structural evolution of archean rocks in the western wawa subprovince minnesota refolding of precleavage nappes during d2 transpression recent mapping in the western wawa subprovince the vermilion district and its westward extensions in minnesota has identified a major northeast trending stratotectonic break informally called the leech lake structural disconformity llsd that separates two contrasting terranes north of the llsd are elongate east northeast trending fault bounded panels of volcanic rocks which are mostly north topping and homoclinal south of the llsd large scale northwest trending folds involve basaltic sequences that are stratigraphically overlain by thick sections of dacitic volcaniclastic and turbiditic rocks however the most prominent outcrop scale deformational features are northeast trending vertical folds and associated axial planar cleavage related to transpression in d2 d1 minor folds and cleavage are rare new field data indicate that the large folds in a predominantly sedimentary part of the southern terrane are early formed d0 d1 and nappe like the precise form of the early folds is largely ob

sr nd isotope composition and clay mineral assemblages in eolian dust from the central philippine sea over the last 600 kyr implications for the transport mechanism of asian dust dust transport to the tropical subtropical northwestern pacific over the past 600 kyr was investigated using radiogenic isotopes 87sr 86sr and end together with the clay mineral composition of eolian dust preserved in a sediment core obtained from the philippine sea 12 30 n 134 60 e these data revealed the influence of two prevailing dust sources namely the asian deserts and nearby volcanic arcs e g the luzon arc with average contributions of around 70 and 30 respectively from each the clay mineral composition of the core resembled dust from the central asian deserts cads e g the taklimakan desert as in the north central pacific but published aerosol data collected near the study site during winter spring have the mineralogical signature of dust originating from the east asian deserts eads these data indicate that the relative contribution of ead dust increases with the northeasterly surface winds associated with the east asian winter monsoon eawm during winter spring but the prevailing westerlies and trade winds that carry dust from the cads is the dominant transport agent in the overall dust budget of the study site the results of this study contradict the prevailing view that direct dust transport by the eawm winds in spring dominates the annual flux of eolian dust in the northwest pacific

the sedimentary expression of oceanic anoxic event 1b in the north atlantic abstract the aptian albian oceanic anoxic event 1b contains the record of severalperturbations in the global carbon cycle and multiple black shale levels particularly in the western tethys the local lithological expression of anoceanic anoxic event depends on palaeogeographical and depositional settingas well as on regional palaeoclimate marine sediments at a particular locationmay therefore be more or less organic rich or not at all and they may consistof different lithologies in most studies however much of the lithologicalvariability associated with oceanic anoxic events is left unaccounted for and thus the exact processes leading to the enrichment of organic matter in thesemarine sediments and their subsequent preservation in the geological recordare unknown this study focuses on the local sedimentary processes behindthe deposition of organic rich sediments at deep sea drilling project site 545and ocean drilling program sites 1049 and 1276 in the north atlantic duringoceanic anoxic event 1b although speci cally dealing with the sedimentsdeposited during this particular event at these localities it is expected that thesame processes were responsible for determining the exact sedimentaryproducts at localities in similar settings as well as during other similar eventsin the mesozoic here it is shown that the deposition of organic richsediments during oceanic anoxic event 1b was a consequence of theenhanced productivity favoured by upwelling and by riverine nutrientinput or aeolian fertilization of the euphotic zone depending ongeographical location slope instability processes resulted in the transfer ofpart of these organic rich sediments from the shelf to deep sea depocentres asmud laden organic rich turbidites especially in the northern north atlantic the so called black shales are much more varied than their name implies the end product of sedimentation during an oceanic anoxic event at aparticular location is commonly the result of several equi nal processes actingon a local scale rather than the direct result of basinal or even globalmechanisms keywords aptian albian kilian event north atlantic oae 1b oceandrilling program oceanic anoxic event paquier event

petrogenesis of intermediate volcanic assemblages from the shebandowan greenstone belt superior province evidence for subduction during the neoarchean abstract research on the petrogenesis of andesites and their implications for geodynamic setting are an important facet to understanding controversial tectonic processes during the archean the genesis of archean intermediate volcanic rocks and their relationship to mantle and crust derived melts can either support subduction dominated tectonic processes or plume crust interactions this study describes the lithogeochemistry and nd isotopic composition of intermediate volcanic assemblages in the shebandowan greenstone belt of the wawa abitibi terrane that were deposited prior to deformation and tectonic assembly of the superior province the intermediate rocks of the shebandowan greenstone belt are unique in that they are voluminous are relatively weakly deformed and are low metamorphic grade and contain significant amounts of magnesian andesites and adakites the major and trace element geochemistry of the intermediate assemblages share many of the geochemical characteristics of modern volcanic and continental arcs these features include enriched th nb and th la ratios steeply dipping rare earth patterns and pronounced negative ti and nb anomalies on primitive mantle normalized diagrams additionally these rocks also contain distinct positive pb and cs anomalies without evidence of major mobility of these elements during secondary processes neodymium isotopic analyses indicate the interaction with older crust and show good correlations with evolved nd isotopic values with other crustal contamination proxies such as th ce and ti sc ratios modeling mixing and assimilation fractional crystallization interactions between plume derived and crustal melts reveal that plume crust interactions cannot explain the compositional array obtained from the intermediate rocks in the shebandowan greenstone belt a compilation of u pb geochronology for the shebandowan greenstone belt reveals that tholeiitic komatiite dominated strata are slightly older than the intermediate dominated strata given that these domains are structurally separated it is very likely that the shebandowan greenstone belt was formed in two different geodynamic settings these different geodynamic settings have important implications for the metallogeny of the belt and explain the relative enrichment of au and ni cu mineralization in the shebandowan greenstone belt relative to other ca 2720 ma assemblages in the wawa abitibi terrane

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

fluctuations of eolian flux and ocean productivity in the mid latitude north pacific during the last 200 kyr abstract in order to understand fluctuations in terrestrial and marine environments a sedimentary core h3571 was investigated from the hess rise located in the mid latitude north pacific under the north westerly wind system the 18 o grain size and grain shape of type 1 quartz suggest that this quartz is of aerosol origin good correlation between al and aerosol quartz in content and mass accumulation rate mar indicates that the alumino silicate minerals in the sediments are mainly transported by wind mar of mineral aerosol maraerosol varies from 156 to 732 mg cm 2 kyr 1 during the last 200 kyr the maraerosol maxima occur in oxygen isotope stage ois 4 to latest ois 5 middle ois 6 moderate maxima occur in early ois 1 2 late ois 3 and middle ois 3 these maxima are ascribed to reduced precipitation during the summer monsoon and to strengthened wind speed during the winter monsoon the mean organic carbon total nitrogen atomic ratio is 7 2 suggesting that the organic matter in the core h3571 is also mainly of marine origin the mar of organic carbon marorganic exhibits two prominent maxima in ois 2 and 4 and relatively high values in middle and late ois 6 enhanced primary productivity is most likely to be responsible for the high burial rate of organic carbon in the sediments carbonate and phosphorus inputs with aerosol into sea surface have played a minor role through dissolution in diminishing pco2 in surface water during glacial times on the other hand the aerosol silica supply to the ocean may have some potential to affect the burial of biogenic silica into sediments the effect of mineral aerosol on the ocean carbon cycle would be greater in the coastal and hemipelagic regions of the western pacific and equatorial atlantic as compared with that in the hess rise regime

rock albedo and monitoring of thermal conditions in respect of weathering some expected and some unexpected results broadly speaking there is at least within geomorphic circles a general acceptance that rocks with low albedos will warm both faster and to higher temperatures than rocks with high albedos reflectivity influencing radiative warming upon this foundation are built notions of weathering in respect of the resulting thermal differences both at the grain scale and at the scale of rock masses here a series of paving bricks painted in 20 per cent reflectivity intervals from black through to white were used to monitor albedo influenced temperatures at a site in northern canada in an attempt to test this premise temperatures were collected for five months for the rock surface and the base of the rock the blocks being set within a mass of local sediment resulting thermal data did indeed show that the dark bricks were warmer than the white but only when their temperatures were equal to or cooler than the air temperature as brick temperature exceeded that of the air so the dark and light bricks moved to parity indeed the white bricks frequently became warmer than the dark it is argued that this negating of the albedo influence on heating is a result of the necessity of the bricks both white and black to convect heat away to the surrounding cooler air the darker brick being hotter initially convects faster than the white as a product of the temperature difference between the two media thus where the bricks become significantly hotter than the air they lose energy to that air and so their respective temperatures become closer the albedo influence being superceded by the requirement to equilibrate with the surrounding air it is argued that this finding will have importance to our understanding of weathering in general and to our perceptions of weathering differences between different lithologies copyright 2005 john wiley sons ltd

salt weathering simulations under hot desert conditions agents of enlightenment or perpetuators of preconceptions because of access difficulties and inhospitable environmental conditions our understanding of rock weathering in hot deserts has been strongly influenced by laboratory simulations however a risk exists that results may come to owe more to experimental design than to actual environmental conditions experienced at the atmosphere rock surface interface this was especially true in early salt weathering simulations that seemingly sought to reinforce the orthodoxy of a physically dominated weathering environment driven by extremely high absolute temperatures and large diurnal temperature ranges however improvements in environmental sensors over the last 20 years have established the complexity of desert climates and the importance of microclimatic controls and allowed considerable refinement of experimental design this overview evaluates the implications of recent simulation studies and presents new information on possible fatigue effects of differential thermal expansion of salts and the salt weathering of test blocks under compressive loading in doing so it demonstrates how physical rock properties change during experimentation the importance of short term surface temperature fluctuations distinctions between the weathering of unconfined debris and larger rock surfaces the importance of moisture and salt applications that replicate their availability in deserts the importance of rock thermal properties in controlling their weathering response in environments dominated by radiative heating and cooling and the overall complexity of weathering regimes

alteration and geochemical patterns in the 3 7 3 8 ga isua greenstone belt west greenland abstract volcanic rocks of the 3 7 3 8 ga isua greenstone belt have undergone heterogeneous poly phase post magmatic alteration resulting in mobilisation of many elements including lree and th in contrast nb ta ti zr y and hree were relatively immobile during alteration processes the degree of element mobility appears to have been controlled by chemical composition primary volcanic structures carbonate and silica enrichment and proximity to ultramafic units and shear zones on the basis of the geochemical characteristics of the least altered samples two distinct associations have been recognised in structurally separated lithotectonic sequences these magmatic associations are a low hfse association tio2 0 20 0 40 wt zr 12 30 ppm nb 0 13 0 80 ppm y 6 14 ppm in the central arc sequence resembling tertiary boninites and a high hfse association tio2 0 50 1 14 wt zr 34 77 ppm nb 1 2 2 7 ppm y 11 28 ppm in the outer and inner arc sequences comparable to phanerozoic island arc basaltic to picritic volcanic rocks these two geochemically distinct sequences were likely to have been juxtaposed as a consequence of phanerozoic style plate tectonic processes operating in the early earth the isua volcanic rocks are characterised by sub chondritic nb ta 10 16 ratios post magmatic alteration can be ruled out as the cause of these low ratios rather these ratios reflect a compositional characteristic of the paleoarchean mantle source s the sub chondritic nb ta ratios may have resulted from either preferential sink of nb into the core as a weakly siderophile element or preferential retention of nb in the subducted oceanic crust during subduction zone petrogenetic processes alternatively the building blocks of the earth were not composed of ci like chondritic material

effects of direct and indirect heating on the validity of rock weathering simulation studies and durability tests rock surface and subsurface temperature responses in samples exposed to direct heating insolation under natural hot desert conditions reveal considerable variability between lithologies related to differences in thermal properties especially albedo and thermal conductivity however when the same samples are heated indirectly by air in an oven based environmental cabinet lithological differences in temperature response disappear and all samples attain temperatures similar to the air temperature within the cabinet rates and patterns of rock decay produced in such environmental cabinets may not therefore reflect those encountered under natural conditions where breakdown is related to micro environmental conditions at the rock air interface and where rock temperature is one of the most important controlling factors in addition to implications for assessment of weathering effectiveness use of only indirect forms of heating affects the determination of comparative rock durability because all rock types are cycled through the same temperature regimes because temperature exerts such a major control on rock breakdown through its control on physical and chemical weathering processes all significant factors influencing it must be included in the design of weathering simulations and durability tests

daytime rock surface temperature variability and its implications for mechanical rock weathering tenerife canary islands summary summer and winter rock surface temperature measurements are presented from three sites along an altitudinal gradient significant between and within site variability is recognised related to insolation cloud cover and air temperature differences maritime influences and time of year the variability argues against the use of a single rock temperature regime to characterise hot desertic environments in for example weathering simulation studies superimposed upon diurnal patterns of heating and cooling are numerous short 3 15 minutes and medium term 1 2 hours fluctuations related to wind speed and cloud cover variations rates of surface temperature change are very high during these fluctuations 3 c minute and it is proposed that they may enhance the operation of a number of mechanical rock weathering mechanisms

laboratory simulation of the wick effect in salt weathering of rock the wick effect is the upward migration of saline solutions into rocks and their subsequent crystallization lower carboniferous sandstone blocks of rectangular shape have been subjected to this process in the laboratory using a range of salt types a range of salt concentrations and various mixtures of salts some treatments produced severe disintegration notably sodium carbonate and a mixture of sodium carbonate with magnesium sulphate whereas other salts including sodium chloride and gypsum were much less effective the debris produced by this experimental salt weathering included appreciable quantities of silt sized material which were analysed with a laser granulometer such material could provide a source for desert loess

geodynamic setting crustal architecture and vms metallogeny of ca 2720 ma greenstone belt assemblages of the northern wawa subprovince superior province the greenstone belts along the northern margin of the wawa subprovince of the superior province vermilion shebandowan winston lake manitouwadge formed at ca 2720 ma and have been interpreted to be representative of a rifted arc to back arc tectonic setting despite a common inferred tectonic setting and broad similarities these greenstone belts have a significantly different metallogeny as evidenced by different endowments in volcanogenic massive sulphide vms magmatic sulphide and orogenic gold deposits in this paper we examine differences in geodynamic setting and crustal architecture as they pertain to the metallogeny of each greenstone belt by characterizing the regional scale trace element and isotopic nd and pb geochemistry of each belt the trace element geochemistry of the vermilion greenstone belt vgb shows evidence for a transition from arc like to back arc mafic rocks in the soudan belt to plume driven rifted arcs in the ultramafic bearing newton belt the shebandowan greenstone

pericontinental crustal growth of the southwestern abitibi subprovince canada u pb hf and nd isotope evidence the abitibi subprovince is widely regarded as a classic example of neoarchean continental crust formed in an ensimatic setting however sialic crust as old as 2 93 ga occurs in the adjacent wawa subprovince and the two subprovinces are thought to have formed a contiguous block since the initiation of abitibi magmatic activity at 2 75 ga a detailed geochemical u pb geochronological and nd hf isotope study of plutonic and volcanic rocks from the southwestern abitibi provides evidence for the involvement of older crust during magma genesis near the abitibi wawa boundary kapuskasing structural zone inherited zircons dated at ca 2 85 ga occur both in 2747 ma tonalite and 2700 ma granodiorite of the rice lake batholith part of the larger kenogamissi plutonic complex igneous zircons from this batholith display large intrasample variations in 176 hf 177 hf which we attribute to mixing of magmas derived from mantle juvenile crust and older crustal sources nd isotope data for felsic volcanic and plutonic rocks in this region indicate a dominantly juvenile source however two older felsic volcanic units 2739 and 2729 ma show nd isotope evidence of significant crustal contamination post tectonic plutonic units that were emplaced at 2676 and 2662 ma also contain inherited zircons but none are older than 2 76 ga in contrast tonalitic units dated at 2744 and 2715 ma from the round lake plutonic complex located 150 km east of the kapuskasing structural zone lack zircon inheritance and display less intrasample hf isotope variability in zircons our data suggest that the influence of older sialic crust during abitibi volcanic and plutonic activity is restricted both in space and time similar evidence for an older crustal influence occurs elsewhere in the southwestern abitibi near the kapuskasing structural zone the data collectively suggest that an approximately 75 km wide belt of abitibi crust adjacent to this structure was underlain by older wawa crust from 2 75 ga onward this crustal geometry is consistent with development of the abitibi sub province at the edge of a wawa protocraton perhaps as the result of rifting of this older continental block

a review of the superior province of the canadian shield a product of archean accretion abstract the superior province consists of northern and southern high grade gneiss subprovinces and a central region of alternating granite greenstone and metasedimentary belts subprovinces are commonly fault bounded and display contrasting lithological assemblages metamorphic and structural styles geophysical characteristics and ages they are comparable to phanerozoic suspect terranes the middle and late archean rocks of the superior province are of mantle and juvenile crustal origin with little evidence of inheritance of components older than ca 3 1 ga high grade gneiss subprovinces are mainly deeper level equivalents of the supracrustal rich belts but one minnesota river valley is part of an older ca 3 6 ga terrane that was juxtaposed late in the tectonic history granite greenstone terranes are characterized by low grade volcano sedimentary sequences tholeiitic komatiitic submarine lava plain tholeiitic calc alkalic submarine to subaerial central complexes early platform type quartz arenite stromatolitic carbonate late timiskaming type shoshonitic alkalic volcanic fluvial sediment that range in age from ca 3 0 ga to 2 7 ga the volcanics represent oceanic island arc and continental arc volcanism the quartz arenite carbonate sequences deposition on relatively stable early formed ca 3 0 ga crust and the timiskaming type sequences deposition in pull apart basins developed along strike slip faults late archean ca 2 75 2 70 ga greenstone sequences occur throughout the superior province middle archean ca 3 0 2 8 ga sequences are common in northern and central superior province rare or absent in the south volcanism was accompanied by mafic to trondhjemitic plutonism the metasedimentary belts consist of variably metamorphosed volcanogenic turbidites with detrital zircons ranging in age from ca 3 0 ga to 2 7 ga the metasediments were deposited after major volcanism and probably represent accretionary prisms late archean orogenesis accompanied and followed by calc alkalic plutonism youngs southward from about 2 73 2 72 ga to 2 70 2 68 ga it involved large scale north south compression and dextral transpression and displays thin to thick skinned transitions the contemporaneity of events along the lengths of the belts and their southward younging coupled with the evidence of major compression are consistent with subduction driven oblique accretion of oceanic and continental volcanic arcs accretionary sedimentary wedges older microcontinental fragments etc in a convergent margin setting analogous to parts of the pacific rim differences eg abundance of komatiites and tonalitic plutonic suites are attributable to a hotter archean mantle

weathering of superficial limestone debris in a hot desert environment abstract weathering of superficial limestone debris is described from stone pavements on the hamada de meski in southeast morocco the dominant features are due to surface and subsurface solution mechanical weathering and aeolian action have only a limited effect microfeatures produced by solution include solution facetting microrills solution pits case hardening micropitting or vesicular weathering and possibly surface crazing such microforms are the most likely representatives of a truly arid karst

tectonic affinity of nisutlin and anvil assemblage strata from the teslin tectonic zone northern canadian cordillera constraints from neodymium isotope and geochemical evidence we present geochemical and isotopic data for nisutlin assemblage metasedimentary rocks and anvil assemblage greenstones from the teslin tectonic zone of the northern canadian cordillera this study aims to establish the tectonic setting of formation for the sedimentary and basaltic protoliths of these highly deformed and metamorphosed rocks and thereby place constraints on the origin of these enigmatic rocks for which differing tectonic models have been proposed for the nisutlin assemblage metasedimentary rocks the geochemical and isotopic data show that two widely different source regions contributed detritus to the original sediments one source region was felsic upper crustal material with nd isotopic compositions compatible with ultimate derivation from the north american continent depleted mantle model age tdm 2 5 2 8 ga the second source region is deduced to be chemically primitive crust basaltic andesitic with a short crustal residence history 0 9 ga for the anvil assemblage greenstones immobile trace element abundances are dissimilar to within plate oceanic arc and normal mid ocean ridge basalts and similar to calc alkaline basalts in active continental margin settings we interpret the paleosetting for the nisutlin assemblage to be at the outermost margin of the ancestral north american continent in an area which received detrital input from the distal north american craton in the early paleozoic however this area also received detritus from a chemically and isotopically juvenile magmatic arc source a source type not known from paleozoic metasedimentary rocks from the miogeoclinal sequence on the basis of similar nd isotopic relationships recorded elsewhere in deformed paleozoic rocks of the orogen we infer that these geochemical signals reflect tectonic processes of regional extent the trace element geochemistry of the anvil assemblage greenstones does not support a correclation with known paleozoic greenstones of the slide mountain terrane which some tectonic models have advocated

depositional setting and deformation of massive sulfide deposits iron formation and associated alteration in the manitouwadge greenstone belt superior province ontario the base metal deposits of the manitouwadge greenstone belt provide a classic example of the difficulties encountered in petrogenetic studies of mineralization in complex metamorphosed and polydeformed terranes the belt comprises a mafic to felsic volcanic succession in which the felsic rocks are interleaved with iron formation and massive sulfide deposits a synvolcanic trondhjemite was a magma source for felsic volcanism and heat source for hydrothermal activity the belt was affected by four phases of ductile deformation including d 1 faulting that dissected the area of known economic mineralization into two tectonic blocks and repeated part of the mineralized sequence the regional map pattern is determined by d 3 folds including the manitouwadge synform based on cu zn pb proportions style of mineralization and relationships to iron formation and alteration zones the orebodies can be divided into three main types 1 cu rich stockwork disseminated orebodies which are the lowest in the stratigraphy hosted by the orthoamphibole garnet cordierite gneiss and in the geco mine area by sillimanite muscovite quartz schist surrounding the main orebody 2 massive and semimassive zn cu pb orebodies on iron formation horizons at middle stratigraphic levels these include the two largest orebodies of the bolt and 3 massive and semimassive zn pb cu orebodies interpreted as highest in the stratigraphy which are hosted by iron formation type 1 orebodies represent subsurface conduits for mineralizing fluids that supplied deposits higher in the stratigraphy type 2 orebodies are sea floor precipitates or near sea floor replacement deposits formed during the peak of hydrothermal activity and base metal deposition type 3 orebodies formed during waning hydrothermal activity all rocks have been metamorphosed to upper amphibolite facies including two zones of synvolcanic hydrothermal alteration orthoamphibole garnet cordierite gneiss forms a strata bound sheet of regional extent mantling synvolcanic trondhjemite in the stratigraphic footwall structural hanging wall to mineral deposits the second alteration unit sillimanite muscovite quartz schist occurs in close proximity to massive sulfide deposits mostly in the stratigraphic hanging wall structural footwall the precursors of altered units were mafic and felsic volcanic reeks despite the unusual extent and concordance of alteration zones at manitouwadge geochemical trends from least to intensely altered are similar to those recorded in alteration pipes in the abitibi camp extensive orthoamphibole bearing gneiss at manitouwadge may be partly a function of high metamorphic grade allowing orthoamphibole hornblende coexistence in relatively calcic bulk rock compositions bulk rock compositions that produced orthoamphibole bearing assemblages at manitouwadge might at a lower metamorphic grade be considered incipient alteration the strata bound character of alteration suggests that hydrothermal activity was focused on aquifer horizons consisting of permeable poorly consolidated volcaniclastic deposits

flux and grain size variation of eolian dust as a proxy tool for the paleo position of the intertropical convergence zone in the northeast pacific abstract a 328 cm long piston core kodos 02 01 02 collected from the northeast equatorial pacific at 16 12 n 125 59 w was investigated for eolian mass fluxes and grain sizes to test these proxies as a tool for the paleo position of the intertropical convergence zone itcz the eolian mass fluxes of the lower interval below 250 cm 15 5 7 6 ma are very uniform at 5 1 mg cm2 103 yr while those of the upper interval above 250 cm from 7 6 ma are over 2 times higher than the lower interval at 12 1 mg cm2 103 yr the median grain size of the eolian dusts in the lower interval increases from 8 4 to 8 0 downward while that of the upper interval varies in a narrow range from 8 8 to 8 6 the determined values compare well in magnitude to those of central pacific sediments for the upper interval and equatorial and southeast pacific sediments for the lower interval this result suggests a possibility that the study site had been under the influence of southeast trade winds at its earlier depositional period due to the northerly position of the itcz and subsequently of the northeast trade winds for a later period when the upper sediments were deposited this interpretation is consistent with a mineralogical and geochemical study published elsewhere that assigned the provenance of the study core dust to central south america for the lower interval and to asia for the upper interval this study suggests that the distinct differences in eolian mass flux and grain size observed across the itcz can be used to trace the paleo latitude of the itcz

north american margin origin of quesnel terrane strata in the southern canadian cordillera inferences from geochemical and nd isotopic characteristics of triassic metasedimentary rocks new geochemical and nd isotopic data from triassic ca 220 ma clastic metasedimentary rocks assigned to the quesnel terrane quesnellia in southeastern british columbia show that detritus was derived from both primitive and evolved sources twenty four samples yield end 2 2 0 values between 9 1 and 5 6 independent of sample location these samples have eu anomalies between 0 6 and 1 0 la n yb n ratios between 3 8 and 11 4 la sc ratios ranging from 0 38 to 4 76 and th sc ratios between 0 09 and 1 62 this range of isotopic and geochemical values overlaps that of samples from upper paleozoic to mesozoic rocks of the north american miogeocline and upper triassic nicola group volcanic rocks of the quesnel terrane the range in nd isotopic and geochemical values supports the interpretation that detritus was derived from both continental north america evolved cratonic source and a volcanic arc primitive source developing on the continental margin these data do not support previous interpretations of the quesnel terrane as an intraoceanic arc the inferred depositional link between north america and the quesnel arc in triassic time is ca 40 ma older than the hypothesized obduction of the quesnel terrane onto the north american continental margin and when combined with existing geological information strongly supports a pericratonic nonexotic origin for the quesnel terrane in southeastern british columbia

neogene history of the south pacific tradewinds evidence for hemispherical asymmetry of atmospheric circulation rea d k and bloomstme m k 1986 neogene history of the south pacific tradewmds evidence for hemlsphermal asymmetry of atmospherm circulation palaeogeogr palaeochmatol palaeoecol 55 55 64 eohan dust grains extracted from southeast pacific pelagic sediments provide a neogene record of southern hemisphere atmospherm processes the mass accumulation rate of dust has been low and generally constant at 1 4 mg cm 2 103 y since the late ohgocene eohan grains ze data show an increase from 8 20 3 40 t m older sediments to 7 20 6 80 t m younger materml this shift occurred about 10 5 m y ago and reflects a s gmfmant increase in the intensity of atmospheric circulation then there s no obwous response to the onset of northern hemisphere glacmtmn 2 5 m y ago m these eohan records from the south pacific compamson with existing lnformatmn from the northern hemisphere suggests that the southern hemisphere has had more intense atmospheric circulation throughout the neogene and that this asymmetry reached its greatest extent between 10 5 and 2 5 ma

magmatic affinity of modern and ancient subalkaline volcanic rocks determined from trace element discriminant diagrams when dealing with ancient subalkaline volcanic rocks the alkali total iron magnesium afm diagram is of limited use in assigning a tholeiitic versus calc alkaline affinity because these eleme

extracting the silicate mineral fraction from ancient carbonate assessing the geologic record of dust abstract the climatic influence of eolian dust particles 63 m is well recognized in the cenozoic earth system but less so for the pre cenozoic in ancient carbonate rocks that formed isolated from fluvio deltaic influx the silicate mineral fraction can in some cases represent atmospheric dust here we present a methodology for sequential extraction of carbonate organic matter pyrite and iron oxide from pre cenozoic carbonate strata to isolate the eolian fraction and illustrate the application to stratigraphic sequences from a late paleozoic carbonate buildup and ramp setting

nd isotope systematics of 2 7 ga adakites magnesian andesites and arc basalts superior province evidence for shallow crustal recycling at archean subduction zones abstract an association of adakite magnesian andesite ma and nb enriched basalt neb volcanic flows which erupted within normal intra oceanic arc tholeiitic to calc alkaline basalts has recently been documented in 2 7 ga wawa greenstone belts large positive initial nd values 1 95 to 2 45 of the adakites signify that their basaltic precursors with a short crustal residence were derived from a long term depleted mantle source it is likely that the adakites represent the melts of subducted late archean oceanic crust initial nd values in the ma 0 14 to 1 68 nb enriched basalts and andesites neba 1 11 to 2 05 and normal intra oceanic arc tholeiitic to calc alkaline basalts and andesites 1 44 to 2 44 overlap with but extend to lower values than the adakites large tightly clustered nd values of the adakites together with th ce and ce yb systematics of the arc basalts that rule out sediment melting place the enriched source in the sub arc mantle accordingly isotopic data for the ma neba and normal arc basalts can be explained by melting of an isotopically heterogeneous sub arc mantle that had been variably enriched by recycling of continental material into the shallow mantle in late archean subduction zones up to 200 ma prior to the 2 7 ga arc if the late archean wawa adakites ma and basalts were generated by similar geodynamic processes as their counterparts in cenozoic arcs involving subduction of young and or hot ocean lithosphere then it is likely that late archean oceanic crust and arc crust were also created and destroyed by modern plate tectonic like geodynamic processes this study suggests that crustal recycling through subduction zone processes played an important role for the generation of heterogeneity in the archean upper mantle in addition the results of this study indicate that the nd isotope compositions of archean arc and plume derived volcanic rocks are not very distinct whereas phanerozoic plumes and intra oceanic arcs tend to have different nd isotopic compositions

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

structural history of the manitouwadge greenstone belt and its volcanogenic cu zn massive sulphide deposits wawa subprovince south central superior province structural analysis of the manitouwadge greenstone belt integrated with detailed mapping and geochronological and petrographic studies reveals a complex early deformation history that significant

trace element geochemistry and petrogenesis of felsic volcanic rocks associated with volcanogenic massive cu zn pb sulfide deposits volcanogenic massive cu zn pb sulfide vms deposits occur primarily in subaqueous rift related environments e g oceanic fore arc arc back arc continental margin or continental are hosted primarily by bimodal mafic felsic volcanic successions and are typically associated with felsic volcanic rocks with specific geochemical characteristics fi alkalic dacites and rhyodacites despite being abundant in the rock record are typically barren some fii calc alkalic rhyodacites and rhyolites host vms deposits but most are barren fiii tholeiitic and fiv depleted rhyolites and high silica rhyolites are much less abundant in the rock record but commonly host vms deposits regardless of age and fiii rhyolites appear to host the largest deposits most petrogenetic models proposed for the formation of fii and fiii fiv felsic volcanic rocks link felsic magma genesis to fractionation processes in high level magma chambers now represented by associated subvolcanic intrusions where the magma is also interpreted to have supplied the heat and or metals required to generate and sustain the vms forming convective hydrothermal system however the relatively constant compositions of fii and fiii fiv felsic volcanic rocks within individual areas the high eruptive temperatures at or above liquidus of fiii rhyolites and the bimodality of vms hosting volcanic successions indicate that fractional crystallization within subvolcanic intrusions could not have generated or significantly modified the compositions of fii and fiii fiv magmas this coupled with detailed geological geochemical and geochronological studies indicates that many of these subvolcanic intrusions were emplaced in multiple phases and that the later most voluminous phases often cut ore associated hydrothermally altered rocks a reassessment of the physical conditions responsible for producing the geochemistry of ore associated fii and fiii fiv felsic volcanic rocks and a review of the compositions of felsic volcanic rocks associated with vms deposits that range in age from mesoarchean to cenozoic provide important constraints on models for vms associated felsic volcanic rocks and their relationship to mineralization the compositions of felsic volcanic rocks may be explained by low to moderate degrees of partial melting of mafic sources at a range of depths within rift environments where the mineralogy and composition of the source regions modes and degrees of partial melting pressure and temperature of melting and to a lesser extent subsequent fractionation processes account for the compositional variations from fi through fii to fiii fiv long lived enhanced heat flow and structural permeability of rift environments that allows partial melting to form some fii rhyolites at midcrustal levels 10 15 km and fiii fiv rhyolites at shallow crustal levels 10 km both within the zone of brittle fracture permeability are essential to sustain the high temperature convective hydrothermal systems that are required to form large vms deposits and camps rift environments contain long lived thermal magmatic and structural corridors that focus magma ascent heat flow high temperature convective hydrothermal systems and emplacement of subvolcanic intrusions that are favorable environments for the formation of vms deposits and fii and fiii fiv felsic volcanic rocks

extensive boulder erosion resulting from a range fire on the type pinedale moraines fremont lake wyoming abstract in july 1988 the flatfish range fire burned over the type pinedale moraines at fremont lake wyoming and caused extensive exfoliation of exposed boulder surfaces the mass of exfoliated material from 130 of 1030 boulders investigated was measured and recorded with information concerning factors that could influence the extent of fire induced exfoliation the range in thickness of material removed from 98 randomly selected boulders within the burn area averaged over the entire exposed boulder surface area is 6 1 to

thermal effects of ridge subduction and its implications for the origin of granitic batholith and paired metamorphic belts distribution of temperature and h2o in subduction zones during the course of ridge subduction are investigated numerically in order to constrain the timing and extent of metamorphism and melting within the subducting oceanic crust and the overlying arc crust the model assumes that after ridge subduction the two plates move together without creating a slab window the results suggest that before ridge subduction temperature along the subducting slab starts to rise when the slab is younger than 10 myr a drastic thermal impact occurs associated with subduction of the ridge crest followed by a diffusion stage of the impact the temperature elevation is limited within a few tens of kilometers from the slab crust interface and within 30 myr after ridge subduction although it will last for a longer period if a slab window is formed during the peak stage slab melting occurs and generates a significant amount of granitic melt mainly at depths shallower than 40 km at p t conditions corresponding to low p t metamorphism high p t metamorphism with a significant water flux is also achieved near the interface when a subducting slab is less than 10 myr old before ridge subduction or 20 myr old after ridge subduction consequently the low and high p t metamorphism accompanied by a significant amount of granitic melt is associated closely in time and space with the ridge subduction this model can explain the observed characteristics of the granitic batholith and the paired metamorphic belts through these processes arcs and continents can grow within the short period of time associated with the episodic subduction of ridges

trace element geochemistry of ore associated and barren felsic metavolcanic rocks in the superior province canada reply archaean felsic metavolcanic rocks in the superior province of the canadian shield may be divided into three major groups on the basis of trace element abundances and ratios 1 fi felsic metavolcanic rocks are dacites and rhyodacites characterized by steep ree patterns with weakly negative to moderately positive eu anomalies high zr y low abundances of high field strength elements e g hree y zr hf and high abundances of sr examples occur in the bowman subgroup and skead group in the abitibi belt in the kakagi lake lake of the woods shoal lake and sturgeon lake areas of the wabigoon belt and in the confederation lake area of the uchi belt none of these horizons as known hosts base metal sulphide deposits 2 fii felsic metavolcanic rocks are rhyodacites and rhyolites characterized by gently sloping ree patterns with variable eu anomalies moderate zr y and intermediate abundances of hfs elements and sr examples occur in the misema subgroup of the abitibi belt in the wabigoon lake a

rock temperatures as an indicator of weathering processes affecting rock art to aid rock art conservation rock temperatures have been monitored at different depths and at low 30 min and high 1 min acquisition rates in a painted rock shelter in the ukhahlamba drakensberg park south africa preliminary data for winter cold and dry show that in that season cryoclasty is unlikely to occur rare subzero thermal events and probable reduced moisture availability and thermal shocks are improbable highest measured t t 2 c min 1 high amplitude about 30 c rock temperature cycles accompanied by reversals of the thermal gradient have been observed to occur almost daily and hint at the possibility of thermal stress fatigue copyright 2006 john wiley sons ltd

contour scaling of a sandstone by salt weathering under simulated hot desert conditions a laboratory study has been used to investigate relationships between salts and contour scaling a weathering feature commonly observed on rock surfaces in salt rich environments surface disaggregation and essentially surface parallel cracks were produced in sandstone blocks using 10 per cent solutions of sodium sulphate and magnesium sulphate applied daily to single exposed surfaces for sixty days a control block soaked once in saturated magnesium sulphate and subsequently wetted daily with distilled water showed extensive surface disaggregation but no cracking both surface disaggregation and subsurface cracking were associated with relative concentrations of microcrystalline salt a tentative model of contour scaling is proposed which involves linking together potential cracks by salt induced fracturing of intervening crack stopping grains further control blocks treated respectively with 10 per cent and saturated sodium chloride showed no evidence of subsurface cracking and only limited surface disaggregation of the saturated block

quaternary fluctuations in the northern hemisphere trade winds and westerlies the mass accumulation rate and grain size of the total colian component isolated from pelagic sediment in two north pacific cores piston core kk75 02 under the prevailing westerlies and deep sea drilling project site 503 beneath the trade winds have been used to evaluate changes in the intensity of atmospheric circulation and source area aridity over the past 700 000 yr the eolian grain size a direct indicator of wind intensity fluctuates at periodicities similar to those calculated for the earth s orbital parameters of precession obliquity and eccentricity both sites display greater variability in wind intensity prior to 250 000 yr ago eolian accumulation rates an indicator of source area aridity fluctuate at periodicities similar to those of the glacial interglacial cycles lower eolian accumulation rates during colder glacial times most likely reflect increased glacial age humidity at central asian and central american source areas

the terminology and the concepts of gypsum rich soils abstract many terms in earth sciences and their underlying ideas have been developed in temperate humid countries both geological and climatic reasons cause gypsum rich soils to occur in dry lands soil science has paid little attention to gypseous soils and this limited knowledge is reflected in the direct loan of customary terms of soil science that can lead to misconceptions on the composition and behaviour of soils with large proportions of gypsum elements for discussion on the use of sundry terms about soils containing gypsum are presented here and some of their implicit assumptions discussed some generic terms are examined as well as several expressions used by organizations devoted to soil survey and classification the transformations occurring in gypseous soils are discussed in particular the effects from exposure the refinements herein proposed aim to help understand the role of gypsum in local and global earth surface processes

lead nd and sr isotope records of pelagic dust source indication versus the effects of dust extraction procedures and authigenic mineral growth abstract eolian silicate dust of the 328 cm long piston core kodos 02 01 02 from the northeast equatorial pacific was analyzed for chemical compositions and nd sr and pb isotopic ratios to evaluate their use as hemispheric dust source discriminator and to examine the potential influence of authigenic smectite on these source signals neodymium and sr isotope ratios of the core determine a change from southern to northern hemisphere dust deposition at about 7 6 ma samples deposited between 15 5 and 7 6 ma resemble southeast equatorial pacific surface and down core dust values while younger samples correspond to signatures typical for dust derived from central asia the 15 5 to 7 6 ma lower interval of the core is smecite rich however previously proposed chemical fingerprints for authigenic smectite such as positive eu anomalies or high fe al ratios are not observed in the kodos samples the up to 40 smectite in the kodos core dust are thus interpreted to represent largely detrital smectite and no evidence is found for authigenic modification of nd sr isotopic or element ratio source signals of the dust records lead isotope results of the core lack prominent down core variation with changing source regimes as reported above a compilation of pacific pb isotope dust records reveals that pb isotope ratios vary as a function of silicate dust extraction procedures the step of removing biogenic silica thereby appears critical use of naoh appears most effective while minimally attacking eolian silicate material it is concluded that of the pb isotopic dust records published so far only a few are useful for dust source identification however once the silicate dust extraction procedure is further optimized for retrieving the pristine silicate dust pb isotopic composition specific source signatures should become well resolvable

late cenozoic changes in atmospheric circulation deduced from north pacific eolian sediments abstract isolation and analysis of the eolian component of late cenozoic pelagic sediments from the north pacific provides direct information concerning changes in atmospheric circulation a 50 increase in intensity of both the prevailing westerlies and the tradewinds coincides with increasing pole to equator temperature gradients resulting from the onset of northern hemisphere glaciation at the same time the mass flux of dust from continents to the north pacific increased by a factor of 4 5 apparently reflecting significantly increased continental aridity associated with the late cenozoic glacial ages

komatiite flooding of a rifted archean rhyolitic arc complex geochemical signature and tectonic significance of the stoughton roquemaure group abitibi greenstone belt canada the 0 2 2 km thick archean stoughton roquemaure group srg in the northern volcanic zone of the abitibi greenstone belt quebec canada is composed of tholeiitic basalt komatiitic basalt and komatiite the mafic and ultramafic rocks are pillowed brecciated and massive columnar jointed flows the srg conformably overlies the 2730 ma hunter mine group a volcanic complex dominated by calc alkaline felsic rocks the tholeiitic basalts of the srg resemble morb the komatiitic basalts and komatiites have positive nd values overlapping those of the tholeiitic basalts komatiitic basalts with low al2o3 tio2 ratios 10 and fractionated heavy ree patterns are similar to al depleted komatiites in contrast the komatiites have high al2o3 tio2 20 unfractionated heavy ree patterns and resemble al undepleted munro type komatiites the al depleted komatiitic basalts occur at the base of the srg whereas the al undepleted komatiites are prevalent higher up in the stratigraphy the association of calcalka

cretaceous climate a comparison of atmospheric simulations with the geologic record abstract atmospheric simulations using realistic cretaceous geography 100 million years ago suggest that paleography is an important factor governing the nature of the circulation the simulated cretaceous atmospheric circulations are markedly different both from the present day atmospheric circulation and from the classical hypotheses of a weaker circulation and poleward displacement of circulation features e g the subtropical high therefore they pose specific questions which can be tested against the geologic record aspects of the cretaceous simulations are verified in comparisons with the geologic record the simulations serve to guide areas of future paleoclimatic research and to formulate better the nature of the problem of warm equable climates

surface temperature differences between minerals in crystalline rocks implications for granular disaggregation of granites through thermal fatigue thermal expansion differences between minerals within rocks under insolation have previously been assumed to drive breakdown by means of granular disaggregation however there have been no definitive demonstrations of the efficacy of this weathering mechanism different surface temperatures between minerals should magnify thermal expansion differences and thus subject adjacent minerals to repeated stresses that might cause breakdown through fatigue failure this work confirms the existence of surface temperature differences between minerals in granitic rocks under simulated short term temperature fluctuations so as to discriminate their potential for initiating granular disaggregation the influence of colour as a surrogate for albedo and crystal size as a function of thermal mass are specifically identified because of their ease of quantification four rock types with a range of these properties were examined and subjected to repeated short term temperature cycles by radiative heating and cooling under laboratory conditions results show that while albedo is the main control for overall and individual maximum temperatures crystal size is the main factor controlling higher temperature differences between minerals thus stones with large differences of mineral sizes can undergo magnified stresses due to thermal expansion differences

the early development of an archean submarine caldera complex with emphasis on the mattabi ash flow tuff and its relationship to the mattabi massive sulfide deposit the south sturgeon lake area of northwestern ontario is underlain by an archean submarine caldera complex which is host to six massive sulfide deposits the complex is approximately 30 km in strike length and is partly filled by mesobreccias subaqueous debris flow deposits and other epiclastic rocks as well as five major ash flow tuff units the most voluminous of these the mattabi ash flow tuff is up to 800 m in thickness and can be traced for more than 15 km across the caldera complex based on flow morphology and composition the mattabi ash flow tuff is divisible into two distinct units a bedded quartz crystal and pumice rich unit 150 650 m thick and a massive to poorly bedded ash unit 20 150 m thick the bedded unit is host to the mattabi massive sulfide deposit as well as numerous other massive sulfide occurrences in addition this unit exhibits a pronounced stratigraphic and geochemical cyclicity individual beds flow units can be subdivided into basal quartz and pumice rich lower sections which are overlain by bedded ash tops thicknesses of individual beds vary from 14 to 155 m each bed also exhibits a pronounced zonation of trace elements with high concentrations of zr y and nb at and or near the base gradually decreasing upward into the ash tops the overlying massive ash unit contains no known massive sulfide mineralization and lacks any pronounced geochemical zoning the bedded nature and geochemical zonation of individual flow units can be explained by periodic eruptions from a zoned or layered recharged siliceous magma chamber the difference in flow morphology between the bedded unit and the overlying massive ash flow tuff most likely reflects the deeper submarine nature of the eruptive vents associated with the bedded deposits the periodic and subaqueous nature of the mattabi eruptions is indicated by the presence of exhalites and massive sulfide lenses between flow units the ore lenses which comprise the mattabi deposit formed between eruptive events from high temperature fluids whose origin may be related to processes within the magma chamber

rock temperatures from southeast morocco and their significance for experimental rock weathering studies surface and subsurface rock temperature measurements are presented from three rock types chalk granite and sandstone from a hot desert climate the temperature regimes undergone by each rock type and the differences between them can be best explained by reference to the values of albedo and thermal conductivity for the rocks the significance of thermal properties in influencing rock temperatures suggests that these properties should be taken into account when attempting to simulate desert weathering and also when trying to explain variations in the weathering behavior of different rock types

neoarchean trans subprovince sediment transport in southwestern superior province sedimentological geochemical and geochronological evidence at 2700 ma volcanism spawned by northward directed subduction under wabigoon subprovince canadian shield fed sediment into an adjacent fore arc basin trench system volcanically active island arcs to the south wawa subprovince were transported northward during this interval and at 2690 ma collided with the accretionary complex quetico subprovince metamorphosed sedimentary units intercalated with the ocean floor and island arc volcanic rocks of northern wawa subprovince provided the opportunity to amass data useful in extending the paleogeographic interpretation of the area this study examines the mckellar harbour formation a several kilometre thick assemblage of graded metasandstone beds outcropping to the north of lake superior its sedimentology geochemistry and detrital u pb zircon geochronology were investigated in conjunction with the same attributes of possible correlative units in the region similarities between the mckellar harbour formation and sedimentary rocks composing the fore

application of high field strength elements to discriminate tectonic settings in vms environments high field strength element ratios in felsic volcanic rocks reflect the tectonomagmatic evolution of a region th ta th hf ta hf th yb and ta yb ratios collectively help to define the tectonic environment of volcanism separating oceanic arcs active continental margins and within plate volcanic zones on the basis of the above empirical observations the tectonic environments of selected archean and post archean volcanogenic massive sulfide deposits were reexamined published data sets plotted on discriminant diagrams represent twelve volcanogenic massive sulfide vms deposits from two distinct tectonic environments the volcanic rocks of the kuroko deposits japan san nicolas mexico and bathurst new brunswick canada plot within the active continental margin field on all diagrams whereas volcanic rocks from archean deposits of the superior province canada kidd creek kamiskotia geco winston lake mattabi lyon lake noranda selbaie and south bay plot in the within plate volcanic zone field the discriminant diagrams demonstrate that although the chemical character of rhyolites has not changed significantly since the archean the range of geotectonic setting of vms deposits probably has it is suggested that archean deposits most likely formed in an ensimatic rift environment whereas post archean deposits formed in subduction related rift zones of arc environments subduction related rhyolites of vms deposits are variably enriched in th and the light rare earth elements with respect to ta nb and the heavy rare earth elements

a record of glacial aridity and milankovitch scale fluctuations in atmospheric dust from the pennsylvanian tropics abstract atmospheric dust is an important climatic agent as well as a valuable climatic archive this study documents systematic variations in a single upper pennsylvanian shallow water carbonate buildup of the midland basin west texas that was isolated from fluvio deltaic input and consists almost entirely of carbonate bounded by sequence boundaries thin 0 02 to 1 m intervals of dark pyritic siliciclastic mudrock with subtle pedogenic features occur commonly at the sequence boundaries and are interpreted as loessite deposited during lowstands primarily on the basis of paleogeographic isolation of the buildup the silicate mineral fraction smf extracted from the underlying carbonate which includes quartz clay and trace feldspars and heavy minerals varies in concentration weight from 0 015 to 6 69 in the carbonate this smf contains both fine grained detrital and authigenic silica interpreted to be eolian on the basis of geochemical petrographic and grain size characteristics as well as paleogeography hence the smf is considered a proxy for atmospheric dust whole rock geochemistry suggests that the dust was at least partly derived from uplifts of the ancestral rocky mountains with a possible minor contribution from active volcanic centers located to the present day south and southwest the estimated mean accumulation rate mar of dust in highstand carbonate facies full interglacial relative to carbonate facies that formed during relative fall in sea level suggest that dust flux increased 4 to 10 times accompanying the transition to glacial conditions mars in the siliciclastic mudrock which accumulated at lowstand full glacial to incipient transgression suggest glacial phase increases in dust flux of nearly 400 to 4000 times relative to full interglacial conditions spectral analyses of dust abundance through the study section show variations consistent with milankovitch forcing

geological evolution of the manitouwadge greenstone belt and wawa quetico subprovince boundary superior province ontario constrained by u pb zircon dates of supracrustal and plutonic rocks fifty million years of archean evolution is recorded in the manitouwadge greenstone belt and the wawa quetico boundary region from ca 2720 ma volcanism and subvolcanic plutonism associated with m

mineral deposits of canada a synthesis of major deposit types district metallogeny the evolution of geological provinces and exploration methods wayne d goodfellow editor 1 068 pp geological association of canada mineral deposits division special publication no 5 2007 hardcover isbn 13 978 1 897095 24 9 price members cdn 60 00 non members cdn 80 00 following in the footsteps of other landmark reviews of major ore producing countries such as australia hughes 1990 solomon and groves 1994 and south africa anhaeusser and maske 1986 this substantial 1 000 pages monograph is a great achievement that should be in every geologic research library in the world in many ways it sets a new standard most notably in that all figures and photographs are in color and that the entire volume is available in electronic form both as an included dvd and mostly on the gac website it is common in such compendia to have a spectacular cover photo or frontispiece to catch the reader s attention and this book does not disappoint the frontispiece photo is of a 61 8 kg sample from the dome mine timmins ontario and is stated to contain 20 wt percent gold at today s prices the gold alone would be worth 1 5 million dollars

shebandowan greenstone belt western superior province u pb ages tectonic implications and correlations the shebandowan greenstone belt of the western wawa subprovince consists of successions of volcanic and sedimentary rocks impinging onto the metasedimentary quetico subprovince to the north and cored by a batholithic complex to the south u pb geochronology using mainly zircon and titanite demonstrates a relatively rapid accretion of the greenstone belt in the late archean the oldest ages were obtained for 2750 ma tonalitic gneiss and sporadic 2830 2750 ma detrital or xenocrystic zircons a major phase of greenstone belt construction at 2720 ma formed ultramafic to felsic volcanic rocks and peridotitic gabbroic and anorthositic bodies probably in an extensional arc backarc setting these units are laterally correlative with volcanogenic massive sulfide bearing assemblages in the central wawa subprovince and probably with similar successions in northern minnesota the second major stage of felsic volcanism and plutonism at about 2695 ma was associated with d 1 compression causing thrusting imbrication and sedimentation this was succeeded by the deposition of an unconformable sequence of calc alkalic to alkalic volcanic and sedimentary rocks and emplacement of tonalitic to syenitic plutons at about 2690 ma transpressive deformation d 2 constrained between 2685 and 2680 ma caused the development of locally penetrative structures and deposition of clastic sedimentary packages the emplacement of plutons at 2683 2680 ma concluded the evolution of the greenstone belt titanite and rutile yield ages in the same range as zircon showing that the greenstone belt was situated at high crustal levels by 2680 ma and escaped the younger and intense deformational metamorphic events recorded in greenstone belts farther east in the central wawa subprovince as well as in the immediately adjacent migmatitic quetico subprovince to the north

influence of surface heterogeneities of building granite on its thermal response and its potential for the generation of thermoclasty surface properties especially albedo and aspect are widely accepted as strong influences on the surface thermal response of building stone to insolation however the influence that adjacent areas of stone with very different surface properties may have on the thermal response of a patch of stonework and the ways in which spatial variation in thermal characteristics might enhance stone decay has received relatively little attention this paper examines the differential thermal response of granite used in construction that results from the presence of dark coloured micro granular enclaves within a leucocratic host surface temperatures and temperature differences between enclaves exhibiting mico spalling enclaves with no spalling and the surrounding stone were measured for different aspects and seasons on a 20th century building in madrid these data were used to calculate a number of indices related to short term temperature cycling and temperature gradients that have the theoretical capability of generating irreversible deformation of the stone these indices suggest that micro spalling of enclaves compared to a lack of similar decay on the host rock is related to their differential thermal response to insolation most importantly the lower albedo and thermal conductivity values of the enclaves however these factors are not sufficient on their own to trigger spalling and breakdown was only observed where enclaves also experienced repeated short term surface temperature cycling caused by for example temporary shading by adjacent vegetation these rapid temperature reversals are identified as a key contributory factor to the thermally driven decay observed on some of the enclaves

sedimentary indicators of atmospheric activity in the northern hemisphere during the cenozoic abstract the concentrations and accumulation rates of eolian phases and the mineralogy of sediments from a north pacific core ll44 gpc3 have been used to evaluate changes in eolian sedimentation and atmospheric activity during the cenozoic the quartz content and clay mineralogy of the sediments reflect changing source areas for eolian material whereas the accumulation rates of eolian phases reflect climatic variation and wind intensity eolian sedimentation decreased from 70 to 50 m y ago at the site as it moved north out of the equatorial pacific where it was supplied with eolian debris from north america and africa low rates of eolian sediment accumulation 50 to 25 m y ago reflect the temperate humid environment of the early tertiary and the lack of vigorous atmospheric circulation at that time from 25 to 7 m y ago eolian accumulation increased as the site moved into the influence of the westerlies from 7 to 3 m y ago there was a more rapid increase in accumulation of eolian material at the site which was not accompanied by changes in mineralogy or quartz content and was therefore related to climatic change and more vigorous atmospheric circulation about 2 5 m y ago a dramatic increase in eolian sedimentation accompanied the onset of dry northern hemisphere glaciation

volcanic reconstruction of paleoproterozoic arc volcanoes the hidden and louis formations flin flon manitoba canadathis is a companion paper to dewolfe y m gibson h l and piercey s j 2009 petrogenesis of the 1 9 ga mafic hanging wall sequence to the flin flon callinan and triple 7 massive sulphide deposits flin flon manitoba canada canadian journal of earth sciences 46 this issue the hanging wall to the flin flon callinan and triple 7 volcanogenic massive sulphide deposits of the flin flon district is composed of the hidden and louis formations the contact between these formations is marked by mafic tuff that represents a hiatus in effusive volcanism the formations form a composite volcanic edifice that was erupted and grew within a large volcanic tectonic subsidence structure hosting the deposits that developed within a rifted arc environment the formations are evidence of resurgent effusive volcanism and subsidence following a hiatus in volcanism marked by ore formation since they consist of dominantly basaltic flows sills and volcaniclastic rocks with subordinate basaltic andesite and rhyodacitic flows and volcaniclastic rocks the hidden formation is interpreted to represent a small shield volcano and the louis formation a separate shield volcano that developed on its flank both the hidden and louis volcanic edifices were constructed by continuous low volume eruptions of pillow lava a gradual change from a dominantly extensional environment during the formation of the footwall flin flon formation to a progressively more dominant convergent environment during the emplacement of the hanging wall suggests that the hidden and louis formations are unlikely to host significant volcanogenic massive sulphide type mineralization however synvolcanic structures in the formations define structural corridors that project downwards into the footwall where they encompass massive sulphide mineralization indicating their control on ore formation longevity and reactivation as magma and fluid pathways during the growth of the hidden and louis volcanoes

nb depleted andesites from the pacific antarctic rise as analogs for early continental crust sampling of the pacific antarctic rise close to the foundation hotspot in the south pacific reveals that silicic lavas erupt together with basalts on a 130 km long part of this mid oceanic ridge representing the most extensive occurrence of andesites on the submarine spreading system most of these tholeiitic andesites and dacites have negative nb and ta anomalies a signature that has so far been attributed only to subduction related magmas and the continental crust the silicic lavas formed by fractional crystallization from basalts and assimilation of melts from hydrothermally altered amphibolite in the oceanic crust the presence of andesites with negative nb and ta anomalies on the pacific antarctic rise implies that such magmas are not restricted to subduction zones but can form at a plume influenced mid oceanic ridge the andesites and dacites from the pacific antarctic rise may represent analogs to some precambrian volcanic rocks and early continental crust

new u pb geochronology from timiskaming type assemblages in the shebandowan and vermilion greenstone belts wawa subprovince superior craton implications for the neoarchean development of the southwestern superior province abstract timiskaming type assemblages in the wawa abitibi terrane of the superior craton and other archean cratons worldwide are important because of their spatial and temporal association with world class orogenic gold mineralization especially in the kirkland lake area of ontario these mainly locally derived sedimentary assemblages are deposited in transpressional pull apart basins that developed during the final stages of terrane accretion and are commonly associated with calc alkalic to alkalic volcanic and plutonic rocks the shebandowan and vermilion greenstone belts sgb vgb in the wawa subprovince have significantly less economic base and precious metal mineralization than the greenstone belts of the abitibi subprovince and the timing of deformation and magmatism in the sgb and vgb is less well constrained this study presents new u pb geochronology from the sgb and vgb that demonstrating that the sedimentary and volcanic rocks of the lake vermilion formation in the vgb are coeval with similar rocks in the sgb and their interpreted depositional environment are consistent with these units being timiskaming type assemblages analyses of magmatic zircons in a dacitic tuff breccia from the gafvert lake sequence the volcanic member of the lake vermilion formation provided a high precision u pb age of 2689 7 0 8 ma using thermal ionization mass spectrometry detrital zircon geochronology using la icp ms confirms that the source of the detritus in the lake vermilion formation was locally derived from the gafvert lake metavolcanic lithofacies a similar temporal pattern was observed in many of the timiskaming type sedimentary rocks that were sampled in the sgb the locally derived alluvial fluvial to shallow marine depositional environment in long narrow basins with rapid lateral facies changes described in the sgb and vgb are consistent with deposition in structurally controlled pull apart basins however one sample from the sgb had detrital zircons with ages that were more akin to the age range found to the north in the wabigoon subprovince which is suggestive of trans terrane transport of detritus in a foreland type basin geochemically the timiskaming type volcanic rocks in the vgb and sgb are less enriched in incompatible elements and are comparatively less alkalic than the volcanic rocks in the timiskaming assemblage of kirkland lake this may indicate that the structures that formed the basins within the sgb and vgb in the wawa were not as deeply penetrating as those in the abitibi which may explain the paucity of economic gold mineralization associated with the former the timiskaming type deposits of the northern wawa abitibi terrane are 20 ma older than the timiskaming assemblage in the abitibi subprovince and co depositional with the flysch like deposits of the porcupine assemblage in the southern part of that terrane

u pb dating of minerals in alteration halos of superior province massive sulfide deposits syngenesis versus metamorphism u pb geochronology of igneous zircon from rhyolitic host rocks to the archean kidd creek geco and winston lake massive sulfide deposits in the superior province of ontario shows that volcanism which accompanied mineralization occupied a narrow time span 2717 2 ma 2720 2 ma and 2723 2 ma respectively precise ages of hydrothermal monazite allanite and rutile from alteration zones surrounding the above deposits indicate that these minerals crystallized 40 70 million years after volcanism monazite from kidd creek mine is 2659 3 ma old in agreement with spatially associated 2664 25 ma old rutile monazite from a biotite schist at geoco mine gives a similar age of 2661 1 ma however monazite from a sericite schist which hosts the ore at geco mine is 2675 2 ma old abraded large monazite grains from three units in the winston lake deposit are coeval with biotite crystallization and record an age of 2677 2 ma approximately the same as monazite in the sericite schist at geco data points from allanite fractions from both the winston lake and geco deposits fall on a pb pb isochron that gives an age of 2672 5 ma rutile from winston lake gives a younger age of 2651 6 2 ma and may date retrograde alteration of biotite to chlorite the ca 2676 ma age of monazite from winston lake and in the sericite schist at geco mine probably dates a regional metamorphic event that affected most of the southern superior province the ca 2660 ma old monazite in the biotite schist at geco mine and in the chlorite sericite alteration at kidd creek may date later k metasomatism caused by metamorphically derived fluids that were focussed along old fault structures such fluids were also responsible for local sulfide remobilization monazite and rutile are spatially associated with chlorite and sericite alterations at kidd creek their young ages indicate that these originally syngenetic mineral assemblages may have been significantly affected by regional metamorphism formation of monazite at all three deposits studied was a result of significant ree remobilization during metamorphism the discrete character of syn metamorphic hydrothermal activity in different units of the same deposit as well as its synchroneity among different widely separated deposits requires a mechanism for episodic injection of heat and fluid into the crust on a regional scale these activities are broadly coeval with and probably related to plutonism within adjacent metasedimentary subprovinces and middle to lower crustal metamorphism in the superior province

late cretaceous history of eolian deposition in the mid pacific mountains central north pacific ocean rea d k and janecek t r 1981 late cretaceous history of eolian deposition in the mid pacific mountains central north pacific ocean palaeogeogr palaeoclimatol palaeoecol 36 55 67 eolian dust preserved in deep sea sediment can provide a direct historical record of global atmospheric circulation data from a reasonably complete upper cretaceous section of pelagic sediments recovered at dsdp site 463 in the central north pacific provides a good record of eolian activity during the time period between about 112 hnd 66 m y ago we have isolated the eolian component from these sediments determined its mass accumulation rate and combined these data with the mineralogy of the inorganic fraction determined by others to construct a record of eolian deposition volcanic input is significant during aptian albian and maastrichtian times otherwise continentally derived minerals dominate mass accumulation rates of the continental eolian component range from over 500 mg cm 103yr during the late albian to a low of 5 mg cm2 10 yr during coniacian time for comparison the upper miocene to pleistocene rate averages about 20 mg cm2 103yr the temporal pattern of late cretaceous eolian accumulation of site 463 generally matches known changes in sea level suggesting that source availability is the dominant control of eolian sedimentation during that time

thermal properties as controls on rock surface temperature maxima and possible implications for rock weathering four rock types basalt sandstone granite and chalk are examined with respect to the maximum surface temperatures which they experience when subjected to similar conditions of exposure rock temperature measurements are reported for an urban environment and for two experimental situations in which an infrared lamp is used to simulate heating under cold and hot conditions differences in rock temperatures are discussed with reference to thermal rock properties albedo specific heat capacity and thermal conductivity some natural situations are suggested in which thermal rock properties could conceivably play a role in determining the extent to which rocks would be affected by particular weathering processes

depositional gaps in abitibi greenstone belt stratigraphy a key to exploration for syngenetic mineralization models of greenstone belt development are crucial for exploration allochthonous models predict belts to be a collage of unrelated fragments whereas autochthonous models allow for prediction of syngenetic mineral deposits within specific stratigraphic intervals superior province greenstone belts consist of mainly volcanic units unconformably overlain by largely sedimentary timiskaming style assemblages and field and geochronological data indicate that the abitibi greenstone belt developed autochthonously we describe major revisions to stratigraphy of the abitibi greenstone belt and the implications of an autochthonous development of the volcanic stratigraphy for exploration for syngenetic mineralization the abitibi greenstone belt is subdivided into seven discrete volcanic stratigraphic episodes on the basis of groupings of numerous u pb zircon ages of pre 2750 2750 to 2735 2734 to 2724 2723 to 2720 2719 to 2711 2710 to 2704 and 2704 to 2695 ma we present revised lithotectonic and or stratigraphic nomenclature using these time intervals including 1 isotopic inheritance in younger episodes which indicates that the older episodes 2750 2735 and 2734 2724 ma had greater extent than is presently seen 2 dikes feeding younger volcanic episodes 2706 ma cutting older volcanic units 2734 2724 ma and 3 2710 to 2704 ma mafic to ultramafic sills intruding the 2719 to 2711 ma episode changes to the nomenclature include the identification of pre 2750 ma volcanic episode supracrustal fragments in the northern and southern abitibi greenstone belt and subdivision of the 2719 to 2711 ma 2710 to 2704 ma and 2704 to 2695 ma episodes into lower and upper parts we present the results of this lithostratigraphic subdivision as the first geochronologically constrained stratigraphic and or lithotectonic map of the abitibi greenstone belt many of the volcanic episodes are intercalated with and capped by a relatively thin sedimentary interface zone dominated by chemical sedimentary rocks stratigraphic and geochronological analysis of these zones indicates discontinuous deposition with localized gaps of 2 to 27 m y between volcanic episodes the zones consist of up to 200 m of iron formation chert breccia heterolithic debris flows of volcanic provenance sandstone and or argillite and conglomerate modeling of the time required for deposition of the volcanic units based on rates of magma production in modern arc and plume environments is on the order of 103 to 104 years whereas the time interval between basalt rhyolite cycles is 106 years the sedimentary interface zones are therefore interpreted as condensed sections zones with very low rates of sedimentation in a basinal setting or zones with negligible rates of sedimentation marked by silicification of existing rock types the sedimentary interface zones are therefore considered submarine correlative conformities disconformities or unconformities separating the equivalent of group level stratigraphic and lithotectonic units the unconformity bounded stratigraphic model provides a new regional to deposit scale interpretive model for use in exploration for syngenetic mineralization

petrogenesis of the 1 9 ga mafic hanging wall sequence to the flin flon callinan and triple 7 massive sulphide deposits flin flon manitoba canada a detailed study of the geochemical and isotopic characteristics of the volcanic rocks of the hidden and louis formations which make up the hanging wall to the volcanogenic massive sulphide deposits at flin flon manitoba was carried out on a stratigraphically controlled set of samples the stratigraphy consists of the lowermost dominantly basaltic hidden formation and the overlying dominantly basaltic louis formation of importance petrogenetically is the 1920 unit a basaltic andesite with nb thmn 0 54 0 62 end 1 9ga 3 6 5 9 ehf 1 9ga 8 5 9 6 and 204pb 206pb 23 9 the basaltic flows that dominate the hidden formation have nb thmn 0 16 0 29 end 1 9ga 1 7 4 4 ehf 1 9ga 7 0 11 8 and 204pb 206pb 16 9 18 6 the carlisle lake basaltic andesite top of hidden formation is characterized by nb thmn 0 16 0 14 and 204pb 206pb 21 4 the rhyodacitic tower member bottom of louis formation has nb thmn 0 23 end1 9ga 4 6 ehf1 9ga 9 3 and 204pb 206pb 22 2 the

sandstone weathering a century of research and innovation abstract a review of sandstone weathering research particularly in the past 100 years reveals a trajectory of enquiry from early description and classification of features to development of process based explanations to decreasing scales of investigation and a disparity between understanding of process es and explanations of the genesis of sandstone weathering features developments in expositions on mesoscale weathering features on sandstone surfaces are discussed demonstrating a range of approaches to weathering phenomena field based and laboratory based that must be linked to provide an explanation of observed features on a landform scale throughout the twentieth century a thematic chronology highlights certain trends in research description of forms often in arid and semi arid environments single process form models an emphasis on experimentation difficulties in measuring weathering rates and a persistent emphasis on physical causes of breakdown a new research agenda is promoted in which biodeterioration and chemical processes gain parity a holistic approach based on conceptual modeling of weathering systems gains prominence and scale issues are addressed more rigorously

an unusual sink for rare elements the rhyolite basalt contact of the archean winston lake volcanogenic massive sulfide deposit superior province canada

movement of the intertropical convergence zone during the mid pleistocene transition and the response of atmospheric and surface ocean circulations in the central equatorial pacific this paper investigates the causes of a brief but prominent cooling episode 1 1 0 8 ma that occurred in the equatorial upwelling region of the atlantic and pacific during the mid pleistocene transition mpt using temporal changes in dust provenance regional hydrology and surface productivity recorded in a deep sea sediment core from the central equatorial pacific the 87sr 86sr and nd values of the inorganic silicate fraction indicate deposition of dust from australia and central south america before 0 8 ma but a gradual increase in asian dust deposition after 0 8 ma the change in dust provenance was accompanied by an increased dust flux and a decrease in surface productivity and salinity these changes can be explained by the southward movement of the intertropical convergence zone itcz and north equatorial counter current necc and the direct influence of these features on the site after 0 8 ma our results together with previously published atlantic data suggest the northward position of the itcz between 1 1 and 0 9 ma and the southward position thereafter the meridional movement of the itcz is in phase with the cooling and warming trend in upwelling regions in the equatorial pacific and atlantic which suggests strengthening of southeast trades relative to its northern counterpart between 1 1 and 0 9 ma as a plausible cause of this brief cooling event the southward movement of the itcz from 0 9 to 0 8 ma indicates more significant cooling in the northern hemisphere nh than in the southern hemisphere which is supportive of the interpretation that the nh ice sheet expanded significantly and stabilized after 0 9 ma

neoarchean paleoweathering of tonalite and metabasalt implications for reconstructions of 2 69ga early terrestrial ecosystems and paleoatmospheric chemistry abstract field and laboratory investigations of a 2690 83 ma 207pb 206pb age of saganaga tonalite unconformity exposed in outcrop in northeastern minnesota usa reveal evidence for development of a deep paleoweathering profile with geochemical biosignatures consistent with the presence of microbial communities and weakly oxygenated conditions weathering profiles are characterized by a 5 50 m thick regolith that consists of saprolitized saganaga tonalite and paulson lake succession basaltic metavolcanic rocks retaining rock structure which is cross cut by a major unconformity surface marking development of a successor basin infilled with alluvial deposits the regolith and unconformity are overlain by thick conglomerate deposits that contain both intrabasinal saprock as well as extrabasinal detritus thin section microscopy and electron microprobe analyses reveal extensive hydrolysis and sericitization of feldspars exfoliation and chloritization of biotite and weathering of fe mg silicates and cu fe sulfides weathering of fe ti oxides was relatively less intense than for other minerals and evidence was found for precipitation of fe oxides geochemical analyses of the tonalite assuming immobile tio2 during weathering ti j show depletion of sio2 al2o3 na2o cao mgo and mno and to a lesser degree of k2o relative to least weathered parent materials significant fe was lost from the tonalite a paleoatmospheric pco2 of 10 50 times pal is estimated based on geochemical mass balance of the tonalite profile and assuming a formation time of 50 500 kyr interpretations of metabasalt paleoweathering are complicated by additions of sediment to the profile and extensive diagenetic carbonate dolomite overprinting patterns of release of p and fe and retention of y and cu in tonalite are consistent with recent laboratory experiments of granite weathering and with the presence of acidic conditions in the presence of organic ligands produced for example by a primitive microbial community during weathering cu metal in the profile may document lower po2 than present day at the surface comparison with previous studies of weathered tonalite and basalt denison 2 45 2 22 ga in ontario canada reveal general similarities in paleoweathering with our study as well as important differences related to lower paleoatmospheric po2 and terrestrial biosignature for the older minnesota profile a falling water table in the alpine lake locality is presumed to have promoted formation of this gossan like deep weathering system that extends to 50 m depth

shifts in oceanic and atmospheric boundaries in the tasman sea southwest pacific during the late pleistocene evidence from organic carbon and lithogenic fluxes abstract the fluctuation in primary production and mineral dust accumulation was estimated to better understand marine and terrestrial environments in the tasman sea southwest pacific during the late pleistocene maxima in primary production were observed during late oxygen isotope stage ois 2 middle ois 4 and late ois 6 for core ngc 97 while minimum values were observed in ois 5 on the other hand primary production was low and relatively uniform in cores ngc 100 and 99 during the last 180 kyr these results suggest that the tasman front existed between ngc 99 30 s and ngc 97 35 s during the last 180 kyr and migrated northward by a few degree 2 3 latitude in ois 2 and 4 the mass accumulation rates mars of mineral aerosol mar aerosol estimated from the al concentration increased southward during each ois excluding ois 2 in cores ngc 100 and 99 the mar aerosol was more enhanced during glacials than interglacials in cores ngc 100 and 97 while ngc 99 showed no definite fluctuation these results suggest small northward shifts 2 3 latitude of the high pressure subtropical ridge dividing the tropical easterly circulation from the mid latitude westerlies took place during glacial times these results demonstrate that the boundary between subtropical and temperate features in both ocean and atmosphere consistently migrated by a few degrees between glacials and interglacials in addition profiles of mar of organic carbon biogenic opal and primary productivity were quite similar for cores ngc 97 and s2612 32 19 84 n 157 51 00 e which shows that the boreal and austral transition zones between subtropical and subarctic waters migrated almost synchronously along the latitudinal transect around 160 e during the last 150 kyr kawahata et al j oceanogr 55 1999 521 532 therefore boreal and austral mid latitudes could have probably experienced similar fluctuations in the oceanic and atmospheric environments

a mid archaean island arc complex in the eastern akia terrane godthabsfjord southern west greenland a relict oceanic island arc complex in the eastern akia terrane godthabsfjord southern west greenland constitutes a magmatic and geotectonic link between c 3 05 3 0 ga tonalitic orthogneiss and enclaves of older supracrustal amphibolite the relict arc forms isoclinally folded panels of volcaniclastic meta andesite with major and trace element island arc signatures intercalated with volcano sedimentary schist tholeiitic amphibolite and opx rich cumulate rocks a zircon u pb age of 3071 1 ma obtained from a volcano sedimentary schist is marginally older than the main orthogneisses and is the first depositional age reported from a supracrustal rock within akia terrane granite sheets were emplaced at c 3005 2980 ma synkinematically with the isoclinal folding and were followed by peak metamorphism at 2990 2970 ma with substantial recrystallization of volcanic zircon and mobility of large ion lithophile elements the identification of the arc complex provides new insight into mid archaean continental crustal accretion in west greenland and substantiates previous ideas that the orthogneisses are products of slab melting in convergent plate tectonic settings the presence of the arc complex also implies that archaean high grade orthogneiss amphibolite associations may not represent plate tectonic environments distinct from granite greenstone associations but expose deeper sections of the same convergent systems

evolution of the southern abitibi greenstone belt based on u pb geochronology autochthonous volcanic construction followed by plutonism regional deformation and sedimentation abstract new mapping and u pb zircon geochronological results in the southern abitibi greenstone belt sagb support an autochthonous regional stratigraphy comprised of nine supracrustal assemblages rather than the collage of allochthonous terranes proposed in recent publications based on lithological and geochronological criteria these supracrustal assemblages also encompass the swayze shining tree and montcalm greenstone belts indicating that despite separation by large granitic intrusions they are in fact part of one extensive greenstone belt in conjunction with the mapping the geochronological results support coherent upward facing stratigraphic sections with about 20 of the samples containing inherited zircons with ages similar to those found in underlying assemblages the seven oldest assemblages represent semi continuous volcanism from 2750 to 2697 ma the volcanism is compositionally diverse ranging from komatiite and tholeiitic basalt to calc alkaline mafic to felsic lavas intimate intermingling of the different magma clans occurs throughout much of the stratigraphic section regional fault control on the distribution of the volcanic assemblages provides evidence for early dip slip movement associated with volcanic extension dating back to at least 2725 ma the two youngest assemblages are dominantly sedimentary and were unconformably deposited on the volcanic assemblages in close proximity to regional faults the earlier sedimentary assemblage consists of turbidites and minor iron formation deposited from 2696 to 2692 ma and the youngest one of subaerial conglomerates fluvial sandstones and alkalic to shoshonitic volcanic rocks ranging in age from 2687 to 2675 ma the sedimentary assemblages are broadly contemporaneous with the emplacement of syntectonic granitic plutons regional folding and reactivated movement on the regional faults probably related to accretion of the abitibi to the superior province craton autochthonous repetition of different geodynamic environments over the 50 million years of volcanic activity with five dominantly tholeiitic komatiitic assemblages and two dominantly calc alkaline assemblages as well as the extensive intermingling of these different magma clans in a number of the assemblages appears to be unique to the archean it suggests complex large scale and long lived interaction between mantle plumes and subduction zone magmas the nd isotope data indicate a derivation of the diverse volcanic magmas from homogeneously depleted sources with end 2 5 0 5 demonstrating a lack of contamination by ancient enriched components

two hourly surface change on supra tidal rock marengo victoria australia a traversing micro erosion meter was used to measure rock surface micro topography over 40 cm2 on a supra tidal cliff face from early morning to late evening in late spring from 06 00 hours to 22 00 hours the relative heights of 188 coordinates were obtained using the meter at 2 hour intervals resulting in a data set of 1607 readings monitoring shows that rock surfaces are dynamic entities with significant rise and fall relative to the first measurement at shorter timescales than previously reported the maximum positive rise between readings was 0 261 mm and lowering was 0 126 mm the pattern of change did not relate as expected to environmental variables such as temperature or insolation rather the surface showed greater surface change in the early morning and late afternoon it is hypothesized that this pattern relates to the expansion and contraction of lichen thalli as moisture is absorbed during higher humidity in the morning and late afternoon the implications of these results for weathering studies are considered copyright 2006 john wiley sons ltd

rare earth element mobility in alteration pipes below massive cuzn sulfide deposits abstract a convincing demonstration of trace element mobility should satisfy two criteria 1 the range of trace element concentrations in the rock before and after alteration must be known with confidence and 2 the absolute abundances and the ratios of the mobile trace elements should vary between altered and unaltered rocks these criteria have been applied to the host felsic volcanics and alteration pipes associated with several canadian massive cu zn sulfide deposits although there is no evidence of rare earth element ree mobility in the pervasive low grade alteration envelopes adjacent to the deposits the light and middle ree lree and mree plus y have been systematically mobilized relative to the heavy ree hree and other trace elements in the alteration pipes beneath the ore zones there is evidence of minor lree and mree depletion in the most altered rocks at the south bay mine uchi lake and of significant lree depletion in the alteration pipe beneath the mattabi mine sturgeon lake however the strongest mobility is found at the kidd creek mine where the lree were leached from the rocks in the footwall stringer zone and redeposited in a metasomatic chlorite zone directly beneath the massive ore horizon and the mree and y were preferentially lost from the system producing distinctive chondrite normalized ree patterns with tb yb n ratios less than unity eu2 was found to be more mobile than the trivalent ree especially at kidd creek where there is a marked increase in the magnitude of the eu anomaly in the most altered samples high field strength elements such as u th hf and zr have not decoupled and apparently remained relatively immobile during all but the most intense alteration i e kidd creek preliminary data suggest that the degree of ree mobility increases with the size of the deposit thus ree mobility is a potentially useful method of distinguishing between small and large massive sulfide deposits at an early stage in exploration however this hypothesis requires further testing

geodynamic reconstruction of the winston lake greenstone belt and vms deposits new trace element geochemistry and u pb geochronology the ca 2720 ma winston lake greenstone belt of the wawa abitibi terrane superior province is located on the northern margin of the wawa subprovince and has important regional tectonostratigraphic implications for the development of the neoarchean superior province the metallogenic importance of the belt is evident from the presence of the winston lake pick lake and zenith volcanogenic massive sulfide vms deposits however the chemostratigraphic evolution has not been fully examined at the greenstone belt scale nor have the vms deposits been examined from the perspective of the belt scale petrogenesis and volcanic reconstruction this study 1 reviews the geology and vms mineralization in the winston lake greenstone belt and 2 reconstructs its geodynamic setting and its magmatic and metallogenetic history using new geological trace element and nd isotope data constrained by new u pb geochronology the belt is subdivided into two main lithotectonic assemblages the winston lake assemblage composed of tholeiitic to calc alkalic bimodal volcanic lithofacies and the big duck lake assemblage composed of alkalic to tholeiitic mafic flows and sills the contact between the winston lake and big duck lake assemblages is intruded by the differentiated zenith gabbro which hosts the 0 16 mt zenith vms orebody as a series of xenoliths the variably altered felsic lithofacies of the winston lake assemblage host the 3 1 mt winston lake main and 1 3 mt pick lake zn rich vms deposits the felsic volcanic lithofacies of the winston lake assemblage are fiii type rhyolites and have a bimodal distribution of zr ti indicating two distinct magmas formed by different temperatures of partial melting mafic lithofacies of the winston lake assemblage are typically calc alkalic to transitional between calc alkalic and tholeiitic in composition they have arc to back arc trace element contents with distinctive negative nb and ti anomalies enrichment in the light rare earth elements lree and higher th nb ratios than the mafic rocks from the big duck lake assemblage mafic strata from the big duck lake assemblage have trace element characteristics similar to mature back arc tholeiitic basalts and oib like or oceanic plateau alkalic basalts with high nb th and ti v ratios the chemostratigraphy of the winston lake greenstone belt is consistent with a geodynamic model where arc rifting is followed by back arc development nd isotope data indicate that strata from the winston lake and big duck lake assemblages are juvenile and show no evidence of contamination by significantly older crust therefore crustal contamination signatures in the mafic flows from the winston lake assemblage must have formed by contamination from crust that is of similar age and supports a comagmatic relationship between the mafic and felsic strata the mafic flows of the big duck lake assemblage represent a mature back arc setting with evidence for enriched plume generated basalts in the upper mafic unit the winston vms deposit formed during the early rifting of the arc and the timing is tightly constrained by the hydrothermally altered 2721 2 0 9 ma vms hosting felsic strata and younger postmineralization 2719 4 ma zenith gabbro the zn dominated vms mineralization suggests that temperature of the hydrothermal fluid during discharge was relatively cool 300 c and did not maintain sufficiently high temperatures to precipitate significant amounts of copper relative to zinc this is likely due to adiabatic cooling of the fluid because of a low pressure 0 5 kb sea floor environment and or permeable volcaniclastic strata a u pb age of emplacement of 2692 1 0 7 ma from the syndeformation quartz feldspar porphyry in the big duck lake assemblage indicate it is comagmatic with syndeformation magmatic events typical of other greenstone belts along the northern margin of the wawa abitibi terrane this event is interpreted to represent the timing of terrane accretion of the wawa abitibi terrane to the superior province

back arc basin basalt systematics the mariana east scotia lau and manus back arc basins babs have spreading rates that vary from slow 100 mm yr and extension axes located from 10 to 400 km behind their island arcs axial lava compositions from these babs indicate melting of mid ocean ridge basalt morb like sources in proportion to the amount added of previously depleted water rich arc like components the arc like end members are characterized by low na ti and fe and by high h2o and ba la the morb like end members have the opposite traits comparisons between basins show that the least hydrous compositions follow global morb systematics and an inverse correlation between na8 and fe8 this is interpreted as a positive correlation between the average degree and pressure of mantle melting that reflects regional variations in mantle potential temperatures lau manus hotter than mariana scotia this interpretation accords with numerical model predictions that faster subduction induced advection will maintain a hotter mantle wedge the primary compositional trends within each bab a positive correlation between fe8 na8 and ti8 and their inverse correlation with h2o 8 and ba la are controlled by variations in water content melt extraction and enrichments imposed by slab and mantle wedge processes systematic axial depth as a proxy for crustal production variations with distance from the island arc indicate that compositional controls on melting dominate over spreading rate hydrous fluxing enhances decompression melting allowing depleted mantle sources just behind the island arc to melt extensively producing shallow spreading axes flow of enriched mantle components around the ends of slabs may augment this process in transform bounded back arcs such as the east scotia basin the re circulation by mantle wedge corner flow to the spreading axes of mantle previously depleted by both arc and spreading melt extraction can explain the greater depths and thinner crust of the east lau spreading center manus southern rifts and mariana trough and the very depleted lavas of east scotia segments e8 e9 the crust becomes mid ocean ridge mor like where the spreading axes further away from the island arc and subducted slab entrain dominantly fertile mantle