sedimentary processes in the river dominated mvoti estuary south africa abstract the mvoti river enters the indian ocean on the natal coast of south africa in its lower reaches the river comprises a narrow shallow channel that traverses a broad floodplain at the coast an outlet to the sea is maintained through a sandy barrier across an underlying rock outcrop seawater intrusion through the outlet is prevented by the elevation of the rock outcrop and hence reversing currents and tidal salinity variations typical of estuaries are not developed in the lower reaches of the river sedimentary deposits and processes in the back barrier area are predominantly fluvial and the system is best classified as a river dominated estuary a lack of coastal progradation prevents its definition as a delta the greatest geomorphological impacts in the channel and barrier are caused by extreme river floods sedimentary processes revealed by aerial photography and field measurements in the mvoti show changes in response to discharge variation within the normal range of discharge variation the channel varies in dimension and morphology but no major long term buildup of sediment is evident in the floodplain or channel minor floods deposit muddy overbank deposits during such floods the channel gradient is increased by barrier breaching and channel shortening but wave dominated barrier processes act to close the breach rapidly superimposed on these short term changes is a cyclic pattern driven by major floods which cause lateral channel erosion and overbank deposition post flood recovery involves progressive channel confinement and stabilisation as flow reverts to a single or braided channel and the floodplain is re vegetated after major floods the channel assumes a position in the centre of the floodplain but subsequently it shows a tendency to migrate to the edge of the floodplain and elongate its channel current incorrect perceptions of the river mouth area as an estuary degraded by siltation are based on a comparison of present morphology with typical wave dominated estuaries and lack of recognition of the mvoti as one of a suite of river dominated estuaries the study highlights the need for a suite of universally applicable models not only for estuaries but for transitional fluvio marine environments in general

sources sinks and storage of river sediment in the atlantic drainage of the united states the history of sediment and its movement in the atlantic drainage demonstrate some of the difficulties of modeling sediment on a river basin scale soil erosion was accelerated by a factor of at least 10 when european settlers cleared forests and planted crops although increasing soil conservation practice and decreasing crop farming have since reduced the rates of erosion large quantities of eroded material are still stored on hillslopes and in stream valleys where they continue to augment the sediment loads of the rivers the sediment from this episode of erosion that is largely past can be expected to emerge from storage for many decades and perhaps even several centuries to come the reservoirs that have been built on many of the major rivers trap significant portions of the moving sediment which in some places may be remobilized by large floods essentially all the river sediment that reaches the atlantic coastal zone is trapped in estuaries and coastal marshlands probably less than 5 is deposi

a melt inclusion study of the toba tuffs sumatra indonesia the toba caldera in northern sumatra indonesia is the site of earth s largest quaternary volcanic eruption this eruption dated at 74 ka produced the 2800 km3 youngest toba tuff ytt and ash fall quartz bearing silicic pumices ranging from 68 to 77 wt sio2 indicate that the ytt magma was zoned compositionally and mineralogically prior to the ytt eruption two other silicic quartz bearing tuffs known as the middle toba tuff mtt and the oldest toba tuff ott were erupted from toba at 0 501 ma and 0 840 ma respectively although the volatile contents of the toba magmas are poorly constrained aerosols generated by the ytt eruption are generally thought to have caused a global volcanic winter an evaluation of the pre eruptive dissolved gas contents of the ytt magma is fundamental to understanding the global effects of this eruption we used melt inclusions in quartz crystals to determine the dissolved h2o co2 s cl and f contents of the ytt mtt and ott magmas quartz crystals selected from pumice blocks and welded tuffs that spanned the compositional ranges of the three units were chosen for study major and trace element analyses of melt inclusions were also conducted to characterize melt evolution and provide context to the volatile data melt inclusions from the ytt mtt and ott are rhyolitic in composition 73 77 wt sio2 and have overlapping indistinguishable major element trends inclusions from the large eruptions ytt and ott have similar geochemical relationships where the most evolved melt inclusions occur in the least silicic bulk rock samples and are more evolved than their matrix glasses in contrast the least evolved melt inclusions occur in the most silicic samples and either overlap with or are less evolved than their matrix glasses these patterns can be explained if quartz crystals in the least silicic magmas were inherited from more evolved melt while those in the most silicic melt formed in situ several lines of evidence suggest that crystal settling of early formed quartz crystals in long lived magma bodies was an important process in the ytt and ott magmas trace element data from the ytt melt inclusions have wide ranges rb 250 830 ppm ba 10 485 ppm and mostly support these models however incompatible trace elements are enriched 2 3 over their matrix glass compositions in all samples in the smaller mtt melt inclusions overlapped with the compositional range of the bulk rock samples and are consistent with in situ crystallization ftir analyses indicate that the ytt mtt and ott melts contained about 4 0 5 5 2 0 5 5 and 2 0 5 5 wt h2o respectively co2 contents in all units are generally 100 ppm and cl is 2000 ppm water gradients occur in all 3 tuffs cl gradients are evident only in the ytt and the least silicic samples from all units had no detectable co2 sulfur contents in melt inclusions are low in all samples 32 ppm and overlap with matrix glass s contents applying broad degassing constraints about 1014 g of h2so4 aerosols were likely loaded into the atmosphere during the ytt eruption 2 orders of magnitude less than previous petrologic estimates considerably more cl and f about 1015 g of each may have been part of the ytt aerosol cloud

chemical differentiation of the bishop tuff and other high silica magmas through crystallization processes re examination of petrochemical data for high silica ash flow tuffs suggests that crystal liquid fractionation plays a major role in the differentiation of high silica magmas for the high silica bishop tuff the enrichment and depletion of 27 major and trace elements correlates with the bulk crystal liquid partition coefficients calculated from the data of hildreth in ways that are consistent with crystal fractionation comparison of the bishop tuff with other high silica tuffs and rhyolites with different compositional variations and different phenocryst assemblages shows the correspondence of chemical gradients with mineralogy crystal zoning studies in the cordillera paine granite in southern chile suggest that the evolution of differentiated liquids similar to those in the bishop tuff results from crystal fractionation the physical mechanisms of separation of liquid and crystals for the paine granite and bishop tuff were quite different however differentiation of the high silica ash flows might result from advection of a less dense liquid from a crystallizing boundary into the top of the magma chamber

estimates of p t ph2o and fo2 for lavas from patmos greece and implications for magmatic evolution abstract various geothermometers and geobarometers are used to estimate the conditions at which magmas erupted on patmos crystallized equilibrium phenocryst compositions are used as input data for the calculations and previously reported activity composition relationships for minerals and melts are used the results constitute an internally consistent set of estimates of t p p h 2 o and f o 2 but there are large auncertainties in values of p 2 kbar p h 2 o up to 0 7 kb and f o 2 up to 1 4 log units the ne trachybasalt hy trachybasalt hy trachyandesite q trachyte lavas of the main volcanic series mvs crystallized over a temperature interval of 1173 920 c at 2 4 kbar water contents calculated from p h 2 o ranged from 2 5 in the least evolved magmas to 5 6 in the q trachytes oxygen fugacity about 3 log units above values for the fmq buffer during crystallization of the ne trachybasalt was similar to values for alkaline lavas from arcs and from oceanic islands calculated oxygen fugacities for crystallization of the evolved mvs magmas are lower within about 1 log unit of the fmq buffer and this partly reflects uncertainties in calculation of the activity of annite the ne trachybasalts of the young volcanic series yvs crystallized at 1141 1121 c at values of f o 2 about 2 log units above those defined by the fmq buffer these magmas contained 2 2 3 8 h 2 o prior to eruption crystallization of the yvs magmas was polybaric and occurred over the pressure range 7 2 kbar the higher pressure indicates that magma evolution began in chambers sites at or near the base of the crust about 28 km the results place constraints on models for the evolution of the magmas erupted on patmos the data are consistent with eruption of the mvs magmas from a single chamber sited at a depth of 11 5 km or from several chambers sited over a depth interval of 8 5 to 14 5 km the f o 2 t data do not necessarily indicate that the trachyandesites and q trachytes are unrelated to the ne trachybasalts other factors such as assimilation and degassing prior to eruption can lead to a lowering of f o 2 during evolution polybaric crystallization of the yvs magmas as they traversed crust heated by previous magmatic activity is consistent with evolution via assimilation coupled with fractionation the preservation of xenocrysts of mantle olivine in the primitive mvs and yvs ne trachybasalts requires magma ascent times of less than about 78 days calculated from published diffusion data it is suggested that the yvs ne trachybasalts experienced fractional crystallization in the mantle prior to picking up the xenocrysts the phenocrysts in the mvs ne trachybasalt record low pressure 2 3 kbar crystallization indicating that either a these magmas represent hybrids formed by mixing of a primitive xenocryst bearing magma with a more evolved magma or b they evolved via fractional crystallization within the crust mixing is not consistent with mineralogical and geochemical data and the latter alternative is preferred crystallization occurred rapidly under supercooled conditions when magma ascent was temporarily arrested in low pressure chambers containing less dense evolved magmas hy trachybasalt to q trachyte fractionation probably reflects preferential nucleation and growth along the chamber margins it is apparent that xenocryst bearing magmas can evolve via fractional crystallization and an important implication is that xenolith xenocryst bearing magmas may also assimilate crustal material hence the trace element and isotopic signatures of such magmas do not necessarily reflect those of the upper mantle source region

petrological statistical approach to interpret recent and subrecent lagoon subfacies idku nile delta of egypt abstract an approach combining petrology and statistics cluster analysis is developed to better distinguish a series of subfacies in surficial and short core samples from idku lagoon in the northwestern nile delta egypt the method integrates lithology physical and biogenic structures grain size and composition of the sand size fraction seven lithofacies eight grain size types and six clusters reveal comparable geographic distributions that are a direct response to geomorphic setting and depositional processes both of which have been modified by man although positioned in an arid setting and affected by anthropogenic factors land reclamation pollutants regional subfacies distribution patterns in idku lagoon are largely a function of the spatial configuration of freshwater dominated to brackish to higher salinity dominated near inlet zones typical of lagoons receiving significant freshwater input within idku a northern depositional province near the inlet and along the coastal sand barrier is defined by associations of terrigenous and coarse grained sediment types a southern province bounded by lagoon margins and marshes is characterized by finer grained sediment types with a high biogenic content recording lower energy levels the petrological statistical approach is used to identify and interpret lagoon subfacies in older to 6000 years b p core sections in idku region and in former abu qir lagoon additionally cluster analysis serves to determine specific lagoon subfacies from hand samples alone whether from surface grabs or cores this is based on a comparison of lithofacies and clusters determined for surficial and short core samples in the idku region to test the method a separate cluster analysis also using surficial and short core samples was used to define manzala lagoon subfacies in the northeastern nile delta results are generally comparable to those obtained in the idku study and show a close relation among manzala lagoon subfacies geomorphic configuration and depositional processes the petrological statistical method could be applied to other regions and also to the geological record

the ascent of felsic magmas in dykes abstract the results of a thermal and fluid dynamical analysis are presented that allow geologists to estimate the critical dyke or fracture width w c necessary for the transport of felsic magma through the crust without control by solidification the principal geological variables required to estimate w c are the magmatic viscosity the density and temperature contrasts and t between magma and country rock and the height of ascent h the results show that for typical values of and and for transport distances of 20 to 30 km the critical dyke width is constrained to lie between about 2 and 20 m

pocho volcanic rocks and the melting of depleted continental lithosphere above a shallowly dipping subduction zone in the central andes the late miocene 7 9 to 4 5 ma pocho volcanic field in argentina occurs 700 km east of the chile trench over the modern shallowly dipping andean wadati benioff zone near 32 s latitude in argentina the field is located in the sierra de cordoba which is the easternmost laramide style block faulted range in the sierras pampeanas pampean ranges the arrival of the shallowly dipping slab initiated both volcanism and the uplift of the sierra de cordoba pocho rocks 52 to 68 sio2 feo mgo 2 2 comprise an older 7 5 0 5 ma high k and a younger 5 3 0 7 ma shoshonitic series mineralogic data and fractionation models show that crystallization occurred under hydrous oxidizing conditions which were most extreme in the high k series an unusual pattern of successively lower ree at higher sio2 concentrations can be modeled by sphene apatite and amphibole removal an arc like trace element signature attributed to an arc component is strongest in the younger shoshonitic series an important depleted lower crustal mantle lithospheric source component in both series is indicated by non radiogenic sr and pb isotopic ratios at nd 0 to 2 low rb sr ratios and low u and th concentrations this depleted signature contrasts with the enriched one in potassic back arc central volcanic zone cvz lavas over the steeper subduction zone to the north and is attributed to several processes in the shallow subduction zone first deep crustal mash processes in the nearly normal thickness crust beneath pocho incorporated depleted proterozoic basement components and not complexly mixed structurally thickened crustal components as in the cvz second the association of pocho volcanism with the arrival of the slab allowed little time for modification of the mantle by subduction components third miocene shallowing of the subduction zone beneath the flat slab required thinning of both the astenosphere and the subcontinental lithosphere thus an important subcrustal component could be from blocks removed from the base of the lithosphere to the west and recycled into the asthenosphere similar magmatic sources would have existed during laramide shallow subduction in western north america

diffusional gradients at the crystal melt interface and their effect on the compositions of melt inclusions melt inclusions are widely believed to represent melts from which host crystals grew melt inclusions represent melt adjacent to growing crystals where compositional gradients exist due to preferential incorporation or exclusion of components by the crystallizing mineral the possibility arises therefore that melt in inclusions may differ significantly from melt which was more remote from growing crystals at the time the crystals grew we have tested this possibility by analyzing 45 major minor and trace components in 50 to 400 m diameter melt inclusions in phenocrysts from the rhyolitic bishop tuff california the following observations indicate that the effects of compositional gradients on chemical compositions of melt inclusions are negligible 1 melt inclusions in quartz and sanidine phenocrysts have indistinguishable compositions 2 no correlation is observed between sizes of melt inclusions and their chemical compositions 3 ten melt inclusions in four quartz phenocrysts from a single

ti diffusion in quartz abstract we have measured ti diffusion in quartz under dry 1 atm conditions experiments were performed using synthetic and natural quartz and a tio2 powder source with ti profiles obtained by rutherford backscattering spectrometry rbs over the temperature range 700 1150 c the following arrhenius relation was obtained for diffusion parallel to 001 d ti 7 10 8 exp 273 12 kj mol 1 r t m 2 sec 1 similar diffusivities were obtained for both synthetic and natural quartz and for a range of ti source materials including natural titanite powder and rutile quartz single crystal diffusion couples although ti diffusion appears slightly slower in the direction normal to c this difference is not great using these diffusion parameters calculations indicate that distances over which diffusional alteration of ti concentrations in quartz could occur in a million years would be on order of 500 m at 800 c and 15 m at 600 c the arrhenius relation above should be broadly applicable and may find application in constraining metamorphic histories under conditions where the ti in quartz geothermometer can be reasonably applied this relation can also be used to constrain peak temperatures and cooling histories from observations of exsolved rutile needles in quartz and the width of the ti depleted zone that develops around the growing needles finally these findings may find utility in evaluating crystal residence times in magmatic systems when coupled with observations of the sharpness of zoning patterns in quartz

cathodoluminescence of quartz from sandstones interpretation of the uv range by determination of trace element distributions and fluid inclusion p t x properties in authigenic quartz quartz overgrowths from keuper sandstones of the paris basin were examined using cathodoluminescence cl microscopy and spectroscopy coupled with a scanning electron microscope sem with the use of standard cold cl equipment it was observed that the emission of authigenic quartz is much less intense than that of detrital quartz grains but a reversal of intensity was observed with scanned cl in the 200 800 nm range the main cl emission band of diagenetic quartz is at 330 340 nm in the uv range with other bands in the visible range the determination of trace element distributions in authigenic quartz by in situ analyses and by sims imagery reveals the correlation of the 330 340 nm emission band with the highest al and li contents the cathodoluminescence emission of diagenetic quartz in the uv range appears to be influenced by the coupled substitution of al and li into the crystal two explanations are suggested 1 ai li or both serve as activators and 2 the incorporation of al and li causes lattice defects that lead to an enhancement of the intrinsic luminescence trace element analyses and fluid inclusion studies revealed that quartz overgrowths precipitated from a fluid that partially originated from an li enriched primary brine derived from eastern triassic evaporites of the paris basin the specific cl emission band in the uv range can be linked to the diagenetic environment the chemistry of the fluids appears to be the essential parameter whereas precipitation temperatures do not influence the occurrence of such emissions

quartz and feldspar zoning in the eastern erzgebirge volcano plutonic complex germany czech republic evidence of multiple magma mixing abstract zoned quartz and feldspar phenocrysts of the upper carboniferous eastern erzgebirge volcano plutonic complex were studied by cathodoluminescence and minor and trace element profiling the results verify the suitability of quartz and feldspar phenocrysts as recorders of differentiation trends magma mixing and recharge events and suggest that much heterogeneity in plutonic systems may be overlooked on a whole rock scale multiple resorption surfaces and zones element concentration steps in zoned quartz ti and feldspar phenocrysts anorthite content ba sr and plagioclase mantled k feldspars etc indicate mixing of silicic magma with a more mafic magma for several magmatic phases of the eastern erzgebirge volcano plutonic complex generally feldspar appears to be sensitive to the physicochemical changes of the melt whereas quartz phenocrysts are more stable and can survive a longer period of evolution and final effusion of silicic magmas the regional distribution of mixing compatible textures suggests that magma mingling and mixing was a major process in the evolution of these late variscan granites and associated volcanic rocks quartz phenocrysts from 14 magmatic phases of the eastern erzgebirge volcano plutonic complex provide information on the relative timing of different mixing processes storage and recharge allowing a model for the distribution of magma reservoirs in space and time at least two levels of magma storage are envisioned deep reservoirs between 24 and 17 km the crystallisation level of quartz phenocrysts and subvolcanic reservoirs between 13 and 6 km deflation of the shallow reservoirs during the extrusion of the teplice rhyolites triggered the formation of the altenberg teplice caldera above the eastern erzgebirge volcano plutonic complex the deep magma reservoir of the teplice rhyolite also has a genetic relationship to the younger mineralised a type granites as indicated by quartz phenocryst populations the pre caldera biotite granites and the rhyodacitic schonfeld volcanic rocks represent temporally and spatially separate magma sources however the deep magma reservoir of both is assumed to have been at a depth of 24 17 km the drastic chemical contrast between the pre caldera schonfeld westfalian b c and the syn caldera teplice westfalian c d volcanic rocks is related to the change from late orogenic geotectonic environment to post orogenic faulting and is considered an important chronostratigraphic marker

thermal history of the bandelier magmatic system evidence for magmatic injection and recharge at 1 61 ma as revealed by cathodoluminescence and titanium geothermometry abstract the rhyolitic valles caldera complex new mexico is one of the type examples of resurgent calderas and has experienced two well studied caldera forming eruptions the first formed the lower bandelier tuff lbt at 1 61 ma and the second emplaced the upper bandelier tuff ubt at 1 22 1 26 ma during the time between the lbt and the ubt the much smaller scale cerro toledo rhyolite ctr was sporadically erupted quartz crystals from these stages of activity were imaged with cathodoluminescence microscopy and growth zones in certain quartzes due to varying ti content were revealed crystallization temperatures were obtained with a titanium in quartz geothermometer the lbt quartzes are unzoned with temperatures clustering between 660 and 715 c when a calculated documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsm

silicate melt inclusion evidence for extreme pre eruptive enrichment and post eruptive depletion of lithium in silicic volcanic rocks of the western united states implications for the origin of lithium rich brines to evaluate whether anatectic and or highly fractionated lithophile element enriched rhyolite tuffs deposited in arid lacustrine basins lose enough lithium during eruption lithification and weathering to generate significant li brine resources pre eruptive melt compositions preserved in inclusions and the magnitude of post eruptive li depletions evident in host rhyolites were documented at six sites in the western united states each rhyolite is a member of the bimodal basalt rhyolite assemblage associated with extensional tectonics that produced the basin and range province and rio grande rift an evolving pattern of closed drainage basins and geothermal energy or mineral resources results from the 0 8 ma bishop tuff geothermal in california 1 3 to 1 6 ma cerro toledo and upper bandelier tephra geothermal and 27 9 ma taylor creek rhyolite sn in new mexico 21 7 ma spor mountain tuff be u f and 24 6 ma pine grove tuff mo in utah and 27 6 ma hideaway park tuff mo in colorado support the following conclusions melt inclusions in quartz phenocrysts from rhyolite tuffs associated with hydrothermal deposits of sn mo and be are extremely enriched in li 1 000s of ppm those from spor mountain have the highest li abundance yet recorded max 5 200 ppm median 3 750 ppm forty five to 98 of the li present in pre eruptive magma was lost to the environment from these rhyolite tuffs the amount of li lost from the small volumes 1 10 km3 of li enriched rhyolite deposited in closed basins is sufficient to produce world class li brine resources after each eruption meteoric water leaches li from tuff which drains into playas where it is concentrated by evaporation the localized occurrence of li enriched rhyolites may explain why brines in arid lacustrine basins seldom have economic concentrations of li considering that hydrothermal deposits of sn mo be u and f may indicate potential for li brines in nearby basins we surmise that the world s largest li brine resource in the salar de uyuni 10 mt received li from nearby rhyolite tuffs in the bolivian tin belt

evolution of crystal sizes in the series of dissolution and precipitation events in open magma systems article i nfo we propose a model that describes the evolution of crystal sizes and crystal size distributions csd of igneous phenocrysts in a sequence of dissolution and crystallization events this model is based on the assumption that crystal dissolution is rate limited by diffusion in melt while crystal growth is controlled by the slower kinetic of new nucleation and growth as a result the dissolution rate is inversely proportional to crystal size coming into effect through the curvature of the crystal s surface but the growth rate does not depend on the crystal size closed form analytical solution of equation for csd is obtained we apply results of modeling to quartz and zircon two prime minerals in silicic igneous systems that are widely used in geochemical and isotopic investigations the time series of multiple solution reprecipitation episodes generate concave downward csds and this result fits well with experimental and natural observations on the abundant concave down csd in silicic igneous rocks we suggest that maturation of crystal populations with sizes above several micrometers can not be caused by a size effect on the solubility of the crystals ostwald ripening but is rather driven by thermal oscillations in experiments and in nature the model predicts that mean crystal size increases with time proportionally to t 0 20 which is very close to the published experimental results for quartz maturation with the exponent of 0 19 0 22 our proposed model gives an opportunity to use natural csds for interpretation of pre eruptive magma history when solubilities and diffusion data are available for constituent elements of the dissolving mineral in particular we present time estimates for maturing zircon populations in large volume ignimbrites and estimate that it takes 100 1000 yrs to mature an initially exponential csd to a lognormal csd

geochemical isotopic and single crystal 40ar 39ar age constraints on the evolution of the cerro galan ignimbrites the giant ignimbrites that erupted from the cerro galan caldera complex in the southern puna of the high andean plateau are considered to be linked to crustal and mantle melting as a consequence of delamination of gravitationally unstable thickened crust and mantle lithosphere over a steepening subduction zone major and trace element analyses of cerro galan ignimbrites 68 71 sio2 that include 75 new analyses can be interpreted as reflecting evolution at three crustal levels afc modeling and new fractionation corrected 18o values from quartz 7 63 8 85 are consistent with the ignimbrite magmas being near 50 50 mixtures of enriched mantle 87sr 86sr 0 7055 and crustal melts 87sr 86sr near 0 715 0 735 processes at lower crustal levels are predicated on steep heavy ree patterns sm yb 4 7 high sr contents 250 ppm and very low nb ta 9 5 ratios which are attributed to amphibolite partial melts mixing with fractionating mantle basalts to produce hybrid melts that rise leaving a gravitationally unstable garnet bearing residue processes at mid crustal levels create large negative eu anomalies eu eu 0 45 0 70 and variable trace element enrichment in a crystallizing mush zone with a temperature near 800 850 c the mush zone is repeatedly recharged from depth and partially evacuated into upper crustal magma chambers at times of regional contraction crystallinity differences in the ignimbrites are attributed to biotite zoned plagioclase and other antecrysts entering higher level chambers where variable amounts of near eutectic crystallization occurs at temperatures as low as 680 c just preceding eruption 40ar 39ar single crystal sanidine weighted mean plateau and isochron ages combined with trace element patterns show that the galan ignimbrite erupted in more than one batch including a 2 13 ma intracaldera flow and outflows to the west and north at near 2 09 and 2 06 ma episodic delamination of gravitationally unstable lower crust and mantle lithosphere and injection of basaltic magmas whose changing chemistry reflects their evolution over a steepening subduction zone could trigger the eruptions of the cerro galan ignimbrites

the magmatic hydrothermal transition evidence from quartz phenocryst textures and endoskarn abundance in cu zn skarns at the empire mine idaho usa information about the magmatic to hydrothermal transition is preserved in late stage features of quartz phenocrysts and endoskarn alteration in some cu zn skarn deposits such as the empire mine in idaho important features include 1 quartz phenocrysts with strong resorption textures such as vermicular zones of igneous groundmass cutting primary quartz cathodoluminescence banding 2 anomalous amounts of endoskarn more than 50 of mineralized rock 3 high f activities as evidenced by fluorite as an accessory mineral in igneous rocks in alteration assemblages and in fluid inclusions and by high f in hydroxyl sites in igneous biotite and amphibole and 4 direct association of zn which normally is deposited distally at low temperature with cu in proximal locations and in endoskarn these features are explained by the following model 1 f lowers the solidus temperature of the magma thus changing the timing temperature and duration of hydrothermal fluid exsolution 2 upon magmatic vapor saturation the f rich hydrothermal fluids form bubbles that adhere to quartz phenocrysts and chemically corrode tunnel into the quartz forming vermicular resorption textures 3 f rich hydrothermal fluids also promote the formation of endoskarn silicic rocks are attacked by f rich fluids in the same sense that carbonate wall rocks are dissolved by weakly to moderately acidic hydrothermal fluids 4 low fluid exsolution temperature facilitated by high f activity promotes high zn cu ratios in proximal locations due to the solubility of zn relative to cu at lower temperatures this model may be applicable at other localities such as the world class cu zn skarn antamina mine as well as some tin and rapakivi granites

origin of hybrid ferrolatite lavas from magic reservoir eruptive center snake river plain idaho the mineralogy and geochemical characteristics of intermediate composition ferrolatites and related lavas from the magic reservoir eruptive center central snake river plain have been investigated to evaluate the origin and petrologic significance of these hybrid lavas the ferrolatites are chemically uniform but contain a disequilibrium phenocryst xenocryst assemblage derived in part from mixed rhyolitic and basaltic magmas that are closely represented by extrusive units in the area the hybrid lavas also contain xenoliths of archean granulites and have high 87sr 86sr and low 143nd 144nd ratios all of which suggest significant magma crust interaction quantitative models including magma mixing minor crystal fractionation and crustal contamination very closely reproduce the observed compositions of these ferrolatites closed system fractionation and or simple bulk contamination models are not as successful and can be ruled out it appears that preexisting mafic and silicic magmas from distinct sources e g mantle and crust encounter one another in crustal level magma chambers under conditions where intimate mixing may occur despite wide differences in the physical properties of these liquids

application of a two dimensional electrical tomography technique for investigating landslides along the amman dead sea highway jordan electrical tomography geophysical surveys were conducted with the syscal r2 resistivity instrument at the location of instantaneous rock failure of a few 1 000s m3 along the amman dead sea highway jordan providing a ground image for investigating landslide sites which caused material damage and closed the road this slide occurred along two major fault planes after heavy rainfall in a rock consisting of a succession of shale marl and marly limestone layers which were folded tilted and fractured three electrical tomography profiles were performed along the axis of the slope to assess the landslide risk in such potential unstable areas the results obtained based on two dimensional inversion of field data have allowed mapping of the shale zones at depths which are characterized by a lower resistivity value and have demonstrated that the rupture was initiated at the contact between the shale mass black colored and the massive limestone white yellowish brown colored

prolonged ascent and episodic venting of discrete magma batches at the onset of the huckleberry ridge supereruption yellowstone abstract how exceedingly large volcanic supereruptions begin provides crucial information on the storage ascent and release of silica rich magma in catastrophic events initial fall deposits of the 2 08 ma 2500 km 3 huckleberry ridge eruption are multiply bedded and in several places contain reworked intervals indicating time breaks in the opening phases of the eruption a 2 5 m section of these fall deposits was sampled at nine levels below the earliest ignimbrite member a at mount everts mammoth wyoming we analyzed major and trace elements and volatiles in quartz hosted melt inclusions mis reentrants res unsealed melt inclusions and associated obsidian pyroclasts thick walled shards to establish quartz crystallization and storage depths and melt compositional groupings systematic relationships between rb and other incompatible elements u cl b indicate 55 fractional crystallization between the least and most evolved glass compositions in contrast h 2 o concentrations in mis show scattered relationships with trace elements and are interpreted to reflect variable loss of h 2 o by diffusion through the quartz host during magma ascent the wide h 2 o variations 1 0 4 7 wt in mis from individual fall horizons imply as much as 14 days of diffusive loss reflecting highly variable and surprisingly slow decompression conditions water and co 2 gradients in reentrants however are consistent with final ascent times of 0 3 1 5 m s similar to those represented by mis that we infer to have experienced little to no diffusive h 2 o loss the wide range of ascent rates for co erupted crystals mirrors that of intermittent explosive activity at mount st helens in summer 1980 and implies that the huckleberry ridge magma body was not strongly overpressured at eruption onset restored entrapment pressures and geochemical data for mis provide evidence for six distinct populations of quartz that originally crystallized in geochemically distinct magma domains the compositions of res and obsidian pyroclasts by comparison show that by the onset of eruption the quartz had been brought together into three discrete magma bodies which we interpret to have been cupolas on the roof of the main magma body these cupolas were erupted sequentially and episodically from separate vents to generate the fall deposits before escalating activity led to generation of voluminous pyroclastic flows and this pattern of activity suggests that tectonic triggering may have destabilized multiple magma bodies supereruptions as large as the huckleberry ridge event may start hesitatingly if the parental magma bodies are not strongly overpressured with small scale episodic activity that is modulated by external controls that may leave no other geological evidence for their presence

origin of lamprophyres by the mixing of basic and alkaline melts in magma chamber in beiya area western yunnan china abstract lamprophyres consisting mainly of diopside phlogopite and k feldspar formed in the early tertiary around 60 ma in the beiya area and are characterized by low sio 2 46 50 wt rb 31 45 ppm and sr 225 262 ppm high al 2 o 3 11 2 13 1 wt cao 8 0 8 7 wt mgo 11 5 12 1 wt k 2 o 4 9 5 5 wt tio 2 2 9 3 3 wt and ree 174 177 ppm and compatible elements e g sc cr and ni and hsf elements e g th u zr nb ta ti and y and low 143 nd 144 nd 0 512372 0 512536 middle 87 sr 86 sr 0 707322 0 707395 middle 206 pb 204 pb 18 50 18 59 207 pb 204 pb 15 60 15 65 and 208 pb 204 pb 38 75 38 8 these rocks developed peculiar quartz megacrysts with poly layer reaction zones melt inclusions and partial melted k feldspar and plagioclase inclusions and plastic shapes important features of these rocks include 1 hybrid composition of elements 2 abrupt increase of sio 2 content of the melt recorded by zoned diopside 3 development of sanidine and aegirine augite reaction zones 4 alkaline melt and partial melted k feldspar and plagioclase inclusions 5 deformed quartz inclusions associated with quartz megacrysts 6 the presence of quartz megacrysts in plastic shape with their parent melts 7 the occurrence of olivine high mgo ilmenite and spinel inclusions within earlier formed diopside phlogopite and magnetite median 87 sr 86 sr values between tertiary alkaline porphyries in the beiya area and the western yunnan and tertiary basalt in the western yunnan indicate that the beiya lamprophyre melts were derivative and resulted from the mixing between basic melts that were related to the partial melting of phenocrysts of spinel iherzolite from a mantle source the alkaline melts originated from partial melting along the jinshajiang subduction ductile shear zone at the contact between the buried palaeo tethyan oceanic lithosphere and the upper mantle lithosphere the alkaline melts are composed of 65 sanidine or 70 ab 28 an 2 and 35 sio 2 the melt mixing occurred in magma chambers in the middle shallow crust at 8 10 km before the derivative lamprophyre melts intruded into the shallow cover in beiya area this mixing of basic and alkaline melts might represent a general process for the formation of lamprophyre in the western yunnan

fragmentation phenomena in populations of magmatic crystals fragmentation of crystals is an important mechanism and a component of particle dynamics in igneous and metamorphic rocks that has received surprisingly little attention recent advances in textural analysis extraction techniques digital imaging and computer assisted measurements enable rapid accumulation of 3d data on particle shapes and size distributions this paper reviews fragment size distributions fsd that result from fragmentation lognormal fractal loggamma and weibull discusses their genesis mechanisms and presents relevant examples of fragmentation from experimental physics next the paper considers fsds of feldspars on digitized images of thin sections and on published images and quartz extracted from vesicular pumice by acid from eight well known large volume eruptive units the acid solution of pumice enables examination of volume abundance 3d shapes proportions of fragmented crystals and measurements of their csds and fsds fsds were also measured in samples of welded tuff and a granite disaggregated by electric pulse products of syneruptive shock wave fragmentation and fragmentation by an electric pulse are found to be fractal with large breakage probabilities branching ratios and fractal dimensions of 2 to 3 in contrast most quartz fragments in pumice obey a lognormal distribution and fragmentation is driven by a melt inclusion decrepitation mechanism which results in low breakage probability and small number 2 3 of fragments per breakage cycle these results are consistent with one atmosphere heating experiments of quartz phenocrysts that led to melt inclusion decrepitation and caused quartz to break up into several smaller pieces collectively having lognormal fsd measured melt inclusion size distributions suggest decrepitation of outermost melt inclusions and low survival rate for large inclusions and inclusions with large radius crystal size ratio the modeling of periodic fragmentation of crystals with melt inclusions due to overheating and or decompression which may occur many times during the lifetime of a long lived magma body may explain concave down lognormal csds abundant in igneous rocks the genesis of lognormality can be explained by the fragmentation algorithm of kolmogorov 1941 other algorithms may generate lognormal like loggamma distributions fragmentation serves as an important size limiting factor a nucleation aid and it facilitates isotopic and trace elemental exchange

buoyant replenishment in silicic magma reservoirs experimental approach and implications for magma dynamics crystal mush remobilization and eruption 1 we present new experiments on replenishment of rhyolite magma chambers by rhyolite magma using corn syrup water solutions we emphasize small density contrasts and show that buoyancy is the key controlling factor for whether injections will rise to the top if buoyant or pond at the base if denser during emplacement we observe little or no mixing of the injected liquid with the reservoir liquid as predicted by the fact that our injections have low reynolds numbers 10 typically at later stages the low buoyancy 1 kg m 3 injected liquid which has accumulated at the top of the reservoir undergoes mixing with the reservoir liquid which may originate by the gravitational destabilization of a thin layer of denser resident liquid trapped above the injected liquid layer the presence of a basal crystal mush modeled by acrylic beads in a corn syrup water solution matrix is also considered slightly buoyant injections entrain a small fraction of mush particles to the top of the overlying liquid layer entrainment efficiency increases dramatically for high buoyancy injections we hypothesize that the injected liquid can entrain a maximum quantity of mush particles which corresponds to the amount required for the injected liquid mush particle suspension to attain neutral buoyancy in the resident liquid hence for silicic systems a replenishing melt can entrain up to 12 5 crystals during its ascent through the mush our results have implications for rhyolites bearing crystals with disequilibrium features as they may represent mush crystals remobilized by a replenishing silicic magma

origin of ti rich rims in quartz phenocrysts from the upper bandelier tuff and the tunnel spring tuff southwestern usa four compositionally zoned melt inclusion bearing quartz phenocrysts from the upper bandelier tuff new mexico and the tunnel spring tuff utah were examined in detail by cathodoluminescence laser ablation icp ms and titanium in quartz titaniq thermobarometry in order to reconstruct the conditions of quartz crystallization temperature and tio2 activity atio2 in the magma were estimated from melt inclusion compositions by means of zircon saturation thermometry and an experimentally calibrated tio2 solubility model whereas pressure was estimated with the most recent calibration of the titaniq thermobarometer on the host quartz next to the analyzed melt inclusions all four investigated quartz phenocrysts display a low luminescent ti poor core overgrown by a high luminescent ti rich rim reconstructed p t atio2 conditions suggest that the rimward increase in the ti content of the two quartz crystals from the upper bandelier tuff is due to a combination of increasing temperature increasing atio2 and decreasing pressure with the temperature effect being dominant in one crystal and the atio2 effect being dominant in the other crystal in the two crystals from the tunnel spring tuff the rimward increase in ti content is mostly due to increasing temperature but in one of them a negative pressure change played an equally important role this study demonstrates that in rapidly cooled peraluminous or metaluminous rhyolites the crystallization conditions of quartz phenocrysts can be reconstructed at the scale of individual growth zones which allows to investigate the origin and evolution of such magmas in great detail

timescales of mixing and mobilisation in the bishop tuff magma body perspectives from diffusion chronometry we present two feldspar thermometry and diffusion chronometry from sanidine orthopyroxene and quartz from multiple samples of the bishop tuff california to constrain the temperature stratification within the pre eruptive magma body and the timescales of magma mixing prior to its evacuation two feldspar thermometry yields estimates that agree well with previous fe ti oxide thermometry and gives a 80 c temperature difference between the earlier and later erupted regions of the magma chamber using the thermometry results we model diffusion of ti in quartz and ba and sr in sanidine as well as fe mg interdiffusion in orthopyroxene to yield timescales for the formation of overgrowth rims on these crystal phases diffusion profiles of ti in quartz and fe mg in orthopyroxene both yield timescales of 150 years for the formation of overgrowth rims in contrast both ba and sr diffusion in sanidine yield nominal timescales 1 2 orders of magnitude longer than these two methods the main cause for this discrepancy is inferred to be an incorrect assumption for the initial profile shape for ba and sr diffusion modelling i e growth zoning exists utilising the divergent diffusion behaviour of ba and sr we place constraints on the initial width of the interface and can refine our initial conditions considerably bringing ba and sr data into alignment and yielding timescales closer to 500 years the majority of which are then within uncertainty of timescales modelled from ti diffusion in quartz care must be thus taken when using ba in sanidine geospeedometry in evolved magmatic systems where no other phases or elements are available for comparative diffusion profiling our diffusion modelling reveals piecemeal rejuvenation of the lower parts of the bishop tuff magma chamber at least 500 years prior to eruption timescales from our mineral profiling imply either that diffusion coefficients currently used are uncertain by 1 2 orders of magnitude or that the minerals concerned did not experience a common history despite being extracted from the same single pumice clasts introduction of the magma initiating crystallisation of the contrasting rims on sanidine quartz orthopyroxene and zircon was prolonged and may be a marker of other processes that initiated the bishop tuff eruption rather than the trigger itself

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

assessment of soil liquefaction potential based on geoelectrical imaging a case study abstractdue to the low spatial resolution of s wave velocity vs depth profile derivable from multichannel analysis of surface waves masw for soil liquefaction studies we have developed an alternate novel method for better vs estimation using high resolution electrical resistivity tomography ert data which does not require standard penetration test spt boreholes our method uses popular regression equations for transforming resistivity ert sections into synthetic spt n data sections in turn these are used for getting factor of safety fos sections whose analysis leads to assessment of soil liquefaction hazard potential of a field site the conversion of spt n data into fos sections involves standard cyclic stress and cyclic resistance ratio computations our methodology is illustrated with the help of a field study involving two sites on our iit roorkee campus india the acquired data sets include ert and masw the achieved results including two different regression equations indicate that

a comment on titaniq under pressure the effect of pressure and temperature on the solubility of ti in quartz by jay b thomas e bruce watson frank s spear philip t shemella saroj k nayak and antonio lanzirotti trace concentrations of ti in quartz are used to indicate the pressure and temperature conditions of crystallization in the titaniq geothermobarometer of thomas et al contrib miner petrol 160 743 759 2010 it utilises the partitioning of ti into quartz as an indicator of the pressures and or temperatures of crystal growth for a given value of tio2 activity in the system if temperatures are inferred to 20 c pressure is constrained to 1 kbar and vice versa there are significant contrasts however between the conclusions from titaniq and those for natural quartz as well as other mineral phases in volcanic rocks application of the titaniq model to quartz from the 27 ka oruanui and 760 ka bishop high silica rhyolites where the values of t p and tio2 activity are constrained by other means fe ti oxide equilibria melt inclusion entrapment pressures in gas saturated melts melt and amphibole compositions yields inconsistent results if realistic values are given to any two of these three parameters then the value of the third is wholly unrealistic the model yields growth temperatures at or below the granite solidus pressures in the lower crust or upper mantle or tio2 activities inconsistent with the mineralogical and chemical compositions of the magmas cl imagery and measurements of ti and other elements in quartz are of great value in showing the growth histories and changes in conditions experienced by crystals but direct linkages to p t conditions during crystal growth cannot be achieved

rutile solubility in hydrous rhyolite melts at 750 900 c and 2 kbar with application to titanium in quartz titaniq thermobarometry abstract the solubility of rutile in water saturated haplogranite melts with molar al na k ratios ranging from 0 84 to 1 25 was determined at 750 900 c and 2 kbar in cold seal pressure vessel experiments due to the low diffusivity of ti at these conditions a new method was developed to determine tio2 solubility in this method glasses with tio2 gradients were used as starting material and after the experiments the tio2 content was measured at the contact between rutile bearing and rutile free glass the glasses were either directly equilibrated at the desired p t conditions i e crystallization experiments or first treated at 50 150 c lower temperatures and then subjected to the desired conditions i e dissolution experiments the results obtained in crystallization and dissolution experiments agree well with each other suggesting that equilibrium was attained rutile solubility in peralkaline melts strongly increases with temperature and the amount of excess alkalies according to the relation log tio 2 wt 1 8 ank 0 53 10 000 t 12 8 ank 4 3 in which ank is the deviation of the molar al na k ratio from unity and t is given in kelvin excess alumina does not seem to promote tio2 solubility for natural melt compositions it was found that if ca mg and fe are assumed to be 10 times less effective in promoting tio2 solubility than excess na and k good fits to previous solubility data in silicic 70 wt sio2 melts at upper crustal pressures 10 kbar are obtained application of this extended tio2 solubility model to natural melt inclusions in quartz phenocrysts from five silicic volcanic systems returns tio2 activities that are similar to those calculated with a previous experiment based model and to those calculated from pairs of coexisting fe ti oxides but are up to 2 9 times higher than those calculated with melts and rhyolite melts pressures calculated from ti concentrations in the host quartz using the most recent calibration of the titaniq thermobarometer are in good agreement with independent pressure estimates suggesting that at upper crustal conditions this calibration is valid

titaniq a titanium in quartz geothermometer titanium is one of many trace elements to substitute for silicon in the mineral quartz here we describe the temperature dependence of that substitution in the form of a new geothermometer to calibrate the titaniq thermometer we synthesized quartz in the presence of rutile and either aqueous fluid or hydrous silicate melt at temperatures ranging from 600 to 1 000 c at 1 0 gpa the ti contents of quartz in ppm by weight from 13 experiments increase exponentially with reciprocal t as described by text log left x text qtz text ti right 5 69 pm 0 02 frac 3765 pm 24 t k application of this thermometer is straightforward typically requiring analysis of only one phase quartz this can be accomplished either by epma for crystallization temperatures above 600 c or by sims for temperatures down to at least 400 resulting temperature estimates are very precise usually better than 5 c potentially allowing detailed characterization of thermal histories within individual quartz grains although calibrated for quartz crystallized in the presence of rutile the thermometer can also be applied to rutile absent systems if tio2 activity is constrained

application of cathodoluminescence to magmatic quartz in a tin granite case study from the schellerhau granite complex eastern erzgebirge germany a model of the cooling history of tin bearing granitic magma forming the schellerhau granites eastern erzgebirge germany is shown on the basis of quartz textures similar grain size similar grain habit and correlatable growth textures of phenocrysts in different granite varieties give proof of a common crystallization history before the melts of the schellerhau granite varieties were intruded four nucleation events occurred during crystallization in different crustal levels between about 20 and 1 km depth the parental melt of the schellerhau granites is interpreted to have contained 2 5 wt h2o originally the water content of the melt during the subvolcanic intrusion stage amounted to more than 5 wt and characterizes highly evolved residual melts that enable the formation of tin deposits this study contributes to a better understanding of the development and behaviour of fractionated tin bearing granitic melts and links quartz cathodoluminescence cl with microanalytical studies

the bishop tuff new insights from eruptive stratigraphy the 0 76 ma bishop tuff from long valley caldera in eastern california consists of a widespread fall deposit and voluminous partly welded ignimbrite the fall deposit f exposed over an easterly sector below and adjacent to the ignimbrite is divided into nine units f1 f9 with no significant time breaks except possibly between f8 and f9 maximum clast sizes are compared with other deposits where accumulation rates are known or inferred to estimate an accumulation time for f1 f8 as ca 90 hrs the ignimbrite ig is divided into chronologically and or geographically distinct packages of material earlier packages ig1 were emplaced mostly eastward are wholly intraplinian coeval with fall units f2 f8 lack phenocrystic pyroxenes and contain few or no glass mountain derived rhyolite lithic fragments earlier packages ig2 were erupted mostly to the north and east are at least partly intraplinian interbedded with fall unit f9 to the east contain pyroxenes and have lithic fractions rich in g

quaternary silicic pyroclastic deposits of atitlan caldera guatemala abstract atitlan caldera has been the site of several silicic eruptions within the last 150 000 years following a period of basalt andesite volcanism the silicic volcanism began with 5 10 km3 of rhyodacites erupted as plinian fall and pyroclastic flows about 126 000 yr b p at 85 000 yr b p 270 280 km3 of compositionally distinct rhyolite was erupted in the los chocoyos event which produced widely dispersed plinian fall deposits and widespread mobile pyroclastic flows in the latter parts of this eruption rhyodacite and minor dacite were erupted which compositionally resembled the earliest silicic magmas of the atitlan center as a result of this major eruption the modern atitlan iii caldera formed following this event rhyodacites were again erupted in smaller 5 13 km3 volumes partly through the lake and mafic volcanism resumed forming three composite volcanoes within the caldera the bimodal mafic silicic atitlan volcanism is similar to that which has occurred elsewhere in the guatemalan highlands but is significantly more voluminous mafic lavas are thought to originate in the mantle but rise intrude and underplate the lower crust and partly escape to the surface eventually silicic melts form in the crust possibly partly derived from underplated basaltic material rise crystallize and erupt the renewed mafic volcanism could reflect either regional magmato tectonic adjustment after the large silicic eruption or the onset of a new cycle

millennial timescale resolution of rhyolite magma recharge at tarawera volcano insights from quartz chemistry and melt inclusions most rhyolite eruption episodes of tarawera volcano have emitted several physiochemically distinct magma batches 1 10 km3 these episodes were separated on a millennial timescale the magma batches were relatively homogeneous in temperature and composition at pumice scale 4 cm but experienced isolated crystallisation histories at the sub cm scale matrix glasses have trace element compositions sr ba rb that vary by factors up to 2 5 indicating incomplete mixing of separate melts some quartz hosted melt inclusions are depleted in compatible trace elements sr ti ba compared to enclosing matrix glasses this could reflect re melting of felsic crystals deeper in the crystal pile individual quartz crystals display a variety of cathodoluminescence brightness and ti zoning patterns including rapid changes in melt chemistry and or temperature 50 100 c and point to multi cycle crystallisation histories the tarawera magma system consisted of a crystal rich mass containing waxing and waning melt pockets that were periodically recharged by silicic melts driven by basaltic intrusion

petrology and emplacement dynamics of intrusive and extrusive rhyolites of obsidian dome inyo craters volcanic chain eastern california drilling at obsidian dome has provided continuous core samples of the distal and proximal portions of obsidian dome its conduit and an associated feeder dike both the dome and conduit are chemically and mineralogically zoned and consist of a finely porphyritic high ba low silica rhyolite occurring in the basal portion of the dome and margins of the conduit and a finely porphyritic low ba higher silica rhyolite occurring in the upper portion of the dome and center of the conduit the high ba rhyolite contains two distinct phenocrysts assemblages with two distinct compositions and represents mingled magmas the low ba rhyolite in the dome and conduit contains significantly fewer disequilibrium phenocrysts and is only slightly mingled the dike sampled at 600 m depth as well as a related tephra fall from obsidian dome vent are entirely low ba rhyolite that contain no evidence of magma mingling end members of the mingled magma calculated using two different methods are a 63 silica end member and a silicic end member identical in composition to the dike and tephra fall from obsidian dome vent this silicic end member was the first magma emplaced in the dike and comprised much or all of the first magma vented to the surface during formation of the obsidian dome vent when eruption rates were high magma mingling of mafic and rhyolite magmas occurred during formation of the conduit a comparison of the magma types at obsidian dome with the other 600 year old magma types in the inyo chain demonstrates that the finely porphyritic rhyolites at obsidian dome are similar to the finely porphyritic rhyolites at the other domes all of these originated by mingling of two end members the coarsely porphyritic rhyolites that occur at glass creek and deadman domes are distinctly different from the finely porphyritic rhyolites the two rhyolites can not be related by any fractionation scheme and could not have been in thermal or chemical equilibrium with each other these observations require considerable heterogeneity in the inyo domes magmatic system two possible interpretations of the chemical variation and emplacement sequence are explored in the first interpretation the chemical patterns observed in the surface and subsurface samples at obsidian dome are explained by differential draw up of magma from a stratified dikelike reservoir this differential draw up is the result of changing flow rates during the course of the eruption when the magma initially vented to the surface during the main part of the explosive phase flow rates were very high and the deepest layer of the reservoir was drawn into the conduit where magma mingling occurred during the subsequent effusive phase flow rates were low draw up depths were reduced and only magma from the uppermost layer in the reservoir erupted only slightly contaminated by earlier hybrid magma drawn up similar processes most likely occurred at the other inyo domes however the low ba rhyolite was less abundant and highly viscous coarsely prophyritic rhyolite was near the surface and drawn up as a late pluglike structure an alternate interpretation is that the dike initially consisted of heterogeneous magma domains and that the zonation observed in the conduit of obsidian dome and on the surface of the three inyo domes is the result of the tendency of less viscous magma to encapsulate more viscous magma during sustained flow in a conduit

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

application of electrical resistivity tomography technique for investigation of landslides a case from turkey electrical resistivity imaging is a widely used tool in near surface geophysical surveys for investigation of various geological environmental and engineering problems including landslide in this study an electrical resistivity tomography ert survey was conducted in a landslide area located in the soke district of aydin turkey in 2003 the neogene aged units on the slope next to a newly built school building became unstable due to an excavation work and moved after a heavy rainfall the resulting landslide partly covered the school the authors carried out a 2 d resistivity survey along three profiles over the landslide mass using a wenner configuration it yielded useful information about the geometry and characteristics of the landslide in addition a 2 d synthetic resistivity modelling study was carried out to understand the response of the resistivity method to a landslide problem before the field surveys eight boreholes were also drilled in the landslide area both the drilling and resistivity results indicated the presence of a fault in the site also the resistivity data from the line measured along the axis of the landslide revealed the surface of rupture

catchment controls and human disturbances on the geomorphology of small mediterranean estuarine systems abstract geographic signatures are physical and human induced characteristics or processes that identify comparable or unique features of estuaries along latitudinal gradients in mediterranean areas the microtidal regime and the strong seasonal and inter annual contrasts cause an alternation between relatively high runoff and arid conditions furthermore the long history of human settlement also increases the complexity in the study of these estuarine systems this study investigates these signatures of the estuaries located within the mallorcan eastern coast which are geomorphologically homogeneous because of a similar bedrock geology and holocene history a multi method approach focused on the integration of geomorphometry hydraulics historical sources and statistics was used we explore the role played by catchment morphometric parameters severe flash flood events and human disturbances in controlling the geomorphology of 10 beach barrier enclosed fluvial incised lagoons most of the lagoons discharge into calas ranging in size from 1345 to 17 537 m 2 and their related catchments are representative of the mediterranean hydrological systems multiple regression models illustrate that the size slope and drainage network development of the catchments explain the variance in length r 2 0 67 volume r 2 0 49 area r 2 0 64 circularity r 2 0 72 and average width r 2 0 81 of the lagoons depending on these catchment morphometric variables the shape of the lagoons is also determined by the occurrence of catastrophic flash floods which cause scouring and dredging whereas the ordinary flood events and sea storms promote refilling and sedimentation a historical analysis since 1850 documented 18 flood events 5 of which were catastrophic with destructive effects along the catchments and large morphological changes in coastal lagoons high intensity rainfall up to 200 mm in 2 h the geomorphometry of the catchments and the massive construction of terraces and transverse walls are involved in the generation of catastrophic flood events additionally the lagoons were altered considerably by human intervention for flood control and to allow for an increased amount of human activities within the surrounding areas although the high recurrence of catastrophic flood events causes a persistent difficulty in the human battle to dominate these ecosystems therefore the area occupied by lagoons increased between 1956 and the present time from 31 981 m 2 to 63 802 m 2 because of the high recurrence of catastrophic flood events furthermore tourism demand and a social conservation consciousness have promoted restoration and preservation since the 1990s this study has improved the geomorphological knowledge of small mediterranean estuaries affected by human disturbances in the high energy environment found in mallorca

sedimentology stratigraphy and tectonics of evolving wedge top depozone ariano basin southern apennines italy the late zanclean wedge top ariano basin located in the external sector of the southern apennines was initially characterized by alluvial and fan delta environments and successively southward of the benevento buonalbergo fault by a gradual drowning with coastal and alluvial plains evolving to shelf and marine coastal settings respectively basin evolution continued with a synsedimentary uplift of different sectors resulting in variations in the drainage pattern and basin shape and ultimately leading to complete basin closure and transition to continental depositional environments early pliocene paleogeography prior to the ariano basin activity is due to regional subsidence and subsequent differential uplifts that resulted from geodynamic processes related to both the downgoing apulian slab and the allochthonous orogenic wedge slab break off and the migration of a tear in the southeastward apulian slab occurred producing a strong subsidence in the external sectors of the southern apennines recorded by the development of the ariano basin subsequently out of sequence synsedimentary thrusting related to thin skinned tectonics occurred in the allochthonous units and unconformably overlying wedge top basin deposits producing northeastward migration of the main depocenters in the ariano basin finally renewed thrusting related to the inversion of pre existing normal faults located in the buried apulian platform and enhanced by regional uplift affected the whole tectonic and sedimentary pile as recorded by deformation of the overlying pliocene deposits

melt generation and fluid flow in the thermal aureole of the bushveld complex granite sheets emplaced into the migmatite zone of the eastern contact aureole of the bushveld complex resulted from fluid enhanced incongruent biotite melting of the underlying silverton formation shales during prograde metamorphism ba concentrations are extreme in both the sheets 1000 ppm and the hornfels 800 ppm into which they have been emplaced we conclude that a ba rich hydrothermal fluid induced melting in the aureole and that fluid transport of ba2 and to a lesser extent sr2 and eu2 persisted in the melt zones under subsolidus conditions sr isotope systematics from high ba localities define an errorchron of 2161 106 ma with an initial 87sr 86sr ratio of 0 705 0 001 metasedimentary rocks unaffected by fluid infiltration were homogenized at the same time but with an increased initial ratio suggesting that whereas isotope homogenization was achieved between outcrops permeated by fluids there is no evidence of regional homogenization oxygen isotope compositions of psammitic metasediments in the aureole are uncorrelated with distance from the contact suggesting the infiltrating fluid equilibrated isotopically with the metasediments their elevated 18o values 11 3 12 1 are consistent with a fluid source from devolatilization of the sedimentary lithologies textural analysis at both outcrop and thin section scale of arkose and psammites in the aureole lakenvalei and magaliesberg formations shows that the extent of melting was highly heterogeneous even on the grain scale and resulted from heterogeneously distributed infiltration of aqueous fluid on dilatant cracks and grain boundaries cathodoluminescence imaging of quartz shows a marked difference in the amount of fine structure with that in the melted rocks having uniform luminescence in contrast to that in rocks containing little or no melt which preserve textures inherited from the regionally metamorphosed protolith simple finite difference thermal modelling of the aureole suggests that the width of the melt zone 500 m is inconsistent with conductive heat transfer and hence that the thermal structure has been modified by fluid advection

mineralogy and geothermometry of high temperature rhyolites from the central and western snake river plain voluminous mid miocene rhyolitic ash flow tuffs and lava flows are exposed along the northern and southern margins of the central and western snake river plain these rhyolites are essentially anhydrous with the general mineral assemblage of plagioclase sanidine quartz augite pigeonite hypersthene fayalitic olivine fe ti oxides apatite zircon which provides an opportunity to compare feldspar pyroxene and fe ti oxide equilibration temperatures for the same rocks estimated pyroxene equilibration temperatures based on the geothermometers of lindsley and coworkers range from 850 to 1000 c and these are well correlated with whole rock compositions with the exception of one sample agreement between the two pyroxene thermometers tested is well within 50 c fe ti oxide geothermometers applied to fresh magnetite and ilmenite generally yield temperatures about 50 to 100 c lower than the pyroxene temperatures and erratic results are obtained if these minerals exhibit effects of subsolidus oxidation and exsolution results of feldspar thermometry are more complicated and reflect uncertainties in the thermometer calibrations as well as in the degree of attainment of equilibrium between plagioclase and sanidine in general temperatures obtained using the ghiorso 1984 and green and usdansky 1986 feldspar thermometers agree with the pyroxene temperatures within the respective uncertainties however uncertainties in the feldspar temperatures are the larger of the two and exceed 60 c for many samples the feldspar thermometer of fuhrman and lindsley 1988 produces systematically lower temperatures for many of the samples studied the estimated pyroxene temperatures are considered most representative of actual magmatic temperatures for these rhyolites this range of temperatures is significantly higher than those for rhyolites from many other suites and is consistent with the hypothesis that the snake river plain rhyolitic magmas formed by partial fusion of relatively dry e g granulitic crustal lithologies

cathodoluminescence and trace element zoning in quartz phenocrysts and xenocrysts quartz phenocrysts and xenocrysts are a common component of volcanic rocks but rarely contribute to our understanding of magmatic or eruptive processes due to an apparent internal chemical and structural homogeneity scanning electron microscopy cathodoluminescence imaging sem cl and secondary ion mass spectroscopy ion microprobe analysis sims are used here to demonstrate that quartz crystals in volcanic rocks show hitherto unrecognised internal structural and chemical zoning two contrasting crystal morphologies have been studied porphyritic euhedral bipyramidal quartz crystals in dacite from bonne nuit bay jersey uk show fine scale growth zoning in sem cl zones are narrow 1 40 m wide planar parallel to crystal faces and overgrow more broadly zoned rounded cores these crystals are interpreted to have formed at small degrees of undercooling by diffusion controlled growth quiescent magma conditions are indicated by the preservation of an al rich diffusive boundary layer which has not been removed by melt shearing during convection in contrast rounded and embayed porphyritic quartz grains in a quartz dacite from the esperanza mine e1 salvador northern chile show broad internal sem cl zones with irregular boundaries some of which are truncated by grain margins indicating dissolution crystal rounding may occur by dissolution or melting due to thermal or thermal chemical disequilibrium with surrounding melt and embayments by gas bubble enhanced convective dissolution are consistent with the development of incipient ocelli textures strings of amphibole inclusions adjacent to quartz rims several episodes of rounding can be recognised in some xenocrysts ion microprobe sims analysis of quartz from both samples shows that a1 contents are higher in areas of bright cl emission previous studies of cl in quartz have suggested that several factors control luminescence although a1 substitution for si in sio4 tetrahedra may be partly responsible for sem cl zoning recorded in volcanic quartz additional mechanisms including the effect of growth rate on defect density probably also play a major role

second reply to comment of r s j sparks h e huppert and c j n wilson on evidence for long residence times of rhyolitic magma in the long valley magmatic system the isotopic record in the precaldera lavas of glass mountain

model for the intrusion of batholiths associated with the eruption of large volume ash flow tuffs pyroclastic eruption and the intrusion of batholiths associated with large volume ash flow tuffs may be driven by a decrease in reservoir pressure caused by the low density of the magma column due to vesiculation batholithic intrusion would then be accomplished by the subsidence and settling of kilometer sized crustal blocks through the magma chamber resulting in eventual collapse to form large caldera structures at the surface such a model does not require the formation of a large laterally extensive shallow magma chamber before the onset of large volume ash flow eruptions eruption could commence directly from a deeper reservoir with only a small channelway being opened to the surface before the onset of catastrophic ash flow eruptions of the scale of yellowstone or long valley such a model has wide ranging implications and explains many of the problems inherent in the simple collapse model involving shallow magna chambers as well as the process and timing of batholith intrusion in such cases

the redox state of pinatubo dacite and the ilmenite hematite solvus the oxidation state of the 1991 pinatubo dacite and many other oxidized silicic arc volcanic rocks has been overestimated we reproduce the compositions of magnetite and ferrian ilmenite found in pinatubo dacite by doing crystallization experiments at 780 degrees c 2 2 kbar and nno 1 7 or 0 2 log units the extra components in igneous ilmenite notably geikielite expand the solvus in a way that is not correctly accommodated in current formulations of the iron titanium oxide thermobarometer

experimental constraints on rhyolite melts and the late bishop tuff magma body thermodynamic models are vital tools to evaluate magma crystallization and storage conditions before their results can be used independently however they must be verified with controlled experimental data here we use a set of hydrothermal experiments on the late erupted bishop tuff lbt magma to evaluate the rhyolite melts thermodynamic model a modified calibration of the original melts model optimized for crystallization of silicic magmas experimental results that are well captured by rhyolite melts include a relatively narrow temperature range separating the crystallization of the first felsic mineral and the onset of the ternary minimum quartz plus two feldspars and extensive crystallization over a narrow temperature range once the ternary minimum is reached the model overestimates temperatures by 40 c a known limitation of rhyolite melts at pressures below 110 mpa model and experiments differ in the first felsic phase suggesting that caution should be exercised when applying the model to very low pressures our results indicate that for quartz sanidine plagioclase magnetite and ilmenite to crystallize in equilibrium from lbt magma magma must have been stored at 740 c even when a substantial amount of co2 occurs in the coexisting fluid such temperatures are in conflict with the hotter temperatures retrieved from magnetite ilmenite compositions 785 c for the sample used in the experiments consistent with other recent studies we suggest that the fe ti oxide phases in the late bishop tuff magma body are not in equilibrium with the other minerals and thus the retrieved temperature and oxygen fugacity do not reflect pre eruptive storage conditions

electrical resistivity tomography technique for landslide investigation a review abstract in the context of in situ geophysical methods the electrical resistivity tomography ert is widely used for the near surface exploration of landslide areas characterized by a complex geological setting over the last decade the technological improvements in field data acquisition systems and the development of novel algorithms for tomographic inversion have made this technique more suitable for studying landslide areas with a particular attention to the rotational translational and earth flow slides this paper aims to present a review of the main results obtained by applying ert for the investigation of a wide spectrum of landslide phenomena which affected various geological formations and occurred in different geographic areas in particular significant and representative results obtained by applying 2d and 3d ert are analyzed highlighting the advantages and drawbacks of this geophysical technique finally recent applications of the time lapse ert tl ert for landslide investigation and the future scientific challenges to be faced are presented and discussed

integration of controlled source and radio magnetotellurics electric resistivity tomography and reflection seismics to delineate 3d structures of a quick clay landslide site in southwest of sweden abstractquick clay which is the main cause of landslides that occur in the northern countries liquefies easily and its presence implies an increased risk of landslide geophysical methods have been increasingly used in landslide investigations three dimensional electric resistivity tomography radio magnetotelluric rmt controlled source rmt csrmt and high resolution reflection seismic data were acquired at a quick clay landslide site in the southwest of sweden the main objectives were to evaluate the capability of each method in delineating different subsurface geologic structures that controlled a peculiar and hazardous retrogressive type landslide in the study area a 3d resistivity model from the inversion of csrmt data showed the best correlation with the reflection seismic data and borehole information thanks to the broad frequency range of the data set it better imaged the resistive crystalline bedrock underlying the marine conductive clays and showed considerable correlations with the

oxygen isotope study of the long valley magma system california isotope thermometry and convection in large silicic magma bodies products of voluminous pyroclastic eruptions with eruptive draw down of several kilometers provide a snap shot view of batholith scale magma chambers and quench pre eruptive isotopic fractionations i e temperatures between minerals we report analyses of oxygen isotope ratio in individual quartz phenocrysts and concentrates of magnetite pyroxene and zircon from individual pumice clasts of ignimbrite and fall units of caldera forming 0 76 ma bishop tuff bt pre caldera glass mountain 2 1 0 78 ma and post caldera rhyolites 0 65 0 04 ma to characterize the long lived batholith scale magma chamber beneath long valley caldera in california values of 18o show a subtle 1 decrease from the oldest glass mountain lavas to the youngest post caldera rhyolites older glass mountain lavas exhibit larger 1 variability of 18o quartz the youngest domes of glass mountain are similar to bt in 18o quartz values and reflect convective homogenization during formation of bt magma chamber surrounded by extremely heterogeneous country rocks ranging from 2 to 29 oxygen isotope thermometry of bt confirms a temperature gradient between late 815 c and early 715 c bt the 18o quartz values of early and late bt are 8 33 and 8 21 consistent with a constant 18o melt 7 8 0 1 and 100 c temperature difference zircon melt saturation equilibria gives a similar temperature range values of 18o quartz for different stratigraphic units of bt and in pumice clasts ranging in pre eruptive depths from 6 to 11 km based on melt inclusions and document vertical and lateral homogeneity of 18o melt worldwide five other large volume rhyolites lava creek lower bandelier fish canyon cerro galan and toba exhibit equal 18o melt values of earlier and later erupted portions in each of the these climactic caldera forming eruptions we interpret the large scale 18o homogeneity of bt and other large magma chambers as evidence of their longevity 105 years and convection however remaining isotopic zoning in some quartz phenocrysts trace element gradients in feldspars and quartz and zircon crystal size distributions are more consistent with far shorter timescales 102 104 years we propose a sidewall crystallization model that promotes convective homogenization roofward accumulation of more evolved and stagnant volatile rich liquid and develops compositional and temperature gradients in pre climactic magma chamber crystal melt gas bubbles mush near chamber walls of variable 18o gets periodically remobilized in response to chamber refill by new hotter magmas one such episode of chamber refill by high ti sr ba zr and volatile richer magma happened 103 104 years prior to the 0 76 ma caldera collapse that caused magma mixing at the base mush thawing near the roof and walls and downward settling of phenocrysts into this hybrid melt

a trace element geochemical model for imperfect fractional crystallization associated with the development of crystal zoning abstract although many petrological studies of volcanic rocks have suggested that crystallization proceeds within magma bodies highly compatible trace elements do not display the marked variations and extreme depletions predicted to result from perfect fractional crystallization imperfect crystal liquid separation is a key process in explaining this paradox the presence of suspended crystals greatly affects variations in highly compatible elements and has been quantitatively modeled by assuming perfect equilibrium between the suspended crystals and the liquid equilibrium crystallization and imperfect separation ecis however volcanic rocks generally contain zoned phenocrysts that reflect the absence of solid state equilibration the present study develops a mass balance model for zoned crystallization and imperfect separation zcis the zcis process is more efficient than the conventional ecis process in generating depleted compatible elements these two end member models are able to explain the compositional range of igneous rocks that experienced imperfect fractional crystallization under natural conditions the predicted compositional regions in bivariate trace element diagrams successfully account for the sizes and shapes of the regions defined by whole rock and melt inclusion data from the bishop tuff ca usa

the arsikere granite of southern india magmatism and metamorphism in a previously depleted crust abstract the arsikere granite is a small diapiric potassic pluton intruded into archean gneisses of the western part of the dharwar craton of southern india a rb sr age of 2563 ma indicates that the granite was formed during a period of granulite development at lower crustal levels at least to the south of the dharwar craton schist belts in the craton were metamorphosed to greenschist or amphibolite facies at this time but gneisses underwent no isotopic or other geochemical effects the arsikere granite contains quartz oligoclase highly perthitic alkali feldspar originally precipitated as a single phase f rich biotite plus primary epidote fluorite and f rich muscovite sphene forms large euhedrons which incorporate nearly all of the ti in the rock leaving pure magnetite as the only opaque phase equilibration parameters include temperatures of 700 from feldspars f o 2 10 12 bar biotite and opaques and f oh 10 3 biotite nearby schist belts were metamorphosed at 5 kbar pressure at the same time as granite emplacement if the granite was emplaced at 5 kbar the magma could not have been water saturated perthite an initial 87 sr 86 sr ratio of 0 7021 in the arsikere granite is too low for the magma to have formed by partial melting of rocks with the rb sr ratios of gneisses currently exposed in the craton apparently the magma formed in a lower crust that had been depleted in rb and probably other lithophilic elements several hundred million years earlier at this time the craton also became water poor and inert to further geochemical activity such as resetting isochrons during later metamorphism

cathodoluminescence properties of quartz eyes from porphyry type deposits implications for the origin of quartz hyperspectral cathodoluminescence cl mapping combined with electron probe microanalysis epma and fourier transform infrared spectroscopy was used for the reconstruction ofcrystallization conditions of quartz from porphyry environments quartz eyes from the two porphyry deposits rio blanco chile and climax u s a were studied three peaks are found to be responsible for the total cl emission 1 93 2 05 and 2 72 ev the first two peaks are assigned to o m with m being an alkali ion and oxygen vacancies respectively the 2 72 ev peak shows a linear correlation with the ti concentration determined by epma point measurements in addition a negative correlation between the 1 93 ev emission and the al concentration was observed quartz grains often form clusters in which adjacent grains show identical cl patterns indicating that they crystallized attached to each other and were not disturbed later quartz cores display sector zoning and enrichment in li oh and sometimes al which points to rapid crystallization from an extremely evolved melt quartz rims show high ti and low li and oh contents indicating crystallization from a less evolved melt either at higher temperatures or at higher titanium activities the al and ti distribution patterns are frequently not correlated and both show uneven distribution indicating fast growth from inhomogeneous melts only ti displays sharp transitions and fine oscillatory zoning which can be explained by the higher mobility of al in the quartz lattice the quartz eyes crystallized after magma emplacement under non equilibrium conditions it is likely that the crystallization occurred from the melt enriched in al li and oh and probably other metals and or volatiles on the brink of fluid exsolution subsequent fluid exsolution brought about disequilibrium to the system resulting in dissolution of quartz and redistribution of elements between the melt and the fluid the oh li and other alkali metals and volatiles partitioned into the fluid whereas ti and al remained in the melt resorption of quartz caused by the fluid exsolution continued until equilibrium was reached again after which crystallization of quartz rims began from the water alkali and volatile poor melt with higher ti activity furthermore accumulation of al and ti in the residual melt led to crystallization of extremely al and ti rich quartz

grain size reduction of feldspars by fracturing and neocrystallization in a low grade granitic mylonite and its rheological effect abstract feldspar grain size reduction occurred due to the fracturing of plagioclase and k feldspar myrmekite formation and neocrystallization of albitic plagioclase along shear fractures of k feldspar porphyroclasts in the leucocratic granitic rocks from the yecheon shear zone of south korea that was deformed under a middle greenschist facies condition the neocrystallization of albitic plagioclase was induced by strain energy adjacent to the shear fractures and by chemical free energy due to the compositional disequilibrium between infiltrating na rich fluid and host k feldspar with increasing deformation from protomylonite to mylonite alternating layers of feldspar quartz and muscovite developed the fine grained feldspar rich layers were deformed dominantly by granular flow while quartz ribbons were deformed by dislocation creep with layer development and a more distributed strain in the mylonite lower stresses in the quartz rich layers resulted in a larger size of dynamically recrystallized quartz grains than that of the protomylonite

investigation of the nature of slip surface using geochemical analyses and 2 d electrical resistivity tomography a case study from lapseki area nw turkey the nature and subsurface structure of the slip surface of a landslide was studied on the basis of geochemical analyses and 2 d electrical resistivity tomography ert survey head scarp and lateral slip surfaces of the landslide marked by clear slickensided shear planes were composed of the average amounts of clayey silt 32 5 and sand 67 5 energy dispersive x ray spectroscopy edx data revealed the enrichment of si 23 24 fe 12 2 al 9 51 and c 8 34 in the elemental composition of the disturbed slip surface from x ray diffractometry xrd data six main clay types were determined such as volkonskoite halloysite ferrosilite saponite illite and nontronite the ert survey displayed that the landslide developed as a reactivation on the upper part of an old landslide body

40ar 39ar laser probe ages of bishop tuff quartz phenocrysts substantiate long lived silicic magma chamber at long valley united states laser probe ar 40 ar 39 dating of quartz phenocrysts with rhyolite glass inclusions from the bishop tuff air fall and ignimbrite deposits reveals that the long valley magma system existed as a long lived silicic magma chamber throughout most of the pleistocene sanidine phenocryst and matrix glass analyses show that the bishop tuff eruption occurred at 759 1 to 761 1 ha initial and radiogenic ar isotope ratios indicate isotopic equilibrium between the sanidine phenocrysts and their host melt at the time of eruption the quartz phenocrysts in contrast the most abundant phenocryst phase of the bishop rhyolite crystallized trapped their glass inclusions and became a closed system with respect to ar at 1 89 0 03 to 2 3 0 3 ma consequently the bishop rhyolite magma already resided in the long valley basement and had formed most of its quartz phenocrysts similar to 1 1 m y before its principal eruption providing important constraints on the longevity of large silicic magma chambers

wetting behavior of partial melts during crustal anatexis the distribution of hydrous silicic melts in polycrystalline aggregates of quartz the equilibrium distribution of hydrous silicic melts in polycrystalline aggregates of quartz was characterized in a series of partial melting and melt distribution experiments in the systems quartz albite orthoclase h2o and quartz anorthite h2o at 650 to 1000 mpa and 800 to 900 c near equilibrium textures in these experiments are characterized by very low quartz quartz melt wetting angles and by a substantial number of thin melt films along grain boundaries wetting angles in the h2o saturated experiments are as follows 18 at 800 c 1000 mpa and 12 at 900 c 1000 mpa in the granitic system 18 at 850 c 650 mpa 15 at 900 c 650 mpa and 15 at 900 c 1000 mpa in the quartzanorthite system in the granitic system at 900 c 1000 mpa a decrease of h2o content in melt from 17 wt at saturation to 6 wt results in a slight increase of wetting angle from 12 to 16 these low wetting angles and the observation that many grain boundaries are wetted by melt films indicate that the ratio of quartz quartz to quartz melt interfacial energies ss s1 is high 2 secondary electron imaging of fracture surfaces of melt poor samples provided a three dimensional insight into the geometry of melt at low melt fraction melt forms an interconnected network of channels along grain edges as predicted for isotropic systems with wetting angles below 60 this high permeability geometry suggests that the segregation of granitic melts is not as sluggish as previously anticipated simple compaction calculations for a permeability range of 10 12 to 10 9 m2 indicate that segregation may operate at low to moderate melt fractions below 30 vol within relatively short time scales i e 105 to 106 years quartzmelt textures show significant deviations from the equilibrium geometries predicted for isotropic partially molten systems the most consistent deviation is the pervasive development of crystallographically controlled planar faces of quartz these faces provide definitive evidence for non isotropic quartz melt surface energy for most silicates other than quartz the grain scale distribution of partial melts deviates even more significantly from equilibrium distributions in isotropic systems accordingly in order to describe adequately melt distributions in most natural source regions the equilibrium model should be modified to account for anisotropy of solid liquid interfacial energy

micro analytical perspectives on the bishop tuff and its magma chamber new in situ major and trace element analytical data are presented for crystals sanidine plagioclase biotite orthopyroxene clinopyroxene and matrix glasses from juvenile materials representing the full bishop tuff sequence from the earliest fall unit f1 to the latest ignimbrite package ig2nc these data are combined with published information to investigate the nature and zonation of the pre eruptive bishop magma chamber our data confirm that this magma chamber was a single unitary body that was thermally and compositionally zoned the zonation was largely established prior to the growth of crystals and also prior to mixing in the lower parts of the chamber induced by late stage intrusion of a magma of contrasting composition and slightly higher temperature the bright rim magma sparse mixed swirly and dacitic pumices show enrichments in ba sr and ti that identify these pumices as possible representatives of the bright rim magma a model revised from previously published work for the pre eruptive magma chamber comprises three main parts 1 an upper volumetrically dominant 2 3 relatively unzoned region that was the source of the earlier eastern erupted ignimbrite units and their coeval fall units 2 a volumetrically minor transition zone that shows evidence for minor degrees of mixing and was the dominant source for the latest eastern erupted part of ig1eb sherwin subunit and the earlier part of the northern erupted ignimbrite ig 2na 3 a lower volumetrically subordinate 1 3 region that was affected by mixing with the bright rim invasive magma in the lead up to the eruption and fed later northern erupted units ingress of the bright rim magma introduced orthopyroxene and bright rimmed zircon crystals and induced partial resorption then overgrowth of rims enriched in ti sr and ba on sanidine and quartz and development of zoning in clinopyroxene based on pumice proportions and associated crystal and glass chemistries through the eruptive sequence we infer that the roof and floor of the magma chamber were stepped down to the north such that the transition zone magma formed the floor of the southern part of the melt dominant chamber and the roof of the northern part our data reinforce the previous concept of a single compositionally and thermally zoned bishop magma chamber and additionally support a temporally constrained role for pre eruptive magma mixing and the introduction of melts and minerals with contrasting compositions to the resident bishop magma

microstructures and composition of melt inclusions in a crustal anatectic environment represented by metapelitic enclaves within el hoyazo dacites se spain abstract this article reports microstructures and compositions of melt inclusions in anatectic metapelites found as enclaves within el hoyazo dacites in the neogene volcanic province of southeastern spain the enclaves represent fragments of continental crust partially melted at 800 850 c and 5 7 kbar and brought to surface rapidly within the host volcanics while they still were in a molten state rapid cooling produced the solidification of silicate melt to glass in the rock matrix and in inclusions within minerals melt inclusions mi are present within nearly all mineral phases in the enclaves and their associated microstructures indicate a primary or pseudo secondary origin the entrapment mechanisms of mi within plagioclase were associated with 1 the presence of micron sized solids mostly graphite on the surface of growing crystals 2 partial resorption of crystals generation of embayments and later growth in the presence of melt and 3 entrapment of melt during crystal growth within crystallographic controlled planar structures e g on crystal faces melt inclusions in garnet are commonly associated with regularly oriented planar discontinuities filled with glass interpreted either as spaces left between adjacent mineral growth spirals or as crystallographic controlled cracks generated in between stages of mineral growth melt was trapped or percolated along these microstructures and later on necking down phenomena individualized inclusions with negative crystal shape melt inclusions in biotite are abundant show negative crystal shape and parallel cleavage planes melt inclusions in cordierite alkali feldspar and ilmenite are isolated sparse and sometimes rather large the composition of glass from all mi is leucogranitic and peraluminous with small differences among glasses in each mineral host there is some variation in glass composition within each textural location as well compositional heterogeneity can be partially explained by a combination of processes such as generation of boundary layers during mineral growth crystallization of daughter phases and hydrogen loss via diffusion through the host mean glass compositions in the several textural locations however can be tentatively interpreted as reflecting the evolution of melt chemistry during the prograde low to medium pressure anatexis of quartz poor metapelites

zoned quartz phenocrysts from the rhyolitic bishop tuff cathodoluminescence cl reveals growth zones in quartz phenocrysts from the rhyolitic bishop tuff melt inclusions occur in various zones and record the evolving melt composition during zonal growth the zones form an oscillatory pattern between bright and dark cl quartz there are three recognizable patterns of cl zoning in these crystals 1 weakly zoned cores and bright cl rims 2 weakly zoned cores and dark cl rims and 3 no cl intensity difference from core to rim dark cl quartz generally occurs at crystal edges contains most of the melt inclusions and is interpreted as fast growing zones that occur along recognizable crystal edges edge zones are thicker than the same zone on adjacent faces consistent with relatively fast growth of these zones in each successive zone these edge zones decrease in size toward the rim while the zones along the crystal faces increase some of the melt inclusions have bright cl quartz locally associated with them this is interpreted as the postentrapment crystallization of slow growing quartz in the melt inclusions many crystals display zone discordance from the weakly zoned interiors to the rims most of the discordant surfaces are rational and probably are primary growth features pumice clasts from the southern vents are largely compositionally and texturally distinct from those from the northern vents and this distinction is also evident in the quartz cl the crystals that have bright cl rims are all associated with the late erupted northern part of the bishop tuff melt inclusion compositions and cl zoning patterns suggest a common origin for early and middle erupted quartz and the interior zones of late erupted quartz however the bright cl rim on the late erupted quartz indicates an additional stage of crystallization in late erupted magma melt inclusions in individual early erupted crystals have small variations in ba whereas inclusions in late erupted crystals markedly increase in ba toward the rim which is opposite to the normal zoning of sequentially trapped melts expected during closed system crystallization differentiation the quartz zoning features are consistent with the hypothesis of crystal settling in evolving magma that erupted late from northern vents

attenuation of p and s waves in a magma chamber in long valley caldera california shallow earthquakes around the southwest boundary of long valley caldera west of the hilton creek fault are characterized by lack of s waves at regional seismic network stations to the northwest north and northeast and p waves for these same station event combinations are deficient in frequencies higher than about 2 3 hz earthquakes east of the hilton creek fault and southeast of the caldera have normal p and s wave signatures at the same stations these effects are explained by propagation through a magma chamber in the south central part of long valley caldera at depth greater than 7 8 km

coastal lagoons geologic evolution in two phases abstract estuaries formed globally when river valleys and bays were inundated by the rising sea towards the end of the holocene post glacial marine transgression and have been supplied with sediment ever since coastal lagoons estuaries that are partially or wholly cut off from marine influence are said to evolve through sedimentation from an immature unfilled state to a mature filled state at a rate dependent on sediment supply the existence of numerous examples of lagoons that remain unfilled worldwide however despite thousands of years of sedimentation suggests that a discontinuity in the geologic evolution of lagoons occurs before maturity is reached presented here is a hypothesis that geologic evolution takes place in two phases which are defined by changes in physical processes the early phase aligns with the traditional view but ends when a depth threshold is reached in the late phase sedimentation is inhibited by the local energy regime and can only proceed if the lagoon surface area is reduced validation of the existence of these two distinct process based phases of geologic evolution will improve the reliability of predictive models for lagoon shoreline changes and rates of basin fill as well as reduce the risk of misinterpreting past conditions from the geological record

implications of quaternary volcanism at cerro tuzgle for crustal and mantle evolution of the puna plateau central andes argentina the high k tuzgle volcanic center 24 s 66 5 w along with several small shoshonitic centers developed along extensional quaternary faults of the el toro lineament on the east central puna plateau 275 km east of the main front of the andean central volcanic zone cvz these magmas formed by complex mixing processes in the mantle and thickened crust 50 km above a 200 km deep scismic zone tuzgle magmas are differentiated from shoshonitic series magmas by their more intraplate like ti group element characteristics lower incompatible element concentrations and lower 87sr 86sr ratios at a given end underlying mio pliocene volcanic rocks erupted in a compressional stress regime and have back arc like calc alkaline chemical characteristics the tuzgle rocks can be divided into two sequences with different mantle precursors a an older more voluminous rhyodacitic ignimbrite to mafic andestitic 56 to 71 sio2 sequence with la yb ratios 35 la yb ratios are controlled by the mafic components low ratios result from larger mantle melt percentages than high ratios shoshonitic series lavas 52 to 62 sio2 contain small percentage melts of more isotopically enriched arc like mantle sources some young tuzgle lavas have a shoshonitic like component variable thermal conditions and complex stress system are required to produce the tuzgle and shoshonitic series magmas in the same vicinity these conditions are consistent with the underlying mantle being in transition from the thick mantle lithosphere which produced rare shoshonitic flows in the altiplano to the thinner mantle lithosphere that produced back are calc alkaline and intraplate type flows in the southern puna substantial upper crustal type contamination in tuzgle lavas is indicated by decreasing end 2 5 to 6 7 with increasing 87sr 86sr 0 7063 to 0 7099 ratios and sio2 concentrations and by negative eu anomalies eu eu 0 78 in lavas that lack plagioclase phenocrysts trace element arguments indicate that the bulk contaminant was more silicic than the tuzgle ignimbrite and left a residue with a high pressure mineralogy crustal shortening processes transported upper crustal contaminants to depths where melting occurred these contaminants mixed with mafic magmas that were fractionating mafic phases at high pressure silicic melts formed at depth by these processes accumulated at a mid to upper crustal discontinuity decollement the tuzgle ignimbrite erupted from this level when melting rates were highest subsequent lavas are mixtures of contaminated mafic magmas and ponded silicic melts feldspar and quartz phenocrysts in the lavas are phenocrysts from the ponded silicic magmas

the ilmenite titano magnetite assemblage kinetics of re equilibration abstract compositions of coexisting ilmenite and titano magnetite commonly have been used to establish the conditions of formation for igneous and metamorphic rocks buddington lindsley geothermometer oxybarometer temperatures so determined for some rocks are lower than might be expected for magmatic crystallization these low temperatures are the result of re equilibration of the fe ti oxides during slow cooling this process is one in which titano magnetites are oxidized and ilmenites are reduced upon cooling along a buffer curve or in the presence of a fluid of constant composition textural studies indicate that the reduction of the ilmenite hematite phase may be the slower reaction consequently the rate controlling step of the re equilibration the kinetics of the reduction reactions in the two phase region between the joins for the ilmenite hematite and magnetite ulvospinel solid solution series were studied by thermogravimetric analysis at controlledfo2 with experiments conducted near the ni nio and qfm buffers annealed ilmenite ss synthetic charges were reduced isothermally the temperature range for the experiments was 900 1250 c with total gas flow rates of 0 35 and 1 0 cm s kinetic data were collected by measuring the weight change during each experiment as a function of time additionally a cooling rate 0 5 c hr experiment was conducted near the qfm buffer from 1150 to 985 c starting with an ilmenite saturated spinel phase at 1200 c and 0 35 cm s flow rate the reaction mechanism is an interfacial process where mass transport of the reacting gases is the rate controlling step in isothermal experiments at 1100 c and lower diffusion of reactants through a solid product layer was the controlling mechanism the activation energy for this diffusion process is 59 6 kcal mole significant enhancement of diffusion occurs along grain boundaries although the individual phases may re equilibrate internally upon cooling the fe ti contents must remain unchanged for proper use of this mineral indicator i e no external re equilibration it is imperative that the kinetics of the situation be appreciated these preliminary kinetic experiments indicate that extreme caution must be exercised when applying this ilmenite titano magnetite geothermometer oxybarometer these phases may only truly quench in the parameters of formation in the case of certain hypabyssal and extrusive occurrences

refractory inclusions in the prototypical cm chondrite mighei abstract refractory inclusions in the mighei cm2 meteorite are very abundant 35 being found in three thin sections of the meteorite the most common are pyroxene rimmed spinel rich inclusions that occur in a range of structural and textural types some inclusions are simple aggregates of crystals or rimmed crystals ranging from loose clusters of spinel grains to distended chains of pyroxene rimmed spinel knots others are more compact and may have experienced recrystallization or melting these include nodular spinel inclusions with polygonal granular textured spinel interiors and pyroxene rims ribbons of spinel in some cases with hibonite and or perovskite that are again rimmed by pyroxene and refractory spherules four inclusions are complex aggregates of several texturally distinct objects each collectively mighei inclusions are similar to those in murchison but appear to be somewhat more altered volatility fractionated and unfractionated trace element patterns similar to those found in refractory inclusions in other carbonaceous chondrites are represented in mighei inclusions and in addition some mighei inclusions have volatility fractionated pattern types not previously found in refractory inclusions in three of the complex aggregates fundamentally different trace element patterns are present within different portions of each inclusion meaning that these objects accreted from genetically different components that never equilibrated with one another subsequent to accretion bulk inclusion magnesium isotopic compositions show minor mass fractionation effects fmg values range from 2 3 to 7 5 but the average fmg value is indistinguishable from normal 1 8 1 2 there are no correlations between magnesium isotopic composition and textural type or trace element pattern type the diverse inclusion types in mighei represent a variety of origins and histories textures suggest that the nodular and banded inclusions may have experienced solid state recrystallization whereas the porous and chain like varieties and complex aggregates have not magnesium isotopic compositions and trace element abundances suggest that the mighei inclusions are unlikely to be evaporation residues and are more likely to be the products of condensation or recondensation processes

evidence for post depositional diffusional loss of hydrogen in quartz phenocryst fragments within ignimbrites ignimbrite hosted quartz phenocryst fragments contain much lower hydroxyl defect concentration than quartz in igneous rocks pre eruptive and post depositional loss of hydrogen were hypothesized as the main processes for lowering the initial magmatic concentrations of hydroxyl defects the aim of this study was to examine the hydroxyl defect concentration of quartz phenocryst fragments from various vertical positions above the base of pyroclastic density current pdc deposits it aims to record the vertical variations of hydroxyl defect concentrations to have an insight into potential post depositional hydrogen loss of pdc deposits ignimbrite hosted quartz phenocryst fragments were examined from two different ignimbrites in the bukk foreland volcanic area north hungary unpolarized micro ftir measurements on 23 35 unoriented crystal fragments from each sample were performed representing four different vertical positions of each site present results imply that hydroxyl defect concentrations show a pronounced decrease upward from the base of the deposits the initial 12 ppm hydroxyl defect concentration decreases to

location and configuration of magma bodies beneath long valley california determined from anomalous earthquake signals recordings of 281 small earthquakes which occurred recently near the southern edge of long valley caldera at depths from 1 to 15 km are used to map the subsurface geometry of shear wave attenuating bodies in the caldera signatures of these events recorded northwest north northeast and east of long valley with ray paths through the caldera are often anomalous in that s wave arrivals have very low amplitudes and high frequency p and s wave energy is missing for the same station event combinations the volcanic and geothermal history of the region suggests that ray paths for these anomalous signals have passed through magma which absorbed much of the s wave energy and also attenuated the higher frequencies with over 1200 normal and anomalous ray paths through the caldera we have located two apparently massive magma bodies in the central and northwest caldera as well as two more dispersed magma areas in the southern caldera and beneath crowley lake the central magma body extends from 4 5 to at least 13 km beneath the surface and the northwest body is as shallow as 5 5 km these two magma bodies are probably connected below about 8 km secondary arrivals seen on select seismograms are tentatively interpreted as reverberations inside the central magma chamber and are consistent with the interpreted lateral extent of the magma the northwest and central magma bodies lie beneath the northwest and southeast corners of the caldera s resurgent dome and probably connect beneath the dome s center also the shallower parts of these magma bodies and the southern anomalous area lie beneath the surface expression of the medial graben faults suggesting that structural features seen at the surface of the valley may be related to magma location at depth

comagmatic granophyric granite in the fish canyon tuff colorado implications for magma chamber processes during a large ash flow eruption the 27 8 ma fish canyon tuff a vast ash flow sheet 5000 km 3 of uniform phenocryst rich dacite is representative of monotonous intermediate eruptions from a magma chamber that lacked compositional gradients sparse small fragments of comagmatic granophyre in late erupted tuff and postcaldera lava having mineral compositions indistinguishable from phenocrysts in the tuff and precaldera lava like rocks record complex events in the fish canyon chamber just prior to eruption sanidine phenocrysts in the granophyre preserve zoning evidence of mingling with andesitic magma then shattering by decompression and volatile loss accompanying early fish canyon eruptions before overgrowth by granophyre the textural and chemical disequilibria indicate that the eruption resulted from batholith scale remobilization of a shallow subvolcanic chamber contrary to previous interpretations of magma storage and phenocryst growth in the lower crust