a compositional tipping point governing the mobilization and eruption style of rhyolitic magma measurements of the composition dependent viscosity of rhyolitic magma reveal a tipping point that changes the physical properties of the melt and controls the transition between effusive and explosive eruptions calcalkaline rhyolites produce the largest explosive volcanic eruptions but these eruptions can switch repeatedly between being effusive and explosive this is difficult to attribute to the rheological effects of magma water content or crystallinity danilo di genova and co authors report the viscosity of a series of melts spanning the compositional range of the yellowstone rhyolitic volcanic system they find that within a narrow compositional zone melt viscosity increases by up to two orders of magnitude which they propose to be the consequence of melt structure reorganization the authors confirm that such a compositional tipping point exists in the global geochemical record of rhyolites which separates effusive from explosive deposits they conclude that the anhydrous water free composition of calcalkaline rhyolites is decisive in determining mobilization and eruption dynamics of the earth s largest volcanic systems the most viscous volcanic melts and the largest explosive eruptions1 on our planet consist of calcalkaline rhyolites2 3 these eruptions have the potential to influence global climate4 the eruptive products are commonly very crystal poor and highly degassed yet the magma is mostly stored as crystal mushes containing small amounts of interstitial melt with elevated water content5 it is unclear how magma mushes are mobilized to create large batches of eruptible crystal free magma further rhyolitic eruptions6 7 8 can switch repeatedly between effusive and explosive eruption styles and this transition is difficult to attribute to the rheological effects of water content or crystallinity9 10 here we measure the viscosity of a series of melts spanning the compositional range of the yellowstone volcanic system and find that in a narrow compositional zone melt viscosity increases by up to two orders of magnitude these viscosity variations are not predicted by current viscosity models11 12 and result from melt structure reorganization as confirmed by raman spectroscopy we identify a critical compositional tipping point independently documented in the global geochemical record of rhyolites at which rhyolitic melts fluidize or stiffen and that clearly separates effusive from explosive deposits worldwide this correlation between melt structure viscosity and eruptive behaviour holds despite the variable water content and other parameters such as temperature that are inherent in natural eruptions thermodynamic modelling demonstrates how the observed subtle compositional changes that result in fluidization or stiffening of the melt can be induced by crystal growth from the melt or variation in oxygen fugacity however the rheological effects of water and crystal content alone cannot explain the correlation between composition and eruptive style we conclude that the composition of calcalkaline rhyolites is decisive in determining the mobilization and eruption dynamics of earth s largest volcanic systems resulting in a better understanding of how the melt structure controls volcanic processes

formation of patterned ground and fine scale soil development within two late holocene glacial chronosequences jotunheimen norway abstract chronosequences of 250 to 130 years were established on two late holocene glacier forelands in the jotunheimen region of southern norway patterned features occurring within chronologically established time units were studied young patterned features forming 10 20 years after deglaciation are frost active vegetation cover is minimal within the young patterned features consisting of bryophytes organic crusts soil development within patterned ground is also minimal absent because frost action retards horizonization with time and distance from the glaciated ice margin frost activity declines within the patterned features suggesting that a thin active periglacial zone exists near the ice margin initially frost activity decreases at the borders of the features with the centers stabilizing later in time this results in fine scale soil heterogeneity and variations of soil development fine scale pedogenic development is first encountered at the borders of patterned ground that has developed on terrain exposed since the 1930s yet soil development is predominantly absent at the centers of patterned ground with time and distance from the ice margin frost activity declines and allows patterned features to homogenize from border to center positions in regard to soil characteristics across the chronosequences soils within patterned features pedogenically follow previous soil chronosequence studies evolving from usda classifications of entisols into inceptisols frost disturbance within patterned ground however produces a lag effect that results in longer periods of time for pedogenesis to occur and thinner soils than that of the surrounding terrain

mechanisms and timescales of generating eruptible rhyolitic magmas at yellowstone caldera from zircon and sanidine geochronology and geochemistry we constrain the physical nature of the magma reservoir and the mechanisms of rhyolite generation at yellowstone caldera via detailed characterization of zircon and sanidine crystals hosted in three rhyolites erupted during the c 170 70 ka central plateau member eruptive episode the most recent post caldera magmatism at yellowstone we present 238 u 230 th crystallization ages and trace element compositions of the interiors and surfaces i e unpolished rims of single zircon crystals from each rhyolite we compare these zircon data with 238 u 230 th crystallization ages of bulk sanidine separates coupled with chemical and isotopic data from single sanidine crystals zircon age and trace element data demonstrate that the magma reservoir that sourced the central plateau member rhyolites was long lived 150 250 kyr and genetically related to the preceding episode of magmatism which occurred c 256 ka the interiors of most zircons in each rhyolite were inherited from unerupted material related to older stages of central plateau member magmatism or the preceding late upper basin member magmatism i e are antecrysts conversely most zircon surfaces crystallized near the time of eruption from their host liquids i e are autocrystic the repeated recycling of zircon interiors from older stages of magmatism demonstrates that sequentially erupted central plateau member rhyolites are genetically related sanidine separates from each rhyolite yield 238 u 230 th crystallization ages at or near the eruption age of their host magmas coeval with the coexisting zircon surfaces but are younger than the coexisting zircon interiors chemical and isotopic data from single sanidine crystals demonstrate that the sanidines in each rhyolite are in equilibrium with their host melts which considered along with their near eruption crystallization ages suggests that nearly all central plateau member sanidines are autocrystic the paucity of antecrystic sanidine crystals relative to antecrystic zircons requires a model in which eruptible rhyolites are generated by extracting melt and zircons from a long lived mush of immobile crystal rich magma in this process the larger sanidine crystals remain trapped in the locked crystal network the extracted melts plus antecrystic zircon amalgamate into a liquid dominated i e eruptible magma body that is maintained as a physically distinct entity relative to the bulk of the long lived crystal mush zircon surfaces and sanidines in each rhyolite crystallize after melt extraction and amalgamation and their ages constrain the residence time of eruptible magmas at yellowstone residence times of the large volume rhyolites 40 70 km 3 are 1 kyr conservatively 6 kyr which suggests that large volumes of rhyolite can be generated rapidly by extracting melt from a crystal mush because the lifespan of the crystal mush that sourced the central plateau member rhyolites is two orders of magnitude longer than the residence time of eruptible magma

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

fast but spatially scattered smectite formation in the proglacial area morteratsch an evaluation using gis proglacial areas in the alps usually cover a time span of deglaciation of about 150 years time since the end of the little ice age in the 1850s in these proglacial areas soils have started to develop due to the continuous retreat of the morteratsch glacier swiss alps the corresponding proglacial area offers a continuous time sequence from 0 to 150 year old surfaces furthermore an optimal digital dataset about the development of vegetation and soils is available for this area the soils have been developing on glacial till having a granitoidic character we investigated the clay mineral assemblage at 35 sites within the glacier forefield smectite can be used as a proxy for weathering intensity in these environments in the proglacial area the smectite concentration in the topsoil steadily increased with time of weathering however this development displayed a strongly scattered trend the complex interplay of biological physical and chemical processes in pedogenesis and clay mineral evolution limits our ability to predict and interpret landscape dynamics we consequently tried to analyse the role of topographic and vegetation modifications on the smectite content sites not or only slightly prone to erosion flattening slope ridge steepening slope ridge or flat morphology promoted the formation of smectite in addition the texture of the soil material influenced soil moisture and hence the degree of weathering and the development of vegetation although vegetation is not a fully independent factor because it is interrelated to the surrounding environmental conditions it seemed to exert its influence on weathering and consequently the formation of smectite green alder stands and grass heath where moister soils develop that have a finer texture or where more organic acids are produced were correlated with a higher smectite content humus forms serve as a proxy for the soil biota and soil organic matter composition at sites having a eumoder and a higher soil organic matter content the smectite concentration was elevated at these sites the production of chelating compounds or organic acids in the soil is believed to promote the development of smectites via an intermediate stage of hydroxy interlayered minerals and the subsequent removal of the hydroxide polymers in this work we have demonstrated that the topographic signature and the effect of vegetation on the formation of smectite and consequent weathering are pervasive our results will serve as a basis for further spatio temporal modelling

high temperature low h2o silicic magmas of the yellowstone hotspot an experimental study of rhyolite from the bruneau jarbidge eruptive center central snake river plain usa the phase relations have been investigated experimentally at 200 and 500 mpa as a function of water activity for one of the least evolved indian batt rhyolite and of a more evolved rhyolite composition cougar point tuff xv from the 12 8 8 1 ma bruneau jarbidge eruptive center of the yellowstone hotspot particular priority was given to accurate determination of the water content of the quenched glasses using infrared spectroscopic techniques comparison of the composition of natural and experimentally synthesized phases confirms that high temperatures 900 c and extremely low melt water contents 1 5 wt h o are required to reproduce the natural mineral assemblages in melts containing 0 5 1 5 wt h o the liquidus phase is clinopyroxene excluding fe ti oxides which are strongly dependent on fo and the liquidus temperature of the more evolved cougar point tuff sample bjr 940 1000 c is at least 30 c lower than that of the indian batt rhyolite lava sample ibr2 970 1030 c for the composition bjr the comparison of the compositions of the natural and experimental glasses indicates a pre eruptive temperature of at least 900 c the composition of clinopyroxene and pigeonite pairs can be reproduced only for water contents below 1 5 wt h o at 900 c or lower water contents if the temperature is higher for the composition ibr2 a minimum temperature of 920 c is necessary to reproduce the main phases at 200 and 500 mpa at 200 mpa the pre eruptive water content of the melt is constrained in the range 0 7 1 3 wt at 950 c and 0 3 1 0 wt at 1000 c at 500 mpa the pre eruptive temperatures are slightly higher by 30 50 c for the same ranges of water concentration the experimental results are used to explore possible proxies to constrain the depth of magma storage the crystallization sequence of tectosilicates is strongly dependent on pressure between 200 and 500 mpa in addition the normative qtz ab or contents of glasses quenched from melts coexisting with quartz sanidine and plagioclase depend on pressure and melt water content assuming that the normative qtz and ab or content of such melts is mainly dependent on pressure and water activity respectively the combination of results from the phase equilibria and from the composition of glasses indicates that the depth of magma storage for the ibr2 and bjr compositions may be in the range 300 400 mpa 13 km and 200 300 mpa 10 km respectively

post caldera volcanism in situ measurement of u pb age and oxygen isotope ratio in pleistocene zircons from yellowstone caldera the yellowstone plateau volcanic field the site of some of the largest known silicic volcanic eruptions is the present location of ne migrating hotspot volcanic activity most volcanic rocks in the yellowstone caldera 0 6 ma which formed in response to the climactic eruption of 1000 km 3 of lava creek tuff lct have unusually low oxygen isotope ratios ion microprobe analysis of both u pb age and n 18 o in zircons from these low n 18 o lavas reveals evidence of complex inheritance and remelting a majority of analyzed zircons from low n 18 o lavas erupted inside the yellowstone caldera have cores that range in age from 2 4 to 0 7 ma significantly older than their eruption ages 0 5 0 4 ma these ages and the high n 18 o cores indicate that these lavas are largely derived from nearly total remelting of normal n 18 o huckleberry ridge tuff hrt and other pre lct volcanic rocks a post hrt low n 18 o lava shows similar inheritance of hrt age zircons the recycling of volcanic rocks by shallow remelting can change the water content and eruptive potential of magma this newly proposed mechanism of intracaldera volcanism is best studied by combining in situ analysis of oxygen and u pb isotope ratios of individual crystals fl 2001 elsevier science b v all rights reserved

extreme enrichment of se te pge and au in cu sulfide microdroplets evidence from la icp ms analysis of sulfides in the skaergaard intrusion east greenland the platinova reef in the skaergaard intrusion east greenland is an example of a magmatic cu pge au sulfide deposit formed in the latter stages of magmatic differentiation as is characteristic with such deposits it contains a low volume of sulfide displays peak metal offsets and is cu rich but ni poor however even for such deposits the platinova reef contains extremely low volumes of sulfide and the highest pd and au tenor sulfides of any magmatic ore deposit here we present the first la icp ms analyses of sulfide microdroplets from the platinova reef which show that they have the highest se concentrations up to 1200 ppm and lowest s se ratios 190 700 of any known magmatic sulfide deposit and have significant te enrichment in addition where sulfide volume increases there is a change from high pd tenor microdroplets trapped in situ to larger low tenor sulfides the transition between these two sulfide regimes is marked by sharp peaks in au and then te concentration followed by a wider peak in se which gradually decreases with height mineralogical evidence implies that there is no significant post magmatic hydrothermal s loss and that the metal profiles are essentially a function of magmatic processes we propose that to generate these extreme precious and semimetal contents the sulfides must have formed from an anomalously metal rich package of magma possibly formed via the dissolution of a previously pge enriched sulfide other processes such as kinetic diffusion may have also occurred alongside this to produce the ultra high tenors the characteristic metal offset pattern observed is largely controlled by partitioning effects producing offset peaks in the order pt pd au te se cu that are entirely consistent with published d values this study confirms that extreme enrichment in sulfide droplets can occur in closed system layered intrusions in situ but this will characteristically form ore deposits that are so low in sulfide that they do not conform to conventional deposit models for cu ni pge sulfides which require very high r factors and settling of sulfide liquids

pyroxene thermometry of rhyolite lavas of the bruneau jarbidge eruptive center central snake river plain article i nfo the bruneau jarbidge eruptive center of the central snake river plain in southern idaho usa produced multiple rhyolite lava flows with volumes of b10 km 3 to 200 km 3 each from 11 2 to 8 1 ma most of which follow its climactic phase of large volume explosive volcanism represented by the cougar point tuff from 12 7 to 10 5 ma these lavas represent the waning stages of silicic volcanism at a major eruptive center of the yellowstone hotspot track here we provide pyroxene compositions and thermometry results from several lavas that demonstrate that the demise of the silicic volcanic system was characterized by sustained high pre eruptive magma temperatures mostly 950 c prior to the onset of exclusively basaltic volcanism at the eruptive center pyroxenes display a variety of textures in single samples including solitary euhedral crystals as well as glomerocrysts crystal clots and annealed microgranular inclusions of pyroxene magnetite plagioclase pigeonite and augite crystals are unzoned and there are no detectable differences in major and minor element compositions according to textural variety mineral compositions in the microgranular inclusions and crystal clots are identical to those of phenocrysts in the host lavas in contrast to members of the preceding cougar point tuff that host polymodal glass and mineral populations pyroxene compositions in each of the lavas are characterized by single rather than multiple discrete compositional modes collectively the lavas reproduce and extend the range of fe mg pyroxene compositional modes observed in the cougar point tuff to more mg rich varieties the compositionally homogeneous populations of pyroxene in each of the lavas as well as the lack of core to rim zonation in individual crystals suggest that individual eruptions each were fed by compositionally homogeneous magma reservoirs and similarities with the cougar point tuff suggest consanguinity of such reservoirs to those that supplied the polymodal cougar point tuff pyroxene thermometry results obtained using quilf equilibria yield pre eruptive magma temperatures of 905 to 980 c and individual modes consistently record higher ca content and higher temperatures than pyroxenes with equivalent fe mg ratios in the preceding cougar point tuff as is the case with the cougar point tuff evidence for up temperature zonation within single crystals that would be consistent with recycling of sub or near solidus material from antecedent magma reservoirs by rapid reheating is extremely rare also the absence of intra crystal zonation particularly at crystal rims is not easily reconciled with cannibalization of caldera fill that subsided into pre eruptive reservoirs the textural compositional and thermometric results rather are consistent with minor re equilibration to higher temperatures of the unerupted crystalline residue from the explosive phase of volcanism or perhaps with newly generated magmas from source materials very similar to those for the cougar point tuff collectively the data suggest that most of the pyroxene compositional diversity that is represented by the tuffs and lavas was produced early in the history of the eruptive center and that compositions across this range were preserved or duplicated through much of its lifetime mineral compositions and thermometry of the multiple lavas suggest that unerupted magmas residual to the explosive phase of volcanism may have been stored at sustained high temperatures subsequent to the explosive phase of volcanism if so such persistent high temperatures and large eruptive magma volumes likewise require an abundant and persistent supply of basalt magmas to the lower and or mid crust consistent with the tectonic setting of a continental hotspot

storage conditions of the 29 ka rhyolitic guangoche white pumice sequence los azufres volcanic field central mexico abstract rhyolitic magmas in occasions can be related to explosive eruptions in active volcanoes that may not exhibit precursory signals making them very dangerous for the surrounding communities to understand the pre eruptive conditions of such magmas it is important to decipher the mechanisms capable to produce these explosive events in this study we analyzed the pre eruptive conditions of guangoche stratovolcano located to the southwest of the los azufres volcanic field in the central part of the trans mexican volcanic belt during the late pleistocene guangoche generated three plinian subplinian eruptions and some effusive eruptions all of them involving high silica rhyolitic magmas one of these plinian events vei 5 occurred 29 ka and deposited the white pyroclastic sequence wps this eruption ejected 0 7 km3 dre volume of rhyolitic magma and deposited a pumice fallout followed by three pumice rich pyroclastic density currents petrography combined with mineral composition melt inclusions and water saturated phase equilibria experiments were used to determine the evolution of the magma storage of the wps event prior to the eruption the magma was a crystal poor 14 vol rhyolite containing the following mineral assemblage biotite fe ti oxides amphibole sanidine and quartz set in a rhyolitic matrix 77 3 wt sio2 with low ba 121 16 7 ppm eu 0 15 0 02 ppm and sr 37 7 ppm based on fe ti oxythermometers and phase equilibria experiments we determine that the magma was stored between 75 and 100 mpa 3 4 km depth at a temperature of 769 8 c moreover h2o co2 dissolved in quartz melt inclusions and the textural features of the mineral assemblage of the wps products provided insights of the presence of a quartzo feldspathic crystal mush located at minimum depths between 4 3 and 9 5 km 98 218 mpa large sanidine quartz plagioclase and amphibole phenocrysts and mineral clots in the wps rocks represent assimilated parts from this mush by a melt extraction process probably triggered by the arrival of a relatively hotter magma at the base of the crystal mush which in turn caused reheating and partial melting of the quartzo feldspathic crystal mush generating the 29 ka rhyolitic wps magma

satellite and pollen based quantitative woody cover reconstructions for northern asia verification and application to late quaternary pollen data abstract accurate reconstruction of late quaternary vegetation cover is necessary for better understanding of past vegetation dynamics the role of vegetation feedbacks in glacial interglacial climate variations and for validating vegetation and climate models in this paper over 1700 surface pollen spectra from the former soviet union mongolia northern china and northern japan together with data from the advanced very high resolution radiometer avhrr were used to calibrate modern analogue method for quantitatively reconstructing past woody cover from fossil pollen data the avhrr based estimates of woody cover percentages within a 21 21 km window around pollen sampling sites were attributed to the respective modern pollen spectra reconstructions of modern woody cover using the pollen data and best modern analogues bma method matched well to the original avhrr based estimates for both total woody cover r 2 0 77 and its fractions including broad leaved r 2 0 66 needle leaved r 2 0 79 deciduous r 2 0 60 and evergreen r 2 0 76 woody cover discrepancies in the pollen avhrr cross validation may be caused by long distance transport of arboreal pollen patchy forest distributions underrepresentation of larix and populus in pollen records and errors in the avhrr classification the generally strong correlations encourage application of the modern analogue approach for reconstructing late quaternary variations in vegetation cover from northern asian fossil pollen records at the last glacial maximum lgm 21 000 cal yr bp areas presently occupied by boreal forest were much more open suggesting a reduction in total woody cover to below 20 at most modern forest sites pollen records from northern and central siberia suggest a rather quick spread of tree and shrub vegetation after 15 000 cal yr bp presumably in response to increased summer insolation woody cover histories are spatially variable in the modern forest steppe where tree growth is largely controlled by the ratio of annual actual over potential evapotranspiration which serves as an index of moisture availability in northwestern mongolia woody cover percentages decreased between 9000 and 5000 cal yr bp and again between 2000 and 1000 cal yr bp and may be linked to shifts in intensity of the pacific monsoon in contrast pollen data from the kazakhstan forest steppe where atmospheric precipitation is associated with the atlantic westerly flow suggest that woody cover density reached modern levels only during the last millennium

stages of major floral change in japan based on macrofossil evidence and their connection to climate and geomorphological changes since the pliocene abstract in the present study the plant macrofossil stratigraphy of the plio pleistocene sedimentary basins of japan is reviewed and the process of development of modern flora is discussed taxa endemic to the modern flora of central and south china became extinct while plants that have been dominant in the recent cool temperate and subarctic zones of japan increased and or emerged after the late pliocene the floral change was stepwise and the events were concentrated in transition periods of climatic fluctuation and or in a downward shift of the glacial climate these events are represented by the last occurrence of exotic taxa at 3 35 ma 2 9 ma 2 7 2 5 ma 1 2 ma 0 9 ma 0 5 ma and in the late pleistocene local extinctions occurred earlier in northern and inland basins and the first appearance of plants dominant in modern cool temperate and subarctic forests was dependent on the topography of mountains surrounding the basin geomorphological changes that were accompanied by mountain uplifts and sea level changes occurred in and around sedimentary basins during stage of floral changes these alterations along with climate changes likely changed the habitats and migration routes of plants which ultimately resulted in their extinction

spatial biome changes in southwestern japan since the last glacial maximum abstract data from published palynological studies in southwestern japan between 20 ka bp and the present were applied in a biomization procedure for japan the 20 biome maps obtained reveal a transition in biome from cool mixed forest to warm mixed broadleaved evergreen forest and their migration routes during the last glacial maximum southwestern japan was covered with cool mixed forest and the climate was cooler than present the warm mixed broadleaved evergreen forest was established in northern kyushu island and in the coastal areas of the sea of japan at 17 and 7 ka bp respectively there appears to have been a delay in its migration into the chugoku region caused by the environmental changes in the sea of japan before 8 ka bp the relatively weak flow of the tsushima warm current into the sea of japan created a climate resembling continental conditions and the winter temperatures were not high enough to permit the establishment of a warm mixed broadleaved evergreen forest after 8 ka bp warm mixed broadleaved evergreen forest spread into the chugoku region and reached higher altitudes 4 ka bp

formation of low δ18o rhyolites after caldera collapse at yellowstone wyoming usa we present a new model for the genesis of low 18o rhyolites of the yellowstone caldera based on analyses of zircons and individual quartz phenocrysts low 18o rhyolites were erupted soon after the massive caldera forming lava creek tuff eruption 602 ka 1000 km3 and contain xenocrysts of quartz and zircon inherited from precaldera rhyolites these zircons are isotopically zoned and out of equilibrium with their host low 18o melts and quartz diffusion modeling predicts that magmatic disequilibria of oxygen isotopes persists for as much as tens of thousands of years following nearly total remelting of the hydrothermally altered igneous roots of the depressed cauldron in which the alteration resistant quartz and zircon initially retained their 18o values these results link melting to caldera collapse rule out rapid or catastrophic magma meteoric water interaction and indicate wholesale melting rather than assimilation or partial melting

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

density and lithospheric strength models of the yellowstone snake river plain volcanic system from gravity and heat flow data abstract the structure and composition of the yellowstone snake river plain ysrp volcanic system were analyzed using gravity data taken at over 30 000 stations in the ysrp and surrounding region additional constraints were provided by tomographic seismic velocity models new heat flow and temperature information gps derived strain rates earthquake locations and chemical analyses of volcanic rocks p wave velocity models and velocity density data based on petrologic information were used to constrain three dimensional density models rheology and strength properties were calculated at selected locations and compared to earthquake focal depths results of this study suggest that the lower crust of the snake river plain srp has been thickened by the addition of an underplated layer composed primarily of clinopyroxene having a density of 3200 kg m3 a mid crustal high density sill is composed of a series of gabbroic lenses inter fingering with the granitic upper crust this geometry yields a bulk composition comparable to diorite and a density of 2900 kg m3 the mid crustal sill varies from 4 to 11 km in thickness resulting in a series of se nw trending gravity highs observed along the axis of the srp the mid crustal sill extends up to 20 km southeast of the srp volcanic field and causes asymmetry of the gravity field the yellowstone plateau volcanic field density model reveals low density partial melt 10 km beneath the caldera that shallows under the northeastern caldera and continues laterally 20 km north of the caldera boundary and notably increases the previously estimated size of the magma reservoir by 20 the caldera melt body has a density of 2520 kg m3 and a significantly lower value of 2470 kg m3 for the northeastern caldera melt body southwest of yellowstone the crustal section occupied by the mid crustal sill in the srp and the partial melt in yellowstone constitute a transition area between the active yellowstone magma system and the now volcanically quiescent srp with a density of 2820 kg m3 strength models show that the crust of the ysrp becomes progressively stronger and cooler with increasing distance from yellowstone and tectonic earthquakes within the yellowstone caldera are unlikely to nucleate below 4 6 km depth thus limiting the maximum magnitude of earthquakes to m 6 5

rapid weathering processes of a 120 year old chronosequence in the hailuogou glacier foreland mt gongga sw china increasing numbers of young soil chronosequences have become exposed in global alpine areas as glaciers have retreated due to climate warming since the industrial revolution however knowledge on the initial stages of weathering at the decadal time scale is limited our aim is to reveal the weathering processes and influential factors in a 120 year old chronosequence on mt gongga in southwest china sixty nine soil samples and 17 water samples were collected from 6 sites with different exposure ages 0 30 40 52 80 and 120 years mineral compositions were determined using x ray diffractometry and four mineral pools i e 1 exchangeable cations 2 carbonates and apatite 3 biotite and hornblende and 4 refractory minerals were separated using a sequential extraction method the results reveal that the soil particle sizes of 2 mu m clay in the a horizons increased and the particle sizes of 20 2000 mu m sand decreased significantly with time the soil organic carbon accumulation rate was up to 14 g m 2 yr which is relatively high compared with other chronosequences of similar age the weathering can be generally divided into two stages the first stage was dominated by the weathering of carbonates and was present at sites with an exposure age of 52 years the second stage was characterized by the intense weathering of biotite hornblende and apatite and was present at the 80 and 120 year old sites where coniferous trees were the dominant plants the rapid weathering was a result of the interactions of the lithology rapid vegetation succession and climate in the hailuogou chronosequence fine silt was produced in large quantities by the strong glacial abrasion and freeze thaw cycles providing rich materials for the subsequent chemical and biogeochemical weathering the decarbonation and the rapid establishment of the conifer forest due to relatively high temperatures and precipitation promote mineral weathering by decreasing soil ph from 8 5 0 years to 4 8 120 years the high permeability of the soil horizons due to the high content of rock fragments and abundant precipitation allows water and organic acids to infiltrate and dissolve mineral soils above the impervious bedrock this study highlights the importance of carbonate weathering in alpine biogeochemical cycling during the initial stage of weathering in granitoid rock areas furthermore our results indicate that the weathering intensity increases with exposure age due to vegetation succession in the early stages of weathering c 2015 elsevier b v all rights reserved

low δ18o rhyolites from yellowstone magmatic evolution based on analyses of zircons and individual phenocrysts the yellowstone plateau volcanic field is one of the largest centers exchange time to form zoned zircons is between a few hundred and a few thousand years which reflects the residence time of lowo of rhyolitic magmatism on earth major caldera forming eruptions are followed by unusual lowo rhyolites new oxygen isotope magmas after formation and before eruption petrologic and geochemical data from rhyolites belonging to the 2 0 my eruptive history of yellowstone are presented with emphasis on the genesis of lowo magmas erupted after the huckleberry ridge tuff 2 0 ma 2500 km and lava creek tuff 0 6 ma

correction to divergent t ƒo 2 paths during crystallisation of h 2 o rich and h 2 o poor magmas as recorded by ce and u in zircon with implications for titaniq and titaniz geothermometry in the original article the eq 1 and email address of the co author are published incorrectly the correct eq 1 and email address of the co author are given below

mushy magma beneath yellowstone a recent prospective on the yellowstone caldera discounts its explosive potential based on inferences from tomographic studies which suggests a high degree of crystallization of the underlying magma body in this study we show that many of the first teleseismic p wave arrivals observed at seismic stations on the edge of the caldera did not travel through the magma body but have taken longer but faster paths around the edge after applying a number of waveform modeling tools we obtain much lower seismic velocities than previous studies 2 3 km sec v p and 1 1 km sec v s we estimate the physical state of the magma body by assuming a fluid saturated porous material consisting of granite and a mixture of rhyolite melt and water and co 2 at a temperature of 800 c and pressure at 5 km 0 1 gpa we found that this relatively shallow magma body has a volume of over 4 300 km 3 and is about 32 melt saturated with about 8 water plus co 2 by volume

snowline elevation and eolian dust flux in the japanese islands during isotope stages 2 and 4 abstract changes in snowline elevation and dust flux clearly contrast the paleoenvironments of the japanese islands during isotope stages 2 and 4 a lower snowline elevation and a smaller dust flux during isotope stage 4 suggests a climate with a cold and dry summer dominated by winter monsoonal precipitation between 70 and 55 ka a higher snowline elevation and a larger dust flux during isotope stage 2 indicates a climate with a cold and very dry summer with a minimized winter monsoon precipitation especially around 18 ka a drier climate during stage 2 can be explained by 1 a lowering of sea surface temperature in the japan sea by blocking the warm tsushima current during a sea level lowering 2 the extension of sea ice over the northern part of the japan sea and the sea of okhotsk and 3 weakening of the summer monsoon and the southern migration of the polar front the increase in dust flux in both stages 2 and 4 suggests an intensification of westerlies and winter monsoon during these stages a bigger dust flux in stage 2 than stage 4 reflects 1 stronger westerlies and winter monsoon and 2 the emergence of continental shelf which became an important dust source

chemical and thermal zonation in a mildly alkaline magma system infiernito caldera trans pecos texas postcollapse lavas of the infiernito caldera grade stratigraphically upward from nearly aphyric high silica rhyolite 76 sio2 to highly prophyritic trachyte 62 sio2 plagioclase clinopyroxene orthopyroxene magnetite ilmenite and apatite occur as phenocrysts throughout the sequence sanidine biotite and zircon are present in rocks with more than about 67 sio2 major and trace elements show continuous variations from 62 to 76 sio2 modeling supports fractional crystallization of the observed phenocrysts as the dominant process in generating the chemical variation temperatures calculated from coexisting feldspars pyroxenes and fe ti oxides agree and indicate crystallization from slightly more than 1100 c in the most mafic trachyte to 800 c in high silica rhyolite the compositional zonation probably arose through crystallization against the chilled margin of the magma chamber and consequent rise of more evolved and therefore less dense liquid mineral compositions vary regularly with rock composition but also suggest minor mixing and assimilation of wall rock or fluids derived from wall rock mixing between liquids of slightly different compositions is indicated by different compositions of individual pyroxene phenocrysts in single samples liquid solid mixing is indicated by mineral compositions of glomerocrysts and some phenocrysts that apparently crystallized in generally more evolved liquids at lower temperature and higher oxygen fugacity than represented by the rocks in which they now reside glomerocrysts probably crystallized against the chilled margin of the magma chamber and were torn from the wall as the liquid rose during progressive stages of eruption assimilation is indicated by rise of oxygen fugacity relative to a buffer from more mafic to more silicic rocks calculation of density and viscosity from the compositional and mineralogical data indicates that the magma chamber was stably stratified lower temperature but more evolved thus less dense rhyolite overlay higher temperature less evolved and therefore more dense progressively more mafic liquids the continuity in rock and mineral compositions and calculated temperature viscosity and density indicate that compositional gradation in the magma chamber was smoothly continuous any compositional gaps must have been no greater than about 2 sio2

soil carbon accretion along an age chronosequence formed by the retreat of the skaftafellsjokull glacier se iceland abstract climate warming has led to glacial retreat worldwide where surfaces exposed to the atmosphere are subjected to weathering vegetation colonization and new soil formation on young soils developing along the recessional path left by the skaftafellsjokull glacier se iceland we investigated the accretion of soil organic carbon soc and nitrogen n representing an age chronosequence of 120 years in total 54 sampling sites were distributed along three moraines deposited in 1890 1945 and 2003 for comparison soil samples were collected from nearby birch woodlands betula pubescens ehrh representing soils in a mature ecosystem likely to establish on the moraines in the future results show that the average soc and n concentrations increase with time and at faster rates over the latter part of the chronosequence period investigated 1945 1890 after 120 yrs the soil contains 1 1 kg c m 2 in the surface layer 0 10 cm which is still about one third of the 3 2 kg c m 2 in soil under the birch woodlands the n stock estimated at 0 06 kg n m 2 after 120 yrs is almost one fourth of that under the woodlands the data suggest that landscape affects vegetation establishment and in turn both landscape and vegetation affect soil development thus concentrations of soc n and noncrystalline oxalate extractable al and fe are higher within depressions in the proglacial landscape the comparison of soc stock in the moraine soils with that under the birch forest shows that the young proglacial soils still have a large potential to accrete soc within the developing pedosphere with the observed accrual rate of 9 1 g c m 2 yr 1 in the top at 10 cm it may take the moraine soils an additional period of 220 yrs to accrue soc stocks comparable with those under the birch forest given the fact that all icelandic glaciers are receding assessing soc accretion in new soil formation may be important to off setting the greenhouse gas emissions

clay mineral formation in soils of two different chronosequences in the swiss alps two chronosequences of soils developed from postglacial tills at two different sites in the swiss alps were studied with respect to their soil mineralogy and chemistry the age of these soils ranged between 0 and 11 500 years the parent material for both chronosequences was similar but differences were found in the clay fraction within the considered time span podzols developed at both sites however at one site already after about 3000 years and at the other a few years later especially trioctahedral minerals were strongly weathered within the time span of about 11 000 years smectite and regularly interstratified dioctahedral mica smectite could be found in the most weathered horizons at one site the origin of smectite could be traced back to both chlorite and trioctahedral mica which supports the fact that smectite is the end product of chlorite alteration and regularly interstratified mica smectite or even smectite the end product of mica weathering in strongly leached and acidified horizons at the other site smectite was already present in the parent material most presumably due to hydrothermal formation during the first 500 years of soil formation a kind of retrograde podzolisation was observed leading to the elimination of this smectite within the same time increased amounts of dioctahedral minerals were formed and after 11 000 years a small proportion of pedogenic smectite was discernible again main clay mineral transformations occurred at both sites within the first 3000 years of soil development weathering and transformation reactions were most advanced in the e horizon being almost complete after 3000 years at one site the presence of significant amounts of chlorite and or a minimal content of mica of ca 5 seems however to be compulsory in order to detect low charge expandable minerals already after a 3000 year duration of soil formation in the alps otherwise smectite formation is retarded

titaniq recrystallized experimental confirmation of the original ti in quartz calibrations several studies have reported the p t dependencies of ti in quartz solubility and there is close agreement among three of the four experimental calibrations new experiments were conducted in the present study to identify potential experimental disequilibrium and to determine which ti in quartz solubility calibration is most accurate crystals of quartz rutile and zircon were grown from sio2 tio2 and zrsio4 saturated aqueous fluids in an initial synthesis experiment at 925 c and 10 kbar in a piston cylinder apparatus a range of quartz crystal sizes was produced in this experiment both large and small examples were analyzed by electron microprobe to determine whether ti concentrations are correlated with crystal size cathodoluminescence images and epma measurements show that intercrystalline and intracrystalline variations in ti concentrations are remarkably small regardless of crystal size the average ti in quartz concentration from the synthesis experiment is 392 1 ppmw ti which is within 95 confidence interval of data from the 10 kbar isobar of wark and watson contrib mineral petrol 152 743 754 2006 and thomas et al contrib mineral petrol 160 743 759 2010 as a cross check on the ti in quartz calibration we also measured the concentration of zr in rutile from the synthesis experiment the average zr in rutile concentration is 4337 32 ppmw zr which is also within the 95 confidence interval of the zr in rutile solubility calibration of ferry and watson contrib mineral petrol 154 429 437 2007 the p t dependencies of ti solubility in quartz and zr solubility in rutile were applied as a thermobarometer to the experimental sample the average ti in quartz isopleth calculated from the calibration of thomas et al contrib mineral petrol 160 743 759 2010 and the average zr in rutile isopleth calculated from the calibration of tomkins et al j metamorph geol 25 703 713 2007 cross at 9 5 kbar and 920 c which is in excellent agreement with the p t conditions of the synthesis experiment separates of the high ti quartz from the initial synthesis experiment described above were used as starting material in subsequent experiments at 20 kbar at which pressure the solubility of ti in quartz is expected to be significantly lower in the recrystallized quartz these recrystallization experiments were conducted under wet and dry conditions at 925 c and under wet conditions at 850 c both wet and dry recrystallization experiments produced polycrystalline quartzites rutile occurs as inclusions in quartz and as individual crystals dispersed along quartz grain boundaries quartz that grew during the recrystallization experiments has dark cathodoluminescence indicating substantially lower ti concentrations the average ti concentrations in quartz from the recrystallization experiments are within the 95 confidence interval of a linear fit to the 20 kbar data of thomas et al contrib mineral petrol 160 743 759 2010 collectively the results from the synthesis and recrystallization experiments confirm that the ti in quartz concentrations used to calibrate the p t dependencies of ti in quartz solubility in thomas et al s contrib mineral petrol 160 743 759 2010 calibration represent the equilibrium concentrations of ti in quartz

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

comagmatic a type granophyre and rhyolite from the alid volcanic center eritrea northeast africa vermicular to cuneiform barker 1970 typically the granophyric blocks within late pleistocene pyroclastic flow ejecta from the alid volcanic center northeast africa are the rapidly groundmass feldspars radiate off pre existing feldspar crystallized intrusive equivalent of pumice from the pyroclastic flow phenocrysts with which they are in optical continuity phenocryst compositions and geochemical characteristics of the dunham 1965 some workers prefer the term pumice and granophyre are virtually identical silicate melt inclusions micrographic for highly regular interlocking arand other geochemical and geological constraints reveal those processes rangements of quartz and feldspar as in the coarser leading to development of the granophyric texture rhyolitic agraphic granite fenn 1986 lentz fowler 1992 type magma with 2 6 wt dissolved h2o and a temperature though schloemer 1964 has shown that some graphic near 870 c was intruded to within 2 4 km of the surface causing textures can grow by replacement see also augustithis deformation and structural doming of shallow marine and subaerial 1973 most workers agree that phenocryst bearing strata eruptions of crystal poor rhyolite from this shallow magma granophyres typically form by rapid and simultaneous chamber caused degassing which forced undercooling and consequent crystallization of quartz and feldspar from a melt smith granophyric crystallization of some of the magma remaining in the 1974 such crystallization is generally believed to be due intrusion the most recent eruption from alid excavated the cryto pronounced undercooling of the silicate liquid vogt stallized granitic wall of the magma chamber bringing the grano1930 dunham 1965 not necessarily at eutectic temphyric clasts to the surface peratures or compositions fenn 1986 london et al 1989 lentz fowler 1992 granophyric textures are common in epizonal granitic bodies particularly those associated with volcanic rocks buddington 1959 dunham 1965 on occasion they erupt as comagmatic ejecta in pyroclastic deposits e g

rates of weathering and chemical depletion in soils across a chronosequence of lake michigan sand dunes abstract accumulation of soil organic matter and depletion of base cations and trace metals were measured in surface soils i e o horizon and upper 15 cm of mineral soil across a 4150 year soil chronosequence of dune capped beach ridges bordering northern lake michigan within 400 years of beach ridge formation coniferous forest develops soil c and n accumulate to steady state levels of 40 and 1 3 mg ha 1 respectively and the ph of the upper mineral soil decreases from 8 5 to 4 3 as carbonate minerals dissolve after substantial proportions of ca and mg have been removed an incipient spodic horizon can be observed the upper surface of which progressively deepens with increasing soil age analysis of soil strain of the upper mineral soil showed gradual dilation reaching 121 after several centuries of soil development after accounting for soil dilation quantities of ca mg p zn mn fe and v in the upper 15 cm of mineral soil decreased exponentially to low asymptotic levels representing quantities contained in weathering resistant minerals mass balance modeling indicated weathering and elemental losses in the order of decreasing decay constant as ca mg mn zn p v fe al k na ti this sequence is consistent with weathering of carbonates then ferromagnesian minerals then feldspars p levels are tightly coupled with ca losses in soils older than 200 years suggesting that ca rather than fe or al stabilizes p high concentrations of heavy metals in the organic horizon relative to the upper mineral soil indicate atmospheric inputs of industrial pollutants

40ar39ar geochronology of rhyolites erupted following collapse of the yellowstone caldera yellowstone plateau volcanic field implications for crustal contamination abstract single crystal laser probe 40 ar 39 ar dating of 133 grains of sanidine and plagioclase has enabled us to resolve the eruption ages of the upper basin member rhyolites the lava flows and related tuffs that erupted within the yellowstone caldera shortly after its collapse 630 ky ago on eruption of the lava creek tuff two lavas and a tuff that erupted from the eastern ring fracture zone yield an eruptive age of 481 8 ka whereas two flows from the western ring fracture zone yield eruptive ages of 516 7 and 198 8 ka most of the units contain old xenocrysts explaining why previous attempts at dating these earliest post caldera units by the conventional k ar method yielded poorly resolved and in some cases anomalous ages the tuff shows the most severe contamination grains from a single pumice lapilli in the tuff show as large an age range as those from bulk vitrophyre indicating that the xenocrysts were incorporated in the magma prior to its near surface explosive fragmentation diffusion calculations indicate that the xenocrysts could not have remained in the magma for more than a few years without degassing and giving ages indistinguishable from the phenocrysts thus the contamination represented by the xenocrysts probably occurred during fracturing and conduit propagation rather than during caldera collapse which took place more than 100 ky earlier the apparent ages of xenocrysts and their compositions as determined by electron microprobe suggest that the eocene absaroka volcanics are the main contaminant with a single xenocryst probably coming from precambrian basement rocks most of the xenocrysts are difficult to distinguish optically or chemically from feldspar phenocrysts illustrating the necessity of single crystal to date many young volcanic rocks accurately

snake river sr type volcanism at the yellowstone hotspot track distinctive products from unusual high temperature silicic super eruptions a new category of large scale volcanism here termed snake river sr type volcanism is defined with reference to a distinctive volcanic facies association displayed by miocene rocks in the central snake river plain area of southern idaho and northern nevada usa the facies association contrasts with those typical of silicic volcanism elsewhere and records unusual voluminous and particularly environmentally devastating styles of eruption that remain poorly understood it includes 1 large volume lithic poor rhyolitic ignimbrites with scarce pumice lapilli 2 extensive parallel laminated medium to coarse grained ashfall deposits with large cuspate shards crystals and a paucity of pumice lapilli many are fused to black vitrophyre 3 unusually extensive large volume rhyolite lavas 4 unusually intense welding rheomorphism and widespread development of lava like facies in the ignimbrites 5 extensive fines rich ash deposits with abundant ash aggregates pellets and accretionary lapilli 6 the ashfall layers and ignimbrites contain abundant clasts of dense obsidian and vitrophyre 7 a bimodal association between the rhyolitic rocks and numerous coalescing low profile basalt lava shields and 8 widespread evidence of emplacement in lacustrine alluvial environments as revealed by intercalated lake sediments ignimbrite peperites rhyolitic and basaltic hyaloclastites basalt pillow lava deltas rhyolitic and basaltic phreatomagmatic tuffs alluvial sands and palaeosols many rhyolitic eruptions were high mass flux large volume and explosive vei 6 8 and involved h2o poor low 18o metaluminous rhyolite magmas with unusually low viscosities partly due to high magmatic temperatures 900 1 050 c sr type volcanism contrasts with silicic volcanism at many other volcanic fields where the fall deposits are typically plinian with pumice lapilli the ignimbrites are low to medium grade non welded to eutaxitic with abundant pumice lapilli or fiamme and the rhyolite extrusions are small volume silicic domes and coulees sr type volcanism seems to have occurred at numerous times in earth history because elements of the facies association occur within some other volcanic fields including trans pecos texas etendeka parana lebombo the english lake district the proterozoic keewanawan volcanics of minnesota and the yardea dacite of australia

vegetation and climate histories between mis 63 and 53 in the early pleistocene in central japan based on plant macrofossil evidences abstract among the early pleistocene fluvial sediments in japan that yield plant macrofossils the uonuma group in the niigata sedimentary basin provides the most continuous profile without any conspicuous hiatuses and is therefore suitable for high resolution reconstructions of environmental and vegetation histories based on tephro and magneto stratigraphy based on the species composition of plant macrofossil assemblages along with previously reported results on sedimentary environments and pollen records we performed a reconstruction of changes in paleovegetation and paleotemperatures between mis 63 and 53 macrofossil assemblages identified from 33 samples include 89 arboreal and 88 herbaceous taxa in total of which 9 taxa are extinct from japan assemblages from the peat deposits in fluvial backmarshes during glacial stages are composed mainly of wetland herbaceous plants whereas those from the sandy channel fill deposits are characterized by a higher diversity in life forms and habitat preferences during the interval from mis 63 to 53 paleotemperatures fluctuated between a coldest month mean temperature of 4 6 c and 0 9 c and between a mean annual temperature of 6 6 c and 11 0 c which is within the present range for cool temperate deciduous broad leaved forests in japan mis 60 was the coldest of the glacial stages with temperatures nearly equivalent to those during the last glacial maximum major plant extinctions in and around mis 60 were not recorded in the sedimentary basin in response to the temperature decline the relatively indistinct floral changes in and around mis 60 are attributed to easier recovery of flora by migration from glacial refugia in the southern basins after termination of the glacial stage interglacial temperatures during mis 57 55 and 53 were higher than during mis 63 61 and 59 the presence of a maritime environment during the interglacial periods between mis 57 and 53 may have resulted from a greater extent of marine transgression and heat provided by the tsushima warm current flowing into the sea of japan after mis 59

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

parent material and chemical weathering in alpine soils on mt mansfield vermont usa we compared the elemental composition of soil and bedrock samples to determine the extent of chemical weathering and the nature of the soil parent material in alpine soils on vermont s highest summit previously it was unclear whether these soils formed through weathering of bedrock glacial till or eolian sediment or solely through the accumulation of organic matter in eighteen profiles no evidence was found to indicate that soils have developed in glacial till despite evidence that the mountain was completely inundated by the laurentide ice sheet in contrast results strongly support the theory that pedogenesis in this environment involves in situ bedrock weathering under a thickening blanket of acidic organic litter weathering indices reveal an increase in weathering intensity upwards from the bedrock and trends of normalized rare earth elements demonstrate a strong similarity between bedrock and soil samples leaching has concentrated less mobile elements such as al cr la p pb and ti in soil horizons and removed mobile elements such as co fe k mg mn si and zn x ray diffraction reveals that chlorite which is present in all bedrock samples and some saprolites has weathered completely from upper soil horizons and that hydrobiotite vermiculite kaolinite gibbsite and goethite have formed in the soil ratios of immobile elements ce cr nb ta ti y and zr in soil and bedrock samples are however notably different furthermore the moderately mobile trace elements cu mo and sr are actually more abundant in soil than in bedrock and soil concentrations of zr are up to an order of magnitude greater than in bedrock samples together these data argue for at least a modest eolian influx which may have arrived during the regression of lake vermont during the latest pleistocene or from an outwash source in the immediate post glacial period similarly increased ca and na concentrations in soil samples may signify modern deposition of dust bearing ca from agricultural fields and na from roads

soil development along primary succession sequences on moraines of hailuogou glacier gongga mountain sichuan china abstract soil properties related to soil development were measured in six profiles over approximately 180 years of soil development on recessional moraines of the hailuogou glacier sichuan of southwestern china it is hypothesized that soil development is strictly time dependent field and laboratory work indicate that as soil develops from initially coarse gravel outwash the properties undergo a progressive physical and chemical change such that there is a considerable profile differentiation between the youngest and the oldest soils the ph is also highly stratified it decreases with time from 8 5 to 4 2 in the upper mineral soil and increases with depth in all profiles accumulation of soil organic c and n increases with time but the rates of accumulation become slower with time within the investigated timespan soil c and n accumulated to a considerable level of 3 5 and 0 6 kg m2 respectively with mean annual rates of 28 g m2 for carbon and 3 5 g m2 for nitrogen the rapid accumulation of organic c and n accelerates the processes of soil formation but the content of organic c and n did not reach a steady state during the observed timespan the accumulation of soil organic matter results in increased acid production and in the chemical weathering of minerals that promote formation and translocation of the clay fraction and leaching of carbonate it is also directly responsible for development of soil properties such as cation exchange capacity cec and bulk density

monitoring super volcanoes geophysical and geochemical signals at yellowstone and other large caldera systems earth s largest calderas form as the ground collapses during immense volcanic eruptions when hundreds to thousands of cubic kilometres of magma are explosively withdrawn from the earth s crust over a period of days to weeks continuing long after such great eruptions the resulting calderas often exhibit pronounced unrest with frequent earthquakes alternating uplift and subsidence of the ground and considerable heat and mass flux because many active and extinct calderas show evidence for repetition of large eruptions such systems demand detailed scientific study and monitoring two calderas in north america yellowstone wyoming and long valley california are in areas of youthful tectonic complexity scientists strive to understand the signals generated when tectonic volcanic and hydrothermal hot ground water processes intersect one obstacle to accurate forecasting of large volcanic events is humanity s lack of familiarity with the signals leading up to the largest class of volcanic eruptions accordingly it may be difficult to recognize the difference between smaller and larger eruptions to prepare ourselves and society scientists must scrutinize a spectrum of volcanic signals and assess the many factors contributing to unrest and toward diverse modes of eruption

months between rejuvenation and volcanic eruption at yellowstone caldera wyoming rejuvenation of previously intruded silicic magma is an important process leading to effusive rhyolite which is the most common product of volcanism at calderas with protracted histories of eruption and unrest such as yellowstone caldera wyoming long valley caldera california and valles caldera new mexico in the united states although orders of magnitude smaller in volume than rare caldera forming supereruptions these relatively frequent effusions of rhyolite are comparable to the largest eruptions of the 20th century and pose a considerable volcanic hazard however the physical pathway from rejuvenation to eruption of silicic magma is unclear particularly because the time between reheating of a subvolcanic intrusion and eruption is poorly quantified this study uses nanometer scale trace element diffusion in sanidine crystals to reveal that rejuvenation of a near solidus or subsolidus silicic intrusion occurred in 10 mo or less following a protracted period 220 k y of volcanic repose and resulted in effusion of 3 km3 of high silica rhyolite lava at the onset of yellowstone s last volcanic interval the future renewal of effusive silicic volcanism at yellowstone will likely require a comparable energetic intrusion of magma that remelts the shallow subvolcanic reservoir and generates eruptible rhyolite on month to annual time scales

low δd hydration rinds in yellowstone perlites record rapid syneruptive hydration during glacial and interglacial conditions hydration of silicic volcanic glass forms perlite a dusky porous form of altered glass characterized by abundant onion skin fractures the timing and temperature of perlite formation are enigmatic and could plausibly occur during eruption during post eruptive cooling or much later at ambient temperatures to learn more about the origin of natural perlite and to fingerprint the hydration waters we investigated perlitic glass from several synglacial and interglacial rhyolitic lavas and tuffs from the yellowstone volcanic system perlitic cores are surrounded by a series of conchoidal cracks that separate 30 to 100 m thick slivers likely formed in response to hydration induced stress h2o and d h profiles confirm that most d h exchange happens together with rapid h2o addition but some smoother d h variations may suggest separate minor exchange by deuterium atom interdiffusion following hydration the hydrated rinds 2 3 wt h2o transition rapidly within 30 m or by 1 wt h2o per 10 m to unhydrated glass cores this is consistent with quenched hydration fronts where h2o diffusion coefficients are strongly dependent on h2o concentrations the chemical 18o and d systematics of bulk glass records last equilibrium between 110 and 60 c without chemical exchange but with some 18o exchange similarly the 18o of water extracted from glass by rapid heating suggests that water was added to the glass during cooling at 400 c experimental data the thick hydration rinds in perlites measuring hundreds of microns preserve the original d h values of hydrating water as a recorder of paleoclimate conditions measured d values in perlitic lavas are 150 to 191 or 20 40 lower than glass hydrated by modern yellowstone waters this suggests that yellowstone perlites record the low d signature of glacial ice cooling calculations combined with the observed high water diffusion coefficients noted for 60 150 c suggest that if sufficient hot water or steam is available any rhyolite flow greater than 5 m thick can develop the observed 250 m hydration rinds within the expected timescale of cooling weeks years as the process of hydration involves shattering of 30 to 100 m thick slivers to expose unhydrated rhyolite glass the time required for hydration may be even shorter rapid hydration and formation of relatively thick walled glass shards allow perlites to provide a snapshot view of the meteoric water and thus climate at the time of initial alteration perlites retain their initial hydration d h signal better than thin walled ash which in contrast hydrates over many thousands of years with time averaged precipitation

volcanoes erupt stressed quartz crystals author s befus ks manga m stan c tamura n abstract 2019 american geophysical union all rights reserved volcanic eruptions are energetic events driven by the imbalance of magmatic forces the magnitudes of these forces remain poorly constrained because they operate in regions that are inaccessible either underground or dangerous to approach new techniques are needed to quantify the processes that drive eruptions and to probe magma storage conditions here we present x ray microdiffraction measurements of volcanic stress imparted as lattice distortions to the crystal cargo of magma from yellowstone and long valley eruptions elevated residual stresses between 100 and 300 mpa are preserved in erupted quartz multiple volcanic forces could be culpable for the deformation so we analyzed crystals from pyroclastic falls pyroclastic density currents and effusive lavas stresses are preserved in all quartz but cannot be attributed to differences in eruption style instead lattice deformation likely preserves an in situ measurement of the deviatoric stresses required for the brittle failure of viscous crystal bearing glass during ascent

soil development on moraines of mendenhall glacier southeast alaska 1 the moraines and soil morphology abstract soils on a sequence of well drained neoglacial moraines up to 240 years old plus an older soil were sampled to investigate soil development through the initial stages of podzolization pebbles and cobbles in the moraines are about 75 to 80 granitic rock computations based on minerals observed optically and on chemical analyses indicate that plagioclase and quartz are the predominant minerals in the fine earth the climate is perhumid leaching of the moraines may have begun before they were free of glacial ice but little organic matter accumulated under the initial vegetative cover of sparse dwarf fireweed 10 year site as alder thicket developed organic matter accumulated rapidly in oi oe and a horizons 38 year site as spruce trees began to replace alder organic matter was lost from the surface mineral soil to form an e horizon and an incipient bs horizon formed below it an oa horizon formed and the a horizon disappeared 70 and 90 year sites organic acid leaching continued to form a spodic bhs horizon in spruce forest 240 year site and a spodic bh horizon in spruce hemlock forest 240 year site hornblende has been etched slightly within 240 years apatite has been lost from e horizons and free fe presumeably in ferrihydrite has accumulated in b horizons the younger moraine soils both with and without incipient bs horizons are typic cryorthents and the 240 year old and older soils with spodic bhs and bh horizons are typic haplocryods they are expected to accumulate more organic matter and become andic humicryods which is the most common subgroup of soils in the area

soil properties micromorphology and mineralogy of cryosols from sorted and unsorted patterned grounds in the hornsund area sw spitsbergen patterned grounds are probably the most interesting features produced by natural processes acting on the earth s surface such features occur mainly in polar areas and in high mountains indicating that the origin of patterned grounds is related to frost action and cryoturbation in spite of the many studies concerning the mechanism of the formation and the various forms of patterned grounds very little attention has been paid to the qualitative and quantitative analyses of their mineral composition and especially the mineralogy of the clay fraction the analysis of the mineralogy of clay fraction is very important due to the finest particles especially clay minerals may play a crucial role in cryoturbation and cryosegregation as the particles are mainly responsible for accumulation of water and rheological properties of the ground thus the main aim of the present study was to verify the hypothesis that the presence of swelling clay minerals in parent material favors the development of sorted patterned grounds to verify the hypothesis the physical chemical micromorphological and qualitative and quantitative mineralogical properties of cryosols from sorted and unsorted patterned grounds in the hornsund area sw spitsbergen were determined the obtained results show that turbic cryosols from sorted patterned grounds featuring clear frost cracking frost segregation and cryoturbation are characterized by a lack of clearly developed soil horizons loamy texture and low content of soil organic matter haplic cryosols show better developed soil horizonation and contain lower amounts of the silt and clay fractions higher content of the sand fraction and soil organic matter in comparison with turbic cryosols exhibiting strong cryoturbation micromorphological analysis of turbic cryosols indicates frost action manifested by a vesicular microstructure round oval and deformed mammillated vesicles as dominant voids vertically oriented rock fragments and silt and silt clay cappings occurring on rock fragments in addition the occurrence of fe mn nodules showing a sharp boundary indicates mixing of soil material micromorphology of the studied turbic cryosols indicates that cryoturbation prevails over cryosegregation the soil material of the studied cryosols is composed mainly of quartz k feldspar plagioclase dioctahedral mica muscovite and or illite biotite augite hornblende garnet chlorite swelling clays smectite vermiculite goethite and in some cases also calcite and traces of kaolinite majority of the minerals are most likely primary minerals inherited from parent material due to weak chemical weathering in the severe arctic climate conditions and relatively young soils however weak chemical weathering of biotite and formation of vermiculite and mixed layered clay minerals also take place quantitative mineralogical analysis shows that besides texture and moisture the mineral composition of soil material may also play some role in the susceptibility to cryoturbation and the formation of sorted and unsorted patterned grounds however the small differences in mineral content between the studied turbic cryosols and haplic cryosols indicate that the mineral composition of parent material is not a crucial characteristic responsible for the formation of sorted patterned grounds

a stratigraphical basis for the last glacial maximum lgm abstract the last glacial maximum lgm is widely used to refer to the episode when global ice volume last reached its maximum and associated sea levels were at their lowest however the boundaries of the interval are ill defined and the term and acronym have no formal stratigraphical basis this is despite a previous proposal to define it as a chronozone in the marine records on the basis of oxygen isotopes and sea levels spanning the interval 23 19 or 24 18 ka and centred on 21 ka in terrestrial records the lgm is poorly represented since many sequences show a diachronous response to global climate changes during the last glacial cycle for example glaciers and ice sheets reached their maximum extents at widely differing times in different places in fact most terrestrial records display spatial variation in response to global climate fluctuations and changes recorded on land are often diachronous asynchronous or both leading to difficulties in global correlation however variations in the global hydrological system during glacial cycles are recorded by atmospheric dust flux and this provides a signal of terrestrial changes whilst regional dust accumulation is recorded in loess deposits global dust flux is best recorded in high resolution polar ice core records providing an opportunity to define the lgm on land and establish a clear stratigraphical basis for its definition on this basis one option is to define the global lgm as an event between the top end of greenland interstadial 3 and the base onset of greenland interstadial 2 spanning the interval 27 540 23 340 ka greenland stadial 3 this corresponds closely to the peak dust concentration in both the greenland and antarctic ice cores and to records of the global sea level minima this suggests that this definition includes not just the coldest and driest part of the last glacial cycle but also the peak in global ice volume the later part of the lgm event is marked by heinrich event 2 which reflects the onset of the collapse of the laurentide at c 24 ka together with other ice sheets in the north atlantic region a longer and later span for the lgm may be desirable although defining this in chronostratigraphical terms is problematic whichever formal definition is chosen this requires the contribution of the wider quaternary community

magma storage and evolution of the most recent effusive and explosive eruptions from yellowstone caldera between 70 and 175 ka over 350 km3 of high silica rhyolite magma erupted both effusively and explosively from within the yellowstone caldera phenocrysts in all studied lavas and tuffs are remarkably homogenous at the crystal eruption and caldera scale and yield quilf temperatures of 750 25 c phase equilibrium experiments replicate the observed phenocryst assemblage at those temperatures and suggest that the magmas were all stored in the upper crust quartz hosted glass inclusions contain 1 0 2 5 h2o and 50 600 ppm co2 but some units are relatively rich in co2 300 600 ppm and some are co2 poor 50 200 ppm the co2 rich magmas were stored at 90 150 mpa and contained a fluid that was 60 75 mol co2 co2 poor magmas were stored at 50 70 mpa with a more h2o rich fluid x text co 2 40 60 storage pressures and volatiles do not correlate with eruption age volume or style trace element contents in glass inclusions and host matrix glass preserve a systematic evolution produced by crystal fractionation estimated to range from 36 12 to 52 12 wt because the erupted products contain 10 wt crystals crystal poor melts likely separated from evolving crystal rich mushes prior to eruption in the tuffs of bluff point and cold mountain creek matrix glass is less evolved than most inclusions which may indicate that more primitive rhyolite was injected into the reservoir just before those eruptions the presence and dissolution of granophyre in one flow may record evidence for heating prior to eruption and also demonstrate that the yellowstone magmatic system may undergo rapid changes the variations in depth suggest the magmas were sourced from multiple chambers that follow similar evolutionary paths in the upper crust

eruption mechanisms and short duration of large rhyolitic lava flows of yellowstone abstract large volume effusive rhyolite lava flows are a common but poorly understood occurrence from silicic volcanic centers we integrate characterization of lava flow topographic morphology and petrographic textures and zoning of crystals with physical models of viscous fluid flow in order to interpret the eruption durations and discharge rates for the most recent effusive volcanic eruptions from yellowstone these large volume 10 70 km3 crystal poor rhyolite lavas erupted within the yellowstone caldera as 100 200 m thick flows and have a cumulative erupted volume of 650 km3 that is similar to less frequent caldera forming events but occur as individual eruptions spread over 100 ka most of this work is focused on the axisymmetric 124 ka 50 km3 summit lake flow we examined crystallinity major and trace element concentrations oxygen and hydrogen isotopic values and quartz morphology and zoning in samples from the center to margin of this flow water contents down to 0 1 wt and d values of 110 are low and require closed system degassing until near surface lithostatic pressure while major elements are consistent with water undersaturated pre eruptive storage and crystallization at 4 8 km depth we found some evidence for subtle km scale zoning within the lavas but describe significant microscopic scale compositional diversity including sharp boundaries between high ti cores and 200 m thick rims on quartz phenocrysts embayed quartz external morphology and rim growth may be the result of undercooling during coalescence of magma bodies during shallow transport between dikes and sills modeling the emplacement of the lava flow as a simple viscous fluid suggests that emplacement of rhyolite lava at 800 c occurred over 2 to 5 yrs with high discharge rates 100 m3 s such high magma discharge rates are accommodated through 6 km long fissures that allow for slower magma ascent velocities of 10 yr flow durations and significant cooling of the flow front that should result in a more complex compound flow morphology than observed higher temperatures require unrealistically wide 50 m dike widths to accommodate large discharge rates petrographic and isotopic evidence from crystals suggests recharge and merger of individual magma batches occurs on a similar timescale to the eruption duration and may directly cause overpressure and emplacement of these rhyolite lava flows from a shallow ephemeral magma chamber large volume rhyolitic lavas are able to erupt effusively through elongate fissures that utilize preexisting zones of crustal weaknesses such as ring fractures less common explosive eruptions at yellowstone may result when ascending magmas are forced through narrower conduits or when recharge rates are especially high the results of this study provide a unique top down constraint on effusive eruption rates make new interpretations of common petrographic textures and presents a comprehensive model for eruption control

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

geodynamics of the yellowstone hotspot and mantle plume seismic and gps imaging kinematics and mantle flow abstract integration of geophysical and geological data show that the yellowstone hotspot resulted from a mantle plume interacting with the overriding north america plate a process that has highly modified continental lithosphere by magmatic and tectonic processes and produced the 16 17 ma 700 km long yellowstone snake river plain ysrp silicic volcanic system accessibility of the ysrp allowed large scale geophysical projects to seismically image the hotspot and evaluate its kinematic properties using geodetic measurements seismic tomography reveals a crustal magma reservoir of 8 to 15 melt 6 km to 16 km deep beneath the yellowstone caldera an upper mantle low p wave velocity body extends vertically from 80 km to 250 km beneath yellowstone but the anomalous body tilts 60 wnw and extends to 660 km depth into the mantle transition zone we interpret this conduit shaped low velocity body as a plume of up to 3 5 vp and 5 5 vs perturbation that corresponds to a 1 2 partial melt models of whole mantle convection reveal eastward upper mantle flow beneath yellowstone at relatively high rates of 5 cm yr that deflects the ascending plume into its west tilted geometry a geodynamic model of the yellowstone plume constrained by vp and vs velocities and attenuation parameters suggests low excess temperatures of up to 120 k corresponding to a maximum 2 5 melt and a small buoyancy flux of 0 25 mg s i e properties of a cool weak plume the buoyancy flux is many times smaller than for oceanic plumes nonetheless plume buoyancy has produced a 400 km wide 500 m high topographic swell centered on the yellowstone plateau contemporary deformation derived from gps measurements reveals sw extension of 2 3 mm yr across the yellowstone plateau one fourth of the total basin range opening rate which we consider to be part of basin range intraplate extension locally decadal episodes of subsidence and uplift averaging 2 cm yr characterize the 80 year yellowstone caldera monitored history and are modeled as hydrothermal magmatic sources moreover a recent episode 2004 2009 of accelerated uplift of the yellowstone caldera at rates up to 7 cm yr has been modeled as resulting from magmatic recharge of a 10 km deep sill at the top of the crustal magma reservoir regionally gravitational potential energy of the yellowstone swell drives the lithosphere southwest and downhill from the yellowstone plateau 400 km where it coalesces with basin range province wide westward extension based on the geometry and its assumed 660 km depth we extrapolate the plume source southwest to its original location at 17 ma and 600 km southwest and 200 km north of the ysrp importantly this location is beneath the southern part of the columbia plateau flood basalt field of the same age and implies that the yellowstone mantle plume may be the common source for both of these large volcanic fields our time progression model suggests that the original plume head rose vertically behind the juan de fuca plate but at 12 ma it lost the protection of the subducting plate from eastward mantle flow and encountered cooler thicker continental lithosphere becoming entrained in eastward upper mantle flow these results reveal that yellowstone plume plate processes have had a profound effect on late cenozoic geologic evolution and topography of a large part of the western u s

soil development on moraines of mendenhall glacier southeast alaska 2 chemical transformations and soil micromorphology abstract soils on holocene age moraines of the mendenhall glacier in southeast alaska range from morphologically undeveloped to soils having field identified spodic horizons that are more strongly expressed with increasing soil age a soil chronosequence was sampled to study development of spodic features and to compare the expression of these features with chemical and micromorphological properties organic c accumulates rapidly in these soils with o horizons forming within 38 yr organic c is highly correlated with cation exchange capacity r2 0 92 variable charge r2 0 94 extractable acidity r2 0 83 and 1500 kpa water retention r2 0 97 the ph of the 10 yr old pedon is acidic with a soil ph h20 ranging from 5 0 to 6 4 the ph decreases with soil age with the lowest ph in horizons at the organic mineral contact increases in dithionite citrate sodium pyrophosphate and acid oxalate extractable fe feo are most evident in the 240 yr old soil depth trends for these measured properties within pedons are most distinctive for fe which increases from surface mineral horizons a or e to underlying horizons in all pedons the feo fed ratio increases with soil age in b horizons and in pedons 70 yr this ratio ranges from 0 3 to 0 5 in the e horizons and from 0 4 to 0 83 in b horizons immediately below these data indicate a greater proportion of poorly crystalline fe in illuvial horizons with increasing soil age allophane content is low 240 yr old pedon this chronosequence study indicates that spodic development is achieved within a relatively short period of time in soils of this region

experimental examination of two pyroxene graphical thermometers using natural pyroxenes with application to metaigneous pyroxenes from the adirondack mountains new york clinopyroxene with exsolved orthopyroxene and coexisting orthopyroxene with exsolved clinopyroxene inverted pigeonite in metaigneous rocks from the adirondacks new york were experimentally homogenized at temperatures near those inferred for their original crystallization the purposes were several 1 to test the graphical two pyroxene geothermometer of lindsley 1983 2 to test the hypothesis of bohlen and essene 1978 that these were originally igneous pyroxenes and 3 to test whether modal recombination of complexly exsolved pyroxenes yields realistic compositions experiments on fe rich compositions at 930 and 870 c 1 gpa are compatible with the graphical thermometer of lindsley 1983 however this graphical thermometer yields apparent temperatures approximately 50 c too high for experiments at 1050 c and 1100 c 0 mpa this suggests that at intermediate mg fe the augite isotherms for these temperatures lie at lower wollastonite compositions than shown by lindsley the results are however in good agreement with isotherms derived from the solution model of davidson 1985 when these isotherms are applied to a variety of terrestrial and lunar igneous rocks and the metaigneous rocks from the adirondacks temperatures given by augite and pigeonite compositions from coexisting pairs are similar comparison of the experimentally homogenized compositions with modally recombined compositions of bohlen and essene 1978 show that discrepancies between augite and pigeonite temperatures may nevertheless arise if pyroxene grains formed by granular exsolution are not correctly reintegrated

initial stages of weathering and soil formation in the morteratsch proglacial area upper engadine switzerland investigations in alpine soils indicate that mineral weathering is much faster in young soils 1000 yr than in old soils 10 000 yr however little is known about the initial stages of weathering and soil formation i e during the first decades of soil genesis in this study we investigated rock forming minerals weathering at very early stages of soil formation due to the continuous retreat of the morteratsch glacier upper engadine swiss alps the proglacial area offers a full time sequence from 0 to 150 yr old surfaces a low slope and the absence of glacier which might have interrupted soil formation processes contributed to the choice of the morteratsch proglacial valley for this case study the area is well documented regarding vegetation and soils the tectonic unit is the bernina crystalline which is mainly constituted of granitoid rocks consequently the glacial till has an acidic character mineralogical measurements were carried out on the soil fraction 2 mm using xrd and drift for qualitative and quantitative phase analysis in addition chemical analyses of the stream water from the main channel tributaries and of rainwater were performed with a special focus on ca sr and sr isotope ratios 87sr 86sr furthermore the accumulation of organic matter within the time sequence and physical soil properties were measured decreasing grain size with time shows active physical weathering processes soil organic matter has been accumulated during 150 yr at very high rates special emphasis has been given to chemical weathering and to the formation and transformation mechanisms of minerals of special interest were biotite chlorite epidote plagioclase and calcite biotite has been continuously transformed into illite like components within 150 yr the concentration of epidote significantly decreased the high ca sr as well as 87sr 86sr ratios in the stream and spring waters confirmed that ca bearing minerals are weathering and transforming at very high rates in the proglacial area also in cryic ice free environments chemical weathering rates are high leading to the formation and transformation of minerals disseminated calcite in granitoid rocks not confined to sedimentary carbonate rocks also plays a role in subglacial environments it is however not known for how long such an influence is significant and measurable the high ca na and ca sr ratio in the stream and tributary waters showed that calcite contributes to the supply of soluble ca although the ion activity product calculations clearly demonstrated that the waters were undersaturated with respect to this mineral

mountain glaciation in japan and taiwan at the global last glacial maximum abstract montane glaciation in japan and taiwan was maximal in mis 3 4 and glacier extent at the global last glacial maximum lgm was much more limited data from four areas in japan and two in taiwan where the topographical and chronological positions of the terminal moraines are well determined and the chronology is controlled by radiocarbon ams and 10be cosmogenic dates are presented in this paper equilibrium line altitudes elas at global lgm are around 1500 m in the hidaka range hokkaido 2500 m in the northern japanese alps 2700 m in the central japanese alps 2800 m in the southern japanese alps in japan and 3300 m in northern taiwan and 3500 m in central taiwan the elas are mostly determined by maximum discharge accumulation ablation area ratio aar and glacier toe and headwall ratio thar methods the pattern of contours of elas indicates a strong influence of precipitation control on glacier development in this region the ela depression at global lgm in japan was 1100 1300 m except in the northernmost part of the northern japanese alps only 400 m where the present hypothetical ela is extraordinarily low because of abundant snowfall the ela depression at global lgm in taiwan is estimated at about 1100 1300 m without consideration of uplift

chemical denudation and the role of sulfide oxidation at werenskioldbreen svalbard summary this study aims to determine the rate of chemical denudation and the relationships between dominant geochemical reactions operating in the proglacial and subglacial environments of the polythermal glacier werenskioldbreen sw svalbard during an entire ablation season water sampling for major ion chemistry was performed at a proglacial hydrometric station and from subglacial outflows from may to september 2011 these data were combined with measurements of discharge and supraglacial ablation rates the slopes and intercepts in best fit regressions of ca2 mg2 vs so42 and hco3 vs so42 in meltwater from ice marginal subglacial channels were close to the stoichiometric parameters of sulfide oxidation and simple hydrolysis coupled to carbonate dissolution concentrations corrected for input of sea salt this shows that these relationships predominates the meltwater chemistry our findings also show that sulfide oxidation is a better indicator of the configuration of subglacial drainage systems than for instance na and k in the proglacial area and in sub artesian outflows the ion associations represent sulfide oxidation but other processes such as ion exchange and dissolution of ca and mg efflorescent salts may also contribute to the solute variations these processes may cause enhanced fluxes of ca2 and hco3 from glacierized basins during the early ablation and peak flow seasons as the proglacial salts re dissolve the overall chemical denudation rate in the basin for 2011 ranging from 1601 to 1762 meq m 2 yr 1 121 9 to 132 2 t km 2 yr 1 was very high when compared to other svalbard valley glaciers suggesting that the high rate of chemical denudation was mostly caused by the high rates of discharge and ablation chemical weathering intensities 876 and 964 meq m 3 yr 1 exceeded previously reported intensities in svalbard

silent play in a loud theatre dominantly time dependent soil development in the geomorphically active proglacial area of the gepatsch glacier austria climate change over the last century expressed as temperature increase is substantially stronger in the european alps than the average for the northern hemisphere this leads to fast glacial retreat and permafrost degradation and hence to increased rates and risks of mass wasting more extreme floods in spring and lower base flow in summer we do not know enough about the interplay between increased proglacial mass wasting and geomorphic activity on the one hand and soil development on proglacial areas on the other hand both processes affect the attenuation of storm flow provision of base flow and the future geo pedo and biodiversity of alpine valleys however despite the known importance of soil landscape interactions soils and landscapes have so far only been studied in isolation our objective was to assess whether soil development the silent play in a geomorphically active proglacial area the loud theatre was nonetheless dominantly a function of time since glacial retreat as often observed in geomorphically inactive proglacial areas we used conditional latin hypercube sampling to select 97 locations in the gepatsch glacier proglacial area in the west of austria that best cover variation in soil age and topographic position standard soil observations were done in all locations soil development indicators were then related to time since glacial retreat and a range of geomorphic variables results indicate that time since glacial retreat indeed remains an important explanatory variable and that soil development in the gepatsch glacier proglacial area roughly equals that in some other well studied valleys geomorphic variables were found to be significant co determinants of soil development with a strong scale dependency variation in soil properties increased over time and the storage of organic matter in the proglacial area is currently in the order of 330 kg per year

chinese loess record of monsoon climate during the last glacial interglacial cycle the thick loess paleosol succession of central china contains a detailed record of changes in east asian monsoon climate since the late miocene epoch the alternating loess paleosol stratigraphy closely resembles the marine oxygen isotope record implying that episodic dust deposition and pedogenesis are in phase with global ice volume fluctuations and controlled by variations in solar radiation reaching the land surface deposits equivalent to marine isotope stages mis 5 through 1 have been dated by 14c 10be luminescence and magnetic susceptibility and grain size models malan loess mis 4 2 decreases in thickness southeastward from 30 m in the western loess plateau to 5 m east of xi an downwind asian dust is found in japan the north pacific ocean and the greenland ice sheet where it has a chemical signature that points to a primary source in western china during glacial times the mean dust flux in the central loess plateau reached 0 35 mm year whereas in interglacial times it fell to 0 1 mm year times of high dust influx and reduced soil development coincided with strengthened winter monsoon conditions which are inferred from variations in loess grain size times of decreased dust accumulation and strong pedogenesis marked by high values of magnetic susceptibility represent times of strengthened summer monsoon conditions high frequency fluctuations in dust influx during deposition of the malan loess include peaks that likely correlate with north atlantic heinrich events the younger dryas oscillation is recorded in chinese eolian and organic deposits by a shift from cool humid late glacial conditions to cold and dry conditions followed by a return to milder humid climate at the beginning of the holocene warm moist climate associated with a strong summer monsoon characterized the first half of the holocene epoch when a widespread paleosol complex developed on the loess plateau increased dust deposition during the middle to late holocene marked a shift to cooler drier conditions

tomography from 26 years of seismicity revealing that the spatial extent of the yellowstone crustal magma reservoir extends well beyond the yellowstone caldera the yellowstone volcanic field has experienced three of earth s most explosive volcanic eruptions in the last 2 1 ma the most recent eruption occurred 0 64 ma forming the 60 km long yellowstone caldera we have compiled earthquake data from the yellowstone seismic network from 1984 to 2011 and tomographically imaged the three dimensional p wave velocity vp structure of the yellowstone volcanic system the resulting model reveals a large low vp body interpreted to be the crustal magma reservoir that has fueled yellowstone s youthful volcanism our imaged magma body is 90 km long 5 17 km deep and 2 5 times larger than previously imaged the magma body extends 15 km ne of the caldera and correlates with the location of the largest negative gravity anomaly a 80 mgal gravity low this new seismic image provides important constraints on the dynamics of the yellowstone magma system and its potential for future volcanic eruptions and earthquakes

the role of superheating in the formation of glass mountain obsidians long valley ca inferred through crystallization of sanidine the glass mountain obsidians long valley ca are crystal poor 8 vol and highly evolved high sio2 low sr and therefore their formation required extremely efficient separation of melts from a crystal rich source a petrologic and experimental investigation of the mineral phases in glass mountain lavas identifies conditions under which phenocrysts grew and the driving mechanism for crystallization which places constraints on the possible processes that generated the obsidians the obsidian in this study gm 11 is saturated in nine phases sanidine quartz plagioclase titanomagnetite ilmenite zircon apatite allanite biotite and results of high resolution sem compositional mapping and electron microprobe analysis reveal that individual sanidine crystals are normally zoned and span a range of compositions or40 78 sanidines have a granophyric texture characterized by intergrowths of quartz and sanidine mineral phases in the natural sample are compared to h2o saturated phase equilibrium experiments conducted in cold seal pressure vessels over a range of conditions 700 850 c 75 225 mpa and all are found to be plausible phenocrysts comparison of sanidine compositions from the natural sample with those grown in phase equilibrium experiments demonstrates that sanidine in the natural sample occurs in a reduced abundance further comparison with phase equilibrium experiments suggests that sanidine compositions track progressive loss of dissolved melt water cooling suggesting that crystallization in the natural obsidian was driven predominantly by degassing resulting from decompression it is paradoxical that an effusively slowly erupted lava should contain multiple phenocryst phases including sanidine crystals that span a range of compositions with granophyric textures and yet remain so crystal poor to resolve this paradox it is necessary that the solidification mechanism degassing or cooling that produced the sanidine crystals and other mineral phases must have an associated kinetic effect s that efficiently hinders crystal nucleation and growth decompression experiments conducted in this study and from the literature collectively demonstrate that the simplest way to inhibit nucleation during degassing induced crystallization is to initiate degassing cooling from superliquidus conditions and therefore the glass mountain obsidians were superheated prior to crystallization

the timing and origin of pre and post caldera volcanism associated with the mesa falls tuff yellowstone plateau volcanic field abstract we present new sanidine 40ar 39ar ages and paleomagnetic data for pre and post caldera rhyolites from the second volcanic cycle of the yellowstone plateau volcanic field which culminated in the caldera forming eruption of the mesa falls tuff at ca 1 3 ma these data allow for a detailed reconstruction of the eruptive history of the second volcanic cycle and provide new insights into the petrogenesis of rhyolite domes and flows erupted during this time period 40ar 39ar age data for the biotite bearing bishop mountain flow demonstrate that it erupted approximately 150 kyr prior to the mesa falls tuff integrating 40ar 39ar ages and paleomagnetic data for the post caldera island park rhyolite domes suggests that these five crystal rich rhyolites erupted over a centuries long time interval at 1 2905 0 0020 ma 2 the biotite bearing moonshine mountain rhyolite dome was originally thought to be the downfaulted vent dome for the pre caldera bishop mountain flow due to their similar petrographic and oxygen isotope characteristics but new 40ar 39ar dating suggest that it erupted near contemporaneously with the island park rhyolite domes at 1 2931 0 0018 ma 2 and is a post caldera eruption despite their similar eruption ages the island park rhyolite domes and the moonshine mountain dome are chemically and petrographically distinct and are not derived from the same source integrating these new data with field relations and existing geochemical data we present a petrogenetic model for the formation of the post mesa falls tuff rhyolites renewed influx of basaltic and or silicic recharge magma into the crust at 1 2905 0 0020 ma led to 1 the formation of the island park rhyolite domes from the source region that earlier produced the mesa falls tuff and 2 the formation of moonshine mountain dome from the source region that earlier produced the biotite bearing bishop mountain flow these magmas were stored in the crust for less than a few thousand years before being erupted contemporaneously along a 30 km long structurally controlled vent zone related to extracaldera basin and range faults these data highlight the rapidity with which magma can be generated and erupted over large distances at yellowstone

mass fluxes and clay mineral formation in soils developed on slope deposits of the kowarski grzbiet karkonosze mountains czech republic poland abstract weathering mineral formation and transformation processes along slopes are complex in cool mountainous regions undisturbed soil development with a strong vertical leaching element may abruptly change as a result of erosion accumulation lateral water fluxes and aeolian input we investigated soils in the eastern karkonosze mountains that have developed on silicatic slope deposits to date illite vermiculite and chlorite are the minerals that have been detected in the clay fraction although the climate and parent material should be favourable for the formation of smectites expandable phases were not verified so far we investigated if expandable phases could be detected and how they related to elemental fluxes along a short slope sequence 1142 1268 m a s l on the border between the czech republic and poland mass balance calculations indicated intensive mineral weathering together with a significant leaching of mg al ca and mn on the shoulder and foot slope positions in the middle zone which has a concave or undulating surface shape however the mass balances of several elements na k al p revealed a less pronounced leaching corresponding to a lower degree of podsolization and in some cases even accumulation at all sites mass balance calculations and detected soil minerals e g the increase in illite towards the surface together with an increase in al and k indicate some aeolian input kaolinite was detected in all soil horizons its concentration slightly increased towards the soil surface together with the pronounced leaching of ca part of kaolinite originates from plagioclase weathering besides being a weathering product of primary minerals part of the kaolinite is inherited from the parent material and probably is also due to aeolian input in all soils illite was being transformed into vermiculite and smectites through regularly interstratified illite smectite phases in addition the content of chloritic components which increases with depth indicated their concurrent weathering and transformation into smectites amphibole also may have acted as a source of smectites not all smectite is being actively formed in the soil most likely due to slope processes cover beds that affected even the subsoil some smectite has been transferred along the slope part of the smectite also seems to derive from the parent material active formation of expandable clay minerals is related to convex and planar landscape forms this relationship suggests intense element leaching inheritance from the parent material and cover bed mixing processes have contributed to the presence of smectite along the slope zones with predominant vertical transport shoulder foot slopes may repeatedly be interchanged with zones dominated by lateral transport undulating slope concave forms

paleovegetation and climatic conditions in a refugium of temperate plants in central japan in the last glacial maximum abstract paleovegetation and climatic conditions in the last glacial maximum lgm ca 24 4 and 20 1 ka were reconstructed based on plant macrofossils and pollen assemblages deposited in a sandy channel outcropped in the hanamuro river ibaraki prefecture central japan the plant macrofossil assemblages were composed of 31 arboreal and 76 herbaceous taxa occurrence of plants with various habitat preferences exhibited distribution patterns of highly diverse vegetation types depending on geomorphology and humidity in and around the drainage of the hanamuro river rich aquatic and wetland flora indicates an expansion of backmarsh mosaic environments along the river channel in the bottom of the valley wetland forests composed of picea sect picea assignable to picea koyamae and riparian forests dominated by alnus inokumae are well represented in the macrofossil assemblages pinaceous conifers were dominant in mesic or dry places with betula and the other deciduous broadleaved trees macrofossils and pollen indicates that abies veitchii was distributed in mesic locations larix kaempferi and picea jezoensis var hondoensis were on the upper slopes and pinus koraiensis was dominant on the plateau dominant selaginella remotifolia and the other drought intolerant understory herbs indicate closed canopy of mesic coniferous forests while many kinds of meadow and or ruderal plants were indicative of open vegetation along the river and slopes annual mean temperature of the fossil site based on occurrence of selaginella remotifolia was 8 1 c which is observed in present cool temperate zones where deciduous broad leaved trees are dominant this indicates that the distribution limit of subarctic conifers shifted to warmer temperature conditions than at present the overlapping distribution of temperate and subarctic plants occurred widely in the lowlands in the distribution ranges of temperate trees south of around 38 n in japan in the lgm with lower precipitation dryness was an important environmental factor that controlled plant distribution along with temperature water stress confined temperate broad leaved trees to the humid valley bottoms and relieved conifers from competition against broad leaved trees to promote their expansion to warmer regions macrofossils indicate the persistence of temperate plants in humid inland and or northern refugia during the lgm locations conducive to paleolithic human occupation

constraints on melting and magma production in the crust major intrusions of granitic rocks are found in several tectonic settings and in all cases crustal melts may contribute to the volumes of granitic magma high grade metamorphism and partial melting of the crust take place predominantly under fluid absent conditions we present a model for calculating the amounts of melt that may be formed by fluid absent breakdown of micas and amphiboles in common crustal rock types pelitic quartzofeldspathic intermediate and mafic melt proportions depend mainly on the kind of source rock the pressure at which melting takes place the temperature and the hydrous mineral h2o content of the source as a consequence of the pressure dependence of water solubility in silicate melts any given source rock will produce more melt by a given fluid absent reaction at lower pressure at a given pressure higher temperature reactions can produce more melt from a given source rock based on a survey of the compositions of common rock types we show that the amounts of melt can vary from 50vol thus crustal rocks vary widely in their fertility as magma sources depending on the types and amounts of hydrous phases they contain in general muscovite breakdown in pelites will yield only small quantities of melt and lead to migmatite formation biotite breakdown in pelites occurs at higher temperature and because most high grade pelites below granulite grade are biotite rich can yield up to about 50 vol of granitoid melt rocks of intermediate composition and hornblende rich mafic rocks are potentially highly fertile magma sources also provided that the high temperatures necessary for biotite and hornblende breakdown are realized pyroxene rich mafic rocks and quartzofeldspathic rocks are much less potentially fertile data suggest that mechanisms exist for the efficient segregation of melt and restite in systems with 30and probably 20vol melt the pressure temperature history of a region can greatly influence crustal source fertility through its control over the occurrence of subsolidus dehydration and melting equilibria

initial soil development and carbon accumulation on moraines of the rapidly retreating werenskiold glacier sw spitsbergen svalbard archipelago article i nfo the rapid retreat of the werenskiold glacier the svalbard archipelago high arctic is leading to an extensive broadening of the proglacial zone covered with recent moraine till on older glacigenic deposits or directly on bedrock schists to study the type and intensity of initial soil development under a harsh periglacial climate a chronosequence of six soils was established between the glacier front and its terminal moraine on 1 to about 80 year old moraines although the surface layer over the entire area of study is frost active the patterned features are not well developed the succession of vegetation mainly saxifraga sp and lichens starts 5 6 years after deglaciation successively covering up to 30 of the soil surface then stagnating present day soil forming processes within the uppermost soil layer comprise initial weathering of primary minerals chlorites and amphiboles carbonate dissolution and base cation leaching associated with ph lowering accumulation of organic matter and nitrogen and an increase in pedogenically derived fe soil development measures are time related and in general fit a logarithmic model the intensity of transformation including organic carbon and nitrogen accumulation started at high rates comparable to those reported in low arctic and alpine environments however in the fourth fifth decade after deglaciation it reached a quasi steady state low annual precipitation is probably a crucial factor that controls plant succession and leaching of carbonates thus limiting mineral weathering organic matter accumulation and soil development on the werenskiold moraines

strontium isotopes and magma dynamics insights from high temperature rhyolites volcanic rocks often exhibit internal heterogeneity in radiogenic isotopes isotopic disequilibrium between coexisting phenocrysts and isotopic zoning within single crystals has been demonstrated in basalts andesites dacites and rhyolites high temperature snake river type rhyolites appear to be an exception despite the occurrence of snake river plain rhyolites in a region of isotopically highly variable crust and mantle and significant differences from rhyolite unit to rhyolite unit little to no sr isotopic zoning is found within their feldspar phenocrysts and feldspars within a single unit define tightly grouped unimodal populations high temperature rhyolitic magmas possess a unique combination of temperature and melt viscosity although typically 200 c hotter than common rhyolites the temperature effect on viscosity is offset by lower water contents 5 10 6 pa s however magmatic temperatures are in the same range as basaltic andesites and andesites consequently cation diffusion rates are orders of magnitude greater than common rhyolites we hypothesize that this combination of characteristics promotes crystal isotopic homogeneity viscosities are too high to permit crystal transfer between liquids of contrasting 87 sr 86 sr on time scales shorter than those required for diffusive homogenization of sr within phenocrysts 500 10 000 yr this is not true for most magma types in which crystal transfer is rapid 5 10 6 yr

chemical weathering in the foreland of a retreating glacier chemical denudation rates and strontium isotope ratios in streams vary substantially and systematically in the foreland of the retreating bench glacier in south central alaska to study weathering of young glacier sediments we sampled 12 streams draining a chronosequence of till and moraine soils derived from cretaceous metagraywacke metapelite bedrock both sediment age and vegetation cover increase with distance from the glacier cation denudation rates decline with increasing distance from the glacier whereas silica denudation rates increase carbonate dissolution and sulfide oxidation account for roughly 90 of the solute flux from the youngest sediments biotite alteration accounts for 5 11 of the solute flux its peak contribution is found in the glacier outlet stream silicate weathering is the dominant reaction only in the oldest sediments in a laboratory dissolution experiment using fresh glacial sediment carbonate dissolution dominated the solute flux during the first 700 hours paralleling the behavior of young sediments in the field in contrast to trends in the field the silica flux did not increase after the carbonate was exhausted from the reactor a possible reason for this difference is that establishment of vegetation causes an increase in silicate weathering the 87sr 86sr ratio in the glacier outlet stream is greater than that in proglacial streams and in bulk rock due to a greater contribution of biotite weathering in the outlet than in proglacial streams strontium isotope ratios decline with sediment exposure age in the proglacial streams and are consistent with a carbonate source because the dominant weathering reactions in the young sediments are of carbonate and sulfide rather than silicate minerals weathering at the glacier margin is not an important long term sink for atmospheric co2

origin and evolution of silicic magmatism at yellowstone based on ion microprobe analysis of isotopically zoned zircons the origin of large volume yellowstone ignimbrites and smallervolume intra caldera lavas requires shallow remelting of enormous volumes of variably o depleted volcanic and sub volcanic rocks altered by hydrothermal activity zircons provide probes of these processes as they preserve older ages and inherited do values this study presents a high resolution oxygen isotope examination of volcanism at yellowstone using ion microprobe analysis with an average precision of 0 2o and a 10 mm spot size we report 357 analyses of cores and rims of zircons and isotope profiles of 142 single zircons in 11 units that represent majoryellowstone ignimbrites and post caldera lavas many zircons from these samples were previously dated in the same spots by sensitive high resolution ion microprobe shrimp and all zircons were analyzed for oxygen isotope ratios in bulk as a function of grain size by laser fluorination we additionally report oxygen isotope analyses of quartz crystals in three units the results of this work provide the following new observations 1 most zircons from post caldera low do lavas are zoned with higher do values and highly variable u pb ages in the cores that suggest inheritance from pre caldera rocks exposed on the surface 2 many of the higher do zircon cores in these lavas have u pb zircon crystallization ages that postdate caldera formation but pre date the eruption age by 10 20 kyr and represent inheritance of unexposed post caldera sub volcanic units that have do similar to the lava creek tuff 3 young and voluminous 0 25 0 1ma intra caldera lavas which represent the latest volcanic activity atyellowstone contain zircons with both high do and lowdo cores surrounded by an intermediate do rim this implies inheritance of a variety of rocks from high do pre caldera and low do post caldera units followed by residence in a common intermediate do melt prior to eruption 4 major ignimbrites of huckleberry ridge and to a lesser extent the lava creek and mesa falls tuffs contain zoned zircons with lower do zircon cores suggesting that melting and zircon inheritance from the lowdo hydrothermally altered carapace was an important process during formation of these large magma bodies prior to caldera collapse 5 the do zoning in the majority of zircon core rim interfaces is step like rather than smoothly inflected suggesting that processes of solution reprecipitation were more important than intracrystalline oxygen diffusion concave downward zircon crystal size distributions support dissolution of the smaller crystals and growth of rims on larger crystals this study suggests that silicic magmatism atyellowstone proceeded via rapid shallow level remelting of earlier erupted and hydrothermally alteredyellowstone source rocks and that pulses of basaltic magma provided the heat for melting each postcaldera yellowstone lava represents an independent homogenized magma batch that was generated rapidly by remelting of source rocks of various ages and do values the commonly held model of a single large volume super solidus mushy state magma chamber that is periodically reactivated and produces rhyolitic offspring is not supported by our data rather the source rocks for theyellowstone volcanism were cooled below the solidus hydrothermally altered by heated meteoric waters that caused low do values and then remelted in distinct pockets by intrusion of basic magmas each packet of new melt inherited zircons that retained older age and do values this interpretation may have significance for interpreting seismic data for crustal low velocity zones in which magma mush and solidified areas experiencing hydrothermal circulation occur side by side new basalt intrusions into this solidifying batholith are required to form the youngest volcanic rocks that erupted as independent rhyolitic magmas we also suggest that the lava creek tuff

formation rates of smectites derived from two holocene chronosequences in the swiss alps the formation rate of smectitic components in alpine soils is derived from two chronosequences in the swiss alps covering a time span of 11 500 years the soils developed on granitic parent material the lithologies between the two chronosequences investigation areas however showed some distinct differences with respect to the main mineralogy and to a lower extent to the chemistry the chronofunctions of smectitic phase formation g kgclay year were fitted to data using an exponential formation model extensive mineral weathering resulted in significant losses of chlorite and mica and the corresponding formation of smectite and regularly and irregularly interstratified mica smectite this formation is especially pronounced in the early stages of soil formation our investigations reveal that the greatest changes in soil clay mineralogy of alpine soils on granitic or gneiss host material occur within the first 1000 3000 years of soil development at both investigation sites the annual formation rates are in a similar order of magnitude with 0 1 g kg year or even higher at the start of soil formation and with values 0 01 g kg year after about 7000 years the pedogenetic smectites from the e or bs horizons included several populations with various interlayer charges this heterogeneity seems to be related to the nature of their precursors

crystal scale anatomy of a dying supervolcano an isotope and geochronology study of individual phenocrysts from voluminous rhyolites of the yellowstone caldera a voluminous 600 km3 and long lived 520 75 ka phase of rhyolitic eruptions followed collapse of the yellowstone caldera 640 ka whether these eruptions represent a dying cycle or the growth of a new magma chamber remains an important question we use new u th zircon ages and 18o values determined by ion microprobe and sanidine pb isotope ratios determined by laser ablation to investigate the genesis of voluminous post caldera rhyolites the oldest post caldera rhyolites erupted between 520 and 470 ka exhibit extreme age and oxygen isotopic heterogeneity requiring derivation from individual parcels of low 18o melts we find a progressive increase in zircon homogeneity for rhyolite eruptions from 260 to 75 ka with homogeneous low 18o zircon values of 2 7 2 8 that are in equilibrium with low 18o host melts for the majority of the youngest eruptions new sanidine pb isotope data define separate arrays for post caldera rhyolites and the caldera forming tuffs that preceded them indicating that they were not sourced from a mushy lava creek tuff batholith that remained after caldera collapse rather our new age and isotopic data indicate that the post caldera rhyolites were generated by remelting of a variety of intracaldera source rocks consisting of pre lava creek tuff volcanic and plutonic rocks and earlier erupted post lava creek tuff rhyolites batch assembly of low 18o melts starting at 260 ka resulted in progressive homogenization followed by differentiation and cooling up until the last rhyolite eruption 75 ka a trend that we interpret to be characteristic of a dying magma reservoir beneath the yellowstone caldera

magma mixing and the generation of isotopically juvenile silicic magma at yellowstone caldera inferred from coupling 238 u 230 th ages with trace elements and hf and o isotopes in zircon and pb isotopes in sanidine the nature of compositional heterogeneity within large silicic magma bodies has important implications for how silicic reservoirs are assembled and evolve through time we examine compositional heterogeneity in the youngest 170 to 70 ka post caldera volcanism at yellowstone caldera the central plateau member cpm rhyolites as a case study we compare 238u 230th age trace element and hf isotopic data from zircons and major element ba and pb isotopic data from sanidines hosted in two cpm rhyolites hayden valley and solfatara plateau flows and one extracaldera rhyolite gibbon river flow all of which erupted near the caldera margin ca 100 ka the hayden valley flow hosts two zircon populations and one sanidine population that are consistent with residence in the cpm reservoir the gibbon river flow hosts one zircon population that is compositionally distinct from hayden valley flow zircons the solfatara plateau flow contains multiple sanidine populations and all three zircon populations found in the hayden valley and gibbon river flows demonstrating that the solfatara plateau flow formed by mixing extracaldera magma with the margin of the cpm reservoir this process highlights the dynamic nature of magmatic interactions at the margins of large silicic reservoirs more generally hf isotopic data from the cpm zircons provide the first direct evidence for isotopically juvenile magmas contributing mass to the youngest post caldera magmatic system and demonstrate that the sources contributing magma to the cpm reservoir were heterogeneous in 176hf 177hf at ca 100 ka thus the limited compositional variability of cpm glasses reflects homogenization occurring within the cpm reservoir not a homogeneous source

quantitative pollen based climate reconstruction in central japan application to surface and late quaternary spectra abstract climate reconstruction in japan by the best modern analogues method was tested with 285 surface pollen spectra and then applied to the 47 000 years pollen profile from lake mikata central japan both pollen taxa percentages and plant functional type affinity scores were used in the reconstruction of six climate variables the reconstructed values were compared with the estimated modern climate at each surface pollen site in order to evaluate the accuracy of the pollen based reconstruction the reconstruction of thermal parameters is very reliable correlation coefficient r between 0 86 and 0 89 the reconstruction of annual precipitation is less accurate r 0 7 we also proposed a new technique to calibrate reconstructed values into both probability distribution and or confidence regions of observed values the specialized programs for this calibration polcalib and polhist are available at qsr website http www elsevier nl locate quascirev the reconstruction of the late quaternary climate changes around lake mikata shows that the summer and winter temperatures were 5 c lower than present around 40 uncal kyr bp reached a minimum around 20 uncal kyr bp 10 c lower than present and became similar to present day at 8 uncal kyr bp the estimates for annual precipitation show that it was driest around 20 uncal kyr bp

variations in weathering processes and rates with time in a chronosequence of soils from glen feshie scotland chemical and mineralogical characteristics have been determined for a chronosequence of six soil profiles ranging in age from 80 13 000 years bp developed on river terraces in the western cairngorms of scotland the c horizons are similar chemically and mineralogically and the soils have similar pedogenetic histories exchangeable ca and mg decrease with time and base saturation decreases exponentially from 24 6 in the ah horizon of the youngest profile to 2 8 in the comparable horizon of the 10 000 year old profile according to the chronofunction y 3 372 22 612 exp 0 0007365t long term weathering rates of base cations calculated from the loss of these cations relative to zr appear to decrease exponentially with time but this may be due to the method of calculation the magnitude of loss of base cations decreases in the sequence na k mg ca but when the relative mobilities of these elements are considered the loss is in the order mg na ca k this reflects the dissolution of chlorite and loss of mg and the more rapid weathering of plagioclase feldspar and loss of na and ca particularly in the coarse sand fraction than k feldspar the clay fractions although 2 of all horizons also show distinct patterns with age in that chlorite and mica are less abundant in older soils and vermiculite is more abundant the latter phase often having hydroxyaluminium polymers in the interlayer region the chemical and mineralogical trends in the soil sequence are closely associated and are induced by pedogenic weathering

between ice and ocean soil development along an age chronosequence formed by the retreating breiðamerkurjokull glacier se iceland as glaciers in iceland retreat they expose new surfaces for plant succession and soil formation in the foreland of brei amerkurjokull glacier we used a high time resolution chronosequence to study vegetation succession morphological physical and chemical changes in soils and the impact of avifauna on the vegetation and soils developing on the moraines in total 38 sampling sites were distributed along moraines deposited in 1890 1930 1945 1960 1982 1994 2004 and 2012 representing 8 age groups on moraines where the influence of seabirds was apparent soils were collected from bird hummocks one for each age group soil samples were also collected from nearby birch betula pubescens ehrh woodlands representing soils in a potentially future mature ecosystem the results show that mosses and grasses dominated and characterized the vegetation on the moraines with the exception of the two youngest moraines that were non or sparsely vegetated an ac horizon sequence slowly formed yet the a horizon remained thin 2 5 cm bulk density decreased with time since deglaciation from 1 2 g cm 3 down to 0 8 1 0 g cm 3 in the oldest moraines similarly soil ph h2o decreased with time reaching a steady state at the value of 6 after 67 yrs loi loss on ignition soc soil organic carbon and total n nitrogen concentrations along with ph naf increased over the time span investigated the increase in loi soc and n concentrations occurred slowly during the first few decades rates increased after 50 yrs since deglaciation but eolian input appeared to reduce the rates again in the 122 yr old moraine the highest soc and n concentrations were reached in the 82 yr old moraine 1 4 soc 0 07 n and the highest naf values of 9 3 after 67 yrs the lack of shrubs and dwarf shrubs indicated that the long distance from seed sources retarded vegetation succession within the brei amerkurjokull moraines which in turn affected the soil development on the moraines although perhaps to a lesser degree than expected the soil in the bird hummocks was characterized by dense root system and thick a or o horizons 14 cm generated by the dense growth of grasses and herbs accompanied by considerably much higher soc and n values 18 soc 1 1 n after 67 yrs when compared to the surrounding moraine soils additionally bulk density was much lower within the bird hummocks 0 26 0 75 g cm 3 and soil ph h2o was generally lower ranging between 5 2 and 6 2 depending on moraine age this study shows that the point centered input by avifauna into the terrestrial ecosystem is an important factor in locally enhancing vegetation growth and the rates of soil formation increasing the heterogeneity within the moraine soils

magma ascent rates volcanoes can erupt explosively generating high columns of ash and occasional pyroclastic flows or they can erupt slowly forming lava flows and domes this variation reflects significant differences in mass eruption rate e g wilson et al 1980 mass eruption rates in turn are controlled by the rates of magma ascent through the volcanic conduit and the conduit size the magma ascent rate itself is a function of the pressure in the magma storage region the physical properties of the magma such as its density viscosity and crystallinity and the resistance to flow in the conduit that connects the magma storage zone to the surface papale and dobran 1994 mastin and ghiorso 2001 pinkerton et al 2002 sparks et al 2006 a number of important characteristics of volcanic eruptions are affected or controlled by the rate at which magma ascends from depth for example the bubble content i e vesicularity and the degree of crystallization that develop in the melt phase can be significantly different in rapidly vs slowly ascended magma in fact the inability of rapidly ascending magma to effectively lose exsolved gas may be one factor causing an eruption to change from effusive to explosive behavior as recently documented for the soufriere hills eruption on montserrat in the west indies sparks et al 1998 therefore in order to better understand the processes involved and the changes that occur in volcanic eruptions it is important to quantify the rates at which different magmas rise to the surface the fact that the rate of magma ascent controls a number of reactions that occur in volatile rich magmas suggests several ways to study magma ascent rates using reaction data and theoretical flow models one reaction that is a direct result of magma ascent is the exsolution of volatiles from the melt

revised ages for tuffs of the yellowstone plateau volcanic field assignment of the huckleberry ridge tuff to a new geomagnetic polarity event 40 ar 39 ar ages were determined on the three major ash flow tuffs of the yellowstone plateau volcanic field in the region of yellowstone national park in order to improve the precision of previously determined ages total fusion and incremental heating ages of sanidine yielded the following mean ages huckleberry ridge tuff 2 059 0 004 ma mesa falls tuff 1 285 0 004 ma and lava creek tuff 0 639 0 002 ma the huckleberry ridge tuff has a transitional magnetic direction and has previously been related to the reunion normal polarity subchron dating of the reunion event has been reviewed and its ages have been normalized to a common value for mineral standards the age of the huckleberry ridge tuff is significantly younger than lava flows of the reunion event on re union island supporting other evidence for a normal polarity event younger than the reunion event