coupling the wrf model with a temperature index model based on remote sensing for snowmelt simulations in a river basin in the altay mountains north west china

how to resist subduction evidence for large scale out of sequence thrusting during eocene collision in western turkey significant along strike variations have locked large parts of the alpine subduction complex in the eastern mediterranean in the eocene and defined the end of high pressure accretion in western turkey structural analysis reveals that the anatolide belt in western turkey formed under greenschist facies metamorphic conditions in the eocene when a high pressure metamorphic fragment of the adriatic plate the cycladic blueschist unit was thrust onto the imbricated mid crustal units of the anatolian microcontinent the menderes nappes the contact between the cycladic blueschist unit and the menderes nappes the cyclades menderes thrust represents an out of sequence ramp which cuts up section towards the south the lack of alpine high pressure fabrics below the cyclades menderes thrust implies c 35 km of exhumation of the cycladic blueschist prior to its eocene emplacement on top of the menderes nappes structure and geodynamic evolution of the anatolide belt are in striking contrast to the neighbouring aegean and contradict the model of a laterally continuous orogenic zone in which the anatolide microcontinent is interpreted as an eastern extension of the adriatic plate

early to mid silurian extrusion wedge tectonics in the central scandinavian caledonides we present evidence for an extrusion wedge in the scandian fold thrust belt of the central scandinavian caledonides seve nappe complex rb sr multimineral geochronology in synkinematic assemblages indicates simultaneous movements at the normal sense roof shear zone and at the reverse sense floor shear zone between 434 ma and 429 ma a sm nd age of 462 ma from a mylonitic garnet mica schist documents prograde garnet growth and possible incipient subduction pressure temperature pseudosection calculations provide evidence for eclogite facies metamorphic conditions and nearly isothermal decompression at 670 50 c from 17 5 to 14 5 kbar in garnet kyanite mica schists during reverse sense shearing and from 15 to 11 kbar in garnet mica schists during normal sense shearing these data and the presence of decompression related pegmatites dated at 434 ma and 429 ma indicate that the seve nappes form a large scale extrusion wedge this wedge extends along strike for at least 150 km and marks an early stage of ultrahigh pressure metamorphism exhumation and orogenic wedge formation in this part of the scandinavian caledonides predating the major post 415 ma ultrahigh pressure exhumation processes in southwestern norway

an oligocene extrusion wedge of blueschist facies nappes on evia aegean sea greece implications for the early exhumation of high pressure rocks we show that the styra nappe of the cycladic blueschist unit on evia constitutes a wedge of high pressure rocks extruded during early stages of orogeny the nappe pile on evia was assembled during d 2 top to the ssw directed thrusting in restored oligocene coordinates which emplaced the styra and ochi nappes of the cycladic blueschist unit above the almyropotamos nappe between c 33 and 21 ma peak metamorphism of the almyropotamos nappe at c 23 ma occurred at lower metamorphic pressure showing exhumation of the styra nappe during underthrusting and burial of the almyropotamos nappe this exhumation was largely accomplished by the d 2 top to the nne displacing mt ochi normal sense shear zone normal shearing commenced at c 33 ma under peak high pressure metamorphism in the styra and ochi nappes fission track dating indicates slow cooling after d 2 in the styra nappe subsequently the former thrust contact between the almyropotamos nappe and the styra nappe was reactivated as a d 3 top to the ese extensional shear zone and this extensional phase led to the formation of a number of middle to late miocene graben our main conclusion is that there is strong evidence for an oligocene extrusion wedge accomplishing the early exhumation of the styra nappe which demonstrates the importance of extrusion wedges for the initial exhumation of the cycladic blueschist unit

structural and petrological analyses of the frido unit southern italy new insights into the early tectonic evolution of the southern apennines calabrian arc system abstract this study provides new data on the deformation and metamorphic evolution of the jurassic to upper oligocene frido unit an ocean continent transition oct unit belonging to the ligurian accretionary complex lac by means of the integration of structural analysis petrological investigations and a revision of the stratigraphical setting the frido unit representing the main metamorphic component of the lower middle miocene lac in southern italy is characterized by a multistage tectonic evolution including i two progressive deformation phases involving the development under relatively high pressure metamorphic conditions of an early cleavage associated with isoclinal folds within the framework of a dominant se ward tectonic transport ii a third deformation stage involving the growth of lower pressure na amphibole along extensional shear surfaces therefore probably marking the onset of tectonic exhumation and iii two very low temperature deformation phases characterized by the development of kink folds and associated thrusts probably related to the late tectonic emplacement of the accretionary wedge onto the outer sectors of the apennine domain with a prevailing tectonic transport first toward the ne and then toward the nw in order to clarify the metamorphic evolution of the frido unit petrologic analyses were focused on its metasedimentary pelitic succession here mineral parageneses including carpholite well documented for the first time in this study and potassic white mica yielded peak pressure of 1 2 1 4 gpa and temperature around 350 c thus indicating a high pressure very low temperature metamorphism and a p t t path characterized by a rapid exhumation without any greenschist facies overprint in comparison with similar units cropping out in northern calabria tuscany and corsica the frido unit experienced one of the coldest burial exhumation histories

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

no need for lithospheric extension for exhuming u hp rocks by normal faulting abstract extensional deformation is commonly considered most important for exhuming rocks from great depths however the necessary space for extending the lithosphere is usually lacking we show that significant exhumation of u hp rocks occurs in extrusion wedges which have a normal fault at their top and a thrust fault at their base the normal fault at the top of an extrusion wedge is a geometric effect and does not result from lithospheric extension therefore the exhumation of u hp rocks in extrusion wedges allows substantial exhumation beneath a normal fault during horizontal shortening and does not cause lithospheric attenuation

deformation partitioning during transpressional emplacement of a mantle extrusion wedge the ronda peridotites western betic cordillera spain abstract composite tectonic emplacement of the world9s largest outcropping body of subcontinental mantle rocks the ronda peridotites occurred during early miocene continental subduction and as a result of oblique plate convergence partitioning of transpressional deformation between coeval orogen parallel wrenching and orogen perpendicular pure thrusting components is recorded by shear zone kinematics and dynamothermal metamorphism in the footwall to the ultramafic rocks left lateral shear characterizing the deeper high pressure eclogitic portions of the continental subduction system propagated through the mantle into the overlying continental crust of the overriding plate whereas top to the foreland frontal thrusting dominated at the leading edge of the hot peridotite body top to the hinterland shear along the upper contact of the peridotites is consistent with the kinematics expected for an extrusion wedge consisting of subcontinental mantle rocks on the other hand coeval strike parallel extension and thinning of the crustal rocks overlying the peridotites confirms that similarly to other alpine mediterranean examples partitioned transpression resulted in the development of a complex deformation pattern with kinematically linked shear zones aiding exhumation the proposed model provides a new coherent scenario for syn convergence peridotite emplacement and exhumation in the western betic cordillera

structural evolution of the usak gure supra detachment basin during miocene extensional denudation in western turkey the usak gure basin is a ne sw trending extensional basin located in the northern part of the menderes massif in western anatolia the usak gure basin contains a lower to upper miocene volcano sedimentary succession that records the unroofing of the metamorphic rocks of the menderes metamorphic core complex we propose a new structural mechanism based on geological mapping and detailed kinematic fault analysis from each of the evolutionary phases we also propose that north to ne dipping low angle detachment surfaces define the basin boundaries and have identified three stages of deformation throughout the miocene the early miocene deformation phase d 2 is characterized by low angle normal faulting simav detachment fault in the supra detachment usak gure basin which marks the initiation of the extensional tectonics during the latest oligocene the middle miocene deformation phase d 3 refers to volcano tectonic activities during accumulation of the inay group the late miocene deformation phase d 4 is related to late miocene tectonic activity widely responsible for deposition of the asartepe formations and uplift of the metamorphic rocks in the usak basin margin in addition we propose that the eastern part of the menderes massif was delimited by the usak mugla transtensional transfer zone from middle miocene time throughout the eastern part of the menderes metamorphic core complex

coeval high pressure metamorphism thrusting strike slip and extensional shearing in the tauern window eastern alps 1 recent findings for a young 31 5 0 7 ma age of high pressure metamorphism at 90 km depths in the eclogite zone of the tauern window eastern alps prompt the question about the timing of the structural development of the tauern window and its relation to high pressure metamorphism we show that all major structures in the tauern window resulting from strong n s lithospheric shortening and simultaneous minor e w extension began developing coevally with high pressure metamorphism in the eclogite zone large scale strike slip shear zones started to form at 32 30 ma and facilitated the spatial accommodation of simultaneous shortening and extension at least some of the strike slip and extensional shear zones operated into the middle miocene either continuously or intermittently with pronounced activity at 21 15 ma the considerable exhumation of the eclogite zone from 90 km depths into the middle crust and the tectonic development of its framework occurred within only 1 2 ma after eclogitization this is evidenced by almost identical ages for eclogite facies metamorphism and for the development of the major structures that bound the eclogite zone under blueschist and greenschist facies metamorphic conditions we discuss a tectonic model in which considerable transpressional shortening and thickening took place in the present central southern part of the tauern window we propose that the tauern window nucleated here and that most of the regional deformation at 32 30 ma is today found at the periphery of the window and in the adjacent austroalpine units afterward transpression continued the window grew to the e w and n and deformation progressed to those parts of the window ductile deformation in the present day surface level ceased at 15 ma

ductile extrusion of the higher himalayan crystalline in bhutan evidence from quartz microfabrics quartz textures measured from deformed quartz tectonites within the lesser himalaya and higher himalaya crystalline of bhutan show similar patterns orientation and distribution of the quartz crystallographic axes were used to confirm the regional shear sense the asymmetry of c axis and a axis patterns consistently indicates top to the south shearing the obliquity of the texture and the inferred finite strain plane strain to moderately constrictional suggest the strain regime had a combination of rotational and irrotational strain path in most of the samples from the bhutan himalaya the inferred deformation mechanisms suggest moderate to high temperature conditions of deformation that produced the observed crystallographic preferred orientation much higher temperature of deformation is indicated in the quartz veins from a leucogranite the observed ductile deformation is pervasively developed in the rocks throughout the investigated area the intensity of deformation increases only slightly in the vicinity of the main central thrust simultaneous southward shearing within a large part of the higher himalaya crystalline near and above the main central thrust and normal faulting across the south tibetan detachment is explained by the tectonically induced extrusion of a ductily deforming wedge the process of extrusive flow suggested here can be approximated quantitatively by channel flow models that have been used to describe subduction zone processes channel flow accounts for some observed phenomena in the himalayan orogen such as inverted metamorphic sequences near the main central thrust not related to an inversion of isotherms and the syntectonic emplacement of leucogranites into the extruding wedge locally leading to an inversion of isotherms due to heat advection

boundaries of mantle lithosphere domains in the bohemian massif as extinct exhumation channels for high pressure rocks abstract five domains microplates have been recognized by seismic anisotropy in the mantle lithosphere of the bohemian massif the mantle domains correspond to major crustal units and each of the domains bears a consistent fossil olivine fabric formed before their variscan assembly the present day mantle fabric indicates that this process consisted of at least three oceanic subductions each followed by an underthrusting of the continental lithosphere the seismic anisotropy does not detect remnants of the oceanic subductions but it can trace boundaries of the preserved continental domains subsequently underthrust along the paths of previous oceanic subductions the most robust continent continent collision was followed by westward underthrusting of the brunovistulian mantle lithosphere still detectable by seismic anisotropy more than 100 km beneath the moldanubian mantle lithosphere major occurrences of the high pressure ultra high pressure hp uhp rocks follow the ene and nne oriented sutures and boundaries of the mantle lithosphere domains mapped from three dimensional modeling of body wave anisotropy the hp uhp rocks are products of oceanic subductions and the following underthrusting of the continental crust and mantle lithosphere exhumed along the mantle boundaries the close relation of the mantle sutures and occurrences of the hp uhp rocks near the paleosubductions testifies for models interpreting the granulite garnet peridotite association by oceanic continental subduction underthrusting followed by the exhumation of deep seated rocks our findings support the bivergent subduction model of tectonic development of the central part of the bohemian massif the inferences from seismic anisotropy image the bohemian massif as a mosaic of microplates with a rigid mantle lithosphere preserving a fossil olivine fabric the collisional mantle boundaries blurred by tectonometamorphic processes in easily deformed overlying crust served as major exhumation channels of the hp uhp rocks

age and temperature constraints on metamorphism and exhumation of the syn orogenic metamorphic complexes of northern apennines italy abstract the apennine range is a young convergent orogen that formed over a retreating subduction zone syn orogenic metamorphic rocks are exposed in the mid tuscan ridge tuscan coast and tuscan archipelago and provide information about processes of continental subduction and exhumation associated with accretion and retreat apatite and zircon fission track analyses were applied to some of these syn orogenic metamorphic rocks the new low temperature thermochronological data helped to constrain the timing of the metamorphic peak and the age and modality of exhumation of these rocks that were structurally buried at 20 to 40 km depth during the main tectonogenic phase of the northern appenine belt in the giglio and elba islands and in the monti dell uccellina along the coast minimum ages of partially reset zircon samples yielded a first time constraint on the late oligocene age of the metamorphic peak the ca 27 ma obtained at the monti dell uccellina is coeval to that found in the alpi apuane located at the northern termination of the mid tuscan ridge the data from the tuscan archipelago point to a slightly older age in the monti pisani south of the alpi apuane and in the argentario promontary along the coast south of the monti dell uccellina completely reset zircon samples but composed by different populations were behaving as multiple thermochronometers and confirm the already proposed isothermal nature of the exhumation occurred after the metamorphic peak zircon p1 peak indicated that at 13 10 ma rocks were already at shallow crustal levels

continental origin of the bibong eclogite southwestern gyeonggi massif south korea eclogite is a high pressure hp metamorphic rock that provides important information about the subduction of both continental and oceanic crusts in this study we present shrimp zircon u pb isotopic data for a suite of the basement gneisses to investigate the origin of the proterozoic bibong eclogite in the hongseong area south korea zircon grains from the basement felsic gneisses yielded paleoproterozoic protolith ages ranging from ca 2197 to 1880 ma and were intruded by syenite at ca 750 ma a hp regional metamorphic event of triassic age ca 255 227 ma is recorded in the zircon rims of the country rocks which is also observed in the zircons from the eclogite the contacts between the bibong eclogite and its host rocks support an origin for the proterozoic protoliths indicating continental intrusions the hongseong area thus preserves evidence for the triassic collision indicating a tectonic linkage among the northeast asian continents

to be or not to be that is the question the cretan extensional detachment greece we present new structural data from the contact zone between the high pressure phyllite quartzite unit pq and the overlying non high pressure tripolitza unit in east central crete for testing pro

the weak and superfast cretan detachment greece exhumation at subduction rates in extruding wedges low angle normal faults detachments are only efficient agents for bringing rocks from 40 100 km depth back to the earth s surface if they operate with extreme slip rates exceeding 20 km ma 1 here we propose a slip rate of 20 30 km ma 1 for the cretan detachment in the aegean greece the cretan detachment and the subjacent subduction thrust bounded an extruding wedge above the miocene hellenic subduction zone during exhumation the high pressure rocks in the wedge were not significantly deformed very low shear coupling at the bounding faults which are therefore weak is needed to prevent significant deformation in the extruding wedge the proposed slip rate of 20 30 km ma 1 is similar to the subduction rate of 35 45 km ma 1 at the hellenic subduction zone we argue that extruding wedges can only slip at rates similar to subduction rates if there is very low shear coupling at the bounding faults which may also explain the paradox of almost non deformed but very rapidly exhumed rocks

a key extensional metamorphic complex reviewed and restored the menderes massif of western turkey article i nfo this paper provides a review of the structure and metamorphism of the menderes massif in western turkey and subsequently a map view restoration of its neogene unroofing history exhumation of this massif among the largest continental extensional provinces in the world is generally considered to have occurred along extensional detachments with a ne sw stretching direction restoration of the early miocene history however shows that these extensional detachments can only explain part of the exhumation history of the menderes massif and that ne sw stretching can only be held accountable for half or less of the

alpine high pressure metamorphism at the almyropotamos window southern evia greece the alpine orogenic belt of the hellenides has been strongly reworked by ductile and brittle extensional tectonics extensional structures have affected the central aegean region and obliterated much of the original orogenic architecture since at least early miocene times in the area of almyropotamos on the island of evia flanking the western part of the aegean a unique remnant compressional nappe stack involving tertiary metamorphic rocks has been preserved this nappe sequence comprises a high pressure rock unit on top of a lower grade unit the upper unit south evia blueschist belt is thought to be the westward continuation of the cycladic blueschist belt metamor phosed at high pressure conditions during late cretaceous eocene times the underlying unit the almyropotamos unit is a continental margin sequence covered by a flysch and containing lutetian nummulites indicating that this unit accumulated sediments until at least late eocene times in the present study we analyse the petrology of the almyropotamos nappe stack and define the p t conditions of each of the different rock units exposed there the presence of glaucophane law sonite rimmed by epidote and jadeite 70 mol suggest that peak p t conditions in the south evia blueschist belt reached approximately 10 12 kbar and 350 450 c unlike previous studies which estimated that the underlying almyropotamos unit reached only greenschist facies conditions glau cophane relics and si rich phengites were found by us in this unit these indicate that high pressure metamorphism and crustal thickening in this part of the aegean lasted until at least the late eocene or early oligocene we note that in this respect the architecture of southern evia resembles that of north ern greece olympos ossa our structural data indicate that rock units in the almyropotamos area record different folding phases with the south evia blueschist belt having a more complex fold his tory than the underlying almyropotamos unit the entire nappe stack shares large scale folds which are e w trending and locally overturned to the south and which may represent at present coordi nates n s contraction and nappe transport

exhumation of the ultrahigh pressure tso morari unit in eastern ladakh nw himalaya a case study exhumation processes of the ultra high pressure uhp tso morari dome nw himalaya are investigated using structural petrological and geochronological data the uhp tso morari unit is bounded by the low grade metamorphic indus suture zone to the ne and mata unit to the sw three deformation phases d1 d2 and d3 are observed only d3 is common to the uhp unit and the surrounding units in the uhp unit the first deformation phase d1 produced upright folds under eclogitic conditions 20 kbar 580 60 c d1 is overprinted by d2 structures related to a nw se trending open anticline this phase is characterized by blueschist mineral associations and corresponds to the quasi isothermal decompression from a depth of 90 km eclogitic conditions up to 30 40 km the final exhumation phase of the tso morari unit is dominated by tectonic denudation and erosion d3 associated with a slight temperature increase radiochronological analyses indicate that the uhp exhumation process began during the eocene exhumation was fast during d1 d2 and slowed down through d3 in oligocene time the change in the deformation style from d1 d2 to d3 in the tso morari unit coincides with changes in the exhumation rates and in the metamorphic conditions these changes may reflect the transition from an exhumation along the subduction plane in a serpentinized wedge to the vertical uplift of the tso morari unit across the upper crust

crystallization and very rapid exhumation of the youngest alpine eclogites tauern window eastern alps from rb sr mineral assemblage analysis multimineral rb sr internal isochrons from eclogite facies rocks of the eclogite zone tauern window eastern alps consistently yield an early oligocene age of 31 5 0 7 ma this age has been obtained both for late prograde dehydration related eclogitic veins and for rocks variably deformed and recrystallized under eclogite facies conditions 2 0 2 5 gpa 600 c initial sr isotopic equilibria among all phases indicate absence of significant post eclogitic isotope redistribution processes therefore the ages date eclogite facies assemblage crystallization equilibria also prove that no prolonged pre eclogite facies history is recorded in the rocks instead subduction prograde mineral reactions and eclogitization proceeded rapidly fast exhumation immediately after eclogitization with minimum rates 36 mm a is inferred from a 31 5 0 5 ma internal mineral isochron age of a post eclogitic greenschist facies vein assemblage such rates equal typical subduction rates late eocene to early oligocene subduction of the european continental margin with subsequent rapid exhumation of high pressure nappe complexes has previously been recognized only in the western alps the new data signify synchronous continental collision all along the alpine belt our results demonstrate the unique potential of rb sr assemblage system analysis for precise dating of both eclogite facies and post eclogitic events thus for precisely constraining exhumation rates of deep seated rocks and for straightforward linkage of petrologic evidence with isotopic ages

high pressure metamorphism in the aegean eastern mediterranean underplating and exhumation from the late cretaceous until the miocene to recent above the retreating hellenic subduction zone 1 we report 40ar 39ar ages from various tectonic units in the aegean and westernmost turkey on the basis of published geochronologic data and our 40ar 39ar ages we propose that the aegean is made up of several high pressure units which were successively underplated from the late cretaceous until the miocene ages for high pressure metamorphism range from 80 83 ma in parts of the vardar izmir ankara suture zone in the north to 21 24 ma for the basal unit in the cyclades and the external high pressure belt on crete in the south published seismic data suggest that high pressure metamorphism is currently occurring underneath crete younging of high pressure metamorphism in a southerly direction mimics the southward retreat of the hellenic subduction zone we propose that distinct stages of high pressure metamorphism were controlled by the underthrusting of fragments of mainly thinned continental crust and that these punctuated events were superposed on progressive slab retreat by far most of the exhumation of the high pressure units occurred early during the orogenic history in a forearc position

the cretan ophiolite bearing melange greece a remnant of alpine accretionary wedge abstract new data collected in central crete on the ophiolite bearing units result in a better understanding of the role and tectonic significance of these units in the construction of this segment of the hellenides these nappes are composed of three main tectonic units that characterized by different metamorphic facies conditions are represented by an un metamorphosed lower unit a greenschist to hp greenschist facies intermediate unit and a blueschist facies upper unit these chaotic thrust nappes include blocks of oceanic and continental deriving rocks and can be considered as a remnant of an accretionary complex the lower unit represents the toe of the wedge whereas the intermediate and upper units refer to the innermost and deeper subducted portions exhumed and superimposed on top of each other during the early stages of continental collision the structural evolution of the accretionary wedge was controlled by four main contractional deformation events that including distinct groups of structures developed at different crustal levels were driven by sse and ssw directions of tectonic transport our data strongly suggest that the ophiolite bearing tectonic wedge was accreted during the paleogene subduction of a late jurassic cretaceous oceanic realm beneath the continental margin of the pelagonian domain and it was successively involved in the continental collision with the adria block the greenschist to blueschist facies metamorphism and the subsequent exhumation and emplacement of the intermediate and upper units above the frontal portion of the wedge may mainly be due to deep duplexing marking the onset of continental collision we thus suggest that the ophiolite bearing units of crete represent a single suture zone related to the closure of a unique oceanic domain pindos cycladic ocean subducted beneath the internal hellenides platform continental domains thus assuming the significance of a southern oceanic seaway of the largest eastern neotethys developed since the triassic between eurasia and africa

eocene tectonometamorphism on serifos western cyclades deduced from zircon depth profiling geochronology and mica thermochronology abstract phengite bearing metasedimentary sequences preserving relict glaucophane from serifos western aegean are indicative of high pressure conditions during cycladic blueschist metamorphism depth profiling and conventional sims u pb geochronology and o isotope analysis on zircon from highly strained orthogneisses at the base of the sequence reveal xenocrystic zircon with varying degrees of recrystallization one end member population has needle like or prismatic morphologies is internally oscillatory zoned with little to no rim material created during recrystallization these zircons yield triassic to carboniferous ages elevated th u and 18 o mostly ranging between 4 and 11 in marked contrast a separate zircon population has a spongy structure created by complete recrystallization of the pre existing crystal these zircons possess low th u and flat hree patterns and yield eocene ages with 18 o 7 chondrite normalized ree profiles are extremely depleted within this spectrum other zircons show variable states of recrystallization and mixed ages regression of u pb data from three mylonitic orthogneiss samples that exhibit near complete recrystallization and similar age depth profiles yields c 40 ma ages these new data are the first geochronological constraints that successfully demonstrate an eocene metamorphic event in the western cyclades and new 40 ar 39 ar phengitic mica ages of 38 32 ma presented here suggest the metamorphic wedge was exhumed into the shallow crust shortly thereafter

late cenozoic tectono sedimentary evolution of the ulukisla basin progressive basin development in south central turkey the ulukisla basin is one of the most important late cretaceous cenozoic basins in central anatolia the basin is surrounded by the bolkar mountains of tauride platform in the south the nigde massif of central anatolian crystalline complex to the north and the ecemis fault zone and aladag mountains in the east the fact that time interval proposed for the formation of ulukisla basin is quite wide and more than one tectonic regime prevailed in the region have led to various suggestions concerning the evolution of the basin while the suggestions majorly examine the character of the basin during the late cretaceous early cenozoic the number of detailed studies on the status of the basin in the late cenozoic is limited in this study we focused on the less studied late cenozoic evolution to differentiate the tectonic phases that controlled the development of ulukisla basin through structural data and elaborate the responses of sedimentation and paleogeography during this period through detailed facies analyses our findings indicate that the ulukisla basin which started to develop as a supradetachment basin in the late cretaceous has continued its extensional development progressively during its cenozoic history while the relatively well studied early cenozoic sequences represent a marine environment that was rapidly changed shallow to deep sea environment and then gained a shallow character by the middle eocene sedimentary features and fossil contents of the late cenozoic units characterize deposition started in a paralic environment changing into a terrestrial environment rapidly as a result of isolation by the uplifting of surrounding topographies while the basin continues its development under an extensional tectonic regime however the extensional basin history surceased in post middle eocene and post middle miocene probably caused by the closing processes of the different branches of neotethys ocean

the geometry and timing of orogenic extension an example from the western italian alps contacts between rocks recording large differences in metamorphic grade are indicative of major tectonic displacements low p upon high p contacts are commonly interpreted as extensional i e material points on either side of the contact moved apart relative to the palaeo horizontal but dating of deformation and metamorphism is essential in testing such models in the western alps the piemonte ophiolite consists of eclogites t 550 600 c and p 18 20 kbar structurally beneath greenschist facies rocks t 400 c and p 9 kbar mapping shows that the latter form a kilometre wide shear zone the gressoney shear zone gsz dominated by top se movement related to crustal extension rb sr data from micas within different gsz fabrics which dynamically recrystallized below their blocking temperature are interpreted as deformation ages ages from different samples within the same fabric are reproducible and are consistent with the relative chronology derived from mapping they show that the gsz had an extensional deformation history over a period of c 9 myr between c 45 36 ma this overlaps in time with the eclogite facies metamorphism the gsz operated over the entire period during which the footwall evolved from eclogite to greenschist facies and was therefore responsible for eclogite exhumation the discrete contact zone between eclogite and greenschist facies rocks is the last active part of the gsz and truncates greenschist facies folds in the footwall these final movements were therefore not a major component of eclogite exhumation pressure estimates associated with old and young fabrics within the gsz are comparable indicating that during extensional deformation there was no significant unroofing of the hangingwall since there are no known extensional structures younger than 36 ma at higher levels in this part of the alps exhumation since the final juxtaposition of the two units at 36 ma seems to have been dominated by erosion key words deformation age eclogite exhumation rb sr dating tectonic

dating deformation in the gran paradiso massif nw italian alps implications for the exhumation of high pressure rocks in a collisional belt the gran paradiso massif situated in the internal part of the western italian alps records a complex tectono metamorphic history involving high pressure metamorphism and subsequent exhumation dur

zircons from syros cyclades greece recrystallization and mobilization of zircon during high pressure metamorphism zircons were studied from high pressure low temperature metamorphosed meta igneous lithologies from syros these rocks carry several zircon generations related to each other by dissolution reprecipitation processes one generation is pristine zircon that shows growth zoning relatively elevated contents of trivalent cations and high th u ratios the other end member is a skeletal zircon generation with negligible trivalent cation contents and low th u ratios 0 1 texturally between these two there is a range of zircon crystals with complex inclusion populations of y hree th phases and fluid inclusions showing variable progress of replacement recrystallization both end members yield distinct sensitive high resolution ion microprobe shrimp u pb ages the pristine generation has an age of 80 2 1 6ma from a metagabbro and 76 4 2 1ma from a meta plagiogranite dyke the skeletal low th u zircon generation yields an age of 52 4 0 8ma the older late cretaceous zircons are interpreted to date emplacement of the magmatic protoliths in a small segment of oceanic crust the younger eocene age however dates a zircon recrystallization event which possibly coincides with high solubility and mobility of high field strength elements in a high pressure aqueous fluid phase intergrowth relations between zircon and peak metamorphic garnet and excellent agreement of the u pb ages with white mica ar ar ages for the same samples support the conclusion that eocene is the true age of high pressure metamorphism on syros

archimedes revisited a structural test of eclogite emplacement models in the austrian alps high pressure rocks of the eclogite zone tauern window eastern alps formed at 20 kb 600 c uplift was fast without post burial heating extensive near field and far field deformation of the eclogite zone and its surroundings provide evidence for a tectonic uplift mechanism published emplacement models buoyant rise underplating and extension wrench faulting create distinct patterns of crustal deformation and are therefore testable by structural analysis we show that emplacement related deformation and its kinematics are consistent with underplating and extension extension is two phased the first phase may be driven by changes in rate or direction of plate convergence the second phase is due to large scale underplating of continental crust

diapiric exhumation of earth s youngest uhp eclogites in the gneiss domes of the d entrecasteaux islands papua new guinea abstract the woodlark rift in papua new guinea hosts the world s youngest 2 8 ma eclogite facies rocks and extensional deformation has played a key role in exhuming these u hp rocks at rates of 20 mm yr during the eocene papuan arc continent collision australian plate derived continental rocks were subducted to u hp depths there they remained for up to 30 m y until the pliocene when asthenospheric circulation ahead of the west propagating woodlark spreading ridge introduced heat and fluids this caused rocks to break away from the paleosubduction channel recrystallize in the eclogite facies and rise as rayleigh taylor instabilities the diapirs ascended adiabatically undergoing partial melting which lowered their viscosity and increased buoyancy u hp crust ponded near the moho at 2 4 ma thickening the crust to 40 km 11 kb domal uplifts emerged above sea level and these are still underlain by an unusually thick crust 26 km for a rift that has stretched by factor of 3 since 6 ma after ponding they acquired a flat lying foliation during amphibolite facies retrogression vertical shortening accompanied the gravitationally driven outflow of ponded lower crust the weak material was extended parallel to the rift margin thinning ductilely by w k 0 2 and was mechanically decoupled from and orthogonal to plate motion in the rift top e shear fabrics suggest that this flow was westward perhaps driven by isostatic stresses towards a strongly thinned rift corridor ahead of the woodlark spreading ridge at 100 c per m y and were mechanically incorporated into the rift s upper crust final exposure was by normal faulting and minor erosion such exhumation may also apply to other u hp terranes where less evidence for moho ponding is preserved

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

strain deformation temperatures and vorticity of flow at the top of the greater himalayan slab everest massif tibet this paper presents quantitative data on strain deformation temperatures and vorticity of flow at the top of the greater himalayan slab the data were collected from the tibetan side of the everest massif where two low angle normal faults bound the upper surface of the greater himalayan slab the earlier and structurally lower lhotse detachment and the later and structurally higher qomolangma detachment greenschist to sillimanite grade quartz rich metasedimentary rocks exposed in the rongbuk to north col region of the everest massif are characterized by cross girdle quartz c axis fabrics indicating approximate plane strain conditions fabric opening angles progressively increase with depth beneath the overlying lhotse detachment and indicate progressively rising deformation temperatures of 525 625 50 c at depths of 300 600 m beneath the detachment deformation temperatures of c 450 c are indicated by fabric opening angles in epidote amphibolite facies mylonites located closer to the overlying detachment a top down to the north normal shear sense is indicated by the asymmetry of microstructures and c axis fabrics but the degree of asymmetry is low at distances greater than 400 m beneath the detachment and sillimanite grains are drawn into adjacent conjugate shear bands but still appear pristine indicating that deformation occurred at close to peak metamorphic temperatures these quenched fabrics and microstructures indicate rapid exhumation in agreement with previous isotopic dating studies mean kinematic vorticity numbers w m were independently calculated by three analytical methods calculated w m values range between 0 67 and 0 98 and indicate that although a simple shear component is generally dominant particularly in greenschist facies mylonites located between the lhotse and overlying qomolangma detachments there is also a major component of pure shear in samples located at 400 600 m beneath the lhotse detachment pure and simple shear make equal contributions at w k 0 71 our integrated strain and vorticity data indicate a shortening of 10 30 perpendicular to the upper surface of the greater himalayan slab and confirm that the upper surface of the slab is a stretching fault with estimated down dip stretches of 10 40 assuming plane strain deformation measured parallel to the flow plane transport direction

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

modelling tectonic styles and ultra high pressure uhp rock exhumation during the transition from oceanic subduction to continental collision the tectonic styles of the transition from oceanic subduction to continental collision and their implications for exhumation of uhp material are tested in a series of numerical thermal mechanical models that address subduction collision dynamics at constant convergence rate reference models examine the sensitivity to continental mantle lithosphere density pro continental margin temperature and rheology and retro continental margin rheology three tectonic styles are observed 1 continental subduction without significant deformation of the over riding continent favoured by relatively dense mantle lithosphere and a strong retro continental margin 2 deformation and subduction of the leading edge of the retro continent favoured by low density mantle lithosphere and strong retro continental crust and 3 backthrusting of the retro continental margin and subsequent double subduction favoured by low density mantle lithosphere and weak retro continental crust continental u hp material is formed in all three tectonic styles although it is only efficiently exhumed in the first case three mechanisms contribute to u hp exhumation their importance depending on the evolving geometry of the subduction zone the strength of the continental margin crust and the density of the subducting mantle lithosphere weaker hotter continental margins decouple in the subduction channel and are subsequently exhumed by buoyancy and or driven circulation of material and or forced expulsion in response to insertion of strong continent into the subduction channel plunger effect stronger colder continental material is subducted without detachment and is then transported laterally underplating the retro continental mantle lithosphere neither surface erosion nor slab break off are required for uhp exhumation