palinspastic reconstruction and topographic evolution of the eastern alps during late tertiary tectonic extrusion this paper presents a new palinspastic restoration of the eastern alps for neogene time and an attempt to reconstruct the neogene palaeogeology palaeotopography and palaeohydrography in connection with the structural evolution the eastern alps underwent radical horizontal displacement during the neogene due to large strike slip systems and formation of structural windows our palinspastic reconstruction considers a the rearrangement of tectonic units dismembered during tectonic extrusion b the tectonic denudation driven by displacement of the crystalline blocks c geochronological arguments and d the sedimentary record of the syn extrusion basins the rearrangement of tectonic blocks results in a remarkably good fit of highly dismembered zones both in crystalline and sedimentary areas and shows the pre miocene unstretched pattern of the eastern alps reduced to 65 of its present day e w elongation using this structural frame and considering the sedimentary record a set of palaeogeologic and palaeotopographic sketch maps with the palaeo river systems is presented for three time slices pre syn and post extension situation in late oligocene and early miocene times the western eastern alps were already mountainous whereas the eastern part of the orogen formed lowlands or hilly areas enhanced block movement in the course of the extrusion process around the early middle miocene boundary led to the formation of intramontane sedimentary basins and a fault induced reorientation of the drainage pattern which forms the basis of the modern river system in the area east of the tauern window this region where pre miocene land surfaces are preserved probably became a mountainous area not before late miocene time and never reached the elevations of the areas further west

the kinematics of movements along the insubric line and the emplacement of the ivrea zone schmid sm zingg a and handy m 1987 the kinematics of movements along the insubric line and the emplacement of the ivrea zone in h j zwart m martens i van der molen c w passchier c spiers and r l m vissers editors tectonic and structural processes on a macro meso and micro scale tecta a hys 135 47 66 the insubric line west of locamo is characterized by a 1 km thick greenschist facies mylonite belt east of locamo these mylonites are overprinted by a discrete brittle fault the mylonites are derived from basement units of the central alps sesia zone and the southern alps ivrea zone as well as from the permo mesozoic cover of the southern alps canavese sense of shear criteria indicate that the mylonites accomm ated backt s g followed by dextral strike slip motion mylonitization during backtbrusting was synchronous with backfolding of the central alpine nappes under higher metamorphic conditions a horizontal temperature gradient resulted from the rapid juxtaposition of the warm central alpine block against the cold southern alpine block mylonites formed during the later dextral strike slip event are related to large transcurrent displacements in the central alps deduced from regional kinematic considerations thus both mylo t ation events are contempor eous with deformation to the north and south of the insubric line insubric phase extensively modifying the pre insubric crustal configuration of the alps the insubric phase post dates the bergell intrusion 30 m y the emplacement of the geophysical ivrea body is a combined effect of vertical uplift due to e w directed crustal thinning during the early jurassic and underplating by continental crust associated with late cretaceous compression a deep crustal normal fault pogallo line subsequently rotated during tertiary alpine orogenesis separates deeper parts of the southern alpine crust ivrea zone from intermediate crustal levels strona ceneri zone the rigid ivrea body localir ed large strains within the insubric mylonite belt and is responsible for the present curvature of the insubric line in uetion

pore water pressure and streambank stability results from a monitoring site on the sieve river italy to investigate the role of pore water pressures in the stability of a streambank a series of tensiometers and piezometers was installed in a bank of the sieve river tuscany italy fluvial entrainment at the bank toe was monitored by repeated cross profiling erosion pins and marked pebbles fluctuations in matric suction measured at the tensiometers reflected the overall response of pore water pressures to rainfall evapotranspiration rising and drawdown of the river stage and variations in water table an expression was derived for the safety factor with respect to mass movement of the upper bank incorporating the failure criterion for unsaturated soils and the normal mohr coulomb criterion for saturated conditions variations in matric suction have important effects on the stability of the streambank during low flow periods the shear strength term due to the matric suction allows the bank to remain stable at a steep angle however during rainfall and flow events reduction in matric suction and increase in unit weight of the material from vertical and lateral infiltration may be sufficient to trigger a mass failure without development of significant positive pore water pressures during the rising limb of high flow events the factor of safety increases as a consequence of the stabilizing confining pressure of the water in the river despite a reduction in matric suction during drawdown in the river when the suction values are still low and the confining pressure in the river decreases to zero the factor of safety falls to lower values than those experienced prior to the runoff event measurements of fluvial entrainment reveal that although the processes mechanisms and the frequency of retreat of basal and upper bank zones differ significantly the amount of retreat at the bank toe due to fluvial erosion is comparable to that of the upper portion of the bank due to mass failure copyright 1999 john wiley sons ltd

sediment characteristics of an extreme flood 1993 upper mississippi river valley the 1993 mississippi river flood was notable for its high magnitude long duration summer occurrence and low sediment discharge a field survey of a 70 km long reach in the vicinity of quincy illinois revealed that the event was characterized by 100 yr flood had remarkably little sedimentological or geomorphological impact on the flood plain within the study reach because the transport effectiveness of floods in large drainage basins is influenced by event sequencing in the same manner as floods in small watersheds and the cohesive flood plain soils were not susceptible to erosion

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

research focus significance of large displacement low angle normal faults low angle normal faults lanfs or detachment faults dip 30 are a major class of faults that became widely accepted by earth scientists only in the late twentieth century continental lanfs were mapped for nearly 100 yr e g ransome et al 1910 1 but typically were interpreted as odd

thermal evolution and exhumation in obliquely convergent transpressive orogens most p t t path models to date have considered a linear erosion rate for exhumation from burial depth related to isostatic readjustment of crustal thickness a few have discussed extension enhanced exhumation erosional exhumation can only restore lower crustal rocks from the thickened mountain root to their previous original depth in the pre collisional crust one major assumption of all models to date is that the compressive forces responsible for crustal thickening cease before elevation and erosion begins however compression is often still active even if the crustal thickening has stopped further compression of the thickened and strongly deformed orogenic root is responsible for forceful exhumation extrusion of softened rocks upwards hence the rate of exhumation is related to the rate of convergence of colliding plates extrusional exhumation can elevate buried rocks to any depth depending on the action of fault shear systems in the extrusional exhumation models examined here the ascending rocks cool faster because they approach the zero temperature surface conditions more rapidly than by isostatic erosion the exhumation rate is also governed by the angle between the plate boundary and the displacement vector implying that the convergent plate boundaries are regarded as complex transpressive systems in which the degree of obliquity can be expressed by the ratio of pure to simple shear components a low ratio of pure simple shear typical for wrench dominated plate boundaries implies long distance horizontal transport from the buried position in the original orogen and longer periods during which metamorphic heating occurs a high ratio of pure simple shear characteristic for frontal like convergence implies a rapid exhumation without significant heating thus granulites barrovian type and blueschist facies metamorphism are characterised by increasing angle of obliquity 10 30 90 respectively the high temperature limit at low ratio of pure simple shear is the geotherm t and lies at temperatures that would commonly be taken to indicate that addition of mantle heat was required to generate hot geotherms and p t t paths wrench faulting over 100 s of kilometres at reasonable slow convergence rates could lead to extensive dehydration melting and granulite formation in large scale collisional orogens

the efficacy of stream power and flow duration on geomorphic responses to catastrophic flooding abstract geomorphologists have long studied the impacts of extreme floods yet the association between the magnitude of flow parameters discharge velocity shear stress or stream power and resulting geomorphic effectiveness remains vague and non deterministic attempts have been made to include flow duration and total expenditure of stream power in combination with peak unit stream power as important variables but there has been minimal exploration of this hydraulic combination taking advantage of tropical storm irene s rapid track through eastern vermont usa in late summer 2011 this paper presents the array of geomorphic responses to a short duration time to peak of

off river waterbodies on tidal rivers human impact on rates of infilling and the accumulation of pollutants abstract cut off meanders backwater ponds and blocked valley coves are all common features along the tidal reaches of lowland rivers while significant progress has been made to understand sediment dynamics in similar off river environments above the head of tides less is known about the processes driving transport and sedimentation within these systems when tidally influenced to provide insight we combine sedimentological observations with flux analyses for a series of tidal off river waterbodies along the lower connecticut river spanning the river s entire 100 km tidal reach sedimentation rates exhibit a clear seaward increase with growing tidal influence and are an order of magnitude higher than accumulation rates obtained previously from neighboring marsh and subtidal environments a simplified mass balance can relate time series measurements of water level and suspended sediment concentration to observed trends in sedimentation and support flood dominated asymmetry in tidal sediment flux i e tidal pumping as the primary mechanism for enhanced trapping relatively steady rates of deposition are observed in off river waterbodies over the last century with little evidence of deposition dominated by extreme events suspended sediment concentrations rise significantly in the main tidal river with increasing river discharge while tidal range is damped with rising freshwater flow the net result is an optimal freshwater discharge for maximizing the tidal pumping of sediment from the main river into tidal off river waterbodies with more routine discharge events largely responsible for driving long term trends in deposition a sudden shift in lithology towards more inorganic fluvial derived sediment is commonly observed towards the end of the 19th century along with over an order of magnitude increase in the rate of deposition the timing of the onset of rapid infilling occurs contemporaneous with the documented creation and or deepening of tidal tie channels followed shortly after by a rapid rise in heavy metal concentrations related to industrial activity along the river results point to the creation and routine maintenance of tidal inlets increasing the connectivity of off river waterbodies to the main tidal river in recent centuries and enhanced sediment trapping along the floodplain at the most favorable time for capturing legacy contaminants introduced during the industrial era

metamorphic p t paths from pelitic schists and greenstones from the south west tauern window eastern alps petrological data from intercalated pelitic schists and greenstones are used to construct a pressure temperature path followed by the upper schieferhulle ush series during progressive metamorphism and uplift in the south west tauern window italy pseudomorphs of al epidote fe epidote albite oligoclase chlorite after lawsonite and data on amphibole crystal chemistry indicate early metamorphism in the lawsonite albite chlorite subfacies of the blueschist facies at p 7 8 kbar geothermometry and geobarometry yield conditions of final equilibration of the matrix assemblage of 475 25 c 5 6 kbar calculations with plagioclase and phengite inclusions in garnet indicate early garnet growth at pressures of 7 5 kbar garnet zoning patterns are complex and reversals in zoning can be correlated between samples thermodynamic modelling of these zoning profiles implies garnet growth in response to four distinct phases of tectonic activity fluid inclusion data from coexisting immiscible h2o co2 nacl fluids constrain the uplift path to have passed through temperatures of 380 30 c at 1 3 0 2 kbar there is no evidence for metamorphism of ush at pressures greater than 7 5 kbar in this area of the tauern window this is in contrast to pressures of 10 kbar recorded in the lower schieferhulle only 2 3 km across strike a history of differential uplift and thinning of the intervening section during metamorphism is necessary to reconcile the p t data obtained from these adjacent tectonic units

hydroclimatological and geomorphic controls on the timing and spatial variability of floods in new england usa abstract numerous methods exist to express a region s flood regime but because of the various controls on flooding no salient method emerges we have used directional also known as orientation statistics to express some of the hydroclimatological and geomorphic controls on flooding in new england and mapped these statistics for 36 gages to reveal the regional groupings of similarly responding basins directional statistics express the temporal variance of flood timings and characterize the seasonality of floods and thus begin to demonstrate some of the climatic controls on flood timing and their spatial effects contour maps of the vector mean timing of floods indicate the strong control of coastal influences on the hydrologic regime and multiple regression analyses indicate that both the surrogate variables for climate latitude and distance to the coast strongly explain the timing of the vector mean although both the geomorphic variables basin size and altitude are also significant explanatory variables an autumnal flood season exists along coastal locations but disappears moving both inland and northward through the region for many of these coastal locations especially in the south the autumn mode reflects the occurrence of hurricane induced floods which for many basins represent the largest flood in the annual series the strength of the seasonality as expressed by the mean resultant magnitude is controlled primarily by basin size with distance to the coast and altitude also important finally these results suggest that directional statistics are an appropriate method for depicting regional hydrologic regimes and in describing some of the hydroclimatological controls on flood occurrence

itrax description and evaluation of a new multi function x ray core scanner a new automated multi function core scanning instrument named itrax has been developed that records optical radiographic and elemental variations from sediment half cores up to 1 8 m long at a resolution as fine as 200 m an intense micro x ray beam focused through a flat capillary waveguide is used to irradiate samples to enable both x radiography and x ray fluorescence xrf analysis data are acquired incrementally by advancing a split core via a programmable stepped motor drive through the flat rectangular section x ray beam traditional xrf determination of element composition in sediments provides high quality data but it takes a considerable time and normally consumes gram quantities of material that is often only available in limited quantities the itrax core scanner non destructively collects optical and x radiographic images and provides high resolution elemental profiles that are invaluable for guiding sample selection for further destructive detailed sampling this paper presents a description of the construction characteristics and capabilities of the itrax system high resolution itrax data obtained from sediment cores are also presented and compared with results from traditional wavelength dispersive xrf analysis at lower resolution finally some recent technical developments linked to the second generation itrax are presented

kinematics of austro alpine cover nappes changing translation path due to transpression upper and middle austro alpine nappes of the eastern alps the structural uppermost subunits of the alps suffered two major superposed deformations d1 d2 during the eo alpine cretaceous orogeny d1 is characterized by nw to w directed thrusting and nappe internal rock flow d2 by large scale folding and imbrication toward the north and northeast structures strain metamorphic history microfabrics and stretching trajectories indicate that the superposition of d2 over d1 structures can be interpreted as a progressive deformation it is concluded that the emplacement of the nappes follows a curved translation path a model which emphasizes non coaxial deformation structures explains the detachment of the nappes the configuration of the separating thrust planes and the distribution of intense deformation zones the overall kinematic history of the austro alpine nappes fits a model in which strike slip shearing horizontal shortening and vertical lengthening act together continuously over a finite deformation zone transpressional model this model emphasizing a gradually changing strain regime eliminates the space problems encountered in models which consider simple south over north imbrication during the alpine orogeny the study stresses two interpretations 1 1 stretching lineations indicate nappe transport directions 2 2 transpression may be a common feature of orogenic belts

impact of reach geometry on stream channel sensitivity to extreme floods predicting spatial and temporal variations in bank erosion due to extreme floods presents a long standing challenge in geomorphology we develop two methodologies for rapid regional scale assessments of stream reaches susceptible to channel widening the first proposes that channel widening occurs when unit stream power exceeds a critical threshold 300 w m2 the second is motivated by the observation that widening often occurs at channel bends we introduce a new metric the bend stress parameter which is proportional to the centripetal force exerted on a concave bank we propose that high centripetal forces generate locally high bank shear forces and enhance channel bank erosion we test both metrics using the geomorphic signature of tropical storm irene 2011 on the white and the saxtons rivers vermont specifically we test if reaches where significant channel widening occurred during irene required one or both metrics to exceed threshold values we observe two distinct styles of channel widening where unit stream power and bend stress parameter are high widening is usually due to bank retreat elsewhere widening is usually due to the stripping of the upstream end of mid channel islands excluding widening associated with the stripping of the heads of mid channel islands almost all the widening 98 occurred along reaches identified as susceptible to widening the combined metrics identify up to one quarter of the reaches lacking susceptibility to channel widening copyright 2014 john wiley sons ltd

salt wedge dynamics lead to enhanced sediment trapping within side embayments in high energy estuaries off river coves and embayments provide accommodation space for sediment accumulation particularly for sandy estuaries where high energy in the main channel prevents significant long term storage of fine grained material seasonal sediment inputs to hamburg cove in the connecticut river estuary usa were monitored to understand the timing and mechanisms for sediment storage there unlike in freshwater tidal coves sediment was primarily trapped here during periods of low discharge when the salinity intrusion extended upriver to the cove entrance during periods of low discharge and high sediment accumulation deposited sediment displayed geochemical signatures consistent with a marine source numerical simulations reveal that low discharge conditions provide several important characteristics that maximize sediment trapping first these conditions allow the estuarine turbidity maximum etm to be located in the vicinity of the cove entrance which increases sediment concentrations during flood tide second the saltier water in the main channel can enter the cove as a density current enhancing near bed velocities and resuspending sediment providing an efficient delivery mechanism finally higher salinity water accumulates in the deep basin of the cove creating a stratified region that becomes decoupled from ebb currents promoting retention of sediment in the cove this process of estuarine enhanced sediment accumulation in off river coves will likely extend upriver during future sea level rise

petrologic constraints on imbrication metamorphism and uplift in the sw tauern window eastern alps the pressure temperature time deformation pttd history of two tectonic units in the southwest tauern window austria italy is evaluated from p t paths of metamorphism and uplift geochronologic data and observations on fabric development petrologic data indicate burial of the lower schieferhulle lsh to depths of 35 km and the adjacent upper schieferhulle ush to only 24 28 km the units are now separated by only 2 km of section metamorphism was postkinematic in the lsh and synkinematic in the ush correlation of p t path reversals calculated from zoned garnets in the two units however indicates that juxtaposition of the lsh and ush occurred prior to metamorphism temperature time and depth time diagrams for both units show increasing cooling rates and decreasing uplift rates as the rocks approached the surface both the petrologic data and the depth time profiles for the lsh and ush point to a history of differential uplift in the early stages of decompression textural features indicate that the lsh behaved as an essentially rigid body during uplift whereas the ush experienced extensive ductile shearing the pttd data for the lsh and ush are incorporated into a model for continental collision in the eastern alps initial tectonic uplift of the lsh was accompanied by ductile thinning of the ush and overlying austroalpine units final uplift and erosion affected all of the units en masse

fluid inclusion constraints on the kinematics of footwall uplift beneath the brenner line normal fault eastern alps dynamic models of isostatic footwall uplift in response to normal faulting can be divided into those in which uplift is accomplished by flexural failure and those in which uplift occurs via subvertical simple shear each class of model predicts a different incremental strain history that should be recorded in the footwall in the tauern window eastern alps postmylonitic structures in the footwall of the brenner line normal shear zone predominantly consist of closely spaced steep west down and east down microfaults formation of the west down faults before and at greater depths than the east down faults would be consistent with unroofing via subvertical simple shear in contrast formation of the two fault types as a conjugate set would be more indicative of unroofing via elastic processes the field data alone do not provide a sufficient test of the two hypotheses because crosscutting relations are only rarely observed and there is no control on the depth at which the structures formed however both depth and timing constraints on the formation of the late structures can be obtained by correlating the orientations of fluid inclusion lined microfaults with the macroscopic west down and east down faults obtaining density data for the inclusions and correlating these data with previously obtained geochronologic data the results indicate that the west down structures formed at depths of 10 20 km and temperatures 450 c in the mid to late oligocene and that the east down structures formed at 2 to 10 km depth and temperatures of 300 50 c in the mid miocene these data support the hypothesis that a rolling hinge was present in the footwall of the brenner line and that isostatically driven footwall deformation was accomplished predominantly by subvertical simple shear the depths at which west down and east down faulting occurred coupled with the angle of dip of the brenner line yield a minimum lateral displacement on the fault of 15 26 km approximately coeval ductile shearing and brittle faulting at depths of 15 20 km and temperatures in excess of 400 c may reflect local variations in strain rate as the footwall rocks entered the zone of rolling hinge deformation

north south extension within the convergent himalayan region recent work by burg et al 1984 indicates the presence of east west striking gently north dipping normal faults in the higher himalayas and southern tibet that formed during postcollisional convergence of india and tibet these faults extend for at least 800 km along strike we interpret these normal faults as probable late miocene extensional features with perhaps several tens of kilometres of down to the north displacement a simple elastic model suggests that these normal faults may have formed during gravitational collapse of the miocene topographic front between india and tibet in this interpretation gravitational collapse occurred by southward motion relative to india and tibet of a wedge of crustal rocks bounded above by gently north dipping normal faults and below by thrust faults that probably dip north north south extension produced in this way is probably confined to upper crustal levels only and does not reflect regional extension of the entire lithosphere

fluid inclusion constraints on the uplift history of the metamorphosed massive sulphide deposits at ducktown tennessee standard petrographic microthermometric and raman spectroscopic analyses of fluid inclusions from the metamorphosed massive sulphide deposits at ducktown tennessee indicate that fluids with a wide range of compositions in the c o h n s salt system were involved in the syn to post metamorphic history of these deposits primary fluid inclusions from peak metamorphic clinopyroxene contain low salinity h2o ch4 fluids and calcite quartz and pyrrhotite daughter crystals many of these inclusions exhibit morphologies resembling those produced in laboratory experiments in which confining pressures significantly exceed the internal pressures of the inclusions secondary inclusions in metamorphic quartz from veins pods and host matrix record a complex uplift history involving a variety of fluids in the c o h n salt system early fluids were generated by local devolatilization reactions while later fluids were derived externally isochores calculated for secondary inclusions in addition to the chronology of trapping and morphological features of primary and secondary fluid inclusions suggest an uplift path which was concave toward the temperature axis over the p t range 6 3 kbar and 550 225 c immiscible h2o ch4 n2 nacl fluids were trapped under lithostatic to hydrostatic pressure conditions at 3 0 5 kbar and 215 20 c entrapment occurred during alleghanian thrusting and the fluids may have been derived by tectonically driven expulsion of pore fluids and thermal maturation of organic material in lower plate sedimentary rocks which are thought to underlie the deposits episodic fracturing and concomitant pressure decreases in upper plate rocks which host the ore bodies would have allowed these fluids to move upward and become immiscible post alleghanian uplift appears to have been temperature convex uplift rates of 0 10 0 05 mm year 1 from middle ordovician to middle silurian late devonian and 0 07 0 12 mm year 1 from middle silurian late devonian to late permian are suggested by our uplift path and available geochronological data

source conveyance and fate of suspended sediments following hurricane irene new england usa hurricane irene passed directly over the connecticut river valley in late august 2011 intense precipitation and high antecedent soil moisture resulted in record flooding mass wasting and fluvial erosion allowing for observations of how these rare but significant extreme events affect a landscape still responding to pleistocene glaciation and associated sediment emplacement clays and silts from upland glacial deposits once suspended in the stream network were routed directly to the mouth of the connecticut river resulting in record breaking sediment loads fifteen times greater than predicted from the pre existing rating curve denudation was particularly extensive in mountainous areas we calculate that sediment yield during the event from the deerfield river a steep tributary comprising 5 of the entire connecticut river watershed exceeded at minimum 10 40 years of routine sediment discharge and accounted for approximately 40 of the total event sediment discharge from the connecticut river a seriesof surface sediment corestaken in floodplainponds adjacent to the tidalsec

shallow water benthic foraminifera from the polonez cove formation lower oligocene of king george island west antarctica abstract we present the first description of benthic foraminifera from the lower oligocene of the antarctic peninsula sector south shetlands of west antarctica the single assemblage was collected at several sites and has no modern antarctic analogue it is dominated by robust calcareous species and represents a fan delta front system the assemblage includes a group of the most morphologically conservative antarctic foraminifera known from other cenozoic neritic sites around antarctica indicating their presence since at least the eocene despite including some characteristic taxa e g ammoelphidiella sp it is difficult to correlate this assemblage with any particular interval of the ross sea record mainly because of a strong taxonomic imprint of a shallow water environment

neogene glacigenic debris flows on james ross island northern antarctic peninsula and their implications for regional climate history detailed sedimentological and microtextural analyses of newly discovered late neogene diamictites and other coarse grained facies mostly sandwiched between hyaloclastite of the james ross island volcanic group and cretaceous sandstone and mudstone indicate deposition mainly by glacigenic debris flows the deposits on james ross island northern antarctic peninsula constrain the depositional setting ice bed dynamics and regional palaeoclimate the sequences on james ross island vary in age but are mainly late miocene and pliocene unlike neogene sedimentary sequences elsewhere in antarctica those on james ross island are unusually well dated by a combination of 40ar 39ar and 87sr 86sr analyses on fresh interbedded lavas and pristine bivalve molluscs respectively the sr isotopic ages of the debris flows cluster around 4 74 4 89 5 44 5 78 and 6 31 ma and probably date relatively warm periods in the northern antarctic peninsula region when the bivalves lived under ice poor or seasonally ice free conditions the bivalves are often remarkably well preserved lack adhering lithified sediment and in at least two locations are large mainly unfragmented and sometimes articulated suggesting that they were alive immediately prior to their incorporation in subaqueous debris flows at the margins of an advancing glacier these fossiliferous glacigenic debris flows signify episodes of ice expansion during relatively warm periods or interglacials of the late miocene and pliocene the james ross island glacigenic sedimentary successions attain thicknesses of up to 150 m and extend over 4 km laterally the high volume of glacigenic sediment delivery implicit in the james ross island successions indicates that a series of dynamic ice fronts crossed the region during the late miocene and pliocene epochs associated evidence in the form of clast abrasion including striations and faceting and bedrock erosion is indicative of basal sliding and subglacial sediment deformation active at the ice bed interface and wet based temperate or polythermal regimes prior to remobilisation the evidence further suggests two local ice caps on james ross island during the warm periods as well as ice overriding by the antarctic peninsula ice sheet from the west and northwest

zanskar shear zone northeast southwest extension within the higher himalayas ladakh india a complete geologic section through the northwestern himalayas is well exposed in ladakh india the collision between the indian shield and the tibetan platform caused large scale intracrustal thrusting and piling up of the himalayan nappes this compressional event was accompanied by prograde regional metamorphism the metamorphism ranges from low grade anchimetamorphism in the indus suture zone in the northeast to upper amphibolite grade in the higher himalaya tectonic unit in the southwest in the zanskar area a well exposed and morphologically prominent shear zone 2 25 to 6 75 km wide can be followed from the northwest to the southeast for at least 80 km in contrast to the main compressional tectonics this shear zone indicates an extensional event within the higher himalaya tectonic unit the zanskar shear zone involves granitic rocks leucogranites of miocene age and various metasediments and in general separates the late precambrian early cambrian sedimentary sequence phe formation from the underlying crystalline basement zanskar crystalline unit a normal sense of shear has been determined by using asymmetric macroscopic and microscopic structures such as pegmatite boudins feldspar augen and crystallographic fabrics the metamorphic isograds are very close within this shear zone as a result of shear deformation a gradual transition from upper amphibolite to lower greenschist facies occurs within 200 m movement in this zone occurred late in the metamorphic history under greenschist or lower metamorphic conditions the minimum horizontal extension and vertical displacement are on the order of 16 and 19 km respectively

the lepontine alps as an evolving metamorphic core complex during a type subduction evidence from heat flow mineral cooling ages and tectonic modeling new surface heat flow data are presented for the valle maggia region within the high grade metamorphic core of the lepontine alps the steady state values range from 44 4 to 55 2 mw m2 and are anomalously low compared with those measured around the periphery of the lepontine these differences are considered to reflect the combined effects of differential uplift and erosion superimposed on a transient low heat flow regime which has existed since the miocene the uplift denudation history of the lepontine is modeled by using various mineral geochronometers two major pulses of accelerated uplift are recognized at circa 22 m y b p and circa 10 m y b p respectively these events directly coincide with times of dominant crustal convergence in the helvetic and jura stages of a subduction from known pmax tmax conditions of oligocene metamorphism estimates of low mantle heat flow and experimentally determined values of crustal heat production best fit thermal models are presented to explain surface heat flow and mineral cooling age data for the metamorphic core a two stage underplating model is shown to be consistent with the excavation history of the lepontine and with geological and geophysical data from more external parts of the central alps this information is integrated to explain the establishment of a crustal scale duplex in the metamorphic core complex contemporaneous with thin skinned tectonics in the foreland

modes of orogen parallel stretching and extensional exhumation in response to microplate indentation and roll back subduction tauern window eastern alps the tauern window exposes a paleogene nappe stack consisting of highly metamorphosed oceanic alpine tethys and continental distal european margin thrust sheets in the eastern part of this window this nappe stack eastern tauern subdome etd is bounded by a neogene system of shear the katschberg shear zone system kszs that accommodated orogen parallel stretching orogen normal shortening and exhumation with respect to the structurally overlying austroalpine units adriatic margin the kszs comprises a 5 km thick belt of retrograde mylonite the central segment of which is a southeast dipping low angle extensional shear zone with a brittle overprint katschberg normal fault knf at the northern and southern ends of this central segment the kszs loses its brittle overprint and swings around both corners of the etd to become subvertical dextral and sinistral strike slip faults the latter represent stretching faults whose displacements decrease westward to near zero the kinematic continuity of top east to top southeast ductile shearing along the central low angle extensional part of the kszs with strike slip shearing along its steep ends combined with maximum tectonic omission of nappes of the etd in the footwall of the knf indicates that north south shortening orogen parallel stretching and normal faulting were coeval stratigraphic and radiometric ages constrain exhumation of the folded nappe complex in the footwall of the kszs to have begun at 23 21 ma leading to rapid cooling between 21 and 16 ma this exhumation involved a combination of tectonic unroofing by extensional shearing upright folding and erosional denudation the contribution of tectonic unroofing is greatest along the central segment of the kszs and decreases westward to the central part of the tauern window the kszs formed in response to the indentation of wedge shaped blocks of semi rigid austroalpine basement located in front of the south alpine indenter that was part of the adriatic microplate northward motion of this indenter along the sinistral giudicarie belt offsets the periadriatic fault and triggered rapid exhumation of orogenic crust within the entire tauern window exhumation involved strike slip and normal faulting that accommodated about 100 km of orogen parallel extension and was contemporaneous with about 30 km of orogen perpendicular north south shortening of the etd extension of the pannonian basin related to roll back subduction in the carpathians began at 20 ma but did not affect the eastern alps before about 17 ma the effect of this extension was to reduce the lateral resistance to eastward crustal flow away from the zone of greatest thickening in the tauern window area therefore we propose that roll back subduction temporarily enhanced rather than triggered exhumation and orogen parallel motion in the eastern alps lateral extrusion and orogen parallel extension in the eastern alps have continued from 12 to 10 ma to the present and are driven by northward push of adria

parallel thrust and normal faulting in peru and constraints on the state of stress abstract we present evidence for recent normal faulting in the cordillera blanca of peru along planes trending approximately n40 w parallel to the chain this type of faulting suggests that there is an important component of extension perpendicular to the chain and contrasts markedly with the underthrusting of the nazca plate on the west side of peru and with the folding and thrusting observed in the sub andes on the eastern flank of the chain these contrasting styles of deformation and associated stress fields can be explained by buoyancy forces due to the high mountains and crustal roots in so far as this explanation is correct the difference in elevation between zones of normal and thrust faulting can be used to place an upper bound of 500 bars on the average stress difference in the crust

deep crustal break back stacking and slow exhumation of the continental footwall beneath a thrusted marginal basin grenville orogen canada abstract granulite to upper amphibolite facies ductile thrusting in the central gneiss belt grenville orogen ontario represents the tectonic shortening of a continental scale footwall beneath the thrust emplaced central metasedimentary belt during the closure of a postulated back arc basin ca 1 19 1 18 ga break back stacking in the footwall occurred at mid to deep crustal depths ca 35 km within tectonically thickened ca 70 km continental crust and culminated with renewed thrusting at the base of the overlying central metasedimentary belt ca 1 08 1 05 ga the individual mylonite belts which constitute the ductile thrust zones and the scale of penetrative deformation of the intervening crystalline thrust sheets are comparable with the largest known examples of high grade thrust belts elsewhere they reflect the large scale thermal and theological boundary conditions of the deformation flow within individual thrust zones may reflect local boundary conditions such as the rheological behaviour of older thrust sheets and the geometry of interfaces within the thrust stack restoration of the thickness of erosionally removed crustal overburden by break back thrusting may retard the rates of exhumation and cooling of a mid to deep crustal thrust stack

foraminiferal assemblages from ice proximal paleo settings in the whales deep basin eastern ross sea antarctica abstract reconstructions of ross sea paleoenvironments based on foraminifera are hindered by the dearth of actualistic data especially from below the ross ice shelf to fill this gap we used a recently developed well resolved deglaciation record from the whales deep basin of the eastern ross sea to understand the ecological affinities of different foraminiferal assemblages during open water conditions similar to the present two benthic foraminiferal communities are strongly dominated by agglutinated species however in the underlying sediments that represent sub ice shelf and grounding zone proximal settings on the outer continental shelf we identified five different assemblages of calcareous foraminifera by antarctic margin standards these calcareous assemblages are periodically truly abundant along with assemblages dominated by benthic calcareous species that are well known from many antarctic settings i e globocassidulina biora trifarina earlandi and astrononion echolsi two important assemblages are dominated by a heretofore undescribed pustulose morphotype of g biora and poorly known spinose morphotype of t earlandi based on our correlations to the deglacial record these two assemblages live near the grounding line or in environments with especially intense bottom water currents as grounded and floating ice retreated south to the middle continental shelf these later sub ice shelf and grounding zone proximal settings were largely devoid of calcareous foraminifera and instead were inhabited by agglutinated taxa this improved understanding of foraminiferal assemblage distributions from a variety of environments within the eastern ross sea may contribute to better use of foraminiferal data to investigate the evolution of environmental changes in grounding line proximal environments

late oligocene neogene evolution of europe adria collision new structural and geochronological evidence from the giudicarie fault system italian eastern alps the giudicarie fault system giudicarie sensu stricto meran mauls passeier thurnstein and jaufen faults represents a sharp break in the generally e w strike direction of the orogen scale periadriatic fault system and is a key element for understanding the late oligocene neogene evolution of the alpine chain the kinematics timing and magnitude of movements on the giudicarie fault system are presented here on the basis of a detailed structural study of the component fault segments combined with zircon and apatite fission track analysis from closely spaced samples two main tectonic phases are established 1 back thrusting of the austroalpine units over the southern alps around 32 ma recorded by basement and limestone mylonites along the giudicarie and meran mauls faults with transport directions toward 100 110 and 2 later sinistral transpressive displacement characterized by structures at the ductile brittle transition which overprinted the top to e ese thrust related mylonites but also partitioned into a major system of transcurrent faults in the southalpine domain it was during this later event that the periadriatic fault attained its present day geometry however the amount of sinistral displacement along the giudicarie system was only 15 20 km the magnitude is established here from the 15 km sinistral offset of the jaufen mylonites across the passeier brittle fault and the 20 km long gap in the otherwise continuous distribution of oligocene tonalitic lamellae along the giudicarie fault a direct structural connection is also established between the brenner and the jaufen faults this constrains the timing of the second phase since it must postdate the main exhumation phase of the tauern window at 20 18 ma the results of this study argue against an originally straight periadriatic fault the giudicarie fault formed a restraining bend in this part of the periadriatic fault system since at least the late miocene and probably since the late oligocene

late oligocene early miocene glacial record of the ross sea antarctica evidence from dsdp site 270 foraminifera from deep sea drilling project site 270 ross sea antarctica are used to trace an early phase of glaciation during the late oligocene early miocene the central ross sea underwent significant bathymetric and oceanographic evolution with the inception of glaciomarine sedimentation resulting in the sequential development of four contrasting foraminiferal populations assemblage zones gradual climatic change in the ross sector during latest paleogene early neogene time culminated in major ice build up by the late early miocene conclusions derived from our microfaunal studies reaffirm climatic and oceanographic trends interpreted from oxygen isotope data for sub antarctic deep sea sites north of the ross sea intensification of glaciation within the ross sea area may be responsible for the increase in production of antarctic bottom water and associated development of widespread early neogene deep sea hiatuses reported from lower latitude regions

the new north american varve chronology a precise record of southeastern laurentide ice sheet deglaciation and climate 18 2 12 5 kyr bp and correlations with greenland ice core records new glacial varve records from long cores combined with records from key surface exposures and new radiocarbon ages have allowed the correction consolidation expansion and calibration of ernst antevs9 original new england varve chronology nevc in the connecticut valley of new england u s a the varve records have been reformulated with corrections and a new numbering system as the new north american varve chronology navc which is a continuous 5659 yr varve sequence that spans most of the last deglaciation 18 200 12 500 yr bp in the northeastern united states rates of ice recession for separate intervals terminated by abrupt glacial stillstands and readvances have been determined for western new england ice recession history is coupled to varve thickness changes that depict changes in meltwater production in the connecticut valley and show the relationship of changes in ablation rate summer climate variation to glacial readvances and periods of halted and rapid ice recession up to 300 m yr comparison of varve thickness records to greenland ice core climate records show that after 15 000 yr bp climate changes of sub century and longer scales recorded in both records appear identical and synchronous after 15 000 yr bp therefore there was a link between north atlantic climate and marginal processes of the southeastern sector of the laurentide ice sheet lis prior to 15 000 yr bp when the lis was closer to an equilibrium condition retreat rates were generally lower and changes in varve thickness and ablation were more subtle but can still be linked to ice sheet activity only weak relationships between varve thickness changes and greenland climate are evident suggesting that changes in the southeastern lis during this time may have been significantly influenced by climate patterns unique to the north american continent or ice dynamics

palaeoclimatic implications of a storm erosion record from late holocene lake sediments north island new zealand abstract a ca 2250 year storm history has been identified from a high resolution lake sediment record from the east coast of the north island new zealand this event based chronology identifies 340 storms in the pre european record the record is largely one of natural variability without human impacts layers of minerogenic sediment representing the products of individual storm events are clearly visible in lake cores these storm sediment pulses derived mainly from landslides record the frequency and magnitude of storms clusters of pulses identify six periods of high sedimentation and associated erosion before european settlement a d 1878 at least five of these are interpreted as periods of higher rainfall and probably warmer temperatures since historic records show that most large storms are derived from the subtropics tropics most of the storm periods correspond to warm climate intervals previously identified from new zealand and from southern hemisphere palaeoclimatic evidence the mapara 2 period ca 2090 1855 cal yr b p was the stormiest other periods were of shorter duration the mapara 2 period occurred at times of sustained warmth in the tasmanian and chilean tree ring records which might suggest hemispheric warming at this time one storm period burrell which occurred during the historical enso record was at a time of moderately high enso activity three earlier periods also appear to show responses to enso two storm periods correspond to previously proposed new zealand wide periods of increased erosion and sedimentation estimates of palaeo storm rainfalls from relationships between storm rainfall and sediment thickness of historical events suggest that storm pulses ca 12 mm thick represent palaeo storms of ca 450 mm rainfall

on the causes and modes of exhumation and lateral growth of the alps 1 a compilation of the apatite and zircon fission track ages of the alpine chain points to markedly different patterns of cooling and exhumation of the eastern alps compared to the central and western alps the site of exhumation and shortening in the western alps migrated outward whereas it was more stationary in the eastern alps where it created a narrower metamorphic belt a correlation of these observations to the deep structure of the orogen suggests that north directed lower crustal wedging induces northward propagation of the deformation and exhumation front in the middle and upper crust of the central and western alps the absence of such lower crustal wedges in the eastern alps does not induce a similar shift of deformation but rather a long term localization of shortening and exhumation in one and the same area namely the axial zone of the orogen a critical review of the temporal correlations between inferred changes in the erosional efficiency of the alps and tectonic phases points to a negative correlation and hence no erosional control on the shifts of the deformation front of the alps therefore we conclude that changes in the deep structure and rheology of the orogen instead of changes in its erosional efficiency exerted the prime control on the lateral growth of the alps

the alpine geodynamic evolution of penninic nappes in the eastern central alps the eastern central alps consist of several pennine nappes with different tectonometamorphic histories the tectonically uppermost units oceanic avers bundnerschiefer continental suretta and tambo nappes oceanic vals bundnerschiefer show cretaceous early tertiary w directed thrusting with associated blueschist facies metamorphism related to subduction of the pennine units beneath the austroalpine continental crust this event caused eclogite facies metamorphism in the underlying continental adula nappe the gross effect was crustal thickening the tectonically lower continental simano nappe is devoid of any imprint from this event in the course of continent continent collision high t metamorphism and n directed movements occurred both affected the whole nappe pile more or less continuously from amphibolite to greenschist facies conditions crustal thinning commenced during the regional temperature peak a final phase is related to differential uplift under retrograde p t conditions further thinning of the crust was accommodated by e to ne directed extensional deformation

thrust regime and transpression regime tectonics in the tauern window eastern alps below the penninic nappes of the tauern window the deepest level of the alpine thrust system is exposed in the parautochthonous sedimentary sequence of helvetic facies

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

rich shallow water benthic ecosystem in late miocene east antarctica fisher bench fm prince charles mountains abstract a single shell of a pectenoid bivalve was found in the lower part of the fisher bench formation fisher massif prince charles mountains in contrast to glacigenic sediments that form extensive outcrops in this area and are almost barren of foraminifera small pieces of muddy sand attached to this shell contained a rich assemblage of calcareous and siliceous microfossils the diatom assemblage associated with this shell was dominated by marine benthic forms with abundant saeptifera associated with subordinate marine neritic taxa and chaetoceros resting spores benthic foraminifera are very abundant but of low diversity strongly dominated by rosalina globularis with uniform chambers it is the first miocene foraminiferal assemblage reported from east antarctica excluding the ross sea area these new results confirm the early late miocene age of the shell that was dated by sr isotope values in an earlier study and suggest an initial phase of deposition in a shallow water possibly no 10 m marine cold and possibly oligotrophic environment after initial burial in microfossil bearing sediment that was weakly lithified the shell was eroded and transported to be incorporated in fossil poor glacigenic sediments since transport from a nearby location could have been facilitated by glacial and or down slope movements in this fjordal setting the shell is considered para autochthonous based on the antarctic foraminiferal fossil records it appears that through most of the cenozoic those parts of the antarctic continental shelf that were deeper than a few tens of meters with the exception of the ross sea area were mostly unfavorable for development and or preservation of calcareous microfossils

alpine metamorphism in the south east tauern window austria 1 p t variations in space and time the pennine rocks exposed in the south east tauern window austria contain mineral assemblages which crystallized in the mid tertiary late alpine regional metamorphism the pressure and temperature conditions at the thermal peak of this event have been estimated for rocks at four different structural levels using a variety of published and thermochemically derived geobarometers and geothermometers the results are a in the garnet chlorite zone 2 5 km structurally above the staurolite biotite isograd t 490 50 c p 7 1 kbar b within 0 5 km of the staurolite biotite isograd t 560 300c p 7 1 kbar c in the staurolite biotite zone c 2 5 km structurally below the staurolite biotite isograd t 610 30 c p 7 6 1 2 kbar d in the staurolite biotite zone 3 4 km structurally below the staurolite biotite isograd t 630 40 c p 6 6 1 2 kbar the pressure estimates imply that the total thickness of overburden above the basement cover interface in the mid tertiary was c 26 4 km this overburden can only be accounted for by the austro alpine units currently exposed in the vicinity of the tauern window if the altkristallin the middle austro alpine nappe was itself buried beneath an upper austro alpine nappe or nappe pile which was 7 4 km thick at that time the occurrence of epidote margarite quartz pseudomorphs after lawsonite in garnet indicates that part of the mesozoic pennine cover sequence in the south east tauern experienced blueschist facies conditions t 450 c p 12 kbar in early alpine times evidence from the central tauern is used to argue that the blueschist facies imprint post dated the main phase of tectonic thickening d1a and was thus a direct consequence of continental collision combined oxygen isotope and fluid inclusion studies on late stage veins thought to have been at lithostatic pressure and in thermal equilibrium with their host rocks during formation suggest that they crystallized from aqueous fluids at 1 1 0 4 kbar and 420 20 c early alpine late alpine and vein formation p t constraints have been used to construct a p t path for the base of the mesozoic cover sequence in the south east tauern window the prograde part of the p t path between early and late alpine metamorphic imprints is unlikely to have been a smooth curve and may well have had a low dp dt overall the decompression presumably due to erosion which occurred immediately before the thermal peak and possibly also earlier in the tertiary was probably partly or completely cancelled by the effects of early to mid tertiary d2a tectonic thickening the thermal peak of metamorphism was followed by a phase of almost isothermal decompression which implies a period of rapid uplift in the middle tertiary the peak metamorphic p t estimates are compared with the solutions of england s 1978 one dimensional conductive thermal model of the eastern alps and are shown to be consistent with the idea that the late alpine metamorphism was caused by tectonic burial of the pennine zone beneath the austro alpine nappes in the absence of extraneous heat sources such as large intrusions at depth

microstructural and textural development of calcite marbles during polyphase deformation of penninic units within the tauern window eastern alps abstract the evolution of calcite microstructures and crystallographic preferred orientations cpos is well understood due to well constrained experimental studies however the interpretation of naturally deformed calcite marbles is more difficult because of less constrained strain paths a multiphase deformation history and variable p t conditions the penninic units within the tauern window eastern alps have been affected by several deformation events and metamorphic overprint generally three major deformational events can be distinguished d 1 is related to underthrusting of penninic units beneath the austroalpine nappe complex and top to the n nappe stacking within the penninic continental units deformation stage d 2 is interpreted as reflecting the subsequent continent collision between the penninic continental units and the european foreland d 3 is related to the formation of the dome structure of the tauern window this polyphase deformation history can be partly reconstructed by the evolution of calcite microfabrics and cpos three types of calcite fabrics are distinguished within the penninic units of the tauern window and the lower austroalpine unit d 1 fabrics are characterized by equilibrated microstructures and lt cpos the cpos are generally strong and symmetric with one well developed cluster near the z axis of the finite strain ellipsoid these fabrics have locally been overprinted by subsequent amphibolite to greenschist facies metamorphism generally the occurrence of lt fabrics coincides with the occurrence of amphibolite facies metamorphic mineral assemblages in the central part of the tauern window while ht fabrics have been observed outside this area fabrics from the central part of the tauern window have likely been strengthened during subsequent thermal equilibration while the fabrics that have been observed at the peripheral parts have been less affected by subsequent metamorphic overprint therefore d 1 fabrics do not reflect d 1 conditions but subsequent thermal equilibration similar observations have been made for the evolution of d 2 fabrics lt fabrics dominate inside the amphibolite facies isograde ht fabrics occur outside greenschist facies metamorphic conditions the fabrics are characterized by high finite strains near the margins of the tauern window the intensity of which decreases towards the central parts where microstructures are characterized by recrystallization and thermal equilibration due to amphibolite facies metamorphic overprint the strong cpos document this influence the ht fabrics and microstructures within peripheral areas indicate that they have less been affected by this thermal event and therefore are more indicative for the deformational conditions during d 2 d 3 is restricted to distinct shear zones along the tectonic boundaries of the tauern window from the central parts to the shear zone boundaries a clear evolution of microfabrics can be observed in internal parts microstructures are characteristic for intracrystalline plasticity with a dominating activity of r glide twinning was less important during the final phases of deformation on approaching the shear zone boundaries the grain size decreases due to dynamic recrystallization and secondary grain size reduction until ultramylonites are formed within these domains grain boundary sliding seems to have been dominant in conclusion calcite cpos from polyphase areas do not only include information on the deformation conditions but also bear information about the thermal overprint subsequent to the main deformational event

the control of precursor brittle fracture and fluid rock interaction on the development of single and paired ductile shear zones abstract ductile shear zones can occur as relatively isolated single structures as arrays or as characteristic paired zones in continuous glaciated exposures of metagranodiorites from the tauern window eastern alps the control of initial dilatant brittle fracture and associated fluid rock interaction on the geometry of subsequent ductile shear zones can be unequivocally established shearing occurred under amphibolite facies conditions fractures in weakly deformed metagranodiorites are often less than 1 mm thick but extend for tens of metres many are healed joints without shear offset others show minor mm cm discrete dextral offset such brittle faults commonly display a low angle en echelon arrangement with displacement transferred between discrete fracture segments by ductile compressive bridges the geometry of more strongly reactivated zones depends on the degree and heterogeneity of fluid rock interaction which is related to fluid infiltration and veining along the primary fractures with little fluid rock interaction reactivation produces single heterogeneous ductile shear zones centred on and immediately flanking the pre existing fracture with increased fluid rock interaction a bleached halo is developed symmetrically to either side of a central epidote quartz garnet calcite vein ductile shear zones commonly flank this bleached zone to develop a characteristic paired pattern strain is partitioned localizing in the central fracture vein and the flanking shear zones paired zones may anastomose in accordance with changes in the width of the central bleached zone but are always symmetrically spaced with regard to the central fracture vein with increasing deformation the ductile shear zones broaden into the adjacent metagranodiorite but not into the bleached zone which remains preserved as a low strain region paired shear zones can also develop to either side of aplite dykes examples of characteristic paired shear zones usually with a clear central vein are found in many areas ranging from greenschist to eclogite facies suggesting that the mechanism of their formation is quite general

distinguishing subglacial till and glacial marine diamictons in the western ross sea antarctica implications for a last glacial maximum grounding line analyses of lithology stratigraphy and tephra from marine sediment cores collected from the western ross sea during cruises eltanin 32 and 52 and deep freeze 80 and 87 indicate that subglacial till does not extend to the continental shelf edge subglacial till occurs as the lowest unit in most cores landward south of approximately 74 s while seaward of approximately 74 s the lowest diamicton units are glacial marine diamictons glacial marine diamictons are distinguished from subglacial tills by the presence of higher and more variable total organic carbon content downcore distinct tephra layers stratification higher diatom and foraminifera abundances higher sand content and radiocarbon dates in chronological order downcore sand sized tephra layers from two cores on the outer continental shelf are interpreted as single eruptive events one likely to have been derived from the mount melbourne volcano and the other from the pleiades volcano radiocarbon dates from sediment above and below the tephra layer in one of these cores df87 32 show that deposition indicative of open water conditions occurred between 22 and 26 ka in the western ross sea

mechanisms of strain accommodation in plastically deformed zircon under simple shear deformation conditions during amphibolite facies metamorphism abstract this study documents the strain accommodation mechanisms in zircon under amphibolite facies metamorphic conditions in simple shear microstructural data from undeformed fractured and crystal plastically deformed zircon crystals are described in the context of the host shear zone and evaluated in the light of zircon elastic anisotropy our work challenges the existing model of zircon evolution and shows previously undescribed rheological characteristics for this important accessory mineral crystal plastically deformed zircon grains have axis oriented parallel to the foliation plane with the majority of deformed grains having axis parallel to the lineation zircon accommodates strain by a network of stepped low angle boundaries formed by switching between tilt dislocations with the slip systems 010 and 1 10 110 and rotation axis 001 twist dislocations with the rotation axis 001 and tilt dislocations with the slip system 001 and rotation axis 010 the slip system 1 10 110 is newly described for zircon most misorientation axes in plastically deformed zircon grains are parallel to the xy plane of the sample and have 001 crystallographic direction such behaviour of strained zircon lattice is caused by elastic anisotropy that has a direct geometric control on the rheology deformation mechanisms and dominant slip systems in zircon young s modulus and p wave velocity have highest values parallel to zircon 001 axis indicating that zircon is elastically strong along this direction poisson ratio and shear modulus demonstrate that zircon is also most resistant to shearing along 001 thus 001 axis is the most common rotation axis in zircon the described zircon behaviour is important to take into account during structural and geochronological investigations of poly metamorphic terrains geometry of dislocations in zircon may help reconstructing the geometry of the host shear zone s large scale stresses in the crust and possibly the timing of deformation if the isotopic systems of deformed zircon were reset

millennial scale storminess variability in the northeastern united states during the holocene epoch for the purpose of detecting the effects of human activities on climate change it is important to document natural change in past climate1 in this context it has proved particularly difficult to study the variability in the occurrence of extreme climate events such as storms with exceptional rainfall1 previous investigations have established storm chronologies using sediment cores from single lakes2 3 4 5 6 7 8 but such studies can be susceptible to local environmental bias here we date terrigenous inwash layers in cores from 13 lakes which show that the frequency of storm related floods in the northeastern united states has varied in regular cycles during the past 13 000 years 13 kyr with a characteristic period of about 3 kyr our data show four peaks in storminess during the past 14 kyr approximately 2 6 5 8 9 1 and 11 9 kyr ago this pattern is consistent with long term changes in the average sign of the arctic oscillation9 suggesting that modulation of this dominant atmospheric mode may account for a significant fraction of holocene climate variability in north america and europe

evidence for east west crustal extension in the eastern alps implications for the unroofing history of the tauern window the contact between the western border of the tauern window and the overlying austroalpine nappes austria and italy is marked by a structural petrologic and geochronologic discontinuity that developed in the early stages of unroofing of the window within the window pressure temperature time paths j selverstone 1985 indicate that significant ductile thinning occurred shortly after the cessation of thrusting paleocene eocene sense of shear indicators rotated porphyroblasts asymmetric augen and pressure shadows s c fabrics associated with a west plunging stretching lineation indicate that this thinning occurred in response to top to the west low angle normal shear during metamorphism the same sense of normal shear is present in the mesozoic members of the austroalpine sequence west of the window in these rocks however west directed shear occurred at low temperatures 300 c after the thermal peak of metamorphism structural data and the regional geometry imply that the western end of the tauern window is a low angle normal fault brenner line that juxtaposed brittlely deformed rocks of the austroalpine nappes against more ductilely deformed rocks from the window biotite k ar and rb sr data suggest a miocene age for final movement on the brenner line these data indicate a prolonged history of east west extension in the eastern alps that affected all crustal levels early ductile thinning of lower crust followed by mid to upper crustal low angle normal faulting a model is presented that relates the young east west extension to displacement transfer from dextral movement on the periadriatic lineament in this model the brenner line and by analogy the simplon line can be thought of as detachment faults that tectonically unroofed the tauern window and lepontine thermal highs respectively

kinematics of the northern part of the simplon line central alps abstract structural studies were carried out along the northern part of the simplon line in order to constrain the kinematic history of the line during tertiary times the ductile strain accumulated within both basement units and mesozoic cover reveals the upper units sheared towards the west southwest the simplon line can be described as a major shear zone along which the main movement occurred perpendicular to the line this shearing developed during retrograde metamorphic conditions and postdates earlier deformations associated with the high temperature lepontine episode finally it was followed by the formation of the berisal syncline back folding episode which generated some brittle movements towards the south localized at the contact between the lower and upper pennine units i e on the simplon line

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

foraminiferal biostratigraphy and palaeoecology in upper oligocene lower miocene glacial marine sequences 9 10 and 11 crp 2 2a drill hole victoria land basin antarctica abstract three cape roberts project drillholes crp 1 2 2a and 3 penetrated in aggregate a 1500 m succession of glacial marine oligocene lower miocene strata on the margins of victoria land basin the upper 1000 m of which consists of a stack of more than 50 unconformity bounded stratigraphic sequences the benthic foraminiferal biostratigraphy ecology and lithofacies relationships of three contiguous sequences sequences 9 10 and 11 130 27 306 65 mbsf from crp 2 2a were first determined and then tested against motif a a sedimentation model developed for the drillhole succession these sequences apparently represent relatively complete glacial deglacial cycles which span an interval of 450 kyr straddling the oligocene miocene boundary 24 ma sedimentological and paleontological data suggest shoreface inner shelf to outer shelf basin margin settings with deposition under the influence of near shore traction currents subglacial ice contact ice rafting meltwater and turbidity associated with ice margin advance and retreat along with sea level variations in the order of 50 m stratigraphic distribution data for benthic foraminifera are at an average sampling interval of 1 m 1000 to 3000 years which offers stratigraphic resolution at less than orbital cycle frequencies in all major lithofacies within the three sequences taxa recovered represent a restricted immigrant group that repeatedly penetrated the shallow coastal waters during deglacial phases of each cycle and originated in the much more diverse assemblages of west antarctic rift system basins both eurytopic and stenotopic taxa are recognized the former occur in all lithofacies and appear tolerant to a wide range of environmental parameters at and near the seafloor representative genera include trochammina cassidulinoides fursenkoina eponides epistominella cibicides nonionella melonis pullenia elphidium ammoelphidiella and cribroelphidium stenotopic taxa are less common occur mainly in fine grained lithofacies represent maximum oceanicity and coincide with maximum retreat of coastal glaciers and sea level highstands representative genera include quinqueloculina pyrgo triloculina lenticulina marginulina vaginulinopsis nodosaria pseudonodosaria pyrulinoides oolina fissurina parafissurina rosalina anomalinoides and hanzawaia planktic foraminifera are absent our foraminiferal data provide strong support for the motif a model and allow interpretation of intra model facies and events motif a is an idealized glacial stratigraphic sequence construct derived from analysis of the entire upper oligocene lower miocene sequence stack in this model lowstand system tract lst diamictites form the base of the sequence diamictites with microfaunas are considered glaciomarine those without are more likely ice proximal or subglacial fine grained sandstone muddy sandstone and mudstone of mid sequence aggradational transgressive system tract tst and highstand system tract hst strata reflect high stands of sea level inshore penetration of open marine waters and peak recession of ice margins and normally contain the most diverse and abundant microfaunas up to 17 spp sample sediments of the overlying regressive system tract rst display low and upwardly declining foraminiferal diversity in response to glacier ice advance sediment progradation across the basin margin and falling sea level the time variable glacial surface of erosion gse or sequence boundary terminates the regressive system tract rst and demarcates the base of the succeeding stratigraphic sequence

fault slip analysis and late exhumation of the tauern window eastern alps exhumation of the eastern alps from the early tertiary to the late miocene was localized mainly in the tauern window a thermal and structural dome located in front of the dolomites indenter stress inversions based on new structural investigations over the entire tauern window indicate a regional zoning of the paleostress field with a predominance of strike slip states of stress in the core of the investigated area and dominant extensional regimes in the eastern and western borders of the dome few inverse fault structures have been highlighted we propose a two stage deformation history in order to explain the different types of structures that characterise the ductile and the brittle domains during the first stage of exhumation of the tauern window corresponding to the folding event the brittle crust was probably dominated by n s shortening and compression the second stage of exhumation was marked by normal faulting at the borders of the dome and strike slip faulting in the core during the second stage the brittle part of the crust that was previously affected by compressive structures belonging to the first stage was eroded normal faulting associated to e w extension along the eastern and western borders of the tauern window was accommodated by strike slip faulting located in the core of the tauern window yielding e w extension and n s shortening the orientation of the extensional axes and the nature of the stress tensors are similar to the ones inferred for the late stage brittle overprint of the internal basement massifs of the central alps pointing to a possible common large scale state of stress acting well beyond the area of the eastern alps

historically unprecedented erosion from tropical storm irene due to high antecedent precipitation lacustrine sediment archives indicate that flooding during tropical storm irene 2011 in the north eastern united states caused the most severe erosion of any flood in the historic record surpassing that of events with greater precipitation and peak discharges compared to deposition from historic floods irene s event layer was more massive and more enriched in unweathered upland sediments indicating an anomalously high incidence of mass wasting and sediment entrainment precipitation records indicate that neither precipitation intensity nor total accumulation distinguished irene from less erosive historic floods however cumulative precipitation prior to irene exceeded the 95th percentile of all days in the record when allowing for non stationarity in the twentieth century background precipitation we find a four fold increase in the probability of irene like conditions where impacts of extreme rainfall are enhanced by high antecedent precipitation we conclude that irrespective of increases in extreme precipitation the risk of highly erosive flooding in the region is increasing due to the influence of wetter baseline conditions associated with a changing climate copyright 2015 john wiley sons ltd

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

metamorphic pressure estimates and sediment volumes for the alpine orogeny an independent control on geobarometers theories which regard the deep erosion 20 30 km of orogenic belts as an important factor in the thermal development of the continents rely on pressure estimates from metamorphic geobarometers to give an estimate of the depth scale for this process the imprecision of geobarometers and the apparent lack of sediments that would result from this amount of erosion are frequently made arguments for much smaller erosion depths the alps are a well studied young mountain belt and afford the opportunity to compare overburden masses inferred from geobarometry with sediment masses in the surrounding sedimentary basins this comparison suggests that metamorphic geobarometry has not significantly overestimated burial depths and that the average erosion to date has been over 15 km with a maximum of 25 km or more it is probable that the total erosion in the belt will eventually average 20 25 km with a maximum of around 40 km a significant feature of the sediment distribution is that over 50 of the volume is outside the neighbouring along strike sedimentary basins this fact which accounts for previous low estimates of alpine sediment volumes follows from the response of the lithosphere to loading by continental thickening and may be a common feature of post orogenic sedimentation

integrated diagenetic and sequence stratigraphy of a late oligocene early miocene mixed sediment platform austral basin southern patagonia resolving base level and paleoceanographic changes and paleoaquifer characteristics abstract a condensed 20 m thick marine transgressive highstand succession comprises the upper san julian formation upper oligocene lower miocene of the northern retroarc austral basin southern patagonia mixed sediment facies identify a shelf interior setting part of an overall warm temperate regional platform of moderate energy giant oyster dominated skeletal hiatal accumulations along the maximum flooding surface and forming high energy event beds in the highstand succession preserve relict micrite in protected shelter porosity and identify periods of reduced sediment accumulation the stratigraphic distribution of marine derived glaucony and diagenetic carbonates is spatially related to sequence development depositional siderite coincides with prominent marine transgression defining transient mixing of marine and meteoric waters across coastal plain deposits chemically evolved autochthonous glaucony coincides with periods of extended seafloor exposure and transgressions that bracket the marine succession and within the oyster dominated skeletal accumulations seafloor cement likely once magnesian calcite formed in association with an encrusting boring biota along the maximum flooding surface in concert with incursion of cool 11 13 c water the cement is present locally in skeletal event beds in the highstand succession suggesting a possible association with high order base level change and cooler water as the highstand succession coincides with elevated global sea level in the late oligocene early miocene the locally marine cemented glauconitic skeletal event beds in the highstand succession may identify higher order glacio eustatic control local stratal condensation however is best explained by regional differences in basement subsidence in the burial realm carbonate diagenesis produced layers of phreatic calcrete coincident with skeletal rich deposits zeolite clinoptilolite k cement is restricted to the lowermost marine transgressive interval probably due to initial elevated metastability of reworked weathered silicates clay illite cement is restricted to siliciclastic rich intervals wherein skeletal carbonate did not buffer pore water ph diagenetic carbonate geochemistry sr na and 18o and 13c shows that with burial the transgressive and highstand system tracts developed as distinct paleoaquifers resulting from different proximities to meteoric recharge zones