integrated seismic hazard analysis of the wasatch front utah we examined the combined effects of different sources that influence earthquake hazard of the populated wasatch front utah we first evaluated the fault stress interaction of the two largest historic earthquakes of the intermountain seismic belt isb the 1959 hebgen lake montana m s 7 5 and the 1983 borah peak idaho m s 7 3 earthquakes which experienced multisegment normal faulting ruptures estimates of the static stress change for these events revealed an increase in coulomb failure stress in areas of extended aftershocks these observations suggested that fault stress analysis is applicable in evaluating the spatial distribution of aftershocks after large normal faulting earthquakes in the same extensional stress regime of the eastern basin range including the wasatch front utah which encompasses the 370 km long wasatch fault and surrounding faults on the basis of this result we applied the modeling technique to the historically seismically quiescent wasatch fault and examined the relation between the pattern of stress change and the space time distribution of paleoearthquakes ages and locations of the wasatch fault paleoseismic data imply 17 single segment or 11 multisegment ruptures in the past 5 6 kyr we prefer the multisegment model because almost all of the large historical normal faulting earthquakes in the isb were multisegment fitting the along fault displacements by an analytic half ellipse function provides a first order distribution of the displacement over an entire rupture length and allows new estimates of fault slip rates and seismic moment with these data we also estimated the occurrence rate of m w 6 6 wasatch paleoearthquakes and showed that the rate was about three times higher than that inferred by the historical seismicity this result along with new information from a megatrench on the wasatch fault near salt lake city that revealed no scarp forming earthquakes between ca 9 0 and 15 5 ka suggests that large wasatch fault events in the past 5 6 kyr may be clustered the recurrence rate of large earthquakes estimated by the geodetic measured strain on the other hand is three to four times higher than that estimated by the long term fault slip rate this difference together with the observation of a low regional strain rate from historical seismicity suggests that cumulative aseismic deformation may be significant on the wasatch fault we also examined a major consideration for along strike segmentation namely how stress contagion could affect the probability of failure of adjacent faults including paleoearthquake derived fault slip rates global positioning system derived geodetic moment rates and the effect of stress contagion in the earthquake hazard estimation for a specific location in the salt lake valley revealed an increase in the annual frequency of peak ground acceleration 0 25 g by a factor of 1 4 4 0 and 5 4 respectively compared with that derived from historical seismicity only manuscript received 31 may 2001

active faulting at the eurasian north american and pacific plates junction abstract the active faults known and inferred in the area where the major pacific north american and eurasian plates come together group into two belts one of them comprises the faults striking roughly parallel to the pacific ocean margin the extreme members of the belt are the longitudinal faults of islands arcs in its oceanic flank and the faults along the continental margins of marginal seas in its continental flank the available data show that all these faults move with some strike slip component which is always right lateral we suggest that characteristic right lateral either partially or dominantly kinematics of the fault movements has its source in oblique convergence of the pacific plate with continental eurasian and north american plates the second belt of active faults transverses the extreme northeast asia as a continental extension of the active mid arctic spreading ridge the two active fault belts do not cross but come close to each other at the northern margin of the sea of okhotsk marking thus the point where the pacific north american and eurasian plates meet

low melt fraction connectivity of granitic and tonalitic melts in a mafic crustal rock at 800 c and 1 gpa in the absence of an externally applied stress the segregation of small amounts of granitic or tonalitic melts from their residual mafic crystals is possible only if the melt forms an interconnected network phase accordingly this research focuses on melt connectivity at low melt fraction 4 wt or 5 vol connectivity of granitic and tonalitic melts in amphibole rich rock was assessed by performing two types of piston cylinder experiments at 1 gpa and 800 c the first involved annealing samples that consisted of either alternating layers or homogeneous mixtures of calcic amphibole and metaluminous obsidian powder the second type of experiment involved creating diffusion couples here an upper cylinder of amphibole saturated granitic or tonalitic melt was placed against a lower cylinder consisting of an amphibole rich rock containing zero or a small melt granitic or tonalitic fraction the upper part of the diffusion couple was doped with emitter 151sm or 14c and functioned as an infinite melt reservoir the lower part of the diffusion couple was considered to be the host rock the experiments approached textural equilibrium which allowed us to characterize the wetting behaviour of the calcic amphibole by the hydrous silicic melt granitic or tonalitic these particular experiments also provided information concerning diffusive transport because the emitter could diffuse through the connected melt liquid in the amphibole rich rock the dihedral angle measurements show that melt connectivity was achieved this conclusion is based on the fact that the dihedral angles consistently yielded median apparent values of 53 58 for an amphibole rich rock granitic melt system and 46 48 for an amphibole rich rock tonalitic melt system however the frequency distribution of angles is found to be relatively broad the results of the diffusion couple experiments assessed using the radiographic technique complement the dihedral wetting angle measurements by showing that melt connectivity is achieved at a melt fraction less than 4wt 5 vol

analysis of scarp profiles evaluation of errors in morphologic dating morphologic analysis of scarp degradation can be used quantitatively to determine relative ages of different scarps formed in cohesionless materials under the same climatic conditions scarps of tectonic origin as well as wavecut or rivercut terraces can be treated as topographic impulses that are attenuated by surface erosional processes this morphological evolution can be modelled as the convolution of the initial shape with erosion or degradation function whose width increases with time such modeling applies well to scarps less than 10m high formed in unconsolidated fanglomerates to a good approximation the degradation function is gaussian with a variance measuring the degree of rounding of the initial shape this geometric parameter can be called the degradation coefficient a synthetic experiment shows that the degradation coefficient can be obtained by least squares fitting of profiles levelled perpendicular to the scarp gravitational collapse of the free face is accounted for by assuming initial scarp slopes at the angle of repose of the cohesionless materials 30 35 uncertainties in the measured profiles result in an uncertainty in degradation coefficient that can be evaluated graphically because the degradation coefficient is sensitive to the regional slope and to three dimensional processes gullying loess accumulation stream incision etc a reliable and accurate determination of degradation coefficient requires several long profiles across the same scarp the linear diffusion model of scarp degradation is a gaussian model in which the degradation coefficient is proportional to numerical age in that case absolute dating requires only determination of the propotionality constant called the mass diffusivity constant for holocene scarps a few meters high in loose alluvium under arid climatic conditions mass diffusivity constants generally range between 1 and 6 m 2 kyr morphologic analysis is a reliable method to compare ages of different scarps in a given area and it can provide approximate absolute ages of holocene scarplike landforms

disequilibrium melt distribution during static recrystallization melt migration and segregation and the rheology of partially molten rocks in the upper mantle and lower crust strongly depend on the grain scale distribution of the melt current theory for monomineralic aggregates predicts a perfectly regular melt framework but high temperature experiments with rock forming minerals melt show considerable deviations from this predicted geometry disequilibrium features such as fully wetted grain boundaries and large melt patches have been described these were mainly attributed to surface energy anisotropy of the minerals we present static analogue experiments with norcamphor ethanol that allow continuous in situ observation of the evolving liquid distribution the experiments show that all previously reported disequilibrium features can form during fluid enhanced static recrystallization when small grains are consumed there is no need to invoke surface energy anisotropy although this might enhance the effect all disequilibrium features are transitory and evolve back toward equilibrium geometry however because the system undergoes continuous static recrystallization disequilibrium features are always present in a partially molten polycrystalline aggregate and therefore control its properties

fitting degradation of shoreline scarps by a nonlinear diffusion model the diffusion model of degradation of topographic features is a promising means by which vertical offsets on holocene faults might be dated in order to calibrate the method we have examined present day profiles of wave cut shoreline scarps of late pleistocene lakes bonneville and lahontan it may be assumed that these scarps were initially at least as steep as the angle of repose offsets range from 1 to 12 m and present slope angles range from 9 to 29 a parameter called apparent diffusion age defined as half the mean square horizontal extent of the slope function of each profile is plotted as a function of scarp offset the points show a clear trend of apparent age increasing nearly linearly with offset if linear diffusion held and scarps were initially vertical apparent diffusion age would be the same for all the shoreline profiles the increasing trend can only partly be explained by nonvertical initial scarp slope and therefore the rate of transport of material downslope must increase significantly faster than a linear law in the range of slopes spanned by the data the transport law must become linear at small slope to reduce scatter between profiles with varying ambient slopes the transport law adopted for the purpose of dating is k0 1 5s2 where s is local slope the transport coefficient k0 is correlated inversely with fan slope suggesting that there is a dependence on the particle size distribution a table is included that allows easy application of the model to scarps with simple initial shape

geometric relations of dip slip to a faulted ground surface new nomograms for estimating components of fault displacement abstract the throw heave and dip slip components of displacement on a fault scarp can be estimated from two easily collected field measurements when fault dip is known or assumed the vertical separation and slope angle of the original ground surface displaced across the fault nomograms allow graphical determination of slip components for cases where fault dip is in the same or in an opposite direction as the slope of the ground surface the technique has several advantages over a previous method that requires three field measurements those of scarp height scarp slope angle and the slope of the original ground surface the geometric relations of a fault scarp illustrate that although differences between throw and vertical separation of the ground surface are small in the cases of steep fault dips or flat ground surfaces these differences can be greater than commonly assumed

melt segregation and magma interactions during crustal melting breaking out of the matrix abstract differentiation of the continental crust begins with its partial melting the products of crustal melting are silicic hydrous h2o undersaturated granitic liquids that are generated within matrices of residual crystals crustal differentiation requires that felsic magmas form and escape from these solid residua an important question is whether granitic magmas collect into large batches within or near their sources which then give rise to ascent or alternatively bleed out of the sources in smaller streams or pulses we demonstrate that the physical reality is closer to the second alternative and thus question the validity of the concepts of magma segregation and source fertility as they are sometimes visualised granitic plutons contain chemically distinct sub populations formed by source level entrainment of the peritectic assemblages into the melts rapid evacuation at source levels and high ascent rates protect the magmas from wall rock interactions during their tenure at source depths and during their ascent through cool upper crust the existence of different types of granites and hence of clearly defined chemically different magmas within plutons dictates that felsic magmas must separate efficiently from their anatectic sources and must ascend to the sites of their emplacement with minimal chemical interaction with crust through which the magma must move exposed deep crustal sections are typically lithologically diverse with the more fertile rocks commonly forming discrete layers surrounded by rocks with contrasting compositions if the melts were required to segregate and accumulate into large volumes within their hot sources especially by slow gravity driven melt percolation it is very likely that they would be substantially modified by reaction with diverse source rocks thus the processes mooted to occur in melting assimilation storage and homogenisation mash or deep crustal hot dch zones would act to erase original compositional heterogeneities and produce larger batches of more homogeneous magma perhaps carrying evidence of extensive magma mixing from various lines of evidence we conclude that mash and dch zones may not exist and even if they do they cannot form the sources of most granitic magmas the intrinsic heterogeneity in crustal source rocks the likely occurrence of peritectic assemblage entrainment and the inefficiency of magma mixing decree that granitic rocks will retain source inherited chemical and isotopic heterogeneities rapid semi continuous and disequilibrium withdrawal of small magma batches from source rocks means that elements of whole rock trace element chemistry and accessory mineral chemistry will be decoupled from major element variations this also means that a large source with low nominal fertility due to low hydrous mineral content for example could still produce a substantial granitic pluton by additions of individually small increments of magma

spatial patterns of geomorphic surface features and fault morphology based on diffusion equation modeling of the kumroch fault kamchatka peninsula russia abstract remote sensing data sets are widely used for evaluation of surface manifestations in active tectonic areas this study utilizes aster gdem and landsat etm data sets with google earth images draped over terrain models this study evaluates the surrounding surface geomorphology of the study area with these data sets and the morphology of the kumroch fault using diffusion modeling to estimate diffusion constants as well as to estimate slip rates by means of real ground data measured across fault scarps by kozhurin et al 2006 the study area is located southeast of the bezymianny volcano within the central kamchatka depression it is part of the kumroch fault zone the area contains numerous geomorphic features indicative of active deformation such as fault scarps ponds offset streams and glacier moraines the aster gdem and landsat etm data together with google earth imagery were used to create accurate geomorphic maps of specific sites within the study area along the western flank of the east kamchatka range previous studies have estimated the time elapsed since slip initiation of the faulted surface on the kumroch fault and the slip rate by dividing the offset of moraines by the age of the ruptured surface slip rates along the kumroch fault vary from 2 0 mm yr 2 5 mm yr determined from previous 14 c studies with time frames of 11 5 ka to 14 ka other slip rates for the kumroch fault were determined from previous studies through tephra and stratigraphic chronology these produced rates of 0 6 mm yr with time frames of 3 2 ka 10 5 ka models of the evolution of fault scarp morphology provide the amount of time elapsed since slip initiated on a faults surface they may therefore provide more accurate estimates of slip rate than those calculated by dividing scarp offset by the age of the ruptured surface profile modeling of scarps collected by kozhurin et al 2006 show that the scarps were formed by several events distributed over time they were evaluated using a constant slip rate csr solution which yields a value a 1 2 slip rate diffusivity time elapsed since slip initiated on the fault is determined by establishing a value for and measuring total scarp offset for this study csr nonlinear modeling assisted in estimates of which along the kumroch fault range from 8 m 2 ka to 14 m 2 ka slip rates have been estimated to range from 0 6 mm yr to 1 0 mm yr since 3 4 ka 3 7 ka this method provides a quick and inexpensive way to gather data for a regional tectonic study and establish estimated rates of tectonic activity

modification of wave cut and faulting controlled landforms from a casual observation that the form of degraded fault scarps resembles the error function this investigation proceeds through an elementary diffusion equation representation of landform evolution to the application of the resulting equations to the modern topography of scarplike landforms the morphologic observations can be analyzed either in the form of one or more cross strike elevation profiles or in the form of the slope offset plot a point plot of maximum scarp slope versus scarp offset working with either or both of these data representations for nine geologic structures which range in age from 3 to 400 ka b p and in offset from 1 to 50 m we apply analytical solutions for the vertical initial value scarp the vertical continuous offset scarp and the finite slope initial value scarp the model calculations are intrinsically ambiguous yielding as the final answer only the product t in the case of the initial value problem or the product a 1 in the case of the repeated faulting problem here t is the age of a single scarp forming event 2a is the vertical slip rate and is the mass diffusivity a single profile across three sea cliffs along the santa cruz california coast is analyzed as three separate initial value problems a reasonably constrained age for the sea cliff standing above the highway 1 platform returns 11 gkg 1 gkg 1 m2 ka with this we can date the two older sea cliffs in fact we do the converse age estimates for these two older sea cliffs based on a uniform rate of uplift both yield the same as for the lower sea cliff we treat a single profile of the raymond fault in pasadena san marino in terms of the repeated faulting problem for it the uplift rate of r crook and others yields 16 gkg the very substantial preexisting offset across the raymond fault must have been buried leveled some 230 ka b p when the modern topography began to form our analysis of the lake bonneville shoreline scarps reveals a dependence of t on 2a suggestive of nonlinear modification processes this appearance is treated with the finite slope initial value scarp model to determine 1 1 gkg for the lake bonneville shoreline scarps the suggestion of m n machette that approximately 100 000 year old meter high scarps are unobservable in weakly consolidated alluvial terranes of the basin and range and rio grande rift valley provinces can be formulated as 1 gkg the coincidence between this inequality and the lake bonneville shoreline is striking and it suggests that the value of 1 gkg may be generally applicable as a good first approximation to the modification of alluvial terranes within the semiarid regions of the western united states the lake bonneville shoreline is the basis for dating four sets of fault scarps in west central utah the drum mountains fault scarps can be modeled in several different circumstances but the most likely interpretation is that these fault scarps formed as the result of a single episode of normal faulting 3 6 to 5 7 ka b p the younger age is associated with quite low initial slope angles 25 the other three sets of fault scarps show no evidence for finite initial value slopes fault scarps along the eastern base of the fish springs range are very young 3 ka b p we estimate the age of fault scarps along the western flank of the oquirrh mountains to be 32 ka b p which meets the weak geologic constraint that they be older than the lake bonneville shoreline fault scarps along the northeastern margin of the sheeprock mountains are even older 53 ka b p an intriguing consequence of our single event analysis of these scarps is that an 11 5 m offset occurred in a single earthquake

structure of an active arc continent collision area the aleutian kamchatka junction abstract the plate boundary between the north american and pacific plates along the westernmost portion of the aleutian arc is formed by several active dextral strike slip fracture zones fracturing is expressed by fault escarpments visible in reflection seismic profiles and narrow zones of high seismicity the seismicity changes from the aleutian arc where shallow earthquakes occur to intermediate to deep earthquakes in the kamchatka aleutian junction area and to the south in the vicinity of this junction the distribution of earthquakes follows the traces of major aleutian fracture zones down to a depth of 100 km south of the kronotsky peninsula the distribution of earthquakes changes and is similar to other subduction zones the fracture zones cut the western aleutian arc into individual blocks which move along strike slip faults to the west and collide with kamchatka related transtension and transpression has led to the development of pull apart basins and block tilting the fracture zones splay into numerous strike slip faults to the west where they meet the kamchatka margin the main faults of the aleutian fault system can be traced on the kamchatka mys peninsula where deformed pleistocene sediments high uplift rates recent thrust faulting and changes in the drainage system provide evidence for neotectonic activity the fault pattern onshore and offshore in the junction area supports an indentation tectonic model of the collision of aleutian arc slivers with kamchatka

comparison of geodetic and geologic data from the wasatch region utah and implications for the spectral character of earth deformation at periods of 10 to 10 million years the wasatch fault and adjacent fault zones provide an opportunity to compare present day deformation rate estimates obtained from space geodesy with geologic displacement rates over at least four temporal windows ranging from the last millennium up to 10 myr the three easternmost gps sites of the basin and range geodetic network bargen at this latitude define a 130 km wide region spanning three major normal faults extending east west at a total rate of 2 7 0 4 mm yr with an average regional strain rate estimated to be 21 4 nstrain yr about twice the basin and range average on the wasatch fault the vertical component of the geologic displacement rate is 1 7 0 5 mm yr since 6 ka 0 6 mm yr since 130 ka and 0 5 0 7 mm yr since 10 ma however it appears likely that at the longest timescale rates slowed over time from 1 0 to 1 4 mm yr between 10 and 6 ma to 0 2 to 0 3 mm yr since 6 ma the cumulative vertical displacement record across all three faults also shows time variable strain release ranging from 2 to 4 mm yr since 10 ka to 1 mm yr averaged over the past 130 kyr conventional earthquake recurrence models reid type behavior would require an accordingly large variation in strain accumulation or loading rate on a 10 kyr timescale for which there appears to be no obvious geophysical explanation alternatively seismic strain release given a wide range of plausible constitutive behaviors for frictional sliding may be clustered on the 10 kyr timescale resulting in the high holocene rates with comparatively low uniform strain accumulation rates on the 100 kyr timescale wallace type behavior the latter alternative combined with observations at the million year timescale and the likelihood of a significant contribution of postseismic transients implies maxima of spectral amplitude in the velocity field at periods of 10 myr variations in tectonic loading 10 kyr clustered strain release and of 100 years postseismic transients if so measurements of strain accumulation and strain release may be strongly timescale dependent for any given fault system

morphologic dating of scarps formed by repeated slip events along the san andreas fault carrizo plain california morphologic dating of fault scarps determines late cenozoic fault activity by comparing observed topographic profiles with those determined using a calibrated hillslope development model we postulate that the material transport rate along the profile is a function only of local slope and is transport limited morphologic dating of hillslopes bounded by continuously dropping boundaries or cut by continuously slipping faults is used to determine the material transport rate constant the time since the downdrop was initiated or the fault began to slip we calibrated the hillslope development model on the southwest facing scarp southeast of wallace creek along the san andreas fault saf in the carrizo plain california the scarp has been exposed by right lateral offset of a southeast sloping shutter ridge located on the southwest side of the saf and by vertical offset related to secondary deformation we assume that all the observed offset occurs after initial exposure of the scarp by passage of the shutter ridge forward modeling of profile development yielded a mass diffusivity of 8 6 0 8 m2 kyr 1 normal fault slip rates were determined for two graben bounding faults in the northern elkhorn hills in the southeastern carrizo plain by applying the calibrated to the degradation of the scarps to determine the scarp age one fault scarp began to form about 12 kyr ago and the other about 63 kyr ago those ages and estimates of the dip slip along the faults result in slip rates of 1 2 mm yr 1

contrasting eruption styles of the 147 kimberlite fort a la corne saskatchewan canada abstract the cretaceous fort a la corne falc kimberlite field was active over a time span of 20 ma with contemporaneous terrestrial mannville group to marine lower colorado group background sedimentation steep sided pipes craters and positive landform volcanoes such as scoria or tuff cones are thought to have formed during that period the 147 kimberlite is located in the se section of the field s main cluster and is part of the large 377 5 ha orion north volcanic complex based on logging of 25 drill cores the morphology of the country rock kimberlite interface suggests excavation of a complex crater field down to the upper portion of the mannville group sedimentary deposits at least two types of volcaniclastic deposits are identified a main kimberlite unit that is typically characterized by crustal xenolith poor 1 2 normal graded beds possibly deposited as turbidites in a subaqueous environment originating from the nearby 148 tephra cone and infilling the adjacent 147 crater and a second unit located on the ne margin of the 147 kimberlite that represents a thick 60 m sequence of large up to 22 m sedimentary country rock blocks located at least 60 m above their original stratigraphic position we suggest the following time sequence of events crater excavation as a consequence of a shallow magma fragmentation level within the uppermost country rock sequences together with several closely spaced eruptive centres initially formed the complex intercalated crater field subsequently ongoing eruptions with a fragmentation level above the country rock produced the lithic fragment poor main infill of the 148 kimberlite resedimentation from the outer flanks of the 148 tephra cone resulted in the deposition of turbidites in the 147 area a consolidation phase solidified the lowermost portion of the main infill in 147 a subsequent explosion s occurred within the mannville group in the 147 area ejecting large blocks of sedimentary country rocks and fracturing the overlying volcaniclastic main infill finally blocks of the main infill tilted and possibly slumped into the subsidence structure developed above the emptied explosion chamber of 147 the different volcanic deposits reflect a change in eruption style and fragmentation level from highly explosive to spatter activity with little fragmentation potential cap rocks to build up the volatile overpressure necessary to blast the craters were not present at the time of emplacement no diatremes were observed in the study area assuming that the magma properties remained constant over time the change in eruption style has to be attributed to external factors such as water access to the rising magma the volcanic behaviour of the kimberlite magma appears to be comparable to that of other magmatic systems both in eruptive style and production rate no evidence was found for a high possibly plinian production rate or dispersion

does kamchatka belong to north america an extruding okhotsk block suggested by coastal neotectonics of the ozernoi peninsula kamchatka russia this paper addresses one part of an outstanding tectonic problem regarding the nature of the plate boundary between eurasia and north america in northeastern russia in this region the northwestern corner of the pacific plate interacts either simply with the north american plate or more complexly with one or more blocks independent of north america north of this corner evidence of uplift tilting and convergence contradicts the prevailing simpler model on the ozernoi peninsula similar to 150 km north of the subducting pacific plate marine terraces indicate uplift rates of 0 1 to 0 3 mm yr with faster rates to the east historic and paleoseismic records provide evidence for recurring tsunamigenic thrust earthquakes offshore of the ozernoi peninsula the most recent a mw 7 7 earthquake in 1969 a multiplate model where an eastward moving okhotsk block including most of kamchatka is converging with a clockwise rotating bering block better explains these observations than does the unbroken north american plate model

microstructures of melt bearing regional metamorphic rocks the most reliable microstructural criterion for the former presence of felsic melt in regional migmatites is a three mineral quartz k feldspar and sodic plagioclase aggregate in veinlets several other criteria are potentially reliable namely 1 euhedral crystals of feldspar precipitated from liquid or peritectic minerals e g garnet cordierite orthopyroxene k feldspar lining felsic protoleucosomes 2 inclusionfree euhedral overgrowths of feldspar precipitated from liquid or peritectic minerals e g garnet cordierite orthopyroxene k feldspar on residual grains of the same minerals with abundant inclusions in the mesosome 3 aligned euhedral feldspar crystals 4 simple twinning in k feldspar 5 dihedral angles of 60 subtended where a grain of feldspar and or quartz inferred to have pseudomorphed former melt meets two grains of other minerals 6 cuspate volumes of quartz k feldspar or sodic plagioclase especially where surrounded by grains inferred to have been residual during melting 7 veinlets of inferred former melt now mineral pseudomorphs consisting of one of quartz k feldspar or sodic plagioclase preferably though less commonly involving two or three of these minerals along grain boundaries or along inferred former intragranular fractures 8 biotite pseudomorphed by feldspar 9 veinlets of plagioclase that is more sodic than plagioclase grains in the adjacent rock 10 plagioclase with oscillatory zoning 11 microgranophyric intergrowths of quartz and alkali feldspar in patches or veinlets between primary grains 12 symplectic replacement aggregates that can be explained by reactions between peritectic grains and cooling melt and 13 melanosome patches and layers from which leucosome has been extracted however all these criteria must be interpreted with care some other proposed criteria are questionable for example 1 random mineral distributions 2 grain size increase 3 interstitial grains 4 corroded relics of inferred reactant mineral grains surrounded by areas of quartz k feldspar or sodic plagioclase 5 projections into a mineral grain 6 lobes of myrmekite and 7 plagioclase rims with a constant sodic composition occurring on plagioclase cores that are more calcic and or of variable composition

directed blasts and blast generated pyroclastic density currents a comparison of the bezymianny 1956 mount st helens 1980 and soufriere hills montserrat 1997 eruptions and deposits we compare eruptive dynamics effects and deposits of the bezymianny 1956 bz mount st helens 1980 msh and soufriere hills volcano montserrat 1997 shv eruptions the key events of which included powerful directed blasts each blast subsequently generated a high energy stratified pyroclastic density current pdc with a high speed at onset the blasts were triggered by rapid unloading of an extruding or intruding shallow magma body lava dome and or cryptodome of andesitic or dacitic composition the unloading was caused by sector failures of the volcanic edifices with respective volumes for bz msh and shv c 0 5 2 5 and 0 05 km3 the blasts devastated approximately elliptical areas axial directions of which coincided with the directions of sector failures we separate the transient directed blast phenomenon into three main parts the burst phase the collapse phase and the pdc phase in the burst phase the pressurized mixture is driven by initial kinetic energy and expands rapidly into the atmosphere with much of the expansion having an initially lateral component the erupted material fails to mix with sufficient air to form a buoyant column but in the collapse phase falls beyond the source as an inclined fountain and thereafter generates a pdc moving parallel to the ground surface it is possible for the burst phase to comprise an overpressured jet which requires injection of momentum from an orifice however some exploding sources may have different geometry and a jet is not necessarily formed a major unresolved question is whether the preponderance of strong damage observed in the volcanic blasts should be attributed to shock waves within an overpressured jet or alternatively to dynamic pressures and shocks within the energetic collapse and pdc phases internal shock structures related to unsteady flow and compressibility effects can occur in each phase we withhold judgment about published shock models as a primary explanation for the damage sustained at msh until modern 3d numerical modeling is accomplished but argue that much of the damage observed in directed blasts can be reasonably interpreted to have been caused by high dynamic pressures and clast impact loading by an inclined collapsing fountain and stratified pdc this view is reinforced by recent modeling cited for shv in distal and peripheral regions solids concentration maximum particle size current speed and dynamic pressure are diminished resulting in lesser damage and enhanced influence by local topography on the pdc despite the different scales of the blasts devastated areas were respectively 500 600 and 10 km2 for bz msh and shv and some complexity involving retrogressive slide blocks and clusters of explosions their pyroclastic deposits demonstrate strong similarity juvenile material composes 50 of the deposits implying for the blasts a dominantly magmatic mechanism although hydrothermal explosions also occurred the character of the magma fragmented by explosions highly viscous phenocryst rich variable microlite content determined the bimodal distributions of juvenile clast density and vesicularity thickness of the deposits fluctuates in proximal areas but in general decreases with distance from the crater and laterally from the axial region the proximal stratigraphy of the blast deposits comprises four layers named a b c d from bottom to top layer a is represented by very poorly sorted debris with admixtures of vegetation and soil with a strongly erosive ground contact its appearance varies at different sites due to different ground conditions at the time of the blasts the layer reflects intense turbulent boundary shear between the basal part of the energetic head of the pdc and the substrate layer b exhibits relatively well sorted fines depleted debris with some charred plant fragments its deposition occurred by rapid suspension sedimentation in rapidly waning high concentration conditions layer c is mainly a poorly sorted massive layer enriched by fines with its uppermost part laminated created by rapid sedimentation under moderate concentration weakly tractive conditions with the uppermost laminated part reflecting a dilute depositional regime with grain by grain traction deposition by analogy to laboratory experiments mixing at the flow head of the pdc created a turbulent dilute wake above the body of a gravity current with layer b deposited by the flow body and layer c by the wake the uppermost layer d of fines and accretionary lapilli is an ash fallout deposit of the finest particles from the high rising buoyant thermal plume derived from the sediment depleted pyroclastic density current the strong similarity among these eruptions and their deposits suggests that these cases represent similar source transport and depositional phenomena

deformation during terrane accretion in the saint elias orogen alaska the saint elias orogen of southern alaska and adjacent canada is a complex belt of mountains formed by collision and accretion of the yakutat terrane into the transition zone from transform faulting to subduction in the northeast pacific the orogen is an active analog for tectonic processes that formed much of the north american cordillera and is also an important site to study 1 the relationships between climate and tectonics and 2 structures that generate large to great magnitude earthquakes the yakutat terrane is a fragment of the north american plate margin that is partly subducted beneath and partly accreted to the continental margin of southern alaska interaction between the yakutat terrane and the north american and pacific plates causes significant differences in the style of deformation within the terrane deformation in the eastern part of the terrane is caused by strike slip faulting along the fairweather transform fault and by reverse faulting beneath the coastal mountains but there is little deformation immediately offshore the central part of the orogen is marked by thrusting of the yakutat terrane beneath the north american plate along the chugach saint elias fault and development of a wide thin skinned fold and thrust belt strike slip faulting in this segment may be localized in the hanging wall of the chugach saint elias fault or dissipated by thrust faulting beneath a north northeast trending belt of active deformation that cuts obliquely across the eastern end of the fold and thrust belt superimposed folds with complex shapes and plunging hinge lines accommodate horizontal shortening and extension in the western part of the orogen where the sedimentary cover of the yakutat terrane is accreted into the upper plate of the aleutian subduction zone these three structural segments are separated by transverse tectonic boundaries that cut across the yakutat terrane and also coincide with the courses of piedmont glaciers that flow from the topographic backbone of the saint elias mountains onto the coastal plain the malaspina fault pamplona structural zone separates the eastern and central parts of the orogen and is marked by reverse faulting and folding onshore most of this boundary is buried beneath the western or agassiz lobe of the malaspina piedmont glacier the boundary between the central fold and thrust belt and western zone of superimposed folding lies beneath the middle and lower course of the bering piedmont glacier

seismicity and structure of the kamchatka subduction zone the configuration of the pacific plate subducted beneath the kamchatka peninsula and the stress distribution in the kamchatka subduction zone ksz were studied using the catalog of the kamchatka regional seismic network focal mechanism solutions estimated from p wave first motions the formal inversion of long period waveforms and centroid moment tensor solutions to the south of 55 n the slab shows an approximately constant dip angle of 55 to the north of 55 n the dip of the slab becomes shallower reaching 35 the maximum depth of seismicity dm varies from 500 km depth near 50 n to 300 km depth at 55 n the volcanic front is almost linear along the main part of the ksz whereas it is sharply shifted landward to the north of 55 n the variation of dm is apparently consistent with the standard empirical relation dm where is the thermal parameter of the subducted slab to the north of 55 n the slab is offset toward the northwest and it is sharply deformed in a narrow contorted zone which is 30 km wide 56 n 161 e to the north of this contortion dm decreases to 100 km the landward shift of the northern part of the slab is reflected by a sharp deviation of the volcanic front to the northwest which follows the 90 160 km isodepth range of the subducted slab the observed value of dm in the northern segment significantly diverges from the global relation dm we interpret this as an effective decrease of the thermal thickness of the subducted lithosphere

comagmatic granophyre and dacite from karymsky volcanic center kamchatka experimental constraints for magma storage conditions abstract despite a 30 000 years difference in age two caldera forming eruptions at karymsky volcanic center kamchatka karymsky 7900 yr bp and academy nauk ca 40 000 yr bp produced two pyroxene dacites with the same composition and mineralogy granophyric xenoliths of the identical whole rock chemistry were found in basalts erupted within academy nauk caldera in 1996 unlike the dacites however the granophyres are holo crystalline and contain biotite and amphibole large amphibole phenocrysts contain rare inclusions of clinopyroxenes which compositionally overlap with clinopyroxenes in the dacites the al content of the amphibole suggests it grew at a pressure of about 100 mpa results of hydrothermal experiments and petrologic observations indicate that academy nauk and karymsky dacites were last equilibrated at 883 19 c 100 15 mpa and 871 19 c 85 18 mpa respectively both at water saturated conditions the mineral assemblage of granophyre is reproduced by isobaric crystallization of the dacite at 100 mpa implying that the granophyres were sampled from the crystallized silicic reservoir that produced the caldera forming eruption of academy nauk similar chemical compositions of karymsky and academy nauk dacites indicate that both were derived from the same crustal level source the eruptive history of the calderas can best be explained by two 10 12 km 3 dacitic batches that detached from a parental body situated in the lower crust then ascended to 3 4 km depth re equilibrated and erupted

investigation of the h7 ordinary chondrite watson 012 implications for recognition and classification of type 7 meteorites abstract despite the fact that the number of officially classified meteorites is now over 45 000 we lack a clearly defined sequence of samples from a single parent body that records the entire range in metamorphic temperatures from pristine primitive meteorites up to the temperatures required for extensive silicate partial melting here we conduct a detailed analysis of watson 012 an h7 ordinary chondrite to generate some clarity on the textural and chemical changes associated with equilibrium based silicate partial melting in chondritic meteorites to do this we compare the textures in the meteorite with those preserved in metamorphic contact aureoles on earth the most distinctive texture generated by the partial melting that affected watson 012 is an extensively interconnected plagioclase network which is clearly observable with a petrographic microscope enlarged metal troilite grains are encapsulated at widenings in this plagioclase network and this is clearly visible in reflected light together with these features we define a series of other characteristics that can be used to more clearly classify chondritic meteorites as being of petrologic type 7 to provide comprehensive evidence of silicate partial melting and strengthen the case for using simple petrographic observations to classify similar meteorites we use high resolution x ray computed tomography to demonstrate that the plagioclase network has a high degree of interconnectedness and crystallised as large cm scale skeletal crystals within an olivine orthopyroxene clinopyroxene framework essentially pseudomorphing a melt network back scattered electron imaging and element mapping are used to show that some of the clino and orthopyroxene in watson 012 also crystallised from silicate melt and the order of crystallisation was orthopyroxene clinopyroxene plagioclase x ray diffraction data supported by bulk geochemistry are used to show that plagioclase and ortho and clinopyroxene were added to the watson 012 sample by through flowing basaltic melt along with the absence of glass and granophyre this interconnected network of coarse grained skeletal plagioclase indicates that the sample cooled slowly at depth within the parent body the evidence of melt flux indicates that watson 012 formed in the presence of a gravitational gradient and thus at significant distance from the centre of the h chondrite parent body the gravitational gradient at the centre would be zero our interpretation is that incipient silicate partial melting in watson 012 occurred when a region of radiogenically heated h6 material located at considerable depth possibly at 15 20 km from surface was heated by an additional ca 200 300 c in association with a large shock event due to insulation at depth within an already hot parent body the post shock temperature equilibrated and remained above the solidus long enough for widespread equilibrium based silicate partial melting and for melt to migrate although the observed melting may have been facilitated by additional heating from an impact event this is not an example of instantaneous shock melting which produces thermal disequilibrium at short length scales and distinctly different textures a small number of h l and ll chondrites have been previously classified as being of petrologic type 7 with our new criteria to support that classification these represent our best opportunity to explore the transition from high temperature sub solidus metamorphism through the onset of silicate partial melting in three different parent bodies

modelling of melt segregation processes by high temperature centrifuging of partially molten granites i melt extraction by compaction and deformation the present study deals with the experimental modelling of two different mechanisms of crystal melt segregation in crustal rocks 1 the buoyancy driven compaction of the crystal melt matrix and 2 melt filtering in a partially crystalline matrix due to differential stresses these two segregation mechanisms have differing relative efficiencies in the deformation of crustal rocks and result in different texture scales depending on melt fraction melt viscosity and tectonic stresses a centrifuge furnace has been used in the present study for the modelling of melt migration in partially molten granitic rocks samples of beauvoir granite massif central france with a grain size of 0 16 0 5 mm and dimensions of diameter 5 mm length 16 mm were used these samples had been pre fused at temperatures of 1000 1075 c yielding an initial average melt fraction of 45 50 volume per cent the centrifuging of partially melted samples during 6 hr at an acceleration of 1000g g is gravity results in a linear vertical distribution of melt over the length of the sample without the development of a compaction layer the gradient of the melt fraction melt migrates to the top of samples correlates with temperature 1075 c 7 volume per cent mm 1 1050 c 4 volume per cent mm 1 1000 c 1 5 volume per cent mm 1 the calculated rate of melt migration varies from 3x10 5 cm s 1 1075 c to 2x10 6 cm s 1 1000 c differential stresses of 0 7 1 4 mpa have been generated in the centrifuge by putting a piston weight 1 02 2 05 g diameter 4 5 mm on the top of the partially melted sample which is then centrifuged at 1000g the rate of melt squeezing from the sample in this case is about two orders of magnitude higher than that observed without the piston after centrifuging for 6 hr a compaction layer below the piston is formed with a thickness of 2 5 mm and a crystal fraction of 70 65 volume per cent further centrifuging 15 hr does not result in any increase of the compaction layer thickness or volume percentage of crystals in it the comparison of the two segregation mechanisms confirms the much greater efficiency of differential stress induced melt segregation and accumulation in veins and pockets than the compaction mechanism

crustal scale en echelon p shear tensional bridges a possible solution to the batholithic room problem the apparent paradox of voluminous granitoid emplacement in an overall compressional magmatic are has been somewhat alleviated by the idea of pluton emplacement in tension cracks and dilational jogs within arc parallel strike slip fault systems as an alternative hypothesis we propose that an en echelon p shear array provides a continuous batholith scale zone of dilation along the trend of active magmatism and that it is favored by transpressional tectonics in the sierra nevada california the late cretaceous granitoids of the cathedral range intrusive epoch are consistent with emplacement into bridges between p shears because 1 they are elongated oblique to the magmatic trend consistent with p shear orientation within a dextral system 2 they were all emplaced within 5 10 m y along a 300 km trend resulting in a displacement rate of 1 cm yr across the arc and 3 syn to late magmatic dextral shear zones bound and crosscut the plutons as in a p shear tensional bridge

water fluxed melting of the continental crust a review abstract water fluxed melting also known as fluid or water present melting is a fundamental process in the differentiation of continents but its importance has been underestimated in the past 20 years during which research efforts focused mostly on dehydration melting reactions involving hydrate phases in the absence of a separate aqueous phase the presence of a free aqueous phase in anatectic terranes influences all major physical and chemical aspects of the melting process from melt volumes viscosity and ability to segregate from rock pores to melt chemical and isotopic composition a review of the literature shows that melting due to the fluxing of aqueous fluids is a widespread process that can take place in diverse tectonic environments active tectono magmatic processes create conditions for the release of aqueous fluids and deformation driven transient high permeability channels capable of fluxing high temperature regions of the crust where they trigger voluminous melting water fluxed melting can be either congruent in regions at the water saturated solidus or incongruent at suprasolidus p t conditions incongruent melting reactions can give rise to peritectic hornblende or to nominally anhydrous minerals such as garnet sillimanite or orthopyroxene in this case the presence of an aqueous phase is indicated by a mismatch between the large melt fraction generated and the much smaller fractions predicted in its absence the relatively small volumes of aqueous fluids compared to that of rocks imply that melting reactions are generally rock buffered fluids tend to move upwards and down temperature however there are cases in which pressure gradients drive fluids up temperature potentially fluxing suprasolidus terranes crustal regions at conditions equivalent to the water saturated solidus represent a natural impediment to the up temperature migration of aqueous fluids because they are consumed in melting reactions in this case continued migration into supra solidus terranes take place through the migration of water rich melts thus melts become the transport agent of water into supra solidus terranes and responsible for water fluxed melting other processes such as the relatively rapid fluid migration through fractures also allow regional aqueous fluids to by pass the water saturated solidus fluid trap and trigger melting above solidus conditions when aqueous fluids or hydrous melts flux rocks at supra solidus conditions they equilibrate with the surroundings through further melting decreasing water activity and giving rise to undersaturated melts it is in these conditions that hornblende or anhydrous peritectic phases are stabilized unlike dehydration melting the melt fraction generated in this case is not limited by the water contained in hydrous minerals but by the volume of water added to the system unlike melting at the water saturated solidus these melts are capable of rising without freezing and do give rise to upper crustal granitic bodies

tomographic imaging of the p wave velocity structure beneath the kamchatka peninsula summary a total of 5270 shallow and intermediate depth earthquakes recorded by the 32 stations of the regional seismic network of the geophysical service of russia are used to assess the p wave velocity structure beneath the kamchatka peninsula in the western pacific the tomographic inversion is carried out in three steps first a 1 d tomographic problem is solved in order to obtain an initial velocity model based on the 1 d velocity model 3 d tomographic inversions with homogeneous and heterogeneous starting models are obtained the conrad 15 km depth and moho 35 km depth discontinuities determined from the 1 d tomographic inversion and the upper boundary of the subducting slab are taken into account in the heterogeneous starting model for the traveltimes and ray path determinations both velocity structure and hypocentral locations are determined simultaneously in the inversion the spacing of the grid nodes is a half degree in the horizontal direction and 20 50 km in the vertical direction a detailed p wave tomographic image is determined down to a depth of 200 km the resulting tomographic image has a prominent low velocity anomaly that shows a maximum decrease in p wave velocity of approximately 6 per cent at 30 km depth beneath a chain of active volcanoes at depth low velocity anomalies are also observed in the mantle wedge extending down to a depth of approximately 150 km these anomalies are apparently associated with the volcanic activity the sedimentary basin of the central kamchatsky graben to the west of the volcanic front and the accretionary prism at the trench correlate with shallow low velocity anomalies highvelocity anomalies observed at a depth of 10 km may be associated with the location of metamorphic basements in the ganalsky valaginskoe uplift and upper crust of shipunsky cape the results also suggest that the subducted pacific plate has p wave velocities approximately 2 7 per cent higher than those of the surrounding mantle and a thickness of approximately 70 km

large scale deformation related to the collision of the aleutian arc with kamchatka the far western aleutian island arc is actively colliding with kamchatka westward motion of the aleutian arc is brought about by the tangential relative motion of the pacific plate transferred to major right lateral shear zones north and south of the arc early geologic mapping of cape kamchatka a promontory of kamchatka along strike with the aleutian arc revealed many similarities to the geology of the aleutian islands later studies support the notion that cape kamchatka is the farthest west aleutian island and that il has been accreted to kamchatka by the process of arc continent collision deformation associated with the collision onshore kamchatka includes gravimetrically determined crustal thickening and formation of a narrow thrust belt of intensely deformed rucks directly west of cape kamchatka the trend of the thrust faults is concave toward the collision zone indicating a radial distribution of maximum horizontal compressive stress offshore major crustal faults trend either oblique to the kamchatka margin or parallel to major aleutian shear zones these offshore faults are complex accommodating both strike slip and thrust displacements as documented by focal mechtmisms and seismic reflection data earthquake activity is much higher in the offshore region within a zone bounded to the north by the northernmost aleutian shear zone and to the west by an apparent aseismic front analysis of focal mechanisms in the region indicate that the present day arc continent contact zone is located directly east of cape kamchatka in modeling the dynamics of the coiiision zone using thin viscous sheet theory the rhealogical parameters are only partially constrained to values of n the effective power law exponent 2 3 and ar the argand number s 30 these values are consistent with a fnrcarc thermal profile of kamchatka previously determined from heat flow modeling the thin viscous sheet modeling also indicates that onshore thrust faulting is a consequence not only of compressive stresses resulting from the west directed collision but also of sediment induced coupling of the subducting pacific plate

maximum depth of seismicity and thermal parameter of the subducting slab general empirical relation and its application the maximum depth of seismicity dm in subduction zones is limited by some physical mechanisms related to the rheological strength of slab material metastability conditions failure strength etc the main factors controlling these properties are temperature and pressure within the lithosphere sinking into the mantle these p t conditions may be coarsely assessed from thermal models of slab subduction the observed relationship between dm the age of the subducted lithosphere a and the convergence rate v can be used to test the theoretical models and reveal inconsistencies which may indicate changes in failure mechanisms with depth we analyze the relation between dm and the thermal parameter of the descending slab which is a product of the age of the subducted lithosphere and the vertical component of convergence rate v seismicity profiles across the subduction zones of mexico chile kamchatka kuriles japan sumatra new hebrides aleutians tonga and marianas are used to estimate dm the quasi linear part of the dependence dm 240 km and 2000 km corresponds to relatively young and slowly descending slab and is in general agreement with the critical temperature models of deep earthquakes for 2000 km which corresponds to the relatively older lithosphere subducting at a higher rate the dm f dependence is nonlinear the flattening of the empirical dm f curve in the range of 2000 km 3500 km is found to be a direct indication of the influence of the equilibrium ol sp phase transition on dm models invoking the metastable ol sp phase transition as a mechanism which controls the deepest seismicity cannot be definitely constrained by the results of this study the general dependence dm f may be applied as a standard relation between dm a and v for the analysis of deep earthquakes and seismotectonic studies of the subduction zones

hydraulic and acoustic properties as a function of porosity in fontainebleau sandstone laboratory measurements have been made of the permeability k free porosity l compressional velocities vp or ve and compressional attenuations qp or qe in fontainebleau sandstone over a continuous range of porosities from 3 to 28 this large variation was achieved without any composition change fontainebleau sandstone is made of fine quartz grains with regular grain size 250 m permeability was measured with a falling head permeameter velocities and attenuations were obtained either through an ultrasonic experiment for frequencies around 500 khz or through a resonant bar technique experiment for frequencies around 5 khz and in both cases with varying water saturation the results show an excellent correlation between permeability k and total porosity for all our samples for low porosities 3 to 9 permeability in millidarcies is 2 75 10 5 7 33 while for high porosities 9 to 28 permeability k in millidarcies is given by 0 303 3 05 the correlation is also excellent between free porosity and total porosity on the other hand the correlation between acoustic properties and total porosity is not as clear as for hydraulic properties whatever the frequency 500 khz or 5 khz or the water saturation on the average velocity decreases and attenuation roughly increases with increasing total porosity velocity and attenuation values are related to the variation of grain contact structure and two samples with the same porosity and permeability may exhibit different velocities and attenuations the clear correlation between hydraulic properties and porosity is related to constant grain size while the lack of correlation for acoustic properties emphasizes the importance of the microstructure

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

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

morphological analysis of olivine grains annealed in an iron nickel matrix experimental constraints on the origin of pallasites and on the thermal history of their parent bodies two types of pallasites can be distinguished on the basis of the grain shape of olivine rounded or angular it has been suggested that these two types of textures resulted from different degrees of annealing at high temperature in the parent body in order to characterize the kinetics of rounding of olivine grains in an fe ni matrix we carried out a series of annealing experiments using a mixture of olivine and fe ni powder we were able to reproduce at a miniature scale the range of textures in pallasites the rate of rounding was rapid enough to be observed and measured at the scale of a few micrometers to 20 m even though the experiments were performed below the solidus of the fe ni metal for instance grains 14 m in diameter became nearly spherical within 7 days at 1400 oc for the morphological analysis of olivine grains we used two independent techniques the critical diameter method and the gaussian diffusion resample method a new technique specially developed for our study both techniques indicate that the rounding time scale is proportional to the cube of the grain size and that morphological adjustments in our experiments occurred by volume diffusion in the olivine lattice not by surface diffusion along the olivine metal boundaries we used our experimental data to estimate the time scales required for the development of olivine metal textures in natural pallasites we determined that small scale rounding of olivine grains in a solid metal matrix can be produced within relatively short time intervals 100 years to produce rounded olivine grains 0 1 mm in radius at 1300 1400oc

textural immaturity of cumulates as an indicator of magma chamber processes infiltration and crystal accumulation in the rum eastern layered intrusion textural maturity describes the extent to which rocks have approached textural equilibrium for igneous rocks this is a function of the time integrated thermal history in the sub solidus which for cumulate rocks generally translates to the cooling history via the rate of solidification of the accumulating crystal mush the most straightforward way to quantify the textural maturity of orthocumulates sensu lato is to measure the angle subtended at the corners of interstitial grains texturally mature cumulates have angle populations with median values of c 120 whereas texturally immature cumulates have lower medians inherited by the interstitial phase which infills either an impingement texture in the accumulating mush or a texturally equilibrated pore topology textural observations of allivalites from the rum layered suite demonstrate that stratigraphically localized excursions towards textural immaturity are the result of either transient relatively rapid solidification rates perhaps a result of the arrival of cold crystal laden bodies of fluid on the chamber floor or late stage infiltration of fully solidified cumulates by evolved liquids expelled upwards by compaction of underlying horizons these two processes have distinct textural and compositional signatures

lithospheric dismemberment and magmatic processes of the great basin colorado plateau transition utah implied from magnetotellurics 1 to illuminate rifting processes across the transition zone between the extensional great basin and stable colorado plateau interior we collected an east west profile of 117 wideband and 30 long period magnetotelluric mt soundings along latitude 38 5 n from southeastern nevada across utah to the colorado border regularized two dimensional inversion shows a strong lower crustal conductor below the great basin and its transition zone in the 15 35 km depth range interpreted as reflecting modern basaltic underplating hybridization and hydrothermal fluid release this structure explains most of the geomagnetic variation anomaly in the region first measured in the late 1960s hence the transition zone while historically included with the colorado plateau physiographically possesses a deep thermal regime and tectonic activity like that of the great basin the deep crustal conductor is consistent with a rheological profile of a brittle upper crust over a weak lower crust in turn on a stronger upper mantle jelly sandwich model under the incipiently faulted transition zone the conductor implies a vertically nonuniform mode of extension resembling early stages of continental margin formation colorado plateau lithosphere begins sharply below the western boundary of capitol reef national park as a resistive keel in the deep crust and upper mantle with only a thin and weak moho level crustal conductor near 45 km depth several narrow steep conductors connect conductive lower crust with major surface faulting some including modern geothermal systems and in the context of other great basin mt surveying suggest connections between deep magma sourced fluids and the upper crustal meteoric regime the mt data also suggest anisotropically interconnected melt over a broad zone in the upper mantle of the eastern great basin which has supplied magma to the lower crust consistent with extensional mantle melting models and local shear wave splitting observations we support a hypothesis that the transition zone location and geometry ultimately reflect the middle proterozoic suturing between the stronger yavapai lithosphere to the east and the somewhat weaker mojave terrane to the west we conclude that strength heterogeneity is the primary control on locus of deformation across the transition zone with modulating force components

geochemistry of granitic melts produced during the incongruent melting of muscovite implications for the extraction of himalayan leucogranite magmas granites formed from the incongruent melting of muscovite preserve evidence of chemical disequilibrium both between restite and melt and within individual phases during crystallization miocene leucogranites from the himalayas exemplify melt formation from a pelitic source through muscovite breakdown trace elements rb sr and ba reside almost entirely in micas and feldspars in the protolith and therefore are appropriate for quantitative modeling equilibrium between melt and restite was established for sr under fluid phase absent conditions but some disequilibrium is suggested by rb abundances consistent with known diffusion rates for these elements abundances of zr and ce in the granites which provide essential structural constituents of the accessory phases zircon and monazite indicate that the himalayan granite melts were saturated in these elements if formed at temperatures of 670 700 c but slightly undersaturated if formed at somewhat higher temperatures ion microprobe traverses of y and heavy rare earth element abundances across single garnets from himalayan leucogranites provide evidence for disequilibrium between melt and phenocryst during garnet growth thus constraining the evolution of magmatic compositions during melt formation and crystallization in some cases progressive melting of the protolith and crystallization of garnet from the melt appear to have been concomitant indicating that minimum solidus temperatures were maintained throughout the melting event this suggests that thermal buffering rather than melt extraction provided the rate determining step in magma evolution

beginning of melting and composition of first melts in the system qz ab or h 2 o co 2 solidus temperatures have been determined for minimum melt compositions in the system qz sio2 ab naalsi3o8 or kalsi3o8 at p fluid 2 5 and 10 kbar and at various water activities the dry solidus was investigated in a dry argon environment water activities ah2o between 0 0 and 1 0 were obtained by using h2o co2 mixtures the or ab or ratio of first melts increases considerably with decreasing water activity at 10 kbar it is 0 28 in the water saturated system and 0 56 at water activity 0 1 the qz content does not change with changing water activities the ab content of minimum melts formed at high pressures and low ah2o may remain almost constant in ascending magmas that are cooling and crystallizing qz content increases at the expense of the or component solidus temperatures decrease considerably when ah2o increases slightly from zero at 10 kbar the temperature difference between dry melting and the solidus for ah2o 0 1 is 120 c the influence of pure co2 on the solidus is very limited in the investigated p t range the solidus is approximatively 760 c at ah2o 0 5 between 2 and 10 kbar and approximatively 830 c at ah2o 0 3 this means that melting of quartz feldspar assemblages may induce dehydration reactions at p t conditions of the granulite facies

distribution of partial melt in a felsic system the importance of surface energy the texture distribution and infiltration tendency of a quartz albite melt in equilibrium with a synthetic texturally equilibrated quartzite was examined in a series of distribution and infiltration experiments at 1 250 c and 8 kbar hydrostatic pressure wetting angle measurements from melt distribution experiments show a dihedral angle of 60 degrees implying a quartz quartz interfacial energy approximately 1 7 times the quartz melt value because of this specific relationship between interfacial energies the system can achieve its lowest surface free energy state with the melt either in pools or along grain edge intersections possibly forming some interconnected channels stability of melt in pockets and along grain edge intersections was observed in a fourteen day dispersed melt experiment yet melt pools failed to disperse into the quartzite during infiltration experiments comparison of the observed dihedral angle with previously measured surface energy values for the melt and quartz shows excellent agreement and also demonstrates that an aggregate of randomly orientated anisotropic grains acts approximately isotropically

anatexis and metamorphism in tectonically thickened continental crust exemplified by the sevier hinterland western north america the generation of granitoid magmas by partial melting of crustal rocks during continental thickening events is well documented in many geological provinces throughout the world including the late mesozoic sevier belt of western north america we present a thermal and petrologic model of anatexis and metamorphism in regions of crustal thickening where the only mantle contribution is the normal conductive supply of heat through the base of the lithosphere i e advection of mass and energy are excluded we distinguish between formation of migmatites and generation of mobile granitoid magmas and examine the temporal and spatial relationships between these two distinct anatectic processes between anatexis and regional deformation and between anatexis and metamorphism a fundamental conclusion is that if protoliths rich in hydrous minerals are present regional anatexis is the end product of classical barrovian metamorphism in thickened continental crust even in the absence of a free water rich fluid phase barrovian metamorphic facies series are predicted with thickening ratios maximum crustal thickness attained initial crustal thickness as low as 1 3 but mobile granitoid magmas are not formed if this ratio is less than approximately 1 5 above these lower bounds barrovian metamorphism and anatectic granitoid magmatism occur independently of the magnitude of thickening and of the way in which thickening is accomplished both processes are sensitive to a diminished heat supply lowering either moho heat flow or crustal radioactive heat production results in blueschist eclogite metamorphism and inhibits the formation of mobile granitoid magmas we model anatexis under fluid absent conditions and show that with such a constraint migmatization is always a syn kinematic process relative to the crustal thickening event whereas generation of mobile granitoid magmas is in most cases post kinematic relative to crustal thickening but can be syn kinematic if thickening takes more than approximately 50 myr the typical time intervals for melting are consistent with geological observations mobile granitoid magmas are predicted by most of our models within approximately 10 myr of the end of the crustal thickening event this incubation period results primarily from the temperature increase required for the dehydration melting reactions capable of producing large melt fractions to occur the energetic requirements of anatexis are relatively minor compared to conductive crustal thermal budgets as shown by the fact that once the necessary p t conditions are attained melting reactions are completed within time intervals on the order of 1 myr i e 1 2 orders of magnitude smaller than the characteristic time scales of the tectonic processes involved in crustal thickening

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

effect of partial melting on vp and vs in crustal enclaves from mazarron se spain abstract the combination of compressional and shear wave velocity is an important tool in discriminating rock types and identifying residing melts within the continental crust here we report the laboratory measurements for vp and vs obtained in varying conditions up to those exceeding the beginning of melting 950 c at 500 mpa confining pressure on two residual garnet biotite sillimanite cordierite spinel metapelitic enclaves recovered from the neogene dacites of mazarron se spain the enclaves preserve widespread interstitial rhyolitic glass as evidence of primary melt extraction at 500 mpa the experimental vp ranges from 7 21 7 46 km s 1 at room temperature to 5 44 km s at 950 c the mean vs is 4 5 km s at room temperature with shear wave splitting of 0 25 0 3 km s measured along three mutually orthogonal directions when temperature increases the vs evidences a reversible slope change at about 650 c and the shear wave splitting reduces to zero isotropic material at 850 950 c where the sample vs is 3 0 km s the vp anisotropy is 7 10 up to 700 c increasing to 20 at 950 c while the vs anisotropy continuously decreases with temperature from 5 to 7 at room temperature to zero at 950 c no mineral reactions are observed up to 650 700 c however microstructure equilibrates due to the relaxation of the primary glass at the glass transition temperature between 850 c and 950 c a new melting reaction is observed producing biotite spinel ilmenite plagioclase melt at melting the rock becomes isotropic for vs and poisson s ratio increases to 0 30 our seismic data show that the seismic signature of high grade metapelitic rocks is similar to that of mafic materials the evolution of vp and vs at melting conditions is compatible with the geophysical data of the area supporting the hypothesis of the current existence of anatectic melts at intermediate depths of the alboran domain

fault slip rates and initiation age based on diffusion equation modeling wasatch fault zone and eastern great basin models of the evolution of fault scarp morphology provide time elapsed since slip initiated on a faulted surface and may therefore provide more accurate estimates of slip rate than the rate calculated by dividing scarp offset by the age of the ruptured surface to accomplish this task linear and nonlinear models of sediment transport are calibrated from the morphology of lake bonneville shoreline scarps and fault scarps formed by multiple surface rupturing earthquakes along the wasatch fault zone wfz profile modeling of scarps formed by several events distributed through time is done using a constant slip rate csr solution and yields a value of a 1 2 slip rate diffusivity time elapsed since slip initiated on a fault is determined by establishing a value for and measuring total scarp offset csr nonlinear modeling 0 2 8 1 1 m2 kyr wfz of faults along the west slope of the oquirrh mountains indicates a slip rate of 0 1 mm yr since 50 to 65 ka which is corroborated by cosmogenic dating 10be 26al age 75 ka the slip rate along the west flank of the stansbury mountains varies from 0 04 to 0 2 mm yr for time frames of 10 to 100 ka with the most recent rupture on the northern portion of the fault zone 10 ka scarp analysis of the southern end of the nephi segment wfz suggests either temporal clustering or variable slip rate as indicated by differences in the short term 1 3 mm yr for 4 3 ka versus long term 0 4 mm yr for 70 ka slip rates

geochemical evidence for the melting of subducting oceanic lithosphere at plate edges most island arc magmatism appears to result from the lowering of the melting point of peridotite within the wedge of mantle above subducting slabs owing to the introduction of fluids from the dehydration of subducting oceanic crust1 volcanic rocks interpreted to contain a component of melt not just a fluid from the subducting slab itself are uncommon but possible examples have been recognized in the aleutian islands baja california patagonia and elsewhere2 3 4 the geochemically distinctive rocks from these areas termed adakites are often associated with subducting plates that are young and warm and therefore thought to be more prone to melting5 but the subducting lithosphere in some adakite locations such as the aleutian islands appears to be too old and hence too cold to melt6 7 this implies either that our interpretation of adakite geochemistry is incorrect or that our understanding of the tectonic context of adakites is incomplete here we present geochemical data from the kamchatka peninsula and the aleutian islands that reaffirms the slab melt interpretation of adakites2 but in the tectonic context of the exposure to mantle flow around the edge of a torn subducting plate we conclude that adakites are likely to form whenever the edge of a subducting plate is warmed or ablated by mantle flow the use of adakites as tracers for such plate geometry may improve our understanding of magma genesis and thermal structure in a variety of subduction zone environments

liquid segregation parameters from amphibolite dehydration melting experiments we have experimentally obtained some of the parameters necessary for understanding the segregation of silicate liquid from amphibolite undergoing dehydration melting at 1 gpa and 750 1000 c the solidus for this calcic amphibolite 68 mg hb 32 pl an 90 is 750 c amphibolites begin to melt at relatively high temperatures in the garnet absent field but the solidus appears to backbend at 1 gpa coincident with the garnet in boundary hornblende breakdown due to garnet formation releases h 2o and causes melting thus in the garnet present field 1 gpa the amphibolite dehydration melting solidus may be coincident with the h 2o saturated solidus liquid interconnectivity may be achieved at 900 c and 5 vol liquid based on both physical and chemical data from solid rock runs mass balance calculations from powdered rock runs suggest that small amounts 5 15 vol of hydrous 4 wt h 2o low viscosity 10 3 10 4 pa s heavy rare earth element depleted felsic liquid may be segregated during amphibolite dehydration melting at 875 c the rapid breakdown of coarse grained hb cores may lead to the formation of transient h 2o saturated liquids with even lower viscosities 10 2 pa s although comprising only a small portion of the melting cycle these h 2o rich conditions may enhance the segregation of liquid by reduction of liquid viscosities and by mechanical effects on the restite e g increased deformation and liquid fracturing during anatexis of coarse grained natural rocks transient conditions may control the initial stages of liquid segregation

timing and nature of magmatic fabrics from structural relations around stoped blocks abstract structural relations around several large 100 m stoped blocks in the granodiorite of castle creek sierra nevada california suggest that magmatic fabrics formed as or after the space making phase of pluton emplacement had ended the stoped granite blocks are approximately 360 m below the exposed pluton roof magmatic foliations in granodiorite surrounding the blocks commonly follow km scale orientation trends to within 1 m of block contacts where they become deflected parallel to the block boundaries locally undeflected foliations occur within a few centimeters of block contacts mafic enclave fabric ellipsoid intensities 0 2 we draw the following conclusions concerning magmatic fabrics in the granodiorite of castle creek 1 magmatic fabrics formed during and or after the latest stages of pluton emplacement and thus contain little or no information about space making processes 2 magmatic fabrics had poor strain memory and 3 during magmatic fabric formation pluton strains were partially decoupled from host rock strains published data from other plutons indicate that these relationships may be common particularly in the brittle upper crust it follows from these conclusions that even in the best case magmatic fabrics contain only qualitative information about pluton emplacement mechanisms regional tectonics and internal magma chamber processes interpretations of magmatic fabrics must be corroborated by evaluating causes kinematics and magnitudes of syn emplacement host rock deformation in the worst case the causes of magmatic fabrics cannot be uniquely determined

the double seismic zone in kuril kamchatka the tale of two overlapping single zones the classic double seismic zone in the central portion of the kuril kamchatka arc seems to turn into a regular wadati benioff zone with downdip compression and extension in the northeastern and southwestern ends of the arc respectively to delineate this lateral changeover we studied 33 large to moderate sized mb 5 1 earthquakes that occurred at depths shallower than 200 km between 1963 and 1991 these events took place in two regions where the double seismic zone terminates and single seismic zones emerge precise earthquake source parameters including focal depths and mechanisms are determined from a careful analysis of a mixture of analog and digital p and sh waveforms recorded at teleseismic distances our results indicate that the double seismic zone is confined between approximately 46 and 53 n northeast of 53 n intermediate depth earthquakes 70 200 km show only downdip compressional focal mechanisms furthermore the wadati benioff zone there seems to be a continuation of the upper compressional layer of the double seismic zone thus the changeover from a double to a single seismic zone in this case is simply disappearing of the lower extensional sheet of the double seismic zone similarly southwest of 46 n intermediate depth earthquakes show only downdip extensional mechanisms the single seismic zone is unlikely to consist of two layers of extensional seismicity in fact nowhere along the entire arc did we observe two distinct seismogenic layers with a single state of strain in other words these extensional events did not occur in the same seismogenic structure as the upper compressional layer of the double seismic zone however we cannot ascertain whether the single seismic zone in extension is simply a southwestern extension of the lower extensional layer of the double seismic zone lateral variation from a single zone under extension in the southwest to a double seismic zone and finally to a single zone under compression cannot be accounted for by conventional models of a double seismic zone on the other hand the addition of a component of stress transmitted from depths greater than 250 km can explain the observed lateral variation in the state of strain at intermediate depths because the slab between depths of 250 450 km is under extension in the southwestern end of the arc whereas the rest of the arc is under compression vanishing of the lower extensional layer of the double seismic zone toward the northeastern end of the arc is interpreted as a result of compression transmitted from below overshadowing extension caused by effects such as unbending a similar reasoning applies to the southwestern termination of the double seismic zone

information about open system magma chambers derived from textures in magmatic enclaves the kameni islands santorini greece post caldera eruptions of santorini greece over the past 3000 years resulted in the formation of the kameni islands which comprise a series of compositionally similar dacitic lava flows each lava flow has a distinct population of partially crystalline mafic enclaves which we propose were derived from the break up of a layer of replenishing magma responsible for triggering the eruption five of the recent flows erupted in 1570 1939 1940 1941 and 1950 include enclaves of essentially identical andesitic bulk compositions which formed by crystallization of originally aphyric melts prior to eruption detailed examination of angles subtended at the junctions between pairs of plagioclase grains demonstrates that enclaves from each flow have a characteristic textural signature with distinct differences in the extent of quench related modification of the original population of dihedral angles formed by impingement of growing grains these variations suggest that the temperature difference between the host dacite and the replenishing andesite at the time of layer overturn and eruption differed between flows the uniformity of major element compositions of both the replenishing magma and the host dacitic lava flows demonstrates that the critical parameter in determining the timing of layer overturn is the pre eruptive h 2 o content of both host dacite and replenishing magma we suggest that the replenishing magma responsible for two of the three eruptions in the period 1939 1941 was significantly wetter than that responsible for the later 1950 eruption the enclaves with the least amount of quench related modification occur in the 1570 flow we suggest that in this case the intruding magma was relatively dry

a double planed seismic zone in kamchatka from local and teleseismic data the fine structure of a double planed deep seismic zone is studied over a wide area of the kamchatka peninsula this prominent feature of deep seismic zone configuration is ascertained through the analysis of microearthquake hypocenters from the local seismic network of the institute of volcanology of kamchatka and 22 focal mechanism solutions from the formal inversion of long period p and sh waves for events with mh 5 5 additionally 1 1 focal mechanism solutions estimated from the first motion of p waves and 12 centroid moment tensor solutions of harvard university are used the maximum depth of the double seismic zone is 170 180 km the two planes of seismicity are separated by 40 km at a depth of 50 km and by 10 15 km at 180 km depth the focal mechanism solutions of shallow earthquakes show an abrupt change from the thrust events to down dip compressional events at approximately 60 km depth at the upper boundary of the descending slab within the descending slab the earthquakes with down dip tensional axis form the lower plane of the double planed deep seismic zone several earthquakes with down dip tensional axis are discovered in a narrow area of the upper seismic zone at the depth of about 50 km the double seismic zone is revealed clearly in the area between 52 n to 54wn and probably extends up to 56 n

textural maturity of cumulates a record of chamber filling liquidus assemblage cooling rate and large scale convection in mafic layered intrusions textural maturity describes the extent to which a rock has evolved from the initial reaction controlled texture towards textural equilibrium controlled by the minimization of interfacial energy solidification in a magma chamber results in the formation of an impingement texture by the random juxtaposition of planar sided grains orthocumulates in which the initial melt filled pores are pseudomorphed by later crystallizing phases have an ophitic or intersertal texture immediately after complete solidification which then evolves towards solid state equilibrium by rounding of initially planar grain boundaries and an increase in the median dihedral angle subtended at the junctions of two primocrystic grains with the interstitial phase the bulk of the increase in angle occurs just below the solidus temperature in kilometre scale mafic plutons quantification of textural maturity via measurement of dihedral angle populations in troctolitic and gabbroic cumulates from the rum eastern layered intrusion and the skaergaard intrusion demonstrates that the rocks preserve a record of thermal events related to magma chamber replenishment and the onset of chamber wide convection textural maturity is also a function of the liquidus phase assemblage for systems in which only olivine and plagioclase are liquidus i e cumulus phases in the main magma body above the crystal mush the texture is significantly less mature than that in systems in which clinopyroxene is an additional liquidus phase the difference in textural maturity reflects differences in the cooling and solidification rate and demonstrates directly that the liquidus phase assemblage plays a role in determining the thermal history of plutons

fluid absent melting behavior of a two mica metapelite experimental constraints on the origin of black hills granite we have studied experimentally the vapor absent melting behavior introduction of a proterozoic metapelite hp 60 1 from the black hills south peraluminous leucogranites such as the miocene granites dakota to assess whether the high do tourmaline bearing granites of the himalaya and tourmaline granites of the harney of the harney peak suite resulted from muscovite dominated depeak suite in south dakota are widely considered to be hydration melting at 10 kbar samples were sealed with no added the product of muscovite dehydration melting yet few h2o in gold capsules then run in a 0 5 inch 1 27 cm pistonexperimental studies of muscovite dehydration melting cylinder apparatus over the temperature interval 812 975 c reactions have been performed because the low temexperiments were conducted at 10 kbar to allow comparison with peratures of the reactions hinder the approach to equiother metapelite melting studies mass balance calculations imply librium in addition melt fractions generated are typically the melting reaction muscovite biotite plagioclase quartz low resulting in small melt pockets which are very difficult melt alkali feldspar aluminosilicate garnet until to analyze with the electron microprobe in this study muscovite is exhausted 812 c then the reaction biotite we assess the possible genetic relationship between the plagioclase quartz alkali feldspar aluminosilicate tourmaline bearing granites of the harney peak suite melt garnet the inferred muscovite reaction is completed below and the aluminous metasediments these granites intrude 812 c and produces 1 2 wt melt melt production of the although the attempt to investigate the muscovite decontinuous biotite reaction increases steadily with rising temperature hydration melting reaction was hindered by the surto 32 wt in our highest temperature run the low melt prisingly low melt productivity we were able to infer a productivity of the muscovite reaction at 10 kbar suggests that balanced reaction illuminating the dominantly peritectic melting at lower pressures may be necessary to generate mobile melt nature of fluid absent muscovite breakdown under the fractions by muscovite dominated reactions in our starting material conditions investigated in addition melts of hp 60 1 are considerably more mafic than isotopic and trace element studies indicate a genetic the tourmaline bearing granites with average combined tio2 relationship between s type granites and aluminous metamgo feo contents of 1 85 wt and 0 84 wt respectively sediments in the black hills of south dakota where the in particular melts of hp 60 1 are enriched in ti and would harney peak granite hpg intruded proterozoic and probably stabilize biotite rather than tourmaline upon cooling archean schists and metagreywackes undergoing regional arguing against hp 60 1 as a potential source rock for the metamorphism the timing and mode of emplacement of tourmaline granites the hpg and the deformation and regional metamorphic

trenching studies of active faults in kamchatka eastern russia palaeoseismic tectonic and hazard implications the central part of the kamchatka peninsula is characterized by a well defined depression associated with active volcanism aligned ne sw on the east the depression is bounded by a prominent system of active faults known as the east kamchatka fault zone ekfz in order to improve understanding of the behaviour and kinematic role of this fault zone a fieldwork programme including study of trenches was conducted in the north central part of this system aerial photograph analysis ground truthed indicates a westward fault dip with predominantly normal slip while lateral offsets of river terraces and stream channels demonstrate a combined dextral component over 20 excavated pits and natural exposures were examined to confirm a detailed tephra succession extending from the early holocene to recent historic eruptions this chronological framework then provided age control on five past faulting events recognised in three trenches these events took place at about 10 5 6 0 4 5 and in a two event succession within a short time span at 3 3 3 2 ka bp event clustering may be characteristic and fault length displacement values suggest earthquakes of m6 5 thus representing a significant new element in regional seismic hazard evaluations additional to events generated at the subduction interface the relatively long gap in faulting since the two most recent events may also be significant for hazard scenarios and there is a possible link between the faulting and volcanic activity in the depression overall the ekfz together with the nachiki transverse zone farther south is thought to define a regional scale block that is extending eastwards independently from the rest of kamchatka

seismicity of the bering strait region evidence for a bering block newly compiled russian and u s seismological data support an independent bering block in motion relative to the north american plate this motion is likely to be driven by the westward extrusion of southwestern alaska resulting from compression in southern alaska due to subduction of the pacific plate and terrane accretion seismicity extends from central alaska through the bering strait and into chukotka in eastern chukotka several southwest trends are evident some of which continue through the koryak highlands to kamchatka the seismicity outlines the bering block which includes most of the bering sea chukchi peninsula seward peninsula and parts of western alaska focal mechanisms young basaltic volcanism and normal faults in western alaska and chukotka indicate that the bering strait is under northeast southwest extension this in conjunction with thrust faulting in the koryak highlands indicates that the bering block is rotating clockwise relative to the north american plate