characteristics of the antarctic surface mass balance 1958 2002 using a regional atmospheric climate model temporal and spatial characteristics of the antarctic specific surface mass balance ssmb are presented including its components solid precipitation sublimation deposition and melt for this purpose we use the output of a regional atmospheric climate model racmo2 ant horizontal resolution of 55 km for the period 1958 2002 racmo2 ant uses european centre for medium range weather forecasts ecmwf 40 year re analysis era 40 fields as forcing at the lateral boundaries racmo2 ant underestimates ssmb in the high interior of east and west antarctica and overestimates ssmb on the steep coastal slopes otherwise the modeled spatial pattern of ssmb is in good qualitative agreement with recent compilations of in situ observations large scale patterns like the precipitation shadow effect of the antarctic peninsula are well reproduced and mesoscale ssmb patterns such as the strong precipitation gradients on law dome are well represented in the model the integrated ssmb over the grounded ice sheet is 153mmw e a 1 for the period 1958 2002 which agrees within 5 with the latest measurement compilations sublimation and melt remove 7 and

atmospheric processes and climatological characteristics of the 79n glacier northeast greenland abstractthe nioghalvfjerdsfjorden glacier the 79 fjord henceforth referred to as 79n has been thinning and accelerating since the early 2000s as a result of calving episodes at the front of the

seasonal cycles of antarctic surface energy balance from automatic weather stations we present the seasonal cycle of the antarctic surface energy balance seb using 4 years 1998 2001 of automatic weather station aws data the four awss are situated on an ice shelf in the coastal and inland katabatic wind zone and the interior plateau of dronning maud land to calculate surface temperature we use a seb closure assumption for a surface skin layer modelled and observed surface have a root mean square difference of 1 8 k at the plateau aws corresponding to an uncertainty in the seb of 5 w m 2 and 1 k 3 w m 2 at the other sites the effect of wind speed sensor freezing on the calculated seb is discussed at all sites the annual mean net radiation is negative and the near surface air is on average stably stratified differences in the seasonal cycle of the seb are mainly caused by the different wind climates at the aws sites in the katabatic wind zone a combination of clear skies and strong winds forces a large wintertime turbulent transport of sensible heat towards the surface which in turn enhances the longwave radiative heat loss on the coastal ice shelf and on the plateau strong winds are associated with overcast conditions limiting the radiative heat loss and sensible heat exchange during the short antarctic summer the net radiation becomes slightly positive at all sites away from the cold interior the main compensating heat loss at the surface is sublimation in the interior summer temperatures are too low to allow significant sublimation to occur here surface heat loss is mainly due to convection

franciscan complex olistostrome at crescent city northern california an olistostrome and bounding turbidites are exposed within the late mesozoic franciscan complex along the crescent city california coastline facies grade in character from mutti ricci lucchi 1978 mixed facies b c and d to f the olistostrome to mixed a b and e progressing upwards within the franciscan stratigraphic section the facies f unit outcrop is up to 600 m thick and extends 12 km along strike it consists of oblate to tabular blocks up to 200 m in maximum dimension of greenstone tonalite radiolarian chert limestone phyllite and greywacke dispersed in a scaly argillite matrix the olistostromal origin of the unit is indicated by depositional contacts with bounding turbidites by the presence of abundant recycled sedimentary clasts within the unit and by the presence of sedimentary breccias and associated dismembered slump folded turbidites both within the olistostrome and among subjacent turbidites sandstones are chiefly feldspathic litharenites that were very likely derived from the partially dissected late mesozoic sierran klamath magmatic are franciscan rocks record an early pervasive layer parallel flattening strain in such features as extensional faults necking and pinch and swell structures several scales of extensional faulting account for the juxtaposition of turbidites of different facies and or with varying degrees of stratal disruption the formation of sandstone lozenges and the formation of scaly foliation in the olistostrome matrix the latter resulted from the juxtaposition of lenticles with varying concentrations of silt and clay these were ultimately derived from the finer divisions of turbidite beds that were incorporated into the olistostrome the presence of gradational contacts between some sandstone olistoliths and the olistostrome matrix and of sandstone dykes that intrude fractures and associated drag folded turbidite beds indicate that franciscan sediments were not lithified during their early deformation these sediments were deposited in either a trench or trench slope basin and were first deformed either by gravity collapse of the trench slope cover or less likely by vertical loading beneath the toe of the accretionary wedge they later were folded during internal shortening of the growing franciscan accretionary prism

well documented travel history of mesozoic pelagic chert in japan from remote ocean to subduction zone the mino tanba belt in southwest japan a segment of the cordilleran type orogenic chain of jurassic east asia is composed mainly of a middle upper jurassic subduction accretion complex in which triassic and lower jurassic bedded radiolarian cherts occur as large allochthonous units structurally interlayered with middle upper jurassic clastic rocks high resolution microfossil conodont and radiolaria research has identified very low average sedimentation rates of about 0 5 g cm 1000 yr in the chert units similar to those of modern pelagic sediments accumulated in open ocean environments judging from the low average sedimentation rate high purity of biogenic silica long duration of continuous deposition 50 m y and wide along strike extent 1000 km the bedded radiolarian cherts in the mino tanba belt are best understood as ancient pelagic sediments that accumulated in open ocean environments accordingly the alleged origin in smaller marginal basins is untenable upward lithologic change from bedded chert to overlying siliceous mudstone in the uppermost portion of chert sequences suggests the gradual landward approach of the oceanic plate toward a trench the tectonic interlayering of these cherts and coarse grained terrigenous elastics is a secondary feature that was added through duplexing underplating in the subduction zone on the basis of the primary stratigraphy and field occurrence of triassic bedded chert in the mino tanba belt newly proposed are an idealized oceanic plate stratigraphy and a generalized travel history of a cordilleran type bedded chert from its birth at a mid oceanic ridge to its demise at a subduction zone

retreating alpine glaciers increased melt rates due to accumulation of dust vadret da morteratsch switzerland the automatic weather station aws on the snout of the vadret da morteratsch switzerland has delivered a unique 12 year meteorological dataset from the ablation zone of a temperate glacier this dataset can be used to study multi annual trends in the character of the surface energy budget since 2003 there has been a substantial darkening of the glacier tongue due to the accumulation of mineral and biogenic dust the typical surface albedo in summer has dropped from 0 32 to 0 15 we have analysed the implications of the lowered albedo for the energy balance and the annual ablation for the 4 year period 2003 06 the decreased albedo caused an additional removal of about 3 5 m of ice calculations with an energy balance model show that the same increase in ablation is obtained by keeping the ice albedo fixed to 0 32 and increasing the air temperature by 1 7 k our analysis confirms that for retreating glaciers the deposition of dust from exposed side moraines on the glacier surface constitutes an important feedback mechanism the mineral dust stimulates the growth of algae lowers the surface albedo enhances the melt rates and thereby facilitates the further retreat of the glacier snout

spin state of ferric iron in mgsio3 perovskite and its effect on elastic properties abstract recent studies have indicated that a significant amount of iron in mgsio 3 perovskite pv is fe 3 fe 3 fe 10 60 due to crystal chemistry effects at high pressure p and that fe 3 is more likely than fe 2 to undergo a high spin hs to low spin ls transition in pv in the mantle we have measured synchrotron mossbauer spectroscopy sms x ray emission spectroscopy xes and x ray diffraction xrd of pv with all iron in fe 3 in the laser heated diamond anvil cell to over 100 gpa fe 3 increases the anisotropy of the pv unit cell whereas fe 2 decreases it in pv synthesized above 50 gpa fe 3 enters into both the dodecahedral a and octahedral b sites approximately equally suggesting charge coupled substitution combining sms and xes we found that the ls population in the b site gradually increases with pressure up to 50 60 gpa where all fe 3 in the b site becomes ls while fe 3 in the a site remains hs to at least 136 gpa fe 3 makes pv more compressible than mg endmember below 50 gpa because of the gradual spin transition in the b site together with lattice compression the completion of the spin transition at 50 60 gpa increases bulk modulus with no associated change in density this elasticity change can be a useful seismic probe for investigating compositional heterogeneities associated with fe 3

in situ sampled snow particle sizes of the east antarctic ice sheet and their relation to physical and remotely sensed snow surface parameters knowledge of snow properties across antarctica is important in estimating how climate could potentially influence the mass balance of the antarctic ice sheet however measuring these variables has proven to be challenging because appropriate techniques have not yet been developed and extensive datasets of field estimates are lacking the goal of this study was to estimate the relationship between field observed snow particle size parameters from across the east antarctic ice sheet and a suite of spatial datasets i e topography remote sensing data using a principal component analysis pca five snow particle size parameters were correlated to spatial datasets of the following five groups 1 relief properties such as elevation and slope 2 remote sensing data from moderate resolution imaging spectroradiometer modis and synthetic aperture radar sar sensors 3 spatially interpolated data i e 10 m maps of temperature and approximate snow accumulation in kg m 2 a 1 4 field retrieved data on surface roughness and 5 in situ elevation and distance from the coast the results show that the relief parameter slope correlated best with the snow particle length and area r 0 76 r 0 80 further the pca indicated that the different remote sensing parameters correlated differently with the size parameters and that the most common parameter in visual analysis particle length grain diameter is not always the optimal parameter to characterize the snow particle size as for example area correlates better to slope and aspect than length

thermally induced icequakes detected on blue ice areas of the east antarctic ice sheet over a year of seismic observations 5000 short duration icequakes were detected by a permanent broadband station installed at the princess elisabeth base located 180 km inland in eastern dronning maud land east antarctica icequake detection via seismic waveform pattern recognition indicates the presence of two dominating clusters of events totalizing 1500 icequakes the corresponding icequake locations point towards two distinct zones of outcropping blue ice areas bias located respectively at 4 and 1 km from the seismic station both on the leeward side of a nunatak protruding through the ice sheet the temporal occurrence of these icequakes suggests a close genetic link with thermal contraction of ice caused by significant surface cooling controlled in summer by variations in diurnal solar radiation and in winter by strong cooling during cold katabatic regimes further analysis demonstrates the dependence of these icequakes on the absolute surface temperature and on its temporal change besides providing information on the ice fracture mechanics and rheology investigations of thermal icequakes may be regarded as a ground based proxy for the monitoring of the thermal state of bias and characterization of ice sheet ablation zones

experimental evidence for perovskite and post perovskite coexistence throughout the whole d region article i nfo since the phase diagram for fe al bearing mgsio3 compositions at the p t conditions of the core mantle boundary remains ambiguous we investigated the fe distribution among the silicate perovskite pv and post perovskite ppv polymorphs using tandem synchrotron analyses of x ray diffraction and x ray absorption spectroscopy we performed measurements at the fe k edge of the partitioning of iron between pv and ppv up to more than 150 gpa after annealing at about 3300 k we obtain a unique solution for kfe pv ppv of 4 2 0 5 our results evidence that the two silicates should coexist over the whole d region with the main post perovskite phase being largely depleted in fe compared to the perovskite as fe and al have a dominant effect on the phase diagram these new results challenge recent determinations of the temperature profile in the lowermost mantle based on the clapeyron slope of the pv to ppv transition for pure mgsio3 composition also it appears clear that variations in the molar fractions of perovskite and post perovskite phases should be expected radially or laterally in the d region in relation with thermal or compositional heterogeneities this can help explaining the seismological anomalies observed for this mantle region finally we predict a significant increase of the feo activity in the d region which should greatly affect the chemical exchange between mantle and core

a middle permian middle triassic accretionary complex and a late triassic foredeep basin forerunners of an indosinian late triassic thrust complex in the thailand malaysia border area abstract the semanggol formation of nw peninsular malaysia is a middle permian late triassic sequence of predominantly radiolarian chert sandstone and mudstone including turbidites and conglomerate the belt of country occupied by this unit extends into thailand where various names including na thawi formation have been applied to its correlatives fossil evidence particularly radiolarian has established its age but also revealed that it is tectonically complex with numerous out of sequence slices interpreted here to be caused by thrusting the model proposed here involves initially in the middle permian accumulation in the oceanward part of an accretionary complex as palaeotethys began subducting beneath indochina east malaya this regime it is proposed continued until about the end of the middle triassic when sibumasu collided with indochina east malaya bringing an end to subduction but as crustal shortening continued into the late triassic a foredeep basin formed in front of the now inactive subduction zone and accretionary complex and the youngest part of the semanggol formation was deposited during this final stage the whole package of rocks comprising those in the accretionary complex and those deposited in the foredeep basin underwent lateral compression resulting in a thrust complex the semanggol formation and its thailand correlatives occupy part of a n s belt of imbricately thrust deeper water sediments which include slope deposited carboniferous and lower permian beds that belt is interpreted as a series of thrust slices juxtaposing rocks of different ages referred to here as the songkhla semanggol terrane its western boundary is a n s line of inferred thrusting which coincides with a major westward facies change to platform carbonates of middle permian to late triassic age called here the rattaphum kodiang tectonic line

in situ observations of phase transition between perovskite and cairo 3 type phase in mgsio 3 and pyrolitic mantle composition abstract in situ observations of the perovskite cairo3 phase transition in mgsio3 and in pyrolitic compositions were carried out using a laser heated diamond anvil cell interfaced with a synchrotron radiation source for pure mgsio3 the phase boundary between the orthorhombic mg perovskite and cairo3 type phases in the temperature range of 1300 3100 k was determined to be p gpa 130 3 0 0070 0 0030 t 2500 k using platinum as a pressure calibrant we confirmed that the cairo3 type phase remained stable up to pressures of at least 156 gpa and temperatures of 2600 k the consistency of our results with previous theoretical calculations leads us to conclude that the 2700 km seismic discontinuity at the bottom of the lower mantle can be attributed to a phase transition to the cairo3 type phase the phase change from an orthorhombic mg perovskite to a cairo3 type bearing assemblage in a pyrolitic mantle composition was also observed at p 125 gpa which corresponds to the same mantle depth as the seismic discontinuity the phase boundary between the orthorhombic mg perovskite and cairo3 type bearing assemblage was determined to be p gpa 124 4 0 008 0 005 t 2500 k using gold as a pressure calibrant this transition boundary indicates that the temperature at a depth of 2700 km is about 2600 k and the adiabatic temperature gradient in the lower mantle is estimated to be 0 31 k km the partition coefficients and the effect of some elements on the phase equilibrium between the orthorhombic mgsio3 perovskite and cairo3 type mgsio3 were estimated from ab initio calculations our experimental and theoretical results indicate that the d layer consists of a cairo3 type bearing assemblage which is likely to have significant effect on the chemical and thermal evolution of the earth s mantle

east flank of the sibumasu block in nw thailand and myanmar and its possible northward continuation into yunnan a review and suggested tectono stratigraphic interpretation abstract the east flank of the sibumasu block was a passive continental margin and in nw thailand is marked by the absence of the autochthonous middle permian triassic platform carbonates which are widespread across the rest of sibumasu further west instead the carbonates are represented by hemipelagic cherts mudstones and sandstones including turbidites during the northward drift of sibumasu following its early permian rifting from gondwana an accretionary complex was present where palaeotethyan pelagic rocks as old as devonian were subducted beneath the sukhothai volcanic arc at the time of sibumasu s collision with the sukhothai arc beginning in the middle triassic the accretionary complex was thrust westwards across the east flank of sibumasu it is suggested that in the late triassic the thrust pile which had been the accretionary complex underwent erosion and was the source of terrigenous clastic rocks deposited further west in a foredeep basin the boundary of sibumasu s east flank with the permo triassic carbonate platform further west is the arcuate mae ping nam teng fault system notwithstanding later cenozoic strike slip displacement those faults as well as the mae yuam fault are interpreted to have had an earlier history of westward directed indosinian thrusting northwards in myanmar and yunnan the sibumasu permo triassic carbonate shelf continues as the shan plateau and baoshan block the east flank is represented by the changning menglian belt and the palaeotethys cryptic suture in thailand possibly joins with the lancangjiang suture

surface layer response to topographic solar shading in antarctica s dry valleys 1 the effects of topographic shading on local flow transitioning and atmospheric surface layer properties are investigated using observational data from the miers valley one of the dry valleys of antarctica a unique data set was collected during a 9 day period in the summer of 2012 using an eddy covariance system and a sound detection and ranging that provided vertical profiles of wind and turbulence characteristics in the surface layer and the lower part of the boundary layer within the miers valley this data set is ideal for investigating the dynamics of flow transitioning due to topographic shading without the atmosphere experiencing complete darkness the lack of atmospheric humidity soil moisture and surface vegetation in the dry valleys creates an atmosphere within which the microclimatic responses are amplified and as a result the valley atmosphere is extremely sensitive to solar radiation the entire measured valley boundary layer up to 250 m above ground level feels the transition from an unstable to a stable stratification as the surface temperature drops by 10 c in response to the topographic shading wavelet analysis reveals the dynamics of flow deceleration stagnation and oscillations as the flow transitions from an unstable to a stable boundary layer the larger air mass along valley scales to the longer terrain fetch and as the shade is cast over the valley it retains some of the longer wavelengths of the flow the cross valley component influenced by the slopes is quicker to adjust to short period oscillations and takes around three more hours before it couples with the oscillatory pattern of the along valley flow

effect of pressure and composition on lattice parameters and unit cell volume of fe mg sio3 post perovskite we obtained unit cell volumes v for fe sub 0 2 mg sub 0 8 sio sub 3 and fe sub 0 4 mg sub 0 6 sio sub 3 post perovskite ppv over a pressure p range of 80 145 gpa by in situ x ray diffraction xrd measurements in laser heated diamond anvil cells dacs our study suggests that the ppv structure is highly resistant to back transformation to pv and fe sub 0 4 mg sub 0 6 sio sub 3 ppv was preserved down to 80 gpa upon laser heating during decompression before transforming to pure perovskite pv the bulk modulus k sub 0 of ppv was determined to be 215 1 and 198 1 gpa for fe sub 0 2 mg sub 0 8 sio sub 3 and fe sub 0 4 mg sub 0 6 sio sub 3 ppv respectively with a fixed k sub 0 4 the substitution of fe for mg in ppv results in the largest expansion along the b axis among all three axes and the expansion of the b axis is nearly independent of pressure whereas the expansion along the a and c directions slightly decreases with increasing pressure combining our results with previous studies on fe sub x mg sub 1 x sio sub 3 ppv x 0 0 09 0 1 shows that the bulk modulus of ppv decreases with increasing fe content over a composition range x 0 to 0 4 varying from 231 gpa for x 0more to 198 gpa for x 0 4 with zero pressure volumes scaled to composition v sub 0 angstrom sup 3 162 2 19 5x and fixed k sub 0 4 0 the increase of fe content in ppv from x 0 to 0 4 results in a 6 3 increase in density and a 5 3 decrease in bulk sound velocity at 130 gpa less

perspectives on the roles of melanges in subduction accretionary complexes a review abstract melanges play three principal overlapping roles in the architecture of subduction accretionary complexes sacs during and after sac formation first tectonic melanges serve as zones of concentrated deformation within and below the accreted rocks that are assembled during the subduction accretion process these melanges facilitate preservation of inter melange less deformed accretionary units aus beneath the trench side of the sac the initial deformation zone along the decollement at the top of the down going plate is marked by non melange tectonically dismembered formations or thinner units of scaly rock and breccia that separate accreted rocks above from the subducting rocks below olistostromal rocks may be incorporated into the decollement here in the mid arc to inner arc areas of the sac exotic block bearing melanges develop in zones of tectonic fragmentation and mixing of accreting ocean plate stratigraphy in mud diapirs and along out of sequence faults some of which facilitate uplift of high pressure rocks and serpentinite matrix melanges second after accretion the sedimentary tectonic diapiric and polygenetic melange units serve as single block or sheet architectural aus or subunits within larger accreted aus of the sac diapiric melanges and sedimentary olistostromal melanges formed in and above sac fault blocks respectively may become incorporated into the sac during ongoing deformation and become architectural units as well third melanges serve as post subduction stress guides that focus shear strain during continuing and post accretion deformation of sacs allowing ongoing modification of the sac during progressive deformation of the orogen examples of each type of role reveal the importance of all three processes in the current architecture of outer orogenic belts

element partitioning between magnesium silicate perovskite and ferropericlase new insights into bulk lower mantle geochemistry n this study we investigated iron magnesium exchange and transition metal trace element partitioning between magnesium silicate perovskite mg fe sio3 and ferropericlase mg fe o synthetised under lower mantle conditions up to 115 gpa and 2200 k in a laser heated diamond anvil cell recovered samples were thinned to electron transparency by focused ion beam and characterized by analytical transmission electron microscopy atem and nanometer scale secondary ion mass spectroscopy nanosims iron concentrations in both phases were obtained from x ray energy dispersive spectroscopy measurements and nanosims our results are the first to show that recently reported spin state and phase transitions in the lower mantle directly affect the evolution of fe mg exchange between both phases mg perovskite becomes increasingly iron depleted above 70 80 gpa possibly due to the high spin low spin transition of iron in ferropericlase conversely the perovskite to post perovskite transition is accompanied by a strong iron enrichment of the silicate phase ferropericlase remaining in the fe rich phase though nanoparticles of metallic iron were observed in the perovskite bearing runs suggesting the disproportionation of ferrous iron oxide but were not observed when the post perovskite phase was present implications on the oxidation state of the earth and core segregation will be discussed transition trace element ni mn concentrations determined with the nanosims show similar trends and could thus be used to trace the origin of diamonds generated at depth this study provides new results likely to improve the geochemical and geophysical models of the earth s deep interiors

subducted banded iron formations as a source of ultralow velocity zones at the core mantle boundary ultralow velocity zones ulvzs are regions of the earth s core mantle boundary about 1 10 kilometres thick exhibiting seismic velocities that are lower than radial earth reference models by about 10 20 per cent for compressional waves and 10 30 per cent for shear waves it is also thought that such regions have an increased density of about 0 20 per cent ref 1 a number of origins for ulvzs have been proposed such as ponding of dense silicate melt2 core mantle reaction zones3 or underside sedimentation from the core4 here we suggest that ulvzs might instead be relics of banded iron formations subducted to the core mantle boundary between 2 8 and 1 8 billion years ago consisting mainly of interbedded iron oxides and silica such banded iron formations were deposited in the world s oceans during the late archaean and early proterozoic eras we argue that these layers as part of the ocean floor would be recycled into the earth s interior by subduction5 sink to the bottom of the mantle and may explain all of the observed features of ulvzs

late cretaceous early tertiary palaeoclimates of northern high latitudes a quantitative view analyses of plant community structure vegetational and leaf physiognomy and growth rings and vascular systems in wood provide qualitative and quantitative data that can be combined to define non marine palaeoclimatic parameters with better resolution than is available from other principally sedimentological methods application of these techniques to cenomanian through paleocene floras from high palaeolatitudes 75 85 n indicates a polar light regime similar to that of the present plant data suggests cenomanian sea level mean annual air temperatures mats of 10 c and mats of 13 c 5 c and 6 7 c in the coniacian maastrichtian and paleocene respectively evapotranspirational stresses at sea level were low and precipitation was in most part uniform throughout the growing season in the cenomanian with possible seasonal drying occurring by the maastrichtian maastrichtian winter freezing was likely but periglacial conditions did not exist at sea level permanent ice was likely above 1700 m at 75 n in the cenomanian and above 1000 m at 85 n in the maastrichtian these near polar data provide critical constraints on global models of late cretaceous to early tertiary climates

temperatures heating rates and vapour pressures in near surface snow at the south pole a finite volume model is used to simulate 9 years 1995 2003 of snow temperatures at the south pole the upper boundary condition is skin surface temperature derived from routine upwelling longwave radiation measurements while the lower boundary condition is set to the seasonal temperature gradient at 6 5 m depth taken from prior measurements at the south pole we focus on statistics of temperature heat fluxes heating rates and vapour pressures in the top metre of snow but present results from the full depth of the model 6 5 m the monthly mean net heat flux into the snow agrees with results from previous studies performed at the south pole on shorter timescales the heating rates and vapour pressures show large variability the net heat flux into the snow which is between 5wm 2 in the monthly mean can be greater than 20 w m 2 on hourly timescales on sub daily timescales heating rates exceed 40 k d 1 in the top 10 cm of the snow subsurface temperatures and therefore heating rates are more variable during winter april september due to increased synoptic activity and the presence of a strong surface based atmospheric temperature inversion the largest vapour pressures 60 70 pa and vertical gradients of vapour pressure are found in the top metre of snow during the short summer december january in contrast during the long winter the low temperatures result in very small vapour pressures and insignificant vapour pressure gradients the high summertime vapour pressure gradients may be important in altering the isotopic composition of snow and ice on the antarctic plateau

the postperovskite transition the discovery of the postperovskite ppv transition has profound impact on our understanding of the core mantle boundary cmb region unlike perovskite pv the ppv phase has a layered structure of the sio6 octahedra which may lead to a large contrast in some properties with pv recent studies have proposed unusual properties of ppv such as a large positive clapeyron slope a large sensitivity of the transition depth to iron a decrease in bulk sound speed at the transition and a development of significant lattice preferred orientation many of the proposed properties can provide explanations for the intriguing seismic observations at the cmb region yet significant discrepancies still exist however rapid developments in mineral physics will continue to improve our knowledge on the changes across the ppv transition

diverse sources for igneous blocks in franciscan melanges california coast ranges igneous blocks in franciscan melanges are of three chemical petrologic types 1 tholeiitic basalts of both arc and spreading center origin with depletions in light relative to heavy rare earth elements 3 tio 2 1 high y zr and y ti ratios and relict augites that generally have low al and ti and well defined iron enrichment trends 2 basalts of probable seamount origin with marked enrichments in light relative to heavy rare earth elements 5 tio 2 1 lower y zr and y ti than 1 and ti al rich augites showing little if any iron enrichment trends and 3 hypabyssal intrusives having sio 2 52 tio 2 1 flat or only slightly fractionated rare earth abundance patterns and diopsidic augites that are very low in ti and al and show no iron enrichment trends all of the blocks are metamorphosed most are undeformed pumpellyite bearing greenstones and a few contain sodic amphibole lawsonite sodic pyroxene the melanges are probably olistostromal in origin deriving the

surface energy balance in the ablation zone of langfjordjokelen an arctic maritime glacier in northern norway glaciers in northern and southern norway are subject to different daily and seasonal cycles of incoming solar radiation which is presumably reflected in the importance of net solar radiation in their surface energy balance we present a 3 year continuous record from an automatic weather station in the ablation zone of the ice cap langfjordjokelen one of the most northerly glaciers of mainland norway despite its location at 708 n langfjordjokelen was found to have a maritime climate with an annual mean air temperature of 1 08c frequent cloud cover and end of winter snow depths over 3m in all three years the main melt season was may october but occasional melt events occurred on warm cloudy winter days net solar and longwave radiation together accounted for 58 of the melt energy with a positive contribution by net longwave radiation 7 the sensible and latent heat fluxes supplied the remainder of the melt energy cloud optical thickness over langfjordjokelen was larger than on two glaciers in southern norway especially in the summer months this resulted in a smaller contribution of net solar radiation to surface melt on langfjordjokelen the effect of the higher latitude on net solar radiation was found to be small

pervasive near surface stratal disruption in an accretionary prism setting kaczawa complex sw poland the tectonized and metamorphosed mudrocks within the variscan accretionary prism of the kaczawa mountains in sw poland comprise sedimentary melanges together with more coherent stratigraphic units some represent large olistoliths deposited in a submarine trench we infer a trend of progressive near surface stratal disruption in mud dominated deposits due to dewatering that forms a continuum with subduction related tectonic structures imposed on unconsolidated sediment during deeper burial the assemblage of characters suggests that an accretionary prism environment can influence and leave characteristic traces of the total burial history of a trench succession

iron rich perovskite in the earth s lower mantle the equations of state of perovskite with mg sub 0 75 fe sub 0 25 sio sub 3 and mgsio sub 3 compositions have been investigated by synchrotron x ray diffraction up to 130 gpa at 300 k in diamond anvil cells here we show that the addition of 25 fe in mgsio sub 3 perovskite increases its density and bulk sound velocity v phi by 4 6 and 6 7 respectively at lower mantle pressures based on concurrent synchrotron x ray emission and moessbauer spectroscopic studies of the samples the increase in v phi and density can be explained by the occurrence of the low spin fe3 and the extremely high quadrupole component of fe sup 2 combining these experimental results with thermodynamic modeling our results indicate that iron rich perovskite can produce an increase in density and a value of v phi that is compatible with seismic observations of reduced shear wave velocity in regions interpreted as dense stiff piles in the lower mantle therefore the existence of the fe rich perovskite in the lower mantle may help elucidate the cause of the lower mantle large low shear velocity provinces llsvps where enhanced density and v phi are seismically observed to anti correlate with the reduced shear wave velocity

firn air depletion as a precursor of antarctic ice shelf collapse since the 1970s the sudden rapid collapse of 20 of ice shelves on the antarctic peninsula has led to large scale thinning and acceleration of its tributary glaciers the leading hypothesis for the collapse of most of these ice shelves is the process of hydrofracturing whereby a water filled crevasse is opened by the hydrostatic pressure acting at the crevasse tip this process has been linked to observed atmospheric warming through the increased supply of meltwater importantly the low density firn layer near the ice shelf surface providing a porous medium in which meltwater can percolate and refreeze has to be filled in with refrozen meltwater first before hydrofracturing can occur at all here we build upon this notion of firn air depletion as a precursor of ice shelf collapse by using a firn model to show that pore space was depleted in the firn layer on former ice shelves which enabled their collapse due to hydrofracturing two climate scenario runs with the same model indicate that during the 21st century most antarctic peninsula ice shelves and some minor ice shelves elsewhere are more likely to become susceptible to collapse following firn air depletion if warming continues into the 22nd century similar depletion will become widespread on ice shelves around east antarctica our model further suggests that a projected increase in snowfall will protect the ross and filchner ronne ice shelves from hydrofracturing in the coming two centuries

a study of the surface mass balance in dronning maud land antarctica using automatic weather stations we use data from four automatic weather stations awss in dronning maud land east antarctica to study the surface mass balance and its components distinct differences were found between the moisture climates of the high plateau the katabatic wind zone and the coastal ice shelves significant undersaturation occurs year round in the katabatic wind zone while on the high plateau and on the coastal ice shelf the air is usually close to saturation in summer absorption of shortwave radiation at the snow surface enhances surface sublimation at all sites removing 3 9 of the annual solid precipitation significant summer melting is an equally important ablation term near the coast but vanishes inland vertically integrated column drifting snow sublimation was estimated using two different methods this process appears to be similar to or greater in magnitude than surface sublimation because intervals between significant precipitation events may last as long as several months sublimation and melt cause extended periods of surface ablation in summer in summer all ablation processes together remove 15 56 of the solid precipitation or 6 27 on an annual basis

solar heating rates and temperature profiles in antarctic snow and ice observations of temperature maxima at about 10 cm depth in cold antarctic snow during summer have previously been explained by proposing that solar heating is distributed with depth whereas thermal infrared cooling is localized at the surface the solid state greenhouse an increase in temperature from the surface to 10 cm depth t 4 k found by rusin 1961 on the antarctic plateau was successfully reproduced by schlatter 1972 in a combined radiative transfer and heat transfer model

various types of olistostromes in a closing ocean basin tethyan himalaya cretaceous tibet abstract the cretaceous rocks of the central tethyan himalayas display different types of deep sea olistostromes and chaotic deposits which are accompanied by turbidites the deposits were incorporated into an accretionary prism and more or less deformed according to the composition and provenance of their clasts we distinguish four types of olistostromes 1 p type derived from the passive indian continental margin 2 po type derived from both the passive indian margin and ocean floor pelagic sediments and oceanic crust 3 poa type with clasts from the same sources as the po type but also containing material from the active margin along the lhasa block and 4 a and oa type mainly derived from the active margin accretionary prism and magmatic arc the occurrence of these different types of deep sea chaotic deposits in space and time is closely related to the evolution of the neo tethyan basin from a wide open ocean basin to a narrowing remnant and trench basin prior to collision whereas pure p type olistostromes formed when the basin was still wide predominating a type deposits characterize a late stage of basin evolution prior to collision mixed type olistostromes record an intermediate stage of basin evolution and require specific syn sedimentary tectonic activity

effects of fe enrichment on the equation of state and stability of mg fe sio3 perovskite fe rich natural orthopyroxenes with compositions of mg0 61fe0 38ca0 01 sio3 fe 38 and mg0 25fe0 74ca0 01 sio3 fe 74 were studied at pressures up to 155 gpa and temperatures up to 3000 k single phase orthorhombic gdfeo3 type perovskite was synthesized by heating to similar to 2000 k at 63 gpa for the fe 38 composition and at 72 gpa for the fe 74 composition at lower pressures heating both compositions resulted in a mixture of perovskite sio2 and mg fe o these measurements provide new constraints on the dependence of mg fe sio3 perovskite stability on pressure and composition upon further compression and heating at 89 and 99 gpa fe 38 and fe 74 perovskites transformed to two phase mixtures of perovskite and post perovskite consistent with previous findings that increasing fe content lowers the transition pressure the volume of mg fe sio3 perovskites increases linearly with fe content volume data were fit to the birch murnaghan equation of state the bulk modulus at 80 gpa is 550 560 gpa for both fe rich perovskites comparable to or slightly higher than the values measured for mgsio3 perovskite at this pressure indicating that the bulk modulus of perovskite is not strongly sensitive to fe content c 2012 elsevier b v all rights reserved

thermochemical structures beneath africa and the pacific ocean large low velocity seismic anomalies have been detected in the earth s lower mantle beneath africa and the pacific ocean that are not easily explained by temperature variations alone the african anomaly has been interpreted to be a northwest southeast trending structure with a sharp edged linear ridge like morphology the pacific anomaly on the other hand appears to be more rounded in shape mantle models with heterogeneous composition have related these structures to dense thermochemical piles or superplumes it has not been shown however that such models can lead to thermochemical structures that satisfy the geometrical constraints as inferred from seismological observations here we present numerical models of thermochemical convection in a three dimensional spherical geometry using plate velocities inferred for the past 119 million years we show that earth s subduction history can lead to thermochemical structures similar in shape to the observed large lower mantle velocity anomalies we find that subduction history tends to focus dense material into a ridge like pile beneath africa and a relatively more rounded pile under the pacific ocean consistent with seismic observations

the saint daniel melange evolution of an accretionary complex in the dunnage terrane of the quebec appalachians the saint daniel melange is part of a series of melanges located along the baie verte brompton line in the northern appalachians this line marks the suture between rocks of oceanic affinities and those of the ancient passive margin of north america with which they collided during the taconian middle to late ordovician orogeny the saint daniel melange contains a wide variety of lithologies including well bedded to dismembered sedimentary sequences pebbly mudstone olistostromes and slivers of igneous and metamorphic rocks black shales with interbeds of green shale calcareous siltstone or sandstone are the dominant units they exhibit various stages of melange formation such as those present in shallow parts of an accretionary complex units of oceanic origin include sediments derived from the forearc basin and slivers of an ophiolite and of a magmatic arc units derived from sediments of the passive margin of north america are also present the ratio between these various lithologies changes greatly within the melange on a kilometric scale along strike the saint daniel melange is a structural complex in which the various units were assigned a sequential order mimicking a stratigraphic order the saint daniel melange is interpreted as the relict of an accretionary complex because of its actual structural position within the northern appalachians and because all its lithologies and their structural fabric can be found in modern accretionary complexes

late cretaceous blueschist metamorphism in the indus suture zone shangla region pakistan himalaya abstract rb sr and 39ar 40ar phengitic muscovite dating of the transitional blueschist greenschist facies rocks from the shangla region of pakistan himalaya resulted in a concordant ca 80 ma age interpreted as a time of metamorphic peak 39ar 40ar age spectra of sodic amphiboles were unsuitable for precise age determination mass balance calculations show that the k concentration in glaucophane crossite is ca 25 ppm and the k ar budget is dominated by inclusions of phengitic muscovite e w oriented parallel to kohistan arc stretching lineation defined by preferred orientation of amphiboles was accompanied by synkinematic growth of riebeckite rims on the edges of microboudins evolution of the pressure conditions based on the al2o3 content in sodic amphibole shows that this deformational stage was accompanied by a decrease in pressure from ca 700 to ca 400 mpa this together with our dating results strongly suggests 10 km late cretaceous exhumation of the shangla blueschists the exhumation may have been associated with the increase of arc parallel displacement rate due to changes of arc obliquity this led to thinning caused by arc parallel extension and to exhumation of the shangla blueschists a lack of strong eocene metamorphic overprint implies that after the peak metamorphism blueschists were accreted to the kohistan arc which helped to prevent burial and metamorphism during continental collision the final emplacement of the shangla blueschists most likely occurred during the india kohistan arc collision and was accompanied by the weak locally developed greenschist facies overprint

late cretaceous to early tertiary structural elements of west kalimantan abstract recent geological and geophysical mapping in west kalimantan has allowed the definition of three domains with distinct geological and geophysical characteristics which were imprinted on the region by early cretaceous to eocene convergent tectonic events subduction related granitoids intruded low grade regional metamorphic rocks during the early cretaceous forming the schwaner mountains domain extending east west across the southern and central part of west kalimantan this is flanked in the northwest by a complex sequence of sedimentary and volcanic rocks ranging in age from late carboniferous to cretaceous which comprise the northwest kalimantan domain deformed cretaceous flysch deposits east of the northwest kalimantan domain form an accretionary complex representing the southern continuation of the extensive dominantly tertiary accretionary wedge in sarawak the boundary between the cretaceous accretionary domain and rocks of the northwest kalimantan domain is a fault which we interpret as a transform that marked the western limit of late cretaceous southward subduction beneath west kalimantan growth of the accretionary complex resulted in uplift of a ridge of melange and flysch deposits on which a half graben extensional basin formed and accumulated thick lacustrine deposits a sedimentary basin developed between continental rocks to the south and the emergent ridge comprising accretionary complex rocks and outer shelf deposits to the north in the position of a forearc basin as accretion proceeded the locus of underthrusting migrated northward and a second melange ridge and sedimentary basin developed farther to the north the evidence for accretionary processes and the association of these with sedimentary basin formation supports the hypothesis that an ancient south dipping subduction zone existed in the eastern part of west kalimantan during late cretaceous to early tertiary times

chronology of sanbagawa metamorphism by collating age data based on the fossil age of the protoliths radiometric dating of the metamorphic minerals and sedimentary records of erosion at the earth s surface the history of the sanbagawa metamorphism can be summarized as follows 1 the pre metamorphic sedimentary rocks carboniferous jurassic early cretaceous became mixed and formed a thickened packet in the vicinity of an ancient trench through a variety of subduction related tectono sedimentary processes probably in early cretaceous time c 130 120 ma 2 the subducted protoliths underwent progressive metamorphism reaching a maximum depth of c 30 km in late early cretaceous time c 116 10 ma 3 the high p t metamorphic rocks began to rise toward the surface during the interval 110 50 ma with minimum estimates for the average cooling rate around 9 12 c ma and an average uplift rate around 0 4 0 5 mm year 4 finally at some stage after reaching the erosional surface the high p t metamorphic rocks were covered unconformably by the middle eocene c 50 42 ma kuma group on the basis of the present chronological summary of the sanbagawa metamorphism the areal extent of the sanbagawa metamorphism is also discussed with respect to the weakly metamorphosed subduction accretion complex of the next tectonic belt to the south the northern chichibu belt

modeling the isotopic composition of antarctic snow using backward trajectories simulation of snow pit records 1 the quantitative interpretation of isotope records d 18 o dd and d excess in ice cores can benefit from a comparison of observed meteorology with associated isotope variability for this reason we studied four isotope records from snow pits in western dronning maud land dml antarctica covering the period 1998 2001 timing and magnitude of snowfall events on these locations were monitored using sonic height rangers for the distinguished snowfall events we evaluated the isotopic composition of the moisture during transport by combining backward trajectory calculations with isotopic modeling using a rayleigh type distillation model mcim the initial isotope ratio of the moisture was determined frommonthlymeanisotopefields fromageneralcirculation model echam4 the trajectory analysis showed that the southern atlantic ocean is the major moisture sourceforprecipitationindml modelingresultsalongthetrajectoriesrevealedthatmostof the isotopic depletion occurred during the last day of the transport finally a diffusion model was applied to describe the diffusion in the firn layer such that the modeled isotopes couldbecomparedwiththeobservedisotoperecords theresultingmodeledisotopeprofiles were mostly in good agreement with the observed seasonal variability in the snow however at low temperatures especially on the antarctic interior magnitude of the total distillation was underestimated regarding the d excess parameter our results show a large influence of advection height on the final value of d excess in precipitation this in turn points to the importance of the vertical structure of d excess over the oceanic source region which obscures the classical interpretation of this parameter in terms of temperature and relative humidity in the moisture source region

evolution of structures and fabrics in the barbados accretionary prism insights from leg 110 of the ocean drilling program the microstructures and crystal fabrics associated with the development of an amphibolite facies quartzo feldspathic mylonitic shear zone torridon nw scotland have been investigated using sem electron channelling our results illustrate a variety of microstructures and fabrics which attest to a complex shear zone deformation history microstructural variation is particularly pronounced at low shear strains significant intragranular deformation occurs via a domino faulting style process whilst mechanical incompatibilities between individual grains result in characteristic grain boundary deformation accommodation microstructures a sudden reduction in grain size defines the transition to medium shear strains but many of the boundaries inherited from the original and low shear strain regions can still be recognized and define distinctive bands oriented at low angles to the shear zone margin grains within these bands have somewhat steeper preferred dimensional orientations these domains persist into the high shear strain mylonitic region where they are oriented subparallel to the shear zone margin and consist of sub 20 m grains the microstructures suggest that the principal deformation mechanism was intracrystalline plasticity with contributions from grain size reduction via dynamic recrystallization grain boundary migration and grain boundary sliding crystal fabrics measured from the shear zone vary with position depending on the shear strain involved and are consistent with the operation of several crystal slip systems e g prism basal rhomb and acute rhomb planes in a consistent direction probably parallel to a and or m they also reveal the presence of dauphine twinning and suggest that this may be a significant process in quartz deformation a single crystal fabric evolution path linking the shear zone margin fabric with the mylonitic fabric was not observed rather the mylonitic fabric reflects the instantaneous fabric which developed at a particular location for a particular shear strain and original parental grain orientation the mature shear zone therefore consists of a series of deformed original grains stacked on top of each other in a manner which preserves original grain boundaries and intragranular features which develop during shear zone evolution the stability of some microstructures to higher shear strains the exploitation of others at lower shear strains and a continuously evolving crystal fabric mean that the strain gradient observed across many shear zones is unlikely to be equivalent to a time gradient

elasticity composition and temperature of the earth s lower mantle a reappraisal the interpretation of seismological models for the earth s lower mantle in terms of chemical composition and temperature is sensitive both to the details of the methodology employed and also to uncertainties in key thermoelastic parameters especially for the dominant mg fe sio3 perovskite phase here the alternative approaches adiabatic decompression of the lower mantle for comparison at zero pressure with laboratory data and the projection of laboratory data to lower mantle p t conditions for direct comparison with seismological observations are assessed along with the equations of state on which they are based it is argued that adiabatic decompression of the lower mantle is best effected by a strategy in which consistent third order finite strain expressions are required simultaneously to fit the strain dependence of both the seismic parameter and the density this procedure accords due weight to the most robust seismological observations namely the wave speeds and reduces to an acceptable level the otherwise very strong covariance among the fitted coefficients it is demonstrated that this approach can readily be adapted to include the effects of relaxation from the hill average to the reuss lower bound of the aggregate bulk modulus which governs the radial variation of density for the projection of laboratory thermoelastic data to lower mantle p t conditions the preferred equation of state is of the mie gruneisen type involving the addition at constant volume of the pressure along a finite strain principal 300 k isotherm and the thermal pressure calculated from the debye approximation to the lattice vibrational energy a high degree of consistency is demonstrated between these alternative equations of state possible departures of the lower mantle from conditions of adiabaticity and large scale homogeneity are assessed these are negligible for the prem model bullen parameter b 0 99 0 01 but significant for ak135 b 0 94 0 02 reviving the possibility of a substantially superadiabatic temperature gradient experimentally determined thermoelastic properties of the major mg fe sio3 perovskite and mg fe o magnesiowustite phases are used to constrain the equation of state parameters employed in the analysis of seismological information although the scarcity of information concerning the pressure and temperature dependence of the elastic moduli for the perovskite phase remains a serious impediment nevertheless it is demonstrated that the combination of a pyrolite composition simplified to the three component system sio2 mgo feo with molar xpv 0 67 and xmg 0 89 and a lower mantle adiabat with a potential temperature of 1600 k consistent with the preferred geotherm for the upper mantle and transition zone is compatible with the prem seismological model within the residual uncertainties of the thermoelastic parameters for the perovskite phase in particular such consistency requires values for the perovskite phase of ks ks p t and q ln ln v t of approximately 3 8 and 2 and g t near 0 022 gpa k 1 for the lower mantle assemblage more silicic models which have sometimes been advocated can also be reconciled with the seismological data but require lower mantle temperatures which are much higher by about 700 k for pyroxene stoichiometry however the absence of seismological and rheological evidence for the pair of thermal boundary layers separating convection above and below which is implied by such models remains a formidable difficulty under these circumstances the simplest possible model that of grossly uniform chemical composition throughout the mantle is preferred

early deformations at a submarine compressive front the quaternary catania foredeep south of mt etna sicily italy abstract in the catania foredeep south of mt etna oil drilling has revealed the existence at depth of an allochthonous complex emplaced during the middle quaternary at the surface outcropping middle quaternary marine marly clays and sands display complex deformations which are partly synsedimentary and which can be correlated with the emplacement of this allochthonous complex most of these deformations are thought to result from gravitational gliding of slope sediment apron this process probably facilitated by high pore pressure would be in particular the cause of a semi penetrative shear deformation with an eastward vergence in the clays thus our study rules out the classical view of a shallow pre etnean gulf that was steadily filled in before emerging some 400 000 to 300 000 years ago this particular example of neotectonics shows the precocity and complexity of deformations occurring in sediments deposited along the compressive margin of a foreland basin or similarly at an accretionary prism front

deformational history of an outlier of metasedimentary rocks coast plutonic complex british columbia canada the khutzeymateen assemblage records a portion of the polyphase deformation experienced by rocks within the core of the coast plutonic complex this series of deformational events probably took place during late cretaceous to early eocene regional orogenic activity the khutzeymateen assemblage is dominated by metamorphosed graywackes and volcaniclastic material the earliest recognizable deformation involves thrust faulting that juxtaposed rocks of the khutzeymateen assemblage and central gneiss complex the next deformational event produced isoclinal folds f1 a penetrative foliation s1 and a strong mineral lineation l1 both f1 and l1 have a 340 15 orientation peak metamorphism p 450 50 mpa t 650 50 c was synchronous with this isoclinal folding event f1 folding was followed by a brittle chevron folding event f2 with a 335 20 orientation there is a strong lithologic control on the development of f2 minor folds which are developed predominantly within regularly layered qua

equation of state of lower mantle al fe mgsio3 perovskite the compression behavior of various al fe bearing mgsio3 perovskites was investigated by powder x ray diffraction up to 70 gpa on the id30 beamline of esrf grenoble france using diamond anvil cell coupled with co2 laser heating we obtained a reliable equation of state up to typical lower mantle pressures in contrast to fe which essentially increases the room pressure unit cell volume v0 the effect of al is to increase the bulk modulus of silicate perovskite this result contrasts with previous determinations performed at pressures below 10 gpa on samples synthesized in the multi anvil press such a difference can be explained by a change in the substitution mechanism of al in mgsio3 with increasing pressure and temperature in agreement with recent ab initio calculations our results confirm that the earth s lower mantle mg fe si ratio is greater than unity because of the high stiffness of silicate perovskite

structural styles and deformation fabrics of accretionary complexes intricately deformed stratally disrupted and mixed rocks produced at subduction zones have been considered structurally intractable however marine geophysical studies deep sea drilling analyses of subaerially exposed complexes and theoretical advances have recently produced breakthroughs in elucidating the structural enigmas of these accretionary complexes the penrose conference structural styles and deformational fabrics of accretionary complexes assembled specialists from the above and related research areas and addressed the research frontiers of this dynamic topic this conference in eureka california in may 1984 drew participants from great britain france canada japan and new zealand

the geodynamic evolution of the eastern eurasian margin in mesozoic times abstract the cenozoic features of eurasia such as marginal seas and intracontinental deformation are unraveled using available paleomagnetic and field data the late cretaceous shape of eurasia is then reconstructed from the examples of sw japan and south russian far east the major features of the mesozoic eurasian margin suture zones marked by ophiolites or high pressure metamorphic rocks olistostromes characterized by the lithology of the olistoliths calc alkaline magmatism and strike slip faults are outlined correlations of the ophiolitic belts and the olistostromes along the eastern eurasian margin from borneo to siberia allow the definition of four microcontinents the west philippines south japan and the anuy and okhotsk sea microblocks from south to north the mesozoic structure of the eurasian margin is due to three processes 1 1 oceanic subduction and the accretion of subduction complexes 2 2 the collision of these microcontinents with eurasia between the late jurassic and the late cretaceous and 3 3 the reactivation of the ophiolitic sutures by left lateral wrench faulting

stable intermediate spin ferrous iron in lower mantle perovskite iron has the ability to adopt different electronic configurations and transitions in its spin state in the lower mantle can significantly influence mantle properties and dynamics experimental results for two lower mantle perovskite compositions show that the intermediate spin state of iron is stable throughout the bulk of the lower mantle

a model for terrane accretion yukon tanana and slide mountain terranes northwest north america to date many north american cordilleran geologists employing the concept of suspect terranes have emphasized differences in lithology metamorphism styles of deformation and timing of these distinct tectonic units arguing that each evolved separately from its neighbors this practice of focusing on dissimilarity and nomenclature used in terrane analysis may be detrimental to our understanding of the evolutionary relationships between terranes i present a model in which the yukon tanana yt and slide mountain sm terranes which do exhibit certain lithotectonic disparities are correlated within a unifying tectonic framework in which each terrane represents a different crustal level of the same late paleozoic early mesozoic magmatic arc and west dipping subduction complex formed during plate convergence outboard of western north america the sm represents the upper crustal level of the arc and accretionary complex and the heterogeneously metamorphosed and ductilely deformed yt represents the deeper crustal level the teslin suture zone tsz the high p t portion of the yt formed the decollement between the yt sm composite terrane hanging wall and the descending north american plate tsz structural relations thus provide insight into the kinematic interaction of this composite terrane with north america prior to its late stage emplacement onto north america the present day collage of suspect terranes clearly comprises a multitude of structurally dismembered and dissimilar lithotectonic assemblages nonetheless it is possible to see order in the chaos to reassemble the pieces in a tectonically meaningful fashion the yt tsz sm association in yukon may serve as a model for tectonically coherent continental margin expansion

intermediate spin ferrous iron in lowermost mantle post perovskite and perovskite the earth s lowermost mantle displays an important mineralogical transition from perovskite to post perovskite but the spin state of iron in these phases remains poorly known experimental results suggest that iron occurs in the intermediate spin state in both of these phases which implies that changes in physical properties of the lower mantle must be governed by factors other than spin transitions in iron

snow atmosphere coupled simulation at dome c antarctica using a snow atmosphere coupled model the evolution of the surface and near surface snow temperature is modeled at dome c antarctica during the period 20 30 january 2010 firstly the detailed multilayer snow model crocus is run in stand alone mode with meteorological input forcing data provided by local meteorological observations the snow model is able to simulate the evolution of surface temperature with good accuracy it reproduces the observed downward propagation of the diurnal heatwave into the upper 50 cm of the snowpack reasonably well secondly a fully coupled 3 d snow atmosphere simulation is performed with the arome regional meteorological model for which the standard single layer snow parameterization is replaced by crocus in spite of a poor simulation of clouds the surface and near surface snow temperatures are correctly simulated showing neither significant bias nor drifts during the simulation period the model reproduces particularly well the average decrease of the diurnal amplitude of air temperature from the surface to the top of the 45 m instrumented tower this study highlights the potential of snow atmosphere coupled models over the antarctic plateau and the need to improve cloud microphysics and data assimilation over polar regions

a 5 year record of surface energy and mass balance from the ablation zone of storbreen norway a 5 year record of data from an automatic weather station aws operating in the ablation zone of storbreen norway has been used to calculate the local surface energy and mass balance the aws observations cover five mass balance years with an unusually strong mass deficit on storbreen the average energy flux q contributing to melt for the period 2001 06 is 113wm 2 of this the net shortwave radiation flux is the dominant contributor 92wm 2 followed by the sensible heat flux 20 wm 2 and the latent heat flux 9 w m 2 the net longwave radiation 6w m 2 and the subsurface heat flux 2 w m 2 contribute negatively to the budget net radiation thus produces 76 of the melt while the turbulent fluxes and the subsurface heat flux produce 24 of the total melt the seasonal mean incoming shortwave radiation is remarkably constant between the years whereas variations in temperature and reflected shortwave radiation albedo explain most of the interannual variation in melt the modelled ablation compares well with the measured ablation from stake readings the sensitivity of the energy balance model was examined by varying the surface roughness length of momentum and the sensitivity of the calculated melt by perturbations of temperature wind speed and relative humidity

accreted oceanic materials in japan abstract the phanerozoic circum pacific orogenic belts contain numerous ocean derived materials accreted through plate converging processes japanese islands in particular display various kinds of oceanic materials of different origins including fragments of seamounts oceanic reef limestone morb like rocks and oceanic mantle and pelagic sediments the compilation of these rocks in many subduction complexes of late permian to the present led to following conclusions accretion processes work effectively only for materials primarily composing the upper portion of subducting oceanic crust i e layer 1 and layer 2 many fragments of seamount with alkali basalt 600 hot spot seamount 26 oceanic reef limestone 291 morb like basalt 200 and numerous cherts more than 1000 are recognized as ancient oceanic materials accreted to the japanese islands however gabbros and mantle materials of layer 3 and lower parts of the oceanic lithosphere scarcely occur in subduction accretion complexes except for a few examples of back arc basin or fore arc origin accretion occurs episodically in southwest japan oceanic materials were accreted intermittently in 1 a end permian 2 b middle late jurassic 3 c late cretaceous times 4 d at ca 50 ma and 5 e in miocene times while in northeast japan and hokkaido this occurred in b middle late jurassic c late cretaceous and f early cretaceous times in contrast to the general belief on accretion of younger oceanic plates the majority of japanese subduction accretion complexes were formed during the subduction of plates up to 160 ma old the accretionary events in end permian and middle late jurassic times coincide with northward collision of ancient island arcs oceanic rises or seamount chains of hot spot origin with the asian continent accretion relevant to subduction of older plates may be controlled by the collision subduction process of these topographic reliefs on an oceanic plate in addition the chronological coincidence with the continent collision amalgamation between the sino korean and siberian platforms and between the sino korean and yangtze blocks also implies collision induced voluminous supply of elastics from back arc regions and its contribution to the formation of huge accretionary complexes accreted fragments of ancient seamounts are much smaller than the average size of modern seamounts this implies that most parts of a colliding seamount are not accreted but subducted together with the underlying oceanic crust to much deeper levels with respect to the metamorphic grades for japanese subduction complexes oceanic materials have less than 1 vol in the zeolite facies 15 20 in the prehnite pumpellyite metagraywacke facies and ca 30 in the greenschist glaucophane schist facies and albite epidote amphibolite fades this relationship indicates that the major process for landward accretion of oceanic materials is not off scraping or sedimentary mixing at the trench but underplating subcretion at much deeper levels of a subduction zone

a benchmark dataset of in situ antarctic surface melt rates and energy balance abstract surface melt on the coastal antarctic ice sheet ais determines the viability of its ice shelves and the stability of the grounded ice sheet but very few in situ melt rate estimates exist to date here we present a benchmark dataset of in situ surface melt rates and energy balance from nine sites in the eastern antarctic peninsula ap and coastal dronning maud land dml east antarctica seven of which are located on ais ice shelves meteorological time series from eight automatic and one staffed weather station neumayer ranging in length from 15 months to almost 24 years serve as input for an energy balance model to obtain consistent surface melt rates and energy balance results we find that surface melt rates exhibit large temporal spatial and process variability intermittent summer melt in coastal dml is primarily driven by absorption of shortwave radiation while non summer melt events in the eastern ap occur during fohn events that force a large downward directed turbulent flux of sensible heat we use the in situ surface melt rate dataset to evaluate melt rates from the regional atmospheric climate model racmo2 and validate a melt product from the quikscat satellite

lateral growth of the continental crust through deep level subduction accretion a re evaluation of central greek rhodope abstract the rhodope massif of northern greece and southern bulgaria has been variably interpreted as a fragment of pre alpine possibly hercynian or precambrian age continental crust that was actively involved in european margin convergent tectonics during the mesozoic and tertiary alternatively we propose that for central greek rhodope the lithological associations and tectonothermal history are consistent with progressive south directed mesozoic crustal growth through deep level subduction accretion a process which involved the near continuous transferral of material of oceanic and continental margin affinity from footwall to hanging wall within a north directed palaeotethyan subduction system central greek rhodope comprises a sequence of schists gneisses and migmatites of wide compositional variation that have undergone intense tectonic intermixing extensive occurrences of marble are associated with amphibolites variably retrogressed eclogites meta gabbros and ultramafic rocks quartzo feldspathic gneisses are abundant throughout the area and are associated with psammitic meta greywacke sequences pelites and quartzites the presence of intercalated marble slivers and thin manganiferous and iron rich siliceous bands is significant the various components exposed in the subduction accretion complex were first underthrust northwards to deep crustal levels subjected to high pressure eclogite facies metamorphism and underplated to the base of the overriding eurasian plate this latter accretion event was characterised by intense southwest directed ductile thrusting and pervasive amphibolite facies metamorphic overprinting it was accompanied by migmatisation and intracrustal melt generation and followed by subduction related magmatism deep level subduction accretion leads to southward growth of the continental margin which in turn leads to subduction retreat allowing the encroachment of the magmatic arc from the north subsequent extensional tectonic exhumation brought the complex up to its present position within the southern margin of eurasia this new interpretation may have implications for other high grade terrains within convergent and collisional systems that have been assumed to represent ancient or pre existing continental crust if so then the importance of deep level subduction accretion as a mechanism of continental crustal growth has hitherto been underestimated