on the origin and post depositional history of widespread massive ash deposits the case of intermediate brown tuffs ibt of lipari aeolian islands italy abstract we analysed a widespread massive ash unit outcropping on the island of lipari which belongs to the intermediate brown tuffs ibt succession of the aeolian islands italy the use of a multidisciplinary approach that integrates textural petrological and pedological methods allows us to discriminate between syn eruptive and post depositional features the deposits are dominated by uncrystallised blocky glass fragments of homogeneous shoshonitic composition confirming a provenance from hydromagmatic eruptions on the island of vulcano many glass fragments are surrounded by a coating separated by a thin void of syn eruptive origin due to alteration by aggressive acid gases in the eruptive cloud the lack of this coating in the northern part of lipari can be explained as a progressive dispersion of the gases far from the vent and or to post depositional processes the degree of soil development significantly increases from south soil profiles p1 and p2 at valle muria to north p3 and p4 at madoro and chiesa vecchia sites respectively as a response to a decrease in slope steepness which has brought about a progressive deepening of the pedogenetic front on gentler landforms and conversely its rejuvenation on steep slopes the relatively poor to moderate degree of pedogenic evolution of the studied ibt unit is consistent with its emplacement during part of the last glacial period

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

magma storage and ascent at lipari island aeolian archipelago southern italy at 223 81 ka the role of crustal processes and tectonic influence fluid inclusion studies together with volcanological and petrochemical data allow reconstruction of the magma feeding system of basaltic andesitic to andesitic activity during the oldest and intermediate stages of development of lipari island 223 81 ka a major magma storage zone is active during the overall investigated time span at depths of 22 km close to the crust mantle moho transition at which mantle derived mafic magmas tend to accumulate due to neutral buoyancy conditions beneath central type volcanoes m mazzacaruso m s angelo m chirica costa d agosto a shallower magma reservoir is located within the upper crust at 5 5 3 5 km associated with a major lithological discontinuity for fissural type volcanoes timpone ospedale monterosa m chirica tectonic structures are suggested to influence further magma ascent and storage at mid crustal depths 14 km with no ponding at shallower levels partial crustal melting processes at the roofs of the deep magma reservoirs 17 km are invoked to explain the origin of cordierite bearing lavas beneath m s angelo and m chirica costa d agosto volcanoes which were active during the intermediate stages of development of lipari 105 81 ka the generation of felsic anatectic melts in the lower crust could have created density and rheologic barriers to impede the passage of mafic melts and promote their ponding with influence on the subsequent evolution of lipari volcano

modeling the magma plumbing system of vulcano aeolian islands italy by integrated fluid inclusion geobarometry petrology and geophysics an integrated petrological geophysical and fluid inclusion model is presented for the internal structure of the active vulcano island southern tyrrhenian sea the present structure of the magma storage system in the crust consists of two major deep accumulation zones located at 17 21 km and 8 13 km depth plus a minor one at 1 5 km depth beneath fossa cone the deepest magma accumulation zone contains mafic melts and is located at the transition between the upper mantle and a granulitic lower crust this reservoir has been active since the onset of the exposed volcanism and has undergone continuous fractional crystallization crustal assimilation and mixing with primary melts from the mantle slightly differentiated magmas from the deep reservoir feed a shallower accumulation zone in the middle and upper crust or erupt directly to the surface through lateral vents deep melts probably enter the shallowest reservoir shortly before magma outbreak at the surface and may represent the trigger of eruptions according to our model magmatic eruptions at vulcano are related to deep magma dynamics whereas most of the changes in the geochemical and geophysical parameters observed at the active cone in the last century could be due to shallow depth modification of rock permeability possibly as a result of cone gravitative instability and or tectonic events implications for strategies of volcano monitoring and for forecasting eruptions are briefly discussed

silica rich melts in quartz xenoliths from vulcano island and their bearing on processes of crustal anatexis and crust magma interaction beneath the aeolian arc southern italy o 3 6 wt contents two types of inclusions can be distin guishedbasedontheirtimeofentrapmentandincompatibletraceelement ite concentrations one type late ite enrichedinclusions has trace element characteristics that resemble thoseof the metamorphic rocks of the calabro peloritano basement ofthe adjacent mainland other inclusions early ite depleted have variable ba rb sr and cs and low nb zr and rareearth element ree contents their ree patterns areunfractionated with a marked positive eu anomaly geochem ical modelling suggests that the ite depleted inclusions cannotbe derived from equilibrium melting of calabro peloritanometamorphic rocks ite enriched inclusions can be modelledby large degrees 480 of melting of basement gneisses andschists leaving a quartz rich residue represented by the quartz rich xenoliths glass inclusions in quartz rich xenoliths repre sent potential contaminants of aeolian arc magmas interactionbetweencalc alkalinemagmasandcrustalanatecticmeltswithacomposition similar to the analysed inclusions may generatesignificant enrichment in potassium in the magmas however ite contents of the melt inclusions are comparable with orlower than those of vulcano calc alkaline and potassic rocks this precludes the possibility that potassic magmas in theaeolian arc may originate from calc alkaline parents throughdifferent degrees of incorporation of crustal melts

antigorite induced seismic anisotropy and implications for deformation in subduction zones and the tibetan plateau the present study which is a follow up of the journal of geophysical research paper by ji et al 2013a provides a new calibration for both seismic and fabric properties of antigorite serpentinites comparisons of the laboratory velocities of antigorite serpentinites measured at high pressures with crystallographic preferred orientation data measured using electron backscatter diffraction techniques demonstrate that seismic anisotropy in high t serpentinite which is essentially controlled by the antigorite c axis fabric is independent on the operating slip system but strongly dependent on the regime and magnitude of finite strain experienced by the rock extrapolation of the experimental data with both pressure and temperature suggests that vp anisotropy decreases but shear wave splitting vs and vp vs increase with increasing pressure in either cold or hot subduction zones for a cold steeply subducting slab antigorite is most likely deformed by nearly coaxial flattening or trench parallel movements forming trench parallel seismic anisotropy for a hot shallowly subducting slab however antigorite is most likely deformed by simple shear or transpression trench normal seismic anisotropy can be observed when the subducting dip angle is smaller than 30 the geophysical characteristics of the tibetan plateau such as strong heterogeneity in vp vs and attenuation shear wave splitting and electric conductivity may be explained by the presence of strongly deformed serpentinites in lithospheric shear zones reactivated along former suture zones between amalgamated blocks hydrated zones of subducting lithospheric mantle and the crust mantle boundary if the temperature is below 700 c in the region of interest

gypsum formation in non calcareous building sandstone a case study of scrabo sandstone this paper addresses one central issue of building stone research an origin for calcium in gypsum formation in non calcareous sandstones a comparative study of scrabo sandstone from outcrops and a 120 year old building in central belfast shows how weathering has significantly altered the mineralogy preliminary results suggest that the occurrence of gypsum throughout the stone blocks is related to chemical reactions between a pore filling mineral constituent actinolite ca mg amphibole and sulphur oxides from urban pollution these findings advocate an internal source of calcium for gypsum formation and provide new evidence to explain the enhanced decay displayed in some scrabo sandstone copyright 2001 john wiley sons ltd

high resolution quantitative imaging of plagioclase composition using accumulated backscattered electron images new constraints on oscillatory zoning oscillatory zoning in plagioclase is investigated at small scale 10 m using accumulated backscattered electron bse images as high resolution imaging method combined with electron microprobe quantitative analysis gray value profiles across these images can be calibrated for an content with a resolution of 0 5 mol an applied to oscillatory zoned crystals this new application of bse imaging allows better characterization of zoning patterns along a profile and quantification of wavelength amplitude and shape of the oscillations we also obtain high resolution information on the morphology of growth zones boundaries this approach allows us to better classify the different types of oscillations and concentric zoning dissolution is more frequent than usually recognized major resorption surfaces crosscut several growth zones irregular 5 10 m saw tooth zones are delimited by faint wavy dissolution surfaces and must be distinguished from small scale oscillations 1 3 m with straight boundaries this suggests at least two mechanisms for the formation of these zoning patterns faint oscillations are probably caused by local kinetic control whereas wavy dissolution surfaces involve magma chamber dynamics

formation of spinel cordierite feldspar glass coronas after garnet in metapelitic xenoliths reaction modelling and geodynamic implications spinel cordierite k feldspar plagioclase glass form coronas around garnet in metapelitic xenoliths at el hoyazo and mazarron two localities of the neogene volcanic province nvp of se spain the presence of fresh glass quenched melt in all phases shows that corona development occurred under partial melting conditions algebraic analysis of mass balance in the nckfmash system suggests the reaction grt sil bt pl spl crd kfs melt as the most plausible model for the development of coronas in the el hoyazo sample and indicates that biotite was required as reactant for the formation of cordierite the p t conditions for the formation of coronas are estimated at 820 50 c 4 5 0 6 kbar at el hoyazo and 820 50 c 4 0 0 4 kbar at mazarron the el hoyazo xenoliths record a complex p t history characterized by early melt production during heating and additional melting during decompression a local cooling event characterized by minor retrograde reaction and melt crystallization preceded ascent and eruption this study shows that detailed xenolith analysis may be used to track magma evolution in a chamber

seismic velocities anisotropy and shear wave splitting of antigorite serpentinites and tectonic implications for subduction zones 1 antigorite the high temperature ht form of serpentinite is believed to play a critical role in various geological processes of subduction zones we have measured p and s wave velocities vp and vs anisotropy and shear wave splitting of 17 serpentinite samples containing 90 antigorite at pressures up to 650 mpa the new results combined with data for low temperature lt lizardite and or chrysolite reveal distinct effects of lt and ht serpentinization on the seismic properties of mantle rocks at 600 mpa vp 5 10 and 6 68 km s vs 2 32 and 3 67 km s and vp vs 2 15 and 1 81 for pure lt and ht serpentinites respectively above the crack closure pressure 150 mpa the velocity ratio of antigorite serpentinites displays little dependence on pressure or temperature serpentine contents within subduction zones and forearc mantle wedges where temperature is 300 c should be at least twice that of previous estimates based on lt serpentinization the presence of seismic anisotropy high pressure fluids or partial melt is also needed to interpret ht serpentinized mantle with vp 1 81 the intrinsic anisotropy of the serpentinites 3 8 16 9 with an average value of 10 5 for vp and 3 6 18 3 with an average value of 10 4 for vs is caused by dislocation creep induced lattice preferred orientation of antigorite three distinct patterns of seismic anisotropy correspond to three types of antigorite fabrics s l and ls tectonites formed by three categories of strain geometry i e coaxial flattening coaxial constriction and simple shear respectively our results are thought to provide a new explanation for various anisotropic patterns of subduction systems observed worldwide

relationships among crustal structure volcanism and strike slip tectonics in the lipari vulcano volcanic complex aeolian islands southern tyrrhenian sea italy abstract the lipari vulcano volcanic complex lvvc aeolian arc southern tyrrhenian sea italy develops along a strike slip fault system that bisects the aeolian arc the lvvc crustal structure is investigated by applying seismic methods to two data sets p wavefronts generated by local and distant events constrain the shallow velocity structure dss data provide shape and depth of the main crustal discontinuities the obtained velocity model shows that the lvvc shallow structure is characterized by the presence of two sharp lateral discontinuities the northern discontinuity bounds a low velocity basin like structure including the la fossa caldera and mt guardia caldera depressions the southern discontinuity coincides with the southern boundary of a high velocity diffractor located beneath the la fossa cone direct modeling of dss data define three crustal discontinuities showing a complex geometry the intra crustal interfaces and the moho discontinuity show an upheaval beneath the lvvc central sector the estimated crustal velocities are lower than those generally reported for the continental crust this feature is due to the high heat flux and fluid circulation affecting the lvvc area the ratio between the thickness of the upper and lower crust and the presence of the moho upheaval are consistent with that reported for continental areas affected by extensional strain the collected geophysical data combined with volcanological and structural information indicate that a the mt guardia and la fossa caldera depressions represent the surface expression of a single structure whose formation is mainly due to tectonic processes b the lvvc crustal structure and the evolution of the volcanism are consistent with those recognized in zones of transition from arc related to rift volcanism in addition results of a preliminary mechanical analysis based on the available structural data indicate low values of the ratio between magmatic overpressure and tectonic stress this suggests a passive mechanism of mantle upwelling the mantle upwelling is due the post collisional normal strike slip tectonics affecting the aeolian arc

seismic anisotropy and shear wave splitting in lower crustal and upper mantle rocks from the ivrea zone experimental and calculated data to quantify the relationships between anisotropy s wave splitting and tectonics we determined the seismic properties of lower crustal and upper mantle rocks outcropping in the ivrea zone northern italy we obtained p and s wave seismic velocities by laboratory direct velocity measurements and or by calculations based on the modal compositions of the rocks the lattice preferred orientations lpos and the single crystal stiffness coefficients measured p and s wave velocities 6 0 7 5 km s 1 and 3 6 4 2 km s 1 are typical of the lower crust the p wave anisotropy is in the range 0 10 shear wave birefringence is in the range 0 0 0 6 km s 1 with typical values between 0 0 and 0 2 km s 1 in many cases the birefringence is clearly related to fabric elements foliation lineation mafic rocks such as anorthosite or pyroxene bearing gabbros exhibit low p wave anisotropies 5 and low shear wave birefringences less than 0 1 km s 1 in contrast the seismic properties of felsic rocks such as biotite bearing gneisses and mafic rocks such as amphibolites display high vp anisotropy 10 and strong birefringence 0 3 km s 1 biotite and amphibole preferred orientations clearly control seismic anisotropy and particularly shear wave splitting in these rocks maximum splitting is observed in directions parallel to the foliation with the fast split shear wave polarized parallel to the foliation plane to have an overview of the seismic properties of this lower crustal section at a broader scale we calculated from our data the anisotropic seismic properties of several hypothetical samples that are perhaps more representative of the regional anisotropy than each sample individually for instance the average lower crustal sample displays an anisotropy of 5 5 for p waves and a birefringence around 0 14 km s 1 for s waves propagating parallel to the foliation we observe little splitting for waves propagating at high angle to the foliation

the role of the crust in the magmatic evolution of the island of lipari aeolian islands italy volcanic rocks on the island of lipari show the entire range of sr nd pb isotopic compositions displayed by other islands in the aeolian archipelago the rapid isotopic evolution of subaerial volcanic rocks on lipari towards crustal values together with the appropriate isotopic composition of the neighbouring calabrian crust serre indicate that many geochemical characteristics observed in the lavas can be attributed to contamination and mixing with crustal materials and melts interpretation of the data is complicated by the fact that underplating onto the crust mantle boundary and the specific lithologies present in the crustal section differ underneath each individual sector of the island in the central and northern parts of the island metapelitic rocks were incorporated to provide the more radiogenic sr isotopic compositions of some lavas the products from m guardia in the southern part of lipari where activity is restricted to the last 30 40 ka bear geochemical similarities to the island of vulcano where it is proposed that considerable remobilization of the crust took place in the presence of mafic mantle derived melts on lipari the petrogenetic processes of magma mixing and assimilation dominate over fractional crystallization and the observed increase of k2o over na2o can be correlated with contributions from metapelitic crustal lithologies it is suggested that the variability in isotopic composition and the budget of alkalis na2o versus k2o in the lavas can be explained by invoking a heat source from an intruding asthenospheric morb type mantle into a cooler lithospheric crust mantle during the opening of the tyrrhenian basin

s type granitic magmas petrogenetic issues models and evidence abstract despite a perception that it represents a perverse divergence it is perfectly possible to believe in the existence of s and i type granites and the implications for the nature of their protoliths and to disbelieve in the applicability of the restite unmixing model for chemical variation in granitic magmas white and chappell erected the s i classification with impeccable validity the isotopic evidence demands contrasting source reservoirs for s and i type granitic magmas however the major advance was not the classification but the recognition that highly contrasting parental materials must be involved in the genesis of granitic magmas the restite unmixing model is commonly seen as a companion to the s i classification but it is really a separate issue this model implies that the compositions of granites image those of their source rocks in a simple way however there are other equally valid models that can explain the data and none of them represents a unique solution the most cogent explanation for the high grade metasedimentary enclaves in most s type granites is that they represent mid crustal xenoliths restitic enclaves are either rare or absent inherited zircons in s type rocks are certainly restitic however the occurrence of a substantial restitic zircon population does not imply an equally substantial restitic component in the rest of the rock zircon and zirconium behaviours are controlled by disequilibrium and kinetics and zr contents of granitic rocks can rarely be used to infer magma temperatures since the dominant ages among inherited zircons in lachlan fold belt lfb s type granites are ordovician and proterozoic it seems likely that crust of this age but geochemically different from the exposed rocks not only underlies much of the lfb but also forms a component in the granite magma sources the evidence is overwhelming that the dark microgranular enclaves that occur in both s and i type granites are igneous in origin they represent globules of quenched more mafic magma mingled and modified by exchange with the host granitic magma however magma mixing does not appear to be a significant process affecting the chemical evolution of the host magmas likewise the multicomponent mixing models erected for some granitic rock suites are mathematically nonunique and in some cases violate constraints from isotopic studies s and i type magmas commonly retain their distinct identities this suggests limited source mixing limited magma mixing and limited wall rock assimilation though intermediate types certainly exist they are probably relatively minor in volume crystal fractionation probably plays the major role in the differentiation of very many granitic magmas including most s types especially those emplaced at high crustal levels or in the volcanic environment minor mechanisms include magma mixing wall rock assimilation and restite unmixing isotopic variations within plutons and in granite suites could be caused by source heterogeneities magma mixing assimilation and even by isotopic disequilibrium however source heterogeneity coupled with the inefficiency of magma mixing is probably the major cause of observed heterogeneity normal geothermal gradients are seldom sufficient to provide the necessary heat for partial melting of the crust and crustal thickening likewise fails to provide sufficient heat generally the mantle must be the major heat source this might be provided through mantle upwelling and crustal thinning and possibly through the intra and underplating of mafic magmas upper crustal extension seems to have been common in regions undergoing granitic magmatism migmatites probably provide poor analogues of granite source regions because they are mostly formed by fluid present reactions granitic magmas are mostly formed by fluid absent processes where we do see rare evidence for arrested fluid absent partial melting the melt fraction is invariably concentrated into small shear zones veinlets and small dykes thus it seems likely that dyking is important in transporting granitic magma on a variety of scales and at many crustal levels however one major missing link in the chain is the mechanism by which melt fractions in small scale segregations occurring over a wide area can be gathered and focused to efficiently feed much wider spaced major magma conduits answers may lie in the geometry of the melting zones and in the tendency of younger propagating fractures to curve toward and merge with older ones self organization almost certainly plays a role

rapid honeycomb weathering tafoni formation in greywacke s e australia the development of honeycomb weathering on seawalls of non marine lower cretaceous greywacke built in 1943 and 1949 shows that under certain conditions this type of tafoni is a significant factor in the retrogradation of rocky coasts

calculation of partial melting equilibria in the system na2o cao k2o feo mgo al2o3 sio2 h2o nckfmash a thermodynamic model for haplogranitic melts in the system na2o cao k2o al2o3 sio2 h2o nckash is extended by the addition of feo and mgo with the data for the additional end members of the liquid incorporated in the holland powell 1998 internally consistent thermodynamic dataset the resulting dataset with the software thermocalc is then used to calculate melting relationships for metapelitic rock compositions the main forms for this are p t and t x pseudosections calculated for particular rock compositions and composition ranges the relationships in these full system pseudosections are controlled by the low variance equilibria in subsystems of nckfmash in particular the solidus relationships are controlled by the solidus relationships in nkash and the ferromagnesian mineral relationships are controlled by those in kfmash however calculations in nckfmash allow the relationships between the common metapelitic minerals and silicate melt to be determined in particular the production of silicate melt and melt loss from such rocks allow observations to be made about the processes involved in producing granulite facies rocks particularly relating to open system behaviour of rocks under high grade conditions

weathering of rock art at two sites in the kwazulu natal drakensberg southern africa sediments of the karoo basin in southern africa represent one of the world s finest laboratories for investigating sandstone weathering the natural breakdown of these sandstones most notably in the clarens formation is destroying much of the indigenous rock art heritage that exists there in an attempt to elucidate the operative weathering processes a range of micro climatic rock temperature rock moisture rock chemistry and rock property data have been monitored over a 15 year period at two sites in the kwazulu natal drakensberg results suggest that rock moisture regimes and to a lesser extent rock thermal regimes exert the most damaging influence on san paintings it is argued that granular disintegration and the enlargement of existing sandstone pores and bedding planes close to the rock surface facilitate an increasingly dynamic moisture regime which leads to an accelerating rate of weathering recent technological advances in data collection suggest that a re evaluation of environmental controls may be necessary before weathering at a scale appropriate to the deterioration of rock art can be fully understood the continued existence of indigenous rock art in southern africa depends on investigations aimed at the development of techniques for its preservation

crustal evolution of the hercynian belt of western europe evidence from lower crustal granulitic xenoliths french massif central abstract granulite facies lower crustal xenoliths scavenged by the tertiary basaltic pipes of bournac and roche pointue massif central france have been analysed for major and trace elements and radiogenic sr nd isotope ratios they display wide variations in major elements rare earth elements and isotopes 87 sr 86 sr 0 7041 0 7216 nd 11 9 to 1 5 which tend to correlate with the three different rock types encountered basic and acidic meta igneous and metasediments the basic liquids are of calc alkaline affinity and cumulates are abundant there is a gap in silica content between the basic and acid meta igneous xenoliths the isotopic compositions suggest mixing of old pre existing continental crust represented by the metasediments and mantle derived basic melts which represent juvenile addition to the crust during the hercynian orogeny the basic meta igneous rocks have been contaminated during their emplacement into the crust whereas the surrounding metasediments have suffered partial fusion and contamination by the same liquid producing the hercynian granitoids which have nd and sr initial ratios identical to those of the lower crustal xenoliths the residue from melting may be represented by the acid meta igneous rocks some of which have positive eu anomalies these results indicate that an important basaltic underplating event occurred during the evolution of hercynian orogenic belt although the exact timing of the underplating requires further constraint

sr nd pb o isotopic evidence for decreasing crustal contamination with ongoing magma evolution at alicudi volcano aeolian arc italy implications for style of magma crust interaction and for mantle source compositions abstract new isotopic sr nd pb o data are reported for a suite of basalts mgo up to 10 wt to andesites and associated mineral separates from the island of alicudi aeolian arc southern tyrrhenian sea with the aim of investigating the effects of magma wall rock interaction in continental magmatic systems major and trace elements at alicudi exhibit smooth variations suggesting derivation of the entire suite from a single type of parental magma that underwent fractional crystallisation however 87sr 86sr and 18o values decrease while 143nd 144nd increases with increasing sio2 and decreasing mgo moreover phenocryst phases show isotopic disequilibrium relative to whole rocks and groundmass such an unusual isotope vs major and trace element variation and isotopic disequilibria suggest interaction between magmas and crustal wall rocks but the decrease of 87sr 86sr with increasing differentiation excludes assimilation fractional crystallisation processes we suggest that mafic calcalkaline magmas with primitive sr nd o isotopic signatures were intruded into a deep reservoir where they underwent fractional crystallisation contamination occurred shortly before eruption as the magmas ascended to the surface interactions between magmas and wall rocks were more extensive for the basalts than basaltic andesites and andesites generating a positive correlation between mgo and 87sr 86sr ratios the variable degrees of magma wall rock interaction are suggested to depend on the differing capabilities of magmas to dissolve crustal rocks due to variable temperature and viscosity the present study therefore provides sr nd pb o isotopic evidence on an uncommon modality of magma contamination by upper crust the alicudi andesites have the most primitive isotope signatures over the entire aeolian arc in plots of 206pb 204pb vs 87sr 86sr or 143nd 144nd isotopes the bulk of the aeolian volcanoes fall along a curved trend that connects himu mantle reservoir and the upper crust in contrast the alicudi andesites fall outside this trend and plot on a binary trend connecting himu and em1 mantle reservoirs it is suggested that the alicudi source consisted of a hybrid himu em1 mantle that was modified by fluids or melts coming from an oceanic slab these fluids did not change significantly the isotopic signatures of the wedge but generated high lile hfse ratios which were inherited by the alicudi magma in contrast the compositions of other aeolian volcanoes and of central italian magmatism reflect addition of upper crust to a himu or fozo mantle collectively the data record the complex interplay between different mantle reservoirs and the addition of various amounts and types of subduction related components in the southern tyrrhenian sea

co2transfer between the upper mantle and the atmosphere temporary storage in the lower continental crust the co2 atmospheric content has shown large variations over geological times high contents up to one order of magnitude more than present day values ultimately correspond to discrete episodes of mantle degassing either juvenile or subduction related carbon recycling a number of arguments e g the continuous volume increase of carbonate bearing sediments with time suggest that throughout the earth s history juvenile co2 has formed a major contribution to the global carbon budget of the earth the absence of a direct relationship between major volcanic episodes and the average co2 atmospheric content suggests that volcanoes might not be the only way by which mantle co2 is transported to the surface it is proposed that large quantities of juvenile co2 could temporarily be stored in the lower continental crust during major episodes of granulite formation these are primarily caused by magmatic underplating and they result in a vertical accretion of the crust by accumulation of co2 bearing mantle derived magmas most of the co2 migrates through the crust during post metamorphic evolution and isostatic restoration of the normal continental thickness however large quantities of co2 can still be present in some areas notably as high density fluids enclosed in minerals

contour scaling of a sandstone by salt weathering under simulated hot desert conditions a laboratory study has been used to investigate relationships between salts and contour scaling a weathering feature commonly observed on rock surfaces in salt rich environments surface disaggregation and essentially surface parallel cracks were produced in sandstone blocks using 10 per cent solutions of sodium sulphate and magnesium sulphate applied daily to single exposed surfaces for sixty days a control block soaked once in saturated magnesium sulphate and subsequently wetted daily with distilled water showed extensive surface disaggregation but no cracking both surface disaggregation and subsurface cracking were associated with relative concentrations of microcrystalline salt a tentative model of contour scaling is proposed which involves linking together potential cracks by salt induced fracturing of intervening crack stopping grains further control blocks treated respectively with 10 per cent and saturated sodium chloride showed no evidence of subsurface cracking and only limited surface disaggregation of the saturated block

laboratory simulation of rock weathering by salt crystallization and hydration processes in hot arid environments the results of a series of experiments are reported in this paper which were designed to differentiate between the forces of crystal growth and hydration in salt weathering using a single salt hydrate system sodium sulphate five contrasting rock types and several diurnal temperature relative humidity cycles which permitted or inhibited these processes and simulated ground surface climates in hot arid environments it was shown that hydration of sodium sulphate is an effective mechanism of rock disintegration but that it is significantly less destructive than crystal growth pressure crystallization of thenardite na2so4 is in turn more effective in rock weathering than the crystal growth of mirabilite na2so4 10h2o in general rates of disintegration were most rapid where the diurnal temperature range was extreme and relative humidity lowest

p wave tomography of the mantle under the alpine mediterranean area 1 we study the upper mantle p wave velocity structure below the euro mediterranean area down to 1000 km depth by seismic travel time tomography we invert summary residuals constructed with both regional and teleseismic first arrival data reported by the international seismological centre isc 1964 1995 introducing some alternative strategies in the travel time tomographic approach and a new scheme to correct teleseismic data for global mantle structure our high resolution model pm0 5 is parameterized with three dimensional 3 d linear splines on a grid of nodes with 0 5 spacing in both horizontal directions and 50 km vertical spacing we obtain about 26 root mean square rms reduction of residuals by inversion in addition to roughly 31 reduction after summary rays formation and selection sensitivity analyses are performed through several test inversions to explore the resolution characteristics of the model at different spatial scales the distribution of large scale fast anomalies suggests that two different stages of a convection process presently coexist in very close regions the mantle dynamics of western central europe is dominated by blockage of subducted slabs at the 660 km discontinuity and ponding of seismically fast material in the transition zone contrarily in the eastern mediterranean fast velocity material sinks into the lower mantle suggesting that the flow of the cold downwelling here is not blocked by the 660 km discontinuity on a smaller scale the existence of tears in the subducted slab lithospheric detachment all along both margins of the adriatic plate as proposed by some authors is not supported by our tomographic images

the monte guardia eruption lipari aeolian islands an example of a reversely zoned magma mixing sequence the monte guardia rhyolitic eruption 22 ka lipari aeolian islands italy produced a sequence of pyroclastic deposits followed by the emplacement of lava domes the total volume of dense magma erupted was nearly 0 5 km3 the juvenile clasts in the pyroclastic deposits display a variety of magma mixing evidence mafic magmatic enclaves streaky pumices mineral disequilibria and heterogeneous glass composition petrographic mineralogical and geochemical investigations and melt inclusion studies were carried out on the juvenile clasts in order to reconstruct the mixing process and to assess the pre eruptive chemico physical magmatic conditions the results suggest that the different mingling and mixing textures were generated during a single mixing event between a latitic and a rhyolitic end member a denser mixed magma was first erupted followed by a larger volume of an unmixed lighter rhyolitic one this compositional sequence is the reverse of what would be expected from the tapping of a zoned magma chamber the monte guardia rhyolitic magma stored below 200 mpa was volatile rich and fluid saturated or very close to this despite its relatively low explosivity in contrast to previous interpretations there exists the possibility that the rhyolite could rise and erupt without the trigger of a mafic input the entire data collected are compatible with two possible mechanisms that would generate a reversely zoned sequence 1 the occurrence of thermal instabilities in a density stratified salic to mafic magma chamber and 2 the intrusion of rising rhyolite into a shallower mafic sill dike

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

p and s wave anisotropy and shear wave splitting at pressure and temperature in possible mantle rocks and their relation to the rock fabric the seismic properties and their directional dependence have been measured in three potentially mantle derived rocks peridotite ivrea zone italy lherzolitic xenolith massif central france serpentinite the experimental data include the measurement of elastic wave velocities and densities at confining pressures up to 600 mpa and temperatures up to 600 c 600 mpa and the determination of velocity anisotropy and shear wave splitting the petrophysical data can be related to mineral composition and to microstructural characteristics of the rocks macroscopic anisotropy of p and s wave velocities is strongly controlled in the peridodites by the olivine and in the serpentinite by the serpentine antigorite lattice preferred orientation lpo respectively shear wave splitting was found to be an important characteristic of the anisotropic rocks the study shows that for the interpretation of shear wave splitting the direction of wave propagation in relation to the lpos of the major minerals and to the symmetry of their lattice fabric is of great importance in the ivrea peridotite exhibiting rhombic symmetry there is practically no shear wave splitting to be observed for s waves propagating parallel to the olivine 100 axes and the maximum shear wave splitting is not coupled with the direction of highest p wave velocity in the transversely isotropic massif central xenolith shear waves do not split when propagating parallel to the olivine 010 maximum coinciding with the direction of the radial symmetry axis of the olivine fabric the experimental data are principally in accordance with velocity calculations based on the measured olivine lpo and the olivine single crystal stiffness coefficients implications for the interpretation of seismic data are discussed

weathering at high latitudes on the carboniferous old red sandstone petrographic and geotechnical investigations jedburgh abbey church scotland a case study weathering processes and intensity vary according to the predominant environmental conditions as well as the rock s physical and geotechnical properties in a given area jedburgh abbey church has been taken as a representative historical building constructed from carboniferous old red sandstone at humid pre glacial region the research aims to examine weathering processes and intensity under the environmental conditions of high relative humidity and low temperature and to determine the output of weathering through an examination of the rock s petrological and geotechnical properties

rhyolites contaminated with metapelite and gabbro lipari aeolian islands italy products of lower crustal fusion or of assimilation plus fractional crystallization pleistocene lavas from monte s angelo and chiesa vecchia volcanoes on lipari contain two suites of inclusions a metapelitic suite consists of gneisses and granulites with combinations of cordierite garnet corundum hercynite andalusite sillimanite orthopyroxene ilmenite magnetite biotite plagioclase and quartz a gabbroic suite has cumulus texture and contains plagioclase orthopyroxene clinopyroxene and magnetite all megacryst phases in the lavas appear to be derived from rock fragments with the exception of euhedral strongly zoned calcic plagioclase and none has grown by homogeneous nucleation from liquid represented by the groundmass which is peraluminous rhyolite 70 wt sio2 6 wt k2o ground mass microcrysts were nearly all derived from disaggregated metapelites overgrowths of alkali feldspar on plagioclase and of orthopyroxene on clinopyroxene and quartz intergrown with alkali feldspar are the only phases that grew from the rhyolitic liquid euhedral cordierite hercynite and plagioclase at the margins of some rock fragments grew by reaction of metapelite with liquid

volcanological and petrological evolution of vulcano island aeolian arc southern tyrrhenian sea petrological and geochemical data are reported for volcanic rocks from vulcano island the subaerial volcanism 120 ka to present built up a nw se elongated composite structure affected by two intersecting multistage calderas volcanics older than 20 ka consist mostly of high k calc alkaline hkca to shoshonitic sho mafic rocks these magmas interacted significantly with the continental crust which generated variable sr isotopic ratios 0 70412 0 70520 however a major role was also played by input of parental liquids into the magma chamber which prevented further evolution of the magmas hkca sho and potassic ks rocks formed from 20 to 8 ka display a much larger range of sio2 from shoshonites to rhyolites and higher concentrations of incompatible elements with respect to the previous stage sr isotopic ratios show small variations 0 70448 0 70486 mixing of silicic and mafic liquids and fractional crystallization processes fc were the main evolutionary processes during this stage volcanics younger than 8 ka consist of sho and leucite bearing ks mafic rocks with abundant intermediate and silicic products mafic and intermediate rocks display similar incompatible element abundances and sr isotopic ratios as the previous stage volcanics whereas higher 87sr 86sr 0 70494 0 70583 are observed in some rhyolites these products originated from a complex interplay of fc crustal assimilation and magma mixing processes the most mafic rocks show increasing incompatible element abundances rb sr rb ba mg al mg ca and a decrease in large ion lithophile to high field strength element ratios passing from older hkca sho to the younger sho ks volcanics these variations suggest a shifting of magma sources from a slightly metasomatized asthenosphere fertile peridotite to a more strongly metasomatized lithospheric mantle residual peridotite time related petrological and geochemical variations have been used to develop a model for the evolution of the vulcano plumbing system

a geochemical and experimental study of the role of k feldspar during water undersaturated melting of metapelites abstract the production of s type granites has been related to the extraction of melts during water undersaturated melting of metasediments in the lower continental crust if this mechanism is of widespread applicability a chemically distinctive granulitic restite must be left behind with a positive eu anomaly and depleted incompatible element concentrations however little geochemical evidence has been found in support of this hypothesis the rare earth element geochemistry of lower crustal granulites and associated melts will depend on the behaviour of the phases in which ree and trace elements are concentrated i e zircon monazite and k rich feldspar new experimental data on synthetic metapelites show that k feldspar can be a product or a reactant during water undersaturated melting of biotite depending on the h2o k2o of the melt relative to biotite past confusion over the role of k feldspar during melting is due to the reaction being close to degeneracy and changing its stoichiometry in response to only small changes in bulk composition coherent interpretation of the role of k feldspar in different experimental studies requires a better knowledge of phase water contents than has commonly been available the leucosomes formed in some antarctic granulite facies migmatites are likely to have had low h2o k2o ratios which suggests that k feldspar would have been a reactant during melting this could cause the positive eu anomalies observed in the leucosomes through the disequilibrium melting of k feldspar during water undersaturated melting the undersaturation of trace elements and ree in the leucosomes strongly suggests that disequilibrium melting took place caused by the incomplete dissolution of accessory phases monazite and zircon these phenomena give the melts a distinctive geochemical character which has also been seen in the other granulite facies leucosomes analysed to date this geochemical character contrasts with that of s type granites and therefore the production of granulites in the lower crust may not necessarily be associated with this type of magmatism if lower crustal granulite facies migmatites are the source region for peraluminous s type granites then the melts generated must undergo considerable modification during ascent

constraints on melting and magma production in the crust major intrusions of granitic rocks are found in several tectonic settings and in all cases crustal melts may contribute to the volumes of granitic magma high grade metamorphism and partial melting of the crust take place predominantly under fluid absent conditions we present a model for calculating the amounts of melt that may be formed by fluid absent breakdown of micas and amphiboles in common crustal rock types pelitic quartzofeldspathic intermediate and mafic melt proportions depend mainly on the kind of source rock the pressure at which melting takes place the temperature and the hydrous mineral h2o content of the source as a consequence of the pressure dependence of water solubility in silicate melts any given source rock will produce more melt by a given fluid absent reaction at lower pressure at a given pressure higher temperature reactions can produce more melt from a given source rock based on a survey of the compositions of common rock types we show that the amounts of melt can vary from 50vol thus crustal rocks vary widely in their fertility as magma sources depending on the types and amounts of hydrous phases they contain in general muscovite breakdown in pelites will yield only small quantities of melt and lead to migmatite formation biotite breakdown in pelites occurs at higher temperature and because most high grade pelites below granulite grade are biotite rich can yield up to about 50 vol of granitoid melt rocks of intermediate composition and hornblende rich mafic rocks are potentially highly fertile magma sources also provided that the high temperatures necessary for biotite and hornblende breakdown are realized pyroxene rich mafic rocks and quartzofeldspathic rocks are much less potentially fertile data suggest that mechanisms exist for the efficient segregation of melt and restite in systems with 30and probably 20vol melt the pressure temperature history of a region can greatly influence crustal source fertility through its control over the occurrence of subsolidus dehydration and melting equilibria

a new method for calculating seismic velocities in rocks containing strongly dimensionally anisotropic mineral grains and its application to antigorite bearing serpentinite mylonites abstract seismic velocity is one of the most important sources of information about the earth s interior for its proper interpretation we must have a thorough understanding of the dependence of seismic velocity on microstructural elements including the modal composition the crystal preferred orientation cpo the grain shape the spatial distribution of mineral phases etc the conventional voigt reuss and hill averaging schemes take into account only the modal composition and the cpo the information about the earth s interior is thus poorly constrained for a better interpretation it is critical to have a calculation method which accounts for the grain shape and the spatial distribution of mineral phases etc we propose a calculation method which accounts for the grain shape of strongly dimensionally anisotropic minerals like micas and serpentines our method can be applied to a distributed geometrical orientation of mineral grains comparison was made between calculated and measured velocities in three antigorite serpentinite mylonites judging from the root mean square relative error our method provides velocities closer to measured values than the voigt reuss and hill averaging schemes the input of the grain shape considerably improves the prediction of seismic properties however large discrepancies 0 1 km s between measured and calculated velocities can be seen in some directions the discrepancies might come from microstructural elements which were not considered in the calculation layer structures and cracks

effect of pressure on 3d distribution of p wave velocity and attenuation in antigorite serpentinite abstractwe have developed a detailed study on the pressure dependence of p wave velocities and amplitudes on a spherical sample of antigorite serpentinite from val malenco northern italy measurements were done at room temperature and hydrostatic pressures up to 400 mpa in a pressure vessel with oil as a pressure medium the transducer sample assembly allows simultaneous velocity and amplitude measurements on the spherical sample in 132 independent directions three significant directions of the foliated sample were selected to study changes of the directional dependence anisotropy of velocity amplitude and q factor with increasing pressure remarkable differences are observed between the changes of velocity and attenuation anisotropy as pressure is increased although the velocity anisotropy is quite stable through all pressure levels the attenuation anisotropy and the q factor vary significantly in magnitude and orientation the variations are probably caused by the closing of microcracks due to a

constraining the recent plumbing system of vulcano aeolian arc italy by textural petrological and fractal analysis the 1739 a d pietre cotte lava flow 1 the 1739 a d pietre cotte lava flow is part of a sequence of low explosive to weak effusion events occurred at la fossa cone the active vent on vulcano island aeolian arc italy this lava is rhyolitic texturally heterogeneous and contains lati trachytic enclaves these compositions are recurrent in the la fossa volcanic products and are representative of the recent vulcano plumbing system the host lava is vesicular relatively phenocryst free and locally contains microlites and millimeter sized spherulites the enclaves are up to 10 cm in size display angular to spherical shapes and can form the core of spherulites enclaves mostly consist of plagioclase and augitic phenocrysts set in a weakly vesicular groundmass characterized by variable abundance of glass and feldspar microlites field textural and fractal data allow us to constrain the rheological features of the rhyolitic and lati trachytic magmas in situ major trace and volatile element analyses provide evidence for heterogeneities in the glassy matrix and zoning of phenocrysts processes of magma evolution have been quantitatively constrained by using the apparent distribution ratios of trace elements measured between mineral phases and glassy matrices the collected data in combination with petrological and fluid inclusion data from the literature provides evidence for 1 a genetic relationship between the two magmas through assimilation fractional crystallization process 2 a mingling mechanism between an uprising rhyolitic magma and a shallower partly crystallized lati trachytic magma plug 3 the desegregation enclaves at variable scales of the lati trachyte within the rhyolite and 4 the possible eruptive scenarios consequent to a future magmatic unrest

magma underplating of continental crust experiments conducted over the past decade have shown that common mantle melting products have densities at moho pressures that exceed the density of average continental crust in a situation of perfect gravitational equilibrium they would not rise to or near the surface the exact behaviour reflects the coupling of crust to the mantle strong at early periods of magmatic cycle but weak at more evolved stages where crustal melting and degassing commences spreading of underplate magmas in rift zones above subduction zones or even hot spots may perturb the state of the crust over very large areas where dense magmas occur beneath normal 30 km continental crust they may crystallize to form gabbro peridotiteanorthosite complexes dense crustal components may founder with melting assimilation and degassing producing very high temperature fluids rich in h2o co2 co and s halogen species depending on compositions the process acts as density filter cleaning the crust and lowering its mean density this process must have been particularly efficient during the archean when komatiite magmas were common opportunities for magma contamination and mixing processes must abound in situations of large scale underplating when crust is overthickened underplate magmas may crystallize to products with eclogitic affinity with the possibility of their foundering in normal mantle

seismic anisotropy of serpentinite from val malenco italy 2015 american geophysical union all rights reserved serpentinites deformed in mantle subduction zones are thought to contribute significantly to seismic anisotropy of the upper mantle and have therefore been of great interest with studies on deformation preferred orientation and elastic properties here we present a combined study of a classical sample from val malenco italy investigating the microstructure and texture with state of the art synchrotron x ray and neutron diffraction methods and measuring ultrasonic velocities both with a multi anvil apparatus and a novel instrument to measure 3 d velocities on spheres both results from diffraction methods and velocity measurements are compared discussing advantages and disadvantages from spherical velocities elastic tensor properties can be derived by inversion also from quantitative texture measurements elastic properties can be modeled by self consistent averaging good agreement between the velocity and microstructural models is observed

beginning of melting and composition of first melts in the system qz ab or h 2 o co 2 solidus temperatures have been determined for minimum melt compositions in the system qz sio2 ab naalsi3o8 or kalsi3o8 at p fluid 2 5 and 10 kbar and at various water activities the dry solidus was investigated in a dry argon environment water activities ah2o between 0 0 and 1 0 were obtained by using h2o co2 mixtures the or ab or ratio of first melts increases considerably with decreasing water activity at 10 kbar it is 0 28 in the water saturated system and 0 56 at water activity 0 1 the qz content does not change with changing water activities the ab content of minimum melts formed at high pressures and low ah2o may remain almost constant in ascending magmas that are cooling and crystallizing qz content increases at the expense of the or component solidus temperatures decrease considerably when ah2o increases slightly from zero at 10 kbar the temperature difference between dry melting and the solidus for ah2o 0 1 is 120 c the influence of pure co2 on the solidus is very limited in the investigated p t range the solidus is approximatively 760 c at ah2o 0 5 between 2 and 10 kbar and approximatively 830 c at ah2o 0 3 this means that melting of quartz feldspar assemblages may induce dehydration reactions at p t conditions of the granulite facies

magma mixing at lipari aeolian islands italy insights from textural and compositional features of phenocrysts in southern lipari aeolian islands italy the volcanic activity was exclusively rhyolitic in the last 42 ka but the presence of mafic magmas in the magmatic system is revealed by the occurrence of mingling and mixing textures in the silicic deposits the study of textural and compositional zoning of phenocrysts is a powerful tool to unravel magmatic processes especially when bulk rock data are affected by magma mixing in this work we present the results of detailed petrographic and microanalytical investigations carried out on the rhyolitic products and their mafic enclaves with the aim to improve the knowledge of the lipari magmatic system in recent times trace element profiles on phenocrysts were carried out by laser ablation icp ms on the products of eruptions occurred around 22 ka ago mineral chemistry indicated the formation of different mafic magma batches in that period zoning patterns in clinopyroxene and plagioclase phenocrysts in enclaves record mixing between two different mafic magmas this event preceded of less than a few years the syn eruptive mixing with the rhyolite short residence times less than hundreds of years of plagioclase phenocrysts in the mafic magma prior to mixing with the rhyolite were calculated based on measured sr profiles and diffusion kinetics the results evidence the existence in southern lipari of a composite vertically developed magmatic system storing silicic and mafic magmas as relatively small volume batches interacting with each other

a preliminary scanning electron microscope study of honeycomb weathering of sandstone in a coastal environment honeycomb weathering has been observed in a carboniferous sandstone at a coastal location near ballycastle on the north coast of northern ireland specimens of this sandstone have been analysed by x ray diffraction scanning electron microscopy and energy dispersive spectrometry results reveal that calcium sulphate gypsum is the only salt present and is found only at and immediately below the rock surface sem observations suggest that crystallization of salts in pores could easily dislodge quartz grains to promote granular disintegration whilst etching of quartz grain surfaces attests to chemical weathering activity within the rock however the reason for the development of the honeycomb pattern is not known

melt production during granulite facies anatexis experimental data from primitive metasedimentary protoliths we conducted fluid absent partial melting experiments at 0 5 and 1 0 gpa in the temperature range 750 to 1000 c to investigate the influence of bulk rock mg 100mg mg fe and the effects of additional tio2 on the granulite grade anatectic evolution of relatively magnesian metapelites and metagreywackes in these experiments melting began between 780 and 830 c by the incongruent breakdown of biotite to produce quartz saturated granulite facies residual mineral assemblages in equilibrium with h2o undersaturated granitic melt the glass quenched melt compositions produced in this study vary little generally the glasses have compositions similar to those of many natural strongly peraluminous leucogranites the solidus temperatures in both rock types increase with increasing mg but are unaffected by the presence or absence of a tio2 component at 0 5 gpa the metapelites melted at temperatures up to 50 c lower than the equivalent metagreywackes but at 1 gpa there was no discernible difference this study suggests that the fluid absent solidus has a steep positive dp dt slope in metapelites and steep negative dp dt slope in metagreywackes the pattern of melt production with increasing temperature is strongly controlled by the upper limit of biotite stability in tio2 free compositions this was found to increase by 15 to 20 c in the metapelites and by 30 to 40 c in the metagreywackes as a function of increasing mg from 49 to 81 the presence of a tio2 component increases the upper limit of biotite stability by 50 c in the metapelites and by 80 c in the metagreywackes over that observed in the equivalent tio2 free compositions in consequence in the tio2 free samples large pulses of melt up to 35 wt are produced over narrow temperature ranges as little as 15 c in these experiments between 830 and 875 c in the tio2 bearing samples the major pulse of melt production occurs more gradually between 830 and 900 c

temporal evolution of a three component system the island of lipari aeolian arc southern italy the volcanic products from lipari define an evolutionary trend with a high gradient of k enrichment similar to the calc alkaline to potassic volcanism of other islands in the aeolian arc stratigraphic reconstruction of the island based on field and geochronological data indicate that the volcanic activity can be subdivided in two stages the first stage from 223 to 42 ka consists of six eruptive cycles and is characterized by basalts and basalt andesites showing progressive increase in both sio2 and k2o contents with time the second stage consists of four cycles erupted since 42 ka and is marked by an apparent rejuvenation of the geochemical system with the appearance of the first rhyolitic products fractional crystallization assimilation and mixing models suggest that the geochemistry of lipari volcanism evolved with time by a complex interplay between two mantle derived components one sub alkaline and the other alkaline in addition to crustal melts and or crustally derived materials a petrogenetic model in which fractional crystallization was subordinate to mixing best fits the geochemical data and petrographic observations of macro and microscopic features melts from the crustal and mantle end members are almost always present in the system but the relative proportions appear to vary with time the sub alkaline mantle component source of tyrrhenian tholeiites is an important contributor to the early evolution of the volcanism in lipari input from the alkaline mantle component source of the roman comagmatic province increases with time and the crustal component becomes dominant in the later activity the preferred petrogenetic model for the temporal evolution of the volcanic system in lipari involves melting initially caused by an increase in the thermal input related to the opening of the tyrrhenian sea and or to subduction processes the quick rise of the isotherms and almost contemporaneous melting of source materials with different compositions favored complex mixing during ascent of the melts

nanogranite and glassy inclusions the anatectic melt in migmatites and granulites using as a case study a granulite from the kerala khondalite belt india we show that a former anatectic melt can be preserved as tiny 25 m droplets within refractory minerals in this case garnet the melt is either fully crystallized as a qtz ab kfs bt cryptocrystalline aggregate nanogranite or completely glassy in inclusions 15 m both nanogranite and glassy inclusions have a peraluminous ultrapotassic granitic composition that in this case does not correspond to a minimum melt and points to high melting temperatures in agreement with the ultrahigh temperature origin of the rock this discovery indicates that peritectic minerals growing during incongruent melting reactions act as hosts for inclusions of anatectic melt and that in the general case of slow cooling of the crust these inclusions will occur as nanogranite exceptionally in the smallest inclusions glass may be present due to inhibition of crystallization our results extend the frontiers of petrological and geochemical research in crustal melting as the composition of natural anatectic melts can be directly analyzed rather than assumed

magmatic feeding system and crustal magma accumulation beneath vulcano island italy evidence from co2 fluid inclusions in quartz xenoliths 1 pure co2 fluid inclusions are observed in quartz xenoliths from four lava flows in the island of vulcano corresponding to distinct activity stages during the last 120 kyr xenoliths which consist of aggregates of quartz grains are present in lavas of contrasting composition ranging from basaltic andesites to rhyolites two main generations of co2 inclusions are observed early type i inclusions were trapped prior to the ascent of the host xenoliths while type ii inclusions were trapped during the ascent into the host magma fluid inclusions show a bimodal distribution of homogenisation temperatures corresponding to two distinct density intervals 0 89 0 52 g cm 3 type i and 0 42 0 13 g cm 3 type ii type i inclusions indicate pressures of 0 56 0 33 gpa 21 13 km relating to the levels of xenolith entrapment in the host lavas type ii fluid inclusions show considerably lower pressures ranging from 0 14 to 0 03 gpa 5 5 3 km present data suggest ponding of mantle derived magmas in at least two distinct reservoirs located at lower crustal depths and at shallow levels respectively combined fluid inclusion and petrological data suggest that the deep reservoirs were the sites of extensive fractional crystallization mixing with source derived magmas and various degrees of crustal assimilation evolutionary processes also occurred inside shallow magma chambers in which deep magma mixed with residing melts and rested for short periods of time before being erupted to the surface index terms 5480 planetology solid surface planets volcanism 8450 8414 volcanology eruption mechanisms 8434 volcanology magma migration

a la icp ms study of minerals in the rocche rosse magmatic enclaves evidence of a mafic input triggering the latest silicic eruption of lipari island aeolian arc italy the volcanic products of lipari island aeolian arc italy younger than 10 ka are mostly aphyric rhyolitic pumices and obsidians emitted during unusual strombolian type eruptions which ended with the emplacement of lava flows the last volcanic activity on the island dates back to 1230 40 ad with the extrusion of rocche rosse rr obsidian lava flow recently mafic enclaves of latitic to trachytic composition have been identified and an evolution process between these enclaves and the rhyolitic magma has been documented in detail davi m 2007 the rocche rosse rhyolitic lava flow lipari aeolian islands magmatological and volcanological aspects plinius supplement to the european journal of mineralogy 33 1 8 in this work textural and trace element investigation of mineral phases of the rr enclaves such as crystals of clinopyroxene olivine plagioclase alkali feldspar and biotite was carried out to delineate the most recent feeding system of the island since such a reconstruction could be significant in terms of hazard forecasting the results indicate that most of the mineral phases are reversely or oscillatory zoned with respect to both major and trace elements suggesting an early crystallization under low f o 2 conditions from melts of intermediate composition followed by a later growth from a more mafic presumably shoshonitic basaltic magma than that from which their cores crystallized crystals of magnesium rich pyroxene and forsteritic rich olivine are indicative of the presence of this shoshonitic basaltic magma based on microanalytical data it is suggested here that the feeding system of recent lipari volcanic activity was characterized by a shoshonitic basaltic magma originating from a deep reservoir which may have evolved and stopped in the crust generating zoned magma chambers at different depths in which latitic and rhyolitic magmas reside the sudden arrival of a new input of mafic melt may have interacted with these resident fractionated magmas and triggered the eruption a plumbing system of this type has been shown to be active in the southern sector of the aeolian islands since the last 42 ka gioncada a mazzuoli r milton a 2005 magma mixing at lipari aeolian islands italy insights from textural and compositional features of phenocrysts j volcanol geotherm res 145 97 118 peccerillo a frezzotti m l de astis g ventura g 2006 modeling the magma plumbing system of vulcano aeolian islands italy by integrated fluid inclusion geobarometry petrology and geophysics geology 34 17 20 it is concluded that the hazard assessment of lipari island should take into account the arrival of deep and never erupted mafic melts as eruption triggers of more evolved shallower magma bodies

occurrence and origin of andalusite in peraluminous felsic igneous rocks andalusite occurs as an accessory mineral in many types of peraluminous felsic igneous rocks including rhyolites aplites granites pegmatites and anatectic migmatites some published stability curves for and sil and the water saturated granite solidus permit a small stability field for andalusite in equilibrium with felsic melts we examine 108 samples of andalusite bearing felsic rocks from more than 40 localities world wide our purpose is to determine the origin of andalusite including the t p x controls on andalusite formation using eight textural and chemical criteria size compatibility with grain sizes of igneous minerals in the same rock shape ranging from euhedral to anhedral with no simple correlation with origin state of aggregation single grains or clusters of grains association with muscovite with or without rims of monocrystalline or polycrystalline muscovite inclusions rare mineral inclusions and melt inclusions chemical composition andalusite with little significant chemical variation except in iron content 008 171 wt feo compositional zoning concentric sector patchy oscillatory zoning cryptically reflect growth conditions compositions of coexisting phases biotites with high siderophyllite eastonite contents aliv 268 007 atoms per formula unit muscovites with 057 401 wt feo and 002 285 wt tio2 and apatites with 353 018 wt f coexisting muscovite biotite pairs have a wide range of f contents and fbt 1612fms 0015 most coexisting minerals have compositions consistent with equilibration at magmatic conditions the three principal genetic types of andalusite in felsic igneous rocks are type 1 metamorphic a prograde metamorphic in thermally metamorphosed peraluminous granites b retrograde metamorphic inversion from sillimanite of unspecified origin c xenocrystic derivation from local country rocks and d restitic derivation from source regions type 2 magmatic a peritectic water undersaturated t associated with leucosomes in migmatites b peritectic water undersaturated t as reaction rims on garnet or cordierite c cotectic water undersaturated t direct crystallization from a silicate melt and d pegmatitic watersaturated t associated with aplite pegmatite contacts or pegmatitic portion alone type 3 metasomatic water saturated magma absent spatially related to structural discontinuities in host replacement of feldspar and or biotite intergrowths with quartz the great majority of our andalusite samples show one or more textural or chemical criteria suggesting a magmatic origin of the many possible controls on the formation of andalusite excess al2o3 water concentration and fluid evolution high be b li p high f high fe mn ti and kinetic considerations the two most important factors appear to be excess al2o3 and the effect of releasing water either to strip alkalis from the melt or to reduce alumina solubility in the melt of particular importance is the evidence for magmatic andalusite in granites showing no significant depression of the solidus suggesting that the and sil equilibrium must cross the granite solidus rather than lie below it magmatic andalusite however formed is susceptible to supra or sub solidus reaction to produce muscovite in many cases textural evidence of this reaction remains but in other cases muscovite may completely replace andalusite leaving little or no evidence of its former existence

grain size sensitive seismic wave attenuation in polycrystalline olivine 1 in order to investigate the processes responsible for the attenuation of seismic shear waves in the earth s upper mantle four olivine polycrystals ranging in mean grain size d from 3 to 23 m have been fabricated characterized and mechanically tested in torsion at high temperatures and seismic frequencies both the shear modulus which governs the shear wave speed vs and the dissipation of shear strain energy q 1 have been measured as functions of oscillation period to temperature t and for the first time grain size at sufficiently high t all four specimens display similar absorption band viscoelastic behavior adequately represented for 1000 t 1200 or 1300 c and 1 to 100 s by the expression q 1 a tod 1 exp e rt with a 7 5 102 s m 0 26 and e 424 kj mol 1 this mildly grain size sensitive viscoelastic behavior of melt free polycrystalline olivine is attributed to a combination of elastically and diffusionally accommodated grain boundary sliding the latter becoming progressively more important with increasing t and or to extrapolation to the larger mm cm grain sizes expected in the earth s upper mantle yields levels of dissipation comparable with those observed seismologically implying that the same grain size sensitive processes might be responsible for much of the observed seismic wave attenuation the temperature sensitivity of vs is increased substantially by the viscoelastic relaxation allowing the lateral variability of wave speeds to be associated with relatively small temperature perturbations

classification of rock weathering at writing on stone provincial park alberta canada a study in applied geomorphology at writing on stone provincial park in southern alberta canada weathering is causing deterioration and loss of archaeologically important indian rock art a procedure devised for the use of park personnel identified four classes of weathering ranging from largely unweathered rock to severely weathered the technique employed simple visual qualitative assessment and photo interpretation of 50 sample sections of sandstone cliff face covering a total area of 354 m2 schmidt hammer tests indicated large variations in rock strength and provided a numerical basis for the visual assessment about 43 per cent of the cliffs are severely to completely weathered 41 per cent show moderate weathering

primary melt inclusions in andalusite from anatectic graphitic metapelites implications for the position of the al2sio5 triple point anatectic crustal xenoliths in the miocene volcanic rocks of mazarron southeast spain contain andalusite with melt inclu sions an unprecedented finding microstructures indicate that the melt inclusions were trapped during andalusite growth the vola tile content of the peraluminous inclusions is too low cl 0 4 wt f 0 3 wt p 1500 ppm b 850 ppm to have caused a significant reduction of the wet solidus temperature moreover the presence of graphite as observed during partial melting is expected to have raised the temperature of the wet solidus melting temperatures for the inclusions obtained from quartz albite or thoclase haplogranite system 680 790 8c zr 620 705 8c and light rare earth element 615 725 8c thermometry indicate that the stability of andalusite 1 melt is incompatible with the position of the most commonly used andalusite 5 sillimanite equilibrium and that the al2sio5 triple point must be placed at higher tem peratures and pressures

monomineralic glomerocrysts textural evidence for mineral resorption during crystallization of igneous rocks monomineralic aggregates or glomerocrysts are a distinctive feature of many igneous rocks those with crystals joined along prominent euhedral crystal faces form by synneusis while the mineral is crystallizing other glomerocrysts comprised of crystals joined along irregular embayed margins arguably formed while the crystals were being resorbed a model for glomerocryst formation during mineral resorption is described during resorption a boundary layer melt which envelops the dissolving crystals is produced when two or more dissolving crystals come into close proximity the intervening portion their respective boundary layer melts becomes isolated from chemical communication with the surrounding granitic liquid contributions from both dissolving crystals to this isolated portion of the boundary layer melt creates a melt composition that eventually becomes supersaturated with respect to the dissolving crystals this results in crystallization of new material from the intervening melt that bonds th

formation of cordierite bearing lavas during anatexis in the lower crust beneath lipari island aeolian arc italy cordierite bearing lavas cbl 105 ka erupted from the mt s angelo volcano at lipari aeolian arc italy are high k andesites displaying a range in the geochemical and isotopic compositions that reflect heterogeneity in the source and or processes cbl consist of megacrysts of ca plagioclase and clinopyroxene euhedral crystals of cordierite and garnet microphenocrysts of orthopyroxene and plagioclase set in a heterogeneous rhyodacitic rhyolitic groundmass containing abundant metamorphic and gabbroic xenoliths new petrographic chemical and isotopic data indicate formation of cbl by mixing of basaltic andesitic magmas and high k peraluminous rhyolitic magmas of anatectic origin and characterize partial melting processes in the lower continental crust of lipari crustal anatectic melts generated through two main dehydration melting peritectic reactions of metasedimentary rocks 1 biotite aluminosilicate quartz albite garnet cordierite k feldspar melt 2 biotite garnet quartz orthopyroxene cordierite k feldspar melt their position into the petrogenetic grid suggests that heating and consequent melting of metasedimentary rocks occurred at temperatures of 725 t 900 c and pressures of 0 4 0 45 gpa anatexis in the lower crust of lipari was induced by protracted emplacement of basic magmas in the lower crust 130 ky crustal melting of the lower crust at 105 ka affected the volcano evolution impeding frequent mafic magma eruptions and promoting magma stagnation and fractional crystallization processes

microstructures of melt inclusions in anatectic metasedimentary rocks the occurrence of crystallized and glassy melt inclusions mi in high grade partially melted metapelites and metagraywackes has opened up new possibilities to investigate anatectic processes the present study focuses on three case studies khondalites from the kerala khondalite belt india the ronda migmatites spain and the barun gneiss nepal himalaya the results of a detailed microstructural investigation are reported along with some new microchemical data on the bulk composition of mi these inclusions were trapped within peritectic garnet and ilmenite during crystal growth and are therefore primary inclusions they are generally isometric and very small in size mostly 15 m and only rarely reaching 30 m they occur in clusters in most cases inclusions are crystallized nanogranites and contain a granitic phase assemblage with quartz feldspar and one or two mica depending on the particular case study commonly with accessory phases mainly zircon apatite rutile in many cases the polycrystalline aggregates that make up the nanogranites show igneous microstructures e g granophyric intergrowths micrographic quartz in k feldspar and cuneiform rods of quartz in plagioclase further evidence for the former presence of melt within the investigated inclusions consists of melt pseudomorphs similar to those recognized at larger scale in the host migmatites moreover partially crystallized inclusions are locally abundant and together with very small 8 m glassy inclusions may occur in the same clusters both crystallized and partially crystallized inclusions often display a diffuse nanoporosity which may contain fluids depending on the case study after entrapment inclusions underwent limited microstructural modifications such as shape maturation local necking down processes and decrepitation mainly in the barun gneiss which did not influence their bulk composition re homogenized nanogranites and glassy inclusions show a leucogranitic and peraluminous composition consistent with the results of partial melting experiments on metapelites and metagraywackes anatectic mi should therefore be considered as a new and important opportunity to understand the partial melting processes