occurrence stratigraphy and geochemistry of late quaternary tephra layers in the aegean sea and the marmara sea abstract several discrete tephra layers occur in 2 5 10 3 m long cores from the aegean sea whereas a single tephra is identified in 3 5 9 7 m long cores from the marmara sea major and trace element data on these tephras delineate eight distinct groups the geochemical data and multivariate statistics allow the correlation of the tephra layers with six previously described marine tephras from the eastern mediterranean sea potential terrestrial sources are suggested for the others the chronostratigraphy of the tephra layers was established using several radiocarbon dates and the oxygen isotope stratigraphy from two long piston cores four widespread tephra layers occur within the upper quaternary sediments of the aegean sea the two youngest widespread tephra layers were derived from the santorini volcano of south central aegean sea z2 the minoan eruption ca 3 6 ka and y2 the cape riva eruption ca 21 7 ka the y2 tephra is also identified in three piston cores from the marmara sea the two older widespread tephra layers originated from the eruptions which emplaced the campanian ignimbrite of the italian volcanic provinces i e the y5 tephra ca 39 3 ka and from the nisyros volcano of the southeastern aegean sea the consistent occurrence of the nisyros tephra below the y5 tephra confirms similar findings in a lake core on the island of lesbos linear extrapolations using the oxygen isotope stratigraphy suggest an age of 42 44 ka for the nisyros eruption three additional tephra layers with a limited regional distribution are identified in the aegean sea cores two of these tephras originated from the yali volcano of the southeastern aegean sea and from the aeolian islands i e x1 tephra a series of six mugearite tephra beds in the south skiros basin is interpreted as a set of redeposited turbidites

late cretaceous palaeocene subduction collision exhumation of a microcontinent along the northern active margin of the southern neotethys evidence from the alanya massif and the adjacent antalya complex s turkey abstract the alanya massif represents a microcontinent that underwent subduction exhumation related to collision with the larger tauride microcontinent to the north during latest cretaceous palaeocene intermediate structural level blueschist melange in the northwest gundogmus area encompasses ductile deformed meta basaltic rocks meta cherts and minor serpentinite in a lower grade meta mudrock matrix the meta basaltic protoliths mainly formed in a subduction influenced setting together with less common oib and e morb late permian platform slope carbonates were intersliced during late stage brittle thrusting and directly over ridden by a lower grade greenschist facies late permian early triassic aged platform unit the blueschist melange is interpreted as an oceanic subduction complex that was obducted southwards related to microcontinental collision intermediate structural level hp lt blueschist ecologites farther south alanya area indicate that the alanya massif represents variably subducted exhumed continental crust both subduction and exhumation took place during the latest cretaceous prior to late palaeocene early eocene marine transgression late precambrian protoliths of eclogitic hp lt rocks and also similar aged amphibolite facies meta basic intrusions farther southeast anamur area are interpreted to have formed in a panafrican cadomian late stage back arc setting late triassic basaltic rocks in the antalya complex structurally beneath and to the north erupted in a rift setting we restore the mesozoic palaeogeography from north to south as tauride microcontinent antalya rift basin alanya micrcontinent s neotethys the subduction exhumation history may serve as a model for similar active margin collisional settings elsewhere

the application of icp ms methods to tephrochronological problems pearce nicholas westgate j a perkins w t preece s j 2004 the application of icp ms methods to tephrochronological problems applied gechemistry 19 3 pp 289 322 rae2008

geometry and p and s velocity structure of the african anomaly 1 we constrain the geometry and p and s velocity structure of a low velocity anomaly in the lower mantle beneath southern africa we term it the african anomaly on the basis of forward traveltime and waveform modeling of seismic data sampling a great arc across the anomaly from the east pacific rise to the japan sea our collected data set consists of direct s direct p sdiff scs pcp sks and skks phases recorded by three temporary broadband passcal seismic arrays deployed in africa between 1994 and 2002 the tanzania seismic array 1994 1995 the kaapvaal seismic array 1997 1999 and the ethiopia kenya seismic array 2000 2002 for earthquakes occurring in the east pacific rise drake passage south sandwich islands iran hindu kush xinjiang and the japan sea the seismic data provide excellent sampling of the african anomaly in the lower mantle along the specific great arc in order to accurately account for the contributions from the african anomaly we relocate all the events using a global seismic shear velocity tomographic model and seismic data recorded by the global seismographic network and correct for the contributions from the seismic heterogeneities outside the african anomaly the seismic observations suggest that the african anomaly locally extends 1300 km above the core mantle boundary beneath southern africa around 25 n 27 e and exhibits a bell like geometry with both the southwestern and the northeastern flanks dipping toward its center with the lateral dimension of the anomaly increasing with depth the base is about 4000 km wide extending broadly in both the southwestward and the northeastward directions the seismic data can best be explained by a shear velocity structure with average velocity decreases of 5 in the base and 2 to 3 in the mid lower mantle above the base and a compressional velocity structure with a uniform s to p velocity perturbation ratio of 3 1 for the entire african anomaly these geometric and velocity features suggest that the mid lower mantle portion of the african anomaly is an integral component of the very low velocity province and the african anomaly is compositionally distinct and geologically stable

strong heterogeneity caused by deep mantle layering 1 numerical simulations are used to characterize the volumetric heterogeneity associated with proposed chemical layering in the deep mantle a globally continuous undulating layer generates enormous amounts of volumetric heterogeneity which is caused by lateral variations in the layer boundary depth and by strong hot upwellings arising from the top of the layer in the middle lower mantle region in contrast the heterogeneity in the deepest mantle is very weak partial cancellation of the temperature and compositional contributions to seismic velocity could mask the layer itself but the strong signatures of the thermochemical boundary layer and induced upwellings remain even when fields are filtered to approximate the resolution of global seismic tomographic models this distinctive heterogeneity is not observed in global seismic tomographic models dense material that is restricted to discontinuous piles generates heterogeneity that is more consistent although not entirely with seismic observations with strong heterogeneity at the core mantle boundary radial correlation functions display a characteristic narrowing in the vicinity of any chemical layer but are very sensitive to the applied seismic tomographic filtering

the high pressure electronic spin transition in iron potential impacts upon mantle mixing 1 at the rayleigh number appropriate to earth s mantle radial heat transport is dominated by solid state thermal convection because of the large number of physical properties required to determine the rayleigh number and because these properties are expected to be perhaps strong functions of pressure and temperature p t laboratory measurements of them under the high pressure and temperature conditions that occur in the deep earth are of fundamental importance recent experimental data demonstrate that an electronic spin transition in iron that occurs at midmantle depths results in significant changes in the physical properties of the ferropericlase component of mantle mineralogy additional recent results suggest that it may also exist in the dominant perovskite component using control volume based numerical models we investigate the impacts on mantle mixing of this spin transition through its influence on the most important subset of these physical properties namely density thermal expansivity bulk modulus and heat capacity our numerical model results demonstrate that this electronic transition enhances mixing in the lower regions of the lower mantle by enhancing the vigor of rising plumes the lowermost region of the mantle is slightly warmed and the upper mantle slightly cooled by spin induced effects however the spin crossover in the lower mantle appears not to significantly influence mantle layering due to the competition that could exist between the strength of the spin induced thermodynamic properties of ferropericlase and perovskite cold descending thermal anomalies could stagnate at middle to lower mantle depths and lead to the occurrence of mid mantle avalanches

mantle tomography and its relation to temperature and composition we propose a new method to constrain lateral variations of temperature and composition in the lower mantle from global tomographic models of shear and compressional wave speed we assume that the mantle consists of a mixture of perovskite and magnesio wustite in a first stage we directly invert vp and vs anomalies for variations of temperature and composition using the appropriate partial derivatives or sensitivities of velocities to temperature and composition however uncertainties in the tomographic models and in the sensitivities are such that variations in composition are completely unconstrained inferring deterministic distributions of temperature and composition being currently not possible we turn to a statistical approach which allows to infer several robust features comparison between synthetic and predicted ratios of the relative shear to compressional velocity anomalies indicates that the origin of seismic anomalies cannot be purely thermal but do not constrain the amplitude of the variations of temperature and composition we show that we can estimate these variations using histograms of the relative vp and vs anomalies at a given depth we computed histograms for a large variety of cases and found that at the bottom of the mantle variations in the volumic fraction of perovskite from 14 to 10 are essential to explain seismic tomography in the mid mantle anomalies of perovskite are not required but moderate variations up to 6 can explain the observed distributions equally well these trade offs between anomalies of temperature and composition cannot be resolved by relative velocity anomalies alone an accurate determination of temperature and composition requires the knowledge of density variations as well we show that anomalies of iron can then also be resolved 2003 elsevier b v all rights reserved

structural features and shear velocity structure of the pacific anomaly 1 we constrain structural features and shear velocity structure of a low velocity anomaly in the lower mantle beneath the pacific we term it the pacific anomaly on the basis of forward travel time and waveform modeling of the observed direct s sdiff scs sks and skks phases sampling a great arc across the anomaly from eastern eurasia to southern south america after correction for the effects of earthquake mislocation and the seismic heterogeneities outside the pacific anomaly seismic observations suggest that the pacific anomaly along the great arc consists of at least two separated portions with a 740 km wide gap between them the western portion of the anomaly is about 1050 km wide extends at least 740 km above the core mantle boundary cmb and exhibits a trapezoidal shape with lateral dimensions increasing slightly with depth the velocity structure of the western portion varies from 3 0 at the top 740 km above the cmb to 3 5 at 100 km above the cmb and an average shear velocity reduction of 5 in the bottom 100 km of the mantle the eastern portion of the anomaly reaches at least 340 km above the cmb beneath the mid pacific with an 1800 km wide base and has a uniform velocity reduction of 3 waveform modeling further suggests a very low velocity layer with a shear velocity reduction of 10 located at the edge of the western portion of the anomaly combining the latest results from others we present a general picture of structural and velocity structures of the pacific anomaly the structural and velocity features suggest that the anomaly represents a cluster of metastable thermo chemical piles

late cretaceous miocene sedimentary development of the arabian continental margin in se turkey adiyaman region implications for regional palaeogeography and the closure history of southern neotethys abstract the middle cretaceous late miocene sedimentary successions that are exposed on the arabian continental margin near adiyaman provide valuable insights into sedimentary tectonic and climatic processes that affected the southern neotethys and its continental margins deposition in the region began with aptian early campanian shelf carbonates followed by deepening during the mid campanian lithoclastic bioclastic turbidites accumulated along the downfaulted northern margin of the arabian platform during the campanian a flexurally controlled foredeep developed in advance of the emplacement of mesozoic allochthonous continental margin and oceanic rocks during the latest campanian early maastrichtian e g supra subduction zone kocali ophiolite alluvial detritus was shed from the emplaced allochthon in non marine to shallow marine deltaic settings during latest campanian early maastrichtian a marine transgression resulted in the establishment of a shallow marine shelf during the mid maastrichtian during the latest maastrichtian the platform submerged initiating deeper water hemipelagic sedimentation uplift took place during the palaeocene resulting in sediment instability slumping and formation of high density subaqueous gravity flows in response to regional faulting and tilting some areas in the north and the southwest emerged during the early middle eocene generating alluvial fans in a warm humid climate that favoured oxidation and reddening the likely control of the tectonic instability was far field compression related to the latest stages of subduction of the southern neotethys or the initial stages of collision of the arabian and tauride continents an oligocene hiatus is likely to reflect the formation of a collision related forebulge followed by flexural subsidence to form an early miocene foreland basin this was finally over ridden by the northerly active continental margin of the southern neotethys during early mid miocene regional suture tightening mid late miocene and related non marine coarse clastic sedimentation was followed by westward tectonic escape of the anatolian microplate towards the aegean region during plio quaternary time

testing the tracer ratio method for modeling active compositional fields in mantle convection simulations 1 tracer methods are attractive for modeling compositional fields because they offer the potential of zero numerical diffusion composition is typically taken to be proportional to the absolute local concentration of tracers but an increasingly popular method is to have dense and regular tracers with composition being equal to the local fraction of dense tracers this paper tests this ratio method using established benchmarks and by comparing the performance of the two tracer methods and grid based methods for simulating the long term evolution of a convecting mantle with a thick dense stable layer for this scenario the ratio method is found to have several advantages giving sharp stable long term layering with no tracer settling minimal statistical noise and low entrainment even with only 5 tracers per cell the method is equally applicable to finite volume and finite element treatments of the underlying flow entrainment in grid based advection methods is heavily dependent on resolution and numerical details and is reduced 1 order of magnitude by the filter proposed by a lenardic numerical determination of physically correct entrainment rates remains a challenging problem comparing tracer and grid based methods the spatial pattern of the thermal and chemical fields appear to be converging on the finest grids however the estimated entrainment differs significantly

trace element composition of single glass shards in distal minoan tephra from sw turkey volcanic glass from the seventeenth century bc c 3600 bp minoan eruption of santorini thera has been recovered from a 4 cm thick tephra deposit at golhisar golu a small lake in sw turkey analysis of single grains of this glass by laser ablation inductively coupled plasma mass spectrometry la icp ms provides for the first time an accurate determination of the trace element composition of the juvenile glass component of this eruption free from contaminants such as phenocrysts or detrital material individual glass shards 150 m show a large degree of variation in their trace element composition indicative of substantial small scale compositional heterogeneity in the magma this is a result of the proximity of crystallizing phases and provides insights into the chemical evolution of the minoan magma the range of elemental compositions displayed by individual glass shards combined with the consistency of many trace element ratios are characteristics of the minoan glass these features provide a trace element signature for the minoan tephra which will be of value in stratigraphic correlation across the eastern mediterranean

late palaeozoic early cenozoic tectonic development of southern turkey and the easternmost mediterranean region evidence from the inter relations of continental and oceanic units

iron spin transition controls structure and stability of llsvps in the lower mantle abstract seismic tomography models have revealed that there exist two large low shear velocity provinces llsvps beneath africa and the pacific ocean in the earth s lower mantle waveform modeling results suggest both llsvps have steep sharp side boundaries which imply that they probably are compositionally heterogeneous from the ambient mantle when applying the surface plate motion history in the last a few hundred million years ma as the driving mechanism numerical modeling has successfully reproduced the geographical distribution of the two llsvps in thermochemical mantle convection however two prominent seismic features of the llsvps the steep side boundaries and the high elevation can hardly be obtained in previous geodynamic models here we include in our mantle convection model the effects of iron spin transition of ferropericlase which substantially change physical properties of the mantle our results show that iron spin transition plays a dominant role in controlling the structure and stability of llsvps large chemical blocks with steep side boundaries and high elevations up to 1200 km above core mantle boundary cmb emerge in our models with the volume content of ferropericlase 20 such blocks cause a shear wave velocity decrease of 3 5 which is consistent with the seismic observations our results also show that these llsvps are transient structures in the lower mantle which can typically last for a few hundred million years before destroyed by large scale mantle motion

late cretaceous cenozoic subduction collision history of the southern neotethys new evidence from the caglayancerit area se turkey evidence of the subduction collision history of the s neotethys is well exposed in the frontal part of the se anatolian thrust belt and the adjacent arabian continental margin the foreland succession in the study area begins with eocene shelf carbonates ranging from shallow marine to deeper marine without sedimentary input from the tauride continent to the north after a regional hiatus oligocene sedimentation resumed during the early miocene with terrigenous gravity flow deposition in the north lice formation and shallow marine carbonates further south clastic detritus was derived from the tauride continent and oceanic accretionary material the base of the overriding tauride allochthon comprises ophiolite derived debris flows ophiolite related melange and dismembered ophiolitic rocks above this the regional scale bulgurkaya sedimentary melange an olistostrome includes blocks and dismembered thrust sheets of metamorphic rocks limestone and sandstone which include late cretaceous and eocene foraminifera the matrix is mainly strongly deformed eocene oligocene mudrocks hemipelagic marl and sandstone turbidites the thrust stack is topped by a regionally extensive thrust sheet malatya metamorphic unit which includes greenschist facies marble calcschist schist and phyllite representing tauride continental crust beginning during the late mesozoic the s neotethys subducted northwards beneath a backstop represented by the tauride microcontinent malatya metamorphic unit ophiolites formed within the s neotethys and accreted to the tauride active margin large scale sedimentary melange developed along the tauride active margin during eocene oligocene on the arabian margin a sedimentary hiatus and tilting oligocene is interpreted to record initial continental collision the early miocene terrigenous gravity flows represent a collision related flexural foreland basin southward overthrusting of the tauride allochthon took place during early middle miocene associated regional uplift triggered large scale alluvial deposition the foreland folded and faulted in response to suture zone tightening late miocene left lateral strike slip characterised the plio pleistocene

godene zone antalya complex volcanism and sedimentation along a mesozoic continental margin s w turkey the godene zone antalya complex is an assemblage of ophiolitic and associated sedimentary rocks formed on a passive margin during and after the rifting of a mesozoic ocean basin the zone comprises late triassic alkaline mafic submarine lavas and sediments mostly pelagic which are tectonically intercalated with mafic ultramafic plutonic rocks taken to be remnants of an original ophiolitic substratum the godene zone also includes major limestone massifs and tectonised remnants of former carbonate margin facies early triassic rifting initiated a horst graben terrain with localised evaporite and clastic deposition by late triassic time continued extension allowed substantial extrusion of submarine mafic volcanics these were often erupted close to tectonically active fault scarps generating both epiclastic and pyroclastic volcanic breccias several large slivers of continental basement were rifted off to form major offshore massifs which remained as topographic highs throughout the mesozoic during late triassic time exposed parts of the continent bey daglari and the offshore massifs shed siliciclastics mostly turbidites above the mafic lavas offshore reefs also shed material ranging from substantial detached blocks to finer grainedhalobia limestone facies during jurassic to late cretaceous time the whole area underwent passive margin deposition radiolarian pelagic sediments were deposited in deep water above the ophiolitic basement and around the offshore massifs the reef complexes persisted until mid cretaceous time when calcareous pelagic deposition was initiated passive margin conditions were terminated with deposition of ophiolitic clastics and olistostrome melange in the maastrichtian followed by major tectonism

discovery of the late triassic middle carnian rhaetian radiolarians in the volcano sedimentary sequences of the kocali complex se turkey correlation with the other tauride units abstract the kocali complex in se turkey includes pelagic sediments pelagic limestones cherts etc basic volcanic rocks of oceanic crust origin together with platform derived sediments its depositional age was previously assigned as late jurassic early cretaceous in order to study the radiolarian contents of volcano sedimentary sequences in this complex six stratigraphic sections have been measured mainly at the ne and nw adiyaman city radiolarian faunas from these stratigraphic sections reveal that the age of these sequences ranges from middle carnian to rhaetian based on these data the depositional age of the complex is older than the previously assigned lithological characteristics widespread triassic basic volcanic rocks associated with pelagic sediments and radiolarian contents of these sequences have close similarities with the sequences of the alakircay nappe of the antalya nappes in western and central taurides based on taxonomic studies 99 taxa have been determined of which one genus adiyamanium and four species monocapnuchosphaera kocaliensis paronaella speciosa ferresium okuyucui and adiyamanium crassum are described as new

gypsum a joint tomographic model of mantle density and seismic wave speeds 1 gypsum is a 3 d model of mantle shear wave s speeds compressional wave p speeds and density the model is developed through simultaneous inversion of seismic body wave travel times p and s and geodynamic observations while using realistic mineral physics parameters linking wave speeds and density geodynamic observations include the global free air gravity field divergence of the tectonic plates dynamic topography of the free surface and the flow induced excess ellipticity of the core mantle boundary gypsum is built with the philosophy that heterogeneity that most closely resembles thermal variations is the simplest possible solution models of the density field from earth s free oscillations have provided great insight into the density configuration of the mantle but are limited to very long wavelength solutions alternatively scaling higher resolution seismic images to obtain density anomalies generates density fields that do not satisfy geodynamic observations the current study provides a 3 d density model for the mantle that directly satisfies geodynamic and seismic observations through a joint seismic geodynamic inversion process notable density field observations include high density piles at the base of superplume structures supporting the general results of past normal mode studies however we find that these features are more localized and have lower amplitude than past studies would suggest when we consider both fast and slow seismic anomalies in gypsum we find that p and s wave speeds are strongly correlated throughout the mantle however we find a low correlation of fast s wave zones in the deep mantle 1500 km depth with the corresponding p wave anomalies suggesting a systematic divergence from simplified thermal effects in ancient subducted slab anomalies the cratonic lithosphere and d regions are shown to have strong compositional signatures however we argue that temperature variations are the primary cause of p wave speed s wave speed and density anomalies throughout most of the mantle

coupled magmatism mantle convection system with variable viscosity abstract numerical models are presented for the thermal and chemical evolution of the mantle when it is controlled by both magmatism and mantle convection the mantle is modeled as a fluid with temperature and pressure dependent viscosity in a two dimensional square box heated by incompatible radioactive elements that decay with time the influence of phase transitions at 660 km between the upper and lower mantle is also included magmatism is modeled as permeable flow of magma produced upon pressure release partial melting of the convecting mantle materials it is shown that the mantle may exist in one of two regimes at first when the internal heating rate is higher than a threshold the mantle is on a regime where episodic but active magmatism takes place to make the mantle chemically stratified with the upper mantle occupied by magma residue harzburgite and the deeper part of the lower mantle occupied by basaltic materials there is a chemical discontinuity along the 660 km phase boundary mantle convection occurs as a layered convection punctuated by flushing events and is sluggish except at the time of flushing events owing to the compositional buoyancy from the chemical stratification the flushing events induce vigorous magmatic activity as the internal heating rate falls below the threshold owing to the decay of radioactive elements the thermal and chemical state jumps to another regime in this regime magma does not erupt and mantle convection occurs as layered thermal convection in spite of the stirring due to the thermal convection the chemical discontinuity and a portion of the chemical stratification formed in the earlier regime remains for billions of years the numerical models suggest that a mantle convection was much less active than expected from the strong internal heating and chemically distinct reservoirs are formed in the early earth and once formed b the reservoirs have survived convective stirring for billions of years

a community benchmark for 2 d cartesian compressible convection in the earth s mantle benchmark comparisons are an essential tool to verify the accuracy and validity of computational approaches to mantle convection six 2 d cartesian compressible convection codes are compared for steady state constant and temperature dependent viscosity cases as well as time dependent constant viscosity cases in general we find good agreement between all codes when comparing average flow characteristics such as nusselt number and rms velocity at rayleigh numbers near 106 and dissipation numbers between 0 and 2 the results differ by approximately 1 per cent differences in discretization and use of finite volumes versus finite elements dominate the differences there is a small systematic difference between the use of the anelastic liquid approximation ala compared to that of the truncated ala in determining the onset of time dependence there was less agreement between the codes with a spread in the rayleigh number where the first bifurcation occurs ranging from 7 79 10 5 to 1 05 10 6

new evidence and model on the evolution of the southeast anatolian orogen this paper describes the orogenic evolution of the southeast anatolian orogenic belt based mostly on new geologic data collected from its constituent tectonic units in the course of new mapping programs of the past decade the southeast anatolian orogenic segment of the alpides may be divided into three approximately east west trending zones from south to north they are the arabian platform followed by a zone of imbrication and then a zone of nappes the arabian platform includes a mostly marine sedimentary succession deposited from early cambrian to middle miocene time the zone of imbrication is a narrow belt sandwiched between the arabian platform and the zone of nappes it consists of imbricated thrust slices emplaced onto a late cretaceous to early miocene sequence the zone of nappes is the highest tectonic unit consisting of two stacks of nappes simply designated the lower and upper nappes the lower nappe is represented by the slices of a polyphase metamorpbic ophiolitic assemblage and the maden group the upper nappe rests on the lower nappe and is represented by the bitlis and poturge metamorphic massifs southeastern anatolia underwent two major episodes of alpide deformation the first occurred during the late cretaceous period when ophiolite was emplaced on the arabian platform this event was not the consequence of a continental collision the ophiolite obduction onto the arabian platform was followed by a regionwide extension and a new marine transgression over the platform immediately after the ophiolite obduction the second episode of deformation occurred during middle eocene miocene time in two distinct stages as a result of the progressive elimination and complete closure of the ocean s which led to the collision between the zone of nappes located to the north being a part of eurasia and the arabian plate the maden marginal basin formed north of the subduction zone that eliminated the ocean between eurasia and arabia along the southern margin of the taurus belt and abutted the arabian plate much later during the final collision the second episode of deformation formed the present orogenic segment leading to the amalgamation of different tectonic units these amalgamated nappes collided with the arabian plate and welded onto it at the latest stage of the orogenic evolution during the miocene epoch

discovery of bridgmanite the most abundant mineral in earth in a shocked meteorite meteorites exposed to high pressures and temperatures during impact induced shock often contain minerals whose occurrence and stability normally confine them to the deeper portions of earth s mantle one exception has been mgsio 3 in the perovskite structure which is the most abundant solid phase in earth here we report the discovery of this important phase as a mineral in the tenham l6 chondrite and approved by the international mineralogical association specimen ima 2014 017 mgsio 3 perovskite is now called bridgmanite the associated phase assemblage constrains peak shock conditions to 24 gigapascals and 2300 kelvin the discovery concludes a half century of efforts to find identify and characterize a natural specimen of this important mineral

mid mantle heterogeneities and iron spin transition in the lower mantle implications for mid mantle slab stagnation abstract recent high pressure experimental results reveal that the elastic and transport properties of mantle materials are impacted by the electronic spin transition in iron under lower mantle pressure and temperature conditions the electronic transition in ferropericlase fp the second major constituent mineral of the lower mantle material is associated with a smooth increase in density starting from the mid mantle depth to the core mantle boundary cmb the transition also yields softening in the elastic moduli and an increase in the thermal expansivity over the transition zone in the lower mantle although there is not yet robust experimental evidence for spin transition induced density change in the perovskite pv phase the major constituent mineral in the lower mantle the spin transition in the octahedral b site in al free perovskite causes a bulk modulus hardening increase in the bulk modulus in the mineral we have incorporated these physical processes into high resolution 3d spherical control volume models for mantle convection a series of numerical experiments explore how the electronic spin transition in iron modifies the mantle flow and in particular the fate of sinking cold slabs such mid mantle stagnations are prevalent globally in seismic tomographic inversions but previous explanations for their existence are not satisfactory employing density anomalies from the iron spin transition in ferropericlase and density anomaly models for perovskite we study the influence of the spin transition in the minerals of the lower mantle on mantle flow our model results reveal that while the spin transition induced property variations in ferropericlase enhance mixing in the lower depths of the mantle the density anomaly arising from the hardening in the bulk modulus of al free perovskite can be effective in slowing the descent of slabs and may cause stagnation at mid mantle levels a viscosity hill in the lower mantle may further enhance the stagnation effect cold descending slabs can stall in the mid mantle for tens of million years or even longer before penetrating to the lower mantle

electronic spin transitions in iron bearing mgsio3 perovskite the electronic spin state of iron in perovskites with the chemical composition mg0 9375fe0 0625sio3 mg0 8750fe0 1250sio3 and mg0 9375fe0 0625si0 9375fe0 0625o3 have been determined at 0 k and various pressures between 40 160 gpa using ab initio methods the results indicate that ferric iron exhibits a wide range of spin transition pressures between about 60 160 gpa while ferrous iron has a much narrower span between about 130 145 gpa in general the lowest spin transition pressures are associated with the most energetically favorable substitution configurations where iron atoms are closest together the effect of spin state on calculated elastic properties is found to be small c 2006 elsevier b v all rights reserved

thermochemical structures beneath africa and the pacific ocean large low velocity seismic anomalies have been detected in the earth s lower mantle beneath africa and the pacific ocean that are not easily explained by temperature variations alone the african anomaly has been interpreted to be a northwest southeast trending structure with a sharp edged linear ridge like morphology the pacific anomaly on the other hand appears to be more rounded in shape mantle models with heterogeneous composition have related these structures to dense thermochemical piles or superplumes it has not been shown however that such models can lead to thermochemical structures that satisfy the geometrical constraints as inferred from seismological observations here we present numerical models of thermochemical convection in a three dimensional spherical geometry using plate velocities inferred for the past 119 million years we show that earth s subduction history can lead to thermochemical structures similar in shape to the observed large lower mantle velocity anomalies we find that subduction history tends to focus dense material into a ridge like pile beneath africa and a relatively more rounded pile under the pacific ocean consistent with seismic observations

effects of multiple phase transitions in a three dimensional spherical model of convection in earth s mantle numerical models of mantle convection that incorporate the major mantle phase changes of the transition zone reveal an inherently three dimensional flow pattern with cylindrical features and linear features that behave differently in their ability to penetrate the 670 km discontinuity the dynamics are dominated by accumulation of cold linear downwellings into rounded pools above the endothermic phase change at 670 km depth resulting in frequent avalanches of upper mantle material into the lower mantle the effect of the exothermic phase transition at 400 km depth is to reduce the overall degree of layering by pushing material through the 670 km phase change resulting in smaller and more frequent avalanches and a wider range of morphologies large quantities of avalanched cold material accumulate above the coremantle boundary cmb resulting in a region of strongly depressed mean temperature at the base of the mantle the 670 km phase change has a strong effect on the temperature field with three distinct regions being visible 1 the upper mantle containing linear downwellings and pools of cold material in the transition zone and characterized by a high amplitude long wavelength spectrum 2 the midmantle containing quasi cylindrical avalanche conduits and characterized by a low amplitude broad spectrum and 3 the deep mantle containing large pools of cold avalanched material and characterized by a high amplitude ultra red i e long wavelength spectrum the effect on the velocity field is very different flow penetration across the 670 km phase change is strongly wavelength dependent with easy penetration at long wavelengths but strong inhibition at short wavelengths thus when comparing numerical models with long wavelength seismic tomography diagnostics based on the density field such as the radial correlation function are much more sensitive to the effects of phase transitions than those based on the velocity field the amplitude of the geoid is not significantly affected by the partial layering because the contribution from the strong heterogeneity in the transition zone is almost perfectly balanced by the contribution from deflection of the 670 km discontinuity avalanches are associated with geoid lows however a more complex viscosity structure is required to correctly match the sign of the geoid over slabs in earth

the temporal evolution of the active margin along the southeast anatolian orogenic belt se turkey evidence from u pb ar ar and fission track chronology abstract the southeast anatolian orogenic belt saob resulted from the north dipping subduction of the southern neotethyan oceanic lithosphere in late mesozoic and early cenozoic however the timing and the rate of the continental collision are still under debate here we present new u pb ar ar and fission track ages from the i type calc alkaline granitoids esence dogansehir and baskil cutting the goksun ispendere and komurhan ophiolites and also the malatya keban metamorphics representing the tauride active continental margin along the saob in this study high to low temperature thermochronological methods applied to the granitoids are used to understand the temporal and geodynamic evolution of the tauride active continental margin and continental collision between tauride and arabian platforms in the frame of the neotethyan convergence during cretaceous and miocene the u pb zircon ages range from 83 to 88 ma for the baskil and from 81 to 83 ma for the esence granitoids the 39 ar 40 ar ages indicate that these late cretaceous granitoids cooled below 300 c in 6 10 ma the formation ages and the timing of the gradual cooling of the late cretaceous granitoids are similar to metamorphism age and the timing of the exhumation of the hp lt bitlis metamorphics during this stage the combined field geochemistry and geo thermochronological data suggest that the first continental collision event occurred between bitlis puturge micro continents to the south and tauride platform to the north in an oblique subduction zone between 84 and 74 ma the granitoids continued uplifting during early middle eocene together with the exhumation of hp uht berit metaophiolite in an extensional regime related to the opening of the maden back arc basin this period also let the intrusion of the dogansehir arc magmatism intruding the puturge and malatya keban metamorphics berit metaophiolite and maden complex the eocene dogansehir granitoid has similar u pb and 39 ar 40 ar ages suggesting a fast cooling the apatite fission track aft ages for all granitoid bodies suggest that they were mainly cooled or uplifted in two episodes where the first one is in the eocene in an extensional setting the aft data marked the final continental collision between the taurides and the arabian platform first in oligocene and the break off of the subducted slab and the delamination process caused fast uplift of the eastern anatolia during middle to late miocene

neutron activation analysis of mediterranean volcanic rocks an analytical database for archaeological stratigraphy abstract pumice has been used as a serviceable abrasive or religious artifact since antiquity and has therefore been an object of trade by analyzing pumice samples from archaeological excavations and comparing the results to an analytical database it is possible to establish the origin of the sample and thereby get information on the maximum age and the transport route of the pumice sample in addition the deposition of primary tephra deposits can be used as time markers and place constraints on the ages of archaeological materials neutron activation analysis naa was applied to determine the concentrations of 25 elements as ba ce co cr cs eu fe hf k la lu na nd rb sb sc sm ta tb th u yb zn and zr in pumice samples from the mediterranean region milos santorini kos giali and nisyros greece lipari italy and cappadokia turkey it was found that eruption products like pumice or volcanic ash can be correlated in many cases to their volcanic sources by comparison of the typical main and trace elemental concentration patterns chemical fingerprint such a distinction is possible if the volcanic rocks are homogenous enough with respect to the concentrations of geochemically relevant elements using only the pure glass fraction of tephra a sample size of 5 mg is sufficient for identification by naa

on the vertical extent of the large low shear velocity province beneath the south pacific superswell the three dimensional s wave velocity structure beneath the south pacific superswell is obtained from joint broadband seismic experiments on the ocean floor and islands we collected only approximately 800 relative times of long period teleseismic sh waves by using a waveform cross correlation from 76 events occurring from january 2003 to may 2005 we conducted relative time tomography to obtain a 3d structure to depths of 1600 km in the resultant image we find a characteristic distribution of low velocity regions the most prominent features are a large doughnut shaped low velocity region at 800 km depth and an elongated large low velocity region beneath the society to pitcairn hotspots at 1200 km depth our model suggests that a large low shear velocity province rooted in the d00 extends upwards and culminates near the top of the lower mantle beneath the central part of the south pacific superswell although its perfect continuity is not still confirmed

compressible thermochemical convection and application to lower mantle structures a new finite element code for compressible thermochemical convection is developed to study the stability of a chemical layer at the base of the mantle using composition dependent compressibility and a density difference between compositions at a reference pressure a composition dependent density profile is derived together with depth dependent thermal expansion this combination of parameters yields a wide range of dynamic evolutions for the chemical layer the chemical structures are classified into five major categories classical plumes mushroom shaped plume domes ridges and continuous layers and a few abnormal cases such as hourglass shaped plumes and columnar plumes several models have a chemical structure morphologically similar to the african low v s structure in the lower mantle at least at a single time guided by our models several dynamic scenarios are proposed for the dynamic nature of the lower mantle low velocity structures a k a superplumes including plumes at an early stage plume clusters ridges passive piles sluggish domes and high bulk modulus domes we predict seismic velocity anomalies from these dynamic models the thermoelastic parameters used in the conversion are additional constraints we compare the density structure with normal mode inversion the predicted seismic signature observations and the required thermoelastic parameters with mineral physics data among the proposed scenarios only the scenario of high bulk modulus domes satisfies all constraints simultaneously the implication on the geochemistry and mineralogy of lower mantle chemical structures is discussed

silurian anorogenic basic and acidic magmatism in northwest turkey implications for the opening of the paleo tethys abstract the sakarya zone northern turkey is a gondwana derived continental block accreted to northern laurussia during the carboniferous and is regarded as the eastward extension of armorica timing of its detachment from the northern margin of gondwana thus opening of the paleo tethys is poorly known here we report on metagranite and amphibolite with silurian igneous crystallization ages from the early carboniferous high temperature middle to low pressure amphibolite facies metamorphic rocks of the saricakaya massif within the sakarya zone nw turkey the metagranite amphibolite complex is exposed mainly along the southern margin of the saricakaya massif over an area of ca 12 km by 1 5 km the metagranite contains preserved domains of porphyric texture indicative of derivation from a former granite porphyry the amphibolite is devoid of any relict igneous texture both the metagranite and amphibolite are crosscut by late up to 50 cm thick felsic veins uranium pb dating on igneous zircons from both metagranite and amphibolite yielded silurian ages of ca 419 6 to 434 7 ma 2 and on those from a felsic vein an age of 319 5 ma 2 late carboniferous geochemically amphibolite displays anorogenic transitional tholeiitic to alkaline signatures initial ehf values of the igneous zircons from both metagranite and amphibolite show a large variation with medial values of 16 to 9 and 3 to 6 respectively thus the protoliths of amphibolite were derived from melts of depleted mantle and those of the metagranite on the other hand from melts of reworked crustal material we suggest that the silurian anorogenic magmatism is related to a rifting event at the northern margin of gondwana leading to the detachment of the sakarya zone and hence placing an age on the initial opening of the paleo tethys this interpretation is based on i the presence of late silurian to devonian deep sea sedimentary blocks in the paleo tethyan accretionary complexes and ii the resemblance of the u pb age spectra of detrital zircons in the metaclastic sequence of the saricakaya massif to those of cambro ordovician sandstones in jordan gondwana and iii the local occurrence of anorogenic a type granites of late ordovician silurian age in the anatolide tauride block a continental block which rifted from gondwana during the early triassic wholly anorogenic nature of the late ordovician to silurian igneous rocks in the saricakaya massif and reported in literature does not support the opening of the paleo tethys as back arc ocean as suggested in most paleogeographic reconstructions

late triassic rifting and jurassic cretaceous passive margin development of the southern neotethys evidence from the adiyaman area se turkey evidence of rifting and continental break up to form the s neotethys is found within the volcanic sedimentary kocali complex this is a folded thrust imbricated succession that includes lavas volcaniclastic sediments pelagic carbonates radiolarites and manganiferous deposits interbedded ribbon cherts contain radiolarians of late triassic to late jurassic age the lower part of the succession of mid late triassic age tarasa formation is dominated by enriched mid ocean ridge basalt e morb the overlying late triassic to mid jurassic interval konak formation is characterised by intercalations of ocean island basalt and e morb taking account of structural position the basalts erupted within the outer part of a continent ocean transition zone continental break up probably occurred during the late triassic carnian norian early to mid jurassic lavas and volcaniclastic sediments record volcanism probably after continental break up in addition the karadut complex is a broken formation that is located at a relatively low structural position just above the arabian foreland pelagic carbonates redeposited carbonates and radiolarites predominate radiolarians are dated as early to mid jurassic and late cretaceous in age the pelagic carbonates include planktic foraminifera of late cretaceous age the karadut complex resulted from the accumulation of calcareous gravity flows pelagic carbonate and radiolarites in a relatively proximal base of slope setting after continental break up morb and ophiolitic rocks formed within the s neotethys further north tectonic emplacement onto the arabian platform took place by earliest maastrichtian time regional interpretation is facilitated by comparisons with examples of triassic rifting and continental break up in the eastern mediterranean region and elsewhere

optical signatures of low spin fe3 in nal at high pressure the iron spin transition directly affects properties of lower mantle minerals and can thus alter geophysical and geochemical characteristics of the deep earth while the spin transition in ferropericlase has been documented at p 60 gpa and 300 k experimental evidence for spin transitions in other rock forming minerals such as bridgmanite and post perovskite remains controversial multiple valence spin and coordination states of iron in bridgmanite and post perovskite are difficult to resolve with conventional spin probing techniques optical spectroscopy on the other hand can discriminate between high and low spin and between ferrous and ferric iron at different sites here we establish the optical signature of low spin fe3 o6 a plausible low spin unit in bridgmanite and post perovskite by optical absorption experiments in diamond anvil cells we show that the optical absorption of fe3 o6 in new aluminous phase nal is very sensitive to the iron spin state and may represent a model behavior of bridgmanite and post perovskite across the spin transition specifically an absorption band centered at 19 000 cm 1 is characteristic of the 2t2g 2t1g 2a2g transition in low spin fe3 in nal at 40 gpa constraining the crystal field splitting energy of low spin fe3 to 22 200 cm 1 which we independently confirm by first principles calculations together with available information on the electronic structure of fe3 o6 compounds we show that the spin pairing energy of fe3 in an octahedral field is 20 000 23 000 cm 1 this implies that octahedrally coordinated fe3 in bridgmanite is low spin at p 40 gpa

stable intermediate spin ferrous iron in lower mantle perovskite iron has the ability to adopt different electronic configurations and transitions in its spin state in the lower mantle can significantly influence mantle properties and dynamics experimental results for two lower mantle perovskite compositions show that the intermediate spin state of iron is stable throughout the bulk of the lower mantle

extended boussinesq thermal chemical convection with moving heat sources and variable viscosity we have studied with an aspect ratio four box the thermal chemical convective evolution with strongly temperature and depth dependent viscosity and moving heat sources within the extended boussinesq framework in which both adiabatic and viscous heating are included and a depth dependent thermal expansivity is assumed in the equation of state our focus is to show how this type of mantle evolution with an averaged ra of 0 106 may develop with a linear chemical stratification and a uniformly hot mantle as an initial condition the effects of extended boussinesq and depth dependent thermal expansivity are to prevent the effective destruction of the chemical heterogeneities our results show that this initial condition would after the age of the earth lead to a lava lamp mode consisting of a thick chemically stratified and intensely internally heated layer with a thickness of around a quarter of the whole mantle thickness however in this isolated internally convecting layer exceedingly high temperatures greater than 4500 k would be reached in the deep mantle plumes can be launched from the top of this thick denser layer this lava lamp stage would give way to the formation of denser hill like structures at the core mantle boundary then upwellings with deep lower mantle origins can be induced by the interaction of the downwellings with the d layer our simulations show the possibility for some long range mass transfer interaction between these widely separated chemical hills promoted by the fast horizontal flow induced by the sinking currents along the low viscosity zone due to temperature dependent rheology at the core mantle boundary

intermediate spin ferrous iron in lowermost mantle post perovskite and perovskite the earth s lowermost mantle displays an important mineralogical transition from perovskite to post perovskite but the spin state of iron in these phases remains poorly known experimental results suggest that iron occurs in the intermediate spin state in both of these phases which implies that changes in physical properties of the lower mantle must be governed by factors other than spin transitions in iron

deformation of the continental crust the legacy of mike coward this special publication in memory and celebration of the work of professor mike coward is about the deformation of the continental lithosphere the collected papers discuss geometry structural principles processes and problems in a wide range of tectonic settings and thereby reflect the breadth of coward s interests they encompass the evolution of precambrian basement gneiss terrains the geometry and evolution of thrust systems basement involvement and structural inheritance in basins syn orogenic extension salt tectonics the implication of structural evolution on hydrocarbon prospectivity and structural controls on mineralization examples are drawn from the lewisian and moine thrust belt of nw scotland the italian apennines nw himalayas the cyclades oman zagros mountains colombian cordillera carpathians north sea offshore brazil regional studies of the irumide belt central africa taurus mountains turkey greater south america and from the witwatersrand basin of south africa and the antler orogeny of sw usa

a magnetite rich cyprus type vms deposit in ortaklar a unique vms style in the tethyan metallogenic belt gaziantep turkey abstract the ortaklar vms deposit is hosted in the kocali complex consisting of basalts and deep sea pelagic sediments which formed by rifting and continental break up of the southern neotethyan in late triassic the basalts are of nmorb type without notable crustal contamination from the surface to depth the ortaklar deposit consists of a gossan zone a thick massive ore zone and a poorly developed stockwork zone primary mineralisation is characterised by distinctive facies including sulphide breccias proximal graded beds distal stockworks and chimney fragments ore mineral abundances decrease in the order of pyrite magnetite chalcopyrite and sphalerite two distinct phases of mineralisation massive magnetite and massive sulphide are present in the ortaklar deposit textural evidence e g magnetite replacing sulphides and the spatial relationships with the host rocks indicate that magnetite and sulphide minerals were generated in different stages the transition from sulphide to magnetite mineralisation is interpreted to relate to variation in h2s content of ore fluids the 1st stage massive sulphide ore might have formed by early hydrothermal fluids rich in fe and h2s the 2nd stage massive magnetite might have formed by later neutral hydrothermal fluids rich in fe but poor in h2s replacing the pre existing sulphide ore the alteration patterns mineral paragenesis lithological features massive ore stockwork ore gossan of the ortaklar deposit together with its trace elements cu pb zn au ag and ree signatures are all consistent with a cyprus type vms system the 34s values in pyrite and chalcopyrite samples range from 2 6 to 5 7 indicating that the hydrothermal fluids were associated with sub seafloor igneous activity typical of cyprus type vms deposits however magnetite formed later than sulphide minerals in the ortaklar deposit contrasting with typical cyprus type vms deposits where magnetite generally occurs in lower sections consequently although the ortaklar deposit generally conforms to cyprus type deposits it is distinguished from them by its late stage and high magnetite concentration thus the ortaklar deposit is thought to be an exceptional and perhaps unique cyprus type vms deposit

more than just a convoluted table discussion of mediterranean tephra stratigraphy revisited results from a long terrestrial sequence on lesvos island greece by margari et al j volcanol geotherm res 163 2007 34 54 bichler m pearce n j g steinhauser g sterba j h 2009 more than just a convoluted table discussion of mediterranean tephra stratigraphy revisited results from a long terrestrial sequence on lesvos island greece by margari et al j volcanol geotherm res 163 2007 34 54 journal of volcanology and geothermal research 181 3 4 247 250

thermodynamic properties and phase relations in mantle minerals investigated by first principles quasiharmonic theory this research has been motivated by geophysics and materials physics the objective of this research has been to advance materials theory and computations for high pressure and high temperature applications to the point that it can make a difference in our understanding of the earth understanding of the mineralogy composition and thermal structure of the earth evolves by close interaction of three fields seismology geodynamics and mineral physics earth s structure is imaged by seismology which obtains body wave velocities and density throughout the earth s interior fig 1 interpretation of this data relies on knowledge of aggregate properties of earth forming materials either measured in laboratory or calculated in many cases by both however the conditions of the earth s interior especially at the core may be challenging for important experiments and materials computations have emerged to contribute decisively to this field earth s evolution is simulated by geodynamics but these simulations need as input information about rheological and thermodynamic properties of minerals including phase transformation properties such as clapeyron slopes our research has concentrated on the phases of the earth s mantle particularly the deep mantle whose conditions are more challenging for experiments the mantle accounts for 83 of the earth s volume in this article we will review the essential first principles approach used to investigate solids at high temperatures and pressures summarize their performance for mantle minerals fig 2 and point to critical results that have stirred us in the current research path the success is remarkable but some limitations point the way to future developments in this field figure 1 a velocities and density profiles kennett et al 1995 b earth s cross section and c composition and mineralogy of earth s layers figure 2 phases proportions versus depth and or pressure ol mg fe 2sio4 olivine also known as phase mg fe