pyrometamorphic processes at the magma hydrothermal system interface of active volcanoes evidence from buchite ejecta of stromboli aeolian islands italy pyrometamorphic ejecta erupted during recent paroxysmal explosions and hydrothermally altered volcanic and subvolcanic rocks from stromboli volcano aeolian islands italy were studied by combined polarizing microscopy electron microprobe scanning electron microscope x ray diffraction transmission electron microscope and whole rock inductively coupled plasma optical emission spectrometry mass spectrometry analysis the pyrometamorphic ejecta are compositionally heterogeneous at the macroand micro scale and are classified as buchites that is glass coupled with a high temperature low pressure modal mineralogy three distinct facies i e cordierite plagioclase mullite plagioclase palisade and tridymite clinopyroxene are recognized among the buchites whose bulk rock chemistry is compatible with aluminousto silica rich protoliths abundant mineral growth e g plagioclase palisades and clinopyroxene coronae occurs at the contact between the ejecta and the crystal rich host shoshonitic basalt which typically coats the pyrometamorphic blocks mineral constraints pseudoporphyritic microstructures plagioclase relict phenocrysts and major and trace element compositions strongly support the origin of the buchite ejecta as hydrothermally altered rocks from thevancori edifice a period of activity spanning 410 kyr which underwent high temperature low pressure contact metamorphism in the uppermost magmatic system of an active island arc volcano such as stromboli volcanic and subvolcanic rocks usually undergo alteration processes induced by acid sulphate hydrothermal systems the circulation of acidic fluids results in leaching of the stromboli rocks in the upper part of the volcano edifice and depending on the ph temperature and exposure time to the hydrothermal fluids production of different alteration facies the hydrothermally altered stromboli rocks show facies consistent with argillic to silicic alteration containing abundant hydrous sulphate and hydroxy sulphate minerals such as the alunite group minerals hexahydrite millosevichite pickeringite and kieserite the hydrothermally altered wall rocks heated by contact with the basaltic magma of the feeder dyke system of stromboli can easily undergo pyrometamorphic processes inducing partial melting and subsolidus crystallization of the volcanic protoliths this results in the development of buchite rocks at the magma hydrothermal system interface

new unspiked k ar ages of volcanic rocks of the central and western sector of the aeolian islands reconstruction of the volcanic stages abstract a geochronological study of the filicudi salina lipari and vulcano islands aeolian archipelago using the unspiked potassium argon technique provides new age data which combined with stratigraphic correlation better constrain the temporal evolution of volcanism the unspiked k ar age of the oldest exposed lavas on filicudi 219 5 ka is significantly younger than the previous estimation of 1 02 ma in the general context of aeolian volcanism this new date suggests that the volcanism of the western sector of the aeolian archipelago is younger than previously thought geochronological data point out on the rapid transition from calc alkaline to potassic volcanism the distribution of the k ar ages within the salina lipari vulcano group shows that the volcanism started on lipari and propagated over time northward on salina and southward on vulcano geochronological and geophysical data suggest that the onset of volcanism in the central sector of the aeolian arc may be due to a mantle upwelling structure located below lipari a change in the style of the eruptions occurred in the salina lipari vulcano system at about 100 ka from the present low energy magmatic eruptions occurred between 188 and about 100 ka from about 100 ka to the present higher energy eruptions and low energy events due to magma water interaction also occurred this change in the style of activity together with the appearance of evolved products i e rhyolites during the last 50 ka is consistent with the formation of magmatic reservoirs located at shallower depth with respect to those of the 188 100 ka period the new geochronological data and available petrological models reveal that a change in the deep source of the primary magmas occurred in a relatively short time interval

geochemical and b sr nd isotopic evidence for mingling and mixing processes in the magmatic system that fed the astroni volcano 4 1 3 8 ka within the campi flegrei caldera southern italy abstract the astroni volcano was built through seven eruptions that generated pyroclastic deposits and lava domes within the campi flegrei caldera southern italy 4 1 3 8 ka bp whole rock geochemical and b sr nd isotopic investigations were carried out on representative samples of all seven eruptions the products vary from tephriphonolites to phonolites and from latites to trachytes they show textural mineralogical and isotopic evidence of disequilibrium including distinct clinopyroxene populations rounded and or resorbed plagioclase and alkali feldspar and reverse zoned phenocrysts of all these mineral phases the sr nd and b isotopic composition of whole rocks is variable and correlated with the degree of chemical evolution suggesting open system processes in addition to fractional crystallisation moreover significant sr isotopic disequilibrium between the phenocrysts and glass has been documented for one sample the chemostratigraphy of the products indicates that astroni eruptions 1 through 5 were fed by magmas of trachytic to phonolitic composition that were less enriched in radiogenic sr and 11b up section this variability has been interpreted as the result of mingling between at least two distinct magmatic end members one more evolved and the other less evolved another heterogeneous batch of magma resulting from almost complete mixing between the same two end members was drained during eruptions 6 and 7 the more evolved end member characterised by 87sr 86sr 0 7075 143nd 144nd 0 51247 and 11b 8 was very similar to the magma that fed the final phases of the agnano monte spina eruption which occurred a few centuries earlier in the astroni vent area the less evolved end member had 87sr 86sr 0 70726 143nd 144nd 0 51251 and 11b 10 and was likely derived by fractional crystallisation of a mantle derived magma an abrupt decrease in both the sr isotope ratio and the th content detected at the transition between unit 4 and 5 suggests that another magma with a 87sr 86sr ratio intermediate between those of the two identified end members may have been involved in astroni activity the more evolved end member is interpreted as a residue of the agnano monte spina eruption that was invaded by either the intermediate or the less evolved magmatic end member promoting mingling and triggering astroni activity this study of astroni provides insights for both short and long term volcanic hazard assessment as the astroni volcano is the best example of a very close sequence of eruptions from the same vent area in the campi flegrei caldera

predictive regions for geochemical compositional data of volcanic systems abstract in this contribution the theoretical basis to define predictive regions on multivariate compositional data is applied to volcanological geochemical data the method defines a predictive region based on the calculation of the eigenvalues and eigenvectors of the covariance matrix of a logratio transformed data set to circumvent the issue of singularity of the covariance matrix of the raw data due to the closure problem principal components have been used to reduce dimensionality and produce a 2 d display of the transformed data and the confidence ellipse the method was tested in a well studied volcanic sequence from stromboli volcano the vancori period and in the tholeiitic differentiation of thingmuli volcano represented in the afm diagram results of the first example are strongly consistent with previous works suggesting that the methodology reproduces the conventional patterns and potentially could help in the search of hidden patterns in noisy data results of the second example depict a useful approach for the treatment of volcanic geochemical data when plotted in a ternary diagram

repeated recharge assimilation and hybridization in magmas erupted from el chichon as recorded by plagioclase and amphibole phenocrysts abstract compositional and isotopic zoning patterns in plagioclase and amphibole phenocrysts from el chichon record multiple cycles of country rock assimilation magma injection hybridization and mixing laser ablation icp ms and electron microprobe analyses of plagioclase crystals from 7 eruptions spanning 3100 years reveal four types of zoning these compositional and isotopic zones are often associated with textural changes observed in the crystals in thin section e g sieved or patchy regions amphiboles are frequently zoned in al and si and in two magmas may have clinopyroxene rims interestingly most plagioclase show multiple and repeated zoning patterns moreover all magmas contain all zoning patterns and textures and crystals with substantially different sequences of zones occur within mm of one another the most reasonable explanation for the origin of these textures is a frequently recharged chamber plagioclase zones with increasing anorthite contents an and decreasing 87sr 86sr ratios record injection by a hotter possibly wetter and more primitive magma lower 87sr 86sr ratio zones with decreasing an and increasing 87sr 86sr ratios record assimilation of country rock and or hybridization of the host and injected magmas injection of hot magma may provide the heat for country rock assimilation changes in an without corresponding changes in 87sr 86sr ratio likely record slight variations in pressure or temperature during crystallization or the far field thermal effects of magma injection variations in 87sr 86sr ratio unaccompanied by anzoning record assimilation of country rock amphibole zoning patterns also record periodic heating events amphibole with clinopyroxene rims record episodes where the magma was heated beyond the amphibole stability field bulk compositional homogeneity and the juxtaposition of many crystals with disparate zoning patterns in single pumice require the magmatic system to be well mixed strontium diffusion rates indicate that the plagioclase zoning patterns cannot have persisted at magmatic pressures and temperatures for more than 500 years thus cycles of injection and assimilation occur on timescales equal to or shorter than the eruption recurrence interval long term compositional and isotopic homogeneity indicate that there is a balance between recharge assimilation and crystallization

deformation at stromboli volcano italy revealed by rock mechanics and structural geology abstract we approach the reconstruction of the recent structural evolution of stromboli volcano italy and the analysis of the interplay between tectonics gravity and volcanic deformation by tying together structural lithostratigraphic and rock mechanics data we establish that since 100 ka bp the edifice has faulted and jointed mainly along ne striking planes faults mostly dip to the nw with normal displacement taking also into account the presence of a nw trending regional least principal stress and of tectonic earthquake hypocenters inside the cone we suggest that this fracturing can be related to the transmission of tectonic forces from the basement to the cone dyking concentrated along a main ne trending weakness zone nez across the volcano summit resembling a volcanic rift whose geometry is governed by the tectonic field in the past 13 ka stromboli experienced a reorganisation of the strain field which was linked with the development of four sector collapses affecting the nw flank alternating with growth phases the tectonic strain field interplayed with dyking and fracturing related to unbuttressing along the collapse shoulders we propose that tectonics control the geometry of dykes inside the cone and that these in turn contribute to destabilise the cone flanks

cenozoic paleotemperatures and leaf physiognomy a european perspective for 21 european leaf floras with a focus on central europe which span a stratigraphic range from the late eocene to the pliocene paleoclimate estimates have been calculated using five different quantitative techniques a leaf margin analysis lma1 using a regression model based on data from east asia b the multivariate climate leaf analysis multivariate programm clamp technique based on data from east asia and n america c a recently developed multivariate technique based on modern european vegetation elpa d a provisional lma regression model based on the vegetation of several wet localities from n america lma2 and e the coexistence approach ca a technique based on comparisons with the nearest living relatives nlrs of fossil taxa according to our results there seems to be certain discrepancies where the different techniques are compared for paleotemperatures estimates depending mainly on the stratigraphic age of the floras for paleogene floras both multivariate leaf physiognomic techniques are in rather good agreement with ca although both techniques may differ considerably from each other in contrast for the neogene clamp shows a tendency to produce estimates that are considerably colder than ca whereas elpa provides generally warmer estimates and is in better agreement with ca and other independent evidence our results and interpretations add some caveats to temperature reconstructions based on leaf physiognomy especially when applied to european floras from older periods i e paleogene cretaceous possible changes of the relationship between climate and leaf physiognomy over time should be taken into account as a possible source of error whenever such techniques are used there is the possibility that the actual correlation between climate and leaf form may be modified by long time evolutionary responses or floral changes leading to erroneous paleoclimate estimates if a calibration data set is used which is not suited for the region and time interval in question however further research will be needed to test whether such changes in the relationship between climate and leaf physiognomy over time can also be detected on other continents or whether this is a problem restricted to europe

changes in atmospheric co2 concentrations and climate from the late eocene to early miocene palaeobotanical reconstruction based on fossil floras from saxony germany abstract in the present study proxy data concerning changes in atmospheric co2 and climatic conditions from the late eocene to the early miocene were acquired by applying palaeobotanical methods fossil floras from 10 well documented locations in saxony germany were investigated with respect to 1 stomatal density index of fossil leaves from three different taxa eotrigonobalanus furcinervis laurophyllum pseudoprinceps and laurophyllum acutimontanum 2 the coexistence approach ca based on nearest living relatives nlr and 3 leaf margin analysis lma whereas the results of approach 1 indicate changes in atmospheric co2 concentration approaches 2 and 3 provide climate data the results of the analysis of stomatal parameters indicate that the atmospheric co2 concentration was higher during the late eocene than during the early oligocene and increased towards the late oligocene a lower atmospheric pco2 level after the late eocene is also suggested by an increase in marine palaeoproductivity at this time from the late oligocene onwards no changes in atmospheric co2 concentration can be detected with the present data for the considered sites the results of the coexistence approach and of the leaf margin analysis document a significant cooling event from the late eocene to the early oligocene the pco2 decrease from the late eocene to the early oligocene indicated by the stomatal data raised in this study was thus coupled to a temperature decrease which is reflected by the present datasets from the early oligocene onwards however no further fundamental climate change can be inferred for the considered locations the pco2 increase from the early oligocene to the late oligocene which is indicated by the present data is thus not accompanied by a climate change at the considered sites a warming event during the late oligocene is however recorded by marine climate archives according to the present data no change in pco2 occurred during the cooling event at the oligocene miocene boundary which is also indicated by marine data the quality and validity of stomatal parameters as sensors for atmospheric co2 concentration are discussed

north american nonmarine climates and vegetation during the late cretaceous abstract analyses of physiognomy of late cretaceous leaf assemblages and of structural adaptations of late cretaceous dicotyledonous woods indicate that megathermal vegetation was an open canopy broad leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year with a moderate increase at about 40 45 n many dicotyledons were probably large massive trees but the tallest trees were evergreen conifers megathermal climate extended up to paleolatitude 45 50 n mesothermal vegetation was at least partially an open broad leaved evergreen woodland perhaps a mosaic of woodland and forest but the evapotranspirational stress was less than in megathermal climate some dicotyledons were large trees but most were shrubs or small trees evergreen conifers were the major tree element some mild seasonality is evidenced in mesothermal woods precipitational levels probably varied markedly from year to year northward of approximately paleolatitude 65 n evergreen vegetation was replaced by predominantly deciduous vegetation this replacement is presumably related primarily to seasonality of light the southern part of the deciduous vegetation probably existed under mesothermal climate comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational climatic patterns suggested from north american data limited data from equatorial regions suggest low rainfall late cretaceous climates except probably those of the cenomanian had only moderate change through time temperatures generally appear to have warmed into the santonian cooled slightly into the campanian and more markedly into the maastrichtian and then returned to santonian values by the late maastrichtian the early eocene was probably warmer than any period of the late cretaceous latitudinal temperature gradients were lower than at present for the campanian and maastrichtian a gradient of about 0 3 c 1 latitude is inferred equability was high a mean annual range of temperature of about 8 c is inferred for paleolatitude 51 56 n during the campanian most late cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation a brief low temperature excursion and a major long lasting increase in precipitation occurred at the cretaceous tertiary boundary in megathermal climates these events selected for plants that could exist in rainforest environments in mesothermal climates deciduousness and contamitant structural adaptations were selected the events at the cretaceous tertiary boundary had a major and long lasting impact on the evolution of land plants and their ecosystems low precipitation at low to middle late cretaceous latitudes is suggested to be the result of high levels of atmospheric co2 which in turn are probably related to inability of warm saline oceans to store large amounts of carbon conditions appear to have rapidly changed at the cretaceous tertiary boundary when oceanic circulation and stratification may have been fundamentally altered after the boundary the oceans were apparently able to store much greater amounts of carbon and the oceans withdrew large amounts of co2 from the atmosphere in turn more precipitation fell at low to middle latitudes the resulting high biomass vegetation formed a second major carbon reservoir to keep atmospheric co2 low relative to the late cretaceous changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean atmosphere system

multiple sector collapses at stromboli volcano italy how they work this paper demonstrates that four large sector collapses have affected the nw flank of the stromboli volcano in the past 13 ka alternating with growth phases in order to contribute to the evaluation of the critical conditions which trigger lateral collapses a reconstruction of the geometry of each collapse of the volcano edifice in the four stages that preceded the relative collapse events is also presented and a computation of the landslide volume this reconstruction is based on new field data plotted in three dimensions prior to the initial 13 ka collapse the volcano was 1125 100 m high above sea level the collapse had a volume of 2 23 0 87 km3 whereas the pre collapse volcano volume was 218 8 7 7 km3 the next edifice that failed was 900 70 m high a s l the collapse volume was 1 0 54 km3 with a precollapse volcano volume of 201 4 5 4 km3 the edifice then grew to 1000 60 m a s l the third collapse had a volume of 1 08 0 39 km3 and occurred within a volcano with a volume of 209 1 4 6 km3 this was followed by a new growth phase followed by the last collapse with a volume of 0 73 0 22 km3 the volcano volume was about the same as the present one the present active crater zone is at 780 m a s l in the first three collapses sliding surfaces cut the main magma conduit in the last collapse the upper scarp coincided with the conduit location dyking along a main ne trending weakness zone across the volcano summit exerted a lateral force for collapse inception the decrease of the landslide volumes with the age and the concentric scarps of the four collapses suggest that the younger sliding planes tended to become more superficial and to decrease the areal extent this is interpreted as due to a successively weaker eruptive products from dominantly lavas to dominantly pyroclastics and b the feedback effects between collapses and dykes that injected along the lateral segments of the first collapse slide plane

marine continental tephra correlations volcanic glass geochemistry from the marsili basin and the aeolian islands southern tyrrhenian sea italy abstract major minor and trace element analysis of volcanic glass in proximal and distal it is evident that correlation of proximal continental and distal marine tephras at a high level of confidence requires a full complement of major minor and trace element data in conjunction with considerations of the mineralogy and morphology of juvenile deposits these data help define petrological lineages such that precise provenance can be established whilst a precise proximal distal match must be based on identical major minor and trace element concentrations it is clear that resurgent activity from a single volcano can produce magmas with identical compositions in such cases stratigraphic relationships must complement any geochemical study occasionally proximal stratigraphies may be unrepresentative of the complete eruptive history because of a lack of exposure due to burial by more recent effusive and explosive activity or sector collapse which can remove vital stratigraphy particularly on volcanic islands

an experimental investigation of volatile exsolution in evolving magma chambers abstract previous laboratory experiments investigating the fluid dynamics of replenished magma chambers have been extended to model effects resulting from the release of gas turbulent transfer of heat between a layer of dense hot and volatile rich mafic magma overlying cooler more evolved magma can lead to crystallization and exsolution of volatiles in the lower layer small gas bubbles can cause the bulk density to decrease to that of the upper layer and thus produce sudden overturning and initiate mixing followed by further exsolution of gas and explosive eruption these processes have been modelled in the laboratory using a chemical reaction between sodium or potassium carbonate and nitric acid to release small bubbles of co 2 we have investigated both the initial overturning produced by gas release in the lower layer and the subsequent evolution of gas due to intimate mixing of the two layers the latter experiments in which the reactants remained isolated in the two layers until overturning occurred demonstrated unambiguously that the fluxes of chemical components across the interfaces between convecting layers are very slow compared to the flux of heat this shows that the evolution of layers of magma of different origins and composition can take place nearly independently of each other the magmas can coexist in the same stratified chamber until their bulk densities become equal and they mix together the processes illustrated in these experiments could occur in h 2 o bearing magmas such as in the calcalkaline association and in co 2 bearing mafic magmas such as in silica undersaturated suites

understanding the collapse eruption link at stromboli italy a microanalytical study on the products of the recent secche di lazzaro phreatomagmatic activity abstract the secche di lazzaro sdl phreatomagmatic activity with the associated neostromboli sector collapse represents the most powerful activity of the last 6 ky at stromboli as revealed by its present day activity stromboli is one of the most eruptive volcanoes in italy and flank instability along its nw flank is a common process volcano instability is often dramatised by explosive eruptions thus it is of crucial importance to understand the linking between volcano collapse and the plumbing system itself the possible role of pre eruptive magmatic processes as triggers of explosive eruptions can be mainly preserved by minerals and revealed by petrochemical studies we studied the juvenile components scoria and pumice of the pyroclastic deposits from the sdl phreatomagmatic activity with the aim to understand the eruption collapse link the sdl pyroclastic sequence has been investigated in three different outcrops at secche di lazzaro sdl sw sequence at vallone del monaco sdl s and along the old path from stromboli village to the active craters sdl n juvenile components are ks shoshonites similar to the most evolved lavas erupted at the end of the neostromboli potassic period our study indicates that the sdl system is strongly heterogeneous and made up by at least two different sequences sdl n and sdl sw sdl s with different textural characteristics of the deposits and composition of the juvenile components mineral chemistry data show a variable presence of recycled crystals antecrysts possibly deriving from the previous neostromboli activity up to 13 ky ago whole rocks are characterised by small but significant differences between the sdl n and the southern samples pointing out the presence of compositionally different potassic magmas and the crystallization and recycling of slightly different mineral assemblages a clear isotope heterogeneity has been also found and explained by the presence of 10 minimum of less radiogenic antecrysts whereas crustal contamination would have only affected the higher sr radiogenic residual melt these data suggest that the sdl phreatomagmatic eruptions were fed by compositionally distinct potassic magmas which rested and evolved in two shallow magma conduits when the magma supply ceased in the waning phase of the neostromboli activity our results also rule out the occurrence of new arrivals of refreshing magmas in the sdl feeding system as well as other internal magma related causes as triggers for the sdl explosive eruptions accordingly external collapse related causes seem effectively more suitable for triggering the sdl phreatomagmatic eruptions by decompression of the magmatic systems we also suggest the sdl n and sdl sw sdl s sequences are generated by two respective explosive events separated in time and or space they can be respectively related to multiple failures of sciara del fuoco which successively depressurised the sdl n and the sdl sw sdl s magma conduits

mineralization of the northwest quartz pyrite gold veins implications for multiple mineralization events at lepanto mankayan mineral district northern luzon philippines

volcanological and magmatological evolution of stromboli volcano aeolian islands the roles of fractional crystallization magma mixing crustal contamination and source heterogeneity the present paper reports the results of a detailed stratigraphical petrological and geochemical investigation on the island of stromboli aeolian arc southern tyrrhenian sea major and trace element data determined on a large quantity of samples from well established stratigraphic positions indicate that the magmatological evolution of the island through time was more complex than previously known the activity of the exposed part of stromboli which occurred over a time span of about 100 000 years started with the emission of high k calc alkaline hkca volcanics which were covered by calc alkaline ca shoshonitic sho high k calc alkaline hkca and potassic ks products the most recent activity consists of hkca lavas and the present day sho basaltic volcanics emitted by mildly explosive strombolian activity most of the products are lavas with minor amounts of pyroclastic rocks emplaced mainly during the early stages of activity the transition from the sho to the ks cycle was associated with the collapse of the upper part of the volcanic apparatus the transition from ks to the present day sho activity has been found to have occurred at the time of the sliding of the western portion of the volcano that generated the sciara del fuoco depression the rock series cropping out at stromboli show variable enrichment in potassium incompatible trace elements and radiogenic sr which increase from ca through hkca and sho up to ks rocks major trace element and sr isotopic data agree in indicating that the hkca and sho series evolved by crystal liquid fractionation starting from different parental liquids whereas crustal assimilation appears to have been the leading process during the evolution of ks volcanics mixing processes also played a role although they can be well documented only when they occurred between magmas with different isotopic and geochemical characteristics geochemical modelling based on trace element and isotopic data indicates that the mafic magmas of the different volcanic series may be generated by melting of an upper mantle heterogeneously enriched in incompatible elements and radiogenic sr by addition via subduction of different amounts of crustal material geochemical data however are also in agreement with the alternative hypothesis that the most mafic magmas of the different series have been generated by combined processes of fractional crystallization assimilation and mixing of a ca magma in a deep sited magma chamber the mafic magmas formed by these complex processes were successively emplaced in a shallow reservoir where they evolved by simple fractional crystallization hkca and sho series and by assimilation of crustal material ks the occurrence of changes in the geochemical signatures of the magmas at the time of the structural modification of the volcano is believed to favour the hypothesis that the variable composition observed in the volcanic rocks of stromboli is the result of processes occurring within the volcanic system

offshore evidence of large scale lateral collapses on the eastern flank of stromboli italy due to structurally controlled bilateral flank instability abstract new detailed swath bathymetry and long range side scan sonar data on the submerged flanks of stromboli integrated with seismic data and seabed sampling indicate that repeated lateral instability processes occurred on the eastern flank of the volcano although no debris avalanche deposits were known before the high resolution exploration of the seabed this flank of the island is opposite to the northwestern side more evidently affected by repeated flank collapses and this setting is evidence for a structurally controlled bilateral flank instability of the volcanic edifice evidence of at least two large scale lateral collapses is represented by a superficial hummocky megablock field partially outcropping on the middle lower eastern submerged slope and by a chaotic unit estimated volume is 1 2 km3 actually embedded within the volcaniclastic sequence at the foot of the submerged flank a main submarine scar open towards the se is carved in the upper slope on the eastern flank of the island being partially filled with gravity flow deposits owing to the present day depositional setting of the volcano s submerged flank a morphological continuity can be envisaged between this submerged scar and an inferred subaerial one likely encompassing the rina grande depression and several minor nested landslide scars recognized on the eastern stromboli flank a spatial and temporal reconstruction of possible events is proposed the chaotic debris avalanche unit buried within the volcaniclastic apron at the slope base and partially reworked in its distal part within the stromboli canyon floor is thought to be the result of a lateral collapse event called paleostromboli lateral collapse plc as it likely occurred in the earlier stages of the subaerial development of the island affecting a wide sector of the eastern stromboli flank the megablock field might instead result from a more superficial debris avalanche deposit partially eroded by gravity flows currently acting on the seabed it is tentatively related to the recent subaerial scar morphologies affecting the vancori units and for this reason named vancori lateral collapse vlc displaced materials have lower volume and mobility than the plc

reconstruction of the eruptive activity on the ne sector of stromboli volcano timing of flank eruptions since 15 ka a multidisciplinary geological and compositional investigation allowed us to reconstruct the occurrence of flank eruptions on the lower ne flank of stromboli volcano since 15 ka the oldest flank eruption recognised is roisa which occurred at 15 ka during the vancori period and has transitional compositional characteristics between the vancori and neostromboli phases roisa was followed by the san vincenzo eruption that took place at 12 ka during the early stage of neostromboli period the eruptive fissure of san vincenzo gave rise to a large scoria cone located below the village of stromboli and generated a lava flow most of which lies below sea level most of the flank eruptions outside the barren sciara del fuoco occurred in a short time between 9 and 7 ka during the neostromboli period when six eruptive events produced scoria cones spatter ramparts and lava flows the neostromboli products belong to a potassic series ks and cluster in two differently evolved groups after an eruptive pause of 5 000 years the most recent flank eruption involving the ne sector of the island occurred during the recent stromboli period with the formation of the large highly k calc alkaline lava flow field named san bartolo the trend of eruptive fissures since 15 ka ranges from n30 e to n55 e and corresponds to the magma intrusions radiating from the main feeding system of the volcano

mean annual temperature estimation based on leaf morphology a test from tropical south america abstract are models that predict mean annual temperature mat from leaf morphology applicable globally fifteen models that predict mat from leaf morphology were tested on thirty floral samples from tropical south america to determine the degree to which models based on published data that are primarily from other regions are applicable to floras from tropical south america the models included are based on regional data from north america south america and asia of the fifteen models tested five are simple linear regressions six are multiple linear regressions two are canonical correspondence analyses and two are correspondence analyses followed by nearest neighbor analyses for the seven modern floras with mat 21 c every model overestimates mat for the 23 modern floras with mat 21 c all models produce variable results without a systematic error the range of average model errors is 2 7 7 3 c while the absolute extremes of error are 0 and 15 1 c average 95 predictive confidence intervals range from 1 6 to 6 9 c predicted mat falls within the published standard error of the model for 0 67 of the south american test floras evaluating the seven sites with mat 21 c separately from the 23 sites with mat 21 c shows that no equation accurately estimates mat of the majority of low temperature sites but that four equations accurately estimate 50 of high temperature sites the results suggest that at least for sites of unknown or high elevation mean annual temperature of fossil floras from tropical south america may be better predicted from models based on the leaf morphology of tropical south american floras

gushan magnetite apatite deposit in the ningwu basin lower yangtze river valley se china hydrothermal or kiruna type abstract the gushan deposit is one of the typical magnetite apatite deposits associated with dioritic porphyries in the lower yangtze river valley belt of the eastern yangtze craton the origin of this deposit is still uncertain and remains a controversial issue divergent opinions are centered on whether the iron deposits are magmatic or hydrothermal in origin however our field observations and mineralogical studies combined with previous published petrological and geochemical features strongly suggest that the main ore bodies in the gushan magnetite apatite deposit are magmatic specific evidence includes the existence of gas bubbles tubes and miarolitic and amygdaloidal structures melt flow banding structure and the presence of ore breccia new electron microprobe analyses of the pyroxene phenocrysts of the dioritic porphyry genetically associated with the gushan magnetite apatite deposit show that the fe contents in the evolving magma dramatically decrease and then gradually increase because there is no evidence of mafic magma recharge this scenario decreasing fe could be plausibly interpreted by fe rich melts separated from fe poor silicate melts i e liquid immiscibility was triggered by minor addition of phosphorus by crustal contamination the occurrence of massive iron ore bodies can be satisfactorily explained by the immiscible fe rich melt with enormous volatile contents was driven to the top of the magma chamber due to the low density the hot and volatile rich iron ore magma was injected along fractures and spaces between the dioritic intrusions and wall rocks and led to an explosion near the surface resulting in the immediate fragmentation of the roof of the intrusion and wall rocks forming brecciated ores moreover other types of ores can be considered as a result of post magmatic hydrothermal activities our proposed metallogenic model involving the kiruna type mineralization is consistent with the observed phenomenon in the gushan deposit

the evolution of the magmatic system of stromboli volcano during the vancori period 26 13 8 ky stratigraphic changes in bulk rock and mineral chemistry within a volcanic sequence can be used to understand the evolution of the magma storage system beneath the volcano in particular changing eruptive styles and major changes in magma chemistry can be linked to open or closed system behaviour changes in phenocryst mineral chemistry often expressed as core rim zonation patterns or the development of reaction rims combined with thermodynamic analysis of appropriate mineral equilibria can provide powerful insights into the timing of inputs of new more primitive magma the vancori period 26 13 8 ky of the eruptive activity of stromboli has a relatively simple stratigraphy comprising three sub periods lower middle and upper vancori each one beginning and ending with an explosive volcanic event marked by breccias electron microprobe analyses of phenocryst and groundmass minerals olivine clinopyroxene plagioclase fe ti oxides in representative samples from the lower middle and upper vancori phases of activity allow tracking of the evolution of the magma chamber system with time thermodynamic analysis of olivine clinopyroxene mineral equilibria is used to constrain changes in temperature within the magmatic system the main stratigraphic discontinuities within the vancori sequence are clearly reflected by changes in bulk rock and mineral chemistry and evidence of textural and thermodynamic disequilibrium calculated temperatures in the eruptive products on the basis of these data the lower and middle vancori periods of the eruptive history of stromboli appear to be characterised by an open magma chamber system repeatedly re filled with basaltic magma which was continuously being erupted at the end of the middle vancori period the system became closed corresponding to a period of dormancy of the volcano and fractional crystallisation dominated following a major flank collapse of the volcanic edifice the upper vancori eruptive products show the most extreme range in bulk rock chemistry as the chamber was progressively flushed with new basaltic magma d 2005 elsevier b v all rights reserved

deciphering magma mixing the application of cluster analysis to the mineral chemistry of crystal populations abstract cluster analysis a classification technique used to group data in many fields is developed here as a tool to study magma mixing and mixed crystal populations in volcanic rocks the method is based on the quantification of the chemical degree of similarity among populations of mineral chemistry data which allows identification of discrete clusters in order to apply the technique for the particular problem of mixed crystal populations the mineral chemistry of a given crystalline phase is represented by a vector with n coordinates in which each coordinate is a real number that represents the amount of a given component in cations per formula unit present in the phase these vectors are in a set which is a subset of rn the real vector space of n dimensions because mineral chemistry data are a particular case of compositional data i e the components sum to a constant value usually 100 or the numbers of cations per formula unit the conventional euclidean distance cannot be used to quantify how similar the data are in order to apply cluster analysis to avoid this predicament aitchison s metric is proposed to measure similarities instead here average linkage a hierarchical clustering technique combined with the aitchison metric and stoichiometrical constraints is applied to mineral chemistry data this approach is evaluated using well characterized lava samples from the vancori period of activity 26 13 8 ky of stromboli volcano italy in which magma mixing has been identified between a basaltic andesite latite hosted in the magma chamber and a less evolved basaltic recharge magma the results are in agreement with previous interpretations of magma mixing which validates the use of the cluster analysis technique in the context of magma mixing relationships and opens the possibility to expand this methodology to other aspects of igneous petrology

testing the climatic estimates from different palaeobotanical methods an example from the middle miocene shanwang flora of china the miocene shanwang biota from eastern china contains exceptionally well preserved plant fossils with abundant leaf fossils and palynomorphs co occurring at several levels in the sedimentary succession this has provided an ideal opportunity to undertake detailed comparative quantitative palaeoclimate reconstruction based on both mega and microfloral assemblages using various approaches namely the coexistence approach coa leaf margin analysis lma and climate leaf analysis multivariate programme clamp by applying these approaches to the same dataset and using multiple fossil assemblages from different levels we are able to compare results from the different methods of climate prediction clamp and lma give consistently lower temperature mean annual temperature mat predictions than the coa taking errors into account all methods indicate no overall climate change through the sequence studied results from coa show overall agreement in the palaeoclimate parameters obtained using both pollen and leaf datasets indicating a high degree of internal consistency with this method

some limitations in using leaf physiognomic data as a precise method for determining paleoclimates with an example from the late cretaceous pautut flora of west greenland abstract plant parts of the late cretaceous west greenland pautut flora are derived from vegetation growing in lower delta plain delta upland and levee habitats a large river system drained the uplands and deposited leaves from species there and levee areas into a shallow bay setting the large drainage area of the rivers caused a great diversity of species to be preserved in the bay when these upland and levee species are combined with those that grew and were deposited in the lower delta plain areas 12 fern six cycad cycadeoid 1 ginkgoalean 35 conifer and over 85 angiosperm species represent the pautut flora when the paleotemperature derived from the angiosperm leaf margin ratio of the complete pautut flora 8 c is compared to other paleobotanical data and oxygen isotope values warm temperate to subtropical there is a serious discrepancy that puts the leaf physiognomic approach for precisely determining paleoclimate in the cretaceous in serious doubt also paleoclimatic interpretations based on the angiosperm leaf margin data of leaves from the lower delta plain species would indicate slightly cooler conditions than that suggested by the upper delta plain species leaf size would indicate wetter conditions in the lower delta plain even though other leaf features e g drip tips suggest moist conditions did occur in the upper delta plain these preservation enough that regional paleoclimate scenarios drawn from only one depositional setting or loclity can be erroneous a sampling size of less than 30 angiosperm species for a fossil flora also is suspect for reliably indicating climatic conditions unless the flora was originally impoverished of angiosperm species taphonomic factors play a significant role in fossil leaf preservation so collected fossil assemblages must closely represent the original vegetation before paleoclimatic interpretations based on leaf physiognomy can have a degree of credibility a limit to plausibility is especially significant in cretaceous floras because they have a limited diversity due to evolutionary constraints and appear to have consisted of more successional species than younger floras thus displaying intermediate climatic conditions moisture and arctic light levels further restrict determination of paleoclimatic conditions derived from leaf margin ratios and leaf size

estimation of rainfall variables from leaf characters in tropical africa abstract regression models are defined for leaf physiognomic and climate variables from 30 modern equatorial african plant communities herbarium specimens provide physiognomic data for published species lists for the 30 sites climate data are from a variety of published sources by limiting the sampled region to equatorial africa where annual amount and seasonality of rainfall are critical determinants of vegetation leaf physiognomy is found to be related linearly to moisture variables principal components analysis demonstrates that the pattern of variation among leaf variables is primarily a function of mean annual and wet months total of all months with 50 mm rainfall multiple regression models are derived for mean annual rainfall wet months rainfall and the number of dry months accuracy of each model is tested by comparing the adjusted predicted values the value for a case when it is not included in calculation of the regression line to the actual climate values at the 30 sites leaf size is the strongest correlate of moisture the mesophyll size class has the most significant positive relationship with annual and wet months rainfall entire margined species increase with wet months rainfall and temperature acuminate tip and length width ratio are also positively related to mean annual and wet months rainfall rounded base emarginate tip and acute tip are inversely related to rainfall variables regression models derived from modern plants and climate can be used to reconstruct seasonal and annual rainfall from cenozoic african leaf fossils

effects of volatiles on mixing in calc alkaline magma systems the intimate mixing between different magmas of disparate densities characteristic of some calc alkaline magma systems is explained by a new mechanism involving the emplacement of a layer of wet undersaturated mafic magma at the base of a magma chamber containing more differentiated magma turbulent transfer of heat between the mafic magma and the overlying magma leads to crystallization and exsolution of volatiles in the lower layer for an initial water content of a few per cent the bulk density of the mafic magma can become equal to that of the overlying magma causing overturning and intimate mixing of the magmas the mechanism is most probable in the low pressure environment of a high level magma chamber

the interplay of magmatism and tectonics an example based on the satellite scoria cones at llaima volcano chile abstract we present a geochemical and mineralogical study of the satellite scoria cones at llaima volcano chile providing insights on magmatic processes and how these are affected by the local and regional tectonics at llaima we identify two different and distinctive groups of satellite scoria cones with a common magmatic source but different petrological evolutions cones from group 1 the glomeroporphyritic group predominantly occur in the ne flank of the volcano are characterized by basaltic to basaltic andesitic compositions 51 55 wt sio2 and have glomeroporphyritic textures we have interpreted these cones as the product of magma replenishment followed by an unimpeded propagation of their feeder dikes controlled mainly by the regional stress as a result dikes are emplaced parallel to the regional 1 and perpendicular to the axis of local crustal extension cones from the group 2 the pilotaxitic group appear at the ne nw and sw flanks of the volcano they have more evolved compositions 55 60 wt sio2 and textures lacking glomerocrysts their location and morphometric parameters suggest that their feeder dike emplacement is mainly controlled by the stress exerted by the load of the volcanic edifice where the compressional stress hinders magma ascent allowing fractionation and volatile overpressure buildup the characteristic texture of these cones is interpreted as fractionation followed by a single crystallization event upon eruption the lack of scoria cones at the se flank is attributed to the local horizontal compressional stress caused by the local tectonic deformation associated to the liquine ofqui fault zone