geochemical and geochronological evidence for early triassic calc alkaline magmatism in the menderes massif western turkey pan african basement rocks and a paleozoic cover series which were intruded by the protoliths of leucocratic orthogneisses have been recognized in the menderes massif located in the western part of the alpine orogenic belt of turkey this geochemical and geochronological study focuses on the evolution of the menderes massif at the end of paleozoic time geochemical data suggest that the crustally derived leucocratic orthogneisses have chemical composition typical of calc alkaline and s type granite zircon grains which are euhedral with typical igneous morphologies were dated by the 207pb 206pb evaporation method single zircon dating of three samples yielded mean 207pb 206pb ages of 246 5 241 5 and 235 6 ma these ages are interpreted as the time of protolith emplacement in triassic geological and geochronological data suggest that leucocratic granites were emplaced in a period following a metamorphic event related to the closure of the paleo tethys the leucocratic granites were metamorphosed during the alpine orogenesis and transformed into orthogneisses the similar triassic magmatic event at 233 2 ma was also occurred using single zircon evaporation method from granitic gneisses which rest upon the migmatites with tectonic contacts in naxos cycladic complex this indicates that the menderes massif and cycladic complex had a common pre early triassic magmatic evolution

near surface deformation in the new madrid seismic zone as imaged by high resolution sh wave seismic methods over 1 5 kilometers of high resolution sh wave refraction and reflection profiles have been performed in the madrid bend area of northwestern tennessee approximately 8 km north of tiptonville tennessee to establish the existence of neo tectonic near surface deformation the specific area was chosen because of the access it provided to the tiptonville dome a holocene flexure and the trend of contemporary seismicity within the new madrid seismic zone nmsz we believed the highest likelihood of near surface deformation to be over these features partially reversed refraction reflection walk away tests and common depth point cdp seismic profiling using the non traditional sh wave method have traced antiformal flexure and numerous faults into the late eocene and holocene sediments of the tiptonville dome province of the lake county uplift lcu vertical displacements exhibited across the faults range from approximately 3 to 30 m these structures have been interpreted to be neo tectonic features associated with tensional stresses across the tiptonville dome

topographic inversion and changes in the sediment routing systems in the variscan orogenic belt as revealed by detrital zircon and monazite upb geochronology in post collisional continental basins abstract the basal alluvial and fluvial siliciclastic successions within the late carboniferous intracontinental basins of the west central bohemian massif provide an intriguing sedimentary record of changes in paleotopography and paleodrainage systems during and after orogenic collapse we analyze this record using the u pb laser ablation icp ms detrital zircon and monazite geochronology five distinct age groups have been identified across the examined stratigraphic succession i archean paleoproterozoic ii late neoproterozoic iii cambro ordovician iv late devonian and v mid to late carboniferous these age groups indicate mixing of both local and distal extra basinal sources and also point to a two stage post convergent geodynamic evolution of the variscan belt the first stage followed collapse of the central bohemian orogenic plateau at around 346 337 ma and involved rapid cooling at ca 340 320 ma and removal of ca 2 3 km of sedimentary overburden from the top of the plateau no sedimentary record of this erosional event suggests that the river systems transported detritus radially outwards from the inner part of the orogen to its forelands a paleorelief inversion and thus major reorganization of the sediment routing systems were then associated with uplift in the southerly and southwesterly peripheral domains of the orogen at ca 330 310 ma in turn these uplifted domains occupied by rapidly unroofed voluminous granite plutons shed detritus into the bohemian sink this was represented by the former plateau collapsed to relatively low elevations but still with significant internal paleorelief dominated by a system of tens of kilometers long nne ssw trending paleovalleys some of the material was further transported in extensive river systems crossing the former plateau to the northerly variscan foreland basin thus the radial sediment routing system changed into axial unidirectional finally we suggest that these major inversions of paleorelief and changes in the surface processes and paleodrainage systems may have been linked to distinct late orogenic lithospheric mantle delamination events first stage delamination occurred beneath the center of the bohemian massif to cause the plateau collapse denudation and radial sediment transport whereas the second stage delamination occurred along its periphery to cause uplift sourcing the intracontinental basins and unidirectional sediment transport end of deposition and magmatic shutdown at around 305 ma may then define the very cessation of late orogenic vertical movements and the transition to a post orogenic intra plate setting

isotopic dating of pre alpidic rocks from the island of ios cyclades greece the lower tectonic unit of ios provides evidence of an at least four stage metamorphic and intrusive history which well might be generalized for large parts of the internal pelagonian

u pb single zircon ages and geochemistry of metagranitoid rocks in the cycladic blueschists evia island implications for the triassic tectonic setting of greece abstract u pb zircon geochronology geochemical and microstructural analyses were carried out to a metagranitoid suite exposed in the blueschist unit of the attic cycladic zone on evia island concordant zircons from three metagranitoid samples yielded id tims u pb single grain ages of 234 1 2 ma 232 1 ma and 214 0 7 ma which are interpreted to constrain the intrusion of the igneous protolith in late triassic times these age data in combination with previously published early middle triassic protolith ages of meta igneous rocks from other greek islands support magmatic activity in the cycladic area throughout the triassic major and trace element whole rock analyses reveal that the granitic protolith of the evia metagranitoid suite is of a type affinity implying triassic magmatism in an extensional setting along the northern gondwanan margin rather than back arc extension above a subduction zone subsequent alpine subduction and related high pressure metamorphism led to pervasive non coaxial fabrics of the evia metagranitoid which indicate top to the e se shearing this alpine deformation took place under ductile viscous conditions at temperatures close to 450 500 c and differential stresses of 65 15 10 mpa

geochemical constraints on the provenance and depositional setting of sedimentary rocks from the islands of chios inousses and psara aegean sea greece implications for the evolution of palaeotethys the provenance and depositional setting of late palaeozoic and early mesozoic clastic sediments from the eastern aegean archipelago are examined here for the first time using whole rock geochemistry and composition of detrital chrome spinel major and trace element data for late palaeozoic and permo triassic clastic sediments from the lower and upper units of chios are compatible with an acidic to intermediate source minor input of ultra mafic detritus and recycling of older sedimentary components chondrite normalized ree profiles are uniform with light ree enrichments la n yb n c 7 7 negative eu anomalies eu eu c 0 67 and flat heavy ree patterns gd n yb n c 1 5 indicating an upper continental crustal source and or young differentiated arc material detrital chrome spinel from the clastic sediments of chios has cr number cr cr al values between 0 29 and 0 89 and mg number mg mg fe 2 values between 0 24 and 0 70 suggesting a probably mixed ultra mafic source involving ridge peridotites mid ocean ridge type fore arc peridotites and island arc basalts the metasediments from the islands of inousses and psara have similar whole rock chemical signatures to those of chios although no evidence was found for an ultra mafic source we conclude that both the late palaeozoic sediments from the lower and upper units of chios and the metasediments from inousses and psara were deposited in a continental island arc setting until at least late permian times probably at a single palaeotethyan margin they are interpreted to be allochthonous tectonically transported to their present position by late mesozoic to cenozoic orogenic processes

late quaternary earthquake related soft sediment deformation along the belgian portion of the feldbiss fault lower rhine graben system abstract trench investigations along the bree fault scarp in belgium in the framework of a first paleoseismological experience in the area of the lower rhine graben system have not only demonstrated the existence of seismogenic faults almost extending to the present ground surface but also exposed several types of soft sediment deformation affecting sandy sediments and soils of inferred late weichselian to holocene age the observed features include asymmetric folding small scale normal faulting possible sand intrusions and small water escape or load structures establishing a seismic origin for the individual features is not always possible based on their sedimentary characteristics only particularly due to the potential confusion with periglacial phenomena but their abundance the close association of different deformational styles and their vicinity to a known active fault all seem to be compatible with an earthquake induced scenario the features are to some extent comparable to those generated during the recent ms 5 3 roermond earthquake at the opposite side of the roer valley graben stratigraphical and mutual geometrical relationships suggest the occurrence of at least three distinct deformational events since probably 30 000 years and one event before that time since nothing is yet known about their regional distribution however estimating the associated paleomagnitudes from these soft sediment deformations is premature

earthquake faulting related deformation in soil evidenced in s wave shallow reflection data field results from portugal abstract expressions of ductile soft sediment deformations induced by ground movements due to past earthquakes are difficult to recognize in near surface soils we have carried out shallow s wave reflection studies in a seismically active area located northeast of metropolitan lisbon portugal identifying shallow disturbed zones and hidden fault segments in this area is important but quite difficult because of small vertical slips due to earthquakes the holocene alluvial cover hiding the fault segments and a high rate of surficial sedimentation we have performed s wave reflection profiling at two sites vila franca xira and castanheira de ribatejo we detected different but interrelated evidence of soft sediment deformation in the seismic data this evidence includes sharp lateral changes in the s wave velocity field changes in the reflection horizons in stacked sections aligned diffractions in unmigrated sections discontinuities in common offset gathers and discontinuities backscattered and d

finite difference modeling experiments for seismic interferometry in passive seismic interferometry new reflection data can be retrieved by crosscorrelating recorded noise data the quality of the retrieved reflection data is among others dependent on the duration and number of passive sources present during the recording time the source distribution and the source strength to investigate these relations we set up several numerical modeling studies to carry out the modeling in a feasible time we design a finite difference algorithm for the simulation of long duration passive seismic measurements of band limited noise signatures in the subsurface novel features of the algorithm include the modeling of thousands of randomly placed sources during one modeling run the modeling experiments explore the dependency relation between the retrieved reflections and source signature length source positions number of sources and source amplitude variations from these experiments we observed that the positions of the passive sources and the length of the source signals are of direct influence on the quality of the retrieved reflections random amplitude variations among source signals do not seem to have a big impact on the retrieved reflections

tectonics and magmatism in turkey and the surrounding area this volume contains 23 papers from a range of international contributors describing recent research into the tectonics and magmatism of turkey and its surroundings this region is sited at the collision zone between eurasia and afro arabia and as such provides an extraordinarily complete and well exposed record of the staged tectonic evolution of this sector of the alpine himalayan orogen the geological history of this area involves separation of continental fragments from the margin of gondwana their migration across the tethyan oceans the subsequent closure of these oceans and finally the development of the neotectonic regime which continues to evolve to the present day such a comprehensive record is relevant to the understanding of collisional zones worldwide the volume is divided into five sections tethyan evolution neotethyan ophiolites post tethyan basin evolution neotectonics and igneous activity the first two sections deal with tethyan oceans whose growth and subsequent closure dominated the geodynamic framework in the mesozoic and cenozoic the subsequent sections deal with more recent geological developments from the balkan peninsula in the west to the transcaucasus in the east that followed consumption of the tethyan oceans there is a broad mix of papers throughout the volume wide ranging review papers on ocean development and extensional tectonics are followed by detailed descriptions of petrology and geochemistry and geographically focused studies on basin evolution specific aspects of extensional and strike slip tectonics and discussions of the relationship of magmatic activity to the tectonic development of the area tectonics and magmatism in turkey and the surrounding area presents up to date results and ideas from a large number of international contributors on a wide range of current research activity in this region it is essential reading for all geoscientists with an interest in both academic and applied aspects of eastern mediterranean geology

u pb zircon and biostratigraphic data of high pressure low temperature metamorphic rocks of the talea ori tracking the paleotethys suture in central crete greece inherited deformation microfabrics of detrital quartz grains and u pb laser ablation la icpms and id tims ages of detrital zircons separated from the phyllite quartzite unit s l of the talea ori central crete suggest strikingly different source rocks albite gneiss of the lower rogdia beds includes cambrian and neoproterozoic rounded zircons with main u pb age peaks at 628 and 988 ma these and minor paleoproterozoic and archean peaks together with the lack of variscan aged and mesoproterozoic zircons are similar to the age spectra obtained from the phyllite quartzite unit s str of the peloponnesus and eastern crete and from the taurides all of these zircons should be derived from the northeastern passive margin of gondwana cimmeria metatuffites of the uppermost rogdia beds and metasandstone of bali beach on the other hand include euhedral detrital zircons displaying a variscan u pb age spectra at ca 300 ma with concordia ages at 291 3 300 1 ma rogdia and 286 3 300 3 313 2 ma bali both types of metasediments and their zircons are similar to those of the pre alpine basement and overlying tyros beds of eastern crete revealing a provenance at the southern active margin of laurasia thus in central crete the paleotethys suture should be situated inside the rogdia beds magmatic zircons separated from a rhyolite boulder of the lower achlada beds yielded a concordant u pb zircon age at 242 2 ma placing a maximum age for the deposition of the meta conglomerate from which the boulder was collected this age is compatible with an olenekian early anisian age of the underlying vasilikon marble suggested by new findings of the foraminifera meandrospira aff pusilla both the achlada beds and the vasilikon marble can be attributed to the lower tyros beds of eastern crete the alpine deformation led to a pervasive mylonitic foliation which is affecting most of the studied rocks this foliation results from d2 top to the north shearing which post dates the growth of blue amphiboles crossite

geophysical methods applied to fault characterization and earthquake potential assessment in the lower tagus valley portugal abstract the study region is located in the lower tagus valley central portugal and includes a large portion of the densely populated area of lisbon it is characterized by a moderate seismicity with a diffuse pattern with historical earthquakes causing many casualties serious damage and economic losses occurrence of earthquakes in the area indicates the presence of seismogenic structures at depth that are deficiently known due to a thick cenozoic sedimentary cover the hidden character of many of the faults in the lower tagus valley requires the use of indirect methodologies for their study this paper focuses on the application of high resolution seismic reflection method for the detection of near surface faulting on two major tectonic structures that are hidden under the recent alluvial cover of the tagus valley and that have been recognized on deep oil industry seismic reflection profiles and or inferred from the surface geology these are a wnw ese trending fault zone located within the lower tagus cenozoic basin across the tagus river estuary porto alto fault and a nne ssw trending reverse fault zone that borders the cenozoic basin at the w vila franca de xira lisbon fault vertical electrical soundings were also acquired over the seismic profiles and the refraction interpretation of the reflection data was carried out according to the interpretation of the collected data a complex fault pattern disrupts the near surface first 400 m at porto alto affecting the upper neogene and at least for one fault the quaternary with a normal offset component the consistency with the previous oil industry profiles interpretation supports the location and geometry of this fault zone concerning the second structure two major faults were detected north of vila franca de xira supporting the extension of the vila franca de xira lisbon fault zone northwards one of these faults presents a reverse geometry apparently displacing holocene alluvium vertical offsets of the holocene sediments detected in the studied geophysical data of porto alto and vila franca de xira lisbon faults imply minimum slip rates of 0 15 0 30 mm year three times larger than previously inferred for active faults in the lower tagus valley and maximum estimates of average return periods of 2000 5000 years for m 6 5 7 co seismic ruptures

the structural and sedimentary evolution of the arruda and lower tagus sub basins portugal abstract the study discusses the jurassic structural and sedimentary evolution of the arruda and lower tagus sub basins located in the central and southern part of the lusitanian basin of portugal in the last five decades thousands of kilometres of 2d seismic reflection lines were acquired for oil exploration reprocessing and reinterpretation of over 700 km from the study area was carried out after the seismic to well ties based on well logs vsp analysis synthetic seismograms revised petrological analysis and stratigraphic reinterpretation of the wells nine key seismic geologic horizons were mapped and depth converted reinterpretation of the seismic profiles was carried out using outcrop data and reprocessed aeromagnetic and gravimetric data of the study area that was integrated in a gis environment several aspects of the tectonic and sedimentary evolution of the study area were enlightened from the triassic until the late jurassic two rift phases were recognised in agreement with data from other parts of the lusitanian basin the initial rifting phase in the triassic continued until the callovian with three prominent tectonic pulses a first in the late triassic a second in the hettangian and a third from the sinemurian onwards the latter episode lasted until the callovian in the arruda sub basin and at least until the bathonian in the lower tagus sub basin during the middle jurassic the arruda sub basin evolved to a nw deepening carbonate ramp the lower tagus sub basin constituted a platform since the early jurassic limited in the east by the setubal pinhal novo fault and in the west by the cadafais fault the third rifting episode occurred in the late oxfordian early kimmeridgian producing a major n s fault system already recognised by several authors and another important nw se and ne sw fault systems post dating the former

pre alpine evolution of a segment of the north gondwanan margin geochronological and geochemical evidence from the central serbo macedonian massif abstract the serbo macedonian massif smm represents a composite crystalline belt within the eastern european alpine orogen outcropping from the pannonian basin in the north to the aegean sea in the south the central parts of the massif i e southeastern serbia southwestern bulgaria eastern macedonia consist of the medium to high grade lower complex and the low grade vlasina unit new results of u pb la icp ms analyses coupled with geochemical analyses of hf isotopes on magmatic and detrital zircons and main and trace element concentrations in whole rock samples suggest that the central smm and the basement of the adjacent units i e eastern veles series and struma unit originated in the central parts of the northern margin of gondwana these data provided a basis for a revised tectonic model of the evolution of the smm from the late ediacaran to the early triassic the earliest magmatism in the lower complex vlasina unit and the basement of struma unit is related to the activity along the late cadomian magmatic arc 562 522 ma subsequent stage of early palaeozoic igneous activity is associated with the reactivation of subduction below the lower complex and the eastern veles series during the early ordovician 490 478 ma emplacement of mafic dykes in the lower complex due to aborted rifting in the middle ordovician 472 456 ma and felsic within plate magmatism in the early silurian 439 2 ma the third magmatic stage is represented by carboniferous late to post collisional granites 328 304 ma these granites intrude the gneisses of the lower complex in which the youngest deformed igneous rocks are of early silurian age thus constraining the high strain deformation and peak metamorphism to the variscan orogeny the permian triassic 255 253 ma stage of late to post collisional and within plate felsic magmatism is related to the opening of the mesozoic tethys

seismic reflection imaging of tertiary faulting and related post eocene deformation 20 km north of memphis tennessee abstract other than the crittenden county fault zone ccfz little is known about the seismic hazard from earthquake faults within 50 km of memphis tennessee a city that contains a large inventory of older buildings that are vulnerable to moderate and strong earthquake ground shaking to address this lack of knowledge about faulting near memphis we acquired a 4 5 km long mini sosie seismic reflection profile across the boundary between the loess covered bluffs and modern mississippi river flood plain in meeman shelby forest state park north of memphis we imaged a previously unknown reverse thrust fault that displaces paleozoic and cretaceous rocks and upwarps tertiary deposits on the floodplain portion of the profile about 25 km north of downtown memphis the paleozoic and cretaceous rocks are vertically faulted about 70 and 40 m respectively in an up to the west sense of displacement the fault displacement apparently terminates in the basal portion of the paleocene section and causes only an upwarping of the overlying deposits the overlying paleocene and eocene deposits which are probably the youngest deposits imaged are upwarped about 50 60 m with the same sense of displacement as the underlying older units the sense of displacement amplitude and appearance of the fault in the seismic data are very similar to that observed in the seismic reflection images of the ccfz 15 km west of this profile although we have imaged this new fault in only one location its proximity to memphis and similarities to the ccfz leads us to speculate that it may be a parallel structure to the ccfz and thus warrants further study

structural analysis of a complex nappe sequence and late orogenic basins from the aegean island of samos greece the island of samos in the aegean sea exposes high pressure metamorphic rocks of the cycladic blueschist unit which are sandwiched between the mildly blueschist facies kerketas nappe below and the overlying non metamorphic kallithea nappe structural and metamorphic analysis shows that deformation can generally be divided into four main stages 1 eocene and earliest oligocene 0ese wnw oriented nappe stacking d1 and d2 associated with blueschist and transitional blueschist greenschist facies metamorphism m1 and m2 d2 caused emplacement of the blueschist unit onto the kerketas nappe indicating that thrusting occurred during decompression 2 a subsequent history of oligocene and miocene horizontal crustal extension d3 before and after greenschist facies metamorphism m3 ductile flow during d3 was characterized by a high degree of coaxial deformation but in general caused displacement of upper units towards the ene nonetheless the late stage d3 emplacement of the kallithea nappe between 9 and 10 ma had a top to the nw nnw sense of shear 3 a short period of brittle e w crustal contraction d4 occurred between 8 6 and 09 ma 4 a phase of n s directed normal faulting d5 8 6 ma to recent ese wnw directed tectonic transport during d1 through d3 is in contrast to uniform nne sswdirected tectonic transport in the adjacent cyclades greece as well as in the neighbouring menderes massif of western turkey published paleomagnetic data reveal sinistral rotation between the cyclades and western turkey we interpret this rotation as a consequence of diaerential extension between the severely extended aegean and the moderately extended menderes massif during d3 the onset of d3 crustal extension is coeval with a marked change in the thermal structure we propose that the thermal reorganization was associated with the retreat of the subduction zone towards the external hellenides in the early oligocene and a subsequent increase in magmatic activity 1999 elsevier science ltd all rights reserved

structure and evolution of the seismically active ostler fault zone new zealand based on interpretations of multiple high resolution seismic reflection profiles abstract to improve our understanding of active faulting away from the main plate boundary on new zealand s south island we have acquired high resolution seismic data across the ostler fault zone twelve 1 2 km long lines perpendicular to fault strike and a 1 6 km long crossline were collected in a region of the mackenzie basin where surface mapping delineates significant complexity in the form of two non overlapping reverse fault strands separated by a transfer zone characterised by multiple smaller strands and increased folding interpretation of the resultant images includes a 45 55 west dipping principal fault and two 25 30 west dipping subsidiary faults one in the hanging wall and one in the footwall of the principal fault the geologically mapped complexities are shown to be caused by shallow variations in the structure of the principal fault which breaks the surface in the north and south but not within the transfer zone where it forms a triangle zone with associated backthrusting and minor faulting these complexities only extend to 300 m depth structures below this level are markedly simpler and much more 2d in nature with the principal fault strand extending over a much longer distance than the individual strands observed at the surface since longer faults are susceptible to larger earthquakes than shorter ones seismic hazard at the study site may be higher than previously thought multiple surface fault strands that give way to a single more major stand at relatively shallow depths may be a common feature of segmented fault systems the deepest layered reflections at our site are consistent with the presence of a late cretaceous tertiary basin underlying the present day mackenzie basin structural restoration of the seismic images back to the base of quaternary fluvioglacial terraces and back to the top of a late pliocene pleistocene fluviolacustrine unit indicate that compression was initiated prior to the late pliocene and that it has continued at a comparatively steady rate of about a millimetre per year to the present day the fluviolacustrine unit has experienced 440 800 m of along fault vertical offset and 870 1080 m of horizontal shortening since that time our study demonstrates that structural reconstructions based on high resolution seismic reflection data provide critical displacement information that can be used to estimate slip rates

soft sediment deformation within seismogenic slumps of the dead sea basin abstract the late pleistocene lisan formation preserved next to the dead sea provides exceptional 3 d exposures of folds and faults generated during soft sediment slumping and deformation it is possible to generate a range of four different scenarios associated with overprinting in a single slump event the progressive evolution of slump systems may be broadly categorised into initiation translation cessation relaxation and compaction phases thrust packages typically define piggyback sequences during slump translation with back steepening of imbricate faults leading to collapse of folds back up the regional palaeoslope detailed evaluation of slumped horizons may also permit structures to be traced across apparently separate and distinct slumped units the recognition that slumps may be reworked by younger seismically triggered events suggests that in some cases the seismic recurrence interval may be shorter than previously anticipated

the eastern lower tagus valley fault zone in central portugal active faulting in a low deformation region within a major river environment abstract active faulting in the lower tagus valley central portugal poses a significant seismic hazard that is not well understood although the area has been affected by damaging earthquakes during historical times only recently has definitive evidence of quaternary surface faulting been found along the western side of the tagus river the location geometry and kinematics of active faults along the eastern side of the tagus valley have not been previously studied we present the first results of mapping and paleoseismic analysis of the eastern strand of the lower tagus valley fault zone ltvfz geomorphological paleoseismological and seismic reflection studies indicate that the eastern ltvfz is a left lateral strike slip fault the detailed mapping of geomorphic features and studies in two paleoseismic trenches show that surface fault rupture has occurred at least six times during the past 10 ka the river offsets indicate a minimum slip rate on the order of 0 14 0 24 mm yr for the fault zone fault trace mapping geomorphic analysis and paleoseismic studies suggest a maximum magnitude for the eastern ltvfz of m w 7 3 with a recurrence interval for surface ruptures 1 7 ka at least two events occurred after 1175 95 cal yr bp single event displacements are unlikely to be resolved in the paleoseismic trenches thus our observations most probably represent the minimum number of events identified in the trenches

crustal seismic structure beneath portugal and southern galicia western iberia and the role of variscan inheritance abstract the crustal structure in western iberia is the result of a complex geodynamic history most of the surface is covered by rocks dating to the variscan orogeny the coastal ranges dominated by mesozoic structures and mesocenozoic basins covering partially the mainland in this study we present the results of a local earthquake tomographic study performed to image in depth this complex crustal structure down to 24 km depth the obtained tomograms present a good correlation with the surface geology in general with higher vp velocities in the north and lower vp velocities in the south the heterogeneity observed on the surface geology of the galicia tras os montes zone is well marked being a relatively thin layer over the smoother structure of the centro iberia zone ciz the ciz crustal block confined between the porto tomar ferreira do alentejo and the manteigas braganca faults having higher vp values enhancing the contrast to the lusitanian basin to the west the ossa morena zone corresponds to the unit presenting the greater heterogeneity in both vp and vp vs models showing also with a complex transition to the south portuguese zone and a relatively smooth transition to the centro iberian zone unexpectedly the south portuguese zone present an east west velocity variation with no apparent correspondence with the surface geology the transition to the coastal mesocenozoic basins is clearly marked the lower tagus valley corresponding to a 4 km thick low velocity region the relocation inland recorded seismicity in the period 2000 2014 allows cleansing some of the alignments and establish their correlation with some of the active structures in portugal the model features and seismicity pattern reveal the strong role played by the variscan heritage

integrating s wave seismic reflection data and cone penetration test data using a multiangle multiscale approach a cone penetration test cpt is the most common geotechnical testing method used to estimate in situ the strength properties of soil although cpt provides valuable information this information is restricted to the location of the measurement we propose a new concept to integrate shallow s wave reflection seismic data with cpt data in order to obtain laterally continuous subsoil information in this vein a valid quantitative means to relate seismic reflections to cpt data is a primary requirement the approach proposed here is based on the characterization of the scaling behavior of the local fine scale s wave velocity information extracted from the seismic reflection data and the same behavior of the cpt cone resistance the local velocity contrast information is extracted by linearized zoeppritz inversion of the amplitude preserved prestack reflection data we have formulated a multiscale analysis approach employing the continuous wavelet transform in order to quantitatively characterize the nature

closure of the paleotethys in the external hellenides constraints from u pb ages of magmatic and detrital zircons crete abstract paleotethys was a highly mobile oceanic realm pinching into the supercontinent pangea between gondwana and eurasia in the late paleozoic early mesozoic published paleotethyan reconstructions reveal that the time of paleotethys closure and the position of its suture are highly debated we present new magmatic and detrital zircon ages separated from pre alpine basement and permian to triassic cover rocks exposed in the external hellenides of crete these age data reveal variscan and cimmerian docking of microplates along the southern margin of laurasia and help to constrain the time of paleotethys closure 46 of detrital zircons from quartzite in the variscan basement are pennsylvanian with concordant ages at 321 2 ma 310 3 ma and 300 3 ma the basement is unconformably overlain by arc related volcanics of the tyros unit magmatic zircons of which yielded a concordant u pb zircon age at 285 2 ma thus the metasediments of the basement interpreted as former trench sediments were deposited metamorphosed and exhumed in latest carboniferous to early permian times 302 283 ma magmatic activity during this late variscan phase is also indicated by igneous boulders within olenekian meta conglomerates of the tyros unit which yielded concordant u pb zircon ages at 291 2 and 310 2 ma the late variscan orogenic phase is attributed to the collision of the gondwana derived southern minoan terrane smt with laurasia subsequent to northward subduction of paleotethys lithosphere and visean collision of the northern minoan terrane nmt magmatic activity ceased during the late permian but revived in the lower triassic as is indicated by felsic volcanics 249 2 ma concordant u pb zircon and by detrital zircons 242 3 240 5 ma 237 3 ma concordant u pb zircon of the tyros unit at the same time the variscan chain was exhumed and removed as is shown by the detritus in the lower to middle triassic tyros sediments which includes high grade metamorphic rocks and detrital zircons with u pb ages ranging from 280 to 335 ma a significant change in the detrital components occurred in the ladinian when the variscan basement with its permo triassic cover was thrust on top of clastic sediments today represented by the phyllite quartzite unit s str the phyllite quartzite unit s str shows cadomian and older but no variscan detritus because of its position along the northern margin of the cimmerian ribbon continent thus in the eastern mediterranean paleotethys was closed during the ladinian and the related suture in the external hellenides is situated between the variscan basement active margin in the north and the phyllite quartzite unit s str passive margin in the south carnian crustal extension led to subsidence of the variscan cimmerian chain most parts of which merged below sea level this is the reason why 90 of the detritus of the carnian tyros beds are not related to the variscan but to the cadomian and grenvillian basement of the e gondwana derived cimmerian ribbon continent

hydrocarbon prospectivity in the hellenic trench system organic geochemistry and source rock potential of upper miocene lower pliocene successions in the eastern crete island greece results of the current and already published studies suggest that the tortonian in age deposits could serve a major source rocks for both oil and gas beneath the messinian evaporites in the hellenic trench system additionally the strong terrestrial input in pliocene deposits could lead to the production of biogenic gas similar to the po basin in adriatic sea italy in the current study fourteen samples from late miocene faneromeni section and twelve samples from the early pliocene makrilia section in eastern crete were collected in order to evaluate their hydrocarbon generation potential for this purpose rock eval analysis and characterization of the organic matter were performed the results document a clear distinction between the two sections faneromeni section contains organic matter of kerogen type iii whereas the makrilia section contains organic matter of kerogen type iv the hi toc plot diagram in both sections indicates poor oil generating potential with the exception of several samples showing fair to good gas and oil potential although thermal maturities of the samples from the two successions are similar according to the t max values samples from faneromeni succession exhibit higher hydrogen index values indicating a better quality of organic matter in terms of hydrocarbon generation very low obtained concentrations of bitumen mg g of rock as well as the predominance of nso compounds compared to the saturates and aromatics indicate low maturation level the n alkanes profiles exhibit a bimodal distribution indicating a mixed origin marine and terrestrial of the organic matter in both areas terrestrial organic matter input is more pronounced in makrilia section the analysis of saturated biomarkers indicates that faneromeni deposits were accumulated under constant organic matter input in an environment influenced by cyclic changes from marine to lagoon origin and vice versa faneromeni section corresponds to a restricted basin during tortonian with quick and often sea level fluctuations just before the messinian crisis while makrilia section represents a very restricted intramontane basin with strong terrestrial influence

analyzing shallow faulting at a site in the wasatch fault zone utah usa by integrating seismic gravity magnetic and trench data abstract gravity magnetic and seismic surveys were conducted across the wasatch fault zone east of springville utah near the mouth of hobble creek canyon the geophysical data were acquired processed and interpreted to determine possible locations of larger total offset greater than 6 ft 1 8 m shallow normal faults within the fault zone interpretations of the individual data sets were integrated to help eliminate spurious readings and to strengthen the interpretations visual methods of integration along with computer modeling were chosen for this study furthermore the geophysical data were correlated and integrated with available trench data and surface data in addition to verifying locations of known faults the geophysical surveys detected numerous possible additional faults not previously mapped of particular interest is a newly discovered graben structure near the southern end of the site where building of new homes has recently been proposed new structural information about fault densities and styles was also determined from the surveys the fault concentration for this site is 1 3 faults 100 ft 30 5 m or one fault per 77 ft 23 5 m interpreted antithetic faults at the hobble creek site account for 65 of the total while synthetic faults account for 35 with respect to the main fault strand information derived from this study should be useful during planning and development of areas within the wasatch fault zone the characteristics of subsurface deformation can be used to gain a better understanding of the potential for surface rupture at a given site this is also useful in planning appropriate site development and remedial measures to help mitigate hazards associated with large magnitude earthquakes

relative age of cordilleran base metal lode and replacement deposits and high sulfidation au ag epithermal mineralization in the colquijirca mining district central peru at colquijirca central peru a predominantly dacitic miocene diatreme dome complex of 12 4 to 12 7 ma 40ar 39ar biotite ages is spatially related to two distinct mineralization types disseminated au ag associated with advanced argillic alteration and local vuggy silica typical of high sulfidation epithermal ores are hosted exclusively within the volcanic center at marcapunta a second economically more important mineralization type is characterized as cordilleran base metal lode and replacement deposits these ores are hosted in mesozoic and cenozoic carbonate rocks surrounding the diatreme dome complex and are zoned outward from pyrite enargite quartz alunite to pyrite chalcopyrite dickite kaolinite to pyrite sphalerite galena kaolinite siderite alunite samples related to the au ag epithermal ores have been dated by the 40ar 39ar method at 11 3 11 6 ma and those from the cordilleran base metal ores in the northern part of the district smelter and colquijirca at 10 6 10 8 ma the significant time gap 0 5 my between the ages of the two mineralization types in the colquijirca district indicates they were formed by different hydrothermal events within the same magmatic cycle the estimated time interval between the younger mineralization event base metal mineralization at 10 6 ma and the ages of 12 5 ma obtained on biotites from unmineralized dacitic domes flanking the vicinity of the diatreme vent suggest a minimum duration of the magmatic hydrothermal cycle of around 2 ma this study on the colquijirca district offers for the first time precise absolute ages indicating that the cordilleran base metal lode and replacement deposits were formed by a late hydrothermal event in an intrusive related district in this case post au ag high sulfidation epithermal mineralization

syn sedimentary gravity slides growth faults in the coal measures of south wales growth faults are an important class of syn sedimentary fault which have been widely recognized in sub surface studies of hydrocarbon bearing clastic basin successions1 4 they are listric normal faults which are active for a limited period during sediment deposition and therefore affect a discrete sedimentary interval whilst active the faults substantially influence sedimentation and a thicker generally sand dominated succession accumulates on the downthrown side which is consistently towards the basin the faults are not directly related to basement tectonics and instead are thought to originate principally by gravity sliding within the sediment pile5 over pressured undercompacted conditions in buried muds aid development of the faults by reducing the slope required to initiate sliding5 and in some cases associated mud diapirism also contributes by creating steeper slopes6 despite their widespread recognition in sub surface studies relatively few examples have been described from exposed successions7 10 and none from the economically important upper carboniferous coal measures of europe here we describe examples of growth faults recently discovered in an opencast site of the coal measures in south wales and comment on their possible significance

resolving cambrian carboniferous permian and alpine monazite generations in the polymetamorphic basement of eastern crete greece by means of the electron microprobe the electron microprobe based investigation of accessory monazites in polished thin sections is a helpful tool in resolving the geochronology of a polymetamorphic basement the method was applied to variably altered gneisses and micaschists from the retrogressed originally amphibolite facies basement in eastern crete greece the presented data indicate that most monazite formed or recrystallized in response to high fluid activity during alpine low temperature metamorphism this low temperature monazite is characterized by distinctly low yttrium uranium and thorium contents however older grains were able to survive in less retrogressed samples and have been traced with the electron microprobe using microstructural and compositional criteria in situ chemical th u pb dating of these pre alpine monazites provides evidence for an igneous event in the cambrian and two different metamorphic events in the carboniferous and permian

evidence for fault weakness and fluid flow within an active low angle normal fault determining the composition and physical properties of shallow dipping active normal faults dips 35 with respect to the horizontal is important for understanding how such faults slip under low resolved shear stress and accommodate significant extension of the crust and lithosphere seismic reflection images1 and earthquake source parameters2 show that a magnitude 6 2 earthquake occurred at about 5 km depth on or close to a normal fault with a dip of 25 30 located ahead of a propagating spreading centre in the woodlark basin here we present results from a genetic algorithm inversion of seismic reflection data which shows that the fault at 4 5 km depth contains a 33 m thick layer with seismic velocities of about 4 3 km s 1 which we interpret to be composed of serpentinite fault gouge isolated zones exhibit velocities as low as 1 7 km s 1 with high porosities which we suggest are maintained by high fluid pressures we propose that hydrothermal fluid flow possibly driven by a deep magmatic heat source and high extensional stresses ahead of the ridge tip have created conditions for fault weakness and strain localization on the low angle normal fault

cambrian granitoids in pre alpine basement of crete greece evidence from u pb dating of zircon the pre alpine basement of eastern crete consists of at least three sub complexes which show differences in age and grade of pre alpine metamorphism u pb analyses of zircons of two orthogneisses yielded upper intercepts in the concordia diagram at 511 16 ma chamezi crystalline complex and 514 14 ma myrsini crystalline complex these values are interpreted as protolith ages of the gneisses suggesting that parts of the basement underwent cadomian pan african imprints at the northern margin of gondwana the lower intercept ages are attributed to alpine subduction which led to high pressure low temperature metamorphism t ca 300 c brittle ductile deformation and hydrothermal fluid activity due to pervasive alpine fluid migration the zircons of the chamezi crystalline complex display disturbed zonation and solution resulting in 87 radiogenic pb loss ca and al gain and zr depletion

elevator tectonics and orogenic collapse of a tibetan style plateau in the european variscides the role of the bohemian shear zone variscan collision of peri gondwanan terranes led to a doubly vergent crustal wedge that was thicker than 55 km in the area of the bohemian massif this crustal thickness resulted in a highly elevated bohemian plateau with a topographic height 3 4 km the bohemian plateau was covered with unmetamorphic paleozoic strata all of which are today well preserved in the tepla barrandian unit because of crustal scale vertical slip along the bohemian shear zone bsz the bsz forms a subvertical ca 500 km long and up to 2 km wide belt of dip slip mylonites which show several 90 deflections in map view tepla barrandian down movements were active under retrograde metamorphic conditions starting with granulite and ceasing with greenschist facies conditions as slip along the bsz was largely vertical and led to a minimum throw of 10 km this type of crustal scale deformation is referred to as elevator tectonics the elevator style movements caused the juxtaposition of the supracrustal tepla barrandian lid the elevator against high grade rocks of the extruding orogenic root the bsz has further governed the foci of mantle derived plutonism new u pb zircon and monazite tims dating of six plutons suggest that emplacement of mantle derived melts along the bsz lasted for at least 20 m y starting with the emplacement of the klatovy granodiorite at 347 4 3 ma and ceasing with the emplacement of the drahotin pluton at 328 1 ma when taking into account the new ages of synkinematic plutons the simultaneous vertical slip along the individual segments of the bsz north west and central bohemian shear zone is bracketed to the period 343 337 ma elevator tectonics was probably controlled by delamination of thickened mantle lithosphere that caused a dramatic thermal turnover and heating up of the orogenic root the overheated lower crust was thermally softened by anatexis and diffusion creep resulting in channel flow vertical extrusion fast uplift and exhumation of the orogenic root

soft sediment deformation in a tectonically active area the plio pleistocene zarzal formation in the cauca valley western colombia abstract the plio pleistocene zarzal formation corresponds to fluvio lacustrine sediments deposited in an intramontane depression within the colombian andes associated with the cauca romeral fault system it crops out mainly in the cauca valley where numerous field sections have permitted the mapping of the vertical and lateral lithological variations lacustrine deposits of sands silts clays and diatomites are interbedded with fluvial sand and gravel beds and fluvio volcanic mass flows derived from the volcanic central cordillera numerous soft sediment deformation structures are encountered in this formation particularly in fine to medium grained sands silts and clays load structures load casts flame structures pseudonodules water escape structures water escape cusps dish and pillar and pocket and pillar structures soft sediment intrusions clastic sills and dykes disturbed laminites convolute laminations slumps and synsedimentary faulting deformation mechanisms and driving forces are related essentially to gravitational instabilities dewatering liquidization and brittle deformations field and regional geological data show that most of these deformations are related to seismicity and can be interpreted as seismites this area has a geological and recent seismic history and outcrops show both syn and post depositional faulting related to the transpressional regime of this part of the colombian andes which generates strike slip faults and associated local normal faults the drainage pattern within the zarzal formation shows the signature of neotectonics moreover the fine to coarse grained sands of the zarzal formation are lithologies prone to liquefaction when affected by seismic waves the intercalation of the deformed intervals within undisturbed strata confirms the catastrophic nature of the events finally the large areal extent of the deformations and the type of structures are compatible with seismites consequently the existence of seismites in the zarzal formation represents corroboration of tectonic activity in this area during the pleistocene earthquakes with a magnitude higher than 5 can be postulated based upon the proximity of active faults and the types of deformations

a new classification of the turkish terranes and sutures and its implication for the paleotectonic history of the region abstract the turkish part of the tethyan realm is represented by a series of terranes juxtaposed through alpine convergent movements and separated by complex suture zones different terranes can be defined and characterized by their dominant geological background the pontides domain represents a segment of the former active margin of eurasia where back arc basins opened in the triassic and separated the sakarya terrane from neighbouring regions sakarya was re accreted to laurasia through the balkanic mid cretaceous orogenic event that also affected the rhodope and strandja zones the whole region from the balkans to the caucasus was then affected by a reversal of subduction and creation of a late cretaceous arc before collision with the anatolian domain in the eocene if the anatolian terrane underwent an evolution similar to sakarya during the late paleozoic and early triassic times both terranes had a diverging history during and after the eo cimmerian collision north of sakarya the kure back arc was closed during the jurassic whereas north of the anatolian domain the back arc type oceans did not close before the late cretaceous during the cretaceous both domains were affected by ophiolite obduction but in very different ways north directed diachronous middle to late cretaceous melange obduction on the jurassic sakarya passive margin senonian synchronous southward obduction on the triassic passive margin of anatolia from this it appears that the izmir ankara suture currently separating both terranes is composite and that the passive margin of sakarya is not the conjugate margin of anatolia to the south the cimmerian taurus domain together with the beydaglari domain part of the larger greater apulian terrane were detached from north gondwana in the permian during the opening of the neotethys east mediterranean basin the drifting cimmerian blocks entered into a soft collision with the anatolian and related terranes in the eo cimmerian orogenic phase late triassic thus suturing the paleotethys at that time the taurus plate developed foreland type basins filled with flysch molasse deposits that locally overstepped the lower plate taurus terrane and were deposited in the opening neotethys to the south these olistostromal deposits are characterized by pelagic carboniferous and permian material from the paleotethys suture zone found in the mersin melange the latter as well as the antalya and mamonia domains are represented by a series of exotic units now found south of the main taurus range part of the mersin exotic material was clearly derived from the former north anatolian passive margin huglu type series and re displaced during the paleogene this led us to propose a plate tectonic model where the anatolian ophiolitic front is linked up with the samail baer bassit obduction front found along the arabian margin the obduction front was indented by the anatolian promontory whose eastern end was partially subducted continued slab roll back of the neotethys allowed anatolian exotics to continue their course southwestward until their emplacement along the taurus southern margin mersin and up to the beydaglari promontory antaya mamonia in the latest cretaceous paleocene the supra subduction ocean opening at the back of the obduction front troodos type ocean was finally closed by eocene north south shortening between africa and eurasia this brought close to each other cretaceous ophiolites derived from the north of anatolia and those obducted on the arabian promontory the latter were sealed by a maastrichtian platform and locally never affected by alpine tectonism whereas those located on the eastern anatolian plate are strongly deformed and metamorphosed and affected by eocene arc magmatism these observations help to reconstruct the larger frame of the central tethyan realm geodynamic evolution

thermobarometric data from a fossil zircon partial annealing zone in high pressure low temperature rocks of eastern and central crete greece abstract a fossil partial annealing zone of fission tracks in zircon is described from high pressure low temperature hp lt rocks of the phyllite quartzite unit pq on the island of crete greece correlation of regional trends in fission track age populations with independent thermobarometric and microstructural data and with new experimental annealing results allows a calibration of this low temperature thermochronological method to a degree hitherto not available from other field examples the zircon fission track ft ages of samples from the pq across crete range from original detrital signature through reduced to completely reset the annealing is the result of a single heating period related to the hp lt metamorphism with near peak temperatures lasting for only a few million years some time between 24 1 and 20 1 ma in eastern crete where rocks have experienced temperatures of 300 50 c and pressures of 0 8 0 3 gpa zircon ft ages range from 414 24 to 145 10 ma ages above 300 ma occur mostly near the east coast of the island in rocks which have not been heated to above ca 280 c and probably represent a pre variscan source track lengths are already indicative of a substantial annealing at this temperature most of the zircon ft ages from eastern crete scatter within error around the stratigraphic age samples with apparent zircon ft ages significantly younger than the depositional age are only observed in areas where temperatures exceeded ca 320 c towards the west a sudden decrease to very young ages ranging from 17 2 to 18 1 ma reflects a complete resetting at ca 350 c short tracks however are still observed throughout the central and western part of the island ages are consistently below 22 ma thermobarometric data for this area indicate maximum temperatures of 400 50 c and pressures of 1 0 3 gpa only samples from western crete which have been exposed to 400 50 c show exclusively long tracks consequently the high temperature limit of the zircon partial annealing zone zpaz appears to be between 350 and 400 c a significant influence of elevated confining pressure on the stability of fission tracks in zircon is ruled out by the results of annealing experiments at 0 5 gpa and at different temperatures which fit the curves previously obtained by other authors at ambient pressure

provenance of sediments during subduction of palaeotethys detrital zircon ages and olistolith analysis in palaeozoic sediments from chios island greece abstract detrital zircon geochronology and analysis of fossiliferous olistoliths from chios island greece are used here to constrain terrane accretion processes and the provenance of crustal sources for sediments during the subduction of a branch of the palaeotethys ocean u pb ages obtained by ion microprobe shrimp ii analyses of detrital zircons from a carboniferous greywacke belonging to the tectonostratigraphic lower unit of chios gave major age groups of 2150 1890 ma 640 540 ma 505 475 ma and 365 322 ma detrital zircons from a permian triassic sandstone yielded prominent age clusters of 2200 1840 ma 1100 910 ma 625 560 ma and 385 370 ma the lack of zircon ages between 1 8 and 1 1 ga in both samples coupled with the occurrence of ca 2 ga old zircons imply a northern gondwana nw africa source the conodont fauna recovered from an orthoceras bearing limestone lens from the carboniferous succession of the lower unit indicates a late silurian age the fauna is typical of the ludfordian polygnathoides siluricus conodont zone the material has a conodont colour alteration index cai of about 1 2 indicating very low grade thermal alteration of less than 100 c the closest localities with similar conodont bearing limestones are to be found in the balkan region and in the istanbul zone of northern turkey the occurrence of orthoceras limestone can be used as an indicator of palaeosource reconstruction our new zircon ages in conjunction with provenance analysis of silurian to lower carboniferous olistoliths strongly suggest that the clastic succession of chios received its detritus from basement rocks of the sakarya microcontinent in western turkey and time and facies equivalents of palaeozoic units from the istanbul zone in northern turkey and the balkan region due to subduction of a branch of palaeotethys close to the southern active margin of eurasia in late palaeozoic times the multidisciplinary approach of this study underlines the importance of terrane accretion during stepwise closure of palaeotethys

structural and sedimentary evidence from the northern margin of the tauride platform in south central turkey used to test alternative models of tethys during early mesozoic time abstract critical to reconstruction of the tethys ocean is the nature and significance of a reported latest triassic cimmerian tectonic event in the tauride mountains of south central turkey in one published model a cimmerian continental fragment including the tauride platform rifted from the northern margin of gondwana and collided with a eurasian derived anatolide continental fragment during late triassic time causing orogenic deformation of the tauride continental platform in a second published model southward subduction of a palaeotethyan ocean opened a back arc basin associated with rift related uplift of the tauride platform during early triassic time the tauride platform remained as a north facing passive margin from the mid late triassic to late cretaceous without further deformation in a third published model a continental fragment rifted from a tauride anatolide platform in the south opening a small ocean basin ankara izmir ocean to the north by mid late triassic time late triassic deformation and uplift of the tauride platform possibly resulted from far field stress transmission from the cimmerian orogeny that affected the eurasian margin in an additional model a tauride anatolide continent experienced a rift related evolution culminating in a pulse of extension related uplift during the latest triassic followed by seafloor spreading to the north the models are tested using evidence from relatively autochthonous tauride units geyik dag sultan dag and over riding thrust sheets hadim aladag nappe bolkar nappe geological mapping of critical areas and related structural evidence show that most of the deformation in the area can be related to late cretaceous and early cenozoic alpine emplacement of the tauride nappes although late triassic compressional deformation is likely at one locality sedimentary evidence from the cayir formation a widespread latest triassic earliest jurassic clastic sequence shows that it accumulated in a range of non marine to locally shallow marine fluvial to deltaic settings palaeocurrent data indicate mainly southward sediment transport most of the material was derived from lithologies equivalent to those exposed within the underlying tauride platform and within an upper palaeozoic basement unit konya complex to the north a combination of the available structural sedimentary and stratigraphical information from the tauride region and international comparisons lead us to exclude the presence of a palaeotethyan suture of latest triassic age within the taurides rather we explain the late triassic early jurassic tauride geology mainly in terms of the uplift of a basement unit that was located along northern margin of the tauride carbonate platform associated with opening of the izmir ankara ocean to the north

late carboniferous plutonism within the pre alpine basement of the external hellenides kithira greece evidence from u pb zircon dating in memory of theodor doutsos for his invaluable contribution to the understanding of geology of greece u pb zircon dating of three granitic orthogneisses sampled from kithira island sw greece provide the first reliable evidence for carboniferous plutonism within the pre alpine basement of the external hellenides concordant zircons from two samples yielded ages at 324 2 ma and 323 3 ma whereas the third sample yielded a lower intercept age at 320 1 2 ma the concordant ages are interpreted to date the emplacement of the igneous protolith ages of inherited zircons of two orthogneisses range from 2 5 to 2 4 ga indicating late archaean early proterozoic crustal components in combination with published ages for other aegean metagranitoids the new u pb ages provide additional evidence of a temporally restricted period of plutonism in the pre alpine aegean region from 325 to 300 ma comparing the post neoproterozoic evolution of the investigated basement with that of the cycladic and pelagonian basements and of the continental massifs of ne greece and turkey we argue that all these crustal blocks were part of the gondwana derived cimmerian terrane based on the spatial and temporal distribution of late carboniferous aegean plutonism we suggest that this period of magmatic events results from the southward subduction of palaeotethys beneath the marginal fragments of northern gondwana

isotopic dating in metamorphic belts isotopic dating in metamorphic rocks is concerned with the timing of processes whose operation is controlled by continually changing physical conditions of these temperature has a pervasive influence and the use of physical models to elucidate the ways in which temperature is likely to vary is briefly reviewed the central concept of closure temperature is critically discussed and quantitative estimates for biotite and hornblende are evaluated in order to illustrate the factors which control closure temperatures and limit their application in practice the possibility of dating crystallization using minerals which crystallize below their respective closure temperatures is examined taking examples involving k ar rb sr sm nd and u pb analyses the indirect dating of metamorphism via structurally dated plutons is briefly considered and the problems of interpreting both discordant u pb zircon ages and rb sr whole rock isochrons in metamorphosed granites are discussed the value of near concordant zircon ages is emphasized the extent of isotopic equilibration during metamorphism specifically of sr isotopes in metasediments is shown not to be a simple function of metamorphic grade the flow of fluids produced by metamorphic reactions appears to be crucial and there is a potential for dating metamorphism using whole rock samples where such flow can he demonstrated independently the concluding discussion briefly examines existing data for the dalradian and indicates the potential for further progress using both well established and novel approaches

deformation within the cycladic subduction exhumation channel new insights from the enigmatic makrotantalo nappe andros aegean new detailed geological structural mapping coupled with microstructural investigations and amphibole chemistry analyses are used to elucidate the enigmatic tectonic evolution of the makrotantalo nappe on northern andros aegean region on the basis of the new geological map we re evaluate the structural position of samples with previously published metamorphic ages to show that the makrotantalo nappe has been affected by the early eocene high pressure hp metamorphism therefore the makrotantalo nappe is an integral part of the cycladic blueschist unit cbu the early main ductile deformation phase recognized in the mapped area is associated with the emplacement of the makrotantalo nappe over the north cyclades nappe at deep subduction levels during early eocene the subsequent deformation phase occurred at the middle eocene oligocene synchronous with the decompression of blueschist rocks from the stability field of glaucophane to that of actinolite during this phase the nappe pile was folded by map scale folds which were locally transposed by ductile shear zones these shear zones were related with ne directed oblique thrusting and locally either restacked the nappe pile or reworked the early nappe contact our results in combination with previous studies in the northern cyclades show that the top to the ne shearing was dominant at a large part of the cbu during exhumation opposite sw directed shearing was restricted at the upper structural levels of the cbu we suggest that the observed spatial variation in shear sense is compatible with ne rather than sw directed ductile extrusion of the cbu

the timing of partial melting barrovian metamorphism and granite intrusion in the naxos metamorphic core complex cyclades aegean sea greece abstract the relationship between partial melting and granite intrusion in a classic barrovian metamorphic terrane has been assessed thirteen samples were dated by shrimp u pb zircon geochronology from the island of naxos greece one of the aegean metamorphic core complexes the effect of partial melting during peak barrovian metamorphism on naxos is recorded by fine

detrital zircon and micropalaeontological ages as new constraints for the lowermost tectonic unit talea ori unit of crete greece the talea ori unit is the lowermost known tectonic unit of crete and the most external part of the hellenides its stratigraphy ranges from late carboniferous to oligocene and outcrops of the lower part are only known in the talea ori mountains central crete in this area a black sandstone at the base of the galinos beds thought to be the oldest formation contains zircons which were dated using the single grain evaporation method the majority of these grains yielded late carboniferous ages variscan while a small group yielded early proterozoic ages the age distribution of these zircons suggests that at the carboniferous permian boundary not much of the older north gondwanan basement was exposed and that a river system carried detrital material from the variscan belt towards the forming neotethyan rift additionally higher up in the stratigraphy benthic foraminifers miliolids were found in clasts from a conglomerate which was so far thought to be of early triassic age epting m kudrass h r leppig u schaffer a 1972 geologie der talea ori kreta n jb geol palaont abh 141 259 285 these miliolids belong to the species hoyenella inconstans michalik j jendrejakova o borza k 1979 some new foraminifera species of the fatra formation uppermost triassic in the west carpathians geol carpath 30 1 61 91 thus attributing a late triassic carnian norian maximal age to this conglomerate the carbonate platform from which the miliolids bearing clasts come is not known the presence to the north of a continuous hemipelagic record from the carboniferous to the triassic phyllite quartzite and tripali units attributed to the palaeotethys realm allows the talea ori unit and its lateral equivalents the ionian zone to be assigned to the westward continuation of the cimmerian block and therefore to the northern margin of the east mediterranean neotethys ocean

permian triassic palaeogeography of the external hellenides abstract in the external hellenides two crustal types are developed 1 a variscan basement overlain by the tyros unit and 2 a presumably panafrican basement overlain by the phyllite quartzite group late carboniferous early triassic and the plattenkalk group permian oligocene if we accept this assumption the plattenkalk and the phyllite quartzite groups fit well into the permian triassic palaeogeography of the northeastern margin of afro arabia during the permian triassic there is evidence for a siliciclastic fluvio marine system in the western sinai and nile area whereas the early triassic shelf of eastern sinai and israel is dominated by a carbonate platform the western facies association of the plattenkalk and the phyllite quartzite groups represents the northward extension of a fluvio marine system the siliciclastics of the plattenkalk group formed part of a marine delta those of the phyllite quartzite group indicate a turbidite fan system the units of middle and eastern crete represent the seaward continuation of the carbonate platform plattenkalk group and a deep sea realm free of turbidite influx phyllite quartzite group during the permian triassic the different crustal segments were brought together due to dextral strike slip movements of gondwana against the southern margin of the european plate as indicated by a uniform shallow marine facies of the carnian norian

evidence for holocene palaeoseismicity along the basel reinach active normal fault switzerland a seismic source for the 1356 earthquake in the upper rhine graben summary we conducted a palaeoseismic study with geomorphologic mapping geophysical prospecting and trenching along an 8 km long nne ssw trending fault scarp south of basel the city as well as 40 castles within a 20 km radius were destroyed or heavily damaged by the earthquake of 1356 october 18 io ix x the largest historical seismic event in central europe active river incisions as well as late quaternary alluvial terraces are uplifted along the linear basel reinach br fault scarp the active normal fault is comprised of at least two main branches reaching the surface as evident by resistivity profiles reflection seismic data and direct observations in six trenches in trenches the normal fault rupture affects three colluvial wedge deposits up to the base of the modern soil radiocarbon as well as thermoluminescence tl age determinations from other trenches helped to reconstruct the holocene event chronology we identified three seismic events with an average coseismic movement of 0 5 0 8 m and a total vertical displacement of 1 8 m in the last 7800 yr and five events in the last 13 200 yr the most recent event occurred in the interval ad 500 1450 2 and may correspond to the 1356 earthquake furthermore the morphology suggests both a southern and northern fault extensions that may reach 20 km across the jura mountains and across the rhine valley taking this fault length and a 10 km thick seismogenic layer suggests a mw 6 5 or greater event as a possible scenario for the seismic hazard assessment of the basel region

rapid extensional unroofing of a granite migmatite dome with relics of high pressure rocks the podolsko complex bohemian massif the podolsko complex bohemian massif is a high grade dome that is exposed along the suprastructure infrastructure boundary of the variscan orogen and records snapshots of its protracted evolution the dome is cored by leucocratic migmatites and anatectic granites that enclose relics of high to ultrahigh pressure rocks and is mantled by biotite migmatites and paragneisses whose degree of anatexis decreases outwards our new u pb zircon ages indicate that the leucocratic migmatites were derived from early ordovician c 480 ma felsic igneous crust the same age is inferred for melting the proto source of the metapelitic migmatites the relics of high to ultrahigh pressure rocks suggest that at least some portions of the complex witnessed an early variscan subduction to mantle depths followed by high temperature anatexis and syntectonic growth of the podolsko dome in the middle crust at c 340 339 ma subsequently the dome exhumation was accommodated by crustal scale extensional detachments similar c 340 ma ages have also been reported from other segments of the variscan belt yet the significance of this tectonothermal event remains uncertain here we conclude that the 340 ma age post dates the high pressure metamorphism the high temperatures required to cause the observed isotopic resetting and new growth of zircon were probably caused by heat input from the underlying mantle and finally the extensional unroofing of the complex requires a minimum throw of about 8 10 km we use this as an argument for significant early carboniferous palaeotopography in the interior of the variscan orogen

near surface fault detection using high resolution shear wave reflection seismics at the co2crc otway project site australia high resolution near surface shear wave reflection seismic measurements were carried out in november 2013 at the co2crc otway project site victoria australia with the aim to determine and if so where deeper faults reach the near subsurface from a previous p wave 3 d reflection seismic data set that was concentrated on a reservoir at 2 km depth we can only interpret faults up to 400 m below sea level for the future monitoring in the overburden of the co2 reservoir it is important to know whether and how the faults continue in the subsurface we prove that two regional fault zones do in fact reach the surface instead of dying out at depth individual first break signatures in the shot gathers along the profiles support this interpretation however this finding does not imply perforce communication between the reservoir and the surface in the framework of co2 injection the shear wave seismic sections image with high resolution better than 3 m vertically and complementary to existing p wave volumes different tectonic structures similar structures also outcrop on the southern coast of the otway basin both the seismic and the outcrops evidence the complex youngest structural history of the area

raman spectroscopic carbonaceous material thermometry of low grade metamorphic rocks calibration and application to tectonic exhumation in crete greece we present new raman spectra data of carbonaceous material cm to extend the range of the raman spectra of cm thermometer rscm to temperatures as low as 100 8c previous work has demonstrated that raman spectroscopy is an excellent tool to describe the degree of graphitization of cm a process that is independent of pressure but strongly dependent on metamorphic temperature a linear relationship between temperature and the raman parameter r2 derived from the area of the defect band relative to the ordered graphite band forms the basis of a previous thermometer because r2 shows little variability in low temperature samples 330 8c serves as a lower limit on the existing thermometer herein we present raman spectra from a suite of low temperature 100 to 300 8c samples from the olympics mountains and describe other aspects of the raman spectra of cm that vary over this range in particular the raman parameter r1 the ratio of heights of the disordered peak to ordered peak varies regularly between 100 and 350 8c these data together with published results from higher temperature rocks are used to calibrate a modified rscm thermometer applicable from 100 to 700 8c application to low grade metasediments in the otago region in the south island of new zealand gives temperatures consistent with previous estimates demonstrating the reliability of the modified rscm thermometer we apply the modified rscm thermometer to 53 samples from crete to evaluate the role of the cretan detachment fault in exhuming miocene high pressure low temperature metamorphic rocks exposed there the metamorphic rocks below the detachment the plattenkalk and phyllite quartzite units give metamorphic temperatures that range from 250 to 400 8c consistent with previous petrologic estimates we also demonstrate that the tripolitza unit which lies directly above the detachment gives an average metamorphic temperature of about 260 8c the modest break in metamorphic temperature in central crete indicates that the cretan detachment accounts for only 5 to 7 km of exhumation of the underlying hp lt metamorphic rocks which were initially accreted at 35 km we argue that the bulk of the exhumation 28 km out of 35 km total occurred by pervasive brittle stretching and erosion of structural units above the detachment d 2005 elsevier b v all rights reserved

provenance and tectonic setting of carboniferous triassic sandstones from the karaburun peninsula western turkey a multi method approach with implications for the palaeotethys evolution abstract carboniferous triassic siliciclastic sediments of the karaburun peninsula in western turkey were studied to unravel their provenance and the tectonic setting of depositional basins within the palaeotethyan realm a set of complementary techniques including petrography bulk rock geochemistry and single grain analysis of rutile garnet and chrome spinel were applied to provide a diverse dataset for testing existing palaeotectonic models using both established and recently published diagrams we show that tectonic discrimination diagrams of siliciclastic sediments based on major and trace element whole rock geochemical data do yield ambiguous results and are only partly in accordance with regional geological events chondrite normalised ree patterns of upper palaeozoic samples are characterised by enrichment of lree and a flat trend towards hree the degree of fractionation allows for discrimination between sandstones of karaburun lan ybn 8 00 14 79 and adjacent greek islands of chios 5 82 9 23 and inousses 7 40 9 95 petrographic observations and compositional data from single grain analysis indicate significant supply from low to medium grade metamorphic rocks of generally felsic character and minor input of ultra mafic detritus detrital chrome spinels in the lower triassic gerence formation are different in composition and shape compared to chrome spinels in carboniferous permian sandstones they were derived from a very proximal source and exhibit variable but generally high cr and mg numbers consistent with chrome spinels from podiform chromitites that have been formed in an intra oceanic back arc setting above a supra subduction zone we conclude that most of the carboniferous triassic successions were deposited along the southern active margin of eurasia in a continental arc environment during the time period when palaeotethys diminished in size and finally vanished large volumes of detritus were probably derived from rock units located in the present day balkan region and the sakarya zone or equivalent successions that are not present anymore

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

shallow sh wave seismic investigation of the mt angel fault northwest oregon usa abstract the mt angel fault is likely one of the most active faults near the portland metropolitan area and was probably associated with the 1993 scotts mills earthquake sh wave seismic techniques used to image the mt angel fault suggest that the fault offsets late pleistocene gravel 22 to 34 ka at several locations within the study area displacement of the late pleistocene gravel along the strike of the mt angel fault increases from no obvious displacement on the northwest to approximately 18 m on the southeast this trend of increasing offset along the strike of the fault is paralleled by topographic and geomorphic trends a reconnaissance geologic investigation at an anomalous bend in the pudding river near the projected trace of the mt angel fault revealed potential tectonic deformation in sediments younger than the late pleistocene gravel imaged by sh wave data the results of this study have contributed to the paleoseismic record of the mt angel fault laid the groundwork for future geologic investigations along the pudding river and determined potential sites for future paleoseismic trenching investigations

cooling and inferred uplift erosion history of the grenville orogen ontario constraints from 40ar 39ar thermochronology stepwise 40ar 39ar degassing experiments of 57 mineral separates of hornblende muscovite biotite and perthitic microcline have been used in conjunction with petrologic observations to place regional constraints on the postmetamorphic cooling and the inferred uplift and erosion history of the grenville orogen in ontario the 40ar 39ar data support an interpretation of slow nearly uniform cooling 1 4 c m y from temperatures of 500 c to below 150 c in the central gneiss belt cgb hornblendes cooled through ar closure between 930 and 1025 ma whereas in the central metasedimentary belt cmb hornblendes record the following range in 40ar 39ar cooling ages 1104 ma in the frontenac terrane 1007 1067 ma in the sharbot lake terrane 919 1026 ma in the elzevir terrane and 972 ma in the central metasedimentary belt boundary zone regional uplift erosion rates of 0 03 0 14 km m y have been estimated for the grenville orogen in ontario based on the 40ar 39ar data a model retrograde p t path for rocks of the cgb and an upper time constraint provided by flat overlying cambrian and ordovician sediments these erosion rates are consistent with rates estimated for other proterozoic or archean granulite terranes but are an order of magnitude slower than active orogens such as the alps and himalayas a regular variation in hornblende 40ar 39ar cooling ages is observed in rocks that traverse highly strained often mylonitic shear zones that separate the four major terranes of the cmb the pattern of 40ar 39ar ages is interpreted to reflect late tectonic extension consistent with field observations in the central metasedimentary belt boundary zone and elsewhere in the cmb up to 13 km of vertical displacement is inferred for some rocks in the cmb between the time they cooled below closure to argon diffusion in hornblende 500 c and their exposure at the surface 25 c

polyphase magmatic pulses along the northern gondwana margin u pb zircon geochronology from gneiss domes of the pyrenees abstract alkaline granitic dikes intruding the metasedimentary mantle and orthogneiss cores of the aston and hospitalet domes of the axial zone of the pyrenees are subjects of a laser ablation icp ms u pb zircon geochronology study the age spectra recorded by detrital magmatic xenocrystic and inherited zircons reveal a more complex nearly continuous paleozoic magmatic history of the variscan basement of the pyrenees than previously known inherited and detrital zircons of mesoarchean paleoproterozoic to ediacaran ages attest to the peri gondwana location of the cambrian sediments that later form the metamorphic core of the variscan pyrenees the youngest magmatic zircon ages fall into the late carboniferous and earliest permian ranging from ca 306 297 ma and represent the emplacement ages of the dikes and small granite intrusions the age spectra of magmatic xenocrystic zircons contain several maxima middle 475 465 ma and late ordovician 455 445 ma early 415 402 ma and late devonian 385 383 ma early 356 351 ma and middle carboniferous ca 328 ma middle ordovician and middle carboniferous ages are obtained from xenocrystic zircons that were assimilated from the rocks the dikes intruded the aston and hospitalet orthogneisses and the soulcem granite the presence of early mid carboniferous magmatic zircons in several samples lends further support to a wide spread early variscan magmatic activity in the central pyrenees the other age peaks do not have equivalent igneous or metaigneous rocks in the central axial zone but are thought to be present in the pyrenean crust not exposed and yet to be identified the diversity of ordovician devonian and carboniferous up to permian magmatic ages indicates polyphase emplacement of intrusive bodies during pre variscan and variscan orogenies the source of the heat for the devonian to early mid carboniferous magmatic activity remains elusive and may involve intracontinental subduction zone lithospheric scale shearing or a mantle plume tuzo

new detrital zircon age data reveal the location of the rheic suture in the mid german crystalline zone spessart and odenwald crystalline complexes new detrital zircon age data of metasedimentary rocks from the spessart and odenwald basement mid german crystalline zone variscides revealed results which are not compatible with current tectonic models the previously proposed existence of a tectonic window which includes lower plate rhenohercynian rocks within the upper plate saxothuringian zone in the spessart and odenwald basement does not agree with the results of this study this leads to a new course of the rheic suture and therefore a non coherence of the two major fault zones in these complexes the southern spessart crystalline complex accommodates the rheic suture which is most likely explained by a southward displacement of a whole segment of the mid german crystalline zone this displacement might extend over the ruhla crystalline complex a hitherto unknown age spectrum of a unit in the bollsteiner odenwald was found which might indicate a sliver of unidentified material in the variscan collision zone an unknown magmatic age of 350 ma is reported for igneous intrusions in the saxothuringian zone and can be used as an additional indicator to distinguish between laurussia and gondwana related rocks

aspects of the structural evolution of the lusitanian basin in portugal and the shelf and slope area offshore portugal abstract the study provides a regional seismic interpretation and mapping of the mesozoic and cenozoic succession of the lusitanian basin and the shelf and slope area off portugal the seismic study is compared with previous studies of the lusitanian basin from the late triassic to the cretaceous the study area experienced four rift phases and intermittent periods of tectonic quiescence the triassic rifting was concentrated in the central part of the lusitanian basin and in the southernmost part of the study area both as symmetrical grabens and half grabens the evolution of half grabens was particularly prominent in the south the triassic fault controlled subsidence ceased during the latest late triassic and was succeeded by regional subsidence during the early early jurassic hettangian when deposition of evaporites took place a second rift phase was initiated in the early jurassic most likely during the sinemurian pliensbachian this resulted in minor salt movements along the most prominent faults the second phase was concentrated to the area south of the nazare fault zone and resulted here in the accumulation of a thick sinemurian callovian succession following a major hiatus probably as a result of the opening of the central atlantic resumed deposition occurred during the late jurassic evidence for late jurassic fault controlled subsidence is widespread over the whole basin the pattern of late jurassic subsidence appears to change across the nazare fault zone north of the nazare fault fault controlled subsidence occurred mainly along nnw sse trending faults and to the south of this fault zone a nne ssw fault pattern seems to dominate the oxfordian rift phase is testified in onlapping of the oxfordian succession on salt pillows which formed in association with fault activity the fourth and final rift phase was in the latest late jurassic or earliest early cretaceous the jurassic extensional tectonism resulted in triggering of salt movement and the development of salt structures along fault zones however only salt pillow development can be demonstrated the extensional tectonics ceased during the early cretaceous during most of the cretaceous regional subsidence occurred resulting in the deposition of a uniform lower and upper cretaceous succession marked inversion of former normal faults particularly along ne sw trending faults and development of salt diapirs occurred during the middle miocene probably followed by tectonic pulses during the late miocene to present the inversion was most prominent in the central and southern parts of the study area in between these two areas affected by structural inversion fault controlled subsidence resulted in the formation of the cenozoic lower tagus basin northwest of the nazare fault zone the effect of the compressional tectonic regime quickly dies out and extensional tectonic environment seems to have prevailed the miocene compressional stress was mainly oriented nw se shifting to more n s in the southern part

structural style deformation mechanisms and paleodifferential stress along an exposed crustal section constraints on the rheology of quartzofeldspathic rocks at supra and infrastructural levels bohemian massif abstract investigations of variscan shortening of quartzofeldspathic rocks have been carried out along an exposed crustal section located in the western part of the tepla barrandian unit bohemian massif the study focuses on determining differential stress deformation mechanisms and geometry of cadomian metagreywackes and cambrian granitoids which show different grade of variscan barrovian type metamorphism ranging from the greenschist subgreenschist facies boundary semibrittle deformation regime to the high grade amphibolite facies the semibrittle deformation regime t ca 300 c is characterized by large scale thrusting within a folding environment and by similar intensities of cataclasis diffusive mass transfer and crystal plasticity of quartz the latter including low temperature migration recrystallization within cadomian quartz veins of the greenschist facies part dislocation creep of quartz operated at differential stresses ranging from ca 70 mpa in the lowermost greenschist facies to ca 20 mpa in the uppermost greenschist facies these values have been derived by paleopiezometry using the grain size of recrystallized quartz they are interpreted as upper bounds for the bulk stress because of intense diffusive mass transfer within the adjacent metagreywackes a marking increase in recrystallized grain size of quartz occurs within the lower greenschist facies where low temperature grain boundary migration is replaced by subgrain rotation thus causion is needed when applying the recrystallized grain size paleopiezometer to this crustal level pressure solution of quartz and development of discrete crenulation cleavage was common in fine grained metagreywackes of the lower greenschist facies whereas the upper greenschist facies t ca 500 570 c is characterized by increasing intensity of metamorphic reactions grain coarsening and development of a schistosity the entire greenschist facies level forms a suprastructure where viscosity contrasts between mica and quartz rich layers were sufficiently high for buckle folding strain protected intercalated metagranitoids on the other hand do not show pervasive deformation fabrics the amphibolite facies part forms an infrastructure characterized by pervasive mylonitic shearing of both cambrian granitoids and metagreywackes it is suggested that the combination of the following processes has contributed to weaken the amphibolite facies level making nonlocalized flow possible 1 increased recrystallization of feldspar 2 crystal plastic softening of quartz due to high temperature grain boundary migration and activity of prism slip and 3 enhanced diffusive mass transfer in the form of metamorphic reactions the structural breaks at the semibrittle crustal level and at the greenschist amphibolite facies boundary supports the view that rheological boundaries are prone to form major detachment horizons in the continental crust

the tectonometamorphic evolution of high pressure low temperature metamorphic rocks of eastern crete greece constraints from microfabrics strain illite crystallinity and paleodifferential stress abstract analysis of strain paleodifferential stress illite crystallinity and microfabrics of quartz and calcite suggest that multiply alternating late oligocene early miocene n s convergence and n s extension caused significant vertical discontinuities in the grade of high pressure low temperature metamorphism of the phyllite quartzite unit pqu of eastern crete constrictional fabrics and parallelism of d2 stretching lineations and fold axes are attributed to enhanced slab pull forces at greater depth of subduction a major d3 extensional detachment is present in the upper part of the pqu where slates with lowest metamorphic grade diagenesis anchizone transition are resting on top of anchimetamorphic rocks the highest metamorphic grade anchi epizone transition has been determined for skythian rocks on top of pre alpine basement revived n s convergence d4 led to e w trending map scale folds and top to the s directed brittle thrusts there is a clear correlation between d2 related metamorphic grade finite strain differential stress and deformation mechanisms at the anchi epizone transition solution precipitation and dislocation creep of quartz and calcite caused maximum finite strains rxz up to 7 at high strain rates and moderate differential stresses 80 200 mpa at the diagenesis anchizone transition deformation was accommodated by cataclasis dislocation glide and solution precipitation creep resulting in relatively low finite strains rxz

zircon geochronology of basement rocks from the pelagonian zone greece constraints on the pre alpine evolution of the westernmost internal hellenides the pelagonian zone of greece is the westernmost segment of the internal hellenides comprising widespread crystalline basement exposures of granites and orthogneisses we dated these basement rocks in order to identify the major crust forming episodes and to understand the evolutionary history of the area in our study we investigated granites gneisses meta rhyolites and mylonites from the major occurrences of the pelagonian zone we applied single zircon dating techniques such as pb pb evaporation conventional u pb and shrimp the majority of the basement rocks gave permo carboniferous intrusion ages thus emphasizing the importance of this crust forming event for the internal hellenides of greece triassic intrusion ages were obtained however for a meta rhyolite from the western pelagonian zone and two mylonites from the eastern pelagonian zone these ages are interpreted to reflect magmatism accompanying early rifting that led to the subsequent opening of the pindos ocean to the west and the meliata ocean to the east of the pelagonian zone the geochronological results demonstrate that the magmatic episodes during which most of the pelagonian zone crystalline basement formed are predominantly pre alpine in age

triassic rift related meta granites in the internal hellenides greece the serbo macedonian massif is a basement complex in the internal hellenides of northern greece situated between the vardar zone to the west and the rhodope massif to the east the serbo macedonian massif comprises several distinct basement units interpreted as terranes the largest of which is the gondwana derived vertiskos terrane in the northwestern and central parts of the massif a series of leucocratic meta granites intrude the silurian orthogneiss basement of the vertiskos terrane no similar granites are found in any of the other units of the internal hellenides the meta granites have a pronounced crustal within plate signature which is visible in lithology major and trace element geochemistry and the sr isotopic compositions these intrusions were dated using the pb pb single zircon evaporation method and yielded a triassic age of between 240 7 2 6 ma and 221 7 1 9 ma on 17 samples with a mean age of 228 3 5 6 ma the zircons are purely magmatic indicating that ages are primary crystallization ages a rb sr errorchron of the whole rock samples of the arnea granite yielded an age of 231 6 9 9 ma mswd 82 and a mean 87 sr 86 sr initial ratio is 0 7142 indicating a crust dominated source and suggesting an a type origin for the granites the a type meta granites together with mafic intrusive bodies amphibolites in the vertiskos terrane may be evidence of triassic rifting that led to the formation of a branch of neotethys vardar meliata ocean similar rock associations are also exposed in the cyclades and in massifs of the wider eastern mediterranean realm related to the gondwana derived hun terrane indicating that the arnea type granites are representatives of a major regional rifting event in triassic times

the recrystallized grain size piezometer for quartz d 1 0 3 56 0 27 s 1 26 0 13 with no change in slope at the regime 2 3 transition and no effect of temperature or a b stability field another experimental piezometer relation for regime 1 of hirth and tullis 1992 differs in slope suggesting that different recrystallization mechanisms require different piezometer calibrations index terms 3902 mineral physics creep and deformation 5120 physical properties of rocks plasticity diffusion and creep 8030 structural geology microstructures 8159 tectonophysics rheology crust and lithosphere 8164 tectonophysics stresses crust and lithosphere citation stipp m and j tullis the recrystallized grain size piezometer for quartz geophys res lett 30 21 2088 doi 10 1029 2003gl018444 2003

the formation of pangea abstract the making of pangea is the result of large scale amalgamation of continents and micro continents which started at the end of the neoproterozoic with the formation of gondwana as pieces were added to gondwana on its south american antarctica and australia side ribbon like micro continents were detached from its african and south chinese side cadomia in the late neoproterozoic avalonia and hunia in the ordovician galatia in the devonian and cimmeria in the permian cadomia was re accreted to gondwana but the other ribbon continents were accreted to baltica north china laurussia or laurasia finding the origin of these numerous terranes is a major geological challenge recently a global plate tectonic model was developed together with a large geological geodynamic database at the lausanne university covering the last 600 ma of the earth s history special attention was given to the placing of gondwana derived terranes in their original position using all possible constraints we propose here a solution for the variscan terranes another paper deals with the altaids the galatian super terrane was detached from gondwana in the devonian during the opening of paleotethys and was quickly separated into four sub terranes that started to by pass each other the leading terranes collided at the end of the devonian with the hanseatic terrane detached from laurussia in the carboniferous gondwana started to impinge onto the amalgamated terranes creating the variscan chain and the pangean super continent east of spain paleotethys remained opened until the triassic subducting northward under laurasia roll back of the paleotethyan slab triggered the collapse of most of the european variscan orogen which was replaced by series of permian rifts some of them becoming oceanized back arc basins during the triassic major force changes at the pangean plate limits at the end of the triassic provoked its break up through the opening of the proto caribbean central atlantic alpine tethys oceanic seaways

u pb zircon ages for post variscan volcanism in the ligurian alps northern italy abstract ages of permian volcanic rocks from the ligurian brianconnais domain western italian alps have been determined by laser ablation inductively coupled plasma mass spectrometry u pb dating of zircon three major volcanic units yielded zircons that were dated calc alkaline rhyolites 285 6 2 6 ma andesites with inherited cores yielded ages c 476 ma and older and voluminous rhyodacites rhyolites 272 7 2 2 ma following an amagmatic sediment starved time gap of c 14 ma alkaline volcanic activity is recorded at the top of the sequence by k alkaline rhyolites dated at 258 5 2 8 ma the ligurian segment of the southern variscan belt records transtensional and then extensional tectonics associated with the volcanic activity the switch from calc alkaline to alkaline activity corresponds to the transition from a post orogenic to an anorogenic setting in the southern variscides it may represent progressive and increasing delamination of the continental lithosphere accompanied by partial melting of the lithospheric mantle supplementary material technical and data acquisition parameters u th pb isotope analyses and calculated ages of zircons from samples and standard and trace element compositions of selected zircons are available at http www geolsoc org uk sup18322

sedimentary evidence from the south mediterranean region sicily crete peloponnese evia used to test alternative models for the regional tectonic setting of tethys during late palaeozoic early mesozoic time

provenance analysis of the paleozoic sequences of the northern gondwana margin in nw iberia passive margin to variscan collision and orocline development abstract the cantabrian zone of nw iberia preserves a voluminous almost continuous sedimentary sequence that ranges from neoproterozoic to early permian in age its tectonic setting is controversial and recent hypotheses include i passive margin deposition along the northern margin of gondwana or ii an active continental margin or iii a drifting ribbon continent in this paper we present detrital zircon u pb laser ablation age data from 13 samples taken in detrital rocks from the cantabrian zone sequence ranging from early silurian to early permian in depositional age the obtained results together with previously published detrital zircon ages from ediacaran ordovician strata allow a comprehensive analysis of changing provenance through time collectively these data indicate that this portion of iberia was part of the passive margin of gondwana at least from ordovician to late devonian times zircon populations in all samples show strong similarities with the sahara craton and with zircons found in libya suggesting that nw iberia occupied a paleoposition close to those regions of present day northern africa during this time interval changes in provenance in the late devonian are attributed to the onset of the collision between gondwana and laurussia additionally the middle carboniferous to permian samples record populations consistent with the recycling of older sedimentary sequences and exhumation of the igneous rocks formed before and during the variscan orogeny late devonian to permian samples yield zircon populations that reflect topographic changes produced during the variscan orogeny and development of the lithospheric scale oroclinal buckling

geophysical characterization of the ota vila franca de xira lisbon sesimbra fault zone portugal summary this paper focuses on the reprocessing of seismic reflection profiles aeromagnetic and seismicity data to locate and characterize the ota vila franca de xira lisbon sesimbra fault zone the studied structure is sited in the lower tagus valley an area with over 2 million inhabitants that has experienced historical earthquakes causing many casualties serious damage and economical losses e g 1531 january 26 and 1909 april 23 earthquakes whose tectonic sources are mostly unknown the fault zone trends nne ssw to n s is located near the eastern border of the mesozoic lusitanian basin and partially delimits the lower tagus cenozoic basin at the west mostly hidden under the cenozoic sedimentary fill according to the data presented here the normal structures that compose the fault zone were reactivated in cenozoic times with positive inversion and the development of splays towards the east the fault zone shows three distinct segments with different behaviour in conformity with their various orientations relative to the nw se maximum compressive stress the northern segment splays into a series of nne ssw oriented east verging imbricate thrusts which merge to the west into a major reverse fault that resulted from the tectonic inversion of the former normal fault bordering the

middle permian early triassic magmatism in the western pontides nw turkey geodynamic significance for the evolution of the paleo tethys abstract permian triassic magmatic rocks are widely exposed in different tectonic terranes and continental blocks in the aegean region this study is focussed on the istanbul zone and the istranca strandja massif which are located in the western pontides of nw turkey the kirklareli and the tepecik plutons intruded into the metamorphic basement rocks of the istranca massif and the sancaktepe pluton is emplaced into the istanbul paleozoic sedimentary sequences we present new geochemical data for these plutons in order to interpret their petrogenesis and time of emplacement and use this information for geodynamic interpretation the zircon u pb crystallization ages are 268 3 2 1 ma for the kirklareli pluton 249 4 1 5 ma for the tepecik pluton and 257 3 1 5 ma and 253 7 1 75 ma for the the sancaktepe pluton they are high k calc alkaline to shoshonitic granitoids with aluminum saturation index asi values between 0 9 and 1 3 which define them as peraluminous and slightly metaluminous 87sr 86sr i values for the studied plutons range between 0 701123 and 0 707704 143nd 144nd i ratios calculated for crystallization ages are between 0 512052 and 0 512431 and end i values vary from 4 71 to 2 22 tdm model ages range between 0 83 and 1 41 ga these plutons are enriched in liles and lree and depleted in hfses with negative eu anomalies indicating that the melts were derived from mafic crustal sources our new data suggest that the kirklareli pluton was generated in a subduction related magmatic arc and the highly fractionated sancaktepe and tepecik plutons were formed in a back arc setting in response to the northward subduction of the paleo tethys ocean during the mid permian early triassic

calcite twins their geometry appearance and significance as stress strain markers and indicators of tectonic regime a review twin lamellae are a widespread feature in calcites of any type and origin twinning in calcite is an important intracrystalline deformation mechanism with low critical resolved shear stress and virtually no temperature dependence in contrast to most slip systems in rock forming minerals twinning therefore permits intracrystalline deformation at very low temperature and very little confining pressure twinning alone however cannot lead to large strains because only one independent slip system is effectively available twins lead to discontinuous shearing on the grain scale which gives rise to considerable strain incompatibilities at grain boundaries twinning consequently leads to strain hardening detailed observations of the geometry of twin lamellae show that incompatibilities at grain boundaries are eliminated by pressure solution on the grain scale at low temperature and dynamic recovery processes at higher temperatures twins are found in various tectonic environments and record very small strains in rocks deformed under very little cover different twinning strain and twinning stress methods and palaeopiezometers are critically reviewed all methods are limited to strains of less than 15 shortening or extension by twinning twinning nevertheless is an important although not directly measurable contribution to the total strain in highly strained calcite rocks at least up to middle greenschist facies under which conditions it is the most effective contributor to the formation of strong lattice preferred orientations in calcite tectonites the appearance of calcite twin lamellae changes systematically as a function of deformation temperature micro twins and straight narrow 1 5 m but fewer twins are developed above approximately 200 c curved twins twinned twins and completely twinned grains indicate the progressive importance of other slip systems and larger intracrystalline strains are possible at ca 250 c and above ancient straight twin lamellae are modified into irregular geometries by recrystallization and grain boundary migration the appearance of calcite twins is proposed as an approximate but rapid and easy to use geothermometer in low temperature environments

signature of fault zone deformation in near surface soil visible in shear wave seismic reflections small throw seismogenic fault segments hidden in the holocene sediments are crucial but difficult targets in seismic exploration we report here the detection of the deformation pattern and a concealed fault segment in the unconsolidated sediments at vila franca xira portugal through identification in shear wave reflection data of multiple signatures of ductile deformation associated with faulting we find step like changes in the stacking velocity along a shallow subsoil layer boundary indicating synsedimentary faulting we also recognize a consistent distortion in the moveout of the reflection events in the raw shear wave data synthetic modeling of seismic data helps in interpreting these observations and identifying backscattered energy from a steeply dipping shallow fault zone prior to this finding there was no evidence for holocene activity of this fault although the fault is considered to be the most probable source for the disastrous 1531 earthquake

dislocation creep regimes in quartz aggregates abstract using optical and tem microscopy we have determined that three regimes of dislocation creep occur in experimentally deformed quartz aggregates depending on the relative rates of grain boundary migration dislocation climb and dislocation production within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization at lower temperatures and faster strain rates the rate of dislocation production is too great for diffusion controlled dislocation climb to be an effective recovery mechanism in this regime recovery is accommodated by strain induced grain boundary migration recrystallization with an increase in temperature or decrease in strain rate the rate of dislocation climb becomes sufficiently rapid to accommodate recovery in this regime dynamic recrystallization occurs by progressive subgrain rotation with a further increase in temperature or decrease in strain rate dislocation climb remains sufficiently rapid to accommodate recovery however in this regime grain boundary migration is rapid thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation the identification of the three regimes of dislocation creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers in addition the identification of a particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred

testing models of late palaeozoic early mesozoic orogeny in western turkey support for an evolving open tethys model field evidence from north south transects tests three tectonic models for tethys in western turkey for when a late palaeozoic ocean was closing and an early mesozoic ocean opening in model 1 a palaeozoic ocean subducted southwards rifting continental fragments from gondwana and opening a triassic neo tethys to the south closure and collision occurred by latest triassic time in model 2 a wide palaeozoic tethys subducted northwards with an active eurasian margin and a passive gondwana margin the northern gondwana margin rifted in the triassic fragments either remained nearby taurides or drifted northwards e g karakaya attached to a north subducting plate new oceanic crust replaced palaeo tethys with neotethys and back arc marginal basins opened along the south eurasian margin e g kure in model 3 a palaeozoic ocean also subducted northwards opening wide marginal basins a wide southern neotethys opened along the gondwana margin rifted eurasian anatolides and gondwana taurides fragments collided in mid tethys by latest triassic time field evidence from the pontides supports north dipping subduction models model 2 or 3 above key features are a south vergent hp lt accretionary prism magmatic arc and back arc basin system bordering the eurasian margin also evidence from the tauride mountains favours model 2 over model 3 critically the anatolides and taurides appear to have a common history and were unlikely to have been located on opposite sides of tethys as in model 3

constrains on the origin and history of the eastern mediterranean basin abstract the basin formed along the northern passive margin of gondwanaland as a relict of the mesozoic neotethys in early mesozoic time though direct information from the basin itself is meagre the geology of its passive margins and the regional framework of the tethys evolution constrain the formation and history of the basin the eastern mediterranean and its passive margins are interpreted to have formed as a result of several faulting and continental breakup phases from early permian to middle jurassic times before pangaea s complete disintegration this led to the detachment of the eratosthenes and tauride blocks from the margins of the levant and herodotus basins respectively the latter merged in the northeast with the cyprus basin that extended along arabia s northern margin the main rifting probably occurred in the triassic leading to seafloor spreading in the herodotus and cyprus basins while along the levant margin important rifting also occurred in the jurassic during the initial rifting stages extension perpendicular to the levant margin was important but subsequently the tauride block drifted mainly northward the existence of the passive margins and slopes of the eastern mediterranean is documented at least from the end of the middle jurassic until then the basin was probably narrow 200 300 km but during the main phase of the africa laurasia separation it grew to twice its present width or more this scenario depends critically on the interpretation that the tauride block was originally located next to northeastern africa on the western side of the eratosthenes block plate convergence and consumption of the northern portion of the basin have taken place since mid cretaceous times but the active convergent boundary on its northern side formed only in the neogene by modification of earlier structures some intra plate deformation also took place especially in the neogene but it hardly changed the original configuration of the remaining portion of the basin

provenance of upper devonian clastic meta sediments of the bollstein odenwald mid german crystalline zone variscides detrital zircons separated from paragneisses of the northern bollstein odenwald mid german crystalline zone variscides yielded cambrian to upper devonian u pb ages the age of the youngest detrital zircon population 371 3 ma and the lower carboniferous metamorphic overprint indicate an upper devonian depositional age of the paragneiss protolith the age spectra of detrital zircons suggest the latter to be derived from 1 ordovician igneous rocks of the saxothuringian zone 2 a late cadomian magmatic arc tepla barrandian unit and 3 a silurian devonian magmatic arc cadomian igneous activity is also documented by cambrian zircon cores in lower to middle devonian detrital zircons meso and paleoproterozoic detrital zircons which are typical for the old red continent and the rhenohercynian zone are entirely lacking the restricted palaeozoic detrital zircon age spectrum is attributed to a silurian devonian intra arc or trench setting both the lack of mesoproterozoic detrital zircons and the striking similarity of the u pb ages of the detrital zircon obtained from the bollstein odenwald with u pb ages from crystalline rocks of the saxothuringian basement rules out that the bollstein odenwald is forming a tectonic window rhenohercynian lower plate inside the mid german crystalline zone saxothuringian upper plate