mesoscopic faults in the granite of isola del giglio tuscan archipelago abstract faults at the mesoscopic scale in the granite at isola del giglio are examined by considering the strike dip pitch of the striae and minerals on the fault planes the pattern of faulting is areally variable dykes and veins are often parallel to faults suggesting a genetic connection a major system of faults mainly reverse and steeply dipping strikes north northwest and is characterized by the frequent occurrence of crushed tourmaline these faults are often developed along pegmatite veinlets or dykes and were probably produced by a combination of hydraulic and shear fracturing in the final stage of cooling of the granite another prominent phase of faulting is testified to by ene striking fault planes strike slip to oblique slip devoid of tourmaline and mostly coated with chlorite p the prevalence of reverse and strike slip faults over normal faults contradicts the traditional views about dominantly extensional tectonics in this area during the pliocene and quaternary extensional deformation at isola del giglio ended with the granite intrusion crustal melting and extension ended at about 5 ma after which subvertical and strike slip movements became dominant

structural setting of the bay of naples italy seismic reflection data implications for campanian volcanism abstract this paper focuses on the recent tectonic evolution of the bay of naples with the aim of exploring the connection between local tectonics and volcanism we reprocessed the seismic reflection dataset acquired in the area in the late 1973 the new processing was highly successful in obtaining a decisive strong reduction of random noise removal of coherent noise and reduction of spatial aliasing classical interpretative schemes and complex attributes of seismic traces were used to reconstruct fault kinematics and reflector patterns the results show that the faults affecting the bay of naples exhibit prevailing ne structural strikes with the exception of the pozzuoli caldera where nw patterns are also common many faults are subvertical and show seismic evidence of volcanic activity along them a main alignment of conjugate ne sw faults named here as magnaghi sebeto line intersects several submarine volcanic banks and separates the bay into two sectors characterized by important geological geophysical and petrochemical differences the structural configuration of the bay may reflect the occurrence of either oblique extension or a transfer zone of the nw se fault system along which in the campanian lucanian apennine chain great vertical displacements occur

shear in the lower crust during extension not so pure and simple abstract as lower crustal reflectivity appears to be related to extension it is sensible to consider the role of the lower crust in the extension of the lithosphere and in particular the way the lower crust deforms the occurrence of transparent zones wrapped around by reflective bands can be interpreted as low strain regions enclosed within anastomosing shear zones suggesting that deformation in the lower crust is by the relative movements of low strain lozenges along acoustically reflective high strain zones although this deformation can easily accommodate bulk pure shear it can also develop during bulk simple shear a component of subhorizontal simple shear within the lower crust is necessary if deformation in the mantle is localised into shear zones with the geometry and distribution imaged on birps profiles the lower crust may be the critical link in the lithosphere transferring deformation between the relatively strong upper crust and upper mantle and being strongly sheared in the process the form of this shearing is a direct consequence of the way the entire lithosphere extends

the complex 3 d transition from continental crust to backarc magmatism and exhumed mantle in the central tyrrhenian basin geophysical data from the medoc experiment across the northern tyrrhenian backarc basin has mapped a failed rift during backarc extension of cratonic variscan lithosphere in contrast data across the central tyrrhenian have revealed the presence of magmatic accretion followed by mantle exhumation after continental breakup here we analyse the medoc transect e f which extends from sardinia to the campania margin at 40 5 n to define the distribution of geological domains in the transition from the complex central tyrrhenian to the extended continental crust of the northern tyrrhenian the crust and uppermost mantle structure along this 400 km long transect have been investigated based on wide angle seismic data gravity modelling and multichannel seismic reflection imaging the p wave tomographic model together with a p wave velocity derived density model and the multichannel seismic images reveal seven different domains along this transect in contrast to the simpler structure to the south and north the stretched continental crust under sardinia margin abuts the magmatic crust of cornaglia terrace where accretion likely occurred during backarc extension eastwards around secchi seamount a second segment of thinned continental crust 7 8 km is observed two short segments of magmatically modified continental crust are separated by the 5 km wide segment of the vavilov basin possibly made of exhumed mantle rocks the eastern segment of the 40 5 n transect e f is characterized by continental crust extending from mainland italy towards the campania margin ground truthing and prior geophysical information obtained north and south of transect e f was integrated in this study to map the spatial distribution of basement domains in the central tyrrhenian basin the northward transition of crustal domains depicts a complex 3 d structure represented by abrupt spatial changes of magmatic and non magmatic crustal domains these observations imply rapid variations of magmatic activity difficult to reconcile with current models of extension of continental lithosphere essentially 2 d over long distances

the coalification pattern in the northern apennines and its palaeogeothermic and tectonic significance the rocks of the northern apennines predominantly consist of non metamorphic terrigeneous deposits flysches and molasses some of which are preorogenic some synorogenic and others postorogenic with respect to the nappe tectonics miocene as plant fragments frequently occur in these sediments a study of coal rank based on reflectance measurements on vitrinites rm mean value of the random reflectance in non polarized light contributes to the clarification of the relation between the orogenic and the palaeogeothermal development the determination of the rm values of more than 180 samples from outcrops and three deep drillings revealed some important features within the pile of liguride and tuscanide nappes the coal rank increases from the uppermost nappe to the lower nappes until lowgrade metamorphism is reached in the lower tuscanides in the single nappes the rank decreases from the tyrrhenian coast internal zone towards the po plain external zone this regional trend is disturbed only locally by young post coalification tectonics in the uppermost liguride nappe m antola unit a pre oligocene i e pre apenninic thermal event was detected postorogenic heating is connected with the magmatic activity of late miocene to pleistocene age in tuscany except for these preorogenic and postorogenic thermal events the main coalification is generally younger than the emplacement of the nappes in the nappe pile during the apenninic orogeny in the miocene but it is older than the last thrust movements and the final tensional tectonics in the internal zones of the chain for these reasons the main regional thermal event has to be considered as synorogenic or more precisely as late synorogenic

influence of syn sedimentary faults on orogenic structures in a collisional belt insights from the inner zone of the northern apennines italy abstract this paper discusses the possible influence of syn sedimentary structures on the development of orogenic structures during positive tectonic inversion in the inner northern apennines italy examples from key areas located in southern tuscany provided original cartographic structural and kinematics data for late oligocene early miocene thrusts organized in duplex systems verging in the opposite direction of the foreland propagation back thrusts which affected the late triassic oligocene sedimentary succession of the tuscan domain previously affected by pre orogenic structures these latter consist of mesoscopic to cartographic scale jurassic syn sedimentary normal faults and extensional structures which gave rise to effective stratigraphic lateral variation and mechanical heterogeneities structural analysis of both syn sedimentary faults and back thrusts were therefore compared in order to discuss the possible role of the pre existing anisotropies in influencing the evolution of the back thrusts as a result it can be reasonably proposed that back thrusts trajectories and stacking pattern were controlled by relevant syn sedimentary normal faults these latter were reactivated in some cases if properly oriented such an issue adds new inputs for discussing the potential role of structural inheritance during tectonic inversions and helps to better understand the processes suitable for the development of back thrusts in the inner zones of orogenic belts as it is the case of the inner northern apennines

tectono sedimentary analysis of a complex extensional neogene basin formed on thrust faulted northern apennines hinterland radicofani basin italy abstract large nw se oriented neogene quaternary structural depressions up to about 200 km long and 25 km wide have developed on the western side hinterland of the northern apennines over thrust substrate the depressions are now for the most part laterally bounded by normal faults and are longitudinally separated into basins by transfer zones a debate exists in the literature as to whether these basins have developed as half graben under a predominantly extensional regime since late miocene or as thrust top basins under a predominantly compressional regime that has continued until the pleistocene the radicofani basin is one of the best preserved basins it developed mainly during the late miocene early pliocene in the southern half of the siena radicofani structural depression and is now bounded on the east by normal faults that transect a thrust anticline nose in the substrate to the north by a substrate high or transfer zone and to the south and west by quaternary igneous volcanic edifices the basin experienced variable differential tectonic and associated sedimentation along linking normal boundary faults along its eastern margin it shows the development of thick 600 m alluvial fans that developed in relay areas between boundary faults and transverse faults and transfer zones well exposed sections generally show upward transitions from conglomeratic alluvial fans to shoreface sandstone to offshore mudstones locally the transition is marked by deltas primarily characterised by thick gravelly sandy stacked cross sets the thicker sandy gravel to gravelly sand cross sets 5 8 m thick are interpreted as gilbert type deltas interstratified thinner 0 5 1 m thick generally openwork gravelly strata are part of delta topset assemblages and probably represent prograding fluvial bars tectonic movements provided the accommodation space for the total 2700 m thick basin fill sea level fluctuations that led to the repeated development of the cross sets may also have been influenced by climatic or eustatic changes possibly related to the effects of early antarctic glaciations some features of the radicofani basin can be found in both extensional and compressional basins however the position of the basin in the mountain chain and the development of alluvial fans fandeltas and associated deposits along the main boundary fault combined with structural evidence from seismic lines show that during the early pliocene this basin best conforms to existing models of half graben

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

considerations on the seismotectonics of the northern apennines abstract the northern apennines have been subdivided into homogeneous zones on the basis of recent structural evolution and crustal structure in which the earthquake distribution can find a coherent framework these zones whose physiography is in strict connection with their structure are the internal peri tyrrhenian belt the external or main belt the buried belt and the pede alpine homocline earthquake activity has a tendency to cluster along well defined bands particularly in the easternmost border of the peri tyrrhenian belt as well as along the zone between the external belt and the buried belt i e along the padanian margin of the northern apennines a minimum of seismic activity seems to be correlated with some zones of the external belt as well as with the late tertiary and quaternary magmatic province of tyrrhenian southern tuscany the fault plane solutions are coherent with the structural picture a tentative seismotectonic model of the northern apennines is discussed

residual oil as a tool in migration and filling history analysis of petroleum reservoirs ghazal field saudi arabia abstract stepwise extraction and molecular analysis of non recoverable oil from intact reservoir core plugs is used to provide constraints on the accumulation history of petroleum in the permo carboniferous unayzah reservoirs at the ghazal field saudi arabia when integrated with existing tools such as oil geochemistry gas geochemistry stable carbon isotopes fluid inclusions and thermal modeling the sequential extraction approach helped decode a previously unrecognized component of the hydrocarbon accumulation history in particular it indicates that the region received early petroleum charges that were less mature than currently produced light oil and gas condensates possibly from the prolific early silurian qusaiba shale source rock and other sources this has significant implications for prospecting for additional oil particularly in the north northwest of the ghazal region where paleo oil accumulations may have been displaced or spilled the lower portion of the unayzah reservoir unayzah c remained water wet during early filling of the upper reservoir unit unayzah a and appears to have been filled only by a late oil charge anomalous molecular and carbon isotopic behavior of residual oil extracts from the uppermost segment of the unayzah reservoir where the free oil first of the sequential extracts is less mature 0 95 rc and isotopically lighter 13c 31 15 than the adsorbed oil last sequential extract 1 05 rc 13c 29 65 suggests a late oil contribution or bitumen contamination from the overlying khuff formation

geometry of propagating continental rifts reconstruction of past plate configurations through palinspastic restoration of continental margins1 4 requires a detailed knowledge of the geometries of horizontal continental extension extension is often restricted to discrete linear zones termed rifts5 6 and rift models that invoke propagating vertical dykes and cracks7 10 are useful for assessing the relative significance and timing of uplift subsidence and extension in the tectonic evolution of rift basins however many models do not adequately account for the observed asymmetry of rifts i describe here the general three dimensional character of young and aborted continental rifts which can be used to derive a structural model for the propagation of rifts in continental lithosphere the rifts become asymmetric as a consequence of the role played by low angle normal faults in the overall rift geometry

new data and hypothesis on the development of the tyrrhenian basin abstract among those basins which developed during the neogene and quaternary at the rear of the perimenditerranean mountain chains the tyrrhenian basin is the most recently formed comparing the available geological and geophysical data the tyrrhenian domain and its neighbourhoods can be divided into more or less homogeneous sectors namely northern and southern tyrrhenian apenninic chain maghrebides chain apulian and iblean african foreland ionian foreland for each sector the different phenomena involved and the crustal characteristics are discussed the evolution of the domain has been explained by the application of a crustal stretching model developed for continental margins this approach predicts the formation of basinal areas as a result of the europe africa collisional movements within a plastic rigid deformation model taking into account the mass redistribution after collision the model explains both the distension developed within the collisional system and the penecontemporaneous development of compressive and distensive phases as a consequence of the intraplate stresses horizontal shearings affecting the whole lithosphere at different levels occur with delaminations asthenosphere uprising and gradual collapse in the upper crust e w trending and strike slip dextral faults played a primary role in the evolution of the tyrrhenian basin inducing the largest tearings at the end of the major transcurrent systems such an evolution is complicated by the migrating motion of the shear zone from n to s and by the penecontemporaneous stop in the extension from the northern towards the southern domains of outstanding importance is the shear zone which borders the southern tyrrhenian enabling the opening of the basin and allowing the development of the major group of en echelon sub basins with a nw se trend

crustal structure of northern latium central italy from receiver functions analysis new evidences of a post collisional back arc margin evolution abstract the crustal velocity structure in a region of central apennines of italy at the hinge between the highly stretched portion of the monte argentario promontory and the magmatic province of the tolfa domes complex northern latium is discussed in this study s wave velocities at depth have been constrained by the modeling of p wave receiver functions rf from both temporary and permanent broadband seismic stations the computer 3d vs models show a thin crust 19 25 km made of a shallow and thin sedimentary cover a very high velocity and anisotropic layer related to a metamorphic basement and a low vs anisotropic layer in the middle lower crust above a shallow moho discontinuity modeled at about 20 km depth the volcano tectonic evolution of this portion of tyrrhenian back arc margin has been strongly influenced by its peculiar crustal architecture the low vs layer acted as a shear zone in the middle lower crust during the tyrrhenian extension also helping the development of plio quaternary magmatism our findings potentially give new constraints on the evolution of the area and to the general comprehension of back arc development in collisional regions

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

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

crustal structures in the geothermal areas of southern tuscany italy insights from the crop 18 deep seismic reflection lines abstract two deep seismic reflection lines named crop 18a and 18b and roughly nnw sse oriented were acquired to investigate the crust between the larderello and the mt amiata geothermal areas both located in southern tuscany since the early middle miocene southern tuscany has been affected by extensional tectonics and since the pliocene by widespread magmatism presently extension is demonstrated by ne dipping normal faults and brittle shear zones which affect the crust down to the brittle ductile transition in the larderello area these shear zones are seismically evidenced by ne dipping weak reflections and by the loss of the k horizon reflectivity a regional mid crustal high amplitude reflector located at the top of the brittle ductile transition the crop 18a and 18b lines were reprocessed down to 10 s twt down to the crust mantle boundary their reflectivity results are closely related to the direction of the survey a clear decrease in reflectivity occurs when the survey plane intersects the crustal shear zones along strike nevertheless both lines display segments with low reflectivity and homogeneous acoustic impedance which indicate intrusive magmatic bodies at different crustal levels a wide partially crystallised granitoid may be sited at about 7 8 km depth underneath the larderello geothermal field in the lower part of the crust the crop 18a and 18b transects show group of bright reflections mainly related to the occurrence of pressurised fluids and or lithological differences the base of the crust is located at about 20 km depth

sedimentation in the northern apennines corsica tectonic knot northern tyrrhenian sea central mediterranean offshore drilling data from the elba pianosa ridge the northern tyrrhenian sea is located on the collisional zone between the alpine corsica and the northern apennines and is a key area for gaining a better understanding of the complex relationships between these two systems the knowledge of the wide offshore part of this zone located between corsica france and mainland italy is based primarily on the analysis of several seismic profiles tied to the outcropping geology and unpublished preliminary reports of few offshore wells the here presented study of two offshore wells provides a revision of the sedimentology biostratigraphy and petrography of the thick mainly siliciclastic tertiary successions about 3 600 m composing the elba pianosa ridge epr a structural morphological high separating the tuscan shelf to the east from the corsica basin to the west a comparison with similar deposits cropping out in the surrounding onshore areas northern apennines corsica tuscan archipelago piedmont tertiary basin provides additional constraints for refinement of the complex geodynamic and regional setting in which the epr evolved

a review on the driving mechanism of the tyrrhenian apennines system implications for the present seismotectonic setting in the central northern apennines abstract the formation of the tyrrhenian apennines system has been characterized by a complex distribution of major tectonic events such as opening of basins migration and distortion of orogenic belts retreat of trench zones stopping of consuming processes and starting of new subductions the various aspects of each event such as timing location dimension and deformation style impose important constraints on the genetic mechanism in this work we argue that the numerous constraints implied by all events together may be plausibly and coherently explained as effects of the convergence of the confining africa arabia and eurasia plates crucial evidence for discriminating among the various geodynamic hypotheses so far advanced is provided by the structural tectonic information recently provided by crop seismic sections in the study area the proposed evolutionary history is illustrated by several paleogeographic maps which provide a more detailed reconstruction than previous attempts particular attention is paid to describing the tectonic setting developed since the middle pleistocene in the apennines belt and its connection with seismic activity

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

middle upper pleistocene record of 100 ka depositional cycles on the southern tuscany continental margin tyrrhenian sea italy abstract five unconformity bounded depositional sequences have been seismically defined on the tyrrhenian margin offshore southern tuscany italy the set of sequences encompasses a 500 ka interval each sequence recording a 100 ka orbitally driven climate eustatic cycle similarly to most of quaternary continental margins sequences on the southern tuscany margin show an overall regressive motif reflecting shelf sediment progradation basically during the prolonged phases of sea level fall that characterise the middle upper pleistocene 100 ka cyclicity on seismic profiles however progradational units within each sequence display a variable clinoform geometry interpreted as a record of the alternation of highstand falling and lowstand intervals within 100 ka cycles the observed geometric variability is thus used as a key for separating systems tracts otherwise merging into a general progradational regressive sedimentary body composing the bulk of each sequence on a longer term the interplay between sea level changes modulated by 100 ka cycles and regional subsidence controls the stratigraphic architecture and the growth pattern of the continental margin this effect is documented by the overall aggradational retrogradational stacking pattern of sequences superimposed on shelf margin progradation and reflecting the renewal of accommodation space landward of the shelf margin and its exploitation at each cycle

tectonic control on the architecture of a miocene carbonate ramp in the central apennines italy insights from facies and backstripping analyses abstract analyses of facies associations and biotic assemblages integrated with backstripping analysis are presented to improve understanding of the development of a shallow water miocene carbonate ramp in the central apennines italy with special reference to the relationships between tectonic subsidence and the internal architecture of the ramp subsidence curves were calculated for six measured sections located in different sectors of the platform dating is derived from sr isotope analyses from previous studies and regional correlations corrections for eustasy and paleobathymetry were deduced from biota and facies analyses the subsidence curves show rates that vary both in space and time by analysing the vertical motions in different sectors of the ramp over a fixed time span burdigalian to tortonian it was possible to evaluate the control on platform architecture exerted by tectonically induced changes in sea floor bathymetry and highlight the effects of tectonic migration most analysed sites experienced a short period of tectonic uplift or stability followed by a period of slow subsidence this preceded increased subsidence which resulted in drowning of the shallow water carbonate platform the stability uplift is progressively younger towards the north eastern sectors that correspond to progressively more external zones of the foreland relative to the apenninic orogenic belt the subsequent drowning is related to the diachronous down flexure of the adriatic lithosphere due to its eastward retreating subduction under the apennines the small magnitude of the uplift suggests that the formation of a foreland bulge due to subduction related flexure of the adriatic plate was probably not the responsible mechanism hence this uplift is related to the development of proto thrusts or to the propagation of compressive stresses in the foreland these vertical motions influenced the geometry of the platform during the 17 5 16 ma stage during this period the platform was characterised by exceptional progradation of the bryomol dominated proximal outer ramp facies belt this rapid spreading may be induced by the combined effect of increased eutrophic conditions and a contemporaneous decrease in the sea floor bathymetry resulting from the tectonic uplift from the tortonian onwards when the platform became involved in the eastward migrating foredeep system the tectonic subsidence curve records a short period of fast tectonic subsidence rates followed by a period of slow subsidence or slight uplift during basin drowning and infilling respectively

late quaternary fluvial terraces of the romagna and marche apennines italy climatic lithologic and tectonic controls on terrace genesis in an active orogen abstract we synthesize a new fluvial terrace chronostratigraphy of the bidente and musone rivers cast within a broader european framework which forms the basis of a terrace genesis and river incision model for the northern apennines italy our model supported by terrace long profiles correlation to po foreland sediments 15 new radiocarbon dates and published numeric and relative stratigraphic ages highlights how drainage basin substrate drives concurrent formation of strath terraces in the bidente basin and fill terraces in the musone basin quaternary climate change paces the formative geomorphic processes through unsteady discharges of water and sediment in the weathering limited setting represented by the bidente basin siliciclastic detritus carves broad strath surfaces during glacial climates that are preserved as terraces as the river incises during the transition to an interglacial climate in contrast the transport limited and carbonate detritus dominated musone basin sees valleys deeply buried by aggradation during glacial climates followed by river incision during the transition to an interglacial climate incision of these rivers over the past 1 million years has been both unsteady and non uniform these and all po adriatic draining rivers are proximal to a base level defined by mean sea level and have little room for increasing their longitudinal profile concavities through incision particularly in their lower reaches despite periodic glacio eustatic drawdowns as a result the observed incision is best explained by rock uplift associated with active local fault or fold growth embedded in the actively thickening and uplifting apennine foreland

foraminiferal record and high resolution seismic stratigraphy of the late holocene succession of the submerged ombrone river delta northern tyrrhenian sea italy abstract micropalaeontological data integrated with radiocarbon dates and seismic profiles allow for a reconstruction of the late holocene evolution of the ombrone river delta area during the last 6 0 ka seven cores collected in three distinct sectors of the submerged ombrone delta were studied the delta front cores nk7 nk8 bok5 and bok10 and prodelta slope core nk4 which are primarily affected by river input and the middle shelf cores nk2 and nk3 which is progressively less influenced by riverine impact seismostratigraphic interpretation indicated that the majority of the cores intercepted the most recent deposits of the late quaternary depositional sequence unit a whose base is dated at 2 8 100 ka bp the deepest and shallowest cores reveal a record of the ancient and the most recent evolution of the succession respectively although the most complete palaeoenvironmental evidence comes from the middle shelf core nk2 and prodelta slope core nk4 the oldest sedimentary phase is indicated by benthic foraminiferal assemblages and seismic profiles of the middle shelf core and correlates with the late transgressive systems tract unit b the following phase is attributed to the highstand systems tract unit a and spans the last 3 0 ka hierarchical cluster analysis hca q mode of the benthic foraminifera in the cores resulted in 10 foraminiferal assemblages that correspond to four distinct environments with various degrees of river influence

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

enhanced co2 mineral sequestration by cyclic hydraulic fracturing and si rich fluid infiltration into serpentinites at malentrata tuscany italy abstract the magnesite deposits of malentrata tuscany italy were derived from serpentinite silicification carbonation of the ligurian ophiolite and represent a natural analogue of in situ co 2 mineral sequestration carbonation of magnesium silicate minerals e g serpentine olivine at temperatures below 200 c is an exothermal process involving incorporation of carbon dioxide into stable carbonates e g magnesite dolomite serpentinites at malentrata were transformed to a brownish friable rock characterized by the occurrence of opal chromian montmorillonite fe rich magnesite and minor iron sulfides and oxides widespread lenses of cohesive rocks occur within the altered serpentines resulting from the complete silicification of the protolith the pervasive alteration of serpentinite was accompanied by the formation of a network of magnesite and dolomite veinlets and large magnesite dolomite veins along major structures field observations petrography and mineral chemistry define the following crystallization sequence in the major veins i early microgranular fe poor magnesite ii comb textured fe rich magnesite and dolomite cementing the early brecciated magnesite vein infill and iii late quartz chalcedony and rare opal in the cavities the mineral assemblage observed both in veins and in host rock is indicative of low temperature hydrothermal alteration driven by si and co 2 rich fluids under relatively low ph conditions pervasive and cyclic hydraulic fracturing maintained a high structural permeability during the whole hydrothermal event creating conduits for the input and output fluids the concomitant presence of co 2 and silica in the fluid enhanced the congruent dissolution of serpentine and hampered immediate carbonate deposition the mg bearing solutions were focused out of the reactor zone and promoted massive carbonate veining along the main structural discontinuities this two steps reaction dissolution of serpentinite followed by carbonate precipitation outside the reacting volume seems to be very efficient and provide new insights on in situ and ex situ induced mineral carbonation and its industrial applications

age and temperature constraints on metamorphism and exhumation of the syn orogenic metamorphic complexes of northern apennines italy abstract the apennine range is a young convergent orogen that formed over a retreating subduction zone syn orogenic metamorphic rocks are exposed in the mid tuscan ridge tuscan coast and tuscan archipelago and provide information about processes of continental subduction and exhumation associated with accretion and retreat apatite and zircon fission track analyses were applied to some of these syn orogenic metamorphic rocks the new low temperature thermochronological data helped to constrain the timing of the metamorphic peak and the age and modality of exhumation of these rocks that were structurally buried at 20 to 40 km depth during the main tectonogenic phase of the northern appenine belt in the giglio and elba islands and in the monti dell uccellina along the coast minimum ages of partially reset zircon samples yielded a first time constraint on the late oligocene age of the metamorphic peak the ca 27 ma obtained at the monti dell uccellina is coeval to that found in the alpi apuane located at the northern termination of the mid tuscan ridge the data from the tuscan archipelago point to a slightly older age in the monti pisani south of the alpi apuane and in the argentario promontary along the coast south of the monti dell uccellina completely reset zircon samples but composed by different populations were behaving as multiple thermochronometers and confirm the already proposed isothermal nature of the exhumation occurred after the metamorphic peak zircon p1 peak indicated that at 13 10 ma rocks were already at shallow crustal levels

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

magnetic interpretation related to geo magnetic provinces the italian case history abstract a comparison of the results obtained from the geophysical interpretation with the available information regarding the italian geological situation permitted us to establish our so called geo magnetic provinces the relationship between the magnetic characteristics and the tectonic evolution permitted the identification of each of the four following provinces that exist inside the global tectonic confines 1 1 the sardo corso block which represents the eastern boundary of stable europe this province is characterized by medium wavelength low amplitude anomalies that originate in an outcropping basement hercynian granites s l 2 2 the orogenic belt which constitutes the double alps apennines system from a magnetic standpoint this system is characterized by short wavelength low amplitude anomalies that are due to a paleozoic outcropping and or buried acid crystalline basement these anomalies are found to overlie long wavelength medium amplitude regional anomalies that are related to a deep apenninic basement central northern apennines 3 3 the foreland area which occurs from sicily hyblean plateau and apulia northwards to ancona and the po plain this area is characterized by a crystalline basement which is typically differentiated from the standpoint of basicity 4 4 the rifting zone which is represented by the part of the tyrrhenian sea lying south of the 41st parallel discontinuity the ionian abyssal plain and the pantelleria and linosa troughs in the sicily channel the main characteristic of this province is its extreme basicity differentiation in the crystalline basement which is induced by the geochemical processes connected with the deep geodynamic events these phenomena do not permit the correlation of the semioceanic basement of the rifting zone with the continental basement by means of interactive modeling a structural tectonic picture of the basement of the various italian geo magnetic provinces has been obtained the main result was found to be that the orogenic belt basement is undergoing intense tectonic compression and overlies the structural highs of the foreland area which mainly show tensive events

extension uplift of rocks and cooling ages in thinned crustal provinces the larderello geothermal area inner northern apennines italy in extensional tectonic settings vertical movements of the earth s surface are largely controlled by rates of strain extensional strain rates within the larderello geothermal area located in inner parts of the northern apennines have been evaluated together with uplift rates and 40 ar 39 ar cooling ages results indicate that extensional strain rates have been relatively low 5 8 10 17 s 1 since the middle pliocene differential uplift rates are estimated to have been high c 0 2 mm year strain and uplift rates within the larderello region are consistent with the regional tectonic framework the low strain rate rapid uplifting and high heat flow within southern tuscany can be explained by an eastward dipping lithospheric shear maintained since at least middle pliocene times

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

plio quaternary vertical motion of the northern apennines insights from dynamic modeling we test the effects of different geodynamic mechanisms on the pliocene to present day dynamics and in particular on the vertical motions of the northern apennines system by means of two dimensional finite element models we show that the pliocene features of the northern apennines exhumation of deep rocks in western italy and fast subsidence rates in the adriatic foredeep can be adequately reproduced by a model slab characterized by the passive sinking of a negatively buoyant adriatic slab and by the upwelling of buoyant asthenosphere beneath western italy model slab is however not able to account for the quaternary and present day pattern of vertical motion of eastern italy and of the adriatic basin a deep configuration of the system characterized by a detached slab model detach may explain the vertical motions of these areas constrained by uplift of the eastern portions of the apenninic chain by an eastward shift of the foredeep depocenter and by lower subsidence rates in the adriatic basin the tectonic and stratigraphic data showing major differences between the tertiary and the quaternary evolution of the northern apennines are discussed

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

bowl shaped basin related to low angle detachment during continental extension the case of the controversial neogene siena basin central italy northern apennines abstract this paper deals with the tectonic evolution of a bowl shaped neogene basin siena basin located in the inner northern apennines and developed during an articulated tectonic evolution this basin was controversially interpreted by different authors as graben half graben or thrust top basin structural and stratigraphic data from the basin substratum and filling sediments integrated with the interpretation of reflection seismic profiles and borehole logs highlight that the siena basin consists of a tectonic depression with a complex internal architecture such a basin developed on a multilayered substratum deeply affected by extensional tectonics since the middle miocene extensional detachments produced a widespread thinning of the basin substratum and superimposed on contractional structures developed during the northern apennines collisional events extensional detachments accommodated within weak horizons and gave rise to the lateral segmentation of most competent stratigraphic horizons sediments filling the siena basin mainly deposited on the ligurian units the topmost tectonic units forming the tectonic pile in the gap between two laterally segmented geological bodies made up of the triassic siliciclastic succession of the verrucano group such a lateral segmentation produced a synformal structural depression not delimited by faults filled by late serravallian late messinian marine to continental sediments which deposited during the extensional faulting from the latest early pliocene to the middle pliocene the architecture of the basin was modified by an high angle normal fault system which affected the eastern side of the basin and produced new accommodation space for marine sediments in sum the siena basin consists of a sin tectonic basin developed on the hanging wall of staircase extensional detachments later affected by high angle normal to oblique faults the latter faults defined a half graben during the latest evolution of the basin the tectonic evolution of the siena basin made it possible to point out some differences with respect to the types of bowl shaped basins related to extensional detachments and named as supradetachment basins

evidence for shear zones in the lower crust offshore britain lower crustal reflections seen on british institutions reflection profiling syndicate birps deep seismic reflection data recorded offshore the united kingdom are commonly short convex up and crosscutting consequently the lower crust should not be described as layered as much of the reflecting structure is not fully resolved and may be quite complex moreover the lower crustal reflective zone lcrz is not a uniformly reflective layer but contains reflective bands that wrap around nonreflective transparent zones because transparent zones probably correspond to a lack of a reflecting fabric understanding why these features are unreflective may help constrain the cause of the reflectivity of the lower crust although transparent zones may have a variety of explanations e g large shear pods or frozen magma bodies the geometry of reflective bands and transparent zones is perhaps best explained by the geometry of shear zones and low strain lozenges predicted both by combining theoretical lithospheric strength profiles with slip line field theory and by drawing analogies with structures developed in highly tectonised high grade metamorphic terrains this interpretation implies that lower crustal reflections may be from shear zones and also has implications for the way the lower crust deforms in particular extension may be accommodated by the relative movement of low strain lozenges along intervening zones of simple shear the lower crust may be stretched during extension but it must also transfer deformation between the upper crust and the mantle the observation on birps data of mantle reflections interpreted as mantle shear zones implies that deformation in the mantle is localised however the manue reflections are never colinear with faults in the upper crust requiring at least locally a component of sub horizontal bulk strain within the lower crust which may greatly increase the amount of shearing therein and hence perhaps may increase the reflectivity of the lcrz

structural constraints on the tertiary plate tectonic evolution of italy abstract eight cross sections six of which were balanced and restored using the principles of thin skinned tectonics demonstrate the reinterpretation of the apennine and sicilian mountains as a detached fold and thrust belt the thin skinned interpretation constrains the extent of the restored continental margins and the amount percentage direction and timing of tectonic shortening allowing the development of a plate tectonic model late cretaceous and paleogene subduction to the north beneath the corsica sardinia calabria csc microplate causes rifting from se france and the development of oceanic crust between the two in the oligo miocene the late oligocene collision of adria and northernmost csc pins the northern edge of the csc plate causing its counter clockwise rotation and its mid miocene suturing between italy and sicily the n s convergence of africa and europe with counter clockwise rotation of italy causes shortening in the nne ssw direction in italy and sicily from 20 10 ma the n s compression extrudes calabria to the se causing mio pliocene compression in southern italy and eastern sicily at the same time as extension and alkaline volcanism in central italy

mid to late permian microfloristic evidence in the metamorphic successions of the northern apennines insights for age constraining and palaeogeographical correlations recent studies on the stratigraphy of paleozoic successions belonging to key sectors of the inner northern apennines provide data that can be used to propose new hypotheses about the palaeogeography of the western mediterranean domain during post hercynian times we report here the first evidence of mid to late permian guadalupian lopingian palynomorphs in the chronostratigraphically highly debated metamorphic units of the northern apennines the rio marina formation the mt calamita formation and the le cetine formation and consider the stratigraphic implications for the tuscan basement to which the study rocks belong and their palaeogeographical attribution considering their gondwana affinity these results agree with the interpretation that the alpine tethyan sedimentary cycle was already active during the mid to late permian thematic collection this article is part of the apennines and tyrrhenian system collection available at https www lyellcollection org cc the apennines tyrrhenian system

tectonic control on laccolith emplacement in the northern apennines fold thrust belt the gavorrano intrusion southern tuscany italy

carbonate deposition in restricted basins a pliocene case study from the central mediterranean northwestern apennines italy abstract carbonate depositional models are often informed by the study of platforms of good lateral continuity and sizable thickness because of their significance in petroleum geology however spatially restricted and more ephemeral carbonate accumulations can be an important but frequently overlooked component of otherwise siliciclastic dominated or mixed carbonate siliciclastic systems pliocene successions of tuscany and the tyrrhenian shelf northern apennines italy record a regional pulse of nontropical carbonate deposition across several restricted basins that has not yet been precisely constrained in its genesis and correlation this study investigates the stratigraphic expression of these carbonates to extract general aspects applicable to carbonate sedimentation across tectonically structured and physiographically complex shelves analyses of the extension composition facies and sequence stratigraphic architecture of the studied piacenzian carbonate units are complemented by new biostratigraphic and magnetostratigraphic data which document the slightly diachronous development of the carbonates within mediterranean planktonic foraminifera subzones mpl4b and mpl5a and magnetic polarity chron c2an the carbonate units are part of a regionally defined tectonically controlled sequence and represent the first transgressive unit overlying the basal sequence boundary but are also found in the regressive portion of the sequence collectively the units document the establishment of a shallow marine carbonate factory dominated by calcareous red algae the larger benthic foraminifer amphistegina and heterozoan skeletal components along the margins of a complex archipelago like coastal domain a review of the studied successions and other examples from the literature indicates that carbonate accumulations in settings with varied coastal physiography and active partitioning of depocenters are generally characterized by a spatial discontinuity b an overall skeletal association consistent across separate basins but with local variability in dominant skeletal components c preferential accumulation along basin margins or over isolated structural highs not in direct proximity to a hinterland with major drainage systems d predominance of low to moderate energy facies e preferential onset of deposition during transgression with possible development of mixed carbonate siliciclastic facies and f differing internal stratigraphic architecture tied to the specific subsidence and uplift history of coeval individual basins these observations built upon the study of mid piacenzian carbonate units from the central mediterranean contribute to the refinement of carbonate facies models and their application in the fields of sequence stratigraphy and basin analysis

cenozoic and mesozoic structure of the eastern basin and range province utah from cocorp seismic reflection data cocorp seismic reflection data collected from the eastern basin and range in west central utah provide information on cenozoic extensional tectonics mesozoic thrusting and their interrelationships those data show a series of remarkably continuous low angle reflectors that extend more than 120 km perpendicular to strike and can be traced as deep as 15 20 km over that distance none of these events are significantly cut by any high angle normal faults a major detachment beneath the sevier desert can be traced from a surface zone of normal faulting to a depth of 12 15 km with a regional apparent westward dip of 12 tentative correlation of upper and lower plate events suggests 30 60 km of extensional displacement on this detachment whether this structure is a reactivated mesozoic thrust is uncertain west steepening splays off the end of the detachment reach depths of 20 km and may represent a major mesozoic ramp or zones of distributed ductile shearing during extension some events are interpreted to be mesozoic thrusts of which at least one beneath the house range has been reactivated during the cenozoic the snake range decollement dips gently east and has a sense of cenozoic displacement opposite to that of other cenozoic detachments farther east deep events are most numerous beneath the east side of the sevier desert where they occur to depths of 30 km at the top of or perhaps partly within the anomalously low velocity upper mantle

structural evolution of the whipple and south mountains shear zones southwestern united states the whipple and south mountains of the southwestern united states have undergone a strikingly similar sequence of deformations in both ranges gently dipping mylonitic fabrics have been overprinted by successively more brittle structures associated with a low angle detachment fault kinematic indicators reveal that the mylonitic rocks brittle structures and detachment faults are kinematically coordinated and were all formed by top to the northeast shear the structural evolution of both areas can be explained in terms of major shallow dipping shear zones that accommodated tertiary crustal extension we suggest that detachment faults and associated zones of brecciation cataclasis and seismic slip were originally continuous downdip along the low angle shear zones into mylonitic gneisses formed below or near the ductile brittle transition as the mylonites were drawn out from beneath the brittlely extending upper plate they were progressively uplifted above the ductile brittle transition and were overprinted by successively more brittle structures

a new active tectonic model for the construction of the northern apennines mountain front near bologna italy 1 we integrate existing and new geologic data retreating trench extension and accretion tectonics retreat project particularly on the origin growth and activity of the mountain front at bologna italy into a new model that explains apennine orogenesis in the context of a slab rollback upper plate retreat process the bologna mountain front is an actively growing structure driving rock uplift 1 mm year cored by a midcrustal flat ramp structure that accommodates ongoing shortening driven by adria subduction at a rate of 2 5 mm year the data we use are assembled from river terraces and associated pleistocene growth strata geodesy including releveling surveys reinterpretation of published reflection lines and a new high resolution reflection line these data constrain a simple trishear model that inverts for blind thrust ramp depth dip and slip apennine extension is recognized both in the foreland as high angle normal faults and modest stretching in the carapace of the growing mountain front and in the hinterland with larger normal faults that accomplish some crustal thinning as the upper plate retreats this coevolution of extension and shortening shares some notable characteristics with other basement involved collisional orogens including the early tertiary laramide orogeny in the american west and the oligocene to miocene evolution of the alps we propose a possible relationship between underplating and the development of the po as a sag basin as a quaternary phenomenon that may also apply to past periods of apennine deformation tortonian continued shortening on the structure beneath the bologna mountain front represents by far the most important and underappreciated seismogenic source in the front of the northern apennines

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

age constraints on felsic intrusions metamorphism and gold mineralisation in the palaeoproterozoic rio itapicuru greenstone belt ne bahia state brazil u pb sensitive high resolution ion microprobe mass spectrometer shrimp ages of zircon monazite and xenotime crystals from felsic intrusive rocks from the rio itapicuru greenstone belt show two development stages between 2 152 and 2 130 ma and between 2 130 and 2 080 ma the older intrusions yielded ages of 2 152 6 ma in monazite crystals and 2 155 9 ma in zircon crystals derived from the trilhado granodiorite and ages of 2 130 7 ma and 2 128 8 ma in zircon crystals derived from the teofil ndia tonalite the emplacement age of the syntectonic ambrosio dome as indicated by a 2 080 2 ma xenotime age for a granite dyke probably marks the end of the felsic magmatism this age shows good agreement with the ar ar plateau age of 2 080 5 ma obtained in hornblendes from an amphibolite and with a u pb shrimp age of 2 076 10 ma in detrital zircon crystals from a quartzite interpreted as the age of the peak of the metamorphism the predominance of inherited zircons in the syntectonic ambrosio dome suggests that the basement of the supracrustal rocks was composed of archaean continental crust with components of 2 937 16 3 111 13 and 3 162 13 ma ar ar plateau ages of 2 050 4 ma and 2 054 2 ma on hydrothermal muscovite samples from the fazenda brasileiro gold deposit are interpreted as minimum ages for gold mineralisation and close to the true age of gold deposition the ar ar data indicate that the mineralisation must have occurred less than 30 million years after the peak of the metamorphism or episodically between 2 080 ma and 2 050 ma during uplift and exhumation of the orogen

application of revised ray tracing migration to imagine lateral variations of seismic fabric corresponding to different tectonic styles in the northern apennines abstract migration of zero offset seismic sections of deep crust can be done with methods based on ray tracing we modify the classical ray tracing migration method rtm introducing a consistency check to control whether back propagated rays satisfy the condition of strict normal incidence at the migrated reflector a synthetic test shows the effectiveness of the method in particular the control of normal incidence allows elimination of physically inconsistent reflectors from the migrated section then rtm is applied to a crustal seismic profile acquired in central italy using a velocity model obtained from wide angle data that reproduces the gross structures of the apenninic crust the lateral variation of the seismic fabric shown from the migrated section reveals the presence of coexisting extensional and compressional tectonic regimes kinematic diffraction modelling gives additional information about both the distribution of seismic velocities and major active geodynamic processes in the upper lithosphere the migrated section supports the subdivision of northern apennines in two tectonic regions a stretched upper plate tuscany and northern thyrrenian supported by a rise of the asthenosphere and a downwarped lower plate adria subducted below the mountain belt

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

active deformation and volcanism offshore campi flegrei italy new data from high resolution seismic reflection profiles abstract the interpretation of high resolution seismic reflection profiles permitted the identification of many geologic features in the inner shelf of pozzuoli bay this area corresponds to the offshore of campi flegrei a classically active volcanic area that experienced earthquakes and meter scale vertical ground uplift before the 1538 monte nuovo eruption and in the period from 1970 to 1985 the detected undersea features include two small debris flows that are located in a submarine valley in the western part of pozzuoli bay they may be the result of a pyroclastic flow and a pyroclastic surge that entered the sea the younger debris flow in the uppermost marine deposits of pozzuoli bay formed during the 1538 monte nuovo eruption and the older debris flow during the 3 8 ka old averno eruption other features detected by our survey are an undersea 8 m high and 1 km wide cryptodome corresponding to a near surface intrusion located off pozzuoli that warped post 4 ka marine deposits the interpretation of the cryptodome is based on seismic facies analysis deformation geometry and correspondence to a magnetic high it is suggested that this undersea dome formed during the uplift phases associated with the 1538 monte nuovo eruption and the two more recent bradyseismic crises of 1970 1972 and 1982 1984 surface breaking faults with maximum vertical offset of 1 m were recognized in very shallow waters near the coast of pozzuoli it is suggested that some of these faults were active during the 1982 1984 bradyseismic earthquake sequence

modes of stepwise eastward migration of the northern tyrrhenian sea back arc extension evidences from the northern latium offshore italy the structural architecture of a portion of the eastern side of the tyrrhenian sea back arc basin has been defined reinterpreting a public data set made up by seismic reflection profiles a detailed reconstruction of the extensional front migration trough time across the area has been achieved migration has been defined by identifying the generation of unconformities in the graben like basins developed in the area as due to the activation and deactivation of normal faults such phenomena are part of a tectonic process that also involved blocks rotation crustal thinning and stretching syn rift extension affected the area since the early to middle miocene our estimate principally interesting the north westernmost sectors during late miocene and throughout the plio quaternary the extensional front moved stepwise toward the southeastern and eastern sectors widespread postrift conditions established over the whole area since the late pliocene to early pleistocene since the quaternary the locus of active extension further migrated toward the present onshore area where a pronounced volcanic phase developed in this evolutionary framework the rates of observed migration could be correlated with the acceleration of calabrian slab rollback since pliocene furthermore direct evidences of magmatism were not recognized in the offshore although the observed crustal thinning the absence of volcanic bodies in the study area could be related to normal faults which were unable to sufficiently extend the crust in association with lower crust and mantle processes unable to produce melts

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

pliocene and pleistocene exhumation and uplift of two key areas of the northern apennines application of different thermochronological methods to two areas of pronounced relief apuane alps and mt falterona of the northern apennines chain documents an average exhumation rate of about 0 7m m yr this result suggests that the general exhumation of the chain is driven mainly by erosion nevertheless the long term exhumation trend seems to be perturbed by shortterm events at higher exhumation rates the time of increased exhumation rates coincides with onset of intramontane sedimentation documenting a contribution of tectonics local normal faulting to the surface uplift the data indicate an eastward shifting of the onset of topographic relief early pliocene in the apuane alps and early pleistocene in the mt falterona area r 2002 elsevier science ltd and inqua all rights reserved

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

upper mantle properties of the tuscan tyrrhenian area a framework for its recent tectonic evolution abstract within the alpine mediterranean deformational system several interesting features in the physical properties of the upper mantle have been recognized through the regional analysis of surface wave dispersion a large upper mantle anomaly uma here called the tuscan uma has been identified in the area northeast of corsica which includes part of the northern tyrrhenian sea and part of the north central apennines this anomalous upper mantle area together with the upper mantle characteristics of the tyrrhenian sea located further to the south provides a natural framework for comprehensive interpretation of the large data set of geological and geophysical observations such as land and marine geology volcanism gravity magnetic data seismic data and seismology deep temperatures and surface heat flow

constraints on vertical crustal motion for long baselines in the central mediterranean region using continuous gps abstract gps determination of vertical crustal velocity relative to a globally defined reference frame is limited by the accuracy of the reference frame origin and scale however the precision of relative vertical rates at regional distance scales remains largely unexplored we investigated the precision of regional scale vertical velocity estimates using data from seven continuously operating gps stations located in the central mediterranean the stations form a network of aperture 500 km and each has been in operation for at least 5 yr we used published constraints on recent crustal uplift inferred from late quaternary shoreline data to aid in the definition of a local vertical reference frame for gps rates to facilitate an assessment of gps vertical precision we explored different methods of defining the local reference frame the simplest method involves the estimation of a single scalar translation parameter adjusting the reference frame by this simple method yields agreement between cgps and holocene shoreline data sets at the level of 0 2 to 0 4 mm yr relative rates determined using cgps are also consistent with tide gauge records and sea level determined by satellite altimetry at the level of about 0 2 mm yr these results suggest that regional scale relative velocity precision well below the mm yr level is now possible using continuous gps

low angle normal fault lanf zone architecture and permeability features in bedded carbonate from inner northern apennines rapolano terme central italy abstract fault zones have the capacity to be hydraulic conduits within upper crustal levels allowing migration of large volume of fluids through shallow and deeper geological environments low angle normal faults lanfs crosscutting carbonate rocks produce damaged volumes that may have a relevant role in channelling or hosting geothermal fluids therefore deserving of investigation to better predict mining targets deformation along lanfs zones dissecting carbonate successions produces permeable volumes presently exploited in the larderello and monte amiata geothermal areas italy in this paper the architectural and permeability features of an exhumed lanf zone exposed in the northern apennines rapolano terme central italy affecting cretaceous bedded limestone are presented such a fault was not affected by circulation of geothermal fluids but its features could reveal much on the potential impact on fluids migration in the active geothermal areas therefore resulting an intriguing analogue the study lanf zone consists of faults which enucleated at depth 4 km during its earlier stage of evolution dissolution seams often arranged in s c fabric characterised the whole damage zone dissolution seams developed under very low grade metamorphism t 100 150 c as indicated by illite crystallinty analyses fault zone architecture and permeability features changed during the fault growth and exhumation permeability heterogeneity and anisotropy characterised the lanf zone during its development if geofluids circulated within the fault zone it could be an effective barrier during its earlier evolution being accompanied by dissolution seams on the contrary it could play as combined barriers conduits during its later evolution progressively at shallower levels being characterised by intersecting fault planes which define pipe like conduits parallel to the direction of the tectonic transport such a configuration could have the capacity to impact on fluids migration for long paths across the upper crustal levels this adds significant information for predicting deeper geothermal circuits and the location of potential exploitable reservoirs in active tectonic environments

late evolution of the inner northern apennines from the structure of the monti del chianti monte cetona ridge tuscany italy abstract the neogene and quaternary tectonic evolution of the inner northern apennines i e southern tuscany and northern tyrrhenian sea as well as its crustal features i e low crustal thickness neogene quaternary magmatism widespread geothermal anomalies lateral segmentation of the stacked tectonic units extensive deep sedimentary basins are framed in different geodynamic scenarios compressional extensional or both pulsing consequently the basin and range structure that characterises the northern tyrrhenian sea and southern tuscany is considered as a consequence of i out of sequence thrusts and related thrust top basins ii polyphased normal faulting that formed horst and graben structures or iii a combination of both this paper provides a new dataset from a sector of the eastern inner northern apennines i e monti del chianti monte cetona ridge contributing to this scientific debate new fieldwork and structural analysis carried out in selected areas along the ridge allowed to define the chronology of the main tectonic events on the basis of their influence on the marine and continental sedimentation the dataset supports for early miocene serravallian in sequence and out of sequence thrusting thrusting produced complex staking patterns of tuscan and ligurian units extensional detachments developed since later middle miocene and controlled the neogene sedimentation in bowl shaped structural depressions later dissected by normal faults enhancing the accommodation space for pliocene marine deposits in broad nnw trending basins siena radicofani and valdichiana basins in this perspective no data supports for active continuous or pulsing compressional tectonics after late serravalian as a result in the whole inland inner northern apennines the extensional tectonics was continuously active at least since middle miocene and controlled the basins development magmatism and structure of the crust and lithosphere

the miocene of pianosa island key to understanding the opening of the northern tyrrhenian back arc basin central mediterranean the only place where neogene quaternary rocks crop out for the entire tuscan archipelago in the northern tyrrhenian sea is the island of pianosa in particular the miocene deposits record the depositional and tectonic evolution of the northern tyrrhenian region during this time period these deposits are subdivided into two successions separated by a low angle unconformity the older middle burdigalian succession represents a calciturbidite shallow marine system whereas the younger late tortonian early messinian succession comprises a continental alluvial system that evolves upwards into a lagoonal marginal marine environment here we present sedimentological palaeontological and petrographical data that support a new stratigraphic and palaeogeographical framework for reconstructing the opening of the northern tyrrhenian back arc basin the early miocene succession records a pre rift marine depositional phase followed by a late burdigalian langhian erosional phase this was followed by a period of synrift continental marginal deposition as recorded by the late miocene succession terminated by an important phase of uplift probably induced by the start of magmatic activity in the tuscan archipelago area

reconstruction of rocks petrophysical properties as input data for reservoir modeling the worldwide increasing energy demand triggered studies focused on defining the underground energy potential even in areas previously discharged or neglected nowadays geological gas storage co2 and or ch4 and geothermal energy are considered strategic for low carbon energy development a widespread and safe application of these technologies needs an accurate characterization of the underground in terms of geology hydrogeology geochemistry and geomechanics however during pre feasibility study stage the limited number of available direct measurements of reservoirs and the high costs of reopening closed deep wells must be taken into account the aim of this work is try to overcome these limits proposing a new methodology to reconstruct vertical profiles from surface to reservoir base of i thermal capacity ii thermal conductivity iii porosity and iv permeability through integration of well log information petrographic observations on inland outcropping samples and flow and heat transport modelling as case study to test our procedure we selected a deep structure located in the medium tyrrhenian sea italy obtained results are consistent with measured data confirming the validity of the proposed model notwithstanding intrinsic limitations due to manual calibration of the model with measured data this methodology represents a useful tool for reservoir and geochemical modellers that need to define petrophysical input data for underground modelling before the well reopening this article is protected by copyright all rights reserved

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

dynamics of orogenic wedges and the uplift of high pressure metamorphic rocks subduction accretion complexes can be approximated as wedge shaped continua with a rigid buttress behind and a subducting litho spheric slab beneath thick wedges undergoing prograde metamorphism have a negligible long term yield strength and are likely to exhibit a complex nonlinear viscous rheology such a wedge will tend to deform internally until it reaches a stable configuration in which the gravitational forces generated by the wedge geometry balance the traction exerted on its underside by the subducting slab accretion of material at the wedge front will lengthen the wedge and cause it to shorten internally to regain the stable geometry this shortening will be expressed as late out of sequence thrusting backthrusting and folding conversely underplating of sediment or crustal slices will thicken the wedge which may need to extend internally to regain stability extension will cause listric normal faults that may merge downward into zones of ductile extension continued underplating at depth and compensating extension above provides a mechanism for bringing high p low t metamorphic rocks to upper levels in the rear of the wedge where they are commonly observed many major tectonic boundaries in convergent orogens such as the coast range thrust in the franciscan complex major nappe contacts in the alps and the contact between the nevado filabride and higher betic nappe complexes in the betic cordillera show abrupt increases in metamorphic grade downward across them this is consistent with their origin or reactivation as uplift related extensional structures

contribution of numeric dynamic modelling to the understanding of the seismotectonic regime of the northern apennines abstract in this paper we investigate the forces possibly active in the area of the northern apennines by means of two dimensional finite element modelling assuming a viscoelastic rheology the forces included in the models are related to continental convergence between africa and eurasia to negative buoyancy of the subducted adriatic lithosphere and to positive buoyancy of anomalously hot mantle material underneath tuscany model predicted stress distribution is compared with seismotectonic data available for the area of the northern apennines and with earthquakes distribution our results indicate that continental convergence cannot be the only mechanism acting in the study area since it causes insignificant subcrustal stresses in disagreement with intermediate seismicity observed under the apennines asthenospheric upwelling under tuscany back arc region is shown to play a crucial role in the present day dynamics of the tyrrhenian apennines positive buoyancy causes an upwards and eastwards flow that generates extensional bending stresses in tuscany and at the top of the slab under the apennines horizontal pushing of the slab is proposed as an alternative mechanism to slab pull to generate subcrustal stresses activation of slab pull does not result in a significant change in orientation of the principal stress axes at shallow depths with respect to the model in which only asthenospheric diapirism is active therefore the existence of a continuous gravitationally sinking slab cannot be ruled out on the basis of comparison with seismotectonic observations both models successfully reproduce extension in tuscany and compression in the outer margin of the apenninic belt but fail to reproduce extension along the inner portion of the chain our modelling highlights the importance of better constraining the lateral extent of the asthenospheric diapir in order to find out whether the extension and tectonic uplift in the apennines is caused by asthenospheric upwelling as in the area of tuscany

evaluating the geogenic co2 flux from geothermal areas by analysing quaternary travertine masses new data from western central italy and review of previous co2 flux data abstract quantification of carbon fluxes between solid earth and its atmosphere is necessary to understand the global geological carbon cycle some of the main co2 contributors are metamorphism and magmatic mantle degassing co2 is discharged from active and quiescent volcanoes fault zones geothermal systems and co2 rich groundwater here a new method for the estimation of the geogenic flux of co2 from tectonically active regions based on the volume composition and age of travertine deposits is proposed the method is applied to the travertine deposits of western central italy where travertine deposition is driven by degassing of co2 charged groundwater results show that the study areas are characterized since middle pleistocene by diffuse co2 degassing processes with time averaged co2 fluxes ranging between 1 24 0 12 106 mol y 1 km 2 and 1 38 0 42 106 mol y 1 km 2 these values are of the same order of magnitude of carbon dioxide fluxes measured by different methods in western central italy and are higher than the global baseline co2 flux from high heat flow regions the review of the available 234u 230th and 14c data shows that the co2 degassing processes that affects western central italy nowadays were already active at least 350 ka ago proving that this region is a globally relevant case for the study of earth degassing considering the widespread occurrence of travertine deposits in tectonically active areas worldwide the proposed approach can be used as a reliable tool to estimate the co2 flux in different geodynamic settings within system earth

the north tyrrhenian northern apennines post collisional system constraints for a geodynamic model the north tyrrhenian northern apennines post collisional system ntas has been analysed on the basis of marine reflection profiles and bibliographic sources with the aim of providing an up to date geotectonic and evolutive framework consistent with structural data the continental rifting began to affect the most internal western side of the system in the middle upper miocene while the most external eastern zones were touched by rifting only in pleistocene times the birth and development of extensive asymmetric basins took place with a progressive speeding up of rifting towards the external sectors a diachronous regionally extended and eastward rejuvenating unconformity recognizable within the neogene quaternary basins marks the passage from the syn rift to the post rift tectonic regime while the first is everywhere dominated by extension the second one produces vertical movements reflection terminations related to this unconformity are interpreted in terms of vertical tectonic component three zones that experienced different post rift vertical movements are thus recognized in the ntas subsidence in the north tyrrhenian deep water region tectonic stability or alternation of moderate subsidence and uplift in the continental shelf and western tuscany strong uplift in eastern tuscany the updated structural data demonstrate that the ntas upper crust is crosscut by both tyrrhenian dipping and apennine dipping low angle detachment planes above which the upper crustal blocks rotated and experienced extensional transport along two opposite directions to the west and to the east respectively the coexistence of opposite dipping crustal surfaces bears two fundamental implications for the ntas geodynamics first it stresses the importance of the anti apennine transfer faults since they separate crustal blocks of opposite extension polarity secondly it testifies that the extension tectonics not only re utilized former crustal thrust planes but also gave origin to new significant e and ne dipping detachment planes plan and crossview geometries of faults together with considerations on the role of the metamorphic core complexes point to an interpretation of the ntas structure that is more consistent with the anastomosing shear model rather than the simple shear or the delamination ones

displacement and strain patterns of extensional orogens rock fabrics that result from displacement in extensional orogens provide a means of identifying geometric models responsible for extension of continental crust strain compatibility arguments indicate that a finite extension can be accommodated by displacements across 1 planar nonrotating faults or ductile shear zones 2 shear zones which rotate above a horizontal detachment the domino model or 3 shear zones which rotate as a result of a horizontally oriented pure shear stretching component the plastic model listric normal shear zone geometries may develop as the result of a depth dependent change in the pure shear component in the plastic model or the area loss component in the planar shear zone model within the geometric framework of these various models the effects of superposed simple shear pure shear extension and area change on the rock fabric are investigated these displacement components which may be superposed sequentially or simultaneously determine the state of finite strain associated with a given magnitude of tectonic extension the relationships between displacement and strain are expressed as graphs of foliation dip or strain ratio versus shear strain and as graphs of foliation dip or strain ratio versus tectonic extension the shear strain graphs illustrate the effects of the different displacement components on the rock fabric in a single shear zone whereas the tectonic extension graphs better illustrate these effects on the regional scale the shear strain and tectonic extension graphs can be used by field geologists 1 to determine tectonic extension across a region from measurements of strain ratio or orientation and fluctuation of foliation 2 to distinguish between possible extension models from field data and 3 to evaluate the influence of shear zone attitude and thickness upon the amount of displacement applications of these methods are illustrated for field areas in metamorphic core complexes of arizona and in the basin and range province of the north america cordillera

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

extensional fault systems in sedimentary basins a review of analogue model studies abstract scaled analogue models have provided graphic new insights into the progressive development of extensional fault systems this paper reviews recent results of an on going analogue modelling programme and compares the structural styles in the models with examples of natural extensional fault systems four fundamental model styles scaled to simulate deformation in brittle sedimentary rocks in the upper 10 km of the crust are reviewed extension above a basal detachment which undergoes stretching over a limited are produces an asymmetric rift graben bounded by planar faults and in which the internal deformation is accommodated by rotational domino faults these experimental results are directly comparable to structures found in intracontinental rifts extension above a basal detechment which undergoes extension under the whole model and which has no constraints at the ends produces domino style fault arrays in the pre rift sequence and listric growth faults in the syn rift sequence these results compare with highly extended rift basins and terranes such as the basin and range province usa extension above a simple listric fault produces a characteristic hangingwall roll over and crestal collapse graben system at high values of extension superposed crestal collapse grabens occur and a fan of listric growth faults is developed these structures bear striking similarities to growth faults in progradational delta systems ramp flat listric extensional fault systems using sand mica models produce a characteristic family of structures with an upper roll over crestal collapse system a ramp syncline and reverse fault fold zone and a lower roll over crestal collapse system an example of a ramp flat fault system from the gulf coast usa is presented as a comparison with the analogue model results preliminary results of three dimensional extensional model experiments are presented to illustrate the complexities in such fault systems in all of the experimental models it is found that the geometry of the underlying detachment system exerts fundamental control on structures produced in the hangingwall the analogue models illustrated in this review provide valid geometric and kinematic templates for the progressive evolution of extensional fault systems in sedimentary basins

lateral variations in the european lithosphere and seismic activity abstract in the mediterranean region an interesting correlation between the model of the lithospheric structure and the distribution of epicentres of shallow earthquakes with magnitudes larger or equal to 6 5 can be established in some areas these areas namely northern and southern italy the calabrian and hellenic arcs correspond to belts where high rigidity values in the lid are associated with very rapid changes in the lithospheric thickness

seismic markers of the messinian salinity crisis in an intermediate depth basin data for understanding the neogene evolution of the corsica basin northern tyrrhenian sea the messinian salinity crisis msc which widely affected the whole mediterranean basin induced rapid and spectacular palaeoenvironmental changes it led to a major erosion of the onshore areas and the upper parts of the continental shelves and slopes as well as important evaporitic deposits in the offshore deep basins the corsica basin belongs to the so called intermediate depth basin type because of its location between the coastal plain shelf area of east corsica and deeper marine basins in the northern tyrrhenian sea the msc event took place in the corsica basin during a period of active regional tectonics contemporaneous with the opening of the tyrrhenian sea as well as during the development of the corsica basin and the elba pianosa ridge based on the interpretation of high resolution seismic reflection profiles and a new 1 250 000 scale synthetic geological map we establish that the msc is recorded in the corsica basin through the occurrence of two sedimentary formations bounded by three remarkable surfaces these seismic markers suggest local and temporal variations in relative water level and associated depositional environments that differ between the north and south of the corsica basin during the msc the northern sector golo basin was emerged whereas the southern sector orbo basin was often flooded or submerged in the orbo basin the deposits record both an episode of intra msc climate change and regional tectonic events during the msc the corsica basin was a perched lake isolated from the deeper tyrrhenian basins the connection with the tyrrhenian basins was re established during the final stages of the msc before the catastrophic pliocene reflooding initiated by retrogressive erosion during a relative lowstand an extensive network of incised valleys was thus established in the orbo basin allowing the drainage of the corsica basin southwards into the deeper tyrrhenian basins these markers record the active regional tectonic context throughout the msc the orbo basin was strongly subsident along its western rim while its eastern rim was uplifted in turn the golo basin subsided from middle pliocene times onwards while the northern eastern and southern edges of the corsica basin were deformed and uplifted

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