defining a 3 dimensional trishear parameter space to understand the temporal evolution of fault propagation folds abstract the application of trishear in which deformation occurs in a triangular zone in front of a propagating fault tip is often used to understand fault related folding a key element of trishear in comparison to kink band methods is that non uniform deformation within the triangle zone allows the layer thickness and length to change during deformation by varying three controlling parameters independently trishear propagation slip ratio trishear apical angle and fault dip we construct a three dimensional parameter space to demonstrate the variability of resultant geometry feasible with trishear we plot published natural examples in this parameter space and identify two clusters and show that the most applicable typical trishear propagation slip ratio is 2 to 3 while the trishear apical angle varies from 30 to 100 we propose that these findings can help estimate the best fit parameters for natural structures we then consider the temporal evolution of specific geometric examples and factors that increase the complexity of trishear including 1 fault dip changes and 2 pre existing faults to illustrate the applicability of the parameter space and complex trishear models to natural examples we apply our results to a sub surface example from the qaidam basin in northern tibetan plateau

transition from a singly vergent to doubly vergent wedge in a young orogen the greater caucasus the greater caucasus mountains due to their youth 5 ma provide an opportunity for insight into the early stages of orogen development during continent continent collision however their recent tectonic evolution and first order architecture remain unclear here we investigate the evolution of the orogen by integrating new observations of the fluvial geomorphology and neotectonics of the range with prior work on seismicity geodetic strain bedrock geology and foreland basin structure we find that the range contains four zones along strike that differ in structural architecture topography and first order tectonic history in particular two south directed singly vergent zones at the western and eastern tips of the orogen are separated by both a central doubly vergent zone that is dominated by north directed deformation and an eastern doubly vergent zone in which south directed thrusting dominates we hypothesize that the along strike changes in vergence and locus of deformation reflects different stages in the development of a doubly vergent orogen with the tips of the range preserving an early singly vergent form and the center recording a more advanced orogen the differences between the two doubly vergent zones seem to be driven by the initial stages of collision between the structurally thickened crust of the greater and lesser caucasus orogens which initiated at 5 ma

palinspastic reconstruction and topographic evolution of the eastern alps during late tertiary tectonic extrusion this paper presents a new palinspastic restoration of the eastern alps for neogene time and an attempt to reconstruct the neogene palaeogeology palaeotopography and palaeohydrography in connection with the structural evolution the eastern alps underwent radical horizontal displacement during the neogene due to large strike slip systems and formation of structural windows our palinspastic reconstruction considers a the rearrangement of tectonic units dismembered during tectonic extrusion b the tectonic denudation driven by displacement of the crystalline blocks c geochronological arguments and d the sedimentary record of the syn extrusion basins the rearrangement of tectonic blocks results in a remarkably good fit of highly dismembered zones both in crystalline and sedimentary areas and shows the pre miocene unstretched pattern of the eastern alps reduced to 65 of its present day e w elongation using this structural frame and considering the sedimentary record a set of palaeogeologic and palaeotopographic sketch maps with the palaeo river systems is presented for three time slices pre syn and post extension situation in late oligocene and early miocene times the western eastern alps were already mountainous whereas the eastern part of the orogen formed lowlands or hilly areas enhanced block movement in the course of the extrusion process around the early middle miocene boundary led to the formation of intramontane sedimentary basins and a fault induced reorientation of the drainage pattern which forms the basis of the modern river system in the area east of the tauern window this region where pre miocene land surfaces are preserved probably became a mountainous area not before late miocene time and never reached the elevations of the areas further west

coupling and decoupling of crust and mantle in convergent orogens implications for strain partitioning in the crust topographic relief strain partitioning and crust mantle coupling within convergent orogens may be systematically related to the distribution of strength as a function of depth within continental crust this result is obtained by solving analytically for basally driven three dimensional flow within an idealized crust with a laterally invariant depth dependent newtonian viscosity two end member flow states are shown to occur in the first crustal flow is directly coupled to the underlying mantle and is controlled by stresses transmitted vertically through the crust in the second upper crustal to midcrustal flow is decoupled from the underlying mantle and is controlled by stresses transmitted horizontally through the crust this model is applied to deformation of continental crust above plate like mantle that undergoes oblique convergence across a narrow suture if no significant low viscosity zone develops within the crust crustal deformation is coupled to motion of the underlying mantle and a triangular mountain range develops surface shortening occurs at the foot of the mountains normal to the trend of the range while strike slip and extension are partitioned along the axis of the orogen if a low viscosity zone is initially absent but develops during crustal thickening a steep sided flat topped plateau forms crustal deformation is coupled to mantle motions on the plateau flanks but may be strongly decoupled beneath the plateau surface shortening normal to the plateau occurs at the foot of the plateau while surface extension normal to the plateau occurs at the plateau edge if a low viscosity zone is present in the lower crust prior to convergence a wide orogen with low topographic relief develops crustal deformation is decoupled from the mantle except at the edges of the deforming region and surface shortening is partitioned uniformly across the belt this study shows that horizontal and vertical partitioning of strain occur even in the absence of lateral strength variations and that shortening and extension may exist simultaneously in different parts of an orogen similar morphology and strain partitioning can be observed in many real orogenic belts including the eastern alps the tibetan plateau and the lachlan tasman fold belt

cenozoic deformation of iberia a model for intraplate mountain building and basin development based on analogue modeling 1 inferences from analogue models support lithospheric folding as the primary response to large scale shortening manifested in the present day topography of iberia this process was active from the late oligocene early miocene during the alpine orogeny and was probably enhanced by reactivation of inherited variscan faults the modeling results confirm the dependence of fold wavelength on convergence rate and hence the strength of the layers of the lithosphere such that fold wavelength is longest for fast convergence rates favoring whole lithosphere folding folding is associated with the formation of dominantly pop up type mountain ranges in the brittle crust and thickening of the ductile layers in the synforms of the buckle folds by flow the mountain ranges are represented by upper crustal pop ups forming the main topographic relief the wavelengths of the topographic uplifts both in model and nature suggest mechanical decoupling between crust and mantle moreover our modeling results suggest that buckling in iberia took place under rheological conditions where the lithospheric mantle is stronger than the lower crust the presence of an indenter inducing oblique shortening in response to the opening of the king s trough in the north western corner of the atlantic iberian margin controls the spacing and obliquity of structures this leads to the transfer of the deformation from the moving walls towards the inner part of the model creating oblique structures in both brittle and ductile layers the effect of the indenter together with an increase on the convergence rate produced more complex brittle structures these results show close similarities to observations on the general shape and distribution of mountain ranges and basins in iberia including the spanish central system and toledo mountains

correlation of early cretaceous carbon isotope stratigraphy and platform drowning events a possible link the early cretaceous carbonate carbon isotope record is marked by three positive high amplitude 1 5 excursions each covering time spans of more than 106 years they are of late valanginian hauterivian and early and late aptian age in a case study along a transect across the western tethys ocean we identified a coincidence between 13c excursions black shale formation and widespread carbonate platform drowning events we conclude that the 13c excursions reflect a change in partitioning of carbon between the organic and carbonate carbon sinks which was triggered by climate induced ecological changes in cretaceous pelagic and neritic environments episodes of intensified greenhouse climate conditions led to an increase in weathering erosion and runoff rates and to elevated nutrient transfer rates from continents into oceans the resulting increase in oceanic nutrient levels favoured marine phytoplankton production and black shale deposition while conditions for carbonate producing biotas became unfavourable partial choking of carbonate production along river influenced coasts resulted in widespread carbonate platform drowning during times of sea level rise in the valanginian and aptian widespread contemporaneous black shale deposits and drowned carbonate platforms therefore reflect the contrasting response of the marine organic and carbonate carbon pumps to nutrient enhanced phytoplankton productivity the change in marine carbon partitioning is mirrored in a shift of the 13c record towards more positive values the transition to the 13c peak values lasted up to several hundred thousand years the peaks of the excursions also covering a time span of up to several hundred thousand years reflect a new stabilisation of the carbon partitioning between carbonate and organic carbon sinks a renewed intensification of carbonate sedimentation under mesotrophic conditions was facilitated by stabilisation of the sea level rise at a high level decreasing 13c values record increasing carbonate carbon burial rates at constant or decreasing organic carbon accumulation rates these changes contributed to the stabilisation of the marine carbon budget and the global carbon cycle up to millions of years after its initial perturbation

cretaceous palaeomagnetic results from hainan island in south china supporting the extrusion model of southeast asia abstract we report the cretaceous palaeomagnetic results from hainan island south china in hainan island we collected the early cretaceous redbeds of the lumuwan formation at eleven sites we also describe the tectonic kinematics for and around hainan island since the cretaceous deduced from our and previous palaeomagnetic results the palaeolatitude of hainan island is 25 9 n 3 4 3 2 implying that hainan island was situated about 7 north from the present position during the cretaceous the palaeopole of hainan island latitude 77 7 n longitude 162 1 e k 65 6 and a95 4 4 suggests 4 0 5 8 counterclockwise rotation and 14 1 5 5 southward translation relative to the suspected coherent part of the south china block scb since the cretaceous the rotation and translation of similar sense 18 8 7 4 and 7 8 6 9 respectively are detected in the existing palaeomagnetic result from the xinlong formation in guangxi which is situated approximately 400 km north northwest from hainan island the southward translation of both areas seems to have been due to the southeastward extrusion of dissected zones within the southwestern part of the scb in a similar pattern to the indochina block which had resulted from the indentation of india into asia this sw part seems to have slightly rotated counterclockwise because its extrusion was probably smaller in scale than the indochina block and therefore it was dragged out by the indochina block this hypothesis is supported by the existence of a northwest southeast trending fault system parallel to the red river fault

shear stresses on megathrusts implications for mountain building behind subduction zones 1 shear stresses on a subduction megathrust play an important role in determining the forces available for mountain building adjacent to a subduction zone in this study the temperatures and shear stresses on megathrusts in 11 subduction zones around the pacific rim hikurangi tonga izu ogasawara western nankai northeastern japan aleutians western alaska cascadia northern chile southern chile and se asia northern sumatra have been determined the main constraint is that vertical normal stresses beneath the highlands behind the subduction zone are nearly equal to horizontal normal stresses in the plane of a trench or arc normal section for a typical brittle and ductile megathrust rheology frictional shear stress gz for depth z and ductile shear stress a exp b rt at temperature t where a b are rheological parameters treated as constants rheological constants common to all the megathrusts crust mantle b are determined by simultaneously solving for the force balance in the overlying wedge and megathrust thermal structure using a simplex minimization algorithm taking account of the induced mantle corner flow at depth 65 15 km 2 and constant radiogenic heating 0 65 0 3 w m 3 2 throughout the crust the a constants are solved individually for each subduction zone assuming that the maximum depth of interplate slip earthquakes marks the brittle ductile transition the best fit solution shows two groupings of megathrusts with most subduction zones having a low mean shear stress in the range 7 15 mpa crust 0 032 0 006 mantle 0 019 0 004 and unable to support elevations 2 5 km for a typical frictional sliding coefficient 0 5 the low effective coefficients of friction suggest high pore fluid pressures at 95 lithostatic pressure tonga and northern chile require higher shear stresses with crust 0 095 0 024 mantle 0 026 0 007 suggesting slightly lower pore fluid pressures at 81 lithostatic ductile shear in the crust is poorly resolved but in the mantle appears to show a strong power law dependency with b 36 18 kj mol 1 amantle values are sensitive to the precise value of b but are in the range 1 20 kpa the power law exponent n for mantle flow is poorly constrained but is likely to be large n 4 the brittle ductile transition in the crust occurs at temperatures in the range 370 c 512 c usually close to the base of the crust and in the mantle at much lower temperatures 180 c 300 c possibly reflecting a marked change in pore fluid pressure or quasi ductile and subfrictional properties in subduction zones where the subducted slab is older than 50 ma a significant proportion of the integrated shear force on the megathrust is taken up where it cuts the mantle and temperatures are 300 c in much younger subduction zones the stress transmission is confined mainly to the crust the shear stresses particularly in the crust may be kept low by some sort of lubricant such as abundant water rich trench fill which lowers the frictional sliding coefficient or effective viscosity and or raises pore fluid pressure the unusual high stress subduction zone in northern chile lacks significant trench fill and may be poorly lubricated with a mean shear stress 37 mpa required to support elevations 4 km in the high andes however where the crust is thin in sediment starved and poorly lubricated subduction zones such as tonga the mean shear stress will still be low sediment may lubricate megathrusts accommodating underthrusting of continental crust such as in the himalayas or eastern central andes which have a low mean shear stress 15 mpa

a cretaceous pole from south china and the mesozoic hairpin turn of the eurasian apparent polar wander path to contribute to the apparent polar wander path apwp of the south china block and eurasia in general we collected paleomagnetic samples from mesozoic red beds around the city of ya an 30 n 103 e in the western tip of the sichuan basin in this paper we present the results from 373 oriented cores taken from one section representing 3 km of sedimentary rocks the section is dated with continental ostracods and with a magnetostratigraphic correlation between a densely sampled 272 m sequence and the polarity time scale giving an upper jurassic to upper cretaceous or lower tertiary age the remanent direction is remarkably stable throughout the section d 2 0 i 34 2 k 63 1 95 3 6 n 26 28 sites while this fact might suggest that the section has been remagnetized paleomagnetic and rock magnetic tests indicate that the remanence is primary the pole position 78 6 n 273 4 e dp 2 4 dm 4 1 corresponds to a rather low paleolatitude 18 8 2 4 but is consistent with other cretaceous poles from china if one accepts the eurasian apwp of irving and irving 1982 this result would imply that more than 1000 km of shortening took place between south china and eurasia following the acquisition of the remanence however there is no geological evidence for this large shortening we propose that the remanence was acquired within the time corresponding to the tip of the hairpin turn 150 50 ma in the revised apwp of besse and courtillot this issue the local geology suggests that the syncline from which the samples were taken has been rotated by 15 5 counterclockwise which is reflected in a similar discrepancy between the measured paleodeclination and that predicted by the besse and courtillot this issue eurasian apwp after correcting for this rotation the pole position is 70 9 n 225 2 e dp 2 4 dm 6 5 we conclude that eurasia was fully assembled by the end of the jurassic and that the mesozoic eurasian hairpin turn is a real feature

exhumation in a convergent orogen the western tauern window unroofing of the western tauern window involved both low angle detachment faulting brenner fault and enhanced footwall erosion contemporaneous with upright antiformal folding this combination reflects orogen parallel e w extension during continued n s alpine convergence new fission track ages establish the relative chronology of folding and faulting and demonstrate that displacement was not always accommodated on the same surface during exhumation some units migrated from the footwall to the hanging wall of the main detachment fault due to the interplay between folding and faulting the region can effectively be divided into 3 distinct domains 1 the penninic units of the western tauern window were always in the footwall to the fault with maximum exhumation in the core of the dome due to folding and erosion 2 the lower austroalpine unit north of the tauern window was first part of the hanging wall to the brenner fault at a later stage this unit was exhumed by a further 4 5 km as part of the footwall to a more discrete through going fault the silltal fault 3 the middle and upper austroalpine units west of the tauern window were always within the hanging wall exhumation of the footwall from an initial depth of 25 km led to a transition in mechanical behaviour the curviplanar folded ductile shear zone marking the boundary to the tauern window was eventually transected by a more planar discrete brittle fault silltal fault with unit 2 now in the footwall along which the pre existing mylonites were passively exhumed to the surface

spectral analysis of the gravity and elevation along the western africa eurasia plate tectonic limit continental versus oceanic lithospheric folding signals large scale folding is a key mechanism of lithospheric deformation and has been described in many parts of the earth both for the continental and oceanic lithospheres some aspects of this process such as the presence of coupling decoupling between the crustal deformation and the mantle lithosphere or between different lithospheres make it necessary to accurately control the periodic characteristics of the elevation and of the gravity signal 1d spectral analysis of gravity and topography profiles is sensitive to a series of factors the location length and orientation of the profiles as well as the number of samples taken we carry out a systematic analysis of the periodicities in the topography and gravity both 1d and 2d along the western border of the africa eurasia plate tectonic boundary we analyze the sensitivity of the 1d and 2d spectral analysis in order to compare the results along a plate boundary where oceanic and continental lithospheres are in contact with different tectonic kinematic and rheological aspects our 1d spectral results indicate that the greater the profile length the longer the wavelength peaks that are found nevertheless there are some periodic signals that appear in almost all the analyzed profiles 100 250 km for the n s profiles across oceanic plate boundary and 150 250 km where the plate boundary is developed over continental lithospheres the 2d spectral analysis avoids the problems found in relation to the particular location of the profile but the resulting wavelengths are slightly higher than those obtained from the 1d spectral analysis the wavelengths estimated for both oceanic and continental lithospheres at the africa eurasia boundary n250 km show low values of mean mantle strength b1013 pa m he presence of lithospheric folds means that the continental and oceanic lithospheres are mechanically oupled this had previously been suggested for iberia but not for the limit between s iberia and the terceira riple junction the orientation of the lithospheric folds is nw se at the contact between continental lithospheres and nne ssw at the contact between oceanic lithospheres this difference is also reflected in the signal anisotropy and must be related to the rotation of the tectonic stresses in the same direction a large periodic signal wavelength n600 km was also detected both in 1d and 2d spectral results after drawing the filtered values the resulting maps indicate that this signal is related to the transition between continental and oceanic lithospheres and to the significant changes in crustal and or lithospheric thickness from the mid atlantic ridge to the continental margins of western eurasia

the first pacific record of the late aptian warming event carbonate platforms consisting of hermatypic coral rudists and larger foraminifers formed along the margin of the ne japanese islands during the mid late aptian the geographical northern limit of the carbonate platforms extended to c 36 n at that time which is the highest latitude for coral and or rudist formation in the north pacific region this geographical extension of the carbonate platform in the nw pacific indicates extreme climatic warmth in the mid latitudes and strong poleward heat transport systems contemporaneous warming has been detected in european and australian regions as represented by the migration of tethyan fauna toward the boreal realm and the positive excursion of 13 c and negative excursion of 18 o in deep sea carbonates our new constraint on the northern limit of reef growth reinforces the view that an interval of greenhouse like warmth punctuated the late aptian climate

experiments on shortening of a 4 layer model of the continental lithosphere davy ph and cobbold p r 1991 experiments on shortening of a 4layer model of the continental lithosphere in p r cobbold editor experimental and numerical modelling of continental deformation tecronophysics 188 l 25 we present an experimental method for modelhng lithospheric deformation the method is based on a simplified profile of lithosphere rheology where only four layers are considered brittle crust ductile crust brittle mantle and ductile mantle the strengths of the four layers calculated from laboratory determined flow laws depend strongly on geothenns and slightly on strain rates and deformation regimes the rheological profiles of the lithosphere have been recreated in experimental models built with analog materials sand silicone putty and golden syrup which flow under their own weight during lithospheric shortening the style of deformation depends on the relative strengths of the four layers especially those in the mantle of special importance is the existence or non existence of a brittle mantle the initial stages of compression often produce flexures or buckles without local isostatic compensation buckling exerts a strong control on the localisation of thrust faults in later stages the thrusts tend to form at the inflexion points of buckles the style of crustal thickening depends on the relative thicknesses and resistances of the lithospheric layers in 2 layer lithospheric models without resistant mantle shortening was concentrated upon a small number of thrusts widely spaced in 3 layer models shortening was concentrated into a large number of reverse faults more closely spaced and more steeply dipping than before in clayer models a single thrust formed in the brittle mantle motion on this thrust dragged the crustal layers down forming an asymmetric crustal root with steep imbricate slices

deep seismic reflection evidence for continental underthrusting beneath southern tibet the himalaya and adjacent tibetan plateau constituting earth s largest region of elevated topography and anomalously thick crust formed as a consequence of cenozoic collision between india and asia itself considered the archetypal continent continent collision1 3 here we report the first results from an attempt to image the structure of the crust beneath this region using deep seismic reflection profiling our 100 km long profile acquired in the tethyan himalaya shows a mid crustal reflection that prob ably marks the active thrust fault along which the indian plate is underthrusting southern tibet upper crustal reflections with geo metries suggestive of large scale structural imbrication of the upper crust and moho reflections from the base of the double normal thickness crust underlying the region these results lend substantial support to the view that crustal thickening beneath southernmost tibet was accomplished by wholesale underthrusting of indian continental crust beneath the structurally imbricated upper crust comprising the tethyan himalaya

phosphogenesis carbon isotope stratigraphy and carbonate platform evolution along the lower cretaceous northern tethyan margin we distinguish three different stages in the evolution of the tithonian late jurassic to aptian early cretaceous northern tethyan carbonate platform 1 carbonate production in the coral oolite mode late tithonian to early valanginian early barremian to early aptian 2 carbonate production in the crinoid bryozoan mode early valanginian haute rivian late aptian and 3 platform retrogradation and destruction condensation and phosphogenesis that is platform drowning early valanginian to early hauterivian middle hauterivian late hauterivian to early barremian early to early late aptian and latest aptian to earliest albian transitions from the coral oolite mode to the crinoid bryozoan mode and consequently to platform drowning may have been driven by increases in nutrient levels on the shelf phases of relative sea level rise in times of carbonate production in the coral oolite mode are named constructive because of the observed platform regeneration following phases of widespread emersion during late sea level highstands in contrast phases of relative sea level rise in times of platform drowning are termed destructive the 13 c stratigraphies obtained from valanginian hauterivian and aptian albian hemipelagic successions beyond the platform correlate well with the early cretaceous pelagic 13 c record positive excursions in the pelagic 13 c record correspond in time to episodes of platform drowning this suggests the existence of a coupling mechanism between changes in the global carbon cycle and platform drowning in our view the early cretaceous crises in carbonate platform growth were the consequence of reinforced greenhouse conditions which may have been triggered by episodes of extensive flood basalt volcanism strong greenhouse conditions may have induced the following chain of feedback mechanisms enabling the biosphere to return to normal conditions climate warming sea level rise accelerated water cycle intensified weathering nutrient mobilization platform destruction increased productivity increased phosphogenesis and carbon burial weakened greenhouse conditions

postcollisional cooling history of the eastern and southern alps and its linkage to adria indentation indentation of rigid blocks into rheologically weak orogens is generally associated with spatiotemporally variable vertical and lateral block extrusion the european eastern and southern alps are a prime example of microplate indentation where most of the deformation was accommodated north of the crustal indenter within the tauern window however outside of this window only the broad late stage exhumation pattern of the indented units as well as of the indenter itself is known in this study we refine the exhumational pattern with new u th sm he and fission track thermochronology data on apatite from the karawanken mountains adjacent to the eastern periadriatic fault and from the central eastern southern alps apatite u th sm he ages from the karawanken mountains range between 12 and 5 ma and indicate an episode of fault related exhumation leading to the formation of a positive flower structure and an associated peripheral foreland basin in the southern alps apatite u th sm he and fission track data combined with previous data also indicate a pulse of mainly late miocene exhumation which was maximized along thrust systems with highly differential amounts of displacement along individual structures our data contribute to mounting evidence for widespread late miocene tectonic activity which followed a phase of major exhumation during strain localization in the tauern window we attribute this exhumational phase and more distributed deformation during adriatic indentation to a major change in boundary conditions operating on the orogen likely due to a shift from a decoupled to a coupled system possibly enhanced by a shift in convergence direction

topo europe studying continental topography and deep earth surface processes in 4d abstract topo europe is a multidisciplinary international research program that addresses the interaction of processes inherent to the deep earth lithosphere mantle with surface processes erosion climate sea level which together shaped the topography of europe the objective of this programme is to assess neotectonic deformation rates and to quantify related geo risks such as earthquakes flooding landslides rock falls and volcanism research incorporating data interactive modeling focuses on the lithosphere memory and neotectonics with special attention on the thermo mechanical structure of the lithosphere mechanisms controlling large scale plate boundary and intraplate deformations anomalous subsidence and uplift and links with surface processes and topography evolution the topo europe natural laboratories in which these processes are analyzed cover a wide range of geodynamic settings these include the post collisional alpine carpathian pannonian basin system the very active aegean anatolian and apennines tyrrhenian orogens and back arc basins the caucasus levant area in the arabia europe collision zone the iberian peninsula caught up between alpine orogens the meta stable west and central european platform the stable east european platform and the seismically active and elevated scandinavian continental margin the topo europe project is a component of the international lithosphere program a european science foundation eurocores project provides funding for part of the research for a total amount of 13 5 m euro creating new research positions for 60 young researchers

evolution patterns of radiolaria and organic matter variations a new approach to identify sea level changes in mid cretaceous pelagic environments the relation between sea level changes plankton productivity and evolution as well as the occurrence of anoxic sediments provides an interesting avenue of paleooceanographic research in this context we examined mid cretaceous radiolarian faunas carbonate isotopic and organic matter type data of deep sea drilling project and ocean drilling program cores from the north atlantic and samples from outcrops of the western tethys from central and northern italy former studies indicate that an expansion of the oxygen minimum zone caused plankton extinctions at the cenomanian turonian boundary an expanded oxygen minimum zone would destroy deeper habitats of planktic foraminifera causing the extinction of deeper dwelling forms although this model is well established for the cenomanian turonian boundary not much is known about the causes of extinctions and radiations during the entire mid cretaceous aptian turonian we demonstrate that the dimension of the oxygen minimum zone which depends on the relative sea level and the corresponding nutrient supply causes the complex pattern of evolution and radiation of planktic protozoa and the sedimentation of black shales in the mid cretaceous this new depositional model allows correlation of micropaleontologic data and different types of black shales in the pelagic realm within a sequence stratigraphic framework

selective organic matter preservation in burn down turbidites on the madeira abyssal plain 1 oxidized intervals of five organic rich madeira abyssal plain map turbidites deposited during the miocene pliocene and pleistocene all displayed comparable major loss of total organic carbon toc 84 3 1 accompanied by a negative isotopic 13c shift ranging from 0 3 to 2 9 major but significantly lower loss of total nitrogen ntot 61 7 1 also occurred leading to a decrease in toc relative to ntot c ntot and a 1 3 to 2 7 ntot isotopic 15n shift compound specific isotopic measurements on plant wax n alkanes indicate the terrestrial organic component in the unoxidized deposits is 13c enriched owing to significant c4 contribution selective preservation of terrestrial relative to marine organic carbon could account for the 13c behavior of toc upon oxidation but only if a 13c depleted component of the bulk terrestrial signal is selectively preserved in the process although the c ntot decrease and positive 15n shift seems inconsistent with selective terrestrial organic preservation results from analysis of a modern eolian dust sample collected in the vicinity indicate these observations are compatible regardless of the specific explanation for these isotopic observations however our findings provide evidence that paleoreconstruction of properties such as pco2 using the 13c of toc is a goal fraught with uncertainty whether or not the marine sedimentary record considered is contaminated with significant terrestrial input nonetheless despite major and selective loss of both marine and terrestrial components as a consequence of postdepositional oxidation intensive organic geochemical proxies such as the alkenone unsaturation index u37k appear resistant to change and thereby retain their paleoceanographic promise

continental plate collision p t t z conditions and unstable vs stable plate dynamics insights from thermo mechanical modelling there was much debate recently on the mechanisms of continental convergence and related pressure temperature p t conditions both in modeling and petrologic community depending on the mechanisms of convergence subduction collision folding or rt instability one can argue about the possibility of large scale deviations of pressure and temperature in the accretion prism and below it from reference i e lithostatic conditions commonly used for petrologic reconstructions of evolution of exhumed metamorphic rocks these deviations can be caused for example by tectonic overpressure that as suggested in some studies may be responsible for formation of uhp ultra high pressure rocks however overpressure in exhumation zones can be built only in specific collision scenarios associated with plate coupling pure shear folding in this study we analyze conditions that define various mechanisms of convergence and consequently of exhumation these mechanisms can be represented as a superposition of 1 simple shear subduction 2 pure shear collision 3 folding and 4 rayleigh taylor instability we study these scenarios using a thermo mechanical model that accounts for brittle elastic ductile rheology surface processes and metamorphic changes it appears that stable oceanic type subduction may occur in the case of cold lithospheres tmohob550 c and relatively high convergence rates n3 5 cm yr depending on the lower crustal rheology strong or weak either the whole upper and lower crust or only the lower crust can be involved in subduction in case of weak metamorphic rheologies phase changes improve chances for stable subduction pure shear becomes a dominant mechanism when tmohon550 c or convergence rates are lower than 3 cm yr large scale folding is favored in case of tmoho 500 650 c and is more effective in the case of mechanical coupling between crust and mantle e g strong lower crust gravitational rayleigh taylor instabilities overcome other mechanisms for very high values of tmoho n800 c and may lead to development of subvertical cold spots however it is reasonable to assume that in most cases continental collision is initiated at oceanic subduction rate which is rarely slower than 5 cm yr this rate is sufficient to drive continental subduction during the first several myr of collision in this case the subduction channel is characterized by nearly lithostatic pressure conditions large scale zones of tectonic overpressure may be built outside the channel but do not affect the exhumed rocks overpressure may be built inside the channel in the short moment of its closure we suggest that most continental orogenic belts could have started their formation from continental subduction this evokes small tectonic overpressures and thus deep origin of the uhp rocks that may be brought to the surface via the suggested multi level mechanism of exhumation

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

correlations of cave levels stream terraces and planation surfaces along the river mur timing of landscape evolution along the eastern margin of the alps the transition zone of the eastern alps to the pannonian basin provides one of the best sources of information on landscape evolution of the eastern alpine mountain range the region was non glaciated during the entire pleistocene thus direct influence of glacial carving as a landscape forming process can be excluded and relics of landforms are preserved that date back to at least the late neogene in this study we provide a correlation between various planation surfaces across the orogen basin transition in particular we use stream terraces planation surfaces and cave levels that cover a vertical spread of some 700 m our correlation is used to show that both sides of the transition zone uplifted together starting at least about 5 ma ago for our correlation we use recently published terrestrial cosmogenic nuclide tcn burial ages from cave sediments new optically stimulated luminescence osl ages of a stream terrace and u th ages from speleothems minimum age constraints of cave levels from burial ages of cave sediments covering the last 4 ma are used to place age constraints on surface features by parallelizing cave levels with planation surfaces the osl results for the top section of the type locality of the helfbrunn terrace suggest an early wurm development 80 5 3 7 to 68 7 4 0 ka the terrace origin as a penultimate gravel deposit in classical alpine terminology riss is therefore questioned u series speleothem ages from caves nearby indicate formation during marine isotope stages mis 5c and 5a which are both interstadial warm periods as osl ages from the terrace also show a time of deposition during mis 5a ending at the mis 5 4 transition this supports the idea of temperate climatic conditions at the time of deposition in general tectonic activity is interpreted to be the main driving force for the formation and evolution of these landforms whilst climate change is suggested to be of minor importance obvious hiatuses in miocene to pleistocene sediments are related to ongoing erosion and re excavation of an uplifting and rejuvenating landscape

planktonic foraminiferal zonation in the cretaceous yezo group central hokkaido japan abstract the mudstone of the yezo group exposed in central hokkaido yields abundant microfossils of calcareous nannofossils foraminifers radiolarians and dinoflagellates benthic foraminifers consisting of both agglutinated and calcareous species occur abundantly and consistently throughout the sequence while specimens of planktonic foraminifers are generally fewer than benthics in all samples we recognized the following 13 planktonic foraminiferal zones assigned to the late aptian to early campanian in the oyubari and haboro kotanbetsu areas 1 globigerinelloides spp 2 ticinella primula 3 biticinella breggiensis 4 rotalipora subicinensis rotalipora ticinensis 5 rotalipora appenninica 6 rotalipora globotruncanoides 7 rotalipora cushmani 8 whiteinella archaeocretacea 9 helvetoglobotruncana helvetica 10 marginotruncana pseudolinneiana 11 marginotruncana sinuosa 12 contusotruncana fornicata 13 globotruncana arca the globigerinelloides spp to h helvetica zones late aptian to early turonian can be correlated with standard zones in the tethyan regions whereas the assemblages from the m pseudolinneiana to g arca zones lack tropical zonal markers of dicarinella concavata d asymetrica and globotruncanita elevata in many studied sections the scarcity or lack of tropical zonal species during the late turonian to early campanian suggests that the oyubari and haboro kotanbetsu regions in hokkaido were located in the transitional to boreal biogeographical provinces

experimental modelling of orogenic wedges a review abstract experimental modelling applied to the study of orogenic wedge dynamics has been a subject of fruitful research for more than 30 years although the technique dates back as far as the early xix th century on one hand several first order parameters controlling the structural evolution of mountain belts have been intensively investigated using the classic tectonic sandbox models the main parameters are the properties of the basal decollement the deforming material the backstop and fluxes kinematics and surface processes on the other hand the morphological evolution of a mountain relief subjected to changing tectonic or climatic forcing has been addressed using another kind of approach called geomorphic models nowadays the literature is extremely rich particularly for the sandbox technique so that it becomes difficult to have an exhaustive view of the effects of the above parameters on mountain evolution in this article we propose a detailed review of the main results obtained using both tectonic and geomorphic approaches our goal is to provide an almost complete state of the art in the experimental study of relief dynamics to guide present and future researchers in their understanding of mountain belt evolution

footwall uplift in an orogenic wedge the tauern window in the eastern alps of europe abstract in the tauern window tw the deepest structural units of the eastern alps are exposed in a 30 160 km antiform european basement and cover occur under nappes of oceanic penninic units and continental origin austroalpine nappes the tertiary structural history of the tw is related to a rapid uplift of 20 30 km since oligocene times structural mapping revealed 1 detachment and folding of the cover units and stacking of orthogneiss sheets 2 constrictional folding of the entire duplex with amplitudes and half wavelengths of several kilometres 3 backthrusting and backfolding along the northern margin of the tw and 4 displacement along steep dip divergent strike slip faults the strain history is complex and related to all these deformation phases the most uniform structural element is a stretching parallel to the long axis of the tw and its major fold axes strain did not contribute to tw uplift because ductile n s shortening was compensated by e w extension restoration of the tw shows that the exposed structures are not sufficient to explain the tw uplift by analogy with the engadine window and the western alps where seismic data are available a deep seated duplex is suspected the tw uplift is best explained in a dextral transpressive regime

paleomagnetism of mid cretaceous red beds in west central kyushu island southwest japan paleoposition of cretaceous sedimentary basins along the eastern margin of asia abstract a paleomagnetic study was carried out on the mid cretaceous sedimentary strata in west central kyushu island southwest japan to elucidate the origin of sedimentary basins along the asian continental margin in the cretaceous we collected paleomagnetic samples from a total of 34 sites of the mid cretaceous goshonoura group shallow marine clastic deposits in west central kyushu and characteristic remanent magnetizations were recognized from 18 horizons of red beds thermal demagnetization has revealed that the red beds contain three magnetization components with low

subduction and deformation of the continental lithosphere in response to plate and crust mantle coupling physical analogue experiments are used to investigate the effect of plate and intra lithospheric coupling on the efficiency of continental lithosphere subduction and the style of collision key parameters investigated in this study are the degree of plate coupling regulated by the viscosity ratio of the decoupling zone and the surrounding crust and or mantle lithosphere and the depth of decoupling the experimental results show that subduction of the slab is deepest in cases with strong decoupling at the plate interface and at the level of the lower crust of the downgoing plate with upper plate deformation restricted to the area close to the plate contact in these cases the strongly asymmetric orogenic wedge is widest consists of a series of imbricated upper crustal slices derived from the lower plate and lacks a retro wedge in contrast a reduced strength contrast across the plate interface at the depth of either the lithospheric mantle or the ductile crust leads to a combination of subduction and thickening of the mantle lithosphere in both the upper and the lower plates the degree of plate coupling determines the efficiency of subduction of continental lithosphere under conditions of collision of neutrally buoyant lithospheres whereas the vertical position of decoupling horizons within the subducting plate controls the amount of subducted lower crust transfer of strain to the upper plate depends critically on 1 the degree of plate coupling with stronger coupling leading to more deformation and 2 the presence of decoupling horizons within the upper plate which act as strain guides to propagate deformation into the upper plate the experimental results explain the geometry and the sequence of deformation in subduction dominated orogens such as the carpathians or the dinarides and provide a mechanical basis for the transfer of strain to the upper plate

late jurassic early cretaceous intra arc sedimentation and volcanism linked to plate motion change in northern japan the sorachi group composed of upper jurassic ophiolite and lower cretaceous island arc volcano sedimentary cover provides a record of late jurassic early cretaceous sedimentation and volcanism in an island arc setting off the eastern margin of the asian continent stratigraphic changes in the nature and volume of the sorachi group volcanic and volcaniclastic rocks reveal four tectonic stages these stages resulted from changes in the subduction direction of the pacific oceanic plate stage i in the late jurassic was characterized by extensive submarine eruptions of tholeiitic basalt from the back arc basin slab roll back caused rifting and sea floor spreading in the supra subduction zone along the active asian continental margin stage ii corresponded to the berriasian and featured localized trachyandesitic volcanism that formed volcanic islands with typical island arc chemical compositions at the beginning of this stage movement of the pacific oceanic plate shifted from northeastward to northwestward during stage iii in the valanginian submarine basaltic volcanism was followed by subsidence the pacific oceanic plate motion turned clockwise and the plate boundary between the asian continent and the pacific oceanic plate changed from convergent to transform during stage iv in the hauterivian barremian in situ volcanism ceased in the sorachi yezo basin and the volcanic front migrated west of the sorachi yezo basin

the barremian aptian turnover of biota in northwestern europe evidence from belemnites abstract neocomian valanginian barremian and gault aptian albian are lithostratigraphic terms used in the last century to divide the sub chalk cretaceous of northern europe the division is based on significant palaeoceanographic and palaeogeographic changes in the early aptian these changes are linked to a major turnover of marine floras and faunas which occurred simultaneously in the boreal realm the tethys and the indo pacific ocean various floral and faunal elements became extinct in the aptian both in the tethys and in the boreal realm while on the other hand new genera and species evolved marked changes in the diversification rate were observed for organisms with a different mode of life plankton nekton benthos apart from calcareous nannofossils foraminifera and ammonites this turnover also occurs in belemnites and the suborder belemnitina was completely replaced by the suborder belemnopseina the northwestern european barremian is characterised by the very successful belemnite family oxyteuthididae belemnitina which was completely replaced by the genus neohibolites belemnopseina in early aptian times this aptian turnover which is expressed by a homogenisation of marine floras and faunas is best explained by significant palaeoceanographic changes occurring in the early aptian the sea floor spreading rate which increased at the barremian aptian boundary significantly peaked in the late early aptian a mantle plume in the pacific possibly caused an additional production of oceanic crust both processes caused a major sea level rise this in turn resulted in a major change of the palaeoceanographic setting and restricted marginal seas like the northwestern european basins in barremian times became drowned the more open oceanic setting of the aptian enabled cosmopolitan floras and faunas to spread worldwide the aptian saw the radiation of planktonic foraminifera which played only a minor role in pre aptian times these palaeoceanographic changes from restricted marginal seas to a more homogeneous pelagic setting are considered to be the main cause for the significant changes in the composition of belemnite faunas

lithospheric scale analogue modelling of collision zones with a pre existing weak zone lithospheric scale analogue experiments have been conducted to investigate the influence of strength heterogeneities on the distribution and mode of crustal scale deformation on the resulting geometry of the deformed area and on its topographic expression strength heterogeneities were incorporated by varying the strength of the crust and upper mantle analogue layers and by implementing a weak plate or part of a plate between two stronger ones three brittle crust viscous crust strong viscous upper mantle and four brittle crust viscous crust brittle upper mantle strong viscous upper mantle layer models were confined by a weak silicone layer on one side in order to contain but not oppose lateral extrusion experimental results show that relative strength contrasts between converging plates and intervening weak plates control the location and the shape of deformation sites taken as collision orogens if the contrast is small internal deformation of the strong plates through fore and backthrusting occurs early in the deformation history however the bulk system is dominated by buckling that nucleates on the weak plate whose antiformal topography is highest model moho of the bordering stronger plates is deepest under these conditions if the contrast is large deformation remains localized within the weak plate for a larger amount of shortening and develops a root zone below a narrow deformation belt which coincides with the locus of maximum topography implementing a buoyant low viscosity layer above the model moho of the weak plate favours the development of asymmetric model orogens notwithstanding the initial symmetric setup once the asymmetry is established strain remains localized in thrust faults and ductile shear zones documenting foreland directed displacement of the model orogen such laterally and vertically irregular configurations have applications in continent continent collision settings such as the eastern alps first order mechanical boundary conditions recognized from modelling to be favourable to the post early oligocene tectonics of the eastern alps include 1 subtle rather than high strength contrasts between the adriatic indentor and the strongly deformed region comprising penninic and austroalpine units to the north of it 2 decoupling of penninic continental upper crust from its substratum to allow for crustal scale buckling of the tauern window 3 weak mechanical behaviour of the european lower crust during collision to account for its constant thickness along the transalp deep seismic transect and 4 the direct continuation of the basal detachment underlying the fold and thrust belt in the hangingwall of the european plate with a wide ductile shear zone in the core of the orogen which separates the european from the adriatic plate the geological society of london 2005

paleogeography and paleocurrents of the barremian strata in japan ne china and sikhote alin russia abstract barremian strata are exposed in japan ne china and sikhote alin and consist of nonmarine and marine sediments that yield fossil molluscs conchostracans dinosaurs and terrestrial plants because of the interfingering relationship between nonmarine and marine sediments the coast of the eastern margin of the asian continent in barremian time is identified with in these areas these areas were strongly influenced by sea level change the second transgression phase as recognized around japan the tetori group and the severosuchanskaia formation in southern sikhote alin are interpreted to have been deposited under a same barremian gulf whose north facing mouth as interpreted by paleocurrent directions facies relationships and the occurrence of common nonmarine bivalve species the occurrence of ammonites and inoceramids found in the tethys nw europe northern pacific and boreal provinces in southwest japan ne china and sikhote alin provides important evidence for both cold and warm currents originating in the arctic and near the equator respectively both current distributions in southwest japan ne china and sikhote alin during the barremian are inferred from the coriolis force the gulf is identified from the tetori group and the severosuchanskaia formation and is considered therefore to be influenced by the current from the arctic

orocline and syntaxes formation during subduction and collision 1 the present work investigates the formation of curved ranges and syntaxes with scaled laboratory experiments we simulated subduction and collision processes comparable to india asia configuration involving a continental upper plate and a subducting plate composed of an oceanic lithosphere and a continental indenter the experiments reveal that the shape of the mountain range concave straight or convex and the development of syntaxes are controlled by the subduction interface the buoyancy number fb of the upper plate i e thickness and viscosity and the boundary conditions four end members regimes of indentation can be defined depending on the range shape and dynamics of the upper plate the curvature of the range is convex toward the subducting plate with syntaxes for a weak subduction fault and concave without syntaxes for a strong subduction fault convex curvature and syntaxes form by overthrusting of upper plate material on the subducting plate which is faster at the center than at the extremities they are associated with a rather flat slab underthrusting during continental collision low fb experiments show less pronounced curvatures associated to thickening comparable to the early stages of the india asia collision in contrast a thick and weak upper plate high fb leads to gravity collapse that increases the amplitude of the curvature and lateral escape similar to the late evolution of the himalaya tibet system important lateral decoupling on the sides of the indenter enhances the indentation and produces sharper syntaxes

partitioning of crustal shortening during continental collision 2 d thermomechanical modeling partitioning of crustal shortening between the colliding continental plates is highly variable in nature physical controls of such variability remain largely enigmatic and require quantitative understanding in this study we employ 2 d thermomechanical numerical modeling to investigate the influence of the rheological properties of the continental crust on the dynamics and distribution of crustal shortening during continental collision three major physical parameters i the mechanical strength of the upper crust ii the moho temperature and iii the convergence rate are investigated and their influences on crustal shortening partitioning between the lower and upper plates are systematically documented numerical modeling results suggest that a strong upper crust of the lower plate high moho temperature and slow convergence rate favor migration of crustal shortening from the lower to the upper plate our numerical modeling results compare well with natural observations from the alpine orogenic system where variable partitioning of crustal deformation between the plates is documented

subsidence and uplift by slab related mantle dynamics a driving mechanism for the late cretaceous and cenozoic evolution of continental se asia continental se asia is the site of an extensive cretaceous paleocene regional unconformity that extends from indochina to java covering an area of c 5 600 000 km the unconformity has previously been related to microcontinental collision at the java margin that halted subduction of tethyan oceanic lithosphere in the late cretaceous however given the disparity in size between the accreted continental fragments and area of the unconformity together with lack of evidence for requisite crustal shortening and thickening the unconformity is unlikely to have resulted from collisional tectonics alone instead mapping of the spatial extent of the mid late cretaceous subduction zone and the cretaceous paleocene unconformity suggests that the unconformity could be a consequence of subduction driven mantle processes cessation of subduction descent of a northward dipping slab into the mantle and consequent uplift and denudation of a sediment filled late jurassic and early cretaceous dynamic topographic low help explain the extent and timing of the unconformity sediments started to accumulate above the unconformity from the middle eocene when subduction recommenced beneath sundaland throughout continental se asia referred to here as sundaland fig 1 there are almost no upper cretaceous and paleocene strata suggesting that much of the region was elevated during this time cenozoic rocks rest on older rocks with a profound unconformity rocks beneath the unconformity are considered basement and comprise predominantly cretaceous and older granites mesozoic sedimentary rocks accreted ophiolitic and arc rocks and pre mesozoic metamorphic rocks sedimentary rocks above the unconformity are eocene and younger fig 1 and include siliciclastic volcanogenic and carbonate lithologies that were deposited across the region in extensional halfgraben basins and at the sundaland continental margins these deposits are initially commonly terrestrial and their depositional ages are often poorly constrained the unconformity has previously been interpreted as the result of a poorly defined tectonothermal event that occurred throughout indochina and the malay peninsula e g krahenbuhl 1991 ahrendt et al 1993 dunning et al 1995 upton 1999 or as a consequence of continental collision at the sundaland margin e g hall morley 2004 smyth et al 2007 hall 2009 however there has been no attempt to estimate the extent of or describe the unconformity itself or to propose a driving mechanism capable of producing uplift over such a large area in this paper we demonstrate that the area covered by the unconformity is in excess of 5 600 000 km c 2000 by c 2800 km greater than the area of the western united states fig 2 or ten times the size of mainland france and it extends from indochina to se borneo and east java fig 1 and that micro continental collisions in the late cretaceous were coincidental with the onset of regional uplift however from an assessment of the spatial extent of accreted continental crust the corresponding extent of the unconformity fig 1 and regional exhumation trends we suggest that uplift of a late jurassic to early mid cretaceous dynamic topographic low dtl also contributed to the formation of the unconformity uplift was triggered by termination of subduction slab detachment and the resulting dynamic rebound across the region furthermore we support the suggestion hall 2009 that the initiation of cenozoic basin development may have been related to resumption of subduction at c 45 ma from hall r cottam m a wilson m e j eds the se asian gateway history and tectonics of the australia asia collision geological society london special publications 355 37 51 doi 10 1144 sp355 3 0305 8719 11 15 00 the geological society of london 2011 fig 1 a our interpreted extent of the unconformity the core of sundaland as defined by hamilton 1979 and the approximate positions of accreted ophiolitic and arc type rocks and continental fragments added to the margin in the late cretaceous b sedimentary basins and their ages in the region that is affected by the unconformity highlighted basins are the malay nam con son west natuna central sumatra south sumatra kutei barito and se java basins polochan et al 1991 gwang et al 2001 doust noble 2008 smyth et al 2008 simplified lithostratigraphies are shown in figure 6 b clements et al 38

new morphostructural subdivision of the western carpathians an approach integrating geodynamics into targeted morphometric analysis abstract a new quantitative method of morphostructure delimitation based on targeted morphometric analyses and multivariate statistical methods was applied to the western carpathians nine specific morphostructural regions and sixteen subregions were defined as an improvement on the preceding qualitative subdivision of the area the integration of geodynamics into the targeted morphometric analysis represents a prerequisite for better interpretability of the delimited regions the new subdivision of the western carpathians therefore reflects first of all the pliocene quaternary geodynamics that controls the development of the present day relief the results also help to understand the timing of the basic dome like morphostructural formation of the western carpathians which began 4 6 million years ago with the main stage continuing until the late pliocene and accelerated uplift taking place since the middle pleistocene as well as the mechanism of its formation the importance of the middle miocene extension for the development of the basin and mountain mosaic unique to the western carpathians is documented the projection of the older structural boundaries into the new morphostructural regions and the increasing prevalence of the young morpholineament systems n s and w e on the southern and northern periphery of the western carpathians could be an indication of the gradual spreading of the western carpathians into the surrounding lowlands during the last stage of the morphotectonic development

the paradox of drowned carbonate platforms and the origin of cretaceous pacific guyots geochemical stratigraphic and palaeolatitudinal data from deep boreholes drilled through pacific guyots flat topped seamounts help to explain the drowning of these cretaceous shallow water carbonate platforms that once thrived through the accumulation of biogenic and inorganic calcium carbonate sediment in mid oceanic regions the platforms drowned sequentially over a 60 million year interval while they were being transported northward by pacific plate motion through a narrow equatorial zone 0 10 s such platforms were apparently resistant to the effects of cretaceous oceanic anoxic events although the mechanism responsible for drowning remains unknown the tropics have not always been the refuge for atolls that they are today

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

lithospheric scale structures from the perspective of analogue continental collision abstract analogue models were employed to investigate continental collision addressing the roles of 1 a suture zone separating different crustal blocks 2 mid crustal weak layers and 3 mantle strengths these models confirmed that low amplitude lithospheric and crustal buckling is the primary response to shortening with a wavelength mainly controlled by the strong upper crust and or lithospheric mantle with increasing shortening bivergent thrusts formed across the brittle layers equivalent to upper crust at inflection points of the buckles while ductile layers lower crust and mantle continued being folded the resulting geometries displayed pop ups and pop downs above the boundaries sutures between blocks further shortening led to wider thrust bounded deformation zones belts in front of the stronger blocks identified as effective indenters during shortening upward extrusion into belts allowed exhumation of deep material weak layers enhanced strain localisation these modelling results have similarity in large scale structures of modern orogens and are relevant to the understanding of natural collisional processes

a minimum thermodynamic model for the bipolar seesaw 1 the simplest possible model is proposed to explain a large fraction of the millennial climate variability measured in the isotopic composition of antarctic ice cores the model results from the classic bipolar seesaw by coupling it to a heat reservoir in this thermal bipolar seesaw the heat reservoir convolves northern time signals with a characteristic timescale applying the model to the data of grip and byrd we demonstrate that maximum correlation can be obtained using a timescale of about 1000 1500 years higher correlations are obtained by first filtering out the long term variability which is due to astronomical and greenhouse gas forcing and not part of the thermal bipolar seesaw the model resolves the apparent confusion whether northern and southern climate records are in or out of phase synchronous or time lagged

far field strain transmission and contractional step overs abstract in contractional subduction collisional settings convergence is accommodated by the formation of thin and thick skinned thrust and fold belts the transmission of such deformation over larger distances into orogenic foreland areas is influenced by the inherited rheological characteristics of continental lithosphere lateral rheological variations parallel to the strike of continental foreland areas creates contrasting geometries and sequences of deformation that interact during orogenic build up we investigate the far field transmission of strain within a continental lithosphere characterized by a laterally variable rheology through physical analogue modelling rheological weak crustal zones were introduced at distance from an advancing backstop to study the progressive along strike linkage and interference of structures during contraction the results reveal that rheologically weak crustal zones localise far field contractional deformation when the size of weak zones by means of their horizontal extend to depth ratio is large deformation localises at the boundaries of the weak zone where they lead to the formation of large offset faults subsequently the faults migrate along strike into areas that are rheologically stronger when the size of the weak zone is reduced a large scale contractional step over forms in orogenic forelands where rheologically contrasting domains transmit out of sequence deformation by a gradual migration of thrust offsets and fold amplitudes along their strike these results show that crustal scale orogenic step overs do not always reflect variations in the geometry of the plate boundary indenter or along strike gradients in shortening rates such features may also form in response to variations in rheology as the ones created by inherited extensional basins situated at large distances from plate boundaries in the orogenic foreland

quantifying tectonic versus erosive denudation by the sediment budget the miocene core complexes of the alps abstract the denudation budget of the alps is quantified for the main period of lateral extrusion between 22 and 12 ma the relative importance of tectonic denudation increases from w to e from 70 in the lepontine window in the swiss alps to 80 in the tauern window and to more than 95 in the rechnitz window the driving mechanism of tectonic denudation was eastward extrusion due to an unconstrained orogenic margin in the pannonian basin tectonic denudation in the alps was responsible for about 30 of the total exhumation between 22 and 12 ma

decoupling during continental collision and intra plate deformation abstract fundamental aspects of mountain building such as the dominant deformation mechanism strain localisation and topography development in response to the presence of decoupling zones either along boundaries of weak and strong lithospheres or within weak domains of continental lithosphere are studied by analogue lithospheric models scenarios are investigated where a weak part of the lithosphere is bordered on either side by stronger lithospheres geometries of the weak zone vary from box to wedge to graben shaped representing lateral strength variations as a consequence of earlier deformation phases the rheologic and geometric configuration at the onset of shortening is therefore considered as representative for continental collision and intra plate settings the modelling results show that the geometric and topographic evolution of mountain belts through time is sensitive to the presence of decoupling horizons along plate or tectonic boundaries this is because the decoupled boundaries localise strain control the dominant deformation mechanism and hence the locus of uplift and subsidence accordingly decoupled boundaries favour deformation by thrusting and particularly in the case of an initially wedge shaped weak zone the development of mountain belts with overall triangular shape in contrast lithospheres with coupled boundaries dominantly deform by buckling irrespective of the initial geometry of the weak zone as this deformation mechanism affects all model domains it produces a distinguishable pattern of uplift and subsidence controlled by buckling strong decoupling at mid crustal levels within the weak zone favours vertical strain partitioning and the formation of plateau shaped mountains the modelling results suggest that natural collisional systems should respond to an increase in plate coupling through time by widespread uplift of the mountain belt including its foreland basins which were formerly created under decoupled conditions due to the absence of decoupling zones like plate contacts weak domains in intra plate settings are predicted to deform dominantly by buckling

analogue modelling of continental collision influence of plate coupling on mantle lithosphere subduction crustal deformation and surface topography abstract the role of the plate boundary in a continental collisional setting is investigated by lithospheric scale analogue models key variables in this study are the degree of coupling at the plate interface and along the moho of the lower plate as well as the geometry of the plate contact they control the onset of intra plate deformation orogenic architecture amount of mantle lithosphere subduction and basin development in all experiments deformation initiates at the plate interface by the formation of a pop up structure a vertical plate boundary with respect to the shortening direction results in buckling of the lithosphere whereas experiments with an inclined plate boundary show underthrusting and foreland basin development without orogenic wedge formation continental collision and coinciding mantle lithosphere subduction may occur only if the lower crust of the foreland plate is weak enough promoting crust mantle decoupling during decoupling the weak lower crust beneath the orogen thickens significantly by ductile flow as it detaches from the down going mantle lithosphere this lower crustal thickening effects the distribution of upper crustal deformation and topography subduction of weak lower crust is favored when the weak plate interface has a significant thickness 15 km in nature and a high amount of shortening is applied increasing coupling at the plate interface through time leads to intra plate deformation by thickening and gentle folding and influences surface uplift and subsidence above the plate interface the transition from a mechanically decoupled plate boundary with a significant amount of mantle lithosphere subduction towards stronger plate coupling resulting in intra plate deformation and topography development can be recorded in for instance the caucasus the colombian cordillera the pyrenees and the alps thickening of the lower crust as portrayed for the western alps does not demand a strong frictional type behavior of the lower crust but can also be the consequence of ductile processes

middle cretaceous reef collapse linked to ocean heat transport biologically defined fluctuations in cretaceous tropical reef boundaries of the caribbean region record a dynamic rather than stable environmental history these fluctuations may be related to major thermal changes resulting from ocean heat transport with simultaneous poleward movement of surface and subsurface waters on sea level highstands the superheated middle cretaceous tropics cooled the reef line contracted diversity decreased and reef ecosystems collapsed leading to mass extinction geologic data qualitatively test and support the hypothesis of enhanced cretaceous ocean heat transport formulated from general circulation models in these models four times the present day atmospheric concentration of co 2 and twice the present day model value of ocean heat transport cooled the superheated tropics and provided the best match to the distribution of inferred middle cretaceous temperature data these dynamic changes suggest an important role for large scale disturbance in the evolution of tropical ecosystems

decoupling along plate boundaries key variable controlling the mode of deformation and the geometry of collisional mountain belts the consequences of decoupling between weak orogenic wedges and strong adjacent foreland plates are investigated by means of lithospheric scale analogue modeling decoupling is implemented in the three layer models by lubrication of the inclined boundary between a strong foreland and a weak orogenic wedge plate boundaries are orthogonal to the convergence direction experimental results show that strong decoupling between the foreland and the orogenic wedge leads to underthrusting of the former underneath the orogenic wedge and deformation of the orogenic wedge by folding shearing and minor backthrusting shortening is mainly taken up along the main overthrust the decoupled boundary and within the orogenic wedge leaving the indenter devoid of deformation in contrast strong coupling between the foreland and the orogenic wedge favors buckling involving both the weak zone and the strong plates the results of these end member models have implications for collision zones for example the eastern alps in europe such that the switch from localized deformation within the orogenic wedge during the oligocene middle miocene to orogen scale uplift and deformation during the late miocene pliocene involving the foreland and indenter plates respectively is interpreted as reflecting a change from a decoupled to a coupled system

integrated gravity and topography analysis in analog models intraplate deformation in iberia in the western part of the iberian microplate the main topographic highs trend e w to ne sw and are periodically spaced with wavelengths of 250 km conversely in the northeastern part the region of the iberian chain topography is more irregular and strike directions vary from nw se to e w and ne sw we relate this phenomenon to shortening of a continental lithosphere which contains two different well defined domains of lithospheric strength our hypothesis is supported by physical analog models a new processing method has been developed to assist the interpretation of the model results it utilizes spectral analysis of gravity and topography data derived from the experiments folding of the crust and mantle lithosphere yields periodic gravity fluctuations while thickening processes lead to localized gravity lows in this way gravity data can be used to distinguish between the two forms of lithosphere deformation and to correlate areas that underwent the same type of deformation gravity modeling has been performed under full in depth control of the experimental lithosphere structure as such gravity signals from the models may be compared to field gravity data for better understanding the underlying deformation mechanism

late mesozoic cenozoic sedimentary basins of active continental margin of southeast russia paleogeography tectonics and coal oil gas presence abstract various settings took place during the late mesozoic divergent convergent collisional and transform after mid jurassic collision of the siberian and chinese cratons a latitudinal system of post collision troughs developed along the mongol okhotsk suture the uda torom basins and others filled with terrigenous coal bearing molasse the dispersion of pangea creation of oceans during the late jurassic are correlated to the emergence of the east asian submeridional rift system with volcano terrigenous coal bearing deposits the amur zeya basin at that time to the east there existed an andean type continental margin foreland upper bureya partizansk and razdolny and flexural sangjiang middle amur basins were formed along the margin of the rigid massifs during the late jurassic to berriasian during the valanginian mid albian an oblique subduction of the izanagi plate beneath the asian continent occurred producing a transform margin type considerable sinistral strike slip displacements and formation of pull apart basins filled with turbidites the sangjiang middle amur basin the aptian is characterized by plate reorganization and formation of epioceanic island arcs fore arc and back arc basins in sakhalin and the sikhote alin the alchan and sangjiang middle amur basins filled with volcanoclastics during the mid albian a series of terranes accreted to the asian continental margin by the end of the albian the east asian marginal volcanic belt began to form due to the subduction of the kula plate beneath the asian continent during the cenomanian coniacian shallow marine coarse clastics accumulated in the fore arc basins which were followed by continental deposits in the santonian campanian from the coniacian to the maastrichtian a thermal subsidence started in rift basins and continental oil bearing clastics accumulated the amur zeya basin widespread elevation and denudation were dominant during the maastrichtian this is evidenced by thick sediments accumulated in the western sakhalin fore arc basin during the cenozoic an extensive rift belt rmade up of a system of grabens which were filled with lacustrine alluvial coal and oil bearing deposits developed along the east asian margin

transfer of deformation in back arc basins with a laterally variable rheology constraints from analogue modelling of the balkanides western black sea inversion the balance between extension and contraction in back arc basins is very sensitive to a number of parameters related to on going subduction and collision processes this leads to complex back arc geometries where a lateral transition between crustal blocks with contrasting rheologies is often recorded one good example is the back arc region of the balkanides pontides orogens where lateral variations in rheologies are observed between the balkanides moesian block and the pontides western black sea basin the latter opened during cretaceous eocene and has been inverted together with the former starting during late middle eocene the inversion generated contrasting geometries along the orogenic strike with a narrow zone of high deformation in the balkanides moesia region wide areas of thrusting with low offsets in the pontides western black sea basin and a transitional zone characterized by highly curved geometries this overall type of inversion is investigated here by the means of analogue modelling testing the role of inherited crustal geometries during inversion our modelling suggests that the contrasting architecture of inverted structures observed in the balkanides pontides domain are the result of pre existing crustal stretching geometries of various blocks inherited from the cretaceous eocene extension the stretched and weak back arc basins can transfer contraction deformation at large distances explaining structures derived by observational studies the collisional deformation recorded in the pontides was transmitted at large distances that are in the range of the contraction structures observed in the centre and northern part of the western black sea in the light of analogue modelling results we argue that the western black sea was a rheologically weaker domain when compared with the adjacent western onshore at the beginning of the inversion in contrast with previous results derived from numerical modelling studies that argued for a strong west black sea domain at the beginning of inversion

extreme polar warmth during the cretaceous greenhouse paradox of the late turonian δ18o record at deep sea drilling project site 511 1 oxygen isotope data for upper turonian planktonic foraminifera at deep sea drilling project site 511 falkland plateau 60 s paleolatitude exhibit an 2 excursion to values as low as 4 66 vienna peedee belemnite standard pdb coincident with the warmest tropical temperature estimates yet obtained for the open ocean the lowest planktonic foraminifer 1 8 o values suggest that the upper ocean was as warm as 30 32 c this is an extraordinary temperature for 60 s latitude but is consistent with temperatures estimated from apparently coeval mollusc 1 8 o from nearby james ross island 65 s paleolatitude glassy textural preservation a well defined depth distribution in site 511 planktonics low sediment burial temperature 32 c and lack of evidence of highly depleted pore waters argue against diagenesis even solid state diffusion as the cause of the very depleted planktonic values the lack of change in benthic foraminifer 1 8 o suggests brackish water capping as the mechanism for the low planktonic 1 8 o values however mixing ratio calculations show that the amount of freshwater required to produce a 2 shift in ambient water would drive a 7 psu decrease in salinity the abundance and diversity of planktonic foraminifera and nannofossils high planktonic benthic ratios and the appearance of keeled foraminifera argue against lower than normal marine salinities isotope calculations and climate models indicate that we cannot call upon more depleted freshwater 1 8 o to explain this record without more late turonian data especially from outside the south atlantic basin we can currently only speculate on possible causes of this paradoxical record from the core of the cretaceous greenhouse

geodynamics of the western part of the mongolia okhotsk collisional belt trans baikal region russia and mongolia abstract after the western edge of the mongolian microcontinent joined the siberian continent in the region of central mongolia in the earliest permian these two continental blocks remained turned at an angle of about 120 with respect to each other and separated on greater extent of their present day boundary by an enormous gulf of the paleopacific called the mongolia okhotsk ocean closure of this ocean at the early middle jurassic boundary led to the complete collision of siberia and mongolia which by then had already become part of the mongolia north china continent this main collisional episode which lasted through the middle and late jurassic involved thrusting folding and magmatism and produced the mongolia okhotsk belt the onon island arc which was located in the mongolia okhotsk ocean was squeezed between the two major continents inasmuch as the third element the island arc was involved in the collision it is reasonable to distinguish two branches of the mongolia okhotsk suture these branches control the spatial distribution of gold mineralization in the trans baikal region on the southeastern periphery of siberia the crust thickened considerably after the collision and a plateau like uplift formed in the early cretaceous when compression ceased the collisional uplift collapsed and the thrusts were transformed into low angle normal faults the motions on which were responsible for the formation of rift basins and exhumation of metamorphic core complexes

cooling and vertical motions of crustal wedges prior to during and after lateral extrusion in the eastern alps new field kinematic and fission track data from the mur murz fault system new structural and thermochronological zircon and apatite fission track data from the eastern most alps highlight distinct deformation phases affecting the austroalpine unit along a major sinistral strike slip fault system the mur murz fault mmf the data link deformation to vertical motions prior to during and after the main phase of lateral extrusion of the orogen zircon fission track ages document rapid ca 15 c myr and diachronous eastward younging cooling and rock exhumation during the latest cretaceous to paleocene subsequent regional eocene to early miocene cooling below the closure temperature of the apatite fission track system occurred at slow rates ca 2 c myr suggesting that the region was not subject to major surface uplift and erosion during that period fault kinematic analysis along the mmf document pre extrusion nnw sse contraction middle miocene syn extrusion ne sw to nne ssw directed shortening and late miocene e w contraction all phases are characterized by strike slip fault regimes formation of the complex mmf zone triggered the exhumation of small fault bound crustal blocks within the fault zone as documented by middle miocene apatite fission track ages overall ages are similar on both sides of the fault suggesting that lateral extrusion along the mmf was not associated with significant differential vertical motions local pliocene rock cooling and exhumation was probably related to the buttressing effect of the underthrust bohemian basement spur whereas large scale post extrusion surface uplift of the extruding crustal wedges such as the styrian block must have been related to long wavelength deformation processes affecting the easternmost alps

forces driving continental collision reconciling indentation and mantle subduction tectonics two end member classes of models indentation and mantle subduction that have been proposed to explain patterns of crustal deformation during continental collision may be reconciled using a model that includes a combination of indentation from the side and basal forcing from underlying subducting layers measurement of the width of deformation across strike can be used to indicate the predominant forcing mechanism and shows that the combined case is controlled by mantle subduction if the crust is well coupled to the underlying mantle lithosphere or by indentation if the crust and mantle lithosphere are decoupled an increase in the width of deformation with convergence as a result of the effect of gravity on crustal thickening can cause a change in the primary control of an orogenic system from mantle subduction to indentation this transfer may be enhanced by diffusional or convective heating at the base of the thickened crust the india eurasia collision is an example where the deformation width may initially have depended on mantle subduction but is now controlled by the indenter limit

thick skinned tectonics and basement involved fold thrust belts insights from selected cenozoic orogens defining the structural style of fold thrust belts and understanding the controlling factors are necessary steps towards prediction of their long term and short term dynamics including seismic hazard and to assess their potential in terms of hydrocarbon exploration while the thin skinned structural style has long been a fashionable view for outer parts of orogens worldwide a wealth of new geological and geophysical studies has pointed out that a description in terms of thick skinned deformation is in many cases more appropriate this paper aims at providing a review of what we know about basement involved shortening in foreland fold thrust belts on the basis of the examination of selected cenozoic orogens after describing how structural interpretations of fold thrust belts have evolved through time this paper addresses how and the extent to which basement tectonics influence their geometry and their kinematics and emphasizes the key control exerted by lithosphere rheology including structural and thermal inheritance and local regional boundary conditions on the occurrence of thick skinned tectonics in the outer parts of orogens

what drove late mesozoic extension of the northern china mongolia tract the northern china mongolia tract exhibited a tectonic transition from contractional to extensional deformation in late mesozoic time late middle to early late jurassic crustal shortening is widely thought to have resulted from collision of an amalgamated north china mongolia block and the siberian plate but widespread late late jurassic early cretaceous extension has not been satisfactorily explained by existing models some prominent features of the extensional tectonics of the northern china mongolia tract are 1 late jurassic voluminous volcanism prior to early cretaceous large magnitude rapid extension 2 overlapping in time of contractional deformation in the yinshan yanshan belt with development of extensionrelated basins in the interior of the northern china mongolia tract and 3 widespread occurrence of alkali granitic plutonism extensional basins and metamorphic core complexes in the early cretaceous a new explanation is advanced in this study for this sequence of events the collision of amalgamated north china mongolia with siberia led to crustal overthickening of the northern china mongolia tract and formation of a high standing plateau subsequent breakoff at depth of the north dipping mongol okhotsk oceanic slab is suggested as the main trigger for late mesozoic lithospheric extension of that tract slab breakoff resulted in mantle lithospheric stretching of the adjacent northern china mongolia tract with subsequent ascent of hot asthenosphere and magmatic underplating at the base of the crust collectively these phenomena triggered gravitational collapse of the previously thickened crust leading to late late jurassic early cretaceous crustal extension and importantly coeval contraction along the southern margin of the plateau in the yinshan yanshan belt the proposed model provides a framework for interpreting the spatial and temporal relationships of distinct processes and reconciling some seemingly contradictory phenomena such as the synchronous extension of northerly terranes during major contraction in the neighboring yanshan yinshan belt d 2003 elsevier b v all rights reserved

the role of lateral strength contrasts in orogenesis a 2d numerical study in this paper we present a series of thermo mechanical experiments on continent continent collision zones to investigate the role of lateral strength contrasts in terms of collision dynamics and orogen geometries our results show that differences in crustal rheology may lead to a variety of different patterns of deformation and crustal geometries upper plate indentation forms a sequence of foreland propagating thrust units made of brittle upper crust on the lower plate the strong deformation of the lower plate stands in stark contrast to the undeformed upper plate in contrast subduction of strong lithosphere beneath a weak upper plate forms a complex pattern of deformation deformation initiates on the lower plate and forms an antiformal stack made of brittle upper crust before it indents the upper plate hence deformation is present on both the lower and upper plate despite differences in initial strength the outcome of this study has direct implications to natural collision zones where differences in strength between the upper and lower plate exist for example along strike variability of upper vs lower plate shortening in the alps are likely to be controlled by contrasts in crustal strength furthermore we suggest that the antiformal stack in the axial zone of the pyrenees might indicate a strong lower plate at the onset of collision our results may therefore provide important constraints for the rheological state of continents during collision

styles of post subduction collisional orogeny influence of convergence velocity crustal rheology and radiogenic heat production abstract a number of models of continental collision already exist but the role of foregoing oceanic plate subduction or variable coupling between plates still remains to be explored in addition heat generation by radioactive decay may be quite variable for example our geochemical data from low to high grade metamorphic rocks of the lesser and higher himalayan sequences reveal measured heat production values on the order 4 5 w m 3 which is considerably higher than normal inferred upper crustal values 3 therefore we performed 2d numerical experiments of oceanic continental subduction followed by continental collision for varying continental lower crustal strength convergence velocity and radiogenic heating rate oceanic subduction produces thinning and upwarping of the overriding lithospheric wedge such as is observed in andean type collisional settings cascadia and central andes after collision two main orogenic styles develop depending on the values of key parameters either a slow convergence rates weak shear heating and consequently strong rheological coupling between plates and or a weak lower crust generate a two sided thick and narrow symmetrical collisional zone or b high convergence rates strong shear heating and therefore weak rheological coupling between plates and a strong lower crust produce a one sided thin and broad asymmetrical collisional zone in this case a vertical lithospheric body divides two upper crustal wedges that develop distinct deformation patterns in both cases enhanced radiogenic heating favors the formation of midcrustal partially melted channels that propagate toward the surface and the pro foreland partial melting triggers lateral extrusion of metamorphic rocks from different depths 15 23 kbar 700 c on top of coherent lp lt units the geometry of metamorphic isograds inverted shapes of p t paths at different grades and exhumation rates are similar to those observed in parts of the himalayan chain indicating that the models capture the essence of real systems the model results demonstrate that internal heat production rate is a crucial parameter in determining the timing of slab breakoff polarity reversal and exhumation of the inverted metamorphic sequence with respect to the timing of partial melting late stages of some numerical experiments showed interesting geodynamical evolution of the collisional zone with the appearance of polarity reversal roll over of both plates and roll back of the subducting slab irrespective of these details hundreds of km of continental lithosphere are recycled into the mantle in all models supporting the idea that continental crustal consumption is indeed a common and considerable process during collision this affects inferences about extents of convergence and or shortening during orogenesis moreover crustal recycling into the deep mantle during collisional orogeny needs to be considered in models of crustal growth and evolution

structure and provenance of late cretaceous miocene sediments located near the ne dinarides margin inferences from kinematics of orogenic building and subsequent extensional collapse the ne part of the dinarides mountain chain located near their junction with the carpatho balkanides is an area where sedimentary basins associated with the neotethys subduction and collision are still exposed we performed a provenance study based on detrital fission track thermochronology combined with zircon upb magmatic geochronology and existing studies of kinematics and exhumation our study shows rapid sedimentation in the trench and forearc basin overlying the upper european tectonic plate a number of latest cretaceous early paleocene igneous provenance ages show a dominant magmatic source area derived from a late cretaceous subduction related arc this arc shed short time lag sediments in the forearc and the trench system possibly associated with focused exhumation in the serbo macedonian margin this was followed by burial of the trench sediments and a novel stage of middle late eocene exhumation driven by continued continental collision that had larger effects than previously thought the collision was followed by late oligocene miocene exhumation of the former lower adriatic plate along extensional detachments that reactivated the inherited collisional contact along the entire dinarides margin this event re distributed sediments at short distances in the neighboring miocene basins our study demonstrates that the dinarides orogenic system is characterized by short lag times between exhumation and re deposition whereas the upper tectonic plate is significantly exhumed only during the final stages of collision such an exhumation pattern is not directly obvious from observing the overall geometry of the orogen

a warm equable cretaceous the nature of the problem abstract the nature of the problem of warm equable paleoclimates is defined by investigating the mid cretaceous period the problem consists of three components 1 defining precisely the climatic state during any specified interval of geologic time 2 specifying the external climatic forcing factors which may have been important and 3 understanding the climatic response to any specific modifying influence these components are characterized by limitations of critical importance in understanding paleoclimates the nature of the problem of a warm cretaceous is defined both qualitatively and quantitatively within these limits

does subduction polarity changes below the alps inferences from analogue modelling the surface expression of a lateral polarity change of continental mantle lithosphere subduction has been studied by using lithosphere scale physical models key parameters investigated were the degree of lateral coupling between adjacent domains of opposing subduction polarity the width of the zone separating the domains and the lithosphere geometry and rheology the model results illustrate an asymmetric lithospheric structure induced by deformation of the downgoing plates which have been separated by a narrow transition zone a wide and symmetric orogenic wedge overlying a region of thickened mantle lithosphere and hampered subduction characterizes this transition zone in addition interaction between the neighboring subduction domains caused downbending of the upper plates and resulted in the lateral termination of crustal structures and lowering of surface topography the lateral extent of interaction between the domains strongly depends on the degree of coupling between the domains the rheology of the mantle lithosphere and the amount of bulk shortening the modelling results have major implications on the interpretation of seismic and tomographic data from the european alps in terms of the crust and lithosphere geometries it appears that an observed lateral change of subduction polarity at mantle depth can explain the variations of wedge build up between the western central and eastern alps

variability of orogenic magmatism during mediterranean style continental collisions a numerical modelling approach abstract the relationship between magma generation and the tectonic evolution of orogens during subduction and subsequent collision requires self consistent numerical modelling approaches predicting volumes and compositions of the produced magmatic rocks here we use a 2d magmatic thermomechanical numerical modelling procedure to analyse rapid subduction of a narrow ocean followed by mediterranean style collision which is characterized by the gradual accretion of lower plate material and slab migration towards the orogenic foreland our results suggest that magmatism has a large scale geodynamic effect by focusing deformation throughout the entire subduction and collision process the rheological structure and compositional layering of the crust impose a key control on the distribution of magmatic rocks within the orogen compared to previous simplified homogeneous crustal models a compositionally layered crust causes an increase in felsic material influx during continental collision and results in shallower magmatic sources that migrate with time towards the foreland changes in the deformation style may be locally driven by magma emplacement rather than by slab movement our modelling also demonstrates that the migration pattern of the deformation front and the magmatic arc relative to the location of the suture zone may be driven by lower crustal indentation in the overriding plate during early stages of collision the modelling predicts a gradual change in magma source composition with time from typical calc alkaline to ones associated with relamination and eduction during subduction collision and slab detachment this transition explains the compositional changes of magma their temporal and spatial migration as well as the observed link with deformation in the dinarides orogen of central europe selected as a case study

alpine metamorphism in the south east tauern window austria 2 rates of heating cooling and uplift existing geochronological data are reviewed and new rb sr k ar and 39ar 40ar ages are presented including a suite of 33 mica ages from a 20 km north south tunnel section these data are discussed in relation to the thermal history from the overthrusting of the autroalpine nappes c 65 myr ago to the present the earliest phase of metamorphism involving lawsonite crystallization is associated with emplacement of these nappes subsequently temperatures in the rocks beneath rose at a mean rate of 3 6 c myr until the climax of metamorphism at high structural levels published data indicate an age 35 myr for the metamorphic climax in contrast a new 39ar 40ar step heating age of 23 8 0 8 myr on amphibole from near the base of peripheral schieferhulle closely approximates the age of metamorphism and provides the first clear indication that the climax of metamorphism occurred later at deeper structure levels following the climax near isothermal uplift and erosion reduced pressure to c 1 kbar before white mica closure at 19 myr this implies uplift at 3 mm yr along the tunnel section white mica k ar ages vary systematically from 24 myr to 16 5 myr with position relative to a late 4 km amplitude dome whereas biotite rb sr ages are uniform at 16 5 myr across the whole profile doming is thus dated at 16 5 myr with transient uplift rates 5 mm yr at other times uplift rates were 1 mm yr

far field contractional polarity changes in models and nature abstract a change in contractional polarity occurs when the direction of tectonic transport switches along strike this switch is conditioned by lateral variations in rheology or inherited asymmetries such as contrasts in structure or changes in the polarity of subduction zones the parameters controlling contractional polarity changes are less understood in situations when the strain is transferred at large distances from indenters analysing this type of strain transfer is critical for understanding the mechanics of thrusting in fore or back arc settings of orogenic areas comparison of crustal scale analogue modelling with the inversion of the black sea back arc and the formation of the new guinea new britain fore arc suggest that far field changes in contractional polarity are related to rheological contrasts across inherited normal faults the initial extension creates rheological weak zones that localize the subsequent far field contractional deformation along groups of thrusts with opposite vergence along the strike of the system the largest amount of far field contractional deformation is recorded in the transfer zone located between the two indenters moving in opposite directions and is particularly high when inverting oblique extensional systems

litho and biofacies of early cretaceous rudist bearing carbonate sediments in northeastern japan abstract carbonate blocks of late aptian lower cretaceous age occur in the lower yezo group of central hokkaido in northeast japan the shallow water carbonates were emplaced by gravity sliding and rock fall into a deep water flysch basin various lithofacies can be distinguished within the blocks including massive wackestone bedded packstone and micro oncoid grainstone containing corals rudists an oyster gastropods calcareous algae and an orbitolinid foraminifer facies and palaeoecological analyses suggest deposition of low energy biostromes and sand banks in open lagoonal and restricted environments with local higher energy shoals and beaches the presence of calcareous sandstones and abundant insoluble residues in limestones suggest deposition in an attached carbonate platform close to a supply of terrigenous material rather than deposition upon seamounts within an oceanic setting a narrow rimmed shelf in tropical subtropical conditions would have been the depositional environment for these carbonates which were subsequently deformed into blocks and transported into deep water as a result of the tectonic collapse of the platform