birth growth and morphologic evolution of the laghetto cinder cone during the 2001 etna eruption we have undertaken detailed observations of the formation of the laghetto cinder cone a new cone that formed during a 2 week period of intense activity in piano del lago on the upper slopes of mount etna in summer 2001 we describe the events leading to the formation of a small graben the formation of pit craters on the base of the graben the onset of phreatomagmatic activity a transition to intense strombolian activity and a return to phreatomagmatic activity as the eruption came to an end we discuss the reasons for these transitions and describe the morphological development of the cone during these events arcuate cracks on the southern part of the cone were related to withdrawal of magma at the end of the eruption other slope instabilities that developed during the eruption include the formation of small radial grain flows on the outer flanks of the cone and the collapse into the crater of part of the crater rim some of the failure planes we observed were first identified using a flir tm 695 thermal infrared camera this is the first time that infrared thermography has been used to detect instability of volcanic structures results obtained during this test case demonstrate that thermal cameras are a very useful tool for studies of volcanic instability

first whiffs of atmospheric oxygen triggered onset of crustal gold cycle lack of a suitable gold source has long been regarded as a major argument against a palaeoplacer model for the exceptionally well endowed witwatersrand gold province by comparing worldwide witwatersrand type deposits occurrences ranging in age from 3 1 to 1 8 ga we propose that the primary concentration of gold in the continental crust resulted from atmospheric and biological evolution in the mesoarchaean a high au flux off the archaean land surface orders of magnitude greater than today s was a consequence of the chemistry of the mesoarchaean atmosphere and hydrosphere when early life gradually changed from anaerobic anoxygenic to oxygenic photosynthesizers at around 3 0 ga the first whiffs of free oxygen produced by photosynthesis under an overall reducing atmosphere provided the ideal trap for au dissolved in the huge reservoir in meteoric and shallow sea water oxidative precipitation of gold on the surface of the o2 producing microbes probably cyanobacteria could fix huge amounts of gold over large areas some of this microbially mediated gold is still preserved in thin kerogen layers carbon seams that typically developed on erosional unconformities scour surfaces and bedding planes in near shore environments at around 2 9 ga this gold provided the principal source for the very rich placer deposits that formed by the subsequent sedimentary reworking of the delicate microbial mats on aeolian deflation surfaces into fluvial channels and delta deposits represented by meso to neoarchaean auriferous conglomerates tectonic reworking of these first gold rich sediments by orogenic processes explains the temporal peak of orogenic type gold formation at around 2 7 to 2 4 ga with time the strongly gold enriched archaean sediments became progressively eroded covered or tectonically reworked and their role as potential source of younger placer deposits diminished this explains why witwatersrand type deposits younger than 2 4 ga are rare and far less well endowed and effectively missing in the rock record after 1 8 ga

hydrothermal alteration in the witwatersrand goldfields abstract alteration is recorded throughout much of the 3 km thick upper witwatersrand succession in south africa and extends for 300 km around the basin and 50 km into the basin the evidence for this alteration comes from petrography mineralogy geochemistry rock fabrics and stratigraphy the alteration conceived as a giant halo enveloping each major goldfield requires a major hydrothermal event focused on the auriferous upper wits central rand group the scale and nature of the alteration and its relationship to gold distribution on various scales strongly support a hydrothermal model for gold deposition such a model can account for the 50 000 t of gold mined from the witwatersrand goldfields the model works within the context of the major advances in understanding of the geological framework of the witwatersrand basin including the recognition of the importance of post burial processes it is highly significant that the age of witwatersrand sedimentation is much older than 2700 my and thus the host rocks for gold were deposited at least 100 my before the major global archean greenstone gold event the shale units from 40 major mines covering the seven goldfields are examined to establish the nature and distribution of the alteration and to make the connection between the fluid infiltration that caused the alteration and the introduction of gold into the witwatersrand basin in the hydrothermal model described here an auriferous low salinity fluid is produced at about 500 c during the metamorphism of mafic material that was below and adjacent to the witwatersrand basin large shear zones in the footwall of goldfields are the inferred fluid pathways into the upper wits succession and then unconformities smaller shear zones veins and the reef packages guide local fluid flow in this model gold precipitation occurs in response to the reaction of the fluid with carbon and iron bearing rocks that are abundant in the reef packages immediately overlying unconformity surfaces gold precipitation occurred at about 350 c and 10 km depth with the implication of a high geothermal gradient approaching 35 c per km the alteration of the shales but lack of abundant gold in them is predicted from the paucity of appropriate rocks or minerals in the shale units to precipitate gold but fluid infiltration still changed their composition fundamentally the source of the witwatersrand gold its present distribution and the alteration are explained within this hydrothermal model with similarities to the models invoked for other major gold provinces it is worth noting that quartz pebble conglomerate is a poor term for this gold type and has almost certainly limited exploration opportunities globally

observation of so2 degassing at stromboli volcano using a hyperspectral thermal infrared imager abstract thermal infrared tir imaging is a common tool for the monitoring of volcanic activity broadband cameras with increasing sampling frequency give great insight into the physical processes taking place during effusive and explosive event while fourier transform infrared ftir methods provide high resolution spectral information used to assess the composition of volcanic gases but are often limited to a single point of interest continuing developments in detector technology have given rise to a new class of hyperspectral imagers combining the advantages of both approaches in this work we present the results of our observations of volcanic activity at stromboli volcano with a ground based imager the telops hyper cam lw when used to detect emissions of sulfur dioxide so2 produced at the vent with data acquired at stromboli volcano italy in early october of 2015 we have developed an innovative technique based on a curve fitting algorithm to quickly extract spectral information from high resolution datasets allowing fast and reliable identification of so2 we show in particular that weak so2 emissions such as inter eruptive gas puffing can be easily detected using this technology even with poor weather conditions during acquisition e g high relative humidity presence of fog and or ash then artificially reducing the spectral resolution of the instrument we recreated a variety of commonly used multispectral configurations to examine the efficiency of four qualitative so2 indicators based on simple brightness temperature difference btd our results show that quickly changing conditions at the vent including but not limited to the presence of summit fog render the establishment of meaningful thresholds for btd indicators difficult building on those results we propose recommendations on the use of multispectral imaging for so2 monitoring and routine measurements from ground based instruments

anomalous magmatic degassing prior to the 5th april 2003 paroxysm on stromboli 1 a major explosion occurred at stromboli on april 5 2003 being the most powerful event over a period of exceptional eruptive activity lasting from december to july here we describe results from a network of diffusive tubes set up on the stromboli s summit area aimed at a characterisation of plume composition so2 hcl hf prior to and after april 5 data analysis revealed anomalous sulphur degassing 2 3 days before the event when so2 hcl ratios 9 significantly higher than those typical of quiescent degassing 1 were recorded we interpret this exceptional plume signature as an evidence of s rich magmas ascending in the shallow plumbing system and propose high so2 hcl as a potential precursor of major explosions on the volcano the post april 5 phase was characterised by time decreasing so2 hcl and so2 hf plume ratios ascribed to declining magma feeding as a prelude to restoration of normal strombolian activity

stratigraphic control of chemistry and mineralogy in metamorphosed witwatersrand quartzites within metamorphosed quartzites of the witwatersrand supergroup bulk chemistry is the major control on the distribution of metamorphic mineral phases and on their chemistry bulk chemistry is in turn controlled by stratigraphic position pyrophyllite distribution varies directly with whereas feldspar distribution varies inversely with bulk al chloritoid distribution is more complex and varies with both bulk al and bulk fe mg despite the overprint of low grade metamorphism and possibly of other alteration processes both detrital and metamorphic phyllosilicates can be recognized and characterized al in metamorphic white mica and metamorphic chlorite varies with bulk al whereas the composition of detrital white mica is unrelated to bulk chemistry similarly mg in metamorphic chlorite varies with bulk mg bulk chemical variation particularly in al mg and na and thus metamorphic mineral chemistry is controlled by stratigraphic position both within individual stratigraphie units and in the strat

the summit hydrothermal system of stromboli new insights from self potential temperature co2 and fumarolic fluid measurements with structural and monitoring implications accurate and precisely located self potential sp temperature t and co2 measurements were carried out in the summit area of stromboli along 72 straight profiles sp data were acquired every metre and t data every 2 5 m co2 concentrations were acquired with the same density as t but only along seven profiles the high density of data and the diversity of the measured parameters allows us to study structures and phenomena at a scale rarely investigated the shallow summit hydrothermal activity pizzo fossa area is indicated by large positive sp t and co2 anomalies these anomalies are focused on crater faults suggesting that the fracture zones are more permeable than surrounding rocks at stromboli the analysis of the distribution of these linear anomalies coupled with the examination of the geologic photographic and topographic data has led us to propose a new structural interpretation of the summit of stromboli this newly defined structural framework comprises 1 a large pizzo circular crater about 350 m in diameter 2 a complex of two concealed craters nested within the pizzo crater the large and the small fossa craters thought to have formed during the eruption of the pizzo pyroclastites unit the small fossa crater is filled with highly impermeable material that totally impedes the upward flow of hydrothermal fluids and 3 the present complex of active craters on the floor of the fossa short wavelength sp lows are organized in drainage like networks diverging from the main thermal anomalies and converging toward the topographic low in the fossa area inside the small fossa crater they are interpreted as the subsurface downhill flow of water condensed above the thermal anomalies we suspect that water accumulates below the small fossa crater as a perched water body representing a high threat of strong phreatic and phreatomagmatic paroxysms t and co2 anomalies are highly correlated the two types of anomalies have very similar shapes but the sensitivity of co2 measurements seems higher for lowest hydrothermal flux above t anomalies a pronounced high frequency sp signal is observed isotopic analyses of the fluids show similar compositions between the gases rising through the faults of the pizzo and large fossa craters this suggests a common origin for gases emerging along different structural paths within the summit of stromboli a site was found along the large fossa crater fault where high gas flux and low air contamination made gas monitoring possible near the active vents using the alkaline bottle sampling technique

complex metasomatism of an archean placer in the witwatersrand basin south africa the ventersdorp contact reef a hydrothermal aquifer the ventersdorp contact reef is an auriferous conglomerate horizon and economic orebody on top of the late archean witwatersrand supergroup in south africa it differs from the other conglomerate beds reefs in the witwatersrand basin in having a massive metabasalt sequence as its hanging wall and by its intense post depositional alteration a geochemical petrologic and fluid inclusion study of the ventersdorp contact reef reveals a polyphase hydrothermal alteration history regional metamorphism under acidic conditions was followed by potassic alteration along the reef the potassic alteration which also extended into the hanging wall and footwall rocks was subsequently followed by a chloritization episode that was restricted to the reef and its immediate contacts mass balance calculations suggest that the latter alteration required only minor fluid influx from an external source whereas the potassic alteration reflects the progressive dehydration of the siliciclastic footwall rocks and associated hydration of the basaltic hanging wall based on microtextural observations on quartz using sem cathodoluminescence imaging the chloritization event is ascribed to the 2020 ma vredefort impact event that created the necessary secondary permeability in the form of microfractures particularly within the conglomerate bed considering that the ventersdorp contact reef is generally regarded as the most intensely altered reef in the witwatersrand basin the relatively minor fluid infiltration established in this study suggests that contrary to prevailing opinion the other auriferous conglomerate beds might have experienced even less influx of externally derived hydrothermal fluids

rare earth elements in river waters we measured rare earth element ree concentrations in river waters to characterize the suspended and dissolved river flux of the ree to the oceans the ree pattern of river suspended materials is sensitive to drainage basin geology a positive correlation is observed between la yb ratios and nd model ages for the rivers studied major rivers have light ree enriched patterns relative to the north american shale composite nasc with la yb n 1 6 2 7 river water dissolved material 0 2 m is heavy ree enriched relative to suspended material and the most pronounced negative ce anomalies occur in rivers of high ph light ree concentrations vary by approximately 3 orders of magnitude and are inversely related to ph and major cation concentrations from these data we estimate that typical major river runoff has heavy ree depleted suspended material with la yb n 1 9 we conclude that the terrigenous input to the oceans from major rivers is heavy ree depleted relative to shales from the available data average river water dissolved material appears to be heavy ree enriched with la yb n 0 4 estuarine removal processes lower the dissolved ree river flux by approximately 60 and result in a flux that is more heavy ree enriched with la yb n 0 2 calculated oceanic residence times with respect to river input range from 2300 to 21 000 years are shortest for ce and greatest for the heavy ree and la such long residence times may suggest the presence of additional sources of ree in seawater

fluid circulation at stromboli volcano aeolian islands italy from self potential and co2 surveys this work addresses the study of fluid circulation of the stromboli island using a dense coverage of self potential sp and soil co2 data a marked difference exists between the northern flank and the other flanks of the island the northern flank exhibits 1 a typical negative sp altitude gradient not observed on the other flanks and 2 higher levels of co2 the general sp pattern suggests that the northern flank is composed of porous layers through which vadose water flows down to a basal water table in contrast to the other flanks where impermeable layers impede the vertical flow of vadose water in the sciara del fuoco and rina grande le schicciole landslide complexes breccias of shallow gliding planes may constitute such impermeable layers whereas elsewhere poorly permeable fine grained pyroclastites or altered lava flows may be present this general model of the flanks also explains the main co2 patterns concentration of co2 at the surface is high on the porous north flank and lower on the other flanks where impermeable layers can block the upward co2 flux the active upper part of the island is underlain by a well defined hydrothermal system bounded by short wavelength negative sp anomalies and high peaks of co2 these boundaries coincide with faults limiting ancient collapses of calderas craters and flank landslides the hydrothermal system is not homogeneous but composed of three main subsystems and of a fourth minor one and is not centered on the active craters the latter are located near its border this divergence between the location of the active craters and the extent of the hydrothermal system suggests that the internal heat sources may not be limited to sources below the active craters if the heat source strictly corresponds to intrusions at depth around the active conduits the geometry of the hydrothermal subsystems must be strongly controlled by heterogeneities within the edifice such as craters caldera walls or gliding planes of flank collapse as suggested by the correspondence between sp co2 anomalies and structural limits the inner zone of the hydrothermal subsystems is characterized by positive sp anomalies indicating upward movements of fluids and by very low values of co2 emanation this pattern suggests that the hydrothermal zone becomes self sealed at depth thus creating a barrier to the co2 flux in this hypothesis the observed hydrothermal system is a shallow one and it involves mostly convection of infiltrated meteoric water above the sealed zone finally on the base of co2 degassing measurements we present evidence for the presence of two regional faults oriented n41 and n64 and decoupled from the volcanic structures

numerical modeling of lava flow cooling applied to the 1997 okmok eruption approach and analysis 1 throughout february and march of 1997 okmok volcano in the eastern aleutian islands of alaska erupted a 6 km long lava flow of basaltic a a within its caldera a numerical model for lava flow cooling was developed and applied to the flow to better understand the nature of its cooling radiation and convection from the surface as well as conduction to the ground were used to transport the flow s heat to its surroundings in the model internally a conduction only approach moved heat from the interior outward vesiculation latent heat generation and thermal conductivity changes with temperature are among the other factors that were dynamically accounted for results indicate that ambient temperature fluctuations on the scale of days to weeks must be taken into account to create an accurate short term prediction of lava surface temperature daily data of rainfall and ambient temperature as opposed to yearly averages greatly increased the accuracy of the model furthermore convective cooling of the lava surface was observed to be a dominant heat loss process during the first 200 days indicating the convective heat transfer coefficient is a prime determinant of the accuracy of the model for predicting surface temperatures over a longer cooling period 2 years thermal conductivity and porosity proved to be among the dominating factors for heat loss because of the limiting role of conductive heat flow in the interior the model s flexibility allows application to flows other than the 1997 okmok eruption

paroxysmal activity at stromboli lessons from the past the persistent normal activity of stromboli is occasionally interrupted by sudden and highly energetic explosive events called strombolian paroxysms these phenomena together with landslide generated tsunamis represent the most hazardous manifestations of present day volcanic activity at stromboli the most recent paroxysms on 5 april 2003 and 15 march 2007 have drawn attention to these energetic events because they significantly threatened inhabitants and tourists historical accounts and field evidence indicate however that even larger paroxysms in terms of volume dispersal of products and intensity of explosive phenomena occurred in the recent past during these paroxysms incipiently welded spatter deposits mantled the north and south rims of the sciara del fuoco down to low elevations extending much farther than the similar deposits from recent observed events 5 april 2003 and 15 march 2007 in order to identify characterize and discriminate among products of these outstanding spatter forming eruptions more than 50 stratigraphic sections were measured and sampled stratigraphic sedimentological and radiometric 14c data indicate that only two paroxysms produced spatter that reached very low elevations and inhabited areas the first occurred in the 16th century and the last in ad 1930 analysis of texture and deposit components reveals that the early phases of the two eruptions were driven by distinctly different eruptive dynamics both identified paroxysms are at least one order of magnitude greater than any similar event observed by monitoring systems at stromboli these two large paroxysms were the most powerful volcanic events at stromboli in the last eighteen centuries

witwatersrand gold deposits formed by volcanic rain anoxic rivers and archaean life the witwatersrand gold deposit is the largest in the world thermodynamic calculations show that such rich accumulations of gold could be linked to abundant volcanism primitive life and the oxygen free atmosphere of the archaean the witwatersrand basin in south africa is one of the best preserved records of fluvial sedimentation on an archaean continent1 the basin hosts the worlds biggest gold resource in thin pebble beds but the process for gold enrichment is debated2 3 4 5 mechanical accumulation of gold particles from flowing river water is the prevailing hypothesis2 6 yet there is evidence for hydrothermal mobilization of gold by fluids invading the metasedimentary rocks after their burial3 4 7 earth s atmosphere three billion years ago was oxygen free8 but already sustained some of the oldest microbial life on land9 here i use thermodynamic modelling and mass balance calculations to show that these conditions could have led to the chemical transport and precipitation of gold in anoxic surface waters reconciling the evidence for fluvial deposition with evidence for hydrothermal like chemical reactions i suggest that the release of sulphurous gases from large volcanic eruptions created acid rain that enabled the dissolution and transport of gold in surface waters as sulphur complexes precipitation of the richest gold deposits could have been triggered by chemical reduction of the dissolved gold onto organic material in shallow lakes and pools i conclude that the witwatersrand gold could have formed only during the archaean after the emergence of continental life but before the rise of oxygen in the earth s atmosphere

dynamics of the december 2002 flank failure and tsunami at stromboli volcano inferred by volcanological and geophysical observations 1 the 2002 effusive flank eruption at stromboli volcano started on december 28 after several months of strong explosive activity at the summit craters on december 30 the seismic network recorded two large flank failures and associated tsunami waves this is the first time that a flank collapse and tsunami and their associated phenomena have been recorded by a multi disciplinary monitoring system volcanological and geophysical monitoring as well as thermal surveys performed immediately before and after the failure allowed us to define and interpret the sequence of events the still on going eruption has provided for the first time the opportunity to look into the dynamics of stromboli s effusive eruptions flank failure and landslide formation and their potential hazard

onset of the persistent activity at stromboli volcano italy stromboli known worldwide as the lighthouse of the mediterranean is commonly believed to have been in a state of persistent activity for the past 2000 2500 years however historical sources older than 1000 a d are not accurate enough to assess if the activity of the volcano was exactly the same as we see at present in order to attempt to identify the onset of the present eruptive regime and assess if it has been maintained with the same characteristics through time stratigraphic and radiometric studies of the recent tephra deposits were undertaken up to 4 m deep stratigraphic trenches dug at a height of approximately 500 m on the ne flank of the volcano exposed a conformable tephra pile containing charcoal fragments one of the most interesting finds was the discovery of a 7 cm thick weathered bed rich in organic matter thin palaeosol approximately 3 m below the surface the sequence underneath the palaeosol consists of decimetre thick lapilli fallout beds alternating with ash deposits bearing small charcoals with calibrated ages of between the fourth century b c and the first century a d the sequence above the palaeosol is charcoal free and consists of coarse ash deposits with discrete centimetre thick lapilli fallout beds composed of crystal poor golden pumice and subordinate crystal rich black scoriae similar to scoria pumice pairs emitted during the more energetic explosions of the present day activity the data collected indicate that between the third and seventh centuries a d after a period of quiescence the activity resumed with an eruptive style identical to the present one we conclude that the lighthouse of the mediterranean actually began its activity in a period much later than previously thought

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

lava effusion rates from hand held thermal infrared imagery an example from the june 2003 effusive activity at stromboli a safe easy and rapid method to calculate lava effusion rates using hand held thermal image data was developed during june 2003 at stromboli volcano italy we used a forward looking infrared radiometer flir to obtain images of the active lava flow field on a daily basis between may 31 and june 16 2003 during this time the flow field geometry and size where flows typically a few hundred meters long were emplaced on a steep slope meant that near vertical images of the whole flow field could be captured in a single image obtained from a helicopter hovering at an altitude of 750 m and 1 km off shore we used these images to adapt a thermally based effusion rate method previously applied to low and high spatial resolution satellite data to allow automated extraction of effusion rates from the hand held thermal infrared imagery a comparison between a thermally derived 0 23 0 87 m3 s 1 and dimensionally derived effusion rate 0 56 m3 s 1 showed that the thermally derived range was centered on the expected value over the measurement period the mean effusion rate was 0 38 0 25 m3 s 1 which is similar to that obtained during the 1985 86 effusive eruption and the time averaged supply rate calculated for normal non effusive strombolian activity a short effusive pulse reaching a peak of 1 2 m3 s 1 was recorded on june 3 2003 one explanation of such a peak would be an increase in driving pressure due to an increase in the height of the magma contained in the central column we estimate that this pulse would require the magma column to attain a height of 190 m above the effusive vent which is approximately the elevation difference between the vent and the floor of the ne crater our approach gives an easy to apply method that has the potential to provide effusion rate time series with a high temporal resolution

relationship between detrital zircon age spectra and the tectonic evolution of the late archaean witwatersrand basin south africa abstract shrimp u pb detrital zircon age spectra for 14 samples from the west rand and central rand groups of the witwatersrand basin indicate that felsic source rocks mostly formed at 3090 3060 and 3000 2870 ma with a smaller proportion formed prior to 3100 ma provenance evaluation indicates that source rocks have largely vanished through erosion such that greenstone terrains extending from the amalia kraaipan belt in the southwest to the murchison belt in the northeast are models of but not the actual source areas analysis of detrital zircon age modes reveals that the west rand and central rand groups record different basins the west rand group is characterised by age subpopulations with a much smaller range and less complex distribution than those in the central rand group furthermore detrital zircon age spectra for the west rand group generally decrease in complexity up section whereas they become increasingly more complex in the central rand group it is concluded that the source area for the west rand group is consistent with a passive margin setting with the decrease in complexity up section of zircon age spectra being the consequence of increasing maturity of the hinterland conversely the source area of the central rand group was far more dynamic with an increasing age range of source rocks being exposed through time pulsed tectonic rejuvenation of the source area is implied contemporaneous emplacement uplift and erosion of granitoids supports a magmatic fold thrust belt as the source and a complementary retroarc basin setting detrital xenotime grains record the ages of high u granitoids emplaced in the fold thrust belt during deposition of the central rand group and are much closer to depositional ages than are detrital zircon grains change from a passive margin to a retroarc basin across the west rand central rand boundary is emphasised by change from simple to increasingly complex detrital zircon age spectra this study establishes that detrital zircon geochronology can overcome the problem of overly quartzose compositions in archaean sandstones due to severe chemical weathering and authigenic alteration thereby enabling distinction between passive margin and retroarc basin stages through systematic changes in the age complexity of the source area

vent discrimination at stromboli volcano italy eruptive activity at stromboli volcano was significantly elevated over background levels in may 2001 during 63 h of observation eight vents produced on average 17 explosions h with an average repose interval of 3 min during this period the stromboli vents exhibited consistent seismic and acoustic signatures based on cross correlation cluster analysis dendrogram clustering based on waveform cross correlation was used to illustrate the complexity of the near surface plumbing system of stromboli s multi vent edifice cross correlations of displacement seismograms produced by explosions at specific craters such as the northeast crater nec form dense waveform clusters with correlation coefficients between 0 96 and 0 99 while displacement waveforms from other craters such as the southwest crater swc exhibit loose clusters with correlations between 0 88 and 0 96 the inconsistency of swc events as compared to the nec suggests that the vent system there is more heterogeneous cluster linkage distance between the nec cluster and the central crater cc cluster is shorter than the linkage distance between the nec and swc clusters indicating that nec and cc are more closely related infrasonic observations were used to locate vent explosions confirming that the clusters of events are associated with specific vents or craters qualitative analyses of acoustic waveforms from approximately 500 explosions reveal that impulsive acoustic signals were associated with short mechanically simple ground displacement responses these events may correspond to the bursting of an individual gas slug similar degassing mechanisms from vents in the nec and the cc show common characteristics in their displacement waveforms

lava effusion a slow fuse for paroxysms at stromboli volcano questo lavoro ha analizzato i risultati del monitoraggio termico delle eruzioni di stromboli del 2002 2003 e 2007 ed ha mostrato come prima di ogni parossisma il volume di lava eruttato nel corso dell attivita effusiva sia stato confrontabile questa osservazione ha fatto ipotizzare l esistenza di una decompressione critica nel sistema di alimentazione superficiale del vulcano raggiungibile anche lentamente che innesca la veloce risalita del magma ricco in gas responsabile dei parossismi durante l attivita effusiva a questa decompressione critica e associabile una soglia di volume di magma emesso che diventa la misura discriminante per valutare la fase critica del vulcano e predire il parossisma

recovery of spectral emissivity from thermal infrared multispectral scanner imagery acquired over a mountainous terrain a case study from mount etna sicily the estimation of ground radiance and emissivity from thermal infrared multispectral scanner tims data is strongly dependent on the atmospheric correction applied to these data since such corrections are a function of the atmospheric path between the sensor and ground correction techniques that do not consider the topographic variations within a scene can introduce appreciable error in the estimation of the atmosphere effects in this paper we describe the development and application of a variable elevation atmospheric correction procedure our objective was to incorporate changes in target altitude into a general atmosphere correction strategy this procedure was tested on a tims data set acquired over mt etna italy in july 1986 the methodology adopted in this study is based on the use of the lowtran radiative transfer code and a digital elevation model dem registered to the image data the image data are divided into a series of layers based on elevation and a separate atmosphere correction is applied to each layer maps of emissivity estimates derived with the variable elevation approach were compared with geologic maps of the etna flow fields prior to the variable elevation correction the emissivity spectra of long lava flows appeared to vary with elevation following the variable elevation correction many of these spectral artifacts were removed from the emissivity maps in addition the variable elevation correction increased our ability to discriminate individual lava flows

multiple sulphur and iron isotope composition of detrital pyrite in archaean sedimentary rocks a new tool for provenance analysis abstract multiple s 34 s and 33 s and fe 56 fe isotope analyses of rounded pyrite grains from 3 1 to 2 6 ga conglomerates of southern africa indicate their detrital origin which supports anoxic surface conditions in the archaean rounded pyrites from meso to neoarchaean gold and uranium bearing strata of south africa are derived from both crustal and sedimentary sources the latter being characterised by non mass dependent fractionation of s isotopes 33 s as negative as 1 35 and large range of fe isotope values 56 fe between 1 1 and 1 2 most sediment sourced pyrite grains are likely derived from sulphide nodules in marine organic matter rich shales sedimentary exhalites and volcanogenic massive sulphide deposits some sedimentary pyrite grains may have been derived from in situ sulphidised fe oxides prior to their incorporation into the conglomerates as indicated by unusually high positive 56 fe values sedimentary sulphides without significant non mass dependent fractionation of s isotopes were also present in the source of some conglomerates the abundance in these rocks of detrital pyrite unstable in the oxygenated atmosphere may suggest factors other than high p o 2 as the cause for the absence of significant non mass dependent fractionation processes in the 3 2 2 7 ga atmosphere rounded pyrites from the c 2 6 ga conglomerates of the belingwe greenstone belt in zimbabwe have strongly fractionated 34 s 33 s and 56 fe values the source of which can be traced back to black shale hosted massive sulphides in the underlying strata the study demonstrates the utility of combined multiple s and fe isotope analyses for provenance reconstruction of archaean sedimentary successions

archean foreland basin tectonics in the witwatersrand south africa the witwatersrand basin of south africa is the best known of archean sedimentary basins and contains some of the largest gold reserves in the world sediments in the basin include a lower flysch type sequence and an upper molassic facies both of which contain abundant silicic volcanic detritus the strata are thicker and more proximal on the northwestern side of the basin which is at least locally bound by thrust faults these features indicate that the witwatersrand strata may have been deposited in a foreland basin and a regional geologic synthesis suggests that this basin developed initially on the cratonward side of an andean type arc remarkably similar phanerozoic basins may be found in the southern andes we suggest that the continental collision between the kaapvaal and zimbabwe cratons at about 2 7 ga caused further subsidence and deposition in the witwatersrand basin regional uplift during this later phase of development placed the basin on the cratonward edge of a collision related plateau now represented by the limpopo province similarities are seen between this phase of witwatersrand basin evolution and that of active basins north of the tibetan plateau e g the tarim and tsaidam basins the geologic evidence does not appear so compatible with earlier suggestions that the witwatersrand strata were deposited in a rift or half graben

the composition and depositional environments of mesoarchean iron formations of the west rand group of the witwatersrand supergroup south africa this paper documents the sedimentological setting mineralogy and geochemistry of several iron formation units interbedded with siliciclastic strata of the mesoarchean witwatersrand supergroup well known for its world class conglomerate hosted au u deposits four major iron formation beds with associated magnetic mudstones are present in two distinctly different lithostratigraphic associations namely shale and diamictiteassociated iron formation the shale association is represented by the water tower and contorted bed iron formations in the parktown formation of the hospital hill subgroup in the lower part of the succession and the diamictite association by the promise and silverfield iron formations in the overlying government subgroup the iron formation units have been subjected to lower greenschist facies metamorphism oxide magnetite and limited hematite carbonate and silicate facies iron formations are recognized the iron formations typically overlie major transgressive flooding surfaces in the succession and in turn form the base of progradational coarsening upward increments of sedimentation comprising magnetic mudstone nonmagnetic shale and interbedded siltstone quartzite the upward transition from iron formation into magnetic mudstone is accompanied by a change in mineralogical composition from hematite magnetite iron formation at the base in the most distal setting through magnetite siderite and siderite facies iron formation in the transition zone to magnetic mudstone the siderite with associated ankerite displays highly depleted 13c values suggesting crystallization via iron respiration in presence of organic carbon the iron formations display positive postarchean australian shale normalized eu and y anomalies with depletion in light rare earth elements relative to heavy rare earth elements indicating precipitation from marine water with a high temperature hydrothermal component integration of sedimentological petrographic and geochemical results indicates that the shale associated iron formation was deposited during the peak of transgression when reduced iron rich hydrothermal waters entered the witwatersrand basin over a limited vertical extent due to neutral buoyancy with the top of the plume occurring below the photic zone it is suggested that chemolithoautotrophic iron oxidizing bacteria which would have been able to exploit the difference in chemistry between the iron enriched plume water and ambient ocean water to fuel metabolic activity in the presence of limited free molecular oxygen were responsible for precipitation of initial ferric iron oxyhydroxides the vertical facies associations in the iron formations most likely developed in response to the limited vertical extent of the hydrothermal plume with from distal to proximal hematite preserved where the base of the plume was not in contact with the basin floor magnetite where the plume water was in contact with bottom sediment iron rich carbonates where organic carbon input was high iron rich alumosilicates where siliciclastic input became significant in more proximal settings and iron poor sediment above the top of the plume diamictite associated iron formations in the witwatersrand are inferred to have been deposited in a fashion similar to the shale associated iron formations with the exception that major transgressions and hydrothermal plume invasion were preceded by glacial ice cover the climate warming and increased volcanic activity required could have been related to increased tectonic activity inferred for the witwatersrand supergroup during deposition of the glacially associated iron formations

geochemistry of archean shales from the witwatersrand supergroup south africa source area weathering and provenance with a few exceptions shales from the archean witwatersrand supergroup 2800 ma in south africa are depleted in na ca lile ree and hfse compared to phanerozoic shales cr co and ni are enriched in all witwatersrand shales and fe and mg are high in shales from the west rand groups wrg and lower central rand group crg shales from the crg and uppermost wrg are enriched in na al lile ree hfse and transition metals relative to shales from the lower wrg chondrite normalized ree patterns for all witwatersrand shales are enriched in light ree and exhibit small to moderate negative eu anomalies a positive correlation of ree and al2o3 contents in the shales suggests that ree are contained principally in clay minerals relative to shales from the crg shales from the wrg exhibit depletions of na ca and sr a feature probably reflecting intense chemical weathering of their source rocks cia indices in witwatersrand shales are variable chiefly 70 98 even within the same shale unit such variations reflect chiefly variable climatic zones or rates of tectonic uplift in source areas with perhaps some contribution from provenance and element remobilization during metamorphism compared to present day upper continental crust all but the orange grove roodepoort and k8 shales appear to have been derived from continental sources depleted in lile ree and hfse and enriched in transition metals computer mixing models based on six relatively immobile elements th hf yb la sc co and four source rocks indicate that the relative proportions of granite basalt and komatiite increased with time in sediment source areas at the expense of tonalite the contributions of basalt and komatiite appear to reach a maximum during deposition of the booysens shale and granite during deposition of the k8 shales and possibly during deposition of the orange grove shales

pathways for neoarchean pyrite formation constrained by mass independent sulfur isotopes it is generally thought that the sulfate reduction metabolism is ancient and would have been established well before the neoarchean it is puzzling therefore that the sulfur isotope record of the neoarchean is characterized by a signal of atmospheric mass independent chemistry rather than a strong overprint by sulfate reducers here we present a study of the four sulfur isotopes obtained using secondary ion ms that seeks to reconcile a number of features seen in the neoarchean sulfur isotope record we suggest that neoarchean ocean basins had two coexisting significantly sized sulfur pools and that the pathways forming pyrite precursors played an important role in establishing how the isotopic characteristics of each of these pools was transferred to the sedimentary rock record one of these pools is suggested to be a soluble sulfate pool and the other pool atmospherically derived elemental sulfur is suggested to be largely insoluble and unreactive until it reacts with hydrogen sulfide we suggest that the relative contributions of these pools to the formation of pyrite depend on both the accumulation of the insoluble pool and the rate of sulfide production in the pyrite forming environments we also suggest that the existence of a significant nonsulfate pool of reactive sulfur has masked isotopic evidence for the widespread activity of sulfate reducers in the rock record

characterizing high energy explosive eruptions at stromboli volcano using multidisciplinary data an example from the 9 january 2005 explosion abstract stromboli is well known for its persistent normal explosive activity consisting of intermittent mild to moderate strombolian explosions that typically occur every 10 20 min all tephras erupted during this activity usually fall back into the crater terrace and consist of volatile poor scoriae fed by highly porphyritic hp magma more occasionally large explosions or paroxysms eject a greater quantity of tephra mainly consisting of hp scoriae and pumice clasts of low porphyritic lp magma but also including large lithic blocks in addition to this activity between 2004 and 2006 high energy explosions displaying an intermediate eruptive style between that of normal and paroxysmal explosions in terms of column height duration and tephra dispersal were observed to occur at a frequency of one to eight events per year while many volcanological geochemical and geophysical studies have focused in the last few years on the two end members of activity i e normal or paroxysmal a detailed investigation on these intermediate types of events has not been carried out yet here we report of a study on the 9 january 2005 explosion one of the high energy explosions during which the main fountaining phase lasted nearly a minute causing ejection of coarse bombs up to a height of 120 m and of ash and lapilli to 200 m an accompanying ash plume rose up to 500 m at the end of the explosion we present a multidisciplinary approach that integrates the results from analysis of live camera images with compositional and textural characterization of the erupted products major element composition of glassy groundmass and 3d views of textures in the erupted scoriae support the hypothesis based on volcanological observations that this explosion falls between normal and paroxysmal activity for which we use the term intermediate by comparing the video camera images of the 9 january 2005 explosion with volcanological features of other high energy explosions that occurred at stromboli between june 2004 and october 2006 we find that three additional events can be considered intermediate explosions suggesting that this type of activity may be fairly common on this volcano the results of this study although preliminary given our limited dataset clearly indicate that the methodology used here can be successfully applied to better define the range of eruptive styles typifying the normal explosive activity potentially improving our capability of eruption forecasting and assessing volcanic hazard at stromboli

the stromboli volcano landslides of december 2002 a seismological description 1 we analyse seismograms of the slump episodes at stromboli on december 30 2002 using a simple single force model we estimate the volume involved in the individual subevents and attempt a chronological reconstruction of the whole process our results indicate the occurrence of two main events that could be interpreted as a submarine slump which caused the observed tsunami and a subaerial slump which did not produce destructive sea waves a total volume of about 20 106 m3 results for the submarine event which developed over about 2 minutes with several distinct detachments the first and largest displacing a volume of 10 8 106 m3 the second subaerial slump involved at least 2 5 106 m3 in about 90 s a large long period pulse is also recognizable in the seismograms of the stromboli station we tentatively interpret this feature as tilt caused by the water load associated with the inundation in the ficogrande area on the northeastern side of the island

provenance and geochemical variations in shales of the mesoarchean witwatersrand supergroup abstractnew major and trace element data are presented for low grade metamorphosed marine shale units of the highly auriferous mesoarchean witwatersrand supergroup in the kaapvaal craton south africa comparison of the most altered with the least altered samples revealed that postdepositional modification of shale chemistry was significant only near contacts with over and underlying coarser grained siliciclastic rocks and along cross cutting faults veins and dikes away from such zones the shale composition can be used to draw inferences on sediment provenance and paleoweathering in the source region and or on intrabasinal erosion surfaces as well as on the likely tectonic setting of the depositional basins the shale composition is highly variable both laterally within and vertically across stratigraphic units the shales are characterized by a high chemical index of alteration chemical index of weathering and index of compositional variability all of which suggest that the source area was lit

integrating puffing and explosions in a general scheme for strombolian style activity strombolian eruptions are among the most common subaerial styles of explosive volcanism worldwide distinctive features of each volcano lead to a correspondingly wide range of variations of magnitude and erupted products but most papers focus on a single type of event at a single volcano here in order to emphasize the common features underlying this diversity of styles we scrutinize a database from 35 different erupting vents including 21 thermal infrared videos from stromboli italy etna italy yasur vanuatu and batu tara indonesia from puffing through rapid explosions to normal explosions with variable ejection parameters and relative abundance of gas ash and bombs using field observations and high speed thermal infrared videos processed by a new algorithm we identify the distinguishing characteristics of each type of activity and how they may relate and interact in particular we record that ash poor normal explosions may be preceded and followed by the onset or the increase of the puffing activity while ash rich explosions are emergent i e with inflation of the free surface followed directly by emission of increasingly large gas pockets overall we see that all strombolian activities form a continuum arising from a common mechanism and are modulated by the combination of two well established controls 1 the length of the bursting gas pocket with respect to the vent diameter and 2 the presence and thickness of a high viscosity layer in the uppermost part of the volcanic conduit

episodic concentration of gold to ore grade through earth s history abstract concentration of gold to economic ore grades has been highly episodic through earth s history with different sedimentary magmatic and hydrothermal processes having operated as principal driving forces at different times comparison of the various types of gold deposits their secular and spatial distribution and the amounts of gold contained in them combined with thermodynamic considerations reveals that the formation of gold deposits reflects fundamental changes in environmental conditions biological evolution and styles of large scale tectonism over the past four billion years here i suggest that most of the gold in the earth s crust was first concentrated at around 2 9 billion years ga ago by early photosynthesising microbes under an oxygen deficient atmosphere sedimentary reworking of auriferous microbial mats provided the source for the richest known gold palaeoplacers between 2 9 and 2 7 ga and an overall gold enrichment of coeval marine sediments only after modern style plate tectonics had begun to operate sediments enriched in gold had been accreted along active plate margins subducted and subcontinental lithospheric mantle had been correspondingly metasomatised did the formation of larger orogenic porphyry type and epithermal and to a lesser extent also other hydrothermal gold deposits become possible thus the principal secular peak in orogenic gold formation at 2 75 2 55 ga can be explained

the 5 april 2003 vulcanian paroxysmal explosion at stromboli volcano italy from field observations and thermal data abstract the 5 april 2003 paroxysmal explosion at stromboli volcano was one of the strongest explosive events of the last century it occurred while the effusive eruption begun on 28 december 2002 and finished on 22 july 2003 was still on going and the summit craters of the volcano were obstructed in this paper we present a reconstruction of the sequence of events based on thermal and visual images collected from helicopter before during and immediately after the paroxysm one month before the blast ash emission and temperature increase at the bottom of the summit craters were observed an increasing amount of juvenile components in the emitted ash during march suggested that the magma level within the crater was rising accordingly hot degassing vents at the bottom of the summit craters were not persistent and the craters remained almost entirely obstructed by talus accumulation until the paroxysm occurred three minutes before the explosion we recorded a significant increase in temperature inside crater 1 accompanied by a thicker gas plume thirty two seconds before the blast reddish ash was emitted from crater 1 the paroxysm produced a vulcanian explosion that opened the feeder conduit obstructed for over three months the blast was accompanied by a shock wave recorded by the ingv seismic network at 07 13 37 gmt explosions with hot material started from crater 1 and after 15 s propagated to crater 3 about 100 m away the velocity of ejecta was 80 m s 1 and increased when the eruptive plumes from both craters merged together during the vulcanian phase an eruptive column rose 1 km above the top of the volcano and explosions continued mainly at crater 3 the paroxysm lasted about 9 min with bombs up to 4 m wide falling on the village of ginostra on the west flank of the island and destroying two houses this event signalled the start of the declining phase of the effusive eruption suggesting that the feeder conduit was returning to its former steady conditions with open vents and continuous mild strombolian activity

characterisation of the 1997 vulcanian explosions of soufriere hills volcano montserrat by video analysis the activity of convention at montserrat soufriere hills volcano montserrat during the period 1995 1999 included numerous violent explosions two major cycles of vulcanian explosions occurred in 1997 a first of 13 explosions between 4 and 12 august and a second of 75 between 22 september and 21 october the explosions were short lived events lasting a few tens of seconds during which partial fountain collapse generated pyroclastic surges and pyroclastic flows and buoyant plumes ascended 3 15 km into the atmosphere each explosion discharged on average 3 105 m3 dense rock equivalent dre of magma draining the conduit to depths of 1 2 km the paper focuses on the first few seconds of three explosions of the 75 that occurred in september october 1997 6 october 1997 at 17 50 7 october 1997 at 16 02 and 9 october 1997 at 12 32 physical parameters such as exit velocities magmatic water contents and magma pressures at fragmentation are estimated by following and modelling the ascent of individual momentum dominated finger jets visible on videos during the initial stages of each explosion the model treats each finger jet as an incompressible flow sustained by a steady flux of gas and particles during the few seconds of ascent and produces results that compare favourably with those using a multiphase compressible code run using similar eruptive parameters each explosion reveals a progressive increase in eruptive intensity with time jet exit velocities increasing from 40 m s 1 at the beginning of the explosion up to 140 m s 1 after a few seconds modelling suggests that the first magma to exit was largely degassed whereas that discharged after a few seconds contained up to 2 wt water magma overpressures up to 10 mpa are estimated to have existed in the conduit immediately prior to each explosion progressive increases in jet exit velocity with time over the first few seconds of each explosion provide direct evidence for strong pre eruptive gradients in water content and magma pressure in the upper reaches probably 100 500 m of the conduit fountain collapse occurred during the first 10 20 s of each explosion because the discharging jets had bulk densities up to 100 times that of the atmosphere and were unable to entrain enough air to become buoyant such high eruptive densities were due to the presence of partially degassed magma in the conduit

thermal precursors in satellite images of the 1999 eruption of shishaldin volcano shishaldin volcano unimak island alaska began showing signs of thermal unrest in satellite images on 9 february 1999 a thermal anomaly and small steam plume were detected at the summit of the volcano in short wave thermal infrared avhrr advanced very high resolution radiometer satellite data this was followed by over 2 months of changes in the observed thermal character of the volcano initially the thermal anomaly was only visible when the satellite passed nearly directly over the volcano suggesting a hot source deep in the central crater obscured from more oblique satellite passes the zenith angle needed to see the anomaly increased with time presumably as the thermal source rose within the conduit based on this change an ascent rate of ca 14 m per day for the thermal source was estimated until it reached the summit on around 21 march it is thought that strombolian activity began around this time the precursory activity culminated in a sub plinian eruption on 19 april ejecting ash to over 45 000 ft 13 700 m the thermal energy output through the precursory period was calculated based on geometric constraints unique to shishaldin these calculations show fluctuations that can be tied to changes in the eruptive character inferred from seismic records and later geologic studies the remote location of this volcano made satellite images a necessary observation tool for this eruption to date this is the longest thermal precursory activity preceding a sub plinian eruption recorded by satellite images in the region this type of thermal monitoring of remote volcanoes is central in the efforts of the alaska volcano observatory to provide timely warnings of volcanic eruption and mitigate their associated hazards to air traffic and local residents

textural and geochemical discrimination between xenotime of different origin in the archaean witwatersrand basin south africa abstract xenotime ypo4 of detrital diagenetic and hydrothermal origin within siliciclastic rocks of the archaean witwatersrand basin south africa has been identified on the basis of petrography and in situ ion microprobe shrimp age data the chemical composition of xenotime determined by in situ electron microprobe analysis can be correlated with its origin this allows the origin of any xenotime grain to be assessed by a non destructive microanalytical method prior to ion microprobe geochronology the main chemical discriminators are mree hree abundance normalised hree slope and eu anomaly and in some cases u and th contents igneous detrital xenotime 2800 ma is distinguished from diagenetic 2780 ma and hydrothermal

observations of seismic volcanic signals at stromboli volcano italy abstract digital recordings of ground motion during a seismic operation organized at stromboli volcano italy from may 31 1986 to june 26 1986 have been studied the amplitude of background seismic noise is greater at the summit than at the base of the volcano and the spectra calculated on different days are dominated by at least two frequencies 2 0 and 6 0 hz with subdominant frequencies at 4 1 4 8 and 8 hz according to their waveform and their spectral content three types of discrete volcanic signals are distinguishable the first type is characterized by a dominant frequency at 2 hz and a subdominant frequency at 4 1 hz the second type also has a dominant peak frequency at 2 hz with two important subdominant frequencies at 5 and 8 hz the type 3 has a sharp dominant frequency at 6 hz and subdominant frequency at 3 2 hz the frequencies observed for discrete signals and ground noise suggest that they are produced by the same repeated mechanism which probably has a volcanic origin the discrete signals are linked to explosions at the active vents within the craters

formation of metal in grosvenor mountains 95551 and comparison to ordinary chondrites abstract siderophile element abundances in individual metal grains in the ungrouped chondrite grosvenor mountains gro 95551 and in the ordinary chondrites tieschitz h3 6 soko banja ll4 and allegan h5 were measured with laser ablation inductively coupled plasma mass spectrometry matrix metal in gro 95551 falls into two distinct compositional groups a high ni group with 7 2 0 4 wt ni and a low ni group with 3 7 0 1 wt ni indicating that kamacite taenite equilibration at 1020 k was followed by rapid cooling the nonrefractory siderophile elements p co cu ga ge as pd and au also partition between the high ni and low ni metal in a manner consistent with kamacite taenite fractionation but the refractory siderophiles ru re os ir and pt show correlated variations that are unrelated to kamacite taenite partitioning and indicate that variations in refractory components of the metal were not completely erased during equilibration at 1020 k the ni normalized bulk metal composition of gro 95551 is refractory depleted and volatile rich relative to bencubbin and related metal rich chondrites but bears strong similarities to equilibrated ordinary chondrite metal gro 95551 represents a new chondrite type with chemical affinity to the ordinary chondrites individual metal grains in unequlibrated ordinary chondrites also have correlated variations in refractory siderophile contents that cannot be produced by redox processes alone these variations span three orders of magnitude and diminish with increasing metamorphic grade of the ordinary chondrites

geochemical precursors of the activity of an open conduit volcano the stromboli 2002 2003 eruptive events 1 marked increases of co2 h2 and he dissolved in thermal waters and changes in the dissolved carbon isotopic composition were observed at stromboli before the 28 december 2002 eruption and before a violent explosive paroxysm occurred on 5 april 2003 high anomalous co2 flux values were recorded at the crater rim since a week before the eruption onset the first anomalies in the thermal waters dissolved co2 amount appeared some months before the eruption when magma column rose at a very high level in the conduit high peaks of dissolved h2 and he were recorded a few days before the paroxysm carbon isotopic composition indicates a magmatic origin of the dissolved co2 whose increase together with those of h2 and he is attributed to an increasing output of deep gases likely produced by depressurization of a rising batch of a deep gas rich magma whose fragments have been emitted during the explosion

geochemistry of precambrian and paleozoic siliciclastic rocks from the iberian range ne spain implications for source area weathering sorting provenance and tectonic setting abstract the major and trace element chemical composition of precambrian and paleozoic shales and sandstones from the iberian range spain has been investigated to determine the provenance and tectonic setting of these rocks as well as to appraise the influence of the weathering hydraulic sorting and recycling processes upon source rock signature the samples studied belong to a prograde sequence from diagenesis to anchizonal grade and are mainly composed of quartz illite mica phases and or kaolinite with chlorite feldspars and carbonates as minor components the major element distribution chemical index of alteration cia indices reflects that recycling processes have been important in homogenizing the composition of shales and sandstones the higher cia indices observed in the silurian and devonian shales 80 and 85 respectively compared with those of precambrian to ordovician and the carboniferous age about 70 indicate that their source area underwent more intense chemical weathering processes possibly due to climatic and or tectonic variations alternatively the source area of the silurian and devonian shales may have been composed of recycled sedimentary materials mineral fractionation is mainly observed in coarser rocks through zircon apatite and xenotime accumulation although the shales are not free of these phases the zircon content of the fine grained rocks is not high enough to affect rare earth element ree contents but phosphate minerals apatite and xenotime at least partially control the ree distribution the influence of apatite and xenotime are slightly higher in the precambrian shales as the phosphate concentration produces a decrease in the la sm ratios chondrite normalized ree patterns and negative eu anomaly size of the studied rocks are similar to that of post archean australian shales paas indicating that they originally come from a differentiated silicic source the higher ree contents in the studied shales in relation to paas indicate that recycling processes in the iberian range sources were probably more intense than that of paas the slight differences among the ree patterns of the different groups of shales probably do not reflect changes in source area composition but instead suggest variations in mineral sorting chemical weathering and or sediment recycling the th sc co th cr th cr v v ni ratios support a primitive silicic source for these rocks with the higher th sc and lower co th in cambrian and ordovician shales indicating a higher proportion of felsic material in their primitive source area the compositional maturity of analyzed sandstones is typical of cratonic environments and their la sc th and zr contents reflect their passive continental margin setting

flexural partitioning of the late archaean witwatersrand foreland system south africa abstract the witwatersrand basin is part of a retroarc foreland system formed during the late archaean in response to crustal thickening along the northern margin of the kaapvaal craton this foreland system may be partitioned into foredeep forebulge and back bulge flexural provinces the preserved sedimentary fill occupies the region of the flexural foredeep and displays a typical transition from underfilled deep and shallow marine to overfilled fluvial and alluvial fan phases loading in the witwatersrand thrust belt took place in relation to the oblique convergence of two compressional stress fields as a result the foredeep is restricted along the strike to a distance of the witwatersrand foreland system formed on a newly cratonized continental lithosphere which gave the basin a small flexural wavelength i e 490 km from the center of orogenic loading to the axis of the back bulge relative to most phanerozoic counterparts the forebulge unconformity may be associated with the lack of dynamic loading which is probably a common feature for all precambrian retro foreland systems due to the lower rates of subduction associated with the early stage of plate tectonic processes

rare earth element geochemistry of australian paleozoic graywackes and mudrocks provenance and tectonic control abstract in the paleozoic graywackes of eastern australia there is an increase in the total abundance of rare earth elements ree a light to heavy ree ratio and a decrease in the chondrite normalized eu anomaly with the increase in sio2 al2o3 and k2o na2o ratios this is due to the change in the dominant source rocks from andesite to dacite to granite gneiss and sedimentary rocks similarly an increase in total ree and a decrease in eu anomaly is also seen in the associated mudrocks with the increase in total clay content this correlation in paleozoic sedimentary rocks suggests that the ree characteristics of terrigenous sedimentary rocks reflect the depositional tectonic setting of the basin the oceanic island arc type graywackes are characterised by their lower total ree abundance only slight enrichment of lree over hree and the absence of a negative eu anomaly on chondrite normalised plots the continental island arc type graywackes are discriminated by their higher ree abundance and la yb ratio the presence of a small negative eu anomaly on the chondrite normalised plots and the significant enrichment of eu compared to paas post archean average australian shale the sedimentary rocks deposited on andean type active continental margins passive margins platform and cratonic basins are all characterised by the high enrichment of lree over hree and the presence of a pronounced negative eu anomaly on chondrite normalised plots and can not be discriminated from each other by ree patterns alone

multiple sulfur isotopes and the evolution of the atmosphere interest in multiple sulfur isotope analyses has been fueled by recent reports of mass independent sulfur isotope signatures in the geologic record a non zero multiple isotopic signature of sulfur 33s and 36s is produced primarily through photochemical reactions and it is an almost perfect tracer of the source of sulfur once the signature is passed on to a given sulfur reservoir it will be preserved unless there is addition of sulfur with a different 33s or 36s in the geological record this signature has been used to study the evolution of the earth s atmosphere and to trace movement of sulfur through geological systems early in earth s history recently small but significant mass independent signatures have been reported for some younger samples raising the possibility of additional applications of multiple isotope studies the purpose of this review is to introduce and discuss the implications of multiple isotope studies and to focus attention on these anomalous but not uncommon isotopic signatures

image processing of explosive activity at stromboli abstract a new way to study the dynamics of explosive behaviour at different vents of stromboli volcano is proposed the method is based on computer processing of images taken by an infrared film camera at a rate of 4 pictures per second each picture has been digitized by use of an image scanner with a 75 d p i dots per inch resolution and 256 levels of gray then processed and the total mass of the ejected material has been calculated for each photograph with this procedure the flux of ejected matter throughout every single explosive event has been reconstructed the analysis of trajectories made on adequate samples of ejecta has allowed us to evaluate the ejection velocity the mode of the mass flux distribution and the mean value of the velocities calculated for individual particles quantify the kinetic energy of an explosion vents nos 1 and 3 which remained active after the last effusive eruption of 1985 1986 show several explosive patterns the energy of which is measured the observed flux distributions have been checked both numerically and experimentally by modelling impulsive events the computer simulations of the mass distributions have allowed us to speculate on the possible explosive dynamisms two different models have been used a single impulse model confirms the behaviour actually shown by one of the two vents while the behaviour of the other is better depicted by a cumulative trend of successive impulses in rhythmic sequence moreover through the experimental approach we have had the opportunity to test the overall resolution of the method the observed matter flux distribution has then been associated to the seismic signals in order to correlate the dynamics involved in the explosions with the seismic source mechanisms