sulfur diffusion in basaltic melts abstract we measured the diffusion coefficients of sulfur in two different basaltic melts at reduced conditions i e in the sulfide stability field temperatures from 1225 c to 1450 c pressures of 0 5 and 1 gpa and water concentrations of 0 and 3 5 wt although each melt is characterized by slightly different sulfur diffusion coefficients the results can be combined to create a general equation for sulfur diffusion in anhydrous basalts d 2 19 10 4 exp 226 3 58 3 r t where d is the diffusion coefficient in m2s 1 the activation energy is in kj mol 1 r is the gas constant and t is the temperature in k sulfur diffusion in basalts with 3 5 wt water is a factor of three to seven higher than in anhydrous melts and can be described by d 5 91 10 7 exp 130 8 82 6 r t at the conditions of this study the pressure does not measurably affect sulfur diffusion sulfur diffusion in dry basaltic melts is one order of magnitude higher than sulfur diffusion in dry andesitic and dacitic melts whereas sulfur diffusion in hydrous basaltic and andesitic melts is within the same order of magnitude when compared to the diffusivity of other volatile species in nominally dry basaltic melts sulfur diffusion appears to be two times lower than co2 diffusion and two orders of magnitude lower than h2o diffusion

geochemical variations in the cocos plate subducting beneath central america implications for the composition of arc volcanism and the extent of the galapagos hotspot influence on the cocos oceanic crust new geochemical data from the cocos plate constrain the composition of the input into the central american subduction zone and demonstrate the extent of influence of the galapagos hotspot on the cocos plate samples include sediments and basalts from ocean drilling program odp site 1256 outboard of nicaragua gabbroic sills from odp sites 1039 and 1040 tholeiitic glasses from the fisher ridge off northwest costa rica and basalts from the galapagos hotspot track outboard of central costa rica site 1256 basalts range from normal to enriched morb in incompatible elements and have pb and nd isotopic compositions within the east pacific rise morb field the sediments have similar 206pb 204pb and only slightly more radiogenic 207pb 204pb and 208pb 204pb isotope ratios than the basalts altered samples from the subducting galapagos hotspot track have similar nd and pb isotopic compositions to fresh galapagos samples but have significantly higher sr isotopic composition indicating that the subduction input will have a distinct geochemical signature from galapagos type mantle material that may be present in the wedge beneath costa rica gabbroic sills from sites 1039 and 1040 in east pacific rise epr crust show evidence for influence of the galapagos hotspot 100 km beyond the morphological hotspot track

seismic velocity structure of the slab and continental plate in the region of the 1960 valdivia chile slip maximum insights into fluid release and plate coupling the south central chilean subduction zone has witnessed some of the largest earthquakes in history making this region particularly important for understanding plate coupling here we present the results of a local earthquake tomography study from a temporary local seismic network in the villarrica region between 39 and 40 s where the largest coseismic displacement of the 1960 valdivia earthquake occurred a lowvelocity anomaly and high vp vs values occur under the coastal region indicating mantle serpentinisation and or underthrusting of forearc material further east a high velocity anomaly is observed interpreted as normal high velocity mantle under the active volcanic arc a low velocity anomaly together with high vp vs ratios 1 8 and higher likely images fluid ascent beneath the volcanoes close to the subducting valdivia fracture zone the coastal low velocity anomaly extends further inland where it interrupts and shifts the high velocity anomalies associated with normal fast mantle velocities this may indicate enhanced fluid presence along this part of the margin probably caused by a stronger hydration of the incoming plate along the valdivia fracture zone this is consistent with geochemical fluid proxies u th pb ce ba nb in young volcanic rocks displaying peak values along the volcanic front at llaima and villarrica volcanoes and with recent gps measurements which suggested a local reduction in plate coupling in this region the shift in the high velocity anomaly underlying the central part may be caused by a north to south decrease in plate age and hydration across the valdivia fracture zone and may explain why a central valley is absent in this segment of the margin the low la yb ratios in the volcanic rocks from villarrica and llaima suggest that the high slab derived fluid flux causes elevated degrees of melting beneath these volcanoes providing an explanation as to why these are amongst the most active volcanoes in south america

insights from trace element geochemistry as to the roles of subduction zone geometry and subduction input on the chemistry of arc magmas subduction zones of continental transitional and oceanic settings relative to the nature of the overriding plate are compared in terms of trace element compositions of mafic to intermediate arc rocks in order to evaluate the relationship between subduction parameters and the presence of subduction fluids the continental chilean southern volcanic zone svz and the transitional to oceanic central american volcanic arc cava show increasing degrees of melting with increasing involvement of slab fluids as is typical for hydrous flux melting beneath arc volcanoes at the svz the central segment with the thinnest continental crust lithosphere erupted the highest degree melts from the most depleted sources similar to the oceanic like nicaraguan segment of the cava the northern part of the svz located on the thickest continental crust lithosphere exhibits features more similar to costa rica situated on the caribbean large igneous province with lower degrees of melting from more enriched source materials the composition of the slab fluids is characteristic for each arc system with a particularly pronounced enrichment in pb at the svz and in ba at the cava a direct compositional relationship between the arc rocks and the corresponding marine sediments that are subducted at the trenches clearly shows that the compositional signature of the lavas erupted in the different arcs carries an inherited signal from the subducted sediments

upper lithospheric structure of the subduction zone offshore of southern arauco peninsula chile at 38 s velocities 8 4 km s 1 in the trench outer rise area the top of incoming oceanic plate is pervasively fractured and likely hydrated as shown by extensional faults horst and graben structures and a reduction of both crustal and mantle velocities these slow velocities are interpreted in terms of extensional bending related faulting leading to fracturing and hydration in the upper part of the oceanic lithosphere the incoming mocha fz coincides with an area of even slower velocities and thinning of the oceanic crust 10 15 thinning suggesting that the incoming fracture zone may enhance the flux of chemically bound water into the subduction zone slow mantle velocities occur down to a maximum depth of 6 8 km into the upper mantle where mantle temperatures are estimated to be 400 430c in the overriding plate the tomographic model reveals two prominent velocity transition zones characterized by steep lateral velocity gradients resulting in a seismic segmentation of the marine fore arc the margin is composed of three main domains 1 a 20 km wide frontal prism below the continental slope with vp 3 5 km s 1 2 a 50 km area with vp 4 5 5 5 km s 1 interpreted as a paleoaccretionary complex and 3 the seaward edge of the paleozoic continental framework with vp 6 0 km s 1 frontal prism velocities are noticeably lower than those found in the northern erosional chile margin confirming recent accretionary processes in south central chile

crustal xenoliths from calbuco volcano andean southern volcanic zone implications for crustal composition and magma crust interaction crustal xenoliths in the 1961 andesite flow of calbuco volcano in the southern southern volcanic zone ssvz of the andes consist predominantly of pyroxene granulites and hornblende gabbronorites the granulites contain plagioclase pyroxene magnetite amphibole and have pronounced granoblastic textures small amounts of relict amphibole surrounded by pyroxene plagioclase magnetite glass symplectites are found in some specimens these and similar textures in the gabbronorites are interpreted as evidence of dehydration melting mineral and bulk rock geochemical data indicate that the granulites are derived from an incompatible trace element depleted basaltic protolith that underwent two stages of metamorphism a moderate pressure high temperature stage accompanied by melting and melt extraction from some samples followed by thermal metamorphism after entrainment in the calbuco andesite lavas high nd t values 4 0 to 8 6 nd isotope model ages of 1 7 2 0 ga and trace element characteristics like chondrite normalized la yb and la nb 1 indicate that the protoliths were oceanic basalts similar oceanic metabasalts of greenschist to amphibolite facies are found in the paleozoic metamorphic belt that underlies the chilean coastal ranges mineral and bulk rock compositions of the gabbronorite xenoliths indicate that they are cognate crystallizing from the basaltic andesite magma at calbuco crystallization pressures for the gabbros based on total al contents in amphibole are 6 8 kbar these pressures point to middle to lower crustal storage of the calbuco magma neither granulite nor gabbro xenoliths have the appropriate geochemical characteristics to be contaminants of calbuco andesites although an ancient sedimentary contaminant is indicated by the lava compositions the presence of oceanic metabasaltic xenoliths together with the sedimentary isotopic imprint suggests that the lower crust beneath the volcano is analogous to the coastal metamorphic belt which is an accretionary complex of intercalated basalts and sediments that formed along the paleozoic gondwanan margin if this is the case the geochemical composition of the lower and middle crust beneath the ssvz is significantly different from that of most recent ssvz volcanic rocks

geochemistry of the active azufre planchon peteroa volcanic complex chile 35 15 s evidence for multiple sources and processes in a cordilleran arc magmatic system

temperature dependence of sulfide and sulfate solubility in olivine saturated basaltic magmas abstract the sulfur concentration at pyrrhotite and anhydrite saturation in primitive hydrous basaltic melt of the 2001 2002 eruption of mt etna was determined at 200 mpa t 1050 1250 c and at log fo2 from fmq to fmq 2 2 fmq is fayalite magnetite quartz oxygen buffer at 1050 c au sample containers were used a double capsule technique using a single crystal olivine sample container closed with an olivine piston embedded in a sealed au80pd20 capsule was developed to perform experiments in s bearing hydrous basaltic systems at t 1050 c pyrrhotite is found to be a stable phase coexisting with melt at fmq fmq 0 3 whereas anhydrite is stable at fmq 1 4 fmq 2 2 the s concentration in the melt increases almost linearly from 0 12 0 01 to 0 39 0 02 wt s at fes saturation and from 0 74 0 01 to 1 08 0 04 wt s at anhydrite saturation with t ranging from 1050 1250 c the relationships between s concentration at pyrrhotite and or anhydrite saturation mgo content of the olivine saturated melt t and log fo2 observed in this study and from previous data are used to develop an empirical model for estimating the magmatic t and fo2 from the s and mgo concentrations of h2o bearing olivine saturated basaltic melts the model can also be used to determine maximum s concentrations if fo2 and mgo content of the melt are known the application of the model to compositions of melt inclusions in olivines from mt etna indicates that the most primitive magmas trapped in inclusions might have been stored at log fo2 slightly higher than fmq 1 and at t 1100 1150 c whereas more evolved melts could have been trapped at t 1100 c these values are in a good agreement with the estimates obtained by other independent methods reported in the literature

multiple subduction components in the mantle wedge evidence from eruptive centers in the central southern volcanic zone chile in the andean central southern volcanic zone basalts from small eruptive centers near the large composite center volcan villarrica are poor in fluid mobile elements such as b cs rb k pb ba and u compared with concurrently erupted villarrica basalts new 1 0 be and u series isotopic data for these centers show that fluid mobile element poor small eruptive center basalts have small 1 0 be 9 be ratios 1 6 1 9 10 1 1 and 2 3 8 u 2 3 0 th activity ratios near 1 0 whereas basalts from villarrica show 2 3 8 u enrichment and larger 1 0 be 9 be ratios 4 0 6 4 10 1 1 these results suggest that small eruptive center basalts include materials derived from the subducted lithosphere that were stored in the mantle wedge for 350 k y to 3 m y that these materials are poor in fluid mobile elements may reflect fluid expulsion during solidification or their formation in an initially hotter subduction setting in contrast the composite center basalts sample materials rich in fluid mobile elements that were recently transferred into the mantle wedge from the subducted lithosphere the results confirm that mantle wedges in subduction zones include subducted materials added to the wedge over both long and short time scales

sulfur bearing magmatic accessory minerals almost all magmas contain sulfide or sulfate bearing phases in most natural samples the sulfur bearing phase is a sulfide which typically is pyrrhotite fe1 x s or pyrite fes2 although chalcopyrite cufes2 pentlandite fe ni 9s8 sphalerite zns or molybdenite mos2 may be present as well sulfate minerals are rare at magmatic conditions and anhydrite caso4 is the most common other magmatic so4 bearing minerals include the sodalite group minerals hauyne simplified formula na ca 4 8 al6si6 o s 24 so4 cl 1 2 scapolite minerals silvialite ca na 4al6si6o24 so4 co3 and s bearing apatite ca5 po4 3 f cl oh barite baso4 has been mentioned in rare cases marchev 1991 sulfur bearing minerals usually constitute a negligible fraction of the mineral assemblage in magmatic rocks and thus can be classified as accessory minerals the crystallization of sulfide sulfate and s bearing minerals strongly depends on melt composition temperature and pressure and the s speciation in melt which in turn is strongly dependent on the prevailing oxygen fugacity baker and moretti 2011 this volume wilke et al 2011 this volume irrespectively of the low abundance of s bearing minerals the evolution of sulfur in magmas may be evaluated from the occurrence of sulfides and sulfates these minerals are critical for estimating the activity of various sulfur bearing species in magmas and can be used to constrain the oxygen fugacity and the s concentration in the melt e g pre eruptive sulfur concentration in melts the presence of either sulfide or sulfate in silicate melt indicates that the predominant dissolved sulfur species in the melt are s2 or s6 respectively typically one of these species is dominant but there are conditions where s2

comparative mass balance of volcanic edifices at the southern volcanic zone of the andes between 33 s and 46 s volcano edifice volume calculations are presented for 65 volcanoes of the 1400 km long chilean southern volcanic zone svz as a basic step in subduction zone mass budgets volume calculations are performed in a geographical information system that integrates digital elevation models based on of shuttle radar topography mission as well as aster gdem topographic data landsat satellite images and geological maps the method of volume calculation is straightforward for isolated morphologically well defined stratovolcanoes uncertainties increase for volcanic edifices that formed on pre existing rugged terrain for multi phase eruptive centers as well as for eroded edifices a revised segmentation of the arc is used to describe the spatial volume distribution of extruded magma along the svz and to discuss controlling tectonic factors peak volumes between arc and back arc are offset by 400 km the total volcanic extrusion is in the range of 10 13 km3 km ma major differences between the svz and the central american subduction system are notable with regard to volcano density and maximum volumes

crust magma interactions and the evolution of arc magmas the san pedro pellado volcanic complex southern chilean andes field petrographic and trace element data indicate that volcanic rocks of the quaternary san pedro pellado complex lat 36 s chile have incorporated a silicic component that may be derived from the crust isotope ratios of sr nd and pb vary little among the volcanic rocks this is due primarily to the limited isotopic contrast between the mesozoic tertiary crust and the young magmas isotope and element compositions of san pedro pellado rocks are similar to those reported from other localities in the southern volcanic zone of the chilean andes we suggest that crustal assimilation is a significant process in the genesis of differentiated volcanic rocks in the southern volcanic zone the san pedro pellado example illustrates the importance of considering all types of evidence not just isotopic data in the evaluation of crustal contributions to arc magmas

micromechanical modeling of the effective elastic properties of oolitic limestone a new micromechanical approach to analytical modeling of oolitic limestone is proposed limestone is modeled as a multiphase composite consisting of sparry calcite matrix spherical oolitic inhomogeneities oblate spheroidal pores of aspect ratio 0 2 and concave pores in the shape of superspheres the concavity factor is the key parameter affecting overall properties maxwell s homogenization scheme is used to calculate effective bulk and shear moduli of this multiphase composite as functions of total porosities the results are in good agreement with experimental data available in the literature

crustal sources involved in continental arc magmatism a case study of volcan mocho choshuenco southern chile volcan mocho choshuenco a pleistocene holocene basaltic andesite to dacite shield volcano located at lat 40 s in the southern volcanic zone svz of the andes is built on the thinnest svz continental crust 30 km which consists largely of paleozoic sedimentary and metamorphic rocks and mesozoic plutons sr pb nd and o isotopic ratios of mocho choshuenco lavas 87 sr 86 sr 0 70399 to 0 70422 206 pb 204 pb 18 57 to 18 61 207 pb 204 pb 15 60 to 15 63 208 pb 204 pb 38 45 to 38 57 143 nd 144 nd 0 512787 to 0 512881 18 o 5 8 to 6 8 standard mean ocean water are similar to those of other svz centers and exhibit no correlation with indices of differentiation however incompatible trace element systematics indicate that evolved lavas have been contaminated by crustal plutonic rocks by 5 to 15 rb ba k ba rb la and k la ratios increase with increasing sio 2 content as a result of assimilation of orogenic calc alkalic plutonic rocks enriched in rb and k relative to ba and la xenoliths of plutonic rocks recovered from mocho choshuenco lavas are slightly more radiogenic in 87 sr 86 sr less radiogenic in 143 nd 144 nd and comparable in pb isotopic ratios and they have variable 18 o contents 87 sr 86 sr 0 70482 to 0 70557 206 pb 204 pb 18 60 to 18 64 207 pb 204 pb 15 60 to 15 62 208 pb 204 pb 38 53 to 38 56 143 nd 144 nd 0 512686 18 o 3 3 to 5 5 smow contamination of mocho choshuenco parental magmas by crustal melts with small isotopic contrast imposed little variation on isotopic heterogeneities existing in the parental compositions these heterogeneities probably were produced during magma crust interaction at the crust mantle boundary or in the lower crust

arc magma compositions controlled by linked thermal and chemical gradients above the subducting slab 1 global arc magmatism is sustained by a continuous fluid flux that is returned to the mantle in subduction zones despite considerable advances in simulations of melting processes models of arc magmatism remain incompletely tested against erupted products here we show that a suite of primitive volcanic rocks from across the southern chilean arc preserves the signature of a systematic down slab gradient in fluid chemistry the chemical gradient is consistent with predictions from modeling geothermometry and experiments we infer that increasing slab surface temperatures cause the sub arc slab flux to become less water rich and increasingly dominated by hydrous melts over a distance of a few kilometers behind the arc front this change exerts a first order control on magma chemistry and implies discrete melt transport pathways through subduction zones our results replicate patterns in other arcs implying common sub arc slab surface temperature ranges in thermally diverse subduction zones

the oxidation state of sulfur in magmatic fluids abstract sulfur compounds in volcanic gases are responsible for the global cooling after explosive eruptions and they probably controlled the early evolution of the earth s atmosphere we have therefore studied the oxidation state of sulfur in aqueous fluids under the pressure and temperature conditions and oxygen fugacities typical for magma chambers 0 5 3 kbar 650 950 c ni nio to re reo 2 buffer conditions sulfur speciation was determined by raman spectroscopy of quenched fluids trapped as inclusions in quartz our results show that sulfur in hydrothermal fluids and volcanic gases is much more oxidized than previously thought and in particular some explosive eruptions may release a significant fraction of sulfur as so 3 or its hydrated forms in the pressure range from 500 to 2000 bar the equilibrium constant k 1 of the reaction 2h 2 s 3o 2 2so 2 2h 2 o in aqueous fluids can be described by lnk 1 57 1 7 1 173 480 7592 t 1 where t is temperature in kelvin the equilibrium constant k 2 for the reaction so 2 o 2 so 3 in aqueous fluids where so 3 may include hydrated forms such as h 2 so 4 was found to be strongly pressure dependent with lnk 2 5 2 5 7 19 243 5993 t 1 at 1500 bar lnk 2 11 1 1 3 25 383 1371 t 1 at 2000 bar and lnk 2 22 1 2 2 37 082 2248 t 1 at 2500 bar our data imply that volcanoes may directly inject hexavalent sulfur in the form of h 2 so 4 into the atmosphere not only on earth but possibly also on venus and on mars when it was still tectonically active remote measurements from satellites may have underestimated the sulfur yield of some recent eruptions moreover the mechanisms of the interaction of volcanic gases with the stratosphere need to be reconsidered

geochemical variations in andean basaltic and silicic lavas from the villarrica lanin volcanic chain 39 5 s an evaluation of source heterogeneity fractional crystallization and crustal assimilation at 39 5 s in the southern volcanic zone of the andes three pleistocene recent stratovolcanoes villarrica quetrupillan and lanin form a trend perpendicular to the strike of the andes 275 to 325 km from the peru chile trench basalts from villarrica and lanin are geochemically distinct the latter have higher incompatible element abundances and la sm but lower ba la and alkali metal la ratios these differences are consistent with our previously proposed models involving a a west to east decrease in an alkali metal rich high ba la slab derived component which causes an across strike decrease in degree of melting or b a west to east increase in the contamination of subduction related magma by enriched subcontinental lithospheric mantle silicic and mafic lavas from the stratovolcanoes have overlapping sr nd and o isotopic ratios silicic lavas also have geochemical differences that parallel those of their associated basalts e g rhyolite from villarrica has lower la sm and incompatible element contents than high sio2 andesite from lanin at each volcano the most silicic lavas can be modelled by closed system fractional crystallization while andesites are best explained by magma mixing apparently crustal contamination was not an important process in deriving the evolved lavas basaltic flows from small scoria cones 20 35 km from villarrica volcano have high incompatible element contents and low ba la like lanin basalts but trend to higher k rb 356 855 and lower 87sr 86sr 0 70361 0 70400 than basalts from either stratovolcano however all basalts have similar nd pb and o isotope ratios the best explanation for the unique features of the cones is that the sources of svz magmas e g slab derived fluids or melts of the subcontinental lithospheric mantle have varying alkali metal and radiogenic sr contents these heterogeneities are not manifested in stratovolcano basalts because of extensive subcrustal pooling and mixing this model is preferable to one involving crustal contamination because it can account for variable sr isotope ratios and uniform nd and pb isotope ratios among the basalts and the divergence of the cones from across strike geochemical trends defined by the stratovolcanoes

three dimensional density model of the nazca plate and the andean continental margin 1 we forward modeled the bouguer anomaly in a region encompassing the pacific ocean 85 w and the andean margin 60 w between northern peru 5 s and patagonia 45 s the three dimensional density model that reproduces the gravity field is a continental scale representation of density structure to 410 km depth that characterizes the mantle and crust of the oceanic nazca plate subducted slab and continental margin with a minimum number of bodies we predefined the density of each body after studying the dependency of density on composition of crustal and mantle materials and pressure temperature conditions appropriate for the andean setting a database of independent geophysical information constrains the geometry of the top of the subducted slab locally the moho of the oceanic and continental crusts and indirectly the lithosphere asthenosphere boundary underneath the continental plate other boundaries notably the intracrustal density discontinuity separating upper from lower crust below the continent were not constrained and their geometry is the result of fitting the observed and calculated bouguer anomaly during forward modeling this contribution presents the model to the andean geoscientific community and contains some tools like a sensitivity analysis that helps potential users of the model to interpret its results we describe and discuss some of these results in order to illustrate the application of the model to the study of a wide range of phenomena e g modification of oceanic plate structure by hot spots shape of the subducted slab thermal structure of the continental lithosphere compensation mechanism and formation of orogenic relieve causes of andean segmentation

eruptive stratigraphy of the tatara san pedro complex 36 s southern volcanic zone chilean andes reconstruction method and implications for magma evolution at long lived arc volcanic centers

petrological insights into shifts in eruptive styles at volcan llaima chile tephra and lava pairs from two summit eruptions ad 2008 and 1957 and a flank fissure eruption ad 1850 are compared in terms of textures phenocryst contents and mineral zoning patterns to shed light on processes responsible for the shifts in eruption style during typical eruptive episodes at volcan llaima andean southernvolcanic zone chile the mineralogy and whole rock com positions of tephra and lavas are similar within eruptive episodes suggesting a common magma reservoir for strombolian paroxysms and lava effusion the zoning profiles and textures of plagioclase record successive and discrete intrusions of volatile rich mafic magma accompanied by mixing of these recharge magmas with the resident basaltic andesitic crystal mushes that are commonly present at shallow levels in the llaima system each recharge event destabil izes the plagioclase in equilibrium with the resident crystal mush melt and stabilizes relatively an rich plagioclase as is recorded by the numerous resorption zones lavas typically have 15 20 vol more phenocrysts than the tephra differences in plagioclase and olivine textures and zoning combined with different phenocryst contents indicate that a greater volume fraction of recharge magma is present in the explosively erupted magma than in subsequent effu sively erupted magma we propose that strombolian paroxysms at volcan llaima are triggered by interactions with large volume frac tions of recharge magma which decrease the bulk viscosity and in crease the volatile contents of the erupted magmas leading to the conditions required for the fragmentation of basaltic andesite lava effusion ensues from reduced interactions with the recharge magma after it has partially degassed and crystallized thereby impeding rapid ascent this process could be operating at other steady state basaltic volcanoes wherein shallow reservoirs are periodically re filled by fresh volatile rich magmas

volatile sulphur and chlorine major and trace element geochemistry of mafic to intermediate tephras from the chilean southern volcanic zone 33 43 s here we present the first systematic investigation of volatile geochemistry along the southern volcanic zone svz of chile holocene olivine hosted melt inclusions in the most mafic tephras sampled from 16 volcanoes along the volcanic front of the svz between 33 s and 43 s were analysed for pre eruptive sulphur chlorine and major element contents these results are combined with trace element compositions of the host whole rocks the highest fractionation corrected gas contents occur in the least degassed melt inclusions from small monogenetic cones of los hornitos cabeza de vaca and apagado from both the transitional and the southern central svz reaching 3 000 g g s and 1 400 g g cl while the lowest abundances of 1 100 g g s and 600 g g cl were found in the central svz at volcan lonquimay volcan llaima and volcan villarrica chlorine co varies with trace element indicators for the degree of melting and or source enrichment such that the lowest cl contents are found in high degree melts from the most depleted mantle sources the size of the volcanic edifices correlates inversely with cl abundances in the melt this could reflect more extensive degassing during ascent through the complex magma plumbing systems beneath the stratovolcanoes or greater dilution during larger degrees of melting of more depleted sources or a combination of these factors compared to other subduction zones the svz melt inclusions exhibit cl and s abundances in the same range as most of those from the central american and those from the marianas arcs

time dependent deformation behaviors of weak sandstones abstract time dependent deformation behavior of rocks has a significant impact on the stability of rock slopes or underground constructions this paper presents systematic experimental data regarding time dependent deformation of a typical weak sandstone known as the mushan sandstone the observed deformations are further separated to distinguish elastic and viscoplastic behaviors of the weak sandstone through the use of multi staged loading creep unloading reloading tests the stress path is designed to be a purely hydrostatic loading followed by a pure shear so that the deformations induced by these two types of stresses can be distinguished for elastic behavior although the nonlinear stress strain relations vary according to the applied hydrostatic stress these stress strain relations can be normalized by the applied hydrostatic stress or the bulk modulus and converted into a single consistent stress strain curve inelastic behavior is then obtained by subtracting the elastic deformation from the total deformation as a result the characteristics of the viscoplastic deformation are that 1 the direction of the viscoplastic flow is time independent and 2 it has a similar direction to the conventionally defined plastic flow as such the viscoplastic potential has a similar shape to the plastic potential but the size of the former changes with time while the latter has a size that is time independent meanwhile through the calculation of irreversible work direct evidence of orthogonality between the yield surface and the plastic flow as well as the viscoplastic flow is observed thus it is reasonable to assert that the yield surface the plastic potential and the viscoplastic potential all have the same geometry consequently the associated flow rules are applicable to modeling the time dependent deformational behavior of weak sandstones

calbuco volcano and minor eruptive centers distributed along the liquine ofqui fault zone chile 41 42 s contrasting origin of andesitic and basaltic magma in the southern volcanic zone of the andes calbuco volcano is a late pleistocene holocene composite stratovolcano located at 41 20 s in the southern region of the southern volcanic zone of the andes ssvz 37 46 s in contrast to basalt and basaltic andesite which are the dominant lava types on the volcanic front from 37 to 42 s calbuco lavas are porphyritic andesites which contain a wide variety of crustal xenoliths they have sio2 contents in the 55 60 range and have comparatively low k2o rb ba th and lref abundances relative to other ssvz centers incompatible element abundance ratios are similar to those of most ssvz volcanics but 87sr 86sr and 143nd 144nd are respectively higher and lower than those of adjacent volcanic centers basalts from nearby osorno stratovolcano 25 km to the northeast are similar to other basaltic ssvz volcanoes however basalts from several minor eruptive centers mec located east of calbuco and osorno volcano along the liquine ofqui fault zone lofz are enriched in ba nb th and lree and have higher la yb and lower ba la k la and rb la 87sr 86sr and 143nd 144nd in mec basalts are respectively lower and higher than those of osorno and calbuco lavas we suggest that mec basalts were produced by lower extents of mantle melting than basalts from osorno and other ssvz stratovolcanoes probably as a result of lower water content in the source of mec basalts calbuco andesites formed from basaltic parents similar to osorno basalts by moderate pressure crystallization of a hornblende bearing assemblage accompanied by crustal assimilation hornblende stability in the calbuco andesites was promoted by the assimilation of hydrous metasedimentary crustal rocks which are also an appropriate endmember for isotopic trends together with magma storage at mid crustal depths the unique characteristics of calbuco volcano i e the stability of hornblende at andesitic sio2 contents low 143nd 144nd and high 87sr 86sr and abundant crustal xenoliths provide evidence for crustal assimilation that is not apparent at more northerly volcanoes in the ssvz