paleomagnetism of jurassic to miocene sediments from the apenninic carbonate platform southern apennines italy evidence for a 60 counterclockwise miocene rotation abstract the tectonic evolution of the apennine belt southern tyrrhenian sea system is addressed through a paleomagnetic study of lias to langhian sediments from the apenninic carbonate platform southern apennines italy reliable paleomagnetic data gathered from 21 sites document a regional scale post langhian 80 counterclockwise ccw rotation since previous studies of the plio pleistocene clays spread over the orogen had shown a 20 ccw rotation we conclude that the southern apennines rotated by 60 during middle late miocene our data provide evidence that the southeastward drift of calabrian block and synchronous spreading of the southern tyrrhenian sea induced saloon door like deformation of the southern apennines and sicily which underwent similar magnitude although opposite in sign orogenic rotations a paleomagnetically derived paleogeographic reconstruction shows that at 15 ma late langhian the alpine apennine belt collided with a nne oriented carbonate platform corridor surrounded by oceanic basins we speculate that both the end of the corsica sardinia rotation and the eastward jump of the locus of back arc extension from the liguro provencal to the tyrrhenian sea may have been consequences of this event

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

new constraints on the bending of the gibraltar arc from palaeomagnetism of the ronda peridotites betic cordilleras spain

evolution of retreating subduction boundaries formed during continental collision retreating subduction boundaries formed where the rate of subduction exceeds the rate of overall plate convergence appear to be commonly developed features within regions of early or incomplete continent continent collision they are characterized by regional extension within the overriding plate and at their leading edge by thin skinned arcuate thrust belts that are concave towards the overriding plate as is illustrated by examples from the mediterranean region the formation of retreating subduction boundaries is intimately related to the process of continental collision during the early stages of collision retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary retreating plate boundaries can also form before the main collision and the associated thrust belts emplaced as precollisional accretionary assemblages because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab slab pull subduction usually ceases when and only when thick buoyant continental crust enters the subduction zone thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted in some cases retreating subduction boundaries may escape into the open ocean where they form nearly isolated local tectonic systems in these systems the rate of subduction is approximately compensated by the rate of upper plate extension and migration of the system across the oceanic region may be very rapid for example the horseshoe seamounts located about 800 km offshore in the eastern north atlantic may be the active expression of an east dipping westwardly migrating retreating subduction boundary that has evolved from the betic cordillera rif system active in miocene time and may now be progressing across the atlantic at approximately 50 mm yr an analogous situation may be represented by the scotia arc system a westward dipping retreating subduction system located between the south american and antarctic plates which may have escaped into the south atlantic ocean from a zone of crustal shortening in the andes and is now progressing across the atlantic at a rate of about 80 mm yr

magnetostratigraphy across the berriasian valanginian stage boundary early cretaceous at cehegin murcia province southern spain abstract the berriasian valanginian stage boundary near the town of cehegin in the eastern subbetic cordillera of spain is documented by a detailed ammonite zonation in pelagic limestones two magnetostratigraphic sections spanning the uppermost ammonite subzone of the berriasian and the lower two zones of the valanginian yielded identical magnetic polarity patterns remanent magnetization is predominantly carried by magnetite and characteristic directions were obtained by thermal demagnetization the mean characteristic directions from both sites have an inclination of 48 however the site declinations are divergent 030 and 074 due to the tectonic disturbance of the region the cehegin polarity pattern can be correlated by means of ammonite and calpionellid zonation to the magnetostratigraphies of the berriasian stratotype and several italian sections thereby enabling a unique correlation to the m sequence magnetic polarity time scale the berriasian valanginian stage boundary is in the middle of normal polarity chron m15n

alpine orogenic p t t deformation history of the catena costiera area and surrounding regions calabrian arc southern italy the nappe edifice of north calabria revised with insights on the tyrrhenian apennine system formation 1 the nappe structured belt of calabria constitutes the eastward termination of the southern branch of the alpine mediterranean belt that delimits the northern edge of the africa plate contrasting hypotheses for the origin and tectonic significance of the north calabrian nappe edifice have been proposed and kinematic data from north calabria have been used to support different interpretations of the alps apennines linkage and the polarity of the tethyan subduction in the apennine region we reconstruct the architecture of the north calabria nappe edifice through a multidisciplinary approach which integrates structural investigations with metamorphic thermobarometry and 40ar 39ar geochronology results from this study indicate that north calabria consists of a tertiary nappe stack resulting from superimposed top to the west extensional shearing late oligocene to middle miocene in age onto a previously structured top to the east compressional belt eocene to oligocene in age this study also documents that the top to the west extensional tectonics was achieved by means of regionally sized extensional detachment fault systems stretching apart and translating as allochthonous fragments the previously accreted units thinning operated by top to the west extensional detachment tectonics also resulted in the direct juxtaposition of non alpine or slightly alpine metamorphosed units upper plate complex onto the previously exhumed deep seated portions of the orogenic wedge metamorphosed under blueschist facies metamorphic conditions lower plate complex these findings support a new tectonic scenario for the orogenic history of north calabria which may be adequately framed within the tertiary apennine tyrrhenian system evolution

tectonics of the umbria marche romagna arc central northern apennines italy new paleomagnetic constraints we present the results of a paleomagnetic study carried out on 32 sites from mainly messinian clayey sediments distributed throughout the external umbria marche romagna arc umra these data together with published results from coeval sediments demonstrate that this arc is an orocline in its central northern sector bending not well constrained in time was due to about 15 clockwise rotations of the central part of this arc and to counterclockwise rotations farther north in this latter area post messinian counterclockwise rotations are of the same amplitude as those calculated for some classic mesozoic paleomagnetic sections in northern umbria suggesting a plio pleistocene age for the rotations reported from the older sequences

paleomagnetic data from umbria italy implications for the rotation of adria and mesozoic apparent polar wander paths abstract sixteen new jurassic and cretaceous paleomagnetic sampling sites are located in northern umbria along three river valleys bosso burano sentino the late jurassic and early cretaceous data are consistent in declination but not inclination with previously published data from these valleys early jurassic data from eight sites give site mean declinations which are significantly different from the two site mean declinations of this age which were previously available comparison of the data with cretaceous and jurassic mean directions from the southern alps indicate 20 anticlockwise rotation relative to the southern alps of this part of northern umbria during neogene deformation of the umbrian fold and thrust belt if the umbrian mean directions are rotated to compensate for the tectonic rotation the early jurassic and cretaceous umbrian and southern alpine pole positions coincide closely with a recently derived african apparent polar path apwp implying that adria moved with africa since at least early jurassic times the late jurassic umbrian and southern alpine poles however are not consistent with current apwps and imply rapid apparent polar wander in both african and north american coordinates from high latitude to lower latitude between bathonian and oxfordian times

hierarchical bayesian lithology fluid prediction a north sea case study seismic 3d amplitude variation with offset avo data from the alvheim field in the north sea are inverted into lithology fluid classes elastic properties and porosity lithology fluid maps over hydrocarbon prospects provide more reliable estimates of gas oil volumes and improve the decision concerning further reservoir assessments the alvheim field is of turbidite origin with complex sand lobe geometry and appears without clear fluid contacts across the field the inversion is phrased in a bayesian setting the likelihood model contains a convolutional linearized seismic model and a rock physics model that capture vertical trends due to increased sand compaction and possible cementation the likelihood model contains several global model parameters that are considered to be stochastic to adapt the model to the field under study and to include model uncertainty in the uncertainty assessments the prior model on the lithology fluid classes is a markov random field that captures local vertical horizonta

paleomagnetic evidence for a neogene two phase counterclockwise tectonic rotation in the northern apennines italy paleomagnetic directions have been determined for a new collection of early oligocene and late miocene pliocene epiligurian clastic sediments from the frontal portions of the northern apennines these results are combined with cenozoic data from the literature to evaluate whether rotations of units in this region are related to the oligomiocene corsica sardinia rotation and or to younger phases of deformation of the apennine chain when corsica sardinia moved counterclockwise ov the coast of france the ligurian units located at its front were presumably pushed eastward and rotated counterclockwise above a main boundary thrust onto the adria africa margin we propose that about 24 out of a total of 52 of rotation observed in the epiligurian units can be related to the oligo miocene motion of the corsica sardinia block in partial agreement with previous conclusions and the remaining 28 to the pliocene tectonic phase at the apennine chain front which may have re activated thrust planes in the adria africa succession below the ligurian wedge 2000 elsevier science b v all rights reserved

a structural and palaeomagnetic study of a section through the eastern subbetic southern spain a well exposed 2 km section through the eastern subbetic immediately to the south of the crevillente wrench fault zone can be divided into an upper thrust sheet of triassic rocks a middle thrust sheet of cenomanian turonian basinal sediments and a lower thrust sheet of jurassic limestones unconformably overlain by upper cretaceous palaeocene sediments structural relationships suggest that the middle sheet overthrust the lower sheet and both units were subsequently folded and imbricated this sequence was then overthrust by the upper sheet incorporating a footwall duplex of cenomanian turonian sediments these structures can be related to the complex deformation associated with a single overthrusting event the dominant thrust transport direction is to the east strongly oblique to the overall trend of the orogen however a palaeomagnetic study isolates stable components which indicate no cumulative vertical axis rotation of the thrust sheets the section is cut by strike slip faults whose displacements appear to be relatively minor the triassic rocks of the upper thrust sheet form a highly disrupted thrust sheet extending over much of the subbetic rather than being local to the crevillente fault zone this section through the subbetic can be interpreted as the result of a major east directed thrust of basinal sediments of the median subbetic over marginal shelf facies of the internal subbetic strongly oblique to the general ese trend of the orogen the shortened sequence is cut by a later set of strike slip faults which are probably related to movement on the crevillente fault

mantle dynamics in the mediterranean the mediterranean offers a unique opportunity to study the driving forces of tectonic deformation within a complex mobile belt lithospheric dynamics are affected by slab rollback and collision of two large slowly moving plates forcing fragments of continental and oceanic lithosphere to interact this paper reviews the rich and growing set of constraints from geological reconstructions geodetic data and crustal and upper mantle heterogeneity imaged by structural seismology we proceed to discuss a conceptual and quantitative framework for the causes of surface deformation exploring existing and newly developed tectonic and numerical geodynamic models we illustrate the role of mantle convection on surface geology a coherent picture emerges which can be outlined by two almost symmetric upper mantle convection cells the downwellings are found in the center of the mediterranean and are associated with the descent of the tyrrhenian and the hellenic slabs during plate convergence these slabs migrated backward with respect to the eurasian upper plate inducing a return flow of the asthenosphere from the backarc regions towards the subduction zones this flow can be found at large distance from the subduction zones and is at present expressed in two upwellings beneath anatolia and eastern iberia this convection system provides an explanation for the general pattern of seismic anisotropy in the mediterranean first order anatolia and adria microplate kinematics and may contribute to the high elevation of scarcely deformed areas such as anatolia and eastern iberia more generally the mediterranean is an illustration of how upper mantle small scale convection leads to intraplate deformation and complex plate boundary reconfiguration at the westernmost terminus of the tethyan collision

magnetic fabric of pleistocene clays from the tyrrhenian arc a magnetic lineation induced in the final stage of the middle pleistocene compressive event we present the results of an analysis of the anisotropy of magnetic susceptibility ams in early pleistocene clay sediments from the southern apennines and its foreland apulia measurements were performed on samples from different tectonic units the apulian unit the bradano unit and the apenninic belt the ams is characterized by a dominant magnetic foliation parallel to the bedding plane in all cases pointing to a primary sedimentary magnetic fabric no lineation is found in the clays from the apulian unit whereas the inner part of the bradano unit and the apenninic belt show a clear nw se trending magnetic lineation which is perpendicular to the main compressive stresses known for this area there is a very consistent wnw ese trending magnetic lineation for the clays from the southern apennines and the calabrian block to the south correction of this lineation with the established tectonic rotations shows that the lineation is clearly of postrotational origin and reflects the latest stages of deformation the lineation is linked to middle and late pleistocene tectonics its alignment occurred in the final stages of the compressive event affecting the tyrrhenian arc system for the sant arcangelo basin in the southern apennines anomalous trends of magnetic lineation compressive stress were established

a major late tortonian rotation phase in the crotone basin using ams as tectonic tilt correction and timing of the opening of the tyrrhenian basin abstract paleomagnetic studies of sediments from the calabro peloritan block in southern italy consequently imply a 15 clockwise rotation for the late tortonian to middle pleistocene sedimentary cover but the results of older sediments are generally less consistent earlier paleomagnetic results of tortonian sites from the basilicoi section crotone basin northern calabria suggested a major counterclockwise rotation of 97 scheepers 1994 here we studied the basilicoi section in detail and we used anisotropy of the magnetic susceptibility ams to reconstruct the bedding plane needed for tilt correction this reduced the 97 counterclockwise rotation to a 25 counterclockwise rotation the lese section also in northern calabria shows the same counterclockwise rotation in sediments with an age between 10 4 and 8 6 ma thus confirming the results from the corrected basilicoi section a comparison of the magnetostratigraphy and planktonic foraminiferal biostratigraphy with the magneto biostratigraphic framework of the mediterranean late miocene allows a correlation of the basilicoi and lese sections to the gpts and a timeframe for the rotation it is concluded that the 25 counterclockwise rotation phase took place between 7 6 0 1 and 8 6 ma we speculate that the timing of this tectonic phase is related to the opening of the tyrrhenian sea and the separation of calabria from sardinia we compare our results with those of odp leg 107 and we suggest an age between 8 6 and 7 8 ma for the timing of the opening of the tyrrhenian sea

east west thrusting and anomalous magnetic declinations in the sierra gorda betic cordillera southern spain abstract structural and palaeomagnetic studies in the sierra gorda sierra de loja located in the external zone of the betic cordillera indicate that westward directed thrusting is not associated with significant rotations about a vertical axis detailed mapping and slip vector analysis show that the sierra gorda is a thrust complex composed of three thrust sheets the uppermost thrust places early jurassic pelagic carbonates on top of jurassic to oligocene sediments that form a large doubly plunging footwall syncline the eastern limb of this syncline has been overturned and is tectonically thinned as a result of the overthrusting palaeomagnetic results from mesozoic and tertiary sediments both within and around the perimeter of the sierra gorda indicate that 1 the average remanence vector of the seven late jurassic localities sampled within the sierra gorda has a direction d 328 and i 38 that is not significantly different from the expected declination for the upper jurassic of stable iberia and 2 there is no significant difference between the remanences in the two upper thrust sheets indicating that differential rotation did not occur during the initiation and displacement on the thrusts in contrast the one late jurassic site that was sampled to the west of the sierra gorda is rotated like the rest of the subbetics 60 clockwise of the reference direction the unrotated directions obtained in the sierra suggest either that it has rotated in a clockwise sense concordant with the rest of the subbetic zone and has then been backrotated or that it has never rotated relative to stable iberia in the latter simpler hypothesis the unrotated declinations may be explained in terms of orthogonal convergence along an irregular continental margin

counter clockwise rotations in the southern apennines during the pleistocene paleomagnetic evidence from the matera area sediments from late pliocene to early pleistocene age have been sampled at six different localities sections 38 sites in the matera area which is in the southern part of peninsular italy basilicata three of the localities are from the apenninic belt the other three from the bradano unit both of them west of the earlier sampled apulian unit stepwise thermal demagnetisation revealed that usually two important components contribute to the natural remanent magnetisation nrm of these clay sediments a low temperature lt component removed between 100 and 300 320 c and a high temperature ht component removed between 300 320 and 430 450 c the ht component is a characteristic remanent magnetisation chrm for the sediments and has a clear primary pre folding origin in fresh unweathered sediments the lt component is identical in direction to the ht component but there is evidence that moderate weathering replaced a high intensity primary lt component with a low intensity secondary lt magnetisation the ht magnetisation is affected by this weathering process in a decrease of its intensity a counter clockwise deflection in declination is observed for the sites sampled in the apenninic belt the ht directions reveal a 23 counter clockwise rotation relative to the magnetic north dm 336 6 and im 57 2 sites in the bradano unit have no tectonic rotation dm 359 1 and im 56 3 earlier sampled sites from the apulian unit also showed no tectonic rotation dm 359 4 and im 57 0 paleomagnetic data support the hypothesis that the southern apennines rotated in the middle late pleistocene after the major phase of extension in the southern part of the tyrrhenian basin and contemporaneous with a regional compressional phase

late pliocene continental magnetochronology in the guadix baza basin betic ranges spain abstract the late pliocene shallow lacustrine sequences in the guadix baza basin betic ranges southeast spain are a suitable setting for mammal chronology because of the abundance of rich mammal bearing sites stratigraphic superposition of late ruscinian and villanyian vertebrate fossils makes the galera section very appropriate for magnetostratigraphic dating sediments are characterized by a weak but measurable magnetization predominantly carried by magnetite other remanence carriers such as iron sulphides and hematite may be significant only in some particular lithologies such as dark palustrine organic silts and red alluvial beds respectively direct correlation of the galera section to the geomagnetic polarity time scale provides a reliable dating of the late ruscinian and villanyian mammal units the ruscinian villanyian boundary mn15 mn16 is found to occur in the lower gauss chron and approximately correlates to the 3 3 ma cooling event observed in stable isotope and planktonic foraminifera deep sea records the earliest occurrence of late villanyian assemblages mn17 in the lower part of the matuyama chron allows dating of the early late villanyian boundary mn6 mn17 to approximately 2 4 2 6 ma based on the presence of late villanyian assemblages underlying the base of the olduvai chron a maximum age of 1 95 ma top of c2r is attributed to the villanyian biharian mn17 mmq boundary a 300 kyr sedimentary gap in the galera section is suggested to correlate with a probable early villanyian hiatus an hypothesis that agrees with the absence of fossils of this age elsewherein the baza formation

kinematics of a twisted core complex oblique axis rotation in an extended terrane betic cordillera southern spain 1 the sierra de las estancias is a metamorphic core complex that developed during the late oligocene to early miocene extensional collapse of the betic cordillera structural and paleomagnetic analysis shows that the northern half of the complex has been strongly modified by rotation about an inclined axis requiring reassessment of the kinematics of the extensional phase of deformation the extensional tectonic event produced two major detachment faults associated mylonitic foliation and lineation and pervasive sets of shear bands and brittle normal faults with a top to ne shear sense an older foliation was largely transposed and reoriented during this event the regional foliation now defines a broad antiform with a steep north dipping limb and the trend of shear related lineations swings from nne to ene from the southern gently dipping limb into the north dipping limb the remanent magnetization in a suite of near vertical early miocene mafic dikes intruded into the north dipping limb has a declination of 243 and an inclination of 27 assuming that the dikes were originally vertical a rotation of approximately 50 about an inclined ssw plunging axis preserves the near vertical orientation of the dikes and brings the remanence into agreement with the expected orientation for an early miocene age correction for this rotation brings the foliation and lineation in the surrounding schists into orientations subparallel to those on the present southern limb of the antiform and the dikes into a vertical e w orientation the corrected orientation of the shear related lineation nne normal faults and dikes suggests that the original direction of extension during the late orogenic extensional event in the internal betic cordillera may therefore have been around nne ssw rather than e w as currently accepted the observed net tectonic rotation can be decomposed into a series of geologically plausible rotations involving domino style rotation due to slip on the late brittle normal faults tilting about the regional fold axis related to thrust ramping onto the iberian margin during miocene collision and a 30 clockwise rotation about a vertical axis related to oblique convergence with the iberian margin

correction to apparent and true polar wander and the geometry of the geomagnetic field over the last 200 myr 1 in the paper apparent and true polar wander and the geometry of the geomagnetic field over the last 200 myr by jean besse and vincent courtillot journal of geophysical research 107 b11 2300 doi 10 1029 2000jb000050 2002 the data in the top part of table 4 were incorrect the correct table 4 is given here journal of geophysical research vol 108 no b10 2469 doi 10 1029 2003jb002684 2003

a 125 post early serravallian counterclockwise rotation of the gorgoglione formation southern apennines italy new constraints for the formation of the calabrian arc abstract the southern apennines calabro peloritane block and sicilian maghrebides form a 700 km long orogenic bend known as calabrian arc cifelli et al 2007 the bending of this orogenic system was realized progressively through opposite sense rotation of the two limbs counterclockwise ccw in the southern apennines and clockwise cw in the sicilian maghrebides synchronous to the miocene to present opening of the tyrrhenian sea despite the wealth of paleomagnetic data from the southern apennines the main miocene rotational phase still remains poorly constrained in time and more importantly data from the most internal paleogeographic domains of the belt are completely lacking the gorgoglione formation a middle miocene piggy back deposit of the southern apennines unconformably resting over the internal sicilide unit offers the unique opportunity to document the deformation pattern of the most internal units and reconstruct the incipient tectonic phases leading to the formation of the calabrian arc new paleomagnetic and biostratigraphic data from the gorgoglione fm reveal a post early serravallian 125 ccw rotation with respect to stable africa such a large rotation affecting the gorgoglione fm and consequently the underneath allochthonous sicilide nappe exceeds by 45 the maximum mean ccw rotation previously reported for the southern apennines we propose that the additional 45 ccw rotation measured in the sicilide unit is the result of an earlier late miocene phase of deformation related to the onset of the tyrrhenian sea opening and affecting the most internal paleogeographic domains of the southern apennines our reconstructed tectonic scenario confirms and emphasizes the central role of the ionian slab in the geodynamic evolution of the central mediterranean

a portable local loop vlf transmitter for geological fracture mapping a portable low power very low frequency vlf transmitter using a large square loop antenna has been designed assembled and tested by the geological survey of canada gsc for geological studies of fracture patterns in igneous rock masses standard laboratory equipment consisting of a signal generator a 1100 w power amplifier and several high power tuning capacitors was used for the purpose field tests at the chalk river facilities of atomic energy of canada limited have demonstrated a remarkable similarity between survey results obtained using the vlf signals from the local loop transmitter and from distant us navy vlf transmitters the local loop was used to simulate the fields from navy stations naa in cutler maine and nss in annapolis maryland conductor axes mapped by using these navy stations and by using the loop antenna yielded almost identical results a survey was also done in the same area with the local loop placed in such a manner that the direction of the vlf field was at 45 to the field directions from naa and nss in this case the same conductor axes were located with only minor shifts in position indicating that conductors whose axes lie within 45 of the direction of the primary horizontal magnetic field are mapped thus it is probably sufficient to have two sources with orthogonal vlf fields to map all vlf conductors in an area since in most areas at least one navy vlf station can be used the local loop transmitter can be used to generate a signal at right angles to the direction from the navy transmitter to allow a more complete vlf survey coverage

tertiary extensional tectonics in tuscany northern apennines italy abstract two extensional events have been recognized in the tertiary evolution of tuscany the first event occurred in the period between the late oligocene and late tortonian and caused a stretching of 120 or greater the second event occurred between the late tortonian and quaternary periods and caused a stretching not greater than 10 the first event is characterized by the exhumation of middle crust rocks and therefore by the development of core complexes the most significant structures of the first event are low angle normal faults which characterize the upper plate of the core complexes and ductile shear zones which characterize the lower plate the low angle normal faults tend to die out in the late triassic evaporite level which constitutes the main detachment of the core complexes the main structures of the second extensional event are high angle normal faults which dissect all the previous tectonic features these faults border tectonic depressions which were the site of clastic sedimentation from late tortonian to quaternary time these normal faults may tend to flatten in a seismic lozenge shaped band explained as an active extensional shear zone which is located at the brittle ductile boundary a similar explanation is given for the detachment located in the late triassic evaporite level during the first extensional event while the first extensional event is in the framework of the northern apennine post collisional evolution the second extensional event because it affects an already stretched crust could be attributed to the southern tyrrhenian opening which began during late tortonian

tectonic and sedimentary evidence for synchronous and out of sequence thrusting larache acilah area western moroccan rif syn tectonic turbidites were analysed using measured sections structural relationships and bio and litho correlations of sedimentary units to determine the tectonic evolution of the alpine thrust belt of the northwestern moroccan rif the external zones of the northwestern moroccan rif contain two tertiary turbidite sequences which can be sub divided into type i ii and iii turbidite packages sensu mutti 1984 one turbidite sequence the acilah sandstone oligocene earliest miocene is found at the leading edge of the tangier thrust sheet while a second the sidi mrait flysch is seen in the underlying prerif thrust sheet the lower sidi mrait flysch was probably deposited in a foredeep basin at the end of the eocene early oligocene the advancing thrust front incorporated the foredeep basin deposits into the thrust belt subsequent turbidite deposition occurred in piggyback basins palaeocurrent directions indicate sediment transport from sse to nnw along troughs elongated parallel to the tectonic strike creation of piggyback basins turbidite onlap relationship unconformities and structural relationships indicate that complex synchronous and out of sequence thrusting accompanied the overall foreland progressing deformation sequence

jurassic magnetostratigraphy 3 bathonian bajocian of carcabuey sierra harana and campillo de arenas subbetic cordillera southern spain abstract four sections in majocian bathonian middle jurassic pelagic limestone with standard ammonite zonation have yielded magnetic polarity sequences magnetic directions in these red to white limestones were obtained by thermal demagnetization and were stable from about 300 c to in excess of 450 c the polarity patterns indicate that the majority of the bajocian and bathonian is characterized by quite frequent reversals of the magnetic field lengthy periods of constant polarity particularly constant normal polarity were not observed the average frequency of reversals is about 6 per ammonite zone which roughly may be interpreted as a frequency of a reversal every 260 000 years a rate comparable to that of the miocene pliocene paleolatitudes of these sites 25 28 are about 10 south of their present positions variable clockwise block rotations within the subbectic region have rotated these sites relative to stable iberia

interpretation of ground vlf em data in terms of inclined sheet like conductor models the response of two dimensional inclined sheet like conductors with low conductance values to plane wave electromagnetic fields in the very low frequency vlf range has been evaluated by using a numerical technique the conductance values of the conductors considered are appropriate for those produced by water and or clay filled fracture and shear zones in the precambrian crystalline rocks of the canadian shield the surrounding host rock was assumed to be resistive with resistivities in the 1 10 k m range to reflect the high resistivities over the shield areas no overburden was assumed in this analysis

origin of the western subbetic arc south spain palaeomagnetic and structural evidence abstract an integrated structural and palaeomagnetic study in late cretaceous eocene rocks of the western subbetic arc in the betic cordillera of southern spain shows that the change in fold trend around the arc is significantly greater than the variation in primary magnetic declination this suggests that the arcuate geometry is not primarily a consequence of differential rotation the area has experienced a regional clockwise rotation of at least 40 which was most probably imposed during oblique wnw directed convergence along the southern iberian margin in early miocene time before the arcuate structure was formed kinematic indicators associated with the arcuate folds and thrust traces arc for the most part consistently wnw directed suggesting that the arc is not primarily a result of variations in the direction of tectonic transport the arcuate structure was probably initiated without significant rotation by the wnw directed indentation of the curved western end of the alboran domain into the iberian margin and was then tightened involving up to about 35 of further rotation in different segments of the arc finally one sector in the arc was rotated anticlockwise by about 40 with respect to the rest of the region reorientating the magnetic declinations the fold trends and the kinematic indicators this rotation was associated with local sinistral shear

implications of a combined biostratigraphic and palaeomagnetic study of the umbrian maiolica formation abstract the study of a 275 5 m thick section of white pelagic limestones occupying the valley of the fonte del giordano river on the southern slope of mt montagnola has yielded a biostratigraphically controlled clear magnetic reversal pattern after thermal cleaning the magnetic stratigraphy of the lower 131 m of the section calpionellid zones is correlatable with the m sequence of oceanic magnetic anomalies between m 19 and m 14 the reversal stratigraphy of the upper 81 5 m of the section radiolaria zone has also been tied to the oceanic polarity time scale by making linear interpolation for a missing 63 m thickness underneath it besides the fonte del giordano section two berriasian outcrops each with a different bedding attitude were studied at gubbio and near cagli for tectonic tilt test giving positive results the mean palaeomagnetic pole position for the late jurassic early cretaceous after bedding correction is 19 1 288 2 k 148 7 95 10 2 n 3 confirming the presence of a large swing in the polar path a common behaviour of apparent polar wandering for the peri adriatic region during this time

the 125 150 ma high resolution apparent polar wander path for adria from magnetostratigraphic sections in umbria marche northern apennines italy timing and duration of the global jurassic cretaceous hairpin turn a new high resolution apparent polar wander path apwp segment has been obtained from the magnetostratigraphy of four kimmeridgian to lower aptian sections in the northern apennines italy the use of paleomagnetic data for determination of the adria apwp was hampered by the large local rotations linked to apennine tectonics characterized by folds and thrusts developed during the neogene to overcome this problem we have computed relative rotations between time overlapping sections and realigned them in a common declination reference frame namely the bosso section we synthesized a new high resolution 150 to 125 ma apwp for adria which has a similar shape to the time equivalent segment of the synthetic apwp of africa of besse and courtillot j besse v courtillot apparent and true polar wander and the geometry of the geomagnetic field over the last 200 myr j geophys res 107 b11 2002 doi 10 1029 200jb000050 a 26 clockwise rotation of our combined adria apwp places it in almost perfect overlap with african data of same age confirming that the adria promontory moved coherently with africa during this time span whereas the counterclockwise rotation of adria with respect to africa was introduced later most probably during apennines orogenesis finally we discuss in relation with worldwide plate evolution the peculiar shape of our apwp which displays a hairpin turn during berriasian time and dates the main late jurassic early cretaceous change in plate motion at around anomaly m16

modeling and inversion of magnetic and vlf em data with an application to basement fractures a case study from raigarh india we present modeling of magnetic and very low frequency electromagnetic vlf em data to map the spatial distribution of basement fractures where uranium is reported in sambalpur granitoids in the raigarh district chhattisgarh india radioactivity in the basement fractures is attributed to brannerite u ti fe complex and uranium adsorbed on ferruginous matter the amplitude of the 3d analytical signal of the observed magnetic data indicates the trend of fracture zones further the application of euler 3d deconvolution to magnetic data provides the spatial locations and depth of the source fraser filtered vlf em data and current density pseudosections indicate the presence of shallow and deep conductive zones along the fractures modeling of vlf em data yields the subsurface resistivity distribution of the order of less than 100 ohm m of the fractures the interpreted results of both magnetic and vlf em data agree well with the geologic section obtained from drilling

paleomagnetism of the umbrian marches orogenic belt abstract the eower cretaceous maiolica formation was investigated in a regional paleomagnetic study in order to clarify the role of the umbrian marches region in western mediterranean tectonics this area has been considered as a semi autonomous microplate by some authors and as an allochthonous overthrust block by others oroclinal bending has been inferred from earlier paleomagnetic results of the scaglia formation in spite of weak natural remanent magnetizations nrm stable characteristic remanent magnetization chrm directions were defined for 31 sites the site mean directions are well grouped d 306 i 37 95 5 but are not uniform fisher statistics are therefore not applicable the nonuniformity of directions is partially due to regional and local variations but is not related to the orientation of the fold axes as suggested by several authors it is possible that the umbrian marches region has suffered thrust decollement on the underlying triassic evaporites during the late tertiary orogeny but this was not accompanied by large scale translation or rotation relative to the assumed autochthonous parts of the adriatic promontory

new gps constraints on active deformation along the africa iberia plate boundary abstract we use velocities from 65 continuous stations and 31 survey mode gps sites as well as kinematic modeling to investigate present day deformation along the africa iberia plate boundary zone in the western mediterranean region the gps velocity field shows southwestward motion of the central part of the rif mountains in northern morocco with respect to africa varying between 3 5 and 4 0 mm yr consistent with prior published results stations in the southwestern part of the betic mountains of southern spain move west southwest with respect to eurasia 2 3 mm yr the western component of betics motion is consistent with partial transfer of nubia eurasia plate motion into the southern betics the southward component of betics motion with respect to iberia is kinematically consistent with south to southwest motion of the rif mountains with respect to africa we use block modeling constrained by mapped surface faults and seismicity to estimate the geometry and rates of strain accumulation on plate boundary structures our preferred plate boundary geometry includes one block between iberia and africa including the sw betics alboran sea and central rif this geometry provides a good fit to the observed motions suggesting a wide transpressive boundary in the westernmost mediterranean with deformation mainly accommodated by the gloria azores fault system to the west and the rif tell lineament to the east block boundaries encompass aspects of earlier interpretations suggesting three main deformation styles i extension along the ne sw trending trans alboran shear zone ii dextral strike slip in the betics corresponding to a well defined e w seismic lineament and iii right lateral strike slip motion extending west to the azores and right lateral motion with compression extending east along the algerian tell we interpret differential motion in the rif alboran betic system to be driven both by surface processes related the africa eurasia oblique convergence and sub crustal dynamic processes associated with the long history of subduction of the neotethys ocean lithosphere the dextral slip identified in the betic mountains in southern spain may be related to the offshore fault that produced the great 1755 lisbon earthquake and as such may represent a significant seismic hazard for the west mediterranean region

paleomagnetic constraints on the plio pleistocene geodynamic evolution of the external central northern apennines italy abstract we report on new paleomagnetic results obtained from 27 sites sampled in the plio pleistocene sequences at the external front of the central northern apennines previous analyses of miocene messinian sediments indicated that the present shape of the northern apenninic arc is due to the oroclinal bending of an originally straight belt oriented around n320 and that vertical axis rotations accompanied the migration of the thrust fronts toward the adriatic foreland f speranza et al j geophys res 102 1997 3153 3166 we tried to provide new paleomagnetic constraints for the timing and rates of the oroclinal bending process during the pliocene and the pleistocene the results suggest that ccw rotations observed in the northern part of the studied area are possibly younger than 3 ma no regional rotation is recorded in the pliocene and pleistocene sediments from the southern part of the study area analogously to the messinian sediments of the acquasanta domain of speranza et al f speranza et al j geophys res 102 1997 3153 3166 a local significant ccw rotation 23 10 is identified in the early pleistocene sediments that crop out along the adriatic coast between ascoli and pescara indicating differential motion of the thrust sheets this rotation must be younger than 1 43 ma

from pore pressure prediction to reservoir characterization a combined geomechanics seismic inversion workflow using trend kriging techniques in a deepwater basin to optimize drilling decisions and well planning in overpressured areas it is essential to carry out pore pressure predictions before drilling knowledge of pore pressure implies knowledge of the effective stress which is a key input for several geomechanics applications such as fault slip and fault seal analysis and reservoir compaction studies it is also a required input for 3d and 4d seismic reservoir characterization because the seismic response of shales and sand depends on their compaction history the effective stress will govern the sedimentary seismic response this is in contrast to normally pressured regimes where the depth below mudline or overburden stress is typically used to characterize the compaction effect

paleomagnetic evidence for a post eocene 90 ccw rotation of internal apennine units a linkage with corsica sardinia rotation we report on an extensive paleomagnetic study 36 sites of the tuscan nappe succession from the northern apennines arc aimed to reconstruct the tectonic evolution of the internal sector of this chain we analyzed eocene pelagic foreland ramp deposits scaglia toscana formation and oligocene lower miocene siliciclastic turbidites macigno and falterona formations paleomagnetic results show that the internal sector of the northern apennines underwent large counterclockwise ccw rotations with respect to the adria africa foreland a decrease in the rotation magnitude was observed from the southern to the northern sector of the arc from 91 to 36 this trend is opposite to that observed in the more external units of northern apennines and demonstrates that the oroclinal bending model which has been proposed for the external units of the chain is not appropriate to explain the evolution of the internal sector of the arc on the basis of the observed paleomagnetic pattern we propose a new tectonic model in which the tuscan and falterona cervarola units in the southern area were first rotated ccw along with the corsica sardinia block during its lower miocene rotational drifting and were later involved in the main phases of rotational emplacement and translation toward the outermost sector umbria domain thus yielding the final curved shape of the northern apennines chain data from this study represent the first paleomagnetic evidence of the influence of the corsica sardinia ccw rotation in the apennines orogenic wedge deformation in the general framework of the geodynamic evolution of the central mediterranean subduction system

paleogene magnetic stratigraphy in umbrian pelagic carbonate rocks the contessa sections gubbio the umbrian sequence of pelagic carbonate rocks provides an opportunity for precise correlation between paleogene biostratigraphy and geomagnetic polarity history the red to pink paleocene to middle eocene scaglia rossa limestone the varicolored upper eocene scaglia variegata limestone and the gray green oligocene scaglia cinerea marlstone form a 250 m thick continuous exposure in the contessa valley near gubbio italy magnetostratigraphic lithostratigraphic and biostratigraphic investigations in three sections covering the entire paleogene have confirmed and dated the geomagnetic reversal sequence for most of this period the ferromagnetic mineral in the scaglia cinerea is magnetite and af demagnetization to peak fields of 20 mt is sufficient to define the characteristic remanent magnetization the scaglia variegata and pink scaglia rossa samples contain an additional hematite component which is very pronounced in dark red paleocene scaglia rossa samples changes of magnetic mineralogy take place in these limestones during heating especially above 500 c however thermal demagnetization is effective in isolating the characteristic remanence vectors which form almost antipodal clusters of directions representing normal and reversed polarities the directions are rotated counterclockwise partly due to post oligocene tectonism paleontological zonations of planktic foraminifera and calcareous nannofossils were hampered by poor preservation but the major epoch and stage 29 as in the gubbio bottaccione section paleocene eocene just above anomaly 25 eocene oligocene between anomalies 13 and 15 oligocene miocene just below anomaly 6c these correlations require slight modifications to previous conclusions on paleogene sea floor spreading rates

widespread neogene remagnetization in jurassic limestones of the south iberian palaeomargin western betics gibraltar arc abstract palaeomagnetic investigations in upper jurassic carbonate rocks from the western subbetics betic cordillera southern spain testify to a widespread neogene remagnetization progressive thermal and alternating field demagnetization analyses reveal the presence of two stable components of the natural remanent magnetization nrm the nrm is dominated by a pervasive neogene overprint which always shows normal polarity and maximum unblocking temperatures of 450 c throughout the whole region studied the primary jurassic component however can also be isolated in many outcrops this component has low intensity values and maximum unblocking temperatures of about 550 c showing both normal and reversed polarities palaeomagnetic and rock magnetic analyses indicate that both primary jurassic and secondary neogene components are carried by magnetite the incremental fold test performed in all sampling localities demonstrates that the remagnetization occurred during some stage of the neogene deformation of the subbetics being pre syn or post folding in the various folds studied

paleomagnetically determined rotations in the western sicilian fold and thrust belt new paleomagnetic data from the west sicilian fold and thrust belt indicate large scale clockwise rotations during tectonic transport for the platform and seamount paleogeographic units of the fold and thrust belt panormide and trapanese units there is a general consistency in the magnitude of rotation along strike suggesting the existence of large coherent structural units for the panormide platform clockwise rotations in the range of 90 to 140 relative to the underlying iblean parautochthon are recorded along 125 km of outcrop strike in the case of the trapanese unit clockwise rotations in the range of 47 to 70 relative to iblei are recorded along about 90 km of outcrop strike intervening basinal paleogeographic units imerese and sicanian units show clockwise rotations of similar magnitude although few reliable data are available from these units palinspastic reconstruction of the thrust belt incorporating the rotations and arguments for the present orientation of the margins of the paleogeographic units implies that the panormide platform and trapanese seamounts were originally elongated more or less north south relative to the present orientation of iblei the two units apparently coalesced to the south and were discontinuous to the north they and their intervening basins were part of a passive continental margin which occupied a large part of the area that was subsequently rifted to form the tyrrhenian sea

styles of back arc extension in the central mediterranean in the central mediterranean two back arc basins the liguro provencal lpb and the tyrrhenian basin tb opened progressively and consecutively from the late eocene oligocene to the present evolution in space and time of rifting and drifting processes along three different transects across these basins shows differences in the style of extension lpb opened with the formation of a narrow single rift while in the tb deformation and magmatism is spread over a wide area moreover at the northern end of the tb the locus of extension progressively migrated towards the east whereas in the southern tb the locus of extension and magmatism migrated inside the basin inducing continental break up and drifting of the previously formed older conjugate basins we propose that these different styles of back arc extension depend upon internal conditions such as prerift rheology linked with its geological heritage and external conditions e g the style of subduction

late neogene evolution of the taza guercif basin rifian corridor morocco and implications for the messinian salinity crisis abstract magnetostratigraphic and biostratigraphic results are presented from neogene deposits in the taza guercif basin located at the southern margin of the rifian corridor in morocco this corridor was the main marine passageway which connected the mediterranean with the atlantic during messinian times correlation of the biostratigraphy and polarity sequence of the taza guercif composite section to the astronomical time scale allows an accurate dating of three subsequent events in the rifian corridor 1 the oldest marine sediments marking the opening of the rifian corridor were deposited at 8 ma at this age a deep 600 m marine basin developed in the taza guercif area marked by deposition of precession controlled turbidite marl cycles 2 paleodepth reconstructions indicate that a rapid 5 m ka shallowing of the marine corridor took place at the tortonian messinian boundary at an age of 7 2 ma this shallowing phase is primarily related to active tectonics although a small glacio eustatic sea level lowering also took place 3 the taza guercif basin was emergent at an age of 6 0 ma and subsequently continental sedimentation continued well into the early pliocene we suggest that shallowing and restricting the marine passageway through the rifian corridor actually initiated the messinian salinity crisis well before the deposition of the messinian evaporites in the mediterranean

on the post 25 ma geodynamic evolution of the western mediterranean during the neogene and quaternary western mediterranean geodynamics were dominated by the eastward migration of the apenninic arc and associated back arc basins the migration was controlled by retreat of the apenninic slab and was associated with boudinage of the lithosphere in the back arc area palaeo reconstruction of the kinematics of the arc suggests about 775 km of migration from the late oligocene to present along a transect from the gulf of lions to calabria a maximum of 135 km of n s converge occurred between africa and europe during the same time span the western mediterranean was thus mainly shaped by the migration of the slab related to west directed subduction it is hypothesized that minor n s convergence deformed the arc but was not the cause of its formation 1998 elsevier science b v all rights reserved