miocene progressive forearc extension in the central mediterranean abstract miocene extensional sedimentary basins are being increasingly recognized in central mediterranean however the paleogeographic reconstruction of the paleo tyrrhenian during this time span results a difficult task because the subsequent pliocene quaternary backarc opening moved away these older sedimentary basins our study outlines principal deformation events recorded by sediments that were deposited within minor basins of the tyrrhenian sea region and provides constraints on the duration of these events the interpretation of seismic profiles wells and outcrops data together with a review of the middle upper miocene successions permitted us to recognize miocene third order depositional sequences reconstruct the fault pattern and furnish a detailed evolution of the sedimentary basins that preceded the pliocene quaternary tyrrhenian high stretching based on the stratigraphic and tectonic constraints together with the age migration of the depocenters we reconstructed a detailed paleogeographic evolution of central mediterranean sedimentary basins architecture and fault pattern indicate a system of approximately n s oriented normal faults and approximately e w transform faults that were active since the late oligocene two period of extensional transtensional tectonics late oligocene lower burdigalian and upper langhian tortonian were interrupted by a compressional event late burdigalian lower langhian tacking in account the position of the miocene volcanic arc sardinia we propose that the coeval sedimentary basins developed in the central mediterranean as forearc extensional transtensional basins during the progressive collision with the african plate and before the tyrrhenian backarc opening unlike published late oligocene tortonian reconstructions of the western central mediterranean realm that report a linear migration of backarc extension our results support a geodynamic model characterized by a progressive deformation of the forearc extension in the overriding plate

survival of ancient landforms in a collisional setting as revealed by combined fission track and u th he thermochronometry a case study from corsica france abstractthe age of high elevation planation surfaces in corsica is constrained using new apatite u th he data field observations and published work zircon fission track apatite fission track aft data and landform stratigraphical analysis thermal modeling results based on aft and u th he data and the eocene sediments uncomformably overlapping the variscan crystalline basement indicate that present day elevated planation surfaces in corsica are the remnants of an erosion surface formed on the basement between 120 and 60 ma during the alpine collision in the paleocene eocene the variscan crystalline basement was buried beneath a westward thinning wedge of flysch and the eastern portion was overridden by the alpine nappes resetting of the apatite fission track thermochronometer suggests an overburden thickness of 4 km covering variscan corsica protected by soft sediment the planation surface was preserved in the latest oligocene to miocene times the surface was re exposed and offset by

fiamme degassing structures and their implications for the post emplacement temperatures and h2o contents of high grade ignimbrites abstract a new process in post emplacement ignimbrite degassing is proposed from observations of unusual structures in a high grade ignimbrite in sardinia the structures consist of fiamme decorated above and below by vesicles termed here fiamme degassing structures fds the relative volumes of vesicles and fiamme have a positive linear correlation and the ratio between the volume of vesicles above and below fiamme asymmetry ratio is 1 wt at

tension gash like back arc basin opening and its control on subduction rollback inferred from tertiary faulting in sardinia 1 the tertiary reactivation of the paleozoic basement in ne sardinia is shown to reflect transtensional back arc tectonics related to the western mediterranean subduction rollback during the algero provencal basin opening the left lateral nuoro fault which is the prevailing structure in central sardinia operated as radial transfer between the west sardinian rift and northern tyrrhenian basin subsequently it contributed to a tension gash like opening of the southern tyrrhenian basin as conjugate fault to a right lateral fault set in se sardinia resulting antithetic rotations with respect to the arc are revealed by reoriented dikes in the basement the tension gash like opening of the southern tyrrhenian basin determined the gulf shape of the east sardinian margin and the arc shape of its calabrian counterpart this structural control on the southern tyrrhenian rollback scenario suggests that tension gash like opening of back arc basins represents an intrinsic aspect of subduction rollback

crustal thinning in the northern tyrrhenian rift insights from multichannel and wide angle seismic data across the basin extension of the continental lithosphere leads to the formation of rift basins or rifted continental margins if breakup occurs seismic investigations have repeatedly shown that conjugate margins have asymmetric tectonic structures and different amount of extension and crustal thinning here we compare two coincident wide angle and multichannel seismic profiles across the northern tyrrhenian rift system sampling crust that underwent different stages of extension from north to south and from the flanks to the basin center tomographic inversion reveals that the crust has thinned homogeneously from 24 km to 17 km between the corsica margin and the latium margin implying a factor of 1 3 1 5 on the transect 80 km to the south the crust thinned from 24 km beneath sardinia to a maximum of 11 km in the eastern region near the campania margin factor of 2 2 the increased crustal thinning is accompanied by a zone of reduced velocities in the upper crust that expands progressively toward the southeast we interpret that the velocity reduction is related to rock fracturing caused by a higher degree of brittle faulting as observed on multichannel seismic images locally basalt flows are imaged intruding sediment in this zone and heat flow values locally exceed 100 mw m2 velocities within the entire crust range 4 0 6 7 km s which are typical for continental rocks and indicate that significant rift related magmatic underplating may not be present the characteristics of the pre tectonic syn tectonic and post tectonic sedimentary units allow us to infer the spatial and temporal evolution of active rifting in the western part of the southern transect thick postrift sediments were deposited in half grabens that are bounded by large fault blocks fault spacing and block size diminish to the east as crustal thinning increases recent tectonic activity is expressed by faults cutting the seafloor in the east near the mainland of italy the two transects show the evolution from the less extended rift in the north with a fairly symmetric conjugate structure to the asymmetric margins farther south this structural evolution is consistent with w e rift propagation and southward increasing extension rates

ordovician alluvial fan to marine shelf transition in sw sardinia western mediterranean sea tectonically sardic phase influenced clastic sedimentation abstract a localized lower ordovician early caledonian structural event sardic phase is recorded in sw sardinia by an angular and erosional unconformity faulting and mild folding this event was accompanied by sedimentation of a transgressive clastic unit puddinga beds which is particularly well developed along a major fault system gonnesa fault zone there the puddinga beds range from basal interfingering fans some formed by coarse carbonate and schist clasts others by schist clasts only to fluvio lacustrine mud and gravelly sandstone to coastal muddy and sandy deposits and to fossiliferous restricted marine shelf sediments the existence of the slightly compressive sardic phase in sw sardinia and quasi coeval calc alkaline volcanism and an extensional structural phase sarrabese phase in central east sardinia suggest transcurrent faulting the calc alkaline acid volcanism is also interpreted by some authors to indicate that the rifted basins developed in backarc position the non volcanic sequence of sw sardinia analyzed in this paper was probably formed in basins developed on the northern margin of the gondwanaland craton this sardinian system may be the eastward extension of transcurrent rifts which have also been recently reported from nw spain structural activity has been the predominant control on sedimentation however worldwide recurring low sea level stands may have influenced the sedimentation of the lower part of the puddinga beds and the deglaciation of the saharan ice sheet has contributed to the uppermost ordovician early silurian deepening of the euxinic shelf

late pleistocene coastal evolution of san giovanni di sinis west sardinia western mediterranean abstract the upper pleistocene succession of coastal deposits outcropping at san giovanni di sinis west sardinia has been studied since the 1960s however the absence of consistent radiometric ages has allowed the production of competing stratigraphic subdivisions of these deposits with different isotopic stage ois mis attributions the succession is composed of sandy to gravelly shallow marine coastal aeolian and alluvial fan plain deposits facies analysis and log correlations show the presence of three unconformities t1 t2 t3 always overlain by shallow marine deposits cutting through the substrate alluvial fan or aeolian sediments we have collected three samples for optically stimulated luminescence osl dating at the top of each shallow marine deposit the succession is composed of four unconformity bounded units u1 u2 u3 u4 and the new osl dates indicate the presence of three different sea level highstands the first unit u1 which is composed of shallow marine to aeolian deposits and overlies transgressive surface t1 is related to a marine transgression during ois 7 186 13 ky unit 2 is composed of continental deposits and formed during ois 6 unit 3 represents ois 5 and overlies a transgressive surface t2 more precisely subunit u3a is related to ois 5e 120 10 ky eu tyrrhenian or eemian sensu strictu and is characterized by shallow marine to aeolian deposits developed during both transgressive and highstand phases the following bay deposits of subunit 3b are associated with ois 5c 100 5 ky and record a second transgressive event t3 and highstand phase occurred during the neo tyrrhenian the succession of san giovanni di sinis ends with continental deposits of unit 4 associated to a sea level fall that took place at the beginning of the last glacial phase ois 4

sedimentary response to intra arc extension controls on oligo miocene deposition sarcidano sub basin sardinia the oligo miocene sardinian rift is a rare example of a well exposed intra arc basin comprising several independent depocentres synthesis of field observations from one such depocentre the sarcidano sub basin in central sardinia not only allows a new and integrated sedimentological and tectonostratigraphic history for the area but also provides insights into controls on syn and post rift sedimentation in intra arc settings initial rifting during the late rupelian early chattian oligocene occurred on nw se trending normal faults and produced a half graben topography which controlled the dispersal of locally supplied coarse continental clastic sediments latest chattian aquitanian miocene ne sw trending normal faulting defined a more complex block topography that remained underfilled in all areas except those which received voluminous ignimbritic volcanic material subsequent marginal and shallow marine sedimentation progressively infilled the fault topography as sea level rose deposition of coarse clastic sediments eroded from fault scarps was focused in the hanging wall depocentres of the intersecting fault trends whilst platform carbonates became established in topographically higher areas protected from clastic sedimentary supply finally as the relative rise in sea level drowned sediment source areas in the burdigalian deeper marine marlstones dominated sedimentation the results demonstrate that the sarcidano sub basin was dominated by a mixed volcanic siliciclastic carbonate basin fill with abrupt facies changes developed in response to complex fault defined topography relative rise in sea level and an episodic volcanic supply whilst the rift structure largely controlled the provenance supply and accumulation of sediments relative sea level primarily controlled the types of facies that developed

early stage rifting of the northern tyrrhenian sea basin results from a combined wide angle and multichannel seismic study extension of the continental lithosphere leads to the formation of rift basins and ultimately may create passive continental margins the mechanisms that operate during the early stage of crustal extension are still intensely debated we present the results from coincident multichannel seismic and wide angle seismic profiles that transect across the northern tyrrhenian sea basin the profiles cross the corsica basin france to the latium margin italy where the early rift stage of the basin is well preserved we found two domains each with a distinct tectonic style heat flow and crustal thickness one domain is the corsica basin in the west that formed before the main rift phase of the northern tyrrhenian sea opening 8 4 ma the second domain is rifted continental crust characterized by tilted blocks and half graben structures in the central region and at the latium margin these two domains are separated by a deep 10 km sedimentary complex of the eastern portion of the corsica basin travel time tomography of wide angle seismic data reveals the crustal architecture and a subhorizontal 15 17 1 km deep moho discontinuity under the basin to estimate the amount of horizontal extension we have identified the pre syn and post tectonic sedimentary units and calculated the relative displacement of faults we found that major faults initiated at angles of 45 50 and that the rifted domain is horizontally stretched by a factor of 1 3 8 10 mm a the crust has been thinned from 24 to 17 km indicating a similar amount of extension 30 the transect represents one of the best imaged early rifts and implies that the formation of crustal scale detachments or long lived low angle normal faults is not a general feature that controls the rift initiation of continental crust other young rift basins like the gulf of corinth the suez rift or lake baikal display features resembling the northern tyrrhenian basin suggesting that half graben formations and distributed homogeneous crustal thinning are a common feature during rift initiation

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

geodynamic history and mantle evolution recorded in cenozoic lavas of sardinia two cenozoic magmatic cycles occurred in sardinia separated by a 5 myr gap oligo miocene subduction related calc alkaline magmatism associated with sardinia migrating from the european continental margin to its current location and plio pleistocene intraplate alkaline magmatism associated with the opening of the southern tyrrhenian basin based on an integration of new and published geochemical data on the cenozoic volcanic rocks of sardinia and regional tectonics we propose that a northward propagating slab tear formed south of sardinia at the end of the oligo miocene cycle this was responsible for the transition from subduction controlled calc alkaline to extension controlled mildly alkaline to peralkaline magmatism in the sulcis area sw sardinia and for the end of the oligo miocene magmatism the inflow of hotter material from the european asthenospheric reservoir ear through the slab window could have produced the minor ear type alkaline lavas that erupted at the end of the oligo miocene cycle and at the beginning of the plio pleistocene cycle the dominant younger plio pleistocene lavas with emi type compositions probably formed from decompression melting of a shallower lithospheric mantle with little influence from the ear forming event supplementary material a summary of sulcis rocks petrography representative whole rock analysis of sulcis rocks sr nd and pb isotope analytical methods and results a list of sources of whole rock geochemical data from the literature and complementary diagrams are available at https doi org 10 6084 m9 figshare c 4447802

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

the maritime alps arc in the ligurian and tyrrhenian systems abstract after late eocene meso alpine collision between the european and adria plates the maritime alps underwent further deformations linked to the apennine orogenesis and consistent with a stress field developed during anticlockwise rotation the western limit of the rotated sector is east of the argentera massif and to the southwest represents the northwestern margin of the post eocene ligurian sphenochasm the sinistral rotation of the maritime alps initially occurred contemporaneous with the opening of the ligurian basin about 30 19 ma and probably continued during the subsequent opening of the tyrrhenian basin about 10 0 ma the rotating block comprises the northwestern part of the adria indenter and a part of the paleo european plate namely the maritime alps corsica and sardinia if a convenient configuration is assumed for the moho of the adria margin and suitable poles are chosen for subsequent rotations then a simplified model of rigid body can explain the rotation structures in the maritime alps the apennines and po plain subsurface compressional arcs the late foreland directed transport of nappes in the western alps the presence of extensional and dextral transcurrent structures and the general uplift of the lithospheric mantle between the ligurian sea and the ivrea body as to the causes of rotation two alternatives subduction or asthenosphere uplift are discussed chronological and mechanical arguments seem to favour the latter

middle pleistocene to holocene coastal evolution of nw sardinia mediterranean sea italy abstract the middle pleistocene holocene sardinian stratigraphy has been revised to identify the roles played by sea and climate changes in controlling sedimentation the succession dated through optically stimulated luminescence quartz k feldspar and 14 c the most recent was grouped into eight major stratigraphic units mainly represented by coastal dunes shallow marine and alluvial systems these units range in age from mis 8 300 ka to mis1 6 ka little information is available for the period between mis 8 and 6 the available data however allow some comments on climate changes over the last 125 ka the last interglacial mis 5 is subdivided into five substages e a mis5e eemian is considered the climate optimum of this interglacial sea level was 4 6 m higher than today and climate conditions were warmer and more humid mis 5c is the second high stand peak sea level was about 1 5 m above the modern level and paleoclimatic and paleogeographic conditions were similar to the present during mis 4 at the beginning of the glacial phase a climatic deterioration occurred temperatures dropped by 6c relative to mis 5e in about 5 ka and sea level fell about 60 m this led to a progressive disruption of inland vegetation cover and to repeated valley slope denudation the sea level fall created the accommodation space for fan development in sheltered and cliffed areas where debris flows developed and filled almost completely the terminal parts of the narrow coastal valleys coves in wider areas however coastal dune fields developed contemporaneous presence of alluvial fan and dune systems is associated with the local morphology that could mitigate or amplify moist conditions within a generally arid environment during mis 3 several climate fluctuations occurred wet arid d o h events however the shallow sardinian shelf was continuously sufficiently exposed to become the source area of bioclastic sands these sands were blown inland and formed extensive dunefield systems dunes dominated the west coasts of sardinia under cold and relatively dry conditions in some areas these dunefield systems were eventually almost completely dismantled and reworked into water flow dominated alluvial fans by catastrophic rainfall events thus the local climate quickly switched from arid to humid conditions no record of the last glacial maximum deposits mis 2 was observed along the nw sardinian coast during the holocene transgression mis1 coastal dune systems developed and progressively migrated inland and temperature rose to reach the present day condition

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

arguments for the pre rift uplift and rift propagation in the ligurian provencal basin northwestern mediterranean in the light of pyrenean provencal orogeny the cenozoic provencal orogeny and the subsequent opening of the ligurian provencal basin were caused by a geodynamic mechanism that originated in the cretaceous it is evident from the arguments presented that 1 regional doming preceded rifting of the continental margin and this uplift widened and or migrated during the ensuing opening of the ligurian provencal basin 2 clastic sedimentation on the provencal platform was initiated during the early cenomanian 3 deformation in the provencal block which varies from late cretaceous to miocene reflects a migration of the north south compression from west to east accross the block 4 the languedoc provencal fold belt was initiated during the eocene as a result of tectonic uplift and sinistral displacement of the paleozoic basement toward the north significant geologic features of the region associated with these events include 1 similarities in shape of the languedoc virgation and the provencal thrust front with the shape of geophysical features over the golfe du lion 2 the unusual width of the young stretched continental margin in the golfe du lion 3 the distinctive v shaped form of the ligurian oceanic crust and 4 the concordance in age of the earliest post rift deposits which increasingly young toward the east and magnetic anomalies that parallel the basin axis these events and structures are attributed to the uplift of a paleozoic block situated to the south in the golfe du lion and previously buried under the mesozoic cover the development of this crustal uplift since upper aptian and its northeastwards migration and or gradual widening account for both sedimentary events and tectonic deformation that occurred on the provencal platform until upper eocene and the later stage of rifting and formation of the provencal margin in the ligurian provencal basin the synthesis of marine data as well as relevant terrestrial data indicates that rifting propagated towards the gulf of genoa while the corsica sardinia block rotated to the southeast

geodynamic control on orogenic and anorogenic magmatic phases in sardinia and southern spain inferences for the cenozoic evolution of the western mediterranean abstract the genetic relationships between orogenic i e subduction related and anorogenic i e intra plate cenozoic igneous phases have been investigated in two regions of the western mediterranean area sardinia and southern spain in sardinia the orogenic magmatism 38 12 ma is followed by the anorogenic volcanism mostly since about 6 ma whereas in southern spain the anorogenic volcanism follows the orogenic phase 34 6 ma after a gap of 0 4 ma in the betic calatrava districts the older orogenic magmatism tholeiitic calcalkaline and more potassic products of both areas is related to the subduction of the ionian oceanic lithosphere which developed beneath the paleo european iberian continental margin probably since middle late eocene this subduction system migrated southeastwards with time up to its present position in the eolian calabrian arc and the betic alboran regions along the apennine maghrebide belt relics of subducted lithosphere are geophysically recorded as nearly vertical bodies down to 500 600 km flattening for several hundreds of kilometres under the tyrrhenian sardinia and betic calatrava areas respectively these relics of subducted slabs which pond over large areas of the mantle transition zone appear to play a significant role also in the genesis of the younger anorogenic magmas whose major volcanic fields lie above the frontal part of the subducted slab where convective instabilities and upward mantle flow components are geophysically supported by laboratory and 3d numerical models this dynamic response to subduction involving localised mantle upwellings and remobilization of pre existing mantle components may have been a fundamental factor in the generation of anorogenic magmas due to slab roll back and inter arc extension in both eolian tyrrhenian and betic alboran regions the magma sources of the previous orogenic phases can be completely replaced by fresh mantle diapirs from whic h anorogenic magmas will be generated these magmas are invariably characterised by oib isotopic signatures himu and emi which are classically interpreted as long term recycling of oceanic crust plus variable sedimentary components via ancient pre paleozoic subduction events we propose that the recent cenozoic subduction from which the orogenic series was generated also had a dynamic influence on the younger anorogenic magmatism by remobilization of long term isolated mantle components which resulted in the secular evolution of oib type magmas in this view the on going subduction processes of the mediterranean orogenic belts did not provide chemical ingredients to the mantle sources of the anorogenic magmas but induced reactivation of older metasomatised mantle domains ultimately triggering magma genesis

post rift sequence architecture and stratigraphy in the oligo miocene sardinia rift western mediterranean sea abstract rift basins provide important sedimentary archives to reconstruct past tectonic and climatic conditions understanding their sedimentary history is however largely hampered by the competing influence of tectonic versus climatic forcing the aim of this study is to comprehend the effects of local to regional tectonic and global climatic eustatic changes on shallow marine depositional systems in the sardinia rift western mediterranean sea for this purpose the stratigraphic and depositional relations of a mixed siliciclastic carbonate ramp at the porto torres basin margin were studied along extensive proximal to distal transects three depositional sequences ds1 to ds3 of late burdigalian to early serravallian age have been identified which are separated by erosional unconformities each contains a lower transgressive part and an upper regressive part the former includes shoreface sandstone ds2 or coral reef ds3 deposits on the proximal ramp and channelized sheet sandstone ds1 or basinal mudstone ds2 ds3 deposits on the distal ramp typically recording an upsection trend of sediment starvation the latter is represented by basinward prograding coralline red algal carbonate wedges due to enhanced shallow water carbonate production rates in the long term the depositional evolution from ds1 to ds3 reveals basin margin progradation associated with decreasing siliciclastic supply integrated calcareous nannoplankton foraminiferal pectinid biostratigraphy links the depositional sequences to third order sea level cycles and allows to correlate the erosional unconformities at the top of ds1 and ds2 with the bur 5 lan 1 and lan 2 ser 1 sequence boundaries the improved sequence stratigraphic framework enables better regional and global correlations this shows that rhodalgal carbonate slopes started prograding in the western branch of the sardinia rift during the late burdigalian because 1 of a worldwide bloom of rhodalgal facies and 2 decreasing tectonic activity at the transition from the syn rift to the post rift stage caused a continuous reduction of the siliciclastic sediment input

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

mantle dynamics in the mediterranean the mediterranean offers a unique opportunity to study the driving forces of tectonic deformation within a complex mobile belt lithospheric dynamics are affected by slab rollback and collision of two large slowly moving plates forcing fragments of continental and oceanic lithosphere to interact this paper reviews the rich and growing set of constraints from geological reconstructions geodetic data and crustal and upper mantle heterogeneity imaged by structural seismology we proceed to discuss a conceptual and quantitative framework for the causes of surface deformation exploring existing and newly developed tectonic and numerical geodynamic models we illustrate the role of mantle convection on surface geology a coherent picture emerges which can be outlined by two almost symmetric upper mantle convection cells the downwellings are found in the center of the mediterranean and are associated with the descent of the tyrrhenian and the hellenic slabs during plate convergence these slabs migrated backward with respect to the eurasian upper plate inducing a return flow of the asthenosphere from the backarc regions towards the subduction zones this flow can be found at large distance from the subduction zones and is at present expressed in two upwellings beneath anatolia and eastern iberia this convection system provides an explanation for the general pattern of seismic anisotropy in the mediterranean first order anatolia and adria microplate kinematics and may contribute to the high elevation of scarcely deformed areas such as anatolia and eastern iberia more generally the mediterranean is an illustration of how upper mantle small scale convection leads to intraplate deformation and complex plate boundary reconfiguration at the westernmost terminus of the tethyan collision

extensional collapse related to compressional uplift in the alpine chain off northern tunisia central mediterranean abstract geophysical and geological marine data recently collected allow to outline the structure of the basement involved fold thrust belt developed during the late cenozoic between sardinia and tunisia along the africa europe plate boundary by integrating these with inland data it is possible to document step by step the progression of crustal thickening from north to south and the collapse of the first uplifted northern units while collision was still going on the geodynamic setting suggests that coupled extensional collapse and fold thrust propagation were driven by island arc drifting above a southward retreating subduction zone

mineralogical and fluid inclusion studies of low sulfidation epithermal veins at osilo sardinia italy several precious metal bearing low sulfidation epithermal veins occur in the rolling topography of the osilo area northern sardinia the sa pala de sa fae and the sa pedra bianca veins were subject to intense diamond drilling exploration in the mid 1990 s the veins extend for 1 3 km dip steeply and range from 1 to 10 m in width high k calc alkaline volcanic deposits containing plagioclase phenocrysts along with lesser pyroxene amphibole magnetite olivine and sanidine form the main host rocks gold grades in drill intersections range from 50 m from the vein the assemblage albite fe chlorite illite pyrite montmorillonite calcite k feldspar prevails regionally and its formation is attributed to minor metasomatism of the country rock involving the addition of water carbon dioxide and hydrogen sulfide at distances 10 m from the vein the assemblage quartz k feldspar pyrite illite dominates forming an alteration envelope that cross cuts regional alteration quartz and k feldspar increase in abundance towards the vein quartz is the main vein mineral and it displays a range of morphologies and textures including crustiform colloform banding quartz pseudomorphs of platy calcite breccias and coarse euhedral crystals electrum and argentite which are the main gold and silver minerals deposited during the early stages of vein mineralization with rhomb shaped crystals of k feldspar adularia pyrite plus lesser marcasite arsenopyrite stibnite and sphalerite are the other sulfide phases in veins kaolinite halloysite jarosite form a late assemblage overprinting earlier hydrothermal alteration it is mostly restricted to shallow depths of a few meters except near veins most of this assemblage likely formed from weathering and oxidation of sulfides microthermometric measurements were made on quartz hosted two phase liquid vapor inclusions containing 75 liquid mean homogenization temperatures 750 measurements range from 220 to 250 c and ice melting temperatures 550 measurements range from 0 0 to 2 3 c the presence of co existing vapor rich and liquid rich inclusions with quartz pseudomorphs of platy calcite indicate that boiling conditions existed slight vapor bubble expansion of a few fluid inclusions subjected to crushing experiments indicates inclusion fluids contained variable but low concentrations of dissolved gas this study shows that gold silver mineralization formed in subvertical channels from ascending solutions at 250 c at around 300 to 450 m below the paleo water table in a typical low sulfidation epithermal environment hydrothermal solutions that produced vein mineralization and related alteration were dilute 4 1 equivalent wt nacl and 4 wt co2 near neutral ph reduced and at times boiling

a magnetovariational study in sardinia abstract a study of geomagnetic field time variations with a magnetometric array was performed in sardinia during the summer of 1988 nine fluxgate magnetometers with digital acquisition systems were employed to cover the main structural features of the island the recordings do not show significant variations in the amplitudes of the horizontal components of the bay like events whereas the vertical component amplitudes show a strong southward increase fourier maps were drawn at significant periods and induction arrows and z h pseudosections were derived

anatomy of a submarine channel system and related fan in a foramol rhodalgal carbonate sedimentary setting a case history from the miocene syn rift sardinia basin italy abstract during aquitanian burdigalian times thick mixed carbonate siliciclastic successions were deposited in basins located on the grabens and half grabens along the oligo miocene sardinia rift basin locally active tectonics sea level variations and ecological factors combined to control the development and distribution of foramol carbonate factories as well as the remobilisation and the redeposition of carbonate sediments into the adjacent deeper areas in the isili basin foramol rhodalgal carbonate factories developed on submerged structural highs which resulted from pre and syn sedimentary tectonics these carbonate factories were periodically shaved mainly during negative sea level oscillations and the sediments removed were funnelled towards the basin through a complex submarine channel network which included a tributary belt one main channel isili channel and the related fan the isili channel is up to 1 km wide 60 100 m deep and includes two stacked channel complexes each built up by several minor order channel units complex strata geometries characterise the isili channel and its related architectural elements e g overbank levee margin and channel thalweg which also include up to 15 m high bedforms individual channel complexes were temporally related to individual fan systems whose spatial distribution and internal geometry were strongly controlled by the type and rate of sediment accumulation and in turn by relative sea level oscillations facies associations include sandy to cobble sized gravity flow and bottom current deposits as well as megabreccias characterised by impressive displaced and tilted blocks which resulted from major channel margin collapses detailed analysis has led to the reconstruction of the internal geometry and depositional architecture of these carbonate bodies and to the determination of the main controlling factors the dimension and distribution of channel and channel related depositional bodies have been accurately determined this information provides a useful tool to analyse less extensively exposed analogues and to model foramol shelf to basin transitions and related channel and fan systems

a two stage rifting in the basins of the corsica sardinian straits abstract a set of seismic and field data from the corsica sardinian straits allowed us to define three well separated oligocene deep basins the castelsardo and porto torres basins forming the northern end of the sardinian graben and the bonifacio basin on the continental shelf of the bonifacio straits a seismostratigraphic investigation of these three basins revealed two major tectonic events a first oligocene to middle aquitanian rifting phase followed by oceanic spreading in the western mediterranean and then a second rifting event between corsica and sardinia in lower burdigalian time the first rifting is noticed in the three basins but the second one only in the porto torres and castelsardo basins

an archaeometric contribution to the study of ancient millstones from the mulargia area sardinia italy through new analytical data on volcanic raw material and archaeological items from hellenistic and roman north africa the main quarrying area of the mulargia ignimbrite used mainly to produce rotary millstones during the hellenistic and roman age has been identified and sampled in order to update and complete the petrographic and geochemical database by employing standard analytical methods optical microscopy and icp aes ms spectrometry the combination of petrographic and geochemical data concerning the tertiary rhyodacitic to rhyolitic ignimbrites outcropping in central west sardinia previously very poor form a helpful tool for future work on this important typology of volcanic millstones the data bank obtained has been used to verify the geological source of eight millstones discovered in different rural settlements of hellenistic numidia and roman africa proconsularis supposed by archaeologists to be made of ignimbrite from mulargia the results of the petro archaeometric study confirmed a sardinian origin for these millstones and represent one of the very few analytical proofs of their effective export to north africa

influence of the subducting plate velocity on the geometry of the slab and migration of the subduction hinge abstract geological observations indicate that along two active continental margins east asia and mediterranean major phases of overriding plate extension resulting from subduction hinge retreat occurred synchronously with a reduction in subducting plate velocity in this paper results of fluid dynamical experiments are presented to test the influence of the velocity of the subducting plate on the hinge migration velocity and on the geometry of the slab results show that hinge retreat decreases with increasing subducting plate velocity in addition phases of hinge retreat alternate with phases of hinge advance for relatively high subducting plate velocities due to interaction of the slab with the bottom of the box simulating the upper lower mantle discontinuity such slab kinematics could explain the episodic behaviour of back arc opening observed in convergent settings the geometry of the slab and the kinematics of subduction are significantly affected by the velocity of the subducting plate three subduction modes with accompanying slab geometry can be recognized a relatively low subducting plate velocity is accompanied by relatively fast hinge retreat with backward sinking of the slab and a backward draping slab geometry with increasing subducting plate velocity hinge migration is relatively small resulting in subvertical sinking of the slab and a folded slab piling geometry for a very high velocity the hinge migrates forward resulting in forward oriented subduction vectors and a forward draping slab geometry

petrographic and geochemical investigations on the volcanic rocks used in the punic roman archaeological site of nora sardinia italy the research focuses on the geochemical and petrographic characterisation of volcanics that were used in the roman city of nora archaeological site these rocks formed during the late eocene miocene orogenic sardinian magmatic activity 38 15 ma were used as construction materials ashlars decorative frame etc and as aggregate in the ancient mortars of some important buildings of nora e g roman theatre first century ad several samples coming from the roman theatre taken as study cases and other ancient buildings and artefacts of nora village were studied and chemically petrographically analysed to define their provenance analytical data of major and trace elements by xrf method were compared with those of several volcanics coming from the sector around the nora archaeological site and from sulcis area frequented in ancient times by romans to highlight the geochemical discriminant markers or affinities between the sample populations of volcanics factorial analysis was used taking some significant variables sio2 na2o k2o l o i al2o3 rb ba sr the results of this research allow also defining the aspects of stone quarry extraction and construction technologies used in the roman period

thermochronological evidence for mesozoic tertiary tectonic evolution in the eastern sardinia apatite fission track analyses on samples from eastern sardinia document a complex tectonic history whose reconstruction is problematic because of the reactivation of faults and structures at different times from jurassic to miocene the oldest ages 150 154 ma have been detected on the southern margin of the gulf of orosei and are related to the extensional tectonics that characterize the european passive margin during early and middle jurassic times thermal modelling of these data allows reconstruction of the burial history of the mesozoic basin and estimation of a sedimentary thickness of 2000 m part of these sediments was eroded during the following uplift documented by mid cretaceous fission track ages a further exhumation episode of eocene age has been revealed by fission track data on granite samples and has been inferred to be related to the alpine orogenic phase this tectonic episode caused the exhumation of crustal blocks bound by faults that were finally reactivated during the late oligocene early miocene

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

la structure de la marge occidentale de la sardaigne et la fragmentation de l ile au cenozoique abstract sardinia is commonly considered as part of a continental arc during the early miocene 21 19 ma anticlockwise rotation of the island and oceanic drifting led to the opening of the western mediterranean basin among the structures inherited from the rifting phase late oligocene the 30 40 km wide n s sardinian graben is the salient tectonic feature of the island it divides the hercynian basement into two blocks the main eastern massif and on the western side the nurra massif and the iglesiente sulcis further west the continental margin extends 100 km towards the western mediterranean basin the western continental margin is divided by a large median nw se fracture zone into two areas a northern part where the two sets of faults coexist and a southern part where the ne sw set progressively disappears towards the south the southwestern margin of the island is therefore affected only by the remaining broadly nw se faults the median fracture is a composite zone consisting of an array of normal faults locally featuring a narrow graben it runs from the bottom of the slope and presumably the ocean continent boundary to the southern end of a small ne sw graben underlying the continental shelf of oristano at its northern end the oristano shelf graben is bounded by another major nw se fracture the south bounding fault of the campidano graben this fault runs from the gulf of oristano to the gulf of cagliari and separates the iglesiente sulcis block from the eastern sardinian massif the island is thus crossed from the bottom of the western slope to the gulf of cagliari by a continuous set of nw se enechelon faults this en echelon system is contemporaneous with the rifting phase in the western mediterranean basin and delineates three crustal blocks through the sardinian basement although this set of faults displays mainly extensional activity apparent flower structures are present in some seismic records from the western margin suggesting left lateral strike slip displacement in plio quaternary times a new extensional event overprinted the earlier structures in the campidano area the fragmentation of the sardinian basement is therefore still active the displacement of blocks related to the opening of the nw se plio quaternary campidano graben is indeed transformed at both ends by two strike slip structures along the ichnusa seamount at the southern end and to the north along a reactivated ne sw hercynian fault the latter runs across the eastern massif from the gulf of oristano to the capo comino to the east and is accompanied by plio quaternary basic volcanics hence except for brief and low intensity miocene compressive events sardinia appears to be mostly affected by extension and fragmentation from the end of the oceanic drifting to the recent therefore the corso sardinian block does not seem to transmit the compressional stress to southern europe due to the northward displacement of the african plate

mineralogical and stable isotope studies of kaolin deposits shallow epithermal systems of western sardinia italy large kaolin deposits hosted by miocene silicic pyroclastic rocks in northwestern sardinia represent hydrothermal alteration formed within 200 m of the miocene paleosurface boiling hydrothermal fluids ascended steeply dipping faults that are enveloped by altered rock the broadly stratiform kaolin deposits constitute advanced argillic alteration that was produced in a steam heated zone near the paleosurface overlying the deeper hydrothermal systems the deeper zones represent two distinct types of epithermal systems weakly acidic inferred low sulfidation systems at tresnuraghes and acidic high sulfidation systems at romana tresnuraghes is characterized at depth by chalcedony quartz barite veins within a 50 m wide zone of k feldspar quartz illite alteration and overlying local occurrences of chalcedony sinter which define the paleosurface kaolin deposits near the paleosurface are characterized by zonation outward and downward from an inner shallow zone of kaolinite 1t opal dickite alunite 20 m diam grains to an outer deeper kaolinite 1m montmorillonite cristobalite this zonation indicates formation by descending acidic fluids the system evolved from ascending weakly acidic or neutral fluids that boiled to produce h2s rich vapor which condensed and oxidized within the near surface vadose zone to form steam heated acid sulfate waters and kaolin alteration at romana veins at depth contain chalcedony or quartz and minor pyrite and are enclosed in up to 20 m wide zones of kaolinite 1t quartz alteration near hydrothermal vents along the paleosurface chalcedonic silica is enclosed within a zone of kaolinite 1t alunite 50 m diam grains quartz opal dickite cristobalite kaolin quarries near the paleosurface display outward and downward zoning to kaolinite 1t opal cristobalite and then to montmorillonite kaolinite 1t opal consistent with formation by descending low ph fluid the siliceous and advanced argillic alteration along steep conduits formed from acidic ascending magmatic hydrothermal fluids whereas the near surface kaolin formed from steam heated meteoric waters alteration mineral assemblages and stable isotope data provide evidence of the temperature and source of hydrothermal fluids barite from tresnuraghes average 18o 17 1 34s 18 8 one alunite sample from romana 18o 12 0 d 3 34s 16 7 and quartz from both localities 18o 15 9 22 0 formed in hydrothermal feeders source fluids were likely mixtures of meteoric water and minor magmatic fluid similar to other epithermal systems kaolinite dickite minerals from the kaolin deposits 18o 16 6 21 4 d 43 to 53 formed from steam heated meteoric water having d 20 per mil consistent with the presence of anomalous hg and fine grained na and fe poor alunite the laterally extensive kaolin deposits in sardinia and possibly similar deposits elsewhere in the world appear to represent the uppermost parts of large hydrothermal systems that may be prospects for gold at depth

a synchronous alpine and corsica sardinia rotation 1 we report on the paleomagnetism of 34 sites from lower oligocene middle miocene sediments exposed in the tertiary piedmont basin tpb northern italy the tpb is formed by a thick 4000 m and virtually undeformed sedimentary succession unconformably lying upon alpine nappes decapitated by extensional exhumation which in turn are tectonically stacked over the adriatic foreland paleomagnetic directions from 23 mostly oligocene sites were chronologically framed using new biostratigraphic evidence from calcareous nannoplankton our data along with published paleomagnetic results show that the tpb rotated 50 counterclockwise with respect to africa in aquitanian serravallian times the rotation was likely driven by underneath nappe stacking and was synchronous with further bending of the alpine chain both the rotation magnitude and its timing are similar to those documented for the corsica sardinia microplate therefore the formation of the western alpine arc or at least part of its present day curvature occurred during the rollback of the apenninic slab and related back arc spreading of the liguro provencal basin and drift of the corsica sardinia block this suggests a common dynamics driving both the alpine and the apennine slab motions paleomagnetic data also document that the adriatic plate has undergone no paleomagnetic rotation since mid late miocene times anisotropy of magnetic susceptibility data suggests that the tpb an enigmatic basin arising from a controversial tectonic setting formed in an extensional regime characterized by a stretching direction approximately orthogonal to the main trend of the underlying chain

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

upper plate deformation as marker for the northern step fault of the ionian slab tyrrhenian sea central mediterranean abstract the eastern tyrrhenian margin etm the active boundary of the tyrrhenian sea backarc basin is the key for understanding the geodynamics of the central mediterranean numerous seismic tomography studies have been carried out in this region proposing different reconstructions of the lower subducting plate and cause of the slab break off existing beneath the southern apennines however the area and mode of the recent deformation of the tyrrhenian sea are still not fully defined and understood in this study we combine the analysis of a recent seismic tomography model and geological data in order to understand the relationship between the subducting lower plate and the tectonic evolution of the sedimentary basins formed on the upper plate with this aim we interpreted a large data set of seismic reflection profiles and several well logs the results consist in 2d and 3d geological models of the basins sedimentary infill and fault networks taking into account the geological data of the etm and those of the adjacent inner flank of the apennines we observe i a system of linked sedimentary basins developed on a narrow deformation belt bounded by transform fault zones ii a polyphase rifting within the upper plate iii an abrupt change of the direction of extension 90 from ne oriented in the lower pleistocene to se oriented in the middle pleistocene since these etm features are not the typical expressions of the current backarc extensional models we propose a link between the evolution of upper plate and the onset and development of a step subduction transform edge propagator fault along the northern margin of the ionian slab

oligo miocene half graben structure in western sardinian shelf western mediterranean reflection seismic and aeromagnetic data comparison abstract an improved model of the tectonic structure of the central sector of the western sardinian shelf off the gulf of oristano from integrated interpretation of seismic and magnetic data is presented from the analysis of the aquapulse seismic reflection profiles and sparker and airgun high resolution seismic data it was possible to define the major structural features of the study area that were previously not extensively known from these analyses it was possible to recognize a prevalently nne trending extensional system the interpretation of the aeromagnetic data was performed by the analytic signal method and euler deconvolution technique in the geological context of the study area these methods show a high resolution power by solving sharp lateral magnetic discontinuities like subvertical structures and basement steps the results of the magnetic interpretation were taken as a support for the seismic interpretation and they allowed a better definition of the tectonic structure of the study area this structure of extensional type is considered as a western conjugate branch of the oligo miocene sardinian rift its evolution is related to the oligo miocene andesitic volcanism at the bottom and with a marine infilling that at the top is messinian in age

extension and compression related basins in central italy during the messinian lago mare event abstract during the messinian lago mare event in the central mediterranean area compression and extension related basins developed as a consequence of the post tortonian evolution of the tyrrhenian apennines system all these syn tectonic sedimentary basins were characterized by different subsidence rates and sedimentary processes several sections located in different tectonic domains from the tyrrhenian to the adriatic margin of the apennine chain have been investigated s valentino in abruzzo citeriore roccamorice penscosansonesco roccacaramanico and le vicenne sections are located in compression related basins foreland basin system while the tolfa blera sections and the sedimentary succession of mondragone 1 well drilled in the garigliano coastal plain are located in extension related basins hinterland or back arc basins the recognition of ostracod assemblages with paratethyan affinities allows them to be referred to the messinian lago mare event loxoconcha djaffarovi zone this result allows us to consider the tyrrhenian rifting the accretion of the apennine thrust belt and the increase in subsidence rate during the flexuration of the foreland domain as synchronous processes due to the same geodynamical process taking into account the thicknesses of the analysed sedimentary basins different total subsidence rates have been computed for both the compression and extension related basins the syn rift basins that developed on the eastern margin of the northern tyrrhenian basin volterra val di fine and tolfa blera basins recorded a mean total subsidence rate of 1 25 mm a whereas higher subsidence rates affected the eastern margin of the central tyrrhenian basin 5 mm a garigliano coastal plain the differences in horizontal stretching and total subsidence rates that affected the tyrrhenian extensional area correspond to different migration rates of the apennine orogenic system in the northern 10 mm a and central apennines 40 mm a this difference in the total syn rift subsidence rate fits in well with the segmentation model of the tyrrhenian apennines system along a nne ssw lithosphere discontinuity which crosses the system from ancona northern apennines to the r selli lineament in the tyrrhenian basin

the valencia trough and the origin of the western mediterranean basins abstract evolutionary models for the valencia trough must be necessarily related to the neogene present geodynamics of the western mediterranean basins all these basins occupy new space created in the wake of the westward translation of the alboran block and the counter clockwise rotation of the corso sardinian block this escape tectonics microplate dispersal model can account for the co existence and progressive migration of compressional and extensional strain fields within the africa europe broad zone of convergence in this escape tectonics model the valencia trough has resulted in a complex evolution which includes 1 latest oligocene early miocene rifting along the catalan valencian margin due to the opening of the gulf of lions 2 almost simultaneous early miocene transpressive thrusting in the balearic margin related to the initiation of displacement of the alboran block and 3 late miocene generalized extension as a consequence of the opening of the south balearic basin

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

earthquake relocation in the ligurian sea western mediterranean geological interpretation abstract relocated epicenters are computed with a model based on complex local structure i e oceanic floor in the central ligurian basin and thinned continental margins by superposing these relocated earthquakes on a basement bathymetric map the structural relations are clearly demonstrated compressive stress towards the west northwest is confirmed in the northern ligurian basin by focal mechanism study according to our results most of the earthquakes appear to be shallow and linked to rejuvenation of older distensive and strike slip structures on margins as in the basin by a compressional motion

the cenozoic fold and thrust belt of eastern sardinia evidences from the integration of field data with numerically balanced geological cross section newly collected structural data in eastern sardinia italy integrated with numerical techniques led to the reconstruction of a 2 d admissible and balanced model revealing the presence of a widespread cenozoic fold and thrust belt the model was achieved with the forc software obtaining a 3 d 2 d time numerical reconstruction of the continuous evolution of the structure through time the mesozoic carbonate units of eastern sardinia and their basement present a fold and thrust tectonic setting with a westward direction of tectonic transport referred to the present day coordinates the tectonic style of the upper levels is thin skinned with flat sectors prevailing over ramps and younger on older thrusts three regional tectonic units are present bounded by two regional thrusts strike slip faults overprint the fold and thrust belt and developed during the sardinia corsica block rotation along the strike of the preexisting fault ramps not affecting the numerical section balancing this fold and thrust belt represents the southward prosecution of the alpine corsica collisional chain and the missing link between the alpine chain and the calabria peloritani block relative ages relate its evolution to the meso alpine event eocene oligocene times prior to the opening of the tyrrhenian sea tortonian results fill a gap of information about the geodynamic evolution of the european margin in central mediterranean between corsica and the calabria peloritani block and imply the presence of remnants of this double verging belt missing in the southern tyrrhenian basin within the southern apennine chain the used methodology proved effective for constraining balanced cross sections also for areas lacking exposures of the large scale structures as the case of eastern sardinia

history of subduction and back arc extension in the central mediterranean summary geological and geophysical constraints to reconstruct the evolution of the central mediterranean subduction zone are presented geological observations such as upper plate stratigraphy hp lt metamorphic assemblages foredeep trench stratigraphy arc volcanism and the back arc extension process are used to define the infant stage of the subduction zone and its latest back arc phase based on this data set the time dependence of the amount of subducted material in comparison with the tomographic images of the upper mantle along two cross sections from the northern apennines and from calabria to the gulf of lyon can be derived further the reconstruction is used to unravel the main evolutionary trends of the subduction process results of this analysis indicate that 1 subduction in the central mediterranean is as old as 80 myr 2 the slab descended slowly into the mantle during the first 20 30 myr subduction speeds were probably less than 1 cm year x1 3 subduction accelerated afterwards producing arc volcanism and back arc extension and 4 the slab reached the 660 km transition zone after 60 70 myr this time dependent scenario where a slow initiation is followed by a roughly exponential increase in the subduction speed can be modelled by equating the viscous dissipation per unit length due to the bending of oceanic lithosphere to the rate of change of potential energy by slab pull finally the third stage is controlled by the interaction between the slab and the 660 km transition zone in the southern region this results in an important re shaping of the slab and intermittent pulses of back arc extension in the northern region the decrease in the trench retreat can be explained by the entrance of light continental material at the trench

climate changes and human impact on the mistras coastal barrier system w sardinia italy abstract integrated archaeological and geological studies conducted on mistras coastal barrier system of central sardinia showed that it developed as transgressive systems during the final stages of the holocene sea level rise final stage of the holocene climate optimum about 6300 6000 cal y bp and become regressive prograding from about 2500 cal y bp when sea level reached the present elevation the regression of the coast was however not continuous but characterized by distinct transgressive regressive phases t r associated to precise climatic fluctuations tied with global eustatic and climatic phases the first regression occurred between 2500 and 1900 cal y bp this time interval known as roman warm coincides with the phoenician punic and roman attendance of the west sardinia coast at that time areas close to the coastal cities had to host landings and perhaps ports probably located at short distance from the shoreline archaeological excavations and findings have documented that in the mistras area punic constructed a long boulder structure probably dated from the 4th century bce to better protect an incipient lagoon used as the harbour of the city of tharros this had the effect to modify the normal behaviour of the beach system that transformed from spit to barrier lagoon during the second regressive phase the well established beach lagoon system developed quasi continuously for 1200 y 650 and 1850 ce this progradation started during a new warm period medieval and continued favoured by gentle sea level fall occurred during the cold little ice age time during this time after the abandonment of the city of tharros and of the sinis peninsula the mistras area was poorly populated as consequence there was no more an active harbour and large sandy dunes developed and nourished the shore allowing a no man influence progradation of the coast the third stage is the current one and begun about 165 y ago post 1850 ce after the relative sea level rise occurred after the end of the little ice age geological and archaeological data of western sardinia barrier lagoon systems revealed that the mistras barrier lagoon evolution was human influenced since the punic time the study pointed that little human activities on the coast could influence its natural behaviour and landscape and that little climatic changes both positive and negative can induce progradation or erosion of the system as well

miocene rotation of sardinia new paleomagnetic and geochronological constraints and geodynamic implications the miocene rotation of sardinia western mediterranean remains poorly constrained despite a wealth of paleomagnetic data primarily due to poor chronostratigraphic control however this rotation is contemporaneous with the opening of the liguro provencal back arc oceanic basin and its history is key to understanding the kinematics of opening of the western mediterranean we address this issue through paleomagnetic and 40ar 39ar geochronological investigations of miocene volcanic sequences in sardinia precise age control allows secular variation of the geomagnetic field to be evaluated these data provide constraints on the rotational history of this continental microplate sardinia rotated 45 counterclockwise with respect to stable europe after 20 5 ma aquitanian which is a marked increase over the estimate of 30 derived from prior paleomagnetic studies rotation was essentially complete by 15 ma about 30 of rotation occurred between 20 5 and 18 ma burdigalian corresponding to the period of maximum volcanic activity in sardinia the observed rotation validates palinspastic models derived from a morphological fit of basin margins and indicates high rates of opening up to 9 cm yr 1 in the southern part of the basin between 20 5 and 18 ma

escalation of salinity levels in the quaternary aquifers of the ganga alluvial plain india a detailed water quality analysis was carried out in the quaternary aquifer system of the marginal alluvial plain ganga plain in bah tahsil agra district india the electrical conductivity of 50 samples each from dug wells hand pumps and tube wells was analysed for the study of salinity levels in shallow intermediate and deep aquifers out of 50 20 samples of each were also analysed for other chemical constituents such as na k cl f and tds the analyses show drastic changes in the salinity levels of shallow intermediate and deep aquifers the deep aquifers are more saline compared to the shallow and intermediate aquifers on the contrary the concentration of chemical constituents such as na k cl and f was more in the shallow aquifers compared to the deep aquifers moreover there is an indication that the salinity and concentration of the above chemical constituents also escalate with time in each aquifer the chemical constituents such as na k cl f and tds range from 51 to 165 mg l 1 to 14 mg l 224 to 1 459 mg l 0 to 1 5 mg l and 750 to 2 650 mg l respectively over a 3 year period the salinity levels have sharply increased and the average f level has increased by 0 1 0 3 mg l an attempt has been made here to discuss the factors causing the variation and escalation of chemical constituents and salinity in the water of the three aquifers

integrated chronostratigraphy of an intra arc basin 40ar 39ar datings micropalaeontology and magnetostratigraphy of the early miocene castelsardo basin northern sardinia italy the chronostratigraphy of the lower miocene deposits of northwestern sardinia is refined in the castelsardo basin the combination of new 40ar 39ar isotopic datings 19 micropalaeontological datings calcareous nannofossils planktonic and large benthic foraminifers and 16 palaeomagnetic polarity measurements led to a new chronostratigraphic framework the continental deposits of the first megasequence valledoria and casteldoria members are possibly aquitanian the overlying marine sediments are early burdigalian vaginella depressa molasse the marine transgression can be dated to around 19 7 ma marine conditions ceased 18 83 0 13 ma the age of the index aerial 2 ignimbrite the continental part of the second megasequence lacustre unit is early middle burdigalian between 18 8 and 18 ma the overlying marine part campulandu and sedini members is middle late burdigalian the second marine transgression began in the earliest late burdigalian during the chron c5dr reversal at the time of the eustatic bur 4 event the castelsardo basin went through two main extensional tectonic episodes the first one occurred as the valledoria member was deposited and possibly dates back to the aquitanian the second one occurred as the uppermost part of the vaginella depressa molasse was deposited during the early burdigalian the second extensional episode is related to a rapid rotation of sardinia palaeomagnetic results confirm that corsica and sardinia acted as a single block which suffered a 28 17 ccw rotation after 19 2 ma the castelsardo basin is held to be an aquitanian early burdigalian intra arc rift basin that later evolved in a thermally controlled subsident margin of the ligurian provencal basin during the middle late burdigalian

heat flow in the valencia trough geodynamic implications abstract as part of the valsis project 110 heat flow determinations were obtained in the axial deep part of the valencia trough during the valsis 1 cruise of the r v le suroit in 1988 the data gathered data provide a fairly comprehensive view of the regional heat flow pattern regional heat flow increases from a value of 66 4 mw m2 to the north of menorca to 88 4 mw m2 in the southern part of the rift between valencia and ibiza a simple rifting model assuming uniform stretching of the lithosphere during a single rifting event from 28 to 22 ma ago satisfactorily describes the observed heat flow and depth to sea floor in the northern part of the trough in contrast the southern valencia trough has high heat flow and shallow sea floor that are difficult to reconcile with predictions of a uniform lithospheric stretching model even allowing for an initial elevation a thin hot lithosphere or a multi episode history of rifting non homogeneous lithospheric stretching models assuming for example large scale dike intrusion or a greater extension of the mantle than in the crust provide potential explanations of the high heat flow and shallow sea floor in the southern valencia trough yet these models remain poorly constrained

plate tectonic evolution of the mediterranean middle east region abstract an interpretive model for the mesozoic cenozoic plate tectonic evolution of the mediterranean and adjacent areas is illustrated by a series of paleoposition maps at selected intervals between the late triassic and recent this interval witnessed an important period of tensional development during the triassic and jurassic that fragmented pangea after its late paleozoic consolidation a number of oceanic areas evolved through jurassic time all of which have since been consumed during the alpine orogeny during the cretaceous and tertiary sea floor spreading geometry in the north and south atlantic resulted in convergence between africa and eurasia that controlled the evolution of the mediterranean and adjacent middle east areas from the late mesozoic to recent the interpretation departs from several previous ones in the following respects 1 1 the eastern mediterranean and adjacent middle east area are interpreted to have developed as two seaways with an intervening continental sliver derived from africa that now comprises central turkey and west iran these seaways persisted from the late triassic to late cretaceous by which time they were largely consumed by northward subduction 2 2 spreading that produced the present eastern mediterranean sea developed during the late cretaceous driving the tripolitza eratosthenes iskenderun continental fragments northward from africa to collision with central turkey as the preceding southern arm of the mesozoic tethys sea floor was entirely consumed initial block faulting in this zone occurred during the jurassic and early cretaceous but without subsidence reaching clearly bathyal depths until the cenomanian turonian this differs from the timing of events in the ionian sequence of the pindic nappe of crete which shows a change from shallow carbonate shelf in the triassic to deep basin in the liassic to the north of equivalent platform facies of the tripolitza nappe 3 3 moesia and rhodope are concluded to have been a single plate until a rifting event that started during the late jurassic the balkan mountains are interpreted to represent an alpine inversion of this mesozoic rift system that extended west from the black sea basin 4 4 the eastern carpathian microcontinental sliver is concluded as continuing southward as the serbo macedonian massif that separates rhodope from the vardar zone rather than as rhodope itself 5 5 the scutari pec lineament is considered as representing a major discontinuity between the apulia pannonian plate and adjacent greece and turkey ophiolites to the northwest of this lineament originated in a single oceanic area the vardar zone ophiolites to the southeast of this lineament evolved from two oceanic areas those of interior greece and northern anatolia and the associated ankara melange relating to the vardar zone the former north arm of tethys and the pindos southern anatolia zagros oman ophiolites relating to a former south arm of mesozoic tethys 6 6 based on the history of development of various elements of the alpine system there is a strong suggestion that important dextral movement took place along a major strike slip fault system reaching from the middle east to the central alps between late cretaceous and middle eocene times

benthic foraminiferal proxies of environmental changes during the pre messinian salinity crisis of the sinis basin w sardinia mediterranean sea abstract the messinian succession cropping out in a marginal basin of the mediterranean sea sinis basin w sardinia was studied in its benthic foraminiferal content in order to investigate the main palaeoenvironmental changes occurring a shallowing upward depositional trend from an upper bathyal circalittoral environment to a coastal lagoon was recognized during the pre messinian salinity crisis in the lower part of the analyzed succession capo san marco formation upper bathyal circalittoral conditions are suggested by species with a wide depth range such as cibicidoides pseudoungerianus melonis pompilioides oridorsalis umbonatus bolivinids and buliminids in the middle part of this formation the progressively shallowing environment is indicated by the low abundance of planktonics coupled with the upward increase of shallow water epiphytic species lobatula lobatula elphidium crispum e macellum ammonia beccarii hanzawaia boueana the progressive marine restriction led to the development of hypohaline conditions typical of lagoonal environments as suggested by ammonia tepida and oligotypic macrofaunas the succession stops with the deposition of laminated limestones barren in fossils sinis laminated limestone formation a mixed siliciclastic carbonate platform torre del sevo formation characterized by fluvial deposits intercalated in the marine succession developed as suggested by benthic foraminifera ostracods very rare planktonic species and macrofaunas sinis laminated limestone formation and torre del sevo formation constituted part of the terminal carbonate complex strongly eroded by the messinian erosional surface mes at its top the palaeoecological conditions in the sinis basin were intermittently suitable for sustaining full marine biota indicating that this marginal basin was not constantly desiccated during the pre messinian salinity crisis

miocene subduction related magmatism in southern sardinia sr nd and oxygen isotopic evidence for mantle source enrichment abstract subduction beneath southern sardinia in miocene times gave rise to a suite of basalts basaltic andesites high k andesites and rhyolitic ignimbrites the monte arcuentu volcanic complex is a typical product of this activity although the volcanic rocks display some tholeiitic affinities in terms of k 2 o sio 2 relations they resemble calc alkaline lavas of the aeolian and aegean arcs the most mafic members of the suite have moderately high ni 164 ppm and cr 550 ppm contents and high mgo 10 wt and are therefore mantle derived mantle normalised trace element patterns show high k rb ba and th but low nb and ta characteristic of subduction related magmas sr contents in almost all samples are particularly low 165 265 ppm 87 sr 86 sr i values range from 0 7054 to 0 7113 whilst nd i is between 0 9 and 8 8 the sr nd isotopic field overlaps those of the high k rocks of roccamonfina and the roman volcanic province and extends that of the aeolian islands and the aegean arc correlations of radiogenic isotope ratios with sio 2 values in bulk rocks are much stronger than with mgo conventionally analysed 18 o whole rock values range from 6 4 in basalt to 12 4 in a high k andesite however 18 o values for clinopyroxene phenocrysts analysed by a laser fluorination method range from 6 17 to 7 46 good correlations are seen between 18 o cpx values and both mgo and sio 2 differences between 18 o whole rock and 18 o cpx values are probably due to late stage alteration of the groundmass and cast doubt on the validity of petrogenetic interpretations based solely on whole rock oxygen isotope analysis the sr nd o isotopic variation can be modelled either by contamination of mantle derived magmas by hercynian continental crust or by extensive enrichment of the mantle source by subducted sediments in the 18 o cpx vs 87 sr 86 sr i diagram crustal contamination hyperbolae are concave upward because of the low sr contents of the monte arcuentu magmas so both crustal contamination trends and mantle enrichment trends can generate the same isotopic relationships however the strong correlations of radiogenic isotopic ratios with sio 2 and the weak correlations with mgo are most easily explained by extensive 2 10 mantle enrichment by subducted siliceous sediments the correlation between sio 2 and 87 sr 86 sr i for the monte arcuentu magmas is very unusual within subduction related magmatism whereas that between 18 o and 87 sr 86 sr appears to show that the suite forms an end member composition for many island arc and active continental margin volcanic suites

subduction triggered magmatic pulses a new class of plumes article i nfo a variety of atypical plume like structures and focused upwellings that are not rooted in the lower mantle have recently been discussed and seismological imaging has shown ubiquitous small scale convection in the uppermost mantle in regions such as the mediterranean region the western us and around the western pacific we argue that the three dimensional return flow and slab fragmentation associated with complex oceanic subduction trajectories within the upper mantle can generate focused upwellings and that these may play a significant role in regional tectonics the testable surface expressions of this process are the outside arc alkaline volcanism topographic swell and low velocity seismic anomalies associated with partial melt using three dimensional simplified numerical subduction models we show that focused upwellings can be generated both ahead of the slab in the back arc region though five times further inward from the trench than arc volcanism and around the lateral edges of the slab in the order of 100 km away from slab edges vertical mass transport and by inference the associated decompression melting in these regions appears strongly correlated with the interplay between relative trench motion and subduction velocities the upward flux of material from the depths is expected to be most pronounced during the first phase of slab descent into the upper mantle or during slab fragmentation we discuss representative case histories from the pacific and the mediterranean where we find possible evidence for such slab related volcanism

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

sedimentation and volcanism linked to multiphase rifting in an oligo miocene intra arc basin anglona sardinia three extensional phases can be recognized in the northern anglona area of the oligo miocene sardinian rift during a fifteen million year period which spanned corsica sardinia continental microplate separation and western mediterranean back arc basin opening in response to this multiphase rifting a complex facies architecture involving clastic carbonate and volcanic rocks developed integrated onshore facies and structural analysis dating and offshore seismic data are here used to reconstruct the tectono stratigraphic history of the anglona area initial late oligocene extension created a half graben geometry with syn rift clastic deposits shed locally from fault bounded highs passing laterally to lacustrine marlstones calc alkaline volcanic activity subsequently predominated as volcanic centres developed along one half graben bounding fault voluminous pyroclastic and epiclastic material was supplied to the adjacent half graben accommodation space and was deposited in marginal to marine conditions second phase mid aquitanian early burdigalian extensional faulting recognized from localized clastic syn rift stratal wedges truncated and subdivided the half graben the syn rift sediments were sealed by a regionally correlated ignimbrite that in turn was offset by late second phase faulting third phase extensional fault movement which reactivated the original fault trend then occurred a perched lake developed in the resultant topography coeval with the progressive marine transgression of lower areas as sea level rose during mid burdigalian times reefal carbonates and grainstones developed on fault block highs whilst calcarenites and marlstones were deposited in hangingwall locations initial extension was coeval with the formation of the sardinian proto rift and the initiation of the western mediterranean basin second phase faulting occurred as the corsica sardinia microplate rotated to its present position during western mediterranean back arc basin spreading final extension can be correlated to a second major extension phase along the oligo miocene sardinian rift following back arc basin opening as extension was transferred towards the fore arc in anglona the main influence of multiphase tectonism was on rift topography providing accommodation space and localized uplifted source areas varying relative sea level mainly controlled the broad types of facies belts that developed contemporaneous calc alkaline volcanism played a major role in the supply of basin filling material and in changing the topography locally

pantelleria rift crustal extension in a convergent intraplate setting the pantelleria rift system is a wide zone of post miocene northwest trending grabens and horsts beneath the sicily strait the central grabens host volcanics of predominantly alkalic composition which are exposed on the islands of pantelleria and linosa on the maltese islands along the northeastern shoulder of the rift an oligocene miocene carbonate succession exposed above sea level allows structural analysis and determination of shallow crustal stresses within the otherwise largely submarine rift system an older northeast trending set of normal faults is probably the expression of an oligocene miocene crustal extension event which produced continental rifts in western europe and led to passive margin formation in the western mediterranean younger northwest trending grabens of the pantelleria rift system cut the older faults almost at right angles and define a zone of lithospheric stretching between tunisia and sicily the northwest trending grabens which subsided dramatically since the beginning of pliocene time appear to be connected by east trending dextral and more rarely north trending sinistral transforms displacement along the transforms is probably in the order of a few kilometres in situ stress measurements carried out on the maltese islands show maximum horizontal compression sh parallel to the rift this suggests that in general 1 vertical and 2 horizontal and parallel to the rift are of about the same magnitude both exceed 3 sh which trends northeasterly slight intraplate convergence in a nw se direction seems to be more than balanced by extension in a ne sw direction neotectonics of the region possibly reflects an asthenospheric flow pattern which became established during the messinian salinity crisis the mechanism of recent intraplate deformation of the pelagian shelf has relevance for the understanding of more anciently subsided platforms of the apulian plate

ignimbrite correlation using whole rock geochemistry an example from the sulcis sw sardinia italy ignimbrites are useful chronological markers in the geological record at local and regional scales they also provide information on the dynamics of the eruption that produced them making their study of great importance in terms of volcanic hazard assessment however their study is usually hampered by their lateral variation and discontinuity when stratigraphic and lithologic criteria are not sufficient for correlation purposes the use of multiple complementary correlation tools may be necessary to correctly determine their areal extension volume and facies variations whole rock geochemistry is considered one of the less reliable correlation techniques due to the pyroclastic nature of these deposits and their emplacement dynamics these may introduce vertical and horizontal geochemical heterogeneity in the final deposit in addition the occurrence of zoned ignimbrites due to magma supply of changing composition is common in this work we show that if appropriately used whole rock geochemistry can be a valid and highly useful tool for ignimbrite correlation we provide an example from the study of an ignimbrite sequence containing 18 units sensu lato in the sulcis region sw sardinia italy a protocol has been developed for unit recognition based on successive simple binary diagrams where the whole rock composition of a problem sample can be plotted immobile trace elements have been preferentially used to minimize effects of element mobilization associated with alteration and weathering the diagrams provided here are designed for the sulcis but the methodology followed to develop them may be applied to other study areas

late oligocene to pliocene extension in the maltese islands and implications for geodynamics of the pantelleria rift and pelagian platform

siliciclastic carbonate sequences of miocene grabens of northern sardinia western mediterranean sea abstract the small crustal block of sardinia island western mediterranean underwent major rifting events during oligocene early miocene aquitanian early burdigalian and plio pleistocene times sedimentation in the resulting extensional and transtensional basins was affected by both local tectonic and worldwide sea level changes the mixed siliciclastic carbonate sequences which developed are readily comparable with those predicted by sequence stratigraphy this paper focuses on the post volcanic uppermost burdigalian to lower messinian sedimentation at the confluence between a main n s trending basin and a secondary sw ne trending graben in northern sardinia silty marlstones of late burdigalian early langhian age characterize the central part of the main basin whereas variable siliciclastic and carbonate sequences affected by up to three major transgression and regression cycles developed at its margins and at the confluence with the smaller graben differential movements along the main boundary fault led to rotation of blocks which localized narrow elongated offshore algal carbonate platforms low sea level stand led to deep erosion type 2 sequence boundary of these carbonates and to the formation of siliciclastic sandy lowstand wedges high sea level stand led to re establishment of algal platforms at the shelf margin which were bounded farther inland by siliciclastic carbonate mixed parasequences although it is not possible to date directly every stratigraphic unit local sequences are well structured and can be tentatively correlated with reported worldwide transgressive regressive events

industrial mineral occurrences associated with cenozoic volcanic rocks of sardinia italy geological mineralogical geochemical features and genetic implications the most important industrial mineral im deposits associated with the cenozoic volcanics of sardinia include kaolin bentonite and zeolites though of less significance perlite and potassium feldspar are also important in local and national markets bentonite and to a lesser extent kaolin and perlite form economically viable deposits and zeolites appear as very important industrial mineral commodities for future economic development the market situation for potassium feldspar is still under evaluation for use in ceramics all these deposit types occur as alteration products of cenozoic volcanic rocks which were emplaced during three main volcanic cycles in the eocene ec 55 to 51 ma oligocene miocene omc 32 to 13 ma and pliocene pleistocene ppc 5 to 0 1 ma kaolin bentonite zeolites and potassium feldspar occur as alteration products of the omc volcanites perlite occurs as an alteration product of the ppc volcanites all deposits have generally derived from the alteration of the most acidic members of the cenozoic volcanic rocks rhyolites to rhyodacites but differences among the associated ore forming phenomena are recognized hydrothermal sensu stricto deuteric alteration and weathering are the most important processes involved in ore formation weathering although of minor importance can also contribute to enhance the alteration of the deposits formed by hydrothermal and deuteric processes the extent and type of occurrences are mainly controlled by the local geological and structural features and the environmental geochemical conditions kaolin occurs in three main districts at romana and tresnuraghes it is hosted within ignimbritic sequences while at serrenti furtei it is found in pyroclastic flows and ash flow tuffs kaolin formed by hydrothermal processes occurs in high sulfidation romana and serrenti furtei and low sulfidation tresnuraghes type epithermal systems the alteration is proximal to the feeder conduits and structural setting controls kaolin formation bentonite is widespread throughout sardinia deposits occur as stratiform mineral bodies in situ altered within poor welded pumice rich and ash rich layers and also as distal fall out deposits as lenticular bodies interlayered within the miocene sedimentary sequences the former originated by deuteric alteration and formation is mainly controlled by lithology whereas the second type originated by weathering which altered the volcanic ash lenses deposited in lacustrine and or fluvial deltaic environments

topography of the calabria subduction zone southern italy clues for the origin of mt etna 1 calabria represents an ideal site to analyze the topography of a subduction zone as it is located on top of a narrow active wadati benioff zone and shows evidence of rapid uplift we analyzed a pattern of surface deformation using elevation data with different filters and showed the existence of a long wavelength 100 km relatively positive topographic signal at the slab edges the elevation of mis 5 5 stage marine terraces supports this pattern although the record is incomplete and partly masked by the variable denudation rate we performed structural analyses along the major active or recently reactivated normal faults showing that the extensional direction varies along the calabrian arc and laterally switches from arc normal within the active portion of the slab to arc oblique or even arc parallel along the northern and southern slab edges this surface deformation pattern was compared with a recent high resolution p wave tomographic model showing that the high seismic velocity anomaly is continuous only within the active wadati benioff zone whereas the northern and southwestern sides are marked by low velocity anomalies suggesting that large scale topographic bulges volcanism and uplift could have been produced by mantle upwelling we present numerical simulations to visualize the three dimensional mantle circulation around a narrow retreating slab ideally similar to the one presently subducting beneath calabria we emphasize that mantle upwelling and surface deformation are expected at the edges of the slab where return flows may eventually drive decompression melting and the mount etna volcanism

the messinian salinity crisis new seismic evidence in the west sardinian margin and eastern sardo provencal basin west mediterranean sea abstract we processed and interpreted a newly acquired geophysical dataset ws10 project integrated with vintage seismic profiles to study the evolution of the sardinian passive margin of the sardo provencal basin the most prominent features of the area of study are a consequence of the messinian salinity crisis msc which produced a thick salt layer in the deep basin complex halokinetic tectonics deformed the overlying messinian upper unit uu and the pliocene quaternary pq sediments sometimes also bending the sea bottom a thinner autochthonous salt in the uu suggests at least one further low stand during the late msc the messinian erosional surface mes separates the erosional truncation of the pre messinian sedimentary sequence from the overlaying plio pleistocene sequence with a clear angular discordance which almost completely masks possible earlier erosional events the mes is present across the middle and upper slopes of the sardinian margin and can be easily recognized down to the lower slope where it interfingers with the messinian evaporites which gradually thicken basinward we propose a correlation between the main erosional surface of the lower slope and the salt layer recognized in the uu as a consequence of a falling stage during the last part of the msc the seismic profiles now available along the west sardinian margin provide novel and crucial information to correlate the messinian depositional units in the deep basin with those present in the lower continental slope and with the erosional surface of the middle and upper slopes our data and interpretation highlight the main units of the messinian trilogy and further internal sequences that are probable related to cyclic fluctuations during their deposition

burial and exhumation of corsica france in the light of fission track data 1 the mesozoic and cenozoic exhumation and cooling history of corsica is reconstructed by fission track ft data on basement and sedimentary rocks apatite ages are 105 16 ma zircon ages are 160 145 ma the jurassic and cretaceous ages show that parts of the variscan basement escaped alpine influence the basement was thermally affected by rifting prior to jurassic opening of the ligurian piedmont ocean then it cooled to near surface temperatures in paleocene eocene times subduction buried parts of the basement and overlying flysch to greater depth in the oligocene both collapse of the nappe stack and rifting prior to opening of the ligurian provencal basin affected the apatite ft system of the basement in different partly overlapping areas causing a complex age pattern the study shows that thorough analysis of ft data and thermal modeling allow to assign age populations to distinct cooling processes even when several thermotectonic events contributed to generate an intricate age pattern

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

styles of back arc extension in the central mediterranean in the central mediterranean two back arc basins the liguro provencal lpb and the tyrrhenian basin tb opened progressively and consecutively from the late eocene oligocene to the present evolution in space and time of rifting and drifting processes along three different transects across these basins shows differences in the style of extension lpb opened with the formation of a narrow single rift while in the tb deformation and magmatism is spread over a wide area moreover at the northern end of the tb the locus of extension progressively migrated towards the east whereas in the southern tb the locus of extension and magmatism migrated inside the basin inducing continental break up and drifting of the previously formed older conjugate basins we propose that these different styles of back arc extension depend upon internal conditions such as prerift rheology linked with its geological heritage and external conditions e g the style of subduction

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

thermochronologic evidence for the exhumational history of the alpi apuane metamorphic core complex northern apennines italy 1 the apennine range is a young convergent orogen that formed over a retreating subduction zone the alpi apuane massif in the northern apennines exposes synorogenic metamorphic rocks and provides information about exhumation processes associated with accretion and retreat u th he and fission track ages on zircon and apatite are used to resolve exhumational histories for the apuane metamorphic rocks and the structurally overlying very low grade macigno formation stratigraphic metamorphic and thermochronologic data indicate that the apuane rocks were structurally buried to 15 30 km and 400 c at about 20 ma exhumation to 240 c and 9 km depth below sea level occurred at 10 13 ma by 5 ma the apuane rocks were exhumed to 70 c and 2 km the macigno and associated tuscan nappe were also structurally buried and the macigno reached its maximum depth of 7 km at 15 to 20 ma stratigraphic evidence indicates that the apennine wedge was submarine at this time thus we infer that initial exhumation of the apuane was coeval with tectonic thickening higher in the wedge as indicated by synchronous structural burial of the tuscan nappe from 6 to 4 ma thinning at shallow depth is indicated by continued differential exhumation between the apuane and the tuscan nappe at high rates after 4 ma differential exhumation ceased and the apuane and the tuscan nappe were exhumed at similar rates 0 8 km ma which we attribute to erosion of the apennines following their emergence above sea level

seismic structure of the central tyrrhenian basin geophysical constraints on the nature of the main crustal domains in this work we investigate the crustal and tectonic structures of the central tyrrhenian back arc basin combining refraction and wide angle reflection seismic was gravity and multichannel seismic mcs reflection data acquired during the medoc mediterraneo occidental 2010 survey along a transect crossing the entire basin from sardinia to campania at 40 n the results presented include a 450 km long 2 d p wave velocity model obtained by the traveltime inversion of the was data a coincident density model and a mcs poststack time migrated profile we interpret three basement domains with different petrological affinity along the transect based on the comparison of velocity and velocity derived density models with existing compilations for continental crust oceanic crust and exhumed mantle the first domain includes the continental crust of sardinia and the conjugate campania margin in the sardinia margin extension has thinned the crust from 20 km under the coastline to 13 km 60 km seaward similarly the campania margin is also affected by strong extensional deformation the second domain under the cornaglia terrace and its conjugate campania terrace appears to be oceanic in nature however it shows differences with respect to the reference atlantic oceanic crust and agrees with that generated in back arc oceanic settings the velocities depth relationships and lack of moho reflections in seismic records of the third domain i e the magnaghi and vavilov basins support a basement fundamentally made of mantle rocks the large seamounts of the third domain e g vavilov are underlain by 10 20 km wide relatively low velocity anomalies interpreted as magmatic bodies locally intruding the mantle