curie isotherm depth from aeromagnetic data constraining shallow heat source depths in the central aeolian ridge southern tyrrhenian sea italy the salina lipari and vulcano volcanic ridge and the surrounding sea sectors aeolian archipelago southern tyrrhenian sea italy are characterized by vents responsible for a recent 40 ka 1889 1890 ad effusive and explosive subareal activity and repeated 56 to 7 ka in age submarine explosive eruptions from source areas located between lipari and vulcano a spectral depth estimation of the magnetic bottom using a fractal method on aeromagnetic data from vulcano lipari and salina volcanic ridge allows us to constrain the curie isotherm depth the elevated portion of the isotherm is between 2 and 3 km below salina and vulcano and about 1 km below lipari the curie depth results in the context of other geological and geophysical evidence suggest that the rise of the curie isotherm is mainly due to the occurrence of shallow heat sources such as magma ponds and associated hydrothermal systems the short wavelength magnetic anomaly field reflects magnetic contrasts from highly magnetized volcanic bodies low magnetization sediments and hydrothermally altered rocks borehole temperature data verify the curie temperature derived from the magnetic methods on the island of vulcano we conclude that the whole vulcano lipari and salina volcanic ridge is active and should be monitored

basin development examples from the united kingdom and comments on hydrocarbon prospectivity abstract analysis of on and offshore basins in the ukcs using a variety of structural modelling techniques including and now confirmed by deep seismic reflection profiles has shown that basins develop on linked fault systems these fault systems comprise both steep and shallow dipping faults which can have either dip or strike slip displacements while linked fault systems are common to all basins they are developed to different degrees and hence produce a variety of structural expression within and between the basins this allows basins to be classified either in terms of their dominant structural elements or seen as a mechanical and geological continuum as the basin grows changes in crustal thickness in the upper brittle crust can take place either on linked staircase arrays of low angle listric faults or on steeper planar domino faults or commonly on a combination of both linked by crustally conservative strike slip systems the development of the controlling basement elements effects the distribution and pattern of internal deformation in the evolving sedimentary fill resulting in a characteristic basin architecture this architecture has profound implications for exploration in both extensional and strike slip basins providing possibilities for the prediction of trap geometry and distribution as well as opportunities for new plays

neogene tectonostratigraphy and kinematics of calabrian basins implications for the geodynamics of the central mediterranean abstract a new structural model for the calabrian arc southern italy is presented based on a systematic analysis of basin kinematics combined with a review of the literature on basement structure three tectonic patterns can be distinguished a nw se trending oblique thrust zones determining a set of n130 trending segments b sw ne to e w trending thrust zones and c radial and concentric tensional fault systems in the southern tyrrhenian back arc area these faults combined with dome shaped uplift centres determine the actual arc patterns a and b can be regarded as the on shore representation of the calabrian accretionary wedge system the kinematics of various types of basins such as piggy back pull apart and complex oblique strike slip basins are connected to these patterns the patterns a and b can be linked to the middle miocene early pliocene development of oblique convergent crustal shear zones strike slip cycle whereas pattern c can be linked to the pleistocene collapse of the southern tyrrhenian basin and concentric uplift of the arc our structural model has considerable implications for the understanding of the kinematic evolution of the central mediterranean we propose a model in which the evolution is characterized by an alternation of the translation of the calabrian lithosphere element either to the southeast gravitationally or to the northeast compression combining a our analyses of basin evolution b the structural model and c some considerations concerning kinematics of the central mediterranean with the geodynamic mechanisms as proposed in literature we present a model which consists of a geodynamic cycle comprising the following three stages 1 a tension stage with back arc basin opening related to the diapiric inflow of asthenosphere material and roll back of the subducted ionian slab resulting in gravitational displacement of the calabrian element to the southeast 2 a transpression stage with oblique overthrusting towards the northeast upon the southern apennines and 3 a compression stage with ne sw compression due to oblique dextral shear along the north african margin plate rupture lithosphere split and back arc basin collapse

gravity modelling of the litho asthenosphere system in the central mediterranean abstract the results of the 2 5 d gravity modelling of the litho asthenosphere system in the central mediterranean along two regional geotransects are presented and their possible implications for the geodynamical evolution of this area are discussed particularly gravity data on the tyrrhenian and provencal balearic basins were interpreted introducing significant constraints by means of several main petro physical parameters tied to the litho asthenospheric evolution during the extensive tectonics by this approach based on the model of mckenzie and bickle in j petrol 29 pp 625 679 1988 and white and mckenzie in j geophys res 94 b6 pp 7685 7729 1988 the estimation of the vertical density distribution in the lithosphere asthenosphere system has been possible significant differences in the gravity anomaly field occur when different density models of asthenospheric upwelling are considered this depends on factors like the thermal regime the stretching of the lithosphere and its thickness before it the obtained results contributed to the validation of models interpreting the origin of the tyrrhenian and ligurian provencal basins as related to a passive extensional process rather than to the presence of an active upwelling asthenosphere beneath the central mediterranean basins

density changes in upwelling mantle abstract gravity modelling of the litho asthenosphere system in regions involved in extensional tectonics requires an accurate estimation of the vertical density profile in the upwelling asthenosphere to this end the calculation of the variation of several parameters is needed i e the degree of thermal anomaly in the asthenosphere the amount of stretching the thickness of the lithosphere before stretching and the variation of melt fraction generated by adiabatic decompression therefore knowledge of melt density and of the residual mantle rock composition is necessary in order to have the information to calculate the density of the uprising mantle these calculations allow to partially solve the problem related to ambiguity of the gravity interpretation and to provide information about the structural features of the upwelling mantle

magmatic and tectonic sources at vulcano aeolian islands southern italy a geodetic model based on two decades of gps observations abstract an update of the surface ground deformation field over the lipari vulcano complex has been provided by analyzing all the available gps observations collected in the last two decades the geodetic velocity field referred to a fixed eurasian frame shows a remarkable negative velocity gradient between the southernmost stations velocity values of 9 0 mm yr and the northernmost ones resulting in a n s contraction of 4 5 mm yr in addition all the gps stations show subsidence with rates decreasing from the northernmost stations 10 0 mm yr to the southernmost ones 4 8 mm yr modelling of geodetic data demonstrates that the observed surface deformation field results from the joint contribution of regional tectonic and local magmatic sources such a dataset is unable to uniquely constrain the magmatic source indeed the three performed models m1 m2 and m3 produce statistically equivalent deformation sources the source modeled in m1 is spatially coincident with that of m3 and both are located beneath the vulcanello cone at depth of 4 km bsl conversely the source modeled in m2 is placed at depth of 0 76 km bsl beneath the northern rim of the la fossa crater integration of these results with geochemical and petrological data already available from literature suggests however that the m1 m3 source placed beneath the vulcanello cone should be the preferred model

temperature and density of the tyrrhenian lithosphere and slab and new interpretation of gravity field in the tyrrhenian basin abstract the gravity anomaly field of the tyrrhenian basin and surrounding regions reflects the complex series of geodynamic events active in this area since the oligocene miocene they can resume in lithospheric thinning and asthenospheric rising beneath the tyrrhenian basin coexisting with the roll back subduction of the african plate margin westward sinking beneath the calabrian arc the geographic closeness between these processes implies an intense perturbation of the mantle thermal regime and an interference at regional scale between the related gravity effects a model of the litho asthenospheric structure of this region is suggested showing a reasonable agreement with both the evidences in terms of regional gravity anomaly pattern and the results concerning thermal state and petro physical features of the mantle the first phase of this study consisted of the computation of the isotherms in the crust mantle system beneath the tyrrhenian basin and afterwards of the density distribution within the partially melted upwelling asthenosphere the second phase consisted of a temperature density modelling of the slab subducting beneath the calabrian arc finally a 21 2 interpretation of gravity data was carried out by including as constraints the results previously obtained thus the final result depicts a model matching both gravity thermal and petrographic data they provide a a better definition of the thermal regime of the passive mantle rise beneath the tyrrhenian basin by means of the estimation of the moderate asthenospheric heating and b a model of lithospheric slab subducting with rates that could be smaller than generally suggested in previous works

early stage rifting of the northern tyrrhenian sea basin results from a combined wide angle and multichannel seismic study extension of the continental lithosphere leads to the formation of rift basins and ultimately may create passive continental margins the mechanisms that operate during the early stage of crustal extension are still intensely debated we present the results from coincident multichannel seismic and wide angle seismic profiles that transect across the northern tyrrhenian sea basin the profiles cross the corsica basin france to the latium margin italy where the early rift stage of the basin is well preserved we found two domains each with a distinct tectonic style heat flow and crustal thickness one domain is the corsica basin in the west that formed before the main rift phase of the northern tyrrhenian sea opening 8 4 ma the second domain is rifted continental crust characterized by tilted blocks and half graben structures in the central region and at the latium margin these two domains are separated by a deep 10 km sedimentary complex of the eastern portion of the corsica basin travel time tomography of wide angle seismic data reveals the crustal architecture and a subhorizontal 15 17 1 km deep moho discontinuity under the basin to estimate the amount of horizontal extension we have identified the pre syn and post tectonic sedimentary units and calculated the relative displacement of faults we found that major faults initiated at angles of 45 50 and that the rifted domain is horizontally stretched by a factor of 1 3 8 10 mm a the crust has been thinned from 24 to 17 km indicating a similar amount of extension 30 the transect represents one of the best imaged early rifts and implies that the formation of crustal scale detachments or long lived low angle normal faults is not a general feature that controls the rift initiation of continental crust other young rift basins like the gulf of corinth the suez rift or lake baikal display features resembling the northern tyrrhenian basin suggesting that half graben formations and distributed homogeneous crustal thinning are a common feature during rift initiation

two dimensional modeling of the p t t paths of regional metamorphism in simple overthrust terrains quantitative modeling of metamorphic p t t paths in thrust belts has so far been limited to one dimensional simplification we have developed a two dimensional time dependent finite element procedure capable of tracing and updating fault and strata boundaries during faulting for modeling thermal evolution of overthrust terrains we show that the two dimensionality of an overthrust and the speed and duration of thrusting have significant effects on the p t t paths of rocks in orogenic belts the results suggest that petrological studies of p t paths of rocks from different lateral positions in an orogenic belt along with two dimensional modeling procedure can put strong constraints on models of regional tectonic processes

mauna loa volcano is not a methane source implications for mars 1 thirteen years of continuous atmospheric carbon dioxide and methane measurements at the mauna loa observatory in hawaii are used to determine the methane emission rate from the summit of mauna loa volcano we find no measurable methane emissions coming from the summit area with a 95 confidence upper limit of 9 t ch4 yr 1 recent studies have detected 10 ppb ch4 in the martian atmosphere requiring emissions of about 300 t ch4 yr 1 volcanic activity has been suggested as a source of abiogenic ch4 on mars either by magmatic degassing or reactions in hydrothermal fluids heated by a magma intrusion the most recent lava flows on mars 2 my ago are on the tharsis shield volcanoes which may still be active if mauna loa is a valid terrestrial analog our findings suggest that volcanic activity is not a significant source of methane to the martian atmosphere

new unspiked k ar ages of volcanic rocks of the central and western sector of the aeolian islands reconstruction of the volcanic stages abstract a geochronological study of the filicudi salina lipari and vulcano islands aeolian archipelago using the unspiked potassium argon technique provides new age data which combined with stratigraphic correlation better constrain the temporal evolution of volcanism the unspiked k ar age of the oldest exposed lavas on filicudi 219 5 ka is significantly younger than the previous estimation of 1 02 ma in the general context of aeolian volcanism this new date suggests that the volcanism of the western sector of the aeolian archipelago is younger than previously thought geochronological data point out on the rapid transition from calc alkaline to potassic volcanism the distribution of the k ar ages within the salina lipari vulcano group shows that the volcanism started on lipari and propagated over time northward on salina and southward on vulcano geochronological and geophysical data suggest that the onset of volcanism in the central sector of the aeolian arc may be due to a mantle upwelling structure located below lipari a change in the style of the eruptions occurred in the salina lipari vulcano system at about 100 ka from the present low energy magmatic eruptions occurred between 188 and about 100 ka from about 100 ka to the present higher energy eruptions and low energy events due to magma water interaction also occurred this change in the style of activity together with the appearance of evolved products i e rhyolites during the last 50 ka is consistent with the formation of magmatic reservoirs located at shallower depth with respect to those of the 188 100 ka period the new geochronological data and available petrological models reveal that a change in the deep source of the primary magmas occurred in a relatively short time interval

the deep seismicity of the tyrrhenian sea summary l he study reappraises the deep seismicity of the tyrrhenian sea careful examination of the quality of reported hypocentres shows that the earthquakes define a zone dipping nw about 200 km along strike 50 km thick and reaching a depth of about 500 km the zone is slightly concave to the nw at a depth of 300 km but contrary to many previous reports is not tightly concave nor are there significant spatial gaps in the seismicity which is effectively continuous with depth seismicity is however concentrated in the depth interval 250 300 km where the dip of the seismic zone changes from 70 above 250 km to a more gentle dip of 45 at greater depths seven fault plane solutions are available for the largest earthquakes in this depth interval all of them consistent with a p axis down the dip of the seismic zone and all of them requiring movement on faults out of the plane of the subducting slab two deep earthquakes near naples lie well outside the main zone of activity for one of which a fault plane solution is available that has ap axis not aligned with the dip of the seismic zone the tightly concave slabgeometry favoured by other reports is supported mainly by the location of these events near naples which we think may represent deformation in a separate probably shallower dipping piece of subducted lithosphere the lack of shallow seismicity and particularly of thrust faulting earthquakes at the surface projection of the benioff zone suggests that active subduction has ceased estimates of the convergence rate responsible for subduction in the last 10 myr far exceed the present convergence rate of africa and eurasia suggesting that the subduction was related instead to the stretching and thinning of the crust in the tyrrhenian sea

volcanological implications of crystal chemical variations in clinopyroxenes from the aeolian arc southern tyrrhenian sea italy crystal chemistry and structural data for clinopyroxene from the aeolian islands southern tyrrhenian sea italy were determined with the aim of obtaining geobarometric information and exploring implications for the structure of volcanic plumbing systems cell and m1 site volumes for clinopyroxenes which are known to decrease with increasing pressure of crystallization revealed variable values both within some single islands and along the entire arc indicating polybaric conditions of crystallization the lowest cell and m1 volumes were found at filicudi plotting close to values of clinopyroxenes from high pressure ultramafic xenoliths entrained in alkali basalts indications of high pressure crystallization were also found at salina and to a lesser extent at alicudi all situated in the western sector of the aeolian arc the central and eastern islands of lipari vulcano panarea and stromboli generally show higher values of cell parameters suggesting crystallization in shallow magma chambers these islands are characterized by the occurrence of large calderas which are apparently lacking at salina and filicudi time related variations were observed for cell and m1 volumes of clinopyroxene for some islands at salina the early erupted products display low values of cell parameters with respect to later activity thus indicating a decrease in crystallization pressure with time a similar although less striking pattern is observed at alicudi and lipari an overall increase in cell parameters with time was observed at the scale of the entire arc the observed variations in clinopyroxene structural parameters highlight the significance of pyroxene crystal chemistry for petrogenetic and volcanological interpretation correlation with time and the structural characteristics of volcanoes suggest significant regional and temporal modifications in the plumbing systems of aeolian volcanoes clinopyroxenes from filicudi and the older salina crystallized at high pressure in deep magma chambers in the lower crust or at the mantle crust boundary the lower crystallization pressure in the younger salina is interpreted as evidence of upward migration of magma chambers with time similar evolution can be envisaged for alicudi instead the entire evolutionary history of the central and eastern islands was dominated by low pressure crystallization with formation of calderas and generation of abundant acid products that are scarce or absent in the western islands evolution of the plumbing system of single volcanoes and of the aeolian arc in general is probably related to modification of stress regimes and or thinning of the arc basement due to the effect of uprising mantle material above the ionian subduction zone

a 550 km long moho traverse in the tyrrhenian sea from o b s recorded pn waves six obs deployed on a 550 km line in the tyrrhenian sea furnish reversed and overlapping profiles from 43 shots at 12 km intervals head waves recorded from a 8 km s refractor the moho permitted the computation of the crustal thickness which shows this basin to be underlain by an oceanic type of crust at least in two 100 km wide regions variations of pn arrival times mirror strong topographical changes of the moho differences in dips at the extremities towards corsica and calabria are documented

heat flow in the balearic and tyrrhenian basins western mediterranean we present the results of three detailed heat flow surveys which are used to investigate the variations of heat flow and age of the balearic and tyrrhenian basins in the western mediterranean analysis of 12 measurements within a 10 km radius from 40 01 4 55 e in the balearic abyssal plain shows a mean heat flow of 92 10 mw m 2 after correction for the effects of sedimentation this value agrees well with the predictions of plate cooling and high extension stretching models for crust of the late oligocene age proposed for the basin a similar survey with 18 measurements around 40 16 n 11 19 e in the western tyrrhenian gives a flux of 134 8 mw m 2 while the third survey of 26 measurements in the southern tyrrhenian abyssal plain at 37 17 n 12 58 e yields a slightly higher heat flow of 151 10 mw m 2 these values are within the range predicted by simple plate cooling models for the late miocene ages of the deep tyrrhenian basin thus our observations suggest that although the mode of crustal formation of these deep marginal basins is less well defined than that of the major ocean basins the thermal signature is similar also the trend of increasing heat flow from west to east through the balearic and tyrrhenian basins is in agreement with models of the formation of the western mediterranean behind an eastwardly migrating trench system in all three areas the measured flux shows significant local variability in the two westernmost surveys this can be attributed to the presence of buried high conductivity salt structures but in the third area se tyrrhenian the magnitude of the variations is several times greater than can be attributed to steady state thermal refraction alone instead evidence exists for localized hydrothermal activity linked to the small topographical relief within the survey area

uplift and extension at the gulf of suez indications of induced mantle convection reconstruction of tectonic movements since the initiation of the gulf of suez rift indicates that there has been 25 27 km of extension the uplift bordering rift indicates that lithosphere heating greatly exceeds that producible by uniform lithosphere extension i propose that small scale convection induced by the rifting augments the heating introduced by extensional rifting and produces the broad uplifts flanking the rift

continental collision and basin opening in southern italy a new plate subduction in the tyrrhenian sea an analysis of the spatial distribution of the seismicity of the southern tyrrhenian sea is presented with the aim of putting constraints on the geometry of the complex benioff zone of this area by relocating the earthquakes that occurred in the period 1985 1990 the data set used in this analysis is based on information from ing isc and neis databases in order to ensure the quality of epi hypocentral locations we based our selection of earthquakes on both the available number of p and s readings at least eight p and two s pickings and the epicentral distances of the stations reporting the event 5 such a selection enabled us to obtain a catalogue of 450 well located events with focal depths of up to 500 km the seismogenetic volumes estimated from the distribution of hypocentres of the whole seismicity analysed were interpreted according to a recent geodynamic model proposed for this area this has led us to the hypothesis of an active nw se oriented subduction of the lithosphere generated and stressed by the opening of the tyrrhenian basin

relationships among crustal structure volcanism and strike slip tectonics in the lipari vulcano volcanic complex aeolian islands southern tyrrhenian sea italy abstract the lipari vulcano volcanic complex lvvc aeolian arc southern tyrrhenian sea italy develops along a strike slip fault system that bisects the aeolian arc the lvvc crustal structure is investigated by applying seismic methods to two data sets p wavefronts generated by local and distant events constrain the shallow velocity structure dss data provide shape and depth of the main crustal discontinuities the obtained velocity model shows that the lvvc shallow structure is characterized by the presence of two sharp lateral discontinuities the northern discontinuity bounds a low velocity basin like structure including the la fossa caldera and mt guardia caldera depressions the southern discontinuity coincides with the southern boundary of a high velocity diffractor located beneath the la fossa cone direct modeling of dss data define three crustal discontinuities showing a complex geometry the intra crustal interfaces and the moho discontinuity show an upheaval beneath the lvvc central sector the estimated crustal velocities are lower than those generally reported for the continental crust this feature is due to the high heat flux and fluid circulation affecting the lvvc area the ratio between the thickness of the upper and lower crust and the presence of the moho upheaval are consistent with that reported for continental areas affected by extensional strain the collected geophysical data combined with volcanological and structural information indicate that a the mt guardia and la fossa caldera depressions represent the surface expression of a single structure whose formation is mainly due to tectonic processes b the lvvc crustal structure and the evolution of the volcanism are consistent with those recognized in zones of transition from arc related to rift volcanism in addition results of a preliminary mechanical analysis based on the available structural data indicate low values of the ratio between magmatic overpressure and tectonic stress this suggests a passive mechanism of mantle upwelling the mantle upwelling is due the post collisional normal strike slip tectonics affecting the aeolian arc

timescales of pre eruptive magmatic processes at vulcano aeolian islands italy during the last 1000 years abstract an integrated petrological and geochemical study on plagioclase crystals erupted at vulcano island aeolian islands southern italy over the past 1000 years allowed us to draw a detailed model of the internal structure of the volcanic system in which modes of magma interaction and timescales of storage at crustal depth are shown the integration of compositional textural and temporal record preserved in plagioclase crystals provides evidence for an articulated plumbing system constituted by several reservoirs connected at the crust mantle boundary here a basaltic shoshonitic magma resides and is thought to feed the shallow magma reservoir of both la fossa and vulcanello centers finally triggering eruptions throughout injections from depth textural and micro compositional data on plagioclase crystals suggest the presence of three main magma levels located between ca 17 and 2 km of depth beneath la fossa cone which were intermittently reactivated over the whole period of activity considered plagioclase textures and compositional zoning indicate that the shallow

triassic jurassic development of the st george s channel basin offshore wales uk abstract isopach maps and backstripped tectonic subsidence plots from the triassic jurassic of the st george s channel basin reveal significant departures from current models of extensional basin development i rifting was highly protracted with discrete increments of crustal extension spanning ca 120 my ii substantial syn kinematic sediment on the footwalls of major faults records pure shear sub seismic scale deformation to have been important during regional triassic extension forward modelling of depth converted seismic interpretations is used to test the notion of combined pure and simple shear and to quantify the distribution of crustal extension between large and sub seismic scale faults the models indicate that triassic subsidence was generated by ca 2 5 km extension on major faults and 10 km extension by sub seismic scale faulting in fault bounded compartments jurassic extension was dominated by large scale faults whereas in the areas of overlap between major fault segments jurassic extension was taken up chiefly by sub seismic scale faulting comparison of measured vitrinite reflectance vr and vr modelled from heatflow history yielded by the forward models supports this scheme of episodic pure shear dominated extension this research highlights the inherent difficulty in using seismic interpretation in isolation from quantitative subsidence and or thermal history data to identify syn and post kinematic sedimentary sequences furthermore it provides an opportunity to more fully reconstruct mesozoic basin development in the west of uk area which in the cheshire central and east irish sea basins is largely precluded by erosion of post triassic strata

the role of the crust in the magmatic evolution of the island of lipari aeolian islands italy volcanic rocks on the island of lipari show the entire range of sr nd pb isotopic compositions displayed by other islands in the aeolian archipelago the rapid isotopic evolution of subaerial volcanic rocks on lipari towards crustal values together with the appropriate isotopic composition of the neighbouring calabrian crust serre indicate that many geochemical characteristics observed in the lavas can be attributed to contamination and mixing with crustal materials and melts interpretation of the data is complicated by the fact that underplating onto the crust mantle boundary and the specific lithologies present in the crustal section differ underneath each individual sector of the island in the central and northern parts of the island metapelitic rocks were incorporated to provide the more radiogenic sr isotopic compositions of some lavas the products from m guardia in the southern part of lipari where activity is restricted to the last 30 40 ka bear geochemical similarities to the island of vulcano where it is proposed that considerable remobilization of the crust took place in the presence of mafic mantle derived melts on lipari the petrogenetic processes of magma mixing and assimilation dominate over fractional crystallization and the observed increase of k2o over na2o can be correlated with contributions from metapelitic crustal lithologies it is suggested that the variability in isotopic composition and the budget of alkalis na2o versus k2o in the lavas can be explained by invoking a heat source from an intruding asthenospheric morb type mantle into a cooler lithospheric crust mantle during the opening of the tyrrhenian basin

heat flow heat production and fission track data from the hercynian basement around the provencal basin western mediterranean abstract in the complex structural framework of the western mediterranean hercynian areas are expected to be thermally preserved from the recent tectonic evolution the thermal regime of these areas is studied using heat flow heat production and fission track data the surface heat flow is significantly higher in corsica 76 10 mw m 2 than in the maures and esterel 58 2 mw m 2 neither heat production nor erosion subsequent to the alpine orogeny in corsica can explain such a difference it is suggested that a deep thermal source related to the asymmetric evolution of the provencal basin could explain the higher heat flow in corsica a model of thermal structure based on the present day thermal regime of the maures and esterei is proposed for the stable hercynian crust in this area the mantle heat flow is 20 25 mw m 2 and the temperature at moho level is 375 500 c depending on the thermal parameter distribution with depth

tectono stratigraphic modelling of the sardinian margin of the tyrrhenian sea rifting of the east sardinia passive margin was characterised by a southeastward migration of the site of extension through time in the first stage of rifting 9 7 ma lithospheric thinning was mainly localised near sardinia crustal and subcrustal thinning factors averaged across the whole transect were 1 12 and 1 5 respectively at 7 ma i e immediately before the onset of the messinian salinity crisis the basin floor was at depths of up to 1000 m in the west and less than few hundred metres in the east during the second stage of rifting between 7 and 5 ma the site of main extension was located in the central part of the future margin with average crustal and subcrustal thinning factors of 1 18 and 1 63 respectively at 5 ma after the termination of the messinian salinity crisis the morphology of the basin floor had changed substantially with depths in general between 700 and 1000 m extension during the last rifting stage before oceanic crust formation at 3 5 ma was mainly concentrated in the southeastemmost part of the profile average crustal thinning factors increased dramatically to i 95 while the subcrustal one remained almost unchanged 1 64 the analysis of temporal changes of thinning factors shows that the opening of the tyrrhenian oceanic basin can be adequately explained with a depth dependent pure shear geometry with crustal and subcrustal thinning being accommodated on the same vertical column subcrustal thinning factors in the initial stages of rifting were higher than the crustal ones but the two become comparable approaching break up the regional compensation of changing loads coupled with a very deep depth of necking is consistent with the observed subsidence trend and basin stratigraphy

a seismic refraction experiment in the tyrrhenian sea summary we present the results of two 100 km long reversed seismic refraction lines shot in the tyrrhenian sea using explosive sources and oceanbottom receivers the results have been interpreted using ray tracing through laterally varying structures the more easterly line t2 was shot in the central part of the tyrrhenian abyssal plain in a water depth of 3 5 km the crust here is shown to be oceanic in character but to exhibit significant lateral heterogeneity the upper part of the crust layer 2 contains a steep velocity gradient from about 4 to over 6 km s l at a depth of typically 2 km the lower part of the crust layer 3 contains a smaller velocity gradient from 6 6 to 6 9 km s l at the base of the crust total crustal thickness is between 6 and 8 km the other line t1 carried out in the cornaglia basin in 2 7 km of water reveals a more complicated velocity structure we conclude that its southern half is underlain by oceanic crust similar to that observed at t2 however its northern half appears to be underlain by crust of similar thickness but in which seismic velocities increase slowly with depth from 4 9 km s l immediately below the superficial sediments to 6 3 km s l at the moho we interpret this latter structure as thinned continental crust surprisingly neither the seafloor topography nor the depth to moho reflect the transition from oceanic to continental crust we infer from these results that although the southern and eastern parts of the tyrrhenian basin were formed primarily by seafloor spreading much of the basin north of about 40 n and probably including some areas with water depths in excess of 3 km is underlain by thinned continental crust the evolution of the northern part of the tyrrhenian basin must therefore have occurred chiefly through a process of continental extension which in some areas has reduced crustal thickness to as little as 6 8 km south of 40 n

rapid subsidence of small oceanic basins a study of the marsili basin central mediterranean many small backarc basins show subsidence rates significantly greater than those in major ocean basins of similar ages in this study we test by numerical modeling the hypothesis that small backarc basins are formed by the same fundamental processes as major oceanic basins i e by accretion spreading and cooling and that the rate of subsidence is modified and accelerated by lateral heat loss from the hot subbasinal asthenosphere to the surrounding cooler continental lithosphere bathymetric seismic and drilling data in the marsili basin a small and young backarc basin in the central mediterranean are used to constrain the models the results of this analysis confirm the above hypothesis they further suggest that for actively spreading backarc basins the most rapid subsidence occurs in a zone near the margin of the basin during the earliest stage of basin spreading whereas after spreading terminates the location for rapid subsidence migrates towards the basin center

extension in south central british columbia mechanical and thermal controls abstract geological data indicate that the omineca belt in the canadian cordillera experienced a rapid episode of extension between 58 and 48 ma following a compressional event and crustal thickening in the early tertiary restored crustal sections have been constructed using listric fault geometries to infer that the amount of eocene extension affecting the southern omineca belt exceeded 50 at the end of compression in the early tertiary the omineca and intermontane belts of southern british columbia reached a crustal thickness of 60 km isostatic compensation implies that these belts formed elevated ranges this is consistent with sediment deposition west of these ranges and the absence of in situ sedimentary basins the stress induced by topography and crustal thickening is calculated the calculations show that the stress in homogeneously thickened lithosphere is small and that tensile stress in the crust is compensated by compression in the mantle removal of the mantle lithosphere induces a stress field that is tensile throughout the lithosphere this local stress field combined with stress induced at the plate boundary by the oblique impingement of the kula farallon ridge controlled the position and direction of crustal extension in south central british columbia the present high heat flow on the west flank of the omineca belt 80 mw m 2 is interpreted as the relict of eocene extension following removal of the lithospheric mantle

contribution of controlled source seismology to the study of seismogenesis examples from the italian transitional area abstract the shallow seismicity in the italian region is dependent on the lithospheric and especially on the crustal structure the major contribution to the definition of crustal features as well as of their lateral variations which in this area are very large has been given so far by the profiles of deep seismic soundings wide angle reflection it has been found that the shape of the velocity depth functions is a good indicator of the crustal type this study illustrates the comparison of the velocity functions with the depth distribution of seismic foci the analysis was done in active seismic zones where the hypocentral depth is known with fair accuracy both the events contained in the general catalogue of italian earthquakes and the micro earthquakes were used the chosen zones are located in different geological settings it has been found that different shapes of the velocity depth curve correspond to different depths of the most active seismic layer the role of velocity inversions seems particularly meaningful to mark the transition from the brittle to the ductile regime when the strongest seismicity is in the upper crust when the lower crust or the upper mantle appears to be the source of the main seismicity different shapes of the velocity functions are observed finally a further different type of velocity distribution is obtained in zones of high geothermal flow where only very shallow and low magnitude events are recorded

migration of the seismic aseismic transition during uniform and nonuniform extension of the continental lithosphere we investigate the thermal and seismic implications of two extreme configurations of lithospheric extension one extreme treats the extension as being approximately uniform with depth the upper crust extending by the rotation of fault bounded blocks above a diffusely deforming lower crust in the other extreme crustal extension occurs only above a low angle fault dip less than about 10 very low angle shear zones that initially move aseismically within a uniformly extending lithosphere may be raised through the depth range that is normally seismically active without cooling appreciably the condition for this to occur is that extension should take place faster than about 10 14 s in contrast extension accommodated entirely above a very low angle shear zone rapidly brings that zone to temperatures at which it should be seismically active even if initial movement on it were aseismic the different thermal histories implied by the two configurations of extension offer the possibility of distinguishing between modes of extension by observations of temperature time and pressure temperature paths on rocks close to low angle faults

volcanological and geochemical evolution of filicudi aeolian islands south tyrrhenian sea italy this paper reports on field petrological geochemical and isotopic characteristics of volcanic rocks from filicudi island aeolian arc southern tyrrhenian sea with particular attention to the recognition of temporal and geochemical variations of magma activity the filicudi volcano consists of basaltic basaltic andesitic and high k andesitic lavas and pyroclastic deposits it represents the emergent part of a complex structure parallel to the main regional structural lineaments stratigraphic investigations and dating have defined four main cycles of activity interrupted by periods of quiescence the main stratigraphic sequences reconstructed on filicudi display irregular variations of rock evolution over time with recurrent reversals to more basic compositions magmas erupted from different vents during the first three cycles of activity display overall similar petrological and geochemical characteristics some major and trace elements define slightly scattered correlations with silica sr abundances are particularly scattered with a large range of values in basic rocks sr isotope ratios range between 0 704270 and 0 704740 and do not exhibit good correlations with geochemical parameters fractional crystallization associated with several episodes of mixing processes and crust assimilation are considered to be responsible for the complex evolution of the filicudi magma mafic magmas erupted during the last cycle of activity at la canna centre show increasing k na mg al rb sr and decreasing ba nb ba rb ratios in respect to the older basalts these characteristics are considered to reflect a derivation from a different mantle source

structural evolution of the tyrrhenian back arc basin abstract the tyrrhenian basin has developed as a marginal basin through drifting of the calabrian sicilian arc system towards the east southeast the main structural features of the basin result from this movement the tensional structures normal faults of the margins are mainly aligned n10 to n30 e the transform faults are oriented n110 n120 e except for a previous structuralization linked to the western mediterranean rifting and drifting the first extensional movements affected the tyrrhenian area as early as lower miocene time during the post burdigalian nevertheless the main rifting phase which led to oceanic accretion was initiated during the late tortonian the narrow central oceanic area generated mainly around the early pliocene is restricted to the rift s axis the marginal basin type of evolution of the tyrrhenian sea is most probably directly linked to subduction of the ionian lithosphere nevertheless interferences between collision in the surrounding apennines calabria or sicilides and subduction processes have dominated this special back arc basin evolution since late tortonian time the tyrrhenian arc shows a regional n120 e oriented tensional pattern short compressional events occur briefly in middle pliocene and middle pleistocene times correlated with brief paroxysmal phases of extension and subsidence the deformation depends on the presence of a subduction zone parallel to the calabrian arc swell which allows the migration of the unblocked segments of the arc in a n120 e direction

the calabrian arc and the ionian sea in the dynamic evolution of the central mediterranean in the central mediterranean area it is possible to recognize three main realms the tyrrhenian sea the pelagian block and the ionian block these domains are limited by important fracture zones that are easily recognizable on land and offshore these fracture zones can be grouped into four main trends 1 the nw se trend which is characterized by dextral horizontal movements 2 the ne sw trend which is generally characterized by sinistral lateral horizontal movements 3 the e w trend which also shows dextral shear movements and 4 the n s trend which is characterized by normal faults only the tyrrhenian sea realm is characterized by a thinned crust of oceanic type and is connected to the apenninic chain by means of listric faults from a geophysical point of view the area shows a high heat flow which follows the main structural trends and positive gravimetric anomalies which are compatible with seismic refraction data and can be explained by the proposed model the pelagian block shows a continental crust about 20 km thick which progressively increases beneath the sicilian chain here an abrupt interruption with the tyrrhenian block takes place in the pelagian realm rifting processes developed according to the nw se and n s trend the n s trend characterizes the westernmost zone of the realm where volcanic processes and a relatively high heat flow can also be observed the ionian block is characterized by the following a thinned crust 17 20 km which increases 40 km towards the southern calabrian chain a thick sedimentary sequence high positive bouguer anomalies 300 mgal and very low heat flow 50 mw m 2 geophysical and structural analyses allowed us to evaluate the post tortonian evolution of the whole area under consideration this evolution resulted in continental crust formation according to a rigid plastic deformation model according to our model the ionian block can be considered as a domain characterized by a thinned continental crust and affected by intrusive material derived from the upper mantle furthermore this domain of probably jurassic age can be considered as a pelagic basin bordered by the pelagian block to the west and by the apulian block to the east northeast this basin according to its position with respect to the apenninic and sicilian chains has not been affected by tectogenesis and still represents a site of continuous sedimentation from a kinematic point of view the ionian realm can be linked with the pelagian block shifting towards the east northeast whereas it is limited towards the north by an e w fracture zone which regulates the opening of the tyrrhenian sea and the counterclockwise rotation of the apenninic chain according to the proposed model the opening of the tyrrhenian sea can be considered as a megaextension fracture which developed parallel to the maximum principal stress direction and evolved as a triangular shaped structural feature in preparing the model the authors have taken into account a large set of data collected both on land and offshore

shear wave attenuation in the lithosphere beneath italy and surrounding regions tectonic implications more than 700 waveforms produced by 51 shallow earthquakes and recorded at regional distances 250 1400 km by the italian seismic network have been analyzed to characterize the amplitude and frequency contents of the crustal and uppermost mantle shear waves lg and sn respectively the crustal phase lg efficiently propagates through the relatively stable adriatic continental crust while it is not observed along propagation paths crossing major physiographic features like the apennine chain and the basinal domain of the tyrrhenian and ionian seas similar to lg efficient sn propagation is observed in the uppermost mantle beneath the po plain and the adriatic sea efficient sn transmission is also observed across the northern ionian sea and sicily and in the area between sardinia and the northern coasts of africa sn are efficiently transmitted across the sicily channel and rather efficient sn propagate beneath the ligurian sea on the contrary inefficient sn transmission characterizes the uppermost mantle beneath the apennines the western margin of the italian peninsula and the southern tyrrhenian sea shear wave attenuation suggests the presence of asthenospheric material in the uppermost mantle probably related to the present day extension along the apennine chain and in the tyrrhenian basin this interpretation is consistent with the presence of extensive neogene and quaternary volcanic activity in these areas and related high heat flow proposed lithospheric delaminatioh processes beneath the apennines and subduction beneath the tyrrhenian sea can reasonably explain the observed high attenuation zones in the uppermost mantle in contrast a high strength mantle lid is inferred to underlay the po plain the adriatic sea and the northern ionian sea the available waveforms also indicate that a continuous mantle lid is present beneath sicily and the extensional domain of the sicily channel as well as in the marine area south of sardinia

evolution of the pannonian basin system 1 tectonics the carpathian arc formed during cretaceous to miocene time by continental collision between europe and smaller continental fragments following southward and westward subduction of ocean floor during the last stages of thrusting in the outer carpathians a set of discrete basins formed behind the carpathian loop these basins are regions of middle to late miocene extension and are connected to each other and to areas of coeval shortening in the outer carpathian thrust belt by a system of strike slip faults sinistral northeast trending and dextral northwest trending sets of conjugate shears reflect overall east west extension of the intra carpathian region during middle to late miocene time palinspastic reconstruction of the basins indicates about 100 50 km of east west extension across the intra carpathian region during this time we interpret the vienna basin which is superimposed partly on the flysch nappes of the outer west carpathians as the result of thin skinned extensional tectonics above a shallow detachment surface within the crust extension of upper crustal rocks above this detachment was probably accomodated by thrusting of the outermost nappes of the west carpathians over the european platform extension of basins farther inside the carpathian loop probably involved rocks at deeper crustal levels and within the upper mantle the most internally situated basins formed by extensional processes that involved the entire lithosphere thus the depth to which extension occurred seems to be closely related to the proximity of each basin to the active thrust front in the carpathians this can be related to the geometry of the subduction zone extension within the intra carpathian basins began first in the northernmost basins and migrated southward and eastward over a ten million year period palinspastic reconstruction of the basins at three different times during the miocene 17 5 16 5 and 13 0 ma predicts eastward migration of the zone of thrusting and shortening within the carpathian mountains to accomodate the synchronous eastward and southward migration of areas of extension from these reconstructions about 120 60 km of east west shortening is predicted across the outer east carpathians from about 17 5 ma until present both predictions are in good agreement with the timing and magnitude of shortening in the carpathian thrust belt as determined directly from rocks within the belt from this we infer a close relationship for middle to late miocene extension of the intra carpathian region and middle to late miocene crustal shortening within the outer carpathians during middle and late miocene time deformation of the pannonian fragment was dominated by extensional and wrench tectonics except along a narrow zone in the outer carpathian thrust belt middle and late miocene thrusting in the carpathians is interpreted as the result of simple shear caused by relative motion between europe and the overriding pannonian fragment at the subduction boundary rather than of regional compression of lithospheric rocks at depth the initiation of extensional tectonics within the intra carpathian region in middle miocene time can be related to reorganization of major fragment boundaries of the eastern european alpine system

extremal bounds on geotherms in eroding mountain belts from metamorphic pressure temperature conditions summary we present a technique based on linear programming for inverting metamorphic pressure temperature pt information from one or more stratigraphic horizons in an eroded mountain belt to determine maximum and minimum bounds on geotherms as a function of time in the orogen these extremal bounds characterize the set of all possible geotherms at a particular time in the history of the mountain belt consistent with the metamorphic data using synthetic pt data generated from several assumed initial thermal profiles we demonstrate the sensitivity of the extremal bounds determined by this inverse technique to the number distribution and accuracy of the pt measurements we conclude that 20 myr after orogeny the set of all possible geotherms is reasonably well constrained reconstruction of tight bounds on possible geotherms as early as 10 myr after the orogeny requires accurate pt measurements from more than one structural horizon finally we provide an example of extremal bounds consistent with real metamorphic pt data from the lower schieferhulle in the tauern window of the austrian alps combined with estimates of the mechanical strength of the continental lithosphere supporting the alps derived from gravity observations our results suggest that the temperature at the elastic ductile transition in continental lithosphere exceeds 540 c

some unsolved birps problems summary birps has 8000 km of records around britain that are relevant to the rheology of continents and to faulting of the lithosphere problems include the need to measure seismic velocities with better resolution and to eliminate multiples in deep water the question are blank bits of records due to noise increase or to geology and the need to know the physics of the origin of deep reflections in order to answer geologists questions

tectonic evolution of the corsica apennines alps region studied by the method of successive approximations paleotectonic and paleogeographic maps are often very complex users find it difficult to evaluate the extent to which the features shown are based on reliable geologic data and it is not generally possible to estimate uncertainties in shapes and positions in the scientific tradition of designing simple models to represent complex reality this study uses systematically simplified palinspastic models to study the tectonic evolution of the central mediterranean the prime constraint is northwestward motion of the african continent toward europe at 7 5 km m y in the first approximation model only unidirectional plate motion is allowed and the model is unable to generate both the alpine and apennine orogenic belts at right angles to each other the second approximation allows rotations it is surprising how well this very simple model with its rigidly restrictive rules reproduces the known evolution of the central mediterranean this agreement allows some optimism that the second approximation is correctly modeling the primary features of the tectonic evolution of the central mediterranean revising the shapes of the tectonic entities in a third approximation would allow the final pattern to mimic even more closely the present tectonic situation in the mediterranean but here the advantages of rigid simplification would start to diminish the first conclusion of the paper is thus that strongly simplified models are useful in tectonic studies and are justified in light of the uncertainties simplified models are used to explore the recently proposed ancient apennine hypothesis in which apennine deformation begins with a reversal of subduction polarity at about 100 90 ma this view contrasts with the standard young apennine hypothesis in which subduction reversal and the onset of apennine orogensis do not occur until 35 30 ma study of the simplified tectonic models leads to the second conclusion of the paper that the ancient apennine hypothesis honors regional constraints as well as the standard view does the simplified modeling suggests specific tests in alpine corsica for choosing between the young apennine and ancient apennine hypotheses

dome growth rates eruption frequency and assessment of volcanic hazard insights from new u th dating of the panarea and basiluzzo dome lavas and pyroclastics aeolian islands italy abstract new geochronological data are presented and discussed together with field data in order to reconstruct the geo volcanological evolution of panarea island attention is focused on the discrepancies between geochronological data compared with field evidence field data provide evidence that the panarea dome was continuously built up without a significant break in volcanic activity continuous extrusion of new magma allowed the dome to emerge subaerially subaerial effusive activity followed with the alternation of exogenous and endogenous phases of growth that led to the formation of radial and tangential lava lobes and plugs the younger volcanic products are represented by a thick succession of pyroclastic products discontinuously outcropping all over the island dated here for the first time samples were dated through the u th disequilibrium method which is also able to provide information on the geological processes at the origin of u th fractionation the chronology of the volcanic events at panarea suggests that the volcanic activity developed through two main phases effusive activity mainly characterized the first phase of the dome growth while during the second phase explosive activity prevailed the second phase occurred from 31 7 to 20 2 ka assessing the age of the first phase is more difficult the age of 155 12 ka which is in the same time span obtained from k ar or ar ar methods is not consistent with field evidence furthermore although the alignment of the points on the isochron is very good the initial value of the 230th 232th ratio is very low and does not have a clear meaning our data strongly suggest that the age of 155 12 ka is not realistic two alternative scenarios are proposed implying a revision of the geological and geochronological evolution of the island together with the significance of the marine terraces on panarea

modern tectonic regime in the tyrrhenian area observations and models summary the rapid opening since 10 ma of the tyrrhenian sea in a context of convergence between eurasia and africa remains a puzzling geodynamic problem one of the most plausible scenarios proposed by malinverno ryan 1986 attributes extension to southward and eastward migration of the trench resulting from subduction of the african adriatic lithosphere below the european lithosphere at present subduction only continues along the calabrian arc a compilation of recent strain and stress indicators by rebai philip taboada 1992 indicates that an extensional regime still prevails in the tyrrhenian sea whereas compression dominates north and south of this area in an earlier paper bassi sabadini 1994 used a numerical model to demonstrate the necessity of a trench suction force acting along the subduction trench to produce the present extension in the tyrrhenian domain this study however did not discuss in detail the tectonic regime in the different areas composing the domain nor the match between the observations and the model in this paper we first review the constraints provided by the observations compiled by rebaiet al 1992 and by more recent measurements we then investigate how much of the observed tectonic regime can be understood in terms of plate interaction forces using thin plate models bird 1989 the geometry and heterogeneous lithospheric properties of the models are constrained by observations the best constrained boundary conditions are held constant the remaining are regarded as parameters that we tune in order to fit the observations our results indicate that the present day tectonic regime in the tyrrhenian area can be explained as a consequence of trench retreat associated with the subduction of ionian oceanic lithosphere under the calabrian arc combined with a rotation of the apennines possibly related to a rotation of the adriatic microplate this study supports therefore the model of malinverno ryan 1986 and suggests moreover that rotation of the apennines is an ongoing process which is supported by seismological and geodetic data but remains to be understood in terms of geodynamics a discrepancy between observations and models is observed in western sicily which can be attributed to modelling limitations the weak extensional activity of the corsica sardinia block however is not explained by this model

volcanological and petrological evolution of vulcano island aeolian arc southern tyrrhenian sea petrological and geochemical data are reported for volcanic rocks from vulcano island the subaerial volcanism 120 ka to present built up a nw se elongated composite structure affected by two intersecting multistage calderas volcanics older than 20 ka consist mostly of high k calc alkaline hkca to shoshonitic sho mafic rocks these magmas interacted significantly with the continental crust which generated variable sr isotopic ratios 0 70412 0 70520 however a major role was also played by input of parental liquids into the magma chamber which prevented further evolution of the magmas hkca sho and potassic ks rocks formed from 20 to 8 ka display a much larger range of sio2 from shoshonites to rhyolites and higher concentrations of incompatible elements with respect to the previous stage sr isotopic ratios show small variations 0 70448 0 70486 mixing of silicic and mafic liquids and fractional crystallization processes fc were the main evolutionary processes during this stage volcanics younger than 8 ka consist of sho and leucite bearing ks mafic rocks with abundant intermediate and silicic products mafic and intermediate rocks display similar incompatible element abundances and sr isotopic ratios as the previous stage volcanics whereas higher 87sr 86sr 0 70494 0 70583 are observed in some rhyolites these products originated from a complex interplay of fc crustal assimilation and magma mixing processes the most mafic rocks show increasing incompatible element abundances rb sr rb ba mg al mg ca and a decrease in large ion lithophile to high field strength element ratios passing from older hkca sho to the younger sho ks volcanics these variations suggest a shifting of magma sources from a slightly metasomatized asthenosphere fertile peridotite to a more strongly metasomatized lithospheric mantle residual peridotite time related petrological and geochemical variations have been used to develop a model for the evolution of the vulcano plumbing system

lower crustal extension across the northern carnarvon basin australia evidence for an eastward dipping detachment asymmetry and strain partitioning along conjugate margins are often explained in terms of detachment faults nevertheless cogent evidence for their existence remains limited furthermore even when inferred detachment faults are imaged seismically it is difficult to demonstrate that differential displacement has occurred across these surfaces we present tectonic and stratigraphic evidence from the northern carnarvon basin northwest australia that documents the existence of an intracrustal eastward dipping detachment by integrating sequence stratigraphy with kinematic and isostatic models of basin development we conclude that the northern carnarvon basin was formed as a consequence of four extension events 1 a broadly distributed late permian event 2 a predominantly localized rhaetian event responsible for the inception of the barrow and dampier subbasins 3 a localized callovian fault reactivation within the barrow dampier subbasins and 4 a tithonian valanginian event that generated large post valanginian regional subsidence across the northern carnarvon basin with only minor accompanying brittle deformation and erosional truncation the regional distribution and amplitude of the post valanginian subsidence are not consistent with the minor amounts of tithonian valanginian brittle upper crustal extension observed on the margin large portions of the platform were emergent or at very shallow water depths prior to the tithonian valanginian extension to match the distribution and magnitude of the post valanginian thermal type subsidence requires significant lower crustal and mantle extension across the northern carnarvon basin such a distribution of extension implies the existence of an eastward dipping intracrustal detachment having a ramp flat ramp geometry that effectively thinned the lower crust and lithospheric mantle the detachment breached the surface close to the position of the continent ocean boundary west of the exmouth plateau the flat component of the detachment occurred at midcrustal depths 15 km across the plateau and ramped beneath the australian continent lower crustal ductile extension provides a viable mechanism to generate large regional subsidence with little attendant brittle deformation which may explain the paradox that both sides of many conjugate margins appear to be the upper plate

tectonic evolution of the north sea basin crustal stretching and subsidence summary the lithospheric stretching model for the formation of sedimentary basins was tested in the central north sea by a combined study of crustal thinning and basement subsidence patterns a profile of crustal structure was obtained by shooting a long range seismic experiment across the central graben the main axis of subsidence a seabed array of 12 seismometers in the graben was used to record shots fired in a line 530 km long across the basin the data collected during the experiment were interpreted by modelling synthetic seismograms from a laterally varying structure and the final model showed substantial crustal thinning beneath the graben subsidence data from 19 exploration wells were analysed to obtain subsidence patterns in the central north sea since jurassic times changes in water depth were quantified using foraminiferal assemblages where possible and observed basement subsidence paths were corrected for sediment loading compaction and changes in water depth through time the seismic model is shown to be compatible with the observed gravity field and the small size of observed gravity anomalies is used to argue that the basin is in local isostatic equilibrium both crustal thinning and basement subsidence studies indicate about 70 km of stretching across the central graben during the mid jurassic to early cretaceous extensional event this extension appears to have occurred over crust already slightly thinned beneath the graben and the seismic data suggest that total extension since the early permian may have been more than 100km the data presented here may all be explained using a simple model of uniform extension of the lithosphere

subsidence crustal structure and thermal evolution of georges bank basin a geophysical study of georges bank basin defines a deep crustal structure that is interpreted in terms of the basin s tectonic and thermal history gravity models along three basin cross sections delineate two zones of crustal thinning at the basement hinge zone and oceanic crustal margins these two zones bound rift stage crust about 25 km thick which underlies the central portion of the basin subsidence analysis of the basin using data from multichannel seismic reflection lines and two cost wells suggests a rifting and uniform extensional origin two dimensional finite difference modeling of the basin defines a crustal structure that concurs with the gravity and subsidence studies the resulting isotherms show no major changes in the thermal structure since the ate jurassic in some areas of the basin temperatures sufficient for oil generation are determined from maturation studies of jurassic sediments hydrocarbon generation is questionable however because of the probable lack of proper and sufficient kerogen in the jurassic deposits

thermo mechanical modeling of the tyrrhenian sea lithospheric necking and kinematics of rifting we present the results of quantitative forward modeling of the sardinian rifted margin of the tyrrhenian sea the purpose of this study is to investigate the thermo mechanical structure that affects the thinning of the lithosphere across the margin the role of lithospheric necking during basin formation constrained by basement topography moho depth and gravity anomalies is modeled for different compensation models independent constraints are obtained from the analysis of the predicted thermal structure a deep level of necking 25 km is required to explain the observed crustal geometries and gravity anomaly signature the model predicts spatial and temporal variations in rheology during extension with important implications for kinematics of lithospheric thinning prerift lithospheric conditions strain rate and temperature during extension appear to be the key controls on the style of lithospheric rifting and necking in the tyrrhenian sea a forward model for basin stratigraphy is presented for the polyphase history of the tyrrhenian rifting this model provides quantitative estimates of time space dependent crustal thinning and rates of extension

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

thermal state and deep earthquakes in the southern tyrrhenian the geodynamic processes in the southern tyrrhenian are approached by comparing the thermal structure with the seismic activity subsidence data are used to determine the boundaries of the oceanic domains in the abyssal area the regional pattern of the surface heat flux reflects lateral variations of structural properties of the lithosphere in the oceanic domain a mean heat flux of 160 mw m 2 is observed to which a convective component of about 100 mw m 2 should be added if an ocean plate cooling model is applicable for a pure shear stretching model the heat flux values of the continental margins indicate a thinning factor of 3 5 4 0 the maximum frequency of seismic events occurs in the 200 350 km depth interval and the energy released is maximum between 250 and 300 km most earthquakes are confined within a 30 50 km thick zone the slab dip angle is about 65 in the 100 400 km depth range characterised by predominant down dip compression then both the slab and the maximum compression axis slightly deflect down to 500 km depth where the deepest event occurs under the hypothesis that the seismic activity is confined within portions of downgoing lithosphere which have a temperature below a depth dependent critical value calculations for a 60 70 km thick slab sinking at a velocity of 6 10 2 m yr 1 yield a thermal structure compatible with the distribution of the deepest seismic activity such a thermomechanical picture and the correlation between the slab dip angle and the total tectonic subsidence of the oceanic domain are typical features of a young marginal basin and are related to the drag stress in the vicinity of the downgoing lithosphere

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

crustal thinning and subsidence in the north sea we present here the results of a detailed study of subsidence and crystal thinning across the central graben of the north sea basin two independent lines of evidence have been used to test how well the uniform extensional model1 2 can account for the evolution of the north sea basin a long range seismic profile was shot perpendicular to the central graben from edinburgh to southern norway and data were analysed from 11 exploration wells situated close to the seismic line fig 1 the estimates of the increase in surface area due to extension from the crustal structure determined using the seismic data and from the well subsidence patterns are both compatible with a simple uniform extensional mechanism for the post palaeozoic evolution of the north sea

amincissement de la croute et accretion au centre du bassin tyrrhenien d apres la sismique refraction seismic refraction lines were carried out in the deep central area of the tyrrhenian basin and near the foot of adjacent margins using air guns as seismic source and pop up bottom seismographs pubs valuable correlations between refraction and reflection data enable us to identify messinian and pre messinian series beneath plio quaternary series on stretched margins toward the middle of the basin detritic to volcanodetritic series overlay the acoustic basement the p wave velocity depth distributions inferred from synthetic seismograms on most of the profiles are similar to those computed for oceanic areas especially for spreading zones such as the atlantic ridge the east indian ridge the reykjanes ridge progressive velocity increasing with depth velocity inversions within the crust moho depth of 10 11 km low pn velocity of 7 73 km s 1 suggesting the existence of an abnormal mantle layer 3 is 7 km deep probably including a 2 km thick layer 3b 7 44 km s 1 our data are in good agreement with the assumption of a recent accretion beneath the central basin of the tyrrhenian sea along a cross section at 40 n latitude running from the sardinian to the apenninic margins the moho discontinuity rapidly rises from 27 km to 11 km depth beneath the central tyrrhenian basin the 6 0 km s 1 granitic layer beneath sardinia disappears east of the central fault and reappears again along the facing apenninic margin

residual topography lithospheric structure and sunken slabs in the central mediterranean abstract the central mediterranean comprises subduction collision and backarc extension all in a relatively small area in this paper we analyze the topography of this region examining the influence of subducting slabs on overriding plates we take the observed surface elevation remove the contribution of the crust to it and use the residual topography to identify regions that are unusually low unusually high or normal then we calculate lithospheric thickness where local isostasy applies the results provide information about the structure of the lithosphere in this complex region and about the vertical tectonics in particular we found a difference between the south tyrrhenian subduction zone and the apennines consistent with the processes of slab rollback and slab break off respectively in the south tyrrhenian the edge of the oceanic plate is strongly pulled down whereas the edge of the overriding plate the calabrian peninsula is uplifted this opposite trend indicates weak plate coupling that is the subducting slab which is rapidly rolling back hangs almost entirely on the oceanic plate and the overriding plate is free in contrast in the apennines high residual topography and uplifting are detected on both sides of the mountain belt consistent with complete break off of the subducted lithosphere

volcanological evolution of the rivi capo volcanic complex at salina aeolian islands magma storage processes and ascent dynamics lava flows and pyroclastic deposits from strombolian fallout related to the activity of the rivi and capo volcanoes which are representative of early subaerial volcanoes on salina aeolian islands have been investigated through a geological petrological approach our geological field survey shows that rivi and capo volcanoes are part of a single n50 e aligned volcanic complex here named rivi capo volcanic complex rcvc stratigraphically specific rock sampling has allowed reconstruction of the magma feeding processes through time whole rock major element compositions together with core to rim profiles of plagioclase and clinopyroxene crystals show a general evolution toward more basic compositions through the three formations constituting the capo volcano and within the rivi center melts simulations and mass balance modeling suggest that the rcvc rocks are the result of fractional crystallization of plagioclase clinopyroxene and olivine ca 45 of solid removed from a primary magma in addition to fractional crystallization continuous recharge and mixing with more basic magma coming from deeper parts of the magmatic plumbing system contributed to the final volcanic rock compositions our textural and microanalytical data on plagioclase and clinopyroxene crystals allow the definition of a multilevel magmatic storage system with reservoirs at 20 and 3 km below sea level when processes of magma differentiation ascent and storage are considered together with the stratigraphic position of each sample a history of continuous modification of the rcvc plumbing system can be constructed volcanism may have been characterized by fissure type eruptions during the early stages lower capo lower rivi and middle capo formations gradually changing later to central type volcanism upper capo and upper rivi formations

evolution and genesis of calc alkaline magmas at filicudi volcano aeolian arc southern tyrrhenian sea italy petrological trace element and sr nd pb isotopic data are reported for volcanic rocks from the island of filicudi aeolian arc southern tyrrhenian sea the volcano consists of several monogenic and polygenic centres built up through four major phases of explosive and effusive activity started before 1 ma rock composition ranges from calc alkaline basalts to high k andesites there is a negative correlation between silica and mgo cao tio2 feototal and a positive trend for k2o na2o and p2o5 lile and hfse increase with silica whereas ferromagnesian trace elements have an opposite tendency incompatible elements such as zr ba rb la display well defined positive correlations on elemental variation diagrams weak correlations are shown by the other incompatible elements sr and compatible elements define negative roughly curvilinear trends with incompatible elements 87 sr 86 sr is poorly but significantly variable 0 704016 0 704740 and shows overall higher values in the mafic than in the sialic rocks nd isotope ratios range from 0 512670 to 0 512760 and are negatively correlated with 87 sr 86 sr pb isotope ratios cluster around 206 pb 204 pb 19 31 19 67 207 pb 204 pb 15 64 15 69 208 pb 204 pb 39 11 39 47 major trace element and isotopic variations reveal complex multistage polybaric evolutionary processes for the filicudi magmas it is clear that crystal liquid fractionation processes determined many of the petrologic and geochemical characteristics of these magmas however elemental variations when coupled with isotopic variations in particular sr isotopes demonstrate that mixing processes and interaction of the magmas with older crustal material also played an important role when compared with other aeolian arc volcanoes filicudi shows petrological and geochemical characteristics similar to those of the nearby islands of salina and alicudi the three islands consist of calc alkaline rocks but the degree of magma evolution increases going from the alicudi to salina these variations are likely related to the plumbing system of the three volcanoes however trace element and isotopic evidence also suggests significant variations of primary magmas which reveal a zoned source which suffered different types of metasomatism d 2003 elsevier b v all rights reserved

geothermal structure of the tyrrhenian sea over 200 heat flow measurements have been carried out in the tyrrhenian sea mostly since 1977 as part of the heat flow map for italy and surrounding seas italian program as well as part of the french italian tyrrhenia program all data have been corrected for the influence of the plio quaternary sedimentation measured heat flow values were evaluated according to the sedimentary environment following criteria outlined by sclater et al 1980 in this way areas affected mainly by shallow thermal effects in the zones with maximum density of data have been displayed filtering out these shallow contributions the major regional geothermal trends were obtained the tyrrhenian basin can be divided in two distinct regions with different geothermal characteristics the northern part of the basin appears to be connected with the continental structures involved in the interaction between the corsica and tuscan margins the maximum heat flow area located offshore civitavecchia is related to the tensile structures of the tuscan geothermal province the most important thermal features of the central and southern part are located along the central belt trending nw se the lowest heat flow values are located in the peri tyrrhenian areas and are related to the continental margins of the basin while the maxima are connected with the stretched and thinned area localized in the bathyal plain taking into account the heat flow data as well as other geological and geophysical information an evolutionary model for the tyrrhenian sea is presented suggesting a generalized stretching of an initially continental crust accompanied by intensive rifting phases which may have favoured the onset of oceanic type crust

source parameters and three dimensional attenuation structure from the inversion of microearthquake pulse width data qp imaging and inferences on the thermal state of the campi flegrei caldera southern italy the three dimensional p wave attenuation structure of the campi flegrei caldera and the estimate of source parameters for 87 local microearthquakes is obtained by the nonlinear inversion of pulse width and rise time measurements by using the method described by zollo and de lorenzo this issue source radii represent the better resolved parameters with values ranging from 70 m to 230 m the dip and strike angles defining fault orientations are usually affected by larger uncertainties and are well constrained only for 11 events the dip fault is usually confined in the range 30 60 with an average uncertainty of 12 the fault strikes mainly range between 60 and 60 and seem to define preferential directions oriented radially from the symmetry axis of the ground deformation stress drop estimates indicate rather low values 0 01 1 mpa which suggest low strength properties of the incoherent and brittle materials filling the caldera primarily yellow tuffs the three dimensional qp images obtained from the inversion of p pulse durations show two significant low qp anomalies between 0 and 1 km of depth in the north eastern sector and at 2 3 km of depth in the central eastern sector of the caldera the high degree of spatial correlation of the low qp zone and low vs as inferred by aster and meyer 1988 at 0 1 km in depth and other geophysical and geochemical observations suggest that this anomaly can be related to the presence of densely fractured porous and fluid filled rocks in the ne sector of the caldera the deeper low qp anomaly is interpreted as being related to a dominant thermal effect we used the surface and deep borehole temperature measurements available in the area to obtain a local calibration curve to convert qp in temperature at campi flegrei the retrieved t qp map shows a high thermal deep disturbance 450 500 c at depths between 2 and 3 km in the eastern sector of the caldera where the most recent eruptive activity is concentrated the present day temperature field retrieved by qp images has been interpreted by using a three dimensional thermal conduction model assuming an extended heat source initial temperature of 800 c located underneath the attenuation anomalous region the results indicate that the qp inferred temperature field can be related to the heat conduction effect of one or more molten bodies whose top should be at about 4 km depth consistent with recent seismic estimates of the magma chamber top at campi flegrei ferrucci et al 1992 this study suggests that the present thermal state and rock rheology of the inner caldera could be controlled by the cooling of molten bodies that originally intruded at depths of 1 4 1 6 km during one or more recent time of 10 kyr eruptive events

temporal evolution of a three component system the island of lipari aeolian arc southern italy the volcanic products from lipari define an evolutionary trend with a high gradient of k enrichment similar to the calc alkaline to potassic volcanism of other islands in the aeolian arc stratigraphic reconstruction of the island based on field and geochronological data indicate that the volcanic activity can be subdivided in two stages the first stage from 223 to 42 ka consists of six eruptive cycles and is characterized by basalts and basalt andesites showing progressive increase in both sio2 and k2o contents with time the second stage consists of four cycles erupted since 42 ka and is marked by an apparent rejuvenation of the geochemical system with the appearance of the first rhyolitic products fractional crystallization assimilation and mixing models suggest that the geochemistry of lipari volcanism evolved with time by a complex interplay between two mantle derived components one sub alkaline and the other alkaline in addition to crustal melts and or crustally derived materials a petrogenetic model in which fractional crystallization was subordinate to mixing best fits the geochemical data and petrographic observations of macro and microscopic features melts from the crustal and mantle end members are almost always present in the system but the relative proportions appear to vary with time the sub alkaline mantle component source of tyrrhenian tholeiites is an important contributor to the early evolution of the volcanism in lipari input from the alkaline mantle component source of the roman comagmatic province increases with time and the crustal component becomes dominant in the later activity the preferred petrogenetic model for the temporal evolution of the volcanic system in lipari involves melting initially caused by an increase in the thermal input related to the opening of the tyrrhenian sea and or to subduction processes the quick rise of the isotherms and almost contemporaneous melting of source materials with different compositions favored complex mixing during ascent of the melts

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

the relationship between geology and landforms along a coastal mountain front northern calabria italy the geomorphology of the central coastal range a north south trending horst along the west coast of northern calabria is governed largely by major faults fault scarps and the distribution of principal rock types as well as by a variety of slope processes operative in a mediterranean climate segments of the major rivers and streams have three principal orientations parallel to major faults in the study area northwest right oblique slip faults oldest e w oblique slip faults ne left oblique slip faults and north south right oblique normal faults youngest all of which cut pre tertiary metamorphic rocks mesozoic limestone miocene molasse and calcarenite small underfit alluvial fans composed chiefly of locally derived debris flow detritus are present at the mouths of large west flowing canyons some of which reach eastward to the crest of the mountain range not only do the north south normal faults displace rocks and structures of all orientations but they also make steep scarps in the small alluvial fans and in sediments of the coastal plain locally some of the scarps are buried by recent debris flow deposits incipient young rivers utilized the weaknesses along the major faults and cracks as avenues of erosion smaller streams and gullies generally flowed westward downflank of the north trending horst and incised thereby deep v shaped canyons some of them have captured older sw flowing canyons locally they were guided in other directions where they encountered faults or tectonic fractures the rocks present a varied resistance to erosion depending upon the degree of cementation by groundwater salts upon the orientation of the foliation and upon the rocks themselves thus mica schist with a relatively flat foliation forms nearly vertical sea cliffs but the sea cliffs are more gentle where the foliation is steep or dips towards the sea therefore downslope movements are facilitated by seaward slip on foliation schistosity bedding and fault surfaces and are evinced especially by large and deep pre holocene landslides sackung in phyllite having areal dimensions up to 2 km2 other downslope processes include surficial creep and soil slip particularly of highly fractured phyllite and schist block sliding and rock falls

seismic reflectivity of the whipple mountain shear zone in southern california the whipple mountains shear zone of southeastern california comprises part of the whipple mountains metamorphic core complex of the north american cordillera the 3 9 km thick shear zone displays excellent exposures of ductilely deformed mid tertiary mylonitic gneisses as well as kinematically related but younger cataclasites which underlie a major low angle normal fault the whipple detachment fault prominent crustal reflections beginning at 3 4 s were recorded on calcrust seismic profiles southwest of the whipple mountains in order to interpret these seismic reflections and to understand why detachment faults are imaged on some profiles but not on others we collected oriented rock specimens from all major structural units in the whipple mountains and determined p wave velocities for these samples parallel to three principal fabric directions under laboratory induced confining pressures up to 500 mpa using a geologic section through the mylonitic gneisses from a previous investigation we then constructed a detailed acoustic impedance section for the whipple mountain shear zone based upon laboratory results this section was in turn used to compose two dimensional synthetic reflection seismograms for comparison with the calcrust records significant impedance contrasts are enhanced by the opposing fabric orientations between the interlayered but structurally isolated relict domains of nonmylonitized rocks and the surrounding mylonitic gneisses the finite thickness and lateral extent of these rock units cause constructive interference in seismic modeling to create the seismic fabric of strong laterally discontinuous but subparallel reflections as seen in the calcrust profiles southwest of the whipple mountains chloritic breccias beneath the whipple detachment fault wdf have much lower seismic impedance than that of rocks occurring both structurally above and below however the significant thinning of the chloritic breccia zone to the southwest of the whipple mountains may have caused the poor image of the wdf on the calcrust profiles the absence of a detachment reflection is thus not necessarily indicative of the absence of a subsurface fault zone

odp leg 107 in the tyrrhenian sea insights into passive margin and back arc basin evolution leg 107 of the ocean drilling program drilled a west northwest east southeast transect of seven sites across the tyrrhenian sea the youngest of the sub basins of the mediterranean sea sites 654 653 652 and 656 document the rifting and subsidence of the sardinia passive continental margin on the upper margin site 654 we cored a classic transgressive sequence subaerial conglomerates overlain by oyster bearing sands overlain by marine marl comparison between the recovered lithologies and seismic reflection profiles suggests that the synrift sediments on the upper margin are tortonian late miocene to messinian latest miocene in age whereas synrift sediments on the lower margin are messinian to pliocene in age during the messinian desiccation of the mediterranean sites 654 and 653 now on the upper sardinian margin apparently occupied a basinal setting where they received nannoplankton bearing clays interbedded with laminated gypsum sites 656 and 652 now on the lower sardinia margin were apparently higher standing during the desiccation event their messinian facies are subaerial and lacustrine respectively we infer from these lines of evidence that tilting and subsidence occurred more than a million years earlier on the upper margin than on the lower margin such diachroneity can be interpreted in terms of migration of the zone of maximum extension above a rolling back subduction zone or in terms of extension of continental crust by shear along a deep detachment fault sites 655 651 and 650 were drilled into two small basalt floored basins of the central and eastern tyrrhenian emplacement of basaltic crust in the central tyrrhenian vavilov basin apparently began more than a million years before emplacement of basaltic crust in the eastern tyrrhenian marsili basin this observation is compatible with previous suggestions that the tyrrhenian has grown southeastward in response to rollback of the down going slab that currently dips northwestward under the toe of italy at the easternmost site high vesicularity of the basalt and benthic foram assemblages in the oldest sediments imply that the basalt erupted in water shallower than 2 500 m it has apparently subsequently subsided to its present depth of 4 100 m below sea level nearly three times as fast as normal subsidence of crust formed at a mid ocean ridge

a numerical study of a mantle plume beneath the tharsis rise reconciling dynamic uplift and lithospheric support models 1 the tharsis rise is an area of extensive volcanism containing the most significant long wavelength topographic and areoid anomalies on mars the mechanism for supporting this large topographic expression and correlating areoid remains controversial the two main competing ideas are dynamic support by a deep mantle plume and a volcanically constructed lithosphere followed by lithospheric flexure while both of these models separately can account for specific features of tharsis neither explain its entirety most of the support of the tharsis topographic anomaly is best explained by a volcanic structure modifying the lithosphere however this raises the important question of the origin of the heat source for volcanic construction leading to possible small scale convection this demonstrates that the remaining topography and areoid not accounted for in lower end members of volcanically constructed surface loads is consistent with a deeper mantle plume source our results show we can produce about 15 and 18 of the total tharsis long wavelength areoid and topography anomaly with a plume forming in a strong temperature dependent rheology additionally our plume model has a 165 km thick rheological lithosphere within the range for present day estimates on mars and generates about 1 partial melting more than sufficient to provide a heat source for recent volcanism this implies both a model with dynamic support from a plume and a volcanically constructed lithosphere not only can coexist but offer an explanation for both the surface anomalies and heat needed for the minor amount of recent volcanic activity at tharsis rise

statistical comparison of palaeomagnetic directional records from lake sediments summary this paper presents three statistical methods for testing the reproducibility or compatibility of palaeomagnetic directional records in undated cores of sediment these methods are based on a the intrinsic equations curvature and torsion as functions of arc length of the curve defining changes in direction b an f test derived from multiple linear regression theory and c the construction and comparison of confidence bands all methods utilize a projection of palaeomagnetic unit vectors on to the tangent plane to their mean direction since preliminary alignment to a common depth scale is necessary both for method b and for subsequent pooling of data some theoretical results are presented for this problem allowing for the possibility of missing segments in either core methods b and c are applied to two cores from loch lomond scotland both methods show that after suitable relative rotation and alignment these palaeomagnetic directional records are indeed compatible demonstrating that the loch lomond sediments can provide reliable palaeosecular variation data of high quality

magma storage conditions and differentiation of the mafic lower pollara volcanics salina island aeolian islands italy implications for the formation conditions of shoshonites and potassic rocks crystallization experiments of basaltic andesite mafic endmember from the 24 ka lower pollara eruption salina aeolian islands italy were investigated at 200 mpa 950 1100 c in the h2o activity ah2o range 0 3 to 1 and at two ranges of oxygen fugacity fo2 between fmq to fmq 1 and fmq 2 to fmq 3 3 log bars fmq is fayalite magnetite quartz comparison of the produced phase assemblages and phase compositions with the natural sample reveals that the storage conditions were 1050 c 2 8 wt h2o in the melt ah2o 0 5 and relatively oxidizing fmq 2 5 the composition of plagioclase in the groundmass indicates a period of cooling to 950 c the overall differentiation trends of the salina volcanics can be explained by fractional crystallization close to h2o saturated conditions 5 wt h2o in the melt at 200 mpa and most likely by accumulation of plagioclase i e in basaltic andesites and by various degree of mixing mingling between the corresponding differentiates the slightly elevated k2o contents of the most mafic basaltic andesites that can be found in the lowermost unit of the lower pollara pyroclastics reveal earlier processes of moderately hydrous fractional crystallization at higher temperature 1050 c fractional crystallization with decreasing influence of h2o causes a moderate decrease of mgo and a significant increase of k2o relative to sio2 in the residual liquids it is exemplarily shown that the crystallization of sio2 rich phases at high temperature and low ah2o of only moderately k2o rich calc alkaline basalts can produce shoshonitic and high potassic rocks similar to those of stromboli and volcano this suggests that the observed transition from calc alkaline to shoshonitic and high potassic volcanism at the aeolian arc over time can be initiated by a general increase of magmatic temperatures and a decrease of ah2o in response to the extensional tectonics and related increase of heat flow and declining influence of slab derived fluids

evolution of the pannonian basin system 2 subsidence and thermal history analysis of sedimentation and thermal data indicates that for most parts of the pannonian basin observed heat flow thermal gradients rates of thermal subsidence and vitrinite reflectance are about twice those predicted by assuming a uniform extension model for basin formation in late miocene time a modified extension model whereby large amounts of heat are added to the uppermost mantle during extension roughly equivalent to replacing the entire sub crustal lithosphere by asthenosphere produced results in good agreement with observation and could also account for periods of uplift observed during extension crustal extension beneath most parts of the basin is estimated to have been about 80 to 170 1 8 to 2 7 although in the deepest parts of the basin deeper than 4 km crustal extension could have been much greater analysis of extension within the danube and zala basins indicates that the late miocene extension in these basins involved the entire lithosphere but subsidence and heat flow data are not well enough constrained to determine if extra heating is required during extension on the basis of tectonic and structural data the vienna basin has been interpreted as the result of thin skinned extensional tectonics above a shallow detachment surface within the upper crust royden et al this issue analysis of thermal and subsidence data from the northern vienna basin suggests that little or no heating occurred during basin extension these data are consistent with a thin skinned extensional origin for the vienna basin and are in better agreement with this interpretation than with the assumption of a uniformly extended lithosphere beneath the basin this study emphasizes the need for good thermal subsidence and structural data in making reconstructions of extensional and thermal histories of sedimentary basins when such data are available it is found that a simple uniform extension model does not explain very well the evolution of some sedimentary basins such as the vienna and pannonian basins in the first instance the basin is thought to be the result of upper crustal extension only due to its special tectonic setting in the second instance the extra heating during extension is due to some unknown processes in the lower lithosphere that may be a general feature of lithospheric extension thus lithospheric extension and associated heating may be distributed in a variety of ways not all extensional sedimentary basins form in the same way application of a uniform subsidence model to basins for which good thermal subsidence and structural data are not available or not properly analysed can lead to reconstructions of thermal histories in error by a factor of 2 or more

ground deformation of the southern sector of the aeolian islands volcanic arc from geodetic data abstract the deformation pattern and the dynamics of the southern sector of the aeolian archipelago are investigated a study on the ground deformation measured over the last 20 years in the trilateration geodetic network between the islands of vulcano and lipari has been conducted analysis of the relative displacements and the uniform strain tensor parameters as well as the comparison between areal dilatation and the vertical variations deduced by precise levelling allow distinguishing different phases associated both with the regional dynamics and the local volcanic context of the area these phases however appear to be closely interrelated the analysis of the deformation pattern allows to constrain the predominance of a roughly e w trending extension and a n s contraction at a regional scale this regime is consistent with right lateral movements along a nw se striking fault system

oblique rifting in salina lipari and vulcano islands aeolian islands southern italy a structural analysis carried out on the volcanic products of the islands of salina lipari and vulcano aeolian archipelago points out that the large scale tectonic setting is dominated by nw se trending right lateral extensional strike slip faults and by n s to ne sw trending normal faults and fractures this fault pattern generates pull apart type structures developing between different right hand overlapping fault segments and a characteristic extensional imbricate fan geometry at the tip of the major strike slip faults all the structures representing the surface expression of an active crustal discontinuity which controls the evolutionary history of the magmatism of the three islands are kinematically compatible with a n100 e extension related to a rifting process affecting southern italy

thermal evolution of a rift basin the tyrrhenian sea existing geological and geophysical data support the view that the opening of the tyrrhenian sea was by rifting of a formerly continuous continental lithosphere which began in upper miocene on the upper sardinian margin and migrated southeastward to the calabria margin heat flow across the tyrrhenian sea shows a pronounced asymmetry from about 50 70 mw m 2 over the sardinian margin to more than 150 mw m 2 over its southeastern margin off southern italy and calabria in this study we use the newly acquired data from ocean drilling program leg 107 heat flow seismic velocity and bathymetric data to constrain a group of models that supposes the tyrrhenian sea opened by detachment of a formerly continuous lithosphere along a southeastern facing low angle normal fault specific models tested include 1 the wernicke model in which thinning and extension of the continental lithosphere are supposed to be accomplished by simple shear along a large scale gently dipping detachment fault zone which cut through the entire lithosphere and 2 the delamination model in which the low angle detachment fault is supposed to cut only the upper and middle crust but to merge subhorizontally into the lower crust below which concurrent pure shear may occur a versatile two dimensional finite element procedure is used to evaluate the tectonic and thermal evolution of these models and the results are compared with observations to test the validity of the models delamination models with large pure shear components in the lower lithosphere and the wernicke model predict heat flow within 1 of the measurements the wernicke model however predicts a basin configuration much too deep in comparison with bathymetry and a subbasinal lithospheric thickness substantially different from rayleigh wave dispersion results the delamination model with a large component of pure shear in the subbasinal lower lithosphere on the other hand predicts satisfactorily both the bathymetry and the lithospheric thickness beneath the basin

geochemistry of the submarine gaseous emissions of panarea aeolian islands southern italy magmatic vs hydrothermal origin and implications for volcanic surveillance the marine sector surrounding panarea island aeolian islands south italy is affected by widespread submarine emissions of co2 rich gases and thermal water discharges which have been known since the roman age on november 3rd 2002 an anomalous degassing event affected the area probably in response to a submarine explosion the concentrations of minor reactive gases co ch4 and h2 of samples collected in november and december 2002 show drastic compositional changes when compared to previous samples collected from the same area in the 1980s in particular the samples collected after the november 3rd phenomenon display relative increases in h2 and co and a strong decrease in the ch4 contents while other gas species show no significant change the interaction of the original gas with seawater explains the variable contents of co2 h2s n2 ar and he which characterize the different samples but cannot explain the large variations of co ch4 and h2 which are instead compatible with changes in the redox temperature and pressure conditions of the system two models both implying an increasing input of magmatic fluids are compatible with the observed variations of minor reactive species in the first one the input of magmatic fluids drives the hydrothermal system towards atypical more oxidizing redox conditions slowly pressurizing the system up to a critical state in the second one the hydrothermal system is flashed by the rising high t volcanic fluid suddenly released by a magmatic body at depth the two models have different implications for volcanic surveillance and risk assessment in the first case the november 3rd event may represent both the culmination of a relatively slow process which caused the overpressurization of the hydrothermal system and the beginning of a new phase of quiescence the possible evolution of the second model is unforeseeable because it is mainly related to the thermal baric and compositional state of the deep magmatic system that is poorly known