paleoclimatology and paleoecology across the eocene oligocene boundary thrace basin northeast aegean sea greece abstract the detailed biostratigraphic and ichnological analysis of the upper eocene lower oligocene forearc sedimentary sequence in the southern greek part of the thrace basin on lemnos island reveals a relationship between eco sedimentary factors and the base level dynamics influencing calcareous nannofossils and trace fossil assemblages the lower part of the 350 m thick succession was deposited in a sand rich submarine fan system and upper part in a shelf environment it contains nannofossil assemblages and distributions typical of the np19 np21 biozones the eocene oligocene e o boundary top of np20 biozone is clearly distinguished within the upper parts of the turbidite system where a decrease in water temperature salinity nutrient supply and oxygenation level is also revealed additionally 19 ichnospecies mostly graphoglyptids typical of deep sea fan deposits have been distinguished the trace fossil diversity and abundance decrease upward reflecting the impact of the changing depositional environments from basin floor fans to slope systems and then shelfal environments the regional basin fill history rather than global climatic changes was probably the fundamental controlling factor on the distribution of graphoglyptids and other trace fossils across the e o boundary

sequence stratigraphy tectonics and depositional history in eastern thrace basin nw turkey abstract the eastern thrace basin forms the eastern portion of the turkish thrace basin in nw turkey the pre tertiary crystalline basement shows platform and deep basin depositional morphology which results in facies pattern and thickness distribution localization during the early stages of basin development in middle to late eocene time normal fault controlled early and lateral reverse fault controlled later stage tectonic events characterize basin geometry and the present topography respectively the early stage normal faulting caused subsidence and sediment accumulation in the late eocene and early oligocene while later stage tectonic events caused intense deformation and structuration in the early to middle miocene as a result southeastern and northern regions were folded or uplifted and deeply eroded outcrop well log core and reflection seismic studies reveal that the sedimentary succession can be subdivided into five characteristic depositional sequences bounded at their base by unconformities these unconformities were dated using paleontological data the sequence boundaries underlying consecutively sequences 1 2 3 and 5 were dated at 39 5 36 30 and 25 5 ma from older to young in order of succession corresponding to the major erosional breaks between the middle and upper eocene the upper eocene and the lower oligocene the lower and upper oligocene and the upper oligocene and the lower miocene the sequence boundary underlying sequence 4 was determined to lie within the late oligocene succession and as an age designation could not be assigned it was termed intra sequence boundary isb the first two sequences correspond to relative sea level rises and a normal fault controlled tectonism coincides with them reefal carbonates coarse grained clastics and marine shales with abundant volcanic flows or layers represent the sedimentary facies of these two early sequences the third and fourth sequences correspond to either a decreased relative rise of sea level or a relative still stand of sea level and a sediment induced subsidence related to thermal relaxation provides accommodation prograding delta sediments of varying extent constitute the sedimentary packages of these two sequences the depositional sequence 5 which makes up the uppermost part of the sedimentary succession in the basin corresponds to a relative sea level fall and a tectonic style shaped by lateral and inversion faulting characterizes this period nonmarine alluvial fan fluvial channel and various lagoonal deposits constitute the sedimentary facies of this last sequence porous reefal limestones and shallow marine beach sandstones of sequence 1 and deltaic sandstones of sequences 3 and 4 provide good reservoir rocks for the hydrocarbons produced in the study area the marine shales and marls of the second and the third sequences provide good source rocks as they are rich in disseminated organic matter content although the non marine alluvial and fluvial channel deposits of sequence 5 are good reservoirs they lack effective seals the time interval in which sequence 5 was deposited represents a period of major structural and trap development in the basin

a precise late neoproterozoic u pb zircon age for the syntectonic perelle quartz diorite guernsey channel islands uk a precise u pb zircon age of 611 4 2 0 1 1 ma has been determined for the foliated quartz diorite at perelle bay guernsey uk channel islands the age is based on the analysis of single zircons half of a single grain and groups of two and three zircons the age is nearly 100 ma younger than that suggested by other workers based on 207 pb 206 pb dates of large multi grain fractions of zircon and thus rules out this intrusion as the earliest marker of the onset of cadomian magmatism in the north armorican massif a 611 ma crystallization age for the perelle quartz diorite is consistent with previous detailed fabric development studies that suggested magmatic fabrics within the pluton are largely overprinted by similarly oriented solid state deformation fabrics resulting from syntectonic emplacement during cadomian orogenesis the u pb age is approximately 8 15 ma older than 40 ar 39 ar hornblende dates for the pluton consistent with the emplacement of the intrusion followed by slow cooling in a region of moderate to high ambient crustal temperatures these new data emphasize the fact that periods of pluton emplacement are considerably briefer than periods of deformation and thus syntectonic intrusions do not date regional deformational events but only mark events within a period of regional tectonism the ability to analyse single zircons and selected portions of single zircons using ultra low blank u pb analytical techniques documents the feasibility of determining precise emplacement ages of other neoproterozoic granitoids that contain a significant percentage of xenocrystic zircon

crustal velocity structure of the northeastern tibetan plateau from ambient noise surface wave tomography and its tectonic implications abstract broadband seismic data from the regional seismic network operated by the china earthquake administration and 32 temporary seismic stations are used to image the crustal velocity structure in the northeast tibetan plateau empirical rayleigh and love wave green s functions are obtained from interstation cross correlation of continuous seismic records group velocity dispersion curves for rayleigh and love waves between 10 and 50 s are obtained using the multiple filter analysis method with phase matched processing the group velocity variations of rayleigh and love waves overall correlate well with the major geologic structures and tectonic units in the study region shear wave velocity structures were then inverted from rayleigh and love wave dispersion maps the results show that the songpan ganzi terrane is associated with a low velocity at depth greater than 20 km the northern qilian orogen with higher elevation and thicker crust compared to the southern qilian orogen is also dominated by low velocity at depth greater than 25 km however there is no clear evidence of the low velocity mid to lower crust beneath the southern qilian orogen as the crustal flow model predicts the low velocity zone lvz beneath the northern qilian orogen may suggest that the crustal thickening and surface uplift of the northern qilian orogen are related to the lvz and the lvz may be considered as an intracrustal response to bear the ongoing deformation in the northern qilian orogen online material figures of crustal topography number of group velocity measurements checkerboard tests for nets stations and 1d velocity models

dextral rotations and tectonomagmatic evolution of the southern rhodope and adjacent regions greece abstract palaeomagnetic measurements deduced from eocene oligocene miocene and pliocene formations exposed in the greek rhodope and surrounding areas reveal significant clockwise rotations displaying an apparent systematic increase in magnitude from thrace westwards and a decrease northwards the pelagonian zone in the west has suffered no rotation at least since the late miocene a transition from rotated to unrotated regions seems to exist close to the western boundary of the vardar zone no rotations are apparent earlier than the mid oligocene parts of the rhodope may have been rotated clockwise by 12 during the late oligocene additional clockwise rotations occurred after the early miocene it is proposed that at least the post early miocene rotations were the result of plate tectonic motions in the north aegean area initiated by middle miocene times and continuing to the present day southward stretching and bending of the ductile part of the lithosphere was accomplished at brittle upper crustal levels by the detachment translation and rotation of the upper plate of the rhodope core complex the serbomacedonian element possibly followed by further fragmentation and rotation of individual blocks

deep seismic imaging of the cadomian thrust wedge of northern brittany abstract the armor seismic profile ar1 ar2 crosscuts the major units of the cadomian domain 600 540 ma of northern brittany and extends the offshore swat 10 profile birps ecors program we thus have a combined 95 km long nnw sse section for describing the regional scale structure of the cadomian crust in the area following reprocessing and migration of the southern end of the swat 10 profile so that it could be compared with the ar1 ar2 armor profile a structural interpretation of the composite profile was carried out taking into account gravity modelling and magnetotelluric soundings the swat 10 armor profile reveals the existence of steeply dipping thrust faults in the upper crust representing a thrust wedge with a gently northwest dipping sole this cadomian thrust system continues below the unmetamorphosed brioverian and palaeozoic sediments of central brittany and beyond the southern end of the profile in the central armorican domain it supports previous interpretations of dominant oblique type thrusting during cadomian tectonics proposed on the basis of geological field evidence and confirms the existence of a major northwest dipping thrust fault that brings the volcanic arc formations of the saint brieuc unit onto the metasediments of the saint malo unit the profile also emphasises the regional extent of a thrust wedge at the scale of the whole cadomian domain of northern brittany

faulting of lemnos island a mirror of faulting of the north aegean trough northern greece abstract a detailed analysis of the faulting on lemnos island since the miocene was achieved by grouping the recorded meso scale faults and their slickenlines into different groups replacing them with mean representative fault planes mrfp and lineations mrfl and finding the stress tensors driven to the activation of the different mrfp mrfl pairs the oldest recognized fault activity followed the late oligocene n s contraction and uplift d1 event as the latter is implied by e w to ene wsw buckle folds in the upper eocene lower oligocene molasse type sediments it was an early middle miocene strike slip to transpression deformation d2 event associated with n s contraction that also affected the lower miocene volcanogenic rocks the next fault activity was dated in middle late miocene and caused a wnw ese extension d3 event this deformation suggests that a during the late eocene oligocene the north aegean trough was developed as a fore arc basin between the rhodopian magmatic arc and its subduction accretion complex to the south and b during the late oligocene middle miocene the north aegean trough as the whole hellenic hinterland was subjected to the transpression s l deformation and lateral extrusion because of the late collisional processes between apulia and eurasia plates and the retreating of the hellenic orogen from late miocene to pliocene a ne sw extension to right lateral transtension d4 event dominated the north aegean trough indicating that the retreating of the hellenic orogen was completely balanced by a back arc extension the deformation facilitates the westward propagation of the north anatolian fault into the north aegean sea since the early pleistocene the deformation of the north aegean trough is related to a nne ssw back arc extension d5 of the present day hellenic subduction zone and the dominant ene wsw to e w faults along the north aegean trough function as normal to oblique right lateral normal faults

u pb geochronology and hf nd isotope compositions of the oldest neoproterozoic crust within the cadomian orogen new evidence for a unique juvenile terrane new u pb dates combined with nd and hf isotopic data from rocks within the port morvan area of the baie de st brieuc region of brittany identify a unique portion of the neoproterozoic cadomia terrane two gneisses near port morvan yielded u pb dates of 754 6 0 8 ma and 746 0 0 9 ma ages that are more than 130 myr older than the oldest units formed during the main phase of early cadomian magmatism two trondhjemite boulders from the monogenetic facies of the cesson conglomerate yielded identical ages of 665 2 0 5 ma and 665 5 0 7 ma and a cobble from the polygenetic facies yields a 207pb 206pb date of 637 2 ma individual detrital zircons from a sandstone associated with the cesson conglomerates yield concordant u pb dates ranging from 650 3 ma to 624 1 0 6 ma initial nd values for the rocks in this region range from 5 0 to 6 6 indicative of a substantial input from depleted mantle initial hf values determined on zircons from these neoproterozoic rocks including the detrital zircons range from 6 7 to 14 5 consistent with the nd isotopic results maximum initial hf values for two 2 ga icartian gneisses considered basement to cadomia average 8 4 and 8 7 in contrast to the results of the port morvan rocks 616 608 ma syn tectonic intrusions from normandy and the british channel islands all have negative initial nd values 10 4 to 8 3 consistent with significant contamination by ancient crust such as the 2 ga gneisses the oldest arc related magmas should have interacted most extensively with cadomian basement buffering younger mantle derived magmas that were generated in subsequent magmatic episodes the rocks within the port morvan region are thus inconsistent as examples of the earliest cadomian intrusions as they show no evidence of interaction with 2 ga basement instead the older ages and mantle like isotopic composition of these rocks suggest they are part of an independent terrane that formed prior to and independently from the cadomian arc possible terrane scale structural boundaries have recently been identified including the newly recognized port morvan thrust fault and the nw dipping main cadomian thrust

latest cretaceous forearc basin development along an accretionary convergent margin south central alaska upper cretaceous sedimentary strata exposed in south central alaska provide insight on tectonic processes that shaped the northern pacific margin following accretion of the wrangellia composite terrane the largest addition of crust to north america over the past 100 m y sedimentologic geochronologic biostratigraphic and petrographic data from the matanuska formation permit reconstruction of the tectono sedimentary history of strata in a forearc basin constructed upon accreted oceanic arc crust the matanuska formation consists of 3 km of sedimentary strata exposed in the northern chugach mountains matanuska valley and southern talkeetna mountains of interior south central alaska measured stratigraphic sections and lithofacies analyses demonstrate that mass slumps and slides debris flows and turbidity currents deposited campanian maastrichtian sandstone conglomerate and mudstone on a gullied trenchward dipping submarine ramp benthic foraminifera inoceramid bivalves and nereites ichnogenera indicate deposition mainly at bathyal water depths sandstone and conglomerate petrofacies are characterized by monocrystalline quartz plagioclase feldspar and volcanic lithic fragments q39f40l21 qm29f40lt32 lm25lv42ls32 and qm42p54k4 jurassic cretaceous arc plutons exposed north of the basin were an important sediment source based on u pb zircon ages of granitoid clasts from conglomerate and detrital zircons from sandstone coeval arc plutons were unroofed relatively quickly judging by the presence of 77 71 ma detrital zircons in sandstone and 79 77 ma granitic clasts in conglomerate together with maastrichtian 71 65 ma ammonite and foraminifera fossils sparse paleozoic triassic detrital zircons indicate minor sediment contribution from inboard sources including the yukon tanana composite terrane and recycled jurassic cretaceous sedimentary strata kahiltna assemblage new data from the upper matanuska formation together with recent studies from age equivalent strata exposed in the alaska range and wrangell mountains provide an exceptional example of basin development along a subduction margin shortly following accretion of an oceanic arc forearc basin development was dominated by subsidence and sediment gravity flow deposits enriched in plutonic and volcanic clasts eroded from both remnant and coeval arc plutons within the arc newly recognized conglomerate in the northern talkeetna mountains records erosion of coeval and remnant arc source terranes to the south and precambrian paleozoic sources to the north farther inboard syndepositional shortening prompted thrust top basin development and accumulation of alluvial lacustrine strata derived from both the former continental margin to the north and accreted oceanic rocks to the south regional subsidence and basin development terminated during late maastrichtian early paleocene time coincident with subduction of progressively younger oceanic lithosphere inboard of an oceanic spreading center

detrital supply from subduction accretion complexes to the eocene oligocene post collisional southern thrace basin nw turkey and ne greece abstract the thrace basin is a large mostly eocene oligocene post collisional sedimentary basin which developed following the closure of the vardar izmir ankara oceanic domain latest cretaceous paleocene sandstone petrologic data framework and heavy mineral analyses and the synthesis of preexisting and new sedimentological observations along representative stratigraphic sections show that the basin fill of the southern thrace basin was mostly derived from the izmir ankara and biga intra pontide subduction accretion complexes to the south proximal facies consistently show northward paleocurrents whereas most paleocurrent indicators measured downcurrent point to an eastward paleoflow likely the result of the deflection of primary gravity flows originated along the southern margin of the basin detrital contributions from the rhodopian basement complex to the west are virtually absent within the southern thrace basin fill conversely rhodopes derived eocene proximal facies in northeastern greece are characterized by a series of coarse grained fan deltas prograding eastward and likely feeding the basin plain turbidites of the depocentral portion of the thrace basin now concealed in the subsurface to the north of our study area arenites of the southern thrace basin are mostly lithic arkoses and arkosic litharenites provenance from the izmir ankara and biga suture zones to the south is characterized by ophiolitic granitoid gneissic low grade metamorphic and extrabasinal carbonate rock fragments as well as by picotite and glaucophane the application of detailed petrographic observations for discriminating paleo vs neovolcanic and penecontemporaneous vs noncoeval terrigenous sands lead to a substantial revision of the geodynamic interpretation of the thrace basin formerly considered a forearc basin a significant penecontemporaneous volcanic component is common in the upper eocene lower oligocene section and can be related to extensive post collisional volcanism following the closure of the vardar izmir ankara ocean the coexistence of pure neovolcanic layers crystal tuffs and cinerites and hybrid arenites rich in penecontemporaneous carbonate grains with sands derived from a continental basement and ophiolitic suites indicates the presence of episutural basins where shallow water carbonates were deposited on top of the exhuming subduction accretion prism these carbonates were mixed with penecontemporaneous neovolcanic and terrigeneous components and redeposited in deeper marine environments

a geophysical study of the manila trench luzon philippines 1 crustal structure gravity and regional tectonic evolution the manila trench subduction zone is an active convergent plate margin between the south china sea and the northern philippines the trench trends northerly and is associated with a volcanic arc an east dipping benioff zone beneath luzon and a well developed fore arc basin system the luzon trough fore arc basins lie landward of the manila trench and contain up to 4 5 km of cenozoic sediments offscraping and accretion of turbidite sediments deposited in the manila trench have resulted in the upbuilding and outbuilding of an accretionary prism which forms the seaward margin of the fore arc basin system the uplifted zambales ophiolite and its offshore extension form the landward side of the fore arc basin multichannel seismic reflection profiles reveal that folding and thrust faulting of trench strata occur at the base of the trench slope the major structural decollement at the manila trench usually forms near the unconformity separating the hemipelagic sediments from the turbidite sediments subduction and perhaps underplating of the basal hemipelagic trench sediments accompany the deformation and accretion of the overlying clastic deposits faulting and uplift occur within a narrow zone of the fore arc where seamounts associated with the relict spreading center of the south china sea basin have presumably been subducted north of lingayan gulf the fore arc is disrupted by active fault systems that trend north and northwest offshore from the luzon central valley and from the southern cordillera central based on regional geological and tectonic observations we infer that subduction probably began at the manila trench in late oligocene to middle miocene time the long term average convergence rate at the manila trench is estimated to be between 10 and 20 mm yr and may be slowing in the north owing to the collision of taiwan with eurasia

the tertiary geodynamical evolution of the aegean arc a paleomagnetic reconstruction abstract the paleomagnetic results obtained in the last 5 6 years from tertiary formations in the aegean domain indicate that the lower miocene arc was almost rectilinear with an e w trend and that its curvature has been acquired tectonically in two major phases during the middle miocene a first phase of deformation is characterized by rotations occurring at the two terminations of the arc clockwise in the west epirus anticlockwise in the east southeastern anatolia a second phase of rotation occurring in the last 5 ma about a pole situated in the southern adriatic sea has affected only the northwestern part the data also indicate that the antalya basin has not been involved in the geodynamical evolution of the arc so that the bey daglari represent its easternmost unit a more complex rotational pattern is observed in the internal zones the large rotations measured in evia 48 and skyros 26 probably occurred in the last 5 ma and result from rotation of fault bounded blocks in a shear zone connecting the north aegean trough to the external arc in the izmir region in the karaburun peninsula of western anatolia and in the island of lesbos significant counterclockwise clockwise or null rotations of coherent blocks have taken place during the neotectonic extensional regime furthermore the values of the inclination obtained from both sedimentary and volcanic oligo miocene formations are systematically shallower than expected on the basis of a geocentered dipole field this suggests that the entire studied area has undergone a northward drift of over 1000 km since the middle miocene

petrofacies and provenance of late mesozoic forearc basin northern and central california data from the great valley group sequence represent the most complete information regarding sandstone petrology of sediment derived from a magmatic arc this information is useful in documenting tectonic and magmatic events within the arc and related terranes and forms the basis for the establishment of petrostratigraphic units for mapping and correlation sandstone and conglomerate compositions are controlled by changes in provenance many of which were basinwide and synchronous clay mineral composition is controlled primarily by burial metamorphism careful attention to sample collection sample preparation and petrographic techniques is essential for uniform results seven petrographic parameters p f lv l m qp q q f and l listed in decreasing importance to petrofacies discrimination define eight petrofacies stony creek platina lodoga grabast boxer cortina los gatos and rumsey listed in approximate order of decreasing age the upper jurassic lower cretaceous petrofacies stony creek platina and lodoga contain higher lithic contents supracrustal sources whereas the upper cretaceous petrofacies especially the rumsey contain higher proportions of plutoniclastic components quartz feldspar and micas the proportion of potassium feldspar increases from near zero in the upper jurassic to nearly 50 of all feldspars in the uppermost cretaceous the lower part of the great valley group upper jurassic and lower cretaceous contains significant quantities of sedimentaclastic and metamorphiclastic material eroded from accreted and deformed terranes tectonic highlands formed by the arc arc collision nevadan orogeny that occurred prior to initiation of the franciscan great valley sierra nevada arc trench system the klamath mountains area provided a major proportion of this detritus ophiolite and serpentinite detritus was deposited locally near the base of the great valley group as a result of deformation along the east side of the growing franciscan subduction complex volcaniclastic detritus was fed into the entire forearc basin as magmatism increased in the sierra nevada area during the cretaceous as the volcanic cover was stripped off plutoniclastic and metamorphiclastic detritus from the underlying batholithic terranes was provided in abundance to the forearc basin crustal components were more continental in the southern sierra nevada and more oceanic in the northern sierra nevada as demonstrated by the higher proportions of metamorphiclastic detritus and by the more felsic nature of volcaniclastic detritus to the south by the middle of the late cretaceous extensive batholithic terranes provided potassium feldspar rich arkosic detritus to the entire forearc basin by the paleogene arc magmatism had migrated eastward sufficiently that deeper levels of the california part of the arc were exposed by erosion tectonic activity decreased in the forearc basin and the basin was filled to sea leve in most parts

morphology displacement and slip rates along the north anatolian fault turkey 1 geological and geomorphological offsets at different scales are used to constrain the localization of deformation total displacement and slip rates over various timescales along the central and eastern north anatolian fault naf in turkey the naf total displacement is reevaluated using large rivers valleys 80 15 km and structural markers pontide suture 85 25 km tosya vezirkopru basins 80 10 km these suggest a neogene slip rate of 6 5 mm yr over 13 myr the river network morphology shows offsets at a range of scales 20 m to 14 km across the main fault trace and is also used to estimate the degree to which deformation is localized at a smaller scale the morphology associated with small rivers is offset by 200 m along the naf the age of these features can be correlated with the holocene deglaciation and a slip rate of 18 3 5 mm yr is determined this is consistent with a rate of 18 5 mm yr deduced independently from the 14c dating of stream terrace offsets over the short term gps data gives a similar rate of 22 3 mm yr all our results tend to show that most of the deformation between the anatolian and eurasian lithospheric plates has been accommodated along or very close to the active trace of the naf the difference between the neogene and the holocene slip rate may be due to the recent establishment of the current plate geometry after the creation of the naf

late cenozoic tectonics and stratigraphy of northwestern anatolia the effects of the north anatolian fault to the region in northwest anatolia there is a mosaic of different morpho tectonic fragments within the western part of the right lateral strike slip north anatolian fault naf zone these were developed from compressional and extensional tectonic regimes during the paleo and neo tectonic periods of turkish orogenic history a ne sw trending left lateral strike slip fault system adapazari karasu fault extends through the northern part of the sakarya river valley and began to develop within a n s compressional tectonic regime which involved all of northern anatolia during middle eocene to early middle miocene times since the end of middle miocene times this fault system forms a border between a compressional tectonic regime in the eastern area eastwards from the northern part of the sakarya river valley and an extensional tectonic regime in the marmara region to the west the extension caused the development of basins and ridges and the incursions of the mediterranean sea into the site of the future sea of marmara since late miocene times following the initiation in late middle miocene times and the eastward propagation of extension along the western part of the naf a block north anatolian block began to form in the northern anatolia region since the end of pliocene times the adapazari karasu fault constitutes the western boundary of this block which is bounded by the naf in the south the northeast anatolian fault in the east and the south black sea thrust fault in the north the northeastward movement of the north anatolian block caused the formation of a marine connection between the black sea and the aegean mediterranean sea during the pleistocene

nd isotopic evidence for juvenile crust in the carolina terrane southern appalachians nd isotopic analyses of whole rock samples from the older portion of the carolina terrane one of the largest terranes in the appalachian orogen demonstrate that part of this terrane is composed of juvenile mantle derived crust these data suggest that the terrane may not have originally been built upon old evolved basement material but rather may have been built upon oceanic crust a recent study by other workers demonstrates a more crustally evolved nd isotopic signature for younger components of the carolina terrane these data may indicate that the terrane interacted with evolved crust at a later time possibly by amalgamation with a more evolved crustal fragment before final accretion to laurentia rather than indicating a primary old basement a juvenile nature for the older portion of the terrane contrasts with models that suggest it is an evolved crustal fragment that formed in a continental margin setting a scenario proposed to explain the high proportion of felsic volcanic rocks within the terrane it is herein suggested that carolina is a chemically evolved but isotopically juvenile crustal fragment because it remained in an oceanic setting for an unusually long time in this regard the carolina terrane is similar to some of the large accreted terranes in the canadian cordillera such as wrangellia and alexander the presence of juvenile crust in the carolina terrane documents that at least part of the southern appalachian orogen is not composed solely of reactivated pre existing continental crust the importance of this part of the orogen in terms of the volume of juvenile phanerozoic crustal material in north america may be larger than previously thought however until additional major appalachian terranes have been isotopically characterized the volume of juvenile crust in the whole orogen remains unknown the isotopic make up of a terrane can be an important aspect of terrane analysis as different terranes may have significantly different isotopic compositions while even widespread pieces of a single terrane should have very similar isotopic characteristics the nd isotopic data for the carolina terrane form the beginning of an isotope database for terranes in the southern appalachians

petrology and geochemistry of siliciclastic rocks of mixed feldspathic and ophiolitic provenance in the northern apennines italy provenance in clastic sedimentary rocks in the northern apennines is determined by integrated petrographic and geochemical criteria thus mafic poor arkoses in the gottero formation senonian paleocene deposited prior to the alpine orogeny were derived from granitic provenance in the sardinian corsican massif in the gottero formation chemical criteria distinguish between very low input of detrital mafic material and co c and ni added entirely by adsorption on clay minerals post alpine orogeny feldspathic sandstones in the macigno formation mid oligocene lower miocene and cervarola formation lower miocene reflect a more diverse provenance of granitic metamorphic ophiolitic and sedimentary rocks in the apennines and alps the macigno and cervarola rocks are distinguished by serpentine gabbro and diabase fragments and higher chlorite contents than in the gottero rocks chemically the macigno and cervarola rocks contain distinctive signatures expressed in higher mgo co cr and ni contents of the mafic ultramafic detritus a wider range and more scattered cr and ni variation and higher niggli ti for a given niggli al alk content the mgo co cr and ni abundances indicate up to 10 ultramafic ophiolitic detritus in the macigno and cervarola sandstones and up to 17 ophiolitic detritus in associated shales estimated by comparison of mixtures of feldspathic sands with ligurian peridotites up to 10 basaltic ophiolitic detritus in these sediments is suggested by cao and fe2o3 total abundances petrographic data indicate that a major part of the detritus in the macigno and cervarola formations is from alpine granitic basement of calc alkaline granite to tonalite plutons and gneisses but apart from higher ba in macigno and cervarola sandstones than in the gottero sandstones this is difficult to identify chemically the trace elements cr ni ba rb ce la y co cu ga pb and zn generally have positive correlations with niggli al alk a chemical surrogate measure of sheet mineral clays micas and chlorites content whereas sr which is associated with carbonate and feldspar shows negative correlation with al alk an olistostrome unit contains the most weathered detritus but otherwise shows similar chemical variation to the other formations methods to 1 identify separately mafic and ultramafic inputs 2 recognize in shales co cr and ni derived from ophiolitic sources and non ophiolitic sources 3 estimate the minimum mafic ultramafic proportion in a sediment may have general application elsewhere in sedimentary and metasedimentary rocks

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

weathering and sediment generation in the archean an integrated study of the evolution of siliciclastic sedimentary rocks of the 3 2ga moodies group barberton greenstone belt south africa abstract alluvial and braided fluvial deposits of the 3 2 ga moodies group in the barberton greenstone belt south africa are analyzed petrographically and geochemically to identify their source rocks provenance and assess the degree and type s of weathering required to produce the observed moodies sediment compositions conglomerate sandstone and shale data give somewhat differing pictures of provenance and weathering due to derivation from different components within the source terrane and size and compositional fractionation during transport the results suggest that shale geochemistry provides the most accurate estimate provenance although both rare earth element and trace element th sc zr cr and ti data must be used in combination to give the best results the source area for moodies group sediments was dominated by tonalite felsic volcanic rock komatiite basalt and granite based on mineralogical and major element divergence from estimated source area composition the moodies group sediments are remnants of an aggressive weathering environment labile materials such as komatiite basalt and coarse plagioclase grains decomposed almost entirely to clays and solutes and the chemical index of alteration for moodies shale is well above the global average an aggressive weathering environment in the archean may have been achieved by increased rainfall higher temperatures and or higher atmospheric p c o 2 more likely a combination of these conditions worked to offset the inhibitory weathering effects of a plant free environment

revision of the cretaceous paleogene stratigraphic framework facies architecture and provenance of the xigaze forearc basin along the yarlung zangbo suture zone abstract new field investigation structural analysis review of biostratigraphy stratigraphic framework facies architecture provenance and flow direction of the cretaceous paleogene sedimentary strata in southern tibet resulted in reinterpretation of the evolution of the xigaze forearc basin xfb the xfb is comprised by flysch dominant xigaze group consisting of ngamring chongdoi and sangzugang formations and of the shallow marine cuojiangding group padana qubeiya quxia and gyalaze formations with their ages herein revised as the albian coniacian and the santonian ypresian respectively the deep sea flysch represented by the ngamring formation constitutes the early sedimentary fill of the xfb it was subdivided into five megasequences ms1 ms5 in order the early submarine fan facies stage channel submarine fan stage the mature submarine fan stage the highstand submarine fan stage and outer fan pelagic stage the paleocurrent flows were eastwards and westwards during the early and late stages of basin development and northwards and southwards during its middle stage indicating typical forearc basin sedimentation with longitudinal supply and lateral filling provenance studies point to multiple sources with andesitic debris sourced from the jurassic lower cretaceous yeba formation and sangri group formed in the volcanic island arc chains in the southern gangdese the four periods of the xfb development are 1 the formation of the xfb basement by the xigaze ophiolite and completed before the aptian the coeval deposits on the shelf are the sangzugang formation carbonate 2 the earliest xfb deposits of the earliest aptian age ca 125 120 ma represented by the chongdoi formation related to the residual forearc 3 composite forearc developed represented by the late albian late cenomanian flysch megasequences ms1 ms2 and the turonian coniacian flysch megasequences ms3 ms5 respectively and 4 the final stage of the xfb development started the terminal forearc stage represented by the late late cretaceous early paleogene shallow marine cuojiangding group and terminated during middle ypresian when the gyalaze formation was deposited

fission track evidence for late oligocene and mid miocene activity along the north anatolian fault in south western thrace apatite fission track ft analyses of sandstone samples collected across the trace of the ganos segment of the north anatolian fault naf in south western thrace turkey indicate that a significant structural discontinuity was in existence at least by the latest oligocene such discontinuity had a complex kinematic history as exhumation south of it occurred during the latest oligocene and north of it during the mid miocene our data imply that early pliocene westward propagation of the naf in the marmara region followed a pre existing structural discontinuity such discontinuity could be related to the development of the intra pontide suture marking the terminal closure of the intra pontide ocean during the oligocene

neogene subsidence and stratigraphy of the simeulue forearc basin northwest sumatra abstract interpretation of new multi channel seismic data reveals the neogene subsidence history of the simeulue forearc basin located off northwestern sumatra the trench parallel elongated basin extends over 260 km in nw se direction and 100 km in sw ne direction maximum water depth is about 1300 m and the neogene sedimentary fill shows a thickness of up to 5 s two way traveltime we identified three stages of subsidence evolution after the formation of a regional basal neogene unconformity which are characterized by changing accumulation space sedimentation rates source areas and tectonic phases an early mid miocene stage is marked by occurrence of subsidence in several half grabens forming along the western border of the basin during the late miocene pliocene this small scale subsidence changed to a steadily subsiding trench parallel trough the present setup of the forearc region under the influence of strike slip faults due to oblique subduction is active at least since this time as evidenced by wrench faulting at the end of this stage subsidence expanded significantly eastwards drowning a large carbonate platform that evolved in the then shallow southern and eastern parts of the basin presently the central part of the simeulue basin is subject to inversion probably related to reactivation of early mid miocene half grabens

timing aegean extension evidence from in situ u pb geochronology and cathodoluminescence imaging of granitoids from nw turkey abstract the biga peninsula of nw turkey hosts granitoid plutons that record the timing of extension in the aegean region here we focus on three plutons the kozak eybek and kestanbol and apply new methods to obtain a detailed tectonic history of their generation and exhumation in situ in thin section ion microprobe zircon geochronology and color cathodoluminescence cl imaging of zircon grains and whole thin sections show these granites experienced magma mixing brittle deformation and significant fluid rock interactions zircon ages range from the late eocene to late miocene with two ages from a single grain that are permian the late eocene early oligocene ages record the end stages of subduction during the closure of a branch of the neo tethyan ocean whereas late oligocene late miocene ages record the plutons extension and exhumation we present a model in which kozak eybek and kestanbol magmas were initially generated by fluid flux melting from dehydration of the subducting anatolide tauride block as evidenced by the late eocene to early oligocene ages late oligocene ages document the initiation of extension in the biga peninsula region and correlate to ages timing exhumation of the kazdag massif early miocene ages indicate continued aegean extension in the southern biga peninsula region at this time

a review of tectonics and sedimentation in a forearc setting hellenic thrace basin north aegean sea and northern greece abstract exposure of the forearc region of the north aegean sea greece offers insight into evolving convergent margins the sedimentary fill of the thrace basin during the late eocene to oligocene time provides a record of subduction driven processes such as growth of magmatic arcs and construction of accretionary complexes this large sediment repository received sediment from two sources the southern outboard basin margin reflects the active influence of the exhumed accretionary prism e g pindic cordillera or biga peninsula while the northern inboard margin records the effect of the magmatic arc in the rhodope region the forearc basin sedimentary fills shoal upward into shallow marine strata but are dominated mainly by deep marine facies the depositional trend and stacking pattern are dominated by progradational patterns this trend which is observed in both basin margins is related to tectonic deformation rather than sea level fluctuations additional evidence for this tectonic uplift comes from the backstripping analysis the accretionary complex provided material into the forearc basin this material was transported northeast and formed a sand rich turbidity system that evolved upslope into shallow marine deposits stratigraphic data indicate that this turbidity system exhibits a successive landward inboard migration of the depocenter provenance data utilizing sandstone petrography conglomerate clast composition and bulk rock geochemistry suggest that this system reflects an increased influx of mafic material into the basin volcanic arc derived material was transported south and east and accumulated in deep marine settings both stratigraphic and provenance data indicate a seaward outboard migration of the basin depocenter and a significant increase in felsic detritus into the forearc

palaeomagnetism in greece cenozoic and mesozoic components and their geodynamic implications abstract an important number of palaeomagnetic data have been obtained in greece during the last 20 years these data can be schematically divided into two groups according to their age when plate movements are fairly well constrained the cenozoic provides a dense network of palaeomagnetic directions the general pattern displays eastward declinations broadly distributed over a large distance from the ionian islands to the western greek rhodope and westward declinations less accurately constrained in space and time in the southern and eastern aegean and in western anatolia emphasis is given to the evaluation of this dataset by comparing it with new concepts of the regional tectonics in the mesozoic palaeozoic more scarcely covered reliable information is provided about latitudinal movements resulting in a suggested palaeolatitude of 15 20 n for almost all studied areas a model proposing prevailing counterclockwise rotations in the internal hellenides and strong clockwise rotations for the external hellenides appears plausible finally issues for future research are outlined for example mio pliocene formations from central greece the pindos ophiolites and palaeocene upper cretaceous data should receive further attention

eocene stratigraphic evolution of the thrace basin turkey abstract this paper explains the primary basin evolution processes of the thrace basin which started opening during early middle eocene stratigraphic and tectonic models for different parts of the basin have been constructed and basin scale stratigraphic correlations were established by using outcrop well and seismic data initial deposits of eocene in the thrace basin show irregular depositional patterns associated with various lithofacies deposited under the control of various tectonostratigraphic settings first a compressional regime started after the collision of the sakarya continent with the rhodope pontide fragment in late cretaceous paleocene enabled initiation of transtensional stress which was responsible for the creation of necessary accommodation space for deposition of the initial thrace sediments in the northern and eastern part of the thrace basin the lower middle eocene hamitabat formation was deposited in this kind of transtensional setting and can be divided into various lithostratigraphic units an unconformity identified within hamitabat formation from seismic and well data divides it to two major units in early eocene the thrace basin was deepening eastwards and deposition was initiated between finger shaped paleo highs aligned in an e w direction thus synchronous erosional and depositional events in different parts of the basin formed various facies associated with a variety of depositional environments during the same time interval a regional unconformity at the base of lower eocene between karaagac and hamitabat formations can be correlated from south to north moreover the unconformity between lower middle eocene deposits and the middle eocene limestones of southern thrace is correlative with the unconformity between the hamitabat formation and overlying upper eocene limestones at northern regions this unconformity has a correlative conformity within the gazikoy or kesan formations in central thrace where continuous deposition took place during eocene without interruption

late precambrian thrust and wrench zones in northern brittany france abstract brioverian units of northern brittany armorican massif france were deformed and metamorphosed during a late precambrian tectonic episode the cadomian orogeny kinematic study strain and displacement in the st cast st brieuc area shows that this tectonic episode was characterized by the obduction of a back arc basin over a continental margin around 580 590 ma ago strain pattern analysis reveals a constant interaction between ssw directed imbricated thrust zones and ductile sinistral wrench zones trending n 50 e the arcuate pattern of cadomian structures in this area results from such an interaction thickening as a result of the thrusts induced migmatization and the development of a high temperature belt around 540 ma in the st malo guingamp area

chromium and nickel in shale of the taconic foreland a case study for the provenance of fine grained sediments with an ultramafic source abstract to test the suitability of using shale geochemistry as a provenance indicator of a source with an ultramafic component we used i c p mass spectrometry to analyze 130 samples from seven localities from newfoundland to new york these samples represent mud from the foreland basin produced during the collision of the taconic are with north america in the ordovician the sandstones in the flysch contain detrital chromite and other detritus that indicate that the source contained ultramafic rocks presumably from ophiolites emplaced during collision this setting is an ideal test case for examining the spatial and temporal variation in cr and ni geochemistry of shale derived from ophiolite bearing highlands shale samples with high concentrations of cr and ni have a cr ni ratio of 1 4 which is approximately the cr ni ratio for ultramafic rocks 1 6 suggesting only minor geochemical partitioning but sandstones have a cr ni ratio of 3 0 suggesting significant sedimentary fractionation analyses of samples taken upsection in a single stratigraphic section suggest that proximity to the source influences cr and ni concentrations a decrease in cr and ni concentrations through time suggests that uplift and erosion of the thrust complex non ophiolitic diluted the ultramafic signal we attribute significant along strike variation in cr and ni concentrations to the relative proportion of ultramafic rocks in the source region this case study shows that cr and ni geoch mistry of shale from basin strata can be used to determine the lateral and temporal variability of ultramafic rocks in an active orogenic setting

gravity modellings of the cadomian active margin of northern brittany abstract the geometrical relationships existing between the saint brieuc saint malo and guingamp units which form the cadomian active margin of northern brittany have been determined by gravity analyses and 2 5d modelling correlated with other geophysical magnetic seismic etc and geological observations automatic structural analyses were performed before modelling to identify lateral gravity discontinuities averaged density measurements were used for 2 5d gravity modelling along six profiles across the arcuate geological and gravity shape of the cadomian basement this study allowed the third dimension to be obtained through correlating each profile with its neighbours we propose that orthogneiss formations equivalent to the port morvan orthogneiss constitute the saint brieuc upper crustal unit below the lanvollon formation 2 5d gravity modelling outlines downward geological differences in the western and eastern parts of the ploufragan complex as previously indicated by surface mapping these results stress the necessity for distinguishing between the guingamp and saint malo units

a fore arc origin for the thrace basin nw turkey hydrocarbon bearing thrace basin occupies much of the european part of turkey the middle eocene to oligocene sequence in the centre of the basin exceeds 9 km in thickness based on the stratigraphy structure and the regional context of this basin we propose that it developed as a fore arc basin between the medial eocene and the oligocene above the northward subducting intra pontide ocean its post miocene history has been dominated mainly by wrench tectonics resulting from the activity of the now deactivated northwestern strand of the present day north anatolian fault zone

possible strand of the north anatolian fault in the thrace basin turkey an interpretation the north anatolian fault is a 1200 km long major transform fault bounding the anatolian plate on its north side the fault formed during the late middle miocene as a broad shear zone with a number of strands splaying westward in a horsetail pattern later movement became localized along a central strand and the southerly and northerly splays became inactive the west northwest striking thrace strike slip fault system is one of these right lateral presently inactive splays it consists of three subparallel strike slip faults from north to south these are the kirklareli luleburgaz and babaeski fault zones which extend for about 130 km through the thrace basin the thrace fault zone probably connected to the southeast with the presently active northern strand of the north anatolian fault in the marmara sea to the northwest the zone may have extended to the plovdiv graben zone in bulgaria the cenozoic thrace basin contains middle eocene to pliocene sedimentary rocks the thrace right lateral wrench fault system formed prior to the pliocene and had become inactive by the pliocene strike slip fault zones with normal and reverse separation are detected by seismic reflection profiles and subsurface data as the system became inactive the motion on the north anatolian fault zone began to be accommodated in the marmara sea region thus the thrace fault system represents the oldest strand of the north anatolian fault to the west of istanbul releasing bend extensional structures and restraining bend compressional structures are abundant along the fault zones several hydrocarbon producing anticlines lie en echelon to the luleburgaz fault zone regionally the thrace fault ystem has a horsetail shape with the various strands becoming younger southward

coeval plutonism and metamorphism in a latest oligocene metamorphic core complex in northwest turkey a metamorphic core complex of latest oligocene age crops out in the kazdag mountain range in northwest turkey the footwall of the core complex consists of gneiss amphibolite and marble metamorphosed at 5 1 kbar and 640 50 c the average muscovite and biotite rb sr ages from the gneisses are 19 ma and 22 ma respectively and imply high temperature metamorphism during latest oligocene times the hangingwall is made up of an unmetamorphosed lower tertiary oceanic accretionary melange with upper cretaceous eclogite lenses the hangingwall and footwall are separated by an extensional ductile shear zone two kilometres thick mylonites and underlying high grade metamorphic rocks show a n trending mineral lineation with the structural fabrics indicat ing down dip top to the north shear sense the shear zone the accretionary melange and the high grade metamorphic rocks are cut by an undeformed granitoid with a 21 ma rb sr biotite age analytically indistinguishable from the rb sr biotite ages in the surrounding footwall gneisses the estimated pressure of the metamorphism and that of the granitoid emplacement indicate that the high grade metamorphic rocks were rapidly exhumed at 24 ma from a depth of 14 km to 7 km by activity along the shear zone the subsequent exhumation of the metamorphic rocks to the surface occurred during pliocene quaternary times in a transpressive ridge between two overstepping fault segments of the north anatolian fault zone the high grade metamorphic rocks of the kazdag range are surrounded by voluminous calc alkaline volcanic and plutonic rocks of late oligocene early miocene age which formed above the northward dipping hellenic subduction zone the magmatic arc setting of the core complex and stratigraphic evidence for subdued topography in northwest turkey prior to the onset of extension suggest that the latest oligocene regional extension was primarily related to the roll back of the subduction zone rather than to the gravitational collapse

u pb geochronological constraints on the timing of plutonism volcanism and sedimentation jersey channel islands uk uranium lead dates for single and small multiple grain zircon separates are presented for the main geological units from jersey british channel islands a turbiditic sandstone from the jersey shale formation brioverian supergroup contains detrital zircons of a variety of ages ranging from c 2 6 to 0 6 ga the youngest zircons yielded nearly concordant u pb dates of 586 7 3 0 ma and 587 1 2 7 ma providing a maximum depositional age for the unit zircons from overlying volcanic rocks anne port rhyolite give an upper intercept date of 582 8 3 2 7 ma considered to be the age of eruption the undeformed sw jersey granite which intrudes and locally thermally metamorphoses the folded jersey shale formation is dated at 580 2 3 1 6 ma these dates constrain tightly the timing of deposition of the jersey shale formation and the age of deformation on jersey and indicate a dynamic arc environment during the late neoproterozoic zircons from the nw jersey granite define an upper intercept date of 482 7 1 6 ma similar to the previously reported 40 ar 39 ar hornblende date of c 473 ma confirming a renewed pulse of magmatism during the ordovician in this sector of cadomia

controls on active forearc basin stratigraphy and sediment fluxes the pleistocene of hawke bay new zealand detailed high resolution documentation of forearc basin fi ll is scarce in the literature in this geological and geophysical study we investigated the pleistocene sedimentary record of the tectonically active hawke bay forearc domain of the hikurangi subduction margin of new zealand interpretation of an extensive seismic refl ection data set that is correlated with marine cores and onshore geological maps identifi es the detailed stratigraphic architecture of the last 1 1 m y this analysis reveals the infl uences and interactions of tectonic deformation climate eustasy and isostasy on forearc basin sedimentation eleven 100 k y depositional sequences are recognized in the basin fi ll thus highlighting the dominance of pleistocene climate eustasy on sequence development the stacking pattern and isopach maps of sequences exhibit an overall retrogradational trend and an arcward migration of depocenters these trends progressively develop a basinwide diachronous and composite erosion unconformity formed by the lateral succession and landward encroachment of the 12 sequence bounding unconformities s12 to s1 among these the s5 surface ca 430 ka is an angular unconformity that separates major megasequences of the sedimentary record the forearc domain evolved from a series of ridge parallel basins to a succession of connected basins that have progressively developed around major growing thrust faulted ridges since ca 430 ka this change in basin confi guration and associated signifi cant increase of the preserved sediment fluxes occurred synchronous with the reactivation of major out of sequence thrusts and the completion of the mid pleistocene transition

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

petrography and geochemistry of lower carboniferous greywacke and mudstones in northeast junggar china implications for provenance source weathering and tectonic setting abstract northeast junggar occupies an important position that links east junggar and chinese altai numerous magmatic and sedimentary rocks of the paleozoic in this area recorded the final amalgamation processes of east junggar and chinese altai this study analyzes the petrological and geochemical characteristics of sandstones and mudstones from the early carboniferous nanmingshui formation in northeast junggar the provenance and tectonic setting of these clastic rocks are discussed petrography indicates that the composition and texture maturity of the sandstones are low the components of the sandstones are mainly volcanic fragments 61 87 feldspars 9 30 and monocrystalline quartz 2 18 with a few polycrystalline quartz and other minerals slice observation indicates that the majority of the volcanic fragments of sandstones are basic intermediate volcanic rocks with a few dacite and felsic plutonic fragments the detrital modes of the sandstones reflect that these sandstones are derived from undissected arcs a low to moderate chemical index of alteration and the al2o3 cao na2o k2o diagram reflect a low to moderate weathering degree in the source area trace and rare earth element e g la th hf sc cr co and eu contents and their ratios suggest that the source rocks of the clastic rocks are intermediate basic rocks with some felsic rocks compared with sandstones the source rocks for mudstones are more felsic the petrography and geochemistry characteristics of the clastic rocks suggest that the proximal dulate arc should be the primary source area mixing calculations based on ree data suggest that approximately two thirds of the sandstone fragments are intermediate basic volcanic rocks the contents of the major and trace elements as well as the stratum features of the clastic rocks manifest that these clastic rocks resemble sedimentary rocks in a back arc basin the formation of this back arc basin is caused by the southward subduction of the zaysan erqis ocean

chronostratigraphy and tectonic deformation of the north ecuadorian south colombian offshore manglares forearc basin abstract forearc basins in convergent margins contain a nearly continuous record of sedimentation and deformation their chronostratigraphy reflects the manner in which the basin accommodates loads and vertical and horizontal motion caused by eustasy tectonics and sedimentation during plate convergence along the north ecuador and south colombia nesc margin 1 3 5 n thick cenozoic sedimentary sequences accumulated over blocks of oceanic basement that accreted between the late cretaceous and early cenozoic thus forming the onshore borbon and tumaco basins and the offshore pacific frontal basin based on morphology and seismic data analysis the nesc forearc basin named manglares basin consists of five acoustic units of sedimentary nature units a e separated by unconformities u1 u5 resting over the interpreted oceanic basement unit f by integrating these data with regionally compiled chronostratigraphic charts of the onshore borbon and tumaco basins and the geology of gorgona island we propose a model for the tectonic and stratigraphic evolution for the manglares basin and its oceanic basement this model shows that 1 unconformity u5 between units f and e marks a tectonic phase that may correlate with the accretion of the oceanic basement of the manglares basin to the northern andes possibly between the late cretaceous and paleocene 2 a marked change in seismic facies between units e and d associated with major tectonic unconformity u4 is compatible with the incaic compressive phase that affected the andes during the late eocene early oligocene 3 this tectonic phase likely peaked during the latest oligocene earliest miocene u3 and later during the middle miocene u2 4 the regional middle miocene erosion period u2 marked a change in the tectono sedimentary evolution of the forearc basin compressive deformation ceased in the southern margin segment which underwent long term basin subsidence while compression and uplift increased in the central and northern segments

rapid early middle miocene exhumation of the kazdag massif western anatolia apatite fission track analyses indicate that the kazdag massif in northwestern anatolia was exhumed above the apatite partial annealing zone between 20 and 10 ma i e early middle miocene with a cluster of ages at 17 14 ma the structural analysis of low angle shear zones high angle normal faults and strike slip faults as well as stratigraphic analysis of upper plate sedimentary successions and previous radiometric ages point to a two stage structural evolution of the massif the first stage encompassing much of the rapid thermal evolution of the massif comprised late oligocene early miocene low angle detachment faulting and the associated development of small supradetachment grabens filled with a mixture of epiclastic volcaniclastic and volcanic rocks kucukkuyu fm the second stage plio quaternary has been dominated by i strike slip faulting related to the westward propagation of the north anatolian fault system and ii normal faulting associated with present day extension this later stage affected the distribution of fission track ages but did not have a component of vertical normal movement large enough to exhume a new partial annealing zone the thermochronological data presented here support the notion that neogene extensional tectonism in the northern aegean region has been episodic with accelerated pulses in the early middle miocene and plio quaternary

time span of plutonism fabric development and cooling in a neoproterozoic magmatic arc segment u pb age constraints from syn tectonic plutons sark channel islands uk abstract new u pb zircon and titanite dates from syn tectonic plutons on the british channel island of sark constrain the time span of plutonism fabric development and cooling in this part of the neoproterozoic cadomian magmatic arc the tintageu leucogneiss is a mylonitic unit that was dated previously at 615 6 4 2 2 3 ma the port du moulin quartz diorite which intruded the tintageu unit contains a high strain solid state deformation fabric that is less intense than but parallel to fabrics in the leucogneiss and yields a u pb zircon date of 613 5 2 3 1 5 ma the little sark quartz diorite also displays solid state deformation fabrics in addition to relict magmatic textures and yields a u pb zircon date of 611 4 2 1 1 3 ma the north sark granodiorite is largely penetratively undeformed exhibits mainly magmatic fabrics and textures and has a u pb zircon date of 608 7 1 1 1 0 ma two fractions of titanite from each intrusion are essentially concordant and are identical within error with mean dates of 606 5 0 4 ma port du moulin quartz diorite 606 2 0 6 ma little sark quartz diorite 606 4 0 6 ma north sark granodiorite the new u pb data in combination with previous u pb and 40 ar 39 ar data and previous field studies confirm the syn tectonic nature of the sark plutons and quantify the time span ca 7 m y required for intrusion and sufficient crystallization of each body to record incremental strain during waning deformation titanite u pb and hornblende 40 ar 39 ar dates mark final cooling about 2 m y after intrusion of the last pluton

ophiolitic source rocks for taconic age flysch trace element evidence flysch generated along the appalachian orogen during the ordovician taconic orogeny ranges in age from late arenig to early caradoc allochthonous flysch and from late llanvirn to ashgill autochthonous flysch sandstones in these units are dominantly lithic arenites with a heavy mineral suite containing common to abundant mg rich chromite north of the canada united states border the only reasonable sources for the chromite were the lower ultramafic units of obducted ophiolites trace element analyses cr ni v cu ti zr y of flysch sandstones indicate a striking increase in cr and ni concentrations from the united states appalachians to the canadian appalachians in the united states units cr is in the range of 10 to 50 ppm canadian flysch units average an order of magnitude more cr these results suggest that ophiolite obduction either did not occur or was of minor importance during the taconic orogeny in the united states appalachians the difference in ophiolite abundance between the canadian and united states appalachians suggests a fundamental difference in tectonic style along the orogen a feature that must be accommodated by plate tectonic models new models will probably need to consider both obliquity of subduction and geological complexity of the ordovician collision zone in order to explain the spatial distribution of obducted ophiolite sheets

comment on maravelis et al accretionary prism forearc interactions as reflected in the sedimentary fill of southern thrace basin lemnos island ne greece

the negative eu anomaly in archean sedimentary rocks implications for decomposition age and importance of their granitic sources abstract a negative correlation between eu anomaly eu eu and chemical index of weathering ciw is found for archean pelites in both greenstone belts and high grade terrains from southern africa western greenland north america western australia and china a similar negative correlation betweeneu eu and chemical index of alteration cia is also found for worldwide young deep sea sediments from various tectonic settings the increase in the indices of weathering and alteration coincide with both shifts in mineral composition and mineral decomposition from plagioclase k feldspar to mica kaolinite and from amphibole to chlorite smectite juvenile crustal materials from local sources are only slightly decomposed due to little or no transport they are characterized by low ciw cia and negligible eu anomalies in contrast crustal materials from large provenance areas have usually suffered long transport and recycling which results in decomposition of high temperature minerals and large ciw cia values that are negatively correlated with significant negative eu anomalies thus the observed trends are interpreted as mainly reflecting increasing contributions of recycled and decomposed materials from large provenances relative to juvenile crustal additions through arc magmatism at local sources in this context there is no obvious distinction between archean greenstone and high grade metasediments and young deep sea sediments the large provenance areas have contained a significant proportion of granitic and rhyolitic materials which in part have not resisted decomposition and erosion due to their occurrence in shallow crustal layers granites received their distinctive negative eu anomaly from equilibration with a feldspar rich residuum the negative eu anomaly of archean metaclastic sediments apparently increased with decreasing age trends of minimum and averageeu eu values of metaclastic sediments evolving with time are calculated for the archean and lead us to infer that the negative eu anormaly eu eu

permo carboniferous conglomerates in the trinity peninsula group at view point antarctic peninsula sedimentology geochronology and isotope evidence for provenance and tectonic setting in gondwana field observations from the trinity peninsula group at view point on the antarctic peninsula indicate that thick southward younging and overturned clastic sedimentary rocks comprising unusually coarse conglomeratic lenses within a succession of fine grained sandstone mudstone couplets are the deposits of debris and turbidity flows on or at the foot of a submarine slope three detrital zircons from the sandstone mudstone couplets date deposition at 302 3 ma at or shortly after the carboniferous permian boundary conglomerates predominantly consist of quartzite and granite and contain boulders exceeding 500 mm in diameter zircons from granitoid clasts and a silicic volcanic clast yield u pb ages of 466 3 ma 373 5 ma and 487 4 ma respectively and have corresponding average ehft values between 0 3 and 7 6 a quartzite clast conglomerate matrix and sandstone interbedded with the conglomerate units have broadly similar detrital zircon age distributions and hf isotope compositions the clast and detrital zircon ages match well with sources within patagonia however the age of one granite clast and the ehf characteristics of some detrital zircons point to a lesser south africa or ellsworth mountain like contribution and the quartzite and granite dominated composition of the conglomerates is similar to upper palaeozoic diamictites in the ellsworth mountains unlike detrital zircons large conglomerate clasts limit possible transport distance and suggest sedimentation took place on or near the edge of continental crust comparison with other upper palaeozoic to mesozoic sediments in the antarctic peninsula and patagonia including detrital zircon composition and the style of deformation suggests deposition of the trinity peninsula group in an upper plate basin on an active margin rather than a subduction related accretionary setting with slow extension and rifting punctuated by short periods of compression

reply to comment by caracciolo et al on maravelis et al 2015 accretionary prism forearc interactions as reflected in the sedimentary fill of southern thrace basin lemnos island ne greece

neoproterozoic shear zone tectonics within the icartian basement of guernsey and sark channel islands the channel islands of guernsey and sark are amongst the few localities within the neoproterozoic cadomian orogenic belt where palaeoproterozoic basement is exposed basement units collectively referred to as icartian comprise orthogneisses e g the c 2000 ma icart granite gneiss metasediments and amphibolites on guernsey the protolith to the icart granite gneiss was intruded into metasediments already deformed during a d 1 deformation event both were variably deformed during a d 2 event within an approximately north south trending steeply dipping oblique dextral shear zone on sark metasediments and amphibolites carry a d 1 fabric not necessarily correlatable with that on guernsey which was deformed during d 2 to form recumbent gently inclined folds and tectonic fabrics which locally carry top to the south kinematic indicators early cadomian quartz diorites which intruded the icartian basement carry variably developed magmatic and moderate temperature 400 550 c ls solid state fabrics which are similarly oriented to d 2 basement structures this indicates that the quartz diorites were emplaced and deformed during a protracted d 2 event published 40 ar 39 ar amphibole cooling ages of c 600 ma from guernsey and sark quartz diorites and a host icartian amphibolite are consistent with reworking of basement units during the cadomian orogeny the contrasting kinematic pattern during cadomian deformation implies that a flat lying shear zone on sark may have accommodated oblique dextral strike slip movement on guernsey with an overall southerly direction of tectonic transport deformation most likely occurred in the hanging wall of a major south dipping neoproterozoic subduction zone

the korudag anticlinorium in the south thrace basin northwest turkey a super giant petroleum trap complex the sedimentary sequence of the south thrace basin northwest turkey comprises upper cretaceous holocene sediments in this basin the korudag anticlinorium which is the subject of this study is located between the aegean sea in the west and the sea of marmara to the east the anticlinorium which is approximately 300 km 186 mi long and 40 km 25 mi wide was formed by effects of the neotethys subduction accretion complex and istranca massif collision during the late early miocene the korudag anticlinorium was deformed to its present day structure by the oldest splay of the north anatolian fault upper middle miocene and the northern branch of the north anatolian fault naf n not earlier than 200 ka organic geochemical analysis oil and gas to source rock correlation and basin modeling studies suggest that the korudag anticlinorium should be charged by hydrocarbons generated from the karaagac ceylan regionally and mezardere formations gas and oil are being produced from the korudag anticlinorium and its subparallel anticlines in the north marmara degirmenkoy seymen cayirdere karacali yulafli tekirdag sevindik and vakiflar gas plus oil fields mapping done as part of this study indicates that the korudag anticlinorium has not yet been tested and explored comprehensively

basement types of the thrace basin and a new approach to the pre eocene tectonic evolution of the northeastern aegean and northwestern anatolia a review of data and concepts in northwestern turkey the pre eocene basement of the thrace basin consists of the strandja rhodope metamorphics in the north northwest the istanbul zonguldak paleozoic sequence in the northeast a tectonic mixture of the fragments from the sakarya continent and pre upper cretaceous ophiolites in the southeast and the uppermost cretaceous paleocene transgressive sediments the ophiolites belong to a dogger early cretaceous oceanic basin the northeastern vardar ocean between the rhodope and sakarya continents the ne trending oceanic branch closed diachronously during the early late malm to the northeast but during latest early cretaceous to late cretaceous time toward the main vardar ocean in the southwest during the final closure the suture zone acted as a strike slip fault zone the latest cretaceous paleocene transpressional to transtensional activities caused the juxtaposition of different basement types and the development of a tectonic mixed zone the biga armutlu ovacik zone between the rhodope and sakarya continents under the regional n s compression on the plate overlying the north northeastward dipping vardar subduction zone the southwestward escape of an area of crust bounding by the wnw trending balkan thrace dextral fault zone to the north and the ne trending biga armutlu ovacik sinistral zone to the southeast caused a triangular shaped and isolated depression area for the deposition of the uppermost cretaceous paleocene transgressive sediments in a transtensional setting the tectonically bounded depression area constitutes also a necessary accommodation space for the deposition of the initial deposits of early eocene age in the thrace basin

from tethys to eastern paratethys oligocene depositional environments paleoecology and paleobiogeography of the thrace basin nw turkey the oligocene depositional history of the thrace basin documents a unique paleogeographic position at a junction between the western tethys and the eastern paratethys as part of the tethys shallow marine carbonate platforms prevailed during the eocene subsequently a three staged process of isolation started with the oligocene during the early rupelian the thrace basin was still part of the western tethys indicated by typical western tethyan marine assemblages the isolation from the tethys during the early oligocene is reflected by oolite formation and endemic eastern paratethyan faunas of the solenovian stage the third phase reflects an increasing continentalisation of the thrace basin with widespread coastal swamps during the late solenovian the mollusc assemblages are predominated by mangrove dwelling taxa and the mangrove plant avicennia is recorded in the pollen spectra the final continentalisation is indicated by the replacement of the coastal swamps by pure freshwater swamps and fluvial plains during the late oligocene mammal zone mp 26 this paleogeographic affiliation of the thrace basin with the eastern paratethys after 32 ma contrasts all currently used reconstructions which treat the basin as embayment of the eastern mediterranean basin

accretionary prism forearc interactions as reflected in the sedimentary fill of southern thrace basin lemnos island ne greece architecture of the well exposed ancient forearc basin successions of northeast aegean sea greece provides useful insights into the interplay between arc magmatism accretionary prism exhumation and sedimentary deposition in forearc basins the upper eocene lower oligocene basin fill of the southern thrace forearc basin reflects the active influence of the uplifted accretionary prism deep marine sediments predominate the basin fill that eventually shoals upwards into shallow marine sediments this trend is related to tectonically driven uplift and compression field stratigraphic sedimentological petrographic geochemical and provenance data on the lower oligocene shallow marine deposits revealed the accretionary prism i e pindic cordillera or biga peninsula as the major contributor of sediments into the forearc region field investigations in these shallow marine deposits revealed the occurrence of conglomerates with 1 mafic and ultramafic igneous rock clasts 2 low grade metamorphic rock fragments and 3 sedimentary rocks the absence of felsic volcanic fragments rules out influence of a felsic source rock geochemical analysis indicates that the studied rocks were accumulated in an active tectonic setting with a sediment source of mainly mafic composition and palaeodispersal analysis revealed a ne nne palaeocurrent trend towards the rhodopian magmatic arc thus these combined provenance results make the accretionary prism the most suitable candidate for the detritus forming these shallow marine deposits

evolution of the se asian continent from u pb and hf isotopes in single grains of zircon and baddeleyite from large rivers to better understand the evolution of the se asian continent 235 single zircon and baddeleyite grains from large rivers were dated by the u pb chronometer and 148 of these grains were simultaneously analyzed for hf isotopes this combination of methods is applied to sand samples from the mekong irrawaddy salween and red rivers which sample the continent on the plate scale u pb dates and hf isotopic signatures of these grains resolve the age spectra of crust and they elucidate source characteristics of magmas involved in continental growth and recycling for sufficient statistical coverage more than 80 of zircons and baddeleyites from each river sample were analyzed representing an erosion area of about 1 6 106 km2 our analyses reveal five different proterozoic crustal growth events occurring at about 2 5 ga 2 3 ga 1 9 ga 1 1 ga and 0 8 ga however none of these basement terrains is exposed in se asia being entirely covered by phanerozoic sediments the data also substantiate granitoid magmatism during the caledonian indosinian and himalayan orogenies initial hf isotope signatures ehfi obtained for grains lying less than 15 discordant in the concordia diagram range between 13 3 and 16 7 plotting in both the domains of strongly lile depleted and enriched reservoirs relative to a chondritic evolution of the mantle approximately half of the grains crystallized in magmas derived from significantly depleted mantle sources and about 18 formed in magmas showing nearly chondritic signatures ehfi 1 37 to 1 59 27 grains the remaining grains yield strongly negative ehfi documenting the incorporation of important amounts of melts generated from crust formed during the paleoproterozoic events at 2 3 and 1 9 ga which seem to have produced the dominant mass of the se asian continent all younger orogenic cycles are characterized by substantial melting of continental material which probably dominate over juvenile crust addition an exception are the irrawaddy terrains where substantial mantle input characterizes post collisional magmatism since 50 ma

a combined petrographical geochemical provenance study of the newland formation mid proterozoic of montana a provenance study was conducted on the mid proterozoic newland formation in which petrographical features of sandstones and geochemical characteristics of shales were integrated to arrive at an internally consistent interpretation sandstones of the newland formation are typically arkosic sands and arkoses with very well rounded quartz and feldspar grains and only minor amounts of extrabasinal rock fragments the predominant feldspar types are k spar and microcline feldspar grains are smaller than quartz grains and feldspars show little alteration due to weathering detrital modes of newland sandstones qfl diagrams indicate that they were derived from a stable cratonic source these petrographical features imply a source area dominated by granites and granitoid gneisses semi arid to arid climate tectonic quiescence and overall peneplain conditions shales of the newland formation are dominated by illite quartz silt and fine crystalline dolomite they have small la th rations relatively large hf contents and small contents of cr co and ni all indicative of derivation from crust of granitic composition small tio 2 al 2 o 3 ratios also suggest source rocks of granitic composition the average chemical index of alteration cia for newland shales is 71 8 which in light of the probable granitoid source indicates modest amounts of chemical weathering relatively large sio 2 contents and large k 2 o na 2 o ratios reflect derivation from stable cratonic areas and tectonic quiescence thus in general the petrography of sandstones and geochemistry of shales provides the same provenance clues for the newland formation one notable discrepancy between the two approaches is that the sandstones indicate an arid to semi arid climate with very minor chemical weathering whereas the cia of the shales indicates at least modest amounts of chemical weathering this indicates on one hand the need to better calibrate the cia with a large variety of muds from modern climatic settings and on the other hand the possibility that this discrepancy is due to transport segregation

discussion unraveling the provenance of eocene oligocene sandstones of the thrace basin north east greece by caracciolo et al 2011 sedimentology 58 1988 2011

unravelling provenance from eocene oligocene sandstones of the thrace basin north east greece new sandstone petrology and petrostratigraphy provide insights on palaeogene middle eocene to oligocene clastics of the thrace basin in greece which developed synchronously with post cretaceous collision and subsequent tertiary extension sandstone petrofacies are used as a tool to unravel complex geodynamic changes that occurred at the southern continental margin of the european plate identifying detrital signals of the accretionary processes of the rhodope orogen as well as subsequent partitioning related to extension of the rhodope area followed by oligocene to present aegean extension and wide magmatic activity starting during the early oligocene sandstone detrital modes include three distinctive petrofacies quartzolithic quartzofeldspathic and feldspatholithic major contributions are from metamorphic basement units represented mostly by low to medium grade lithic fragments for the quartzolithic petrofacies and high grade metamorphic rock fragments for the quartzofeldspathic petrofacies volcaniclastic sandstones were derived from different volcanic areas with a composition varying from dominantly silicic to subordinate intermediate products mainly rhyolitic glass spherulites and felsitic lithics evolution of detrital modes documents contributions from three key source areas corresponding to the two main crystalline tectonic units i the variegated complex ultramafic complex in the initial stage of accretion quartzolithic petrofacies ii the gneiss migmatite complex quartzofeldspathic petrofacies and iii the circum rhodope belt the volcaniclastic petrofacies is interbedded with quartzofeldspathic petrofacies reflecting superposition of active volcanic activity on regional erosion the three key petrofacies reflect complex provenance from different tectonic settings from collisional orogenic terranes to local basement uplift and volcanic activity the composition and stratigraphic relations of sandstones derived from erosion of the rhodope orogenic belt and superposed magmatism after the extensional phase in northern greece provide constraints for palaeogeographic and palaeotectonic models of the eocene to oligocene western portions of the thrace basin clastic detritus in the following sedimentary assemblages was derived mainly from provenance terranes of the palaeozoic section within the strongly deformed rhodope massif of northern greece and south east bulgaria from the epimetamorphic units of the circum rhodope belt and from superposed late eocene to early oligocene magmatism related to orogenic collapse of the rhodope orogen the sedimentary provenance of the rhodope palaeogene sandstones documents the changing nature of this orogenic belt through time and may contribute to a general understanding of similar geodynamic settings

biostratigraphic data from the cetmi melange northwest turkey palaeogeographic and tectonic implications abstract the cetmi accretionary melange is cropping out in the biga peninsula of northwest turkey it is characterised by an isolated position relatively far from the accretion complexes of the nearest suture zones which raises the question of its lateral correlations a detailed biostratigraphic investigation of the limestone and radiolarite blocks and the matrix of the cetmi melange allowed to propose a solution for this palaeogeographic problem scarce red nodular limestones in the han bulog facies represent the oldest lithology in the melange their late scythian ladinian age is based on chiosella gondolleloides the co occurrence of gladigondolella sp and nicoraella cf kockeli and paragondolella fuelopi light grey limestone blocks are a characteristic feature of the cetmi melange they occur in two distinct facies facies a consists of packstone to grainstone and is characterised by unsorted and poorly washed pelbiosparites facies b consists of wackestone to packstone and is characterised by poorly washed biopelmicrites to biopelsparites the foraminiferal assemblage of facies a containing triasina hantkeni is of late norian to rhaetian age the foraminiferal assemblage of facies b never contains t hantkeni and is characteristic of a late triassic carnian to norian rhaetian age radiolarian cherts are widely distributed in the cetmi melange they record fully pelagic sedimentation from the upper bajocian to the aptian the matrix of the cetmi melange consists of brown to black shales sometimes silty or siliceous intercalated with dark grey greywackes palynomorphs of one sample of brownish silty shale yielded an early to middle albian age based on the co occurrence of several dinoflagellate cysts the age of the matrix representing the youngest lithology within the melange and of the unconformable overlaying section latest albian cenomanian indicate that the melange forming process stopped between the early albian and the latest albian cenomanian at a regional scale the cetmi melange has little in common with the melanges from the izmir ankara and intra pontide sutures of northwestern turkey precluding a direct correlation on the other hand the cetmi melange shares several characteristics with the melange like units of the eastern rhodope zone bulgaria and greece like a major cenomanian transgression the reworking of triassic limestones and middle jurassic lower cretaceous radiolarians and the absence of jurassic cretaceous passive margin lithologies the occurrence of rhodopian units on the biga peninsula suggests that the studied units represent an isolated fragment of the rhodope zone in nw turkey

coupling of early tertiary extension in the great valley forearc basin with blueschist exhumation in the underlying franciscan accretionary wedge at mount diablo california in the california coast ranges east of san francisco post 3 5 ma folding and erosion of the mount diablo anticline have created unusual three dimensional exposures of late mesozoic cenozoic stratigraphic and structural relations among rocks of the franciscan subduction complex coast range ophiolite and great valley forearc basin these relations offer new insights into the kinematics of late cretaceous early tertiary synsubduction extension attenuation and blueschist exhumation within the ancestral california forearc region map relations and subsurface data reveal that marine strata of the great valley forearc basin northeast of mount diablo accumulated in an 100 km long north south trending extensional graben system normal faults in the graben system cut steeply downsection through late cretaceous and early tertiary growth strata and terminate against the clayton marsh creek fault which is at a low angle to bedding and is interpreted to be the basal detachment for part of the graben system the clayton marsh creek fault in turn is linked to a system of faults that juxtapose blueschist facies rocks of the underlying ancestral franciscan accretionary prism against attenuated remnants of forearc crust that were never deeply buried including the coast range ophiolite and basal great valley strata these faults are the local expression of the coast range fault in this area franciscan rocks exposed beneath the faults were metamorphosed at 20 km depths after 108 ma based on jadeitic pyroxene and 108 ma detrital zircons u pb in metagraywackes apatite fission track data indicate that these blueschist facies rocks were subsequently uplifted and exhumed from 9 km to 3 km depths in latest cretaceous early tertiary time coeval with the subsidence and extension in the structurally overlying forearc graben system much of their earlier rise from 20 km to 9 km depth presumably also occurred coeval with graben development although our data cannot determine this directly these relations demonstrate that the california forearc around mount diablo was in an extensional regime undergoing active sedimentation during major franciscan exhumation and thus support models for exhumation of franciscan blueschist facies rocks via synsubduction extensional processes rather than via erosional processes

precise u pb zircon ages from alderney channel islands growing evidence for discrete neoproterozoic magmatic episodes in northern cadomia the northernmost exposures of rocks formed during the late neoproterozoic cadomian orogeny in the channel islands northern france region occur on alderney the island mainly comprises foliated quartz diorite once considered to be 2 ga pre cadomian basement and an undeformed basic to intermediate plutonic complex a precise age of 610 2 ma based on u pb analyses of single and small groups of zircons for the foliated fort tourgis quartz diorite demonstrates that the oldest rocks were emplaced and deformed during a cadomian magmatic event the age is virtually identical to ages from similar foliated syntectonic quartz diorite bodies on the islands of guernsey and sark and at la hague north normandy indicating that this magmatic and deformational event was regional in extent discordant zircon xenocrysts define an upper intercept age of c 2 ga indicating the presence of palaeoproterozoic basement at depth single zircons from the undeformed bibette head granodiorite give a precise u pb age of 572 1 ma this age is closely similar to that for the emplacement of the northern igneous complex of guernsey the emerging data indicate that cadomian magmatism in the northern channel islands region was not a protracted continuum but occurred during two distinct short lived events separated by c 30 40 my

secular geochemical variations of the lower cretaceous siliciclastic rocks from central tibet china indicate a tectonic transition from continental collision to back arc rifting abstract fifty five lower cretaceous siliciclastic rocks from central tibet were analyzed for major and trace elements in an attempt to evaluate their provenance and the type of tectonic setting in which they were deposited the spatial temporal variation of both sediment maturity indices sio 2 al 2 o 3 la v and zr tio 2 the ratios of immobile trace elements cr th th sc th co la sc and la co and sio 2 k 2 o na 2 o eu eu gd yb n and ferromagnesian contents displays that the berriasian valanginian bv sediment could have been derived from northern orogenic source areas whereas the hauterivian lower barremian hb sediment could have been closely related to the syndepositional volcanism in the northern lhasa block itself the na 2 o al 2 o 3 k 2 o al 2 o 3 relations also place approximately half of hb samples in the field of volcanic rocks of back arc rifting origin whereas little volcanic clasts exist in the bv rocks there are distinct signatures that the mafic ultramafic materials in the bv rocks were derived from oceanic island basalts ophiolites in the bangong nujiang suture therefore the collisional orogen due to the qiangtang lhasa collision should have played a key role in supply of the sediments during bv time bimodal sedimentary basaltic and rhyolitic tuffs with respective distinguished geochemical features exist in the hb sequence therefore a distinct tectonic transition from continental collision to back arc rifting in central tibet is believed to have occurred during early cretaceous time extreme depletion of na of most lower cretaceous samples compared to the upper crust and their high average chemical index alteration cia values and th u ratios point out the source rocks formed in tropical climatic regions with little tectonic uplift although the weathering degree of the source rocks for hb samples could likely have been affected by the syndepositional volcanism during middle cretaceous time the entire southern eurasian margin could have been characterized by a series of back arc rift basins including those in kohistan and ladakh

cadomian tectonics in northern brittany a contribution of 3 d crustal scale modelling abstract both available and newly acquired geological and geophysical data processed in the framework of the armor project have been used to construct a 3 d geometric and geological model of the cadomian domain of northern brittany the major results of the data processing are presented and discussed relative to a composite profile transecting the studied domain and constructed from the surface geology reflection seismics magnetotelluric soundings and gravimetric data they are then extrapolated at regional scale through a series of cross sections compiled from the surface geology and gravimetric data and calibrated onto the composite profile the 3 d crustal scale models were computed according to two procedures the first using a strim matra datavision modeler defines various interfaces through correlation between adjacent cross sections and is well adapted to the 3 d representation of geological structures the second based on voronoi diagrams leads to a volumetric model of the geological units and is a powerful tool for calculating 3 d geophysical responses of the model when the physical properties of the rock units are known the tectonic implications of the computed 3 d crustal scale geometry of the cadomian domain are then discussed in terms of volcanic arc thrusting with special emphasis being placed on the obliquity of the shortening direction by reference to the thrust fault trend finally the data are used to demonstrate the reactivation of some cadomian faults during the deposition of ordovician sandstones and following the emplacement of the paleozoic dolerite dyke swarm of northern brittany

tectonic stages along a traverse cross cutting the rhodopian zone greece in a cross section along the rhodopian zone from the greece bulgarian border through the postalpine basins in the xanthi area to thasos island detailed structural mapping and collection of field data enable us to determine a sequence of tectonic stages that affected this area this allows us to propose a model of continental collision during the early eocene ne sw directed movements produced a southwest facing pile of crystalline nappes with internal deformation comprising nw and ne trending isoclinal folds and a ne sw trending stretching lineation after a short time interval nappe movements started again under brittle deformation conditions and produced composite thrust sheets wnw and nne trending chevron folds and thick cataclasite late erogenic uplift and extension caused the formation of nw and ne trending normal faults these faults bounded the oligocene flysch and molasse basins and provided pathways for voluminous magmatic suites this tectonic process was interrupted at the oligocene miocene boundary by a late orogenic compression reflected in nw open folds and dissolution cleavages subsequently differential uplift and subsidence associated with nw and ne trending normal faults has continued up to the present time from the early pliocene new fragmentation and thinning of the crust reflected in wnw listric faults and nne transfer faults has affected the southern parts of the rhodopian zone nappe forming movements are the result of a progressive collisional process involving a kimmerian microcontinent lying between the eurasia and apulia continents in the final stages of this collision uderplating processes led to regional uplift and extension additional extensional movements were related to the formation of the aegean back arc basin caused by the late cenozoic hellenic subduction zone

u pb geochronology and sm nd isotopic composition of proterozoic gneisses channel islands uk gneissic units of the channel islands united kingdom have traditionally been considered to be palaeoproterozoic basement to the late neoproterozoic cadomia terrane based on lithological correlations and imprecise or ambiguous isotopic data a new precise u pb date of 2061 2 ma based on analyses of single zircons for the icart granitic orthogneiss of guernsey confirms a palaeoproterozoic age of its igneous protolith the nd depleted mantle model age t dm of this gneiss is 2220 ma only slightly older than its crystallization age indicating that it represents juvenile crust other gneisses from guernsey have similar t dm ages ranging from 2210 to 2370 ma suggesting that they are also exposures of juvenile palaeoproterozoic crust a component from a penetratively deformed orthogneiss from sark previously correlated with icartian gneisses on guernsey yields a u pb zircon date of 616 4 2 ma this crystallization age demonstrates that the protolith was a cadomian intrusion and that penetrative deformation and amphibolite facies metamorphism in the northern channel islands were cadomian in age the use of gneissic features as a means of invoking the antiquity of many other undated gneissic units in the region is thus considered unreliable the presence of 2170 7 ma zircon xenocrysts within the sark orthogneiss combined with its initial e nd 615 9 5 are strong evidence that pre cadomian basement was a significant source component and that documenting the extent and age of pre cadomian basement may be possible by indirect geochemical methods

cretaceous to cenozoic sequential kinematics in the forearc arc transition effects of changing oblique plate convergence and the san andreas system with implications for the la paz fault southern baja california mexico we studied metasediments and mylonitic arc granitoids from the forearc arc transition of southern baja california mexico thin section analyses and field evidence show that metamorphism of the forearc arc transition is of the high t p active margin type the heat was provided by cretaceous arc intrusions field observations and thin section analyses including the time temperature deformation path demonstrate that the study area was first affected by dextral ductile shearing followed by ductile sinistral possibly transpressive strike slip parallel to the magmatic arc during the cretaceous both intervals are related to changing oblique plate convergence and thus identified as trench linked strike slip effects the geometric relationship between arc dipping foliation stretching lineation and shear sense indicates that the arc may have been pressed onto the rocks of the study area during sinistral shearing the sinistral interval lasted up until regional cooling early cenozoic because the la paz fault is closely associated with the forearc arc transition it must have the same cretaceous to early cenozoic kinematic history the northern segment of the la paz fault is a modern brittle strike slip fault interpreted as a dextral synthetic fault of the san andreas system which opened the gulf of california mar de cortes golfo de california we found no evidence for miocene basin and range extension

the cadomian active margin north armorican massif france a segment of the north atlantic panafrican belt abstract within the european variscan belt the armorican massif northwestern france contains an isolated fragment of the north atlantic panafrican belt the cadomian block mostly unaffected by variscan deformation this block is composed of neoproterozoic rocks ranging in age from 620 to 540 ma brioverian locally overlying a composite basement of icartian 2000 ma or pentevrian 750 ma age the cadomian tectonics the last magmatic manifestations of which are dated at around 540 ma were sealed by a cover of early cambrian rocks in normandy and early ordovician rocks in brittany five units are distinguished in this cadomian block tregor saint brieuc guingamp saint malo and fougeres although the units are bound by major faults the overall coherence of their different protolithic characteristics suggests that they can be fitted into a simple geodynamic model the tregor unit represented by the north tregor batholith of crustal affinity and its icartian host rock probably reflects an early cadomian evolution the saint brieuc unit essentially made up of magmatic rocks of juvenile affinity includes two assemblages juxtaposed by the cadomian tectonics 1 a volcanosedimentary succession formed in a typical island arc setting reflecting subduction around 610 ma and 2 a volcanic plutonic complex emplaced around 590 ma in an extensional active continental margin of pentevrian age the guingamp unit predominantly migmatitic includes a tectonic slice of deep origin the extrusion of which accompanied the exhumation of the migmatites it may represent the trace of a possible suture the saint malo unit is composed of brioverian detrital rocks the significance of which is uncertain passive continental margin or accretionary prism it is structured around a late migmatitic dome 540 ma the fougeres unit corresponds to the outer domain of the cadomian orogeny it was only weakly deformed by cadomian tectonics and is intruded by the large mancellian batholith of crustal origin dated at 540 ma together the structural units are interpreted in the framework of an evolving active margin juxtaposing continental margin marginal basin and volcanic arc before being shortened during the cadomian convergent tectonics

river dominated shelf edge deltas delivery of sand across the shelf break in the absence of slope incision shelf edge deltas record the potential magnitude of sediment delivery from shallow water shelf into deep water slope and basin floor and if un incised represent the main increment of shelf margin growth into the basin for that period the three dimensional complexity of shelf edge delta systems and along strike variability at the shelf edge in particular remains understudied the permian triassic kookfontein formation of the tanqua karoo basin south africa offers extensive three dimensional exposure 100 km2 and therefore a unique opportunity to evaluate shelf edge strata from an outcrop perspective analysis of stratal geometry and facies distribution from 52 measured and correlated stratigraphic sections show the following i in outer shelf areas parasequences are characterized by undeformed river dominated storm wave influenced delta mouth bar sandstones interbedded with packages showing evidence of syn depositional deformation the amount and intensity of soft sediment deformation increases significantly towards the shelf edge where slump units and debris flows sourced from collapsed mouth bar packages transport material down slope ii on the upper slope mouth bar and delta front sandstones pinch out within 2 km of the shelf break and most slump and debris flow units pinch out within 4 km of the shelf break iii further down the slope parasequences consist of finer grained turbidites characterized by interbedded thin tabular siltstones and sandstones the results highlight that river dominated shelf edge deltas transport large volumes of sand to the upper slope even when major shelf edge incisions are absent in this case transport to the upper slope through slumping debris flows and un channellized low density turbidites is distributed evenly along strike

late cretaceous blueschist facies metamorphism in southern thrace turkey and its geodynamic implications a blueschist facies tectonic sliver 9 km long and 1 km wide crops out within the miocene clastic rocks bounded by the strands of the north anatolian fault zone in southern thrace nw turkey two types of blueschist facies rock assemblages occur in the sliver i a serpentinite body with numerous dykes of incipient blueschist facies metadiabase ii a well foliated and thoroughly recrystallized rock assemblage consisting of blueschist marble and metachert both are partially enveloped by an upper eocene wildflysch which includes olistoliths of serpentinite metadiabase upper cretaceous and palaeogene pelagic limestone upper eocene reefal limestone radiolarian chert quartzite and minor greenschist field relations in combination with the bore core data suggest that the tectonic sliver forms a positive flower structure within the miocene clastic rocks in a transpressional strike slip setting and represents an uplifted part of the pre eocene basement the blueschists are represented by lawsonite glaucophane bearing assemblages equilibrated at 270 310 c and 0 8 gpa the metadiabase dykes in the serpentinite on the other hand are represented by pumpellyite glaucophane lawsonite assemblages that most probably equilibrated below 290 c and at 0 75 gpa one metadiabase olistolith in the upper eocene flysch sequence contains the mineral assemblage epidote pumpellyite glaucophane recording p t conditions of 290 350 c and 0 65 0 78 gpa indicative of slightly lower depths and different thermal setting timing of the blueschist facies metamorphism is constrained to c 86 ma coniacian santonian by rb sr phengite whole rock and incremental 40 ar 39 ar phengite dating on blueschists the activity of the strike slip fault post dates the blueschist facies metamorphism and exhumation and is only responsible for the present outcrop pattern and post miocene exhumation 2 km the high p t metamorphic rocks of southern thrace and the biga peninsula are located to the southeast of the circum rhodope belt and indicate late cretaceous subduction and accretion under the northern continent i e the rhodope massif enveloped by the circum rhodope belt the late cretaceous is therefore a time of continued accretionary growth of this continental domain