constraining the relative strengths of high grade metamorphic rocks using foliation refraction angles an example from the northern new england appalachians foliation refraction angles are used to estimate effective viscosity contrasts between metapelitic and metapsammitic layers in amphibolite facies metaturbidites in the presidential range of the white mountains in eastern new hampshire an early formed foliation developed during km scale nappe folding consistently displays larger bedding foliation angles in metapelitic units than metapsammitic units suggesting that the metapelitic units had higher effective viscosities during this deformation we collected bedding foliation angle measurements from a combination of outcrops and locally derived boulders to test the hypothesis that foliation refraction angles could be used to estimate the effective viscosity ratio between different rock types at high metamorphic grades our results show that the metapelitic layers were between 2 and 3 times more viscous than the metaspsammitic layers which we attribute to the presence of large up to 15 cm long abundant up to 30 vol effectively rigid andalusite porphyroblasts in the metapelitic layers we present a methodology for using foliation refraction angles to determine the effective viscosity ratios of different rock types address the practical limitations we encountered and suggest this method is an easy way of estimating the strength contrast between different rock types finally we hypothesize that metamorphism resulting in porphyroblast growth can strengthen large crustal volumes during orogenesis

lateral variations of thermo mechanical properties in the tyrrhenian northern apennine region abstract we present lithospheric strength profiles calculated for a transect running from the island of corsica in the west to the apennine foredeep in the east strength profiles are constructed at locations selected on the basis of the availability of seismic heat flow gravity data and earthquake foci distribution rheological modelling points to the presence of strong lateral variations in the thermo mechanical state of the lithosphere the tyrrhenian tuscany area has a low rigidity in relation with the intense stretching active from the early miocene and with very high heat flow associated with asthenospheric rise on the contrary hinterland corsica and apenninic foreland areas adriatic area show a higher level of lithospheric strength effective elastic thickness estimates confirm this scenario exhibiting a strong reduction from the northern tyrrhenian to the inner apennines and then an abrupt increase in correspondence of the adriatic plate the distribution of earthquake focal depths confirms the presence of a brittle rheology in the first kilometres of the crust in the tuscany area whereas close to the plate boundary much lower thermal gradients partly induced by the westward plunging adriatic plate enable seismic activity to occur at larger depths

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

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

regional evaluation of the coalbed methane potential of the foothills mountains of alberta canada abstract coal is present in the alberta foothills mountains in five zones the kootenay gething gates brazeau and coalspur coal zones for coalbed methane cbm evaluation purposes they can be divided into shallow less than 1000 m depth and deep greater than 1000 m depth coal zones the potential gas content of all shallow coal zones totals about 878 10 9 m 3 31 tcf of cbm which is considered an inferred initial in place coalbed methane resource estimate based on limited data the limited amount of data on formation testing and measured gas content indicate that the inferred resource is bordering on the speculative category the gas content of all deep coal zones deeper than 1000 m totals 2 8 10 12 m 3 about 99 tcf of in place coalbed methane gas consequently the total ultimate coalbed methane resource could be 3 7 10 12 m 3 130 tcf however coalbed methane recovery from deep coals is generally not attempted because of the high cost of drilling and the low permeability that results from high overburden load and stress the only limited foothills coalbed methane production has been from the southern alberta kootenay coal zone which is very prospective for coalbed methane production the shallow gates coal zone in the central and northern foothills is also prospective but needs to be better tested the best potential for coalbed methane in the coalspur coal zone is in the edson area entrance syncline and triangle zone the kootenay and gates coal zones are not well defined in the northern part of the calgary nts 82o map sheet

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

active geodynamics of the central mediterranean sea tensional tectonic evidences in western sicily from mantle derived helium 1 we report results on the measured high 3he 4he isotope ratio in western sicily interpreted together with the heat data the study of this sector of the europe africa interaction is crucial to a better understanding of the tectonics and the geodynamical evolution of the central mediterranean area the estimated mantle derived helium fluxes in the investigated areas are up to 2 3 orders of magnitude greater than those of a stable continental area the highest flux found in the southernmost area near the sicily channel where recent eruptions of the ferdinandea island occurred 20 miles out to sea off sciacca has been associated with a clear excess of heat flow our results indicate that there is an accumulation of magma below the continental crust of western sicily that is possibly intruding and out gassing through roughly n s trending deep fault systems linked to the mantle that have an extensional component although the identification of these faults is not sufficiently constrained by our data they could possibly be linked to the pre existing faults that originated during the mesozoic extensional transtensional tectonic phases

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

the legacy of the european geotraverse abstract the european geotraverse egt created a 4600 km profile across europe from north cape norway to tunisia not only did this produce the first comprehensive cross section to a depth of 450 km of continental lithosphere covering an eighth of the earth s circumference it covered the geological history of europe from the archaean to the present egt built up a detailed knowledge of the crust and upper mantle of europe by integrating geological and geophysical information in a coherent way continuously along a single profile it illuminated the dramatic contrast between the thickness and complexity of the lithosphere of western europe and that of fennoscandia which remain in isostatic equilibrium and elucidated the multilayered elements of thickened alpine crust and lithosphere and the dynamics of the western mediterranean nine years on the legacy of egt is the platform it provided for major scientific advances that have stemmed from it the greatest being through europrobe projects the pancardi project has discovered the subducted slab beneath the carpathian arc in the process of tearing apart from the lithosphere uralides has discovered the urals orogen is almost perfectly preserved since the palaeozoic and the tesz project has elucidated the complex evolution of the transitional region between the baltic shield and the caledonian and variscan crustal terranes of western europe the scientific advances of egt were matched by its achievement in mobilising an international workforce from every discipline of the earth sciences friendships made in that endeavour are another legacy of egt and many of those who started their research careers in egt are now leading europrobe projects and other collaborative ventures we all owe a great debt to professor stephan mueller who founded and led the european geotraverse and was its enduring inspiration

why is the ligurian basin mediterranean sea seismogenic thermomechanical modeling of a reactivated passive margin 1 the seismic activity of the ligurian basin the northeastern termination of the western mediterranean basin is larger than in surrounding regions even though recent geodetic studies attest that this area is subject to very low levels of deformation this basin is an example of a type of passive margins that cannot be considered solely as inert sites of sedimentation and of progressive subsidence and that are reactivated in a compressive pattern other examples include the kwanza basin angola and the brazil margin we investigated by means of 2 d thermomechanical modeling the structural and rheological heterogeneities that can lead to concentration of strain in this marginal basin we deduced that the deformation of the basin is due to its particular geometric features narrow and with a thick surrounding continental crust related to its position at the southern termination of the alps this sharp transition in terms of both geometry and rheological contrast is a main factor in explaining the weakness of the margin we discuss the importance of buoyancy forces versus tectonic forces as well as thermal effects on the observed reactivation influence of contrast in rheology between an oceanic type crust and continental crust is also studied geodynamical implications are proposed for the region the good agreement between the predicted localized deformation and the observed seismicity distribution should help improve seismic hazard assessment in the region

preliminary heat flow density data from tunisia and the pelagian sea heat flow density values at 78 sites in tunisia and the pelagian sea are derived from oil exploration wells bottom hole temperatures bht are systematically corrected for mud circulation cooling effects either by a horner technique when several temperature records are available at a given depth or by a statistical method based on the comparison of all bht with test temperatures dst that are representative of the actual formation temperatures thermal conductivities are estimated from detailed studies of stratigraphic and geophysical logs an inverse technique is used to estimate heat flow density for each borehole as well as interpolated temperatures at constant depths results are discussed with maps that include heat flow density data in neighbouring areas algeria and the strait of sicily the general trend corresponds remarkably to the recent structural evolution of the tunisian margin with high values in the pelagian sea and decreasing values toward the stable platform

deep structure of the north tyrrhenian sea from multi channel seismic profiles and on land wide angle reflection refraction seismic recording lisa cruise geodynamical implications we present a lithospheric section of the northern tyrrhenian basin based on principal observations along a transect from corsica island to tuscany margin offshore crustal structure observations come from the lisa deep seismic cruise composed by multi channel seismic profiles and wide angle reflection refraction seismic data other parts of the section are constrained by published data from different geophysical sources a great detachment between alpine corsica and hercynian corsica constitutes the base of the corsica basin the end of this detachment is probably located below the elba island in the ductile lower crust where we observed an east dipping reflector interpreted as ductile shear zone similar detachments have been observed beneath the punta ala basin on the tuscany margin our section shows a thin crust below corsican basin 15 km thick and a thicker crust below the pianosa ridge 25 km between elba island and the tuscany coast the moho reflections shallow to 23 km depth as identified on the mcs profiles and from the modelling of the wide angle reflection refraction seismic date an asthenospheric mantle uplift produces a significant heat flow below the tuscany margin the base of the lithosphere is located at 75 km depth below the corsica margin at 50 km below the corsica basin and as shallow as 30 km below the tuscany margin the shift observed between the corsica basin and the tuscany coast suggests an asymmetric lithospheric thinning which involves a detachment fault located at the base of the corsican basin

the middle ordovician to early silurian voyage of the dashwoods microcontinent west newfoundland based on new u pb and 40ar 39ar geochronological and kinematic constraints the dashwoods microcontinent is an important tectonic segment in the peri laurentian setting of the newfoundland appalachians in order to better understand the tectonic history of dashwoods during the ordovician taconic orogeny we have undertaken field mapping microscopic studies and u pb and 40 ar 39 ar geochronological studies along the northern little grand lake fault lglf and western baie verte brompton line cabot fault zone bcz boundaries oblique dextral ductile deformation in the bcz occurred from late middle ordovician into the early silurian based on the presence of a late syn tectonic pegmatite dike 455 12 ma and a foliated granodiorite sheet 445 8 0 6 ma deformation is coeval with oblique sinistral accretion along the eastern margin of dashwoods which means that dashwoods and its notre dame arc had a southward translation with respect to the laurentian margin and the then present iapetus ocean during the late ordovician dextral movement along the bcz continued after the collision of dashwoods with the laurentian margin deformation along the little grand lake fault is bracketed between 463 5 ma and 440 ma these ages combined with other geological arguments indicate that motion probably took place during the late ordovician to earliest silurian contemporaneous with the southward translation of dashwoods a possible explanation is that the snooks arm arc moved independently from and faster southwards than the notre dame arc with its dashwoods infrastructure thereby underthrusting the dashwoods along the little grand lake fault our new u pb geochronological data including a muscovite granite 463 5 ma a schistose muscovite granite 459 17 21 ma and a tectonized tonalite 458 20 ma add to the geochronological database of the voluminous second phase of the notre dame arc additionally in all but one of our u pb samples inherited grains of mesoproterozoic circa 1 0 ga age have been obtained their regional presence fortifies the possible relationship of the dashwoods microcontinent with the long range inlier in western newfoundland furthermore it introduces a potential link with the blair river inlier in cape breton island

on the origin and consequences of crustal scale extension between africa and sicily since late miocene insights from the kaboudia area western pelagian sea abstract the eastern tunisian shelf is located between the gulf of hammamet and the gulf of gabes and belongs to the pelagian domain which underwent a continuous ne directed extension and crustal thinning since late miocene this geodynamic process induced the formation of nw striking normal faults and associated grabens both in the tunisian atlas and the pelagian domain including the sicily channel rifting zone scrz in this study we combine regional stratigraphy from seismic reflection profiles focal mechanisms space geodetic measurements gnss and thermal indicators from well data to propose a backward tectonic reconstitution of the pelagian domain the thinning of the continental crust is demonstrated by gravity inversion integrating published seismic refraction profiles by completing the interpretation of tectono stratigraphic records we highlight a northeastward propagation of extension prevailing within the pelagian shelf from messinian to plio quaternary times we suggest that extensional tectonics is explained by 1 eastward slab tearing between the african continental lithosphere and the tethyan oceanic slab allowing asthenospheric upwelling and 2 forces arising from relative motions between nubia and the hyblean malta block the decoupling of these domains since late miocene likely results from a combination of the nw directed plate convergence inherited rheological contrasts within the continental crust and weakening arising from mantle flow induced by the tethyan slab rollback and tearing

mise en evidence d importantes variations regionales du flux de chaleur en algerie evaluation of heat flow in 230 oil wells using temperature measurements bottom hole temperature and temperature of fluids in drill stem test and various rock porosity data reveals a high heat flow average 82 19 mw m 2 associated with the algerian sahara basins the isopleth map exhibits significant regional variations overprinted by short wavelength anomalies that in general are related to the local geological structure on a regional scale we observe an essentially north south zonation that is not directly related to the major structural units except for the northern alpine domain the southern area at the border of the hoggar precambrian basement is characterized by very high heat flow values 90 130 mw m 2 the anomalies define a major axis generally east west which seems to affect the northern part of the african plate from the canaries to libya locally some relationships with extensional miocene pliocene quaternary volcanism suggest an association with recent mantle thermal events

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

a cross section of the lithosphere along the european geotraverse southern segment from the alps to tunisia abstract the european geotraverse southern segment egt s is a 200 300 km wide strip from the alps to tunisia which crosses the youngest tectonic provinces of europe where continued alpine compression is accompanied by recent extension e g in the ligurian sea and sicily channel the geophysical research along the egt s has been nearly continuous both on land and sea from 1982 to 1987 with deep seismic sounding dss experiments and collection of heat flow gravity magnetic seismological and seismotectonic data the new dss and seismic reflection data testify to the asymmetry of the alpine edifice the deepest part of the crust mantle boundary is found beneath the internal and external crystalline massifs where the european moho disappears after a steep flexure in the seismic reflection data the continuation of the moho discontinuity into the southern alpine domain is however evident in the seismic refraction data seismic evidence and heat flow data indicate incipient rifting in the ligurian sea which is underlain by a mantle with an anomalously low pn velocity of only 7 5 km s the palaeozoic crust of the sardinia corsica block exhibits a bowl shape with a rather undifferentiated internal structure average p wave velocity of 6 3 6 4 km s crustal thickness increases from 20 km at its margins to more than 30 km beneath the centre of the islands a thinned crust with thrusted blocks in its upper part characterizes the sardinia channel finally the preliminary dss results from tunisia show an abrupt deepening of the moho from 20 to approximately 35 km in the tell area very low average crustal velocity which requires a velocity inversion within the lower crust and subcrustal reflectors revealing a structured upper mantle

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

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

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

tectonic and litho stratigraphic controls on kaolin deposits within volcanic successions insights from the kaoliniferous district of north western sardinia italy abstract in northwestern sardinia a tertiary calc alkaline volcanic succession linked to the subduction of insubric oceanic crust and subsequent post collisional slab break off crops out and hosts several kaolin deposits we have undertaken field and laboratory studies to establish how the tertiary geodynamic setting of the western mediterranean and the composition and texture especially porosity of the volcanic rocks control the geometry and quality of the deposits massive andesites dacites and mildly welded rhyodacitic ignimbrites are the precursors of the kaolin kaolin deposits from the andesites contain pyrite and jarosite and the deposits which formed from the dacites contain up to 5 alunite the amounts of pyrite and alunite are negligible in deposits which formed from ignimbrite fracture controlled fluid dominated systems izawa 1986 responsible for the formation of the deposits are linked to nnw sse trending normal faults which formed during burdigalian to serravallian extension following on from collision between adria and europe corsica sardinia crust four types of deposit morphology bedform mushroom fault parallel and funnel are recognised based on the attitude fracturing and porosity of the precursor rock the remarkable funnel morphology was generated by repeated hydrothermal eruptions

analogue modelling of late miocene early quaternary continental crustal extension in the tunisia sicily channel area abstract we adopt analogue modelling to investigate continental crustal stretching by simulating a late miocene early quaternary extensional event occurred in tunisia and in the sicily channel the analogue model of the continental crust is composed of a lower ductile crust and an upper brittle crust including a low viscosity layer to simulate the presence of evaporites in our models the extension is driven by tectonic stresses and not solely by gravity all models are run under the same boundary conditions with a moveable lateral edge different physical hypotheses are tested to interpret the origin and geometry of this rifting event that affected the sw sector of the mediterranean basin the modelling of the continental crustal stretching produces small tectonic troughs with regular spacing that simulates the pattern observed in the atlasic rift system tunisia as well as a large rift zone involving bulk crust thinning simulating the features of the sicily channel rift zone in accordance with geological and geophysical data extension in the atlasic rift zone is controlled at depth by the triassic evaporite layer and by inherited diapiric structures that create rheological soft points in the upper crust the best accordance between models and nature are thus obtained when combining crustal scale stretching decoupling level within the upper crust and pre structuration inheritance of the evaporitic layer we propose that the ne trending extensional event occurring since the pliocene to the early quaternary in the tunisian pelagian sea area was driven by a transient eastward migration of the tunisia pelagian ionian area acting as a micro plate with an undefined southern boundary due to a far field pull of the western hellenic dinaride subduction

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

crustal velocity and strain rate fields in italy and surrounding regions new results from the analysis of permanent and non permanent gps networks summary we present a new geodetic velocity solution for italy and the surrounding areas obtained from an analysis of continuous and survey mode global positioning system observations collected between 1991 and 2002 we have combined local regional and global networks into a common reference frame velocity solution providing a new detailed picture of the regional scale deformation field in the central mediterranean our velocity estimates are computed with respect to a new stable eurasian reference frame constraining the kinematics of the greater african eurasian plate boundary system in the study area we provide strain rate values for the main seismotectonic districts which are in good agreement with the seismic deformation inferred from earthquake focal mechanisms the southern tyrrhenian area calabria the apennines the southeastern alps the southern dinarides and the albanides display deformation rates at the order of 20 30 nanostrain yr 1 the corsica sardinia block moves according to eurasian plate motions and there is no indication that the opening of the tyrrhenian is still active the pelagian and sicilian domains are separated by a northwest southeast discontinuity the sicily channel rifted area and marginally significant relative motion between the pelagian plateau and the african plate is also observed the southern tyrrhenian is affected by north south compression and accommodates up to 50 per cent of the africa eurasia relative plate motion whereas the calabrian arc exhibits 2 mm yr 1 northwest southeast extension the observed deformation pattern suggests the presence of a major approximately north south tectonic discontinuity separating the sicilian and calabrian domains an extensional boundary observed along peninsular italy coincides with the distribution of seismogenic faults along the axis of the apennines this boundary separates a tyrrhenian and an adriatic domain with diverging velocities orientated north nnw ward and northeastward respectively the apennines are extending perpendicularly to the chain axis at rates of less than 3 mm yr 1 and only in the outer northern apennines indications of active shortening are observed insignificant deformation is observed in the western po plain and the western alps while the central and eastern alps display north south shortening the eastern adriatic domain is shortening perpendicular to the dinaric front with strain rates increasing from north to south the locus of collision between the aegean balkan system and the adriatic and ionian domains is marked by the kephalonia fault system which accommodates up to 20 1 mm yr 1 of right lateral motion the deformation pattern observed in the peri adriatic domain is well described by a counter clockwise rotation of the adriatic microplate around a pole located in the western alps

heat flow measurements in 17 perialpine lakes thirty eight heat flow measurements were carried out in 17 perialpine lakes to supplement the scanty information concerning the thermal conditions in the crust underlying central europe a probe of the corer type was built which allowed the measurement of 11 temperatures at equally spaced subbottom intervals to a maximum penetration of 10 5 m measurements of this type were made in lake constance greifensee lake zurich lake zug lake lucerne baldeggersee lake biel lake murten lake neuch tel lake geneva lac d9annecy lac de bourget lago maggiore lago di lugano lago di como lago d9iseo and lago di garda after retrieval of the probe a sediment core was collected for samples on which thermal conductivity was measured with the needle probe method after treating the material to remove exsolved gas pubbles continuous seismic reflection and reflection profiles in all of these lakes provided a set of parameters for gradient correction due to heat flow refraction additional corrections were applied on the basis of palynologically determined sedimentation rates and for the influence of the last period of glaciation final heat flow values obtained in this manner are given the lesser values are generally found in the more western lakes north of the alps the higher values are found in the more eastern lakes north and south of the alps the higher values are partially confirmed by earlier measurements in lakes but show considerable discrepancy with measurements from the central alps this could be explained by the underthrusting of a cold wedge under the aar and gotthard massif in the late miocene and early pliocene which then would lower the temperature gradient in the central alps

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

testing models of orogen exhumation using zircon u th he thermochronology insight from the ligurian alps northern italy testing models of orogen exhumation requires precise constraint of the time temperature paths of the exhumed rocks the zircon u th he zhe thermochronometer has a closure temperature of 140 210 c and can provide temporal constraints on the exhumation history of rocks through a thermal range which crucially corresponds the onset of brittle behaviour of an exhuming orogen we performed zhe analyses to test the existing contradictory models for the exhumation of the ligurian alps the zhe ages indicate a very rapid 1 3 6 8 mm yr and southward migrating exhumation of the orogen between 32 and 25 ma these high exhumation rates are unique within the alpine belt and cannot be reconciled with existing geodynamic models of the evolution of the ligurian alps we propose a model of tectonic denudation via detachment accomplished in the shallowest crust 5 km as a result of the last orogenic phase of extension

linking the northern alps with their foreland the latest exhumation history resolved by low temperature thermochronology the evolution of the central alpine deformation front subalpine molasse and its undeformed foreland is recently debated because of their role for deciphering the late orogenic evolution of the alps its latest exhumation history is poorly understood due to the lack of late miocene to pliocene sediments we constrain the late miocene to pliocene history of this transitional zone with apatite fission track and u th he data we used laser ablation inductively coupled mass spectrometry for apatite fission track dating and compare this method with previously published and unpublished external detector method fission track data two investigated sections across tectonic slices show that the subalpine molasse was tectonically active after the onset of folding of the jura mountains this is much younger than hitherto assumed thrusting occurred at 10 8 6 5 ma and potentially thereafter this is contemporaneous with reported exhumation of the external crystalline massifs in the central alps the jura mountains and the subalpine molasse used the same detachments as the external crystalline massifs and are therefore kinematically coupled estimates on the amount of shortening and thrust displacement corroborate this idea we argue that the tectonic signal is related to active shortening during the late stage of orogenesis

geothermal structure of the tyrrhenian sea over 200 heat flow measurements have been carried out in the tyrrhenian sea mostly since 1977 as part of the heat flow map for italy and surrounding seas italian program as well as part of the french italian tyrrhenia program all data have been corrected for the influence of the plio quaternary sedimentation measured heat flow values were evaluated according to the sedimentary environment following criteria outlined by sclater et al 1980 in this way areas affected mainly by shallow thermal effects in the zones with maximum density of data have been displayed filtering out these shallow contributions the major regional geothermal trends were obtained the tyrrhenian basin can be divided in two distinct regions with different geothermal characteristics the northern part of the basin appears to be connected with the continental structures involved in the interaction between the corsica and tuscan margins the maximum heat flow area located offshore civitavecchia is related to the tensile structures of the tuscan geothermal province the most important thermal features of the central and southern part are located along the central belt trending nw se the lowest heat flow values are located in the peri tyrrhenian areas and are related to the continental margins of the basin while the maxima are connected with the stretched and thinned area localized in the bathyal plain taking into account the heat flow data as well as other geological and geophysical information an evolutionary model for the tyrrhenian sea is presented suggesting a generalized stretching of an initially continental crust accompanied by intensive rifting phases which may have favoured the onset of oceanic type crust

three dimensional numerical modeling of contemporary mantle flow and tectonic stress beneath the central mediterranean the structure density and effective viscosity of the crust and uppermost mantle beneath the central mediterranean influence lithospheric deformation mantle flow and tectonic stress state to estimate the contribution of buoyancy forces to regional dynamics three dimensional finite element models are developed to determine contemporary uppermost mantle flow and tectonic stresses we use density models for the crust and uppermost mantle derived from s wave seismic velocities and constrained by gravity data the viscosity model is constrained by the observed strain rate and regional heat flow data the modeled movement of the uppermost crust is consistent with the northeast oriented motion of the lithosphere and is in an agreement with the geodetic measurements the modeled flow patterns of the lower crust and uppermost mantle are consistent with the regional observations the models predict i northwest oriented movements beneath the southeast part of the adriatic sea region ii the northeastern subduction beneath the western part of the adriatic sea iii the upwelling beneath the tyrrhenian sea and its eastern coast iv the western movement of the ionian sea sub plate and v the subduction beneath the western calabria region our models predict also a distinct compressional regime along the northeast part of the italian peninsula and to the east of sicily and a tensional regime beneath the tyrrhenian sea umbria marche region and ionian sea the predicted tectonic stress regimes in the northern and central apennines are in agreement with stress regimes derived from earthquake fault plane solutions changes in the predicted crustal stress pattern and magnitude are likely to be caused by buoyancy driven mantle circulation beneath the region rather than by gravitational potential energy differences in the crust itself based on the model results we conclude that the buoyancy forces play an important role in the contemporary tectonics of the region

thick skinned tectonics within the intracontinental easternmost atlas foreland and thrust belt tunisia meso cenozoic kinematics and implications for regional geodynamics the transition zone between western and central mediterranean domains presents a key area to investigate kinematic interactions within the adjacent orogen systems such as the easternmost atlas foreland and thrust belt analysis of gravity and seismic data revealed a highly structured basement characterizing a series of structural highs and lows delimited by high angle n s e w and nw se extensional faults this basement architecture is inherited from successive extensional events related to the openings of the triassic early cretaceous tethys oceans i e alpine tethys ligurian tethys and mesogea throughout this period this mosaic of continental blocks significantly controlled the thickness and facies distributions early stages of diapirism took place along these basement faults and allowed maximum subsidence in minibasins revealed by the development of growth strata in response to the late cretaceous eocene shortenings these extensional faults have been reactivated as trasnpressional shear zones giving rise to narrow popup structures in addition gravity modeling indicates crustal thinning and deep rooted faults affecting the crust south of the zaghouan thrust and along e w transfer zones from the late miocene a drastic change in the stress regime is attributed to the effect of the adjacent sicily channel on the study area this promotes crustal thinning basin subsidence and channeling up of mantle derived helium along lithospheric scale weak zones our results give rise to new insights into the reactivation of inherited weakness zones of southern tethys margin in response to the complex interaction between african and eurasian plates accommodated by subduction rollback collision and slab segmentation

thermorheological model for the european central alps brittle ductile transition and lithospheric strength a two dimensional thermorheological model of the central alps along a north south transect is presented thermophysical and rheological parameters of the various lithological units are chosen from seismic and gravity information the inferred temperature distribution matches surface heat flow and results in moho temperatures between 500 and 800 c both european and adriatic lithospheres have a jelly sandwich structure with a 15 20 km thick brittle upper crust overlying a ductile lower crust and a mantle lid whose uppermost part is brittle the total strength of the lithosphere is of the order of 0 5 1 0 1013 n m 1 if the upper mantle is dry or slightly less if the upper mantle is wet in both cases the higher values correspond to the adriatic indenter

cenozoic denudation of corsica in response to ligurian and tyrrhenian extension results from apatite fission track thermochronology 1 the island of corsica france occupies a unique position in the western mediterranean since it has recorded both the cenozoic alpine orogenic history of the area as well as subsequent extensional collapse and oceanic basin formation we present 41 new apatite fission track aft ages and 23 measurements of track length distributions from corsica in order to elucidate its cenozoic thermal and morphological evolution aft ages vary from 10 5 0 8 ma to 53 8 4 1 ma and form a clear spatial pattern oldest ages are encountered in the southwest of the island with a broad band of ages between 20 and 30 ma running across the mountainous central area and ages 20 ma confined to the eastern half of the island samples along the western and northwestern coasts record kilometer scale erosional denudation linked to rifting in the ligurian provencal basin whereas samples from close to the extensionally inverted alpine deformation front record a later cooling phase related to tyrrhenian extension the eastward younging pattern of aft ages suggests the migration of a wave of erosional denudation from west to east across the island apparently controlled by the migrating locus of extension our aft data therefore support models of mediterranean extension controlled by slab roll back

compositional and thermodynamic variability in a stratified magma chamber evidence from the green tuff ignimbrite pantelleria italy the green tuff ignimbrite pantelleria is compositionally zoned from pantellerite at the base to comenditic trachyte at the top the variation apparently representing an inverted vertical zonation in the pre eruptive reservoir the main phenocryst assemblages are alkali feldspar olivine clinopyroxene ilmenite apatite in the trachytes and alkali feldspar aenigmatite clinopyroxene quartz in the rhyolites thermodynamic modelling indicates that the temperature range was 900 700 c fo2 fmq 1 5 to fmq 0 5 where fmq is fayalite magnetite quartz buffer and asio2 relative to quartz saturation 0 74 1 00 melt water contents ranged from 1 wt in the trachytes to 4 wt in the pantellerites matrix glass analyses in the more evolved rocks are highly variable showing that compositional layers in the upper parts of the reservoir formed by fractional crystallization were mixed during eruption the proportion of rhyolitic to trachytic melts increasing towards the top of the reservoir some areas of glass have low al2o3 contents 5 16 5 46 wt and high feo contents 9 66 10 02 wt making them the most evolved melts yet reported from pantelleria the new glass data reveal how whole rock analyses do not truly reflect the complete range of melt compositions in the pre eruptive reservoir the trachytes contain 40 modal phenocrysts which with relatively high ba contents and positive eu anomalies are considered to have originated in a feldspar accumulitic layer phenocrysts in the trachytes are commonly heavily resorbed inferred to be a result of heating by influxes of intermediate composition magma which however were not erupted it is argued that magmas of intermediate composition were present in the green tuff reservoir but were efficiently trapped in a crystal rich layer below the green tuff magmas which was eventually erupted during a resurgent phase as the montagna grande trachyte

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