posteruptive impacts of pyroclastic deposits from basaltic andesite stratovolcanoes on surface water composition volcanic ash deposition following explosive eruptions can pose significant hazards for water quality human health agriculture and infrastructure functionality many studies have examined how fresh ash deposition may lower the ph of and introduce a range of potentially toxic elements into exposed surface waters however no study has yet determined the effects on water composition as a result of mechanical pyroclast disaggregation and production of new fresh particle surfaces and increasingly fine grained particles such disaggregation could result from natural posteruptive processes such as debris avalanches lahars or fluvial aeolian transport and human activities such as cleanup efforts or mining of pyroclastic deposits the posteruption time scales of pyroclast disaggregation may vary from months in moist tropical or temperate environments to years or decades in arid settings here we show for the first time in experimental studies that mechanical milling of pyroclasts will introduce a range of elements into exposed waters including al which can be toxic at elevated levels and na which increases the electrical conductivity of solutions the ph of leaching solutions also increases by several log units such dramatic changes on the experimental scale may have implications for surface water composition in posteruptive settings necessitating longer term risk assessments for ecosystem health and consideration of the role of pyroclastic deposits in element cycling in volcanically active regions

magmatic processes revealed by textural and compositional trends in merapi dome lavas syn eruptive degassing of volcanoes may lead to syn eruptive crystallization of groundmass phases we have investigated this process using textural and compositional analysis of dome material from merapi volcano central java indonesia samples included dome lavas from the 1986 88 1992 93 1994 and 1995 effusive periods as well as pyroclastic material deposited by the november 1994 dome collapse with total crystallinities commonly in excess of 70 phenocrysts 1 microlites the liquids present in merapi andesites are highly evolved rhyolitic at the time of eruption feldspar microlites in dome rocks consist of plagioclase cores ab63an29or8 surrounded by alkali feldspar rims ab53an5or42 compositional pairs which are not in equilibrium a change in the phase relations of the ternary feldspar system caused by degassing best explains the observed transition in feldspar composition a small proportion of highly vesicular airfall tephra grains from the 1994 collapse have less evolved glass compositions than typical dome material and contain rimless plagioclase microlites suggesting that the 1994 collapse event incorporated less degassed partially liquid magma in addition to fully solidified dome rock as decompression drives volatile exsolution rates of degassing and resultant microlite crystallization may be governed by magma ascent rate microlite crystallinity is nearly identical among the 1995 dome samples an indication that similar microlite growth conditions ph2 o and temperature were achieved throughout this extrusive period however microlite number density varied by more than a factor of four in these samples and generally increased with distance from the vent low vent ward microlite number densities and greater microlite concentrations down flow probably reflect progressively decreasing rates of undercooling at the time of crystal nucleation during extrusion of the 1995 dome comparison between dome extrusion episodes indicates a correlation between lava effusion rate and microlite number density suggesting that extrusion slowed during 1995 crystal textures and compositions in the 1992 93 and 1994 domes share the range exhibited by the 1995 dome suggesting that transitions in crystallization conditions i e rates of undercooling determined by effusion rate are cyclic q 2000 elsevier science b v all rights reserved

the geochemical evolution of clinopyroxene in the roman province a window on decarbonation from wall rocks to magma abstract we present results from magma carbonate interaction experiments designed to shed light on the geochemical evolution of clinopyroxene in the roman province central italy atmospheric pressure experiments were performed at 1140 1160 and 1180 c under nno mh and air oxygen buffering conditions the starting materials were a shoshonite and a phonotephrite doped with different amounts of cao and cao mgo whose stoichiometric proportions reproduced the assimilation by magmas of calcite and dolomite respectively the results show that clinopyroxenes spinels and residual glasses are ubiquitous phases in all run products calcite doped runs crystallize more clinopyroxene than dolomite doped runs at the same conditions this leads to the formation of strong desilicated cao rich melts showing compositions comparable to those of magmatic skarns during magma carbonate interaction the content of fe3 in clinopyroxene increases with increasing fo2 promoting the substitution of al for si in tetrahedral site local charge imbalances are also compensated by the incorporation of highly charged cations such as ti into the crystal lattice according to this cation substitution al ca fe3 ti rich clinopyroxenes of the skarn environment testify to continuous co2 fluxes produced by the thermal decomposition of carbonate wall rocks nevertheless the oxidative capacity of co2 progressively decreases from the skarn shells towards the interior of the magma chamber driving the crystallization of si fe2 mg rich clinopyroxenes

relations among subduction parameters clues to the dynamics of the subduction process are found in the many measurable parameters of modern subduction zones based on a critical appraisal of the geophysical and geological literature 26 parameters are estimated for each of 39 modern subduction zones to isolate causal relationships among these parameters multivariate analysis is applied to this data set this analysis yields empirical quantitative relations that predict strain regime and strike slip faulting in the overriding plate maximum earthquake magnitude benioff zone length slab dip arc trench gap and maximum trench depth excellent correlation is found between length of the benioff zone and the product of convergence rate and age of the downgoing slab this relationship is consistent with the conductive heating model of molnar et al 1979 if the model is modified in one respect the rate of heating of the slab is not constant it is substantially slower during passage of the slab beneath the accretionary prism and overriding plate the structural style in the overriding plate is determined by its stress state though the stress state of overriding plates cannot be quantified one can classify each individual subduction zone into one of seven semiquantitative strain classes that form a continuum from strongly extensional class 1 back arc spreading to strongly compressional class 7 active folding and thrusting this analysis indicates that strain class is probably determined by a linear combination of convergence rate slab age and shallow slab dip interplate coupling controlled by convergence rate and slab age is an important control on strain regime and the primary control on earthquake magnitude arc parallel strike slip faulting is a common feature of convergent margins forming a forearc sliver between the strike slip fault and trench optimum conditions for the development of forearc slivers are oblique convergence a compressional environment and a continental overriding plate the primary factor controlling presence of strike slip faulting is coupling strongly oblique convergence is not required the rate of strike slip faulting is affected by both convergence obliquity and convergence rate maximum trench depth is a response to flexure of the underthrusting plate the amount of flexural deflection at the trench depends on the vertical component of slab pull force which is very sensitive to slab age and shallow slab dip shallow slab dip conforms to the cross sectional shape of the overriding plate which is controlled by width of the accretionary prism and duration of subduction deep slab dip is affected by the mantle trajectory established at shallow depth but may be modified by mantle flow much of the structural complexity of convergent margins is probably attributable to terrane juxtaposition associated with temporal changes in both forearc strike slip faulting and strain regime empirical equations relating subduction parameters can provide both a focus for future theoretical studies and a conceptual and kinematic link between plate tectonics and the geology of subduction zones

the behavior of cu zn and pb during magmatic hydrothermal activity at merapi volcano indonesia abstract understanding the behavior of cu zn and pb in magmatic hydrothermal systems is essential in developing models for the genesis of hydrothermal ore deposits in subduction environments a commonly held view is that the metals originate in magmas of intermediate to felsic composition from which they partition directly into exsolving aqueous fluids in this paper we build on the results of an earlier study in which we showed that fe cu co and ni at merapi volcano indonesia were transferred from a mafic melt to an immiscible sulfide melt and then to a magmatic volatile phase which carried them to the surface here we examine the pathways taken by the volatile phase and the behavior of cu zn and pb in the upper part of the magmatic system beneath merapi volcano based on the composition of a suite of silicate melt inclusions and thermodynamic modeling we show that the mafic melt did not hybridize with the resident felsic melt but instead transferred metals to the latter by exsolving a magmatic volatile phase which dissolved the cu rich sulfide melt and then percolated upwards through the felsic melt enriching it in cu and pb it is this fluid which transported the metals to the surface and potentially also to subsurface environments of ore formation

finite difference calculation of traveltimes in three dimensions the traveltimes of first arriving seismic rays through most velocity structures can be computed rapidly on a three dimensional numerical grid by finite difference extrapolation head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 11 percent are found between the results of this technique and ray tracing for a complex but smooth model this scheme has proven useful for earthquake location and shows promise as an inexpensive well behaved substitute for ray tracing in forward modeling and kirchhoff inversion applications

a re examination of the evidence for a plio pleistocene marine transgression on the chiltern hills iii deposits a petrological re examination of the deposits that wooldridge and linton used as evidence for a plio pleistocene marine transgression on the chiltern hills indicates that many are fluvial and some have been reworked in a periglacial climate however those from little heath and rothamsted hertfordshire and lane end buckinghamshire are confirmed as marine and plio pleistocene subsidence during the pleistocene is suggested by the northeasterly decline in height of the few truly marine deposits

magmatic hydrothermal evolution and devolatilization beneath merapi volcano indonesia abstract at merapi volcano indonesia explosive eruptions lasting several months result from injections of reduced mafic magmas and are interspersed by periods of lava dome growth and collapse quiescent degassing assimilation of wall rock and fractional crystallization lasting a few years silicate melt inclusions and volcanic gases were analyzed to study processes of magmatic volatile exsolution and volcanic degassing during periods of quiescent degassing at merapi volcanic gases were sampled at merapi in 1994 during a phase of quiescent degassing and in 2006 at the end of a dome growth and collapse explosive eruption silicate melt inclusions were collected and analyzed from lavas and scorias for their major element and volatile components solubility relationships between h 2 o and co 2 in melt inclusions demonstrate that melt was being trapped beneath merapi to depths reaching 19 km host amphibole geobarometry indicates crystallization pressures reaching up to 26 km hence there is evidence of deep pooling and crystallization of magma beneath merapi at appreciable depths using a mass balance model of magmatic volatile exsolution we demonstrate that the magma degassing from 19 km to the surface approaches closed system behavior compared to the bulk magmatic volatiles analyzed in melt inclusions volcanic gases had similar amounts of co 2 were enriched in h 2 o and s and depleted in cl and f we thus propose that the magmatic volatile phase was initially exsolved from the magma as a supercritical fluid and that it subsequently exsolved into a h 2 o cl f rich brine and co 2 s rich vapor according to the h 2 o nacl model brine vapor exsolution occurred at 5 km in depth for a 5 wt nacl 900 c to 1000 c fluid although the presence of h 2 s so 2 and co 2 may cause the supercritical fluid to unmix at greater depths magma at shallower depths exsolved a brine and a vapor directly from the melt the volcanic gases at merapi thus represent the vapor fraction of a magmatic volatile phase as brine ponded below the surface we further suggest that carbon dioxide liberated by the magmatic assimilation of limestone as proposed by other studies fluxed the melt thereby promoting co 2 enrichment of the melt and h 2 o degassing finally we propose that merapi volcanic gases are enriched in sulfur compared to the modeled volatile phase composition because deep reduced mafic magma supplies sulfur to the shallow magmatic plumbing system

topographic slope as a proxy for seismic site conditions and amplification we describe a technique to derive first order site condition maps directly from topographic data for calibration we use global 30 arc sec topographic data and v s 30 measurements here v s 30 refers to the average shear velocity down to 30 m aggregated from several studies in the u s as well as in taiwan italy and australia v s 30 values are correlated against topographic slope to develop two sets of parameters for deriving v s 30 one for active tectonic regions where topographic relief is high and one for stable shields where topography is more subdued by taking the gradient of the topography and choosing ranges of slope that maximize the correlation with shallow shear velocity observations we can recover to first order many of the spatially varying features of sitecondition maps developed for california our site condition map for the low relief mississippi embayment also predicts the bulk of the v s 30 observations in that region despite rather low slope ranges we find that maps derived from the slope of the topography is often well correlated with other independently derived regional scale site condition maps but the latter maps vary in quality and continuity and subsequently also in their ability to match observed v s 30 measurements contained therein alternatively the slope based method provides a simple approach to uniform site condition mapping

hydrous basalt limestone interaction at crustal conditions implications for generation of ultracalcic melts and outflux of co 2 at volcanic arcs abstract high degassing rates for some volcanoes typically in continental arcs e g colli albani volcanic district etna vesuvius italy merapi indonesia popocatepetl mexico are thought to be influenced by magma carbonate interaction in the crust in order to constrain the nature of reaction and extent of carbonate breakdown we simulated basalt limestone wall rock interactions at 0 5 1 0 gpa 1100 1200 c using a piston cylinder and equal mass fractions of calcite caco3 and a hydrous 4 wt h2o basalt in a layered geometry contained in aupd capsules all experiments produce melt fluid calcite clinopyroxene plagioclase calcic scapolite spinel with increasing t plagioclase is progressively replaced by scapolite clinopyroxene becomes cats rich and fluid proportion as inferred from vesicle population increases at 1 0 gpa 1200 c our hydrous basalt is superliquidus whereas in the presence of calcite the experiment produces calcite clinopyroxene scapolite melt with the consumption of calcite with increasing t and decreasing p melt on a volatile free basis becomes silica poor 58 1 wt at 1 0 gpa 1100 c to 34 9 wt at 0 5 gpa 1200 c and cao rich 6 7 wt at 1 0 gpa 1100 c to 43 7 wt at 0 5 gpa 1200 c whereas al2o3 drops e g 19 7 at 1100 c to 12 8 wt at 1200 c at 1 0 gpa as clinopyroxene becomes more cats rich high t or low p melt compositions are ultracalcic potentially presenting a new hypothesis for the origin of ultracalcic melt inclusions in arc lava olivines wall rock calcite consumption is observed to increase with increasing t and decreasing p at 0 5 gpa our experiments yield carbonate assimilation from 21 6 to 47 6 between 1100 and 1200 c using measured co2 outflux rates for mts vesuvius merapi etna and popocatepetl over a t variation of 1100 to 1200 c at 0 5 gpa we calculate 6 92 of magmatic input estimates undergo this extent of assimilation suggesting that up to 3 of the current global arc co2 flux may be crustally derived application of the assimilation extent bracketed in this study to the estimated elevated number of carbonate assimilating arc magmatic systems active during the late cretaceous to early paleogene suggests that magma induced upper plate decarbonation alone had the potential to contribute up to 2 7 10 14 5 6 10 15 g y co2 assuming no dilution and complete gaseous release of all assimilated carbon using an estimated assimilation extent averaged from current systems gives a slightly lower though still significant value of 5 5 10 14 g y of excess co2 being released into the atmosphere

the genesis of refractory melts in the formation of oceanic crust refractory primary liquids arising in various oceanic plate tectonic settings are characterized by high mgo sio2 ca na low tio2 and generally low incompatible element abundances relative to primary liquids parental to morb we propose that the former melts segregate from upper mantle peridotite which has earlier been depleted by extraction of picritic melts which were parental to morb a compositional range in the second stage melts is expected depending on the extent of previous depletion of the peridotite the temperature and pressure of melt segregation and the possible influence of volatile phases c h o present during melting

a conceptual model for block and ash flow basal avalanche transport and deposition based on deposit architecture of 1998 and 1994 merapi flows the 1998 block and ash flow baf deposits on the western flanks of merapi were described both immediately following emplacement and after one and two wet seasons of erosion this afforded a unique combination of data on deposit morphology and internal structure from proximal to distal reaches the deposits of the basal avalanches from individual baf events were classified into three major and two minor facies in channelised reaches primarily resulting from effects of channel confinement and slope termination reaches were classified into three facies related to preevent topography the deposit facies architecture was interpreted to understand particle transport and deposition within the framework of granular flow systematics the transport model we propose for these basal avalanches involves unsteady flow conditions generated by pulses of collapse as the source and or by development of kinetic waves during the granular flow the coarsest clasts along with low density material migrated to the wave pulse fronts within these flows whereas in bulk flow grain dispersive pressures and kinetic sieving result in coarsest clasts being buoyed to the flow top with this tendency being greatest on higher slopes greater kinetic energy and with greater flow confinement maximising particle collisions deposition begins as the flow reaches near its full extent an initial pulse or flow wave freezes rapidly from its base upward and its rear forward as it looses kinetic energy and dispersive pressure such that an upper higher energy part of the flow is still able to move downstream over the frozen base later waves or pulses then accrete progressively horizontally upslope banking up onto or overtopping earlier deposited sediment hence the overall flow freezes from its front to its tail at termination reaches in unconfined areas the overflowing upper part of flow gradually deposits from its base upward resulting in a slightly tapering sheet formed deposit marked by a front made up of wood fragments and large boulders on sudden slope breaks in termination areas piling up of sediment occurs in flat reaches producing whaleback type forms as the flows rapidly lost competence one implication of this model is that each kinetic wave or flow pulse crest developed within the basal avalanche represents a portion of greater flow depth or stage height hence development of these crests control the ability of parts of the basal avalanche to escape from confined channels and generate unexpected hazards

origin of high silica liquids at stromboli volcano aeolian islands italy inferred from crustal xenoliths high silica igneous xenoliths granophyre and obsidian fragments with sio2 ca 75 wt and high silica glass sio2 between ca 64 and 75 wt within glass bearing tonalitic and dioritic xenoliths have been discovered at stromboli they are well beyond the silica range of the volcanic rocks erupted during the subaerial activity of the volcano the granophyre and the obsidian fragments occur within the petrazza pyroclastics high k andesite pumiceous scoriae of the paleostromboli i period 61 ka whereas the glass bearing tonalites and diorites are hosted in the omo basaltic andesite lava flows of the paleostromboli ii period 64 55 ka the obsidian represents an extremely evolved liquid derived from low pressure fractional crystallization of high k calc alkaline magmas of stromboli coupled with minor assimilation of upper crust or terrigenous sediments the other studied high silica products have an anatectic origin the granophyre composition is compatible with a genesis by low degree melting of leucotonalites similar to some calabrian arc lithotypes partial melting of crustal rocks from the stromboli basement is also demonstrated by interstitial glass in the tonalite and diorite xenoliths textural evidence and the presence of variable glass compositions suggest that in these plutonic xenoliths the melt chemistry was controlled by dehydration melting of biotite and non modal melting of local mineralogy high degree undercooling of granophyre melt and of the partially melted xenoliths is consistent with rapid rise of the host magmas leading to eruption whether partial melting was initiated during stoping and transport of xenoliths within the rising magma or in situ during magma storage within the crust has not been unequivocally established

carbonate assimilation at merapi volcano java indonesia insights from crystal isotope stratigraphy recent basaltic andesite lavas from merapi volcano contain abundant complexly zoned plagioclase phenocrysts analysed here for their petrographic textures major element composition and sr isotope composition anorthite an content in individual crystals can vary by as much as 55 mol an

sr isotope disequilibrium in columbia river flood basalts evidence for rapid shallow level open system processes geochemical variability among columbia river basalt group flood lavas has been attributed to two different origins derivation from heterogeneous mantle and modification of mantle derived magmas by open system processes involving continental crust we present in situ analyses of sr isotopes from core to rim transects of plagioclase phenocrysts and groundmass from each major columbia river basalt group formation and show that plagioclase crystals are usually internally zoned in 87 sr 86 sr and are in 87 sr 86 sr disequilibrium with their host groundmass these data unequivocally demonstrate that columbia river basalt magmas regardless of the nature of mantle sources were modified by opensystem processes operating at crustal depths one dimensional diffusion modeling indicates that observed isotopic heterogeneities cannot have existed at magmatic temperatures for more than a few years or decades in general results indicate that these flood basalt magmas were erupted while still in the process of assembly a typical columbia river flood basalt magma melt plus phenocrysts therefore only attains its final geochemical identity just before or during eruption a fact that is generally obscured when evaluating conventional whole rock isotope analyses

mechanical erosion of xenoliths by magmatic shear flow 1 we focus on the role of mechanical erosion by magmatic shear flow in the formation of xenoliths occurring in lava flows the process is analyzed by combining the physics of fragmentation and erosion to the concept of rock mass the conditions for the country rock fragmentation are analyzed as a function of the magma viscosity strain rate and tensile strength of the rock mass in reservoirs mechanical processes play a subordinate role and thermal erosion processes prevail in conduits intermediate and silicic magmas may erode and eventually fragment good to poor quality country rock masses basalts may erode poor quality country rocks a crystal rich magma has more chance to break up the conduit walls with respect to a vesiculated melt the variety of xenoliths of a lava reflects a set of wall rocks with similar mechanical properties and may not mirror the stratigraphy of the substratum of a volcanic area

pseudotachylite on impact marks of block surfaces in block and ash flows at merapi volcano central java indonesia surfaces of meter sized blocks in the 1998 block and ash flow deposits of merapi volcano are partially covered by centimeter sized randomly orientated impact marks which consist of an outer glassy pseudotachylite underlain by a cataclastic layer whole rock pseudotachylite melt inclusion in plagioclase and host rock groundmass compositions indicate that the pseudotachylite was generated by remelting of bulk rock on block impact the occurrence and distribution of this new type of collision related pseudotachylite on volcanic block surfaces demonstrate that blocks were transported by chaotic rotation saltation and tumbling the random orientation of impact marks suggests grain flow as the dominant process rather than any other currently discussed pyroclastic flow mechanism in addition the chaotic orientation of striations is interpreted as reflecting momentum transfer having been dominated by short lived intergranular collisions the blocks have apparently been transported in the collisional regime of grain flow

passive infrared remote sensing evidence for large intermittent co2 emissions at popocatepetl volcano mexico abstract passive infrared ftir and correlation spectrometer cospec measurements were conducted at popocatepetl volcano during february 10 to 26 1998 from sites 4 to 17 km distant from the summit volcano behavior was relatively quiet and so 2 flux averaged 1670 1420 t day 51 measurements relatively small for popocatepetl concurrent hcl so 2 and hf so 2 ratios were 0 17 0 01 and 0 031 0 003 respectively about the same as ratios measured from 1994 to 1997 the amount of co 2 in the volcanic plume was quantified using fascode in which atmospheric co 2 is numerically subtracted from the total infrared spectrum to obtain the residual magmatic co 2 surprisingly co 2 so 2 mass ratios rose dramatically to values as high as 140 about 30 times higher than typical values of 2 to 8 measured from 1994 to 1996 these excursions in high co 2 so 2 ratios were short lived lasting no longer than about 0 5 to 3 0 h but co 2 flux occasionally exceeded 100 000 t day we estimate that the average co 2 so 2 ratio for the period was about 23 yielding an average co 2 flux of roughly 38 000 t day chemical and petrographic analyses of lava and pumice erupted during explosions on june 30 1997 and january 1 1998 show conclusively that popocatepetl produces mixed products formed by injection of mafic magma into a more silicic chamber at temperatures and pressures of roughly 1040 c and 5 kbar in addition popocatepetl eruptive products include xenoliths of metamorphosed carbonate rocks containing wollastonite and other calc silicate minerals indicating reaction of magma with cretaceous limestone underlying the volcano using a normal co 2 so 2 ratio of 4 for reference we calculate an average excess co 2 production of 32 000 t day for 17 days this would require assimilation of only 5 10 4 km 3 of limestone an amount easily accessible in the 3 km thick cretaceous section beneath the volcano we also examine two scenarios in which excess co 2 is produced by degassing of subjacent basalt magma but these explanations seem less plausible to us because many other volcanoes are underlain by carbonate sequences short duration bursts of co 2 flux and increased co 2 so 2 ratio might be observed at other sites if simultaneous real time measurements of major gas species are made

inter and intracrystalline isotopic disequilibria techniques and applications in the last 20 years we have seen a significant expansion of techniques related to geochemical and isotopic microsampling of materials in the earth sciences from constraining pre eruptive histories of flood basalt magmas to identifying the natal rivers of origin of anadromous fishes these techniques have had significant impacts in a wide variety of scientific fields nowhere has the impact been greater than in identifying the sources processes and timing of processes involved in igneous magmatic systems both technique refinements and the development of new technologies have aided in advancing microsampling applications thus allowing for a better understanding of the sources and mechanisms responsible for changing geochemical and isotopic signatures in natural systems in this chapter we focus on the techniques and technologies associated with radiogenic isotope microsampling and review applications of these techniques as utilized in scientific investigations isotope microsamping is a logical extension of earlier studies that evaluated individual components of magmas and magma systems including melts and minerals from the use of petrographic microscopes and the later introduction of the electron microprobe the focus on internal chemical variations in melts and minerals is critical to assessing the petrogenetic histories of igneous rocks even today these technologies are used to ensure that further trace element and isotopic analyses are undertaken in a textural and major element context for trace elements and isotopes early studies e g cortini and van calsteren 1985 confirmed variations in the melt and mineral components of many igneous rocks but focused on mineral or glass separates potential information associated with isotopic variations retained by individual crystals or internal variations within individual crystals was lost later studies such as geist et al 1988 focused on isotope variations within single megacrysts to constrain mixing scenarios between basaltic andesitic and rhyolitic magmas and davidson et al 1990 used

joint inversion of active and passive seismic data in central java seismic and volcanic activities in central java indonesia the area of interest of this study are directly or indirectly related to the subduction of the indo australian plate in the framework of the merapi amphibious experiments meramex a network consisting of about 130 seismographic stations was installed onshore and offshore in central java and operated for more than 150 days in addition 3 d active seismic experiments were carried out offshore in this paper we present the results of processing combined active and passive seismic data which contain traveltimes from 292 local earthquakes and additional airgun shots along three offshore profiles the inversion was performed using the updated lotos 06 code that allows processing for active and passive source data the joint inversion of the active and passive data set considerably improves the resolution of the upper crust especially in the offshore area in comparison to only passive data the inversion results are verified using a series of synthetic tests the resulting images showan exceptionally strong low velocity anomaly 30 per cent in the backarc crust northward of the active volcanoes in the upper mantle beneath the volcanoes we observe a low velocity anomaly inclined towards the slab which probably reflects the paths of fluids and partially melted materials in the mantle wedge the crust in the forearc appears to be strongly heterogeneous the onshore part consists of two high velocity blocks separated by a narrow low velocity anomaly which can be interpreted as a weakened contact zone between two rigid crustal bodies the recent java mw 6 3 earthquake 2006 05 26 utc occurred at the lower edge of this zone its focal strike slip mechanism is consistent with the orientation of this contact

collection and three dimensional modeling of gps and tilt data at merapi volcano java we study here the deformations associated with the november 1996 to march 1997 eruption period at mount merapi central java one of the most active volcanoes in indonesia this activity period includes a vertical explosion on january 17 and an increase of the lava dome volume by about 3 106 m3 two global positioning system gps campaigns have been carried out on a six benchmark network at the beginning and at the end of the period relative displacements with respect to the reference point show an average subsidence of 6 5 cm a multicomponent tilt station installed on the southeast flank 3 km from the summit recorded a tilt of 11 1 0 7 rad in the tangential direction and 0 9 0 4 rad in the radial direction these data are interpreted using a three dimensional 3 d elastic model based on the mixed boundary element method and a near neighbor monte carlo inversion interpretation of tilt data requires an accurate mesh for discretizing the 3 d topography the final result supports a horizontal elliptic magma source located 8 5 0 4 km below the summit and 2 0 4 km to the east of it in particular the data cannot be consistent with the location of a magma chamber determined from seismic activity analysis i e 2 km below the summit the computed depth depends strongly on the source shape and cannot be constrained properly because of the small amount of data the computed deflation of 11 2 106 m3 is about 3 times larger than the observed increase in the lava dome volume this difference is attributed to rock avalanches and pyroclastic flows on the flanks of the volcano

the 1984 nuee ardente deposits of merapi volcano central java indonesia stratigraphy textural characteristics and transport mechanisms for many centuries merapi volcano has generated hot avalanches of blocks lapilli and ashes derived from the destruction of partially solidified viscous lava domes merapi type nuees ardentes on 15 june 1984 at least four nuees ardentes came down the southwest slope of the merapi the first and the last being responsible for more than 99 of the deposits which are now exposed the first nuee ardente a merapi type nuee ardente was produced by the destruction of the dome travelled 7 km from the crater leaving a measured deposit 2 7 m thick 4 km from the crater near its upper depositional limit regularly increasing to a maximum measured thickness of 12 m at the front of the deposit the lower contact is sharp non erosive with pines still rooted in the underlying paleosol the deposit consists of 50 ash 33 lapilli and 17 blocks with two subpopulations one rosin and one normal and is finespoor with less than 4 of fine ash d finer than 4 the deposit displays reverse population grading of both vesiculated and massive clasts and of the maximum grain size the maximum size significantly increases regularly down current over most of the exposed length of unit 1 and bed thickness increases for the entire length of the deposit the deposit of the second nuee ardente is only 6 21 cm thick and of very limited lateral extent it is a normally graded coarse to fine ash with a finespoor base the third unit consists of fines poor normally graded coarse ash exposed in low amplitude 20 40 cm 12 m wavelength dunes the deposit of the fourth nuee ardente rests in sharp erosive contact on the underlying unit increasing in thickness down flow it consists of transitional coarse and fine grained strata 6 130 c cm thick dipping 5 10 down flow the deposit made up of two subpopulations one rosin and one normal is normally graded over the entire bed but coarsegrained strata are reversely graded the relative content of vesiculated clasts increases up bed in both strata types from 12 at the base to 40 at the top the characteristics of unit 1 suggest that it accumulated from a concentrated suspension of cohesionless solids exhibiting non newtonian behavior where dispersive pressure played an important role in the suspension of the clasts units 2 and 3 were probably deposited from dilute turbulent suspensions whereas the upper unit 4 is a classic example of deposition from a high density turbulent suspension leading to the formation of multiple traction carpets driven by the overlying lower density surge the horizontal distance travelled by a hot rock avalanche may be influenced by its transport mechanism debris flows are mobile on very low slopes as low as 1 whereas grain flows even density modified grain flows require relatively high slopes more than 6 at merapi to maintain their mobility if the present merapi dome were to collapse and produce a debris flow its present volume coupled with the minimal 1 5 km vertical drop could travel a distance ranging between 15 and 30 km however if transport were by grain flow mechanisms the mass could come to rest as it reaches a 5 10 slope

magma recharge processes of the yandangshan volcanic plutonic caldera complex in the coastal se china constraint from inter grain variation of sr isotope of plagioclase abstract in situ sr isotope of plagioclase can be used to elucidate the details of magmatic processes here we report in situ sr isotopic compositions of plagioclase from the intra caldera porphyritic quartz syenite and mafic microgranular enclave of the yandangshan caldera se china plagioclase phenocrysts from porphyritic quartz syenite show consistent initial 87sr 86sr ratios 0 7088 0 7091 plagioclases in groundmass of mafic microgranular enclave have low initial 87sr 86sr ratios 0 7080 0 7081 in contrast the plagioclase phenocrysts of mafic microgranular enclave show relatively variable initial 87sr 86sr ratios of 0 7081 0 7088 which exhibit distinct inter grain variation with high values similar to the plagioclase phenocrysts in porphyritic quartz syenite and low values similar to the plagioclase in groundmass however the initial 87sr 86sr ratios of individual plagioclases from phenocrysts and groundmass show insignificant intra grain variation furthermore initial 87sr 86sr ratios 0 7080 0 7088 of plagioclase from phenocrysts and groundmass of mafic microgranular enclave are within and lower than the whole rock initial 87sr 86sr ratios 0 7082 0 7088 while the values of plagioclase phenocrysts from the porphyritic quartz syenite are within and higher than the whole rock initial 87sr 86sr ratios 0 7086 0 7089 therefore we propose that the inter grain sr isotope variation of plagioclase is related to magma recharge events which induce chemical and physical exchanges between the recharge magma and the host magma and the remobilization of crystal mush in magma reservoir furthermore our study shows that whole rock sr isotopic compositions could not represent the end members and they may be a result of the assemblage of rock forming minerals such as plagioclase with different initial sr isotopic ratios

finite difference calculation of travel times the travel times of the first arriving seismic waves through any velocity structure can be rapidly computed on a two or three dimensional numerical grid by finite difference extrapolation from point to point wavefronts rather than the traditional rays are tracked head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 03 per cent are found between the results of this technique and raytracing for a complex two dimensional model this scheme is useful for the windowing of finite difference calculations to increase computing speed and promises to aid in earthquake location tomographic inversion and kirchhoff migration in structures that have strong lateral velocity gradients

crustal differentiation processes at krakatau volcano indonesia anak krakatau is a basaltic andesite cone that has grown following the famous caldera forming 1883 eruption of krakatau it breached sea level in 1927 and since the 1950s has been growing at an average rate of similar to 8 cm a week we present new major and trace element data combined with whole rock delta o 18 sr and nd isotope data for 1883 1993 and 2002 krakatau eruptive products and the surrounding crust bombs erupted from anak krakatau during 2002 contain frothy metasedimentary and plutonic xenoliths that show variable degrees of thermal metamorphism plastic deformation and partial melting contact metamorphic minerals such as cordierite and tridymite in metasedimentary xenoliths are consistent with high temperature metamorphism and incorporation at mid to upper crustal depth energy constrained assimilation and fractional crystallization modelling of whole rock data suggests that the anak krakatau magmas have a genetic relationship with the 1883 eruption products the geochemical impact of crustal contaminants on whole rock compositions is apparently small and we conclude that low levels of assimilation of a quartzo feldspathic sediment are recorded in anak krakatau magmas plagioclase phenocrysts from the 2002 eruption exhibit disequilibrium textures and complex compositional zoning however and are also isotopically variable with a total range in sr 87 sr 86 of 0 center dot 7043 0 center dot 7048 as determined by in situ laser ablation inductively coupled plasma mass spectrometry this suggests that although shallow crustal assimilation appears to have had a limited effect on whole rock chemistry a complex late stage differentiation history is recorded within the magma s cargo of crystals and xenoliths

using p s amplitude ratios for seismic discrimination at local distances we used a dense seismic network to test the p s amplitude ratio discriminant for earthquakes and explosions at distances from 20 to 200 km in a complex tectonic setting we used data from several hundred seismic stations in northern wyoming to observe 22 earthquakes 37 mining blasts and 24 borehole shots and compared their p s amplitude ratios frequencies of 6 8 hz and above achieved the best discrimination results for single shot borehole explosions whereas 6 8 and 8 10 hz passbands were best for mining blasts the p s method appears valid for 50 200 km but fails at distances 50 km geologic heterogeneities and path effects have a large effect on amplitude measurements even after magnitude and distance amplitude corrections are applied geologic boundaries between source and receiver that cause sharp lateral discontinuities in seismic velocity can alter the measured p s ratio to the point that an event could be misidentified the source geology is a factor as well with noticeable amplitude differences between shots in bedrock and shots in sediment we tested the discrimination performance of the average log p s values of a network of seismometers which should reduce the discrimination errors caused by these heterogeneities relative to a single station by bootstrapping the single station measurements over varying sample sizes we found that averaging three or four stations achieved significantly better discrimination than just one or two stations finally we corrected the signal amplitude to remove prephase noise to improve p s discrimination results this shows promise for improving event discrimination with only simple corrections online material table of event information and figure showing waveforms overlaid with amplitude windows

high temperature contact metamorphism of calc silicate xenoliths in the kiglapait intrusion labrador calc silicate xenoliths occur as part of a xenolith and autolith swarm in the lower zone of the kiglapait intrusion labrador all xenoliths are lighter colored than the local troctolite host rock and are surrounded by a 1 2 cm thick reaction zone of clinopyroxenite the typical mineral assemblage in calc silicate xenoliths is diopside forsterite monticellite spinel and one also contains akermanite reaction zones are dominated by diopside and spinel all clinopyroxene compositions are fassaitic with high concentrations of al 2 o 3 4 12 wt tio 2 1 4 wt and calculated fe 2 o 3 fe 3 fe 2 in addition clinopyroxene grains locally display extreme zoning in si al ti and x mg akermanite contains up to 1 5 wt na 2 o textures in the xenoliths are complex with most containing highly irregular intergrowths of diopside forsterite and monticellite akermanite and forsterite are separated locally by a coarse symplectic intergrowth of diopside and monticellite which resulted from a retrograde reaction the dominant assemblage probably represents the production of monticellite from calcite clinopyroxene forsterite until calcite was consumed these reactions require metamorphic temperatures of 900 c and pressures 0 4 kbar such that the xenoliths were probably derived from the roof of the magma chamber whole rock compositions reflect either substantial chemical exchange with the kiglapait magma or a very impure dolomitic protolith the clinopyroxenite reaction zones were produced primarily by assimilation of carbonate by the kiglapait magma in combination with the effects of magma undercooling near the xenoliths

magma chambers emplaced in carbonate substrate petrogenesis of skarn and cumulate rocks and implications for co2 degassing in volcanic areas crystal rich lithic clasts occurring in volcanic deposits are key tools to understand processes of storage cooling and fractionation of magmas in pre eruptive volcanic systems these clasts represent snapshots of the magma chamber host rock interface before eruption and provide information on crystallization differentiation and degrees of interaction between magma and wall rock in this study we have focused on the petrology of clasts of cumulate and skarn rocks from the colli albani volcanic district with the aim of shedding light on magma carbonate interaction and co2 emission in volcanic areas by means of phase relations bulk rock chemistry mineral compositions and isotope data we have identified different types of cumulates and skarns cumulates containing either clinopyrox

broadband rayleigh wave dispersion curve and shear wave velocity structure for yucca flat nevada the geology near a seismic source has a major effect on seismic waves recorded at distance this can be especially true in the case of man made explosions due to increased geologic heterogeneity at shallow depths and interactions with the free surface yucca flat yf a sedimentary basin on the nevada national security site has hosted hundreds of well recorded underground nuclear tests as such it should be an ideal natural laboratory for the study of shallow explosions unfortunately basin wide models of such important physical properties as compressive and shear wave velocity are not available with sufficient fidelity to maximize the potential of the studies we attempt to remedy this situation by creating a new shear wave velocity model of yf this model was generated by inverting rayleigh wave phase velocity dispersion measurements because no single dataset provided a dispersion curve of the necessary frequency bandwidth for shallow intermediate and deep basin depths simultaneously we combined three dispersion curves with complementary bandwidths from three data sources the datasets in order of low frequency to high were 1 underground nuclear tests at yf recorded on regional seismic networks 0 14 0 4 hz 2 a multimode spatially averaged coherency microtremor array located on yf 0 2 20 hz and 3 several refraction microtremor remi linear arrays also on yf 2 5 50 hz compared to previous work our model is characterized by slower velocities the known geologic boundaries such as the depth of the basin and water table are prominent at reasonable locations

an evolving magma chamber within extending lithosphere an integrated geochemical isotopic and zircon u pb geochronological study of the gushan granite eastern north china craton the gushan granite located in the jiaobei terrane of the eastern north china craton carries mafic micro granular enclaves mmes and zoned k feldspar phenocrysts and is a typical example of magma gener ation and evolution in an extensional setting here we present whole rock major and trace element geochemistry sr nd isotopes and zircon u pb and hf isotope data on the granite and its enclaves the granite was emplaced at 120 ma it is high in sio2 k 2 o n a 2o lile and lree but low in mgo and hfse the granite are also marked by high initial 87 sr 86 sr 0 7103 and low end t 18 5 to 18 9 and zircon ehf t 16 6 to 22 0 values these features indicate that the host granite was mainly derived from ancient north china craton lower crust field petrographic and compositional studies indicate that mmes are products of mafic felsic magma interactions in the generation of the granite in the relatively late magmatic history available data suggest that enriched lithospheric mantle was a suitable candidate for the mafic magma end member involved in the magma interaction process internal sr nd isotopic variations within k feldspar phenocrysts are also evaluated to decipher the magmatic history in spite of a protracted cooling history and evidence of subsolidus alteration the k feldspar phenocrysts preserve marked primary sr nd isotopic variations initial 87 sr 86 sr ratios increase from the cores 0 7100 0 7102 to rims 0 7105 0 7110 whereas end t values show decrease from the cores 17 7 to 20 5 to rims 21 1 to 27 0 the overall isotopic profiles across the k feldspar phenocrysts are consistent with a continuous magma contamination process highly negative nd isotopic values of some k feldspar rims suggest that the precambrian basement rocks in the upper crust are potential candidates for the contam inant these results indicate that isotopic heterogeneity could be preserved within single crystal from much older slower cooled plutonic rocks and those isotopically zoned minerals are effective recorders of open magma system based on petrographic geochemical and isotopic studies we envisage multiple magmatic pulses mafic felsic magma interaction and continuous assimilation during the formation of the gushan granite a model involving lithospheric thinning and mantle crust interaction in an exten sional setting is proposed to account for the generation of the gushan granite and its enclaves

the ion microprobe as a tool for obtaining strontium isotopes in magmatic plagioclase a case study at okataina volcanic centre new zealand abstract we investigated the potential of multi collector secondary ion mass spectrometry mc sims as a tool for obtaining sr isotopic compositions in plagioclase a ubiquitous mineral in igneous rocks that serves as a recorder of crystallization history mc sims allows for high spatial resolution analysis 12 m in this study of isotopes and therefore improves the temporal scale at which fluctuations in crystallization conditions can be recognized ultimately improving our understanding of rates of magmatic processes plagioclase crystals from two young rhyolitic deposits from two major eruptive complexes tarawera and haroharo of the okataina volcanic centre in new zealand were analysed results were corrected for matrix effects using linear modelling of mc sims data versus an contents as well as 87sr 86sr ratios acquired via laser ablation inductively coupled plasma mass spectrometry la mc icp ms corrected mc sims sr isotopic ratios had an average 2 uncertainty of 0 0008 per spot and were homogeneous in okataina plagioclase at high spatial resolutions average la mc icp ms 87sr 86sr ratios of plagioclase from both intra caldera volcanic complexes tarawera 87sr 86sr 0 7056 and haroharo 87sr 86sr 0 7054 suggest similar magma sources and similar assimilation and fractional crystallization processes for the two complexes overall homogeneity of plagioclase excluding relict cores indicates no significant changes in contributions i e crustal assimilation mafic influx to the system during the majority of plagioclase crystal growth furthermore lack of 87sr 86sr ratio fluctuations in plagioclase rims suggest interaction between the resident silicic magma and the intruding mafic magma that triggered the eruptions was largely limited to volatile and heat transfer using appropriate standards and analysis this mc sims method can be used to detect short lived open system events in magma reservoirs where differences in 87sr 86sr isotopic ratios are significant

the origin of k feldspar megacrysts hosted in alkaline potassic rocks from central italy a track for low pressure processes in mafic magmas abstract in situ sr isotope and microchemical studies were used to determine the provenance of k feldspar megacrysts hosted in mafic alkaline potassic ultrapotassic rocks and in differentiated rocks from two nearby volcanic apparatus in central italy at monte cimino volcanic complex mafic leucite free ultrapotassic megacryst bearing rocks of olivine latitic composition are associated with evolved latite and trachyte here latites and trachytes straddle the sub alkaline field age corrected 87sr 86sr values sri of the analysed cimino olivine latites vary from 0 71330 and 0 71578 and strongly increase at constant mg value latite and trachyte have lower sri than olivine latites ranging between 0 71331 and 0 71361 sri of k feldspar megacrysts from olivine latites are between 0 71352 and 0 71397 but core and rim 87sr 86sr ratios within individual megacryst are indistinguishable in all the mafic rocks the megacrysts are not in isotopic equilibrium with the hosts k feldspar megacrysts from both the latite and trachyte have similar sr isotope compositions sri 0 71357 0 71401 to those in the olivine latites however sri of megacryst in the trachyte vary significantly from core to rim sri from 0 71401 to 0 71383 as with the olivine latites the k feldspar megacrysts are not in isotopic equilibrium with bulk rock compositions of the latite or trachyte at vico volcano megacryst bearing rocks are mafic leucite free potassic rocks mafic leucite bearing ultrapotassic rocks and old trachytic rocks the mafic leucite bearing and leucite free rocks are a tephri phonolite and an olivine latite respectively a megacryst in vico trachyte is isotopically homogeneous sri core 0 71129 rim 0 71128 and in equilibrium with the host rock sri bulk rock 0 71125 sri of megacryst from tephri phonolite is clearly not in isotopic equilibrium with its host sri bulk rock 0 71158 and it increases from core sri 0 71063 to rim sri 0 71077 a megacryst in vico olivine latite is isotopically homogeneous sri core 0 71066 rim 0 71065 but not in equilibrium with the host rock sri bulk rock 0 71013 the sr isotope microdrilling technique reveals that cimino megacrysts were crystallised in a cimino trachytic magma and were subsequently incorporated by mixing mingling processes in the latitic and olivine latitic melts a model invoking the presence of a mafic sub alkaline magma which was mixed with the olivine latite is proposed to justify the lack of simple geochemical mixing relation between cimino trachytes and olivine latites this magmatological model is able to explain the geochemical characteristics of cimino olivine latites otherwise ascribed to mantle heterogeneity the similarity of core sri of megacrysts hosted in vico tephri phonolite and olivine latite suggests that the k feldspar megacrysts are co genetic isotopic equilibrium between megacryst and vico host trachyte indicates that the trachyte is the parent of this megacryst on the contrary the megacrysts hosted in tephri phonolite and olivine latite do not derive from the old trachytic magma because no diffusion process may explain the core to rim sr isotope increase of the xenocryst hosted in the tephri phonolite the megacrysts hosted in the vico mafic rocks might derive from a trachytic melt similar in composition to the old vico trachytes

the nevados de payachata volcanic region 18 s 69 w n chile subduction related volcanism in the nevados de payachata region of the central andes at 18 s comprises two temporally and geochemically distinct phases an older period of magmatism is represented by glaciated stratocones and ignimbrite sheets of late miocene age the pleistocene to recent phase 0 3 ma includes the twin stratovolcanoes volcan pomerape and volcan parinacota the nevados de payachata volcanic group and two small centers to the west i e caquena and vilacollo both stratovolcanoes consist of an older dome and flow series capped by an andesitic cone the younger cone i e v parinacota suffered a postglacial cone collapse producing a widespread debris avalanche deposit subsequently the cone reformed during a brief second volcanic episode a number of small relatively mafic satellitic cinder cones and associated flows were produced during the most recent activity at v parinacota at the older cone i e v pomerape an early dome sequence with an overlying isolated mafic spatter cone and the cone forming andesitic dacitic phase mostly flows have been recognized the two nevados de payachata stratovolcanoes display continuous major and trace element trends from high k2o basaltic andesites through rhyolites 53 76 sio2 that are well defined and distinct from those of the older volcanic centers petrography chemical composition and eruptive styles at v parinacota differ between pre and post debris avalanche lavas precollapse flows have abundant amphibole at sio2 59 wt and lower mg numbers than postcollapse lavas which are generally less silicic and more restricted in composition compositional variations indicate that the magmas of the nevados de payachata volcanic group evolved through a combination of fractional crystallization crustal assimilation and intratrend magma mixing isotope compositions exhibit only minor variations pb isotope ratios are relatively low 206pb 204pb 17 95 18 20 and208pb 204pb 38 2 38 5 87sr 86sr ratios range 0 70612 0 70707 143nd 144nd ratios range 0 51238 0 51230 and 18osmow values range from 6 8 o to 7 6 o smow a comparison with other central volcanic zone centers shows that the nevados de payachata magmas are unusually rich in ba up to 1800 ppm and sr up to 1700 ppm and thus represent an unusual chemical signature in the andean arc these chemical and isotope variations suggest a complex petrogenetic evolution involving at least three distinct components primary mantle derived melts which are similar to those generated by subduction processes throughout the andean arc are modified by deep crustal interactions to produce magmas that are parental to those erupted at the surface these magmas subsequently evolve at shallower levels through assimilation crystallization processes involving upper crust and intratrend magma mixing which in both cases were restricted to end members of low isotopic contrast

temporal variation of mineralogy and petrology in cognate gabbroic enclaves at arenal volcano costa rica gabbroic enclaves ejected during the current eruption phase a 1 and during the latest prehistoric eruption phase a 2 of arenal volcano show systematic variations in texture mineralogy and composition as a function of host rock chemistry and timing of eruption the most differentiated enclaves occur in the more differentiated a 2 lavas enclaves in the a 1 volcanics are consistently less evolved within the current a 1 eruption the most mafic enclaves are amphibole bearing rocks that were erupted during the first 2 3 years of activity 1968 1970 these enclaves occur in the most differentiated a 1 volcanics and are not in equilibrium with their host rocks they crystallized from a hydrous melt that was slightly more mafic than anything erupted during the current cycle we interpret the enclaves as sidewall crystallization products of a melt possibly a high alumina basalt that was immediately parental to the a 1 lavas enclaves that occur in a 1 rocks erupted after 1970 and all of the a 2 enclaves are amphibole free and less mafic than the early a 1 enclaves their chemistry suggests that they formed during the early to intermediate crystallization of their host lavas none of the enclaves contain minerals that might have equilibrated with a primary mantle derived melt geothermometry is consistent with geochemistry with amphibole bearing a 1 enclaves yielding the highest pyroxene temperatures ave 1090 c and a 2 enclaves the lowest ave 1030 c geobarometry suggests mid to upper crustal depths for the crystallization of all enclaves the enclaves are cognate and reflect pre eruptive crystallization of arenal magmas they record evolution from a hydrous basaltic magma to the drier basaltic andesites that characterize the current eruption volatiles appear to have been lost due to depressurization during the slow ascent of the magmas through the upper levels of the crust following the initial explosive eruption volatile loss and depressurization resulted in the destabilization and the progressive resorption of amphibole the a 2 lavas may represent the long term fractionation products of basaltic andesite magmas similar in composition to the a 1 lavas anorthitic plagioclase commonly thought of as a phase stabilized by high ca na and high water pressure continued to crystallize in a system with relatively low ca na and which had dehydrated and or depressurized to the point at which amphibole was no longer stable this suggests that compositional characteristics other than high ca na or high water content may have stabilized the anorthite in the basaltic and basaltic andesite melts at arenal we speculate that the high alumina content of the arenal magmas may be the stabilizing factor

historical eruptions of merapi volcano central java indonesia 1768 1998 abstract information on merapi eruptive activity is scattered and much is remotely located a concise and well documented summary of this activity has been long needed to assist researchers and hazard mitigation efforts and the aim of this paper is to synthesize information from the mid 1700s to the present a descriptive chronology is given with an abbreviated chronology in a table that summarizes events by year assigns preliminary volcanic explosivity index vei ratings and hartmann classifications and provides key references the history of volcano monitoring is also outlined the study reveals that a major difference in eruption style exists between the twentieth and nineteenth centuries although the periodicity between larger events seems about the same during the twentieth century activity has comprised mainly the effusive growth of viscous lava domes and lava tongues with occasional gravitational collapses of parts of oversteepened domes to produce the nuees ardentes commonly defined as merapi type in the 1800s however explosive eruptions of relatively large size occurred to vei 4 and some associated fountain collapse nuees ardentes were larger and farther reaching than any produced in the twentieth century these events may also be regarded as typical eruptions for merapi the nineteenth century activity is consistent with the long term pattern of one relatively large event every one or two centuries based on the long term eruptive record deduced by others from volcanic stratigraphy it is uncertain whether or not a recurrence time model continues to apply to merapi but if so merapi could soon be due for another large event and its occurrence with only modest or inadequately appreciated precursors could lead to a disaster unprecedented in merapi s history because the area around the volcano is now much more densely populated

faster better shear wave velocity to 100 meters depth from refraction microtremor arrays current techniques of estimating shallow shear velocities for assessment of earthquake site response are too costly for use at most construction sites they require large sources to be effective in noisy urban settings or specialized independent recorders laid out in an extensive array this work shows that microtremor noise recordings made on 200 m long lines of seismic refraction equipment can estimate shear velocity with 20 accuracy often to 100 m depths the combination of commonly available equipment simple recording with no source a wavefield transformation data processing technique and an interactive rayleigh wave dispersion modeling tool exploits the most effective aspects of the microtremor spectral analysis of surface wave sasw and multichannel analysis of surface wave masw techniques the slowness frequency wavefield transformation is particularly effective in allowing accurate picking of rayleigh wave phase velocity dispersion curves despite the presence of waves propagating across the linear array at high apparent velocities higher mode rayleigh waves body waves air waves and incoherent noise two locations illustrate the application of this technique in detail coincident with a large accelerometer microtremor array in reno nevada and atop a borehole logged for shear velocity in newhall california refraction equipment could duplicate microtremor results above 3 hz but could not estimate velocities deeper than 100 m refraction microtremor cannot duplicate the detail in the velocity profile yielded by a suspension logger but can match the average velocity of 10 to 20 m depth intervals and suggest structure below the 100 m logged depth of the hole eight additional examples from southern california and new zealand demonstrate that the refraction microtremor technique quickly produces good results from a wide range of hard and soft sites

fluid ascent and magma storage beneath gunung merapi revealed by multi scale seismic imaging abstract magma is fed to a volcano through a complex plumbing system that involves not only shallow structures beneath the volcano edifice but also deep structures and processes within the underlying crust and upper mantle this paper summarizes seismic experiments carried out over many years at gunung merapi in central java these have resolved the 3d seismic velocity structure of the merapi edifice and provided a 3d structural image of the lithosphere and subduction zone beneath central java earthquake locations reveal that with distance from the trench the dip of the subducting slab steepens from nearly horizontal 0 150 km through 45 150 250 km to 70 250 km the slab appears as a 30 km thick double layer of seismicity in a depth range of 80 km to 150 km and it can be identified seismically to a depth of more than 600 km the active volcanoes of merapi sumbing and lawu are located at the edge of a large low velocity body that extends from the upper crust to the upper mantle beneath central java shear wave signals recorded above this anomaly are strongly attenuated compared to neighboring areas the anomalous body has a detected volume of 50 000 km3 and a decrease in p and s velocities relative to adjacent regions of up to 30 the resulting vp vs ratio of up to 1 9 is unusually high for lower crust additionally the anomaly extends along a 45 degree slope downward from beneath the volcanic arc and meets the slab at 100 km depth we interpret this sloping anomaly as a pathway for fluids and partial melts increased seismicity is observed at depths of 100 km possibly as a result of dehydration of the subducting slab with related fluid releases causing partial melting of overlying mantle material the large velocity reduction and high vp vs ratio in the region are consistent with an increase in temperature a reduction of shear strength and the presence of fluids or melts of 13 to 25 vol the detected strong anomaly beneath central java is unique in size and amplitude compared to other subduction zones the geophysical evidence suggests that this segment of the arc has a high magma flux and is thus capable of developing even larger shallow crustal reservoirs and more voluminous explosive eruptions in the future

boundary layer crystallization in a basaltic magma chamber evidence from rishiri volcano northern japan the evolution of basaltic magma by mushy boundary layer processes introduction in a magma chamber is documented for an alkali basalt kutsugata the evolution of magma chambers is of major petrologic lava from rishiri volcano northern japan on the basis of zoning interest and has been studied extensively experimental patterns of plagioclase phenocrysts and their spatial distribution in and theoretical studies that have investigated the cooling the lava plagioclase phenocrysts with complex zoning patterns can of magma chambers have demonstrated that a magma be divided into four types type 1 is characterized by an extremely chamber solidifies through formation of a mushy boundan rich core an71 90 which is commonly corroded and filled with ary layer composed of crystals and interstitial melt along sodic plagioclase type 2 has an ab rich core surrounded by a calcic the chamber walls e g brandeis jaupart 1986 turner mantle characteristic of partial dissolution type 3 is characterized by et al 1986 marsh 1988 tait jaupart 1992 layered igneous complexes e g morse 1969 shirley 1987 an ab rich core that is commonly surrounded by a reversely zoned mcbirney 1996 provide useful information on how slightly calcic mantle type 4 has an ab rich core without a calcic mafic magma chambers evolve and consolidate but they mantle the an rich cores of the type 1 plagioclase are too calcic do not offer much insight into the instantaneous state of to have crystallized from a liquid represented by any whole rock a chamber because those intrusions integrate processes composition at the estimated temperatures of the kutsugata magma that occurred over long solidification times mcbirney system the an rich cores are inferred to have been formed in a noyes 1979 tait 1988 volcanic products such as mushy boundary layer along the wall of a magma chamber where lava flows and tephra deposits can sample the inthe magma was relatively cool and rich in water because of significant stantaneous state of a magma chamber there are a few olivine fractionation and possibly because of addition of water studies along this line of approach tait 1988 de silva expelled from the chilled margin and or groundwater from the 1989 nakada et al 1994 these studies focused on surrounding crust the ab rich cores of types 2 4 plagioclase crystal aggregates in volcanic products and concluded phenocrysts are interpreted to have crystallized in the main magma that the crystal formation in a mushy boundary layer body of the reservoir the types 2 and 3 ab rich cores were brought plays a dominant role in magmatic evolution in a magma to the mushy layer by convection the temporal and spatial variations reservoir however these studies were mostly on silicic of zoning patterns of plagioclase phenocrysts in basaltic lava flows magmas and there are significant differences in physical give useful information on the evolution of mafic magma chambers and chemical features between silicic and mafic magma chambers in this paper the magmatic evolution of an alkali basalt kutsugata lava from rishiri volcano northern japan is studied the kutsugata lava is divided into three lava flows on the basis of whole rock chemical

recharge in volcanic systems evidence from isotope profiles of phenocrysts strontium isotope ratios measured from core to rim across plagioclase feldspar crystals can be used to monitor changes in the isotope composition of the magma from which they grew in samples from three magma systems from convergent margin volcanoes sudden changes in major element composition petrographic features and strontium isotope composition were found to correspond to discrete magmatic events most likely repeated recharge of more mafic magma with lower ratios of strontium 87 to strontium 86 into a crustally contaminated magma

geothermal systems on the island of java indonesia abstract this paper presents an overview of the geothermal systems on the island of bali indonesia physicochemical data of hot springs and shallow geothermal wells were collected from four geothermal locations penebel batur banjar and banyuwedang the concentrations for the three main anions varied significantly indicating a different geothermal history the values for cl ranged from 0 1 to 1000 mg l for hco3 from 20 to 2200 mg l and for so42 from 0 1 to 500 mg l although the island of bali is underlain by carbonate rocks a carbonate host rock for the geothermal reservoirs could not be confirmed because the ca2 mg2 hco3 molar ratios were approximately 0 4 well below 1 0 and the k mg ratios were approaching those of a calc alkaline rock reservoir the hco3 of the thermal waters correlated with ca2 mg2 sr2 and k indicating water rock interaction in the presence of carbonic acid phase separation was inferred for the bedugul and banjar geothermal systems because of relatively high b cl ratios boron isotopes were determined for selected samples with values ranging from 11b of 1 3 to 22 5 nbs 951 the heavy 11b of 22 5 together with a low b cl ratio indicated seawater input in the banyuwedang geothermal system the hydrogen and oxygen isotopic composition of the thermal water plotted along the global meteoric water line gmwl and close to the mean annual value for precipitation in jakarta indicating a meteoric origin of the geothermal water comparison of the si na k na k ca and na li geothermometers with actual reservoir temperature measurements and physicochemical considerations led to the conclusion that the na li thermometer provided most reliable results for the determination of geothermal reservoir temperatures on bali using this thermometer the following reservoir temperatures were calculated 1 penebel bedugul from 235 to 254 c 2 batur 240 c and 3 banjar 255 c due to seawater input this thermometer could not be applied to the banyuwedang geothermal system there application of a sio2 thermometer indicated a reservoir temperature below 100 c

sr isotope disequilibrium during differentiation of the bandelier tuff constraints on the crystallization of a large rhyolitic magma chamber the 1 61 ma otowi member of the bandelier tuff jemez mountains volcanic field new mexico is a caldera forming high silica rhyolitic ignimbrite with a precursor fallout deposit the otowi member has high rb sr ratios the 87 rb 86 sr ratios from sanidines and glasses range from 14 to 570 most sanidines from glomerocrysts in the ignimbrite have 87 sr 86 sr i 0 7052 0 7056 whereas the ratios from glasses from glomerocrysts range from 0 7052 to 0 7079 quartz phenocrysts containing glass inclusions from both the initial fallout and the ignimbrite are markedly more radiogenic at 87 sr 86 sr i 0 7105 0 7113 despite having much lower rb sr ratios than glomerocryst glasses these relations require that the inclusion glasses are more contaminated with proterozoic country rock than are glomerocryst glasses textural isotopic and trace element data support a model in which crystals grow in a boundary layer with the most inclusion rich quartz grains closest to the magma country rock contact phenocrysts and glomerocrysts represent fragments from different zones of the chamber9s crystalline carapace disseminated throughout the magma prior to eruption an important implication of these results is that glass inclusions do not necessarily represent precursor magma compositions hence extrapolation of measured volatile contents of inclusion glasses to the entire volume of an erupted magma should be approached with caution

interaction between ultrapotassic magmas and carbonate rocks evidence from geochemical and isotopic sr nd o compositions of granular lithic clasts from the alban hills volcano central italy abstract magma carbonate rock interaction is investigated through a geochemical and sr nd o isotope study of granular lithic clasts ejecta from the alban hills ultrapotassic volcano central italy some samples group 1 basically represent intrusive equivalents of alban hills magmas a few samples group 2 are ultramafic have high mgo 30 to 40 wt and 18o and originated by accumulation of mafic phases that crystallised from ultrapotassic melts during assimilation of dolomitic rocks group 3 ejecta consist of dominant k feldspar and show major element compositions similar to phonolites which however are absent among the alban hills volcanics finally another group group 4 contains corroded k feldspars surrounded by a microgranular to porphyritic matrix made of igneous minerals k feldspar foids clinopyroxene phlogopite plus wollastonite garnet and some cuspidine group 4 ejecta are depleted in sio2 and enriched in cao with respect to group 3 the analysed ejecta have similar 143nd 144nd 0 51204 0 51217 as the alban hills lavas whereas 87sr 86sr 0 70900 0 71067 is similar to lower whole rocks 18o ranges from 7 0 to 13 2 reaching maximum values in ultramafic samples a positive correlation with cao is observed in single rock groups large ion lithophile element lile abundances and ree fractionation are generally high and extreme values of th u and lree are found in some group 3 and group 4 rocks mineralogical petrological and geochemical data reveal extensive interaction between magma and carbonate wall rocks involving both dolostones and limestones these processes had dramatic effects on magma compositions especially on phonolites which were transformed to foidites evidence of such a process is found in group 4 samples in which k feldspar is observed to react with a matrix that represents strongly undersaturated melts formed by interaction between silicate magma and carbonates trace element data also testify to a very important role for f co2 h2o s fluids during magma wall rock interaction fluid transfer was responsible for extreme enrichments in th u and lree especially observed in group 3 and group 4 rocks implications of these processes for potassic magma evolution in central italy are discussed

empirical dependence of seismic ground velocity on the weight of explosives shotpoint site condition and recording distance for seismic refraction data in this study we have constructed an empirical least squares model for maximum seismic ground velocity vertical component as a function of source size and distance from explosions in drillholes and bodies of water this model is intended in part for use in designing explosion seismic experiments in order to produce acceptable signal to noise ratios at larger distances 10 km and to avoid damaging human structures at smaller distances 1 km data consist of velocities recorded by 120 portable seismographs from 159 shots fired by the u s geological survey in alaska and arizona results show that maximum ground velocity amplitude not necessarily first arrival amplitude decreases with distance and the functional dependence changes with distance for example at 3 km amplitudes decrease as r 2 but at 73 km they decrease as r 1 results also show a strong dependence on site conditions at the shotpoint for example a drillhole shot in wet alluvium produces amplitudes that are four times larger than a drillhole shot in dry alluvium ground velocities are proportional to the square root of the weight of explosives

derivation of the chalk superficial deposits of the north downs england an application of discriminant analysis abstract stepwise discriminant analysis was used on particle size and heavy mineral data from 276 sediment samples including 39 from published sources to distinguish between palaeocene and plio pleistocene deposits found above the cretaceous chalk in southeast england and to determine parent materials of the soils and superficial deposits of the central north downs of 71 known cases in situ deposits 85 9 were correctly classified using textural data sig 99 9 and 89 7 of 29 known cases sig 99 9 using heavy mineral data the best textural discriminating variables were sand graphic mean clay and graphic skewness and the best heavy mineral discriminants were kyanite plus staurolite andalusite and garnet discriminant analysis has achieved good differentiation between marine plio pleistocene sands clay with flints loess and palaeocene groups and allowed objective classification of sediments of unknown origin the distribution of parent materials revealed strongly upholds the earlier interpretation z geomorphol 39 1995 433 that in the central north downs except where palaeocene residuals survive the superficial cover above the chalk consists of in situ clay with flints sensu stricto beneath plateau drift and loess clay with flints is seen as residual and plateau drift as a pleistocene soliflucted deposit textural affinities of reading beds clay and clay with flints elicited by a third discriminant analysis using additional published data from 22 samples suggest their common derivation from chalk residua

structural and geochemical interactions between magma and sedimentary host rock the hovedoya case oslo rift norway two end member conceptual models are used to describe deformation of the earth s crust induced by magma intrusion mode i fracturing assumes tensile or opening mode elastic deformation while mode ii fracturing assumes plastic shear mode deformation around a viscous indenter field observations of both mechanisms exist but it remains unclear which mechanism dominates in which conditions we describe intrusion geometries host rock deformation and geochemical magma host rock interactions around 53 exceptionally preserved tephrite basanite permian dike segments of 0 5 to 30 cm thickness these thin dikes that is dikelets intruded late ordovician carbonate rich sedimentary rocks on hovedoya island oslo rift norway dikelets emplaced in preexisting fractures dominantly created cavities ahead of their narrow tapering tips and are associated with bent host rock broken bridges and stepped segmented geometries other tips are blunt with dense brittle fracturing around them also cross sectional intrusion segment opening profiles deviate from parabola shaped profiles typical for elastic media the observations demonstrate that dominant opening mode host rock deformation can coexist with shear mode deformation locally alignment of most dikelet segments along the dominant host rock fracture directions highlights the control of local structural orientations on magma emplacement analysis of bulk major and trace element compositions in situ micro xrf sample analysis and carbon and oxygen stable isotope compositions suggests that thermochemical interactions between magma and the carbonate rich host rock produced a low viscosity mixture of magma pore water and gas we propose that such low viscosity hybrid fluid may assist in the intrusion of magma in sedimentary rocks by filling the cavity ahead of propagating sheet intrusion tips

u th and ra disequilibria sr nd and pb isotope and trace element variations in sunda arc lavas predominance of a subducted sediment component the time scales of magma formation transfer and storage beneath island arc volcanoes are important because of the insights they provide into the physical processes of magma formation and evolution with possible links to the prediction of eruptive hazards here we present new mass spectrometric u th and ra and sr nd and pb isotope data along with major and trace element data from 19 lavas along the sunda arc indonesia the lavas range in sio2 from 49 to 75 and the combination of high sio2 and low 143nd 144nd indicates an important role for shallow level contamination by ancient crustal materials in sumatra diagrams of 143nd 144nd versus th ce and u th versus 87sr 86sr reveal negative trends which allow contributions from both subducted sediments and fluids to be identified the fluid component as expressed in elevated u th 238u 230th and 226ra 230th o ratios is ubiquitous in all of the lavas including near primary lavas from galunggung sr isotope data indicate that the fluids had variable composition and derived from altered oceanic crust and the u th and ra isotope data suggest that some fluid components must have been added less than 8 000 years ago tholeiitic lavas from flores have the lowest th contents in the arc and accordingly the highest 226ra 230th o and 238u 230th for these there is evidence that both u and ra addition probably occurred less than a few thousand years ago this suggests that the onset of melting was linked to fluid fluxing and cannot have been due to decompression alone in contrast the sediment component may have been added as a partial melt and sediment addition can account for the observed along arc variations in sr nd pb and th isotopes there is no requirement in our data for an oib component in the mantle wedge increases in sio2 in the galunggung lavas are accompanied by decreases in both 238u 230th and 226ra 230th o which are inferred to reflect mixing with melts of pre existing mafic lavas mixing and differentiation must have occurred faster than could be recorded by either the 238u 230th or 226ra 230th systems there is little evidence in our data for any effect of the australia indonesia collision on the composition of the lavas across arc trends in lava composition indicate an increasing relative contribution from subducted sediment a correspondingly weaker fluid signal and probable decreases in the degree of partial melting residual aluminous clinopyroxene or garnet may become important in controlling ree and u th fractionation in the far back arc

textural and mineral chemistry constraints on evolution of merapi volcano indonesia abstract we analyze and compare the textures of merapi lavas basalts and basaltic andesites ranging in age from proto merapi through modern activity with the goal of gaining insights on the temporal evolution of merapi s magmatic system analysis of textural parameters such as phenocryst and microphenocryst crystallinity coupled with crystal size distribution theory provides information about the storage and transport of magmas we combine textural analyses with geochemical investigations for a comprehensive comparison of erupted lavas over time the chemical analyses identify crystal growth processes in magma chambers and underline differences between sample groups our work suggests the occurrence of two distinct histories presumably associated with at least two generally distinct types of rheological behaviors and storage transport systems these behaviors are associated with different plagioclase growth patterns with both groups influenced by late stage shallow decompression degassing induced microlite crystallization both groups contain amphibole crystals that indicate an early period of mid crustal to deep crustal storage of water rich magmas dome lavas from the 20th century eruptive activity indicate quasi steady state nucleation and growth evolution interspersed with episodes of reheating and textural coarsening suggesting residence in magma storage at multiple depths both 10 km and

rapid determination of initial 87sr 86sr and estimation of the rb sr age of plutonic rocks by la icpms of variably altered feldspars an example from the 1 14 ga great abitibi dyke ontario canada abstract sr isotope analysis of plutonic rocks is an important method for deriving the provenance and age of ancient magmatic episodes and the petrogenetic processes operating during intrusive activity we determined the 87 sr 86 sr isotopic compositions of fresh and variably altered feldspars from the 1 14 ga gabbroic great abitibi dyke ontario canada through the use of laser ablation inductively coupled plasma mass spectrometry la icpms the data show an alteration trend between fresh low rb plagioclase with 87 sr 86 sr ratios of 0 7045 and high rb alkali feldspar with 87 sr 86 sr ratios of 0 7059 which may be used to constrain the 87 sr 86 sr ratio of the mantle source this trend is incompatible with simple mixing and instead has age significance as post intrusive alteration through hydrothermal circulation starts immediately following emplacement la icpms analysis allows rapid estimation of initial 87 sr 86 sr ratios and intrusive age suitable for sample screening and selection for more precise dating for the great abitibi dyke the rb sr age estimate of emplacement of 1 10 0 23 ga 2 is concordant with the precise u pb emplacement age of the dyke 1140 6 2 0 ma the most altered high rb alkali feldspars return younger ages suggesting that post intrusive alteration lasted several hundred million years this study highlights the need for microanalysis to differentiate between alteration and magmatic processes on basis of sr isotopic signatures and outlines a rapid method to determine initial 87 sr 86 sr ratios and to estimate rb sr ages of plutonic rocks in terranes with long histories of multiple intrusive magmatic episodes

textural and micro petrological variations in the eruptive products of the 2006 dome forming eruption of merapi volcano indonesia implications for sub surface processes the interplay between magma ascent degassing and changing magmatic properties are widely recognized as critical factors controlling the style of silicic volcanic eruptions microlite textures in samples from the prolonged dome forming eruption of merapi in 2006 provide a record of changing magmatic ascent conditions and shallow conduit processes throughout the eruption analysis of microlite textural parameters including measurements of areal number density na mean microlite size crystal aspect ratio and groundmass crystallinity combined with the monitoring record and field observations indicate that magma ascent paths change between continuous ascent at varying rates from a deeper magma storage region to ascent being temporarily stalled at shallow depths in the latter stages of the eruption supporting the idea of an ephemeral shallow magma storage region at merapi plagioclase microlite compositions show evidence of decompression induced degassing often displaying rims of anorthoclase and more k rich alkali feldspar sanidine anorthite contents also support the textural data of later erupted magma being temporarily stalled at shallow depths crystal size distributions csds are interpreted to show that both growth dominated and nucleation dominated crystallisation regimes existed during the 2006 eruption resulting from changing conditions of undercooling t during variable magma ascent paths by contrast microlite textural analysis and feldspar microlite compositions of samples from the fast growing lava dome of the second phase of the 2010 eruption prior to the cataclysmic events on 5 november indicate faster ascent rates a crystallisation regime more strongly dominated by nucleation due to high t and interaction of the 2010 magma with more hotter magma from depth

geochemical characterization of ophiolitic soils in a temperate climate a multivariate statistical approach abstract the geochemical characterization of ophiolitic soils in a temperate climate based on the nature of basic bedrock has been scarcely investigated in this work we have taken into account major minor and trace element data and clay silt sand and organic matter contents of ophiolitic soils collected from several places in tuscany central italy where the chemical nature of the bedrocks is known thus using data belonging to three groups of soils collected on serpentinitic gabbroic and basaltic bedrocks we have studied the influence of the bedrock on the chemical character of the soils we have applied discriminatt analysis techniques to find a classification rule both to discriminate the groups originally determined and to assign new samples to one of these groups furthermore starting from a large number of variables defining the overall chemical character of soil samples we have found that only a few variables contribute to discriminate the three groups

the nevados de payachata volcanic region 18 s 69 w n chile ii evidence for widespread crustal involvement in andean magmatism volcanism extending over 11 ma is represented in the rocks of the nevados de payachata region culminating in the formation of two large composite stratocones within the last 500 000 years chemically distinct mafic magmas are erupted at a number of parasitic centers these cannot be related to each other by crystal fractionation and do not appear to be direct parents for the differentiated suites of the composite cones two distinct trends are defined by the intermediate and evolved rocks a high lile large ion lithophile element tio2 and ce yb lineage among the youngest rocks including the two major stratocones and a more typical calc alkaline trend among the older 1 ma rock types within individual volcanic centers differentiation involves fractionation of plagioclase pyroxene and hornblende with biotite and k feldspar in the more evolved rock types isotopic compositions sr pb nd o vary little with differentiation from basaltic andesite to rhyolite or with age contamination during differentiation from basalt to rhyolite may occur but the most mafic rocks erupted in the region are already enriched in incompatible trace elements and therefore may be insensitive to the effects of interaction with the crust the majority of data are similar to baseline compositions cenozoic parental magmas from other parts of the central andes and may reflect a relatively homogeneous magma source or source mixture throughout this central volcanic zone cvz which is distinct from the southern and northern andes and from island arc volcanic rocks

an overview of the seismicity of merapi volcano java indonesia 1983 1994 abstract from 1982 to 1995 merapi volcano java indonesia experienced two main eruptive cycles from 1984 to 1986 and from 1992 to 1994 each cycle had a duration slightly larger than 2 years four major eruptive events occurred in 1984 1986 1992 and 1994 these eruptions were monitored by a telemetered seismic network we present an overview of the seismicity observed between 1983 and 1995 from seismological observations several types of characteristic events are recognised volcanotectonic earthquakes are standard microearthquakes either shallow an aseismic zone is situated between two seismic zones at a depth between 1 5 and 2 5 km below the summit we postulate that it is a small shallow magma reservoir where magma injected from below can be stored temporarily we try to relate seismic observations during both eruptive cycles to the initial injection of deep magma to the superficial magma system the first eruption in each case seems to involve magma enriched in gas that extrudes the content of the conduit and explodes the old dome a regular outflow of magma follows the initial explosion and gradually a dome is building up then it stops and a period of repose is observed later a second episode of dome growth occurs the height of the dome reaches a maximum corresponding to a state of lithostatic equilibrium the time delay of more than 2 years between the beginning and the end of a cycle may result from crystallisation in a volatile rich magma and from the building up of pressure in the superficial magma pocket some important events like the collapse of the dome on 22 november 1994 are not preceded by any seismic precursor when it reaches a large volume the dome is not stable and is likely to collapse by gravity for instance after the sudden influx of matter or gas or after a heavy rain on merapi tremors are observed but do not always precede a dangerous event

constraints from phase equilibrium experiments on pre eruptive storage conditions in mixed magma systems a case study on crystal rich basaltic andesites from mount merapi indonesia mount merapi is one of indonesia s and the world s most hazardous volcanoes existing constraints on the location and the crystallization conditions of its pre eruptive magma reservoir based on mineral and glass thermobarometry and geophysical surveys are inconclusive yet of immediate importance for future hazard mitigation here we use two series of phase equilibrium experiments to quantify the conditions of pre eruptive magma storage and magma recharge in merapi s upper crustal reservoir 1 to characterize crystallization at total equilibrium conditions 2 to characterize crystallization at local equilibrium conditions between crystal rims and host melt we demonstrate that this experimental approach can constrain pre eruptive crystallization conditions and their variation in crystal rich mixed magma systems such as that of merapi for which standard crystallization experiments and mineral thermobarometry fail in agreement with geophysical estimates we infer that mount merapi s pre eruptive reservoir partially crystallizes at 100 200 75 mpa and thus at relatively shallow depths of c 4 5 to 9 km magmas are stored at 925 950 25 c with a melt h2o content of 3 4 wt and a vapour phase with an xh2o h2o h2o co2 of 0 5 0 6 0 1 pre eruptive recharge magmas in contrast have a temperature 950 to 1000 c a higher melt h2o content of 4 5 wt and a vapour phase with a higher xh2o of 0 8 0 1 we hypothesize that these variations in melt h2o content and vapour xh2o between resident and pre eruptive recharge magmas relate to variable degrees of open system degassing of magma parcels en route into the reservoir rather than to variations in volatile fluxing of the stored magmas

effects of volatile behaviour on dome collapse and resultant pyroclastic surge dynamics gunung merapi 2010 eruption in 2010 gunung merapi central java indonesia generated two violent eruption sequences on 26 october and 5 november culminating in widespread pyroclastic density currents pdcs associated with the destruction of lava domes tephra from pdc deposits were analysed to examine pre dome collapse volatile behaviour and evidence of carbonate assimilation secondary ion mass spectroscopy sims depth profiles of plagioclase phenocrysts reveal that the 7 li 30 si ratios in 26 october products are higher in the glass compared to the crystal indicating a build up of li in the groundmass not observed in the 5 november samples higher li in the groundmass suggests gas accumulation and rapid development of conduit overpressure in the shallow plumbing system prior to the initial 26 october explosion which was only captured through the behaviour of quickly diffusing li and not h 2 o following the explosion induced decompression juvenile magma rapidly ascended in great volume to generate extremely destructive pdcs following subsequent dome collapses particularly on 5 november additionally 26 october tephras contain carbonate grains in the ash component and abundant co 2 within the lava lapilli groundmass glass which supports previous studies indicating assimilation of calc silicate lithologies by the merapi magma at depth in the plumbing system prior to the onset of 2010 activity

magma mixing and crustal recycling recorded in ternary feldspar from compositionally zoned peralkaline ignimbrite a gran canaria canary islands miocene ignimbrite a on gran canaria contains three compositional endmember fiamme types two rhyolites and one trachyte each of which crystallized distinct feldspar various textural and compositional criteria are interpreted as reflecting a complex scenario within the magma chamber in which the crystals formed about 25 30 of the feldspar phenocrysts contain evidence for magma mixing in the form of 1 partial to severe dissolution resorption rims 2 distinct zones of drastically different compositions and 3 overgrowth textures on formerly resorbed crystals four major types of zoning in the oligoclase to anorthoclase feldspars of ignimbrite a include a normal and a reversely zoned type and two complexly zoned types the feldspars with normal and reverse zonation show only minor compositional amplitudes between individual zones ab or 4 whereas the complexly zoned types show compositional differences between zones of up to 18 mol ab and 20 mol or and are commonly associated with an internal dissolution surface complex zoning with large compositional amplitudes and dissolution textures is taken as evidence of crystal movements within the magma and across compositional boundaries between magma batches a multiple step cycle model involving growth and transport of a crystal into another magma batch and its return to the original host magma is suggested by the data moreover feldspars from one rhyolite compositional group are found to be substantially elevated in 18o suggesting an input of a high 18o component to this rhyolite the other endmember rhyolite appears to be related to the endmember trachyte by mainly crystal fractionation of anorthoclase feldspar this observation is consistent with trace element and rare earth element concentrations for the magma endmembers and their feldspars where contamination led to a depletion in incompatible trace elements and light rare earth elements in the contaminated rhyolite and its feldspar phenocrysts we suggest that the combination of textural and compositional variation in ternary feldspar of peralkaline rhyolitic systems is well suited to reconstruct dynamic processes such as magma mixing and contamination in evolving rhyolitic magma chambers

merapi central java indonesia an outline of the structural and magmatological evolution with a special emphasis to the major pyroclastic events abstract merapi volcano in the central part of java is regarded as the most active and most dangerous volcano in indonesia on the basis of field studies and geochronological data its history is divided into four periods ancient middle recent and modern merapi according to our preliminary age data the ancient period may have begun around 40 000 y bp and lasted until 14 000 y bp when the middle period begun the recent period begun around 2200 y bp and was replaced by the modern period after the eruption of 1786 during the middle merapi stage a mount st helens type edifice collapse occurred our data suggest that his event is younger than 6700 y bp and older than 2200 y bp during the recent merapi stage violent magmatic to phreatomagmatic eruptions twice interrupted the growth of the volcano the older gumuk phreatoplinian deposits cover the entire cone charcoal found within these deposits gave 14c ages of 2200 and 1470 y bp the overlying sambisari ash deposits were emplaced by violent pyroclastic surges directed towards the south i e to the present location of the town of yogyakarta they buried the shivaitic temple of sambisari at the start of the 15th century modern merapi is characterised by the persistent growth of a summit dome periodically interrupted by partial or total collapse of the dome to generate frequent merapi type nuees ardentes blocks and ash flows and associated surges or more exceptionally fall back st vincent type nuees ardentes scoria flows in contrast previous stages were characterised by effusion of long lava flows alternating with violent explosive phases generating essentially st vincent type nuees ardentes merapi lavas are calc alkaline with a compositional range between 49 5 and 60 5 wt sio2 moreover high k basaltic andesites represent about 90 of merapi lavas disequilibrium features are common in the mineralogical assemblage plagioclase orthopyroxene clinopyroxene olivine amphibole titanomagnetite scarce alkali feldspar macroscopic and microscopic textural heterogeneities are related to magma mixing that may have buffered the compositions of lavas and caused the restricted range of compositions our studies of past activity at merapi provide some insights into future activity and to related volcanic hazards it is clear that merapi has the potential of eruptions much more powerful than observed during the historic period

time dependent geochemistry of clinopyroxene from the alban hills central italy clues to the source and evolution of ultrapotassic magmas abstract we investigated chemical and isotopic compositions of clinopyroxene crystals from well age constrained juvenile scoria clasts lava flows and hypoabyssal magmatic ejecta representative of the whole eruptive history of the alban hills volcanic district the alban hills is a quaternary ultra potassic district that was emplaced into thick limestone units along the tyrrhenian margin of italy alban hills volcanic products even the most differentiated are characterised by low sio2 content we suggest that the low silica activity in evolving magmas can be ultimately due to a decarbonation process occurring at the magma limestone interface according to the liquid line of descent we propose the differentiation process is driven by crystallisation of clinopyroxene leucite apatite magnetite coupled with assimilation of a small amount of calcite and or with interaction with crustal co2 by combining age chemical data strontium and oxygen isotopic compositions and ree content of clinopyroxene we give insights into the evolution of primitive ultrapotassic magmas of the alban hills volcanic district over an elapsed period of about 600 kyr geochemical features of clinopyroxene crystals consistent with data coming from other italian ultrapotassic magmas indicate that alban hills primary magmas were generated from a metasomatized lithospheric mantle source in addition our study shows that the 87sr 86sr and lree hree of alban hills magmas continuously diminished during the 600 35 ka time interval of the alban hills eruptive history possibly reflecting the progressive depletion of the metasomatized mantle source of magmas

highly explosive 2010 merapi eruption evidence for shallow level crustal assimilation and hybrid fluid abstract the processes responsible for the highly explosive events at merapi central java indonesia have been investigated through a petrological mineralogical and geochemical study of the first stage tephra and pyroclastic flows sampled in october and november 2010 and second stage ash sampled shortly after the 5 6th november 2010 paroxysmal subplinian eruption several chemical and physical parameters suggest that the magma assimilated calc silicate xenoliths derived from the surrounding carbonate bearing crust javanese limestone the bulk volcanic samples have highly radiogenic 87 sr 86 sr 0 70571 0 70598 ratios that approach the compositional field of material similar to the calc silicate xenoliths the 2010 plagioclase phenocrysts from the pyroclastic flow and tephra reveal anorthite cores up to an 94 97 with low feo contents 0 8 wt and 18 o enrichment 6 5 18 o the major and trace elements of the silicic glasses and phenocrysts plagioclase low al augite and titanomagnetite the sr isotopic compositions of the bulk samples and plagioclases erupted in 2010 can be explained by complete digestion of the 1998 and 2006 calc silicate xenoliths the bulk assimilation proceeded through binary mixing between a calcic melt representing crustal assimilant cao up to 10 5 wt and cao al 2 o 3 up to 1 2 and the deep source hydrous k rich melt similarly to the 1998 and 2006 calc silicate xenolith composition the 2010 crustal assimilant is enriched in mn mno up to 0 5 wt zn v and sc contents in contrast the hydrous k rich melt is enriched in volatiles cl up to 0 37 wt and bulk h 2 o co 2 up to 5 1 wt al 2 o 3 tio 2 and ree contents consistent with its derivation from deep source this hydrous k rich melt may have been saturated with an aqueous cl rich fluid at about 200 mpa a pressure consistent with the level of the crustal assimilation we estimated that the pre eruptive basaltic andesite magma assimilated from 15 to 40 wt of the calc silicate crustal material corresponding to introduction of additional 0 19 to 2 1 mt of co 2 to the magma experimental leaching of the ash samples documents the release of an aqueous fluid enriched in cl na ca cd sb and zn during the paroxysmal subplinian eruption the paroxysmal eruption may have been produced by saturation of the pre eruptive basaltic andesite magma with hybrid aqueous carbonic nacl hcl rich fluid due to bulk assimilation creating elevated partial pressure of co 2 at shallow crustal conditions of about 200 mpa in contrast mildly explosive block and ash flows typical merapi type may result from selective assimilation of the carbonate bearing xenoliths and lower co 2 partial pressure that may not lead to explosive degassing

textural history of recent basaltic andesites and plutonic inclusions from merapi volcano mt merapi in central java is one of the most active stratovolcanoes on earth and is underlain by a multistage plumbing system crystal size distribution analyses csd were carried out on recent merapi basaltic andesites and co eruptive magmatic and plutonic inclusions to characterise the crystallisation processes that operate during storage and ascent and to obtain information on respective time scales the basaltic andesites exhibit log linear kinked upwards csd curves for plagioclase and clinopyroxene that can be separated into two main textural populations large plagioclase phenocrysts 1 6 mm make up one population but correspond to crystals with variable geochemical composition and reflect a period of crystal growth at deep to mid crustal levels this population was subsequently influenced by crystal accumulation and the onset of crustal assimilation including the incorporation of high ca skarn derived xenocrysts textural re equilibration is required for these crystals to form a single population in csd a second episode of crystal growth at shallower levels is represented by chemically homogenous plagioclase crystals 1 6 mm in size crustal assimilation is indicated by for example oxygen isotopes and based on the csd data crystallisation combined with contamination is likely semi continuous in these upper crustal storage chambers the csd data observed in the basaltic andesite samples are remarkably consistent and require a large volume steady state magmatic system beneath merapi in which late textural equilibration plays a significant role plagioclase csds of co eruptive magmatic and plutonic inclusions may contain a third crystal population 1 mm not found in the lavas this third population has probably formed from enhanced degassing of portions of basaltic andesite magma at shallow crustal levels which resulted in increased crystallinity and basaltic andesite mush inclusions a suite of coarse plutonic inclusions is also present that reflects crystallisation and accumulation of crystals in the deep merapi plumbing system as deduced from csd patterns and mineral assemblages

pervasive assimilation of carbonate and silicate rocks in the hortavaer igneous complex north central norway the intrusive complex at hortav r represents a magma transfer zone in which multiple pulses of gabbroic and dioritic magmas evolved along fe and alkali enrichment trends extreme alkali enrichment resulted in nepheline normative and sparse nepheline bearing monzodioritic and monzonitic rocks more evolved monzonitic and syenitic rocks are silica saturated and in some cases quartz bearing previous and current research recognized an abundance of clinopyroxene and other ca rich phases such as scapolite grossular rich garnet and igneous textured calcite among the mafic and intermediate rocks even the most pyroxene rich samples contain low sc concentrations which suggests early intense fractionation of clinopyroxene these features and the alkali enrichment are consistent with assimilation of carbonate rich host rocks carbon isotope ratios of the igneous textured calcite indicate an origin of the carbon from host rocks rich in calcite consistent with assimilation however low end values 3 4 to 10 2 and moderate initial 87 sr 86 sr values 0 7052 to 0 7099 indicate the need for assimilation of quartzofeldspathic rocks as well models of combined assimilation and fractional crystallization indicate that assimilation of simple end members either carbonate or silicate cannot explain the entire data set instead variable proportions of carbonate and silicate materials were assimilated with the most pronounced assimilation effects in the mafic rocks the reasons for variable degrees of assimilation are as yet uncertain it is possible that assimilation of calc silicate rocks with variable carbonate silicate proportions resulted in the range of observed compositions however the importance of carbonate assimilation in mafic rocks compared to felsic ones suggests that assimilation of carbonates was predominant at high temperature and or mafic magma compositions and assimilation of silicates was predominant at lower temperature and or felsic magma compositions we suggest that the ability of the mafic magma to dissolve higher proportions of carbonate contaminants is the result of the magma s ability to form clinopyroxene as a product of assimilation in any case extensive carbonate assimilation was possible because co2 escaped from the system d 2004 elsevier b v all rights reserved

oxygen isotope heterogeneity of arc magma recorded in plagioclase from the 2010 merapi eruption central java indonesia chemical and isotopic compositions of magmatic crystals provide important information to distinguish between deep juvenile and crustal contributions in this work high resolution multicollector secondary ion mass spectrometry data reveal strong variations of 18o values in three plagioclase crystals 800 1700 m from two representative basaltic andesite samples of the 2010 merapi eruption central java indonesia the 18o values from 4 6 to 7 9 are interpreted to reflect oxygen isotope heterogeneity in the melt composition during plagioclase growth the lowest 18o values 4 6 6 6 are found in anorthite rich cores an82 97 whereas higher 18o values 5 7 to 7 9 are found in anorthite poorer zones an33 86 typically in crystal rims combining these new plagioclase 18o data with 18o of calc silicate crustal xenoliths erupted between 1994 1998 the composition of glass inclusions hosted by the anorthite rich plagioclase an82 92 available experimental data and the results of thermodynamic modelling using the magma chamber simulator code we conclude that the abundant anorthite rich cores crystallized from a mantle derived hydrous basaltic to basaltic trachyandesite melt that recharged a deeper 200 600 mpa magma storage zone whereas lower anorthite zones crystallized at shallower levels 100 200 mpa the oxygen isotope variations in the plagioclase are explained by a two stage model of interaction of the hydrous mafic mantle derived magma 1 with old crustal rocks depleted in 18o due to high temperature alteration that yielded the low 18o values in the anorthite rich cores at deep levels 13 20 km and later 2 with 18o enriched carbonate material that yielded the high 18o values in anorthite poorer zones at shallow levels 4 5 9 km thermodynamic modelling is consistent with 18 wt assimilation of crustal calc silicate material at 925 950 c and 100 200 mpa by the 2010 merapi basaltic andesite magma prior to eruption timescales for plagioclase phenocryst growth and residence in the magmatic plumbing system are 34 years the combined data thus reveal efficient magma recharge and crustal assimilation processes that characterize the open system magma storage and transport systems associated with the 2010 merapi eruption

p and s velocity structure of the crust and the upper mantle beneath central java from local tomography inversion here we present the results of local source tomographic inversion beneath central java the data set was collected by a temporary seismic network more than 100 stations were operated for almost half a year about 13 000 p and s arrival times from 292 events were used to obtain three dimensional 3 d vp vs and vp vs models of the crust and the mantle wedge beneath central java source location and determination of the 3 d velocity models were performed simultaneously based on a new iterative tomographic algorithm lotos 06 final event locations clearly image the shape of the subduction zone beneath central java the dipping angle of the slab increases gradually from almost horizontal to about 70 a double seismic zone is observed in the slab between 80 and 150 km depth the most striking feature of the resulting p and s models is a pronounced low velocity anomaly in the crust just north of the volcanic arc merapi lawu anomaly mla an algorithm for estimation of the amplitude value which is presented in the paper shows that the difference between the fore arc and mla velocities at a depth of 10 km reaches 30 and 36 in p and s models respectively the value of the vp vs ratio inside the mla is more than 1 9 this shows a probable high content of fluids and partial melts within the crust in the upper mantle we observe an inclined low velocity anomaly which links the cluster of seismicity at 100 km depth with mla this anomaly might reflect ascending paths of fluids released from the slab the reliability of all these patterns was tested thoroughly

minor and trace element zoning in plagioclase implications for magma chamber processes at parinacota volcano northern chile textural and compositional zoning in plagioclase phenocrysts in a sample from parinacota volcano chile was investigated using backscattered electron images and electron microprobe analysis of major and trace elements large 2 mm oscillatory zoned crystals type i with resorption surfaces of moderate an discontinuities 10 an and decreasing trace element contents sr mg ti towards the rim reflect melt differentiation and turbulent convection in the main magma body early recharge with a low sr mafic magma is seen in the core small scale sr variations in the core indicate limited diffusion and thus residence and differentiation times of the magma shorter than a few thousand years smaller crystals type ii with low trace element an ratio reflect the influence of an h2o rich melt probably from a differentiated boundary layer closed system in situ crystallisation mafic magma recharge and the role of a water rich differentiated boundary layer can be distinguished from the an trace element relationships crystals apparently move relatively freely between different parts and regimes in the magma chamber evidence for convective crystal dispersion high sr type ii crystals indicate an earlier input of sr rich mafic magma recharge of two distinct mafic magma types is thus identified high sr and low sr which must have been present at increasing recharge rates with time in the plumbing system throughout the volcano s history

thermal weakening of the carbonate basement under mt etna volcano italy implications for volcano instability abstract the physical integrity of a sub volcanic basement is crucial in controlling the stability of a volcanic edifice for many volcanoes this basement can comprise thick sequences of carbonates that are prone to significant thermally induced alteration these debilitating thermal reactions facilitated by heat from proximal magma storage volumes promote the weakening of the rock mass and likely therefore encourage edifice instability such instability can result in slow gravitational spreading and episodic to continuous slippage of unstable flanks and may also facilitate catastrophic flank collapse understanding the propensity of a particular sub volcanic basement to such instability requires a detailed understanding of the influence of high temperatures on the chemical physical and mechanical properties of the rocks involved the juxtaposition of a thick carbonate substratum and magmatic heat sources makes mt etna volcano an ideal candidate for our study we investigated experimentally the effect of temperature on two carbonate rocks that have been chosen to represent the deep heterogeneous sedimentary substratum under mt etna volcano this study has demonstrated that thermal stressing resulted in a progressive and significant change in the physical properties of the two rocks porosity wet i e water saturated dynamic poisson s ratio and wet vp vs ratio all increased whilst p and s wave velocities bulk sample density dynamic and static young s modulus dry vp vs ratio and dry dynamic poisson s ratio all decreased at temperatures of 800 c the carbonate in these rocks completely dissociated resulting in a total mass loss of about 45 and the release of about 44 wt of co 2 uniaxial deformation experiments showed that high in situ temperatures 500 c significantly reduced the strength of the carbonates and altered their deformation behaviour above 500 c the rocks deformed in a ductile manner and the output of acoustic emissions was greatly reduced we speculate that thermally induced weakening and the ductile behaviour of the carbonate substratum could be a key factor in explaining the large scale deformation observed at mt etna volcano our findings are consistent with several field observations at mt etna volcano and can quantitatively support the interpretation of 1 the irregularly low seismic velocity zones present within the sub volcanic sedimentary basement 2 the anomalously high co 2 degassing observed 3 the anomalously high vp vs ratios and the rapid migration of fluids and 4 the increasing instability of volcanic edifices in the lifespan of a magmatic system we speculate that carbonate sub volcanic basement may emerge as one of the decisive fundamentals in controlling volcanic stability