sub ice topography in patriot hills west antarctica first results of a newly developed high resolution fm cw radar system we present a newly developed high resolution frequency modulated continuous wave fm cw radar system for sounding the sub ice topography the system working in the frequency range from 200 to 400 mhz was developed to measure thickness and internal layers in cold ice with a resolution better than 1 m this system has the potential to measure accumulation rates an important input for improved knowledge of the mass balance of polar ice sheets first measurements for the test calibration and optimization of the new ice sounder were made in december 2005 near the ellsworth mountains specifically in patriot hills west antarctica at 80 18 s 81 22 w the complete radar system was installed on a ski mounted support frame and towed by hand across the ice surface the measurement results show the capability of this system to measure ice thickness up to 1000 m and to define internal layers within the ice body

experimental constraints on coesite abundances in eclogite and implications for the x seismic discontinuity we have experimentally tested the possibility that the coesite stishovite transition in eclogite bodies is responsible for the x discontinuity a locally observed low impedance jump in seismic wave velocities at 260 330 km depth we determined phase relations and free sio2 abundances in three natural analog eclogite compositions that simulate different subduction scenarios in terms of pressure temperature conditions and whether or not melt extraction occurred eclogitic compositions representing residues after either shallow or deep melting contain either no coesite or else too little 4 wt to produce the observed impedance contrast for the x discontinuity only an unmodified mid ocean ridge basalt morb composition was found to contain just enough coesite 6 8 wt to be consistent with the expected impedance contrast when it transforms to stishovite however we assert that morb cannot remain compositionally unmodified during subduction down to 300 km fluid loss due to dehydration reactions during the transformation from basalt to eclogite lowers bulk sio2 content in addition the morb wet solidus intersects the coesite stishovite boundary at 290 km implying that at greater depths a melt phase should be present before stishovite stability is reached our data indicate that melt generation is an efficient means of lowering the free sio2 content in the mineral assemblage this study also confirms previous work indicating that exsolution of sio2 from the ca eskola ca0 5alsi2o6 component in clinopyroxene is not a feasible mechanism for producing significant stishovite upon reaching its stability field we conclude that the coesite stishovite transition in eclogite bodies is not a viable petrological explanation for the x discontinuity

upper mantle seismic shear discontinuities of the pacific 1 shear wave impedance discontinuities are inventoried for eight paths connecting circum pacific earthquakes with seismic stations on hawaii and oahu in addition to the transition zone discontinuities we observe a consistent impedance decrease at a depth of 80 km that marks the transition from the fast seismic lid to the low velocity zone the interval over which this transition occurs is less than 30 km the requisite impedance decrease ascribed almost entirely to diminished velocities in the low velocity zone exceeds predictions for peridotite chemistries of appropriate lithospheric age in all cases the transition is better matched by lithosphere of roughly half of the true age four paths show clear evidence of the x discontinuity an impedance increase of 3 8 near 300 km depth the only viable explanations would require extensive eclogite or basalt depleted mantle in the upper mantle of the western pacific the impedance contrast of the 410 km discontinuity which depends on the modal fraction of mantle olivine does not signal the presence of either although a mixture of the two remains a possibility we find no evidence of a low velocity layer atop of the 410 km discontinuity if present it is either consistently thin 15 km highly variable in thickness topography in excess of 60 km or has little impedance contrast 2 3 with overlying mantle the apparent absence of melt atop the 410 km discontinuity an intermittent and weak 520 km discontinuity and a thinned transition zone are consistent with relatively dry conditions in the deep upper mantle of the central pacific

the eclogite garnetite transformation at high pressure and some geophysical implications mineral assemblages displayed by morb and alkali poor olivine tholeiites have been investigated over the pressure interval 4 6 18 gpa at 1200 c both compositions crystallize to form normal eclogites between 4 6 and 10 gpa and there is little change in the relative proportions of garnet and pyroxene over this range however the proportion of garnet increases rapidly above 10 gpa as pyroxene dissolves in the garnet structure and pyroxene free garnetites stishovite are produced by 14 15 gpa dependent upon composition the garnetite facies for both compositions possess zero pressure densities of 3 75 g cm3 implying that subducted oceanic crust remains appreciably denser than surrounding mantle to depths exceeding 600 km it is demonstrated that the seismic velocity distributions in the mantle between 400 and 650 km are inconsistent with anderson s hypothesis that this region is of eclogitic composition

ultrahigh pressure metamorphic rocks from the chinese continental scientific drilling project i petrology and geochemistry of the main hole 0 2 050 m the main hole mh of the chinese continental scientific drilling project ccsd in southern sulu has penetrated into an ultrahigh pressure uhp metamorphic rock slice which consists of orthogneiss paragneiss eclogite ultramafic rock and minor schist recovered eclogites have a uhp metamorphic mineral assemblage of garnet omphacite rutile phengite kyanite coesite epidote ultramafic rocks contain garnet olivine clinopyroxene orthopyroxene ti clinohumite phlogopite gneisses and schists contain an amphibolite facies paragenesis but their zircons have coesite garnet omphacite or jadeite and phengite inclusions indicating that eclogites and gneisses have been subjected to in situ uhp metamorphism using available geothermobarometers p t estimates of 3 1 4 4 gpa and 678 816 c for eclogites were obtained if surface outcrops and neighboring shallow drill holes are considered together we suggest that a huge supracrustal rock slab 50 km long 100 km wide 5 km deep was subducted to a depth 100 km and then exhumed to the surface the depth interval 0 2 050 m of the ccsd mh can be divided into six lithological units unit 1 consists of alternating layers of quartz rich and rutile rich eclogites with thin interlayers of gneiss and schist eclogites of unit 1 are characterized by nb ta sr and ti depletions low mg number and general lree enrichment unit 2 comprises rutile and ilmenite rich eclogite and minor normal eclogite and is characterized by high tio2 total fe v co and sr and very low sio2 alkali zr ba nb ta and total ree contents and lree depleted ree patterns with slightly positive eu anomalies unit 3 contains ultramafic rock and minor mgo rich eclogite protoliths of uhp rocks from units 1 2 and 3 represent a layered mafic to ultramafic intrusion at crustal depth units 4 and 6 consist of interlayered eclogite and paragneiss the eclogites are characterized by th u nb ta and ti depletion and k enrichment and lree enriched ree patterns paragneisses show nb ta sr and ti depletions and lree enriched ree patterns occasionally with slightly negative eu anomalies indicating that their protoliths represent metamorphic supracrustal series unit 5 consists mainly of orthogneisses showing distinct nb ta sr and ti depletions and lree enriched ree patterns with pronounced negative eu anomalies suggesting granitic protoliths in conclusion it is proposed that the southern sulu uhp belt consists of a series of meta supracrustal rocks a layered mafic ultramafic complex and granites

eclogite facies relics and inferred ultrahigh pressure metamorphism in the north dabie complex central eastern china mineral assemblages and microstructures of a newly identified retrogressed eclogite sensu lato in the north dabie complex ndc central eastern china indicate early very high pressure metamorphic relics preserved in a dominant amphibolite facies host where no eclogite sensu stricto has been positively identified before the investigated eclogitic rock shows distinct multistage recrystallization with granulite and amphibolite facies assemblages overprinting eclogite facies relics the minimum temperature for the eclogite facies metamorphism is estimated to be 800 820 c a spectacular microstructure of oriented quartz needles 2 20 m wide 5 200 m long in matrix ca na clinopyroxene implies the prior existence of a non stoichiometric supersilicic omphacite stabilized at ultrahigh pressure uhp 25 kbar conditions although no coesite or coesite pseudomorphs have been found in the samples the absence of coesite may be due to the lack of free silica at uhp conditions or the consumption of silica during retrograde reactions the inferred uhp conditions metamorphism is further supported by sm nd ages that are equivalent to triassic metamorphic ages from uhp eclogites in the southeastern dabie mountains this finding expands the uhp terrane northward about 50 km spatial distribution of subduction collision related uhp rocks includes parts of the ndc

the orthorhombic to high p monoclinic phase transition in mg fe pyroxenes can it produce a seismic discontinuity the orthorhombic to high p monoclinic phase transition in mg fe sio 3 pyroxene with a mantle relevant composition x fs 0 1 is expected to occur at 300 km depth woodland and angel 1997 however the divariant nature of the phase transition in the mg fe system leaves the question open as to whether this transition occurs over a narrow enough pressure interval to cause a seismic discontinuity new experimental results with binary mg fe pyroxenes constrain the divariant loop to be 0 2 gpa wide at the composition of x fs 0 4 and on the order of 0 15 gpa for a mantle relevant composition this implies that the phase transition will be complete over a depth interval of about 5 6 km in the mantle and it is concluded that the divariant loop of the orthorhombic to high p monoclinic phase transition in mg fe sio 3 pyroxene is indeed narrow enough to produce a jump in seismic velocities the experimentally observed metastable behavior of orthopyroxene could further reduce the effective depth interval of this phase transition the expected location of this phase transition coincides with a small magnitude seismic discontinuity the x discontinuity occasionally observed in seismic profiles at 300 km depth and thus provides a viable petrologic explanation for the origin of this discontinuity if it truly exists

stability of anhydrous phase b experimental studies and implications for phase relations in subducting slab and the x discontinuity in the mantle 1 we have experimentally determined the equilibrium boundary of the reaction forsterite fo periclase per anhydrous phase b anh b at 900 1600 c and we used the retrieved gibbs free energy of formation of anh b to calculate the stability field of anh b stishovite sti with respect to the mg2sio4 polymorphs the results suggest the possibility of the reaction sequence wadsleytite anh b sti ringwoodite with increasing pressure at temperature below 600 c this might lead to an eye shaped splitting of the 410 km discontinuity within the interior of a sufficiently cold slab such as would prevail in a 140 myr old slab subducting at an angle of 60 with a rate of 14 cm yr e g tonga the equilibrium boundary of anh b sti with respect to the wadsleyite and ringwoodite has respectively positive and negative slope in the p t space the reaction of fo per to anh b seems to offer a viable explanation of the so called x discontinuity that has been observed at 275 345 km depth in several subcontinental and subduction zone environments it is suggested that periclase could form locally by the dissolution of silica in mantle fluid or precipitate from a hydrous melt that became enriched in mgo due to the incongruent melting of olivine at pressures of 6 8 gpa

the mineralogy and the origin of deep geospheres a review abstract the structure and composition of inner geospheres are considered in light of new data on the structural transformations of minerals under high pressure more than 100 tetrahedral complexes in silicates of the earth s crust give way to no more than 20 structural types of minerals of this class in the earth s mantle the main difference in their structures is associated with the transformation of si tetrahedra into si octahedra new data on the structural transformations of minerals in deep geospheres indicate that the mineralogical diversity of the earth s crust is substantially richer than that of deep geospheres however mantle mineralogy is not as primitive as was supposed even twenty or thirty years ago the results of recent seismological investigations and quantum mechanical calculations allow the assumption that there exists a new previously unknown phase transformation under the conditions in the earth s inner core according to seismic tomography maps for various depth levels and available data on geophysical discontinuities mineral composition and phase transformations in the mantle it is proposed that the latter can be subdivided into six geospheres the cornerstone of the new concept lies in the recognition of middle mantle between 840 and 1700 km which is separated from the upper and lower mantle by boundary zones 170 and 500 km thick respectively the first approach to the origin and geological history of deep seated geospheres is discussed

density of morb eclogite in the upper mantle in order to study the role of eclogite subducted oceanic crust in geodynamics we carried out high pressure experiments on natural mid oceanic ridge basalt morb using a multi anvil apparatus we determined phase relations of morb as a function of pressure and temperature in the temperature range of 1200 1700 c and pressures from 5 to 14 gpa the present results differ from a previous high pressure study of morb earth planet sci lett 77 1986 245 conducted at 1200 c as follows 1 coesite coe or stishovite st appears throughout the studied pressure range and 2 the clinopyroxene garnet cpx gar ratio is smaller particularly in the low pressure range 12 gpa our results show that the calculated bulk density of subducted oceanic crust increases discontinuously at around 9 gpa due to the coesite stishovite phase transition the density is considerably higher than estimates based on the previous experiments at pressures less than 12 gpa thus the role of eclogite in driving subduction should be more important than previously thought on the other hand the density difference between peridotite and eclogite in ascending mantle plumes becomes smaller as temperature increases a result of the increase in clinopyroxene garnet sio2 ratio in eclogite with increasing temperature as eclogite is still denser than peridotite even under subsolidus conditions recycled oceanic crust entrained in ascending plumes must be sustained by the upward flow of ambient peridotite in mantle plumes

fate of the subducted farallon plate inferred from eclogite xenoliths in the colorado plateau we present the first finding of the high pressure mineral coesite in lawsonite bearing eclogite xenoliths from the colorado plateau united states the presence of coesite in these xenoliths supports the hypothesis that the eclogite formed in a low temperature high pressure environment such as envisaged inside subducted oceanic lithosphere ion microprobe u pb dating of micrometer scale zircons in the eclogites yields ages ranging from 81 ma to 33 ma the two extremes in age likely indicating the age of crystallization during subduction related metamorphism and the age of recrystallization by the host magmatic event respectively these observations conclusively demonstrate that certain eclogite xenoliths from the colorado plateau originated as fragments of the subducted farallon plate which had been residing in the upper mantle since the late cretaceous this is the first conclusive evidence that any eclogite xenoliths can be directly linked to a known subducted plate

broadband array observations of the 300 km seismic discontinuity 1 intermittent seismic discontinuities near 250 300 km depth beneath south america and the pacific basin are detected with high resolution seismic array methods that use ss and pp precursors recorded at the high lava plains seismic experiment and the earthscope transportable array the transformation of coesite to stishovite in an eclogite rich mantle composition produces a seismic discontinuity near 300 km depth lateral changes in basalt fraction of the upper mantle will thus produce an intermittent seismic discontinuity the sensitivity of the precursors to intermittent seismic structure is addressed using an axisymmetric finite difference model of wave propagation in the mantle these numerical experiments find that the precursors are sensitive to structures 500 km in lateral extent and that the observations of this discontinuity are plausibly tied to lateral variations in basaltic composition of the upper mantle related to dynamics such as plumes and subduction

eclogite facies relics and a multistage breakdown in metabasites of the ktb pilot hole ne bavaria implications for the variscan tectonometamorphic evolution of the nw bohemian massif complex reaction textures in coronitic metagabbros and retrograded eclogites of the ktb pilot and an adjacent drilling provide evidence for a multistage metamorphic history in the variscan basement of the nw bohemian massif the eclogites show complete metamorphic recrystallization leaving no textural or mineral relics of their igneous precursors in contrast textural relics of the igneous protolith are still preserved in the metagabbros where the metamorphic overprint under high pressure conditions achieved only partial replacement of the initial assemblage plagioclase augite amphibole olivine or orthopyroxene ilmenite to form the eclogite facies assemblage garnet omphacite kyanite zoisite quartz rutile the garnets in the metagabbros occur in the typical necklace fashion at the borders between the original plagioclase and mafic phase domains in the same rocks omphacite formed by a topotactic reaction mechanism replacing igneous augite as well as in smaller grains at the margins of the texturally igneous clinopyroxene where it occurs without fixed orientation with respect to the relict phase both eclogites and metagabbros show a partial breakdown under high pressure granulite transitional to high pressure amphibolite facies conditions during which omphacite broke down to vermicular symplectites of diopside plagioclase a later pervasive medium pressure metamorphism under amphibolite facies conditions led to the development of assemblages dominated by hornblende plagioclase titanite phases prevailing in the overwhelming majority of the surrounding metabasites subsequent vein associated retrogression produced minerals typical of the greenschist to zeolite facies all metamorphic stages may be represented in a single thin section but although the overall reaction sequence is apparent the obvious disequilibrium in the rocks makes the use of conventional geothermobarometry difficult however calculations made by assuming an approach to domainal equilibrium show that both the eclogite facies and early breakdown occurred above 10 kb as the metamorphic unit hosting these particular metabasites is generally characterized by pressures below 10 kb these results have important implications for understanding the tectonometamorphic evolution of the region the relationship between the studied rocks and other units in the nw bohemian massif exhibiting a multistage metamorphic evolution is discussed and possible tectonic models evaluated

experimental study on the non darcy flow characteristics of soil rock mixture this study aims at investigating the flow characteristics of soil rock mixtures srm with different rock block percentage a self developed servo controlled permeability testing system was developed and used to carry out the permeability testing cylindrical srm specimens 50 mm diameter and 100 mm height with staggered rock block proportions 20 30 40 50 60 and 70 by mass were produced via compaction tests with different hammer strike counts to roughly insure the same void ratio from the test results the non darcy flow characteristic of srms was first proposed the relationship between hydraulic gradient and the seepage velocity obeys a power function with good correlation the increasing trend of the seepage velocity gets much more obvious with increasing hydraulic gradient with the increase of the rock block percentage the average permeability coefficient decreases to a minimum at a rock block percentage of 40 as the rock block percentage continues to increase above 40 the permeability increases again the critical hydraulic gradient decreases gradually with the increase of rock block percentage the variation of permeability for srm specimens is the result of soil matrix properties combined with rock blocks and rock soil interfaces the research results can be helpful to predict the subsurface erosion and piping hazards in soil rock mixture stratum

quartz exsolution in clinopyroxene is not proof of ultrahigh pressures evidence from eclogites from the eastern blue ridge southern appalachians u s a oriented quartz needles in clinopyroxene have become one of the diagnostic indicators of ultrahigh pressure uhp metamorphism the presence of apparently exsolved quartz is taken as evidence of decompression of a non stochiometric ca eskola component ca0 5 0 5alsi2o6 caes that is presumed to be stable only at uhp conditions eclogite from the eastern blue ridge north carolina contains clinopyroxene jd20cats5ac5caesdi65hd5 with oriented needles of quartz and calcic amphibole that appear to have exsolved together the quartz amphibole intergrowths are surrounded by 1 5 m haloes of neoformed pyroxene jd10cats10ac5caesdi70hd5 the modes of quartz amphibole and clinopyroxene haloes were determined using bse images and reintegrated with the host clinopyroxene viewing the quartz and amphibole needles down the c axis of the pyroxene host provides a better estimate of their proportions than in prismatic sections reintegrated pyroxene compositions were nearly identical to the analyzed host pyroxene with no caes component clinopyroxene with caes solid solution has been repeatedly synthesized at uhp conditions however examination of the phase equilibria usually cited as evidence for caes stability at conditions of 25 kbar shows that clinopyroxene with 10 mol caes is stable well within the quartz field and provides a pressure minimum similar to the albite jadeite quartz barometer exsolution of quartz and associated amphibole is commonplace in clinopyroxene from the blue ridge eclogite that lacks coesite or other evidence for uhp metamorphism the presence of a diluted 5 10 caes component in clinopyroxene does not require uhp conditions

adiabatic temperature profile in the mantle abstract the temperature at the 410 km discontinuity is re evaluated by comparing the depth of the discontinuity with the olivine wadsleyite transition pressure obtained using in situ x ray diffraction experiments by katsura et al 2004a and equation of state eos of mgo by tange et al 2009 tange scale and matsui et al 2000 the newly estimated temperature is 1830 48 k 70 k higher than that by our previous estimation the eoses of the major mantle minerals olivine wadsleyite ringwoodite and perovskite are also recalculated using the tange scale the adiabatic temperature gradient is calculated using the thermal expansion coefficient obtained from these eoses the adiabatic temperature gradient gradually decreases with increasing depth without a phase transition and abruptly increases in association with phase transitions the adiabatic temperature gradients are found to be 04 0 5 and 0 3 k km in the upper and lower parts of the mantle respectively the temperatures at a depth of 200 km the bottom of the mantle transition zone the top of the lower mantle and a depth of 2700 km are found to be 1720 40 2010 40 1980 40 and 2730 50 k the mantle potential temperature is found to be 1610 35 k

estimating unconfined compressive strength and elastic modulus of a fault breccia mixture of weak blocks and strong matrix determination of the compressive strength and elastic modulus of rocks from direct methods requires a large number of regularly shaped specimens weak rocks are usually not suitable for preparing smooth specimens and at best the preparation of such specimens is tedious time consuming and expensive fault breccias have very poor engineering properties and fall within the category of weak rocks these rocks usually cause problems not only in construction works but also in slopes or in underground works for this reason knowing the physical and mechanical properties of fault breccia is very important in rock engineering however little published material on the geomechanical properties of fault breccias is available geomechanical characterization of complex geological mixtures of competent blocks and weak matrix geomaterials such as melanges sheared serpentinites fault rocks and coarse pyroclastics is relatively new the term block in matrix rocks for complex geo materials was firstly described by raymond 1 as blocks of one lithology enclosed in materials of another lithology medley 2 introduced the term bimrocks a contraction of the term block in matrix rocks and defined a bimrock as a mixture of rocks composed of geotechnically significant blocks within a bonded matrix of finer the expression geotechnically significant means that there is mechanical contrast between blocks and matrix such as the ratio tan block tan matrixx2 the range in block sizes is between 5 and 75 of the characteristic

fill placement on slopes underlain by franciscan melange distress in two housing developments was caused by a deep bedrock landslide triggered by placement of a large upslope fill the large fill was placed to create a visual barrier between the upslope development and downslope housing developments and to balance the cut and fill quantities for the upslope site this case history presents some of the ramifications of fill placement on natural slopes surrounded by urban areas such as overstressing underlying weak material that may exist below the depth of borings typically conducted for single family residences and office complexes the importance of surface and subsurface information in a formation known locally as franciscan complex melange which is a block in matrix rock formation common to the area the shear behavior of serpentinite which is part of the franciscan complex and the importance of natural and man made changes to a slope such as rainfall surficial grading home construction and fill placement it also illustrates the importance of locating the critical slope cross section before construction and the proper use of back analyses in a landslide investigation doi 10 1061 asce gt 1943 5606 0000394 2011 american society of civil engineers ce database subject headings landslides shear strength slope stability subsurface investigations case studies fills author keywords landslides shear strength slope stability subsurface investigation serpentinite franciscan complex melange block in matrix rock

evaluating the geomechanical properties of misis fault breccia turkey abstract this study investigated the correlations between the uniaxial compressive strength ucs elastic modulus e or the differential stress and density p and s wave velocity volumetric block proportion vbp average block diameter d block average block diameter factor abdf aspect ratio and roundness the results were evaluated by both simple and multiple regression analysis simple regression analysis results show no correlation between ucs e or and the other examined parameters except s wave velocity a correlation was however found between ucs and s wave velocity for 25 and 75 vbp other significant models including density p and s wave velocity and textural properties for the prediction of ucs and were found by multiple regression analysis from these results it is concluded that the strength of the misis fault breccia cannot be defined by a single parameter such as vbp as is the case for some bimrocks it is also concluded that the models developed by multiple regression analysis can be used to predict the ucs and of the misis fault breccia the multiple regression models including two or three independent variables are the most practical equations using these equations to predict the ucs and of the fault breccia is easier faster and cheaper than conducting triaxial or uniaxial compressive strength tests

the contribution of geostatistics to the characterisation of some bimrock properties abstract this paper introduces a geostatistical approach for characterising the morphological and spatial variability of rock inclusions in bimrocks and for attempting their direct mechanical characterization through an indirect description deduced by image analysis of outcrop images the study was carried out on the shale limestone chaotic complex slcc bimrock which is affected by several slope stability problems in the disused santa barbara open pit mine tuscany italy due to its complex heterogeneity the mechanical characterization of slcc was based on a limited number of non conventional shear tests bimtests due to the relevant influence of rock inclusions on bimrock strength the study focused on identifying the possible image parameters characterising content and variability of rock inclusions in each sampled picture a two step analysis was carried out for a identification of an image parameter centimetric scale that is able to grasp some property of rock fragment shape and size spatial distribution b verification of the correlation at the outcrop scale multimetric scale between the bimrock strength parameters and the new regionalised variables rev describing image properties related to rock fragment distribution a geostatistical approach was adopted for both steps but applied to two different problems at two different scales with different variables an extensive sampling of outcrop pictures was carried out and a variogram analysis was performed on the rock fragment indicator variable i b x y defined at the image scale and obtained through the digital segmentation of the collected pictures a very good link was observed between the geostatistical model parameters and the content size and spatial variability of rock fragments shown in every picture the values of the total sill of the block indicator variograms were then assumed as a new rev c tot x y defined all over the sllc outcrop a cross covariance was computed between the variogram total sill and the friction angle x y and cohesion c x y at the scale of the whole outcrop area and a preliminary analysis showed a likely correlation

experimentally based water budgets for dehydrating slabs and consequences for arc magma generation phase diagrams of hydrous mid ocean ridge mor basalts to 330 km depth and of hydrous peridotites to 250 km depth are compiled for conditions characteristic for subduction zones a synthesis of our experimentally determined phase relations of chlorite lawsonite epidote zoisite amphibole paragonite chloritoid talc and phengite in basalts and of phase relations from the literature of serpentine talc chlorite amphibole and phase a in ultramafics permits calculation of h2o contents in hydrous phase assemblages that occur in natural compositions this yields the information necessary to calculate water budgets for descending slabs starting from low grade blueschist conditions 10 20 km depth with h2o contents between 5 and 6 wt for hydrated oceanic crust complete dehydration is achieved between 70 and 300 km depth as a function of individual slab geotherms hydrous phases which decompose at depth below volcanic arcs are lawsonite zoisite chloritoid and talc phengite in mafic compositions and chlorite and serpentine in peridotite approximately 15 35 of the initially subducted h2o are released below volcanic arcs the contribution of amphibole dehydration to the water budget is small 5 20 and occurs at relatively shallow depth 65 90 km in any predicted thermal structure dehydration is a combination of a stepwise and a continuous process through many different reactions which occur simultaneously in the different portions of the descending slab such a dehydration characteristic is incompatible with single phase dehydration models which focus fluid flow through a unique major dehydration event in order to explain volcanic fronts as a consequence of continuously progressing dehydration water ascending from the slab will be generally available to depth of ca 150 200 km the fluid rising from the subducting lithosphere will cause partial melting in the hot portion of the mantle wedge we propose that the volcanic front simply forms above the mantle wedge isotherm where the extent of melting is sufficient to allow for the mechanical extraction of parental arc magmas thermal models show that such an isotherm ca 1300oc locates below volcanic fronts slab surface depths below such an isotherm are compatible with the observed depths of the slab surface below volcanic fronts 1998 elsevier science b v all rights reserved

evaluating safety of concrete gravity dam on weak rock scott dam scott dam is owned and operated by pacific gas electric co pge this condition caused design changes during construction numerous subsequent special investigations and several corrections and additions a main stumbling block to clarification of the dam safety issue for scott dam has always been difficulty in characterizing the foundation material this paper discusses an approach to this problem as well as how the safety of the dam was subsequently confirmed following a comprehensive program of research investigations and analysis from 1991 to 1997

elevation change and ice flow at horseshoe valley patriot hills west antarctica patriot hills is located at 80 18 s 81 22 w at the southernmost end of the heritage range ellsworth mountains west antarctica a comparison of glacier elevation data and ice velocities obtained by the differential global positioning system in the period 1996 97 is presented ablation accumulation rates measured at a network of stakes in horseshoe valley show average accumulation of 70 kg m 2 a 1 in the central part of the valley and a maximum ablation of 170 kg m 2 a 1 at the edge of the blue ice area close to patriot hills changes in the surface elevation of the glacier measured at 81 stakes in the period 1995 97 show a mean thickening of 0 43 0 42 m a 1 which considering the uncertainties indicates that the ice sheet around patriot hills is in near steady state surface velocities in combination with ice thicknesses obtained by ground based radio echo sounding are used to compute the ice flux across the horseshoe valley transect a total outflow of 0 44 0 08 km 3 a 1 is obtained considering a catchment area for horseshoe valley of 1087 km 2 upstream from the flow transect and a net accumulation rate of 100 kg m 2 a 1 a total input of 0 11 0 04 km 3 a 1 by snow accumulation is obtained accepting a near equilibrium condition for the ice sheet the flux difference i e 0 33 km 3 a 1 must be supplied by flow from the inland ice sheet through ice cliffs located in mountain gaps in the heritage range if horseshoe valley is not in steady state but is thickening the positive mass balance could be due to increased snow accumulation or enhanced ice flow from the interior of the ice sheet new data are needed to elucidate this

an approach to predicting the overall strengths of unwelded bimrocks and bimsoils the strength of geological materials is a fundamental property used in the design of civil engineering works including projects constructed in complex geological mixtures or fragmented rocks such as melanges fault rocks coarse pyroclastic rocks breccias and sheared serpentines these and other often chaotic mechanically and or spatially heterogeneous rock masses are composed of relatively strong rock blocks surrounded by weaker matrix rocks these common rock mixtures known as bimrocks block in matrix rocks or bimsoils when the matrix material is soil like are very difficult to evaluate it is almost impossible to recover high quality undisturbed drill core samples or to prepare laboratory specimens perform laboratory studies and evaluate geomechanical parameters such as cohesion internal friction angle and uniaxial compressive strength from these complex mixtures there is sparse literature describing empirical and laboratory studies on strength of bimrocks hence this study was devised to develop a preliminary bim strength criterion a generalized conceptual empirical approach for predicting the overall strength of unwelded bimrocks and bimsoils the approach considered fundamental rules of rock and soil mechanics and the reported mechanical behavior of bimrocks as a function of volumetric block proportion vbp as reported in literature in addition cores of artificial bimrock were prepared in the laboratory for uniaxial and triaxial compression testing empirical equations useful for predicting the strength of bimrocks were devised which depend on practical charts and input parameters such as parameter a defined to relate the contact strength between matrix and blocks the predictive equations were calibrated by using the literature database the predictive performance of the preliminary bim strength criterion for bimrocks and bimsoils was checked by using the established database and was found to have high predictability although erring slightly on the conservative side