the uwekahuna ash member of the puna basalt product of violent phreatomagmatic eruptions at kilauea volcano hawaii between 2800 and 210014c years ago abstract kilauea volcano s reputation for relatively gentle effusive eruptions belies a violent geologic past including several large phreatic and phreatomagmatic eruptions that are recorded by holocene pyroclastic deposits which mantle kilauea s summit area and the southeast flank of adjacent mauna loa volcano the most widespread of these deposits whose original distribution can be reconstructed is the uwekahuna ash member of the puna basalt a basaltic surge and fall deposit emplaced during two or more eruptive episodes separated by a few decades to several centuries the first episode occurred between 2770 70 and 2265 50 14 c yr ago it included two major pyroclastic surges each preceded by unusually vigorous lava fountaining from a vent near the volcano s summit before the second eruptive episode 2110 120 14 c yr ago plants had re colonized the rainforest environment northeast of the summit and at least two lava flows from mauna loa had buried parts of the first episode deposits the second episode also began with vigorous lava fountaining followed by widespread lithic ashfall a third major surge and finally a fourth fountaining event before the final pumice deposit could be significantly reworked it was partly buried by picritic basalt flows that are unusual in kilauea s summit area in proximal areas the uwekahuna ash member is more than 1 m thick locally 5 m and includes lithic blocks up to 0 8 m in diameter coarse primarily lithic debris was deposited around the vent by laterally expanding surges fallout deposits accumulated preferentially to the northeast under the influence of high altitude counter tradewinds the area devastated by surges and originally buried by at least 15 cm of the uwekahuna was about 420 km 2 the bulk volume of the deposits was approximately 0 3 km 3 including less than 0 1 km 3 of juvenile material juvenile constituents are olivine tholeiitic basalts similar in major element composition to typical kilauea summit lava flows but variations in both major elements and trace elements suggest that the eruptions tapped more than a single uniform source region we infer that the eruptions which produced the uwekahuna were driven by water interacting with a fluctuating magma column magma withdrawal episodes may have been accompanied by large volume submarine effusive eruptions and by summit collapse the volume extent and character of the uwekahuna deposits underscore the hazards posed by relatively infrequent but potentially devastating explosive eruptions at kilauea as well as at other basaltic volcanoes

molecular and stable carbon isotopic compositions of saturated fatty acids within one sedimentary profile in the shenhu northern south china sea source implications abstract this study examined the distributions and stable carbon isotopic compositions of saturated fatty acids safas in one 300 cm long sedimentary profile which was named as site4b in shenhu northern south china sea the concentrations of total safas in sediments ranged from 1 80 to 10 16 g g g fa g dry sediment and showed an even over odd predominance in the carbon chain of c12 to c32 mostly with n c16 and n c18 being the two major components the short chain fatty acids scfas n c12 to n c18 mainly from marine microorganisms had average 13c values of 26 7 to 28 2 whereas some terrigenous sourced long chain fatty acids lcfas n c21 to n c32 had average 13c values of 29 6 to 34 1 the other lcfas n c24 n c26 n c28 average 13c values are 26 1 to 28 0 as well as n c19 and n c20 safas average 13c values are 29 1 and 29 3 respectively showed a mixed signal of carbon isotope compositions the relative bioproductivity calculation marine vs terrigenous demonstrated that most of organic carbon accumulation throughout the sedimentary profile was contributed by marine organism the high marine productivity in shenhu south china sea may be related to the hydrocarbon seepage which evidenced by diapiric structures interestingly there is a sever fluctuation of terrigenous inputs around the depth of 97 cm below the seafloor bsf probably resulting from the influence of the dansgaard oeschger events and the younger dryas event as revealed by 14c age measurements

a reappraisal of the 1835 eruption of cosiguina and its atmospheric impact in the great january 1835 eruption of cosiguina volcano nicaragua andesitic magma and lithic material were erupted over a period of at least three days proximal facies consist of clastogenic lava scoria fall and lithic ash fall produced by phreatomagmatic to vulcanian or plinian activity together with surge deposits and lithic block falls pyroclastic flow deposits covered some flanks of the volcano and entered the sea in the gulf of fonseca little record exists of the distal ash fall thus the total bulk volume erupted can only be roughly constrained to 2 9 5 6 km3 furthermore the amount of juvenile material is thought to be small a recent study of volatiles in 1835 scoria suggests sulfur release from the magma was negligible this reappraisal indicates that the cosiguina eruption probably had little global climatic impact despite its violent nature the magnitude of the eruption was modest the eruption occurred too late to initiate the northern hemisphere cooling trend form 1828 1836 dry fogs and other atmospheric optical phenomena usually observed after eruptions that contribute significantly to the stratospheric aerosol burden were not recorded after 1835

ignimbrites of basaltic andesite and andesite compositions from tanna new hebrides arc tanna island is part of a large volcanic complex mainly subsided below sea level on land two series of hydroclastic deposits and ignimbrites overlie the subaerial remains of a basal mainly effusive volcano the older tanna ignimbrite series oti late pliocene or pleistocene in age consists of ash flows and ash and scoria flow deposits associated with fallout tephra layers overlain by indurated pumice flow deposits phreatomagmatic features are a constant characteristic of these tuffs the younger late pleistocene pyroclastics the siwi sequence show basal phreatomagmatic deposits overlain by two successive flow units each comprising a densely welded layer and a nonwelded ash flow deposit whole rock analyses of 17 juvenile clasts from the two sequences vitric blocks from the phreatomagmatic deposits welded blocks scoriaceous bombs and pumices from the ignimbrites show basaltic andesite and andesite compositions sio2 53 60 in addition 296 microprobe analyses of glasses in these clasts show a wide compositional range from 51 to 69 sio2 dominant compositions at 54 56 58 5 and 61 62 sio2 characterize the glass from the oti glass compositions in the lower phreatomagmatic deposits from the siwi sequence also show multimodal distribution with peaks at sio2 55 57 5 61 62 and 64 whereas the upper ignimbrite has a predominant composition at 61 62 sio2 in both cases mineralogical data and crystal fractionation models suggest that these compositions represent the magmatic signature of a voluminous layered chamber the compositional gradient of which is the result of fractional crystallization during two major eruptive stages probably related to two caldera collapses the oti and siwi ignimbrites represent large outpourings from these magmatic reservoirs the successive eruptive dynamics from phreatomagmatic to plinian emphasize the role of water in initiating the eruptions without which the mafic and intermediate magmas probably would not have erupted

the volcano sedimentary succession of the archean sodium group ventersdorp supergroup south africa volcanology sedimentology and geochemistry abstract the volcano sedimentary succession of the sodium group in the south western corner of the kaapvaal craton rests unconformably on basement granites and is usually correlated with the middle ventersdorp supergroup this neoarchean 2700 ma large igneous province lip has been interpreted as deposited in a tectonic escape basin scenario following the collision of the zimbabwe and kaapvaal cratons or alternatively in a mantle plume induced cratonic rift basin the basaltic komatiitic to andesitic dacitic volcanic sequence and the accommodated sedimentary deposits developed in a graben to half graben setting within a cratonic failed rift system the sodium group sedimentary facies and geochemistry of volcanic rocks correlate well with the ventersdorp supergroup the major and trace element and ree geochemistry correspond with previously published results crow and condie 1988 grobler et al 1989 and the sr and nd isotopy confirms crustal contamination of the sodium group magmatic rocks a preliminary weighted mean 207 pb 206 pb zircon age of 2739 39 ma for a tuff in the upper ongers river formation is reported for the lower part of the sodium group the ongers river t kuip and omdraaivlei formations reflect sedimentation and volcanism in a rift induced graben setting with fast sedimentation from horst flanks and high burial rates in the graben valleys and subsequently a less pronounced topography post graben environment accompanying explosive phreatomagmatic and effusive mafic to acidic bimodal volcanism with abundant pyroclastics delivered ample material for graben fill deposits repeated horst reactivation has episodically exposed the basement to renewed erosion sedimentation along graben flanks comprised alluvial fans mass flow deposits braided river and related modes of deposition in distal shallow lakes volcaniclastic suspension and current sedimentation low density turbidites and stromatolitic reefs were accumulated

post glacial microbialite formation in coral reefs of the pacific atlantic and indian oceans abstract the occurrence of microbialites in post glacial coral reefs has been interpreted to reflect an ecosystem response to environmental change the greater thickness of microbialites in reefs with a volcanic hinterland compared to thinner microbial crusts in reefs with a non volcanic hinterland led to the suggestion that fertilization of the reefal environment by chemical weathering of volcanic rocks stimulated primary productivity and microbialite formation using a molecular and isotopic approach on reef microbialites from tahiti pacific ocean it was recently shown that sulfate reducing bacteria favored the formation of microbial carbonates to test if similar mechanisms induced microbialite formation in other reefs as well the tahitian microbialites are compared with similar microbialites from coral reefs off vanuatu pacific ocean belize caribbean sea atlantic ocean and the maldives indian ocean in this study the selected study sites cover a wide range of geological settings reflecting variable input and composition of detritus the new lipid biomarker data and stable sulfur isotope results confirm that sulfate reducing bacteria played an intrinsic role in the precipitation of microbial carbonate at all study sites irrespective of the geological setting abundant biomarkers indicative of sulfate reducers include a variety of terminally branched and mid chain branched fatty acids as well as mono o alkyl glycerol ethers isotope evidence for bacterial sulfate reduction is represented by low 34s values of pyrite 43 to 42 enclosed in the microbialites and compared to seawater sulfate slightly elevated 34s and 18o values of carbonate associated sulfate 21 9 to 22 2 and 11 3 to 12 4 respectively microbialite formation took place in anoxic micro environments which presumably developed through the fertilization of the reef environment and the resultant accumulation of organic matter including bacterial extracellular polymeric substances eps coral mucus and marine snow in cavities within the coral framework tof sims analysis reveals that the dark layers of laminated microbialites are enriched in carbohydrates which are common constituents of eps and coral mucus these results support the hypothesis that bacterial degradation of eps and coral mucus within microbial mats favored carbonate precipitation because reefal microbialites formed by similar processes in very different geological settings this comparative study suggests that a volcanic hinterland is not required for microbialite growth yet detrital input derived from the weathering of volcanic rocks appears to be a natural fertilizer being conductive for the growth of microbial mats which fosters the development of particularly abundant and thick microbial crusts

pressure temperature fluid evolution in eburnean metabasites and metapelites from tamanrasset hoggar algeria abstract tamanrasset central hoggar algeria is part of the 2000 ma eburnean terrane in which spectacular examples of granulite grade metapelites and metabasites occur reactional textures in metabasites supplemented by geothermobarometry fluid inclusions and mineral equilibria indicate a complex metamorphic history characterized by a strong decompression during postpeak uplift peak metamorphic pressure temperature pt conditions of 800 c and 10 kbar respectively were followed by rapidly decreasing pressure to 700 c and 6 kbar at nearly constant temperature during which time the rocks acquired their present mineral assemblages and textures garnet pyroxenites this isothermal decompression path was followed by nearly isobaric cooling throughout this history water activity remained consistently low documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usep

recent sedimentary hopanoids in the northwestern pacific alongside the japanese islands their concentrations and carbon isotopic compositions two hopanoids 17b h 21b h hop 22 29 ene diploptene and 17b h 21b h bishomohopanoic acid bbc32ha are the most abundant among the pentacyclic triterpenoids found in recent sediments of the pacific ocean alongside the japanese islands the concentration of diploptene normalized to organic carbon content is higher in sediments where c37 polyunsaturated alkene a biomarker of haptophytes is in high concentration suggesting that the diploptene may be associated with the accumulation of marine organic matter in open marine settings d 13 c values of bbc32 ha range from 23 8 to 19 4 relative to pdb being enriched in 13 c relative to diploptene 31 6 to 26 3 by 5 9 the isotopic diaerence indicates the presence of at least partially diaerent sources for the two hopanoids while diploptene is derived from cyanobacteria and chemotrophic bacteria in the water column or sediment bishomohopanoic acid may be produced mainly by heterotrophs in the sediment using marine organic matter in contrast the d 13 c values of the two hopanoids from river and bay sediments are similar 31 to 29 indicating a common source derived from soil components terrestrial plants or bacteria in soils 2000 elsevier science ltd all rights reserved

an organic geochemical assessment of oceanographic conditions at manop site c over the past 26 000 years eleven sediment samples taken downcore and representing the past 26 kyr of deposition at manop site c 0 57 2 n 138 57 3 w were analyzed for lipid biomarker composition biomarkers of both terrestrial and marine sources of organic carbon were identified in general concentration profiles for these biomarkers and for total organic carbon toc displayed three common stratigraphic features in the time series 1 a maximum within the surface sediment mixed layer 4 ka 2 a broad minimum extending throughout the interglacial deposit and 3 a deep pronounced maximum within the glacial deposit using the biomarker records a simple binary mixing model is described that assesses the proportion of terrestrial to marine toc in these sediments best estimates from this model suggest that 20 of the toc is land derived introduced by long range eolian transport and the remainder is derived from marine productivity the direct correlation between the records for terrestrial and marine toc with depth in this core fits an interpretation that primary productivity at site c has been controlled by wind driven upwelling at least over the last glacial interglacial cycle the biomarker records place the greatest wind strength and highest primary productivity within the time frame of 18 to 22 kyr b p diagenetic effects limit our ability to ascertain directly from the biomarker records the absolute magnitude that different types of primary productivity have changed at this ocean location over the past 26 kyr

reconstructing eruptions from historical accounts makaturing c 1765 philippines abstract for some volcanoes the only evidence for past eruption is provided by historical accounts when interpreted carefully these have the potential to be a rich source of information and yet they have so far been under utilised in reconstructing eruption histories the navigator thomas forrest describes a large eruption at makaturing volcano southern philippines in approximately 1765 that he considers the catalyst for the local iranun population transitioning from an agrarian society to long distance piracy and slave raiding within the historical literature the eruption is attributed to large scale physical impacts around the volcano and disruptions to trading routes and livelihoods that ultimately changed the course of southeast asia s history however no such eruption or impacts are recognised in the scientific literature or in eruption databases and fieldwork to the region remains difficult here we reinterpret the account of forrest from a multi disciplinary perspective with a historian and physical volcanologists working together to incorporate the greatly needed local context into identifying credible volcanic processes and impacts associated with the reported activity we used a novel approach to eruption reconstruction by cross referencing deposits and impacts inferred from the historical record with stochastic tephra dispersal modelling that considered multiple eruption sources and characteristics we found that forrest s account was best characterised by an eruption of vei 4 between may and october with plume heights in the range of 12 to 16 km while at least one eruption of this size was required to reproduce the impacts described in the historical record it may have formed part of a longer sequence of multiple repeated eruptions in this way such an eruption could have acted as a tipping point for a local population already on the verge of socio political and economic collapse disproportionately affecting regions on a much larger scale than the reported deposits suggest there remains a disconnect between the eruption characteristics recorded in historical accounts and those reproduced by numerical modelling for which we propose alternative interpretations of the historical record unfortunately given the minimal details available about the eruption this discordance is unlikely to be resolved even when geological studies are possible however a valuable benefit of the probabilistic modelling approach presented here is that it highlights the likely direction of tephra dispersal and deposition during a future eruption of makaturing supporting rapid tephra hazard assessment in the event of future unrest

thermal properties of granulite facies rocks in the precambrian basement of finland and estonia abstract we present results of heat production thermal conductivity and p wave velocity measurements of 252 rock samples from five granulite facies areas in finland and estonia these compositionally mainly intermediate archaean and palaeoproterozoic metamorphic rocks have relatively high heat production values mean values averaged by areas range from 0 57 to 2 24 w m 3 the lowest values are in the varpaisjarvi area which is the oldest and most mafic and where the highest metamorphic pressure occurred 8 11 kbar whereas the highest heat production is found in the turku granulite belt where the metamorphic pressure was 4 6 kbar the heat production decreases with the increase of the metamorphic pressure however a general numerical relationship cannot be presented because of considerable variations in heat production data there is no significant difference in the metamorphic temperatures of the studied granulites and therefore no dependence on temperature is found further our data suggest no relationship between heat production and p wave velocity the mean thermal conductivity of granulites varies from 3 0 to 3 5 w m 1 k 1 slightly elevated thermal conductivity values in the varpaisjarvi and lapland granulite areas can be attributed to higher sillimanite and quartz contents respectively

factors controlling the types of microbial consortia in cold seep environments a molecular and isotopic investigation of authigenic carbonates from the south china sea authigenic carbonates were recovered from several locations of the south china sea continental slope at a 470 m to 770 m water depth the sources of seeping fluids the time involved in carbonate formation and the potential driving forces are increasingly understood but little is known about the biogeochemical processes that occur during this type of carbonate precipitation here a molecular and isotopic investigation of authigenic carbonates was conducted to determine the factors controlling the types of microbial consortia in cold seep environments the studied carbonates were one aragonitic crust and three high mg calcitic tubular concretions from specific sites a significant input of biogenic methane to the carbon pool during the precipitation of the carbonates was suggested by the presence of c 13 depleted molecular fossils of methanotrophic archaea with delta c 13 values as negative at 141 5 and sulfate reducing bacteria with delta c 13 values as negative at 128 5 the methane was primarily oxidized in an anaerobic process the predominant consortia were anme 2 assemblages in the aragonitic carbonate sample tvg3 c2 whereas high mg calcitic carbonates samples tvg14 c2 and tvg8 c5 were dominated by anme 1 assemblages according to the specific biomarkers observed taking the favored environments for specific aom consortia and crystallization conditions for aragonite and calcite together the factors selecting for specific aom communities appear to be constrained by their biogeochemical settings accordingly higher alkalinity abundant sulfate concentration and being closer to the water sediment interface conditions favor the precipitation of aragonite over high mg calcite c 2013 elsevier b v all rights reserved

stability and instability of quiescently active volcanoes the case of masaya nicaragua quiescently active volcanoes are enigmatic due to their restlessness but lack of eruptive activity i present a model of coupled conduit convection and foam accumulation to explain degassing behavior of masaya an active volcano in nicaragua that is currently emitting large amounts of gas but not erupting gas rich magma is transported through a conduit 2 6 m in radius and then released into a shallow reservoir the magma is degassed in the reservoir and forms a foam 1 3 m thick at the top with bubbles 20 60 m in diameter the foam layer is stable because the input of gas into the foam is balanced by gas release through a vent to the surface if the foam layer is destabilized the volcano can erupt explosively the most likely cause of foam destabilization is a large injection of volatile rich magma from deeper levels into the shallow conduit reservoir system thereby increasing magma fluxes and gas fluxes exsolving large gas bubbles and reducing surface tension of the magma

basaltic thermals and subplinian plumes constraints from acoustic measurements at shishaldin volcano alaska the 1999 basaltic eruption of shishaldin vol cano alaska usa included both strombolian and sub plinian activity as well as a pre subplinian phase inter preted as the local coalescence within a long foam in the conduit although few visual observations were made of the eruption a great deal of information regarding gas ve locity gas flux at the vent and plume height may be inferred by using acoustic recordings of the eruption by relating acoustic power to gas velocity a time series of gas velocity is calculated for the subplinian and pre subplinian phases these time series show trends in gas velocity that are inter preted as plumes or for those signals lasting only a short time thermals the subplinian phase is shown to be com posed of a thermal followed by five plumes with a total expelled gas volume of 1 5 10 7 m 3 the initiation of the subplinian activity is probably related to the arrival of a large overpressurised bubble close to the top of the magma column a gradual increase in low frequency 0 01 0 5 hz signal prior to this trigger bubble may be due to the rise of the bubble in the conduit this delay corresponds to a reservoir located at 3 9 km below the surface in good agreement with studies on other volcanoes the presence of two thermal phases is also identified in the middle of the pre subplinian phase with a total gas release of 4 3 10 6 m 3 and 3 6 10 6 m 3 gas veloc ity at the vent is found to be 82 m s 1 and 90 m s 1 for the subplinian plumes and the pre subplinian thermals respectively the agreement is very good between estimates of the gas flux from modelling the plume height and those obtained from acoustic measurements leading to a new method by which eruption physical parameters may be quantified fur thermore direct measurements of gas velocity can be used for better estimates of the so2 flux released during the eruption

quaternary volcanic stratigraphy of managua nicaragua correlation and source assignment for multiple overlapping plinian deposits a tephrochronological study that began as an active fault mapping program in managua nicaragua following the 1972 earthquake has yielded information with broader geologic relevance seven principal widespread quaternary air fall deposits the managua sequence have been defined the deposits are basaltic or rhyodacitic span probably 11 km 3 dense rock equivalent and are classified as plinian or phreatoplinian regardless of chemical composition two of the units were radiocarbon dated at 6 600 yr b p and 21 000 yr b p as a result of this study ages of the other layers are not as well constrained but are estimated on the basis of soil development and position in the section correlation and source assignment were particularly difficult because of incomplete exposure and similarity of physical and chemical features but they were accomplished with a combination of detailed measurement and sampling at managua reconnaissance mapping and sampling at potential vent areas and application of petrographic mineralogic and chemical correlation methods the close similarity among the rhyodacite pumices posed the greatest difficulty for correlation cluster analysis applied to multielement xrf chemical analyses of pure glass separates gave the best results the clarification of the managua sequence has revealed the local geologic history of managua has characterized the average largest recent nicaraguan eruptions and has defined time stratigraphic markers used for archaeologic and engineering purposes additionally it has provided a regional framework within which to interpret and correlate more detailed studies of individual nicaraguan volcanoes

volcanology and eruptive styles of barren island an active mafic stratovolcano in the andaman sea ne indian ocean barren island india is a relatively little studied little known active volcano in the andaman sea and the northernmost active volcano of the great indonesian arc the volcano is built of prehistoric possibly late pleistocene lava flows dominantly basalt and basaltic andesite with minor andesite intercalated with volcaniclastic deposits tuff breccias and ash beds deposited by pyroclastic falls and surges which are exposed along a roughly circular caldera wall there are indications of a complete phreatomagmatic tephra ring around the exposed base of the volcano a polygenetic cinder cone has existed at the centre of the caldera and produced basalt basaltic andesite aa and blocky aa lava flows as well as tephra during historic eruptions 1787 1832 and three recent eruptions 1991 1994 95 2005 06 the recent aa flows include a toothpaste aa flow with tilted and overturned crustal slabs carried atop an aa core as well as locally developed tumuli like elliptical uplifts having corrugated crusts based on various evidence we infer that it belongs to either the 1991 or the 1994 95 eruptions the volcano has recently 2008 begun yet another eruption so far only of tephra we make significantly different interpretations of several features of the volcano than previous workers this study of the volcanology and eruptive styles of the barren island volcano lays the ground for detailed geochemical isotopic and petrogenetic work and provides clues to what the volcano can be expected to do in the future

kuwae 1425 a d the forgotten caldera in vanuatu tongoa and epi islands once formed part of a larger landmass kuwae which was partly destroyed during a cataclysmic seismo volcanic event that is recorded in local folklore it led to the formation of a 12 kmlong and 6 km wide oval shaped submarine caldera with two distinct basins and a total area of 60 km2 at the level of the rim the age ofthis eniption 1420 1430 a d and the structure of the related collapse are discussed and a composite log 143 m of the pyroclastics surrounding the caldera is presented they comprise thick hydromagmatic deposits belonging to a terminal hydromagmatic phase of the pre caldera edifice which grade upwards into two major sequences of pyroclastic flow deposits clearly related to the caldera event collapse near the caldera edge was at least in the range 650 to 950 m and may have been as much as 800 to 1100 m the volume of rocks engulfed during the caldera formation is 32 39 km3 suggesting the same volume of magma was erupted even if two coalescent collapse structures were formed it is worth noting that the kuwae caldera is not a reactivated structure but the result of a single event of short duration which occurred in the first half of the fifteenth century this event is one of the seven biggest caldera forming events during the last 10 000 years and is comparable with the santorini minoan eruption and the crater lake eruption

compositional similarities of non solvent extractable fatty acids from recent marine sediments deposited in differing environments abstract five recent sediment samples from a variety of north american continental shelves were analyzed for fatty acids fas in the solvent extractable solex lipids as well as four types of non solvent extractable nonex lipids the nonex lipids were operationally defined by the succession of extraction procedure required to recover them the complete procedure included i very mild acid treatment ii hf digestion and iii saponification of the sediment residue following exhaustive solvent extraction the distribution pattern and various compositional parameters of solex fas in the five sediments were divided into three different groups indicating the difference of biological sources and also diagenetic factors and processes among the three groups of samples nevertheless the compositions of the corresponding nonex fas after acid treatment were surprisingly very similar this was also true for the remaining nonex fa groups in the five sediment samples the findings implied that most of the nonex fas reported here are derived directly from living organisms it is also concluded that a large part of nonex fas are much more resistant to biodegradation than we have thought so that they can form the large percentage of total lipids with increasing depth of water and sediments

stable carbon isotopic variation of long chain n alkanoic acids in the equatorial pacific sediments over the last 40 ma implications for expansion of c4 grassland in south america abstract the stable carbon isotope ratio 13 c values of sedimentary long chain c 20 n alkanoic acids from the equatorial pacific iodp sites u1331 1338 were measured for historical reconstruction of c 4 plant contribution from south america over the last 40 ma the values for c 30 and c 32 acids ranged between 36 9 and 25 4 suggesting that they likely originated from higher plant wax associated with c 3 dominated vegetation the molecular distribution of alkanoic acids in the sediments showed a marked change across the intertropical convergence zone itcz indicating a potential contribution from the northern hemisphere to the sediments located at 10 n in contrast the abundances of n alkanoic acids significantly decreased in the sediments at 13 c values suggest that the differences in the core locations possibly caused north and southward shifts of ca 1 0 n and ca 0 5 s from the equator respectively the corrected 13 c values of c 30 and c 32 acids did not cross the c 3 end member threshold until 1 7 ma despite the onset of c 4 plants in central south america at ca 7 ma this implies that vegetation in the low latitudes of south america was less affected by hydrological changes induced by the uplift of the andes during the late miocene

isotopic data upb rbsr pbpb and smnd on mafic granulites from finnish lapland abstract a combined approach using several methods pb pb u pb rb sr sm nd on granulitic rocks selected from classic areas in northern finland is presented the results show that the emplacement of igneous rocks and the granulitic metamorphism occurred nearly coevally 1 9 2 0 ga this result which is supported by field observations means that these rocks are not ideal for comparing the response of the various parent daughter pairs to the high grade metamorphism or for checking the special geochronological possibilities of each method nevertheless because of the coherence of results from rocks of different origins a discussion is possible the bulk of the mafic granulite was certainly derived from upper mantle sources or short lived crustal mafic materials granulites of the granulitic belt and anorthosites are thought to have originated from two distinct mantle sources reflecting mantle heterogeneities at that time

the precambrian of finnish lapland evolution and regime of metamorphism the precambrian crust of northern finland has been the subject of detailed geochemical and petrological studies the geochemical data and the present day geotectonic setting suggest the existence of an old island arc system with the west inari schist zone tana river belt as an outer tholeiitic arc the granulite complex as a calcalkaline inner arc and a stable continental block granite gneiss complex kola nucleus in the northeast

description of the polar profile transect display abstract the polar profile transect display attempts to integrate all the existing aeromagnetic gravimetric geological and geochemical investigations with the results of the deep seismic and electromagnetic studies carried out along the polar profile our description is based on the stage of joint interpretation reached at the second earth science study centre the nearly 440 km long ne sw trending polar profile traverses archaean and early proterozoic parts of the baltic shield the thickness of the crust varies between 40 and 50 km and consists of three distinct crustal layers a geological interpretation based on the various geophysical results is given for the uppermost 10 14 km thick layer in the central part of the profile the overthrust early proterozoic lapland granulite belt forms a wedge shaped body reaching the middle crust the upper crust is underlain by a transparent layer 16 18 km thick with a smooth increase in velocity and density a reflective lowermost 10 21 km thick layer has a high velocity gradient the crust mantle has a pronounced topography

compositions and phase relations of calcic amphiboles in epidote and clinopyroxene bearing rocks of the amphibolite and lower granulite facies central massachusetts usa calcic amphiboles coexisting with epidotegroup minerals zoisite clinozoisite epidote and or clinopyroxene plagioclase quartz garnet occur in amphibolites and calc silicate rocks that underwent amphibolite to lower granulite facies metamorphism in the acadian metamorphic high of central massachusetts usa across the region peak metamorphic conditions range from about 580 c and 6 2 kbar to 730 c and 6 3 kbar the coexistence of most ca amphiboles with fe3 rich epidote group minerals suggests the presence of fe3 in most of these amphiboles an empirical fe3 estimation for the microprobe analyses is based on two constraints the na ca content of the m4 sites of ca saturated gravimetrically analyzed hornblendes gives the relation ca m4 c 1 479 na m4 c 2 c corrected the second constraint is the stoichiometric equation ca m4 na m4 fm 15 where fm is the sum of all cations exclusive of ca na and k solving the two equations simultaneously gives 20 185 0 479 ca m4 1 479 fm starting with the uncorrected values of ca m4 u and fm m4 u u uncorrected of the all ferrous formula the normalization factor nf for calculating the corrected cations of the ferric formulas is 20 185 0 478 ca m4 u 1 479 fm u from the deficient oxygen the fe3 content which is equal to 2 23 ox can be calculated determinations of fe3 contents of four hornblende separates by mossbauer spectroscopy are in agreement with the calculated values the ca amphiboles show systematic changes in composition with increasing grade of metamorphism within the amphibolite and lower granulite facies zones increasing edenite and tschermakite substitution increasing ti content and increasing fe2 fe2 mg ratio in addition the coexisting clinopyroxenes are also characterized by an increase in fe2 fe2 mg ratio in quartz free rocks with coexisting ca amphibole and plagioclase there is an increase in the ratio x ab x ed where x ab na na ca in plagioclase and x ed na in the amphibole a site these chemical changes in mineral composition together with the disappearance of epidote at the transition to granulite facies metamorphic conditions are attributed to the continuous reaction albite epidote fe mg hornblende fe mg clinopyroxene anorthite naalsi 1 hbl h2o

pyroclastic flow deposits on venus as indicators of renewed magmatic activity radar bright deposits on venus that have diffuse margins suggest eruptions that distribute debris over large areas due to ground hugging flows from plume collapse we examine deposits in eastern eistla western eistla phoebe and dione regiones using magellan data and earth based radar maps the radar bright units have no marginal lobes or other features consistent with viscous flow their morphology radar echo strength polarization properties and microwave emissivity are consistent with mantling deposits comprised of few cm or larger clasts this debris traveled downhill up to 100 km on modest slopes and blanketed lava flows and tectonic features to depths of tens of cm to a few meters over areas up to 40x103 km2 there is evidence for ongoing removal and exhumation of previously buried terrain a newly identified occurrence is associated with a ridge belt south of ushas mons we also note radar bright streaks of coarse material west of rona chasma that reflect the last traces of a deposit mobilized by winds from the formation of mirabeau crater if the radar bright units originate by collapse of eruption columns with coarse fragmental material entrained and fluidized by hot gases then their extent suggests large erupted volatile co2 or h2o amounts we propose that these deposits reflect the early stage of renewed magmatic activity with volatile rich disrupted magma escaping through vents in fractured regions of the upper crust rapidly eroding under venus surface conditions or buried by subsequent eruptions these markers of recently renewed activity have disappeared from older regions

major and transition trace element abundances in the khondalite suite of the granulite belt of lapland fennoscandia evidence for an early proterozoic flysch belt abstract the granulite belt of lapland comprises two main units the more extensive unit the khondalite suite is formed of approximately equal proportions of sillimanite garnet gneisses and garnet gneisses which include impersistent layers of quartz rich gneisses calc silicate rocks and metavolcanics the less extensive unit the charnockite complex corresponds to several tholeiitic and calc alkaline series each of them ranging from gabbro to tonalite an attempt has been made to elucidate the primary features of the khondalite suite and its depositional environment major and transition trace element variations suggest that it has an overall sedimentary parentage and that it corresponded to a graywackeshale sequence turbidites original clastic sediments were mainly derived from an eroded continental crust and in lesser amount from contemporary volcanism the geochemical trends for alkalies seem to indicate that this crust was relatively silicic and that it had undergone previous granite forming events taking into consideration the geological setting the geometry and the facies of these sedimentary formations we propose to reinterpret the granulite belt of lapland as a flysch belt located at a plate junction and pre dating a continent continent collision with subducted oceanic crust

reflection seismic measurements across the granulite belt of the polar profile in the northern baltic shield northern finland abstract reflection seismic measurements were carried out in 1985 on the central part of the polar refraction seismic profile in northern finland the survey was planned and executed jointly by the universities of helsinki uppsala and hamburg using digital equipment with a total of 144 channels by repeating the shots and moving the geophone spreads every day we were able to observe a 42 50 km recording spread referred to reflection elements a line of 84 km total length through the source receiver midpoints was recorded we processed the results up to normal moveout corrected time sections a number of reflectors dipping 8 15 to the northeast were recorded in the lapland granulite belt range these represent a system of sheared granulites which were observed on the surface in the southern part of the profile from gravity modelling the bottom of the dipping layers coincides with the lower boundary of the granulites between the depths of 22 and 35 km the crust in this area seems to be transparent to seismic signals this leads to the assumption that the middle part of the crust is characterized by gentle velocity and density gradients the crust mantle boundary seems to be a layered moho with good reflectors lying at depths between 40 and 44 km

petrology of tholeiitic lavas from tanna island new hebrides importance of cumulative processes in island arc magmatism tanna one of the southernmost islands of the new hebrides volcanic arc is made of late pliocene to recent island arc tholeiitic basalts and andesites with sio2 contents ranging from 45 to 57 these lavas are highly porphyritic 30 50 in volume phenocrysts of plagioclase are the most abundant together with olivine and clinopyroxene the groundmass contain plagioclase augite olivine magnetite and glass pigeonite tridymite sanidine and rarely biotite may also occur the olivines and clinopyroxenes show an iron enrichment from the cores of phenocrysts to their rims and the groundmass crystals but their compositional variations are not correlated with the mg fe ratio of bulk host rocks the most fe rich compositions being found in mg rich lavas plagioclase compositions range from an95 to an60 in the basalts and an60 to an50 in the andesites but within each group they are not correlated with sio2 or na2o contents of host lavas consequently the bulk major element compositions of tanna volcanic rocks cannot be considered as primarily controlled by crystal separation from successive liquids the oxyde sio2 variations diagrams and the modal compositions and mineral chemistry show that crystal accumulation is the predominant mechanism accounting for bulk rock compositions however this does not exclude fractional crystallization the variation of the calculated groundmass mineralogy strongly suggest the occurrence of crystal removal mainly clinopyroxene and magnetite

towards a more practical two feldspar geothermometer the thermodynamic basis of several recent attempts to formulate a simple two feldspar geothermometer is discussed together with a review of earlier empirical geothermometers and ones based on experimental studies in the ternary feldspar system it is shown that double binary thermometers which involve the combination of regular solution mixing models for the binary alkali feldspar system with ideal mixing in plagioclases do not give a satisfactory representation of two feldspar relations especially for albite rich compositions where a critical point exists thermometers based on mixing parameters for ordered alkali feldspar frameworks are even more unjustified both because low plagioclases are certainly non ideal and because of uncertainty in knowing the degree of al si order in the alkali feldspar when exchange equilibrium was achieved a thermodynamic thermometer requires knowledge of ternary activities which are at present unknown experimental determinations of relationships in the ternary feldspar system are reviewed and the correct general form of the thermometer constructed using mainly the experimental data of seck 1971a and smith and parsons 1974 chemographic tests for equilibrium between feldspar pairs are suggested and petrographie features discussed in an appendix new values are given of margules parameters calculated for binary disordered alkali feldspars from recent solvus data up to 15 kbars and their physico chemical basis examined we suggest that accurate representations of the mixing properties of disordered alkali feldspars using margules parameters are at present premature

biogeochemical formation of calyx shaped carbonate crystal fans in the subsurface of the early triassic seafloor abstract the kuh e dena sedimentary section in iran developed on the southwestern margin of the neotethys ocean the fossil and bioturbation lean early triassic section late dienerian to early smithian is typified by finely laminated calcareous shales that are interbedded with laterally extending carbonate beds which are mostly composed of calyx shaped carbonate crystal fans the calyxes consist of fibrous crystals that apparently formed within the subseafloor in soft water saturated sediment by displacive growth rare earth element and yttrium patterns indicate that calyx shaped crystals precipitated from anoxic pore waters biomarker patterns of the carbonate beds reveal major input of lipids from prokaryotes that typically occur within layered benthic microbial mats i e cyanobacteria anoxygenic phototrophic bacteria sulphate reducing bacteria and methanogenic archaea along their length the fibrous crystals of the calyxes reveal a trend of increasing 13 c carb values from 2 7 to 3 3 suggesting that archaeal methanogenesis affected the carbonate pool apart from the putative benthic prokaryotes molecular fossils of halophilic most likely planktic archaea were detected in the carbonate beds low pristane to phytane ratios 0 8 and the presence of halophilic archaea are in accord with the lack of bioclasts and bioturbation which likely reflects increased salinities the former presence of a benthic microbial mat with cyanobacteria underlain by anoxygenic phototrophic bacteria sulphate reducing bacteria and methanogenic archaea is in accordance with studies on living microbial mats in hypersaline low oxygen marine environments the early triassic subseafloor seems to have been a sink for carbon driven by biologically induced formation of secondary diagenetic carbonate

a giant underwater encrusted stalactite from the blue hole lighthouse reef belize revisited a complex history of biologically induced carbonate accretion under changing meteoric and marine conditions a late pleistocene to holocene submerged and encrusted speleothem exhibits a complex history including a meteoric phase and two marine phases a combined study using petrography mineralogy and inorganic and organic geochemistry as well as geochronology has shown that phototrophic and heterotrophic biological activity impacted carbonate precipitation during all phases of carbonate accretion the stalactite formed ca 30 m below modern sea level at a marginal overhang in the blue hole of lighthouse reef atoll unlike purely meteoric speleothems the belize example consists of a meteoric core a marine aragonite crust and a serpulid micrite rich outer crust as a result of postglacial flooding of the karst cave the core of the stalactite has a tufaceous texture containing algal or microbial remains and consists entirely of low magnesium calcite formed 19 55 10 68 kyr bp the texture suggests that the stalactite formed at the cave entrance and hence the former cave ceiling had apparently collapsed earlier during the pleistocene oxygen 18o and carbon 13c isotopes across the core suggest a trend towards drier conditions and reduced soil and plant cover after the last glacial maximum the marine aragonite crust consists of stacked botryoids in which individual crystals up to 700 lm have dark terminations enriched in high magnesium calcite this crust accreted from 10 82 to 9 95 kyr bp in warm shallow water during the early holocene thermal optimum carbonate accretion rates were considerable and averaged 125 m yr the crust has a dense laminated texture on one side and a porous shrubby texture on the other the presence of n c16 1 5 n c17 1 6 and 10me c16 fatty acids in the laminated crust suggests that sulfate reducing bacteria contributed to aragonite formation in an environment that was less open than the formation environment of the porous crust where these biomarkers are lacking n c16 1 5 n c17 1 6 or are less abundant 10me c16 enrichment of 34s and 18o in carbonate associated sulfate cas relative to seawater sulfate also suggests sulfate reduction during carbonate formation the greater contribution of heterotrophic processes to aragonite precipitation in the laminated crust is also reflected in 13c values as low as 1 3 whereas no such depletion is observed in the aragonite of the porous crust 13c values as low as 0 0 a pronounced isotopic variability and excursions to positive 13c values as high as 3 5 0 in the inner half of the laminated crust indicate an episodic local impact of photosynthesis on aragonite precipitation whereas the lack of such excursions in the porous crust 13c values as high as 1 5 0 is again best explained by a more open environment of formation after a ca 5 kyr hiatus from 4 39 kyr bp a biogenic crust of abundant serpulids and finely crystalline microbial and detrital carbonate consisting of high magnesium calcite and aragonite accreted on the outer surface of the stalactite outermost crust accretion was probably influenced by the inundation of the lighthouse reef lagoon that started to shed abundant fine grained carbonate sediment into the blue hole the stalactite broke off the cave ceiling either before or after the formation of the outermost crust likely due to seismic movements along the nearby plate boundary the study demonstrates that like speleothems from the terrestrial realm submerged stalactites may have had complex histories with great potential as paleoenvironmental archives

first insights into mid holocene environmental change in central vanuatu inferred from a terrestrial record from emaotfer swamp efate island abstract here we present the first terrestrial record of mid holocene environmental changes in vanuatu this preliminary multi proxy analysis of core tfer 06 from emaotfer swamp efate island indicates changes in environmental conditions are mainly related to variations in climate over the last 6500 cal yr bp drier periods are broadly correlated with an increase in sustained el nino events recorded in the pacific on a decadal timescale the earliest change is the disappearance of mangroves adjacent to the site around 3200 cal yr bp this could well be due to both local tectonic uplift with subsequent hydrostatic adjustment and the onset of a drier period from c 3250 2500 cal yr bp the prevailing drier conditions can be linked to more persistent el nino conditions local volcanic events had limited ecological impact on the area freshwater diatoms indicate a hydroseral succession species living on submerged plants being common in muds from c 3250 1500 cal yr bp but rare in fibrous peat deposited later palaeoecological indicators of human impact have not been identified throughout this work

geochemistry vs seismo tectonics along the volcanic new hebrides central chain southwest pacific abstract compositional variations major and trace element of pleistocene to present rocks along the volcanic new hebrides central chain southwest pacific are presented and discussed using a new set of analyses we focus in particular on the anomalous mg k lile and lree rich and al and si poor character of the basalts from aoba and santa maria volcanoes and to a lesser extent from ambrym volcano all located in the area where the d entrecasteaux zone collides with the arc in addition we note a compositional transition from normal arc basalts to boninite related high mg andesites at the southern termination of the nhcc the peculiar composition of the rocks of the volcanoes facing the d entrecasteaux zone has traditionally been related more or less directly to the collision subduction occurring in this area we present an alternative hypothesis of a strong geochemical anomaly under santa maria and aoba volcanoes unrelated to this collision in this model a westward and upward invasion of dupal type enriched mantle corroborated by the pattern of intermediate seismicity occurs under this part of the arc in strong contrast to the usual pacific type morb mantle source present under all other volcanoes of the nhcc such a dupal type source may explain the anomalous geochemistry of the resulting volcanic products

shallow magma mingling driven strombolian eruptions at mt yasur volcano vanuatu 1 mt yasur volcano vanuatu has been increasingly recognized for its high frequency strombolian eruptions strombolian activity is often regarded as a product of the rapid ascent of gas slugs originating from a deep magma which mingle with a batch of shallow magma upon eruption heterogeneous crystal distribution as well as bimodal bubble size distributions in the eruptive products generally supports this view here the strombolian activity at mt yasur is analyzed a rheological investigation indicates that the basaltic andesitic eruptive products contain an apparently homogeneous glass phase and yet exhibit evidence of a distinct range of glass transition temperatures with multiple peaks occurring in individual samples such anomalous behavior is proposed to result from the mingling of magmas with contrasting oxidation states the unstable nature of the measured glass transition behavior leads us to the inference that mingling is located in the shallow parts of the eruptive conduits partly driven by rejuvenation of material slumped from the crater walls into an open conduit system the dynamics of this process may expose the periodicity of the eruptions themselves

k rb sr ba u and th geochemistry of the lapland granulites fennoscandia lile fractionation controlling factors the lile geochemical patterns of the three main lithological units graywacke shale metasedimentary sequence tholeiitic metaigneous rocks and migmatitic rocks of the lapland granulite belt are described k ba sr and th concentrations in metasediments are nearly similar to average continental crust whereas rb and u are unevenly impoverished in particular graphitic metashales and calcsilicate rocks are not significantly depleted in uranium tholeiitic metaigneous rocks comprises metavolcanics which present k rb ratios similar to metasediments and metaplutonics with lile abundances close to those of the low k tholeiites migmatites show wide range in lile content metatexites and diatexites have higher k rb th and u concentrations and similar k rb ratios with respect to equivalent unmobilized rocks potassic pegmatoids are strongly enriched k rb ba and th but moderately in sr and u plagioclasic pegmatoids and ferromagnesian restites are rich in sr and poor in other lil elements

collecting field data in volcanic landscapes using small uas suas drones abstract the last several years have seen a very rapid increase in the development and availability of unmanned aerial vehicles systems uav or uas more commonly called drones uas are remotely operated aerial vehicles that can be fixed wing planes helicopters or aerial systems with multiple propellers small versions of uas here called suas in particular have become so prevalent that they can be easily purchased at general retail stores this paper seeks to review and summarize the use of suas in volcanic research given their size low cost and relative durability suas provide a light weight tool platform that is easy to transport to field locations quick to set up and easy to launch and control they require very little launch and recovery space because of these characteristics suas are useful in collecting immediate and real time aerial data especially in remote inaccessible dynamic and or hazardous volcanic environments in volcanic areas suas have been used for mapping sample collection thermal imaging magnetic surveys slope stability studies and as platforms for sensors to measure outgassing of co 2 and so 2 they are also becoming invaluable for real time hazard assessment during and after an eruption they are however limited by their flight time which is greatly affected by wind speeds since they are predominately made of plastic they are also impacted by the high thermal temperatures found in active volcanic areas which can degrade their structure and performance with continued technological improvement however suas have the potential to dramatically improve our ability to collect field data because of additional natural technological and legal challenges related to their use it is critical that users be aware of and adhere to all national and local laws associated with suas

hypersaline conditions during deposition of the calcare di base revealed from archaeal di and tetraether inventories abstract the calcare di base is a widespread messinian carbonate formation in the mediterranean especially in sicily and calabria italy the environmental conditions under which these limestones were deposited their formation mechanism and the timing of deposition are a matter of debate in order to shed new light on their formation the lipid biomarker inventories of calcare di base from four locations in sicily and calabria were studied following petrographical and mineralogical characterization of the limestone samples the mineralogy is chiefly calcite the microfabric is mostly peloidal and partly laminated or brecciated deposition took place at high salinity as confirmed by numerous pseudomorphs after halite long chain n fatty acids were the most abundant lipid biomarkers in samples from all sites but isoprenoid alcohols were also abundant the most prominent archaeal compounds were diphytanyl glycerol diethers dgds and glycerol dibiphytanyl glycerol tetraethers gdgts among these archaeol and gdgt 0 caldarchaeol predominated respectively other gdgts were virtually absent minor amounts of c 20 25 dgd extended archaeol a biomarker for halophilic archaea were detected in all samples the 13 c values of caldarchaeol avg 20 and archaeol avg 11 varied widely indicating that these compounds derived from distinct archaeal precursor lipids based on lipid biomarker patterns the calcare di base had been previously considered to represent a normal marine deposit in contrast to the evaporitic gypsum and halite deposits in messinian successions the archaeal biomarker inventories from the calcare di base samples reported here in conjunction with the occurrence of pseudomorphs after halite reveal that deposition took place in a hypersaline environment

likelihood of basaltic eruptions as a function of volatile content and volcanic edifice size a simple physical model is used to link eruption likelihood in continental regions to the size and shape of the volcanic edifice as well as to magma density and volatile content a volcanic edifice acts as a surface load and modifies the stress field in upper crustal levels including the magma chamber it affects the critical magma overpressure for reservoir failure as well as the conditions of dyke ascent from reservoir to surface calculations are made for dyke ascent in the stress field due to an overpressured reservoir beneath an edifice different edifice shapes are investigated from shield volcanoes with gentle slopes to stratovolcanoes with steeper flanks beneath a mature volcanic edifice magmatic overpressures required for reservoir failure are large but not large enough for a dyke to reach the central vent area at the summit thus basaltic summit eruptions can only occur if the amount of dissolved volatiles exceeds some threshold value which increases with edifice size and hence must be in explosive regimes unless magma is able to degas at shallow depths for mature volcanic systems edifice collapse or destruction may lead to renewed basaltic activity through the central vent area

factors controlling 13c contents of sedimentary organic compounds principles and evidence the carbon isotopic composition of any naturally synthesized organic compound depends on 1 the carbon source utilized 2 isotope effects associated with assimilation of carbon by the producing organism 3 isotope effects associated with metabolism and biosynthesis and 4 cellular carbon budgets these factors are reviewed and quantitative considerations summarized particularly with regard to active and passive modes of carbon assimilation by phytoplankton and the existence of discernible regularities in isotope effects associated with lipid biosynthesis it is concluded that n alkyl lipids are in general depleted in 13c by about 1 5 relative to polyisoprenoid lipids produced by the same organism the effects of biological reworking on isotopic compositions of organic carbon are examined and it is suggested that enrichment of 13c in sedimentary organic carbon may result from loss of ch4 from zooplanktonic gut communities isotopic methods for estimation of ancient co2 levels are considered and a hyperbolic form favored for the relationship between concentrations of dissolved co2 and isotopic fractionation

a global synthesis of lava lake dynamics abstract active lava lakes represent a variety of open vent volcanism in which a sizable body of lava accumulates at the top of the magma column constrained by the vent and or crater geometry the longevity of lava lakes reflects a balancing of cooling and outgassing occurring at the surface and input of hot and gas rich magma from below due to their longevity and relative accessibility lava lakes provide a natural laboratory for studying fundamental volcanic processes such as degassing convection and cooling this article examines all seven lakes that existed at the time of writing in 2018 located in the pacific antarctica africa and south and central america these lakes span all tectonic environments and a range of magma compositions we focus on analysis of the lake surface motion using image velocimetry which reveals both similarities and contrasts in outgassing and lake dynamics when comparing the different lakes we identify two categories of lake behavior organized erta ale nyiragongo k lauea after 2011 and erebus and chaotic villarrica masaya marum this division does not map directly to lake size viscosity gas emission rate or temperature instead when examined together we find that the lakes follow a linear relationship between average surface speed and the ratio of total gas flux to lake surface area this relationship points to the combined importance of both flux and lake size in addition to the total volume of gas emission and suggests that a shared deep mechanism controls the supply of heat and gas to all lakes on the other hand the differences between chaotic and organized lakes highlight the important role of the geometry of the conduit lake transition which superimposes a shallow signal on that of the deep circulation the spatial patterns of surface motion we document suggest that the release of gas bubbles at chaotic lakes is more efficient i e bubbles are less likely to be retained and recycled compared with organized lakes in addition the data presented here indicate that the solidified crust of organized lakes plays a role in regulating convection and outgassing in lava lakes

sources of long chain fatty acids in deep sea sediments from the bering sea and the north pacific ocean abstract the distributions and compound specific carbon isotope ratios of long chain n fatty acids and long chain n alkanes in two sedimentary cores collected from the north pacific ocean and the bering sea have been examined long chain fatty acids were further fractionated into three sub fractions esterified free and polar to investigate their sources the 13 c values of these fractions clarified the sources of different fatty acids the esterified fraction had lighter 13 c values 30 1 0 70 similar to those of the long chain n alkanes 30 2 1 08 consistent with a mainly terrestrial plant origin in contrast the long chain fatty acids except c 28 from the polar and free fractions had heavier isotopic values 27 5 1 06 suggesting a mixed origin from terrestrial and marine organisms the esterified fatty acids from the north pacific ocean and the bering sea can be used as terrestrial biomarkers

caldera development during the minoan eruption thira cyclades greece the well known caldera of thira santorini greece was not formed during a single eruption but is composed of two overlapping calderas superimposed upon a complex volcanic field that developed along a ne trending line of vents before the minoan eruption of 1400 b c thira consisted of three lava shields in the northern half of the island and a flooded depression surrounded by tuff deposits in the southern half andesitic lavas formed the overlapping shields of the north and were contemporaneous with and in many places interbedded with the southern tuff deposits although there appears to be little difference between the composition of magmas erupted differences in eruption style indicate that most of the activity in the northern half of the volcanic field was subaerial producing lava flows whereas in the south eruptions within a flooded depression produced a sequence of mostly phreatomagmatic tuffs many of these tuffs are plastered onto the walls of what appears to have been an older caldera most probably associated with an eruption of rhyodiacitic tephra 100 000 years ago the minoan eruption of about 1400 b c had four distinct phases each reflecting a different vent geometry and eruption mechanism the minoan activity was preceded by minormore eruptions of fine ash 1 the eruption began with a plinian phase from subaerial vent s located on the easternmost of the lave shields 2 vent s grew toward the sw into the flooded depression subsequent activity deposited large scale base surge deposits during vent widening by phreatomagnetic activity 3 the third eruptive phase was also phreatomagmatic and produced 60 of the volume of the minoan tuff this activity was nearly continuous and formed a large featureless tuff ring with poorly defined bedding less

la pacana caldera and the atana ignimbrite a major ash flow and resurgent caldera complex in the andes of northern chile the recently discovered la pacana caldera 60 35 km is the largest caldera yet described in south america this resurgent caldera of pliocene age developed in a continental platemargin environment in a major province of ignimbrite volcanism in the central andes of northern chile at about 23 s latitude collapse of la pacana caldera was initiated by the eruption of about 900 km3 of the rhyodacitic atana ignimbrite the atana ignimbrite was erupted from a composite ring fracture system and formed at least four major ash flow tuff units that are separated locally by thin air fall and surge deposits all four sheets were emplaced in rapid succession about 4 1 0 4 ma ago caldera collapse was followed closely by resurgent doming of the caldera floor accompanied by early postcaldera eruptions of dacitic to rhyolitic lava domes along the ring fractures the resurgent dome is an elongated asymmetrical uplift 48 5 12 km which is broken by a complex system of normal faults locally forming a narrow discontinuous apical graben later postcaldera eruptions produced large andesitic and dacitic stratocones along the caldera margins and dacitic domes on the resurgent dome beginning about 3 5 ma ago and persisting into the quaternary hydrothermally altered rocks occur in the eroded cores of precaldera and postcaldera stratovolcanoes and along fractures in the resurgent dome but no ore deposits are known a few warm springs located in salars within the caldera moat appear to be vestiges of the caldera geothermal system

build up and depositional dynamics of an arc front volcaniclastic complex the miocene tepoztlan formation transmexican volcanic belt central mexico volcanic terrains such as magmatic arcs are thought to display the most complex surface environments on earth ancient volcaniclastics are notoriously difficult to interpret as they describe the interplay between a single or several volcanoes and the environment the early miocene tepoztlan formation at the southern edge of the transmexican volcanic belt belongs to the few remnants of this ancestral magmatic arc and therefore is thought to represent an example of the initial phase of evolution of the transmexican volcanic belt based on geological mapping detailed logging of lithostratigraphic sections palaeocurrent data of sedimentary features and anisotropy of magnetic susceptibility mapping of two dimensional panels from outcrop to field scale and geochronological data in an area of ca 1000 km 2 three periods in the evolution of the tepoztlan formation were distinguished which lasted around 4 myr and are representative of a volcanic cycle edifice growth phases followed by collapse in a magmatic arc setting the volcaniclastic sediments accumulated in proximal to medial distances on partly coalescing aprons similar to volcanic ring plains around at least three different stratovolcanoes these volcanoes resulted from various eruptions separated by repose periods during the first phase of the evolution of the tepoztlan formation 22ae 8t o 22 ae2 ma deposition was dominated by fluvial sediments in a braided river setting pyroclastic material from small andesitic dacitic composite volcanoes in the near vicinity was mostly eroded and reworked by fluvial processes resulting in sediments ranging from cross bedded sand to an aggradational series of river gravels the second phase 22ae 2t o 21 ae3 ma was characterized by periods of strong volcanic activity resulting in voluminous accumulations of lava and tuff which temporarily overloaded and buried the original fluvial system with its detritus continuous build up of at least three major volcanic centres further accentuated the topography and in the third phase 21ae 3t o 18 ae8 ma mass flow processes represented by an increase of debris flow deposits became dominant marking a period of edifice destruction and flank failures

plinian airfall deposits of basaltic composition two widespread scoria fall deposits locally known as the fontana lapilli and san judas formation are demonstrated to have issued from masaya caldera complex nicaragua and to be the first documented plinian airfall deposit of basaltic composition data from maps of median grain size average maximum pyroclast diameter and average maximum diameter of lithic fragments provide conclusive evidence of the plinian nature of both deposits the volume within the 1 mm isopach of the fontana lapilli is 12 km3 3 4 km3 dense rock equivalent and within the san judas formation it is 1 2 km3 0 35 km3 dre theoretical eruption parameters calculated for the fontana lapilli and san judas formation respectively include muzzle velocity 170 m s and 150 m s column height 50 km and 18 km volume eruption rate 2 105 m3 s and 1 104 m3 s and duration 2 h and 10 h these are all similar to the calculated parameters for silicic plinian eruptions basaltic magmas are generally considered incapable of erupting in the manner characteristic of plinian eruptions recognition of them argues that factors other than high viscosity may be of fundamental importance

molecular and isotopic abundances of long chain n fatty acids in open marine sediments of the western north pacific abstract molecular abundance and compound specific carbon isotope ratios of long chain n fatty acids lcfas ranging from c20 to c30 are reported for open marine sediments of the western north pacific a positive correlation r2 0 94 is observed between total organic carbon toc and lcfa concentrations although the toc concentrations varied from 0 34 to 2 62 wt in dry sediment the relatively uniform ratio of lcfas to toc 0 74 0 12 mg gc is similar to that of the central pacific reported by ohkouchi et al ohkouchi n kawamura k kawahata h taira a 1997 latitudinal distributions of terrestrial biomarkers in the sediments from the central pacific geochim cosmochim acta 61 1911 1918 and in a core sample from the tropical central pacific by prahl et al prahl f g muehlhausen l a lyle m 1989 an organic geochemical assessment of oceanographic conditions at manop site c over the past 26 000 years paleoceanography 4 495 510 on the other hand lcfa concentrations in riverine and estuarine sediments are apparently higher than in open marine sediments carbon isotopic compositions of individual lcfas in open marine sediments are similar 26 1 for n c24 and n c26 being more enriched in 13 c than bay and riverine sediments by up to 6 terrestrial c3 higher plants commonly have a 13 c value of 26 in bulk organic carbon and because lipid components including fatty acids are known to be depleted in 13 c by several per mil compared to bulk organic matter this study indicates that the open marine sedimentary lcfas are not derived from normal terrestrial c3 higher plants rather the isotopic composition is consistent with a mixed source of c4 and c3 terrestrial higher plants and or marine organisms low carbon preference index cpi values of the lcfas and the isotopic difference between the northern and southern samples suggest that the lcfas of this study are likely to be related to marine primary productivity even though lcfas have often been used to infer a terrestrial higher plant input to marine sediments

dispersal and characteristics of pyroclastic fall deposits from mt misery volcano west indies mt misery volcano near the northern end of the lesser antilles island arc produced late quaternary airfall layers that have different dispersal patterns these are controlled by a the style of explosive activity which determined the heights of the eruption columns and b a layered atmospheric system with contrasted bipolar wind directions at different altitudes isopach and isopleth maps are given for 10 eruptions belonging to the mansion series 41 730 1 750 yrs b p basaltic strombolian type scoria fall deposits were dispersed mainly by surface lower tropospheric winds to the nw and w in contrast green and brown andesitic sub plinian and plinian falls with higher eruption columns were dispersed to the se and e by upper tropospheric winds thinly laminated phreatomagmatic ashes within the mansion series are again dispersed to the nw and controlled by surface winds

giant tuff cone and 12 km wide associated caldera at ambrym volcano vanuatu new hebrides arc abstract ambrym in the new hebrides arc has been considered as an effusive basaltic volcano the present paper discusses the general structure of this edifice which consists of a basal shield volcano topped by an exceptionally large tuff cone surrounding a 12 km wide summit caldera dacitic pyroclastic flow deposits are exposed in the lower part of the tuff series they grade upward into composite sequences of bedded surtseyan type hyaloclastites ash flow deposits and fallout tephra which are essentially basaltic in composition in such a way that the tuff cone may be considered as mainly basaltic the relationship between the eruption of pyroclastics and the collapse event precludes a classical model of caldera formation at a basaltic volcano in which quiet subsidence i e kilauea type is the dominant mechanism interpretation of the tuff series implies intervention of external water and suggests both explosive and collapse mechanisms a model of caldera formation which assumes an enlargement of the ring fracture during a first plinian and dacitic then essentially hydrobasaltic eruption is proposed

fluctuation of biogenic and abiogenic sedimentation on the shatsky rise in the western north pacific during the late quaternary abstract sedimentation of biogenic and abiogenic components was studied in cores ngc108 36 36 85 n 158 20 90 e water depth 3390 m and s2612 32 19 84 n 157 51 00 e water depth of 2612 m from the shatsky rise to understand fluctuations in primary productivity and abiogenic sedimentation in the mid latitude of the western north pacific during the late quaternary the mean c organic n atomic ratio of 6 0 7 8 in both cores indicates that organic matter is mainly marine in origin organic carbon is positively correlated with biogenic opal in core ngc108 in contrast to a weak correlation in core s2612 although the maxima of paleoproductivity estimates in both cores generally occur during glacial times the paleoproductivity estimates biogenic opal carbonate ratios and the c organic c carbonate ratios have always been higher in core ngc108 than in core s2612 during the last 180 kyr suggesting that the surface water at site ngc108 could have been influenced more by subarctic water mass than at site s2612 however the opal carbonate ratio in core s2612 remains fairly constant relative to that in core ngc108 which might mean that the transition zone between subarctic and central water was narrower in latitude in at the oxygen isotope stage ois 2 3 boundary ois 4 and ois 6 sedimentation of 13 inorganic elements has been measured in both cores these elements are classified into four groups based on correlation between each element in content 1 terrigenous components al ti fe 2 biogenic calcareous material ca sr 3 biogenic scavenged elements mg zn cr be and 4 the other elements mn ba cu ni the terrigenous mass accumulation rates were elevated in ois 2 3 and 4 and late ois 6 in core ngc108 while they were higher in early ois 1 ois 2 4 and 6 in core s2612 mno 2 and ba might be redistributed during the sub surface reduced condition especially precipitation of particle reactive be which could be accelerated by both enhanced terrigenous input and biogenic vertical transport has fluctuated largely in response to climatic change because of its short residence time on the order of the oceanic mixing time

a structural outline of the yenkahe volcanic resurgent dome tanna island vanuatu arc south pacific abstract a structural study has been conducted on the resurgent yenkahe dome 5 km long by 3 km wide located in the heart of the siwi caldera of tanna island vanuatu arc south pacific this spectacular resurgent dome hosts a small caldera and a very active strombolian cinder cone the yasur volcano in the west and exhibits an intriguing graben in its central part detailed mapping and structural observations make it possible to unravel the volcano tectonic history of the dome it is shown that following the early formation of a resurgent dome in the west a complex collapse caldera plus graben occurred and this was associated with the recent uplift of the eastern part of the present dome eastward migration of the underlying magma related to regional tectonics is proposed to explain this evolution

a geochemical and geophysical investigation of the hydrothermal complex of masaya volcano nicaragua abstract masaya volcano nicaragua is a persistently active volcano characterized by continuous passive degassing for more than 150 years through the open vent of santiago crater this study applies self potential soil co 2 and ground temperature measurements to highlight the existence of uprising fluids associated to diffuse degassing structures throughout the volcano the diffuse degassing areas are organized in a semi circular pattern and coincide with several visible and inferred surface volcanic structures cones fissure vents and likely consist of a network of buried faults and dykes that respectively channel uprising flow and act as barrier to gravitational groundwater flow water depths have been estimated by multi scale wavelet tomography of the self potential data using wavelets from the poisson kernel family compared to previous water flow models our water depth estimates are shallower and mimic the topography typically less than 150 m below the surface between 2006 and 2010 the depths of rising fluids along the survey profiles remained stable suggesting that hydrothermal activity is in a steady state this stable activity correlates well with the consistency of the volcanic activity expressed at the surface by the continuously passive degassing when compared to previous structural models of the caldera floor it appears that the diffuse degassing structures have an important effect on the path that shallow groundwater follows to reach the laguna de masaya in the eastern part of the caldera the hydrogeological system is therefore more complex than previously published models and our new structural model implies that the flow of shallow groundwater must bypass the intrusions to reach the laguna de masaya furthermore these diffuse degassing structures show clear evidence of activity and must be connected to a shallow magmatic or hydrothermal reservoir beneath the caldera as such the heat budget for masaya must be significantly larger than previously estimated

the sources and deposition of organic matter in the late quaternary pigmy basin gulf of mexico abstract the concentration and carbon isotopic composition 13c of sedimentary organic carbon corg n c ratios and terrigenous and marine 13corg endmembers form a basis from which to address problems of late quaternary glacial interglacial climatic variability in a 208 7 m hydraulic piston core dsdp 619 from the pigmy basin in the northern gulf of mexico while interpretations of sedimentary 13corg time series records are often not unique paired analyses of 13corg and n c are consistent with the hypothesis that the corg in the pigmy basin is a climatically determined mixture of c3 photosynthetic terrigenous and marine organic matter confirming the earlier 13corg model of sackett 1964 a high resolution 1 4 2 9 ka sample 13corg record shows that sedimentary organic carbon in interglacial oxygen isotope sub stages 1 and 5a b are enriched in 13c average 1 values are 24 2 1 2 o and 22 9 0 7 o relative to pdb respectively while glacial isotope stage values 2 are relatively depleted 25 6 0 5 concentrations of terrigenous and marine sedimentary organic carbon are calculated for the first time using 13corg and corg measurements and empirically determined terrigenous and marine 13corg endmembers the net accumulation rate of terrigenous organic carbon is 4 3 2 6 times higher in isotope stages 2 4 than in sub stages 1 and 5a b recording higher erosion rates of terrigenous organic material in glacial times the concentration and net accumulation rates of marine and terrigenous corg suggest that the nutrient bearing plume of the mississippi river may have advanced and retreated across the pigmy basin as sea level fell and rose in response to glacial interglacial sea level change

pendant bioconstructions cemented by microbial carbonate in submerged marine caves holocene se sicily abstract unusual pendant bioconstructions occur within two submerged caves in the plemmirio marine protected area south of syracuse se sicily these cm to dm sized bioconstructions project downward from the cave roofs the main framework builders are serpulids belonging to the genera protula semivermilia and josephella encrusting bryozoans corals hydrozoans and sponges are subordinately present whereas bivalves and brachiopods are overall rare these faunal associations are characteristic of the studied caves but only in some places they form small bioconstructions that are cemented by microbial carbonates made up by autochthonous peloidal to clotted peloidal and aphanitic micrite the autochthonous micrite stabilizes the pendant bioconstructions herein referred to as biostalactites the microbial carbonate reveals high contents of bacterial lipid biomarkers among the most abundant compounds are mono o alkyl glycerol ethers mages and branched fatty acids 10 me c16 0 iso and anteiso c15 0 and c17 0 interpreted as biomarkers of sulfate reducing bacteria other compounds preserved in the autochthonous carbonates include lipids derived from marine zoo and phytoplankton brassicasterol dinosterol and monounsaturated short chain fatty acids unspecified marine bacteria saturated and monounsaturated short chain fatty acids and land plants long chain fatty acids long chain alcohols stigmasterol sitosterol and campesterol the observed lipid biomarker signatures are remarkably similar to those of post glacial reefal microbialites where microbialite formation in cavities of the coral framework was also mediated by sulfate reducing bacteria in the submerged caves of plemmirio marine protected area serpulid colonies apparently occur preferentially where freshwater is seeping through crevices in the limestone the consequent nutrification is believed to favor serpulid aggregation and the growth of other skeletal i e bryozoans and corals and soft bodied organisms i e sponges and ascidiae the resultant accumulation of biomass and its taphonomy provide niches for sulfate reducing bacteria which induce carbonate precipitation cementing and stabilizing the biostalactites the finding of pendant cemented bioconstructions in the mazzere and granchi caves of the plemmirio marine protected area reveals that sulfate reducing bacteria are involved in microbialite formation in various cryptic environments the formation of such peloidal to clotted peloidal microcrystalline carbonates in cryptic ecosystems is a significant factor for the stabilization of different kinds of bioconstructions spanning from small biostalactites to large reefs

fracture zone scale variation of trace elements and stable isotopes in calcite in a crystalline rock setting abstract with an aim to increase the understanding about the isotopic and chemical heterogeneity of calcites in water conducting fracture zones with different crystalline wall rock compositions at different depths we present trace element chemistry isotopic composition 18o 13c 87sr 86sr and biomarkers of euhedral low temperature fracture coating calcite paleohydrogeological fluctuations and wall rock influence on the hydrochemistry in the deep groundwater are explored samples are from several fracture zone sub fractures at 360 to 740 m retrieved during an extensive core drilling campaign in sweden calcite generally showed fracture zone specific values of 13c 18o and 87sr 86sr which indicates precipitation from relatively homogeneous fluid similar to the modern groundwater at the site at the same event in each fracture zone 18o and 13c in the different fracture zones were consistent with precipitation from waters of different salinity and decreasing organic input with depth respectively the latter is also supported by biomarkers showing clear indications of srb related organic compounds e g iso and anteiso c17 0 branched fatty acids except in the deepest zone in contrast to the isotopes variation in trace elements within the fracture zones was generally up to several orders of magnitude manganese and ree as oppose to the other metals were higher in the shallow fracture zones 112 1130 and 44 97 ppm respectively than in the deeper 28 272 and 5 11 ppm respectively in agreement with the groundwater composition although the rock types varied between and within the different fracture zones this had insignificant influence on the trace element chemistry of the calcites co variation was generally relatively large for many trace elements with isometric logratio correlation generally better than 0 75 which indicates that their variation in the calcites is due to variation of ca in the fracture water but other local factors especially uptake in co precipitating minerals clay minerals barite pyrite and zeolites but also microbial activity and metal speciation may have influenced the metal incorporation into calcite these detailed studies of fracture calcite are of importance for the understanding of variation in fluid chemistry and trace metal uptake in fracture zones adding together with hydrochemical studies detailed information optimal for site characterisation

age discrepancy between molecular biomarkers and calcareous foraminifera isolated from the same horizons of northwest pacific sediments abstract recent observations show that establishment of molecular level radiocarbon stratigraphy is increasingly critical for paleoceanographic studies especially to enable comparable discussion about past ocean and climate changes inferred from multiple proxy records based on lipid biomarkers and calcareous foraminiferal microfossils so far although we have interesting evidence that there are temporal and spatial age offsets between the algal alkenone biomarker used for sst sea surface temperature estimates and planktonic foraminifera in regions with high sedimentation rates less is known about such age offsets in the settings of lower sedimentation in this study to investigate the potential of biomarkers as an alternative dating proxy to foraminifera in a low sedimentation rate setting we measured radiocarbon ages of 17 different lipid biomarkers fatty acids fas n alkanes and alkenones bulk total organic matter toc and foraminifera from two sections 12 15 cm and 21 24 cm depth of a surface sediment core in the northwest pacific the sedimentation rate estimated from the toc ranged from 10 5 cm kyr in the core top to 0 9 cm kyr in the lower part of the core the ages of the fas detected at 12 15 cm depth ranged from 530 yr bp c 18 to 3250 yr bp c 28 the 14 c analysis of the fas could be divided into two groups fas c 16 c 18 derived from marine organisms and those c 24 c 26 c 28 derived from terrestrial higher plants the high molecular weight hmw fas ages were older 2550 yr bp c 24 to 3250 yr bp c 28 than those of the low molecular weight lmw fas 530 yr bp c 18 to 1820 yr bp c 16 at 21 24 cm depth the alkenone ages were 7100 7300 yr younger than those of the planktonic foraminifera in this horizon the alkenone 14 c age 7500 yr bp and the alkenone estimated sst 15 3 c suggest that these alkenones were produced in this region during the holocene the alkenone 14 c age was also in good agreement with those of the lmw fas c 14 ic 15 aic 15 c 16 and c 18 1 derived from marine plankton and bacteria similarly the toc age was 5700 yr younger than that of the planktonic foraminifera these age differences are large compared with those estimated for the horizon at 12 15 cm depth which was characterized by a relatively higher sedimentation rate these trends between ages of alkenones toc and planktonic foraminifera are not comparable to the results from sites with high sedimentation rates such as the benguella upwelling system mollenhauer g eglinton t i ohkouchi n schneider r r muller p j grootes p m et al 2003 asynchronous alkenone and foraminifera records from the benguela upwelling system geochim cosmochim acta 67 2157 2171 or the bermuda rise drift deposit ohkouchi n eglinton t i keigwin l d hayes j m 2002 spatial temporal offsets between proxy records in a sediment drift science 289 1224 1227 which are significantly different sedimentary settings from our site the radiocarbon results from these high sedimentation rate regions suggest that the alkenones are several thousand years older than the coexisting planktonic foraminifera on the other hand the age offsets between alkenones and planktonic foraminifera at our site are larger than those from the other sites and the alkenones are younger than the planktonic foraminifera

mafic pyroclastic flows at santa maria gaua volcano vanuatu the caldera formation problem in mainly mafic island arc volcanoes at santa maria volcano new hebrides island arc extensive ash and scoria flow deposits overlie the mainly effusive pre caldera cone hydromagmatic features characterize these deposits the composition of juvenile clasts ranges from basalt to acid andesite dacite sio2 51 63 6 with a dominant basaltic composition the stratigraphic position of this pyroclastic series and its spatial distribution around a 8 5 km 6 km wide caldera provide evidence of a relationship between this series and the caldera formation in addition these pyroclastic deposits are co genetic to parasitic cones and lava flows developed along faults concentric to the caldera both series result from a compositionally layered magma reservoir the subordinate differentiated magmas being the result of fractional crystallization from the basalts a model of caldera formation which implies a large hydromagmatic eruption at the central vent and minor magma withdrawal by flank eruptions is proposed this model emphasizes the importance of mafic hydroclastic eruptions in the caldera forming event and contradicts a model implying only quiet subsidence a process often proposed for the formation of calderas in island are volcanoes of mainly mafic composition

magma and volatile supply to post collapse volcanism and block resurgence in siwi caldera tanna island vanuatu arc v24c 04 allen s r 2005 complex spatterand pumice rich pyroclastic deposits from an andesitic caldera forming eruption the siwi pyroclastic sequence tanna vanuatu bulletin of volcanology 67

tectonic styles of early proterozoic ore deposition in the fennoscandian shield the early proterozoic metallogenic events of the fennoscandian shield are connected with two major stages of crustal evolution the karelian continental development 2 5 2 1 ga and the svecofennian orogeny 2 0 1 75 ga the karelian continental development was dominated by deposition of terrestrial sediments and tholeiitic volcanism on archaean crust a tensional regime probably associated with a mantle plume and partial melting of the upper mantle culminated in the generation of an ene wsw trending rift zone which was intruded by tholeiitic magma 2 44 ga ago some 15 layered igneous bodies hosting cr pge ni cu and fe v ti deposits are known in the kemi suhanko and koillismaa belts these mafic ultramafic bodies originally formed either several lopoliths or one single layered igneous complex with a minimum length of 260 km nw se and nnw sse trending dolerite dykes intruded the rifted and attenuated archaean crust 2 25 2 0 ga ago preceding ocean opening the coeval ne sw trending dolerite dykes in the northern part of the shield are interpreted as manifestation of an aulacogen the failed arm of a triple armed rift system oceanic crust is preserved in 1 96 ga old ophiolite complexes the cu co zn ni and cr contents of the outokumpu type deposits derive from hydrothermal leaching of oceanic crust and were discharged together with chemogenic cherts and carbonates from ascending hydrothermal fluids on the seafloor above fissure vents in the northern part of the shield rifting and probably ocean opening resulted in the formation of the layered tholeiitic sedimentary complex of the petsenga ni cu district intruded by mineralized mafic ultramafic magma the age of this event is poorly constrained the basin was subsequently closed and continental collision of the kola suture was accompanied by southward obduction of the lapland granulite belt on the archaean crust during the svecofennian orogeny the divergent continental margin was converted into an active margin early subduction of oceanic crust produced oceanic island arcs intruded by 1 93 1 9 ga old tonalites and trondhjemites subsequent subduction of oceanic crust generated 1 9 1 87 ga old continental island arcs associated with massive sulphide cu zn pb ag au deposits the island arcs were accreted to the archaean crust in a concave belt containing the ore districts of kiruna skellefte vihanti pyhasalmi aijala orijarvi and bergslagen bimodal volcanic suites with felsic calc alkaline and mafic tholeiitic volcanites are attributed to rifting of the overriding plate above subduction zones ni cu deposits in synorogenic 1 9 1 87 ga old mafic ultramafic intrusions occur in linear fault controlled belts at the margin of the archaean crust the generation of ni bearing tholeiitic to komatiitic magma is explained by partial melting of the mantle wedge above the early subduction zone magma differentiation and magma upwelling along transcurrent faults on the continental margin sulphur was probably assimilated from the supracrustal wall rocks 1 89 1 87 ga old early svecofennian granitoids are associated with porphyry type cu mo au deposits widespread late svecofennian s type 1 84 1 75 ga granitic magmatism generated minor mo u w sn and ree deposits emphasis is laid on the importance of geotectonic models as a basis for further exploration in the fennoscandian shield

the phlegraean fields structural evolution volcanic history and eruptive mechanisms abstract the main event within the volcanic history of the phlegraean fields was the eruption about 35 000 years ago of a huge alkali trachytic ignimbrite 80 km 3 dre followed by caldera collapse the pre caldera activity evidence from geothermal wells and surface outcrops changed from submarine to subaerial shortly before the ignimbrite eruption the caldera was subsequently invaded by the sea and became progressively filled with tuffites and subordinate submarine flows in its northern half the last submarine explosive activity dates back to 12000 10500 yr with the eruption of mostly hydroplinian yellow tuffs recent mostly subaerial activity consists of a series of explosive eruptions whose volume decreases with time until the last eruption of mt nuovo in 1538 a d two peaks in recent activity occur at 10000 8000 and 4700 3000 years ago during post caldera activity eruptive vents migrated from the caldera rim toward the center where there are two distinct zones of recent vents minor collapses occurred within the caldera after the main eruptions often they are eccentric to the vent and displaced toward the caldera center phlegraean explosive activity is characterized by water magma interaction eruptive events without a hydromagmatic component are extremely rare in most cases the evolved trachytic magmas interacted with surface water either the sea or intracaldera lakes however there is evidence of interaction of magma with deep seated aquifers for some plinian events explosivity i e the efficiency of the transformation of thermal into kinetic energy during magma water interaction is largely controlled by the primary fragmentation of the magmatic melt

carbon chain length distribution in n alkyl lipids a process for evaluating source inputs to lake qinghai abstract lake sediments generally contain a mixture of terrestrial and aquatic source inputs and determining the major inputs is important for understanding geological records in paleoenvironment and paleoclimate research in this study we describe the distribution of n alkanes and n fatty acids fas in representative modern plants from around lake qinghai we found a significant difference in the average length of n fa carbon chains acl fa 16 32 in terrestrial 23 3 and aquatic plants 18 6 the results reveal that acl fa 16 32 may essentially serve as a proxy for evaluating the major source inputs to lake sediments assessment of surface sediments from the lake showed that the fas originated from a mixture of inputs with the aquatic source input predominant at most sites additionally the d values of sediment mid chain n acids c 22 showed a relationship with the acl fa 16 32 proxy an increased fa acl corresponded to more negative hydrogen isotope ratio values we suggest that different sources should be considered and acl fa 16 32 could be a potential calibration proxy before using d values to extract reliable isotopic information from lake water more attention should be paid to source inputs and their relationship to other geochemical proxies in future studies of lake sediments

estimation of the near surface velocity structure of the yasur yenkahe volcanic complex vanuatu small aperture array measurements of seismic noise at seven sites around yasur volcano vanuatu are performed to estimate the vp and vs velocities of the shallow structure the spatial autocorrelation spac and the frequency wavenumber f k methods are used to determine rayleigh phase velocity dispersion curves phase velocities computed with the spac method vary between 580 m s and 960 m s at 1 hz and between 270 m s and 420 m s at 15 hz f k dispersion curves show velocities of 300 340 m s and 800 940 m s at 1 hz and 200 230 m s at 15 hz an inversion technique based on the use of the neighbourhood algorithm has been used to calculate the one dimensional velocity model at each site velocity models reach 200 m deep and mainly contain two layers and a half space for sites close to the siwi caldera rims comparisons with geology and hydrothermal system studies suggest that the two layers highlighted in models may correspond to two large pyroclastic sequences related to caldera collapses based on the flank of an old volcano results obtained for the other three sites located inside the caldera show the influence of the hydrothermal system on p and s wave velocities for these sites fluid circulation inside the volcanic deposits causes lower velocities at depth to obtain a near surface velocity model of the volcanic structure each 1d velocity model is spatially extrapolated according to the surface geology results highlight four distinct areas the siwi caldera edges with high velocities and the resurgent block the ash plain and the yasur edifice with lower velocities at depth

mafic plinian volcanism and ignimbrite emplacement at tofua volcano tonga tofua island is the largest emergent mafic volcano within the tofua arc tonga southwest pacific the volcano is dominated by a distinctive caldera averaging 4 km in diameter containing a freshwater lake in the south and east the latest paroxysmal vei 5 6 explosive volcanism includes two phases of activity each emplacing a high grade ignimbrite the products are basaltic andesites with between 52 wt and 57 wt sio2 the first and largest eruption caused the inward collapse of a stratovolcano and produced the tofua ignimbrite and a sub circular caldera located slightly northwest of the island s centre this ignimbrite was deposited in a radial fashion over the entire island with associated plinian fall deposits up to 0 5 m thick on islands 40 km away common sub rounded and frequently cauliform scoria bombs throughout the ignimbrite attest to a small degree of marginal magma water interaction the common intense welding of the coarse grained eruptive products however suggests that the majority of the erupted magma was hot water undersaturated and supplied at high rates with moderately low fragmentation efficiency and low levels of interaction with external water we propose that the development of a water saturated dacite body at shallow 6 km depth resulted in failure of the chamber roof to cause sudden evacuation of material producing a plinian eruption column following a brief period of quiescence large scale faulting in the southeast of the island produced a second explosive phase believed to result from recharge of a chemically distinct magma depleted in incompatible elements this similar but smaller eruption emplaced the hokula ignimbrite sheet in the northeast of the island a maximum total volume of 8 km3 of juvenile material was erupted by these events the main eruption column is estimated to have reached a height of 12 km and to have produced a major atmospheric injection of gas and tephra recorded in the widespread series of fall deposits found on coral islands 40 80 km to the east in the direction of regional upper tropospheric winds radiocarbon dating of charcoal below the tofua ignimbrite and organic material below the related fall units imply this eruption sequence occurred post 1 000 years bp we estimate an eruption magnitude of 2 24 1013 kg sulphur release of 12 tg and tentatively assign this eruption to the ad 1030 volcanic sulphate spike recorded in antarctic ice sheet records

terrigenous plant wax inputs to the arabian sea implications for the reconstruction of winds associated with the indian monsoon author posting the authors 2005 this is the author s version of the work it is posted here by permission of elsevier b v for personal use not for redistribution the definitive version was published in geochimica et cosmochimica acta 69 2005 2547 2558 doi 10 1016 j gca 2005 01 001

structure and composition of the precambrian crust along the polar profile in the northern baltic shield abstract along the 500 km long polar profile the continental crust of the northern baltic shield consists of several archaean and early proterozoic crustal segments in the south in the karelian province the upper crust consists of a 3 1 2 6 ga old archaean substratum with a 0 6 km thick low to medium grade volcanosedimentary cover here shallow basin facies rocks of the central lapland complex have been thrust northwards onto the karasjok kittila greenstone belt the repeatedly folded cover rocks form linear troughs between domes and culminations of granitoids the 47 48 km thick crust of the karelian province is of a shield type it is characterised by a low velocity layer interpreted as a horizon of decollement below the supracrustal and granitoid rocks in the lapland granulite belt early proterozoic high grade metapelites and metapsammites with minor metaigneous intercalations have been thrust to the southwest they are separated from the underlying karelian province by the tectonic mixture zone of the tanaelv belt in the interpretations two alternative models are given for the shape of the lapland granulite belt it is either a synformal nappe or a ne dipping body pinching out at depth and overthrust from the north by the archaean inari terrain both the lapland granulite belt and the inari terrain have a 42 44 km thick crust with a relatively thin lower crust marked by lower seismic velocities the early proterozoic polmak pasvik pechenga belt separates the archaean inari terrain from the archaean sorvaranger terrain in the north this belt is interpreted as a suture zone which continues to depth it may either dip steeply towards irregularities in the moho or form a sw dipping low angle plane below the lapland granulite belt the northernmost part of the baltic shield is concealed beneath a 0 7 km thick very low grade metamorphic late proterozoic cover this cover is divided into two parts by the trollfjord komagelv strike slip fault here the crust is again of a normal shield type with a thickness of 42 46 km

inverting the source mechanism of strombolian explosions at mt yasur vanuatu using a multi parameter dataset abstract the source mechanism of strombolian explosions at mt yasur vanuatu is analyzed using a unique data set which enables us to combine different methodologies the novelty of the approach presented here lies in the combination of seismic acoustic and doppler radar data thus using infrasound and doppler radar observations we are able to provide independent estimates of the volume of the eruptive source in the following we show that a correlation exists between source volume and the maximum particle velocity of the expelled volcanic products in order to determine the source location and the associated mechanism and to compare those two methods we use time reversal imaging and moment tensor inversion while the first method also applies to extended sources the latter might be biased by its intrinsic point source approximation we show that time reversal imaging can deliver an estimate of the source depth without any a priori assumptions even in an unfavorable scenario in terms of topography and receiver setup the inverted source mechanism retrieved from moment tensor inversion is found to be largely isotropic with minor deviatoric components the inverted source location points towards an area to the north west of the active craters indicative of a common feeder system of the activity at mt yasur however it is also evident that to fully locate the source of strombolian activity at yasur location precision must be enhanced

latitudinal distribution of terrestrial lipid biomarkers and n alkane compound specific stable carbon isotope ratios in the atmosphere over the western pacific and southern ocean abstract we investigated the latitudinal changes in atmospheric transport of organic matter to the western pacific and southern ocean 27 58 n 64 70 s molecular distributions of lipid compound classes homologous series of c15 to c35 n alkanes c8 to c34 n alkanoic acids c12 to c30 n alkanols and compound specific stable isotopes 13c of c29 and c31 n alkanes were measured in marine aerosol filter samples collected during a cruise by the r v hakuho maru the geographical source areas for each sample were estimated from air mass back trajectory computations concentrations of tc and lipid compound classes were several orders of magnitude lower than observations from urban sites in asia a stronger signature of terrestrial higher plant inputs was apparent in three samples collected under conditions of strong terrestrial winds unresolved complex mixtures ucm showed increasing values in the north pacific highlighting the influence of the plume of polluted air exported from east asia n alkane average chain length acl distribution had two clusters with samples showing a relation to latitude between 28 n and 47 s highest acl values in the tropics whilst a subset of southern samples had anomalously high acl values compound specific carbon isotopic analysis of the c29 25 6 to 34 5 and c31 n alkanes 28 3 to 37 revealed heavier 13c values in the northern latitudes with a transition to lighter values in the southern ocean by comparing the isotopic measurements with back trajectory analysis it was generally possible to discriminate between different source areas the terrestrial vegetation source for a subset of the southernmost southern ocean is enigmatic the back trajectories indicate eastern antarctica as the only intercepted terrestrial source area these samples may represent a southern hemisphere background of well mixed and very long range transported higher plant organic material

pyroclastic density currents at etna volcano italy the 11 february 2014 case study abstract on 11 february 2014 a considerable volume 0 82 to 1 29 106 m3 of unstable and hot rocks detached from the lower eastern flank of the new southeast crater nsec at mt etna producing a pyroclastic density current pdc this event was by far the most extensive ever recorded at mt etna since 1999 and has attracted the attention of the scientific community and civil protection to this type of volcanic phenomena usually occurring without any clear volcanological precursor and especially toward the mechanisms which led to the crater collapse the pdc flow dynamics and the related volcanic hazard we present here the results of the investigation carried out on the 11 february 2014 collapse and pdc events data were obtained through a multidisciplinary approach which includes the analysis of photograph images from visible and thermal surveillance cameras and the detailed stratigraphic textural and petrographic investigations of the pdc deposits results suggest that the collapse and consequent pdc was the result of a progressive thermal and mechanical weakening of the cone by repeated surges of magma passing through it during the eruptive activity prior to the 11 february 2014 events as well as pervasive heating and corrosion by volcanic gas the collapse of the lower portion of the nsec was followed by the formation of a relatively hot up to 750 c dense flow which travelled about 2 3 km from the source stopping shortly after the break of the slope and emplacing the main body of the deposit which ranges between 0 39 and 0 92 106 m3 this flow was accompanied a relatively hot cloud of fine ash that dispersed over a wider area the results presented may contribute to the understanding of this very complex type of volcanic phenomena at mt etna and in similar volcanic settings of the world in addition results will lay the basis for the modeling of crater collapse and relative pdc events and consequently for the planning of hazard assessment strategies aimed at reducing the potential risks to scientists and tens of thousands of tourists visiting etna s summit areas every year

the role of komatiites in plate tectonics evidence from the archaean and early proterozoic crust in the eastern baltic shield abstract the early archaean continental crust of the eastern part of the baltic shield had been submitted to repeated rifting during the archaean and the early proterozoic the newly formed rifting belts evolved by sagduction and seemingly subduction in the archaean and subduction and collision in the lapland fold belt and in the svecokarelides of the central baltic shield the comparative evolution of these domains suggests that sagduction compatible with plate motion is a process competitive with subduction it is postulated what the sagduction subduction duality characterizing the archaean is equivalent to the intracontinental marginal orogenies encountered in proterozoic and phanerozoic times and that both represent at different periods variations in crustal interaction within an overall plate tectonic framework

the 1245 yr bp asososca maar new advances on recent volcanic stratigraphy of managua nicaragua and hazard implications abstract asososca maar is located at the western outskirts of managua nicaragua in the central part of the active n s trending and right lateral nejapa miraflores fault that marks an offset of the middle america volcanic arc it constitutes one of the 21 vents aligned along the fault between the chiltepe volcanic complex to the north and ticomo vents to the south asososca consists of an east west elongated crater filled by a lake which is currently used for supplying part of managua with drinking water 10 of the capital city demand the crater excavated the previous topography allowing the observation of a detailed holocene stratigraphic record that should be taken into account for future hazard analyses we present a geological map together with the detailed stratigraphy exposed inside and around asososca crater aided by radiocarbon dating of paleosols the pre existing volcanic sequence excavated by asososca is younger than 12 730 255 250 yr bp and is capped by the phreato plinian masaya tuff 2 are dominated by accidental clasts including basaltic to basaltic andesitic olivine bearing scoriae lapilli porphyritic and hypocrystalline andesite blocks and lapilli altered pumice lapilli and ash and ignimbrite fragments juvenile fragments were only identified in size fractions smaller than 1 in proportions lower than 25 and consist of black moss like fused shape and poorly vesiculated fresh glass fragments of basaltic composition sio2 48 the asososca tephra is interpreted as due to the emplacement of several pyroclastic surges originated by phreatomagmatic eruptions from asososca crater as suggested by impact sags geometry and dune crest migration structures according to radiocarbon dating these deposits were emplaced at 1245 125 120 yr bp the stratigraphic position of the asososca tephra and the well preserved morphology of the crater indicate that asososca is the youngest vent along the nejapa miraflores fault explosive eruptions might therefore occur again along this fault at the western outskirts of managua such kind of activity together with the strong seismicity associated to the active fault represents a serious hazard to urban infrastructure and a population of ca 1 3 million inhabitants

the salazie cirque ignimbrite piton des neiges volcano reunion island chronostratigraphy description and significance of lithic fragments and eruptive mechanisms abstract an ignimbrite sequence in the salazie cirque is characterized by a pyroclastic flow unit composed of basal breccias layers a1 and a2 a welded tuff layer b and an upper ashy layer layer c this eruption began a new eruptive cycle in the piton des neiges volcanic complex the second stage of a differentiation series characterized by the emission of undersaturated lava the paleogeography of the volcano s eastern flank is reconstituted at about 150 000 y b p from the distribution of ignimbrite deposits that partially fill two large erosion cirques the salazie protocirque and the marsouins protocirque the total volume of these deposits is only a few km3 and no evidence indicates a related caldera collapse basal breccias are composed of 1 juvenile magmatic clasts yielding a mugearitic composition and normative nepheline and 2 xenoliths representative of the different units in a 1500 2000 m thick volcanic pile which include differentiated lavas first stage of differentiated series basaltic lava flows and plutonic rocks oceanite series the appearance of hydrothermal parageneses only in subsurface facies emphasizes the striking role of volcanotectonic structures in mineralized fluid circulation the common features of magma mixing abnormal mineralogical associations reverse zonings disequilibrium features in layer b are interpreted as resulting from the assimilation of highly differentiated foreign rocks by the mugearite magma during and after the course of the eruption the salazie cirque ignimbrite is of the overflowing type non plinian characterized by high emplacement temperatures a model is proposed for its formation 1 rising of a mugearitic eruption column 2 vesiculation of magma at shallow depth beneath the plug 3 increase of magma pressure and eruption of a mixture of gas magmatic blocks and xenoliths down slope deposition of fines depleted heterogenous lithic rich flow layer a1 4 explosion flashing of the gas rich upper part of the magma column and eruption of the main welded tuff unit with segregation of a basal non fines depleted lithic concentration zone during flow layer a2 and elutriation of an ash cloud fall layer c 5 effusive phase

eruption transport and deposition of ignimbrite a case study from mexico abstract the acatlan ignimbrite covers 150 km 2 around a vent situated 40 km southwest of guadalajara mexico the upper and main ignimbrite flow unit is compositionally zoned and has white or pink rhyolitic pumice in its lower part and black andesite in its upper these parts are believed to have been erupted continuously from the same magma chamber this zonation has been important in correlating an extremely coarse lithic rich deposit a co ignimbrite lag fall deposit with this ignimbrite the co ignimbrite lag fall deposit indicates that the flow unit formed by continuous collapse of an explosive eruption column and enables the source vent to be located the vertical compositional grading of the flow unit also provides a means of testing the various proposed mechanisms of ignimbrite emplacement turbulent vs high concentration flow the preservation of compositional zonation and other features in the deposit indicate that flow was not turbulent details of the grain size distribution indicate that laminar flow was important early in the flow history when collapsing material from the eruption column was superimposed in stratigraphical sequence initial high gas flow rates associated with flow segregation and formation at the site of column collapse rapidly decayed away from vent and later in its history the flow degassed to a semi rigid plug overriding a sheared basal layer

families of similar events and modes of oscillation of the conduit at yasur volcano vanuatu abstract we examined one year of seismic recordings collected in 2008 during a temporary experiment at yasur volcano vanuatu the volcano has a permanent strombolian activity that was at a relatively high level during most of our experiment with commonly at least one explosion per minute associated with this activity the network recorded intense seismicicity with hundreds of transients per day video recordings indicate that most of the high frequency transients are directly related to the strombolian explosions they also outline the presence of fewer signals which are not accompanied by any surface activity the classification of transient events recorded at a station close to the summit indicates that a significant part of the events exhibit waveform similarity this technique allows the identification of characteristic repeating events among the hundreds of thousands of transients recorded during the experiment most of the families of similar events are groups of explosion quakes eqs but a few are groups of long period events related to deeper processes by scanning the 9 months of continuous data available at the summit station with master events extracted from these families we reconstruct their temporal evolution our results show that several families dominate the activity with a few of them lasting for several months we show that their temporal evolutions can be used to probe changes in the structure or activity of the volcano we observe that a major change was induced by a m 7 3 subduction earthquake which occurred on april 9 2008 about 80 km from the volcano while this event did not change significantly the surface morphology of the volcano nor the intensity of the eruptive activity it interrupted the families as none of them is present both before and after the event this change in the waveforms can be explained by a drop in the seismic velocity of the volcano caused by the distal event numerous other transitions between families are observed sudden or progressive these can be interpreted as representative of changes in the eruptive dynamics the presence of similar eqs especially for impulsive explosions indicates that the source mechanism is reproducible and has a stable location for some periods this favors a source process based on the oscillation of the conduit or oscillation of the edifice in response to the explosive decompression of gas slugs at the free surface of the conduit our results suggest that the seismic activity of yasur is characterized by the presence of dominant modes of resonance of the conduit which may be influenced both by external and internal factors

evidence for molecular structural variations in the cytoarchitectures of a jurassic plant in this study we investigate the molecular structural characteristics of organic remains in various cellular organelles from a 180 ma jurassic royal fern belonging to the osmundaceae family of ferns and compare their carbon isotopic compositions to a now living species of royal fern osmunda regalis we discovered molecular structural variations indicated by raman and infrared spectral parameters obtained from various fossilized cellular organelles the organic remains preserved in the chromosomes and cell nuclei show marked structural heterogeneities compared to the cell walls during different stages of the cell cycle the fossil and extant fern have similar 13 c values obtained from bulk samples supporting evolutionary stasis in this plant lineage and an unchanged metabolic pathway of carbon assimilation since the jurassic the organic remains in the cellular organelles of the fossil seem to be less heterogeneous than those in the extant fern likely due to the preferential preservation of certain cellular compounds during fossilization taphonomic processes appear to have diminished the subcellular isotopic heterogeneities our research sheds light on the functioning of ancient plant cellular organelles during mitosis provides insights to the taphonomic processes operating at molecular and isotopic levels and shows the practicability of in situ techniques in studying the evolution and behaviors of ancient cells

strombolian surface activity regimes at yasur volcano vanuatu as observed by doppler radar infrared camera and infrasound abstract in late 2008 we recorded a continuous multi parameter data set including doppler radar infrared and infrasound data at yasur volcano vanuatu our recordings cover a transition in explosive style from ash rich to ash free explosions followed again by a phase of high ash discharge to assess the present paradigm of strombolian behavior in this study we investigate the geophysical signature of these different explosive episodes and compare our results to observations at stromboli volcano italy to this end we characterize yasur s surface activity in terms of material movement temperature and excess pressure the joint temporal trend in these data reveals smooth variations of surface activity and regime like persistence of individual explosion forms over days analysis of all data types shows ash free and ash rich explosive styles similar to those found at stromboli volcano during ash free activity low echo powers high explosion velocities and high temperatures result from the movement of isolated hot ballistic clasts in contrast ash rich episodes exhibit high echo powers low explosion velocities and low temperatures linked to the presence of colder ash rich plumes furthermore ash free explosions cause high excess pressure signals exhibiting high frequencies opposed to low amplitude low frequency signals accompanying ash rich activity to corroborate these findings we compare fifteen representative explosions of each explosive episode explosion onset velocities derived from doppler radar and infrared camera data are in excellent agreement and consistent with overall observations in each regime examination of infrasound recordings likewise confirms our observations although a weak coupling between explosion velocity and excess pressure indicates changes in wave propagation the overall trend in explosion velocity and excess pressure however demonstrates a general correlation between explosive style and explosion intensity and points to stability of the uppermost conduit on timescales shorter than at stromboli volcano

formation of the mid fifteenth century kuwae caldera vanuatu by an initial hydroclastic and subsequent ignimbritic eruption in the mid fifteenth century one of the largest eruptions of the last 10 000 years occurred in the central new hebrides arc forming the kuwae caldera 12x6 km this eruption followed a late maar phase in the pre caldera edifice responsible for a series of alternating hydromagmatic deposits and airfall lapilli layers tuffs related to caldera formation 120 m of deposits on a composite section from the caldera wall were emitted during two main ignimbritic phases associated with two additional hydromagmatic episodes the lower hydromagmatic tuffs from the precaldera maar phase are mainly basaltic andesite in composition but clasts show compositions ranging from 48 to 60 sio2 the unwelded and welded ashflow deposits from the ignimbritic phases and the associated intermediate and upper hydromagmatic deposits also show a wide compositional range 60 73 sio2 but are dominantly dacitic this broad compositional range is thought to be due to crystal fractionation the striking evolution from one eruptive style hydromagmatic to the other magmatic with emission of a large volume of ignimbrites which occurred either over the tuff series as a whole or at the beginning of each ignimbritic phase is the most impressive characteristic of the caldera forming event this strongly suggests triggering of the main eruptive phases by magma water interaction a three step model of caldera formation is presented 1 moderate hydromagmatic sequences hd 1 4 and magmatic fallout deposits activity from a central vent probably over a period of months or years affected an area slightly wider than the present caldera at the end of this stage intense seismic activity and extrusion of differentiated magma outside the caldera area occurred 2 unhomogenized dacite was released during a hydromagmatic episode hd 5 this was immediately followed by two major pyroclastic flows pfd 1 and 2 the vents spread and intense magma water interaction at the beginning of this stage decreased rapidly as magma discharge increased subsequent collapse of the caldera probably commenced in the southeastern sector of the caldera 3 dacitic welded tuffs were emplaced during a second main phase wfd 1 5 at the beginning of this phase magma water interaction continued producing typical hydromagmatic deposits hd 6 caldera collapse extended to the northern part of the caldera previous c14 dates and records of explosive volcanism in ice from the south pole show that the climactic phase of this event occurred in 1452 a d

carbon and hydrogen isotopic compositions of sterols from riverine and marine sediments the sources marine algae terrestrial c3 and c4 plants of sterols deposited to sediments along a riverine marine transect from ohtsuchi river in iwate prefecture japan to the northwestern pacific ocean were estimated using carbon d 13 c and hydrogen isotopic compositions dd in surface sediments in marine sediments algal sterols such as 24 methylcholesta 5 22 dien 3b ol had d 13 c values of 222 7 6 0 4 and dd values of 2292 6 3 in contrast sterols derived from multiple potential sources such as 24 methylcholest 5 en 3 b ol and 24 ethylcholest5 en 3b ol were gradually enriched in 13 c from riverine 230 7 and 230 5 respectively to marine sediments 222 3 and 224 4 respectively but showed little variation in dd values 2262 6 1 these isotopic signatures suggest that 24 methylcholest 5 en 3b ol and 24 ethylcholest 5 en 3b ol are derived from c3 plants 90 and c4 plants 10 in the riverine sediments and marine algae 30 c3 plants 30 and c4 plants 40 in the open marine sediments thus dual isotopic compositions d 13 c dd of sterols allow determinations of the proportions of three biological sources in which the relative contribution of c3 plants decreases while that of marine algae and c4 plants increases from riverine to marine sediments these results indicate that d 13 c dd signatures of sterols provide a useful tool for interpreting the sources of sedimentary organic matter and for understanding the transport and mixing processes of distinct biological sources in riverine marine environments quantitative assessment of organic matter inputs from marine algae and terrestrial plants to riverine and marine sediments is important for understanding the burial and mixing processes affecting organic matter at continental margins and for estimating marine primary productivity and carbon flux associated with biogeochemical cycles in surface environments marine algae and terrestrial c3 and c4 plants are major primary producers and potential sources for sedimentary organic matter in river dominated coastal environments molecular and isotopic compositions of sedimentary organic materials should reflect both variations in the input of marine algae relative to terrestrial plants and in the proportions of c3 and c4 terrestrial plant inputs many previous studies have estimated the relative contribution between two biological sources marine algae vs terrestrial plants or terrestrial c3 vs c4 plants for sedimentary organic materials from riverine or coastal to marine environments based on biomarker assessments e g laureillard and saliot 1993 mannino and harvey 1999 carbon isotopic compositions of bulk organic carbon e g wada et al 1987 carreira et al 2002 and specific biomarkers including lignin derived com1