facies analysis of a pliocene river dominated deltaic succession siena basin italy implications for the formation and infilling of terminal distributary channels the recent recognition and description of terminal distributary channels in ancient delta front deposits have led to important progress when it comes to understanding delta construction processes the plan view shapes of both modern and ancient river dominated deltas and sediment dispersal within deltas deltaic deposits fed by terminal distributary channels can be observed in the extensive outcrops approximately up to 300 m wide and 50 to 70 m thick in the central sector of the pliocene siena basin in tuscany italy stratigraphic constraints indicate that the deposition occurred in relatively shallow marine settings was not affected by tidal effects and was influenced only locally by wave action as a consequence these rock exposures provide an opportunity to investigate the facies assemblage of an ancient delta complex which was built up almost exclusively as the result of river related processes the studied deltaic succession is composed of vertically stacked parasequence like units which are invariably characterized by the lack of coarse grained distributary channel deposits at the top and an extensive network of terminal distributary channels that controlled the deltaic deposition these deposits were interpreted previously as deep water turbidites this study provides new elements for the correct distinction between hyperpycnal dominated delta fronts and basinal turbidite deposits the terminal distributary channel facies documented in this study are more complex than those investigated in previous research the channels are often passively filled during abandonment phases and not just due to the aggradation and lateral upstream migration of mouth bars as classically proposed moreover the frequent occurrence of mudstone beds just above the basal channel scours may be indicative of an abandonment phase after the channel incision and before its infilling with subsequent implications for the formational and infilling mechanisms of terminal distributary channels furthermore the channel fills are often the result of alternating depositional and erosional phases leading to a complex stratigraphic arrangement

early proterozoic nappe formation an example from sodankyla finland northern baltic shield the central lapland greenstone belt comprises rift related metavolcanic and metasedimentary rocks representing one of the largest supracrustal belts in the baltic shield the sodankyla area in the central part of the belt represents a complex thrust duplex within a nappe overlying belomorian archaean basement and autocthonous luirojoki calc silicate rocks here an early d 1 schistosity is axial planar to at least three coaxial generations of southward verging subhorizontal e w plunging d 1 folds associated with major southwards thrusting d 2 is represented by broad map scale upright ne trending folds in the south and crenulations in the north staurolite grade metamorphism represented by post tectonic andalusite staurolite kyanite assemblages occurred after d 2 folding later d 3 deformation was limited to local nw trending folds and sinistral faults the internal nappe like structure of the central lapland greenstone belt suggests that it represents the foreland of a large collisional complex cored by the lapland granulite 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

driving mechanism of tectonic activity in the northern apennines quantitative insights from numerical modeling 1 it is shown by numerical modeling that the recent deformation pattern observed in the northern apennines mainly characterized by progressive eastward migration and bowing of the belt thrusting activity along its external front and tensional tectonics in the internal area can be reproduced at a first approximation by applying a belt parallel se nw compression to the chain which is simulated as a structural system characterized by a high mechanical strength and decoupled from the surrounding zones the above compressional regime obtained by imposing kinematic boundary conditions to the model causes the outward escape of crustal wedges from the chain in particular the northeastward displacement of the romagna marche umbria units and the counterclockwise rotation and northwestward displacement of the ligurian units this kinematics produces compressional to transcompressional strain along the external front of the chain and tensional to transtensional strain in the internal area in line with the observed features that concern both strain style and orientation of principal strains evidence and arguments supporting the kinematic boundary conditions and the model parameterization adopted in modeling are discussed numerical experiments have also been carried out to evaluate the influence of major features of the model parameterization and boundary conditions we have adopted in modeling and to provide insights into the possible influence of strong decoupling earthquakes in the central apennines on tectonic and seismic activity in the northern apennines

climatic and tectonic signature in the fluvial infill of a late pliocene valley siena basin northern apennines italy abstract incised valleys entirely filled with fluvial deposits are rarely described in the literature and even rarer are accounts of incised valleys whose filling is not driven by relative sea level changes valleys of this type have not been widely recognized in the stratigraphic record because they are likely to occur in areas undergoing intense erosion or to be encased within alluvial deposits with no strong lithologic contrast in this paper an upper pliocene fluvial valley fill encased within shallow marine middle pliocene deposits and pre neogene bedrock eastern siena basin northern apennines italy and accumulated in response to tectonics and climate changes is described the recognition of this fluvial body up to 40 m thick in an incised valley setting is based on its overall geometry lithofacies characteristics gravel composition and fossil content upvalley fill is represented by amalgamated gravels emplaced by heavily sediment laden flows whereas downvalley fill shows a more organized depositional style and consists of two fining upward successions notable is the presence at the top of the lower succession of decameter thick floodplain fines which extend from one valley wall to another and have no fine grained correlatives in the upvalley fill valley incision resulted from a drop in relative sea level arising from late middle pliocene regional uplift stratigraphic and paleontological data constrain valley filling to the late pliocene early pleistocene time span such a filling stemmed from an increase in sediment supply which resulted from the interplay between uplift of the chianti ridge and a climatic change toward humid conditions as recorded in the coeval strata of the adjacent valdarno basin beyond the regional significance an important implication of the case study is that the incision and filling factors need not be genetically related moreover the stratigraphic architecture of the studied fluvial fill is discussed in terms of the relations between sediment supply and sediment storage en route from the source area to the depositional site and their association with tectonic movements specifically the valley wide floodplain fines are thought to record the response of the fluvial system to a tectonic rejuvenation of catchments which modified the valley gradient and promoted upstream gravel storage whereas the overlying gravels manifest the reestablishment of a new equilibrium river profile

superimposed brittle structures in the late orogenic extension of the northern apennine results from the carrara area alpi apuane nw tuscany this paper presents data on the geometric and kinematic features of brittle faults in the carrara area alpi apuane nw tuscany italy providing the first paleostress determination in a key region of the northern apennine meso and microfault analyses point out the presence of brittle structures formed during a polyphase deformation and characterized by an older stage ds1 with an interfering system of strike slip and normal faulting followed by the ds2 stage developing normal faults locally showing apenninic trend nw se as a whole the brittle structures are related to the late pliocene middle pleistocene evolution of the thyrrenian side of the northern apennine

the structure of the moho in the northern apennines evidence for an incipient slab tear fault abstract this study investigates the geometry of the crust mantle boundary along the northern apennines italy and its relationship to the tectonic evolution of a retreating subduction system using receiver function analysis from teleseismic records the moho depth was computed beneath 26 seismic stations located in key positions along the orogen the results show a relatively shallow 20 km moho in the tyrrhenian side as expected from an extended overriding plate and a deeper moho 40 km in the subducted adriatic plate sw dipping 15 45 beneath the chain stations deployed on the northeastern edge of the plio quaternary extensional basins provide maximum moho depth estimates thus supporting the hypothesis that these basins define the zone where the two plates separate at depth in addition an abrupt change in the moho depth is recognized along strike of the orogen attributed to a 45 km wide trench normal deformation zone that crosses the northern apennines in the proximity of the livorno sillaro lineament this zone is interpreted as an incipient lithospheric tear fault which accommodates varying rates of trench retreat along the length of the subduction zone

no tectonic rotation of the tuscan tyrrhenian margin italy since late messinian extensive paleomagnetic sampling of 38 late miocene and pliocene sites has been carried out in the western tuscan basins in italy these basins are located along the tyrrhenian margin and the studied formations were deposited at the same time as the opening of the tyrrhenian sea the laboratory analyses show that in most of the sites pseudo single domain magnetites are the main magnetic carrier the paleomagnetic data obtained from 27 suitable sites indicate that the tuscan tyrrhenian margin has not been affected by significant regional rotation since at least the late messinian early pliocene about 5 5 m y these data demonstrate that the rotations previously measured in the meso cenozoic units of the apennines and of the apulia foreland cannot be directly related to the late messinian pliocene phases of rifting in the tyrrhenian sea moreover the data presented here conflict with published results from coeval formations in the apennines and sicily in areas subjected to strong thrusting and shortening in these areas the rotations control the orientation of the main compressional structures and give rise to the typical arcuate shape of the apenninic chain we suggest that the tectonic evolution of the northern tyrrhenian sea apenninic chain system involved thrusting and shortening of the external eastern domains with rotations of the allochthonous units followed by gravitational collapse of the western sector this second phase involved no tectonic rotation of the newly formed extensional basins

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

heterogeneous brittle ductile deformation at shallow crustal levels under high thermal conditions the case of a synkinematic contact aureole in the inner northern apennines southeastern elba island italy abstract we present an example of interaction between magmatism and tectonics at shallow crustal levels in the late miocene the metamorphic units of the eastern elba island northern apennines were intruded at very shallow crustal levels by a large pluton 60 km 2 with the development of an hectometre sized contact aureole defined by growth of low pressure high temperature mineral assemblages p max max 650 c structural data show that the contact aureole is associated with a km sized antiform of the foliation and by several metre to decametre thick high strain domains consisting of strongly foliated rocks containing synkinematic ht lp mineral assemblages and ductile shear zones of variable thickness these shear zones are characterized by a mylonitic foliation variably overprinted by cataclasis quartz microfabrics indicate that the dynamic crystallization processes progressively changed from grain boundary migration associated with the thermal peak of contact metamorphism to subgrain rotation and bulging recrystallization the latter mostly associated with the cataclastic overprint these transitions of recrystallization mechanisms in quartz are related to a progressive decrease of temperature during deformation deformation accompanied the development and cooling of the contact aureole which recorded the switch from high temperature ductile to low temperature brittle conditions the geometry of the studied deformation structures is consistent with the constraints of the regional tectonic evolution and its local interaction with the localized and transient thermal anomaly related to the coeval emplacement of igneous rocks

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

vein development during folding in the upper brittle crust the case of tourmaline rich veins of eastern elba island northern tyrrhenian sea italy abstract detailed structural analysis of tourmaline rich veins hosted in the contact aureole of the 6 ma porto azzurro granite in southeastern elba island northern tyrrhenian sea is presented using geometric features of the veins the physical conditions at the time of vein formation are estimated namely the stress ratio 2 3 1 3 driving stress ratio r p f 3 1 3 and fluid overpressure p o p f 3 two vein sets a veins and b veins have been recognized based on orientation and thickness distributions and infilling material analysis of vein pole distributions indicates 0 57 and r 0 24 for the a veins and 0 58 and r 0 47 for the b veins and fluid pressures less than the intermediate stress magnitude analysis of geometric features of the veins gives estimated fluid overpressures of between 16 mpa a veins and 32 mpa b veins we propose a model for the tectonic environment of vein development in which formation of secondary permeability in the deforming thermal aureole of the porto azzurro pluton was controlled by ongoing development of fracture systems in the hinge zone of a regional nnw sse trending fold that favored transport and localization of hydrothermal fluids

alpine tectonothermal evolution of the tuscan metamorphic complex in the larderello geothermal field northern apennines italy on the internal tyrrhenian side of the northern apennines high heat flow and geothermal gradient in the larderello geothermal field are evidence of a large scale thermal anomaly related to the emplacement of a large batholith of pliocene age extending from the upper to middle crust these intrusions relate to the miocene to recent northern apennines magmatism which developed as a result of crustal extension and upwelling of the asthenosphere at the base of the thinned crust in the subsurface of the larderello geothermal field medium and high grade metamorphic rocks tuscan metamorphic complex cored in several geothermal wells have previously been considered to be variscan basement new structural and petrographic data on these metamorphic rocks indicate an alpine tectonometamorphic history and provide evidence that medium to high grade mineral assemblages are related to pliocene thermal metamorphism centred on intrusions at shallow depth these data allow a new interpretation of the tuscan metamorphic complex as a tectonic wedge of the late palaeozoic triassic units and in particular highlight the considerable extent of pliocene thermal metamorphism and hydrothermal circulation as a result of convective cooling of intrusions

the dynamics of back arc extension an experimental approach to the opening of the tyrrhenian sea the e w opening tyrrhenian sea developed after the cretaceous palaeogene alpine collision nearly perpendicular to the motion of the african plate as a back arc of the adria ionian westward subduction three driving mechanisms have been proposed to explain the dynamic evolution of the tyrrhenian apennine system 1 the northward indentation of the african plate 2 the retreating subduction of the adria ionian lithosphere and 3 the gravitational collapse of the alpine post collisional wedge in order to define the relative contribution of each of these mechanisms in the neogene dynamic of the tyrrhenian apennine system we performed 3 d laboratory experiments in which we simulated a retreating subduction process in a compressional regime oriented perpendicularly to the direction of subduction in this framework we also tested the influence of the gravitational collapse of the overriding plate experiments were constructed using dry sand and silicone putties to simulate brittle upper crust and ductile lower crust upper mantle respectively these layers floated on a high density low viscosity glucose syrup which simulated the asthenosphere the main conclusion of our experiments is that large scale continental extension similar to that observed in the tyrrhenian area could be reproduced perpendicular to the shortening direction induced by the indentation of the african plate in this framework extensional processes are indeed possible if the trench retreat velocity is higher than the rate of shortening induced by the advancing african plate our experimental results indicate that this high trench retreat velocity could be explained by the coexistence of the gravitational collapse of the post alpine wedge with a slab pull process linked to the retreating subduction of the adria ionian plate while the first mechanism is predominant in the northern tyrrhenian area the second one seems to be important in the latest stage of extension and oceanic accretion of the southern tyrrhenian area

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

dating of deformation phases using k ar and 40ar 39ar techniques results from the northern apennines abstract paleozoic to oligocene metasedimentary rocks present in the alpi apuane region of the northern apennines italy have been sequentially deformed during a tertiary progressive deformation in an attempt to date the individual deformation episodes over 50 conventional k ar and 1140 ar 39ar incremental gas release analyses have been carried out on fine grained white micas separated from samples whose structural settings were well known mineralogy x ray diffractometry and thin section analyses indicate that the constituent muscovite and phengite formed under metamorphic conditions of 3 4 kbars and 300 400 c during all deformational phases pre existing micas were variably crenulated during each subsequent deformational phase both k ar and 40ar 39ar analyses were carried out on 0 6 2 m 2 6 m and 6 20 m size separates of the phengitic white mica although the k ar apparent ages range from 11 to 27 ma and are consistent with available stratigraphic constraints the 40ar 39ar age spectra display variable internal discordancy these isotopic data indicate that 1 both the k ar and 40ar 39ar total gas ages decrease as the degree of crenulation increases 2 the k ar and 40ar 39ar total gas ages decrease as grain size decreases 3 for each sample characteristics of the 40ar 39ar age spectra depend upon grain size with fine sizes yielding discordant patterns which systematically increase in apparent age from low to high temperature and 4 phengitic micas associated with earliest structures yield generally older ages than micas associated with later structures the isotopic results are interpreted to indicate that the major deformation phase d1 occurred at approximately 27 ma with subsequent pulses ending by c 10 ma these results may be combined with finite strain data to suggest that the region was deformed at strain rates between 10 15 and 10 14 s 1 a 27 ma age indicates mid oligocene initiation of plate tectonic activity in the western mediterranean and concomitant deformation in the northern apennines

fault plane solutions and seismicity of the italian peninsula abstract a new fault plane solution map of the italian peninsula is presented in this paper the earthquakes analyzed are included in the period 1905 1980 with magnitudes ranging 4 7 75 earthquakes are located in the crust while 31 are related to the deep and intermediate zone of the calabrian arc the large seismic events of the italian peninsula are generally associated with normal faulting while strike slip motion is mostly related to small earthquakes located along lateral segments of the mountain chain the deep and intermediate earthquakes of the tyrrhenian sea indicate predominant down dip compression and strike slip motion at the boundaries of this benioff zone this last is interpreted as a remnant of a subduction zone active since oligocene extending to 500 km depth with a very small lateral size about 300 km the present tectonics of this benioff zone is strongly conditioned by the lateral bending more so than the gravitational sinking process the coexistence of thrust and normal faulting motion associated to the earthquakes within a few tens of kilometers of each other seems to be explained by the strong lateral inhomogeneities of the crustal rocks present in this region more so than to the depth of the seismogenetic zone and the nature of the faulting process

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

shock effects on the k ar system of plagioclase feldspar and the age of anorthosite inclusions from north eastern minnesota abstract artificial shock pressures up to 52 5 gpa have no influence on the k ar system of plagioclase feldspar the 40ar 39ar analysis of feldspar labradorite an67 from anorthosite of north eastern minnesota shocked up to 45 gpa in vacuo to prevent massive entrapment of atmospheric argon shows that the age spectra and the argon diffusion properties remain unaltered similar feldspar samples labradorite an51 from nain labrador shocked in air up to 52 5 gpa and dated by the conventional k ar method also yield the same age as unshocked samples but with a higher atmospheric argon contribution the minnesota anorthosite has an 40ar 39ar age of 1075 10 m y no information on a possible previous history of the anorthosite became apparent

rheology of the northern apennines lateral variations of lithospheric strength abstract a thermorheological wsw ene profile along the northern apennines is presented the variations in rheology are estimated using two different models the conventional model in which only frictional sliding and power law creep are taken into account and a new model in which in addition to the previous two mechanisms a high pressure brittle fracture mechanism is included upper and lower bounds for the rheology are considered a hard case where the lower crust is mafic granulite and the lithospheric mantle is dry peridotite and a soft case where the lower crust is felsic granulite and the lithospheric mantle is wet peridotite important differences in lithospheric rheological structure are inferred between the western and the eastern sectors of the chain in the former a creme brulee structure generally applies in the latter a jelly sandwich structure applies these rheological models therefore are not alternative but end members of a continuous spectrum of rheological behaviours

recent and active tectonics of the external zone of the northern apennines italy we present a comprehensive study of the recent and active tectonics of the external part of the northern apennines italy by using morphotectonic geological structural and stratigraphic analysis compared with the current seismicity of the region this analysis suggests that the external part of the northern apennines is characterised by presence of three major systems of quaternary compressive structures corresponding to 1 the apenninic watershed 2 the apennines po plain margin pede apenninic thrust front and 3 the emilia ferrara and adriatic fold systems buried below the po plain geological data and interpreted seismic sections indicate a roughly n s quaternary deformation direction with rates 2 5 mm year the shortening decreased since the pliocene when our data indicate compression in a nnw sse direction and rates up to 7 mm year the trend and kinematics of the structures affecting the apennines po plain margin and the po plain subsoil fit well the pattern of the current seismicity of the area as well as recent gps and geodetic levelling data pointing to a current activity of these thrust systems controlled by an overall compressive stress field close to the apenninic watershed earthquake focal mechanisms indicate that shallow extension is associated to deep compression the extensional events may be related to a secondary extensional stress field developing on the hangingwall of the thrust system affecting the apenninic watershed alternatively this thrust system may have been recently deactivated and overprinted by active normal faulting deeper compressive events are related to the activity of both a major basement thrust that connects at surface with the pede apenninic thrust front and a major moho structure

the tectonic significance of italian magmatism an alternative view to the popular interpretation the tyrrhenian rift zone has been the site of widespread magmatism since late tortonian times a pronounced asymmetrical distribution reflecting the tectonic structure characterizes italian magmatism sodic basalts occur on the western tyrrhenian flank and transitional morb basalts occur in the tyrhenian sea the eastern flank however is characterized by k alkaline and hk to ultra alkaline e g carbonatites and melilitites rocks major trace elements and isotopic compositions allow two major magmatic lineages to be identified one relating to a non radiogenic basaltic end member and the other to a mantle end member enriched in ca with high lile hfse ratio and high sr isotopic ratios their mantle sources are located within the lithosphere thermal boundary layer tbl and the metasomatized phlogopite carbonate asthenosphere at the base of the tbl respectively the composition and spatial distribution of volcanism and relative mantle sources tend to map the geometry of the lithospheric mantle and to define a pronounced increase in depth from less than 60 km to about 100 km across the boundary between the thinned tyrrhenian lithosphere and the adriatic lithosphere a mechanism of intra continental passive rifting which drives mantle upwelling is sufficient to satisfy the petrological and geochemical constraints and the observed tectonic environment without requiring a subduction plane

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

structural styles chronology rates of deformation and time space relationships in the umbria marche thrust system central apennines italy structural interpretation of geological and geophysical data available for the central apennines italy allowed us to draw balance and restore three geological profiles across the external zones of the umbria marche thrust system and to evaluate the timing and rates of deformation in a roughly 4 ma time window from late messinian to late pleistocene time from this data set we established a general correlation between spacing l and thickness d of the thrust sheets which was used as a depth correction factor for deriving local versus regional depths to the sole thrust and a time space relationship between the closing time of activity of each thrust and the distance x from a reference point within the system

response of meltwater runoff to air temperature fluctuations on keqikaer glacier south slope of tuomuer mountain western china flow records of meltwater runoff provide information about the movement of water through the ice and about glacial ablation this study indicates that the lag time required for a maximum correlation between daily discharge and air temperature and the sensitivity of meltwater response to air temperature changes during the ablation period for different proportions of the base flow to examine how glaciers respond to climatic changes and the hydrological characteristics of the large glaciers in the tuomuer mountain area western china observations have been undertaken in this region since june 2003 by means of correlation and cross spectral analysis the relationship between air temperature and meltwater runoff in different months of the ablation period may september on keqikaer glacier in 2004 has been evaluated data have been selected from the 1st to the 30th for every month and the calculated hourly discharges of the meltwater runoff for each day were utilized from these data we conclude that for keqikaer glacier the meltwater runoff has a greater sensitivity to air temperature in may july and august than in june and september however the lag time is shorter in june july and august than it is in may and september

surface movements in bologna po plain italy detected by multitemporal dinsar abstract we studied the surface deformations affecting the southeastern sector of the po plain sedimentary basin in particular the area of bologna to this aim an advanced dinsar technique referred to as dinsar sbas small baseline subset has been applied this technique allows monitoring the temporal evolution of a deformation phenomenon via the generation of mean deformation velocity maps and displacement time series from a data set of acquired sar images in particular we have processed a set of sar data acquired by the european remote sensing satellite ers sensors and compared the achieved results with optical levelling measurements assumed as reference the surface displacements detected by dinsar sbas from 1992 to 2000 are between 10 mm year in the historical part of bologna town and up to 59 mm year in the ne industrial and agricultural areas former measurements from optical levelling referred to 1897 show 2 3 mm year vertical movements this trend of displacement increased in the second half of the 20th century and the subsidence rate reached 60 mm year we compared the more recent levelling campaigns in 1992 and late 1999 and dinsar results from 1992 to 1999 the standard deviation of the difference between levelling data projected onto the satellite line of sight and dinsar results is 2 mm year this highlights a good agreement between the measurements provided by two different techniques the explanation of soil movements based on interferometric results ground data and geological observations allowed confirming the anthropogenic cause surface effect due to the overexploitation of the aquifers and highlights a natural tectonic subsidence

cover thrust reactivations related to internal basement involvement during neogene quaternary evolution of the northern apennines up to recently the neogene quaternary evolution of the northern apennines italy has been described by the classic model of a migrating eastward compressive external front with an extensional regime in the back areas connected with the tyrrhenian basin formation however in the last few years new structural data have been collected in the internal marine and continental episutural basins and in the external exposed thrust belt a complex structural evolution has now been reconstructed with coeval main tectonic phases that affect both areas with stress field change four main tectonic phases have been identified since late tortonian times these are dated as messinian late pliocene middle and late pleistocene the thrust belt has a complex evolution detected in a wide external area of the chain after the first emplacement of the main thrust sheets with reactivations and out of sequence thrusting these reactivation phases fit very well with the compressive phases affecting the sediments of the internal basins suggesting a direct relationship within a single evolutive model the increased knowledge of the deep structure of the northern apennines through geophysical and subsurface data acquired in the last few years indicates the basement involvement at least for the internal side of the northern apennines this basement involvement also played an important role in the tectonic evolution of the external sector of the apennines in this paper a new model is proposed that integrates field data geophysical evidence and geodynamic constraints the thrust reactivations and the out of sequence structures of the external area are related to internal crustal thrust activity the deformed sediments of the neogene quaternary basins are dating the thrust activity all the evidences point to a late neogene rejuvenation of the tectonic evolution but some inferences can be drawn on the development of the foredeep

the tectonic expression slab pull at continental convergent boundaries examination of five thrust belt systems developed at continental subduction boundaries suggests that they comprise two distinct groups that display pronounced and systematic differences in structural style topographic elevation denudation metamorphism postcollisional convergence and foredeep basin geometry and facies the distinctive geological features developed within each thrust belt group appear to be causally linked to the relative rates of subduction and convergence via the magnitude of horizontal compressional stress transmitted across the subduction boundary at subduction boundaries where the rate of overall plate convergence is less than the rate of subduction termed here retreating subduction boundaries the transmission of horizontal compressive stress across the plate boundary is small and regional deformation of the overriding plate is by horizontal extension the tectonic expression of these retreating subduction boundaries includes topographically low mountains little erosion or denudation low grade to no metamorphism little to no involvement of crystalline basement in shortening little to no postcollisional convergence anomalously deep foredeep basins and a protracted history of flysch deposition within the adjacent foredeep basin analysis of deflection and gravity data across three retreating subduction boundaries apennine carpathian and hellenic systems shows that subduction is driven by gravitational forces acting on dense subducted slabs at depths between about 40 and 80 km carpathians 50 and 150 km apennines and 50 and 250 km hellenides the total mass anomalies represented by the slabs are approximately 3 1012 6 1012 and 12 1012 n m respectively the slabs are partially supported by flexural stresses transmitted through the subducted lithosphere to the foreland and partially supported by dynamic viscous stresses in the asthenosphere at subduction boundaries where the rate of overall plate convergence is greater than the rate of subduction termed here advancing subduction boundaries the transmission of horizontal compressive stress across the plate boundary is large and regional deformation of the overriding plate is by horizontal shortening the tectonic expression of these advancing subduction boundaries includes topographically high mountains antithetic thrust belts large amounts of erosion and denudation exposure of high grade metamorphic rocks at the surface extensive deformation of crystalline basement to midcrustal depths protracted postcollisional convergence tens of millions of years and a protracted history of molasse deposition within the adjacent foredeep basins analysis of gravity and deflection data across two advancing subduction boundaries developed within the continental lithosphere western to eastern and southern alps and himalayas shows that the thrust sheets have been translated for great distances over the foreland lithosphere relative to the point at which the subduction forces are applied thus obscuring any flexural and gravity signals from the subducted slab however it appears that far field stresses presumably related to global plate motions drive most of the convergent motion across these subduction boundaries the concept that orogenic belts formed above retreating subduction boundaries have recognizable tectonic signatures that differ from those of orogenic belts formed above advancing subduction boundaries suggests that it may be possible to interpret the plate boundary settings in which ancient orogenic belts evolved appendix b is available with entire article on microfiche order from the american geophysical union 2000 floridaavenue n w washington d c 20009 document t92 004 2 50 payment must accompany order

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

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

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

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

mare versus lago mare marine fishes and the mediterranean environment at the end of the messinian salinity crisis during the late messinian c 5 5 ma ago after evaporitic sedimentation and before the pliocene flooding the mediterranean recorded a major environmental change testified by deposition of non marine sediments of the so called lago mare facies such deposits are widespread in the mediterranean basin usually characterized by molluscs and ostracodes of brackish affinity here we present marine fish remains from lago mare deposits of central italy the fossils represented by both articulated skeletons and otoliths were collected from nine stratigraphic horizons of the upper portion of the lago mare sequence of cava serredi tuscany marine euryhaline fishes strongly dominate the assemblages but fully marine stenohaline fishes belonging to the families myctophidae and bythitidae are also present the fossil fish remains are associated with classic lago mare ostracodes and molluscs these fossil fishes clearly demonstrate that normal marine conditions were present at least during the upper interval of the lago mare event implying that the marine refilling of the mediterranean was intra messinian rather early pliocene we argue in favour of the necessity of a new palaeoenvironmental interpretation for the post evaporitic messinian of the mediterranean

the terminology of structures in thrust belts abstract a review of structures and geometric relationships recognized in thrust belts is presented a thrust is defined as any contractional fault a corollary being that thrusts must cut up section in their transport direction flats are those portions of a thrust surface which were parallel to an arbitrary datum surface at the time of displacement and ramps are those portions of thrusts which cut across datum surfaces ramps are classified on the basis of their orientation relative to the thrust transport direction and whether they are cut offs in the hangingwall or footwall of the thrust lateral variations in the form of staircase trajectories are joined by oblique or lateral ramps which have a component of strike slip movement an array of thrusts which diverge in their transport direction may form by either of two propagation models these are termed piggy back propagation which is foreland directed and overstep propagation which is opposed to the thrust transport direction an array of thrust surfaces is termed an imbricate stack and should these surfaces anastamose upwards a duplex will result the fault bounded blocks are termed horses a duplex is bounded by a higher roof thrust and a lower floor thrust the intersection of any two thrust planes is termed a branch line thrusts can be classified on the basis of their relationship to asymmetric fold limbs which they cut a further classification arises from whether a particular thrust lies in the hangingwall or footwall of another one the movement of thrust sheets over corrugated surfaces or the local development of thrust structures beneath will fold higher thrust sheets these folds are termed culminations and their limbs are termed culmination walls accommodation of this folding may require movement on surfaces within the hangingwall of the active thrust these accommodation surfaces are termed hangingwall detachments and they need not root down into the active thrust this category of detachment includes dip slip hangingwall drop faults which are developed by differential uplift of duplex roofs and out of the syncline thrusts which develop from overtightened fold hinges back thrusts as well as forming as hangingwall detachments may also form due to layer parallel shortening above a sticking thrust or by rotation of the hangingwall above a ramp

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

the zuccale fault elba island italy a new perspective from fault architecture the zuccale fault central eastern elba island has been regarded since the 1990s as a low angle normal fault that records neogene crustal extension in the inner tyrrhenian side portion of the northern apennines the flat lying attitude of the fault zone and the strong excision of thick nappes were the main reasons for this interpretation previous structural and petrographic studies have focused primarily on the fault rocks themselves without map scale investigation of the structural setting and deformation structures in the hanging wall and footwall blocks furthermore despite the complex history proposed for the zuccale fault the timing of deformation has not yet been constrained by radiometric age data we present the findings of recent geological studies on eastern elba island that provide significant new insight on the nature and tectonic significance of the zuccale fault we document in detail the architecture of breccias and cataclasites that comprise the zuccale fault our new observations are consistent with a purely brittle deformation zone that crosscuts older early middle and late miocene regional and local tectonic structures the activity on the fault postdates emplacement of the late miocene porto azzurro pluton and it displaces a previously formed nappe stack 6 km eastward without any footwall exhumation or hanging wall block rotation these new data raise questions about the development of misoriented faults in the upper crust

symmetry of pebble deformation involving solution pits and slip lineations in the northern alpine molasse basin abstract deformation features on pebbles of the alpine molasse basin are most clearly developed in carbonate components ductile distortion is small most of the pebbles moved against each other to produce solution pits and slip lineations on the pebble surfaces the complete lineation field has a triaxial geometry from a compressional axis of divergence with maximum solution fields of diverging lineations extend to meet at a plane of convergence their ends bend away from an intermediate axis towards an extensional axis of convergence the strain symmetry is pure shear for orthogonal lineation field axes uniaxial compression and extension representing special cases the angle between the divergent and the convergent axes decreases from 90 to 0 with the transition from pure to simple shear for molasse pebbles angles between 90 and 60 were usually observed regional compression developed perpendicular to the alpine structures and parallel to bedding with increasing deviations near the alpine border zones are recorded of vertical and horizontal extension and of compression perpendicular to bedding and horizontal extension perpendicular to the rhinegraben existing at the northern border of the molasse basin

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

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

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

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

the miocene pliocene boundary in the mediterranean area new insights from a high resolution micropalaeontological and cyclostratigraphical study cava serredi section central italy abstract tuscany central italy is a key area for studying the messinian salinity crisis and overlying lower pliocene deposits due to the high number and excellence of the outcrops although the miocene pliocene transition is well exposed and suitable for detailed analyses a high resolution integrated stratigraphic study of such a crucial time span for the geological history of the mediterranean has never been attempted in the fine basin central tuscany the cava serredi section is one of the best exposures of the upper messinian lower pliocene transition of the northern apennines the miocene pliocene boundary corresponds to a surface separating thinly laminated lacustrine lago mare marls from homogeneous circalittoral to upper bathyal marly clays detailed quantitative micropalaeontological analyses have been performed on 111 samples from the 22 m thick lower pliocene succession they resulted in the improvement of the biostratigraphic resolution of the basal zanclean interval due to the recognition of several chronologically constrained bioevents typical of the mediterranean region and based on benthic and planktonic foraminifera and calcareous nannofossils moreover to unravel cyclical patterns of deposition and given that the investigated succession shows no evident lithological pattern micropalaeontological analyses have been coupled with calcium carbonate content variations the latter revealed more regular fluctuations which are especially evident if the exclusive contribution of the planktonic foraminifer fraction p caco 3 is considered spectral analysis of the caco 3 curve indicates that sedimentation occurred under the control of earth s precession this datum is also confirmed by the cyclical patterns of neogloboquadrina acostaensis and sphenolithus spp among foraminifers and nannofossils respectively according to the proposed cyclostratigraphic and astrochronological reconstruction the lower pliocene interval of the cava serredi section consists of eight precession controlled cycles ranging from the i cycle 510 5 33 ma to the i cycle 494 5 16 ma finally the comparison with other astronomically calibrated sections including the zanclean gssp eraclea minoa sicily allowed us to prove the completeness of the basal zanclean interval of the study section and to state that pliocene re flooding after the messinian salinity crisis occurred synchronously with respect to other deeper sectors of the mediterranean basin

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

strain rates in northwestern italy from spatially smoothed seismicity 1 this work presents seismic strain rate maps for the western alps and northern apennines northern italy as derived from an earthquake catalog collecting both historical and instrumental data strain rates are calculated on the basis of the rate of seismic moment release using the anderson method unlike previous applications which determined the total strain rate associated with specific seismogenic sources we have employed an innovative zoneless approach based on a spatially smoothed seismicity method in addition a monte carlo simulation procedure is applied to allow for uncertainty in the input data e g magnitude to moment conversion seismogenic thickness maximum earthquake magnitude strain rate maps are developed by summing the moments of the earthquakes reported in the catalog and by using two different earthquake recurrence relations our results indicate that deformation rates are quite high ranging from about 2 to 12 10 9 yr 1 in the northern apennines and from 0 5 to 6 10 9 yr 1 in the western alps these values however are 1 order less than those derived from global positioning system measurements suggesting that a portion of the recent deformation in northwestern italy is related to aseismic processes the discrepancies between seismic and geodetic strain rates may also indicate that the record of seismicity may not provide a sufficient time window for assessment of secular rates of moment release or secular deformation rates and rates of recurrence of large magnitude earthquakes in the study area

fault sourced alluvial fans and their interaction with axial fluvial drainage an example from the plio pleistocene upper valdarno basin tuscany italy abstract the present study deals with the fault sourced alluvial fan deposits of the plio pleistocene upper valdarno basin northern apennines italy different phases of alluvial fan aggradation progradation and backstep are discussed as possible effects of the interaction among fault generated accommodation space sediment supply and discharge variations affecting the axial fluvial drainage the upper valdarno basin located about 35 km se of florence is filled with 550 m palustrine lacustrine and alluvial deposits forming four main unconformity bounded units i e synthems the study alluvial fan deposits belong to the two uppermost synthems montevarchi and torrente ciuffenna synthems and are early to middle pleistocene in age these deposits are sourced from the fault bounded ne margin of the basin and interfinger with axial fluvial deposits alluvial fan deposits of the montevarchi synthem consist of three main intervals i a lower interval which lacks any evidence of a depositional trend and testify balance between the subsidence rate i e fault activity and the amount of sediment provided from the margin ii a coarsening upward middle interval pointing to a decrease in subsidence rate associated with an augment in sediment supply iii a fining upward upper interval locally preserved documenting a phase of tectonic quiescence associated with a progressive re equilibration of the tectonically induced morphological profile the basin scale unconformity which separates the montevarchi and torrente ciuffenna synthems was due to the entrance of the arno river into the basin as consequence of a piracy this event caused a dramatic increase in water discharge of the axial fluvial system and its consequent embanking such an erosional surface started to develop in the axial areas and propagated along the main tributaries triggering erosion of the alluvial fan deposits alluvial fan deposits of the torrente ciuffenna synthem accumulated above the unconformity during a phase of tectonic quiescence and show a fining upward depositional trend this trend was generated by a progressive decrease in sediment supply stemming out from upstream migration of the knickpoints developed during the embanking of the axial system

late pliocene quaternary evolution of outermost hinterland basins of the northern apennines italy and their relevance to active tectonics abstract we examine the tectonic evolution and structural characteristics of the quaternary intermontane mugello casentino and sansepolcro basins in the northern apennines fold and thrust belt these basins have been classically interpreted to have developed under an extensional regime and to mark the extension compression transition the results of our study have instead allowed framing the formation of these basins into a compressive setting tied to the activity of backthrust faults at their northeastern margin syndepositional activity of these structures is manifested by consistent architecture of sediments and outcrop scale deformation after this phase the mugello and sansepolcro basins experienced a phase of normal faulting extending from the middle pleistocene until present basin evolution can be thus basically framed into a two phase history with extensional tectonics superposed onto compressional structures analysis of morphologic features has revealed the occurrence of fresh fault scarps and interaction of faulting with drainage systems which have been interpreted as evidence for potential ongoing activity of normal faults extensional tectonics is also manifested by recent seismicity and likely caused the strong historical earthquakes affecting the mugello and sansepolcro basins qualitative comparison of surface information with depth converted seismic data suggests the basins to represent discrete subsiding areas within the seismic belt extending along the axial zone of the apennines the inferred chronology of deformation and the timing of activity of normal faults have an obvious impact on the elaboration of seismic hazard models

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

neogene to quaternary rifting and inversion in corsica retreat and collision in the western mediterranean 1 stratigraphic structural and fission track data have been integrated in order to unravel the neogene to quaternary tectonic evolution of northeastern corsica results indicate that during early to middle miocene the study area was affected by a rapid cooling at low temperatures accompanied by exhumation and rifting basin inversion occurred during the tortonian again followed by extension in the messinian to early pliocene compressional deformations are finally recorded by early pliocene to quaternary deposits alternating rifting and inversion events are recorded not only in northeastern corsica but also in many peri tyrrhenian regions this alternation can be explained in terms of intraplate propagation of the compressional stress related to the africa europe convergence and to a discontinuous slab retreat along the apennine subduction system a pause in the slab retreat implies a break of the back arc extension in the upper plate and it allows a temporary propagation of africa europe compression

fluid seepage variability across the external northern apennines italy structural controls with seismotectonic and geodynamic implications abstract the relations between fluid seeps and tectonic structures have been targeted in some key areas of the axial sector and partly at the edge of the exposed northern apennines pede apennine margin in the axial zone fluid seepage is dominated by methane venting which may occur in the form of dry seeps or associated with mineral springs surface venting is linked to the presence of foreland dipping normal faults or related to reservoirs localised at inactive anticlines the pede apennine margin is instead dominated by thrusting and mud volcanism the two different categories of fluid seepage appear strongly coupled to the dissimilar stress fields compressional or extensional operating in these sectors pressure data inferred from deep wells delineate an overall fluid pressure increase from the axial zone toward the pede apennine margin possibly as a result of the growth of tectonic compaction in this direction the increase of fluid pressure at the pede apennine margin is thus interpreted as the primary control on the transition from dry vents to mud volcanism the intimate association between seepage modes and distinct tectonic structures involves relevant consequences on fluid fault interactions and seismotectonics and also shows connections with processes dictating the internal deformation of evolving fold and thrust belts

a sagging along the eastern chianti mts italy abstract a deep seated gravitational slope deformation dgsd affects the eastern side of the chianti mts ridge it develops in an n s to nw se direction and is 10 km wide and 3 4 km long this area corresponds to the eastern side of a main antiform characterised by east verging folds and thrusts involving bedrock of the mesozoic paleogene tuscan units particularly sandstones containing interlayered highly fractured and deformed ligurian rocks shales and limestones with olistostromes the foot of the slope is characterised by tilted plio pleistocene deposits unconformably sealing the bedrock structures as folds thrusts and faults the most significant morphological features are a main escarpment trenches several secondary and counter slope escarpments that together indicate large scale gravitational phenomena the main escarpment is responsible for the headward retreat of the slope and is deeply segmented by numerous arcuate niches that reveal differential movements of single blocks the dgsd is also dissected by sw ne trending streams that often deepen inside the n s trenches minor landslides due to local instability are also present at the foot of the slope the older continental pliocene deposits of the upper valdarno basin crop out although tilted by tectonic movements the deposits have not been severely affected by gravitational deformations this indicates that the movement is a typical sagging a large landslide at an embryonic stage affecting the upper part of the slope but not reaching the valley bottom the deformations are absorbed in the rock mass which is also partially drained by stream incision that prevents high pore pressure the occurrence of down slope and down movement facing escarpments and up slope and up movement facing counter slope escarpments indicate a sagging characterised by a listric spoon shaped geometry the dgsd has a style similar to crustal extensional tectonics such as morton and black s crustal attenuation model although few chronological indications of movements are present the fact that late pleistocene debris deposits widespread in the northern and central apennines are not found at the contact between the escarpment and the trenches suggests a post glacial activity for at least part of the movements recognizing embryonic stage collapse is of primary importance in assessing geological hazard and risk because rapid evolution and collapse could follow

new data on the paleogeography of southern tuscany italy since late miocene time in order to add new data to the knowledge of the paleogeography of southern tuscany and the tuscan shelf a multidisciplinary study on the petrology and distribution of magmatic clasts of the widely exposed messinian pliocene and quaternary sediments in southern tuscany was carried out the magmatic clasts consist of porphyric aplites and subordinate granite porphyries which derive from eroded subvolcanic acidic bodies the porphyric aplite clasts were analyzed in detail to define their textural petrographic and chemical major and trace elements sr and nd isotopic composition features the porphyric aplite clasts show strong affinities with the 8 4 7 9 ma old capo bianco aplite whereas the granite porphyry clasts have affinities with the portoferraio porphyry ca 8 ma which intruded the cretaceous and paleogene flysch units and the ophiolitic unit in central western elba island northern tyrrhenian sea the present outcrops of the capo bianco aplite in central elba island cannot be considered as the source rock for the late messinian gravels because at that time such capo bianco aplite located at the lower portion of the laccolitic stack was there buried at several kilometers depth however other capo bianco like aplitic bodies outcropped during the latest miocene in the host rocks above and also around the 6 8 ma m capanne pluton in the western elba areas the exposure of such bodies was made possible by the activation of the central elba detachment fault cef due to the uplift of the m capanne pluton this uplift displaced a significant portion of the cover including the upper portion of the laccolithic stack of the granitoid body at about 6 7 ma thus allowing the erosion of the lower part of the laccolith complex made up of the capo bianco aplite and of the portoferraio porphyry and leaving still buried the m capanne pluton the paleogeographic picture of southern tuscany arising from the collected evidences is the following during late messinian the clasts were dispersed by a ssw nne trending complex fluvial system in the colline metallifere area the early pliocene extensional tectonics cut off the detrital inputs from the messinian source areas because of the onset of the piombino channel and of the campiglia gavorrano ridge during the pliocene the clasts were cannibalized from the previous sedimentary units and reached the easternmost areas due the eastward progressive uplift of the colline metallifere likely connected with the coeval magmatic intrusions finally the quaternary regional uplift allowed a drainage reversal and a backward displacement of the aplitic clasts toward the tyrrhenian coast these data point to a rapidly evolving drainage pattern in southern tuscany during the considered time interval which was mostly driven by the intrusion and uplift of the messinian to quaternary plutons the morpho tectonic evolution is well framed also within the models since long accepted for the northern apennine geodynamics characterized by an overall eastward shift of the orogenic front

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

tectonic regime granite emplacement and crustal structure in the inner zone of the northern apennines tuscany italy a new hypothesis abstract geological and geophysical data on the inner part of the northern apennines and the deep 4 km geothermal wells contained therein have been reviewed in order to better characterize the tectonic regime of the region the area is affected by neogene quaternary igneous activity reduced crustal thickness high heat flow and active geothermal systems the available information leads to the following conclusions 1 at present part of the chain including its inner regions are undergoing extensional activity a tectonic situation in southern tuscany dating back to the late tortonian however the simple model of solely extensional tectonics cannot exhaustively account for the phenomena observed in the area as there is ample evidence of compressive events of pliocene and pleistocene ages 2 the geophysical data indicate reduced lithosphere thickness and the uprising of the asthenosphere to shallow crust levels the upper crust has been intruded by many granite bodies and the brittle ductile transition is probably very shallow an integrated geophysical model which accounts for heat flow seismic gravimetric and magnetic data indicates that a regional strong reflector rather than coinciding with the beginning of the ductile crust more likely indicates the presence of deep brines rather than a gneiss core complex and a generalized post collision extensional model cameli et al 1993 we support a more complex geodynamic framework including compressive phases of the internal zone and re activation of the thrust of the apennines as a consequence of crustal thrust emplacements from the late tortonian in the frame of a subducting delaminated lithosphere

seismotectonic zoning in east central italy deduced from an analysis of the neogene to present deformations and related stress fields this paper concerns the space time evolution of the late miocene to present contractional and extensional deformations within east central italy with an analysis of the pattern and orientation of the related stress field an insight into the cover basement relations and a discussion of the seismotectonic implications the pattern and orientation of the deformation and stress fields have remained unchanged since late miocene time and have been always characterized by the coexistence and parallelism in contiguous areas in a given time of shortening to the east and elongation to the west with time during a multistage deformation history both the contraction and the extension fields have moved eastward basement involved tectonics with a west dipping multiple detachment system would have allowed the progressive eastward shift of crustal slices corresponding at the surface to well defined tectonic domains with consequent crustal thinning in the tuscan zone and crustal thickening beneath the apennine mountain chain by comparing macroseismic epicenters hypocenters and focal mechanisms with crustal structure and independently known active faults it appears evident that the pattern frequency and distribution of the crustal seismicity are tectonically controlled and that a contraction extension pair is active also at the present time in fact along the adriatic coastline contractional deformation prevails with involvement of pleistocene layers whereas beneath the apennine range extensional deformation prevails both t axes in the inner domain and p axes in the outer domain are oriented southwest northeast or west south west east northeast and this coaxiality reflects the situation depicted by the geologic stress field on this basis we have produced a seismotectonic zoning of east central italy with three distinct domains intramountain seismic zone isz foothills seismic zone fsz and coastal seismic zone csz a plausible explanation for the genesis of the active seismic deformations of east central italy is that the locally intense extensional upper crustal seismicity of the intramountain seismic zone is confined to the hanging wall of a major west dipping active extensional discontinuity whereas the less frequent contractional seismic activity of the coastal seismic zone is within the hanging wall of an outer major active west dipping contractional discontinuity an area of overlap between these two zones is represented by the foothills seismic zone where superposed epicentral patterns from different surfaces of weakness at different depths are the predictable result of the asymmetry of the deformation

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

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

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

did the mediterranean marine reflooding precede the mio pliocene boundary paleontological and geochemical evidence from upper messinian sequences of tuscany italy abstract the events related to the messinian salinity crisis are among the most deeply investigated of earth s history according to the current hypothesis of neogene paleogeographic evolution approximately 5 5 ma ago after evaporitic sedimentation and before the mio pliocene boundary the mediterranean was characterized by the widespread development of non marine environments inhabited by molluscs and ostracods of brackish affinity the messinian post evaporitic deposits that testify such a dramatic environmental change are commonly referred to as lago mare and have been reported from several outcrops and boreholes throughout the entire mediterranean basin the origin of lago mare conditions is commonly interpreted as the result of the synergistic effect of both the humid climatic conditions and change of the drainage patterns at the mediterranean scale with the capture of paratethyan brackish waters a few recent studies however suggest that such a scenario probably represents an oversimplification of the original context from both a paleogeographical and paleoenvironmental point of view unfortunately the results of these studies have never been commonly accepted and the proposed evidences have been considered questionable in this paper we describe the fish assemblages from the lago mare deposits of two localities cava serredi and podere torricella located in the neogene hinterland basins of tuscany central italy these assemblages consists of a mixture of marine euryhaline and stenohaline taxa suggesting that the depositional environments were characterized by permanently open connections with a marine basin filled with normal marine waters in order to better define the paleontological significance of these upper messinian fish assemblages the oxygen carbon and strontium isotopic composition of fish otoliths and other fossils has been measured these isotopic compositions are strongly indicative of the presence of normal marine conditions close to the depositional environments testified by the sedimentary sequences thereby implying that the interpretation of the geochemical results are consistent with those derived from the paleoecological analyses of the fish assemblages based on the integrated paleoichthyological geochemical approach discussed in this paper it is possible to unambiguously demonstrate that normal marine rather than fresh or brackish waters were present in the mediterranean at least during the upper part of the lago mare event providing an unquestionable evidence that the marine refilling of the basin preceded the mio pliocene boundary

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

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

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

emplacement of foreland thrust systems emplacement driving mechanisms for thrust systems have been briefly reviewed and compared with distinctive structural styles in thrust belts a b type mode which implies a push from the rear and an elastic brittle behavior of the rock mass appears to be suitable as a general model for the emplacement of thrust sheets in thin skinned fold and thrust belts where stratal shortening of sedimentary covers and imbrication of upper level crustal rocks occur in such an environment that the mechanical behavior of the crustal section involved the mode and timing of deformation and the geometry of thrust systems are all strongly dependent upon the coupling between induced tectonic strain and transient close to lithostatic pore fluid pressure buildup over a critical areal extent the model presented here does not require a weak basal horizon for the detachment of thrust sheets and pore pressure pp does not need to be high at once under the entire length of the thrust wedge rather the transient buildup of pp and hence the spatial and temporal progressive weakening of the rock mass are directly coupled with deformation

geometric and kinematic complexities in the marche abruzzi external zones central apennines italy in the central apennines italy three major domains can be recognized the umbria and marche pelagic domains and the lazio abruzzi carbonate platform their mesozoic tertiary sequences are separated by major low angle thrust systems which superpose the umbria domain onto both the marche and lazio abruzzi domains the lazio abruzzi platform onto the marche sequence and all of them onto the apulia foreland

magma emplacement in a thrust ramp anticline the gavorrano granite northern apennines italy 1 magma emplacement in the upper crust is often associated with crustal extension whereby space for intrusions is made by dilation along transtensive and strike slip faults the lenticular shape of several intrusions indicates that a further mechanism for magma intrusion is laccolith emplacement with roof uplift of the overburden additionally melts exploit rheological discontinuities e g sedimentary layering during their ascent we present an emplacement model for intrusion of the shallow level gavorrano granite northern apennine italy which is located at the core of an open anticline the shape of the intrusion and structural features of the host rocks are indicative of a synkinematic emplacement in a growing thrust anticline space was provided by the opening of dilatation zones at the core of anticline as a consequence of different amounts of translation between hanging wall and footwall units which were separated by evaporitic rocks these evaporitic units acted as major decollement layers analog models provide results in good agreement with the structural setting of the anticline and emphasize the possibility that melts filled the dilatation zone with the decollement layers further facilitating intrusion

palinspastic restoration and paleogeographic reconstruction of the peri tyrrhenian area during the neogene abstract this paper presents the results of research carried out on the paleogeographic and geodynamic post collisional evolution of the peri tyrrhenian area from the southern alps to sicily during this post collisional evolution a back arc area thrust belt foredeep system developed in which the following tectono sedimentary zones can be distinguished from the external to the internal ones the foreland zone connected to the foredeep through a slope generally controlled by normal faults the foredeep an assymmetric depression with strong subsidence related to the compressional activity of the thrust zone the chain whose outward migration from the late oligocene onward was discontinuus with important stages of crisis partially connected to the mechanical response of different crustal thicknesses existing in the foreland the discontinuous satellite basins developed within the thrust belt the back arc basins developed in the inner part of the chain where the superposition of the extensional tectonics over previous compressional domains causes the fragmentation of the thrust belt leading to its destruction according to this model seven palinspatic maps are discussed regarding the following time intervals late oligocene 25 24 m y burdigalian 22 20 m y langhian 17 16 m y serravallin 15 13 m y tortonian 10 9 m y late messinian 5 5 5 3 m y and early pliocene 5 3 4 6 m y during five of these time intervals significant geodynamic modifications occurred in the whole peri tyrrhenian area leading to paleogeographic changes in any case the geodynamic evolution of the whole area seems clearly controlled by the activity of important bundles of tectonic lines transversal to the chain which in the same time interval in the outermost part of the thrust belt separated areas with different values of shortening and in tthe most internal zones separated segments having different amount of extension these tectonic lines certainly have a crustal significance and have probably acted along previous formed discontinuities