kinematic reconstructions and magmatic evolution illuminating crustal and mantle dynamics of the eastern mediterranean region since the late cretaceous the relationship between subduction dynamics and crustal deformation in the mediterranean region has been recently studied using three dimensional 3d numerical models such models require however a detailed information concerning the past geological evolution we use stratigraphic petrologic metamorphic structural paleomagnetic and magmatic data to build new kinematic reconstructions of the eastern mediterranean region since the late cretaceous using the principle of non rigid domains the motions of the 56 deforming domains defined in this work are calculated based on published paleomagnetic rotations the directions and amounts of displacement on crustal scale shear zones and the burial and exhumation histories of the main metamorphic units extracted from these reconstructions paleotectonic maps and lithospheric scale cross sections illustrate that the present day subduction zone has been continuously retreating southward since the late cretaceous and has accreted several small continental domains in the process we find evidence for two back arc related extensional events 1 slow extension along the balkans and the pontides in the late cretaceous while the trench was long and linear and 2 faster extension in the rhodope aegean west anatolian region since the eocene oligocene rapid rotation of the hellenides between 15 and 8 ma probably indicates a slab tearing event below western anatolia that could have further accelerated this extensional kinematics spatial distribution and the geochemical signature of magmatic centers integrated in these reconstructions allow us to trace mantle related processes revealing the deep dynamics that controls both the magma genesis and the crustal deformation

40ar 39ar and oxygen isotope studies of polymetamorphism from tinos island cycladic blueschist belt greece petrological oxygen isotope and 40ar 39ar studies were used to constrain the tertiary metamorphic evolution of the lower tectonic unit of the cyclades on tinos polyphase high pressure metamorphism reached pressures in excess of 15 kbar based on measurements of the si content in potassic white mica temperatures of 450 500 c at the thermal peak of high pressure metamorphism were estimated from critical metamorphic assemblages the validity of which is confirmed by a quartz magnetite oxygen isotope temperature of 470 c some 40ar 39ar spectra of white mica give plateau ages of 44 40 ma that are considered to represent dynamic recrystallization under peak or slightly post peak high pressure metamorphic conditions early stages in the prograde high pressure evolution may be documented by older apparent ages in the high temperature steps of some spectra eclogite to epidote blueschist facies mineralogies were partially or totally replaced by retrograde greenschist facies assemblages during exhumation oxygen isotope thermometry of four quartz magnetite pairs from greenschist samples gives temperatures of 440 470 c which cannot be distinguished from those deduced for the high pressure event the exhumation and overprint is documented by decreasing ages of 32 28 ma in some greenschists and late stage blueschist rocks and ages of 30 20 ma in the lower temperature steps of the ar release patterns of blueschist micas almost flat parts of ar ar release spectra of some greenschist micas gave ages of 23 21 ma which are assumed to represent incomplete resetting caused by a renewed prograde phase of greenschist metamorphism oxygen isotope compositions of blueschist and greenschist facies minerals show no evidence for the infiltration of a 18o enriched fluid rather the compositions indicate that fluid to rock ratios were very low the isotopic compositions being primarily controlled by those of the protolith rocks we assume that the fundamental control catalysing the transformation of blueschists into greenschists and the associated resetting of their isotopic systems was the selective infiltration of metamorphic fluid a quartz magnetite sample from a contact metamorphic skarn taken near the miocene monzogranite of tinos gave an oxygen isotope temperature of 555 c and calculated water composition of 9 1 the value of 18o obtained from this water is consistent with a primary magmatic fluid but is lower than that of fluids associated with the greenschist overprint which indicates that the latter event cannot be directly related to the monozogranite intrusion

eclogite blueschist relationships as evidenced by mineral equilibria in the high pressure metabasic rocks of sifnos cycladic islands greece

timing kinematics and cause of aegean extension a scenario based on a comparison with simple analogue experiments abstract since the early 1970s most geodynamic models proposed for the eastern mediterranean consider that the initiation of extension in the aegean during the late middle miocene or later was a direct consequence of the westward extrusion of anatolia away from the arabia eurasia collision front in the late 1990s a few models have taken into account the increasing evidence for an earlier initiation of aegean extension arising mostly from the analysis of deformation within the various alpine metamorphic complexes of the area based largely on our own investigations we first present a review of the data that reliably constrain the minimum age for the initiation of extension in these complexes it shows that regional scale extension with a pattern of stretching orientations similar to that of the pliocene pleistocene was already strongly active in the aegean before the onset of arabian indentation into eurasia lower miocene vs middle or upper miocene this implies that the initiation of aegean extension did not result from the lateral extrusion of anatolia instead extension may have started owing to a process of gravity spreading of the continental lithosphere that had previously been thickened during alpine collision the main arguments favouring this interpretation are presented and a preliminary scenario is proposed for the neogene evolution of the eastern mediterranean in which lateral extrusion of anatolia occurred lately during southward spreading of the aegean lithosphere in order to test this hypothesis further physical experiments simulating the horizontal spreading of a continental lithosphere toward a free boundary have been carried out the analysis of various elements of the deformation field displacements strain rotations fault pattern and kinematics both in the experiments and in the aegean domain reveals an excellent agreement between the two not only do early stages of aegean extension appear to fit the gravity spreading hypothesis but so does the recent to present internal deformation of the aegean transverse e w active shortening observed in the northern aegean is commonly taken as one of the most striking pieces of evidence that aegean extension results from the lateral extrusion of anatolia the experiments indicate that such transverse shortening may equally develop as a result of pure gravity spreading associated with a pattern of faults and rotations that compares well with that of the northern aegean pure dextral shearing along some strands of the north aegean trough fault system and the related development of an asymmetric pattern of faults in the northern aegean are eventually the only features that evidently arise from the extrusion of anatolia since less than 3 ma finally we argue that during the early stages of aegean extension since at least 21 ma and until ca 11 ma the distribution of extensional strain on a regional scale has been controlled by the distribution of earlier thickening post thickening thermal weakening through partial melting of deep levels of the crust probably accounts for the localization of extensional strain within the areas of thick crust restoring the aegean in its most likely configuration at the onset of bulk crustal extension suggests that 1 the extensional strain rate remained roughly constant or has eventually decreased since the onset of aegean extension and 2 the amounts of extension before and after 16 ma have been roughly equal

dating the evolution of c s microstructures a combined 40ar 39ar step heating and uv laserprobe analysis of the alpine roffna shear zone abstract a technique combining 40ar 39ar step heating analyses in situ uv laserprobe dating and electron microprobe chemical characterization has been developed to unravel the relationships between microstructures metamorphism and k ar systematics this technique has been applied to white micas of a discrete shear zone in the roffna metarhyolite in the suretta nappe se switzerland neoformed phengites from the roffna metarhyolite crystallised in shear zones during tertiary alpine deformation under blueschist and greenschist facies conditions in situ 40ar 39ar uv laser dating of white micas defining the schistosity and c planes yield systematically younger isotopic dates in the c planes which are also correlated with decreasing celadonite content i e si al ratio these results suggest that the timing of the high pressure deformation event is preserved in the schistosity high si micas appear to have lost no ar later deformation was localised preferentially in c planes giving younger 40ar 39ar dates probably related to a later period of phengite growth the age sequence is broadly consistent with the textural constraints and geological field relations

non stoichiometry of interlayer cations in micas from low to middle grade metamorphic rocks in the ryoke and the sanbagawa belts japan micas in 17 pelitic k feldspar free and 8 psammitic k feldspar bearing rocks from the wazuka and the asemi gawa areas in the ryoke and the sanbagawa metamorphic terrains respectively were analyzed on an electron probe microanalyzer the deficiency of alkali cations in the low to middle grade metamorphic micas is ascribed to the illite substitution kxii aliv xii vacancy siiv

superimposed tectono metamorphic episodes of jurassic and eocene age in the jadeite uplift myanmar as revealed by 40ar 39ar dating abstract the myanmar jadeite uplift forms an important link between the indo burma range and the tagaung myitkyina belt two contrasting ages of jurassic 152 4 1 5 ma of glaucophane from blueschist and eocene 44 8 1 1 and 45 0 1 3 ma of phengitic muscovites from quartz schists in the uplift were yielded using 40 ar 39 ar dating the jurassic age of the glaucophane even older than the forming age of the jadeitite from recent relevant literatures and for the reason of possible excess argon involved is interpreted as the lower limit of the subduction age previous studies correlated this subduction with the woyla intra oceanic arc or the incertus arc to the west the eocene ages of phengitic muscovites are interpreted as the time of an intra continental shearing deformation event against the timing of hp lt metamorphism as previously suggested combined with other studies it is suggested that the tagaung myitkyina belt and the indo burma range belonged to a single belt which has been separated by the sagaing fault leaving the jadeite uplift straddling along the fault between the belt and the range we propose a rapid exhumation model for the myanmar jadeitite at 45 ma coeval with onset of the sagaing fault

tectono metamorphic evolution of syros and sifnos islands cyclades greece abstract miocene exhumation of metamorphic rocks in the aegean sea is partly a consequence of post orogenic extension if the post orogenic mechanism of exhumation is rather well understood the earlier syn orogenic eocene exhumation is still largely enigmatic previous authors have argued in terms of extension or compression new structural and petrological data on sifnos and syros islands show that exhumation of high pressure low temperature hp lt rocks involves crustal scale extensional ductile shear zones during the eocene we observe a continuum of top to the ne and e ductile shear from the eocene in the blueschist facies to the miocene in the greenschist facies this deformation is distributed in the eclogites and blueschists whereas it is rather localised along ductile shear zones in the greenschists eclogites which are preserved only at the top of the structural pile are exhumed with a cold retrograde p t path in the lower part of the structural pile we observe a progressive retrogression of eclogites in blueschist then greenschist facies this lower part of pile is subsequently exhumed with p t paths showing a nearly isothermal decompression before cooling p t t deformation data suggest that the cycladic blueschists are progressively exhumed by a continuum of accretion at the base of the orogenic wedge and by a partly non coaxial extensional deformation above distributed during the syn orogenic stage then localised during the post orogenic stage we then compare the mechanism of syn orogenic exhumation of crete and the cyclades and we discuss a simple geodynamic scenario for the aegean domain and the external hellenides which accounts for 1 the southward migration of the hellenic trench and arc during the cenozoic 2 the p t t deformation data for the cycladic blueschists and the phyllite quartzite nappe and 3 the transition from syn orogenic to post orogenic in the cyclades

coesite and pure pyrope in high grade blueschists of the western alps a first record and some consequences a pyrope quartzite originally described by vialon 1966 from the dora maira massif was resampled and reinvestigated garnet up to 25 cm in size phengite kyanite talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz the garnet is a pyrope almandine solid solution with 90 to 98 mol mg end member it contains inclusions of coesite which has partially inverted to quartz resulting in a typical radial cracking of the host garnet around the inclusions several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite

extraneous argon in high pressure metamorphic rocks distribution origin and transport in the cycladic blueschist unit greece the 40ar 39ar geochronological technique has significantly contributed to the study of crustal deformation however the frequent occurrence of extraneous argon in high pressure terrains can make the interpretation of 40ar 39ar ages problematic this contribution attempts to i characterize the distribution and origin of extraneous argon in the cycladic blueschist unit cbu greece by applying the 40ar 39ar dating technique on three cycladic islands syros tinos and ios which span a complete transect of the cbu and ii discuss regional implications for the tectonometamorphic evolution of the cbu our results combined with ages available in the literature show that periods of peak burial conditions 55 49 ma and syn 45 38 ma to post orogenic exhumation 37 21 ma are well constrained in the cbu by the 40ar 39ar method moreover variscan apparent ages are preserved in the cycladic basement of ios indicating that the 40ar 39ar system was not completely reset during the eocene metamorphic episode additionally our 40ar 39ar data show that the occurrence of extraneous argon is heterogeneously distributed in the cbu while high pressure rocks of syros and tinos are only locally affected extraneous argon is clearly evidenced in the cbu of ios yielding geologically meaningless ages up to 900 ma on each island the most affected ages were obtained in microstructures where fluid circulation is enhanced such as shear bands or strain shadows around garnets we suggest that the cycladic basement a polymetamorphic continental unit behaved as an argon reservoir that has been mobilized by fluid circulation at the eocene these argon enriched fluids have then heterogeneously contaminated metamorphic rocks when percolating through the cbu finally we claim that a minimum closure temperature of 550 c must be accepted for the phengites of the cbu and conclude that volume diffusion is not the main process resetting the argon isotopic system in high pressure rocks compare to recrystallization enhanced by fluid circulation and deformation

continental subduction intracrustal shortening and coeval upper crustal extension p t evolution of subducted south iberian paleomargin metapelites betics se spain abstract the nevado filabride complex represents the basement and permo triassic cover of the south iberian passive margin metamorphosed during miocene continental subduction under the alboran crustal domain it forms a nappe stack with the thick calar alto unit 6 km thick sandwiched between the ragua unit below and the bedar macael unit above the nappe stacking occurred by ductile flow along basal syn metamorphic shear zones structural analysis of the calar alto unit together with thermobarometric data of samples from both the bottom and top of the unit served us to understand the tectonic significance of this episode of intracrustal shortening in the context of a strongly extended orogen multiequilibrium thermobarometry shows that the calar alto schist underwent a prograde p t path at mantle depths from 1 6 gpa at 450 500 c to 1 0 gpa at 550 570 c during the growth of the schistosity s1 parallel to the compositional layering after detachment from the downgoing slab and underplating the unit underwent nearly isobaric cooling by up to 250 c from peak metamorphic conditions the main crenulation cleavage s2 and the mylonitic foliation sm developed within the crustal nappe stack during decompression and heating sm at the base of the unit grew between 0 8 gpa at 400 c and 0 4 gpa at 500 c while s2 at the top of the unit developed between 0 6 gpa at 300 c and 0 2 gpa at 400 c these shortening structures developed simultaneously to the activity of overlying middle miocene extensional detachments intracrustal shortening and coeval upper crustal extension resulted in a mode of exhumation where the material rise entailed an important horizontal component of displacement at rates of approximately 15 mm year being exhumed along an s shaped p t path after peak metamorphic conditions and its detachment from the subducting slab

the two stage aegean extension from localized to distributed a result of slab rollback acceleration back arc extension in the aegean which was driven by slab rollback since 45 ma is described here for the first time in two stages from middle eocene to middle miocene deformation was localized leading to i the exhumation of high pressure metamorphic rocks to crustal depths ii the exhumation of high temperature metamorphic rocks in core complexes and iii the deposition of sedimentary basins since middle miocene extension distributed over the whole aegean domain controlled the deposition of onshore and offshore neogene sedimentary basins we reconstructed this two stage evolution in 3d and four steps at aegean scale by using available ages of metamorphic and sedimentary processes geometry and kinematics of ductile deformation paleomagnetic data and available tomographic models the restoration model shows that the rate of trench retreat was around 0 6 cm year during the first 30 my and then accelerated up to 3 2 cm year during the last 15 my the sharp transition observed in the mode of ex

subduction and exhumation of continental crust insights from laboratory models summary when slivers of continental crust and sediment overlying oceanic lithosphere enter a subduction zone they may be scraped off at shallow levels subducted to depths of up to 100 200 km and then exhumed as high pressure hp and ultra high pressure uhp rocks or subducted and recycled in the mantle to investigate the factors that influence the behaviour of subducting slivers of continental material we use 3 d dynamically consistent laboratory models a laboratory analogue of a slab upper mantle system is set up with two linearly viscous layers of silicone putty and glucose syrup in a tank a sliver of continental material also composed of silicone putty overlies the subducting lithosphere separated by a syrup detachment the density of the sliver viscosity of the detachment geometry of the subducting system attached plate versus free ridge and dimensions of the sliver are varied in 34 experiments by varying the density of the sliver and viscosity of the detachment we can reproduce a range of sliver behaviour including subduction subduction and exhumation from various depths and offscraping sliver subduction and exhumation requires sufficient sliver buoyancy and a detachment that is strong enough to hold the sliver during initial subduction but weak enough to allow adequate sliver displacement or detachment for exhumation changes to the system geometry alter the slab dip subduction velocity pattern of mantle flow and amount of rollback shallower slab dips with more trench rollback produce a mantle flow pattern that aids exhumation steeper slab dips allow more buoyancy force to be directed in the up dip direction of the plane of the plate and aide exhumation of subducted slivers slower subduction can also aide exhumation but if slab dip is too steep or subduction too slow the sliver will subduct to only shallow levels and not exhume smaller slivers are most easily subducted and exhumed and influenced by the mantle flow

styles and regimes of orogenic thickening in the peloritani mountains sicily italy new constraints on the tectono metamorphic evolution of the apennine belt the peloritani mountains constitute the sicilian portion of the calabria peloritani arc italy a tectono metamorphic edifice recording the history of the subduction exhumation cycle during tertiary convergence between the african and european plates here we describe the kinematic and the petrological characteristics of the major shear zones bounding the lowermost continental derived metamorphic units cropping out in the eastern portion of the peloritani mountains both meso and micro scale shear sense criteria indicate a top to the sse tectonic transport during a general evolution from ductile to brittle deformation conditions quantitative thermobarometry on texturally equilibrated phengite chlorite pairs crystallized along the shear bands indicates pressure of 6 8 kbar at temperatures of 360 440 c for the structurally highest units and 3 4 kbar at 380 440 c for the lowest ones this documents an overall inverse type nappe arrangement within the tectonic edifice and a transition from an alpine 13 18 c km 1 to a barrovian type 28 36 c km 1 geothermal gradient during the progress of the alpine orogenic metamorphism in the peloritani mountains the integration of these results allows the peloritani mountains to be considered as a constituent element of the apennine orogenic domain formed during the progressive space time transition from oceanic to continental subduction at the active convergent margin

trends in uk extreme sea levels a spatial approach the majority of studies of long term sea level change have concentrated on the trend in mean sea level which is just one constituent of the trend in extreme sea level by fitting a spatial model to sea level annual maxima from 62 uk sites extreme sea level trend estimates are obtained for the entire british coastline these estimates exhibit smooth but significant spatial variation which arises from a combination of eustatic extreme sea level change and local vertical land movements once the latter effect is removed eustatic extreme sea level trends are found to have no significant spatial variation and to be similar in value to trends in uk eustatic mean sea level

aegean tectonics strain localisation slab tearing and trench retreat abstract we review the geodynamic evolution of the aegean anatolia region and discuss strain localisation there over geological times from late eocene to present crustal deformation in the aegean backarc has localised progressively during slab retreat extension started with the formation of the rhodope metamorphic core complex eocene and migrated to the cyclades and the northern menderes massif oligocene and miocene accommodated by crustal scale detachments and a first series of core complexes mccs extension then localised in western turkey the corinth rift and the external hellenic arc after messinian times while the north anatolian fault penetrated the aegean sea through time the direction and style of extension have not changed significantly except in terms of localisation the contributions of progressive slab retreat and tearing basal drag extrusion tectonics and tectonic inheritance are discussed and we favour a model 1 where slab retreat is the main driving engine 2 successive slab tearing episodes are the main causes of this stepwise strain localisation and 3 the inherited heterogeneity of the crust is a major factor for localising detachments the continental crust has an inherited strong heterogeneity and crustal scale contacts such as major thrust planes act as weak zones or as zones of contrast of resistance and viscosity that can localise later deformation the dynamics of slabs at depth and the asthenospheric flow due to slab retreat also have influence strain localisation in the upper plate successive slab ruptures from the middle miocene to the late miocene have isolated a narrow strip of lithosphere still attached to the african lithosphere below crete the formation of the north anatolian fault is partly a consequence of this evolution the extrusion of anatolia and the aegean extension are partly driven from below asthenospheric flow and from above extrusion of a lid of rigid crust

diffusional isotopic exchange across an interlayered marble schist sequence with an application to tinos cyclades greece marble schist contacts are frequently characterized by fine scale interlayering which prevents the application of semi infinite layer width assumptions to advection diffusion models of isotope profiles using a finite layer width boundary condition we show that the minimum width w of a layer required in order that diffusional exchange at both boundaries will not mutually interfere is given by the relation w k dt 1 2 where d is the effective diffusion coefficient t is the duration of the diffusion and k is a constant determined by the initial compositional step and the noise i e natural homogeneity and or analytical accuracy when this condition is not satisfied a solution of the diffusion equation for a multilayer transition zone containing several schist and marble layers of different finite widths is applicable application of this refinement of the diffusion model to an oxygen isotope profile from tinos cyclades greece gives 10 4 dt 10 2 m2 this dt range and a dt value of 10 1 m2 previously determined for sifnos indicates that rocks undergoing the oligocene miocene greenschist facies overprint of eocene high pressure metamorphic rocks in the cyclades were characterized by extremely low porosities permeability perpendicular to marble schist contacts was sufficiently low to prevent advection into the marbles correspondingly it is suggested that the layer parallel schistosity permitted infiltration of the fluids required for the hydration reactions of the metamorphic overprint

exhumation of high pressure metamorphic rocks the exhumation of high pressure metamorphic minerals necessitates the removal of overburden which was present at the time of metamorphism assuming metamorphism during an orogenic phase and exhumation during an uplift phase the model presented here is based on postulating continuous deformation at the active margin of an ocean continent interaction accepting the conclusion that coesite bearing eclogites and other high pressure minerals were formed when a sliver of continental crust was subducted down to 100 km i propose that their uplift was caused by a shift of the beniofff zone the high pressure slab now accreted to the continental lithosphere was lifted up the ramp of a benioff zone when ocean lithosphere was thrust under the continent the geology of the western alps illustrates this model

oxygen isotope geothermometers for metamorphic rocks the chicago mineral carbonate oxygen isotope fractionation curves have been combined with mineral water fractionation data for jadeite zoisite and rutile and new data for grossular water to provide a set of self consistent mineral pair calibrations the a coefficients in the equation 1000 in a 106t 2 of the new mineral pair fractionations are jadeite zoisite grossular rutile quartz 1 69 2 00 3 03 5 02 jadeite 0 31 1 34 3 33 zoisite 1 03 3 02 grossular 1 99 the isotopic fractionation properties of natural pyralspite garnet ca fe mg mn 3al2si3o12 can be approximated by those of the grossular end member appropriate substitutions also yield coefficients for the solid solution minerals sodic pyroxene and epidote e g aquartz sodic pyroxene 2 75 1 06xjd aquartz epidote 2 00 0 75xps where xjd and xps are the mole fractions of the jadeite and pistacite components respectively the new data set is particularly suitable for the geothermometry of metamorphic rocks 18o data from minerals of the high pressure metamorphic rocks of the sesia zone of italy and cyclades complex of greece yield well constrained mean temperatures of 572 and 478d c respectively type iii blueschist metabasalts of the franciscan formation of california give mean quartz garnet temperatures of 354d c

relation between the intensity of deformation and retrogression in blueschist metapelites of tinos island greece evidenced by chlorite mica local equilibria the late greenschist deformation of the cycladic blueschists unit on tinos island evolves along a ne sw gradient of non coaxial strain across a major extensional shear zone deformation is more intense and the greenschist overprint is also more severe close to the shear zone that separates the cycladic blueschists from the upper ophiolitic unit in the ne of the island the compositional variability of chlorite and k white mica kwm in metapelites sampled along a ne sw cross section is characteristic of their p t conditions of crystallization and is mainly characterized by variations of their si al fe and mg contents due to the tschermak substitution siiv fe mg vi alvialiv multi equilibrium p t estimates based on the assumption of local equilibrium indicate that each sample recorded a part of the p t history which depends on the distance to the contact to the main shear zone i e the intensity and the pattern of deformation the combination of p t estimates obtained from all the samples collected along the transect provides a continuous p t path which is composed of two parts it provides insights on the syn and post orogenic exhumation for some of the cycladic blueschists in particular we could distinguish two stages in the exhumation process a first stage in the blueschist facies occurred along a cold p t path during the construction of the hellenides the second exhumation stage occurred along a warmer p t path during the formation of the aegean sea between the two stages of exhumation there is a thermal reequilibration of the crust and a partial thermal overprint of the blueschist parageneses

low angle faults above and below a blueschist belt tinos island cyclades greece new observations from the island of tinos greece allow a better definition of the structural position of the alpine eocene blueschist belt exposed in the islands of the aegean sea these blueschists over a significant part of the aegean sea are delimited from below by a low angle thrust fault while from above they are delimited by a low angle normal type fault which omits a substantial crustal interval both underlying and overlying rocks were not affected by the high metamorphism the rapid uplift and exhumation of the high rocks was therefore mainly the result of fault movements rather than erosion and whole crust uplifting the low angle normal fault apparently had a major role in the uplift of the blueschists

ion probe and fluid inclusion evidence for co seismic fluid infiltration in a crustal detachment we have investigated the geochemical pattern of fluid infiltration in the extensional detachment of tinos island cyclades greece ion microprobe o isotope analyses and fluid inclusion studies have been conducted in strain fringes developing around pyrite blasts in the mylonite of the shear zone micro scale traverses in quartz and calcite fibres show that 18o increases from 17 18 to 20 21 in 1 mm towards the blast drops of 3 in 200 m then rises again in the direction of growth 18o variations are interpreted as transient influxes of exotic fluids into the shear zone between periods of closed system buffering by the host rock fluid inclusions trapped in the fibres show fluctuating salinities 0 4 wt nacl eq and densities that reflect drops of the pore pressure from lithostatic 1 to hydrostatic 0 4 values during fringe growth isotopic and microthermometric data are consistent with models of seismic pumping developed for compressive shear zones we therefore suggest that co seismic pore pressure variations developed suction forces sufficient to drive large scale fluid migration in the tinos detachment as in convergent tectonic settings

phase relations of epidote blueschists phase diagrams have been computed for minerals in the system ncmash using the optimised thermodynamic data base of berman 1988 augmented by data on glaucophane and pumpellyite to illustrate the relationships between rocks containing epidote and sodic amphibole and those containing assemblages characteristic of neighbouring metamorphic facies the stoichiometries of stable bounding equilibria yield a simple list of mineral parageneses that serves to define an epidote blueschist facies and surrounding metamorphic facies the calculations suggest that when iron free the pairs zoisite glaucophane and clinozoisite glaucophane do not possess a stability field the natural fe bearing paragenesis of epidote sodic amphibole occupies a closed field in the pt diagram whose size increases dramatically as the ratio fe3 al in the minerals is increased where garnet is involved in bounding reactions such as with respect to eclogite and garnet bearing albite epidote amphibolite the epidote blueschist field decreases in size as the ratio fe2 mg is increased the classic blueschist to greenschist transition reaction is best developed in rocks with large fe3 and fe2 contents and is possibly metastable in mgal rich rocks in the latter a wedge of albite epidote actinolite barroisite amphibolite separates the epidote blueschist from the greenschits paragenesis field a first occurrence of garnet divides the epidote blueschist field into a lower temperature garnet free zone and a higher temperature garnet bearing zone although the temperatures calculated for this garnet isograd seem high the locations of all the facies boundaries are influenced by h2o activity however even minor amounts of co2 in the fluid phase x co2 0 005 render the epidote sodic amphibole paragenesis metastable so that facies boundaries cannot be shifted by varying the co2 content of the fluid phase below 600 c no mutual boundaries exist between the amphibolite facies and the epidote blueschist and eclogite facies respectively the calculated low pressure limit for the eclogite paragenesis pyralspite omphacite jd 50 quartz typical metabasite compositions is 12 to 14 kbars with h2o activity 0 9 or 1 5 to 2 kbar lower for jd 30

the lavrion pb zn ag rich vein and breccia detachment related deposits greece involvement of evaporated seawater and meteoric fluids during postorogenic exhumation

tephra horizons identified in the western north atlantic and nordic seas during the last glacial period extending the marine tephra framework abstract geochemically distinct volcanic ash tephra deposits are increasingly acknowledged as a key geochronological tool to synchronize independent paleoclimate archives recent advances in the detection of invisible crypto tephra have led to the ongoing establishment development and integration of regional tephra lattices these frameworks offer an overview of the spatial extent of geochemically characterized tephra from dated eruptions a valuable tool for precise correlation of paleorecords within these areas here we harness cryptotephra analysis to investigate the occurrence of two well known tephra markers from the last glacial period i e fmaz ii 1 26 7 ka b2k and naaz ii ii rhy 1 55 3 ka b2k in marine sediment cores from the nordic irminger and labrador seas in addition we assess the imprint of bioturbation on two of these tephra deposits using computed tomography ct imagery we have successfully identified fmaz ii 1 in the nordic and irminger seas the tephra deposit is a visible deposit in the nordic seas whereas it appears as a single high concentration peak within the fine grained shard size fraction i e 25 80 m in the irminger sea both horizons are primary airfall deposits and this study is the first to identify a fmaz ii 1 deposit of isochronous nature in the irminger sea region in addition we have identified a new tephra horizon in the irminger sea which is stratigraphically associated with fmaz ii 1 and geochemically similar to the known 2 jpc 192 1 population we discuss its potential to serve as a new reference tie point for correlations in the region lastly we have successfully identified naaz ii ii rhy 1 of isochronous nature in both the irminger and labrador sea the layers are interpreted to be deposited by either direct airfall or by sea ice drifting past the sites compared to the existing frameworks which previously mainly focused on sites east of iceland our findings expand the knowledge and utility of the fmaz ii 1 and naaz ii ii rhy 1 horizons

episodic slab rollback fosters exhumation of hp uhp rocks summary the burial exhumation cycle of crustal material in subduction zones can either be driven by the buoyancy of the material by the surrounding flow or by both high pressure and ultrahigh pressure rocks are chiefly exhumed where subduction zones display transient behaviours which lead to contrasted flow regimes in the subduction mantle wedge subduction zones with stationary trenches mode i favour the burial of rock units whereas slab rollback mode ii moderately induces an upward flow that contributes to the exhumation a regime that is reinforced when slab dip decreases mode iii episodic regimes of subduction that involve different lithospheric units successively activate all three modes and thus greatly favour the exhumation of rock units from mantle depth to the surface without need for fast and sustained erosion

structural evolution of andros cyclades greece a key to the behaviour of a flat detachment within an extending continental crust the continental crust extends in a brittle manner in its upper part and in more distributed ductile manner in its lower part during exhumation of hp metamorphic rocks brittle features superimpose on earlier ductile ones as a result of the progressive localization of deformation the islands of tinos and andros are part of the numerous metamorphic core complexes exhumed in the aegean domain they illustrate two steps of a gradient of finite extension along a transect between mt olympos and naxos this study confirms the main role of boudinage as an initial localizing factor at the brittle ductile transition and emphasizes the continuum of strain from ductile to brittle during exhumation early low angle semi brittle shear planes superimpose onto precursory ductile shear bands whereas steeply dipping late brittle planes develop by progressive steepening of structures or sliding across en echelon arrays of veins the comparison between tinos and andros allows us to propose a complete dynamic section of the aegean extending continental crust and emphasizes that the strain localization process depends on both its rheological stratification and its compositional heterogeneity

on the role of isostasy in the evolution of normal fault systems the footwalls of west dipping normal faults that separate the west central colorado plateau from the basin and range province record at least 5 7 km and perhaps as much as 15 20 km of west side up neogene uplift with an axis just 10 20 km west of undeformed plateau strata the uplift is expressed as folding and steep faulting in pre tertiary cratonic and disconformably overlying neogene strata forming a basement cored anticline and coincident topographic high on the western margin of the plateau the authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin profound isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains calling into question several assumptions fundamental to existing models of the evolution of normal fault systems

dating polygenetic metamorphic assemblages along a transect across the western alps multichronometric analyses were performed on samples from a transect in the french italian western alps crossing nappes derived from the brianconnais terrane and the piemonte liguria ocean in an endeavour to date both high pressure hp metamorphism and retrogression history twelve samples of white mica were analysed by 39ar 40ar stepwise heating complemented by two samples from the monte rosa nappe 100 km to the ne and also attributed to the brianconnais terrane one sm nd and three lu hf garnet ages from eclogites were also obtained white mica ages decrease from c 300ma in the westernmost samples zone houille re reaching c 3008c during alpine metamorphism to 548ma in the internal units to the east which reached c 5008c during the alpine orogeny the spatial pattern of eocene k ar ages demonstrates that si rich hp white mica records the age of crystallization at 47 48ma and retains ar at temperatures of around 5008c paleocene early eocene lu hf and sm nd ages recording prograde garnet growth before the hp peak confirm eclogitization in eocene times petrological and microstructural features reveal important mineralogical differences along the transect all samples contain mixtures of detrital syn d1 and syn d2 mica and retrogression phases d3 in greatly varying proportions according to local variations in the evolution of pressure temperature fluid activity deformation p t a d conditions samples from the zone houille re mostly contain detrital mica the abundance of white mica with si46 45 atoms per formula unit increases eastward across the whole traverse phengitic mica grown during hp metamorphism defines the d1 foliation syn d2 mica is more si poor and associated with nappe stacking exhumation and hydrous retrogression under greenschist facies conditions syn d1 phengite is very often corroded overgrown by or intergrown with syn d2 muscovite most importantly syn d2 recrystallization is not limited to s2 schistosity domains micrometrescale chemical fingerprinting reveals muscovite pseudomorphs after phengite crystals which could be mistaken for syn d1 mica based on microstructural arguments alone the cl k ratio in white mica is a useful discriminator as d2 retrogression was associated with a less saline fluid than eclogitization as petrology exerts the main control on the isotope record constraining the petrological and microstructural framework is necessary to correctly interpret the geochronological data described in both the present study and the literature our approach which ties geochronology to detailed geochemical petrological and microstructural investigations identifies 47 48ma as the age of hp formation of syn d1 mica along the studied transect and in the monte rosa area cretaceous apparent mica ages which were proposed to date eclogitization by earlier studies based on conventional thermochronology are due to ar inheritance in incompletely recrystallized detrital mica grains the inferred age of the probably locally diachronous greenschist facies low si syn d2 mica ranges from 39 to 43ma coexistence of d1 and d2 ages and the constancy of non reset d1 ages along the entire transect provides strong evidence that the d1 white mica ages closely approximate formation ages volume diffusion of ar in white mica activation energy e 250 kj mol 1 pressure adjusted diffusion coefficient d 050 03 cm2 s 1 has a subordinate effect on mineral ages compared with both prograde and retrograde recrystallization in most samples

structural and thermochronometric evidence for multi stage exhumation of southern syros cycladic islands greece abstract the attic cycladic metamorphic core complex province was formed during miocene to recent regional back arc extension in response to slab rollback and gravitational collapse the development of several metamorphic core complexes along extensional low angle detachment faults resulted in the exhumation of lower plate rocks and the tectonic denudation of the upper plate that is only sparsely exposed throughout the aegean sea one of these areas is in southern syros where the tectonic configuration includes three tectonometamorphic units separated by two detachment faults the lower plate cycladic blueschist unit underwent late cretaceous eocene hp lt metamorphism and subsequent greenschist facies overprint during oligo miocene times the tectonically overlying greenschist facies upper unit is a tectonic sliver between the cycladic blueschist unit and the structurally highest unit the vari unit which is dominated by quartzofeldspathic gneisses that are affected by four distinct deformation events d1 d4 the late cretaceous upper greenschist facies d1 episode is related to late cretaceous eocene subduction while d2 d4 fabrics were formed in response to late cenozoic extension and exhumation field relations and structural data suggest that the late miocene brittle vari detachment juxtaposes both vari unit and upper unit against the cycladic blueschist unit mylonitic rocks observed at the base of vari unit along the contact with upper unit and zircon and apatite u th he thermochronometry corroborate this scenario with lower plate cycladic blueschist unit rocks recording rapid cooling at 8 10 ma in contrast cooling ages from the vari unit cluster at 13 15 ma indicating rapid exhumation coeval with activity along the livadi detachment on the neighboring island of tinos these data document new evidence that vari unit was affected by a major middle miocene phase of exhumation and an older semi brittle episode both unrelated to late miocene detachment faulting revealing that crustal extension occurred in multiple stages and in a protracted episodic fashion similar to other parts of the cyclades

rb sr isotope studies on tinos island cyclades greece additional time constraints for metamorphism extent of infiltration controlled overprinting and deformational activity this study presents new rb sr age data concerning the metamorphic evolution of the attic cycladic crystalline belt which represents a complex polymetamorphic terrane within the alpidic orogenic belt of the hellenides two major groups of tectonic units can be distinguished metamorphism in parts of the upper units is commonly considered as a cretaceous event in contrast the group of lower units experi enced tertiary high pressure metamorphism which was followed by a medium pressure overprint we focus on the island of tinos where a representative spectrum of the rock units found in the cyclades is exposed in three tectonic units the upper unit the intermediate unit and the basal unit the complete range of tectono metamorphic and magmatic events affecting the attic cycladic crystalline belt is documented by numerous petrological and tectonic studies phyllites and phyllonites from the ophiolitic upper unit yielded rb sr apparent ages phengite whole rock between c 92 and 21 ma the older age differs from the cretaceous dates reported for upper unit rocks elsewhere in the cyclades it is suggested that the sequence studied belongs to the jurassic ophiolites of the hellenides rather than to cretaceous occurrences the spread to younger ages is related to non pervasive rejuvenation and resetting of the rb sr system during tectonic juxtaposition of the upper unit over the intermediate unit the youngest age obtained so far for a sample from the upper unit 21 ma is believed to approximate the timing of tectonic juxtaposition which probably occurred during a regional greenschist facies episode producing a pervasive overprint in the struc turally lower tectonic unit the major phyllite meta gabbro serpentinite sequence of the upper unit is inter preted as an emplacement related ductile shear zone which experienced reworking under brittle conditions in the intermediate unit a gradient in rb sr ages from top c 40 ma to the bottom c 22 ma was recog nized which is interpreted to represent greater effects of fluid infiltration and overprinting in the lower parts of this unit possibly controlled by variable intensity of deformation which might be related to tectonic jux taposition onto the basal unit we suggest that synmetamorphic stacking of all three tectonic units took place during an oligocene miocene greenschist event extensional deformation continued after tectonic stacking and after intrusion of the main granite as is indicated by a rb sr whole rock isochron 15 1 0 6 ma for a ductilely deformed garnet bearing leucogranite from the marginal parts of the main undeformed pluton application of the rb sr dating technique provided no unequivocal evidence that previously pub lished eocene k ar and 40 ar 39 ar dates for high pressure phengites from the lower units are significantly contaminated with excess argon

the tectono metamorphic evolution of a dismembered ophiolite tinos cyclades greece the six exposures of the upper tectonic unit of the cycladic massif occurring on the island of tinos are shown to comprise a metamorphosed dismembered ophiolite complex the common stratigraphic section consisting of tens of metres thick tectonic slices of mafic phyllites overlain by serpentinites and gabbros is considered to have been derived by a combination of thrusting during obduction and subsequent attenuation by low angle normal faults all rock types show evidence of a phase of regional greenschist facies metamorphism which in the case of the phyllites is accompanied by penetrative deformation the greenschist facies metamorphism in gabbros is preceded by high temperature sea floor amphibolite facies alteration whereas in the serpentinites the antigorite forsterite greenschist facies assemblage overprinted an earlier low temperature lizardite serpentinite trace element patterns of the mafic phyllites and a harzbur gitic origin of meta serpentinites suggest a supra subduction zone ssz affinity for the ophiolitic suite 5 o values of phyllites gabbros and serpentinites range from 6 to 15 o model calculations indicate that such values are consistent with low temperature 50 200 c alteration of parent rocks by sea water at varying water rock ratios this would agree with the early low temperature mineralogy of the serpentinites but the early high temperature alteration of the gabbros would require the presence of o enriched sea water the following overall history is suggested for tinos ophiolitic slices 1 oceanic crust was generated at a supra subduction zone spreading centre with high temperature alteration of gabbros 2 tectonic distur bance its early hot stages recorded in an amphibolitic shear zone at the base of serpentinites brought the already cooled ultramafics into direct contact with sea water and caused low 7 serpentinization 3 tectonism after cooling involved thrusting which caused repetition and inversion of the original order of the oceanic suite 4 regional metamorphism of all the ophiolite components at greenschist facies conditions 450 c overprinted the early alteration mineralogy it was probably induced by continued thrusting and piling up of nappes the tinos ophiolite dated as late cretaceous and genetically related to other low pres sure rock units of the same age in the aegean differs in age and degree of dismemberment and metamor phism from ophiolites in mainland greece

granite intrusion in a metamorphic core complex the example of the mykonos laccolith cyclades greece abstract the aegean domain is a well suited place to study the formation of metamorphic core complex mcc and to investigate the role of syn tectonic granites on their development in the northern cyclades the mykonos delos rhenia mcc is characterized by the intrusion of a kilometer scale late miocene pluton of i type granitoids within a migmatitic gneiss dome new combined ams anisotropy of magnetic susceptibility and microstructural studies on the mykonos granitoids together with recently published thermochronological data allow us to use the granitoids as strain markers the mykonos granitoids form a laccolith like intrusion with a n70 e long axis the laccolith is strongly asymmetric with an outlying root zone to the sw and a major body mainly developed to the ne the laccolith construction is due to successive pulses of more or less differentiated magma that intruded the cycladic blueschist unit the attitude of stretching markers suggests an important about 60 vertical axis local rotation phenomenon in the cycladic upper crust during the exhumation of the mykonos mcc structural data suggest a four stage evolution of the mykonos mcc i a first stage characterized by flat shearing toward the n ne and by the formation of a domal structure in migmatitic paragneisses with multi scale generation of folds with axes either perpendicular or parallel to the regional stretching as a result of the interplay between regional n20 e directed extension and ew shortening ii a second stage marked by the emplacement of the mykonos laccolith at 13 5 0 3 ma at the top of the migmatitic paragneisses iii the third stage corresponding to the development of protomylonitic foliations and lineations in the whole laccolith in high to medium temperature conditions and iv the late stage marked by an acceleration of the exhumation of the mykonos mcc this exhumation was accommodated by important rotations of upper crustal blocks during the end of the exhumation processes around 10 ma deformation localized at the top of the laccolith in semi ductile conditions and then in brittle conditions in the major detachment plane our study shows that the cycladic plutonism event had no role on the initiation of the mcc however the geometry of the mykonos intrusion supports that the magmas are sucked into the direction of regional extension and that the intrusion of magmas has caused an acceleration of the last stages of the mcc development this acceleration was marked by a very fast exhumation of the laccolith after its emplacement

crenulation cleavage formation evolving diffusion deformation and equilibration mechanisms with increasing metamorphic grade abstract an integrated microstructural and chemical study of crenulation cleavages developed in chlorite to garnet zone schists from the wenchuan maowen shear zone central china has resulted in the recognition of the deformation and equilibration mechanisms operating during their formation at a range of temperatures deformation during crenulation cleavage formation at chlorite to biotite zone temperatures 520 c is essentially a solution deposition process in which transport occurred by a combination of localized advection and grain boundary diffusion recrystallization and hence equilibration of muscovite in discrete cleavages is recognized by distinct compositional differences between muscovite from different domains crenulation cleavages developed in garnet zone schist are characterized by homogeneous muscovite compositions across domains and microstructures related to intracrystalline deformation indicating an increasing importance of volume diffusion and diffusive equilibration of mica at temperatures greater than 520 c

crustal scale geometry and kinematics of late orogenic extension in the central aegean cyclades and ewia island abstract the aegean continental domain is known to be the site of widespread back arc extension since at least the middle miocene overprinting structures related to the mesozoic cenozoic hellenic orogeny features attributed to early thrusting include the overall ductile deformation within two broad belts that have suffered hp lt metamorphism across the aegean this study summarizes the results of a structural study in the central aegean area cyclades and evvia island examining in particular the relationship between ductile and brittle deformation on a regional scale extension appears to be responsible for most of the ductile deformation within hp rock units that have experienced penetrative greenschist facies and higher grade metamorphic overprinting on each island studied progressive extensional deformation has occurred through the development of a major normal sense detachment zone down to depths of about 18 25 km the geometry of the extensional system on the scale of the central aegean is described taking into account the characteristic features of the regional scale ductile strain field at least two probably three subparallel major north dipping detachment zones are identified trending nw se in the northwestern cyclades and e w in the southeastern cyclades both with initial dips estimated at around 30 45 the present geometry of the extensional system implies that these detachment zones and related metamorphic core complexes interfere with each other two main evolutionary models are considered which can account for such a kinematic link between parallel detachment zones structural data favour the sequential development of synthetic major detachments zones in a direction opposite to the sense of dip of the detachments early oligocene lower miocene detachment type extension in the area studied is related to a late orogenic post thickening back arc setting

fluid rock interaction and thermal evolution during thrusting of an alpine metamorphic complex tinos island greece this study examines the fluid rock interaction and thermal evolution along a thrust that juxtaposes calcite rich marbles of high p t metamorphic unit of the attic cycladic massif greece on top of a lower grade dolomite marble unit the tertiary thrust represents a major phase of tectonic movement related to the decompression of the alpine orogen in the hellenides the stable isotope signatures of the thrust plane and adjacent sections of the footwall and hanging wall rocks are characterized by significant carbon and oxygen isotope depletions the depletion is most pronounced in calcite but is almost entirely missing in coexisting dolomite the isotopic patterns in the thrust zone can be explained by the infiltration of an externally derived water rich h2o co2 ch4 fluid x c x co 2 x ch 4 0 05 at water rock ratios on the order of 0 1 to 0 5 by weight the fluid induced calcite recrystallization is viewed as an important rheological control during thrusting the temperature evolution of the footwall hanging wall and mylonitic tectonic contact was determined by calcite dolomite solvus thermometry histograms of calcite dolomite temperatures are interpreted as indicating a heating of the footwall dolomite marble during the thrusting of the hotter upper plate conversely the hanging wall marble unit was cooled during the thrusting the calcite dolomite thermometry of the thrust plane gives temperatures intermediate between the initial temperatures of the lower and upper marble units and this leads to the conclusion that conductive heat transfer rather than fluid infiltration controlled the thermal evolution during thrusting

deciphering subduction from exhumation in the segmented cycladic blueschist unit central aegean greece the cycladic blueschist unit cbu represents the northern passive margin of the adria continental block and ophiolites that are the remnants of the pindos ocean which were affected by high pressure low temperature metamorphism in the blueschist and eclogite facies during the eocene prior to the lutetian the ophiolitic and margin units were thrust towards the sw inside a ne dipping subduction zone two subsequent exhumation stages are characterized by top to the ne senses of shear i from mantle depths to lower crustal levels before 37 ma which was accommodated by an extensional inversion of the vardar suture zone and ii from deep crustal levels to the near surface between 30 and 20 ma which was accommodated by the north cycladic detachment it is during this late stage of ductile exhumation that the central cyclades core complex was exhumed segmentation of the cbu by normal faults started at 12 ma as recorded by the low temperature thermochronometers and was coeval with block rotation and folding with ns trending axes which were predominantly controlled by the myrthes ikaria strike slip fault in the centre of the cyclades a map restoration of the cbu geometry prior to segmentation has been carried out using available structural and paleomagnetic data the restoration shows that following the cbu exhumation from mantle depths to crustal levels a single core complex was exhumed along a single ne dipping detachment

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

uplift and exhumation of high pressure metamorphic terrains the example of the cycladic blueschist belt aegean sea the cycladic blueschists emerged from a depth of more than 50 km during the tertiary these rocks are now covered only by a thin fraction of the synmetamorphic overburden upper plate remnants of the upper plate include low p crystalline rocks and sediments which have been juxtaposed onto the lower plate blueschists in several stages since the early miocene the low angle contacts operated as normal faults which removed the overburden from above the cycladic blueschists detailed investigations on tinos island indicate that the fractured blocks of the upper plate lying above a low angle normal fault did not rotate this shows that the faults initiated as rather gently dipping fractures similar structures were also reported from other blueschist terrains kinematic analysis of such flat lying faults implies that the synmetamorphic overburden should be mostly located several hundred kilometers away from the present exposure of the blueschists considering that the cycladic blueschist belt exposes successively shallower units in the west and that rocks of the upper plate have an anatolian nature we suggest that these blueschists were dragged from beneath turkey we recognize that the blueschist unit has undergone further thrusting in the final stage of the exhumation as have its counterparts elsewhere in the hellenides the emergence of the blueschists in the tertiary was concomitant with continental collision and thrusting in the hellenides the operation of low angle normal faults with large extensional displacements occurred within this context of collision tectonics this extension occurred parallel to the strike of the convergent orogen

metamorphic core complexes of cordilleran type in the cyclades aegean sea greece the islands of ios and naxos in the cycladic archipelago greece contain elongate domes over which a pervasive north to north northeast stretching lineation is warped these islands may be metamorphic core complexes of cordilleran type involving middle crustal rocks drawn upward and outward from underneath the sedimentary basins now 100 km to the south from ca 25 ma onward during uplift the crystalline rocks now exposed on the islands were deformed noncoaxially in the deeper levels of a major shallow dipping ductile shear zone this shear zone may have connected with low angle normal faults in its upper levels because it is probable that its later history involved the metamorphic complexes being dragged out from under a stretching and fracturing upper plate composed mainly of unmetamorphosed sedimentary and ophiolite suite rocks this model can be extended to explain the exhumation of the high pressure low temperature metamorphic rocks on crete which with the cyclades forms a distended paired metamorphic belt separated by an active sedimentary basin

ductile thrusting recorded by the garnet isograd from blueschist facies metapelites of the ile de groix armorican massif france

map view restoration of aegean west anatolian accretion and extension since the eocene 1 the aegean region greece western turkey is one of the best studied continental extensional provinces here we provide the first detailed kinematic restoration of the aegean region since 35 ma the region consists of stacked upper crustal slices nappes that reflect a complex paleogeography these were decoupled from the subducting african adriatic lithospheric slab especially since 25 ma extensional detachments cut the nappe stack and exhumed its metamorphosed portions in metamorphic core complexes we reconstruct up to 400 km of trench perpendicular ne sw extension in two stages from 25 to 15 ma the aegean forearc rotated clockwise relative to the moesian platform around euler poles in northern greece accommodated by extensional detachments in the north and an inferred transfer fault se of the menderes massif the majority of extension occurred after 15 ma up to 290 km by opposite rotations of the western and eastern parts of the region simultaneously the aegean region underwent up to 650 km of post 25 ma trench parallel extension leading to dramatic crustal thinning on crete we restore a detachment configuration with the mid cycladic lineament representing a detachment that accommodated trench parallel extension in the central aegean region finally we demonstrate that the sakarya zone and cretaceous ophiolites of turkey cannot be traced far into the aegean region and are likely bounded by a pre 35 ma n s fault zone this fault became reactivated since 25 ma as an extensional detachment located west of lesbos island the paleogeographic units south of the izmir ankara sava suture however can be correlated from greece to turkey

exhumation of deep crustal metamorphic rocks and crustal extension in arc and back arc regions we adress the problem of exhumation of metamorphic rocks in arc and back arc positions based on observations of the aegean and tyrrhenian back arc regions in both regions back arc extension has been active for 25 ma at least while convergence and crustal thickening was going on at the thrust front compressional structures are reworked in the back arc domain as extensional flat lying detachments which allow unroofing of the metamorphic pile metamorphic rocks suffer first a dynamic burial during nappe stacking and then fast exhumation when they reach the extensional region we describe a continuous process of burial and exhumation that is contemporaneous with the migration of the thrust front toward external zones the front of extension follows behind at approximately one hundred kilometers at the convergence front continuous subduction of a cold oceanic slab or continuous accretion of continental units keeps a cool p t gradient and hp lt metamorphic rocks are formed at depth the overall cool environment leads to a deep brittle ductile transition and thus to a resistant crust which can sustain its large thickness while the thrust front propagates forward parts of the accretionary wedge which were formed earlier enter the back arc domain which can be already under extension and which is warmer because of a greater distance to the cold slab and the presence of the volcanic arc the brittle ductile transition rises in the thick crust which then becomes unstable and subsequently collapses the exhumation history of metamorphic rocks below detachments is two fold 1 a constantely thickening crust is unroofed by flat lying detachments which rework early thrusts this first period is characterized by a good preservation of hp lt parageneses 2 the second period is when rocks are in the zone of crustal scale extension of the back arc region deep crustal metamorphics are exhumed below flat lying detachements which affect the whole crust

the geological signature of a slab tear below the aegean in this paper we explore the geology of the aegean region in the miocene to identify the geological signature of a first order slab tear observed in all tomographic models from 15 to 8 ma the tear is associated spatially and timely with a fast clockwise rotation of the external hellenides alkaline volcanism high temperature metamorphic domes with a predominance of north dipping detachments and south westward migration of granitoid intrusions these features suggest a warmer geodynamic environment during the rotation and the impact of a hot mantle flow associated with the tear the 8 ma duration between the first high temperature metamorphic domes in the centre of the archipelago and the beginning of the fast rotation may correspond to the time needed for the slab to bend stretch and finally tear

pressure temperature path of sanbagawa prograde metamorphism deduced from grossular zoning of garnet the zonal structure of prograde garnet in pelitic schists from the medium grade garnet zone and the higher grade albite biotite zone was examined to investigate the evolution of prograde p t paths of the sanbagawa metamorphism the garnet studied shows a bell shaped chemical zoning of the spessartine component which decreases in abundance from the core towards the rim almandine and pyrope contents and xmg mg mg fe2 increase monotonously outwards the general scheme of the zonal structure for grossular content xgrs ca fe2 mn mg ca can be summarized as 1 xgrs increases outwards inner segment and reaches a maximum at an intermediate position between the crystal core and the rim then decreases towards the outermost rim outer segment 2 the inner segment of garnet in the garnet zone samples tends to have a higher xgrs xsps values for a given xsps than those in the albite biotite zone samples 3 average xsps at the maximum xgrs position in the albite biotite zone samples ranges from 0 02 to 0 12 and is lower than that in the garnet zone samples 0 13 0 32 4 the maximum xgrs in the albite biotite zone samples 0 34 0 39 on average tends to be higher than that in the garnet zone samples 0 26 0 36 and 5 differences of xgrs between the maximum and rim in the albite biotite zone samples are between 0 10 and 0 14 and higher than those in the garnet zone samples 0 11 these facts imply that albite biotite zone materials a were recrystallized under lower dp dt conditions at an early stage of the prograde metamorphism b began their exhumation under higher p t conditions and c have been continuously heated during exhumation for a longer duration than the garnet zone materials the systematic changes of prograde p t paths can be interpreted as documenting the evolution of the sanbagawa subduction zone

dynamics of orogenic wedges and the uplift of high pressure metamorphic rocks subduction accretion complexes can be approximated as wedge shaped continua with a rigid buttress behind and a subducting litho spheric slab beneath thick wedges undergoing prograde metamorphism have a negligible long term yield strength and are likely to exhibit a complex nonlinear viscous rheology such a wedge will tend to deform internally until it reaches a stable configuration in which the gravitational forces generated by the wedge geometry balance the traction exerted on its underside by the subducting slab accretion of material at the wedge front will lengthen the wedge and cause it to shorten internally to regain the stable geometry this shortening will be expressed as late out of sequence thrusting backthrusting and folding conversely underplating of sediment or crustal slices will thicken the wedge which may need to extend internally to regain stability extension will cause listric normal faults that may merge downward into zones of ductile extension continued underplating at depth and compensating extension above provides a mechanism for bringing high p low t metamorphic rocks to upper levels in the rear of the wedge where they are commonly observed many major tectonic boundaries in convergent orogens such as the coast range thrust in the franciscan complex major nappe contacts in the alps and the contact between the nevado filabride and higher betic nappe complexes in the betic cordillera show abrupt increases in metamorphic grade downward across them this is consistent with their origin or reactivation as uplift related extensional structures

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

exhumation of high pressure rocks a review of concepts and processes the exhumation of high pressure metamorphic rocks requires either the removal of the overburden that caused the high pressures or the transport of the metamorphic rocks through the overburden exhumation cannot be achieved simply by thrusting or strike slip faulting it may be caused by erosion of shortened and thickened crust but this is unlikely to be the only mechanism for exhuming rocks from depths greater than about 20 km one or more of the following additional mechanisms may be involved 1 corner flow of low viscosity material trapped between the upper and lower plates in a subduction zone can cause upward flow of deeply buried rock and may explain some occurrences of high pressure tectonic blocks in melange this process does not however appear to be adequate to explain the exhumation of regional high pressure terrains 2 buoyancy forces acting directly on metamorphic rock bodies may cause them to rise relative to more dense surroundings this is likely to be the most important mechanism of exhumation of crustal rocks subducted into the mantle but cannot explain the emplacement of coherent tracts of high density metamorphic rock into shallow crustal levels some high pressure blocks emplaced at shallow levels in accretionary terrains may have been entrained in diapiric intrusions of low density mud or serpentinite 3 extension driven by the forces associated with contrasts in surface elevation may explain the exhumation and structural setting of many high pressure terrains extension may occur in the upper part of an accretionary wedge thickened by underplating or it may affect the whole lithosphere in a region of intracontinental convergence if surface elevation has been increased by the removal of a lithospheric root in the second case extension may be accompanied by magmatism and an evolution towards higher temperature during decompression of the metamorphic terrain

from static alteration to mylonitization a nano to micrometric study of chloritization in granitoids with implications for equilibrium and percolation length scales strain accommodation in upper crustal rocks is often accompanied by fluid mediated crystallization of phyllosilicates which influence rock strength and shear zone formation the composition of these phyllosilicates is frequently used for pressure temperature time constraints of deformation events although it is often highly heterogeneous even in mylonites this study investigates the reactions producing a phyllosilicate chlorite in and below grenschist facies conditions and the variations in chlorite composition along a strain gradient in the variscan bielsa granitoid axial zone pyrenees compositional maps of chlorite including iron speciation are compared to nanostructures observed by transmission electron microscopy in increasingly strained samples and related to mechanisms of fluid percolation in the bielsa granitoid altered at the late variscan alpine age shear zones are found with high strain gradients the undeformed granitoid exhibits local equilibria pseudomorphic replacement and high compositional heterogeneities in chlorite this is attributed to variable reaction mechanisms at nanoscale and element supply little interconnected intra and inter grain nanoporosity and isolation of fluid evolving in local reservoirs in samples with discrete and mm sized fractures channelized fluid triggered the precipitation of homogeneous alpine chlorite in fractures preserving late variscan chlorite within the matrix in low grade mylonites where brittle ductile deformation is observed micro and nanocracks and defects allows the fluid percolating into the matrix at the scale of hundreds of m this results in a more pervasive but incomplete replacement of late variscan chlorite by alpine chlorite despite the high strain in studied granitoids deformed under greenschist facies conditions local equilibria and high compositional heterogeneities in phyllosilicates as chlorite are therefore preserved according reaction mechanisms and element mobility controlled by i matrix fracture porosity contrasts at nanoscale and ii the location and interconnection of nanoporosity between crystallites of phyllosilicates this preservation influences our ability to reconstruct the pre and syn kinematic metamorphic history of granitic rocks in low grade units of orogens

age resetting of hanging wall rocks above a low angle detachment fault tinos island aegean sea the central aegean region has been affected by extensional tectonics since at least the oligo miocene on tinos island cyclades greece a low angle normal fault places low grade metamorphic rocks the upper unit above high pressure rocks the cycladic blueschist unit k ar and 40ar 39ar ages were obtained by us on white micas amphiboles and whole rock samples separated from various metamorphic rocks representing different structural levels of the hanging wall the hanging wall upper unit is commonly thought to have resided at shallow crustal levels since late cretaceous times but our geochronological data supported by previously published rb sr dating brocker m franz l 1998 rb sr isotope studies on tinos island cyclades greece additional time constraints for metamorphism extent of infiltration controlled overprinting and deformational activity geol mag 135 3 369 382 indicate severe age resetting of the base of the hanging wall during tertiary times amphiboles from the top of the hanging wall section yielded late cretaceous ages which correlate well with other cretaceous upper unit rocks in the cyclades their preservation implies that tertiary age resetting was mainly confined to the lower part of the upper unit while upper parts retained older ages the base of the hanging wall section where age resetting and ductile deformation are most pronounced is taken to represent a part of a thick extensional shear zone that operated in low greenschist facies conditions during tertiary time the results of one dimensional thermal modeling suggest that warm footwall rocks emerging from great depth subsequently to hp lt metamorphism may have supplied the heat required for the metamorphism and ductile deformation at the base of the hanging wall the model also indicates that only minor cooling of the footwall during decompression is allowed if the footwall is to warm up the hanging wall this is a priori consistent with the isothermal decompression path of footwall blueschists and eclogites deduced from previous petrological studies on tinos

geodetic determination of the kinematics of central greece with respect to europe implications for eastern mediterranean tectonics we use a new satellite laser ranging global positioning system slr gps solution at seven sites in anatolia and aegea to obtain a better definition of the extrusion motion of the anatolian aegean block with respect to europe we show that this motion can be described in a first approximation by a counterclockwise rotation which transfers most of the motion of arabia to anatolia we combine 78 displacement vectors obtained at common points of two triangulation nets measured in central greece in 1895 and 1975 with the slr gps measurements to compute the velocity field over greece with respect to europe these measurements indicate that central greece is a zone of extension between the anatolian aegean counterclockwise rotation to the south and the northern greece clockwise rotation to the north this extension is principally localized within the gulf of corinth to the east but is distributed to the west we then extrapolate this velocity field to the whole aegea and western anatolia using recently published gps results as well as the slr results the narrow dextral north anatolian fault which limits the velocity field to the north progressively gives way to a much wider boundary zone where extension becomes dominant we show that the collision between the mediterranean ridge and africa began 3 6 ma and we describe the modifications that this collision has produced on the kinematic pattern both in aegea and on the mediterranean ridge