hf isotopic composition and age constraints on the evolution of the archean central uchi subprovince ontario canada the archean uchi subprovince located in the northwestern superior province comprises greenstone belts and granitoid complexes that formed in the course of a multistage history between about 3000 and 2690 ma the earliest volcanic plutonic complexes were assembled into a microcontinent which then progressively grew by the addition of magmatic arcs and tectonic slivers a major compressional orogeny concluded this evolution at around 2700 ma lu hf isotopic compositions for well dated zircon populations from volcanic and plutonic rocks of the central part of the subprovince have hf values that range from 6 1 to 1 4 these results show that the bulk of the province was derived predominantly from depleted mantle sources but there is a superimposed trend showing involvement of the oldest greenstone and crustal sequences in the generation of the youngest magmatic complexes the temporal and isotopic relationships of the uchi subprovince contrast with the situation observed in the southern abitibi greenstone belt which developed within a time span of less than 80 m y in an intraoceanic setting and exhibits quite uniform depleted mantle like isotopic values revealing only very subordinate degrees of recycling of older crust

the oxygen isotope composition petrology and geochemistry of mare basalts evidence for large scale compositional variation in the lunar mantle to investigate the formation and early evolution of the lunar mantle and crust we have analysed the oxygen isotopic composition titanium content and modal mineralogy of a suite of lunar basalts our sample set included eight low ti basalts from the apollo 12 and 15 collections and 12 high ti basalts from apollo 11 and 17 collections in addition we have determined the oxygen isotopic composition of an apollo 15 kreep k potassium ree rare earth element and p phosphorus basalt sample 15386 and an apollo 14 feldspathic mare basalt sample 14053 our data display a continuum in bulk rock delta o 18 values from relatively low values in the most ti rich samples to higher values in the ti poor samples with the apollo 11 sample suite partially bridging the gap calculation of bulk rock delta o 18 values using a combination of previously published oxygen isotope data on mineral separates from lunar basalts and modal mineralogy determined in this study match with the measured bulk rock delta o 18 values this demonstrates that differences in mineral modal assemblage produce differences in mare basalt delta o 18 bulk rock values differences between the low and high ti mare basalts appear to be largely a reflection of mantle source heterogeneities and in particular the highly variable distribution of ilmenite within the lunar mantle bulk delta o 18 variation in mare basalts is also controlled by fractional crystallisation of a few key mineral phases thus ilmenite fractionation is important in the case of high ti apollo 17 samples whereas olivine plays a more dominant role for the low ti apollo 12 samples consistent with the results of previous studies our data reveal no detectable difference between the delta o 17 of the earth and moon the fact that oxygen three isotope studies have been unable to detect a measurable difference at such high precisions reinforces doubts about the giant impact hypothesis as presently formulated

influence of cohesion on river bed scour in the wake region of piers abstractstudies on scour in the wake region of piers in cohesive sediments containing gravel were not reported in literature to the best of our knowledge results from the laboratory experiments based study on the process of wake scour are presented here the sediment used for the experiment were of two types 1 fine gravel mixed with clay in proportions varying from 20 to 60 by weight and 2 fine gravel and fine sand in equal proportion by weight mixed with clay in proportions varying from 20 to 60 by weight the experiments revealed that the process of scour as well as depth shape and geometry of scour hole developed in such cohesive sediment were significantly different from that of cohesionless sediments proportion of clay fraction and unconfined compressive strength of cohesive sediment mixture were found to be the most significant variables controlling the depth of scour in the wake of piers on the basis of dimensional considerations relationships have been proposed for the estimation

interior of the moon the presence of garnet in the primitive deep lunar mantle new trace element data have been generated by inductively coupled plasma mass spectrometry icp ms for 65 high and low ti mare basalts from the apollo 11 12 14 15 and 17 landing sites these data demonstrate that ratios of the high field strength elements and yttrium are generally chondritic in the mare source regions for the low ti basalts but nonchondritic in the high ti basalts and potassium rare earth elements and phosphorus kreep such differences can be explained by addition and subtraction respectively of ilmenite this interpretation is consistent with derivation of the basalts from lunar magma ocean lmo cumulates through which late stage ilmenite has sunk and mixed with earlier magma ocean products compositional differences between the mare basalts and volcanic glass beads suggest that at least some of the latter were derived from a garnet bearing source region siderophile and chalcophile element data suggest that the garnet bearing source escaped the lmo melting event and thus represents primitive moon material the remaining glasses are generally very low ti vlt and appear to have been derived from early lmo cumulates i e olivine and orthopyroxene similar to the vlt basalts the remaining glasses were derived from below the lmo cumulates and as the magmas rose they underwent sequential assimilation to varying degrees initially of an ilmenite rich cumulate followed by a kreep component this study presents geochemical evidence for the existence of garnet in a mare source and demonstrates the likelihood that the lmo was not whole moon thus preserving primitive lunar material which has acted as the source region for at least some of the volcanic glasses

flume experiments on scour downstream of wood stream restoration structures abstract river restoration aims to improve physical natural form and processes of a river techniques to control the riverbed stabilize channel alignment protect stream banks and rebuild the natural habitat are an important part of river restoration projects rivers can be stabilized and habitat restored through techniques such as rebuilding meanders and pool riffle sequences and managing large wood structures that limit channel width to accelerate the normal flows through the constricted section are referred to as stream deflectors single wing double wing and triangular deflectors are the most commonly used types of this measure log frame deflectors consist of a triangular log frame filled with rock deflector constructions singly or in series in low gradient meandering streams divert base flows toward the center of the channel and under certain conditions increase the depth and velocity of flow thereby creating scour pools and enhancing fish habitat scour characteristics and morphologies downstream of log frame deflectors have been analyzed at the hydraulic laboratory of the university of pisa all experiments have been carried out in clear water conditions the results showed that the tailwater depth plays an important role on scour characteristics in addition it was experimentally proven that using log frame deflectors instead of log deflectors result in a better river bank protection in this case for all the tested hydraulic conditions the scour hole never occurred close to the channel bank useful empirical relationships have been proposed in order to evaluate the main features of the scour geometry

effect of grade control structures at various stages of their destruction on bed sediments and local channel parameters abstract grade control structures gcss represent the typical management of torrential streams preventing massive bed erosion and bedload transport the original and present geometric and sedimentary parameters of 18 gcss at various stages of their destruction since the 1970s were evaluated to determine the relationship between the former and present day components of the managed mohelnice river the western carpathians czech republic the latest changes in the gcs geometry related scour holes and bed surface grain size of sedimentary wedges were caused by the 2010 flood event of 20 50 r i discharge no relationship exists between the bed surface grain sizes and the present water drop or the present equilibrium channel slope of the sedimentary wedge a significant downstream coarsening of the largest grain size percentile represented by d 95 is detected through the sequence of gcss also statistically insignificant trends in downstream coarsening were observed for d 16 d 50 and d 84 grain sizes however the investigated sequence is still passable for grain diameters up to 200 mm during high magnitude floods similar to the 2010 event as documented by the development of a confluent gravel bar downstream of the sequence bedload transport simulations provide the highest bedload transport rates for the initial stage of the uppermost studied channel reach without the presence of gcss 30 000 kg min 1 for q 50 grade control structures reconstruction in the 1970s significantly decreased transport rates 2000 kg min 1 for q 50 owing to the erosion of gcs crests and an increase in related equilibrium channel slope damage on gcss can lead to an increase in bedload transport intensity 13 000 kg min 1 for q 50 significant linear relationships exist among the present parameters of the scour holes length of scour hole maximum scour depth and horizontal distance between the point of maximum depth and the gcs crest a statistical significant power relationship exists between the parameters of maximum scour hole depth and the present drop height showing adjustments of maximum scours to the present stage of gcss and the last flood event

meteomod a numerical model for the calculation of melting crystallization relationships in meteoritic igneous systems the meteomod model is a computer program designed to calculate melting crystallization relationships in igneous systems compositionally similar to ordinary chondrites and basaltic achondrites the core of meteomod is a set of empirically calibrated equations called geothermometers which describe equilibria between silicate melt and minerals such as olivine orthopyroxene pigeonite augite plagioclase and metallic fe in terms of pressure temperature and liquid compositions the silicate mineral geothermometers are calibrated from a database containing the compositions of melts and minerals produced in melting experiments on 113 meteoritic and 141 synthetic systems the metallic iron silicate melt geothermometer is calibrated from a database of 396 melting experiments the meteorite melting model or meteomod calculates crystallization temperatures and contents of major end members in mineral solid solutions with accuracies of 10 15 c and 1 2 mol respectively input parameters for the program are 1 increment in crystallization degree 2 one of 12fo2 buffers routinely used in petrology 3 shift from the buffer in log units if any 4 a choice of equilibrium or fractional crystallization trajectory 5 terminal crystallization degree 6 contents of ten major elements in wt 7 a set of minor and trace elements in parts per million 8 the number of initial compositions to be modeled in a single computation run the output consists of a series of tables that list equilibrium temperatures o fugacities and proportions of melt and minerals and their compositions as a function of the degree of crystallization the results of application of meteomod to modeling of melting crystallization of the st severin ll chondrite are compared with the experimental data of jurewicz et al 1995

origin of high magnesian andesites in the setouchi volcanic belt southwest japan ii melting phase relations at high pressures melting phase relations of an augite olivine high magnesian andesite and an augite olivine basalt from the miocene setouchi volcanic belt in southwest japan have been studied under water saturated water undersaturated and under anhydrous conditions both the andesite and the basalt are characterized by low feo mgo ratios 0 86 and 0 76 in weight respectively and qualify as primary magmas derived from the upper mantle the andesite melt coexists with olivine orthopyroxene and clinopyroxene at 15 kbar and 1030 c under water saturated conditions and at 10 kbar and 1070 c under water undersaturated conditions 7 wt h2o in the melt the basalt melt also coexists with the above three phases at 11 kbar and 1305 c under anhydrous conditions and at 15 kbar and 1205 c in the presence of 4 wt water present studies indicate that high magnesian andesite magmas may be produced even under water undersaturated conditions by partial melting of mantle peridotite it is suggested that two types of high magnesian andesites in the setouchi volcanic belt augite olivine and bronzite olivine andesites were produced by different degrees of partial melting augite olivine andesite magmas whose mantle residual is lherzolite were formed by lower degrees of partial melting than bronzite olivine andesite magmas which coexist with harzburgite the basalt magmas which were often extruded in close proximity to the high magnesian andesite magmas are not partial melting products of a mantle peridotite which had previously melted to yield high magnesian andesite magmas

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

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

on the connection between mare basalts and picritic volcanic glasses the evolution of the major element compositions of mare basaltic liquids and coexisting crystals in low pressure fractionation processes has been modeled in order to examine the postulated link between picritic volcanic glasses and mare basalts existing models of equilibrium and fractional crystallization longhi 1977 1982 have been modified to include expressions for the cr spinel liquidus surface and the boundary between the armalcolite and ilmenite surfaces average molar partition coefficients for armalcolite liquid pairs are also included in the modifications results of the calculations show that most mare basalts are not derived by simple low pressure fractionation from parents with the compositions of picritic glasses as tabulated by delano 1986a also there is no indirect evidence as yet for posteruption fractionation of picritic magmas in the form of sufficiently magnesian mare type olivines at the apollo 12 and 15 landing sites however the calculations do suggest that luna 24 ferrobasalt and apollo 11 high k basalts could have been derived by simple near surface fractionation of known picritic compositions also xenocrystic olivines with mare like concentrations of tio2 and cao in high ti basalt 74275 provide evidence for the existence of a picritic magma at the apollo 17 site more importantly the calculations indicate that the picritic magmas would have fractionated to produce basalts with bulk and mineral compositions generally similar to those of mare basalts these latter results favor the hypothesis that mare basalts have fractionated nonprimary compositions and that the small number of observed linkages between basalts and picritic parents is a consequence of limited sampling

local scouring and morphological adjustments in steep channels with check dam sequences this paper describes bed profile and grain size distribution adjustments in a mountain river maso di spinelle river italian alps stabilized by a sequence of boulder check dams the control works were originally designed to simulate the geometry of natural step pool channels where tumbling flow is the dominant hydraulic regime local scouring downstream of 29 drop structures is analysed through the use of nondimensional parameters where maximum scour depth and scour length are normalised to the drop height prior laboratory data reveal a pattern similar to field scours where complex interactions occur between drop height critical flow depth and step spacing the linkage between scour length and depth is also discussed there seems to be a maximum step height for impinging jets that is approximately twice the drop height this maximum may explain the upper limit of the steepness factor found in high gradient step pool streams if such a maximum upper limit is confirmed by further studies this may aid designs of foundation heights for transverse control works in steep channels

reduction of bend scour by an outer bank footing flow field and turbulence river bank protection is a costly but essential component in river management outer banks in river bends are most vulnerable to scour and erosion previous laboratory experiments illustrated that a well designed horizontal foundation of a vertical outer bank protruding into the cross section called a footing can reduce the scour depth and thereby protect the bank this paper provides detailed experimental data in a reference experiment without footing and an experiment with footing carried out under similar hydraulic conditions which suggest a delicate interaction between bed topography downstream and cross stream velocity and to lesser extent turbulence the presence of the outer bank footing modifies this delicate interaction and results in a more favorable configuration with respect to bank stability including reduced maximum scour depth more uniformly distributed downstream velocity and weaker cross stream circulation cells

nd o and sr isotopic constraints on the origin of precambrian rocks southern black hills south dakota abstract the nd o and sr isotopic characteristics of precambrian metasedimentary metavolcanic and granitic rocks from the black hills of south dakota are examined two late archean granites 2 5 2 6 ga have t dm ages of 3 05 and 3 30 ga suggesting that at least one of the granites was derived through the melting of significantly older crust early proterozoic metasedimentary rocks have t dm ages that range from 2 32 to 2 45 ga these model ages in conjunction with probable stratigraphic ages ranging from 1 9 to 2 2 ga indicate that mantle derived material was added to the continental crust of this region during the early proterozoic previous studies of the harney peak granite complex have reported u pb and rb sr ages of about 1 71 ga and most granite samples examined in this study have sr isotopic compositions consistent with that age two granite samples taken from the same sill however give two point rb sr and sm nd ages of 2 08 0 08 and 2 20 0 20ga 2200 nd 15 5 respectively in addition whole rock and apatite samples of the spatially associated tin mountain pegmatite give a sm nd isochron age of 2000 100 ma 2200 nd 5 8 1 8 the sm nd o and rb sr isotopic systematics of these granitic rocks have been complicated to some degree by both crystallization and post crystallization processes and the age of the pegmatite and parts of the harney peak granite complex remain uncertain processes that probably complicated the isotopic systematics of these rocks include derivation from heterogeneous source material assimilation mixing of ree between granite and country rock during crystallization via a fluid phase and post crystallization mobility of sr the nd isotopic compositions of the pegmatite and the harney peak granite indicate that they were not derived primarily from the exposed metasedimentary rocks

petrogenesis of primitive and evolved basalts in a cooling moon experimental constraints from the youngest known lunar magmas abstract we have conducted high temperature experiments over a range of pressures to constrain the petrogenesis of the youngest sampled lunar magmas which have contrasting primitive and evolved compositions our results indicate that at 3 ga melting still occurred within the same mantle depth range that produced crystalline mare basalts for the previous 1 ga although our data cannot support or confirm that the shallowest extents of melting moved deeper into the mantle by 3 ga as is predicted by most thermal evolution models furthermore melting still occurred in regions with low abundances of heat producing elements basaltic lunar meteorite nea 003a has some of the lowest abundances of incompatible trace elements among all mare basalts and no negative eu anomaly our experiments show that nea 003a is multiply saturated with olivine and low ca pyroxene on its liquidus at 1 1 gpa 215 km and 1330 c if the primitive nea 003a liquid composition is a minimally modified melt the relatively low mg of its source region 73 75 its lack of a eu anomaly and its chondritic initial nd isotopic composition indicate its source region likely escaped mixing during mantle overturn with later stage magma ocean cumulates that formed after plagioclase saturation this condition would require the sources of the ultramafic glasses to have experienced cumulate mixing or for assimilation of later stage magma ocean cumulates by the ultramafic glass parental magmas before eruption in order to account for their higher mg s and deeper negative eu anomalies alternatively nea 003a may have undergone some fractional crystallization in which case its more primitive source region would be deeper than 215 km and may approach the depth range of the ultramafic glass source regions iron and incompatible trace element rich basaltic lunar meteorites lap 02205 nwa 032 479 and nwa 4734 have nearly identical bulk compositions and have a multiple saturation point on their high pressure liquidus at

an archean metamorphic core complex in the southern slave province basement cover structural relations between the sleepy dragon complex and the yellowknife supergroup archean rocks in the fenton lake brown lake area southern slave province are subdivided into two lithotectonic domains a supracrustal domain which consists mainly of the archean yellowknife supergroup and a gneiss granite domain the latter is composed of gneissic and metaigneous rocks of the sleepy dragon complex determined to be basement to the yellowknife supergroup and granite plutons including the 2641 3 5 ma suse lake granite and the 2583 5 1 ma morose granite volcanic rocks of the cameron river belt and greywacke mudstone turbiditic metasedimentary rocks of the burwash formation constitute the supracrustal domain a late archean amphibolite to greenschist facies ductile to local brittle high strain zone separates the domains kinematic indicators demonstrate that the zone experienced two kinematically opposed episodes of displacement the older episode involved pre to synthermal peak thrusting of the supracrustal rocks over the gneiss granite domain thrusting is kinematically an

magmatic evolution of the moon although incomplete because of the imperfect and somewhat random sampling of rock types by the apollo and luna missions 1969 1976 the history of lunar magmatism has been reconstructed by numerous researchers over the past three decades these reconstructions have illustrated the continuous nature of lunar magmatism from 4 6 to approximately 2 0 ga and the large influence of early differentiation and catastrophic bombardment on lunar mantle dynamics magmatism and eruptive style in this review we group magmatism into multiple stages of activity based on sampled rock types and evaluate the models for each stage stage 1 is early lunar differentiation and associated magmatism partial melting of the moon soon after accretion was responsible for producing an anorthositic crust and a differentiated lunar interior the extent of lunar melting and mantle processing depends strongly on the mechanisms that induced melting estimates for the time over which melting and crystallization occurred range from tens to hundreds of millions of years stage 2 is the disruption of lunar magma ocean cumulates soon after the crystallization of most of the lunar magma ocean the cumulate pile experienced gravitational overturn this resulted in transport of late forming cumulates into the deep lunar mantle and mixing of magma ocean cumulates on a variety of scales stage 3 is the post magma ocean highland magmatism whereas the ferroan anorthositic crust was probably produced during the crystallization of a magma ocean the slightly younger mg suite and alkali suite plutonic rocks may have been generated by decompressional melting of early magma ocean cumulates during cumulate pile overturn a kreep and crustal signature was incorporated into these primitive basaltic magmas through assimilation near the base of the lunar crust or through melting of a hybridized mantle the alkali suite could represent either the differentiation products of mg suite parental magmas or a separate but contemporaneous episode of basaltic magmatism stage 4 is pre basin volcanism sample analysis and remote sensing data indicate that early lunar volcanism kreep basalts and high alumina basalts was contemporaneous with periods of highlands plutonism and catastrophic bombardment of the lunar surface the relationship between early stages of lunar volcanism and the contemporaneous plutonism is not clear the kreep basalts may be volcanic equivalents to both the mg suite and alkali suite stage 5 is the late remelting of magma ocean cumulates and eruption of mare basalts basin associated eruption of mare basalts occurred during and following the late stages of catastrophic bombardment this volcanic activity was possibly an extension of the thermal event that initiated pre basin volcanism mare basalts exhibit a wide range of composition resulting from near surface fractionation of chemically distinct primary basaltic magmas most likely mare basalts were produced by small to moderate degrees of partial melting of hybrid cumulate sources in the deep lunar mantle alternatively the mixed chemical signatures observed in many mare basalts may be interpreted as indicating assimilation of late stage evolved cumulates by melts produced deep in the cumulate pile the wide range of compositions exhibited by the mare basalts compared with earlier episodes of basaltic magmatism may reflect the thermal regime in the lunar mantle that limited the extent of partial melting and melt source homogenization

local scour associated with angled spur dikes a series of experiments were conducted in which the volume of the scour hole associated with model spur dikes was measured in a laboratory flume under clear water overtopping flows spur dike models were angled at 45 90 and 135 to the downstream channel sidewall with contraction ratios of 0 125 and 0 250 the main goals of the experiments were to evaluate the effect of the three angles on the volume of scour and potential aquatic habitat and on minimizing erosion adjacent to the streambanks the experiments showed that of the three angles tested the least erosion of the bed in the near bank region was associated with the spur dikes with 90 angles while the greatest volume of the scour hole was associated with the 135 spur dikes it was concluded that spur dikes with 135 angles showed the best potential for providing improved aquatic habitats while minimizing the potential for erosion of the channel bank

lunar volcanic glasses and their constraints on mare petrogenesis abstract volcanic glasses from the apollo 11 14 15 and 16 landing sites have been analyzed for major elements and ni by electron microprobe the 19 varieties of volcanic glass define two distinct chemical arrays that provide new insights into a the petrogenesis of mare basalts and b the structure of the deep lunar interior a simple model is proposed whereby mare basaltic liquids may have been derived from two isolated cumulate systems occurring at depths of 300 km and 400 km each system was itself composed of two lithologic components low ti vs high ti that underwent hybridization assimilation or mixing to generate the large compositional range of magmas observed within each array while the distribution of the two components within each system was locally heterogeneous data indicate that the components themselves were chemically uniform on at least a regional scale the surface correlated volatiles associated with the lunar volcanic glasses seem to have come from some other reservoir within the moon the simplicity of the chemical relationships observed among the lunar volcanic glasses allow specific predictions to be made we believe that they should readily reveal any strengths or weaknesses of this new model

pristine lunar glasses criteria data and implications major element analyses of several thousand glasses from all of the apollo landing sites have resulted in the identification of 25 groups of pristine i e volcanic glass the nickel in these pristine glasses is shown to be indigenous not meteoritic contamination and to be correlated with mg the chemical data indicate that these glasses are consistently better candidates for primary magmas than the majority of crystalline mare basalts the pristine glasses support the view that assimilative processes ringwood and kesson 1976 involving two cumulate systems in the differentiated mantle operated during mare petrogenesis the reality of those assimilative interactions is evident by the occurrence of two linear arrays among the chemistries of the glasses data suggest that these cumulate components in the differentiated mantle persist for lateral distances of at least 1000 km and therefore appear to be products of a vast magma ocean that existed early in lunar history alternative hypotheses claiming that the highlands crust and mare source regions were produced by serial magmatism without a magma ocean have not yet considered all of the constraints derived from the pristine glasses

assimilation by lunar mare basalts melting of crustal material and dissolution of anorthite we discuss techniques for calculating the amount of crustal assimilation possible in lunar magma chambers and dikes based on thermal energy balances kinetic rates and simple fluid mechanical constraints assuming parent magmas of picritic compositions we demonstrate the limits on the capacity of such magmas to melt and dissolve wall rock of anorthitic troctolitic noritic and kreep quartz monzodiorite compositions significant melting of the plagioclase rich crustal lithologies requires turbulent convection in the assimilating magma and an efficient method of mixing in the relatively buoyant and viscous new melt even when this occurs the major element chemistry of the picritic magmas will change by less than 1 2 wt diffusion coefficients measured for al2o3 from an iron free basalt and an orange glass composition are 10 12 m2 s 1 at 1340 c and 10 11 m2 s 1 at 1390 c these rates are too slow to allow dissolution of plagioclase to significantly affect magma compositions picritic magmas can melt significant quantities of kreep which suggests that their trace element chemistry may still be affected by assimilation processes however mixing viscous melts of kreep composition with the fluid picritic magmas could be prohibitively difficult we conclude that only a small part of the total major element chemical variation in the mare basalt and volcanic glass collection is due to assimilation fractional crystallization processes near the lunar surface instead most of the chemical variation in the lunar basalts and volcanic glasses must result from assimilation at deeper levels or from having distinct source regions in a heterogeneous lunar mantle

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

are ureilites residues from partial melting of chondritic material the answer from magpox calculations performed using magpox show that no bulk compositions having chondritic ca al ratio and within the range of chondritic si mg ratios can produce the olivine pigeonite ureilites which constitute 65 of those for which modal abundances are known as residues of single stage equilibrium partial melting calcium aluminum ratios of 2 3 5 ci are required in addition all the ureilites could not have formed from a single composition at various degrees of reduction because they show no correlation between pigeonite olivine ratio and mg ratio materials with various al mg ratios ranging from subchondritic to superchondritic are required if these materials are primitive i e created by nebular processes rather than planetary igneous processes they are unknown in the meteorite record excess accretion relative to chondrites of 5 10 mol of a high temperature condensate component which was itself almost completely depleted in corundum due to early fractionation could create the necessary compositions the plausibility that such processes occurred on a parent body sized scale is difficult to assess in contrast lodranites can be produced as residues of 3 30 equilibrium partial melting of an average ordinary chondritic composition at the appropriate level of reduction although many features of ureilites suggest that they are relatively primitive residues produced by low degrees of melting of chondritic materials and thus resemble lodranites and other groups of primitive achondrites their predominantly pigeonite olivine mineralogy remains difficult to explain within this simple scenario

the origin and evolution of lunar high ti basalts periodic melting of a single source at mare tranquillitatis abstract five groups of basalts a b1 b2 b3 d with three principal ages exist at the apollo 11 site these range from the low k low rare earth element ree groups b1 b2 and b3 to the low k high ree group d basalts to the high k high ree group a basalts the group a basalts are the only high k 0 2 wt k2o basalts and youngest with an age of 3 59 02 ga groups b3 and b1 are 3 71 02 and 3 67 02 ga respectively group b2 basalts are the oldest at 3 85 02 ga group d basalts have not been dated fractionation modelling for major and trace elements indicates that the b1 basalts could have formed from a b3 like parent liquid the b2 and d basalts can also be related to liquids similar to the b3 b1 composition through the presence of varying amounts of modal whitlockite thus the entirety of low k high ti basalts at apollo 11 may have formed through melting of the same source region the group a basalt compositions are consistent with formation from a different parent liquid with the composition of apollo 11 orange glass modelling of major and trace elements in the apollo 11 orange glass indicate that the composition of the group a basalts is consistent with fractionation of this glass coupled with some assimilation 7 5 15 of an evolved kreep like material however this component is much younger than primitive kreep 4 4 ga this neukreep component similar to the composition of quartz monzodiorites described from the apollo 15 site probably represents evolved material formed during plutonism prior to the formation of the apollo 11 orange glass liquid

northwest africa 773 lunar mare breccia with a shallow formed olivine cumulate component inferred very low ti vlt heritage and a kreep connection abstract lunar meteorite northwest africa 773 herein referred to as nwa773 is a breccia composed predominantly of mafic volcanic components including a prominent igneous clast lithology the clast lithology is an olivine gabbro cumulate which on the basis of mineral and bulk compositions is a hypabyssal igneous rock related compositionally to volcanic components in the meteorite the olivine gabbro lithology exhibits cumulus textures and in our largest section of it includes some 48 olivine fo 64 to fo 70 average fo 67 27 pigeonite en 60 fs 24 wo 16 to en 67 fs 27 wo 6 11 augite en 50 fs 17 wo 33 to en 47 fs 13 wo 40 2 orthopyroxene en 70 fs 26 wo 4 11 plagioclase an 80 to an 94 and trace barian k feldspar ilmenite cr spinel re merrillite troilite and fe ni metal the mg fe ratios of the mafic silicates indicate equilibration of fe and mg however the silicates retain compositional variations in minor and trace elements that are consistent with intercumulus crystallization accessory mineralogy reflects crystallization of late stage residual melt both lithologies breccia and olivine cumulate of the meteorite have very low ti vlt major element compositions but with an unusual trace element signature compared to most lunar vlt volcanic compositions i e relative enrichment in light ree and large ion lithophile elements and greater depletion in eu than almost all other known lunar volcanic rocks the calculated composition of the melt that was in equilibrium with pyroxene and plagioclase of the cumulate lithology exhibits a kreep like ree pattern but at lower concentrations melt of a composition calculated to have been in equilibrium with the cumulate assemblage plus excess olivine yields a major element composition that is similar to known green volcanic glasses one volcanic glass type from apollo 14 in particular green glass b type 1 has a very low ti concentration and ree characteristics including extremely low eu concentration that make it a candidate parent melt for the olivine gabbro cumulate we infer an origin for the parent melt of nwa773 volcanic components by assimilation of a trace element rich partial or residual melt by a magnesian vlt magma deep in the lunar crust or in the mantle prior to transportation to the near surface accumulation of olivine and pyroxene in a shallow chamber eruption onto a volcanic surface and incorporation of components into local predominantly volcanic regolith prior to impact mixing of the volcanic terrain and related hypabyssal setting and ejection from the surface of the moon volcanic components such as these probably occur in the oceanus procellarum region near the site of origin of the green volcanic glasses found in the apollo 14 regolith

lithospheric structure in northwestern canada from lithoprobe seismic refraction and related studies a synthesis the snorcle refraction wide angle reflection r war experiment snore 97 included four individual lines along the three transect corridors a combination of snore 97 results with those from earlier studies permits generation of a 2000 km long lithospheric velocity model that extends from the archean slave craton to the present pacific basin using this model and coincident near vertical incidence nvi reflection data and geological information an interpreted cross section that exemplifies 4 ga of lithospheric development is generated the velocity structural models correlate well with the reflection sections and provide additional structural compositional and thermal constraints geological structures and some faults are defined in the upper crust at a larger scale the seismic data identify a variety of orogenic styles ranging from thin to thick skinned accretion in the cordillera and crustal scale tectonic wedging associated with both paleoproterozoic and mesozoic collisions models of poisson

the systematics of light lithophile elements li be and b in lunar picritic glasses implications for basaltic magmatism on the moon and the origin of the moon lunar picrites represented by high mg volcanic glasses are thought to be products of either partial melting of the deep lunar mantle followed by rapid ascent or polybaric partial melting initiated in the deep lunar mantle the near primary compositions of these volcanic glasses provide us with a unique perspective for evaluating basaltic magmatism the characteristics and evolution of the lunar mantle and the origin of the moon the light lithophile elements lle li be b in planetary materials have been used to estimate planetary compositions and evaluate magmatic processes ion microprobe analyses of these glasses for lles were conducted using a cameca 4f ion microprobe this suite of glass beads ranged in tio2 from 0 3 to 17 wt seventy one individual glass beads were analyzed for the lles in addition core rim analyses of individual glass beads were made the lles show a wide range of variability with li ranging from 1 2 to 23 8 ppm be ranging from 0 06 to 3 09 ppm and b ranging from 0 11 to 3 87 ppm b be ranges from 0 40 to 4 6 li be ranges from 2 7 to 41 7 although 90 of the li be values range from 14 to 30 both b be and li be values for the picritic glasses are less than chondrite be nd for the glasses ranges from 04 to 06 and are similar to chondrite 058 traverses across individual beads indicate that they are generally homogeneous with regards to lles regardless of tio2 content the individual glass groups show limited variations in lle characteristics the exceptions to this observation are the a17 vlt and the a15 yellow glasses at individual apollo sampling sites the lle content is generally correlated to tio2 the high ti glasses are displaced toward higher li at similar b and be relative to the very low ti glasses lle concentrations also parallel the enrichments of other lithophile elements such as ba zr sr and rees as noted for other trace element characteristics glasses from each sampling site have similar lle signatures for example the apollo 14 glasses generally have higher lle concentrations relative to glasses of similar tio2 content from other sites the lle data support mantle inhomogeneity and lunar magma ocean lmo cumulate overturn models suggested by previous studies a kreep component had been incorporated into some of these picritic glasses this is consistent with other trace elements and probably reflects the recycling of kreep and or other late stage lmo cumulates into the deep lunar mantle the picritic glasses are compositionally distinct from the crystalline mare basalts in lles they are not related by either fractional crystallization or partial melting processes this suggests that they were derived from distinctively different mantle sources estimates of the bulk compositions of the earth and the moon have previously been made based on the assumption that the ratio of li to be is a direct measure of the ratio of the high temperature condensates htc refractory components to the mg silicates less refractory components in a planet we assert that if li be is to be used to estimate bulk moon composition the picritic glasses provide fewer pitfalls and a better estimate than the crystalline mare basalts differences in partition coefficients d for li and be indicate that fractional crystallization and partial melting will modify the libe ratio estimates based on the picritic glasses infer a higher li be for the bulk moon than estimated from the mare basalts this would indicate that the bulk moon is less refractory than previously calculated by li be and approaches the bulk composition of the earth

geometry of scour holes associated with 90 spur dikes the stable pools formed by spur dikes can be a significant factor for improving aquatic habitat in unstable degraded streams prediction of the volume and geometry of the scour hole associated with a spur dike yields information that is valuable for assessing the potential benefit to the aquatic habitat volumes of the scour hole in the vicinity of model spur dikes were measured in a laboratory flume under clear water overtopping flows spur dike length flow depth and shear velocity ratio were varied in the experiments and found to significantly influence the volume of the scour hole for overtopping flows the ratio of the flow depth to the spur dike height was found to be an important control on the geometry of the resulting scour hole at higher flow depth to spur dike height ratios the location of the maximum depth of scour changed from the upstream point of the dike toward the channel bank and caused a secondary scour zone to form downstream of the spur dike a preliminary technique is proposed to predict the volume of scour for spur dikes perpendicular to the bank

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

geochemistry of the archean yellowknife supergroup the archean yellowknife supergroup slave structural province canada is composed of a thick sequence of supracrustal rocks which differs from most archean greenstone belts in that it contains a large proportion 80 of sedimentary rocks felsic volcanics of the banting formation are characterized by hree depletion without eu anomalies indicating an origin by small degrees of partial melting of a mafic source with minor garnet in the residua granitic rocks include synkinematic granites hree depleted low 87sr86sr i post kinematic granites negative eu anomalies high 87sr86sr i and granitic gneisses with ree patterns similar to the post kinematic granites sedimentary rocks turbidites of the burwash and walsh formations have similar chemical compositions and were derived from 20 mafic intermediate volcanics 55 felsic volcanics and 25 granitic rocks jackson lake formation lithic wackes can be divided into two groups with group a derived from 50 mafic intermediate volcanics and 50 felsic volcanics and group b characterized by hree depletion derived almost exclusively from felsic volcanics ree patterns of yellowknife sedimentary rocks are similar to other archean sedimentary ree patterns although they have higher lanybn these patterns differ significantly from typical post archean sedimentary ree patterns supporting the idea that archean exposed crust had a different composition than the present day exposed crust

multi chronometric ages and origin of archaean tonalitic gneisses in finnish lapland a case for long crustal residence time the tojottamanselka gneisses of the koitelainen region northern finland have been dated by the sm nd and the common pb methods the sm nd data of seven samples from a small area 100 m 100 m define an isochron oft 3 06 0 12 2 ga with correspondingind 0 50848 9 2 orend t 3 7 1 8 this age is in good agreement with the zircon u pb discordia age 3 1 ga reported by kroner et al 1981 and is interpreted as the time of magmatic emplacement the distinctly negativeend t value is found for the first time for archean tonalitic gneisses and implies derivation of these magmas by remelting of continental material with a long 200 500 ma crustal residence time a few samples on the other hand possessend t values close to zero hence they are thought to be derived by partial melting of basaltic sources with nearchondritic ree distribution patterns

neodymium and lead isotope evidence for enriched early archaean crust in north america there has been considerable debate as to whether isotopically enriched continental crust was an important geochemical reservoir in earliest archaean times fundamental questions such as the volume of the early crust its composition and the effect of its formation and or recycling on mantle geochemistry have still to be answered the most direct clues to the nature of the earliest crust and mantle are obtained from the isotope systematics of old rocks1 5 here we report neodymium and lead isotope measurements and uranium lead zircon geochronology from archaean gneisses of the slave province northwest territories canada the gneisses contain zircons with cores older than 3 842 gyr one sample of tonalitic gneiss has a nd chondritic model age of 4 1 gyr and an end 3 7 gyr of 4 8 this is the oldest reported chondritic model age for a terrestrial sample and provides evidence for strongly enriched pre 3 8 gyr crust a reservoir complementary to the depleted mantle already in existence by 3 8 gyr before present2 6

lunar regional dark mantle deposits geologic multispectral and modeling studies clementine five channel uv visible uvvis data have been used to study seven regional dark mantle deposits dmds on the moon the dmds were mapped in distribution to determine their extent and stratigraphic relationship to other geologic units based upon the spectral properties for each dmd the crystallization of the beads in each deposit was inferred and used to estimate cooling rates in the volcanic plumes that emplaced the deposits deposits with a high concentration of glasses reflect volcanic plumes that had low optical densities and high cooling rates whereas deposits dominated by crystallized beads indicate plumes with slower cooling rates due to higher optical densities spectral data from each of the regional dmds show that their glass crystallized bead ratio can be estimated based upon their 415 750 and 750 950 nm values and comparison to laboratory spectra for the beads patches of young dark mantle in the sinus aestuum dmd represent one extreme with the bluest color highest 415 750 and weakest glass band absorption lowest 750 950 of all the dmds at the other extreme is the aristarchus plateau dmd with the reddest color and strongest glass band absorption the other nearside dmds including taurus littrow sulpicius gallus rima bode and mare vaporum lie between these two extremes due to intermediate mixtures of the crystallized beads and glasses with other local soils the orientale ring dmd on the western limb is dominated by volcanic glasses and is spectrally similar to the localized dmds found in alphonsus crater we have identified a central vent for the orientale ring dmd and model the eruption as degassing of a near surface dike to produce a 20 km high umbrella shaped plume with ejection velocities of 360 m s and deposition of the glasses at an average radius of 80 km from the vent although we cannot identify the exact sources for the other regional dmds probably because they are buried beneath younger mare the eruptions most likely resulted from dikes breaching the surface and producing a volcanic plume dominated by larger greater than submillimeter hot clasts that formed mare and sinuous rules the small percent of clasts that form the volcanic beads are carried by the expanding gas cloud to large distances in some cases 100 km to produce the observed continuous regional dmds the lack of basalt samples that can be petrologically related to the volcanic glasses may be a result of their spatial separation with the basalts flowing into the basins while the beads are deposited both into the basins and on the adjacent highlands

genesis of granitoid batholiths of peninsular malaysia and implications for models of crustal evolution evidence from a ndsr isotopic and upb zircon study nd sr and u pb isotopic data for the late triassic west coast province batholiths and permian to triassic east coast province batholiths of peninsular malaysia allow estimates of the ages of the crustal fragments comprising the peninsula to be made initial nd and sr values for granitoids from the west coast province range from 6 to 10 and 160 0 716 to 660 0 751 respectively nd model ages calculated based on a depleted mantle evolution model tdmnd range from 1300 ma to 1800 ma and are in general agreement with the mid proterozoic upper intersection ages of u pb zircon reverse discordia 1500 1700 ma initial nd and sr values for granitoids from the east coast province range from 0 8 to 6 and 10 0 705 to 130 0 714 respectively calculated tdmnd ages of 900 1400 ma for these granitoids are comparable to two u pb zircon reverse discordia intercepts that yield 800 ma and 1350 ma the general agreement of u pb zircon inheritance ages and tdmnd ages are interpreted to correspond to the proterozoic crust formation ages of the continental fragments represented by the west coast and east coast batholithic provinces mid proterozoic 1300 1900 ma crust formation ages are commonly shown by other phanerozoic continental margin plutonic and volcanic belts the ubiquitous mid proterozoic crust formation ages and the absence of archaean signatures suggest voluminous juvenile additions to the continental crust in the mid proterozoic such ages at continental margins would imply that many continental blocks had achieved very much their present day extent by the mid proterozoic

apollo 15 yellow brown volcanic glass chemistry and petrogenetic relations to green volcanic glass and olivine normative mare basalts abstract apollo 15 yellow brown glass is one of twenty five high mg primary magmas emplaced on the lunar surface in pyroclastic eruptions forty spherules of this glass were individually analyzed by electron microprobe and inaa for major and trace elements e g sc v cr co la ce nd sm eu ho tm yb lu hf ta and u the abundances demonstrate that this primary magma was produced by partial melting of differentiated cumulates in the lunar mantle models are developed to explain the possible source regions of several apollo 15 and apollo 12 low ti mare magmas as being products of hybridization involving three ancient differentiated components of a primordial lunar magma ocean a early olivine orthopyroxene cumulates b late stage clinopyroxene pigeonite ilmenite plagioclase cumulates and c late stage inter cumulus liquid isotopic constraints on sm nd fractionation and least squares tests of potential mixing models require models of apollo 15 yellow brown glass and apollo 12 and 15 olivine mare basalts involving low f 3 cumulate remelting of sources in which olivine and orthopyroxene are residual phases models of the apollo 15 green glass composition indicate higher 4 7 degrees of melting but with only a slight preference for orthopyroxene rich relative to orthopyroxene free sources the modeled dependence on residual orthopyroxene in mare source regions places source depths at 400 km or greater in order to maintain olivine and orthopyroxene on the liquidus hybridization at such depths would likely result from convective overturn of the primordial magma ocean and suggests that separate fractionating masses were positioned at various depths our models for developing hybridized source regions of primary low ti mare magmas do not require selective contamination of primary liquids the preferred model for apollo 15 yellow brown glass is presented as the commingling of 95 early cumulate olivine orthopyroxene 1 9 clinopyroxene 0 27 pigeonite 1 7 plagioclase 0 02 ilmenite and 0 56 trapped liquid respective proportions for the apollo 15 olivine mare basalt source model are 98 5 0 37 0 0 79 0 16 and 0 13 and the proportions used for the preferred apollo 12 olivine mare basalt model are 97 6 0 73 0 24 0 77 0 42 and 0 21 our preferred model for the green glass source composition f 0 07 requires the commingling of 97 4 early olivine orthopyroxene 0 18 clinopyroxene 1 32 pigeonite 0 85 plagioclase and 0 28 trapped liquid

origin of high magnesian andesites in the setouchi volcanic belt southwest japan i petrographical and chemical characteristics high magnesian andesites of middle miocene age occur in southwest japan forming an obvious volcanic belt these andesites have low feo mgo ratios 0 546 0 931 and are rich in ni 101 312 ppm co 30 0 45 1 ppm and cr 208 756 ppm they are relatively aphyric phenocrysts 10 vol and the phenocrysts of magnesian olivine fo88 are in equilibrium with the host high magnesian andesite magmas on the basis of the fe mg exchange partitioning these features suggest that the high magnesian andesites are not differentiated or accumulative they appear to represent primary andesites generated in the upper mantle these southwest japanese high magnesian andesites are rich in incompatible elements and show light rare earth enrichment relative to boninites suggesting that the former is derived from a less depleted mantle source than the latter

oxidation states and ascent history of the apollo 17 volcanic beads as inferred from metal glass equilibria abstract the composition mode of occurrence and relationships of metal blebs in the apollo 17 74001 2 core have been examined to provide insight into variations in oxidation states during ascent and eruption of the lunar volcanic glasses the 74001 2 core is composed of 99 orange volcanic glasses and their crystallized equivalents black beads with olivine phenocrysts metal blebs and in the upper 8 cm of the core lithic fragments composing the remaining 1 in an analysis of this core twenty nine metal blebs larger than 4 m in size were discovered in thin sections taken along the length of the 68 cm deep core these blebs are classified into three types on the basis of their shape composition and distribution fourteen of the metal blebs were found trapped inside or between olivine phenocrysts type i blebs microprobe analyses showed that these spherical blebs have a homogeneous composition of 85 fe 14 ni and 1 1 co from core to rim six type ii rounded blebs were discovered trapped inside volcanic beads their core compositions are similar to the type i but near the rim these blebs have a sharp decrease in fe and increase in ni content in the lower half of the 74001 2 core where the beads are predominantly black many contain 5 m amoeba shaped type iii metal blebs type iii blebs are composed of fe with trace amounts of ni two angular metal fragments could not be classified into any of the three types we propose that the type i blebs formed initially at 4 0 km depth and 1 3 log units below iw at a pressure of 200 bars and a temperature of 1320 c by the formation of c o gas during graphite oxidation once trapped by olivine phenocrysts the blebs were buffered from further reactions with the melt the type ii blebs remained in contact with the melt during ascent and experienced loss of fe to the surrounding melt phase by oxidation reactions which range from 1 3 to 0 9 log below iw finally type iii blebs formed either by exsolution of fe during crystallization in the fire fountain or by loss of volatiles originally coordinated with fe to the volcanic gas phase under the reduced conditions in the fountain

exploring the lunar mantle with secondary ion mass spectrometry a comparison of lunar picritic glass beads from the apollo 14 and apollo 17 sites abstract the major element characteristics of lunar picritic beads indicate that their composition approaches that of primary basaltic liquids and therefore may be our best geochemical mineralogical probes of the lunar interior the picritic magmas appear to represent partial melting of a variety of mantle mineral assemblages secondary ion mass spectrometry sims analysis of individual glass beads collected from the apollo 14 a 14 and apollo 17 a 17 landing sites shows that although there is substantial major minor tio 2 al 2 o 3 and trace element variation at each site the glasses from each site have distinguishable trace element signatures ba sr lree hree the incompatible element characteristics of glasses of nearly identical major element chemistry are strikingly different between sites the contrast between the a 14 and a 17 glasses appears to be the result of a higher kreep component in all the a 14 glasses the incorporation of evolved kreep component into high mg magmas is not a result of either assimilation or magma mixing but incorporation during the partial melting episode that produced the picritic magmas this is a more thermally efficient mechanism for incorporation of the kreep component into a picritic magma calculated mantle chemistries based upon glass compositions low degrees of partial melting and mineralogical components used in previous models suggest that the difference between a 14 and a 17 mantle sources is a 0 1 1 4 kreep intercumulate melt this difference will increase with an increase in the degree of partial melting in the model calculations this intercumulate melt may interstitially reside in an evolved high ti cumulate component the juxtaposition of evolved high ti cumulates kreep and primitive low ti cumulates mantle components has been attributed to original mantle inhomogeneities density contrasts during magma ocean crystallization and sinking of high density evolved cumulates into less dense primitive cumulates within the context of either magma ocean or serial magmatism type models regardless of the model the trace element signatures of glasses and the basalts indicate that the character of the a 14 mantle source is intrinsically different from that of the a 17 mantle source this indicates large scale lateral and vertical inhomogeneities in the lunar mantle

scour of clear water rock w weirs in straight rivers abstractscour characteristics downstream of rock w weir structures were studied in a horizontal straight channel and under clear water conditions for each structure different hydraulic conditions were considered including densimetric froude numbers water drops and tailwaters results showed that the tailwater depth plays an important role in predicting the scour parameters dimensional analysis was used to derive equations to predict the maximum scour depth and length and the maximum dune height and length selected tests were conducted with an open w weir in this case results show that the maximum scour depth decreases and its location shifts downstream with respect to classical w weirs three types of scour morphology were classified type a characterized by one scour hole and two ridges type b with two scour holes and two ridges and type c characterized by only one scour hole and one ridge

anatexis of lunar cumulate mantle in time and space clues from trace element strontium and neodymium isotopic chemistry of parental apollo 12 basalts abstract in an effort to elucidate the processes of lunar mantle melting and the magma evolution of mare basalts within oceanus procellarum on the western lunar near side we have analyzed seven fine grained to vitrophyric apollo 12 basalts for trace elements five of these also have been analyzed for nd and sr isotopic compositions these samples represent all three main groups identified among the apollo 12 mare basalts and have been proposed as parental melts to their respective groups i e olivine pigeonite and ilmenite basalts the sources for these low ti mare basalts are postulated to have formed from crystallization of a global magma ocean li be systematics combined with ree data indicate that the specific sources for the apollo 12 low ti mare basalts were generated after 82 94 crystallization of this lunar magma ocean in fact it seems that all mare basalts analyzed from the apollo collections were generated from cumulates precipitated in the last 20 of the magma ocean chemical compositions of fine grained pigeonite and olivine basalts are consistent with 7 9 nonmodal in proportions not defined by experimental petrology and phase equilibria melting of a source consisting of 48 olivine 30 calcic clinopyroxene and 22 pigeonite as per neal et al 1994b sm nd and rb sr abundance data also suggest that the pigeonite and olivine basalt source contained from 0 3 to 0 5 trapped residual liquid from the magma ocean the compositions of the two fine grained ilmenite basalts are consistent with 5 7 partial melting of a source with subequal proportions of olivine 45 5 and pigeonite 42 5 and lesser amounts of clinopyroxene 11 5 and entrained plagioclase 0 5 furthermore the ilmenite source was nearly devoid of trapped liquid isotopic systematics of the apollo 12 fine grained parental basalts are consistent with their derivation from two distinct mantle source regions both of these sources were lree depleted for extended periods of time up to 600 million years for the ilmenite basalt source and up to 900 million years for the pigeonite and olivine basalt source due in part to the relatively small proportion of low sm nd trapped residual magma ocean liquid in the source by integrating this information on parental low ti apollo 12 basalts with mare basalt and picritic glass data from other landing sites as well as telescopic and remote sensing data we propose a model for melting of the lunar interior the upper 400 500 km of the lunar mantle is a consequence of incipient melting of the moon and formation of a global magma ocean this magma ocean became progressively enriched in incompatible elements as it precipitated the cumulate upper mantle this incompatible earliest extensive mare magmas high ti mare basalts were generated at shallow depths in the mantle from cumulate source regions that had trapped relatively large proportions of this incompatible element enriched residual magma ocean liquid these source regions also contained the late crystallizing phase ilmenite and thus generated high ti magmas the trapped liquid component contained elevated abundances of heat producing elements k u and th increasing the fertility of associated source regions with time melting moved progressively deeper in the mantle to source regions with less of the residual heat producing magma ocean liquid due to density contrasts the ilmenite bearing upper portions of the lunar mantle sank into the cumulate pile possibly carrying more fertile material with it and allowing melting of more mg enriched source regions to form the high ti picritic glass beads thus the major controlling factors in the melting of the lunar interior could be the proportion of trapped magma ocean liquid in the cumulate source and the sinking of more fertile ilmenite bearing material into the lower mantle

mantle derivation of archean amphibole bearing granitoid and associated mafic rocks evidence from the southern superior province canada amphibole bearing late archean 2 73 2 68 ga granitoids of the southern superior province are examined to constrain processes of crustal development the investigated plutons which range from tonalite and diorite to monzodiorite monzonite and syenite share textural mineralogical and geochemical attributes suggesting a common origin as juvenile magmas despite variation in modal mineralogy the plutons are geochemically characterized by normative quartz high al2o3 15 wt na rich fractionation trends mol na2o k2o 2 low to moderate rb generally 150 ppm are comagmatic with the evolved granitoids and indicate that the suites are mantle derived isotopic studies of archean monzodioritic rocks have shown lree enrichment and initial 143nd 144nd ratios indicating derivation from mantle sources enriched in large ion lithophile elements lile shortly before melting mineral assemblages record lower ph2o with increased alkali contents of the suites this evidence in conjunction with experimental studies suggests that increased alkali contents may reflect decreased ph2o during mantle melting these features indicate that 2 73 ga tonalitic rocks are derived from more hydrous mantle sources than 2 68 ga syenitic rocks and that the spectrum of late archean juvenile granitoid rocks is broader than previously recognized comparison with phanerozoic and recent plutonic suites suggests that these archean suites are subduction related

lunar magma transport phenomena abstract an understanding of the most significant events during the first ga or so of lunar history global differentiation associated with a lunar magma ocean lmo and the later generation of about 107 km3 of mare basalts depends profoundly on magma transport dynamics lmo evolution is dominated by the characteristics of hard turbulent convection of a fluid undergoing phase change quench protocrust formed at the ocean surface in early times is repeatedly disrupted by bolide impact ocean body tides and associated crustal foundering during this epoch the ocean temperature is set by the balance between convective heat brought to the surface and brown body radiation from the surface at later times the convective flow is organized into a number of regimes from top to bottom these include conductive crustal lid a viscous sublayer an inertial core a lower viscous sublayer and a mushy cumulate region crystal settling and flotation is restricted to the viscous sublayer regions dilatancy pumping may prevent the efficient expulsion of intercumulus melt during cumulate formation typical velocities within the inertial region are of order 10 m s because late stage ti rich cumulates are dense relative to the earlier mg rich cumulates hyper to sub solidus convection tends to mix lmo crystallization products numerical simulations that account simultaneously for compositional and thermal buoyancy effects indicate a characteristic mixing time 200 ma statistical measures of mixing variance and spatial correlation length quantify the details of mixing the darcy percolative and vein drain models of melt extraction are briefly discussed because compaction lengths are small 102 m the rate of melt extraction is governed by the balance between melt buoyancy and darcy friction differential melt matrix velocities are of order 10 km ma for nominal values appropriate for mare basalt melt extraction from a heterogeneous mixed lmo source transport of magma through the lunar lithosphere via a connected crack network seems highly probable for the range of inferred discharge rates applicable for lunar mare volcanism lmv 103 to 107 m3 s typical fracture widths and ascent speeds are 10 1 to 50 m and 10 1 to 10 m s respectively a simple model is proposed to evaluate the extent of fractionation as magma traverses cold lunar lithosphere if apollo green glasses are primitive and have not undergone significant fractionation en route to the surface then mean ascent rates of 10 m s and cracks of widths 40 m are indicated lunar tephra and vesiculated basalts suggest that a volatile component plays a role in eruption dynamics the predominant vapor species appear to be co co2 and cos near the lunar surface the vapor fraction expands enormously and vapor internal energy is converted to mixture kinetic energy with the concomitant high speed ejection of vapor and pyroclasts to form lunar fire fountain deposits such as the apollo 17 orange and black glasses and apollo 15 green glass

petrology and provenance of a very low titanium picrite clast in lunar highland regolith breccia 15295 clast 100 in regolith breccia 15295 could be a key to resolving the relationship s between mare basalts and lunar picritic glasses the clast is basaltic with texture mineralogy mineral compositions and calculated bulk composition suggesting that it crystallized in a thick lava flow or shallow intrusive body from a very low titanium vlt basaltic magma the estimated bulk composition of clast 15295 100 is primitive i e magnesian compared to those of known vlt basalts and is very close to those of vlt picritic green glasses especially the apollo 14 a green glass from these similarities we infer that clast 15295 100 is a crystalline product of a picritic magma similar to the apollo 14 a glass clementine and m3 remotely sensed data of the lunar surface were used to find areas that have chemical compositions consistent with those of clast 15295 100 not only near the apollo 15 site but in a broad region surrounding the site two regions are consistent with clast s 15295 100 compositional data the larger region is in southern mare imbrium and a smaller region is in the eastern half of sinus aestuum these locations should be considered as candidates for future missions focusing on sample science

a magma ocean on vesta core formation and petrogenesis of eucrites and diogenites abstract available evidence strongly suggests that the hed howardite eucrite diogenite meteorites are samples of asteroid 4 vesta abundances of the moderately siderophile elements ni co mo w and p in the hed mantle indicate that the parent body may have been completely molten during its early history during cooling of a chondritic composition magma ocean equilibrium crystallization is fostered by the suspension of crystals in a convecting magma ocean until the crystal fraction reaches a critical value near 0 80 when the convective system freezes and melts segregate from crystals by gravitational forces the extruded liquids are similar in composition to main group and stannern trend eucrites and the last pyroxenes to precipitate out of this ocean before convective lockup span the compositional range of the diogenites subsequent fractional crystallization of a main group eucrite liquid which has been isolated as a body of magma produces the nuevo laredo trend and the cumulate eucrites the predicted cumulate mineral compositions are in close agreement with phase compositions analyzed in the cumulate eucrites thus eucrites and diogenites are shown to have formed as part of a simple and continuous crystallization sequence starting with a magma ocean environment on an asteroidal size parent body that is consistent with vesta

scour on alluvial bed downstream of grade control structures this paper describes an approach for predicting local scour downstream of grade control structures the developed analysis applies the incomplete self similarity iss theory for deducing some physically based dimensionless groups controlling the geometrical pattern of the scour profile the scour measurements available in the literature in conjunction with numerous unpublished data allow a multiregressive calibration of the iss relationships the experimental sample includes different bed grain size distributions and scales of the erosive phenomenon the results prove that the ratio between the upstream water head and the weir height is able to explain the measurements of scour depth carried out in both small and large scale installations this estimation of maximum scour depth was improved introducing variables representative of both the jet contraction and the bed particle grain size distribution variables related to the longitudinal sizes of the scour profile tend to be predicted with more accuracy than those related to the scour depth and appear more influenced by the coarsest component of the alluvial bed

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

ion microprobe studies of trace elements in apollo 14 volcanic glass beads comparisons to apollo 14 mare basalts and petrogenesis of picritic magmas abstract the major element geochemistry of picritic lunar glass beads indicates that they represent primary basaltic liquid compositions and as such provide unique information concerning the origin of mare basalts and characteristics of the lunar interior this study used ion microprobe techniques for trace element analysis of individual glass beads representing seven compositionally distinct types of picritic glass beads from the apollo 14 site high ti glasses 17 11 tio2 red black orange intermediate ti glasses 5 4 tio2 yellow low ti glasses 2 8 tio2 lap low alkali picritic papike et al 1989 very low ti glasses ba sr 1 of these glasses are different from low ti mare basalts at other sites but are similar to crystalline basalts at the apollo 14 site the intermediate to high ti picritic glasses exhibit a flat to slightly positive lree slope and a negative hree slope the orange glass has a higher total ree abundance and a slightly larger negative eu anomaly than the red black and yellow glasses relative to the apollo 17 high ti glasses apollo 14 high ti glasses are enriched in ree lree hree y v zr sr ba and ba sr and are similar in alkali elements li rb co and sc trace element modeling within the context of liquid lines of descent and major element characteristics indicates that the picritic glass beads at the a 14 site are not related by low pressure fractional crystallization to each other or to crystalline basalts at the apollo 14 or other landing sites a possible exception is the relationship between lap and basalts of the high al basalt suite the wide range of primary magma compositions and the lack of petrogenetic linkage via crystal fractionation to crystalline basalts indicates that either a wide compositional range of evolved mare basalts has not yet been sampled or a unique mechanism is selectively tapping these picritic magmas directly from their mantle source region the wide range of major and trace element characteristics of the volcanic glass beads is consistent with derivation from mineralogically distinct sources which consist of varying proportions of olivine orthopyroxene clinopyroxene ilmenite plagioclase kreep component the evolved kreep component may have been incorporated into these primary picritic magmas by either assimilation fractional crystallization type processes afc or by hybridization of the mantle source the former appears less likely due to the general systematic increase in incompatible elements relative to ti concentration and the apparent lack of crystallization that is required in afc type models the hybridization processes may be the result of sinker mechanisms as proposed by ringwood and kesson 1976 a manifestation of original mantle inhomogeneities or a magma ocean stirred by large impacts

petrogenesis of mare basalts a record of lunar volcanism returned rock and soil samples from our nearest planetary neighbor have provided the basis for much of our understanding of the origin and evolution of the moon of particular importance are the mare basalts which have revealed considerable information about lunar volcanism and the nature of the mantle as well as post magma generation processes this paper is a critical review of the petrogenetic models for the generation of mare basalts formulated over the last twenty years we have used all available mare basalt analyses to define a six fold classification scheme using tio2 contents as the primary division i e 1 wt very low ti or vlt 1 6 wt low ti 6 wt high ti a secondary division is made using al2o3 contents i e 11 wt low al 11 wt high al and a tertiary division is defined using k contents i e 2000 ppm low k 2000 ppm high k such divisions and subdivisions yield a classification containing twelve categories of which six are accounted for by the existing apollo and luna collections therefore we present our discussions in the form of six mare basalt rock types 1 1 high ti low al low k referred to as high ti low k 2 2 high ti low al high k referred to as high ti high k 3 3 low ti low al low k referred to as low ti 4 4 low ti high al low k referred to as high alumina 5 5 low ti high al high k referred to as vhk 6 6 vlt low al low k basalts referred to as vlt a variety of post magma generation processes have been invoked such as fractional crystallization either alone or combined with wallrock assimilation to explain the compositional ranges of the various mare basalt suites in order to evaluate these proposed petrogenetic processes this review is by rock type and is non site specific but for each rock type reference to particular lunar sample return missions is brought forth this permits a comparison of similarities and differences of broadly similar rock types correlated with geography on the moon which in turn allows a more thorough petrogenetic evaluation high ti mare basalts i e high ti low al low k are found at apollo 11 and apollo 17 sites however the a 11 basalts contain lower tio2 abundances a considerably larger range in trace element contents and the only occurrence of high ti high k mare basalts fractional crystallization and source heterogeneity within each site are the keys to understanding the petrogenesis of the high ti basalts low ti basalts including both low al k and high al k varieties are found at apollo 12 14 and 15 and luna 16 sites the low ti basalts exhibit a wide range of major and trace element compositions and require source heterogeneity fractional crystallization and some assimilation the high alumina mare basalts i e low ti high al low k are found at apollo 14 and luna 16 sites and exhibit a wide range of major and trace element compositions however in these examples source heterogeneity is not a major factor indeed fractional crystallization coupled with kreep assimilation particularly for the apollo 14 variants can explain the compositional ranges of these high alumina basalts the vhk mare basalts i e low ti high al high k have been sampled only at the apollo 14 locale and are products of a parental highalumina magma assimilating lunar granite very low ti vlt mare basalts i e vlt low al low k are found at apollo 17 and luna 24 sites fractional crystallization has had a major influence upon the range in vlt compositions but luna 24 vlt basalts have been derived from a source slightly different in composition from that for apollo 17 vlt varieties for example the luna 24 vlt basalts generally exhibit positive eu anomalies a unique property for mare basalts which almost always have negative eu anomalies the concept of a lunar magma ocean lmo is generally accepted and source modelling of all basalts invokes a mafic lmo cumulate source this is the only unifying model for mare basalt petrogenesis but the semantics and logistics of it are and will be debated for many years for example major convective overturn of the lmo appears plausible but whether this occurred on a local or planet wide scale to produce source heterogeneity remains to be determined

a three component model for the bulk composition of the moon abstract using detailed analyses of lunar pristine glasses as a basis delano 1986 we present a suite of models of lunar bulk composition which are based on the following assumptions i that the early moon differentiated into two primary reservoirs 1 an feo rich magma ocean and 2 an olivine rich residuum of fo90 and ii that this magma ocean then differentiated into an olivine dominated cumulate fo80 and a primitive liquid composition ppg thus in these models the bulk composition of the moon is given by a mixture of three components an early olivine residuum a later olivine orthopyroxene cumulate and ppg liquid with the constraint that the moon possess a ci chondritic mg al ratio our model lunar compositions are grossly similar to the lunar composition of ringwood et al 1987 and when projected from feo they appear very similar to the composition of the earth s upper mantle again when projected from feo our model magma ocean compositions are very similar to the bulk lunar composition derived by taylor 1982 remelting of cumulates from the magma ocean can produce the mare basalts and the pristine glasses remelting of the early residuum may be the source of the highly magnesian olivines found in the lunar highlands our ability to relate such diverse chemistries as the earth s mantle and taylor s moon is relatively model independent the model compositions discussed above are generated by assuming that the cumulate formed by equilibrium crystallization to better determine if there is a significant difference between the feo contents of the earth and the moon we have also calculated bulk lunar compositions whose cumulate component is formed by fractional crystallization a more realistic approximation we find that if the mg si ratios of the earth and moon are similar and if the early residue is dominated by olivine then the bulk silicate moon is 25 to 50 enriched in feo over the earth s upper mantle 10 to 13 wt feo for the moon as compared to 8 wt for the earth again the ultimate basis for this estimate of lunar feo is the set of lunar pristine glasses a characteristic of all our models is that refractory lithophile elements such as ca and al are calculated to be 2 to 3 times ci in the bulk silicate moon these abundances are largely determined by our requirement that the moon possess a chondritic mg al ratio to emphasize this point we discuss the implications of the choices of various mg al and mg si ratios in the calculation of bulk planetary compositions

the electrical structure of the slave craton the slave craton in northwestern canada a relatively small archean craton 600400 km is ideal as a natural laboratory for investigating the formation and evolution of mesoarchean and neoarchean sub continental lithospheric mantle sclm excellent outcrop and the discovery of economic diamondiferous kimberlite pipes in the centre of the craton during the early 1990s have led to an unparalleled amount of geoscientific information becoming available over the last 5 years deep probing electromagnetic surveys were conducted on the slave using the natural source magnetotelluric mt technique as part of a variety of programs to study the craton and determine its regional scale electrical structure two of the four types of surveys involved novel mt data acquisition one through frozen lakes along ice roads during winter and the second using ocean bottom mt instrumentation deployed from float planes the primary initial objective of the mt surveys was to determine the geometry of the topography of the lithosphere asthenosphere boundary lab across the slave craton however the mt responses revealed completely serendipitously a remarkable anomaly in electrical conductivity in the sclm of the central slave craton this central slave mantle conductor csmc anomaly is modelled as a localized region of low resistivity 10 15 v m beginning at depths of f80 120 km and striking ne sw where precisely located it is spatially coincident with the eocene aged kimberlite field in the central part of the craton the so called corridor of hope and also with a geochemically defined ultra depleted harzburgitic layer interpreted as oceanic or arc related lithosphere emplaced during early tectonism the csmc lies wholly within the ne sw

geochemistry and origin of the regan intrusive suite and other granitoids in the northeastern slave province northwest canadian shield the regan intrusive suite of about 100 plutons of tonalite granodiorite and quartz diorite intruded the yellowknife supergroup and migmatite terrain in the northwest slave structural province 2 59 ga ago rare earth element ree trace element and major element analyses from 39 representative whole rocks from the suite suggest it was derived by batch melting of the crust producing a parental magma of tonalitic or granodioritic composition by analysing ree from different parts of a zoned pluton it was concluded that ree distribution was controlled by early separation of quartz diorite from the parent magma by flow differentiation and that the bulk of the ree were contained in early cumulate accessory apatite and monazite the residual magma was further fractionated in pipelike magma chambers during ascent into more leucocratic rocks chondrite normalized ree patterns of single lithology plutons are similar to lithologies in zoned plutons and it is proposed they initially segregated during ascent

basaltic magmatism on the moon a perspective from volcanic picritic glass beads abstract it is widely accepted that basaltic magmas are products of partial fusion of periodotite within planetary mantles as such they provide valuable insights into the composition structure and processes of planetary interiors those compositions which approach primary melt compositions provide the most direct information about planetary interiors and serve as a starting point to understand basaltic evolution within the collection of lunar samples returned by the apollo and luna missions are homogeneous picritic glass beads of volcanic origin these picritic glasses are our closest approximations to primary magmas as such these glass beads provide a unique perspective concerning the origin of mare basalts the characteristics of the lunar interior and processes in the early differentiation of the moon we have obtained trace element data for these picritic glasses using sims techniques these data and literature isotopic and experimental data on the picritic glasses are placed within the framework of mare basaltic magmatism the volcanic glasses are very diverse in their trace element characteristics for example they have a wide range of ree pattern shapes and concentrations like the crystalline mare basalts all picritic glasses have a negative eu anomaly unlike the crystalline mare basalts there is little correlation between the size of the eu anomaly and overall ree concentrations trace element differences among the various glasses suggests that a kreep component was incorporated into their mantle source this implies large scale mixing of the lunar magma ocean derived cumulate pile subtle differences among glasses suggest that local mixing of sources may also have been an important process preservation of subtle chemical differences in the picritic glasses and crystalline basalts may be interpreted as indicating that they were produced by small to moderate degrees of partial melting and that the lunar mantle did not experience extensive melting during episodes of mare volcanism several lines of evidence are consistent with the view that the picritic glasses were derived from mantle sources that were compositionally distinct from the sources for crystalline mare basalts these are parallel but no common liquid lines of descent chemical differences between picritic glasses and the more primitive crystalline mare basalts experimental studies indicating that the picritic glasses are multiply saturated at depths greater than that of the mare basalts differences in lead isotopic data and the mode of eruption i e fire fountaining for glass beads these data also provide circumstantial evidence that suggests that the picritic glasses were derived from a source somewhat more volatile rich than that of the mare basalts several petrogenetic models are suggested by the trace element characteristics of the picritic glasses 1 1 partial melting of heterogeneous lunar mantle at depths greater than 300 km to produce the parental magmas picritic for both the mare basalts and picritic glasses picritic magmas represented by glass beads were erupted to the surface with small degrees of fractional crystallization while mare basalts were produced by larger degrees of fractional crystallization 15 30 of similar but not identical picritic magmas 2 2 picritic magmas represented by the glass beads were generated at depths greater than 400 km in a volatile enriched relative to the mare basalt source heterogeneous mantle while mare basalts are fractional crystallization products of picritic magmas generated at depths of less than 400 km 3 3 the picritic magmas represented by the glass beads represent polybaric melting that initiated at depths of at least 1000 km a primitive mantle component or less processed cumulate mantle components may have been involved in the generation of the picritic glasses in any of these models

thermal and magmatic evolution of the moon as with all science our continually developing concepts of lunar evolution are firmly tied to both new types of observations and the integration of these observations to the known pool of data this process invigorates the intellectual foundation on which old models are tested and new concepts are built just as the application of new observational tools to lunar science in 1610 galileo s telescope and 1840 photography yielded breakthroughs concerning the true nature of the lunar surface the computational and technological advances highlighted by the apollo and post apollo missions and associated scientific investigations provided a new view of the thermal and magmatic evolution of the moon 1 1 pre apollo view of the thermal and magmatic evolution of the moon many of the early views of the moon manifested in mythology and art throughout the world were primarily tied to lunar and terrestrial cycles and the relationships between the sun and the moon prophetically myths involving the lunar deities mwuetsi from zimbabwe and coyolxauhqui from mexico told of rather violent or catastrophic events in which the moon was expunged from the earth numerous ancient scientific observations were made about the nature of the moon ranging from those uncovered in early neolithic sites that correctly identified mare crisium and mare humorum to the insights made by greek philosophers such as anaxagoras ca 500 428 b c and democritus ca 460 370 b c who attached terrestrial analogues to its character stone mountains with the advent of the telescope 1610 and photography 1840 as scientific tools for lunar exploration semiquantitative data could be collected that would provide an intellectual foundation for scientific interpretation initially modern terrestrial geological analogs were extended to the moon lunar highlands volcanic craters seas combined with the rigors of computational modeling these observational data were extended to predict the original thermal state of the moon and its thermal and magmatic history its proximity to the earth

live bed scour at submerged weirs abstractweirs or bed sills are low head hydraulic structures used for bed stabilization raising upstream water level and reducing flow velocity during high flow events the weir is fully submerged in the river and scouring occurs both upstream and downstream of the weir for a fully submerged weir the scour mechanism around the weir is dependent on approach flow intensity clear water scour conditions or live bed scour conditions and flow regimes surface flow regime or impinging jet regime over the weir the fast evolution of underwater mobile topographies and propagating bedforms increase the complexities of the scour process and the difficulties for scour measurement at the submerged weir under live bed scour conditions this paper develops a measurement and data processing technique for the study of scour at submerged weirs under extreme measurement environments and investigates the scour process both upstream and downstream of submerged weirs under live bed scour conditions the experiments are

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

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

investigation of the archaean crust by single grain dating of detrital zircon a greywacke of the slave province canada u pb dating of single zircon grains from a graywacke of the point lake area of the archaean slave structural province in canada indicates that this sediment is derived from two sources 1 the ancient shield parts of which are at least 3100 ma old which is the basement of the slave province supracrustal rocks and 2 younger rocks about 2700 ma old this implies the creation of large amounts of acidic to intermediate rocks during the 2700 ma event it also indicates that magma generation and intracontinental sedimentary basin formation and deepening are strongly related

deciphering basaltic magmatism on the moon from the compositional variations in the apollo 15 very low ti picritic magmas picritic glass beads of volcanic origin have been interpreted as representing extremely primitive lunar magmas that approach primary magma compositions based on this they have been used for developing models for lunar magmatism estimating the mineralogical and chemical characteristics of their mantle sources constraining the dynamics and structure of the lunar mantle developing models for lunar core formation reconstructing the bulk composition of the moon and evaluating the genetic relationships between the earth and the moon yet we still do not truly understand many aspects of the compositional diversity among individual glass types or even within a single glass type using high precision ion microprobe techniques we have analyzed a total of forty very low ti glass beads from the apollo 15 a15 site and twenty additional picritic glass beads from other sampling sites for a suite of highly compatible ni co weakly compatible to weakly incompatible mn cr v and highly incompatible ce ti zr nb elements within the a15 very low ti glass population ni and co concentrations are positively correlated exhibit limited fractionation of ni co and are distinctive for individual glass groups as defined by major elements manganese is also colinear with both ni and co the highly incompatible elements also appear to be generally colinear with ni co and mn although there are distinguishable compositional offsets in the glass populations the ni co ratio does not differ dramatically among the very low ti glasses from other sampling sites although incompatible element concentrations may differ significantly these trace element data eliminate fractional crystallization and partial melting of a homogeneous source under extremely low fostaggered2 conditions as possible models for the origin of the compositional variations observed in the a15 very low ti glass population these data are consistent with the generation of these magmas through partial melting of a spatially restricted heterogeneous lunar magma ocean lmo cumulate sequence the compositional variation in these magmas can be produced by at least two different melting processes 1 partial melting of a cumulate sequence consisting of relatively early cumulates with a higher proportion of an intercumulus melt component green glass a d e and later cumulates with lower proportions of an intercumulus melt component green glass c 2 different degrees of partial melting of a cumulate sequence small degrees of partial melting less than 5 of a more primitive cumulate mantle source will generate one group of magmas green a d e whereas a group of other picritic magmas green c were produced by larger degrees of partial melting 10 to 20 of a mineralogically similar but a more evolved cumulate mantle source in both models the green b glass group is formed by either cumulate commingling or magma mixing processes these magmas cannot be rapidly transported from the source region to the lunar surface in a single eruptive event without extensive fractional crystallization yet the colinear relationship among ni co and mn is not compatible with extensive and variable fractional crystallization therefore a polybaric melting model as suggested by longhi 1992b appears to be the only alternative to producing relatively unfractionated apollo 15 very low ti picritic magmas with high pressure signatures the trace element data provides additional constrains for this type of model

turbulence and vorticity in a laboratory channel bend at equilibrium clear water scour with and without stream barbs abstractlaboratory flume experiments were conducted to study the flow field and sediment dynamics in a mobile bed channel bend with and without the presence of stream barbs upstream angled submerged groynes this paper presents spatial distributions of the vorticity field and the turbulent reynolds shear stresses kinetic energy and integral scales the objectives of the present paper were to 1 advance understanding of the role that vorticity and turbulence play in the erosion process in channel bends with and without barbs and 2 optimize barb design for reducing erosion along the outer bank regions of channel bends through consideration of flow field turbulence and vorticity results indicate that 1 increased z vorticity occurred in the outer bank scour zone for all runs with and without barbs 2 for the runs without barbs and with moderately sized barbs increased streamwise cross stream reynolds stress uv was found to coincide with locations of scour and 3 for the run with large barbs

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

sediment control by submerged vanes a procedure is developed for a rational design of a system of submerged vanes for depth control in alluvialriver channels the vanes are vertical smallaspect ratio foils installed on the channel b

lunar meteorite queen alexandra range 94281 glass compositions and other evidence for launch pairing with yamato 793274 abstract lunar meteorite queen alexandra range 94281 is remarkably similar to yamato 793274 pairing in the conventional earth entry sense is difficult to reconcile with the 2500 km separation between the find locations for these two samples nonetheless both of these regolith breccias are dominated by very low ti vlt mare basalt the pyroxenes of which feature exsolution lamellae on a remarkably coarse scale typical lamella width 0 5 1 m by mare standards the pyroxenes also show similar compositional variations e g fe vs ti trends which confirm parentage from vlt mare basalt plots using al2o3 or feo as a tracer of the highland component indicate indistinguishable internal mare highland geochemical mixing trends the same two distinctive glass types dominate the mare glass populations of both breccias glass type yq1 features 0 37 0 63 wt tio2 10 17 wt mgo and 9 11 wt al2o3 glass type yq2 features higher tio2 0 99 1 22 wt which is inversely correlated with mgo 12 6 13 8 wt and nearly constant 8 8 wt al2o3 all of these similarities suggest that y 793274 and que 94281 are a launch pair which we designate yq most of these similarities also extend to another mare breccia meteorite elephant moraine 87521 however the eet 87521 mare basalt is unusually v poor 88 g g whereas the yq mare component contains 166 g g queen alexandra range 94281 features a variety of textural domains discrete patches of dark matrix material appear to represent clods of mature regolith that have been mixed with a coarser relatively immature material interior to a frothy fusion crust are areas of massive glass that probably formed as a splash coating on que 94281 when it was still on the moon the coarse yq and eet 87521 pyroxene exsolution features imply relatively slow cooling in either a very shallow sill or an unusually thick ponded lava and or later annealing within a cryptomare mare pyroclastic glasses including the two yq varieties are systematically mgo rich compared to crystalline mare basalts this disparity may be a consequence of limited survival of graphite the main fuel for explosive volcanism during formation of the mare source regions as magma ocean cumulates graphite 2 2 g cm3 survived preferentially in regions that avoided extensive early melting and thus remained mgo rich an apparent bimodality in the tio2 contents of mare volcanics especially the pyroclastic glasses also seems a plausible consequence of petrogenesis by remelting of magma ocean cumulates cumulates deposited after the magma ocean evolved to ilmenite saturation had vastly higher tio2 contents than cumulates deposited shortly before the yq regolith s subequal proportions of mare and highland matter are consistent with derivation from a terrain close to a mare highland boundary however a similar mixture might also develop through vertical mixing in a cryptomare or a region of thin mare coverage thus unfortunately the yq bulk composition is not a very useful clue to the identity of the source crater

3d flow and sediment dynamics in a laboratory channel bend with and without stream barbs abstracta series of laboratory flume experiments were performed to study the effect of stream barbs on flow field dynamics and sediment erosion in a 135 mobile bed channel bend stream barbs also known as spur dikes or submerged groynes are low profile linear rock features that redirect high velocity flow away from the outer bank of channel bends unlike emergent groynes the submerged nature of these structures creates a unique combination of horizontal shear plunging type flow and vertical shear at the groyne tip spatially dense high frequency velocity data were collected and analyzed to describe the pattern and magnitude of three dimensional 3d velocity throughout the bend and in the vicinity of the stream barbs this paper demonstrates that the outer bank region particularly between barbs may still be at risk of erosion or even increased erosion greater than the same case without barbs if stream barbs generate excessive secondary velocities because of their size and layout that are op

pseudobrookite group oxide solutions and basaltic melts abstract orthorhombic bbmm r2 1 x 3 rx2 ti1 xo5 r3 r2 ti m1 ti r2 r3 2m2o5 solid solutions were first recognized in lunar rocks and then identified as such on earth even though they are less common than ilmenite and magnetite s l there is strong field experimental and theoretical evidence that they are not geological oddities besides pseudobrookite oxide solutions may have had a critical role in the petrogenesis of the mare basalts and lunar picritic glasses as a source of tio2 and may be present in other planetary bodies as well as materials they are of particular theoretical and practical interest because of the cation order disordering phenomena that affect their physical and mechanical properties and participation in the tio2 slag smelting process x ray crystallography and spectroscopy studies have shown that all the cations are in octahedral coordination occupying two nonequivalent sites with a 1 2 ratio evaluation of site fractions configurational entropy in r2 1 x 3 rx2 ti1 xo5 solutions and of the known properties of pseudobrookite group mgti2o5 suggests that r23 tio5 solutions may reach cation random distribution and thus entropy maxima at lower temperatures than r2 ti2o5 rich solid solutions as a result the entropy contribution to their thermodynamic stability may depend upon the r 2 r 3 ratio on the basis of computations experiments and chemography of mineral equilibria it is inferred that 1 assemblages of pseudobrookite group ti oxide ilmenite rutile olivine and pyroxene s should be expected under lower crust and upper mantle conditions in the earth and conceivably in other planetary bodies including the earth s moon 2 reactions between pseudobrookite group ti oxide and olivine orthopyroxene and pseudobrookite group ti oxide or ilmenite can produce ilmenite or olivine saturated ti enriched liquids 3 lack of either ilmenite or pseudobrookite group ti oxide saturation in melts which are in equilibrium with orthopyroxene and olivine enriches these melts in tio2 4 the assemblage olivine orthopyroxene rutile has a large stability field and is probably replaced by olivine orthopyroxene ilmenite with increasing pressure and temperature and olivine orthopyroxene pseudobrookite group ti oxide with decreasing pressure and increasing temperature 5 lunar source regions nominally saturated in olivine orthopyroxene and pseudobrookite group ti oxide or ilmenite may produce the range of tio2 content in the lunar pristine glasses which apparently cannot be derived by partial melting of model late stage lunar magma ocean oxide silicate assemblages or equivalent bulk compositions

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

effectiveness of grade control structures in reducing erosion along incised river channels the case of hotophia creek mississippi abstract herein we undertake a geomorphological analysis in which spatial and temporal trends of bed and bank erosion along an 18 km length of hotophia creek mississippi are estimated for the period between 1961 and 2050 the evaluation was undertaken for two scenarios of channel response to channelization during 1961 1963 one scenario represents the actual response of the channel and includes the effects of installing a series of grade control structures gcs between 1980 and 1996 while the other represents a hypothetical scenario in which the channel is left to adjust naturally this allows the effectiveness of gcs in reducing in channel erosion to be assessed the analysis relies on the availability of channel survey data to develop empirical bed and bank response models for each adjustment scenario supplemented by bank stability modelling to predict future rates of bank erosion results indicate that channel erosion rates decline nonlinearly with respect to time since 1961 for both adjustment scenarios however by the year 2050 the with gcs adjustment scenario results in the cumulative removal of some 663 000 9 extra tonnes of sediment relative to the without gcs scenario most 63 of this excess is derived from enhanced bed erosion during 1976 1985 and 1985 1992 with the remainder derived from increased bank erosion during 1985 1992 detailed analysis of the patterns of erosion and deposition and their association with the gcs provides evidence to support the view that gcs installed along hotophia creek have for the most part been ineffective in reducing channel erosion rates this is because the gcs were installed too late to prevent bed degradation caused by the 1961 1963 channelization migrating upstream in addition some structures have disrupted the downstream transmission of bed material from eroded reaches upstream exacerbating bed degradation and bank erosion in incised reaches downstream

mantle derived archaean monozodiorites and trachyandesites the 2 680 2 750 myr old1 5 intrusive granite greenstone terranes6 8 in the rainy lake region ontario and in and adjacent to the vermilion district minnesota of the superior province in north america include a wide variety of volcanic and intrusive rocks with initial pb sr and nd isotope ratios close to those for the mantle4 5 9 12 the isotopic constraints require the production of large volumes of silica oversaturated magmas from silica undersaturated mantle within 100 200 myr we present here geochemical data on monzodiorites and trachyandesites from the rainy lake area which are strongly enriched in large ion lithophile elements lile we conclude that they are derived by direct melting of the mantle at depths of 50km in either anhydrous or hydrous conditions their rare earth element ree abundances and initial 143nd 144nd ratios suggest that their mantle sources were enriched in lile shortly before melting the monzodiorites trachyandesites and their granodioritic derivatives may comprise up to 20 of the exposed igneous rocks in the rainy lake region and vermilion district if these rocks are as abundant in other archaean terranes a significant part of the early continental crust could have formed by direct melting of lile enriched mantle

presidential address presented 2000 august 28 chicago illinois usa the eucrite vesta story many lines of evidence indicate that meteorites are derived from the asteroid belt but in general identifying any meteorite class with a particular asteroid has been problematical one exception is asteroid 4 vesta where a strong case can be made that it is the ultimate source of the howardite eucrite diogenite hed family of basaltic achondrites visible and near infrared reflectance spectra first suggested a connection between vesta and the basaltic achondrites experimental petrology demonstrated that the eucrites the relatively unaltered and unmixed basaltic achondrites were the product of approximately a 10 melt studies of siderophile element partitioning suggested that this melt was the residue of an asteroidal scale magma ocean mass balance considerations point to a parent body that had its surface excavated but remains intact modern telescopic spectroscopy has identified kilometer scale vestoids between vesta and the 3 1 orbit orbit resonance with jupiter dynamical simulations of impact into vesta demonstrate the plausibility of ejecting relatively unshocked material at velocities consistent with these astronomical observations hubble space telescope images show a 460 km diameter impact basin at the south pole of vesta it seems that nature has provided multiple free sample return missions to a unique asteroid major challenges are to establish the geologic context of the hed meteorites on the surface of vesta and to connect the remaining meteorites to specific asteroids

hydraulic evaluation of w weir for river restoration various structural measures have been advocated for river restoration and habitat improvement schemes the w weir is one such structure that can be used in mobile bed alluvial rivers to diversify habitat and provide grade control laboratory studies have been carried out in a large scale meandering channel with a mobile bed to investigate their effects on flow and sediment transport processes a w weir placed immediately downstream of a riffle section created a strongly three dimensional flow pattern and high turbulence zones two adjacent scour holes of different depths and substrate are formed under clearwater and live bed conditions the continuity of sediment transport along the channel was not interrupted by the structure and the upstream afflux is minimal overbank flow significantly influenced the action of the weir and the scour hole was shifted closer to the structure in a relatively tight bend followed by a short crossover reach the weir may affect bed load transport pathways in the downstream bend finally the study provides insights to guide their design for restoration projects

petrogenesis of the apollo 14 high alumina basalts implications from ion microprobe analyses abstract in this study ion microprobe analyses of individual minerals are used to investigate the petrogenesis of the apollo 14 high al basalts we use trace element concentrations from individual minerals in the apollo 14 high al basalts to evaluate both endogenic and exogenic models the data show that if the apollo 14 high al basalts were produced by melting within the lunar mantle these basalts cannot be related to one another by closed system fractional crystallization of a single basaltic melt rather the trace element data show that variable amounts of a kreep component were added to the basalts by either assimilation mixing into mantle sources or impact melting single stage assimilation fractional crystallization models can only explain the data from this study if an excessively large mass of urkreep is assimilated into the parent magma before olivine crystallization alternatively the trace element data can be explained if the apollo 14 high al basalts were produced by melting multiple al rich mantle sources that contain different amounts of urkreep finally for impact melting to be a relevant process the data require that multiple large impact melts be formed from mixed kreep rich target lithologies the resulting impact melts must then crystallize to produce basalts with igneous textures high al2o3 concentrations uniform major element compositions and a wide range of incompatible trace element concentrations

petrogenesis of mantle derived lile enriched archean monzodiorites and trachyandesites sanukitoids in southwestern superior province reply in southwestern superior province diorite monzodiorite and trachyandesite sanukitoids occurring within syn to post tectonic intrusive complexes and within greenstone belts have the following chemical characteristics 55 60 wt sio2 mgo 6 wt mg 0 60 ni and cr both 100 ppm na2o k2o 6 wt sr and ba both 600 1800 ppm and rare earth element ree patterns that are strongly light rare earth element lree enriched cen 80 250 ybn 4 10 and show no eu anomalies sanukitoids and their granodioritic derivatives constitute at least 5 of the exposed crust in the study area the sanukitoids cannot be derived by melting fractionation or crustal contamination of basalts or lamprophyres that are coeval with the sanukitoids crustal contamination of komatiites fails to explain the high large ion lithophile element lile contents of the sanukitoids rather we suggest that the sanukitoids were derived by hydrous melting of lile enriched mantle peridotite at pressures between 10 and

an 1800 km cross section of the lithosphere through the northwestern north american plate lessons from 4 0 billion years of earth s history the lithoprobe slave northern cordillera lithospheric evolution snorcle study across northwestern north america in combination with related crustal studies has been synthesized into an 1800 km long cross section of the lithosphere that is constrained by high resolution geophysical data seismic reflection refraction electromagnetic potential fields and detailed bedrock geology the cross section offers one of the longest continuous profiles of the continental lithosphere anywhere in the world that is constrained by combined geophysical measurements and electromagnetic properties and exposed bedrock geological relationships the primary conclusion of the study is that during all major orogenic episodes recorded from archean to present in that part of earth s lithosphere the crust and perhaps much of the mantle was reorganized and redistributed rather than being differentiated from the mantle at the time of orogenesis the observed subsurface geometries of relict subduction zones accretion

exploring the moon s surface for remnants of the lunar mantle 1 dunite xenoliths in mare basalts a crustal or mantle origin remotely sensed observations from recent missions e g grail kaguya chandrayaan 1 have been interpreted as indicating that the deep crust and upper mantle are close to or at the lunar surface in many large impact basins e g crisium apollo moscoviense if this is correct the capability of either impact or volcanic processes to transport mantle lithologies to the lunar surface should be enhanced in these regions somewhat problematic to these observations and interpretations is that examples of mantle lithologies in the lunar sample collection apollo program luna program lunar meteorites are at best ambiguous dunite xenoliths in high ti mare basalt 74275 are one of these ambiguous examples in this high ti mare basalt olivine occurs in three generations olivine associated with dunite xenoliths olivine megacrysts and olivine microphenocrysts the dunite xenoliths are anhedral in shape and are generally greater than 800 m in diameter the interior of the xenoliths are fairly homogeneous with regard to many divalent cations for example the mg mg mg fe 100 ranges from 82 to 83 in their interiors and decreases from 82 to 68 over the 10 30 m wide outer rim titanium and phosphorus x ray maps of the xenolith illustrate that these slow diffusing elements preserve primary cumulate zoning textures these textures indicate that the xenoliths consist of many individual olivine grains approximately 150 200 m in diameter with low ti al and p cores these highly incompatible elements are enriched in the outer fe rich rims of the xenoliths and slightly enriched in the rims of the individual olivine grains highly compatible elements in olivine such as ni exhibit a decrease in the rim surrounding the xenolith an increase in the incompatible element depleted cores of the individual olivine grains and a slight decrease in the interior rims of the individual olivine grains inferred melt composition liquid lines of descent and zoning profiles enable the reconstruction of the petrogenesis of the dunite xenoliths preservation of primary magmatic zoning ti p al and lack of textures similar to high pressure mineral assemblages exhibited by the mg suite shearer et al 2015 indicate that these xenoliths do not represent deep crustal or shallow mantle lithologies further they are chemically and mineralogically distinct from mg suite dunites identified from the apollo 17 site more likely they represent olivine cumulates that crystallized from a low ti mare basalt at intermediate to shallow crustal levels the parent basalt to the dunite xenolith lithology was more primitive than low ti basalts thus far returned from the moon furthermore this parental magma and its more evolved daughter magmas are not represented in the basalt sample suite returned from the taurus littrow valley by the apollo 17 mission the dunite xenolith records several episodes of crystallization and re equilibration during the last episode of re equilibration the dunite cumulate was sampled by the 74275 high ti basalt and transported over a period of 30 70 days to the lunar surface

integrated nd isotopic and u pb detrital zircon systematics of clastic sedimentary rocks from the slave province canada evidence for extensive crustal reworking in the early to mid archean abstract a combined u pb geochronology and nd isotopic analysis of clastic metasedimentary rocks from the archean slave province northwest territories canada is presented a series of clastic sedimentary rocks with deposition age of 3 13 ga to 2 58 ga was collected from the west central slave province these samples include conglomerates as well as finer sedimentary rocks such as greywacke arkose and quartzite although it is generally agreed that the nd model age t dm of clastic sedimentary rocks represents the average sedimentary provenance age t dm of samples studied here is generally older than the average u pb age of detrital zircons extracted from the same sample rather there seems to be a better 1 1 relationship between the t dm and u pb age of the oldest zircon from each sample a simple model relationship between u pb geochronology and t dm suggests that such correlation is a result of archean crustal evolution of the slave province being dominated by crustal reworking i e intracrustal processes rather than addition of juvenile materials from the mantle one exception is the period between 3 1 and 3 2 ga during which period a significant portion of detrital zircons have u pb ages exceeding the t dm indicating a large input of juvenile material and or decreasing level of crustal reworking an alternative explanation for the u pb vs t dm trend may be a mixing of older mafic juvenile crust containing no zircon and younger felsic juvenile crust however the general lack of extensive pre 2 8 ga mafic crust in the slave province makes this scenario unlikely the results of this study cannot constrain the change in the volume of continental crust at any given period of time since the addition of juvenile crust may always be counterbalanced by recycling of crustal material back into the mantle however a dominance of crustal reworking during the early to mid archean strongly implies that a large part of ancient crust was lost during the younger tectonomagmatic events since the majority of zircon may be lost during crustal reworking processes unless they are preserved as an inherited core absence of a large quantity of ancient detrital zircon cannot be used as evidence for the lack of large sialic crust existing on the early earth

relict subduction zones in canada 1 relict subduction zones that are interpreted on 10 lithoprobe deep seismic reflection profiles in canada provide key observational evidence that lithosphere plate interactions have operated with essentially the same resultant geometry for at least 2 7 gyr subduction zone reflections are generally found beneath known collisional belts and their orientations are often consistent with the locations of exposed arcs sutures and subduction complexes they project from the lower crust into the upper mantle and provide key geometric relationships between the crust moho and upper mantle the interpretation of subduction zone reflections as being syntectonic establishes a minimum age for the overlying lower crust and mantle wedge and precludes inferred formation of the moho and upper mantle by postorogenic delamination in these areas the orientation of subduction zone reflections may be synthetic or antithetic to exposed sutures indicating juxtaposition by subcretion or by delamination respectively the mantle wedge above the subduction zone reflections may exhibit sparse reflectivity subduction zone reflections commonly dip toward the craton indicating a preferred dip of subduction during the last stages of convergence within an orogen or else a higher likelihood of preservation beneath older domains interpreted ages of the canadian examples range from recent to neoarchean 2 7 ga providing observational evidence that plate tectonics or similar processes have been active since at least the neoarchean the locations and geometries of these relict subduction zones provide a snapshot of accretion boundaries in the mantle and establish a framework for the neoarchean recent accretionary architecture of the north american lithosphere