a large scale lateral spreading its genesis and quaternary evolution in the coastal sector between cogoleto and varazze liguria italy abstract the results of a study carried out on a coastal area of central western liguria northern italy where metamorphosed basic and ultrabasic rocks outcrop are presented the study indicates that a wide area 16 km 2 was involved in a large scale deep seated gravitational slope deformation dsgsd this movement has special features related to the lithology and structure of the involved rock mass to the plio quaternary uplifting and brittle tectonics affecting an area where a paleosurface was recognised and to the continental shelf dynamics the particular geometry of the dsgsd was recognised on the basis of detailed analyses of the above mentioned aspects due to its characteristics the deep seated deformation can be classified as a lateral spreading the current altitude of the pliocene marine clay outcrops and their deposition bathymetry allowed estimation of the uplift rate of the coastal area the altitudinal variations of an ancient marine terrace which was displaced by the dsgsd were used to reconstruct the chronology of the gravitational movement a final issue concerns the very large scale and the particular kind of phenomenon both of which are certainly new in liguria

tectonics and seismicity in the northern apennines driven by slab retreat and lithospheric delamination abstract understanding how long term subduction dynamics relates to the short term seismicity and crustal tec tonics is a challenging but crucial topic in seismotectonics we attempt to address this issue by linking long term geodynamic evolution with short term seismogenic deformation in the northern apennines this retreating subduction orogen displays tectonic and seismogenic behaviors on various spatiotemporal scales that also characterize other subduction zones in the mediterranean area we use visco elasto plastic seismo thermo mechanical stm modeling with a realistic 2d setup based on available geological and geophysical data the subduction dynamics and seismicity are coupled in the numerical modeling and driven only by buoyancy forces i e slab pull our results suggest that lower crustal rheology and lithospheric mantle temperature modulate the crustal tectonics of the northern apennines as inferred by previous studies the observed spatial distribution of upper crustal tectonic regimes and surface displacements requires buoyant highly ductile material in the subduction channel beneath the internal part of the orogen this allows protrusion of the asthenosphere in the lower crust and lithospheric delamination associated with slab retreat the resulting surface velocities and principal stress axes generally agree with present day observations suggesting that slab delamination and retreat can explain the dynamics of the orogen our simulations successfully reproduce the type and overall distribution of seismicity with thrust faulting events in the external part of the orogen and normal faulting in its internal part slab temperatures and lithospheric mantle stiffness affect the cumulative seismic moment release and spatial distribution of upper crustal earthquakes the properties of deep sub crustal material are thus shown to influence upper crustal seismicity in an orogen driven by slab retreat even though the upper crust is largely decoupled from the lithospheric mantle our simulations therefore highlight the effect of deep lower crustal rheologies self driven subduction dynamics and mantle properties in controlling shallow deformation and seismicity

late shortening and extensional structures and veins in the western margin of the taconic orogen new york to vermont abstract along the western margin of the taconic orogen in new york and vermont undeformed quartz calcite veins commonly occur in the belt of melange that formed beneath the westward advancing taconic allochthon during the middle late ordovician taconic orogeny the veins have mineral slickenfibers recording either reverse or normal slip in new york the reverse motion veins recording the latest phase of shortening are crosscut by the normal motion veins and faults the shortening indicated by the reverse motion veins is correlated with the convergence along the champlain thrust in vermont which is also crosscut by a significant strike parallel normal fault fluid inclusion data from the veins complemented by stable isotope data lead to a reconstruction of the sequence of events in the context of a cooling of the fluids which is consistent with crosscutting relationships among the veins following cessation of the convergence there was regional extension of the western margin of the taconic orogen

oligocene to present kilometres scale subsidence and exhumation of the ligurian alps and the tertiary piedmont basin nw italy revealed by apatite u th he thermochronology correlation with regional tectonics the ligurian alps segment of the alpine apennine orogen in nw italy is unconformably covered by upper eocene to holocene sediments in the tertiary piedmont basin tpb and po plain these sediments dip towards the north demonstrating the erosional nature of the southern border of the succession and implying that the adjacent orogenic belt formed the substratum rather than the margin of the sedimentary basin apatite u th he and fission track thermochronology shows that the orogen first subsided and was buried at 4 km from 30 to 26 ma and began its exhumation thereafter from 26 ma to present this upward movement was contemporaneous with subsidence in the northern tpb the couple exhumation in the s and subsidence in the n migrated northwards through time vertical movements in the area are similar to those reconstructed in corsica in both cases the onset of exhumation b

the western mediterranean extensional basins and the alpine orogen the western mediterranean late oligocene miocene basins alboran valencia and provencal basins are a coherent system of interrelated troughs in all basins normal faults and thermal subsidence migrated toward the east progressively moving to the miocene to pleistocene algerian and tyrrhenian basins all those troughs appear elements of the back arc opening related to the eastward roll back of the w directed apennines maghrebides subduction zone similarly to western pacific back arc settings these late oligocene early miocene basins nucleated both within the betic cordillera e g alboran sea and in its foreland valencia and provencal troughs the n40 70 direction of grabens is oblique to the coexisting n60 80 trending orogen and shows its structural independence from the orogenic roots thus as the extension cross cuts the orogen and developed also well outside the thrust belt front the westernmost basins of the mediterranean had to develop independently from the alps betics orogen therefore the alboran extension considered a classic example of a basin generated by the collapse of an orogen cannot be ascribed to the detachment or annihilation of the lithospheric root in contrast with the eastward migrating extensional basins the betic balearic thrust front was migrating westward producing interference or inversion structures

former carboniferous overburden in the northern appalachian basin a reconstruction based on vitrinite reflectance abstract elevated vitrinite reflectance values have been observed in the upper devonian west falls group of the northern new york appalachian basin in new york lopatin modeling suggests that the high thermal maturity of these and associated strata was caused by the presence of a devonian and carboniferous overburden that has subsequently been eroded from the northern appalachian basin devonian overburden reconstructed from extrapolation of stratigraphic data thickens from west 0 4 km to east 2 0 km across the field area in contrast carboniferous overburden reconstructed by lopatin modeling thins from west 2 0 3 4 km to east 0 7 1 2 km the inferred geometry of a northeasterly thinning wedge of sediment is compatible with the existing distribution of late paleozoic sediments in the appalachian basin and suggests the northern part of the basin experienced only moderate subsidence during carboniferous time

migration of orogenic fluids through the siluro devonian helderberg group during late paleozoic deformation constraints on fluid sources and implications for thermal histories of sedimentary basins abstract fluid inclusion data and fracture filling cement fabrics in deformed but non overthrusted carbonate and siliciclastic rocks of the siluro devonian helderberg group central appalachians indicate post cementation late paleozoic migration of high pressure high temperature fluids void filling quartz and calcite cements contain secondary two phase fluid inclusions liquid vapor which occur in annealed microfractures most melting temperatures last occurrence of ice are 20 to 25 c which correspond to salinities of greater than 22 equivalent wt nacl pressure corrected liquid vapor homogenization temperatures are 200 to 300 c and greatly exceed maximum paleotemperatures 150 c given by conodont cai values vitrinite reflectance illite crystallinity or temperatures calculated from known sedimentary overburden completely cemented sandstone and limestone also have multiple crosscutting trains of secondary hydrocarbon inclusions hydrocarbon inclusions occur along deformation microstructures in cements some hydrocarbon inclusion trains crosscut cement filled fractures the nature of occurrence of the secondary inclusions suggests that fluids moved along intracrystalline deformation microstructures either during or after late paleozoic deformation rare fractures contain transported skeletal grains exotic clasts lithologies different from wall rock recemented clasts of fracture filling cement and mud cement clasts contain solid inclusions of mud and skeletal fragments and indicate several episodes of particle transport cementation and refracturing prior to final fracture filling and cementation these fracture fills locally crosscut stylolites coarse grained poorly sorted clastic fracture fills suggest migration of rapidly moving fluids which were capable of transporting clasts through fracture conduits under deep burial conditions conduction calculations place upper limits on size and duration of thermal anomalies which were caused by extrabasinal fluids these calculations indicate that hot fluid migration events most likely were short lived heat transfer by extraformational fluids moving along faults and fractures may have been the mechanism by which thermal anomalies developed in the helderberg group stratigraphic constraints suggest that likely sources for the hot brines are overthrusted terranes to the east of the study area possible stratigraphic horizons which were sources for the overpressured hot fluids may have been thick cambrian shales which are important detachment horizons for major late paleozoic thrust sheets in the eastern valley and ridge province east of the study area fluids may have migrated during thrusting along thrust faults which ramp upwards from east to west into stratigraphically higher units thrust faults ultimately die out in devonian units some of the dissolved ions in the secondary two phase inclusions may have been incorporated when shale derived fluids moved through silurian evaporites or cambro ordovician carbonates which contain evidence of cryptic evaporites potential source rocks for secondary hydrocarbon inclusions may have been lower silurian through lower devonian strata based on lopatin modeling and assuming that migration occurred during late paleozoic deformation this study may help to explain many apparently anomalous geologic phenomena in deformed foreland basin sediments it also has implications for tracking migration pathways for fluids which facilitate regional scale deformation in fold and thrust belts and how tectonic fluids may affect the rocks through which they move

provenance of oligocene synorogenic sediments of the ligurian alps nw italy inferences on belt age and cooling history mineral chemistry 40ar 39ar geochronology on white micas and apatite fission track thermochronology aftt are applied here to study the provenance of the synorogenic molare formation lowermost unit of the tertiary piedmont basin clastic sequence the molare formation was deposited during transgression onto the ligurian alps nappe stack in the early oligocene depositional facies show that clastic distribution remained transversal with local sources located just landward from the coastline phengite mineral chemistry together with 40ar 39ar data clearly shows two distinctive source areas each one mirroring the composition of the basement directly beneath the clastic sequence amphibole mineral chemistry allows second order provenance distinctions within each sector reflecting heterogeneous metamorphic evolution of the bedrock complexes integrated 40ar 39ar dating and aftt suggest that following a fast cooling exhumation episode of the ligurian alps during the oligocene very little net uplift has since occurred this is due to a period of general subsidence from the oligocene late miocene followed by comparable uplift from late miocene pliocene to the present in general our data provide an image of the ligurian alps during the oligocene which is very similar to the present day one

appalachian stress study 2 analysis of devonian shale core some implications for the nature of contemporary stress variations and alleghanian deformation in devonian rocks detailed stress measurements in three boreholes penetrating horizontally bedded devonian silt stones sandstones and limestones above a prominent salt decollement in the appalachian plateau of western new york have revealed variations in horizontal stress magnitudes which correlate with lithologic and stratigraphic units in all wells high differential stress levels up to 20 mpa were found in shales of very high clay content contrary to the proposition that such materials have negligible long term strength elastic modulus data show that stiffer beds generally host higher stress levels and suggest that sand shale stress contrasts result in large part from elastic shortening of the section in response to regional ene compression no correlation between stress and poisson s ratio was found however a major systematic drop in stress level within the generally massive shales which occurs across a group of sand beds near the base of the rhinestreet formation appears to be of different origin the stress offset corresponds to the top of a section which we conclude on the basis of local and regional total strain data derived from chlorite fabric measurements once hosted abnormally high pore pressures the total strain data also suggest the entire section above the salt has been uniformly shortened during alleghanian compression to explain the stress discontinuity two kinematic patterns for alleghanian deformation of the devonian section are proposed both involving abnormal pore pressure development in the sub rhinestreet section in response to limited drainage of fluid drainage of this paleo overpressure is the best available explanation of the stress offset although an additional remnant stress component must also be present to satisfy the stress data precisely

the thermal history of the new york basement determined from 40ar 39ar k feldspar studies constraints on the thermochronologic evolution of the new york crystalline basement are mainly restricted to the high temperature early cooling history following 1 1 ga grenville metamorphism u pb methods and the late cooling history fission track methods the thermal history for the one billion years between these intervals is herein assessed using 40ar 39ar hornblende muscovite biotite and k feldspar thermochronology hornblende preferred ages suggest cooling below 450 500 c between ca 900 and 950 ma total gas ages of biotites range from 746 1060 ma and their age spectra complexity is probably related to younger thermal events and or excess argon a single muscovite analysis yields a preferred age of 854 ma argon isotope analyses of k feldspar provide a quantitative evaluation of the thermal history between 175 and 350 c multi diffusion domain thermochronology on highly variable k feldspar results yield internally consistent thermal histories and along with geologic constraints suggest thermal maxima of 275 350 c at ca 700 470 450 and 300 ma combining all of the k feldspar analyses provides an internally consistent thermal history for the region and allows for the following inferences reheating at 700 ma associated with late precambrian rifting during the formation of the iapetus ocean apparently affected the entire adirondack region with the highest temperatures occurring in the eastern part of new york local reheating in the ordovician is inferred to have affected the eastern adirondack mountains and probably resulted from the combined effects of burial during the early paleozoic emplacement of taconic thrust sheets and migration of hot fluids along normal faults during the taconic orogeny high paleotemperatures for the devonian section of eastern new york are related to maximum burial of the basement during the carboniferous at ca 300 ma

the collisional knot in liguria a series of 8 new seismic refraction profiles were computed as extensions of the borehole controlled reflection profiles of the po plain into the northern apennines and the ligurian alps they help to more clearly define the subsurface structure of this intricate ligurian knot in particular it has been possible to identify a number of high velocity bodies and they may be correlated with such geological entities as the adriatic mesozoic ophiolites of the apenninic liguride nappes and ophiolites or mesozoic carbonates underlying the antola flysch in the alpine part of the knot when combining the refraction and reflection lines these bodies appear to be bounded by important dislocation surfaces such as the padanide sole thrust plio pleistocene the villalvernia varzi line oligo miocene the ottone levanto line oligo miocene and the volpedo valle salimbene fault oligo miocene reactivated as a transfer fault in the plio pleistocene the 3d geometry may be interpreted in terms of regional kinematics and is compatible with a model that envisages an oligo early miocene nw translation of the adriatic indenter coupled with collapse in the provencal ligurian sea and rotation of the sardinia liguria complex into the roll back of the adriatic subduction zone the refraction interpretations extending to a depth of 15 km are supplemented by data on the moho configuration obtained for the european geotraverse the moho appears to be dissected into a series of patches which may be interpreted in terms of the shallow crustal configuration and its history in particular the deepest patch appears to be terminated by the volpedo valle salimbene fault which consequently would displace the entire crust

exhumation of alpine high pressure rocks insights from petrology of eclogite clasts in the tertiary piedmontese basin ligurian alps italy the study of late and postorogenic sedimentary basins is a powerful tool to understand uplift exhumation and erosion of an orogen in the ligurian alps high pressure ophiolitic rocks are directly overlain by the sediments of the tertiary piedmontese basin tpb the conglomerates at the bottom of the tpb succession contain clasts of metaophiolites and metasediments which display deformation structures acquired at peak metamorphic conditions ranging from eclogite to blueschist facies the deformation events prevalently recorded by the high pressure rocks of the ligurian alps are either related to subduction and peak metamorphism or to the late stage greenschist collision the main structures which accomplish the early exhumation of such high pressure terrains are only locally recorded and poorly explored further information on these early tectonic events can be gathered through the study of the clasts in the conglomerates in this paper we present a textural and petrologic outline and some thermobarometric estimates of the main types of high pressure clasts sampled and their comparison with the high pressure equivalents presently exposed in the ligurian alps in particular some clasts displaying a na amphibole white mica epidote sphene blueschist foliation superimposed to an eclogitic garnet na clinopyroxene rutile tectonitic assemblage have been studied in detail this kind of rock records a pressure temperature p t path implying cooling during exhumation whereas the high pressure bedrocks are characterized by either isothermal decompression or initial heating and subsequent cooling we conclude that the blueschist foliation of these clasts most likely developed along shear zones and or contacts among different slices formed during tectonic coupling of warm uprising eclogite units with cooler blueschist slices during the early stages of exhumation

modeling of the temperature sensitivity of the apatite u th he thermochronometer apatite u th he apparent ages will generally reflect residence for extended periods at temperatures where helium is neither quantitatively retained nor lost by diffusion to characterize the response of apatite he ages to thermal histories involving partial he retention we explored solutions to the he production diffusion equation under thermally static conditions the analytical solution to this equation coupled with published diffusivity data demonstrates that the zone of partial he retention extends from about 40 c to 85 c this zone lies at temperatures 35 c cooler than the analogous fission track partial annealing zone he ages within the partial retention zone ultimately achieve a balance between he production and loss yielding a steady state age both the ultimate age and the time it takes to achieve this age are temperature dependent for example an apatite held at 75 c equilibrates to an age of 2 ma after 17 myr regardless of whether equilibrium is approached from a higher or a lower initial he age for representative dynamic thermal histories we evaluated apatite he ages using a numerical solution to the ingrowth diffusion equation the results illustrate the sensitivity of he ages to various geologic histories and are useful for understanding he age elevation relationships and for testing time temperature paths derived from apatite fission track length distributions in addition although he diffuses rapidly from apatite at shallow crustal temperatures modeling of ambient temperature fluctuations indicates that he ages are nearly unaffected by surficial processes

halimeda dominance in the coastal wedge of pietra di finale ligurian alps italy the role of trophic conditions the middle to late miocene mixed carbonate siliciclastic coastal wedge of the pietra di finale unconformably overlying the ligurian alps succession displays a carbonate portion dominated by halimeda and porites fragments that fall in the photozoan assemblages photozoan assemblages typically develop under tropical and oligotrophic conditions while hetorozoan assemblages tend to thrive in high nutrient settings the pietra di finale formation shows however that high weathering and an increase of nutrient inputs related to alpine uplift and humid climatic conditions promoted halimeda over the seagrass carbonate factory in the photic zone the successful halimeda proliferation was due to its efficient competition for nutrients especially nitrogen thus the pietra di finale formation represents an interesting counter intuitive example in which increased nutrient concentrations promoted instead of inhibited a photozoan over a seagrass related heterozoan carbonate production

long lasting transcurrent tectonics in sw alps evidenced by neogene to present day stress fields abstract the sw alps are an active orogen undergoing intra mountainous extension and peripheral compression we discuss the significance of syn orogenic extension based on a comparison of paleo stress derived from fault slip data inversion reflecting the long term

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

distribution of seismic coupling on the subducting plate boundary in northeastern japan inferred from gps observations abstract many global positioning system gps stations of the geographical survey institute and tohoku university in northeastern japan observed clear coseismic and postseismic deformations associated with the m7 5 1994 far off sanriku earthquake applying the geodetic inversion algorithm given by yabuki and matsu ura geophys j int 1992 109 363 376 to the observed gps data we estimate in this paper the spatial distributions of the coseismic and postseismic slip on the boundary between the subducting pacific plate and the overriding continental plate it is noted that the coseismic slip estimated in this paper denotes the slip for a period between the day before and the day after the main shock the inversion for coseismic slip shows that the main shock was thrust faulting typical for interplate earthquakes which is consistent with the results of other seismological studies the short term postseismic deformation std observed for a period of ca 10 days between the main shock and its largest aftershock shows that the initially high deformation rate was lowered rather rapidly in comparison with the subsequent long term deformations ltd lasting longer than 1 year which decreased at an almost constant low rate the observed data of std can be explained by postseismic slip distributed approximately on the same region as the faulting area of the main shock where the moment release during this period is ca 16 of that estimated for the coseismic slip the region of the sliding causing ltd is found to have significantly expanded southward and downward or westward on the plate boundary the moment released by the postseismic sliding for nearly 1 year amounts approximately to 80 of that released by the coseismic slip in addition to the contribution from uniform steady sliding due to the relative plate motion furthermore we find from the inversion analysis a locked region to the south of the long term postseismic sliding region on the plate boundary the amount of nominal back slip estimated is so large that the locked region of the plate boundary is considered to have been tightly coupled for the year of 1995 this study demonstrates that the gps observation only for ca 1 year can distinguish the decoupled region due to the postseismic sliding around the source area of the main shock from the coupled one of the plate boundary

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

late miocene to present exhumation in the ligurian alps southwest alps with evidence for accelerated denudation during the messinian salinity crisis detrital apatite u th he and fission track thermochronometry are applied to constrain the exhumation history of the ligurian alps southwest alps exhumation of the ligurian alps is recorded from ca 11 ma and continues until present more than 4 km of exhumation is recorded at an average rate of 0 4 0 2 mm yr exhumation is accommodated along a north dipping thrust at the foot of the ligurian margin combined u th he and fission track thermal modeling show a phase of accelerated denudation between 7 and 5 ma associated with the base level drop during the messinian salinity crisis

testing models of orogen exhumation using zircon u th he thermochronology insight from the ligurian alps northern italy testing models of orogen exhumation requires precise constraint of the time temperature paths of the exhumed rocks the zircon u th he zhe thermochronometer has a closure temperature of 140 210 c and can provide temporal constraints on the exhumation history of rocks through a thermal range which crucially corresponds the onset of brittle behaviour of an exhuming orogen we performed zhe analyses to test the existing contradictory models for the exhumation of the ligurian alps the zhe ages indicate a very rapid 1 3 6 8 mm yr and southward migrating exhumation of the orogen between 32 and 25 ma these high exhumation rates are unique within the alpine belt and cannot be reconciled with existing geodynamic models of the evolution of the ligurian alps we propose a model of tectonic denudation via detachment accomplished in the shallowest crust 5 km as a result of the last orogenic phase of extension

the arc of the western alps in the light of geophysical data on deep crustal structure recently two international deep seismic campaigns in the western and central alps etude continentale et oceanique par reflexion et refraction sismique progetto strategico crosta profonda ecors crop roure et al 1996b and national research program 20 nrp 20 pfiffner et al 1997 have been completed here we present a synoptic interpretation of the wealth of geophysical data about deep crustal structure of the alps collected during the past 40 years including the two above mentioned geophysical projects the tectonic reinterpretation of the ecors crop high resolution seismic transect is based on an evaluation of the deep crustal structure by integrating new and literature data on surface geology combined with previously published interpretations regarding the central alps schmid et al 1996 this study reveals substantial differences in geometry and kinematics between transects across the western and central alps respectively at depth the transition between the central and western alps is marked by the western limits of an adriatic lower crustal wedge shaped structure and the northeastern limits of a similar structure made of european lower crustal material at the surface it coincides with a corridor of dextral strike slip along the tonale and simplon lines in addition the thickness of the seismogenic zone shows a remarkable variation from over 40 km beneath the penninic realm of the western alps to less than 20 km in the central alps the formation of the western alpine arc was initiated during convergence and collision before 35 myr ago when the adriatic micro plate moving northward with respect to the european foreland caused sinistral transpression in the western alps while the central and eastern alps underwent head on convergence and collision during the post collisional stage i e after 35 myr ago the arcuate shape of the western alps was accentuated by wnw directed movement and anticlockwise rotation of the adriatic microplate decoupled from the central and eastern alps along the tonale simplon dextral shear zone this led to wedging of lower crustal slices both in the western alps and in the central alps the new tectonic interpretation of the ecors crop transect allows a kinematic model to be established for crustal shortening in the western alps during the past 35 myr the ivrea mantle plays the role of a backstop in our tectonic model we distinguish three episodes of post collisional crustal shortening along the ecors crop transect from 35 to 30 ma the brianconnais basement was back thrusted over the gran paradiso units leading to 30 km of crustal shortening first episode in the early miocene movements concentrated mainly along the penninic frontal thrust and resulted in about 60 km shortening second episode post 12 ma shortening within the external massifs is associated with folding in the jura mountains when the crust was shortened by an additional 30 km third episode

early cretaceous uplift and erosion of the northern appalachian basin new york based on apatite fission track analysis abstract the thermal history of outcropping devonian sediments of the northern appalachian basin new york has been investigated using fission track analysis of detrital apatites from 57 sandstone samples based on lengths and apparent age measurements using fission tracks in apatite it is concluded that lower devonian sediments presently at the surface in the catskill region were cooled rapidly from temperatures higher than about 110 c during early cretaceous times 120 140 ma ago in the western part of new york wellsville buffalo data from late devonian sediments are consistent with cooling at the same time as that identified for the catskill region but from lower temperatures in the range of approximately 80 110 c the maximum temperature these sediments experienced since deposition for a pre uplift paleogeothermal gradient of 25 35 c km the confined track length data indicates uplift and erosion of 2 3 km for western new york and greater than 3 4 km for the catskill region a differential uplift pattern which is consistent with the historical stratigraphic data from the region this conclusion is at variance with earlier interpretations put forth by others rapid broad scale uplift and erosion of the scale identified imply that large volumes of sediment could have been supplied from the northern appalachian basin during the early cretaceous this timing for the dominant post devonian cooling phase in the basin is not accounted for by recent models of the tectonic evolution of the appalachian orogen but is compatible with the change from carbonate to siliciclastic deposition in the atlantic coastal plain it is suggested that this style of broad regional uplift without significant deformation is characteristic of a tectonic regime associated with and subsequent to continental rifting apatite fission track analysis is shown to be a basic tool in providing fundamental limits for thermal history assessment in regional tectonic problems

cenozoic denudation of corsica in response to ligurian and tyrrhenian extension results from apatite fission track thermochronology 1 the island of corsica france occupies a unique position in the western mediterranean since it has recorded both the cenozoic alpine orogenic history of the area as well as subsequent extensional collapse and oceanic basin formation we present 41 new apatite fission track aft ages and 23 measurements of track length distributions from corsica in order to elucidate its cenozoic thermal and morphological evolution aft ages vary from 10 5 0 8 ma to 53 8 4 1 ma and form a clear spatial pattern oldest ages are encountered in the southwest of the island with a broad band of ages between 20 and 30 ma running across the mountainous central area and ages 20 ma confined to the eastern half of the island samples along the western and northwestern coasts record kilometer scale erosional denudation linked to rifting in the ligurian provencal basin whereas samples from close to the extensionally inverted alpine deformation front record a later cooling phase related to tyrrhenian extension the eastward younging pattern of aft ages suggests the migration of a wave of erosional denudation from west to east across the island apparently controlled by the migrating locus of extension our aft data therefore support models of mediterranean extension controlled by slab roll back

kinematics of back arc inversion of the western black sea basin 1 back arc basin evolution is driven by processes active at the main subduction zone typically assuming the transition from an extensional back arc during the retreat of a mature slab to a contractional basin during high strain collisional processes such a transition is observed in the black sea where the accurate quantification of shortening effects is hampered by the kinematically unclear geometries of cenozoic inversion by means of seismic profiles interpretation quantified deformation features and associated syn tectonic geometries on the romanian offshore this study demonstrates that uplifted areas observed by exploration studies form a coherent thick skinned thrust system with n ward vergence thrusting inverted an existing geometry made up by successive grabens that were inherited from the cretaceous extensional evolution the shortening started during late eocene times and gradually affected all areas of the western black sea basin during oligocene and miocene times deformation being coherently correlated across its western margin the mechanism of this generalized inversion is the transmission of stresses during the collision recorded in the pontides balkanides system syn tectonic sedimentation in the western black sea demonstrates that this process was continuous and took place through the onset of gradual shortening migrating northward although the total amount of shortening is roughly constant in an e w direction individual thrusts have variable offsets deformation being transferred between structures located at distance across the strike of the system the black sea example demonstrates that the vergence and offset of thrusts can change rapidly along the strike of such a compressional back arc system this generates apparently contrasting geometries that accommodate the same orogenic shortening

episodic exhumation in the western alps oligocene to miocene clastic sediments of the tertiary piedmont basin northwest italy were derived from erosion of western alps source rocks detrital white micas from dif ferent stratigraphic units and from sands of three present day rivers draining the internal western alps have been analyzed by 40 ar 39 ar geochronology our data suggest a wide spread fast cooling and exhumation event prior to ca 38 ma followed by a 30 m y period of slower cooling and exhumation combined with erosion of crustal rocks with uniform 40 ar 39 ar signatures these processes have resulted in a pattern of regularly increasing lag time up section