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

the evolution of the southern menderes massif in sw turkey as revealed by zircon dating this geochronological study concentrates on the evolution of the southern part of the menderes massif a metamorphic core complex in w turkey by dating single zircons with the pb pb evaporation and the u pb methods we have analysed zircons from granitic augen gneisses of the core as well as from quartzites of the metasedimentary envelope zircons from the granitic core gneisses are euhedral with typical igneous morphologies the single zircon ages of these gneisses indicate a time span for magmatic activity from 520 to 570 ma with a major event at about 550 ma some gneisses contain older zircons of c 660 ma which are interpreted as inherited grains zircons from the quartzites are detrital as indicated by their rounded shapes and pitted surfaces their ages vary from 526 to 2094 ma these data partially coincide with the ages of the gneisses but also indicate an older source region for the sediments neither a tertiary origin nor metamorphic overgrowth is documented in the pb ages of the zircons the results suggest that the southern part of the menderes massif developed during a major magmatic episode in latest proterozoic times thus suggesting a relation with other pan african regions in n africa

on the hellenic subduction zone and the geodynamic evolution of crete since the late middle miocene abstract in recent syntheses of the geodynamic evolution of the aegean area the hellenic subduction zone and in particular its initiation plays a central role two basic aspects of the recent comprehensive model put forward by le pichon angelier and co workers are a initiation of subduction along the hellenic arc is inferred to have taken place approximately 13 ma ago whereas several others have suggested approximately 5 ma and b migration of the trench system to the south southwest giving rise to an extensional regime in the back arc region which led to general subsidence and formation of the present day aegean sea new data on the structure of the upper mantle underneath the aegean area indicate that the former aspect requires modification the seismic velocity structure indicating a northward dipping slab down to a depth of at least 600 km and the depth distribution of earthquake hypocenters can not be reconciled with straightforward initiation of subduction approximately 13 ma ago estimates of about 5 ma for the time of initiation of the present subduction zone are even more difficult to reconcile assuming 400 km as an upper bound for the effect of stretching of the aegean sea and of other processes contributing to the separation of crete from the eurasian mainland we arrive at an age for the hellenic subduction zone of at least 26 ma as to aspect b geological data of crete lend strong support to the idea that on crete compressional tectonics is of much greater importance than current models imply combining geophysical and geological data we propose a modification of the tectonic evolution for the cretan segment of the hellenic arc whereas the basic process of extension caused by a migrating trench system roll back in a land locked basin remains a very useful and sound concept the tectonics of the margins of a region subject to stretching in this case crete may be more complicated than hitherto thought in our model the documented fragmentation of crete into several basins which started about 12 ma ago is not attributed to initiation of subduction but to inception of the roll back process compressional tectonics on crete is taken to be associated with deformation of the crust resulting from the overall tensional stress regime

spatial and temporal relationships between mid tertiary magmatism and extension in southwestern arizona cenozoic magmatism in southwestern arizona which is within the basin and range tectonic province occurred almost entirely between 15 and 25 ma volcanic rocks typically consist in ascending order of 1 a thin sequence of mafic to intermediate lava flows 2 voluminous felsic lava flows and pyroclastic rocks with minor to moderate amounts of intermediate to mafic lava flows and 3 basalt and andesite volcanic rock sequences rest disconformably on pre tertiary bedrock in most areas but locally overlie substantial coarse clastic debris that was deposited immediately before and during earliest magmatism prevolcanic clastic debris is interpreted as a consequence of local early normal faulting in most regions tilting related to extension began later and occurred during or after eruption of felsic volcanic rocks and before the end of younger mafic volcanism extension generally ended before about 17 ma except in a northwest trending belt adjacent to the relatively unfaulted and topographically elevated transition zone tectonic province which is adjacent to the colorado plateau rapid cooling of metamorphic core complexes and tilting of young basalts and coarse clastic rocks continued in this belt until as recently as 11 ma extension was extreme in this belt whereas it was generally moderate to slight in other parts of southwestern arizona large magnitude extension was not associated with areas of greatest igneous activity and rapid cooling and exhumation of core complexes postdated local magmatism these relationships are inconsistent with theories that relate genesis of metamorphic core complexes to magma intrusion in the upper crust except for young extension in this northwest trending belt there are no apparent regional migration trends for either magmatism or extension within southwestern arizona lack of substantial extension before magmatism and general lack of magmatism during youngest extension are inconsistent with the hypothesis that magmatism was the product of decompression melting during lithospheric extension the long duration and large magnitude of extension adjacent to the transition zone tectonic province and within an area of earlier crustal thickening are consistent with the hypothesis that extension was driven by the gravitational potential energy of elevated land mass and crustal roots regional magmatic heating apparently weakened the lithosphere and triggered extension but did not control extension locally

unroofing of active metamorphic core complexes in the d entrecasteaux islands papua new guinea metamorphic core complexes in the d9entrecasteaux islands are forming as a result of active extension at the western end of the woodlark basin spreading center high grade metamorphic rocks exist in the cores of gneissic domes including eclogites formed at minimum depths of 45 75 km i e 13 21 kbar high temperatures were maintained during uplift of basement rocks from 13 21 kbar t 730 900 c through 7 11 kbar t 570 730 c to 5 6 kbar t 730 c subsequent rapid cooling 100 c m y of the basement occurred between 1 and 2 ma on the basis of 40 ar 39 ar geochronology the core zone rocks were transected by kilometre scale amphibolite facies ductile shear zones active at depths of 25 35 km extensive intrusion of granodiorite plutons occurred and the age of granodiorite intrusions constrains late stage shear zone activity to 2 ma and younger unroofing was accomplished by faults and shear zones bounding the gneiss domes juxtaposing them against ultramafic rocks and sedimentary deposits surface uplift continues today and has led to topographic elevations of up to 2 5 km

continental extension from core complexes to rigid block faulting extension of overthickened continental crust is commonly characterized by an early core complex stage of extension followed by a later stage of crustal scale rigid block faulting these two stages are clearly recognized during the extensional destruction of the alpine orogen in northeast corsica where rigid block faulting overprinting core complex formation eventually led to crustal separation and the formation of a new oceanic backarc basin the ligurian sea here we investigate the geodynamic evolution of continental extension by using a novel fully coupled thermomechanical numerical model of the continental crust we consider that the dynamic evolution is governed by fault weakening which is generated by the evolution of the natural state variables i e pressure deviatoric stress temperature and strain rate and their associated energy fluxes our results show the appearance of a detachment layer that controls the initial separation of the brittle crust on characteristic listric faults and a core complex formation that is exhuming strongly deformed rocks of the detachment zone and relatively undeformed crustal cores this process is followed by a transitional period characterized by an apparent tectonic quiescence in which deformation is not localized and energy stored in the upper crust is transferred downward and causes self organized mobilization of the lower crust eventually the entire crust ruptures on major crosscutting faults shifting the tectonic regime from core complex formation to wholesale rigid block faulting

neotectonics of the thakkhola graben and implications for recent activity on the south tibetan fault system in the central nepal himalaya the thakkhola graben is one of many north trending rifts that define the neogene structural pattern of the southern tibetan plateau lying at the southern margin of the plateau and extending to the crest of the himalaya the graben provides an opportunity to evaluate the kinematic relationships between east west extensional strain in southern tibet and north south extensional strain in the himalaya neotectonic and structural mapping of the dangardzong fault along the western margin of the graben reveals a southward decreasing component of normal slip coupled with a southward increasing component of right lateral slip that affects pleistocene basin fill sediments we present 14c ages for river terraces in the thakkhola graben that provide a ca 17 2 ka minimum age on the latest stage of dangardzong fault movement near the southern termination of the graben the dangardzong fault apparently offsets the annapurna detachment an early miocene strand of the east striking south tibetan fault system however the dangardzong fault itself terminates against a young i e younger than ca 17 2 ka strand of the south tibetan fault system the dhumpu detachment structural relationships among the dangardzong annapurna and dhumpu faults suggest that the dangardzong structure is a tear fault in the south tibetan allochthon that accommodates differential amounts and rates of displacement along the south tibetan fault system thus although the south tibetan fault system first developed as part of the structural architecture of the himalaya in miocene time at least some strands have been active as recently as the pleistocene in a regional context the south tibetan fault system serves to accommodate the strain gradient between extension in tibet and shortening in the himalaya

progressive development of the buyuk menderes graben based on new data western turkey oblique and normal fault systems exposed in the buyuk menderes graben bmg region record two successive and independent complex tectonic events the first group tectonic event is defined by an e w extension related to n s contraction and transpression this group is responsible for the development of nw and ne trending conjugate pairs of oblique faults which controlled early middle miocene basin formation between the early middle miocene and plio quaternary strata exists an unconformity indicating a period of folding uplift and severe erosion associated with n s shortening the second group of events was the change in tectonic regime from e w extension to n s extension which controlled the formation of the buyuk menderes graben by three progressive pulses of deformation the first pulse of extensional deformation was initially recorded in the region by the exhumation of the deep part of the menderes massif mm with the development of the e trending buyuk menderes detachment fault bmdf the minimum age of this pulse is constrained by the older plio quaternary fluviatile deposits of the buyuk menderes graben that range in age from the plio pleistocene boundary interval to late pleistocene the second pulse which is marked by the rapid deposition of alluvial deposits initiated the formation of approximately e w trending high angle normal faults synthetic and antithetic to the buyuk menderes detachment fault on the northern margin during holocene times these faults are interpreted as secondary steeper listric faults that merge with the main buyuk menderes detachment fault at depth the third pulse was the migration of the buyuk menderes graben depocentre to the present day position by diachronous activity of secondary steeper listric faults these steeper faults are the most seismically active tectonic elements in western turkey according to the stratigraphic and structural data the n s extension in the buyuk menderes graben region produced a progressive deformation phase with different pulses during its plio quaternary evolution with migration of deformation from the master fault to the hangingwall the formation of diachronous secondary synthetic and antithetic steeper faults on the upper plate of the buyuk menderes detachment fault hence the southward migration of the deformation and of the buyuk menderes graben depocentre should be related to the evolution of detachment in the region the presence of the seismically active splays of secondary faults implies an active detachment system in the region this young plio quaternary n s extension in the buyuk menderes graben may be attributed to the combined effects of the two continuing processes in aegean region the first process is back arc spreading or probably the roll back of african slab below the south aegean arc which seems to be responsible for the change in the stress tensor from e w extension to n s extension the second and later event is the southwestward escape of the anatolian block along its boundary fault that is the north anatolian fault naf

continuing evolution of the pacific juan de fuca north america slab window system a trench ridge transform example from the pacific rim abstract many subduction margins that rim the pacific ocean contain complex records of cenozoic slab window volcanism combined with tectonic disruption of the continental margin the series of slab windows that opened beneath california and mexico starting about 28 5 ma resulted from the death of a series of spreading ridge segments and led to piecewise destruction of a subduction regime the timing and areal extent of the resultant slab window volcanism provide constraints on models that depict the subsequent fragmentation and dispersal of the overlying continental margin the initial pioneer slab window thermally weakened the overlying western transverse ranges and california borderlands region starting about 28 5 ma a second thermal pulse occurred in the same region starting about 19 ma during growth of the monterey slab window this additional heating combined with the capture of a partially subducted monterey plate fragment by the cocos plate initiated the pulling apart and rotation of the adjacent continental margin similarly the capture of guadalupe and magdalena plate fragments by the pacific plate and initiation of the guadalupe magdalena slab window about 12 5 ma are coeval with baja california pulling away from the mexico continental margin with the break along the comondu arc in crust already thermally weakened by about 10 my of volcanism in coastal california distributed crustal extension and subsidence accompanied the new transform plate boundary and continued until the slab windows cooled and plate motion coalesced along a through going system of strike slip faults the transform boundary continues to evolve and forward modeling predicts an instability with the current configuration as a result of convergence between the sierra nevada and peninsular ranges batholiths starting about 2 my in the future the instability may be resolved by a shift in the locus of transform motion from the san andreas fault to the eastern california shear zone or by breaking off another fragment of the mojave or southern sierra nevada crustal blocks and translating it northward

exhumation with a twist paleomagnetic constraints on the evolution of the menderes metamorphic core complex western turkey 1 much remains to be understood about the links between regional vertical axis rotations continental extension and shortening in western turkey miocene vertical axis rotations have been reported that occur simultaneously with the extensional exhumation of the menderes metamorphic core complex which has been related to back arc extension in the eastern part of the aegean back arc in this paper we explore the spatial and temporal relationships between vertical axis rotations in southwestern turkey and extensional unroofing of the menderes massif to this end we provide a large set of new paleomagnetic data from western turkey and integrate these with the regional structural evolution to test the causes and consequences of oroclinal bending in the aegean region the lycian nappes and bey daglari are shown to rotate 20 between 16 and 5 ma defining the eastern limb of the aegean orocline this occurred contemporaneously with the exhumation of the central menderes massif along extensional detachments and after the latest oligocene to early miocene exhumation of the northern and southern menderes massifs exhumation of the latter two was not associated with vertical axis rotations the lower miocene volcanics in the region from lesbos to usak to the north of the central menderes massif underwent a small clockwise rotation insignificant with respect to eurasia this shows that exhumation of the central menderes massif was associated with a vertical axis rotation difference between the northern and southern menderes massifs of 25 30 this result is in excellent agreement with the angle defined by the trends of buyuk menderes and alasehir detachments as well as the angle defined by the regionally curving stretching lineation pattern across the central menderes massif these structures define a pivot point rotation pole for the west anatolian rotations the rotation of the southern domain including the southern menderes massif the lycian nappes and bey daglari must have led to n s contraction east of this pole the eastern limit of the rotating domain is formed by the transpressional couple of the aksu thrust and kirkkavak fault in the center of the isparta angle previously reported clockwise rotations in the volcanic fields near afyon may be the result of distributed n s shortening east of the pivot point the precise accommodation of this shortening history remains open for investigation late oligocene to early miocene extension in the eastern part of the aegean back arc was ne sw oriented and likely bounded by a discrete transform this transform may be associated with an early evolution of the eastern aegean subduction transform edge propagator fault oroclinal bending in the west anatolian region is likely related to a reconnection of the eastern part of the aegean orocline with the african northward moving plate in tandem with roll back in the aegean back arc comparable to a recently postulated scenario for western greece

supradetachment basin evolution during continental extension the aegean province of western anatolia turkey we present a detailed structural and stratigraphic record of a neogene quaternary supradetachment sedimentary succession in the aegean extensional province of western anatolia and we compare its tectonic features and evolution to those of other well documented supradetachment basins around the world the sedimentary fill of the alasehir basin records the uplift and exhumation of a core complex in the footwall of a detachment fault within the central menderes massif accumulation of footwall derived clastic sediments in this basin started ca 20 ma shortly after the initiation of the approximately e w trending alasehir detachment and its shear zone and continued until ca 2 ma major sedimentary facies types include fluvial and alluvial fan deposits debris flow and mass flow deposits and locally developed lacustrine rocks these sedimentary units were accumulated largely in distal depocenters within the extending basin as the low angle 15 28 detachment faulting created little accommodation space near the basin margins while producing high back shed topography in the uplifted menderes core complex the drainage system was dominated mainly by extension parallel transverse streams during the main phases of basin evolution extension parallel scissor hinge faulting produced differential uplift and subsidence in the adjacent fault blocks changed the direction of sediment transport and drainage patterns over short distances and resulted in the local uplift of the older basin strata these processes led to the development of subbasins with lateral variations in basement topography strata thickness and sedimentary facies distribution and generated a segmented basin architecture high angle synthetic and antithetic faults that formed extensively after 3 ma caused back tilting of the sedimentary strata formation of half grabens with their own axial drainage systems and development of angular unconformities with the onset of this crustal scale block faulting the detachment fault ceased to operate and the quaternary gediz graben started to develop at the northern end of the alasehir supradetachment basin our comparative evaluation of select basins shows a maximum sediment thickness of 3 km average extension rates of 6 to 8 9 mm yr 1 and accumulation rates of 0 1 0 2 mm yr 1 uncorrected for compaction in supradetachment basins in general the rates and amounts of extension the geometry of detachment faulting the rates of footwall uplift and the kinematics and interplay of different fault systems are the most important factors controlling three dimensional structural architecture and evolution of supradetachment basins

u pb and 40ar 39ar geochronology of the symvolon granodiorite implications for the thermal and structural evolution of the rhodope metamorphic core complex northeastern greece north aegean continental lithosphere was thickened by southwest vergent thrusting and continental subduction within the alpine collisional orogen but has subsequently been greatly extended on a northeast southwest axis in the back arc of the hellenic subduction zone crosscutting relationships with two granodiorite bodies emplaced at 31 33 ma the xanthi and eastern vrondou plutons constrain a pre mid oligocene origin of alpine convergent structures in northeastern greece post alpine thinning of the north aegean nappe pile began in earliest miocene time and has been accommodated by a succession of distinct structural systems the earliest of these the symvolon shear zone appears to represent a midcrustal coaxial rupture of the falakron marble series a carbonate platform 5000 m thick that was subducted northeastward beneath high grade rocks of the rhodope metamorphic province in late alpine time zircon and titanite u pb dates and hornblende 40ar 39ar dates obtained in this study constrain the intrusion and incipient mylonitization of the symvolon or kavala granodiorite within the symvolon shear zone at 21 22 ma following its emplacement the symvolon body resided at temperatures between 300 c and 500 c for 5 7 m y during which coaxial deformation may have continued within a widening symvolon rupture the strymon valley detachment a regionally south west dipping low angle normal fault succeeded the symvolon shear zone in middle miocene time southwestward displacement of the serbo macedonian gneiss complex by as much as 80 km in the hanging wall of this detachment facilitated the unroofing of the rhodope metamorphic core complex including the falakron marble series and several tertiary plutons in its footwall biotite and k feldspar 40ar 39ar dates from 11 1 0 2 ma to 15 5 0 3 ma yielded by symvolon granodiorite samples document the cooling of the rhodope core complex below 150 c 300 c during its southwestward progressive exhumation in the footwall of the strymon valley detachment

understanding basin sedimentary provenance evidence from allied phytogeographic and heavy mineral analysis of the palaeocene of the ne atlantic the drilling of hydrocarbon exploration wells in the faroe shetland basin has provided an expanding sample resource that provides material for testing recently developed palynology based sediment transport analysis this technique has been verified by comparison with heavy mineral analysis both approaches have been used to identify sediment sources and input points along the strike of the palaeocene west shetland platform integration of heavy mineral and palynological data has provided a basis for understanding arenaceous and argillaceous sediment distribution and sourcing in addition to a source from the western greenland side of the basin four argillaceous and four arenaceous sedimentary sources have been identified along the strike of the west shetland platform these vary in temporal and spatial distribution and thus provide a history of sediment source evolution this analysis supports a persistent difference in source between the corona basin and the flett and judd sub basins although source variation and overlap between basins is evident transfer zones represent both conduits for and barriers to effective sediment transport both palynological and heavy mineral evidence identifies the former presence of late namurian westphalian strata on the west shetland platform which were removed by subsequent erosion

an active bivergent rolling hinge detachment system central menderes metamorphic core complex in western turkey two symmetrically arranged detachment systems delimit the central menderes metamorphic core complex and define a bivergent continental breakaway zone in the anatolide belt of western turkey structural analysis and apatite fission track thermochronology show that a large east trending syncline within the alpine nappe stack in the central part of the orogen is related to late miocene early pliocene to recent core complex formation the syncline formed as a result of two opposite facing rolling hinges in the footwalls of each of the two detachments back rotation of the syncline limbs suggests that the detachments rotated from an initial dip of 408 608 to a currently shallow orientation of 08 208

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

late cenozoic extension in northeastern greece strymon valley detachment system and rhodope metamorphic core complex the strymon valley detachment system accommodated at least 25 km of extension at the northern margin of the aegean extensional province from middle miocene through early pliocene time the primary detachment surface is exposed as a gently southwest dipping low angle normal fault similar to those widely known in core complex settings of the u s basin and range province for more than 150 km along strike from the aegean sea coast in northeastern greece northward into the struma valley of southern bulgaria hanging wall rocks in the strymon valley detachment system moved in a s53 w direction relative to the footwall resulting ultimately in the tectonic unroofing of the rhodope metamorphic core complex several segments of the strymon valley detachment have previously been interpreted as thrust faults formed during a miocene compressional event our results negate the principal evidence for this event and imply instead that extensional deformation has characterized the northern aegean region since at least middle miocene time displacement ceased on the strymon valley detachment with the late pliocene development of the strymon and drama basins we propose that those basins together with the other principal basins of the northern aegean region are subsiding above an active northeast dipping extensional detachment zone that forms a unified kinematic system with the western offshore continuation of the dextral north anatolian strike slip fault the north aegean trough if this hypothesis is correct then the north aegean trough the western strands of the north anatolian fault and the principal modern depocenters of the northern aegean region may all have originated no earlier than late pliocene time

evolution of lithospheric strength after thrusting modeling of an eroding thrust belt indicates that immediately after thrusting the lithosphere is about twice as strong as unthickened cratonic lithosphere but after 10 to 20 m y it becomes weaker than cratonic lithosphere reaching a minimum of 40 to 70 of cratonic strength 30 to 100 m y after thrusting this may explain why rifting of thrust belts commonly occurs several tens of million years after thrusting ceases relative weakening results from 1 elevation of the geotherm caused by burial of radioisotope enriched surface rocks and 2 replacement of strong mantle rocks by weak crustal rocks in the lithospheric column low denudation rates enhance weakening by allowing radioisotope enriched rocks to remain buried longer our modeling indicates that 1 magmatism after thrusting is favored by high concentrations of heat producing elements in the lower plate and by slow denudation rates and 2 factors that affect denudation rate such as climate and the development of external drainage can significantly influence evolution of a thrust belt

geochemistry geochronology and cathodoluminescence imagery of the salihli and turgutlu granites central menderes massif western turkey implications for aegean tectonics abstract the menderes massif western turkey is an important metamorphic core complex located in the aegean region geochemical and geochronological data from this extensional domain facilitates our understanding of large scale extension of the earth s lithosphere s type peraluminous granites salihli and turgutlu that intrude the alasehir detachment which bounds the northern edge of the central menderes massif may have been generated due to subduction of the eastern mediterranean floor along the hellenic trench in situ th pb ion microprobe monazite ages from the granites range from 21 7 4 5 ma to 9 6 1 6 ma 1 higher uncertainty in the ages is attributed to monazite common pb but the range is consistent with cathodoluminescence cl imagery that document complex textures within the samples salihli and turgutlu granites share many similar characteristics including multiple generations of plagioclase some with shocked cores plagioclase replacing k feldspar and the development of myrmekite evidence for fluid interaction and multiple generations of microcracks and microfaults the granites may have evolved from compositionally distinct magma sources as salihli samples in general contain allanite as the major accessory mineral whereas turgutlu granites contain monazite however the cl imagery document similar alteration textures the youngest turgutlu monazite grain 11 5 0 8 ma is located in the rim of a k feldspar grain close to myrmekite and the youngest salihli monazite grain 9 6 1 6 ma is located in the outer edge of an altered plagioclase crystal these ages likely time episodes of deformation as the granites were subjected to exhumation along the alasehir detachment ages reported here are similar to dates constraining extension reported elsewhere in the aegean but indicate a level of complexity when linking movement within the menderes massif to the large scale geodynamic processes that created other metamorphic core complexes in the region difficulties exist in linking the ages obtained from the granites to specific tectonic events due to the presence of secondary alteration textures generations of mineral growth and multiple episodes of deformation

subduction and the depth of convection in the mediterranean mantle 1 we tie together geological data paleotectonic reconstruction plate motion and tomographic analysis to unravel the history of subduction and back arc extension of the eastern and central mediterranean in these two regions extensional processes started contemporaneously around 30 myr ago but with marked differences in the eastern region the aegean basin opened slowly 1 cm yr behind a shallow dipping slab 40 45 the corresponding high velocity anomaly extends inside the upper mantle and can be also followed in the midmantle down to a depth of at least 1500 km its descent into the midmantle initiated most probably during the late cretaceous and the trench moved northeastward following the path of the eurasian plate and under the persistent push of the african plate conversely in the central mediterranean region subduction initiated later and the motion of the subducting slab is confined to the upper mantle causing punctuated and rapid episodes of back arc extension provencal and tyrrhenian basins behind a slab that dips steeply 75 we explore the causes that control how the slab subducted and interacted with the lower more viscous part of the mantle

40ar 39ar and rb sr geochronology of high pressure metamorphism and exhumation history of the tavsanli zone nw turkey geochronological investigations in high and ultra high pressure metamorphic rocks are problematic since firstly the low temperatures lead to fine grain size and disequilibrium assemblages and secondly the problem of excess argon affects 40ar 39ar systematics the most commonly used isotopic system the tavsanli zone is a belt of high pressure low temperature hp lt rocks spanning nw turkey and is one such region where previous geochronological studies have produced a range of estimates for the age of hp lt metamorphism raising the question of whether they are geologically significant this study presents new data from the tavsanli zone 40ar 39ar ages are in the range 60 ma to 175 ma whilst rb sr ages are restricted to 79 7 ma to 82 8 ma confirming the presence of excess argon detailed ultra violet laser ablation microprobe uvlamp studies have revealed younger 40ar 39ar ages in the cores of coarser white micas which in conjunction with 40ar 39ar ages from the finest grained lithologies and the rb sr white mica crystallisation ages constrain the post hp lt metamorphism exhumation rates of these rocks petrological and regional constraints suggest that syn subduction exhumation and cooling took place initially by synchronous subduction and exhumation by underplating this is followed by a phase of syn continent continent collision at a rate of approximately 1 5 mma 1 and exhumation to the surface via thrusting the 40ar 39ar hornblende data from a granodiorite intruding the hp lt rocks constrain the later parts of exhumation path this study highlights the importance of a multi system geochronological approach when attempting to determine the history of hp lt rocks

tectono stratigraphic evolution of the ne sw trending superimposed selendi basin implications for late cenozoic crustal extension in western anatolia turkey abstract selendi basin is located in the eastern part of western anatolia that is the easternmost part of the aegean extensional province in western anatolia crustal extension resulted in exhumation of the mid crustal units the menderes massif synchronously with volcano sedimentary basin formation the stratigraphic and tectonic features of the volcano sedimentary succession reflect the exhumation processes and the modes of extension we present new stratigraphical sedimentological structural and 40ar 39ar age data from the neogene volcano sedimentary fill of the ne sw trending selendi basin the data show that crustal extension in the region occurred in four distinct episodes and accommodated the exhumation of the menderes massif and the basin formation throughout the late cenozoic late oligocene to early miocene detachment faulting the simav detachment fault sdf is attributed to the first episode clastic sedimentation and bimodal volcanism of 20 0 17 5 ma the hacibekir group age was formed in the hanging wall of the sdf during the exhumation of northern menderes massif in the footwall during second episode the menderes collapse occurred and was manifest by formation of the gediz detachment fault gdf during the middle miocene activity on the gdf has resulted in the exhumation of the central menderes massif in the bozdag area during this period the hanging wall of the gdf was dissected by ne sw trending high angle oblique slip cross faults and accommodated clastic to lacustrine carbonate deposition and syn sedimentary bimodal volcanism of 16 15 ma the inay group the third episode is represented by formation of nw se trending sinistral and ne sw trending dextral strike to oblique slip faults and associated dip to oblique slip normal faults during the late miocene indicating that the area was deformed under a strike slip tectonic regime the faults localized alluvial sedimentation the kocakuz formation and basaltic volcanism of 7 8 ma the kabaklar basalt in the selendi basin the last episode commenced by the start of the plio quaternary this period is represented by the currently active n s extensional tectonic regime that resulted in the formation of e w trending high angle normal faults that controls the present day e w trending graben type basin formation e g gediz and simav grabens and the quaternary 1200 60 ka basaltic volcanism

a comparison of geodetic and finite strain pattern in the aegean geodynamic implications abstract a comparison of the active strain pattern of the aegean constrained by global positioning system measurements and the oligo miocene finite strain field shows some striking similarities in terms of direction and rates of extension the geometry of extension at crustal scale is also very similar with north dipping normal faults connecting near the brittle ductile transition to shallow north dipping shear zones this pattern of extension is not significantly modified by the recent extrusion of the motion of anatolia and aegea the persistence over more than 25 myr of the same pattern of extension suggests that the cause for extension resides within the aegean lithosphere gravitational collapse allowed by extensional boundary conditions after 30 ma slab retreat is the primary cause for post orogenic extension in the aegean and western anatolia

geometric and temporal evolution of an extensional detachment fault hohhot metamorphic core complex inner mongolia china the early cretaceous hohhot metamorphic core complex and its master hohhot detachment fault are 400 km west of beijing in the daqing shan mountains of inner mongolia the complex developed across the east trending yinshan fold and thrust belt within 4 m y following cessation of thrusting ca 125 ma see note added in proof in main text postcontractional extension was initiated within a mid crustal zone of mylonitic and ductile shear that was in part controlled by carboniferous strata sandwiched between its proterozoic and archean crystalline basement and an overlying thrust sheet of similar crystalline rocks the hohhot detachment fault appears to have rooted into deep kinematically active levels of the mid crustal shear zone higher inactive levels of the mylonitic section were transected by the fault and carried upward in its footwall geometries of the footwall mylonitic rocks indicate localized ramp flat geometries of the fault within and across them the crosscut top of the mylonitic sequence defines a mylonitic front that departs from the gently south dipping detachment fault and dips northward into its footwall early cretaceous extension was widespread elsewhere in northern china and was particularly pronounced in the yunmeng shan core complex north of beijing the gravitational collapse of orogenically thickened crust acting in concert with localized centers of deep seated plutonism appear to have led to the development of isolated metamorphic core complexes within a broad region of more distributed extensional deformation

extensional folding in the alasehir gediz graben western turkey the broad folds exposed in the syn extensional sedimentary rocks of the alasehir graben western turkey have been recently interpreted as contractional in origin our field mapping of these folds suggests that they are the products of extensional tectonics the field evidence includes the presence of several longitudinal extensional folds such as a rollover anticline and drag folds that are related to normal faults in the area the extensional nature of these folds negates the previous interpretation and consequently suggests extensional tectonics in the region was not interrupted by short lived contractional tectonics

the 40ar 39ar age of extensional ductile deformation and granitoid intrusion in the northern menderes core complex implications for the initiation of extensional tectonics in western turkey the simav detachment fault in the northern part of menderes core complex in western turkey separates cover sequence rocks with brittle deformation from high grade metamorphic core rocks and young granitoid intrusions the timing of shear zone formation and the intrusion of syn tectonic granitoids is constrained by 40ar 39ar geochronology on muscovite from mylonitic gneiss and biotite from the egrigoz granitoid 40ar 39ar data indicate that mylonitic deformation occurred at 22 86 0 47 ma whilst the cooling age of the granitoid is 20 19 0 28 ma the intrusion and cooling of the egrigoz granitoid occurred between 23 20 ma these data demonstrate that extensional deformation in the northern menderes core complex began before early miocene times and represents an early stage in the tertiary extensional tectonics of western turkey

influence of varying upper ocean stratification on coastal near inertial currents the influence of varying horizontal and vertical stratification in the upper layer o 10 m associated with riverine waters and seasonal atmospheric fluxes on coastal near inertial currents is investigated with remotely sensed and in situ observations of surface and subsurface currents and realistic numerical model outputs off the coast of oregon based on numerical simulations with and without the columbia river cr during summer the directly wind forced near inertial surface currents are enhanced by 30 60 when the near surface layer has a stratified condition due to riverine water inputs from the cr comparing model results without the cr for summer and winter conditions indicates that the directly wind forced near inertial surface current response to a unit wind forcing during summer are 20 70 stronger than those during winter depending on the cross shore location which is in contrast to the seasonal patterns of both mixed layer depth and amplitudes of near inertial currents the model simulations are used to examine aspects of coastal inhibition of near inertial currents manifested in their spatial coherence in the cross shore direction where the phase propagates upward over the continental shelf bounces at the coast and continues increasing upward offshore toward surface and then downward offshore at the surface with magnitudes and length scales in the near surface layer increasing offshore this pattern exhibits a particularly well organized structure during winter similarly the raypaths of clockwise near inertial internal waves are consistent with the phase propagation of coherence showing the influence of upper layer stratification and coastal inhibition

pattern of normal faulting in the gediz graben sw turkey hanging wall deformation of the fault systems controlling the southern margin of the gediz graben were investigated separately within the plio quaternary and neogene predominantly miocene deposits of the graben fill fault styles observed in both packages share many similarities in terms of geometry and comprise conjugate fault sets that show clustering of strike orientations predominantly around wnw ese but also sw ne and nw se directions the main difference between the two units is observable in terms of fault dips and rake of the slickenside lineations measured on the exposed fault planes both measurements show a uni modal distribution for the plio quaternary deposits but a tri modal distribution for the neogene deposits this variation is probably related to the geometrical modification of the older faults by the process of domino style back rotation in the hanging wall of higher order faults similarities among the two units are not limited to geometrical aspects of the fault systems but also counts for the orientation of the principal stress axes that controlled the deformation during the deposition of each sedimentary package inversion of the fault slip data showed that approximately n s oriented extension which varies in the range of nnw sse and nne ssw controlled the faulting during the accumulation of the entire graben fill with almost no evidence of change in the state of stress during the graben evolution however some heterogeneity in terms of stress field is observable among the fault systems formed within the same time frame this heterogeneity is probably related to poorly defined direction of extension in the graben indeed low ratio in the order of 0 25 suggests that 2 and 3 are close in magnitudes and the direction of extension is not well constraint with a potential of 2 3 axes permutations local stress field anomalies related to fault segment interaction could also contribute to the observed heterogeneity

the three dimensional thermo mechanical signature of ridge subduction and slab window migration we present a series of three dimensional numerical models investigating possible thermal and mechanical effects of ridge subduction and slab window migration ridge subduction is a fundamental process of plate tectonics and the geologic manifestations in the overriding lithosphere have been investigated in many convergent margin settings many of the geologic effects of slab window migration e g anomalous high t metamorphism in the forearc non arc like magmatism in the volcanic arc are explained primarily by the introduction of a region of hot upwelling asthenospheric mantle in the subduction zone environment using end member boundary conditions and idealized geometries our models address the thermal and corresponding mechanical manifestations of slab window migration and our results provide a general agreement with observations from interpreted regions of slab window migration our models show that protracted heating in the forearc region should result in protracted high temperature metamorphism associated rheologic weakening and strain partitioning and changes in the topographic uplift pattern in regions affected by slab window migration although these models are idealized they do provide valuable insight into the geodynamics of slab window environments and provide a valuable starting point for further exploration

the black mountains turtlebacks rosetta stones of death valley tectonics the black mountains turtlebacks expose mid crustal rock along the western front of the black mountains as such they provide keys to understanding the tertiary structural evolution of death valley and because of the outstanding rock exposure they also provide valuable natural laboratories for observing structural processes there are three turtlebacks the badwater turtleback in the north the copper canyon turtleback and the mormon point turtleback in the south although important differences exist among them each turtleback displays a doubly plunging antiformal core of metamorphic and igneous rock and a brittle fault contact to the northwest that is structurally overlain by miocene pleistocene volcanic and or sedimentary rock the turtleback cores contain mylonitic rocks that record an early period of top southeastward directed shear followed by top northwestward directed shear the earlier formed mylonites are cut by and locally appear concurrent with 55 61 ma pegmatite we interpret these fabrics as related to large scale basement involved thrust faults at the turtlebacks now preserved as areally extensive metamorphosed basement over younger cover contacts the younger and far more pervasive mylonites record late tertiary extensional unroofing of the turtleback footwalls from mid crustal depths available geochronology suggests that they cooled through 300 8c at different times 13 ma at badwater 6 ma at copper canyon 8 ma at mormon point at mormon point and copper canyon turtlebacks these dates record cooling of the metamorphic assemblages from beneath the floor of an 11 ma tertiary plutonic complex collectively these relationships suggest that the turtlebacks record initiation of ductile extension before 14 ma followed by injection of a large plutonic complex along the ductile shear zone ductile deformation continued during extensional uplift until the rocks cooled below temperatures for crystal plastic deformation by 6 8 ma subsequent low angle brittle fault slip led to final exposure of the igneous and metamorphic complex the turtleback shear zones can constrain models for crustal extension from map view as well as cross sectional perspectives in map view the presence of basement involved thrust faults in the turtlebacks suggest the black mountains were a basement

pliocene and quaternary regional uplift in western turkey the gediz river terrace staircase and the volcanism at kula abstract along the upper reaches of the gediz river in western turkey in the eastern part of the aegean extensional province the land surface has uplifted by 400 m since the middle pliocene this uplift is revealed by progressive gorge incision and its rate can be established because river terraces are capped by basalt flows that have been k ar and ar ar dated at present the local uplift rate is 0 2 mm a 1 uplift at this rate began around the start of the middle pleistocene following a span of time when the uplift was much slower this was itself preceded by an earlier uplift phase apparently in the late late pliocene and early early pleistocene when the uplift rate was comparable to the present the resulting regional uplift history resembles what is observed in other regions and is analogously interpreted as the isostatic response to changing rates of surface processes linked to global environmental change we suggest that this present phase of surface uplift amounting so far to 150 m is being caused by the nonsteady state thermal and isostatic response of the crust to erosion following an increase in erosion rates in the late early pleistocene most likely as a result of the first large northern hemisphere glaciation during oxygen isotope stage 22 at 870 ka we suggest that the earlier uplift phase responsible for the initial 250 m of uplift resulted from a similar increase in erosion rates caused by the deterioration in local climate at 3 1 ma this uplift thus has no direct relationship to the crustal extension occurring in western turkey the rate and sense of which are thought not to have changed significantly on this time scale our results thus suggest that the present often deeply incised landscape of western turkey has largely developed from the middle pleistocene onwards for reasons not directly related to the active normal faulting that is also occurring the local isostatic consequences of this active faulting are instead superimposed onto this background of regional surface uplift modelling of this surface uplift indicates that the effective viscosity of the lower continental crust beneath this part of turkey is of the order of 1019 pa s similar to a recent estimate for beneath central greece the lower uplift rates observed in western turkey compared with central greece result from the longer typical distances of fluvial sediment transport which cause weaker coupling by lower crustal flow between offshore depocentres and eroding onshore regions that provide the sediment source

detached strata in a tertiary low angle normal fault terrane southeastern california a sedimentary record of unroofing breaching and continued slip miocene sedimentary strata exposed in the eastern chemehuevi mountains southeastern california record development of an evolving low angle normal fault system the sequence includes more than 1 km of conglomerate and sandstone with rare interbedded monolithologic breccia and volcanic flows clasts of peach springs tuff in basal units indicate that this succession is younger than 18 ma these rocks have been displaced by a regionally extensive low angle normal fault the chemehuevi detachment and are folded and faulted structural reconstructions and the character of associated fault rocks indicate that the chemeheuvi fault was initiated at a low angle and that the footwall was progressively unloaded through thinning and displacement of its cover during extensional deformation the syntectonic sedimentary rocks described here provide evidence that movement continued on the gently dipping 15 sup 0 fault even after part of the fault was breached and the footwall eroded the conglomerates and sandstones were deposited by stream flow and debris flow on alluvial fans synsedimentary faulting is suggested by angular discordance below one monolithologic breccia bed and by local coarsening upward sequences clast types reveal progressive unroofing of hanging wall rocks to exposer the chemehuevi fault zone from which chloritic brecciated granite clasts were derived clasts weremore then derived from both the hanging wall and the footwall footwall debris being dominant high in the section distinctive clasts show that late displacement on this evolving fault system was on the order of 1 to 5 km less

pan african high pressure metamorphism in the precambrian basement of the menderes massif western anatolia turkey the menderes massif is made up of pan african basement and a paleozoic to early tertiary cover sequence imbricated by late alpine deformation the precambrian basement comprises primarily medium to high grade schists paragneisses migmatites orthogneisses metagranites charnockites and metagabbros high pressure relics in the pan african basement are divided into two groups eclogites and eclogitic metagabbros the mineral assemblage in the eclogites is omphacite jd 44 garnet clinozoisite rutile the eclogites occur as pods and boudinaged layers in the basement schists and paragneisses inclusions found in the cores of the garnets indicate a medium pressure protolith the eclogitic metagabbros are closely related to precambrian gabbroic stocks the igneous texture and relic magmatic phases are preserved in these high pressure rocks which are characterized by the mineral assemblage omphacite jd 25 garnet rutile kyanite the p t conditions of the pan african high pressure metamorphism in the eclogites are estimated to be 644 c with a minimum pressure of approximately 15 kbar the eclogites are partly to completely retrograded to garnet amphibolites by a barrovian type overprint which developed under isothermal decompression conditions for this post eclogitic event the p t estimates are 7 kbar and 623 c the eclogite relics provide strong support for a correlation of the menderes massif with the bitlis massif in terms of common pan african high pressure evolution

monazite ages and the evolution of the menderes massif western turkey the menderes massif experienced polyphase deformation but distinguishing pan african events from alpine tectono metamorphic evolution and discriminating eocene oligocene shortening from recent extension remain controversial to address this monazite in garnet bearing rocks from the massif s gordes central and cine sections were dated in thin section in situ using the th pb ion microprobe method cambro ordovician monazite inclusions in cine and central menderes massif garnets are 450 m y older than matrix grains monazites in reaction with allanite from the kuzey detachment which bounds the northern edge of the central menderes massif are 17 5 ma and 4 5 1 0 ma the pliocene result shows that dating of monazite can record the time of extension the kuzey detachment might have exhumed rocks a lateral distance of 53 km at a rapid rate of 12 mm year assuming the present 20 ramp dip pliocene monazite crystallization at 450 c and a geothermal gradient of 25 c km assuming an angle of 60 the rate decreases to 5 mm year with the detachment surface at 21 km depth in the pliocene two gordes massif monazites show a similar allanite monazite reaction relationship and are 29 6 1 1 ma and 27 9 1 0 ma suggesting that the cenozoic extension in the gordes massif and possibly the entire menderes massif might have begun in the late oligocene

alpine high p low t metamorphism of the afyon zone and implications for the metamorphic evolution of western anatolia turkey abstract carpholite chloritoid pyrophyllite association occurs widely in the triassic metaclastic rocks of the afyon zone in west central turkey fe mg carpholite is associated with rare aragonite pseudomorphs and glaucophane in marbles and metabasites respectively the afyon zone consists stratigraphically of a pan african basement and an overlying mesozoic cover sequence the pan african basement which shows barrovian type amphibolite facies metamorphism comprises garnet mica schists intruded by sodic amphibole bearing metagabbros and leucocratic metagranites it is unconformably overlain by a continuous metasedimentary sequence extending from triassic to early palaeocene this cover sequence begins with metaconglomerates which pass upwards into phyllites fe mg carpholite occurs within this metaclastic sequence as rosette like crystals in metapelites and fibres in quartz segregations the metaclastic rocks are succeeded by metamorphosed platform carbonates grading into latest mesozoic metamorphosed pelagic limestones which in turn progress up to a late mesozoic early tertiary olistostrome this sequence is tectonically overlain by the blueschists of the tavsanli zone fe mg carpholite bearing assemblages imply temperatures of about 350 c and minimum pressures of 6 9 kbar corresponding to burial depths of about 30 km for the mesozoic passive continental margin sediments and the underlying pan african supracrustal metasediments and metaintrusives the metamorphic rocks of the afyon zone are unconformably overlain by upper palaeocene lower eocene sedimentary rocks indicating a paleocene age for the regional hp lt metamorphism this implies continuous younging of hp lt metamorphism in the anatolides related to northward subduction of the anatolide tauride platform beneath the sakarya zone from north to south this involved the tavsanli zone campanian 80 5 ma the afyon zone palaeocene the menderes massif middle eocene and the lycian nappes late cretaceous eocene all of which were probably derived from the frontal part of the anatolide tauride platform

rift segment interaction and its relation to hydrocarbon exploration in continental rift systems 1 in both the early stages of continental rifting and the onset of sea floor spreading in the more advanced rifting longitudinally continuous rifting is accomplished by the propagation and linkage of isolated pockets of extension in the early continental rift phase these isolated pockets of deformation are defined as rift segments rift segments initially are distributed in a loose association of in line and en echelon geometry their propagation interaction and linkage into a continuous rift system creates a variety of rift geometries including rift splays gaps offsets passes and large scale transfer zones an understanding of these geometries and their associated fault patterns is critical for effective hydrocarbon exploration in these zones

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

intrusion age of pan african augen gneisses in the southern menderes massif and the age of cooling after alpine ductile extensional deformation

dynamics and structural development of metamorphic core complexes the development of metamorphic core complexes mccs in a thickened continental lithosphere is studied using fully coupled thermomechanical numerical code accounting for elastic brittle ductile properties of constituent rocks for mccs to develop the middle lower crust and the sub moho mantle are required to be weak enough to flow laterally so as to simultaneously feed the exhuming dome and enable the moho to keep a flat geometry the conditions are satisfied with initial moho temperatures of 800 c or higher with crustal thicknesses of 45 km or greater and with initial effective viscosities lower than 1020 pa s and 1022 pa s in the lower crust and the underlying mantle respectively a compositional mainly density anomaly with the properties of granite is placed centrally in the crust to localize strain at the onset of deformation during a first stage of upper crust necking the deformation pattern is relatively symmetrical and dominated by graben formation in the upper crust when the first ductile layers reach the surface a second stage of dome amplification and widening occurs dome amplification is accommodated by horizontal flow in the ductile crust giving an early symmetrical pattern of conjugate shear zones with no obvious detachment zone the system then rapidly becomes asymmetric with the localization of a detachment zone along one dome limb further accommodating dome widening thus the exhumation process of a metamorphic dome results in the progressive development of a detachment zone depending on initial moho temperature the detachment zone can migrate in space or die out and be replaced by a new one with an opposite dip

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

development of three genetically related basins associated with detachment style faulting predicted characteristics and an example from the central mojave desert california three types of sedimentary basins may develop in large magnitude detachment type extensional systems possible early miocene examples of these basin types have been identified in association with northeast directed extension on the central mojave metamorphic core complex southern california from west to east the basins are 1 the tropico basin a flexural basin formed on the unextended footwall behind and bounded by the detachment breakaway zone 2 the pickhandle basin a supradetachment half graben bounded to the southwest by the detachment breakaway and to the northeast by the hanging wall and 3 the clews basin an intra hanging wall basin that formed on the upper plate of the detachment system different basin types may be recognized by the nature and geometry of their strata the footwall flexural basin should be shallow and areally extensive with basin fill dominated by fine grained low energy deposits the supradetachment basin typically will be elongate normal to the extension direction and characterized by a thick sequence of volcanic and coarse grained deposits that reflect its fault controlled margins intra hanging wall basins may be of half or full graben geometry and will vary in dimension depending on the spacing of the transfer elements recognition of these basin types is potentially useful in delineating features of the extensional system that are important to its reconstruction including the detachment breakaway zone and the boundaries of the extensional system parallel and normal to the extension direction

tertiary sedimentary rocks associated with the harcuvar core complex in arizona u s a insights into paleogeographic evolution during displacement along a major detachment fault system abstract geologic mapping and analysis of oligocene miocene sedimentary rocks in the upper plate of the buckskin rawhide detachment fault system west central arizona reveals a complex paleogeographic history during fault displacement involving shifting sediment source areas and multiple drainage reversals within the study area four upper plate fault blocks are capped by homoclinal sedimentary sections that display fanning dip relationships indicating concurrent tilting and sedimentation during deposition of these strata upper plate sedimentation was intermittently confined to separate half graben while at other times rapid rates of aggradation relative to fault displacement resulted in burial of ridges separating sub basins four sedimentary assemblages recognized within the study area can be correlated between fault blocks on the basis of lithologic similarity stratal position provenance paleocurrent data and sparse geochronologic constraints the basal assemblage consists of lacustrine rocks and interfingering fluvial strata composed of detritus derived from the granitic terrane surrounding the northern part of the study area these sediments were deposited during the earliest stages of tilting of upper plate fault blocks and inferred displacement along the buckskin rawhide detachment fault system the lower assemblage which directly overlies the basal assemblage consists of fine grained lacustrine deposits sandy conglomerate and breccia during lower assemblage deposition mass flow dominated alluvial fans were derived from source areas consisting mainly of mesozoic and paleozoic rocks exposed to the south of the study area these source areas may have been associated with the breakaway fault of the detachment system or with fault blocks stranded above structurally elevated parts of the footwall tilting of fault blocks continued during deposition of the lower assemblage and strongly affected dispersal patterns and lithofacies distributions lacustrine sediments were deposited mainly within large deep sub basins and with few exceptions lower assemblage streams followed half graben axes the middle assemblage consists of conglomerate and sandstone deposited by an extensive south directed stream system that probably flowed off undistended parts of the hanging wall across extended parts and locally onto the footwall tilting of upper plate fault blocks continued during middle assemblage deposition but rapid burial of escarpments by sediment permitted relatively unobstructed southward drainage the upper assemblage consists of sandy conglomerate deposited by a northeast directed system of broad shallow streams these deposits display a variety of clast types including tertiary mylonitic sedimentary and volcanic rocks that were eroded from the upwarped footwall of the core complex and overlying klippen upper assemblage streams maintained relatively consistent northeasterly flow even during the early stages of deposition when some fault blocks were still rotating

asymmetric extension of the middle proterozoic lithosphere mount isa terrane queensland australia abstract the middle proterozoic mount isa basin of the mount isa terrane hosts several large pb zn ag deposits and is arguably one of the richest mineral provinces in the world the deformed remnants of this basin extend from the eastern margin of the leichhardt river fault trough through to the murphy tectonic ridge in the far north of the terrane the mount isa basin initially evolved in response to nw se directed extension during the mount isa rift event this event began before 1708 ma and had ceased by 1653 ma a sag basin continued to evolve thereafter until 1595 ma regional analysis of the highest level cover rocks of the mount isa basin reveals a notable difference in the locus of syn rift sedimentation syn rift magmatism and post rift subsidence although crustal extension was widespread across the mount isa basin tectonic subsidence was focussed along the n s oriented mount isa rift approximately 3 5 km of fluvial to shallow marine clastic sediments were deposited into isolated rift basins bimodal volcanism and emplacement of shallow level plutons occurred along the western and northwestern margins of the mount isa rift magmatic provinces mark the locus of significant subcrustal lithospheric thinning asthenospheric upwelling and mafic underplating within these magmatic provinces the syn rift sequences are fewer and thinner 750 2000 m and were dominantly deposited in subaerial environments suggesting a relatively stable uplift and subsidence history the position of maximum subcrustal lithospheric extension is determined by the position of greatest post rift subsidence this occurred beneath the northern mount isa terrane where the thickest post rift sequences are preserved and the depositional history is more protracted we propose that the evolution of the mount isa basin is a consequence of asymmetric extension of the middle proterozoic lithosphere

a tibetan model for the early tertiary western united states a comparative study of the geology of the early tertiary western united states and the modern tibetan and turkish iranian plateaux indicates that these three regions situated in the hinterland of major orogenic belts share a common taphrogenic evolutionary path both the tibetan and turkish iranian plateaux have high mean elevations above sea level 5 km and 2 0 2 5 km respectively have experienced fast uplift and widespread unroofing during the last 10 8 ma and are undergoing extension nearly perpendicular to the plate convergence direction successive accretionary and collisional events accompanied by significant shortening and underplating during the formation of these plateaux resulted in the generation of overthickened continental crust 50 km that is currently in the process of extending a two stage magmatism characterized by widespread calc alkaline volcanism followed and or overlapped by bimodal basaltic to rhyolitic volcanism occurs synchronously with crustal extension and thinning the plateaux in general have an internal closed drainage system and are drained by antecedent rivers near their edges the early tertiary western us cordillera displayed similar geological and geomorphic features to those observed in the tibetan and turkish iranian plateaux in the aftermath of a prolonged mesozoic orogeny and underwent an orogenic collapse starting around mid tertiary time a n trending crustal welt with a maximum thickness of 60 km and an elevation around 3 km formed a highland with alpine flora in the hinterland of the cordilleran orogenic belt and separated internal drainage basins and saline lakes on the east from major flood plains of antecedent river systems on the west this highland subsequently became the locus of crustal extension metamorphic core complex formation and wide spread calcalkaline volcanism 9ignimbrite flare up9 this early stage of orogenic collapse was followed by the basin and range extension characterized by block faulting and bimodal volcanism starting around 18 16 ma the basin and range extension and associated subsidence resulted in development of the great basin with a mean elevation of 1 5 km above sea level and a crustal thickness of 30 km similarities in the post orogenic evolutionary paths of these three regions indicate that continental lithosphere reacts to overthickening in a consistent way through large scale crustal remobilization and extensional collapse regardless of the mode and nature of its orogenic build up

metasedimentary and igneous xenoliths from tallante betic cordillera spain inferences on crust mantle interactions and clues for post collisional volcanism magma sources abstract the deep seated xenolith association exhumed in the pliocenic volcano of tallante betic cordillera spain includes protogranular mantle peridotites felsic metasedimentary crustal rocks as well as cumulus igneous rocks such as norites and amphibole phlogopite clinopyroxenites the whole xenolith suite equilibrated at the same pressure 0 7 0 9 gpa representing the local crust mantle boundary moho characterized by extreme lithological heterogeneity this heterogeneity resulted from orogenic processes that induced the juxtaposition of crustal rocks variably depleted in fusible components within mantle domains including metasomes as it is commonly observed in orogenic mantle massifs of the mediterranean area in this contribution we report new mineral compositions of igneous parageneses recorded in these xenoliths and we present sr nd isotope data on both igneous and metasedimentary xenoliths that integrate those from the literature sr nd isotopes coherently indicate a restitic character of the metasedimentary xenoliths which according to model ages were affected by partial melting in paleozoic times sr nd isotopic errorchrons on the igneous xenoliths on the other hand qualitatively indicate tertiary ages which are corroborated by u pb zircon datings of one norite xenolith and two composite xenoliths having zircon bearing norite veinlets the new data are discussed proposing that moho lithologies of tallante could provide significant source compositions for the genesis of the neogene volcanics of the betic area which included calcalkaline lavas as well as more potassic products such as lamproites

book review the techniques of modern structural geology volume 2 folds and fractures john g ramsay and martin i huber academic press london 1987 xi 309 398 pp price stg17 50 us 34 50 paperback

stratigraphy of upper cretaceous palaeogene sequences in the southern and eastern menderes massif western turkey the stratigraphy of the uppermost levels of the menderes massif is controversial and within its details lie vital constraints to the tectonic evolution of south western turkey our primary study was carried out in four reference areas along the southern and eastern menderes massif these areas lie in the upper part of the menderes metamorphic cover and have a clear stratigraphic relationship and contain datable fossils the first one in the akbuk milas area is located south east of bafa lake where the milas then kizilagac and kazikli formations are well exposed there the milas formation grades upwards into the kizilagac formation the contact between the kizilagac and the overlying kazikli formation is not clearly seen but is interpreted as an unconformity the milas and kizilagac formations are also found north of mugla in the region of yatagan and kavaklidere in these areas the milas formation consists of schists and conformably overlying platform type emery and rudist bearing marbles rudists form the main palaeontological data from which a santonian campanian age is indicated the kizilagac formation is characterized by reddish greyish pelagic marbles with marly pelitic interlayers and coarsening up debris flow deposits pelagic marbles within the formation contain planktonic foraminifera and nanoplankton of late campanian to late maastrichtian age the kazikli formation is of flysch type and includes carbonate blocks planktonic foraminifera of middle palaeocene age are present in carbonate lenses within the formation in the serinhisar tavas area mesozoic platform type marbles yilanli formation belonging to the cover series of the menderes massif exhibit an imbricated internal structure two rudist levels can be distinguished in the uppermost part of the formation the first indicates a middle late cenomanian age and the upper one is santonian to campanian in age these marbles are unconformably covered by the palaeocene early eocene zeybekolentepe formation with polygenetic breccias in the cal denizli area the menderes massif succession consists of cherty marbles and clastic rocks with metavolcanic lenses the lower middle eocene alvan formation lies unconformably on this sequence and is interpreted as equivalent to the marble horizons at serinhisar but with pelagic facies the alvan formation consists of shale mafic volcanic rock lenses of limestone and blocks of recrystallized limestone the alvan formation is dated here for the first time by early middle eocene foraminifera and nanoplankton from the matrix of the formation an angular unconformity exists between the upper cretaceous and lower tertiary sequences suggesting that a phase of deformation affected the southern and eastern part of the menderes massif at this time this deformation may be caused by initial obduction of the lycian ophiolite onto the passive margin to the north of the menderes carbonate platform during the latest cretaceous drowning of the platform led to termination of carbonate deposition and deposition of deep water flysch like clastic sediments

how the harcuvar mountains metamorphic core complex became cool evidence from apatite u th he thermochronometry apatite u th he ahe data from 60 km of exposed footwall in the harcuvar mountains metamorphic core complex arizona reveal a higher precision late stage cooling history than previously reported for this complex and others in the region progressively younger ahe ages recorded with distance along the slip direction show two distinct trends separated by a sharp inflection at structurally shallower levels ages decrease from ca 23 to 15 ma toward the northeast defining an estimated slip rate of 2 6 0 1 0 2 km m y samples from the structurally deepest 35 km of footwall yield concordant ages of ca 15 ma 2 error limits the effects of mineralizing fluids advection of isotherms toward the surface and flexure induced erosion are considered but are unlikely to have influenced the ages therefore it is suggested that the fault slip rate must have increased ca 15 ma to a rate of 30 km m y evidence for an increased slip rate ca 15 ma has also been observed in other metamorphic core complexes nearby and this increase is attributed to the thermal effects of a slab free window on the extending lithosphere

late orogenic crustal extension in the northern menderes massif western turkey evidence for metamorphic core complex formation the simav metamorphic core complex of the northern menderes massif western turkey consists of a plutonic tertiary and metamorphic precambrian core footwall separated from an allochthonous cover sequence hanging wall by a low angle ductile to brittle extensional fault zone i e detachment fault the core rocks below the detachment fault are converted into mylonites with a thickness of a few hundred metres two main deformation events have affected the core rocks the first deformational event d1 was developed within the precambrian metamorphic rocks the second event d2 associated with the tertiary crustal extension includes two distinct stages stage one is the formation of a variably developed ductile mylonitic deformation d2d in metamorphic and granitic core rocks under greenschist facies conditions the majority of the mylonites in the study area have foliations that strike nnw to nne and dip sw to se stretched quartz and feldspar grains define the mineral lineation trending sw ne direction and plunging gently to sw the kinematic indicators indicate a top to ne sense of shear stage two formation of brittle deformation d2b that affected all core and cover rocks d2b involves the development of cataclasites and high angle normal faults an overall top towards the north sense of shear for the ductile mylonitic fabrics in the core rocks is consistent with the n s regional extension in western turkey

the liaonan metamorphic core complex southeastern liaoning province north china a likely contributor to cretaceous rotation of eastern liaoning korea and contiguous areas abstract the mesozoic liaonan metamorphic core complex mcc of the southeastern liaoning province north china is an asymmetric cordilleran style complex with a west rooting master detachment fault the jinzhou fault a thick sequence of lower plate fault related mylonitic and gneissic rocks derived from archean and early cretaceous crystalline protoliths has been transported ese ward from mid crustal depths u pb ages of lower plate syntectonic plutons ca 130 120 ma 40 ar 39 ar cooling ages in the mylonitic and gneissic sequence ca 120 110 ma and a cretaceous supradetachment basin attest to the early cretaceous age of this extensional complex the recent discovery of the coeval and similarly west rooting waziyu mcc in western liaoning darby b j davis g a zhang x wu f wilde s yang j 2004 the newly discovered waziyu metamorphic core complex yiwulushan western liaoning province north china earth science frontiers 11 145 155 indicates that the gulf of liaoning which lies between the two complexes was the center of a region of major crustal extension clockwise crustal rotation of a large region including eastern liaoning province and the korean peninsula with respect to a non rotated north china block has been conclusively documented by paleomagnetic studies over the past decade the timing of this rotation and the reasons for it are controversial lin et al lin w chen y faure m wang q 2003 tectonic implication of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china journal of geophysical research 108 b 6 epm 5 1 to 5 17 proposed that a clockwise rotation of 22 5 10 2 was largely post early cretaceous in age and was the consequence of extension within a crustal domain that tapers southwards towards the bohai sea of which the gulf of liaoning is the northernmost part paleomagnetic studies of early cretaceous strata ca 134 120 ma in the yixian fuxin supradetachment basin of the waziyu mcc indicate the non rotation of north china and the basin zhu r x shao j a pan y x shi r p shi g h li d m 2002 paleomagnetic data from early cretaceous volcanic rocks of west liaoning evidence for intracontinental rotation chinese science bulletin 47 1832 1837 such upper plate non rotation supports our conclusion that the lower plates of the waziyu and liaonan metamorphic core complexes were displaced ese ward in an absolute sense away from the stable north china block thus contributing to the rotation of korea and contiguous areas rotation is inferred to have affected only the upper crust above mid crustal levels into which we believe the jinzhou and waziyu detachment fault zones flattened if this is the case the regional tan lu fault that lies between the two core complexes was truncated at mid crustal depth since in areas to the south it forms the boundary between the north and south china lithospheric blocks it is noteworthy that the two extensional complexes lie not far north of the bohai bay the area proposed by lin et al lin w chen y faure m wang q 2003 tectonic implication of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china journal of geophysical research 108 b 6 epm 5 1 to 5 17 as the site of the pole of rotation for korea s clockwise displacement lin et al lin w chen y faure m wang q 2003 tectonic implication of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china journal of geophysical research 108 b 6 epm 5 1 to 5 17 were unaware of the liaonan and waziyu mcc s and argued that most of the regional block rotation was post early cretaceous and in part early cenozoic however the ca 130 120 ma ages of the two liaoning mcc s and a songliao basin mcc xujiaweizi the latter discovered only by recent drilling through its younger stratigraphic cover support our and some korean coworkers conclusions that most of the clockwise rotation was early cretaceous

sediment thicknesses of the western anatolia graben structures determined by 2d and 3d analysis using gravity data abstract western turkey is tectonically one of the most active and rapidly deforming regions of continental crust in the world the most pronounced structural and morphological features of this region are defined by normal faulting in an e w direction which creates the boundaries of the buyuk menderes kucuk menderes and gediz grabens the graben systems may have become active between 11 7 ma and are now deeper than the surrounding topography the gediz and buyuk menderes grabens exhibit negative bouguer gravity anomalies the bouguer gravity anomalies increase towards the center of the aegean sea in a regional sense the grabens are filled with recent sediments giving rise to relative negative gravity anomalies these anomalies were interpreted using 2d and 3d gravity inversion techniques in order to determine the depth to the metamorphic basement inversion of geophysical anomalies implies fitting the observed data to theoretical anomalies possibly produced by subsurface bodies inversion of gravity anomalies is a non linear problem in the sense that body parameters are not linearly related to the anomalies gravity anomalies caused by structures are mostly determined by a 2d model which has an n sided polygonal cross section for non linear problems theoretically it is more suitable to determine the parameters of the structure by a series of juxtaposing prisms or vertical dykes extending to infinity rather than using a single n side polygonal model the depths to the top surfaces of a rectangular prisms with infinite depth represent the relief of the basement the basement relief can be computed on the basis of density contrast if the reference depth is assessed as a result of 3d analysis of the bouguer gravity map the maximum thickness of sedimentary cover appears to be more than 2 0 and 1 5 km for the gediz and buyuk menderes grabens respectively towards the saraykoy kizildere area the sedimentary thickness cover thickens to more than 2 0 km 2d analysis of the bouguer gravity profiles indicate that the maximum thickness of the sedimentary cover is between 2 5 and 3 5 km in the buyuk menderes graben and between 0 5 and 2 0 km in the gediz graben

sedimentation of the neogene recent alasehir gediz continental graben system used to test alternative tectonic models for western aegean turkey abstract the alasehir gediz graben exemplifies clastic sedimentation in a long lived continental half graben in a semi arid setting developed within relatively incompetent metamorphic rocks early miocene to recent rift related sediments are exhumed on both flanks of the graben allowing detailed three dimensional study during the early miocene small fan delta lobes were shed northwards from the rugged menderes metamorphic massif into a bordering lacustrine basin during early to mid miocene time large alluvial fans prograded northwards into this basin through drainage to the aegean sea was established as the basin widened and filled discrete lobes of coarse alluvial fan sediments of latest miocene pliocene age also shedding northwards are likely to have been climatically influenced quaternary alluvium party infills the modern alasehir rift basin the sedimentary information can be used to test two alternative tectonic models for the alasehir graben in the first model an e w graben bounded by high angle faults was active during latest miocene recent time whereas earlier miocene sedimentation was controlled by n s faulting related to a n s compressional stress regime in the second hypothesis the alasehir graben was initiated much earlier in the early miocene and was then either continuously or episodically active until recent our results especially facies and palaeocurrent data from alluvial sediments indicate that clastic sedimentation was controlled by mainly e w faulting in a n s stress regime assuming the early miocene clastic sediments are correctly dated this supports the second long lived extension model however rather than steady state extension for ca 15 ma the sedimentary evidence and regional context are consistent with a pulsed extension model whereby initial early to mid miocene extension and related clastic sedimentation was followed by a second phase of extension in latest miocene pliocene time the driving force of initial early miocene extension was probably gravity spreading towards a south aegean subduction zone whereas the inferred second extension pulse is seen as being triggered by westward tectonic escape of anatolia towards the extending aegean back arc region

are turtleback fault surfaces common structural elements of highly extended terranes abstract the death valley region of the u s a contains three topographic surfaces resembling the carapace of a turtle these three surfaces are well exposed along the black mountain front and are named the badwater copper canyon and mormon point turtlebacks it is widely accepted that the turtlebacks are also detachment surfaces that separate brittlely deformed cenozoic volcanic and sedimentary rocks of the hanging wall from the strongly mylonitic ductilely deformed pre cenozoic rocks of the footwall we have found a turtleback like detachment surface along the southern margin of the alasehir gediz graben in western anatolia turkey this surface qualifies as a turtleback fault surface because it a is overall convex upward and b separates brittlely deformed hanging wall cenozoic sedimentary rocks from the ductilely to brittlely deformed strongly mylonitic pre cenozoic footwall rocks the surface named here horzum turtleback contains striations that overprint mylonitic stretching lineations indicating top to the ne sense of shear this suggests that the northeasterly directed cenozoic extension in the region resulted in a ductile deformation at depth and as the crust isostatically adjusted to the removal of the rocks in the hanging wall of the detachment fault the ductilely deformed mylonitic rocks of the footwall were brought to shallower depths where they were brittlely deformed the turtleback surfaces have been considered unique to the death valley region although detachment surfaces rollover folds and other extensional structures have been well observed in other extended terranes of the world the presence of a turtleback fault surface in western anatolia turkey suggests that the turtleback faults may be common structural features of highly extended terranes

the origin and evolution of the menderes massif w turkey a rubidium strontium and oxygen isotope study the menderes massif located in the alpine orogen of western turkey has three litho structural units a basal gneiss core a schist mantle covering the gneiss core and an overlying marble mantle this study reports isotopic data from samples of metasediments and migmatites from the southern type a and of tonalitic to granitic metaigneous rocks from the northern menderes massif type b type a rocks define a rb sr whole rock isochron age of 502 10 ma and an initial87sr 86sr ratio of 0 71174 73 this is interpreted as the age of migmatization type b rocks give a rb sr whole rock isochron age of 471 9 ma with an initial87sr 86sr ratio of 0 70684 25 which we interpret as the intrusion age k white micas from rock type a give an average rb sr mineral age of 56 1 ma which can be interpreted as the formation age of the alpine mineral paragenesis k white micas from rock type b give rb sr mixed ages of 120 230 ma between alpine and pan african orogenies biotites from both rock types yield an average rb sr age of 37 1 ma which is interpreted as an alpine cooling age the oxygen isotope ratios of type a rocks range from 10 4 to 14 6 and of type b from 8 9 to 11 8 the oxygen and strontium isotopic compositions together clearly distinguish rocks of types a and b compositions of type a rocks suggest a crustal origin type b rocks have compositions transitional between those of crustal and mantle derived materials

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

tectonics of mid tertiary extension along a transect through west central arizona large magnitude miocene extension in west central arizona occurred primarily along three imbricate northeast dipping normal faults the structurally highest of these faults the gently dipping buckskin rawhide detachment fault accommodated approximately 66 km of crustal extension whereas the two structurally lower faults accommodated a total of about 20 km extension due to this large magnitude extension an area at the earth s surface that was 10 to 20 km wide is now over a 100 km wide and crystalline rocks with mid tertiary mylonitic fabrics uncovered by detachment faulting are exposed over roughly 2000 km in the harcuvar metamorphic core complex most of the upper plate of the buckskin rawhide detachment fault was largely undeformed by internal extension only the thin tapered end of the upper plate was highly extended during extension the lower plate must have flexed to conform to the listric underside of the upper plate and to have flattened to its present subhorizontal form as it was uncovered grooves on the underside of the upper plate were apparently imposed on the pliable lower plate as it was denuded forming extension parallel folds in the lower plate low flexural strength characterized the lower plate during denudation and a highly mobile low viscosity deeper crust must have effectively decoupled the upper crust from the mantle lithosphere

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

evolution of the miocene sedimentary fill of the gediz graben sw turkey abstract the gediz graben is a continental extensional basin filled with miocene to recent sediments the evolution of the graben can be expressed in terms of two phases i miocene half graben phase and ii post miocene graben phase the miocene half graben phase was governed by the southern margin structure evolution of which significantly controlled the stratigraphic variability in the basin alluvial fluvial and lacustrine systems developed in the graben as a function of distance to the southern margin thus alluvial deposits with coarse grained facies dominate the southern margin and grade into finer fractions of fluvial and or lacustrine deposits to the north this depositional architecture repeated three times during the miocene and deposited alasehir caltilik and gediz formations these formations depict distinct thickness and grain size decrease from south to north to emphasize the half graben configuration for the favour of the southern margin the post miocene graben phase started with the faulting of the northern margin this resulted in relatively balanced partitioning of the subsidence between the two margins although the preceding asymmetry was inherited by the graben sediment influx became bipolar and alluvial fan systems developed along the both margins

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

metamorphic evolution partial melting and miocene exhumation of lower crust in the edough metamorphic core complex west mediterranean orogen eastern algeria abstract the edough massif is the easternmost crystalline massif of the maghrebides which represent the southeastern part of the west mediterranean orogen it emerges from below the greenschist facies tellian units that represent the thrusted mesozoic to eocene passive paleomargin of northern africa deposited on the thinned continental crust the top of the crystalline pile of the edough massif is characterised by metasedimentary rocks affected by medium to high pressure 12 14 kbar and medium temperature metamorphic conditions of ca 600 c the northern part of the massif as well as the overlying allochthonous amphibole peridotite unit in the north is characterised by high pressure granulite facies t 800 c and p 12 kbar nearly isothermal decompression is documented in metapelites by late to post kinematic crystallisation of sillimanite and andalusite overprinting kyanite the core of the dome comprises essentially diatexite and granite gneisses a late low pressure evolution and overprinting 2 3 kbar took place in paleozoic rocks in proximity to granite gneisses the predominant igneous mineralogy of granite gneisses suggests that they represent synmetamorphic and syn kinematic sheeted intrusions generated through a high degree melting of metasediments geochronology of the metamorphic rocks u pb on monazite sm nd on garnet wr pairs 40 ar 39 ar on amphiboles and micas yields ages bracketed between 24 and 16 ma suggesting that regional metamorphism of the edough massif took place during the late tertiary synchronous with the greenschist facies metamorphism recorded in the overlying mesozoic tellian units the edough massif represents a metamorphic core complex exhumed through tectonic denudation assisted by syn to late metamorphic low angle n dipping normal ductile shear zones an exhumation rate of 6 8 km ma and associated cooling rate of 200 300 c ma is implied we conclude that the edough massif represents part of the former thinned continental crust of africa involved in a late eocene northward subduction beneath the suboceanic domain that separated paleo europe and africa in mesozoic time the upward syn metamorphic tectonic emplacement at 40 45 km depth of slices of spinel peridotites detached from the lower mantle may be responsible for the local granulite facies occurrences their emplacement is a consequence of the long lived transtensional sinistral then dextral kinematics having taken place between the african and european plates