first evidence of high pressure metamorphism in the cover series of the southern menderes massif tectonic and metamorphic implications for the evolution of sw turkey abstract the menderes massif occupies a large part of western turkey it is tectonically overlain by nappes of the izmir ankara suture zone including the bornova flysch zone on its northern flank the afyon zone on its eastern border and the lycian nappes on its southern flank the discovery of magnesiocarpholite kyanite assemblages in the mesozoic cover sequence of the southern menderes massif leads to the very first consideration that a major high pressure hp metamorphic event affected the massif during its alpine evolution estimations of minimum pressure temperature conditions about 10 12 kbar and 440 c suggest a minimum burial of 30 km for the metasedimentary rocks of the menderes massif similar to that for the eocene dilek blueschists which belong to the cycladic complex this finding of high pressure rocks within the menderes cover series as well as the recent description of low grade high pressure parageneses in the basal thrust sheets of the overlying lycian nappe complex has strong implications for the tectono metamorphic evolution of these units the characteristics of this high pressure metamorphism and the deformation features observed in the southern menderes massif allow consideration of a fast burial during alpine subduction and nappe stacking three high pressure units were piled up during the eocene collision of the sakarya continent and the tauride menderes block the lowermost unit consists of the imbricated core and cover of the menderes massif the intermediate unit is the cycladic blueschist complex dilek and samos regions and the uppermost unit is made of the lycian nappes the retrogression of high pressure parageneses from the menderes massif follows an isothermal decompression path and the associated deformation is characterized by a severe stretching oriented n s to ne sw during the high pressure event and its exhumation we propose a tectono metamorphic model in three main stages 1 the southward translation of the high pressure lycian nappes and the burial of the menderes and cycladic metasediments to a depth of at least 30 km to allow their eocene high pressure metamorphism 2 a northward continuum of deformation responsible for top to the north fabrics associated with the main menderes metamorphism peak paleocene eocene and its progressive cooling late eocene north verging folding thrusting imbrication of core and cover series and n s to ne sw intense stretching associated with the menderes high pressure metamorphism and its exhumation these top to the north to top to the northeast movements are probably related to the northward backthrusting of the lycian nappes reactivating the contact between the menderes massif and the lycian nappes as a top to the ne shear zone that allowed exhumation of the lycian high pressure rocks 3 oligo miocene n s extension during which the final exhumation of the metamorphic rocks along kilometre scale low angle detachments occurred

experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

metamorphic evolution of the attic cycladic metamorphic belt on naxos cyclades greece utilizing 40ar 39ar age spectrum measurements 40ar 39ar age spectrum analysis of phengite separates from naxos part of the attic cycladic metamorphic belt in greece indicates that cooling following high pressure low to medium temperature metamorphism m1 occurred about 50 ma ago phengite has 40ar gradients that suggest that part of the scatter observed in conventional k ar ages was caused by diffusion of radiogenic argon from the minerals during a younger metamorphism m2 in central naxos this metamorphism m2 has overprinted the original mineral assemblages completely and is associated with development of a thermal dome excellent 40ar 39ar plateaus at 15 0 0 1 ma 11 8 0 1 ma and 11 4 0 1 ma obtained on hornblende muscovite and biotite respectively from the migmatite zone indicate that relatively rapid cooling followed the m2 event and that no significant thermal overprinting occurred subsequent to m2 toward lower m2 metamorphic grade 40ar 39ar plateau ages of hornblendes increase to 19 8 0 1 ma concomitantly the proportion of excess 40ar in the spectra increases as well we propose that the peak of m2 metamorphism occurred beween 15 0 and 19 8 ma ago k ar ages of biotites from a granodiorite on the west coast are indistinguishable from those found in the metamorphic complex and hornblende k ar ages from the same samples are in the range 12 1 13 6 ma as the latter ages are somewhat younger than most ages obtained from the metamorphic complex intrusion of the granodiorite most likely followed the peak of the m2 metamorphism the metamorphic evolution of naxos is consistent with rapid crustal thickening during the cretaceous or early tertiary causing conditions at which supracrustal rocks experienced pressures in the range 900 1500 mpa transition to normal crustal thicknesses ended the m1 metamorphism about 50 ma ago the m2 metamorphism and granodiorite intrusion occurred during a period of heat input into the crust possibly related to the migration of the hellenic volcanic ar c in a southerly direction through the area

exemples de melange de magmas en contexte plutonique les enclaves des tonalites granodiorites du massif de bono sardaigne septentrionale in calc alkaline orogenic plutons the dark xenoliths and their host rocks must be considered the expression of partial mixing of magma three associations of this type have been investigated and are illustrated by the bono pluton northern sardinia a composite pluton including three intrusives of different nature tonalitic to granodioritic and containing a very large number of basaltic xenoliths of magmatic origin detailed mineralogical analysis of the two end members in each association coupled with geochemical data has determined the major petrogenetic mechanisms intervening in the mixing process in a plutonic setting temperature equilibration mechanical exchanges of crystals chemical exchanges etc the most important result of this article however is to show that each intrusion is related to a specific group of xenoliths that is characterized by constant feot mgo the latter reflects the different composition of basaltic components and it is concluded that each intrusive event is associat

geochemistry and petrogenesis of late miocene granitoids cyclades southern aegean nature of source components abstract neogene igneous activity in the aegean region comprised both extrusive volcanism and intrusive granitoid plutonism granitoid plutonism in the cyclades was established in the mid miocene period and lasted until late miocene 18 to 9 ma the timing of granitoid intrusion was associated with the initiation of extensional tectonics in the aegean these intrusions form a broad belt about 200 km long running from the west lavrium and serifos to the eastern aegean both s type and i type granitoids are present the former generally being emplaced earlier than the i types 15 to 8 3 ma major and trace element variations reveal that three end member components are involved in the granitoids but the proportions of these vary in the different plutons initial isotopic compositions of all the granitoids are typical of crust derived magmas from heterogeneous metasedimentary sources i type 87 sr 86 sr 0 7091 0 712 e nd 6 4 to 10 4 s type 0 710 0715 e nd 7 5 to 10 1 three end member sources have been identified 1 one end member appears to be a metasedimentary biotite gneiss greywacke type such as that forming the metamorphic core complexes naxos and paros this is a dominant but not the only component in the s types 2a major trace element and sr nd isotopic composition correlations of the s type granitoids with basement gneiss require an extra source of sr and ca having lower initial 87 sr 86 sr indicating a more depleted metasedimentary source at depth due to possible interaction of metamorphic fluids with marbles and amphibolites and infiltration through the gneissic units at mid crustal levels 2b a possible second end member could be the marble component as indicated by the buffered values of the initial sr isotopic ratios major element variation of the mafic microgranular quartz diorites and tonalites enclaves are compatible with dehydration melting of a mafic source similar to the amphibolites island arc tholeiites at medium pressure 8 kb conditions 3 amphibolite is another end member which may contribute mostly to the source of the younger intrusions along the western flank of the arc

segmented african lithosphere beneath the anatolian region inferred from teleseismic p wave tomography summary lithospheric deformation throughout anatolia a part of the alpine himalayan orogenic belt is controlled mainly by collision related tectonic escape of the anatolian plate and subduction roll back along the aegean subduction zone we study the deeper lithosphere and mantle structure of anatolia using teleseismic finite frequency p wave traveltime tomography we use data from several temporary and permanent seismic networks deployed in the region approximately 34 000 p wave relative traveltime residuals measured in multiple frequency bands are inverted using approximate finite frequency sensitivity kernels our tomograms reveal segmented fast seismic anomalies beneath anatolia that corresponds to the subducted portion of the african lithosphere along the cyprean and the aegean trenches we identify these anomalies as the subducted aegean and the cyprus slabs that are separated from each other by a gap as wide as 300 km beneath western anatolia this gap is occupied by slow velocity perturbations that we interpret as hot upwelling asthenosphere the eastern termination of the subducting african lithosphere is located near the transition from central anatolia to the eastern anatolian plateau or arabian eurasian collision front that is underlain by large volumes of hot underplating asthenosphere marked by slow velocity perturbations our tomograms also show fast velocity perturbations at shallow depths beneath northwestern anatolia that sharply terminates towards the south at the north anatolian fault zone nafz the associated velocity contrast across the nafz persists down to a depth of 100 150 km hence our study is the first to investigate and interpret the vertical extent of deformation along this nascent transform plate boundary overall the resolved upper mantle structure of anatolia is directly related with the geology and tectonic features observed at the surface of the anatolian plate and suggest that the segmented nature of the subducted african lithosphere plays an important role in the evolution of anatolia and distribution of its tectonic provinces

constraints on the kinematics of post orogenic extension imposed by stretching lineations in the aegean region abstract new kinematic data from shear zones of tertiary age in the metamorphosed basement of the aegean region in combination with published kinematic lithological and palaeomagnetic data have enabled us to determine a detailed kinematic evolution of the region during post orogenic extension in the aegean three distinct stages are recognised firstly extension of both the western and eastern aegean started in the late oligocene early miocene 36 25 ma ago initially in an 023 direction stage two started shortly after this with the division of the aegean crust into the west aegean block a coupled assemblage of small blocks bound on its northwestern and southeastern margins by the scutari pec line and mid cycladic lineament fracture zones respectively between 25 ma and 3 ma the west aegean block underwent 30 clockwise rotation whilst the eastern aegean underwent on average 19 anticlockwise rotation rotation of the west aegean block as a semi coherent block was aided by the relative coolness of the block compared to the warmer eastern aegean region as the crust thinned and rotated the nw se trending faults which characterise the west aegean block were cross cut by e w trending faults in the latest miocene pliocene the thermal front migrated westwards into the west aegean block and the mid cycladic lineament ceased activity the final kinematic stage marked the start of the subdivision of the west aegean block into two portions in the pliocene the southeastern portion nw cycladic area coupled with the sw cycladic area to form a central aegean block that started to translate southwest the northern and western portion rotated a further 10 15 clockwise whilst the southeastern rim rotated anticlockwise these data demonstrate that aegean post orogenic extension is not dominated by a single block rotation or radial spreading event but is characterised by the sequential formation and reformation of lithospheric scale blocks that have developed in response to large scale partitioning of rotational strain

the strontium and oxygen isotopic record of hydrothermal alteration of syenites from the abu khruq complex egypt hydrothermal convection initiated by emplacement of the gabbro syenite complex of abu khruq into the egyptian basement 89 ma ago systematically altered the trace element and isotopic compositions of the syenites the scale of sr transport in migrating solutions was far larger than the scale of sr isotopic equilibration within rocks as a result sr exchange was heterogeneous in the syenites an effect which can be observed on three different scales within grains of a single mineral species heterogeneities are related to grain boundaries and microfractures through which fluids migrated among minerals within rock samples heterogeneities are related to differences in susceptibility to sr alteration among samples within a single unit heterogeneous alteration is apparently related to differences in permeability close to fracture zones during the early stages of alteration radiogenic sr derived from the country rocks was added to the syenites causing small net changes in concentration 5 ppm ave some rb sr mineral isochrons from single rock samples yield the emplacement age because isotopic equilibration of this added sr sometimes occurred within rock specimens however regressions of the whole rock rb sr data yield apparent ages that are about 10 ma too old later stage alteration involved larger changes in whole rock sr concentration 45 ppm ave but had little further effect on the isotopic relationships because the sr was derived from cogenetic gabbros rather than the country rocks alterations of rb sr and sr isotopic compositions are not well correlated with changes in 18o 16o ratio because mineralogy played an important role in decoupling trace element and oxygen isotopic alteration in general the absence of such correlations for whole rock data is not diagnostic of rocks with unaltered trace element and isotopic compositions mineral scale sr isotopic heterogeneities associated with grain boundaries and microfractures may be the most unambiguous evidence of trace element mobility

exhumation of high pressure rocks driven by slab rollback rocks metamorphosed under high pressure hp and ultra high pressure uhp conditions in subduction zones come back to the surface relatively soon after their burial and at rates comparable to plate boundary velocities in the mediterranean realm their occurrence in several belts related to a single subduction event shows that the burial exhumation cycle is a recurrent transient process using the calabria apennine and aegean belts as examples we show that the exhumation of hp rocks is associated in time and space with the subduction of small continental lithosphere blocks that triggers slab rollback creating the necessary space for the exhumation of the buoyant continental crust that was deeply buried just before the buoyancy force of the subducted crust increases until this crust detaches from the downgoing slab it then exhumes at a rate that depends directly on the velocity of trench retreat to become part of the overriding plate heated from below by the asthenosphere that flows into the opening mantle wedge the exhumed crust weakens and undergoes core complex type extension responsible for a second stage of exhumation at a lower rate the full sequence of events that characterizes this model crust mantle delamination slab rollback and trench retreat hp rock exhumation asthenosphere heating and core complex formation arises entirely from the initial condition imposed by the subduction of a small continental block no specific condition is required regarding the rheology and erosion rate of hp rocks the burial exhumation cycle is transient and can recur every time a small continental block is subducted

ground penetrating radar facies of inferred tsunami deposits on the shores of the arabian sea northern indian ocean abstract the occurrence of tsunami waves that affected the shores of the arabian sea including the gulf of oman coastline has been proven by historical reports and sedimentological investigations the damaging effect of such extensive events should not be underestimated in this region in our study we present an investigation of coarse to fine grained marine tsunami deposits in the vicinity of fins sultanate of oman using ground penetrating radar gpr the sedimentary setting along the beach section preserves evidence boulder block deposits as well as trenching results for possible high energy wave impacts the investigated area s environment is representative of conditions which lead to the best possible gpr data quality arid conditions no interference due to electrical power lines and an elevated study area 5 10 m a m s l which eliminates the low frequency noise of the ground and the possibility of salt water in the gpr data 3d visualisation of gpr results from four study areas show e g wedging out of sediments and fining inland features as well as several erosion features at the base of the deposit these findings corroborate the hypothesis of inferred tsunami deposits furthermore the presented gpr investigation technique provides new insights regarding the spatial distribution and internal architecture of palaeo tsunami deposits in comparable tsunami prone regions worldwide

regional implications of geochemistry and style of emplacement of miocene i type diorite and granite delos cyclades greece abstract the miocene plutons of the cyclades were emplaced in a subduction setting during regional back arc extension of continental crust that led to flat lying mid crustal detachment faulting mapping of the island of delos shows that quartz diorite and tonalite were emplaced as dykes in country rock of schist and marble within shear zones parallel to the extension direction mafic magmas were followed by numerous small batches of felsic magma with magmatic and ductile deformation synchronous with magma emplacement late granite dykes occupy brittle fractures in the more deformed rocks mafic and intermediate rocks show a bimodal distribution of incompatible trace elements with one group of broadly tholeiitic character and the other with substantial enrichment in sr nb and hfse but low th and ba these differences appear to be inherited from two distinct mafic sources that are different from the mafic source for the plutons of the eastern cyclades voluminous granodiorite results from these mafic magmas fractionating and or mixing with felsic crustal material some of which was derived by anatexis of a sedimentary protolith indicated by high b and mn some late granites appear derived from partial melting of hercynian paragneiss regionally the shear zones appear to be feeders to more extensive granitic plutons located at space produced at ramps in detachment fault zones the shear zones parallel the mid cycladic lineament a broad zone of displacement between two crustal blocks rotating in opposing directions as rollback took place at the hellenic subduction zone distinctive geochemical features in miocene igneous rocks suggests that these two blocks had quite different geological histories the localisation of plutonism and core complexes near the mid cycladic lineament suggests that this crustal scale shear played a role in bringing subduction derived magmas to mid crustal levels the heat supplied by the mafic magmas promoted ductile deformation high in the crust where extension was concentrated leading to the formation of core complexes the regional extension resulted in progressive shallowing of the position of the granite solidus within the crust leading to welding of the mid cycladic lineament which is no longer seismically active

geochemistry of enclaves and host granites from the nelas area central portugal abstract tonalitic granodioritic and monzogranitic enclaves occur in the hercynian peraluminous porphyritic biotite granite and biotite muscovite granite from the nelas region some variation diagrams show linear trends but others show dispersion the enclaves generally have closely similar isotopic signatures to those of the host granites they contain xenocrystic plagioclase with the same composition as phenocrysts of the host granite and have biotite as the sole ferromagnesian phase with a composition typically similar to that of the host granite however some cores of enclaves have biotite slightly chemically distinct from that of rims the modelling of major and trace elements of granodioritic enclaves and hybrid host granite indicate that they result from simple mingling mixing between a tonalitic magma and the host granite magma microgranular enclaves are thus interpreted to be globules of a more mafic magma probably from an enriched mantle source partial equilibration has been achieved between these enclaves and the host granite

the hellenic subduction zone a tomographic image and its geodynamic implications new tomographic images of the hellenic subduction zone demonstrate slab penetration in the aegean upper mantle to depths of at least 600 km beneath greece the lower part of the slab appears to be detached at a depth of about 200 km whereas it still seems to be unruptured beneath the southern aegean schematically we derive minimum time estimates for the duration of the hellenic subduction zone that range from 26 to 40 ma this is considerably longer than earlier estimates which vary between 5 and about 13 ma

the basement of the mount athos peninsula northern greece insights from geochemistry and zircon ages the mount athos peninsula is situated in the south easternmost part of the chalkidiki peninsula in northern greece it belongs to the serbo macedonian massif smm a large basement massif within the internal hellenides the south eastern part of the mount athos peninsula is built by fine grained banded biotite gneisses and migmatites forming a domal structure the southern tip of the peninsula which also comprises mount athos itself is built by limestone marble and low grade metamorphic rocks of the chortiatis unit the northern part and the majority of the western shore of the mount athos peninsula are composed of highly deformed rocks belonging to a tectonic melange termed the athos volvi suture zone avz which separates two major basement units the vertiskos terrane in the west and the kerdillion unit in the east the rock types in this melange range from metasediments marbles and gneisses to amphibolites eclogites and peridotites the gneisses are tectonic slivers of the adjacent basement complexes the melange zone and the gneisses were intruded by granites ierissos ouranoupolis and gregoriou the ouranoupolis intrusion obscures the contact between the melange and the gneisses the granites are only slightly deformed and therefore postdate the accretionary event that assembled the units and created the melange pb pb and u pb shrimp dating of igneous zircons of the gneisses and granites of the eastern athos peninsula in conjunction with geochemical and isotopic analyses are used to put athos into the context of a regional tectonic model the ages form three clusters the basement age is indicated by two samples that yielded permo carboniferous u pb ages of 292 6 2 9 ma and 299 4 3 5 ma the main magmatic event of the granitoids now forming the gneiss dome is dated by pb pb ages between 140 0 2 6 ma and 155 7 5 1 ma with a mean of 144 7 2 4 ma a within error identical age of 146 6 2 3 ma was obtained by the u pb shrimp method this late jurassic age is also known from the kerdillion unit and the rhodope terrane the rather undeformed granites are interpreted as piercing plutons the small granite stocks sampled have late cretaceous to early tertiary ages of 66 8 0 8 ma and 68 0 1 0 ma u pb shrimp 62 8 3 9 ma pb pb the main accretionary event was according to these data in the late jurassic since all younger rocks show little or no deformation the age distribution together with the geochemical and isotopic signature and the lithology indicates that the eastern part of the mount athos peninsula is part of a large scale gneiss dome also building the kerdillion unit of the eastern smm and the rhodope massif this finding extends the area of this dome significantly to the south and indicates that the tectonic boundary between the smm and the rhodope massif lies within the avz

geochemical constraints on the bimodal origin of high himalayan leucogranites major and trace element and rb sr isotope systematics of the manaslu leucogranite central nepal have been examined to constrain the role of mineral fractionation and fluids in peraluminous granite petrogenesis biotite and tourmaline are for the most part mutually exclusive with a predominance of two mica leucogranites over tourmaline leucogranites the 87sr86sr initial isotopic ratios sri indicate that leucogranitic melts were derived from two different sources the two mica leucogranites having a metagreywacke origin with sri 0 752 nd 15 such a bimodal nature of the source zone does not directly influence the magmatic evolution except that probably the higher initial boron content in the metapelitic rocks may increase the na2ok2o ratio in contrast the amount of water present during melting principally controls in part anatectic processes and element behaviour water saturated conditions probably occured during melting of metagreywackeous rocks and favoured crystallization of two mica leucogranites whereas water absent conditions prevailed during melting of metapelitic layers and favoured biotite plagioclase and monazite fractionation in the source zone and tourmaline crystallization in the leucogranite

tectonic significance of deformation patterns in granitoid rocks of the menderes nappes anatolide belt southwest turkey deformation fabrics in proterozoic cambrian granitic rocks of the cine nappe and mid triassic granites of the bozdag nappe constrain aspects of the tectonometamorphic evolution of the menderes nappes of southwest turkey based on intrusive contacts and structural criteria the proterozoic cambrian granitic rocks of the cine nappe are subdivided into older orthogneisses and younger metagranites the deformation history of the granitic rocks documents two major deformation events an early pre alpine deformation event dpa during amphibolite facies metamorphism affected only the orthogneisses and produced predominantly top to ne shear sense indicators associated with a ne trending stretching lineation the younger metagranites are deformed both by isolated shear zones and by a major shear zone along the southern boundary of the cine submassif we refer to this alpine deformation event as da3 da3 shear zones are associated with a n trending stretching lineation which formed during greenschist facies metamorphism kinematic indicators associated with this stretching lineation reveal a top to south sense of shear the greenschist facies shear zones cut the amphibolite facies structures in the orthogneisses 207pb 206pb dating of magmatic zircons from a metagranite which crosscuts orthogneiss containing amphibolite facies top to ne shear sense indicators shows that dpa occurred before 547 2 1 0 ma such an age is corroborated by the observation that mid triassic granites of the cine and bozdag nappes lack dpa structures the younger top to south fabrics formed most likely as a result of top to south alpine nappe stacking during the collision of the sakarya continent with anatolia in the eocene

petrology mineral chemistry and sr nd pb isotopic compositions of granitoids in the central menderes metamorphic core complex constraints on the evolution of aegean lithosphere slab abstract plutonic associations in the central menderes metamorphic core complex are suitable rocks in order to understand the magma forming processes in extended terrains syn extensional salihli and turgutlu granitoids have granodioritic composition and contain monzonitic and monzodioritic microgranular enclaves they are transitional metaluminous peraluminous and high k calc alkaline in character and are located on i and s type transition salihli and turgutlu granodiorites are geochemically similar to each other while their microgranular enclave chemistry is in contrast with low sio2 and high mg values mineral chemistry data from granodiorites and mafic microgranular enclaves confirm their shallow emplacement at about 7 km geochemical modelling suggests that syn extensional granitoids were derived from the mixing of mantle and lower crustal components which were finally modified by a significant amount of upper crustal contamination and fractional crystallization processes at shallow crustal levels early middle miocene syn extensional granitoids across the aegean region form a magmatic belt associated with roll back of the aegean lithosphere slab roll back induced magmatism together with ductile deformation in western turkey ceased after cooling of the salihli granodiorites at 12 2 ma but core complex related magmatism was continuous in the cycladic metamorphic core complex during late miocene and was followed by an active arc volcanism in the southern aegean such abrupt change from ductile to brittle mode of extension in western turkey can be explained by opening of a slab window on the aegean lithosphere slab which would lead to upwelling of fertile subslab asthenospheric mantle forming transitional and finally oib type basalts

geochemistry and geochronology of hp melanges from tinos and andros cycladic blueschist belt greece abstract u pb zircon geochronology sr nd isotope and bulk rock geochemistry have been applied to meta igneous and meta sedimentary rocks from high pressure metamorphic melanges exposed on the cycladic islands of tinos syros and andros ion microprobe shrimp u pb zircon dating of 7 samples representing meta igneous blocks tinos a blackwall zone tinos and chlorite talc schists from block matrix contacts syros and tinos yielded cretaceous ages of c 80 ma many of the criteria commonly used to distinguish between magmatic or metamorphic zircon genesis internal structure th u ratio ree characteristics ti in zircon thermometry enclosed mineral phases do not provide unambiguous constraints for the mode of formation however a magmatic origin for cretaceous zircon of meta gabbros and eclogites is considered likely supporting evidence for a previously suggested metamorphic origin for c 80 ma zircon in eclogite has not been found zircon of the same age occurring in chlorite talc schists is presumably related to non magmatic processes well defined cretaceous age groups clustering at c 79 ma also occur in the detrital zircon populations of 2 quartz mica schists representing the melange matrix on tinos and suggest a much later time for sediment accumulation than previously assumed the importance of c 57 ma zircon ages remains unclear but may record either hp metamorphic processes or a post 57 ma depositional age the youngest age group in a third quartz mica schist from tinos collected outside the main melange occurrences clusters at c 226 238 ma in all clastic metasediments from tinos most data points plot along the concordia between c 300 and 900 ma single data points indicate concordant ages of c 2 5 ga 2 3 ga and 1 ga respectively the youngest 206 pb 238 u age group that has been recognized in a felsic paragneiss from andros indicates an age of 163 1 3 9 ma and mostly represents overgrowths around zircon with ages in the range from 272 to 289 ma single data points of other inherited cores provided 206 pb 238 u ages of c 630 and c 930 ma meta gabbros from tinos show a large compositional variability and were found at 4 locations each with distinct compositional characteristics suggesting different crystallization histories different sources and or significant post magmatic disturbance the geochemistry of melange blocks and the identical u pb zircon ages suggest that the block matrix associations on tinos and syros can be grouped together on a broader regional scale there seem to be similarities between some meta igneous rocks from tinos and evvia field relationships indicate that the melanges occurring in southern andros and northern tinos can be correlated but supporting geochemical and or geochronological evidence for this interpretation could not be established previously published jurassic ages for mafic and felsic melange blocks from andros suggest a genetic relationship to the ophiolite occurrences exposed in the larger balkan region a similar regional correlation is also considered likely for the cretaceous meta gabbros from tinos and syros but cannot be documented with certainty

stacking of nappes with different pressure temperature paths an example from the menderes nappes of western turkey pressure temperature p t paths have been estimated from metapelitic rocks in the lowermost cine nappe and the directly underlying bozdag nappe of the anatolide belt in western turkey peak metamorphic conditions in the lowermost cine nappe are 670 to 730 c 6 2 to 6 3 kb prograde garnet grt i growth occurred largely before and during the formation of the regional s p a foliation the suffix pa indicates a pre alpine age formation of a second garnet generation grt ii which discordantly overgrew grt i followed at 550 to 620 c 6 4 to 6 5 kb peak metamorphic conditions in the underlying bozdag nappe vary from 480 to 540 c 6 1 to 7 6 kb at the base to 610 to 660 c 8 5 to 10 8 kb at the top of the nappe and attest to an inverted metamorphic field gradient in the bozdag nappe differential thermodynamic modelling gibbs method yielded a prograde path for garnet growth during the formation of s p a because d p a structures formed during prograde metamorphism we relate them to crustal shortening which was associated with a top to the north northeast shear sense in present day coordinates this event caused deformation of the cine and bozdag nappes under different metamorphic conditions we propose that the cine nappe was heated by granitoid intrusions before being emplaced above a foreland unit we speculate that the bozdag nappe belonged to the lower parts of this foreland unit cross cutting relationships of d p a structures with dated granites indicates an age of 540 to 550 ma for this tectonometamorphic event the final juxtaposition of the cine nappe and bozdag nappes and also the inversion of the metamorphic field gradient in the bozdag nappe occurred during greenschist facies conditions during the alpine orogeny in the eocene

45 m y of aegean crust and mantle flow driven by trench retreat the available seismic anisotropy data in the aegean shallow mantle and their relationship with crustal deformation are used for deciphering the lithosphere scale flow pattern driven by rollback of the hellenic subduction slab in the north and central aegean the directions of mantle seismic anisotropy trend parallel to stretching lineations in core complexes of the overlying crust suggesting that crust and mantle have undergone the same direction of flow at the scale of the entire aegean crustal extension is controlled by dextral rotation around a pole located at scutary pec albania that is related to the hellenic trench retreat the intensity of mantle anisotropy increases as a function of distance from the pole and of amount of rotation surface geology reveals that this rotating flow pattern resulted in strains accumulated since 45 ma a slab tear model is suggested to integrate the observed variations of geological events in time and space to subduction dynamics

supra pan african unconformity between core and cover series of the menderes massif turkey and its geological implications abstract well preserved primary contact relationships between a late proterozoic metasedimentary and the metagranitic core and palaeozoic cover series of the menderes massif have been recognized in the eastern part of the cine submassif on a regional scale metaconglomerates occur as laterally discontinuous channel fill bodies close the base of the metaquartzarenite directly above the basement the pebbles in the metaconglomerates consist mainly of different types of tourmaline rich leucocratic granitoids tourmalinite and schist in a sandy matrix petrographic features geochemical compositions and zircon radiometric ages 549 6 3 7 552 3 3 1 ma of the diagnostic clasts of the metaconglomerates e g leucocratic granitoids and tourmalinites show excellent agreement with their in situ equivalents 549 0 5 4 ma occurring in the pan african basement as stocks and veins the correlation between clasts in the metaconglomerates and granitoids of the basement suggests that the primary contact between the basement and cover series is a regional unconformity supra pan african unconformity representing deep erosion of the pan african basement followed by the deposition of the cover series hence the usage of core cover terminology in the menderes massif is valid consequently these new data preclude the views that the granitic precursors of the leucocratic orthogneisses are tertiary intrusions

the oldest rocks of greece first evidence for a precambrian terrane within the pelagonian zone the pelagonian zone in greece represents the westernmost belt of the hellenide hinterland internal hellenides previous geochronological studies of basement rocks from the pelagonian zone have systematically yielded permo carboniferous ages in this study we demonstrate for the first time the existence of a precambrian crustal unit within the crystalline basement of the pelagonian zone the u pb single zircon and shrimp ages of these orthogneisses vary from 699 7 ma to 713 18 ma which identify them as the oldest rocks in greece these late proterozoic rocks which today occupy an area of c 20 100 km are significantly different from the neighbouring rocks of the pelagonian zone they are therefore interpreted as delineating a terrane named here the florina terrane during the permo carboniferous florina was incorporated into an active continental margin where it formed part of the basement for the pelagonian magmatic arc the activity of this arc was dated in this study by single zircon pb pb ages as having taken place at 292 5 ma and 298 7 ma during the alpine orogeny florina together with the pelagonian zone eventually became a constituent of the hellenides geochemically the florina orthogneisses represent granites formed at an active continental margin because of the late proterozoic ages this late proterozoic active continental margin can be correlated to a pan african or cadomian arc as the gneisses contain inherited zircons of late to middle proterozoic age the original location of florina was probably at the northwestern margin of gondwana similar to other gondwana derived terranes such as east avalonia florina approached the southern margin of eurasia during palaeozoic times where it became part of an active continental margin above the subducting palaeotethys these interpretations further indicate that terrane accretion was already playing an important role in the early pre alpine evolution of the hellenides

tectonic significance of synextensional ductile shear zones within the early miocene alacamdag granites northwestern turkey synextensional granitoids may have significant structural features leading to the understanding of the evolution of extended orogenic belts one of the highly extended regions the aegean region includes a number of metamorphic core complexes and synextensional granitoids that developed following the alpine collisional events the alacamdag area in northwestern turkey is one of the key areas where miocene granites crop out along the boundary of various tectonic units structural data from the early miocene alacamdag granites demonstrated two different deformation patterns that may provide insights into the development of granitic intrusions and metamorphic core complexes 1 steeply dipping ductile shear zones caused emplacement of syn tectonic granite stocks they include kinematic indicators of a sinistral top to the sw displacement this zone has also juxtaposed the izmir ankara zone and the menderes massif in the west and east respectively 2 gently dipping ductile shear zones have developed within the granitic stocks that intruded the schists of the menderes massif on the structurally lower parts kinematic data from the foliated granites indicate a top to the ne displacement which can be correlated with the direction of the hanging wall movement documented from the simav and kazdag metamorphic core complexes the gently dipping shear zones indicate the presence of a detachment fault between the menderes massif and the structurally overlying izmir ankara zone mesoscopic to map scale folds in the shallow dipping shear zones of the alacamdag area were interpreted to have been caused by coupling between ne sw stretching and the accompanying nw se shortening of ductilely deformed crust during early miocene times one of the ne trending shear zones fed by granitic magmas was interpreted to form the northeastern part of a sinistral wrench corridor which caused differential stretching between the cycladic and the menderes massifs this crustal scale wrench corridor the izmir balikesir transfer zone may have controlled the asymmetrical and symmetrical extensions in the orogenic domains the combination of the retreat of the aegean subduction zone and the lateral slab segmentation leading to the sinistral oblique slip tearing within the eurasian upper plate appears to be a plausible mechanism for the development of such extensive ne trending shear zones in the aegean region

magma interaction processes in syn extensional granitoids the tertiary menderes metamorphic core complex western turkey abstract western turkey which forms the eastern part of the aegean region was subjected to continental extension that led to formation of metamorphic core complexes and associated syn extensional granitoids this study deals with petrogenesis of the syn extensional early miocene alacamdag ag and middle miocene salihli sg granitoids and associated mafic microgranular enclaves mme in order to better understand the time progressive evolution of the mantle sources beneath the extended continental crust in western turkey ag and sg granitoids consist of undeformed and ductility deformed granitoids together with abundant mmes they are calc alkaline to high k calc alkaline rocks that are metaluminous to slightly peraluminous mg of ag host rocks is slightly lower than that of sg host rocks ag host rocks have higher na 2 o ba rb rb la and lower al 2 o 3 cao mgo tio 2 zr y values than those of the sg host rocks ag and sg host rocks differ from those of mmes with their lower al 2 o 3 cao mgo fe 2 o 3 tio 2 sr v mg and higher sio 2 values mmes are intermediate corresponding to monzonite monzodiorite in ag and diorite in sg compositions and are more mafic with respect to their host rocks in the primitive mantle pm normalized trace element patterns host rock and mme samples have similar trace element patterns all of these rocks are enriched in large ion lithophile elements liles cs rb ba th k and sr and strongly depleted high field strength elements hfses ta nb p ti compared to the primitive mantle the isotope ratios of the syn extensional ag and sg rocks display increasing radiogenic strontium and decreasing radiogenic neodymium isotopic values for the ag and sg host rocks and mme samples are 87 sr 86 sr ag host 0 708835 0 710206 and e nd t ag host 5 36 to 7 36 87 sr 86 sr ag mme 0 709107 0 709801 and e nd t ag mme 5 36 to 7 36 87 sr 86 sr ag mme 0 709107 0 709801 and e nd t ag mme 5 55 to 6 51 87 sr 86 sr sg host 0 712200 0 712408 and e nd t sg host 8 03 to 8 61 87 sr 86 sr sg mme 0 712028 0 712351 and e nd t sg mme 7 57 to 8 48 syn extensional granitoids in western turkey were mainly affected by crustal contamination fractional crystallization and magma mixing mingling mm processes magma mixing mingling partial mixing appear to have larger affects on the compositional range of the magmas than those generated by partial melting crustal contamination and fractional crystallization mafic and felsic magmas forming syn extensional granitoids have also undergone metasomatism chemical equilibrium and diffusional exchange processes during cooling syn extensional granitoids have been derived from a hybrid magma that originated from mixing of coeval lower crustal derived felsic magma and lithospheric mantle derived mafic magmas during extensional processes

o sr isotopic variations in miocene granitoids from the aegean evidence for an origin by combined assimilation and fractional crystallization sr o and d h isotopic compositions have been analyzed in miocene metaluminous to slightly peraluminous i type granitoids of the central aegean individual plutonic complexes display significant variations in their 18o and initial87sr 86sr compositions d and 18o compositions of minerals and whole rocks are mostly in the magmatic range some samples from naxos and mykonos delos show low d and 18o values characteristic of meteoric water hydrothermal interaction but as a whole the changes in 18o and sr isotopic compositions as a result of hydrothermal alteration were slight even in instances where marked alteration is petrographically observable consequently the bulk rock variations of 18o from 8 1 to 12 0 and of87sr 86sr from 0 70438 to 0 71450 may be regarded as primary and indicative of the conditions of their evolution heterogeneous isotopic compositions observed in the individual plutons of serifos ikaria samos and kos may be caused by the multiple intrusion of chemically and isotopically distinct magma pulses with high viscosities and relatively rapid consolidation in most cases preventing complete homogenization the granitoids of serifos ikaria and kos display weak correlations between the initial87sr 86sr and 18o and 1 sr the granitoid province shows a positive correlation between87sr 86sr and 18o and a non linear relationship between87sr 86sr and 1 sr whereby 1 sr increases more rapidly than the isotopic ratio as the degree of fractionation of the rocks increases it is argued that assimilation of older continental material by mantle derived arc magmas with combined fractionation afc is the most plausible model to explain the chemical and isotopic characteristics of the granitoids and the geological situation in which rock types trend from granodiorites in the south west near the inferred oligocene miocene suture to granites in the center and monzonites in the north east of the province

the faroe bank channel deep water overflow in the late 1950s it was recognised that a considerable transport of water from the deeper reaches of the norwegian sea into the atlantic takes place through the faroe bank channel which thereby serves as an important source for the renewal of the north atlantic deep water consequently substantial efforts have over the past decades been dedicated towards quantifying the overflow as well as clarifying the underlying dynamics in the present review an attempt is made to summarise the main body of the observational results as well as some theoretical considerations regarding the dynamical mechanisms the most prominent characteristic of the faroe bank channel overflow is that it is a persistent phenomenon with a yearly average deep water viz t 5degreesc transport of around 2 sv using inviscid rotating hydraulics the flow through the controlling section at the sill furthermore can be reasonably well predicted on the basis of upstream conditions in the norwegian sea after passing the threshold the descending overflow plume is subject to intense mixing a process very much in the focus of ongoing research c 2004 elsevier ltd all rights reserved

ductile brittle transition along the alasehir detachment fault and its structural relationship with the simav detachment fault menderes massif western turkey abstract western turkey has experienced extensional deformation since the tertiary an early phase of extensional deformation resulted in the formation of detachment faults in the northern part of the menderes massif the alasehir and simav detachment faults the footwalls of these two detachment faults are mid crustal level rocks the alasehir detachment fault developed in metamorphic rocks and in a syn extensional intrusion the salihli granodiorite the salihli granodiorite shows a gradual change from undeformed isotropic granodiorite to protomylonite mylonite and ultramylonite towards its upper structural levels the deformed granodiorite in turn grades into a cataclastic zone whose uppermost part is the alasehir detachment surface this gradual upward change from the undeformed granodiorite to a brittlely deformed detachment surface suggests that tertiary extension resulted in a ductile deformation at depth and the ductilely deformed granitoids were brought to shallower depths where they were brittlely deformed the metamorphic wall rocks of the intrusion are also mylonitized structurally upward a similar transition has also been found in the footwall of the simav detachment fault the upper part of which is also a cataclastic zone leading to the simav detachment fault separating the low grade metamorphic rocks and or non metamorphic rocks in its hanging wall from mainly high grade metamorphic rocks and syn tectonic granitoids in its footwall during ductile extension greenschist facies grade mylonitic deformation developed in the metamorphic rocks and the granitoids shear sense indicators along the two shear zones show top to n ne sense shear consistent with the regional cenozoic extension direction in western turkey available radiometric age data from the granitoids in the footwall of the two detachment faults suggest that the cenozoic extension in western turkey was initiated in oligocene to early miocene and the simav detachment fault is older than the alasehir detachment fault extensional features of these detachment faults suggest that the simav detachment fault characterise the earlier stage of the tertiary extensional tectonics of the menderes massif and later stage of this deformation resulted in the development of the alasehir detachment fault

slab detachment control on mafic volcanic pulse and mantle heterogeneity in central mexico seismic tomography studies and plate reconstructions suggest that the farallon slab broke off shortly before subduction ended off southern baja california however the progress of detachment in time and space and its consequences on the volcanism of central mexico have not so far been considered here i use the neogene geologic record of central mexico to propose a lateral propagation of slab detachment beneath the trans mexican volcanic belt during the late miocene i suggest that the trace of the detachment is expressed by a short 2 3 m y eastward migrating pulse of mafic volcanism that took place from ca 11 5 to ca 6 ma to the north of the pliocene quaternary volcanic arc as hot subslab material flowing into the slab gap produced a transitory thermal anomaly in the mantle wedge slab detachment of the deeper and denser part of the plate was initiated in the southern gulf of california area by the incoming of progressively younger oceanic lithosphere at the paleotrench that produced an increasing coupling between the magdalena microplate and the overriding north american plate the tear in the slab propagated eastward from the gulf of california to the gulf of mexico paralleling the southern mexico trench system the decrease in the rivera north america convergence rate between ca 9 and 7 ma appears to be related to the loss of slab pull after the detachment sparse oceanic island type basalts emplaced since the end of the miocene in the trans mexican volcanic belt are located above a trench parallel slab window between the inferred detachment trace and the leading edge of the present slab which has been detected seismically in this context the occurrence of these unusual intraplate magmas is easily explained by the infiltration of enriched asthenosphere into the subarc mantle