on vertical advection truncation errors in terrain following numerical models comparison to a laboratory model for upwelling over submarine canyons 1 submarine canyons which indent the continental shelf are frequently regions of steep up to 45 three dimensional topography recent observations have delineated the flow over several submarine canyons during 2 4 day long upwelling episodes thus upwelling episodes over submarine canyons provide an excellent flow regime for evaluating numerical and physical models here we compare a physical and numerical model simulation of an upwelling event over a simplified submarine canyon the numerical model being evaluated is a version of the s coordinate rutgers university model scrum careful matching between the models is necessary for a stringent comparison results show a poor comparison for the homogeneous case due to nonhydrostatic effects in the laboratory model results for the stratified case are better but show a systematic difference between the numerical results and laboratory results this difference is shown not to be due to nonhydrostatic effects rather the difference is due to truncation errors in the calculation of the vertical advection of density in the numerical model the calculation is inaccurate due to the terrain following coordinates combined with a strong vertical gradient in density vertical shear in the horizontal velocity and topography with strong curvature

reappraisal of the palaeomagnetism of the miocene intramontane pag and drnis sinj basins external dinarides croatia abstract this paper presents palaeomagnetic results from the miocene offshore pag and the twin onshore drnis sinj basins earlier magnetostratigraphic results were published from both basins which documented that the lake sediments were good targets for palaeomagnetism from the pag basin we sampled the oldest and youngest segments of the 1200 m long crnika section and obtained statistically different palaeomagnetic directions from the two parts during a repeated visit to the section it was revealed that modern gravity driven creeping can account for this i e the results from the pag basin should be rejected from regional tectonic interpretation the overall mean palaeomagnetic direction for the drnis sinj basin has excellent statistical parameters its high quality is further supported by positive regional fold tilt and reversal tests based on seven geographically distributed localities the results suggests 13 20 ccw rotation with respect to africa and 21 27 with respect to stable europe during the last 15 million years as the external dinarides are the loci of a complicated network of miocene and even younger tectonic zones we cannot export the observed rotation for the whole unit but consider our results as one step in obtaining robust kinematic constraints for the post oligocene tectonic history of the external dinarides

the drift history of adria and africa from 280 ma to present jurassic true polar wander and zonal climate control on tethyan sedimentary facies article i nfo the orogenic belts surrounding the undeformed adriatic sea represent the margins of an area known as adria the african promontory we have undertaken a critical appraisal of paleomagnetic data from regions of adria considered parautochthonous relative to africa obtained either from biostratigraphically dated sed imentary rocks corrected for inclination shallowing or from igneous rocks that are regarded as free from any inclination shallowing bias paleomagnetic directions were used to calculate paleomagnetic poles for compar ison with coeval and inclination flattening free paleomagnetic poles from stable africa visual coherence of paleopoles for several time slices from the early permian to the eocene supports the construction of a com posite apparent polar wander path apwp valid for parautochthonous adria and stable africa this compos ite apwp is compared to previous apwps finding good agreement with the global apwp of kent and irving 2010 both apwps show a remarkable and rapid polar shift of 40 in the jurassic that other apwps tend to underestimate we interpret this shift to represent a major episode of true polar wander tpw from 183 ma in the early jurassic to 151 ma in the late jurassic using a simple zonal climate model the drift motion of adria attached to africa appears to be consistent with the distribution of permian cretaceous sed imentary facies on adria

dynamics of tethyan carbonate platforms tethyan carbonate platforms are relatively short lived depositional systems which were born developed died and sometime resurrected in a tectonically active area in contrast with pericratonic platforms which are generally huge in size hundreds of kilometers across and show wide facies belts very gentle slopes ramps and transitional boundaries tethyan carbonate platforms are smaller tens of kilometers and have steep slopes generally faulted boundaries and abrupt facies changes it appears clear that the overall control on these two contrasting systems is the geodynamic milieu relatively stable in the first case where eustatic oscillations and long term subsidence are probably the main dictators quite dynamic and aggressive in the second one where carbonate platforms developed through the entire geodynamic spectrum rifting transtension transpression and collision of the wilson cycle primary controls on tethyan carbonate platforms appear to be tectonics most important and eustatic sea level oscillations which determine their emplacement growth and decay their overall shape and architecture are a function of these factors secondary factors affecting tethyan carbonate platform evolution are physiography oceanographic conditions and biology as a function of geologic time especially across the mesozoic tertiary boundary facies and facies distribution and to a lesser extent their shape are controlled by thesemore variables less

paleomagnetism of the istria peninsula yugoslavia 280 core samples were collected from upper jurassic cretaceous and eocene sediments outcropping in the istria peninsula yugoslavia due to the very low intensities of the initial natural remanent magnetizations more than 50 of the collection consisting mainly of rock samples of jurassic and eocene sediments was not suitable for paleomagnetic studies the cretaceous samples yield a mean paleomagnetic pole lat 53 long 275 and 95 4 8 which is significantly different from the african and european paleomagnetic poles of the same age the position of the istria peninsula on the autochthonous adriatic platform allows the result to be interpreted as applicable to all the autochthonous periadriatic region this new paleomagnetic result indicates that the autochthonous adriatic platform rotated counterclockwise over an angle of about 30 with respect to africa in post mesozoic times

liquid core structure and pkp station anomalies derived from pkp bc propagation times abstract pkp bc travel time residuals in the distance range 148 5 155 5 have been extracted from the catalogues of the international seismological centre and inverted to retrieve possible heterogeneities or anisotropy at the base of the liquid core and pkp bc station anomalies a binning has first been applied to the data to minimize the biases that result from the uneven sampling of the earth by the pkp bc rays and from the heterogeneities in the source regions for the liquid core structure the data reveal weak heterogeneities with travel time delays slightly higher near the south pole and lower beneath southeast asia but most of these variations stay below the error bar level the search for anisotropy at the base of the liquid core also leads to inconclusive results with a weak tendency for lower velocities in the direction of the earth s rotation axis station anomalies appear to be by far the major contribution to the pkp bc residuals their values are compared with the p station corrections and with the values predicted by lower mantle tomographic models they show that the lower mantle makes an important contribution to the pkp residuals at medium wavelengths these delays are generally underpredicted by tomographic models

formation and exhumation of ultra high pressure rocks during continental collision role of detachment in the subduction channel 1 uhp rocks commonly form and exhume during the transition from oceanic subduction to continental collision their exhumation in subduction channels depends on the balance between down channel shear traction and up channel buoyancy thermal mechanical upper mantle scale numerical models are used to investigate how variations in material properties of the subducting continental margin affect this balance changes in shear traction leading to crustal decoupling detachment are investigated by varying the onset of strain weakening thermal parameters and convergence velocity variations in buoyancy force are investigated by modifying subducted material density and volume the model results are interpreted in terms of the exhumation number e which expresses the role of the pressure gradient channel thickness effective viscosity and subduction velocity peak metamorphic conditions exhumation velocity and timing of exhumation are temporally and spatially variable and are sensitive to the evolution of e the models reproduce natural ptt constraints and indicate that neither slab breakoff nor surface erosion is required for uhp exhumation

eoalpine and mesoalpine tectonics in the southern alps according to structural and stratigraphic data eoalpine and mesoalpine tectonics can be clearly recognized in the southern alps and distinguished from the better known neoalpine deformation

magnetostratigraphy of the jurassic cretaceous boundary in the maiolica limestone umbria italy the magnetic stratigraphy of a 110 m section of the early cretaceous maiolica pelagic limestone in the bosso valley umbria italy shows clearly defined magnetozones that are correlated with the geomagnetic polarity record derived from the m sequence marine magnetic anomalies m19 to m14 and possibly m13 using an established paleontological zonation of this section based on calpionellids the position of the jurassic cretaceous boundary is located close to the base of the negative magnetozone corresponding to anomaly m17

two layer tidal modeling of the yellow and east china seas with application to seasonal variability of the m2 tide 1 the baroclinic response of tide and tidal currents in the yellow and east china seas is investigated using a two layer numerical model seasonal variability in the m2 tide especially the smaller summer amplitudes prevailing along the korea tsushima strait kang et al 1995 is investigated by a series of numerical experiments with varying degrees of stratification specific to winter and summer model results show that the summer amplitudes of the m2 tide around the southwestern tip of the korean peninsula and korea tsusima strait decrease with a peak decrease of about 14 cm off the southwestern tip of the korean peninsula while the summer amplitudes in other coastal regions tend to increase this seasonal variability generally coincides with the observations these models results indicate that seasonal stratification has several noticeable effects on the tides including varying degrees of current shear varying frictional dissipation and varying barotropic energy flux in particular it drives complicated seasonal variability in the m2 tide with a peak amplitude modulation of nearly 5 off the southwestern tip of the korean peninsula the seasonal variation of barotropic m2 energy flux through the eastern entrance of the yellow sea is thought to induce the corresponding variability in the m2 amplitude in the korea tsusima strait with smaller amplitudes found in the summer

deep subduction and rapid exhumation role of crustal strength and strain weakening in continental subduction and ultrahigh pressure rock exhumation 1 the exhumation of crustal ultra high pressure uhp material depends on temporal and spatial variations in its detachment within the subduction channel this dependence is investigated using numerical models with variable initial crustal strengths representing a range of initial crustal compositions and parameterized strain weakening representing a range of processes that reduce effective crustal viscosity during deformation competition between down channel shear traction favoring subduction and up channel buoyancy favoring exhumation is expressed as the exhumation number e which can vary with time and position along the channel exhumed lower strength crust which resists subduction owing to weak down channel traction records peak conditions 38 kbar given sufficient strain weakening exhumation proceeds at 60 km ma 1 indicating that buoyancy e 1 drives exhumation in these models in all models exhuming uhp material forms a deforming ductile plume with a range of possible structural relationships predicted between exhumed uhp and hp materials

shallow and deep rotations in the miocene alps mapping and the construction of balanced cross sections reveal dextral rotation in addition to n s contraction during the late middle to late miocene jura phase both at the northern and the southern front of the central alps jura and lombardic southern alps respectively these rotations may be ascribed to one and the same shallow domain or sublid rotated clockwise around a pivot somewhere at the southwestern end of the aar massif in a crude first approximation model the sublid may be considered rigid although the data indicate differential rotations and longitudinal stretching within the lid the eastern boundary of the sublid crosses the alps at the giudicarie brenner line which according to very recent data in the jura phase formed a kinematically linked system whereas from innsbruck to the northwest it is postulated to join as a diffuse or accommodation zone the eastern tip of the jura in the southwest the lombardic thrusts enter into the interior of the western alps from there to the southwestern end of the jura the lid boundary is tentatively chosen arbitrarily to pass somewhere near the northern end of the belledonne massif a similar sublid though less well substantiated may comprise the tauern and the venetian southern alps the rotational components are superimposed on elements of internal strain particularly transverse contraction and longitudinal stretching due to simple dextral shear and lateral escape the model of dextrally rotating sublids pulls together a number of hitherto unexplained structures and opens new perspectives on such recalcitrant problems as the eastward disappearance of the jura and the adige embayment in the southern alps dextral rotation of such shallow sublids may be considered to constitute mode 1 of the dextral component at the europa adria plate boundary there is also a mode 2 that affects its deep parts at the surface its manifestation is a dextral belt of en echelon folds and pull apart domains that crosses the sublids diagonally it consists of the massifs line in the west and the neo pustertal line in the east they approximately join in the brenner area where they cross and interfere with the sublid boundaries the combined massifs pustertal line describes an arcuate partial northern boundary of the adriatic plate with an apparent center of sinistral rotation in central italy this sinistral rotation may be responsible for the contractional features in the southern part of the western alps which cannot be accounted for by se nw adria europa convergence it could have caused the development of the fold and thrust belts of sisteron castellane and nice these arcs in turn suggest the action of more or less independent shallow sublids also in this part of the alps

the alpine evolution of the southern alps around the giudicarie faults a late cretaceous to early eocene transfer zone abstract data supporting relevant late cretaceous early eocene sinistral displacement along the giudicarie fault zone and a minor neogene dextral displacement along the periadriatic lineament are discussed the pre adamello structural belt is present only in the internal lombardy zone located w of the adamello massif this belt is unknown in the dolomites and surrounding areas located to the e of the giudicarie lineament upper cretaceous early eocene thick syntectonic flysch deposits of lombardy and giudicarie are well preserved along the southern and eastern border of the pre adamello belt s vergent alpine orogen towards the e in the dolomites and in the carnic alps and external dinarides only incomplete remnants of flysch deposits aptian albian and turonian maastrichtian in age are present they can be considered as equivalent to those of lombardy and giudicarie formerly in connection to each other along the n giudicarie corridor to the s the syntectonic flysch deposits are laterally replaced by the calcareous red pelagites of the scaglia rossa and by the carbonate shelf deposits of the friuli to the e and bagnolo to the s carbonate platforms the different location in the southern structural accretion of the eastern and western opposite blocks the dolomites versus the pre adamello belt can be related to the cretaceous eocene convergence in this frame the n giudicarie fault has been considered as part of a former transfer zone which produced the sinistral lateral displacement of the southern alps front for an amount of some 50 km during the late eocene to early oligocene the transfer zone was mostly sealed by the paleogene adamello batholith oligocene to neogene compressional evolution inverted the n giudicarie fault into a backthrust of the austroalpine units over the south alpine chain

new cretaceous paleomagnetic results from the foreland of the southern alps and the refined apparent polar wander path for stable adria abstract the central western and the eastern southern alps are separated by the triangular shaped adige embayment which belongs to stable adria and was the site of pelagic sedimentation from the tithonian through maastrichtian the first part of this study presents paleomagnetic results from the tithonian cenomanian biancone and turonian maastrichtian scaglia rossa formations sampled at 33 geographically distributed and biostratigraphically dated localities the new and high quality paleomagnetic results from the adige embayment are then combined with coeval paleomagnetic directions from autochthonous istria marton et al 2008 which also belongs to stable adria the combined data set which for the late albian maastrichtian time period is constructed similarly to the synthetic african curve by besse and courtillot 2002 2003 reveals an important tectonic event late aptian early albian characterized by 20 ccw rotation and sedimentary hiatus comparison between paleomagnetic declinations inclinations expected in an african framework i e with the assumption that adria is still an african promontory leads to the following conclusions the time distributed tithonian and berriasian 150 135 ma paleomagnetic directions exhibit the african hairpin with an inclination minimum and a sudden change from cw to ccw rotation at 145 ma concerning the younger ages the declinations for adria continue to follow the african trend of ccw rotation till the end of cretaceous however the tithonian maastrichtian declination curve for stable adria is displaced by 10 from the african curve as a result of two rotations the first an about 20 cw rotation of adria with respect to africa took place between the maastrichtian and the mid eocene during this time the orientation of adria remained the same while africa continued its ccw rotation the younger rotation 30 ccw changed the orientation of adria relative to africa as well as to the present north

reappraisal of paleomagnetic data from gargano south italy vandenberg j 1983 reappraisal of paleomagnetic data from gargano south italy in e mcclelland brown and j vandenberg editors palaeomagnetism of orogenic belts tectonophysics 98 29 41 the platform limestones of apulia italy outcropping in the gargano peninsula have been restudied paleomagnetic research has been carried out on upper cretaceous lower cretaceous and jurassic rocks despite the low intensities of the nrm 10 100 pa m all samples 268 could be cleaned by stepwise a f and or thermal demagnetization treatments nrm directions could be determined accurately and reproducibly for 85 of the samples using a sct cryogenic magnetometer and double precision measuring procedures nrm of the jurassic limestone is carried by secondary haematite and the results are therefore rejected from further consideration the upper and lower cretaceous limestones have an nrm carried by magnetite minor bedding tilt corrections improve the grouping of the site mean results the upper cretaceous scaglia limestone turonian senonian reveals a characteristic mean direction of decl 327 7 incl 38 2o a ss 4 3 21 sites while the lower cretaceous maiolica limestone neocomian aptian albian reveals a characteristic mean direction of decl 303 1 o incl 35 1 as s 8 7o 8 sites the cretaceous results show a post aptian albian counterclockwise rotation of about 25 which is expressed by the smeared distribution of the late cretaceous site mean results and a post senonian i e tertiary counterclockwise rotation of the same amount with respect to the pole these results are in excellent agreement with contemporaneous paleomagnetic results from other peri adriatic regions a tertiary counterclockwise rotation of all the stable adriatic block is strongly supported by the new results

coeval blueschist exhumation along thousands of kilometers implications for subduction channel processes we herein focus on understanding what controls the detachment and migration of oceanic crustal slices along subduction zones we provide evidence for the coeval middle to late cretaceous exhumation of oceanic blueschists in the same neotethyan subduction zone across more than 3000 km from depths around 30 40 km over a short time interval similar to 25 ma compared to the duration of subduction 100 ma we stress the importance of such a geodynamic process and suggest that this exhumation was promoted by a regional scale change in the long term interplate mechanical coupling on the basis of geological and geophysical evidence we propose that the upward migration of oceanic fragments in subduction zones is normally inhibited and only occurs discontinuously as the subduction channel opens up in response to a major change in plate geodynamics slab geometry and dynamics mantle wedge and slab hydration or a combination of these

40ar 39ar mineral ages within metamorphic clasts from the kuma group eocene central shikoku japan implications for tectonic development of the sambagawa accretionary prism abstract the sambagawa metamorphic belt exposed in central shikoku records a high p t metamorphism it is comprised by the oboke nappe and the structurally overlying internally imbricated besshi nappe complex the besshi nappe complex locally is unconformably overlain by the kuma group eocene which consists of conglomerates and subordinate sandstones and mudstones clasts within kuma conglomerates exposed in the kamegamori district include low grade schists derived from the unconformably underlying sambagawa complex and high grade metamorphic rocks of uncertain provenance including garnet amphibolite and oligoclase bearing pelitic schist 36 ar 40 ar vs 39 ar 40 ar isotope correlation ages recorded by hornblende from two amphibolite clasts are 131 1 4 9 ma and 156 8 4 3 ma these are interpreted to date post metamorphic cooling through temperatures required for intracrystalline retention of argon and are older than cooling ages previously reported from any presently exposed segments of the sambagawa terrane plateau ages of 108 8 0 7 ma and 115 7 0 6 ma are recorded by muscovite from two clasts of schist muscovite within a proximal basement exposure of unconformably underlying sambagawa pelitic schist records a plateau age of 78 7 0 5 ma combined with isotopic ages previously reported for the sambagawa terrane 40 ar 39 ar data from clasts in the kuma group suggest that metamorphic culmination within a high grade source terrane occured at c 185 145 ma sectors of this complex cooled through c 500 c at c 150 ma other portions cooled through c 500 c at c 130 ma contrasts in the cooling ages likely reflect internal imbrication within the source terrane the besshi nappe complex reached peak metamorphic conditions at c 100 90 ma and experienced relatively rapid uplift and cooling at c 85 75 ma the besshi nappe complex was structurally emplaced onto the oboke nappe which attained peak metamorphic conditions at c 75 ma subsequently the entire sambagawa section was exhumed and most high grade metamorphic rocks were removed the eocene kuma group was unconformably deposited over the sambagawa terrane at c 50 ma

balancing cross sections with kinematic constraints the dolomites northern italy balancing of structural cross sections is often hindered by a limited database or tectonic complications in such cases kinematic constraints may help to better constrain the construction of a cross section and its extrapolation to depth the kinematic implications of a known structure generally at the surface have to be considered for the unknown structure and for the internal consistency of a cross section a key point is the quantification of shortening of the known structure the extrapolation of this parameter allows balancing in an approximate way emphasizing major structures while minor structures are either neglected or treated in a simplified way with this approach a quick overview can be achieved on how much leeway for interpretation exists critical points for testing various working hypotheses become more evident and the trial and error effort during the construction of a balanced section is considerably shortened still the implications the observed structures have on the deeper crustal levels can be assessed this concept is applied to a section across the italian dolomites a brittle fold and thrust belt lacking reflection seismic data so far and thus with a poorly known deep structure still active south vergent alpine thrusting is oriented approximately perpendicular to previous dinaric thrusting the ramp flat style is dominant due to rheological constrasts within the stratigraphic sequence thanks to kinematic balancing based on surface data three alpine thrust systems could be identified each defining a thrust sheet with its particular basement unit and its sedimentary part superposition of the two more external basement units led to the presently observed high elevation of the triassic sequence in the dolomites shortening since late miocene times amounts to more than 50 km retrodeformation of alpine thrusting is a key for better understanding the previous dinaric structures and kinematics

paleomagnetism and the adriatic promontory a reappraisal the geodynamic evolution of the western mediterranean area was influenced strongly by the adriatic promontory of the african plate which can be outlined at present by current seismicity and by facies and ophiolite distributions paleomagnetic results from different parts of the promontory contribute useful information about its past history the evaluation of these data is made difficult by the lack of a well defined apparent polar wander path for africa this has resulted in occasional overinterpretation of some paleomagnetic studies results from umbria and the southern alps cover a long enough period of time to define part of an apw path and support the idea that the promontory moved as an adjunct to the african plate during the late mesozoic and early cenozoic a conservative evaluation of cretaceous paleomagnetic data the most abundant for the promontory as a whole shows no strong evidence for previously proposed counterclockwise rotations of sicily or the southern alps relative to the african plate paleomagnetic data however suggest about 17 degrees counterclockwise rotation of autochthonous gargano and istria and about 25 degrees counterclockwise rotation of allochthonous umbria tectonic rotation of the middle part of the promontory appears to have occurred without significant rotation of its northern and southern extremities

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

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

late oligocene neogene evolution of europe adria collision new structural and geochronological evidence from the giudicarie fault system italian eastern alps the giudicarie fault system giudicarie sensu stricto meran mauls passeier thurnstein and jaufen faults represents a sharp break in the generally e w strike direction of the orogen scale periadriatic fault system and is a key element for understanding the late oligocene neogene evolution of the alpine chain the kinematics timing and magnitude of movements on the giudicarie fault system are presented here on the basis of a detailed structural study of the component fault segments combined with zircon and apatite fission track analysis from closely spaced samples two main tectonic phases are established 1 back thrusting of the austroalpine units over the southern alps around 32 ma recorded by basement and limestone mylonites along the giudicarie and meran mauls faults with transport directions toward 100 110 and 2 later sinistral transpressive displacement characterized by structures at the ductile brittle transition which overprinted the top to e ese thrust related mylonites but also partitioned into a major system of transcurrent faults in the southalpine domain it was during this later event that the periadriatic fault attained its present day geometry however the amount of sinistral displacement along the giudicarie system was only 15 20 km the magnitude is established here from the 15 km sinistral offset of the jaufen mylonites across the passeier brittle fault and the 20 km long gap in the otherwise continuous distribution of oligocene tonalitic lamellae along the giudicarie fault a direct structural connection is also established between the brenner and the jaufen faults this constrains the timing of the second phase since it must postdate the main exhumation phase of the tauern window at 20 18 ma the results of this study argue against an originally straight periadriatic fault the giudicarie fault formed a restraining bend in this part of the periadriatic fault system since at least the late miocene and probably since the late oligocene

from rifting to drifting tectonic evolution of the south alpine upper crust from the triassic to the early cretaceous abstract the tectonic evolution of the south alpine rifted margin is discussed on the base of four palinspastic upper crustal profiles extension related to the movements between adria and europe began in the norian after variscan orogeny late carboniferous to middle permian orogenic collapse and continental scale wrenching from the late triassic to the early liassic stretching was mostly limited to the lombardian basin during this time extension was mainly controlled by four major listric faults symmetrically centred around the late carboniferous early permian collio grabens smaller faults which also started in the norian were progressively de activated during the late triassic after the middle liassic faulting in the lombardian basin gradually ceased and the site of extension shifted westwards i e towards the future site of crustal separation extension was then controlled by a set of west dipping normal faults oceanic crust was formed not later than 157 ma the overall extension along the profile which had a final length of 290 km was 52 km which corresponds to a stretching factor of 1 22 for the whole length of the preserved margin the strain rate is ca 1 10 16 s the sedimentation history suggests that the extension of the south alpine margin was a continuous process from the norian to the middle jurassic the changes in tectonic pattern are related to progressive hardening of the lithospheric segment undergoing slow extension

tectonic mode switches and the nature of orogenesis abstract the birth and death of many mountain belts occurs in lithosphere that over rides major subduction zones here the tectonic mode shortening versus extension can abruptly switch even during continuous and otherwise smooth convergence if the hinge line of the foundering slab rapidly retreats i e rolls back the foundering slab creates a gravitational potential well into which the orogen collapses this motion coupled with stress guides can pull the orogen apart a slowing of roll back or of hinge retreat means that the subduction flexure may subsequently begin to be pushed back or be pushed over by the advancing orogen the consequence of such changes in relative motion is that orogenic belts are affected by abrupt tectonic mode switches the change from push to pull leads to a sudden change from horizontal extension to horizontal shortening potentially throughout the entire mass of the orogenic lithosphere that over rides the subducting slab the sequencing of these tectonic mode switches affects the thermal evolution of the orogen and thus fundamentally determines the nature of orogenesis this insight led to us to our quite different views as to how orogens work it is evident that orogens affected by abrupt push pull mode switches are characterized by high pressure metamorphism whereas orogens affected by abrupt pull push mode switches are characterized by high temperature metamorphism magmatism and anatexis

southward extrusion of eclogite bearing mafic ultramafic bodies in the sanbagawa belt central shikoku japan abstract several mafic rock masses which have experienced eclogite facies metamorphism are distributed in flat lying non eclogitic schists in an intermediate structural level thermal core of the sanbagawa belt the largest iratsu mass and an associated peridotite the higashi akaishi mass extend e w for about 8 km and n s for about 3 km and are surrounded by pelitic basic and quartz schists the iratsu mass consists of metabasites of gabbroic and basaltic origin with intercalations of ultramafic rocks felsic gneiss quartz schist and metacarbonate the iratsu mass can be divided into two layers along a wnw trending metacarbonate layer the higashi akaishi mass consists of peridotite with intercalations of garnet clinopyroxenite it is situated beneath the western half of the iratsu mass and their mutual boundary dips gently or steeply to the n or ne these masses underwent eclogite and subsequent epidote amphibolite facies metamorphism as has been reported elsewhere the iratsu higashi akaishi masses and the surrounding rocks underwent ductile deformation under epidote amphibolite facies or lower p t metamorphic conditions their foliation generally trends wnw and dips moderately to the nne and the mineral lineation mostly plunges to the n and ne in non eclogitic schists surrounding the iratsu higashi akaishi masses the foliation generally trends wnw and dips gently or steeply to the n or s and the mineral lineation mostly plunges to the nw n and ne kinematic analysis of deformation structures in outcrops and oriented samples has been performed to determine shear senses consistent top to the north normal fault displacements are observed in peridotite layers of the higashi akaishi mass and eclogite bearing epidote amphibolite layers of the iratsu mass top to the northeast or top to the northwest displacements also occur in non eclogitic pelitic quartz schists on the northern side of the iratsu mass in the structural bottom of the iratsu higashi akaishi masses and to the south reverse fault top to the south movements are recognized in serpentinized peridotite and non eclogitic schists these observations provide the following constraints on the kinematics of the rock masses 1 northward normal displacement of iratsu relative to higashi akaishi 2 northward normal displacement of non eclogitic schists on the north of the iratsu mass and 3 southward thrusting of the iratsu higashi akaishi masses upon non eclogitic schists in the south the exhumation process of the iratsu higashi akaishi masses can be explained by their southward extrusion

why is terrestrial subduction one sided subduction of the lithosphere at convergent plate boundaries takes place asymmetrically the subducted slab sinks downward while the overriding plate moves horizontally one sided subduction in contrast global mantle convection models generally predict downwelling of both plates at convergent margins two sided subduction we carried out two dimensional 2 d numerical experiments with a mineralogical thermomechanical viscoelastic plastic model to elucidate the cause of one sided subduction our experiments show that the stability intensity and mode of subduction depend mainly on slab strength and the amount of weak hydrated rocks present above the slab two sided subduction occurs at low slab strength sin 0 15 the weak interface is maintained by the release of fluids from the subducted oceanic crust as a consequence of metamorphism the resulting weak interplate zone localizes deformation at the interface and decouples the strong plates facilitating asymmetric plate movement our work suggests that high plate strength and the presence of water are major factors controlling the style of plate tectonics driven by self sustaining one sided subduction processes

cretaceous palaeomagnetic results from murge apulia southern italy tectonic implications summary the adriatic area is of key importance in the reconstruction of the kinematic history of the mediterranean region concerning its relative position with respect to the african plate palaeomagnetic studies marton veljovic 1983 vandenberg 1983 have found evidence that autochthonous istria and gargano rotated counter clockwise with respect to africa after the cretaceous however the geodynamic role of the southern part of apulia has remained unclear in order to decide whether the boundary between the adriatic microplate and africa may be drawn between gargano and murge and whether the different parts of apulia could have undergone differential rotations after the cretaceous we carried out palaeomagnetic investigations in murge and the salentina peninsula in the field several carefully selected facies were collected and oriented with a magnetic compass at eight geographically distributed localities 46 sites 224 cores and 13 hand samples because of extremely weak nrm several sites failed to yield a meaningful palaeomagnetic signal this category comprises all sites younger than the turonian bauxite horizon and also six sites of cenomanian early turonian age samples from the remaining sites were subjected to detailed thermal and af demagnetization kirschvink 1980 and subtracted vector analysis and irm experiments including the thermal demagnetization of three component irm as a result we were able to demonstrate that some of the sites are devoid of overprint on the other hand there were sites with unremovable overprint the latter were rejected from tectonic evaluation despite the sometimes high degree of clustering of the individual nrms within a site so were those with unstable remanence eventually a cenomanian turonian palaeomagnetic mean direction was calculated for murge on a locality before tectonic correction d 327 i 44 k 55 95 17 n 3 after tectonic correction dc 327 ic 38 k 76 95 15 and a site before tectonic correction d 324 i 41 k 44 95 6 5 after tectonic correction dc 327 ic 40 k 42 95 6 7 basis and a palaeomagnetic pole latitude 56 longitude 261 was computed from the tectonically corrected locality mean direction since coeval palaeomagnetic poles for murge gargano and istria cluster we conclude that the stable part of the adriatic region moved in a highly integrated manner their displacement with respect to africa has manifested itself in a moderate ccw rotation since the turonian

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

palaeomagnetic evidence for tertiary counterclockwise rotation of adria abstract with the aim of obtaining tertiary palaeomagnetic directions for the adriatic foreland of the dinaric nappe system we carried out a palaeomagnetic study on platform carbonates from stable istria from the northwestern and the central dalmatia segment of imbricated adria despite the weak to very weak natural remanences of these rocks we obtained tectonically useful palaeomagnetic directions for 25 sites from 20 localities all exhibit westerly declinations both before and after tilt correction concerning the age of the magnetizations we conclude that five subhorizontal and magnetite bearing eocene localities from stable istria are likely to carry primary remanence whereas three tilted and hematite bearing ones were remagnetized in the northwestern segment of imbricated adria the cluster of the mean directions improved after tectonic correction indicating pre tilting magnetization in contrast maastrichtian eocene platform carbonates from central dalmatian were remagnetized in connection with the late eocene oligocene deformation or miocene hydrocarbon migration based on the appropriate site locality means we calculate mean palaeomagnetic directions for the above three areas and suggest an alternative interpretation of the data of kissel et al j geophys res 100 1995 14999 for the flysch of central dalmatia the four area mean direction define a regional palaeomagnetic direction of dec 336 inc 52 k 107 95 9 from these data we conclude that stable istria in close coordination with imbricated adria must have rotated by 30 counterclockwise in the tertiary relative to africa and stable europe we suggest that the latest miocene early pliocene counterclockwise rotations observed in northwestern croatia and northeastern slovenia were driven by that of the adriatic foreland i e the rotation of the latter took place between 6 and 4 ma

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

apparent polar wander path for adria extended by new jurassic paleomagnetic results from its stable core tectonic implications abstract as a continuation of a systematic paleomagnetic research in the northern part of stable adria which provided a well defined apparent polar wander apw path for the cretaceous eocene we present new paleomagnetic results for the jurassic these new data were obtained from 15 geographically distributed localities from the trento platform eastern southern alps using standard paleomagnetic approach the lower jurassic shallow water carbonates are not considered for tectonic interpretation due to inconsistent inclinations the middle and upper jurassic rosso ammonitico provided excellent kinematic constraints with the new jurassic results an apw is now defined for adria for the 167 40 ma interval it is well constrained for timing of important changes like the speed and the sense of rotations this apw suggests that the cw rotation and southward shift changed to the opposite at 155 1 5 3 ma signifying a dramatic change in the life of the neo tethys from opening to closing the latter is manifested in fast ccw rotation and northward movement of adria up to 102 9 2 4 ma and moderate displacements in the same manner in post 103 ma times combined data sets from stable istria and the foreland of the southern alps point to an approximately 15 cw rotation with respect to africa at the end of the cretaceous and an about 25 in the ccw sense after the eocene

new paleocene eocene paleomagnetic results from the foreland of the southern alps confirm decoupling of stable adria from the african plate abstract from the undeformed foreland of the southern alps paleocene through early miocene rocks mostly biostratigraphically well dated sediments with sub horizontal bed attitude were collected for a paleomagnetic study from 23 geographically distributed localities the samples were subjected to standard paleomagnetic measurements and evaluation while the miocene samples are unstable most of the older localities yielded statistically well defined paleomagnetic directions these are interpreted as primary for the compact marls supported by positive between locality tilt and reversal tests this large group of localities is characterized by ccw rotated declinations with respect to the present north combined with paleomagnetic directions of corresponding age from stable istria these allow definition of the apw for stable adria for the 61 6 33 9 ma interval which is significantly displaced from the coeval segment of the african apw due to the decoupling of the former to the latter by a moderate ccw rotation this post eocene final separation exact age is not constrained directly but estimated as end of miocene was preceded by a small cw rotation of adria with respect to africa suggested by unchanged orientation of the former across the cretaceous paleocene boundary while the latter continued its ccw rotation

the tectonic development of the northern adriatic region constrained by jurassic and cretaceous paleomagnetic results abstract in the northern adriatic region there is a clear boundary between the weakly deformed stable core of the adriatic microplate and its tectonically complicated ne margin the external dinarides which are further subdivided on stratigraphic and structural grounds although most authors distinguish an adriatic and a dinaridic realm within the external dinarides the relationship and the present boundary between the realms are matters of discussion the aim of this study was to obtain paleomagnetic directions from different parts of the northern adriatic segment of the external dinarides and discuss their bearing on the different types of the tectonic models for this purpose we carried out standard paleomagnetic measurements on biostratigraphically well controlled samples from 28 localities from the adriatic mainland and the northern adriatic islands and from one middle jurassic locality representing the stable core of the adriatic microplate in addition six localities from the northern adriatic islands earlier studied paleomagnetically were biostratigraphically updated and thus included in the data set for the northern adriatic islands an albian d i 333 48 k 44 95 9 and a cenomanian santonian d i 334 46 k 188 95 5 paleomagnetic direction was defined they are in perfect agreement with coeval paleomagnetic directions from stable adria thus the paleomagnetic data clearly support the models which conceive the area as the imbricated margin of the adriatic microplate the early d i 338 49 k 118 95 11 the middle d i 342 54 k 112 95 7 and the late d i 336 42 k 62 95 16 jurassic paleomagnetic directions all representing the tectonic units of the adriatic mainland suggest an about 30 cw rotation of this belt of the external dinarides with respect to stable adria the difference can be interpreted as inherited from the differencial rotations of two independent carbonate platforms an adriatic and a dinaric alternatively thrusting of the more internal belt of the external dinarides above the adriaticum may be responsible for the difference

detrital remanence inclination errors and anhysteretic remanence anisotropy quantitative model and experimental results summary we suggest that inclination errors in detrital remanent magnetization drm may be recognized and corrected by measurement of the anisotropy of anhysteretic remanent magnetization arm arm anisotropy reflects directional variations in the remanence capacity of relatively fine grained magnetic particles in rocks or sediments generally the same particles that carry the stable component of drm relative vertical and horizontal drm magnitudes are controlled by this directional remanence capacity as well as by the alignment efficiency of the particle magnetic moments which in turn is governed by the relative intensities of the vertical and horizontal components of the ambient magnetic field thus the respective vertical and horizontal components of palaeointensity and therefore palaeofield inclination may be obtained by normalizing the measured drm components by parallel arm intensities synthetic sediments containing silica kaolin and sized magnetite powders have previously been found to acquire experimental drm with an inclination error that is a direct function of kaolin concentration further experiments have now shown that arm anisotropy in the synthetic sediments is also a direct function of kaolin content and thus a correlation exists between drm inclination errors and arm anisotropy multiplying the measured drm vector by the inverse of the arm anisotropy matrix yields an improved estimate of the actual laboratory depositional field in all cases for samples with acicular 0 5 m magnetite this procedure reduces a mean inclination error of over 5 to less than 0 5 samples with subequant magnetite of slightly larger grain size 0 75 m exhibit similar arm anisotropy 10 per cent but somewhat larger inclination errors 10 we interpret this in terms of stronger horizontal alignment but weaker particle anisotropies for the larger more equant magnetites

shrimp u pb zircon dating of quartz bearing eclogite from the sanbagawa belt south west japan implications for metamorphic evolution of subducted protolith in order to decipher the origin of eclogite in the high p t sanbagawa metamorphic belt shrimp u pb ages of zircons from quartz bearing eclogite and associated quartz rich rock metasandstone were determined one zircon core of the quartz rich rock yields an extremely old provenance age of 1899 79 ma suggesting that the core is of detrital origin eight other core ages are in the 148 134 ma range and are older than the estimated age for trench sedimentation as indicated by the youngest radiolarian fossil age of 139 135 ma from the sanbagawa schists ages of metamorphic zircon rims 132 112 ma from the quartz rich rock are consistent with metamorphic zircon ages from the quartz bearing eclogite indicating that eclogite facies metamorphism peaked at 120 110 ma these new data are consistent with both the iratsu eclogite body and surrounding highest grade sanbagawa schists undergoing coeval subduction zone metamorphism and subsequent re equilibration under epidote amphibolite facies conditions during exhumation

thermal consequences of a subduction boundary jump a numerical model for generating subduction related clockwise pressure temperature paths 1 clockwise pressure temperature p t paths with a temperature increase after peak p have been reported from a number of subduction related metamorphic belts around the world however an adequate tectonic interpretation of these paths has been lacking one of the principal difficulties is the lack of a sufficient heat source to account for the post peak p temperature rise however two dimensional thermal calculations incorporating accretion of a thick metamorphic unit in a subduction zone reveal that in general an accreted sheet with a width of several kilometers experiences a post accretion heating without having to appeal to any special internal heat source the heating effect is due to the spatial shift of the subduction boundary or subduction boundary jump this heating can account for the generation of subduction related clockwise p t paths within thick metamorphic units for such units the styles of clockwise p t paths vary considerably and can be used as a general indicator of the exhumation rate by considering the balance between conduction and advection during exhumation in contrast a thin unit with a width of 1 km tends to record a nonclockwise p t path regardless of its exhumation rate this is because the thinness decreases the potential both for post accretion heating and for maintaining the higher achieved temperature during exhumation in addition a subduction boundary jump can cause a post accretion transition of metamorphic p t conditions from high to low p t ratios and it may therefore be incorrect to use peak t metamorphic conditions as an indicator of the geotherm along the coeval subduction boundary

tertiary extension in the southern trento platform southern alps italy the southern trento platform southern alps ne italy was the locus of abundant mafic volcanism associated with paleogene extensional tectonics during the pal eocene and throughout the eocene a nnw sse trending graben the alpone agno graben aag developed in the eastern lessini mountains the graben was filled with basaltic volcaniclastics calcarenites and lava flows the aag is a half graben system probably bounded by rotational listric normal faults most faults in the graben dip towards the wsw paleostress analysis within the aag shows that during the eocene the direction of horizontal extension was ene wsw the volcanic activity continued into the oligocene however the relation between oligocene tectonics and volcanism remains unclear gravimetric and magnetic anomalies in conjunction with the crustal thickness variations suggest a locus of lithospheric thinning slightly off axis from the aag this can be explained by an overall asymmetric extensional geometry dominated by a wsw dipping detachment fault the paleogene geodynamic scenario of the trento platform suggests that the aag developed as a foreland extensional response to the active collisional convergence between the european and adriatic plates neogene compressional tectonics reactivated some of the paleogene normal faults as strike sup faults

on the formation and evolution of the pannonian basin constraints derived from the structure of the junction area between the carpathians and dinarides 1 the large number and distribution of rollback systems in mediterranean orogens infer the possibility of interacting extensional back arc deformation driven by different slabs the formation of the pannonian back arc basin is generally related to the rapid miocene rollback of a slab attached to the european continent a key area of the entire system that is neglected by kinematic studies is the connection between the south carpathians and dinarides in order to derive an evolutionary model we interpreted regional seismic lines traversing the entire serbian part of the pannonian basin the observed deformation is dominantly expressed by the formation of miocene extensional detachments and half grabens the extensional geometries and associated synkinematic sedimentation that migrated in time and space allow the definition of a continuous and essentially asymmetric early to late miocene extensional evolution this evolution was followed by the formation of few uplifted areas during the subsequent latest miocene quaternary inversion the present day extensional geometry changing the strike across the basin is an effect of the clockwise rotation of the south carpathians and apuseni mountains in respect to the dinarides our study infers that the carpathian rollback is not the only mechanism responsible for the formation of the pannonian basin an additional middle miocene rollback of a dinaridic slab is required to explain the observed structures furthermore the study provides constraints for the pre neogene orogenic evolution of this junction zone including the affinity of major crustal blocks obducted ophiolitic sequences and the sava suture zone

reconciling plate tectonic reconstructions of alpine tethys with the geological geophysical record of spreading and subduction in the alps article a new reconstruction of alpine tethys combines plate kinematic modelling with a wealth of geological data and seismic tomography to shed light on its evolution from sea floor spreading through subduction to collision in the alps unlike previous models which relate the fate of alpine tethys solely to relative motions of africa iberia and europe during opening of the atlantic our reconstruction additionally invokes independent microplates whose motions are constrained primarily by the geological record the motions of these microplates adria iberia alcapia alkapecia and tiszia relative to both africa and europe during late cretaceous to cenozoic time involved the subduction of remnant tethyan basins during the following three stages that are characterized by contrasting plate motions and driving forces 1 131 84 ma intra oceanic subduction of the ligurian part of alpine tethys attached to iberia coincided with eo alpine orogenesis in the alcapia microplate north of africa these events were triggered primarily by foundering of the older 170 131 ma neotethyan subduction slab along the ne margin of the composite african adriatic plate subduction was linked by a sinistral transform system to e w opening of the valais part of alpine tethys 2 84 35 ma subduction of primarily the piemont and valais parts of alpine tethys which were then attached to the european plate beneath the overriding african and later adriatic plates nw translation of adria with respect to africa was accommodated primarily by slow widening of the ionian sea 3 35 ma recent rollback subduction of the ligurian part of alpine tethys coincided with western alpine orogenesis and involved the formation of the gibraltar and calabrian arcs rapid subduction and arc formation were driven primarily by the pull of the gravitationally unstable retreating adriatic and african slabs during slow convergence of africa and europe the upper european iberian plate stretched to accommodate this slab retreat in a very mobile fashion while the continental core of the adriatic microplate acted as a rigid indenter within the alpine collisional zone the subducted lithosphere in this reconstruction can be correlated with slab material imaged by seismic tomography beneath the alps and apennines as well as beneath parts of the pannonian basin the adriatic sea the ligurian sea and the western mediterranean the predicted amount of subducted lithosphere exceeds the estimated volume of slab material residing at depth by some 10 30 indicating that parts of slabs may be superposed within the mantle transition zone and or that some of this subducted lithosphere became seismically transparent

clasts of high grade sanbagawa schist in middle eocene conglomerates from the kuma group central shikoku south west japan middle eocene conglomerates which overlie the sanbagawa metamorphic rocks contain clasts of metamorphic rock with isotope ages of 120 85 ma which fall within the age range reported from the sanbagawa metamorphic rocks they were derived from the chlorite to oligoclase zones of the sanbagawa metamorphic belt clasts of garnet amphibolite and oligoclase biotite schist show a mineral assemblage similar to the highest grade sanbagawa schists however the metamorphic temperatures estimated by various mineralogical thermometers show that some of the clasts were formed at higher temperatures than the in situ sanbagawa metamorphic rocks such higher grade rocks were at the surface by the middle eocene and for the most part they have been eroded away cretaceous and post cretaceous sediments overlie or are in fault contact with the sanbagawa metamorphic rocks which suggests that rocks in the belt were uplifted and eroded from the latest cretaceous to middle eocene time after strike slip movement along the median tectonic line since the middle eocene the belt has experienced relatively slow uplift which was locally around 2 km in central shikoku

large scale thin skinned thrusting in the southern alps kinematic models the tectonics of the southern alps are dominated by thrusting on extensive ramp flat systems and by folding some of which is ramp folding basement slivers are involved that frontally are not thicker than 5 km the most unequivocal section is that of the grigna mountains east of lake como for which kinematic modeling based on material balance considerations results in a shortening of 40 km it is separated from the grona section in the west and the valtorta section in the east by probably pre existing transverse zones that cut through the important decollement horizons and define blocks of different depths to basement local tectonics across these transverse zones change abruptly while over all shortening remains constant in particular both east and west of the grigna section basement ramp folds were wedged into the very incompetent raibl beds provoking back thrusting of the thick hauptdolomit and higher sediments with the substitution of the original cover of the frontal limb of the basement fold this new kinematic interpretation is compatible with the information facilitates the construction of balanced sections and is required for lateral constancy of shortening

miocene to present major fault linkages through the adriatic indenter and the austroalpine penninic collisional wedge alps of ne italy

new paleomagnetic results from the upper cretaceous red marls of the pieniny klippen belt western carpathians evidence for general ccw rotation and implications for the origin of the structural arc formation abstract the pieniny klippen belt pkb is a narrow arcuate structure separating the central and outer western carpathians formed during several cenozoic deformational stages the primary aim of this study was to obtain paleomagnetic constraints for the mechanism of formation of the arc we investigate albian santonian red pelagic marls from 14 localities distributed along a strike length of ca 400 km ams measurements reveal a pattern characteristic of weakly deformed sedimentary rocks and magnetic lineations do not correlate with the general strike of the pkb paleomagnetic analysis revealed well defined hematite based ancient magnetization components at 13 localities which are dated using fold and inclination tests a within locality fold test is negative for two localities exhibiting large ccw rotations of similar magnitude situated at the two ends of the pkb remanences of pre folding age were documented for 11 localities with an overall mean paleomagnetic direction of d 311 i 53 and 95 11 the indicated general ccw rotation most probably took place during the miocene together with western central and outer carpathians paleolatitudes for the pkb indicate a considerable separation from the southern margin of stable europe leaving space for coordinated rotation a paleomagnetic oroclinal test involving all localities with primary magnetizations was negative when localities with monoclinal steep dips are omitted due to possible declination bias the overall mean paleomagentic direction does not change significantly but correlation is observed between the general trend of the pkb and the paleomagnetic declinations thus we conclude that the present shape of the arc can be partly due to oroclinal bending this must have happened before oligocene since paleomagnetic declinations for neighboring paleogene basins in the central and outer western carpathians reveal a uniform ccw rotation of ca 50 magnitude irrespective of the position of the localities in relation to the carpathian arc

ordovician continental margin terranes in the lachlan orogen australia implications for tectonics in an accretionary orogen along the east gondwana margin 1 four continental margin turbidite black shale terranes of the lachlan orogen in the southern tasmanides of eastern australia formed in two major systems along the east gondwana margin and constrain the ordovician assembly of this accretionary orogen key features are the dissimilar stratigraphies of the adjacent bendigo and melbourne terranes in the western system the dissimilar stratigraphies of the adjacent melbourne and albury bega terranes that reflect juxtaposition of the two systems during the middle devonian and the presence of the albury bega terrane both west and east of the macquarie arc in the eastern system that also includes the ocean floor narooma terrane and igneous ocean crust terrane s repetition of the albury bega terrane either side of the arc requires either rifting or orogen parallel strike slip duplication of a once contiguous package terrane interactions began in the earliest gisbornian with early docking uplift deformation and exchange of detritus amalgamation occurred in the earliest silurian benambran orogeny with accretion in the middle devonian over 40 myr discrete turbidite terranes aligned along the gondwana margin in two systems were converted into a very wide orogen characterized by the along strike juxtaposition of superficially similar terranes

paired metamorphic belts revisited abstract the modern plate tectonics regime is characterized by a duality of thermal environments one representing the subduction zone and the other representing the arc backarc or orogenic hinterland this duality is the hallmark of one sided asymmetric subduction and the characteristic imprint of one sided subduction in the geological record is predicted to be the broadly contemporaneous occurrence of two contrasting types of metamorphic belt one of high dt dp type and the other low dt dp type the broadly contemporaneous occurrence of granulite and ultrahigh temperature metamorphism with eclogite high pressure granulite metamorphism in the geological record since the neoarchean era is evidence of dual thermal environments and indicates that subduction has operated on earth since that time classic paired metamorphic belts in which an inboard high dt dp metamorphic belt is juxtaposed against an outboard low dt dp metamorphic belt along a tectonic contact such as the ryoke and sanbagawa belts in japan are found in phanerozoic accretionary orogens of the circum pacific generally they appear to result from juxtaposition of terranes with different metamorphic facies series that may or may not be exactly contemporaneous and that may or may not be far traveled this is a consequence of the difference between globally continuous subduction generating a low to intermediate dt dp environment in the subduction zone and a high dt dp environment in the arc backarc system and metamorphic imprints in the geological record that represent discrete events due to changes in plate kinematics or subduction boundary dynamics or as a result of collision of ridges arcs or continents with the upper plate at the trench the concept of paired metamorphic belts may be generalized and extended more widely than in the original proposition to subduction to collision orogenic systems in addition to accretionary orogenic systems in this wider application the term paired metamorphic belts may be used for penecontemporaneous belts of contrasting type of metamorphism that record different apparent thermal gradients one warmer and the other colder juxtaposed by plate tectonics processes brown 2009 this extends the original concept of miyashiro 1961 beyond the simple pairing of high dt dp and low dt dp metamorphic belts in circum pacific accretionary orogens and makes it more useful in the context of our better understanding of the relationship between thermal regimes and tectonic settings this is particularly useful in subduction to collision orogenic systems where the suture and lower plate materials will register the imprint of low to intermediate dt dp and the upper plate will register penecontemporaneous high dt dp metamorphism commonly manifested at shallow crustal levels by the occurrence of granites in the rock record

thermal model for approach of a spreading ridge to subduction zones and its implications for high p high t metamorphism importance of subduction versus ridge approach ratio 1 the approach of oceanic ridges to subduction zones finally resulting in ridge subduction is observed on the present earth s surface the thermal effects of the ridge approach event are studied using a two dimensional numerical model around subduction zones with particular emphasis on the implications for the associated high p high t metamorphism the ridge approach occurs when the subduction rate v is larger than the half spreading rate at the ridge the difference between the two rates represents the ridge approach rate to the trench u which is newly incorporated in the present thermal model the calculated thermal structure along the slab surface when a ridge reaches the trench generally depends only on u v when shear heating or mantle flow is not taken into account if u v is small or the ridge approach is slow compared to the subduction rate the thermal effect of the ridge approach is large enough to explain the hot general p t conditions of high p high t metamorphism relative to the steady state conditions predicted by numerical simulations in addition when the ridge is close to the trench the subduction stage p t paths experienced by high p high t metamorphic rocks show a strongly curved trajectory with the dp dt progressively increasing with pressure this suggests that the slope of petrologically determined subduction p t paths may indicate if ridge approach contributed to the formation of the metamorphic rocks

the motion of adria during the late jurassic and cretaceous new paleomagnetic results from stable istria abstract the motion of adria the largest lithospheric fragment in the central mediterranean region has played an important role in the tectonic development of the surrounding mountain chains and even of distant areas like the eastern alps or the pannonian basin the available paleomagnetic data were insufficient to constrain this motion except in a general way in this paper new paleomagnetic results are presented from one of the stable parts of adria which emerge from the adriatic sea the results were obtained on weakly magnetic platform carbonates of the mud supported type collected from 21 geographically distributed localities the results combined with mean paleomagnetic directions from selected localities from a pioneer study in istria that were chosen using statistical criteria were divided into three age groups tithonian aptian albian cenomanian turonian coniacian the paleomagnetic poles calculated for each of them tithonian aptian n 47 e 275 k 67 95 9 4 n 5 albian cenomanian n 58 e 253 k 145 95 4 3 n 9 turonian coniacian n 63 e 261 k 50 95 7 3 n 9 reveal a moderate shift during the cretataceous which is comparable with that calculated from the african reference poles however the istrian apparent polar wander path is slightly displaced from the african curve as a consequence of about 10 counterclockwise rotation of istria with respect to africa this rotation angle is more that 10 smaller than the difference measured for the mid late eocene between the paleomagnetic direction of platform carbonates from istria and the african reference direction this difference may be the consequence of a small clockwise rotation of istria with respect to africa most probably at the end of cretaceous

new stepping stones dugi otok and vis islands in the systematic paleomagnetic study of the adriatic region and their significance in evaluations of existing tectonic models abstract the external dinarides from which several conflicting tectonic models were published are the more tectonized ne margin of autochthonous adria dugi otok and vis islands belong to this margin from the two islands a new paleomagnetic study is presented based on 48 geographically distributed and biostratigraphically controlled cretaceous carbonate sediment localities the results suggest that the two islands certainly moved in co ordination after the mid albian which was the time of resumed sedimentation after a period of emersion although some relative movement could have occurred earlier the new post aptian paleomagnetic results are in perfect agreement with recently published paleomagnetic results from stable adria and from the more northerly adriatic islands this consistency suggests that all these areas moved together from the albian on while the coastal range of the external dinarides seems to have moved independently thus autochthonous adria together with the adriatic islands is established as a crustal block within the central mediterranean region which rotated significantly in ccw sense in post cretaceous times

alpine geodynamic evolution of passive and active continental margin sequences in the tauern window eastern alps austria italy a review the penninic oceanic sequence of the glockner nappe and the foot wall penninic continental margin sequences exposed within the tauern window eastern alps have been investigated in detail field data as well as structural and petrological data have been combined with data from the literature in order to constrain the geodynamic evolution of these units volcanic and sedimentary sequences document the evolution from a stable continent that was formed subsequent to the variscan orogeny to its disintegration associated with subsidence and rifting in the triassic and jurassic the formation of the glockner oceanic basin and its consumption during the upper cretaceous and the paleogene these units are incorporated into a nappe stack that was formed during the collision between a penninic zentralgneis block in the north and a southern austroalpine block the venediger nappe and the storz nappe are characterized by metamorphic jurassic shelf deposits hochstegen group and cretaceous flysch sediments kaserer and murtorl groups the eclogite zone and the rote wand modereck nappe comprise permian to triassic clastic sequences wustkogel quartzite and remnants of platform carbonates seidlwinkl group as well as jurassic volcanoclastic material and rift sediments brennkogel facies covered by cretaceous flyschoid sequences nappe stacking was contemporaneous to and postdated subduction related high pressure eclogite and blueschist facies metamorphism emplacement of the eclogite bearing units of the eclogite zone and the glockner nappe onto penninic continental units zentralgneis block occurred subsequent to eclogite facies metamorphism the eclogite zone a former extended continental margin was subsequently overridden by a pile of basement cover nappes rote wand modereck nappe along a ductile out of sequence thrust low angle normal faults that have developed during the jurassic extensional phase might have been inverted during nappe emplacement

upper cretaceous and palaeogene magnetic stratigraphy and biostratigraphy from the venetian southern alps abstract four sections of upper cretaceous eocene pelagic limestones from the belluno basin of the venetian alps italy yield well defined magnetic stratigraphies the correlation of magnetozones with nannofossil and foraminiferal zonations generally agrees well with that obtained from the type section at gubbio 1 the magnetostratigraphy supplements the palaeontology as a means of stratigraphic correlation variations in sedimentation rate and in the duration of hiatuses are clearly documented for the four different locations in the basin