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

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

seismic evidence of mylonite reflectivity and deep structure in the kettle dome metamorphic core complex washington the first direct test of the seismic reflectivity of mylonites is provided by a seismic reflection profile over a mylonite zone exposed in the kettle dome metamorphic core complex northeastern washington the mylonite zone developed at mid crustal levels and has undergone a minimum of retrogression and cataclasis during uplift downdip projection of the exposed mylonite zone into the seismic profile indicates that the compositionally layered mylonite zone is reflective and traceable to at least 5 km depth as a complex zone of multicyclic reflections the seismic data also show that the crust beneath the kettle dome is characterized by abundant strongly reflective moderately dipping layers down to at least 18 km these layers can be interpreted in terms of compressional or extensional orogenic events or a combination of both models for the structure and genesis of metamorphic core complexes must take these data into account

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

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

pyroclastic flow deposits of the 1991 eruption of volcan de colima mexico the april 16 1991 eruption of volcan de colima represents a classical example of partial dome collapse with the generation of progressively longer runout merapi type pyroclastic flows that traveled up to 4 km along the el cordoban gullies east central and west the flows filled the gullies with block and ash flow deposits up to 10 m thick of which after 7 years of erosion only remnants remained in the el cordoban west and east gullies the el cordoban central gully however provided a well preserved and incised longitudinal section of the 1991 deposits the deposits were emplaced as proximal and distal facies separated by a change in slope angle from 30 to 20 the proximal facies consists of massive clast supported flow units up to 1 m thick with andesite blocks locally supported by a matrix of coarse ash and devoid of segregation structures or grading the distal facies consists of a massive matrix supported deposit up to 8 m thick which contains dispersed andesite blocks in a fine ash matrix in the distal facies a train of blocks marks flow unit upper boundaries and although sorting is poor some grading is present thin finely stratified or dune bedded layers of fine ash material are locally present above or below units of both facies sedimentologic parameters show that the size or fraction of large pyroclasts larger than 1 decreases from proximal to distal facies as the percentage of matrix 0 to 4 increases especially immediately beyond the break in slope we propose that the propagation of the colima pyroclastic flows is critically dependent on local slope angle the presence of erodible slope debris and the decrease in grain size with distance from the vent the progressive fining is probably caused by some combination of erosion clast breakup and deposition of larger pyroclasts and is itself influenced by the slope angle in the proximal region the flows moved as granular avalanches in which interacting grains ground each other and erosion occurred to produce an overriding dilute ash cloud the maximum runout distance of the avalanches was controlled by the angle of repose of the material and the volume and grain size of source and eroded material because the slope angle is close to the repose angle for this debris granular avalanches were not able to propagate far beyond the change in slope if however an avalanche had enough mass in finer grain size fractions at least part of the flow continued beyond the break in slope and across the volcano apron propagating in a turbulent state and depositing surge layers or in an otherwise settling modified state and depositing block and ash flow layers

forced folding above shallow magma intrusions insights on supercritical fluid flow from analogue modelling abstract magma emplacing at shallow crustal levels may cause significant deformation in the overlying country rock i e forced folding fracturing and faulting both at a local and or regional scale to get insights into these processes we investigated in the laboratory the development of forced folds and associated fracture fault networks an analogue magma simulated by polyglycerols was intruded into a sand pack representing the brittle crust the scaled analogue models reproduced different 3d deformation structures depending on the model parameters e g magma viscosity injection rate volumetric flux and the rheology and thickness of the host and cover rocks however all models support the observation that the emplacement of shallow magmatic bodies may result in the growth of dome shaped forced folds and associated development of tensional and compressional deformation in the host rock although the models involve simplifications these results provide useful hints for geothermal research as fractures and faults associated with magma emplacement can significantly influence the distribution and migration of superhot geothermal fluids these structures can therefore be considered potential targets for geothermal and or ore deposit exploration in this perspective the results of analogue models may provide useful geometric constraints for field work numerical modelling and particularly seismic interpretation allowing production and a better understanding of integrated conceptual models concerning the circulation of supercritical fluids

chronology of deformation and analogue modelling of the plio pleistocene tiber basin implications for the evolution of the northern apennines italy abstract the late miocene quaternary hinterland basins located in the western sector of the northern appennines have been considered either as the surficial effect of the back arc extension related to the tyrrhenian basin opening or related to late orogenic gravity spreading conversely some authors recently suggested that they formed in a compressional regime and underwent a complex tectonic history in this frame the controversial origin of these hinterland basins is the subject of this paper a structural study of the plio pleistocene continental tiber basin tb one of the most important ones has been carried out allowing to establish the role of lateral compressional and extensional deformations both of which have been affecting the continental deposits during basin evolution on the basis of field mapping and structural analysis the development during early middle pliocene of the three main branches constituting the tb has been referred to a compressive regime related to the emplacement of a crustal thrust the area was only later during the early pleistocene affected by extension characterised by nw se trending normal faults as well as fault controlled basins these structures in fact obliquely cross cut the nnw trending older tb branches the area was further affected by a ne oriented shortening phase at the boundary between early and middle pleistocene which produced the partial inversion of the southwestern tb branch deruta terni sector the pleistocene tectonic evolution of this sector has been also investigated by means of analogue modelling experiments whose results support the hypothesised tectonic evolution a succession of stress fields ranging from tb development up to middle late pleistocene has been reconstructed they are characterised by a ne to ene trending direction of compression or extension and the variation through time of the stress field led to the reactivation of suitably oriented pre existing structures the proposed tectonic evolution of the tb indicates a rejuvenating of thrust activity in the study area as well as a retard of normal faulting with respect to the hypotheses proposed by previous authors

mapping capable faulting hazard in a moderate seismicity high heat flow environment the tuscia province southern tuscany northern latium italy abstract this study is focused on potential evidence of capable faulting affecting southern tuscany northern latium a region of high heat flow and moderate to low seismicity here we refer to this region as tuscia the latin name for the land of the etruscans the review of the evidence for active tectonics in this area has allowed us to identify several potentially active capable faults mapped using a combination of analysis of digital terrain models with remote sensing and local geological information derived from bibliographic data and different scale maps active and capable faulting is certainly more evident in the eastern sector of tuscia chianti cetona ridge pienza amiata and bolsena caldera however even in the western tuscia e g colline metallifere and tyrrhenian coast capable faulting may be hypothesized along numerous structural elements the characterization of active faulting potential in terms of geometry slip types and rates in such a high heat flow environment beyond its usefulness in improving the assessment of fault displacement and earthquake hazard also helps to improve knowledge of the stress field and structural setting of the many geothermal fields in the area this allows new useful insights into geothermal exploitation and hazard e g induced triggered seismicity moreover this new knowledge of active tectonics and capable faults of the hinterland sector of the northern apennines may also provide useful insights into the siting processes of highly hazardous and strategic structures and more generally in land use planning and management of infrastructures especially during emergencies

upper crustal structure of the larderello geothermal field as a feature of post collisional extensional tectonics southern tuscany italy abstract reflection seismic profiles crossing the larderello geothermal field permit the distinction of three different seismic facies units in the upper continental crust the upper 3 4 km of the crust is characterized by low reflectivity its base corresponding to a reflector referred to as the k horizon and recognized in many other areas of southern tuscany beneath this reflector a seismic facies of 0 8 1 0 twt thickness is characterized by strong convergent and divergent reflections forming a lozange shaped geometry the lowermost seismic facies is characterized by almost horizontal reflections based on the distribution of the hypocentral microearthquakes temperature data recorded in deep boreholes and the geometry of normal faults the k horizon is explained here as a kinematically active rheological boundary which separates a brittle upper part from a ductile lower part according to this hypothesis the k horizon and the lozange reflections could originate from a mylonite band located at the contact between two geological bodies characterized by different rheological behavior it is inferred that this horizon acts as a decoupling plane in the upper continental crust it developed as a consequence of the extensional tectonics and the high heat flow which characterize southern tuscany

seismic reflectivity of mylonite zones in the crust deep fault zones are characterized by mylonitic rocks with strong preferred orientation of constituent minerals and retrograde mineral assemblages sonic velocities are consequently lower for propagation directions normal to mylonite foliation than in surrounding unmylonitized rocks synthetic seismograms computed for low velocity near horizontal thick mylonite zones of complex laminated geometry show multicyclic reflections with amplitudes up to twice those generated by a single interface seismic characteristics of mylonite zones are sufficient to produce reflections in crystalline rocks provided noise levels are relatively low

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

continental fault structure and the shallow earthquake source plate boundaries in continental crust are generally less sharply defined than in the oceans with seismicity spread over broad areas interplate displacements appear to be largely accommodated by networks of major fault zones a simple 2 level model for these important structures accounts for the depth distribution of most continental earthquakes and for the observed range of faulting styles and associated rock deformation textures the model consists of a seismogenic frictional slip regime overlying quasi plastic mylonite belts wherein shearing is largely accommodated aseismically due mainly to the changing response of quartz to deformation with increasing temperature shear resistance increases with depth to a peak value in the vicinity of the frictiona1 quasi plastic transition and then decreases rapidly the depth to which microseismic activity extends appears inversely related to regional heat flow and can be satisfactorily modelled as the frictional quasi plastic transition for different geotherms using laboratory determined flow laws for quartz bearing rocks larger earthquake ruptures m 5 5 tend to nucleate near the base of the seismogenic regime in the region inferred to have the highest shear resistance and concentration of distortional strain energy consideration is also given to the depression of isotherms and seismic activity in regions of thrusting and to the question of the downward continuation of major fault zones through the lithosphere decoupling of the upper crust on flat lying shear zones may accompany higher level dip slip and perhaps in some circumstances strike slip faulting being favoured by above average continental heat flow and a high quartz content in the middle or deep crust the average level of deviatoric stress within the seismogenic regime remains an outstanding problem

structure and late cenozoic evolution of the upper lithosphere in southwest tuscany italy abstract geological and geophysical data on southwest tuscany are reviewed in order to define the structure and evolution of the upper lithosphere from the miocene to the quaternary petrologic studies reveal the existence below all of tuscany of hercynian and older polyphased metamorphic rocks and of hercynian granite whose top is an important seismic reflecting horizon the basement is characterized by ne sw trending structures in contrast with the main nw se alpine structures of the uppermost levels the heat flow map shows two broad areas with values higher than 80 mw m2 reaching maximum values of 10 5 and 15 h f u in the geothermal areas which are also characterized by negative bouguer anomalies a landsat study revealed a ne sw band of subcircular structures passing through larderello and coinciding with a regional fault system and a steep rise in the moho petrologic geochemical and radiometric data on the tuscan igneous rocks show that partial melting took place in the tuscan crust at different levels and to varying degrees from the miocene to quaternary producing a continuous alpine granitic layer the known tuscan intrusive bodies and two batholiths below the larderello and mt amiata geothermal fields represent culminations of the alpine granite the rise of the tuscan magmas was closely correlated to a post tortonian tensional tectonics and followed its n e migration tensional tectonics started after the last compressional phase 10 11 ma b p as a consequence of the anticlockwise rotation of italy the opening of the tyrrhenian sea and the swelling of the mantle below southwest tuscany

holocene slip rate for the western segment of the castle mountain fault alaska the western segment of the castle mountain fault poses a significant seismic hazard to the most populated region of south central alaska we identify a previously unrecognized margin of a postglacial outwash channel that is offset right laterally 36 4 m across the western segment of the castle mountain fault this offset occurred after glaciers withdrew from the lowland 11 300 15 380 cal yr b p and after outwash channel margins were cut and stabilized 11 210 13 470 cal yr b p using these ages and the measured separation we obtain a maximum slip rate of 3 0 0 6 mm yr 1 and a minimum slip rate of 2 8 0 7 mm yr 1 these are the first lateral slip rates for the castle mountain fault established by a field measurement based on timing of the most recent earthquake 670 60 yr b p the castle mountain fault could have accumulated an average single event slip of about 1 9 m extremes range from 1 3 to 2 6 m the fault consists of two segments a surface rupturing earthquake likely will be limited to the 62 km long western segment area magnitude regression calculations suggest that such an earthquake on the western castle mountain fault would have a moment magnitude of 6 9 to 7 3

tectonics of the punta bianca promontory insights for the evolution of the northern apennines northern tyrrhenian sea basin the structural setting of the eastern headland of the la spezia gulf punta bianca promontory provides some constraints on the contractional and extensional framework of the northern apennines northern tyrrhenian sea basin geodynamic system and allows a detailed reconstruction of a complex evolutionary path out of sequence thrusting is supposed in the inner side of the chain two different extensional events are identified the older early middle miocene may be related to the imbrication of the deeper metamorphic units of the apenninic thrust wedge younger extension fits very well into an eastward asymmetrical faulting framework related to the opening of the northern tyrrhenian sea basin from the late miocene to the pliocene pleistocene well exposed low angle normal faults developed during this event extensional structures were then overprinted and reactivated by a mainly strike slip regime in the quaternary

seismic depth imaging of a geothermal system in southern tuscany this work represents a case study concerning the application of reflection seismic imaging methods in the context of geothermal exploration our goal is to obtain accurate structural images of a geothermal active area in southern tuscany these images will be required in subsequent studies as the input for geological model building and numerical simulation of the heat transport and fluid flow the target region exhibits great geologic complexity including strong velocity contrasts lateral nearsurface inhomogeneities fracture zones and significant topography those features are typical for a volcanic hard rock environment and pose significant challenges to conventional seismic imaging methodology therefore we apply a sophisticated and robust depth imaging workflow to previously acquired surface seismic data within our workflow we focus on estimating the seismic velocities of the predominant rock units and subsequently carry out kirchhoff pre stack depth migration and fresnel volume migration to obtain high resolution images of the subsurface our results demonstrate that the applied methodology provides a valueable tool for imaging in a complex environment such as a volcano geothermal area in detail the resulting reflector images show the main horizons that delineate the tuscan sedimentary rocks in the target region the images from standard kirchhoff migration can be significantly enhanced by utilizing fresnel volume migration which eliminates migration artefacts and provides a better result moreover we obtain the migration velocities and depths for an important regional reflector known as the k horizon which is of major interest for geothermal characterization

extensional shear zones as imaged by reflection seismic lines the larderello geothermal field central italy the larderello geothermal field is located in the inner northern apennines in an area which has been subject to extension since the early miocene the latest extensional episode pliocene present has resulted in the formation of nw trending nedipping listric normal faults whose geometry is controlled down to f3 km by borehole data in this paper we integrate a new interpretation of seismic reflection lines with existing seismic field and borehole data to analyse the relations among listric normal faults the top of the brittle ductile transition and the migration of geothermal fluids in accordance with previous interpretations we consider the strong reflector k horizon marking the top of the reflective mid lower crust and located at a depth of 3 5 km in the geothermal area to represent the top of the brittle ductile transition its reflectivity most probably derives from the presence of overpressured fluids we identify three main nw trending nedipping extensional brittle shear zones showing listric geometry and soling out in the vicinity of the k horizon the latter appears to be dislocated in correspondence of the soling out of the shear zones these shear zones because of the associated intense fracturing represent the most natural channels of upward migration of geothermal fluids from the magmatic sources located below the k horizon we suggest that these two conclusions that listric normal faults root at or near the brittle ductile transition and that they act as preferential upward migration paths for magmatic fluids may be of general validity for geothermal fields located in extensional settings d 2002 elsevier science b v all rights reserved

fluid flow within the damage zone of the boccheggiano extensional fault larderello travale geothermal field central italy structures alteration and implications for hydrothermal mineralization in extensional settings the neogene extensional province of southern tuscany in central italy provides an outstanding example of fossil and active structurally controlled fluid flow and epithermal ore mineralization associated with post orogenic silicic magmatism characterization of the hydrodynamic regime leading to the genesis of the polysulphide deposit known as filone di boccheggiano hosted within the damage zone of the boccheggiano fault is a key target to assess modes of fossil hydrothermal fluid circulation in the region and more generally to provide inferences on fault controlled hydrothermal fluid flow in extensional settings we provide a detailed description of the fault zone architecture and alteration mineralization associated with the boccheggiano ore deposit and report the results of fluid inclusion and stable oxygen isotope studies this investigation shows that the boccheggiano ore consists of an adularia illite type epithermal deposit and that sulphide ore deposition was controlled by channelling of hydrothermal fluids of dominantly meteoric origin within the highly anisotropic permeability structure of the boccheggiano fault the low permeability structure of the fault core compartmentalized the fluid outflow preventing substantial cross fault flow with focused fluid flow occurring at the hangingwall of the fault controlled by fracture permeability fluid inclusion characteristics indicate that ore minerals were deposited between 280 and 350 c in the upper levels of the brittle extending crust lithostatic pressure in the order of 0 1 gpa abundant vapour rich inclusions in ore stage quartz are consistent with fluid immiscibility and boiling and quartz ore vein textures suggest that mineralization in the boccheggiano ore deposit occurred during cyclic fluid flow in a deformation regime regulated by transient and fluctuating fluid pressure conditions results from this study i predict a strongly anisotropic permeability structure of the fault damage zone during crustal extension and ii indicate the rate of secondary structural permeability creation and maintenance by active deformation in the hangingwall of extensional faults as the major factor leading to effective hydraulic transmissivity in extensional terranes these features intimately link ore grade mineralization in extensional settings to telescoping of hydrothermal flow along the hangingwall block s of major extensional fault zones

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

deformation pattern in the central mediterranean and behavior of the african adriatic promontory abstract the adriatic platform has been described in the literature both as an africa promontory moving in close connection with the main continent and as an independent microplate this evident incongruity is mainly due to the wide spectrum of kinematic hypotheses proposed on the basis of paleomagnetic data and to the fact that the adriatic africa transition is not marked by any clear decoupling fracture or by any interruption of lithological facies along the marginal belts apennines maghrebides and dinarides hellenides in this work it is argued that the counterclockwise rotation of the adriatic plate driven by africa pushing beneath the calabrian arc and southern tyrrhenian may coherently account for all major plio quatemary events in the central mediterranean