magma enclave interactions in the east carpathian subvolcanic zone romania petrogenetic implications abstract the east carpathian volcanic arc is made up of two extrusive sectors separated by a subvolcanic zone the east carpathian subvolcanic zone ecsz consists of calc alkaline shallow intrusions sills laccoliths and dykes emplaced in the precambrian metamorphic basement or in its paleogene cover during the pannonian pontian time span all intrusions contain enclaves of magmatic metamorphic or sedimentary origin the magmatic rocks in the ecsz have been divided into three groups group i rocks are ubiquitous but occur only as mafic cognate enclaves showing cumulate features group ii rocks basaltic andesites andesites microdiorites and dacites are the most widespread occurring both as enclaves and host rocks group iii comprises only enclave poor rhyolitic host rocks major and trace element analyses of both cognate enclaves and their host rocks have been done in order to get information about the evolution of the magmas in the ecsz microprobe analyses of the main mineralogical phases and microscopic investigation of the relationships between the enclaves and their host rocks have been used to decipher the processes that took place during magma differentiation differentiation trends and mineralogical composition of cognate enclaves and host rocks indicate that clinopyroxene and amphibole fractionation in mid crustal magmatic chambers represented the most widespread evolutionary process in the study area xenolith assimilation evidenced at microscopic scale took place mostly by liquid liquid and solid liquid interdiffusion and locally may be quantitatively important mixing processes have been inferred for dacites and for garnet bearing andesites

the stratigraphy of a proximal late hercynian pyroclastic sequence the vilancos region of the pyrenees volcanic activity the result of crustal differentiation during the hercynian orogeny generated eight explosive eruptions in the vilancos region of the spanish pyrenees the volcanic products comprise the erill castell volcanic formation of stephanian age which crops out as a 20 km long wnw trending strip 2 km wide dipping steeply to the south the vilancos region represents a small fragment of an originally extensive regional terrain of silicic centres the explosive eruptions mainly generated strongly peraluminous and phenocrystal garnet bearing subaerial ignimbrite facies proximal intra formational breccias represent a substantial volume of the preserved erupted product and one phreatoplinian deposit is exposed mass flow deposits are common and small volume basalt andesite and rhyolite lava flows minor tuffs and palaesols also occur electron microprobe data show that each garnet bearing member of the vilancos region has a distinct garnet composition this is used as geochemical fingerprinting tool to aid mapping and correlation between proximal intra formational breccias and ignimbrite of the same eruption within one debris flow deposit the vilancos breccia member at least three garnet populations occur two of these are derived from pyroclastic members within the mapped region the other comes from an unexposed rhyolite lava source

contrasting patterns of early twenty first century glacier mass change in the himalayas glaciers are among the best terrestrial climate indicators an important water resource in mountains1 2 and a major contributor to global sea level rise3 4 in the hindu kush karakoram himalaya region hkkh a paucity of appropriate glacier data has prevented a comprehensive assessment of current regional mass balance5 however there are indirect evidences of a complex pattern of glacial responses5 8 in reaction to heterogeneous climate change signals9 here we provide the first coherent data set of detailed glacier thickness changes over the hkkh during 2003 2009 by combining satellite laser altimetry and a global elevation model in the eastern central and south western parts of the hkkh glacier wastage is widespread with regional thinning rates up to 0 66 0 09 m a 1 in the jammu kashmir region conversely in the karakoram glaciers are close to balance with only a slight thinning of 0 07 0 04 m a 1 regionally averaged thinning rates under debris mantled ice are similar to those of clean ice despite insulation by debris covers the 2003 2008 specific mass balance for our hkkh study region is 0 21 0 05 m a 1 water equivalent we significantly less negative than the global average of 0 7 m a 1 we for glaciers and ice caps4 10 this difference is mainly an effect of the balanced glacier mass budget in the karakoram the corresponding hkkh sea level contribution is 0 035 0 009 mm a 1 amounting to 1 of the present day sea level rise11 our 2003 2008 mass budget of 12 8 3 5 gt a 1 is more negative than recent satellite gravimetry based estimates of 5 6 gt a 1 over 2003 2010 ref 12 for the mountain catchments of the indus and ganges basins13 the glacier imbalance contributes 3 5 and 2 0 respectively to the annual average river discharge13 and up to 10 for the upper indus basin14

the volcanogenetic significance of garnet bearing minor intrusions within the borrowdale volcanic group eskdale area cumbria a number of garnetiferous minor intrusions have been mapped within the borrowdale volcanic group they underlie garnetiferous extrusive volcanic rocks which occur toward the top of a sequence of ignimbrite and lava the airy s bridge formation which is the product of a major caldera forming eruptive episode garnet and whole rock geochemistry indicate that most of the intrusions are indistinguishable from garnetiferous dacite forming the final eruptive unit of the airy s bridge formation a co magmatic link is therefore postulated one of the intrusions which intrudes the airy s bridge formation is distinct and may be related to the later eskdale pluton it is suggested that following the emplacement of ignimbrites forming the basal half of the airy s bridge formation caldera collapse partially sealed a fissure conduit system and degassed garnet bearing magma was intruded as dykes and sills and locally extruded as a post explosive lava dome it is also postulated that garnet crystallized in a high level magma chamber p

origin and evolution of a peraluminous silicic ignimbrite suite the violet town volcanics the violet town volcanics are a 373 ma old comagmatic s type volcanic sequence mainly comprising crystal rich intracaldera ignimbrites rock types vary from rhyolites to rhyodacites all containing magmatic cordierite and garnet phenocrysts variation in the suite is primarily due to fractionation of early crystallized quartz plagioclase and biotite plus minor accessory phases in a high level magma chamber prior to eruption early magmatic crystallization occurred at around 4 kb and 850 c with melt water contents between 2 8 and 4 wt this high temperature markedly water undersaturated restite poor granitic magma was generated by partial melting reactions involving biotite breakdown in a dominantly quartzofeldspathic source terrain leaving a granulite facies residue

origin and evolution of mid cretaceous garnet bearing intermediate and silicic volcanics from canterbury new zealand abstract the mt somers volcanics are part of a suite of mid cretaceous 89 2 ma intermediate to silicic volcanics erupted onto an eroded surface of torlesse sediments rock types vary from basaltic andesite to high silica rhyolite andesites are medium to high k with phenocrysts of plagioclase orthopyroxene and pigeonite dacites are peraluminous and commonly contain granulite facies xenoliths and garnet xenocrysts equilibrium mineral assemblages indicate metamorphic pressures of close to 6 kbar at 800 c rhyolites are peraluminous with phenocrysts of quartz sanidine plagioclase biotite garnet and orthopyroxene the ferromagnesian phases show textural evidence of magmatic crystallization and are chemically distinct from xenocryst phases in dacites equilibrium assemblages indicate that early magmatic crystallization occurred at close to 7 kbar 20 km depth at above 850 c with melt water contents of less than 3 5 major element contents trace element contents and an initial 87 sr 86 sr ratio of 0 7085 indicate that the rhyolites formed by partial melting of dominantly quartzo feldspathic torlesse sediments leaving a granulite facies residue the chemical variation displayed by the rhyolites is best explained by fractional crystallization of the observed high pressure phenocryst assemblage most elements show a compositional gap between rhyolite and dacite the major element trace element and sr isotope compositions of the intermediate lavas are best explained by assimilation of lower crustal material combined with fractional crystallization in mantle derived tholeiitic magmas magmatism was the result of heat and magma flux from the mantle during the change from compressive to extensional tectonics after the culmination of the rangitata orogeny

sm nd garnet age for the ordovician borrowdale volcanic group english lake district garnets separated from andesites and dacites of the calc alkaline borrowdale volcanic group are highly enriched in heavy rare earth elements hree relative to their host rocks d gt yb from 9 in andesite to 37 in dacite sm nd ratios and d gt lree show a wide range probably resulting from small quantities of an ree rich impurity in the separates the four garnet host rock pairs analysed yield sm nd ages identical within analytical error of a weighted mean of 457 4 ma the borrowdale group overlies upper llanvirn sediments and is unconformably overlain by mid caradoc the age of 457 ma is considered to be the best estimate available for the age of the llandeilo as the samples analysed are from the lower part of the group the age suggests that a lower palaeozoic timescale intermediate between those of gale et al 1979 and mckerrow et al 1980 might be the most appropriate

are strongly peraluminous magmas derived from pelitic sedimentary sources igneous compositions that require the presence of a phase more aluminous than biotite are here designated as strongly peraluminous ps such compositions are common but subordinate in felsic rocks and exceedingly rare in more mafic rocks the term s type has been applied to many igneous rocks based largely or even solely upon their ps compositions neglecting or placing less emphasis on other criteria for sedimentary parentage in chappell and white s i and s type classification system the s type designation was in fact initially restricted to granites which were thought to have been derived from a chemically mature strongly weathered pelitic shaly source application of chappell s and white s criteria together with others based upon isotopic and phase equilibria considerations leads to the following conclusions about ps igneous rocks worldwide 1 very few ps rocks are derived entirely from pelitic sources 2 a majority are derived largely from intermediate to felsic crustal sources including

calculated relationships between activity of alumina and phase assemblages of silica saturated igneous rocks petrogenetic implications of magmatic cordierite garnet and aluminosilicate abstract many peraluminous igneous rocks are characterized by the presence of al rich minerals such as cordierite garnet and aluminosilicate polymorphs clearly one of the important thermodynamic intensive variables controlling the stability of these minerals relative to al poor phases such as ortho and clinopyroxene must be the activity of al 2 o 3 a al 2 o 3 in the melt calculated phase relationships of anhydrous mineral assemblages in equilibrium with quartz saturated liquids show that at crustal pressures less than about 10 kbar garnet cordierite and aluminosilicate are only likely to crystallize from melts in which a al 2 o 3 is up to one order of magnitude higher than that required for orthopyroxene clinopyroxene crystallization in spite of this peraluminous granitoid liquids saturated with orthopyroxene garnet or orthopyroxene cordierite do not ordinarily contain significantly larger amounts of excess al al in excess of that required to form feldspars than peraluminous liquids saturated with orthopyroxene clinopyroxene these observations indicate that there must be profound compositional controls on the activity coefficient of al in silicic melts and the strongest of such controls appears to be the total alkali content of the melt the activity coefficient of al in silicic melts varies directly with total alkali oxide content so that alkali poor melts can become markedly peraluminous without ever becoming saturated in aluminous phases whereas alkali rich melts of similar normative corundum content can crystallize garnet cordierite or even aluminosilicate because activity of alumina in a silicic melt is not a simple function of excess al content classification schemes for silicic igneous rocks based on model mineralogical assemblages which reflect the value of the thermodynamic effective concentration of al during crystallization convey more petrologic information than those based on chemical parameters such as normative corundum content or alumina saturation index

the significance of garnet in the permo carboniferous volcanic rocks of the pyrenees garnet occurs within rhyolitic to dacitic lavas ignimbrites and volcaniclastic sediments of the pyrenean calc alkaline permo carboniferous volcanic rocks on the basis of texture and major and trace element composition the garnet is interpreted as having a phenocrystal as opposed to a xenocrystal or restite origin the pyrenean silicic volcanics are strongly peraluminous consistent with derivation as a partial melt from a sedimentary source they were erupted contemporaneously with the hercynian thermal anomaly which produced regional granulite facies metamorphism and anatectic granites the late hercynian granodiorites were also intruded at about this time geochemical data suggest that the petrogenesis of the volcanic rocks differed from that of the granodiorites ree garnet matrix partition coefficients for garnets from a welded rhyolitic ignimbrite are similar to those reported for other phenocrystal garnets in rhyolites ree abundances imply that the garnets crystallized from a hree depleted melt and this is considered to reflect the effects of garnet in the restite experimental constraints suggest that the garnet crystallized at pressures 4 5kb implying that the rhyolites originated from 14 17km depth and were erupted rapidly from these depths in order for the garnet to survive these figures place constraints on the thermal regime prevailing in the late stages of the hercynian orogeny

recycling processes in granite granodiorite complex genesis the querigut case studied by ndsr isotope systematics abstract using the isotopic rb sr and sm nd petrogenetic tracers we have studied the calc alkaline plutonic complex of querigut pyrenees france which is famous for its acid to mafic rock association and is a typical post tectonic hercynian granitoid its age of 280 m y is already known 2 23 24 and our purpose is to examine the relationship between its different petrographic units and the problem of their source composition the sm nd isotopic results rule out any genetic process involving a unique homogeneous source and imply the presence of old recycled continental materials in contrast the rb sr isotope system seems to have been homogenized by hot fluids maybe post magmatic this is also true for pb isotopes as shown previously by michard vitrac et al 18 on the basis of the isotopic results and the major element data a model of combined fractional crystallization assimilation of country rocks is proposed for the basic part of the complex in contrast acid parts are mainly the result of the continental anatexis this study also constrains the basement s age 1200 1900 m y of the area and suggests a scheme for the gological history of the eastern pyrenees

caldera like structures related to permo carboniferous volcanism of the catalan pyrenees ne spain abstract the permo carboniferous volcanism of the catalan pyrences produced calc alkaline orogenic rocks with a predominance of rhyolitic and rhyodacitic pyroclastic deposits on the basis of the regional stratigraphic tectonic relationships and facies analysis of sedimentary and pyroclastic deposits the existence of four permo carboniferous basins which acted as volcanotectonic depressions has been deduced the origin of these basins seems to be related to the movement of regional strike slip faults which formed during the permo carboniferous compressive deformation caldera like structures which in some cases affected the entire basin occurred in each basin these caldera like structures seem to follow a similar pattern in three of these basins each taking place when the basin structure was already developed and continental sedimentation had started volcanism caused a high subsidence rate during the most important explosive periods by a mechanism similar to that of caldera collapse but after the subsidence structure has been established moreover a caldera structure formed by the collapse of a central volcanic edifice is also suggested in the western margin of the fourth basin

interannual flow dynamics driven by frontal retreat of a lake terminating glacier in the chinese central himalaya abstract most lake terminating glaciers in the himalaya retreat rapidly due to periodic frontal ice loss at their terminus but long term observations are still limited regarding their flow dynamics which is crucial for understanding the processes of ice mass loss and proglacial lake growth we present multi decadal surface velocity dynamics of the longbasaba glacier a rapid retreating lake terminating glacier in the chinese himalaya using an image feature tracking method applied on optical satellite images between 1989 and 2018 we show that in companion with rapid retreat 51 7 m a 1 its lower 5 km tongue experienced high interannual fluctuations in velocity comprising periodic acceleration and slowdown in 1989 1995 and 2001 2010 and a recent remarkable acceleration since 2012 the temporal variation of longitudinal velocity distribution indicates an upward propagation of the lake ward acceleration namely a downglacier inversion of strain from compression to extension this propagation is coupled to the retreat of the glacier front and occurs along the lowermost 1 1 5 km lake adjacent section as the proglacial lake expands the most recent acceleration of the near lake section since 2012 has likely facilitated a dynamic thinning on its upper sections where flow acceleration started two years later in 2014 this pattern contrasts markedly with a nearby decelerating land terminating glacier which has experienced a much slower retreat rate 7 8 m a 1 and the same magnitude of mean thinning rate at its lower part since 2000 our results confirm the strong influence of the proglacial lake on ice flow dynamics and suggest that lake ice interactions are important to consider when analyzing interpreting or modeling dynamics of rapidly retreating lake terminating glaciers in the himalayas as well as around the world

controls on the mineralogy of s type volcanic and plutonic rocks abstract far from being simply two mica granites s type rocks contain highly diverse mineral assemblages the most important chemical factors influencing the mineralogy of an s type rock are peraluminosity bulk feo mgo mg mg fe k na ca and the fugacities of volatile species such as h2o hf h3bo3 and o2 however it is not just initial melt chemistry that determines the mineral assemblage the pressure and temperature of crystallization exert major effects as magmas evolve the p t conditions volatile fugacities and melt chemistry change often leading to changes in stable mineralogy many s type granites and silicic volcanic rocks contain partly or completely re equilibrated mineral assemblages recognition of these may provide important information about early crystallization conditions and the nature of the magma source terrains

almandine garnet phenocrysts in a 1 ga rhyolitic tuff from central india we report on the newly discovered almandine garnet phenocrysts in rhyolitic ignimbrites sukhda tuff in the precambrian churtela shale formation of the chhattisgarh supergroup in central india shrimp ages of igneous zircon from the ignimbrites range from 990 ma to 1020 ma these ignimbrites exhibit characteristic eutaxitic texture with compacted curvilinear glass shards with triple junctions quartz commonly embayed bluish cathodoluminescence and albite altered but retaining ghosts of twinning are common phenocrysts others are apatite ilmenite rutile magnetite zircon monazite and garnet there are no metamorphic or granitic xenoliths in the ignimbrites garnet grains occur as isolated broken isotropic crystals with sharp or corroded boundaries in a very fine grained groundmass of volcanic ash that consists principally of albite quartz magnetite and glass they do not have any systematically distributed inclusions a few have penetratively intergrown phenocrysts of apatite ilmenite rutile and zircon which we interpret as subophitic texture extensive sem bse imaging of more than 100 grains and electron microprobe traverses across about 30 grains showed no zoning or systematic compositional variability common metamorphic garnets are usually zoned with respect to fe mg mn and typically have mineral inclusions we infer therefore that these observed garnets are not metamorphic xenocrysts the average major oxide composition of analysed garnets from five different horizons within the sukhda tuff spanning approximately 300 m of the stratigraphic section have very small standard deviation for each element which is suggestive of a single magmatic source phenocrysts of quartz including those in contact with coexisting garnets show blue scanning electron cl indicating rapid cooling from high temperature this suggests that adjacent coexisting garnets are not slowly cooled restites we conclude on the basis of texture mineral chemistry and absence of any indicative xenoliths or xenocrysts that these almandine garnets al 78 7 py 12 3 gr 7 4 sp 1 6 are phenocrysts within the sukhda tuff almandine of such composition is stable under high pressure we infer that almandine crystallized at lower crustal depths in a magma that ascended very rapidly and may have erupted explosively

modeling the collapse of hebes chasma valles marineris mars physical modeling and detailed mapping of hebes chasma provide new insights into the crustal composition and origin of the valles marineris region of equatorial mars hebes chasma is a 315 km long and 8 km deep closed depression containing distinctive landforms that include diapirs and extensive allochthonous flows that end in pits a central puzzle of hebes chasma is how and where 10 5 km 3 of missing material disappeared our physical models tested the hypothesis that the chasma formed by collapse and removal of material from below gravity driven collapse in the models reproduced all the chasma9s main landforms as subsidence evolved from early sagging of the upper surface to inward collapse and removal of material to emergence of diapirs and low gradient flows the models and geologic evidence suggest that hebes mensa arched upward diapirically and raised deep stratigraphy almost level with the chasma rim if the chasma indeed collapsed by subsurface drainage as occurred in the models the upper 8 10 km of deposits at hebes must have been solid to depths of 5 km but viscous at greater depths the materials removed could not have consisted mainly of basalt flows instead they probably were a mixture of hydrated and nonhydrated salts water ice liquid water and insoluble likely basaltic particles the proportions of these constituents are unknown but constrained because the material drained from the subsiding chasma and apparently contributed to the outburst floods released down neighboring echus chasma and kasei valles

glacier surface velocities in alpine terrain from optical satellite imagery accuracy improvement and quality assessment the worldwide retreat of mountain glaciers has important consequences for the water food and power supply of large and densely populated areas in south and central asia successful mitigation of the hydrological impacts on societies as well as assessing glacier related hazards require large scale monitoring of glacier dynamics however detailed glaciological data from the asian highlands are lacking due to its size and difficult accessibility we have applied a novel technique for precise orthorectification co registration and sub pixel correlation of advanced spaceborne thermal emission and reflection radiometer aster satellite imagery to derive surface velocities of himalayan glaciers our approach allows for the correction of offsets due to attitude effects and sensor distortions as well as elevation errors if a digital elevation model dem from the shuttle radar topography mission srtm was used for orthorectification after post processing the error on the displacements is on the order of 2 4 m per correlation translated into annual velocities this error is reduced increased when the correlated images are more less than a year apart through application of a filtering procedure and several quality tests the consistency of the results is validated to provide confidence in the remotely sensed velocity measurements despite the lack of ground control this novel approach allows fast easy and economically viable acquisition of detailed glaciological data in areas of difficult access and provides a means for large scale monitoring of glaciers in high mountainous terrain

an andesitic sill complex in the southern permian basin volcanogenetic model and stratigraphic implications subvolcanic intrusions are highly variable in shape and structure and occur in nearly all parts of the upper crust as a result of extensive volcanic activity processes of subvolcanics interacting with the host rock are insufficiently understood as they are rarely exposed in the southernmost part of the flechtingen altmark subprovince sub volcanic rocks of the flechtingen volcanic complex fvc are exposed in several quarries it is built up of silicic tuffs ignimbrites and lava flows but also of intermediate lavas and extended sill sheets additionally major granitic intrusions exposed by drillings are associated with the fvc in the mammendorf quarry a sill intruded in between lithified turbiditic series of early carboniferous visean serphukovian age at the base and widely consolidated volcanoclastic deposits of late carboniferous late pennsylvanian age at the top various magma host rock interactions were found indicating brittle and ductile deformation patterns occurring at the basal contact and secondary fluidal mixing predominantly occurring at the top contact most probably caused by fluids accompanying the intruding magma we present an extended volcanogenetic model for the fvc volcanic activity initiated at 302 3 ma with fallout deposits represented by mostly re deposited silicic ashfall deposits of the flechtingen formation and cumulated in depositing major ignimbrite series most likely forming a caldera later the sills intruded at the rheological boundary of the lithified mississippian turbiditic series and the partly consolidated volcanoclastic series finally major granitic intrusions emplaced in the basement rocks at around 298 4 ma the study contributes to clarify stratigraphic constraints of late carboniferous to early permian continental deposits and sheds light on stratigraphy of significant late paleozoic volcanic deposits of the flechtingen altmark subprovince in the southern permian basin

the origin of garnets in andesitic rocks from the northland arc new zealand and their implication for sub arc processes an unusual andesitic suite from the miocene volcanic arc in northland new zealand comprises pyroxene andesite and garnetbearing hornblende pyroxene hornblende and biotite hornblende andesites garnet crystals occur as 1 10 mm single crystals or more commonly as two or more annealed crystals and as garnetite lenses the andesitic rocks also contain enclaves of high mgo pyroxenite hornblendite and pyroxene hornblende gabbro as well as highal2o3 hornblende gabbro garnet hornblende gabbro and anorthosite garnet crystals in the andesitic volcanic rocks and in the enclaves show comparable compositional ranges zoning patterns and inclusions which indicate that they share a common petrogenetic history they can be grouped into four distinct types on the basis of mode of occurrence chemical composition and zoning patterns which leads to their interpretation as antecrysts rather than orthocrysts the compositions of the garnets as well as their included mineral assemblages reflect a petrogenetic trend from high temperature pyroxene bearing high mg garnet to low temperature fe rich garnet at relatively constant pressure well preserved zoning patterns in particular those of the caand mg rich garnets reflect processes within a deep crustal arc environment later assimilation is suggested by some zoning patterns that show decreasing ca and increasing fe and mn contents the garnets are interpreted as being derived by disintegration of discrete but closely related cumulate material that formed at pressures of 8 10 kbar the host volcanic rocks and their garnet crystals together with the enclaves thus represent a consanguineous mixture of liquid and solid components that developed where subduction related magmas ponded and interacted at or near the base of the crust together they represent a rare snapshot of the processes and components that produce arc type rocks

the origin of pyrenean hercynian volcanic rocks france spain ree and smnd isotope constraints reply abstract the hercynian orogeny of the pyrenees generated a suite of basalt to rhyolite calc alkaline volcanic rocks that were erupted subaerially these melts may either have been generated above a subduction zone or by lower crustal melting after input of mantle derived magmas in an extensional environment sm nd garnet whole rock mineral isochrons date a rhyolitic ignimbrite from the coll de oli ignimbrite member at 313 14 ma 2 mswd 0 7 and a rhyolitic lava of the coll de pi region at 320 2 ma 2 mswd 0 2 these ages suggest that some of the volcanism was synchronous with high temperature low pressure metamorphism and partial melting deep in the hercynian crust as seen in rocks now exposed in the axial and northern pyrenean zones and dated by u pb on zircon at between 309 5 and 315 5 ma the silicic volcanic rocks are peraluminous and have highly fractionated ree patterns with low abundances of the hree and la yb n 70 mineral and whole rock ree abundances suggest derivation of the silicic rocks by partial melting of a metasedimentary source in equilibrium with garnet and or garnet fractionation in melts derived from peraluminous sources nd isotope compositions of the entire volcanic rock suite mafic silicic compositions are within the same range as those of sediments metamorphosed during the hercynian orogeny and hercynian basement rocks they have mid proterozoic depleted mantle model sm nd ages and do not exhibit mixing trends with mantle sources even the most mafic of the volcanic rocks appear to have interacted extensively with the crust analysis of the chemistry of the volcanic rocks does not unequivocally constrain the hercynian tectonic setting of the pyrenees

evaluation of garnet discrimination diagrams using geochemical data of garnets derived from various host rocks abstract this work is an attempt to evaluate six different garnet discrimination diagrams one binary diagram and five ternary diagrams commonly used by many researchers the mineral chemistry of detrital garnet is a useful tool in sedimentary provenance studies yet there is no clear cut understanding of what garnet type originates from which host lithology several discrimination diagrams exist for garnet showing distinct compositional fields separated by strict boundaries that are thought to reflect specific types of source rocks for this study a large dataset was compiled n 3532 encompassing major element compositions of garnets derived from various host lithologies including metamorphic igneous and mantle derived rocks in order to test the applicability of the various discrimination schemes the dataset contains mineral chemical data collected from the literature complemented with some new data n 530 from garnet bearing metamorphic and ultramafic rocks in austria and norway discrimination of the tested diagrams only works for a small group of garnets derived from mantle rocks granulite facies metasedimentary rocks and felsic igneous rocks for other garnet types the assignment to a certain type of host rock remains ambiguous this is considered insufficient and therefore the evaluated diagrams should be used with great care we further apply compositional biplot analysis to derive some hints towards future perspectives in detrital garnet discrimination

stable isotopic evidence for large scale seawater infiltration in a regional metamorphic terrane the trois seigneurs massif pyrenees france oxygen isotopic analyses of 95 metamorphic and igneous rocks and minerals from a hercynian metamorphic sequence in the trois seigneurs massif pyrenees france indicate that all lithologies at higher metamorphic grades than the andalusite in isograd have relatively homogeneous 18o values the extent of homogenization is shown by the similarity of 18o values in metacarbonates metapelites and granitic rocks 11 to 13 and by the narrow range of oxygen isotopic composition shown by quartz from these lithologies these values contrast with the 18o values of metapelites of lower metamorphic grade 18o about 15 homogenization was caused by a pervasive influx of hydrous fluid mass balance calculations imply that the fluid influx was so large that its source was probably high level groundwaters or connate formation water hydrogen isotopic analyses of muscovite from various lithologies are uniform and exceptionally heavy at d 25 to 30 suggesting a seawater origin many lines of petrological evidence from the area independently suggest that metamorphism and anatexis of pelitic metasediment occurred at depths of 6 12 km in the presence of this water rich fluid the composition of which was externally buffered deep penetration of surface waters in such environments has been hitherto unrecognized and may be a key factor in promoting major anatexis of the continental crust at shallow depth three types of granitoid are exposed in the area the leucogranites and the biotite granite quartz diorite are both mainly derived from fusion of local paleozoic pelitic metasediment because all these rocks have similar whole rock 18o values 11 to 13 the post metamorphic biotite granodiorite has a distinctly different 18o 9 5 to 10 0 and was probably derived from a deeper level in the crust rare mafic xenoliths within the deeper parts of the biotite granite quartz diorite also have different 18o 8 0 to 8 5 and possibly represent input of mantle derived magma which may have provided a heat source for the metamorphism