late miocene holocene canyon incision in the western altiplano northern chile tectonic or climatic forcing abstract major fluvial incision 600 1000 m affecting the coastal cordillera and central depression of northern chile is analysed to evaluate supposed coeval uplift of the altiplano and or climatic changes in the atacama desert the timing of the beginning of incision is constrained by the age of deposition of the central depression top in the north 18 19 s this top corresponds to fluvial gravels accumulated between 11 9 0 6 ma and 8 3 0 5 ma which are genetically related to semiarid climate and to an eastward poorly dissected parallel drainage network that developed between 15 0 0 6 and 11 2 0 6 ma thus gravel deposition ended at 11 9 11 2 ma to the south 19 20 s the central depression top corresponds to c 6 ma alluvial deposits stratigraphically determined canyon ages and knickzone locations indicate that southward dissection began later and or developed under a regime of lower erosion capacity owing to drier climate vertical incision rate evolution is compatible with eastward knickzone migration dissection required a considerable altitude difference between ancient and present day river base levels which was achieved predominantly by basin infill on an already partially elevated bedrock therefore subsequent incision would have been triggered by local semiarid climatic periods rather than by contemporaneous surface uplift exoreic canyons occur when climatic conditions in the catchments are arid semiarid whereas endoreism is developed when these conditions in catchments are hyperarid

cenozoic tectonic evolution in the central andes in northern chile and west central bolivia implications for paleogeographic magmatic and mountain building evolution a review of available stratigraphic structural and magmatic evolution in northernmost chile and adjacent peru and bolivia shows that in this region 1 compression on the paleogene intra arc during the middle eocene incaic phase formed the nne ssw oriented incaic range along the present day precordillera and western cordillera and 2 post incaic tectonic conditions remained compressive until present contrasting with other regions of the andes where extensional episodes occurred during part of this time lapse a late oligocene early miocene peak of deformation caused further uplift the incaic range formed a pop up structure bounded by two thrusts systems of diverging vergencies it represented a major paleogeographic feature that separated two domains with different tectonic and paleogeographic evolutions and probably formed the andean water divide this range has been affected by intense erosion and was symmetrically flanked by two major basins the pampa del tamarugal and the altiplano magmatic activity remained located along the previous late cretaceous early eocene arc with slight eastward shift further compression caused westvergent thrusting and uplift along the western eastern cordillera bounding the altiplano basin to the east by another pop up shaped ridge eastward progression of deformation caused eastvergent thrusting of the eastern cordillera and subandean zone

tracing the migration of mantle co2 in gas fields and mineral water springs in south east australia using noble gas and stable isotopes abstract geochemical monitoring of co2 storage requires understanding of both innate and introduced fluids in the crust as well as the subsurface processes that can change the geochemical fingerprint of co2 during injection storage and any subsequent migration here we analyse a natural analogue of co2 storage migration and leakage to the atmosphere using noble gas and stable isotopes to constrain the effect of these processes on the geochemical fingerprint of the co2 we present the most comprehensive evidence to date for mantle sourced co2 in south east australia including well gas and co2 rich mineral spring samples from the otway basin and central victorian highlands cvh 3he 4he ratios in well gases and co2 springs range from 1 21 to 3 07 ra and 1 23 3 65 rc ra respectively we present chemical fractionation models to explain the observed range of 3he 4he ratios he ne ar kr xe concentrations and 13c co2 values in the springs and the well gases the variability of 3he 4he in the well gases is controlled by the gas residence time in the reservoir and associated radiogenic 4he accumulation 3he 4he in co2 springs decrease away from the main mantle fluid supply conduit we identify one main pathway for co2 supply to the surface in the cvh located near a major fault zone solubility fractionation during phase separation is proposed to explain the range in noble gas concentrations and 13c co2 values measured in the mineral spring samples this process is also responsible for low 3he concentrations and associated high co2 3he which are commonly interpreted as evidence for mixing with crustal co2 the elevated co2 3he can be explained solely by solubility fractionation without the need to invoke other co2 sources the noble gases in the springs and well gases can be traced back to a single end member which has suffered varying degrees of radiogenic helium accumulation and late stage degassing this work shows that combined stable and noble gas isotopes in natural gases provide a robust tool for identifying the migration of injected co2 to the shallow subsurface

geohazard map of cover collapse sinkholes in the tournaisis area southern belgium abstract this paper reports the methodology developed to draw up a geohazard map of cover collapse sinkhole occurrences in the tournaisis area in this area carboniferous limestones are overlain by a mesocenozoic cover mainly consisting of marls sand and clay the thickness of this cover ranges from a few meters to more than 100 m the surficial morphology of the area does not show any karstic evidence except for the occurrence of these collapses from a paleogeographical point of view a developed quaternary karst is not conceivable in the area recent works suggested that the collapses are set off from reactivated paleokarsts the paleokarsts studied in the area proved to be the result of a particular weathering of the limestone the organization of these paleokarsts seems very low and mainly guided by the limestone fracturing as for most induced sinkholes the reactivation of these paleokarsts is linked to the lowering of piezometric heads in most of the area a thick cover and intensive land use mask potential surface hints of the buried paleokarsts and of the fracturing of the bedrock aerial photographs and remote sensing techniques have therefore shown little results in delineating collapse hazard zones up to now the study of the surficial morphology is also of little help in order to draw up the geohazard map in such a difficult context hydrogeological data and geological mapping information could only be used these informations are based on a limited number of boreholes and piezometers and are thus only valid on a regional scale records of former collapses were also available these records were of great interest since sinkhole distribution is obviously clustered in the area bedrock roof and cover formation floor altitudes were digitized and adapted to produce digital thematic maps piezometric heads were imported from a calibrated groundwater model of the aquifer these data and a digital elevation model of the area were integrated into a geographical information system gis to produce a coherent 3 d description of the area on a regional scale parameters such as the dewatering of the limestone and the thickness of the cover formation where sinkholes occurred were then estimated density of former collapses was also computed this showed that zones of high sinkhole occurrence coincide with zones of heavy lowering of piezometric heads combining the density of former collapses with the dewatering of the limestone enabled us to delineate zones of low moderate and high collapse hazard

multiphase development of the atacama planation surface recorded by cosmogenic 3he exposure ages implications for uplift and cenozoic climate change in western south america the atacama planation surface is an extensive west dipping surface developed between 16 s and 27 s along the pacific margin of south america it is considered to have formed between 16 and 7 5 ma and to have important chronostratigraphic significance here we present new cosmogenic 3he exposure dates of boulders on the planation surface using pyroxene and amphibole exposure ages display good within and between site consistency and range from 22 to 1 2 ma with ages of ca 14 6 7 and 3 ma recurring at more than one site on the planation surface the 14 6 ma peak records the cessation of the main period of planation surface development but contrary to popular opinion the younger ages reflect subsequent modification of the planation surface by alluvial activity comparison with other climate proxies for western south america suggests that since 14 6 ma a predominantly hyperarid climate interspersed with short lived phases of more intense runoff driven by global climate change has prevailed the longevity and composite nature of the atacama planation surface suggest that regionally extensive planation surfaces may have a multiphase history are unlikely to have any chronostratigraphic significance and cannot be used to reconstruct uplift histories

a review on natural and human induced geohazards and impacts in karst karst environments are characterized by distinctive landforms related to dissolution and a dominant subsurface drainage the direct connection between the surface and the underlying high permeability aquifers makes karst aquifers extremely vulnerable to pollution a high percentage of the world population depends on these water resources moreover karst terrains frequently underlain by cavernous carbonate and or evaporite rocks may be affected by severe ground instability problems impacts and hazards associated with karst are rapidly increasing as development expands upon these areas without proper planning taking into account the peculiarities of these environments this has led to an escalation of karst related environmental and engineering problems such as sinkholes floods involving highly transmissive aquifers and landslides developed on rocks weakened by karstification the environmental fragility of karst settings together with their endemic hazardous processes have received an increasing attention from the scientific community in the last decades concurrently the interest of planners and decision makers on a safe and sustainable management of karst lands is also growing this work reviews the main natural and human induced hazards characteristic of karst environments with specific focus on sinkholes floods and slope movements and summarizes the main outcomes reached by karst scientists regarding the assessment of environmental impacts and their mitigation

ophiolitic basement to the great valley forearc basin california from seismic and gravity data implications for crustal growth at the north american continental margin the nature of the great valley basement whether oceanic or continental has long been a source of controversy a velocity model derived from a 200 km long east west reflection refraction profile collected south of the mendocino triple junction northern california in 1993 further constrained by density and magnetic models reveals an ophiolite underlying the great valley great valley ophiolite which in turn is underlain by a westward extension of lower density continental crust sierran affinity material we used an integrated modeling philosophy first modeling the seismic refraction data to obtain a final velocity model and then modeling the long wavelength features of the gravity data to obtain a final density model that is constrained in the upper crust by our velocity model the crustal section of great valley ophiolite is 7 8 km thick and the great valley ophiolite relict oceanic moho is at 11 16 km depth the great valley ophiolite does not extend west beneath the coast ranges but only as far as the western margin of the great valley where the 5 7 km thick great valley ophiolite mantle section dips west into the present day mantle there are 16 18 km of lower density sierran affinity material beneath the great valley ophiolite mantle section such that a second deeper present day continental moho is at about 34 km depth at mid crustal depths the boundary between the eastern extent of the great valley ophiolite and the western extent of sierran affinity material is a near vertical velocity and density discontinuity about 80 km east of the western margin of the great valley our model has important implications for crustal growth at the north american continental margin we suggest that a thick ophiolite sequence was obducted onto continental material probably during the jurassic nevadan orogeny so that the great valley basement is oceanic crust above oceanic mantle vertically stacked above continental crust and continental mantle

uplift of the altiplano puna plateau a view from the west 1 the western flank of the central andean plateau is a crustal scale monoclinal fold expressed in the geomorphology and in the westward tilt of fore arc basin strata data from three fore arc basins quantify the magnitude and time of displacement of the plateau system relative to the fore arc from 18 30 s to 22 s there is a single monocline strand there other authors documented 2000 m 500 m of early and middle miocene structural relief growth across small scale monoclines and our data reveal 810 m 640 m of 11 5 ma relief growth and 400 m 170 m relief growth since 5 ma across a long wavelength monoclinal fold limb this structural relief growth since 11 ma approximates the topographic relief growth between the fore arc and the altiplano plateau from 22 s to 24 s there are two subparallel long wavelength monoclines structural relief on the east side of the fore arc increased by 2840 m 2510 m during 17 10 ma and by 2320 m 1050 m since 10 ma some part of this monoclinal limb rotation led to topographic uplift of the adjacent puna plateau rotation across the western monocline could have increased the altitude of the fore arc basins by 900 m since 6 ma and may result from intense heating of the eastern margin of the cold and strong atacama lithosphere block although the wavelengths of the monoclines vary along strike and through time the monoclinal style of deformation dominated the uplift history of the eastern fore arc of the central andes throughout the neogene

late cenozoic deformation and uplift of the western flank of the altiplano evidence from the depositional tectonic and geomorphologic evolution and shallow seismic activity northern chile at 19 30 s 1 we analyze the west vergent thrust system wts along the western flank of the altiplano in northern chile 18 s 21 s in our study area 19 20 s 19 50 s the wts consists of three thrust propagation monocline folds flexures developing growth strata the relative uplift accommodated by the flexures is rapid between 26 and 8 ma 0 1 mm yr diminishing to 0 02 mm yr after 8 ma approximately 2000 m of relative surface uplift was accommodated by the flexures since the late oligocene sedimentological and geomorphological analysis shows that westward tilting of the forearc occurred after 10 ma coeval with the shifting of deformation from the altiplano to the sub andean zone where the underthrusting of the brazilian craton would have resulted in crustal thickening surface uplift in the orogen and westward ductile subcrustal flow forearc tilting is accommodated by east vergent thrusts ets issued from the benioff zone beneath the central depression emerging into the western cordillera contributing 500 1400 m of surface uplift the wts connects the ets in the brittle ductile crustal transition 25 km depth continuing farther east as the altiplano low velocity zone configuring the western altiplano as a crustal scale fault bend fold forearc tilting would be caused by westward ductile flow in the lower crust pushing the rigid forearc in the ets meanwhile between 19 s and 21 s the wts accommodates dextral strike slip and 3 km of n s shortening occurred in the coastal cordillera transcurrence and strain partitioning are probably the result of slight plate convergence obliquity strong coupling within the interplate zone westward continental concavity and high elevation opposing horizontal contraction

noble gas isotopic compositions and water gas chemistry of soda springs from the islands of bioko sao tome and annobon along with cameroon volcanic line west africa abstract chemical and isotopic compositions are reported for water and co 2 and noble gases in groundwater and soda springs from bioko principe sao tome and annobon all islands located in the off shore part of the cameroon volcanic line in west africa the soda spring waters are of ca mg hco 3 type with d and 18 o values that range from 20 to 8 and 5 4 to 2 7 respectively indicative of a meteoric origin co 2 is the main gas species in the springs 13 c co 2 values vary from 2 8 to 5 0 overlapping the observed mantle c range 3 to 8 co 2 3 he ratios 3 9 10 9 suggest that most c 90 in the samples is derived from the mantle neon has atmospheric isotopic compositions while ar is slightly enriched in radiogenic 40 ar 3 he 4 he ratios 3 0 to 10 1 10 6 or 2 1 to 7 2 r a where r a is the atmospheric ratio of 1 4 10 6 are much higher than those for typical crustal fluids 10 8 but lower than those expected for fluids derived from high 3 he 4 he hotspots like loihi and iceland this precludes significant contributions of such fluids in the source regions of the gases and by inference in the magmatism of these oceanic islands alternatively approximately 90 of the he in sao tome gases is inferred to be derived from a source similar to the morb source the 3 he 4 he ratio for the bioko gas 6 6 10 6 may be derived from a source with a higher time integrated u th 3 he ratio than the morb source

an electrical resistivity imaging based strategy to enable site scale planning over covered palaeokarst features in the tournaisis area belgium abstract since the beginning of the 20th century more than 150 sinkhole occurrences mainly dropout or cover collapse sinkholes have been reported in the tournaisis area south eastern belgium land use planning in such a context has to take into account hazards linked with sinkhole subsidence and collapse management maps drawn at a regional scale point out zones where karstic risks have to be taken into account when dealing with infrastructure or building projects however karst hazard is highly variable in three dimensions at the local scale therefore for such purposes an accurate methodology is needed to detect and delineate covered karst features especially when located in urbanized areas as geophysical investigations are sensitive to contrasts in physical properties of soils these methods can be useful to detect such targets the specific karstic context encountered in the tournaisis area strongly guides the choice of investigation techniques electrical resistivity imaging eri methods were tested on a well known site where dropout sinkholes occurred formerly this site was also studied using static cone penetration tests cpt and boreholes a 3d inverted resistivity model was computed based on the 2d eri models obtained after inversion resistivity profiles were extracted at each cpt location and compared to geotechnical results to determine an empirical and site specific resistivity law that allows discrimination between weathered zones and sound limestone performance tests were conducted to evaluate the potential of the proposed methodology for two typical engineering problems based on two current hypotheses borehole data were used as ground truth similar performance tests were also computed using the cpt depth to bedrock model the results of these performance tests are compared and discussed finally an eri based investigation strategy is proposed to assess karst hazard in palaeokarstic context such as encountered in the tournaisis area at the scale needed for building and infrastructure purposes

a comprehensive approach to karst identification and groutability evaluation a case study of the dehou reservoir sw china abstract yunnan province in sw china has one of the most developed karst terrains in china and has been historically affected by sinkholes and other instability phenomena caused by unpredictable cavity formation and well developed underground hydraulic conduits during construction of a karst seepage control reservoir project grouting of a 4 6 km long anti seepage curtain in yunnan province some typical detection methods electromagnetic and water injection tests failed to map the complex geo structural karst zones clearly resulting in considerable grout loss and excessive leakage during the grouting phase of this project to deal with this limitation a comprehensive approach including a new drilling process monitoring system borehole electrical resistivity tomography borehole sonic logging and water injection tests is employed to identify the general characterization geometry and spatial distribution of karst zones along the anti seepage curtain additionally a deep belief network dbn model replaced the empirical relationships typically used to predict the grouting quantity for groutability evaluation in karstified areas the dbn algorithm is trained by data collected using this comprehensive approach rate of penetration rock permeability resistivity and p wave velocities and two previous grouting quantities as input data the lessons learned in this case study permit us to define an effective comprehensive approach for delineating the general characterization of karst zones between two boreholes and locations of potential conduits for grout flow through the borehole the proposed dbn model can predict the grouting quantity for karst regions and the accuracy of prediction is greatly affected by previous grouting quantity rather than the collected parameters

discussion on development and morphometry of sinkholes in coastal plains of apulia southern italy preliminary sinkhole susceptibility assessment by e bruno d calcaterra m parise engineering geology 99 2008 198 209

geographical distribution of 3 he 4 he ratios in the chugoku district southwestern japan we have collected 34 hot spring and mineral spring gases and waters in the chugoku and kansai districts southwestern japan and measured the 3he 4he and 4he 20ne ratios by using a noble gas mass spectrometer observed 3he 4he and 4he 20ne ratios range from 0 054 ratm to 5 04 ratm where ratm is the atmospheric 3he 4he ratio of 1 39 10 6 and from 0 25 to 36 8 respectively they are well explained by a mixing of three components mantle derived radiogenic and atmospheric helium dissolved in water the 3he 4he ratios corrected for air contamination are low in the frontal arc and high in the volcanic arc regions which are consistent with data of subduction zones in the literature the geographical contrast may provide a constraint on the position of the volcanic front in the chugoku district where it was not well defined by previous works taking into account the magma aging effect we cannot explain the high 3he 4he ratios of the volcanic arc region by the slab melting of the subducting philippine sea plate the other source with pristine mantle material may be required more precisely the highest and average 3he 4he ratios of 5 88 ratm and 3 8 1 6 ratm respectively in the narrow regions near the volcanic front of the chugoku district are lower than those in kyushu and kinki spot in southwestern japan but close to those in ne japan this suggests that the magma source of the former may be related to the subduction of the pacific plate in addition to a slight component of melting of the philippine sea slab

hepburn spa cold carbonated mineral waters of central victoria south eastern australia hepburn spring is the major cold carbonated mineral spring of the spa country of central victoria in south eastern australia the spring occurs in a small tributary valley of the loddon river 15 km away from the crest of the great dividing range the waters are effervescent have an alkalinity of around 1 500 mg l as hco3 are mildly acidic and have high iron concentrations hepburn spring is one of nearly 100 small cold low flow carbonated mineral water springs that occur in the region hepburn spring has been protected since 1865 in one of 34 special mineral spring reserves by world standards the spring is small and not highly developed but it retains much of its charm due to the bushland forest setting the bedrock of the region consists of indurated arkosic sandstones interbedded with carbonaceous shales and slates the rocks are folded and cut by swarms of strongly developed meridional fissure fault systems hepburn spring is situated on the fault and fold axes associated with the cornish line and gold mines have dewatered the spring on several occasions after dewatering events the water level and flow recovered first and then the water composition and effervescence the origin of the effervescent waters has attracted much attention hypotheses include both a volcanic and a rock water reaction origin the second hypothesis involves weathering of the carbonaceous and sometimes pyritic rock mass which contains only a few percent carbonate this process produces high bicarbonate groundwater throughout central victoria the hepburn waters are a variant of these waters and it is suggested that controls on the carbonate solubility and redox conditions in the fissures flow systems results in effervescent waters as the waters ascend

gis based susceptibility mapping of karst depression in gypsum a case study from sivas basin turkey a method is presented for mapping of collapse susceptibility using geographical information system gis collapses in karst terrains are very serious geological hazards and can damage engineering structures and cause groundwater contamination preparation of collapse susceptibility maps will serve to successful urban planning in karst terrains susceptibility of collapses and the effects of collapse related factors such as geological and hydrological lithology tectonic activity drainage systems springs topographical slope angle slope aspect elevation land use distance from roads and settlement areas and vegetation cover were evaluated using gis field observations and remote sensing data of landsat thematic mapper tm satellite images a susceptibility map was constructed using the frequency ratio techniques as a result all factors had a relatively positive effect on the susceptibility map in the study area the validation of the susceptibility map was checked by considering actual collapses for this purpose degree of fit df was calculated and the values obtained indicated the high quality of map

metallogeny structural evolution post mineral cover distribution and exploration in concealed areas of the northern chilean andes abstract mineral exploration of prospective areas concealed by extensive post mineralization cover is growing being very complex and expensive the projection of rich and giant paleocene to early oligocene porphyry cu mo belts in northernmost chilean andes 17 5 19 5 s has major exploration potential but only a few minor deposits have been reported to date due to the fact that the area is largely covered by post mineral strata we integrate the cenozoic stratigraphic structural and metallogenic evolution of this sector in order to identify the most promising regions related to lesser post mineral cover and the projection of different metallogenic belts the paleocene to early eocene metallogenic belt extends along the precordillera with ca 30 km wide and includes porphyry cu prospects and small cu mo au ag vein and breccia pipe deposits geochronological data indicate an age of 55 5 ma for an intrusion related to one deposit and ages from 69 5 to 54 5 ma for hydrothermal alteration in one porphyry cu prospect and largest known cu deposits the middle eocene to early oligocene porphyry belt in the western cordillera farther east is associated with 46 44 ma intrusions it is estimated to be 40 km wide but is largely concealed by thick post mineral cover the youngest miocene to early pliocene metallogenic belt also in the western cordillera is well exposed and includes au ag epithermal and polymetallic veins and manto type deposits the oligocene holocene cover consists of a succession of continental sedimentary and volcanic rocks that overall increase in thickness from 0 to 5000 m from west to east these strata are subhorizontal in the west and folded faulted towards the east miocene gentle anticlines and monocline flexures extend along strike for 30 60 km in the precordillera and were generated by propagation of high angle east dipping blind reverse faults with at least 300 900 m of oligocene bedrock offset the thickness of cover exceeds 2000 m in the eastern central depression whereas it is generally less than 1000 m in the precordillera along the paleocene to early eocene porphyry cu belt and it can reach locally up to 5000 m in the western cordillera above the middle eocene to early oligocene belt in the studied andean segment the miocene to early pliocene metallogenic belt is superimposed on the paleocene to oligocene belts in a 40 50 km wide zone this overlap may be explained by an accentuated migration of the magmatic front from east to west since ca 25 ma as a consequence of subduction slab steepening after a period of magmatic lull and flat subduction from ca 30 35 to 25 ma the identified areas of lesser cover thickness are prone to exploration for concealed deposits especially along the projection of major porphyry cu mo belts

progressive evolution of a fault related fold pair from growth strata geometries sant llorenc de morunys se pyrenees abstract new structural stratigraphical mapping constrains the three dimensional kinematics and mechanisms of eocene oligocene growth folding at sant llorenc de morunys ne ebro basin spain a 1 km wide sub vertical panel of syntectonic alluvial gravels passes southwards via a highly asymmetrical growth fold pair to shallowlydipping strata the axial surface of the anticline comprises either continuous or en echelon segments while that of the syncline is concave and usually continuous while converging upwards the axial surfaces do not define growth triangles principal and subsidiary growth unconformities and thickness changes occur across both axial surfaces and the common limb dips within the common limb decrease up stratigraphy and up dip mesostructures indicate that internal deformation was ongoing during folding at all stratigraphical levels and concentration of cleavage in the syncline indicates that this hinge was essentially fixed sequential restoration of three profiles shows that folds amplified principally by limb rotation but incorporated minor passive hinge migration particle movement vectors generated by section restoration are arcuate about a hinterland pinpoint a new trishear model of fault propagation folding involving non rigid limb rotation reproduces the rounded hinge forms thickening geometries and limb dip variations observed simple kink band migration models fixed axis and constant thickness theories do not replicate these features

uplift of the western altiplano plateau evidence from the precordillera between 20 and 21 s northern chile 1 we present a quantitative reconstruction of uplift of the western flank of the altiplano plateau central andes one of the largest monoclines on the earth on the basis of an analysis of tectonic structures syntectonic deposits and geophysical data uplift occurred on a west vergent slowly propagating system of high angle reverse faults merging into a joint detachment that ramps down to midcrustal levels below the plateau edge the upper ramps determine local fold geometries while the lower ramp controls large scale surface tilting and uplift at 20 s this fault system was active between 30 ma and 5 10 ma with maximum shortening rates of 0 22 mm yr between 17 and 10 ma it generated some 2600 m of surface uplift with only minor shortening of 3000 m its activity was largely synchronous to eruption of large volume ignimbrites from a midcrustal source geophysical data indicate that the fault system localized deformation at the boundary between a cool strong forearc crust and a presumably fluid rich and or partially molten zone underneath the plateau area the systematic relation between crustal melting and shortening with uplift at the western plateau margin can be traced along most of the plateau flank with a stepwise decrease in age of deformation and magmatism toward the south indicating discontinuous addition of plateau segments crustal thickening to as much as 70 km from westward underthrusting in the back arc parts of the plateau isostatically compensated the tectonic surface uplift and monocline formation with respect to a stable forearc which only reacted with minor tilting

helium isotope systematics at nevado del ruiz volcano colombia implications for the volcanic hydrothermal system abstract we have collected 14 water and gas samples from 9 thermal springs and gas vents near nevado del ruiz volcano colombia the 3 he 4 he and 4 he 20 ne ratios vary significantly from 0 98 r atm where r atm is the atmospheric 3 he 4 he ratio of 1 4 10 6 to 6 30 r atm and from 0 37 to 7 0 respectively the 3 he 4 he ratio corrected for air contamination decreases with increasing distance from the central crater of the volcano to the sampling site the trend is very similar to that observed at ontake volcano japan a hydrodynamic porous media dispersion model can explain the 3 he 4 he trend the temporal variations in the 3 he 4 he ratio at four sites provide useful information on the apparent velocity of the magmatic fluid flow brought on by a volcanic eruption the estimated value of several tens m day 1 agrees well with the inferred velocity of flow in oshima volcano japan and is comparable to the largest rate of groundwater movement in a deep sedimentary basin

fault related folding drainage network evolution and valley incision during the neogene in the andean precordillera of northern chile abstract we describe neogene drainage network development before during and after regional folding in the precordillera of the andes of northern chile 18 19 s the drainage network developed on an extensive regular erosional surface formed on oligocene miocene ignimbrites oxaya formation the folding affecting the rocks of the precordillera is represented by the oxaya anticline oa which trends n to nw is 50 km long and 30 km wide the fold is gentle west vergent and has resulted in an uplift of the hinge zone by up to 850 m it formed by the propagation on its western border of a subvertical east dipping blind reverse fault ausipar fault af the folding occurred in the middle late miocene essentially between 11 7 0 7 and 10 7 0 3 ma its maximum duration was 2 my two phases of drainage development are recognised in the precordillera an initial lower middle miocene 19 12 ma parallel drainage network is well preserved and synchronous with fluvial and lacustrine sedimentation in the central depression the network was poorly structured and attained maximum incision of to 250 50 m the minimum long term rate of incision was 36 7 m my folding generated the progressive abandonment and fossilisation of the initial parallel drainage network which became trellissed and concentrated in a few deeply incised valleys in the anticline hinge the lluta and azapa main valleys present a total incision of 1650 50 and 1605 50 m respectively whereas the cardones valley presents 595 50 m during folding river incision at the fold hinge was equal to or greater than the amplitude of the folding which is 790 50 m in the lluta valley and 715 50 m in the azapa valley consequently the long term rate of synfolding incision was much greater than 395 25 lluta valley and 358 25 m my azapa valley the cardones valley was fossilised approximately in the middle of the folding after folding 11 to 0 ma the incision in the lluta and azapa rivers was 610 100 and 640 100 m and with a rate of 56 9 and 58 9 m my respectively the postfolding incision rate is approximately twice than of the prefolding incision rate this implies an acceleration of valley incision since the late miocene which is considered as consequence of regional uplift of the andean forearc

sedimentary fill of the chile trench 32 46 s volumetric distribution and causal factors the chile trench of the convergent continental margin of central chile is a sediment filled basin that stretches over 1500 km in a north south direction the sediment fill reflects latitudinal variations in climate as well as in the morphology and geology of chile but also of sediment transport processes to the trench and within the trench we try to untangle these signals by calculating the total volume and the latitudinal volume distribution of trench sediments and by relating this distribution to a number of factors that affect this pattern the volume calculation is based on a model geometry of the top of the subducting oceanic plate that is buried beneath trench sediments and the sea floor as measured by swath bathymetry we obtain the model geometry of the subducting plate by interpolating between depth converted seismic reflection profiles that cross the trench the total volume of the trench fill between 32 and 46 s is calculated to be 46000 500 km 3 the resulting latitudinal volume distribution is best explained by a sedimentation model that alternates between 1 glacial phases of high sediment flux from southern chile combined with active latitudinal sediment transport within the trench and 2 interglacial phases over which sediment input is dominated by local factors supplementary material top of the oceanic basement tob grid is available as ascii raw data files xyz at www geolsoc org uk sup18664

a case of man induced ground subsidence and building settlement related to karstified gypsum oviedo nw spain this paper presents the research carried out to shed light on a sudden settlement and its consequences that occurred in the city of oviedo ground subsidence in the ventanielles area led to severe damage and the subsequent demolition of two buildings with 362 flats resulting in losses of 18 million euros the investigation allowed the identification of a buried sinkhole filled with up to 13 m of fluvial sediments linked to the dissolution of a paleogene gypsum unit with a maximum thickness of 18 m and containing metre sized cavities the triggering process that reactivated the paleosinkhole was found to be the pumping of water from a confined aquifer related to excavation work during the construction of a nearby underground parking lot this extraction modified the natural hydrological regime the compaction and migration of alluvial sand towards the karstic cavities were the main subsidence mechanisms responsible for the structural damage aggravated by the poor quality of the buildings and the geotechnical behaviour of the supporting ground

the early andean magmatic province eamp 40ar 39ar dating on mesozoic volcanic and plutonic rocks from the coastal cordillera northern chile abstract the early andean magmatic province eamp consists of about 150 000 km 3 of volcanic and plutonic units in the coastal cordillera of northern chile and southern peru and represents a major magmatic mesozoic event in the world for which the precise age of the thick volcanic series was unknown thirty 40 ar 39 ar analyses were carried out on primary mineral phases of volcanic and plutonic rocks from northern chile 18 30 24 s reliable plateau and mini plateau ages were obtained on plagioclase amphibole and biotite from volcanic and plutonic rocks despite widespread strong alteration degree in the arica tocopilla and antofagasta 700 km apart regions the ages obtained on lava flows constrain the volcanic activity between 164 and 150 ma and no n s migration of volcanism is observed the uppermost lava flows of the volcanic sequence at the type locality of the la negra formation extruded at ca 153 150 ma suggesting the end of the volcanic activity of the arc at that time the oldest volcanic activity occurred probably at ca 175 170 ma in the iquique area although no plateau age could be obtained the plutonic bodies of the same regions were dated between ca 160 and 142 ma indicating that they were partly contemporaneous with the volcanic activity at least one volcanic pulse around 160 ma is evidenced over the entire investigated reach of the eamp according to the ages found in arica tocopilla michilla and mantos blancos regions the episodic emplacement of huge amounts of subduction related volcanism is observed throughout the whole andean history and particularly during the jurassic southern peru northern chile and southern argentina these events probably correspond to periodic extensional geodynamic episodes as a consequence of particular subduction conditions such as change of obliquity of the convergence change in the subduction angle slab roll back effect or lower convergence rate that remain to be precisely defined

hydrogeological characterization and modelling of weathered karst aquifers applicability to dewatering operations in limestone quarries limestone aquifers represent an important part of groundwater resources in the world they are usually considered as fractured karstic rock formations however a different type called weathered or ghost rock karst aquifer has recently been highlighted in this particular type of aquifer the karst is not expressed as open conduits but consists in zones made of a residual alterite resulting from the in situ partial dissolution of limestone these particular structures are crucial in some areas because they actually govern groundwater flow and transport in the aquifer they have however never been studied from a hydrogeological perspective in this study we present a methodology to characterize and model such aquifers results show that the ghost rock features are usually organized into networks and that their hydraulic properties are variable within each feature according to the limestone weathering intensity measurements in a specific aquifer in belgium are presented the modelling approach derived from the common equivalent porous medium approach enables to spatially distribute the variable hydraulic properties within the features from the hard fresh rock to the alterite in finite difference grids the method allows creating models including thousands of features and respecting correct connectivity relations the approach is considered at different scales with varying grid cells sizes results show that the induced error increases significantly when the size of the grid cells exceeds the width of the main features controlling flow the approach is applied on a case study consisting in dewatering operations in an exploited quarry located in a weathered karst aquifer presented results provide new insights regarding characterization and modelling of this kind of aquifers and highlight their importance in hydrological studies

mapping a bedrock surface under dry alluvium with shallow seismic reflections shallow seismic reflection techniques were used to image the bedrock alluvial interface near a chemical evaporation pond in the texas panhandle allowing optimum placement of water quality monitor wells the seismic data showed bedrock valleys as shallow as 4 m and accurate to within 1 m horizontally and vertically the normal moveout velocity within the near surface alluvium varies from 225 m s to 400 m s all monitor well borings near the evaporation pond penetrated unsaturated alluvial material on most of the data the wavelet reflected from the bedrock alluvium interface has a dominant frequency of around 170 hz low cut filtering at 24 db octave below 220 hz prior to analog to digital conversion enhanced the amplitude of the desired bedrock reflection relative to the amplitude of the unwanted ground roll the final bedrock contour map derived from drilling and seismic reflection data possesses improved resolution and shows a bedrock valley not interpretable from drill data alone

natural gas association with water and oil as depicted by atmospheric noble gases case studies from the southeastern mediterranean coastal plain a model for the equilibrium distribution of atmospheric noble gases ang between natural gas and water phases was extended to include the gas oil relationship the basic assumption is that the ang are introduced into hydrocarbon systems via recharge or seawater theoretical ang patterns of natural gas at equilibrium with water fall between the air pattern and that of air saturated water theoretical ang patterns of natural gas degassed from oil which had previously equilibrated with a water phase cover a wide range including the range calculated for gas water equilibration ang patterns in natural gas which fall outside the overlapping range may thus indicate association of the gas with oil the model was tested in the case of hydrocarbon systems of the southeastern mediterranean coastal plain other geochemical evidence indicates that the ashdod sadot shallow gas wells are not related to oil the relative ang abundances in gas samples from these wells lie within the range predicted for gas water association the relative ang abundances in samples degassed from oils of the helez kokhav oilfield are similar to specific patterns predicted for the degassing of oil which was previously associated with water published and new analyses of methane dominated natural gas samples from california japan and northern israel also reveal ang patterns of the type predicted by the model the results of the case studies support our hypothesis that water is responsible for transport of atmospheric noble gases into subsurface hydrocarbon systems this forms the basis for identification of oil associated natural gases via ang study

stable isotope geochemistry of cold co2 bearing mineral spring waters daylesford victoria australia sources of gas and water and links with waning volcanism abstract mineral springs in the victorian central highlands australia have high co 2 contents and naturally effervesce 13 c values of co 2 gas and dissolved inorganic carbon are 10 6 to 7 0 and 5 9 to 0 1 respectively with a net 13 c of 8 to 3 the carbon in these waters was derived from a mantle source associated with local pliocene to recent basaltic newer volcanic province rocks previously reported 3 he 4 he 1 2 3 1 relative to air and high he ne ratios are also consistent with the presence of magmatic volatiles silica contents imply that the waters were never heated above 130 c and that the system is not hydrothermal the occurrence of carbonated mineral springs in a relatively small region of the newer volcanics province where volcanic activity ceased several thousands of years ago may be due to the presence of late intrusions combined with deep circulation of water through deeply weathered and fractured ordovician basement a region of low seismic velocity under the daylesford area potentially images those intrusions most spring waters have 18 o and 2 h values of 8 to 6 and 45 to 35 respectively and lie to the left of the local and global meteoric water lines the anomalously low 18 o values results from co 2 exsolution at low temperatures which strongly partitions 18 o into the gas the lack of waters lying to the right of the local meteoric water line also implies that water rock interaction at elevated temperatures did not occur the 2 h values are lower than contemporary meteoric water suggesting that the waters may have recharged under colder climate conditions several thousand years ago the local ordovician rocks are gold bearing the present spring system is cold and would not efficiently transport au however volcanic is waning and the spring systems at the time of volcanism may have been hotter and able to redistribute au

trench parallel shortening in the northern chilean forearc tectonic and climatic implications in the central andes the frictional coupling between south america and the subducting nazca plate occurs beneath the coastal cordillera of northern chile one of the most distinctive characteristics of the coastal cordillera is a suite of ew topographic scarps located between 19 and 21 6 s latitude these scarps are associated with predominantly south dipping reverse faults that have almost pure dip slip and produce shortening parallel to the plate boundary limited geochronology as well as more regional studies indicate that the scarps formed during the late miocene and early pliocene though some show activity extending into the quaternary in several areas the scarps dammed local drainages producing internally drained basins that accumulated evaporites this relationship indicates that the coastal cordillera was probably moister during the late miocene and pliocene than it is today and also indicates that the coastal cordillera has been significantly uplifted or that the coastal escarpment of northern chile has advanced significantly eastward since the pliocene the limited latitudinal extent of the ew scarps and their location symmetrically about the axis of topographic and wadati benioff zone symmetry suggest that they owe their origin to the concave seaward shape of the continental margin due to prior formation of the bolivian orocline

origin of carbon in fumarolic gas from island arcs abstract we have measured 3 he 4 he ratios 13c values and co 2 3 he ratios of fumaroles and hot spring gases in three volcanic areas in japan the 3 he 4 he ratios 13c values and co 2 3 he ratios vary from 02 05 ratm 9 7 to 2 7 and from 7 74 109 to 1 18 1011 respectively based on these data and those in the literature we present the first quantitative estimates of the upper mantle sediment and limestone including slab components in co2 of volcanic and hydrothermal fluids from subduction zones taking compiled c isotopic data of limestone and organic sediment assuming that the co 2 3 he ratio and 13c value of mid ocean ridge basalt morb are representative of the upper mantle component and that later isotopic and elemental fractionations are minimal it is possible to deconvole each fraction of c on the basis of simple mixing equations up to 20 of the carbon in high temperature volcanic gases in subduction zones is derived from a morb type source while the major fraction of the gases is attributable to co2 produced by decarbonation of subducted marine limestone and slab carbonate

sustainable development and anthropogenic induced geomorphic hazards in subsiding areas in many areas of the world subsidence related to the lowering of the water table is modifying the landscape and provoking costly environmental hazards this article is protected by copyright all rights reserved we consider the dead sea the earth s lowest lake as a model its water level was 395 m bmsl in the 1960s due to water diversions in the catchment area as of 2016 the level has dropped to about 430 m bmsl here as in other parts of the anthropocene world from china to iran to turkey to canada and the united states consequences of human interventions are rapidly modifying the environment aggressive geomorphic processes leading to accelerated degradations are taking place and affecting landforms and infrastructures this article is protected by copyright all rights reserved in tectonic terms the lake is a pull apart basin resulting from the motion of the dead sea transform fault since the 1960s a slice of brine of about 35 km3 had been lost the water table is dropping more rapidly in the lake than in the coastal zone creating an ever increasing head difference consequently groundwater moves towards the sea to compensate for the imbalance provoking the reactivation of the area s paleo channels with subsidence sinkholes and landslides this article is protected by copyright all rights reserved since the 1980s industrial touristic infrastructure has covered newly emerging lands in geomorphic hazards prone areas of the coastal zone this article is protected by copyright all rights reserved time series analysis of high to very high resolution visible radar satellite images acquired from the 1970s to present revealed major landscape evolution such dynamic systems prevailing in the last decades permitted the study of human environment interactions to help minimizing their effects this article is protected by copyright all rights reserved major deformations of an industrial dike were analysed and quantified the results underline the necessity in the anthropocene of careful analysis of relevant data sources acquired before and during subsidence particularly in karst topography zones and prior to the development of major human activities in economically appealing environments around the world this article is protected by copyright all rights reserved

a multicriteria approach to karst subsidence hazard mapping supported by weights of evidence analysis soil subsidence collapse is a major geohazard occurring in karst regions it occurs as suffosion or dropout sinkholes developing in the overburden overlying karst less frequently it corresponds to a breakdown of karst void ceiling i e collapse sinkhole this hazard can cause significant engineering challenges therefore decision makers require the elaboration of methodologies for reliable predictions of such hazards e g karst subsidence susceptibility and hazards maps planning strategies priority areas for detailed investigations this study aims at developing a methodological framework for the evaluation of potential conditioning factors controlling the occurrence of sinkholes in a context of limestone karst potential conditioning factors are first determined based on underlying physical processes for different geological contexts barren and mantled karsts then the relevance of each factor is evaluated against a set of representative karst subsidence locations using the weight of evidence theory and relevant factors are tested for independence relevant and independent factors are finally weighed and combined together i e superimposed to achieve karst subsidence susceptibility models the best model i e the one showing the highest predictability is determined by a receiver operating characteristic roc curve analysis which is performed using a set of independent and representative karst subsidence locations the method is applied to one case study where mantled karst setting prevails val d orleans south of paris results show higher susceptibility in mantled karst with significant role of the overburden lithology presence absence of low permeability layer and position of the karst piezometric surface within the overburden the limited area of barren karst shows a low susceptibility although this approach was developed for a specific karst context it can easily be replicated in other karst contexts e g interstratal karst chalk or evaporitic karsts which are known to be highly susceptible to karst subsidence even if some of the conditioning factors will be different

doline probability map using logistic regression and gis technology in the central ebro basin spain in the surroundings of zaragoza karstification processes are especially intense in covered karst areas where fluvial terraces lie directly on tertiary evaporites since the beginning of quaternary these processes have lead to the development of collapse and subsidence dolines with a wide range of sizes which have significant economic impacts to reduce economic impact and increase safety a regional analysis of this phenomenon is needed for spatial management therefore a probability map of dolines was developed using logistic regression and geographic information system gis techniques this paper covers the selection of input data manipulation of data using the gis technology and the use of logistic regression to generate a doline probability map the primary variable in the doline development in this area is geomorphology represented by the location of endorheic areas and different terrace levels secondary variables are the presence of irrigation and the water table gradient

helium and neon isotope systematics in carbon dioxide rich and hydrocarbon rich gas reservoirs the isotopic compositions and elemental abundances of helium and neon were measured in three natural gas reservoirs in the pannonian sedimentary basin of hungary kismarja a co2 rich reservoir and szeghalom south and szeghalom north both ch4 dominated reservoirs are located on topographic basement highs close to the derecske sub basin in eastern hungary mantle derived neon has been identified in mixed ch4 co2 reservoirs in the vienna basin austria this study establishes that mantle derived neon and helium are a characteristic feature of gas reservoirs throughout the neogene extensional basins of hungary and austria regardless of the dominant active gas composition 3he4he ratios within these samples are attributable to a two component mixing between mantlederived and crustal radiogenic helium the percent contribution of mantle derived 4he varies from 2 3 to 17 in contrast neon isotopic ratios indicate that the gases contain a significant component of atmosphere derived neon in addition to the mantle and crustal derived components 20ne 21ne and 22ne abundances can be corrected for this atmospheric contribution calculated contributions of mantle and crustal derived 21ne are between 3 6 21 and 1 37 respectively 20ne22nec and 21ne22nec ratios derived for these atmosphere corrected components correlate with measured r ra values and plot along a single two component mixing line between crustal and mantle isotopic endmembers this is consistent with a model in which simple mixing occurs between crustal and mantle endmembers with fixed he ne ratios the mixing line is defined by a hyperbolic constant k where k 4he22ne rad 4 he22ne mntl with a mean value of 67 3 11 8 based on estimated values of 0 47 for 21ne22nerad and 1 62 0 03 107 for 4he21ne rad kennedy et al 1990 values of 7 61 106 for he22ne rad and 11 3 104 for 4he22ne mntl can be calculated for the pannonian basin gases this 4he22ne mntl value is indistinguishable within error from the value of 8 04 104 calculated for rare gases in natural gases from the vienna basin these results clearly establish that the continental expression of mantle derived rare gases in continental extensional systems in austria and hungary is distinct and consistently different from that of gases discharging at the spreading ridges where best estimates of 4he22ne mntl are 8 1 11 3 times higher 9 10 105 staudacher et al 1989 given the remarkable agreement in the continental expression of mantle derived gases throughout the pannonian and vienna basins it is difficult to attribute the observed neon enrichment helium depletion with respect to morb gases to fractionation related to lithospheric transport processes kinetic fraction ation processes involved in transport through the crust might be expected to produce a much wider variation in the observed he ne elemental ratios the consistent order of magnitude neon enrichment observed throughout these gas fields instead implies that mantle derived fluids in these continental extensional systems may be sourced in a region of the mantle distinct from that supplying the mid ocean spreading ridges

evaluating and comparing methods of sinkhole susceptibility mapping in the ebro valley evaporite karst ne spain abstract multiple sinkhole susceptibility models have been generated in three study areas of the ebro valley evaporite karst ne spain applying different methods nearest neighbour distance sinkhole density heuristic scoring system and probabilistic analysis for each sinkhole type separately cover collapse sinkholes cover and bedrock collapse sinkholes and cover and bedrock sagging sinkholes the quantitative and independent evaluation of the predictive capability of the models reveals that 1 the most reliable susceptibility models are those derived from the nearest neighbour distance and sinkhole density these models can be generated in a simple and rapid way from detailed geomorphological maps 2 the reliability of the nearest neighbour distance and density models is conditioned by the degree of clustering of the sinkholes consequently the karst areas in which sinkholes show a higher clustering are a priori more favourable for predicting new occurrences 3 the predictive capability of the best models obtained in this research is significantly higher 12 5 82 5 than that of the heuristic sinkhole susceptibility model incorporated into the general urban plan for the municipality of zaragoza although the probabilistic approach provides lower quality results than the methods based on sinkhole proximity and density it helps to identify the most significant factors and select the most effective mitigation strategies and may be applied to model susceptibility in different future scenarios

probabilistic sinkhole modelling for hazard assessment a method for quantitatively assessing sinkhole susceptibility spatial probability and hazard spatio temporal probability has been developed and independently tested in a 50 km2 sector of the ebro valley evaporite karst three genetic types of sinkholes have been mapped in the floodplain and a terrace surface 947 small cover collapse sinkholes type 1 terrace large collapse sinkholes type 2 floodplain and large subsidence depressions type 3 floodplain the type 1 sinkhole inventory includes two temporal populations 447 sinkholes formed before 24 november 2005 and 500 between that date and 2 november 2006 sinkhole susceptibility models have been elaborated analysing the statistical relationships between the sinkholes of the 2005 inventory and a set of potential conditioning factors the independent evaluation validation of the susceptibility models by means of several strategies random sequentially excluded and temporal has allowed us to select the most significant variables for each sinkhole type and assess quantitatively the quality of models which are reasonable for the three sinkhole types validation has also provided information on the contribution of specific variables and the effect of changing their accuracy to the prediction capability of models susceptibility models for type 3 sinkholes have been validated satisfactorily with the 2006 sinkhole inventory temporal validation the best susceptibility model has been transformed into a hazard map considering the frequency of sinkholes that occurred in each susceptibility class between 2005 and 2006 as well as their average size the susceptibility and hazard models obtained could be used as an objective basis for the application of mitigation measures either of preventive or corrective nature copyright 2008 john wiley sons ltd

layer cake depth conversion part i in areas of uniform lithology which have not undergone tectonic inversion or severe structural deformation depth conversion can often be performed according to some simple mathematical function e g average velocity as a linear function of depth in areas where there are dramatic changes of velocity such as thick carbonate or evaporite units alternating with thick clastic units as those found in the southern north sea basin then simple functions cannot adequately cope with the inherent velocity inversions and are inadequate for depth conversion

actual extension of sinkholes considerations about geophysical geomorphological and field inspection techniques in urban planning projects in the ebro basin ne spain abstract aerial photographs historical cartographies and field inspection are useful tools in urban planning design on mantled karst because they permit a wide time interval to be analyzed in the case of zaragoza city several works have confirmed the interest of these approaches in configuring the urban planning code and therefore represent a promising technique nevertheless some caveats should be taken into account when using this kind of information a detailed analysis is presented comparing in a case study from the surroundings of zaragoza geomorphological historical analysis and field inspection with geophysical data field inspection in a noncultivated area permits the constraint of the presence of karst indicators below the geomorphological resolution of aerial photographs and shows results consistent with geophysical surveys the studied case shows an inner zone coinciding with the sinkhole mapped from aerial photographs that correlates with changes in the position of the substratum and changes in thickness of alluvial sediments the integrated analysis permits us to define an external subsidence ring around the geomorphological sinkhole whose surface is twice the size of the inner zone this outer ring is indicated by geometrical changes in gpr profiles increases of thickness of the conductive shallower unit toward the collapse and small collapses on marginal cracks these results support the higher extension of karst hazards linked to sinkholes with respect to their geomorphological expression and the needed detailed analysis to constrain the real sinkhole size or the use of security radii surrounding this surficial evidence when geomorphological data is used for the hazard analyses or the urban planning at karstic zones

abrupt change in the dip of the subducting plate beneath north chile no large tsunamigenic earthquake has occurred in north chile since 1877 and the region has been largely recognized as a mature seismic gap1 2 3 4 5 6 7 8 9 at the southern end of the seismic gap the 2007 mw 7 7 tocopilla earthquake ruptured the deeper seismogenic interface whereas the coupled upper interface remained unbroken4 6 7 seismological studies onshore show a gently varying dip of 20 to 30 of the downgoing nazca plate3 6 which extends from the trench down to depths of 40 50 km here we study the lithospheric structure of the subduction zone of north chile at about 22 s using wide angle seismic refraction and reflection data from land and sea complemented by hypocentre data recorded during the 2007 tocopilla aftershocks7 our data document an abrupt increase in the dip of the subducting plate from less than 10 to about 22 at a depth of approximately 20 km the distribution of the 2007 aftershocks indicates that the change in dip acted as a barrier for the propagation of the 2007 earthquake towards the trench which in turn indicates that the subduction megathrust is not only segmented along the trench but also in the direction of the dip we propose that large magnitude tsunamigenic earthquakes must cross the barrier and rupture the entire seismogenic zone

intraplate deformation in central australia the link between subsidence and fault reactivation abstract central australia has experienced two intraplate orogenic events involving significant north south shortening the late neoproterozoic to early cambrian petermann orogeny and the devonian to carboniferous alice springs orogeny in each event pre existing structures inherited from mesoproterozoic terrain amalgamation were reactivated and basement rocks exhumed from beneath thick sedimentary successions accumulated in the centralian superbasin the pattern of fault reactivation during these events shows a striking similarity to the pattern of subsidence in the overlying basin immediately prior to the petermann orogeny the centralian superbasin was thickest in the vicinity of the musgrave block the region in which deformation was subsequently localised at the same time crustal scale faults elsewhere in central australia that were covered by a relatively thin sheet of sediment remained inactive despite being favourably oriented to accommodate the north south shortening between the petermann and alice springs orogenies subsidence patterns shifted such that fault systems in the arunta block and also those in the southern musgrave block were buried by significant thicknesses of sediment whereas the major structures that were exhumed during the petermann orogeny were not significantly buried during the alice springs orogeny reactivation once again occurred along the most deeply buried faults even in the instances where those faults had remained inactive during the earlier petermann orogeny importantly the major petermann aged structures that were not buried during renewed subsidence remained inactive during the alice springs orogeny the record of reactivation implies that the presence of pre existing crustal scale faults alone was insufficient to localise deformation rather fault reactivation appears to have required a priming process that modulated the strength of the lithosphere on a regional scale the correspondence between the distribution of basement fault reactivation and subsidence patterns during both the petermann and alice springs orogenies implies a link between relatively thick sedimentation and long term lithospheric weakening we show that this link is compatible with the thermal effects of a thick sedimentary blanket in the context of central australia the mechanical impact of basin formation is likely to be enhanced by the presence of regionally elevated heat production in the proterozoic basement

the andean orogenic period and its major structures in central and northern peru the andean orogenic period began in the albian and consisted of at least 6 discrete compressional phases which are albian to late miocene in age deformation migrated progressively toward the amazonian foredeep the major andean structures in central and northern peru are related to the eocene incaic early miocene quechua 1 and late miocene quechua 3 phases the maranon thrust and fold belt mtfb which bounds the western cordillera to the ne rose in the eocene it was reactivated partly by the quechua 1 phase which also folded the altiplano farther e and possibly part of the eastern cordillera the sub andean thrust and fold belt stfb is related to the quechua 3 phase in both mtfb and stfb the imbricate thrusts merge at depth in large decollement faults gravity sliding does not play a dominant role for these faults have to be rooted westward in the pre andean basement the corresponding crustal shortening played a significant part in the creation of the sialic root of the andes

volcano tectonic setting of the intraplate pliocene holocene newer volcanic province southeast australia role of crustal fracture zones 1 the pliocene holocene newer volcanic province in victoria southeast australia is a wide volcanic field site of the most recent volcanic activity of australia the intraplate signature and the localization on the northern side of the southern ocean have been used in the past to ascribe the volcanic activity either to the presence of a mantle hot spot or to thermal anomalies inherited from the seafloor spreading that separated australia from antarctica during the gondwana breakup the spacing and distribution of groups of eruption points suggests the presence of a 32 km deep mantle thermal anomaly alignments of eruption points indicate a strong tectonic control on magma emplacement mainly along nw se mesozoic cenozoic structures and along n s palaeozoic and e w late cretaceous structures this volcano tectonic setting relates to the interference of the left lateral kinematics of the major n s trending faults associated with the tasman fracture zone and the extensional structures of the otway basin this interpretation is also coherent with stress in situ data and focal mechanisms of earthquakes shmax oriented n150 this interpretation enhances the role of the tasman fracture zone a major sinistral transform on the reactivation of transtensional structures and on triggering the magmatism of the newer volcanic province

development and validation of sinkhole susceptibility models in mantled karst settings a case study from the ebro valley evaporite karst ne spain abstract a preliminary sinkhole susceptibility analysis has been carried out in a stretch 50 km 2 in area of the ebro valley alluvial evaporite karst ne spain a spatial database consisting of a sinkhole layer and 27 thematic layers related to causal factors was constructed and implemented in a gis three types of sinkholes were differentiated on the basis of their markedly different morphometry and geomorphic distribution large subsidence depressions 24 large collapse sinkholes 23 and small cover collapse sinkholes 447 the susceptibility models were produced analysing the statistical relationships between the mapped sinkholes and a set of conditioning factors using the favourability functions approach the statistical analyses indicate that the best models are obtained with 6 conditioning factors out of the 27 available ones and that different factors and processes are involved in the generation of each type of sinkhole the validation of two models by means of a random split strategy shows that reasonably good predictions on the spatial distribution of future dolines may be produced with this approach around 75 of the sinkholes of the validation sample occur on the 10 of the pixels with the highest susceptibility and about 45 of the area can be considered as safe

age of supergene oxidation and enrichment in the chilean porphyry copper province twenty five samples of supergene alunite collected from deeply developed supergene profiles in porphyry copper deposits and prospects between latitudes 20 degrees and 27 degrees s in northern chile yield k ar ages ranging from about 34 to 14 ma therefore supergene oxidation and enrichment processes were active from the early oligocene to the middle miocene a minimum of 20 m y supergene activity at individual deposits lasted for at least 0 4 to 6 2 m y the early oligocene supergene activity affected deposits in the paleocene porphyry copper belt whereas early and middle miocene supergene processes are documented in the early cretaceous paleocene and late eocene to early oligocene porphyry copper belts middle miocene oxidation also affected the oldest epithermal gold silver deposits in the maricunga belt farther east supergene activity commenced no less than 11 m y after generation of each porphyry copper deposit because of the time required to unroof the copper bearing parts of the system supergene activity throughout northern chile ceased at approximately 14 ma the geologic features of deposits and prospects and their morphotectonic positions present latitudes and present elevations display no obvious correlations with the supergene chronology exploration for major cumulative enrichment blankets should not be carried out either beneath thick sequences of piedmont gravels or ignimbrites of oligocene through middle miocene age unless their accumulation is demonstrably late in the documented history of supergene activity or in porphyry copper provinces such as those of central chile and northwestern argentina which formed after approximately 14 ma the uplift responsible for efficient cumulative copper enrichment is difficult to correlate convincingly with the brief pulses of compressive tectonism postulated for northern chile and contiguous areas unless their effects were much more prolonged intensifying aridity is confirmed as the likely reason for the cessation of supergene activity in northern chile and tectonic uplift was its most probable cause however more fundamental global controls producing a period of chemical weathering followed by worldwide dessication also may have played a role

assessing the risk of subsidence of a sinkhole collapse using ground penetrating radar and electrical resistivity tomography abstract in segovia province spain there are numerous carbonate rock outcrops that are affected by karstification processes in which there are numerous galleries caves and sinkholes this is the case of the sima de madrona a sinkhole collapse caused by the sinking of dolostone the objective of this study was to ascertain the existence and the characteristics of cavities and galleries as well as to evaluate the risk of subsidence in the area by applying shallow and non invasive geophysical techniques ground penetrating radar and electrical resistivity tomography the joint combination of these two independent shallow geophysical techniques has provided the best combination of investigation depth up to 8 m and resolution needed to image small to medium 1 to 4 m size cavities the associated risks are evident because the cavities found herein affect various anthropic structures a highway and crop fields

sinkhole formation above underground limestone quarries a case study in south limburg belgium abstract historical records were used for the compilation of a database of sinkholes resulted from collapses of abandoned shallow underground limestone quarries mines in two villages in belgian south limburg during the last 350 years the formation of such sinkholes caused at least 38 casualties but more often it caused a change in topography and damage to public and private property the objective of this study is to better understand the spatial and temporal patterns of quarry collapse related sinkholes in the study area apart from sinkhole locations and ages the compiled database provides information on the dimensions of the area affected and the damage caused by sinkhole formation as well as the causal factors of sinkholes one hundred seventy three sinkholes have been reported since 1665 but most 80 reported sinkholes postdate 1965 sinkhole dimensions provided information on the type of collapse seven large sinkholes displacing a total sediment volume of 480 000 m3 resulted from large scale roof breakdown after pillar failure the smaller sinkholes were the result of fall of the overburden into galleries after local roof collapse or suffosion of a solution pipe in total these small sinkholes displaced 12 300 m3 of sediment at present almost all large underground quarries in the study area have been affected by sinkholes these features were caused by natural and anthropogenic factors and occur in zones with thin roofs where pillars were affected by pillar robbing or on locations with inappropriate sewerage systems above quarries the formation of sinkholes was often reported in spring during years with high moisture contents in the overburden caused by high groundwater recharge or above average precipitation with increasing time since quarry abandonment quarries become more susceptible to pillar creep and bending of the roof hence if no appropriate mitigation measures are taken to reduce such deterioration processes the number of sinkholes is expected to increase

seismic stratigraphy and structural analysis of the northern east china sea shelf basin interpreted from multi channel seismic reflection data and cross section restoration analysis of multi channel seismic data from the northern east china sea shelf basin ecssb reveals three sub basins socotra domi and jeju basins separated by structural highs hupijiao rise and faulted basement blocks these sub basins show a typical rift basin development faulted basement and syn rift and post rift sedimentation separated by unconformities four regional unconformities including the top of acoustic basement have been identified and mapped from multi channel seismic data faults in the acoustic basement are generally trending ne parallel to the regional structural trend of the area the depths of the acoustic basement range from less than 1000 m in the northwestern part of the domi basin to more than 4500 m in the socotra basin and 5500 m in the jeju basin the total sediment thicknesses range from less than 500 m to about 1500 m in the northwest where the acoustic basement is shallow and reach about more than 5500 m in the south interpretation of seismic reflection data and reconstruction of three depth converted seismic profiles reveal that the northern ecssb experienced two phases of rifting followed by regional subsidence the initial rifting in the late cretaceous was driven by the nw se crustal stretching of the eurasian plate caused by the subduction of the pacific plate beneath the eurasian plate extension was the greatest during the early phase of basin formation estimated rates of extension during the initial rifting are 2 6 5 and 3 5 in the domi jeju and socotra basins respectively a regional uplift terminated the rifting in the late eocene early oligocene rifting and extension although mild resumed in the early oligocene while fluvio lacustrine deposition continued to prevail the estimated rates of extension during the second phase of rifting are 0 7 0 8 and 0 5 in the domi jeju and socotra basins respectively a second phase of uplift in the early miocene terminated the rifting marking the transition to the post rift phase of regional subsidence regional subsidence dominated the study area between the early miocene and the late miocene an inversion in the late miocene interrupted the post rift subsidence resulting in an extensive thrust fold belt in the eastern part of the area uplift and subsequent erosion were followed by regional subsidence highlights this paper presents 2d seismic mapping of the northern east china sea shelf basin structural and stratigraphic evolution of the basin have been investigated we have also reconstructed three depth converted seismic reflection profiles cross section restoration provided quantitative information about extension rates

tectonic and magmatic evolution of the andes of northern argentina and chile abstract two orogenic cycles both with different evolution are developed in the western margin of the south american continent in northern argentina and chile the paleozoic hercynic cycle and the meso cenozoic andean cycle the hercynic cycle a wide marine basin extending westward of the cordillera oriental which developed in cambrian ordovician times marks the beginning of this cycle in contrast to peru and bolivia where this basin developed between two precambrian blocks the western margin of this basin in northern argentina and chile is still unknown the ordovician sedimentation and accompanied volcanism ends with the ocloyic deformation phase and its synkinematic granitic plutonism two basins were developed in the silurian devonian separated by the puna arc uplifted during this ocloyic phase the shallow water marine terrigeneous sediments which were deposited in them were deformed by a new tectono magmatic associated phase chanic phase carboniferous to lower permian marine carbonates were deposited west of the puna arc and red beds east of it later on during the permian to triassic a magmatic belt was developed along the cordillera occidental the rhyolites ignimbrites and the granitic to granodioritic related intrusives are well represented in chile although the overall geologic history of this period is known many problems concerning its origin and relations to plate tectonics are still unsolved the andean cycle during this cycle a series of magmatic arc systems related to the subduction of the pacific crust was built up along the western margin of south america huge volumes of calc alkaline lavas and related plutons were emplaced since the jurassic along belts parallel to the present coastline showing a general eastward migration trend up to the lower cretaceous an ensialic back arc basin was formed east of this magmatic arc thousands of meters of marine and continental sediments were deposited in it this basin disappeared during the middle cretaceous probably as a result of the final opening of the atlantic and the active westward movement of the south american plate since middle cretaceous times the magmatic arc has been the fundamental paleogeographic element the arc progressively migrated stepwise eastward each step marked by a tectonic phase subduction related crustal erosion could explain the lack of fore arc petrotectonic assemblages the eastward magmatic polarity which characterizes this section of the andes could also be explained by such a mechanism

a multidisciplinary approach in sinkhole analysis the quinis village case study ne italy abstract during the last recent years in quinis a small village sited in the alta val tagliamento valley friuli venezia giulia region ne italy the inhabitants faced with instability phenomena related to the presence of soluble rocks in the subsurface the evaporite bedrock is mainly mantled in fact by high thickness deposit this paper explains the methodological approach that we used to identify the instabilities in a very complex geo structural environment where the urbanization limits the applicability of several investigation techniques different methods were used to define the bedrock morphology to characterize the mantling deposits and to identify the processes behind what emerged from the study is a mandatory multidisciplinary approach to characterize the subsoil because each technique is not able individually to take to a unique result the data collected allowed to draft a geo hydrogeological conceptual model of the quinis village the lessons learned even if with some site specific dependency demonstrate the importance of broad spectrum investigations which are essential to understand the subsurface characteristics avoiding relevant socio economic impact and supporting an adequate future territorial planning

late pliocene age for the atacama desert implications for the desertification of western south america the atacama desert forms one of the major hyperarid deserts of the world previous studies suggest that desertification commenced at 14 ma during global climate desiccation sedimentologic data from middle miocene to upper pliocene successions in the modern atacama desert indicate that a semiarid climate persisted from 8 to 3 ma punctuated by a phase of increased aridity at ca 6 ma as such hyperaridity did not commence until the late pliocene implications are 1 that the rain shadow generated by the andean cordillera has had a minor influence on climate change and 2 that the upwelling north flowing cold humboldt current although important in establishing the generally arid climate of western south america did not control the shift to hyperaridity the formation of the hyperarid atacama desert in the late pliocene accompanied the development of the current phase of aridification in the sahara and namib deserts and is attributed to a phase of global climate cooling

tectonics of the jurassic early cretaceous magmatic arc of the north chilean coastal cordillera 22 26 s a story of crustal deformation along a convergent plate boundary the tectonic evolution of a continental magmatic arc that was active in the north chilean coastal cordillera in jurassic early cretaceous times is described in order to show the relationship between arc deformation and plate convergence during stage i circa 195 155 ma a variety of structures formed at deep to shallow crustal levels indicating sinistral arc parallel strike slip movements from deep crustal levels a sequence of structures is described starting with the formation of a broad belt of plutonic rocks which were sheared under granulite to amphibolite facies conditions bolfin complex the high grade deformation was followed by the formation of two sets of conjugate greenschist facies shear zones showing strike slip and thrust kinematics with a nw se directed maximum horizontal shortening i e parallel to the probable late jurassic vector of plate convergence a kinematic pattern compatible to this plate convergence is displayed by nonmetamorphic folds thrusts and high angle normal faults which formed during the same time interval as the discrete shear zones during stage ii 160 150 ma strong arc normal extension is revealed by brittle low angle normal faults at shallow levels and some ductile normal faults and the intrusion of extended plutons at deeper levels during stage iii 155 147 ma two reversals in the stress regime took place indicated by two generations of dikes an older one trending ne sw and a younger one trending nw se sinistral strike slip movements also prevailed during stage iv until 125 ma when the atacama fault zone originated as a sinistral trench linked strike slip fault the tectonic evolution of the magmatic arc is interpreted in terms of coupling and decoupling between the downgoing and overriding plates the structures of stages i and iv suggest that stress transmission due to seismic coupling between the plates was probably responsible for these deformations however decoupling of the plates occurred possibly due to a decrease in convergence rate resulting in extension and the reversals of stages ii and iii

mantle derived volatiles in continental crust the massif central of france co2 rich gases and groundwaters from springs and boreholes originating within the basement of the massif central have variable3he 4he ratios with correspondingr ra values ranging from 0 8 to 5 5 and 0 3 to 2 8 respectively indicating the presence of a significant component of mantle helium molar concentrations of rare gases in the co2 rich gases are approximately 5 orders of magnitude greater than in the waters and suggest that a near surface henry s law fractionation has occurred between exsolving co2 and water 13c values of the co2 rich gases are in the range 4 2 to 6 1 i e in that range normally attributed to mantle carbon but which could also represent an average crustal composition and therefore do not discriminate between mantle and crustal sources c 3he ratios show 4 orders of magnitude variation from 1 4 1012 to 5 108 and compared to a mantlec 3he ratio of 109 indicate that either a complex fractionation has occurred between mantle helium and mantle co2 or more likely that mantle rare gases have been diluted by large quantities of co2 with an average crustal carbon isotope composition the regional distribution of3he and c does not show any obvious relationship to age or proximity of volcanic centres or major faults suggesting that mantle derived c and he components decoupled from their silicate melt sources at some depth the results from this area of active fluid circulation suggest that c isotope data derived from metamorphic terrains should be interpreted with great caution but that input of some mantle derived carbon is expected to accompany crustal extension

cover collapse sinkholes in the tournaisis area southern belgium abstract in the tournaisis area southern belgium cover collapse sinkholes have been reported since the beginning of this century in this area the relatively flat lying carboniferous limestone is overlain by an unconformable mesocenozoic cover recent research has shown that these sinkholes developed from reactivated paleokarsts the intensive pumping for domestic and industrial water supply combined with the dewatering due to deep limestone quarries operations resulted in the lowering of groundwater levels this triggered the reactivation of paleokarstic systems and thus the occurrence of cover collapse sinkholes these sudden and unexpected collapses have already had major impacts in the region in 1977 about thirty sinkholes opened up along the escaut river downstream from the city of tournai as a consequence the groundwater was polluted by an extensive loss of river water into the carboniferous aquifer more recently a house and industrial facilities were severely damaged by such cover collapse sinkholes in this context a geoharzard map would be a valuable tool as far as regional development is concerned this points at the importance to develop methods to locate and characterize hidden paleokarsts a study site has been chosen in an area where sinkholes have been opening up for about ten years a geophysical survey of the site which included electrical resistance mapping of the area has shown weakness lineaments these lineaments are parallel to a main fault affecting the region

multidisciplinary approach for urban planning in alluvial karstic zones case study from the central ebro basin spain abstract constructive design on inhomogeneous ground often faces geotechnical problems particularly under ongoing karst processes namely subsidence or collapses careful analysis of this kind of problems by means of different techniques together with accurate geological models is needed for correct urban planning in this work the main results obtained during an urban planning study in the proximities of zaragoza city ne spain are presented several independent approaches give results that can only be clearly interpreted when integrated as a whole the first approach is related to historical geomorphological analysis from maps and series of aerial photographs the second approach is an intensive geophysical survey gpr magnetometry gravimetry em the third approach includes the analysis of subsoil characteristics by means of trenches boreholes and dynamic penetration tests prior studies failed in the correct characterization of this area mainly because of the difficulties in interpreting the obtained data the discussion of this work analyzes the sensitivity of techniques and reliability of the obtained results and the importance of correctly defining the geological geotechnical model the presented methodology responds to the main potential problems to be analyzed in complex alluvial environments linked to karst activity and can be applied in similar contexts where different approaches must be integrated to obtain realistic geological models

karst collapse susceptibility mapping considering peak ground acceleration in a rapidly growing urban area abstract karst collapse occurrences represent a geological hazard that can cause damage to man made structures in the present study a karst collapse susceptibility map was produced using a multivariate statistical method and a geographical information system the case under study is the northern suburbs of athens greece the karstic features of the study area were recorded physical processes slope angle and aspect hydrographic network springs lithology tectonic features along with anthropogenic road network and land use parameters were chosen as major factors affecting the karst collapse occurrences the innovative method was combining karst collapse occurrences with seismic hazard assessment which was achieved by calculating peak ground acceleration pga the pga was determined for a return period of 475 years corresponding to a 90 probability of not being exceeded in 50 years the logistic regression lr method was applied to evaluate these factors slope angle pga lithology and distance to springs and roads were statistically significant for the applied model among these factors the slope angle and pga have a negative effect while the lithology and distance to springs and roads have a positive effect on the karst collapse occurrences the validation of the applied lr model indicated that the results are reliable and that the produced map is accurate the karst collapse susceptibility map was classified into four classes the areas of very high and high susceptibility were observed mainly in the eastern and southwestern parts of the study area almost 30 of the existing urban growth boundary of the study area is located in areas of very high and high susceptibility the karst collapse susceptibility map can be used by planners and engineers for sustainable urban development

time depth relationships for multilayer depth conversion the conversion of seismic time to depth through the use of analytical functions has been a common procedure in seismic work for many decades with the exception of recent examples dealing with the linear function none of the published time depth relationships corresponding to these functions is applicable to multilayer depth conversion the present work redresses this situation it presents formulae applicable to multilayer depth conversion for a large number of analytical functions the derivation is based on a procedure generally similar to that presented by japsen 1993 most of the functions considered date back to a publication by kaufman in 1953 and earlier publications a number of other functions hitherto not known in the industry are also presented

magmatic arc tectonics in the central andes between 21 and 25 s abstract in northern chile four magmatic arc systems each displaced towards the east in relation to the previous one developed in sequence since the lias this migration of the magmatic arc from the coastal cordillera to the western cordillera probably was a consequence of tectonic erosion of the continental margin within each of these systems tectonic deformation took place contemporaneously to magmatic activity as the continental crust of the upper plate has been weakened in the area of the magmatic arc by the igneous processes it is relatively sensitive to the stresses introduced by plate convergence a very important factor for the deformation in the magmatic arc is the angle of convergence obliqueness which may cause shortening if obliqueness is small

coupled tectonic evolution of andean orogeny and global climate abstract the largest tectonic relief breaking the earth s surface 13 km vertically is at the subduction margin of the andes which generates routinely megathrust earthquakes mw 8 5 and drives the paradigmatic andean orogen here we present key geologic evidence to reassess first order features of geomorphology and tectonics across the central andes where the orogen includes the altiplano plateau and attains its maximum integrated height and width the andean subduction margin has a stepped morphology dominated by the low relief atacama bench which is similar to a giant uplifted terrace slopes gently over a width of 60 100 km from the andes to the pacific and runs over more than 1000 km of coastal length we find that the genesis of stepped morphology at the andean seaboard is due to concomitant development of large west vergent thrusts parallel to the subduction interface and increasing aridity in the atacama desert which keeps an unprecedented large scale record of interplaying tectonics and cenozoic climate change incorporating our results with published geological knowledge demonstrates that andean orogeny is characterized by trench perpendicular bivergent and trench parallel bilateral growth over the past 50 myr associated with positive trench velocity toward the continent trench advance and subduction of a wide slab under south america we hypothesize that a global plate tectonic reorganization involving long lasting viscous mantle flow has probably forced both andean orogeny and global climate cooling since 50 ma in contrast two important stepwise pulses of increasing aridity and trench perpendicular andean growth appear to be results of changes in erosion rates due to global late eocene and middle miocene cooling events

influence of geomorphological constraints and exploitation techniques on stone quarry spatial organisation abstract the lutetian limestones were used to build numerous historical monuments in the north east part of france in rheims laon and soissons areas more than 400 underground quarries have been inventoried by research in the regional archives on old maps and by several months of ground prospecting actually most of these underground quarries are abandoned only 3 are now open in the soissons area in the rheims region the last active quarry located at courville village was closed in 2005 because of the safety conditions the aim of the study was to demonstrate the importance of geomorphological context on the fracturing network and on the quarry spatial organisation underground topography fracturing network measurement aerial mapping and analysis of the geomorphological features show the high connection between natural constraints and extraction choices and may explain the progressive disappearance of building stone quarries in a part of the studied area in the east of the studied area where the usable limestone has a weak thickness and important mechanical distension stress the galleries direction depends on fracturing network in contrast in the west soissons area limestone shows thick homogeneous facies that allow a rational extraction using room and pillars mining system

seismic reflection character of the hikurangi subduction interface new zealand in the region of repeated gisborne slow slip events summary we use seismic reflection data to map the geometry and character of the subduction interface in the gisborne area of the hikurangi subduction margin new zealand which experiences repeated shallow 15 km slow slip events the reflection character and geometry in this area is highly variable which we interpret to be related to the subduction of seamounts and underthrust sediments three zones of high amplitude interface reflectivity hrz 1 2 and 3 are interpreted to be the result of fluid rich sediments that have been entrained with subducting seamounts the interface above the hrz zones is shallower than the surrounding areas by 2 4 km due to the warping of the interface to accommodate seamount subduction these zones of high amplitude reflectivity and shallower interface geometry correlate broadly with locations of recorded slow slip events from 2002 to 2008 we hypothesize that effective stresses on the interface may be lower along the northeast margin in areas of high amplitude reflectivity due to 1 the enhanced underthrusting of fluid rich sediment 2 reduced overburden stresses where the interface has been warped to shallower depths to accommodate seamount subduction and 3 potential fluid flow concentration effects leading to overpressure along these shallower interface corrugations from our observations we propose localized reductions in effective stress caused by interface structural relief may be a potential factor in promoting shallow slow slip events

the depositional evolution of diapir and fault bounded rift basins examples from the lusitanian basin of west iberia new data on the evolution of rift basins is presented after analysing the late jurassic stratigraphy of the central lusitanian basin west iberia well outcrop and regional 2d seismic reflection profiles are used to investigate the differences in stratigraphic signature between diapir and fault bounded sub basins during the late jurassic syn rift phase surface rupturing in fault bounded sub basins resulted in the formation of tectonic scarps from which footwall derived gravity flows were sourced in contrast the diapir bounded bombarral alcobaca sub basin evolved as a distal bowl shaped depocentre with an axis located up to 10 km away from its basin margins low gradient marginal slopes developed in the bombarral alcobaca sub basin during the late jurassic rifting while growing salt pillows limited the vertical propagation of basement normal faults differences in tectonic evolution basin physiography and sediment input are the main factors responsible for the distinct sedimentary evolutions recorded in the study area 1 transverse footwall derived sediment fans predominant in fault bounded regions give place to axial southwards prograding fluvial to shallow marine units in the diapir bounded sub basins 2 growing salt pillows absent in the fault bounded sub basins formed barriers to and limited the development of transverse drainage systems

late neogene lacustrine record and palaeogeography in the quillagua llamara basin central andean fore arc northern chile abstract the cenozoic quillagua llamara basin northern chile central andes is an asymmetrical intramassif fore arc basin with a relatively wide northern sector separated from a narrower southward extension by a basement threshold the northern sector was characterised by a noticeable oligocene late neogene alluvial fan and lacustrine dominated deposition which resulted in sequences up to 900 m thick whereas the southern sector was often a bypass zone with thinner fluvial and lacustrine sediment accumulation the basin infill includes two third order alluvial lacustrine unconformity bounded units which include other higher frequency 4th to 5th order sequences the evolution of the late miocene pliocene lacustrine episodes in the quillagua llamara basin was not only controlled by the regional variations from arid to hyperarid palaeoclimate conditions due to the combined influence of the pacific high pressure cell the rain shadow effect exerted by the rising andes and the northward flowing cold oceanic currents but also by a the extensional tectonics and evolution and uplift of the fore arc region which defined the location and size of the depocentres b the resulting basement palaeorelief which affected sediment thickness and facies distribution during the late basin infill episodes and c the tectonic modifications of watersheds water divides and drainage networks in the precordillera which caused considerable changes of water income in the lacustrine systems understanding of this regional tectonosedimentary evolution is a necessary first step before analysing of the low to high order lacustrine sequence changes in the region lacustrine water supply was very sensitive to tectonics even gentle tectonic tilting and uplifting in critical water divide zones could result in changes in water balance in the lacustrine basins and trigger variations in the depositional record the very conspicuous lacustrine regime changes recorded in the quillagua llamara basin infill cannot be considered in themselves conclusive proof of an exclusive climatic forcing since they took place close to either major regional drainage changes or to gentle but noticeable tectonic reactivation in the fore arc region