flexure of lithosphere beneath apennine and carpathian foredeep basins evidence for an insufficient topographic load the pliocene foredeep basin external to the apennine thrust belt and the late miocene foredeep basin external to the outer east carpathians are considered typical molassic foredeeps that formed contemporaneously with thrusting in the adjacent mountain belts a simple mechanical model in which the response of the lithosphere to loading was approximately by a semi infinite broken elastic plate overlying a weak fluid was used to analyze the deflection of the foreland lithosphere beneath the apennine and outer east carpathian foredeep basins along three transects perpendicular to the thrust belts comparison between the calculated and observed depth to basement suggests that the emplacement of thrust sheets onto the foreland lithosphere during mountain building failed to pr duce a sufficient load to create the observed foredeep basins and observed topography regardless of the position of the slab end or the flexural rigidity assumed for the foreland lithosphere we infer that an additional subsurface load must be present and that its magnitude must be roughly equal to the load created by that part of the thrust belt that is above sea level for the two apennine transects an acceptable fit to the shape and size of the observed foredeep basin was generated by assuming effective elastic plate thicknesses of 8 and 15 km 4 9 and 9 3 mi and applied vertical forces of 2 1015 dynes cm and 1 3 1015 dynes cm at the slab end for the carpathian transect an effective plate thickness of 30 km 18 6 mi and an applied force of 1 5 215 1015 dynes cm generated an acceptable fit this study suggests a method whereby an estimate of the depth to autochthonous basement rocks beneath overthrust belts can be made in some areas where this information is not available from seismic or drilling data such an approach may enable exploration geologists to determine if crystalline rocks encountered in drilling overthrust terranes are a part of the autochthonous basement or if they are part of an overthrust sheet in the latter situation oil bearing sequences of sedimentary rocks might lie below crystalline rocks contained in the allochthonous sheet

flexure of the continental lithosphere beneath apennine and carpathian foredeep basins the formation and development of foredeep basins adjacent to marginal fold and thrust belts are thought to be the result of flexural loading of the foreland lithosphere by migrating thrust sheets1 and this concept has formed the basis for many recent studies of the deformation of the continental lithosphere and consequent evolution of foreland basins2 7 the preservation of foredeep basins after the associated mountain belt has been greatly reduced by erosion suggests that an additional load independent of the topography must act on the lithosphere of the subducted slab6 to determine whether such an additional load might be present in some very young orogenic belts we constructed transects through the apennine and outer flysch carpathian thrust belts of the mediterranean region fig 1 using a simple elastic model which assumes a semi infinite broken elastic plate of constant flexural rigidity overlying a weak fluid we show that the topographic loads present along these transects are insufficient to cause the observed plate deflection this suggests that there is an additional load or downward force acting on the plate to produce the observed plate deflection beneath the foredeep troughs we suggest that this extra load resulted from either the negative bouyancy contrast between the subducted slab and the surrounding asthenosphere or modification of the crustal structure within the overriding plate due to the initiation of backarc rifting in the hinterland

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

forward modeling of the southern apennines forward kinematic modeling has been developed to reconstruct the successive geometries of geological sections the method is tested here on a geological section across the southern apeninnes where syntectonic neogene deposits are of help in determining the timing of the deformation that progressively affected more eastern parts of the apulian margin well known triassic and paleogene decollement levels induced thin skinned tectonics in the mesozoic and cenozoic sedimentary cover but the basement geometry is only poorly revealed by subsurface data two distinct hypotheses have been tested 1 thin skinned tectonics and 2 basement involved tectonics the shortening of the prism is estimated to be between 170 and 210 km whether or not the basement is involved in the imbricated stack of thrust sheets the results are discussed in the light of regional constraints i e regional flexure uplifts etc which favor basement involved structures at depth in addition to the effects of compression other phenomena affected the geometry of the prism and have to be taken into account because of the recent uplift of the belt the inner parts of the apenninic wedge have emerged and undergone erosion part of this eroded material has been simultaneously trapped in piggyback basins which record both the geometric and temporal evolution of the prism normal faulting also affected the western part of the southern apennines reactivating older thrust as detachment surfaces along which block rotation occurred

role of subsurface loads and regional compensation in the isostatic balance of the transverse ranges california evidence for intracontinental subduction bouguer gravity anomalies in the transverse ranges of southern california show a pronounced asymmetry in north south profiles across the mountains and a characteristic shape which is largely insensitive to variations in the topographic load along strike while individual gravity topography profile pairs could be consistent with a number of isostatic compensation mechanisms the unusual relationship between gravity and topography in the san bernardino mountains severely limits the class of acceptable models if the bouguer gravity field is caused by flexure of the crust mantle boundary the simplest solution consistent with the data in the western transverse ranges the san gabriel mountains and the san bernardino mountains models the great valley and mojave provinces to the north as a 50 km thick elastic plate supporting the mountains which are underthrust by a much weaker plate to the south the best fit to the gravity data in the san bernardino mountains requires a terminal bending moment on the southern plate beneath the mountains the magnitude of the terminal bending moment decreases to the west in the san gabriel and western transverse ranges we equate the load responsible for this terminal moment with the high velocity slablike feature mapped in the upper mantle beneath the transverse ranges using seismic tomography the coupling between the subsurface load and the overlying lithosphere suggests that the slab represents lithospheric subduction with an extremely small density contrast rather than a small scale convective feature

first paleomagnetic results from mio pliocene series of the hellenic sedimentary arc abstract paleomagnetic measurements have been conducted on the mio pliocene series along the external sedimentary hellenic arc in order to detect the presence or absence of rotational deformations in different sections of the arc in the central eastern part of the arc crete and rhodes paleomagnetic directions are very closely aligned along the north south direction showing that this portion of the arc has not undergone significant rotation since at least 7 m y for crete and 4 m y for rhodes in the western and northwestern parts results from south peloponnesos zakinthos kephallinia and corfu indicate that this section of the arc has undergone a clockwise rotation detailed analysis of the data from the three ionian islands shows that their rotation began about 5 m y b p and has proceeded since then at roughly 5 m y giving a total amplitude of about 26 it is suggested that the beginning of this rotation is related to the lower pliocene compressive phase which most probably initiated the tectonic activity of the present day ionian margin

seismotectonics of the calabrian arc abstract relocation of intermediate and deep earthquakes of tyrrhenian sea area through joint hypocenter determination for the period 1962 1979 has allowed a more detailed definition of the geometry of this peculiar benioff zone earthquakes dip along a quasi vertical plane to 250 km depth there is a 50 dip in the 250 340 km depth range and a low dip angle to 480 km depth the structure sketched from the hypocenters is almost continuous but most energy has been released in the 230 340 km depth interval an evaluation of fault plane solutions of intermediate earthquakes in this area indicates predominance of down dip compressions in the central part of the slab at the border strike slip motion occurs independent of depth some earthquakes that occurred at intermediate depth less than 100 km along the ionian margin of calabria show predominance of reverse faulting with the p axis oriented se nw however shallow earthquakes in the calabria sicily region indicate a more complex motion with predominance of normal faulting a possible interpretation of these features according to the available geological history which involves subduction of continental lithosphere is discussed

deflection gravity anomalies and tectonics of doubly subducted continental lithosphere adriatic and ionian seas three profiles across the southern adriatic and northern ionian seas span an intermediate foreland area that is or has recently been subducted both westward under the apennine calabrian thrust belt and eastward under the hellenide belt gravity and deflection data from the base of the pliocene along the three profiles are qualitatively similar to those predicted for a thin elastic sheet subject to end loads at both plate ends more detailed analysis of the profiles shows very good agreement between observations and predictions if the intermediate foreland lithosphere is treated as a thin elastic sheet with an effective elastic thickness between about 15 and 20 km equivalent to a flexural rigidity between 2 1022 and 6 1022 nm these results coupled with seismicity data suggest that active convergence within the hellenides extends as far north as southwestern yugoslavia analysis of the northernmost profile across the southern adriatic sea shows a well constrained elastic plate thickness of 14 km and an initial water depth prior to loading of about 1 km the distance between the two subduction systems on this profile is estimated at about 275 km analysis of the two more southerly profiles yields a minimum effective elastic plate thickness of about 15 km but no maximum value could be determined the initial water depths for these two profiles are well constrained at 1 3 and 1 6 km prior to loading and the distance between the two subduction systems is estimated at about 175 km on both profiles along the northwest trend of the two opposing subduction systems the change in distance between the two systems occurs abruptly and the hellenic subduction system appears to be segmented into a series of northwest trending roughly linear subduction segments the calculated deflection profiles also show pronounced asymmetry on the northernmost profile and an opposite sense of asymmety on the southernmost profile

stratigraphy and tectonics offshore of puglia italy southern adriatic sea abstract the structural and stratigraphic framework of puglia offshore between the gargano promontory and the town of brindisi southern adriatic sea has been analysed based on 1700 km of multichannel seismic profiles and 10 exploratory wells the area includes two different geodynamic settings 1 part of the undeformed apenninic foreland apulian carbonate platform consisting mainly of shallow water mesozoic carbonates and 2 part of the southern adriatic basin which represents the foredeep of the hellenic thrust system a mesozoic slope buried by tertiary clastics and corresponding to the edge of the apulian carbonate platform is observed on seismic data the present physiography of the escarpment is the result of an erosional retreat mainly developed during the tertiary and related to the subsidence of the south adriatic basin at the same time carbonate facies belts as evidenced by well data seem to suggest that in some sectors of the margin the original mesozoic physiography has been preserved and fossilized three seismostratigraphic units separated by regional or local unconformities have been distinguished in the neogene clastic sequence of the south adriatic basin significant deformations in the sedimentary cover are represented by various antiforms one of these antiforms named the gondola ridge is an elongated positive structure deforming the pre tertiary basement the western sector of the gondola ridge belongs to a major e w strike slip lineament extending on land in the gargano promontory in the eastern part of the area in question some tectonic features resembling pop up like and thrust antiforms are arranged along an arcuate pattern named here grifone trend the grifone trend structures indicate a post pliocene tectonism probably related to the late stages of the dinaric hellenic orogenesis the recent westward migration of the hellenic fold and thrust belt can be demonstrated by the south adriatic foredeep shift during the last 5 6 million years

constraints on the structure of the himalaya from an analysis of gravity anomalies and a flexural model of the lithosphere the intracontinental subduction of india beneath the himalaya presents several similarities to that occurring at island arcs we study one of those similarities by analyzing gravity anomalies across the himalaya assuming that the topography is supported by the indian elastic plate flexed under the weight of both the overthrust mountains and the sediments in the ganga basin we first examine in detail the effects of each of the following parameters on the configuration of the elastic plate and on the gravity anomalies the flexural rigidity the position of the northern end of the elastic plate the amount of underthrusting of such a plate beneath the range and the density contrasts between the crust and mantle and between the sediments and the crust a plate with a constant flexural rigidity of about 0 7 1025 n m between 0 2 and 2 0 1025 n m allows a good fit to the data from the lesser himalaya and the ganga basin such a plate however cannot underthrust the entire himalaya instead the gravity anomalies show that the moho steepens from only about 3 beneath the lesser himalaya to about 15 beneath the greater himalaya this implies a smaller flexural rigidity beneath the greater himalaya 0 1 to 1 0 1023 n m than beneath the ganga basin and the lesser himalaya even with a thin weak plate beneath the greater himalaya the weight of the mountains depresses the plate too much unless an additional force or moment is applied to the plate the application of a bending moment unit length to the end of the plate of about 0 6 1018 n m is adequate to elevate the indian plate and to bring the calculated gravity anomalies in agreement with those observed both the smaller flexural rigidity and the bending moment can be understood if we assume that part or all of the indian crust has been detached from the lower lithosphere that underthrusts the greater himalaya we study the tectonic implications of these results by means of a series of idealized balanced cross sections from the collision to the present that reproduce several important features of the geology of the himalaya and predict an amount of eroded material comparable to that in the ganga basin and the bay of bengal these cross sections include high grade metamorphic rocks near the main central thrust and a steeper dip of it there than in the lesser himalaya they predict rapid uplift only in the greater himalaya and at the foot of the lesser himalaya

gravity anomalies and flexure of the lithosphere at mountain ranges the bouguer gravity anomaly over the himalayan alpine and appalachian mountains is characterized by a generally asymmetric gravity low which spans the mountains and associated foreland basins the minimum of the gravity low is generally systematically displaced from the region of greatest topographic relief and shows no obvious relationship to surface geology in addition the alps and appalachians are associated with a generally symmetric gravity high that is unrelated to the topographic relief together the gravity low and high form a characteristic positive negative anomaly couple the steep gravity gradient between the positive and negative couple correlates with the insubric line and its equivalents in the alps and the brevard zone in the southern appalachians this gravity anomaly couple is interpreted as evidence for flexure of the continental lithosphere by subsurface buried and surface topographic loading the magnitude of the subsurface load is estimated from the integrated excess mass represented by the positive anomaly and the magnitude of the surface load from the topography by combining these loads the flexure of the lithosphere and the associated bouguer gravity anomaly are calculated for different assumed values of the elastic thickness te of continental lithosphere the best fitting value of te for the himalayas is 80 100 km for the alps 25 50 km and for the appalachians 80 130 km the model calculations suggest that the main contribution to the gravity couple in the alps and appalachians arises not from surface loads such as thrust sheets and nappes but from subsurface loads however in the case of the himalayas the topography appears to be a sufficient load to explain the observed asymmetric gravity low when subsurface loads do exist therefore we would not expect a close correlation between mountain topographic relief and depth to the m discontinuity as required by classical models of isostasy rather the m discontinuity is expected to relate to the center of mass of all the loads acting on the lithosphere the surface and subsurface loads inferred from the gravity anomaly play a major role in the development of mountains and foreland basins the emplacement of large subsurface loads represents the primary event in the alps and appalachians while in the himalayas the emplacement of the surface load is the primary event the emplacement of the subsurface load probably marks the initiation of foreland basin development the regional characteristics of the basin are controlled by the primary load while local variations are controlled by the secondary thrust sheet loads subsequent movement of either load will produce migration of the basin depocenter the origin of the subsurface load is not clear but its association with the insubric line in the alps and the brevard zone in the appalachians suggests that it may be related to the obduction of crustal blocks flakes onto the underlying plate during continental collision or possibly to the preloaded crustal structure of the underlying plate

adriatic flexure and seismotectonics in southern italy abstract the morphological features of the mesozoic platform in the apulo garganic region and beneath the southern apennines have been tentatively interpreted as consequences of the flexure of the adriatic lithosphere to make a rough quantitative check of this hypothesis and to provide a possible interpretation to the main seismotectonic features in this area the flexural pattern of a thin elastic lithospheric plate loaded at one edge by a bending moment has been determined the satisfactory fit between the theoretical results and observations mainly relating to the morphology of the mesozoic platform the distribution of vertical movements and the concentration of strongest earthquakes within a narrow band in the apennines leads us to think that the tectonic premise is feasible

is the adriatic an african promontory seismicity patterns and fault plane solutions for the largest recent earthquakes in the adriatic region are used to test the hypothesis that the adriatic is a promontory of the african continental mass the horizontal projections of the slip vectors for the 24 best constrained focal mechanisms trend at a high angle to those predicted for the africa eurasia collision and so the adriatic cannot be thought of as a promontory of africa the slip vectors define an instantaneous pole of rotation that describes anticlockwise rotation of the adriatic relative to eurasia the adriatic is a stable continental block moving within the broad zone of deformation between africa and eurasia

assessing and calibrating the atr ftir approach as a carbonate rock characterization tool abstract atr ftir attenuated total reflectance fourier transform infrared spectroscopy can be used as a rapid and economical tool for qualitative identification of carbonates calcium sulphates oxides and silicates as well as quantitatively estimating the concentration of minerals over 200 powdered samples with known concentrations of two three four and five phase mixtures were made then a suite of calibration curves were derived that can be used to quantify the minerals the calibration curves in this study have an r2 that range from 0 93 0 99 a rmse root mean square error of 1 5 wt and a maximum error of 3 10 wt the calibration curves were used on 35 geological samples that have previously been studied using xrd x ray diffraction the identification of the minerals using atr ftir is comparable with xrd and the quantitative results have a rmsd root mean square deviation of 14 and 12 for calcite and dolomite respectively when compared to xrd results atr ftir is a rapid technique identification and quantification takes

gravity anomalies flexure of the indian plate and the structure support and evolution of the himalaya and ganga basin bouguer gravity anomalies along four profiles across the western himalaya and ganga basin show large deviations from local isostatic equilibrium a deficit of mass characterizes the ganga basin and an excess underlies the lesser himalaya both can be understood if the indian plate is flexed down by the distributed load of part of the mountains the cross sectional shape of the ganga basin seems to be controlled by the deflection of the indian plate which we compute assuming the indian plate to overlie an inviscid fluid from the shapes of both bouguer anomaly profiles and the basement topography we place bounds on the flexural rigidity of such a plate if the ganga basin is a steady state feature then the age of the basal sediments in a given locality should be proportional to the distance of that locality from the southern edge of the basin if the rate of convergence of india and the himalaya were constant that rate should equal the distance divided by the corresponding age we find a rate of 10 to 15 mm a for the last 15 to 20 ma which is consistent with a large part of the 50 mm a rate of convergence between india and eurasia being absorbed by the eastward extrusion of parts of tibet profiles of bouguer gravity anomalies show only a small peak or plateau over the southern edge of the lesser himalaya implying that the boundary between the light sediments of the ganga basin and the heavier crustal rocks of the lesser himalaya is not sharp and that there exists some light material beneath the range we infer that some sediment deposited in the ganga basin has been underthrust beneath the lesser himalaya but the quantity is small most of this sediment probably is scraped off the indian plate to make the foothills of the range we find that the load of the high himalaya is too large to be supported solely by elastic stress in the indian plate if the flexural rigidity of the plate is constant and if no other external forces act on the plate the observed gradient in bouguer gravity anomalies increases from an average of about 1 mgal km over the ganga basin and lesser himalaya to about 2 mgal km over the high himalaya this increase in the gravity gradient implies that the moho dips more steeply 10 15 beneath the high himalaya than beneath the lesser himalaya 2 3 we interpret this steepening of the moho to be due to a weakening of the plate which allows it to bend more sharply beneath the high himalaya than farther south with the inclusion of a weak segment of indian plate beneath the high himalaya calculated anomalies show a somewhat increased gradient beneath the high himalaya but when the weight of the entire himalaya is used as a load on the plate calculated anomalies are more negative than observed therefore an external force system is needed to support much of the weight of the high himalaya as well as to bend the plate sufficiently beneath the high himalaya the magnitudes of the bending moment and the force per unit length that must be applied to the end of the plate are compatible with their sources being gravity acting on a part of india s mantle lithosphere stripped of its crust and underthrust beneath southern tibet

thrust loads and foreland basin evolution cretaceous western united states two dimensional modeling of loading during the formation of the idaho wyoming thrust belt shows that regional isostatic compensation by flexure of an elastic lithosphere is sufficient to control the formation of a foreland basin the flexural rigidity of the lithosphere is inferred to have been approximately 1023 nm 1030 dyne cm on the basis of palinspastic comparison of predicted downwarping due to the thrust plate loads to the shape of the sedimentary wedge on the west side of the cretaceous western interior seaway erosion of part of the uplifted thrust plates redistributed the load depositing it farther to the east thereby causing subsidence over a much wider area than could have been accomplished only by the loading by thrust plates paleotopography after major cretaceous thrust events was calculated the resulting mountainous terrain gentle alluvial plain and flat sea floor correspond well with the topography of the modern foreland thrust belt and basin system in the andes of south america and to paleogeographic reconstructions in the western united states thrust belt topography is controlled by the subsurface geometry of the thrust faults particularly the positions of ramp zones and by isostatic subsidence

constraints on the structure of brooks range and colville basin northern alaska from flexure and gravity analysis tectonic thickening of the crust within the adjacent brooks range fold thrust mountain belt has been suggested as a probable cause for rapid subsidence of the colville basin in the early cretaceous a simple mechanical model in which the response of the lithosphere to loading was approximated by a semi infinite broken elastic plate overlying a weak fluid was used to analyze deflection of the basement beneath the colville basin comparison between the calculated and observed depth to basement suggests that the emplacement of thrust sheets onto the lithosphere during mountain building cannot produce a load sufficient to create the observed basin geometry and observed topography regardless of the position of the slab end or flexural rigidity assumed for the lithosphere an additional subsurface load capable of producing a deflection of the foreland basin roughly equal to the depression caused by the topographic load of the brooks range is required bouguer gravity data from the region are characterized by an asymmetric gravity low which spans the brooks range and colville basin and a gravity high to the south gravity modeling is consistent with a subsurface load with a mass of approximately 2 5 1013 g cm located beneath the southern brooks and the yukon koyukuk province to the south the origin of the subsurface load is interpreted as obduction of crustal blocks onto an old rifted continental margin during attempted continental a type subduction the colville basin was also influenced by the contemporaneous development of the northern arctic continental margin loading by subsurface and topographic loads to the south and loading on the continental margin to the north resulted in the formation of the barrow arch just offshore of northern alaska a best fitting value for mechanical thickness of the lithosphere beneath the colville basin is approximately 65 km

polar basal melting on mars if ice is present throughout the cryosphere anywhere on mars thermodynamic considerations suggest that it is most likely at the poles given this condition the deposition of dust and h2o at the polar surface will ultimately result in a situation where the equilibrium depth to the melting isotherm has been exceeded melting ice at the base of the cryosphere until thermal equilibrium is once again established should deposition persist the polar deposits will ultimately reach a thickness where melting will occur at their actual base at this point the cap may reach a state of equilibrium where the deposition of any additional ice is balanced by geothermal melting thermal calculations yield basal melting thicknesses that are consistent with the inferred 4 6 km thickness of the present north polar cap however in the south the deposits appear sufficiently thin 1 2 km that geothermal melting is likely to be relegated to a depth that lies well below the regolith polar cap interface similar conclusions are reached from consideration of the polar caps theoretical equilibrium profiles in the north a basal yield stress characteristic of ice at or near the melting point is indicated while in the south it appears the cap has yet to achieve the necessary height for significant deformation to occur at its base the potential importance of basal melting is illustrated through the discussion of four examples 1 the origin of the major polar reentrants 2 the removal and storage of an ancient martian ice sheet 3 the mass balance of the polar terrains and 4 the possibility of basal melting at temperate latitudes this analysis suggests that the process of basal melting may play a key role in understanding the evolution of the martian polar terrains and the long term climatic behavior of water on mars

ionian sea western greece its structural outline deduced from drilling and geophysical data abstract this paper outlines the preliminary structural results obtained by the compilation of geological drilling and geophysical data in western greece most external geotectonic zones of the hellenides are included in the geological setting of the marine and insular domain of western greece ionian pre apulian and apulian zones the gavrovo and pindus zones make a restricted contribution to the marine geological framework continental shelf of southwest peloponesus besides the geographical setting of the geotectonic units their general tectonic characteristics allow the following remarks to be made the main tectonic events younger than eocene are well marked in both ionian and pre apulian zones the detrital sequence shows a fast pinch out towards the apulian platform where the plio quaternary clastic layers overlap what are probably late mesozoic or early tertiary limestones taking into consideration general tectonic features we can distinguish a northern area and a southern one separated by a fault trending 30 n located on the western margin of kephallinia lefkas islands 1 a in the northern area we observe a strong tangential tectonism decreasing towards the apulian platform with transitional characteristics on the pre apulian zone paxos where asymmetrical folding occurs 2 b in the southern area from lefkas kephallinia islands to the s w cape of peloponesus the tangential tectomism is well masked by strong vertical faulting attributed to young plio quaternary deformations the fast subsidence induces huge diapiric structures in the ionian zone salt walls originating from triassic layers intersect a thick pleistocene sequence

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

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

tertiary geodynamical evolution of northwestern greece paleomagnetic results abstract paleomagnetic results have been obtained from 29 sites sampled in lower to upper oligocene flysch sections of the ionian zone in northwestern greece they indicate a clockwise rotation of about 45 of the entire region a comparison with previously published results relative to both younger and older formations shows that this rotation has occurred in two phases of comparable amplitude one during middle miocene and the other during pliocene and quaternary separated by a period of at least 7 ma during which no significant rotation has occurred no major rotation has occurred during the entire paleocene and eocene stages this large measured rotation implies a horizontal displacement of at least 100 km in epirus possible mechanisms involving a rotation of the nappe sheets rotation of the basement or a combination of the two are discussed the two phases of paleomagnetic rotation can be correlated with the tertiary and quaternary calc alkaline volcanic activity in the aegean sea a palinspastic reconstruction shows that the orientation of the major structures now striking n155 was almost east west in the middle miocene at the epoch of their formation

neogene to quaternary sedimentary basins in the south adriatic central mediterranean foredeeps and lithospheric buckling up to several kilometers deep sedimentary basins of neogene to quaternary age are found in the south adriatic between the apennines and the dinarides albanides they are the apennines foredeep the central adriatic basin and the south adriatic basin two regional seismic lines 260 and 170 km long across the entire system provide hitherto unavailable constraints on the kinematics and dynamics of basin development the apennine foredeep imaged along the lines formed in middle to late pliocene times through a rapid westward tilting of the basin floor a paleobathymetry of few kilometers was created in which allochthonous bodies were emplaced and sediments deposited unaffected by deformation and farther rotations the central and south adriatic basins formed in neogene to quaternary times and are both characterized by strong subsidence in their central parts gradually diminishing toward the edges in the sw and ne depocenters did not shift laterally through time subsidence rates increase through time and subsidence continued also following the end of main shortening episodes in the dinarides albanides the central and south adriatic basins form two crustal scale synclines with subsidence concentrated in their central parts basins geometries and subsidence patterns indicate that the adriatic crust has undergone episodes of buckling since miocene times wavelengths and amplitudes of such folds change along strike corresponding to mechanical changes of the folded medium

the gulf of taranto southern italy seismic stratigraphy and shallow structure abstract interpretation of seismic profiles across the gulf of taranto southern italy allows us to discuss the seismic stratigraphy and to define the shallow geological structure of this complex area of the northern ionian sea the apulian slope is a down faulted passive margin covered by irregular unconsolidated plio quaternary sediments the sedimentary fill rests on presumed discontinuous upper miocene deposits and on mesozoic and cainozoic strata acoustic basement the taranto valley is a thickly sedimented trench like feature that is the submerged extension of the onshore bradanic fore deep the eastern calabrian margin intensively cut by normal faulting comprises a lower acoustic sequence representing the widespread allochtonous apenninic units these units overthrust towards the east the unconsolidated taranto submarine valley sedimentary fill creating a sinuous nw se trending thrust front