diapiric transfer of melt in kilauea iki lava lake hawaii a quick efficient process of igneous differentiation kilauea iki lava lake formed in 1959 is a large pond of picritic basalt average mgo content 15 34 by weight which has cooled and crystallized as a small self roofed magma chamber repeated drilling of the upper crust of the lake down to its molten core and more recent 1981 drilling through the thermal maximum and part way through the lower crust have made it possible to monitor the differentiation processes in the lake in detail differentiation processes recognized as active in the lake include rather inefficient settling of the larger 2 10 mm olivine phenocrysts formation of segregation veins and formation of diapir like vertical olivine rich bodies all processes which occur in one or more of the other kilauean lava lakes as well in addition most of the central part of kilauea iki has been affected by diapiric melt transfer in this process relatively low density liquid present at 1145 1160 c rose from within the loose crystal mush at the base of the lens of melt and intruded the equivalent thermal horizon at the top of the lens of melt passing through the hotter but denser melt in the core of the lake without mixing the source volume from which the low density liquid was extracted is depleted in tio 2 and other incompatible elements and enriched in feo and cao the upper part of the lake shows the opposite effects the crystalline assemblage present was olivine augite minor plagioclase the crystallinity of both the source and receiving layers was low enough that no obvious textural imprint was left by the transfer process the principal evidence for its occurrence is the chemical zonation of the lake seen in core from depths of 13 to 80 m diapiric melt transfer was active from 1960 to 1971 and has affected most of the central part of the lake from 13 m to at least 80 m the process ran simultaneously with the other three main differentia tion processes but started and stopped independently of the others calculations suggest that between 21 and 42 wt liquid has been extracted from the depleted zone at 56 78 m in the center of the lake making this a very efficient process of chemical differentiation

a new scheme for the very deep geological disposal of high level radioactive waste a case is presented for reconsidering deep borehole disposal for high level radioactive waste hlw in the light of recent discoveries about the hydrogeology and hydrogeochemistry of the continental crust a new multi barrier concept is proposed for very deep elevated temperature disposal of vitrified hlw spent fuel and ex military and other fissile materials which involves melting and recrystallization of a granitic host rock utilizing the heat from the waste this scheme is fundamentally different from previously proposed borehole disposal scenarios in its key aspects particularly in utilizing only partial melting and a surviving container the perceived advantages of the scheme are discussed in general and in relation to previous deep disposal ideas particularly from the standpoint of safety it is concluded that the scheme offers a potentially safer and environmentally more acceptable option for the permanent disposal of high level waste

how summit calderas collapse on basaltic volcanoes new insights from the april 2007 caldera collapse of piton de la fournaise volcano in april 2007 piton de la fournaise volcano experienced a caldera collapse during its largest historical eruption we present here a structural analysis both of the caldera and the surrounding area and precise gps data recorded with a dense gps network specifically dedicated to the analysis of deformation related to the summit collapse structures despite a collapse of more than 300 m in the central zone the geometry of the new caldera is similar in map view to that of the pre existing collapsed structure which was formed from the coalescence of several pit craters the caldera shows an asymmetric inner geometry with sub vertical walls in the nw quadrant and steep scarps composed of inward tilted blocks in the southern half the presence of preserved polished surfaces on the lower part of the sub vertical scarp indicates that it corresponds to the caldera north western ring fault the april 2007 caldera collapse led to the development and the reactivation of concentric fractures on the caldera rim mostly along the southern limit of the caldera gps data show that fractures result from radial extensional stresses that are restricted within the first tens of meters of the caldera edge gps data also reveal that the caldera collapse was coeval with a centripetal deflation whose magnitude is largest along the southern half of the caldera the displacements recorded by gps result from both a general deflation due to magma withdrawal from piton de la fournaise s summit magma chamber and additional local effects related to the caldera collapse comparison of the caldera collapses at piton de la fournaise miyakejima and fernandina reveals striking similarities with cyclic seismic signals accompanying small scale deflation inflation cycles this strongly suggests a common mode of collapse hence we propose a unifying model of caldera collapse in basaltic setting in which the inward deflation due to magma withdrawal from the magma chamber prevents the collapse of the caldera roof until the gravitational stress acting on the rock column above the magma chamber exceeds the shear strength along pre existing ring faults the downward displacement stops when the pressure increase into the magma chamber is able to again sustain the rock column the succession of 1 inward deflation that prevents the collapse 2 collapse due to gravitational stress and 3 stopping of the downward motion is repeated many times the frequency of the cycles is influenced by the rate of magma withdrawal and by the amount of intrusion of magma along the ring faults

contact partial melting of granitic country rock melt segregation and re injection as dikes into ferrar dolerite sills mcmurdo dry valleys antarctica numerous interconnected granitic dikes 530 cm in width and hundeds of meters in length cut ferrar dolerite sills of the mcmurdo dry valleys antarctica the source of the granitic dikes is partial melting of granitic country rock which took place in the crust at a depth of about 2 3 km adjacent to contacts with dolerite sills sustained flow of doleritic magma through the sill generated a partial melting front that propagated into the granitic country rock granitic partial melts segregated and collected at the contact in a melt rich nearly crystal free reservoir adjacent to the initial dolerite chilled margin this dolerite chilled margin was subsequently fractured open in the fashion of a trapdoor by the granitic melt evacuating the reservoir to form an extensive complex of granitic dikes within the dolerite sills at the time of dike injection the dolerite was nearly solidified unusually complete exposures allow the full physical and chemical processes of partial melting segregation and dike formation to be examined in great detail the compositions of the granitic dikes and the textures of partially melted granitic wall rock suggest that partial melting was characterized by disequilibrium mineral dissolution of dominantly quartz and alkali feldspar rather than by equilibrium melting it is also unlikely that melting occurred under water saturated conditions the protolith granite contains only 7 vol biotite and estimated contact temperatures of 900 9508c suggest that melting was possible in a dry system granite partial melting under closed conditions extended tens of meters away from the dolerite sill yet melt segregation occurred only over less than one half a meter from the dolerite chilled margin where the degree of partial melting was of the order of 50 vol this segregation distance is consistent with calculated length scales expected in a compaction driven process we suggest that the driving force for compaction was differential stress generated by a combination of volume expansion as a result of granite partial melting contraction during dolerite solidification and relaxation of the overpressure driving dolerite emplacement on a purely chemical basis the extent of melt segregation necessary under fractional and batch melting to match the rb concentrations between melt and parent rock is a maximum of 48 and 83 vol melt respectively

the collapse of barðarbunga caldera iceland lying below vatnajokull ice cap in iceland bar arbunga stratovolcano began experiencing wholesale caldera collapse in 2014 august 16 one of the largest such events recorded in the modern instrumental era simultaneous with this collapse is the initiation of a plate boundary rifting episode north of the caldera observations using the international constellation of radar satellites indicate rapid 50 cm d 1 subsidence of the glacier surface overlying the collapsing caldera and metre scale crustal deformation in the active rift zone anomalous earthquakes around the rim of the caldera with highly nondouble couple focal mechanisms provide a mechanical link to the dynamics of the collapsing magma chamber a model of the collapse consistent with available geodetic and seismic observations suggests that the majority of the observed subsidence occurs aseismically via a deflating sill like magma chamber

understanding caldera structure and development an overview of analogue models compared to natural calderas abstract understanding the structure and development of calderas is crucial for predicting their behaviour during periods of unrest and to plan geothermal and ore exploitation geological data including that from analysis of deeply eroded examples allow the overall surface setting of calderas to be defined whereas deep drillings and geophysical investigations provide insights on their subsurface structure collation of this information from calderas worldwide has resulted in the recent literature in five main caldera types downsag piston funnel piecemeal trapdoor being viewed as end members despite its importance such a classification does not adequately examine a the structure of calderas particularly the nature of the caldera s bounding faults and b how this is achieved including the genetic relationships among the five caldera types various sets of analogue models specifically devoted to study caldera architecture and development have been recently performed under different conditions apparatus materials scaling parameters stress conditions the first part of this study reviews these experiments which induce collapse as a result of underpressure or overpressure within the chamber analogue the experiments simulating overpressure display consistent results but the experimental depressions require an exceptional amount of doming seldom observed in nature to form therefore these experiments are not appropriate to understand the structure and formation of most natural calderas the experiments simulating underpressure reveal a consistent scenario for caldera structure and development regardless of their different boundary conditions these show that complete collapse proceeds through four main stages proportional to the amount of subsidence progressively characterized by 1 downsag 2 reverse ring fault 3 peripheral downsag 4 peripheral normal ring fault the second part of this study verifies the possibility that these latter calderas constitute a suitable analogue to nature and consists of a comprehensive comparison of the underpressure experiments to natural calderas this shows that all the experimental structures as well as their progressive development are commonly observed at natural calderas highlighting a consistency between models and nature as the shallow structure of experimental calderas corresponds to a precise architecture at depth it provides a unique key to infer the deeper structure of natural calderas recognizing diagnostic surface features within a caldera will thus allow it to be categorized within a precise structural and evolutionary context the general relationship between the evolutionary stage of a caldera and its d s diameter subsidence ratio allows such a quantification with stage 1 calderas characterized by d s 40 stage 2 by 18 the four stages adequately explain the architecture and development of the established caldera end members along a continuum where one or more end members downsag piston funnel piecemeal trapdoor may correspond to a specific stage while such a continuum is controlled by progressive subsidence specific collapse geometries will result from secondary contributory factors roof aspect ratio collapse symmetry pre existing faults these considerations allow proposing an original classification of calderas incorporating their structural and genetic features

linking magma transport structures at kīlauea volcano identifying magma pathways is important for understanding and interpreting volcanic signals at k lauea volcano seismicity illuminates subsurface plumbing but the broad spectrum of seismic phenomena hampers event identification discrete long period lp events dominate the shallow 5 10 km plumbing and deep 40 km tremor has been observed offshore however our inability to routinely identify these events limits their utility in tracking ascending magma using envelope cross correlation we systematically catalog non earthquake seismicity between 2008 and 2014 we find that the lps and deep tremor are spatially distinct separated by the 15 25 km deep horizontal mantle fault zone mfz our search corroborates previous observations but we find broader band 0 5 20 hz tremor comprising collocated earthquakes and reinterpret the deep tremor as earthquake swarms in a volume surrounding and responding to magma intruding from the mantle plume beneath the mfz we propose that the overlying mfz promotes lateral magma transport linking this deep intrusion with k lauea s shallow magma plumbing

location and size of the shallow magma reservoir beneath kīlauea caldera constraints from near source vp vs ratios we present high resolution compressional wave to shear wave velocity ratios vp vs beneath k lauea s summit caldera by applying an in situ estimation method using waveform cross correlation data for three similar earthquake clusters we observe high vp vs ratios 1 832 and 1 852 for two event clusters surrounded by the low background vp vs value of 1 412 at 2 1 km depth below the surface these high and low vp vs ratios can be explained by melt and co2 filled cracks respectively based on a theoretical crack model the event cluster with the highest vp vs ratio consists of long period events that followed the 1997 east rift zone eruption indicating their association with fluid and magma movement the depths of the two clusters with high vp vs ratios are consistent with the magma reservoir location inferred from geodetic observations their locations east and north of halema uma u crater suggest a horizontal extent of a few kilometers for the reservoir

shallow conduit system at kilauea volcano hawaii revealed by seismic signals associated with degassing bursts 1 eruptive activity at the summit of kilauea volcano hawaii beginning in march 2008 and continuing to the present time is characterized by episodic explosive bursts of gas and ash from a vent within halemaumau pit crater these bursts are accompanied by seismic signals that are well recorded by a broadband network deployed in the summit caldera we investigate in detail the dimensions and oscillation modes of the source of a representative burst in the 1 10 s band an extended source is realized by a set of point sources distributed on a grid surrounding the source centroid where the centroid position and source geometry are fixed from previous modeling of very long period vlp data in the 10 50 s band the source time histories of all point sources are obtained simultaneously through waveform inversion carried out in the frequency domain short scale noisy fluctuations of the source time histories between adjacent sources are suppressed with a smoothing constraint whose strength is determined through a minimization of the akaike bayesian information criterion abic waveform inversions carried out for homogeneous and heterogeneous velocity structures both image a dominant source component in the form of an east trending dike with dimensions of 2 9 2 9 km the dike extends 2 km west and 0 9 km east of the vlp centroid and spans the depth range 0 2 3 1 km the source model for a homogeneous velocity structure suggests the dike is hinged at the source centroid where it bends from a strike e 27 n with northern dip of 85 west of the centroid to a strike e 7 n with northern dip of 80 east of the centroid the oscillating behavior of the dike is dominated by simple harmonic modes with frequencies 0 2 hz and 0 5 hz representing the fundamental mode 11 and first degenerate mode 12 21 of the dike although not strongly supported by data in the 1 10 s band a north striking dike segment is required for enhanced compatibility with the model elaborated in the 10 50 s band this dike provides connectivity between the east trending dike and the new vent within halemaumau pit crater waveform inversions with a dual dike model suggest dimensions of 0 7 0 7 km to 2 6 2 6 km for this segment further elaboration of the complex dike system under halemaumau does not appear to be feasible with presently available data

calderas and caldera structures a review abstract calderas are important features in all volcanic environments and are commonly the sites of geothermal activity and mineralisation yet it is only in the last 25 years that a thorough three dimensional study of calderas has been carried out utilising studies of eroded calderas geophysical analysis of their structures and analogue modelling of caldera formation as more data has become available on calderas their individuality has become apparent a distinction between caldera caldera complex cauldron and ring structure is necessary and new definitions are given in this paper descriptions of calderas based on dominant composition of eruptives basaltic peralkaline andesitic dacitic rhyolitic can be used and characteristics of each broad group are given styles of eruption may be effusive or explosive with the former dominant in basaltic calderas and the latter dominant in andesitic dacitic rhyolitic and peralkaline calderas four end member collapse styles occur plate or piston piecemeal trapdoor and downsag but many calderas have multiple styles features of so called funnel and chaotic calderas proposed in the literature can be explained by other collapse styles and the terms are considered unnecessary ground deformation comprises subsidence or collapse essential characteristics of a caldera and uplifting doming and fracturing due to tumescence and or resurgence frequent but not essential collapse may occur on pre existing structures such as regional faults or on faults created during the caldera formation and the shape of the collapse area will be influenced by depth size and shape of the magma chamber the final morphology of a caldera will depend on how the caldera floor breaks up whether collapse takes place in one event or multiple events whether vertical movement is spasmodic or continuous throughout the eruptive sequence and whether blocks subside uniformly or chaotically at one or more collapse centres a meaningful description of any caldera should therefore include number of collapse events presence or absence of resurgence caldera floor coherency caldera floor collapse geometry and dominant composition of eruptives

deep volcanic tremor and magma ascent mechanism under kilauea hawaii deep harmonic tremor originating at depths around 40 km under kilauea was studied using records accumulated since 1962 at the hawaii volcano observatory of the u s geological survey the deep source of the tremor was determined by onset times and confirmed by the relative amplitude across the island wide network of seismometers the period of tremor was conclusively shown to be determined by the source effect and not by the path or station site effect because the period would change considerably in time but maintained uniformity across the seismic net during the tremor episode the tremor appeared to be primarily composed of p waves we interpret the observed period and amplitude in terms of the stationary crack model of aki et al 1977 and find that the seismic moment rates for deep tremors are considerably larger than those for shallow tremors suggesting more vigorous transport for the former we propose a kinematic source model which may be more appropriate for deep tremor according to this model a measurable quantity called reduced displacement is directly proportional to the rate of magma flow a systematic search for deep tremor episodes was made for the period from 1962 through 1979 and the amplitude period and duration of the tremor were tabulated we then constructed a cumulative reduced displacement plot over the 18 year period the result shows a generally steady process which does not seem to be significantly affected by major eruptions and large earthquakes near the surface the total magma flow estimated from the reduced displacement is however one order of magnitude smaller than that estimated by swanson 1972 it may be that most channels transport magma aseismically and only those with strong barriers generate tremor

the orestes melt zone mcmurdo dry valleys antarctica spatially distributed melting regimes in a contact melt zone with implications for the formation of rapakivi and albite granites

a tensile shear crack model for the mechanism of volcanic earthquakes abstract temporary seismic observations were carried out for about 1 month at miyakejima island on the izu bonin arc after an eruption on october 3 1983 more than 3000 seismic events were observed and they are classified into 4 different categories short period earthquakes long period earthquakes isolated tremors and continuous tremors two active source regions of the short period earthquakes were located along the old caldera rim of the miyakejima volcano one region was very close to the eruptive fissures another was about 1 2 km northwest of the fissures almost all the earthquakes in the former region showed dilatant first motions of p waves at all the stations in the island on the other hand almost all events in the latter region showed compressive first motions of p waves at all the stations the first motions of p waves for these earthquakes cannot be explained by the quadrant type pattern due to a double couple force system nucleation of a tensile crack coupled with a shear crack a tensile shear crack model is proposed as a source mechanism of the short period earthquakes moment tensor elements of tensile and shear cracks have been determined by the least squares method using observed p and s wave data results suggest that tensile cracking opening or closing is dominant for generating those earthquakes in comparison with shear cracking the strikes of the tensile cracks for the earthquakes are shown to be nearly parallel to the strike of the fissures the earthquakes that occurred in the northwestern region of the fissures are considered to be generated by a sudden opening of tensile shear cracks due to the excess pressure of intrusive magma in contrast the earthquakes occurring beneath the fissures are probably generated by a sudden closing of tensile shear cracks and this suggests that the magmatic pressure under the fissures rapidly decreased after the eruption moment tensor analysis of the tensile shear crack model in this study demonstrates the non double couple source mechanism for volcanic earthquakes related to magmatic activity

granite recrystallization the key to the nuclear waste problem we report the outcome of high temperature high pressure experiments showing that granite can be partially melted and completely recrystallized on a time scale of years as opposed to millennia as widely believed this could prove the key to secure very deep borehole disposal in the continental crust for small to moderate volumes of particularly problematic radionuclides removal of these problematic isotopes from spent nuclear fuel and other forms of high level waste could open the way to safe and acceptable disposal of the remaining bulk of high level waste with large volumes of intermediate level waste in geologically shallow conventional repositories

very long period seismic signals and caldera formation at miyake island japan over a period of roughly 40 days starting on 8 july 2000 a caldera structure 1 7 kilometers in diameter developed by means of gradual depression and expansion of the summit crater at miyake island japan at the same time very long period vlp seismic signals were observed once or twice a day source mechanism analyses of the vlp signals show that the moment tensor solutions are smooth step functions over a time scale of 50 seconds with dominant volumetric change components we developed a model to explain the caldera and the vlp signals in which a vertical piston of solid materials in the conduit is intermittently sucked into the magma chamber by lateral magma outflow this model offers potential for making quantitative estimations of the characteristic physical properties of magma systems

kinetics of crystallization of igneous rocks the geochemistry of igneous rocks is discussed with the primary objectives of bringing together the theories underlying the kinetics of crystallization of igneous rocks and illustrating the use of these theories in understanding experimental and observational data the primary purpose of the chapter is to introduce current thinking about the kinetics of igneous rocks and to provide a basis for understanding other work a basic assumption made in the discussion is that the rate of any chemical reaction including the crystallization of igneous rocks is zero at equilibrium and proceeds at a finite rate only at a finite deviation from equilibrium as such an understanding of the processes operating in igneous rocks requires an understanding of how deviation from equilibrium affects the rates and mechanisms of the processes occurring during crystallization these processes are detailed with special emphasis given to nucleation and crystal growth jmt

three dimensional velocity structure of the kilauea caldera hawaii high resolution velocity models 0 5 km resolution of the kilauea caldera region are obtained by the tomographic inversion of both p and s wave arrival times data are from the permanent hawaiian volcano observatory hvo seismic network a broadband seismic network and a temporary array of stations centered on the southern boundary of the caldera a low velocity p wave anomaly is imaged centered on the southeastern edge of the caldera with a velocity contrast of about 10 and a volume of 27 km the vp vs model mimics the spatial extent of the p wave anomaly but is partitioned into two discrete anomalous volumes centered on the southern boundary of the caldera and on the upper east rift of the volcano the corresponding poisson s ratio in these zones is high 0 25 0 32 which is consistent with a densely cracked hot volume which may contain partial melt the large scale features of the models are consistent with results obtained from an earlier larger scale 2 km resolution tomographic image of kilauea volcano based on hvo network data

magma dynamics and collapse mechanisms during four historic caldera forming events 1 four historic caldera forming events were studied to understand the relationship of magma withdrawal processes and caldera subsidence mechanisms two calderas are silicic katmai in 1912 and pinatubo in 1991 and two are basaltic fernandina in 1968 and miyakejima in 2000 all events have sufficient geophysical geologic and petrologic data with which to examine and model magma withdrawal and caldera collapse the data reveal that the magmas erupted at katmai and pinatubo were in a bubbly state in the reservoir immediately before and during caldera collapse the bubbly magma allowed for its efficient extraction from the reservoir causing significant underpressures to develop rapidly particularly in the case of katmai where the erupted rhyolite was voluminous and nearly aphyric and has very low viscosity the rapidly developing underpressures at katmai and pinatubo caused sudden en masse caldera collapse halfway through the climactic eruptions thereby liberating large amounts of seismic energy at fernandina and miyakejima by contrast caldera collapse was initiated early and continued for an extended period of time from weeks to months consisting of a series of discrete subsidence events manifested by large earthquakes at fernandina and by very long period vlp signals at miyakejima systematic changes in earthquake magnitudes and quiescent intervals at both volcanoes reveal changes in friction as collapse took place during extended time intervals

the cooling history of the late pliocene eldzhurtinskiy granite caucasus russia and the thermochronological potential of grain size age relationships abstract isotopic age investigations have been carried out on samples from the late pliocene eldzhurtinskiy granite great caucasus russia in order to elucidate the cooling history of this kilometere sized plutonic body the samples were taken from a horizontal profile from the edge to the centre of the granite and from a vertical profile from the top to a depth of 4570 m the 40ar 39ar results on biotites ranging from 2 5 to 1 2 ma indicate a vertical age zoning of the granite caused by regional uplift an uplift rate of 4 mm a is calculated from the age differences together with the results of fission track dating on apatite and zircon and the present day rock temperatures the biotite ages can be used to evaluate cooling rates below 400 c the cooling rates of about 180 c ma are relatively high and spatially and temporarily fairly uniform throughout the granite a geothermal gradient of 45 c km is derived from uplift and cooling rates this is identical to the present day borehole gradient the 40ar 39ar ages of distinct biotite grain fractions from one and the same sample specimen are discordant generally they show clear age grain size correlation as expected from ar diffusion theory for cooling systems thus the biotite results support the additional detailed thermochronological information the cooling rates in the temperature range of biotite closure based on the grain size age correlations of the biotites are close to 180 c ma they provide evidence that within a certain temperature interval the time temperature path of a rock may be determined exclusively by isotopic dating of different grain size fractions of only one type of mineral

partial melting and recrystallization of granite and their application to deep disposal of radioactive waste part 2 recrystallization abstract a previously published scheme for the high temperature disposal of nuclear waste in deep boreholes requires that granite host rock partially melted by the heat from the waste can be completely recrystallized on the time scale of the cooling of the waste experimental studies of dynamic recrystallization of a typical s type crustal granite were therefore undertaken under the pressure 0 15 gpa and other conditions likely to arise during implementation of this scheme linear cooling experiments at 1 c h 0 1 c h and 1 c day were carried out over the temperature range 800 560 c these demonstrate that the partially melted granite can be fully recrystallized when cooled at 0 1 c h or slower crystal growth rates for the main phases formed during cooling are linearly proportional to total h 2 o content and decrease from alkali feldspar through biotite to quartz recrystallizing the partially melted granite at 0 1 c h compared with 1 c h increases grain size by a factor of 2 5 on the basis of partial melting experiments reported previously by us lithos 2003 this issue for the same granite and the results presented here it is concluded that an s type granite similar to the one studied would be a suitable host rock for the proposed high temperature very deep disposal scheme for radioactive waste

shallow magma accumulation at kīlauea volcano hawai i revealed by microgravity surveys for vertical displacement at the summit of about 1 3 m and 160 gal respectively the volume of magma lost based on grav ity data and assuming a reasonable magma density exceeded the volume of summit col lapse suggesting the creation of 40 90 10 6 abstract using microgravity data collected at k lauea volcano hawai i united states between november 1975 and january 2008 we document signifi cant mass increase beneath the east margin of halema uma u crater within k lauea s summit caldera surprisingly there was no sustained uplift accompanying the mass accumulation we propose that the positive grav ity residual in the absence of signifi cant uplift is indicative of magma accumulation in void space probably a network of interconnected cracks which may have been created when magma withdrew from the summit in response to the 29 november 1975 m 7 2 south fl ank earthquake subsequent refi lling documented by gravity represents a gradual recovery from that earthquake a new eruptive vent opened at the summit of k lauea in 2008 within a few hundred meters of the positive gravity residual maximum probably tapping the reservoir that had been accumulating magma since the 1975 earthquake

experimental study of caldera formation scaled experiments have been carried out on caldera collapse mechanisms using silicone as analogue magma and dry sand as analogue rock experiments were carried out in two and three dimensions using a range of roof aspect ratios thickness width 0 2 to 4 5 appropriate for caldera collapse they reveal a general mechanism of collapse only weakly dependent on the shape of the reservoir for low roof aspect ratios 1 subsidence starts by flexure of the roof and the formation of outward dipping reverse ring faults which in turn trigger formation of peripheral inward dipping normal ring faults the subsidence always occurs asymmetrically in cross section the reverse faults delimit a coherent piston bounded on each side by an annular zone of inwardly tilted strata located between the reverse and normal ring fault sets the surface depression consists of a nondeformed area piston surrounded by an annular extensional zone tilted strata for high aspect ratios 1 multiple reverse faults break up the roof into large pieces and subsidence occurred as a series of nested wedges 2 d or cones 3 d the extensional zone dominates the surface depression in the case where preexisting regional faults do not play a major role the collapse mechanics of calderas probably depends strongly on the roof aspect ratio calderas with low roof aspect ratios are predicted to collapse as coherent pistons along reverse faults the annular extensional zone might be the source of the large landslides that generate intracaldera megabreccias collapse into magma reservoirs with high roof aspect ratios may be the origin of some funnel calderas where explosive reaming is not dominant

controls on the mineralogy of s type volcanic and plutonic rocks abstract far from being simply two mica granites s type rocks contain highly diverse mineral assemblages the most important chemical factors influencing the mineralogy of an s type rock are peraluminosity bulk feo mgo mg mg fe k na ca and the fugacities of volatile species such as h2o hf h3bo3 and o2 however it is not just initial melt chemistry that determines the mineral assemblage the pressure and temperature of crystallization exert major effects as magmas evolve the p t conditions volatile fugacities and melt chemistry change often leading to changes in stable mineralogy many s type granites and silicic volcanic rocks contain partly or completely re equilibrated mineral assemblages recognition of these may provide important information about early crystallization conditions and the nature of the magma source terrains

anticorrelated rb sr and k ar age discordances leuchtenberg granite ne bavaria germany the leuchtenberg granite oberpfalz ne bavaria displays a continuous differentiation trend ranging from mildy peraluminous coarse grained porphyritic biotite granites bg to strongly peraluminous medium to fine grained garnet bearing muscovite granites gmg the rb sr and k ar age determinations of whole rock and mineral samples from the granite and associated intermediate rocks redwitzites have revealed two divergent age gradients rb sr wholerock dates decrease and initial 87sr 86sr ratios increase for successively more evolved subsets of the granite all bg samples 87rb 86sr 2 16 yield a date of 326 2 ma with a low initial 87sr 86sr ratio of 0 70778 0 00013 1 while all gmg samples 87rb 86sr 70 to 1000 yield a younger date of 317 2 ma with an enhanced initial 87sr 86sr ratio of 0 7146 0 0039 the k ar measurements on biotites and muscovites give closely concordant dates for the gmg 326 323 ma and the southern lobe of the bg 324 320 ma the northern lobe of the bg including the redwitzites shows a well defined trend of decreasing k ar dates from 320 ma to 300 ma towards the northwest critical consideration of both isotope systems leads to the conclusion that the rb sr system of the gmg was disturbed by a later hydrothermal event the ca 326 ma whole rock rb sr date for the bg is not in conflict with any of the k ar mineral dates and is taken as approaching the crystallization age of the leuchtenberg granite the k ar age progression within the northern lobe of the bg indicates that this part either cooled down over a protracted period of some 20 ma or experienced reheating at ca 300 ma the study highlights the potential of combined rb sr and k ar dating in deciphering detailed chronology on the scale of a single igneous intrusion

beginning of melting in the granite system qz or ab an h2o the beginning of melting in the system qz or ab an h2 o was experimentally reversed in the pressure range p text h text 2 text o 2 15 kbar using starting materials made up of mixtures of quartz and synthetic feldspars with increasing pressure the melting temperature decreases from 690 c at 2 kbar to 630 c at 17 kbar in the an free alkalifeldspar granite system qz or ab h2o in the granite system qz or ab an h2o the increase of the solidus temperature with increasing an content is only very small in comparison to the alkalifeldspar granite system the solidus temperature increases by 3 c 7 c if albite is replaced by plagioclase an 20 an 40 the difference between the solidus temperatures of the alkalifeldspar granite system and of quartz anorthite sanidine assemblages system qz or an h2o is approximately 50 c

a petrogenetic grid for pelitic schists in the system sio 2 al 2 o 3 feo mgo k 2 o h 2 o a quantitative petrogenetic grid for pelitic schists in the system kfmash that includes the phases garnet chlorite biotite chloritoid cordierite staurolite talc kyanite andalusite sillimanite and pyrophyllite with quartz h2o and muscovite or k feldspar in excess is presented the grid is based on thermodynamic data of berman et al 1985 and berman 1988 for endmember kfash and kmash equilibria and natural fe mg partitioning for the kfmash system calculation of p t slopes and the change in fe fe mg along reactions in the kfmash system were made using the gibbs method in addition the effect on the grid of mno and cao is evaluated quantitatively the resulting grid is consistent with typical buchan and barrovian parageneses at medium to high grades at low grades the grid predicts an extensive stability field for the paragenesis chloritoid biotite which arises because of the unusual facing of the reaction chloritoid biotite quartz h2o garnet chlorite muscovite which proceeds to the right with increasing t in the kfmash system however the reaction proceeds to the left with increasing t in the mnkfash system so the assemblage chloritoid biotite is restricted to bulk compositions with high fe fe mg mn typical metapelites will therefore contain garnet chlorite at low grades rather than chloritoid biotite

viscous boundary of dda for modeling stress wave propagation in jointed rock note roches reference lmr article 2007 010view record in web of science record created on 2007 09 24 modified on 2016 10 14

a hybrid composite dike suite from the northern arabian nubian shield southwest jordan implications for magma mixing and partial melting of granite by mafic magma abstract the arabian nubian shield is an exemplary juvenile continental crust of neoproterozoic age 1000 542 ma the post collisional rift related stage 610 to 542 ma of its formation is characterized among others by the intrusion of several generations of simple and composite dikes this study documents a suite of hybrid composite dikes and a natural example of partial melting of granite by a mafic magma from the northernmost extremity of arabian nubian shield in southwest jordan the petrogenesis of this suite is discussed on the basis of field petrographic geochemical and rb sr isotopic data these dikes give spectacular examples of the interaction between basaltic magma and the granitic basement this interaction ranges from brecciation partial melting of the host alkali feldspar granite to complete assimilation of the granitic material field structures range from intrusive breccia angular partially melted granitic fragments in a mafic groundmass to the formation of hybrid composite dikes that are up to 14 m in thickness the rims of these dikes are trachyandesite latite with alkali feldspar ovoids up to 1 cm in diameter while the central cores are trachydacite to dacite and again with alkali feldspar ovoids and xenoliths from the dike rims the granitic xenoliths in the intrusive breccia have been subjected to at least 33 partial melting a seven point rb sr isochron from one of these composite dikes yields an age of 561 33 ma and an initial 87 sr 86 sr ratio of 0 70326 0 0003 2 and mswd of 0 62 geochemical modeling using major trace rare earth elements and isotopes suggests the generation of the hybrid composite dike suite through the assimilation of 30 to 60 granitic crustal material by a basaltic magma while the latter was undergoing fractional crystallization at different levels in the continental crust

high precision relocation of long period events beneath the summit region of kilauea volcano hawai i from 1986 to 2009 long period 0 5 5 hz lp seismicity has been recorded for decades in the summit region of kilauea volcano hawai i and is postulated as linked with the magma transport and shallow hydrothermal systems to better characterize its spatiotemporal occurrence we perform a systematic analysis of 49 030 seismic events occurring in the kilauea summit region from january 1986 to march 2009 recorded by the 50 station hawaiian volcano observatory permanent network we estimate 215 437 p wave spectra considering all events on all stations and use a station averaged spectral metric to consistently classify lp and non lp seismicity we compute high precision relative relocations for 5327 lp events 43 of all classified lp events using waveform cross correlation and cluster analysis with 6 4 million event pairs combined with the source specific station term method the majority of intermediate depth 5 15 km lps collapse to a compact volume with remarkable source location stability over 23 years indicating a source process controlled by geological or conduit structure

non double couple earthquakes 1 theory historically most quantitative seismological analyses have been based on the assumption that earth quakes are caused by shear faulting for which the equiv alent force system in an isotropic medium is a pair of force couples with no net torque a double couple or dc observations of increasing quality and coverage however now resolve departures from the dc model for many earthquakes and find some earthquakes especially in volcanic and geothermal areas that have strongly non dc mechanisms understanding non dc earth quakes is important both for studying the process of faulting in detail and for identifying nonshear faulting processes that apparently occur in some earthquakes this paper summarizes the theory of moment tensor expansions of equivalent force systems and analyzes many possible physical non dc earthquake processes contrary to long standing assumption sources within the earth can sometimes have net force and torque components described by first rank and asymmetric sec ond rank moment tensors which must be included in analyses of landslides and some volcanic phenomena non dc processes that lead to conventional symmetric second rank moment tensors include geometrically complex shear faulting tensile faulting shear faulting in an anisotropic medium shear faulting in a heteroge neous region e g near an interface and polymorphic phase transformations undoubtedly many non dc earthquake processes remain to be discovered progress will be facilitated by experimental studies that use wave amplitudes amplitude ratios and complete waveforms in addition to wave polarities and thus avoid arbitrary assumptions such as the absence of volume changes or the temporal similarity of different moment tensor com ponents

insights into shallow magmatic processes at kīlauea volcano hawaiʻi from a multiyear continuous gravity time series continuous gravity data collected near the summit eruptive vent at k lauea volcano hawai i during 2011 2015 show a strong correlation with summit area surface deformation and the level of the lava lake within the vent over periods of days to weeks suggesting that changes in gravity reflect variations in volcanic activity joint analysis of gravity and lava level time series data indicates that over the entire time period studied the average density of the lava within the upper tens to hundreds of meters of the summit eruptive vent remained low approximately 1000 1500 kg m3 the ratio of gravity change adjusted for earth tides and instrumental drift to lava level change measured over 15 day windows rose gradually over the course of 2011 2015 probably reflecting either 1 a small increase in the density of lava within the eruptive vent or 2 an increase in the volume of lava within the vent due to gradual vent enlargement superimposed on the overall time series were transient spikes of mass change associated with inflation and deflation of k lauea s summit and coincident changes in lava level the unexpectedly strong mass variations during these episodes suggest magma flux to and from the shallow magmatic system without commensurate deformation perhaps indicating magma accumulation within and withdrawal from void space a process that might not otherwise be apparent from lava level and deformation data alone continuous gravity data thus provide unique insights into magmatic processes arguing for continued application of the method at other frequently active volcanoes

gravity changes and deformation at kīlauea volcano hawaii associated with summit eruptive activity 2009 2012 analysis of microgravity and surface displacement data collected at the summit of k lauea volcano hawaii usa between december 2009 and november 2012 suggests a net mass accumulation at 1 5 km depth beneath the northeast margin of halema uma u crater within k lauea caldera although residual gravity increases and decreases are accompanied by periods of uplift and subsidence of the surface respectively the volume change inferred from the modeling of interferometric synthetic aperture radar deformation data can account for only a small portion as low as 8 of the mass addition responsible for the gravity increase we propose that since the opening of a new eruptive vent at the summit of k lauea in 2008 magma rising to the surface of the lava lake outgasses becomes denser and sinks to deeper levels replacing less dense gas rich magma stored in the halema uma u magma reservoir in fact a relatively small density increase 200 kg m 3 of a portion of the reservoir can produce the positive residual gravity change measured during the period with the largest mass increase between march 2011 and november 2012 other mechanisms may also play a role in the gravity increase without producing significant uplift of the surface including compressibility of magma formation of olivine cumulates and filling of void space by magma the rate of gravity increase higher than during previous decades varies through time and seems to be directly correlated with the volcanic activity occurring at both the summit and the east rift zone of the volcano

rupture in the 4 may 2018 m w 6 9 earthquake seaward of the kilauea east rift zone fissure eruption in hawaii

40ar 39ar and 18o 16o studies of the chegem ash flow caldera and the eldjurta granite cooling of two late pliocene igneous bodies in the greater caucasus mountains russia volcanic and intrusive rocks of the chegem caldera and the nearby eldjurta eldzhurtinskiy granite record a late pliocene episode of silicic magmatism in the north central caucasus mountains surface exposures created by the recent rapid uplift and erosion of the caucasus mountains span a 2 km vertical section of chegem caldera fill and 1150 m of the eldjurta granite cored mineral exploration drillholes in the eldjurta granite extend the sampling to a depth of 4 km the unique sampling range available in these two young igneous bodies affords an excellent opportunity to study their denudation and cooling histories which we examine by means of 40 ar 39 ar and 18 o 16 o measurements on an extensive sample suite total fusion biotite and sanidine ages from eight chegem tuff samples both intracaldera and outflow are analytically indistinguishable with a weighted mean of 2 82 0 02 ma a cross cutting granodiorite porphyry intrusion has a sanidine total fusion age of 2 84 0 03 ma and whole rock incremental heating of a post caldera andesite flow which caps the caldera fill yields an age of 2 82 0 02 ma thus caldera formation and post caldera resurgence and volcanism all occurred within a very short time 50 000 yr biotite total fusion ages of ten eldjurta granite samples including seven from 500 m intervals in the 4 km deep drillhole show a systematic linear decrease in age with depth from 1 90 ma near the roof contact of the granite to 1 56 ma at a depth of 3700 m assuming these ages were set at the same temperature this age depth gradient implies an isotherm migration rate of 13 mm yr between 1 90 and 1 56 ma this migration rate is due to a combination of rapid denudation and downward relaxation of isotherms with cooling rates between 200 and 500 c ma during this period oxygen isotopic compositions of quartz k feldspar plagioclase and biotite from the drillhole samples below the 800 m depth are fairly uniform and record primary igneous 18 o values with little evidence for subsolidus hydrothermal activity however in surface outcrop samples and in the shallowest drillhole sample mineral 18 o values have been lowered by up to 3 by interaction with an external meteoric hydrothermal fluid the primary mineral 18 o values of the eldjurta granite are distinctly higher than the corresponding phenocryst 18 o values in the chegem volcanic rocks indicating that the two bodies evolved as separxate magma batches

partial melting and recrystallization of granite and their application to deep disposal of radioactive waste part 1 rationale and partial melting abstract a high temperature deep borehole disposal scheme for nuclear waste is outlined this requires that granite host rock can be partially melted by the heat from the waste then completely recrystallized both on the time scale of the cooling of the waste experimental studies of non equilibrium partial melting of a typical s type crustal granite were carried out under the conditions likely to arise during implementation of this scheme p 0 15 gpa t 700 850 c the melting relations were determined under h2o saturated and h2o undersaturated conditions melting begins just under 700 c and the amount of melt increases with temperature and especially h2o content up to saturation such that with no added h2o only 5 of melt is produced even at 850 c but the addition of 1 h2o will generate 40 of melt 50 c lower at 800 c the partial melts formed at high degrees of melting e g h2o saturated t 800 c approximate to equilibrium melting but the smaller amounts of melt produced at lower temperatures under h2o undersaturated conditions clearly do not on the basis of these experiments it is concluded from the point of view of partial melting that an s type granite similar to the one studied would be a suitable host rock for the proposed high temperature very deep disposal scheme for radioactive waste

lava lake level as a gauge of magma reservoir pressure and eruptive hazard forecasting volcanic activity relies fundamentally on tracking magma pressure through the use of proxies such as ground surface deformation and earthquake rates lava lakes at open vent basaltic volcanoes provide a window into the uppermost magma system for gauging reservoir pressure changes more directly at k lauea volcano hawai i usa the surface height of the summit lava lake in halema uma u crater fluctuates with surface deformation over short hours to days and long weeks to months time scales this correlation implies that the lake behaves as a simple piezometer of the subsurface magma reservoir changes in lava level and summit deformation scale with and shortly precede changes in eruption rate from k lauea s east rift zone indicating that summit lava level can be used for short term forecasting of rift zone activity and associated hazards at k lauea