jurassic magnetostratigraphy 4 early callovian through middle oxfordian of the krakow uplands poland a magnetic polarity pattern has been constructed for the early callovian through middle oxfordian stages of the jurassic from several ammonite rich magnetostratigraphy sections within the krakow czestochowa wielun region of southern poland these overlapping sections encompass portions of every ammonite from the late early callovian through late middle oxfordian however the presence of several hiatuses and condensed intervals within the shallow marine to pelagic sediments preclude reliable identification of the complete polarity pattern the mean callovian oxfordian pole from these sites is at 74 3 n 200 3 e 95 4 7 the callovian through early oxfordian is dominated by reversed polarity with a minimum of five normal polarity zones the early middle oxfordian is predominantly of normal polarity and the late middle oxfordian is characterized by reversed polarity with several relatively brief normal polarity episodes the callovian and oxfordian stages appear to average a minimum of two magnetic polarity reversals per million years this reversal frequency is similar to the average tertiary record but is less than the reported spacing of callovian and oxfordian magnetic anomalies in the pacific

middle oligocene extension in the mediterranean calabro peloritan belt southern italy insights from the aspromonte nappes pile the calabro peloritan belt constitutes the eastward termination of the southern segment of the alpine mediterranean belt this orogenic system was built up during the convergence between the eurasian and the african plates roughly directed north south since the upper cretaceous it was subsequently fragmented during the opening of the western mediterranean basins since oligocene times the curved shape of the calabro peloritan belt was acquired during the opening of the tyrrhenian basin since tortonian the origin kinematics and significance of the calabro peloritan tectonic pile are still debated our data in the aspromonte massif of southern calabria reveal an alpine history marked by two main superimposed kinematic regimes i a first phase corresponds to the piling up of basement nappes with a top to the se vergence i e in a direction orthogonal to the belt trend and towards the adriatic foreland this external vergence is similar to what is observed in both northeastern sicily and northern calabria in sicily the age of nappe piling is alpine as evidenced by pinched slices of mesozoic sediments in the aspromonte massif thrusting age is less constrained our data suggest remnants of late hercynian structuration before the alpine stacking ii a second phase corresponds to the thinning of the continental crust dated at around 30 ma by both geochronological and stratigraphical data this extension is mainly localized on two low angle detachment contacts with top to the ne displacement the lower one corresponds to the reworking of the former main nappe contact the upper one is a large detachment fault cutting across the pile from upper sedimentary levels down to metamorphic basement extension of similar alpine age and similar internal vergence has been already recognized in other parts of the calabro peloritan arc in the basement nappes of northeastern sicily and in the ophiolitic units of northern calabria coming back to the original geometry and position of the calabro peloritan belt before its bending and the opening of the liguro provencal and tyrrhenian basins we evidence a homogeneous oligocene ne sw extension all along the calabro peloritan segment of the alpine mediterranean belt this tectonometamorphic history is best explained within the framework of the continuous tertiary westward dipping subduction of the tethyan oceanic domain below the european active margin and the progressive eastward retreat of the apennine trench since oligocene times

paleomagnetism of the front range colorado morrison formation and an alternative model of late jurassic north american apparent polar wander a paleomagnetic study of the upper jurassic morrison formation in the front range of central colorado yields high unblocking temperature dual polarity magnetizations with respect to known paleohorizontal the inclinations absolute mean 57 3 degree 95 confidence interval 52 3 degree to 63 1 degree n 8 sites pass tilt and reversal tests whereas the dispersion in declinations can be attributed to apparent or real tectonic rotations and sedimentary processes the site centered colatitudinal locus of possible front range morrison poles partially overlaps the upper pole but it excludes the lower pole from the morrison formation on the colorado plateau as well as the 151 ma glance conglomerate pole from the basin and range province of southeastern arizona the authors offer various explanations for these disparities and suggest an alternative model of late jurassic north american apparent polar wander through approximately 70 degree n which is supported by late jurassic european poles with positive stability tests transferred to north american coordinates

how deep can we find the traces of alpine subduction 1 slab like seismic velocity heterogeneities below the alpine chain interpreted as subducted lithosphere are imaged by tomographic studies down to only about 300 km depth a non negligible discrepancy therefore exists between tomographic and geological data the latter indicating at least 500 km of tertiary convergence at trench yet a recently published tomographic study detects a pronounced high velocity anomaly at the bottom of the upper mantle right below the alpine area combining tomographic images of the mantle geological findings and plate system kinematics we investigate how the presence of this feature in the transition zone below the alps can be traced back to the tertiary alpine subduction and possibly explain the observed discrepancy we propose that a part of the fast velocity body now residing just above the 660 km discontinuity once belonged to the alpine slab torn off by an event occurred at about 30 35 ma

paleomagnetism of middle late jurassic sediments from poland and implications for the polarity of the geomagnetic field abstract paleomagnetic data for the middle late jurassic sediments from nine localities of krakow czestochowa upland belonging to stable europe and from three valleys of the lower subtatric nappe belonging to mobile europe are presented the majority of the rocks investigated comprising limestones stromatolites and radiolarites were found to be normally magnetized natural remanent magnetizations nrm of reversed polarity were found in limestones and stromatolites of middle callovian age from the stable region and in one exposure of oxfordian radiolarites from the mobile region along one of the middle callovian sections studied the nrm direction of the specimens changed from r to n the mean paleomagnetic pole positions obtained for the krakow czestochowa upland lat 72 3 n long 150 4 e 95 7 3 and for the lower subtatric nappe lat 71 7 n long 132 2 e 95 4 3 are consistent with the data for stable europe lat 74 7 n long 147 1 e 95 5 0 the paleomagnetic results presented do not reveal any major relative rotations either within the lower subtatric nappe or between this area and the krakow czestochowa upland the reversed directions of nrm observed indicate the existence of a period of reversed field direction in the middle callovian and perhaps also in the oxfordian

timing of natural remanent magnetization in ferriferous limestones from the swiss jura mountains abstract goethite and hematite are the main magnetic phases contained in two ferriferous middle jurassic beds which are exposed within the mandach structure the major tectonic structure of the eastern tabular jura of northern switzerland the iron oxidic phases in a reddish brown sparry limestone known as spatkalk were formed diagenetically whereas these phases are weathering products in a stratigraphically slightly younger oolitic bed the hematite in the oolitic bed was magnetized after the jura main tectonic event in the miocene whereas the hematite in the spatkalk was magnetized before the miocene the goethites in the oolitic bed carry a pretectonic and in the spatkalk a syntectonic magnetization physical and chemical data show that the goethite which was resistant to remagnetization contains an al substitution of 3 4 mol resulting in a neel temperature of 90 c the remagnetized goethite has an al content of 10 7 mol and a neel temperature of 70 c the different goethite properties indicate that the tectonic formation of the mandach structure occurred under low temperature conditions below 90 c

geological structure of a long living geothermal system larderello italy we have examined the data of 600 geothermal wells and re interpreted approximately 500 km seismic profiles through the field of larderello italy we conclude that the two main seismic reflectors present below the geothermal area host two different fluids 1 superheated steam in the upper h horizon reached by drillholes and 2 supercritical fluid in the deeper k horizon reached by few unproductive or damaged wells the superheated steam has the physical and chemical connotation of the geothermal fluid exploited so far at larderello whereas the supercritical fluid represents a potential unconventional deep seated resource still to be assessed the high temperatures existing in correspondence of the k horizon suggest that the silica rich rocks are close to a plastic state and the fluids should remain confined in a medium sealed to the confining rocks unless occasional fluid overpressure and abrupt high strain rates occur

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

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

exhumation of high pressure rocks driven by slab rollback rocks metamorphosed under high pressure hp and ultra high pressure uhp conditions in subduction zones come back to the surface relatively soon after their burial and at rates comparable to plate boundary velocities in the mediterranean realm their occurrence in several belts related to a single subduction event shows that the burial exhumation cycle is a recurrent transient process using the calabria apennine and aegean belts as examples we show that the exhumation of hp rocks is associated in time and space with the subduction of small continental lithosphere blocks that triggers slab rollback creating the necessary space for the exhumation of the buoyant continental crust that was deeply buried just before the buoyancy force of the subducted crust increases until this crust detaches from the downgoing slab it then exhumes at a rate that depends directly on the velocity of trench retreat to become part of the overriding plate heated from below by the asthenosphere that flows into the opening mantle wedge the exhumed crust weakens and undergoes core complex type extension responsible for a second stage of exhumation at a lower rate the full sequence of events that characterizes this model crust mantle delamination slab rollback and trench retreat hp rock exhumation asthenosphere heating and core complex formation arises entirely from the initial condition imposed by the subduction of a small continental block no specific condition is required regarding the rheology and erosion rate of hp rocks the burial exhumation cycle is transient and can recur every time a small continental block is subducted

tectonic role of ophiolite bearing terranes in the development of the southern apennines orogenic belt new data on ophiolite bearing terranes of the liguride complex together with some information on the terranes of the sicilide complex result in a better understanding of the role and tectonic significance of these units in the construction of the southern apennines orogenic belt the liguride complex is composed of two main tectonic units overlain by a thick turbiditic sequence of late oligocene middle miocene age the uppermost one frido unit is a polydeformed and polymetamorphosed sequence composed of two tectonic subunits of shales and calc schists respectively containing blocks of ophiolite garnet gneiss amphibolites and granitoids this unit is thrust over the un metamorphosed terranes calabro lucano flysch unit consisting of a broken formation with blocks of late jurassic ophiolite and their sedimentary cover cretaceous eocene pelagic sediments and late oligocene volcaniclastic deposits the frido unit underwent hp lt metamorphism p 8 10 kb t 400 500 c resulting in glaucophane and lawsonite assemblages in the ophiolitic rocks and aragonite in the meta limestones and calc schists followed by greenschist fades metamorphism p 4 kb t 300 350 c from a structural point of view units of the liguride complex comprise structures developed at different structural levels indicating progressive non coaxial deformation in response to tectonic transport towards the n ne the ophiolite bearing terranes of the liguride complex can be considered as a remnant of an accretionary complex in which the calabro lucano flysch unit represents the toe of the wedge where frontal accretion processes occur and the frido unit is a deeper portion emplacement of the frido unit is explained as being due to formation of a deep duplex structure during the early stage of continental collision processes the polarity of tectonic transport provides new evidence that the liguride complex represents a suture zone between the apulian and the calabrian blocks the age of collision appears to be not older than late oligocene the allochtonous terranes of the liguride and sicilide complexes therefore represent a complete accretionary wedge which records first subduction of the neotethys ocean beneath the calabrian europe continental margin and later continental collision with the african block

origin and timing of the post variscan gabbro granite complex of porto western corsica the post variscan complex of porto consists of metaluminous to slightly peraluminous a type biotite granites mingled with gabbro dioritic rocks and late dykes with basaltic to trachyandesitic composition u pb zircon dating by la icp ms on two mafic intrusive samples constrains the time of the gabbro granite crystallisation at 281 3 ma and 283 2 ma hornblende 40ar 39ar ages from a late trachyandesite dyke date the dyking event at 280 2 ma which is within error the u pb zircon ages of the intrusives biotite granites show variable major and trace element compositions and similar initial end 0 3 to 0 9 whole rock chemistry variations and trace element compositions of plagioclase and allanite indicate that the granites are genetically linked essentially through fractional crystallisation of feldspars and minor allanite on the basis of whole rock chemistry e g initial end 4 9 to 1 7 and trace element clinopyroxene compositions we have ascertained that the mafic intrusives and basic dykes formed from isotopically depleted mantle source derived melts with similar trace element signature these basic melts experienced slightly different evolutionary histories controlled by fractional crystallisation and crustal contamination mainly by the acid magma that gave rise to the associated biotite granites but also by the enclosing older variscan granitoids u pb zircon data suggest that the porto complex was affected by hydrothermal fluid circulation at 259 9 ma

structure kinematics and metamorphism in the liguride complex southern apennines italy abstract the liguride complex of south italy is the remains of a cretaceous paleogene accretionary wedge which was emplaced onto the african margin during early miocene time transport directions of thrust sheets and nappes in the internal zone are roughly towards the present day northeast transport directions match well with the corresponding slip vectors derived from relative motion of the calabria sardinia corsica block with respect to africa including adria during late eocene to oligocene time deformation of the internal zone included extensive underthrusting followed by underplating of already lithified sediments ophiolitic rocks and continental basement on to the base of an accretionary wedge down to depths in places exceeding 30 km overthickening by massive underplating caused late paleogene gravity driven extension within the accretionary wedge the contact between the lower ophiolitic nappe and the upper ophiolitic nappe is an extensional fault zone of this age transport directions during the gravity driven deformation do not match plate derived slip vectors it is inferred that the gravitational potential of the wedge dominated the kinematics of the late palaeogene extensional deformation

reply to comment by robert f butler steven r may and david r bazard on high latitude paleomagnetic poles from middle jurassic plutons and moat volcanics in new england

cross shore grain size and sorting patterns for the bed profile variation at a dissipative beach hasaki coast japan abstract three field observations were conducted in three consecutive years on a sandy beach on the east coast of japan sediment cores were collected from the shoreline to the end of the offshore bar region each core was subdivided into layers and the sorting and skewness were analyzed using predefined trask coefficients the correlations between sediment properties that is median diameter sorting and skewness with respect to the change in the bed profile are discussed in this paper the weekly bed profiles offshore wave conditions and wave energy along the bed profile during the observation periods are discussed two significant sediment types were observed finer well sorted sediment and coarser poorly sorted sediment both coarser skewed the latter sediment properties were observed near the shoreline and at deeper elevations of the cross shore bed profile finer well sorted sand was transported away from and toward the coast depending on the wave intensity which causes in depth materials of coarser poorly sorted sediments to reappear with time the offshore bar and trough region has a limited erosional depth due to the existence of poorly sorted coarser materials which has been confirmed using weekly bed profile measurements the sediment properties have a direct influence on the change of the bed profile

geometry of eclogite facies structural features implications for production and exhumation of ultrahigh pressure and high pressure rocks western gneiss region norway 1 well preserved eclogite facies structural features in metamorphosed gabbro and diorite gneiss in baltica crust formed at a minimum depth of 60 70 km during the scandian orogeny allow direct inferences to be made regarding the geometry of folds kinematics and original structural orientations related to production and exhumation of high pressure rocks folds associated with eclogite facies fabrics are isoclinal to tubular with axes parallel to the trend of a stretching lineation strain estimates and l s or l s fabrics indicate that these structures were formed in a constrictional strain field locally they are well preserved in eclogite facies mylonite zones at least 40 m thick that cut proterozoic gabbro and adjacent gneiss where steeply dipping they show a north side up shear sense across a younger northeast trending shallowly plunging amphibolite facies anticlinorium formed in a constrictional noncoaxial strain field where original structural facing direction can be inferred small circle rotation of the eclogite facies lineation about the anticline axis indicates that the relative motion vector of baltica with respect to overlying imbricated crust and laurentia was oriented 320 in a present day reference frame this result is identical to the orientation of the relative motion vector estimated from paleomagnetic plate reconstructions and consistent with late silurian to early devonian oblique sinistral convergence between baltica and laurentia results of this study indicate that coherent baltica crust at 60 70 km depth experienced subvertical and horizontal shortening while extending toward the foreland during tops southeast thrusting parallel to plate motion high pressure rocks were progressively imbricated and stacked along eclogite facies mylonite zones with the deforming zone separating coherent baltica crust from imbricated basement above the constrictional strains under eclogite facies conditions are interpreted to have resulted from stretching associated with sinking of the cool dense mantle lithosphere

paleomagnetism and late diagenesis of jurassic carbonates from the jura mountains switzerland and france a crucial fold test for magnetizations measured in bajocian through kimmeridgian limestones from the jura mountain region shows that rare blue gray limestones found in this sequence preserve a prefolding magnetization in contrast tan limestones which predominate in this sequence contain secondary magnetizations acquired after folding in the late miocene the postfolding magnetizations in tan limestones appear to be carried in goethite and because reversed as well as normal polarity directions are present the magnetization in these limestones is probably a post miocene pre brunhes 700 000 yr chemical remanent magnetization crm field relations between tan and blue gray limestones which are present in some cases in the same rock unit for example the hauptrogenstein suggest that the tan limestones may have formed from alteration of blue limestones whereas goethite pseudomorphs after pyrite are found in tan limestones the occurrence of pyrite in the blue limestones supports this model indicating that goethite could have formed from oxidation of pyrite abundant meteoric water probably was available for such an oxidation process during uplift of these strata subsequent to deformation natural remanent magnetization in blue limestones appears to be carried in magnetite the positive fold test for the characteristic magnetization in these rocks is significant at the 99 confidence level k values for 24 site mean directions before and after tilt correction are 9 3 and 43 2 respectively the simplest interpretation for the origin of observed remanence in magnetite in the blue limestones is a primary magnetization of depositional or biogenic origin characteristic directions in these rocks yield a mean paleopole position of 77 7n 148 4e k 26 0 a95 5 9 this pole is in reasonable agreement with one other upper jurassic pole from western europe and with other middle to upper jurassic poles from the atlantic bordering continents after rotation of these continents to a reconstructed configuration for middle to late jurassic time

geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy abstract serri g innocenti f and manetti p 1993 geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 117 147 the neogene quaternary magmatism of the northern apenninic arc took place in four phases separated in space and time which become progressively younger from west to east phase i 14 ma phase ii 7 3 6 0 ma phase iii 5 1 2 2 ma phase iv 1 3 0 1 ma this magmatism is the result of the activation of three physically separate sources 1 the adriatic continental crust extracted from the mantle in the late proterozoic 2 a strongly refractory recently k enriched harzburgitic mantle located in the mechanical boundary layer mbl of the lithosphere and 3 a recently metasomatized cpx rich mantle compositionally variable from iherzolite to wehrlite clinopyroxenite interpreted as an ephemerally k enriched asthenosphere the adriatic continental crust is the dominant source of the acid plutonic and volcanic rocks of the tuscan region the acid magmatism is mostly found inside an ellipsoidal area about 150 300 km centred on giglio island here defined as the tuscan crustal dome within this area mantle derived magmas unaffected by important crustal contamination processes and mixing with crustal anatectic melts have so far not been found pure crustal magmas are rare but are represented for example by some of the san vincenzo and roccastrada rhyolites virtually all the tuscan acid centres show evidence of mixing with potassic mantle derived magmas major and trace elements as well as 87 sr 86 sr and 143 nd 144 nd data on primitive rocks mg 65 reveal two groups of mantle derived magmas these define two distinct mantle enrichment trends both essentially due to the additions of k rich components which metasomatized separate compositionally diverse upper mantle sectors in both cases the most remarkable mineralogical effect of these enrichment processes is the production of variable amount of phlogopite through reaction between fluids and or melts with the mantle the rocks of group i ol hy and q normative lamproites ultrapotassic high mg latites ultrapotassic shoshonites and shoshonites saturated trend are considered to be derived by partial melting at low pressure 87 sr 86 sr 0 717 ce sr 0 3 and k 2 o na 2 o 6 7 and low ratios of 143 nd 144 nd 0 5121 0 5120 and ba la 87 sr 86 sr 0 712 and k 2 o na 2 o 8 9 values and low 143 nd 144 nd ba la 0 10 ratios these constraints do not allow to exclude a complete identity between the k rich components which metasomatized the mantle sources of the saturated and undersaturated trend magmas the geochemical and isotopic features of the components that metasomatized the mantle sources of the northern apenninic arc magmatism can be explained by a geodynamic process which causes a large amount of crustal materials to be incorporated within the upper mantle we propose that the delamination and subduction of the adriatic continental lithosphere related to the still ongoing northern apennine continental collision provide a viable mechanism to explain the genesis and eastward discontinuous migration of the magmatism in central italy the subduction of delaminated lithospheric mantle with lower crustal slivers would have exposed uppermost mantle adriatic mbl and crustal units previously imbricated in the apennine chain to the heating advected by the upwelling of a recently and ephemerally k enriched asthenospheric mantle wedge and by the underplating of magmas derived from it we consider that the diapiric uprising of a hot crustally contaminated asthenosphere occurs in the wake left above the sinking of the adriatic delaminated subducting continental lithosphere the delamination subduction process of the adriatic lithosphere has probably started in the early middle miocene but earlier than 15 14 ma ago as indicated by the age and petrologic characteristics of the first magmatic episode sisco lamproite of the northern apennine orogenesis

paleomagnetism of jurassic sediments as evidence for oroclinal bending of the inner west carpathians abstract the jurassic carbonates from the krizna nappe contain a pre tectonic characteristic component of remanence the declinations for individual nappe fragments differ and form a fan like pattern they are close to the tectonic vergencies measured in the field which suggests that the arcuate structure of the inner carpathians results from an oroclinal bending of an originally straight belt

p wave tomography of the mantle under the alpine mediterranean area 1 we study the upper mantle p wave velocity structure below the euro mediterranean area down to 1000 km depth by seismic travel time tomography we invert summary residuals constructed with both regional and teleseismic first arrival data reported by the international seismological centre isc 1964 1995 introducing some alternative strategies in the travel time tomographic approach and a new scheme to correct teleseismic data for global mantle structure our high resolution model pm0 5 is parameterized with three dimensional 3 d linear splines on a grid of nodes with 0 5 spacing in both horizontal directions and 50 km vertical spacing we obtain about 26 root mean square rms reduction of residuals by inversion in addition to roughly 31 reduction after summary rays formation and selection sensitivity analyses are performed through several test inversions to explore the resolution characteristics of the model at different spatial scales the distribution of large scale fast anomalies suggests that two different stages of a convection process presently coexist in very close regions the mantle dynamics of western central europe is dominated by blockage of subducted slabs at the 660 km discontinuity and ponding of seismically fast material in the transition zone contrarily in the eastern mediterranean fast velocity material sinks into the lower mantle suggesting that the flow of the cold downwelling here is not blocked by the 660 km discontinuity on a smaller scale the existence of tears in the subducted slab lithospheric detachment all along both margins of the adriatic plate as proposed by some authors is not supported by our tomographic images

opposite vergence of nappes and crustal extension in the french italian western alps in the internal pennine zone of the french italian western alps dora maira monviso rocciavre massifs and queyras region the structural trends define an apparent dome geometry that is truncated to the east by the po basin this geometry is classically interpreted as a backthrusting system the kinematic history of the area has been investigated using structural metamorphic and geochronologic data on the basis of which two main deformation episodes have been distinguished that occurred under differing metamorphic conditions 1 the first deformation occurred under greenschist facies metamorphism it caused a regional scale foliation and an ew trending lineation that lie parallel to ductile deformation zones and thrust contacts sense of shear indicators associated with the lineation indicate contradictory top to the east and top to the west senses of shear from these it is deduced that coeval east and west vergent thrust faulting accommodated major displacements between nappes phengite ar ar data yield late eocene early oligocene ages for the greenschist facies metamorphism 2 the second deformation caused the widespread development of high angle shear bands and normal faults on opposite sides of the dora maira massif resulting in the apparent dome geometry of the massif a steep 50 80 network of west dipping normal faults is particularly well developed on the west side of the dora maira massif differences of 2 3 kbar and 100 150 c between juxtaposed monviso rocciavre and queyras nappes implies 8 km of vertical displacement along the monviso upper tectonic contact these normal faults formed in a more brittle regime only a post early oligocene age can be estimated from microstructural studies for these final movements these deformations postdate hp lt metamorphism and resulted in the juxtaposition of nappes of distinctly different origin age grade and p t t history a kinematic model is presented in which opposite vergence of nappes followed by large scale crustal extension occurred in response to uplift during the convergence between the european and south alpine plates this model may account for rapid uplift rapid unroofing and cooling of high pressure low temperature rocks thereby explaining the absence of amphibolite facies metamorphism overprint in this part of the alps that may have led to the preservation of coesite bearing rocks in the southern part of the dora maira massif

low latitude oxfordian position of the oravic crustal segment pieniny klippen belt western carpathians palaeogeographic implications abstract the bajocian and the oxfordian kimmeridgian crinoidal limestones of the pieniny klippen belt pkb western carpathians and the bathonian callovian neptunian dykes which cut them were sampled for rock magnetic and palaeomagnetic study the sampled sections were babina mestecko vrsatec bolesovska dolina and szaflary sirm t curves show that the limestone and the dykes from mestecko contain hematite with blocking temperature t b about 650 670 c babina limestone and dykes contain magnetite with t b between 470 and 570 c usually accompanied by small hematite tail sometimes goethite with t b about 80 100 c is seen dykes and limestone from vrsatec contain magnetite with t b of 570 c or hematite with unblocking temperature of 670 c after cleaning of recent soft component by a temperature of 200 c and a field of 10 20 mt the hard component was revealed after tilt correction the locality mean directions found in limestones have scattered declination but similar reversed inclination between 35 and 40 for the bajocian and between 35 and 49 for the oxfordian kimmeridgian an exception was the mean direction for the bajocian limestone from bolesovska dolina which has normal polarity fold test for inclination only showed pre folding inclinations for the bajocian and oxfordian kimmeridgian limestones and scattered inclinations for the in situ and tilt corrected directions for the dykes the mean palaeoinclination calculated for bajocian and oxfordian kimmeridgian by means of inclination only test are 38 5 3 and 42 5 11 2 respectively which corresponds to 21 7 1 5 n and 24 6 5 6 n of palaeolatitude this is about 10 15 lower than the value of inclination expected for that age for the pieniny klippen belt from the jurassic poles for stable europe as positive inclination only fold test proves pre folding age of isolating directions other possibility flattening of inclination should be considered anisotropy of magnetic susceptibility ams and magnetic unhysteretic remanent magnetisation aarm can be used for the evaluation of origin and for the deviation of natural remanent magnetisation nrm the axes of ams are scattered for all localities the degree of anisotropy is low the shape parameter t shows equal distribution of oblate and prolate fabric on the contrary the arm maximum axes are well clustered especially for mestecko and vrsatec the maximum axes are distributed in a vertical plane for mestecko and in horizontal plane for babina and vrsatec this evidences that the aarm fabric is not related to sedimentation and compaction the anisotropy axes are not close to the nrm directions for mestecko they are steeper this excludes an effect of shallowing of nrm on this basis we can assume that more southern palaeolatitude of the pieniny klippen belt than expected is a demonstration of palaeogeography and tectonics and points to a close vicinity of the pkb to the african plate in the jurassic the results from the polish part of pkb which emerged in the latest years showed the same palaeolatitude for the callovian kimmeridgian limestones the low palaeomagnetic inclinations measured in the bajocian crinoidal limestones show that the southward drift may have started earlier than previously expected

palaeomagnetic results from the fold and thrust belt of the western carpathians an overview the western carpathians are separated into an outer and inner carpathians both comprising several nappe systems by the extremely narrow and highly deformed pieniny klippen belt the main phase of deformation and thrusting took place during the late cretaceous in the inner carpathians at the end of cretaceous paleocene in the pieniny klippen belt and in the miocene in the outer carpathians in this paper a large amount of palaeomagnetic results of different quality available from several nappe stacks and from overstep sequences were reviewed and interpreted in terms of tectonics the data suggest that all three main units participated in two phases of anticlockwise rotation starting at 18 5 ma that is the outer carpathian nappes in front of the already consolidated alpine carpathian pannonian block became accreted to the block late cretaceous nappe transport neogene uplift of core mountains and possibly oroclinal bending of pre oligocene age can account for important differences in pre cenozoic palaeomagnetic declinations most of them exhibit less or no anticlockwise rotation suggested by the overstep sequences implying pre cenozoic clockwise rotations of variable angles

the role of true polar wander on the jurassic palaeoclimate from the late carboniferous until the middle jurassic continents were assembled in a quasi rigid supercontinent called pangea the first palaeomagnetic data of south america indicated that the continent remained stationary in similar present day latitudes during most of the mesozoic and even the palaeozoic however new palaeomagnetic data suggest that such a scenario is not likely at least for the jurassic in order to test the stationary versus the dynamic continent model we studied the jurassic apparent polar wander paths of the major continents that is eurasia africa and north america that all in all show the same shape and chronology of the tracks with respect to those from south america we thus present a master path that could be useful for the jurassic pangea one of the most remarkable features observed in the path is the change in pole positions at 197 ma early jurassic which denotes the cessation of the counter clockwise rotation of pangea and commencement of a clockwise rotation that brought about changes in palaeolatitude and orientation until the end of the early jurassic 185 ma here we analyse a number of phenomena that could have triggered the polar shift between 197 and 185 ma and conclude that true polar wander is the most likely in order to do this we used morgan s tectonophysics 94 123 139 1983 grid of hotspots and performed absolute palaeogeographical reconstructions of pangea for the late triassic and jurassic the palaeolatitudes changes that we observe from our palaeomagnetic data are very well sustained by diverse palaeoclimatic proxies derived from geological and palaeoecological data at this time of both the southern and northern hemispheres

geomagnetic polarity in the early cretaceous and jurassic knowledge of the polarity history of the earth s magnetic field during the mesozoic stems primarily from oceanic m sequence magnetic anomalies certain of these anomalies have been biostratigraphically dated from sediments immediately overlying basaltic basement at deep sea drilling project d s d p sites within the m sequence the biostratigraphic control is such that these age estimates are generally imprecise and moreover the sediment ages represent only minimum ages for the basaltic basement itself magnetostratigraphy in sedimentary land sections provides improved age estimates for magnetozones which can then be correlated with m sequence anomalies magnetostratigraphy provides not only enhanced dating of the ocean floor and resolution of the behaviour of the geomagnetic field during the cretaceous and jurassic oceanic quiet zones but also a world wide correlation tool for sedimentary stratigraphy the middle cretaceous is characterized by a long period of normal polarity extending from the early aptian to the early campanian reversed magnetozones corresponding to oceanic anomalies m 0 m 1 and m 3 have been palaeontologically dated as early aptian middle barremian and early barremian respectively magnetozones corresponding to oceanic anomalies m 5 to m 15 are hauterivian to valanginian in age but have not been individually associated with stage boundaries mainly due to poor biostratigraphic control in italian pelagic limestone sections of this age however magnetozones corresponding to oceanic anomalies m 16 to m 22 have been individually correlated to lower berriasian and tithonian palaeontological zones and extrapolation of this correlation gives an age for anomaly m 25 close to the oxfordian kimmeridgian boundary the jurassic 9quiet zone in the oceans is recognized in land sections as an extended period of predominantly normal polarity and although poor biostratigraphic control in this interval limits our knowledge of its duration we consider that it extended through the oxfordian and callovian stages the bathonian and older jurassic stages are characterized by mixed polarity a precise correspondence of magnetozones to ammonite zonations and stage boundaries is only available for the aalenian to pliensbachian interval where the frequency of reversal was apparently very high

plate tectonic evolution of the southern margin of eurasia in the mesozoic and cenozoic abstract thirteen time interval maps were constructed which depict the triassic to neogene plate tectonic configuration paleogeography and general lithofacies of the southern margin of eurasia the aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework the hercynian orogeny was completed by the collision of gondwana and laurussia whereas the tethys ocean formed the embayment between the eurasian and gondwanian branches of pangea during late triassic early jurassic times several microplates were sutured to the eurasian margin closing the paleotethys ocean a jurassic cretaceous north dipping subduction boundary was developed along this new continental margin south of the pontides transcaucasus and iranian plates the subduction zone trench pulling effect caused rifting creating the back arc basin of the greater caucasus proto south caspian sea which achieved its maximum width during the late cretaceous in the western tethys separation of eurasia from gondwana resulted in the formation of the ligurian penninic pieniny magura ocean alpine tethys as an extension of middle atlantic system and a part of the pangean breakup tectonic system during late jurassic early cretaceous times the outer carpathian rift developed the opening of the western black sea occurred by rifting and drifting of the western central pontides away from the moesian and scythian platforms of eurasia during the early cretaceous cenomanian the latest cretaceous paleogene was the time of the closure of the ligurian pieniny ocean adria alcapa terranes continued their northward movement during eocene early miocene times their oblique collision with the north european plate led to the development of the accretionary wedge of the outer carpathians and its foreland basin the formation of the west carpathian thrusts was completed by the miocene the thrust front was still propagating eastwards in the eastern carpathians during the late cretaceous the lesser caucasus sanandaj sirjan and makran plates were sutured to the iranian afghanistan plates in the caucasus caspian sea area a north dipping subduction zone jumped during paleogene to the scythian turan platform the shatski terrane moved northward closing the greater caucasus basin and opening the eastern black sea the south caspian underwent reorganization during oligocene neogene times the southwestern part of the south caspian basin was reopened while the northwestern part was gradually reduced in size the collision of india and the lut plate with eurasia caused the deformation of central asia and created a system of nw se wrench faults the remnants of jurassic cretaceous back arc systems oceanic and attenuated crust as well as tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems

the timing of partial melting barrovian metamorphism and granite intrusion in the naxos metamorphic core complex cyclades aegean sea greece abstract the relationship between partial melting and granite intrusion in a classic barrovian metamorphic terrane has been assessed thirteen samples were dated by shrimp u pb zircon geochronology from the island of naxos greece one of the aegean metamorphic core complexes the effect of partial melting during peak barrovian metamorphism on naxos is recorded by fine

palaeogeographic evolution of the pieniny klippen basin using stratigraphic and palaeomagnetic data from the veliky kamenets section carpathians ukraine abstract a 40 m thick carbonate succession of the bajocian to berriasian age from the veliky kamenets quarry novoselica area pieniny klippen belt ukraine resembles both the czorsztyn and niedzica successions of the pieniny klippen belt traditionally considered ridge slope related deposits a total of 176 individually oriented cores collected from the bottom to the top of the sequence with sampling density dependent on inferred sedimentation rates show multicomponent remanent magnetization with magnetite as a main magnetic carrier thermal demagnetization revealed two main components of natural remanent magnetization nrm a low blocking temperature component s of normal polarity is considered of posttectonic probably thermoviscous origin due to overheating by neogene volcanics a stable high blocking temperature nrm component p shows dual polarity distribution and is considered primary it was possible to recognize 23 polarity zones that have been correlated with a biostratigraphic scale since two significant sedimentary gaps occur at 422 and 860 cm the main hiatus ms from the base the latter comprising the middle callovian early oxfordian time span 6 8 ma an obtained pattern of magnetic reversals presented in this study cannot be considered complete a palaeolatitude of 41 5 is calculated for the mid jurassic part below ms similar to that expected for the european craton at the kamenets locality the mid oxfordian limestone directly overlying the ms has palaeolatitudes around 28 6 this implies a relatively fast opening of the oceanic domain to the north from the kamenets block this conclusion combined with similarity of the kamenets sequence to ridge related sediments of the pieniny klippen belt makes it possible to speculate on the existence of the kamenets ridge a new term a structure of uncertain although possible structural links to the czorsztyn ridge palaeomagnetic declinations suggest 100 counterclockwise rotation of the whole section before the neogene

geochronology and isotope transport systematics in a subsurface granite from the larderello travale geothermal system italy abstract a monzogranite here referred to as the montieri pluton was encountered along two depth profiles from ca 2 to 4 km depth in wells of the larderello travale geothermal system italy we obtained high resolution petrographic and microchemical data on seven fresh samples of the montieri pluton these data are required to correctly interpret the combined isotope data for the rb sr and k ar systems biotite and k feldspar from all samples were analyzed by rb sr and 39ar 40ar rb sr analyses gave extremely variable two point rb sr apparent ages and sr initials indicating that biotite did not equilibrate with feldspar bulk dissolution of k feldspars does not define a rb sr alignment that could have proved a common origin of all k feldspar samples from a single magma batch the leachable fractions of k feldspar separates have much more homogeneous 87sr 86sr ratios around 0 712 which may reflect the isotopic composition of a late stage circulating fluid because of the anatectic origin of the granites from the larderello travale geothermal system it is likely that every k feldspar separate contains at least three isotopically distinct feldspar generations relics of the hercynian gneiss basement pliocene magmatic minerals and hydrothermal retrogression products such heterogeneity can be confirmed and quantified by petrographical observations and electron microprobe analyses the 39ar 40ar age spectra of the biotite samples show some internal discordance because of deviations from stoichiometry biotite discordance can be attributed both to chlorite intergrowths as predicted from the active fluid circulation and to the presence of multiple biotite generations such as have already been documented from other micas from the larderello travale geothermal system and as indeed confirmed by high resolution petrography total k ar biotite ages on cluster around 3 ma and broadly agree with a rb sr age obtained by regressing only the biotite analyses this suggests that the montieri pluton whose known volume is at least 25 km3 was emplaced at that time the k feldspar spectra are strongly discordant no step age approaches the zero age which would be predicted by ar diffusivity modelling the extraneous ar in the feldspars is not excess ar but inherited ar instead ar inheritance in the feldspar separates correlates with inheritance of sr arrhenius trajectories of the apparent ar diffusivities for all seven feldspars are astonishingly identical despite the heterochemism amongst samples however the apparent diffusivity calculated from the step heating experiments led to irreproducible models for the thermal history along the depth profile as well as time scales shorter than the historical record this indicates that ar diffusivities calculated from laboratory experiments must not be extrapolated to geological conditions

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

neogene evolution of the southwestern tyrrhenian sea sardinia basin and western bathyal plain abstract the reprocessing of mcs reflection lines and sampling data across the sw tyrrhenian basin from the sardinia tunisia strait sts to the orosei canyon line ocl show that the acoustic basement of the area is made by variscan crystalline metamorphic rocks covered by a thick sequence of sediments including the messinian interval the pre messinian sequence can be subdivided into three seismic intervals or subunits largely calibrated by sampling data the oldest pre messinian subunit is strongly deformed by compressional and or transpressional structures and the recovered samples are deep water arkosic sediments aquitanian in age however the whole interval may encompass a wider time span probably from late oligocene to langhian this subunit was laid down in a fore arc basin located between a volcanic arc sardinia and an accretionary wedge calabrian peloritanian kabilide or ck units prior to the collision of the latter elements with the continental margin of africa in sicily and tunisia along the so called drepano thrust front dtf coeval to collision the generation of the main sardinia thrust mst occurred carrying the sardinia basement rocks over the ck units and deforming the fore arc basin sediments the intermediate pre messinian sedimentary subunit spans from part of serravallian to part of tortonian it is post tectonic with respect to the underlying subunit but it represents a pre rift succession if related to the overlying one it consists of terrigenous deposits prograding from sardinia to the ene into a basin some hundreds of meters deep which was left in the area after collision the youngest pre evaporitic subunit late tortonian early messinian in age displays wedge shaped reflectors in the sardinia basin and forms the lower portion of a syn rift complex including the messinian and part of the pliocene sediments this succession records the onset of extensional tectonics in the area as also testified by the tortonian age of exumation of the basement while in the tyrrhenian basin north of the ocl intra tortonian to intra pliocene rifting was strong but discontinuous and migrating with time to the east in the sw tyrrhenian basin in contrast rifting was less severe but continuous during the same time interval this emphasizes the role played by the ocl a inherited mesozoic discontinuity reactivated as a transfer zone during the neogene these new data allow correlation of the main miocene deformational events observed in the study area to those of the adjacent emerged areas namely the peloritani and maghrebian units in sicily prior to the pliocene quaternary full development of the southern tyrrhenian sea

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

oxfordian magnetostratigraphy of poland and its correlation to sub mediterranean ammonite zones and marine magnetic anomalies abstract a nearly continuous magnetostratigraphic polarity pattern was compiled from several ammonite zoned carbonate successions of southern poland and from a composite magnetostratigraphy from the iberian range of spain the array of sections spans the middle two thirds of the oxfordian within the sub mediterranean province cordatum through bifurcatus ammonite zones the average paleopole calculated from eight of these polish sections is at 78 5 n 184 9 e p 2 6 m 3 5 the sub mediterranean polarity pattern is consistent with an independent polarity pattern derived from the boreal realm sections of the british isles and improves the inter correlation between these faunal realms cycle stratigraphy published for these ammonite subzones from southern france enabled temporal scaling of the polarity pattern thereby facilitating correlation to marine magnetic anomalies m28 through m33 as modeled from deep tow magnetometer surveys in the western pacific the bases of the middle and upper oxfordian substages as defined in the sub mediterranean zonation in poland correspond approximately to chrons m33 and m29 of that pacific m sequence model

the liguride complex of southern italy a cretaceous to paleogene accretionary wedge abstract the ophiolite bearing allochthonous flysch liguride complex of the southern apennines italy has traditionally been divided into two tectonic units the metamorphic frido unit and the unmetamorphosed cilento unit the two units have hitherto been considered to derive from two distinct paleogeographic domains however the identification of cilento unit sediments within frido unit successions implies that the sediments of both units were coeval deposits within the same sedimentary basin cilento unit sediments also occur as the sedimentary cover of kilometre scale oceanic slices within the liguride complex indicating deposition on oceanic basement and not continental basement as was previously considered thrust transport directions and sediment provenance indicate that during late jurassic time this ocean basin lay to the east of the calabrian terrain and to the west of apulia calabria and apulia representing the european and african margins of neotethys respectively northwestwards subduction of oceanic crust beneath the calabrian terrain from late cretaceous time onwards produced an accretionary wedge which was later emplaced onto the apulian margin during the burdigalian collision of calabria and apulia the liguride complex represents the obducted remains of this accretionary wedge this interpretation contains three important implications for pre tertiary plate tectonic reconstructions of the western mediterranean region these are 1 1 the calabrian continental terrain formed part of the iberian plate on the north margin of neotethys this may have implications for the former location and continuation of the north pyrenean fault 2 2 the existence of a continuation of the eo alpine belt through calabria and the kabylies is placed in doubt thus requiring only one constant polarity nw dipping subduction direction to explain the structures now seen in these regions 3 3 the existence of a transform fault between the europe vergent structures of corsica and the africa vergent structures of calabria this transform must have been active from at least late cretaceous time in a position now occupied by the tyrrhenian sea

crustal section based on crop seismic data across the north tyrrhenian northern apennines adriatic sea abstract using deep seismic reflection data from the italian lithospheric exploration project crop in the central mediterranean region a 400 km long section composed of three different profiles crossing the northern tyrrhenian sea crop m 12a profile the northern apennines crop 03 and the adriatic sea crop m 16 is reconstructed and discussed new data allow us to outline a seismically consistent tectono stratigraphic setting for the crust and upper mantle of the northern apennines thrust belt system and its adriatic foreland time space analysis of the deformation of the investigated chain and identification of existing macrostratigraphic crustal intervals and tectonic units allow a reasonably controlled interpretation of the geodynamic evolution and of the main orogenic stages careful seismic reprocessing and application of advanced techniques to key zones of the explored area such as the tuscan archipelago were determinants in obtaining fundamental information for understanding of the complex lithospheric structures and their evolution profile interpretation supports that the northern apennine chain is dominated by a compressive thrust system crustal extension assumed by some authors as the dominating tectonic process for the whole tuscan apennine area represents a subordinate geodynamic event of the last stage tyrrhenian in the early cretaceous late jurassic the paleogeographic framework consisted of the europe and adria plates separated by the alpine tethys ocean during the late cretaceous early eocene adria europe convergence eo alpine stage and subduction beneath the adria plate closed the alpine tethys sea with the tethyan slab being clearly seismically imaged the first apenninic geodynamic stage occurred in the late oligocene early miocene with the opening of the balearic basin which generated a first lithospheric root of the apenninic chain in the tuscan archipelago area this root is represented by adria verging thrust faults that progressively flatten eastward upper parts of the west verging eo alpine thrust blocks were truncated by the east verging thrust faults of the balearic stage a deeper seismic reflector attributed to the top of the asthenosphere forms a mantle high below the elba island from the late miocene to present the corsica basin and western hinterland area were affected by extensional tectonics related to the tyrrhenian opening whereas compressional tectonics continued in the eastern hinterland and mostly on the eastward migrating foreland with development of a second lithospheric root constituted by high angle thrust faults these faults give rise to a huge basement culmination below the main apennines watershed impressive e directed gravity sliding of sedimentary blocks over their sloping basement occur generating the umbria marche shallow seismicity crustal shortening of the apennines system amounts to 170 km 14 km of which are due to the eo alpine stage 71 km to the balearic and 85 km to the tyrrhenian one in the frame of africa europe convergence the tyrrhenian apennines tectonodynamics were mainly conditioned by the mesozoic paleogeography

tectonics of the punta bianca promontory insights for the evolution of the northern apennines northern tyrrhenian sea basin the structural setting of the eastern headland of the la spezia gulf punta bianca promontory provides some constraints on the contractional and extensional framework of the northern apennines northern tyrrhenian sea basin geodynamic system and allows a detailed reconstruction of a complex evolutionary path out of sequence thrusting is supposed in the inner side of the chain two different extensional events are identified the older early middle miocene may be related to the imbrication of the deeper metamorphic units of the apenninic thrust wedge younger extension fits very well into an eastward asymmetrical faulting framework related to the opening of the northern tyrrhenian sea basin from the late miocene to the pliocene pleistocene well exposed low angle normal faults developed during this event extensional structures were then overprinted and reactivated by a mainly strike slip regime in the quaternary

extensional faulting in an intraoceanic subduction complex working hypothesis for the palaeogene of the alps apennine system abstract within the ophiolite complexes exposed in the ligurian alps and apennines nw italy several extensional detachment faults are identified which overprint late cretaceous high pressure metamorphic fabrics developed in an intraoceanic subduction system one of these detachment faults is the sestri voltaggio line which marks an 8 kbar pressure gap between blueschist facies ophiolites and calcareous sediments of the sestri voltaggio zone and underlying eclogite fades ophiolites and metasediments of the voltri massif radiometrie and stratigraphie constraints suggest that extension has occurred during the late paleocene to possibly early eocene from the middle eocene onward compressional tectonics prevailed again resulting in westerly directed imbrications in the ligurian alps and easterly directed folding and thrusting in the ligurian apennines a strong correlation is identified between the africa europe convergence rate and the stability of the accretionary wedge i e the paleocene extension coincides with a period of strongly reduced convergence velocities whilst the middle eocene transition to compressional tectonics concurs with an acceleration of the convergence rate this inferred relation between convergence rate and style of internal deformation matches very closely the results from mechanical models addressing the stability of orogenic wedges with a strain rate dependent rheology and provides the basis for a working hypothesis on the palaeogene evolution of the alps apennine orogenic system

comment on high latitude paleomagnetic poles from middle jurassic plutons and moat volcanics in new england and the controversy regarding jurassic apparent polar wander for north america by mickey c van fossen and dennis v kent

a paleomagnetic pole position of late jurassic early cretaceous dolerites from hinlopenstretet svalbard and its tectonic implications abstract paleomagnetic examination of late jurassic early cretaceous dolerites hinlopenstretet reveal a mean paleofield direction d 181 i 71 95 4 2 k 117 9 17 sites 96 samples which is argued to represent a deuteric magnetization formed at the time of cooling the resultant paleopole 66 n 200 e dp 7 dm 8 accords with paleomagnetic poles of similar age for north america after taking into account post jurassic continental separation the result from the present study is interpreted to represent a late jurassic early cretaceous paleopole for eurasia the similarity of the paleopoles from cratonic north america and eurasia in its pre drift configuration at about 145 ma makes it reasonable to conclude that relative displacement due to extension between eurasia and north america prior to the onset of sea floor spreading must have taken place after 145 ma and before the start of sea floor creation in the cretaceous

new berriasian palaeopole from the central west carpathians tatra mountains southern poland does it look apulian summary a palaeomagnetic study was carried out in the northern part of the central west carpathians in the tatra mts 20 e 49 n berriasian pelagic carbonates from the krizna nappe fatricum were investigated at three localities 166 samples embracing a 100 m vertical section a mixed polarity pre folding magnetite related component was calculated for 87 samples representing the lower and middle berriasian the palaeopole 152 e 63 n is located close to the coeval eurasian palaeopole implying a net post berriasian 15 20 clockwise tectonic rotation of the krizna nappe in the investigated area relative to stable europe berriasian palaeolatitudes from the tatra mts are similar to those from the pieniny klippen belt and northern calcareous alps but systematically higher than in the transdanubian and italian apulian sections taking into account the fact that palaeomagnetic data from the overlying ter tiary rocks indicate 60 counter clockwise rotation of the central west carpathians after the oligocene the krizna nappe must have rotated clockwise before the eocene probably during the late cretaceous thrusting available palaeomagnetic data point to a palaeotectonic affinity of the central west carpathi ans and northern calcareous alps in the mesozoic the central west carpathians and northern calcareous alps reveal a rotation pattern that is predominantly clockwise whereas areas be longing to the apulian plate e g transdanubian mts southern alps and appenines show mostly counter clockwise rotations

map view retrodeformation of an arcuate fold and thrust belt the jura case 1 the mechanism of arcuate mountain range formation is a matter of debate here we perform a map view restoration of a detailed three dimensional model of the jura arc a typical arcuate mountain range in the foothills of the swiss and french alps this retrodeformation is performed using the unfold surface balanced program based on a block mosaic method it results in a displacement field divergent toward the deformation front this displacement field suggests counterclockwise rigid rotations in the horizontal plane up to 30 in the southern internal jura and a corresponding vertical axis rotation or shear strain of the savoie molasse basin hinterlandward we also predict a 10 clockwise vertical axis rotation of the molasse basin in switzerland all these rotations agree with those documented by paleomagnetic data the former are taken to result from a substantial decrease in shortening at the southern jura end while the divergence of displacements is interpreted to result from variations in the detachment level distribution

hp lt metamorphism in the volparone breccia northern corsica france evidence for involvement of the europe corsica continental margin in the alpine subdution zone the alpine belt in corsica france is characterized by the occurrence of stacked tectonic slices derived from the corsica europe continental margin which outcrop between two weakly or non metamorphic tectonic domains the autochthonous domain of the hercynian basement to the west and the balagne nappe ophiolitic unit belonging to the nappes superieures to the east these slices including basement rocks permian granitoids and their palaeozoic host rocks late carboniferous permian volcano sedimentary deposits coarse grained polymict breccias volparone breccia and middle eocene siliciclastic turbidite deposits were affected by a polyphase deformation history of alpine age associated with a well developed metamorphic recrystallization this study provides new quantitative data about the peak of metamorphism and the retrograde p t path in the alpine corsica the tectonic slices of volparone breccia from the balagne region previously regarded as unmetamorphosed were affected by peak metamorphism characterized by the phengite chlorite quartz albite assemblage using the chlorite phengite local equilibria method peak metamorphic p t conditions coherent with the low grade blueschist facies are estimated as 0 60 0 15 gpa and 325 20 c moreover the retrograde p t path characterized by a decrease of pressure and temperature is evidence of the first stage of the exhumation path from the peak metamorphic conditions to greenschist facies conditions 0 35 0 06 gpa and 315 20 c the occurrence of metamorphic peak at high pressure low temperature hp lt conditions is evidence of the fact that these tectonic slices derived from the corsica europe continental margin were deformed and metamorphosed in the alpine subduction zone during their underplating at 20 km of depth into the accretionary wedge and were subsequently juxtaposed against the metamorphic and non metamorphic oceanic units during a complex exhumation history

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

the age of the paludi formation a major constraint to the beginning of the apulia verging orogenic transport in the northern sector of the calabria peloritani arc a stratigraphic revision of the paludi formation cropping out in northern calabria on the north eastern side of sila massif has confirmed that it has been deposited between two main tectonic phases actually the formation is involved only by top to the north east thrusts different from those separating the crystalline and ophiolitic nappes of northern calabria and rests unconformably on the sila unit the uppermost nappe of the tectonic stack in the frame of the interpretation of northern calabria as a fragment of the alps the paludi formation play the role of a deposit post dating the eo alpine tectonic phases and pre dating the apenninic orogenic transport therefore the aquitanian age of the formation obtained by nannofloras analyses can be considered the minimum age to the apulia verging orogenic transport witnessed by top to north east thrusts it fairly corresponds to the age referred to the lucanian ocean closure

paleomagnetic implications on the evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we first re examined the apparent polar wander curves for stable eurasia and africa since the triassic these curves were then combined together with curves of north and south america according to the kinematics of the atlantic ocean and a synthetic polar wander curve was given then most of the paleomagnetic results from the tethys mobile belt from the atlantic to the pamirs were analysed several groups of plates microplates and blocks can be seen first relatively stable regions like maghreb and sicily which have not moved much then we have a group formed by iberia sardinia italy and to a lesser extent corsica and the western and central alps for these blocks movements are anticlockwise rotations chiefly driven by the anticlockwise rotation of africa but they are sometimes stronger to the east a major change takes place the north of the aegean sea and the ionian zone are clockwise rotated and these rotations are recent oligocene miocene for the first part pliocene to the present for the second part a major problem arises in turkey caucasus and iran paleomagnetic results indicate a position far to the south of eurasia and at the same time geological evidence is in favour of a position close to eurasia we discuss these discrepancies

paleomagnetism of the middle jurassic summerville formation east central utah the paleomagnetism of the late callovian summerville formation was analyzed to obtain a late middle jurassic paleomagnetic pole for north america a total of 281 samples were collected from 35 sedimentary horizons sites in a single locality in the san rafael swell area of east central utah fifteen site mean characteristic remanent magnetization chrm directions pass the reversals test and define at least five polarity zones within 52 m of stratigraphic section suggesting that the chrm was acquired upon or soon after deposition magnetizations of some specimens are complex and several horizons yield anomalous site mean directions data analysis included filtering to provide different combinations of virtual geomagnetic poles for calculation of the paleomagnetic pole however editing the data did not change the pole position by more than 5 the preferred paleomagnetic pole position is 56 3 n 133 4 e a95 7 2 n 11 sites the summerville formation paleomagnetic pole is located near the 172 ma corral canyon pole and is statistically indistinguishable from the 151 ma glance conglomerate and 149 ma lower morrison poles the paleomagnetic pole from the summerville formation is located at a much lower latitude and more easterly longitude than the paleomagnetic pole obtained from the 165 ma moat volcanics of new england we propose that the jurassic north american apparent polar wander path is an age progressive band at 55 n to 65 n latitude extending from 11 e longitude at 172 ma to 150 e longitude at 149 ma

a palaeomagnetic study of 143 ma kimberlite dikes in central new york state summary a palaeomagnetic study of 143 ma serpentinized kimberlite dikes near ithaca new york yields a dual polarity high unblocking temperature and high coercivity magnetization which passes the reversal test and two baked contact tests the mean pole position 58 n 203 e a95 3 8 n 7 differs from published late jurassicearly cretaceous north american poles currently used to define the apparent polar wander path the angular dispersion in mean directions 3 5 is low but the presence of reversals argues that the ithaca kimberlites magnetization should represent sufficient time for averaging of palaeosecular variation similar findings apparently typify palaeomagnetic studies of other serpentinized kimberlite supporting the suggestion that thermo chemical remanent magnetization in this lithology prolongs the duration of magnetization acquisition sufficiently to average secular variation per dike a consistent but weak foliation in anisotropy of arm parallels the n s and vertical orientation of the ithaca dikes but is apparently unrelated to the northwest down or southeast up remanence the ithaca kimberlites pole may therefore record a previously undocumented sharp bend or cusp at 143ma and the initiation of a cretaceous and cenozoic interval of apparent polar wander that generally follows a great circle along the 200 e meridian to geographic north a coeval 145 ma kimberlite pole from southern africa transferred to north america agrees with the ithaca kimberlites pole position whereas reported poles from the berriasian stratotype southern france and 144ma svalbard dolerites provide less diagnostic tests of the ithaca kimberlites pole due in part to uncertainties in europe north america reconstructions

paleomagnetism of the upper proterozoic and devonian rocks from the klodzko metamorphic complex in the west sudetes sw poland tectonic implications for the variscan belt of central europe abstract the klodzko metamorphic complex kmc consists of upper proterozoic metaigneous and metasedimentary rocks forming a stack pile thrusted over the givetian and overlain by frasnian fammenian sediments magnetomineralogical experiments show that the magnetic minerals are secondary the paleomagnetic experiments identified three components of the natural remanent magnetization labeled a1 a2 and m the mean pole positions calculated in situ correspond with the baltica upper devonian a1 plats 18 plonge 317 permo carboniferous a2 plats 39 plonge 2 and triassic jurassic m plats 60 c plonge 308 segments of the apparent polar wander path apwp for baltica this indicates that the region studied was situated close to the baltica plate at least since the upper devonian and was not folded after this period

paleomagnetism and tectonics of the jura arcuate mountain belt in france and switzerland abstract goethite and hematite in ferriferous oolitic beds of callovian age from the jura mountains switzerland france carry either pre and or post tectonic magnetization the frequent pre tectonic origin of goethite magnetization indicates a temperature range during formation of the arcuate jura mountain belt below the goethite neel temperature of about 100 c the scatter of the pre tectonic paleomagnetic directions d 11 5 e i 55 5 95 4 7 which reside both in goethite and hematite provides strong evidence that the arcuate mountain belt was shaped without significant rotation the paleomagnetic results support tectonic thin skinned models for the formation of the jura mountain belt

alpine structural and metamorphic signature of the sila piccola massif nappe stack calabria italy insights for the tectonic evolution of the calabrian arc combined structural and petrographical investigations coupled with 40ar 39ar geochronology were carried out in the sila piccola massif of the calabrian arc in order to define the structural geometry and map out the major structural and metamorphic breaks within the exposed nappe sequence on the basis of the contrasting alpine pressure temperature p t and structural signatures the nappe stack can be divided in two major tectonic complexes bounded by a flat lying ductile to brittle extensional shear zone the upper complex consists of a nappe like structure where a major top to the east compressional shear is recorded the lower tectonic complex consists of an ophiolite bearing sequence showing typical high p low t parageneses mg carpholite and na amphibole the 40ar 39ar geochronology on phengites in equilibrium with blueschist minerals provided a minimum age estimate for the blueschist event in the lower complex rocks at the oligocene eocene boundary around 35 ma ductile to brittle top to the west extensional shear accompanied the nearly isothermal retrogression and exhumation of the lower complex rocks reworking the previous nappe contacts with shear localization along the upper lower tectonic complex discontinuity the 40ar 39ar dating indicates that this postnappe stacking tectonic evolution took place from 30 ma onward it is proposed that exhumation of the deep seated rocks occurred below a top to the west extensional detachment active during convergence and orogenic complex formation synorogenic extension the age of this detachment is bracketed between 30 ma and the post orogenic neogene basin sedimentation middle upper miocene the revised structural and metamorphic scenario is here integrated into a new tectonic evolutionary reconstruction which involves an early high p low t top to the east crustal thickening episode during the construction of the apennine orogenic wedge eocene oligocene followed and overprinted by a top to the west extensional shear probably active from the late oligocene

neogene and quaternary rollback evolution of the tyrrhenian sea the apennines and the sicilian maghrebides reconstruction of the evolution of the tyrrhenian sea shows that the major stage of rifting associated with the opening of this basin began at similar to10 ma it involved two episodes of back arc extension which were induced by the rollback of a west dipping subducting slab the first period of extension 10 6 ma was prominent in the northern tyrrhenian sea and in the western part of the southern tyrrhenian sea the second period of extension mainly affected the southern tyrrhenian sea began in the latest messinian 6 5 ma and has been accompanied by subduction rollback at rates of 60 100 km myr 1 slab reconstruction combined with paleomagnetic and paleogeographic constraints indicates that in the central apennines the latest messinian 6 5 ma arrival of a carbonate platform at the subduction zone impeded subduction and initiated a slab tear and major strike slip faults these processes resulted in the formation of a narrow subducting slab beneath the ionian sea that has undergone faster subduction rollback and induced extreme rates of back arc extension

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

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

tomographic constraints on the geodynamic evolution of the italian region in this paper we present p wave tomographic images of the mantle beneath italy obtained by inverting 6000 teleseismic p and pkp wave arrival times accurately repicked recorded in the time period 1988 1994 by the stations of the national seismic network of the istituto nazionale di geofisica we pay great attention in the data selection and picking procedure of seismic phases to obtain a very high quality data set the data were inverted with the well established aki christofferson husebye tomographic technique different reference models and residuals computation have been tried to verify the stability of the results the high quality of the repicked arrival times allows us to enhance the definition of the deep structures beneath both the alps and the apennines looking for their lateral and vertical continuity down to 800 km depth the main finding of this study is a continuous high velocity body located between 250 and 670 km depth beneath the entire apenninic system dipping toward the tyrrhenian area which continues upward segmented in two main anomalies in the northern apenninic and the calabrian arcs we interpret this high velocity feature as the subducted oceanic lithosphere between the eurasian and african plates dipping down to the upper lower mantle boundary beneath the tyrrhenian sea the retrieved images of the lithosphere subducting beneath apennines are reliable in terms of thickness about 80 90 km and p wave velocity contrast 2 4 higher than the normal mantle furthermore our tomographic images which focus on the deep geometry and continuity of the velocity structures provide new keys to understanding the geodynamic evolution of the italian region the segmentation of the high velocity slab upward suggests a complex evolution of the arc trench system and the initially continuous subduction of the ionian adriatic plate progressively developed in subordinate arcs probably due to lateral heterogeneity of the subducting lithosphere

kinematics of the alpine arc and the motion history of adria the alps have been interpreted traditionally in terms of north or northwest directed convergence between africa and europe1 with adria the continental underpinnings of the adriatic sea and northern italy acting as a promontory of the african continent2 this has been supported by recent analyses of africa europe relative plate motions3 5 which indicate dominantly north south directed convergence during the tertiary phase of intracontinental shortening we show here however that kinematic indicators from alpine tectonites are difficult to reconcile with this motion history figs 1 and 2 and are explained best by roughly west northwest directed adria europe motion since about 70 million years ago combined with an arc normal pattern of motion driven by local body forces this implies that adria has moved independently of both africa and europe since at least the late cretaceous

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

magnetostratigraphic correlation of the oxfordian kimmeridgian boundary a magnetic polarity pattern for boreal and sub boreal ammonite zones of the upper oxfordian to lower kimmeridgian was established and confirmed in four british sections including the proposed global boundary stratotype section and point gssp on the isle of skye scotland to define the base of the international kimmeridgian stage a coeval pattern for sub mediterranean ammonite zones was compiled from seven sections in poland one german section and multi section composites from france and spain the mean paleopole for the european craton excluding spain at the oxfordian kimmeridgian boundary is 74 2 n 181 3 e 95 3 8 the common magnetic polarity scale enables inter correlation of ammonite subzones among these three faunal provinces and to the marine magnetic anomaly m sequence the proposed gssp at the base of the pictonia baylei zone is near the base of an extended interval dominated by reversed polarity which is interpreted to be chron m26r this gssp level projects to the lower to middle part of the epipeltoceras bimammatum subzone which is the middle subzone of this e bimammatum zone in the sub mediterranean standard zonation in contrast the traditional placement of the oxfordian kimmeridgian boundary in that sub mediterranean standard zonation base of sutneria platynota zone is at the base of chron m25r or nearly 1 million years younger