the origin and age of the metamorphic sole from the rogozna mts western vardar belt new evidence for the one ocean model for the balkan ophiolites abstract this study brings new geochronological and petrochemical data from the metamorphic sole beneath the rogozna mts western vardar ophiolite belt the rogozna metamorphic sole is located at the base of a serpentinite nappe and consists of amphibolites and talc chlorite schists the rogozna amphibolites are medium to fine grained rocks with nematoblastic texture and pronounced foliation they consist of green amphibole 70 vol with variable silica contents 6 4 to 7 8 si apfu as well as mg molmg mg fe tot 0 53 to 0 77 and variably albitized plagioclase 30 vol ab 24 ab 98 amphibolites are overprinted by a retrograde assemblage containing actinolite epidote clinoclore sericite chlorite and magnetite the amphibolites formed due to metamorphism of two basaltic suites subalkaline tholeiitic and alkaline subalkaline tholeiitic amphibolites possess low zr nb y th hf tio 2 and p 2 o 5 values and a lree depleted pattern typical for the n morb normal mid ocean ridge basalt to bab back arc basalt origin alkaline amphibolites show elevated concentrations of zr nb y th hf tio 2 and p 2 o 5 with a lree enriched pattern typically displayed by oib ocean island basalt amphibolites were crystallized during intra oceanic thrusting at temperatures between 685 c and 765 c and at a depth of 12 17 km 40 ar 39 ar cooling ages of amphibole ranging from 165 to 170 ma slightly postdate the sole formation talc chlorite schists are related to retrograde greenschist facies metamorphism they consist of fe rich talc and cr rich chlorite peninite diabantite pseudomorphs after amphibole and morb type cr al spinel surrounded by al and mg poor ferrit chromite the occurrence of ferrit chromite is related to earlier amphibolite facies metamorphism chlorite pseudomorphs after amphibole were formed at 300 410 c this study suggests that there is no essential difference in the emplacement age of the dinaric and west vardar ophiolite belts supporting the interpretation involving a single mesozoic ocean in the balkan sector

the nappe structure of the central northern calcareous alps and its disintegration during miocene tectonic extrusion a contribution to understanding the orogenic evolution of the eastern alps the classical concept of the nappe structure of the central northern calcareous alps nca is in contradiction with modern stratigraphic structural metamorphic and geochronological data we first perform a palinspastic restoration for the time before miocene lateral tectonic extrusion which shows good continuity of structures facies and diagenetic metamorphic zones we present a new nappe concept in which the tirolic unit practically takes the whole area of the central nca and is divided into three subunits nappes lower and upper tirolic subunit separated by the upper jurassic trattberg thrust and the metamorphic ultra tirolic unit the hallstatt iuvavic nappe s formed the highest unit but were completely destroyed by erosion after nappe stacking remnants of the hallstatt nappes are only represented by components of up to 1 km in size in middle upper jurassic radiolaritic wildflysch sediments hallstatt melange belonging to the tirolic unit destruction of the continental margin started in middle to upper jurassic time and prograded from the oceanic side towards the shelf the original substratum of the external nappes bavaric units of the nca was largely the austroalpine crystalline basement of the internal nappes tirolic units the weakly metamorphosed palaeozoic sequences greywacke zone and equivalents eocene movements caused limited internal deformation in the tirolic unit

the northeast brazilian rift system the northeast brazilian rift basins provide important data critical to the understanding of continental rifting processes associated with the opening of the south atlantic these basins represent the locus of intersection of the southern and equatorial branches and some basins yield substantial chronostratigraphic data that constrain the temporal and spatial interaction of the rift phases similar data are not found in its counterpart in africa especially for the neocomian these early cretaceous rift basins of northeast brazil illustrate key three dimensional geometries of intracontinental rift systems mainly controlled by the basement structural framework during the main rift phase syn rift ii neocomian early barremian extensional deformation was distributed over three main rift axes 1 the gabon sergipe alagoas gsa trend 2 the reconcavo tucano jatoba rtj trend and 3 the cariri potiguar cp trend during this phase extensional deformation jumped west from the easternmost basins gsa trend to a series of ne trending intracratonic basins rtj and cp trends characterized by a set of asymmetric half grabens separated by basement highs transfer faults and or accommodation zones these basins are typically a few tens of kilometers wide and trend ne sw roughly perpendicular to the main extension direction during the neocomian preexisting upper crustal weakness zones like the dominantly ne sw trending shear zones of the brazilian pan african orogeny controlled the development of intracrustal listric normal faults internal transverse structures such as transfer faults and accommodation zones were also controlled by the local basement structural framework the megashear zones of pernambuco brazil and ngaundere africa seem to have behaved like a huge accommodation zone accommodating extensional deformation along the rtj gsa trends with simultaneous extension along the cp trend during the late barremian syn rift phase iii a significant change in rifting kinematics occurred when the cp trend was aborted and major rifting initiated at the equatorial branch during the aptian while the equatorial branch and benue trough africa experienced the main rift phase the rtj trend was aborted and the gsa trend developed a transitional phase between the rift and drift stage the gsa trend and the offshore potiguar basin represent the site of continued evolution into passive margin basins following the main rift episode

how many oceans meliata vardar and pindos oceans in mesozoic alpine paleogeography the timing of rifting and subduction in the meliata vardar and pindos zones of the hellenic dinaric carpathian region indicates that they cannot be considered remnants of a single ocean basin in contrast to several recently published mesozoic paleogeographies sea floor spreading in the meliata zone culminated in middle triassic ladinian time and ceased in the late triassic and subduction occurred from this time until late jurassic closure in contrast sea floor spreading in the vardar zone began in early jurassic time and culminated in the middle jurassic and subduction occurred from latest jurassic time in the pindos zone sea floor spreading was initiated in the early triassic with late jurassic and early tertiary subduction

the tectonic evolution of the south atlantic from late jurassic to present an improved tectonic database for the south atlantic has been compiled by combining magnetic anomaly geosat altimetry and onshore geologic data we used this database to obtain a revised plate kinematic model starting with a new fit reconstruction for the continents around the south atlantic we present a high resolution isochron map from chron m4 to present fit reconstructions of south america and africa that require rigid continental plates result in substantial misfits either in the southern south atlantic or in the equatorial atlantic to achieve a fit without gaps we assume a combination of complex rift and strike slip movements 1 along the south american parana chacos basin deformation zone 2 within marginal basins in south america salado colorado basin and 3 along the benue trough niger rift system in africa these faults are presumed to have been active before or during the breakup of the continents our model describes a successive unzipping of rift zones starting in the southern south atlantic between 150 ma tithonian and approximately 130 ma hauterivian rifting propagated to 38 s causing tectonic movements within the colorado and salado basins subsequently between 130 ma and chron m4 126 5 ma the tip of the south atlantic rift moved to 28 s resulting in intracontinental deformation along the parana chacos basin deformation zone between chron m4 and chron mo 118 7 ma rifting propagated into the benue trough and niger rift inducing rift and strike slip motion after chron mo the equatorial atlantic began to open while rifting and strike slip motion still occurred in the benue trough and niger rift since chron 34 84 ma the opening of the south atlantic is characterized by simple divergence of two rigid continental plates

regional framework structural and petroleum aspects of rift basins in niger chad and the central african republic c a r abstract this paper overviews the regional framework tectonic structural and petroleum aspects of rifts in niger chad and the c a r the data base is from mainly proprietary exploration work consisting of some 50 000 kilometres of seismic profiles 50 exploration wells one million square kilometres of aeromagnetics coverage and extensive gravity surveys there have been 13 oil and two oil and gas discoveries a five phased tectonic history dating from the pan african orogeny 750 550 my b p to the present suggests that the western central african rift system wcas with its component west african rift subsystem was and central african subsystem cas formed mainly by the mechanical separation of african crustal blocks during the early cretaceous among the resulting rift basins in niger chad and the c a r seven are in the was grein kafra tenere tefidet termit bongor and n dgel edgi and three doba doseo and salamat are in the cas the was basins in niger and chad are all extensional and contain more than 14 000 m of continental to marine early cretaceous to recent clastic sediments and minor amounts of volcanics medium to light oil 20 api 46 api and gas have been discovered in the termit basin in reservoir source and seal beds of late cretaceous and palaeogene age the most common structural styles are extensional normal fault blocks and transtensional synthetic and antithetic normal fault blocks the cas doba doseo and salamat are extensional to transtensional rift basins containing up to 7500 m of terrestrial mainly early cretaceous clastics heavy to light oil 15 39 api and gas have been discovered in doba and doseo basins source rocks are early cretaceous lacustrine shales whereas reservoirs and seals are both early and late cretaceous dominant structural styles are extensional and transtensional fault blocks transpressional anticlines and flower structures the existence of a total rift basin sediment volume of more than one million cubic kilometres with structured reservoir source and seal rocks favours the generation migration and entrapment of additional significant volumes of hydrocarbons in many of these basins

the rift to break up evolution of the gulf of aden insights from 3d numerical lithospheric scale modelling abstract the gulf of aden provides an ideal setting to study oblique rifting since numerous structural data are available onshore and offshore recent surveys showed that the spatio temporal evolution of the gulf of aden rift system is dominated by three fault orientations displacement orthogonal wsw rift parallel wnw and an intermediate e w trend the oldest parts of the rift that are exposed onshore feature displacement orthogonal and intermediate directions whereas the subsequently active necking zone involves mainly rift parallel faults the final rift phase recorded at the distal margin is characterised by displacement orthogonal and intermediate fault orientations we investigate the evolution of the gulf of aden from rift initiation to break up by means of 3d numerical experiments on lithospheric scale we apply the finite element model slim3d which includes realistic elasto visco plastic rheology and a free surface despite recent advances 3d numerical experiments still require relatively coarse resolution so that individual faults are poorly resolved we address this issue by proposing a simple post processing method that uses the surface stress tensor to evaluate stress regime extensional strike slip compressional and preferred fault azimuth the described method is applicable to any geodynamic model and easy to introduce our model reproduces the observed fault pattern of the gulf of aden and illustrates how multiple fault directions arise from the interaction of local and far field tectonic stresses in an evolving rift system the numerical simulations robustly feature intermediate faults during the initial rift phase followed by rift parallel normal faulting at the rift flanks and strike slip faults in the central part of the rift system upon break up displacement orthogonal as well as intermediate faults occur this study corroborates and extends findings from previous analogue experiments of oblique rifting on lithospheric scale and allows new insights in the timing of fault successions of the gulf of aden and continental rifts in general

temporal and spatial correlations between changes in plate motions and the evolution of rifted basins in africa we present the results of a backstripping study incorporating over 200 wells in 14 different basins or groups of basins located on the african interior or continental margins these results presented as mean tectonic subsidence rates averaged over appropriate periods are compared with the opening histories and changes in plate motions of the atlantic and indian oceans and the tethys mediterranean area for seven time steps from the late jurassic until present the results indicate a temporal and spatial correlation between phases of rapid subsidence in african basins and changes in plate motions and therefore are promising in terms of applicability of large scale plate motions in the studies of paleo stresses in sedimentary basins especially at times of initial rifting and formation of subduction zones reactivation of the basins appears to be primarily controlled by the orientation of the basin and underlying basement structures with respect to the stress direction the basins are preferably formed within weaker zones mostly pan african shear zones and the distance from the active plate boundary to the weak zone plays a minor role in whether or not it will be reactivated the presence of three important hot spots which were active during the early stages of break up of gondwana may have been important in preweakening the lithosphere at their sites this may have played an additional role in the localization of the basin deformation

a flow law for dislocation creep of quartz aggregates determined with the molten salt cell we have used the molten salt cell to conduct an experimental study on the rheology of a natural quartzite containing 0 15 wt water co axial deformation experiments were conducted at constant piston displacement rates approximating constant strain rates at low strain the strengths of our natural quartzite measured in the molten salt cell are approximately half those measured at the same conditions in solid media because unlike solid confining media molten salt does not contribute to the strength of the sample it reduces the friction on the moving piston and it allows clear identification of the hit point we have limited the experimental conditions to those required for dislocation creep and have used only steady state flow stresses measured during climb accommodated dislocation creep to calculate the flow law parameters two flow laws were determined one for samples containing minor amounts of melt 1 2 and one for melt free samples in both cases the power law stress exponent n is 4 0 0 9 which is greater than that previously reported in flow laws for dislocation creep of quartz aggregates determined in solid media the activation energy q is 137 34 kj mol 1 for samples with melt and 223 56 kj mol 1 for those without within the range of previously determined values for quartz aggregates containing 0 1 wt water the pre exponential term a is 1 1 10 4 2 mpa ns 1 for samples without melt and 1 8 10 8 2 mpa ns 1 for those with melt the lower strengths measured in the molten salt cell indicate that previous piezometer relations for quartz experimentally determined in solid media are not correct extrapolation of the flow law for melt free aggregates to natural strain rates predicts higher strengths than most previous quartz flow laws however accurate extrapolation requires determining the dependence of flow stress on fh2o and or ah

long term evolution of the west african transform margin estimates of denudation from benin using apatite thermochronology the benin continental margin was formed during the breakup of gondwana through oblique rifting along transform faults the evolution of topography following breakup directly affects the evolution of sedimentary basins which has major implications for hydrocarbon exploration in the region quantitative constraints on erosion across benin are limited to the cenozoic based on analysis of dissected lateritic palaeolandscapes to resolve the mesozoic erosion history we have obtained apatite fission track and single grain u th sm he data from 18 samples collected across a 600 km long transect through benin we invert these data including available geological and geomorphological constraints to obtain time temperature paths which are used to estimate magnitudes of denudation over the last 200 myr our study suggests that denudation was focused over a c 300 km long seaward sloping limb of the marginal upwarp and at the southern margin of the interior iullemmeden basin from 140 to 100 ma with lower magnitudes of denudation characterizing the continental interior and post cretaceous evolution of the margin models are consistent with modest burial c 1 km of the iullemmeden basin between 120 and 85 ma and of the continental margin between 85 and 45 ma by the eocene the first order relief of benin had developed with regional erosion rates supplementary information full details of the analytical data and modelling results including the various constraints and further data on denudation and burial magnitudes and rates are available at https doi org 10 6084 m9 figshare c 4220804

tectonosedimentary evolution related to extreme crustal thinning ahead of a propagating ocean example of the western pyrenees 1 in this paper we describe the tectonosedimentary evolution and its subsequent inversion of a basin that underwent extreme crustal thinning in a transtensional setting ahead of a propagating ocean in the western pyrenees the labourd mauleon area situated in the western pyrenees at the termination of the v shaped bay of biscay is an ideal natural laboratory to study how such complex basins evolve in time and space because of a mild inversion of the basin during pyrenean compression the rift structures and their relations to basement rocks and sediments are exposed and can be directly studied in the field the basin shows a complex polyphase evolution that starts with left lateral dominated transtension in latest jurassic early aptian time this event is overprinted by a late aptian early albian extension that is related to the counterclockwise rotation of iberia away from europe leading to the opening of the bay of biscay during this stage the late triassic to jurassic carbonate platform was stretched salt migrated and detachment faults exhumed upper and lower crustal and mantle rocks to the seafloor the final structure of the basin resembles a sag basin floored by exhumed rocks overlain by extensional allochthons and compartmentalized by n40 to n60 transfer faults the sedimentary architecture is characterized by late aptian synrift sediments e g urgonian limestones that were deposited in fault bounded basins and are overlain by thick latest aptian to albo cenomanian sediments e g flysch noir that define a sag sequence the complex tectonosedimentary evolution of the basin is associated with salt tectonics and overprinted by a major magmatic thermal event that postdates mantle exhumation

origin of a major aeromagnetic anomaly in the middle niger basin nigeria abstract a composite magnetic anomaly map was compiled from existing half degree aeromagnetic sheets of the southeastern sector of the middle niger nupe basin the map which has the international geomagnetic reference field i g r f epoch date 1 january 1974 removed is dominated by an elongated e w negative anomaly aligned along latitude 9 other prominent features include an e w trending positive anomaly which flanks the negative anomaly to the south and a large negative zone in the southeast corner of the map previous gravity results for parts of this area suggested that a positive residual gravity anomaly which appears to correspond to this magnetic low is caused by schists of intermediate composition which are overlain by cretaceous nupe sandstones however a combined application of werner deconvolution and forward modelling techniques on selected profiles across the major e w anomaly lead to the conclusion that the anomaly may be caused by predominantly basic rocks at depths which vary between 4 km and 6 km well below the base of the sediments which are generally not more than 2 km thick the presence of large bodies of basic rocks indicated by these results suggest that a deep seated rift may exist in the crust under the basin

three dimensional laboratory modelling of rifting application to the baikal rift russia abstract continental rifting is treated as a mechanical instability developing under horizontal tectonic tension the instability results in strain localization and the formation of a neck which is interpreted as a rift zone at the scale of the whole lithospheric plate this process occurs in plane stress conditions and can therefore be modelled to a first approximation by a one layer plate whose properties represent integral over thickness properties of the real lithosphere we have designed a scaled experimental single layer lithosphere model having elasto plastic rheology and lying upon a liquid substratum to study its behaviour under axial horizontal tension in a homogeneous plate the instability develops along a linear zone oriented at an angle of 60 to the tension axis this orientation is preserved even when the divergent displacement of the plate boundaries is not plain parallel but rotational in the latter case the strain localization zone is rapidly propagating when the plate length to width ratio is less than 2 5 the necking develops along two branches conjugated at an angle of about 120 which is frequently observed in actual rift systems if the model contains a local weak zone hot spot or fault zone the rift junction is located at this zone in the lithospheric models comprising strong cratonic and weak segments strain localization depends on the configuration of the boundary between different lithospheres the necking starts to form within the weak segment in the vicinity of the cratonic promontories and propagates in opposite directions again at an angle of ca 60 to the tension axis in the models containing both a strong lithosphere and local weak zones the rift configuration depends on their shape and relative positions with necking always going through the weak zones in a set of models we have reproduced the geometry of the boundary between the siberian craton and the thermally much younger 100 ma sayan baikal lithosphere in the baikal rift area in these models we were able to obtain the well known three branch configuration of the baikal rift system only by introducing a weak zone in the area of lake baikal such a zone simulates the paleozoic suture existing in this area as in nature two wide outer branches eastern and western are oblique to the regional tension axis whereas the central one is narrow and orthogonal to the tension direction in nature and in the model rifting starts in the central branch corresponding to lake baikal the modelling also predicts the formation of a fourth oblique ns trending branch to the south of baikal although poorly expressed in the field this branch has some seismotectonic and magmatic manifestations the orientations of all four branches with respect to each other and with respect to the regional tension direction are remarkably similar in nature and in the model

ultra high pressure metamorphism and orogenesis an alpine perspective article i nfo the pressure temperature time deformation evolution of the high to ultra high pressure units of the western alps has been progressively refined in the last 40 years leading to several paradigm shifts in the understanding of orogenesis this set of information combined with cretaceous tertiary plate kinematic reconstructions and mesozoic palaeogeography indicates that the western alps represent the amalgamation of a cretaceous and an eocene orogen which developed at the expense of the adriatic and european rifted margins respectively in the cretaceous nne directed drift of the adriatic plate parallel to the inherited jurassic structural trends led to the development of a highly oblique subduction boundary in this setting the canavese zone and parts of the sesia zone derived from the hyper extended adriatic margin underwent deformation and metamorphism at conditions ranging from sub greenschist to eclogite facies a lower eocene switch to nnw directed motion perpendicular to the rift related jurassic structural trends culminated in the collision between the proto alps and the brianconnais block at ca 44 ma as a result the brianconnais domain and parts of its hyper extended margin preserved in the u hp piemonte units were accreted to the orogen continued convergence was subsequently accommodated by subduction of the more external valaisan basin and of the thinned european margin the arrival of thick european continental crust at the subduction zone at ca 35 30 ma marked the onset of the final continental collision to a first order the orogen grew through the progressive episodic accretion of units located towards north westerly positions accretion of subducting units at the front of the orogen was coeval with kinematic reworking of tectonic contacts in the hangingwall units locally resulting in renewed deformation metamorphism

madagascar s escape from africa a high resolution plate reconstruction for the western somali basin and implications for supercontinent dispersal accurate reconstructions of the dispersal of supercontinent blocks are essential for testing continental breakup models here we provide a new plate tectonic reconstruction of the opening of the western somali basin during the breakup of east and west gondwana the model is constrained by a new comprehensive set of spreading lineaments detected in this heavily sedimented basin using a novel technique based on directional derivatives of free air gravity anomalies vertical gravity gradient and free air gravity anomaly maps also enable the detection of extinct mid ocean ridge segments which can be directly compared to several previous ocean magnetic anomaly interpretations of the western somali basin the best matching interpretations have basin symmetry around the m0 anomaly these are then used to temporally constrain our plate tectonic reconstruction the reconstruction supports a tight fit for gondwana fragments prior to breakup and predicts that the continent ocean transform margin lies along the rovuma basin not along the davie fracture zone dfz as commonly thought according to our reconstruction the dfz represents a major ocean ocean fracture zone formed by the coalescence of several smaller fracture zones during evolving plate motions as madagascar drifted southwards and offshore tanzania is an obliquely rifted rather than transform margin new seismic reflection evidence for oceanic crust inboard of the dfz strongly supports these conclusions our results provide important new constraints on the still enigmatic driving mechanism of continental rifting the nature of the lithosphere in the western somali basin and its resource potential

a three dimensional 3d structural model for an oil producing basin of the brazilian equatorial margin abstract hydrocarbon discoveries in regions such as the brazilian equatorial margin equatorial africa and french guiana have recently confirmed their importance as new exploration frontiers the mundau sub basin located on the brazilian equatorial margin is an oil and gas producing region with four producing fields in shallow water xareu atum espada e curima in order to understand the structural and seismic stratigraphic frameworks of an oil producing area of the brazilian equatorial margin this work addresses the 3d geometry and spatial distribution of main faults in the curima and espada fields the occurrence of hydrocarbons in the mundau sub basin is compared with fields in other parts of the brazilian equatorial basin and in equatorial africa data from 12 wells and a 3d post stack time migrated multichannel seismic volume are used to define nine 9 main seismic stratigraphic units the syn rift mundau formation units 1 2 3 and 4 the transitional paracuru formation unit 5 and the drift ubarana uruburetama and itapage members units 6 and 7 tibau and guamare formations units 8 and 9 the study area is dominated by nw se planar normal faults basinward dipping that formed multiple half grabens and tilted blocks with small anticlines and synclines genetically related to a transtensional system three types of plays are recognised in the mundau sub basins structural combined structural stratigraphic and stratigraphic turbiditic in the eastern part of the region where the basement is shallow no oil was found conversely oil was discovered in an anticlinal trap formed on a hanging wall block analogous to fields in cote d ivoire ghana transform margin this work shows that combined traps on footwall blocks are successful plays near the shelf break of the mundau sub basin in similarity with the espoir and baobab fields in ivory coast basin furthermore turbiditic reservoirs in drift units are analogous to the stabroek block in guyana and prospects in the gulf of guinea the structural and petroleum play analyses in this work are therefore crucial to understand the multiple geological processes leading to the trapping of hydrocarbons in the larger equatorial atlantic ocean

modeling suggests that oblique extension facilitates rifting and continental break up 1 in many cases the initial stage of continental break up was and is associated with oblique rifting that includes break up in the southern and equatorial atlantic separation from eastern and western gondwana as well as many recent rift systems like gulf of california ethiopia rift and dead sea fault using a simple analytic mechanical model and advanced numerical thermomechanical modeling techniques we investigate the influence of oblique extension on the required tectonic force in a three dimensional setting while magmatic processes have been already suggested to affect rift evolution we show that additional mechanisms emerge due to the three dimensionality of an extensional system focusing on non magmatic rift settings we find that oblique extension significantly facilitates the rift process this is due to the fact that oblique deformation requires less force in order to reach the plastic yield limit than rift perpendicular extension the model shows that in the case of two competing non magmatic rifts with one perpendicular and one oblique to the direction of extension but otherwise having identical properties the oblique rift zone is mechanically preferred and thus attracts more strain

on late oligocene to pliocene depocentre migrations and the evolution of the carpathian pannonian system abstract the late oligocene to pliocene evolution of foredeep basins of the eastern alps carpathians fold and thrust belt is marked by pronounced internal to external and lateral depocentre shifts the latter shifts covering a present along arc distance of 1700 km portray accelerating rates of foredeep depocentre migration particularly so in the late early and in the middle miocene from about 7 to about 45 cm yr lateral depocentre migration came to a close at the beginning of the late miocene the subsequent late miocene to pliocene foredeep infill history was characterized by exponentially increasing accumulation rates in the intersection area of the east european ukrainian and moesian platforms successive steps in the evolution of the foredeep basins had pronounced counterparts in the intra carpathian area the beginning of acceleration of foredeep depocentre migration in latest early miocene times was coeval with the inception of intra carpathian extensional tectonics the extremely rapid middle miocene depocentre shift coupled with a change in direction of foredeep depocentre migration corresponded with maximum extension in the intra carpathian area the ensuing end of foredeep depocentre migration around the middle late miocene transition was coeval with the end of extension of the intra carpathian area which in turn was followed by the inception of overall thermal subsidence at about 11 5 ma the timing of and spatial relationships between discrete coeval events in arc and intra arc evolution put unambiguous geological constraints on geodynamic modelling of the evolution of the carpathian pannonian system it is speculated that the geological observations may best be understood in terms of the surficial effects of lateral migration of slab detachment such effects would mirror the dominant role of a concentrating slab pull taken to result in e g a time progressive acceleration of foredeep depocentre migration

the western alps from the jurassic to oligocene spatio temporal constraints and evolutionary reconstructions abstract despite extensive research in the last 150 years the regional tectonic reconstruction of the western alps has remained controversial the curved orogenic belt consists of several ribbon like continental terranes sesia austroalpine internal crystalline massifs brianconnais which are separated by two or more ophiolitic sutures piemonte valais antrona lanzo canavese high pressure hp metamorphism of each terrane occurred during distinct orogenic episodes at 65 ma in the sesia austroalpine at 45 ma in the piemonte zone and at 35 ma in the internal crystalline massifs it is suggested that these events reflect individual accretionary episodes which together with kinematic indicators and the speed and direction of plate motions provide constraints for the discussed reconstruction model the model involves a prolonged orogenic history that took place during relative convergence of europe and adria here considered as a promontory of the african plate the first accretionary event involved the sesia austroalpine terrane final closure of the piemonte ocean occurred during the eocene 45 ma and involved ultra high pressure uhp metamorphism of the piemonte oceanic crust incorporation of the brianconnais terrane in the accretionary wedge occurred thereafter possibly during or after subduction of the valais ocean in the late eocene 45 35 ma this subduction was terminated at ca 35 ma when the internal crystalline massifs i e the assumed internal parts of the brianconnais terrane were buried into great depths and underwent hp and uhp metamorphism

tertiary subduction and slab break off model of the carpathian pannonian region abstract this paper illustrates the application of multidisciplinary data analysis to the carpathian pannonian region and presents a new tertiary development model that incorporates all multidisciplinary parameters during the late cretaceous eocene the future carpathian orogen was part of the larger alpine carpathian orogen formed by the southeastward subduction 135 55 ma of the penninic ocean and the ultimate collision 55 40 ma of the european and adriatic continents the subduction in the alpine region ended by the slab break off of the subducting oceanic lithosphere from the continental one and by the related magmatism 43 24 ma while the eocene alps were under continental collision the eocene remnant carpathian flysch basin rcfb was still subducting the carpathians and eastern parts of the alps started to occupy the region of the present carpathians during the early miocene the oceanic plate underlying the rcfb subducted southwestwards later westwards while the northeastward and eastward migration velocity of the accreting plate boundary decreased through time the slower subduction rate caused a steeper dip of the subducting slab the beginning of the eggenburgian 22 19 ma and following duration of extension in the orogenic hinterland accompanied by the asthenosphere upwelling the onset of the crustally derived volcanism above the risen asthenosphere and the younger mantle derived volcanism progressively less contaminated by the crustal material all contemporaneous with a shortening in the carpathian accretionary wedge the subduction of the rcfb finally led at the end of the early miocene to a collision with the continental margin along the westernmost part of the present carpathian arc the subduction roll back of the subducting slab of the rcfb under the advancing inner carpathians the oblique closure of the basin the progressive change of the subduction to collision from the west to the east along the carpathian arc drove a scissors like break off of the subducting oceanic slab along the west carpathians the break off in the east carpathians was driven by the weight of a subducting oceanic slab and buoyancy of the attached continental slab the break off started in the west of the carpathian arc in the early miocene ran along the arc to its present position in the bend area between the east and south carpathians and separated the oceanic slab that subducted passively under its own weight from the european continental margin the lateral propagation rate of the slab tear decreased with time the break off related volcanism was synchronous with the final stages of the collision

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

evolution of seaward dipping reflectors at the onset of oceanic crust formation at volcanic passive margins insights from the south atlantic seaward dipping reflectors sdrs have long been recognized as a ubiquitous feature of volcanic passive margins yet their evolution is much debated and even the subject of the nature of the underlying crust is contentious this uncertainty significantly restricts our understanding of continental breakup and ocean basin forming processes using high fidelity reflection data from offshore argentina we observe that the crust containing the sdrs has similarities to oceanic crust albeit with a larger proportion of extrusive volcanics variably interbedded with sediments densities derived from gravity modeling are compatible with the presence of magmatic crust beneath the outer sdrs when these sdr packages are restored to synemplacement geometry we observe that they thicken into the basin axis with a nonfaulted diffuse termination which we associate with dikes intruding into initially horizontal volcanics our model for sdr formation invokes progressive rotation of these horizontal volcanics by subsidence driven by isostasy in the center of the evolving sdr depocenter as continental lithosphere is replaced by more dense oceanic lithosphere the entire system records the migration of 10 km thick new magmatic crust away from a rapidly subsiding but subaerial incipient spreading center at rates typical of slow oceanic spreading processes our model for new magmatic crust can explain sdr formation on magma rich margins globally but the estimated crustal thickness requires elevated mantle temperatures for their formation

post rift stratigraphic architectures along the african margin of the equatorial atlantic part i the influence of extension obliquity abstract we investigated the variability of the first order crustal structure and early post rift stratigraphy of six segments of the african equatorial atlantic margin using sub surface data seismic and wells extension obliquity of the segments varies from 0 for the west ivory coast and ghana transform segments to 30 for the togo benin oblique segment and 75 for the east ivory coast normally divergent segment the sierra leone and liberia segments underwent probably deformation during both the early jurassic rifting of the central atlantic and the early cretaceous rifting of the equatorial atlantic with contrasted divergence obliquities for segments that underwent a single rifting we show that the higher the obliquity the wider the crustal thinning domain this has a major influence on the first order geometry of all the post rift horizons including the present day slope the lower the obliquity the larger the differential subsidence across the margin and the steeper the present day slopes of post rift horizons this also has a major influence on the flexural isostatic response of the lithosphere to thermal and erosion sedimentation driven un loads during the early post rift narrow transform segments underwent higher flexural and or thermal uplifts in the proximal domain than wider divergent segments along the same margin divergent segments therefore may preserve early post rift deposits in their proximal domains whereas they are not preserved on nearby transform segments

comparison of the rift and post rift architecture of conjugated salt and salt free basins offshore brazil and angola namibia south atlantic abstract this study presents a regional comparison between selected 2d seismic transects from large conjugated salt and salt free basins offshore southern brazil campos basin santos basin pelotas basin and southwest africa kwanza basin northern and southern namibe basin walvis basin tectonic stratigraphic interpretation of the main rift and post rift units free air gravity data and flexural isostatic backstripping were used for a comprehensive basin to basin documentation of key mechanisms controlling the present day differences in conjugated and neighbouring south atlantic basins a significant variation in the tectonic sedimentary architecture along strike at each margin and between the conjugated basins across the south atlantic reflects major differences in 1 the structural configuration of each margin segment at transitional phase between rifting and breakup as emphasized in the highly asymmetric settings of the large santos salt basin and the conjugated salt free southern namibe basin 2 the post breakup subsidence and uplift history of the respective margin segment which caused major differences for example between the campos and espirito santo basins and the conjugated northern namibe and kwanza basins 3 variations in the quantity and distribution of post breakup margin sediments which led to major differences in the subsidence history and the related present day basin architecture for example in the initially rather symmetric siliciclastic pelotas and walvis basins and 4 the deposition of aptian evaporites in the large rift and sag basin provinces north of the rio grande rise and walvis ridge highly contrasting the siliciclastic basins along the margin segments south of the ridges the resulting present day architecture of the basins can be generally classified as i moderately symmetric salt free and magma rich in the northern part of the southern segment i highly asymmetric salt bearing and magma poor vs salt free and magma rich in the southern part of the central segment and iii moderately symmetric to asymmetric salt rich and magma poor in the central part of the central segment of the south atlantic

complex structural pattern of the alpine dinaridic pannonian triple junction due to the political boundaries between the central european countries on one hand and the thick tertiary cover in the pannonian basin on the other the eastward continuation of the alpine and dinaridic units has been ambiguous and poorly documented based on comparative analyses the aim of the present paper is to define the pre tertiary structural units in the junction area of the alpine dinaridic and pannonian regions in the sw part of the pannonian basin and to draw conclusions on the continuation of the alpine and dinaridic units according to diagnostic characteristics of the periadriatic lineament system the balaton lineament system may be considered as its direct eastern continuation north of the periadriatic balaton lineament system the transdanubian range unit due to its pre tertiary paleogeographic setting shows mainly south alpine facies relations however its present structural position is identical to that of the upper austroalpine nappes between the periadriatic balaton and zagreb zemplin lineament systems heterogeneous structural units are juxtaposed forming the sava composite unit in the northern part of this composite unit non metamorphosed nappes occur which can be considered the eastern continuation of the south alpine units these nappes are overthrust onto internal dinaridic units in the tertiary the zagreb zemplin mid hungarian lineament separates the sava unit from the tisza unit showing close affinity to the tethyan margin of the eurasian plate during the early stage of the alpine evolution

flat versus steep subduction contrasting modes for the formation and exhumation of high to ultrahigh pressure rocks in continental collision zones abstract flat and steep subduction are end member modes of oceanic subduction zones with flat subduction occurring at about 10 of the modern convergent margins and mainly around the pacific continental margin subduction normally follows oceanic subduction with the remarkable event of formation and exhumation of high to ultrahigh pressure hp uhp metamorphic rocks in the continental subduction collision zones we used 2d thermo mechanical numerical models to study the contrasting subduction collision styles as well as the formation and exhumation of hp uhp rocks in both flat and steep subduction modes in the reference flat subduction model the two plates are highly coupled and only hp metamorphic rocks are formed and exhumed in contrast the two plates are less coupled and uhp rocks are formed and exhumed in the reference steep subduction model in addition faster convergence of the reference flat subduction model produces extrusion of uhp rocks slower convergence of the reference flat subduction model results in two sided subduction collision the higher lower convergence velocities of the reference steep subduction model can both produce exhumation of uhp rocks a comparison of our numerical results with the himalayan collisional belt suggests two possible scenarios 1 a spatially differential subduction collision model which indicates that steep subduction dominates in the western himalaya while flat subduction dominates in the extensional central himalaya and 2 a temporally differential subduction collision model which favors earlier continental plate flat subduction with high convergence velocity in the western himalaya and later flat subduction with relatively low convergence velocity in the central himalaya

tectonostratigraphic development of the interior sudan rifts central africa abstract in the muglad melut and blue nile rift basins of interior sudan three major episodes of rifting concomitant subsidence and nonmarine nonvolcanic sedimentation are recognized these three rifting cycles which spanned 140 to 95 ma fl 95 to 65 ma f2 and 65 to 30 ma f3 resulted in the accumulation of up to 5400 4200 and 5400 m of sediments respectively in the muglad basin the best known and largest of the sudan rift basins each rifting cycle consists of 1 a basal sandstone unit at least near rift margins that is followed by 2 an upward coarsening section of lacustrine shale grading through marginal lacustrine mudstone and sandstone into fluvial mudstone and sandstone and 3 a capping blanket of fluvial and alluvial sandstone the shale dominated portions of these cycles were deposited in a closed drainage basin during active faulting the fluvial and alluvial blanket sands were deposited in an open drainage basin during the thermal sag phase following each tectonic cycle the early cretaceous f1 intracontinental rifts of interior sudan were linked to major rifts spreading centres in the proto south atlantic by the dextral wsw trending central african shear zone and to the indian ocean via the nw trending anza rift in kenya in the muglad basin f1 deformation involved high strain rates rapid syn rift crustal stretching and subsidence and the formation of deep fault bounded tensional and transtensional pull apart basins during the f2 and f3 deformations the rates of subsidence and stretching were much lower and were focused within smaller geographic areas structural elements include asymmetric half grabens and less common full grabens with central highs the three superimposed tectonic episodes resulted in the subsidence of nnw to nw trending rift sub basins this gave rise to a wide variety of normal fault geometries displacements and growth histories planar domino style and listric normal f1 fault arrays are modeled the rotated f1 basement blocks typically are asymmetric and low standing and favour ne directed growth and material transport the f2 and f3 normal faults which have both ne and sw directed polarities often are listric and decouple younger syn rift strata from older f1 rotated and locked planar basement faults palinspastic restorations and forward modeling of three regional cross sections suggest that f1 faults account for 65 80 of total crustal extension stretching factors across the interior sudan rifts vary between 1 25 and 1 40 this range is considered to be a minimum since restored sections do not cross f3 depocenters total crustal extension across the muglad plus the melut rift basins exceeds 75 km

geodynamic evolution of the central dinarides abstract the central part of the dinarides unlike the northwestern and southeastern dinarides shows a consistent pattern in the distribution of the large tectonostratigraphic units from southwest apulia to northeast the following five main units originating in different parts of the mesozoic tethys can be distinguished 1 adriatic dinaridic carbonate platform formations 2 carbonate clastic units flysch bosniaque of the passive continental margin 3 ophiolite bearing formations of the dinaridic ophiolite zone also containing radiolarites greywackes and shales including melange formations and overstepped late jurassic to cretaceous cover sequences 4 active continental margin units represented by upper cretaceous palaeogene trench sediments with blueschists tectonized ophiolite melange alpine medium pressure metamorphic rocks originated from upper cretaceous palaeogene sediments and alpine synkinematic granitoids 5 a nappe consisting of allochthonous palaeozoic triassic formations which is thrust onto the ophiolites and genetically related sedimentary formations the frontal parts of this nappe directly overlie the northeastern margin of the adriatic dinaridic carbonate platform i e the external dinarides the evolution of the central dinarides was controlled by a sequence of tectonic events which took place within the alpine cycle 1 rifting processes lasting some 40 50 ma which started in the late permian and ended in the norian 2 opening of the oceanic dinaridic tethys commenced in the late triassic and persisted for some 70 80 ma until the end of the jurassic 3 subduction processes and emplacement of ophiolites started in late jurassic early cretaceous times during the closing phase of the dinaridic ocean or dinaridic tethys the palaeozoic triassic nappe was emplaced on the ophiolites the thrusting was accompanied by alpine metamorphism 120 100 ma 4 the main alpine deformational event and medium pressure metamorphism with synkinematic granite plutonism took place in late eocene early oligocene times when the ophiolite and palaeozoic triassic nappes were emplaced on the adriatic dinaridic carbonate platform which at the same time was deformed resulting in the development of the external dinarides fold and thrust belt

paradigms new and old for ultrahigh pressure tectonism regional ultrahigh pressure uhp metamorphic terranes exhibit a spectrum of lithological structural and petrological characteristics that result from the geodynamic processes that formed and exhumed them at least six geodynamic processes can be envisioned to have carried continental rocks to mantle depths i continental margin subduction ii microcontinent subduction iii sediment subduction iv intracontinental subduction v subduction erosion and vi foundering of a crustal root most of these processes have been investigated through numerical or analog models and most have been invoked for one or more specific occurrences of uhp rocks at least six geodynamic processes can be envisioned to have exhumed uhp continental rocks i eduction ii microplate rotation iii crustal stacking iv slab rollback v channel flow and vi trans mantle diapirs most of these processes have also been investigated through numerical or analog models and all have been invoked to explain the exhumation of at least one uhp terrane more detailed and systematic field investigations are warranted to assess the predictions of numerical models and more sophisticated and realistic numerical models are required to replicate and explain the petrological structural and chronological data obtained from uhp terranes

salt diapir reactivation and normal faulting in an oblique extensional system vulcan sub basin nw australia oblique extension and salt diapirism have their own distinct mechanisms that control the geometry and kinematics of structures in this study we document a geological phenomenon from the vulcan sub basin in nw australia that combines these processes a salt diapir reactivated in an oblique extensional system detailed structural analysis of this natural example with a focus on normal fault systems allows characterization of the oblique extensional system and investigation of how the pre existing structural fabrics and salt diapir control deformation and interact with each other under oblique extension after comparison with forward modelling results and using constraints from geological evidence our fault strike analysis indicates that the neogene flexural extension orientation in the oblique extensional system is around 347 revealing a perpendicular relationship between extension direction and fault strikes from the deformation zone the salt diapir reactivated during neogene extension strongly influences local structure in the oblique extensional system by altering fault strikes stepping patterns deformation zone width and fault density indicative of a stress strain concentration effect of the salt diapir owing to its extremely low strength these results provide valuable insights into the understanding of oblique extensional systems the geomechanical role of salt during extension and the neogene tectonic evolution of nw australia supplementary material dominant seismic frequency analysis uninterpreted seismic profiles additional structural and isochron maps a 3d view of fault systems and original measurements of the fault system are available at http doi org 10 6084 m9 figshare c 3148321

constraining south atlantic growth with seafloor spreading data recent models of south atlantic opening history focus on early plate divergence by incorporating intracontinental deformation which is poorly constrained aiming to avoid the uncertainties in this approach we model the entire divergence history with a joint inversion for seafloor spreading data for this history the pre campanian motion parameters are the first to feature formal uncertainty estimates we date the onset of spreading at 138 ma with movement along intracontinental accommodation zones leading to the assembly of south america by 123 ma and africa by 106 ma part of the ridge in the agulhas basin jumped westward soon afterward toward the bouvet plume initiating the motion of a short lived malvinas plate the ne georgia and maud rises and agulhas plateau formed as a large igneous province over the plume farther north part of the ridge jumped eastward toward the tristan plume around 94 93 ma but seems not to have resulted in independent plate motion our results show that the south atlantic grew by diachronous breakup of continents on just two plates cretaceous intracontinental deformation in south america and africa can be interpreted in terms of the accommodation of stress associated with northward propagation of this process the pattern of accommodation is usually envisaged as focusing all of the strain in narrow belts with our rotations a commonly used set of such belts accounts instead for just 42 67 of the implied total strain we suggest that the remainder was accommodated at all scales within the continental interiors and the extended continental margins

controls of inherited lithospheric heterogeneity on rift linkage numerical and analog models of interaction between the kenyan and ethiopian rifts across the turkana depression inherited rheological structures in the lithosphere are expected to have large impact on the architecture of continental rifts the turkana depression in the east african rift connects the main ethiopian rift to the north with the kenya rift in the south this region is characterized by a nw se trending band of thinned crust inherited from a mesozoic rifting event which is cutting the present day n s rift trend at high angle in striking contrast to the narrow rifts in ethiopia and kenya extension in the turkana region is accommodated in sub parallel deformation domains that are laterally distributed over several hundred kilometers we present both analog experiments and numerical models that reproduce the along axis transition from narrow rifting in ethiopia and kenya to a distributed deformation within the turkana depression similarly to natural observations our models show that the ethiopian and kenyan rifts bend away from each other within the turkana region thus forming a right lateral stepover and avoiding a direct link to form a continuous n s depression the models reveal five potential types of rift linkage across the pre existing basin three types where rifts bend away from the inherited structure connecting via a 1 wide or 2 narrow rift or by 3 forming a rotating microplate 4 a type where rifts bend towards it and 5 straight rift linkage the fact that linkage type 1 is realized in the turkana region provides new insights on the rheological configuration of the mesozoic rift system at the onset of the recent rift episode

dynamics and thermodynamics of the mean transpolar drift and ice thickness in the arctic ocean abstracta theory for the mean ice thickness and the transpolar drift in the arctic ocean is developed asymptotic expansions of the ice momentum and thickness equations are used to derive analytic

late miocene extension in coastal sonora mexico implications for the evolution of dextral shear in the proto gulf of california oblique rift abstract the timing kinematics and processes responsible for the rapid transition from subduction to oblique rifting and the localization of the pacific north america plate boundary in the gulf of california are not well understood well exposed volcanic rocks deposited between 15 and 10 ma in the sierra bacha coastal sonora mexico preserve a record of late miocene deformation on the eastern rifted margin of the gulf of california and offer new insights into the timing and kinematic evolution of oblique rifting detailed geologic mapping fault kinematic analysis u pb and 40ar 39ar geochronology and paleomagnetic data reveal that the 2 km thick composite volcanic section is cut by a series of southwest dipping domino style normal faults and uniformly tilted down to the northeast palinspastic cross section restoration suggests that the region experienced ca 55 60 northeast southwest directed extension between 11 7 and 10 9 ma fault kinematic data reflect relatively minor dextral transtension either following or during the later stages of extension paleomagnetic results indicating modest clockwise vertical axis block rotation suggest that dextral shear was concentrated in the southwest of the study area near the modern coastline these results support an emerging model in which dextral strain was not ubiquitous across sonora and did not initiate immediately following the 12 5 ma transition from subduction to oblique rifting instead strain east of the baja california microplate at this latitude evolved from extension dominated transtension prior to 8 ma to dextral shear dominated transtension by 7 6 ma the onset of dextral shear in coastal sonora likely resulted from an increase in rift obliquity due to a change in relative plate motion direction at 8 ma the increase in rift obliquity and resultant onset of significant strike slip faulting played a crucial role in facilitating subsequent plate boundary localization and marine incursion in the northern gulf of california by 6 ma and continental rupture at 2 1 ma

tertiary paleomagnetic results and structural analysis from the transdanubian range hungary rotational disintegration of the alcapa unit abstract we carried out an integrated paleomagnetic and structural study in the transdanubian range western and central hungary as a result the tertiary tectonic history of this area can be characterized by three events of counterclockwise ccw rotation and four or five phases of brittle deformation the change of the orientation of stress axes between phases is mainly apparent and reflects the rotation of the faults predating a particular rotation event the first two rotation events r1 and r2 were probably governed by the rollback mechanism of the subducting european plate we suggest that these rotations were taking place from 18 17 and 16 14 5 ma respectively i e simultaneously with the rotations of the north hungarian paleogene basin and the main part of the western carpathians however the angle of both rotations was less in the transdanubian range due to increasing distance from the subduction front the differential rotation was accommodated by extensional faulting by formation of a graben system on the other hand the youngest rotation event r3 seems to be connected to the renewed rotation of the adriatic plate around 5 ma our combined data set strongly supports earlier conclusions namely that the different subunits of the eastern alpine western carpathian northern pannonian unit alcapa did not form a rigid unit although they moved in similar manner

cenozoic granitoids in the dinarides of southern serbia age of intrusion isotope geochemistry exhumation history and significance for the geodynamic evolution of the balkan peninsula two age groups were determined for the cenozoic granitoids in the dinarides of southern serbia by high precision single grain u pb dating of thermally annealed and chemically abraded zircons 1 oligocene ages kopaonik drenje eljin ranging from 31 7 to 30 6 ma 2 miocene ages golija and polumir at 20 58 20 17 and 18 06 17 74 ma respectively apatite fission track central ages modelling combined with zircon central ages and additionally local structural observations constrain the subsequent exhumation history of the magmatic rocks they indicate rapid cooling from above 300 c to ca 80 c between 16 and 10 ma for both age groups induced by extensional exhumation of the plutons located in the footwall of core complexes hence miocene magmatism and core complex formation not only affected the pannonian basin but also a part of the mountainous areas of the internal dinarides based on an extensive set of existing age data combined with our own analyses we propose a geodynamical model for the balkan peninsula the late eocene to oligocene magmatism which affects the adria derived lower plate units of the internal dinarides was caused by delamination of the adriatic mantle from the overlying crust associated with post collisional convergence that propagated outward into the external dinarides miocene magmatism on the other hand is associated with core complex formation along the southern margin of the pannonian basin probably associated with the w directed subduction of the european lithosphere beneath the carpathians and interfering with ongoing dinaridic hellenic back arc extension

south atlantic fits and intraplate boundaries in africa and south america abstract the misfit problems raised by the pre drift reconstructions of the south and equatorial atlantic compel us to resort to intraplate deformations it is shown that acceptable deformations of the african plate in line with the benue trough and the transafrican rifts and shear zones provide a far from satisfactory solution to the geometrical misfit problems in the south atlantic these problems can instead be alleviated by considering a degree of deformation of the south american plate along an intraplate boundary in line with the parana province the rio grande rise and the walvis ridge in spite of the scarcity of field observations in this area of south america we show that such a deformation cannot be ruled out but it will have to be associated with deformations in the equatorial atlantic and in other areas of the african and south american plates

oblique rifting of the equatorial atlantic why there is no saharan atlantic ocean rifting between large continental plates results in either continental breakup and the formation of conjugate passive margins or rift abandonment and a set of aborted rift basins the nonlinear interaction between key parameters such as plate boundary configuration lithospheric architecture and extension geometry determines the dynamics of rift evolution and ultimately selects between successful or failed rifts in an attempt to evaluate and quantify the contribution of the rift geometry we analyze the early cretaceous extension between africa and south america that was preceded by 20 30 m y of extensive intracontinental rifting prior to the final separation between the two plates while the south atlantic and equatorial atlantic conjugate passive margins continued into seafloor spreading mode forming the south atlantic ocean basin cretaceous african intraplate rifts eventually failed soon after south america broke away from africa we investigate the spatiotemporal dynamics of rifting in these domains through a joint plate kinematic and three dimensional forward numerical modeling approach addressing 1 the dynamic competition of atlantic and african extensional systems 2 two stage kinematics of the south atlantic rift system and 3 the acceleration of the south america plate prior to final breakup oblique rifts are mechanically favored because they require both less strain and less force in order to reach the plastic yield limit this implies that rift obliquity can act as selector between successful ocean basin formation and failed rifts explaining the success of the highly oblique equatorial atlantic rift and ultimately inhibiting the formation of a saharan atlantic ocean we suggest that thinning of the last continental connection between africa and south america produced a severe strength velocity feedback responsible for the observed increase in south america plate velocity

subduction evolution of the dinarides and the cretaceous orogeny in the eastern alps hints from a new paleotectonic interpretation

geodynamic evolution of ophiolites from albania and greece dinaric hellenic belt one two or more oceanic basins all the geological constraints for an exhaustive reconstruction of the triassic to tertiary tectonic history of the southern dinaric hellenic belt can be found in albania and greece this article aims to schematically reconstruct this long tectonic evolution primarily based on a detailed analysis of the tectonic setting the stratigraphy the geochemistry and the age of the ophiolites in contrast to what was previously reported in the literature we propose a new subdivision on a regional scale of the ophiolite complexes cropping out in albania and greece this new subdivision includes six types of ophiolite occurrences each corresponding to different tectonic units derived from a single obducted sheet these units are represented by 1 sub ophiolite melange 2 triassic ocean floor ophiolites 3 metamorphic soles 4 jurassic fore arc ophiolites 5 jurassic intra oceanic arc ophiolites and 6 jurassic back arc basin ophiolites the overall features of these ophiolites are coherent with the existence of a single though composite oceanic basin located east of the adria pelagonian continental margin this oceanic basin was originated during the middle triassic and was subsequently early jurassic affected by an east dipping intra oceanic subduction this subduction was responsible for the birth of intra oceanic arc and back arc oceanic basins separated by a continental volcanic arc during the early to middle jurassic from the uppermost middle jurassic to the early cretaceous an obduction developed during which the ophiolites were thrust westwards firstly onto the neighboring oceanic lithosphere and then onto the adria margin

evidence of magmatic activity related to middle jurassic and lower cretaceous rifting from northeastern brazil ceara mirim k ar age palaeomagnetism petrology and sr 1bnd isotope characteristics the mesozoic magmatic activity in the easternmost part of ne brazil ceara mirim is mainly represented by two pyroxene tholeiitic dykes only few dykes have alkaline character k ar ages and palaeomagnetism data indicate that ceara mirim dykes are of middle jurassic 175 160 ma and early cretaceous 140 130 ma age both middle jurassic and lower cretaceous dykes have high incompatible element concentrations and tio2 with the lower contents generally confined to the middle jurassic dykes rare tholeiitic dykes low in tio2 and incompatible elements are present sr 1bnd isotopic and other chemical data do not support appreciable crustal contamination and in a 87sr86sr vs 143nd144nd diagram almost all the dykes plot in a narrow area of the enriched quadrant of the mantle array tholeiitic and alkaline ceara mirim dykes are related to different parent magmas probably originating by different degrees of melting of garnet peridotite mantle sources characterized by distinct sr 1bnd isotope compositions and small scale chemical heterogeneities ceara mirim tholeiitic dykes show close mineralogical chemical and isotopic similarities with the lower cretaceous high tio2 tholeiites from maranhao sardinha intrusives and parana northern province basins in general chemical and sr 1bnd isotope data for high and low tio2 brazilian mesozoic tholeiites appear to be related to time integrated enriched and depleted mantle components respectively subcontinental mantle heterogeneity is believed to be due to variable enriched components related to metasomatic processes the ceara mirim jurassic dykes correlate well in terms of composition and tectonic setting with the analogue tholeiitic dyke swarms from the benue trough and can be related to the opening of the central atlantic ocean the lower cretaceous ceara mirim magmatic activity corresponds to the coeval one of the benue trough and can be related to the early rifting events responsible for the opening of the equatorial domain of the south atlantic whose oceanic crust formed between 120 and 100 ma

tectonic control of the oil rich large igneous carbonate salt province of the south atlantic rift abstract the early cretaceous south atlantic magmatic province samp which includes the parana etendeka lip produced about 8 million km 3 of tholeiitic basalt and diabase over an area of 4 million km 2 huge pre salt oil reserves discovered in 2007 by petrobras in non marine carbonates are estimated at more than 45 billion barrels here we show the close causal relationship of the southward increasing width of the wedge shaped south atlantic rift with the similarly southward increase in igneous activity in the thicknesses of non marine carbonate and salt and in the size of oil reserves all controlled mainly by south america s early clockwise rotation away from africa about a pole in its northeast large diabase dike swarms transversal to the rift witness to south america s rotation that opened in its wake the southward widening south atlantic rift westward increasing pressure on the equatorial margin by south america s clockwise rotation forced open the benue trough and created pre late aptian folds in the demerara plateau and in brazil s solimoes upper amazonas basin prerift and synrift volcanic activity increases southward culminating in the parana etendeka lip and in the offshore volcanic sdrss that continue southward to the cape basin berriasian valanginian rift sediments deposited from about 145 ma 10 ma before the flood basalts of the parana etendeka lip the largest transversal dike swarm continued in the proto walvis ridge that separated the central south atlantic endorheic rift basin from the sea in the south erosion and leaching of basalts supplied ca mg and sio 2 to the endorheic basin for the deposition of non marine carbonates and authigenic clays basalt flows intercalated with carbonates nearly until salt deposition about 113 ma hypogenic leaching of carbonates by mantle derived co 2 created optimal reservoirs supergiant oil deposits occur where the widest endorheic basin and the volcanic province overlap

rifted margin architecture and crustal rheology reviewing iberia newfoundland central south atlantic and south china sea abstract crustal rheology controls the style of rifting and ultimately the architecture of rifted margins here we review the formation of three magma poor margin pairs iberia newfoundland the central segment of the south atlantic rift and the south china sea by integrating observational data into a numerical forward modelling framework we utilise a 2d version of the finite element code slim3d which includes nonlinear temperature and stress dependent elasto visco plastic rheology and is able to reproduce a wide range of rift related deformation processes such as flexure lower crustal flow and faulting extension in cold strong or thin crust is accommodated by brittle faults and ductile shear zones that facilitate narrow rifts with asymmetric fault geometries hot weak or thick continental crust is dominated by ductile deformation and often extends symmetrically into a wide rift system this simple recipe provides the standard framework to understand initial rift geometry however it is insufficient to account for the dynamics of intermediate and late rift stages that shape the final margin architecture asymmetric conjugate margins where one side is wide and the other narrow can be formed via both wide and narrow rift styles which we reproduce with weak and strong crustal rheologies respectively exemplified by the iberia newfoundland conjugates and the central south atlantic we define three characteristic rift phases an initial phase of simultaneous faulting an intermediate phase of rift migration that involves sequential fault activity and finally the breakup phase crustal rheology plays an overarching role in governing the dynamics of these asymmetric margins we illustrate that weak rheologies generally prolong the phase of simultaneous faulting while rift migration is enabled by initial fault asymmetry as well as relatively weak crust formation of the predominantly symmetric and wide margins of the south china sea was controlled by extraordinarily weak crust that extended the phase of simultaneous faulting until breakup the weak crustal rheology of this region relates to the south china sea s pre rift history where plate convergence lead to crustal thickening and magmatic additions in a back arc regime shortly before the onset of rifting

tectono stratigraphic and kinematic evolution of the southern apennines calabria peloritani terrane system italy abstract temporal controls such as sedimentation ages in foredeep and wedge top basins combined with information about stratigraphic and metamorphic evolution ages and characterization of magmatic rocks deep structures burial and exhumation histories allowed us to obtain kinematic estimations of the southern apennines calabria peloritani terrane system evolution from the late oligocene to recent calculated thrust front velocities suggest to subdivide the orogenic evolution in main five kinematic stages characterized by different velocity trends nine kinematic complexes from a to i i e sets of tectonic units deformed in the same time range are determined according to foredeep ages these complexes bounded by main regional thrust faults encompass one or more tectonic sub units and successions of different paleoenvironment domains paleogeographic evolution model indicates according to available paleomagnetic data a counterclockwise rotation with a mean angle of 60 for the apennine platform carbonates whereas a mean angle of 20 for the eastern sector of the apennine platform and western side of apulian platform shortening estimations for the apennine successions show values ranging between 55 and 88 and a linear best fit indicating an increase from 60 nw sector to ca 90 se sector such high values are consistent with a deformation dominated by a thin skinned tectonics on the contrary the low value of 28 calculated for mt alpi suggests an exhumation ruled by high angle deep seated structures characterized by limited displacements tectonic vergences referred to middle late miocene late miocene and pliocene middle pleistocene when restored indicate an average eastward tectonic transport finally tectonic evolution is summarized in eleven schematic cross sections and corresponding paleogeographic maps

the late jurassic to present evolution of the andean margin drivers and the geological record 1 uncommonly long lived subduction and variable plate geometry along the south american andean plate margin resulted in diverse relationships between magmatic flux and extensional and contractional deformation as recorded by the overriding continental plate convergence velocities absolute overriding plate velocities and subducting slab ages were resolved along the trench from 170 ma to the present using a recently developed kinematic global plate model to identify any relationship between subduction conditions deformation style and magmatic features in the overriding plate key correlations reflect the dependence of macroscopic crustal strain style on subduction mechanism and relative plate vectors extensional back arc basins involving mafic oceanic crust developed only when the overriding plate velocity of south america was directed away from the trench and the modeled age of the subducting slab was older than 50 myr the development of fold and thrust belts and uplift of major plateaus was accompanied by trench normal convergence velocities in excess of 4 cm yr parameters investigated in this study revealed no correlation with the timing of major magmatic events nor was any correlation observed with the structural style of fold and thrust belts

tectono sedimentary evolution of the eastern gulf of aden conjugate passive margins narrowness and asymmetry in oblique rifting context abstract here we focus on the yet unexplored eastern gulf of aden on socotra island yemen southeastern oman and offshore conjugate passive margins between the socotra hadbeen shfz and the eastern gulf of aden fracture zones our interpretation leads to onshore offshore stratigraphic correlation between the passive margins we present a new map reflecting the boundaries between the crustal domains proximal necking hyper extended exhumed mantle proto oceanic and oceanic domains and structures using bathymetry magnetic surveys and seismic reflection data the most striking result is that the magma poor conjugate margins exhibit asymmetrical architecture since the thinning phase upper rupelian burdigalian their necking domains are sharp 40 10 km wide and their hyper extended domains are narrow and asymmetric 10 40 km wide on the socotra margin and 50 80 km wide on the omani margin we suggest that this asymmetry is related to the migration of the rift center producing significant lower crustal flow and sequential faulting in the hyper extended domain throughout the oligo miocene rifting far field forces dominate and the deformation is accommodated along ew to n110 e northward dipping low angle normal faults convection in the mantle near the shfz may be responsible of change in fault dip polarity in the omani hyper extended domain we show the existence of a northward dipping detachment fault formed at the beginning of the exhumation phase burdigalien it separates the northern upper plate oman from southern lower plate socotra island and may have generated rift induced decompression melting and volcanism affecting the upper plate we highlight multiple generations of detachment faults exhuming serpentinized subcontinental mantle in the ocean continent transition associated to significant decompression melting final detachment fault may have triggered the formation of a proto oceanic crust at 17 6 ma and induced late volcanism up to 10 ma finally the setting up of a steady state oceanic spreading center occurs at 17 ma

evidence for jurassic subduction from the northern calcareous alps berchtesgaden austroalpine germany the closure of the western part of the neotethys ocean started in late early jurassic the middle to early late jurassic contraction is documented in the berchtesgaden alps by the migration of trench like basins formed in front of a propagating thrust belt due to ophiolite obduction these basins propagated from the outer shelf area hallstatt realm to the interior continent hauptdolomit dachstein platform realm the basins were separated by nappe fronts forming structural highs this scenario mirrors syn orogenic erosion and deposition in an evolving thrust belt active basin formation and nappe thrusting ended around the oxfordian kimmeridgian boundary followed by the onset of carbonate platforms on structural highs starved basins remained between the platforms rapid deepening around the early late tithonian boundary was induced by extension due to mountain uplift and resulted in the reconfiguration of the platforms and basins erosion of the uplifted nappe stack including obducted ophiolites resulted in increased sediment supply into the basins and final drowning and demise of the platforms in the berriasian the remaining early cretaceous foreland basins were filled up by sediments including siliciclastics the described jurassic to early cretaceous history of the northern calcareous alps accords with the history of the western carpathians the dinarides and the albanides where 1 age dating of the metamorphic soles prove late early to middle jurassic inneroceanic thrusting followed by late middle to early late jurassic ophiolite obduction 2 kimmeridgian to tithonian shallow water platforms formed on top of the obducted ophiolites and 3 latest jurassic to early cretaceous sediments show postorogenic character

the pindos fold and thrust belt greece inversion kinematics of a passive continental margin continuous exposure in the pindos mountain chain greece and the detailed stratigraphic measurements in the area enable us to construct eight balanced cross sections across the pindos fold and thrust belt pftb and to approach quantitatively some parameters which controlled foreland evolution the 160 km wide passive continental margin of the apulian continent in greece was progressively shortened from east to west at rates of 6 mm year between the early oligocene and late eocene from the rear to the frontal part of the wedge fault bend folds duplexes and imbricates were formed while strain was partitioned into faulting 34 layer parallel shortening 23 and buckling 9 foreland subsidence and internal deformation of the orogenic wedge are strongly affected by two parameters of equal importance the thrust load of the overthrusted microcontinents and the rigidity of the underthrusted apulian passive margin changes in the thickness of the pre orogenic sediments and reactivated transform faults induced salients during the lower miocene the orogenic wedge in the peloponnese suffered additional uplift and westward gravitational gliding induced by the intracontinental subduction of the palaeozoic rift zone of the phyllite quartzite series which was reactivated and returned to the earth s surface during the hellenic orogeny

a quantitative analysis of transtensional margin width abstract continental rifted margins show variations between a few hundred to almost a thousand kilometres in their conjugated widths from the relatively undisturbed continent to the oceanic crust analogue and numerical modelling results suggest that the conjugated width of rifted margins may have a relationship to their obliquity of divergence with narrower margins occurring for higher obliquity we here test this prediction by analysing the obliquity and rift width for 26 segments of transtensional conjugate rifted margins in the atlantic and indian oceans we use the plate reconstruction software gplates www gplates org for different plate rotation models to estimate the direction and magnitude of rifting from the initial phases of continental rifting until breakup our rift width corresponds to the distance between the onshore maximum topography and the last identified continental crust we find a weak positive correlation between the obliquity of rifting and rift width highly oblique margins are narrower than orthogonal margins as expected from analogue and numerical models we find no relationships between rift obliquities and rift duration nor the presence or absence of large igneous provinces lips

abrupt plate accelerations shape rifted continental margins rifted margins are formed by persistent stretching of continental lithosphere until breakup is achieved it is well known that strain rate dependent processes control rift evolution yet quantified extension histories of earth s major passive margins have become available only recently here we investigate rift kinematics globally by applying a new geotectonic analysis technique to revised global plate reconstructions we find that rifted margins feature an initial slow rift phase less than ten millimetres per year full rate and that an abrupt increase of plate divergence introduces a fast rift phase plate acceleration takes place before continental rupture and considerable margin area is created during each phase we reproduce the rapid transition from slow to fast extension using analytical and numerical modelling with constant force boundary conditions the extension models suggest that the two phase velocity behaviour is caused by a rift intrinsic strength velocity feedback which can be robustly inferred for diverse lithosphere configurations and rheologies our results explain differences between proximal and distal margin areas and demonstrate that abrupt plate acceleration during continental rifting is controlled by the nonlinear decay of the resistive rift strength force this mechanism provides an explanation for several previously unexplained rapid absolute plate motion changes offering new insights into the balance of plate driving forces through time

recognizing remnants of magma poor rifted margins in high pressure orogenic belts the alpine case study magma poor rifted margins are being increasingly recognized in present day atlantic type systems however findings of fossil areas floored by exhumed mantle or hyper extended crust are comparatively rare within orogenic belts that were originated through the inversion of pre existing rifted margins this discrepancy may be due to the common reactivation of lithological contacts during subduction orogeny potentially masking pre orogenic relationships and most importantly to the frequent lack of a preorogenic layer cake architecture hindering retro deformation of multiply deformed tectonic units this study outlines a methodology to detect sections of magma poor hyper extended rifted margins without a layer cake architecture in multiply deformed metamorphosed terrains this approach is defined by comparison to well studied examples of fossil analogues preserved in weakly deformed parts of alpine orogens in the latter domains continental basement and hydrated peridotites were exhumed at the basin floor during jurassic rifting along long offset detachment systems extensional geometries locally resulted in tectonic sampling of laterally discontinuous slivers of allochthonous continental basement and pre rift sediments fromthe hanging wall blocks lithostratigraphic associations consisting of continental basement rocks directly juxtaposed with syn to post rift meta sediments and or serpentinized subcontinental mantle are widespread within sections of alpine type orogenic belts that underwent high to ultra high pressure metamorphism however similar associations may arise from a variety of processes other than rift related lithospheric thinning in magma poor environments including subduction melange dynamics or deposition of sedimentary melanges along convergent divergent margins the partial preservation of rift related lithostratigraphic associations may still be assessed despite the lack of biostratigraphic evidence by 1 the consistency of the lithostratigraphic architecture over large areas despite pervasive alpine deformation which rules out chaotic mixing during subduction exhumation 2 the presence of clasts of basement rocks in the neighboringmeta sediments indicating the original proximity of the different lithologies 3 evidence of brittle deformation in continental basement and ultramafic rocks pre dating alpine metamorphism indicating that theywere juxtaposed by fault activity prior to the deposition of post rift sediments and 4 the similar alpine tectono metamorphic evolution of ophiolites continental basement and meta sediments a re assessment of basement cover relationships in the north western alps following this approach combined with published studies on exhumedmantle domains sampled in the rest of thewestern alps indicates that several tectono metamorphic units fromthemost deformed metamorphosed part of the belt between the canavese line and the penninic front sample hyper extended lithosphere related to the jurassic opening of the western tethys relative plate motion during cretaceous tertiary basin inversion was largely accommodated at the transition between areas floored by hyper extended crust or hydrated subcontinental mantle and domains consisting of thicker continental crust as a result distal margins were preferentially subducted whereas the proximal domains and the brianconnais paleo high underwent relatively minor deformation and metamorphism the high pressure alpine tectono metamorphic units were probably detached from the downgoing lithosphere along a hydration front that is typically observed in present day distal margins the recognition of preserved pre alpine relationships between continental basement post rift sediments and or serpentinized ultramafic rocks calls for a re assessment of the relative role of subduction and rifting dynamics in establishing the present day orogen architecture

late cretaceous intra oceanic magmatism in the internal dinarides northern bosnia and herzegovina implications for the collision of the adriatic and european plates abstract the kozara mountains of northern bosnia and hercegovina form part of the internal dinarides and host two tectonically juxtaposed ophiolitic successions of different age the southern part of the kozara mountains exposes the western vardar ophiolitic unit which was obducted onto the adriatic margin in the late jurassic the northern part exposes a bimodal igneous succession that was thrust onto the western vardar ophiolitic unit during the latest cretaceous to early paleogene this bimodal igneous succession comprises isotropic gabbros doleritic dikes basaltic pillow lavas and rhyolites pelagic limestones intercalated with pillow lavas yielded a campanian globotruncanid association consistent with concordant u pb ages on zircons from dolerites and rhyolites of 81 39 0 11 and 81 6 0 12 ma respectively chondrite normalised rare earth element patterns of the bimodal igneous rocks show enrichment of lree over hree primitive mantle normalised multi element diagrams do not reveal significant depletion of hfse the end t and initial 87sr 86sr isotopic values range from 4 4 to 6 3 and from 0 70346 to 0 70507 respectively suggesting an intraoceanic origin the bimodal igneous succession is unconformably overlain by maastrichtian to paleocene siliciclastics that contain abundant ophiolitic detritus suggesting reworking of the campanian magmatics an eocene turbiditic sandstone succession unconformably covers both the western vardar ophiolitic unit and the late cretaceous bimodal igneous successions these observations suggest that the adriatic plate and the europe derived tisza and dacia mega units were still separated by a deep basin floored by oceanic lithosphere until the campanian and that its closure did not occur before the maastrichtian to earliest paleogene this late cretaceous oceanic domain probably represented a remnant of the vardar ocean or alternatively the alpine tethys possibly the traces of both oceanic domains were connected in the area

slip history of the la cruz fault development of a late miocene transform in response to increased rift obliquity in the northern gulf of california abstract the gulf of california rift has accommodated oblique divergence of the pacific and north america plates in northwestern mexico since miocene time due to its infancy its rifted margins preserve a rare onshore record of early continental break up processes and an opportunity to investigate the role of rift obliquity in strain localization we map rift related structures and syn tectonic basins on southern isla tiburon a proximal onshore exposure of the rifted north america margin we integrate analysis and geochronology of syn tectonic sedimentary basins and mapping of crosscutting relationships to characterize the style and timing of fault activity on southern isla tiburon an early phase of extension initiated between 19 17 ma and 12 2 ma subsequently these normal faults and related basins were cut by the la cruz strike slip fault and buried by deposits of the la cruz basin an elongate fault controlled trough coextensive with the la cruz fault crosscutting relationships show that the nw striking la cruz fault accrued 5 2 km of dextral slip 8 4 ma the la cruz fault and parallel tiburon transform were kinematically linked to detachment faulting that accommodated latest miocene to pliocene oblique opening of the offshore upper tiburon pull apart basin the onset of strike slip faulting on isla tiburon was synchronous with the 8 6 ma onset of transform faulting and basin formation along 1000 km of the reconstructed pacific north america plate boundary this transition coincides with the commencement of a clockwise azimuthal shift in pacific north america relative plate motion that increased the obliquity of the gulf of california rift and formed the gulf of california shear zone the record from the proto gulf of california illustrates how highly oblique rift geometries where transform faults are kinematically linked to pull apart basins enhance the ability of continental lithosphere to rupture and ultimately hasten the formation of new oceanic rift basins

how much magma is required to rift a continent article i nfo article history many continental rifts are associated with and preceded by the formation of large igneous provinces partial melting of a large region of anomalously hot upwelling mantle isrequired to explain these huge volumes of pre and syn rift basaltic magma the uplift associated with a shallow region of hot mantle is often invoked as a cause of the rift push force that may drive the observed extension the rift push force is likely to be an order of magnitude toosmall todrive tectonicstretching of normal continentallithosphere but may besufficient to drive opening of lithosphere cutting dikes intrusion of a sequence of such dikes along a narrow zone may provide enough heat to significantly weaken the lithosphere here we use a newly developed 2d numerical approach in which magma filled dikes open in continental lithosphere in response to an evolving model stress field and the advection and diffusion of heat is tracked to investigate the relation between the volume of magma and the amount of lithospheric weakening the available rifting force lithospheric structure and parameters controlling magma flux are varied in the numerical simulations for continental lithosphere 60 km thick hl h1200 c heat diffusion is unimportant and only a small amount of magma is required 10 20 m y similar to magmatic rifts like the red sea

evolution of the adriatic carbonate platform palaeogeography main events and depositional dynamics abstract the adriatic carbonate platform adcp is one of the largest mesozoic carbonate platforms of the perimediterranean region its deposits comprise a major part of the entire carbonate succession of the croatian karst external or outer dinarides which is very thick in places more than 8000 m and ranges in age from the middle permian or even upper carboniferous to the eocene however only deposits ranging from the top of the lower jurassic toarcian to the top of the cretaceous can be attributed to the adcp defined as an isolated palaeogeographical entity although the entire carbonate succession of the karst dinarides was deposited within carbonate platform environments there were different types of carbonate platforms located in different palaeogeographical settings carboniferous to middle triassic mixed siliciclastic carbonate deposits were accumulated along the gondwanian margin on a spacious epeiric carbonate platform after tectonic activity culminating by regional middle triassic volcanism recorded throughout adria the african promontory a huge isolated carbonate southern tethyan megaplatform abbreviated as stm was formed with the area of the future adcp located in its inner part tectonic disintegration of the megaplatform during the middle to late early jurassic resulted in the establishment of several carbonate platforms including the adriatic apenninic and apulian separated by newly drowned deeper marine areas including the adriatic basin as a connection between the ionian and belluno basins lagonero basin and the area of the slovenian and bosnian troughs the adcp was characterised by predominantly shallow marine deposition although short or long periods of emergence were numerous as a consequence of the interaction of synsedimentary tectonics and eustatic changes also several events of temporary platform drowning were recorded especially in the late cretaceous when synsedimentary tectonics became stronger leading up to the final disintegration of the adcp the thickness of deposits formed during the 125 my of the adcp s existence is variable between 3500 and 5000 m the end of adcp deposition was marked by regional emergence between the cretaceous and the palaeogene deposition during the palaeogene was mainly controlled by intense synsedimentary tectonic deformation of the former platform area some carbonates mostly eocene in age were deposited on irregular ramp type carbonate platforms surrounding newly formed flysch basins and the final uplift of the dinarides reached its maximum in the oligocene miocene the adriatic carbonate platform represents a part although a relatively large and well preserved one of the broader shallow water carbonate platform that extended from ne italy to turkey although its continuity is somewhat debatable in the area near albanian greece boundary this large carbonate body which was deformed mostly in the cenozoic including a significant reduction of its width needs a specific name and the central mediterranean carbonate platform is proposed abbreviated to cmcp although the local names such as adcp for its nw part should be kept to enable easier communication and to facilitate description of local differences in platform evolution

accommodation of transpressional strain in the arabia eurasia collision zone new constraints from u th he thermochronology in the alborz mountains north iran the alborz range of n iran provides key information on the spatiotemporal evolution and characteristics of the arabia eurasia continental collision zone the southwestern alborz range constitutes a transpressional duplex which accommodates oblique shortening between central iran and the south caspian basin the duplex comprises nw striking frontal ramps that are kinematically linked to inherited e w striking right stepping lateral to obliquely oriented ramps new zircon and apatite u th he data provide a high resolution framework to unravel the evolution of collisional tectonics in this region our data record two pulses of fast cooling associated with sw directed thrusting across the frontal ramps at 18 14 and 9 5 7 5 ma resulting in the tectonic repetition of a fossil zircon partial retention zone and a cooling pattern with a half u shaped geometry uniform cooling ages of 7 6 ma along the southernmost e w striking oblique ramp and across its associated nw striking frontal ramps suggests that the ramp was reactivated as a master throughgoing n dipping thrust we interpret this major change in fault kinematics and deformation style to be related to a change in the shortening direction from ne to n nne the reduction in the obliquity of thrusting may indicate the termination of strike slip faulting and possibly thrusting across the iranian plateau which could have been triggered by an increase in elevation furthermore we suggest that 7 6 m y old s directed thrusting predated inception of the westward motion of the south caspian basin

style of rifting and the stages of pangea breakup pangea results from the progressive amalgamation of continental blocks achieved at 320 ma assuming that the ancient concept of active versus passive rifting remains pertinent as end members of more complex processes we show that the progressive pangea breakup occurred through a succession of rifting episodes characterized by different tectonic evolutions a first episode of passive continental rifting during the upper carboniferous and permian led to the formation of the neo tethys ocean then at the beginning of triassic times two short episodes of active rifting associated to the siberian and emeishan large igneous provinces lips failed the true disintegration of pangea resulted from 1 a triassic passive rifting leading to the emplacement of the central atlantic magmatic province 200 ma lip and the subsequent opening of the central atlantic ocean during the lowermost jurassic and from 2 a lower jurassic active rifting triggered by the karoo ferrar lip 183 ma which led to the opening of the west indian ocean the same sequence of passive then active rifting is observed during the lower cretaceous with in between the parana etendeka lip at 135 ma we show that the relationships between the style of rifts and their breakdown or with the type of resulting margins as magma poor or magma dominated are not straightforward finally we discuss the respective role of mantle global warming promoted by continental agglomeration and mantle plumes in the weakening of the continental lithosphere and their roles as rifting triggers

episodic formation of neotethyan ophiolites tibetan plateau snapshots of abrupt global plate reorganizations during major episodes of supercontinent breakup abstract neotethyan ophiolites along the bangong nujiang and yarlung tsangpo sutures tibetan plateau consist of mantle peridotite cumulates isotropic gabbro diabase plagiogranite and basaltic lava they comprise morb iab oib and boninitic rocks and mostly belong to supra subduction zone ssz type compositionally different rocks crystallized synchronously over a distance of 2000 km along the bangong nujiang and yarlung tsangpo sutures during the short periods of 190 182 and 132 120 ma respectively resembling the izu bonin mariana ibm proto arc the early jurassic bangong nujiang ophiolites formed in forearc settings during subduction initiation while the middle jurassic early cretaceous bangong nujiang ophiolites and the early cretaceous yarlung tsangpo ophiolites formed in forearc settings at pre existing subduction zones crystallization of the neotethyan ssz ophiolites from the eastern mediterranean middle east tibetan plateau to southeast asia and formation of the associated metamorphic rocks temporally coincided with major supercontinent breakup events 1 initial breakup of pangea in central atlantic and westernmost tethys 190 ma 2 separation of west and east gondwana 170 160 ma and initial opening of piemont ligurian tethys 175 164 ma 3 initial breakups of east and west gondwana 135 125 ma and 4 final breakup of gondwana 104 96 ma far field forces associated with abrupt global plate reorganizations may have triggered subduction initiation or transient interplate coupling decoupling at pre existing subduction zones leading to episodic formation of the neotethyan ssz ophiolites and rapid exhumation of metamorphic rocks in subduction zones the formation events of neotethyan ssz ophiolites and associated metamorphic rocks represent snapshots of global plate reorganizations during the major episodes of supercontinent breakup

quantifying the thermo mechanical impact of plume arrival on continental break up abstract the arrival of a plume head at earth s continental lithosphere is often considered to be an important factor for continental break up however the impact of plume impingement on strength and duration of a rift remains unclear in this study we quantify the mechanical and thermal influence of a plume i e lithosphere erosion on continental break up to do that we apply the three dimensional numerical code slim3d that features realistic elasto visco plastic rheology we model the thermo mechanical response of a segment of earth s lithosphere that is affected both by extension as well as plume related lithosphere erosion in order to evaluate the influence on the overall force budget we find that lithosphere erosion leads to a moderate lithospheric strength reduction of several tn m in a force limited environment however this strength reduction may have strong influence on the timing of continental break up or it may even control whether continental break up takes place at all additional reduction of the lithospheric strength is likely due to the massive emplacement of dikes that follows intensive melting within the plume head

dynamic processes controlling evolution of rifted basins abstract the extension of the lithosphere controlling the development of rifted basins is driven by a combination of plate boundary forces frictional forces exerted on the base of the lithosphere by the convecting asthenosphere and deviatoric tensional stresses developing over upwelling branches of the asthenospheric convection system although mantle plumes are not a primary driving force of rifting they play an important secondary role by weakening the lithosphere and by controlling the level of rift related volcanic activity a distinction between active and passive rifting is only conditionally justified the extension of the lithosphere depending on its rate and magnitude and the potential temperature of the asthenosphere can cause by adiabatic decompression partial melting of the lower lithosphere and upper asthenosphere in rift systems the level and timing of volcanic activity is highly variable the lack of volcanic activity implies passive rifting an initial passive rifting stage can be followed by a more active one during which magmatism plays an increasingly important role magmatic destabilization of the moho may account for the frequently observed discrepancy between upper and lower crustal extension factors combined with evidence for thermal thinning of the mantle lithosphere this suggest that the volume of the lithosphere is not necessarily preserved during rifting as advocated by conventional stretching models the structural style of rifts is controlled by the rheological structure of the lithosphere the availability of crustal discontinuities that can be tensionally reactivated the mode orthogonal or oblique and amount of extension and the lithological composition of pre and syn rift sediments simple shear extension prevails in rifts that subparallel the structural grain of the basement pure shear extension is typical for rifts cross cutting the basement grain pre existing crustal and mantle lithospheric discontinuities contribute to the localization of rift systems the duration of the rifting stage of extensional basins is highly variable stress field changes can cause abrupt termination of rifting in major rift systems progressive strain concentration on the zone of future crustal separation entails abandonment of lateral rifts depending on constraints on lateral block movements crustal separation can be achieved after as little as 9 my and as much as 280 my of rifting activity syn rift basin subsidence is controlled by isostatic adjustment of the crust to mechanical stretching of the lithosphere its magmatic inflation and thermal attenuation of the mantle lithosphere post rift basin subsidence is governed by thermal reequilibration of the lithosphere asthenosphere system deep seated thermal anomalies related to syn rift pull up of the asthenosphere lithosphere boundary have decayed after 60 my by about 65 and after 180 my by about 95 the magnitude of post rift subsidence is a function of the rift induced thermal anomaly and crustal density changes the potential temperature of the asthenosphere and initial water depths intraplate stresses can have an overprinting effect on post rift subsidence stretching factors derived from post rift subsidence analyses must be corrected for such effects

kinematics of retreating subduction along the carpathian arc romania kinematic axes and resultant vectors of displacement along the carpathian arc and the apuseni mountains aid in the reconstruction of retreating subduction along the carpathians the recent vertical position of the subducted slab below the vrancea area of the eastern carpathians represents the final rollback stage of a small fragment of oceanic lithosphere formerly situated between the moesian and east european plates the ages and locations of the eruption centers of the andesitic volcanic chain along the carpathian arc in the overriding plate as well as the thrust directions are used as markers to reconstruct the rollback area of the subducted slab between the moesian and east european plates

continental rifting parallel to ancient collisional belts an effect of the mechanical anisotropy of the lithospheric mantle analysis of major rift systems suggests that the preexisting structure of the lithosphere is a key parameter in the rifting process rift propagation is not random but tends to follow the trend of the orogenic fabric of the plates systematically reactivating ancient lithospheric structures continental rifts often display a clear component of strike slip deformation in particular in the early rifting stage moreover although the close temporal and spatial association between flood basalt eruption and continental breakup suggests that mantle plumes play an important role in the rifting process there is a paradox between the pinpoint thermal and stress perturbation generated by an upwelling mantle plume and the planar geometry of rifts these observations suggest that the deformation of the lithosphere especially during rifting is controlled by its preexisting structure on the other hand 1 the plasticity anisotropy of olivine single crystal and aggregates 2 the strong crystallographic orientation of olivine observed in mantle xenoliths and lherzolite massifs and 3 seismic anisotropy data which require a tectonic fabric in the upper mantle coherent over large areas suggest that preservation within the lithospheric mantle of a lattice preferred orientation lpo of olivine crystals may induce a large scale mechanical anisotropy of the lithospheric mantle we use a polycrystal plasticity model to investigate the effect of a preexisting mantle fabric on the continental breakup process we assess the deformation of an anisotropic continental lithosphere in response to an axi symmetric tensional stress field produced by an upwelling mantle plume by calculating the deformation of textured olivine polycrystals representative of the lithospheric mantle at different positions above a plume head model results show that a lpo induced mechanical anisotropy of the lithospheric mantle may result in directional softening leading to heterogeneous deformation during continental rifting this mechanical anisotropy may induce strain localisation in domains where extensional stress is oblique 30 55 to the preexisting mantle fabric this directional softening associated with olivine lpo frozen in the lithospheric mantle may also guide the propagation of the initial instability that will follow the preexisting structural trend the preexisting mantle fabric also controls the deformation regime imposing a strong strike slip shear component a lpoinduced mechanical anisotropy may therefore explain the systematic reactivation of ancient collisional belts during rifting structural inheritance the plume rift paradox and the onset of transtension within continental rifts fl 2001 elsevier science b v all rights reserved

a genetic link between transform and hyper extended margins abstract the similarity between the geometry of the west african and south american coastlines is among one of the strongest natural observations supporting the plate tectonic paradigm however using classical plate tectonic approaches to model these conjugate transform margins results in a high degree of variability in palaeogeographic reconstructions using state of the art 3d coupled thermo mechanical numerical models we simulate for the first time crustal deformation at the onset of oceanisation along large offset oblique margins our models show that obliquity causes oceanic rift propagation to stall resulting in an apparent polyphased tectonic evolution and in some circumstances leads to the formation of hyper extended margins as a result conjugate margins located at the edge of future fracture zones are highly asymmetric from rifting to spreading with their lengths differing by a factor of 5 to 10 before the final phase of break up occurs accounting for this discrepancy should ameliorate future palaeogeographic reconstructions

deep structure of the argentine margin inferred from 3d gravity and temperature modelling colorado basin abstract following previous work on the colorado basin using a 3d crustal structural model we now investigate the presence of lower crustal bodies at the base of the crust using 3d lithospheric gravity modelling and calculations of the conductive thermal field our first study highlighted two fault directions and depocentres associated with thinned crust nw se in the west and ne sw at the distal margin fault relative chronology argues for two periods of extension 1 nw se faulting and thinning in the western colorado basin and 2 ne sw faulting and thinning related to the continental breakup and formation of the ne sw striking volcanic margins of the atlantic ocean in this study the geometry of modelled high density lower crustal bodies lcbs enables the reproduction of the gravimetric field as well as of the temperature measured in wells down to 4500 m the modelled lcbs correlate with geological observations 1 nw se lcbs below the deepest depocentres in the west 2 ne sw lcbs below the distal margin faults and the seaward dipping reflectors thus the proposed poly phased evolution of the margin could as well correspond to two emplacement phases of the lcbs the calculated conductive thermal field fits the measured temperatures best if the thermal properties thermal conductivity and radiogenic heat production assigned to the lcbs correspond to either high grade metamorphic rocks or to mafic magmatic intrusions to explain the possible lithology of the lcbs we propose that the two successive phases of extension are accompanied by magma supply emplaced 1 in the thinnest crust below the older nw se depocentres then 2 along the ne sw continentward boundary of the distal margin and below the volcanic seaward dipping reflectors the south african conjugate margin records only the second ne sw event and we discuss hypotheses which could explain these differences between the conjugate margins

the origin of along rift variations in faulting and magmatism in the ethiopian rift the geological record at rifts and margins worldwide often reveals considerable along strike variations in volumes of extruded and intruded igneous rocks these variations may be the result of asthenospheric heterogeneity variations in rate and timing of extension alternatively pre existing plate architecture and or the evolving kinematics of extension during breakup may exert first order control on magmatism the main ethiopian rift mer in east africa provides an excellent opportunity to address this dichotomy it exposes along strike several sectors of asynchronous rift development from continental rifting in the south to incipient oceanic spreading in the north here we perform studies of volcanic cone density and rift obliquity along strike in the mer by synthesizing these new data in light of existing geophysical geochemical and petrological constraints on magma generation and emplacement we are able to discriminate between tectonic and mantle geodynamic controls on the geological record of a newly forming magmatic rifted margin the timing of rift sector development the three dimensional focusing of melt and the ponding of plume material where the rift dramatically narrows each influence igneous intrusion and volcanism along the mer however rifting obliquity plays an important role in localizing intrusion into the crust beneath en echelon volcanic segments along strike variations in volumes and types of igneous rocks found at rifted margins thus likely carry information about the development of strain during rifting as well as the physical state of the convecting mantle at the time of breakup