gravity modelling of the litho asthenosphere system in the central mediterranean abstract the results of the 2 5 d gravity modelling of the litho asthenosphere system in the central mediterranean along two regional geotransects are presented and their possible implications for the geodynamical evolution of this area are discussed particularly gravity data on the tyrrhenian and provencal balearic basins were interpreted introducing significant constraints by means of several main petro physical parameters tied to the litho asthenospheric evolution during the extensive tectonics by this approach based on the model of mckenzie and bickle in j petrol 29 pp 625 679 1988 and white and mckenzie in j geophys res 94 b6 pp 7685 7729 1988 the estimation of the vertical density distribution in the lithosphere asthenosphere system has been possible significant differences in the gravity anomaly field occur when different density models of asthenospheric upwelling are considered this depends on factors like the thermal regime the stretching of the lithosphere and its thickness before it the obtained results contributed to the validation of models interpreting the origin of the tyrrhenian and ligurian provencal basins as related to a passive extensional process rather than to the presence of an active upwelling asthenosphere beneath the central mediterranean basins

density changes in upwelling mantle abstract gravity modelling of the litho asthenosphere system in regions involved in extensional tectonics requires an accurate estimation of the vertical density profile in the upwelling asthenosphere to this end the calculation of the variation of several parameters is needed i e the degree of thermal anomaly in the asthenosphere the amount of stretching the thickness of the lithosphere before stretching and the variation of melt fraction generated by adiabatic decompression therefore knowledge of melt density and of the residual mantle rock composition is necessary in order to have the information to calculate the density of the uprising mantle these calculations allow to partially solve the problem related to ambiguity of the gravity interpretation and to provide information about the structural features of the upwelling mantle

state of stress in the southern tyrrhenian subduction zone from fault plane solutions summary in this paper we present revised locations and original focal mechanisms computed for intermediate and deep earthquakes that occurred within the southern tyrrhenian subduction zone between 1988 and 1994 in order to improve our knowledge of the state of stress for this compressional margin in particular we define the stress distribution within a large portion of the descending slab between 40 and about 450 km depth the seismicity distribution reveals a continuous 40 50 km thick slab that abruptly increases its dip from subhorizontal in the ionian sea to a constant 70 dip in the tyrrhenian we computed focal mechanisms for events with magnitudes ranging from 2 7 and 5 7 obtaining the distribution of p and t axes for many events for which centroid moment tensor cmt solutions are not available thus enabling the sampling of a larger depth range compared to previous studies we define three portions of the slab characterized by different distributions of p and t axes a general down dip compression is found between 165 and 370 km depth whereas in the upper part of the slab 40 165 km depth the fault plane solutions are strongly heterogeneous below 370 km the p axes of the few deep events located further to the north have a shallower dip and are not aligned with the 70 dipping slab possibly suggesting that they belong to a separated piece of subducted lithosphere there is a good correspondence between the depth range in which the p axes plunge closer to the slab dip 70 and the interval characterized by the highest seismic energy release 190 370 km

temperature and density of the tyrrhenian lithosphere and slab and new interpretation of gravity field in the tyrrhenian basin abstract the gravity anomaly field of the tyrrhenian basin and surrounding regions reflects the complex series of geodynamic events active in this area since the oligocene miocene they can resume in lithospheric thinning and asthenospheric rising beneath the tyrrhenian basin coexisting with the roll back subduction of the african plate margin westward sinking beneath the calabrian arc the geographic closeness between these processes implies an intense perturbation of the mantle thermal regime and an interference at regional scale between the related gravity effects a model of the litho asthenospheric structure of this region is suggested showing a reasonable agreement with both the evidences in terms of regional gravity anomaly pattern and the results concerning thermal state and petro physical features of the mantle the first phase of this study consisted of the computation of the isotherms in the crust mantle system beneath the tyrrhenian basin and afterwards of the density distribution within the partially melted upwelling asthenosphere the second phase consisted of a temperature density modelling of the slab subducting beneath the calabrian arc finally a 21 2 interpretation of gravity data was carried out by including as constraints the results previously obtained thus the final result depicts a model matching both gravity thermal and petrographic data they provide a a better definition of the thermal regime of the passive mantle rise beneath the tyrrhenian basin by means of the estimation of the moderate asthenospheric heating and b a model of lithospheric slab subducting with rates that could be smaller than generally suggested in previous works

crustal features along a w e tyrrhenian transect from sardinia to campania margins central mediterranean abstract the tyrrhenian sea is a neogene back arc basin formed by continental extension at the rear of the eastward migrating apennine subduction system its central part generated from tortonian to pliocene includes the sardinia rifted margin to the west an area with large volcanoes in the deep central sector and the campania rifted margin to the east a reprocessing of some 2000 km of mcs lines a new swath bathymetric map and a review of previous geological and geophysical data allow to analyse the nature and distribution of continental vs oceanic crust in this area which evolved in a short time span the central portion of the southern tyrrhenian sea is characterized by moho at about 10 km depth north of magnghi and vavilov smts this thinned crustal domain include a wide continent ocean transition with the occurrence of extensional allochthons and of serpenitinzed sub continental mantle recalling other well known rifted margins as the iberia one sectors floored by oceanic crust should occur mainly in the southern part of the study area but they do not appear related to discrete spreading ridges the continent ocean boundary cannot be drawn unequivocally in the area due also to the occurrence of widespread and huge magmatic manifestations not related to oceanic spreading these portions of the southern tyrrhenian sea represents therefore a complex oceanic back arc basin surrounded by magma rich rifted continental margins the abundant igneous manifestations and the very high stretching rates observed in the area may be related to the fact that the present tyrrhenian area was occupied by an orogenic domain affected by shortening until middle miocene times which is just before the late miocene onset of back arc extension the lithosphere in the region had then to be rheologically weak abundant generation and ascent of magmas mostly of ocean island basalt type was favoured by the large lithospheric permeability induced by strong extensional deformations

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

the deep seismicity of the tyrrhenian sea summary l he study reappraises the deep seismicity of the tyrrhenian sea careful examination of the quality of reported hypocentres shows that the earthquakes define a zone dipping nw about 200 km along strike 50 km thick and reaching a depth of about 500 km the zone is slightly concave to the nw at a depth of 300 km but contrary to many previous reports is not tightly concave nor are there significant spatial gaps in the seismicity which is effectively continuous with depth seismicity is however concentrated in the depth interval 250 300 km where the dip of the seismic zone changes from 70 above 250 km to a more gentle dip of 45 at greater depths seven fault plane solutions are available for the largest earthquakes in this depth interval all of them consistent with a p axis down the dip of the seismic zone and all of them requiring movement on faults out of the plane of the subducting slab two deep earthquakes near naples lie well outside the main zone of activity for one of which a fault plane solution is available that has ap axis not aligned with the dip of the seismic zone the tightly concave slabgeometry favoured by other reports is supported mainly by the location of these events near naples which we think may represent deformation in a separate probably shallower dipping piece of subducted lithosphere the lack of shallow seismicity and particularly of thrust faulting earthquakes at the surface projection of the benioff zone suggests that active subduction has ceased estimates of the convergence rate responsible for subduction in the last 10 myr far exceed the present convergence rate of africa and eurasia suggesting that the subduction was related instead to the stretching and thinning of the crust in the tyrrhenian sea

heat flow heat production and lithospheric thermal regime in the iberian peninsula abstract the first heat flow and heat production maps of the iberian peninsula and its margins using previously acquired data are presented the surface heat flow map includes 553 determinations carried out on water and mining exploration wells oil exploration wells and on the seafloor the surface heat flow varies noticeably from the iberian mainland 65 10 mw m 2 to the atlantic and the mediterranean margins where the heat flow reaches values of about 40 50 mw m 2 and 80 100 mw m 2 respectively the heat production map consists of 664 determinations carried out on rock samples from the variscan iberian massif and the betics the higher values are obtained for granitic rocks 2 5 3 5 w m 3 whereas metasediments and basic rocks reach values of 1 2 5 w m 3 and nearly zero respectively the lithospheric structure deduced for the iberian peninsula by combining heat flow heat production and elevation data indicates that most of the iberian mainland is characterized by a lithospheric thickness of 110 5 km this value is maintained across the west atlantic margin whereas towards the mediterranean margin the lithospheric thickness decreases down to 60 40 km this study also suggests that the heat production in the southern variscan iberian massif must be noticeably higher 3 7 0 5 w m 3 than in the rest of the areas in order to fit the measured heat flow crustal thickness and elevation data

heat flow in the balearic and tyrrhenian basins western mediterranean we present the results of three detailed heat flow surveys which are used to investigate the variations of heat flow and age of the balearic and tyrrhenian basins in the western mediterranean analysis of 12 measurements within a 10 km radius from 40 01 4 55 e in the balearic abyssal plain shows a mean heat flow of 92 10 mw m 2 after correction for the effects of sedimentation this value agrees well with the predictions of plate cooling and high extension stretching models for crust of the late oligocene age proposed for the basin a similar survey with 18 measurements around 40 16 n 11 19 e in the western tyrrhenian gives a flux of 134 8 mw m 2 while the third survey of 26 measurements in the southern tyrrhenian abyssal plain at 37 17 n 12 58 e yields a slightly higher heat flow of 151 10 mw m 2 these values are within the range predicted by simple plate cooling models for the late miocene ages of the deep tyrrhenian basin thus our observations suggest that although the mode of crustal formation of these deep marginal basins is less well defined than that of the major ocean basins the thermal signature is similar also the trend of increasing heat flow from west to east through the balearic and tyrrhenian basins is in agreement with models of the formation of the western mediterranean behind an eastwardly migrating trench system in all three areas the measured flux shows significant local variability in the two westernmost surveys this can be attributed to the presence of buried high conductivity salt structures but in the third area se tyrrhenian the magnitude of the variations is several times greater than can be attributed to steady state thermal refraction alone instead evidence exists for localized hydrothermal activity linked to the small topographical relief within the survey area

rifted margin formation in the south tyrrhenian sea a high resolution seismic profile across the north sicily passive continental margin a new 150 km long seismic line across the continental margin of north sicily has been acquired and interpreted the overall structure of the margin is controlled by extension which caused crustal thinning and widespread normal faulting two main thinned zones are observed in the south in correspondence with the cefalu basin and farther to the north at the continent ocean transition zones of thinned crust coincide with zones of intense normal faulting extension began in late tortonian times and caused the opening of the cefalu basin controlled by a northward dipping listric fault messinian stretching affected most of the future margin and provoked a widening of the cefalu basin and normal faulting in the north following a phase of relative quiescence in the early pliocene renewed extension determined further opening of the cefalu basin and subordinate normal faulting in the north here however the record is unclear because of the emplacement of the calc alkaline sisifo volcano with associated volcanoclastic deposits breakup took place in the late pliocene and was followed by the deposition of postrift pleistocene sediments at the lithospheric scale the sites of extension thinning did not migrate during rifting on the smaller scale on the contrary the cefalu basin displays a remarkably systematic pattern of migration toward the foot wall of the listric fault which controlled the opening of the basin the spacing of 4 6 km between faults is also quite systematic elongation experienced by the continental part of the margin presently 97 km has been derived by comparing the present day and the preextensional lengths and is 10 km the corresponding strain rate is 5 10 16 s 1

heat flow heat production and fission track data from the hercynian basement around the provencal basin western mediterranean abstract in the complex structural framework of the western mediterranean hercynian areas are expected to be thermally preserved from the recent tectonic evolution the thermal regime of these areas is studied using heat flow heat production and fission track data the surface heat flow is significantly higher in corsica 76 10 mw m 2 than in the maures and esterel 58 2 mw m 2 neither heat production nor erosion subsequent to the alpine orogeny in corsica can explain such a difference it is suggested that a deep thermal source related to the asymmetric evolution of the provencal basin could explain the higher heat flow in corsica a model of thermal structure based on the present day thermal regime of the maures and esterei is proposed for the stable hercynian crust in this area the mantle heat flow is 20 25 mw m 2 and the temperature at moho level is 375 500 c depending on the thermal parameter distribution with depth

tectono stratigraphic modelling of the sardinian margin of the tyrrhenian sea rifting of the east sardinia passive margin was characterised by a southeastward migration of the site of extension through time in the first stage of rifting 9 7 ma lithospheric thinning was mainly localised near sardinia crustal and subcrustal thinning factors averaged across the whole transect were 1 12 and 1 5 respectively at 7 ma i e immediately before the onset of the messinian salinity crisis the basin floor was at depths of up to 1000 m in the west and less than few hundred metres in the east during the second stage of rifting between 7 and 5 ma the site of main extension was located in the central part of the future margin with average crustal and subcrustal thinning factors of 1 18 and 1 63 respectively at 5 ma after the termination of the messinian salinity crisis the morphology of the basin floor had changed substantially with depths in general between 700 and 1000 m extension during the last rifting stage before oceanic crust formation at 3 5 ma was mainly concentrated in the southeastemmost part of the profile average crustal thinning factors increased dramatically to i 95 while the subcrustal one remained almost unchanged 1 64 the analysis of temporal changes of thinning factors shows that the opening of the tyrrhenian oceanic basin can be adequately explained with a depth dependent pure shear geometry with crustal and subcrustal thinning being accommodated on the same vertical column subcrustal thinning factors in the initial stages of rifting were higher than the crustal ones but the two become comparable approaching break up the regional compensation of changing loads coupled with a very deep depth of necking is consistent with the observed subsidence trend and basin stratigraphy

from tectonic reconstruction to upper mantle model an application to the alpine mediterranean region abstract de jonge m r wortel m j r and spakman w 1993 from tectonic reconstruction to upper mantle model an application to the alpine mediterranean region in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 53 65 the seismic velocity structure of the upper mantle and lithosphere in the mediterranean region is very complex many areas with anomalous p wave velocities can be recognized by means of seismic tomography in view of the complicated tectonic evolution of the peri mediterranean orogens and basins this is not surprising in this study we will show results of a modelling approach we have recently developed to predict this structure in this approach we make a quantitative connection between the tectonic evolution on one hand and the present seismic velocity structure on the other our model predicts the evolution of temperature distributions in the lower lithosphere and upper mantle by simulating the flow of material inferred from a kinematic description of lithosphere scale processes from the modelled present thermal state the endpoint of an evolution we calculate expected seismic velocity anomalies that can be compared with results obtained by seismic tomography thus the method enables us to compare the implications of geological reconstructions describing the past tectonic processes with seismological results for the present structure the predicted mantle models show a good correlation with the tomographic results obtained for the mantle this means we can verify many features present in the tectonic scenarios with the seismologically determined deep structure

rapid subsidence of small oceanic basins a study of the marsili basin central mediterranean many small backarc basins show subsidence rates significantly greater than those in major ocean basins of similar ages in this study we test by numerical modeling the hypothesis that small backarc basins are formed by the same fundamental processes as major oceanic basins i e by accretion spreading and cooling and that the rate of subsidence is modified and accelerated by lateral heat loss from the hot subbasinal asthenosphere to the surrounding cooler continental lithosphere bathymetric seismic and drilling data in the marsili basin a small and young backarc basin in the central mediterranean are used to constrain the models the results of this analysis confirm the above hypothesis they further suggest that for actively spreading backarc basins the most rapid subsidence occurs in a zone near the margin of the basin during the earliest stage of basin spreading whereas after spreading terminates the location for rapid subsidence migrates towards the basin center

a seismic refraction experiment in the tyrrhenian sea summary we present the results of two 100 km long reversed seismic refraction lines shot in the tyrrhenian sea using explosive sources and oceanbottom receivers the results have been interpreted using ray tracing through laterally varying structures the more easterly line t2 was shot in the central part of the tyrrhenian abyssal plain in a water depth of 3 5 km the crust here is shown to be oceanic in character but to exhibit significant lateral heterogeneity the upper part of the crust layer 2 contains a steep velocity gradient from about 4 to over 6 km s l at a depth of typically 2 km the lower part of the crust layer 3 contains a smaller velocity gradient from 6 6 to 6 9 km s l at the base of the crust total crustal thickness is between 6 and 8 km the other line t1 carried out in the cornaglia basin in 2 7 km of water reveals a more complicated velocity structure we conclude that its southern half is underlain by oceanic crust similar to that observed at t2 however its northern half appears to be underlain by crust of similar thickness but in which seismic velocities increase slowly with depth from 4 9 km s l immediately below the superficial sediments to 6 3 km s l at the moho we interpret this latter structure as thinned continental crust surprisingly neither the seafloor topography nor the depth to moho reflect the transition from oceanic to continental crust we infer from these results that although the southern and eastern parts of the tyrrhenian basin were formed primarily by seafloor spreading much of the basin north of about 40 n and probably including some areas with water depths in excess of 3 km is underlain by thinned continental crust the evolution of the northern part of the tyrrhenian basin must therefore have occurred chiefly through a process of continental extension which in some areas has reduced crustal thickness to as little as 6 8 km south of 40 n

heat flow and depth versus age for the mesozoic northwest atlantic ocean results from the sohm abyssal plain and implications for the bermuda rise abstract heat flow in the sohm abyssal plain is measured to be 53 mw m 2 at an age of 163 ma this is 25 higher than predicted by conductive cooling models even though the sediment corrected basement depth of 6 5 km at this location is normal for its age an analysis of existing heat flow depth and geoid anomalies in the northwest atlantic shows that there is little correlation between heat flow and depth throughout the entire region depth and geoid are clearly related to the bermuda swell while the associated heat flow anomaly once adjusted for variations with age is limited to 5 mw m 2 and only decays to the south this means that the bermuda swell is probably not caused by extensive thermal reheating within the lithosphere but instead by dynamic uplift at its lower boundary due to the convective upwelling of a mantle plume the regionally high heat flow in the northwest atlantic may be a thermal remanent of previous plumes which passed beneath this region early in its history therefore depth and heat flow anomalies from this region cannot be used to provide constraints on steady state parameters of the lithosphere such as the presence or absence of a long term boundary layer at its base

the galapagos spreading center at 86 w a detailed geothermal field study appendix is available with entire article on microfiche orderfrom american geophysical union 2000 florida avenue n w washington d c 20009 document j80 013 01 00 payment mustaccompany order we report here measurements of the heat flow field of the galapagos spreading center on crust of age less than 1 0 m y the 443 measurements in an area of about 570 km2 reveal the general planform of the geothermal flux and permit the first truly areal estimate of the near axis conductive heat flux the intrusion process and associated hydrothermal circulation dominate the surface heat flow pattern with circulation apparently continuing beyond the limits of our survey the areal average of the conductive heat flux is 7 1 0 8 hfu 295 33 mw m2 about one third the heat flux predicted by plate models the remaining heat is apparently removed by venting of hydrothermal waters at the spreading axis and through basalt outcrops and hydrothermal mounds off axis the pattern of surface heat flux is lineated parallel to the axis and the strongly lineated topography sharp lateral gradients in the heat flow greater than 10 hfu km near escarpments and commonly expressed as high heat flow at the tops of the scarps and lower heat flow in the valleys may indicate a local concentration of the circulation by surface fault systems and or variable sediment thickness

heat flow and seismic observations in the northwestern banda arc results of heat flow measurements in the centers of three basins in the nw banda arc carried out during the indonesian dutch snellius ii expedition in 1985 all show high heat flow values the average heat flow in the north buru basin on the outside of the arc is 161 mw m2 two small ns to nw se elongated subbasins situated in the lucipara basin show heat flow values of 175 and 134 mw m2 respectively the high heat flow measured in both the north buru and lucipara basins is interpreted to be the result of recent ew strike slip movement in the northwestern banda arc

subsidence history crustal structure and thermal evolution of the valencia trough a young extensional basin in the western mediterranean the valencia trough is an extensional basin that began rifting during the late oligoceneearly miocene yet it is located within a region of compression between the european and african plates seismic reflection seismic refraction well gravity and geoid data have been used to determine the relative importance of extensional and compressional processes in controlling the structure and evolution of the trough although the trough appears symmetric on bathymetric maps seismic and gravity and geoid data indicate a fundamental asymmetry in its deep crustal and upper mantle structure two dimensional flexural backstripping techniques have been used to estimate the total amount of crustal stretching along a transect of the trough between the catalan coastal ranges and mallorca there is good agreement between the predicted depth to the mono based on a stretching model and the seismically constrained depth beneath the catalan margin but poor agreement beneath mallorca the seismic moho beneath mallorca can be explained by a model in which the crust was modified by the flexural effects of thrust fold loading geoid data suggest that the differences in the crustal structure between the two margins extend into the upper mantle the catalan margin is characterized by a thermal and mechanical boundary which marks the transition between cold unstretched lithosphere and hot thin lithosphere while mallorca is located above a broad region of lithospheric thinning the subsidence history and amount of crustal thinning in the catalan margin resemble that of typical atlantic type nonvolcanic margin however a narrow transition zone 60 km the lack of any evidence for a conjugate margin and the absence of oceanic crust suggest fundamental differences in the way that extensional processes may occur in convergent plate settings

probabilistic tectonic heat flow modeling for basin maturation assessment method and applications tectonic modeling is often neglected in the basin modeling workflow and heat flow is most times considered a user input such heat flows can therefore result in erroneous basin modeling outcomes resulting in false overoptimistic identification of prospective areas or failure to identify prospects this is particularly true for areas with limited data control such as frontier basin areas or deep unexplored plays in mature basins three major factors obstruct routinely use firstly because of the focus of most tectonic models on lithosphere scale processes a large range of models including the mckenzie rift model fail to take into account effects which are of paramount importance for basement heat flow such as transient effects of sediment infill and erosion and changes in crustal heat production over time secondly lithosphere tectonic models often fail to allow inversion of basin data making forward tectonic modeling a cumbersome exercise non vertical sediment movements and 2d and 3d loading effects can play an important role hampering a unique inversion thirdly lithosphere tectonic models generally fail to aid the user to understand the sensitivity of the model results in terms of basin maturation for permissible ranges of tectonic model parameters and for uncertainties in tectonic scenarios such as absence or presence of underplating or two layered stretching vs a mckenzie model for this reason we have developed a multi 1d probabilistic tectonic heat flow model which is capable of calculating tectonic heat flows incorporating a variety of tectonic scenarios the model is capable of inversion of burial histories calibrated to temperature and maturity data calibration and sensitivity analysis is done through monte carlo sampling analysis using an experimental design technique for computational efficiency the tectonic heat flows can easily be used as input for basin modeling in commercially available 3rd party software 2009 elsevier ltd all rights reserved

cretaceous collision and indentation in the west carpathians view based on structural analysis and numerical modeling 1 a model of indentation of a rigid promontory into weak metasedimentary rocks during cretaceous convergence is suggested for tectonic evolution of southern part of west carpathians an early arcuate cleavage fan has developed in front of northward moving southern rigid basement block the interaction of the moving indenter with western stationary basement promontory is responsible for development of the boundary parallel shear zone along which the main southern indenter is shifted to the east this results in development of a new steep transpressional cleavage overprinting the early fabric eastward displacement of the southern indenter causes the development of a thrust zone parallel to the margin of the eastern stationary promontory a proposed numerical model of the deformation of a thin viscous sheet in front of oval rigid indenter reliably simulates the development of the observed deformation pattern modeled discrete partitioning between the western promontory and the indenting block fully agrees with the observed secondary cleavage associated with the transpressional shear zone our numerical model interconnects this complex kinematic frame with finite strain pattern which was to date possible only for simple boundary conditions in addition the model explains the polyphase cleavage patterns in terms of complex shapes of promontories and changes in movements of indenting blocks

interbasin deep water exchange in the western mediterranean owing to its nearly enclosed nature the tyrrhenian sea at first sight is expected to have a small impact on the distribution and characteristics of water masses in the other basins of the western mediterranean the first evidence that the tyrrhenian sea might in fact play an important role in the deep and intermediate water circulation of the entire western mediterranean was put forward by hopkins 1988 there an outflow of water from the tyrrhenian sea into the algero provencal basin was postulated in the depth range 700 1000 m to compensate for an observed inflow of deeper water into the tyrrhenian sea however this outflow the tyrrhenian deep water tdw was undetectable since it would have hydrographic characteristics that could also be produced within the algero provencal basin a new data set of hydrographic tracer lowered acoustic doppler current profiler ladcp and deep float observations presented here allows us now to identify and track the tdw in the algero provencal basin and to demonstrate the presence and huge extent of this water mass throughout the western mediterranean it extends from 600 m to 1600 1900 m depth and thus occupies much of the deep water regime the outflow from the tyrrhenian is estimated to be of the order of 0 4 sv sv 10 6 m 3 s 1 based on the tracer balances this transport has the same order of magnitude as the deep water formation rate in the gulf of lions the tyrrhenian sea effectively removes convectively generated deep water western mediterranean deep water wmdw from the algero provencal basin mixes it with levantine intermediate water liw above and reinjects the product into the algero provencal basin at a level between the wmdw and liw thus smoothing the temperature and salinity gradients between these water masses the tracer characteristics of the tdw and the lowered adcp and deep float observations document the expected but weak cyclonic circulation and larger flows in a vigorous eddy regime in the basin interior

apparent shear band geometry resulting from oblique fold sections abstract small scale shear zones inclined at intermediate angles to an earlier anisotropy are often observed in deformed rocks they are traditionally described as shear bands c bands extensional crenulation cleavage or normal kink bands formed as a result of extension along the anisotropy their asymmetries are widely used to describe the large scale kinematics of deformation and the deformational history of a given area we demonstrate that when various three dimensional fold structures are observed on two dimensional outcrop surfaces or in thin section they can appear geometrically identical we have developed a simple technique that allows the geometrical evaluation of any section across a cylindrical fold of arbitrary geometry the ranges of planar sections on which a fold exhibits shear band like geometry are presented on a stereographic projection in order to simplify the determination of critical orientations we demonstrate that for any fold geometry there are two distinct groups of sections showing shear band like geometry with opposite senses of shear criteria systematically arranged around the axial plane and which are inclined at a high angle to the major anisotropy we provide a field example from western carpathians where kinematic analysis mainly based on apparent extensional shear bands led to overemphasis of the role of post orogenic extension on the final structural pattern of the belt

oligo miocene rotation of sardinia kar ages and paleomagnetic data of tertiary volcanics abstract conventional k ar dating was carried out on mineral separates mostly plagioclases from middle tertiary volcanics of sardinia along with paleomagnetic studies the close agreement of dates from the two methods establishes the rotation age of sardinia relative to europe within a rather short time span of 1 5 ma between 20 5 and 19 ma from correlation of our results with the geomagnetic time scale it is suggested that the rotation took place shortly after the magnetic anomaly 6

interpretation of heat flow density of the apennine chain italy the apennine chain is a consequence of the continental collision between europe and africa characterized by several compressive phases with events of intense shortening during one of these phases from early oligocene to early miocene the continental crust broke into various segments which became packed one over the other forming an adriatic verging structure of imbricated listric wedges this event is thermally modeled in the southern apennines by the successive overthrust of two slabs of 7 km total thickness and explains the low heat flow density hfd 40 mw m 2 observed there in the northwestern apennines modeling is on the basis of the overthrusting of a slab 10 km thick which reduced the hfd of the steady lithosphere 63 mw m 2 observed on the iblean platform to 50 4 mw m 2 from the late miocene onwards tensional tectonism developed in the internal areas of the chain application of mckenzie s simple stretching model shows that the high regional heat flow 100 mw m 2 obtaining by filtering the observed data is explained by a stretching of the lithosphere of a factor 3 1

heat flow in the western mediterranean thermal anomalies on the margins the seafloor and the transfer zones the western mediterranean basin has been formed by miocene back arc extension and is underlain by a thin and young lithosphere this young lithosphere is warm as testified by an overall elevated offshore heat flow heat flow within the western mediterranean is however highly variable and existing data are unevenly distributed and poorly studied in the central part of the liguro provencal and algero balearic basins this central part is floored by a young oceanic crust bordered by different continental margins cut by transform faults and filled by up to 8 km of sediments we present a total of 148 new heat flow data collected during the medsalt and westmedflux cruises in 2015 and 2016 and aligned along seven regional profiles that show an important heat flow variability on the basin scale but also locally on the margins a new heat flow map for the western mediterranean outlines the following regional features 1 a higher average heat flow in the algero balearic basin compared to the liguro provencal basin 94 13 mw m2 and 78 16 mw m2 respectively and 2 a regional thermal asymmetry in both basins but with opposed heat flow trends up to 20 of this heat flow difference can be explained by sediment blanketing but age and heterogeneity of ocean crust due to an asymmetric and polyphased opening of the basins are believed to have given the major thermal imprint estimates of the age of the oceanic crust based on the new heat flow suggest a considerably younger west algerian basin 16 23 ma compared to the east algerian basin and the west sardinia oceanic floor 31 37 ma on the margins and ocean continent transitions of the western mediterranean the new heat flow data point out the existence of two types of local anomalies length scale 5 30 km 1 locally increased heat flow up to 153 mw m2 on the gulf of lion margin results from thermal refraction of large salt diapirs and 2 the co existing of both low 110 mw m2 heat flow areas on the south balearic margin suggests a heat redistribution system we suspect the lateral heat advection is resulting from a regional fluid circulation in the sediments associated to the widespread plio pleistocene volcanism on the south balearic margin

heat flow and lithospheric thinning in the ligurian basin n w mediterranean we present preliminary results of 78 new heat flow measurements collected on a transect across the central ligurian basin south france to corsica margins the basin wide flux has an average of 79 21 mwm 2 with significant local and regional variability correction for the deposition of up to 5 km of post rift sediment gives a mean value of 102 mwm 2 which is similar to values for normal oceanic crust of the same age 21 ma the total tectonic subsidence tts calculated for the region with probable oceanic crustal structure is comparable to or somewhat greater than 21 ma crust of the major ocean basins the heat flow data overall are compatible with the observed tts in showing substantial lithospheric thinning but do not tightly constrain thermal models of continental extension and rifting

morphogenesis of the sw balearic continental slope and adjacent abyssal plain western mediterranean sea we present the seafloor morphology and shallow seismic structure of the continental slope south east of the balearic promontory and of the adjacent algero balearic abyssal plain from multibeam and chirp sonar data the main purpose of this research was to identify the sediment pathways from the balearic promontory to the algero balearic deep basin from the early pliocene to the present the morphology of the southern balearic margin is controlled by a sw ne structural trend whose main expressions are the emile baudot escarpment transform fault and a newly discovered wsw ene trend that affects the sw end of the escarpment and the abyssal plain we relate the two structural trends to right lateral simple shear as a consequence of the miocene westward migration of the gibraltar arc newly discovered steep and narrow volcanic ridges were probably enabled to grow by local transtension along the transform margin abyssal plain knolls and seahills relate to the subsurface deformation of early stage halokinetic structures such as salt rollers salt anticlines and salt pillows the limited thickness of the overburden and the limited amount of deformation in the deep basin prevent the formation of more mature halokinetic structures such as diapirs salt walls bulbs and salt extrusions the uppermost sediment cover is affected by a dense pattern of sub vertical small throw normal faults resulting from extensional stress induced in the overburden by subsurface salt deformation structures shallow gas seismic character and the possible presence of an active polygonal fault system suggest upward fluid migration and fluid and sediment expulsion at the seafloor through a probable mud volcano and other piercement structures one large debris flow deposit named formentera debris flow has been identified on the lower slope and rise of the south formentera margin based on current observations we hypothesize that the landslide originating the formentera debris flow occurred in the holocene perhaps in historical times

modern tectonic regime in the tyrrhenian area observations and models summary the rapid opening since 10 ma of the tyrrhenian sea in a context of convergence between eurasia and africa remains a puzzling geodynamic problem one of the most plausible scenarios proposed by malinverno ryan 1986 attributes extension to southward and eastward migration of the trench resulting from subduction of the african adriatic lithosphere below the european lithosphere at present subduction only continues along the calabrian arc a compilation of recent strain and stress indicators by rebai philip taboada 1992 indicates that an extensional regime still prevails in the tyrrhenian sea whereas compression dominates north and south of this area in an earlier paper bassi sabadini 1994 used a numerical model to demonstrate the necessity of a trench suction force acting along the subduction trench to produce the present extension in the tyrrhenian domain this study however did not discuss in detail the tectonic regime in the different areas composing the domain nor the match between the observations and the model in this paper we first review the constraints provided by the observations compiled by rebaiet al 1992 and by more recent measurements we then investigate how much of the observed tectonic regime can be understood in terms of plate interaction forces using thin plate models bird 1989 the geometry and heterogeneous lithospheric properties of the models are constrained by observations the best constrained boundary conditions are held constant the remaining are regarded as parameters that we tune in order to fit the observations our results indicate that the present day tectonic regime in the tyrrhenian area can be explained as a consequence of trench retreat associated with the subduction of ionian oceanic lithosphere under the calabrian arc combined with a rotation of the apennines possibly related to a rotation of the adriatic microplate this study supports therefore the model of malinverno ryan 1986 and suggests moreover that rotation of the apennines is an ongoing process which is supported by seismological and geodetic data but remains to be understood in terms of geodynamics a discrepancy between observations and models is observed in western sicily which can be attributed to modelling limitations the weak extensional activity of the corsica sardinia block however is not explained by this model

heat flow data and shallow thermal regime on mallorca and menorca western mediterranean abstract the first heat flow density values acquired on the balearic islands are presented a total of 39 thermal gradient determinations were carried out 23 on mallorca and 16 on menorca the sampling points consist of water exploration wells whose depths range between 100 m and 250 m most of the thermometric logs are strongly affected by water circulation through the formation and or through the borehole heat flow density measurements have been performed from 18 boreholes where conductive heat transport is inferred thermal conductivity values were obtained from 52 available well core samples covering the main lithologies present in the area after topographic and paleoclimatic corrections surface heat flow values ranging from 24 13 mw m 2 to 88 23 mw m 2 for mallorca and from 46 6 mw m 2 to 92 20 mw m 2 for menorca are obtained a well defined positive thermal anomaly associated to upward ground water flow is described on mallorca water flowing through the mesozoic basement would be responsible for an overall cooling effect affecting the northeastern half of the island where the lower heat flow values are measured water perturbations on menorca are mainly due to hydraulic connection through the borehole taking into account the effects of the regional ground water flow background heat flow densities of about 70 80 mw m 2 for mallorca and 75 90 mw m 2 for menorca are proposed

heat transfer through the sediments of the mounds hydrothermal area galapagos spreading center at 86 w heat transfer processes at the mounds area of the galapagos spreading center at 86 w are revealed by temperatures measured at 10 m intervals in the 30 10m sediment at each of 12 holes at dsdp leg 70 sites 506 509 and by temperatures of up to five thermistors on eleven 8 12 m long piston cores the 325 needle probe values show a significant linear increase of thermal conductivity with depth in each core about half of the temperature thermal resistance profiles are nonlinear and are fit to a steady state vertical pore water advection model results indicate high and variable total heat flow and localized hydrothermal discharge at 10 8 m s associated with individual mounds recharge is indicated at similar rates in the low heat flow belt 5 km south of the mounds and is suggested at slower rates in the intermediate heat flow 0 17 0 42 w m2 belt surrounding the mounds heat flow high possible slow entrained recharge within 100 m of discharging mounds is suggested also suggested is strong local discharge along the major fault bounding the mounds crustal block to the north about 95 km north of the spreading axis at dsdp site 510 temperatures in the 114 m sediment cover on 2 7 m y crust are linear consistent with the suggestion that the hydraulic resistance of this layer is sufficient to seal off free hydrothermal exchange between basement and bottom water the combination of heat flow data and the physical properties data of karato and becker this issue suggests that 50 m of sediment may be a threshold thickness for sealing of hydrothermal circulation within basement where the topography is smooth we suggest that the formation of mounds may be associated with the forced localization of hydrothermal discharge through the sediment as its thickness approaches this threshold value

thermo mechanical modeling of the tyrrhenian sea lithospheric necking and kinematics of rifting we present the results of quantitative forward modeling of the sardinian rifted margin of the tyrrhenian sea the purpose of this study is to investigate the thermo mechanical structure that affects the thinning of the lithosphere across the margin the role of lithospheric necking during basin formation constrained by basement topography moho depth and gravity anomalies is modeled for different compensation models independent constraints are obtained from the analysis of the predicted thermal structure a deep level of necking 25 km is required to explain the observed crustal geometries and gravity anomaly signature the model predicts spatial and temporal variations in rheology during extension with important implications for kinematics of lithospheric thinning prerift lithospheric conditions strain rate and temperature during extension appear to be the key controls on the style of lithospheric rifting and necking in the tyrrhenian sea a forward model for basin stratigraphy is presented for the polyphase history of the tyrrhenian rifting this model provides quantitative estimates of time space dependent crustal thinning and rates of extension

evidence for the multi stage formation of the south western valencia trough a basin evolution model for the south western valencia trough is established using thermal and palaeo thermal data bottomhole temperature and drillstem test data from oil wells have been used to determine the geothermal gradient in the study area a combination of well log data and x ray diffractometry analyses carried out on rock samples from the ibiza marino well has allowed an estimation of the bulk thermal conductivity and heat flow density integrating these data with previous seafloor heat flow measurements yields a regional surface heat flow density of about 90 100 mw m 2 vitrinite reflectance data available from the ibiza marino well have been used as a palaeo thermal constraint for the proposed tectonic models two different modelling approaches are tested a single rift phase model and a multi phase formation model the single rifting phase which considers different eroded thicknesses is ruled out as it does not match the observed data a multi stage evolution coherent with the geological and geophysical data is proposed and consists of three mesozoic rifting events palaeogene compression to which erosion of about 5 km of late jurassic and cretaceous sediments is related and a neogene rifting event that gave rise to the present day valencia trough surface heat flow vitrinite data and eroded thickness are successfully integrated in the proposed model

thermal state and deep earthquakes in the southern tyrrhenian the geodynamic processes in the southern tyrrhenian are approached by comparing the thermal structure with the seismic activity subsidence data are used to determine the boundaries of the oceanic domains in the abyssal area the regional pattern of the surface heat flux reflects lateral variations of structural properties of the lithosphere in the oceanic domain a mean heat flux of 160 mw m 2 is observed to which a convective component of about 100 mw m 2 should be added if an ocean plate cooling model is applicable for a pure shear stretching model the heat flux values of the continental margins indicate a thinning factor of 3 5 4 0 the maximum frequency of seismic events occurs in the 200 350 km depth interval and the energy released is maximum between 250 and 300 km most earthquakes are confined within a 30 50 km thick zone the slab dip angle is about 65 in the 100 400 km depth range characterised by predominant down dip compression then both the slab and the maximum compression axis slightly deflect down to 500 km depth where the deepest event occurs under the hypothesis that the seismic activity is confined within portions of downgoing lithosphere which have a temperature below a depth dependent critical value calculations for a 60 70 km thick slab sinking at a velocity of 6 10 2 m yr 1 yield a thermal structure compatible with the distribution of the deepest seismic activity such a thermomechanical picture and the correlation between the slab dip angle and the total tectonic subsidence of the oceanic domain are typical features of a young marginal basin and are related to the drag stress in the vicinity of the downgoing lithosphere

secondary cleavages in ductile shear zones abstract secondary cleavages developed at late stages in ductile shear zones show several features that are inconsistent with progressive simple shear in the zone these are the orientation of a single secondary cleavage oblique to the shear zone boundaries conjugate sets with opposite senses of shear and multiple sets with the same sense of shear these features can be explained if the bulk flow is partitioned into slip along discrete failure planes parallel to the primary foliation s coaxial stretching along the foliation and spin

cretaceous evolution of a metamorphic core complex the veporic unit western carpathians slovakia p t conditions and in situ40ar 39ar uv laser probe dating of metapelites alpine metamorphism related to the development of a metamorphic core complex during cretaceous orogenic events has been recognized in the veporic unit western carpathians slovakia three metamorphic zones have been distinguished in the metapelites 1 chloritoid chlorite garnet 2 garnet staurolite chlorite 3 staurolite biotite kyanite the isograds separating the metamorphic zones have been modelled by discontinuous reactions in the system k2o feo mgo al2o3 sio2 h2o kfmash the isograds are roughly parallel to the north east dipping foliation related to extensional updoming along low angle normal faults thermobarometric data document increasing p t conditions from c 500 c and 7 8 kbar to c 620 c and 9 10 kbar reflecting a coherent metamorphic field gradient from greenschist to middle amphibolite facies 40ar 39ar data obtained by high spatial resolution in situ ultraviolet uv laser ablation of white micas from the rock slabs constrain the timing of cooling and exhumation in the late cretaceous mean dates are between 77 and 72 ma however individual white mica grains record a range of apparent 40ar 39ar ages indicating that cooling below the blocking temperature for argon diffusion was not instantaneous the reconstructed metamorphic p t t path is clockwise reflecting post burial decompression and cooling during a single alpine orogenic cycle the presented data suggest that the veporic unit evolved as a metamorphic core complex during the cretaceous growth of the western carpathian orogenic wedge metamorphism was related to collisional crustal shortening and stacking following closure of the meliata ocean exhumation was accomplished by synorogenic orogen parallel extension and unroofing in an overall compressive regime

thermal origin of the hawaiian swell heat flow evidence and thermal models the lithospheric reheating hypothesis for the origin of the hawaiian swell has been tested by heat flow measurements along the swell between hawaii and midway ninety five measurements at eight carefully selected sites show that the heat flux on the swell increases systematically from near normal values 52 2 mw m 2 near hawaii to values near midway 59 2 mw m 2 about 20 25 higher than normal for lithosphere of that age 110 m y this heat flow pattern is qualitatively consistent with a deep seated thermal anomaly created in a lithospheric plate moving across a fixed heat source modeling of the heat flow and bathymetry data on the hawaiian swell strongly suggest that the swell is caused by a rapid heating within 40 to 50 km depth of normal 90 m y old lithosphere over a relatively broad 500 1000 km region near hawaii this model is also consistent with gravity and geoid anomalies associated with the swell which require a low density region in the lower lithosphere and with flexure studies of seamounts in the hawaiian chain which indicate that the rigidity of the lithosphere is not significantly reduced by the reheating appendices a c are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j82 005 1 00 payment must accompany order

regional scale tectonic evolution and the seismic velocity structure of the lithosphere and upper mantle the mediterranean region we present a numerical modeling approach designed for the verification of tectonic reconstructions and for a quantitative analysis of the seismic velocity structure of the lower lithosphere and upper mantle in this forward modeling procedure we use published reconstructions of the tectonic evolution of a region to predict the thermal structure from which we calculate physical quantities like p wave velocity basin subsidence and basement heat flow we show an application of this approach to two reconstructions of the late mesozoic and cenozoic evolution of the mediterranean region the resulting synthetic velocity models are tested against seismological models of the mantle structure obtained independently by delay time tomography subsidence and heat flow predictions are compared with actual observations to further constrain the geological assumptions underlying the forward models the mantle models predicted from reconstructions of the evolution of the mediterranean region correlate with major features in the tomographic images from our model results we conclude that the present distribution of seismic velocities in the mediterranean region is largely determined by the tectonic evolution during at least the last 40 m y this means we can verify processes represented in different tectonic scenarios with the seismologically determined velocity structure seen from a different perspective the model results contribute to understanding the causes of the velocity structure imaged by delay time tomography by showing how the tectonic evolution results in this structure

heat flow in the alboran sea western mediterranean abstract the results of the first regional heat flow survey carried out in the alboran basin are presented the survey consists of 98 heat flow measurements obtained using a violin type probe 697 nautic miles of gravity profiles 1446 nautic miles of bathymetric survey and 22 gravity cores a remarkable difference in heat flow patterns exists between the western wab and eastern eab parts of the alboran basin the average heat flow in the wab is 69 6 mw m 2 with a generally increasing trend towards the centre and to the east in contrast the heat flow pattern in the eab shows an average value of 124 8 mw m 2 and it is maintained rather constant for the overall area superimposed on this general pattern there are some local thermal anomalies associated with hydrothermal activity which have been detected in the central wab up to 123 mw m 2 in the south alboran basin sab up to 153 mw m 2 and in the djibouti bank db up to 254 mw m 2 after corrections for thermal refraction sedimentation and cooling of volcanic bodies the resulting heat flow distribution in the wab is smoother but still shows the increasing trend towards the centre and to the east in the eab the application of these corrections did not lead to any noticeable changes a 1 d approach that combines heat flow data crustal structure and elevation shows a dramatic decrease in lithospheric thickness from the wab 50 90 km to the eab 38 40 km likewise the resulting crustal thickness is around 14 16 km in the central part of the wab increasing towards the borders of the basin whereas in the eab the crustal thickness varies between 12 5 and 14 5 km in its western part and between 10 and 11 5 km in its eastern part

marine tectonics processes at mid ocean ridges the use of multibeam echo sounders and various side looking sonar systems has greatly increased our knowledge and understanding of mid ocean ridge mor processes since the last iugg review on mid ocean ridge research macdonald 1983 the extensive use of swath mapping tools such as sea beam deep tow seamarc i and ii the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions this review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid ocean ridges in the last four years certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews because of the exponential growth in the number of publications related to mors during 1982 1986 only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text references published prior to 1982 were added only where appropriate

a spatial domain stokes flow model for the gravity and topography of the middle latitudes of venus a new modeling strategy is developed and applied to the long wavelength gravity topography and internal density structure of venus geodynamic modeling of planetary scale phenomena is usually carried out in the wavenumber transform domain spherical harmonics or fourier transforms however because of limitations associated with the gravity and topography data available for venus a spatial domain approach is preferable smoothed representations of the gravity and topography of venus are developed in terms of quadratic b splines on 10 centers in latitude and longitude over the latitude interval from 45 s to 45 n these models reproduce 83 6 and 98 3 of their respective data variances a similarly constructed model is then presented for the dynamic support of gravity and topography on venus internal mass anomalies are specified at two discrete depths 50 and 500 km with lateral variations determined by two constraints 1 that the slow viscous flow induced by the anomalies will distort the free surface into a form matching the observed topography and 2 that the sum of the gravitational effects of the internal anomalies plus that due to the surface distortion they cause will match the observed gravity there are four major features evident in the gravity and topography data sets atla beta ovda and thetis regiones all four have compensating mass patterns consistent with a mantle plume origin the surficial flow pattern associated with this model does not resemble terrestrial plate tectonic patterns

a land locked back arc basin preliminary results from odp leg 107 in the tyrrhenian sea abstract the odp leg 107 drilled a series of eleven holes across the tyrrhenian sea probably one of the youngest of the mediterranean sea sub basins four sites have documented the evolution of the sardinia passive type continental margin and shown that tilting and subsidence occurred earlier on the upper margin than on the present lower margin three sites have been drilled into the two small deep basins of the central tyrrhenian the results show that both basins are floored by basaltic basements and strongly support the model of back arc basin growth by seaward southeast in this case retreat of the downgoing hinge line plate

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

heat flow and geodynamics in the tyrrhenian sea the present heat flow in the southern tyrrhenian sea appears as a transient thermal wave that has migrated eastward in time the higher heat flow in the south eastern side of the basin confirms the suggestion of an eastward migrating rift punctuation of the tyrrhenian backarc extension in lithospheric boudins is accompanied by a concentrated increase in heat flow generated by asthenospheric intrusions and related magmatism progressively moving eastward the migration of the asthenosphere in the same direction could explain these phenomena

the effects of sedimentation and compaction on oceanic heat flow summary the estimation of environmental effects forms an important part of the interpretation of oceanic heat flow measurements in particular the perturbations associated with sedimentation and surface temperature changes must be taken into account analytical solutions can be obtained only for individual simplified versions of these problems whereas any real example is complicated by the process of sediment compaction which changes the bulk thermal properties with depth a physical model is developed which uses sediment porosity trends to predict the thermal parameters and material advection rates for an evolving sediment basement system these values are then used in a numerical solution to the heat flow equation to give estimates of the perturbed surface heat flux through time in addition to variations in sedimentation rate sediment type radioactive heat production and surface temperature changes are considered heat flow corrections may vary by up to a factor of 2 according to sediment type while radioactive heat production can offset the effects of sedimentation by as much as 40 per cent the results also indicate that alterations determined from simple analytical models tend to over estimate the true perturbation to the flux

a precautionary note on shear bands as kinematic indicators the orientation of shear bands relative to foliations defined by elongated mineral aggregates is often used to determine the large scale sense of displacement in ductile faults data from contact strain zones at the bases of large overthrust complexes in the eastern alps and the betic cordilleras demonstrate that there is not always a simple geometrical relation between shear band orientation and sense of vorticity in bulk non coaxial flow in addition to single shear band sets that show displacements synthetic with the large scale displacement there are single sets with antithetic displacements and conjugate sets the last two observations are at variance with published data and interpretations and cast doubts on the general applicability of shear bands as indicators of large scale flow kinematics

thermal evolution of a rift basin the tyrrhenian sea existing geological and geophysical data support the view that the opening of the tyrrhenian sea was by rifting of a formerly continuous continental lithosphere which began in upper miocene on the upper sardinian margin and migrated southeastward to the calabria margin heat flow across the tyrrhenian sea shows a pronounced asymmetry from about 50 70 mw m 2 over the sardinian margin to more than 150 mw m 2 over its southeastern margin off southern italy and calabria in this study we use the newly acquired data from ocean drilling program leg 107 heat flow seismic velocity and bathymetric data to constrain a group of models that supposes the tyrrhenian sea opened by detachment of a formerly continuous lithosphere along a southeastern facing low angle normal fault specific models tested include 1 the wernicke model in which thinning and extension of the continental lithosphere are supposed to be accomplished by simple shear along a large scale gently dipping detachment fault zone which cut through the entire lithosphere and 2 the delamination model in which the low angle detachment fault is supposed to cut only the upper and middle crust but to merge subhorizontally into the lower crust below which concurrent pure shear may occur a versatile two dimensional finite element procedure is used to evaluate the tectonic and thermal evolution of these models and the results are compared with observations to test the validity of the models delamination models with large pure shear components in the lower lithosphere and the wernicke model predict heat flow within 1 of the measurements the wernicke model however predicts a basin configuration much too deep in comparison with bathymetry and a subbasinal lithospheric thickness substantially different from rayleigh wave dispersion results the delamination model with a large component of pure shear in the subbasinal lower lithosphere on the other hand predicts satisfactorily both the bathymetry and the lithospheric thickness beneath the basin

structural framework and crustal characteristics of the sardinia channel alpine transect in the central mediterranean abstract the submerged area located between the sardinia channel and the western sicily offshore has been investigated based on deep crustal and conventional seismic lines with the aim of illustrating the relationships between the crust and its overlying crystalline and sedimentary thrust wedge analyses of seismic attributes and reflector pattern supported by dredge hauls also provided data in areas where stratigraphic and lithologic control is absent crustal geometries tectonic processes and timing of the deformation are discussed here north of the elimi chain central sardinia channel the reflecting body consists of superposed tectonic wedges of crystalline rocks and their meso cenozoic carbonatic and terrigenous cover sardinian and kabilian calabrian units the kabilian calabrian units overthrust the maghrebian apenninic units along the drepano thrust front elimi chain which is traceable on land in eastern sicily nebrodi peloritani mountains this lineament roots on the crustal mantle discontinuity where the local superposition of two different crusts occurs the thrust front of the crystalline kabilian calabrian units marks the boundary between thick skinned and thin skinned tectonics in the chain the apenninic segment of the chain develops between the elimi sector and the sciacca offshore south west sicily the crust is not as thick as expected in alpine chain areas suggesting pre orogenic thinning of the african continental crust the accretionary wedge is a southeast vergent embricate fan consisting of four groups of thrust units formed by carbonate basinal and platform ramps with duplex geometries the mesozoic carbonate units are detached from the crystalline basement not involved in the deformation the tertiary terrigenous rocks are their roof thrust the upper miocene clastic terrigenous successions sealing most of the structures appear in turn detached and piled up the intramountain plio pleistocene basins display tectonic features that point out the area underwent both extensional and contractional tectonics

architecture and neogene to recent evolution of the western calabrian continental margin an upper plate perspective to the ionian subduction system central mediterranean the western calabria continental margin forms the transition between the pliocene to recent marsili spreading center and continental calabria all parts of the upper plate of the ionian subduction zone integrating high resolution and crustal seismic images constrained by gravity modeling we provide a detailed reconstruction of the architecture of the margin and develop a new scheme for its miocene to present evolution this time span encompasses the continent continent collision between africa and eurasia subsequent orogenic collapse and rifting apart between the two continental masses and the pliocene to recent emplacement of oceanic crust in the vavilov and marsili basins the crust of the margin thins from the calabria coast 25 km to the marsili continent ocean transition 12 km on the whole upper and lower crusts thin proportionally with pure shear geometry the continental margin is covered by an oligocene to present sedimentary succession reaching a maximum thickness of 6 0 km in the paola basin during the miocene the continental margin experienced regional shortening accommodated by a large number of mainly west vergent thrusts possibly associated with the late stages of the kabilo calabrian chain shortening continued through pliocene to recent but was accommodated by a limited number of west vergent thrust faults located in the western part of the margin and by a few tens of kilometers wide syncline located in the eastern part of the profile the accommodation space created in the syncline core hosted a 4 5 km thick plio quaternary sedimentary succession the paola basin no significant extensional fault is observed along the profile miocene to recent subsidence was controlled by 1 a short wavelength component related to shortening and responsible for the formation of the paola basin syncline and possibly contributing to the uplift of onshore calabria and 2 a long wavelength component responsible for the regional subsidence and oceanward tilting of the calabria margin short wavelength subsidence ended in the late pliocene but long wavelength downward movements persisted and even accelerated during late pliocene to quaternary times when the present day bathymetry was achieved both horizontal deformations and vertical movements are difficult to explain in the context of a normal back arc basin without taking into consideration patterns of secondary mantle flow generated by the retreat of the subducting slab