sandstone matrix olistostrome deposited on intra subduction complex serpentinite franciscan complex western marin county california abstract detailed field mapping in the franciscan complex in western marin county california offers insight into the origins and development of melanges as well as accretionary complex architecture from structurally high to low the study area units comprise a structurally high sandstone matrix olistostrome serpentinite a structurally intermediate sandstone matrix olistostrome early cretaceous nicasio reservoir terrane greenstone and coherent cretaceous greywacke all exhibiting prehnite pumpellyite burial metamorphism the structurally high sandstone matrix olistostrome includes volcanic blocks up to 700 m in diameter and chert blocks up to 100 m in diameter whereas the structurally intermediate olistostrome unit comprises a lithic rich sandstone matrix enclosing volcanic blocks 1 20 m in diameter the youngest detrital zircons in the high olistostrome and the coherent greywacke have u pb ages of 20 m y older than the inferred depositional ages of the units themselves suggesting that the bulk of the detritus comprising these units was derived by exposure and sedimentary recycling of significantly older previously accreted sediments the matrix of both olistostrome units exhibits minimal strain with weak local development of pressure solution cleavage these findings demonstrate introduction of franciscan exotic blocks and development of franciscan block in matrix fabrics through sedimentary sliding and support sedimentary interpretations for more highly strained shale and serpentinite matrix melanges additionally these data suggest that sandstone matrix olistostromes melange may constitute a larger part of the franciscan and other accretionary complexes than previously believed the structurally high olistostrome preserves a depositional contact on serpentinite verifying an intra subduction complex origin for the serpentinite the serpentinite lacks block in matrix structure and likely represents a tectonically emplaced unit derived from the subducting plate as a coherent nappe rather than a sedimentary serpentinite deposit multi kilometer scale west vergent overturned folds with subhorizontal fold axes deform the nappes of the field area and a later generation of open northeast trending folds overprints the earlier folds

on the origin and post depositional history of widespread massive ash deposits the case of intermediate brown tuffs ibt of lipari aeolian islands italy abstract we analysed a widespread massive ash unit outcropping on the island of lipari which belongs to the intermediate brown tuffs ibt succession of the aeolian islands italy the use of a multidisciplinary approach that integrates textural petrological and pedological methods allows us to discriminate between syn eruptive and post depositional features the deposits are dominated by uncrystallised blocky glass fragments of homogeneous shoshonitic composition confirming a provenance from hydromagmatic eruptions on the island of vulcano many glass fragments are surrounded by a coating separated by a thin void of syn eruptive origin due to alteration by aggressive acid gases in the eruptive cloud the lack of this coating in the northern part of lipari can be explained as a progressive dispersion of the gases far from the vent and or to post depositional processes the degree of soil development significantly increases from south soil profiles p1 and p2 at valle muria to north p3 and p4 at madoro and chiesa vecchia sites respectively as a response to a decrease in slope steepness which has brought about a progressive deepening of the pedogenetic front on gentler landforms and conversely its rejuvenation on steep slopes the relatively poor to moderate degree of pedogenic evolution of the studied ibt unit is consistent with its emplacement during part of the last glacial period

the mutual interaction between continental scale ice sheets and atmospheric stationary waves the great continental ice sheets of the pleistocene represented significant obstacles to the northern hemisphere midlatitude westerlies they must therefore have forced large changes in the atmospheric circulation and consequently also in the patterns of accumulation and melting over the ice sheets themselves a simplified threedimensional coupled ice sheet stationary wave model is developed in order to understand the ice sheet s response to the circulation changes that it induces consistent with ice age climate simulations the ice sheet topography induces an anticyclonic circulation over the ice sheet causing a slight warming over the western slopes and a stronger cooling over the remainder the modeled feedbacks significantly affect the ice sheet configuration with the most important influences being the patterns of summer temperature and the topographically induced precipitation field the time evolution of the ice sheet is also changed by the atmospheric feedbacks and the results suggest the possibility of multiple equilibrium solutions

sensitivity experiments for the antarctic ice sheet with varied sub ice shelf melting rates ice sheet modelling is an important tool for predicting the possible response of ice sheets to climate change in the past and future an established ice sheet model is sicopolis simulation code for polythermal ice sheets and for this study the previously grounded ice only model was complemented by an ice shelf module the new version of sicopolis is applied to the antarctic ice sheet driven by standard forcings defined by the searise sea level response to ice sheet evolution community effort a crucial point for simulations into the future is to obtain reasonable initial conditions by a palaeoclimatic spin up which we carry out over 125 000 years from the eemian until today we then carry out a set of experiments for 500 years into the future in which the surface temperature and precipitation are kept at their present day distributions while sub ice shelf melting rates between 0 and 200 m a 1 are applied these simulations show a significant but not catastrophic sensitivity of the ice sheet grounded ice volumes decrease with increasing melting rates and the spread of the results from the zero to the maximum melting case is similar to 0 65 m s l e metres sea level equivalent after 100 years and similar to 2 25 m s l e after 500 years

the north american cordillera an impediment to growing the continent wide laurentide ice sheet abstractthis study examines the evolution of a continental scale ice sheet on a triangular representation of north america with and without the influence of the cordilleran region simulations are conducted using a comprehensive atmospheric general circulation model asynchronously coupled to a three dimensional thermomechanical ice sheet model the atmospheric state is updated for every 2 106 km3 increase in ice volume and the coupled model is integrated to steady state in the first experiment a flat continent with no background topography is used the ice sheet evolves fairly zonally symmetric and the equilibrium state is continent wide and has the highest point in the center of the continent this equilibrium ice sheet forces an anticyclonic circulation that results in relatively warmer cooler summer surface temperatures in the northwest southeast owing to warm cold air advection and radiative heating due to reduced cloudiness the second experiment includes a simplified representation of t

role of model initialization for projections of 21st century greenland ice sheet mass loss model simulations of the greenland ice sheet contribution to 21st century sea level rise are performed with a state of the art ice sheet model parallel ice sheet model pism the climate forcing fields are obtained from the european union s seventh framework programme project ice2sea in which three regional climate models are used to dynamically downscale two scenarios a1b and e1 from two general circulation models echam5 and hadcm3 to assess the sensitivity of the projections to the model initial state four initialization methods are applied in these experiments the simulated contribution to sea level rise by 2100 ranges from an equivalent of 0 2 to 6 8 cm the largest uncertainties arise from different formulations of the regional climate models 0 8 3 9 cm and applied scenarios 0 65 1 9 cm but an important source of uncertainty is the initialization method 0 1 0 8 cm these model simulations do not account for the recently observed acceleration of ice streams and consequent thinning rates the changing ice discharge that may result from the spatial and temporal variability of ocean forcing or the feedback occurring between ice sheet elevation changes and climate forcing thus the results should be considered the lower limit of greenland ice sheet contributions to sea level rise until such processes have been integrated into large scale ice sheet models

spatial and seasonal effects of temperature variability in a positive degree day glacier surface mass balance model this doctoral dissertation presents a study of the glacial history of the north american cordillera using numerical ice sheet modelling calibrated against field evidence this area characterized by the steep topography of several mountain ranges separated by large inter montane depressions was once covered by a large scale ice mass the former cordilleran ice sheet because of the irregular topography on which the ice sheet formed geological studies have often had only local or regional relevance thus leaving the cordilleran ice sheet least understood among pleistocene ice sheets in terms of its extent volume and dynamics here i present numerical simulations that allow quantitative reconstructions of the former ice sheet evolution based on approximated physics of glacier flow these simulations show that the geometry of the last glacial maximum cordilleran ice sheet was largely controlled by sharp contrasts in regional temperature precipitation and daily temperature variability associated with the presence of mountain ranges however this maximum stage appears short lived and out of balance with contemporaneous climate during most of the simulated last glacial cycle the north american cordillera is characterized by an intermediate state of glaciation including isolated glaciers and ice caps covering major mountain ranges the largest of which is located over the skeena mountains the numerically modelled cordilleran ice sheet appears in constant imbalance with evolving climate conditions while the complexity of this transient response transcends that encapsulated in two dimensional conceptual models of ice sheet growth and decay this thesis demonstrates the potential of numerical ice sheet modelling to inform on ice sheet history and former climate conditions over a glacial cycle given that ice sheet models can be calibrated against field constraints

birth death and resurrection the life cycle of suprasubduction zone ophiolites 1 suprasubduction zone ssz ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites this sequence includes the following 1 birth which entails the formation of the ophiolite above a nascent or reconfigured subduction zone this stage is typically characterized by the eruption of arc tholeiite lavas and the formation of layered gabbros and sheeted dike complex 2 youth during which is continued melting of refractory asthenosphere depleted during birth occurs in response to fluid flux from the subducting slab with extensional deformation of the older plutonic suite eruption of refractory lavas and the intrusion of wehrlite pyroxenite 3 maturity with the onset of semistable arc volcanism typically calc alkaline as the subduction zone matures and stabilizes and the intrusion of quartz diorite and eruption of silicic lavas and 4 death which is the sudden demise of active spreading and ophiolite related volcanism which in many cases is linked to collision with an active spreading center and the onset of shallow underthrusting of the buoyant spreading axis expressed as dikes and lavas with oceanic basalt compositions that crosscut or overlie rocks of the older suites 5 resurrection with emplacement by obduction onto a passive margin or accretionary uplift with continued subduction the early stages 1 3 may be diachronous and each stage may overlap in both time and space the existence of this consistent progression implies that ophiolite formation is not a stochastic event but is a natural consequence of the ssz tectonic setting

tectonic controls on rates and spatial patterns of glacial erosion through geothermal heat flux abstract glacial erosion has shaped many mountain belts during the cold periods of the late cenozoic the rate of glacial erosion is sensitive to the subglacial environment including both the subglacial hydrology and the basal thermal regime geothermal heat from underlying bedrock is a major contributor to glacier energy budgets controlling ice dynamics at the ice bed interface by changing the basal temperature and the supply of meltwater despite the known influence of geothermal heat on the subglacial environment its impact on glacial erosion has received little study the geothermal heat flux in glaciated mountain ranges varies widely as a function of the tectonic setting therefore if glacial erosion is sensitive to geothermal heat flux the evolution of glaciated landscapes may depend upon tectonically controlled geothermal gradients we explore the impact of geothermal heat flux on the rates and spatial patterns of glacial erosion in mountain ranges using numerical models we couple a sliding dependent glacial erosion model with the parallel ice sheet model pism to simulate the evolution of a synthetic glacial landscape we find a robust tendency for increasing glacial erosion with increasing geothermal heat flux the spatial pattern of erosion also varies with the magnitude of geothermal heat flux at low geothermal heat flux glacial erosion is consistently focused in major valleys as geothermal heat flux increases the area of significant glacial erosion expands into higher elevations and the rate of erosion increases the location of maximum erosion migrates up valley as geothermal heat flux increases suggesting that glacial erosion tends to produce distinct landscapes as a function of geothermal heat flux our finding suggests that active mountain belts with high geothermal heat flux will express the glacial buzzsaw effect in which high elevation topography is preferentially removed by glacial erosion glaciers at passive margins with low geothermal heat flux in contrast will tend to incise deep valleys at relatively low elevations previous work on the interaction between tectonics and landscape evolution has focused on relief generation and fracturing of rocks our results introduce a novel potential linkage between tectonics and erosion based on the sensitivity of glacial erosion to geothermal heat

simulations of northern hemisphere ice sheet retreat sensitivity to physical mechanisms involved during the last deglaciation a 3 dimensional thermomechanical ice sheet model is used to simulate the evolution of the geometry of northern hemisphere ice sheets through the last deglaciation the ice sheet model is forced by a time evolving climatology provided by the linear interpolation through time of climate snapshots simulated by the lmd5 3 atmospheric general circulation model agcm at different periods of the last deglaciation 21 15 9 6 and 0 kyr bp the agcm is driven by insolation atmospheric co2 content ice sheet configuration and sea surface temperatures although our approach is able to produce the complete continental ice retreat our simulated deglaciation presents a phase lag with reconstructions based on observational evidences this suggests that physical mechanisms related to climate forcing and or ice sheet internal dynamics are not properly represented the influence of millennial scale forcing feedback mechanisms between ice sheet elevation and surface mass balance and parameterization of the ice flow is also tested through a set of sensitivity experiments the rapid variability has a strong impact on the evolution of the ice volume because of nonlinear effects in temperature mass balance relationships fennoscandia appears to be strongly sensitive to the small scale ice sheet instability both ice sheets are to some extent sensitive to an increased basal sliding

u pb ages of detrital zircons in pacheco pass metagraywackes sierran klamath source of mid cretaceous and late cretaceous franciscan deposition and underplating 1 using laser ablation icp ms techniques u pb ages are reported for 338 detrital zircons separated from four franciscan metagraywacke samples from imbricate thrust sheets cropping out in the pacheco pass area east central california coast ranges structurally higher slabs are clastic quartz albite bearing rocks typified by neoblastic lawsonite jadeitic pyroxene the lowest exposed slab lacks jadeitic pyroxene but contains traces of newly grown pumpellyite and lawsonite in addition to abundant quartz albite studied specimens contain moderate amounts of phengite titanite chlorite stilpnomelane carbonate iron oxides rock fragments and carbonaceous matter these diablo range clastic sediments were deposited in mid cretaceous and late cretaceous time the highest allochthon unit i was deposited after 102 ma unit iv was deposited after 90 102 ma and unit v was deposited after 86 ma metagraywacke depositional accretionary ages within slab iv young upward but ages of the slabs decrease progressively downward in the four sample aggregate most zircons have igneous ages falling in the 135 170 ma range with a smaller population at 85 120 ma the rocks contain rare zircons of middle proterozoic late archean ages a minor source in northern california and nw nevada seems likely for the pacheco pass metagraywackes but the sierran klamath calcalkaline arc provided most of the clastic debris judging by the volcanic nature of lithic clasts in these eastern belt metagraywackes and because massive sierran plutonism occurred at 85 120 ma the abundant 135 170 ma zircons probably were derived chiefly from the eroding comagmatic volcanic arc rather than from the less voluminous jurassic arc plutons

nappes tectonics of oblique plate convergence and metamorphic evolution related to 140 million years of continuous subduction franciscan complex california this paper presents a new synthesis of franciscan complex tectonics with the emphasis on the pre san andreas fault history of these rocks field relations suggest that the franciscan is characterized by nappe structures that formed during sequential accretion at the trench the presence of these structures along with other field relations including the lack of evidence for large offset of conglomerate suites indicates that strike slip fault systems of large displacement 500 km did not cut the franciscan complex during subduction regional geology and comparisons to modern arc trench systems suggest that strike slip faulting associated with oblique subduction took place inboard east of the franciscan in the vicinity of the magmatic arc the franciscan varies along strike because individual accreted elements packets of trench sediment seamounts etc did not extend the full length of the trench different depths of underplating distribution of post metamorphic faulting and level of erosion pro

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

counterclockwise p t t paths from amphibolites franciscan complex california relics from the early stages of subduction zone metamorphism overprinting mineral relationships in amphibolites from the franciscan complex california suggest metamorphic evolution from high temperature amphibolite facies to the blueschist facies with increasing p t ratio a counterclockwise p t t path early formed pargasitic amphiboles are both crosscut and rimmed by subcalcic hornblendes that are in turn cut or rimmed by sodic amphiboles some amphibolites are overprinted successively by eclogite and blueschist facies assemblages clinopyroxenes are zoned with increasing jadeite component from core to rim multiple generations of phengites are present in the same sample and are more si rich with each successive generation of growth garnets in eclogite overprinted amphibolites are zoned with an initial mgo increase away from the core to a maximum mgo zone followed by mgo decrease toward the rim garnets in other amphibolites show continually increasing mgo from core to rim several samples representative of the variety of franciscan amphibolites are describ

intraoceanic unroofing of eclogite facies rocks in the omachi seamount izu bonin frontal arc electron microscope and electron microprobe observations of amphibolites from the omachi seamount in the izu bonin frontal arc show that they contain micrometer sized inclusions of omphacite kyanite indicating eclogite facies metamorphism the garnet zoisite amphibolite was subjected to metamorphic conditions of 600 700 c and 2 gpa in the early stage of metamorphism these metabasites were subducted to a depth of 70 km beneath the izu bonin arc and were exhumed together with serpentinite schist their intraoceanic unroofing was probably induced by backarc extension of the upper plate whose axes were intersected and cooled by the newly formed izu bonin subduction system this intraoceanic exhumation associated with suprasubduction extension can be a modern analogue for ancient on land eclogite terranes accompanied by ophiolites

positive degree day factors for ablation on the greenland ice sheet studied by energy balance modelling ice ablation is related to air temperature by the positive degree day factor variations of the positive degree day factor in west greenland are studied using an energy balance model to simulate ablation under different conditions degree day factors for simulated and measured ice ablation at nordbogletscher and qaman rssup sermia agree well with values around 8 mm d 1 c 1 degree day factors for snow are less than half those for ice energy balance modelling shows that degree day factors vary with summer mean temperature surface albedo and turbulence but there is only evidence of large positive degree day factors at lower temperatures and with low albedo 0 3 the greatest effect of albedo variations 0 3 0 7 is at lower temperatures while variations in turbulence have greater effect at higher temperatures current models may underestimate runoff from the greenland ice sheet by several tenths because they use a degree day factor for melting ice that is too small for the colder parts of the ice sheet i e the upper ablation area and the northerly margin

tectonic accretion versus erosion along the southern chile trench oblique subduction and margin segmentation 1 the southernmost tip of south america is an active continental margin where oblique convergence between plates transcurrent motion and tectonic rotation on land make the geodynamic setting more complex than that of the central andes a multichannel seismic data set has been used in conjunction with multibeam and altimetry data to clarify the regional architecture of the continental margin from 50 s to 57 s despite the thick sedimentary section in the trench and the slow plate convergence rate peculiar of typical accretionary margins seismic reflection profiles image widely varying frontal wedge morphologies different rates of accretion a high degree of structural diversity and different modes of continental building offscraping underplating tectonic erosion correlation between structural parameters depth of the decollement level width of the wedge accretionary rates moho depth suggests large scale structural control on margin geometry and structural diversity the transition from tectonic accretion to erosion and general structural variations do not show any gradual trend but rather they occur along oblique structural trends that produce a tectonic segmentation of the margin this is mainly related to tectonic processes on the overriding plate block rotations along strike slip faults while local disturbances on the incoming plate seamounts fracture zones and oceanic fabric relative orientation add further structural complexity altimetry data in conjunction with structural analysis suggest that large scale tectonic variations and structural development are related to trench parallel gravity anomaly variations and ultimately to basal friction on the plate interface strong negative gravity anomalies are associated with sedimentary basins wide wedges and accretionary domains while positive gravity anomalies mainly refer to transverse structural highs and narrow wedges

clay minerals oxyhydroxide formation element leaching and humus development in volcanic soils a weathering sequence with soils developing on volcanic trachy basaltic parent materials with ages ranging from 100 115 000 years in the etna region served as the basis to analyse and calculate the accumulation and stabilisation mechanisms of soil organic matter som the transformation of pedogenic fe and al the formation and transformation of clay minerals the weathering indices and by means of mass balance calculations net losses of the main elements although the soils were influenced by ash depositions during their development and the soil on the oldest lava flow developed to a great extent under a different climate leaching of elements and mineral formation and transformation could still be measured leaching of major base cations coupled with a corresponding passive enrichment of al or fe was a main weathering mechanism and was especially pronounced in the early stages of soil formation due to mineral or glass weathering with time the weathering indexes such as the k ca ti ratio tend to an asymptotic value chemical and mineralogical changes between 15 000 and 115 000 years in the a and b horizons were small in contrast to this the accumulation of newly formed itm imogolite type materials and ferrihydrite showed a rather linear behaviour with time weathering consisted of the dissolution of primary minerals such as plagioclase pyroxenes or olivine the breakdown of volcanic glass and the formation of secondary minerals such as itm and ferrihydrite the main mineral transformations were volcanic glass imogolite kaolinite clay fraction in the most weathered horizons a very small amount of 2 1 clay minerals could be found that were probably liberated from the inner part of volcanic glass debris the rate of formation and transformation of 2 1 clay minerals in the investigated soils was very low no major changes could be observed even after 115 000 years of soil evolution this can be explained by the addition of ash and the too low precipitation rates in general soil erosion played a subordinate role except possibly for the oldest soils 115 000 years the youngest soils with an age 2000 years had the highest accumulation rate of organic c about 3 0 g c m2 year after about 15 000 years the accumulation rate of organic c in the soils tended to zero soil organic carbon reached an asymptotic value with abundances close to 20 kg m2 after about 20 000 years in general the preservation and stabilisation of som were due to poorly crystalline al and fe phases pyrophosphate extractable kaolinite and the clay content these parameters correlated well with the organic c imogolite type material did not contribute significantly to the stabilisation of soil organic matter

chemical weathering of palaeosols from the lower palaeolithic site of valle giumentina central italy abstract the major archaeological site of valle giumentina abruzzo contains a well dated lower palaeolithic pedosedimentary sequence that provides an excellent opportunity to study the relationships among soil weathering volcanism and climate change at the glacial interglacial and submillennial timescales in central italy and the mediterranean area during the middle pleistocene as well as the human environment interactions of some of the earliest settlements in central southern europe high resolution analyses of geochemistry and magnetic susceptibility revealed the presence of eleven palaeosols ten of which s2 s11 were formed between 560 and 450 ka based on 40ar 39ar dating of sanidine in tephras i e spanning marine isotope stages mis 14 12 the evolution of the major and trace element composition suggests that the palaeosols were mainly formed by in situ weathering of the parent material the major phases of soil weathering occurred during the mis 13 interglacial period s8 and s6 as well as during episodes of rapid environmental change associated with millennial climatic oscillations during the mis 14 and 12 glaciations s11 and s2 respectively although global forcing such as orbital variations solar radiation and greenhouse gas concentrations may have influenced the pedogenic processes the volcanism in central italy climate change in the central mediterranean and tectono sedimentary evolution of the valle giumentina basin also impacted and triggered the formation of most palaeosols which provided subsistence resources for the lower palaeolithic human communities this study highlights the importance of having high resolution palaeoenvironmental records with accurate chronology as close as possible to archaeological sites to study human environment interactions

investigation of soils developed on volcanic materials in nisyros island greece abstract soils that are forming on volcanic parent materials have unique physical and chemical properties and in most cases on wet and humid climates are classified as andisols the main purpose of this study is to examine if the soils that are forming on volcanic materials under a dry mediterranean climate in nisyros island greece meet the requirements to be classified as andisols soils from seven sites were sampled and examined for their main physico chemical properties and selective dissolution analysis dithionite citrate bicarbonate dcb extractable al and fe al d fe d acid ammonium oxalate extractable al fe and si al o fe o and si o and sodium pyrophosphate extractable al and fe al p fe p were measured in addition al and si were determined after reaction with hot 0 5 m naoh al naoh and si naoh and with tiron c 6 h 4 na 2 o 8 s 2 al t and si t p retention was also measured the soils are characterised by coarse texture low organic matter content low values of cation exchange capacity cec and high ph values values of si o al o and fe o are less than 0 022 0 09 and 0 35 respectively highlighting the lack of noncrystalline components the ratio fe d fe o 100 fe d is quite high expressing the degree of crystallisation of free iron oxides for all samples tested values of the al o 1 2fe o index are extremely low naoh and si t arising 2 76 and 2 18 respectively indicate the presence of silica in amorphous forms p retention values are very low

the impact of climate vegetation interactions on the onset of the antarctic ice sheet a global coupled atmosphere vegetation model and a dynamic ice sheet model were employed to study the impact of climate vegetation interactions on the onset of the antarctic ice sheet during the eocene oligocene transition we found that the co2 threshold for antarctic glaciation is highly sensitive to the prevailing vegetation in our experiments the co2 threshold is less than 280 ppm if the antarctic vegetation is dominated by forests and between 560 and 1120 ppm for tundra and bare ground conditions the large impact of vegetation on inception is attributed to the ability of canopies to shade the snow covered ground which leads to a weaker snow albedo feedback and higher summer temperatures however the overall effect of canopy shading on the antarctic climate also depends on features like local cloudiness and atmospheric meridional heat transport our results suggest that vegetation feedbacks on climate are crucial for the timing of the antarctic glaciation

basalt weathering in an arctic mars analog site abstract the martian surface has undergone chemical and physical weathering in the past and these processes may continue intermittently today to explore whether martian rocks are likely to retain features indicative of weathering we investigated how basaltic material weathers on earth specifically we investigated weathering of a quaternary aged basaltic flow at the sverrefjell volcano in svalbard above the arctic circle this flow weathered since deglaciation under cold dry

sensitivity of the modeled present day greenland ice sheet to climatic forcing and spin up methods and its influence on future sea level projections 1 the accuracy of the modeled present day greenland ice sheet gris is crucial for future projections of gris changes in this study we present a detailed evaluation of the modeled present day gris sensitivity to different present day climatology data sets and spin up methods and further assess the influence of the modeled present day gris on future sea level projections our study demonstrates that with present day climatology data sets derived from the regional atmospheric climate model racmo2 the modeled ice volume area and elevation of the gris agree substantially better with observations compared to simulations with present day climatology data sets from temperature parameterizations and era interim reanalysis with transient spin up the simulated rates of ice elevation changes for the 1993 2010 period are closer to observations than those with steady state spin up these results indicate that the racmo2 forcing and transient spin up may be preferable for use in the ice sheet model moreover our results reveal that the present day climatology data sets and spin up methods affect future sea level projections using transient spin up the ice sheet model estimates a range of 26 mm in projected sea level rise by 2098 under the a1b emissions scenario due to different present day climatology data sets compared to the results with transient spin up the estimated sea level rise by 2098 is reduced by 5 21 mm with steady state spin up this discrepancy is attributed mainly to differences in ice thickness and ice velocity between the modeled present day gris with transient and steady state spin ups and the effect of paleoclimatic changes with transient spin up

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

what caused the low water phase of glacial lake agassiz abstract first order modeling suggests that a low water phase in late glacial lake agassiz can be explained through changes in the balance between evaporation precipitation and runoff rather than drainage the low water moorhead phase is often attributed to drainage through outlets opened by isostatic depression and retreat of the laurentide ice margin however new data indicate that the proposed outlets were ice covered during the moorhead phase instead the lake water levels dropped to the moorhead phase before the start of the younger dryas chronozone and remained there until 11 3 ka thus drainage seems to be an implausible explanation for younger dryas aged low water levels in lake agassiz an alternative explanation is that evaporation equaled or exceeded water inputs from the adjacent ice margin and the deglaciated parts of the drainage basin to evaluate whether this hypothesis is plausible we constructed a simple model that considers the paleo basin geometry hydrology and meltwater production from the adjacent ice margin modest hydrologic changes within the range of present day variability coupled with low meltwater production produce a closed basin shifts in the location of the polar jet driven by increased arctic albedo may explain our inferred hydrologic changes

subduction zone infancy examples from the eocene izu bonin mariana and jurassic california arcs a new model for the earliest stages in the evolution of subduction zones is developed from recent geologic studies of the izu bonin mariana ibm arc system and then applied to late jurassic ophiolites of cailfornia the model accounts for several key observations about the earliest stages in the evolution of the ibm system 1 subduction nucleated along an active transform boundary which separated younger less dense lithosphere in the west from older more dense lithosphere to the east 2 initial arc magmatic activity occupied a much broader zone than existed later 3 initial magmatism extended up to the modern trench over a region now characterized by subnormal heat flow 4 early are magmatism was characterized by depleted tholeiitic and ultra depleted boninitic magmas indicating that melting was more extensive and involved more depleted mantle than is found anywhere else on earth 5 early arc magmatism was strongly extensional with crust forming in a manner similar to slow spreading ridges and 6 crust production rates were 120 to 180 km 3 km ma several times greater than for mature arc systems these observations require that the earliest stages of subduction involve rapid retreat of the trench we infer that this resulted from continuous subsidence of denser lithosphere along the transform fault this resulted in strong extension and thinning of younger more buoyant lithosphere to the west this extension was accompanied by the flow of water from the sinking oceanic lithosphere to the base of the extending lithosphere and the underlying asthenosphere addition of water and asthenospheric upwelling led to catastrophic melting which continued until lithosphere subsidence was replaced by lithospheric subduction application of the subduction zone infancy model to the late jurassic ophiolites of california provides a framework in which to understand the rapid formation of oceanic crust with strong arc affinities between the younger sierran magmatic arc and the franciscan subduction complex provides a mechanism for the formation and subsidence of the great valley forearc basin and explains the limited duration of high t high p metamorphism experienced by franciscan melanges

the influence of sub glacial bed evolution on ice extent a model based evaluation of the last glacial maximum pukaki glacier new zealand abstract a potential complication in using glacier extent to estimate paleoclimatic conditions is the influence of glacier bed evolution on changes in ice extent over time here we examine this issue through model based reconstructions of the last glacial maximum lgm pukaki glacier southern alps new zealand whose lgm extents are exceptionally well defined by lateral and terminal moraines using the well dated moraine limits as an empirical constraint on maximum ice extents we employ a one dimensional glacier flowline model driven by a mass balance model in order to evaluate the influence of climate and glacier bed profile on the extent of the lgm pukaki glacier the lgm glacier bed is buried by lateglacial and post glacial sediment so we calculate bed profiles using a modified version of the one dimensional model and available geologic constraints a best fit to the moraine record occurs with a lgm temperature of 7 8 c cooler than present with precipitation ranging from 80 to 100 of present levels modeling of the bed profile evolution indicates that bed changes alone could account for kilometer scale changes in glacier width and length

development and spatial distribution of soils on an active volcano mt etna sicily abstract as a large active volcano mt etna presents a complex soil forming environment with a spatial diversity of lava flow age tephra deposition local climate and agriculture following a review of previous published research on etna s soils this paper analyses physical and chemical data for 23 profiles between 120 m and 1030 m elevation on all flanks of the volcano with the aim of characterising the soils and determining the extent to which the chief controls on their nature and geography may be identified soils are sampled across a chronosequence of lava flows dating from 72 yr to between 28 ka and 42 ka bp which occur in conditions of diverse land use and local climate ages of flows 3000 yr are only broadly constrained the majority of soils comprise mostly tephra chief soil processes inferred have been identified in previous published research on mt etna accumulation of soil organic matter rapid loss of na and production of fine grained materials particularly those inferred to be of short range order other developments are soil structural formation and evidence of increasing soil mesofaunal activity despite the complexity of environmental diversity and spatial variation in tephra deposition a number of soil properties including material

the treatment of meltwater retention in mass balance parameterisations of the greenland ice sheet retention of melt water runoff by percolation and or refreezing in the snowpack cannot be neglected when studying the surface mass balance of the greenlandice sheet in this paper we make a detailed comparison of several treatments proposed in the literature to account for this process in large scale mass balanceparameterizations the melt on the greenland ice sheet is calculated with a revised degree day model using updated datasets of surface elevation and precipitationrate on a 5 km grid crucial model parameters are recalibrated by comparing mass balance characteristics with available observations on a regional basis wediscuss the role of meltwater retention in the light of the overall mass balance of the greenland ice sheet and its sensitivity to climatic change and displaypatterns of effective retention fractions for the various methods as a main conclusion it appears that overall results are quite similar for the various models butthat meltwater retention has a large spatial variation not described by the simple treatments using the most comprehensive retention model the sensitivity of therunoff is found to be 0 35 mm deg c of sea level change per year we also present a new map of the different zones facies that characterize the accumulationarea of the greenland ice sheet that is useful for interpreting field data and calibrating satellite observations

modeling the evolution of the juneau icefield between 1971 and 2100 using the parallel ice sheet model pism we study the evolution of the juneau icefield one of the largest icefields in north america 3700 km 2 using the parallel ice sheet model pism we test two climate datasets 20 km weather research and forecasting model wrf output and data from the scenarios network for alaska planning snap derived from spatial interpolation of observations good agreement between simulated and observed surface mass balance was achieved only after substantially adjusting wrf precipitation to account for unresolved orographic effects while snap s climate pattern is incompatible with observations of surface mass balance using the wrf data forced with the rcp6 0 emission scenario the model projects a decrease in ice volume by 58 68 and a 57 63 area loss by 2099 compared with 2010 if the modeled 2070 99 climate is held constant beyond 2099 the icefield is eliminated by 2200 with constant 1971 2010 climate the icefield stabilizes at 86 of its present day volume experiments started from an ice free state indicate that steady state volumes are largely independent of the initial ice volume when forced by identical scenarios of climate stabilization despite large projected volume losses the complex high mountain topography makes the juneau icefield less susceptible to climate warming than low lying alaskan icefields

initial results of the searise numerical experiments with the models sicopolis and icies for the greenland ice sheet searise sea level response to ice sheet evolution is a us led multi model community effort to predict the likely range of the contribution of the greenland and antarctic ice sheets to sea level rise over the next few hundred years under global warming conditions the japanese ice sheet modelling community is contributing to searise with two large scale dynamic thermodynamic models sicopolis and icies here we discuss results for the greenland ice sheet obtained using both models under the forcings surface temperature and precipitation scenarios defined by the searise effort a crucial point for meaningful simulations into the future is to obtain initial conditions that are close to the observed state of the present day ice sheet this is achieved by proper tuning during model spin up from the last glacial interglacial cycle to today experiments over 500 years indicate that both models are more sensitive exhibit a larger rate of ice sheet mass loss to future climate warming based on the a1b emission scenario than to a doubling in the basal sliding speed ice sheet mass loss varies between the two models by a factor of 2 for sliding experiments and a factor of 3 for climate warming experiments highlighting the importance of improved constraints on the parameterization of basal sliding and surface mass balance in ice sheet models

the snow mountain volcanic complex an on land seamount in the franciscan terrain california the snow mountain volcanic complex in the franciscan terrain of northern california is a 1 1 2 to 2 km thick sequence of altered submarine pillow lavas pillow breccias diabase and interbedded sediments forming a klippe that structurally overlies nearby rocks of the franciscan assemblage the coast range ophiolite and great valley sequence all of the snow mountain rocks bear a weak overprint of blue schist facies metamorphism the volcanic rocks were deposited on top of 200 300 m of interbedded turbiditic greywacke shale and radiolarian chert which are interpreted as an interfingering abyssal fan and pelagic sequence the volcanic pile is therefore supracrustal and is not an ophiolitic fragment formed at a mid ocean spreading center rather it is probably the remnant of a former seamount the lavas are mostly titanium rich transitional basalts minor associated rocks include rhyolite and peralkaline rhyolite relict clinopyroxenes in the basaltic rocks are all titanium aluminum rich augites thes

block in matrix fabrics that lack shearing but possess composite cleavage planes a sedimentary melange origin for the yuwan accretionary complex in the ryukyu island arc japan while melanges have been taken to be a significant component of accretionary complexes the use of this term has been mostly descriptive given the lack of consensus concerning their genesis however many workers have interpreted asymmetric shear fabrics in melanges as evidence of a tectonic origin i e giving rise to tectonic melanges in contrast to olistostromes which are considered to be purely sedimentary in origin due at least in part to the lack of such shear fabrics it is still uncertain whether accretionary processes include those that involve the intense shearing of oceanic lithologies along with for example the incorporation and entrapment of exotic blocks by muddy matrices during sediment deposition and deformation in axial deep sea trench settings here we argue that the so called block in matrix fabrics that characterize accretionary complexes are primarily sedimentary in origin and are distinct from shear fabrics represented by tectonic melanges we also propose that following their accretion subsequent recycling of such oceanic materials is a common feature within evolving accretionary prisms lastly we draw attention to the observation that d1 pressure solution cleavage planes notably widespread in the lower cretaceous yuwan complex amami oshima island in the ryukyu arc sw japan are absent from the minor asymmetric shear structures that often characterize tectonic melanges in contrast we suggest that the yuwan complex represents the effects of broadly symmetric flattening this scenario is supported by our observation that the number of sedimentary and deformation events differs significantly compared to the single phase of shearing expected in tectonic melanges d minus 1 d 1 pressure solution and axial planar cleavages are only observed in exotic blocks and exhibit older accretionary deformation events within a preexisting accretionary prism of the existing structural associations sd1 is the oldest predating the d 1 sedimentary episode and it represents an oceanic sedimentary phase associated with the formation of a distinct type of block in matrix fabric produced by the accumulation of debris flows at seamount margins sd2 represents a succeeding sedimentary episode characterized by trench axis debris flow including oceanic inclusions derived from collapsed material from an older accretionary prism the resulting sd2 block in matrix fabric is one of the main lithologic components of the amami oshima yuwan complex here the sd2 episode typically includes an igneous fabric consisting of nonexotic intrusive and extrusive basalts within a terrigenous matrix suggesting that the yuwan prism may have also been associated with a trench trench ridge triple junction d1 coaxial deformation is observed to overprint all of the episodes represented although it has not destroyed or significantly sheared their respective fabrics especially in regard to the main sd2 block in matrix structures which are therefore considered to represent original sedimentary structures

unmetamorphosed sedimentary melange with high pressure metamorphic blocks in a nascent forearc basin setting abstract melanges crop out within unmetamorphosed basal great valley group gvg forearc basin strata and between gvg and the underlying coast range ophiolite cro in the san francisco bay region of coastal california these melanges include high pressure hp metamorphic blocks of the franciscan subduction complex that structurally underlies the unmetamorphosed cro as well as blocks of gvg and cro the matrix consists of foliated shale and serpentinite locally interleaved at centimeter scale the melanges strike and dip parallel to bounding gvg sandstones and conglomerates the matrix locally consists of sedimentary breccia and conglomerate made up of clasts of serpentinite and shale gvg sandstones within and bounding the melanges have detrital serpentinite clasts the field relationships indicate a sedimentary origin of the melanges as olistostromal deposits within latest jurassic to earliest cretaceous basal gvg the melanges correlate to units along the eastern margin of the northern coast ranges about 250 km to the north with restoration of post subduction dextral faulting and differ from the latter in the higher proportion of shale stronger matrix foliation and common occurrence of hp blocks similar units may have mistakenly been assigned to the franciscan owing to the foliated nature of the matrix and occurrence of hp blocks this and the broad distribution of localities indicate that these deposits are more widespread than previously believed exhumation rates of coarse grained hp melange blocks may have been 2 to 10 mm yr or higher based on the ages of similar blocks in the coast ranges burial depth of the blocks and depositional age of the enclosing strata exhumation and deposition of franciscan blocks in these gvg melanges predates preserved accretion of similar materials in the adjacent franciscan by at least 30 m y suggesting subduction erosion of previously accreted material or exhumation of the blocks in forearc serpentinite shale diapirs

structural styles in mesozoic and cenozoic melanges in the western cordillera of north america the term melange is currently used to describe several different kinds of mudstone rich rocks that are broadly characterized by an obscure stratigraphy stratal disruption or a chaotic block in matrix fabric four types of melange which can be defined in outcrop on the basis of mesoscopic fabric and lithologic composition are particularly widespread and distinctive type i includes sequences of originally interbedded sandstone and mudstone that record incipient to thorough disruption and fragmentation of strata accomplished largely by layer parallel extension type ii consists of similarly deformed thin layers of green tuff radiolarian ribbon chert and minor sandstone originally interbedded with black mudstone disruption in both types i and ii which probably occurred while the sediments were incompletely consolidated has been ascribed to either imbricate faulting in accretionary wedges or gravitationally driven deformation type iii comprises inclusions of diverse shapes sizes and compositions enveloped in a locally scaly pelitic matrix the ultimate source of fragments is obscure because the majority were not derived by either the progressive disruption of interbedded sediments or in situ tectonic plucking and abrasion of adjacent rocks although some type iii melanges may have originated deep within accretionary prisms final emplacement as olistostromes muddy debris flow deposits or mud diapirs seems likely type iii melanges are mechanically analogous to scaly sheared serpentinites many probably have been tectonically remobilized or even intruded into shallow level fault zones type iv consists of lenticular inclusions bounded by an anastomosing network of subparallel faults their fabric records progressive slicing in brittle fault zones each of the four types of melange described here could in theory have formed in a variety of settings on or within an accretionary wedge at an active convergent margin none can yet be singled out as a uniquely diagnostic subduction melange

new evidence for polyphase metamorphism of glaucophane schist and eclogite exotic blocks in the franciscan complex california and oregon abstract the early metamorphic history of high grade exotic blocks in the franciscan complex may be more complicated than previously supposed the different assemblages of high grade glaucophane schist eclogite amphibolite and hornblende schist are commonly considered to have formed at the same time from essentially unmetamorphosed oceanic crust however new textural and mineralogical data presented here suggest that high grade glaucophane schist and eclogite have replaced an earlier epidote amphibolite facies assemblage that is identical to the primary assemblages in many of the hornblende rich blocks at least some of the hornblende rich blocks may therefore be well preserved remnants of the earlier metamorphism comparison of the mineral assemblages and element partitioning in the mixed assemblage blocks suggests that the glaucophane schist and eclogite metamorphism took place at slightly lower temperatures but at the same or higher pressures than the earlier hornblende forming stage

metamorphism of franciscan tectonostratigraphic assemblage pacheco pass area east central diablo range california coast ranges the pacheco pass area well known for the relatively high pressure low temperature mineral assemblages developed in a well ordered section of chiefly metaclastic strata was restudied in order to elucidate the geologic paragenetic and textural relationships among the various lithologic units the mapped 7 minute quadrangle extends from 4 km west of the range crest eastward to the ortigalita fault tectonic contact of the franciscan assemblage with coeval great valley strata semicontinuous metachert beds underlain by scraps of na cpx and or na amphibole bearing metabasaltic rock mark the base of terrigenous tectonostratigraphic units evidently decoupled from the downgoing oceanic crust capped plate underplating along newly recognized bedding plane faults has juxtaposed members of an apparently conformable franciscan sedimentary sequence four depositional units each consisting of monotonous metagraywacke and interlayered metashale are stacked within the accretionary section from top down these are tectonostratigraphic members a b c and d unit d differs from overlying members in possessing a greater abundance of bluestone greenstone pods minor serpentinite bodies and rare metaconglomerate lenses varying degrees of stratal disruption indicate that it has been arrested in the transformation to broken formation the ortigalita fault is nearly vertical strikes north northwest and exhibits apparent dextral offset it truncates the east west striking gonzaga fault and other franciscan structures the topographic low occupied by san luis reservoir is a cenozoic tectonic depression sited at a releasing bend on the ortigalita fault newly acquired textural chemical mineralogic and areal relations of albitic and jadeitic pyroxene bearing franciscan metagraywacke near pacheco pass demonstrate that 1 na cpx and na amphibole are metamorphic minerals not clastic materials 2 pumpellyite is a minor neoblastic phase in albite bearing metagraywacke west of pacheco pass and in the north western corner of the quadrangle but it does not occur in jadeitic pyroxene bearing metaclastic rocks 3 higher textural grade metagraywacke specimens generally contain higher modal proportions of jd 4 abundance textural grade and chemistry of na cpx are not related to tectonostratigraphic units and 5 because of sluggish reaction rates albite persisted metastably into the higher pressure jadeitic pyroxene quartz p t field production of na cpx resulted from a reaction of the sort ab chl jd iws qtz gln h 2 o irregular oscillatory zoning within single jadeitic pyroxene prisms and variable jd ab modes for rocks of the same bulk composition reflect growth governed by diffusion rather than recrystallization within a p t transition zone high pressure overstepping of the phase boundary explains variable modal proportions of ab and jd as well as chemical heterogeneity of the jd elevated p attended metamorphism of na cpx bearing rocks exposed in the pacheco pass area as indicated by the wide spread coexistence of quartz and naalsi 2 o 6 rich pyroxene inferred physical conditions of prograde metamorphism were 150 50 c at 7 8 kbar or more franciscan rocks in the east central diablo range underwent subduction zone metamorphism accompanying paleo pacific lithospheric plate descent during mid cretaceous convergence underplating contraction and sequestering of the tectonostratigraphic assembly at depths of 25 30 km during underflow followed by gradual rise took place under conditions of refrigeration due to protracted descent of the oceanic slab paleogene diapiric uplift and extension followed indicating more complete decoupling of the buoyant trench complex from the downgoing plate finally passage of the east pacific rise triple junction in neogene time initiated the present dextral slip regime in the california coast ranges

modelling the short term response of the greenland ice sheet to global warming a two dimensional vertically integrated ice flow model has been developed to test the importance of various processes and concepts used for the prediction of the contribution of the greenland ice sheet to sea level rise over the next 350 y short term response the mass balance is modelled by the degree day method and the energy balance method the lithosphere is considered to respond isostatically to a point load and the time evolution of the bedrock follows from a viscous asthenosphere according to the ipcc is92a scenario with constant aerosols after 1990 the greenland ice sheet is likely to cause a global sea level rise of 10 4 cm by 2100 ad it is shown however that the result is sensitive to precise model formulations and that simplifications as used in the sea level projection in the ipcc 96 report yield less accurate results our model results indicate that on a time scale of a hundred years including the dynamic response of the ice sheet yields more mass loss than the fixed response in which changes in geometry are not incorporated it appears to be important to consider sliding as well as the fact that climate sensitivity increases for larger perturbations variations in predicted sea level change on a time scale of hundred years depend mostly on the initial state of the ice sheet on a time scale of a few hundred years however the variability in the predicted melt is dominated by the variability in the climate scenarios

distribution of displacement on and evolution of a young transform fault system the northern san andreas fault system california this paper presents a working model for the spatial and temporal distribution of dextral slip on the northern san andreas fault system of coastal california based primarily on field relations in the san francisco bay area and offers insight into the evolution of a young transform fault system a fundamental difference between this and previous models of slip distribution is that this model assigns negligible slip to the pilarcitos fault which has been suggested to have 120 to 250 km of post early miocene dextral slip in previous models because separation on the san francisco peninsula reach of the san andreas fault is about 25 km and displacement on the san andreas fault in central california is 310 to 320 km more than 250 km of late cenozoic dextral slip must be accommodated east of the san francisco peninsula the distribution of this dextral slip is constrained by offset late cenozoic and basement units slip distribution combined with ages of offset features and plate boundary kinematic constraints show that the distribution of slip rates on groups of faults along the transform boundary has changed in an irregular fashion through time in contrast to existing models that propose progressive eastward migration of active faulting in the san andreas system in addition to the shifting patterns of displacement a migrating transition zone connecting the eastern faults of the strike slip system to the mendocino triple junction may have resulted in distributed dextral faulting and shortening in the northernmost and youngest part of the transform fault system

detrital zircon evidence for progressive underthrusting in franciscan metagraywackes west central california we present new u pb ages for detrital zircons separated from six quartzose metagraywackes collected from different franciscan complex imbricate nappes around san francisco bay all six rocks contain a broad spread of late jurassic cretaceous grains originating from the klamath sierra nevada volcanic plutonic arc units young structurally downward consistent with models of progressive underplating and offscraping within a subduction complex the youngest specimen is from the structurally lowest san bruno mountain sheet at 52 ma it evidently was deposited during the eocene none of the other metagraywackes yielded zircon ages younger than 83 ma zircons from both el cerrito units are dominated by ca 100 160 ma grains the upper el cerrito also contains several grains in the 1200 1800 ma interval these samples are nearly identical to 97 ma metasedimentary rock from the hunters point shear zone zircon ages from this melange block exhibit a broad distribution ranging from 97 to 200 ma with only a single pre mesozoic age the albany hill specimen has a distribution of pre mesozoic grains from 1300 to 1800 ma generally similar to that of the upper el cerrito sheet however it contains zircons as young as 83 ma suggesting that it is significantly younger than the upper el cerrito unit the skaggs spring schist is the oldest studied unit its youngest analyzed grains were ca 144 ma and it is the only investigated specimen to display a significant paleozoic detrital component sedimentation and subduction accretion of this tract of the trench complex took place along the continental margin during early to early late cretaceous time and perhaps into eocene time franciscan and great valley deposition attests to erosion of an andean arc that was active over the entire span from ca 145 to 80 ma with an associated accretionary prism built by progressive underthrusting we use these new data to demonstrate that the eastern franciscan complex in the northern and central coast ranges is a classic accretionary prism where younger structurally lower allochthons are exposed on the west and older structurally higher allochthons occur to the east in the heavily studied san francisco bay area

first evidence for the presence of andisols in the dry hot environment of the arabian shield abstract saudi arabia has many volcanoes and extensive basaltic lava fields known as harrats located along the western part of the arabian shield sub parallel to the red sea the soils developed on these volcanic materials have not yet been investigated forty representative soil profiles were selected from six harrats and their morphological and physicochemical properties as well as their mineralogical compositions were characterized using standard chemical xrd sem and tem techniques the main objective of this study was to determine if the soils developed from basaltic rocks in the harrats of the arabian shield are andisols the results revealed that all representative profiles had volcanic glass content that ranged from 15 to 40 p retention capacity 35 and acid oxalate extractable a1o 1 2 feo that ranged from 0 44 to 2 20 the crystalline clay minerals were dominated by smectite kaolin kaolinite halloysite and mica illite whereas chlorite hydroxy interlayered vermiculite ch hiv palygorskite ca zeolites and pseudo chlorite were present as minor components small amounts of allophane imogolite and ferrihydrite made up the poorly crystalline clay minerals all representative profiles satisfied the criteria for andic soil properties and were classified as torrands due to the presence of an aridic soil moisture regime in the area paleoclimatic conditions that existed in the arabian peninsula over the last few thousand years are consistent with the formation of andic and or vitric soil properties because of this andisols developed from pyroclastic parent materials and are now present in dry hot conditions the presence of andisols in the study area was demonstrated and was mainly attributed to the influence of pleistocene paleoclimatic conditions

paleoglaciological reconstructions for the tibetan plateau during the last glacial cycle evaluating numerical ice sheet simulations driven by gcm ensembles abstract the tibetan plateau is a topographic feature of extraordinary dimension and has an important impact on regional and global climate however the glacial history of the tibetan plateau is more poorly constrained than that of most other formerly glaciated regions such as in north america and eurasia on the basis of some field evidence it has been hypothesized that the tibetan plateau was covered by an ice sheet during the last glacial maximum lgm abundant field and chronological evidence for a predominance of local valley glaciation during the past 300 000 calendar years that is 300 ka coupled to an absence of glacial landforms and sediments in extensive areas of the plateau now refute this concept this furthermore calls into question previous ice sheet modeling attempts which generally arrive at ice volumes considerably larger than allowed for by field evidence surprisingly the robustness of such numerical ice sheet model results has not been widely queried despite potentially important climate ramifications we simulated the growth and decay of ice on the tibetan plateau during the last 125 ka in response to a large ensemble of climate forcings 90 members derived from global circulation models gcms using a similar 3d thermomechanical ice sheet model as employed in previous studies the numerical results include as extreme end members as an ice free tibetan plateau and a plateau scale ice sheet comparable in volume to the contemporary greenland ice sheet we further demonstrate that numerical simulations that acceptably conform to published reconstructions of quaternary ice extent on the tibetan plateau cannot be achieved with the employed stand alone ice sheet model when merely forced by paleoclimates derived from currently available gcms progress is however expected if future investigations employ ice sheet models with higher resolution bidirectional ice sheet atmosphere feedbacks improved treatment of the surface mass balance and regional climate data and climate reconstructions

collision propagation in papua new guinea and the solomon sea the mountain system in papua new guinea png is growing by accretion of australian margin strata to the front of the papuan fold and thrust belt in the south and by accretion of exotic terranes along its ne margin presently the finisterre terrane is being accreted along the ne margin of png and the collision point is migrating eastward within the solomon sea east of the collision point the new britain trench marks the tectonic front between the solomon sea and south bismarck sea plates whereas to the west the tectonic front lies in the southern part of the papuan fold and thrust belt present day sedimentary environments within the western solomon sea are inferred from interpretation of seismic reflection data similar facies are observed accreted to the front of the finisterre terrane in the markham valley the frontal leron formation is largely fluvial and shallow marine and the erap complex contains elements of turbidites and pelagic deposits there appears to be a smaller volume of coarse proximal marine strata accreted to the front of the finisterre terrane than is expected from interpretation of reflection profiles in the western solomon sea this difference may be attributed to a combination of submarine erosion in the markham canyon partial incorporation of these deposits into the erap complex and a difference in depositional rates and products carried to the solomon sea in the past relative to what is observed today based on plate motions alternative collision geometries and the youngest dates available for the erap complex we determine a rate of progression of the collision point of about 212 km m y during the past 1 m y

simulation of the metamorphic and deformational history of the metamorphic sole of the oman ophiolite emplacement of ophiolites onto less dense continental crust is an enigma the rates of emplacement the mechanisms of emplacement and the stress and temperature histories of the rocks are all incompletely understood the oman ophiolite is well exposed and has been studied extensively by field geologists an integrated thermal and kinematic model of the temperature stress rock type and displacement fields during the early stages of the emplacement of the oman ophiolite is developed here to explain field relations and provide insight into the development of the metamorphic rocks at the base of the ophiolite the thermal evolution was calculated by a finite difference algorithm for heat conduction considering heats of metamorphic reactions deformational heating and heat advection by rock the stress and displacement fields were calculated by an analytical model using a velocity boundary condition power law constitutive relations and a brittle frictional sliding relationship in simulations involving young hot subducted lithosphere a wider portion of the subduction zone deforms by power law creep and deformation occurs at lower stresses and slower strain rates minimizing the deformational heating compared to colder older subducted lithosphere dehydration occurs at an accelerated rate in younger hotter lithosphere removing heat from the subducted plate at an earlier stage and causing the zone of brittle deformation to propagate downward more rapidly power law creep of subducted basaltic rocks is limited to temperatures greater than 500 c and occurs at differential stresses of the order of 100 mpa the simulations predict that metamorphic field gradients and the spatial distribution of rock types in the metamorphic sole of tethyan ophiolites might be used to infer the emplacement direction of the ophiolite

coupling of early tertiary extension in the great valley forearc basin with blueschist exhumation in the underlying franciscan accretionary wedge at mount diablo california in the california coast ranges east of san francisco post 3 5 ma folding and erosion of the mount diablo anticline have created unusual three dimensional exposures of late mesozoic cenozoic stratigraphic and structural relations among rocks of the franciscan subduction complex coast range ophiolite and great valley forearc basin these relations offer new insights into the kinematics of late cretaceous early tertiary synsubduction extension attenuation and blueschist exhumation within the ancestral california forearc region map relations and subsurface data reveal that marine strata of the great valley forearc basin northeast of mount diablo accumulated in an 100 km long north south trending extensional graben system normal faults in the graben system cut steeply downsection through late cretaceous and early tertiary growth strata and terminate against the clayton marsh creek fault which is at a low angle to bedding and is interpreted to be the basal detachment for part of the graben system the clayton marsh creek fault in turn is linked to a system of faults that juxtapose blueschist facies rocks of the underlying ancestral franciscan accretionary prism against attenuated remnants of forearc crust that were never deeply buried including the coast range ophiolite and basal great valley strata these faults are the local expression of the coast range fault in this area franciscan rocks exposed beneath the faults were metamorphosed at 20 km depths after 108 ma based on jadeitic pyroxene and 108 ma detrital zircons u pb in metagraywackes apatite fission track data indicate that these blueschist facies rocks were subsequently uplifted and exhumed from 9 km to 3 km depths in latest cretaceous early tertiary time coeval with the subsidence and extension in the structurally overlying forearc graben system much of their earlier rise from 20 km to 9 km depth presumably also occurred coeval with graben development although our data cannot determine this directly these relations demonstrate that the california forearc around mount diablo was in an extensional regime undergoing active sedimentation during major franciscan exhumation and thus support models for exhumation of franciscan blueschist facies rocks via synsubduction extensional processes rather than via erosional processes

the effect of a holocene climatic optimum on the evolution of the greenland ice sheet during the last 10 kyr the holocene climatic optimum was a period 8 5 kyr ago when annual mean surface temperatures in greenland were 2 3 c warmer than present day values however this warming left little imprint on commonly used temperature proxies often used to derive the climate forcing for simulations of the past evolution of the greenland ice sheet in this study we investigate the evolution of the greenland ice sheet through the holocene when forced by different proxy derived temperature histories from ice core records focusing on the effect of sustained higher surface temperatures during the early holocene we find that the ice sheet retreats to a minimum volume of 0 15 1 2 m sea level equivalent smaller than present in the early or mid holocene when forcing an ice sheet model with temperature reconstructions that contain a climatic optimum and that the ice sheet has continued to recover from this minimum up to present day reconstructions without a warm climatic optimum in the early holocene result in smaller ice losses continuing throughout the last 10 kyr for all the simulated ice sheet histories the ice sheet is approaching a steady state at the end of the 20th century

early cretaceous transition from nonaccretionary behavior to strongly accretionary behavior within the franciscan subduction complex 1 during subduction at the franciscan trench beginning at 170 160 ma and continuing to the present marine sedimentary and lesser volcanic rocks have been underthrust accreted and metamorphosed to form the franciscan accretionary wedge the south fork mountain schist sfms forms the eastern margin and structural top of the wedge and so was apparently the first unit of substantial size to accrete into the franciscan new u pb ages of detrital zircons and 40ar 39ar ages of metamorphic white micas indicate that the sfms accreted surprisingly late in the time span of franciscan subduction probably at ca 123 ma at least parts of the valentine spring formation and yolla bolly terrane accreted soon thereafter therefore accretion of the sfms apparently marks a fundamental transition from virtually nonaccretionary behavior to strongly accretionary behavior in the franciscan forearc about 75 of modern forearcs are nonaccretionary so recognition of an early nonaccretionary period is consistent with modern examples the franciscan mafic high grade exotic blocks and related very small slabs which yield ca 132 to 169 ma metamorphic ages are the only well documented rock record of the early 40 m y long nonaccretionary period and represent very sparse accretion during that interval the transition into an accretionary regime at ca 123 ma was essentially synchronous with the end of the late jurassic early cretaceous magmatic lull in the sierra nevada magmatic arc with the waning of early cretaceous faulting and warping within the great valley forearc basin and possibly with changes in motion vectors of the pacific and farallon plates

dynamics of orogenic wedges and the uplift of high pressure metamorphic rocks subduction accretion complexes can be approximated as wedge shaped continua with a rigid buttress behind and a subducting litho spheric slab beneath thick wedges undergoing prograde metamorphism have a negligible long term yield strength and are likely to exhibit a complex nonlinear viscous rheology such a wedge will tend to deform internally until it reaches a stable configuration in which the gravitational forces generated by the wedge geometry balance the traction exerted on its underside by the subducting slab accretion of material at the wedge front will lengthen the wedge and cause it to shorten internally to regain the stable geometry this shortening will be expressed as late out of sequence thrusting backthrusting and folding conversely underplating of sediment or crustal slices will thicken the wedge which may need to extend internally to regain stability extension will cause listric normal faults that may merge downward into zones of ductile extension continued underplating at depth and compensating extension above provides a mechanism for bringing high p low t metamorphic rocks to upper levels in the rear of the wedge where they are commonly observed many major tectonic boundaries in convergent orogens such as the coast range thrust in the franciscan complex major nappe contacts in the alps and the contact between the nevado filabride and higher betic nappe complexes in the betic cordillera show abrupt increases in metamorphic grade downward across them this is consistent with their origin or reactivation as uplift related extensional structures

geochemical evidence for the tectonic setting of the coast range ophiolite a composite island arc oceanic crust terrane in western california the middle to late jurassic age coast range ophiolite cro of california contains two geochemically distinct volcanic rock associations that formed in different tectonic settings volcanic rocks from the southern cro point sal cuesta ridge stanley mountain llanada quinto creek and del puerto and parts of the northern cro healdsburg elder creek are similar to low k tholeiites and calc alkaline rocks of the island arc suite the thin volcanic sections of these ophiolite remnants suggest formation by intra arc rifting in contrast volcanic rocks from stonyford seamount and paskenta in the northern cro are transitional subalkaline metabasalts with geochemical characteristics similar to enriched mid ocean ridge basalts or ocean island tholeiites these rocks are associated with tithonian radiolarian cherts and may be part of the franciscan complex alternatively they may represent a change in tectonic setting within the cro during the late jurassic regardless the cro as currently conceived cannot be considered a single terrane with one mode of origin

relationship between sediment supply and avulsion frequency in braided rivers the interplay between sediment supply s s sedimentation rate s r and the frequency of channel avulsion a f exerts a primary control on alluvial architecture in order to investigate the effect of sediment supply on avulsion frequency four froude scale model experiments of an aggrading braided river were undertaken in which the magnitude of s s was progressively increased over an eightfold range the value of a f increases at a rate slower than the increase in s s contrary to the trend previously reported by bryant falk and paola in their experimental study on alluvial fan dynamics these results suggest that the relationship between a f and s s is dependent upon bed slope and that the response of a f to an increase in s s in unconfined braided rivers may be different than that on steep alluvial fans

subducted sedimentary serpentinite melanges record of multiple burial exhumation cycles and subduction erosion abstract serpentinite matrix melanges give insight into large scale convergent plate margin processes particularly because of the derivation of the serpentinite from oceanic mantle similar to shale matrix melanges a field geologist may easily recognize the sedimentary origins of little deformed serpentinite matrix melanges but melanges within accretionary prisms have undergone significant deformation and recrystallization of matrix serpentinite melanges of the franciscan subduction complex of california have a seemingly intact and foliated matrix such exposures contrast sharply with the granular undeformed sedimentary serpentinite melanges of the coeval great valley group gvg forearc basin deposits that depositionally overlie coast range ophiolite that structurally overlies the franciscan nonetheless franciscan serpentinite melanges display evidence of sedimentary origins including sedimentary breccia composed of exotic block material tolay ridge sedimentary serpentinite breccia panoche pass road basal serpentinite conglomerate with exotic clasts sunol regional wilderness and serpentinite sandstones and conglomerates including a basal conglomerate overlying coherent metagraywacke tiburon peninsula these examples record two burial exhumation cycles to blueschist facies depths in addition a melange breccia in the panoche pass area may have components that record three burial exhumation cycles to blueschist or greater depth exhumation rates for various cycles ranged from about 1 2 to 10 mm year the tiburon peninsula serpentinite melange occupies the structurally highest horizon in the franciscan of the san francisco bay area and regional field relationships indicate deposition at ca 100 ma apparently about 65 ma of subduction erosion non accretion followed initiation of franciscan subduction in this region the oldest franciscan serpentinite melanges are at least 35 ma younger than sedimentary serpentinites of the gvg subduction erosion may have facilitated reworking of forearc sedimentary serpentinite deposits into the trench evidence of multiple burial exhumation cycles indicates reworking of subduction complex material consistent with existence of clastic units that have fossils indicative of significantly older ages than detrital zircon ages

allophane aluminum and organic matter accumulation across a bioclimatic sequence of volcanic ash soils of argentina an investigation was conducted to study al fractions organic matter accumulation and their effects on physicochemical properties in soils derived from volcanic ash at the andinopatagonian region in sw neuquen argentina five sites were selected in a climatic biosequence ranging from nothofagus forest with a udic soil moisture regime at the footslope of the andes mountain range to grass shrub steppe with a xeric soil moisture regime in the hills and plains the morphological characteristics showed young pedons containing andic mollic and cambic horizons a change from low bulk density from 0 82 mg m 3 in andisols under a udic regime to medium density values of 1 1 mg m 3 in xerands and xerolls was observed this was related to a lower rate of weathering probably coinciding with a lower content of allophane and higher clay crystallization and to a decrease in total soil organic carbon corg the rate of soil weathering was estimated from acid oxalate extractable al which together with corg significantly explained the bulk density variation r2 0 7091 p 0 00002 soil acidity varied from moderately and strongly acidic in andisols with a udic soil moisture regime to slightly acid and almost neutral in xerands and xerolls the higher base concentration and low soil acidity in xerolls were attributed to less leaching due to lower mean annual precipitation however phnaf and corg were the variables which significantly explained the phwater variation r2 0 7806 p 0 0000 this showed that soil acidity was closely related to al activity and organic matter content rather than to base content the lower c n ratios in the surface horizons of the xerands and xerolls versus the andisols with a udic soil moisture regime suggested that the rate of mineralization was faster under warmer conditions with xeric moisture regime than with udic moisture regime there was also a remarkable difference in the humic c fulvic c ratio in a horizons which may reflect the input of vegetation residues indicating a sensible contribution of the cover of grass shrub steppe to the formation of humic substances the acid oxalate extractable si and al values reflected a low rate of weathering which decreased when mean annual precipitation decreased and a xeric soil moisture developed being also higher under nothofagus forest than under grass shrub steppe which reflects the possible effect of the mean annual precipitation gradient 2000 700 mm and vegetation types on soil weathering the differences in type and quantity of organic matter input with a higher organic matter content and lower humic c fulvic c ratio under nothofagus indicate a more reactive organic matter which may be somewhat responsible for the weathering degree no significant relationship between acid extractable al and corg was found suggesting that organically bound al is not dominant the detection of higher allophane estimations in soils with the highest corg levels may indicate that the anti allophanic hypothesis probably does not apply to these soils

simulations of the greenland ice sheet 100 years into the future with the full stokes model elmer ice it is likely that climate change will have a significant impact on the mass balance of the greenland ice sheet contributing to future sea level rise here we present the implementation of the full stokes model elmer ice for the greenland ice sheet which includes a mesh refinement technique in order to resolve fast flowing ice streams and outlet glaciers we discuss simulations 100 years into the future forced by scenarios defined by the searise sea level response to ice sheet evolution community effort for comparison the same experiments are also run with the shallow ice model sicopolis simulation code for polythermal ice sheets we find that elmer ice is 43 more sensitive exhibits a larger loss of ice sheet volume relative to the control run than sicopolis for the ice dynamic scenario doubled basal sliding but 61 less sensitive for the direct global warming scenario based on the a1 b moderate emission scenario for greenhouse gases the scenario with combined a1b global warming and doubled basal sliding forcing produces a greenland contribution to sea level rise of 15cm for elmer ice and 12cm for sicopolis over the next 100 years