the permian triassic transition and the onset of mesozoic sedimentation at the northwestern peri tethyan domain scale palaeogeographic maps and geodynamic implications the main aim of this paper is to review middle permian through middle triassic continental successions in european secondly areas of middle late permian sedimentation the permian triassic boundary ptb and the onset of triassic sedimentation at the scale of the westernmost peri tethyan domain are defined in order to construct palaeogeographic maps of the area and to discuss the impact of tectonics climate and sediment supply on the preservation of continental sediment at the scale of the western european peri tethyan basins the upper permian is characterised by a general progradational pattern from playa lake or floodplain to fluvial environments in the northern variscan belt domain areas of sedimentation were either isolated or connected to the large basin which was occupied by the zechstein sea in the southern variscan belt during the late permian either isolated endoreic basins occurred with palaeocurrent directions indicating local sources or basins underwent erosion and or there was no deposition these basins were not connected with the tethys ocean which could be explained by a high border formed by corsica sardinia palaeorelief and even parts of the kabilia microplate the palaeoflora and sedimentary environments suggest warm and semi arid climatic conditions at the scale of the whole study area an unconformity more or less angular is observed almost everywhere between deposits of the upper permian and triassic except in the central part of the germanic basin the sedimentation gap is more developed in the southern area where in some basins upper permian sediment does not occur the large sedimentary supply erosion and or lack of deposition during the late permian as well as the variable palaeocurrent direction pattern between themiddle late permian and the early triassic indicate a period of relief rejuvenation during the late permian during the induan all the intra belt basins were under erosion and sediment was only preserved in the extra belt domains the northern and extreme southern domains in the northern domain the central part of the germanic basin sediment was preserved under the same climatic conditions as during the latest permian whereas in the extreme southern domain it was probably preserved in the tethys ocean implying a large amount of detrital components entering themarinewaters mesozoic sedimentation began in the early olenekian the ephemeral fluvial systems indicate arid climatic conditions during this period three distinct areas of sedimentation occur a northern and southern domain separated by an intra belt domain the latter accumulated sediments during the early middle permian and experienced erosion and or no deposition conditions between the middle late permian and the beginning of mesozoic sedimentation dated as anisian to hettangian at the top of the lower triassic another tectonically induced more or less angular unconformity is observed the hardegsen unconformity which is dated as intra spathian and is especially found in the north european basins this tectonic activity created new source areas and a new fluvial style with marine influences at the distal part of the systems during the anisian and ladinian continental sedimentation was characterised by a retrogradational trend in other words the fluvial system evolved into fluvio marine environments attesting to a direct influence of the tethys ocean in the southern and northern domains both at the end of the olenekian spathian and during the anisian the presence of palaeosols micro andmacrofloras indicate less arid conditions throughout this domain

mica liquid trace elements partitioning and the granite pegmatite connection the st sylvestre complex western french massif central abstract we constrain the genetic relation between granite and pegmatite parental melts from the variscan saint sylvestre leucogranite complex and associated pegmatite bodies massif central france through compositions of micas using mica trace element concentrations and available partition coefficients for li rb ba cs and f we calculated the trace element contents of granitic and pegmatitic melts at equilibrium with micas biotite in leucogranites and pegmatites ranges mostly from fe biotite to siderophyllite more evolved facies contain protolithionite and zinnwaldite and lepidolite occurs in the most fractionated pegmatite white micas have homogeneous compositions from muscovite to li phengite in granites biotite and muscovite trace element distributions are clustered in pegmatites mica trace element contents globally follow differentiation from the least to the most evolved body the reconstructed pegmatitic and granitic melts present strong compositional similarities such as enrichments in li rb cs and depletion in ba that suggest a similar origin however micas are shown to have selectively equilibrated with the last melt or fluid in contact and so trace element concentrations of early magmatic liquids are rarely preserved inversion of the mica data constrains the composition of parental melts and the trace element evolutions during crystallization leucogranite and pegmatite melts show mutual incompatible element evolutions inconsistent with a parent daughter genetic relation the data and the modelling suggest that they represent non cogenetic melts generated by discrete episodes of partial melting differentiation is thus inherited from source processes rather than being the consequence of fractional crystallization of a common parental melt magma we suggest that both the leucogranites and the pegmatites originate from partial melting of a heterogeneous source rather than pegmatites being the product of granite crystallization

mechanisms of crustal anatexis a geochemical study of partially melted metapelitic enclaves and host dacite se spain to shed light on the mechanisms of crustal anatexis a detailed geochemical study has been conducted on minerals and glasses of quenched anatectic metapelitic enclaves and their host peraluminous dacites at el hoyazo se spain anatectic enclaves composed of plagioclase biotite sillimanite garnet glass k feldspar cordierite graphite formed during the rapid heating and overstepped melting of a greenschist facies metapelite and finally equilibrated at 850 508c and 5 7 kbar glass appears as melt inclusions within all mineral phases and in the matrix of the enclaves and has a major element composition similar to that of peraluminous leucogranites melt inclusions and matrix glasses have normative quartz orthoclase albite compositions that plot in the vicinity of h2o undersaturated haplogranite eutectics melt inclusions show some compositional variability with high li cs and b low y first row transition elements frte and rare earth elements ree and zircon and monazite saturation temperatures of 665 7508c they are interpreted as melts produced by muscovitebreakdown melting reactions at the onset of the process of rapid melting and mostly under h2o undersaturated conditions compared with melt inclusions matrix glasses show less compositional variability lower large ion lithophile element contents higher y frte and ree and higher zircon and monazite saturation temperatures 695 8158c they are interpreted as former melts recording the onset of biotite dehydration melting matrix glasses in the dacite are compositionally different from glasses in the enclaves hence the genetic connection between metasedimentary enclaves and dacite is not as straightforward as previous petrographic and bulk major element data suggest this opens the possibility for some alternative interpretation this study shows the following 1 melt inclusions provide a window of information into the prograde evolution of anatexis in the enclaves 2 melting occurred for the most part under h2o undersaturated conditions even if because of the rapid heating the protolith preserved most of the structurally bound h2o contained at greenschist facies up to the beginning of anatexis such that the excess h2o maximized the amount of h2o undersaturated melt generated during anatexis 3 although a large proportion of accessory minerals are currently shielded within major mineral phases they have progressively dissolved to a considerable extent into the melt phase along the prograde anatectic path as indicated by the relative clustering of accessory mineral saturation temperatures and closeness of these temperatures to those of potential melting reactions 4 the dacite magma was probably produced by coalescence of melts

a rise in the carbonate compensation depth of western tethys in the carnian late triassic deep water evidence for the carnian pluvial event the upper triassic of the lagonegro basin southern apennines southern italy is represented by hemipelagic cherty limestones of the calcari con selce formation deposited in an oceanic setting two stratigraphic sections petina chiana and pignola 2 representative of the evolution of the lagonegro basin during the carnian have been studied in detail with a multidisciplinary approach in the pignola 2 section within the calcari con selce formation a unique interval composed of green shales and radiolarites has been identified the absence of carbonate deposition within this interval is interpreted as evidence of a contemporaneous shallowing of the carbonate compensation depth conodont and palynomorph biostratigraphy constrain the age of this interval to the julian tuvalian lower carnian upper carnian boundary the age and characteristics of this interval suggest correlation with a putative climatic event known as the carnian pluvial event which has also been recognized in continental and shallow marine successions from different european localities this event is thus now documented also in a deep marine setting like the continental and shallow water settings it is characterized by a sudden input of siliciclastics petina chiana and pignola 2 integrate current knowledge of the carnian distribution of conodonts paragondolella praelindae kozur to date known only from the lower tuvalian has now been documented from the uppermost julian moreover a drastic turnover was recorded between julian and tuvalian conodont assemblages which is clearly associated with the carnian pluvial event thus a biotic crisis oceanographic changes associated with the rise of the carbonate compensation depth increased rainfall and an anomalous siliciclastic input occur contemporaneously at the time of the carnian pluvial event a similar pattern is associated with perturbations of the carbon cycle that occur during the jurassic and cretaceous e g in the early aptian thus it is hypothesized that the carnian pluvial event may have analogous causes

middle upper triassic carbonate platforms in minorca balearic islands implications for western tethys correlations abstract in order to progress in the knowledge of the middle to upper triassic evolution of the western tethys realm an integrated approach which includes new sedimentological sequence stratigraphic and biostratigraphic data has been accomplished in the carbonate marine successions muschelkalk facies of that age in minorca balearic islands spain the new biostratigraphy which includes six successive ammonoid biozones allowed to assign these carbonate successions to the uppermost anisian lower carnian interval the integration of the new chronostratigraphic framework with the sedimentological analysis allowed to recognize five main successive stages of carbonate platform evolution 1 initial marine transgression and shallow ramp development uppermost anisian 2 carbonate ramp drowning anisian ladinian boundary 3 prevalence of open sea conditions ladinian early carnian 4 abrupt sea level drop intra lower carnian and 5 shallow carbonate ramp and transition to sabkha systems keuper facies furthermore the sequence stratigraphic analysis allowed to divide some of these stages into depositional sequences minorca was located in the westernmost tethys area during the triassic in a key paleogeographic location close to the present day iberia sardinia and the cottian and southern alps the new data have allowed an interregional comparative analysis among these areas with recognition of major suprarregional events and episodes in the framework of the western tethys evolution

multiple sources of the early mesozoic gouli batholith eastern kunlun orogenic belt northern tibetan plateau linking continental crustal growth with oceanic subduction orogenic belts have been among the most important locations to investigate the growth of continental crust cc the eastern kunlun orogenic belt ekob which contains widespread permian triassic granitoids is volumetrically comparable to the cenozoic gangdese magmatic belt in the tibetan plateau and is an ideal region to investigate the mechanism of the paleozoic mesozoic cc growth in this region the gouli batholith at the eastern end of the ekob consists of the synchronous xiangride granodiorite asiha quartz diorite ca 242 ma and adamellite the granodiorite and quartz diorite both of which contain magmatic enclaves show medium high k calc alkalic and metaluminous signatures and have similar rare earth element and trace element patterns to those of bulk cc besides the xiangride granodiorite displays distinct adakitic signatures average sr y of 47 the sr nd isotopic values for the different types of rocks are roughly similar 87sr 86sr i 0 708167 0 713553 end t 6 8 to 5 3 while hf isotopes are distinguishable with ehf t granodiorite 0 3 to 5 1 and ehf t diorite 1 6 to 0 7 these geochemical and petrographic signatures suggest that the granodiorite originated from the partial melting of subducting oceanic crust and terrigenous sediments and the quartz diorite and enclaves formed via the mixing of slab derived magma and enriched mantle derived melt further comprehensive analyses of the spatial and temporal distribution of regional magmatic rocks metamorphism and sedimentary facies reveal that the gouli batholith and most of the permian triassic granitoids in the ekob formed during the subduction of the paleo tethys ocean instead of subsequent syn collision setting thus we contend that the permian triassic cc growth of the ekob occurred in a slab subduction setting and that both oceanic slab and subcontinental mantle significantly contributed to this process

melt segregation and magma interactions during crustal melting breaking out of the matrix abstract differentiation of the continental crust begins with its partial melting the products of crustal melting are silicic hydrous h2o undersaturated granitic liquids that are generated within matrices of residual crystals crustal differentiation requires that felsic magmas form and escape from these solid residua an important question is whether granitic magmas collect into large batches within or near their sources which then give rise to ascent or alternatively bleed out of the sources in smaller streams or pulses we demonstrate that the physical reality is closer to the second alternative and thus question the validity of the concepts of magma segregation and source fertility as they are sometimes visualised granitic plutons contain chemically distinct sub populations formed by source level entrainment of the peritectic assemblages into the melts rapid evacuation at source levels and high ascent rates protect the magmas from wall rock interactions during their tenure at source depths and during their ascent through cool upper crust the existence of different types of granites and hence of clearly defined chemically different magmas within plutons dictates that felsic magmas must separate efficiently from their anatectic sources and must ascend to the sites of their emplacement with minimal chemical interaction with crust through which the magma must move exposed deep crustal sections are typically lithologically diverse with the more fertile rocks commonly forming discrete layers surrounded by rocks with contrasting compositions if the melts were required to segregate and accumulate into large volumes within their hot sources especially by slow gravity driven melt percolation it is very likely that they would be substantially modified by reaction with diverse source rocks thus the processes mooted to occur in melting assimilation storage and homogenisation mash or deep crustal hot dch zones would act to erase original compositional heterogeneities and produce larger batches of more homogeneous magma perhaps carrying evidence of extensive magma mixing from various lines of evidence we conclude that mash and dch zones may not exist and even if they do they cannot form the sources of most granitic magmas the intrinsic heterogeneity in crustal source rocks the likely occurrence of peritectic assemblage entrainment and the inefficiency of magma mixing decree that granitic rocks will retain source inherited chemical and isotopic heterogeneities rapid semi continuous and disequilibrium withdrawal of small magma batches from source rocks means that elements of whole rock trace element chemistry and accessory mineral chemistry will be decoupled from major element variations this also means that a large source with low nominal fertility due to low hydrous mineral content for example could still produce a substantial granitic pluton by additions of individually small increments of magma

distribution of chemosynthetic biological communities in monterey bay california we report the first quantitative evaluation of the distribution of seafloor chemosynthetic biological communities on a regional scale the results are based on the analysis of video images and navigation from 792 benthic remotely operated vehicle dives conducted on the continental margin in monterey bay california these communities are common occurring within 5 of the 25 m square grid cells within which there have been bottom observations within 45 km of the bay9s head and within 9 of the visited cells that are below 550 m water depth although it has been previously assumed that these communities are associated with fluid seepage from faults they are not more common within known fault zones surprisingly the communities in monterey bay occur preferentially on steep slopes which are commonly sites of recent erosion

melt segregation in the continental crust before melt will segregate from its restite and source there must be both a driving force and space into which the melt can move the continental crust is anisotropic and in most cases is subject to deviatoric stresses during melting under these conditions melt segregation begins when an interconnected network of melt forms and the source becomes permeable melt is driven by pressure gradients from its restite toward dilatant sites set up in the heterogeneously deforming source the source is continually drained of melt and so need never contain more melt than that required to maintain permeability 26 where the solid matrix breaks down and diapirism can occur

new paleontological evidence of the carnian strata in the mežica area karavanke mts slovenia conodont data for the carnian pluvial event abstract the carnian carbonate succession in the me ica area called raibl beds karavanke mts slovenia on the north of the periadriatic line in the eastern alps includes three clastic horizons of marly shaly rocks the most interesting is the second clastic horizon that contains unique layers or lenses of micritic limestone although many samples were collected for conodonts only one single sample yielded well preserved carnian julian specimens the monospecific conodont fauna is marked by elements of nicoraella budaensis that enables us to reconstruct a multielemental apparatus the sporomorph associations of the first and the second clastic horizons are well correlated to the humid sub phases in the raibl beds the recovered conodont fauna verifies the julian age of the second clastic horizon in the me ica area and it provides new significant information for definition of the carnian pluvial event in the karavanke mts

insights into the complexity of crustal differentiation k2o poor leucosomes within metasedimentary migmatites from the southern marginal zone of the limpopo belt south africa differentiation of the continental crust is the result of complex interactions between a large number of processes which govern partial melting of the deep crust magma formation and segregation and magma ascent to significantly higher crustal levels the anatectic metasedimentary rocks exposed in the southern marginal zone of the limpopo belt represent an unusually well exposed natural laboratory where the portion of these processes that operate in the deep crust can be directly investigated in the field the formation of these migmatites occurred via absent incongruent melting reactions involving biotite which produced cm to m scale k2o poor garnet bearing stromatic leucosomes with high ca na ratios relative to their source rocks field investigation combined with geochemical analyses and phase equilibrium modelling designed to investigate some aspects of disequilibrium partial melting show that the outcrop features and compositions of the leucosomes suggest several steps in their evolution 1 melting of a portion of the source with restricted plagioclase availability due to kinetic controls to produce a magma melt entrained peritectic minerals in variable proportions relative to melt 2 segregation of the magma at near peak metamorphic conditions into melt accumulation sites mas a k a future leucosome 3a reequilibration of the magma with a portion of the bounding mafic residuum via chemical diffusion h2o k2o which triggers the co precipitation of quartz and plagioclase in the mas 3b extraction of melt dominated magma to higher crustal levels leaving peritectic minerals entrained from the site of the melting reaction and the minerals precipitated in the mass to form the leucosome in the source the key mechanism controlling this behaviour is the kinetically induced restriction of the amount of plagioclase available to the melting reaction this results in elevated melt h2o and k2o and chemical potential gradient for these components across the leucosome mafic residuum contact the combination of all of these processes accurately explains the composition of the k2o poor leucosomes these findings have important implications for our understanding of melt segregation in the lower crust and minimum melt residency time which according to the chemical modelling is 5 years we demonstrate that in some migmatitic granulites the leucosomes constitute a type of felsic refractory residuum rather than evidence of failed magma extraction this provides a new insight into the ways that source heterogeneity may control anatexis this article is protected by copyright all rights reserved

isotopic disequilibrium during melting of granite and implications for crustal contamination of magmas the assumption that the isotopic ratios of anatectic melts generated in response to crust magma interaction are equivalent to the bulk source rock from which they are derived was tested experimentally via dehydration melting of a proterozoic biotite granite heating of the coarse grained granite at 1250 c for durations of 1 to 48 h produced extreme disequilibrium among simultaneously generated mafic and felsic melts quenched to glass and whole rock 87sr 86sr ratios in situ microdrill sr isotopic analyses across gradational contacts between mafic high 87sr 86sr and felsic low 87sr 86sr glass register significant isotopic and chemical heterogeneity on the submillimetre scale our experiments suggest that during the early stages of wall rock melting when the rate of heating may exceed melting rates isotopic equilibrium may not be maintained thus producing contaminant liquids having isotopic compositions different from the bulk source rock if isotopic equilibrium is not attained during partial melting in the crust current geochemical models of open system magmatic processes may require modification

disequilibrium melting during crustal anatexis and implications for modeling open magmatic systems contamination of ascending mantle derived magmas by the continental crust was investigated and modeled for a suite of volcanic rocks and entrained crustal xenoliths from the central andes using bulk geochemical compositions for mantle derived and crustal end members as dictated by traditional approaches the assumption that the crustal contaminant in these open magmatic systems is a single composition was assessed through in situ analysis of quenched anatectic melt trapped within its crustal xenolith our results show for the first time significant chemical and sr isotopic disequilibrium between melt and source over submillimeter length scales in a natural system sampled glass is rhyolitic in nature enriched in large ion lithophile elements lile and depleted in heavy rare earth elements hree analysis of the melt for its 87sr 86sr composition revealed isotopic heterogeneity ranging from 0 7164 to 0 7276 the isotopic disequilibrium between melt and source is understood to reflect the melting of minerals with different rb sr and therefore 87sr 86sr more quickly than the isotopic composition can diffusively equilibrate between melt and minerals our results suggest that the mechanism of crustal anatexis produces contaminating melts which are geochemically heterogeneous both spatially and temporally furthermore time scales of sr diffusion and anatectic melt segregation promote the preservation of isotopic disequilibrium at the micro submillimeter and macro crustal scale this highlights the need for detailed microscopic investigations coupled with petrogenetic modeling in order to develop more robust characterization and quantification of contamination in open magmatic systems

element concentrations in granitic magmas ghosts of textures past the geochemistry of granitic rocks appears to contain information about some aspects of the pre anatectic textures of the protoliths there are marked contrasts in the covariations between ba a proxy for melting proportion in the protolith and the p 2 o 5 tio 2 y zr and ce concentrations in i and s type granitic magmas rocks these contrasts are interpreted as features resulting from the interplay between differences in the locations of accessory mineral grains in the protoliths their solubilities in the granitic melts and the degree of foliation developed in the protoliths it is inferred that s type protoliths are more highly foliated with accessory minerals concentrated into the biotite rich layers that form the foci for partial melting i type protoliths appear to have less pronounced foliation and a more random distribution of both hydrous mafic silicates and accessory grains supplementary material a list of data sources and tables of analyses of granitic rocks are available at www geolsoc org uk sup18682

ichnology and sedimentology of the triassic carbonates of north west sardinia italy the classical middle to upper triassic carbonate sections at monte santa giusta and punta del lavatoio north west sardinia italy referred to the muschelkalk and keuper lithofacies group are revisited and their trace fossil content is investigated for the first time a combined ichnological and sedimentological study reveals insights into the depositional environments regional context palaeogeography and sequence stratigraphy the results indicate deposition on a homoclinal carbonate ramp with broad facies belts all recognized trace fossils are also known from time equivalent deposits of germany and thus indicate a close affinity between the north west sardinian triassic and the germanic basin only a few trace fossils are particularly abundant and these indicate opportunistic colonization by their producers which is probably related to restricted endobenthic conditions due to reduced oxygen and or increased salinity the trace fossil association can be grouped into a softground suite belonging to the cruziana ichnofacies and a firmground suite of the glossifungites ichnofacies this discrimination enables an interpretation of the northern monte santa giusta section as a carbonate ramp with extensive tidal flats and abundant carbonate accumulation in a relatively proximal position whereas the southern punta del lavatoio section exhibits broad lagoonal environments with reduced sedimentation in a deeper and more tethys influenced area the sardinian sections are ichnologically similar to the anisian ladinian succession known from the tatra mountains but differ from it by having a slightly higher ichnodiversity which again can be attributed to a less restricted lagoonal environment this study demonstrates the importance of integrating trace fossil analysis in sedimentological and palaeontological investigations of carbonate systems

the anatectic effect on the zircon hf isotope composition of migmatites and associated granites zircon hf isotope composition is widely used to trace the growth and evolution of continental crust however it is controversial whether the hf isotope composition of magmatic zircons can faithfully reflect that of their sources especially for s type granites in order to provide an insight into this issue we have revisited the published lu hf isotope data of zircons from well studied migmatites and associated granites in the sulu orogen and the cathaysian terrane respectively the results show greatly elevated 176hf 177hf ratios by more than 10e units for newly grown zircon domains compared to the relict zircon domains this indicates considerable contributions from non zircon hf to anatectic melts during crustal anatexis and subsequent magmatism furthermore this more radiogenic hf isotope signature was not erased during magmatic processes such as crystal fractionation during melt ascent and emplacement the budget of hf isotopes in source rocks with respect to mineral lu hf ratios suggests the involvement of hf bearing major minerals in anatectic reactions by dissolving hf bearing major minerals into the anatectic melts the significant hf isotope variations in some anatectic and magmatic zircon domains from the migmatites and granites suggest not only the source heterogeneity but also the variable non zircon hf contributions as such the hf isotope compositions of anatectic and magmatic zircons are substantially dictated by the mass balance between the non zircon hf from anatectic reactions and the zircon hf from the dissolution of protolith zircons into the anatectic melts they are primarily controlled by p t conditions and mechanism of crustal anatexis and the magmatic processes during melt evolution the present study highlights the important contribution of non zircon hf to the anatectic and magmatic zircon domains in this regard the greatly elevated 176hf 177hf ratios for newly grown zircon domains in the migmatites and granites cannot reflect the hf isotope compositions of their source rocks such a deviation must be kept in mind when linking relatively depleted hf isotope compositions to the nature of source rocks in petrogenetic interpretation and to the growth of continental crust the contribution of non zircon hf can also better account for the variable hf isotope compositions often shown by zircons from s type granites

characterizing the continental basement of the central andes constraints from bolivian crustal xenoliths a critical factor in understanding the development of active continental margins is knowledge of the crustal basement on which magmatic arcs are built this study reports results from a whole rock geochemical and zircon u pb geochronological study of a suite of crustal xenoliths from the bolivian altiplano central andes that provide new insight into the evolution and composition of the continental basement beneath the region the xenoliths are hosted in pliocene pleistocene trachyandesitic to dacitic lavas that erupted from monogenetic volcanic centers in the andean backarc region and comprise both igneous and metamorphic lithologies including diorites microgranites gneisses garnet mica schists granulites quartzites and dacites the xenolith suite exhibits significant sr isotopic heterogeneity with values extending from 0 7105 to 0 7368 pb isotopic signatures reflect the crustal domains previously constrained from scattered exposures of basement rocks throughout the region ion microprobe u pb dating of cores and rims from zircon separates from two of the sampled xenoliths reveals predominant early phanerozoic age peaks ca 500 ma population 1 late mesoproterozoic age peaks 1 0 1 2 ga population 2 and paleoproterozoic age peaks 1 7 1 9 ga population 3 populations 1 and 2 are well documented throughout the andes and correspond to periods of supercontinent formation e g rodinia at ca 1 0 ga and breakup population 3 which is poorly represented in the zircon record of the andes as a whole may record geological events during the construction of the paleoproterozoic amazonian craton the presence of the three age peaks in the detrital zircon population record of a single crustal xenolith demonstrates the important role of crustal recycling in the construction of the modern day andean margin the lithological character of the xenoliths and their detrital zircon ages are inconsistent with current understanding of the eastern extent of the arequipa antofalla basement block beneath the bolivian altiplano and instead indicate that it terminates further to the west than previously assumed

palynological correlation of carnian humid pulses throughout western tethys abstract the carnian pluvial event is an upper triassic swing toward increased rainfall best documented in the tethys tropical belt and mainly recognized on its effects on sedimentary systems as the demise of carbonate platforms and the enhanced siliciclastic supply in some portions of western tethys and particularly in the raibler schichten of the northern calcareous alps and in the dolomites the carnian pluvial event is recorded by four discrete siliciclastic pulses in the raibler schichten three siliciclastic intervals are documented and take the name of first second and third shale in order to correlate these pulses at the basinal scale the study of the palynological assemblages in a section of the raibler schichten near rubland austria and of the classical succession of the lunz nappe have been carried out more than eighty palynomorph species are recorded most of them correspond to typical carnian morphospecies of the carnian pluvial event in europe on the base of their stratigraphic distribution three different palynomorph assemblages are described aulisporites astigmosus assemblage lagenella martinii assemblage and granuloperculatipollis rudis assemblage a fourth older assemblage is also informally defined a palynostratigraphic correlation between the nca the germanic basin and the dolomites has been obtained the four siliciclastic pulses recognized in the raibler schichten and lunz are also found in the dolomites and yield the same palynological associations the base of the schilfsandstein that record the carnian pluvial event in the germanic basin is correlated to the second or third siliciclastic pulse first or second shale of the raibler schichten siliciclastic pulses are thus correlated throughout western tethys and can thus be interpreted as short lived humid climate wiggles within the carnian pluvial event a quantitative analysis of the carnian successions of the nca highlights a shift toward hygrophytic elements in the uppermost julian and an abrupt return to xerophytic associations in the lower tuvalian the palynological hygrophytic associations that characterize the aulisporites astigmosus and lagenella martinii assemblages are present in many other parts of europe and middle east suggesting that the carnian pluvial event determined a humid climate perturbation in a wide area of the northern hemisphere spanning from tropical to high latitudes

andean cenozoic volcanic centers reflect basement isotopic domains isotopic data for quaternary volcanic centers from lat 17 5 to 22 s in northern chile provide evidence for crustal contributions to arc magma genesis in the central andes and delineate basement domains crustal thickness distance from trench height of volcanic edifices above the seismically active subduction zone and sediment supply to the trench are all constant along this segment of the arc the only significant variable is crustal age paleozoic in the south proterozoic in the north pb isotopic compositions of quaternary lavas in the northern sector are lower 206 pb 204 pb 17 89 18 28 and sr and o isotope ratios are less variable 87 sr 86 sr 0 7058 0 7077 18 o 6 5 8 4 than in the southern sector 206 pb 204 pb 18 59 18 79 87 sr 86 sr 0 7053 0 7083 18 o 6 4 9 3 for rocks similar in bulk composition from 53 to 74 wt sio 2 together these features are interpreted to reflect interaction of magmas with crustal contaminants of different isotopic character rather than changes in the mantle source of central andean are magmas resulting from either subduction erosion or involvement of old enriched lithosphere

source of the zhawulong granitic pegmatite type lithium deposit in the songpan ganze orogenic belt western sichuan china constrants from sr nd hf isotopes and petrochemistry abstract the zhawulong ore field hosts lots of rare element pegmatite dikes and is an important producing area for lithium resources in the songpan ganze orogenic belt sgob east tibet this paper aims to evaluate the sources and ore forming processes for granite and pegmatite in the zhawulong ore field as well as the petrogenetic links between these rocks using petrography whole rock major and trace element analysis and sr nd hf isotope analysis in this ore field pegmatites are common as dike swarms that emanate from the external and or internal contact zone of the zhawulong granitic pluton and strata of the triassic xikang group showing close spatial relationships measured values of k rb vs zr hf and cs contents indicate geochemical affinities between granite and pegmatite which suggests that the pegmatite was generated by processes involving high fractional crystallization from the residual parental magma of the host granite additionally the granite have high 87sr 86sr i values 0 711064 to 0 716105 negative end t values 9 6 to 9 1 and ehf t values 32 6 to 2 0 and ancient nd and hf model ages 1 2 3 1 ga which indicate a continental crustal source metasedimentary rocks of the xikang group are rich in li 95 ppm rb 124 ppm nb 15 ppm and cs 17 ppm and their rare earth element ree patterns show moderate enrichment in light rees and a negative eu anomaly eu eu 0 64 revealing characteristics similar to those of granite the coeval nature and close spatial relationships between the zhawulong granite and other syn orogenic s type granites indicate that the formation of this granite was related to crustal melting the petrology and geochemical signatures of the zhawulong rare metal bearing granite pegmatite imply that it was generated by the partial melting of metasedimentary rocks during the late triassic orogeny assembly and was further enriched in li through processes involving high fractional crystallization

volcanic rocks from the bolivian altiplano insights into crustal structure contamination and magma genesis in the central andes lavas from quaternary minor volcanic centers behind the central andean volcanic arc in bolivia form a compositional continuum with rocks from the arc front extending to more primitive compositions the lavas show petrographic and geochemical evidence for deep crustal contamination during differentiation sr nd and pb isotopic data from centers within 30 km of each other encompass the entire range found in the central volcanic zone of the andes the most mafic rocks are largely typical of arc magmas elsewhere and may represent parental magmas to the porphyritic andesites and dacites erupted from stratovolcanoes along the arc to the west andean arc magmas therefore undergo considerable contamination during ascent through the thick crust the only basalts lacking petrographic evidence for contamination are picrobasalts from chiar kkollu that form the most primitive end member of the compositional spectrum these rocks resemble ocean island basalts in some respects indicating that variations in crustal contamination across the strike of the arc may be superimposed on variations in the mantle source composition

isotopic disequilibrium in migmatitic hornfels of the gennargentu igneous complex sardinia italy records the formation of low 87sr 86sr melts from a mica rich source isotopic disequilibrium is increasingly recognized as a common feature of magmatic systems but the details of the mechanism s underpinning the development of isotopic disequilibrium during partial melting processes are not fully understood partial melting of mica rich lithologies may be predicted to generate melts enriched in radiogenic sr compared to the bulk protolith compositions due to the typically high rb sr ratio coupled with low melting temperature of mica in crustal rocks here we report a puzzling case study where the sr isotope composition of the melt fraction leucosome of partially molten metapelites migmatites is instead less radiogenic than the restitic component melanosome the examined migmatites fringe 50 m wide zone a low pressure 200 mpa high temperature 1050 c quartz dioritic intrusion which was emplaced in the gennargentu igneous complex sardinia italy at 306 26 ma bulk rock rb sr dating the migmatites derive from anatexis of the muscovite rich metapelitic wall rocks they include a quartzo feldspathic leucosome and a melanosome containing cordierite k feldspar plagioclase biotite fe ti oxide minerals and both corundum and hercynite the leucosome has a less radiogenic sr and more radiogenic nd isotope composition than the melanosome 87sr 86sr 306 ma 0 71068 and 0 71536 end 306 ma 6 4 and 9 2 respectively with bulk migmatite samples having intermediate compositions the significantly lower content of mica in the migmatites compared to the protolith indicates that muscovite and to a lesser extent biotite largely contributed to melt formation however the leucosome volume 50 estimated through mass balance calculations is considerably higher than the amount of melt 10 vol generally produced by mica dehydration melting in the crust suggesting that partial melting was enhanced by an external hydrous fluid the o isotope composition of the migmatites is lower than the typical metapelite values 10 but overlaps with the 18o range of the quartz diorites 8 8 9 9 suggesting that such a hydrous fluid was released from the quartz dioritic intrusion we put forward a model whereby the anatexis temperature conditions t 800 c favored the preservation of isotopic disequilibrium of micas and plagioclase in the protolith in this context the leucosome formed by the preferential melting of less radiogenic plagioclase rather than more radiogenic micas the melt was then efficiently separated from the melanosome containing restitic biotite and peritectic k feldspar and magnetite derived from mica breakdown during the anatectic process the quartz diorite provided not only the heat budget but also the fluid amount responsible for i the hydration of the pelitic country rock ii the increase of melt fraction and iii the higher mobility of anatectic magma

a spectrum of disequilibrium melting preserved in lava hosted partially melted crustal xenoliths from the wudalianchi volcanic field ne china abstract disequilibrium melting has been established as a common process occurring during crustal anatexis and thus demonstrates that crustal assimilation is not a closed system observations of extreme compositional heterogeneity within partial melts derived from crustal xenoliths have been documented in several recent examples however the retention or transfer of elements to and from residues and glasses and their relative contributions to potential crustal contaminants warrants further investigation recent eruptive products of the huoshaoshan volcano in the holocene wudalianchi volcanic field of northeast china contain crustal xenoliths which preserve a spectrum of partial melting both petrographically and geochemically thus providing an excellent natural example of crustal anatexis correlations exist between the volume of silicic glass preserved within the xenoliths and bulk rock sio2 70 83 wt al2o3 8 16 wt glass 87sr 86sr 0 715 0 908 abundances of elements common in feldspars and micas sr ba rb and elements common in accessory minerals y zr nb these correlations are likely associated with the consumption of feldspars and micas and the varying retention of accessory phases during partial melting the xenoliths which contain greater volumes of silicic glass and residual quartz interpreted as being the most melted were found within pahoehoe lava whilst the least melted xenoliths were found within scoria of the summit cone of huoshaoshan thus it is interpreted that the extent of melting is linked to the immersion time in the lava which we estimate to be on the order of days however the least partially melted samples display geochemical evidence in support of melt loss evidenced by the relatively depleted nature of their whole rock compositions and the larger difference between whole rock and glass yet the more melted samples appear to have experienced less melt loss thus the extent of melting cannot be linked linearly to the volume of melt loss which occurs small scale mm mingling and transfer of material from the enclosing lava to the xenolith are observed however modelling of potential contaminant compositions is inconsistent with crustal contamination during lava petrogenesis it is thus more likely that any crustal contamination in these eruptives is extremely localized within this open magmatic system and most likely occurs at the contact zone between the xenolith and host lava

self subduction of the pangaean global plate one of the most striking and rare occurrences in the earth s history is the amalgamation of most of the continental lithosphere into one supercontinent the most recent supercontinent pangaea lasted from 320 to 200 million years ago here we show that after the continental collisions that led to the formation of pangaea plate convergence continued in a large wedge shaped oceanic tract we suggest that plate strain at the periphery of the supercontinent eventually resulted in self subduction of the pangaean global plate when the ocean margin of the continent subducted beneath the continental edge at the other end of the same plate our scenario results in a stress regime within pangaea that explains the development of a large fold structure near the apex of the palaeotethys ocean extensive lower crustal heating and continental magmatism at the core of the continent as well as the development of radially arranged continental rifts in more peripheral regions of the plate

a model that helps explain sr isotope disequilibrium between feldspar phenocrysts and melt in large volume silicic magma systems feldspar phenocrysts of silicic volcanic rocks are commonly in sr isotopic disequilibrium with groundmass in some cases the feldspar is more radiogenic and in others it is less radiogenic several explanations have been published previously but none of these is able to accommodate both senses of disequilibrium we present a model by which either more or less radiogenic feldspar or even both within a single eruptive unit can originate the model requires a magma body open to interaction with biotite and feldspar bearing wall rock magma is incrementally contaminated as wall rock melts incongruently biotite preferentially melts first followed by feldspar such melting behavior which is supported by both field and experimental studies first contaminates magma with a relatively radiogenic addition followed by a less radiogenic addition feldspar phenocrysts lag behind melt groundmass of volcanic rock in incorporating the influx of contaminant thus resulting in sr isotopic disequilibrium between the crystals and melt the sense of disequilibrium recorded in a volcanic rock depends on when eruption quenches the contamination process this model is testable by isotopic fingerprinting of individual feldspar crystals for a given set of geologic boundary conditions specific core to rim sr isotopic profiles are expectable moreover phenocrysts that nucleate at different times during the contamination process should record different and predictable parts of the history initial results of sr isotopic fingerprinting of sanidine phenocrysts from the taylor creek rhyolite are consistent with the model more tests of the model are desirable

geochemical and isotopic disequilibrium in crustal melting an insight from the anatectic granitoids from toledo spain in the hercynian anatectic complex of toledo act the anatectic granitoids include leucogranitic leucosomes leucogranitic massifs and restite rich granites they show a broad range of initial sr and nd isotope ratios from 0 711 to 0 720 and 0 51164 to 0 51203 respectively which clearly indicate the absence of isotopic homogenization in the melts broadly the ranges reflect the isotopic variation of the metapelitic protoliths if crustal melting occurs under water undersaturated conditions as is the case of the act the generated melts do not isotopically and chemically equilibrate with the granulitic residuum the preservation of heterogeneities could arise through a number of processes 1 duration of the process in which the presence of melts with disequilibrium features and the high solid content of several of the granites in the act point to a very short lived magmatic system 2 limited diffusion in which poorly segregated and volatile undersaturated granitoids have a very restricted opportunity for isotopic and chemical homogenization and 3 magma dynamics in which the low melting rates the high restite and low water contents and the silica rich composition of these granites together with the small volume and high viscosity values of the melts seriously restrict the physical processes leading to homogenization

isotope disequilibrium during anatexis a case study of contact melting sierra nevada california the geochemical consequences of contact melting were investigated in the sierra nevada batholith where trachyandesite magmas have intruded and melted the host granitic rocks partial melting of the granite varies from 10 20 at contact regions to 50 70 in a granite block within the trachyandesite thermal modelling suggests that the temperature of the granite block exceeded its solidus within 3 months of trachyandesite intrusion reached a maximum of 1000 c after ca 1 5 yr and remained above 500 c for ca 40 yr sr nd and pb isotope data of granitic melts record marked sr isotope and to a lesser extent pb isotope disequilibrium both within different glass fractions and between glasses and their source rb sr isochron calculations on residual mineral glass pairs fail to yield the age of melting obtained by40ar 39ar dating 11 9 ma sr and pb isotope data of glasses establish that major rock forming minerals of the granite had not attained isotope equilibrium before the onset of melting consequently the isotopic composition of the successive liquid fractions originating from granite melting depended on the relative contribution of each mineral to the elemental budget of the melts the extrapolation of these results to the petrogenesis of crustal melts and more generally to studies of crustal evolution suggests that isotope disequilibrium during anatexis and high grade metamorphism may be a common characteristic of many geologic settings if future studies substantiate these results some geochemical models of crustal melting and assimilation may need revision in addition marked sr isotope disequilibrium in the residual mineral phases within the partially melted granite raises concerns about the reliability of radiometric dating in metamorphic terranes

the changing climate framework and depositional dynamics of triassic carbonate platforms from the dolomites abstract the triassic of the dolomites offers a valuable opportunity to investigate the relationships between climate fluctuations and the changing depositional dynamics of carbonate platforms the reconstruction of the large palaeoclimatic modification is based on the synthesis of multiple sedimentological palaeobotanical pedological and geochemical proxies the triassic climate fluctuations were generally fast in nature and were probably associated with a latitudinal shift of the monsoon belts during the triassic the dolomites were placed at an intertropical northern latitude of about 16 18 and were generally dominated by dry climate and elevated temperature at least five pulses toward moister climate are however documented dated to early olenekian middle anisian late ladinian middle carnian and late norian times within this variable climatic scenario the carbonate systems record a global evolutionary trend from late permian early triassic regional shelves rich in loose micrites and bio calcarenites to anisian ladinian synsedimentary cemented steep sided 35 40 high relief platforms and back to carnian low angle ramps moist transgressive episodes were surprisingly prone to the spreading of corals and other colonial reef organisms probably because of the reduced space competition by syndepositional cementation structures the permo triassic boundary extinction dramatically impacted on the calcified organism communities but the carbonate depositional architecture nevertheless stayed almost unaffected through the boundary the early triassic and earliest anisian were commonly associated with hyperhaline sometimes evaporitic conditions intervals of moister climate and efficient river discharge are however documented by earliest induan and early olenekian sediments the latter terrigenous deposits matched a crisis in the carbonate production after a return to arid conditions during the anisian a fluctuation toward moister climate developed associated to a massive continental vegetation cover the anisian tectonic activation of the region fragmented the previous carbonate shelf triggering the development of three generations of fast prograding but globally backstepping isolated platforms recording an increasing role of the synsedimentary cementation a dry climate dominated the late anisian and early ladinian interval at the time a fast subsidence pulse was associated with platform drowning and basinal anoxia only a few aggrading pinnacles were able to survive providing the nuclei for larger prograding platforms during a dry climate interval massive syndepositional cementation generated a major source of carbonate carbonate production stayed active through the ladinian magmatic phase but the onset of volcanism was associated with a large modification in the platform carbonate facies which became dominated by automicrites moist climate phases are well documented again during the late ladinian followed by a return to dry conditions the late ladinian early carnian platforms prograded toward the eastern dolomites depocentre eventually infilling almost the whole of the accommodation space the middle portion of the carnian recorded renewed sharply moist phases associated with the demise of the rimmed platforms and with the return to loose sediment ramps at least four separated humid fluctuations can be identified in this carnian interval alone climate then returned to persistent aridity until the late norian moist phase

incongruent melting of biotite to spinel in a quartz free restite at el joyazo se spain textures and reaction characterization in the grt bt sil restitic xenoliths of el joyazo cerro de hoyazo hercynitic spinel is a minor phase commonly associated with biotite the possible reaction relationships among biotite and spinel are studied in reaction textures developed around biotites at their contact with patches of fibrolitic sillimanite and rhyolitic melt in these textures resorbed biotite crystals about 1 mm long are rimmed by a layer of glass 5 mm away from the reaction texture biotite is chemically zoned cores bt 1 have xmg 0 35 0 02 and ti 0 58 0 01 atoms whereas the outer rims bt 2 have xmg 0 45 0 01 and ti up to 0 68 atoms the hercynite rich spinel spl has low zno content 0 80 wt and xmg 0 26 0 04 the chemical compositions of the mix aggregate represent linear combinations between sillimanite and a silica rich melt this melt melt 1 is different from that of the layer around biotite melt 2 which is also richer in ca and alkalis garnet rims grt have low ca and mn and xmg 0 14 plagioclase is characterized by large homogeneous cores pl 1 an31 2 and more calcic rims pl 2 an49 6 matrix analysis in the 9 component al ca fe k mg mn na si ti 9 phase bt1 bt2 grt spl ilm melt2 mix pl1 pl2 system provides the mass balance in mole units

anatexis and metamorphism in tectonically thickened continental crust exemplified by the sevier hinterland western north america the generation of granitoid magmas by partial melting of crustal rocks during continental thickening events is well documented in many geological provinces throughout the world including the late mesozoic sevier belt of western north america we present a thermal and petrologic model of anatexis and metamorphism in regions of crustal thickening where the only mantle contribution is the normal conductive supply of heat through the base of the lithosphere i e advection of mass and energy are excluded we distinguish between formation of migmatites and generation of mobile granitoid magmas and examine the temporal and spatial relationships between these two distinct anatectic processes between anatexis and regional deformation and between anatexis and metamorphism a fundamental conclusion is that if protoliths rich in hydrous minerals are present regional anatexis is the end product of classical barrovian metamorphism in thickened continental crust even in the absence of a free water rich fluid phase barrovian metamorphic facies series are predicted with thickening ratios maximum crustal thickness attained initial crustal thickness as low as 1 3 but mobile granitoid magmas are not formed if this ratio is less than approximately 1 5 above these lower bounds barrovian metamorphism and anatectic granitoid magmatism occur independently of the magnitude of thickening and of the way in which thickening is accomplished both processes are sensitive to a diminished heat supply lowering either moho heat flow or crustal radioactive heat production results in blueschist eclogite metamorphism and inhibits the formation of mobile granitoid magmas we model anatexis under fluid absent conditions and show that with such a constraint migmatization is always a syn kinematic process relative to the crustal thickening event whereas generation of mobile granitoid magmas is in most cases post kinematic relative to crustal thickening but can be syn kinematic if thickening takes more than approximately 50 myr the typical time intervals for melting are consistent with geological observations mobile granitoid magmas are predicted by most of our models within approximately 10 myr of the end of the crustal thickening event this incubation period results primarily from the temperature increase required for the dehydration melting reactions capable of producing large melt fractions to occur the energetic requirements of anatexis are relatively minor compared to conductive crustal thermal budgets as shown by the fact that once the necessary p t conditions are attained melting reactions are completed within time intervals on the order of 1 myr i e 1 2 orders of magnitude smaller than the characteristic time scales of the tectonic processes involved in crustal thickening

geochemical constraints on the petrogenesis of granitoids in the east kunlun orogenic belt northern tibetan plateau implications for continental crust growth through syn collisional felsic magmatism early triassic syn collisional granitoids with mafic magmatic enclaves mmes crop out along the entire east kunlun orogenic belt ekob at the northern margin of the tibetan plateau they are andesitic in composition and enriched in light rare earth elements lrees with a flat heavy ree hree pattern their average composition resembles that of the bulk continental crust the enclosed mmes have the same mineralogy as their host granitoids but contain a greater mode of mafic minerals amphibole and biotite and thus have higher hree abundances zircon u pb dating shows that both the granitoid hosts and mmes have the same crystallization age of similar to 250 ma and indistinguishable bulk rock sr nd pb hf isotope compositions i sr of 0 7080 0 7116 varying pb 206 pb 204 i of 18 53 19 32 essentially constant epsilon nd t of 5 3 to 2 1 and a small range of positive epsilon hf t mostly 1 7 5 2 the complete isotopic overlapping between the granitoid hosts and the mmes is understood to reflect that the mmes are disintegrated cumulates formed at an early stage of the granitoid magma evolution within the same magmatic system the isotopic data set reveals that the granitoids are variably evolved melts produced by partial melting of the subducted paleo tethyan oceanic crust with terrigenous sediments under amphibolite facies conditions in response to the continental collision c 2014 elsevier b v all rights reserved

triassic ammonoid biostratigraphy an overview abstract the triassic chronostratigraphic scale was built on two centuries of research on ammonoid biostratigraphy and biochronology two triassic stage bases and all of the triassic substages are currently defined by ammonoid bioevents the study of triassic ammonoids began during the late 1700s and in 1895 edmund von mojsisovics wilhelm waagen and carl diener published an essentially complete triassic chronostratigraphic scale based on ammonoid biostratigraphy this scale introduced many of the triassic stage and substage names still used today and all terminology of stages and substages subsequently introduced has been based on ammonoid biostratigraphy early triassic ammonoids show a trend from cosmopolitanism induan to latitudinal differentiation olenekian and the four lower triassic substage griesbachian dinerian smithian and spathian boundaries are globally correlated by widespread ammonoid biotic events middle triassic ammonoids have provinciality similar to that of the olenekian and provide a basis for recognizing six middle triassic substages late triassic ammonoids provide a basis for recognizing three stages divided into five substages the main uncertainty for the future of triassic ammonoid biostratigraphy is not the decline of the ammonoids as a tool for dating and correlation of triassic strata but rather the dramatic decrease in the number of specialists due to the lack of replacement of experienced palaeontologists who started their activity in the 1950s and 1960s

unravelling the complexity of magma plumbing at mount st helens a new trace element partitioning scheme for amphibole volcanoes at subduction zones reside above complex magma plumbing systems where individual magmatic components may originate and interact at a range of pressures because whole rock compositions of subduction zone magmas are the integrated result of processes operating throughout the entire plumbing system processes such as mixing homogenisation and magma assembly during shallow storage can overprint the chemical signatures of deeper crustal processes whereas melt inclusions provide an effective way to study the uppermost 10 15 km of the plumbing system challenges remain in understanding magma intrusion fractionation and hybridisation processes in the middle to lower crust 15 30 km depth which commonly involves amphibole crystallisation here we present new insights into the mid crustal plumbing system at mount st helens usa using multiple regression methods to calculate trace element partition coefficients for amphibole phenocrysts and thus infer the trace element compositions of their equilibrium melts the results indicate vertically distributed crystal fractionation dominated by amphibole at higher pressures and in intermediate melts and by plagioclase at lower pressures variations in nb zr and ree concentrations at intermediate sio2 contents suggest repeated scavenging of partially remelted intrusive material in the mid crust and mixing with material from geochemically diverse sources amphibole is an effective probe for deep crustal magmatism worldwide and this approach offers a new tool to explore the structure and chemistry of arc magmas including those forming plutonic or cumulate materials that offer no other constraints on melt composition

extreme mineral scale sr isotope heterogeneity in granites by disequilibrium melting of the crust abstract the broadest ranges of initial sr isotopic ratios 87 sr 86 sr i ever reported within a single igneous rock 2 10 2 are preserved within the late miocene laccolith pluton dyke felsic complex of elba island italy for these units the integration of textural and crystal scale isotope data allows tracing the evolution of the 87 sr 86 sr i of the melt from the emplacement level back to the earliest pre emplacement crystallization stage the rock matrix minerals record the 87 sr 86 sr i composition of the magma at the emplacement level 0 715 0 716 k feldspar megacrysts representing an earlier phase crystallized at depth record a rim to core increase of sr isotopic ratios from values similar to those of the matrix to significantly higher ones 0 719 remarkably biotites hosted within megacrysts representing the first crystallization stage have extreme and contrasting 87 sr 86 sr i values in the different intrusive units biotites within megacrysts from the laccolith record the lowest ratio in the intrusive complex 0 710 while those in the megacrysts from the pluton and associated felsic dyke have the highest 87 sr 86 sr i 0 732 this time transgressive record of isotopic variation in the magma reflects episodic recharge and mixing of magma batches formed by disequilibrium melting of crustal sources that produced melts through different reactions as temperature was increasing the progression from muscovite to biotite dominated fluid absent melting generates melts with increasing 87 sr 86 sr while at higher temperatures the progression from biotite to hornblende dominated melting reactions results in a decrease in the 87 sr 86 sr of the melt

climatic and biotic change in the late triassic generally arid conditions that pervaded much of europe and north america during the late triassic were interrupted by a wet monsoonal climatic phase during middle and late carnian times extensive fluviatile sandstones deposited at this time throughout the region occur within a thick sequence of playa lake mudstones the sandstones occasionally contain kaolinite suggesting a humid climate an extreme 13 c depletion in a shallow marine sequence of this age in israel has been interpreted as evidence for an influx of freshwater a widespread change from carbonates to clastics in marine sequences at this time may also be climate related water course cave systems in limestone areas exposed during the late triassic indicate high levels of runoff during the middle and late carnian the marine invertebrate fauna shows a significant turnover at the end of the early carnian the terrestrial fauna and flora were relatively unaffected at this time but subsequently diversified prior to a major biotic turnover at the carnian norian boundary these periods of biotic change appear to be synchronous with the onset and cessation of a carnian humid phase the change to a monsoonal climate during this interval has been documented over more than 90 of longitude between 5 and 50 north of the triassic equator it may have been caused by rising atmospheric co 2 levels due to volcanism associated with the incipient dispersal of pangaea

interference between pluton expansion and non coaxial tectonic deformation three dimensional computer model and field implications abstract structures in orogenic belts are greatly controlled by interactions between pluton related and tectonic related strain fields however many aspects of the geometry and evolution of these structures are poorly known for example 1 what is the geometry of these structures if regional deformation is coaxial 2 how does this geometry change with progressive deformation this paper describes a three dimensional simulation of strain shape and magnitude as well as foliation and lineation patterns formed by interactions between pluton expansion and homogeneous coaxial deformation this simulation suggests that interactions between pluton expansion and regional uniaxial shortening generate patterns that are distinct from the patterns produced by regional uniaxial extension or regional non coaxial deformation for example shortening produces doughnut shaped constrictional rings about the pluton whereas extension produces apple shaped flattening regions around the pluton in addition shortening produces one continuous doughnut shaped low strain region around the pluton on the other hand extension creates two separate ellipsoidal low strain regions at the ends of the pluton furthermore shortening forms foliation rings that have triangular two dimensional sections and lineation is concentric around the axis of maximum shortening in contrast extension produces two separate foliation and lineation cones at the ends of the pluton all these structural and strain elements migrate away from the pluton with increasing expansion rates and towards the pluton with increasing tectonic deformation rates although structural studies around plutons should always integrate microstructural radiometric and field measurements simulation generated patterns can be used to evaluate 1 origin geometry and evolution of structures around plutons 2 mechanisms that explain inclusion trails within porphyroblasts 3 contribution of pluton related strains to strains measured in the country rock and 4 type and three dimensional orientation of regional kinematic schemes

post collisional magmatism in the late miocene rodna bârgău district east carpathians romania geochemical constraints and petrogenetic models abstract post collisional magmatism in the late miocene rodna b rg u subvolcanic district east carpathians gave rise to a wide variety of rock compositions allowing recognition of four groups of calcalkaline rocks with distinctive petrography mineral chemistry whole rock geochemistry and sr nd hf isotope features new u pb zircon datings together with literature data indicate that the emplacement of the four rock groups was basically contemporaneous in the 11 5 8 ma time span the low potassium group lkg includes the most abundant lithotypes of the area ranging from basaltic andesite to dacite characterized by k poor tschermakitic amphibole weak enrichment in lile and lree relatively low 87 sr 86 sr coupled with relatively high 143 nd 144 nd and 176 hf 177 hf the high potassium group hkg includes amphibole bearing microgabbro amphibole andesite and amphibole and biotite dacite with k richer magnesio hastingsite to hastingsite amphibole more marked enrichments in incompatible elements higher 87 sr 86 sr and lower 143 nd 144 nd and 176 hf 177 hf these two main rock groups seem to have originated from similar juxtaposed mantle sources with the hkg possibly related to slightly more enriched domains with higher h 2 o reflected by the higher modal amphibole with respect to lkg with higher plagioclase amphibole ratios the evolution of the two rock series involved also open system processes taking place mainly in the upper crust for the hkg in the lower crust for lkg magmas in addition limited occurrences of generally younger strongly evolved peraluminous rhyolites and microgranites acid group and sialic dominated leucocratic andesites and dacites lad group were also recognized to the opposite outermost areas of the district these two latter rock groups were generated by the melting of a basic metamorphic crustal source respectively in hydrous and anhydrous conditions favored by the heat released by mantle melts from the adjoining central area the peculiar distribution of the products of the four rock groups in well defined sectors argues for a strong control of the local crustal tectonic regime on magmatism influenced by the change from a transpressional to trastensional stage