geochemistry of shallow aquifers and soil gas surveys in a feasibility study at the rivara natural gas storage site po plain northern italy abstract a geochemical survey in shallow aquifers and soils has been carried out to evaluate the feasibility of natural gas ch 4 storage in a deep saline aquifer at rivara mo northern italy this paper discusses the areal distribution of co 2 and ch 4 fluxes and co 2 ch 4 rn he h 2 concentrations both in soils and shallow aquifers above the proposed storage reservoir the distribution of pathfinder elements such as 222 rn he and h 2 has been studied in order to identify potential faults and or fractures related to preferential migration pathways and the possible interactions between the reservoir and surface a geochemical and isotopic characterization of the ground waters circulating in the first 200 m has allowed to investigation of i the origin of the circulating fluids ii the gas water rock interaction processes iii the amount of dissolved gases and or their saturation status in the first 200 m the presence of ch 4 rich reducing waters are probably related to organic matter peat bearing strata which generate shallow derived ch 4 as elsewhere in the po plain on the basis of isotopic analysis no hints of thermogenic ch 4 gas leakage from a deeper reservoir have been shown the 13 c co 2 both in ground waters and free gases suggests a prevalent shallow origin of co 2 i e organic and or soil derived the acquisition of pre injection data is strategic for the natural gas storage development project and as a baseline for future monitoring during the gas injection withdrawing period such a geochemical approach is considered as a methodological reference model for future co 2 ch 4 storage projects

age of emplacement of the schistes lustres nappe alpine corsica abstract structural studies in the schistes lustres nappe west of bastia corsica demonstrate the existence of a tectonic melange in which km scale blocks and smaller lozenges of basement granite gneiss thick layered marble and dismembered mesozoic ophiolite are enveloped in a matrix of calc schist and blueschist the main s1 foliation is developed in both block and matrix and is concordant with lithologie contacts blueschist facies metamorphism was syn kinematic with the main foliation the s1 in the schistes lustres was refolded about ene wsw trending tight similar and monoclinal fold axes f2 these second folds verge to the southeast and show km scale axial culminations and depressions that are reflected by topography and residual bouguer gravity anomalies parautochthonous hercynian basement tenda corte complex beneath the western edge of the schistes lustres nappe contains a mylonitic foliation which is concordant with the main foliation in the schistes lustres the intensity of deformation in the basement decreases away from this contact and undeformed granites are found 3 km to the west whole rock samples of the deformed basement immediately beneath the schistes lustres yield an rb sr isochron diagram n 4 which has an age of 105 8 ma 1 and initial 87 sr 86 sr ratio of 0 7228 0 0005 1 this result is more precise than our preliminary age and initial ratio estimate of 98 14 and 0 7296 0 0068 respectively cohen et al 1979 it is similar to a recently published mid cretaceous 90 ma 40ar 39ar age from glaucophane mineral separates we interpret this date as the age of a metamorphic overprint related to the emplacement of the schistes lustres nappe and associated ophiolites the formation of the main foliation and blueschist facies metamorphism these results indicate that the mid cretaceous blueschist facies metamorphism documented in the western alps formerly extended farther south of its present terminus the data are consistent with mid cretaceous obduction of tethyan oceanic crust onto the present day eastern continental margin of corsica we postulate that during eocene early oligocene time a polarity flip occurred outboard of the obducted crust and a new southfacing subduction zone developed this change in polarity was responsible for the development of southeast vergent second folds and for the resetting of 40ar 39ar and k ar geochronologic clocks described in the literature

calibrating fluvial erosion laws and quantifying river response to faulting in sardinia italy abstract it is now widely accepted that rivers modify their erosion rates in response to variable rock uplift rates resulting in changes in channel slope that propagate upstream through time therefore present day river morphology may contain a record of tectonic history the simple stream power incision model can in principle be used to quantify past uplift rates over a variety of spatial and temporal scales nonetheless the erosional model s exponents of area and slope m and n respectively and bedrock erodibility k remain poorly constrained in this paper we will use a geologically and geomorphically well constrained plio pleistocene volcanic landscape in central sardinia italy to calibrate the stream power erosion equation and to investigate the slip rate of faults that have been seismically quiescent in the historic past by analysing digital elevation models geological maps and landsat imagery we have identified the geomorphic expression of several volcanic features eruption centres and basaltic lava flows and three normal faults with 6 to 8 km fault traces within the outcrop downstream river longitudinal profiles show a similar transient response to relative base level fall probably as a result of relief inversion at the edge of the volcanic outcrop from measurements of incision local slope and upstream catchment area across eight different rivers we calculate n 1 m 0 50 0 02 and using a landscape age from literature of 2 7 ma bedrock erodibility k 0 10 0 04 m 1 2m myr 1 there are also knickpoints on rivers upstream of two normal faults and we used numerical inverse modelling of the longitudinal profiles to predict the slip rate of these faults since 2 7 ma the results from the inverse model show that the erosional parameter values derived in this study can produce theoretical longitudinal profiles that closely resemble observed river profiles upstream of the faults the lowest misfit theoretical longitudinal profiles were generated by a model of temporally discontinuous footwall uplift with consistently low throw rates

the temporal and spatial distribution of foraminiferans in marine benthic sediments of the clyde sea area scotland abstract the numbers of benthic foraminiferans at four sites in the clyde sea area showed no consistent temporal variation throughout 1993 in the finest surface sediments numbers ranged between 200 and 400 cells cm 3 compared to only 25 50 cells cm 3 in the coarsest sediments on two occasions high populations of cells less than 63 m were found in the surface layers these were thought to represent recruitment peaks since these juvenile cells grew rapidly when maintained in the laboratory a total of 56 taxa were identified from the region the greatest diversity being recorded in the finest sediments rose bengal stained foraminiferans i e presumed living were found below the anoxic oxic boundary the fate of these cells was considered by examining their ability to migrate through fine sediments and their capacity to survive based on evidence of pseudopodial activity periods of anoxia this study has highlighted the numerical importance of foraminiferans particularly in fine surface coastal sediments but questions whether the high populations of stained cells found in deeper sediments play a significant ecological role

oligo miocene rift of sardinia and the early history of the western mediterranean basin the geodynamic evolution of the western mediterranean basin in spite of many studies is still uncertain there is some consensus for interpreting this basin as a kind of small oceanic marginal basin its opening has generally been related to a subduction process which was active during the oligocene miocene somewhere east of sardinia corsica1 7 as the margins of the basin are deeply buried below miocene to present sediments direct lithological and stratigraphical data which could explain the events responsible for its formation are rare8 10 or missing altogether to obtain such data detailed field studies have been undertaken in sardinia fig 1 and the first results are presented here this approach is justified by the fact that in that island oligocene and miocene sediments were deposited in a rift fossa tettonica sarda of verdabasso11 which is the easternmost arm of the complex rift system that affected the european plate during oligocene and miocene times one of these arms evolved towards a small oceanic basin the western mediterranean or algero provencal basin while others such as the gulf of valencia and the sardinia rift aborted and remained at the rift stage its exceptional exposures make it possible to examine the sardinia rift to clarify the sequence of events which created it and to establish a sedimentological model which we believe is directly applicable to the western mediterranean basin

fluid geochemistry of the sardinian rift campidano graben sardinia italy fault segmentation seismic quiescence of geochemically active faults and new constraints for selection of co2 storage sites abstract sardinia is typically seismically quiescent displaying an almost complete lack of historical earthquakes and instrumentally recorded seismicity this evidence may be in agreement with the presence of a ductile layer in the northern sector of the island as suggested by the he isotopic signature in fluids rising to the surface through quiescent fault systems the fault systems have been found to be segmented and therefore isolated in fluid circulation the study of fluid behaviour along fault systems becomes strategically important when applied to solve some geological risk assessments such as rn indoor or to define geological structures like potential co 2 storage sites both of these have been recently requested by the exploitation in italy of the euratom directive and the evolution of the kyotoprotocol policy four water dominated hydrothermal areas of sardinia located along regional fault systems were considered campidano graben tirso valley logudoro and casteldoria a fluid geochemical survey was carried out taking into account physical chemical and environmental parameters major elements within gaseous and liquid phases a few minor and trace elements selected isotope ratios 2 h 18 o 13 c 3 he 4 he 222 rn concentration and some dissolved gases two different fluids have been recognised as regards both water chemistry and dissolved gases i co 2 rich gases poor in he and rn with a relatively high 3 he 4 he ratio up to r r a 2 32 associated with na hco 3 cl thermal and cold groundwater ii gases rich in he and n 2 poor in co 2 and rn with a low 3 he 4 he ratio associated with alkaline thermal and cold waters the distribution of these two groups of fluids characterises the sardinian tectonic systems in fact gas fluxes are not homogeneous being mainly related to the different fault segments and to the areas where quaternary basalts crop out the underground geochemical evolution of the sardinian fluids as a function of the geological and tectonic systems provides some suggestions for solving one of the most important problems co 2 geological sequestration in order to reduce the co 2 excess produced by human activity the best geological disposal sites are reservoirs with low hydraulic conductivity sealed to fluid movement or aquifers characterised by maximum ph buffering capacity of their mineralogical matrix the knowledge of the role of faults as permeability barriers or as deep fluid uprising pathways is prerequisite

fault plane solutions and seismicity of the italian peninsula abstract a new fault plane solution map of the italian peninsula is presented in this paper the earthquakes analyzed are included in the period 1905 1980 with magnitudes ranging 4 7 75 earthquakes are located in the crust while 31 are related to the deep and intermediate zone of the calabrian arc the large seismic events of the italian peninsula are generally associated with normal faulting while strike slip motion is mostly related to small earthquakes located along lateral segments of the mountain chain the deep and intermediate earthquakes of the tyrrhenian sea indicate predominant down dip compression and strike slip motion at the boundaries of this benioff zone this last is interpreted as a remnant of a subduction zone active since oligocene extending to 500 km depth with a very small lateral size about 300 km the present tectonics of this benioff zone is strongly conditioned by the lateral bending more so than the gravitational sinking process the coexistence of thrust and normal faulting motion associated to the earthquakes within a few tens of kilometers of each other seems to be explained by the strong lateral inhomogeneities of the crustal rocks present in this region more so than to the depth of the seismogenetic zone and the nature of the faulting process

crustal anomalies under the tunisian seismograph array using teleseismic p waves abstract the object of this study is to understand the anomalies in the crustal structure under the seismograph array of tunisia using teleseismic p waves at epicentral distances 30

benthic foraminifera in the nazare canyon portuguese continental margin sedimentary environments and disturbance abstract living rose bengal stained benthic foraminifera were investigated from thirteen stations ranging from 146 4976 m water depth in the nazare canyon located on the western iberian continental margin the total standing stocks tss species assemblages and in sediment distributions are compared between stations located on the highly disturbed axis of the upper 4000 m in addition the community changes were investigated in relation to water depth and bio available organic carbon overall low total standing stocks of foraminifera were found in the disturbed canyon axis which experiences frequent sediment resuspension and gravity flows at the upper canyon axis station at 1118 m a rather exceptional fauna was recovered dominated by a species of technitella that made up 75 of the tss the highest tsss were recorded in the upper canyon terrace stations where fine grained sediment and organic carbon are able to accumulate standing stocks on the terraces decreased with increasing water depths the quiescent terrace stations recorded high abundances of infaunal species including melonis barleeanum globobulimina spp and chilostomella oolina the occurrence of these species reflects the low pore water oxygen concentrations and high bio available carbon supply several tubular bathysiphon species were found in the upper canyon terrace stations instead the deepest stations of the lower canyon were dominated by another large agglutinated protozoan saccorhiza ramosa the change in the arborescent tubular foraminiferal community may reflect the increase in sediment oxygenation with increasing water depth in the canyon bathysiphon spp occurring in sediments with higher bio available carbon flux and s ramosa inhabiting more oligotrophic areas

plate tectonics and orogenic research after 25 years a tethyan perspective abstract orogeny the process by which the earth s prominent mountain ranges are constructed has been a central topic of interest in the earth sciences since at least the end of the 18th century the recognition that strains and displacements of very considerable magnitude occur along all of the three dimensions within an orogenic belt during its evolution has grown gradually during the last two centuries emphasis on primary vertical movements dominated the ideas on the nature of orogeny during the first half of the 19th century whereas compression and consequent uplift across mountain belts were believed to be the main cause for their origin during the subsequent one hundred years or so that were spent under the dominance of the fixist contraction theory mobilist tectonicians realised that continental drift in places also required motion along the trend of orogenic belts but this view did not gain general acceptance recognition of significant strike slip motion parallel or subparallel with mountain ranges evolved independently and mostly within the fixist camp by the 1960 s presence of important motions both along and across mountain belts had become common knowledge but no theoretical basis existed to account for them all

salt tectonics and crustal tectonics along the eastern sardinian margin western tyrrhenian new insights from the metyss 1 cruise abstract the tyrrhenian sea is usually interpreted to be a neogene back arc basin that opened by continental rifting and oceanic spreading caused by the eastward migration of the apennine subduction system during miocene and pliocene times rifting of the southern tyrrhenian sea started first along the eastern sardinian margin during the middle to late miocene times including the messinian the metyss project aims at better constraining the relationships between crustal tectonics salt tectonics and sedimentation from messinian times to present day the metyss 1 cruise 2009 allowed to acquire about 1200 km of hr seismic reflection profiles along the eastern sardinian margin western tyrrhenian sea this data set clearly illustrates that this area has been highly dissected during the rifting stage by n s trending normal faults delineating ridges and basins as previously described the messinian seismic markers uu and mu locally display fan shaped stratal geometries but the mechanism responsible for such geometries salt tectonics or rifting has yet to be carefully deciphered we also mapped the spatial distribution of the mobile salt the highly variable thickness of the small confined salt basins may be related to the initial pre messinian basin geometry to the fact that salt deposition was syn rift or to salt movement southeastward salt tectonics is vigorous in unconfined basins and appears to have started early during the uu deposition more surprisingly our data demonstrate that some of the major faults have been significantly reactivated during the post rift period up to late quaternary time as shown by bathymetric scarps and associated debris flows moreover some of this post rift deformation can be evidenced within the plio quaternary sequence by a regional unconformity the post miocene deformation style varies greatly between different areas of the margin and can also be strongly influenced by the presence or absence of mobile messinian salt

sedimentary labile organic carbon and pore water redox control on species distribution of benthic foraminifera a case study from lisbon setubal canyon southern portugal abstract rose bengal stained benthic foraminifera were studied from 11 cores collected along two depth transects off southern portugal one in the lisbon setubal canyon and the other along the canyon edge the total standing stocks and distribution of foraminifera were investigated in relation to sediment and pore water geochemistry nitrate was used as a redox indicator sedimentary chlorophyll a and cpe chloroplastic pigment equivalents contents as a measure of labile organic matter and total organic carbon as a measure of bulk organic matter availability the canyon sediments were enriched in organic carbon and phytopigments at all water depths in comparison with the canyon edge water depth seemed to control sedimentary phytopigment content but not total organic carbon no significant correlation was seen between pigment and total organic carbon content the abundance of calcareous foraminifera correlated with the phytodetritus content whereas a weaker correlation was observed for the agglutinated taxa therefore calcareous foraminifera appear to require a fresher food input than agglutinated taxa the foraminiferal species composition also varied with pigment content and nitrate penetration depth in the sediment in line with the trox concept phytopigment rich surficial cpe content 20 g cm3 sediments with a shallow nitrate penetration depth 1 cm depth were inhabited by generally infaunal species such as chilostomella oolina melonis barleeanus and globobulimina spp as the nitrate penetration increased to 2 cm depth in sediment and the pigment content remained relatively high 15 g cm3 uvigerina mediterranea and uvigerina elongatastriata became dominant species with declining cpe content and increasing nitrate penetration depth the foraminiferal assemblages changed from the mesotrophic cibicides kullenbergi uvigerina peregrina assemblage to the oligotrophic abyssal assemblage mainly consisting of agglutinated taxa

could middle ordovician carbonate shelf depositional patterns in appalachian orogene indicate collision along an irregular continental margin abstract analysis of lower to middle ordovician carbonate successions and the conodonts they contain from tennessee to new york show that 1 in the northern great valley strike parallel disconformable contacts occur between lower and middle ordovician and within middle ordovician carbonate units 2 apparent maximum extent of unconformities along tectonic promontories and 3 relatively rapid subsidence and transgression at promontories diachronous early paleozoic collisional events at an irregular continental margin might explain these observations initial taconic collisions may have occurred at the virginia promontory resulting in uplift and erosion of the knox beekmantown shelf in whiterockian time followed by rapid subsidence and transgression uplift and erosion possib y related to continued convergence migrated southwest and at least as far northeast as lexington virginia beyond lexington shelf deposition continued relatively uninterrupted on the east side of the great valley collision at the new york promontory could have produced the two pre blackriverian and pre rocklandian middle ordovician intervals of uplift and erosion on the beekmantown shelf these unconformities are greatest near newburgh new york and decrease in magnitude northeastward and southwestward west of reading pennsylvania in the great valley carbonate shelf deposition remained virtually continuous thus between reading and lexington in the pennsylvania reentrant continuous deposition during early paleozoic collisions suggests that an irregular outline of the continenta margin may have controlled patterns of sedimentation during collision tectonics end of article last page 1171

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

extensional tectonics on sardinia italy insights into the arc back arc transitional regime although the tectonic features and stress regime typical for accretionary complexes and back arc domains have been widely documented so far few are known on the transitional zone separating these two systems here we report on structural analysis and anisotropy of magnetic susceptibility ams results from eocene pliocene sediments exposed in western sardinia from late oligocene to middle miocene the studied area was located between the alpine apennine wedge to the east which was undergoing shortening and accretion and the liguro provencal basin undergoing extension and spreading we find that prior to the formation of the liguro provencal basin the middle eocene lower oligocene sediments cropping out at the southwesternmost edge of sardinia were subjected to ne sw shortening in present day coordinates in agreement with recently reported geological information conversely the upper oligocene pliocene sedimentary sequences record a different evolutionary stage of extensional processes upper oligocene middle upper burdigalian sediments clearly show a n s oriented magnetic lineation that can be related to extensional direction along the prevalent e w oriented normal faults on the other hand no magnetic lineation has been detected in upper burdigalian serravallian sediments which mark the end of the first rifting process in sardinia which likely coincides with the rift to drift transition at the core of the liguro provencal basin finally a ne sw extension is observed in two tortonian pliocene sites at the northwestern margin of the nnw sse oriented campidano graben our study confirms that ams may represent a valuable strain trajectory proxy and significantly help to unravel the characters of temporally superimposed tectonic events

model for a passive to active continental margin transition implications for hydrocarbon exploration this paper proposes a model for the transition of a passive atlantic type continental margin to an active one with reverse polarity prior to its ultimate collision with an island arc or continent significant morphological and stratigraphic patterns which are believed to characterize this transition include 1 reactivation as reverse faults of preexisting listric normal faults not gulf coast type growth faults but those affecting basement as well that were established during the margin s most recent period of extension 2 landward migration with time of this fault rejuvenation 3 development of deeper water shallower water deeper water or deeper water unconformity deeper water stratal assemblages on the margin 4 regional flexure of the continental margin a in to that known for the outer rise area of oceanic plates landward of the subduction zone and 5 landward migration of major unconformities coeval with continental margin flexure this model creates implications for hydrocarbon exploration because 1 it predicts the presence or absence of unconformities and thus potential stratigraphic traps among units of a particular basin 2 provides spatial and temporal constraints for secondary porosity development in potential reservoirs 3 allows more accurate interpretations to be made of thermal or burial history diagrams constructed for the purpose of determining relative thermal maturities of potential source units and 4 helps distinguish between basement reactivation and decollement or gulf coast type growth faulting the orogenic phase of the margin s development however may later overprint or conceal these morphological and stratigraphic patterns to the extent that they might be unrecognizable because they have implications from both academic and economic perspectives the role of these patterns in the margin s evolution should not be overlooked

gravity anomalies and flexure of the lithosphere at mountain ranges the bouguer gravity anomaly over the himalayan alpine and appalachian mountains is characterized by a generally asymmetric gravity low which spans the mountains and associated foreland basins the minimum of the gravity low is generally systematically displaced from the region of greatest topographic relief and shows no obvious relationship to surface geology in addition the alps and appalachians are associated with a generally symmetric gravity high that is unrelated to the topographic relief together the gravity low and high form a characteristic positive negative anomaly couple the steep gravity gradient between the positive and negative couple correlates with the insubric line and its equivalents in the alps and the brevard zone in the southern appalachians this gravity anomaly couple is interpreted as evidence for flexure of the continental lithosphere by subsurface buried and surface topographic loading the magnitude of the subsurface load is estimated from the integrated excess mass represented by the positive anomaly and the magnitude of the surface load from the topography by combining these loads the flexure of the lithosphere and the associated bouguer gravity anomaly are calculated for different assumed values of the elastic thickness te of continental lithosphere the best fitting value of te for the himalayas is 80 100 km for the alps 25 50 km and for the appalachians 80 130 km the model calculations suggest that the main contribution to the gravity couple in the alps and appalachians arises not from surface loads such as thrust sheets and nappes but from subsurface loads however in the case of the himalayas the topography appears to be a sufficient load to explain the observed asymmetric gravity low when subsurface loads do exist therefore we would not expect a close correlation between mountain topographic relief and depth to the m discontinuity as required by classical models of isostasy rather the m discontinuity is expected to relate to the center of mass of all the loads acting on the lithosphere the surface and subsurface loads inferred from the gravity anomaly play a major role in the development of mountains and foreland basins the emplacement of large subsurface loads represents the primary event in the alps and appalachians while in the himalayas the emplacement of the surface load is the primary event the emplacement of the subsurface load probably marks the initiation of foreland basin development the regional characteristics of the basin are controlled by the primary load while local variations are controlled by the secondary thrust sheet loads subsequent movement of either load will produce migration of the basin depocenter the origin of the subsurface load is not clear but its association with the insubric line in the alps and the brevard zone in the appalachians suggests that it may be related to the obduction of crustal blocks flakes onto the underlying plate during continental collision or possibly to the preloaded crustal structure of the underlying plate

the origin of modern agglutinated foraminiferal assemblages evidence from a stratified fjord loch etive a silled 145 m deep fjord on the scottish west coast provides an example of modern benthic foraminiferal assemblages at intermediate depths i e below the intertidal zone and above the ccd consisting almost exclusively of organic cemented agglutinated forms since such faunas from intermediate depths are rare in modern oceans but relatively common in the fossil record the present study allows new insights into one kind of ancient environment for which there are few modern analogues the strong dominance of agglutinated forms both living and in some dead assemblages of foraminifera to the exclusion of calcareous taxa is attributed to the unusual oceanographic conditions these include a combination of restricted deep water renewals and strong influence of freshwater which drains through large areas relative to the size of the loch of vegetated land the result is calm bottom water conditions with commonly occurring oxygen depletion although not anoxic brackish water throughout the water column salinity 28 in the deeper parts and organic rich mostly terrestrially derived sediments with geochemical properties which to a much larger degree than open marine ones are controlled by local input this environment supports low abundance and low diversity live assemblages mainly restricted to the surface 1 cm of sediment the dead assemblages show similar faunal characteristics but the calcareous components are due to carbonate dissolution even more reduced one of the calcareous species in loch etive is elphidium albiumbilicatum its occurrence is the first record in british waters and it matches the previously suggested southern limit of its distribution analysis of a 90 cm long core representing sediments deposited over the past two centuries shows the presence of a calcareous dominated assemblage including more marine species with a higher diversity in the lower part this suggests that loch etive is in the process of going from a marine to a more terrestrial dominated environment the relatively high sedimentation rate 0 5 cm per yr the apparent lack of smearing through bioturbation and the presence of faunal changes in response to reduced marine influence over the past centuries shows that loch etive has a good potential for performing high resolution climatic studies

the gross structure of the crust under corsica and sardinia as part of the european geotraverse project egt a number of international cooperative seismic refraction surveys were carried out along the n s segment from the ligurian sea across the islands of corsica and sardinia to the sardinian channel between sardinia and north africa from 1982 to 1985 for all the experiments offshore explosions served as energy sources ranging from 200 to 1125 kg the main result is that the crust in the ligurian sea is of transitional type with a thickness of only 18 km the two continental blocks of corsica and sardinia have a maximum crustal thickness of 33 and 34 km with average crustal velocities of 6 4 and 6 3 km s respectively other results are that the internal crustal structure as derived from the available data in both islands is rather undifferentiated with only local evidence for a more steplike interface in the lower crust corsica 6 3 to 6 6 km s sardinia 6 5 to 6 8 km s there are also indications of a slight velocity inversion under the southwestern part of sardinia farther south in the sardinian channel the crustal thickness decreases again to 20 km a significant feature is the observed pn velocity this parameter increases from the relatively low value of 7 5 km s in the north ligurian sea to 7 7 km s and 7 9 km s for corsica and sardinia and finally to 8 0 km s under the sardinian channel these values reflect the tectonic evolution of that part of the mediterranean sea

geochemistry of the high pco2 waters in logudoro sardinia italy abstract a geochemical study of the high pco2 waters in logudoro northern sardinia was carried out starting from regional hydrogeochemical prospecting for geothermal energy based on the major dissolved components and some minor elements this preliminary investigation led to the identification of five different lithologies marking the different aquifers the high pco2 waters can be divided into the less saline tds

development of tectonostratigraphy in distal part of foreland basin in southwestern taiwan abstract in the young and active tectonic belt of southwestern taiwan reconstructed stratigraphy in the distal part of the foreland basin reveals at least two regional unconformities with the younger ones covering the areas farther from the mountain belt in contrast with the previously proposed monotonous basin development the temporal spatial distribution of the unconformities indicates the back and forth migration of the foreland basin margin three distinct episodes of rapid subsidence during the foreland basin development have also been identified the onset of the basin development can be well constrained by the initial rapid subsidence at 4 4 4 2 ma which happened only in the proximal part of the basin this was followed by two younger episodes of rapid subsidence events at 2 1 8 ma and 0 45 ma which were encountered initially in the areas progressively farther from the orogenic belt we propose a model of episodic tectonic evolution in the distal part of the foreland basin in southwestern taiwan during each episode of rapid subsidence uplifting that corresponds to the forebulge began with a concurrent rapid subsidence in the areas closer to the basin center and was followed by rapid subsidence and deposition of widespread strata onlapping toward the basin margin part of the widespread strata and its overlying deposits would be eroded in the beginning of the next episode when the forebulge shifted toward the orogenic belt in general rate of forebulge migrating away from the orogenic belt during the early stage was slower than that derived from a previously proposed kinematic model of a steady migration of the orogenic belt this might be due to a rifted and weaker lithosphere beneath the foreland basin once the foreland basin migrated onto the less stretched lithosphere the basin would expand rapidly into the craton

gravity constraints on the structure of the northern margin of tunisia implications on the nature of the northern african plate boundary summary bouguer gravity data were analysed to determine the general crustal and upper mantle structure in northern tunisia residual gravity anomalies were determined by removing the gravitational effect of crustal thickness variations imaged by regional seismic experiments residual gravity anomalies contain short wavelength anomalies superimposed on a long wavelength component that decreases in amplitude northward towards the tunisian coastline an edge enhancement analysis e g enhanced analytic signals of the short wavelength anomalies suggests a previously unknown east west trending gravity anomaly south of 37 n with source depths of between 3 and 7 km modelling of residual and bouguer gravity anomalies indicate that there are two possible solutions for the residual gravity decrease in northern tunisia 1 thickening of cenozoic and mesozoic sediments north of a strike slip fault or 2 a crustal and uppermantle low density zone interpreted as being crustal material of the remnant subducted african plate the latter result is favoured based on seismic tomographic images of the mediterranean region which implies that subducting material exists under the african coast geological interpretations suggesting that the tell atlas may be a thrust wedge accreted by underplating of the african continental crust and seismic refraction models indicating a thinning of sediments in northern tunisia the east west trending gravity anomalies south of 37 n correspond to an important structural feature that may be related to either a structural boundary e g a transform fault or subduction beneath the african plate

experiments on basin inversion above reactivated domino faults abstract results are presented from scaled sand box experiments which investigate the structural inversion of half graben basins generated by the contractional reactivation of extensional domino fault systems the overburden was deformed above a series of rigid basement fault blocks that were extended in a domino manner the models were constructed from either 1 sand with mica interlayers anisotropic behaviour 2 pure sand isotropic behaviour or 3 a sand clay mixture behaviour with increased competence during the extensional phase of deformation sand or alternating sand mica layers were deposited in teh half grabens associated with individual domino faults to simulate a syn extensional stratigraphic sequence together with a component of overall subsidence after termination of the extensional phase sand layers were added to represent a post rift passive subsidence stratigraphy subsequent contraction of the experimental configuration resulted in progressive reactivation of the domino fault system which was accompanied by back rotation of both the footwall and hanging wall in each of the individual fault blocks this produced null points along the profile section of the fault planes which separated net contraction above from net extension below continued shortening of the system led to further contraction being accommodated along footwall shortcut faults it is suggested that these shortcuts developed in response to 1 the accommodation of space problems generated by increased bed length in the graben acquired during extension and 2 by more efficient low angle fault trajectories in keeping with coulomb failure during horizontal to subhorizontal compression during inversion in the anisotropic model folding in the footwall partially suppressed the initiation of footwall shortcut faults footwall shortcut faulting did not occur in experiments where the dips of the original extensional faults were decreased before the inversion in all inversion experiments the contractional deformation associated with the shortening of the half graben was concentrated in the footwall to each domino basin bounding fault a control experiment in which an undeformed sand pack was deposited above an extended series of basement fault blocks revealed that the early extensional architecture formed in the other experiments had a profound influence on the resultant inversion geometries the results show clear similarities to interpreted examples of natural basin inversion structures associated with reactivated domino fault systems as well as to inferred strike slip induced flower structures

evaluation of stresses in two geodynamically different areas stable foreland and extensional backarc areas which are geodynamically different have different behaviors both in their thermal regime and seismic activity a stable area has a geotherm which can be considered as standard extensional and compressional areas have respectively high and low temperature gradients the italian region includes different geodynamical areas and all such situations are present we consider the apulian platform as an example of a stable area and the tuscany latium as an example of an extensional area for both of them the present geotherms are calculated taking into account for the tuscany latium its thermal history assuming that each region is subject to a constant strain rate the stresses are calculated as functions of depth and time the rheological behavior is assumed to be linear viscoelastic with viscosity dependent on temperature and elastic parameters dependent on lithology the geothermal profile and the rheological structure of the lithosphere remarkably affect the processes of stress accumulation which control the distribution of seismic activity the abrupt decrease of the temperature gradient at the moho produces considerably higher stress values with respect to the case of uniform gradient thus favoring subcrustal seismicity in the case of a standard temperature gradient subcrustal seismicity is predicted and a gap in seismicity indicating a soft intracrustal layer exists if there is a discontinuity in rheology by contrast in the case of a high temperature gradient subcrustal seismicity is not to be expected even in the presence of a discontinuity in rheology since subcrustal temperatures are already too high to permit a sufficient stress accumluation

evidence for reversal of basin polarity during carbonate ramp development in the mesoproterozoic borden basin baffin island distribution of facies in the lower half of the bylot supergroup suggests overall westward deepening of the mesoproterozoic borden basin in marked contrast the upper half of the succession records a reversal in the overall bathymetric trend such that the eastern portion underwent relative deepening as the west experienced relative shallowing strata deposited during this reversal belong to the victor bay formation a ramp composed predominantly of limestone karsting of carbonate strata and development of an angular unconformity in the west contrast with back stepping and drowning of the ramp in the east followed by mantling by deep water limestone carbonaceous carbonate and turbidites increased accommodation space during this time via both tectonic subsidence and eustatic sea level rise led to a profusion of stromatolite pinnacle reefs and large biostromes the reversal of basin polarity is best reconciled with development of a distal foreland basin superimposed on the borden aulacogen crustal rethickening and uplift occurred along reactivated basement faults during an eastward directed compressional event and could be related to thrusting of similar age and vergence in the coppermine river group of northwestern canada

crustal structure beneath the tell and atlas mountains algeria and tunisia through the analysis of gravity data abstract bouguer and isostatic residual gravity anomaly maps were analyzed for the general crustal structure under the tell and atlas mountains of algeria and tunisia two dimensional gravity models and profiles of topography free air and bouguer gravity anomalies were constructed to provide estimates of the crustal thickness and the degree of isostatic compensation the thickest crust 38 40 km was found beneath the saharian atlas in northern algeria whereas under the tunisian atlas it is approximately 34 36 km there is little evidence of crustal thickening due to the formation of the tell mountains large amplitude negative bouguer small amplitude positive free air gravity and small amplitude positive isostatic residual gravity anomalies suggest that saharian and tunisian atlas are partially isostatically compensated with regions of possible overcompensation in algeria the boundary between the saharian and tunisian atlas is characterized by negative isostatic residual anomalies suggesting overcompensation and a thick crustal root however the cause may be low density material in the upper crust the amplitude and width of bouguer gravity anomalies and two dimensional gravity models across the saharian and tunisian atlas indicate that there was a greater amount of crustal shortening in algeria than in tunisia

cretaceous flexural history of northern oman mountain foredeep united arab emirates an important feature of the middle cretaceous arabian continental margin was the regional upwarping in the foreland of the northern oman mountains we interpret this upwarp as an early expression of a cratonward migrating peripheral swell associated with the emplacement of the semail ophiolite onto the margin subsurface stratigraphic data indicate that the swell was expressed during the cenomanian and attained its maximum relief during the turonian by the santonian further downflexure of the margin took place around an axis west of the study area burying the then inactive turonian swell beneath the deposits of the westward expanding foreland basin we suggest that establishment of the later more cratonward flexural regime took place abruptly rather than as a continuo sly migrating wave the middle cretaceous swell axis paralleled the present day axis of the oman mountains the upwarp was slightly asymmetric to the east and loosely constrained estimates of its width and height are 150 km and 244 93 mi and 800 ft respectively the dimensions suggest an anomalously low flexural rigidity 1022 n m for the middle cretaceous continental lithosphere we attribute this low apparent rigidity to the combined effects of remnant thermal and mechanical processes of an earlier rifting event and compression of the margin during the cretaceous emplacement of the semail ophiolite the small dimensions of the middle cretaceous swell suggest that other continental margins with similar geologic histories may also have narrow extinct swells buried beneath foreland deposits such swells may have significant impact on the entrapment of hydrocarbons as we propose for the sajaa margham trend

the geometrical evolution of normal fault systems abstract the purpose of this paper is to examine the kinematic behaviour of normal fault systems and see what general conditions govern their geometrical evolution we pay particular attention to seismological and surface data from regions of present day active normal faulting as the instantaneous three dimensional geometry at the time of fault movement is better known in active regions than in areas where the faults are now static most normal faults are concave upward or listric this shape can be produced by geometric constraints either because the faults reactivate curved thrusts or because they must be curved to accommodate rotations another effect which will produce curved faults is the variation of rheology with depth brittle failure at shallow depths produces less fault rotation than does distributed creep in the lower part of the crust an important geometric feature of normal faulting is the uplift of the footwall the amount of such uplift is related not only to the elastic properties of the lithosphere but also to the throw and dip of the fault a striking feature of active normal faults is that they occur in groups in which all the faults dip in the same direction this behaviour arises because the faults cannot intersect if they do one must cease to be active the rotation which such fault systems produce reduces the dip of the faults until a new steeply dipping fault is formed once a new fault cuts pre existing faults the earlier faults become locked and a new set of faults must propagate rapidly across the whole region involved many of these geometric constraints also apply to thrust faulting

focused and diffuse effluxes of co2 from mud volcanoes and mofettes south of mt etna italy abstract several sites with anomalous emissions of carbon dioxide were investigated in the region south of mt etna volcano in order to assess the types of emission focused and or diffuse their surface extension and the total output of co 2 most of the studied emissions are located on the southwest boundary of mt etna near the town of paterno they consist of three mud volcanoes known as salinelle one spring with bubbling gas acqua grassa and one area of diffuse degassing pescheria another site naftia lake with remarkable gas emissions bubbling gas into a lake as well as adjacent areas of diffuse soil degassing is located further southwest of mt etna in an area of extinct quaternary volcanism on the northwest margin of hyblean mts in all of these areas the origin of the highest co 2 emissions is clearly magmatic and degassing to the atmosphere occurs mostly through tectonic structures probably at a regional scale the magmatic source that feeds anomalous degassing in the above areas is likely to be the same that feeds volcanic activity at mt etna focused degassing was measured at each emission vent using devices that measure the air speed whereas diffuse soil degassing was measured using the accumulation chamber method in total 712 measurements were carried out 146 in focused degassing vents 566 on diffuse degassing areas single co 2 output values ranged from 1 8 10 5 to 1 68 kg s 1 in the case of diffuse degassing areas statistical analyses allowed to discriminate between biogenic co 2 and co 2 deriving from a magmatic hydrothermal source only the efflux values from the latter source were considered in the output estimates the total estimated output thus obtained was about 2 61 kg s 1 relevant to a total surface of about 146 500 m 2 which includes only the magmatic co 2 emissions this value is comparable with that of most non volcanic emissions from geothermal and or faulted areas of central southern italy as well with the co 2 output from some of the volcanic areas of italy

helium isotopes in alpine regions abstract the isotopic composition of helium has been determined for a variety of groundwaters from springs and boreholes in the alps and adjacent regions the main alpine block in france italy switzerland and austria is characterized by a virtual absence of mantle derived 3he in near surface groundwaters in contrast adjacent areas where crust has been thinned by extension to the west in the rhone valley and ardeche to the north in the rhine valley and to the east in the vienna and pannonian basins mantle derived helium is clearly identified helium and undoubtedly other gases are introduced by melts whose generation is associated with crustal thinning however the surface distribution of mantle helium covers a much larger than that of associated surface volcanics this probably results from the dispersion of helium following its solution in groundwaters the po and the molasse neogene sedimentary basins developing by loading on the south and the north sides of the alps respectively have helium with typical crustal composition and a mantle component cannot be resolved these results clearly indicate the control of tectonics on the distribution of helium isotopes in the alpine regions

a tensile flexural model for the initiation of subduction we argue that subduction may be initiated at passive continental margins without shortening the lithosphere overcoming the lithosphere s high compressive strength requires special circumstances and these make it difficult to explain the nearly complete recycling of old sea floor instead we present a model that predicts tensile decoupling of the continental and oceanic lithosphere passive rifting and foundering of the seafloor beneath material welling up in the rift this occurs because the lithosphere in a new ocean basin establishes mechanical continuity with the continent at a depth comparable to mid ocean ridges later subsidence at the margin is therefore inhibited by flexure which implies shear stresses that promote fault slip and tensile stresses necessary to balance the component of the plate s weight directed down the margin slope we show that this tension can more than offset ridge push in our model an important additional tension arises from basal shear tractions resisting the plate s motion away from the mid ocean ridge although these tractions cannot be evaluated with confidence slip on a high angle fault decouples the oceanic and continental lithosphere when shear stresses arising from flexure and the applied tension exceed the lithosphere s shear strength under these loads a passive rift then forms allowing a mantle column to rise to the height of mid ocean ridges over 3 km above the old seafloor and flow onto the surface in a gravity current this load flexes the plate downwards which enhances the flow and lets the old oceanic lithosphere founder this model is consistent with the presence of oceanic material in continental forearcs and the youth of ophiolites when they are obducted as both might be explained by rifting a margin and underthrusting the juvenile crust formed there boninites in ophiolite complexes and tectonites at their bases show depleted and hydrated geochemistries consistent with the melting of rifted mantle lithosphere that receives volatiles from foundering oceanic crust

the cenozoic graben system of sardinia italy geodynamic evolution from new seismic and field data abstract a tectono sedimentary scenario for the southern sardinia italy cenozoic graben system is proposed using field observations and the interpretation of onshore and offshore seismic profiles the major structural events are tied to the general geodynamic evolution of the western central mediterranean thus the extensional late oligocene aquitanian event is a consequence of an apenninic westward subduction process associated with a volcanic arc 29 30 to 15 16 my which is particularly well exposed in sardinia deposition of sub aerial clastics was followed by transgression of the rift depression at the beginning of the aquitanian subduction terminated at the opening of the oceanic provencal basin and the rotation of sardinia corsica during burdigalian time 20 21 to 15 16 my the messinian compressional event ne sw oriented documented from microtectonic data strongly affected the oligo miocene basin the superimposed plio quaternary campidano graben which is probably related to the formation of the tyrrhenian basin contains more than 600 m of syntectonic deposits a change in polarity of the master faults bounding the oligo miocene rift created a central horst type twist zone separating two depocenters in the oristano and cagliari regions emplacement of large volcanic bodies and inversion of the basin during the messinian in cagliari area has reduced the areas with potential for hydrocarbon exploration the two remaining prospective zones are the oristano sub basin and the offshore south of cagliari where burial of lower miocene marine organic matter may have been sufficient to generate hydrocarbons potential reservoirs could be pre rift mesozoic or eocene strata but are mainly excellent miocene sands derived from erosion of the granitic basement in tilted blocks

heat flow in the tectonic provinces crossed by the southern segment of the european geotraverse abstract several published and unpublished surface heat flow density hfd data sets have been reviewed to obtain a valid hfd estimate for the main tectonic provinces crossed by the european geotraverse southern segment egt s and to produce a regional hfd map for this area because the quality and areal distribution of the data are rather heterogeneous particular care has been devoted to data validation and processing we used a geostatistical approach to estimate the regional range of influence of the hfd data in the various tectonic provinces the hfd map has been obtained using an automatic interpolation technique kriging hfd values generally higher than 100 mw m 2 are observed in the post eocene rifting areas such as the rhine graben the tyrrhenian ligurian provencal and balearic basins the younger part of the sardinia rift the central part of the sardinia tunisia channel and the pantelleria rift system the alps show values ranging between 50 and 90 mw m 2 and a mean value of about 70 mw m 2 whereas the molasse basin lying on their northern front exhibits a mean hfd significantly more elevated 87 mw m 2 the northern apennines separate the low hfd about 40 mw m 2 foreland po basin from the internal zones of the chain which shows higher hfd values and a tensional stress regime values higher than 200 mw m 2 pertain to areas recently affected by magmatic and volcanic activity such as the tuscany latium geothermal area and the oceanic tyrrhenian basin the atlas zone shows an hfd trend with values around 75 mw m 2 whereas the pelagian block and the northern edge of the saharan platform display higher values the hercynian crust of sardinia and southern corsica is characterized by a value of about 60 mw m 2 the higher values found along the western corsica and sardinia margins are probably due to a thermal event related to recent tectonic phases of the ligurian provencal and sardo balearic rifting a remarkably good correspondence between the hfd field and the bouguer gravity anomaly strongly supports the existence of transient thermal regimes in the recent deformational areas of the egt s as opposed to the steady regime mostly affecting the central and northern segments of the egt

structural evolution of djebel debadib anticline a clue to the regional tectonic style of the tunisian atlas djebel debadib is a northeast trending anticline in the tunisian atlas near el kef tunisia the core of the anticline consists of a deformed triassic gypsum matrix breccia containing clasts of supratidal dolomite terrigeneous clastic rocks and ophites metabasites locally low grade metasedimentary rocks occurring as clasts in the evaporite may represent fragments of basement rock plucked from salt subcrop during deep seated flowage the multiply deformed triassic rocks are juxtaposed against cretaceous or younger rocks and jurassic and neocomian strata are not present in outcrop these characteristics have been cited in many studies to suggest a history of diapirism to explain both the internal structure of the triassic rocks and the contact relations with the younger rocks a previously unreported unconformity developed on the triassic rocks and overlain by aptian albian strata indicates that an important period of piercement occurred during the early cretaceous for the djebel debadib diapir from the mid cretaceous to the late eocene the continental margin of northern tunisia was a regional basin in which a thick sequence of carbonate rocks was deposited beginning in late oligocene time sandy clastic sediments accumulated on the older carbonate rocks above a regional unconformity and during the middle miocene atlas orogeny numerous northeast southwest folds deformed the rocks of the tunisian trough including the diapiric triassic masses these folds commonly boxlike in geometry were extensively faulted during the late miocene and pliocene a four phase tectonic model is recognized for the tunisian atlas 1 early mesozoic rifting of the north african continental margin 2 diapiric emplacement of the late triassic liassic evaporites into overlying strata beginning in the early cretaceous 3 folding of the cover strata in response to regional compression culminating in the middle miocene atlas orogeny 4 the development of transvers grabens during late orogenic normal faulting latest miocene to recent a major regional decollement is not considered necessary to account for the shortening of the sedimentary cover during the middle miocene deformation rather the principal driving mechanism of regional crustal shortening was the reactivation of early mesozoic normal faults as reverse faults that displaced basement rocks this model implies that the small amount of shortening recorded in the tunisian atlas involved active shortening and structural thickening of basement and the concurrent deformation of the sedimentary cover

timing and mode of emplacement of the roberts mountains allochthon antler orogeny this antler model involves incipient subduction of continental crust and miogeoclinal strata beneath an accretionary wedge composed primarily of oceanic sedimentary rocks and lesser outer shelf strata under thrusting and sediment obduction three phases of associated tectonism are 1 first emplacement phase in which only oceanic crust is subducted evidenced primarily by foreland epeirogeny 2 second emplacement phase in which incipient subduction of continental crust occurs and a flysch trough is formed 3 post emplacement phase of isostatic uplift of continental margin and allochthon accompanied by molasse sedimentation the first two phases associated with compressive movements of the antler orogeny of nevada occurred between mid frasnian and mid osagean time this interval equals about 23 m y based on c a sandberg9s estimates of the duration of conodont zones overlap of the surface trace of the roberts mountains thrust by the kinderhookian webb formation preceded final emplacement of the allochthon ordovician devonian and kinderhookian units in the allochthon as mapped in the carlin pinyon range area by smith and ketner overlie the oldest antler flysch kinderhookian age and are interpreted to have been encased within the antler clastic wedge during osagean time

rare earth elements in waters from the albitite bearing granodiorites of central sardinia italy with the aim of contributing to the knowledge of the geochemical behaviour and mobility of the rare earth element ree in the natural water systems the ground and surface waters of the ottana orani area central sardinia italy were sampled the study area consists of albititic bodies included in hercynian granodiorites the waters have ph in the range of 6 0 8 6 total dissolved solid tds of between 0 1 and 0 6 g l and major cation composition dominated by ca and na whereas predominant anions are cl and or hco3 the ph and the major element composition of the waters are the factors affecting the concentration of ree in solution the concentrations of ree y in the samples filtered at 0 4 m vary between 140 and 1600 ng l with la of between 14 and 314 ng l and yb of between 6 and 12 ng l a negative ce anomaly especially marked at high ph is observed in the groundwaters the surface waters show lower ree concentrations which are independent of ph and negligible ce anomaly speciation calculations carried out with the eq3nr computer program showed that the complexes with the co32 ligand are the dominant ree species at ph in the range of 6 7 8 6 the ree3 ions dominate the speciation at ph 6 7 and only in the light ree lree the relative concentrations of ree in water roughly reflect those in the aquifer host rocks however when concentrations of ree in water are normalised relative to the parent rocks a preferential fractionation of heavy ree hree into the water phase can be observed suggesting the greater mobility and stability of hree in aqueous solution

systematic review of geochemical data from thermal springs gas vents and fumaroles of southern italy for geothermal favourability mapping abstract in recent years two research projects specifically conceived by italian institutions of research to promote the implementation of the use of geothermal energy in southern italy has allowed the review of most data on chemical and isotopic compositions of natural thermal manifestations in the territory of italy two large databases one for thermal springs and co2 rich springs and a second one for fumarolic condensates and associated gas phase have been produced and are available on line with data spanning in time from the early 70 s to the present we have used those data after careful evaluation of the quality and reliability of them to produce correlation diagrams and isodistribution maps of some relevant geochemical geothermal parameters such as pco2 in thermal springs co2 and 13c in co2 of gas phases 3he 4he ratio and he in this way we have been able to delimit the areal patterns of thermal anomalies potentially related with geothermal reservoirs the cross correlation among the many parameters 40 selected has allowed the overview on the circulation of fluids at shallow crust in one of the most active tectonic boundary of the earth between the african and the eurasian continents shallow circulation of hot fluids is particularly active in the roman comagmatic province the neapolitan area and sicily both at etna aeolian archipelago and pantelleria island in the sicily channel where active geothermal systems are already known whose areal extension is probably much larger than what envisaged at present the geothermometric evaluation of data has not allowed to clearly identity new areas apart from those already known but nevertheless some areas in the inner apennines as well as sicily and sardinia have shown anomalous 3he 4he values that point to the presence of mantle fluids located inside the crust being most of active volcanic islands likely much smaller than the thermal anomaly they are associated with a futuristic perspective of utilizing geothermal fluids off shore is suggested moreover the database and the proposed maps can be a useful tool both scientific community and stakeholders to perform geothermal favourability maps and to identify potential new areas interesting from a geothermal perspective

analogous tectonic evolution of the ordovician foredeeps southern and central appalachians new stratigraphic data suggest that the diachronous evolution of the ordovician foredeeps in the southern and central appalachians was remarkably similar stratigraphic features that characterize the middle ordovician sevier basin in tennessee and the middle and late ordovician martinsbuirg basin in pennsylvania are in identical ascending order 1 disconformity on the knox group beekmantown group 2 shelf carbonates 3 slope deposits 4 submarine fan turbidites and 5 contourites and muddy turbidites we propose that diachronous attempted subduction of the north american craton beneath southeastern microplates and or volcanic arcs resulted in uplift and erosion of the western shelf followed by its rapid subsidence basinward migration of eastern and northeastern terrigenous source areas and associated submarine fan turbidites resulted from continued convergence and filled the basins finally tectonic stabilization and lowering of the source area is recorded by contourites and muddy turbidites the evolutionary model proposed for the sevier and martinsburg basins closely resembles present day tectonics of the timor foredeep and the adjoining sahul shelf north of australia similar comparisons have also been made for ordovician basins in the northern appalachians analogous tectonic mechanisms therefore appear to have operated diachronously along the eastern margin of north america from tennessee to new england and possibly to newfoundland during ordovician time

evidence for crustal assimilation by turbulently convecting mafic alkaline magmas geochemistry of mantle xenolith bearing lavas from northern sardinia abstract alkali basalt trachybasalt and basanite magmas containing abundant xenoliths of upper mantle origin were erupted during the plio pleistocene 2 4 0 14 ma in northern sardinia the magmas are enriched in k rb th and ba relative to mid ocean ridge basalts morb and most ocean island basalts oib resulting in high k nb th nb ba nb and rb nb ratios the large number of spinel peridotite inclusions in these lavas suggests that these chemical features cannot be explained by combined assimilation and fractional crystallization within the continental crust however volcanic rock chemistry can be explained by the assimilation of sialic rocks by turbulently convecting mafic magmas during their ascent to the surface fractionation of ba and k from the light rare earth elements lree is required to explain the positive correlation of k la and ba la with 87 sr 86 sr i consequently bulk assimilation of crystalline basement rocks by rising hot basaltic magmas cannot explain the observed chemical trends and preferential melting of a low melting quartzo feldspathic crustal component probably occurred leaving the ree in residual phases such as apatite zircon sphene and amphibole alternatively large ion lithophile element lile enrichment may have been related to interaction of rising mafic lavas with metasomatized lithospheric mantle or enriched asthenosphere

passive margin evolution initiation of subduction and the wilson cycle we have constructed finite element models at various stages of passive margin evolution in which we have incorporated the system of forces acting on the margin depth dependent rheological properties and lateral variations across the margin we have studied the interrelations between age dependent forces geometry and rheology to decipher their net effect on the state of stress at passive margins lithospheric flexure induced by sediment loading dominates the state of stress at passive margins this study has shown that if after a short evolution of the margin time span a few tens of million years subduction has not yet started continued aging of the passive margin alone does not result in conditions more favourable for transformation into an active margin although much geological evidence is available in support of the key role small ocean basins play in orogeny and ophiolite emplacement evolutionary frameworks of the wilson cycle usually are cast in terms of opening and closing of wide ocean basins we propose a more limited role for large oceans in the wilson cycle concept