the chemical composition of ree y th u rich accessory minerals in peraluminous granites of the erzgebirge fichtelgebirge region germany part ii xenotime xenotime from a geochemically heterogeneous series of mildly to strongly peraluminous granites of the erzgebirge germany displays extended compositional variability with respect to abundances of hree y u and th with few exceptions the maximum and minimum concentrations for the lanthanides and actinides exceed those noted for this mineral from other geologic environments xenotime chemistry is dominated by the theoretical end members hree po 4 and ypo 4 90 mol in total typical xenotime grains from the erzgebirge granites and from other granites worldwide contain 70 80 mol ypo 4 and 16 25 mol hree po 4 this study documents the occurrence of xenotime abnormally rich in hree in place of y with up to 45 mol hree po 4 substitutions of thorite coffinite th u pb sio 4 brabantite ca th u po 4 2 and monazite la sm po 4 are of minor importance reaching maximum levels of 5 6 mol each with a total contribution typically th u super 4 ca super 2 the total lanthanide and actinide contents in xenotime and host granite are not strongly correlated however formation of xenotime unusually rich in hree occurs only in the a type limica granites that are strongly enriched in these elements the shapes of hree patterns of xenotime and host rock are similar which combined with mass balance calculations indicate the importance of this mineral in affecting the hree as well as y evolution of late stage granitic melts late xenotime may show strong y ho fractionation thus recording the decoupling of y and the hree which can occur in the latest stages of crystallization of evolved granites and which may be associated with deuteric alteration

the transition from peraluminous to peralkaline granitic melts evidence from melt inclusions and accessory minerals fractional crystallization of peraluminous f and h2o rich granite magmas progressively enriches the remaining melt with volatiles we show that at saturation the melt may separate into two immiscible conjugate melt fractions one of the fractions shows increasing peraluminosity and the other increasing peralkalinity these melt fractions also fractionate the incompatible elements to significantly different degrees coexisting melt fractions have differing chemical and physical properties and due to their high density and viscosity contrasts they will tend to separate readily from each other once separated each melt fraction evolves independently in response to changing t p x conditions and further immiscibility events may occur each generating its own conjugate pair of melt fractions the strongly peralkaline melt fractions in particular are very reactive and commonly react until equilibrium is attained consequently the peralkaline melt fraction is commonly preserved only in the isolated melt and mineral inclusions we demonstrate that the differences between melt fractions that can be seen most clearly in differing melt inclusion compositions are also visible in the composition of the resulting ore forming and accessory minerals and are visible on scales from a few micrometers to hundreds of meters

composition and origin of intermediate solid solutions in the system thorite xenotime zircon coffinite abstract a comprehensive survey of the accessory mineral assemblages in variscan granites of the german erzgebirge and pan african granites from jordan revealed the occurrence of intermediate solid solutions of the tetragonal thorite xenotime zircon coffinite mineral group with partially novel compositions these solid solutions preferentially formed in evolved and metasomatically altered p poor leucogranites of either i or a type affinity thorite from the erzgebirge contained up to 18 8 wt y2o3 16 1 wt zro2 and 23 3 wt uo2 xenotime and zircon have incorporated th in abundances up to 36 3 wt and 41 8 wt tho2 respectively extended compositional gradation with only minor gaps is confined to hydrated members of this mineral group and is observed to exist between thorite and xenotime thorite and coffinite and y hree bearing thorite and zircon complex hydrous solid solutions containing elevated abundances of three or more of the endmembers are subordinate previously reported intermediate solid solutions between anhydrous zircon and xenotime and anhydrous zircon and thorite are not observed and are in conflict with experimental work demonstrating very limited miscibility between anhydrous species of endmember composition the majority of hydrous intermediate solid solutions in the th y zr u system are likely thermodynamically unstable instead they are probably metastable responses to unusual physico chemical conditions involving various parameters and conditions the relative importance of which is incompletely known leaching and dissolution of preexisting accessory phases during interaction with f bearing hydrous fluids enriched in th y hree zr and or u and common deposition of the various elements at disequilibrium supersaturation seems to play a key role but other processes may be of similar importance experimental work involving hydrous conditions and complex systems composed of more than two endmembers are needed to shed light into the stability relations of the chemically uncommon compositions treated in this study

residence of ree y th and u in granites and crustal protoliths implications for the chemistry of crustal melts a systematic study with laser ablation icp ms scanning electron microscopy and electron microprobe revealed that 70 95 wt of ree except eu y th and u in granite rocks and crustal protoliths reside within reeythu rich accessories whose nature composition and associations change with the rock aluminosity the accessory assemblage of peraluminous granites migmatites and high grade rocks is composed of monazite xenotime in low ca varieties apatite zircon thorthosilicate uraninite and betafite pyrochlore metaluminous granites have allanite sphene apatite zircon monazite and thorthosilicaie peralkaline granites have aeschinite fergusonite samarskite bastnaesite fluocerite allanite sphene zircon monazite xenotime and th orthosilicate granulite grade garnets are enriched in nd and sm by no less than one order of magnitude with respect to amphibolite grade garnets granulitegrade feldspars are also enriched in lree with respect to amphibolite grade feldspars accessories cause non henrian behaviour of ree y th and u during melt solid partitioning because elevated fractions of monazite xenotime and zircon in common migmatites are included within major minerals their behaviour during anatexis is controlled by that of their host settling curves calculated for a convecting magma show that accessories are too small to settle appreciably being separated from the melt as inclusions within larger minerals biotite has the greatest tendency to include accessories thereby indirectly controlling the geochemistry of ree y th and u we conclude that ree y th and u are unsuitable for petrogenetical modelling of granitoids through equilibrium based trace element fractionation equations

effect of degassing on sulfur contents and δ 34 s values in somma vesuvius magmas sulfur contents and 34s values of somma vesuvius magmas are consistent with syneruptive open system degassing at temperatures of 800 850 c for plinian pumices and 1100 1200 c for lavas the extent of degassing appears to be greater in lavas than in pumices the key parameter controlling the 34s 32s ratio of somma vesuvius volcanics is the average magma oxidation state which generally varies from 0 85 to 1 20 nno units for lavas and from 1 20 to 1 40 nno units for pumices consequently s contents and 34s values of magmas constitute a potentially valuable tool in estimating their average redox conditions the results of this study may help in risk mitigation when the vesuvius magmatic system evolves toward eruptive conditions

a possible earthquake triggered mega boulder slide in a chilean mio pliocene marine sequence evidence for rapid uplift and bonebed genesis the type area of the bahia inglesa formation north central chile is structurally complex as a result of active margin subduction at the peru chile trench inliers of subaerially exposed mesozoic igneous basement are unconformably overlain by a mid miocene to late pliocene marine siliciclastic sequence which has become known for its abundance of fossil vertebrates found concentrated in a phosphatite on an omission surface mega boulders derived from one of the largest inliers occur exclusively within this bonebed which appears to have formed after major localized uplift caused removal of a significant thickness of unconsolidated sediment the mega boulders were probably dislodged by a high magnitude earthquake event that accompanied tilting of the sea floor and their emplacement was an integral part of the processes involved in genesis of the bonebed

monitoring of active but quiescent volcanoes using light hydrocarbon distribution in volcanic gases the results of 4 years of discontinuous monitoring in the campi flegrei italy abstract during the period from january 1991 to january 1994 the 10 yr geochemical monitoring in the campi flegrei southern italy usually performed using the inorganic gas fraction was implemented by discontinuous monitoring of the hydrocarbon gas fraction the measured compositions have revealed the presence of significant amounts of at least 11 hydrocarbon species related to alkane alkene and aromatic classes thermodynamic calculations showed the possible existence of partially independent equilibria within the c1 c2 c3 and c1 c2 c3 c4 alkane systems as well as among alkene alkane pairs at redox conditions controlled by the geothermal feo fe1 5o redox buffer system at temperatures between 200 and 400 c and ph2o controlled by the presence of a saline brine unlike the constancy of the measured and calculated inorganic temperature equilibrium temperature based on organic species has displayed fluctuations and a significant increase starting from the second half of 1993 according to their apparent correlation with other independent observations such as the measured increases of vapor fraction h2s co2 and h2 n2 ratios on the monitored fumarole in addition to a general increase of dissolved co2 in the campi flegrei groundwaters the observed variations of the organic parameters were interpreted as the result of a general increase in acid bearing gas flux throughout the re equilibration zone

brazilian structural provinces an introduction abstract the territory of brazil coincides almost entirely with the south american platform the crystalline core of the continent its basement is composed of ancient metamorphic and igneous rocks and it has not suffered any tectonic regeneration since the beginning of the phanerozoic sedimentary rocks with almost horizontal bedding cover this crystalline basement this latter shows ages as old as early precambrian although ages between 500 and 1000 m y are conspicuously frequent the cratonic areas became consolidated more than 1700 m y ago whereas the fold belts formed essentially between 500 and 1700 m y ago the sedimentary cover accumulated from the early silurian in three large intracratonic basins until the platform became completely stabilized a late jurassic to early cretaceous reactivation caused by the break up of the ancient gondwana continent created another basin sequence chiefly along the atlantic continental margin based on the nature of the crystalline basement rocks and the sedimentary cover ten structural provinces can be distinguished 1 rio branco province in the north of the country occupied by the guyana shield and still only poorly known with an important fold belt developed during the so called transamazonian cycle 2000 200m y with high grade metamorphic rocks and only slight influence of later events 2 tapajos province in central brazil corresponding to the amazonas or guaporecraton showing chiefly precambrian crystalline rocks and behaving as an cratonic area during the phanerozoic 3 sa o francisco province located on the atlantic shield with its basement covered by rocks of different ages chiefly affected by the brasiliano cycle between 1000 and 500 m y and constituting another cratonic area 4 tocantins province between the amazonas and sa o francisco cratons with the oldest rocks in its centre ages over 2600 m y and at the eastern and western borders metamorphic sequences of various fold belts and almost no phanerozoic deposits 5 mantiqueira province located along the southern part of the atlantic coast affected chiefly by the brasiliano folding cycle 6 borborema province in the northeast brazilian fold belt affected by the brasiliano cycle in a very complex way and with important faulted zones it was reactivated in phanerozoic times when also sedimentary covers accumulated 7 amazonas province represented by the amazonas sedimentary basin syneclise and subdivided into four parts by three important arcs 8 parnaiba province coinciding with the piauf maranha o syneclise and filled with a rather thick sedimentary sequence 9 paranaprovince the sedimentary basin of southern brazil in which the well known late paleozoic glaciation features are found and which possesses an extensive cover of basaltic rocks of late jurassic to early cretaceous age 10 coastal province and continental margin the youngest structural unit developed during the separation of the continent and represented by rift valleys and coastal basins filled with mesozoic cenozoic deposits of various kinds

sedimentary features of tsunami backwash deposits in a shallow marine miocene setting mejillones peninsula northern chile abstract miocene shoreface sandstones in the caleta herradura half graben northern chile contain an exceptionally coarse deposit that based on sedimentologic and stratigraphic features is regarded as having been laid down during a tsunami event by non cohesive and sediment laden subaqueous density flows interpretations of the principal sediment depositing mechanisms effective in the tsunami surges rely largely on field observations of deposit geometry and internal sedimentary characteristics this example comprises two erosively based sedimentation units that were probably deposited by successive waves in the tsunami wave train the lower unit consists of a clast supported polymodal boulder bearing breccia composed mostly of angular clasts and fewer well rounded clasts framework components are mostly chaotic but may also exhibit either inverse to normal grading or crude normal grading laterally changes in characters of depositional facies are common and abrupt the sand sized bioclastic rich matrix is poorly sorted and very similar to the underlying lower shoreface bioclastic sandstone implying that soft sediments eroded at the lower erosional surface contributed to the tsunami deposit the bulk of the upper unit is a poorly sorted breccia bearing sandstone pebbles and cobbles are scattered massive or normally graded sporadic outsized boulders emplaced as debris fall deposits may occur along the erosional base an array of signatures such as unusually coarse grain size in comparison to the surrounding deposits erosional bases the mixed sources of sediments multiple erosional and depositional events normal size grading or massive texture are all considered distinctive features of tsunamigenic deposits backwash deposition is indicated by the incorporation within the tsunami deposits of sediments derived from mixed sources such as angular clasts from nearby subaerial settings rounded clasts reworked from beach gravels and bioclastic sand eroded from older and unconsolidated shoreface deposits notwithstanding the absence of soft sediment deformation features the marked facies change from a lower shoreface into an upper shoreface environment through the tsunamiites provides directional information about the origin of the tsunami wave it was most likely produced by a sea floor fault displacement associated with an episode of sudden probably coseismic coastal uplift

u pb dating of the madeira suite and structural control of the albite enriched granite at pitinga amazonia brazil evolution of the a type magmatism and implications for the genesis of the madeira sn ta nb ree cryolite world class deposit the madeira sn nb ta deposit corresponds to the albite enriched facies of madeira granite madeira suite that is part of a ne sw alignment of three granitic bodies structural analyses suggest that the albite enriched granite emplacement and development of related structures occurred in a different tectonic setting than earlier facies of the granitic bodies in the ne sw alignment and that the structure was dominated by a n ne trending shortening related to a left lateral motion along a ne sw corridor within a riedel shear three types of structures flat lying near vertical fractures and geodes miaroles concentrated the last magmatic related fluid in the albite enriched granite u pb in situ zircon dating of the albite enriched granite yielded an age of 1 822 22 ma the other granitic plutons of the madeira suite agua boa granite topaz granite facies and europa per alkaline granite formed at 1 825 14 ma 1 831 11 ma and 1 839 10 ma respectively the granite bodies of the madeira suite occur in an area occupied by a cauldron complex composed of volcanic sequences iricoume group and associated a type granites mapuera suite and their formation was controlled by the reactivation of the cauldron structures and the pre existing structures the gap between the cauldron complex and the madeira suite is no greater than 35 ma the geological evolution was reanalyzed from the perspective of an entire extensional environment where three successive episodes of a type magmatism and basin formation urupi formation occurred the data and interpretations of this work imply crucial constraints on the petrologic models proposed for the albite enriched granite and consequently on the genesis of the madeira deposit

the volcanic and geothermally active campi flegrei caldera an integrated multidisciplinary image of its buried structure the campi flegrei caldera in southern italy is one of the greatest geohazard areas on earth evidence of an active magmatic and geothermal system is provided by ongoing ground uplift with volcano tectonic and long period lp seismicity the persistent degassing of 1500 tonnes of co2 per day the presence of hot fumaroles at temperatures of 90 150 c brine rich aquifers with total dissolved solids up to 33 g l 1 and high thermal gradients in the crust with temperatures reaching 420 c at 3 050 m b s l since the 1940s more than 100 exploratory boreholes have been drilled in the area to depths of 80 3 100 m by the azienda geologica italiana petroli agip and the societa anonima forze endogene napoletane safen to date however no systematic reanalysis of the drilling data has been carried out and the buried volcanic structure has not been updated using the most recent scientific results and previous findings by integrating unpublished data from the agip and safen reports with published information from geological volcanological petrological petrophysical and geophysical studies this paper presents an improved picture of the campi flegrei caldera that will be useful for volcanic hazard assessment and mitigation in the naples area and for future research planning the results suggest that intra caldera activity has been influenced by how the magmatic system at depths greater than about 4 km has determined the transfer of magma volatiles and heat to the overlying geothermal system and ultimately to the surface in particular intriguing is that the most volcanically active central eastern sector of the caldera which is subject to intense bradyseismic ground movement and gas emission coincides with a structurally delimited subsurface rock volume characterized by an uprising of the 100 c isotherm a deep water supply to the shallower aquifer the early disappearance of secondary calcite lp seismicity and high seismic s wave attenuation in this area we also document evidence of repeated injection at depths of c 1 5 3 0 km of isolated and small volume batches of magma where occurred their crystallization and degassing shallow intrusions and degassing of magma are thus identified as two of the key processes that drive unrest in campi flegrei

what induced the exceptional 2005 convection event in the northwestern mediterranean basin answers from a modeling study 1 open sea convection occurring in the northwestern mediterranean basin nwmed is at the origin of the formation of western mediterranean deep water wmdw one of the main mediterranean water masses during winter 2004 2005 a spectacular convection event occurred observed by several experimental oceanographers it was associated with an exceptionally large convection area and unusually warm and salty wmdw explanations were proposed tentatively relating the unusual characteristics of this event to the eastern mediterranean transient emt or to the atmospheric conditions during winter 2004 2005 in the nwmed they could however not be supported until now here we used numerical modeling to understand what drove this convection event the control simulation performed for the period 1961 2006 reproduces correctly the long term evolution of the mediterranean sea circulation the emt and the nwmed convection event of 2004 2005 sensitivity simulations are then performed to assess the respective contributions of atmospheric and oceanic conditions to this event the weakness of the winter buoyancy loss since 1988 in the nwmed prevented strong convection to occur during the 1990s enabling heat and salt contents to increase in this region this resulted in the change of wmdw characteristics observed in 2005 the strong buoyancy loss of winter 2004 2005 was responsible for the intensity of the convection observed this winter in terms of depth and volume of newly formed wmdw the emt did not fundamentally modify the convection process but potentially doubled this volume by inducing a deepening of the heat and salt maximum that weakened the preconvection stratification

tsunami sculpturing of the pebble beach wave cut platform crescent city area california abstract bedrock sculpturing of semilithified st george formation sandy mudstone exposed on a wave cut platform has produced a variety of erosional forms that include surface scratches made by beach debris ripple like ridges that reflect differential erosion of bedrock potholes and scallop shaped pockets and grooves which may be straight or sinuous straight grooves form by preferential incision of regional joints sinuous grooves are not fracture controlled are oriented parallel to wave run up orthogonal to the coast and exist as closely spaced subparallel nonconnecting internally drained grooves that are best developed on higher platform ramparts and benches sinuous grooves have a mean length of 258 cm mean maximum width of 14 cm and mean width length ratio of 0 08 they are not as deeply incised as straight grooves do not serve as conduits for low tide runoff during winter months and typically terminate by shallowing and narrowing in both seaward and landward directions sinuous appeara

calculations of asteroid impacts into deep and shallow water contrary to received opinion ocean impacts of small 500 m asteroids do not produce tsunamis that lead to world wide devastation in fact the most dangerous features of ocean impacts just as for land impacts are the atmospheric effects we present illustrative hydrodynamic calculations of impacts into both deep and shallow seas and draw conclusions from a parameter study in which the size of the impactor and the depth of the sea are varied independently for vertical impacts at 20 km s craters in the seafloor are produced when the water depth is less than about 5 7 times the asteroid diameter both the depth and the diameter of the transient crater scale with the asteroid diameter so the volume of water excavated scales with the asteroid volume about a third of the crater volume is vaporised because the kinetic energy per unit mass of the asteroid is much larger than the latent heat of vaporisation of water the vaporised water carries away a considerable fraction of the impact energy in an explosively expanding blast wave which is responsible for devastating local effects and may affect worldwide climate of the remaining energy a substantial portion is used in the crown splash and the rebound jet that forms as the transient crater collapses the collapse and rebound cycle leads to a propagating wave with a wavelength considerably shorter than classical tsunamis being only about twice the diameter of the transient crater propagation of this wave is hindered somewhat because its amplitude is so large that it breaks in deep water and is strongly affected by the blast wave s perturbation of the atmosphere even if propagation were perfect however the volume of water delivered per metre of shoreline is less than was delivered by the boxing day 2004 tsunami for any impactor smaller than 500 m diameter in an ocean of 5 km depth or less near field effects are dangerous for impactors of diameter 200 m or greater hurricane force winds can extend tens of kilometers from the impact point and fallout from the initial splash can be extremely violent there is some indication that near field effects are more severe if the impact occurs in shallow water

liquidus equilibria in the system k2o na2o al2o3 sio2 f2o 1 h2o to 100 mpa ii differentiation paths of fluorosilicic magmas in hydrous systems we investigated phase equilibria in the six component system na2o k2o al2o3 sio2 f2o 1 h2o at 100mpa to characterize differentiation paths of natural fluorine bearing granitic and rhyolitic magmas topaz and cryolite are stable saturating solid phases in calcium poor systems at 100mpa the maximum solidus depression and fluorine solubility in evolving silicic melts are controlled by the eutectics haplogranite cryolite h2o at 6408c and 4 wt f and haplogranite topaz h2o at 6408c and 2 wt f topaz and cryolite form a binary peralkaline eutectic at 6608c 100mpa and fluid saturation the low temperature nature of this invariant point causes displacement of multiphase eutectics with quartz and alkali feldspar towards the topaz cryolite join and enables the silicate liquidus and cotectic surfaces to extend to very high fluorine concentrations more than 30 wt f for weakly peraluminous and subaluminous compositions the differentiation of fluorine bearing magmas follows two distinct paths of fluorine behavior depending on whether additional minerals buffer the alkali alumina ratio in the melt in systems with micas or aluminosilicates that buffer the activity of alumina magmatic crystallization will reach either topaz or cryolite saturation and the system solidifies at low fluorine concentration in leucogranitic suites precipitating quartz and feldspar only the liquid line of descent will reach topaz or cryolite but fluorine will continue to increase until the quaternary eutectic with two fluorine bearing solid phases is reached at 5408c 100mpa and aqueous fluid saturation the maximum water solubility in the haplogranitic melts increases with the fluorine content and reaches 12 5 0 5 wt h2oat the quartz cryolite topaz eutectic composition a continuous transition between hydrous fluorosilicate melts and solute rich aqueous fluids is not documented by this study our experimental results are applicable to leucocratic fluorosilicic magmas in multicomponent systems however the presence of calcium may severely limit enrichment of fluorine by crystallization of fluorite

the thorite mineralization in the madeira sn nb ta world class deposit pitinga brazil abstract the world class sn nb ta madeira deposit is located in the pitinga mine northern brazil the deposit is associated with the albite enriched granite facies of the a type madeira granite 1820 ma the mine commercially extracts tin cassiterite nb and ta u pb pyrochlore and columbite fluorine cryolite y ree xenotime zr zircon u u pb pyrochlore and zircon and th thorite are potential byproducts this work presents a detailed study of thorite mineralization in the albite enriched granite subfacies the albite enriched granite core the albite enriched granite border and associated pegmatites the madeira deposit is revealed in this work to be among the largest th deposits in the world with 164 mt of homogeneously dispersed ore average grade of 759 ppm tho2 in the rock and higher concentrations up to 1 8 wt tho2 in small pegmatites average of 0 51 wt tho2 thorite compositions are either close to the thorite pole or correspond to relatively limited substitutions in the thorite zircon xenotime coffinite solid solution system the concentration of fe in thorite ranges from 0 11 wt to 29 56 wt fe2o3 and in many cases is considered to be of structural nature as well as part of the content of f up to 6 02 wt f thorites of all subfacies were strongly affected by hydrothermal alteration related to f rich low temperature aqueous fluids the hydration of thorite allowed the introduction of m3 cations y ree fe and al and f and caused losses in si and th contents average of 48 wt tho2 the alteration also created a fe rich halo in thorite with associated secondary minerals likely th fe hydroxyfluorides and y th fe fluorcarbonates the th u average ratios in bulk rock are 1 85 in the albite enriched granite border 3 82 in the albite enriched granite core and 19 85 in the associated pegmatites this variation reflects a pattern of magmatic evolution with higher availability of u in earlier stages and u depletion in later stages in pitinga the th and u mineralization are divided into different minerals formed at distinct stages of magma evolution this feature is related to fluorine enrichment and high alkalinity of the magma that strongly inhibited the early crystallization of zircon as well as columbite and favored the early appearance of u pb pyrochlore when crystallization of hydrous silicates reduced alkalinity crystallization of zircon from a magma depleted in u nb ta and lree became intense accompanied by thorite and xenotime

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

intrusion and deformation at campi flegrei southern italy sills dikes and regional extension 1 the campi flegrei volcanic district in southern italy has been uplifted since 1968 by a net maximum of 3 m during the intervals 1968 1972 and 1982 1984 the uplift represents a permanent deformation against a background rate of subsidence of about 17 mm a 1 previous models have reproduced the observed vertical deformation but not the full pattern of horizontal movements the 1982 1983 deformation is here reanalyzed in terms of a penny shaped sill on its own with a tabular surface protrusion or in an extensional stress field it can be explained best by the intrusion of a sill of 0 03 0 04 km3 at a depth of 2 75 km in a crust that is being stretched ese wnw at a strain rate of about 5 6 10 5 a 1 the sill s volume is similar to the common volumes of campi flegrei s eruptions since the neapolitan yellow tuff nyt caldera was formed 15 6 ka ago this similarity and the permanent nature of the uplift favor magmatic intrusion as the primary source of unrest sill formation may thus reflect the spreading of magma at a level of neutral buoyancy or along lateral discontinuities in the crust the southern part of the caldera has been shielded from post nyt eruptions despite some 33 m of permanent uplift since roman times precursors to eruptions may thus be related not to caldera wide uplift but to the preceding conditions that determine whether magma ascends beneath the southern part of the caldera favoring sill intrusion or elsewhere favoring an eruption

high and low temperature alteration of uranium and thorium minerals um ara granites south eastern desert egypt abstract the um ara area in the south eastern desert of egypt contains a number of uranium occurrences related to granitic rocks u rich thorite thorite and zircon are the main primary uranium and thorium bearing minerals found in mineralized zones of the um ara alkali feldspar granites uranophane is the most common secondary uranium mineral u rich thorite contains blebs of galena has rims of uranophane and contains inclusions of zr rich thorite electron probe microanalysis epma provides an indication of a range of solid solution between thorite and zircon in which intermediate phases such as th rich zircon and zr rich thorite were formed these phases have higher sum of all cations per formula 2 05 to 2 06 apfu for 4 oxygen atoms than that of ideal thorite and zircon this is attributed to the presence of substantial amount of interstitial cations such as ca u and al in these phases some zircon grains are stoichiometric in composition other altered grains display lower sio 2 and zro 2 contents enrichment of th and u in altered zircon preferentially involves coupled substitution ca 2 th u 4 2zr 4 2si 4 implying that significant u and th may enter the zr and si position in zircon negative correlation of zr vs hf and al may indicate that hf and al have been introduced to the zircon during later fluid alteration rather than during the primary magmatic event a two stage metallogenetic model is proposed for the alteration processes and origin of u and th bearing minerals in the um ara alkali feldspar granite 1 the first stage was dominated by hydrothermal alteration and accompanied by albitization k feldspathization desilicification chloritization hematitization silicification argillization fluoritization and corrosion of primary u bearing minerals solid solution between thorite and zircon occurred during this stage the second stage occurred at the near surface profile where circulating meteoric water played an important role in mobilizing the early formed primary u bearing minerals uranium was likely transported as a calcium uranyl carbonate complexes when these complexes lost their stabilities by precipitation of calcite they decomposed in the presence of silica to form uranophane

coconuts in miocene turbidites in new zealand possible evidence for tsunami origin of some turbidity currents fossil coconuts are recorded in proximal turbidites of middle miocene age in eastern north island new zealand this is apparently the first record of coconuts in turbidites the rocks can be assigned to a mid submarine fan environment and are part of the accretionary prism of the late cenozoic volcanic arc in northern new zealand the climate was marginally tropical these turbidites may have been formed by the surge of sediment and debris carried offshore by tsunamis

hydrothermal activity and subsoil complexity implication for degassing processes at solfatara crater campi flegrei caldera the solfatara area and its fumaroles are the main surface expression of the vigorous hydrothermal activity within the active campi flegrei caldera system at depth a range of volcanic and structural processes dictate the actual state of the hydrothermal system below the crater the presence of a large variety of volcanic products at shallow depth including pyroclastic fallout ash beds pyroclastic density current deposits breccias and lavas and the existence of a maar related fault system appears to exert major controls on the degassing and alteration behavior adding further to the complexity of this environment variations in permeability and porosity due to subsoil lithology and alteration effects may further influence fluid flow towards the surface here we report results from a field campaign conducted in july 2015 that was designed to characterize the in situ physical temperature humidity and mechanical permeability strength stiffness properties of the solfatara crater subsoil the survey also included a mapping of the surficial hydrothermal features and their distributions finally laboratory measurements porosity granulometry of selected samples were performed our results enable the discrimination of four main subsoils around the crater 1 the fangaia domain located in a topographic low in the southwestern sector 2 the silica flat domain on the western altered side 3 the new crust domain in the central area and 4 the crusted hummocks domain that dominates the north east and south parts these domains are surrounded by encrusted areas reworked material and vegetated soil the distribution of these heterogeneous subsoils suggests that their formation is mostly related to i the presence of the fangaia domain within the crater and ii a system of ring faults bordering it the subsoils show an alternation between very high and very low permeabilities a fact which seems to affect both the temperature distribution and surficial degassing a large range of surface temperatures from 25 up to 95 degrees c has been measured across these surfaces with the hottest spot corresponding to the mud pools the area of new crust formation and the crusted hummocks in the subsoil the distribution of temperature is more complex and controlled by the presence of coarser and more permeable sandy pebbly levels these act as preferential pathways for hot hydrothermal fluid circulation in contrast low permeability fine grained levels act as thermal insulators that remain relatively cold and hinder fluid escape to the surface hot gases reach the surface predominantly along vertical fractures when this occurs mound like structures can be formed by a cracking and healing process associated with significant degassing it is anticipated that the results presented here may contribute to an improved understanding of the hazard potential associated with the ongoing hydrothermal activity within the solfatara crater at this site the permeability of the near surface environment and its changes in space and time can affect the spatial and temporal distribution of gas and heat emission particularly in areas where reduction in permeability occurs it can produce pore pressure augmentation that may result in explosive events

chemical and isotopic compositions of minerals and waters from the campi flegrei volcanic system naples italy abstract based on their 34 s signature sulfate minerals and native sulfur around fumaroles and hot water pools from the campi flegrei volcanic area derive from supergenic oxidation of volcanic h 2 s their mean 34 s value 0 2 1 7 matches with that of fumarolic h 2 s at solfatara 0 3 0 3 as well as with the 34 s of 1 4 obtained for total sulfur in fresh trachyte from the area all 34 s values indicate a mostly deep seated origin for sulfur thermal waters were analysed for major and minor chemistry and for oxygen hydrogen and sulfur isotope compositions pools at pisciarelli are filled with evaporated meteoric water heated by rising magmatic gases the water 18 o 3 8 1 3 and 2 h 6 5 2 2 values in these steam heated waters are controlled by mixing and evaporation effects and the 34 s value of dissolved sulfate 1 3 0 3 basically agrees with supergenic oxidation of deep seated h 2 s as the major source of sulfur instead water from thermal springs and wells elsewhere in the campi flegrei appears to be a mixture between dilute meteoric and saline marine components the latter may be local seawater from the bay of pozzuoli the 18 o and 2 h values of waters sampled during 1993 1994 range from 5 6 to 0 3 and from 33 to 3 4 respectively the 34 s values of dissolved sulfate range between 0 1 and 19 5 in general sulfate is probably derived essentially from two sources both within the volcanic cover i e oxidation dissolution of pyrite and anhydrite and marine water an occasional source of water and sulfate is represented by magmatic gases which directly interact with shallow meteoric water as in the case of the hotel tennis well yielding steam heated water with 18 o 1 5 0 2 2 h 17 1 and 34 s 0 1

hydrothermal alteration of surficial rocks at solfatara campi flegrei petrophysical properties and implications for phreatic eruption processes abstract solfatara crater is located within the campi flegrei caldera to the west of naples italy it is one of the largest fumarolic manifestations known and the rocks hosting the hydrothermal system are affected by intense hydrothermal alteration alteration can result in changes of degassing behavior and in the formation of a cap rock thereby increasing the probability of phreatic eruptions here we investigate the effects of alunitic solfataric alteration on the mineralogy the physical properties porosity density permeability and the mechanical properties strength of the rocks involved as well as its influence on fragmentation and ejection behavior our results show that the pristine mineralogy of deposits from the vicinity of the solfatara cryptodome and from pisciarelli is almost completely replaced by amorphous silica and alunite the differences in the degree of alteration among the samples series are reflected in the investigated properties and behavior as well as in the analysis of the experimentally generated particles alunitic alteration increases porosity and permeability whereas it reduces density elastic wave velocity and strength leading to higher fragmentation and ejection speeds for the sample series examined in this study our results also show that alteration results in the generation of a high fraction of fines particle sizes

first observations of the fumarolic gas output from a restless caldera implications for the current period of unrest 2005 2013 at campi flegrei 1 the fumarolic gas output has not been quantified for any of the currently deforming calderas worldwide due to the lack of suitable gas flux sensing techniques in view of resumption of ground uplift since 2005 and the associated variations in gas chemistry campi flegrei in southern italy is one of the restless calderas where gas flux observations are especially necessary here we report the first ever obtained estimate of the campi flegrei fumarolic gas output based on a set of multigas surveys performed in 2012 and 2013 with an ad hoc designed measurement setup we estimate that the current campi flegrei fumarolic sulphur s flux is low on the order of 1 5 2 2 tons day suggesting substantial scrubbing of magmatic s by the hydrothermal system however the fumarolic carbon dioxide co2 output is 460 160 tons day mean sd which is surprisingly high for a dormant volcano in the hydrothermal stage of activity and results in a combined fumaroles soil co2 output of 1560 tons day assuming magma to be the predominant source we propose that the current co2 output can be supplied by either i a large 0 6 4 6 km3 deeply stored 7 km magmatic source with low co2 contents 0 05 0 1 wt or ii by a small to medium sized 0 01 0 1 km3 but co2 rich 2 wt magma possibly stored at pressures of 100 to 120 mpa independent geophysical evidence e g inferred from geodetic and gravity data is needed to distinguish between these two possibilities

experimental investigations on the explosivity of steam driven eruptions a case study of solfatara volcano campi flegrei steam driven eruptions both phreatic and hydrothermal expel exclusively fragments of non juvenile rocks disintegrated by the expansion of water as liquid or gas phase as their violence is related to the magnitude of the decompression work that can be performed by fluid expansion these eruptions may occur with variable degrees of explosivity in this study we investigate the influence of liquid fraction and rock petrophysical properties on the steam driven explosive energy a series of fine grained heterogeneous tuffs from the campi flegrei caldera were investigated for their petrophysical properties the rapid depressurization of various amounts of liquid water within the rock pore space can yield highly variable fragmentation and ejection behaviors for the investigated tuffs our results suggest that the pore liquid fraction controls the stored explosive energy with an increasing liquid fraction within the pore space increasing the explosive energy overall the energy released by steam flashing can be estimated to be 1 order of magnitude higher than for simple argon gas expansion and may produce a higher amount of fine material even under partially saturated conditions the energy surplus in the presence of steam flashing leads to a faster fragmentation with respect to gas expansion and to higher ejection velocities imparted to the fragmented particles moreover weak and low permeability rocks yield a maximum fine fraction using experiments to unravel the energetics of steam driven eruptions has yielded estimates for several parameters controlling their explosivity these findings should be considered for both modeling and evaluation of the hazards associated with steam driven eruptions

isotopic study of the origin of sulfur and carbon in solfatara fumaroles campi flegrei caldera abstract isotopic study of the origin of sulfur and carbon in the hottest solfatara fumaroles of campi flegrei caldera southern italy was carried out on gas samples collected between 1983 and 1988 i e during and after the 1982 1984 seismo volcanic crisis the results for sulfur h2s the first ever reported on these gases indicate a mean 34 s of 0 3 0 3 range 0 7 to 0 1 versus canyon diablo troilite standard consistent with an igneous derivation of this element from either active magma degassing or and leaching of reduced sulfur bearing minerals in the volcanic layers the lack of peculiar 34s variation during and after the crisis suggests that the chemical variation of h2s and s c ratio in the fumaroles increase and then decrease by a factor 3 were not due to a changing origin of sulfur the mean 13c of carbon co2 over the period of survey 1 6 0 2 range 1 9 to 1 3 versus pdb standard is similar to the values obtained before the crisis since 1970 such an isotopic constancy requires a large and stable source of carbon feeding the fumaroles the measured 13c values are much higher than those typical of primary mantle magmatic carbon 6 2 and plot within the 13c range for marine carbonates 0 2 such high values may reflect either a 13c fractionation during degassing of co2 from the underlying 5 km depth magma chamber or b the contribution of heavy co2 of sedimentary origin derived from either thermometamorphism of mesozoic limestone series embedding the magma chamber or possibly past contamination of the local mantle by subducted sediments various arguments among which volcanological evidence of an isolated and cooling magma reservoir which would have been extensively degassed and so depleted in 13c along with time the low 3he 4he ratios and the broad 13c enrichment of volcanic fluids in the region and geochemical evidence of crust magma fluid interactions suggest that a considerable fraction 60 of co2 in solfatara fumaroles derives from carbonate sediments in the basement the contribution of magma derived co2 may be higher within the central part of the caldera including solfatara crater than toward its western margin where fumarolic and geothermal well gases exhibit lower 3he 4he ratios and still higher 13c values such a geochemical pattern is consistent with the central distribution of ground deformation and seismicity during the 1982 1984 crisis and with the idea of a residual magma body confined beneath the central part of the structure alternatively higher 13c and lower 3he 4he ratios toward the western margin may result from dilution of solfatara type gas during progressively deeper water boiling finally accepting that solfatara co2 derives from simple crustal mixing between magmatic and sedimentary carbon its constant isotopic composition together with the constant he isotope ratio would restrict the possibility of magma intrusion and or higher magmatic gas input as mechanisms responsible for the 1982 1984 events however this conclusion would no more hold true if the magma itself or even its mantle source were previously contaminated by crustal carbon

rare element mineralization related to precambrian alkali granites in the arabian shield five examples of disseminated rare element mineralization with sufficient resource potential to warrant exploration all are characterized by enrichment in a suite of granitophile elements which typically includes nb ta sn rare earth elements y th u and zr but they differ in size geometry mode of occurrence and lithology two types of mineralization the jabal sa id type is characterized by high total iron to total alkali ratios and high k 2 o na 2 o ratios the ghurayyah type is characterized by major oxide abundances approximating those of typical alkali granites both types evolved from alkali granite magmas formed by high temperature dry melting of late proterozoic island arc crust indicated resources range from 6 million metric tons jabal tawlah and umm al birak through or 20 million metric tons jabal sa id and jabal hamra to 440 million metric tons ghurayyah the highest average grades from nb 3 400 ppm sn 380 ppm y 5 200 ppm and zr 37 000 ppm occur at jabal tawlah the highest ta grades 200 ppm at ghurayyah and the highest u 130 ppm and th 830 ppm grades at jabal sa id modified journal abstract

geochemical monitoring of the thermal waters of the phlegraean fields abstract thermal waters from the phlegraean fields pf caldera area have been periodically sampled and analysed during the period 1990 1999 for major chemical constituents and chemico physical parameters to define the most useful variables for geochemical surveillance the variations observed in waters from different locations were compared with ground movements and microseismic events recorded at the time of observation the discontinuous monitoring of the hydrothermal system of the pf has given indications about the geochemical variations brought about by changes in the chemical and physical characteristics of the deep aquifers because of the complexity of the pf geothermal system in each sampling location different variations have been observed and then evaluated on the basis of the different kinds and degrees of deep fluid supply characterising waters sampled in the different zones in some cases a good correspondence between vertical soil movements and chemical changes in the waters has been observed in particular in pools and wells located around the solfatara crater interesting variations in some chemical parameters ph ammonia and or so 4 2 cl ratios have been recorded variations can be observed in all of the sampling locations but pools and wells located near the solfatara crater are the best sites for detecting changes occurring in the deep hydrothermal system and possibly in the activity of the underlying magma chamber

geology and uranium thorium mineral deposits of the bokan mountain granite complex southeastern alaska abstract the bokan mountain kendrick bay uranium thorium deposits are associated with a late jurassic peralkaline granite ring dike complex the uranium thorium deposits form pipe like bodies along contacts or occur as pods in en echelon northwest striking shear zones the host intrusive is a multiphased body consisting mainly of riebeckite granite porphyry and subordinately of pegmatite aplite aegirine granite porphyry and eight other lesser rock types the ore is closely associated with an albitized aegirine syenite the ore consists of thorium and rare earth rich rock containing uranothorite uraninite and generally less than 2 of sulfide species about 100 000 tons 89 000 t of ore have been mined at an average grade of about 1 u3o8 and nearly 3 tho2 mainly from the ross adams pipe the pipe itself lies along the contact of aegirine syenite and aegirine granite porphyry it is as much as 24 m across and was mined along strike for over 300 m the ore in shear zones occurs in lenses as much as 3 m thick and 30 m in strike length wallrock alteration within and adjacent to orebodies consists of pervasive hydrothermal albite and lesser amounts of chlorite fluorite calcite quartz sericite and tourmaline hematite is present in the outer distal parts of the ore zones the minerals produced to date occur within the outer annular zone of the bokan granite complex in which aegirine is present as the major alkali ferro magnesian mineral ore emplacement occurred during the first subsidence event in association with devolatilization of the magma chamber the pod like ore zones appear to have formed during regional faulting synchronous with magma crystallization and subsequent hydrothermal events subsequent magma crystallization yielded riebeckite granites that were depleted in u and th filling temperatures in ore stage fluid inclusions within quartz range from 320 to 331 c with pressure corrections increasing the temperature of formation to 420 c or higher depending on dissolved gas content sulfur isotopic analyses on pyrite galena sphalerite and pyrrhotite indicate disequilibrium but 34sh2s is estimated at 7 6 carbon and oxygen isotopic analyses on ore stage calcite yield 18oh2o of 6 8 to 8 1 and 13c c of 4 3 to 7 0 the oxygen and carbon isotopic data support a magmatic origin for the calcite and associated thorium uranium deposits

co2 and h2s concentrations in the atmosphere at the solfatara of pozzuoli the co2 and h2s concentration in the solfatara atmosphere has been measured the concentrations of both gases are higher neraby the more active areas and decrease away from them a sharp horizontal and vertical gradient of the co2 content has been recognized

mechanisms of activity and unrest at large calderas large caldera collapses represent catastrophic natural events second only to large meteoritic impacts in addition some calderas are densely populated making the risk extreme even for moderate eruptions understanding caldera mechanisms unrest and the danger of eruption is therefore a crucial challenge for earth sciences several key features of caldera behaviour have yet to be fully understood through a combination of case studies and theoretical modelling the following topics are addressed in this volume the conditions required to produce and to release large volumes of magma erupted during caldera formation how magmatic feeding systems evolve before and after a caldera has formed the processes that limit the behaviour of precursors to eruptions how pre emptive precursors can be distinguished from those that drive unrest without an eruption and given that post collapse eruptions may occur across a wide area the optimum procedures for designing hazard maps and mitigation strategies

new mineral names the following new minerals are discussed in this issue langbanshyttanite pseudolyonsite and yangzhumingite these new minerals have been described in the european journal of mineralogy and are reported here n v chukanov i v pekov e jonsson n v zubkova y e filinchuk d i belakovskiy and d yu pushcharovsky 2011 langbanshyttanite a new low temperature arsenate mineral with a novel structure from langban sweden eur j mineral 23 675 681 the new mineral langbanshyttanite was discovered in a specimen from the langban mine filipstad district varmland county bergslagen ore province sweden the carbonate hosted langban deposit 59 86 n 14 27 e is together with related occurrences in the western part of the palaeoproterozoic bergslagen ore province in south central sweden characterized by anomalously pb as ba be sb rich metamorphosed stratabound fe and mn oxide ores with associated skarn units sulfide assemblages as well as abundant vein and fissure hosted mineral assemblages the name is for langbanshyttan which is the old name of both the mine mining village and smelter that in more recent times has been known plainly as langban langbanshyttan actually means langban s smelter or langban s furnace langbanshyttanite occurs as a very late low temperature species in the deposit it crystallized during the last stage of hydrothermal activity involving metal remobilization in the langban system post dating regional metamorphism of the volcanic hydrothermal ores and their host rocks based on existing evidence these minerals formed at very low temperature and pressure in this case most likely below 70 c the mineral formed in fractures and corrosion veinlets post dating calcite in a mn oxide bearing mn silicate rich rock associated late stage minerals are calcite antigorite sparse euhedral trigonite and a few microscopic aggregates of a so far unidentified as bearing mineral typically both calcite and antigorite exhibit evidence of being partly corroded away prior to langbanshyttanite formation trigonite coeval with langbanshyttanite occurs as sparse euhedral crystals the groundmass to the veinlets or fractures mainly consists

oceanic impacts a growing field of fundamental geoscience the importance of oceanic impacts of collisional events and resulting energy release are briefly described data collection methods from the eltanin a mesosiderite projectile deep water impact are presented

source processes of the thermal waters from the phlegraean fields naples italy by means of the study of selected minor and trace elements distribution abstract the geochemical characteristics of hydrothermal waters from the phlegraean fields p f naples italy were analysed for minor and trace elements selectively mobilised in hydrothermal systems such as b f hg as pb and tl the water samples collected from a shallow aquifer likely to be fed by deeper fluids showed various geochemical features resulting from the mixing of three components 1 surface waters of meteoric origin 2 hot deep waters deriving from water rock interaction and including deep waters of marine origin 3 magmatic fluids rising from the local magma chamber lying a few kilometres below the town of pozzuoli this setting although very complex provides a reliable means of studying the distribution of the investigated trace elements in particular within the phlegraean area high contents of b 0 1 48 mg l f 0 5 8 mg l as 16 6050 g l and hg 0 7 232 g l were observed the levels of thallium in the springs close to solfatara about 7 g l were in line with those normally recorded in hydrothermal areas whereas high levels of this element up to 23 3 g l were identified in other wells of the study area lead 1 3 to 29 1 g l appears to be anomalous with respect to its normal content in groundwater about 1 g l owing to the presence of high density brines at depth which enhance the solubility of pb in volcanic rocks under hydrothermal conditions the distribution of the investigated trace elements in the phlegraean fields thermal area is probably related to the different ascent pathways of the fluids clearly apart from the influence exerted by anomalous thermal conditions each element shows a different behaviour depending on its geochemical affinity with mineral phases and as a consequence of the different enthalpy values which determine ion partitioning in gaseous phases based on geochemical evidences and on the distribution of minor and trace elements the source processes of the investigated hydrothermal waters were defined five main groups were identified 1 acid sulphate waters resulting from mixing of meteoric water with magmatic gases mainly h 2 s 2 high sulphate chloride waters from a deep reservoir located in the major upflow zone 3 waters associated with significant degassing of magmatic co 2 4 waters from a deep geothermal neutral chloride reservoir resulting from heating of marine water modified by water rock interaction processes 5 cold waters from the inner area influenced by low temperature water rock interaction processes

chemical and isotopic signatures of the basement rocks from the campi flegrei geothermal field naples southern italy inferences about the origin and evolution of its hydrothermal fluids abstract the campi flegrei naples campanian plain southern italy geothermal system is hosted by quaternary volcanic rocks erupted before during and after the formation of the caldera that represents one of the major structural features in the neapolitan area the volcanic products rest on a mesozoic carbonate basement cropping out north east and south of the area chemical major minor and trace elements and stable isotope c h o analyses were conducted on drill core samples recovered from geothermal wells mf 1 mf 5 sv 1 and sv 3 at depths of 1100 to 2900 m the study was complemented by petrographic and sem examination of thin sections the water which feeds the system is both marine and meteoric in origin mineral zonation typical of a high temperature geothermal system exists in all the geothermal wells measured temperatures in wells are as high as 400 c the chemical composition of the waters suggests the existence of two reservoirs a shallow reservoir depth 2000 m of hypersaline water the drill cores are mainly hydrothermally altered volcanics of trachy latitic affinity but some altered pelites and limestones are also present published na mg and k concentrations of selected geothermal waters indicate that the hydrothermal fluids are in equilibrium with their host rocks with respect to k feldspar albite sericite and chlorite the measured 18 o smow values of rocks range from 4 3 to 16 5 the measured d smow values range from 79 to 46 the calculated isotopic composition of the fluids at equilibrium with the samples vary from 1 to 8 3 18 o and from 52 to 1 d the estimated isotopic composition of the waters at equilibrium with the studied samples confirmed the existence of two distinct fluid types circulating in the geothermal system the shallower has a marine water signature while the deeper water has a signature consistent both with magmatic and meteoric origins in the latter case the recharge of this aquifer likely occurs at the outcrop of the mesozoic limestones surrounding the campanian plain after infiltration the water percolates through evaporitic layers becoming hypersaline and d depleted

native sulfur sulfates and sulfides from the active campi flegrei volcano southern italy genetic environments and degassing dynamics revealed by mineralogy and isotope geochemistry abstract we investigated sulfur bearing minerals from the campi flegrei caldera southern italy in relation to the increase of hydrothermal activity phenomena since 2006 aimed at providing insights into the volcanic system dynamics mineral encrustations and muds were sampled between 2013 and 2015 at the long standing degassing crater of the solfatara tuff cone and its recently restless north eastern pisciarelli slope deep seated sulfides were further separated from two drill cores agip s mofete boreholes 1500 m and 2695 m depth the mineral assemblage and texture of sampled encrustations were determined by x ray diffraction optical and scanning electron microscopy and x ray microanalysis by energy dispersive spectrometry native sulfur and alunite dominate among the newly formed mineral phases other minerals are mostly alunogen and locally pickeringite potassium alum hematite and pyrite mereiterite and amarillite sporadically occur the mud pools are rich in gypsum potassium alum and pyrite quartz and argillic phases locally with analcime are dispersed in the outcropping rocks 34 s values were determined for shallow subsurface native sulfur 5 5 to 0 0 and alunite 1 7 to 0 2 as well as for the deep seated pyrite 3 3 to 7 4 in the depth range 1500 2695 m 18 o values were measured for shallow native alunite 4 2 to 7 0 pisciarelli alunite was finally analyzed for its 87 sr 86 sr ratio and 143 nd 144 nd ratios 0 707517 6 and 0 512459 6 respectively textural and isotopic data constrain the genesis of alunite at the expense of k feldspars through rock alteration by hydrothermal fluids we suggest that the caldera is a low sulfidation system hosting acid sulfate deposits in its active degassing area the acid sulfate environment developed on an argillitic facies that thins outwards and is characteristic for steam heated and magmatic steam environments these environments developed in relation to the fractured settings that facilitates the gas emissions from deeper levels and the meteoric infiltration from surface to depth newly determined 34 s data are lower than previously published values suggesting a progressive decrease in the sulfur isotopic composition through time at least since 1956 the isotopic variation is associated with a lowering of the so 2 h 2 s ratio and the widening of the surface of co 2 degassing in the absence of significant changes in the average co 2 flux values and in the carbon and helium isotope compositions native sulfur and sulfates move from sulfur isotope equilibrium to disequilibrium we ascribe this transition to enhanced so 2 scrubbing due to a high rock permeability that facilitates a faster gas ascent rate in the shallow crust

columbite solubility in granitic melts consequences for the enrichment and fractionation of nb and ta in the earth s crust the behaviour of niobium and tantalum in magmatic processes has been investigated by conducting mnnb2o6 and mnta2o6 solubility experiments in nominally dry to water saturated peralkaline aluminium saturation index a s i 0 64 to peraluminous a s i 1 22 granitic melts at 800 to 1035 c and 800 to 5000 bars the attainment of equilibrium is demonstrated by the concurrence of the solubility products from dissolution crystallization mn doped and nb or ta doped experiments at the same pressure and temperature the solubility products of mnnb2o6 ksp nb and mnta2o6 ksp ta at 800 c and 2 kbar both increase dramatically with alkali contents in water saturated peralkaline melts they range from 1 2 10 4 and 2 6 10 4 mol2 kg2 respectively in subaluminous melt a s i 1 02 to 202 10 4 and 255 10 4 mol2 kg2 respectively in peralkaline melt a s i 0 64 this increase from the subaluminous composition can be explained by five non bridging oxygens being required for each excess atom of nb5 or ta5 that is dissolved into the melt the ksp nb and ksp ta also increase weakly with al content in peraluminous melts ranging up to 1 7 10 4 and 4 6 10 4 mol2 kg2 respectively in the a s i 1 22 composition columbite tantalite solubilities in subaluminous and peraluminous melts a s i 1 02 and 1 22 are strongly temperature dependent increasing by a factor of 10 to 20 from 800 to 1035 c by contrast columbite tantalite solubility in the peralkaline composition a s i 0 64 is only weakly temperature dependent increasing by a factor of less than 3 over the same temperature range similarly ksp nb and ksp ta increase by more than two orders of magnitude with the first 3 wt h2o added to the a s i 1 02 and 1 22 compositions whereas there is no detectable change in solubility for the a s i 0 64 composition over the same range of water contents solubilities are only slightly dependent on pressure over the range 800 to 5000 bars the data for water saturated sub and peraluminous granites have been extrapolated to 600 c conditions at which pegmatites and highly evolved granites may crystallize using a melt concentration of 0 05 wt mno 70 to 100 ppm nb or 500 to 1400 ppm ta are required for manganocolumbite and manganotantalite saturation respectively the solubility data are also used to model the fractionation of nb and ta between rutile and silicate melts predicted rutile melt partition coefficients increase by about two orders of magnitude from peralkaline to peraluminous granitic compositions it is demonstrated that the nb2o5 ta2o5 activity coefficient ratio in the melt phase depends on melt composition this ratio is estimated to decrease by a factor of 4 to 5 from andesitic to peraluminous granitic melt compositions accordingly all the relevant accessory phases in subaluminous to peraluminous granites are predicted to incorporate nb preferentially over ta this explains the enrichment of ta over nb observed in highly fractionated granitic rocks and in the continental crust in general

the origin of the fumaroles of la solfatara campi flegrei south italy abstract the analysis of gaseous compositions from solfatara campi flegrei south italy fumaroles since the early 1980s clearly reveals a double thermobarometric signature a first signature at temperatures of about 360 c was inferred by methane based chemical isotopic geoindicators and by the h2 ar geothermometer these high temperatures close to the critical point of water are representative of a deep zone where magmatic gases flash the hydrothermal liquid forming a gas plume a second signature was found to be at around 200 240 c at these temperatures the kinetically fast reactive species h2 and co re equilibrate in a pure vapor phase during the rise of the plume a combination of these observations with an original interpretation of the oxygen isotopic composition of the two dominant species i e h2o and co2 shed light on the origin of fumarolic fluids by showing that effluents are mixture between fluids degassed from a magma body and the vapor generated at about 360 c by the vaporization of hydrothermal liquids a typical andesitic water type d 20 18o 10 and a co2 rich composition x co 2 0 4 has been inferred for the magmatic fluids while for the hydrothermal component a meteoric origin and a co2 fugacity fixed by fluid rock reaction at high temperatures have been estimated in the time the fraction of magmatic fluids in the fumaroles increased up to 0 5 at each seismic and ground uplift crisis bradyseism which occurred at campi flegrei suggesting that bradyseismic crises are triggered by periodic injections of co2 rich magmatic fluids at the bottom of the hydrothermal system

geological record and reconstruction of the late pliocene impact of the eltanin asteroid in the southern ocean in 1995 an expedition on board the research vessel fs polarstern explored the impact site of the eltanin asteroid in the southern ocean the only known asteroidimpact into a deep ocean basin analyses of the geological record of the impact region place the event in the late pliocene 2 15 myr and constrain thesize of the asteroid to be 1 km the explosive force inferred for this event places it at the threshold of impacts believed to have global consequences and its studyshould therefore provide a baseline for the reconstruction and modelling of similar events which are common on geological timescales

monitoring active fumaroles through time lapse electrical resistivity tomograms an application to the pisciarelli fumarolic field campi flegrei italy abstract volcanoes are usually monitored through observations of many physical and chemical phenomena in the most dangerous cases as the one of the campi flegrei caldera italy great amount of data are collected both in discrete or continuously and regularly stored however how to transform such mass of data in a deeper understanding of the volcano dynamics is still an open question dissimilar information are in fact always hard to compare but just integrating all the available knowledge hazardous events could be prevented in a reliable way fluids as water and gasses mobilized in the subsoil by the heat induced by deep magmatic sources are widely recognized as the first engine of similar occurrences and the volcanic gas emissions represent together with the seismic activity one of the most considered precursors at the same time the electrical geophysical methods are the most applied in order to detect and characterize the fluid patterns in the subsoil so the integration of geoelectrical and geochemical observations should represent one of the most pursued approach in volcanoes monitoring on the contrary standard way to compare such data has been not yet codified the ert tomograms capability to individuate that parts of the subsoil where gasses cumulate is well understood in literature however we look for indications about its proficiency in associating the electrical resistivity changes relative to these zones once compared to the geochemical time series to deep related contributes distinguishing them from the seasonal ones the electrical signature of the fluid patterns reconstructed through a time lapse ert approach could be of relevance to better characterize the volcanic phenomena and their origins in this paper a first test of ert and geochemical time series integration was performed to enhance the understanding of the pisciarelli fumarolic field evolution now the most active area in the whole campi flegrei caldera

chemical and isotopic gas emissions at campi flegrei evidence for an aborted period of unrest the hydrothermal system beneath campi flegrei an explosive caldera in southern italy is quantified by analyzing gas samples collected since 1983 during and after 2 years of intense earthquake swarms and dramatic uplift of the caldera center these gas samples were obtained from both land and submarine fumaroles as well as a few samples from water wells at the bocca grande fumarole in solfatara crater near the center of campi flegrei large variations were measured in the amount of water vapor hydrogen sulfide nitrogen and hydrogen gases methane and hydrogen chloride some variations could be controlled partly by a change in heat flux from a deep source to a surficial hydrothermal system possible evidence of a change in heat flux comes from subsurface temperatures calculated from a water carbon monoxide reaction the calculated temperatures changed most in 1989 1990 concurrent changes were measured in concentrations of hydrogen sulfide nitrogen and hydrogen no change was noted in helium or carbon isotopes which could have indicated a change in emission of magmatic gases i suggest the changes in gas chemistry since 1985 could be evidence of an aborted period of unrest which was characterized as a change in gas emissions but did not progress far enough to produce uplift or earthquake swarms as pointed out by other researchers the ratio of helium isotopes which implies the presence of magma is uniform across an area that includes campi flegrei the distribution of carbon isotopes which is nonuniform correlates with limestone outcrops and the presence of shallow thermal sources

rate of diffuse carbon dioxide earth degassing estimated from carbon balance of regional aquifers the case of central apennine italy central italy is characterized by an anomalous flux of deeply derived co2 in the western tyrrhenian sector of central italy co2 degassing occurs mainly from focused emissions vents and strong diffuse degassing and thermal springs whereas in the eastern apennine area deep co2 is dissolved in cold groundwaters of regional aquifers hosted by mesozoic carbonate evaporite formations influx of deep co2 into 12 carbonate aquifers 12 500 km2 of the central apennine is computed through a carbon mass balance that couples aquifer geochemistry with isotopic and hydrogeological data mass balance calculations estimate that 6 5 1010 mol yr 1 of inorganic carbon are dissolved in the studied aquifers approximately 23 of this amount derives from biological sources active during the infiltration of the recharge waters 36 comes from carbonate dissolution while 41 is representative of deep carbon sources characterized by a common isotopic signature 13c 3 the calculated deep co2 influx rate ranges from 105 to 107 mol yr 1 km 2 increasing regionally from east to west in the study area

the eltanin asteroid impact possible south pacific palaeomegatsunami footprint and potential implications for the pliocene pleistocene transition large asteroid impacts are rare and those into the deep ocean are rarer still the eltanin asteroid impact around 2 51 0 07 ma occurred at a time of great climatic and geological change associated with the pliocene pleistocene boundary numerical models of the event indicate that a megatsunami was generated although there is debate concerning its magnitude and the region wide extent of its influence we summarise the existing evidence for possible eltanin megatsunami deposits in antarctica chile and new zealand while also examining other potential sites from several locations mainly around the south pacific region in reviewing these data we note that these events were unfolding at the same time as those associated with the pliocene pleistocene boundary and as such most of the geological evidence from that time has a climatic interpretation the potential climatic and geological ramifications of the eltanin asteroid impact however have failed to be considered by most researchers studying this time period although we are not advocating that all geological activity at that time is connected with the eltanin asteroid impact it raises interesting questions about the role potentially played by such catastrophic events in contributing to or even triggering epochal transitions copyright 2012 john wiley sons ltd

mineralogical geochemical and isotopic features of tuffs from the cfddp drill hole hydrothermal activity in the eastern side of the campi flegrei volcano southern italy abstract a 506 m drill hole has been recently drilled in the framework of the campi flegrei deep drilling project cfddp and the international continental scientific drilling program icdp with the intention of coring the subsurface in the eastern sector of the campi flegrei caldera the borehole located in the western district of the neapolitan city bagnoli plain 3 km to the east of the most active volcanic area and about 5 m above sea level is now targeted for monitoring purposes this paper reports the results obtained from the analysis of two short cores collected at depths of 443 and 506 m below the ground level the cores sampled two pre caldera tuffs observations performed by optical and scanning electron microscopy energy dispersive spectroscopy and powder x ray diffraction were used to achieve data on the primary lithology both primary and secondary mineralogical assemblages and the relationship between texture and secondary mineralization sr isotope ratios were determined on selected primary feldspars whereas 13c and 18o analyses were performed on carbonates from veins and filled voids in tuffs our results provide information on the hydrothermal system in the eastern sector of the caldera that was not among the goals in the previous drilling programs secondary mineralization suggests a saline hydrothermal environment characterized by fluids that progressively evolved from boiling toward more alkaline and cooler conditions a paleo temperature of ca 160 c has been inferred from authigenic mineral occurrences and calculated on the basis of equilibria between cored calcites and fluids presently emitted at the surface by using carbon and oxygen isotope data the temperature measured at the bottom of the drilling is about 80 c

evolution of uranium fractionation processes through time driving the secular variation of uranium deposit types uranium deposit types have evolved considerably from the archean to the present the major global drivers were 1 change of geotectonic conditions during the late archean 2 strong increase of atmospheric oxygen from 2 4 to 2 2 ga and 3 development of land plants during the silurian other significant variations of uranium deposit types are related to unique conjunctions of conditions such as those during phosphate sedimentation in the cretaceous earth s uranium fractionation mechanisms evolved through four major periods the first from 4 55 and 3 2 ga corresponds to formation of a thin essentially mafic crust in which the most fractionated trondheimite tonalite granodiorite ttg rocks attained uranium concentrations of at most a few parts per million moreover the uranium being essentially hosted in refractory accessory minerals and free oxygen being absent no uranium deposit could be expected to have formed during this period the second period from about 3 1 to 2 2 ga is characterized by several widespread pulses of highly fractionated potassic granite strongly enriched in u th and k late in this period peraluminous granite was selectively enriched in u and to a lesser extent k these were the first granite and pegmatite magmas able to crystallize high temperature uraninite the erosion of these granitic suites liberated thorium rich uraninite which would then be concentrated in placer deposits along with pyrite and other heavy minerals e g zircon monazite fe ti oxides within huge continental basins e g witwatersrand south africa and bind river canada the lack of free oxygen at that time prevented oxidation of the uraninite which formed the oldest economic uranium deposit types on earth but only during this period the third period from 2 2 to 0 45 ga records increased oxygen to nearly the present atmospheric level tetravalent uranium from uraninite was oxidized to hexavalent uranium forming highly soluble uranyl ions in water uranium was extensively trapped in reduced epicontinental sedimentary successions along with huge quantities of organic matter and phosphates accumulated as a consequence of biological proliferation especially during the late paleoproterozoic a series of uranium deposits formed through redox processes the first of these developed at a formational redox boundary at about 2 0 ga in the oklo area of gabon all known economically significant uranium deposits related to na metasomatism are about 1 8 ga in age the high grade large tonnage unconformity related deposits also formed essentially during the late paleoproterozoic to early mesoproterozoic the last period 0 45 ga present coincided with the colonization of continents by plants the detrital accumulation of plants within continental siliciclastic strata represented intraformational reduced traps for another family of uranium deposits that developed essentially only during this period basal roll front tabular and tectonolithologic types however the increased recognition of hydrocarbon and hydrogen sulfide migration from oil or gas reservoirs during diagenesis suggests potential for sandstone hosted uranium deposits to be found within permeable sandstone older than the silurian large uranium deposits related to high level hydrothermal fluid circulation and those related to evapotranspiration calcretes are only known during this last period of time probably because of their formation in near surface environments with low preservation potential

mineral control of arsenic content in thermal waters from volcano hosted hydrothermal systems insights from island of ischia and phlegrean fields campanian volcanic province italy this paper documents arsenic concentrations in 157 groundwater samples from the island of ischia and the phlegrean fields two of the most active volcano hosted hydrothermal systems from the campanian volcanic province southern italy in an attempt to identify the environmental conditions and mineral solution reactions governing arsenic aqueous cycling on ischia and in the phlegrean fields groundwaters range in composition from nacl brines which we interpret as the surface discharge of deep reservoir fluids to shallow depth circulating fluids the latter ranging from acid sulphate steam heated to hypothermal cold bicarbonate groundwaters arsenic concentrations range from 1 6 to 6900 g l 1 and from 2 6 to 3800 g l 1 in the phlegrean fields and on ischia respectively they increase with increasing water temperature and chlorine contents and in the sequence bicarbonate groundwatersbsteam heated groundwatersbnacl brines according to thermochemical modeling we propose that high as concentrations in nacl brines form after prolonged water rock interactions at reservoir t fo2 and fh2s conditions and under the buffering action of an arsenopyrite pyrite pyrrhotite rock assemblage on their ascent toward the surface nacl brines become diluted by as depleted meteoric derived bicarbonate groundwaters giving rise to hybrid water types with intermediate to low as contents steam heated groundwaters give their intermediate to high as concentrations to extensive rock leaching promoted by interaction with as bearing hydrothermal steam 2005 elsevier b v all rights reserved

characterization of the volcanic and hypabissal rocks of the paleoproterozoic iricoume group in the pitinga region and balbina lake area amazonian craton brazil petrographic distinguishing features and emplacement conditions abstract the iricoume group 1 897 to 1 875 ma is a widespread volcanic sequence in the amazonian craton south american platform in the pitinga region it consists of acidic to intermediate ignimbrites with cogenetic surge and ash fall deposits associated to hypabissal and effusive acidic rocks in the balbina lake area it consists of acidic to intermediate effusive rocks crystal rich ignimbrites and pumice rich ignimbrites detailed petrographic studies of phenocrysts and crystal fragments provided characterization and distinctive features of pyroclastic effusive and hypabissal rocks the phenocrysts of hypabissal rocks were affected by high temperature resorption and flow related physical fragmentation the effusive rocks can have a considerable content of crystal fragments due to intense dissolution and fragmentation of the phenocrysts and the pyroclastic rocks crystal fragments are generated mainly by decompression mechanic fragmentation dissolution and resorption of quartz and feldspar crystals may have acted at pressure conditions between 500 mpa and 100 mpa in response to rapid decompression in the magma ascent the viscosity values of 7 5 10 log pa s for anhydrous conditions decrease exponentially with estimated water addition the amount of phenocrysts and their intratelluric character in the volcanic units of iricoume group can be related to a magma chamber with high content of crystals we suggest that even with the addition of water in the magma the viscosities had a drastic increase with progressive crystal growth due to the viscosity dependence on the solid fraction and the deposits were generated by the extrusion of viscous lava and pyroclastic flows

evolution of pliocene to recent abyssal sediment waves on bounty channel levees new zealand abstract levees bordering bounty channel 900 km east of new zealand accommodate a 400 m thick sequence maximum of sediment waves that have formed since pliocene times these bedforms with amplitudes of 2 17 m and wavelengths of 0 6 6 km occur in 4100 4900 m of water and were formed by turbidity currents as indicated by their restriction to levee backslopes the frequent occurrence of turbidites in cores and the preferential but not exclusive development of waves on the left bank levee in accord with the southern hemisphere coriolis deflection the wave field was instigated in the late pliocene when glacially lowered sea level allowed rivers draining the southern alps of south island to discharge directly into bounty channel and its attendant canyons the field grew vertically through the coalescence of small waves into larger bedforms that continually migrated across and up levee backslopes at an average rate of 5 6m 100 yrs wave growth decreased into the late pleistocene probably in response to progressive containment of turbidity currents as the relief of bounty channel increased to 200 m or more the glacial periods of wave growth were interrupted by interglacial interludes of quiescence when the field was draped mainly by pelagic calcareous ooze

rb sr dating of the bokan mountain granite complex and its country rocks seven out of 11 whole rock samples of the bokan granitic complex give a rb sr isochron date of 151 5 ma late jurassic as a minimum age for the complex this result is discordant with published early to middle jurassic k ar and u pb dates for the same unique peralkaline rock suite a late jurassic age is tenable if excess radiogenic ar and a trace of xenocrystic zircon are postulated to explain the previously reported results and the u pb data are reinterpreted to give an age between 156 6 and granitic country rock for the complex is dated by rb sr at 432 19 ma early silurian in agreement with published k ar dates