kinematics and geometry of miocene low angle detachments and exhumation of the metamorphic units in the hinterland of the northern apennines italy abstract this paper deals with the lateral segmentation crustal boudinage and exhumation of the metamorphic units in the hinterland of the northern apennines during the late miocene extension the study area mt leoni area is part of the middle tuscan ridge a regional morpho tectonic feature in which the deepest tectonic units of the northern apennines are broadly exposed crustal seismic profiles and deep boreholes indicate that the middle tuscan ridge coincides with the outcropping part of a laterally discontinuous geological body mainly made up of hp lt and greenschist facies metamorphic units extensional detachments characterised by top to the east sense of shear and staircase geometry produced the lateral segmentation of the metamorphic units their activity can be ascribed to late tortonian late messinian times geometry and kinematics of the extensional detachments have been compared with the miocene extensional structures developed at shallow depths in the overthickened crust of the northern apennines allowing understanding of the extensional tectonic evolution which reorganised the hinterland northern apennines collisional belt

tectono sedimentary characteristics of late miocene quaternary extensional basins of the northern apennines italy abstract extensional and compressional regimes exist at the same time in adjacent parts of the northern apennines italy and the former regime succeeded the latter at the same place as the thrust mountain front moved eastward since miocene times numerous extensional basins have developed west of the present mountain divide the westernmost ones formed over attenuated continental crust since late miocene and have been subjected to several subsidence and uplift events with rates of subsidence generally faster than rates of sedimentation they contain continental deposits overlain by gypsum bearing upper miocene marine sequences and siliciclastic marine pliocene deposits these basins were affected by shallow magmatism and are still experiencing high geothermal gradient and late to post magmatic activities such as in the renowned thermal region of larderello to the east closer to the present mountain divide the extensional basins formed later from pliocene to quaternary contain continental fluvial and lacustrine deposits and have not experienced near surface magmatic activities the sedimentary fill architecture of the apennine extensional basins is similar to that of other european american and african extensional or transtensional systems for instance a common characteristic is the prevalence of large alluvial fan deposits at the hanging wall shoulder of half grabens coarser smaller alluvial fans at the footwall shoulder and some fluvial deposits introduced longitudinally unlike the african rifts though the sedimentary facies distribution of extensional basins which developed in active orogenic zones such as in the apennines may be strongly affected by uplifting steep mountain slopes and can have large thick coarse alluvial fans also on the footwall side of the half grabens

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

extensional and strike slip tectonics across the monte amiata monte cetona transect northern apennines italy and seismotectonic implications abstract this paper deals with the structural evolution along a transect across the inner northern apennines monte amiata volcano geothermal area monte cetona mainly focussing on the post orogenic middle miocene quaternary structures the tectonic setting of the study area derives from the superimposition of three main faulting events the first and second events developed during the middle late miocene and early middle pliocene respectively and took place in response to extensional tectonics the third faulting event developed in a transcurrent transtensional setting during the quaternary quaternary faults mainly strike ne sw and show left lateral kinematics with a minor dip slip normal component they caused the monte amiata volcanic eruptions 300 190 ka and controlled the widespread pleistocene and present hydrothermal fluids circulation quaternary strike slip faults have been documented in the monte amiata monte cetona area for the first time in this paper correlation with the adjoining areas e g vulsini region identifies the quaternary strike slip faulting recognised in the study area as a feasible source for the seismic activity in the monte amiata region where the origin of diffuse low magnitude seismicity is still under debate and poorly understood

evolution and depocentre migration in thrust top basins inferences from the messinian velona basin northern apennines italy abstract a structural study of the thrust related messinian velona basin is presented this basin developed in the hinterland area of the northern apennines between two n trending and e verging thrust anticlines the montalcino castelnuovo dell abate anticline to the west and the ripa d orcia anticline to the east the architecture of the basin and the deformation affecting the syntectonic sedimentary deposits show that the velona basin was affected by two strong compressive phases during the messinian the results of this study fit well into the structural evolution of the nearby hinterland basins indicating a neogene tectonic scenario dominated by compression the evolution of the velona basin is compared with simple models of thrust top basins whose development is controlled by the kinematics of two competing thrust anticlines the westward directed depocentre migration recognized in the velona basin is related to a higher displacement rate along the eastern thrust fault ripa d orcia thrust anticline whereas the deformations at the opposite basin margin are related to the montalcino castelnuovo dell abate thrust anticline the general models of thrust top basin evolution presented here were successfully applied to the velona basin case and may be compared with other natural examples as well

rapid incremental assembly of the monte capanne pluton elba island tuscany by downward stacking of magma sheets the late miocene monte capanne pluton elba island italy is characterized by the widespread occurrence of euhedral k feldspar megacrysts for which variations in size and abundance have been determined at 392 stations the variability of megacryst distribution defines three main facies characterized by low san piero facies high sant9andrea facies and intermediate san francesco facies megacryst abundance the three facies show minor yet systematic differences in whole rock major and trace element contents isotopic composition and biotite mineral chemistry with no detectable link between chemical variabilities and megacryst abundance these results along with the reconstruction of the crystallization sequence suggest that the facies formed at depth as distinct magma batches with their own peculiar geochemical features which were preserved after ascent and emplacement the new geological map based on k feldspar megacryst distribution thus reveals the composite structure of the pluton which was built up incrementally by downward stacking of three slightly different magma batches resulting in a sheeted pluton in the intermediate shallow crust the three magma batches were emplaced in a short time sequence in order to have internal magmatic contacts preserved thus giving a new perspective to the ongoing geochronological efforts to unravel age differences between internal plutonic facies

restricted rifting and its coexistence with compressional structures results from the crop 3 traverse northern apennines italy a geological interpretation of the deep seismic reflection line crop 3 italian program crosta profonda deep crust profile no 3 which crosscuts the northern apennines from the tyhrrenian to the adriatic coast is presented the profile images the lithosphere up to 15 s twt and highlights several peculiarities a the lower crust is bedded by discontinuous sub parallel reflective markers which terminate at 7 s beneath the western side of the profile b in the same area a notable reflection is recognizable at 10 s and is interpreted as the top of the asthenosphere c east plunging shear zones are recognizable throughout the crust by contrast the adriatic outer side of this line shows a reflections deepening westward from 13 to 15 s twt related to the base of the crust 33 38 km depth b the absence of thick bedding of reflective markers within the lower crust and c tectonic structures affecting the basement which are different from those which deform the cover of the northern apennines geological interpretation is based on the eastward migration of ductile shear zones which have been recognized on the seismic line the bending of the outer zone crust is considered to be a consequence of the rifting process with the application of pushing forces against the adriatic lithosphere which cannot escape toward east

tectonics of the umbria marche romagna arc central northern apennines italy new paleomagnetic constraints we present the results of a paleomagnetic study carried out on 32 sites from mainly messinian clayey sediments distributed throughout the external umbria marche romagna arc umra these data together with published results from coeval sediments demonstrate that this arc is an orocline in its central northern sector bending not well constrained in time was due to about 15 clockwise rotations of the central part of this arc and to counterclockwise rotations farther north in this latter area post messinian counterclockwise rotations are of the same amplitude as those calculated for some classic mesozoic paleomagnetic sections in northern umbria suggesting a plio pleistocene age for the rotations reported from the older sequences

the development and behaviour of low angle normal faults during cenozoic asymmetric extension in the northern apennines italy abstract movements on low angle normal faults lanf are not predicted by traditional anderson byerlee frictional fault mechanics our investigations centre on three normal fault systems active at distinct times during the regional extension of the northern apennines with each showing different degrees of crustal exhumation these are from e to w the altotiberina fault system umbria the radicofani fault system tuscan mainland and the zuccale fault system isle of elba regional extension has been a continuous process since middle miocene migrating progressively from west to east with deformation accommodated by a set of e to ne dipping lanf and more steeply sw dipping antithetic structures the lanf acted as regional detachments accommodating a majority of the extension in the northern apennines with individual faults exhibiting several kilometres of displacement regionally the stress field has been characterised by a vertical 1 and a ne sw tuscan mainland and umbria to e w elba trending 3 where exposed at the surface the main lanf detachments possess a well developed fault core of foliated fault rocks in which fluids have played a key role in weakening due to reaction softening and the onset of stress induced solution precipitation mechanisms we speculate that the e dipping normal faults initiated with relatively low angles of dip due to differential drag generated by mantle flow following slab retreat and roll back beneath the apennine chain

how and why the present tectonic setting in the apennine belt has developed the building of the apennine belt slowed down or ceased around the early pleistocene since then the belt has undergone strong uplift and considerable distortion this change from belt normal to belt parallel shortening has been determined by the fact that the continental adriatic domain adria was almost completely surrounded by buoyant orogenic structures in that context the mobility of adria underwent a considerable reduction whereas uplift and deformation of its southern part was strongly emphasized as an effect of the convergence of the confining plates around the middle pleistocene the deformation pattern in the peri adriatic zones changed again in response to acceleration of adria the outer adriatic sector of the apennine belt underwent belt parallel shortening accommodated by uplift and outward escape of upper crustal wedges the separation between the extruding wedges and the almost stable inner belt has generated a series of extensional or transtensional fault systems along the axial part of the apennines which now correspond to the main seismogenic sources the spatio temporal distribution of major tectonic events in the study area can plausibly be explained as an effect of the least action principle thematic collection this article is part of the apennines and tyrrhenian system collection available at https www lyellcollection org cc the apennines tyrrhenian system

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

geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy abstract serri g innocenti f and manetti p 1993 geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 117 147 the neogene quaternary magmatism of the northern apenninic arc took place in four phases separated in space and time which become progressively younger from west to east phase i 14 ma phase ii 7 3 6 0 ma phase iii 5 1 2 2 ma phase iv 1 3 0 1 ma this magmatism is the result of the activation of three physically separate sources 1 the adriatic continental crust extracted from the mantle in the late proterozoic 2 a strongly refractory recently k enriched harzburgitic mantle located in the mechanical boundary layer mbl of the lithosphere and 3 a recently metasomatized cpx rich mantle compositionally variable from iherzolite to wehrlite clinopyroxenite interpreted as an ephemerally k enriched asthenosphere the adriatic continental crust is the dominant source of the acid plutonic and volcanic rocks of the tuscan region the acid magmatism is mostly found inside an ellipsoidal area about 150 300 km centred on giglio island here defined as the tuscan crustal dome within this area mantle derived magmas unaffected by important crustal contamination processes and mixing with crustal anatectic melts have so far not been found pure crustal magmas are rare but are represented for example by some of the san vincenzo and roccastrada rhyolites virtually all the tuscan acid centres show evidence of mixing with potassic mantle derived magmas major and trace elements as well as 87 sr 86 sr and 143 nd 144 nd data on primitive rocks mg 65 reveal two groups of mantle derived magmas these define two distinct mantle enrichment trends both essentially due to the additions of k rich components which metasomatized separate compositionally diverse upper mantle sectors in both cases the most remarkable mineralogical effect of these enrichment processes is the production of variable amount of phlogopite through reaction between fluids and or melts with the mantle the rocks of group i ol hy and q normative lamproites ultrapotassic high mg latites ultrapotassic shoshonites and shoshonites saturated trend are considered to be derived by partial melting at low pressure 87 sr 86 sr 0 717 ce sr 0 3 and k 2 o na 2 o 6 7 and low ratios of 143 nd 144 nd 0 5121 0 5120 and ba la 87 sr 86 sr 0 712 and k 2 o na 2 o 8 9 values and low 143 nd 144 nd ba la 0 10 ratios these constraints do not allow to exclude a complete identity between the k rich components which metasomatized the mantle sources of the saturated and undersaturated trend magmas the geochemical and isotopic features of the components that metasomatized the mantle sources of the northern apenninic arc magmatism can be explained by a geodynamic process which causes a large amount of crustal materials to be incorporated within the upper mantle we propose that the delamination and subduction of the adriatic continental lithosphere related to the still ongoing northern apennine continental collision provide a viable mechanism to explain the genesis and eastward discontinuous migration of the magmatism in central italy the subduction of delaminated lithospheric mantle with lower crustal slivers would have exposed uppermost mantle adriatic mbl and crustal units previously imbricated in the apennine chain to the heating advected by the upwelling of a recently and ephemerally k enriched asthenospheric mantle wedge and by the underplating of magmas derived from it we consider that the diapiric uprising of a hot crustally contaminated asthenosphere occurs in the wake left above the sinking of the adriatic delaminated subducting continental lithosphere the delamination subduction process of the adriatic lithosphere has probably started in the early middle miocene but earlier than 15 14 ma ago as indicated by the age and petrologic characteristics of the first magmatic episode sisco lamproite of the northern apennine orogenesis

horizontal gravity gradient an aid to the definition of crustal structure in north america a map of the magnitude of the horizontal bouguer gravity gradient over the north american continent is used to delineate lateral discontinuities in upper crustal density and or thickness associated with such processes as suturing and rifting the usefulness of gradient trends in mapping major structural boundaries which are sometimes poorly exposed or completely buried is demonstrated by examples such as the buried southward extension of the grenville front and buried boundaries of the superior province gradient trends also draw attention to poorly known structures which may have major tectonic significance and to a continent wide structural fabric which may provide a record of the tectonic growth of the north american continent

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

tectonic burial and young 10 ma exhumation in the southern apennines fold and thrust belt italy in the southern apennines fold and thrust belt thermal indicators record exhumation of sedimentary units from depths locally in excess of 5 km the thrust belt is made of allochthonous sedimentary units that overlie a 6 8 km thick carbonate footwall succession the latter continuous with the foreland apulian platform is deformed by reverse faults involving the underlying basement therefore a switch from thin skinned to thick skinned thrusting occurred as the apulian platform carbonates and the underlying thick continental lithosphere were deformed during the latest shortening stages apatite fission track data showing cooling ages ranging between 9 2 1 0 and 1 5 0 8 ma indicate that exhumation marks these late tectonic stages probably initiating with the buttressing of the allochthonous wedge against the western margin of the apulian platform pliocene pleistocene foreland advancing of the allochthonous units exceeds the total amount of slip that based on cross section balancing and restoration could be transferred to the base of the allochthon from the underlying thick skinned structures this suggests that emplacement of the allochthon above the western portion of the apulian platform carbonates was followed by gravitational readjustments within the allochthonous wedge coeval and partly associated with thick skinned shortening at depth the related denudation processes are interpreted to have played a primary role in tectonic exhumation

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

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

epithermal precious metal deposits of italy an overview epithermal precious metal deposits have only quite recently been added to the metallogenic view of italy it was only in the late 1980s that two districts were recognized in sardinia and southern tuscany previously long known for a large variety of other commodities the sardinian epithermal precious metal district is associated with the oligocene miocene sardinian calc alkaline magmatic cycle the most relevant areas include the au deposit at furtei already in production and the osilo prospect where extensive exploration is under way the deposit at furtei contains at least six tonnes of gold metal the mineralogy of the deposit and of the alteration assemblages is typical of the acid sulfate high sulfidation class of volcanic hosted epithermal deposits fluids associated with alteration and mineralization have moderate temperatures 200 300 c and low salinities less than 6 wt nacl equivalent high temperature high salinity fluids similar to porphyry style systems also circulated at furtei at osilo a number of quartz veins containing up to several ppm au have been identified the alteration assemblage includes adularia and illite i e is typical of low sulfidation deposits fluid inclusion homogenization temperatures range from 198 to 270 c with salinities of less than 4 wt nacl equivalent

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

tertiary extensional tectonics in tuscany northern apennines italy abstract two extensional events have been recognized in the tertiary evolution of tuscany the first event occurred in the period between the late oligocene and late tortonian and caused a stretching of 120 or greater the second event occurred between the late tortonian and quaternary periods and caused a stretching not greater than 10 the first event is characterized by the exhumation of middle crust rocks and therefore by the development of core complexes the most significant structures of the first event are low angle normal faults which characterize the upper plate of the core complexes and ductile shear zones which characterize the lower plate the low angle normal faults tend to die out in the late triassic evaporite level which constitutes the main detachment of the core complexes the main structures of the second extensional event are high angle normal faults which dissect all the previous tectonic features these faults border tectonic depressions which were the site of clastic sedimentation from late tortonian to quaternary time these normal faults may tend to flatten in a seismic lozenge shaped band explained as an active extensional shear zone which is located at the brittle ductile boundary a similar explanation is given for the detachment located in the late triassic evaporite level during the first extensional event while the first extensional event is in the framework of the northern apennine post collisional evolution the second extensional event because it affects an already stretched crust could be attributed to the southern tyrrhenian opening which began during late tortonian

extension and compression in the northern apennines italy hinterland evidence from the late miocene pliocene siena radicofani basin and relations with basement structures 1 the northern apennines na hinterland area is characterized by a complex neogene quaternary tectonics where both crustal extension associated with the tyrrhenian basin opening and crustal shortening in the onshore area took part in the deformation analysis of synorogenic deposits preserved in the nnw trending siena radicofani basin srb extending along a large part of the na hinterland documents the evolution of deformation of this sector during the last 9 ma information from subsurface geology deep seismic lines commercial seismic lines and deep wells surface geology mapping and structural analysis and from analogue modeling was integrated and used to infer the tectono sedimentary history of the srb and its relation with structures in the substratum as well as the possible implications for the evolution of the na hinterland the results we obtain indicate that the srb and the adjoining hinterland basins were bounded by thrust anticlines controlling basin development and deformation seismic lines across the srb display various examples of compressional structures affecting the basin fill and the substratum such as thrust anticlines and reverse faults notably these basin scale structures exhibit a good correlation with those observed in the field and are consistent with the kinematics of the outcrop scale compressional structures the thrust anticlines bounding the basins are often cored by triassic evaporites burano formation suggesting that this weak layer decoupling the sedimentary cover from the underlying crystalline basement controlled their evolution in this circumstance three series of scaled brittle ductile physical models have been used to investigate the development of a basement cover system with a decollement ductile layer at the base of the sedimentary cover these models simulate the evolution of the northern apennines hinterland where the basement is involved in the thrusting and the sedimentary cover is shortened above a basal ductile layer given by the burano formation longitudinal models cross sections display similar deformation patterns to those observed in the na hinterland such as characteristic wavelength of both basement and cover structures as well as detachment and fault propagation folding in the cover extensional tectonics is instead found to control sedimentation in the southern part of the srb at 8 ma or representing recent deformation the older extensional event is here related to the forelandward propagation of tyrrhenian related extension that could reactivate suitably oriented basement thrusts transfer zones produced a differential propagation of extension such that along strike sectors of the hinterland were eventually deformed by different stress fields analysis of the srb and of other adjoining basins reveals that the na hinterland experienced alternated periods of forward and backward migration of the compression extension transition in our interpretation the competition between extension and compression in the hinterland is related to the nnw directed africa pelagian indentation responsible for the lateral extrusion of the na and the contemporaneous opening of the tyrrhenian basin in the inner zone increased marginal loading at the foreland promoting reactivation of hinterland thrusts may have influenced this process as well

crustal section based on crop seismic data across the north tyrrhenian northern apennines adriatic sea abstract using deep seismic reflection data from the italian lithospheric exploration project crop in the central mediterranean region a 400 km long section composed of three different profiles crossing the northern tyrrhenian sea crop m 12a profile the northern apennines crop 03 and the adriatic sea crop m 16 is reconstructed and discussed new data allow us to outline a seismically consistent tectono stratigraphic setting for the crust and upper mantle of the northern apennines thrust belt system and its adriatic foreland time space analysis of the deformation of the investigated chain and identification of existing macrostratigraphic crustal intervals and tectonic units allow a reasonably controlled interpretation of the geodynamic evolution and of the main orogenic stages careful seismic reprocessing and application of advanced techniques to key zones of the explored area such as the tuscan archipelago were determinants in obtaining fundamental information for understanding of the complex lithospheric structures and their evolution profile interpretation supports that the northern apennine chain is dominated by a compressive thrust system crustal extension assumed by some authors as the dominating tectonic process for the whole tuscan apennine area represents a subordinate geodynamic event of the last stage tyrrhenian in the early cretaceous late jurassic the paleogeographic framework consisted of the europe and adria plates separated by the alpine tethys ocean during the late cretaceous early eocene adria europe convergence eo alpine stage and subduction beneath the adria plate closed the alpine tethys sea with the tethyan slab being clearly seismically imaged the first apenninic geodynamic stage occurred in the late oligocene early miocene with the opening of the balearic basin which generated a first lithospheric root of the apenninic chain in the tuscan archipelago area this root is represented by adria verging thrust faults that progressively flatten eastward upper parts of the west verging eo alpine thrust blocks were truncated by the east verging thrust faults of the balearic stage a deeper seismic reflector attributed to the top of the asthenosphere forms a mantle high below the elba island from the late miocene to present the corsica basin and western hinterland area were affected by extensional tectonics related to the tyrrhenian opening whereas compressional tectonics continued in the eastern hinterland and mostly on the eastward migrating foreland with development of a second lithospheric root constituted by high angle thrust faults these faults give rise to a huge basement culmination below the main apennines watershed impressive e directed gravity sliding of sedimentary blocks over their sloping basement occur generating the umbria marche shallow seismicity crustal shortening of the apennines system amounts to 170 km 14 km of which are due to the eo alpine stage 71 km to the balearic and 85 km to the tyrrhenian one in the frame of africa europe convergence the tyrrhenian apennines tectonodynamics were mainly conditioned by the mesozoic paleogeography

the crustal structure of the northern apennines central italy an insight by the crop03 seismic line in this paper the crop03 deep seismic reflection profile in the northern apennines is described and re considered in light of new geophysical data and interpretations made available in the last five years particularly from heat flow measurements aeromagnetics tomography active stress determination and passive seismology the crustal structure of the northern apennines is shown to be composed of two distinct domains to the west is the tyrrhenian domain and to the east is the adriatic domain these domains have distinctive geological and geophysical characteristics that exhibit distinct reflectivity patterns at all crustal levels in the tyrrhenian domain the upper oligocene lower miocene compressive structures are no longer recognizable because they are dissected by subsequent extensional tectonic features the seismic profile highlights the strong asymmetry of extensional deformation and the upper crust is affected by a set of six major east dipping low angle normal faults in the adriatic domain compressive tectonics have acted since the middle miocene and the pattern of shallow contractional structures is well preserved the geological interpretation of the seismic data supports a thick skinned style of deformation where the basement is involved in the major thrust sheets the good quality of seismic data also allows for determining the total shortening produced by the contractional structures in the central part of the profile at the border between the tyrrhenian and adriatic domains seismic data shows the presence of an intermediate sector the sector consists of a highly reflective window where the refraction data indicate a local doubling of the crust for about 30 km a scenario is presented that attempts to describe the geodynamics that drove the tectonic evolution of the northern apennines since the upper oligocene

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

studying travertines for neotectonics investigations middle late pleistocene syn tectonic travertine deposition at serre di rapolano northern apennines italy middle late pleistocene tectonic activity has been inferred through studies on travertine deposits exposed in a tract of the hinterland northern apennines a detailed study on the relationships between tectonics and travertine deposition coupled with 230th 234u age determination of travertines at cava oliviera quarry located close to serre di rapolano village southern tuscany northern apennines allowed us to recognise pleistocene faults whose activity has been referred to 157 24 ka at least travertine deposition was tectonically controlled by wsw ene striking oblique and normal faults associated to a main fault named as the violante fault this structure dissected a regional normal fault known as the rapolano fault early middle pliocene in age which bounded the eastern side of the pliocene siena basin and gave rise to space accommodation for clayey and sandy marine sediments hydrothermal circulation and related travertine deposition was favoured by the damaging enhancement due to the fault fault intersection tectonic activity has been also documented by deformation recorded by travertines which suggest a main tectonic event between 64 5 and 40 5 ka the tectonic activity described for the study area agrees with the quaternary tectonic evolution documented in the surrounding areas e g mt amiata and mt vulsini as well as the tyrrhenian margin of the central apennines indicating that a widespread tectonic activity affected the inner part of the apennines until the latest quaternary

highly extended terrains lateral segmentation of the substratum and basin development the middle late miocene radicondoli basin inner northern apennines italy 1 this paper deals with the evolution of sedimentary basins not delimited by normal faults with a substratum characterized by an upward concave shape and with infilling sediments synclinally deformed we describe the middle late miocene radicondoli basin representing an example of such bowl shaped basins its tectonic origin is controversial being related both to compression and extension these opposite interpretations bear significant consequences on the geodynamic context in which the inner northern apennines developed during the middle late miocene the results of our structural studies carried out in the substratum and infilling sediments indicate that the radicondoli basin is an example of a hanging wall basin developed in an extensional setting extensional tectonics determined the lateral segmentation of the substratum competent levels i e tuscan nappe and verrucano group and the consequent collapse of overlying less competent levels i e the ligurian units with the formation of a bowl shaped tectonic depression here the syntectonic sediments serravallian late messinian are deformed in a large syncline characterized by minor gravity driven folds with vergences toward the depocenter and traces of their axial planes parallel to the basin margins this paper highlights the role of the competence contrast during the postcollisional tectonic evolution and the influence of substratum lateral segmentation for the accommodation of syntectonic sediments

new constraints on the evolution of the inner northern apennines by k ar dating of late miocene early pliocene compression on the island of elba italy

migration of geothermal fluids in extensional terrains the ore deposits of the boccheggiano montieri area southern tuscany italy an integrated study based on fluid inclusion 18o composition and structural analyses was carried out on a pliocene fossil hydrothermal system located to the south of the present active larderello geothermal field in the boccheggiano montieri area the study area is typified by mineralized cataclastic levels related to late oligocene early miocene thrust surfaces and to the following two generations of normal faults of miocene and pliocene ages respectively within the damage zone of the pliocene boccheggiano fault the mineralization is mainly made up of quartz and pyrite quartz pb zn sulfides or quartz pb zn sulfides fluorite carbonates assemblages occur instead in the older cataclastic levels two generations of liquid rich fluid inclusions were recognized in quartz and fluorite the first one with homogenization temperatures ranging between 172 and 331 c and salinity between 0 0 and 8 8 wt naclequiv records the early stage of hydrothermal activity the second generation of fluid inclusions documents a later stage with homogenization temperature from 124 to 288 c and salinity from 0 2 to 1 9 wt naclequiv fluid inclusions analyses also indicate that mixing of fluid with distinct salinities and or temperatures was a widespread process during the early stage and that fluid temperatures decreased moving from the boccheggiano fault toward the more distal and older cataclastic levels the 18o values of water in equilibrium with hydrothermal quartz which range from 5 7 to 0 1 are related to the circulation of meteoric water mixed with saline water that leached the evaporite level and enriched in 18o through water rock interaction and or with magmatically derived fluids results indicate that the damage zone of the pliocene boccheggiano fault represented the main channel for the flow of meteoric water which was heated at depth then mixed with high salinity fluids and finally ascend to infiltrate along the older cataclastic levels our results based on fluid inclusions oxygen isotopic compositions and structural analyses indicate that a single fluid flow path run through the damage zone of the boccheggiano fault and the older cataclasites which were thus hydraulically connected

thrust belt development in the central apennines italy northward polarity of thrusting and out of sequence deformations in the gran sasso chain the lazio abruzzi carbonate platform overrides the outermost sectors of the foreland fold and thrust belt of the central apennines of italy along an arcuate thrust front which swings from e w to nnw sse orientation the e w striking north verging thrust faults of the gran sasso cut in their footwall the n s oriented east verging imbricates of the marche thrust belt and the adjacent adriatic foredeep our field mapping of the gran sasso imbricate system shows an array of six major thrust faults crosscutting each other in such a way that oblique propagation of higher thrust faults across the preexisting thrust sheets causes rethrusting of earlier imbricated units decapitation of previous folds and superposition of younger on older beds deformation in the gran sasso thrust belt mainly occurred between messinian and middle pliocene times and is partly synchronous with the development of the marche thrust belt thus implying that shortening resulted from a complex combination of northward and eastward propagating thrust systems increasing west to east shortening along the gran sasso thrust front indicates large differential anticlockwise rotation by decoupling along a n s transpressive right lateral shear zone this mechanism could have been induced by the maiella foreland uplift acting as a buttress against which the lazio abruzzi carbonate platform was stacked and forced to rotate anticlockwise with consequent shortening by out of sequence thrust propagation

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

out of sequence thrusts out of sequence thrusts oost are those thrusts which do not obey the foreland propagating or in sequence deformation style they include both isolated thrusts which develop hindward of the thrust front and sequences of break back thrusts which propagate from the foreland to the hinterland two end members of a series of oost types are recognized 1 older in sequence thrusts which are reactivated along their entire length and 2 completely new thrusts which propagate through already deformed thrust sheets between the two end members are thrusts composed partially of reactivated in sequence thrust sequences and partially of new entirely out of sequence segments oosts can be initiated for a variety of reasons including 1 keeping the orogenic wedge at critical taper 2 break back sequences from the suture zone in the overriding plate 3 ramping to overcome a sticking point which inhibits in sequence thrust propagation and 4 during simultaneous displacement along two stacked thrusts culminations which bow up segment of the upper thrust may be chopped through to permit continued displacement on the upper thrust many different types of thrust behavior including gravity sliding plucking and derivation of isolated horses from ramps may mimic some of the characteristics of oosts consequently it may be difficult to conclusively prove an oost origin for a complex thrust geometry

geometry and kinematic evolution of inversion structures positive inversion structures form by the compressional reactivation of preexisting extensional structures experimental models and observations of natural structures are used to develop quantitative models for the geometry and kinematic evolution of inversion structures in this paper i analyze two main formation mechanisms of inversion structures 1 fault propagation folding on planar faults and 2 fault bend folding on listric faults inversion structures formed by fault propagation folding occur in the southern north sea the central montana platform and the kangean basin during extension a broad fault propagation or drape fold develops above the master fault with the fault subsequently breaking through the fold synextensional growth units deposited in the hanging wall typically thicken into the basin compressional reactivation results in slip reversal on the master and secondary faults their rotation to shallower dips and the development of a compressional fault propagation fold inversion structures formed by fault bend folding on listric faults occur in the taranaki basin and possibly in the southern north sea rollover folding in the hanging wall occurs during extension possibly accompanied by a small component of fault propagation folding in the vicinity of the fault tip deformation is primarily localized along a system of antithetic faults synextensional growth sediments typically thicken into the fault but also show thinning in the immediate vicinity of the fault during compression the extensional fold is first unfolded and then folded into a compressional fault bend fold the characteristic variations in bed geometry and thickness provide predictive models for interpreting the subsurface geometries of these two classes of inversion structures in areas with poor seismic data these models are particularly useful in exploring for structural traps in the complex and relatively unexplored synextensional growth units

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

flexural behavior of the continental lithosphere in italy constraints imposed by gravity and deflection data a procedure is developed that systematically matches observations of plate flexure and gravity anomalies at simple convergent boundaries to the bestfitting two dimensional flexural geometry obtained by a thin elastic sheet of specified elastic strength the procedure allows analytical solution for three independent variables one of which is the initial preflexure elevation of the reference surface and two of which are related to the vertical forces and bending moments that act on the plate application to four profiles constructed across the apennine convergent system in italy shows that the observed depth of the basal pliocene surface which marks the base of the foredeep basin and the observed bouguer gravity anomalies can be fit by a two dimensional elastic plate model with an effective elastic thickness of about 20 km on three profiles and about 10 km on the fourth profile the initial elevation prior to flexure is determined to have been about 1000 m below sealevel on all profiles large bending moments and or vertical shear forces are required to act at the effective plate ends in order to maintain the observed deflection moments between 0 5 1017 and 3 1017 n and shear forces between 3 1012 and 3 1012 n m gravity modelling indicates that on the two northernmost profiles these terminal forces can not be supplied by a static mass at crustal depths and suggests that on all four profiles the terminal forces are supplied by anomalously dense material present at depths of 75 150 km beneath and west of the west coast of italy this dense material probably corresponds to westward subducted lithosphere of the adriatic plate extending from the northern apennines to the southern apennines and calabria this study suggests that in subduction systems like the apennines that are characterized by backarc extension forces acting on subducted lithosphere at depth can be expressed at the surface in the geometry of the foredeep basin that forms adjacent to the subduction zone

three dimensional moho topography in italy new constraints from receiver functions and controlled source seismology in complex tectonics regions seismological geophysical and geodynamic modeling require accurate definition of the moho geometry various active and passive seismic experiments performed in the central mediterranean region revealed local information on the moho depth in some cases used to produce interpolated maps in this paper we present a new and original map of the 3 d moho geometry obtained by integrating selected high quality controlled source seismic and teleseismic receiver function data the very small cell size makes the retrieved model suitable for detailed regional studies crustal corrections in teleseismic tomography advanced 3 d ray tracing in regional earthquake location and local earthquake tomography our results show the geometry of three different moho interfaces the european adriatic ionian and tyrrhenian the three distinct moho are fashioned following the alpine and apennines subduction collision and back arc spreading and show medium to high frequency topographic undulations reflecting the complexity of the geodynamic evolution

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

tectonic control on travertine and calcareous tufa deposition in a low temperature geothermal system sarteano central italy this paper presents an integrated study directed toward an understanding of the tectonic control on the hydrothermal circulation and resulting deposition of middle late pleistocene travertine in a low temperature geothermal field of southern tuscany located in the sarteano area central italy the study area is characterized by thermal springs c 25 c and related continental carbonate deposits structurally controlled by sw ne trending oblique to strike slip faults dissecting previous normal faults sedimentological stratigraphical data and 230 th 234 u radiometric age determination for the travertine indicate that continental carbonates were deposited in a tectonically controlled perched spring system from 268 22 ka at least to the present the hydrothermal system is and was characterized by meteoric waters with a minor contribution from fluids of deeper origin meteoric waters infiltrated to depth through tectonically damaged zones of mesozoic and cenozoic carbonate rocks and overheated as a result of localized anomalous geothermal gradient then fluids enriched in bicarbonate sulphate moved up along highly fractured rock masses at the intersection between strike slip faults and normal faults this paper highlights the use of continental carbonates in the reconstruction of palaeohydrothermal systems in terms of the location of the main conduits for hydrothermal fluid flow age of faulting and physical properties of hydrothermal fluids

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

geological and geophysical study of a thin skinned tectonic wedge formed during an early collisional stage the trasimeno tectonic wedge northern apennines italy the presence of a set of well known turbidite successions deposited in progressively e migrating foredeep basins and subsequently piled up with east vergence makes the northern apennines of italy paradigmatic of the evolution of deepwater fold and thrust belts this study focuses on the early apenninic collisional stage early miocene in age which led to the accretion of the turbidites of the trasimeno tectonic wedge ttw in the central part of the northern apennines based on the interpretation of previously unpublished seismic reflection profiles with new surface geology data and tectonic balancing we present a detailed tectonic reconstruction of the ttw in the study area the ttw is characterized by a w dipping shaly basal decollement located at a depth of 1 5 km the tectonic wedge is c 5 km thick at its central western part and tapers progressively eastwards to c 1 km the total shortening balanced along a 33 km long cross section is c 60 km including 20 km 40 of internal imbrication c 23 km of horizontal ene wards translation along the basal decollement and c 17 km of passive translation caused by the later shortening of footwall units deformation balancing constrained through upper aquitanian upper burdigalian c 21 16 ma biostratigraphy provides an average shortening rate of c 8 6 mm a 1 internal shortening of the ttw shows an average shortening rate of c 4 mm a 1 for this period

tectono metamorphic evolution of the siliciclastic units in the middle tuscan range inner northern apennines mg carpholite bearing quartz veins related to syn metamorphic syn orogenic foliation abstract this paper accounts for a new finding of high pressure low temperature hp lt metamorphism documented in continental derived rocks exposed in the central part of the middle tuscan range representing the easternmost location in the tyrrhenian region where blueschist facies metamorphism has been documented it describes the development mechanism of mg carpholite bearing quartz veins in the framework of the deformational events described for the inner northern apennines the hp lt peak metamorphism can be estimated in p 1 1 gpa and t 370 420 c as supported by the mineralogical assemblage consisting of quartz muscovite chloritoid pyrophylite hematite chlorite paragonite ti oxides documented in the aluminous metasediments pelites and quartzose sandstones of the triassic verrucano succession this paragenesis defines the s 1 schistosity an axial planar tectonic foliation associated to map and mesoscale isoclinals folds f 1 s 1 schistosity is a composite foliation resulted from a non coaxial progressive deformation associated to the de 1 collisional event late oligocene early miocene mg carpholite bearing quartz veins developed as tension gashes in en echelon arrays within brittle ductile shear zones the development of quartz veins was guaranteed by the high volumes of si rich fluids produced by the dynamic recrystallization process on the siliciclastic rocks

belt bending driven by lateral bending of subducting lithospheric slab geophysical evidences from the northern apennines italy abstract many of the mountain belts displaying a curved shape are oroclines i e are produced after progressive bending of an originally straight fold and thrust belt the bending process was previously explained as a consequence of several possible events taking place in the crustal orogenic wedge such as occurrence of obstacles non coaxial deformation and movements on wrench faults recent paleomagnetic results from the northern apenninic arc document that this belt is properly an orocline and results from late messinian early pliocene bending of a messinian straight belt foredeep system tomographic images in turn show the presence of a high velocity body interpreted as subducted slab in the upper mantle beneath the northern apennines between 35 and 670 km depth down to 100 km this body displays an arcuate shape which closely mirrors the geological outlines while it appears to be straight and parallel to the messinian pre rotated belt at depth we explore here the possibility that the arcuate shape of the northern apennines is a consequence closely following in time of much deeper processes than previously suggested i e the lateral bending of the subducting adriatic 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

lake formation characteristics and evolution in retroarc deposystems a synthesis of the modern andean orogen and its associated basins lake deposystems are commonly associated with retroarc mountain belts in the geological record these deposystems are poorly characterized in modern retroarcs placing limits on our ability to interpret environmental signals from ancient deposits to address this problem we have synthesized our existing knowledge about the distribution morphometrics and sedimentary geochemical characteristics of tectonically formed lakes in the central andean retroarc large active mountain belts such as the andes frequently create an excess of sediment to the point that modeling and observational data both suggest their adjacent retroarc basins will be rapidly overfi lled by sediments lake formation requiring topographic closure demands special cohen email arizona edu current address department of earth and environmental sciences university of kentucky lexington kentucky 40506 0053 usa cohen a mcglue m m ellis g s zani h swarzenski p w assine m l and silva a 2015 lake formation characteristics and evolution in retroarc deposystems a synthesis of the modern andean orogen and its associated basins in decelles p g ducea m n carrapa b and kapp p a eds geodynamics of a cordilleran orogenic system the central andes of argentina and northern chile geological society of america memoir 212 p 309 335 doi 10 1130 2015 1212 16 for permission to copy contact editing geosociety org 2014 the geological society of america all rights reserved on december 5 2014 memoirs gsapubs org downloaded from