early cambrian back arc volcanism in the western taurides turkey implications for rifting along the northern gondwanan margin the lower cambrian tommotian go ebakan formation in western central anatolia is made up of slightly metamorphosed continental to shallow marine clastic rocks with pillowed and massive spilitic lavas and dolerite dykes spilitic lavas commonly amygdaloidal are albite and pyroxene phyric with the metamorphic mineral paragenesis albite calcite sericite epidote tremolite chlorite dolerite dykes mainly include plagioclase and pyroxene as primary minerals and tremolite epidote chlorite as low grade secondary minerals geochemical data show that the spilitic lavas and dolerite dykes are sub alkaline of oceanic tholeiitic basalt character and display a tholeiitic fractional trend characterized by an increase in feo mgo and zr and tio2 in variation diagrams they are characterized by relatively high zr y 2 4 5 relatively high th yb 0 15 1 0 and la nb 0 5 2 5 both show marked negative nb and ti anomalies relative to th and la ce implying a subduction related chemistry chondrite normalized ree patterns display slight enrichment of light ree spilitic lavas la yb n 0 79 1 56 dolerite dykes la yb n 0 89 3 50 fairly comparable with morb the geochemical similarity of the spilitic lavas and dolerite dykes suggests a co genetic origin la nb ratios of both types are slightly higher than average morb values and were possibly formed in the early stages of back arc basin development petrogenetic modelling suggests the mafic rocks of the formation were formed by 9 batch melting of spinel lherzolite in shallower depths c 60 km taken together the data suggest that the early cambrian mafic rocks of the taurus units were developed in a back arc basin along the northern edge of gondwana above the southward subducting oceanic lithosphere and may represent initial rifting that resulted in separation of the peri gondwanan terranes

volcanic and climatic controls on fluvial style in a high energy system the lower cretaceous matasiete formation golfo san jorge basin argentina abstract the cretaceous chubut group in the golfo san jorge basin patagonia argentina comprises up to 6000 m of continental sediments at the base of the succession an extensive saline alkaline lacustrine unit pozo d 129 fm grades laterally towards the basin margin into the fluvial matasiete fm hauterivian aptian the matasiete fm comprises up to 650 m of siliciclastic and pyroclastic deposits in its type area where three members have been distinguished the following facies associations were identified 1 single fluvial channels 2 multistorey fluvial channels 3 proximal floodplain 4 distal floodplain 5 pyroclastic ash fall and ground surge deposits additional observations in the time equivalent pozo d 129 fm provide evidence for 6 shallow lacustrine and 7 deep lacustrine facies associations the floodplain association contains paleosols with abundant carbonate concretions and fine pyroclastic tuffs paleosols are mostly vertisols characterized by deep desiccation cracks slickensides and carbonate nodules these observations coupled with the occurrence of shallow water oolitic grainstones in the lacustrine pozo d 129 fm indicate a semiarid environment tree trunks up to 1 m in diameter and 15 m long preferentially located near channel margins provide evidence for vegetated riverbanks the exposures of the matasiete formation in the san bernardo fold belt show individual channel belts containing straight meandering and braided channels evidence of changes in fluvial style attributable to base level control has not been observed the most dramatic changes in fluvial architecture which were comparatively short lived were provoked by intermittent pyroclastic deposition on the floodplain the reduced infiltration capacity of the floodplain and the concomitant increase in sediment load increased runoff as well as volume and flashiness of the discharge which favoured the development of shallow multichannel rivers the fluvial system abruptly changed from single ribbon channels to a braided system which notably increased the width thickness ratio of sandbodies

groundwater recharge connectivity between a hills and plains area of western taiwan using water isotopes and electrical conductivity water isotopes d 18o as well as electrical conductivity were employed to clarify hydrological relationships among precipitation stream water and groundwater in the douliou hills dlh of taiwan they are also used to evaluate the importance of groundwater recharge sources in the proximal fan of choshuichi alluvial plain csap which is connected to the eastern extreme of the dlh results indicate that the most important source of groundwater in the dlh comes from summer precipitation in most cases the summer precipitation recharges stream water via base flow based on 18o and ec values groundwater in the proximal fan of the csap can be divided into groundwater from 5 wells nearby the dlh near dhl group and groundwater from 6 wells nearby the choshui stream near cs group semi quantitative results calculated by ternary end member mixing analysis emma for 18o and electrical conductivity values indicate that for the near dlh group precipitation in the csap contributes 40 50 of water to the proximal fan groundwater while dlh groundwater donates 20 55 and choshui stream water 0 29 precipitation in the csap is the most important recharge source dlh groundwater s contribution is more notable in deep groundwater and choshui stream water s contribution decreases with distance from the choshui stream for the near cs group anthropogenic pollution adds ions to the groundwater restricting the effectiveness of the ternary emma approach this study provides new insights into groundwater recharge in the csap it should be applicable to future studies of hill and plains water connectivity in other regions

shear stresses on megathrusts implications for mountain building behind subduction zones 1 shear stresses on a subduction megathrust play an important role in determining the forces available for mountain building adjacent to a subduction zone in this study the temperatures and shear stresses on megathrusts in 11 subduction zones around the pacific rim hikurangi tonga izu ogasawara western nankai northeastern japan aleutians western alaska cascadia northern chile southern chile and se asia northern sumatra have been determined the main constraint is that vertical normal stresses beneath the highlands behind the subduction zone are nearly equal to horizontal normal stresses in the plane of a trench or arc normal section for a typical brittle and ductile megathrust rheology frictional shear stress gz for depth z and ductile shear stress a exp b rt at temperature t where a b are rheological parameters treated as constants rheological constants common to all the megathrusts crust mantle b are determined by simultaneously solving for the force balance in the overlying wedge and megathrust thermal structure using a simplex minimization algorithm taking account of the induced mantle corner flow at depth 65 15 km 2 and constant radiogenic heating 0 65 0 3 w m 3 2 throughout the crust the a constants are solved individually for each subduction zone assuming that the maximum depth of interplate slip earthquakes marks the brittle ductile transition the best fit solution shows two groupings of megathrusts with most subduction zones having a low mean shear stress in the range 7 15 mpa crust 0 032 0 006 mantle 0 019 0 004 and unable to support elevations 2 5 km for a typical frictional sliding coefficient 0 5 the low effective coefficients of friction suggest high pore fluid pressures at 95 lithostatic pressure tonga and northern chile require higher shear stresses with crust 0 095 0 024 mantle 0 026 0 007 suggesting slightly lower pore fluid pressures at 81 lithostatic ductile shear in the crust is poorly resolved but in the mantle appears to show a strong power law dependency with b 36 18 kj mol 1 amantle values are sensitive to the precise value of b but are in the range 1 20 kpa the power law exponent n for mantle flow is poorly constrained but is likely to be large n 4 the brittle ductile transition in the crust occurs at temperatures in the range 370 c 512 c usually close to the base of the crust and in the mantle at much lower temperatures 180 c 300 c possibly reflecting a marked change in pore fluid pressure or quasi ductile and subfrictional properties in subduction zones where the subducted slab is older than 50 ma a significant proportion of the integrated shear force on the megathrust is taken up where it cuts the mantle and temperatures are 300 c in much younger subduction zones the stress transmission is confined mainly to the crust the shear stresses particularly in the crust may be kept low by some sort of lubricant such as abundant water rich trench fill which lowers the frictional sliding coefficient or effective viscosity and or raises pore fluid pressure the unusual high stress subduction zone in northern chile lacks significant trench fill and may be poorly lubricated with a mean shear stress 37 mpa required to support elevations 4 km in the high andes however where the crust is thin in sediment starved and poorly lubricated subduction zones such as tonga the mean shear stress will still be low sediment may lubricate megathrusts accommodating underthrusting of continental crust such as in the himalayas or eastern central andes which have a low mean shear stress 15 mpa

crustal scale structural architecture in central chile based on seismicity and surface geology implications for andean mountain building 1 we document a crustal scale structural model for the central chile andes based on seismicity and surface geology which consists in a major east verging ramp detachment structure connecting the subduction zone with the cordillera the ramp rises from the subducting slab at 60 km depth to 15 20 km below the western edge of the cordillera extending eastward as a 10 km depth flat detachment this structure plays a fundamental role in the andean orogenesis because most of the shortening has been accommodated by structures rooted in it and allows the distribution of crustal thickening in a simple shear deformation mode indeed despite shortening distribution being very asymmetric 16 km versus 70 km in the western and eastern side respectively the western side is higher and thicker than what is expected yield strength envelopes show strong rheological control on this structure vp and vp vs variations in the upper mantle and in the deepest limit of the seismogenic interplate contact mark the intersection of the ramp with the slab which coincides with the blueschist eclogite transition therefore subduction processes would control the depth where the major east verging structure may merge with the slab such a ramp flat structure is observed in other parts of the chilean margin hence it seems to be a first order feature in the andean subduction zone this structure delimitates upward the rocks transmitting part of the plate convergence stress from the plate interface and controls mountain building tectonics thus playing a key role in the andean orogeny

recharge sources and hydrogeochemical evolution of groundwater in alluvial basins in arid central australia summary it is necessary to define the role of various sources of recharge in the surficial alluvial aquifer system in arid alice springs in central australia for future management of water resources in the region multiple sources of natural recharge include infiltration from ephemeral stream flow in the todd river groundwater throughflow between connected alluvial basins regional groundwater flow from the underlying tertiary aquifer and diffuse recharge in addition treatment storage and irrigation reuse of alice springs waste water has resulted in additional recharge of effluent via infiltration water resource management plans for the region include effluent reuse through soil aquifer treatment sat within one of the connected alluvial basins with the purpose of managing the excess waste water overflows while also supplementing groundwater resources for irrigation and protecting their quality hydrogeochemical tracers chloride and the stable isotopes of water were used in a three member mixing model to define and quantify the major recharge sources the mixing model was not sensitive enough to quantify minor contributions from effluent in groundwater that were identified only by an evaporated isotopic signature the contribution of the multiple recharge sources varied spatially with proximity to the recharge source with todd river effluent and town basin throughflow contributing to the inner farm basin groundwater the outer farm basin was largely influenced by the todd river the inner farm basin throughflow and the older tertiary aquifer while inner farm groundwater throughflow contains an effluent component only outer farm basin groundwater near the interface between the two basins clearly illustrated an effluent signature aside from this effluent recharge was not evident in the outer farm basin indicating that past unmanaged recharge practices will not mask signs of managed aquifer recharge through the soil aquifer treatment sat operation the long term impact of effluent recharge is a shift from sodium and calcium as co dominant cations in the groundwater as evident in the outer farm basin to dominance by sodium alone as typical for the inner farm basin

vertical extrusion and horizontal channel flow of orogenic lower crust key exhumation mechanisms in large hot orogens a large database of structural geochronological and petrological data combined with a bouguer anomaly map is used to develop a two stage exhumation model of deep seated rocks in the eastern sector of the variscan belt an early sub vertical fabric developed in the orogenic lower and middle crust during intracrustal folding followed by the vertical extrusion of the lower crustal rocks these events were responsible for exhumation of the orogenic lower crust from depths equivalent to 18 20 kbar to depths equivalent to 8 10 kbar and for coeval burial of upper crustal rocks to depths equivalent to 8 9 kbar following the folding and vertical extrusion event sub horizontal fabrics developed at medium to low pressure in the orogenic lower and middle crust during vertical shortening fabrics that record the early vertical extrusion originated between 350 and 340 ma during building of an orogenic root in response to se directed saxothuringian continental subduction fabrics that record the later sub horizontal exhumation event relate to an eastern promontory of the brunia continent indenting into the rheologically weaker rocks of the orogenic root indentation initiated thrusting or flow of the orogenic crust over the brunia continent in a north directed sub horizontal channel this sub horizontal flow operated between 330 and 325 ma and was responsible for a heterogeneous mixing of blocks and boudins of lower and middle crustal rocks and for their progressive thermal re equilibration the erosion depth as well as the degree of reworking decreases from south to north pointing to an outflow of lower crustal material to the surface which was subsequently eroded and deposited in a foreland basin indentation by the brunia continental promontory was highly noncoaxial with respect to the se oriented saxothuringian continental subduction in the early visean suggesting a major switch of plate configuration during the middle to late visean

estimation of evapotranspiration losses in the vadose zone using stable isotopes and chloride mass balance method this study used stable isotope and chloride data of porewater to evaluate water fluxes through the vadose zone and thereby estimate evapotranspiration water losses in parts of the nabogo catchment of the white volta basin in ghana the overall objective was to develop a framework so that the recharge regime can be properly conceptualized for numerical hydrological modeling unsaturated zone material was sampled at regular intervals of 50 cm to a maximum depth of 300 cm in four different locations in the study area rainwater groundwater and surface water were simultaneously sampled and analyzed for their 18o and 2h characteristics porewater extracted from the unsaturated zone material was analyzed for the 18o and 2h and chloride content and profiles were created to gauge the isotopic evolution of precipitation and estimate evaporative losses at each interval of the sampling the chloride mass balance technique was used to estimate the fraction of infiltrating water remaining at each interval of the sampling transpiration losses through the entire profile were then estimated this study finds that the vertical infiltration of water through the vadose zone is dominated by piston flow and a mixture of piston and preferential flows in the shallow subsurface 0 0 3 0 m evaporative losses estimated from stable isotope data fall in the range of 29 3 52 4 322 3 576 4 mm year of the annual precipitation with an average of 40 or 440 mm year estimated vadose zone recharge at the maximum depth of sampling ranges between 11 1 and 185 mm year with an average of 32 9 mm year representing 1 1 18 5 and 3 29 of the annual precipitation respectively estimated transpiration losses within this interval range between 29 1 290 mm year and 69 5 695 mm year with an average of 54 7 547 mm year of the annual precipitation transpiration losses appear to increase down the profile and apparently account for a significant percentage of water losses in the vadose zone a significant proportion of the original precipitation is lost within the upper 300 cm 3 m of the vadose zone the water table fluctuations method was independently used to estimate saturated zone groundwater recharge and indicates that recharge rates range between 64 65 and 151 2 mm year with an average of 102 5 mm year which respectively represent 5 9 13 7 and 9 3 of the average annual precipitation in the area the apparently higher estimates from the water table fluctuations method may arise from uncertainties in the specific yield values used for the vadose zone material

evolution of the san jorge basin argentina the san jorge basin although small is the most important hydrocarbon producing basin in argentina remaining untested potential is high because of the presence of good source rock favorable structural complexity and multiple reservoirs reservoir quality is commonly low because of the highly tuffaceous sandstones the sedimentary fill of the basin is closely related to its tectonic history northwest southeast trending grabens formed and filled during a triassic and early jurassic early rift phase climaxing with a pervasive middle jurassic volcanic episode continued growth and filling of the basin occurred during a late jurassic earliest cretaceous late rift phase and cretaceous early and late sag phases late cretaceous early tertiary extension set up many of the present day structural traps along normal faults middle tertiary andean compression produced the narrow north south san bernardo structural belt which exhibits reversed movement on older normal graben bounding faults and on local low angle thrust faults marked early to middle tertiary erosion produced a significant unconformi y within cretaceous beds around basin margins origin of upper jurassic and lowermost cretaceous sedimentary fill is primarily lacustrine or fluvial in origin lacustrine organic rich black shales are fringed by oolitic and other limestones and fluvial deltaic sandstones derived mostly from the north a significant southern source of sand existed during the valanginian interbedded marine shales occur mostly to the west toward a presumed marine seaway connection to the northern magallanes basin middle to upper cretaceous sedimentary rocks sourced mostly from the north are mainly fluvial sandstone shale successions with some minor lacustrine influence reservoir quality glauconitic sands were deposited during a late cretaceous early tertiary marine incursion from the atlantic after development of a lower tertiary regional unco formity relatively undisturbed younger tertiary sediments completed the basin fill lower cretaceous lacustrine shales of the d 129 formation are the best source rocks yet identified however most hydrocarbon production occurs above the source in middle and upper cretaceous sandstones along the basin flanks the most obvious hydrocarbon emplacement mechanism is vertical migration along reactivated graben faults

tectonic development of the north patagonian andes and their related miocene foreland basin 41 30 43 s 1 the northern patagonian andes have been constructed through multiple mechanisms that range from tectonic inversion of extensional structures of early to middle jurassic age in the main andes to oligocene in the precordilleran region these have acted during two distinctive orogenic stages first in late early cretaceous and later in miocene times late oligocene extension separates these two contractional periods and is recorded by half grabens developed in the retroarc region the last contractional stage coexists with an eastward foreland expansion of the late miocene arc whose roots are presently exposed as minor granitic stocks and volcanic piles subordinately in the main andes east of the present arc as a consequence of this orogenic stage a foreland basin has developed having progressed from 18 ma in the main north patagonian andes where the mountain front was flooded by a marine transgression corresponding to the base of the nirihuau formation to 11 ma in the foreland area cannibalization of this foreland basin occurred initially in the hinterland and then progressed to the foreland zone blind structures formed a broken foreland at the frontal zone inferred from growth strata geometries during pliocene to quaternary times most of the contractional deformation was dissipated in the orogenic wedge at the time when the arc front retracted to its present position

relics of an early panafrican metabasite metarhyolite formation in the brno massif moravia czech republic the brno massif in moravia czech republic is an important exposure of precambrian basement in central europe it includes large volumes of cadomian granitoids and a narrow fault bounded zone with metagabbros metadiorites and metabasalts this so called central basic belt also contains some metarhyolites one of these was dated by means of the zircon evaporation method at 725 15 ma chemical and isotope data show that the dated rock represents a mantle derived magma which is cosanguinous with surrounding morb type metabasites the data suggest that the brno massif hosts the oldest metabasite complex currently known in central europe its formation apparently coincides with the main period of ocean floor spreading and island arc formation in the panafrican orogens this lends further support to the theory that the brno massif is a gondwana derived element

identification of sources and causes of leakage on a zoned earth dam in northern taiwan hydrological and isotopic evidence abstract seepage through an earth dam body must be regulated as a well planned process if it is not properly managed the abnormal seepage may cause dam failure this study employed stable isotopic and statistical methods to identify the source and cause of an abnormal leakage on the zoned earth dam of the xin shan reservoir located in northern taiwan water samples from the dam area over a 2 a period were collected and analyzed for their stable o and h isotope compositions in addition a 4 a period of hydrological data including rainfall reservoir level well level seepage of filter drainage and leakage were statistically analyzed with a stepwise multiple regression approach both the stable isotopic and hydrological results indicate that the abnormal leakage on the dam shell comes from the filter drainage in the dam the reason for abnormal leakage is due to unexpected and significant precipitation sourced water flowing into the dam s body the dam filter fails to drain out the incoming water sufficiently thus generating the abnormal seepage in addition the defect in the dam filter may also cause the drainage filter to drain off reservoir seepage inadequately therefore it is suggested that checking the filter function and preventing excessive precipitation sourced water from flowing into the dam are the two top priorities for the follow up remedial strategy of the dam

neoproterozoic and cambro ordovician magmatism in the variscan klodzko metamorphic complex west sudetes poland new insights from u pb zircon dating the klodzko metamorphic complex kmc in the central sudetes consists of meta sedimentary and meta igneous rocks metamorphosed under greenschist to amphibolite facies conditions they are comprised in a number of separate tectonic units interpreted as thrust sheets in contrast to other lower palaeozoic volcano sedimentary successions in the sudetes the two uppermost units the orla gologlowy unit and the klodzko fortress unit of the kmc contain meta igneous rocks with supra subduction zone affinities the age of the kmc was previously assumed to be early palaeozoic devonian based on biostratigraphic findings in the lowermost tectonic unit our geochronological study focused on the magmatic rocks from the two uppermost tectonic units exposed in the sw part of the kmc two orthogneiss samples from the orla gologlowy unit yielded ages of 500 4 3 1 and 500 2 4 9 ma interpreted to indicate the crystallization age of the granitic precursors a plagioclase gneiss from the same tectonic unit intimately interlayered with metagabbro provided an upper intercept age of 590 1 7 2 ma which is interpreted as the time of igneous crystallization from the topmost klodzko fortress unit a metatuffite was studied which contains a mixture of genetically different zircon grains the youngest 207pb 206pb ages which cluster at ca 590 600 ma are interpreted to indicate the maximum depositional age for this metasediment the results of this study are in accord with a model that suggests a nappe structure for the kmc with a middle devonian succession at the base and upper proterozoic units at structurally higher levels it is suggested here that the kmc represents a composite tectonic suture that juxtaposes elements of pre variscan basement intruded by the lower ordovician granite against a middle palaeozoic passive margin succession the new ages combined with the overall geochemical variation in the kmc indicate the existence of rock assemblages representing a gondwana active margin the recognition of neoproterozoic subduction related magmatism provides additional arguments for the hypothesis that equivalents of the tepla barrandian domain are exposed in the central sudetes

the margins of laurussia in central and southeast europe and southwest asia the continuation of the laurussian margin into central and southeast europe and southwest asia is defined by the rheic suture which becomes harder to trace to the southeast because of complex post variscan strike slip displacements and tectonic stacking linked to the cimmerian and alpine cycles the uncertain extent of the neoproterozoic baikalian orogeny fringing baltica ambiguous early paleozoic paleobiogeographic data and strike slip activity complicate the distinction of the tornquist suture from the transeuropean suture zone there is growing evidence for the incorporation of the brunovistulian malopolska and west moesian terranes into the late neoproterozoic cambrian baltican margin the istanbul zonguldak terrane along with the bitesh and east moesia terranes may have been part of the avalonian terrane assemblage although an arabian nubian shield or baltica provenance cannot be excluded the terranes of the armorica terrane assemblage bordering the rheic suture include the outer carpathian tatra getic and balkan terranes in southeast europe and sakarya and the anatolide tauride terrane in turkey further east the rheic suture may be present in the caucasus in all probability between the greater caucasus and the scythian platform or alternatively between the greater caucasus and transcaucasia alborz in northern iran is interpreted as a distal part of transcaucasia the location of the rheic suture in the southeast part of the turan domain of central asia is poorly constrained

long lasting cadomian magmatic activity along an active northern gondwana margin u pb zircon and sr nd isotopic evidence from the brunovistulian domain eastern bohemian massif manuscript published version available in international journal of earth sciences 2016 doi 10 1007 s00531 016 1416 y

the liquine ofqui fault zone a long lived intra arc fault system in southern chile abstract plate reconstructions for the cenozoic document relatively steady right oblique subduction of the farallon nazca plate beneath the chilean continental margin the kinematic signature recorded along the intra arc liquine ofqui fault zone lofz a major feature of the southern andes may help to understand the way in which the nazca south america slip vector has been partitioned into strain and displacement along and across the continental margin the lofz consists of two nne trending right stepping straight lineaments a strike slip duplex at the right step and curved features which splay off the straight lineaments toward the northwest the lofz runs mostly through heterogeneously deformed cenozoic plutonic rock of the north patagonian batholith and patchy metamorphic wall rock early cenozoic volcano sedimentary rocks and dyke swarms found in close spatial association with the strike slip duplex are believed to have developed in strike slip related basins quaternary volcanoes are aligned parallel to the lofz both ductile and brittle kinematic indicators within centimeter to meter wide high strain zones document late cenozoic dextral shear deformation contrasting left lateral deformation recorded on older and wider mylonitic zones suggests that the lofz may be a long lived shear zone that accommodated continental scale deformation arising from the farallon nazca south america plate convergence a block rotation pattern as indicated by paleomagnetic data is consistent with the geometry and cenozoic kinematics of the lofz

a water isotope approach to assessing moisture recycling in the island based precipitation of taiwan a case study in the western pacific 1 this study employs a dual isotope and three end member linear mixing model to semiquantitatively assess vapor contributions of advection transpiration and evaporation to precipitation and to compare the extent of moisture recycling including transpiration and evaporation among areas of various topographic types in taiwan an island located in the western pacific the three topographic types examined are the mountainous regions foothill regions as represented by two reservoir stations and coastal plains results indicate that the moisture fractions from advection and evapotranspiration in mountain precipitations are about 63 and 37 respectively and those in precipitation of plain and foothill regions are about 69 and 31 respectively moreover transpiration accounts for most of the recycling moisture while evaporation offers minor contribution since the transpiration fraction of recycling moisture is higher in forest mountain area than in plain foothill region topographic type is the major factor affecting the extent of transpiration nevertheless the two reservoirs examined in this study do not offer significant contribution of recycling moisture to local precipitation in addition to topographic type temperature and rainfall may be two other factors controlling the extent of transpiration transpiration would be promoted in greater rainfall regions but reduced in higher temperature areas additionally about 25 of precipitation in plain foothill region is of relocated moisture from evapotranspiration induced from forest mountains it should be noted that this isotope based approach has its limitations and should be applied with caution

tectonic evolution of the north patagonian andes 41 44 s through recognition of syntectonic strata abstract the north patagonian fold thrust belt 41 44 s is characterized by a low topography reduced crustal thickness and a broad lateral development determined by a broken foreland system in the retroarc zone this particular structural system has not been fully addressed in terms of the age and mechanisms that built this orogenic segment here new field and seismic evidence of syntectonic strata constrain the timing of the main deformational stages evaluating the prevailing crustal regime for the different mountain domains through time growth strata and progressive unconformities controlled by extensional or compressive structures were recognized in volcanic and sedimentary rocks from the cordilleran to the extra andean domain these data were used to construct a balanced cross section whose deep structure was investigated through a thermomechanical model that characterizes the upper plate rheology our results indicate two main compressive stages interrupted by an extensional relaxation period the first contractional stage in the mid cretaceous inverted jurassic lower cretaceous half graben systems reactivating the western canadon asfalto rift border 500 km away from the trench at a time of arc foreland expansion for this stage available thermochronological data reveal forearc cooling episodes and global tectonic reconstructions indicate mid ocean ridge collisions against the western edge of an upper plate with rapid trenchward displacement widespread synextensional volcanism is recognized throughout the paleogene during plate reorganization retroarc paleocene eocene flare up activity is interpreted as product of a slab rollback and fore to retroarc oligocene slab asthenospheric derived products as an expression of enhanced extension the second stage of mountain growth occurred in miocene time associated with nazca plate subduction reaching nearly the same amplitude than the first compressive stage extensional weakening of the upper plate predating the described contractional stages appears as a necessary condition for abnormal lateral propagation of deformation

heterogeneous extrusion and exhumation of deep crustal variscan assembly geochronology of the western tatra mountains northern slovakia abstract the nature and style of mid crustal assembly and exhumation during continental collision has been investigated in the tatra mountains of the western carpathians the pre alpine basement of the western carpathians represents the easternmost exposure of the variscan orogen in europe which marks the collision of laurasia with gondwanian affiliated terranes during the palaeozoic the tatric crystalline unit of the western tatra in northern slovakia displays an inverted metamorphic sequence where a high grade unit comprising migmatites with relicts of eclogite has been thrust over a lower grade mica schist unit new geochronological and thermochronological data together with published thermobarometry illuminate the metamorphic history of the western tatra the upper unit eclogites with occasionally preserved omphacite record near isothermal decompression from 1 6 gpa to 1 0 1 2 gpa at 750 800 c which lead to intensive re equilibration at high pressure granulite facies conditions comparable to the peak metamorphic conditions of the host migmatite both eclogite and migmatite shared a retrograde p t path following the insertion of the eclogite assemblage into the migmatites the metamorphic evolution of the lower unit mica schist is constrained to peak p t conditions of 0 6 0 8 gpa and 640 and 660 c followed by retrogression this suggests that different rock types of the western tatra metamorphic core shared only their exhumation path from mid crustal levels id tims sm nd dating of garnet from eclogite yields a whole rock garnet isochron age of 337 10 ma with an initial e nd isotopic composition of 8 3 in situ u pb dating of monazite from a migmatite surrounding the eclogite shows one age population of c 380 ma whereas monazite from a migmatite away from the eclogite preserves a robust 340 11 ma age which is indistinguishable from sm nd garnet age and u pb age of zircons in the anatectic leucosome of the migmatite 347 7 ma a younger monazite age population from the migmatite of 300 16 ma is consistent with 40 ar 39 ar mica ages of c 310 ma this argues for a contemporaneous and likely shared exhumation path of the assemblage pair in situ monazite total pb analyses from the lower unit mica schists yields xenocrystic and c 370 ma ages but no geochronologic evidence for peak variscan tectonism exhumation of the deep crustal root occurred most probably in a two stage process the timing of the high pressure eclogite facies metamorphism before the onset of exhumation into the mid crust was likely between c 380 ma and 360 ma subsequent exhumation into the middle crust was coeval with migmatite generation at c 340 ma and garnet diffusion modeling suggest 30 c ma cooling rates the exhumation was likely tectonically forced by the action of a rigid indentor which prompted the weak lower crust to be heterogeneously extruded to mid crustal levels at a time coeval with anatexis and subsequently extruded with mid crustal material to the upper crust

distribution timing and causes of andean deformation across south america the andean orogeny in south america has lasted over 100 ma it comprises the peruvian incaic and quechuan phases the nazca and south american plates have been converging at varying rates since the palaeocene the active tectonics of south america are relatively clear from seismological and global positioning system gps data horizontal shortening is responsible for a thick crust and high topography in the andes as well as in se brazil and patagonia we have integrated available data and have compiled four fault maps at the scale of south america for the mid cretaceous late cretaceous palaeogene and neogene periods andean compression has been widespread since the aptian the continental margins have registered more deformation than the interior for the peruvian phase not enough information is available to establish a tectonic context during the incaic phase strike slip faulting was common during the quechuan phase crustal thickening has been the dominant mode of deformation to investigate the mechanics of deformation we have carried out 10 properly scaled experiments on physical models of the lithosphere containing various plates the dominant response to plate motion was subduction of oceanic lithosphere beneath continental south america however the model continent also deformed internally especially at the margins and initial weaknesses

sedimentology and alluvial architecture of the bajo barreal formation upper cretaceous in the golfo san jorge basin outcrop analogues of the richest oil bearing fluvial succession in argentina abstract this study addresses the sedimentology architecture and dimensions of fluvial deposits in the bajo barreal formation upper cretaceous in the codo del senguerr anticline golfo san jorge basin argentina the stratigraphic framework of the 450 650 m thick alluvial succession was carried out through description and interpretation using 18 detailed sedimentary logs along a 4 5 km wide exposure where 314 fluvial channels were analysed the bajo barreal formation is a high accommodation fluvial succession dominated by fine grained floodplain deposits with isolated to vertically stacked sheet like low sinuosity or braided fluvial channels of limited lateral mobility clustered in several coeval channel belts in which fluvial channels were relocated by avulsion the lower member consists of reworked ash fall materials preserved in floodplain areas 78 floodplain sandstones 4 and fluvial channels 18 the mean thickness of sandbodies is 2 96 m n 118 and mean true width is 112 m mean w t 43 with thicker and wider sandbodies in upper levels of the member the upper member consists of grey siltstones and mudstones preserved in extensive lowland areas 78 and fluvial channels 19 with scarce preservation of sandstones in the proximal floodplain 3 fluvial channels are narrow low sinuosity sheets with comparable thickness mean 3 21 m n 196 but greater width than those of the lower member mean width 147 m mean w t 50 paleoflow data from 298 fluvial sandbodies indicates a paleoflow direction toward the se az 112 rivers flowed parallel to inherited early cretaceous normal faults and are oriented to high angle 70 to the current axis of the codo del senguerr anticline suggesting that the uplift of the anticline occurred after the deposition of the formation the variation in geometry of fluvial channels in both members of the bajo barreal formation could help in planning and developing primary and or enhanced oil recovery projects in nearby oilfields and provide data necessary for modelling the subsurface connectivity of hydrocarbon reservoirs

petrogenesis and tectonic setting of cadomian felsic igneous rocks sandikli area of the western taurides turkey in the sandikli afyon region western taurides the late proterozoic rocks of the sandikli basement complex are composed of low grade meta sedimentary rocks guvercinoluk formation intruded by felsic rocks kestel cayi porphyroid suite kcps the kcps is a deformed and highly sheared dome shaped rhyolitic body with a granitic core quartz porphyry dikes intrude both the slightly metamorphic igneous and the sedimentary rocks of the basement complex both the quartz porphyries and rhyolites were converted into mylonites with relict igneous textures geochemical data show that these felsic igneous rocks are subalkaline and mainly granitic in composition with sio2 72 wt and al2o3 11 5 wt the chondrite normalized incompatible trace element patterns are characterized by distinct negative rb nb sr p ti and eu with enrichment in th u la ce nd sm and zr the ree patterns of the felsic rocks indicate a strong enrichment in lree but display slightly flat hree patterns according to geochemical characteristics and petrogenetic modeling extrusive and intrusive rocks of the kcps were probably derived from an upper continental crustal source partial melting of granites felsic rocks by 18 20 fractional melting plus 18 20 rayleigh fractional crystallization which seems to be the most effective igneous process during the crystallization of the kcps single zircon age data from the granitoids and fossils from the disconformably overlying sedimentary successions indicate that the metamorphism and the igneous event in the taurides are related to the cadomian orogeny based on the geological geochemical and petrogenetic correlation of the post collisional granitoids it is further suggested that the tauride belt in western central turkey was in a similar tectonic setting to the gondwanan terranes in north africa younger granitoids and southern europe spain france bohemia brno massifs during the late cadomian period

along strike segmentation of the andean foreland causes and consequences abstract thrust belts of tertiary age characterize the east flank of the andes and part of the adjacent foreland from venezuela to the southern tip of south america this foreland deformation comprises three basically different structural styles 1 thin skinned thrust belts detached within the sedimentary cover 2 thick skinned thrust belts with an inferred basal detachment in the basement at 10 20 km depth and 3 foreland basement thrusts which possibly affect the entire crust alternating foreland structural styles along the orogen often with sharp boundaries produce a segmentation of the andean foreland the changes in structural style are interpreted to be primarily controlled by inherited stratigraphic and structural features of the south american plate for instance thin skinned thrust belts appear to require a more or less conformable sedimentary cover at least some 3 km thick over a metamorphic crystalline basement unaffected by mesozoic extension in areas of mesozoic rifting normal faults have been reactivated during tertiary contraction resulting in the formation of thick skinned thrust belts the basement becomes involved even if potential decollement levels are present deep seated foreland basement thrusts tend to form over basement arches with a thin sedimentary cover the three basic structural styles are unequally efficient in terms of shortening thin skinned belts are typically shortened by 40 70 thick skinned belts by 20 35 and areas of foreland thrusts by less than 10 the structural segmentation of the foreland therefore implies strong along strike variations in the amount of shortening available estimates of shortening along the central andes actually suggest that shortening does not vary steadily but has several maxima and minima strongly and weakly shortened foreland segments correlate poorly with the segmentation of the subducted plate in steeper and subhorizontal segments flat slabs but closely with lithospheric structure the most strongly shortened segment coincides with thick mantle lithosphere suggesting that shortening of the edge of the south american plate has resulted in substantial underthrusting of lithospheric mantle beneath part of the andes this underthrusting of thick lithosphere may have caused steepening of a formerly flat slab in the arica bend region to the normal 25 30 dip presently observed

stable isotopic characteristic of taiwan s precipitation a case study of western pacific monsoon region abstract the stable oxygen and hydrogen isotopic features of precipitation in taiwan an island located at the western pacific monsoon area are presented from nearly 3 500 samples collected during the past decade for 20 stations results demonstrate that moisture sources from diverse air masses with different isotopic signals are the main parameter in controlling the precipitation s isotope characteristics the air mass from polar continental pc region contributes the precipitation with high deuterium excess values up to 23 and relatively enriched isotope compositions e g 3 2 for 18o during the winter with prevailing northeasterly monsoon by contrast air masses from equatorial maritime em and tropical maritime tm supply the precipitation with low deuterium excess values as low as about 7 and more depleted isotope values e g 8 9 and 6 0 for 18o of tm and em respectively during the summer with prevailing southwesterly monsoon thus seasonal differences in terms of 18o d and deuterium excess values are primarily influenced by the interactions among various precipitation sources while these various air masses travel through taiwan secondary evaporation effects further modify the isotope characteristics of the inland precipitation such as raindrop evaporation reduces the deuterium excess of winter precipitation and moisture recycling increases the deuterium excess of summer precipitation the semi quantitative estimations in terms of evaluation for changes in the deuterium excess suggest that the raindrop evaporation fractions for winter precipitation range 7 to 15 and the proportions of recycling moisture in summer precipitation are less than 5 additionally the isotopic altitude gradient in terms of 18o for summer precipitation is 0 22 100 m greater than 0 17 100 m of winter precipitation the greater isotopic gradient in summer can be attributed to a higher temperature vs altitude gradient relative to winter the observed spatial and seasonal stable isotopic characteristics in taiwan s precipitation not only contribute valuable information for regional monsoon research crossing the continent ocean interface of east asia but also can serve as very useful database for local water resources management

using oxygen hydrogen and tritium isotopes to assess pond water s contribution to groundwater and local precipitation in the pediment tableland areas of northwestern taiwan summary environmental isotopes including stable hydrogen and oxygen and radioactive tritium isotopes are employed to assess groundwater sources in the taoyuan chungli tableland tct northwestern taiwan we evaluate the contribution to groundwater resources of copious ponds distributed throughout the tct results indicate that both precipitation and pond water are the end sources of proximal shallow groundwater p sgw in the tct recharge of p sgw to deep groundwater in the proximal fan region p dgw is obvious because values of p dgw are similar to those of p sgw and no barrier restricts p sgw entering p dgw however the infiltration of precipitation or pond water to shallow groundwater in the mid and distal fan regions md sgw is restricted somewhere because of impermeable confining layers overlying the md sgw in addition apart from the upstream recharge of the p sgw md sgw overlying the deep groundwater in the mid distal fan regions md dgw contributes to md dgw through barrier layer leakage between md sgw and md dgw overall values indicate that pond sourced moisture accounts for about 6 of precipitation in the studied tableland this contribution fraction is larger than that in the western plains or reservoir catchments of taiwan the calculations also indicate that precipitation and pond water respectively contribute 51 and 49 to p sgw among the 49 contribution from pond water to p sgw 46 is from direct infiltration and the remaining 3 is via the evaporation precipitation process the fractional results clearly indicate that pond water is a vital source of both local precipitation and groundwater

using hydrogen oxygen and tritium isotopes to identify the hydrological factors contributing to landslides in a mountainous area central taiwan over a 1 year period 343 samples including precipitation creek pond and groundwater were collected from june 2003 to may 2004 analyses were performed for stable oxygen and hydrogen isotope compositions selected samples were also analyzed for tritium the goal was to identify possible hydrologic factors contributing to a severe landslide in the li shan area central taiwan the isotope characteristics indicate that groundwater from fu shou shan farm located up slope from the landslide area is a major source for slope groundwater in addition to precipitation the groundwater is mainly recharged by pond water at fu shou shan farm according to the calculation of a two end member equation with 18o the contribution of farm groundwater to slope groundwater is significantly higher than that of precipitation up to a factor of five the estimated drainage efficiency of the existing system is only 23 draining off the slope groundwater in the up slope region to decrease farm groundwater flow into the slope area is a feasible strategy to effectively reduce the risk of landslide

the dynamic relationship between ground water and the columbia river using deuterium and oxygen 18 as tracers abstract deuterium and oxygen 18 were used as natural tracers to investigate the hydraulic relationship between the columbia river and the blue lake gravel aquifer near portland oregon a time series of stable isotope data collected from surface and ground waters during a march 1990 aquifer test confirms that the river and aquifer are hydraulically connected calculations based on simple mixing show that the river contributed 40 50 of the yield of three wells after 5 6 days of pumping data collected during august 1990 show that the river contributed 65 80 of the yield of one well after 22 days of pumping and indicate that the contribution of the river was still increasing

assessing groundwater sources and their association with reservoir water using stable hydrogen and oxygen isotopes a case study of the taipei basin northern taiwan the purpose of this isotopic study is to identify groundwater sources in taipei basin tpb and their association with water of the feitsui reservoir ftr northern taiwan to this end water samples including precipitation catchment surface water tpb groundwater ftr water and catchment surface water of ftr were analyzed for stable hydrogen and oxygen isotope compositions 2h and 18o isotopic results support previous reports that dahan stream and xindian stream waters are the major recharge sources of tpb groundwater these recharge regions are located along the southern border of the tpb further isotopic evidence finds that water from the southern hills catchment area of the tpb also recharges tpb groundwater and most importantly indicates that tpb groundwater is highly related to ftr water however for caution s sake future comprehensive study is needed to confirm hydrological connectivity between the ftr water and tpb groundwater

late neoproterozoic to early palaeozoic palaoegeography of the holy cross mountains central europe an integrated approach study of geochemistry examination of isotope ages of detrital minerals palaeomagnetic analysis and a study of the trilobites were performed to provide constraints on the palaeogeographical position of the holy cross mountains in late ediacaran early palaeozoic time the geochemical results indicate an active continental margin or continental island arc provenance of the ediacaran sediments sediments from a passive continental margin were deposited here during the cambrian and ordovician the palaeomagnetic pole isolated from cambrian rocks of the malopolska region of the holy cross mountains corresponds to the cambrian segment of the baltic apparent polar wander path isotope age estimations indicate that cambrian sediments of the malopolska region contain detritus not only from a latest neoproterozoic source but also from sources with ages of c 0 8 0 9 ga 1 5 ga and 1 8 ga the malopolska brunosilesia dobrugea and moesia terranes which originally developed near the present southern edge of baltica and were partly involved in the cadomian orogen were dextrally relocated along its trans european suture zone margin the first stage of this movement took place as early as latest ediacaran time while baltica rotated anticlockwise anticlockwise rotation of baltica at the cambrian ordovician boundary implies further dextral movement of the malopolska block

the late jurassic to present evolution of the andean margin drivers and the geological record 1 uncommonly long lived subduction and variable plate geometry along the south american andean plate margin resulted in diverse relationships between magmatic flux and extensional and contractional deformation as recorded by the overriding continental plate convergence velocities absolute overriding plate velocities and subducting slab ages were resolved along the trench from 170 ma to the present using a recently developed kinematic global plate model to identify any relationship between subduction conditions deformation style and magmatic features in the overriding plate key correlations reflect the dependence of macroscopic crustal strain style on subduction mechanism and relative plate vectors extensional back arc basins involving mafic oceanic crust developed only when the overriding plate velocity of south america was directed away from the trench and the modeled age of the subducting slab was older than 50 myr the development of fold and thrust belts and uplift of major plateaus was accompanied by trench normal convergence velocities in excess of 4 cm yr parameters investigated in this study revealed no correlation with the timing of major magmatic events nor was any correlation observed with the structural style of fold and thrust belts

using stable hydrogen and oxygen isotopes to reveal monsoonal and related hydrological effects on meteoric water in the western pacific monsoon region a case study of the ilan region northeastern taiwan abstract this study analyzes the isotopic compositions 2h and 18o of meteoric waters including precipitation and stream water to reveal what major hydrological processes affect the hydrological regime of the ilan region northeastern taiwan the isotopic results indicate monsoonal flows as the fundamental factors affecting studied precipitation and stream water summer precipitation sourced from southerly air mass exhibits lower and deuterium excess de values than winter precipitation sourced from northerly air masses the 18o and de values are respectively 7 7 and 8 for summer precipitation and 3 3 and 24 for winter precipitation furthermore semi quantitative estimations using de evidence indicate that summertime southerly air masses generally contribute more to stream water than wintertime northerly air mass flows approximately 54 vs 46 however the contribution fractions are controlled by the orientation of catchments to the windward side of respective monsoonal flows northern catchments located on the windward side of southerly air masses receive about 60 of their water from precipitation condensed from the southerly air masses and 40 from the northerly air masses by comparison southern catchments located on the windward side of northerly air masses receive about 59 of their water from northerly air masses and 41 from southerly air masses additionally catchment effect induced from value is notable in stream basins with high elevations but this is not related to catchment sizes besides this altitude effect which is determined in terms of 18o values was derived using data from four precipitation stations of northern taiwan it ranges from 2 5 to 3 0 per 100 m depending on the season moreover based on the de evidence secondary evaporation effects are apparent with moisture recycling influencing inland summer precipitation and raindrop evaporation influencing inland winter precipitation

chronological constraints on the pre orogenic history burial and exhumation of deep seated rocks along the eastern margin of the variscan orogen bohemian massif czech republic key lithological units of the high grade eastern margin of the bohemian massif were dated using the u pb and pb pb methods on zircons in order to establish a chronological framework for the geodynamic evolution of the variscan orogenic root the protolith ages for metagranitoids orthogneisses and granulites of thickened lower and middle crust reveal the existence of magmatic activity that occurred over a 100 million year time interval from cambro ordovician to early devonian times probably related to discontinuous intracontinental rifting of neoproterozoic crust our geochronological data suggest that the eastern part of the orogenic root represents thermally softened and rifted neoproterozoic crust preserved farther to the east as the brunia microcontinent zircon ages for felsic granulites high grade gneisses of the lower crust and of a syn convergence granodioritic intrusion in the upper crust indicate that thickening and exhumation of the crust occurred during a narrow time interval between 370 and 340 ma exhumation of the lower crust to mid crustal levels was a localized process that occurred at 340 ma and was associated with crustal scale folding in the internal part of the root as well as orogenic channel flow along the eastern collisional margin both types of exhumation mechanisms were driven by deep level wedging indentation of the easterly brunia continent followed by deposition of heavy minerals and pebbles derived from high pressure rocks in the adjacent foreland basin final orogenic development was characterized by ne sw dextral transpressive shearing parallel to the brunia margin as well as dextral trans tension associated with activity along the elbe lithospheric fault these processes affected the marginal parts of the orogenic root and were accompanied by 330 to 325 ma old syntectonic granitoid intrusions along reactivated lithotectonic boundaries rotation of the assembled orogenic belt accompanied by lithospheric faulting driven by westerly subduction roll back may be the most plausible model to explain late deformation of the orogenic root

patagonian broken foreland and related synorogenic rifting the origin of the chubut group basin abstract the central patagonia is characterized by prominent continental deposits that belong to the cretaceous chubut group basin whose tectonic setting remains controversial it has been interpreted as a foreland basin an extensional basin and even as a sag stage of a rift event related deposits outcrop as part of the patagonian broken foreland east of the patagonian andes particulary the san bernardo fold and thrust belt between 42 and 48 s as the main sector of the broken foreland constitutes a nnw trending intraplate belt located 450 km away from the trench coincidentally at these latitudes 1200 km east of the trench intraplate deformation has caused tectonic inversion of mesozoic basins presently located at the atlantic offshore area additionally at the san jorge gulf area this orogenic system interferes with a conspicuous e w extensional system transversally disposed to the andean strike mainly active between the late early cretaceous and late paleocene we carried out an integrated analysis from structural 2 d and 3 d seismic data at the san bernardo ftb and the adjacent rio mayo basin studying sections of the chubut group basin to unravel the different evolutionary stages thus surface and subsurface evidence of syn compressional deposition indicate the development of a broken foreland basin related to the formation of the san bernardo ftb suggesting an initial growth during the late early cretaceous and probably up to the late paleocene our results imply that the cretaceous compression acted in concert with transversal foreland extension hence we propose a syncontractional rift reactivation of a potential lithospheric anisotropy triggered by regional contraction finally the origin of compression during this time is discussed in relation to multiple processes that go from high convergence between plates and trenchward motion of south america collision of mid ocean ridges to potential dip changes in the subducted slab as suggested by arc expansion

geology and geochemistry of the pre early cambrian rocks in the sandikli area implications for the pan african evolution of nw gondwanaland abstract the pre early cambrian sandikli basement complex in western central anatolia comprises a low grade meta sedimentary succession guvercinoluk formation and meta rhyolites intruded by meta quartz porphyry rocks kestel cayi porphyroid suite the guvercinoluk formation consists of alternation of meta siltstones and meta sandstones with olistostromal conglomerates rare black chert and cherty meta dolomite lenses the kestel cayi porphyroid suite is a deformed highly sheared dome shaped rhyolitic body with quartz porphyry rocks quartz porphyry dykes intrude both the volcanic carapace and the meta sedimentary rocks of the guvercinoluk formation both the meta quartz porphyry rocks and meta rhyolites are typically mylonitic with relict igneous textures geochemical data indicate that the felsic rocks of the kestel cayi porphyroid suite are subalkaline and display characteristic features of post collisional i type granitoids the basement complex is unconformably overlain by variegated conglomerates mudstones and arkosic sandstones with andesitic lavas followed by siliciclastic rocks and carbonates that yielded early middle cambrian fossils based on the geochemical characteristics of the felsic rocks of kestel cayi porphyroid suite and the depositional features of the associated sediments it is suggested that the sandikli basement complex is related to a post collisional extension event in nw gondwanaland similar occurrences elsewhere have been related to a transition from continental plate convergence to continental plate divergence along the pan african belt

early cambrian location and affinities of the brunovistulian terrane central europe in the light of palaeomagnetic data the brunovistulian was one of the first tectonic units of central europe to be defined as a terrane in spite of extensive studies the early palaeozoic palaeogeographical position and provenance of this unit remains unclear a palaeomagnetic study of the lower cambrian red beds and a study of the trilobite fauna were performed to provide constraints on the palaeogeographical position of the terrane in early cambrian time good quality palaeomagnetic data obtained from the lower cambrian red beds suggest the mixed nature of the early cambrian geomagnetic field and a nearly equatorial position a palaeolatitude of c 7 of the brunovistulian terrane in the early cambrian comparison of this palaeolatitude with existing palaeogeographical models leads to the conclusion that at this time the brunovistulian terrane was separated by a great distance from the avalonian margin of gondwana the terrane was located within the cadomian belt occupying a position north of the present day northern margin of africa it was coupled to the present day southern margin of baltica during the cambrian when baltica moved along the cadomian margin of gondwana another possibility is that the brunovistulian terrane could have remained near this margin of baltica since grenvillian time and was incorporated into the cadomian orogen

neogene uplift of central eastern patagonia dynamic response to active spreading ridge subduction the chile triple junction ctj episodically migrated northward during the past 14 ma from 54 s to its present day position at 46 30 s as different almost trench parallel spreading segments entered in subduction this migration resulted in the opening of an asthenospheric window below patagonia inducing a disturbance in the regional mantle convection on the overriding plate the middle miocene time corresponds to a major change in the central patagonian basin dynamics with a transition from subsidence to generalized uplift the detailed mapping and the morphological study of post middle miocene terraces evidence regional scale trench parallel tilt histories that differ depending on latitude south of 46 30 s the slopes of the fluvial terraces indicate a change from northward to southward tilt during late miocene terraces younger than the early pliocene do not show any trench parallel tilt north of 46 30 s in contrast only northward tilt active until the pleistocene is recorded we use a semianalytical model of dynamic topography which suggests that the northward migration of the chile triple junction should be accompanied by a dynamic uplift of the central patagonian basin uplift would cause both north directed and south directed tilt north and south of the triple junction respectively with values of 0 1 0 2 500 km east of the trench tilt measured in the southeastern part of the central patagonian basin 0 1 is comparable to values predicted using the semianalytical model the dynamic topography associated to the chile ridge subduction may have exerted a major control on the neogene dynamics of patagonia

a geodynamic model linking cretaceous orogeny arc migration foreland dynamic subsidence and marine ingression in southern south america abstract this study synthesizes the tectonomagmatic evolution of the andes between 35 30 s to 48 s with the aim to spotlight early contractional phases on andean orogenic building and to analyze their potential driving processes we examine early tectonic stages of the different fold thrust belts that compose this andean segment additionally we analyzed the spatio temporal magmatic arc evolution as a proxy of dynamic changes in andean subduction during critical tectonic stages of orogenic construction this revision proposes a hypothesis related the existence of a continuous large scale flat subduction setting in cretaceous times with a similar size to the present largest flat slab setting on earth this potential process would have initiated diachronically in the late early cretaceous and achieved full development in late cretaceous to earliest paleocene times constructing a series of fold thrust belts on the retro arc zone from 35 30 s to 48 s moreover we assess major paleogeographic changes that took place during flat slab full development in maastrichtian danian times at this moment an enigmatic atlantic derived marine flooding covered the patagonian foreland reaching as far as the andean foothills based on flexural and dynamic topography analyses we suggest that focused dynamic subsidence at the edge of the flat slab may explain sudden marine ingression previously linked to continental tilting and orogenic loading during a high sea level global stage finally flat subduction destabilization could have triggered massive outpouring of synextensional intraplate volcanic rocks in southern south america and the arc retraction in late paleogene to early neogene times

identification of groundwater sources of a local scale creep slope using environmental stable isotopes as tracers summary water plays an important role for slope stability and typically consists of local precipitation lp and original slope groundwater osgw high amount of the osgw leads the slope groundwater sgw easily to exceed the critical level that causes slope failure in a heavy raining event this study was to verify the source and significance of the osgw for a creep slope adjoining a hydropower plant northern taiwan by an environmental stable isotope approach isotope results indicate that the source of the osgw derived from leaking of the water transporting system of the power plant the leaking fraction in the sgw is as high as 70 80 high leaking component in the sgw indicates that the leaking water rather than local precipitation is the crucial factor for the mass movement of the creep slope since the mass movement poses a potential threat to the hydropower plant safety the most important measure for the remedial project is to perform a comprehensive check and repair the leak of the water transporting system

risk faults in stable crust of the eastern bohemian massif identified by integrating gnss levelling geological geomorphological and geophysical data abstract it is difficult to identify and assess the recently active faults representing a risk factor for key human activities in the areas of stable crust with slow tectonic deformation and reduced seismicity we face the problem in the eastern bohemian massif central european variscides at a contact with the eastern alpine western carpathian orogenic belt through building its integrated geodynamic model based on the long term gnss data cross checked with the results from existing levelling geological surveys geophysical surveys and a new geomorphological analysis the model shows differently moving crustal blocks determining the intervening boundary zones as the main risk regions where weak earthquakes are also usually concentrated primarily diendorf cebin tectonic zone nectava konice fault hana faults b la fault and bulhary fault shear zone the maximum horizontal gnss differential velocities in the exposed bohemian massif reach up to 1 5 2 0 mm yr 1 the up thrusted segments of the western carpathians move individually 2 mm yr 1 the integration of a number of full area datasets corresponding to various dimensions and depth levels of crustal processes allowed us to highlight the important fault zones as driving elements of regional geodynamics

production of jurassic rhyolite by anatexis of the lower crust of patagonia abstract the mid jurassic marifil and chon aike volcanic rocks of eastern patagonia are part of one of the largest silicic igneous provinces known rb sr geochronology indicates eruptive ages of 175 190 ma for the marifil complex mostly toarcian aalenian the majority of the rocks are isotopically uniform with initial 87sr 86sr 0 7067 0 0003 and endt 4 2 primary magmas of andesitic composition were generated by partial melting of mafic grenvillian lower crust indentified by depleted mantle model ages of 1150 1600 ma lower crustal pyroxene granulite xenoliths can be modelled as residual jurassic source although they may alternatively be co genetic cumulates the dacite rhyolite suite formed by crystal liquid fractionation processes from the primary andesites involving multistage crystallization and re melting during magma ascent with the later stages of evolution being explicable by fractional crystallization of plagioclase amphibole and accessory minerals the province represents large scale lower crustal reworking associated with the unique tectonic and igneous environment of gondwana break up

fault inversion vs new thrust generation a case study in the malargue fold and thrust belt andes of argentina abstract the reverse reactivation of pre existing normal faults has been documented in many orogens in other cases the lack of sub surface information has allowed the construction of both inversion and non inversion structural models we will analyze the possibility of fault inversion in one such case in the malargue fold and thrust belt in the andes of argentina in order to address this issue we modeled fault inversion vs new thrust generation using the reactiva 2 4 software and varying the physical parameters for the pre existing fault and the host rock the results of modeling are compared to the possible sub surface characteristics of faults in the malargue fold and thrust belt we show that the orientation of these structures in the andean stress field makes them likely to reactivate if the pre existing fault planes present a low coefficient of friction and or fluid overpressure both are expectable in the geological setting in which the structures are found we conclude that fault inversion cannot be dismissed and should be taken into account for structural models of the malargue fold and thrust belt our results can be extended to other orogens with similar characteristics

brunovistulian terrane bohemian massif central europe from late proterozoic to late paleozoic a review the brunovistulian terrane represents a microcontinent of enigmatic proterozoic provenance that was located at the southern margin of baltica in the early paleozoic during the variscan orogeny it represented the lower plate at the southern margin of laurussia involved in the collision with the armorican terrane assemblage in this respect it resembles the avalonian terrane in the west and the istanbul zone in the east there is a growing evidence about the presence of a devonian back arc at the margin of the brunovistulian terrane the early variscan phase was characterized by the formation of devonian extensional basins with the within plate volcanic activity and formation of narrow segments of oceanic crust the oldest visean flysch of the rheic rhenohercynian remnant basin protivanov andelska hora and horni benesov formations forms the highest allochthonous units and contains together with slices of silurian bohemian facies clastic micas from early paleozoic crystalline rocks that are presumably derived from terranes of armorican affinity although provenance from an active brunovistulian margin cannot be fully excluded either the development of the moravo silesian late paleozoic basin was terminated by coal bearing paralic and limnic sediments the progressive carboniferous stacking of nappes and their impingement on the laurussian foreland led to crustal thickening and shortening and a number of distinct deformational and folding events the postorogenic extension led to the formation of the terminal carboniferous early permian boskovice graben located in the eastern part of the brunovistulian terrane in front of the crystalline nappes the highest allochthonous westernmost flysch units locally with the basal slices of the devonian and silurian rocks thrusted over the silesicum in the nw part of the brunovistulian terrane may share a similar tectonic position with the giessen harz nappes the silesicum represents the outermost margin of the brunovistulian terrane with many features in common with the northern phyllite zone at the avalonia armorica interface in germany

mountain building and mantle dynamics 1 mountain building at convergent margins requires tectonic forces that can overcome frictional resistance along large scale thrust faults and support the gravitational potential energy stored within the thickened crust of the orogen a general dynamic model for this process is still lacking here we propose that mountain belts can be classified between two end members first those of slab pull type where subduction is mainly confined to the upper mantle and rollback trench motion lead to moderately thick crustal stacks such as in the mediterranean second those of slab suction type where whole mantle convection cells conveyor belts lead to the more extreme expressions of orogeny such as the largely thickened crust and high plateaus of present day tibet and the altiplano for the slab suction type deep mantle convection produces the unique conditions to drag plates toward each other irrespective of their nature and other boundary conditions we support this hypothesis by analyzing the orogenic volcanic and convective history associated with the tertiary formation of the andes after 40 ma and himalayas after collision at 55 ma based on mantle circulation modeling and tectonic reconstructions we surmise that the forces necessary to sustain slab suction mountain building in those orogens derive after transient slab ponding from the mantle drag induced upon slab penetration into the lower mantle and from an associated surge of mantle upwelling beneath africa this process started at 65 55 ma for tibet himalaya when the tethyan slab penetrated into the lower mantle and 10 myr later in the andes when the nazca slab did this surge of mantle convection drags plates against each other generating the necessary compressional forces to create and sustain these two orogenic belts if our model is correct the available geological records of orogeny can be used to decipher time dependent mantle convection with implications for the supercontinental cycle

deduction of groundwater flow regime in a basaltic aquifer using geochemical and isotopic data the golan heights israel case study summary groundwater flow paths through shallow perch and deep regional basaltic aquifers at the golan heights israel are reconstructed by using groundwater chemical and isotopic compositions groundwater chemical composition which changes gradually along flow paths due to mineral dissolution and water rock interaction is used to distinguish between shallow perched and deep regional aquifers groundwater replenishment areas of several springs are identified based on the regional depletion in rainwater 18 o values as a function of elevation 0 25 per 100 m tritium concentrations assist in distinguishing between pre bomb and post bomb recharged rainwater it was found that waters emerging through the larger springs are lower in 18 o than surrounding meteoric water and poor in tritium thus they are inferred to originate in high elevation regions up to 20 km away from their discharge points and at least several decades ago these results verify the numerically simulated groundwater flow field proposed in a previous study which considered the geological configuration water mass balance and hydraulic head spatial distribution

use of stable water isotopes to assess sources and influences of slope groundwater on slope failure this study employs stable oxygen and hydrogen isotopes as natural tracers to assess the headwater of a landslide next to a drainage divide and the importance of the slope s headwater in the study area the study is undertaken near wu she township in the mountains of central taiwan because a reservoir is located on the other side of the divide this study evaluates the relationship between the reservoir water and headwater of the landslide as well over a 1 year period water samples from september 2008 to september 2009 including local precipitation lp wu she reservoir s water wsrw slope groundwater sgw upper reach stream water ustw and down reach stream water dstw were analysed for deuterium d and oxygen 18o stable isotopes results indicate that wsrw is the predominant component in sgw approximately 70 of sgw originates from wsrw and 30 from lp based on a two end member mass balance mixing model for 18o the similar two end member mixing model is also employed to assess the contributions of ustw and sgw to dstw model results indicate that sgw is the major source of dstw with a contribution of about 67 accordingly about 47 of dstw sources from the wsrw in short owing to reservoir leakage wsrw contributes the greater part of both sgw and dstw plentiful wsrw in sgw threatens the stability of the slope in the divide area to avoid subsequent continuous slope failure necessary mitigation steps are required copyright 2011 john wiley sons ltd