archean nain and southeastern rae provinces and evolved in four stages 0 deposition of platformal supracrustal assemblages followed by subduction related arc magmatism in the margin of the rae province i crustal thickening and nappe tectonics ii sinistral transpression and formation of the abloviak shear zone iii uplift on steeply dipping east verging mylonites along the eastern orogenic front u pb geochronology on zircon and monazite from major rock units and syntectonic intrusions indicates that arc magmatism at ca 1880 ma was followed by 40 ma of deformation and high grade metamorphism from ca 1860 to 1820 subsequent uplift and final cooling occurred ca 1795 1770 ma several ages of mineral growth that correspond to distinct structural and metamorphic events have been recognized 1 1858 1853 ma zircon and monazite dates are interpreted as the minimum age of stage i and peak metamorphic conditions 2

precise u pb ages for grenvillian and pre grenvillian thrusting of proterozoic and archean metamorphic assemblages in the grenville front tectonic zone canada while the position of the grenville front is placed at a structural feature associated with the onset of high grade rocks when approached from the north the time of first metamorphism in these rocks is in general pre grenvillian and highly variable at killarney amphibolite to granulite grade rocks were metamorphosed lineated and foliated to their present front parallel configuration mainly by 1453 6 ma north of north bay amphibolite grade migmatites have been subjected to a pre 2650 ma metamorphism granulite grade gneisses south of the grenville front near val d or record a 2640 ma metamorphic event south of chibougamau mafic enclaves in tonalite south of the front were converted to migmatitic amphibolite at about 2680 to 2690 ma in central labrador a 1650 ma foliated granite is present south of the grenville front and at least some of the banding is this old at the atlantic coast granulite facies metamorphism in front parallel gneisses predates a 1790 1662 ma deformation in contrast each of these areas shares a near common age of second metamorphism that is variable in degree and accompanies nw directed thrusting or crustal loading near killarney on georgian bay titanite records an episode of 977 2 ma partial resetting the degree of which increases with distance into the grenville province here grenvillian deformation where present is manifest as feldspar porphyroclastic fabric with strong se plunging lineations near north bay archean pegmatites in the grenville front zone were similarly deformed at 988 10 ma and strongly rodded ductile amphibolite underwent late melting to produce postlineation tonalite in which new zircon tips grew at 987 2 ma a 991 4 ma cooling age for titanite in this melt is analytically identical to the zircon growth age hence rapid cooling occurred south of chibougamau new zircons grew in high pressure coronite in response to tectonic loading at 995 6 ma and in central labrador melt pods that developed in 1650 granites in response to thrusting record a zircon new growth age of 995 2 ma titanite in the granitic host rock has an analytically identical age of 992 4 ma again indicating rapid cooling this second event is recorded by 28 titanite and zircon analyses for samples up to 225 km apart that record a 1651 5 ma to 988 5 ma two age mixing line grenville resetting at about 1037 19 ma in the grenville front zone on the labrador coast is indicated but major thrusting is pre 1662 ma u pb isotopic results indicate that the grenville front zone is characterized along its length by partially reset u pb systems high pressure assemblages local melting and rapid cooling crustal loading and shearing with lead loss related to mechanically induced recrystallization and local heat that was rapidly terminated by rebound and cooling are required

carbonate clumped isotope evidence for latitudinal seawater temperature gradients and the oxygen isotope composition of early cretaceous seas abstract in this study we investigated early cretaceous valanginian ca 135 million years ago climate from subtropical to boreal palaeolatitudes combined carbonate clumped isotope and oxygen isotope data derived from sub arctic boreal and sub tropical fossil belemnite rostra mollusca cephalopoda provide new palaeotemperature estimates as well as a constraint on the oxygen isotope composition of seawater our belemnite data reveal balmy high latitude marine temperatures ca 22 c and warm sub tropical temperatures ca 31 c supplementing our clumped isotope based temperature estimates with published tex86 data results in a conservative reconstruction of a latitudinal temperature gradient that is reduced compared to modern conditions we find that modelling efforts are close to reproducing tropical temperatures when high pco2 levels are considered warm polar temperatures imply however that data model discrepancies remain early cretaceous seawater oxygen isotope values show a modern profile and are much more positive up to 1 5 smow than typically assumed based on our findings if the positive cretaceous seawater 18o values are not considered carbonate 18o thermometry would underestimate temperatures most acute at middle and tropical latitudes

late cretaceous climate in the canadian arctic multi proxy constraints from devon island abstract arctic climate in the late cretaceous has long been recognized to have been warm and wet relative to the present but quantitative assessments of paleoclimate have been challenging due in part to disagreements between proxies in marine and terrestrial environments this study provides a first multiproxy evaluation of late cretaceous 93 90 ma to 73 72 ma paleoclimate and paleohydrology from devon island in the canadian high arctic modern location 76 17 n 91 12 w late cretaceous location 71 30 n 24 30 w surface temperatures are reconstructed at 12 6 to 20 6 c for the ocean and 11 7 to 16 9 c over land using glycerol dialkyl glycerol tetraether gdgt based proxies measured from marine tex86 and terrestrial samples mbt 5me these proxies are likely skewed toward warm month temperatures based on novel analysis and interpretation of biomarkers in sediment and co occurring marine vertebrate coprolites the hydrogen isotopic composition 2h of precipitation is constrained to have varied from 123 to 82 vsmow using evidence from n alkanes likely derived from higher plants 18o of shelfal marine surface water is constrained to have been between 10 5 to 3 4 using phosphate oxygen isotopes of marine vertebrate teeth and coprolites from these marine salinity is modeled to have varied from 10 psu and 30 psu indicative of periodic freshwater influx these estimates indicate that large marine vertebrates lived and fed at least intermittently in near shore brackish waters finally the arctic was similarly warm in both the late cretaceous and paleocene eocene but the late cretaceous isotopic composition of precipitation at devon island was enriched in the heavy isotope of hydrogen by up to 60 to 70 relative to arctic eocene sites the combination of techniques used here reduces uncertainties related to the application of proxies to an environment without a modern analogue providing novel paleoclimatic constraints on the late cretaceous arctic region

the significance of titanite and apatite u pb ages constraints for the post magmatic thermal hydrothermal evolution of a batholithic complex berens river area northwestern superior province canada abstract titanite apatite and in one case rutile from a suite of twenty seven samples representing the major phases of an extensive and well dated archean plutonic domain of the northwestern superior province have been dated by u pb to determine the temporal progress of thermal and hydrothermal events accompanying and following major plutonism and to assess the isotopic behaviour of these geochronometers most samples contain 1 dark brown titanite with 350 20 ppm u showing shapes and textural relationships indicative of a primary magmatic origin and yielding ages corresponding either to the time of magmatic crystallization or to that of secondary metamorphic or magmatic events known in the area 2 pale titanite with 30 2 ppm u showing textural evidence for a secondary origin by breakdown of biotite hornblende oxide or older titanite and yielding ages that in general post date the major plutonic and metamorphic events in the area 3 apatite containing 30 5 ppm u occasionally up to 150 ppm u showing igneous shapes and textural relationships but yielding post magmatic ages similar to those of coexisting pale titanite 4 rutile in one sample postdating the ages of coexisting titanite and apatite the common coexistence of two noncoeval titanite generations demonstrates that the often invoked mechanism of pb diffusion during slow cooling in this case has no general validity the distribution of primary dark titanite ages however could be explained by late closure to diffusion or alternatively as the result of resetting by the thermal or hydrothermal effects caused by younger plutonic activity the ages of the secondary pale titanites probably reflect crystallization during discrete retrogressive events promoted by moderate heating or enhanced fluid activity the correspondence between pale titanite and apatite ages suggests that the same processes also caused the isotopic resetting of apatite on a regional scale the data pattern permits the identification of domains characterized by differences in the length and intensity of the thermal and hydrothermal processes the most protracted activity is recorded in northern domains of the berens river area whereas the gold mineralized red lake area in the south underwent a very rapid decline of the thermal hydrothermal activity these data also highlight important differences between the red lake and other gold camps of the superior province such as hemlo and val d or where hydrothermal activity locally associated with mineralization occurred as much as 30 80 m y after the major orogenic developments

age and tectonic implications of paleoproterozoic granitoid intrusions within the nain province near nain labrador u pb zircon age determinations from three granitoid intrusions in the nain region formerly assigned to the well known 1 35 1 29 ga mesoproterozoic nain plutonic suite nps indicate that they

middle cretaceous greenhouse hydrologic cycle of north america we present a paleolatitudinal precipitation reconstruction for the greenhouse setting of mid latitude north america based on the oxygen isotopic composition of sphaerosiderites found in middle cretaceous wetland paleosols our reconstructed middle cretaceous d 18 o values of precipitation are 4 less than values from comparable modern low elevation coastal settings free of monsoons the data fit a conceptual model in which the precipitation source for the eastern margin of the cretaceous western interior seaway of north america is an 18 o enriched oceanic coastal jet in this subtropical tropical setting midcretaceous precipitation rates are interpreted to range from 2500 to 4100 mm yr

extremely high sea surface temperatures at low latitudes during the middle cretaceous as revealed by archaeal membrane lipids the middle cretaceous 125 88 ma greenhouse world was characterized by high atmospheric co 2 levels the general absence of polar ice caps and much higher global temperatures than at present both 1 8 o based and model based temperature reconstructions indicate extremely high sea surface temperatures ssts at high latitudes however there are a number of uncertainties with sst reconstructions based on 1 8 o isotope data of foraminifera due to diagenetic overprinting effects and tenuous assumptions with respect to the 1 8 o value of cretaceous seawater the paleoecology of middle cretaceous marine organisms and seawater ph here we applied a novel sst proxy i e text tetraether index of 86 carbon atoms based on the membrane lipids of marine crenarchaeota derived from middle cretaceous sedimentary rocks deposited at low latitudes the text proxy indicates that tropical ssts in the proto north atlantic were at 32 36 c during the early albian and late cenomanian early turonian this finding agrees with sst estimates based on 1 8 o paleothermometry of well preserved foraminifera as well as global circulation model calculations the text proxy indicates cooler ssts 27 32 c for the equatorial pacific during the early aptian which is in agreement with sst estimates based on 1 8 o paleothermometry

modelling equable climates of the late cretaceous can new boundary conditions resolve data model discrepancies late cretaceous maastrichtian climate and vegetation is modelled using the hadcm3l fully coupled atmosphere ocean model and the triffid dynamic vegetation model we investigate data model inconsistencies in the high latitudes and continental interiors by exploring the sensitivity of modelled terrestrial climate to vegetation treatment changing atmospheric pco2 levels and the representation of arctic seaway connections we expand on previous work by using millennial scale gcm runs with dynamic vegetation to allow for improved representations of ocean heat transport and terrestrial boundary conditions incorporating realistic vegetation drives high latitude warming particularly during summer through reductions in surface albedo and induced atmosphere ocean feedbacks resulting regional warming can exceed 10 c as pco2 rises some regions cool as deciduous to evergreen change increases albedo incorporating enhanced arctic connectivity reconfigured ocean heat transport drives widespread terrestrial warming of 3 c and 5 c regionally applying sensitivities in combination significant palaeobotanical data model inconsistencies in the northern high latitudes and continental interiors remain further work is required to resolve climate and vegetation model deficiencies and improve the interpretation and geographic distribution of quantitative climate sensitive geological proxies

paleoclimatic tracers an investigation using an atmospheric general circulation model under ice age conditions 2 water isotopes the linear relationship observed between the water isotopic contents of precipitation and surface air temperatures leads to the use of the water isotopes h218o and hdo in paleoclimatology applied to the measurements of the isotopic content of paleowaters like groundwaters and deep ice cores this relationship is used to infer paleotemperatures however this interpretation of paleo isotopic contents is only valid if the isotope temperature relationship is not affected by climate change to address this problem we have developed a water isotope modeling inside an atmospheric general circulation model agcm and performed simulations of both the present day and last glacial maximum lgm climatic conditions agcms are indeed the only appropriate tools able to account the whole complexity of the atmospheric circulation for the present day climate preliminary results for january were presented by joussaume et al 1984 and are complemented by new simulations performed for both february and august climatic conditions with a higher resolution version of the model model results are well corroborated by observations they also exhibit some effects of the atmospheric circulation on the isotopic fields for the simulated lgm climate the model results compare well with paleoclimatic data of water isotopic contents except for a higher than observed spatial variability the overall patterns of the simulated 18o temperature relationship for the lgm climate are practically unchanged which tends to comfort the use of water isotopes in paleoclimatology however concerning the deuterium excess i e the relationship between oxygen 18 and deuterium the model results are not sufficiently valid to allow a discussion of the use of deuterium excess in paleoclimatology

extrapolation of tectonic boundaries across the labrador shelf u pb geochronology of well samples near saglek fiord a northerly trending boundary between the early archean saglek block and the middle archean hopedale block extends between drill sites which respectively sampled uivak amphibolite gneiss with u pb zircon intercept ages of 3742 12 and 2752 42 ma and migmatitic lister gneiss with concordant ages of for restite and for leucosome titanite ages of ca 2508 ma are common to both rocks a nearby metapsammitic gneiss has detrital zircon and monazite ages of 2681 5 2700 4 ca 2730 and 2750 2 ma representing high grade metamorphism related to the hopedale saglek collision and metamorphic monazite of ca 2560 ma age representing metamorphism of the sediment during reactivation of the saglek hopedale suture two hundred kilometres southeast a gneissic granite records a protolith age of 3170 ma and late proterozoic pb loss near the nain makkovik boundary 1269 4 ma zircons indicate a significant extension of the nain platonic suite south of the makkovik boundary a foliated g

revisiting the equable climate problem during the late cretaceous greenhouse using paleosol carbonate clumped isotope temperatures from the campanian of the western interior basin usa abstract greenhouse climates such as the late cretaceous period provide important reference frames for understanding modern anthropogenic climate change upper cretaceous terrestrial climate proxies have been interpreted as evidence for equable climates with reduced seasonal variations in temperature however climate models have largely failed to reproduce these reconstructions unless parameters such as atmospheric co2 concentrations are set to unreasonable values to help resolve such model proxy disagreements we reconstruct mean annual range in temperature mart for the campanian 75 ma kaiparowits south central utah and two medicine northwest montana formations using warmest mean monthly temperature reconstructions from the clumped isotope composition of paleosol carbonate nodules and reconstructions of local mean annual air temperatures from other methods an evaluation of the applicability of bulk elemental soil geochemistry temperature proxies in these deposits supports the use of previous leaf physiognomy based estimates of mean annual temperature for our mart reconstructions we test the validity of several common assumptions made in reconstructing mart in two novel ways first mart is commonly calculated as twice the difference between local mean annual air temperature and warmest mean monthly temperature and we validate this method by estimating modern mart for a range of environments using climate reanalysis data second we constrain the effect of radiative soil heating on our soil carbonate temperature estimates by showing that for most environments likely to be preserved in the geologic record summer soil temperatures are 9 c larger than previous proxy reconstructions of late cretaceous mart these results add to a growing body of literature showing that terrestrial mart during ancient greenhouse periods was not significantly different from modern seasonal temperature variations finally the similarity in mart between the kaiparowits and two medicine formations suggests that latitudinal changes in mart did not contribute to the faunal provincialism that has been proposed by some paleontologists