permian continental basins in the southern alps italy and peri mediterranean correlations the late carboniferous to permian continental successions of the southern alps can be subdivided into two main tectono sedimentary cycles separated by a marked unconformity sealing a middle permian time gap generally estimated at over 10 ma the lower cycle 1 between the variscan crystalline basement and the early permian is mainly characterised by fluvio lacustrine and volcanic deposits of calc alkaline acidic to intermediate composition which range up to a maximum thickness of more than 2 000 m the upper cycle 2 which is devoid of volcanics is mostly dominated through the mid late permian by alluvial sedimentation which covered the previous basins and the surrounding highs giving rise to the subaerial verrucano lombardo val gardena groden red beds up to about 800 m thick the palaeontological record from the terrigenous deposits of both the above cycles consists mainly of macro and microfloras and tetrapod footprints the age of the continental deposits is widely discussed because of the poor chronological significance of a large number of fossils which do not allow reliable datings however some sections are also controlled by radiometric calibrations the comparison with some selected continental successions in southern europe allows to determine their evolution and set up correlations a marked stratigraphic gap shows everywhere between the above mentioned cycles 1 and 2 as in the southern alps the gap reaches the greatest extent during the mid permian near the illawarra reversal geomagnetic event 265 ma in western europe however such as in provence and sardinia the discussed gap persists upwardly to late permian and early triassic or slightly younger times i e to the onset of the alpine sedimentary cycle even though in northeastern spain iberian ranges balearic islands this gap results clearly interrupted by late guadalupian lopingian deposits the above two major tectonosedimentary cycles reflect in our view two main geodynamic events that affected the southern europe after the variscan orogenesis the late carboniferous early permian transformation of the gondwana eurasia collisional margin into a diffuse dextral transform margin and the middle late permian opening of the neotethys ocean with the onset of a generalised extensional tectonic regime and the progressive westward marine ingression

origin and paleoenvironmental reconstruction of phosphorus bearing sandstones of the cambrian xinji formation southwestern margin of the ordos basin china increasing exploration interest in oil and gas hosted by early cambrian strata has focused research efforts on early cambrian sandstones the origin of phosphorus and the paleoenvironment of phosph

from present rivers to old terrigenous sediments the evolution of the drainage system in the eastern southern alps terra nova 22 218 226 2010 abstract the eastern southern alps are presently dominated by southward drainage systems feeding the venetian friulian plain confined to the south of the insubric lineament following the assumption that river sediments reflect in the first instance the rocks outcropping in their catchments the comparison between present fluvial and old terrigenous sediments lets us to evaluate changes in provenance since the late miocene when the basement exhumation along the valsugana thrust system took place as indicated by apatite fission track data this tectonic event determined the onset of the main drainage systems the evolution of which has been depicted tracking the petrographic signatures from the present back to the late miocene provenance data show important episodes of stream piracy and watershed migration in response to tectonic uplift in the southern alps as well as to the messinian salinity crisis and the quaternary glaciations terra nova 00 1 9 2010

lateral extrusion in the eastern alps part 1 boundary conditions and experiments scaled for gravity lateral extrusion encompasses extensional collapse gravitational spreading away from a topographic high in an orogenic belt and tectonic escape plane strain horizontal motion of wedges driven by forces applied to their boundaries in the eastern alps it resulted from 1 an overall northerly compression apulia against eurasia 2 a strong foreland bohemian massif 3 lack of constraint along a lateral boundary carpathian region and 4 a previously thickened gravitationally unstable thermally weakened crust eastern alpine orogenic belt six indentation experiments reproduce lateral extrusion at lithospheric scale the models have two to four lithospheric layers with a mohr coulomb rheology for the upper and a viscous rheology for the lower crust the lithosphere rests upon a low viscosity asthenosphere a broad indenter a narrow deformable area and a weakly constrained eastern margin fullfill as closely as possible conditions in the eastern alps indentation produces both thickening in front of the indenter and escape of triangular wedges lateral variations in crustal thickness become attenuated by gravitational spreading the overall fault pattern includes domains of reverse strike slip oblique normal and pure normal faults strike slip faults in conjugate sets develop serially the narrow width of the deformable area and the strength of the foreland determine the angles between the sets gravitational spreading produces a rhombohedral pattern of oblique and pure normal faults along the unconstrained margin opposite the unconstrained margin the indenter front shows thrusts and folds intersecting with the conjugate strike slip sets a triangular indenter favors spreading high velocity of indentation favors escape high confinement limits lateral motion inhibits spreading and favors thickening lateral extrusion in the eastern alps is best modeled by 1 a weak lateral confinement 2 a broad and straight indenter 3 a narrow width of the deformable area and 4 a rigid foreland crustal thickening lateral escape and gravitational spreading all contribute to the overall deformation

miocene pliocene tectonic evolution of the slovenian periadriatic fault implications for alpine carpathian extrusion models the periadriatic line pal is a remarkable several hundred kilometer long fault system of the alpine orogen its dextral character was documented by several authors using diverse criteria but detailed kinematics and timing of movements had not been investigated along its whole length structural and paleomagnetic measurements mapping and stratigraphic and sedimentological studies have helped to unravel the miocene pliocene evolution of the slovenian segment of the pal brittle deformation was characterized by nw se to n s compression and perpendicular tension deformation has resulted in dextral strike slip faulting folding and tilting of beds the first transpressional event corresponds to the first phase of lateral extrusion of the east alpine western carpathian northern pannonian block in the early miocene 24 17 5 ma after a short period of transtension during the karpatian 17 5 16 5 ma dextral transpression reoccurred during the middle miocene to pliocene and lasted up to the quaternary middle miocene dextral slip can be connected to the second phase of extrusion the highly deformed rocks within the dextral shear zones show variable clockwise sometimes counterclockwise rotations the mechanism of rotation seems to be complex ranging from regional rotation to local folding due to pure or simple shear domino type rotation

sea floor phosphorites along the central california continental margin early to middle miocene phosphorites are patchily distributed along the continental margin of central california at water depths of 200 to 2 000 m between cape san martin and point reyes greater concentrations of phosphorites are present along the lower continental slope off pescadero point on sur knoll and on twin knolls at water depths of 1 000 to 1 400 m no phosphorites were found on cordell bank or in monterey bay nor along the walls of adjacent submarine canyons the dominant mineral of these miocene phosphorites is carbonate fluorapatite francolite associated minerals include glauconite dolomite detrital silicates and minor pyrite most of the central california margin phosphorites are conglomeratic and contain a multitude of microdiscontinuity surfaces implying repeated alternations of deposition erosion reworking and cementation both orthochemical and allochemical phosphorites are recognized petrographically samples from offshore pescadero are mostly oolitic phosphorites whereas those collected from sur and twin knolls are predominantly microsphorites many samples also contain volcanic glass shards as well as opaque organics they have been extensively silicified and are intensely bioturbated sem observations reveal micron size euhedral crystals of apatite that are distinctly hexagonal and commonly are intergrown or stacked indicating in situ precipitation and or recrystallization of an amorphous precursor bacterialike structures were also observed suggesting the possibility of microbially mediated precipitation of apatite geochemically the central california margin samples are typical phosphorites p 2 o 5 content ranges from 11 5 to 31 0 percent and averages 24 4 percent major element si al fe ca mg k c analyses are consistent with published values for phosphorites but do indicate slight relative enrichments trace element concentrations are also typical for marine phosphorites with the exception of mn which is significantly depleted and sr which is greatly enriched whereas uranium values range from 47 to 170 ppm averaging 90 ppm organic carbon values range from 0 45 to 2 65 percent with darker colored phosphorites enriched in organic carbon relative to lighter colored samples the miocene central california margin phosphorites originated primarily by direct physio and or biochemical precipitation of apatite within oxygen depleted near surface sediments although subsequent recrystallization during burial may also have occurred polytaxic paleoceanographic conditions appear to have dominated during phosphogenesis but may have been repeatedly interrupted by episodes of increased oceanic circulation during glacial events times of transition from interglacial to glacial modes are believed to have been critical to phosphogenesis diagenetic formation of these phosphorites occurred along impinging dysaerobic 0 1 1 0 ml l o 2 oxygen minimum zones where internal nutrient recycling may have provided sufficient in situ organic material phosphorous and sufficiently high ph values to allow apatite precipitation central california margin phosphorites are a potential natural resource however their patchy distribution and occurrence at relatively great water depths make them economically less attractive than well known on land accumulations in central california as well as submarine deposits off the southern california shore that occur at much shallower 330 m water depths and in higher concentrations

origin of the lower cambrian phosphatic bed at vassbo sweden an extensive phosphatic bed characterized by a black apatite cemented sandstone is developed in the uppermost part of the lower cambrian formation over the entire vassbo area sweden the thickness of the layer is generally 0 1 m increasing in places to 0 2 m the lower boundary of the bed is transitional to a sandstone the upper boundary displays a contact that is both sharp and irregular with a middle cambrian bituminous black shale the phosphatic bed was diagenetically formed by inorganic in situ precipitation of apatite in a sandstone at a depth of about 0 2 m below the sediment water interface where reducing conditions were developed as a result of oxygen consumption during the degradation of organic matter sulphur isotope data from associated pyrite suggest that organic processes such as bacterial sulphate reduction were also involved in the formation of the phosphatic bed the depositional environment of the bed was a marine shelf with a zero to very low sedimentation rate the upper part of the apatite cemented sandstone was partly reworked by bottom currents as demonstrated by a board containing numerous pebbles sedimentological as well as chemical data confirm a southern hemisphere position of the baltic shield in the early cambrian in which an oceanic upwelling and high organic productivity was the probable source of the phosphorus along the palaeo west coast

surface kinematics in the alpine carpathian dinaric and balkan region inferred from a new multi network gps combination solution abstract the understanding of the intraplate tectonics of central europe requires a detailed picture of how stress is transferred from the interaction of the eurasian nubian and anatolian plates to the alpine carpathian pannonian and dinaric regions recent strain distribution is controlled by the adria horizontal push by the vrancea vertical slab pull and associated horizontal displacements and by the aegean anatolia extension and slab roll back we present a horizontal velocity field for the alpine carpathian pannonic dinaric and balkan regions resulting from a new combination of seven different gps networks formed from permanent and campaign stations dedicated velocity profiles in two specific regions are studied in detail one is the alpine pannonian region with a detailed picture of the ns indentation of the adria microplate into the southern alps in ne italy the deformation in the tauern window and the eastwards kinematics of a pannonian plate fragment the second study region includes transylvania the southern carpathians up to the aegean sea and albania where a major right lateral shear deformation exists as a consequence of the ne convergence of the apulia platform towards the dinarids and the ssw motion of macedonia western bulgaria and rumania related to the hellenic arc dynamics in the eastern mediterranean the profiles in the alpine pannonian area indicate that a velocity drop of 2 5 0 4 mm yr associated with the adria indentation concentrates on a segment of some 50 km south of the periadriatic fault the deformation becomes extensional by a similar amount just north of the periadriatic fault in the tauern window where the updoming of the tauern window implies vertical motion which could well be associated with surface extension in the ew profile we observe a sudden velocity change of 1 5 0 2 mm yr in 20 km corresponding to the right lateral lavant fault which seems to mark the border between dominant indentation kinematics to the west and dominant extrusion kinematics to the east three profiles are considered in southern and eastern europe one across the lower adriatic sea from apulia in italy to the southern dinarides which enables it to constrain the velocity drop associated with the subduction of the adria microplate into the dinarides to 3 2 0 5 mm yr in 140 km the second profile is longitudinal and constrains the velocity inversion of 7 4 1 0 mm yr in 350 km associated with right lateral shear faults in albania the third profile crosses the transylvania region with a shortening of 2 3 1 0 mm yr in 220 km and the wallachian moesian region up to the chalcidic peninsula in n greece this lower part of the profile implies an extensional stretch of the upper crust of 3 2 0 9 mm yr in 440 km culminating in the hellenic arc strain rate maps are presented in this regional scale showing the excellent agreement between fault plane solutions of crustal earthquakes and the eigenvectors of the gps derived two dimensional strain rate tensor three profiles are considered in the balkan and se carpathians one across the lower adriatic sea from apulia in italy to the southern dinarides which enables to constrain the velocity drop associated to the subduction of the adria microplate into the dinarides to 3 2 0 5 mm yr in 140 km the second profile is longitudinal and constrains the velocity inversion of 7 4 1 0 mm yr in 350 km associated to right lateral shear faults in macedonia a highly seismic region the third profile crosses the transylvania with a shortening2 3 1 0 mm yr in 220 km and the wallachian moesian region up to the chalcidic peninsula in n greece this lower part of the profile implies an extensional stretch of the upper crust of 3 2 0 9 mm yr in 440 km culminating in the hellenic arc

modeling surface gps velocities in the southern and eastern alps by finite dislocations at crustal depths abstract the indentation of the adria plate into the southern and eastern alps is an ongoing collisional process accompanied by seismicity surface and rock uplift and lateral escape we present a 3d quantitative description of the process by combining gps and structural data with an elastic dislocation model horizontal velocities of 70 austrian and italian permanent gps stations in the eastern and southern alps serve as boundary condition on the free surface of an elastic half space containing six rectangular faults each with a uniform slip rate the geometry of the rectangular faults and the slip rate vector are constrained by least squares taking into account the structural setting of the area and the geographic distribution of the velocity data we find that the surface velocities of the order of some mm yr require reverse north side of the tauern window transpressional giudicarie north alpine wrench corridor pustertal dinarides and normal brenner fault slips ranging from 10 to 30 mm yr at crustal depths the regional stress pattern computed from fault plane solutions agrees with the principal directions of our rectangular fault planes the model although constrained by horizontal velocities only predicts a pattern of vertical motion which qualitatively agrees with known phenomena such as the surface uplift in the tauern window area of the order of up to few mm yr if the heat on the shearing fault planes is removed mostly by upwards diffusion the absence of large heat anomalies on the earth s surface suggests for nominal geotherms shear stresses and concentration of subcrustal radiogenic elements that the time of initiation of the slip dates to pliocene hence more recent than late oligocene miocene time of collision of the adria indenter

present day stress field and deformation in eastern austria we analysed fault plane solutions and borehole breakouts in the eastern part of the eastern alps and found a heterogeneous stress field which we interpret as a transition zone of three different stress provinces the western european stress province with nw to nnw sh orientation and mainly strike slip faulting regime the adriatic stress province with a radial stress pattern and thrust faulting to strike slip faulting regime and the dinaric pannonian stress province with ne sh orientation and strike slip faulting regime the western pannonian basin seems to be a part of the transition zone with wnw to nw sh orientation a stress regime stimulating strike slip faulting prevails in the eastern alps the south bohemian basement spur as a major tectonic structure with a high rheological contrast to surrounding units has a strong influence on the stress field and exhibits the highest seismicity at its tip due to stress concentration from a constructed vertical stress orientation profile we found stress decoupling of the northern calcareous alps from the underlying european foreland both the molasse and the flysch helvetic zone are considered as candidates for decoupling horizons due to stress orientation observations and due to their rheological behaviour from seismological and rheological data we suggest a horizontal stress decoupling across the eastern alps caused by a weakened central alpine lithosphere

thermal and tectonic evolution of the southern alps northern italy rifting coupled organic matter maturity analysis and thermokinematic modeling the southern alps were characterized by strong variations both in space and time of heat flow during mesozoic rifting the regional thermal history was reconstructed using organic matter om maturity data from outcropping sediments one dimensional 1 d thermal modeling performed on selected successions suggests that om maturity was mainly controlled by high geothermal gradients heat flow peaks of 85 to 105 mw m2 in the middle jurassic and differential burial during norian early jurassic extensional phases the results of 1 d modeling show an eastward increase of heat flow peak values these results were compared with those obtained with two dimensional 2 d thermokinematic models the models show a time shift ca 10 ma in the heat flow peak aalenian bajocian for 2 d and bajocian for 1 d modeling however the bajocian age was a priori imposed on 1 d models available geochemical data could be fitted assuming aalenian bajocian peak ages consequently this misfit is not alarming the eastward increase in heat flow peak values is tentatively explained with an eastward increase of radiogenic heat production in the crust instead of with differential stretching the comparison of paleothermal data and numerical modeling was done to gain knowledge on the potentials and limitations of numerical modeling in frontier areas although some differences do exist in the results of geochemical and thermokinematic models we can conclude that if a reasonable knowledge of the thermal parameters of both covers and basement is available thermokinematic modeling can provide useful first order estimates in frontier areas of heat flow and temperature evolution through time

the significance of silica precipitation on the formation of the permeable impermeable boundary within earth s crust the hydrological system within earth s crust is divided into the permeable zone and the underlying much less permeable zone in this study we investigated the solubility and precipitation kinetics of silica in water under the conditions of the kakkonda geothermal field japan where well wd 1a penetrates the boundary between the hydrothermal convection zone and the heat conduction zone we found that quartz solubility has a local minimum at the depth of the hydrological boundary at 3100 m depth 380 c and 24 mpa in the case of either hydrostatic conditions or fluid pressure increase above hydrostatic at deeper levels the hydrothermal experiments reveal that rapid quartz precipitation occurs via nucleation when fluids are brought from the liquid region to the supercritical region the preferential precipitation of quartz at a specific depth plays a significant role in forming and sustaining the permeable impermeable boundary in the crust

natural arsenic contamination in waters from the pesariis village ne italy high arsenic as concentrations 900 g l were measured in ca mg so4 waters from springs and drainages in the village of pesariis in the carnic alps ne italy oxidation of the outcropping arsenian marcasite ore deposits of the area is proposed as the mechanism for as release into oxygenated waters during runoff nevertheless the limited extension of the ore deposit and the relatively low as content of the mineralization suggest that sulfide weathering might not be the only process responsible for the highest as concentration in groundwaters an additional mechanism involves as adsorption onto ferric iron particulate during oxidation the drawdown in reducing environment at depth during water infiltration and the release of ferrous iron and sorbed arsenic to the water columns by reductive dissolution of hydrous ferric oxides hfo this yields the observed fe as correlation newly formed hfo precipitates when groundwaters discharge to aerated conditions leading to the removal of as which strongly partitions into the iron rich sediments adsorbed onto the surface of amorphous fe2o3 xh2o the calculated and measured as concentration in sediments exceeds 10 by weight furthermore geochemical and isotopic data indicate that the as rich reservoir partly mixes with shallower aquifers commonly tapped for drinking supply representing a natural hazard for inhabitants

balancing cross sections with kinematic constraints the dolomites northern italy balancing of structural cross sections is often hindered by a limited database or tectonic complications in such cases kinematic constraints may help to better constrain the construction of a cross section and its extrapolation to depth the kinematic implications of a known structure generally at the surface have to be considered for the unknown structure and for the internal consistency of a cross section a key point is the quantification of shortening of the known structure the extrapolation of this parameter allows balancing in an approximate way emphasizing major structures while minor structures are either neglected or treated in a simplified way with this approach a quick overview can be achieved on how much leeway for interpretation exists critical points for testing various working hypotheses become more evident and the trial and error effort during the construction of a balanced section is considerably shortened still the implications the observed structures have on the deeper crustal levels can be assessed this concept is applied to a section across the italian dolomites a brittle fold and thrust belt lacking reflection seismic data so far and thus with a poorly known deep structure still active south vergent alpine thrusting is oriented approximately perpendicular to previous dinaric thrusting the ramp flat style is dominant due to rheological constrasts within the stratigraphic sequence thanks to kinematic balancing based on surface data three alpine thrust systems could be identified each defining a thrust sheet with its particular basement unit and its sedimentary part superposition of the two more external basement units led to the presently observed high elevation of the triassic sequence in the dolomites shortening since late miocene times amounts to more than 50 km retrodeformation of alpine thrusting is a key for better understanding the previous dinaric structures and kinematics

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

ediacaran cambrian phosphorites from the western margins of gondwana and baltica the late ediacaran mid cambrian occurrence s of phosphorites in the wes tern mediterranean region west gondwana and southern sweden north west baltica are related to the poleward drift of west gondwana and thenorthern drift of baltica as a result these regions crossed subtropical andtemperate palaeolatitudes of the southern hemisphere in which oceanicupwelling and high organic productivity were the probable sources of phos phorus along their western margins a parallel south west north east migra tion trend of evaporites and delayed time transgressive phosphorites pointto distal upwelling environments associated with shallower arid conditions concentration of hardground derived phosphate accumulations took placeby repeated alternations of low sedimentation rates and condensation in situ early diagenetic and microbially mediated precipitation of amorphousand cryptocrystalline carbonate bearing francolite winnowing and poly phase reworking of previously phosphatized skeletons and hardground derived clasts thicker phosphorites of economic importance display aspiculate sponge thromboid consortium that points to a distinct benthiccommunity developed on suboxic slope to basinal substrates for mostphosphorite samples an up to ten fold enrichment in rare earth elementconcentration relative to post archaean average australian shale re ects sig ni cant incorporation of rare earth elements and yttrium after deposition considerable scavenging took place from anoxic pore waters followingreductive dissolution of iron oxides as evidenced from the medium rareearth element enrichment in most samples this contrasts with the rare pre servation of primary sea water features such as cerium depletion andyttrium enrichment in phosphatized thrombolites from the shallower realms for example montagne noire the data are consistent with phosphogenesisafter upwelling and transgression of nutrient rich suboxic anoxic ferrugi nous waters over more oxygenated rifting settings and inland portions of anevolving passive margin

permian triassic boundary magnetostratigraphy from the southern alps italy palaeomagnetic investigations of permian triassic boundary sections in the dolomites provided a magnetostratigraphy for the uppermost part of the permian bellerophon formation to the lower triassic werfen formation magnetite was the dominant magnetic component in most of the samples while the presence of hematite was characteristic for the tesero horizon which is regarded as the immediate permian triassic boundary layer the palaeomagnetic results are consistent with earlier studies of permian and triassic sediments and volcanites in the southern alps the mean characteristic remanence directions indicate deposition and remanence acquisition at a shallow northerly palaeolatitude and a counterclockwise rotation a zone of reversed polarity occurs at the top of the permian sequence and a polarity change from reverse to normal polarity shortly above the base of the werfen formation the onset of a tectonically controlled sedimentary cycle marks the beginning of the basal triassic normal polarity zone which corresponds to most of griesbachian time the record of geomagnetic polarity across the permian triassic boundary confirms the apparent continuity as found by sedimentologic biostratigraphic investigations which emphasise a gradual lithic transition with no evidence for a time gap at the boundary

from rifting to drifting tectonic evolution of the south alpine upper crust from the triassic to the early cretaceous abstract the tectonic evolution of the south alpine rifted margin is discussed on the base of four palinspastic upper crustal profiles extension related to the movements between adria and europe began in the norian after variscan orogeny late carboniferous to middle permian orogenic collapse and continental scale wrenching from the late triassic to the early liassic stretching was mostly limited to the lombardian basin during this time extension was mainly controlled by four major listric faults symmetrically centred around the late carboniferous early permian collio grabens smaller faults which also started in the norian were progressively de activated during the late triassic after the middle liassic faulting in the lombardian basin gradually ceased and the site of extension shifted westwards i e towards the future site of crustal separation extension was then controlled by a set of west dipping normal faults oceanic crust was formed not later than 157 ma the overall extension along the profile which had a final length of 290 km was 52 km which corresponds to a stretching factor of 1 22 for the whole length of the preserved margin the strain rate is ca 1 10 16 s the sedimentation history suggests that the extension of the south alpine margin was a continuous process from the norian to the middle jurassic the changes in tectonic pattern are related to progressive hardening of the lithospheric segment undergoing slow extension

fast slip with inhibited temperature rise due to mineral dehydration evidence from experiments on gypsum anomalously low heat flow around active faults has been a recurrent subject of debate over past decades we present a series of high velocity friction experiments on gypsum rock cylinders showing that the temperature of the simulated fault plane is efficiently buffered due to large scale endothermic dehydration reaction the tests were performed at 1 mpa normal stress and a velocity of 1 3 m s 1 while measuring the temperature close to the sliding surface and the relative humidity around the sample the temperature close to the sliding surface is remarkably stable at 100 c during the dehydration reaction of gypsum microstructural and x ray diffraction investigations show that dehydration occurs at the very beginning of the test and progresses into the bulk as slip increases in the hottest parts of the sample anhydrite crystal growth is observed the half thickness of the dehydrated layer ranges from 160 m at 2 m slip to 5 mm at 68 m slip thermodynamic estimates of the energy needed for the dehydration to occur yield values ranging from 10 to 50 of the total mechanical work input the temperature plateau is thus well explained by the energy sink due to the dehydration reaction and the phase change from liquid water into steam we suggest that similar endothermic reactions can efficiently buffer the temperature of fault zones during an earthquake this is a way to explain the low heat flow around active faults and the apparent scarcity of frictional melts in nature

a mechanical model for complex fault patterns induced by evaporite dehydration and cyclic changes in fluid pressure complex fault patterns i e faults which exhibit a diverse range of strikes may develop under conditions where a regional tectonic stress field is weak or absent e g polygonal faults the present paper considers a complex system of synsedimentary faults in the umbria marche apennines italy geometrically similar to polygonal fault systems developed during an early jurassic extensional episode this particular fault pattern differs from many extensional fault systems as it lacks structures that are developed with a classical bimodal conjugate andersonian geometry a conceptual and mechanical model is proposed to explain the development and evolution of the complex fault pattern in which it is proposed that faulting is primarily controlled by the development of volumetric instability in triassic evaporites due to dehydration processes anhydritisation during burial the lithological architecture of the triassic evaporites comprising interbedded ca sulphate layers and dolostones played a fundamental role in controlling the deformation processes cyclic fluid overpressure build up release and the coexistence of brittle and brittle ductile flow processes led to horizontal isotropic and non plane extensional strain fields within the dehydrating rock mass which favoured the development of complex deformation patterns the mechanical model proposed shows that the studied fault pattern developed under a stress field consistent with almost homogeneous stress intensities within the horizontal plane the data presented show that local strain fields and transient fluid pressure conditions have been dominant over weak regional extensional tectonics the findings are relevant to many other areas where complex faulting patterns including polygonal faults occur in association with evaporite or clay rich sedimentary sequences

a low temperature ductile shear zone the gypsum dominated western extension of the brittle fella sava fault southern alps based on structural and fabric analyses at variable scales we investigate the evaporitic gypsum dominated comeglians paularo shear zone in the southern alps friuli it represents the lateral western termination of the brittle fella sava fault missing dehydration products of gypsum and the lack of annealing indicate temperatures below 100 c during development of the shear zone despite of such low temperatures the shear zone clearly exhibits mylonitic flow thus evidencing laterally coeval activity of brittle and viscous deformation the dominant structures within the gypsum rocks of the lower bellerophon formation are a steeply to gently s dipping foliation a subhorizontal stretching lineation and pure shear dominated porphyroclast systems a subordinate simple shear component with dextral displacement is indicated by scattered clasts both meso and microscale structures are characteristic of a subsimple shear type of deformation with components of both coaxial and non coaxial strain shortening in a transpressive regime was accommodated by right lateral displacement and internal pure shear deformation within the comeglians paularo shear zone the shear zone shows evidence for a combination of two stretching faults where stretching occurred in the rheologically weaker gypsum member and brittle behavior in enveloping lithologies

present day lithospheric strength of the eastern alps and its relationship to neotectonics 1 we calculate the present day lithospheric strength of the eastern alps along the new reflection seismic profile transalp to examine vertical and lateral strength variations and their implications on neotectonic activity of the eastern alps the large scale geometry of the eastern alps and the spatial distribution of upper and lower crustal layers and the lithospheric mantle is constrained by the deep seismic line two rheological models coupled to a kinematic thermal model that accounts for the thermal evolution of the eastern alps for the last 30 myr are investigated for the present day lithospheric configuration in the eastern alps models with strong model a and weak model b crustal rheologies predict the european and the adriatic plates to be stronger than the central zone of the orogen comprising the region between the inntal fault and the periadriatic fault model a is characterized by a brittle ductile boundary between 14 and 9 km depth and strong coupling of the mechanically strong lower crust to the upper mantle whereas model b suggests the presence of a thick decoupling zone between the upper crust and the upper mantle and a shallower brittle ductile boundary 7 10 km of these end member scenarios model a is in better agreement with neotectonic data including seismicity down to the upper lower crust boundary within the adriatic plate uplift of the central zone of the eastern alps and the southern alps and eastward escape of fault bound blocks such deformation pattern is best explained by lateral extrusion upon north south compression supporting a strong weak strong configuration of tectonic units along the transalp line

geochemical record of methane seepage in authigenic carbonates and surrounding host sediments a case study from the south china sea abstract sediments at marine methane seep sites provide potential archives of past fluid flow that serve to explore seepage activities over time three gravity cores d 8 d f and d 7 were collected from seep sites on the northern slope of the south china sea where gas hydrates were drilled in the subsurface various carbon and sulfur contents 13c values of total inorganic carbon 13ctic 34s values of chromium reducible sulfur 34scrs trace element contents grain size and ams 14c dating of planktonic foraminifera in the sediments were determined to explore the availability of related proxies at seeps and to trace past methane seepage activities evidence for the presence of methane seepage and consequently anaerobic oxidation of methane comes from the occurrence of 13c depleted authigenic carbonate nodules 13c values as low as 49 discovered at an interval of 150 200 cm in core d 7 this finding is supported by high s c ratios and molybdenum enrichment in the same interval however low contents of crs and negative 34scrs values are present it is suggested to reflect a transient methane seepage event which continued for about 1 ka based on the 14c ages cores d 8 and d f have 13ctic values close to zero low s c ratios and crs contents negative 34scrs values and no trace element enrichment suggesting a negligible impact of methane seepage on the sediments the negative 34scrs values of the studied seep impacted and background sediments suggest that the application of 34scrs alone as a proxy to identify aom related process may be insufficient sediment carbon sulfur trace element systematics and 14c ages used here have the potential to be a promising tool to recognize transient methane seepages and constrain their timescales

far field effects of late miocene subduction in the eastern carpathians e w compression and inversion of structures in the alpine carpathian pannonian region kinematic and paleostress data constrain a late miocene e w compressional event that affected the entire alpine carpathian pannonian system after 9 ma and prior to 5 3 ma the maximum horizontal compression directions obtained from 110 stations show a mean 1 orientation of 083 deformation is mainly strike slip e w directed compression followed early to middle miocene upper plate extension in the pannonian basin which was caused by the retreating subduction boundary in the outer carpathians this compressional event terminated early to middle miocene eastward lateral extrusion of the eastern alps and reverted strike slip faults which bounded earlier extruded wedges such as the salzachtal ennstal fault the periadriatic fault the mur murz vienna basin fault system and strike slip faults in the western carpathians e w compression caused the reorientation of the extension direction of the alpine crustal stack east directed tectonic unroofing of the metamorphic domes in the central eastern alps terminated between 9 and 6 ma and early to middle miocene orogen parallel e w extension switched to late miocene n s extension which parallels modern topographic slopes in the pannonian basin the change from synrift extension to late miocene compression during the postrift phase caused the pronounced postrift subsidence by stress induced downward flexure of the loaded lithosphere we relate late miocene e w compression to coeval late stage west directed subduction of the european plate below the eastern carpathians slab pull of the subducted plate caused subduction roll back and upper plate extension of the pannonian area up to the middle miocene subduction slowed down and ceased when up to 60 km thick buoyant continental crust entered the subduction zone during the short period of continued convergence e w directed compressive stress was transmitted across the subduction boundary into the upper plate compressive stress was transferred through the uppermost brittle crust of the earlier extended pannonian region into the eastern alps up to 1400 km behind the subduction zone e w compression terminated during the pliocene when the pliocene to recent nnw sse compressive stress field was established in central europe

present state of tectonic stress of the friuli area eastern southern alps stress orientations are determined for the friuli area from focal mechanisms using the inversion technique of gephart and forsyth 1984 the data consist of 244 fault plane solutions selected for the period 1988 1995 where the data coverage was poor this period was extended to 1978 1996 local magnitude ranges from 2 0 to 4 3 and the depths extend from 4 to 16 km the friuli area is subdivided into five seismotectonic zones on the basis of tectonic characteristics seismic activity and focal mechanisms and for each zone a stress tensor is determined the results show that the active tectonic stress in the friuli area is heterogeneous and conditioned by the complex structural pattern which is characterized by two indented tectonic wedges the western and central parts of the area are mainly affected by a compressional state of stress while in the eastern part a strike slip state of stress prevails the orientation of the principal stresses varies from the western to the eastern part of the area and differences are also noticeable with depth in the central part of the friuli area the maximum compressional stress is n s trending at shallow depths 10 km changing to nw se at deeper levels the maximum compressional stress is nw se oriented in the western part while in the eastern part it is n s oriented

the structure of the hallstatt evaporite body northern calcareous alps austria a compressive diapir superposed by strike slip shear based on old detailed mining maps and own observations in the hallstatt salt mine we reinterpret the structure of the hallstatt evaporite body of the upper permian to lower triassic haselgebirge fm within the northern calcareous alps nca the haselgebirge fm represents a rocksalt mylonite with abundant lenses of sulphates mudstones and limestones in comparison to published results of analogue modeling we interpret the present shape of the hallstatt body as a wnw ese elongated compressive teardrop like diapir this is overprinted by nne ssw shortening and dominantly sinistral shearing along a w trending shear zone the internal structure shows steeply dipping rock units and foliation earlier dextral ductile shear fabrics of likely late early cretaceous age are preserved in sulphate rocks and are subsequently overprinted by mylonitic fabrics in rocksalt and cataclastic fabrics in other rocks the low strength of halite results in recent subvertical shortening and a strain rate e of 8 10 10 s 1 is deduced from deformed subhorizontal boreholes this value is similar to such strain rates 10 10 to 10 9 s 1 estimated by the halite grain size distribution from other salt mines in the nca and thus indicative of sub recent formation of the halite microfabrics

thermal history of the carnic alps southern alps austria and its palaeogeographic implications abstract the thermal history of the carnic alps southern alps austria has been investigated by means of organic petrology clay mineralogy and microthermometry in the tectonic framework of the carnic alps the metamorphic overprint from the lower anchizone up to the epizone is exposed in a continuous n s trending metamorphic section the metamorphic zonation is disturbed by shear zones related to the strike slip movement of the periadriatic lineament all obtained data a methodical correlation and a numeric 1d simulation of the burial history result in the model of a multistage thermal history 1 a variscan tectonothermal event caused a syntectonic anchi to epizonal metamorphism with the development of local overpressured zones characterized by convective heat transfer 2 major strike slip faults operating during the sedimentation of the late carboniferous molasse are related to enhance the heat flow 3 the alpine metamorphic overprint shows the same intensity as the variscan event 4 high temperature fluid inclusion phases are related to oligocene plutonic activity along the periadriatic lineament these data from the carnic alps are discussed in a general framework of the non to low grade metamorphic units of the internal alps and carpathians in the uppermost tectonic units of the eastern and southern alps a spatial and temporal shift of the alpine very low grade metamorphic overprint from north to south is observed this zonation indicates the pannonian transdanubian range which suffered no alpine metamorphism as an exotic block inside an alpine heated domain the gailtal line as a segment of the periadriatic lineament separates two terrains with the same alpine overprint

discontinuous fault zones abstract many tectonic faults and tension fractures are at least initially composed of separate segments this note deals with a little explored reason for this phenomenon which in faulting has obvious implications both for the migration of hydrocarbons and for the sealing capacity of faults theoretical arguments based on coulombmohr s theory of shear failure and on a theorem for the integrability of vector fields lead to the expectation that in general non uniform and truly three dimensional stress fields will impede the formation of smooth coherent fault surfaces this is in contrast to the stress fields that are associated with plane deformation examples are given and special attention is drawn to the role of tectonic stress fields with horizontal principal stresses that change with depth in magnitude and direction

constraints on the active tectonics of the friuli nw slovenia area from cgps measurements and three dimensional kinematic modeling we use site velocities from continuous gps cgps observations and kinematic modeling to investigate the active tectonics of the friuli nw slovenia area data from 42 cgps stations around the adriatic indicate an oblique collision with southern friuli moving nnw toward northern friuli at the relative speed of 1 6 to 2 2 mm a we investigate the active tectonics using 3dmove a three dimensional kinematic model tool the model consists of one indenter shaped fault plane that approximates the adriatic plate boundary using the fault parallel flow deformation algorithm we move the hanging wall along the fault plane in the direction indicated by the gps velocities the resulting strain field is used for structural interpretation we identify a pattern of coincident strain maxima and high vorticity that correlates well with groups of hypocenters of major earthquakes including their aftershocks and indicates the orientation of secondary active faults the pattern reveals structures both parallel and perpendicular to the strike of the primary fault in the eastern sector which shows more complex tectonics these two sets of faults probably form an interacting strike slip system

polyphase metamorphism in the eastern carnic alps n italy s austria clay minerals and conodont colour alteration index evidence thermal evolution of the palaeozoic triassic sequences of the carnic alps has been characterized by b cell dimension and kubler index illite crystallinity of k white micas ki arkai index ai of chlorites clay mineral assemblages and conodont colour alteration index cai data indicate at least two metamorphic events variscan and alpine in the older event high anchizonal conditions predominated although epizonal conditions were reached over wide areas it was characterized by low intermediate pressure facies the thermal peak was mainly due to an extensional regime during the bashkirian a younger thermal overprint generated by alpine orogeny was of lower grade reaching high diagenetic anchizonal conditions characterized by high pressure facies inverted metamorphic patterns are associated with middle to late miocene thrusting hydrothermal alteration in the northern part of the region can be linked with emplacement of oligocene plutons and high heat flow along the periadratic lineament