reflection and refraction seismics in areas of complex geology an example in the northern apennines an experimental survey employing refraction wide angle reflection seismic techniques dss deep seismic soundings was carried out in the northern apennines north italy the main objective of the experiment was the application of dss to better define the structure of the upper crust down to about 15 km depth in the crucial alps apennines boundary zone a second objective was to understand the potential of dss as a complementary tool in areas of complex geology where the results of near vertical reflection nvr are generally poor the results of the experiment show that dss if properly planned can continuously follow deep markers and therefore impart a greater significance to faint and discontinuous nvr as well as data on the p wave velocity of the seismic units

on the hellenic subduction zone and the geodynamic evolution of crete since the late middle miocene abstract in recent syntheses of the geodynamic evolution of the aegean area the hellenic subduction zone and in particular its initiation plays a central role two basic aspects of the recent comprehensive model put forward by le pichon angelier and co workers are a initiation of subduction along the hellenic arc is inferred to have taken place approximately 13 ma ago whereas several others have suggested approximately 5 ma and b migration of the trench system to the south southwest giving rise to an extensional regime in the back arc region which led to general subsidence and formation of the present day aegean sea new data on the structure of the upper mantle underneath the aegean area indicate that the former aspect requires modification the seismic velocity structure indicating a northward dipping slab down to a depth of at least 600 km and the depth distribution of earthquake hypocenters can not be reconciled with straightforward initiation of subduction approximately 13 ma ago estimates of about 5 ma for the time of initiation of the present subduction zone are even more difficult to reconcile assuming 400 km as an upper bound for the effect of stretching of the aegean sea and of other processes contributing to the separation of crete from the eurasian mainland we arrive at an age for the hellenic subduction zone of at least 26 ma as to aspect b geological data of crete lend strong support to the idea that on crete compressional tectonics is of much greater importance than current models imply combining geophysical and geological data we propose a modification of the tectonic evolution for the cretan segment of the hellenic arc whereas the basic process of extension caused by a migrating trench system roll back in a land locked basin remains a very useful and sound concept the tectonics of the margins of a region subject to stretching in this case crete may be more complicated than hitherto thought in our model the documented fragmentation of crete into several basins which started about 12 ma ago is not attributed to initiation of subduction but to inception of the roll back process compressional tectonics on crete is taken to be associated with deformation of the crust resulting from the overall tensional stress regime

interplay between subduction retreat and lateral extrusion tectonics of the western carpathians 1 analysis of brittle microstructures reveals three tertiary deformation events in the western carpathians 1 late paleogene bedding parallel extension 2 oligocene to middle miocene nne ssw compression and ese wnw extension 3 post mid miocene nw se extension these regional deformations applied to crustal blocks in the intra carpathian region resulted from forces which were induced by the coupled plate tectonic processes of subduction retreat beneath the carpathian arc and lateral extrusion from the eastern alps toward the carpathian region material flow from the alps spread toward east and ne guided by sinistral strike slip zones along the ne trending continental margin subduction retreat was terminated by mid miocene soft collision of the inner western carpathians with the european foreland ongoing subduction retreat beneath the eastern carpathians caused post mid miocene back arc extension forming the pannonian basin extension spread into the western carpathians by reactivating the extrusion related strike slip faults as normal faults

rheological stratification of the lithosphere abstract the rheology of the lithosphere is estimated on the basis of pore pressure dependent frictional failure in the brittle regime and power law steady state creep in the ductile regime different petrological models of the continental and oceanic lithosphere combined with different geotherms and thicknesses are used to generate models covering a variety of geodynamic situations results show that the depth dependence of lithospheric rheology varies with the tectonic province and that in many instances the continental lithosphere has one at the bottom of the crust or two the previous one plus another at mid crustal levels soft ductile layers sandwiched between brittle layers the depth distribution of geophysical parameters seismicity seismic wave velocity and electrical conductivity matches the theological predictions well the lithospheric rheological profiles are used to analyze observed variations in the structural style of deformed continental margin and oceanic terranes in the southeastern canadian cordillera the large scale characteristics of the system show a satisfactory agreement with the inferred rheological structure sub horizontal decollements should be the rule rather than the exception where the lithospheric rheology is strongly stratified

the arcs of the western alps and the northern apennines an updated view abstract the arcs of the western alps and the northern apennines and the link between them are in the process of being investigated using the european geotraverse and they have historically been interpreted in many different ways new information particularly geophysical further constrains possible models both arcs have evolved in several stages sometimes complexly interrelated and sometimes independent of each other compressional belts produced in these stages have either been of the push arc type indentation into a deformable mass or the pull arc type backward migration of hinge of a subduction zone leading to small extensional basins known as back arc basins and pores with an arcuate mountain range on the subduction side extensional periods with the possible formation of pull arcs in the alps comprise the gosau period between the eo and meso alpine push arc phases and the oligocene lull period between the meso and the neo alpine push arc phases in the northern apennines remainders of the meso alpine nappes were involved in oligocene early miocene pull arc formation associated with spreading in the balearic sea followed by push arc formation particularly in the middle miocene and by renewed pull arc formation from the latest late miocene to the present during all of these developments the moho was modified by such processes as lithospheric stretching asthenospheric intrusions subhorizontal shearing and isostatic uplift the present moho configuration is consequently a collage of moho patches formed at different intervals both push and pull arcs are laterally bounded by complementary strike slip or transform zones these too were modified in the course of history and their final geometry is consequently of a very complex nature in the alps for instance the insubric fault zone appears to have been the main dextral transform fault of the neogene push arc until it was sinistrally kinked by the giudicarie fault zone and probably deactivated dextral transpression being briefly transferred to the en echelon brachyanticlines of the late alpine windows in the case of the oligocene apennines the sinistral rotations of corsica and sardinia otherwise hard to understand may be attributed in part to sinistral transform motions along the eastern border zone of the oligocene early miocene balearic extension

seismic anisotropy and mantle creep in young orogens summary seismic anisotropy provides evidence for the physical state and tectonic evolution of the lithosphere we discuss the origin of anisotropy at various depths and relate it to tectonic stress geotherms and rheology the anisotropy of the uppermost mantle is controlled by the orthorhombic mineral olivine and may result from ductile deformation dynamic recrystallization or annealing anisotropy beneath young orogens has been measured for the seismic phase pn that propagates in the uppermost mantle this anisotropy is interpreted as being caused by deformation during the most recent thermotectonic event and thus provides information on the process of mountain building whereas tectonic stress and many structural features in the upper crust are usually orientated perpendicular to the structural axis of mountain belts pn anisotropy is aligned parallel to the structural axis we interpret this to indicate mountainparallel ductile i e creeping deformation in the uppermost mantle that is a consequence of mountain perpendicular compressive stresses the preferred orientation of the fast axes of some anisotropic minerals such as olivine is known to be in the creep direction a consequence of the anisotropy of strength and viscosity of orientated minerals in order to explain the anisotropy of the mantle beneath young orogens we extend the concept of crustal escape or extrusion tectonics to the uppermost mantle we present rheological model calculations to support this hypothesis mountain perpendicular horizontal stress determined in the upper crust and mountain parallel seismic anisotropy in the uppermost mantle require a zone of ductile decoupling in the middle or lower crust of young mountain belts examples for stress and mountain parallel pn anisotropy are given for tibet the alpine chains and young mountain ranges in the americas finally we suggest a simple model for initiating mountain parallel creep

segmentation and configuration of subducted lithosphere in italy an important control on thrust belt and foredeep basin evolution the apennine foredeep basin system located on continental crust consists of four roughly parallel basin segments each containing a flexural outer rise and an inner trough that deepens continuously toward the thrust belt flexural modeling of subsidence data across the basin indicates that this foredeep basin results mainly from deep subsurface loads acting on the subducted slab from within the subduction zone rather than from the topographic load of the apennine mountains the geometry of the four basin segments observed within the apennine foredeep is thus inferred to reflect subduction of segmented lithosphere where each lithospheric segment corresponds to a segment of the foredeep basin beneath the basin and in the foreland the lithosphere is continuous segmentation occurs only at depth beneath the thrust belt this pattern olf segmentation of the subducted lithosphere at depth is reflected in the large scale geometry of the outer part of the apennine thrust belt and appears to control it similarly the pattern of segmentation also appears to control the position of the eastern limit of back arc type extension in western italy these relations strongly suggest a genetic relation between subduction zone processes foredeep basin geometry and thrust belt evolution in which the configuration of the subducted lithosphere largely controls the large scale surface deformation observed in the apennine system

fold uplift and synkinematic stratal architectures in a region of active transtensional tectonics and volcanism eastern tyrrhenian sea the detailed stratigraphic analysis of synkinematic stratal architectures permits the calculation of fold uplift rates and the reconstruction of fold kinematics this approach was applied to active folds in the bay of pozzuoli eastern tyrrhenian sea this area features late quaternary volcanism shallow magmatic intrusions and transtensional tectonics seismostratigraphic analysis of synkinematic strata is constrained by a physical correlation to an already established stratigraphic succession in the neighboring campi flegrei and by tephra layers in a gravity core located in pozzuoli bay a stratigraphic resolution in thousands of years was established structural and stratigraphic analyses yield quantitative data on the timing of fold inception kinematics and the amount and rates of uplift the folds extend over 2 km and display a curved axial pattern and wedge shaped packages of synkinematic strata the rate of fold uplift ranges from 1 to 20 mm yr the structures feature limb rotation kinematics and decreasing uplift rates the uplift rates and geometry of the pozzuoli bay folds suggest that they are of tectonic origin and are a product of detachment folding their limited longitudinal extent and arcuate axial trends are compatible with an east trending left transtensional shear zone that was active along the eastern tyrrhenian sea during the late quaternary a relative sea level curve was calculated for an anticline culminating in the city of pozzuoli this relative sea level curve highlights the relationship between the deformation timing and the genesis of related abrupt changes in sedimentary facies and erosional surfaces

delineation of the north central italian upper mantle anomaly the italian peninsula is the focus of intense deformational tectonic activity it is underlain by mantle material whose inferred relatively anomalous properties1 2 are not inconsistent with the seismic volcanic and thermal activity that is manifested in this region the most effective geophysical tool for mapping the structure of the uppermost 200 300 km of the earth is the observation and analysis of seismic surface wave dispersion on a regional scale here we synthesize the interpretations of rayleigh wave dispersion measurements made by several authors each for different parts of north central italy3 8 to delineate the lateral extent of the upper mantle anomaly in this region

ground motion and stress accumulation driven by density anomalies in a viscoelastic lithosphere some results for the apennines summary we provide the analytical formulation for calculating the displacement and stress field forced by internal sources in a stratified self gravitating viscoelastic earth this model is specialized to study the rate of vertical motion and shear stress accumulation produced by lithospheric density anomalies these sources are allowed to vary in the lateral direction we show that sphericity plays a crucial role for elongated lithospheric anomalies while self gravitation produces minor deviations from a gravitating earth when the model is applied to the apennines we get for lithospheric viscosity ranging between 10 and loz3 pas the subsidence of the plate underlying the active front of the overthrusting load to be around 0 5 1 0 mm yr this is consistent with the amount of sedimentation in the adriatic foredeep the deformation pattern is very peculiar with the largest subsidence localized beneath the active front of the topography our model enlightens the impact of discontinuities of tectonic phases on vertical motions in collision zones if lithospheric viscosity is around 10 pa s vertical motions decay drastically on time scales of 105yr if lateral migration of density anomalies comes to an end for higher viscosities deformation rates are maintained longer this correlation between horizontal and vertical motions suggests that altimetric geodetic surveying along levelling lines of a few hundred kilometers can be an important tool to constrain the tectonics of the studied region results are also shown for vertical motions along a transect perpendicular to the apennines when the crustal structure inverted from bouguer gravity data is considered analysis of the stress field induced by an overthrusting load shows that principal stress differences of a few bar or a few tenths of mpa can be accumulated on time scales of 102 103yr these low values agree with the average stress drop of earthquakes in the appalachians and northern apennines where our modelling can be applied we find that lateral density variations certainly contribute to intraplate stresses but they are less efficient in triggering earthquakes than other mechanisms such as transcurrent motions along active plate margins seismicity induced by lateral variations of crustal and lithospheric density must be moderate characterized by long return times these results are in agreement with the recorded seismicity in the northern apennines where the largest earthquakes have return times of lo2 yr if shear stress is forced by an overthrusting load we find that the largest rate of stress accumulation in the crust is concentrated beneath the active front close to the boundary with the ductile lithosphere discontinuities of tectonic phases play an important role in controlling the amount of shear stress due to density anomalies

on the thermal regime of some tectonic units in a continental collision environment in romania an analysis of the evolution of the main tectonic units in romania shows that the thermal regime of the lithosphere should be derived according on the one hand to the particular tectonic interactions the various tectonic units have been involved in and on the other hand to the investigated depth interval a steady state conduction model of the crustal temperature field based on the heat flow distribution and information on the structure is presented for the romanian territory it shows large lateral thermal variations between tectonic units as a result of different geological and thermal histories within the frame of a complex modelling of the thermal evolution of the lithosphere in the east carpathians as proposed in this study the zero order thermal effects of the pre miocene oceanic subduction of the eurasian plate are evaluated the deep thermal structure of the subducted slab is derived and shown to be compatible with the velocity structure of the lithosphere and the intermediate depth seismicity of the vrancea area

the tyrrhenian apennines system structural setting and seismotectogenesis abstract the available geological geophysical and seismological data of the tyrrhenian apennines system are briefly reviewed and synthesized in a number of sketch maps integrating and comparing these data a large scale simple shear kinematic model is proposed for the tyrrhenian apennines system that is here interpreted as an oblique asymmetric passive continental margin developed during the progressive counterclockwise rotation of the adriatic foreland from the late miocene to the present in the frame of this working hypothesis the thinning and stretching of the tyrrhenian crust were accommodated by progressive eastward motion of extensional allochthonous slices bounded by low angle west dipping oblique shear zones rotating above a common detachment that penetrates into the mantle lithosphere at any given time the most external eastward moving slice is bounded by a transtensional shear zone at the top and by a transpressional one at the bottom the displacement within the hanging wall of the transtensional shear zone is accommodated by high angle normal faults and en echelon grabens the displacement within the hanging wall of the transpressional shear zone is instead accommodated by co axial en echelon sets of folds thrusts and high angle strike slip faults thus the development of the late miocene pliocene pleistocene contractional strain field of the apennines of italy might not be a consequence of complex subduction processes but subordinate to the deformation processes that lead to the progressive opening of the tyrrhenian sea the seismicity of the crustal apennines of italy is analyzed in the frame of the above history of progressive deformation and a seismotectogenetic model is outlined

architectural complexity of a carbonate transgressive systems tract induced by basement physiography three dimensional exposure of the plio pleistocene calcarenite di gravina formation around matera horst italy permits analysis of the architecture and internal complexities of carbonate sedimentary bodies around a palaeoisland spatial organization of the different lithosomes along with their skeletal composition sedimentary structures and bedding patterns helps decipher the key factors that controlled platform architecture and distribution of heterogeneities basement physiography type and loci of carbonate production bottom currents and changes in accommodation relative sea level changes resulted from high frequency glacioeustatic cycles that punctuated an overall tectonically induced transgression topographic relief fragmentation of the limestone basement and wave energy controlled lithoclastic supply basement physiography and relative sea level changes determined the area available for carbonate producing biotas and thus the amount and type of skeletal sediments on the moderately dipping south western margin waves and associated currents re distributed the lithoclasts derived from coastal abrasion bioclasts mostly derived from epiphytic seaweed production in the shoreface infralittoral prisms resulted from downdip transport progradation and longshore transport which controlled along strike continuity of the prisms where basement continuity was interrupted at the margin of the palaeoisland a lithoclastic fan was deposited from dumping sediments carried by shore parallel currents fan shaped skeletal bodies coalesced to form an apron on the steeper northern side of the palaeoisland when a structural platform was flooded and epiphytic carbonates were shed red algae contribution depended on the available oligophotic area which in turn was controlled by high frequency sea level cycles basement physiography and apron aggradation the internal architecture of this apron resembles a low stand wedge but it accumulated during transgression deeper water contour parallel currents formed a lithosome at the foot of the structural relief interpreted as drift deposits it is composed of shallow water benthonic skeletal components planktonic foraminifera and some limeclasts

seismotectonics of the calabrian arc abstract relocation of intermediate and deep earthquakes of tyrrhenian sea area through joint hypocenter determination for the period 1962 1979 has allowed a more detailed definition of the geometry of this peculiar benioff zone earthquakes dip along a quasi vertical plane to 250 km depth there is a 50 dip in the 250 340 km depth range and a low dip angle to 480 km depth the structure sketched from the hypocenters is almost continuous but most energy has been released in the 230 340 km depth interval an evaluation of fault plane solutions of intermediate earthquakes in this area indicates predominance of down dip compressions in the central part of the slab at the border strike slip motion occurs independent of depth some earthquakes that occurred at intermediate depth less than 100 km along the ionian margin of calabria show predominance of reverse faulting with the p axis oriented se nw however shallow earthquakes in the calabria sicily region indicate a more complex motion with predominance of normal faulting a possible interpretation of these features according to the available geological history which involves subduction of continental lithosphere is discussed

deflection gravity anomalies and tectonics of doubly subducted continental lithosphere adriatic and ionian seas three profiles across the southern adriatic and northern ionian seas span an intermediate foreland area that is or has recently been subducted both westward under the apennine calabrian thrust belt and eastward under the hellenide belt gravity and deflection data from the base of the pliocene along the three profiles are qualitatively similar to those predicted for a thin elastic sheet subject to end loads at both plate ends more detailed analysis of the profiles shows very good agreement between observations and predictions if the intermediate foreland lithosphere is treated as a thin elastic sheet with an effective elastic thickness between about 15 and 20 km equivalent to a flexural rigidity between 2 1022 and 6 1022 nm these results coupled with seismicity data suggest that active convergence within the hellenides extends as far north as southwestern yugoslavia analysis of the northernmost profile across the southern adriatic sea shows a well constrained elastic plate thickness of 14 km and an initial water depth prior to loading of about 1 km the distance between the two subduction systems on this profile is estimated at about 275 km analysis of the two more southerly profiles yields a minimum effective elastic plate thickness of about 15 km but no maximum value could be determined the initial water depths for these two profiles are well constrained at 1 3 and 1 6 km prior to loading and the distance between the two subduction systems is estimated at about 175 km on both profiles along the northwest trend of the two opposing subduction systems the change in distance between the two systems occurs abruptly and the hellenic subduction system appears to be segmented into a series of northwest trending roughly linear subduction segments the calculated deflection profiles also show pronounced asymmetry on the northernmost profile and an opposite sense of asymmety on the southernmost profile

the origin of the apenninic arcs abstract the apennine area is composed of a variety of arcs some of them forming the mountain chain and some of them being submerged below the po plain and the adriatic sea the structure of the apennine mountain belt is that of a succession of northeast east and southeastward directed arcs corresponding to single thrust sheets each arc is limited by n s oriented dextral transcurrent faults data from volcanology gravimetry and reflection seismic surveys show that an important section of the upper mantle is involved in these features the geodynamic reconstruction during neogene times i e the period of apenninic up building suggests that a unique arc existed from oligocene to middle miocene times as a result of the rotation of the sardo corso continental block this arc was successively disrupted in several segments which advanced and shortened differentially as a function of the resistance to the orogenic expansion opposed by the rigid adriatic foreland this new tectonic phase which is responsible for most of the apenninic features has been triggered by the differential evolution of anomalous mantle domes in the tyrrhenian area from post middle miocene times onwards

tephrochronological study in the quaternary val d agri intermontane basin southern apennines italy in the south eastern depocentre of the val d agri basin southern apennines a volcanic ash layer crops out interbedded within poorly structured alluvial fan deposits of late pleistocene age textural depositional and pedological features of this weathered layer suggest a primary deposition from a pyroclastic fall out of volcanic ash chemical analyses of feldspars show an alkali trachytic composition and accessory minerals association allow to correlate this tephra layer with the regionally dispersed y 7 marine tephra layer tufo verde epomeo eruption ischia volcano dated at 56 4 ka the val d agri tephra here described for the first time was deposited during mis stage 3 its recovery and characterization permit to contribute to regional correlation of the mediterranean climatic and volcanic events from marine to continental successions and to describe landscape evolution of the southern apennines during glacial interglacial cycles

sedimentary and tectonic evolution of plio pleistocene alluvial and lacustrine deposits of fucino basin central italy abstract the fucino basin was the greatest lake of the central italy which was completely drained at the end of 19th century the basin is an intramontane half graben filled by plio quaternary alluvial and lacustrine deposits located in the central part of the apennines chain which was formed in upper pliocene and in quaternary time by the extensional tectonic activity the analysis of the geological surface data allows the definition of several stratigraphic units grouped in lower units and upper units the lower units upper pliocene are exposed along the northern and north eastern basin margins they consist of open to marginal lacustrine deposits breccia deposits and fluvial deposits the upper units lower pliocene holocene consist of interbedded marginal lacustrine deposits and fluvial deposits thick coarse grained fan delta deposits are interfingered at the foot of the main relief with fluvial lacustrine deposits most of the thickness of the lacustrine sequences more than 1000 m thick is buried below the central part of the fucino plain the basin is bounded by e w wsw ene and nw se fault systems velino magnola fault e w and tremonti celano aielli fault wsw ene and s potito celano fault nw se in the north the trasacco fault the pescina celano fault and the serrone fault nw se in the south east the geometry and kinematic indicators of these faults indicate normal or oblique movements the study of industrial seismic profiles across the fucino basin gives a clear picture of the subsurface basin geometry the basin shows triangular shaped basin fill geometry with the maximum deposits thickness toward the main east boundary fault zones that dip south westward serrone fault trasacco fault pescina celano fault on the basis of geological surface data borehole stratigraphy and seismic data analysis it is possible to recognize and to correlate sedimentary and seismic facies the bottom of the basin is well recognized in the seismic lines available from the good and continuous signals of the top of meso cenozoic carbonate rocks the shape of sedimentary bodies indicates that the filling of the basin was mainly controlled by normal slip along the nw se boundary faults in fact the continental deposits are frequently in on lap contact over the carbonate substratum several disconformable contacts occurred during the sedimentary evolution of the basin the main faults with antithetic and synthetic fault planes displace the whole sedimentary sequence up to the surface indicating a recent faults activity 1915 avezzano earthquake ms 7 0 the stratigraphic and tectonic setting of the fucino basin and neighboring areas indicates that the extensional tectonic events have had an important role in driving the structural sedimentary evolution of the plio quaternary deposits the geometry of the depositional bodies of the fault planes and their relationships indicate that the fucino basin was formed as a half graben type structure during plio quaternary extensional events some internal complexities are probably related to the fold and thrust structures of the apenninic orogeny formed in messinian time in this area and to a different activity timing of the e w and wsw ene fault systems and the nw se fault systems we believe based on the similarity of the surface characteristics that the structural setting of the fucino basin can be extrapolated to the other great intramontane basins in central italy e g rieti l aquila sulmona sora isernia basins

87sr 86sr ratios in permo carboniferous sea water from the analyses of well preserved brachiopod shells abstract sr isotopic analyses of well preserved portions of permo carboniferous brachiopods distributed globally confirm the general shape of the sr isotope age curve established by previous workers for this time interval there is little variation between the sr isotopic composition of unaltered portions of brachiopods and that of portions of the same shell interpreted to be diagenetically altered based on cathodoluminescence elemental and stable isotopic data however the sr isotopic composition in diagenetically altered micritic matrix adjacent to the shell is more radiogenic the sr isotopic composition in the unaltered portions of calcitic megafossils has potential as a stratigraphie tool

the calabrian arc and the ionian sea in the dynamic evolution of the central mediterranean in the central mediterranean area it is possible to recognize three main realms the tyrrhenian sea the pelagian block and the ionian block these domains are limited by important fracture zones that are easily recognizable on land and offshore these fracture zones can be grouped into four main trends 1 the nw se trend which is characterized by dextral horizontal movements 2 the ne sw trend which is generally characterized by sinistral lateral horizontal movements 3 the e w trend which also shows dextral shear movements and 4 the n s trend which is characterized by normal faults only the tyrrhenian sea realm is characterized by a thinned crust of oceanic type and is connected to the apenninic chain by means of listric faults from a geophysical point of view the area shows a high heat flow which follows the main structural trends and positive gravimetric anomalies which are compatible with seismic refraction data and can be explained by the proposed model the pelagian block shows a continental crust about 20 km thick which progressively increases beneath the sicilian chain here an abrupt interruption with the tyrrhenian block takes place in the pelagian realm rifting processes developed according to the nw se and n s trend the n s trend characterizes the westernmost zone of the realm where volcanic processes and a relatively high heat flow can also be observed the ionian block is characterized by the following a thinned crust 17 20 km which increases 40 km towards the southern calabrian chain a thick sedimentary sequence high positive bouguer anomalies 300 mgal and very low heat flow 50 mw m 2 geophysical and structural analyses allowed us to evaluate the post tortonian evolution of the whole area under consideration this evolution resulted in continental crust formation according to a rigid plastic deformation model according to our model the ionian block can be considered as a domain characterized by a thinned continental crust and affected by intrusive material derived from the upper mantle furthermore this domain of probably jurassic age can be considered as a pelagic basin bordered by the pelagian block to the west and by the apulian block to the east northeast this basin according to its position with respect to the apenninic and sicilian chains has not been affected by tectogenesis and still represents a site of continuous sedimentation from a kinematic point of view the ionian realm can be linked with the pelagian block shifting towards the east northeast whereas it is limited towards the north by an e w fracture zone which regulates the opening of the tyrrhenian sea and the counterclockwise rotation of the apenninic chain according to the proposed model the opening of the tyrrhenian sea can be considered as a megaextension fracture which developed parallel to the maximum principal stress direction and evolved as a triangular shaped structural feature in preparing the model the authors have taken into account a large set of data collected both on land and offshore

late caledonian extension in the scandinavian caledonides the roragen detachment revisited abstract this paper concerns the interplay of compression and extension during palaeozoic collisional orogeny in scandinavia and focuses on a small old red sandstone basin in the central scandes at roragen early devonian sediments are preserved there in a half graben located in the western limb of a major late upright antiform the latter the vigelen antiform exposes proterozoic crystalline rocks in the core and folds the entire caledonian tectonostratigraphy of the lower middle and upper allochthons mylonites related to the eastward directed thrust assembly of these allochthons have been mapped over the antiform they occur in the western limb of the fold in the footwall of a high angle w dipping normal fault the latter separating the old red sandstones from the caledonian nappes these thrust generated mylonites exhibit a suite of superimposed down to nw shear sense indicators in the footwall of the fault displacement on this roragen detachment is inferred to be about ten kilometers reflection seismic profiling across the northern extension of the vigelen antiform in the storlien area indicates that this major longitudinal fold developed in the hanging wall of a sole thrust that dips very gently westwards beneath this part of the mountain belt it is argued here that the early devonian roragen half graben may have developed during thrust stacking of the vigelen antiform providing evidence of scandian upper crustal extension accompanying the emplacement of the thrust sheets onto the baltoscandian platform in the southern scandes full crustal extension would have occurred thereafter leading to the development of the mid devonian basins in the hinterland of westernmost norway

differential rotation between lithosphere and mantle a consequence of lateral mantle viscosity variations the description of plate motions in the so called hotspot reference frame introduces a global rotation of the lithosphere with respect to the mantle this rotation called toroidal field of degree 1 is roughly westward it reaches an amplitude of about 2 cm yr and has been consistently found in the different generation of plate tectonic models various authors have tried to relate this observation to the deceleration of the earth s rotation to polar wander or to tidal drag however these different physical mechanisms cannot explain the requested amplitude in this paper we compare the values of this rotation vector using different relative plate motion models expressed in the hotspot reference frame in a model earth with lateral viscosity variations a differential rotation is predicted the observed net lithospheric rotation is consistent with the dynamics of a model earth where the asthenospheric viscosity below the oceans is at least one order of magnitude lower than underneath the continents this relative westward drift of the lithosphere may account for the significant structural differences between east or west dipping subduction zones

a proposal for the kinematic modelling of w dipping subductions possible applications to the tyrrhenian apennines system in w dipping subduction zones there is a general eastward progression of the back arc basin accretionary wedge foredeep complex with the forward progression early stages of the complex are revealed by slices of upper crust and sedimentary cover abandoned to the west left floating above a new section of mantle a major shear zone should form at the new moho separating upper crust slices of earlier accretionary stages and the eastward flowing mantle the mantle wedging at the top of the subduction plane could be responsible for the uplift of the central parts of the belt the retreating of the subduction hinge is interpreted as due to the push generated by the eastward mantle flow detected in the hot spot reference frame the foredeep depth is mainly a function of the radius of curvature of the subduction hinge the frontal wedge is constructed from the stacking of the upper layers of the subducting plate and the syntectonic clastics that fill the foredeep which are progressively involved in thrusting and later by extension in order to preserve volume balance the lithosphere of the eastern plate before subduction has to be the same size as that which has been subducted due to the longer length of the arc with respect to the original length of the linear margin between the two converging plates laterally stretched subducted lithosphere is predicted at depth w dipping subductions usually have a short life probably due to their inherent capability to produce new lateral heterogeneities of the lithosphere the thin back arc which are a key factor in controlling and generating new subductions both e and w dipping this model is applied to the apennines tyrrhenian sea system

transfer zones in an oblique back arc basin setting insights from the latium campania segmented margin tyrrhenian sea new multichannel seismic reflection profiles were acquired to unravel the structure of a portion of the eastern margin of the tyrrhenian basin this extensional feature is part of an oligocene to present back arc basin in the hangingwall of the west directed apennines subduction system the basin provides excellent conditions to investigate the early stage processes leading to the development of rifted passive margins and to the emplacement of oceanic crust in an oblique setting the interpreted post stack migrated seismic profiles highlight the geometry and kinematics of the pontine escarpment that connects the latium campania continental margin to the vavilov basin the latter is the main feature of the area related to the early pliocene extension of the tyrrhenian sea several morphological variations are pointed out along strike mirroring different structural settings of the margin itself a steeper margin to the north corresponds to high angle possibly transtensional faults whereas a smooth slope in the southern portion corresponds to several more distributed listric faults this work contributes to the understanding of the interplay between extensional and transtensional tectonics along the margins of an oblique back arc basin

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

lower adriatic sea seismic sequence january 1986 spatial definition of the seismogenic structure abstract in january 1986 a swarm like seismic sequence main shock m l 4 8 took place in the lower adriatic sea this sequence was recorded by the italian telemetered seismological network using a digital acquisition system using additional data collected by other italian yugoslavian and albanian institutions 15 shocks of the sequence were located by means of the master event technique and for two of them a focal mechanism solution was obtained we attempted to frame our results within the knowledge available in the literature the adriatic microplate is regarded by many authors as a whole block nevertheless it exhibits moderate seismicity the question has arisen as to whether it can be considered an african promontory or whether it behaves independently the area actived by the sequence is rather small less than 10 km in diameter owing to the low level of seismic energy release and does not show any particular trends the focal mechanisms are consistent with the recent stress field in the adriatic area inferred from previous studies which indicate a compression axis oriented ne sw

the main characteristics of the lithosphere asthenosphere system in italy and surrounding regions we present a summary of the available information on rayleigh wave dispersion data for the italian area the dispersion curves can be grouped into two main families according to their shape one with an almost linear trend in the period range from 40 to 150 sec the other with a relatively flat portion in the period range from 40 to 80 sec the inversion of these data shows that there are strong lateral variation in the lithosphere system a very rapid transition in the lithospheric thickness from about 130 km to about 30 km as well as in the s wave velocity of the lithosphere and asthenosphere

the umbria marche arcuate fold belt italy abstract in this paper the structural setting of the umbria marche fold belt is briefly described the basement cover relationships and the primary or secondary origin of the arcuate shape are also discussed mainly on the basis of structural data it is suggested that the umbria marche fold belt can hardly be the result of a thin skinned tectonics under little overburden but one or more deep seated detachment levels must have worked thick skinned tectonics during the mio pliocene transpressional phase furthermore an orocline origin for the arcuate shape of the fold belt resulting from a progressive history of oblique right lateral shearing is suggested during the first deformative stage stage 1a late miocene the cover detached from the basement is deformed by a nw se trending linear fold belt whilst the basement is deformed by oblique right lateral shear then stage 1b the linear fold belt is progressively bent by right lateral dragging in correspondence with the deep seated shear zones during the second deformative stage stage 2 early piocene the cover deforms in connection with the basement the northern and the central sectors of umbria marche apennines undergo a prevailing shortening accomodated by nw se nnw sse dip slip thrusting the southern sector undergoes a prevailing right lateral shearing accommodated by nne ssw oblique thrusting

paleomagnetism of the umbrian marches orogenic belt abstract the eower cretaceous maiolica formation was investigated in a regional paleomagnetic study in order to clarify the role of the umbrian marches region in western mediterranean tectonics this area has been considered as a semi autonomous microplate by some authors and as an allochthonous overthrust block by others oroclinal bending has been inferred from earlier paleomagnetic results of the scaglia formation in spite of weak natural remanent magnetizations nrm stable characteristic remanent magnetization chrm directions were defined for 31 sites the site mean directions are well grouped d 306 i 37 95 5 but are not uniform fisher statistics are therefore not applicable the nonuniformity of directions is partially due to regional and local variations but is not related to the orientation of the fold axes as suggested by several authors it is possible that the umbrian marches region has suffered thrust decollement on the underlying triassic evaporites during the late tertiary orogeny but this was not accompanied by large scale translation or rotation relative to the assumed autochthonous parts of the adriatic promontory

the european african collision and its effects on the lithosphere asthenosphere system abstract in the european area lateral changes in the shear wave velocities of the lithosphere asthenosphere system are quite pronounced gravity data imply a positive density contrast 0 03 0 07 g cm 3 in the upper mantle related to almost aseismic lithospheric roots which seem to characterize many orogenic belts the analysis of a transect along the longitudinal axis of the alps seems to indicate that relevant lateral variations in density are also present in the lithospheric part of the mantle

tracing deep fluid source contribution to groundwater in an active seismic area central italy a combined geothermometric and isotopic δ13c perspective abstract an understanding of the origin and migration pathways of geofluids in an active seismic area is of paramount importance in terms of societal challenges such as mitigation of seismic hazards this study investigates the relationship between the stable isotope ratio 13c 12c of deep co2 and geothermometry in selected groundwater samples located close to extensional faults in central italy the temperature range is inferred from an equation based on the na li ratio and chemical geothermal modelling 113 130 c globally the calculated temperature range agrees with that resulting from deep boreholes in the northern apennines an alternative method is also included to better evaluate the difference in isotopic composition between the aqueous and gaseous 13c co2 at deep condition a review of previously published data shows that monitoring of the isotopic composition of the dissolved inorganic carbon dic in springs fed by meteoric origin located in seismically active areas must take into account mass and isotopic balance to correctly evaluate the component and the role of deep fluid during seismic events in particular the coupled and corrected isotope and geothermometrical monitoring of the springs could help to distinguish between deep gas or deep fluid contributions to shallow aquifers the results of this study indicate that faults play a crucial role in controlling the migration of crustal fluids in addition they reveal that possible evaluation of potential seismic precursors mandatorily requires a long period of monthly monitoring

propagation anomalies in northwestern italy by inversion of teleseismic residuals travel time residuals of teleseismic p waves were analysed in order to elucidate the crust upper mantle structure in northwestern italy and the western alpine arc using digital data obtained from both fixed seismograph networks operating in nw italy notably liguria piedmont and temporary arrays with the aid of cross correlation techniques reliable travel time residuals were calculated which were then inverted to obtain models of propagation anomalies the reliability of the inversion procedure was tested using synthetic data the model thus obtained appears to be stable and shows strong lateral heterogeneities at a litho asthenospheric level in particular it confirms the high velocity contrast caused by the ivrea body in the shallower layers and the presence of alpine roots reaching down to at least 200 km a statistical analysis performed on the propagation times of rays crossing the resulting four layered model reveals rms below 0 1 s

tomographic images of the upper mantle below central europe and the mediterranean results from delay time tomography of the european mediterranean upper mantle are discussed and where possible interpreted in terms of geodynamic processes slab like positive velocity anomalies of which the locations correlate well with deeper seismicity are found beneath spain the tyrrhenian basin and the aegean these structures are interpreted as images of subducted slabs large aseismic regions with positive velocity anomalies are found beneath the western mediterranean italy the alps dinarides the pannonian basin northern greece and the aegean these anomalies can also be linked to subducted lithosphere from the anomaly patterns it is deduced that subduction occurred below the western mediterranean and along both sides of the adriatic micro plate beneath the dinarides and northern greece the velocity structures suggest detachment of the slab from the surface

odp leg 107 in the tyrrhenian sea insights into passive margin and back arc basin evolution leg 107 of the ocean drilling program drilled a west northwest east southeast transect of seven sites across the tyrrhenian sea the youngest of the sub basins of the mediterranean sea sites 654 653 652 and 656 document the rifting and subsidence of the sardinia passive continental margin on the upper margin site 654 we cored a classic transgressive sequence subaerial conglomerates overlain by oyster bearing sands overlain by marine marl comparison between the recovered lithologies and seismic reflection profiles suggests that the synrift sediments on the upper margin are tortonian late miocene to messinian latest miocene in age whereas synrift sediments on the lower margin are messinian to pliocene in age during the messinian desiccation of the mediterranean sites 654 and 653 now on the upper sardinian margin apparently occupied a basinal setting where they received nannoplankton bearing clays interbedded with laminated gypsum sites 656 and 652 now on the lower sardinia margin were apparently higher standing during the desiccation event their messinian facies are subaerial and lacustrine respectively we infer from these lines of evidence that tilting and subsidence occurred more than a million years earlier on the upper margin than on the lower margin such diachroneity can be interpreted in terms of migration of the zone of maximum extension above a rolling back subduction zone or in terms of extension of continental crust by shear along a deep detachment fault sites 655 651 and 650 were drilled into two small basalt floored basins of the central and eastern tyrrhenian emplacement of basaltic crust in the central tyrrhenian vavilov basin apparently began more than a million years before emplacement of basaltic crust in the eastern tyrrhenian marsili basin this observation is compatible with previous suggestions that the tyrrhenian has grown southeastward in response to rollback of the down going slab that currently dips northwestward under the toe of italy at the easternmost site high vesicularity of the basalt and benthic foram assemblages in the oldest sediments imply that the basalt erupted in water shallower than 2 500 m it has apparently subsequently subsided to its present depth of 4 100 m below sea level nearly three times as fast as normal subsidence of crust formed at a mid ocean ridge

petrogenesis and tectonic setting of the roman volcanic province italy abstract the volcanism in the roman province of italy can be modelled by the partial melting of heterogeneously enriched mantle sources the heterogeneity was created by materials derived from a subducted slab which can still be traced geophysically beneath the central apennines new petrographical and chemical data are presented for the high k calc alkaline and the shoshonitic volcanics of the campania region primary magmas are present only locally the existence of spatial zonation in the volcanism of campania is documented for the first time the shoshonitic leucite basanitic and leucititic volcanics of the phlegraean fields procida ischia and the somma vesuvius areas are at similar degrees of evolution about two times richer in nb and ba than those of northwestern campania and the latium part of the roman province accordingly distinct north western and south eastern subprovinces can be defined the evaluation of enrichment factors that is the abundance ratio between the average contents of each element in the relatively primitive lavas of the low k and the high k suites shows that the mantle sources prior to k metasomatism were different in the two sub provinces of the roman province in the north western one they resembled the sources of ocean island tholeiites and moderately enriched mor basalts in the south east they were similar to those of ocean island alkaline lavas and enriched morb s modelling based on k p ce sr rb ba th sm eu gd y nb and 87 sr 86 sr was carried out it indicates that the range of mantle sources of the volcanics in northwestern campania and latium can be modelled by the addition of 3 to 20 of materials derived by partial melting of carbonaceous pelites to a sr enriched mantle wedge comparable to the honolulu mantle source least enriched in nb the production of sr enriched mantle wedge requires either the action of fluids produced by dehydration of subducted oceanic crust or a small amount of metasomatism caused by the presence of carbonatite melts the near absence of ti ta nb yb and the highly fractionated ree in the metasomatizing component requires the presence of residual garnet and accessory ti rich minerals during the partial melting of the subducted sediments the writers propose that the mantle wedge overlying the subducted slab was hybridized by melts produced by partial fusion of subducted material derived from the continental crust probably sediments this process played a dominant role in the generation of the mantle sources from which the high k calc alkaline shoshonitic leucite basanitic and leucititic magmas of the roman province were derived

crustal extension in the northern apennines the transition from compression to extension in the alpi apuane core complex an interpretation of northern apennine geology is presented which relates the temporal and spatial occurrence of both compressional and extensional deformation features in terms of the changing dynamic evolution within an accretionary wedge after a model proposed by platt 1986 followed by the initiation and development of continental rifting during cretaceous to eocene time an accretionary wedge formed as remnant tethyan oceanic crust subducted beneath the rotating corsica sardinia microplate microplate collision during the oligocene was characterized by the rapid imbrication of buoyant continental crust of the italian continental margin the record of which is preserved within the duplex structure geometry of the alpi apuane region the overthickened wedge geometry returned to a more stable configuration by developing extensional features during the miocene both listric normal faults at upper crustal levels and shear zones indicating evidence of distributed ductile extensional strain at mid crustal levels are recorded it is proposed that large scale regional extension with associated volcanism beginning in the messinian was represented by the intrusion of asthenospheric material from the subducted plate into the already attenuated accretionary complex further rifting perhaps aided by subduction and back arc processes in the southern apennines led to the formation of the tyrrhenian sea as an oceanic basin both the apennines and north american core complexes record evidence of crustal thickening followed by crustal thinning and finally of continental rifting this suggests that the similar histories of these regions with vastly different plate tectonic settings may both be explained by processes linked to the changing internal dynamics of accretionary wedges

the deep seismicity of the tyrrhenian sea the deep seismicity of the tyrrhenian sea is analysed using data from a new instrumental catalogue of the seismicity of the italian area we use algorithms for the determination of absolute and relative hypocentral locations and for the evaluation of the geometry and coherence of the state of stress within the subducting slab the structure of the benioff zone although simpler than previously indicated reveals anomalous traits both in the seismicity distribution and in the stress geometry confirming that standard subduction models cannot be applied in the tyrrhenian region the velocity anomaly and the location of few isolated events indicate that the subducted slabs extend to the north along the apenninic chain approximately to the latitude of the irpinia region in central italy 42 n

is there a correlation between lithosphere structure and the statistical properties of seismicity the elastic parameters and the thickness of the lithospheric part of the mantle the lid are correlated with the seismicity of italy and surrounding areas through the estimation of several statistical parameters in particular the intensity of the flow of seismic events deprived of aftershocks reveals concentrations associated with large gradients in the lithospheric thickness the average depth of crustal shocks tends to be very shallow in areas of thin and soft low shear wave velocities lid the positive influence probably reflecting the thermal state in the lithosphere is very large in connection with the thin and soft lid and where strong gradients in lid thickness are observed and is small in connection with a thick and hard lid high shear wave velocities

paleomagnetically determined rotations in the western sicilian fold and thrust belt new paleomagnetic data from the west sicilian fold and thrust belt indicate large scale clockwise rotations during tectonic transport for the platform and seamount paleogeographic units of the fold and thrust belt panormide and trapanese units there is a general consistency in the magnitude of rotation along strike suggesting the existence of large coherent structural units for the panormide platform clockwise rotations in the range of 90 to 140 relative to the underlying iblean parautochthon are recorded along 125 km of outcrop strike in the case of the trapanese unit clockwise rotations in the range of 47 to 70 relative to iblei are recorded along about 90 km of outcrop strike intervening basinal paleogeographic units imerese and sicanian units show clockwise rotations of similar magnitude although few reliable data are available from these units palinspastic reconstruction of the thrust belt incorporating the rotations and arguments for the present orientation of the margins of the paleogeographic units implies that the panormide platform and trapanese seamounts were originally elongated more or less north south relative to the present orientation of iblei the two units apparently coalesced to the south and were discontinuous to the north they and their intervening basins were part of a passive continental margin which occupied a large part of the area that was subsequently rifted to form the tyrrhenian sea

horizontal shear flow in the mantle beneath the tonga arc in the tonga subduction zone a systematic shear deformation in which deep material moves relatively to the south is superimposed on the mode of down dip shortening which is characteristic of the region we interpret this observation together with a tectonic reconstruction in terms of the interaction between the subducting lithospheric slab and a horizontal shear flow in the mantle