petrological geochemical and statistical analysis of eocene oligocene sandstones of the western thrace basin greece and bulgaria abstract the rhodopian orogen developed since the late cretaceous early eocene during accretionary processes following the closure of the vardar ocean basin a branch of neotethys through a multidisciplinary approach including sandstone petrology and geochemistry of the clastic and volcanoclastic sediments we reconstruct the unroofing history of the rhodopian orogen and characterize the formation and the evolution of the western portions of the thrace basin in greece and bulgaria between the late eocene and oligocene detrital modes of 127 sandstone samples provide evidence of three distinctive petrofacies quartzolithic quartzofeldspathic and volcanoclastic the petrographic composition gives evidence of contributions from three key source areas corresponding to the three main tectonic units the circum rhodope belt the variegated complex ultramafic complex and the gneiss migmatite complex the three petrofacies reflect multiple provenance from different tectonic settings as they evolve from quartzolithic to quartzofeldspathic to volcanoclastic corresponding to collisional orogen crustal block uplift and volcanic arc settings respectively geochemical data on major elements and trace elements are used to discuss the efficacy of tectonic setting discrimination diagrams and compare them to the dickinson model as well as to distinguish and characterize i petrographically homogeneous gneiss supplied subbasins and ii volcanic contributions to sandstone composition multivariate statistical techniques are used to unravel the complex web of factors controlling sediment composition biplot analysis highlights the influence of two independent processes 1 mixing between carbonate and silicate phases and 2 evolution from mafic to felsic source rocks the latter indicates progressively increasing supply rates from deeper crustal levels the compositional evolution of the sandstone suites of thrace basin in ne greece and se bulgaria is strictly related to various geodynamic stages of the rhodope region provenance analysis of thrace sandstones provide an example of the changing nature of orogenic belt sand associate basins through time and may contribute to the general understanding of similar geodynamic settings

buried granites within the mid north sea high a gravity survey of the uk sector of the north sea reveals the presence of three gravity lows over the mid north sea high seismic data eliminate the possibility that these lows are due either to thicker sediments or to salt structures consequently the anomalies may be related to buried granites within the palaeozoic basement gravity modelling demonstrates that the amplitude and shape of the observed anomalies may be explained by buried batholith shaped bodies with densities appropriate for granites the tectonic influence of the buried granites may explain to some extent the continued stability of the mid north sea high throughout much of the development of the north sea basins

dextral rotations and tectonomagmatic evolution of the southern rhodope and adjacent regions greece abstract palaeomagnetic measurements deduced from eocene oligocene miocene and pliocene formations exposed in the greek rhodope and surrounding areas reveal significant clockwise rotations displaying an apparent systematic increase in magnitude from thrace westwards and a decrease northwards the pelagonian zone in the west has suffered no rotation at least since the late miocene a transition from rotated to unrotated regions seems to exist close to the western boundary of the vardar zone no rotations are apparent earlier than the mid oligocene parts of the rhodope may have been rotated clockwise by 12 during the late oligocene additional clockwise rotations occurred after the early miocene it is proposed that at least the post early miocene rotations were the result of plate tectonic motions in the north aegean area initiated by middle miocene times and continuing to the present day southward stretching and bending of the ductile part of the lithosphere was accomplished at brittle upper crustal levels by the detachment translation and rotation of the upper plate of the rhodope core complex the serbomacedonian element possibly followed by further fragmentation and rotation of individual blocks

role of continental crust in petrogenesis of orogenic volcanic associations abstract orogenic volcanic rocks form a continuous spectrum between tholeiitic associations of island arcs and calc alkaline associations of continental margins and collision zones although these settings show a wide variation in plate convergence rate depth of scismic zone nature and age of subducted and over riding lithosphere the compositional characteristics of the volcanic association is correlated most strongly with crustal thickness tholeiitic associations dominated by basaltic rocks and with high feott mgo and low k2o for a given sio2 content are restricted to island arcs with crustal thickness less than 20 km more calc alkaline associations dominated by andesitic rocks with lower feot mgo and higher k2o for a given sio2 content occur in areas where crustal thickness exceeds 20 km these suggest that 1 fractional crystallization occurring within the continental crust may be the major mechanism responsible for variations within orogenic volcanic associations and 2 formation of calc alkaline associations may require the presence of continental crust these relationships suggest that calc alkaline magmas may be derived from more tholeiitic magmas by fractional crystallization possibly combined with crustal melting or contamination the extension of these processes might be responsible for formation of silicic ignimbrites occurring in continental areas where the crustal thickness exceeds 30 km in areas of crustal extension

mantle discontinuity structure beneath china mantle reflectivity profiles obtained from long period recordings of multiple scs reverberations from intermediate and deep focus earthquakes surrounding china reveal remarkably sharp images of china deep structure the tibetan plateau and fold belts to the north are underlain by a midlithospheric low velocity zone lvz evidenced by coincident g lid lvz boundary and l base of the lvz reflectors and a thickened lithosphere consistent with uniform thickening as the dominant mode of north south deformation the mantle beneath northeastern china mongolia and southeastern russia has a typically cratonic reflectivity signature with h hales and deep l lehmann discontinuities the sino korean paraplatform of eastern china is a region of active extensional tectonics as expressed by an oceanic reflectivity pattern at shallow depths a g discontinuity at 80 km but a more continental structure below the southern sea of japan korean peninsula yellow sea and bordering regions of the china mainland are underlain by a 5 4 impedance decrease near 330 km depth that we interpret as the upper limit of dense silicate melt atop the 410 km discontinuity produced at the subduction zones to the east regional inversion of the reflection coefficient of the 410 km discontinuity r 410 reveals a pronounced high beneath mongolia and north to northwestern china which is best explained by increased upper mantle olivine content signifying extensive basalt depletion in a tectosphere that extends below the 410 km discontinuity a low value of r 660 associated with topographic depression of the 660 km discontinuity beneath eastern asia is consistent with a horizontally inclined slab atop the phase transition marking the seismic discontinuity reflection defocusing is an alternative but requires 38 km of intermediate scale topography within the depressed region exceeding the amplitude of the depression by a factor of 1 5 2 either mechanism requires strong heterogeneity far west of seismically active slabs two lower mantle reflectors one beneath southern honshu kyushu and the sea of japan the other below shantung province china and the yellow sea correlate with horizontally elongated velocity anomalies in western pacific seismic tomography models we speculate that they may represent slabs stagnating below the 660 km discontinuity

cenozoic metallogeny of greece and potential for precious critical and rare metals exploration abstract the cenozoic metallogeny in greece includes numerous major and minor hydrothermal mineral deposits associated with the closure of the western tethyan ocean and the collision with the eurasian continental plate in the aegean sea which started in the cretaceous and is still ongoing mineral deposits formed in four main periods oligocene 33 25 ma early miocene 22 19 ma middle to late miocene 14 7 ma and pliocene pleistocene 3 1 5 ma these metallogenic periods occurred in response to slab rollback and migration of post collisional calc alkaline to shoshonitic magmatism in a back arc extensional regime from the rhodopes through the cyclades and to arc related magmatism along the active south aegean volcanic arc invasion of asthenospheric melts into the lower crust occurred due to slab retreat and were responsible for partial melting of metasomatized lithosphere and lower crustal cumulates these geodynamic events took place during the collapse of the hellenic orogen along large detachment faults which exhumed extensive metamorphic core complexes in mainly two regions the rhodopes and the cyclades the detachment faults and supra detachment basins controlled magma emplacement fluid circulation and mineralization the most significant mineralization styles comprise porphyry epithermal carbonate replacement reduced intrusion related gold intrusion related mo w and polymetallic veins porphyry and epithermal deposits are commonly associated with extensive hydrothermal alteration halos whereas in other cases alteration is of restricted development and mainly structurally controlled porphyry deposits include cu au cu mo au re mo re and mo w variants epithermal deposits include mostly high and intermediate sulfidation hs and is types hosted in volcanic rocks although sedimentary and metamorphic rock hosted mineralized veins breccias and disseminations are also present the main metal associations are cu au ag te and pb zn au ag te in hs and is epithermal deposits respectively major carbonate replacement deposits in the kassandra and lavrion mining districts are rich in au and ag and together with reduced intrusion related gold systems played a critical role in ancient economies finally hundreds of polymetallic veins hosted by metamorphic rocks in the rhodopes and cyclades significantly add to the metal endowment of greece

subduction kinematics and dynamic constraints the kinematics of subduction zones shows a variety of settings that can provide clues for dynamic understandings two reference frames are used here to describe the simple 2d kinematics of subduction zones in the first the upper plate is assumed fixed whereas in the second frame upper and lower plates move relative to the mantle relative to a fixed point in the upper plate u the transient subduction hinge h can converge diverge or be stationary similarly the lower plate l can converge diverge or be stationary the subduction rate vs is given by the velocity of the hinge h minus the velocity of the lower plate l vs vh vl the subduction rate 1 increases when h diverges and 2 decreases when h converges combining the different movements at least 14 kinematic settings can be distinguished along the subduction zones variable settings can coexist even along a single subduction zone as shown for the 5 different cases occurring along the apennines subduction zone apart from few exceptions the subduction hinge converges toward the upper plate more frequently along e or ne directed subduction zone whereas it mainly diverges from the upper plate along w directed subduction zones accompanying backarc extension before collision orogen growth occurs mostly at the expenses of the upper plate shortening along e ne directed subduction zones whereas the accretionary prism of w directed subduction zones increases at the expenses of the shallow layers of the lower plate the convergence shortening ratio is 1 along e or ne directed subduction zones whereas it is 1 along accretionary prisms of w directed subduction zones backarc spreading forms in two settings along the w directed subduction zones it is determined by the hinge divergence relative to the upper plate minus the volume of the accretionary prism or in case of scarce or no accretion minus the volume of the asthenospheric intrusion at the subduction hinge since the volume of the accretionary prism is proportional to the depth of the decollement plane the backarc rifting is inversely proportional to the depth of the decollement on the other hand along e or ne directed subduction zones few backarc basins form e g aegean andaman and can be explained by the velocity gradient within the hangingwall lithosphere separated into two plates when referring to the mantle the kinematics of subduction zones can be computed either in the deep or in the shallow hotspot reference frames the subduction hinge is mostly stationary being the slab anchored to the mantle along w directed subduction zones whereas it moves w or sw ward along e or ne directed subduction zones surprisingly along e or ne directed subduction zones the slab moves out of the mantle i e the slab slips relative to the mantle opposite to the subduction direction kinematically this subduction occurs because the upper plate overrides the lower plate pushing it down into the mantle as an example the hellenic slab moves out relative to the mantle i e sw ward opposite to its subduction direction both in the deep and shallow hotspot reference frames in the shallow hotspot reference frame upper and lower plates move westward relative to the mantle along all subduction zones this kinematic observation casts serious doubts on the slab negative buoyancy as the primary driving mechanism of subduction and plate motions w directed subduction zones rather provide about 2 3 times larger volumes of lithosphere re entering into the mantle and the slab is pushed down this opposite behavior is consistent with the down dip extension seismicity along e ne directed subduction zones and the frequent down dip compression along the w directed subduction zones subduction kinematics shows that plate velocity is not dictated by the rate of subduction along the w directed subduction zones the rate of subduction is rather controlled i by the hinge migration due to the slab interaction with the easterly trending horizontal mantle wind along the global tectonic mainstream ii by the far field plate velocities and iii by the value of negative buoyancy of the slab relative to the country mantle alternatively e ne nne directed subduction zones have rates of sinking chiefly determined i by the far field velocity of plates and ii by the value of negative buoyancy of the slab relative to the country mantle along this type of subduction the subduction hinge generally advances e ne ward toward the upper plate decreasing the subduction rate but it moves w sw ward relative to the mantle all this indicates that subduction zones have different origin as a function of their geographic polarity and the subduction process is more a passive feature rather than being the driving mechanism of plate motions a rotational component combined with mantle density and viscosity anisotropies seems more plausible for generating the global tuning in the asymmetry of subduction zones

iron partitioning in a pyrolite mantle and the nature of the 410 km seismic discontinuity pyrolite1 is a hypothetical mixture of distinct minerals which iswidely believed to represent the composition of the earth s mantle the main pressure induced phase transformations of the olivine component of pyrolite occur at about 13 5 gpa to and 24 gpa to mgsio3 rich perovskite magnesiowustite 2 3 which are thought to be responsible for the seismic discontinuities at 410 and 660 km depths in the mantle recent seismological studies however have demonstrated that the 410 km seismic discontinuity is sharper in some areas than that expected from the to transformation in mantle olivine with a fixed composition4 5 6 7 moreover some mineral physics studies suggest that the seismic velocity jump at the 410 km discontinuity is inconsistent with that associated with the to transformation in olivine8 9 here we present a phase equilibria study of a material having pyrolite composition at pressures of 6 16 gpa we found that the iron content in olivine changes significantly with increasing pressure as a result of the formation of a relatively iron rich majorite phase at these pressures this variation in iron content can overcome or at least reduce both of the above difficulties encountered with the pyrolite model of mantle composition by showing that the component mineral systems cannot be treated as separate

error bars for the global seismic q profile the radial attenuation profile of the earth is needed to account for dispersion effects when interpreting seismic velocities and can provide important constraints on composition to date most radial q models have been produced using traditional damped inversions of free oscillation and surface wave data because such inversions can severely underestimate the model uncertainties that are needed to guide mineralogical and dynamic interpretation and because the quality of data has continued to improve we revisit this seismic inverse problem using a model space search approach already proven effective with similar data we do indeed observe model uncertainties at least an order of magnitude greater than earlier estimates at the same time we find that q is determined well enough to confirm that the data favor several important features previously disputed because of questions of consistency these include shear attenuation that drops significantly in the lower third of the lower mantle and bulk attenuation that is negligible in the inner core but stronger in the outer core and lower mantle than suggested by most models d 2004 elsevier b v all rights reserved

porphyry and epithermal deposits in greece an overview new discoveries and mineralogical constraints on their genesis abstract greece hosts a variety of magmatic hydrothermal ore deposits prospects with porphyry and epithermal styles playing a major role in its total gold endowment these deposit types are mainly clustered in two areas the rhodope and attico cycladic massifs and formed from about 33 ma to the pleistocene as a result of back arc extension in the aegean sea metamorphic core complex formation and contemporaneous post subduction and arc magmatism in the serbo macedonian massif porphyry cu au deposits include skouries fisoka tsikara vathi and gerakario causative intrusives are oligocene to miocene granodiorites to monzonites gold and pge mineralization is associated with potassic alteration of the intrusives in the eastern rhodope massif and the ne aegean islands porphyry prospects occur at pagoni rachi konos hill myli melitena west thrace fakos sardes and kaspakas limnos island and stypsi lesvos island mineralization is associated with oligocene to miocene subvolcanics of calc alkaline to shoshonitic affinity feature of these prospects which they share in common with several porphyry au only systems is their shallow depth of emplacement the presence of potassic sodic calcic and or phyllic alteration a strong epithermal overprint their low cu content an extreme re enrichment the multistage introduction of au the presence of banded quartz veinlets and the local presence of tourmaline new discoveries of porphyry style mineralization at king arthur st philippos and aisymi increases the gold potential in west thrace high intermediate sulfidation epithermal au ag polymetallic deposits prospects overprint and or occur laterally from porphyry style mineralization where they are spatially associated with lithocaps of advanced argillic alteration high intermediate sulfidation au ag epithermal mineralization at perama hill mavrokoryfi and pefka in west thrace and at pterounda mesotopos and megala therma on lesvos island is controlled by steeply dipping extensional faults within volcanic rocks without any obvious genetic relationship to spatially related porphyry style mineralization polymetallic epithermal deposits and prospects contain critical and energy critical metals e g te se bi sb in ge and ga which may be considered as by products in the attico cycladic area porphyry mo w mineralization occurs as sheeted quartz veins and stockworks cutting a potassic to sericitic altered miocene granodiorite stock in the lavrion district bonanza grade au and or ag rich veins with epithermal affinities crosscut metamorphic rocks at lavrion and on syros tinos antiparos and anafi islands milos island is characterized by shallow submarine volcanic hosted is hs epithermal au ag te and base metal deposits antimony as ag au deposits prospects on chios samos and kos islands in the eastern aegean sea indicate the potential for carlin style mineralization in greece several factors played a role to the metal endowment of the aegean porphyry epithermal systems magma fertility in the source regions depth of emplacement of causative intrusives relative contribution of mantle versus crustal material redox state of subduction related magmas and physico chemical fluid conditions at the site of ore deposition

new paleomagnetic data from oligocene formations of northern aegea new paleomagnetic data obtained from volcanic and plutonic formations in thrace northern aegea show that this region has not undergone any significant rotation since the lower oligocene the mean value of the inclination is shallower than expected on the basis of a geocentered dipole field implying a large northward drift of about 1000 km although a comparison with published data from bulgaria leads to a puzzling large shortening between these two regions the measured shallow inclinations are coherent with most of other paleomagnetic studies from oligocene formations throughout the entire mediterranean area together with published results from chalkidiki peninsula our data suggest that the circum rhodopean belt was almost rectilinear and trending e w in lower oligocene time

3d subduction dynamics a first order parameter of the transition from copper to gold rich deposits in the eastern mediterranean region the natural variability of geometry and dynamics of subduction zones leads to a variety of mantle and crustal processes that may influence the genesis of ore deposits in the overriding plate these complex interactions cannot be fully represented by two dimensional 2d models but require that the spatial and temporal evolution of ore deposits be examined in a detailed 3d tectonic framework we compare and discuss the geodynamic and metallogenic evolution of the eastern mediterranean subduction zone since the late cretaceous by integrating a newly compiled metallogenic database with a recent kinematic reconstruction model the resulting paleotec tonic maps identify 1 a late cretaceous cu rich metallogenic period with large deposits formed above a linear and stable subduction zone that produced large amounts of potentially fertile magmas in a narrow magmatic arc and 2 a late eocene miocene pb zn followed by au rich metallogenic period with generally smaller deposits spread over a wide back arc basin that was opened due to subduction retreat and lateral slab tearing supported by high resolution numerical modeling the proposed dynamic arc and back arc metallogenic models emphasize 1 the influence of 3d slab dynamics and associated asthenospheric flow on ore distribution in space and time and 2 the importance of exhuming metamorphic domes in extensional back arc setting to focus metal bearing fluid circulations these models differ from collision and post collision models and may be valid on the western and eastern terminations of the whole tethyan orogenic belt i e mediterranean and southeast asia where fast 3d subduction dynamics has influenced the geodynamic and metallogenic evolution of the overriding plate

constraining the kinetics of mantle phase changes with seismic data summary in a system where two phases coexist a seismic wave can disrupt the pre existing equilibrium and induce a re equilibration process because the kinetics of the phase change is not instantaneous the transformation induces an attenuation of the wave that can be quantified using an appropriate physical theory kinetics of earth s phase transitions are not well known in this paper we show that they can be constrained by seismic attenuation data we quantify the influence of a phase transition upon seismic mode attenuation and body wave reflexion coefficient we perform a numerical application for the olivine to wadsleyite transition at 410 km depth assuming a phase loop thickness of 10 km we show that the relaxation time that controls the frequency band of attenuation and the velocity at which the interface evolves when submitted to a pressure disequilibrium is likely larger than 7000 s for this kinetics slower than typical seismic waves periods the transformation loop does not affect s waves attenuation but potentially that of p waves and normal modes

anatomy of an intruded coal ii effect of contact metamorphism on organic δ13c and implications for the release of thermogenic methane springfield no 5 coal illinois basin abstract concerns about the present day accelerated rate of carbon input to the atmosphere have prompted the search for comparable events throughout earth s history recent research has attempted to determine the cause of such events represented as negative 13 c excursions within the sedimentary record and their subsequent effect on the earth it has been suggested that such excursions could be the result of the large scale release of 13 c depleted thermogenic methane produced by the intrusion of large igneous provinces lips into organic rich rocks and or coal e g mcelwain et al 2005 svensen et al 2004 2007 our study asserts that if intrusions result in significant release of 13 c depleted thermogenic methane from intruded coals 13 c enriched coal should be observed adjacent to the intrusions in this study values of bulk organic 13 c 13 c org are reported for fifteen samples along a coal transect in the illinois basin where a pennsylvanian age coal the springfield or no 5 coal is intruded by a permian ultramafic dike the samples reveal significant bulk geochemical and petrographic changes within the alteration halo for example volatile matter vm decreases towards the intrusion whereas fixed carbon fc and vitrinite reflectance r r both increase accompanied by the development of natural coke both isotropic and anisotropic mosaic structure devolatilization vacuoles and carbonate mineralization reflectance levels and coke development are consistent with exposure to temperatures 450 500 c despite the high level of alteration of the organic matter no significant change is observed in 13 c org values across the transect vary by less than 0 5 along this transect 13 c org does not correlate with r r and does not appear to be influenced by maceral composition the intruded coals show no evidence of pyrolytic carbon that could influence 13 c org the relatively high vm contents of the intruded coals compared to coals that have undergone normal burial maturation and the lack of any trend in 13 c org approaching the intrusion raises questions about previously published models of the effects of large scale igneous intrusions on atmospheric composition and 13 c org excursions associated with oceanic anoxic events this study underscores the importance of the use of organic petrography in combination with isotope geochemistry to determine if contact metamorphosed coals and organic rich shales could have released a significant amount of 13 c org depleted volatiles leading to negative 13 c org excursions in the sedimentary record

evidence of bulk attenuation in the asthenosphere from recordings of the bolivia earthquake radial modes excited by the 9 june 1994 bolivia earthquake are analyzed to improve constraints on bulk attenuation in the earth s interior using data recorded at 53 stations quality factors for six radial modes are determined the new observations are combined with previously published surface wave and normal mode attenuation measurements and inverted for radial variations in shear and bulk attenuation q 1 r and q 1 r the consequences of restricting finite q to specific regions of the earth s interior are investigated using a layered model parameterization the optimal model is characterized by 1 no bulk attenuation in the core 2 a ratio of bulk to shear dissipation in the asthenosphere 30 consistent with the presence of partial melt and 3 a ratio in the remainder of the mantle 1 consistent with solid state mechanisms of attenuation

detrital supply from subduction accretion complexes to the eocene oligocene post collisional southern thrace basin nw turkey and ne greece abstract the thrace basin is a large mostly eocene oligocene post collisional sedimentary basin which developed following the closure of the vardar izmir ankara oceanic domain latest cretaceous paleocene sandstone petrologic data framework and heavy mineral analyses and the synthesis of preexisting and new sedimentological observations along representative stratigraphic sections show that the basin fill of the southern thrace basin was mostly derived from the izmir ankara and biga intra pontide subduction accretion complexes to the south proximal facies consistently show northward paleocurrents whereas most paleocurrent indicators measured downcurrent point to an eastward paleoflow likely the result of the deflection of primary gravity flows originated along the southern margin of the basin detrital contributions from the rhodopian basement complex to the west are virtually absent within the southern thrace basin fill conversely rhodopes derived eocene proximal facies in northeastern greece are characterized by a series of coarse grained fan deltas prograding eastward and likely feeding the basin plain turbidites of the depocentral portion of the thrace basin now concealed in the subsurface to the north of our study area arenites of the southern thrace basin are mostly lithic arkoses and arkosic litharenites provenance from the izmir ankara and biga suture zones to the south is characterized by ophiolitic granitoid gneissic low grade metamorphic and extrabasinal carbonate rock fragments as well as by picotite and glaucophane the application of detailed petrographic observations for discriminating paleo vs neovolcanic and penecontemporaneous vs noncoeval terrigenous sands lead to a substantial revision of the geodynamic interpretation of the thrace basin formerly considered a forearc basin a significant penecontemporaneous volcanic component is common in the upper eocene lower oligocene section and can be related to extensive post collisional volcanism following the closure of the vardar izmir ankara ocean the coexistence of pure neovolcanic layers crystal tuffs and cinerites and hybrid arenites rich in penecontemporaneous carbonate grains with sands derived from a continental basement and ophiolitic suites indicates the presence of episutural basins where shallow water carbonates were deposited on top of the exhuming subduction accretion prism these carbonates were mixed with penecontemporaneous neovolcanic and terrigeneous components and redeposited in deeper marine environments

the tertiary geodynamical evolution of the aegean arc a paleomagnetic reconstruction abstract the paleomagnetic results obtained in the last 5 6 years from tertiary formations in the aegean domain indicate that the lower miocene arc was almost rectilinear with an e w trend and that its curvature has been acquired tectonically in two major phases during the middle miocene a first phase of deformation is characterized by rotations occurring at the two terminations of the arc clockwise in the west epirus anticlockwise in the east southeastern anatolia a second phase of rotation occurring in the last 5 ma about a pole situated in the southern adriatic sea has affected only the northwestern part the data also indicate that the antalya basin has not been involved in the geodynamical evolution of the arc so that the bey daglari represent its easternmost unit a more complex rotational pattern is observed in the internal zones the large rotations measured in evia 48 and skyros 26 probably occurred in the last 5 ma and result from rotation of fault bounded blocks in a shear zone connecting the north aegean trough to the external arc in the izmir region in the karaburun peninsula of western anatolia and in the island of lesbos significant counterclockwise clockwise or null rotations of coherent blocks have taken place during the neotectonic extensional regime furthermore the values of the inclination obtained from both sedimentary and volcanic oligo miocene formations are systematically shallower than expected on the basis of a geocentered dipole field this suggests that the entire studied area has undergone a northward drift of over 1000 km since the middle miocene

kinetics of the olivine ringwoodite transformation and seismic attenuation in the earth s mantle transition zone abstract in regions of the mantle where multi phases coexist like at the olivine wadsleyite ringwoodite transitions the stress induced by the seismic waves may drive a mineralogical reaction between the low to high pressure phases a possible source of dissipation in such a situation the amount of attenuation critically depends on the timescale for the phase transformations to reach equilibrium relative to the period of the seismic wave here we report synchrotron based measurements of the kinetics of the olivine to ringwoodite transformation at pressure temperature conditions of the co stability loop for iron rich olivine compositions both microstructural and kinetic data suggest that the transformation rates are controlled by growth processes after the early saturation of nucleation sites along olivine grain boundaries transformation time data show an increase of reaction rates with temperature and iron content and have been fitted to a rate equation for interface controlled transformation g k 0 t exp n x fa exp h a p v r t 1 exp g r r t where x fa is the fayalite fraction the exponential factor n 9 7 ln k 0 9 1 m s 1 x fa 1 and h a 199 kj mol assuming v 0 cm 3 mol including these new kinetic results in a micro mechanical model of a two phase loop ricard et al 2009 we predict q k 1 and q 1 significantly higher than the prem values for both body waves and normal modes this attests that the olivine wadsleyite transition can significantly contribute to the attenuation of the earth s mantle transition zone

ammonium enrichment associated with diagenetic alteration in tertiary pyroclastic rocks from greece the ammonium ion has been measured in fresh volcanic rocks in vitric tuffs and in tuffs which have undergone secondary alteration the ammonium content of fresh lavas of a wide range of composition is shown to be negligible in contrast high concentrations of ammonium are found in pyroclastic rocks that have undergone diagenetic alteration data are given for three types of diagenetic alteration namely 1 hydration 2 zeolitization and 3 alteration to secondary k feldspar different levels of ammonium enrichment are associated with each type hydrated vitric tuffs from kozani in northern greece and heraklion in crete contain from 158 to 390 ppm nh 4 zeolitized ash and lapilli tuffs from santorini and from lefkimi ne greece are much lower in their ammonium content ranging from 12 to 56 ppm tuffs containing secondary k feldspar in addition to zeolites from metaxades n e greece have ammonium contents from 51 to 512 ppm measurements of fixed and exchangeable ammonium were used to distinguish between the ammonium held by zeolites and that held by k feldspars in the clinoptilolite and mordenite bearing tuffs from santorini and lefkimi most of the ammonium is in cation exchangeable form and must be held by the zeolites by contrast in the feldspar bearing tuffs from the metaxades area almost all the ammonium is fixed and it is inferred to be held mainly by secondary k feldspar

post stishovite transition in hydrous aluminous sio2 abstract lakshtanov et al 2007 showed that incorporation of aluminum and some water into sio2 significantly reduces the post stishovite transition pressure in sio2 this discovery suggested that the ferroelastic post stishovite transition in subducted morb crust could be the source of reflectors scatterers with low shear velocities observed in the mid to upper lower mantle a few years later a similar effect was observed in anhydrous al bearing silica in this paper we show by first principles static calculations and by molecular dynamics using inter atomic potentials that hydrogen bonds and hydrogen mobility play a crucial role in lowering the post stishovite transition pressure a cooperative redistribution of hydrogen atoms is the main mechanism responsible for the transition pressure reduction in hydrous aluminous stishovite the effect is enhanced by increasing hydrogen concentration this perspective suggests a potential relationship between the depth of seismic scatterers and the water content in stishovite

attenuation tomography of the upper mantle we present qsadr17 a global shear wave attenuation model of the upper mantle synthetic tests confirm that large scale shear attenuation anomalies are resolved in the whole upper mantle with limited vertical smearing 50 km qsadr17 shows strong correlation with surface tectonics down to 200 km depth with low attenuation beneath continents and high attenuation beneath oceans the attenuation signal near 250 km depth is dominated by a high quality factor along subduction zones attenuating anomalies are found beneath mid ocean ridges down to 150 km and under most pacific hotspots from the lithosphere down to the transition zone the presence of broad attenuating anomalies at 150 km depth in the pacific ocean suggests that several thermal plumes pond in the asthenosphere evidence for compositional heterogeneities is found in the lithosphere at the base of cratons and in a number of active regions

the impact of variability in the rheological activation parameters on lower mantle viscosity stratification and its dynamics the recently discovered spin state crossover in iron in major mantle minerals at high pressures should exert dramatic influences on transport properties such as the activation creep parameters in the deep mantle wentzcovitch et al 2009 have computed the elastic parameter of ferropericlase that is affected by this crossover the bulk modulus at high realistic conditions using first principles density functional theory plus hubbard u as a consequence of the spin crossover there is a significant softening of the bulk modulus and an attendant reduction of the activation energy in the creep law using a parameterized model capturing the basic physics we have studied the dynamical consequences within the framework of a 2 d cartesian convection model our models reveal a series of asthenospheres and are characterized first by a low viscosity channel below the 670 km boundary second asthenosphere caused by an increase of temperature and decrease in grain size reduction superplascity with the post spinel transition which results in partially layered convection further the variability of the rheological parameters leads to the prevalent formation of viscosity minimum at a depth of about 1600 km third asthenosphere caused by spin crossovers followed by a viscosity hill in the bottom half of the lower mantle the latter due to the increase of the activation energy in some low spin irons at the bottom of the mantle our numerical simulations reveal a tendency to the formation of small scale convection below the 670 km boundary and bigger stabilized plumes and or plume clustering in the deep lower mantle other material properties at the bottom of the mantle decrease of thermal expansivity radiative thermal conductivity also exert significant influence on the multi scale lower mantle plume dynamics

evolution and geodynamic significance of the tertiary orogenic volcanism in northeastern greece the tertiary volcanism of eastern macedonia and western thrace greece developed in association with the sedimentary basin which formed from eocene to oligocene along the southern margin of the rhodope massif the volcanic products ranging in composition from basaltic andesites to rhyolites show an overall calc alkaline orogenic affinity while chemical characteristics identify different groups of rocks probably reflecting minor differences among parent magmas the observed evolution within any group of rocks is compatible with fractional crystallization processes acting on relatively shallow magma bodies the sr isotopic composition of rhyolitic member shows an initial87sr 86sr ratio comparable with that of basaltic andesites reinforcing the hypothesis of a crystal liquid line of descent geochemical and petrographic evidence on the whole suggests that the investigated orogenic association developed on an active continental margin characterized by a relatively thick crust acting as a density filter for the basic magmas and facilitating their storage and fractionation within the crust itself minor contamination by interaction with host materials may also have occurred stratigraphic and k ar geochronological data indicate that the volcanic activity started in upper eocene and reached its maximum development in upper oligocene from lower miocene the volcanism shifted southward in the central aegean area and in part of western anatolia coming to an end by middle miocene the southward migration of the volcanic front has been interpreted as a consequence of the increase in the dipping of the benioff zone due to the decrease of penetrative strength after the main phase of continental collision

mantle layering from scs reverberations 2 the transition zone this is the second paper in a four part sequence that examines the nature of mantle layering using the scsn phases and internal reflections observed within the reverberative interval of sh polarized seismograms mantle reflectivity profiles for 18 seismic corridors sampling portions of indonesia australia and the western and central pacific are constructed from low frequency 25 mhz scs reverberations i e scsn type phases reflected once from internal mantle discontinuities modeling the reflectivity profiles using synthetic seismograms yields precise path specific estimates of the travel times to the 410 km and 660 km discontinuities and their reflection coefficients the data are consistent with an olivine dominated model of the transition zone marked by two major phase transitions having average apparent depths of 414 2 km and 660 2 km and impedance contrasts of 0 046 0 010 and 0 072 0 010 respectively the interpath variations observed in the reverberation travel times imply that the topography on the two discontinuities is of the order of 20 km peak to peak and is negatively correlated consistent with an endothermic transition at 660 km whose clapeyron slope magnitude is comparable to that of the 410 km exothermic transition in the case of the 660 km discontinuity we have been able to supplement these long wavelength 1500 5000 km observations with an estimate of intrapath topography inferred from the frequency dependence of the 660 km reflection coefficient which gives peak to peak variations less than 40 km on scale lengths of 500 1500 km for the 660 km discontinuity the observed topography is significantly less than the dynamic topography expected for a simple compositional interface in regions of subduction however we do observed an intriguing negative correlation between the apparent depth and the reflection coefficient of the 660 km discontinuity which may involve small compositional variations plausible explanations for this correlation include heating of an initially cool chemical boundary layer gravitationally trapped above an endothermic phase transition loss of reflected energy due to local curvature or roughness of the reflector and or extreme topography occurring on a small compositional component to the discontinuity 40 of the total impedance contrast by stripping the 410 km and 660 km peaks from the composite path reflectivity profile we identify three minor reflectors at mean depths of 520 710 and 900 km the shallowest may mark the phase spinel phase transition the 710 km discontinuity can be attributed to the ilmenite gamet perovskite phase transition although changes in perovskite symmetry can potentially provide explanations for both the 710 km and 900 km features

40ar 39ar geochronology of magmatism and hydrothermal activity of the madjarovo base precious metal ore district eastern rhodopes bulgaria the madjarovo volcanic complex and ore district comprise alteration styles from potassium silicate advanced argillic and sericite alteration to adularia sericite alteration mineralization with a close and unambiguous spatial relationship to specific magmatic events new 4 ar 39ar laser fusion and incremental heating experiments on nine sanidine biotite adularia k feldspar and alunite samples constrain the ages and time span of lavas and tepluas comprising the complex and their relationship to the hydrothennal activity these results demonstrate that high k calc alkaline to shoshonitic volcanic activity began c 32 7 ma and terminated c 500 ka later with the extrusion of quartz latite lavas at 32 2 ma the final stage of volcanism was accompanied by intrusion of cornpositionally similar monzonite stocks and trachytic dykes c 32 2 32 1 ma and associated barren advanced argillic and sericite alteration lithocap and adularia sericite base precious metal vein mineralization a probable thermal event at c 12 13ma disturbed the ages of alunite and sericite bearing alteration at low stratigraphic levels however field relations combined with a plateau age of 32 1 0 2 ma from adularia in low sulphidation veins that cross cut lithocap indicate that hydrothermal activity including baseand precious metal vein deposition was coeval with the youngest magmatic activity although most recent models of epithermal systems emphasize close spatial association among volcanic and plutonic events alteration and deposition of ore hedenquist lowenstern 1994 sillitoe 1993 1995 only rare combinations of geological events provide examples where relationships between igneous rocks porphyry and epithermal systems both high and low sulphidation are exposed this is mainly because young epithermal systems are poorly exposed whereas older deposits are eroded or deformed hedenquist arribas 1999 cooke simmons 2000 most economic epithermal ore deposits are tertiary and conventional k a r dating cannot precisely constrain the timing of magmatism alteration and mineralization at the 95 confidence level the precision of 4 ar 39ar age determinations of krich minerals is typically better than i0 5 thus for the oligocene materials of this investigation differences in age of about 200 ka may be distinguished e g marsh et al 1997 singer march

the oligocene xanthi pluton northern greece a granodiorite emplaced during regional extension the xanthi pluton is one of a series of oligocene subduction related granodiorites in northern greece its emplacement was controlled by major faults it is located on the ene trending kavala komotini fault zone which probably originated as a strike slip fault geophysical data show that the pluton is laccolith shaped extending many kilometres south of the fault andesitic dykes several million years older than the pluton indicate a ne sw directed extensional stress field mineral lineations plunging to the sw reflect continued extension during cooling of the pluton subsequent jointing and dykes of aplite and lamprophyre reflect continued extension although this could result from extensional pull apart at a bend during dextral strike slip motion on the kavala komotini fault there is no evidence for subsequent strike slip deformation furthermore two similar laccolithic plutons are unrelated to the kavala komotini fault and the regional extent of thick oligocene sediments suggests an extensional environment during the extension that created a ramp space along the listric fault bounding the xanthi basin into which the granite was intruded the kavala komotini fault acted as a transfer fault reactivation of early joints occurred during late oligocene early miocene compression faults within the pluton parallel to the kavala komotini fault accompanied extension during neogene basin formation emplacement of subduction related magma into ramp space developed along listric faults to produce laccolith like plutons may be a common feature of back arc extension

an exploratory study of the viscoelasticity of phase transforming material attenuation and modulus dispersion are typically associated with shear stress and strain time dependent volume changes accompanying pressure variations can give rise to bulk modulus attenuation and dispersion phase transformations in a two phase region are candidates for such phenomena here we report laboratory data that are consistent with bulk modulus softening as pressure is cycled in a region of coexisting olivine and spinel we use fay70for30 olivine as our sample experiments are performed in a multi anvil high pressure apparatus deformation dia using synchrotron nsls x ray radiation as the probing tool pressure is up to 12 gpa and temperature is up to 1450 c measurements were carried out within the binary loop where the olivine and spinel phases coexist we apply a uniaxial oscillation stress onto the sample and young s modulus and q sup 1 are measured at frequencies of 0 1 0 01 hz our results indicate that the sinusoidal force applied to the sample in olivine ringwoodite region has much lower bulk modulus and higher q sup 1 than in the single phase regions our data are consistent with the diffusion controlled model of jackson i 2007 physical origins of anelasticity and attenuation in rock in price g d ed mineral physics treatise on geophysics elsevier where the characteristicmore time decreases with decreasing strain less

kinetics of the olivine spinel transformation in subducting lithosphere experimental constraints and implications for deep slab processes abstract the persistence of metastable olivine to depths greater than 400 km in subducting slabs has implications for the generation of deep focus earthquakes the magnitude of buoyancy forces driving plate motion and the state of stress in the slab the depth to which metastable olivine can survive in a subduction zone and the depth interval over which transformation to or mg fe 2sio4 occurs have been evaluated from experimental kinetic data for the mg2geo4 and ni2sio4 transformations and the mg2sio4 transformation the data were extrapolated using a kinetic model for grain boundary nucleation and interface controlled growth under non isothermal and non isobaric conditions the results predict that metastable mg1 8fe0 2sio4 olivine survives to depths greater than 500 km in the cold interior of rapidly subducting slabs of old lithosphere the onset of transformation to mg fe 2sio4 spinel depends only on growth kinetics and coincides with the 550 50 c isotherm including the effects of latent heat production causes the transformation to occur by a runaway process over a very narrow depth interval at the onset of transformation high nucleation rates and low growth rates are consistent with the formation of very fine grained reaction products which are required for the transformational faulting mechanism of deep focus earthquakes when olivine crosses the equilibrium boundaries at higher temperatures e g higher than 700 c at 400 km depth transformation to or occurs much closer to equilibrium at a depth controlled by nucleation kinetics in this case the effect of latent heat production on the transformation kinetics is small and microstructural evolution is unlikely to result in transformational faulting below the depth of olivine breakdown cold slabs are likely to have a complex rheological structure owing to temperature dependent microstructural evolution during the phase transformation

small scale variations of 87 sr 86 sr isotope composition of barite in the madjarovo low sulphidation epithermal system se bulgaria implications for sources of sr fluid fluxes and pathways of the ore forming fluids the madjarovo ore district is located in the volcanic rocks of the oligocene madjarovo shield volcano and underlying precambrian and palaeozoic high grade metamorphic rocks of the rhodope massif bulgaria it is situated in the eastern part of a large tertiary magmatic metallogenic belt which resulted from the cretaceous collision of serbo macedonian and rhodope massifs with the pelagonian microplate the low sulphidation base and precious metal mineralisation at madjarovo 32 1 ma formed shortly after the cessation of the shoshonitic and high k calc alkaline volcanic and intrusive activity 32 6 32 2 ma and is spatially and temporally related to late monzonite trachyte intrusions the strontium isotope composition of five barite samples hosted in the volcanic sequence is used to characterise the source s of sr in associated base and precious metal mineralisation and to infer fluid fluxes and pathways of the ore forming fluids the 87sr 86sr compositions for barite samples from ore veins fall in the range 0 70854 0 70955 with the lowest and highest values found in the smaller brecciated veins barite from a thin vein in the basal latite lava flow has the most radiogenic 87sr 86sr isotope composition likely reflecting the involvement of more radiogenic metamorphic basement rocks the least radiogenic composition was determined for barite from a similar vein high in the volcanic pile 500 600 m above the metamorphic basement barites from large veins taken from different stratigraphic positions in the host lavas have almost identical isotopic compositions in the range 0 70883 0 70899 the 87sr 86sr values for barite within the deposit are higher than those for host magmatic rocks 0 70775 0 70863 but lower than those of the metamorphic basement 0 7110 0 7278 it is concluded that strontium in the fluids is a mixture of predominantly magmatic strontium and a variable amount of more radiogenic sr from the metamorphic basement rocks the ore bearing fluid may have been derived from a shallow 1 4 km silicic pluton with an initial 87sr 86sr value 0 7080 because of the short distance to the site of deposition the fault focused ore fluids maintained homogeneous strontium predominantly magmatic strontium isotope ratios with slight contribution s of more radiogenic strontium from the metamorphic basement rocks larger variations in the small brecciated veins can be explained by more extensive fluid rock interaction with local host metamorphic or volcanic rocks

anatomy of an intruded coal i effect of contact metamorphism on whole coal geochemistry springfield no 5 pennsylvanian coal illinois basin abstract if time and heating rate are important agents in coal maturation one might expect to see differences in chemical changes in response to maturation depending on the means of increased rank using a suite of samples obtained from an intruded pennsylvanian age coal in southern illinois we present whole coal chemical data comparing these data to extant geochemical data for coals that have undergone normal burial maturation we evaluated the hypothesis that if coal alteration occurs rapidly due to intrusion rather than gradually burial maturation then different relationships are seen in chemical composition proximate and ultimate analyses and vitrinite reflectance the pennsylvanian age asturian westphalian d springfield no 5 coal is mined at the big ridge mine near eldorado southern illinois this high volatile b bituminous coal was intruded by an ultramafic igneous intrusion during the early permian alteration occurs out to 1 2 dike thickness and includes an increase in random vitrinite reflectance rm from levels 0 7 to over 5 3 loss of liptinites and formation of devolatilization vacuoles and fine mosaic texture decreases in volatile matter vm and increases in fixed carbon fc appear to be less than would be expected for the level of reflectance seen within the alteration halo carbonate minerals have a major influence on proximate analyses but even following the removal of carbonates the decrease in vm is still less than would be seen in coals of similar vitrinite reflectance that were altered by normal burial maturation carbonate mineralization also contributes to variability in ultimate analysis values approaching the intrusion particularly for c and o after carbonate removal data for these coals do not appear to follow the normal burial coalification tracks when plotted on a van krevelen diagram and on a seyler chart these differences suggest that a slightly different maturation pathway may have been followed by these coals and by others that were altered rapidly by intrusion

the effect of strain energy on growth rates during the olivine spinel transformation and implications for olivine metastability in subducting slabs we have studied growth kinetics during the transformation of mg1 8fe0 2sio4 san carlos olivine to its high pressure polymorphs wadsleyite phase and ringwoodite phase at 800 1200 c and nominal pressures of 16 20 gpa in experiments in which a large 500 600 m olivine single crystal contained in a matrix of either fine grained olivine or nacl was transformed reaction rims of wadsleyite ringwoodite form on the margins of the single crystal by incoherent grain boundary nucleation and interface controlled growth contrary to theoretical expectations the growth rate of these reaction rims decreases sharply as a function of time for instance at 1100 c and 18 gpa growth ceases on an experimental timescale after the rim width reaches 20 25 m in order to explain this observation we develop an elastic model based on the theory of a misfitting inclusion comparing the results of this model with the experimental data suggests that elastic strain energy which develops because of the large volume decrease associated with the transformation is responsible for the decreasing growth rates on the other hand experimental and theoretical results suggest that elastic strain energy is relatively unimportant when grains of the product phase are randomly dispersed and distinct reaction rims do not form this is the case when the nucleation rate is low the growth rate is fast and the reactant olivine is fine grained on a geological timescale in subducting lithosphere where the grain size of the olivine is large the growth rates of grain boundary nucleated reaction rims are likely to be controlled by viscoelastic relaxation therefore current kinetic models of olivine metastability in subducting slabs which are based on simple extrapolations of experimental data and on the assumption that the growth rate is constant at fixed temperature and pressure need to be reevaluated

reflectivity of the 410 km discontinuity from pp and ss precursors a number of studies have confirmed the global existence of a transition zone discontinuity at 410 km depth by aligning large numbers of long period seismograms on a surface reflection phase before stacking in particular ss and pp precursors from the 410 km discontinuity termed p410p and s410s have revealed long wavelength topography of this discontinuity here we extend these techniques to examine the reflection coefficient of the 410 km discontinuity using our measurements of p410p and s410s amplitudes we constrain the impedance contrasts across the 410 km discontinuity we also show lateral variations in the p wave impedance contrast at 410 km which is typically low under north america and china and higher beneath the north pacific the s wave impedance contrast shows less variability on the regional scale however analysis of p410p and s410s amplitudes over smaller areas by binning traces into spherical caps shows that the s wave reflection coefficient varies over much shorter scale lengths than that for p waves the different patterns of variation for p410p and s410s reflection amplitudes could be due to the presence of melt water or other chemical heterogeneities in the transition zone other factors such as temperature or mantle olivine content variations could also influence precursor amplitudes but they would be expected to lead to correlated variations and so they cannot explain all the variation that we observe

experimental constraints on the depth of olivine metastability in subducting lithosphere the hypothesis that metastable olivine persists in some subducting slabs into the transition zone has wide implications for mantle dynamics and rheology in order to evaluate this possibility we derive new thermo kinetic subduction zone models to predict the extent of olivine metastability within the stability fields of its high pressure polymorphs wadsleyite and ringwoodite our updated models improve on previous work by incorporating experimental kinetic data on realistic mantle compositions mg fe 2sio4 rather than analogue systems furthermore latent heat due to the transformation is fed back into both the kinetics and the thermal model we also consider the effects of transformation stress on growth kinetics and the possibility of an intracrystalline transformation mechanism previously thought to be important only at high shear stresses our models predict significantly smaller wedges of metastable olivine than previous work in the case of tonga for example where high values of lithospheric age 100 140 million years and convergence rate 14 cm per year are most favorable for metastability models considering only grain boundary nucleation and interface controlled growth predict olivine metastability to 600 km depth in contrast to 660 km predicted previously by kirby et al rev geophys 34 1996 261 when intracrystalline transformation is considered the depth of metastability is further reduced by as much as 100 km due to the large increase in the density of nucleation sites inhibition of growth by transformation stress can increase the depth interval over which the transformation takes place but is unlikely to be a dominant factor especially if the intracrystalline mechanism operates these results indicate that the existence of metastable olivine at depths corresponding to those of the deepest earthquakes 680 km requires subduction of old lithosphere 100 million years and a high vertical subduction velocity 15 cm per year such conditions currently may only be achieved in the very northern part of the tonga subduction zone yet earthquakes occur at depths down to 680 km in other subduction zones in which lithospheric age and or subduction velocity are relatively low e g indonesia and the marianas therefore mechanisms other than transformational faulting in metastable olivine must operate to cause the deepest earthquakes

phase transitions and short timescale sinusoidal motions abstract while the effects of phase transitions of mantle materials are considered in convection studies models of geophysical processes that occur on shorter timescales such as seismic normal modes and earth tides often ignore these effects a common justification is that the latent heat released from the material changing phase could not conduct away from the boundary on timescales shorter than those of convection and thus the phase transition would not proceed in this study we first examine the behavior of a phase boundary to a periodic pressure perturbation by solving the heat equation if all the latent heat is released at an infinitely thin boundary we find that the phase transitions do not proceed however if the latent heat is released over a region of 1 5 km thickness which might occur due to the divariant nature of the phase boundaries then some of the material changes phase regardless of the period of the forcing we apply these results to predictions of seismic normal mode center frequencies and elastic love numbers the perturbations to the normal mode frequencies can be two orders of magnitude greater than the differences between the observed frequencies and those predicted using the preliminary reference earth model however we have not considered kinetics the energetics of the mechanisms of the phase transitions in this formulation this work suggests a greater knowledge of the kinetics near equilibrium phase boundaries is required because the kinetics may be the limiting factor in these short period small amplitude motions

on the geodynamics of the aegean rift abstract the aegean rift is considered to be either a classic backarc basin or the result of the westward escape of anatolia or the effect of a gravitational collapse of an over thickened lithosphere here these models are questioned we alternatively present a number of geodynamic and magmatic constraints suggesting a simple model for the genesis of the extension as being related to the differential advancement of the upper lithosphere over a heterogeneous lower african plate the greek microplate overrides the ionian oceanic segment of the african plate faster than the anatolian microplate over the thicker levantine more continental segment this setting is evidenced by gps velocity gradient in the hangingwall of the hellenic cyprus subduction system and requires a zone of rifting splitting the hangingwall into two microplates this mechanism is unrelated to the replacement of retreated slab by the asthenosphere as typically occurs in the backarc of west directed subduction zones the supposed greater dehydration of the ionian segment of the slab is providing a larger amount of fluids into the low velocity channel at the top of the asthenosphere allowing a faster decoupling between the greek microplate and the underlying mantle with respect to the anatolian microplate slab ruptures associated with the differential retreat controlled by the inherited lithospheric heterogeneities in the lower plate and the proposed upwelling of the mantle suggested by global circulation models would explain the occurrence and coexistence of slab related and slab unrelated magmatism

possible causes of abnormal vitrinite reflectance values in paralic deposits of the carboniferous in the achterhoek area the netherlands abstract vitrinite reflectance data r m are presented for coals from two wells in the netherlands these data are grouped according the allied sedimentary sequences three groups of sedimentary sequences are distinguished thin coal seams covered by sands show suppressed r m values relatively high values are found in thick coal seams covered by shales coal seams with irregular sequences do not show abberant values it is suggested that the low reflectance values are caused by relatively more intense biodegradation during the early diagenesis due to continuous refreshment of te ambient watermass in sediments covered by a stagnant watermass biodegradation has not progressed as far leaving vitrinite precursors relatively rich in oxygen vitrinites produced in these environments have a high r m value the redoxpotential is a predominant factor governing the diagenetic processes

strength of mg fe 2sio4 wadsleyite determined by relaxation of transformation stress abstract the growth of a reaction rim around a crystal undergoing a polymorphic phase transformation generates elastic strain energy as a consequence of the reaction volume change the strain energy inhibits the transformation by counteracting the chemical free energy driving force for growth stress relaxation enables growth to continue at a rate controlled primarily by the mechanical properties of the rim we studied this process in high pressure experiments in order to constrain the rheology of wadsleyite one of the high pressure polymorphs of olivine single crystal spheres of san carlos olivine surrounded by a quasi hydrostatic pressure medium of nacl or au were partially transformed to wadsleyite at 1100 c and 16 17 gpa to determine the rate of growth as a function of time microstructural observations indicate that the relict olivine remains largely undeformed while the wadsleyite rims deform by dislocation creep application of an elastoplastic model to fit the observed decrease in growth rates with time constrains the yield strength of wadsleyite at these conditions to between 4 and 6 gpa a decrease in growth rates was also observed in another study in which varying amounts of water were added to the samples kubo t ohtani e kato t shinmei t fujino k 1998a experimental investigation of the transformation of san carlos olivine single crystal phys chem miner 26 1 6 kubo t ohtani e shinmei t fujino k 1998b effects of water on the transformation kinetics in san carlos olivine science 281 85 87 modeling these results gives values for the yield strength of wadsleyite between 2 and 5 gpa under various conditions a strength difference of 1 gpa is indicated by experiments at 1030 c conducted under nominally dry 200 ppm h2o and water added 500 ppm h2o conditions supporting the hypothesis that hydrolytic weakening is an important process in wadsleyite the calculated yield strengths for wadsleyite indicate that it is three to six times stronger than olivine at the same conditions based on an extrapolation of the low temperature plasticity flow law for olivine these results imply a strong increase in the strength of subducting slabs in the mantle transition zone provided that the deformation mechanism is the same as in the experiments furthermore inhibition of growth by transformation stress may be an important factor in extending the depth range over which metastable olivine transforms to its high pressure polymorphs in subducting slabs

revisiting the thermally metamorphosed coals of the transantarctic mountains antarctica abstract petrographic and geochemical data for late permian coals and carbonaceous shales from the transantarctic mountains antarctica source polar rock repository prr were used to evaluate maturation levels and assess the effects of contact metamorphism coals were evaluated for locations in the southern transantarctic mountains the central transantarctic mountains and south victoria land including samples from the buckley mt glossopteris and queen maud formations and the weller coal measures these formations have been intruded by sills and dikes of the jurassic ferrar group 177 183 ma associated with the breakup of gondwanaland proximate 129 samples total sulfur 69 analyses vitrinite reflectance analysis 92 and petrographic composition 34 were determined one third of the samples have 50 ash yields dry basis a subset of samples 87 with 7 thus vm does not reveal true rank of the antarctic coals vitrinite reflectance rr typically surpasses that of inertinite the vm rr relationship for these coals does not follow that of coals matured by normal burial maturation but more closely follows that of intruded coals coke textures including isotropic coke and anisotropic mosaics vacuoles pyrolytic carbon and coked bitumen are observed indicating alteration by contact metamorphism and providing insights to the rank of the coal at the time of intrusion coarse grained circular and fine grained lenticular mosaic textures suggest coal rank at the time of intrusion was medium volatile bituminous coal maximum vitrinite reflectance 1 2 this would imply a burial depth by time of intrusion of 5 5 5 km assuming 25 c km or 4 km assuming 34 c km modern day background reflectance levels of 2 5 rr indicate continued post intrusion maturation possibly due to exposure to higher regional heat flow coals and carbonaceous shales from the polar rock repository prr can provide reliable petrographic and maturation data using reflectance to help decipher the burial history for various parts of the transantarctic mountains however geochemical data must be used with caution due to the high original inorganic content and possible formation of gypsum and changes in vm during long term storage hcl treatment removes some of the neoformed minerals but samples should be treated extensively with hcl hf to remove all silicate minerals prior to proximate and ultimate analysis to ensure more reliable data

the geodynamics of the aegean and anatolia introduction the complexity of the plate interactions and associated crustal deformation in the eastern mediterranean region is reflected in many destructive earthquakes that have occurred throughout its recorded history many of which are well documented and intensively studied the eastern mediterranean region including the surrounding areas of western turkey and greece is indeed one of the most seismically active and rapidly deforming regions within the continents fig 1 thus the region provides a unique opportunity to improve our understanding of the complexities of continental tectonics in an actively collisional orogen the major scientific observations from this natural laboratory have clearly been helping us to better understand the tectonic processes in active collision zones the mode and nature of continental growth and the causes and distribution of seismic volcanic and geomorphological events e g tsunamis and their impact on societal life and civilization the tectonic evolution of the eastern mediterranean region is dominated by the effects of subduction along the hellenic aegean arc and of continental collision in eastern turkey anatolia and the caucasus northward subduction of the african plate beneath western turkey and the aegean region is causing extension of the continental crust and volcanism in the overlying aegean extensional province eastern turkey has been experiencing crustal shortening and thickening as a result of northward motion of the arabian plate relative to eurasia and the attendant postcollisional magmatism taymaz et al 1990 1991a b mcclusky et al 2000 2003 dilek pavlides 2006 and references therein fig 2 the resulting combination of forces the pull from the subduction zone to the west and push from the convergent zone to the east is causing the turkish plate to move southwestward bounded by strike slip fault zones the north anatolian fault zone nafz to the north and the east anatolian fault zone eafz to the south interplay between dynamic effects of the relative motions of adjoining plates thus controls large scale crustal deformation and the associated seismicity and volcanism in anatolia and the aegean region taymaz et al 2004

effects of rapid thermal alteration on coal geochemical and petrographic signatures in the springfield no 5 coal illinois basin abstract igneous intrusion into a coal bed can change the geochemical and petrographic properties of the coal including vitrinite reflectance maceral petrographic composition optical texture mineralogy stable isotope composition trace element composition and bulk geochemistry the intent of this study was to evaluate petrographic and geochemical changes in an intruded coal and compare them to trends seen in coals altered by normal burial maturation thereby evaluating whether or not the intruded coals followed a different maturation pathway the current study reports petrographic bulk geochemical proximate ultimate leco total organic carbon toc and rock eval pyrolysis data for a suite of samples from the springfield no 5 coal pennsylvanian desmoinesian in the southern part of the illinois basin where the coal had been intruded by a permian age peridotite dike petrographic analysis shows an increase in vitrinite reflectance rm from background levels of 0 55 0 63 up to 4 80 a loss in ability to differentiate liptinite macerals formation of isotropic coke and at the dike coal contact development of fine grained mosaic anisotropic coke texture volatile matter vm content decreases and fixed carbon fc content ash and mineral matter parr formula increase approaching the intrusion contact carbon increases whereas nitrogen hydrogen and oxygen decrease approaching the intrusion the presence of carbonate minerals confirmed by x ray diffraction and petrographic analysis has a significant impact on proximate and ultimate data however even after removal of carbonates trends for vm vs rm c vs rm and h vs c do not follow typical trends associated with normal burial coalification approaching the contact leco toc rock eval free oil content s1 remaining hydrocarbon potential s2 co2 from pyrolysis of the organic matter s3 and hydrogen hi and oxygen oi indices decrease whereas thermal maturity tmax c increases s2 vs rm and tmax vs rm diverge from the pathways seen in previous studies of coals that have undergone normal burial maturation geochemical data from this study suggest that the intruded springfield no 5 coal may have followed a maturation track that differed from that seen under normal burial maturation perhaps due to the geologically rapid high heating event associated with the emplacement of the intrusion it is also suggested here that the natural coke textures produced by this rapid geological heating may differ from those observed for metallurgical cokes produced under standard industrial coking conditions typically in an industrial coke oven a coal of this initial rank ro 0 6 would produce an isotropic coke rather than the fine grained circular anisotropic coke seen here however as variations in heating rate duration of heating maximum temperatures attained hydrothermal conditions and pressure are mostly unknown for the intrusive event it is not unreasonable to suggest that differences in these variables contributed to the higher anisotropy of the coke alternatively the development of this texture may reflect pre heating of the coal during the intrusion event

is the palea kavala bi te pb sb au district northeastern greece an intrusion related system abstract intrusion related gold systems are generally characterized by a au bi te sn w metal assemblage genetically linked to the emplacement of granitoids the palea kavala ore system greece consists of 150 minor fe mn pb zn ag fe mn au fe as au fe cu au and bi te au occurrences that occur primarily in quartz calcite sulfide veins hypogene mineralization or as supergene bodies in overlapping zones centered on the 21 22 ma granodioritic kavala pluton which intrudes metamorphic rocks of the paleozoic rhodope metamorphic core complex the pluton consists mostly of granodiorite with lesser amounts of diorite tonalite and monzodiorite which was emplaced along the regional e w trending kavala komotini fault the recently discovered 4 km long e w trending so called kavala vein is a sheeted quartz vein system of bi te pb sb au mineralization that crosscuts the kavala pluton and the schists and gneisses of the rhodope massif the kavala vein system is comprised of quartz with lesser amounts of k feldspar plagioclase and muscovite quartz sericite pyrite alteration is pervasive but minor kaolinite is also present pyrite 5 of vein volume contains inclusions of tetradymite some gold bearing bismuthinite and cosalite sulfur isotope values n 27 of pyrite from the kavala and chalkero veins as well as pyrite and galena from garizo hill fe mn pb vein range from 1 9 to 1 0 with one outlier of 4 6 and suggest a magmatic sulfur source homogenization temperatures th of type i two phase aqueous liquid vapor and type ii three phase h2o co2 rich fluid inclusions that homogenize into the liquid phase in quartz from the kavala and chalkero veins range from 216 0 to 420 0 c n 216 and 255 7 to 414 0 c n 112 respectively the th of type iii two phase aqueous liquid vapor which homogenize into the vapor phase ranges from 210 4 to 323 4 c n 28 the salinities of type i and type ii inclusions range from 15 9 to 22 6 wt nacl equiv and 5 5 to 11 2 wt nacl equiv respectively eutectic temperatures of 58 5 to 44 3 c for type i inclusions suggest the presence of appreciable cacl2 in addition to nacl clathrate melting temperatures for type ii inclusions of 56 7 c indicate that co2 is the major component of the gaseous phase however up to 6 ch4 is present in some inclusions the presence of a zoned metallogenetic district centered on bi te pb sb au mineralization within the kavala pluton the presence of both magnetite and ilmenite in the kavala pluton and the two high temperature high salinity immiscible carbonic and aqueous fluids associated with the kavala and chalkero veins are consistent with them being part of an intrusion related gold system that formed along the ilmenite magnetite buffer

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

late cenozoic volcanic evolution of the northeastern aegean region abstract late cenozoic volcanism occurred in an extensional tectonic regime in the northeastern aegean activity commenced in northeastern greece during the early oligocene and in northwestern turkey during the late oligocene early miocene the beginning of activity was characterized by calc alkaline intermediate acid volcanism however alkaline intermediate basic volcanism became dominant from the late miocene until the pleistocene this change in nature of volcanism is not related to a change of regional tectonic regime as previously thought instead we propose that the volcanic evolution reflects an increasing asthenospheric contribution facilitated by a thinned extended lithosphere arising from the regional extensional tectonics

aberrations in the coalification patterns of the offshore coalfields of northumberland and durham united kingdom abstract the offshore extensions of the northumberland and durham westphalian coalfields are formed of continuous and linked sequences of sediments which lie in contrasting structural regimes respectively basin and block the coalfields have suffered different geothermal histories offshore northumberland basin sediments endured low heating rates and low maximum temperatures to give seams which even at the base of the succession hardly reached vitrinite reflectances of roil 0 60 apart from raised values due to igneous activity the offshore durham block succession was exposed to higher temperatures and heating rates due to the proximity of the lower devonian weardale granite underlying the block which was re activated during carboniferous times these geothermal conditions not only led to higher levels of reflectance and steeper maturation gradients offshore in the block succession than offshore in coals of the basin but also produced contrasting relationships between correlations of vitrinite oil reflectance and volatile matter yield of coals for the two structural zones and probably also for other property relationships as well reflectance profiles have been modified due to three circumstances first considerable variation locally in the raising of reflectance levels caused by igneous activity second lowering of vitrinite reflectance values due to arenaceous sediments being deposited immediately on top of vitrinite precursors within the coal forming organic matter and third possible interference from liptinite rich accumulations within coal seams or near to them in the succession which exuded aliphatic materials relatively early in coalification which were then absorbed by vitrinites or more likely deposition of the vitrinite precursors in a marine near marine and calcium rich environment so reducing reflectance values on coalification similar contrasting property relationships to those described here may have been produced by lower devonian granitoid bodies which have been identified on the north sea high if they also were re activated during the carboniferous

kinetics of the post garnet transformation implications for density and rheology of subducting slabs abstract mechanisms and kinetics of the post garnet transformation in natural pyrope were examined at 28 1 31 3 gpa and 1320 2150 k by time resolved x ray diffraction measurements using synchrotron radiation combined with microstructural observations of the recovered samples the water content of samples recovered was estimated to be approximately 400 wt ppm h 2 o from infrared spectroscopic measurements the transformation occurs by the grain boundary reaction and reaction rims are formed along the grain boundaries of parental garnet grains decomposed post garnet assemblages consisting of mg and ca perovskites aluminous phase and stishovite show very fine grained symplectic texture analyses of kinetic data obtained have revealed that growth rates in the post garnet transformation are strongly time dependent extrapolations of the present kinetic data suggest that the post garnet transformation cannot complete at less than ca 1730 k even under geological timescales because of the slow growth kinetics due to the presence of the metastable garnet subducting slabs become buoyant in the lower mantle at less than ca 1730 k for the basaltic crust and at ca 1400 1600 k for the underlying peridotite layer rheological weakening of the basaltic crust is expected in the lower mantle through grain size reduction by the metastable post garnet transformation occurring under large overpressure conditions the kinetics of the post garnet transformation significantly affect both the density and rheology of subducting slabs in the lower mantle and possibly has important roles in the mixing and survival of chemically differentiated slab materials

the influence of heating rates on organic matter in laboratory and natural environments abstract this contribution to the festschrift relates to one of marie theresa mackowsky s industrial interests heating rate but it is not solely focussed within the field of industrial coking one intention is to stress the importance of heating rate in the natural environment to illustrate its broad pervasiveness first discussed however are the effects of heating rate on the appearance optical properties and molecular structures of organic matter in laboratory experiments before considering instances of the influence of heating rate variation on sedimentary organic matter within the natural environment notable illustrations within igneous provinces in the midland valley of scotland and north east england are described heating rate is obviously only one of a number of factors involved in the ultimate development of coal rank or level of organic metamorphism but the instances cited here emphasize that heating rate is not only an important factor in industrial carbonisation but is also a widely effective contributor to the variable maturation of crustal organic matter

interpretation of vitrinite reflectance depth profiles in the northern denison trough bowen basin australia abstract the denison trough bowen basin australia is a mature hydrocarbon province that contains permian to triassic coal and gas bearing sediments deposited in deltaic to shallow marine shelf conditions the sandstone reservoirs of the permian aldebaran sandstone freitag formation and catherine sandstone of the northern denison trough ndt were evaluated for their co2 storage potential as part of the queensland government s zerogen co2 capture and storage project which found that diagenetic processes acting on the sandstones have resulted in poor permeability and reduced porosity making them unsuitable for large scale injection and storage in this area to better understand the factors acting to degrade these reservoirs the purpose of the current study was to establish a thermal maturity framework for the permian sandstone reservoirs of the northern denison trough based on vitrinite reflectance measurements of coals and rock eval analysis of coals and shales from the aldebaran sandstone through to the catherine sandstone mean maximum vitrinite reflectance of coals rmax ranges from 0 55 to 0 93 and estimated maximum burial temperatures calculated from vitrinite reflectance fall between 83 oc 125 oc calculation of palaeotemperatures from vitrinite reflectance data has been hampered by inversions of depth reflectance profiles at the top of the aldebaran sandstone and scatter in vitrinite reflectance data this has been attributed to depositional effects including the major marine flooding surfaces at the top of the aldebaran sandstone that have affected vitrinite reflectance evolution in the ndt producing low reflecting fluorescing perhydrous vitrinite near marine flooding surfaces and subhydrous vitrinite when oxidising conditions prevailed a vitrinite reflectance difference of up to 0 2 rmax is detected in an isometamorphic coal an equivalent palaeotemperature difference of approximately 19 oc the abundance of perhydrous vitrinite has resulted in largely suppressed vitrinite reflectance throughout the examined permian interval in the northern denison trough and the presence of both perhydrous and subhydrous vitrinite introduces an error in palaeotemperature calculation in high volatile bituminous coals rock eval analysis provides supporting and calibrating maturity data tmax over the studied interval ranges from 421 oc to 447 oc generating a positive broadly linear correlation between rmax and tmax that is applicable specifically to the ndt tmax suppression was also detected in perhydrous coals hydrogen index serves to evaluate the level of vitrinite reflectance suppression through an inverse relationship between the two parameters the rock eval data confirms the oil generation potential of coals in the ndt while shales associated with the same stratigraphic intervals have lower hydrocarbon generation potential this study brings new insights into the thermal maturity framework in the ndt and highlights the importance of reliable vitrinite reflectance data for calculation of maximum burial temperatures particularly in underexplored or frontier areas

influence of a basic intrusion on the vitrinite reflectance and chemistry of the springfield no 5 coal harrisburg illinois abstract the springfield no 5 coal a pennsylvanian age high volatile b bituminous rank coal in the carbondale formation is mined in the southeastern section of the illinois basin intruded into this coal is a 10 1 m wide basic dike that is near vertical through the extent of the mined coal bed and strikes n 22 w the intrusion and the effects it had on the coal were studied petrographically and geochemically using a published heat flow model by carslaw and jaeger 1959 carslaw h s jaeger j c 1959 conduction of heats in solids oxford university press in conjunction with thin section microscope analysis a contact temperature of 600 c was determined vitrinite reflectance was measured for a suite of coal samples collected distal to the intrusion vitrinite reflectance values rose uniformly from the ambient reflectance values of 0 69 at just greater than one dike thickness away to 5 at the dike coal contact the increase in reflectance values for samples within 1 2 times dike thickness is concordant with data published by bostick and pawlewicz 1984 bostick n h pawlewicz m j 1984 paleotemperatures based on vitrinite reflectance of shales and limestones in igneous dike aureoles in the upper cretaceous pierre shale walsenburg colorado in woodward j g meissner f f clayton j l eds hydrocarbon source rocks of the greater rocky mountain region rocky mountain association of geologists pp 387 392 on the effects of mafic intrusions into cretaceous age shales in walsenburg colorado comparison of colorado data with data from these sites indicates that despite differences in intrusion temperature timing or coal rank at time of the intrusion ambient mean vitrinite reflectance values remain unchanged at just greater than one dike width from an intrusion

the effect of early alpine thrusting in late stage extensional tectonics evidence from the kulidzhik nappe and the pelevun extensional allochthon in the rhodope massif bulgaria abstract in the northeastern rhodope massif the kulidzhik nappe exposes a unique juxtaposition of a high grade basement allochthon onto a low grade mesozoic unit and the counterpart pelevun extensional allochthon belonging to the same unit the kulidzhik nappe tectonostratigraphy comprises structurally upward i a lower unit consisting of high grade basement orthogneisses ii a low grade greenschist phyllite unit consisting of jurassic extrusive rocks and metasedimentary rocks iii the nappe allochthon built by the lower high grade basement unit orthogneisses and iv eocene sedimentary rocks and oligocene volcanic cover rocks the pelevun extensional allochthon is heterogeneous and consists of mesozoic low grade unit marbles and greenschists and the upper high grade basement unit we have combined structure and kinematics with lithological information and 40 r 39 r geochronology to constrain the tectonic evolution and regional significance of the kulidzhik nappe and the pelevun extensional allochthon mineral chemistry reveals igneous phases of the granitic protolith of the allochthonous orthogneisses with textures related to ductile deformation and metamorphism higher than 500 c their trace element patterns are indistinguishable from the high grade basement orthogneisses in the eastern rhodope mineral chemistry of the metamorphic assemblage in the underlying greenschists is consistent with medium grade greenschist facies metamorphism at temperatures well below 450 c whose geochemistry defines transitional morb to iat affinities with a strong arc imprint the greenschist s composition is extremely similar to the composition of a supra subduction zone jurassic arc extrusive suite that occurs in the low grade unit of the eastern rhodope the structural elements in all of the tectono metamorphic units and the nappe surface indicate top to the nne tectonic transport deformation evolved from ductile to brittle conditions coevally with a progressive decrease from lower amphibolite to weak greenschist facies metamorphism towards the structural top two klippen gave plateau 40 r 39 r mica ages of 154 23 0 66 ma and 156 70 0 81 ma respectively which reflect cooling following the greenschist facies event below 350 c during shallow crustal level thrust emplacement and exhumation of the kulidzhik allochthon the hanging wall pelevun extensional allochthon preserves an internal nne directed ductile tectonic transport trend but is underlain by a ssw directed ductile brittle extensional detachment and has experienced ne sw brittle extension on high angle normal faults an amphibole 40 r 39 r inverse isochron age of 156 58 0 60 ma constrains a late jurassic upper greenschist facies tectono metamorphic event whereas a white mica plateau age of 39 66 0 47 ma provides evidence for middle eocene cooling and exhumation of the pelevun extensional allochthon in the hanging wall of the detachment we relate the kulidzhik nappe to late jurassic crustal deformation during arc continental margin collision that involved nne directed nappe staking and metamorphism of continental margin basement and island arc units the nappe shares a tectono metamorphic history with the nappes of the adjacent strandzha massif implying a region wide early alpine orogenic system our results reveal a record of early alpine thrust tectonics and show the significance of crustal accretion related assembly for the tectonic evolution of the rhodope massif both the late jurassic thrusting event and the subsequent cretaceous thrusting event thickened the rhodope crust creating crustal instability which influenced tertiary crustal extension

tertiary granitoids of rhodope northern greece magmatism related to extensional collapse of the hellenic orogen abstract many granites that occur in orogenic belts such as the himalaya the hercynides or caledonides are thought to result from anatexis of the lower parts of over thickened thrust stacked crustal units just preceding termination of the orogenic cycle numerous tertiary granitoids occur in the rhodope zone of northern greece and adjacent regions of bulgaria a belt regarded as an eastern extension of the alpine system these granites could also be regarded as syn or late tectonic crustal melts in that some have been emplaced as sheet like bodies along major alpine thrust planes and show a strong marginal foliation parallel to the pervasive alpine compressional fabrics in detail however the geochemistry of the granitoids their timing and relationships with country rocks suggest they have been emplaced in an extensional regime that is related to the collapse of the hellenic orogen and more particularly to the crustal thinning that the aegean region has suffered since the mid tertiary rather than being products of crustal thickening it is suggested that their petrogenesis is related to the elevation of thermal gradients during the extensional phase which initiated thermal breakdown of hydrous minerals in the lithosphere and lower crust that had existed metastably during compression and the subduction of cool ocean lithosphere beneath the region in the late mesozoic early tertiary

a seismic model of a partially molten inner core fearn et al 1981 recently proposed a mechanism whereby the inner core contains a significant fraction of liquid we construct a model of a partially molten inner core compatible with seismic observation specifically we develop an improved model of bulk anelasticity including the effect of thermal and material diffusion and show that it is quantitatively capable of explaining the observed anelasticity also studies of the reflection of seismic waves from the inner core boundary are used to estimate the mass fraction of liquid in the inner core

effect of dynamic melting on acoustic velocities in a partially molten peridotite abstract the mechanical effect of materials with a zero shear modulus aggregated with solids with non zero shear moduli has been the primary motivation for why partially molten rocks should have lowered shear wave velocities we propose that elastic softening associated with the process of melting must also be considered in this view seismic waves propagating in regions of partial melting perturb the thermodynamic state and drive solid to liquid and liquid to solid thereby lowering the effective elastic moduli we present measurements of young s modulus for a mantle peridotite klb1 at lvz pressures and temperatures and seismic frequency that support this model the model predicts that the softening of elastic modulus is controlled by the pressure dependence of melt fraction f p and not the percentage of melt present in contrast to previous models the p wave velocity is decreased by nearly the same percentage as the s wave velocity

a geophysical study of the granites and the sedimentary basins of the xanthi area n greece intrusive features of varying size can be interpreted from the aeromagnetic map of the xanthi area in n greece

paleogene collision related basalts and basaltic andesites in the eastern rhodopes bulgaria yanev y mavroudchiev b and nedyalkov r 1989 paleogene collision related basalts and basaltic andesites in the eastern rhodopes bulgaria j volcanol geotherm res 37 187 202 high k calc alkaline and shoshonitic basalts basaltic andesites sior 49 53 wt represented by a total of 10 specimens and one absarokite sample are studied petrologically and geochemically trace elements and ree basalt phenocrysts include clinopyroxene an ore mineral and plagioclase olivine biotite sanidine and absarokite phenocrysts are represented by olivine clinopyroxene and orthopyroxene collisional basalts basaltic andesites differ from those in the active continental margin settingin their increasedabundances of some lll elements rb cs ba as well as th and u in the high kl ti klp k sr rb sr and ba sr ratios negative nb anomaly and low abundances of most fe mg elements ti y yb sc ni co cr their ree patterns are moderately fractionated and the rocks show a negative eu anomaly higher p and cr abundances lower yb content and a positive eu anomaly however are characteristic ofthe absarokite the basalts basaltic andesites represent highly crust contaminated melts formed at moderate s and high p11 6 whereas the absarokite shows some features indicative of mantle derived melts

effect of phase transitions on compressional wave velocities in the earth s mantle the velocities of seismic waves in the earth are governed by the response of the constituent mineral assemblage to perturbations in pressure and stress the effective bulk modulus is significantly lowered if the pressure of the seismic wave drives a volume reducing phase transformation a comparison between the amount of time required by phase transitions to reach equilibrium and the sampling period thus becomes crucial in defining the softening and attenuation of compressional waves within such a two phase zone these phenomena are difficult to assess experimentally however because data at conditions appropriate to the earth s deep interior are required here we present synchrotron based experimental data that demonstrate softening of the bulk modulus within the two phase loop of olivine ringwoodite on a timescale of 100 s if the amplitude of the pressure perturbation and the grain size are scaled to those expected in the earth the compressional wave velocities within the discontinuities at 410 520 and possibly 660 km are likely to be significantly lower than otherwise expected the generalization of these observations to aluminium controlled phase transitions raises the possibility of large velocity perturbations throughout the upper 1 000 km of the mantle

unravelling provenance from eocene oligocene sandstones of the thrace basin north east greece new sandstone petrology and petrostratigraphy provide insights on palaeogene middle eocene to oligocene clastics of the thrace basin in greece which developed synchronously with post cretaceous collision and subsequent tertiary extension sandstone petrofacies are used as a tool to unravel complex geodynamic changes that occurred at the southern continental margin of the european plate identifying detrital signals of the accretionary processes of the rhodope orogen as well as subsequent partitioning related to extension of the rhodope area followed by oligocene to present aegean extension and wide magmatic activity starting during the early oligocene sandstone detrital modes include three distinctive petrofacies quartzolithic quartzofeldspathic and feldspatholithic major contributions are from metamorphic basement units represented mostly by low to medium grade lithic fragments for the quartzolithic petrofacies and high grade metamorphic rock fragments for the quartzofeldspathic petrofacies volcaniclastic sandstones were derived from different volcanic areas with a composition varying from dominantly silicic to subordinate intermediate products mainly rhyolitic glass spherulites and felsitic lithics evolution of detrital modes documents contributions from three key source areas corresponding to the two main crystalline tectonic units i the variegated complex ultramafic complex in the initial stage of accretion quartzolithic petrofacies ii the gneiss migmatite complex quartzofeldspathic petrofacies and iii the circum rhodope belt the volcaniclastic petrofacies is interbedded with quartzofeldspathic petrofacies reflecting superposition of active volcanic activity on regional erosion the three key petrofacies reflect complex provenance from different tectonic settings from collisional orogenic terranes to local basement uplift and volcanic activity the composition and stratigraphic relations of sandstones derived from erosion of the rhodope orogenic belt and superposed magmatism after the extensional phase in northern greece provide constraints for palaeogeographic and palaeotectonic models of the eocene to oligocene western portions of the thrace basin clastic detritus in the following sedimentary assemblages was derived mainly from provenance terranes of the palaeozoic section within the strongly deformed rhodope massif of northern greece and south east bulgaria from the epimetamorphic units of the circum rhodope belt and from superposed late eocene to early oligocene magmatism related to orogenic collapse of the rhodope orogen the sedimentary provenance of the rhodope palaeogene sandstones documents the changing nature of this orogenic belt through time and may contribute to a general understanding of similar geodynamic settings

seismic evidence for water deep in earth s upper mantle water in the deep upper mantle can influence the properties of seismic discontinuities in the mantle transition zone observations of converted seismic waves provide evidence of a 20 to 35 kilometer thick discontinuity near a depth of 410 kilometers most likely explained by as much as 700 parts per million of water by weight

absorption band q model for the earth body wave surface wave and normal mode data are used to place constraints on the frequency dependence of q in the mantle with a simple absorption band model it is possible to satisfy the shear sensitive data over a broad frequency range the quality factor qs is proportional to in the band and to and 1 at higher and lower frequencies respectively as appropriate for a relaxation mechanism with a spectrum of relaxation times the parameters of the band are q min 80 0 15 and width 5 decades the center of the band varies from 101 seconds in the upper mantle to 1 6 103 seconds in the lower mantle the shift of the band with depth is consistent with the expected effects of temperature pressure and stress high qs regions of the mantle are attributed to a shift of the absorption band to longer periods to satisfy the gravest fundamental spheroidal modes and the scs data the absorption band must shift back into the short period seismic band at the base of the mantle this may be due to a high temperature gradient or high shear stresses a preliminary attempt is also made to specify bulk dissipation in the mantle and core specific features of the absorption band model are low q in the body wave band at both the top and the base of the mantle low q for long period body waves in the outer core an inner core qs that increases with period and low qp qs at short periods in the middle mantle the short period qs increases rapidly at 400 km and is relatively constant from this depth to 2400 km the deformational q of the earth at a period of 14 months is predicted to be 463

bulk attenuation in the earth s mantle due to phase transitions abstract the calculated bulk attenuation due to phase transition from mineral physics data is reported here with relaxation time less than 1 s the calculated value for a pyrolite mantle is consistent with the inverted bulk attenuation of the upper mantle from seismic observations the two important mechanisms of phase transitions diffusion controlled and kinetics controlled have different relaxation time as indicated by the models here the diffusion controlled is more likely to contribute to the observed seismic bulk attenuation than the kinetic controlled process based on the available diffusivity and kinetics data the correlation between the bulk attenuation and relaxation time emphasizes the importance of a number of parameters in the mineral physics database such as fe mg diffusivity and kinetics in olivine wadsleyite ringwoodite perovskite mg ca al si diffusivity and kinetics in pyroxene garnet ca perovskite some of which are still unknown

qlm9 a new radial quality factor qμ model for the lower mantle abstract we employ a niching genetic algorithm to invert 30 000 differential scs s attenuation values for a new spherically symmetric radial model of shear quality factor q with high sensitivity to the lower mantle the new radial q model qlm9 possesses greater sensitivity to q at large mantle depths than previous studies on average lower mantle q increases with depth which supports models of increasing viscosity with depth b m steinberger a r calderwood mineral physics constraints on viscous flow models of mantle flow j conf abs 6 2001 2001 there are two higher q regions at 1000 and 2500 km depth which roughly correspond to high viscosity regions observed by forte and mitrovica a m forte and j x mitrovica deep mantle high viscosity flow and thermochemical structure inferred from seismic and geodynamic data nature 410 1049 1056 2001 there is a lower q layer at the core mantle boundary and a relatively low q region in the mid lower mantle with several caveats we infer a divergence of the solidus and geotherm in the lower mantle and a convergence within d by relating q to homologous temperature

no significant post eocene rotation of the moesian platform and rhodope bulgaria implications for the kinematic evolution of the carpathian and aegean arcs abstract the region located between the carpathian balkan and aegean arcs the moesian platform and bulgarian rhodope is generally assumed to have been stably attached to the east european craton during the cenozoic evolution of these arcs the kinematic evolution of this region is however poorly constrained by paleomagnetic analysis in this paper we provide new paleomagnetic data 800 volcanic and sedimentary samples from 12 localities showing no significant post eocene rotation of the moesian platform and rhodope with respect to eurasia therefore confirming the stability of this region we compare this result to a provided review of paleomagnetic data from the south carpathians tisza block and the aegean region the tisza block underwent 68 4 16 7 of middle miocene 15 10 ma clockwise rotation with respect to the moesian platform in line with previous rotation estimates based on structural geology the stability of the moesian platform during middle miocene eastward emplacement of the tisza block into the carpathian back arc supports dextral shear along the southern carpathians recorded by 13 6 ma clockwise strike slip related rotations in foreland deposits the new reference direction for the moesian platform and rhodope allows accurate quantification of the rotation difference with the west aegean domain at 38 0 7 2 occurring between 15 and 8 ma to accommodate this rotation we propose that the pivot point of the west aegean rotation was located approximately in the middle of the rotating domain rather than at the northern tip as previously proposed this new scenario predicts less extension southeast of the pivot point in good agreement with estimates from aegean structural geology northwest of the pivot point the model requires contraction or extrusion that can be accommodated by the coeval motion of the tisza block around the northwestern edge of the moesian platform

reflection properties of phase transition and compositional change models of the 670 km discontinuity seismic observations of the amplitude ratio amplitude p 670p amplitude p p suggest a reflection coefficient r 7 13 for reflections from the underside of the 670 km discontinuity this can be compared with calculated reflection coefficients to constrain the nature of the mantle transition region velocity and density profiles through the transition region were calculated for olivine pyroxene garnet and olivine garnet model mineral assemblages for models with identical upper and lower mantle compositions the computed reflection coefficients from the phase transitions pertinent to the 670 km discontinuity are less than 0 5 these phase transitions produce their maximum r if they are effectively discontinuous which gives r 2 3 except for the garnet to perovskite transformation which gives r 8 in general given realistic impedance contrasts across a phase transition the change in material properties must occur over a region less than 3 km thick for r to be of the order of 5 a discontinuous change in chemical composition at 670 km depth coupled with a change in phase can also produce a reflection coefficient of the observed magnitude r 2 3 for a first order change in phase at 670 km with different iron concentrations on each side of the discontinuity and r 4 6 for cases with a discontinuous increase in silica content based on our analysis the thermal and chemical boundary layers which would occur across such a chemical discontinuity would probably have negligible effects on the reflection coefficient thus although limited by considerable uncertainties the mineralogical and seismic data suggest a two layered model of the mantle with a discontinuous change in both phase and composition at 670 km

geochemical and petrographic alteration of rapidly heated coals from the herrin no 6 coal seam illinois basin abstract coals altered by rapid heating events i e those intruded by dikes and sills are thought to follow a different geochemical maturation pathway than coals altered through diagenesis if an igneous intrusion alters the petrographic and geochemical properties of a coal the effect should also be observable in the coal s molecular structure in this study we evaluate whether coals altered by rapid heating follow distinct maturation trends from coals that were altered by slower heating burial maturation petrographic geochemical and micro ftir analyses were performed on a series of pennsylvanian illinois basin coal samples collected at various distances from a permian igneous dike standard coal characterization techniques including vitrinite reflectance and proximate and ultimate analyses provide valuable insights on the maturation pathways experienced by rapidly heated coals these techniques were coupled with reflectance micro ftir to provide a better understanding of the molecular changes that occur in the coal structure during relatively short lived intensive heating events with decreasing distance to the intrusion coals have higher mean random vitrinite reflectance values rr within the dike alteration zone coking textures similar to those observed in industrial cokes are observed within 2 m of the intrusion geochemical data for hcl treated coals indicate an overall loss of h o and n and an increase in c approaching the dike intruded coals have higher volatile matter vm yields at high rank than coals of similar rank that result from normal burial maturation when plotted on a van krevelen diagram or seyler chart intruded coals follow different coalification trends than coals matured through normal burial diagenesis reflectance micro ftir analysis of collotelinite shows increased aromaticity with rank both the ratio of the aromatic ch stretching band at 3100 3000 cm 1 versus the aliphatic chx stretching bands between 3000 and 2800 cm 1 ar1 and the ratio of the aromatic out of plane deformation bands between 900 700 cm 1 versus the aliphatic chx band ar2 increase with increasing rr within the 3000 2800 cm 1 region there is an increase in the area under the asymmetric ch3 peak at 2960 cm 1 relative to the asymmetric ch2 peak at 2920 cm 1 with increased rank within the 900 700 cm 1 region the overall intensity of the 750 cm 1 peak aromatic rings with four adjacent h atoms relative to the 870 cm 1 peak aromatic rings with one isolated h atom increases up to 2 5 rr likely reflecting a lower degree of substitution dos of alkyl groups on aromatic ring sites the prevalence of the 750 cm 1 peak at high rank may represent a lower degree of condensation of aromatic rings in the structure of intruded coals compared to normally matured coals

the aegean sea we summarize briefly the main features of a kinematic model of evolution of the aegean area since 13 ma the formation of the aegean sea by extensional tectonics is related to the subduction of the mediterranean floor below the hellenic arc we then make a quantitative estimate of vertical movements in the aegean area on the basis of geological data and demonstrate that the outer arc was built since the beginning of this episode of subduction by vertical uplift the easiest way to explain the uplift is by underplating finally we discuss briefly the dynamics of the subduction marginal sea formation processes in this continental collision framework

2 hydrothermal ore deposits related to post orogenic extensional magmatism and core complex formation the rhodope massif of bulgaria and greece abstract the rhodope massif in southern bulgaria and northern greece hosts a range of pb zn ag cu mo and au ag deposits in high grade metamorphic continental sedimentary and igneous rocks following a protracted thrusting history as part of the alpine himalayan collision major late orogenic extension led to the formation of metamorphic core complexes block faulting sedimentary basin formation acid to basic magmatism and hydrothermal activity within a relatively short period of time during the early tertiary large vein and carbonate replacement pb zn deposits hosted by high grade metamorphic rocks in the central rhodopean dome e g the madan ore field are spatially associated with low angle detachment faults as well as local silicic dyke swarms and or ignimbrites ore formation is essentially synchronous with post extensional dome uplift and magmatism which has a dominant crustal magma component according to pb and sr isotope data intermediate and high sulphidation pb zn ag au deposits and minor porphyry cu mo mineralization in the eastern rhodopes are predominantly hosted by veins in shoshonitic to high k calc alkaline volcanic rocks of closely similar age base metal poor high grade gold deposits of low sulphidation character occurring in continental sedimentary rocks of synextensional basins e g ada tepe show a close spatial and temporal relation to detachment faulting prior and during metamorphic core complex formation their formation predates local magmatism but may involve fluids from deep mantle magmas the change in geochemical signatures of palaeogene magmatic rocks from predominantly silicic types in the central rhodopes to strongly fractionated shoshonitic bulgaria to calc alkaline and high k calc alkaline greece magmas in the eastern rhodopes coincides with the enrichment in cu and au relative to pb and zn of the associated ore deposits this trend also correlates with a decrease in the radiogenic pb and sr isotope components of the magmatic rocks from west to east reflecting a reduced crustal contamination of mantle magmas which in turn correlates with a decreasing crustal thickness that can be observed today hydrogen and oxygen isotopic compositions of the related hydrothermal systems show a concomitant increase of magmatic relative to meteoric fluids from the pb zn ag deposits of the central rhodopes to the magmatic rock hosted polymetallic gold deposits of the eastern rhodopes

a geophysical investigation of post alpine granites and tertiary sedimentary basins in northern greece the geology of the rhodope region of northern greece consists of crystalline basement rocks of the rhodope massif in which tertiary extensional basins and granitic intrusions of oligocene age occur widely geophysical modelling has highlighted the close spatial relationship of the tertiary sedimentary basins and post tectonic granites of closely similar age geochemical data for selected granites are used to support the suggestion that there is a close genetic relationship between the episode of granite intrusion and the tectonic development of extensional basins

notes on the mechanisms of coal metamorphism in the pennsylvania anthracite fields abstract charred devolatilized megasporinite and featureless vitrinite with devolatilization pores filled with pyrolytic carbon suggest that eastern pennsylvania anthracites may have been altered by to localized episodes of metamorphism from superheated steam co2 co hydrocarbons in addition to the pervasive regional metamorphism based on the extant vitrinite textures the lack of mesophase anisotropic textures and on comparisons to laboratory studies of the thermoplasticity of bituminous coals the rank at the time of metamorphism would have been high volatile c or lowermost high volatile b bituminous the temperature of alteration would have been in the 350 400 c range corresponding to the critical point of steam 374 15 c and 22 1 mpa about 1 km depth it is speculated that while increased pressure would have prolonged the duration of fluid properties fluidity is still a transient property and the vitrinite would have returned to a solid state after a few hours the heat would have persisted dissipating over the course of days to months to years depending upon the depth and ambient pre heating geothermal gradient but contributing to the coal metamorphism long after the vitroplast solidified

metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere earth s deepest earthquakes occur as a population in subducting or previously subducted lithosphere at depths ranging from about 325 to 690 km this depth interval closely brackets the mantle transition zone characterized by rapid seismic velocity increases resulting from the transformation of upper mantle minerals to higher pressure phases deep earthquakes thus provide the primary direct evidence for subduction of the lithosphere to these depths and allow us to investigate the deep thermal thermodynamic and mechanical ferment inside slabs numerical simulations of reaction rates show that the olivine spinel transformation should be kinetically hindered in old cold slabs descending into the transition zone thus wedge shaped zones of metastable peridotite probably persist to depths of more than 600 km laboratory deformation experiments on some metastable minerals display a shear instability called transformational faulting this instability involves sudden failure by localized superplasticity in thin shear zones where the metastable host mineral transforms to a denser finer grained phase hence in cold slabs such faulting is expected for the polymorphic reactions in which olivine transforms to the spinel structure and clinoenstatite transforms to ilmenite it is thus natural to hypothesize that deep earthquakes result from transformational faulting in metastable peridotite wedges within cold slabs this consideration of the mineralogical states of slabs augments the traditional largely thermal view of slab processes and explains some previously enigmatic slab features it explains why deep seismicity occurs only in the approximate depth range of the mantle transition zone where minerals in downgoing slabs should transform to spinel and ilmenite structures the onset of deep shocks at about 325 km is consistent with the onset of metastability near the equilibrium phase boundary in the slab even if a slab penetrates into the lower mantle earthquakes should cease at depths near 700 km because the seismogenic phase transformations in the slab are completed or can no longer occur substantial metastability is expected only in old cold slabs consistent with the observed restriction of deep earthquakes to those settings earthquakes should be restricted to the cold cores of slabs as in any model in which the seismicity is temperature controlled via the distribution of metastability however the geometries of recent large deep earthquakes pose a challenge for any such models transformational faulting may give insight into why deep shocks lack appreciable aftershocks and why their source characteristics including focal mechanisms indicating localized shear failure rather than implosive deformation are so similar to those of shallow earthquakes finally metastable phase changes in slabs would produce an internal source of stress in addition to those due to the weight of the sinking slab such internal stresses may explain the occurrence of earthquakes in portions of lithosphere which have foundered to the bottom of the transition zone and or are detached from subducting slabs metastability in downgoing slabs could have considerable geodynamic significance metastable wedges would reduce the negative buoyancy of slabs decrease the driving force for subduction and influence the state of stress in slabs heat released by metastable phase changes would raise temperatures within slabs and facilitate the transformation of spinel to the lower mantle mineral assemblage causing slabs to equilibrate more rapidly with the ambient mantle and thus contribute to the cessation of deep seismicity because wedge formation should occur only for fast subducting slabs it may act as a parachute and contribute to regulating plate speeds wedge formation would also have consequences for mantle evolution because the density of a slab stagnated near the bottom of the transition zone would increase as it heats up and the wedge transforms to denser spinel favoring the subsequent sinking of the slab into the lower mantle

kinetics of melting in peridotite from volume strain measurements abstract partial melting in the earth s mantle involves a combination of processes such as ionic diffusion and solid liquid transition these processes yield an array of characteristic times for the melting kinetics both the magnitude and time constant of melt induced volume strain affect seismic velocity attenuation and buoyancy in situ monitoring of samples during melting are enabled by multi anvil high pressure devices coupled with synchrotron x ray radiation in this study the volume strain induced in a sample from melting is measured as a function of time using x ray images we find a doubling of the effective thermal expansion for only 2 melt both from our data and from thermodynamic models of peridotite the characteristic time of melting is determined to be less than one second these findings have a direct impact on the effect of melting on seismic velocities

lateral growth of the continental crust through deep level subduction accretion a re evaluation of central greek rhodope abstract the rhodope massif of northern greece and southern bulgaria has been variably interpreted as a fragment of pre alpine possibly hercynian or precambrian age continental crust that was actively involved in european margin convergent tectonics during the mesozoic and tertiary alternatively we propose that for central greek rhodope the lithological associations and tectonothermal history are consistent with progressive south directed mesozoic crustal growth through deep level subduction accretion a process which involved the near continuous transferral of material of oceanic and continental margin affinity from footwall to hanging wall within a north directed palaeotethyan subduction system central greek rhodope comprises a sequence of schists gneisses and migmatites of wide compositional variation that have undergone intense tectonic intermixing extensive occurrences of marble are associated with amphibolites variably retrogressed eclogites meta gabbros and ultramafic rocks quartzo feldspathic gneisses are abundant throughout the area and are associated with psammitic meta greywacke sequences pelites and quartzites the presence of intercalated marble slivers and thin manganiferous and iron rich siliceous bands is significant the various components exposed in the subduction accretion complex were first underthrust northwards to deep crustal levels subjected to high pressure eclogite facies metamorphism and underplated to the base of the overriding eurasian plate this latter accretion event was characterised by intense southwest directed ductile thrusting and pervasive amphibolite facies metamorphic overprinting it was accompanied by migmatisation and intracrustal melt generation and followed by subduction related magmatism deep level subduction accretion leads to southward growth of the continental margin which in turn leads to subduction retreat allowing the encroachment of the magmatic arc from the north subsequent extensional tectonic exhumation brought the complex up to its present position within the southern margin of eurasia this new interpretation may have implications for other high grade terrains within convergent and collisional systems that have been assumed to represent ancient or pre existing continental crust if so then the importance of deep level subduction accretion as a mechanism of continental crustal growth has hitherto been underestimated