insights from quartz cathodoluminescence zoning into crystallization of the vinalhaven granite coastal maine the vinalhaven intrusive complex provides field and petrographic evidence for multiple replenishments of mafic and silicic magmas mingling and limited mixing and rejuvenation of granite quartz in granitic rocks preserves a record of those processes in the form of cathodoluminescence cl zoning which is related to concentration of titanium and to temperature of crystallization using the new titaniq ti in quartz geothermometer injection of mafic melts into partly crystalline vinalhaven granite resulted in partial quartz resorption followed by higher temperature growth from h2o undersaturated melt this is shown by steep rimward increases in cl intensity and ti content across discordant boundaries that truncate older growth zones quartz zoning in granite affected by mafic magmas displays large rimward jumps in ti content whereas quartz in granitic feeders and in granite far from mafic rocks typically displays broad rims with decreasing ti contents consistent with slow cooling without thermal disruptions due to mafic recharge

implications of pre eruptive magmatic histories of zircons for u pb geochronology of silicic extrusions zircons in silicic magmas begin to crystallize 10 s to 100 s of thousands of years ka prior to their eruption u pb and u th dating for zircons from 32 young extrusions indicate a range of mean pre eruption ages from 33 to 247 ka with a median of 92 ka explosive large volume widespread eruptions show a narrower range and a younger median of 70 ka these results indicate that the difference between initial zircon growth and eruption age measured by other e g 40ar 39ar techniques is in excess of the achievable analytical uncertainty for eruptions 30 million years ma and likely for eruptions of up to 300 ma protracted pre eruption zircon growth is well established by an increasing number of studies on magma process time scales but this source of eruption age bias has been largely ignored in chronostratigraphic applications of high precision u pb data until intrinsic properties of zircons or their host deposits enable a priori estimates of pre eruption age bias it is prudent to expand the uncertainties attending all u pb zircon ages interpreted as deposition ages in e g chronostratigraphic studies by 0 200 ka

phase equilibrium constraints on the viscosity of silicic magmas 1 volcanic plutonic comparison by using recently determined experimental phase equilibria we show that the viscosity of granitic magmas emplaced at upper crustal levels is approximately constant at 104 5 pa s irrespective of their temperature and level of emplacement magmas crystallizing as granitic plutons are not water poor and thus not more viscous than their extrusive equivalents instead comparison between pre eruption magma viscosities of extrusive silicic intermediate and intrusive granitic magmas shows that the former are on average slightly more viscous given the typical strain rates in silicic magma chambers magma rheological behavior is expected to be dominantly newtonian bubbles having a minor rheological influence at depth although exceptions can exist thus whether a silicic intermediate magma is erupted or frozen at depth depends primarily on the rheological properties of surrounding terranes or on external tectonic factors but not on the rheology of the magma itself however preemptive viscosities of extrusive magmas rarely exceed 106 pa s which suggests that crystal melt mushes with higher viscosities cannot leave the magma storage regions beneath volcanoes the narrow range of viscosities displayed by silicic intermediate magmas results from both the strong control that pressure exerts on volatile solubilities in silicate melts and thermal limitations required to produce acid magmas considerations of the relationships between magma crystallinities bulk sio2 and preemptive melt h2o contents show that the higher the melt h2o content is the higher the maximum crystallinity that a given magma will be while still being potentially erupted an empirical correlation is proposed that enables us to estimate preemptive melt h2o contents of erupted magmas by knowing their crystallinity and bulk sio2

magma extraction pressures and the architecture of volcanic plumbing systems abstract the deposits of large volcanic eruptions provide the sole record of the architecture of magmatic plumbing systems in the moments when large pools of crystal poor eruptible magma are present in the crust it is widely accepted that silicic magmas form by segregation of melt rich crystal poor magma from a crystal rich source however the depths at which segregation takes place and the distribution of the magma within the crust are not well constrained we present a new approach to calculate pressures at which crystal poor eruptible magma is extracted from a crystal rich source i e mush we apply the approach to a sequence of large 50 km3 eruptions from the taupo volcanic zone tvz new zealand which were part of a volcanic flare up we compare the calculated extraction pressures with pre eruptive storage pressures for the same units our results show that storage and extraction pressures do not always coincide instead eruptible magma can be completely segregated from the crystal rich source and stored at shallower levels in the crust prior to eruption in the case of the tvz flare up repeated input of material and heat probably coupled with tectonic extension gradually conditioned the crust and allowed extraction of eruptible magma over a growing range of pressures with time our approach has the potential to reveal important information on the structure and distribution of magmatic systems within the shallow crust

soil and sediment properties affecting the accumulation of mercury in a flood control reservoir abstract mercury accumulations in some fish species from grenada lake in north mississippi exceed the food and drug administration standards for human consumption this large flood control reservoir serves as a sink for the skuna and yalobusha river watersheds whose highly erodible soils contribute to excessively high sediment yields and impaired water quality this study was conducted to characterize the distribution of total hg in watershed soils and determine the relationship between the easily transportable clay organic c oc and fe oxide fractions and the movement of hg from upland sources to reservoir sinks cores were collected from soils of different land use representative of the three soil orders alfisols entisols and vertisols found in the watersheds sediment cores were collected from the yalobusha river and grenada lake in the laboratory soil cores were sampled by horizon while sediment cores were sampled in 10 cm increments these samples were characterized for total hg particle size distribution oc fe oxide contents and ph mercury concentrations ranged from 10 to 112 g kg 1 in the soil profiles with average regression coefficient r 2 values of 0 104 0 362 and 0 06 for hg versus clay oc and fe oxides respectively river sediment cores had hg concentrations ranging from 0 to 38 g kg 1 and significant 1 level r 2 values of 0 611 0 447 and 0 632 versus clay oc and fe oxides respectively mercury concentrations in the lake sediment ranged from 0 to 125 g kg 1 the r 2 values for hg versus clay oc and fe oxides in the lake sediment were 0 813 0 499 and 0 805 respectively all significant at the 1 level these results indicate that total hg is poorly correlated with the clay oc and fe oxide fractions at depth in the soil profiles because maximum hg concentrations occur in the surface horizons due to atmospheric in fall the statistically significant r 2 values for hg versus these components in the sediment cores are the result of particulate clay fe oxides and finely divided oc sorption of hg from solution during the runoff and sediment transport process the higher correlations for the lake sediment reflect an enrichment of the hg laden clay fraction relative to stream sediment through flocculation and sedimentation processes in the slack water environment of the reservoir

geometry forced coherent structures as a model of the kuroshio large meander abstract the bimodality of the kuroshio path south of japan is presented from a new viewpoint of direct interaction of current with local coastal geometry by solving the barotropic quasi geostrophic equation in a channel with steplike coastal geometry we demonstrate that the model kuroshio can actually show the localized bimodal behavior for a reasonable range of inlet current speed the amplitude of the large meander is approximately given by 2umax in contrast to all nonlocal model results our local coherent structures have nothing to do with the basin size geometry such as kyushu and the izu ogasawara ridge in general the present study suggests that even a small feature of coastline geometry may trigger a big change in a nearshore current

extraction of crystal poor rhyolite from a hornblende bearing intermediate mush a case study of the caldera forming matahina eruption okataina volcanic complex the matahina ignimbrite 160 km3 rhyolite magma 330 ka was deposited during a caldera forming eruption from the okataina volcanic centre taupo volcanic zone tvz new zealand juvenile clasts are divided into three groups group 1 the dominant crystal poor rhyolite type group 2 a minor coarse grained mingled mixed intermediate type and group 3 a rare fine grained basalt the ignimbrite consists of the group 1 type and is divided into three members a lower and middle member which is high silica crystal poor 10 vol rhyolite and the upper member which is low silica and slightly more crystal rich up to 21 vol cognate crystal rich up to 50 vol basalt to intermediate pumice occurs on top of lag breccias and within lithic rich pyroclastic density current deposits along the caldera margin groups 2 and 3 several lines of evidence indicate that the intermediate clasts represent the cumulate complement to the melt rich rhyolite 1 continuity in the compositions of plagioclase orthopyroxene hornblende and oxides and normal zoning of individual phenocrysts 2 the silicic glass from the intermediate magma interstitial melt overlaps compositionally with the bulk rock rhyolite and glass 3 high zr and a slight positive eu anomaly in the intermediate magma relative to quenched enclaves from other intermediate tvz eruptions indicates zircon and plagioclase accumulation respectively 4 an increase in the cl contents in glass from the least evolved to most evolved is consistent with the concentration of volatiles during magma evolution most of the compositional variations in the low to high silica rhyolites can be accounted for by continued rayleigh fractionation up to 15 following melt extraction from the underlying mush under varying fo2 fh2o conditions to form a slightly compositionally zoned rhyolitic cap this link to the varying fo2 fh2o conditions is evidenced by the strong correlation between key geochemical parameters e g dy y that qualitatively reflect fh2o conditions presence or absence of hornblende biotite and fo2 estimated from fe ti oxide equilibrium magma mingling mixing between the basalt andesite and the main slightly compositionally zoned rhyolitic magma occurred during caldera collapse modifying the least evolved rhyolite at the lower portion of the reservoir and effectively destroying any pre eruptive gradients

late pleistocene granodiorite source for recycled zircon and phenocrysts in rhyodacite lava at crater lake oregon abstract rhyodacite tephra and three lavas erupted 27 ka interpreted to be early leaks from the climactic magma chamber of mount mazama contain ubiquitous resorbed crystals antecrysts that were recycled from young granodiorite and related plutonic rocks of the same magmatic system the shallow composite pluton is represented by blocks ejected in the 7 7 ka climactic eruption that formed crater lake caldera plagioclase crystals in both rhyodacite and granodiorites commonly have cores with crystallographically oriented fe oxide needles exsolved at subsolidus conditions at least 80 of plagioclase crystals in the rhyodacite are antecrysts derived from plutonic rocks other crystals in the rhyodacite notably zircon also were recycled sims 238 u 230 th dating indicates that zircons in 4 granodiorite blocks crystallized at various times between 20 ka and 300 ka with concentrations of analyses near 50 70 110 and 200 ka that correspond to periods of dacitic volcanism dated by k ar u th ages of zircon from a rhyodacite sample yield similar results no analyzed zircons from the granodiorite or rhyodacite are pre quaternary zircon minimum ages in blocks from different locations around the caldera reflect ages of nearby volcanic vents and may map the distribution of intrusions within a composite pluton survival of zircon in zircon undersaturated hydrous magma and of fe oxide needles in plagioclase suggests that little time elapsed from entrainment of antecrysts to the 27 ka eruption of the rhyodacite the 27 ka rhyodacite is an example of young silicic magma that preserved unstable antecrysts from a known source early during growth of a large high level magma chamber in contrast the voluminous 7 7 ka climactic rhyodacite pumice is virtually lacking in zircon indicating dissolution of any granodioritic debris in the intervening period mineralogical evidence of assimilation may be destroyed in hot vigorously growing silicic magma bodies such as ultimately produced the climactic eruption of mount mazama

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

quantum magmatism magmatic compositional gaps generated by melt crystal dynamics compositional gaps are common in volcanic series worldwide the pervasive generation of compositional gaps influences the mechanical and thermal properties of the crust and holds clues on how our planet differentiates we have explored potential mechanisms to generate these gaps using numerical simulations coupling crystallization kinetics and multiphase fluid dynamics of magma reservoirs we show that gaps are inherent to crystal fractionation for all compositions as crystal liquid separation takes place most efficiently within a crystallinity window of 50 70 vol crystals the probability of melt extraction from a crystal residue in a cooling magma chamber is highest in this crystallinity window due to 1 enhanced melt segregation in the absence of chamber wide convection 2 buffering by latent heat of crystallization and 3 diminished chamber wall thermal gradients this mechanical control of igneous distillation is likely to have played a dominant role in the formation of the compositionally layered earth9s crust by allowing multiple and overlapping intrusive episodes of relatively discrete or quantized composition that become more silicic upward

crystallisation ages in coeval silicic magma bodies 238u 230th disequilibrium evidence from the rotoiti and earthquake flat eruption deposits taupo volcanic zone new zealand abstract the timescales over which moderate to large bodies of silicic magma are generated and stored are addressed here by studies of two geographically adjacent successive eruption deposits in the taupo volcanic zone new zealand the earlier caldera forming rotoiti eruption 100 km3 magma at okataina volcano was followed within months at most by the earthquake flat eruption 10 km3 magma from nearby kapenga volcano both generated non welded ignimbrite and coeval widespread fall deposits the rotoiti and earthquake flat deposits are both crystal rich high silica rhyolites with sparse glass bearing granitoid fragments also occurring in rotoiti lag breccias generated during caldera collapse here we report 238u 230th disequilibrium data on whole rocks and mineral separates from representative rotoiti and earthquake flat pumices and the co eruptive rotoiti granitoid fragments using tims and in situ zircon analyses by sims multiple grain zircon controlled crystallisation ages measured by tims from the rotoiti pumice range from 69 3 ka 350 ka with a pronounced peak at 70 90 ka the weighted mean of isochrons is 83 14 ka in accord with the tims data one glass bearing rotoiti granitoid clast yielded an age of 57 8 ka by tims controlled by th rich phases that however are not apparently present in the juvenile pumices another glass bearing rotoiti granitoid yielded sims zircon model ages peaking at 60 90 ka having a similar age distribution to the pumice age data from pumices are consistent with a published 64 4 ka eruptive age now modified to 62 2 ka but chemical and or mineralogical data imply that the granitoid lithics are not largely crystalline rotoiti rhyolite but instead represent contemporaneous partly molten intrusions reflecting different sources in their chemistries and mineralogies similarly although the earthquake flat eruption immediately followed and probably was triggered by the rotoiti event age data from juvenile material are significantly different a multiple grain zircon controlled crystallisation age measured by tims from a representative pumice is 173 5 ka while sims model ages range from 70 26 34 ka to 350 ka with a peak at 105 ka these age data coupled with previously published geochemical and isotopic data show that the rotoiti and earthquake flat deposits were erupted from independent unconnected magma bodies

degassing of the h2o rich rhyolites of the okataina volcanic center taupo volcanic zone new zealand the taupo volcanic zone tvz new zealand is the most active region of rhyolitic volcanism on earth with 50 rhyolitic eruptions and 780 km3 of magma erupted in the past 60 k y here we use analyses of quartz hosted melt inclusions from eight eruptions in the okataina volcanic center ovc of the tvz to constrain magmatic volatile contents pressures and temperatures of quartz crystallization and degassing of h2o cl and minor co2 from the rhyolitic magmas the ovc melt inclusions trapped volatile rich melts with 6 wt h2o and 0 27 wt cl our data indicate that vapor saturated crystallization of quartz occurred at low temperatures 760 805 c over a wide range of pressures 50 200 mpa for some eruptions variations in volatiles and major and trace elements provide evidence for simultaneous crystallization and partial loss of h2o cl and co2 into a vapor phase using the combination of melt inclusion and pumice glass volatile contents we calculate minimum volatile emissions of 3 1011 to 8 1012 kg h2o and 7 109 to 4 1010 kg cl during the ovc eruptions we estimate that emissions from the smaller volume 100 of the global arc h2o flux and as much as 90 of the global arc cl flux these results underscore the importance of individual magmatic provinces in creating large temporal variations in global arc volatile fluxes to earth s hydrosphere

analysis of late holocene faulting within an active rift using lidar taupo rift new zealand abstract high quality light detection and ranging lidar data collected across the rangitaiki plains the fastest extending section of the onshore taupo rift new zealand reveal 122 active fault traces and provide new constraints on displacements displacement rates and paleoearthquakes of the normal faults in the rift the identified lineaments are scarps that record vertical offset of geomorphic surfaces e g beach ridges meander channel floors river terraces etc and trend parallel or sub parallel to other active faults in the rift these lineaments are interpreted to be active faults active fault traces trend 060 and their lengths range from 0 25 to 6 km they mainly traverse and displace a diachronous landscape of

variations of current path velocity and volume transport of the kuroshio in relation with the large meander abstract the variations of the kuroshio current path and their relations with current velocity volume transport and upstream position of the kuroshio are examined using sea level data after the long time non large meander nlm path during 1963 75 the kuroshio takes a large meander lm path during most of 1975 91 1975 80 1981 84 1986 88 and 1989 91 the study of these meanders confirms the description of the path of the kuroshio based on the three typical paths and the transitions between them with an exception being the 1981 84 lm path the formation and decay of the large meander are associated with velocity and position of the kuroshio in the tokara strait south of kyushu a small meander precursor of the large meander seems to be formed southeast of kyushu in relation with a temporary increase of kuroshio velocity and a northward shift of the kuroshio in the tokara strait an eastward propagation of the small meander leading to the lm formation is associated with remaining in the northe

hornblende cummingtonite and biotite hydrogen isotopes direct evidence of slab derived fluid flux in silicic magmas of the taupo volcanic zone new zealand abstract hornblende cummingtonite and biotite d values from rhyolitic and mingled mixed mafic rocks from the central taupo volcanic zone were determined in an effort to characterize the isotopic composition of the dissolved fluid of magmas in this predominantly rhyolitic volcanic zone hand samples were obtained from pyroclastic flow airfall and lava flow deposits as well as co eruptive cognate plutonic blocks mineral d values range from 88 to 35 smow standard mean ocean water cummingtonite phenocryst d overlaps with hornblende from the same rocks while biotite values are consistently 7 more negative than hornblende phenocrysts from the same hand sample calculated volcanic steam d values ca 46 to 25 are consistent with an island arc crustal source ca 40 to 15 with a negligible to absent mantle ca 100 to 60 component earlier researchers suggested that the taupo volcanic zone fluid flux included dilute concentrations of slab derived phases i e co 2 cl similar to back arc volcanic systems at other convergent margins however the island arc type fluid composition estimated from the minerals we studied is similar to hornblende and biotite compositions from pyroclastic deposits and volcanic fumaroles from the kamchatka and japanese arcs the silicic rocks from the 2 0 1 0 ma mangakino caldera the most inland caldera system we studied have the lowest d hornblende and biotite suggesting that silicic volcanism distal to the subduction trench was derived from a back arc like i e mixture of mantle and slab fluid however we found that the currently active more proximal locus of silicic volcanism reflects typical arc like fluid compositions our results further suggest that the composition of volcanic steam migrating through the upper crust was similar in composition to regional meteoric waters ca 45 to 23

tracking the evolution of large volume silicic magma reservoirs from assembly to supereruption the most voluminous silicic volcanic eruptions in the geological past were associated with caldera collapses above giant silicic magma reservoirs the thermal evolution of these subcaldera magma reservoirs controls the volume of eruptible magma and eruptive style here we combine high precision zircon u pb geochronology trace element analyses of the same mineral grains and mass balance modeling of zircon trace element compositions allowing us to track the thermal and chemical evolution of the oligocene fish canyon tuff magma reservoir colorado united states as a function of absolute time systematic compositional variations in u pb dated zircons record 440 k y of magma evolution an early phase of volumetric growth was followed by a period of cooling and crystallization during which the fish canyon magma approached complete solidifi cation subsequent remelting due to underplated andesitic recharge magmas began 219 45 k y prior to eruption and led to the generation of 5000 km3 of eruptible crystal rich 45 vol dacite age equivalent but compositionally different zircons in an andesite enclave from late erupted fish canyon tuff tie the growth and thermal evolution of the upper crustal reservoir to a lower crustal magma processing zone our results demonstrate that the combination of high precision dating and trace element analyses of accessory zircons can reveal invaluable information about the chemical and thermal histories of silicic magmatic systems and provides critical input parameters for fl uid dynamic modeling

plutonic xenoliths reveal the timing of magma evolution at hualalai and mauna kea hawaii 238 u 230 th and u pb dating of zircons from leucocratic plutonic xenoliths indicating that lava stratigraphy is an incomplete monitor of magmatic evolution within subsurface res ervoirs our results indicate that diorites from mauna kea record postshield evolution over tens of thousands of years when the depth of magma storage increased and highly evolved lavas began erupting in contrast diorites and syenogabbros from hualalai record generation of evolved alkalic magma during the shield stage and growth of a deep composite pluton abstract hawaiian volcanoes evolve through stages that have been delimited by the compositions of their erupted lavas new in situ 238 u 230 th and u pb dating of single zircons from leucocratic plutonic xenoliths erupted at mauna kea and hualalai volcanoes hawaii reveals that impor tant episodes of magmatic evolution are not necessarily refl ected in the stratigraphy or com positions of erupted lavas zircons from mauna kea diorites form a heterogeneous population with apparently bimodal ages of ca 125 ka and ca 65 ka suggesting fractionation intrusion and crystal recycling about the time of transition of postshield volcanism from basaltic to hawaiitic compositions hualalai syenogabbros and diorites record extreme fractionation and generation of alkalic magma at 41 9 ka and 261 28 ka indicating that alkalic magma was generated 130 000 yr before the shield to postshield transition inferred from lava stra tigraphy and that coeval evolution of chemically distinct magma reservoirs at shallow and deep levels may have characterized the shield stage these episodes at hualalai did not cause eruption of evolved lavas indicating that extreme differentiation in hawaiian volcanoes is not necessarily followed by eruption of highly evolved magma

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

bimodality of the kuroshio abstract a barotropic ocean model is used to study the bimodal behavior of the kuroshio to the south of japan by considering the combined effects of the beta plane the kyushu coastal perturbation the izu ridge and the sw ne tilted coastline the two frequently observed meander patterns have been numerically verified as the two quasi steady solutions contained n the model the small meander state is identified as an upstream disturbance largely forced by the izu ridge its width decreases as the strength of the current increases the large meander state is forced by the presence of both the kyushu wedge and the izu ridge topography for small volume transports the large meander state behaves like the small meander state in that the meander width decreases as the current speed increases for large volume transports it behaves like a lee rossby wave in that the width of the meander increases as the current speed increases the birth of the large meander state occurs as a consequence of the ocean spin do

rapid remobilization of magmatic crystals kept in cold storage we lack thermal histories for magma reservoirs but here the magma under mount hood oregon usa is shown to have been too cold to mobilize for most of the time it has been stored which implies that magma mobilizes at which point it can be imaged geophysically very quickly prior to eruption this paper presents a novel approach to constraining the thermal history of the subsurface magma bodies that feed eruptions by combining temporal information from a variety of sources kari cooper and adam kent combine timescales derived from uranium series disequilibria textural information and trace element zoning in crystals they show that at mount hood oregon only a small fraction of the total storage duration has been spent at temperatures above the critical crystallinity the point at which magma is easily mobilized they conclude that largely liquid bodies that could be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption the processes involved in the formation and storage of magma within the earth s upper crust are of fundamental importance to volcanology many volcanic eruptions including some of the largest result from the eruption of components stored for tens to hundreds of thousands of years before eruption1 2 3 although the physical conditions of magma storage and remobilization are of paramount importance for understanding volcanic processes they remain relatively poorly known4 5 eruptions of crystal rich magma are often suggested to require the mobilization of magma stored at near solidus conditions6 7 8 however accumulation of significant eruptible magma volumes has also been argued to require extended storage of magma at higher temperatures7 8 9 what has been lacking in this debate is clear observational evidence linking the thermal and therefore physical conditions within a magma reservoir to timescales of storage that is thermal histories here we present a method of constraining such thermal histories by combining timescales derived from uranium series disequilibria crystal sizes and trace element zoning in crystals at mount hood oregon usa only a small fraction of the total magma storage duration at most 12 per cent and probably much less than 1 per cent has been spent at temperatures above the critical crystallinity 40 50 per cent at which magma is easily mobilized partial data sets for other volcanoes also suggest that similar conditions of magma storage are widespread and therefore that rapid mobilization of magmas stored at near solidus temperatures is common magma storage at low temperatures indicates that although thermobarometry calculations based on mineral compositions may record the conditions of crystallization they are unlikely to reflect the conditions of most of the time that the magma is stored our results also suggest that largely liquid magma bodies that can be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption

identifying the crystal graveyards remaining after large silicic eruptions abstract the formation of crystal poor high silica rhyolite via extraction of interstitial melt from an upper crustal mush predicts the complementary formation of large amounts of typically unerupted silicic cumulates however identification of these cumulates remains controversial one hindrance to our ability to identify them is a lack of clear predictions for complementary chemical signatures between extracted melts and their residues to address this discrepancy we present a generalized geochemical model tracking the evolution of trace elements in a magma reservoir concurrently experiencing crystallization and extraction of interstitial melt our method uses a numerical solution rather than analytical thereby allowing for various dependencies between crystallinity partition coefficients for variably compatible and or incompatible elements and melt extraction efficiency results reveal unambiguous fractionation signatures for the extracted melts while those signatures are muted for their cumulate counterparts our model is first applied to a well constrained example searchlight pluton usa and provides a good fit to geochemical data we then extrapolate our results to understanding the relationship between volcanic and plutonic silicic suites on a global scale utilizing the navdat database to identify crystal accumulation or depletion signatures for each suite we suggest that many large granitoids are indeed silicic cumulates although their crystal accumulation signature is expected to be subtle

rapid cooling and cold storage in a silicic magma reservoir recorded in individual crystals silicic volcanic eruptions pose considerable hazards yet the processes leading to these eruptions remain poorly known a missing link is knowledge of the thermal history of magma feeding such eruptions which largely controls crystallinity and therefore eruptability we have determined the thermal history of individual zircon crystals from an eruption of the taupo volcanic zone new zealand results show that although zircons resided in the magmatic system for 103 to 105 years they experienced temperatures 650 to 750 c for only years to centuries this implies near solidus long term crystal storage punctuated by rapid heating and cooling reconciling these data with existing models of magma storage requires considering multiple small intrusions and multiple spatial scales and our approach can help to quantify heat input to and output from magma reservoirs

fault controls on the geometry and location of the okataina caldera taupo volcanic zone new zealand abstract okataina caldera is located within the taupo rift and formed due to collapse following eruptions at 325 and 61 ka gravity seismic reflection topographic and geological data indicate that active rift faults pass into the caldera and have influenced its location and geometry the caldera has a minimum gravity anomaly of 50 mgal is elongate north south with an inferred minimum depth to caldera floor of 3 0 5 km at the rift axis and occupies a 10 km hard linked left step in the rift the principal rift faults 55 75 dip define the location and geometry of the northwest and southeast caldera margins and locally accommodate piecemeal collapse segments of the east and west margins of the caldera margin are near vertical 70 90 dip trend north south and are inferred to be faults formed by the reactivation of a pervasive mesozoic basement fabric i e faults and or lithological contacts the fault sets which define the caldera geometry predate it while the step in the rift across the okataina volcanic centre ovc is at least as old as the caldera within the ovc displacement on rift faults induced by gravitational caldera collapse at 61 ka exceeds tectonic displacement since this time by at least a factor of two collapse along pre existing rift faults and in particular mesozoic basement fabric are important for caldera formation elsewhere in the taupo volcanic zone

origin of quartz clusters in vinalhaven granite and porphyry coastal maine we use the crystallographic orientations of quartz crystals as determined with ebsd to provide new evidence for the formation of clustered quartz crystals during magma crystallization vinalhaven is dominated by granite with minor porphyry that formed when granite remelted during input of coeval basalt cl zoning suggests that most quartz clusters in granite and porphyry formed by synneusis the swimming together of preformed crystals in granite most quartz pairs in clusters have random orientations only about 10 have parallel or esterel twin orientations porphyry has fewer quartz clusters and all pairs have approximately parallel or esterel twin orientations cl zoning of quartz pairs in porphyry indicates that they attached prior to a major remelting event interpretation of the vinalhaven quartz clusters leads us to propose that oriented synneusis occurs during crystal accumulation on a magma chamber floor during hindered settling some quartz crystals should have come into contact along their dipyramidal faces once in contact continued settling and loss of interstitial melt may have rotated some quartz crystals such that lattices on their dipyramidal faces matched producing parallel and esterel twin orientations and creating strong bonds between pairs only a small proportion of pairs with matched dipyramidal faces formed in the granite and during rejuvenation to produce porphyry only these oriented pairs survived hence the presence of oriented synneusis in a plutonic rock may demonstrate a history of crystal accumulation

synneusis of kilauea iki olivines olivine phenocrysts in the picritic scoria that erupted from kilauea iki in 1959 occur as glomeroporphyritic aggregates of 2 16 crystals the compositions and three dimensional textures of the olivines vary within an aggregate and within individual lapilli the attachment of crystals from different environments indicates that these aggregates formed by synneusis the swimming together of crystals most of the crystals are attached along faces with their a crystallographic axes parallel and their c axes either parallel or perpendicular so that the structural mismatch and interfacial energy are minimized observed facial attachments are consistent with fluid dynamical interactions of crystals falling with their large 010 faces horizontal the aggregates formed in a liquid rich magma rough computations suggest that the minimum aggregation time could be on the order of minutes aggregation of very small crystals suggests that the yield strength was less than 3 dynes cm 2 the textures of the aggregates are similar to those of cumulate peridotites

a flower like glomerophyric diorite porphyry from central china constraints on the unusual texture abstract an unusual texture with plagioclase phenocrysts clustered as flower like glomerocrysts has been discovered in the wulong diorite porphyry at the southern margin of north china craton the rock consists mainly of plagioclase and amphibole with the former as dominant phenocryst two groups of the plagioclase phenocrysts have been distinguished flower like glomerocrysts fg type and single isolated phenocrysts sp type chemical compositions of both fg and sp type plagioclases are similar in anorthite contents an35 45 which are slightly higher than the matrix an25 35 calculation of the plagioclase crystallization time based on crystal size distribution csd program shows that the fg type crystals have been formed within a longer timescale 226 2782 years than the sp type crystals 98 1910 years the concave down csds and lack of small crystals for fg type plagioclases suggest that coarsening may have been involved in contrast a concave up csd within the size of 3 10 mm plagioclase indicating that a rejuvenation kinetic process after coarsening a possible formation history for the unusual flower like plagioclase glomerocrysts was proposed as follows 1 initial nucleation and growth of single crystals in a confined environment 2 ascent of early crystals with magma upwelling and radial coarsening at the roof layer of magma chamber 3 remobilization of dense crystal mush and final emplacement at shallow level of crust 4 rapid cooling and extensive nucleation and growth of matrix 5 post magmatic alteration and metamorphism it is likely that the morphologic diversity of plagioclase glomerocrysts are largely influenced by variation of undercooling degrees the second step is the most important for the formation of the flower like glomerophyric texture which requires an environments of relatively low undercooling degree

deciphering magmatic processes in calc alkaline plutons using trace element zoning in hornblende hornblende in the kuna crest lobe kcl of the tuolumne intrusive complex tic and the upper zone of the wooley creek batholith wcb precipitated over a temperature range of 835 to 700 c and thus has the potential to record magmatic processes we measured trace element concentrations in hornblende from the wcb from the kcl of the tic and from one sample from an adjacent interior unit of the tic to compare and contrast magmatic processes in these two mid crustal intrusions in both systems the magmatic amphibole is magnesiohornblende in which ti zr hf nb sr ba and rare earth elements ree typically decrease from crystal interiors to rims an indication of compatible behavior of these elements and the size of the negative eu anomaly decreases in the kuna crest lobe hornblende from individual mapped units differs in trace element abundances and zoning trends some samples contain at least two distinct hornblende populations which is particularly evident in the shapes of ree patterns in contrast compositions of hornblende from all structural levels of the upper wcb and related dacitic roof zone dikes form a single broad array and the ree patterns are essentially indistinguishable regardless of rock type from quartz diorite to granite in the wcb zr hf ratios in hornblende are consistent with crystallization from a melt with chondritic zr hf values in contrast most hornblende in the kcl has zr hf values lower than expected from crystallization from a melt with chondritic values suggesting that zircon fractionation occurred before and during crystallization of the hornblende simple fractional crystallization models indicate that ree high field strength elements sr and ba were compatible in kcl and wcb magmas as hornblende grew these trends require removal of hornblende plagioclase zircon ilmenite biotite the uniform variations of trace element concentrations and patterns in the upper wcb and roof zone dikes indicates crystallization from a large magma body that was compositionally uniform probably stirred by convection caused by influx of mafic magmas at the base of the zone coint et al 2013a 2013b cf burgisser and bergantz 2011 in contrast in the kcl each analyzed sample displays distinct hornblende compositions and zoning patterns some of which are bimodal these features indicate that each analyzed sample represents a distinct magma and that individual magmas were variably modified by fractionation and mixing hornblende trace element contents and zoning patterns prove to be powerful tools for identification of magma batches and for assessing magmatic processes and thereby relating plutonic rocks to hypabyssal and volcanic equivalents

structure and variability of the kuroshio current in tokara strait four years of mooring array measurements in tokara strait south of kyushu japan from 1992 to 1996 are used to analyze the structure and temporal variability of the kuroshio current the mean kuroshio current in tokara strait shows a nearly permanent subsurface double core structure possibly due to topographic blockage effects the dominant variations of the kuroshio in tokara strait are separated into long term variability typically 100 day period and short term variability 10 days to 1 month according to spectrum and wavelet analysis the long term variability has a large horizontal scale across the strait with a striking twofold banded structure in spatial correlations this is due to the north south kuroshio axis shift that advects the double core structure of the mean current the axis shift can be indexed with the northeastward current velocity at the northernmost station a composite analysis using this index shows well defined northward and southward axis shift structures of the kuroshio current from the composite of the topex poseidon sea level anomaly in terms of this index the kuroshio axis shift and the current structure change are associated with a dipole shape sea level anomaly east of tokara strait on the other hand the short term variability of high kinetic energy only has a small horizontal scale within the northern part of the current which is related to frontal variability there exists a deep southwestward undercurrent below 600 m in the northern part of tokara strait flowing along the isobaths the undercurrent becomes stronger during the northward shift of the kuroshio axis while it almost disappears during the southward shift

high silica granites terminal porosity and crystal settling in shallow magma chambers abstract high silica 70 wt sio2 granites hsgs are important carriers of highly incompatible elements thus understanding their origin is relevant to understanding how the composition of the continental crust evolves we examined a large scale geochemical study of plutons in the peninsular ranges batholith in southern california usa to better understand the petrogenetic relationships between hsgs and the batholith using highly incompatible and compatible elements we show that hsgs represent residual liquids within a felsic 69 72 wt sio2 magmatic crystal mush at crystal fractions of 50 60 and residual liquid fractions of 40 50 trace element systematics show that separation of the hsg liquid from the crystal mush is inefficient such that no more than 70 80 of the hsg is fully extracted and the remaining greater than 20 30 remains trapped in cumulate mush we find little evidence of more efficient liquid crystal segregation which suggests that compaction induced segregation may be too slow to be important on a large scale instead the terminal porosity of 20 30 coincides with theoretical maximum packing fraction of unimodal particles settled out of suspension 0 74 which may indicate that crystal settling perhaps in the form of hindered settling drives segregation of viscous silicic melts and crystals unlike compaction settling operates on timescales of 1 10 ky fast enough to generate large volumes of hsg and complementary cumulates with trapped melt before magma chambers freeze many felsic plutons may thus be cumulates but because of trapped melt they are difficult to geochemically distinguish from plutons whose compositions fall along liquid lines of descent the approach here using a combination of highly incompatible and compatible elements provides a way of identifying and quantifying trapped melt fractions finally we show that hsgs appear to form only in the shallow crust

basalt triggering of the c ad 1305 kaharoa rhyolite eruption tarawera volcanic complex new zealand abstract the ad 1305 kaharoa eruption episode of tarawera volcanic complex was the largest 4 km3 magma eruption in new zealand in the last 1000 years high silica 76 sio2 rhyolite was erupted from seven vents along an 8 km linear zone to form pumiceous pyroclastic deposits and lava domes initial vent clearing explosions were followed by a series of plinian pumice eruptions that spread tephra downwind and pyroclastic density current deposits over the volcano slopes the early pyroclastic eruptions were followed by extrusion of a dome in the summit vent and the migration of further plinian activity to adjacent vents the episode finished with the extrusion of three summit lava domes accompanied by block and ash flows two main types of rhyolite were erupted 1 a low zr low sr high rb type comprising the early plinian pyroclastics and 2 a high zr high sr low rb type comprising the late eruptives including the summit domes basaltic material basalt and basaltic andesite is commonly present as free clasts within the kaharoa pyroclastic deposits along with rare clasts of granodiorite diorite gabbro and olivine clinopyroxenite the basaltic clasts are often veneered by kaharoa rhyolite basaltic material is also common as inclusions within rhyolite pumices along with olivine and augite xenocrysts derived from the basalt the basaltic clasts and inclusions contain complexly zoned plagioclase and corroded olivine commonly with a reaction rim consistent with disequilibrium caused by magma mixing some basaltic clasts and inclusions are hornblende free others contain groundmass hornblende plumes of brown glass often extend from hornblende bearing basaltic inclusions into the surrounding rhyolite these plumes demonstrate magma mixing as does the presence of rhyolitic glass and quartz xenocrysts in some basaltic inclusions most basaltic inclusions have crenulate boundaries suggesting they were fluidal when coming into contact with the rhyolite magma diorite gabbro and olivine clinopyroxenite clasts have mineralogy similar to the basalts commonly contain patches of fine grained basaltic material and are considered co magmatic with the basalts intrusion of basalt magma into the base of the rhyolite magma chamber appears to have occurred for some time before the kaharoa eruptions began allowing considerable mixing with the rhyolite magma transfer of water to some basalt inclusions and formation of hornblende in their groundmass conversely the hornblende free basalt inclusions did not have time to react with the rhyolite magma and must have been intruded shortly before the start of the eruption intrusion of this hornblende free basalt appears to have triggered the kaharoa eruption after the magma chamber had been primed by the earlier intrusions

magmatic perturbations in the okataina volcanic complex new zealand at thousand year timescales recorded in single zircon crystals abstract using single crystals to trace the chemical evolution of a magmatic system has long been a goal of igneous petrology crystals utilized for in situ dating hold great potential to link compositional and temporal information to better understand the evolution of a magmatic system if micron scale zoning of trace elements within a single zircon can be directly associated with volcanic events in magmatic systems then new insights into long term maintenance and storage of eruptible magma can be unlocked this study presents new data that directly links the geochemical history recorded in individual zircon crystals with over 50 000 yrs of changing physical and chemical conditions within a magma reservoir trace elements hf and y in zircon have not diffusively equilibrated with their host melt so that they store information about the melt when that zone crystallized thus different stages of growth can be associated with discrete time periods in the magmatic system zircon from the two most recent rhyolite eruptions kaharoa and whakatane within the okataina volcanic complex ovc new zealand have both isotopic age and trace element signatures that correspond with distinct changes in the temperature and phase assemblage of pulses of erupted magma within the caldera system this discrete change is associated with caldera collapse and reflects a change from cold wet source rhyolite to a relatively hotter and drier source rhyolite and back the kaharoa and whakatane eruptions are separated by 4000 yrs and 15 km distance yet the zircon populations record the same distinct thermal and chemical pulse that occurred following caldera collapse suggesting an interconnected magmatic system that houses at least small volumes of rhyolite melt for timescales of 10 3 to 10 5 yrs that is periodically extracted during eruption

mercury contamination of active channel sediment and floodplain deposits from historic gold mining at gold hill north carolina usa a reconnaissance investigation of mercury contamination associated with historic gold mining in north carolina usa revealed high concentrations of mercury in channel and floodplain sediments downstream from the gold hill mining district the most intense period of mining activities in this region occurred in the 1840s and 1850s when mercury amalgamation was used to recover fine gold particles from milled ore this paper evaluates mercury concentrations measured in active channel sediments and two cores recovered from historic floodplain deposits of the lower portion of dutch buffalo creek mercury concentrations in these cores range from 0 01 to 2 2 mg kg with maximum concentrations more than 35 times background levels a later peak in copper concentrations is associated with the operation of a large copper mine between 1899 and 1906 following the most intense periods of mining both mercury and copper concentrations decrease upcore to constant levels of about twice pre mining background concentrations results suggest that vertical trends in mercury and other trace metals provide a useful tool for interpreting rates of historic floodplain sedimentation in the piedmont of north carolina

trace element indicators of crystal accumulation in silicic igneous rocks abstract if fractional crystallization coupled with some crustal assimilation afc is the dominant process for generating evolved magmas in the earth s crust large quantities of igneous cumulates must be present in the rock record however despite some reported occurrences intermediate to silicic rocks characterized by an unambiguous crystal accumulation signature have remained elusive the signature is expected to be subtle in viscous silicic magmas and sensitive criteria need to be developed to test whether these cumulates are truly rare or simply difficult to discern we propose models that use specific trace element concentrations and ratios zr ba eu eu and zr hf within a well constrained framework for the physical extraction of liquid from crystals mostly occurring between 50 and 70 vol crystals to identify silicic cumulates the results of these models indicate that crystal accumulation or melt extraction has occurred in multiple natural examples around the world both in plutonic and volcanic realms however these examples were selected because they represent conditions that are most favorable high amount of melt extraction well constrained initial liquid compositions for unambiguously identifying cumulate residue in many cases we show that the trace element signature for crystal accumulation will remain largely concealed in addition the different liquid lines of descent related to the various tectonic settings on earth dry reduced in hot spots divergent margins and wetter more oxidizing in arc environments will lead to different trace element evolution and each criterion must be applied on a case by case basis despite these limitations the undeniable but subtle presence of silicic cumulates in the mid to upper crust lends support to the idea that igneous differentiation is dominantly driven by melt extraction from partially crystalline reservoirs

on kuroshio front fluctuations in the east china sea using satellite and in situ observational data fluctuations of the kuroshio front in the east china sea and their relation to variations of the kuroshio stream around the tokara strait are investigated using consecutive satellite images sea level data as well as water temperature records from a japan meteorological agency buoy station and a ferryboat which crosses the tokara strait meanders of the kuroshio front with typical horizontal scales of 100 to 150 km and wave periods of 14 to 20 days are found to appear ubiquitously in the east china sea the front meanders originate upstream over the continental slope and evolve rapidly while propagating downstream at speeds of 20 to 26 cm s 1 downstream southwest of kyushu the fully developed meanders sometimes take the form of warm filaments and when the volume transport of the kuroshio is large they may develop into shed off warm eddies previous observations based on ferryboat temperature records have revealed the repeated northward migration of a clear sea surface temperature sst front across the tokara strait it is shown that this northward migration of the sst front corresponds to the passage of the kuroshio front meanders across the tokara strait and that the unclear southward migration of the sst front is due to the presence of mixed water behind each meander the kuroshio front meanders in the east china sea are further found to be closely related to the north southward movement of the entire kuroshio stream in the tokara strait a lag of about 10 days exists between the time the front meanders reach the tokara strait and the kuroshio stream there shifts to its northernmost position

late stage mafic injection and thermal rejuvenation of the vinalhaven granite coastal maine the vinalhaven intrusive complex consists mainly of coarse grained granite inward dipping gabbro diorite sheets and a fine grained granite core small bodies of porphyry occur throughout the coarsegrained granite the largest porphyry body roughly 0 5 km by 2 5 km occurs with coeval gabbro hybrid rocks and minor finegrained granite in the vinal cove complex which formed during the waning stages of solidification of the coarse grained vinalhaven granite porphyry contacts with surrounding coarse grained granite are irregular and gradational compositions of whole rocks and minerals in the porphyry and the coarse grained granite are nearly identical neighboring phenocrysts in the porphyry vary greatly in degree of corrosion and reaction indicating that the porphyry was well stirred thermal rejuvenation of a silicic crystal mush by a basaltic influx can explain the composition and texture of the porphyry comparable rejuvenation events have been recognized in recent studies of erupted rocks weakly corroded biotite phenocrysts in the porphyry require that hydrous interstitial melt existed in the granite during remelting field relations along with thermal calculations suggest that cooling and crystallization of coeval mafic magma could have generated the porphyry by thermal rejuvenation of granite crystal mush containing about 20 melt field relations also suggest that some of the porphyrymatrix may represent new felsic magma that was emplaced during remelting

the kuroshio structure and transport estimated by the inverse method abstract structure and transport of the kuroshio are examined by the inverse method based on a dataset around the tokara strait subsurface velocities measured by a shipborne acoustic doppler current profiler are used together with ctd sections across the kuroshio to estimate the absolute flow fields the dataset was obtained along a closed line south off the kyushu by the r v chofu maru in september 1987 the kuroshio transport through the tokara strait was 28 109 kg s 1 at the time of observations the transport of warm water eddy south of the kuroshio is estimated at larger than 39 109 kg s 1 but its precise value is difficult to determine because of strong transport dependency on the solution rank the result also suggests a southward flow below the kuroshio off cape toimisaki and in the tokara strait in the section east of amamioshima island a broad northward flow is suggested on the continental slope

decoupled crystallization and eruption histories of the rhyolite magmatic system at tarawera volcano revealed by zircon ages and growth rates we obtained u th disequilibrium age data on zircons from each of the four rhyolite eruptions that built tarawera volcano in the last 22 ka within the okataina volcanic center ovc caldera new zealand secondary ion mass spectrometry analyses on unpolished euhedral crystal faces that lack resorption features show that crystal growth variously terminated from near eruption age to 100 ka prior to eruption age depth profiling of crystals reveals long periods of continuous 34 ka and discontinuous growth 90 ka growth hiatuses of up to 40 ka duration occur but do not all relate to obvious resorption surfaces age differences up to similar magnitude are found on opposing faces of some crystals suggesting episodes of partial exposure to melts these features are best explained by periodic complete or partial sub solidus storage and or inclusion in larger crystal phases followed by rapid liberation prior to eruption this is supported by high abundances of u and th 500 2 000 ppm in some zircons consistent with periods of high crystallinity 70 in the magmatic system based on crystal melt partitioning contemporaneous but contrasting rim ward trends of these elements within crystals even in the same lava hand sample require synchronous growth in separate melt bodies and little connectivity within the system but also significant crystal transport and mixing prior to eruption many crystals record continuity of growth through the preceding 60 ka ovc caldera collapse and subsequent eruptions from tarawera this demonstrates a decoupling between eruption triggers such as shallow crustal extension and mafic intrusion and the crystallization state of the ovc silicic magmatic system the data highlights the need to distinguish between the time for accumulation of eruptible magma and the long term magma residence time based on the age of crystals with high closure temperatures when assessing the potential for catastrophic eruptions

formation of rhyolite at the okataina volcanic complex new zealand new insights from analysis of quartz clusters in plutonic lithics granitoid lithic clasts from the 0 7 ka kaharoa eruption at the tarawera volcano okataina volcanic complex taupo volcanic zone new zealand provide insight into the processes of rhyolite formation the plutonic lithic clasts of the kaharoa eruption consist of 1 quartz phenocrysts which are often grouped into clusters of two to eight quartz grains 2 plagioclase phenocrysts mostly an 40 with up to an 60 cores and 3 interstitial alkali feldspar quartz orientations obtained through electron backscatter diffraction ebsd methods show that 78 of the 82 analyzed clusters have at least one pair of quartz grains with the dominant dipyramidal faces matched variations in cathodoluminescence cl zoning patterns of the quartz suggest that quartz clusters came together after initial crystal growth and that many quartz crystals were subject to one or more resorption events the process of quartz crystals with different magmatic histories coming together into common relative orientations to form clusters is indicative of oriented quartz synneusis and suggests a history of crystal accumulation the quartz clusters are interpreted to have formed as part of a crystal cumulate mush within a shallow magma chamber where quartz crystals rotated into contact along their dominant dipyramidal faces during hindered settling and or compaction the preservation of oriented quartz clusters from the kaharoa plutonic lithics thus provides evidence for synchronous shallow pluton formation from a cumulate mush during active silicic volcanism this result is consistent with models whereby melt rich high silica rhyolite formation occurs via interstitial melt extraction from a low silica rhyolite mush in the shallow crust

timing and conditions of formation of granitoid clasts erupted in recent pyroclastic deposits from tarawera volcano new zealand abstract granitoid clasts in pyroclastic deposits of the 0 7 ka kaharoa eruption from the intra caldera tarawera volcano of the okataina volcanic centre ovc new zealand provide an insight to the plutonic processes beneath one of the most productive quaternary rhyolite centers on earth sims u th data for 79 granitoid zircon crystals from six clasts reveal a unimodal age spectrum yielding a weighted average model age of 208 4 ka mswd 1 2 n 72 the remaining crystals are at secular equilibrium and u pb analyses indicate that a few of these outliers date back to 750 ka a period significantly longer than the known volcanic record at ovc probably 550 ka in contrast zircon crystallization in co erupted pumice and lava of the 0 7 ka kaharoa event and that of the three preceding rhyolite eruptions occurred mostly during 0 50 ka reflecting a separate magmatic history brittle deformation features incipient alteration and low 18o whole rock compositions 3 are consistent with a shallow solid intrusion that has interacted with meteoric hydrothermal fluids however 18o sims analyses of zircons 5 4 0 2 n 11 are consistent with magmatic compositions and thus meteoric interaction occurred post emplacement the kaharoa granitoids contrast with those ejected in the 40 60 ka caldera forming rotoiti event that were partly molten and display zircon age spectra indistinguishable from those for co erupted pumices suggesting the latter were derived from contemporaneous crystal mush the 0 7 ka kaharoa case shows that zones of the magmatic system remained solid despite frequent and voluminous magma production that included caldera forming events such long lived sub solidus zones in magma systems would act as barriers to melt connectivity and interaction with country rock but are also a potential source for antecrysts xenocrysts in subsequent eruptions this exemplifies how plutonic and volcanic evolution can diverge even in close proximity

kuroshio meanders in the east china sea abstract an array of seven inverted echo sounders was moored along and across the kuroshio in the east china sea for more than one year the data from this array show evidence of energetic meanders with periods of 7 11 and 16 days the respective phase velocities of these meanders are 28 20 and 17 km day 1 downstream the 7 and 16 day waves are intermittent but the 11 day waves are present throughout the deployment the instability responsible for these waves is investigated with a spectral numerical model applied to a background state representing the kuroshio in this region the fastest growing instability from the model has e folding growth time of 2 days period of 12 days and phase velocity of 18 km day 1 downstream it appears to be a close representation of the 11 day wave seen in the observational data such a model has been previously used to represent meanders in the gulf stream at similar latitudes off the east coast of the united states the kuroshio meanders have approximately half the

texture spatial distribution and rate of reservoir sedimentation within a highly erosive cultivated watershed grenada lake mississippi 1 while more than 75 000 dams nationwide have served a multitude of purposes over the past 50 years current emphasis is being placed on decommissioning those aged infrastructures considered environmentally harmful grenada lake a relatively large flood control reservoir in mississippi is located in a highly erodible region of the united states and is fed by historically unstable stream channels through a variety of stratigraphic analyses postimpoundment sediments are identified in the reservoir showing that the lake has lost a nominal 3 of its flood storage capacity since its inception in 1954 a simple sediment budget constructed for the yalobusha river s contribution of channel derived sediments shows that about 76 of this sediment remains stored upstream about 16 is stored in the reservoir and about 8 has exited the lake sediment delivery ratios known to be low for relatively large watersheds appear to be unaffected by upstream channel instabilities and aggressive channelization projects