u pb geochronological constraints for paleoproterozoic evolution of the core zone southeastern churchill province northeastern laurentia abstract the core zone of the southeastern churchill province northeastern laurentia is a composite of paleoproterozoic lithotectonic domains assembled in the vise between obliquely colliding archean superior and north atlantic cratons between ca 1860 and 1810 ma detailed geological and u pb geochronological studies of domains in the southern core zone highlight significant differences in archean and paleoproterozoic geology between domains and constrain timing and models for paleoproterozoic assembly in the south central part of the core zone crossroads and orma domains consist of late archean granite greenstone terrane crust crossroads domain also contains a significant number of granite charnockite intrusions belonging to the 1840 1810 ma de pas batholith magmatism pre dates and overlaps with ca 1820 1775 ma high grade metamorphism and attendant deformation in marked contrast orma domain which occurs to the east of crossroads domain contains only local evidence of paleoproterozoic de pas related intrusions and appears to have mainly escaped paleoproterozoic metamorphism and penetrative deformation a model compatible with available data suggests the de pas batholith is a continental magmatic arc formed above an east dipping subduction zone paleoproterozoic metamorphism and deformation is concentrated in regions contiguous with arc magmatism west of crossroads domain and separated from it by the lac tudor shear zone mckenzie river domain is dominated by archean orthogneiss 80 m y older than gneisses in crossroads and orma domains minor amounts of paleoproterozoic supracrustal rocks absent in domains to the east and 1815 ma tonalite it does not contain de pas intrusions u pb geochronology suggests juxtaposition of the mckenzie river domain with domains to the east may have occurred around 1810 ma one possible model envisages the mckenzie river domain as a piece of reassembled superior craton crust incompletely rifted from the superior margin during ca 2 17 ga rifting domains occurring east of the lac tudor shear zone are interpreted to be exotic with respect to the superior craton

reworking of sialic crust as represented in late archean age gneisses northern labrador regionally reworked sialic crust has been recognized in the form of 2 800 m y old nebulitic rocks kiyuktok gneisses with high initial 87sr 86sr ratios 0 7081 and pb isotope ratios that suggest a history of the source back to at least 3 500 m y b p the field geochemical and isotopic data are consistent with these rocks having formed by in situ mobilization of granitic components in the 3 600 m y old uivak gneisses by the introduction of aqueous fluids some 2 800 m y ago contemporary but subordinate tonalitic granodioritic orthogneisses derived from discrete intrusive bodies have contrasting sr isotope compositions some display low initial 87sr 86sr ratios 0 7030 that suggest derivation from a source with mantlelike sr isotope composition however most of the late archean age intrusive rocks display higher initial 87sr 86sr ratios 0 7056 0 7059 recognition of these contrasting isotopic patterns suggests that processes of late archean crust formation and stabilization in the north atlantic craton were more complex than previously realized crustal reworking due to interaction of old crust with aqueous fluids must have been accompanied by the introduction of granitic melts derived by melting of ancient deep crustal rocks or contamination of juvenile granitic melts by ancient deep crustal material

apollo 16 impact melt splashes petrography and major element composition we made petrographic and major element chemical analyses of 50 impact melt splash ims samples from the apollo 16 landing site to assess their origin and the nature of their subregolith source these melts possess volumes that are significantly larger than those of agglutinates but smaller than those represented by fragments of generally holocrystalline melt sheets most of these melts occur as splashes that drape various host rocks the majority appear to have been deposited onto their hosts inside growing crater cavities or during ballistic flight and subsequently piggy backed to their collection site s macroscopically ims s exhibit a glassy appearance but display varied crystallinity under the microscope schlieren rich glasses dominate the holohyaline areas most ims s contain generally feldspathic monomineralic and lithic clasts while purely regolithic materials i e agglutinates are absent crystalline portions are predominately spherulitic but definitive criteria to distinguish between crystallization from a melt or solid state devitrification are lacking more than half of the ims s possess a distinct crystallization front that we attribute to devitrification chemically most ims s are fairly homogeneous on the scale of a thin section variation among samples is much greater e g al2o3 varied from 24 to 32 wt feo from 2 to 6 wt such a wide range of melt compositions suggests that more than one impact generated these 50 ims s the chemistry of most ims s is unlike the local regolith and appears to represent varied mixtures of vha impact melt breccias and anorthosite i e are dimict like the host rocks are predominantly dimict breccias 70 or one of their component lithologies vha impact melt breccias and anorthosite because of the short surface residence times for these samples determined from microcrater populations on all samples and absolute exposure ages of 10 specimens many ims s might be associated with south ray and baby ray craters in the absence of absolute chronological ages for melt formation we cannot distinguish between a young scenario in which the melts were formed during excavation of south ray and or baby ray craters and an old scenario in which previously formed melts were exposed as part of the discontinuous ejecta of either or both of these craters we prefer the former in part because of the tight compositional cluster of most ims s in either case we conclude that most of these samples or their progenitors resided at depth within the south ray and or baby ray targets furthermore the cayley formation in the southern part of the apollo 16 landing site is a polymict deposit predominantly composed of vha impact melt breccias and anorthosites both lithologies must be intimately mixed as they are in dimict breccias and large coherent units of individual lithologies appear to be limited to 50 m in dimensions

an integrated approach to understanding apollo 16 impact glasses chemistry isotopes and shape the major and minor element abundances were determined by electron microprobe in 1039 glasses from regoliths and regolith breccias to define the compositional topology of lunar glasses at the apollo 16 landing site in the central highlands of the moon while impact glasses with chemical compositions similar to local materials i e apollo 16 rocks and regoliths are abundant glasses with exotic compositions i e transported from other areas of the moon account for up to 30 of the population a higher proportion of compositionally exotic angular glass fragments exists when compared to compositionally exotic glass spherules ratios of non volatile lithophile elements i e al ti mg have been used to constrain the original source materials of the impact glasses this approach is immune to the effects of open system losses of volatile elements e g si na k four impact glasses from one compositionally exotic group low mg high k fra mauro lmhkfm were selected for 40ar 39ar dating the individual fragments of lmhkfm glass all yielded ages of 3750 50 ma for the time of the impact event based on the petrography of these individual glasses we conclude that the likely age of the impact event that formed these 4 glasses as well as the possible time of their ballistic arrival at the apollo 16 site from a large and distant cratering event perhaps in the procellarum kreep terrain zeigler et al 2004 is 3730 40 ma close to the accepted age for imbrium

evolution of depleted mantle the lead perspective abstract isotopic data have established that compared to estimated bulk earth abundances the sources of oceanic basaltic lavas have been depleted in large ion lithophile elements for at least several billions of years various data on the tertiary mesozoic gorgona komatiite and cretaceous oka carbonatite show that those rocks also sample depleted mantle sources this information is used by analogy to compare pb isotopic data from 2 6 billion year old komatiite and carbonatite from the suomussalmi belt of eastern finland and munro township ontario that are with associated granitic rocks and ores that should contain marked crustal components within experimental error no differences are detected in the isotopic composition of initial pb in either of the rock suites these observations agree closely with sr and nd data from other laboratories showing that depleted mantle could not have originated in those areas more than a few tenths of billions of years before the rocks were emplaced on a world wide basis the pb isotope data are consistent with production of depleted mantle by continuous differentiation processes acting over approximately the past 3 billion years the data show that pb evolution is more complex than the simpler models derived from the rb sr and sm nd systems the nature of the complexity is still poorly understood

pre grenvillian and grenvillian lithotectonic regions in eastern labrador correlations with the sveconorwegian orogenic belt in sweden the trans labrador batholith groswater bay terrane and lake melville terrane are three major crustal segments located adjacent to or within the grenville province in eastern labrador each crustal segment is a distinct lithotectonic entity displaying contrasts with each other in proportions of rock types structural style and metamorphic imprint together they indicate a unilateral polarity to the region partly reflecting grenvillian tectonism which sliced the region into thrust bound blocks in all three crustal segments an archean or aphebian gneissic basement is inferred onto or adjacent to which ca 1900 1700 ma supracrustal rocks were deposited deformation metamorphism and granitoid pluton emplacement were partly coeval with and partly postdated the supracrustal assemblages in the north tectonothermal effects can be assigned to hudsonian ketilidian orogenesis but their peak was 50 100 ma later farther south post tectonic granitoid plutons and layered mafic intrusions were emplaced at about

the northern margin of the grenville province in western labrador anatomy of an ancient orogenic front abstract in western labrador the northern margin of the grenville province known as the grenville front tectonic zone abuts against the superior foreland zone composed of an archean gneiss terrain and against the churchill foreland zone composed of weakly metamorphosed and deformed aphebian supracrustals in both terrains a similar tectonic style is developed in which aphebian rocks from within the grenville orogen have been thrust northwards over the adjacent foreland the grenville front is marked by mylonite phyllonite zones in the archean gneisses of the superior foreland whereas in the supracrustals it is characterized by cleavage folding grenvillian deformation involved 3 episodes of which two gave rise to northeast trending structural elements and are interpreted to be part of a single protracted event involving northerly translation of rocks from within the orogen towards the foreland a third deformation comprised large scale crossfolds and may be related to the formation of a major arcuate thrust salient spatially the northeast trending structural elements occur in the grenville front tectonic zone while the crossfolds dominate in the interior of the orogen a zone of interference structures related to the two fold trends occurs in the southern part of the grenville front tectonic zone the hudsonian front westerly limit of hudsonian deformation in the churchill province passes through the churchill foreland zone in the study area there grenvillian structures are superimposed on older hudsonian structures elsewhere in the area studied however all deformation and metamorphism of aphebian rocks is of grenvillian age metamorphic zones in pelitic rocks indicate a progressive increase in grade towards the interior of the grenville orogen the occurrence of the mineral pair kyanite k feldspar preceding the assemblage sillimanite k feldspar in the prograde sequence indicates that peak metamorphic conditions may have exceeded 8 kb and 700 c such elevated pressures during metamorphism may have been achieved by stacking of thrust slices in the grenville front tectonic zone both deformation and postorogenic uplift were diachronous in the grenville province deformation was initiated in the high grade core of the orogen and migrated northwards towards the margin whilst uplift occurred earlier in the margin than in the core

spatial variations of surface water chemistry and chemical denudation in the erdalen drainage basin nordfjord western norway abstract this study conducted over an investigation period of six years 2004 2010 focuses on spatial variation in chemical components of drainage water from sub areas within a confined drainage basin of 79 5 km 2 erdalen drainage basin inner nordfjord western norway for detection of spatial diversity and relation to environmental factors the erdalen drainage basin is homogenously composed of gneisses which is reflected in a homogenous relative as a percentage chemical composition of surface water across the entire drainage basin system at the same time the mean annual tds values of surface water sampled in creeks draining defined subsystems within erdalen show a rather high spatial variability the main controls of this spatial variability are i differences in slope deposit regolith thickness ii differences in slope angle iii differences in areal regolith cover iv differences in vegetation cover v differences in snow cover and ground frost conditions and vi differences in elevation m a s l altogether the mean annual tds values in erdalen are rather low which can be explained by i the shallow thickness of regolith across the very steep drainage basin ii the small percentage of surface areas showing a significant cover of regolith iii the cool climate in the fjord landscape of western norway and iv the weathering resistance of the predominant gneisses within erdalen the annual chemical denudation rates in erdalen are in a similar range of magnitude to rates published for numerous other cold environment catchments worldwide despite the rather low mean annual tds values chemical denudation is a comparably important and spatially very variable denudational process and should therefore not be neglected when studying slope development as well as slope and catchment wide denudation rates and mass budgets in this kind of steep mountainous cold climate drainage basins

the composition and evolution of the continental crust rare earth element evidence from sedimentary rocks the composition of the present day upper crust inferred from the uniformity of sedimentary rock r e e rare earth element patterns is close to that of granodiorite a revised andesite model is used to obtain total crustal composition the lower crust is the composition remaining assuming that the upper crust one third of the total is derived from intracrustal partial melting the upper crustal r e e pattern has pronounced eu depletion eu eu 0 64 the lower crustal pattern has eu enrichment eu eu 1 17 and the total crust has no eu anomaly relative to chondritic abundances the eu depletion in the upper crust is attributed to retention of eu in plagioclase in the lower crust because plagioclase is not stable below 40 km 10 kbar the anomaly is intracrustal in origin the archaean upper crust has a different r e e pattern to that of the present day upper crust being lower in total r e e and la yb ratios and lacking an eu anomaly these data are used to infer the archaean upper crustal composition which resembles that of the present day total crust except that ni and cr contents are higher the archaean crustal composition can be modelled by a mixture of tholeiites and tonalite trondhjemites the latter have steep light r e e enriched heavy r e e depleted patterns consistent with equilibration with garnet and hence probable mantle derivation there is little reason to suppose that the archaean lower crust was different in composition from the upper crust except locally where partial melting episodes occurred the r e e evidence is consistent with isotopic and geological evidence for a low continental growth rate in the early archaean a massive increase to about 70 of the total crust between about 3000 and 2500 ma b p and a slow increase until the present day the change from archaean to post archaean r e e patterns in the upper crust is not isochronous but is reflected in the sedimentary rock r e e patterns at differing times in different continents on the basis of a model composition for the mantle 36 of the potassium 30 of uranium 15 of lanthanum and 3 of ytterbium are concentrated in the present continental crust this enrichment is related to ionic size and valency differences from common mantle cations e g mg fe pre 3 9 ga b p crusts were obliterated by meteorite bombardment no geochemical evidence exists for primordial anorthositic sialic or mafic crusts

stratigraphic architecture and infill history of a deglaciated bedrock valley based on georadar seismic profiling and drilling the sediment fill of a silled bedrock valley in western norway has been investigated with respect to stratigraphy and infill history using a combination of mapping georadar seismic profiling and drilling a small outlet glacier occupies the head of the valley that displays a stepwise down valley profile and terminates in a lake at 29 m above sea level the valley is surrounded by high steep bedrock slopes and is characterized by a series of filled basins each limited by sills of bedrock or moraine accumulations till glacial outwash and or rockslide deposits fill in the lower half of the two larger basins fan delta deposits fringed by the deposits of alluvial fans and colluvial cones dominate the upper fill of most basins fan delta deposits interfinger downstream with lake sediments in the larger basins and fluvial deposits comprise the top fill the overall infill pattern was controlled by deglaciation as well as basin size and shape an overall decreasing sediment supply following deglaciation is shown in the fill of a larger basin down valley whereas a recently increasing sediment supply during glacier growth is reflected primarily in an upstream basin only the lowermost basin was exposed to a sea level drop from 75 m above sea level to the present lake level associated with incision and river migration this observation is in contrast to the basins above marine influence where incision has been limited due to fixed downstream sills resulting in insignificant erosion except for some fan head entrenchment it follows that the fills of these small valley basins display progradational and aggradational trends of deposition and paraglacial reworking has been limited additionally the study demonstrates that georadar profiling combined with other methods is very useful for comprehensive investigation of valley basins

evidence for transition from a continental forearc to a collisional pro foreland basin in the eastern trans hudson orogen detrital zircon provenance analysis in the labrador trough canada abstract the new quebec orogen nqo is the best preserved supracrustal belt of the deeply eroded paleoproterozoic trans hudson orogen and thus constitutes an exceptional window to investigate one of the most ancient wilson cycle sedimentary records within the manikewan paleo ocean it consists of a paleoproterozoic supracrustal belt that underwent reworking when the superior craton collided with an archean to paleoproterozoic microcontinent core zone terrane during the trans hudsonian orogeny within the nqo the western and central parts of the labrador trough comprise greenschist facies sedimentary and volcanic sequences kaniapiskau supergroup inferred to represent the rifted margin of the superior craton whereas the laporte group eastern part composed of similar successions but metamorphosed to higher grades remains of unclear origin competing models purport that the laporte group is either a deeper higher grade exposure of the kaniapiskau supergroup or an exotic terrane large scale sampling petrography and shrimp u pb detrital zircon geochronology provide insights to elucidate the sedimentary provenance and depositional environments for both zones kaniapiskau supergroup detrital zircons yield ages older than 2 5 ga showing a signature typical of the archean superior craton with a main peak at 2 72 ga there is a gap of more than 150 ma between detrital zircon ages and the interpreted depositional age suggesting a divergent environment like a rift and passive margin in contrast detrital zircons from the laporte group yield ages as young as 1834 2 4 ma and a dominant age peak at 1 84 ma the presence of age peaks at 2 2 2 4 ga suggests that the core zone exotic terrane is the main source area and the metamorphic monazite ages previously dated at 1793 2 ma point to a relative short depositional time the presence of an andean type magmatic arc in the western part of the core zone terrane supports the interpretation of an eastward subduction at 1860 1830 ma furthermore a lag time between crystallization and deposition ages within the laporte group points to convergent and collisional settings with a 40 ma transition from continental forearc basin to collisional pro foreland basin marking the consolidation of the columbia supercontinent in northeastern laurentia

environmental controls rates and mass transfers of contemporary hillslope processes in the headwaters of two glacier connected drainage basins in western norway the role of hillslopes functioning as the key elements for sediment production storage and transfers is particularly important within headwater systems in cold climate mountain landscapes that are considered to react sensitively to climate change and human impact environmental controls rates and sedimentary mass transfers of the contemporary slope processes were explored within the headwater systems of the parabolic shaped and glacier connected erdalen and bodalen drainage basins in western norway the identified relevant contemporary processes in both drainage basins include rockfalls and boulder falls snow avalanches slush flows debris flows slow mass movements and creep processes wash and chemical denudation and fluvial transport of solutes suspended sediments and bedload these denudational processes were analyzed based on an extensive geomorphic monitoring program conducted over a period of four years 2009 2012 combined with detailed geomorphological mapping and in depth studies of the most important slope processes a range of different monitoring and field techniques was applied the results show that the intensity of contemporary denudational processes in erdalen and bodalen is rather low and appears to be in a range of magnitude comparable to a number of other cold climate environments situated in the higher latitudes of the northern hemisphere the present day spatio temporal pattern of the denudational slope processes occurring in the headwater systems is controlled by a complex combination of meteorological and morphometric factors a comparison of the different denudational slope processes according to their annual mass transfers reveals the highest relative importance for rockfalls snow avalanches slope wash and chemical slope denudation in erdalen as well as for rockfalls chemical slope denudation snow avalanches and debris flows in bodalen the revealed differences between the single headwaters regarding the absolute and relative importance of the denudational slope processes are seen as a consequence of the different glacially inherited valley morphometries however due to the generally low process intensities the postglacial modification of the inherited glacial relief is altogether minor in both valleys

wide angle seismic transect across the torngat orogen northern labrador evidence for a proterozoic crustal root a refraction wide angle reflection seismic transect across the labrador peninsula covers the core zone of the se churchill province the paleoproterozoic torngat orogen and the archean nain province including a portion of the labrador continental margin an airgun array was used as source and 11 ocean bottom seismometers and 16 land stations recorded the shots forward modeling of travel times and amplitudes reveals a deep asymmetric crustal root beneath the torngat orogen with a crustal thickness of 49 km and with p wave velocities of 6 9 7 0 km s the geometry of the velocity model and the root can be best explained by either westward dipping subduction or westward underthrusting of the nain crust gravity modeling suggests a correlation of the crustal root with a gravity low that extends 100 km in an e w direction and 200 km from north to south the preservation of the crustal root is attributed to the lack of postorogenic heating and ductile reworking consistent with the lack of abundant postcollisional magmatism in the se churchill province a discontinuity possibly cutting through the entire crust is interpreted as a zone of major transcurrent shearing associated with the main phase of deformation west of the torngat orogen the crustal thickness in the core zone of the churchill province varies between 35 and 38 km p wave velocities of 5 8 7 0 km s east of the orogen the crystalline crust in the nain province is 38 km thick velocities from 5 8 to 6 9 km s but thins to 9 km in the shelf area of the labrador margin where it is covered with up to 8 km of sediments no high velocity zone was found beneath the thinned continental crust at the margin

an overview of the upb geochronology of the paleoproterozoic torngat orogen northeastern canada abstract the paleoproterozoic torngat orogen northern labrador and northeastern quebec canada is the result of oblique collision between the nain north atlantic and rae cratons a comprehensive set of u pb ages allows the chronology of events to be closely bracketed subduction occurred below the nain craton from ca 1910 1870 ma and collision between the cratons may have occurred between 1869 and 1844 ma sinistral deformation continued along the intervening abloviak shear zone until ca 1824 ma and convergence was ultimately impeded by the partial subduction of the southern rae craton post collisional isostatic uplift of the southern rae craton initiated deformation in the komaktorvik zone ca 1798 ma a prominent bend in the abloviak shear zone may be the result of differential uplift of the western side of the orogen in the south sinistral strike slip and east as well as west side up deformation continued episodically in the komaktorvik zone until at least 1710 ma the tectonic development of the orogen can be explained in terms of modern plate tectonic processes

a nd and o isotope study of the ree rich peralkaline strange lake granite implications for mesoproterozoic a type magmatism in the core zone ne canada it is well established that a type granites enriched in high field strength elements such as zr nb and the ree form in anorogenic tectonic settings the sources of these elements and the processes controlling their unusual enrichment however are still debated they are addressed here using neodymium and oxygen isotope analyses of samples from the 1 24 ga strange lake pluton in the paleoproterozoic core zone of quebec labrador an a type granitic body characterized by hyper enrichment in the ree zr and nb age corrected end values for bulk rock samples and sodic amphiboles mainly arfvedsonite from the pluton range from 0 6 to 5 7 and 0 3 to 5 3 respectively the end values for the napeu kainiut quartz monzonite which hosts the pluton range from 4 8 to 8 1 the 147sm 144nd ratios of the suite and the host quartz monzonite range from 0 0967 to 0 1659 large variations that can be explained by in situ fractionation of early lree minerals strange lake and late hydrothermal hree remobilization oxygen isotope analyses of quartz of both strange lake and the host yielded 18o values between 8 2 and 9 1 which are considerably higher than the mantle value of 5 7 0 2 bulk rock oxygen isotope analyses of biotite gneisses in the vicinity of the strange lake pluton yielded 18o values of 6 3 8 6 and 9 6 the negative end values and positive 18o values of the strange lake and napeu kainiut samples indicate that both magmas experienced considerable crustal contamination the extent of this contamination was estimated assuming that the contaminants were sedimentary derived rocks from the underlying archean mistinibi para gneiss complex which is characterized by low end and high 18o values mixing of 5 15 of a gneiss having an end value of 15 and a 18o value of 11 with a moderately enriched mantle source end 0 9 18o 6 3 would produce values similar to those obtained for the strange lake granites based on analogies between the nain plutonic suite and the gardar alkaline igneous province sw greenland we conclude that the strange lake pluton and associated ree mineralized anorogenic bodies formed from a combination of subduction induced fertilization of the sublithospheric mantle crustal extension and in situ magma evolution

composition of the cayley formation at apollo 16 as inferred from impact melt splashes chemical data for impact melt splashes ims collected at the apollo 16 landing site show that ni concentrations and feo ni cr ni and co ni correlations are consistent with a chondritic meteoritic component present at levels between approximately 1 5 and 11 wt like apollo 16 soils the ims are intermediate in composition to apollo 16 rocks the chemical data for the ims are consistent with two main compositional groups the group a ims 28 samples are chemically distinct from local apollo 16 soils and are very similar to mixtures of anorthosite and low sc vha lscvha impact melt rocks calculated to a meteorite free basis their average sc concentration la sc mgo sc and tio2 mgo ratios and mg value are 6 1 ug g 1 94 9800 0 066 and 0 74 respectively the group b ims seven samples have chemical equivalents among the soils five samples are chemically very similar to mature apollo 16 soils from the central and southern parts of the landing site two are more similar to soils 67601 and 67941 from north ray crater generally the group b ims and soils are enriched in a composition similar to anorthositic norite 67215 or mixtures thereof with anorthosite as compared to the group a ims the average sc concentration la sc mgo and tio2 mgo ratios and mg value for the subgroup of five are 9 3 ug g 1 41 5780 0 124 and 0 66 respectively the corresponding values for the subgroup of two are 7 5 ug g 1 04 7400 0 090 and 0 71 respectively the group b ims and most soils have a minor high ti component not present in the group a ims if this component is high ti mare basalt its average concentration is approximately 1 6 wt the seven group a ims that have been dated by rare gas methods all have approximately 2 m y exposure ages an age generally associated with south ray crater these seven and potentially most group a ims are likely quenched samples of the melt volume produced by the south ray impact the chemical signature of the impacting projectile is chondritic and its average concentration for the group a ims is 7 3 wt like large coherent melt sheets from terrestrial impacts the impact melt volume of the south ray impact as represented by the group a ims is homogeneous with respect to target lithologies target lithologies at south ray crater which are represented by the host rocks for the ims include anorthosite lscvha impact melt rocks hscvha impact melt rocks and dimict breccias with the exception of 61016 the melt portion of analyzed dimict breccias has the hscvha composition implying that the dimensional scales of lscvha type of rocks and anorthosite in the south ray target do not extend to the 1 10 cm scale observed for the hscvha dimict breccias the compositional difference between group a ims and surface soils from the southern part of the landing site implies stratigraphic variation in the dominant type of vha impact melt rock within the cayley formation chemical data and mixing model results are consistent with a model in which hscvha rocks dominate lscvha rocks in the surface layer the lscvha rocks dominate hscvha rocks in the layer beneath the south ray impact penetrated both layers as both types of vha impact melt rocks are traceable as ejecta material its impact melt volume was formed primarily from the lower layer to give the observed composition of the group a ims that the north ray impact also sampled the lower layer is indicated by the chemical affinities of soils 67601 and 67941 with the lscvha composition away from north ray crater most soils have chemical affinities with the hscvha composition reflecting soil development primarily from the surface layer estimated average compositions give tio2 mgo sc and la concentrations of 0 69 and 7 1 wt and 10 5 and 21 2 ug g respectively for the surface cayley layer and 0 38 and 5 9 wt and 6 1 and 11 8 ug g respectively for the subsurface cayley layer an average composition estimated for the descartes formation from soil compositions has tio2 mgo sc and la concentrations of 0 25 and 3 5 wt and 7 7 and 2 2 ug g respectively the cayley formation is more kreepy more magnesian and less aluminous than the descartes formation

paleoproterozoic lithotectonic divisions of the southeastern churchill province western labrador the southeastern churchill province secp is a paleoproterozoic system of orogens that formed during collision of the nain and superior cratons with a composite lithotectonic terrane that now forms the medial metamorphic plutonic core zone of the secp in western labrador the core zone consists of reworked archean gneisses paleoproterozoic supracrustal rocks and variably deformed 1 83 1 81 ga granitic plutons it is subdivided into three paleoproterozoic lithotectonic domains mckenzie river crossroads and orma which are separated from each other by dextral transpressive high strain zones crossroads and orma domains are thought to be derived from archean high grade granite greenstone terrane crust whereas mckenzie river domain is inferred to have been part of an archean orthogneiss terrane dominated by the ca 2776 ma flat point gneiss u pb geochronological data indicate that the igneous precursor of the flat point gneiss is 80 ma older than the oldest tonalite granite intrusions in crossroad

some things we can infer about the moon from the composition of the apollo 16 regolith randy l korotev department of earth and planetary sciences and mcdonnell center for the space sciences washington university st louis missouri 63130 usa author s e mail address rlk levee wustl edu received 1996 september 16 accepted in revised form 1997 may 12 abstract characteristics of the regolith of cayley plains as sampled at the apollo 16 lunar landing site arereviewed and new compositional data are presented for samples of 1 mm fines soils and 1 2 mm rego lith particles as a means of determining which of the many primary igneous and secondary crystalline brec cias lithoiogic components that have been identified in the soil are volumetrically important and providing anestimate of their relative abundances more than 3 x 106 combinations of components representing nearly everylithology that has been observed in the apollo 16 regolith were systematically tested to determine which com binations best account for the composition of the soils conclusions drawn from the modeling include the fol lowing at the site mature soil from the cayley plains consists of 64 5 2 7 components representing prebasin materials anorthosites feldspathic breccias and a small amount 2 6 1 5 of total soil ofnonmare mafic plutonic rocks mostly gabbronorites on average these components are highly feldspathic with average concentrations of 31 32 a1203 and 2 3 feo and a molar mg mg fe ratio of 0 68 theremaining 36 of the regolith is syn and postbasin material 28 8 2 4 mafic impact melt breccias mimbs i e lkfm and vha basalts created at the time of basin formation 6 0 1 4 mare derived material impact and volcanic glass crystalline basalt with an average tio2 concentration of 2 4 and 1 postbasin meteoritic material the mimbs are the principal 80 90 carrier of incompatible traceelements rare earths th etc and the carrier of about one half of the siderophile elements and elementsassociated with mafic mineral phases fe mg mn cr sc most 71 of the fe in the present regolithderives from syn and postbasin sources mimbs mare derived material and meteorites thus althoughthe bulk composition of the apollo 16 regolith is nominally that of noritic anorthosite the noritic part themimbs and the anorthositic part the prebasin components are largely unrelated there is compositionalevidence that 3 4 of the soil is th rich material such as that occurring at the apollo 14 site and one frag ment of this type was found among the small regolith particles studied here if regolith such as that repre sented by the apollo 16 ancient regolith breccias was a protolith of the present regolith such regolith cannotexceed 71 of the present regolith the rest must be material added or redistributed since closure of theancient regolith breccias the postclosure material includes the mare derived material and the apollo 14 like component compositions of all mature surface soils from apollo 16 even those collected 4 km apart on the cayleyplains are very similar which is in stark contrast to the wide compositional range of the lithologies of whichthe soil is composed this uniformity indicates that the ratio of mimbs to feldspathic prebasin componentsis not highly variable in the megaregolith over distances of a few kilometers that there are no large sub surface concentrations of pure mafic impact melt breccia and that the intimate mixing is inherent to thecayley plains at a gross scale thus the mixing ofmafic impact melt breccias and feldspathic prebasin com ponents must have occurred during formation and deposition of the cayley plains such uniformity could nothave been achieved by small postdeposition impacts into a stratified megaregolith using this conclusion asone constraint and the known distribution of th on the lunar surface as another and the assumption that the im brium impact is primarily responsible for formation of the cayley plains arguments are presented that theapollo 16 mimbs derive from the imbrium region and consequently that one fourth of the apollo 16 regolithis primary imbrium ejecta in the form of mafic impact melt breccias

holocene hillslope development in glacially formed valley systems in nordfjord western norway abstract large areas of the norwegian fjord landscapes are covered by hillslopes that reflect the influence of glacial inheritance from the last glacial maximum lgm the focus of this paper is two fold 1 analyze the spatio temporal variability of relevant denudational slope processes and process intensities over the holocene and 2 detect holocene modification of the glacial valley morphometry research was performed on hillslope systems within two steep parabolic shaped and glacier fed tributary valleys erdalen and bodalen located on the western side of the jostedalsbreen ice cap in western norway orthophoto delineation high resolution mapping tls detailed geomorphological information and spatial data analysis were combined with dating techniques and geophysical investigations calculated holocene rockwall retreat rates at selected slope test sites range from 0 38 to 0 67 mm yr 1 with a mean value of 0 53 mm yr 1 slightly higher values were found in erdalen with a mean rockwall retreat rate of 0 57 mm yr 1 compared to 0 50 mm yr 1 in bodalen valley wide holocene rockwall retreat rates of 0 38 0 50 mm yr 1 are consistent with other estimates of holocene rockwall retreat rates in cold mountain environments it is shown that the glacial inheritance of topography is the most important factor controlling valley development since the lgm and that sediment storage capacity is primarily conditioned by valley morphometry compared to contemporary rates the results indicate enhanced denudation activity and intensity immediately following deglaciation and during the little ice age the overall tendency of landscape development is postglacial widening of the parabolic shaped valley morphometry through rockwall retreat with associated debris accumulation beneath rockwalls as a result the glacially sculpted topography has not yet adapted to denudational processes acting under holocene environmental conditions

composition structure and age of the apollo 16 subregolith basement as deduced from the chemistry of post imbrium melt bombs irregularly shaped slag like impact melt bombs with variolitic crystallization texture mostly 1 to 10 cm in size occur throughout the regolith of the apollo 16 landing site we have analyzed 16 samples from stations 11 and 13 near north ray crater using the microscope electron microscope microprobe neutron activation and 40ar 39ar age dating techniques we interpret the melt rocks as rapidly quenched high velocity ejecta glass bombs from impact craters less than 1 5 km in diameter located in the vicinity of the apollo 16 landing site a comparison between glass bombs and typical regolith samples from various sampling stations reveals differences in their bulk chemical compositions more than 80 of the glass bombs cannot be derived from the melting of the regolith but can be produced by melting the subregolith basement the differences in chemical composition of metal particles in glass bombs and regolith samples are consistent with these findings mixing calculations show that the glass bombs were formed by melting of two or more of the most abundant lithologies granulites feldspathic melt breccias anorthosites and various mafic melt breccias of vha and lkfm affinity that constitute the subregolith basement from these results we conclude that the subregolith basement represents a polymict megabreccia target the glass bombs are post cayley in age they were produced by several different impact events more than 370 ma ago by which they were emplaced in proximity to the north ray crater area they were buried under a younger regolith layer until the north ray impact event 50 ma ago brought them up to the lunar surface again and since then they have been exposed to cosmic radiation

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

sm and gd isotopic shifts of apollo 16 and 17 drill stem samples and their implications for regolith history abstract the isotopic compositions of sm and gd in lunar regolith samples from the apollo 16 and 17 deep drill stems showed clear isotopic shifts in 150 sm 149 sm e 124 to 191 for a 16 and 37 to 111 for a 17 and 158 gd 157 gd e 107 to 169 for a 16 and 31 to 84 for a 17 corresponding to neutron fluences of 5 68 9 03 10 16 n cm 2 for a 16 and 1 85 5 04 10 16 n cm 2 for a 17 the depth profiles of neutron fluences suggest that the regoliths at both sites were due to incomplete mixing of three different slabs which experienced individual two stage irradiation before and after deposition of the upper slabs the variations in ree compositions provide chemical evidence for incompletely vertical mixing of regoliths especially at upper layers of the two sites the thermal neutron energy index estimated from the combination of sm and gd isotopic shifts defined as e sm e gd shows a small variation 0 61 0 64 in the a 16 core except for the surface layer on the other hand a large variation in e sm e gd 0 67 to 0 83 in the a 17 core may result from complicated history such as two stage irradiation and incomplete mixing during the gardening processes isotopic enrichments of 152 gd and 154 gd correlated with eu gd elemental abundances and neutron fluences were also observed in almost all of 15 samples showing evidence of neutron capture from 151 eu and 153 eu respectively

the protocontinental nature and regional variability of the central metasedimentary belt of the grenville province lead isotope evidence the lead isotopic compositions of sulphide samples mainly galenas from a representative set of mineral deposits within the central metasedimentary belt of the grenville province have been determi

review of crustal architecture and evolution in the ungava peninsula baffin island area connection to the lithoprobe ecsoot transect within the trans hudson orogen in northern quebec and southern baffin island parautochthonous archean basement and paleoproterozoic cover as well as allochthonous accreted paleoproterozoic units are exposed in a series of antiformal culminations and complementary synclinoria the parautochthonous rocks of the superior province margin and two assemblages of accreted paleoproterozoic units ungava and meta incognita crustal terranes define a basic tripartite crustal architecture which is characterized by polyphase deformation and metamorphic histories early structures and mineral assemblages are recognized in all three crustal components and shown to be temporally distinct the earlier structures and assemblages are overprinted by younger elements and mineral assemblages that are related to at least three regional contraction episodes and one thermal event that are common to all crustal components of the orogen close correlation of regional aeromagnetic data in northern quebec and southern baffin island with the three crustal components offers a first order approximation of the distribution of basement lithological units across hudson strait continuation of the aeromagnetic domains beneath ungava bay to northeastern quebec and northern labrador allows for the southward extrapolation of the tripartite trans hudson orogen crustal architecture into the lithoprobe eastern canadian shield onshore offshore transect area

low and high temperature weathering budgets in kamchatka peninsula in the general attempt to link chemical weathering global geochemical cycles and climate the study of riverine erosion in the active volcanic arc of kamchatka provides important informations as it was shown by several authors louvat and allegre 1997 and dessert 2003 chemical weathering of silicate rocks and in particular basalts is acting as a major contribution to the global fluxes derived from continental weathering and then to the global carbon cycle in such a case the atmospheric co2 consumption flux derived from basalts represents 30 of the global flux from all silicates and acts as an important regulation system of the earth s environment dessert 2003 the global budget investigated is based on co2 consumption taking place during low temperature chemical weathering of basaltic rocks occurring in soils and river systems but a substantial amount of alkalinity of river waters in volcanic context is derived from higher temperature water rock interactions occurring during hydrothermal circulation however in all the previous river studies the river chemistry was systematically corrected from the high temperature component to evaluate the co2 consumption rate although in certain rivers the alkalinity derived from high temperature water rock interaction was not negligible here we adopt another approach and by focusing on a volcanic province particularly impacted by hydrothermalism we chose not to subtract the hydrothermal component to the weathering budget and to consider both fluxes of low temperature and high temperature chemical interactions as an example the high temperature weathering explains almost 30 of the global cationic rate in kamchatka depending on the origin of co2 atmospheric or volcanic and the abundance of sulfuric acid as a proton donor oxidation of sulfide minerals and degassing the impact of the two chemical weathering processes have distinct consequences in the long term carbon cycle perspective

the nain churchill boundary and the nain plutonic suite a regional perspective on the geologic setting of the voisey s bay ni cu co deposit northern labrador is the site of two major lithotectonic elements of eastern canadian shield geology first it encompasses a paleoproterozoic continental suture zone archean rocks of the nain province tectonically juxtaposed against paleoproterozoic and reworked archean rocks of the churchill province the nain churchill suture evolved between 1860 and 1740 ma impressing upon the archean and paleoproterozoic rocks a regional metamorphic and tectonic signature referred to as the torngat orogen an important component of the torngat orogen is the tasiuyak gneiss a paleoproterozoic metasedimentary unit that occupies most of the eastern margin of the churchill province second northern labrador is the site of a world renowned terrane of mesoproterozoic anorogenic igneous rocks the nain plutonic suite that sits astride the suture and acts as a stitching batholith between the nain and churchill provinces the nain plutonic suite comprising amalgamated granitic anorthositic dioritic and troctolitic intrusions largely obscures the suture for nearly half of its total length the suite evolved between 1350 and 1290 ma and is interpreted as a product of magmatism associated with limited intracontinental rifting of the conjoined nain churchill crust above a mantle plume the voisey s bay ni cu co deposit serendipitously discovered in 1993 resides within one of the oldest troctolitic intrusions of the nain plutonic suite a 1334 ma intrusion that transgresses a contact between archean and paleoproterozoic gneisses genetic controls on the setting of mineralization have been built upon the nain churchill boundary as a zone of weakness that was exploited by mantle magmas and have implicated the tasiuyak gneiss as a crustal sulfur source although the archean paleoproterozoic junction at voisey s bay is presently interpreted as representing the nain churchill boundary in reality the provincial affinity of the archean gneisses is equivocal this uncertainty dictates caution in assigning the nain churchill boundary as the convenient transcrustal conduit that allowed the voisey s bay mafic intrusions rapid transit from their mantle staging area modeling the sulfide deposit as being solely a result of sulfur saturation of mafic magma by proximal paleoproterozoic tasiuyak paragneisses is also questionable because other genetic processes may have been responsible for example desilication of gneiss is strongly indicated by aluminous refractory minerals in vestiges of fused tasiuyak gneiss the spatial distribution of the mineralized rock at voisey s bay apparently within the subchamber plumbing system feeding a larger intrusion and within remnants of the larger intrusion itself may serve as a paradigm for similar deposits in the nain area but the preerosional comparative morphology of that larger intrusion relative to the better preserved ones may never be known a thorough understanding of the setting and genesis of the voisey s bay deposit will better facilitate establishing exploration targets in other parts of the nain region in labrador as a whole and in other geologically similar regions of the world

composition and evolution of the lunar crust in the descartes highlands apollo 16 samples from the north ray crater ejecta blanket apollo 16 were investigated by petrographic microscope electron microprobe instrumental neutron activation and xray fluorescence analyses and 40ar 39ar and rb sr dating techniques nine major groups of monomict and polymict breccias were defined on the basis of microscopic texture and these were further subdivided into chemical subgroups on the basis of characteristic elements such as al mg fe cr ree ni and co the polymict breccias fragmental breccias granulitic breccias and impact melt breccias are the result of multiple impact induced mechanical mixing and melting and of thermal and impact metamorphism of rock and mineral clasts derived from primordial igneous crustal rocks for calculations of mixing models it was found that end members consisting of the pristine igneous rock components present as discrete samples at the apollo 16 site and supplemented by kreep dunite and a meteoritic component yield the best fits for the composition of polymict breccias the end member rocks a re ferroan anorthosite various magnesian gabbronorites including sodic ferrogabbro and feldspathic lherzolite and spinei troctolite the following model is proposed for the composition and stratigraphy of the target for north ray crater the lower section of the stratigraphy is composed of a megabreccia with clasts of highly feldspathic polymict breccias kreep free old eastern highland rock suite interpreted as nectaris ejecta descartes formation the top section contains kreep bearing polymict breccias kreep bearing young western highland rock suite and appears to be similar to the lithologies found in the cayley plains this material interpreted as cayley formation may be a distant facies of imbrium basin ejecta deposits of the imbrium basin the petrographic differences between these two major selenographic units the descartes and the cayley formations in the apollo 16 area are more distinct than the chemical differences the petrographic and chemical composition of the primordial igneous upper crust in the regions of the nectaris and imbrium basins has been calculated by subtraction of the kreep and meteoritic components from the bulk composition of the descartes and cayley materials the nectaris crust which is better constrained consists of 86 87 a northosite 4 sodic ferrogabbro 0 5 1 3 feldspathic lherzolite 6 8 regular magnesian gabbronorite 1 8 2 8 dunite and 0 1 spinel troctolite a model for the evolution of the upper lunar crust in the descartes highlands is proposed on the basis of isotope ages and clast matrix relationships of polymict breccias essential features of this model in sequenial order are 1 development of multiple layers of kreep free early feldspathic fragmental megabreccias and impact melt sheets on the primordial crust in the time period from 4 4 aeons to the time of the nectaris impact which could have occurred as late as 3 85 aeons ago 2 excavation of these megabreccias by the nectaris event and deposition of a nectarian feldspathic fragmental megabreccia in the descartes area 3 introduction of kreep basaltic material into the upper crust mainly west and northwest of the descartes site and formation of kreepy impact melt sheets most probably from 4 05 to 3 80 aeons ago 4 imbrium impact at 3 8 aeons ago and deposition of kreep bearing imbrian feldspathic fragmental breccias at the descartes site which form the cayley formation and 5 redeposition mixing and melting of all preexisting breccias yielding kreep bearing and kreep poor post cayley fragmental breccias and melt ejecta glass bombs as the result of small impacts craters 1 5 km in diameter in the cayley plains and the descartes mountains respectively

chemical denudation in arctic alpine latnjavagge swedish lapland in relation to regolith as assessed by radio magnetotelluric geophysical profiles chemical denudation in arctic alpine latnjavagge swedish lappland in relation to regolith as assessed by radio magnetotelluric geophysical profiles

sr and nd isotope geochronology geologic history and origin of the adirondack anorthosite abstract we have analyzed samples from the adirondack marcy massif for rb sr and sm nd isotopes in an attempt to determine directly the primary crystallization age of a proterozoic massif type anorthosite rock suite the oldest age obtained 1288 36ma is from a 4 point sm nd isochron defined by igneous textured whole rock and mineral separate data from a local layered sequence gradational from oxiderich pyroxenite to leuconorite this age is older than silver s 1969 1113 ma zircon age of associated charnockites but is within the window of permissible anorthosite ages based on previous geochronology and field relationships as such 1288 ma may represent the time of crystallization of the massif for the most part however both sm nd and rb sr isotopic systems did not survive granulite facies metamorphism internal isochrons based on whole rocks and minerals yield ages between 995 and 919 ma these isotopic data suggest that the granulite fades metamorphism experienced by the massif was a prograde event that occurred a minimum of 100 ma and as much as 350 ma after crystallization of the massif the relatively large range in rb abundance and in calculated initial 87 sr 86 sr 0 7039 0 7050 and 143 nd 144 nd ratios among anorthosite suite rocks particularly those at or near the contacts of the marcy massif is explicable by variable contamination with crustal materials and or fluids derived from surrounding acidic metaplutonic rocks paragneisses and marbles despite uncertainies caused by crustal contamination and metamorphic resetting of primary ages marcy samples have epsilon nd values between 0 44 and 5 08 implying a source for the massif with long term depletion in light rare earth elements a probable source material would be depleted mantle

intensity and spatio temporal variability of fluvial sediment transfers in an arctic oceanic periglacial environment in northernmost swedish lapland latnjavagge catchment abstract intensity and spatio temporal variability of fluvial sediment transfers and mechanical fluvial denudation were analyzed in the periglacial latnjavagge catchment 9 km 2 950 1440 m a s l 68 20n 18 30e in arctic oceanic northernmost swedish lapland the present day rates of fluvial sediment transfer are low the mean annual mechanical fluvial denudation rate at the inlet of lake latnjajaure as calculated after five years of process monitoring 2000 2004 and excluding a rare rainfall event which caused 3 2 times higher suspended sediment transport during one day as compared to the total mean annual suspended sediment transport is 2 3 t km 2 yr 1 in years without rare rainfall events most of the total annual sediment load is transported in a few days during annual snowmelt runoff in the calculation of longer term sediment budgets rare rainfall events like the july 20th 21st 2004 event have to be considered as essential components reliable estimation of the recurrence intervals of such events is problematic the pattern of ice patches and snow fields within the valley the steepness of streams and channels and the location of areas showing slushflow activity are the major factors controlling spatial variability of mechanical fluvial denudation in the drainage basin the five lakes in latnjavagge especially lake latnjajaure are significant sediment traps and ground below 1300 m a s l is protected by a very stable and closed vegetation cover and rhizosphere across the entire lower catchment

pegmatitic pods in the mealy mountains intrusive suite canada clues to the origin of the olivine orthopyroxene dichotomy in proterozoic anorthosites the anorthositic members of the mealy mountains intrusive suite mmis labrador canada are host to 0 5 5 m diameter pegmatitic pod like segregations originally described as graphic granite pods u pb zircon geochronology confirms that the pods are coeval with the 1650 1630 ma emplacement age range for the mmis yielding ages of 1654 6 8 to 1628 6 3 5 ma petrographic and geochemical analysis of five pods from anorthositic rocks of the mmis reveals that the pods have a diverse compositional range from monzodiorite to granite varying from fe rich and si poor to fepoor and si rich compositions fe rich si poor pods in the mmis and other massifs e g laramie anorthosite complex tend to be hosted by olivine bearing anorthosites whereas si rich fe poor pods are hosted by pyroxene bearing anorthosites each pod shows a range of graphic myrmekitic and symplectitic textures along with distinctive mineral assemblages e g apatite and zircon and highly enriched trace element compositions evolved mineral assemblages high concentrations of fe ti and p and in some cases sio2 and 10 1000 chondrite enrichment in light rare earth elements u th and rb indicate that many of the pods are highly fractionated the array of textural intergrowths provides clues about the final stages of crystallization in the pods and by extension the anorthosites macroscopic quartz k feldspar graphic intergrowths indicate high viscosity fluid bearing and significantly undercooled magmatic conditions whereas microscopic myrmekitic plagioclase quartz and symplectitic plagioclase orthopyroxene intergrowths on primary grain boundaries indicate replacement of phases in the presence of reactive fluids in assessing the nature of these pegmatitic pods based on field petrographic and geochemical evidence we conclude that they represent the fluid bearing late stage crystallization products of a residual liquid in the massif anorthosite system the fe and si compositional variations observed in these late stage pods can be linked to a fundamental olivine pyroxene dichotomy observed in most proterozoic anorthosite massifs suggesting that pulses of magma experience variable contamination in amount and or composition leading to varying differentiation paths a range of lithologies monzonites monzonorites ferrodiorites and jotunites observed in similar pod like structures as well as dykes and plutons has been observed in other proterozoic anorthosite massifs and all have at one time or another been interpreted as the residual liquids of anorthosite crystallization our observation of in situ pods with similar compositions to all of the aforementioned lithologies and displaying textures indicative of late stage crystallization supports the notion that all of these associated lithologies can be interpreted as comagmatic with but variably contaminated and isolated residual

the case for a younger imbrium basin new 40ar 39ar ages of apollo 14 rocks petrographically and chemically well characterized rocks of the apollo 14 landing site 12 impact melt breccias 3 clast free impact melt rocks 2 granulitic rocks 1 cataclastic noritic anorthosite 1 shocked gabbronorite 1 mare basalt and 1 plagioclase single crystal have been dated by the 40ar 39ar technique the samples represent two different formations at the apollo 14 site 1 small lithic clasts 10 specimens from fragmental breccia 14063 ejected from the 26 ma old cone crater and one clast mare basalt from cone crater soil 14140 and 2 large rock samples 10 specimens collected throughout the regolith of the landing site the first group of samples has exposure ages close to 26 ma and 40ar 39ar ages ranging from 3 86 to 4 09 ga which indicates that breccia 14063 was assembled 3 86 ga ago the second group of samples displays lower 40ar 39ar ages ranging from 3 73 to 3 85 ga we interpret breccia 14063 as part of a nectarian megabreccia unit which was incorporated into the fra mauro formation as a megablock by secondary mass wasting of the ejecta blanket of a local pre imbrian crater the remaining samples are thought to represent clasts of the apollo 14 subregolith basement megabreccia defined as the fra mauro formation consequently the reported ages of these clasts confirm previous suggestions that the fra mauro formation and therefore the imbrium basin is only 3 75 ga old and not 3 85 ga as commonly assumed

geochemical comparison of impact glasses from lunar meteorites alha81005 and mac88105 and apollo 16 regolith 64001 abstract most glasses that occur in lunar highland regolith are quenched droplets of impact melt the chemical compositions of these glasses are equivalent in the absence of volatile losses to the original target materials the compositional range of impact glasses in a regolith reflects the chemical diversity that existed throughout the region up to the time of system closure e g breccia formation since these glasses are a product of widespread and random sampling both in terms of space and time they can be used for geochemical exploration of the moon the major element compositions of impact glasses occurring in three samples of lunar feldspathic regolith alha81005 mac88105 apollo 16 64001 have been determined by electron microprobe the glass populations among these three unrelated samples are compositionally distinct while most of the impact glasses within each of these three samples are compositionally similar to the regolith in which they are found up to 40 of the impact glasses are different some of the compositionally exotic glasses were ballistically transported from other areas of the moon and thereby provide information about the compositional range of regoliths that exist elsewhere since the geological setting of the apollo 16 region is well known compared to the source areas of the lunar meteorites the apollo 16 glasses provide a ground truth for interpretations the thirty four impact glasses in meteorite alha81005 overlap the compositional range of feldspathic regoliths represented by all of the lunar highland meteorites i e y86031 y82192 y791197 mac88105 alha81005 and are compositionally distinct from highland regoliths sampled by apollo 14 apollo 16 apollo 17 and luna 20 a small proportion of alha81005 glasses contain a mare component no kreep glasses were observed due to their scarcity only ten impact glasses in lunar meteorite mac88105 were analyzed the spherules occur in two broadly defined compositional groups one group of glasses is similar to the bulk composition of mac88105 whereas the other group is more mafic all of these glasses are distinct from highland regoliths sampled by apollo 14 apollo 16 and apollo 17 and luna 20 a low ti mare glass was also analyzed in mac88105 no kreep glasses were observed the two hundred and fifty three aluminous impact glasses analyzed in apollo 16 regolith 64001 display a prominent grouping of compositions equivalent to the local regolith in addition about 10 of the glasses in 64001 are distinct from the local regolith and chemically resemble the lunar highland meteorites alha81005 mac88105 these glasses may record the chemical composition of an ancient regolith that occurred in the apollo 16 region prior to the arrival of kreep and mare components twentythree percent of the glasses in 64001 have high ti mare affinities these mare glasses are clearly exotic to the apollo 16 site and have been transported from distances of at least 300 km

seasonal and annual variations of surface water chemistry solute fluxes and chemical denudation in a steep and glacier fed mountain catchment in western norway erdalen nordfjord abstract conducted during an investigation period of six full years 2004 2010 this study focuses on inter and intra annual temporal variations of surface water chemistry solute fluxes solute yields and chemical denudation in a steep cold climate and glacier fed drainage basin system in the fjord landscape of western norway the selected erdalen drainage basin 79 5 km2 is considered a typical valley system of the nordfjord region in western norway and is connected to the jostedalsbreen ice cap through two outlet glaciers the mean annual chemical denudation rate in erdalen is 6631 kg km 2 yr 1 which is of a similar range of magnitude for annual chemical denudation rates as a number of other cold regions catchments worldwide inter and intra annual temporal variations of surface water chemistry solute gross concentrations solute gross yields and chemical denudation rates are clearly determined by the combined effects of inter and intra annual temporal variations of precipitation solar radiation and air temperature intra annual temporal variations of surface water total dissolved solids tds values reflect the dilution of base flow from the drainage basin by i thermally controlled snowmelt in spring april june ii thermally determined glacier melt in summer july august and iii more frequent and more intense rainfall events in autumn september november the highest monthly solute gross yields over the year comprising 43 of the total annual solute gross yield are recorded in the spring period three month period from april to june which is due to high runoff during spring snowmelt and comparably higher tds values than during major glacier melt in summer july august in autumn september november comparably high amounts of ion poor rainwater in combination with a fast surface drainage saturation overland flow of a significant share of rainwater during heavy rainfall events and lower air temperatures as well as lower solar radiation inputs lead to comparably lower tds values in surface water than are found in spring

the southeastern churchill province synthesis of a paleoproterozoic transpressional orogen the paleoproterozoic southeastern churchill province secp is located in the northeastern canadian shield of labrador and quebec the secp formed through the oblique collisions of the archean nain and superior cratons with a third intervening archean block the core zone the belt has a tripartite structure comprising the torngat orogen to formed by nain craton core zone collision in the east the core zone in the centre and the new quebec orogen nqo formed by superior craton core zone collision in the west the secp thus records transpressional development on the flanks of the superior and nain cratons as they indented northwards to form the larger trans hudson nagssugtoqidian orogenic belt to the north principal stages of tectonic development were 1 2 2 2 1 ga crustal rifting of nain and superior cratons 2 ca 1 9 ga subduction under eastern nain craton 3 ca 1 87 1 85 ga collision of nain craton and core zone to form the to 4 1 845 1 820 ga sinistral transpression in the to and subduction under the western core zone and 5 1 82 1 77 ga collision of superior craton and core zone to form the nqo in association with dextral transpression crustal scale cross sections of the secp have been developed from reflection and refraction seismic data the western part of the nqo is dominantly west vergent and associated with an imbricate thick skinned thrust stack that ramps from the base of the crust the core zone is characterized by a 35 40 km thick crust and pervasive east dipping fabrics related to westerly thrusting the to is a narrow doubly vergent belt associated with a 48 km thick crust that forms a crustal root with a moho relief of 12 km the root is interpreted to result from attempted subduction of the core zone under the nain craton possibly as a result of mid crustal wedging by the nain craton the to was the site of intense convergence that resulted in excision of juvenile crust possibly including tectonic removal of the axial magmatic arc as a result the middle to lower levels of the secp consist largely of refractory archean lithosphere this may account for the lack of widespread post collisional plutonism in the secp and the preservation of the to root

role of river suspended material in the global carbon cycle the reaction of ca derived from silicate weathering with co2 in the world s oceans to form carbonate minerals is a critical step in long term climate moderation ca is delivered to the oceans primarily via rivers where it is transported either as dissolved species or within suspended material the relative importance for climate moderation of riverine dissolved ca vs suspended ca transport stems from the total ca flux and its climate dependence data in the literature suggest that within uncertainty global riverine dissolved ca flux is equal to suspended material ca flux to determine how these fluxes depend on temperature and rainfall a 40 yr field study was performed on 4 catchments

age and origin of early proterozoic dolerite dykes in south west greenland samples of three dolerite dykes from south west greenland give a pooled weighted mean rb sr whole rock isochron age of 2 130 65 ma initial 87sr 86sr ratios are 0 70155 0 00018 for one of the dykes naujat and 0 70277 0 00012 for the other two torssut and akinaq a fourth dyke qaqarssuaq did not yield an isochron torssut samples have significantly lower initial 207pb 204pb ratios than samples from the naujat dyke indicating that the torssut dyke has been affected by crustal contamination

compositional variation in apollo 16 impact melt breccias and inferences for the geology and bombardment history of the central highlands of the moon abstract high precision data for the concentrations of a number of lithophile and siderophile elements were obtained on multiple subsamples from 109 impact melt rocks and breccias mostly crystalline from the apollo 16 site compositions of nearly all apollo 16 melt rocks fall on one of two trends of increasing sm concentration with increasing sc concentration the eastern trend lower sm sc mg fe and sm yb ratios consists of compositional groups 3 and 4 of previous classification schemes these melt rocks are feldspathic poor in incompatible and siderophile elements and appear to have provenance in the descartes formation to the east of the site the western trend higher sm sc mg fe and sm yb ratios consists of compositional groups 1 and 2 these relatively mafic kreep bearing breccias are a major component 35 of the cayley plains west of the site and are unusual compared to otherwise similar melt breccias from other sites in having high concentrations of fe ni metal 1 2 the metal is the carrier of the low ir au 0 3 chondritic siderophile element signature that is characteristic of the apollo 16 site four compositionally distinct groups 1m 1f 2db and 2nr of western trend melt breccias occur that are each represented by at least six samples compositional group 1 of previous classification schemes the poikilitic or lkfm melt breccias can be subdivided into two groups group 1m represented by six samples including 60315 is characterized by lower al2o3 concentrations higher mgo and alkali concentrations and higher mg fe and cr sc ratios than group 1f represented by fifteen samples including 65015 group 1m also has siderophile element concentrations averaging about twice those of group 1f and ir au and ir ni ratios that are even lower than those of other western trend melt rocks ir au 0 24 0 03 ci normalized at the mafic extreme of group 2 vha melt breccias the melt lithology occurring as clasts in feldspathic fragmental breccias from north ray crater group 2nr is compositionally distinct from the melt lithology of dimict breccias from the cayley plains group 2db in having higher concentrations of sc cr and heavy rare earth elements and lower concentrations of siderophile elements the distinct siderophile element signature high absolute abundances low ir au ratio suggest that the four groups of mafic melt breccia are all somehow related ratios of some lithophile elements also suggest that they are more closely related to each other than they are to melt breccias from other apollo sites however none of the breccia compositions can be related to any of the others by any simple process of igneous fractionation or mixing involving common lunar materials thus the origin of the four groups of mafic melt breccia is enigmatic if they were produced in only one or two impacts then a mechanism exists for generating regimes of impact melt breccia in a single impact that are substantially different from each other in composition for various reasons including the problem of delivering large volumes of four different types of melt to the apollo 16 site it is unlikely that any of these breccias were produced in basin forming impacts if they were produced in as many as four crater forming impacts then the unusual siderophile element signature is difficult to explain possible explanations are 1 1 the four groups of melt breccia all contain metal from a single earlier impact 2 2 they were each formed by related metal rich meteoroids or 3 3 some common postimpact process has resulted in metal of similar composition in each of four melt pools within a compositional group most intrasample and intersample variation in lithophile element concentrations is caused by differences among samples in the proportion of a component of normative anorthosite or noritic anorthosite in most cases this compositional variation probably reflects variation in clast abundance for group 2db and probably 2nr differences in abundance of a component of ferroan anorthosite estimated al2o3 32 accounts for the compositional variation for groups 1m and 1f the anorthositic component is more mafic estimated al2o3 26 some group 2 samples may be related by a troctolitic component of varying abundance

genesis of the precambrian copper rich caraiba hypersthenite norite complex brazil caraiba the largest brazilian copper deposit under exploitation consists mostly of disseminated and remobilised bornite and chalcopyrite hosted in early proterozoic norite and hypersthenite the mafic igneous complex comprises multiple intrusions of dykes veins and breccias of norites and hypersthenites with minor proportions of amphibolised gabbronorite and peridotite xenoliths transported by the magma from deeper levels in the lithosphere the country rocks are high grade gneisses granulites and metasediments compositions of plagioclase an60 40 and orthopyroxene en70 60 fall in a narrow range similar to the koperberg suite from the okiep copper district south africa and to that in many massif type anorthosites whole rock major and trace element geochemistry indicate a parental magma enriched in fe lree p k and cu negative nb anomalies on multi element plots and fractionated ree patterns along with sulphide sulphur isotopes in the range 34s 1 495 to 0 643 suggest a primary mantle lithosphere source although a lower crustal source for the gabbronorite and peridotite xenoliths cannot be excluded geochronological and field evidence indicate that both norite and hypersthenite are likely to have been emplaced during a major sinistral transcurrent partly transpressional shearing event associated with the waning stage of evolution of the early proterozoic salvador curaca orogen

shock metamorphism of carbonaceous chondrites abstract we have studied shock effects in carbonaceous chondrites using optical microscopy of thin sections and find that our petrographic classification of progressive shock metamorphism in ordinary chondrites can also be applied to carbonaceous chondrites we find that sixty nine carbonaceous chondrites can be assigned to four shock stages si to s4 largely on the basis of shock effects in olivine the least shocked chondrite groups are cm2 and co3 thirty six out of thirty eight members are classified as shock stage s1 differences between the mean shock levels of certain groups of chondrites e g co3 and cv3 are probably due to stochastic differences in the sampling of their parent bodies however there is an overall tendency for the mean shock level of carbonaceous chondrites and ordinary chondrites to increase with increasing petrologic type that may reflect real differences in the shock level of near surface materials on their parent bodies caused by intrinsic variations in the chemical and physical properties of these materials petrologic type 2 and 3 chondrites are more porous and richer in volatiles than types 4 to 6 the greater porosity of types 2 3 causes higher post shock temperatures and melting at lower pressures and the higher volatile contents ensure that strongly shocked material is more readily dispersed on release from high pressure we suggest that type 2 3 material shocked above 20 30 gpa normally escapes from the parent asteroids and forms particles that are too small to survive as meteorites in the cv3 group there is a correlation between the degree of chondrule flattening and the intensity of shock metamorphism analogous to that discovered in ordinary chondrites by sneyd et al 1988 suggesting that shock rather than static overburden pressure is responsible for chondrule flattening we infer that the correlations are due to collapse of pores under shock pressures of at least 5 10 gpa and that shock is an important process affecting many physical properties of type 2 4 chondrites

contemporary suspended sediment dynamics within two partly glacierized mountain drainage basins in western norway erdalen and bodalen inner nordfjord abstract this paper focuses on environmental controls spatiotemporal variability and rates of contemporary fluvial suspended sediment transport in the neighboring partly glacierized and steep erdalen 79 5 km 2 and bodalen 60 1 km 2 drainage basins in the fjord landscape of the inner nordfjord in western norway field work including extended samplings and measurements was conducted since 2004 in erdalen and since 2008 in bodalen the distinct intra and inter annual temporal variability of suspended sediment transport found is mostly controlled by meteorological events with most suspended sediment transport occurring during pluvial events in autumn september november followed by mostly thermally determined glacier melt in summer july august and by mostly thermally determined snowmelt in spring april june extreme rainfall events 70 mm d 1 in autumn can trigger significant debris flow activity that can cause significant transfers of suspended sediments from ice free surface areas with sedimentary covers into main stream channels and is particularly important for fluvial suspended sediment transport in years with occurring relevant debris flow activity the total annual drainage basin wide suspended sediment yields are strongly determined by these single extreme events the proportion of glacier coverage followed by steepness of slopes and degree of vegetation cover in ice free surface areas with sedimentary covers are the main controls for the detected spatial variability of suspended sediment yields the contemporary sediment supply from glacierized surface areas and the jostedalsbreen ice cap through different defined outlet glaciers shows a high spatial variability the fact that the mean annual suspended sediment yield of bodalen is with 31 3 t km 2 yr 1 almost twice as high as the mean annual suspended sediment yield of erdalen 16 4 t km 2 yr 1 is to a large extent explained by the higher proportion of glacier coverage in bodalen 38 of the drainage basin surface area as compared to erdalen 18 of the drainage basin surface area and by a significantly higher sediment yield from the glacierized area of the bodalen drainage basin compared to the glacierized surface area in erdalen when looking at the total annual mass of suspended sediments being fluvially exported from both entire drainage basin systems the total amount of suspended sediments coming from the ice free drainage basin surface areas altogether dominates over the total amount of suspended sediments coming from the glacierized surface area of both drainage basins drainage basin wide annual suspended sediment yields are rather low when compared with yields of other partly glacierized drainage basin systems in norway and in other cold climate environments worldwide which is mainly due to the high resistance of the predominant gneisses towards glacial erosion and weathering the altogether only small amounts of sediments being available within the entire drainage basin systems the stable and nearly closed vegetation cover in the ice free surface areas with sedimentary covers and the efficiency of proglacial lakes in trapping sediments supplied by defined outlet glaciers both contemporary and long term suspended sediment yields are altogether supply limited contemporary suspended sediment transport accounts for nearly two thirds of the total fluvial transport and accordingly plays an important role within the sedimentary budgets of the entire erdalen and bodalen drainage basins

the poisonous rocks of karkevagge abstract the black schist in karkevagge swedish lapland has been reported to weather easily and produce a poisonous effect on vegetation this research was an investigation of that phenomenon as part of a larger study of weathering in karkevagge in july 1999 soil and plant samples were collected downslope of a poisonous boulder samples from the adjacent unaffected slope served as references biomass plant elemental composition and soil fertility were determined most plants within 1 4 m downslope of the poison boulder were dead and effects on plant growth could be seen to about 6 m plants near the boulder had elevated levels of k b al cd se and fe and lower levels of ca mn and ba compared to reference plants in the soil near the poison boulder extractable s cd and fe and salt contents were greater while ph and extractable cl p ca mg k ba ni and cr were lower than in the reference soil at 10 m downslope of the boulder soil and plant chemistry was more similar to the reference materials but some effects were still noted elemental analyses of the poison boulder and soil revealed no particular plant toxins although contents of fe and s were higher and ca lower than in reference materials we believe the poison is sulfuric acid which forms as a consequence of pyrite oxidation the dark color of the boulder is consistent with a pyrite bearing lithology and other field observations and laboratory analyses support the hypothesis coatings on local rocks include jarosite gypsum and copiapite secondary minerals associated with pyrite oxidation and weathering accelerated by sulfuric acid radiocarbon dating indicates that the rock fell off the cliff some time before 245 14 c years bp

fluxes of high versus low temperature water rock interactions in aerial volcanic areas example from the kamchatka peninsula russia abstract volcanic areas play a key role in the input of elements into the ocean and in the regulation of the geological carbon cycle the aim of this study is to investigate the budget of silicate weathering in an active volcanic area we compared the fluxes of the two major weathering regimes occurring at low temperature in soils and at high temperature in the active volcanic arc of kamchatka respectively the volcanic activity by inducing geothermal circulation and releasing gases to the surface produces extreme conditions in which intense water rock interactions occur and may have a strong impact on the weathering budgets our results show that the chemical composition of the kamchatka river water is controlled by surface low temperature weathering atmospheric input and in some limited cases strongly imprinted by high temperature water rock reactions we have determined the contribution of each source and calculated the rates of co 2 consumption and chemical weathering resulting from low and high temperature water rock interactions the weathering rates between 7 and 13 7 t km 2 yr for cations only and atmospheric co 2 consumption rates 0 33 0 46 10 6 mol km 2 yr for kamchatka river due to rock weathering in soils low temperature are entirely consistent with the previously published global weathering laws relating weathering rates of basalts with runoff and temperature in the kamchatka river co 2 consumption derived from hydrothermal activity represents about 11 of the total hco 3 flux exported by the river the high temperature weathering process explains 25 of the total cationic weathering rate in the kamchatka river although in the rivers non affected by hydrothermal activity the main weathering agent is carbonic acid reflected in the abundance of hco 3 in rivers in the region most impacted by hydrothermalism the protons responsible for minerals dissolution are provided not only by carbonic acid but also by sulphuric and hydrochloric acid a clear increase of weathering rates in rivers impacted by sulphuric acid can be observed in the kamchatka river 19 of cations are released by hydrothermal acids or the oxidative weathering of sulphur minerals our results emphasise the important impact of both low and high temperature weathering of volcanic rocks on global weathering fluxes to the ocean our results also show that besides carbonic acid derived from atmospheric co 2 hydrochloric acid and especially sulphuric acid are important weathering agents clearly sulphuric acid with hydrothermal activity are key parameters that cause first order increases of the chemical weathering rates in volcanic areas in these areas accurate determination of weathering budgets in volcanic area will require to better quantify sulphuric acid impact

petrography geochemistry and nd isotope systematics of metaconglomerates and matrix rich metasedimentary rocks implications for the provenance and tectonic setting of the labrador trough canada the new quebec orogen consists of a supracrustal belt that was reworked when the superior craton collided with the core zone terrane during the paleoproterozoic trans hudson orogeny within the new

apollo 17 regolith 71501 262 a record of impact events and mare volcanism in lunar glasses thirteen glasses from apollo 17 regolith 71501 262 have been chemically analyzed by electron microprobe and isotopically dated with the 40ar 39ar dating method we report here the first isotopic age obtained for the apollo 17 very low titanium vlt volcanic glasses 3630 40 ma twelve impact glasses that span a wide compositional range have been found to record ages ranging from 102 20 ma to 3740 50 ma the compositions of these impact glasses show that some have been produced by impact events within the apollo 17 region whereas others appear to be exotic to the landing site as the data sets that include compositions and ages of lunar impact glasses increase the impact history in the earth moon system will become better constrained

the gravity field over the ungava bay region from satellite altimetry and new land based data implications for the geology of the area gravity data were obtained along two transects on the southern coast of ungava bay which provide continuous gravity coverage between leaf bay and george river the transects and the derived gravit

on the origin of impact glass in the apollo 16 regolith this study addresses the issue of what fraction of the impact glass in the regolith of a lunar landing site derives from local impacts those within a few kilometers of the site as opposed to distant impacts 10 or more kilometers away among 10 323 fragments from the 64 210 lm grain size fraction of three apollo 16 regolith samples 14 are impact glasses that is fragments consisting wholly or largely of glass produced in a crater forming impact another 16 are agglutinates formed by impacts of micrometeorites into regolith we analyzed the glass in 1559 fragments for major and minor element concentrations by electron probe microanalysis and a subset of 112 of the fragments that are homogeneous impact glasses for trace elements by secondary ion mass spectrometry of the impact glasses 75 are substantially different in composition from either the apollo 16 regolith or any mixture of rocks of which the regolith is mainly composed about 40 of the impact glasses are richer in fe mg and ti as well as k p and sm than are common rocks of the feldspathic highlands these glasses must originate from craters in maria or the procellarum kreep terrane of the feldspathic impact glasses some are substantially more magnesian greater mgo feo or have substantially lower concentrations of incompatible elements than the regolith of the apollo 16 site many of these however are in the range of feldspathic lunar meteorites most of which derive from points in the feldspathic highlands distant from the procellarum kreep terrane these observations indicate that a significant proportion of the impact glass in the apollo 16 regolith is from craters occurring 100 km or more from the landing site in contrast the composition of glass in agglutinates on average is similar to the composition of the apollo 16 regolith consistent with local origin 2010 elsevier ltd all rights reserved

the shabogamo intrusive suite labrador sr and nd isotopic evidence for contaminated mafic magmas in the proterozoic abstract the shabogamo intrusive suite comprises numerous bodies of variably metamorphosed gabbro which intrude archean and proterozoic sequences at the junction of the superior churchill and grenville structural provinces in western labrador combined sm nd and rb sr systematics in two bodies ranging from unmetamorphosed to lightly metamorphosed document a crystallization age of about 1375 m y and suggest that both bodies crystallized from magmas with similar nd and sr isotopic compositions this age is in accordance with the existence of a regional magmatic event in the churchill province at approximately 1400 m y rb sr systematics in two bodies of amphibolite grade gabbro suggest a regional metamorphic event at about 950 m y corresponding to the waning stages of grenville activity sm nd systematics in these high grade bodies are affected to a much lesser degree than rb sr initial ratios for143nd 144nd and87sr 86sr are lower and higher respectively than bulk earth values at 1375 m y both these displacements are in the direction of older crustal material at 1375 m y and a model is proposed to produce the shabogamo magma by mixing a mantle derived magma with a partial melt of crustal rocks approximately 4 1 by volume young volcanic rocks with anomalous nd and sr isotopic ratios which have previously been taken as evidence for enriched mantle may be interpreted similarly

cobalt and nickel concentrations in the komatiite component of apollo 16 polymict samples abstract some estimates for the concentrations of co and ni in the primitive mafic component of apollo 16 breccias and soils are large comparable to concentrations in terrestrial komatiites these estimates may be erroneously high because the contribution from meteoritic contamination of the samples has been underestimated however even if the correction for meteoritic co and ni is valid and the calculated residual ni is not of meteoritic origin the ni is presently carried by fe ni metal while the fe and mg are carried by mafic silicates if any large scale separation of metal and silicate phases has occurred the concentration ratio of ni to fe mg in the mafic silicates of the ancient crust in the vicinity of the apollo 16 site has not been preserved by apollo 16 rocks apollo 16 polymict breccias and soils contain much higher concentrations of siderophile elements and fe ni metal than other nonmare samples from the moon thus it is likely that the ni mg fe ratio estimated for the komatiite component from apollo 16 samples is high compared to the actual ratio for the lunar crust

water chemistry and its diversity in relation to local factors in the latnjavagge drainage basin arctic oceanic swedish lapland the chemistry of precipitation snow pack and surface water has been analysed on 205 samples collected during the 2001 field season at 25 selected sites within the latnjavagge drainage basin in arctic oceanic northern swedish lapland additionally daily discharge and yield of dissolved solids have been calculated for several subcatchments and the entire latnjavagge catchment during the years 2000 2001 and 2002 chemical water analysis included the components ca2 mg2 na k fe2 mn2 cl no3 so42 and po43 with so42 and ca2 being the dominant ones in the surface water solute concentrations and chemical denudation were low but showed significant differences within the basin in areas of shade longer snow cover frozen ground and thin regolith concentrations over the summer were perceptible but so low that solutes brought into the basin from precipitation could be detected in the surface water in one locality it was even found that lake water could reflect snowmelt to such an extent that the solute concentration was less than that of summer precipitation the highest concentrations were found at a radiation exposed w facing vegetated moderately steep slope with relatively thick regolith that was thawed at the time of snowmelt in early june in such well drained sites with continuous subsurface water flow a maximum of contact between water and mineral particles could take place the concentration values revealed differences in the rate of thawing of frozen ground between shaded areas and or areas at higher altitude on the one hand and radiation exposed areas on the other a comparison with published results from karkevagge a few kilometres to the northwest as well as from other periglacial locations indicates that the chemical denudation values from latnjavagge are more representative of periglacial oceanic environments than the values from the karkevagge catchment which shows especially high chemical denudation rates the investigation in latnjavagge stresses the importance of spatial variability within even small catchments of homogeneous lithology as it demonstrates that solute concentrations from different subbasins can differ substantially dependent on exposure to radiation duration of snow cover and frozen ground conditions regolith thickness and possibly also to vegetation cover and slope angle as factors steering water turbulence and retention of drainage

isotopic evidence from the eastern canadian shield for geochemical discontinuity in the proterozoic mantle most workers agree that proterozoic anorthosite massifs represent the crystallization products of mantle derived magmas1 2 although the composition of the parental melts is a major unsolved petrological problem3 as mantle derived rocks the massifs can be used as geochemical probes of their late precambrian upper mantle sources we report here nd and sr isotopic compositions of anorthosites and related rocks from the grenville and nain provinces of the eastern canadian shield here 75 of the earth s known anorthosite is found in a 1 600 km belt from the adirondack mountains of northern new york state to the eastern coast of labrador4 fig 1 the results indicate that the massifs were derived from at least two distinct mantle source regions which were established before 1 650 myr ago and were episodically involved in magmatism over 500 myr one reservoir below the grenville province and probably below much of the eastern superior province was isotopically similar to the depleted modern day mid ocean ridge basalt morb source the other reservoir was chondritic to moderately enriched and is most easily identified in the nain province but may have occurred scattered throughout the superior province

the mealy dykes labrador petrology age and tectonic significance the mealy dykes constitute a major olivine diabase swarm in the mealy mountains grenville province labrador the dykes intrude anorthosites and monzonites of the mealy mountains complex and outcrop over an area of at least 4000 km2 the swarm strikes east northeast and may constitute the largest group of unmetamorphosed diabase dykes in the grenville province the mealy dykes are moderately iron rich olivine tholeiites typically nonporphyritic thick dykes have coarse grained interiors that show some fractionation but variations in bulk chemical composition are relatively modest olivine fo47 fo27 plagioclase cores an63 an47 rims an47 an30 and low ca augite are the principal silicate minerals coexisting magnetite and ilmenite suggest that solidus temperatures were about 980 c and that subsolidus oxide re equilibration continued to near 530 c or perhaps lower a whole rock rb sr errorchron age for the mealy dykes yielded 1380 54 ma sr1 0 7028 0 0002 which within precision estimates i

the chemical weathering regime of karkevagge arctic alpine sweden abstract karkevagge is a valley located in swedish lapland at approximately 68 n and represents an arctic alpine landscape it is a presently periglacial glaciated trough incised into essentially horizontal metamorphic rocks some of which are presumably pyrite rich a set of coordinated studies was undertaken to investigate the nature of chemical weathering and pedogenesis in the valley and upon the abutting ridges august 1996 water quality measures reveal considerable spatial variation in solute totals with the highest total dissolved solute abundances being correlated with high sulfate abundances ridge crest soils exhibited poor horizonation but more extensive development of secondary clay minerals developed in situ than was found in valley flank and valley bottom soils valley soils exhibited multiple thin horizons many of which were buried and are taken to reflect great paraglacial and periglacial instability favorable microenvironments in the valley permit significant development of spodosols coarse debris along and across the valley bears both weathering rinds and rock coatings rock coatings in the valley include several types of iron films sulfate crusts carbonate skins and heavy metal skins karkevagge represents a mild arctic environment which does not preclude substantial chemical weathering in locations where abundant pyrite rich bedrock and water coincide this weathering follows pathways which are eminently expectable given that weathering of the pyrite rich rock permits generation of sulfuric acid which in turn weathers muscovite mica and calcite in local schists and marble respectively zones of intense chemical weathering also generate clearly visible deposits of gypsum and iron sulfate deposits such as jarosite not all arctic and or alpine environments are likely to be so active chemically but the results from karkevagge clearly show that dismissal of chemical weathering in cold regions on the basis of presumed first principles is erroneous consequently chemical weathering in such environments merits substantially more attention than it has hitherto received

models of convergent boundary tectonics implications for the interpretation of lithoprobe data physical models of convergent boundary processes can provide insights into compressional orogens such as those studied by lithoprobe we summarize the qualitative tectonic style of a series of mode

combining impact sensor field and laboratory flume measurements with other techniques for studying fluvial bedload transport in steep mountain streams the timing and rate of fluvial bedload transport are of central importance within sediment budget studies and in many applications in river science and engineering during the years 2010 2011 and 2012 detailed field measurements with portable impact sensors as a non invasive technique for indirectly determining fluvial bedload transport intensity were conducted in two instrumented and supply limited drainage basin systems erdalen and bodalen in the fjord landscape in western norway additional field measurements with portable impact sensors were carried out in 2010 and 2011 in selected transport limited fluvial systems in the coast mountains of western canada the collected impact sensor field data were calibrated with laboratory flume experiments the data from the impact sensor field measurements in western norway and the flume experiments were combined with field data from continuous discharge monitoring repeated surveys of channel morphometry and sediment texture particle tracer measurements helley smith samplings underwater video filming and biofilm analyses the combination of methods and techniques applied provides insights into the temporal variability and intensity of fluvial bedload transport in the selected mountain streams i in the transport limited systems with generally high bedload transport rates during high discharge and with bedload material moving in clusters over the impact sensor plates impact sensor data based on a 1 s measuring interval provide the opportunity to detect the start and end of bedload transport thus to identify discharge thresholds for sediment entrainment and to roughly estimate the intensity and relative intensity of change of bedload transport during the measuring period ii in the supply limited systems with low bedload transport rates and bedload components moving separately as single particles over the impact sensor plates impact sensor data with a 1 s measuring interval allow the detection of the start and end of transport of bedload components 11 3 mm thus the identification of discharge thresholds for possible entrainment of particles the quantification of the number of particles 11 3 mm moving over the impact sensor plates during the measuring period the rough estimation of grain sizes of the particles moving separately over the impact sensor plates and the calculation of the total mass of the bedload material 11 3 mm moving over the impact sensor plates during the measuring period iii when combined with other methods and techniques helley smith sampling particle tracer measurements biofilm analyses underwater video filming which provide information on the active bedload transport channel width on discharge thresholds for possible entrainment of particles of different grain sizes and on transport rates of bedload material 11 3 mm total rates of fluvial bedload transport covering all given grain sizes of the bedload material can be calculated for the supply limited mountain streams with generally low bedload transport the higher measured annual bedload yield in bodalen 13 6 t km 2 yr 1 compared to erdalen 2 6 t km 2 yr 1 reflects a higher level of slope channel coupling in bodalen than in erdalen

the archean gneiss complex of northern labrador 2 mineral ages secondary isochrons and diffusion of strontium during polymetamorphism of the uivak gneisses strontium isotope systematics of minerals from the ca 3600 ma old uivak gneisses and of compositionally layered uivak i gneisses which define secondary isochrons are the result of sr isotopic homogenization during thermal events ca 2800 ca 2500 and ca 1800 ma ago the strontium isotope data provide information about the thermal history of the archean gneiss complex in northern labrador the scale of sr isotopic equilibration and mechanisms of sr diffusion during polymetamorphism the mineral data indicate that biotite and amphibole were both partially open to sr diffusion during the hudsonian orogeny ca 1800 ma ago however cooling rates and closure to diffusion of sr in these phases varied throughout the terrane potassium feldspars were largely closed to diffusive loss of sr during the 1800 and 2500 ma events and they record evidence of a ca 2800 2900 ma thermal event ages defined by secondary isochrons correlate with variations in the widths of the gneissic layers and correspond with geolog

weathering implications of water chemistry in an arctic alpine environment northern sweden this paper reports on some of the chemical characteristics of late melt season water from karkevagge valley of the boulders above the arctic circle in northern sweden included in the analyses were temperature electrical conductivity ph so4 no3 k sio2 mg mn na fe and al these were measured in rain late lying snow and water from the major stream and lake as well as from pond tributary and seep sources in the valley a total of 71 samples was collected at 57 sites between august 6 and august 23 1996 for the purpose of characterizing the present weathering regime within this classic u shaped glacial valley evidence of chemical weathering included increases in solute concentrations over precipitation inputs and a source related wide variation in water chemistry the dominant anion measured in surface water was so4 that along with the presence of caso4 coatings on streambeds indicates that pyrite oxidation may contribute to the weathering regime high so4 concentrations were associated with gypsum coated streambeds and seeps that emerge from the bedrock low so4 concentrations were associated with tributaries flowing primarily on fresh rock and originating from melting snow estimated chemical denudation rate for the valley corrected for atmospheric inputs was 19 2 tons km2 yr although this is lower than previously reported our research supports earlier work indicating that chemical weathering is a major component of mass wasting in this arctic alpine environment

sr nd and pb isotopes in proterozoic intrusives astride the grenville front in labrador implications for crustal contamination and basement mapping abstract we report sr nd and pb isotopic compositions of mid proterozoic anorthosites and related rocks 1 45 1 65 ga and of younger olivine diabase dikes 1 4 ga from two complexes on either side of the grenville front in labrador anorthositic or diabasic samples from the mealy mountains grenville province and harp lake nain churchill provinces complexes have very similar major minor and trace element compositions but distinctly different isotopic signatures all mealy mountains samples have isr 0 7025 0 7033 end 0 6 to 5 6 and pb isotopic compositions consistent with derivation from a mantle source depleted with respect to nd sm and rb sr pb isotopic compositions for the mealy mountains samples are slightly more radiogenic than model mantle compositions all harp lake samples have isr 0 7032 0 7066 end 0 3 to 4 4 and variable but generally unradiogenic 207pb 204pb and 206pb 204pb compared to model mantle suggesting mixing between a mantle derived component and a u depleted crustal contaminant crustal contaminants are probably a variety of archean high grade quartzofeldspathic gneisses with low u pb ratios and include a component that must be isotopically similar to the early archean 3 6 ga uivak gneisses of labrador or the amitsoq gneisses of west greenland this would imply that the ancient gneiss complex of coastal labrador and greenland is larger than indicated by present surface exposure and may extend in the subsurface as far west as the labrador trough if harp lake and mealy mountains samples were subjected to the same degree of contamination as suggested by their chemical similarities then the mealy contaminants must be much younger probably early or middle proterozoic in age the labrador segment of the grenville front therefore appears to coincide with the southern margin of the archean north atlantic craton and may represent a pre mid proterozoic suture

sediment sources spatiotemporal variability and rates of fluvial bedload transport in glacier connected steep mountain valleys in western norway erdalen and bodalen drainage basins abstract contemporary fluvial bedload transport rates are still very difficult to measure and as a result of this in many sites only quantitative data on suspended and solute transport are included in sediment budget studies carried out for defined drainage basin systems the presented analysis of fluvial bedload dynamics in different defined subsystems of the glacier connected erdalen 79 5 km 2 and bodalen 60 1 km 2 drainage basins in the steep fjord landscape of western norway provides insights into i detectable relevant sediment sources ii instream channel storage of bedload material iii spatiotemporal variability and controls of bedload transport rates and bedload yields and iv the absolute and relative importance of fluvial bedload transport within the sedimentary budgets of these steep cold climate mountain valleys rockfalls snow avalanches stream channel bank erosion and fluvial transfers through small tributaries draining slope systems are relevant sediment sources for fluvial bedload transport in the main stream channels whereas the main outlet glaciers in both drainage basins are not of importance as all bedload material delivered directly from these outlet glaciers is trapped within proglacial lakes narrow valleys within both drainage basin systems are characterized by a higher intensity of slope channel coupling and display higher rates of sediment supply from slopes into the main stream channels than wider valleys snow avalanches are the most important sediment source in erdalen whereas fluvial transfers through small tributaries followed by snow avalanches are most important in bodalen longer term instream channel storage is not of great importance in the steep bodalen drainage basin but currently plays an important role within the erdalen drainage basin which is characterized by a stepped longitudinal main valley bottom profile favoring deposition of bedload material within less steep main channel reaches the mean annual bedload yields 2010 2013 are 2 4 t km 2 y 1 for the entire erdalen and 13 3 t km 2 y 1 for the entire bodalen drainage basin which are comparably low values for steep and partly glacierized drainage basin systems because of supply limited conditions the intensity of fluvial bedload transport is generally much more related to the availability of sediments than to channel discharge fluvial bedload transport accounts for about one third of the total fluvial transport and accordingly plays an important role within the sedimentary budgets of both drainage basin systems