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

geophysical exploration for geothermal low enthalpy resources in lipari island italy abstract integrated geophysical surveys were performed in two sites fossa di fuardo and terme di san calogero in lipari island southern italy with the intent of the exploration of low enthalpy geothermal fluids both sites show strong geochemical and geologic evidences of hydrothermal activity the geophysical methods consist of two microgravimetric surveys two 2d geoelectric profiles a seismic reflection profile and a five seismic refraction profiles the seismic methods allowed us to locate the main subsurface seismic discontinuities and to evaluate their geometrical relationships the gravity field was used to constraint the seismic discontinuities while the electric prospecting let discriminate more conductive areas which could correspond to an increase in thermal fluid circulation in the investigated sites the results obtained by the different geophysical methods are in good agreement and permit the definition of a reliable geo structural model of the subsurface setting of the two investigated areas a low enthalpy geothermal reservoir constituted by a permeable pyroclastic and lava sequence underlying two shallow impermeable formations was found at fossa del fuardo the reservoir is intersected by some sub vertical faults fractures that probably play an important role in convoying the thermal water up to the surface at the other site terme di s calogero the geophysical surveys showed that an intense circulation of fluids affects the subsurface of the area this circulation concentrates along a ene trending fault located at a little distance from the thermal resort the hot fluids may upraise along the fault if the width of the ascent area is smaller than 20 m

three s type volcanic suites from the lachlan fold belt southeast australia the concept that granitoids of the lachlan fold belt in southeast australia are derived from either igneous or sedimentary source rocks i or s type can be extended to volcanic rocks of the same age three suites of late silurian s type volcanics are described two of which can be matched quite closely with plutonic equivalents a large part of the paleozoic continental margin volcanic activity in southeast australia consisted of the magmatic recycling of old metasedimentary crust probably of late proterozoic age the three volcanic suites are moderately to strongly peraluminous with the corresponding presence of al rich minerals variation within the volcanic suites is ascribed chiefly to progressive removal of restite or source material residual from partial melting the most mafic suite the hawkins suite contains plagioclase cordierite orthopyroxene biotite and quartz as restite components with less abundant almandine these rocks are chemically equivalent to mafic biotite rich and cordierite bearing granitoids from parts of the berridale and murrumbidgee batholiths garnet is absent from the goobarragandra suite volcanics which are a little more felsic and close in compositon to granitoids of the young and maragle batholiths the s type character of the laidlaw suite is less pronounced although a sedimentary source seems to be established such a source would be less mature than those for the other two volcanic suites the laidlaw suite resembles but cannot be closely identified with felsic s type granitoids of the murrumbidgee and berridale batholiths low grade regional metamorphism in most of the volcanic rocks has resulted in much mineralogical alteration and mobility of alkali and alkaline earth elements despite this alteration unaltered rocks are present in all three suites compositional data for the phenocryst phases within the unaltered rocks has allowed estimation of some intensive parameters hawkins suite volcanics were extruded directly from their source region and preserve phenocryst equilibria established at 5 6 kbar at 800 c the laidlaw and goobarragandra suites reequilibrated at lower pressures than their source before extrusion the laidlaw suite reequilibrated at estimated temperatures of 725 730 c o2 of 10 15 5 to 10 14 bars and h2o of 2 to 2 5 kbar differing mineral compositions in the three suites are related to differing source rock compositons and oxygen fugacities relative biotite and orthopyroxene mg is possibly pressure dependent

roman comagmatic province central italy evidence for subduction related magma genesis geochemical data on mafic volcanics show that important affinities exist between the roman and the calc alkaline rocks from the aeolian arc south tyrrhenian sea these affinities together with the close association of calc alkaline and k rich volcanics in the aeolian arc and in the naples area the continuity in the variation of abundances of incompatible elements from calc alkaline to potassic suites and the similarity in terms of major element geochemistry support a genetic relationship of the roman magmatism and the subduction processes that affected the apennines in tertiary time and are still active under the aeolian arc in the genetic model presented here both calc alkaline and k rich magmas were generated within a mantle heterogenously enriched in lil elements composition of the mantle was modified by addition of material probably sediments dragged down by the undergoing slab the geochemical and petrological differences displayed by the calc alkaline and k rich volcanics are accounted for by the different conditions of melting as well as by chemical and isotopic heterogeneities of the source 26 references 3 figures 1 table

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

fe rich cordierites from acid volcanic rocks an optical and x ray single crystal structure study low cordierites from volcanic rocks of tuscany italy lipari italy and of the cerberean cauldron australia were investigated both single crystal structure refinements and optical data indicate that the italian samples contain only low concentrations of volatiles 0 4 and provide additional information about the crystal structure of fe rich cordierites with increasing fe mg substitution the mean t11 al o distance decreases slightly which is probably not caused by substitution of smaller cations on t11 but by angular distortion of the tetrahedron

volcanological implications of crystal chemical variations in clinopyroxenes from the aeolian arc southern tyrrhenian sea italy crystal chemistry and structural data for clinopyroxene from the aeolian islands southern tyrrhenian sea italy were determined with the aim of obtaining geobarometric information and exploring implications for the structure of volcanic plumbing systems cell and m1 site volumes for clinopyroxenes which are known to decrease with increasing pressure of crystallization revealed variable values both within some single islands and along the entire arc indicating polybaric conditions of crystallization the lowest cell and m1 volumes were found at filicudi plotting close to values of clinopyroxenes from high pressure ultramafic xenoliths entrained in alkali basalts indications of high pressure crystallization were also found at salina and to a lesser extent at alicudi all situated in the western sector of the aeolian arc the central and eastern islands of lipari vulcano panarea and stromboli generally show higher values of cell parameters suggesting crystallization in shallow magma chambers these islands are characterized by the occurrence of large calderas which are apparently lacking at salina and filicudi time related variations were observed for cell and m1 volumes of clinopyroxene for some islands at salina the early erupted products display low values of cell parameters with respect to later activity thus indicating a decrease in crystallization pressure with time a similar although less striking pattern is observed at alicudi and lipari an overall increase in cell parameters with time was observed at the scale of the entire arc the observed variations in clinopyroxene structural parameters highlight the significance of pyroxene crystal chemistry for petrogenetic and volcanological interpretation correlation with time and the structural characteristics of volcanoes suggest significant regional and temporal modifications in the plumbing systems of aeolian volcanoes clinopyroxenes from filicudi and the older salina crystallized at high pressure in deep magma chambers in the lower crust or at the mantle crust boundary the lower crystallization pressure in the younger salina is interpreted as evidence of upward migration of magma chambers with time similar evolution can be envisaged for alicudi instead the entire evolutionary history of the central and eastern islands was dominated by low pressure crystallization with formation of calderas and generation of abundant acid products that are scarce or absent in the western islands evolution of the plumbing system of single volcanoes and of the aeolian arc in general is probably related to modification of stress regimes and or thinning of the arc basement due to the effect of uprising mantle material above the ionian subduction zone

fault plane solutions and seismicity of the italian peninsula abstract a new fault plane solution map of the italian peninsula is presented in this paper the earthquakes analyzed are included in the period 1905 1980 with magnitudes ranging 4 7 75 earthquakes are located in the crust while 31 are related to the deep and intermediate zone of the calabrian arc the large seismic events of the italian peninsula are generally associated with normal faulting while strike slip motion is mostly related to small earthquakes located along lateral segments of the mountain chain the deep and intermediate earthquakes of the tyrrhenian sea indicate predominant down dip compression and strike slip motion at the boundaries of this benioff zone this last is interpreted as a remnant of a subduction zone active since oligocene extending to 500 km depth with a very small lateral size about 300 km the present tectonics of this benioff zone is strongly conditioned by the lateral bending more so than the gravitational sinking process the coexistence of thrust and normal faulting motion associated to the earthquakes within a few tens of kilometers of each other seems to be explained by the strong lateral inhomogeneities of the crustal rocks present in this region more so than to the depth of the seismogenetic zone and the nature of the faulting process

geochemical evidence for relict degassing pathways preserved in andesite andesitic arc volcanoes degas large quantities of volatiles evidence for vapour transport in the erupted lavas is rarely preserved and poorly understood but is crucial for understanding eruption style we present geochemical evidence for the transport of metal bearing vapour in shear zones preserved in lavas erupted from soufriere hills volcano montserrat textural evidence suggests that shear induced brittle failure occurred in a narrow zone at the conduit wall or in the lava dome elevated metal concentrations cu au ag pb zn within the zones indicate that the fractures acted as a transient pathway for metal bearing magmatic gases during slip frictional heating to temperatures of 1000 c caused partial melting at the slip surface resorption of volatiles and metals into the partial melt preserved the geochemical signature of magmatic vapour in the shear zone cordierite which is highly unusual in volcanic rocks crystallised from the peraluminous partial melt with metal bearing sulphides and oxides the shear zones provide the first geochemical evidence for vapour segregation and transport through viscous andesite magmas and provide an insight into controls on eruption style

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

petrology and geochemistry of volcanic rocks from the island of panarea implications for mantle evolution beneath the aeolian island arc southern tyrrhenian sea abstract major trace element and radiogenic isotope sr nd pb data are reported for a suite of rocks from the panarea volcano a large structure that is largely hidden below sea level and outcrops only as a group of small islands between lipari vulcano and stromboli in the eastern aeolian arc the exposed rocks mostly consist of high potassium calc alkaline hkca andesites dacites and some rhyolites shoshonitic basalts have been collected from submarine centres mafic calc alkaline ca rocks occur as thin layers of late erupted strombolian scoriae major and trace element data are scattered but define generally linear trends on inter element diagrams sr isotope ratios do not display significant increase with evolution although rough positive trends of 87sr 86sr versus sio2 and rb sr can be recognised within some units the mafic rocks display varying enrichment in potassium from ca to shoshonitic compositions and are characterised by variable abundances of incompatible trace elements which increase with potassium there is an increase of 87sr 86sr ratios and a decrease of 143nd 144nd and 206pb 204pb ratios from ca to hkca and shoshonitic mafic rocks the scattered and incomplete nature of the outcrops make it difficult to constrain magmatic evolution at panarea geochemical and isotopic data suggest that afc and mixing were important evolutionary processes however geochemical modelling does not support the possibility that the first order compositional variations observed in the mafic rocks are the result of these processes and suggests a genesis in a heterogeneous mantle source recent studies have highlighted strong differences in terms of incompatible trace element ratios and isotopic signatures between the western central and the eastern aeolian arc rocks from the western islands alicudi filicudi salina vulcano have typical magmatic arc geochemical signatures and relatively unradiogenic sr isotope compositions by contrast the eastern island of stromboli has a more radiogenic sr isotope signature and shows trace element abundances and ratios that are intermediate between arc and intraplate compositions panarea mafic rocks have geochemical and isotopic signatures that are intermediate between those observed in the two sectors of the arc the late erupted ca scoriae of panarea have trace element and isotopic compositions similar to those of the mafic rocks from the western islands of filicudi and alicudi whereas the hkca and shoshonitic mafic rocks have isotopic and trace element signatures that are closer to those of stromboli this reflects the particular position of panarea which is sited midway between the western central arc and stromboli according to some recent views subduction of the ionian sea plate is actively occurring beneath the eastern aeolian arc with rollback of the subduction zone toward the southeast the tindari letoianni malta escarpment fault zone is considered to be the boundary between the active subducting plate in the east and the african plate and western aeolian arc in the west it is suggested that the rollback of the ionian plate generated inflow of mantle material from below the western arc into the mantle wedge above the subducting ionian slab this situation generated a hybrid mantle beneath panarea which resulted in a mixture of western type and resident eastern arc mantle materials the latter had a composition akin to the source of stromboli magmas early hkca and shoshonitic magmatism tapped such a hybrid source whereas the younger ca activity has been derived from melting of unmodified western type mantle material the late eruption of ca rocks with a composition similar to western arc can be explained by assuming that a continuing inflow process had increased the amount of western type mantle with time thus favouring the late appearance of ca magmas this hypothesis accounts for the overall decrease of potassium with time which is the opposite of the trend observed in other aeolian islands

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

models of mediterranean back arc basin formation during and mainly after the tertiary continental collisions regions of extension and subsidence developed within the alpine mediterranean orogenic belt in the rear part of the contemporaneously active arcs mediterranean back arc basins are characterized by a hot upper mantle overlain by crust transitional from continental to oceanic which reflects their different stages of maturation the four basins considered here are in order of increasing maturity the pannonian basin the aegean basin the alboransouth balearic basin and the tyrrhenian basin back arc extension is not a rigid plate opening but rather an areal expansion associated with progressive bending of the arc the most successful models suggested for the evolution of mediterranean back arc basins imply updoming of the asthenosphere accompanied by lithospheric attenuation stretching and dyke intrusion the force behind asthenospheric updoming is under debate active and passive mechanisms have been suggested it seems however certain that gravity plays an important role in initiating and maintaining back arc extension basin subsidence is an isostatic response to structural changes of the lithosphere and to conductive decay of the associated heat anomaly a quantitative model for basin formation can be obtained only if the subsidence history is well documented

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

volcanological and geochemical evolution of filicudi aeolian islands south tyrrhenian sea italy this paper reports on field petrological geochemical and isotopic characteristics of volcanic rocks from filicudi island aeolian arc southern tyrrhenian sea with particular attention to the recognition of temporal and geochemical variations of magma activity the filicudi volcano consists of basaltic basaltic andesitic and high k andesitic lavas and pyroclastic deposits it represents the emergent part of a complex structure parallel to the main regional structural lineaments stratigraphic investigations and dating have defined four main cycles of activity interrupted by periods of quiescence the main stratigraphic sequences reconstructed on filicudi display irregular variations of rock evolution over time with recurrent reversals to more basic compositions magmas erupted from different vents during the first three cycles of activity display overall similar petrological and geochemical characteristics some major and trace elements define slightly scattered correlations with silica sr abundances are particularly scattered with a large range of values in basic rocks sr isotope ratios range between 0 704270 and 0 704740 and do not exhibit good correlations with geochemical parameters fractional crystallization associated with several episodes of mixing processes and crust assimilation are considered to be responsible for the complex evolution of the filicudi magma mafic magmas erupted during the last cycle of activity at la canna centre show increasing k na mg al rb sr and decreasing ba nb ba rb ratios in respect to the older basalts these characteristics are considered to reflect a derivation from a different mantle source

water contents of silicic to intermediate magmas silicic to intermediate magmas have water contents that range from 1 wt to around 7 wt depending on the character and depth of the magma source type of melting reaction and the degree of differentiation the condition of water saturation is rare implying that crustal magma genesis generally takes place under fluid absent conditions or that any fluid present must contain volatile species other than h2o the source and quantity of water present during partial melting profoundly affect the types of melting reactions residues and magmas as well as subsequent magma evolution for s type granitic magmas melting reactions involving muscovite breakdown in pelites yield low temperature wet melts that form veins pockets and small plutons in regional metamorphic terranes biotite breakdown in pelites near the amphibolite granulite facies transition yields hotter magmas with variable water contents these are emplaced at medium to high levels under granulite facies conditions biotite breakdown in quartzofeld spathic rocks yields high temperature dry magmas emplaced as subvolcanic batholiths and volcanics

the spinel and quartz associations in high grade xenoliths from tallante s e spain and their potential use in geothermometry and barometry remarkable spinel quartz associations are observed in some xenoliths found in the basaltic rocks from tallante the main primary parageneses are quartz plagioclase sillimanite spinel garnet ilmenite graphite quartz plagioclase garnet orthopyroxene spinel ilmenite

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

growth history of garnet in pelitic schists of the sanbagawa metamorphic terrain in central shikoku abstract during the prograde metamorphism of the sanbagawa metamorphic terrain in central shikoku garnet has grown in the pelitic schists whilst maintaining surface equilibrium with coexisting minerals such as chlorite and epidote etc in the quartz albite layer it has grown euhedrally in the micaceous layer its crystal morphology varies according to the different minerals in contact and their different orientations garnet enclosed in or sandwiched between micas is always ellipsoidal extended parallel to the basal planes of the micas however when the edge of a garnet has intruded at an acute angle into the micas euhedral garnet has grown it is concluded that the growth of garnet at the interface with micas ceased when the 110 surface of garnet came into contact with the basal plane of the micas in the tectonic c axis direction other models such as chloritization resorption pressure solution and mechanical erosion or grinding do not adequately explain the origin of the flattened garnet during retrograde metamorphism chloritization and resorption of garnets took place in the matrix resulting in the rough and irregular surface of garnet garnets included in albite porphyroblasts have been largely unaffected by the retrograde metamorphism

geochemical consequences of intense pulse like degassing during the onset of the central atlantic magmatic province the triassic jurassic boundary tjb ismarked by one of the five largestmass extinctions of the phanerozoic and the eruption of a large igneous province the central atlanticmagmatic province camp the tjb is characterized by a carbonate production crisis by negative excursions in the carbon isotopic ratio of buried organic matter and by successive peaks in atmospheric co2 herewe use the numerical model geoclimto explore the possible connections between the camp emplacement and the observed carbon cycle perturbations different degassing scenarios linked to the camp eruption are explored we show that the emission of realistic amounts of co2 that follow a geologically constrained degassing scenario as short termpeaks less than 10 ka leads to successive decrease in carbonate production as observed in the geological record we also calculate the evolution of carbon isotopes and show that our model reproduces the amplitude of the isotopic excursion with a volcanic degassing of co2 characterized by a carbon isotopic composition of 20 such low values could be associated to carbon pools of light isotopic composition located at the transition zone cartigny p 2010 earth and planetary science letters v 296 p 329 339 and not necessarily to biogenicmethane release finally themodel predicts a succession of short term co2 rises with an amplitude in close agreement with available proxy based reconstructions

petrology of felsic granulites metapelites metabasics ultramafics and metacarbonates from southern calabria italy prograde metamorphism uplift and cooling of a former lower crust

persistent polybaric rests of calc alkaline magmas at stromboli volcano italy pressure data from fluid inclusions in restitic quartzite nodules a fluid inclusion study has been performed on quartzite nodules of stromboli volcano hosted by calc alkaline lavas of both the strombolicchio 200 ka and paleostromboli ii 60 ka periods the nodules are mainly composed of quartz crystals with subordinate plagioclase and k feldspar small interstitial minerals such as plagioclase k feldspar clinopyroxene biotite and quartz are also found together with glass muscovite epidote and zircon occur as accessory minerals different quartzite nodules occur 1 equigranular polygonal granoblastic quartzite nodules forming a polygonal texture with clear triple points 2 inequigranular polygonal granoblastic quartzite nodules and 3 break up nodules with strongly resorbed quartz these quartzites are restites from partial melting involving felsic crustal rocks at the magma wall rock contact restitic quartz re crystallises at variable and generally high temperatures leading to the formation of quartzites with different textures quartz grains contain five types of fluid inclusions distinguished on the basis of both fluid type and textural phase relationships at room temperature type i are two phase liquid vapour co2 rich fluid inclusions they are primary and subordinately pseudosecondary in origin and have undergone re equilibration processes type ii mono phase two phase vapour liquid vapour co2 rich fluid inclusions are the most common and based on their spatial distribution and shape they can be divided into two subclasses type iia and type iib type ii inclusions are secondary or pseudosecondary and they are assumed to have formed after decrepitation of type i inclusions and cracking of the host quartz type iii inclusions are mono phase vapour they possibly contain co2 at very low density and surround the inner rims of quartz grains type iv two phase silicate melt inclusions contain glass co2 rich fluid some of them are cogenetic with type ii inclusions finally type v two phase liquid vapour aqueous inclusions are both vapour rich and liquid rich aqueous inclusions microthermometric experiments were performed on both type i and ii inclusions type i inclusions homogenise to liquid between 20 and 30 5 c type iia inclusions homogenise to vapour in the 24 to 30 c range with a maximum peak of frequency at 29 c type iib inclusions also homogenise to vapour between 14 and 25 c there appears to be no difference in homogenisation temperature distribution between the strombolicchio and paleostromboli ii samples the trapping pressures of the fluid inclusions have been obtained by combining the microthermometric data of the strombolicchio and paleostromboli ii samples with the pressure temperature volume i e density characteristics for a pure co2 system the data on the early inclusions type i suggest an important magma rest at a pressure of about 290 mpa i e about 11 km depth type iia co2 inclusions suggest that a second magma rest occurred at a pressure of about 100 mpa i e about 3 5 km depth whereas type iib inclusions were trapped later at a shallower depth during the final magma upwelling no pressure depth differences seem to occur between the strombolicchio and paleostromboli ii periods indicating the same polybaric rests for the calc alkaline magmas of stromboli despite their significantly different ages this persistence in magma stagnation conditions from 200 to 60 ka suggests a similar plumbing system for the present day strombolian activity

evidence of crustal melting events below the island of salina aeolian arc southern italy quartz rich xenoliths hosted in the basaltic andesitic and andesitic lavas of monte dei porri in the island of salina contain fluid and melt inclusions whose study makes it possible to trace back the magma ascent path of this volcano moreover they are a source of information about the anatectic processes that occurred under this island the texture mineralogy and whole rock chemistry of these rocks exhibit the typical characteristics of a residual rock which went through several melt extraction events the chemistry of melt inclusions hosted inside quartz grains sio 2 72 7 al 2 o 3 9 0 13 5 cao 0 2 4 3 k 2 o 3 1 mgo feo t 1 5 supports the hypothesis that a progressive and continuous anatectic processes affected a peraluminous high grade metamorphic rock gneiss or micaschist that constituted the calabro peloritani basement and generated a quartz bearing residue the fluids trapped inside these inclusions are rarely composed of high density co 2 with a homogenization temperature to liquid phase th l within the range 26 2 31 0 c corresponding to densities of 520 to 690 kg m 3 more commonly they are made up of low density co 2 with a homogenization temperature to vapour phase th v within the range 13 2 31 0 c corresponding to density values of 150 to 460 kg m 3 it is proposed that during ascent batches of magma rising from the mantle sampled various fragments of a residual rock from a depleted metamorphic basal layer and carried them to the surface magmas probably stopped inside at least two distinct reservoirs located at different depths 12 7 km and between 1 7 and 4 7 km in which they underwent fractional crystallization the ascent speed of the xenolith bearing magmas from the deeper storage area to the shallower reservoir was fairly high as confirmed by the low number of high density fluid inclusions preserved that show re equilibration features and by the contemporaneous presence of denser cumulitic ol cpx opx xenoliths in the host lava

evidence for a major change in silicon cycling in the subarctic north pacific at 2 73 ma the initiation of northern hemisphere glaciation in the subarctic north pacific at 2 73 ma was marked by an abrupt cessation of high opaline accumulation considered to result from an increased stratification of the water column that should have led to higher utilization of nutrients in the surface ocean we present a new stable si isotope based record of si utilization that is hard to reconcile with this model a drop in 30si 28si by 0 4 at 2 73 ma is coincident with an increase in bulk n isotope composition the contrasting utilization records cannot have been both caused by a hydrographic change alone excluding a change in the si n export ratio these results either imply a relative increase in silicic acid supplied to the surface waters or a change in its si isotope composition while it is impossible to distinguish between these two possibilities both imply a regional or global change in the si biogeochemical cycle potentially caused by an enhanced storage of si in the underlying deep waters of the pacific

beginning of melting in the granite system qz or ab an h2o the beginning of melting in the system qz or ab an h2 o was experimentally reversed in the pressure range p text h text 2 text o 2 15 kbar using starting materials made up of mixtures of quartz and synthetic feldspars with increasing pressure the melting temperature decreases from 690 c at 2 kbar to 630 c at 17 kbar in the an free alkalifeldspar granite system qz or ab h2o in the granite system qz or ab an h2o the increase of the solidus temperature with increasing an content is only very small in comparison to the alkalifeldspar granite system the solidus temperature increases by 3 c 7 c if albite is replaced by plagioclase an 20 an 40 the difference between the solidus temperatures of the alkalifeldspar granite system and of quartz anorthite sanidine assemblages system qz or an h2o is approximately 50 c

disequilibrium crystal liquid processes at hamblin cleopatra volcano lake mead area nevada abstract the 60 km 3 hamblin cleopatra stratovolcano produced shoshonite latite and trachyte lavas throughout its miocene eruptive history low silica rhyolite and silica undersaturated hawaiite erupted before and after lavas of the hamblin cleopatra volcano shoshonite latite and trachyte resulted from contamination of felsic trachyte to low silica rhyolite anatectic liquids with crystals from hawaiite most of the entrained crystals were not in equilibrium with liquid represented by groundmass but were mingled with liquid shortly before eruption crystal aggregates are common inclusions in the lavas and are sources of the contaminating minerals the resulting bulk compositions of these porphyritic lavas form a continuum that resembles a liquid line of descent as dictated by mass balance

volcanic history of lipari aeolian islands italy during the last 10 000 years abstract examination of the volcanic stratigraphy of deposits younger than 10 000 years on lipari indicates four principal periods of volcanic activity related to specific centers the products from each different volcanic center are defined as volcano stratigraphic unit vsu from the oldest these are the canneto dentro gabellotto fiume bianco forgia vecchia and monte pilato rocche rosse vsus the study of textures and dispersal of the deposits permitted the vents to be localized and the recent volcanic history of lipari to be reconstructed the oldest event formed a small explosion breccia cone with a final obsidian lava in the canneto dentro area immediately afterward a complex series of explosions produced the widespread dry surge deposits of the gabellotto fiume bianco sequence this activity ended with the extrusion of a domical lava flow the renewal of activity occurred in the pirrera area with an explosive eruption that produced explosion breccia deposits the last eruptions from this vent were coeval with the first eruption of m pilato the rim of the explosion breccia cone was partially destroyed by the forgia vecchia lava flow m pilato cone grew in a very short period of time due to a continuous swarm of explosive events after a short repose time a series of more energetic and superficial explosions occurred through a vent slightly to the south the extrusion of the rocche rosse lava flow about 729 a d ended this cycle of activity all the volcanic centers follow a quite similar stochastic pattern starting with a fall or surge eruption and ending with effusion of viscous rhyolitic lavas the four centers are aligned along either nw se or ne sw fault systems according to the structural pattern of the island they can be placed into two groups the canneto dentro gabellotto centers and the forgia vecchia m pilato centers a long quiescence 3 500 years separates the activity of these two groups while inside of each the activities were nearly contemporaneous or in rapid succession

high δ18o and possible pre eruptional rb sr isochrons in cordierite bearing neogene volcanics from se spain o and sr isotope data are reported for cordieritebearing dacites and andesites forming part of the neogene volcanic province of se spain the almandine bearing biotite cordierite labradorite dacite from the cerro del hoyazo with its numerous inclusions of metamorphic and igneous rocks has been studied in some detail a syngenetic derivation of the hoyazo dacite magma and part of its inclusions interpreted as restite by means of anatexis of semi pelitic rocks has previously been proposed

evolution and genesis of calc alkaline magmas at filicudi volcano aeolian arc southern tyrrhenian sea italy petrological trace element and sr nd pb isotopic data are reported for volcanic rocks from the island of filicudi aeolian arc southern tyrrhenian sea the volcano consists of several monogenic and polygenic centres built up through four major phases of explosive and effusive activity started before 1 ma rock composition ranges from calc alkaline basalts to high k andesites there is a negative correlation between silica and mgo cao tio2 feototal and a positive trend for k2o na2o and p2o5 lile and hfse increase with silica whereas ferromagnesian trace elements have an opposite tendency incompatible elements such as zr ba rb la display well defined positive correlations on elemental variation diagrams weak correlations are shown by the other incompatible elements sr and compatible elements define negative roughly curvilinear trends with incompatible elements 87 sr 86 sr is poorly but significantly variable 0 704016 0 704740 and shows overall higher values in the mafic than in the sialic rocks nd isotope ratios range from 0 512670 to 0 512760 and are negatively correlated with 87 sr 86 sr pb isotope ratios cluster around 206 pb 204 pb 19 31 19 67 207 pb 204 pb 15 64 15 69 208 pb 204 pb 39 11 39 47 major trace element and isotopic variations reveal complex multistage polybaric evolutionary processes for the filicudi magmas it is clear that crystal liquid fractionation processes determined many of the petrologic and geochemical characteristics of these magmas however elemental variations when coupled with isotopic variations in particular sr isotopes demonstrate that mixing processes and interaction of the magmas with older crustal material also played an important role when compared with other aeolian arc volcanoes filicudi shows petrological and geochemical characteristics similar to those of the nearby islands of salina and alicudi the three islands consist of calc alkaline rocks but the degree of magma evolution increases going from the alicudi to salina these variations are likely related to the plumbing system of the three volcanoes however trace element and isotopic evidence also suggests significant variations of primary magmas which reveal a zoned source which suffered different types of metasomatism d 2003 elsevier b v all rights reserved

monte guardia sequence a late pleistocene eruptive cycle on lipari italy this paper documents a complex sequence of interbedded lapilli fall base surge and pyroclastic flow deposits here named the monte guardia sequence that erupted from volcanic centers in the southern part of lipari aeolian island arc radiocarbon data from ash flow tuffs above and below this sequence bracket its eruption between 22 600 and 16 800 years ago geologic evidence however suggests that this single eruptive cycle had a more restricted duration of years to tens of years the basis for our interpretations comes from data measured at 38 detailed sections located throughout the island the monte guardia sequence rests on a series of lower rhyolitic endogenous domes in the southern part of lipari and it covers the oldest lavas lahars and pyroclastic flows in the north only in the northeast part of the island is it covered by younger deposits which there consist of lapilli tuffs and lavas of the monte pilato rhyolitic cycle the deposit ranges in thickness from more than 60 m surrounding the vents in the south to less than a few decimeters at 10 km distance in the north throughout most of the island the monte guardia sequence overlies a thin andesitic lapilli fall layer which is a key bed for correlation this lapilli tuff probably erupted from a volcanic center on another island of the aeolian arc possibly salina the principal activity of the monte guardia sequence started with an explosion that formed a continuous breccia blanket covering most of the island some pumiceous blocks within this breccia are composed of alternating bands of acidic and andesitic composition suggesting that the initiation of pyroclastic activity could have been triggered by magma mixing typical monte guardia sequence consists of explosive products that grade from magmatic pumice fall to phreatomagmatic base surge character the eruptive cycle is characterized by a number of energy decreasing megarhythms that start with a lapilli fall bed and end with a base surge set that progresses through sand wave massive and planar beds isopach maps of the fall and surge deposits indicate that both types were directed to the northwest by prevailing winds existing topographic relief was an additional factor that affected the emplacement of surge products at the end of the cycle andesitic pyroclastic flows and rhyolitic endogenous domes were emplaced above the monte guardia deposits near the vent

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

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

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

geochemical characteristics of the south tuscany italy volcanic province constraints on lava petrogenesis abstract three suites of volcanic rocks from radicofani mts cimini and mt amiata south tuscany italy were analyzed for major and trace element contents and sr isotopic composition all samples are silica saturated hypersthene normative and some are peraluminous samples from radicofani and the less evolved mts cimini samples have high mg numbers 74 5 66 3 consistent with the fosteritic rich nature of their olivine phenocrysts and high bulk rock abundances of ferromagnesian trace elements all samples are highly enriched in light ree 150 315 chondrites compared to heavy ree 9 15 chondrites and have negative eu anomalies eu eu 0 92 0 44 87 sr 86 sr ratios are high and variable radicofani 0 7137 0 7150 mts cimini 0 7128 0 7138 mt amiata 0 7119 0 7131 a distinctive feature of the radicofani samples is that with decreasing age the rocks increase in k2o content but decrease in la ce these south tuscany rocks have geochemical characteristics of the calc alkaline and alkaline series namely in addition to the high k rb cs ba and lree contents they have high ratios of incompatible elements relative to the high field strength ions such as ti zr hf nb and hree when compared to an estimated primitive mantle composition in general the geochemical characteristics of south tuscany volcanics are consistent with mixing between crustal derived material and mantle derived magma the mantle derived component was unusually rich in radiogenic sr and incompatible elements and had geochemical features similar to basic lavas of the high k series in the roman province

complex interaction of aluminous metasedimentary xenoliths and siliceous magma an example from mt amiata central italy aluminous silica deficient metasedimentary xenoliths in siliceous lavas of mt amiata have preserved composite zoning patterns indicative for complex processes of magma rock interaction petrographic observations and small scale mineralogical and chemical differences between up to five distinct zones including the core and envelope of lava provide evidence that quartz poor muscovite biotite schists are considered to be the most likely parent rocks and it is believed that release of volatiles from decomposing micas played a significant role in the high temperature metamorphic evolution of the xenoliths and their interaction with the magma the conditions favourable for assimilation were enhanced by injection of mafic magma into the magma chamber although this concurrent operation of magma mixing precludes a quantitative estimate of contamination from the wall rocks which was probably of minor importance the present example indicates that dry acid magma may potentially become more mafic by interaction with partially melted hydrous rocks

character of the stress field in the calabrian arc and southern apennines italy as deduced by geological seismological and volcanological information abstract three crustal sections located in key zones of the calabrian arc and southern apennines have been drawn on the basis of the available geological geophysical seismological and volcanological data the purpose is to gather information on the state of stress at different crustal levels and to test to which extent data sampled at different time intervals may be consistently compared the analysis allows for the individualization of the following sectors 1 1 peri tyrrhenian belt marked by a tensional state of stress down to the moho depth 2 2 apenninic chain subjected to tension only in its shallow portions and to a compressive regime at depth 3 3 external chain internal foretrough characterized by a deep compressive regime which is expressed at the surface in its outermost zone only 4 4 external foretrough foreland with tensional processes in the whole crust compressional processes are linked to the activity of a deep shear zone which causes the thrusting of the tyrrhenian crust over the adriatic crust and which seems to control the present distortion of the calabrian arc the analysis suggests a change in the stress field and deformation mechanisms from the uppermost to the lowermost levels of the crust and an eastward migration with time of the compressional events these facts would explain the contrasting evidence sometimes given by stress constraints derived from geological seismological and volcanological data

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

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