origin of late archean granite geochemical evidence from the vermilion granitic complex of northern minnesota the 2 700 ma vermilion granitic complex of northern minnesota is a granite migmatite terrane composed of supracrustal metasedimentary rocks mafic rocks tonalitic and granodioritic plutonic rocks and granite the metasedimentary rocks are predominantly graywacke which has been regionally metamorphosed to garnet sillimanite muscovite bearing biotite schist and has locally undergone anatexis the mafic rocks form early phases within the complex and are of two types 1 basaltic amphibolite and 2 monzodiorite and essexite rich in large ion lithophile elements lile the members of the early plutonic suite form small bodies that intrude the metasedimentary rocks and mafic rocks producing an early migmatite the granite is of two distinct varieties 1 white garnet muscovite biotite leucogranite s type chappell and white 1974 and 2 grayish pink biotite magnetite lac la croix granite i type the leucogranite occurs in the early migmatite and in paragneissic portions of the complex whereas the lac la croix granite is a late stage intrusive phase that invades the early migmatite and metasediment producing a late migmatite and forms a batholith this study focuses specifically on the origin of granite in the vermilion granitic complex chemical mass balance calculations suggest that the s type two mica leucogranite had a metagraywacke source and that the i type lac la croix granite formed via partial fusion of calc alkaline tonalitic material which may have been similar to rocks of the early plutonic suite this model is satisfactory for petrogenesis of similar late archean post kinematic granites throughout the canadian shield

trace element behavior during partial melting of iberian orthogneisses an experimental study abstract the determination of the exact protolith from which every leucogranite is derived may be a hard task the trace element composition of both the leucogranite and their likely source rock can be a way to establish this relationship this hypothesis is checked in an experimental study on the partial melting of two iberian orthogneisses the ollo de sapo and the tormes dome gneisses several runs between 700 and 900 c at 0 6 and 1 0 gpa with added water ranging from 2 wt to 10 wt have been carried out in piston cylinder devices their results show that two gneisses of virtually the same major and trace element composition yield partial melts of closely similar major element composition but extremely different trace element composition above all ree these differences are produced because of several factors mainly the asi value of melts which in turn depends on minor differences in the composition in the main oxides of the gneisses and the phosphorus hosted in the feldspars of the gneisses the consequence of these minor changes is that the dissolution of the trace element bearing accessories mainly apatite can be delayed until higher temperatures are achieved so melts formed under these circumstances are depleted in ree th and y gneisses of relatively low aluminosity and phosphorus rich feldspars will produce ree poor melts saturated in p 2 o 5 at low temperatures because neither apatite nor other phosphates dissolve in contrast gneisses of relatively high aluminosity and phosphorus poor feldspars will produce ree rich melts subsaturated in p 2 o 5 at low temperatures for this reason using the trace element composition of peraluminous granites as the only way to establish their protoliths is not recommended

the nature age and petrogenesis of the cartier batholith northern flank of the sudbury structure ontario canada abstract the cartier batholith exposed about 50 km northwest of sudbury ontario canada is a late archean k rich granitic batholith along with the levack gneiss complex it forms the footwall of the north range of the sudbury igneous complex the cartier batholith dominantly monzogranitic to granodioritic is relatively homogeneous unfoliated and contains k feldspar megacrysts it shows several distinctive chemical features including high concentrations of zr th u and lree and low concentrations of nb ti and hree several discriminants suggest a post orogenic tectonic environment for the batholith this inference is consistent with a u pb age of 2642 1 ma obtained on zircon only slightly younger than the inferred timing of high grade metamorphism of the levack gneiss complex the cartier batholith could have formed as a result of approximately 33 partial melting of the levack gneiss complex

simplified process modeling of river avulsion and alluvial architecture connecting models and field data abstract modeling is an invaluable tool for studying sedimentary basin filling and for understanding depositional processes with long recurrence intervals including channel avulsion simplified modeling approaches such as cellular models and process analogue experiments are particularly useful for efficiently exploring alternative hypotheses and evaluating first order controls on river avulsion and alluvial architecture here we review the history and current state of the art in simplified avulsion and alluvial architecture models with a particular focus on how results and insights from these models can be incorporated into field and subsurface studies and vice versa simplified avulsion and alluvial architecture models have proliferated in the past decade providing a wide variety of models to serve as a basis for future coupled field modeling studies we compare features of leading models and discuss avenues for effectively pairing model capabilities with hypotheses and field data outstanding questions highlighted by recent modeling efforts include 1 what thresholds control avulsion initiation in different systems 2 how do floodplain processes and topography influence avulsion dynamics and alluvial architecture 3 what factors determine where avulsion channels stabilize answering these questions will require targeted modeling efforts coupled to data from ancient systems hence our model comparison emphasizes features that can be used to choose or design fit for purpose models and we outline how quantitative data useful for model selection and validation can be obtained from modern systems and ancient deposits matching model goals with targeted questions and model parameters and predictions with quantitative field data will help tighten communication between field and model oriented sedimentary geologists facilitating advances in our understanding of river avulsion and alluvial architecture

petrogenesis of alkalic and calcalkalic volcanic rocks of mormon mountain volcanic field arizona the cenozoic mormon mountain volcanic field mmvf of northern arizona is situated in the transition zone between the basin and range and the colorado plateau it is composed of alkalic to sub alkalic basalts and calcalkalic andesites dacites and rhyodacites despite their spatial and temporal association the basalts and the calcalkalic suite do not seem to be co genetic the petrogenesis of primitive mmvf basalts can be explained as the result of different degrees of partial melting of a relatively homogenous incompatible element enriched peridotitic source the variety of evolved basalt types was the result of subsequent fractional crystallization of olivine spinel and clinopyroxene from the range of primitive basalts crustal contamination seems to have occurred but affected only the highly incompatible element abundances the formation of mmvf calcalkalic rocks is most readily explained by small to moderate amounts of partial melting of an amphibolitic lower crust this source is lree enriched but depleted in rb and relatively unradiogenic sr 87sr 86sr 0 7040 calcalkalic rhyodacites may also be derived from andesitic parents by fractional crystallization the overall petrogenesis of the mmvf complex is the result of intra plate volcanism where mantle derived magmas intrude and pass through thick continental crust

the significance of source versus process in the tectonic controls of magma genesis arculus r j 1987 the significance of source versus process in the tectonic controls of magma genesis in s d weaver and r w johnson editors tectonic controls on magma chemistry j volcanol geotherm res 32 1 12 despite the association of certain characteristic trace element signatures with particular tectonic environments of eruption there are accumulating data which would result in significant tectonic misassignments ambiguity of signals appears in active arc back arc systems of the southwestern pacific and particularly in some intracontinental plate suites given the selective preservation of continental as opposed to oceanic lithosphere inappropriate paleotectonic inferences are probable using trace element criteria alone strong relative fractionation of the alkalis and alkaline earth elements aee with respect to the rare earth elements ree in the majority of arc related magmas and a number of intraplate continental basalts is strongly suggestive of the involvement of hydrous fluids at some stages in the respective petrogenetic processes occurring in these two tectonic regimes in contrast fractionation of high field strength elements hfse such as nb and ta with respect to the ree in the same suites is most readily explained by the involvement at some stage in the magma formation process of high sio2 melts a number of widely applied tectonic discriminants makes use of aee hfse fractionation but the processes and sources involved in subduction zone petrogenesis may be duplicated during interaction of mantle derived basalt with the heterogeneous components of continental lithosphere both mantle and crust a significant role for both volatile dominated fluids and silicate melts is implicated in collision and some intracontinental plate magmatism

application of channel belt scaling relationships to early middle jurassic source to sink system evolution in the southern junggar basin abstract a wide range of key scaling relationships obtained from modern fluvial systems can be used to estimate the drainage areas in ancient source to sink systems in this study these relationships are applied to reconstruct source to sink systems of the early middle jurassic xishanyao formation in the southern junggar basin where meandering fluvial and deltaic successions are developed both the lower channel belt thickness and the bankfull channel belt thickness are measured and are used to estimate the scale of drainage systems that were associated with the seven fluvial systems in three sequences sequence 1 2 and 3 in ascending order the results indicate that the channel belt thickness had significant variation through time and space the average values of the bankfull thickness of the seven fluvial systems are translated into drainage area which range from 63 000 157 000 km2 and the maximum drainage length which range from 559 to 934 km the delta volume of the seven fluvial systems range from 2 01 km3 to 10 35 km3 from sequence 1 to sequence 3 detrital mineral compositions of sandstones show a gradual change from lithic arkose to feldspathic litharenite provenance fields on ternary plots and the characteristics of sandstone components show that the sandstone sources gradually shifted from the southwest dominated yilinhabierga mountains to the southeast dominated bogda mountains sediment provenance analysis together with paleogeographic maps and analysis of sedimentary records suggests that orogenic building of the bogda mountains was responsible for the progressive eastward shifting of the main fluvial channels and for the modification of drainage areas the mismatched pattern of channel sizes between the rivers developed in the early middle jurassic and in the modern northern tian shan front is due to late cenozoic north south crustal shortening which had caused the drainage network reorganization and the evolution of fluvial styles our work provides a complete profile of sediment dispersal from source to sink for better understanding of the paleogeographic evolution in the southern junggar basin this source to sink approach could also be applicable to other lacustrine basins in china

temporal and compositional differences between subsolidus and anatectic migmatite leucosomes from the quetico metasedimentary belt canada migmatites in the quetico metasedi mentary belt contain two types of leucosome 1 layer parallel leucosomes that grew during deformation and prograde metamorphism these are enriched in si02 sr and eu but depleted in ti02 fe203 mgo cs rb ree sc th zr and hf relative to the quetico metasediments 2 discordant leucosomes that formed after the regional folding events when metamorphic temperatures were at their peak these are enriched in rb ba sr and eu but display a wide range of lree th zr and hf contents relative to the quetico metasediments layer parallel leucosomes formed by a sub solidus process termed tectonic segregation this stress induced mass transfer pfocess began when the quetico sediments were deformed during burial and continued whilst the rocks were both stressed and heterogeneous sub solidus leucosome compositions are consistent with the mobilization of quartz and feldspar from the host rocks by pressure solution the discordant leucosomes formed by partial melt ing of the quetico metasediments possibly dur ing uplift of the belt the range of composition displayed by the anatectic leucosomes arises from crystal fractionation during leucosome emplacement some anatectic leucosomes pre serve primary melt compositions and have smooth ree patterns but those with negative eu anomalies represent fractionated melts and others with positive eu anomalies represent accumulations of feldspar plus trapped melt

extracting palaeoflood data from coarse grained pleistocene river terrace archives an example from se spain field based palaeoflood event reconstruction has the potential to contribute to the development of our understanding of long term landscape evolution however the reconstruction of past flow event histories magnitude and frequency over long term quaternary timescales is fraught with difficulties here we make a preliminary exploration of some of the practicalities of flood reconstruction from fluvial terrace archives using commonly available sedimentological and geomorphological observations from a field perspective we utilize manning and palaeostage indicators to reconstruct historic events that can be used as benchmarks for a lesser used competence based approach which is applied to coarse grained strath terrace deposits we evaluate the results against gauged records for extreme and catastrophic events that affected the same region in 1973 and 2012 the findings suggest that the competence approach is most effectively applied to terrace deposits if the channel geometry is taken into account when sampling both in cross section and in longitudinal section and calibrated against the sedimentology for palaeo flow depth problems can arise where constrictive channel geometries allow boulder jams to develop acting as sediment traps for the coarsest material and leading to downstream boulder starvation useful sites to target for palaeoflood reconstruction therefore would be upstream of such constrictive reaches where the coarsest transportable bedload has been effectively trapped sites to avoid would be downflow where the deposited material would poorly represent palaeoflood competence underestimation from maximum boulder preservation and limited section exposure issues would appear to outweigh possible overestimation concerns related to fluid density and unsteady flow characteristics such as instantaneous acceleration forces flood data derived from river terrace deposits suggests that basal terrace geometries and coarse boulder lags common to many terrace sequences are likely the result of extreme flow events which are subsequently filled by lesser magnitude flood events in this environmental setting copyright 2016 john wiley sons ltd

geology and geochemistry of huronian rhyolites and low ti continental tholeiites from the thessalon region central ontario bimodal volcanism associated with early phases of huronian rifting in central ontario dated about 2450 ma produced low ti tholeiitic basalts and two varieties of crustally derived calc alkaline rhyolite early tholeiites are characteristically highly evolved have mg values from 30 to 50 and display pronounced enrichment in large ion lithophile elements lile and light rare earth element lree in comparison with modern oceanic basalts fractionated heavy rare earth element hree patterns and low ti zr p nb ba and k abundances ti zr ratios rise progressively in early basalts and associated basaltic andesite fractionates from about 35 in early flows to 55 in central units late basalts also carry enriched lile and lree but in contrast to early types have average mg values greater than 50 and lower rare earth element ree abundances with flat hree patterns they also display negative ba nb and p anomalies on chondrite normalized distribution diagrams but lack low k zr and ti contents

melt related metasomatism in mafic granulites of the quetico subprovince ontario constraints from o sr nd isotopic and fluid inclusion data mafic granulites in the archean quetico subprovince north of manitouwadge ontario occur as isolated lenses or discontinuous layers in spatial association with tonalitic leucosomes in metasedimentary rocks and exhibit concentric zoning from a biotite rich margin to an orthopyroxene rich outer zone and a clinopyroxene rich central zone with internal orthopyroxene bearing leucosomes and rarely patches of relict amphibolites within the clinopyroxene rich zone microstructural and microchemical evidence suggests that the mafic granulites formed from amphibolites by combined infiltration diffusion processes in the presence of a p f bearing silicate melt p 2o5 melt 0 24 0 28 wt and ac o 2 rich hypersaline fluid the whole rock and mineral 18 o values of the mafic granulites 8 9 v smow indicate oxygen isotope equilibration between amphibolites 6 6 6 9 and associated tonalitic leucosomes 9 5 10 at 700 800 c strontium and nd isotope data and u pb zircon ages confirm isotopic homogenization at the leucosome amphibolite boundaries during the peak granulite facies metamorphism at about 2650 ma texturally early co2 rich fluid inclusions in quartz and garnet yield p t conditions similar to those of the peak granulite facies metamorphism hypersaline fluid inclusions occur in textural coexistence with the early co2 rich inclusions but are invariably low in homogenization temperatures 178 234 c this study shows that silicate melts not only provide a conduit for co2 rich fluids but also interact directly with country rocks for the formation of granulites also the o sr nd isotope data show that the documented mobility of rare earth elements in the quetico granulite zone is localized in scale and related to anatexis of local metasedimentary rocks during the granulite facies metamorphism resume les granulites mafiques dans la sous province de quetico archeenne au nord de manitouwadge en ontario apparaissent sous forme de lentilles isolees ou de couches discontinues associees spatialement a des leucosomes tonalitiques dans les roches metasedimentaires elles exhibent un zonage concentrique evoluant d une marge riche en biotite a une zone externe riche en orthopyroxene et a une zone centrale riche en clinopyroxene incluant des leucosomes internes contenant un orthopyroxene occasionnellement sont rencontrees des plages d amphibolites relictuelles dans la zone riche en clinopyroxene les analyses microstructurales et microchimiques suggerent que les granulites mafiques derivent d amphibolites transformees par les processus combines d infiltration diffusion en presence d un magma silicate contenant p et f p2o5 magma 0 24 0 28 par poids et d un fluide riche en co2 hypersalin

geochemical constraints on the genesis of hercynian two mica leucogranites from the massif central france abstract late hercynian two mica leucogranites dated at 340 280 3a old occur across the entire massif central france and form dykes and stocks up to 130 km in length they are peraluminous molecular al 2 o 3 na 2 o k 2 o cao asi 1 16 1 25 and have low initial nd 8 2 to 6 1 indicating derivation from the metasedimentary lower crust as sampled in crustal xenoliths nd 340 8 6 to 4 3 nd 280 9 0 to 4 8 their high sio 2 70 78 wt p 2 o 5 up to 0 5 rb and ga and low ba sr and ree are mainly a result of partial melting processes rather than fractionation partial melting was initiated by underplating of the lower crust by mantle derived basic magmas between 360 and 270 ma and was intensified by granulite facies metamorphism between 300 and 280 ma from this model there is little similarity between the genesis of two mica leucogranite in the massif central and that in the himalaya with which it has previously been compared

global assessment of pure crystalline plagioclase across the moon and implications for the evolution of the primary crust recent advancements in visible to near infrared orbital measurements of the lunar surface have allowed the character and extent of the primary anorthositic crust to be studied at unprecedented spatial and spectral resolutions here we assess the lunar primary anorthositic crust in global context using a spectral parameter tool for moon mineralogy mapper data to identify and map fe bearing crystalline plagioclase based on its diagnostic 1 25 m absorption band this allows plagioclase dominated rocks specifically anorthosites to be unambiguously identified as well as distinguished from lithologies with minor to trace amounts of mafic minerals low spatial resolution global mosaics and high spatial resolution individual data strips covering more than 650 targeted craters were analyzed to identify and map the mineralogy of spectrally pure regions as small as 400 m in size spectrally pure plagioclase is identified in approximately 450 targets located across the lunar surface diviner thermal infrared tir data are analyzed for 37 of these nearly monomineralic regions in order to understand the compositional variability of plagioclase an in these areas the average an for each spectrally pure region is estimated using new laboratory measurements of a well characterized anorthite an96 sample diviner tir results suggest that the plagioclase composition across the lunar highlands is relatively uniform high in calcium content and consistent with plagioclase compositions found in the ferroan anorthosites an94 98 our results confirm that spectrally pure anorthosite is widely distributed across the lunar surface and most exposures of the ancient anorthositic crust are concentrated in regions of thicker crust surrounding impact basins on the lunar nearside and farside in addition the scale of the impact basins and the global nature and distribution of pure plagioclase requires a coherent zone of anorthosite of similar composition in the lunar crust supporting its formation from a single differentiation event like a magma ocean our identifications of pure anorthosite combined with the grail crustal thickness model suggest that pure anorthosite is currently observed at a range of crustal thickness values between 9 and 63 km and that the primary anorthositic crust must have been at least 30 km thick

incongruent dissolution of ree and sr rich apatite in peraluminous granitic liquids differential apatite monazite and xenotime solubilities during anatexis the relative solubilities of monazite mnz xenotime xno and apatite ap ree and sr rich and ree and sr poor have been studied in peraluminous granitic liquids in month long experiments at 750 c and 200 mpa ph20 in contrast with the high solubility of the apatite 0 7 wtojop205 in strongly peraluminous liquids monazite and xenotime have much lower solubilities 0 05 wt jop205 in mildly to strongly peraluminous compositions p205 in the liquid is 0 03 0 04 wt joat xenotime saturation and 0 02 0 05 wt jo at monazite saturation in keeping with the low p in the glasses re203 contents are below emp detection thresholds 50 08 wt jo for all conditions of experiments saturation of liquid at equilibrium and local saturation around apatite apatite dissolves incongruently crystallizing ree rich monazite on its surface 1 4 m iong grains resulting in similar low ree contents in liquids monazite precipitation occurs along the margins of dissolving apatite crystals even though the bulk liquid is not monazite saturated the abundance of monazite microcrystals increases with the ree content of the apatite and the degree of apatite dissolution the reaction relationship ap liqi mnz liq2 stemming from differences in relative solubilities greater than an order of magnitude between apatite and monazite results in the dissolution of much smaller amounts of ree into peraluminous liquids than expected by simple evaluation of apatite ree contents the amount of ree contributed from apatite directly to peraluminous granitic liquid is related to the amount of apatite dissolved by simple mass balance only if the total ree content of the apatite is sufficiently low that monazite saturation in liquid 50 100 ppm re203 at 750 c is avoided during dissolution of sr rich apatite the sr partitions into the liquid and at 750 c and 200 mpa ph20 the diffusion coefficient of sr in liquid is 2 x 10 10 cm2js r2 0 659 the reaction relationships described above may have application to some textural features observed in natural igneous rocks for example clusters of monazite microcrystals might be indicators of dissolved apatite monazite morphology can be used to distinguish the source of its ree and the general petrological process rock anatexis or magma crystallization under which the monazite formed in addition monazite microcrystals could serve as nucleation sites for other minerals which might explain their common inclusion in biotite and amphibole within granitoids

towards a quantitative method for estimating paleohydrology from clast size and comparison with modern rivers abstract an outcrop based methodology is presented to reconstruct bankfull depth of fluvial channels from clast size based on well established geomorphological procedures results obtained from a lower old red sandstone ludlovian to emsian example from the midland valley basin scotland are calibrated against existing methodologies for reconstruction of bankfull channel depth in fluvial sandstones which utilize preserved channel thickness and preserved dune foreset height the proposed methodology can be applied to pebbly sandstones and conglomerates of fluvial origin it does include significant uncertainties but these are of a range similar to the existing approaches for reconstructing bankfull depth in sandy fluvial systems estimates of bankfull channel depth can be used to reconstruct paleo drainage area using paleo discharge data derived from geomorphological regional curves these regional hydraulic geometry curves are constructed for modern rivers with specific hydro physiographic catchment properties and constrain the relationship between bankfull depth and discharge and bankfull depth and drainage area by comparing the results of outcrop datasets with the regional curves from similar inferred climate regimes an estimate of paleo discharge and paleo drainage area can be derived utilizing these paleohydrological approaches from outcrops of fluvial strata allow quantitative constraints to be placed on paleogeographic reconstructions give a better understanding of paleoclimate and help to constrain provenance studies in addition comparison of the drainage areas and bankfull discharges obtained from this analysis for lower old red sandstone fluvial systems with global data for modern rivers reveals good agreement this indicates that using region specific hydraulic geometry curves to reconstruct ancient fluvial systems can be applied to large rivers interpreted to have a dryland setting possibly sourced from another climatic region as is commonly the case in modern dryland river systems it is recommended that by integrating several techniques more accurate estimates of paleohydrology can be obtained to better reconstruct ancient fluvial environments

pressure effect on ti or p rich accessory mineral saturation in evolved granitic melts with differing k2o na2o ratios the solubility of ti and p rich accessory minerals has been examined as a function of pressure and k2o na2o ratio in two series of highly evolved silicate systems these systems correspond to a alkaline varying from alkaline to peralkaline with increasing k2o na2o ratio and b strongly metaluminous essentially trondhjemitic at the lowest k2o na2o ratio and remaining metaluminous with increasing k2o na2o ratio to 3 the experiments were conducted at a fixed temperature of 1000 c with water contents varying from 5 wt at low pressure 0 5 gpa increasing through 5 10 wt at 1 5 2 5 gpa to 10 wt at 3 5 gpa pressure was extended outside the normal crustal range so that the results may also be applied to derivation of hydrous silicic melts from subducted oceanic crust for the alkaline composition series the tio2 content of the melt at ti rich mineral saturation decreases with increasing pressure but is unchanged with increasing k content at fixed pressure the p2o5 content of the alkaline melts at apatite saturation increases with increased pressure at 3 5 gpa only but decreases with increasing k content and peralkalinity for the metaluminous composition series termed as trondhjemite based series t series the tio2 content of the melt at ti rich mineral saturation decreases with increasing pressure and with increasing k content at fixed pressure the p2o5 content of the t series melts at apatite saturation is unchanged with increasing pressure but decreases with increasing k content the contrasting results for p and ti saturation levels as a function of pressure in both compositions point to contrasting behaviour of ti and p in the structure of evolved silicate melts ti content at ti rich mineral saturation is lower in the alkaline compared with the t series at 0 5 gpa but is similar at higher pressures whereas p content at apatite saturation is lower in the t series at all pressures studied the results have application to a type granite suites that are alkaline to peralkaline and to i type metaluminous suites that frequently exhibit differing k2o na2o ratios from one suite to another

ree fractionation and nd isotope disequilibrium during crustal anatexis constraints from himalayan leucogranites abstract the processes controlling rare earth element ree behaviour during crustal anatexis have profound implications not only for ree abundances of crustally derived granites but also for their model nd ages for typical protoliths of anatectic granites such as are exposed in metapelites from the high himalayan crystalline series hhcs a high proportion 90 of bulk rock lree and mree are sited in the accessory phases apatite and monazite and of hree in garnet and apatite mass balance constraints indicate that observed ree abundances of himalayan leucogranites cannot be generated from ree deficient reactant phases in their metasedimentary protoliths muscovite biotite plagioclase and quartz but must result from the dissolution of accessory phases ree and th abundances in anatectic melts are modelled by combining empirical expressions for monazite apatite and zircon solubilities as a function of temperature melt composition and melt water content with analysed accessory phase ree abundances this approach which allows the contribution to the melt from each accessory phase to be identified successfully predicts himalayan leucogranite trace element abundances the lree and th concentrations of a metapelite derived melt are buffered by monazite stability although apatite dissolution contributes up to 10 of lree to the melt together with 50 of the mree and 90 of the hree zircon contributes a negligible proportion of ree to the melt during anatexis dissolution of monazite and apatite in the melt results in 1 increasing ree abundances and lree hree ratios with increasing temperature of melting 2 a negative eu anomaly in the melt 3 high sm nd ratios in the melt relative to its metasedimentary protolith and 4 nd isotope disequilibrium between the melt and its protolith all of these features are observed in the ree geochemistry of himalayan leucogranites the combined effects of sm nd fractionation and nd isotope disequilibrium during anatexis imply that model nd ages calculated for anatectic granites derived from apatite and monazite bearing protoliths should be treated with considerable caution

hybridisation in middle proterozoic high level ring complexes aland sw finland abstract the 1800 ma ring complexes of the aland archipelago sw finland were emplaced shortly after the cessation of the major svecofennian orogenic activity during a subsequent period of continuous but episodic mantle crust interaction and crustal adjustment culminating in the 1600 1500 ma rapakivi event chemical data for these complexes indicate that their range of compositions are a result of a complex mixing sequence at depth involving an alkaline lamprophyric magma an aluminous hfs element enriched tholeiitic magma associated with anorthositic magmatism and contamination by a disrupted crystallines mid crustal rapakivi granite body the complexes represent premature local tappings of a developing rapakivi granite source region in the lower crust contamination was a result of thermo mechanical stoping by a hot alkaline basic magma impounded beneath a granite sheet rapakivi granite genesis in southern finland is considered to be an integral part of both lower crustal and upper mantle responses and evolution subsequent to svecofennian orogenic development

post collision a type granites of homrit waggat complex egypt petrological and geochemical constraints on its origin abstract the homrit waggat complex hwc is a ring complex which belongs to the younger granite province of the nubian shield it comprises a central biotite granite encircled by an intermediate ring of mylonitized pink granite both of which have been emplaced by cauldron subsidence in a granodiorite body the mylonitized pink granite is locally cut across by hypersolvus coarse grained red granite the mylonitized pink granite is characterized by fully developed mylonitic fabrics and suffered inflation and flattening due to a ballooning effect which suggests that it has experienced stronger ductile deformation than the granodiorite and biotite granite the hw granites are mildly peraluminous highly fractionated and enriched in rb nb y ree except eu and f with corresponding depletion in mg fe ti ca sr and ba ree fractionation patterns and eu eu values decrease from granodiorite la yb n 6 24 6 69 eu eu 0 95 1 56 to biotite granite la yb n 2 48 4 68 eu eu 0 25 0 75 the mylonitized pink and red granites display flat patterns and large negative eu anomalies la yb n 0 33 1 09 eu eu 0 01 0 07 respectively although accessory minerals e g apatite allanite and fluorite exerted some control on ree concentrations volatile transfer largely controls ree abundances particularly hree heavy rare earth element geochemical data indicate that the granites of hwc are post collision a types the less fractionated granodiorite has an i type and volcanic arc geochemical signature least squares analyses of major elements and modelling of rees indicate that the hw a type granites were formed through two stages of differentiation a first stage crystalmelt fractionation was dominated by the removal of plagioclase biotite quartz and apatite from the granodiorite magma to yield the biotite granite further crystal fractionation of the biotite granite liquid with k feldspar as a dominant separating phase in addition to plagioclase biotite and quartz gave rise to the mylonitized pink granite second stage volatile phase transfer occurred during the second stage of fractionation in the magma chamber the red granite represents the last crystallizing granite type from a residual volatile rich fluids which accumulated and emplaced as ring dykes in the solidified part of the mylonitized pink granite

the geochemistry of phosphorus in different granite suites of the western carpathians slovakia the role of apatite and p bearing feldspar the geochemical behaviour of phosphorus in granites coupled with compositional variations in apatite discriminate the different genetic suites of variscan granitic rocks in the west carpathian orogenic belt meso variscan granites mostly of stype affinity show a good correlation between sio2 and p2o5 with decreasing amounts of p in the poorly and moderated fractionated granites and increasing phosphorus in the most evolved and late differentiation products the aluminium saturation index asi correlates negatively with bulk p contents in i type granites and positively with p in s type granites the phosphorus content of alkali feldspar mainly kfs is usually very low typically 0 05 wt p2o5 or not detected in the slightly differentiated granites in the latevariscan i s type granitoids phosphorus is hosted mainly in the early magmatic apatite but is present also in the late k feldspar up to 0 15 wt of p2o5 that formed from the residual melts in the postorogenic s type granites the bulk of the phosphorus occurs in alkali feldspar f0 3 wt p2o5 with a minor proportion present in primary early magmatic apatite clusters of small secondary apatite grains with a distinctive composition are distributed in alkali feldspar grains of the post orogenic s type granites this apatite has formed post magmatically from p released from p rich alkali feldspar during decreasing temperature by reaction with a fluid rich in volatiles including f and b and alkali and alkali earth metals a type granites have the lowest bulk phosphorus contents consequently phosphate minerals are relatively rare in this granite type and the alkali feldspar has negligible p2o5 contents except for sr the minor element contents in apatite partly correlate with the bulk composition of their host rocks and partly reflect some thermodynamic properties of melt the mn contents of apatite increase with the peraluminous character of the melt and with decreasing fo2 and so apatite from the s type granites has significantly higher mn contents than apatite from the i type granites apatite from a type granites is enriched in fe and hree reflecting the higher bulk fe and hree content of this granite type apatite from specialized s type granites is enriched in yand hree in general the cl and s content of apatite is higher in the basic members of the i type affinity granitic rocks d 2004 elsevier b v all rights reserved

lower palaeozoic convergent plate margin volcanism on bomlo southwest norwegian caledonides geochemistry and petrogenesis major and trace element analyses of a lower palaeozoic metavolcanic sequence of convergent plate type from bomlo southwest norwegian caledonides are presented and discussed this sequence ranges in age from the upper cambrian through the lower silurian petrogenetic models for the lavas in terms of partial melting and crystal fractionation are discussed two models are presented for the metabasalts in order to explain their different trace element abundances and ratios 1 ree modelling assuming a mantle source with ree abundances twice chondritic suggests progressively more varied sources with time thus the metabasalts from the oldest upper cambrian lower ordovician geitung unit of primitive island arc type and those of the mid ordovician siggjo complex of basin and range type can be modelled in terms of high around 25 and moderate around 5 degrees of partial melting of spinel lherzolite respectively the metabasalts of the post ashgillian vikafjord group of typical continental flood basalts are compatible with moderate c 5 10 degrees of partial melting of spinel and garnet lherzolite sources the supposed lower silurian langevag group of calc alkaline andean type metabasalts grading into alkaline to tholeiitic metabasalts of early marginal basin youngest character require low 2 source heterogeneity produced by subduction zone derived enrichment of lil elements and contemporaneous stabilization of minor phases which accommodate hfs elements this process combined with possible continental contamination may possibly yield the trace element concentrations and ratios of the different metabasalts by partial melting of modally similar mantle sources

influence of phosphate on mobility and adsorption of rees during weathering of granites in thailand abstract the permo jurassic north thai nt granites and the late cretaceous to paleogene western province wp granites in thailand are contrasting in terms of tectonic settings and chemical compositions the nt granites which are dominated by s type features are characterized by lower sio2 contents and higher p2o5 contents than the wp granites in this study in order to compare the mobility and adsorption of rare earth elements rees during weathering of the two granite suites geochemical analyses were conducted on the granite and weathered granites the weathered wp granites show wider ranges of rees y rey contents percentages of ion exchangeable rey and ce anomalies than the weathered nt granites these results indicate that rees were less mobile during weathering of the nt granites than those of the wp granites the low mobility of rees can be explained by the occurrences of residual monazite and secondary ree phosphates which immobilize rees during weathering therefore in the weathered nt granites rees are mostly contained in the phosphate minerals in contrast the weathered wp granites are dominated by ion exchangeable rees adsorbed rees which are likely to exist on the surface of clays previous studies and our study results suggest that the ion exchangeable rees in the weathered granites were probably sourced from weatherable allanite titanite apatite and or ree fluorocarbonate and rarely from monazite and zircon which are resistant to weathering the weathered granites of low phosphate contents potentially show high percentages of ion exchangeable rey although they can be influenced by the degree of hydrothermal alteration or weathering of granites

sedimentology paleoflow dynamics and flood history of jokulhlaup deposits paleohydrology of holocene sediment sequences in southern iceland sandur deposits abstract this paper examines the sedimentology of a series of deposits associated with catastrophic floods caused by subglacial volcanic eruptions in southern iceland a simple model is proposed for the interpretation of the sediments in terms of changes in flow characteristics of the fluid sediment mix a range of sediment types characteristic of these flood flows is identified the predominant one being thick massive homogeneous poorly structured black pumice fine gravels with 65 p rcent silt clay type e and single lithology boulder deposits type f these flood deposits alternate with or are channeled into more normal sandur deposits comprising heterogeneous poorly sorted clast supported imbricated rounded cobble and pebble gravels type g the dominant sediment sequences are interpreted as representing hyperconcentrated fluid sediment mixtures with dispersive stresses acting to create massive poorly sorted nongraded or inversely graded sediments the latter characterized by large surface boulders the vertical changes in sediment type reflect significant changes in flow conditions during transport and subsequent deposition with an initial massive flood surge followed by flow deceleration sediment freezing and dewatering producing a more fluid series of flows the more fluid phases were associated with extensive erosion and channelization cutting deep scour channels marked by residual streamlined hummocks boulder lags and fields of megaripples leading downstream to a washed sandur plain the paper examines some of the problems associated with the application of paleoflow models for determining former flow dynamics the models adopted suggest that most of the flows occurred as relatively mobile low viscosity flows with little internal resistance to shear while sediment concentrations are estimated to have reached about 50 percent by weight with maximum yield strengths between 2 9 103 and 4 2 105 dn cm 2 maximum viscosities ranged between only about 2 and 8 102 poises a range of paleovelocity models applied to the flood sediment indicates flow rates of between abo t 4 and 13 ms 1 with peak discharges reaching a maximum of 3 3 105 m3 s 1 dating of the deposits by 14c dating and tephrochronology indicates that at least 8 major sediment producing jokulhlaups occurred over a 4 000 year period between c 4500 yr bp and 1357 ad hence although relatively rare the effects of these floods still dominate the proglacial landscape probably producing 85 percent of the total thickness of proglacial sandur sediments

badrinath gangotri plutons garhwal india petrological and geochemical evidence for fractionation processes in a high himalayan leucogranite the gangotri leucogranite is the western end of the badrinath granite one of the largest bodies of the high himalayan leucogranite belt hhl it is a typical fine grained tourmaline muscovite biotite leucogranite the petrography shows a lack of restitic phases the inferred crystallization sequence is characterized by the early appearance of plagioclase quartz and biotite and by the late crystallization of the k feldspar this suggests that in spite of being of near minimum melt composition the granite probably had long crystallization or melting interval in agreement with previous experimental studies tourmaline and muscovite have a mainly magmatic origin even though the major element composition is homogeneous there are several geochemical trends when cao decreases there is an increase in na2o rb sn u b f and a decrease in k2o fe2o3 tio2 sr ba zr ree th which are best explained by a fractionation process with early crystallizing phases experimental solubility models for zircon and monazite in felsic melt support a magmatic origin for these two accessory phases as well rb sr isotope data show this granite to have like other hhl heterogeneous isotopic values for sr initial 87sr 86sr ratios calculated at 20 ma range between 0 765 and 0 785 therefore no mixing i e no convection occurred between the different batches of magma in contrast 18o data show little variation 13 04 0 25 implying a source with homogeneous 18o values differences in timing between fluid infiltration and the onset of melting related to differences in temperature of the source could explain why source homogenization occurred for the gangotri and not for the manaslu granite the use of experimental results for solubility and the position of the accessory minerals during melting predict a low viscosity for the melt during its extraction this in turn explains the lack of restitic phases major and accessory in the granite as well as some field features lensoid shape pronounced magmatic layering based on the petrographic and isotopic studies it is suggested that the mechanism of ascent was not diapiric but rather that the melt ascended along several fractures and the level of emplacement was partialy controlled by the density contrast between the melt and host rocks

crystallization and hybridism in microgranitoid enclave magmas microstructural evidence microstructural evidence indicates that many microgranitoid enclaves mafic inclusions in granitoids crystallize from globules of magma that have undergone previous magma mixing hybridism the evidence includes 1 rounded xenocrysts ocelli of quartz rimmed with fine grained aggregates of early formed minerals especially mafic minerals 2 k feldspar megacrysts commonly rimmed with plagioclase rapakivi structure and 3 corroded cores dendritic overgrowths and calcic spikes in plagioclase initial quenching of a magma globule in felsic magma involves rapid temperature equilibration which causes a high rate of nucleation of minerals precipitating from the enclave magma at the time followed by a period of slow cooling during which the nucleation and growth rates of later crystallizing minerals are similar to the much slower rates prevailing in the granitic melt this may result in markedly poikilitic microstructures involving inclusion of the earlier formed finer grained minerals in quartz and or k feldspar which are common in microgranitoid enclaves

phosphorus and the rare earth elements in felsic magmas an assessment of the role of apatite abstract the solubility of fluorapatite in 17 silica rich melts in the system na 2 o k 2 o al 2 o 3 sio 2 with and without cao or caf 2 was determined at 1 kbar water pressure and 750 900 c apatite saturation occurs at levels of dissolved p 2 o 5 ranging between 0 04 0 02 and 0 28 0 13 wt with only 4 values outside the 0 09 0 20 wt range the results demonstrate not only that apatite is a common liquidus phase in felsic melts but also that under most circumstances it remains in the residue during episodes of partial fusion of the crust given a solubility limit of 0 14 wt dissolved p 2 o 5 the mean of the experimental values a source containing as little as 0 05 p 2 o 5 must be 35 melted before apatite is lost from the residue and no longer buffers the melt p 2 o 5 concentration at the saturation value higher abundances of p 2 o 5 in the source postpone the loss of residual apatite to still higher degrees of melting and if the source p 2 o 5 content exceeds 0 14 wt apatite must be residual for all degrees of melting increasing in abundance as melting proceeds the generally secondary influence of apatite on the rare earth element ree patterns of melt and residue is most apparent when garnet and or amphibole is minor or lacking in the residue fractional crystallization of intermediate e g andesitic magmas toward felsic compositions invariably results in saturation in apatite and some consequent depletion of ree in the melt

trapped phosphate melt inclusions in silicate carbonate hydroxyapatite from comb layer alvikites from the kaiserstuhl carhonatite complex sw germany structural and crystal chemical observations on acicular and skeletal silicate carbonate hydroxyapatite crystals schap from comb layer alvikite dykes of the kaiserstuhl carbonatite complex yield strong evidence for their being quenched products as well as being intimately intergrown with calcite they also contain distinctive primary phosphate inclusions in contrast to the host apatite these inclusions are free of si low in lree but enriched in sr and the volatiles f and s and contain a high concentration of na this pronounced fractionation combined with the absence of x ray diffraction and electron diffraction patterns suggests that the phosphate inclusions represent portions of a trapped residual phosphate melt therefore the schap are considered to be the direct liquidus phase of a carbonate phosphate melt that two phosphate phases coexist however presumes strong enrichment of phosphorous in the parental carbonatitic melt since the eutectic would otherwise produce calcite and apatite only the formation of sharply interfaced apatite and calcite comb layers and the occurrence of trapped phosphate melt inclusions in the quench apatites argue for the existence of two immiscible liquids such as a phosphate rich and a carbonate rich melt

fundamental uniformity in the trace element patterns of the volcanics of the kaapvaal craton from 3000 to 2100 ma evidence for the lithospheric origin of these continental tholeiites

preservation of cross strata due to the migration of subaqueous dunes an experimental investigation this experimental investigation examined the controls on the geometry of cross sets formed by subaqueous dunes a range of steady unidirectional flow conditions spanning the field of dune existence was investigated andaggradation rate ranged from 0 mm s 1 to 0 014 mm s 1 data from an ultrasonic depth profiler consist of high resolution temporal and spatial series of bed profiles from which dune height and length migration rate and the depth of trough scour were measured cross set thickness and length were measured from sediment peels the size and shape of dunes from an equilibrium assemblage change continuously individual dunes commonly increase in height by trough scouring and occasionally by being caught up by the upstream dune both types of behaviour occur suddenly and irregularly in time and hence do not appear to depend on dunes further upstream however dune climbing or flattening is a typical response of dunes that disappear under the influence of the upstream dune all types of behaviour occur at any flow velocity or aggradation rate successive dune trough trajectories defined by dunes showing various behaviours affect the geometry of the preserved cross sets mean cross set thickness mean dune height averages 0 33 0 7 and mean cross set length mean dune length averages 0 49 0 08 and both show no systematic variation with aggradation rate or flow velocity mean cross set thickness mean cross set length tends to decrease with increasing flow velocity and froude number therefore allowing a qualitative estimation of flow conditions quantitative analysis of the temporal changes in the geometry and migration rate of individual dunes allows the development of a two dimensional stochastic model of dune migration and formation of cross sets computer realizations produced stacks of cross sets of comparable shape and thickness to laboratory flume observations indicating a good empirical understanding of the variability of dune trough trajectories however interactions among dunes and aggradation rates of the order of 10 2 mm s 1 should be considered in future improved models

apatite solubility in peraluminous liquids experimental data and an extension of the harrison watson model abstract new experimental data at 750 1000 c 2 5 kbar and for peraluminous melt compositions show a dramatic increase of apatite solubilities and phosphorus melt contents when compared to metaluminous or peralkaline compositions harrison and watson 1984 the formation of alumino phosphate units in peraluminous melts qualitatively explains our data a new apatite solubility model incorporating the data for the peraluminous region is presented application of this model to examples of peraluminous felsic suites is discussed

the effect of accessory minerals on the redistribution of lead isotopes during crustal anatexis a model abstract the initial pb isotopic composition of anatectic granites is modelled as a mixture of pb derived from major minerals that have characteristically low 238 u 204 pb and 232 th 204 pb ratios i e feldspars biopyroboles etc with pb contributed from dissolved accessory minerals with characteristically high 238 u 204 pb and 232 th 204 pb ratios i e zircon monazite etc the initial pb isotopic composition of anatectic granites is a function of a the age type modal distribution and heterogeneity in the initial u and th content of the accessory minerals b variation in melt composition and temperature during anatexis c the fraction of the source melted and d the extent to which the melt was homogenized prior to crystallization the differential behavior of accessory minerals during anatexis can explain the common yet enigmatic decoupling of the pb isotopes from other chemical and isotopic systems in granite rocks granitic plutons derived by anatexis of the same source material are not required to have the same initial pb isotopic composition low temperature peraluminous granites are more likely to exhibit homogeneous initial pb isotopic compositions dominated by the pb contained within the major mineral assemblage of the source material in contrast the initial pb isotopic composition of higher temperature metaluminous or peralkaline anatectic granites is more likely to be heterogeneous unless the melts are homogenized during emplacement and will record a larger fraction of the radiogenic pb component contained in the accessory mineral assemblage of the source material heterogeneity in the initial pb isotopic composition of individual granites or granitic suites can preserve the weighted average age of the radiogenic pb present in the accessory mineral assemblage of the source region even if these minerals are entirely dissolved during anatexis the use of isotopic tracer studies in terrane analysis will be optimized by the isotopic characterization of granitic suites

sedimentary processes vertical stratification sequences and geomorphology of the roaring river alluvial fan rocky mountain national park colorado abstract the roaring river alluvial fan formed on 15 july 1982 in rocky mountain national park colorado by a catastrophic flood that was generated by a dam failure the fan covers an area of 0 25 square km has a radial length of 0 7 km and is up to 14 m thick sedimentation occurred in three phases each producing a distinct fan lobe initial sedimentation was by a noncohesive sediment gravity flow which deposited two levees on the proximal boundaries of lobe i the levees consist of a poorly sorted mixture of logs sand pebbles cobbles and boulders the first two lobes were built primarily by sheetflooding which deposited imbricated boulders in trains behind obstacles that formed as jams between boulders or logs and upright trees horizontally laminated granule and sand sedimentation took place down fan from the boulders due to deceleration of the expanding sheetflood thin to medium interbedded sand and cobble pebble gravel couplets were deposited by sheetflooding on the third lobe gravel was transported as bedload by supercritical flow and deposited locally where antidunes broke sand was transported as suspended load and deposited where flood velocity locally decreased due to destruction of antidunes increased roughness or flow separation around the low amplitude gravel bed forms the flood rechannelized at the distal end of lobe iii due to constriction between the fan and the valley margin deposits in the upper rechannelized reaches consist of crudely bedded cobble and pebble gravel and interstratified pebble gravel and backset bedded sand deposition was by supercritical flow in the lower reaches planar cross bedded sandy pebble gravel and climbing ripple horizontal trough cross bedded and backset bedded sand were deposited by supercritical and subcritical flow the flood deposit was modified during waning flood stage and during the three years following the flood by noncatastrophic discharge events these events formed braided distributary channels by erosion into the top of the sheet flood deposits fan building took place mostly by catastrophic unconfined discharge whereas much of the present fan surface consists of braided channels that formed by erosion into the sheetflood deposits by noncatastrophic discharge

the genesis of felsic mafic plutonic associations a sr and nd isotopic study of the hercynian braga granitoid massif northern portugal abstract the late tectonic braga plutonic complex in the centro iberian zone north portugal was emplaced during the hercynian orogeny within a silurian sedimentary sequence and displays an acid basic association which consists of three well defined intrusions the biotite dominant braga granite minor bodies of gabbro to granodiorite composition and the mildly peraluminous gonca leucogranite these three plutonic suites present field relationships indicating a synchronous magmatic emplacement for which a rb sr age of 310 10 ma is obtained the distribution of the three plutonic units along regular curves in major and trace element diagrams suggests that the different units can be genetically related however the rb sr and sm nd isotopic results do not indicate a unique homogeneous source and a simple fractional crystallization process the gabbros have chemical characters high k ba sr and light rare earth elements and low nb ti and zr contents and isotopic compositions sri 0 70497 and nd 2 5 which suggest an alkaline magmatic affinity of shoshonitic type they are probably derived from an enriched mantle source in contrast the peraluminous gonca leucogranite sri 0 70933 and nd 6 8 is more likely the result of crustal anatexis the braga granite and the evolved members of the basic series have an intermediate isotopic composition sri 0 70532 to 0 70733 and nd 3 0 to 6 2 which can be interpreted in terms of an hybridization process between the two previous end members the chemical and sr nd isotopic compositions of the braga plutonic series can be explained by an assimilation fractional crystallization afc model between a mantle derived magma equivalent to the gabbros and a crust derived magma the gonca granite

a large spectral survey of small lunar craters implications for the composition of the lunar mantle a global spectral survey of 4506 immature craters with diameters 1 km was carried out using near ir data from the kaguya spectral profiler to characterize the composition of the lunar megaregolith on the basis of band minima and radiative transfer mixing models small crater spectra fall into three groups 1 mare basalts with strong absorptions at relatively long wavelengths indicating high ratios of high to low ca pyroxene 2 norites containing about 50 plagioclase and with pyroxene assemblages dominated by low ca pyroxene that occur within the south pole aitken basin spa near apollo 14 and other locations near imbrium basin and three major cryptomaria deposits and 3 noritic anorthosites occurring within the feldspathic highlands terrane containing about 20 wt pyroxene with a pyroxene assemblage containing exclusively very low ca pyroxene very few pure anorthosites are present in this survey and there are no occurrences of pyroxene poor olivine rich assemblages models of the composition of basin ejecta incorporate large amounts of mantle material and the spectral results require that that the sampled mantle is orthopyroxenite basin depth diameter ratios used in the models required to match the measured composition are consistent with prior estimates for the largest basins the composition found in the spa and imbrium regions are consistent with mafic impact melt breccias or basaltic impact melts of basin origin for spa we model this composition and find it requires an extremely low impact angle while this is consistent with prior work on an oblique impact for the spa event a more robust solution invokes the production of norite in impact melt seas

estimation of source to sink mass balance by a fulcrum approach using channel paleohydrologic parameters of the cretaceous dunvegan formation canada abstract trunk rivers transport the bulk of the sediment in a source to sink s2s system and total mass passing through any cross section i e fulcrum of a trunk river over geologic time should allow matching of source area sediment delivery budgets to downstream sediment volumes deposited in the basin we analyze the paleohydrology of ancient trunk channels and link downstream deltaic strata of allomember e of the cretaceous dunvegan alloformation in the western canadian sedimentary basin to test the total mass balance fulcrum approach bankfull channel depth and width grain size paleoslope velocity and discharge are derived from outcrop core and well logs some parameter estimates use multiple methods providing a range of values and serve as a cross check of independent methods estimates of annual flood frequency and paleodischarge associated with long term geologic time estimates are derived from chronostratigraphic analysis and allow calculation of cumulative sediment discharge isopach maps are used to measure sink area sediment volumes the results indicate that the trunk river of allomember e was 10 15 m deep and 150 250 m wide carried fine to medium grained 200 microns sand and flowed over a low gradient paleoslope of 4 1 6 1 10 5 annual total sediment discharge is estimated to have ranged from 5 4 to 12 106 m3 within 25 000 years the river is estimated to have transported 135 307 km3 of sediment into the basin this is consistent with the 130 km3 of sediment mapped in the study area however the upper range estimate of sediment delivered into the sink is 2 5 times the measured sediment volume in the map area which if accurate suggests significant sediment escape this supports the hypothesis that in dunvegan time mud was widely dispersed southward along the alberta foreland basin by geostrophic currents associated with storm processes and counterclockwise oceanic gyres in the cretaceous seaway

sedimentological constraints on the late silurian history of the highland boundary fault scotland implications for midland valley basin development the relationship between movement on the highland boundary fault and deposition of the lower old red sandstone in the midland valley basin of scotland is controversial most models favour mid silurian to early devonian sinistral movement on the highland boundary fault and development of a transtensional midland valley basin to constrain highland boundary fault movement during the late silurian we examine the basal lower old red sandstone alluvial succession exposed adjacent to the highland boundary fault a lack of synsedimentary fault movement indicators coupled with an increase in stratal thickness across the fault indicates that the highland boundary fault was not active during lower old red sandstone sedimentation a transtensional basin model cannot be sustained

geochemistry and hf nd isotope characteristics and forming processes of the yuntoujie granites associated with w mo deposit guangxi south china abstract the yuntoujie w mo deposit is so far the only indosinian granite related deposit with an element association of w mo in the nanling ore belt south china the granites in the yuntoujie ore field consist of the yuntoujie batholith and late stage granites the w mo mineralization is associated closely with the late stage granites here we report major and trace element sr nd isotope and zircon hf isotope compositions of the yuntoujie batholith and the late stage granites the yuntoujie batholith and the late stage granites have high sio 2 70 77 74 86 wt and alkaline k 2 o na 2 o 6 27 8 27 wt concentrations and are characterized as peraluminous a cnk 1 1 a nk 1 30 1 43 the yuntoujie batholith and late stage granites feature negative correlation between th y and rb no positive correlation between p 2 o 5 and sio 2 and high a cnk values 1 1 suggesting that they could be classified as s type granites the yuntoujie batholith and the late stage granites might be sourced from the partial melting of proterozoic crust without contribution from juvenile crust as evidenced from the low 143 nd 144 nd values of 0 511942 0 512477 the nd t values of 8 52 to 11 76 falling in the field of nd isotope evolution for the proterozoic crust and the zircon hf t values of 7 19 to 14 89 with the t dm2 ranging from 1713 ma to 2187 ma the major and trace element compositions of the yuntoujie batholith and late stage granites especially the low cao na 2 o and cao mgo feo t ratios and the high rb ba and rb sr ratios further indicate that their sources are predominantly argillaceous sedimentary the trace element characteristics such as the positive correlation between la yb and la and between ba and sr and negative correlation between ba and rb suggest that the late stage granites are the product of highly fractionated melts of the yuntoujie magma chamber moreover 1 the tetrad effect observed in the ree patterns for the late stage tourmaline muscovite monzogranite porphyry and 2 the abundant fluid inclusions in their quartz phenocrysts imply that the processes of the volatile phase exsolution and the fluid melt reaction had taken place in the evolved water saturated magma these geochemical features together with the fact that the yuntoujie magma chamber had survived for 10 myr suggest that the peraluminous magma experienced a prolonged period of crystallization differentiation which plays a key role in the formation of w mo mineralization associated with granites from the observations that the granites in the yuntoujie district were formed about 20 10 ma later than the peak age of the indosinian collisions and that they all fall in the post ceg area in the tectonomagmatic discrimination diagrams we proposed that the yuntoujie granites were formed in the post collisional environment

chronology and petrogenesis of a 1 8 g lunar granitic clast 14321 1062 abstract a study was undertaken to determine the chronology of a pristine granite clast 1062 from apollo 14 breccia 14321 using rb sr sm nd and 39ar 40ar methods the genesis of the granite as constrained by the isotopic results and trace element characteristics is discussed chronology the rb sr internal isochron is slightly disturbed and yields an age of 4 09 0 11 ae 87 rb 0 0139 ae 1 and an imprecise initial i sr 0 702 008 if two data are excluded the age becomes 4 13 0 03 ae and i sr 0 698 003 the whole rock and mineral separates are extremely radiogenic they yield model ages which are relatively well defined the average model age is 4 12 0 03 ae relative to babi 0 69898 the sm nd internal isochron is also slightly disturbed and gives an age of 4 11 0 20 ae 147 sm 0 00654 ae 1 the 39ar 40ar average age of the non magnetic fraction of the sample yields a slightly younger age of 3 88 0 03 ae k ar constants from steiger and a 1977 the concordancy of rb sr and sm nd internal isochrons with the rb sr model age strongly suggests that the granitic clast formed at 4 1 ae ago in the shallow crust and was later excavated and brecciated about 3 88 ae ago petrogenesis isotopic and trace element data of the lunar granite show large k la and rb sr fractionations small sm nd fractionation and the distinct v shaped ree distribution pattern at the time of crystallization a two stage model involving crystal fractionation followed by silicate liquid immiscibility sli is proposed for lunar granite genesis we propose that the granite can be the immiscible acidic liquid produced by sli from a residual liquid which underwent fractionation of ca 3 of phases with ree distribution coefficients similar to those of phosphate minerals from a highly evolved parental magma with ree contents about twice those of the 15405 85 quartz monzodiorite qmd the extreme scarcity of lunar granitic samples and their young formation ages suggest that they are probably not directly crystallized from the differentiation of the primordial magma ocean our isotopic results and trace elements data from other workers suggest that granites qmd and probably mggabbronorites may be genetically related and may have formed in a plutonic environment similar to gabbro granophyre associations in terrestrial layered intrusions such as the skaergaard intrusions

petrogenesis of the hercynian tichka plutonic complex western high atlas morocco trace element and rbzsr and smznd isotopic constraints the late tectonic hercynian tichka plutonic complex in morocco was emplaced in the lower cambrian volcanosedimentary sequence of the western high atlas and displays an exceptional acid basic association which consists of five well defined plutonic intrusions gabbros diorites granodiorites tonalites monzogranites and two types of leucogranites biotite amphibole leucogranites and two mica leucogranites with the exception of the late two mica leucogranites the plutonic suites present field relationships clearly indicating an almost synchronous magmatic emplacement the monzogranites and biotite amphibole leucogranites plot along the same rbzsr isochron and most of them also plot along the same smznd isochron yielding respectively ages of 291 5 ma and 283 24 ma with initial87sr 86sr and143nd 144nd ratios of 0 70348 4 and 0 51243 4 major and trace element data together with the rbzsr and smznd isotopic results rule out any genetic process involving a unique homogeneous source the smznd isotopic heterogeneity even at the scale of one unit implies the existence of contrasting source rocks and the combination of different mechanisms the gabbro and diorite magmas are assumed to be derived from the melting to different degrees of a depleted upper mantle source in a within plate geotectonic environment whereas a combined wallrock assimilation fractional crystallisation model is proposed for the evolution of the diorite suite in contrast the granitoids are mainly the result of the anatexis of a dominant basic to intermediate igneous heterogeneous continental crust

generation of leucogranites via fractional crystallization a case from the late triassic luoza batholith in the lhasa terrane southern tibet abstract leucogranites are important in understanding intracrustal differentiation and regional tectonic evolution but how these rocks form remains a matter of much debate the luoza batholith in the central lhasa subterrane provides an important opportunity to address these issues as this batholith consists of normal calc alkaline s type granodiorites group 1 and highly fractionated s type leucogranites group 2 laser ablation inductively coupled plasma mass spectrometry zircon u pb dating indicates that these rocks were emplaced at ca 221 205 ma the group 1 samples ca 205 ma have low sio2 content 64 67 wt and low differentiation index values di 75 76 and are slightly depleted in ba p sr and ti compared to the group 2 samples ca 221 ma and 213 ma which have high sio2 content 74 75 wt high differentiation index values 91 94 and are significantly depleted in ba p sr and ti samples from group 1 and group 2 exhibit similar zircon ehf t values 15 6 to 1 4 both of which are significantly higher than melts from the pure ancient basement in the central lhasa subterrane 20 5 to 10 6 the group 1 samples can be interpreted as having been derived from the partial melting of metagreywacke within the ancient basement in the central lhasa subterrane with contributions from mantle or juvenile crust derived components whereas the group 2 samples may have formed via varying degrees of fractional crystallization of different minerals e g plagioclase k feldspar biotite zircon allanite monazite titanite and apatite from the parental magmas represented by the granodioritic samples in group 1 in shallow crustal magma chambers in combination with sedimentary records the high temperature and low pressure conditions indicated by the group 1 samples can be geodynamically linked to a back arc extensional setting in response to the southward subduction of the bangong nujiang tethys ocean seafloor our work implies that fractional crystallization is likely a feasible mechanism for the development of leucogranites and for explaining the compositional diversity of the granite during intracrustal differentiation

common trace element characteristics of crustal and mantle derived k rich magmas at mt amiata central italy rare earth and other trace element data are reported for k rich mafic inclusions and siliceous lavas from mt amiata southern tuscany italy which form an almost complete mixing series as a result of magmachamber replenishment despite a wide range of sio2 contents 48 67 wt most of the rocks are equally enriched in light ree 200 300 and heavy ree 10 15 relative to chondritic values whereas intermediate ree are slightly less abundant in the lavas compared with the inclusions eu shows negative anomalies eueu 0 49 0 70 that are most pronounced in the lavas the compatible elements cr v sc and co are found to behave like sr ba and most major elements as they show a distinct inverse correlation with sio2 while cs follows na and li and markedly increases with sio2 however k and a number of other predominantly incompatible elements viz rb zr la ce yb lu nb y hf th and u display surprisingly little or no variation and all of the rocks have unusually high concentrations of many of these elements based on arguments that mixing in the magma chamber was not accompanied by significant selective enrichment of certain elements these chemical characteristics are attributed to the end members which can be identified as a silica saturated tuscan type magma and a primitive silica undersaturated roman type magma of the high k series it is tentatively suggested that the different sources in the lower crust and upper mantle from which the end member magmas are thought to originate were metasomatized by the same fluids prior to melting

the geochemistry of phosphorus in granite rocks and the effect of aluminium phosphorus has been shown to have a profound influence on the evolution of silicate melt systems it also controls the geochemical behavior of rare earths uranium thorium strontium and other elements through the relationships between melt and accessory phosphates based on experimental data harrison and watson 1984 proposed a model of saturation behavior of apatite in crustal melts as a function of temperature and silica content subaluminous granites fit in well with such a model but departures are evident in the case of peraluminous granites a systematic study of the distribution of p2o5 in granitoids from all over the world shows that there are two modes to describe phosphorus enrichment in peraluminous granitic rocks 1 the hoyos type trend which is parallel to the one in harrison and watson s hw model but with higher p2o5 concentrations at the same silica contents and 2 the pedrobernardo type trend implying an increase in phosphorus in the most sio2 rich differentiates of strongly peraluminous low ca granites pedrobernardo type leucogranites are characterized by the presence of rare phosphates or p rich feld spars since they have excess p2o5 over cao to form normative apatite we here propose the term perphosphorous granites high phosphorus contents appear to be due to elevated apatite solubility in peraluminous granitic melts rather than to high amounts of restitic apatite both the hoyos and pedrobernardo type departures from the hw model can be corrected by using the expression p2o5corrected p2o5hw efactor where p2o5hw is the prediction according to the hw model and factor is asi 1 6429t asi being the al2o3 cao na2o k2o molar ratio we suggest that such departures could be caused by a decrease in the ca activity in the melt as a result of increased peraluminousity the pedrobernardo type trend is a limiting case in which ca activity in the melt is nearly zero and calcium instead of phosphorus becomes the essential structural constituent esc of the apatite when this happens phosphorus starts behaving as an incompatible element that is concentrated in late fluids high p2o5 contents are more characteristic of s than other granite types no significant departures from the hw model have been found for i a or m type granites in central iberia granites associated with u sn and w mineralizations usually have high phosphorus contents values of p2o50 5 wt at sio270 wt are good indicators of economic mineralization

evolution of a plume influenced source to sink system an example from the coupled central emeishan large igneous province and adjacent western yangtze cratonic basin in the late permian sw china abstract source to sink paleogeography in a time constrained sequence stratigraphic framework has been reconstructed for the non marine to marine transitional lopingian strata late permian in the western yangtze cratonic basin wycb and the adjacent inner zone of the emeishan large igneous province elip in order to reveal the evolution of a mantle plume influenced cratonic basin the lopingian coal bearing strata can be subdivided into seventeen 4th order sequences and three 3rd order composite sequences representing 6 76 myr paleogeographic reconstructions of the wycb demonstrate the existence of n s trending terrestrial transitional and marine facies belts distributed west to east away from the central elip geomorphological analysis indicates that the western boundary of the source area coincided with the major axis of the uplifted central elip based on sediment flux estimates and modeling bqart model relief of the central elip increased from near sea level in the earliest late permian and reached equilibrium at about 200 m in the latest permian sediment volume backfilling analysis indicates that total tectonic uplift of the central elip in the late permian was more than 500 m evolution of the coupled central elip and wycb can be subdivided into three stages pre eruptive uplift stage pre and syn eruptive subsidence stage and syn and post eruptive uplift stage post eruptive basin filling was controlled by sediment supply that was related to tectonic uplift drainage topography and climate change and basin accommodation that was related to sea level fluctuations and plume induced syn sedimentary tectonics

reflectance spectroscopy of plagioclase dominated mineral mixtures implications for characterizing lunar anorthosites remotely anorthositic rocks dominate the moon s upper crust as remnants of the lunar magma ocean lmo small variations in the mineralogy of these rocks may hold key information about the homogeneity of lmo composition and solidification processes orbital near infrared nir sensors are sensitive to mineralogy but technologic advances have only recently enabled detection of the plagioclase component in crustal rocks based on an absorption band centered near 1250 nm anorthosites occupy a unique mineralogic range that is well suited for nir studies the highly transparent component plagioclase is present in high abundances while the spectrally dominant mafic or oxide minerals are present in only minor abundance as a result spectra of anorthosites are more likely than many other rock types to contain visually discernable signatures from more than one mineral component facilitating their identification and characterization in nir data in support of new nir measurements for the moon we present laboratory spectral analyses of well controlled plagioclase dominated mineral mixtures we focus on the spectral effects of varying mafic and oxide composition and abundance in mixtures with a common plagioclase end member the results demonstrate that plagioclase can be a significant contributor to reflectance spectra when strongly absorbing minerals are present in low abundance we show that the contribution of plagioclase is more pronounced in mixtures with pyroxenes and certain spinels but more easily masked in mixtures containing small amounts of olivine differences in minor mineral composition are clearly expressed in bulk spectra modeling of mixtures using a hapke nonlinear approach accurately estimates mineral abundances in laboratory spectra to within 5 vol for mixtures with 90 vol plagioclase together these results imply that not only should orbital nir data sets be able to discern the presence of plagioclase in anorthositic crustal exposures but also that detailed information about anorthosite mineral assemblages can be reliably accessed in reflectance spectra

the global surface temperatures of the moon as measured by the diviner lunar radiometer experiment abstract the diviner lunar radiometer experiment onboard the lunar reconnaissance orbiter lro has been acquiring solar reflectance and mid infrared radiance measurements nearly continuously since july of 2009 diviner is providing the most comprehensive view of how regoliths on airless bodies store and exchange thermal energy with the space environment approximately a quarter trillion calibrated radiance measurements of the moon acquired over 5 5 years by diviner have been compiled into a 0 5 resolution global dataset with a 0 25 h local time resolution maps generated with this dataset provide a global perspective of the surface energy balance of the moon and reveal the complex and extreme nature of the lunar surface thermal environment our achievable map resolution both spatially and temporally will continue to improve with further data acquisition daytime maximum temperatures are sensitive to the albedo of the surface and are 387 397 k at the equator dropping to 95 k just before sunrise though anomalously warm areas characterized by high rock abundances can be 50 k warmer than the zonal average nighttime temperatures an asymmetry is observed between the morning and afternoon temperatures due to the thermal inertia of the lunar regolith with the dusk terminator 30 k warmer than the dawn terminator at the equator an increase in albedo with incidence angle is required to explain the observed decrease in temperatures with latitude at incidence angles exceeding 40 topography and surface roughness influence temperatures resulting in increasing scatter in temperatures and anisothermality between diviner channels nighttime temperatures are sensitive to the thermophysical properties of the regolith high thermal inertia ti materials such as large rocks remain warmer during the long lunar night and result in anomalously warm nighttime temperatures and anisothermality in the diviner channels anomalous maximum and minimum temperatures are highlighted by subtracting the zonal mean temperatures from maps terrains can be characterized as low or high reflectance and low or high ti low maximum temperatures result from high reflectance surfaces while low minimum temperatures from low ti material conversely high maximum temperatures result from dark surface and high minimum temperatures from high ti materials impact craters are found to modify regolith properties over large distances the thermal signature of tycho is asymmetric consistent with an oblique impact coming from the west some prominent crater rays are visible in the thermal data and require material with a higher thermal inertial than nominal regolith the influence of the formation of the orientale basin on the regolith properties is observable over a substantial portion of the western hemisphere despite its age 3 8 gyr and may have contributed to mixing of highland and mare material on the southwest margin of oceanus procellarum where the gradient in radiative properties at the mare highland contact is broad 200 km

palynology of the stonehaven group scotland evidence for a mid silurian age and its geological implications palynomorphs from the stonehaven group indicate a late wenlock to early ludlow age this is older than the currently accepted pridoli age based on fish and arthropods reasons for this discrepancy are discussed a previous correlative of the stonehaven group has been the old red sandstone of kerrera argyll however palynological assemblages from both kerrera and the adjacent succession at oban are in fact younger than that from stonehaven in being of latest silurian to earliest devonian age the palynomorphs from kerra and oban lie beneath the important geochronological tie point of the lorne lavas and suggest that the silurian devonian boundary is older than currently accepted

fluorine geochemistry in volcanic rock series examples from iceland and jan mayen abstract a new analytical procedure has been established in order to determine low fluorine concentrations 30 100 ppm f in igneous rocks and the method has also proven successful for higher concentrations 100 4000 ppm f fluorine has been measured in a series of olivine tholeiites from the reykjanes peninsula a tholeiite to rhyolitic rock series from kerlingarfjoll central iceland and an alkaline rock series from jan mayen that ranges from ankaramites to trachytes fluorine is not appreciably degassed during extrusion and appears to be insensitive to slight weathering the olivine tholeiites from the reykjanes peninsula have f contents of 30 300 ppm and exhibit linear increases proportional to the incompatible elements k p and ti such incompatible behaviour for f has been confirmed for the less evolved rocks of the other series the tholeiites from kerlingarfjoll 100 2000 ppm f show a linear increase with k2o whereas the f content decreases slightly for the andesitic to rhyolitic rocks the change from a linear increase with k for the tholeiites to a moderate decrease in f for the more evolved rocks is associated with a sharp decrease in p suggesting that apatite controls the f distribution for these rocks when the activity of p is too low to allow for significant control of f by apatite the f abundances increase towards the most k rich rhyolites similar relationships between f k and p are also apparent for the alkaline jan mayen rock series but the shifts in f and p behaviour occur at higher k2o and sio2 concentrations

experimental silicate phosphate equilibria in peraluminous granitic magmas with a case study of the alburquerque batholith at tres arroyos badajoz spain with the actual mineralogy and whole rock p in the granite experimental results presented here establish the p2o5 content of aplite pegmatite facies at tres arroyos peraluminous silicic melt for three potential buffering reactions at 200 mpa h2o and t from 525 to 850 c 1 biotite sarcopside 2 spessartine sarcopside 3 petalite amblygonite montebrasite quartz the first two equilibria are moderately insensitive to t and buffer the p content of melt between 1 30 1 57 wt

estimating abundances of volatile and other mobile components in evolved silicic melts through mineral melt equilibria to variable degrees of accuracy from source partitioning between and earths residual minerals and anatectic melts through melt fractionation partitioning between igneous minerals and residual melts to the end stages of magma solidification where higher concentrations of normally trace elements may promote saturation in their crystalline phases the magmatic abundance of rare alkalis and alkaline earths

evolution of a strongly differentiated suite of phonolites from the klinghardt mountains namibia phonolites of tertiary age occur as eroded tholoids lava flows ignimbrites and coulees in the klinghardt mountains of southern namibia sixty samples have been analyzed for major and trace elements and fourteen of these for 87sr86sr the phonolites lie close to the low pressure cotectics in q ne ks in keeping with their petrography which indicates that most samples have phenocrysts of both nepheline and sanidine na has been variably lost from the rocks during crystallization and devitrification alteration of hypocrystalline specimens the concentrations of other elements except perhaps lree remain unaffected the composition variation within the phonolites is consistent with fractional crystallization of nepheline sanidine and minor clinopyroxene to produce a number of near parallel lineages from similar but not identical parent compositions fractional crystallization results in increasing sio2 na2o zr nb ce rb th y zn pb and ree but decreasing k2o tio2 cao mgo p2o5 ba and sr with differentiation enrichment factors for zr and nb indicate that the most evolved phonolites represent 20 residual liquids a result which is consistent with major element modelling in the evolution of the most differentiated phonolites fractional crystallization was accompanied or followed by volatile transfer causing depletion of th y lree zn and pb relative to zr and nb initial 87sr86sr for most of the phonolites lie in the range 0 7050 0 7057 rising to 0 7080 in the low sr samples this is suggestive of some interaction with crustal rocks but this interaction has no detectable influence on the fractionation controlled compositional evolution of the suite the phonolites are associated on a regional scale with nephelinite and melilitite rocks but there is no favourable evidence for an evolutionary link between these and phonolite alternatively the primitive phonolites may have originated through anatexis of metasomatized nepheline normative crustal rocks

apatite dissolution into peraluminous haplogranitic melts an experimental study of solubilities and mechanisms apatite ap dissolution and solubility in the peraluminous haplogranite system were investigated in three sets of experiments at 750 c and 200 mpa ph2o as functions of ap grain size abundance melt ap ratio and melt asi alumina saturation index mol al2o3 na2o k2o cao between an asi of 1 1 1 metaluminous to mildly peraluminous the solubility of ap as measured by p2o5 in the melt is low 0 1 wt p2o5 which agrees with previous work in equilibrium runs with more strongly peraluminous compositions however ap solubility increases linearly with asi to p2o5 0 63 wt in melt at asi 1 3 and can be denned by a simple equation p2o5 3 4 3 1 asi r 0 833 which agrees within error with previous calculations reported in the literature in experiments where ap grains are sparce and widely separated i e simulating ap distribution in an ap bearing peraluminous protolith undergoing anatexis the dissolution of ap involves transient disequilibrium that promotes higher solubility of p2o5 up to nearly six times the equilibrium values adjacent to ap at a given bulk asi of melt and this increases the al si of melt in the ap dissolution aureole the approach to equilibrium between ap and melt is hastened by increasing the ap melt ratio within the local melt pool e g the capsule or by decreasing ap grain size for a similar melt ap ratio diffusivity calculations using inverse error function methods for the normal diffusion of p and ca yield dp 10 11 cm2 s and dca 10 10 cm2 s confirming prior results that diffusion of p away from ap surfaces is the rate limiting factor in ap dissolution these results combined with previous work at higher temperatures but on similar hydrous melts yield an activation energy e for p diffusion of 16 5 kcal mol and a frequency factor d0 of 1 4 10 3 cm2 s phosphorus diffusion through the melt is accompanied by uphill diffusion of al resulting in an increase of up to 2 wt al2o3 in melt near the ap within the ap dissolution aureole melt contains one additional al cation for every p cation i e al p 1 1 which is suggestive of an associated alpo4 complex the exchange reaction in melt is represented by alpsi 1 in which 2 to4 clusters are created in the place of 1 this exchange should be accompanied by discernable changes in melt properties e g density molar volume viscosity the results have applications to equilibrium and local disequilibrium effects during anatexis of apbearing metapelites and to the saturation limits of ap during crystallization of peraluminous magmas the dissolution of flux bearing minerals such as ap e g those containing p b or f may influence the stability and solubility of other trace element bearing minerals during anatexis of metapelites texture e g grain size and distribution and spacial relationship to other minerals plays an important role in reaction kinetics and at least temporarily in mineral solubilities the disequilibrium behavior of accessory minerals has critical consequences for ree modelling of granites

the petrogenesis of an i type volcanic plutonic suite the st marys porphyrite tasmania the devonian i type st marys porphyrite 388 1ma comprises two petrographically similar units an 800 m thick pyroclastic sheet compositionally dacite and rhyolite and a subvolcanic feeder dyke the pyroclastics are crystal rich and contain in order of decreasing abundance plagioclase quartz biotite augite hypersthene and sanidine phenocrysts in an aphanitic groundmass

accessory minerals and the geochemical evolution of crustal magmatic systems a summary and prospectus of experimental approaches it has recently been recognized that accessory minerals in continental rocks may contain a substantial fraction of the whole rock complement of trace elements and geochemically important isotopes this observation is in itself interesting but its importance is magnified many fold when one considers the possible consequences to the geochemical rearrangement that accompanies crustal melting if for example an accessory phase is insoluble in early formed partial melts it may effectively retain in the residue many incompatible elements e g ree and daughter isotopes e g radiogenic pb that would otherwise be partitioned into the melt in addition should an unmelted accessory mineral e g zircon be entrained in a departing melt fraction it may carry with it radiogenic components pb nd143 hf176 characteristic of the source region the effectiveness of phases such as zircon apatite sphene allanite epidote and monazite in the roles noted above can only be gauged from knowledge of the three fundamental accessory phase parameters i e 1 the solubilities of the accessory minerals in crustal melts 2 the equilibrium mineral liquid partition coefficients for the trace element and isotopes of interest and 3 the diffusivities that govern the rates at which equilibrium will be approached in general these parameters can only be measured in laboratory experiments and relatively few data have been accumulated to date it does seem clear however that apatite generally is residual insoluble during crustal melting and zircon can be depending on melting conditions and abundance of zircon in the source petrographic and geochemical studies indicate that monazite allanite and epidote may also be highly insoluble in some cases but the specific circumstances that promote insolubility remain unknown the few experimentally determined partition coefficients now available for apatite and zircon agree qualitatively with natural rock data on mineral separates however preliminary diffusion measurements and inferences from natural systems suggest that trace element and isotopic equilibrium between undissolved accessories and crustal melts is in fact rarely approached ironically it is this very disequilibrium in the form of preserved diffusion profiles that may afford the most information on time temperature histories of melting events continued experimental interest in the fundamental accessory phase parameters will eventually provide the tools that will enable rigorous assessment not only of the timing and duration of crustal melting episodes but also of the extent of melting and re distribution of trace elements and radiogenic isotopes

alkali feldspars as a main phosphorus reservoirs in rare metal granites three examples from the bohemian massif czech republic phosphorus rich alkali feldspars were found in three peraluminous highly differentiated albite topaz li mica granites in the w and s parts of the bohemian massif the average contents of p2o5 in k feldspars k i ovy kamen 0 57 wt homolka 0 77 wt and podlesi 0 83 wt are higher than the average contents of p2o5 in albites k i ovy kamen 0 23 wt homolka 0 23 wt and podlesi 0 39 wt the analyses of feldspars indicate that partition coefficient of phosphorus between k feldspar and albite range from 1 5 to 2 5 measured data in k feldspars suggest a statistically significant difference from the al3 p5 2 si4 substitution mechanism for higher phosphorus concentration the p content in k feldspars from the podlesi granite represent the highest p content in natural feldspar known to date up to 2 5 wt of p2o5 it is suggested that all studied granites retained nearly all phosphorus of granitic melts and that their alkali feldspars represent major reservoirs of phosphorus

effects of syndepositional faulting and folding on early cretaceous rivers and alluvial architecture lakota and cloverly formations wyoming u s a abstract quantitatively reconstructed paleochannel hydraulics e g channel discharges slopes velocities geometries e g widths depths sinuosities channel patterns and alluvial architecture record the local effects of syndepositional faults and folds these effects are evaluated from lower cretaceous rocks in three areas 1 the northern black hills where the axes of syndepositional folds trend roughly perpendicular to paleoflow 2 the northwestern black hills where the trend of a syndepositional fault is oblique to paleoflow and 3 the wind river basin where the trends of syndepositional faults are nearly parallel to paleoflow in each area channel belt deposits are laterally and vertically connected where local subsidence rates were high producing thick laterally extensive sandstones areas of lower subsidence rates are characterized by isolated or laterally connected channel belt deposits and thinner sandstones surface deformation controlled the positions of some rivers because of the development of antecedent drainages or by directing rivers toward areas of maximum subsidence some reconstructed channel slopes which range from 0 62 10 4 to 5 43 10 4 record surface deformation the three dimensional alluvial architecture was simulated using the model of mackey and bridge 1995 together with quantitatively reconstructed paleochannel parameters in order to provide quantitative insight as to possible conditions and processes that produced the observed alluvial architecture the effects of deformation on channel slopes together with depositional topography were important in controlling avulsion and resultant alluvial architecture the most important condition that governed the alluvial architecture was comparable rates of local subsidence and sediment accumulation paleochannel reconstructions indicate that the rivers were 48 180 m wide and 4 4 13 6 m deep and had discharges of 64 1073 m3s 1 channel deposits all appear to represent point bars and associated channel fills of meandering rivers sinuosities were comparable ranging from 1 1 to 1 4 and show no consistent trends with other channel parameters hence with the exception of two paleochannels out of the thirteen that were reconstructed differences in hydraulic parameters such as slope and sediment transport rate had no discernible effect on channel pattern or sinuosity

partition coefficients for rare earth elements in mafic minerals of high silica rhyolites the importance of accessory mineral inclusions abstract ree concentrations of mafic mineral separates from high silica rhyolites measured by inaa are high and variable compared to electron microprobe analyses of the minerals themselves the mafic phases commonly contain inclusions or have adhering grains of accessory rare earth element ree rich minerals optical and electron microscopic observation revealed discrete grains of chevkinite rare earth titano silicate included within clinopyroxenes from the sierra la primavera mexico rhyolite and monazite grains adhering to ortho and clinopyroxenes from the bishop tuff california during hand picking of mineral separates inclusions are only partly removed as a result the magnitude and variability of true mineral melt partition coefficients for light ree have been overestimated the true ree partition coefficients of la primavera and bishop tuff pyroxenes obtained by microprobe are only slightly higher than they are in lower silica rhyolites and are not as variable as previously thought the partitioning slope is positive as in less silicic systems the relative partitioning behavior of ree in high silica rhyolites is dominated by crystal chemical controls and not by liquid structural effects when a partition coefficient is used for crystallization calculations adhering phases and inclusions should be retained or the minor phases must be accounted for separately alternatively a bulk distribution coefficient can be calculated using whole rock and glass compositions and the glass mode

microstructural evidence of orders of crystallization in granitoid rocks experimental melting studies of granitoid rocks have documented variations in the order of crystallization of minerals depending on the melt composition total pressure and the activity of water and other volatiles in the melt microstructural criteria for independent determination of the order of crystallization are needed to permit application of the experimental data to the evaluation of the conditions of crystallization unfortunately few criteria can be reliably applied to infer either the order of initial crystallization on the order in which minerals cease to crystallize in granitoid rocks most microstructures of granitoid rocks record simultaneous rather than sequential crystallization of minerals grain size criteria e g phenocrysts vs groundmass can be used to infer a partial order of crystallization in many volcanic rocks but the presence of extremely large phenocrysts of k feldspar that from experimental data must be the last mineral to crystallize highlights the dangers inherent in the use of grain size criteria providing it can be determined that included minerals did not form subsequently along cracks or from entrapped melt inclusions those inclusions that are demonstrably and consistently only near the centre of large grains must have ceased to crystallize before the host mineral where the host mineral occurs only as rims on the early formed mineral it is possible to infer both the order of cessation and initiation of crystallization common examples are provided by the rimming produced by a discontinuous reaction relationship most other examples of inclusion relationships could result from simultaneous crystallization microstructures involving moulding and impingement relationships are unreliable as the microstructure is produced only after the minerals have begun to crystallize in the melt or on the melt solid interface as most minerals continue to crystallize right to the solidus they cease to crystallize simultaneously new criteria perhaps involving detailed chemical zoning patterns need to be developed before the orders of crystallization can be reliably determined for granitoid rocks

composition of the lunar highland crust from near infrared spectroscopy near infrared reflectance spectra of the lunar highlands are synthesized to obtain global information about the composition of the lunar near side crust immature exposed surfaces from small fresh craters mountains and massifs and large craters with central peaks are included in a survey of rock types across the lunar near side compositions recognized in these data include anorthosite noritic gabbric and troctolitic mineral assemblages three quarters of the areas studied that represent samples from the upper 1 2 km of lunar crust exhibit noritic compositions with different amounts of pyroxene and or brecciation alteration norites are ubiquitous across the near side and show no spatial clustering associated with any of the major basins in contrast to this noritic megaregolith of the upper crust material representing stratigraphically deeper zones 5 15 km of the lunar crust is dominated by gabbros anorthosites and troctolites with less than a quarter of the areas studied exhibiting a noritic composition the origin of the noritic megaregolith and its relation to deeper crustal material is thus somewhat of an enigma the current limited statistics for areas identified as anorthosites and troctolites are insufficient to derive global spatial distributions gabbroic areas however are notably concentrated in the western hemisphere although incomplete for a global assessment of crustal materials these data demonstrate that the lunar near side crust is clearly mineralogically heterogeneous both laterally and vertically and not well mixed below 1 2 km

dissecting through the metallogenic potentials of precambrian granitoids case studies from the bastar and eastern dharwar cratons india

apatite in igneous systems apatite is a minor but ubiquitous mineral in most igneous rocks although the modal proportion of apatite in common rocks is generally low it can reach high concentrations in enclaves cumulates and other rocks of low abundance i e rocks that constitute a small volume of the crust and mantle e g nelsonites the presence of apatite in most rocks is due not only to its low solubility in naturally occurring melts and aqueous solutions but also to the limited ability of common rock forming minerals to accept the amount of phosphorus that occurs in most rocks into their structure in this paper we will discuss some aspects of the occurrence texture composition physical chemistry and petrogenetic significance of apatite in felsic rocks i e andesite to rhyolite and their plutonic analogs in mafic i e basalts and related rocks and plutonic analogs and ultramafic rocks of the earth s crust and mantle fluorapatite is by far the most common member of apatite family found in igneous rocks however most natural fluorapatite contains some chlorine and hydroxyl as well and these constituents can attain high concentrations in some cases the other halogens bromine and iodine also occur in apatite but their concentrations are much lower than chlorine and fluorine many cations commonly substitute for calcium and phosphorus in apatite however they rarely reach concentrations that warrant the definition of a separate mineral species apatite can be described by the general formula a5 xo4 3z following sommerauer and katz lehnert 1985 the a site accommodates large cations e g ca2 sr2 pb2 ba2 mg2 mn2 fe2 ree3 eu2 cd2 na pan and fleet ch 2 in this volume and comprises two sites that exhibit vii fold

entrainment of gravel from naturally sorted riverbed material the critical dimensionless shear stress ci required to entrain a given size particle di was computed from extensive bedload transport measurements in three self formed rivers that have naturally sorted gravel and cobble bed material the value of ci was determined to be significantly affected by the size distribution of the riverbed material for bed particles between 0 3 to 4 2 times the median diameter of the subsurface bed material d50 the average critical dimensionless shear stress ci is equal to ci 0 0834 di d50 0 872 with a coefficient of determination of 0 980 for bed particles larger than 4 2 times d50 ci appears to approach a constant value of approximately 0 020 in a noneroding channel thus ci varies from 0 25 to 0 020 for a given particle depending on the ratio of di to d50 previous investigations of the hydraulic conditions required to entrain coarse riverbed material have reported critical shear stress values ranging from 0 25 to 0 020 for a given particle size this analysis indicates that virtually all of the variation is due to differences in the subsurface bed material size distribution this analysis shows that ci varies almost inversely proportional to the particle diameter for a nonuniform bed material therefore bed particles between 0 3 to 4 2 times d50 are entrained at nearly the same discharge an investigation of the hydraulic characteristics and bed material mobility of 24 self formed gravel bed rivers in colorado determined that particles as large as the median diameter of the bed surface were entrained by discharges equal to the bankfull stage or less particles as large as the 90th percentile fraction were entrained by the bankfull discharge in nine of the rivers studied consequently in these rivers a significant fraction of the riverbed was entrained rather frequently over a period of years although the transport rate was very small

origin of rhythmic layering in the calamity peak satellite pluton of the harney peak granite south dakota the role of boron abstract the calamity peak satellite granite pluton on the flanks of the harney peak granite south dakota displays prominent mineral and textural layering the latter defined by alternating fine grained and pegmatitic granite superimposed on the fine grained granite layers is a fine scale 0 1 5 cm rhythmic layering defined by modal differences in tourmaline microcline albite and muscovite there is very little variation in the major element mineral compositions in the whole complex analyses by prompt gamma neutron activation gave a b2o3 content of 0 07 in the light layers albite quartz and muscovite and 0 65 in the dark layers tourmaline microcline quartz and albite these contents are essentially proportional to tourmaline abundance in each layer the textural and mineralogic layering is the result of the interplay of tourmaline crystallization and shifts in phase equilibria due to changes in b concentration in the melt initial cotectic crystallization of albite quartz and muscovite increased the activity of fe and mg in the adjacent melt to levels sufficient for tourmaline to form tourmaline crystallization depleted b and decreased the solubility of h2o in the melt causing exsolution of h2o from the melt and further removal of b due to high fluid melt partition coefficient this process also resulted in the precipitation of k feldspar partly at the expense of muscovite and partly due to a slight increase in the solidus temperature once the crystallization front moved to an fe and mg poor region of the melt tourmaline precipitation ceased and the equilibrium shifted back toward quartz muscovite and albite the pegmatitic layers some of which cut across previously formed rhythmic layers and commonly have tourmaline along their borders appear to have crystallized from melt enriched in the exsolved fluid phase

geology and geochemistry of archaean granites in the kalgoorlie region of the eastern goldfields western australia a syn collisional tectonic setting abstract granites in the kalgoorlie region of the archaean yilgarn craton are predominantly biotite granodiorite and monzogranite with some hornblende bearing varieties granites are divided on the basis of field relationships petrography and chemical composition into five supersuites an older supersuite containing four suites pre dates regional folding and four supersuites post date regional folding the potassic composition of the mainly silica rich granites 68 sio2 suggest that the most appropriate source for the majority of supersuites is continental crust with a composition in the range tonalite to granodiorite most supersuites evolved by fractional crystallization mainly of biotite and plagioclase some suites contain synplutonic dykes and microgranite xenoliths that crystallized from enriched mantle derived magmas there was only limited and local chemical interaction between granite and mantle derived magmas geometric and temporal relationships between regional structures and granites indicate that the granites were emplaced during a major orogenic event however s type granites which are widespread in some modern syn collision settings are absent in the kalgoorlie region the predominance of high fo2 i type granites in the study area probably reflects the absence of large graphite bearing metasedimentary accumulations in the lower crustal source regions the distribution of suites and supersuites implies a common source region beneath the kalgoorlie and gindalbie granite greenstone terranes suggesting that they shared a common geological history dating back to late greenstone deposition

a weathering related origin of widespread monazite in s type granites the s type granite suites comprising more than a quarter of the extensively developed granites in the lachlan fold belt australia contain monazite which may be related to the chemical weathering of the sedimentary source rocks we report a process whereby chemical weathering fixes mobile rare earth elements ree in hydrous phosphate phases such as florencite and rhabdophane this material contains up to 50 wt lree and occurs as very small particles 3 m dehydration of these hydrous ree phases during anatexis directly yields monazite the low solubility of phosphorus in s type granite melts inhibits dissolution of both monazite and apatite refractory monazite may be thus entrained and transported in s type granites in a manner similar to processes resulting in inherited zircon since both th and the light ree are major components in monazite materials containing this minute phase may be of widespread geochemical significance in both granites and metamorphic rocks

a quantitative approach to linking drainage area and distributive fluvial system area in modern and ancient endorheic basins abstract regression relationships are derived relating the areal extent of large distributive fluvial systems dfss 30 km in length formed in endorheic basins to contributing drainage area the resulting correlation coefficients vary between 79 and 98 derived correlation values are strikingly similar when stratified by climate large scale tectonic regime and basin context regression equation exponent values range from 0 41 to 0 75 indicating a strong positive relationship between drainage area and dfs area while coefficients account for the influence of external parameters on the derived relationships analysis of the dataset using planform morphology and drainage basin slope as additional variables reveals that regressions for braided bifurcating dfs produce a highly significant relationship the relationship suggests that drainage basin relief influences sediment supply to the sedimentary basin in terms of volume or caliber which in turn affects the depositional gradient of the dfs surface and resultant channel planform an evaluation of the predictive capability of the regression equations reveals that the relationships derived from braided bifurcating dfss perform best with 80 of the predicted values falling within 25 of the measured dfs area value with a third of the predicted values within 10 of the measured dfs area value application of the regression relationships derived here to rock record examples of fluvial deposits interpreted as large dfss show that dfs area can be used as a proxy to predict the surface area of fluvially transported sediment deposited in a sedimentary basin from the contributing drainage basin area the regression relationships for modern drainage areas and corresponding dfs areas from a range of tectonic and climatic settings suggest a measurable link between source and sink in the sedimentary rock record the results provide a potential tool for more accurate reconstruction and prediction of preserved fluvial deposits and basin fill architecture within basin scale climatic and tectonic contexts

chemical evolution of granitic rocks in the east antarctic shield with particular reference to post orogenic granites granitic intrusives of the east antarctic shield range in age from early archaean 3930 ma to cambrian and show systematic variations in chemical and isotopic characteristics many archaean orthogneisses are of tonalitic to granodioritic composition and represent new continental crust derived from the mantle by a two stage process involving hydrous melting of mafic crustal rocks syn orogenic granitic rocks are generally of more potassic composition and were derived by intracrustal melting under lower ph2o conditions they are mostly of more typical i type derived from igneous source materials but there is an increasing proportion of s types derived by melting of sedimentary materials with time late and post orogenic intrusives are mostly granites s s with a type anorogenic affinities and were derived by melting of relatively anhydrous granulite facies lower crustal rocks they are characterised by marked enrichment of y zr nb la and ce relative to p ti and sr and commonly have high f femg znfe and gaal plagioclase apatite and ti minerals were probably residual phases during partial melting as well as being involved in fractional crystallisation whereas other minor phases such as zircon were apparently relatively soluble in the high temperature melts emplacement of a type granites at about 500 ma may have been associated with internal fracturing of gondwanaland before eventual break up

structural setting and geochemistry of archaean i type granites in the bardoc coolgardie area of the norseman wiluna belt western australia abstract regional structures in the bardoc coolgardie area of the archaean norseman wiluna greenstone belt in western australia developed during early large scale thrusting followed by a transpressional regime characterized by enewsw shortening and large scale sinistral strike slip faults structural relationships between granites and greenstone successions indicate emplacement of granitic rocks throughout this deformation history emplacement mechanisms include solid or liquid state diapirism forceful dilation of country rocks and passive stoping i type granites are common and include early and late tectonic intrusions the widespread occurrence of i type granodiorite and monzogranite probably derived by partial melting of lower continental crust or subducted oceanic crust suggests a continental margin setting for the belt alkalic quartz diorite occurs as rounded enclaves in granodiorite and is enriched in ba rb sr ce la p and f which suggests a mantle derived volatile component these quartz diorite melts may have formed by partial melting of metasomatized mantle or alternatively mantle degassing may have lowered solidus temperatures in the source region and thus induced melting emplacement of hot volatilerich quartz diorite melts into the lower crust may have lowered solidus temperatures in the source rocks for granodiorite and monzogranite recent models for archaean gold mineralization suggest that auriferous fluids contained co 2 derived from lower crustal or mantle sources in the bardoc coolgardie area co 2 may have been flushed out during partial melting of the lower continental crust however the origin of the gold in the mineralizing fluids requires some other explanation because gold mineralization is generally a late stage event and took place over a considerably shorter time interval than the formation and emplacement of i type granites

the origin of the dapingzhang volcanogenic cu pb zn ore deposit yunnan province sw china constraints from host rock geochemistry and ore os pb s c o h isotopes abstract the dapingzhang volcanogenic cu pb zn sulfide deposit is located in the lancangjiang tectonic zone within the sanjiang region yunnan province of southwestern china the deposit occurs within a felsic volcanic dome belonging to a mid silurian volcanic belt stretching for more than 100 km from dapingzhang to sandashan the mineralized volcanic rocks are predominantly keratophyre and quartz keratophyre with subordinate spilite the dapingzhang deposit is characterized by well developed vertical zonation with stockwork ores in the bottom disseminated sulfide ores in the middle and massive sulfide ores in the top overlain by a thin layer of chemical sedimentary exhalative rocks chert and barite the re os age of the pyrites from the deposit is 417 23 ma indistinguishable from the age of the associated felsic volcanic rocks the associated felsic volcanic rocks are characterized by negative nb ta anomalies and positive e nd t values 4 4 6 5 similar to the coeval calc alkaline volcanic rocks in the region this observation supports the interpretation that the felsic volcanic rocks associated with the dapingzhang deposit are the derivatives of arc basaltic magma by extensive fractional crystallization the 34 s values of the sulfides from the deposit vary from 1 24 to 4 32 indicating a predominantly magmatic source for the sulfur the sulfides are also characterized by homogeneous and relatively low radiogenic pb isotope compositions 206 pb 204 pb 18 310 18 656 207 pb 204 pb 15 489 15 643 and 208 pb 204 pb 37 811 38 662 similar to the pb isotopic compositions of the associated volcanic rocks the pb isotopic data indicate that mantle derived pb is more prevalent than crust derived pb in the deposit the s pb isotopic data indicate that the important ore forming materials were mainly derived from the associated volcanic rocks the 13 c pdb and 18 o smow values of the associated hydrothermal calcite crystals vary from 2 3 to 0 27 and from 14 6 to 24 4 respectively these values are between the mantle and marine carbonate values the narrow range of the 13 c pdb values for the calcite indicates that carbon bearing species in the hydrothermal fluids were primarily derived from marine carbonates the 18 o values for the hydrothermal fluids calculated from the measured values for quartz are between 2 1 and 3 5 the corresponding d values for the fluids range from 59 to 84 the o h isotopic data indicate mixing between magmatic fluids and seawater in the ore forming hydrothermal system similar to a typical volcanogenic massive sulfide vms deposit the ore forming fluids contained both magmatic fluids and heated seawater the ore metals and regents were derived from the underlying magma as well as felsic country rocks

provenance of lower old red sandstone conglomerates se kincardineshire evidence for the timing of caledonian terrane accretion in central scotland northerly derived conglomerates dominate much of the thick lower old red sandstone ors succession of the ne midland valley of scotland these contain a diverse suite of granitoid boulders the provenance of which can be used to constrain the timing of the post caradoc displacements which juxtaposed the highland border complex against the grampian terrane rb sr muscovite whole rock ages for two mica granite boulders from the crawton group are 473 457 ma confirming the persistence of an ordovician two mica granite source first recognized in the dunnottar group the rb sr muscovite ages are supported by a u pb age of 475 5 ma for monazite separated from one of the clasts a rb sr biotite age of 412 4 ma for a clast of porphyritic biotite granite and geochemical evidence linking this clast to many of the other biotite granite clasts suggests that late silurian granitoids and related hypabyssal intrusions have also made an important hitherto unrecognized contribution to the conglomerates mica whole rock ages for accompanying psammitic clasts suggest the source included metamorphic rocks of up to at least staurolite grade whose uplift overlapped with the intrusion of crustally derived melts the chemistry chronology and sr and nd isotopic compositions of the various igneous clasts are shown to resemble closely the ordovician through to silurian magmatic history of a small area of the grampian terrane in ne scotland this is taken as strong evidence for a pre lower ors juxtaposition of the highland border complex and the grampian terrane to within several tens of kilometres of their present position ashgill silurian terrane displacements are invoked to achieve this discrepancies in the proportions and types of clast occurring in the conglomerates are explained by uplift and unroofing of the grampian terrane prior to docking the involvement of polycyclic sediment perhaps as a local veneer of pre existing sediment on the grampian terrane and the likelihood that the source involved parts of the local grampian terrane which are no longer exposed

structure of some lower old red sandstone conglomerates kincardineshire scotland deposition from late orogenic antecedent streams a thick succession of early lower old red sandstone ors conglomerates and subordinate sandstones are preserved in a small fault bounded basin in the ne midland valley of scotland the conglomerates associated with the northern margin of this basin are distinguished by a complex provenance which involved both reworking of existing gravels and addition of contemporary volcanic and plutonic detritus this may explain their characteristic bimodal texture deposition was in large probably permanent low sinuosity channels with evidence for both periods of uniform high stage flow and repeated flow stage fluctuations variable palaeoflows in the basal part of the succession suggest deposition on wet type alluvial fans supplied by feeder channels with a high sediment and water discharge the thickness of the succession the poorly developed cyclothems despite active syndepositional faulting evidence for rapid aggradation and the inferred scale of channel bars and coarsening upward units produced by bar migration suggest the basin may have been externally drained transverse antecedent streams are invoked to account for the structure of alluvium during the early devonian central scotland lay close to the boundary between regions suffering scandian orthogonal shortening and acadian strike slip shear the tectonic controls which governed the preservation of early lower ors sediments may have been largely uncoupled from those determining the supply and dispersal of the sediment

the sedimentation and paleohydrology of the mesoproterozoic stream deposits in a strike slip basin svinsaga formation telemark southern norway abstract ancient braided fluvial systems were affected by a lack of binding vegetation under variable paleoclimatic conditions and possibly characterized by unique fluvial styles during the precambrian thus the paleohydrological investigations are important in interpreting ancient fluvial systems and a comparison of different fluvial styles systems this study reports new paleohydrological and sedimentological data from the ca 1 17 ga old fluvial deposits svinsaga formation in the fennoscandian shield which is a part of the east european craton the mesoproterozoic svinsaga formation overlies a major unconformity sub svinsaga unconformity in the telemark supracrustal rocks southern norway the unconformity corresponding to a ca 170 ma hiatus ca 1347 1170 ma and carry evidence for ancient periglacial climatic conditions eleven different sedimentary lithofacies and five lithofacies associations were recognized from the svinsaga formation the lithofacies assemblages indicate that the formation represents a relatively high energy braided fluvial environment massive breccias massive and inversely to normally graded conglomerates stratified sandstones and laminated and rippled mudstones were transported by traction currents sediment gravity flows and by suspension the proximal part of the formation contains blockfield blockslope accumulations and waning flood flow cycles these are overlain by hyperconcentrated and debris flow deposits and ephemeral high energy bedforms the distal part of the formation contains dune bedforms and channel lag deposits which indicate waning discharge fluctuations the paleohydrological calculations from the channel fill conglomerates and sandstone bedforms correlate with lithofacies assemblages the estimation of paleoslope and discharge values supports the presence of a fluvial stream rather than an alluvial fan environment the stream power and water velocity systematically decreases towards the distal parts of the formation the abundance of the waning flood flow cycles ephemeral high energy sedimentary deposits and hyperconcentrated and debris flow deposits is a possible indicator of periglacial melt waters in basin margin strike slip fault evolution this melt water combined with abundantly available debris from the non vegetated high topographic landscape

electron microprobe dating of monazite the story abstract this paper is a testimony of how electron microprobe dating of monazite was developed in the early days of this technique in the 90 s five contributions have been collected from nagoya clermont ferrand orleans salzburg and amherst the technique was designed in nagoya by professor suzuki using an old jxa 5a jeol electron microprobe the first results were published in 1991 with great difficulty professor suzuki also created the isochron like pb th diagram to present the data progressive improvement of the method finally allowed the nagoya team to date cenozoic monazite the technique was re discovered in clermont ferrand using a cameca camebax microprobe this team demonstrated the accuracy of the method and proposed statistical tools to improve the precision and to handle multimodal populations the first results were published in 1993 in orleans the french geological survey brgm developed the method with a cameca sx50 to support mapping projects they developed a new method for calculating the age and showed that this technique was very efficient for dating monazite in migmatites in salzburg the first results were obtained in 1996 using a jeol jx 8600 it proved to be very efficient in the alps to distinguish cadomian ordovician variscan and alpine events it allowed this team to directly date a monazite allanite reaction they described for the first time finally the amherst team investigated in detail the technical issues of electron microprobe monazite dating they showed that the best analytical procedures must include at least detailed chemical mapping several interference corrections and special care for background measurements with the help of cameca they designed a specific microprobe for dating named ultrachron with this machine high precision ages can be obtained on well characterized individual grains in thin section giving birth to a new era in geochronology of complex metamorphic rocks

the geochemistry of apatite from the los colorados iron oxide apatite deposit chile implications for ore genesis apatite grains from the los colorados iron oxide apatite ioa deposit the largest ioa deposit in the chilean iron belt cib exhibit significant intracrystalline spatial variability with respect to the concentrations of f cl and oh and trace elements statistical interrogation of the compositional data indicates that individual apatite grains contain spatially discrete f rich and cl rich domains the chemical composition of the f rich domains is consistent with apatite growth from silicate melts whereas the chemical composition of the cl rich domains is consistent with apatite growth from a magmatic hydrothermal fluid that cooled as it percolated outward from the los colorados fault the structural control for emplacement of the ore body into the surrounding brecciated diorite and andesite host rocks apatite in the deposit is intimately intergrown with magnetite and actinolite for which trace element fe h and o stable isotope data indicate a combined magmatic magmatic hydrothermal genesis for the deposit the compositional data for apatite are consistent with a genetic model wherein f rich apatite cores crystallized with magnetite from silicate melt followed by exsolution of a magmatic hydrothermal fluid during decompression of the parent magma experimental studies demonstrate that magmatic hydrothermal volatile phase bubbles preferentially nucleate and grow on the surfaces of apatite and magnetite microlites during decompression of a magma body continued degassing of the melt results in the volatile phase sweeping up apatite and magnetite microlites and forming a magnetite apatite fluid suspension that is buoyant in the magma chamber and ascends from the source magma along faults during regional extension halite saturated fluid inclusions in magnetite which is paragenetically equivalent to apatite at los colorados indicate that the magmatic hydrothermal fluid was a brine which allows this fluid to efficiently scavenge cl p rare earth elements and other fluid compatible elements from the silicate melt during ascent the xcl xf ratio of apatite increases as it grows from the evolving cl rich magmatic hydrothermal fluid during decompression and cooling

climatic and morphologic relationships of rivers implications of sea level fluctuations on river loads the characteristics of 279 rivers that discharge into the world oceans are analyzed in terms of their basin hydrology river discharge morphometry basin slope and area river length extension of the continental shelf seaward of the river mouth and climate precipitation statistically reliable relationships are found between discharge and basin area and between sediment load and a combined function of basin area and slope these functions are used to demonstrate how river hydrologic features would be strongly influenced by sea level fluctuations particularly under the influence of continental shelf emergence a fall in sea level toward a glacioeustatic lowstand would induce the merging of rivers on the subaerial continental shelf thereby allowing giant rivers to form for example rivers of western europe would reorganize themselves into two or three very large rivers sediment concentration carried by these mega rivers would decrease and thus the number of hyperpycnal plumes generated at river

rare earth element distributions among minerals in a granodiorite and their petrogenetic implications a study of the distribution of lanthanide rare earths in a granodiorite from the eastern peninsular ranges batholith southern california reveals that a large fraction of the ree in this rock resides in the accessory phases sphene and allanite the minerals plagioclase alkali feldspar biotite epidote and apatite each contribute approximately 1 or less of each ree to the whole rock with the exception of eu for which plagioclase contributes 7 sphene and allanite together contain 80 to 95 of each ree each of these phases is zoned in ree concentration with substantial decreases from core to margin textural observations argue for relatively early saturation and precipitation of sphene and allanite in the magma ree zoning trends in sphene and allanite and unexpectedly low ree concentrations in largely later crystallizing minerals such as feldspar indicate that the precipitation of sphene and allanite significantly reduced ree concentrations in residual melts these results illustrate the potential that sphene and allanite have for controlling the behavior of ree in granitic magmas available information collectively suggest that the sampled granodiorite existed as a complete melt that the ree contained in the assemblage of phases were derived by direct crystallization from the melt and that the melt behaved essentially as a closed system once crystallization of the phases now present began close correspondences between the major and trace element chemistries of the granodiorite and phenocryst poor lavas from similar tectonic settings support these conclusions the ree pattern of the granodiorite melt appears to have originated at depth and is characteristic of its source regions and derivation mechanism the high liquidus temperature of a granodiorite melt 1000 c indicates the importance of mantle derived components within the sources of batholithic magmas in the peninsular ranges

the origin and significance of the delaney dome formation connemara ireland dalradian meta sediments of the laurentian margin and mafic intrusions thereof in sw connemara ireland tectonically overlie meta rhyolites of the delaney dome formation the two units are separated by the mannin thrust a new u pb age of 474 6 5 5 ma shows that the delaney dome formation is a temporal equivalent of arc volcanic rocks preserved in the adjacent south mayo trough the tourmakeady volcanic group erupted during the collision of an oceanic island arc with the laurentian margin in the grampian orogeny new rare earth and high field strength element data show that the delaney dome formation and tourmakeady volcanic group are chemically similar and arc like in character this suggests that the delaney dome formation is an along strike equivalent of the tourmakeady group strike slip faulted south of the south mayo trough during or after the grampian orogeny further correlation of these units with northern appalachian rhyolites is also possible the delaney dome formation is an extrusive temporal equivalent of intrusions that penetrate the connemara dalradian thus movement along the mannin thrust brought mid crustal plutons and dalradian country rocks tectonically above the extrusive volcanic sequence the mannin thrust is identified as a major imbricating structure within a continental arc but not a terrane boundary

paleocene wilcox cross shelf channel belt history and shelf margin growth key to gulf of mexico sediment delivery abstract shelf margins prograde and aggrade by the incremental addition of deltaic sediments supplied from river channel belts and by stored shoreline sediment this paper documents the shelf edge trajectory and coeval channel belts for a segment of paleocene lower wilcox group in the northern gulf of mexico based on 400 wireline logs and 300 m of whole cores by quantitatively analyzing these data and comparing them with global databases we demonstrate how varying sediment supply impacted the wilcox shelf margin growth and deep water sediment dispersal under greenhouse eustatic conditions the coastal plain to marine topset and uppermost continental slope succession of the lower wilcox shelf margin sediment prism is divided into eighteen high frequency 300 ky duration stratigraphic sequences and further grouped into 5 sequence sets labeled as a e from bottom to top sequence set a is dominantly muddy slope deposits the shelf edge of sequence sets b and c prograded rapidly 10 km ma and aggraded modestly 80 m ma characterizes sequence sets d and e which is associated with smaller 9 10 m thick on average and isolated channel belts this stratigraphic trend is likely due to an upward decreasing sediment supply indicated by the shelf edge progradation rate and channel size as well as an upward increasing shelf accommodation indicated by the shelf edge aggradation rate the rapid shelf edge progradation and large rivers in sequence sets b and c confirm earlier suggestions that it was the early phase of lower wilcox dispersal that brought the largest deep water sediment volumes into the gulf of mexico key factors in this lower wilcox stratigraphic trend are likely to have been a very high initial sediment flux to the gulf because of the high initial release of sediment from laramide catchments to the north and northwest possibly aided by modest eustatic sea level fall on the texas shelf which is suggested by the early flat shelf edge trajectory high amalgamation of channel belts and the low overall aggradation rate of the sequence sets b and c

apatite monazite and xenotime in metamorphic rocks this chapter focuses on phosphates that are significant in metamorphic rocks a quick survey of phosphate mineral descriptions at a commercial mineral web site revealed over 500 phosphate mineral names remarkably only three are common in metamorphic rocks apatite monazite and xenotime and this chapter is restricted to discussion of these minerals apatite monazite and to a lesser extent xenotime have enjoyed intensive study during the previous half century following world war ii considerable study was made of minerals that contain fissionable materials and the sometimes large concentrations of u and th in monazite culminated in a number of seminal papers on the occurrence of that mineral e g overstreet 1967 during the 1970s and early 1980s the study of apatite and monazite turned towards their role as a sink for rees and other trace elements in rocks e g watson 1980 watson and capobianco 1981 throughout this period monazite and to some extent xenotime enjoyed attention as a geochronometer e g parrish 1990 and through today this attention has continued to grow accessory minerals such as monazite xenotime and apatite have come to the forefront of research in metamorphic petrology in recent years for two reasons first it has recently been recognized that trace elements in metamorphic rocks and especially trace element zoning in garnet and other major phases contain considerable detailed information about the reaction history a rock has experienced coupled with the fact that diffusion of many trace elements in metamorphic minerals is in general considerably slower than diffusion of major elements in those same minerals the possibility has recently emerged of recovering details of metamorphic petrogenesis that were previously unattainable inasmuch as accessory minerals play a dominant role in the mass budget of many trace elements attention has naturally turned to their paragenesis it has also recently been discovered that