provenance of the greater himalayan sequence evidence from mafic granulites and amphibolites in nw bhutan abstract mafic granulites and amphibolites in the masang kang area of nw bhutan himalaya have been investigated for their geochemical and isotopic characteristics in order to determine their protolith history bulk rock major and trace element geochemistry indicate that the rocks were originally tholeiitic and alkali basalts with minor ultramafics u pb zircon sims data suggest an age of 1742 39 ma for mafic magmatism the age corrected e nd 1742 values of the rocks are highly variable ranging from high positive 8 4 to negative 3 3 the positive value suggests a primitive magma source similar to that of rift related tholeiites we suggest that the rocks of the masang kang suite were produced during a major late paleoproterozoic thermal event that caused the mobilization and enrichment of the sub continental lithospheric mantle beneath the north indian margin the geochemical signature of these rift related metabasic rocks may have been produced during an earlier episode of oceanic underplating or subduction from which the fluid required to mobilize and enrich the overlying sub lithospheric mantle may have been derived though their occurrence is rare paleoproterozoic igneous rocks within the greater himalayan sequence ghs in addition to sources identified throughout the lhs may have contributed to the detrital zircon population that form the 1 7 1 9 ga peak in the age spectra of the lesser himalayan sequence lhs in addition the coeval paleoproterozoic magmatism in both lhs and ghs suggests that the two lithotectonic units may have belonged to the same continental plate at that time period

comments on a paper by jon d woodhead titled the origin of geochemical variations in mariana lavas a general model for petrogenesis in intra oceanic island arcs

u pb la icp ms dating of apatite in mafic rocks evidence for a major magmatic event at the devonian carboniferous boundary in the armorican massif france apatite is a ubiquitous accessory mineral found in most magmatic rocks and is often the only u bearing mineral available to date mafic rocks because primary zircon and or baddeleyite are not present in this paper u pb la icp ms dating of apatite was applied to seven different dike and sill samples of dolerite from the variscan belt of brittany armorican massif western france these dolerites which are characterized by a within plate tholeiite geochemical signature are organized in several dense swarms across the belt their geochemical compositions are homogeneous although they intrude a large geographical area subdivided into several domains each characterized by different tectonic metamorphic settings their emplacement ages were so far poorly constrained due to the difficulty to date these mafic rocks using either the 40ar 39ar or the u pb methods on classical minerals like mica plagioclase or zircon although the closure temperature of apatite is lower than the emplacement temperature of the magma physical models show that the time needed to solidify and cool these mafic dikes and sills below the apatite closure temperature is basically of the order of 100 years or less consequently the u pb dates obtained on apatite can be interpreted as the emplacement ages for these mafic intrusions our results demonstrate that in all cases the apatite grains do carry enough radiogenic pb to be dated by in situ u pb analyses and yield a 207pb corrected mean age of 363 4 5 8 ma these results reveal the existence of a major and short lived magmatic event in the variscan belt of brittany during the devonian carboniferous transition a feature further highlighted by field evidence beyond the geological implications of these results u pb la icp ms dating of apatite appears to represent an ideal tool to date small size mafic intrusions

coping between crises early triassic early jurassic bivalve diversity dynamics abstract the triassic is bounded by two of the most severe biotic crises but nevertheless this time was for bivalves both a recovery and a diversification period and a moment to fully exploit some of their evolutionary novelties just how and when this was achieved is analyzed in this paper which covers induan to sinemurian bivalve diversity based on a newly compiled database taxonomic diversity and ecospace dynamics are examined separately diversity and evolutionary rates were assessed extinction selectivity was tested using a resampling algorithm and cohort analysis was used to study extinction patterns during the early triassic most bivalve genera were survivors from the permian and they were mainly cosmopolitan epifaunal and semi infaunal endobyssate taxa reclined epifaunal and semi infaunal bivalves increased in diversity during the triassic but from norian on their diversity declined and they were strongly affected by the t j crisis although the triassic jurassic extinction strongly impacted bivalve taxonomic diversity it had little impact on bivalve ecologic diversity not a single bivalve life strategy was eliminated at the end of the triassic the present study does not support previous conclusions that infaunal bivalves suffered greater extinction than epifaunal ones during the t j extinction not all life strategies were equally affected by the extinction event being the deep infaunal burrowers positively selected bivalves with major energetic requirements seem to have been more affected with negative selectivity on fast shallow burrowers the ecologic diversity changes of bivalves during the late triassic and several adaptations of durophagous predators reflect the effects of increasing predation pressure and support a late triassic origin of the mesozoic marine revolution

effectiveness of small size against drilling predation insights from lower miocene faunal assemblage of quilon limestone india abstract the nature of drilling predation although well documented for molluscan fossils is understudied for micromolluscs microbenthos of the quilon limestone shows a lower predation intensity in comparison to the miocene macrobenthos worldwide including coeval formations of the kutch basin the interaction in the microbenthos is more strongly size dependent in contrast to the kutch fauna reduced predation intensity in the microfauna and the existence of negative size refugia support the claim of micromorphy acting as a defense mechanism and highlights the role of size dependent predation in marine benthos

differentiation and compaction in the skaergaard intrusion igneous differentiation processes are constrained from bulk compositions densities and mineral modes of 116 cumulate gabbro samples in a new reference profile through the layered series of the skaergaard intrusion east greenland the stratigraphic distribution of p u and rb in cumulates and residual magma modeled by rayleigh fractionation constrains the final porosities or trapped liquid contents to 30 52 in lza troctolites decreasing to 4 12 at the top of lzb olivine gabbros and remaining low 1 13 4 middle dot 6 on average in the oxide gabbros of lzc mz and uz local variations in trapped liquid content are associated with modal layering leucocratic low density rocks have higher proportions of trapped melt than adjacent melanocratic high density rocks these observations are explained by varying degrees of compaction compaction was most important after the onset of fe ti oxide crystallization because of the high densities of the crystal matrix here computed rates of compaction exceed the rate of crystal accumulation in layers that are metres to a few tens of metres thick in the basal section lza the crystal pile was too thin and the density of the crystal matrix too low to drive the rate of compaction above the high rate of crystal accumulation promoted by initial cooling through the intrusion floor in the overlying section lzb the efficiency of compaction gradually increased as a result of thickening of the crystal pile and lowering of the rate of crystal accumulation the modeling constrains the p2o5 content of the residual magma to 1 middle dot 7 wt at the level of apatite in suggesting that the magma contained 49 wt sio2 and followed a trend of iron enrichment compaction of the uppermost metres to tens of metres of crystal mush at the top of the cumulate pile was an efficient means of differentiation and resulted in layers with variable final porosities and trace element contents depending on the mineralogy and density of the crystal matrix

before the ice biogeography of antarctic paleogene molluscan faunas abstract new identifications are listed of antarctic paleogene molluscan faunas lopez de bertodano and sobral formations seymour island paleocene la meseta formation seymour island eocene mcmurdo sound erratics eocene and king george island oligocene early miocene these show that both cosmopolitan and antarctic subantarctic genera increased regularly as percentages of faunas with time 15 of paleocene genera 30 of eocene genera and 59 of oligocene early miocene genera still live in the antarctic subantarctic region the present major antarctic families of larger molluscs have remained the most diverse ones since middle eocene time and the antarctic fauna was well established by then however mytilidae and veneridae have decreased markedly in diversity mactridae and oysters have disappeared from the antarctic and antarctic trochidae volutidae and conoidea are now distinct guilds of more offshore taxa this reflects the present antarctic ice cover shallow water taxa that are no longer able physically to live in antarctica provide an index of antarctic glaciation glaciation was not extensive on the antarctic peninsula by late eocene time and a few genera of shoreface molluscs still inhabited the king george island area during oligocene early miocene time subduction has left only sparse localities around the margins of the pacific and indian australian plates containing shallow water early paleogene macrofossils almost none are known from the central regions of these plates few data points are available so apparent indications of taxa originating in antarctica are not interpretable new names are provided for two junior homonyms gaimardia zinsmeisteri replacing gaimardia flemingi zinsmeister 1984 prosipho stilwelli replacing aeneator huttoni stilwell and zinsmeister 1992

reworked old crust derived shoshonitic magma the guarany pluton northeastern brazil abstract the 572 ma guarany stock consists of magmatic epidote bearing hornblende monzodiorite to biotite granite that intruded paleoproterozoic orthogneisses about 10 km inland from the coast in northeastern brazil co magmatic diorite enclaves and dikes are abundant throughout the pluton the monzodiorite granite pluton and diorite enclaves are shoshonitic and display continuous trends in variation diagrams they display chemical and isotopic characteristics of crustal melts such as enrichment in incompatible elements high back calculated initial 87 sr 86 sr ratios avg 0 71253 negative end 0 57ga values avg 14 58 as well as high and variable 9 1 to 11 1 vsmow 18 o zircon values correlations between o isotope and whole rock silica contents as well as initial 87 sr 86 sr ratios with 1 sr concentrations suggest hybridization of a lower continental crustal melt with more felsic crustal rocks concomitant with fractional crystallization amphibole chemistry and whole rock zr tio 2 and p 2 o 5 contents suggest magma solidification at a pressure 7 kbar and near liquidus temperature 900 c the parental magma was likely formed by partial melting of old tdm 2 0 ga amphibolitic lower continental crustal rocks in a post collisional setting probably triggered by underplating of mantle derived mafic magma during the period of relaxation after collision

reply to comments on deccan flood basalts at the cretaceous tertiary boundary by h wensink reponse aux commentaires de wensink h parus dans earth planet sci letters nld 1987 85 326 328

the impact of lithification on the diversity size distribution and recovery dynamics of marine invertebrate assemblages lithified marine sediments are not equitably distributed through time raising the possibility that lithification masks biological signals when data from unlithified and lithified sediments are compared or combined using mollusk dominated assemblages from the early cenozoic of the gulf coastal plain we find that lithification conceals small taxa decreases taxonomic resolution and exacerbates the undersampling of rare taxa lithified assemblages appear less diverse and have less even abundance distributions than coeval unlithified samples these limitations cannot be overcome by standardization procedures nor are they likely to be circumvented by collecting larger samples the effects of this bias however can be mitigated by restricting analyses to a single lithification state or to specific size classes since lithification selectively obscures small taxa the magnitude of this bias will be most severe when organisms are particularly small such as in the aftermath of mass extinctions in the study area lithification artificially protracts the recovery period following the cretaceous paleogene mass extinction by 7 m y

in situ u pb zircon geochronology of neogene garnet bearing lavas from slovakia carpatho pannonian region central europe abstract zircons armored in garnet from four neogene lavas of slovakia three andesites and one dacite were dated in situ using excimer laser ablation icp ms for the andesites the 66 analytical points yield a lower intercept age of 13 3 0 1 ma mswd 1 2 which is older than the age of 12 4 0 2 ma recorded for the dacite u pb ages obtained in this study are significantly younger than the lower badenian ages k ar and fission track dating coupled with biostratigraphic correlations classically assumed for the garnet bearing lavas of the western carpathians with a minimum discrepancy of 3 ma accessorily a composite zircon with an inherited core reveals that some pan african crustal component is present at depth garnet bearing andesites and dacites potentially bear critical information about melt generation in the lower crust and possible recycling of pre existing crust into igneous rocks practically the problem is to assess the nature of the melt from which the garnet actually grew for this purpose zircon grains included into garnet may help to clarify the beginning of the magma history it seems likely that zircon was not grown from the bulk dacitic or andesitic melt but rather from a specific rhyolitic batch later mixing and consecutive change in magma chemistry explain that free zircons in the melt were almost totally dissolved whereas zircons shielded into garnets were preserved finally owing to their miocene age the zircon grains armored into garnet preclude any restitic origin for their host and definitely demonstrate the magmatic origin of garnet

petrology and evolution of transitional alkaline sub alkaline lavas from patmos dodecanesos greece evidence for fractional crystallization magma mixing and assimilation petrographic mineral chemical and whole rock major oxide data are presented for the lavas of the main volcanic series of patmos dodecanesos greece these lavas were erupted about 7 m y ago and range in composition from ne trachybasalts through hy trachybasalts and trachyandesites to q trachytes to some extent the ne trachybasalts are intermediate in composition to the alkaline lavas found on oceanic islands and the calc alkaline lavas of destructive plate margins major oxide variation is largely explicable in terms of fractional crystallization involving removal of the observed phenocryst and microphenocryst phases viz olivine plagioclase clinopyroxene and ti magnetite in the mafic lavas plagioclase clinopyroxene mica and ti magnetite in the evolved lavas apatite which occurs as an inclusion in other phenocrysts or as microphenocrysts must also have been removed however mass balance calculations indicate that the chemistry of the hy trachybasalts is inconsistent with an origin via fractional crystallization alone and the complex zoning patterns and resorbtion phenomena shown by phenocrysts in these lavas show that they are hybrids formed by the mixing of 80 77 ne trachybasalt with 20 23 trachyandesite it is estimated that the mixing event preceded eruption by a period of 12 h 2 weeks suggesting that mixing triggered eruption combined fractionation and mixing cannot explain the relatively low mgo contents of the hy trachybasalts and it is concluded that assimilation also occurred assimilation and especially addition of volatiles to the magmas may be responsible for the evolutionary trend from ne normative to hy normative magmas and was probably facilitated by intensified convection resulting from mixing a model is presented whereby primitive magma undergoes fractionation in an intracrustal magma chamber to yield more evolved liquids influx of hot primitive magma into the base of the chamber facilitates assimilation but eventually mixing yields the hy trachybasalts and finally the ne trachybasalts are erupted

apatite phosphorus and titanium in eclogitic garnet from the upper mantle the existence of apatite exsolution lamellae in garnet supports earlier suggestions that garnet is a major repository for p in the mantle and that p is strongly coupled to na ti the bulk p content 250 ppm of mantle eclogites is unexpectedly similar to estimates for the p content 130 220 ppm of the upper mantle both rocks are depleted relative to chondrites and to ocean floor basalts eclogites have either equilibrated with the mantle at large or have undergone secondary melting and based on p contents are unlikely to have had subducted protoliths

comments on deccan flood basalts at the cretaceous tertiary boundary by v courtillot j besse d vandamme r montigny j j jaeger and h cappetta the age of the flood basalts of the deccan area and the length of the interval during which the outpourings took place are not known precisely the authors have tried to date those basalts and estimate how long the volcanic activity lasted on the basis of new paleomagnetic paleontological and geochronological data of the deccan effusives they came to the preliminary conclusion that the volcanic activity may have lasted less than 1 ma and that the majority of the lavas poured out during chron 29r unfortunately the authors were not familiar with our paper on paleomagnetism and radiomettic age determinations of deccan trap lavas 2 in our paper we presented the paleomagnetic data derived from 223 individual lava flows from 16 sections all over the deccan area and gave the k ar age determinations for 13 selected unaltered lava flows we agree that the enormous volume of deccan extrusives poured out in a relatively short interval and that the volcanic activity was probably concerned with the spreading in the central indian ocean in late cretaceous and early tertiary time

a model for monazite melt equilibrium and application to the generation of granitic magmas abstract in order to model the behaviour of zr hf ti p u th y and the rare earth elements ree in the continental crust the parameters which control the equilibria between accessory minerals and granitic melts must be determined this paper proposes equations for the equilibrium between monazite and ca poor felsic melts in a first step all the light ree are considered as a single component and an equation describing monazite solubility is deduced from the available experimental data in a second step the fractionation of ree by monazite is investigated on the basis of a natural example of coexisting monazite and obsidian from macusani peru the solubility of monazite can be used as a thermometer based on the total ree content of natural magmatic rocks application of ree thermometry to various peraluminous rock series suggests that it is a reliable tool for determining temperatures of magmatic processes the equation governing ree fractionation by monazite is used to discuss genetic relationships between a melt and a presumed parental rock using the composition of the monazite in the parental rocks and the ree pattern of the daughter rock this method has been applied successfully to high himalayan manaslu and tibetan slab granites it is suggested that detailed petrographical work on monazite including electron microprobe analyses and sem imaging of its internal structures combined with the model presented here can be a useful tool for deciphering the genesis and the differentiation of peraluminous granitic magmas in the continental crust

samarium neodymium evolution of meteorites we have obtained sm nd data on two differentiated meteorites ibitira a eucrite with distinct basaltic texture and with evidence of crystallization and morristown a group 3a mesosiderite as well as on acapulco an unclassified meteorite with chondritic chemical composition and a highly recrystallized texture we have demonstrated the presence of in situ decay of short lived 146 sm in these meteorites with initial abundance of 146 sm 144 sm from 0 009 to 0 007 for the different meteorites precisely defined 147 sm 143 nd internal isochrons were obtained yielding ages of 4 60 0 03 ae for acapulco 4 47 0 02 ae for morristown and 4 46 0 02 ae for ibitira the corresponding initial 143 nd 144 nd values obtained were 0 2 0 9 2 1 0 7 and 1 6 0 8 u epsilon units detailed consideration of the coupled 147 sm 143 nd and 146 sm 142 nd systematics and of the elevated initial 143 nd 144 nd values indicates the presence of inconsistencies in the data for the two sm nd parent daughter pairs in spite of the precise isochrons we present a model which provides an interpretation of the paired sm nd systematics in terms of an impulsive disturbance the abundance of phosphate with large concentrations of rees controls the ree economy plagioclase with low ree concentrations is assumed to be susceptible to exchange pyroxene is considered to be undisturbed because of the low diffusion coefficients of trace elements the experimental results can be reasonably explained by this model the results indicate that three meteorites studied some with very low ree concentrations including a mesosiderite are relatively ancient objects formed within the first 50 to 100 m y of the solar system by planetary differentiation and impact processes and were subjected to late metamorphism the time of late metamorphism is substantially younger than 4 4 ae and possibly as recent as 3 9 ae this metamorphism has resulted in partial very limited reequilibration between plagioclase and phosphate resulting in the observed shifts in initial 143 nd 144 nd sm nd model ages and the 142 nd 144 nd abundances but preserving the major temporal structures of early original formation and later disturbances these results show the need for care in the interpretation of the parent daughter systematics even when they appear well behaved and the mineral phases are viewed as highly resistant to mild metamorphism

the behaviour of nd and pb isotopes during 2 0 ga migmatization in paragneisses of the central zone of the limpopo belt south africa and botswana we have carried out major and trace element analyses and nd pb isotope measurements on different components of two migmatite outcrops in the limpopo belt lose quarry botswana and palala south africa in order to assess the effect of migmatization during a high grade metamorphic event on sm nd systematics and nd model ages the outcrops studied are located in the mahalapye tshipise straightening zone at the south western part of the limpopo central zone close to its contact with the kaapvaal craton leucosomes of peraluminous granitic composition were formed by incongruent biotite melting in an fe rich metagreywacke lose quarry and in a metapelite palala respectively monazite u pb and garnet sm nd ages yield close to 2 0 ga for the high grade event confirming other recent work in the central zone the chemical compositions of the main mineral phases feldspar biotite and garnet indicate minimum melt formation at t 750 c and low pressure isocon plots and pb isotope data indicate that the partial melts are locally derived however lil trace element distribution between the leucosomes and paleosomes indicate the incomplete equilibration of the nascent melts with the residual feldspars and biotite in the paleosomes sm nd results on leucosomes and paleosomes of the metagreywacke migmatite show considerable scatter when calculated back to 2 0 ga the paleosomes fall in a narrow range of nd 4 and give tdm model ages between 2 45 and 2 66 ga the nd values of leucosomes are on average four units lower causing them to have apparent tdm ages of 2 7 2 92 ga on average 250 ma older than those of the paleosomes the ree th p2o5 and zr budgets of paleosomes and leucosomes indicate dominance of the lree by monazite and the hree by apatite incorporation of proportionally more monazite than apatite into the melt is inferred as the cause for the nd isotope discrepancy and hence the uncertainty of the average protolith mantle derivation age in contrast pb pb results define an apparent age of 2025 29 ma reflecting nearly full pb isotope exchange in the case of the palala metapelitic migmatite the nd values at 2 0 ga of all but two migmatitic constituents cluster between 7 and 9 5 pointing out extensive nd isotope equilibration during migmatization whereas the pb isotopes yield an errorchron date of 2311 65 ma indicating incomplete pb isotope exchange here garnet dominates the hree distribution whereas the lree are controlled by feldspar and monazite considering that nd isotope equilibration was nearly reached during migmatization nd model ages on the whole rocks represent a good approximation of those of the original protolith 3 0 3 2 ga in the regional context the pb isotope data from the lose quarry locality combined with the nd model age uncertain but within the range of 2 5 2 9 are reminiscent of the northern marginal zone of the limpopo belt and the southern zimbabwe craton whereas the nd and pb isotope data from the palala locality are typical for the limpopo southern marginal zone and the northern kaapvaal craton

geochemistry of the lyngdal hyperites s w norway comparison with the monzonorites associated with the rogaland anorthosite complex the lyngdal hyperites lyhy crop out as two small post tectonic intrusions of gabbro noritic to monzonoritic composition at the extreme south of norway they display subophitic textures with plagioclase laths an40 to an58 orthopyroxene en56 to en62 clinopyroxene wo47 5en39fs13 5 ilmenite magnetite and interstitial myrmekite fringes k feldspar quartz apatite and biotite the sio2 content is very constant 50 53 but k2o ranges from 1 to 1 6 in differentiated facies ree patterns are smooth layb n 6 the hyperites define an rbsr isochron of 910 82 ma 2 with an initial ratio of 0 7054 nd is slightly positive 0 to 2 and average lead isotopic initial ratios are 17 45 206pb204pb i and 15 51 207pb204pb i the lyhy represent magmatic liquids that have not fractionated large amounts of plagioclase they are quite comparable to the rocks of the monzonoritic series that occur in the nearby rogaland anorthosite complex 1 the plagioclases have the same composition plagioclase phenocrysts are locally present 2 they display enrichments in tio2 p2o5 and k2o 3 they have comparable ree patterns 4 the isotopic data show that the monzonorites and the lyhy derive from the same isotopic reservoir the lyhy nevertheless differ from the monzonorites by their high al content al2o3 18 5 and their lower feotot content feototfeotot mgo 0 62 the geochemical and isotopic diversity of the monzonoritic magmatism including the lyhy implies that each occurrence represents a distinct magma batch generated from a distinct source the lyhy could tentatively be interpreted as a fe poor mg rich end member of the monzonoritic magmatism occurring to the east of the anorthosite complex

skeletal mineralogy and biodiversity of marine invertebrates size matters more than seawater chemistry it is now well established that seawater chemistry as well as influencing non skeletal marine precipitation calcite and aragonite seas has affected skeletal mineral secretion in some algal and marine invertebrate groups skeletal mineralogy has had a yet more profound consequence on fossil preservation the realization that the fossil record of marine organisms with an aragonite shell is widely depleted in some shelf settings through early effectively syn depositional dissolution missing molluscs effect has led to a re evaluation of the composition diversity ecological and trophic structure of marine benthic communities comparisons of molluscan lagerstatten from calcite and aragonite seas show a similar pattern of skeletal mineralogical loss that is no differences are discernibly linked to changed seawater geochemistry it is notable that the rare mollusc rich skeletal lagerstatten faunas in the fossil record include many small individuals micromolluscs are quantitatively important among modern shell assemblages yet small size is a major source of taphonomic and biodiversity loss in the fossil record in skeletal lagerstatten faunas micromolluscs contribute variably to mollusc biodiversity but appear particularly significant through at least to triassic times they highlight a further missing molluscs effect of taphonomic loss through early dissolution

accessory mineral behavior during differentiation of a granite suite monazite xenotime and zircon in the sweetwater wash pluton southeastern california u s a abstract compositional and textural characteristics of the accessory minerals monazite xenotime and zircon in the sweetwater wash granites and related aplites indicate that these phases not only controlled much of the trace element geochemistry of the suite but that they also record the melt compositional changes that occurred during magmatic differentiation fractionation of monazite due to decreasing saturation levels of its essential structural constituents with falling temperature was likely responsible for an ongoing trend of light rare earth element ree depletion this was accompanied by increasing heavy ree concentrations until xenotime joined the crystallizing assemblage subsequently combined monazite xenotime fractionation resulted in lowering of the entire ree budget zircon which contains inherited cores that were apparently resorbed and rounded during initial anatexis was saturated throughout the differentiation history of the sweetwater wash suite accessory phases in granite and aplite exhibit strong compositional differences at a variety of scales the differences are best displayed by monazite on average crystals in more differentiated rocks aplites are relatively depleted in light ree s and contain higher concentrations of the substituting elements u and th zircon displays complimentary increases in hf and y while xenotime shows a slight increase in th and in gd ho ratios both phases also exhibit higher u concentrations in aplites than in granites these differences in accessory mineral compositions are observed not only between granites and the more differentiated aplites but also within individual thin sections due to in situ fractionation on an even smaller scale strong compositional variations are present within single crystals possibly due to diffusion controlled melt compositional gradients in the regions a adjacent to growing major phases and b adjacent to the growing accessory crystal itself our observations indicate that compositional variations among accessory minerals are potentially useful for tracking of magmatic processes but that the scale of observed variations must be carefully considered

behaviour of apatite during partial melting of metapelites and consequences for prograde suprasolidus monazite growth abstract the suprasolidus behaviour of apatite and monazite is examined for an average metapelite composition using phase equilibria modelling coupled with solubility equations of these minerals both closed and open system scenarios are considered partial melting above the solidus requires apatite and monazite breakdown in order to saturate the anatectic melt in phosphorus and the light rare earth elements in general melt loss is predicted to increase the stability of apatite and monazite at high temperature most apatite is predicted to survive up to ultrahigh temperature conditions except for rocks with low bulk phosphorus concentrations by contrast most monazite is expected to be consumed by uht conditions thorium substitution in monazite is expected to increase the stability of monazite to higher temperatures the presence of lree rich apatite decreases the stability of monazite above the solidus but the breakdown of this apatite during anatexis may generate prograde monazite at the apatite melt interface in local pockets of melt oversaturation however prograde suprasolidus monazite along grain boundaries is expected to be consumed during further partial melting or during melt homogenization when an interconnected melt network develops anatectic melts are predicted to be saturated with respect to apatite except at uht conditions and for rocks with low initial p2o5 bulk concentrations

crystallization of apatite in natural magmas under high pressure hydrous conditions with particular reference to orogenic rock series two separate series of hydrous experiments involving 1 imposing apatite saturation on a series of igneous rock compositions from basanite to rhyolite and 2 crystallizing similar natural rock compositions progressively until apatite appears demonstrate a close dependence between apatite saturation and silica content of the magma and determine p2o5 levels at a given silica value and temperature at which that composition may be expected to crystallize apatite the effect of pressure on apatite solubility is not great and is most significant for silicic compositions

sediment mixing and stratigraphic disorder revealed by the age structure of tellina shells in great barrier reef sediment radiocarbon calibrated amino acid racemization ages of 250 individually dated tellina shells from two sediment cores are used to quantify molluscan time averaging with increasing burial depth in the shallow water carbonate lagoon of rib reef central great barrier reef australia the top 20 cm of sediment contain a distinct essentially modern assemblage with a median age of only 5 yr sediment between 20 and 125 cm are age homogeneous and significantly older than the surface sediment median age 189 yr shell age distributions within layers indicate that the top 125 cm of lagoonal sediment is thoroughly mixed on a subcentennial scale shell size is an important correlate of shell half life and an important determinant of the inferred age of sedimentary layers these results illustrate the importance of bioturbation in these environments indicate that age estimates in this depositional setting are sensitive to specimen choice and document a size dependent bias in death assemblage formation

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

rare earth element abundances in apatite in the bushveld complex a consequence of the trapped liquid shift effect reply the concentrations of the rare earth elements rees in apatite from a 600 m thick sequence toward the top of the bushveld complex south africa have previously been published they show two ranges of compositions in a lower section and an upper section the data were interpreted in terms of liquid immiscibility the evidence for this model is reassessed and an alternative explanation offered that involves the trapped liquid shift effect in this process the true cumulus phase compositions reequilibrated with trapped liquid as it solidified and ree abundances in apatite were variably increased the extent of the change depends on the relative proportions of cumulus apatite and trapped liquid calculations show that if there was 5 apatite and 10 trapped liquid as found in the lower section the ree abundance in the final apatite would have only increased marginally relative to the original cumulus composition however in the upper section where there was only 2 apatite and 25 trapped liquid the ree abundances were increased by a factor of 3 most of the rees are essentially incompatible in the other cumulus phases except apatite and the other phases have little influence on the final concentrations of rees in apatite however for eu which partitions into plagioclase this mineral acts as a major buffering influence and relatively less eu than the other rees entered apatite during the solidification process as a result the calculated final apatite in the upper section developed a large negative eu anomaly as observed in the actual mineral analyses the concept of large scale liquid immiscibility in the upper part of the bushveld complex based on rees in apatite is challenged and an interpretation involving the trapped liquid shift effect is considered more plausible

apatite liquid partition coefficients for the rare earth elements and strontium abstract sixteen sets of apatite liquid partition coefficients dap liq for the rare earth elements ree la sm dy lu and six values for sr were experimentally determined in natural systems ranging from basanite to granite the apatite melt glass assemblages were obtained from starting glasses artificially enriched in ree sr and fluorapatite components these were run under dry and hydrous conditions of 7 5 20 kbar and 950 1120 c in a solid media piston cylinder apparatus an sem equipped electron microprobe was used for subsequent measurement of ree and sr concentrations in coexisting apatites and quenched glasses the resulting partition coefficient patterns resemble previously determined apatite phenocryst groundmass concentration ratios in the following respects 1 the rare earth patterns are uniformly concave downward i e the middle ree are more compatible in apatite than the light and heavy ree 2 dreeap liq is much higher for silicic melts than for basic ones and 3 strontium and therefore eu2 is less concentrated by apatite than are the trivalent ree the effects of both temperature and melt composition on dreeap liq are systematic and pronounced at 950 c for example a change in melt sio2 content from 50 to 68 wt causes the average ree partition coefficient to increase from 7 to 30 a 130 c increase in temperature on the other hand results in a two fold decrease in dreeap liq partitioning of sr is insenstitive to changes in melt composition and temperature and neither the sr nor the ree partition coefficients appear to be affected by variations in pressure or h2o content of the melt the experimentally determined partition coefficients can be used not only in trace element modelling but also to distinguish apatite phenocrysts from xenocrysts in rocks reported apatite megacryst host basalt ree concentration ratios 12 for example are considerably higher than the equilibrium partition coefficients which suggest that in this particular case the apatite is actually xenocrystic a reversal experiment incorporated in our study yielded diffusion profiles of ree in apatite from which we extracted a ree ca interdiffusion coefficient of 2 4 10 14 cm2 s at 1120 c extrapolated downward to crustal temperatures this low value suggests that complete ree equilibrium between felsic partial melts and residual apatite is rarely established

the fossil record and spatial structuring of environments and biodiversity in the cenozoic of new zealand there is increasing evidence to suggest that drivers of bias in the fossil record have also affected actual biodiversity history so that controls of artefact and true pattern are confounded here we examine the role of spatial structuring of the environment as one component of this common cause hypothesis our results are based on sampling standardized analyses of the postmiddle eocene record of shelf molluscs from new zealand we find that spatial structuring of the environment directly influenced the quality of the fossil record contrary to our expectations however we find no evidence to suggest that spatial structuring of the environment was a strong or direct driver of taxic rates net diversity or spatial structuring in mollusc faunas at the scale of analysis stage to stage variation in sampling standardized diversity over the past 40 ma exhibits two superficially independent dynamics a changes in net diversity were associated primarily with changes in origination rate and b an unknown common cause related extinction rate to the quality of the fossil record and indirectly to spatial structuring of the environment we suggest that tectonic drivers manifest as second order sequence stratigraphic cycles are likely to have been a key element of this common cause our perceptions of biodiversity history are influenced strongly by secular biases in the quality of the fossil record e g raup 1976 peters foote 2001 many authors have argued against a literal reading of the record and various techniques to minimize the impacts of sampling biases have been developed e g connolly miller 2001 foote 2003 alroy 2010 in addition however a number of studies have proposed that the relationship between sampling biases and diversity dynamics may be complex these studies have suggested that there are latent common cause factors such as plate tectonics and sea level change which have affected simultaneously the quality of the fossil record and true macroevolutionary history e g newell 1952 sepkoski 1976 smith 2001 peters foote 2002 foote 2003 peters 2005 2006a wall et al 2009 demonstrating potential common causes separating their effects from simple preservation and sampling biases and interpreting them mechanistically are challenging problems that must be solved if palaeobiologists are to resolve true patterns and processes of macroevolutionary change through geological time the aim of the present paper is to examine the role of spatial structuring of the environment and of biodiversity in driving both macroevolutionary dynamics and biases in the fossil record fig 1 specifically we are interested in the extent to which partitioning of marine environments may have influenced biodiversity and the preservation of that diversity in part the study is founded on the expectation that the geographical range and evolution extinction dynamics of organisms occupying a particular habitat will be related to the area and fragmentation of that habitat e g rosenzweig 1995 maurer nott 1998 at the same time we anticipate that the quality of the marine fossil record will be influenced by for example the areal extent and distribution of depositional v non depositional or erosional environments factors that are also likely to affect habitat fragmentation and diversity to test the role of spatial structuring in the common cause hypothesis we use the exemplary well studied and relatively complete fossil record of post middle eocene level bottom shelf molluscs from new zealand e g crampton et al 2003 2006a this record is approximately from mcgowan a j smith a b eds comparing the geological and fossil records implications for biodiversity studies geological society london special publications 358 105 122 doi 10 1144 sp358 8 0305 8719 11 15 00 the geological society of london 2011 40 complete at the species level for the neogene as estimated using two very different approaches cooper et al 2006 crampton et al 2006a in this paper therefore we derive an index for spatial heterogeneity of the environment and adapt established indices of spatial differentiation in the new zealand cenozoic mollusc fauna we then compare time series of these measures to time series of sampling probability a proxy for the quality of the fossil record and sampling standardized estimates of overall species richness origination rate and extinction rate all analyses and computations reported here were undertaken using r r development core team 2010 materials and methods

estimating the rock volume bias in paleobiodiversity studies to interpret changes in biodiversity through geological time it is necessary first to correct for biases in sampling effort related to variations in the exposure of rocks and recovery of fossils with age data from new zealand indicate that outcrop area is likely to be a reliable proxy of rock volume in both stable cratonic regions where the paleobiodiversity record is strongly correlated with relative sea level and on tectonically active margins in contrast another potential proxy the number of rock formations is a poor predictor of outcrop area or sampling effort in the new zealand case

evolution turnovers and spatial variation of the gastropod fauna of the late miocene biodiversity hotspot lake pannon abstract lake pannon constituted the biggest hotspot of biodiversity in the late cenozoic of europe comprising a total diversity of almost 600 gastropod species the gastropod fauna of this huge brackish system which existed over about seven million years from the late miocene to earliest pliocene within the pannonian basin system has been well documented by a great many of taxonomic works in contrast the faunal development within the lake has not been properly addressed from a statistical point of view the present investigation demonstrates that species were not homogeneously distributed across space and time generating uneven and temporally shifting patterns of species richness and degree of point endemism across the lake the faunal compositions of the time intervals analyzed were highly different contrasting simple species accumulation as suggested by the overall numbers shifting patterns of local diversity within the lake reflect changing paleo shorelines resulting from prograding river systems entering and successively diminishing the lake surface area as mainly herbivorous grazers and predominantly shallow water inhabitants the gastropods traced the moving shelf margins and vegetation belts accordingly producing the observed diversity shifts in addition each time interval is characterized by a high degree of provincialism which is considered to reflect high habitat diversity this claim is supported by the complex subaqueous topography and the presence of extensive delta plains produced by the incoming river systems a potential driver for provincialism might be the adaptation of species to distinct water depths and related parameters finally the notable differences among the faunal compositions of the upper pannonian strata and the succeeding lower viviparus beds especially regarding family level indicate an environmental turnover at the transition brackish water species are mostly replaced by typical freshwater elements indicating strong fluvial influence based on our results and latest stratigraphic data we conclude that the viviparus beds were deposited in a different environment replacing lake pannon in the southern pannonian basin in the early pliocene

temporal change in chemistry of magma source under central kyushu southwest japan progressive contamination of mantle wedge volcanism related to subduction of the philippine sea phs plate began in central kyushu at 5 ma after a pause of igneous activity lasting about 10 m y it formed a large volcano tectonic depression the hohi volcanic zone hvz and has continued to the present at a decreasing eruption rate the products are largely andesite and dacite which became enriched in k with time the proportion of tholeiitic to calc alkalic rocks also increases with time calc alkalic high mg basaltic andesites ybbs were erupted in the early stage of the hvz activity 5 3 ma and high alumina basalts kjbs were erupted in the later stage 2 0 ma in contrast to the basalts in the hvz northwest kyushu basalts nwkbs have been erupted on the backarc side of the hvz since 11 ma and hence are not related to the phs plate subduction they are mainly high alkali tholeiitic to alkali basalt that shows no notable chemical change with time nwkb ybb and kjb have morb normalized incompatible element spectra that differ from each other as is well expressed in both nb and sr anomalies the patterns of kjb and nwkb are typical of those for island arc basalt iab and ocean island basalt oib respectively ybb shows a pattern intermediate between the two we suggest that the magma source beneath the hvz changed in composition from an oib type mantle to an iab type mantle as the subduction of phs plate advanced however the magma source remained fertile under northwest kyushu in order to explain the temporal change of source mantle beneath the hvz we propose a model for progressive contamination of the mantle wedge in which three processes contamination by a slab derived component subtraction of magma from the mantle and mixing of the mantle residue and slab derived component are repeated as subduction continues as long as the progressive contamination of mantle wedge proceeds its trace element composition converges at a steady state value for a short period this value does not depend on the initial composition of the mantle wedge but instead on the composition of the slab derived component the trace element composition of the magma produced in such a mantle wedge approaches that of the slab derived component with time but the major element composition is determined by the phase relations of mantle peridotite the slab derived component may be basaltic liquid that is partially melted from rutile bearing eclogite

marine diversity through the phanerozoic problems and prospects the fossil record provides direct evidence of how diversity has changed over time but cannot be taken at face value diversity curves constructed from counting taxa in the rock record are seriously biased by unevenness of geographical and stratigraphical sampling effort inequality in the rock record available for sampling and inconsistent taxonomic practice sample standardization removes some bias but does not overcome more general incompleteness problems modelling that accounts for potential biases is a newer approach but needs accurate estimates of rock record and consistent taxonomic data uncertainty remains over whether the steep rise in diversity over the last 100 ma is real or reflects sampling bias the repeated rise and fall of marine diversity over time correlates closely with the areal extent of sedimentary deposits and independent estimates of the quality of the fossil record implying a common driving factor namely tectonically mediated sea level change however whether changes in diversity are primarily biological in origin or reflect sampling artefact remains contentious there is a distinct possibility that many of the apparent rises and falls in diversity over the phanerozoic including most of the mass extinctions arise either partially or entirely from rock record bias

terrestrial maria the origins of large basalt plateaus hotspot tracks and spreading ridges large lava plateaus which form abruptly within plates without apparent tectonic cause appear to be the terrestrial equivalents of lunar maria deep erosion of lava plateaus reveals that their magma chambers are gabbro and granophyre complexes the classic lopoliths the close association of the deccan plateau with the timing of the terminal cretaceous boundary clay suggests that it is an impact crater large enough to cause pressure relief melting in the asthenosphere basalt then flooded the crater to form a lava lake the terrestrial equivalent of a lunar mare part of the crater rim survives in the amirante ridge the carlsberg oceanic ridge and chagos laccadive hotspot track formed simultaneously with the deccan plateau several other mesozoic and cenozoic lava plateaus are parts of similar arrays of simultaneous features one of those is the southern oregon part of the columbia plateau with its associated continental rifting in the northern basin and range and the yellowstone hotspot track along t

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

an assessment of the contribution of fossil cave deposits to the quaternary paleontological record mammal bearing cave deposits are an important part of the quaternary fossil record but the exact nature of the contribution that caves make to the fossil record is a research area that is largely unexplored to explore this issue late pleistocene species representation in cave versuses non cave deposits was examined additionally this study examined how fossiliferous cave deposits influence perceptions of past biogeographic distributions and evaluated factors that impact the distribution of cave deposits across the united states cave deposits account for a high proportion of the individual species records known from the late pleistocene and caves provide the only late pleistocene records of 14 individual taxa calculated ratios of individual taxonomic records from caves relative to the total number of individual taxonomic records resulted in a value of 0 62 the impact of cave data on understanding of late pleistocene biogeographic distribution patterns vary among individual species of sciurid rodents geographic analyses comparing the distribution of cave and non cave sites in texas suggest a strong relationship between site distribution and specific geologic and hydrologic features ultimately understanding potential biases recorded in distinct depositional settings provides improved frameworks for interpreting the adequacy of the fossil record

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

completeness of the fossil record estimating losses due to small body size size bias in the fossil record limits its use for interpreting patterns of past biodiversity and ecological change using comparative size frequency distributions of exceptionally good regional records of new zealand holocene and cenozoic mollusca in museum archive collections we derive first order estimates of the magnitude of the bias against small body size and the effect of this bias on completeness of the fossil record our database of 3907 fossil species represents an original living pool of 9086 species from which 36 have been removed by size culling 27 from the smallest size class 5 mm in contrast non size related losses compose only 21 of the total in soft rocks the loss of small taxa can be reduced by nearly 50 through the employment of exhaustive collection and preparation techniques

the role of residual melt migration in producing compositional diversity in a suite of granitic rocks abstract we present a quantitative model for in situ crystallization within a solidification zone or boundary layer based on the trace and major element compositions of plutonic igneous rocks and related geochemical data we developed the model to account for the characteristics of a suite of granitic rocks nearly uniform mineral compositions in rocks that range widely in bulk composition e g 58 76 wt sio 2 linear variation and correlation of all major and trace elements analyzed except ba large and apparently random variations in ba concentration these characteristics cannot be explained by any standard petrogenetic model involving fractionation mixing or restite unmixing but are successfully reproduced by our model of residual melt migration we do not attempt to model the entire crystallization history of a pluton but rather only that interval during which melt migration processes have recognizable geochemical effects for the granitic suite the chemical signature of residual melt migration resulted from the change in ba compatibility with the onset of orthoclase crystallization at a granite minimum our results demonstrate that plutonic rocks can develop large compositional variations comparable to those expected to result from extreme differentiation within a large magma body over short distances by melt migration under conditions of high permeability or slow crystallization rate within the solidification zone melt migration is probably a common process that could be overlooked in large plutons if sampling is sparse and if variations in some components that appear random are not considered our model equations yield estimates for parameters that describe the proportions of residual melt that crystallize within and migrate out of the solidification zone values of these parameters can be used to infer information about permeability and melt mobility within the solidification zone the model parameters derived for the granitic suite have a roughly concentric spatial pattern in the pluton suggesting that residual melt was trapped near the margins accumulated in the interior with a zone of enhanced melt mobility and possibly compositional convection in between our model may be of general usefulness because it requires no assumptions about magma chamber geometry or magma dynamics it is applicable to magmas of any composition and the equations could be formulated to include those variables best constrained by a particular suite of plutonic igneous rocks

geochronology geochemistry and sr nd isotopes of the granitic rocks associated with tungsten deposits in beishan district nw china central asian orogenic belt petrogenesis metallogenic and tectonic implications abstract the beishan orogenic belt is an important tectonic unit and a suitable target to investigate and understand the paleozoic tectonic framework of the central asian orogenic belt paleozoic granitic rocks are widely distributed in the area and closely related to the tungsten deposits at hongjianbingshan guoqing yingzuihongshan and yushan to understand the petrogenesis of the intrusions we performed sims zircon u pb o and whole rock major trace element contents and sr nd isotopic analyses two major suites of granitic intrusions associated with tungsten mineralization have been recognized during 424 314 ma and 286 244 ma the former suite shows variable sr nd and o compositions average 87sr 86sr i 0 7149 or 0 7034 end t 6 3 or 7 6 t2dm 1 68 or 0 41 ga 18o 9 3 or 5 9 indicating an ancient crust or a juvenile lower crust origin whereas the latter suite shows a type affinity and the sr nd and o compositions average 87sr 86sr i 0 7125 end t 4 5 t2dm 1 42 ga 18o 6 9 suggest the precambrian metasedimentary strata may have exerted a significant role in the magma source the proposed magma sources combined with the geochemical differences between these two suites of intrusions indicating the silurian carboniferous mineralization such as hongjianbingshan guoqing and yingzuihongshan are closely associated with subduction accretion and generation of gongpoquan arc accretionary system while the permian mineralization including yushan deposit are attributed to continuing accretion and subsequent post collision these tungsten related granitic rocks are enriched in lree and depleted in hree and ba sr nb p eu and ti suggesting they may have experienced advanced fractional crystallization furthermore a spectacular tetrad effect in their ree distribution patterns has been discovered showing the granites are highly evolved rocks with strong hydrothermal interaction the prolonged fractional crystallization and magmatic hydrothermal interactions have contributed to the formation of the silurian permian tungsten mineralization

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

early triassic gulliver gastropods spatio temporal distribution and significance for biotic recovery after the end permian mass extinction a reduction in body size lilliput effect has been repeatedly proposed for many marine organisms in the aftermath of the permian triassic pt mass extinction specifically reduced maximum sizes of benthic marine invertebrates have been proposed for the entire early triassic this concept was originally based on observations on early triassic gastropods from the western usa basin and the dolomites n italy and it stimulated subsequent studies on other taxonomic groups however only a few studies have tested the validity of the lilliput effect in gastropods to determine whether the paucity of large sized gastropods is a genuine signal or the result of a poor fossil record and insufficient sampling in combination with a review of the literature we document numerous new abundant large sized gastropods from the griesbachian outcrops of greenland and from the smithian early spathian interval in the southwestern usa we show that large sized gulliver gastropods i were present soon after the pt mass extinction ii occurred in various basins sedimentary facies and environmental contexts from shallow to deeper settings and iii belong to diverse higher rank taxa focusing on the western usa basin we investigate areas from which microgastropod shell beds were previously presented as being typical however we show that gulliver gastropods do occur in the very same areas insufficient sampling effort is probably the main reason for the rarity of reports of large early triassic gastropods which is supported by preliminary rarefaction based simulations finally it appears that the recently documented middle to late smithian climate shifts and the severe end smithian extinction of nekto pelagic faunas did not reduce maximum shell sizes of gastropods

age of the mulcahy lake intrusion northwest ontario and implications for the evolution of greenstone granite terrains abstract zircon data from a 63 km 2 layered mafic intrusion in the wabigoon subprovince the mulcahy lake gabbro show that the gabbro crystallized at 2733 2 0 9 1 0 ma the largely unaltered and unmetamorphosed gabbro intrudes tholeiites of the crow lake savant lake greenstone belt which were generated over at least a 10 ma time span rb sr and sm nd data were obtained for pristine whole rock and mineral separates from the intrusion the rb sr data show disturbances in the system particularly in the case of pyroxenes samples with low rb sr ratios indicate an initial sr ratio of 0 7007 for an age of 2733 ma the sm nd age is 2744 55ma and an epsilon nd value of 2 6 1 2 indicates a light rare earth element depleted source the sm nd data show less disturbance than the rb sr data granitic and mafic intrusives with similar initial ratios occur 80 km to the south in the quetico subprovince primary hornblende was analyzed for 40 ar 39 ar the age obtained is 2703 20ma clearly younger than the zircon age indicating some argon loss the mulcahy lake gabbro is one of four layered mafic plutons of similar petrographic character and stratigraphic age which are arrayed in an arc in the crow lake savant lake greenstone belt the plutons appear to represent subvolcanic chambers which developed simultaneously and which crystallized at the end of the volcanic cycle all intrude basalts and are intruded in turn by the atikwa batholith a massive granitic intrusion of over 1000 km 2 in area previously published zircon ages for several sample sites within the batholith indicate crystallization at 2731 8 1 3 1 6 ma to 2732 2 2 9ma these data show that the batholith overlaps the age of the gabbros or is at most 5 ma younger this virtual contemporaneity is hidden in the rb sr and sm nd data the cessation of mafic magma production and the immediate if not parallel voluminous production of calc alkaline liquid may represent a process important in the development of greenstone granite belts a process not apparent when ages are not so precisely determined

an example of trondhjemite genesis by means of alkali metasomatism rockford granite alabama appalachians a model for trondhjemite genesis is proposed where granite is transformed to trondhjemite via infiltration by a na rich metamorphic fluid the rockford granite of the northern alabama piedmont serves as the case example for this process and is characterized as a synmetamorphic peraluminous trondhjemite granite suite the major process operative in the conversion of granite to trondhjemite involves cation exchange of na for k in the feldspar and mica phases through a volatile fluid medium whole rock 18o values for the trondhjemites are negatively correlated with atomic proportion k na ratio indicating a partial reequilibration of the altered granitoids with a na and18o rich metamorphically derived fluid biotite decomposition to an al epidote paragonitic muscovite secondary quartz assemblage is also associated with the sodium metasomatism as are apatite replacement by al epidote and secondary zircon crystallization rare albitization of primary magmatic plagioclase and discontinuous grossularite reaction rim growth on magmatic garnet are present in the trondhjemites indicating the mobility of ca during alkali metasomatism the replacement of magmatic phases by me tasomatic phases exemplifies the chemical changes produced during infiltration metasomatism where the trondhjemites are depleted in p2o5 th rb u k2o v sn f mgo pb tio2 feo and li and enriched in cao na2o zr and sr relative to the granites other elements such as cr mno cu zn co ba sio2 ni al2o3 are shown to be relatively immobile during the metasomatism the infiltration metasomatism probably occurred during prograde regional metamorphism when a discrete fluid phase was produced in the surrounding amphibolite grade metasediments foliation planes in the granite apparently served as conduits for fluid flow with reaction enhanced permeability accompanying the 8 molar volume reduction during na for k exchange in the feldspars a source for the na and sr in the metamorphic fluid may have been paragonitic muscovite in the metasedimentary country rocks rubidium and k were probably retained in metasedimentary biotite the silent lake pluton in southeastern ontario is a possible analogue to the alkali metasomatic processes affecting the rockford granite