along arc lateral variation of rb sr and k ar ages of cretaceous granitic rocks in southwest japan cretaceous granitic rocks were emplaced over a distance of 700 km along arc in southwest japan rb sr and k ar ages of a major group of these granitic rocks with ilmenite series ore mineralogy were examined rb sr whole rock ages of 92 8 4 0 ma and rb sr and k ar biotite ages of 80 88 ma were obtained on one group of these granitic rocks from kamo sera area of central hiroshima prefecture the k ar ages of various minerals combined with the rb sr whole rock age give a smooth cooling curve which suggests a 5 to 10 ma time lag between intrusion and cooling at 300 c for the cretaceous granitic rocks the rb sr whole rock and rb sr k ar biotite ages of these granitic rocks become younger eastward along the southwest japan arc and the time lag between the two systems remains constant at 5 to 10 ma over the entire area the along arc age variation does not support the genetical relationship of the cretaceous granitoids with steady state subduction the cretaceous granitic province at the eastern margin of eurasian continent was at least partly formed by an episodic event such as ridge subduction

evolution of the sanbagawa and shimanto high pressure belts in sw japan insights from k ar ar ar geochronology abstract the sanbagawa belt sensu lato in japan is one of the world s classical high pressure hp metamorphic belts and has long been considered to be a coherent hp belt of the cretaceous age however recent progress in detrital zircon geochronology together with the accumulation of abundant phengites k ar ar ar ages revealed that the belt is comprised of two petrotectonic belts sanbagawa sensu stricto hp belt and shimanto hp belt these two belts have distinctly different ages of peak metamorphism and different p t conditions of metamorphism the sanbagawa schists sensu stricto were metamorphosed in the conditions of the pumpellyite actinolite facies through the epidote blueschist to epidote amphibolite facies and up to the eclogite facies during a prograde stage in a subduction zone at 120 115 ma phengite k ar geochronology revealed that the subsequent exhumation after the peak metamorphism took placed in a manner that the higher grade rocks exhumed more rapidly in comparison with the lower grade rocks this is supported by a positive correlation between age and apparent metamorphic gradient that have formed during the post metamorphic peak hydration recrystallization moreover the schists have experienced intense ductile deformation and long term exhumation it took longer than 31 m y to reset the phengite k ar system in contrast the shimanto hp schists were metamorphosed in the epidote blueschist greenschist transitional facies to the epidote amphibolite facies and have experienced a short term deformation for less than 13 m y this short deformation formed a negative correlation between k ar age and apparent metamorphic gradient these two contrasting age temperature relationships suggest different exhumation processes between the two hp belts most likely due to a change in subducting oceanic plates in the cretaceous along the paleo japanese convergent margin

k ar age and chemistry of phengite from the sanbagawa schists in the kanto mountains central japan and their implication for exhumation tectonics abstract epma analyses and k ar age determinations were carried out on phengite in pelitic schist from the sanbagawa metamorphic belt of the kanto mountains central japan phengite from the sanbagawa pelitic schist in the kanto mountains generally occurs as aggregates of fine grained crystals it is extremely fine grained in domains adjacent to relatively rigid garnet and albite porphyroblasts this suggests that deformation induced grain size reduction took place in phengite during the ductile deformation accompanying the exhumation of the host schists epma analysis shows that phengite is chemically heterogeneous at the thin section scale suggesting that it formed during retrograde metamorphism in restricted equilibrium domains the retrograde chemical reaction was promoted by the ductile deformation k ar ages of phengite get younger from the southern unit 82 ma to the northern unit 58 ma in the kanto mountains the age range is similar to that in central shikoku the older schists occur in the higher metamorphic grade zone in central shikoku and in the lower grade zone in the kanto mountains the thermal structures in central shikoku are inverted so that the highest grade zone occurs in the upper or middle parts of the apparent stratigraphic succession in contrast the kanto mountains have a normal thermal structure the higher grade zone is in the lower part of the apparent stratigraphic succession the different tectonic features in exhumation produced the two contrasting age temperature structure relations at the western side of sanbagawa belt in central shikoku and the eastern end of the sanbagawa belt in the kanto mountains that are 800 km distant from each other namely the western sanbagawa belt in central shikoku underwent longer ductile deformation during the exhumation than the eastern sanbagawa belt in the kanto mountains

age k ar phengite temperature structure relations a case study from the ishigaki high pressure schist belt southern ryukyu arc japan the ishigaki high pressure schist belt in the southern ryukyu arc is correlated with the suo high pressure schist belt in southwest japan the former metamorphic sequence is composed mainly of basic and pelitic schists and is subdivided into three zones the lower grade zone a the medium grade zone b and the high grade zone c based on the mineral assemblages of the basic schists the k ar phengite age gives 188 205 ma for zone a 196 206 ma for zone b and 208 220 ma for zone c while the apparent d 002 spacing of carbonaceous materials is 3 590 3 437 a 3 415 3 390 a and 3 387 3 364 a respectively the age d 002 relationships suggest that the ages become older with increasing metamorphic temperature this positive age temperature relationship in the ishigaki area contrasts with a negative relationship in the nishiki area in the suo belt the two areas also display a contrasting thermal structure with the former area having an inverted metamorphic gradient and the latter displaying a normal thermal structure these contrasting age temperature structure relationships in the metamorphic belt could be due to different tectonic styles relating to the exhumation of the metamorphic sequences we suggest that the ages obtained are related directly to the ductile deformation history of the matrix phengite below the closure temperature 500 c during exhumation of the host rocks the duration from the beginning of exhumation to the apparent resetting of the phengite k ar system was different between the two metamorphic sequences and significantly longer in the ishigaki than the nishiki

the pyrope coesite rocks and their country rocks at parigi dora maira massif western alps detailed petrography mineral chemistry and pt path both the coarse and fine grained varieties of the partly coesite bearing pyrope quartzites their interlayered jadeite kyanite rocks and the biotite phengite gneiss country rock common to all of them were subjected to detailed petrographic and textural studies in order to determine the sequence of crystallisation of their mineral constituents which were also studied analytically by microprobe prior to pyrope and coesite growth the mg rich metapelites were talc kyanite chlorite rutile ellenbergerite schists which upon continued prograde metamorphism developed first pyrope megacrysts in silica deficient local environments at the expense of chlorite talc kyanite and subsequently the smaller pyrope crystals with coesite inclusions from reacting talc kyanite based on geobarometrically useful mineral inclusions as well as on experimentally determined phase relations a prograde pt path simplified for water activity 1 is constructed which passes through the approximate pt conditions 16 kbar and 560 c 29 kbar and 720 c and finally up to 37 kbar at about 800 c where the mg rich metapelite was a pyrope coesite rock with phengite kyanite and talc still present during the retrograde path pyrope was altered metasomatically either into phlogopite kyanite quartz or at a later stage to chlorite muscovite quartz both assemblages yield pt constraints the latter about 7 9 kbar 500 600 c the country rock gneisses have also endured high pressures of at least 15 kbar but they provide mostly constraints on the lowest portion of the uplift conditions within the greenschist facies about 5 kbar 450 c microprobe data are presented for the following minerals pyrope ellenbergerite dumortierite unusually mgti rich jadeite vermiculite formed after na phlogopite paragonite and for several generations of phengite chlorite talc phlogopite dravite and glaucophane in the high pressure rocks as well as for biotite chlorite phengites epidote garnet albite and k feldspar in the country rock gneisses an outstanding open problem identified in this study is the preservation of minerals as inclusions within kyanite and pyrope beyond their pt stability limits

coesite and pure pyrope in high grade blueschists of the western alps a first record and some consequences a pyrope quartzite originally described by vialon 1966 from the dora maira massif was resampled and reinvestigated garnet up to 25 cm in size phengite kyanite talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz the garnet is a pyrope almandine solid solution with 90 to 98 mol mg end member it contains inclusions of coesite which has partially inverted to quartz resulting in a typical radial cracking of the host garnet around the inclusions several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite

rbsr and 40ar39ar laser probe dating of high pressure phengites from the sesia zone western alps underscoring of excess argon and new age constraints on the high pressure metamorphism abstract the combined use of the rb sr and 40ar 39ar laser probe methods allows confirmation of the existence of excess argon in phengites from eclogites from the sesia zone western alps despite systematic 40ar 39ar plateau ages 40ar 39ar phengite ages from two different areas show integrated age spreads between 65 4 0 3 ma and 109 5 0 4 ma the youngest 40ar 39ar plateau age 65 9 0 4 ma is concordant with two rb sr phengite whole rock isochron ages from the same outcrop which display a mean age at 64 2 2 5 ma and older than a rb sr biotite whole rock isochron age at 53 0 1 0 ma this age concordance being incompatible with the concept of isotopic closure temperature is probably fortuitous and probably results from an excess argon contamination however the concordance of the rb sr phengite isotopic closure temperature with the temperature reached during the eclogite facies event suggests that the age at 64 2 2 5 ma could be a crystallization age probably contemporaneous with the eclogite facies event in the sesia zone when compared to recent age data from the piemont zone and the dora maira massif the entire data set which needs to be confirmed by extra measurements support diachronous high pressure hp events in the western alps

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

from rifting to drifting africa is splitting apart down the east african rift an analysis of the relative motion of the tectonic plates involved allows the rate of continental rifting to be estimated

chemical features of white micas from the piemonte calc schists western alps and implications for k ar ages of metamorphism abstract anomalously large chemical ranges in muscovite paragonite and muscovite celadonite systems are observed in white micas from the piemonte calcschists in the chisone valley area internal western alps the petrographical and chemical observations on white mica strongly suggest that most mica crystals with high na k ratios in the chlorite zone are of detrital origin and were derived from the pre alpine high temperature metamorphic sequence such the caledonian and or variscan submicroscopic muscovite ms paragonite pg composite aggregates occur in the chlorite zone and their epma analyses give an apparent chemical composition range from ms 0 6 pg 0 4 to ms 0 2 pg 0 8 in the rutile zone the paragonite content of the white micas is less than 20 suggesting that the white micas have been homogenized during the alpine metamorphism even if detrital white micas existed metamorphic mica is also very heterogeneous the total range in si content becomes wider with increasing of metamorphic grade 3 22 3 39 pfu for the chlorite zone 3 07 3 45 pfu for the chloritoid zone and 3 06 3 59 pfu for the rutile zone this clearly indicates that the micas have experienced significant retrogressive chemical reactions during cooling and exhumations of the host schists the detrital white mica in the chlorite zone has not reset well in its k ar system during the alpine subduction related metamorphism the wide range of the white mica k ar ages from 115 to 41 ma must be due to a mixture of various amounts of detrital white mica in the separates this feature is also observed in the chloritoid zone though the age variation is not so large as that in the chlorite zone in contrast the mica in the rutile zone which was higher than 450 c has been reset completely during alpine hp metamorphism

karakoram glacier surge dynamics quincey d j braun m glasser n f bishop m p hewitt k luckman a 2011 geophysical research letters 38 article number l18504

a distributed temperature index ice and snowmelt model including potential direct solar radiation hourly melt and discharge of storglaciaren a small glacier in sweden were computed for two melt seasons applying temperature index methods to a 30 m resolution grid for the melt component the classical degree day method yielded a good simulation of the seasonal patient of discharge but the pronounced melt induced daily discharge cycles were not captured modelled degree day factors calculated for every hour and each gridcell from melt obtained from a distributed energy balance model varied substantially both diurnally and spatially a new distributed temperature index model is suggested attempting to capture both the pronounced diurnal melt cycles and the spatial variations in melt due to the effects of surrounding topography this is accomplished by including a radiation index in terms of potential clear sky direct solar radiation and thus without the need for other data besides air temperature this approach improved considerably the simulation of diurnal discharge fluctuations and yielded a more realistic spatial distribution of melt rates the incorporation of measured global radiation to account for the reduction in direct solar radiation due to cloudiness did not lead to additional improvement in model performance

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

metamorphic evolution of the sesia lanzo zone western alps time constraints from multi system geochronology the sesia lanzo zone is a polymetamorphic unit containing hercynian granulite relics overprinted by eclogite and greenschist facies metamorphism and deformation during the alpine orogeny different parts of the unit record different stages on the p t deformation evolution allowing multi system isotopic studies to unravel the precise timing of the metamorphic history new rb sr white mica and u pb sphene data constrain the age of eclogite facies metamorphism and deformation to 60 70 ma this substantially alters the common view of early to mid cretaceous eclogite facies metamorphism in this unit the new results are more consistent with the established geotectonic framework for the alpine orogeny since they do not require a prolonged period of depressed geothermal gradient at a time when the region was in extension it is also more concordant with recent studies of other units that demonstrate post cretaceous high pressure metamorphism step heated 40ar 39ar analysis of phengites yields good plateaux giving ages older than the corresponding rb sr age such anomalously high ages indicate the presence of radiogenic argon rich fluids in the grain boundary network under the fluid pressure conditions acting during this high pressure metamorphic event the u pb sphene ages are variable in polymetamorphic rocks and show inheritance of older pb or sphene crystals into the high pressure event two monometamorphic assemblages yield concordant ages at 66 1 ma reflecting crystallisation of the eclogite facies assemblage the gneiss minuti complex gmc lies structurally below the eclogitic micaschists and its pervasive greenschist facies fabric yields tightly clustered rb sr white mica ages at 38 39 ma this greenschist event did not affect the majority of the emc the 40ar 39ar ages of micas formed at this time were very disturbed whereas micas surviving from an earlier higher pressure assemblage had their 40ar 39ar system reset the greenschist event did not strongly affect u pb systematics in hercynian age sphenes suggesting that the gmc did not uniformly suffer an eclogite facies metamorphism during the alpine cycle but was juxtaposed against the emc later in the orogeny this model still requires that the locus of deformation and metamorphism and possibly fluid flux moved outboard with time leaving the sesia lanzo basement as a shear bounded unreactive block within the orogenic wedge

geotectonic subdivision and areal extent of the sangun belt inner zone of southwest japan the sangun belt has long been considered to be a major coherent glaucophanitic terrane of permian to triassic age and to be paired with the low p t hida belt to the north however recent progress in geochronology metamorphic geology and tectonics has revealed that the belt is in fact comprised of two geologic units of different ages and with contrasting conditions of formation the older unit is named the renge belt and the younger the suo belt the renge belt is the oldest of the high p t metamorphic belts in the japanese islands and extends from northern kyushu through the san in coastal regions to the hida marginal belt it is characterized by 330 280 ma ages and the association of glaucophane schist to epidote amphibolite facies schists the renge belt is also typically associated with meta ophiolite sequences 470 340 ma including serpentinite the suo belt is characterized by 230 160 ma high p t schists closely related to weakly metamorphosed permian accretionary rocks of the akiyoshi belt metamorphic facies series is from the prehnite pumpellyite facies through the pumpellyite actinolite and glaucophane schist facies to the epidote amphibolite facies the belt is widespread in west kinki to north and central kyushu via chugoku but also stretches further to the southwest and is present in the ishigaki iriomote islands of the southern ryukyu arc throughout this belt there are scattered small blocks or lenses of meta ophiolite whose k ar ages of relict hornblendes are 590 to 220 ma bounded by low angle faults and thrusts both belts define subhorizontal nappes dipping gently north the geotectonic framework in the inner zone of southwest japan is made up of from north to south the hida oki renge akiyoshi suo maizuru plus ultra tamba mino tamba and ryoke belts with a tectonically downward younging polarity this has resulted from stepwise accretions during palaeozoic to mesozoic time

contrasting patterns of early twenty first century glacier mass change in the himalayas glaciers are among the best terrestrial climate indicators an important water resource in mountains1 2 and a major contributor to global sea level rise3 4 in the hindu kush karakoram himalaya region hkkh a paucity of appropriate glacier data has prevented a comprehensive assessment of current regional mass balance5 however there are indirect evidences of a complex pattern of glacial responses5 8 in reaction to heterogeneous climate change signals9 here we provide the first coherent data set of detailed glacier thickness changes over the hkkh during 2003 2009 by combining satellite laser altimetry and a global elevation model in the eastern central and south western parts of the hkkh glacier wastage is widespread with regional thinning rates up to 0 66 0 09 m a 1 in the jammu kashmir region conversely in the karakoram glaciers are close to balance with only a slight thinning of 0 07 0 04 m a 1 regionally averaged thinning rates under debris mantled ice are similar to those of clean ice despite insulation by debris covers the 2003 2008 specific mass balance for our hkkh study region is 0 21 0 05 m a 1 water equivalent we significantly less negative than the global average of 0 7 m a 1 we for glaciers and ice caps4 10 this difference is mainly an effect of the balanced glacier mass budget in the karakoram the corresponding hkkh sea level contribution is 0 035 0 009 mm a 1 amounting to 1 of the present day sea level rise11 our 2003 2008 mass budget of 12 8 3 5 gt a 1 is more negative than recent satellite gravimetry based estimates of 5 6 gt a 1 over 2003 2010 ref 12 for the mountain catchments of the indus and ganges basins13 the glacier imbalance contributes 3 5 and 2 0 respectively to the annual average river discharge13 and up to 10 for the upper indus basin14

karakorum hindukush western himalaya assessing high altitude water resources the high mountains of central and south asia provide irrigation water for their adjacent lowlands the indus irrigation scheme depends on approximately 50 of its runoff originating from snowmelt and glacier melt from the eastern hindukush karakorum and western himalaya the atlas of pakistan indicates that these mountains gain a total annual rainfall of between 200 and 500 mm amounts that are generally derived from valley based stations and not representative for elevated zones high altitude snowfall seems to be neglected and is obviously still rather unknown estimates derived from accumulation pits runoff above 4000 m range from 1000 mm to more than 3000 mm depending on the site and time of investigation as well as on the method applied to assess the vertical spatio temporal distribution of total annual precipitation a combined approach is presented this approach links in situ measurements of snow depth and water equivalent 10 year time series derived from automatic weather stations at elevations between 1500 and 4700 m a s l the spatial distribution and period of snow coverage remotely sensed data and digital elevation models and the runoff characteristics of streams originating from snow or snow ice covered watersheds modified snowmelt runoff model including intermediate snowfall and glacier runoff based on conservative assumptions the vertically changing seasonal ratio between liquid and solid precipitation is calculated using a combined snow cover and ablation model total annual amounts of precipitation are derived for different altitudinal zones amounts of modelled and measured runoff complement the investigation horizontal gradients along the indus gilgit hunza transect indicate the varying dominance of seasonal precipitation regimes monsoonal mediterranean and continental disturbances south of nanga parbat between nanga parbat and batura wall west karakorum rainfall regime 1500 1800 mm year 1 at 5000 m and areas north of batura central asian rainfall regime 600 mm year 1 at 5000 m copyright 2005 john wiley sons ltd

a physically based model of the year round surface energy and mass balance of debris covered glaciers debris covered glaciers respond to atmospheric conditions in different ways from debris free glaciers due to the presence of debris at the surface during the ablation season and at the snow ice interface during the accumulation season understanding the response of debris covered glaciers to a variety of meteorological conditions in a physically sound manner is essential to quantify meltwater discharge and to predict their response to climate change to tackle this issue we developed the crocus deb model as an adaptation of the detailed snowpack model crocus to simulate the energy and mass balance of debris covered glaciers including periods when debris is covered by snow crocus deb was evaluated with data gathered during a field experiment using artificial debris covering the snowpack at col de porte france with very good results in terms of conductive heat flux both at the surface and at the interface between the debris and the underlying dense snow taken as a surrogate for ice with and without snow overlying the debris the model was also evaluated using field data from the debris covered glacier changri nup nepal himalaya this paper introduces the design of the model its performance and its ability to explore relationships between model parameters meteorological conditions and the critical debris thickness

late paleozoic mesozoic tectonic evolution of sw japan a review reappraisal of the accretionary orogeny and revalidation of the collisional model abstract this paper makes a review of the interpretations of the tectonic evolution of sw japan during the last three decades in the late 1970s the dominant model was the so called pacific type orogeny emphasizing the purported absence of nappes and the contrast with the alpine chains and interpreting the evolution as due to a steady oceanic subduction since the paleozoic time in the 80s the discovery of the actual structure made of a pile of large thrust sheets led authors to propose collisional models involving the intermittent underthrusting of buoyant blocks like micro continents at the same time the use of high resolution biostratigraphy allowed several authors to recognize ancient accretionary wedges with a reconstructed ocean plate stratigraphy of individual accreted units especially in the tanba and shimanto zones also precise radiometric dating permitted the distinction of metamorphosed units especially in sanbagawa and shimanto belts as a result of these new data since the 1990s the plate tectonic interpretation of the history of the japanese islands was revised by japanese scientists and presented again in terms of accretionary processes linked to a steadily oceanic subduction with an episodic ridge subduction the so called miyashiro type orogeny the review of different data leads to the following conclusions the structure of sw japan is made of a pile of sub horizontal nappes polydeformed with a geometry similar to the one encountered in collisional orogens the geodynamic mechanisms advocated for the tectonic building within the accretionary orogeny concept miyashiro type orogeny are inappropriate a permanent oceanic subduction with the intermittent collision actually subduction of an active ridge or seamount chain is unable to build such structures as this process induces in fact an acceleration of the tectonic erosion and collapse of the upper plate the underthrusting of a micro continent or mature arc is likely needed the exhumation story of sanbagawa hp schists suggests the setting of a continental subduction the petrological and new geochemical data from the literature strongly support the existence beneath the nappes of accretionary complexes of continental bodies showing affinities with south china from which they were once separated the episodic collision underthrusting of such blocks was responsible for the tectonic piling tectonic erosion plaid likely a major role in removing material during the intervening subduction stages a revised geodynamic model implying the collision of the honshu south kitakami kurosegawa and shimanto blocks is proposed for explaining the three orogenic crises which took place respectively at around 240 130 and 80 60 ma ago in sw japan the paleogeographic position and affinity of the hida block with surrounding units in the hinterland are still unclear more work is needed to solve this question

continuous metamorphic gradient documented by graphitization and k ar age southeast otago new zealand the chrystalls beach brighton coastal section southwest of dunedin new zealand exposes otago schist including the weakly metamorphosed triassic accretionary melange of the chrystalls beach complex and higher grade rocks of a largely felsic arc derived provenance melange zones contain pelagic sediments some of which are manganiferous and metabasites the grade of metamorphism increases progressively from southwest to northeast four mineral zones are recognized largely on the basis of mineral assemblages in psammitic and semipelitic rocks pumpellyite chlorite pumpellyite actinolite epidote actinolite and biotite d 002 data for carbonaceous material b 0 values for phengite and metamorphic phengite k ar ages are reported for 32 pelitic and semipelitic samples remarkably tight correlations are revealed between d 002 for progressively graphitized carbonaceous material k ar ages that range from 184 6 to 138 7 ma and linear distance along the section both the d 002 values and the k ar ages decrease progressively toward the northeast through the four mineral zones and with progressive textural changes all rocks cropping out in the section have undergone a coherent episode of progressive metamorphism associated with terrane collision and have not been disturbed by any later major displacements a convex trend for phengite b 0 values plotted against advancing graphitization suggests p t conditions during metamorphism as in the high pressure intermediate facies series the age of the metamorphic peak is inferred to be 175 155 ma middle to late jurassic with cooling to the mica closure temperature at 155 135 ma late jurassic to early cretaceous unloading denudation and cooling were accompanied by localized hydrothermal events the oldest covering strata were deposited at ca 100 ma and denudation was completed by ca 75 80 ma middle triassic radiolarian nodules in melange zones are dated as preceding the metamorphic peak by about 65 ma associated turbidites contain suspected late middle to early late triassic tube fossils

excess 40ar free phengite in ultrahigh pressure metamorphic rocks from the lago di cignana area western alps abstract ar ar analyses of phengites and paragonites from the ultrahigh pressure metamorphic rocks zoisite clinozoisite schist garnet phengite schist and piemontite schist in the lago di cignana area western alps were carried out with a laser probe step heating method using single crystals and a spot dating method on thin sections eight phengite and two paragonite crystals give the plateau ages of 37 42 ma with 96 100 of 39 ar released each rock type also contains mica crystals showing discordant age spectra with age fractions 20 35 ma significantly younger than the plateau ages phengite inclusions in garnet give ages of 43 2 1 1 ma and 44 4 1 5 ma which are significantly older than the spot age 36 4 1 4 ma from the matrix phengites and the plateau ages from the step heating analyses inclusion ages 43 and 44 ma are consistent with a zircon shrimp age 44 1 ma in this area these results suggest that the oceanic materials that underwent a simple subduction related uhpm form excess 40 ar free phengite and that the peak metamorphism is ca 44 ma or little older we suggest that matrix phengites experienced a retrogression reaction changing their chemistry contemporaneously with deformation related to the exhumation of rocks releasing significant radiogenic 40 ar from the crystals this has lead to the apparent ages of the matrix phengites that are significantly younger than the inclusion age

do debris covered glaciers demonstrate distinctive hydrological behaviour compared to clean glaciers abstract supraglacial debris is known to strongly influence the distribution of glacier surface melt since melt inputs drive the formation and evolution of glacial drainage systems it should follow that the drainage systems of debris covered glaciers will differ from those of debris free glaciers this would have implications for the proglacial runoff regime subglacial erosion and glacier dynamics this paper presents analysis of return curves from 33 successful dye injections into the extensively debris covered miage glacier italian alps it demonstrates that the spatial distribution of supraglacial debris influences the structure and seasonal evolution of the glacial drainage system where the debris cover is continuous melt is lower and the surface topography is chaotic with many small supraglacial catchments these factors result in an inefficient englacial subglacial drainage network beneath continuous debris which drains to the conduit system emanating from the upper ablation zone melt rates are high in areas of clean and dirty ice above the continuous debris runoff from these areas is concentrated by inter moraine troughs into large supraglacial streams which encourages the early season development of an efficient englacial subglacial conduit system downstream of this area drainage efficiency from the debris covered area increases over the melt season but dye trace transit velocity remains lower than from moulins on the upper glacier future runoff models should account for the influence of supraglacial debris on the hydrological system

evidence for motion between nubia and somalia along the southwest indian ridge the east african rift marks the northern boundary of the nubian west african and somalian east african plates and has formed by horizontal stretching due to the separation of these plates1 south of 20 s any expression of deformation or seismicity due to the relative motion of these two distinct plates vanishes although the boundary must continue until it intersects another plate boundary the nearest such boundary is that of the antarctic plate marked by the southwest indian ridge but previous analyses of plate motion data have indicated no significant difference between nubia antarctica and somalia antarctica motion2 3 here we show using a large compilation of plate motion data that nubia antarctica motion does differ from somalia antarctica motion and we determine a relative angular velocity of the two plates that has compact confidence limits our analysis places the pole of rotation near to the southern limit of african seismicity implying that the southern part of the nubian somalian plate boundary is a diffuse zone of convergence up to 2 mm yr 1 whereas up to 6 mm yr 1 of separation is accommodated across the east african rift about half the separation rate of the slowest mid ocean ridge

temporal variations in supraglacial debris distribution on baltoro glacier karakoram between 2001 and 2012 distribution of supraglacial debris in a glacier system varies spatially and temporally due to differing rates of debris input transport and deposition supraglacial debris distribution governs the thickness of a supraglacial debris layer an important control on the amount of ablation that occurs under such a debris layer characterising supraglacial debris layer thickness on a glacier is therefore key to calculating ablation across a glacier surface the spatial pattern of debris thickness on baltoro glacier has previously been calculated for one discrete point in time 2004 using satellite thermal data and an empirically based relationship between supraglacial debris layer thickness and debris surface temperature identified in the field here the same empirically based relationship was applied to two further datasets 2001 2012 to calculate debris layer thickness across baltoro glacier for three discrete points over an 11 year period 2001 2004 2012 surface velocity and sediment flux were also calculated as well as debris thickness change between periods using these outputs alongside geomorphological maps of baltoro glacier produced for 2001 2004 and 2012 spatiotemporal changes in debris distribution for a sub decadal timescale were investigated sediment flux remained constant throughout the 11 year period the greatest changes in debris thickness occurred along medial moraines the locations of mass movement deposition and areas of interaction between tributary glaciers and the main glacier tongue the study confirms the occurrence of spatiotemporal changes in supraglacial debris layer thickness on sub decadal timescales independent of variation in surface velocity instead variation in rates of debris distribution are primarily attributed to frequency and magnitude of mass movement events over decadal timescales with climate regional uplift and erosion rates expected to control debris inputs over centurial to millennial timescales inclusion of such spatiotemporal variations in debris thickness in distributed surface energy balance models would increase the accuracy of calculated ablation leading to a more accurate simulation of glacier mass balance through time and greater precision in quantification of the response of debris covered glaciers to climatic change

carbonaceous material in pelitic schists of the sanbagawa metamorphic belt in central shikoku japan abstract carbonaceous material in pelitic schists of the sanbagawa metamorphic belt in central shikoku japan was separated from the host rocks and its x ray diffraction and chemical composition were studied its crystal structure and chemistry change continously with increasing metamorphic grade and approach those of well ordered graphite near the biotite isograd as graphitization is a rate process the temperature of complete graphitization differs from one metamorphic terrain to another as a function of the duration of metamorphism in an individual metamorphic terraan however the degree of graphitization is a useful indicator of relative metamorphic temperature in lower grade rocks

carbon isotope anomalies and demise of carbonate platforms in the sinemurian early jurassic of the tethyan region evidence from the southern alps northern italy despite its global impact on ecosystems the triassic jurassic boundary event had only a modest effect on the carbonate depositional systems of the southern alps whereas a fundamental reorganization of the same palaeogeographic area took place during the sinemurian age this paper investigates whether or not the well documented demise of sinemurian carbonate platforms in the tethyan region was a response to a global event by examination of carbon isotope anomalies in successions of different facies that record this interval of time a chemostratigraphic transect from lake garda up to the eastern italian border is illustrated by four stratigraphic sections high resolution 20 cm over key intervals chemostratigraphic sampling allowed detection of a major negative 13 c anomaly of 1 5 preceded by a positive excursion both in shallow and deep water successions over the stratigraphical range of the ammonite genus arnioceras a comparison with sections from the uk suggests that the positive excursion belongs to the turneri zone and the succeeding negative excursion falls within the obtusum zone in the deep water belluno basin the negative anomaly occurs in a biogenic chert rich unit recording the onset of mesotrophic conditions in the basin in the platform carbonate successions this major negative carbon isotope excursion is developed within a calcarenitic unit corresponding to the lowest occurrence of the foraminifer paleomayncina termieri this evidence for deepening and transgression across the carbonate platform suggests pre conditioning for drowning hence rather than tectonic subsidence alone environmental factors may have aided the demise of tethyan carbonate platforms during the early jurassic sinemurian age

white mica k ar geochronology of hp uhp units in the lago di cignana area western alps italy tectonic implications for exhumation abstract high pressure and ultra high pressure hp uhp blueschist and eclogite facies metabasaltic and metasedimentary rocks occur in four different tectonic units near lago di cignana western alps we have determined k ar ages for white micas matrix phengite and paragonite from the lago di cignana uhp unit lcu 39 41 ma the lower and upper units of the zermatt saas meta ophiolite lu and uu 37 38 ma and 38 41 ma respectively and the combin unit cu 36 40 ma these k ar ages overlap with single grain ar ar plateau ages 36 42 ma previously determined for phengites from lcu metasediments matrix white micas have been severely deformed during exhumation and their chemistries differ from those of micas included in garnet although individual mica grains in the matrix could have experienced different degrees of deformation which have reset their k ar systems bulk white mica separates provide the average age of all the individual grains in the separate the similarity of ages determined for white micas from the lcu lu uu and cu units regardless of rock type and mineral species suggests that these four units were metamorphosed together as part of a single metamorphic sequence in the piemonte liguria paleosubduction zone and were subsequently exhumed together however present day structural relationship among those units and the limited occurrence of uhp minerals in lcu suggests that the exhumation of lcu was more rapid than that for lu uu and cu the age gaps between the youngest value of white mica k ar ages in each unit and the inferred timing of the metamorphic peak u pb age 44 ma is 5 7 6 and 8 myr for lcu lu uu and cu respectively these intervals are considerably shorter than that determined for the sanbagawa hp metamorphic belt of southwest japan 31 myr the short interval observed for the lago di cignana units that we have studied is consistent with the model of rapid exhumation of the uhp bearing metamorphic domain suggesting the exhumation rate is higher than 18 mm y in the early stage of exhumation from the deepest level ca 120 km to the lower crust ca 30 km

ice ablation and meteorological conditions on the debris covered area of baltoro glacier karakoram pakistan during the recent italian expedition k2 2004 50 years later june july 2004 on baltoro glacier karakoram pakistan glaciological field experiments were carried out on the debris covered area of this high elevation glacier the aim was to investigate the ice ablation and its relations with debris thermal properties and meteorological conditions ablation measurements along the glacier up to about 5000 m and within a dedicated test field were combined with meteorological data from two automatic weather stations located at urdukas 4022 m a s l and at k2 base camp 5033 m a s l in addition temperature measurements of the debris cover at different depth levels along the glacier allowed the calculation of debris surface temperature and of the debris thermal resistance r using the air temperature the local mean lapse rate 0 00758 cm 1 and the measured ablation the degree day factors k at different locations on the glacier were calculated the ice ablation rates were related to debris thickness and elevation they are typically on the order of 4 cm d 1 during the observation period however it was found that the surface topography slope aspect has an influence on the total ablation similar to that of the debris thickness thermal resistance of the debris cover and its distribution over the glacier were estimated finally a best guess estimate of the total meltwater production was calculated from available climate data

a dynamic process for drowning carbonate reefs on the northeastern australian margin drowned carbonate reefs on passive margins are puzzling because of their enormous growth potential compared to typical rates of passive margin subsidence and moderate sea level fluctuations a possible solution to this paradox is that slow processes acting over geologic time weaken reefs and contribute to their ultimate demise the australian northeastern marginal plateaus known for their drowned reefs underwent a period of accelerated tectonic subsidence during the late miocene to pliocene that combined with a sequence of second order global sea level rises outpaced reef growth and drowned the once thriving miocene carbonate platforms however the mechanism for the observed anomalous subsidence of this relatively mature passive margin 1000 km from the nearest plate boundary is uncertain we use a coupled plate kinematic mantle flow model to show that in the late miocene northeastern australia overrode subducted slabs from eocene melanesian subduction north of papua new guinea we find that the rate of surface subsidence induced by the sinking slabs increases the likelihood that relative sea level rises outpaced late miocene reef growth in addition to the well known effects of long term plate processes and short term global sea level and climate change our results demonstrate that deep earth processes can play a substantial role in driving the evolution of passive margins and coral reefs

permian metamorphic event in the alps in addition to the well known variscan and alpine orogenic cycles a permian thermal event occurred in the european alps the geodynamic background of this event is not well understood here we suggest that the event is a reflection of lithospheric thinning accompanied by magmatic underplating causing partial melting of the lower crust and low pressure high temperature metamorphism the event was terminated by early triassic opening of the meliata ocean and was followed by sag stage subsidence during slow lithospheric cooling this last stage of the evolution allowed the onset of the mesozoic marine evolution with the orogen wide formation of triassic carbonate platforms well known from the dolomites and the northern calcareous alps the combined evidence for magmatism metamorphism and late subsidence identifies the permian event of the alps as an excellent example of underplating events suggested as a cause for low pressure high temperature terrains worldwide

evidence for excess argon during high pressure metamorphism in the dora maira massif western alps italy using an ultra violet laser ablation microprobe 40 ar 39 ar technique ultra high pressure eclogite amphibolite grade metamorphism of the dora maira massif in the western alps is a well established and intensively studied event however the age of peak metamorphism and early cooling remains controversial the 40ar 39 ar step heating and laser spot ages from high pressure phengites yield plateau ages as old as 110 ma which have been interpreted as the time of early cooling after the high pressure event recent u pb and sm nd results challenge this assertion indicating a much younger age for the event around 45 ma and hence a radically different timing for the tectonic evolution of the western alps in a new approach to the problem samples from the undeformed hercynian metagranite brossasco were studied using an ultra violet laser ablation microprobe technique for 40ar 39 ar dating the new technique allowed selective in situ analysis at a spatial resolution of 50 urn of quartz phengite biotite and k feldspar the results demonstrate the frequent occurrence of excess argon with high 40ar 39 ar ratios 1000 10000 and a strong relationship between apparent ages and metamorphic textures the highest excess argon ratios are always associated with high closure temperature minerals or large diffusion domains within single mineral phases the best interpretation of this relationship seems to be that excess argon was incorporated in all phases during the high pressure event then mixed with an atmospheric component during rapid cooling and retrogression producing a wide range of argon concentrations and 40ar 36ar ratios step heating analysis of minerals with this mixture would produce linear arrays on a40ar 36ar versus 40ar 36 ar correlation diagram leading to geologically meaningless plateau ages older than the true closure age in the present case some ages in the range 60 110 ma could be explained by the presence of excess argon incorporated around 40 50 ma ago similar results found in other high pressure terrains in the alps may reconcile the argon geochronometer with other systems such as rb sr u pb or sm nd this study therefore calls for an increasing use of high resolution in situ sampling techniques to clarify the meaning of 40ar 36 ar ages in many high pressure terrains

excess argon incorporation in phengite of the mulhacen complex submicroscopic illitization and fluid ingress during late miocene extension in the betic zone south eastern spain abstract 40 ar 39 ar induction furnace and laser step heating of well crystallised post tectonic phengitic mica single grains from gneisses of the mulhacen complex with an early alpine tectonic fabric has resulted in 1 highly scattered integrated ages 2 an abnormally high atmospheric contamination and 3 often anomalously old apparent ages during early 39 ar release that is associated with a high 36 ar air and 37 ar ca contamination this low temperature excess argon 40 ar xs component is probably released from carbonate formed during slight alteration of the mica more than 50 of the samples yielded plateau ages ranging from 15 8 0 4 to 90 1 1 0 ma samples taken only a few metres apart may differ in age by as much as 50 ma a grain that was split over the basal plane yielded plateau ages for each half that differ by 12 the age variation on these different scales is explained by heterogeneous 40 ar xs incorporation during a period with a high transient partial argon pressure in the metamorphic fluid resulting from a late stage reheating event the very swift cooling of 50 100 c ma during exhumation of the mulhacen complex concomitant with late miocene extension may have prevented the equilibration of different 40 ar xs levels in the mica hrtem images of the oldest and youngest phengite specimens show that at least 20 of the lattice is affected by submicroscopic illitisation which is concentrated in several micrometer wide zones and veins that cross cut the basal cleavage these are made up of aggregates of 0 07 0 30 m thick crystallites of three illitic micas types which are chemically and structurally progressively closer to pure illite and occur in different textures the oldest specimen is affected most severely as the veins contain newly formed pseudo illite that does not inherit its crystallographic orientation and chemistry from the host mica in contrast to the youngest sample hrtem aem analyses revealed that phengite and the different illitic micas may be depleted in k the oldest sample is derived from a coarse grained augen gneiss with extensively developed hydraulic cracks which are lacking in the youngest sample a fine grained mylonitic gneiss fluid rock interaction and consequently sub microscopic illitization were therefore more intense in the coarser grained rocks growth of the illitic micas in equilibrium with a high partial 40 ar pressure could account for 40 ar xs incorporation in k vacancies and other lattice imperfections variation in illitisation and associated textural dissimilarities between the oldest and youngest mica permit the different levels of 40 ar xs incorporation that account for the observed age discordance the finding of 40 ar xs plateau ages despite the degassing of intimately intergrown micaceous minerals is interpreted by gas release invoked by in vacuo chemical and structural changes that led to a joint collapse of the lattices of phengite and the illitic micas between 800 c and 1000 c

the secret life of ice sails we present the first dedicated study into the phenomenon of ice sails these are clean ice structures that protrude from the surface of a small number of debris covered glaciers and can grow to heights of over 25 m we draw together what is known about them from the academic exploration literature and then analyse imagery we show here that ice sails can develop by one of two mechanisms both of which require clean ice to become surrounded by debris covered ice where the debris layer is shallow enough for the ice beneath it to melt faster than the clean ice once formed ice sails can persist for decades in an apparently steady state before debris layer thickening eventually causes a reversal in the relative melt rates and the ice sails decay to merge back with the surrounding glacier surface we support our image based analysis with a surface energy balance model and show that it compares well with available observations from baltoro glacier in the karakoram a sensitivity analysis of the model is performed and confirms the results from our empirical study that ice sails require a relatively high evaporative heat flux and or a relatively low sensible heat flux in order to exist

excess argon in phengite from eclogite evidence from dating of eclogite minerals by smnd rbsr and 40ar39ar methods the existence of excess ar in phengites from coesite bearing ultrahigh pressure eclogites of the dabie mountains and su lu terrain china has been confirmed by dating of minerals using sm nd rb sr and 40ar39ar methods 40ar39ar ages of phengites for two samples studied are much older than the sm nd and rb sr mineral isochron ages sample ql 1 has rb sr age of 219 5 0 5 ma sm nd age of 226 3 4 5 ma and phengite 40ar39ar age of 877 5 15 9 ma the corresponding ages for sample zb 4 are 223 9 0 9 ma rb sr 228 4 6 0 ma sm nd and 943 3 12 4 ma 40ar39ar phengite an age of 225 ma based on the sm nd and rb sr mineral isochron ages is consistent with the time inferred from paleomagnetic and geological data for collision of the north china and yangtse blocks and formation of these eclogites we call for greater caution in 40ar39ar dating of phengites from other occurrences of ultrahigh pressure environments

debris thickness patterns on debris covered glaciers abstract many debris covered glaciers have broadly similar debris thickness patterns surface debris thickens and tends to transition from convex to concave up down glacier we explain this pattern using theory analytical and numerical models paired with empirical observations down glacier debris thickening results from the conveyor belt like nature of the glacier surface in the ablation zone debris can typically only be added but not removed and from the inevitable decline in ice surface velocity toward the terminus down glacier thickening of debris leads to the reduction of sub debris melt and debris emergence toward the terminus convex up debris thickness patterns occur near the up glacier end of debris covers where debris emergence dominates ablation controlled concave up debris thickness patterns occur toward glacier termini where declining surface velocities dominate velocity controlled a convex concave debris thickness profile inevitably results from the transition between ablation control and velocity control down glacier debris thickness patterns deviating from this longitudinal shape are most likely caused by changes in hillslope debris supply through time by establishing this expected debris thickness pattern the effects of climate change on debris cover can be better identified

spatial distribution of debris thickness and melting from remote sensing and meteorological data at debris covered baltoro glacier karakoram pakistan a distributed surface energy balance study was performed to determine sub debris ablation across a large part of baltoro glacier a wide debris covered glacier in the karakoram range pakistan the study area is 124 km 2 the study aimed primarily at analyzing the influence of debris thickness on the melt distribution the spatial distribution of the physical and thermal characteristics of the debris was calculated from remote sensing aster image and field data meteorological data from an automatic weather station at urdukas 4022 m a s l located adjacent to baltoro glacier on a lateral moraine were used to calculate the spatial distribution of energy available for melting during the period 1 15 july 2004 the model performance was evaluated by comparisons with field measurements for the same period the model is reliable in predicting ablation over wide debris covered areas it underestimates melt rates over highly crevassed areas and water ponds with a high variability of the debris thickness distribution in the vicinity and over areas with very low debris thickness 0 03 m we also examined the spatial distribution of the energy balance components global radiation and surface temperature over the study area the results allow us to quantify for the study period a meltwater production of 0 058 km 3

monitoring surging glaciers of the pamirs central asia from space the evolution of surging glaciers of the pamirs central asia has been studied using repeat remote sensing surveys in the institute of geography russian academy of sciences since the early 1970s we use images obtained from national resurs f satellites 1972 91 as well as landsat 7 and terra 1999 2006 to provide a basis for monitoring of surging glaciers aimed at developing their inventory studying the causes and mechanisms of surges and examining the timing and extent of glacial catastrophes the inventory from the early 1990s allows identification of 215 glaciers with a dynamically unstable regime we discovered 51 surging glaciers up until 2006 10 more surges had occurred we use stereoscopic deciphering and photogrammetric processing of consecutive satellite images to study the morphology and ice velocity changes of several compound surging glaciers we analyze the results of monitoring of bivachny and oktyabr sky glaciers from 1972 to 1991 and sugran glacier from 1972 to 2006 two surges of sugran glacier occurred during this time an internal surge in 1976 80 and a surge with glacier tongue advance as far as 4 5 km in 2000 05 the role of damming in compound glacier systems is examined satellite based monitoring is now the only method for obtaining initial information about the state and fluctuations of such glaciers

climate change studies in the western himalaya the high himalayan mountains in the north of india are important sources for generating and maintaining the climate over the entire northern belt of the indian subcontinent they also influence extreme weather events such as the western disturbances over the region during winter the work presented here describes some current trends in weather and climate over the western himalaya and suggests some possible explanations in the context of climate change the work also shows how the special features of indian orography in the western himalaya affect climate change in the long term changing the pattern of precipitation over the region data analysis of different ranges of the western himalaya shows significant variations in temperature and snowfall trends in the past few decades possible explanations for the changing climate over the western himalaya are proposed in terms of variations in cloudiness the possible effects of climate change on the number of snowfall days and the occurrences of western disturbances over the western himalaya are also analysed

land subsidence and late glacial environmental evolution of the como urban area northern italy abstract the late glacial and holocene geological and environmental evolution of the como lacustrine palustrine basin has been broadly reconstructed based on a the collection and analysis of more than 100 borehole stratigraphies b the drilling of three new shallow boreholes and the analysis of a new geological section and c several in situ and laboratory analyses mineralogical organic and pollen content 14c dating the long term natural tendency of the ground surface to sink where the como urban area has developed has been verified and assessed this tendency has resulted clearly controlled by the compaction of young unconsolidated sediments accumulated at the hydrologically closed sw tip of lake como the definition of a minimum age for the deglaciation of the basin and for a correlated stratigraphic marker allowed broad quantification of the average velocity of land subsidence during the last ca 17 000 cal bp with a gradient of values close to 2 5 mm yr along the axial zone of the basin toward the present day lake burial depth of archaeological remains related to roman age and levelling monitoring since 1928 are in agreement with this estimate during 1950 1975 because of deep water withdrawal the como area was affected by a human induced accelerated subsidence with velocity 10 20 mm yr one order of magnitude higher than the natural one after a period of deceleration between the end of the 1970s and the end of the 1990s during which some benchmarks even reversed their trend persistent scatterer interferometry psi data provided by tele rilevamento europa tre for the period 1992 2003 and levelling data obtained by apat in 2004 show that during the last decade the subsidence rate has returned to its physiologic long term trend

distribution and significance of extraneous argon in uhp eclogite sulu terrain china insight from in situ 40ar 39ar uv laser ablation analysis in situ 40ar 39ar uv laser ablation analyses of garnet omphacite epidote phengite barroisite and symplectite in a sample of uhp eclogite from qinglongshan sulu terrain china reveal extremely heterogeneous argon isotopic ratios results from the 220 240 ma eclogite indicate a significant and variable extraneous argon signature that is restricted to the early formed phengite and epidote and later formed barroisite individual compositionally zoned phengite grains record a large variation in 40ar 39ar dates 300 1100 ma that are positively correlated with celadonite content these data are consistent with retrograde chemical exchange and argon isotopic repartitioning in response to decreasing partial pressures of argon during decompression consistent with the observation of atmospheric argon ratios in garnet omphacite and symplectite these data support an interpretation that the extraneous ar was incorporated early in the crystallization history of the eclogite and not from a late infiltrating fluid the ultimate source of the extraneous argon remains speculative however on the basis of supporting stable oxygen and hydrogen isotope data from this locality which support a closed isotopic system it is inferred to have been inherited from the protolith of the uhp eclogite

triassic continental rifting of pangaea direct evidence from the alpujarride carbonates betic cordillera se spain abstract evidence is presented for triassic rift related palaeo structures from the alpujarride complex carbonates of the betic cordillera se spain direct evidence of synsedimentary extensional tectonics is provided by macro to meso scale normal faults overstepped by younger strata most faults define domino like horst and graben structures the faults are associated with an expanded synrift sedimentary prism in which soft sediment deformation gravity flow deposits and unconformities are widely developed syntectonic mafic igneous intrusions also occur the age of this phase of extension is constrained as ladinian carnian c 237 216 ma from a palaeogeographical standpoint the thick triassic carbonates of the betic internal zone together with comparable successions in northern calabria southern apennines occupied a belt with elevated subsidence connecting the neo tethys to the east with the eastern north american intracontinental rift system to the west their carbonate facies intermediate between classical alpine and germanic type triassic facies recorded the main episodes of rifting affecting central pangaea

assessing glacier features supporting supraglacial trees a case study of the miage debris covered glacier italian alps the number of debris covered glaciers featuring supraglacial trees is increasing worldwide as a response of high mountain environments to climate warming generally their distribution on the glacier surface is not homogeneous thus suggesting that some glacier parameters influence germination and growth of trees in this study we focused our attention on the widest italian debris covered glacier the miage glacier mont blanc massif we analyzed the ablation area in the range from 1730 to 2400 m a s l where continuous debris coverage is present and trees are found using data obtained by remote sensing investigations and field surveys we defined a record of glacier parameters to be analyzed with respect to the presence and abundance of trees we found that supraglacial trees are present at the miage glacier 1 whenever exceeding a debris thickness threshold 19 cm 2 with a gentle slope 10 3 with a low glacier surface velocity 7 0 m yr and 4 where the vertical changes due to glacier

distribution of debris thickness and its effect on ice melt at hailuogou glacier southeastern tibetan plateau using in situ surveys and aster imagery debris cover is widely present in glacier ablation areas of the tibetan plateau and its spatial distribution greatly affects glacier melt rates high resolution in situ measurements of debris thickness on hailuogou glacier mount gongga southeastern tibetan plateau show pronounced inhomogeneous debris distribution an analysis of transverse and longitudinal profiles indicates that the ground surveyed debris thicknesses and advanced spaceborne thermal emission and reflection radiometer aster derived thermal resistances of debris layers correlate strongly over the entire ablation area across and along glacier patterns of aster derived thermal resistance correspond well with spatial patterns of debris thickness which may reflect large scale variations in the extent and thickness of the debris cover the ice melt rate variability over the ablation area simulated by a surface energy balance model that considered thermal resistance of the debris layer indicates clearly the crucial role of debris and its spatial continuity in modifying the spatial characteristics of melt rates because of the inhomogeneous distribution of debris thickness about 67 of the ablation area on hailuogou glacier has undergone accelerated melting whereas about 19 of the ablation area has experienced inhibited melting and the sub debris melt rate equals the bare ice melt rate in only 14 of the ablation area

excess 40ar transport scale and mechanism in high pressure phengites a case study from an eclogitized metabasite of the dora maira nappe western alps application of the bulk separate furnace heating laser step heating and in situ laser agemapping 40ar 39ar techniques reveals that high pressure phengites from an alpine eclogite of the dora maira basement nappe western alps were pervasively contaminated with excess 40ar to yield ages 130 ma spot fusion dating of individual grains with the 40ar 39ar laserprobe reveals concentric radial patterns with core ages as high as 320 ma showing that this excess component was trapped at an early stage and subsequently remobilized by volume diffusion during a late greenschist thermal pulse the single grains and population from this hand sample retain major differences in apparent ages indicating that the extent of the excess 40ar contamination varies from grain to grain attempt to model these differences in terms of grain size dependent fractional loss falls short and demonstrates that strong cm scale argon isotopic gradients locally prevailed during syn kinematic high pressure metamorphism on petrostructural grounds a model of internal isotopic buffering is outlined whereby the excess 40ar is argued to have been internally derived from within the eclogite protolith itself low intergranular ar diffusion rates due to reduced water activity buffered below unity by the phengite assemblage resulted in the local segregation and partitioning of the excess 40ar along grain boundaries during ongoing ductile deformation supporting evidence for this model comes from the recent literature on fluid and stable isotope behaviour in alpine eclogites and very high pressure metasediments which shows that volatile recycling during high pressure metamorphism may occur on a very limited scale

muscovite k ar ages of the sanbagawa schists japan and argon depletion during cooling and deformation seventy muscovites from schists in the sanbagawa terrain in central shikoku were dated by the k ar method the muscovite ages are consistently older with increasing metamorphic grade within the same zone the ages are significantly younger in schists which have been more severely deformed these k ar age variations could be due to systematic argon depletion during deformation i e to the dynamic recrystallization of muscovites during ductile deformation that formed a large scale recumbent fold during the uplift and cooling argon loss was greater in schists that were more extensively deformed and in the lower grade zone that experienced a longer period of low temperature deformation than the higher grade zone the relationships between age and grain size in a pelitic schist suggest that coarse grained muscovites lost more argon than the finegrained ones there was no significant resetting of ages in the vicinity of major strike slip faults such as the median tecotonic line or near thrust faults the combination of geochronological and geological data constrains the cooling rate of the sanbagawa schists to 9 12 c ma in the oligoclase biotite zone in central shikoku japan

migration of igneous activities related to ridge subduction in southwest japan and the east asian continental margin from the mesozoic to the paleogene abstract in the inner zone of southwest japan the northern part of the median tectonic line mtl granites and their volcanic equivalents were formed in large quantities during the late cretaceous to early tertiary migration of magmatic activity related to ridge subduction is proposed to explain the widely distributed magmatism and its tectonics for this purpose the ages of granitic rocks were carefully inspected according to the criteria of the dating methods and procedures concerned and compiled with the sampling localities they clearly show a trend in rock ages along the mtl in agreement with the general direction of strikes in southwest japan from the trend of the ages and the cooling histories of the bodies it was concluded that the magmatism migrated eastward along the mtl with a rate of 30 km m y this migration concept is extended to the mesozoic igneous rocks of the east asian continental margin there two magmatic belts ranging in age from mesozoic to paleogene are found to become younger northeastward along the margins which is ascribed to the subduction of the farallon izanagi and kula pacific ridges

triassic high strain shear zones in hainan island south china and their implications on the amalgamation of the indochina and south china blocks kinematic and 40ar 39ar geochronological constraints abstract a kinematic and geochronological study has been carried out on the triassic high strain shear zones in hainan island the southern south china block there are wnw and ne trending high strain shear zones with greenschist to amphibolite facies metamorphism in this island kinematic indicators suggest a dextral top to the nne thrust shearing for the wnw trending high strain shear zones and a sinistral top to the se thrust shearing for the ne trending shear zones the quartz c axis orientations of mylonitic rocks exhibit the domination of basal slip and some activation of a rhombohedra gliding system the timing of shearing for these shear zones has been constrained by the 40ar 39ar dating analyses of synkinematic minerals middle triassic 242 250 ma and late triassic early jurassic 190 230 ma have been identified for the wnw and ne trending shear zones respectively a synthesis of these kinematic and thermogeochronological data points to a two stage tectonic model for hainan island that is top to the nne oblique thrusting at 240 250 ma followed by top to the se oblique thrusting at 190 230 ma in combination with the available data from the southern south china and indochina blocks it is inferred that south hainan and north hainan have affinity to the indochina and south china blocks respectively the tectonic boundary between south hainan and north hainan lies roughly along the wnw trending changjiang qionghai tectonic zone probably linking to the song ma and ailaoshan zones the middle triassic structural pattern of hainan island is spatially and temporally compatible with those of the south china and indochina blocks and thus might be a derivation from the amalgamation of the indochina with south china blocks in response to the closure of the paleotethys ocean and subsequent subduction collision

supervised classification of types of glaciated landscapes using digital elevation data abstract automated approaches for identifying different types of glaciated landscapes using digitally processed elevation data were evaluated we tested the ability of geomorphic measures e g elevation relative relief roughness and slope gradient derived from digital elevation models dems to differentiate glaciated landscapes using maximum likelihood classification and artificial neural networks ann the automated methods were trained and validated using an existing quaternary geology map and a manual interpretation of the contour data portrayed on topographic quadrangles the need for such methods arises from efforts to classify types of landscapes e g ecoregions in michigan one fundamental control of the landscape structure in michigan including soil type and vegetation is the underlying sedimentary and landform assemblages produced by an array of glacial processes during the waning phase of the pleistocene traditional methods for identifying different landscapes e g ice contact landscapes stagnation landscapes have relied on printed topographic maps and have been very effective but time consuming the maps resulting from the four supervised classification trials had between 51 and 61 agreement with the original quaternary geology map the output from the maximum likelihood classification had slightly higher agreements than the output from the neural net which is attributed to the generalization inherent in the quaternary geology map compared with the nature of the classifier for the neural net the neural net however identifies significant detail and non linear relationships between classification inputs and output classes future work should incorporate a map of soils into the classification

40ar 39ar mineral age constraints for the tectonothermal evolution of the sambagawa metamorphic belt central shikoku japan a cretaceous accretionary prism abstract the sambagawa metamorphic belt exposed in central shikoku japan is tectonostratigraphically represented by the oboke and structurally overlying besshi nappe complexes oboke units consist of metamorphic rocks largely derived from clastic protoliths sandstone and conglomerate whereas besshi units are dominated by rocks with oceanic protolith affinities shale chert and greenstone whole rock schist samples from low grade oboke units record intermediate temperature 40 ar 39 ar plateau ages of 70 77 ma which are interpreted to closely date attainment of maximum metamorphic conditions whole rock schist samples from besshi units chlorite zone record plateau ages of 85 94 ma suggesting an earlier metamorphic climax within this structural level amphibole within the albite biotite zone in besshi records 36 ar 40 ar vs 39 ar 40 ar plateau isotope correlation ages of 84 87 ma which are interpreted as dating the post metamorphic cooling through temperatures required for intracrystalline retention of argon a slightly older isotope correlation age 94 ma is recorded by amphibole from the higher grade oligioclase biotite zone contrasts in amphibole cooling ages are interpreted as reflecting thrust related metamorphic inversion and resultant earlier cooling of higher grade structural units muscovite from all structural levels of the besshi nappe complex records 40 ar 39 ar plateau ages of 76 89 ma these are interpreted to date post metamorphic cooling through appropriate closure temperatures following structural assembly of the besshi nappe complex protoliths of the besshi units originated at approx 130 ma and attained maximum metamorphic conditions during entrainment in an accretionary complex at approx 90 100 ma higher grade sequences developed at deeper levels along the hanging wall of the accretionary complex during subsequent structural uplift to shallower crustal levels the besshi nappe complex was tectonically emplaced over oboke units

temporal and spatial variation of the surface albedo of the morteratschgletscher switzerland as derived from 12 landsat images this investigation uses landsat images from 12 days in 1999 and 2000 to study the spatial and temporal variation in surface albedo of a glacier with a rugged topography morteratschgletscher switzerland our retrieval method considers all processes that substantially influence the relationship between the satellite signal and the surface albedo the correction for the anisotropy of the reflected radiation field of ice and snow ranges up to 0 10 depending on wavelength band solar zenith angle and surface type we analyzed the uncertainties in the retrieval method and mainly expect errors in satellite derived albedos for areas with large variation in topography and high albedos the latter is due to application of bidirectional reflectance distribution function brdf parameterizations for the anisotropic correction to albedos outside the parameterizations validity on average satellite derived albedos exceed the measured surface albedo by 0 03 the glacier tongue is characterized by bands of low and high albedo relating to ice with higher and lower concentrations of debris the ice albedo shows no dependence on altitude except at 2000 2200 m a s l it increases during summer which is likely associated with rainfall as concluded from a comparison between summer rainfall and measured albedos

glaciological characteristics of the ablation zone of baltoro glacier karakoram pakistan baltoro glacier in the karakoram pakistan is one of the world s largest valley glaciers it drains an area of about 1500 km 2 and is 60km long in 2004 an italian german expedition carried out a glaciological field program on the ablation zone of the glacier focusing on the ablation conditions and the dynamic state of the glacier as baltoro glacier is a debris covered glacier ice ablation also depends on the debris properties stake measurements of ice ablation and debris cover in combination with meteorological data from automatic weather stations close by have been used to determine the local melt conditions results from these calculations have been combined with an analysis of different classes of surface cover and information about precipitation using remote sensing techniques in order to calculate mass fluxes for the upper part of baltoro glacier the dynamic state of the glacier has been investigated by gps based surface velocity measurements along the stake network a comparison of these short term measurements during the melt season with surface velocities computed from feature tracking of satellite images shows a high seasonal variability of the ice motion we have shown that this variability is up to 100 of the annual mean velocity on the basis of these investigations the mass fluxes at the concordia cross section have been quantified this approach can now be used together with the ablation calculations to reconstruct the variability of glacier extent and volume in the past using available climate data from the central karakoram from the comparison of historical measurements and photographs it is shown that the snout of baltoro glacier is oscillating back and forth a couple of hundred metres otherwise it seems not to react with the same magnitude as other glaciers to the climatic change elevation changes at concordia are a few tens of metres at the most

tethyan ophiolites and tethyan seaways tethyan ophiolites have played a major role in the development of the ophiolite concept during the past 200 years and contributed significantly to the formulations of the suprasubduction zone ssz ophiolite paradigm and the plate tectonics theory their melt evolution and magmatic construction witnessed the dispersal of the supercontinent pangaea via continental rifting and seafloor spreading opening and closure of multiple seaways in an eastward widening latitudinal ocean basin neotethys and deep mantle recycling processes through subduction zone tectonics and plume activities neotethyan ophiolites are highly diverse in their crustal mantle structures and compositions pointing to major differences in their melt sources and tectonic settings of magmatic construction the papers in this thematic set demonstrate these differences in the neotethyan ophiolite record through new structural geochemical isotopic and geochronological data and interpretations the jurassic western alpine ophiolites formed in a narrow basin alpine tethys that developed between europe and north africa adria iberia their peridotites represent exhumed continental lithospheric mantle the triassic jurassic and cretaceous ophiolites east of adria formed in different neotethyan seaways and their ssz magmatic construction involved multiple episodes of melting depletion and refertilization of subduction modified oceanic mantle the late cretaceous peri arabian and peri indian ophiolites which are discontinuously exposed along a c 9000 km long belt from sw anatolia to se tibet formed above a trans tethyan subduction accretion system within southern neotethys diachronous collisions of arabia and india with this intraoceanic subduction accretion system in the latest mesozoic and the paleogene respectively resulted in diachronous ophiolite emplacement in the mediterranean and tibetan himalayan orogenic belts thematic collection this article is part of the tethyan ophiolites and tethyan seaways collection available at https www lyellcollection org cc tethyan ophiolites and tethyan seaways

changes in the ablation zones of glaciers in the western himalaya and the karakoram between 1972 and 2015 abstract observed estimates of changes in the himalayan and karakoram glaciers remain ambiguous because of limited knowledge regarding complex glacier behaviour low quality of remote sensing data and sparse ground based monitoring remote sensing has indicated anomalous behaviour of glaciers in the karakoram during the past two decades attracting scientists attention to the region in this context this study has made detailed estimates of changes in thickness and area of two glaciers the sachen in the western himalaya and the burche in the karakoram to facilitate understanding of recent glacier changes and their potential impacts on water resources this study used several datasets including landsat the shuttle radar topographic mission srtm the ice cloud and land elevation satellite icesat and differential global positioning system dgps in situ measurements from the period 1972 through 2015 the extent of debris cover increased significantly between 1972 and 2014 while the total glacierized area decreased slightly further our study estimated thickness changes after removing recognizable biases and seasonal variations computed through comparisons of icesat data with dgps a thinning trend occurred between 2000 and 2015 suggesting that the glaciers in the western part of the karakoram and himalaya regions have not recently gained mass this study also found non uniform variations within different zones of the glaciers avalanches have fed most of the karakoram glaciers providing spatially heterogeneous thickness changes the frequency of observations data quality acquisition time and local weather affect our observations of temporal changes careful assessment of regularly acquired remote sensing and ground based observations should reduce uncertainty regarding estimates of glacier changes for management of water resources and associated hazards

the radiolarian evidence for the accretion of the fu saki formation with the inferred oceanic plate stratigraphy a case of weakly metamorphosed accretionary complex in ishigaki jima southern ryukyu arc japan abstract the island of ishigaki jima located in the western part of the southern ryukyu arc japan is underlain by a basement comprising the tumuru and fu saki formations the former is a pelitic glaucophane schist with a metamorphic age of 220 190 ma and the latter is a weakly metamorphosed accretionary complex composed mainly of chert mudstone and sandstone with minor amounts of limestone and mafic rocks the fu saki formation was weakly metamorphosed at 140 ma latest carboniferous early jurassic microfossils have been obtained from the limestones cherts and siliceous mudstones of this formation but no fossils have been collected from the phyllitic mudstones the radiolarian fauna of the phyllitic mudstones described herein indicates a late pliensbachian early toarcian early jurassic age this result when combined with existing data enables the reconstruction of an oceanic plate stratigraphy showing a succession of in ascending order upper carboniferous triassic cherts sinemurian lower pliensbachian siliceous mudstones and upper pliensbachian lower toarcian phyllitic mudstones and sandstones the radiolarians from the phyllitic mudstones are important in constraining the timing of the accretion of the fu saki formation to the base of the tumuru formation

microtectonics and 39ar 40ar dating of high pressure metamorphic rocks of the south ryukyu arc and their bearings on the pre eocene geodynamic evolution of eastern asia abstract the pre eocene metamorphic rocks found in the yaeyama islands the southern part of the ryukyu arc have disputed relationships with the metamorphic formations of japan and taiwan they are divided into the tomuru and fusaki formations 1 1 the tomuru formation is composed of high pressure hp metamorphic rocks derived from oceanic sediments and the uppermost oceanic crust the first deformation phase is characterized by a synmetamorphic nw se trending stretching lineation l1 kinematic analysis shows that the deformation corresponds to a subhorizontal ductile shear directed along l1 from the northwest to the southeast 2 2 the fusaki formation or chaotic formation is an olistostrome of triassic or lower jurassic radiolarite olistoliths the age of the matrix is assumed to be late jurassic it is slightly schistose and only a s vergent deformation phase is observed it is assumed that the hp schists overthrust the mesozoic olistostrome 39ar 40ar step heating experiments have been carried out on phengite and na amphibole from the tomuru formation phengite and zoned barroisite crossite give well defined plateaus at 225 4 8 ma and 237 6 3 ma respectively they are interpreted as the age of the ductile deformation crossite yields an integrated data of 104 8 8 3 ma interpreted as the age of the thrusting of the hp schists above the chaotic formation the lithostratigraphy petrology microtectonics and 39ar 40ar ages of the hp schists and the chaotic formation are similar to the permian sangun hp schists and the jurassic tanba olistostrome of the inner belt of southwestern japan respectively there the sangun schists also overthrust the tanba olistostrome during the mesozoic orogeny the same tanba like mesozoic olistostrome is also found in taiwan but was intensely deformed and metamorphosed in miocene times the geodynamic collision model proposed to account for the late permian to early triassic orogen of southwestern japan is extended to the south ryukyu and taiwan conversely the mesozoic sanbagawa hp schists and the upper jurassic to lower miocene turbidites and olistostrome sanbosan shimanto zones of southwestern japan are neither exposed in the south ryukyu arc nor in taiwan hypotheses are discussed that call upon tectonic erosion or non deposition to account for this absence

tectonostratigraphic evolution of the jurassic extensional basins of the eastern southern alps and adriatic foreland based on an integrated study of surface and subsurface data successions that characterize the eastern southern alps have been compared with coeval units drilled in the alpine foreland po and veneto plains northern adriatic sea the eastern southern alps are composed of a carbonate platform plateau drowned in the early jurassic trento platform and plateau a basin formed in the early jurassic belluno basin and a carbonate platform that lasted from the jurassic to the cretaceous friuli platform integration of stratigraphic and geophysical data illustrates the extensional architecture of the alpine foreland subsurface at the beginning of the jurassic peritidal successions were widespread everywhere except for the belluno basin a reorganization of the early jurassic paleogeography affected the southern alps around the sinemurian pliensbachian boundary the pliensbachian successions were deposited in the central western areas of the trento platform whereas elsewhere in the same platform and in the northern friuli platform pliensbachian units are missing replaced by an unconformity surface covered by crinoidal sands that have also been found in the subsurface the belluno basin is recognizable in seismic profiles under the veneto plain southward northern adriatic sea and po plain the basin between the trento and the friuli platforms here called the northern adriatic basin possesses a stratigraphy different from that of the belluno basin the northern adriatic basin drowned later and seismic profiles indicate that it was wider and bounded by groups of small synsedimentary faults instead of the major faults displacing the belluno basin the northern adriatic basin can be interpreted as the northeastern extension of the umbro marchean basin of central italy

evidence for late alpine tectonics in the lake garda area northern italy and seismogenic implications we investigated the recent evolution of the po plain alps system by integrating subsurface geophysical data from the po plain with new stratigraphic and structural observations from the southern alps margin inversion of structural data and chronology provided by stratigraphic constraints led to the definition of three tectonic events since the pliocene namely the intra zanclean the gelasian and the middle pleistocene driven by an axis of maximum compression formerly oriented ne intra zanclean and then to the nnw gelasian and middle pleistocene the associated deformation has been accommodated by two sets of faults consisting of nne trending thrust faults mostly represented in the western sector of lake garda and nw trending strike slip faults observed in the southern and eastern sectors the interplay between these two sets of faults is interpreted to produce short w w 6 5 along the nw trending strike slip faults in this framework the newly defined nogara fault and the sant ambrogio fault all pertaining to the nw trending system are regarded as potential candidates for the seismogenic source of the january a d 1117 event the most destructive earthquake in the po plain

cretaceous isochron ages from k ar and 40ar 39ar dating of eclogitic rocks in the tso morari complex western himalaya india abstract the tso morari complex which is thought to be originally the margin of the indian continent is composed of pelitic gneisses and schists including mafic rock lenses eclogites and basic schists eclogites studied here have the mineral assemblage grt omp ca amp zo phn pg qtz rt they also have coesite pseudomorph in garnet and quartz rods in omphacite suggesting a record of ultrahigh pressure metamorphism they occur only in the cores of meter scale mafic rock lenses intercalated with the pelitic schists small mafic lenses and the rim parts of large lenses have been strongly deformed to form the foliation parallel to that of the pelitic schists and show the mineral assemblages of upper greenschist to amphibolite facies metamorphism the garnet omphacite thermometry and the univariant reaction relations for jadeite formation give 13 21 kbar at 600 c and 16 18 kbar at 750 c for the eclogite formation using the jadeite content of clinopyroxene x jd 0 48 phengites in pelitic schists show variable si al and na k ratios among grains as well as within single grains and give k ar ages of 50 87 ma the pelitic schist with paragonite and phengite yielded k ar ages of 83 5 ma k 4 9 wt for paragonite phengite mixture and 85 3 ma k 7 8 wt for phengite and an isochron age of 91 13 ma from the two dataset the eclogite gives a plateau age of 132 ma in ar ar step heating analyses using single phengite grain and an inverse isochron age of 130 39 ma with an initial 40 ar 36 ar ratio of 434 90 in ar ar spot analyses of phengites and paragonites the cretaceous isochron ages are interpreted to represent the timing of early stage of exhumation of the eclogitic rocks assuming revised high closure temperature 500 c for phengite k ar system the phengites in pelitic schists have experienced retrograde reaction which modified their chemistry during intense deformation associated with the exhumation of these rocks with the release of significant radiogenic 40 ar from the crystals the argon release took place in the schists that experienced the retrogression to upper greenschist facies metamorphisms from the eclogite facies conditions

flat plateau and impossible isochrons apparent 40ar 39ar geochronology in a high pressure terrain until recently most ages determined by the 40ar 39ar technique have been represented by the age spectrum and isochron early in the history of the technique a series of criteria were outlined in order to discriminate between spectra which were considered to reflect disturbed isotopic systems and spectra which were considered to reflect the accurate age of the rock or mineral with the advancement of 40ar 39ar instrumentation and the introduction of laser ablation techniques it is now possible to obtain an age from single grains and on a sub grain scale in this case there is no production of an age spectra or determination of a plateau age however isochrons are still readily produced and used in the discussion of ar isotope ratios and specifically excess argon here new data illustrate the possible drawback first of the age spectrum and plateau age in the absence of an independent geochronological constraint in high pressure terranes and second of the accompanying isochron which we demonstrate can be both incorrect and geologically meaningless

an enhanced temperature index glacier melt model including the shortwave radiation balance development and testing for haut glacier d arolla switzerland an enhanced temperature index glacier melt model incorporating incoming shortwave radiation and albedo is presented the model is an attempt to combine the high temporal resolution and accuracy of physically based melt models with the lower data requirements and computational simplicity of empirical melt models represented by the degree day method and its variants the model is run with both measured and modelled radiation data to test its applicability to glaciers with differing data availability five automatic weather stations were established on haut glacier d arolla switzerland between may and september 2001 reference surface melt rates were calculated using a physically based energy balance melt model the performance of the enhanced temperature index model was tested at each of the four validation stations by comparing predicted hourly melt rates with reference melt rates predictions made with three other temperature index models were evaluated in the same way for comparison the enhanced temperature index model offers significant improvements over the other temperature index models and accounts for 90 95 of the variation in the reference melt rate the improvement is lower but still significant when the model is forced by modelled shortwave radiation data thus offering a better alternative to existing models that require only temperature data input

an energy balance model for debris covered glaciers including heat conduction through the debris layer extensive covers of supraglacial debris are often present in glacier ablation areas and it is essential to assess exactly how the debris affects glacier melt rates this paper presents a physically based energy balance model for the surface of a debris covered glacier the model is driven by meteorological variables and was developed using data collected at miage glacier italy during the ablation seasons of 2005 2006 and 2007 the debris surface temperature is numerically estimated by considering the balance of heat fluxes at the air debris interface and heat conduction through the debris is calculated in order to estimate melt rates at the debris ice interface the predicted hourly debris surface temperatures and debris internal temperatures provide a good fit to temperatures measured on rock covered miage glacier r 2 0 94 and the tephra covered glacier on villarrica volcano chile r 2 0 82 the model can also be used to reproduce observed changes in melt rates below debris layers of varying types and thicknesses an important consideration for the overall mass balance of debris covered glaciers

exhumation of triassic hp lt rocks by upright extrusional domes and overlying detachment faults ishigaki jima ryukyu islands abstract the tomuru formation of ishigaki jima in the southernmost part of the ryukyu arc comprises blueschist facies subduction complex rocks metamorphosed in triassic time d1 structures related to subduction blueschist facies mineral growth and possibly early stages of exhumation are deformed by d2 structures that appear to reflect the last stage of exhumation d2 structures define several anticlines with parasitic overturned folds verging away from anticlinal axes the shortening recorded by this deformation appears to reflect upward extrusion relative to flanking material the anticlines are flanked by detachment faults with normal sense of shear parallel to d2 vergence hanging wall rocks that include the fusaki formation an accretionary prism with early cretaceous metamorphic ages and late eocene limestone conglomerate and andesitic volcanics the eocene strata contain metamorphic detritus derived from the tomuru and fusaki formations indicating pre late eocene surface exposure of these units ultramafic rocks and gabbro blocks of the tomuru formation were incorporated by sedimentary sliding into the trench prior to subduction and high pressure metamorphism rather than being emplaced as diapirs along a post metamorphic fault as previously proposed geochronologic metamorphic and thermal considerations suggest exhumation of the tomuru formation to relatively shallow crustal depths prior to or concurrent with early cretaceous metamorphism of the fusaki formation arcward vergent thrusting may have placed the younger and formerly structurally lower subduction complex fusaki formation over the older one tomuru formation d2 extrusional doming began after the emplacement of the fusaki formation at high structural levels the d2 transport directions are subparallel to the strike of the orogen suggesting that the upright extrusion may have occurred along a forearc strike slip fault system this final stage of exhumation concluded in the late eocene with extensional collapse and the development of detachment faults the progression from initial exposure of the tomuru and fusaki formations deposition of late eocene strata extrusional doming and late detachment faulting may have been associated with migrating step overs rather than changes in regional tectonics

calculating ice melt beneath a debris layer using meteorological data generalized numerical models of sub debris ice ablation are preferable to empirical approaches for predicting runoff and glacier response to climate change as empirical methods are site specific and strongly dependent upon the conditions prevailing during the measurement period we present a modified surface energy balance model to calculate melt beneath a surface debris layer from daily mean meteorological variables despite numerous simplifications the model performs well and modelled melt rates give a good match to observed melt rates suggesting that this model can produce reliable estimates of ablation rate beneath debris layers several decimetres thick this is a useful improvement on previous models which are inappropriate for thick debris cover

timing and evolution of middle triassic magmatism in the southern alps northern italy middle triassic magmatism in the southern alps northern italy consists of widespread volcanoclastic deposits basaltic lava flows and intrusive complexes despite their importance in understanding the geodynamic evolution of the westernmost tethys the timing of magmatic activity and the links between the different igneous products remain poorly understood we present a comprehensive high precision zircon u pb geochronology dataset for the major intrusive complexes and several volcanic ash layers and integrate this with a high resolution stratigraphic framework of middle triassic volcano sedimentary successions the main interval of middle triassic magmatism lasted at least 5 07 0 06 myr magmatic activity started with silicic eruptions between 242 653 0 036 and 238 646 0 037 ma followed by a supplementary material isotope dilution thermal ionization mass spectrometry u pb and laser ablation inductively coupled plasma mass spectrometry trace element data tables sample coordinates supplementary geochemical data cathodoluminescence images of isotope dilution thermal ionization mass spectrometry dated zircons and supplementary field documentation are available at https doi org 10 6084 m9 figshare c 4287506