stratigraphy and paleoenvironmental evolution of the dinosaur rich baruungoyot nemegt succession upper cretaceous nemegt basin southern mongolia abstract portions of the dinosaur rich upper cretaceous baruungoyot nemegt succession are exposed in four geographic areas of the nemegt basin mongolia nemegt altan uul bugiin tsav and hermiin tsav lithostratigraphic correlations of these areas employ marker beds and non random stratigraphic patterns of lithology grain size variation and inferred paleoenvironments correlations suggest a minimum thickness of 350 m for the succession exposures at nemegt altan uul and bugiin tsav form a 100 km east west transect along the northern margin of the basin exposing 265 m of section from east to west the transect exposes higher portions of the succession extending from the uppermost baruungoyot formation and encompassing an almost complete section of the nemegt formation which has a minimum thickness of 235 m and can be consistently divided into three informal members lower middle and upper the lower nemegt is well exposed at nemegt and altan uul and is dominated by fluvial deposits the middle and upper nemegt are well exposed at altan uul 2 and bugiin tsav and consist of alluvial plain paludal lacustrine and fluvial deposits as confirmed by earlier studies the baruungoyot and nemegt formations exhibit an interfingering transition at nemegt the hermiin tsav section is a geographic outlier tens of kilometers west southwest of the northern transect it exposes about 150 m of section that overlaps with but is mostly lower stratigraphically than the northern transect the uppermost hermiin tsav section correlates with the lowermost nemegt section and also exhibits an interfingering contact between the baruungoyot and nemegt formations the remaining section at hermiin tsav comprises sediments of the baruungoyot formation 135 m that were deposited in alluvial fan fluvial paludal lacustrine and eolian environments and can be divided into two informal members designated as lower and upper the distribution of facies through the composite section records changes in paleoenvironments during the late cretaceous that may provide insights into the origins of the dinosaurian biostratigraphy

calcite u pb age of the cretaceous vertebrate bearing bayn shire formation in the eastern gobi desert of mongolia usefulness of caliche for age determination

alleged vertebrate eggs from upper cretaceous redbeds gobi desert are fossil insect coleoptera pupal chambers fictovichnus new ichnogenus small egg like structures from the upper cretaceous campanian djadokhta formation of mongolia were previously interpreted as casts of crocodile lizard and turtle eggs or as inorganic nodules identical structures from coeval redbeds at bayan mandahu in northern china indicate the structures are not vertebrate eggs nor of vertebrate origin comparisons with recent and quaternary beetle coleoptera pupal chambers show close similarities in size shape and the presence of a round to irregular exit hole for the adult beetle most importantly the cretaceous structures are enveloped by a thin clay rich zone which is expected if constructed by beetle larvae but inexplicable in any egg or inorganic nodule model additional evidence contradicting a vertebrate egg origin for the structures includes i the structures are too small to have been laid by turtle or crocodile species occurring in the bayan mandahu redbeds ii the structures are isolated not in clutches or pairs and iii unlike newly hatched soft shelled lizard eggs the cretaceous structures are not collapsed and show a round to irregular exit hole rather than a slit it is concluded that the egg like structures are sand casts steinkerns of beetle pupal chambers probably of scarabaeidae tenebrionidae or curculionidae the cretaceous pupal chambers are assigned to a new ichnogenus fictovichnus and new ichnospecies fictovichnus gobiensis and fictovichnus parvus

crustal evolution of the ktb drill site from oldest relics to the late hercynian granites the crustal unit penetrated during the german continental deep drilling program ktb the zone of erbendorf vohenstrauss zev comprises an association of metabasites and paragneisses and orthogneisses that underwent high and medium pressure metamorphic cycles during the early palaeozoic in this summary of the structural petrological geochemical and geochronological information from borehole and surface rocks we show that geological models proposed prior to drilling have had to be significantly modified features of the zev such as the dominant nw se trending structures devonian 370 ma medium pressure amphibolite facies metamorphism 0 6 0 8 gpa 720 c and earlier eclogite stage are directly comparable with those of the nearby bohemicum unit in western bohemia intervening units in contrast exhibit ne sw trending structures and carboniferous 315 325 ma low pressure metamorphism all units are cut by predominantly posttectonic granites mostly 320 ma earlier models to explain this contrast by means of a nappe emplacement of the zev in the narrow time interval between the younger regional metamorphism and granite intrusion could not be substantiated because contrary to predictions the same rock association was present in the whole of the drilled 9 1 km and therefore no nappe boundary was drilled instead it is interpreted that shallow crustal levels reached by the zev subsequent to the devonian event shielded most of it from the effects of the carboniferous metamorphism a lack of expected thermal and baric gradients within the drilled metamorphic pile is a result of repeated stacking of an original 3 km depth section in mesozoic times an important result of the geological investigations of the ktb project is the recognition that the present day geometry of the zev is a result of cold shallow level thin skinned tectonics that in the absence of the view into the third dimension offered by the drill hole could not have been accurately predicted from the fossil high grade assemblages and structures seen at the surface

structural reactivation in plate tectonics controlled by olivine crystal anisotropy structures formed during ancient tectonic events are commonly reactivated during subsequent tectonism numerical models point to mechanical anisotropy arising from the inherited orientation of crystals of the mineral olivine in the lithospheric mantle as the cause of this behaviour

rheological stratification of the lithosphere abstract the rheology of the lithosphere is estimated on the basis of pore pressure dependent frictional failure in the brittle regime and power law steady state creep in the ductile regime different petrological models of the continental and oceanic lithosphere combined with different geotherms and thicknesses are used to generate models covering a variety of geodynamic situations results show that the depth dependence of lithospheric rheology varies with the tectonic province and that in many instances the continental lithosphere has one at the bottom of the crust or two the previous one plus another at mid crustal levels soft ductile layers sandwiched between brittle layers the depth distribution of geophysical parameters seismicity seismic wave velocity and electrical conductivity matches the theological predictions well the lithospheric rheological profiles are used to analyze observed variations in the structural style of deformed continental margin and oceanic terranes in the southeastern canadian cordillera the large scale characteristics of the system show a satisfactory agreement with the inferred rheological structure sub horizontal decollements should be the rule rather than the exception where the lithospheric rheology is strongly stratified

signatures of continental collisions and magmatic activity in central brazil as indicated by a magnetotelluric profile across distinct tectonic provinces broadband and long period magnetotelluric soundings were collected along a 560 km e w profile in a region of central brazil subjected to neoproterozoic collision tectonics and archean to cretaceous magmatic events the profile crosses the northeastern portion of phanerozoic sediments and volcanics of the parana basin the southern extension of the neoproterozoic metasedimentary rocks of the brasilia belt locally pervaded by cretaceous alkaline magmas of the alto paranaiba igneous province apip and neoproterozoic sedimentary cover and exposed archean basement of the southern sao francisco craton 2d conductivity structures derived by joint inversions of the te and tm polarization modes and a separate inversion of the tipper components show signatures of the past tectonomagmatic events that affected the area a gravity defined suture zone beneath the parana basin is detected in the models as a subvertical conductor extending from crustal to upper mantle depths which strengthen the interpretation of a neoproterozoic collision of the sao francisco craton and a continental block beneath the sedimentary basin deep underthrusting of organic graphite bearing metasedimentary rocks composing a fossil suture zone is proposed to explain such increase in electrical conductivity a similar conductivity signature beneath the sedimentary covered region of the sao francisco craton can be tentatively interpreted as another similar cryptic suture zone other isolated high conductivity anomalies at midcrustal depths below the parana and apip provinces are interpreted as fossil residues representing precipitated graphite and sulfide derived from percolating volatiles during the emplacement of cretaceous mafic ultramafic volcanics a very high conductivity wedge into the lower lithosphere is highlighted in the deep mantle beneath the apip volcanic complex coincident with a zone of low velocity defined by seismic tomography geochemical evidence indicates that the alkaline magmatism stemmed from a metasomatized upper mantle at only slightly raised temperatures thus interconnected carbonatite melts of low melting point and graphite in the lithospheric mantle are the most likely candidates to explain this high conductivity the seismic and conductivity anomalies are probably triggered by the same source mechanisms incipient melting because they are plausibly related to the same magmatic process conductivity anomalies at crustal and mantle depths in the southern segment of the sao francisco craton suggest that its lithosphere was significantly affected by the several tectonomagmatic episodes it has experienced throughout its geological history consequently the enhanced conductivity in the lower crust can be genetically related to upwelling volatile rich intrusions whereas upper mantle high conductivity can be related to refertilization by infiltrations of low degree carbonatitic melts from deeper sourced metasomatic processes

one dimensional resistivity modeling of ne japan from stationary wide band magnetotelluric data abstract stationary magnetotelluric mt systems were set up at the esashi station and the mizusawa geodetic observatories of geographical survey institute gsi in ne japan since 1996 continuous 24 h resistivity and phase data have been acquired by the wide band mt measurement devices the data from the two sites were processed by the remote reference technique to minimize the effect of local noise data quality at the mizusawa was sometimes poor but use of the data as reference improved the mt data of the esashi station as a result extremely stable apparent resistivity and phase curves were obtained from the esashi station the resistivity structure of ne japan was estimated using two ways of 1 d modelling procedure by evaluating the stability of apparent resistivity and phase data the modelling suggests the existence of anomalous layers which represent anisotropic or inhomogeneous crust and or upper mantle structures of the ne japan of fore arc these features may relate with cretaceous tectonic events

unraveling middle crust conductive layers in paleozoic orogens through 3d modeling of magnetotelluric data the ossa morena zone case study sw iberian variscides 1 in recent years a number of magnetotelluric mt surveys have been carried out in the southern branch of the iberian variscan massif namely in the ossa morena zone omz and its neighboring areas the south portuguese zone spz and the central iberian zone ciz in order to determine the geoelectrical structure of this transpressive orogen and gain insight into its internal architecture new mt data collected across the omz complete a dense database that covers the whole belt and its boundaries this paper presents an integrative three dimensional model of the available mt data from the apparent resistivities four components impedance phases and geomagnetic transfer functions from 61 stations given the location of the study area near the atlantic ocean coast effect on the data was analyzed as well as the stability of the mesh due to the strong resistivity contrasts a mesh of 80 77 76 cells was finally used with an average cell size of 4 4 km in the horizontal direction and increasing thickness in the vertical direction from 25 m in the shallower layers to 5 km in the deepest ones the most striking feature is in addition to the conductive anomalies associated with the sutures between the spz omz and the omz ciz a conductive layer which spans the whole ossa morena middle to lower crust the top of this conductive layer is interpreted as a major decollement between the granulitic basement and the overlying meta sedimentary pile

a constitutive model for layer development in shear zones near the brittle ductile transition 1 the microstructure of ductile shear zones differs from that of surrounding wall rocks in particular compositional layering is a hallmark of shear zones as layered rocks are weaker than their isotropic protolith when loaded in simple shear layering may hold the key to explain localization of ductile deformation onto ductile shear zones i propose here a constitutive model for layer development a two level mixing theory allows the strength of the aggregate to be estimated at intermediate degrees of layering a probabilistic failure model is introduced to control how layers develop in a deforming aggregate this model captures one of the initial mechanism of phase interconnection identified experimentally by holyoke and tullis 2006a 2006b fracturing of load bearing grains this model reproduces the strength evolution of these experiments and can now be applied to tectonic modeling

are some of the deep crustal conductive features found in sw iberia caused by graphite abstract recent results obtained from two dimensional inversion of magnetotelluric mt data acquired in sw iberia reveal high conductive features at the middle lower levels of the crust the top of these anomalous structures correlates very well with the depth 10 13 km of an important seismic interface that has been interpreted as a regional detachment horizon very shallow and relatively narrow conductors in the ossa morena zone appear to correspond to small scale fluid deposited graphite systems in the preorogenic metasedimentary sequences some of the midcrustal conductors can be ascribed to graphite bearing thrust zones the formation of graphite with variable crystallinity being a consequence of variscan shearing processes deep seated conductors are tentatively interpreted as a result of relatively continuous highly crystalline grain boundary graphite films presumably preserved in basement granulite rocks assuming that graphite occurs as interconnected films calculations indicate that a fraction of 0 006 0 02 of this accessory mineral is enough to explain the range of the electrical resistivity estimated on the basis of mt models the role of graphite on the thermal behaviour of the crust is also discussed the results show that low contents of graphite do not significantly change the thermal behaviour of earth materials

a magnetotelluric study of the damara belt in namibia 2 mt phases over 90 reveal the internal structure of the waterberg fault omaruru lineament abstract magnetotelluric mt observations at some sites in the vicinity of the waterberg fault omaruru lineament wf ol a major tectono stratigraphic zone boundary in the central zone of the damara belt show evidence for strong three dimensional 3d effects we observe very high skew values phases over 90 and a strong correlation of parallel components of the electric and magnetic fields at long periods because of the dense site spacing and good spatial coverage we can positively attribute these effects to local geology and are able to resolve structural detail within the wf ol mapping latorraca s electric characteristic vectors in form of ellipses proved particularly useful in identifying key elements of the conductivity structure for subsequent modelling 3d and 2d anisotropic modelling can reproduce most of the observed 3d effects the conductivity anomalies revealed in the area are i a conductive ring structure in the shallow crust along the northern part of the profile ii an anisotropic region in the upper crust with high conductivity parallel to the wf ol iii anisotropy in the lower crust with a different but undetermined strike direction and iv a shallow elongated conductor sub normal to the wf ol modelling studies further suggest that the anisotropic fault zone is approximately 10 km wide and may reach down to a depth of 14 km or more

an electrical resistivity crustal section from the alps to the baltic sea central segment of the egt abstract electrical resistivity models derived from magnetotelluric and magnetovariational measurements in the past 10 years have been compiled along the central segment of the european geotraverse along the profile low resistivity structures exist particularly in the middle and upper crust and probably mask deeper low resistivity zones these structures can be related to different tectonic units along the profile the prominent features are the two dimensional low resistivity structures at the transition from the moldanubian to the saxothuringian and from the saxothuringian to the rhenohercynian unit of the variscan belt the depth correlation of the low resistivity horizon in the rhenish massif with a seismic low reflectivity band the very high conductance of an upper to middle crustal layer in the north german lowlands and its cessation at the river elbe towards the baltic sea the reduction in the resistivity of these zones is very likely due to graphite at mid crustal depths it is obvious that there exists a general increase of electrical conductance in the upper half of the crust from south to north of the central segment which may be due to increasing accumulation of graphite and successive tectonically controlled ordering processes this phenomenon may by relating it to the growing crustal age from south to north be the indicator of a maturing continental crust

three dimensional magnetotelluric responses for arbitrary electrically anisotropic media and a practical application electrical anisotropy in earth media increases the complexity of magnetotelluric responses magnetotelluric models based on anisotropic media must be developed to fully understand observed data this paper presents a three dimensional algorithm for calculating magnetotelluric responses of arbitrary anisotropic media in the frequency domain using a staggered grid finite difference method the model space is discretized into rectangular blocks with electric fields on the edges of each block and the magnetic fields normal to the faces of each block the electric field helmholtz vector equation that considers a full 3 3 conductivity tensor is calculated numerically under two orthogonal polarizations in calculating the boundary values on the four sides of the three dimensional anisotropic model we adopt different procedures for calculating the two dimensional responses on the sides in the x and y directions the responses for a layered anisotropic model and a three dimensional isotropic model calculated with this algorithm are compared with the corresponding analytical and numerical solutions respectively the comparisons show that the algorithm s approximations are highly precise for a wide frequency band a typical two dimensional anisotropic model and a general three dimensional anisotropic model were also constructed and their responses were calculated these anisotropic models have ordinary structures but can produce phase rolling out of quadrant magnetotelluric responses which indicates that considering electrical anisotropy may improve our interpretation of observed data using this algorithm we can model the observed data from the northern qaidam basin in northern tibet where ultrahighpressure metamorphic rocks are exposed along an old suture and seismic anisotropy was indicated in neighbouring areas the phase tensors of the magnetotelluric sites at this location show large skew angles and the corresponding phase splits are distinct in the off diagonal impedance elements although the isotropic three dimensional electrical structure can model the profile data well the structure shows a sequence of conductive and resistive bodies in the mid lower crust of the north qaidam basin which is very spatially inhomogeneous and a simple intrinsic anisotropic body can also produce similar surficial responses using the three dimensional anisotropic algorithm we found an equivalent anisotropic replacement for this area the results of the three dimensional anisotropy modelling of the magnetotelluric data from the northern tibetan plateau show the valuable applicability of the threedimensional anisotropic algorithm in testing the qualitative presumption of electrical anisotropy

robust characteristics method for modelling multiphase visco elasto plastic thermo mechanical problems abstract we have extended our previous 2d method gerya t v yuen d a 2003 characteristics based marker in cell method with conservative finite differences schemes for modeling geological flows with strongly variable transport properties phys earth planet interiors 140 295 320 which is a combination of conservative finite differences with marker in cell techniques to include the effects of visco elasto plastic rheology self gravitation and a self consistently derived evolving curvilinear planetary surface this code is called i2elvis and can solve a new class of computationally challenging problems in geodynamics such as shear localization with large strains crustal intrusion emplacement of magmas bending of realistic visco elasto plastic plates and core formation by vigorous shell tectonics activities related to a global rayleigh taylor instability of a metal layer formed around silicate rich lower density primordial core during planetary accretion we discuss in detail the computational strategy required the rheological constraints to be satisfied at each time step and spatial location we show analytical benchmarks and examples drawn from comparing between numerical and analogue experiments in structural geology subducting slab bending with a visco elasto plastic rheology and equilibrium spherical configurations from self gravitation we have also tested possibilities of future applications by addressing 3d geometries based on multigrid method and including inertial effects in the momentum equation with tracers in order to simulate meteoritic impact events and eventually earthquake instabilities

shear heating induced lithospheric scale localization does it result in subduction abstract even though it is a well established fact that the earth is currently in a plate tectonics mode the question on how to break lithospheric plates and initiate subduction remains a matter of debate here we focus on shear heating as a potential mechanism to cause lithospheric shear localization and subsequent subduction initiation in oceanic plates it is shown that shear heating under some conditions i facilitates the formation of a lithospheric scale shear zone and ii is capable of stabilizing a lithospheric scale shear zone thus creating the necessary condition for subduction initiation to occur furthermore we demonstrate that not only the localization process is of importance but also the post localization stage where rapidly growing convective instabilities might prevent an incipient subduction zone from developing we develop scaling laws for both the localization and the post localization stages in the case of lithospheric localization the characteristic length scale equals a quarter of the dominant folding wavelength in the lithosphere thus of the order of the competent layer thickness this shows that oceanic lithosphere develops an intrinsic perturbation length scale that is largely independent of smaller scale heterogeneities we compare the subduction initiation potential of wet olivine and dry olivine rheologies and find that for earth like conditions a dry olivine rheology is more likely to result in subduction initiation a large plate age does not always increase the potential for subduction initiation as it increases the potential for convective instabilities to occur instead an optimal plate age exists for shear heating induced subduction initiation which is around 40 ma for a wet olivine rheology

three dimensional modelling of crustal motions caused by subduction and continental convergence in the central mediterranean summary crustal deformation in the central mediterranean is modelled by means of 3 d finite element models assuming a viscoelastic rheology the tectonic mechanisms under investigation are subduction of the ionian oceanic lithosphere beneath the calabrian arc and continental convergence between the african and eurasian blocks very long baseline interferometry vlbi data at the station noto in sicily and the results from global models of plate motions are taken as representative of the motion of the african plate with respect to eurasia while vlbi solutions at matera and medicina in the southern and northern parts of the italian peninsula are geodetic observations that must be compared with modelling results vertical deformation rates are taken from geological and tide gauge records the model that best fits the observations includes the effects of subduction in the southern tyrrhenian and convergence between africa and europe the overthrusting of the tyrrhenian domain onto the adriatic domain results in an eastward component of the velocity at the eastern border of the tyrrhenian domain in agreement with vlbi data from the matera and medicina stations and gps data from northeastern sicily and the eolian islands the highest subsidence rates are obtainedinthe southern tyrrhenian and are of the order of 1 2 1 4 mm yr 1 along the whole adriatic coast of the italian peninsula subsidence in the foredeeps is of the order of 0 2 0 5 mm yr 1 the apenninic chain is rising with rates of the order of 0 2 0 4 mm yr 1 subduction beneath the calabrian arc is responsible for a roll back velocity higher than in the northern areas 2 d models built for the geological past indicate the possibility of roll back velocities of several centimetres per year in particular active rifting in the tyrrhenian and softening of the crust in the back arc basin result in a trench retreat velocity in agreement with geological estimates our results show that numerical modelling can be used to estimate present day deformation rates and the contribution of active tectonics to sea level changes along coastal areas

mantle circulation models with variational data assimilation inferring past mantle flow and structure from plate motion histories and seismic tomography summary mantle convection models require an initial condition some time in the past because this initial condition is unknown for earth we cannot infer the geological evolution of mantle flow from forward mantle convection calculations even for the most recent mesozoic and cenozoic geological history of our planet here we introduce a fluid dynamic inverse problem to constrain unknown mantle flow back in time from seismic tomographic observations of the mantle and reconstructions of past plate motions using variational data assimilation we derive the generalized inverse of mantle convection and explore the initial condition problem in high resolution 3 d spherical mantle circulation models for a time period of 100 myr roughly comparable to half a mantle overturn we present a synthetic modelling experiment to demonstrate that mid cretaceous mantle structure can be inferred accurately from fluid dynamic inverse modelling assuming present day mantle structure is well known even if an initial first guess assumption about the mid cretaceous mantle involved only a simple 1 d radial temperature profile we also demonstrate that convecting present day mantle structure back in time by reversing the time stepping of the energy equation is insufficient to model the mantle structure of the past the difficulty arises because such backward convection calculations ignore thermal diffusion effects and therefore cannot account for the generation of thermal buoyancy in boundary layers as we go back in time inverse mantle convection modelling should make it possible to infer a number of flow parameters from observational constraints of the mantle

dynamic models of continental rifting with melt generation abstract active or passive continental rifting is associated with thinning of the lithosphere ascent of the asthenosphere and decompressional melting this melt may percolate within the partially molten source region accumulate and be extracted two dimensional numerical models of extension of the continental lithosphere asthenosphere system are carried out using an eulerian visco plastic formulation the equations of conservation of mass momentum and energy are solved for a multi component crust mantle and two phase solid melt system temperature pressure and stress dependent rheologies based on laboratory data for granite pyroxenite and olivine are used for the upper and lower crust and mantle respectively rifting is modelled by externally prescribing a constant rate of widening with velocities between 2 5 and 40 mm yr a typical extension experiment is characterized by 3 phases 1 distributed extension with superimposed pinch and swell instability 2 lithospheric necking 3 continental break up followed by oceanization the timing of the transition from stages 1 to 2 depends on the presence and magnitude of a localized perturbation and occurs typically after 100 150 km of total extension for the lithospheric system studied here this necking phase is associated with a pronounced negative topography rift valley and a few 100 m of rift flanks the dynamic part of this topography amounts to about 1 km positive topography this means if rifting stops e g due to a drop of external forces immediate additional subsidence by this amount is predicted solidification of ascended melt beneath rift flanks leads to basaltic enrichment and underplating beneath the flanks often observed at volcanic margins after continental break up a second time dependent upwelling event off the rift axis beneath the continental margins is found producing further volcanics melting has almost no or only a small accelerating effect on the local extension value value for a constant external extension rate melting has an extremely strong effect on the upwelling velocity within asthenospheric wedge beneath the new rift this upwelling velocity is only weakly dependent on the rifting velocity the melt induced sublithospheric convection cell is characterized by downwelling flow beneath rift flanks melting increases the topography of the flanks by 100 200 m due to depletion buoyancy another effect of melting is a significant amplification of the central subsidence due to an increase in localized extension subsidence modelled magma amounts are smaller than observed for east african rift system increasing the mantle temperature as would be the case for a large scale plume head better fits the observed magma volumes if extension stops before a new ocean is formed melt remains present and convection remains active for 50 100 myr and further subsidence is significant

a new species of zangerlia testudines nanhsiungchelyidae from the upper cretaceous redbeds at bayan mandahu inner mongolia and the relationships of the genus zangerlia neimongolensis sp nov is described on the basis of material from the upper cretaceous redbeds at bayan mandahu in inner mongolia zangerlia neimongolensis is similar to zangerlia testudinimorpha in the proportions of the carapace and plastron and presence of a knob at the posterior end of the neural series but differs from it in the arrangement of scutes covering the bridge the placement of zangerlia in the nanhsiungchelyidae is supported by derived features of the bridge peripherals and plastral scutes shared by z neimongolensis basilemys and nanhsiungchelys these are the presence of ventrally expanded sixth inframarginal scutes humeral scutes that are narrow at the midline and expanded laterally pectoral scutes that are wide at the midline and narrow laterally and large rectangular abdominal scutes the skull of zangerlia is more primitive than that of nanhsiungchelys the only other member of the family for which a skull is known it shows extensive emargination of the temporal and

electrical structure of the crust below the deccan flood basalts india inferred from magnetotelluric soundings summary the indian shield has experienced major stable continental region scr earthquakes in the recent past which occurred in the deccan volcanic province until now the deeper crust below the deccan traps where thick basaltic layers cover large areas of the indian shield remains poorly understood a magnetotelluric mt study covering a broad period range was conducted along a n s running profile of 330 km length to achieve more insights into the nature of the crustal electrical structure below the flood basalts after dimensionality analysis and decomposition 2 d inversions for te and tm modes were carried out the basalt cover characterized by at first glance surprisingly low electrical resistivities is found to have an average thickness of 400 m with the exception of central parts of the profile where it reaches up to 700 m the crust is in general highly resistive but several subvertical zones of enhanced conductivity were delineated in the middle to lower crust which are tentatively explained as images of hidden partly reactivated faults fractures of the precambrian basement sensitivity analysis indicates a high resolution of these features an alternative approach incorporating macro anisotropy is additionally considered and corresponding 2 d anisotropic forward modelling confirms the existence of successions of conductive dykes in the deep crust

a simple analytical solution for slab detachment abstract an analytical solution is presented for the nonlinear dynamics of high amplitude necking in a free layer of power law fluid extended in layer parallel direction due to buoyancy stress the solution is one dimensional 1 d and contains three dimensionless parameters the thinning factor i e ratio of current to initial layer thickness the power law stress exponent n and the ratio of time to the characteristic deformation time of a viscous layer under buoyancy stress t tc tc is the ratio of the layer s effective viscosity to the applied buoyancy stress the value of tc n specifies the time for detachment i e the time it takes until the layer thickness has thinned to zero the first order accuracy of the 1 d solution is confirmed with 2 d finite element simulations of buoyancy driven necking in a layer of power law fluid embedded in a linear or power law viscous medium the analytical solution is accurate within a factor about 2 if the effective viscosity ratio between the layer and the medium is larger than about 100 and if the medium is a power law fluid the analytical solution is applied to slab detachment using dislocation creep laws for dry and wet olivine results show that one of the most important parameters controlling the dynamics of slab detachment is the strength of the slab which strongly depends on temperature and rheological parameters the fundamental conclusions concerning slab detachment resulting from both the analytical solution and from earlier published thermo mechanical numerical simulations agree well indicating the usefulness of the highly simplified analytical solution for better understanding slab detachment slab detachment resulting from viscous necking is a combination of inhomogeneous thinning due to varying buoyancy stress within the slab and a necking instability due to the power law viscous rheology n 1 application of the analytical solution to the hindu kush slab provides no order of magnitude argument against slab detachment and therefore supports existing studies suggesting a currently ongoing slab detachment in the hindu kush slab

kinematic interpretation of the 3d shapes of metamorphic core complexes 1 metamorphic core complexes form dome shaped structures in which the ductile crust is exhumed beneath a detachment fault the 3d dome geometry inferred by mapping the schistosity in the exhumed crust can be either elongated normal to the stretching direction or along it in the first case the domes are interpreted as having formed during extension however in the second case they are interpreted either as strike slip transpressive or constrictive extensional structures depending on the geodynamic context numerical models of metamorphic core complexes published to date are all two dimensional and therefore theoretically only apply to domes which are elongated normal to the stretching direction here we explore by means of 3d thermomechanical modeling the impact of 3d kinematic extensional boundary conditions on the shape of metamorphic core complexes we examine the impact of a transtensional step over and of horsetail splay fault kinematics on the dynamics of exhumation finite strain and p t paths and compare them to cylindrical 3d models we show for the first time that domes formed in transtensional step over or at the tip of propagating strike slip faults display a finite strain field which can be interpreted as characteristic of a transpressive domes although no shortening was applied in the far field applying our models to the cyclades we propose that the coeval formation of domes elongated normal and parallel to the stretching during the miocene can be the result of horsetail splay fault kinematics which could correspond to the formation of a tear in the aegean slab

on the discovery of an oviraptorid skeleton on a nest of eggs at bayan mandahu inner mongolia people s republic of china a partial skeleton of oviraptor which means egg thief collected at bayan mandahu inner mongolia people s republic of china in 1990 was lying on top of a nest of eggs of the six known skeletons of this genus from upper cretaceous djadokhtan sediments this is the second occurrence in which the theropods were interacting with the eggs when they were buried by sand and dust during sandstorms two explanations for the association of oviraptor with eggs are that the theropod may have been eating the eggs or it may have been incubating and protecting them evidence presented suggests that the latter hypothesis is more likely it is also conceivable that the female oviraptorid was in the process of laying eggs when she died

the occurrence of psittacosaurus xinjiangensis sereno and chow 1988 in the urho area junggar basin xinjiang people s republic of china a partial specimen of psittacosaurus xinjiangensis from the urho locality in the western junggar basin china extends the known geographical range of p xinjiangensis and documents the adult morphology in this species variation in the number of denticles on the dentary tooth crowns is documented possibly representing a decrease in the number of denticles during growth although a high denticle count remains a diagnostic feature of the species

a magnetotelluric study of the damara belt in namibia 1 regional scale conductivity anomalies abstract the namibian margin is dominated by the late proterozoic to early cambrian fold belts of the damara orogen which wrap around and separate the congo and kalahari cratons this mosaic of relatively soft fold belts and hard cratons apparently controlled the path for the opening of the south atlantic in the early cretaceous the continents split along the coast parallel fold belts of the damara orogen while the inland fold belt damara belt was effected by extension and widespread igneous intrusion but never developed to the rift stage this paper is concerned with the interpretation of magnetotelluric mt data along a 200 km nw se profile across the damara belt in nw namibia the regional two dimensional electrical resistivity model and the induction vector data exhibit three distinctive zones i a generally very resistive upper crust which is typical for the granites and metasediments of the damara belt ii two subvertical conductors in upper to mid crustal levels which correlate with major tectonic zone boundaries and iii a highly conductive middle to lower crust in the southern part of the profile the geometry of the conductive structures could reflect a regional shear system in which upper crustal listric faults pass into a detachment zone in the middle crust we interpret the high electrical conductivity in terms of graphite or other forms of mineralization enrichment along the shear planes this zone of crustal weakness may have originated in pre damara times and had probably experienced several episodes of crustal reactivation before the intrusion of basaltic dike swarms during the cretaceous rifting and magmatism associated with the opening of the south atlantic

3d modelling of electrical anisotropy from electromagnetic array data hypothesis testing for different upper mantle conduction mechanisms abstract upper mantle electrical conductivities provide besides seismic velocities or thermal diffusivities another source of information on upper mantle structure and composition we present the results of a long period magnetotelluric dataset consisting of 64 sites covering an area of 300 km 400 km in central germany mapping electrical conductivities at the base of the lithosphere to seperate the effect of crustal and upper mantle structures we interprete the obtained dataset by 3d conductivity modelling we observe high conductivities and anisotropies at asthenospheric upper mantle depth with main bulk conductivities of 1 2 s m in west east and 4 1 0 3 s m in north south direction differing by about two orders of magnitude in comparing with results from laboratory measurements on electrical conductivites for various conduction mechanisms we are able to confine the conduction mechanisms possibly dominating at these depths with melt volume fractions of 1 only partial melt can be excluded as origin of the high upper mantle conductivities instead conductivity enhancement due to hydrogen diffusion along the olivine 1 0 0 axis is favoured as the dominant conduction mechanism at the base of the lithosphere

magnetotellurics in southwestern sweden evidence for electrical anisotropy in the lower crust magnetotelluric data from measurements conducted on the southwestern part of the baltic shield are analyzed with respect to crustal and upper mantle structures the interpretations have been done using ordinary two dimensional and transverse anisotropic layered models in which distortions of the impedance tensors due to near surface electrical structures are included in the interpretation procedures the anisotropic model is able to explain the gross features of the data whereas the two dimensional model only displays features observed at long periods the two main results from the study with anisotropic models are the interpretation of a possible transverse anisotropic lower crust and a depth to the uppermost conductive layer within the mantle of more than 200 km the minimum depth to the conductive mantle layer is found from a most squares analysis

anomalous phases exceeding 90 in magnetotellurics anisotropic model studies and a field example summary a study of synthetic anisotropic models that explain phases exceeding 90 in magnetotellurics is presented the basic model comprises an anisotropic layer overlain by a shallow local anisotropic block with both structures inserted in a 2 d model the 2 d strike and the anisotropy strikes layer and block differ the influence of the following parameters was analysed anisotropy strike geometry of the block and the layer and anisotropy ratios of the block and the layer we show that according to this model the anomalous phase effect is limited to those sites above the shallow block and does not influence the regional structure which can therefore be recovered these results were applied to field data from a magnetotelluric profile in sw iberia where phases greater than 90 occurred in an area in which alternating bands of schist and graphite rich blackschists crop out giving rise to strong macroanisotropy

djadokhta formation correlative strata in chinese inner mongolia an overview of the stratigraphy sedimentary geology and paleontology and comparisons with the type locality in the pre altai gobi because the bayan mandahu redbeds of inner mongolia share similar sedimentary facies and fossil assemblages with the djadokhta formation of pre altai gobi the two units are interpreted as stratigr

trace fossils on dinosaur bones from upper cretaceous eolian deposits in mongolia taphonomic interpretation of paleoecosystems in ancient desert environments abstract the formation processes of trace fossils including shallow to deep pits notches borings tunnels and channels particularly at the limb joints observed on the surfaces of velociraptor protoceratops ankylosaurid and bagaceratops skeletons from upper cretaceous eolian deposits in the gobi desert mongolia were investigated the median diameters of these structures ranged from 5 25 to 7 68 mm these structures were likely created by insects scavenging on dinosaur carcasses this interpretation is corroborated by the presence of burrows of a size similar to the trace fossils observed on the dinosaur bone surfaces at the same locality broad borings about 32 mm in diameter created by small mesozoic mammals have also been discovered on the ribs and scapulae of a protoceratops skeleton dinosaur skeletons found at two localities tugrikin shireh and khermeen tsav and two formations the djadokhta formation and barun goyot formation exhibited the same type of damage to the limb joints the high frequency of trace fossils at the limb joints suggests that small animals targeted the collagen in the joint cartilage of dried dinosaur carcasses as a source of nitrogen which was relatively scarce in the eolian environments of the gobi desert during the late cretaceous

control of folding by gravity and matrix thickness implications for large scale folding 1 we show that folding of a non newtonian layer resting on a homogeneous newtonian matrix with finite thickness under influence of gravity can occur by three modes 1 matrix controlled folding dependent on the effective viscosity contrast between layer and matrix 2 gravity controlled folding dependent on the argand number the ratio of the stress caused by gravity to the stress caused by shortening and 3 detachment folding dependent on the ratio of matrix thickness to layer thickness we construct a phase diagram that defines the transitions between each of the three folding modes our priority is transparency of the analytical derivations e g thin plate versus thick plate approximations which permits complete classification of the folding modes involving a minimum number of dimensionless parameters accuracy and sensitivity of the analytical results to model assumptions are investigated in particular depth dependence of matrix rheology is only important for folding over a narrow range of material parameters in contrast strong depth dependence of the viscosity of the folding layer limits applicability of ductile rheology and leads to a viscoelastic transition our theory is applied to estimate the effective thickness of the folded central asian upper crust using the ratio of topographic wavelength to moho depth phase diagrams based on geometrical parameters show that gravity does not significantly control folding in the jura and the zagros mountains but does control folding in central asia applicability conditions of viscous and thin sheet models for large scale lithospheric deformation derived in terms of the argand number have implications for the plate like style of planetary tectonics

geoelectric crustal structures off the sw border of the sao francisco craton central brazil as inferred from a magnetotelluric survey summary a magnetotelluric mt survey of the crust beneath sedimentary basins and thrust sheets along the southwestern edge of the sao francisco craton central brazil reveals intricate electrical characteristics that are interpreted in the context of proterozoic collision tectonics and horizontal transport of allochthonous rock units emplacement of cretaceous hypabyssals lavas and diatremes of ultrapotassic mafic composition and occurrence of induced seismicity the data exhibit strong distortions represented by 3 d induction effects and galvanic disturbances resulting from shallow structures frequency and site dependence of electrical strike and inhomogeneous anisotropic layers with smoothly varying phase split conductance and azimuth of the highly conductive direction geoelectrical and orthogonal phase difference directions 2 d inversion and forward modelling characterize three distinct subhorizontal sections showing two anisotropic conductors within a highly resistive crust laterally segmented into unique blocks the model for the uppermost crust section has e w geoelectric directions and a 15 30 s anisotropic zone at a depth of approximately 1 2 km along the entire profile this conducting layer is interpreted to represent a brine filled fracture layer possibly controlled by the present day state of crustal stresses as disclosed from reservoir triggered quakes the mid crust section presents a deeper conducting zone located at depths below 10 km it is defined by stronger mt responses having phase split directions oscillating from wnw ese to e w beneath sites in the central western area parana basin and allochthonous cover units and nne ssw in the northeastern region autochthonous platform units and sanfranciscana basin anisotropy is greater than an order of magnitude in the highly conductive direction with conductance in the range of 250 400 s conjecturally the source of this anomalous feature would come from interconnected grain boundary phases and hypersaline fluids exsolved and precipitated from upwelling cretaceous magma in the central western area favourable trapping of conductors was constrained along a nearly e w direction feasibly associated with relic structures inherited from brasiliano pan african continental collisions along the northeast however the coincidence with superficial nne ssw structural directions suggests a localized direct causal relationship with the trend of extension related to magma emplacement the lower crust has a highly resistive quasi 1 d section along the entire profile that prevails also at uppermost mantle depths thus whereas the brittle crust would have reconciled subhorizontal strain with fluid percolation related to uplift and magma emplacement a mechanically coupled and stronger lower crust upper mantle would have controlled the deep magma generation during cretaceous distention pulses

sineoamphisbaena hexatabularis an amphisbaenian diapsida squamata from the upper cretaceous redbeds at bayan mandahu inner mongolia people s republic of china and comments on the phylogenetic relationships of the amphisbaenia sineoamphisbaena hexatabularis wu et al 1993 is the earliest known amphisbaenian represented by well preserved cranial and postcranial material it reveals a mosaic of generalized lizard like features and amphisbaenian characters most distinctive of the latter are features of cranial consolidation adaptive for a fossorial way of life phylogenetic analyses strongly confirm the monophyly of the amphisbaenia inclusive of s hexatabularis the amphisbaenia is diagnosed by a suite of apomorphic characters the available evidence suggests a probable amphisbaenia macrocephalosauridae relationship within the scincomorpha this is supported primarily by the unique modifications of the palate and temporal region of the skull it is argued here that the amphisbaenia evolved in central asia during the cretaceous in response to the transition from a perennial lacustrine environment to a dry semiarid eolian environment the relatively primitive morphology indicates that s hexatabularis was not permanently subterranean the further derived modifications of later forms are associated with tunneling in an environment of more compact soils

refined models of the conductivity distribution at the transition from the bohemian massif to the west carpathians using stochastic mcmc thin sheet inversion of the geomagnetic induction data although volume 3d modeling solutions has become widespread in recent time thin sheet approximation of earth s conductivity distribution can still serve as a useful tool when quasi 3d conductivity structures in the heterogeneous subsurface are investigated and the available database of observations is limited to long period electromagnetic induction data from large scale deep sounding arrays we present results of stochastic monte carlo markov chains mcmc inversion of long period induction arrows based on the bayesian statistics strategy we concentrated on the different methodological aspects of mcmc for gibbs sampling and for adaptive metropolis algorithm together with convergence of these methods the results are presented on a case study from the transition zone between the bohemian massif and the west carpathians where a phantom effect caused by superposition of the prominent sw ne trending carpathian conductivity anomaly and nw se trending anomalous structure related to the fault system at the eastern boundary of the bohemian massif appears

deriving scaling laws in geodynamics using adjoint gradients abstract whereas significant progress has been made in modelling of lithospheric and crustal scale processes in recent years it often remains a challenge to understand which of the many model parameters is of key importance for a particular simulation determining this is usually done by manually changing the model input parameters and performing new simulations for a few cases such as for folding or rayleigh taylor instabilities one can use thick plate stability analysis to derive scaling laws to obtain such insights yet for more general cases it is not straightforward to do this apart from running many simulations here we discuss a numerically cheaper approach to compute scaling laws using adjoint gradients this method determines the gradients of the model solution versus the model parameters or more precisely quantifies the influence of a large number of parameters on the simulation the required computational effort is nearly independent on the number of model parameters which makes it tractable even for complicated setups here we show how these gradients can be used to derive scaling laws we test the method by reproducing existing scaling laws for a rayleigh taylor instability problem as well as that of folding of a single layer over a weaker basement next we show the applicability of the method to more complicated multilayer folding setups and a 3d subduction problem with 22 parameters the results show that the method can at very little computational overhead give significant insights in the controlling parameters of geodynamic simulations

depositional environments and fades transitions of dinosaur bearing upper cretaceous redbeds at bayan mandahu inner mongolia people s republic of china campanian redbeds near bayan mandahu consist of six lithosomes which in turn comprise twelve lithofacies the distribution of these lithosomes along a 12 km escarpment resolves into three coeval paleogeographic zones representing a proximal to distal depositional gradient zone 1 the most proximal consists of alluvial lacustrine and eolian sediments it is interpreted as an eolian influenced distal alluvial fan or braid plain environment farther basinward zone 2 is dominated by structureless eolian sandstones and caliche profiles with minor occurrences of alluvial lacustrine and eolian dune deposits it is interpreted as a zone of vertically aggrading eolian sand stabilized by vegetation and a high water table zone 3 the most distal is dominated by eolian dune and structureless eolian deposits with lacustrine and interdune fluvial deposits it is interpreted as the southern margin of an eolian dune field that was dominated by transverse and barchan dunes u shaped mature caliche profiles ca

the dynamics of plate tectonics and mantle flow from local to global scales plate tectonics is regulated by driving and resisting forces concentrated at plate boundaries but observationally constrained high resolution models of global mantle flow remain a computational challenge we capitalized on advances in adaptive mesh refinement algorithms on parallel computers to simulate global mantle flow by incorporating plate motions with individual plate margins resolved down to a scale of 1 kilometer back arc extension and slab rollback are emergent consequences of slab descent in the upper mantle cold thermal anomalies within the lower mantle couple into oceanic plates through narrow high viscosity slabs altering the velocity of oceanic plates viscous dissipation within the bending lithosphere at trenches amounts to 5 to 20 of the total dissipation through the entire lithosphere and mantle

long term exhumation history of the inner mongolian plateau constrained by apatite fission track analysis the inner mongolian plateau along the southeastern flank of the wider mongolian plateau is a vast undulating surface ranging in elevation between 900 and 1500 m above sea level the peculiar topography of this area is assumed to be closely related to its complex tectono thermal evolution since late paleozoic the lithospheric structure of the plateau includes three continental blocks the mandula and the bart obo blocks form the southern margin of the central asian orogenic belt in that area and to the south the plateau includes the northern margin of the north china craton apatite fission track aft ages and track length distributions from 13 basement outcrops situated in the main tectonic blocks forming the inner mongolian plateau were determined in order to reconstruct its denudation history the thermal histories inferred from these data imply multi phased differential exhumation burying processes from the late paleozoic to the early cretaceous this complex thermal history is largely related to the early middle triassic closure of the paleo asian ocean the jurassic closure of the mongol okhotsk ocean and the early cretaceous orogenic collapse of the mongol okhotsk belt finally since late cretaceous no further major tectonic movement occurred and the inner mongolian plateau has been largely peneplained

electrical anisotropy in the main central thrust zone of the sikkim himalaya inference from anomalous mt phase abstract the sikkim himalaya in the eastern sector of the himalayan collision belt shows some distinct features such as the occurrence of the main central thrust as a several km wide zone mctz of intense ductile deformation and its deviation from the general east west strike of the himalayan thrusts suggesting that the tectonics of this region could be different from the regional himalayan tectonics we have carried out a mt survey across mctz to understand the tectonics of the region the broadband mt data of the site at the northern boundary of the zone reveals anomalous phase exceeding 90 for frequencies smaller than 1 hz whereas other sites further north of this zone show normal behavior such anomalous phase behavior has been explained earlier in terms of anisotropy in the medium and special configuration of local conductors we have analyzed the observed anomalous phase behavior in terms of anisotropy based on geological consideration that alternating bands of graphitic schists are present within high grade crystalline gneisses at the northern boundary of mctz among various models analyzed a block model of the crustal structure with strong anisotropy contrast between the block and the underlying anisotropic layer provides good fit to the observed data we thus infer that the presence of a localized strongly anisotropic block at the northern boundary of mctz could be a viable explanation for the observed anomalous phase behavior

two dimensional topographic responses in magnetotellurics modeled using finite elements we simulate the magnetotelluric response to two dimensional earth topography using finite elements linear interpolation of the secondary field parallel to strike over triangular elements allows accurate modeling of inclined resistivity boundaries including topographic surfaces to avoid discontinuities in field derivatives or resistivity care must be taken that the nodal values of the field parallal to strike used to obtain the auxiliary secondary fields are kept within uniform earth media the nodal locations may be shifted but the derivatives still are evaluated at the field points of interest correct values may be returned at gentle breaks in slope as well as along straight surfaces the finite element program is verified by comparison with the analytic transverse magnetic response of a hemicylindrical depression and with rayleigh scattering and transmission surface results for transverse electric and transverse magnetic polarization agreement with the other methods generally is excellent with t

thermal mechanical effects of low temperature plasticity the peierls mechanism on the deformation of a viscoelastic shear zone we studied for the first time the effects of low temperature plasticity on the formation of shear zones a thermal mechanical model has been developed for describing the shear deformation of maxwell viscoelastic material with a rheology close to dry olivine we employed a one dimensional model with a half width of l deforming under a constant velocity u at the boundary and the spatially averaged strain rate u l was set to o 10 14 s 1 in addition to diffusion and power law creep we included deformation by low temperature plasticity called the peierls mechanism which is significant at low temperatures and has a strong exponential dependence on the stress when a sufficient magnitude of heat is generated by the rapid conversion from elastically stored energy into viscous dissipation thermal instability takes place and the deformation localizes in a narrow region by comparing the condition for thermal instability we found that the low temperature plasticity inhibits the development of thermal instability in shear zones in case of constant strain rate the peierls mechanism enhances deformation at a significantly lower stress compared to the rheology with solely diffusion creep and power law creep the enhanced deformation by low temperature plasticity produces lower amount of dissipative heating and thus stabilizes the shear zone comparing the stability between constant strain rate and constant stress boundary conditions we found that the peierls mechanism exerts an opposite destabilizing effect in the case of constant stress for dry olivine rheology and realistic magnitude of the strain rate the effect of low temperature plasticity is significant for temperatures between around 800 k and 1000 k this finding suggests that the low temperature plasticity may be crucial in determining the thermal mechanical stability in the shallow portion of slabs

systematics and taxonomic diversity of squamates from the upper cretaceous djadochta formation bayan mandahu gobi desert people s republic of china squamate fossils collected for the sino canadian dinosaur expeditions 1986 1990 include some 70 specimens from the upper cretaceous campanian djadochta formation exposed at the vicinity of bayan mandahu inner mongolia china well preserved skulls jaws postcranial skeletons and even osteodermal armor document a fossil assemblage composed of at least 18 genera in 8 families besides showing considerable taxonomic diversity several families recorded in the assemblage are of importance in understanding the geologic and biogeographic distribution of the relevant groups and the paleoenvironment in which these lizards lived comparison of the gobi lizard assemblage with north american and central asian assemblages is briefly discussed taxonomic differences in the assemblage from that of the upper cretaceous in the north american western interior reflect endemism and suggest a low frequency of interchange of small terrestrial vertebrates between the two regions during campanian time the taphonomic s

adjoint based estimation of plate coupling in a non linear mantle flow model theory and examples we develop and validate a systematic approach to infer plate boundary strength and rheological parameters in models of mantle flow from surface velocity observations based on a realistic rheological model that includes yielding and strain rate weakening from dislocation creep we formulate the inverse problem in a bayesian inference framework to study the distribution of parameters that are consistent with the observations we compute the maximum a posteriori map point gaussian approximations of the parameter distribution around that map point and employ markov chain monte carlo mcmc sampling methods the computation of the map point and the gaussian approximation require first and second derivatives of an objective function subject to non linear stokes equations these derivatives are computed efficiently using adjoint stokes equations we set up 2 d numerical experiments with many of the elements expected in a global geophysical inversion this setup incorporates three subduction zones with slab and weak zone interplate fault geometry consistent with average seismic characteristics with these experiments we demonstrate that when the temperature field is known we can recover the strength of plate boundaries the yield stress and strain rate exponent in the upper mantle when the number of uncertain parameters increases there are trade offs between the inferred parameters these trade offs depend on how well the observational data represents the surface velocities and on the weakness of plate boundaries as the plate boundary coupling drops below a threshold the uncertainty of the inferred parameters increases due to insensitivity of plate motion to plate coupling comparing the trade offs between inferred rheological parameters found from the gaussian approximation of the parameter distribution and from mcmc sampling we conclude that the gaussian approximation which is significantly cheaper to compute is often a good approximation in particular locally around the map point thus the method can be applied to the global problem of inferring non linear constitutive parameters and plate coupling factors for each subduction zone in a global geophysical inversion with known slab structure

dinosaur eggshell and tooth enamel geochemistry as an indicator of mongolian late cretaceous paleoenvironments the late cretaceous fossiliferous beds of mongolia s gobi desert have yielded spectacular articulated remains of a remarkable diversity of fossil mammals lizards turtles birds and non avian dinosaurs paleoenvironmental interpretations of the deposits at these localities have ranged from arid wind blown dune fields to more mesic moist environments among the diversity of fossils dinosaur eggshells and teeth are commonly found at these localities dinosaur eggs like modern avian eggs are constructed of biomineralized calcite caco3 and proteins allowing carbon and oxygen stable isotopes to be quantified to provide information about the environment in which the egg laying animals were living here it is shown that dinosaur eggshell and teeth from the djadokhta and nemegt formations have not been significantly altered and reflect an environment of dry dunes during deposition of the djadokhta formation and a more mesic stream environment for conditions in the nemegt formation carbonate nodules from the same eggshell bearing layers also independently reflect a similar environmental signal this study represents the first geochemical analysis of dinosaur remains from the cretaceous of mongolia and illustrates the potential of utilizing dinosaur fossil geochemistry of both eggs and teeth to reconstruct mesozoic environments

electromagnetic imaging of variscan crustal structures in sw iberia the role of interconnected graphite abstract the western part of the iberian peninsula iberian massif is the best exposed fragment of the variscan orogen in europe its southern half was generated by an oblique collision between three continental terranes belonging to the margins of laurassia avalonia the south portuguese zone spz and gondwana the ossa morena zone omz and the central iberian zone ciz the boundaries between them are considered to be suture zones a 200 km long magnetotelluric profile across the three variscan terranes was done in a nne direction approximately perpendicular to the main tectonic features the results of two dimensional inversion of the mt dataset reveal high conductivity zones coinciding with the transitions spz omz and omz ciz these conductive bodies related to the sutures at depth were interpreted as graphite enrichments along shear planes formed due to the overall transpressive regime a high conductivity layer extending along the whole omz was found at a depth of 15 25 km the top of which spatially correlates with a broad reflector detected by a recently acquired deep seismic reflection profile the high conductivity was interpreted as caused by the precambrian serie negra graphite rich rocks carbon and oxygen x ray mapping with electron microprobe on polished sections of serie negra samples from omz revealed the presence of interconnected graphite which supports the hypothesis that graphite is determinant for the high conductivity two graphite types which help to record the geological evolution were identified graphite accumulations in the schistosity surfaces produced by folding and metamorphism and metallic films of graphite developed along late faults the conductive layer shows blobs of higher conductivity suggesting macro anisotropy additional mylonitisation and shearing produced by thrusting at depth can be the origin of these zones of enhanced conductivity given that the detachment level is located within the serie negra several high resistivity features were found in the upper crust related to devonian and carboniferous successions and probably to some unexposed plutons in the spz and the palaeozoic series of omz plus some granitic intrusions in the ciz a high resistivity zone extending to the whole crust is correlated with extensive late variscan granite intrusions

introduction to the special issue commemorating the 30th anniversary of the royal tyrrell museum of palaeontology with a summary of the museum s early history and its research contributions located just west of drumheller in southern alberta canada the royal tyrrell museum of palaeontology rtmp is nestled among outcrops of the upper cretaceous horseshoe canyon formation exposed along the red deer river valley fig 1 since it officially opened on 25 september 19851 the museum has become one of alberta s must see tourist attractions a significant contributor to the local economy and earned an international reputation for the quality of its palaeontological collections and the research conducted by its scientists the rtmp is unique within canada in being the only government supported museum dedicated to palaeontology and it is one of the few such institutions in the world fig 1 the royal tyrrell museum of palaeontology a front of museum and main entrance circa 2010 looking westwards and with horizontal beds of the upper cretaceous horseshoe canyon formation exposed in the walls of the red deer river valley in the distance b aerial photograph oblique angle and looking to the north northeast the museum sits on top of the number 7 coal seam sensu gibson 1977 and at the base of the horsethief member of the horseshoe canyon formation d a eberth pers comm 2015 that stratigraphic position correlates with an age of about 71 5 ma i e late campanian and lies within the upper part of the edmontosaurus regalis pachyrhinosaurus canadensis dinosaur assemblage zone see eberth et al 2013 fig 6 c the iconic running theropod logo that until recently graced the exterior of the museum below a life sized tyrannosaurid sculpture by brian cooley one of many such sculptures by cooley that have been featured at the museum since its opening in 1985 and with the education wing opened in 2003 as the atco tyrrell learning centre in the background d the cretaceous alberta life sized diorama opened in 2007 an example of a rtmp exhibit that relies heavily on discoveries and interpretations by museum researchers in this case work done in the albertosaurus bonebed and at other localities throughout the horseshoe canyon formation all photographs courtesy of the royal tyrrell museum of palaeontology this special issue of the canadian journal of earth sciences presents a collection of papers commemorating the rtmp s 30th or pearl anniversary our rationale for doing a 30th anniversary volume was two fold first it is an opportunity to showcase the breadth of research conducted by current and former museum scientists as well as by some colleagues having a history of collaboration with the rtmp the 13 invited papers included in this volume are a mix of review and original research papers all thematically focused on the geology and palaeontology of alberta to varying degrees each contribution is the result of work supported by the rtmp and relies on specimens housed in the museum s collections second the 30th anniversary is an opportunity to reflect on the rtmp s history and its research program as is typical for most institutions the rtmp has done little to formally document its own history this year likely will be the last major milestone for which the original generation of museum staff are still working and available to share their recollections about the museum fieldwork and research already deaths and departures have winnowed away part of the original

macro anisotropy of the electrical conductivity of the crust a magnetotelluric study of the german continental deep drilling site ktb summary the interpretation of magnetotelluric mt data collected in the vicinity of the german continental drilling project ktb has revealed two major structures in the earth s crust first a large scale mid crustal layer of enhanced conductivity is required to fit the regional observations of the anomalous vertical magnetic field second the mt impedances of the area close to the ktb namely the crustal unit of the zone erbendorf vohenstraus zev support a model with a highly anisotropic upper to middle crust the extremely high values of anisotropy derived from the mt measurements exceed the values of anisotropy observed on rock samples in the laboratory by an order of magnitude and therefore exclude intrinsic features as a source for the observed anisotropy the regional mid crustal conductor is in agreement with central europe wide observations of high conductivity layers in the crust while the proposed model of well conducting subvertical dykes within a resistive host rock explains the mt observations and agrees with the steeply dipping seismic reflectors the downhole and core observations from the drilling and the model of the tectonic development of this area however the superposition of both structures leaves some unanswered questions

stagnant lid convection on venus the effect of strongly temperature dependent viscosity on convection in the interior of venus is studied systematically with the help of finite element numerical models for viscosity contrasts satisfying experimental constraints on the rheology of rocks venus is likely to be in the regime of stagnant lid convection this regime is characterized by the formation of a slowly creeping very viscous lid on top of the mantle venusian lithosphere and is in agreement with the tectonic style observed on venus stagnant lid convection explains large geoid to topography ratios on venus by the thermal thinning of a thick lithosphere the thickness of the lithosphere can be as large as 400 550 km for beta regio and 200 400 km on average geoid and topography data and experimental data on the rheology of rocks provide constraints on the viscosity of the mantle 10 20 10 21 pa s the convective stresses in the interior 0 2 0 5 mpa the stresses in the lid 100 200 mpa the velocity in the interior 0 5 3 cm yr 1 and the heat flux beneath the lithosphere 8 16 mw m 2 parameterized convection calculations of thermal history of venus are difficult to reconcile with a thick present day lithosphere however a sufficiently thick lithosphere can be formed if a convective regime with mobile plates was replaced by stagnant lid convection around 0 5 b y ago one of the possible explanations for the cessation of venusian plate tectonics is that during the evolution of venus stresses in the lid dropped below the yield strength of the lithosphere this model predicts a drastic drop in the heat flux thickening of the lithosphere and suppression of melting and is consistent with the hypothesis of cessation of resurfacing on venus around 0 5 b y ago

a model of lower crustal electrical anisotropy for the pontiac subprovince of the canadian shield summary magnetotelluric data from the pontiac subprovince of the canadian shield indicate that the crustal electrical conductivity structure of the region is very uniform because the data are distorted by near surface electrical heterogeneities the exact parameters of the resistivity structure may vary for different static shift corrections but the same sequence of layers is retained an approximate one dimensional model of the pontiac based on inversion of the effective impedance recorded at each site consists of a thin conductive weathered layer underlain by at least 12 km of resistive upper crust at 5000 rm or more a mid crustal layer of 200 qm extends to a depth of 25 km or more below which there is evidence of an increase in the bulk resistivity in the lower crust and or upper mantle however this last layer displays marked non one dimensional magnetotelluric responses which appear to be quite uniform along the profile similar responses have been seen in other parts of the canadian shield and the baltic shield this feature in the mt data can be explained by azimuthal electrical anisotropy or by a two dimensional conductive structure the absence of any large vertical magnetic field responses suggests that anisotropy is the more likely cause modelling the anisotropy shows that a ratio of horizontal resistivities between 1 6 and 1 13 is representative of the lower crust and or the upper mantle in the area the higher conductivity is found or electric fields measured in the east west direction subparallel to the tectonic fabric of the shield in this region

fold interaction and wavelength selection in 3d models of multilayer detachment folding abstract many fold and thrust belts are dominated by folding and exhibit a fairly regular fold spacing yet in map view the aspect ratio of doubly plunging anticlines varies considerably from very elongated and sometimes slightly curved cylindrical folds to nearly circular dome like structures in addition the fold spacing often varies significantly around an average value so far it remains unclear whether these features are consistent with a folding instability therefore we here study the dynamics of multilayer detachment folding process by which shortening can be accommodated in thin skinned fold and thrust belts we start by analysing the physics of this process by using both a semi analytical thick plate theory and numerical simulations results show that several different folding modes occur about half of which are affected by gravity and have a wavelength that depends on the background deformation rate non dimensional expressions are derived that predict the dominant wavelength and growth rate of each of these folding modes and mechanical phase diagrams are presented that illustrate the applicability of each of the modes next we perform 3d simulations and compare the results with those of 2d models and analytical theory both 2d and 3d numerical simulations have wavelengths that are in good agreement with the analytical predictions in the high resolution 3d simulations the lateral growth of folds is studied in particular with respect to fold segment interactions and evolution of fold width length aspect ratio the numerical simulations show a number of similarities with the fars region of the zagros fold and thrust belt including a large range of fold aspect ratio and a normally distributed fold wavelength around a dominant one

magnetotelluric inversion for anisotropic conductivities in layered media abstract electrical anisotropy in the earth s crust and upper mantle has recently gained attention as a significant linking factor between electrical models and underlying structural and tectonic patterns this interest has also motivated new methodological studies into the modelling and inversion for electrically anisotropic structures we present an algorithm for the inversion of magnetotelluric data over layered anisotropic conductors which is a straightforward extension of the standard occam 1 d inversion to anisotropic models owing to the essential limitation of magnetotellurics to resolve the complete conductivity tensor we formulate the inversion for azimuthal anisotropy only we treat the non linear inverse problem as a multi criterion minimization of the structure complexity data misfit and anisotropy to constrain the structure complexity we employ the standard roughness penalty as well as non quadratic penalties of the total variation and gradient support type that produce more focused model sections and thus conform better to the idea about sharp non diffuse boundaries of anisotropic structures in the earth application of the anisotropy penalty is crucial for suppressing spurious anisotropy in the inverse models we use a 2 d extension of the heuristic l curve method to estimate the quasi optimal penalty weights with two non linear iteration solvers specifically the reweighted conjugate gradient method and the lagged diffusivity iteration we can arrive at the minimum of the target functional for one selected pair of regularization weights typically after a few tens of iteration steps to demonstrate the inverse solution we present two simple yet not completely trivial synthetic examples the first one based on data generated by a model with two anisotropic layers with discordant strikes and the other showing possible misinterpretations in case a 1 d inversion with anisotropy is formally applied to data produced by simple 2 d block structures field data from the variscan structures in southern portugal bear indications both geological and geophysical on possible crustal anisotropy due to shearing and graphitization we present results of a 1 d anisotropic imaging and a preliminary 2 d modelling for a short section of five sites over an old suture between the south portuguese zone and ossa morena zone aimed at explaining some essentially non 2 d effects in the data as e g systematic frequency variations of the regional strike or phases rolling out of their natural quadrants

artefacts of isotropic inversion applied to magnetotelluric data from an anisotropic earth summary 2 d isotropic approaches are standard for magnetotelluric mt data modelling and inversion unfortunately the real subsurface structure is not isotropic everywhere and one should be aware of the possible consequences of applying an isotropic inversion to data from an anisotropic earth the work presented herein was motivated by discovering an unusual mid to lower crust conductor that appeared to be bent downward into the lithospheric mantle compared to the neighbouring terranes when applying routine 2 d isotropic inversion one major difference between the terranes is the presence of the okavango giant mafic dyke swarm northeastern botswana beneath which the conductor is imaged to be in the lithospheric mantle rather than the lower crust the limited width of the dykes makes them an anisotropic feature rather than a normal 2 d structure at mt scale to examine the possible effects of the dykes synthetic data were generated from an 1 d model accounting for the dyke swarm by using an anisotropic block and then inverted isotropically the synthetic tests showed that the normal 2 d decomposition and strike analysis techniques are not removing these large scale anisotropic effects and that an isotropic inversion result obtained in the presence of an anisotropic structure has to be treated with caution the comparison of the synthetic data with the presented case history strongly suggests that the lithospheric depths of the conductor is an artefact and it is most likely located in the lower crust as everywhere else in the area focused anisotropic inversion of the dyke swarm area supports the assumption of a crustal anisotropic structure related to the okavango dyke swarm that affects the isotropic inversion results

planforms of self consistently generated plates in 3d spherical geometry 1 in the past decade several studies have documented the effectiveness of plastic yielding in causing a basic approximation of plate tectonic behavior in mantle convection models with strongly temperature dependent viscosity strong enough to form a rigid lid in the absence of yielding the vast majority of such research to date has been in either two dimensional or three dimensional cartesian geometry in the present study mantle convection calculations are performed to investigate the planform of self consistent tectonic plates in three dimensional spherical geometry the results are compared to those of similar calculations where a three dimensional cartesian geometry is used we found that when yield stress of the lithosphere is low 20 mpa a great circle subduction zone forms at low intermediate yield stresses 100 mpa plates spreading centers and subduction zones formed and were destroyed over time at high intermediate yield stresses 200 mpa two plates form separated by a great circle boundary that is a spreading centre on one side and a subduction zone on the other side at high yield stresses 400 mpa a rigid lid was observed the great circle subduction zone and the rigid lid are stable over time while at intermediate yield stresses some episodic behavior is observed the spherical cases showed a higher more earth like toroidal poloidal ratio of the surface velocity field than the cartesian cases

lithostratigraphy and depositional environments of the upper cretaceous djadokhta formation ulan nuur basin southern mongolia and its paleoclimatic implication abstract non marine upper cretaceous strata are widely distributed in the gobi basin of southern mongolia and record marked paleoenvironmental and paleoclimatic changes the climate in this region is considered to have changed from humid during the cenomanian to santonian to semi arid during the campanian and returned to humid during the early maastrichtian the change from humid to semi arid climate is well recorded in the djadokhta formation as former division in the ulan nuur basin of the central gobi basin in previous studies the djadokhta formation was formally regarded as being characterized by eolian deposits formed under a semi arid climate however the present study revealed that this formation comprises sub humid fluvial lithofacies in the lower part and semi arid eolian lithofacies in the upper part since the djadokhta formation was initially defined as a succession characterized by eolian lithofacies it is proposed here that the lower part showing fluvial lithofacies should be separated from the djadokhta formation and is newly named as the alagteeg formation the alagteeg formation is characterized by alternating beds of horizontally bedded sandstone and mudstone indicating sandy braided river flood plain and ephemeral lake environments under sub humid climate the djadokhta formation revised division is further subdivided into two parts the lower part is composed of large scale cross stratified sandstone in situ and reworked calcretes and thick mudstone lens suggesting desert environments of broad sand dune fields with few inter dune ephemeral river and pond deposits under semi arid climate on the other hand the upper part comprises structureless sandstone with mature in situ calcretes exotic pebbly sandstone and large sized burrows these lithofacies imply steppe environments with calcic soil development under semi arid climate this change from sub humid to semi arid climate during the campanian is recorded not only in the ulan nuur basin but also in other regions of southern mongolia as well as northern china hence the broad aridification in the mid latitudes of the asian interior during the campanian is inferred

a magnetotelluric profile across the german deep drilling project ktb area two and three dimensional modeling results previous interpretations of magnetotelluric data from the vicinity of the german deep drilling project ktb revealed two major structures a midcrustal layer of increased conductivity and large regional extent and a highly anisotropic upper crust nevertheless a satisfactory combination of both structures explaining all measurements has not yet been achieved mostly due to incomplete and qualitatively poor data simplified superposition of both structures could not yield an explanation of the observations on the basis of a carefully processed new data set we apply different modeling approaches to verify the existence of both structures models calculated with a two dimensional modeling program which allows for general anisotropy as well as a full three dimensional code show that an anisotropic upper crust is overlaying a regional east west striking high conductivity structure nevertheless this continuous conductive midcrustal layer with a conductance decreasing from north to south must be replaced by a quasi anisotropic one at least in the region of the ktb the final model may still be oversimplified considering the complexity of the true but unknown geology in this particular area but it demonstrates which major electrically effective structures could be resolved

a finite element algorithm for electromagnetic induction in two dimensional anisotropic conductivity structures summary electromagnetic fields are computed for a 2 d electrically anisotropic earth using a finite element technique the models consist of a background layered structure containing anisotropic blocks each block and layer may be anisotropic by assigning to them 3 3 conductivity tensors the forward modelling problem leads to a coupled system of two partial differential equations for the strike parallel field components ex and hx they are solved numerically using the finite element fe method the resulting system of linear fe equations is solved using a preconditioned conjugate gradient method subsequently strike perpendicular field components ey and hy at the surface are found by numerical differentiation of ex and hx using spline interpolation the 2 d fe algorithm has been validated by comparison with a 2 d finite difference solution three model types are used to demonstrate the effect of anisotropy upon the magnetotelluric responses horizontal vertical and dipping anisotropy a fourth model simulates the effect of anisotropy in the context of shear and subduction zones the model responses simulate the splitting of apparent resistivity curves at long periods as well as the existence of tensor impedances with significant diagonal elements as has been observed previously

parameters that control lithospheric scale thermal localization on terrestrial planets 1 shear heating induced localization has been suggested as a potentially important mechanism for breaking the lithosphere yet the physical parameters that control the onset of this instability remain unclear we therefore performed systematic 2 d simulations of visco elasto plastic lithospheric deformation in which we addressed the effects of various parameters and we found that a sharp transition exists between localizing and non localizing regimes in a next step we develop a semi analytical model that combines scaling laws with a 1 d lithospheric deformation model we show that the 1 d model successfully predicts the occurrence of shear localization in 2 d models if the thickness of the plastically deforming part of the lower lithosphere is employed as characteristic length scale an application of the 1 d model to the terrestrial planets shows that this type of shear localization is expected to occur most readily on earth

oyu tolgoi mongolia siluro devonian porphyry cu au mo and high sulfidation cu mineralization with a cretaceous chalcocite blanket the oyu tolgoi porphyry cu au mo deposit is located in the gobi desert of southern mongolia the deposit consists of three main mineralized zones north central and south oyu interpreted to constitute at least two separate porphyry copper centers oyu tolgoi is associated with a series of small structurally controlled stocks and dikes of monzonitic and dioritic composition which intrude a sequence of siluro devonian volcanic and sedimentary rocks country rocks consist of pillow basalt and basaltic andesite interbedded with fine grained clastic sedimentary horizons the sequence is interpreted to have formed in a subaqueous island arc volcanic environment which formed part of the extensive paleozoic tuva mongol arc these island arc rocks are covered by carboniferous terrigenous sequences and are intruded by carboniferous syenite and granite and permian alkaline granite much of the area is covered by poorly consolidated cretaceous sedimentary sequences central oyu consists of a multiple phase hydrothermal breccia crosscutting an altered fine grained feldspar porphyry containing porphyry type alteration and mineralization the breccia underwent texture destructive advanced argillic alteration characterized by several associations of quartz alunite dickite pyrophyllite sericite and zunyite plus lesser svanbergite and fluorite these associations overprint earlier formed k silicate and quartz sericite illite assemblages copper mineralization at central oyu is present in a supergene chalcocite blanket that formed at the expense of a pyrite rich hypogene chalcocite covellite tennantite arsenosul vanite sulvanite chalcopyrite bornite sulfide suite that accompanied the advanced argillic alteration event at south oyu a feldspar hornblende porphyry of monzonitic composition intrudes a sequence of fine grained andesite and basaltic andesite hypogene copper gold mineralization occurs as early magnetite rich pyrite poor quartz chalcopyrite bornite stockworks and sheeted veinlets hydrothermal alteration is composed of biotite and k feldspar with apatite and minor albite magnetite averages 7 to 10 vol percent and copper and gold grades vary sympathetically these early assemblages are overprinted by a sericite chlorite event with ore grade copper and erratic gold and molybdenum values and also by structurally controlled pyrite rich advanced argillic alteration k ar ages show that the hypogene copper gold mineralization at south oyu is latest silurian earliest devonian 411 3 ma and that the entire district was intruded by postmineralization syenite during the carboniferous 307 4 ma the supergene chalcocite blanket at central oyu formed in the early cretaceous earliest late cretaceous based on ages for supergene alunite of 117 1 and 93 1 ma which makes central oyu one of the oldest preserved chalcocite blankets in the world chalcocite blanket preservation was favored by climatic desiccation into the late cretaceous and the tertiary it is inferred that significant regional uplift took place at the silurian devonian boundary this synmineral ization uplift and erosion may have been in part responsible for the telescoping of the hydrothermal systems at oyu tolgoi including the superposition of epithermal style associations over higher temperature deeper seated assemblages typical of the porphyry environment