aftsolve a program for multi kinetic modeling of apatite fission track data aftsolve is a computer program for deriving thermal history information from apatite fission track data it implements a new fission track annealing model that takes into account the known kinetic variability among different apatite species to fully utilize this model a fission track worker must obtain data that can be used to infer the kinetic characteristics of each apatite grain from which a measurement was taken such data can consist of etch figure lengths or chemical composition the benefit of this overall approach is that it allows useful information to be derived from previously unusable analyses extends the practical range of geological temperatures constrained by fission track analyses and increases overall confidence in model predictions aftsolve also incorporates the effects of fission track orientation relative to the apatite crystallographic c axis variation in initial track length and the biasing effect of 2 5 2 cf irradiation for enhancing confined horizontal track length detection aftsolve is written for windows operating systems and has a graphical interface that allows interactive input of thermal histories and real time generation of estimates for fission track length distributions and ages for up to six simultaneously modeled kinetic populations it also includes procedures for estimating the range of time temperature histories that are statistically consistent with a data set and constraints entered by the user

role of tectonic sedimentary melange and permian triassic cover units central southern turkey in tethyan continental margin evolution abstract melanges play a key role in the interpretation of orogenic belts including those that have experienced deformation and metamorphism during continental collision this is exemplified by a palaeozoic tectonic sedimentary melange part of the konya complex that is exposed beneath a regionally metamorphosed carbonate platform near the city of konya in central anatolia the konya complex as a whole comprises three units a dismembered latest silurian early carboniferous carbonate platform a carboniferous melange made up of sedimentary and igneous blocks in a sedimentary matrix also known as the halici group or sizma group and an overlying volcanic sedimentary unit earliest permian the palaeozoic carbonates accumulated on a subsiding carbonate platform that bordered the northern margin of gondwana perhaps as an off margin unit the matrix of the melange was mainly deposited as turbidites debris flows and background terrigenous muds petrographic evidence shows that the clastic sediments were mostly derived from granitic and psammitic pelitic metamorphic rocks typical of upper continental crust both extension and contraction related origins of the melange can be considered however we interpret the melange as a carboniferous subduction complex that formed along the northern margin of gondwana related to partial closure of palaeotethys blocks and slices of upper palaeozoic radiolarian chert basic igneous rocks and shallow water carbonates were accreted and locally reworked by gravity processes large up to km sized blocks and slices of shallow water limestone were emplaced in response to collision of the palaeozoic carbonate platform with the subduction zone the overlying volcanic sedimentary unit earliest permian comprises alkaline lava flows interbedded with volcaniclastic debris flows and turbidites volcanogenic shales and tuff the complex as a whole is overlain by shallow water mixed carbonate siliciclastic sediments of mainly late permian age that accumulated on a regional scale shelf adjacent to gondwana successions pass transitionally into lower triassic rift related shallow water carbonates and terrigenous sandstones in the southwest of the area in contrast triassic sediments in the southeast overlie the melange unconformably and pass upwards from non marine clastic sediments into shallow marine calcareous sediments of mid triassic age marking the base of a regional mesozoic carbonate platform during the latest cretaceous early cenozoic the entire assemblage subducted northwards and underwent high pressure low temperature metamorphism and polyphase folding as a part of the regional anatolide unit

tectonic evolution of a part of the tethyside orogenic collage the kargi massif northern turkey the central part of the rhodope pontide fragment one of the major tectonic units in turkey provides critical data for evaluating the cimmeride and alpide evolution of the mediterranean tethysides tectonic events that affected the central part of the rhodope pontide fragment since the end of the paleozoic generated east west trending belts with the event of every episode redeforming and partly obliterating the structures of previous episodes this evolution may be conveniently described in terms of three major episodes 1 two different realms of pre dogger oceanic rocks are present in the area the northern realm coincided with main branch of paleo tethys that was being actively destroyed by south dipping subduction the southern realm the karakaya ocean a back arc basin related to this subduction began opening by rifting of a retroarc carbonate platform during the permo triassic to the west a continental domain with sparse magmatism seperated the two oceanic areas toward the east the two oceans become united by the wedging out of the continental domain these two pre dogger oceans closed during the lias and their remnants were emplaced between the southern margin of laurasia and the fragments of the cimmerian continent 2 the second episode partly overlapped the first with rifting south of the cimmerian continent fragment during the lias this rifting was followed by a transgression which covered the ruins of the cimmeride orogenic belt by the malm this rifting concurrently led to the development of the northern branch of the neo tethys and a south facing atlantic type continental margin a southerly thickening sedimentary prism developed on this margin during the lias to early cretaceous interval 3 the floor of the northern branch of neo tethys began to be consumed along the north dipping subduction zone beneath the previosly constructed continental margin this convergent margin generated a magmatic arc to the north and to the south a subduction accretion complex present width of which approaches 80 km to the south of the subduction accretion complex yet another convergent margin is indicated by the presence of the remnants of an ensimatic arc the northern branch of the neo tethys was totally consumed in the late cretaceous to eocene interval

an interannual link between arctic sea ice cover and the north atlantic oscillation this work investigates links between arctic surface variability and the phases of the winter djf north atlantic oscillation nao on interannual time scales the analysis is based on era reanalysis and model data from the ec earth global climate model our study emphasizes a mode of sea ice cover variability that leads the nao index by 1 year the mechanism of this leading is based on persistent surface forcing by quasi stationary meridional thermal gradients associated thermal winds lead a slow adjustment of the pressure in the following winter which in turn feeds back on the propagation of sea ice anomalies the pattern of the sea ice mode leading nao has positive anomalies over key areas of south davis strait labrador sea the barents sea and the laptev ohkostsk seas associated to a high pressure anomaly over the canadian archipelago baffin bay and the laptev east siberian seas these anomalies create a quasi annular quasi steady positive gradient of sea ice anomalies about coastal line when leading the positive nao phase and force a cyclonic vorticity anomaly over the arctic in the following winter during recent decades in spite of slight shifts in the modes spectral properties the same leading mechanism remains valid encouraging actual models appear to reproduce the same mechanism leading model s nao relative to model areas of persistent surface forcing this indicates that the link between sea ice and nao could be exploited as a potential skill source for multi year prediction by addressing the key problem of initializing the phase of the nao ao arctic oscillation

macroevolutionary history of the planktic foraminifera planktic foraminifera are an abundant component of deep sea sediment and are critical to geohistorical research primarily because as a biological and geochemical system they are sensitive to coupled bio hydro lithosphere interactions they are also well sampled and studied throughout their evolutionary history here we combine a synoptic global compilation of planktic foraminifera with a stochastic null model of taxonomic turnover to identify statistically significant increases in macroevolutionary rates there are three taxonomic diversifications and two distinct extinctions in the history of the group the well known cretaceous paleogene extinction is of unprecedented magnitude and abruptness and is linked to rapid environmental perturbations associated with bolide impact the eocene oligocene boundary extinction occurs due to a combination of factors related to a major reorganization of the global climate system changes in ocean stratification seawater chemistry and global climate recur as primary

evolution of shallow crustal thermal structure from subduction to collision an example from taiwan we study crustal thermal evolution by examining heat flow patterns along a convergent boundary from a young subduction zone to a more structurally mature collision zone more than 8000 km of seismic profiles covering an offshore region of 45 000 km 2 in southern taiwan show widespread bottom simulating reflectors bsrs we derived 1107 bsr based heat flows before combining 42 additional published offshore thermal probe data and 86 on land heat flow data to document the shallow forearc thermal structures from the subduction zone to the collision zone in the subduction zone the geothermal gradient ranges mostly within 30 80 c km and decreases toward the arc due to slab cooling intensive dewatering at the toe sediment blanketing topographic effects and other processes the geothermal gradient ranges mostly from 30 to 90 c km in the collision zone and increases instead of decreases toward the arc possibly caused by exhumation erosion topographically induced ground water circulation and some upper mantle processes related to collision heat flow in the collision zone ranges from 80 to 250 mw m 2 the high heat flow in the collision zone correlates with a shallower seismicity zone and high seismic attenuation while the lower heat flow in the subduction zone might allow the earthquakes to rupture to greater depth the heat flow increases along the topographic high from subduction to collision zone due to increasing geothermal gradients and higher thermal conductivities of the exhumed basement rocks this heat flow variation may generate an artificial exhumation rate pattern if a conventional 30 c km geothermal gradient was used in fission track studies

code numbers for cenozoic low latitude radiolarian biostratigraphic zones and gpts conversion tables abstract code numbers for the radiolarian zonation for the tropical pacific indian and atlantic oceans rp1 rp22 for the paleogene and rn1 rn17 for the neogene are standardized and introduced thirty nine zones are recognized from the lower paleocene to the holocene revision of previously separate upper neogene zonations for the pacific and indian oceans in which the same zonal names were applied to different stratigraphic intervals resulted in a single tropical zonation we change four upper neogene indian ocean zones to subzones and refer to them simply by their code numbers rn12b pterocanium prismatium rn12a anthocyrtidium jenghisi rn11b stichocorys peregrina rn11a phormostichoartus fistula we introduce the name lychnodictyum audax interval zone rn11 for the interval stratigraphically equivalent to the combined stichocorys peregrina and phormostichoartus fistula zones in the indian ocean and to the anthocyrtidium jenghisi zone in the pacific ocean two paleocene zones bekoma bidartensis rp7 and b campechensis rp6 and two subzones stylotrochus nitidus pterocodon poculum rp6c and orbula discipulus rp6b are emended each zone is formally defined and we include a stratigraphically ordered list of radiolarian events falling within each zone mean numerical ages for zonal boundary events were culled from previous literature and converted to the geomagnetic polarity time scale gpts references to the original description and concept herein applied of all included taxa and tables which allow for accurate conversion in simple increments between the different published gptss are included in this paper

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

tectono magmatic evolution of the west philippine mariana region and the origin of boninites re examination of published data on the tectomagmatic evolution of the west philippine mariana region indicate that arc magmatism and back arc extensional pulses are not synchronous but are largely asynchronous arc volcanism ceases within a few million years of the development of a back arc basin and recommences oceanward on a new arc during the final stages in the development of the back arc basin following karig s model we believe that ascent beneath the arc axial chain of a line of diapirs of morb source mantle interferes with processes of arc magma generation and arc magmatism wanes partial melting of the diapirs produces voluminous morb type tholeiites which split the arc and form the crust of a widening back arc basin we show for both the west philippine mariana region and occurrences of boninite like lavas in ophiolites that boninites appear to be erupted after arc magmatism and immediately before eruption of morb type lavas passage of a diapir of hot morb source mantle through refractory sub arc peridotite which has been enriched in lile and h2o will result in limited partial melting of the hydrous peridotite and the restricted production of boninitic magmas these are more likely to erupt modified or only slightly modified by crystal fractionation through the thin forearc crust continued ascent of the morb source mantle diapir will result in it partially melting to yield morb tholeiites which erupt shortly after and in considerably more voluminous amounts than the boninites finally we suggest that forearcs regions are likely to be incorporated into foldbelts and that boninite or low ti lava bearing ophiolites may characterize such regions

the arkot dag melange in arac area central turkey evidence of its origin within the geodynamic evolution of the intra pontide suture zone abstract in northern turkey the intra pontide suture zone is represented by an east west trending belt of deformed and or metamorphic units located at the boundary between the istanbul zonguldak terrane to the north and the sakarya terrane to the south these units can be regarded as issued from the intra pontide domain whose geodynamic history is still a matter of debate along the akpinar arac bayramoren geotraverse located in central turkey an ophiolite bearing melange known as the arkot dag melange is well exposed along the intra pontide suture zone the arkot dag melange plays a key role in the interpretation of the geodynamic history of the intra pontide domain and can be described as a late santonian chaotic sedimentary deposit consisting of an up to 1000 m thick succession of slide blocks of different sizes and lithologies enclosed in a sedimentary matrix consisting of shales coarse grained arenites pebbly mudstones and pebbly sandstones the slide blocks from a few meters to hectometers in size are represented by metamorphic rocks mainly micaschists and gneisses by ophiolites peridotites gabbros iat and babb basalts and cherts and by sedimentary rocks cherts neritic and pelagic limestone marly limestone and ophiolite bearing turbidites the youngest age among the slide blocks has been provided by the ophiolite bearing turbidites where a late coniacian nannofossil assemblage has been found the cherts have provided a wide range of ages from the middle triassic to late cretaceous whereas the fossils found in the limestone indicate late jurassic to early cretaceous ages the matrix of the arkot dag melange even if unaffected by metamorphism shows deformations represented by multiple meters thick cataclastic shear zones at the boundaries of the melange slices or inside of them according to its features the source area of the arkot dag melange was most likely a continental and oceanic thrust sheet emplaced in the late cretaceous onto a continental margin the data collected from the different slide blocks suggest that the intra pontide domain was characterised by an oceanic basin opened at the latest in the early jurassic the opening of the intra pontide oceanic basin was followed by the development of a subduction zone with a subsequent opening of suprasubduction oceanic basin in the middle jurassic early cretaceous the convergence in this suprasubduction oceanic basin started at the early late cretaceous boundary by an obduction process whereas its final closure can be regarded as late paleocene in age

radiolarian stratigraphy across the oligocene miocene transition abstract recently the international union of geological sciences commission on stratigraphy working group on the paleogene neogene boundary proposed that the oligocene miocene boundary be placed at the base of chron c6cn2n at 23 8 ma on the cande and kent 1992 magnetic time scale where it is approximated by planktic foraminifera at the first occurrence of globorotalia kugleri and by calcareous nannofossils at the last occurrence of sphenolithus ciperoensis and the first and last occurrences of sphenolithus delphix and s capricornutus herein we show that in terms of radiolarians the base of chron c6cn2n can be correlated with the upper part of the lychnocanoma elongata zone between the last occurrence of artophormis gracilis 23 94 ma and the first occurrence of cyrtocapsella tetrapera 23 69 ma since the proposed stratotype at lemme carrosio italy does not contain radiolarians at the boundary we re examined 13 dsdp sites and established the stratigraphic sequence of 29 first and last radiolarian occurrences and one evolutionary transition across the boundary nine of these sites contain both calcareous and siliceous microfossils and thus allow for an integrated biostratigraphy paleomagnetic stratigraphy is not available for any of the dsdp cores examined however use of hodell and woodruff s 1994 strontium isotope curve from dsdp site 289 has permitted calibration of several low latitude microfossil datum levels against the geomagnetic polarity scale two new species lychnocanoma apodora and eucyrtidium plesiodiaphanes are described

magma supply in back arc spreading centre segment e2 east scotia ridge segment e2 is situated in the back arc east scotia ridge the segment is unusual in that it has an axial topographic high underlain by a seismically imaged melt lens the axis of the segment which is 70 km long was sampled at 2 km spacing there is strong correlation between compositions and bathymetry and there is no evidence that lateral flow of magmas along dykes within the segment was more than 25 km magmas are more evolved towards the summit indicating that magma fractionation took place within the imaged melt lens na8 0 is roughly constant at 2 6 implying uniform degree of partial melting except for some samples at the summit that have na8 0 2 2 compositions closest to n morb occur at the segment tips and lree hree ratios increase toward the summit none of the magmas were derived from depleted sub arc mantle nevertheless most compositions in the segment were modified by slab derived components the low na8 0 samples have high ba nb compared with the rest of the segment dredged lavas from the lateral flanks of the summit have the most extreme compositions including ones derived from plume mantle and are end members for magma mixing processes that controlled compositions

an oligocene multi species foraminiferal oxygen and carbon isotope record from odp hole 758a indian ocean paleoceanographic and paleo ecologic implications abstract an oligocene basal miocene zones p19 p22 n4 oxygen and carbon isotope stratigraphy is presented based on mixed benthic foraminiferal faunas and different species of planktic foraminifers from eastern indian ocean odp hole 758a lack of covariance in planktic and benthic 18 o ratios indicates that many oligocene sea level fluctuations including the major fall at 30 ma are not of glacio eustatic origin 18 o values suggest that test morphology is a poor indicator of preferred depth habitat of oligocene planktic foraminifers also some groups show considerable shifts in preferred depth habitat reconstructed surface water temperature was nearly constant during the investigated period but even assuming a large antarctic icecap values are unrealistically low 18 20 c most likely water masses with markedly different oxygen isotopic composition existed this poses great problems for quantitative temperature reconstructions planktic foraminiferal species show similar 13 c ratios indicating well mixed surface waters this contrasts with the strong oxygen isotopic gradient which suggests well stratified surface waters during the oligocene the difference in 13 c ratio between the average ratio of planktic foraminiferal species and the benthic foraminifers 13 c p b shows an inverse relation with the known circulation intensity record and thus with productivity this 13 c pattern is interpreted as being caused by the presence of younger bottom waters at this site during periods with lower temperatures and or larger antarctic ice sheets

latest oligocene through early middle miocene diatom biostratigraphy of the eastern tropical pacific abstract study of dsdp sites 71 77 and 495 has allowed the development of a refined diatom biostratigraphy for the latest oligocene through early middle miocene of the eastern tropical pacific which is well correlated to the low latitude zonations for planktonic foraminifers coccoliths and radiolarians six zones and 7 subzones are proposed and correlation with high latitude diatoms zonations for the north pacific the norwegian sea and the southern ocean is suggested by the discovery of selected diatoms in these tropical sediments which were previously thought to be restricted to high latitudes six new species and one new variety of diatoms which are stratigraphically useful are proposed actinocyclus hajosiae n sp a radionovae n sp coscinodiscus blysmos n sp c praenodulifer n sp craspedodiscus rydei n sp thalassiosira bukryi n sp and coscinodiscus lewisianus var robustus n var

analysis of the north anatolian shear zone in central pontides northern turkey insight for geometries and kinematics of deformation structures in a transpressional zone abstract the western part of the north anatolian shear zone at the southern boundary of the central pontides in turkey was investigated in the kursunlu arac area by means of a geological structural field study in this area the north anatolian shear zone results in a transpressional deformation zone that extends between two master faults striking parallel to the main shear direction the main systems of structures identified in the deformation zone appear to be oriented parallel to the directions predicted by riedel theoretical model nevertheless the strain partitioning is more complicated than predicted by theory the structural analysis suggests a polyphase deformation characterized by a steady component of transcurrence associated with alternance of compression and extension along each of theoretical directions the combination of double verging structures can be observed with folds and thrust surfaces root into high angle shear zones according to flower type geometries the discrepancies of directions kinematics and geometries from theoretical models are due to transpressive and or transtensive nature of the deformation according to the observed outcropping structures we propose a conceptual model for the north anatolian shear zone interpreting it as a crustal scale positive flower structure

miocene biochronology and paleoceanography of the north pacific abstract biostratigraphic correlation based on microfossil datum levels directly or indirectly tied to the paleomagnetic time scale provides a high resolution time control for the miocene in the equatorial and middle latitude north pacific faunal changes and abundance fluctuations of planktic foraminiferal species combined with the oxygen pacific faunal changes and abundance fluctuations of planktic foraminiferal species combined with the oxygen isotope record of foraminifers reveal the paleoclimatic and paleoceanographic history the planktic foraminiferal assemblage change in the early miocene extinction of oligocene fauna and rise of a highly diverse neogene fauna appears to be related to increased water mass stratification in the world oceans presumably resulting from the establishment of circum antarctic circulation an increase in the siliceous productivity in the eastern equatorial pacific region between 20 and 18 ma suggests that the vertical and horizontal circulation was intensified at that time climates cooled rapidly during the middle miocene between 14 and 13 ma suggesting the growth of a major east antarctic ice sheet paleoclimatic conditions remained generally cool although oscillating during the late miocene in the late early to middle miocene faunal provincialism developed between low and middle latitudes and by late miocene time a distinct provincialism similar to the present was established

criteria for identifying structures related to true crustal extension in orogens faults and shear zones in orogens may be related to crustal shortening or extension or both true extensional structures should ultimately intersect the earth s surface when traced out in a direction opposite to that of hangingwall transport the present dip of a fault in an orogen and its relation to local layering are unreliable guides the observation of low pressure metamorphic rocks structurally above high pressure metamorphic rocks is not sufficient to diagnose crustal extension a valid metamorphic criterion is the difference in pressure time histories between footwall and hangingwall if the footwall was decompressing faster than the hangingwall during shear zone movement then the shear zone was truly extending the crust the pressure time history can be constrained via the temperature time and pressure temperature histories ideally crustal extension inferred from structural data should be confirmed using diagnostic ptt information

kinematic linkage between internal zone extension and shortening in more external units in the nw alps in the alps a major extensional shear zone unroofed eclogites in its footwall from 30 kbar to c 10 kbar implying of the order of 60 km of relative vertical movement in the period 45 36 ma the horizontal component of divergence was of the order of 100 km we use the foreland basin sedimentary record to prove that the extension was contemporaneous with thrusting in units structurally beneath the eclogites the brianconnais and or external zones this thrust related convergence during that time period was of the order of 44 56 km and therefore of the same order of magnitude as internal zone divergence extension may have been driven by internal density contrasts buoyant continental crust underneath the mafic eclogites or dense subducted slab offset from the orogen can induce extension any dynamic model must account for the comparable magnitudes of extension and shortening in adjacent parts of the orogen relative plate motions in the period 45 36 ma played a subsidiary role

late oligocene to early miocene geochronology and paleoceanography from the subantarctic south atlantic mi2 as well as several other distinctive isotope events our data suggest that the d 18 o maximum commonly associated with the oligocene miocene o m boundary falls within c6cn 2r 23 86 ma the d 13 c maximum coincides within the temporal resolution of our record with c6cn 2n r boundary and hence to the o m boundary comparison of the stable isotope record from site 1090 to the orbitally tuned stable isotope record from odp site 929 across the o m boundary shows that variability in the two records is very similar and can be correlated at and below the o m boundary site 1090 stable isotope records also provide the first deep southern ocean end member for reconstructions of circulation patterns and late oligocene to early miocene climate change comparison to previously published records suggests that basin to basin carbon isotope gradients were small or nonexistent and are inconclusive with respect to the direction of deep water flow oxygen isotope gradients between sites suggest that the deep southern ocean was cold in comparison to the north atlantic indian and the pacific oceans dominance of cold southern component deep water at site 1090 at least until 17 ma suggests that relatively cold circumpolar climatic conditions prevailed during the late oligocene and early miocene we believe that a relatively cold southern ocean reflects unrestricted circumpolar flow through the drake passage in agreement with bathymetric reconstructions index terms 4267 oceanography general paleoceanography 1035 geochemistry geochronology 4870 oceanography biological and chemical stable isotopes keywords paleoceanography 1035 geochronology stable isotopes

subduction and exhumation related structures in the cycladic blueschists insights from south evia island aegean region greece 1 detailed geological mapping structural investigation and amphibole chemistry analyses in southern evia aegean sea greece allow us to place new constraints on the internal structural architecture and tectonic evolution of the cycladic blueschists we show that the early deformation history was related to ese directed thrusting resulting in the stacking of the styra and ochi nappes which constitute the cycladic blueschist unit in evia these early thrust movements initiated just before and proceeded at peak conditions of the eocene high pressure metamorphism subsequent constrictional deformation gave rise to e w trending upright folding accomplished at the early exhumation stage the main ductile stage exhumation occurred during a single deformation phase associated with the decompression of blueschist rocks from the stability field of crossite to that of actinolite this phase was characterized by localization of ductile deformation into a series of major tens of meters thick ene directed shear zones which cut up section in their transport direction and restack the early thrust and fold sequence locally bringing the structurally lower styra nappe over the higher ochi nappe it is suggested that these zones operated as thrusts rather than normal sense shear zones as has been previously argued and were possibly formed during the oligocene ene ward extrusion of the blueschists brittle ductile ne dipping normal faulting of post early miocene age was probably responsible for the final exhumation of rocks

reconstruction of oceanic circulation patterns in the tropical pacific across the early middle miocene boundary as inferred from radiolarian assemblages abstract although there have been attempts to infer neogene oceanic circulation patterns in the tropical pacific on the basis of multiple marine proxies oceanic circulation patterns across the early middle miocene boundary are still poorly understood despite paleoclimate having significantly changed during this interval in this study we reconstruct the changes in tropical oceanic circulation patterns in the pacific across the early middle miocene boundary based on radiolarian assemblages obtained at integrated ocean drilling program site u1335 in the eastern tropical pacific the radiolarian upwelling taxa increased during four intervals 18 4 18 1 ma 16 9 15 7 ma 15 2 14 6 ma 14 2 13 4 ma radiolarian temperature index rti was calculated using the relative abundances of the warm water cluster b1 and cool water taxa cluster b2 in order to evaluate relative temperature fluctuations of the surface water the sea surface temperature index was relatively high from 16 8 to 16 0 ma and gradually decreased from 16 0 to 14 6 ma subsequently the temperature index decreased stepwise at 13 9 and 13 4 ma and became relatively low from 13 4 to 12 7 ma comparison of the rti record in the eastern tropical pacific to the climatic index based on the benthic foraminiferal 18o record shows that variability in the two records follows a roughly similar trend from the early to the middle miocene however the sea surface temperature record does not indicate a sharp increase in warmth in the eastern tropical pacific during the mid miocene climatic optimum 1 mmco 1 as suggested by the benthic isotopic record this is likely because of increased upwelling of cool nutrient rich water at this time beginning in the latest early miocene 17 ma radiolarian assemblages were dominated by different taxa in the eastern and western tropical pacific this pattern is interpreted as indicating a shallower thermocline in the east and a deeper thermocline in the west based on the relative abundance of the upwelling taxa there is an overall increasing trend in this difference since the latest early miocene we tie these events to the effective closure of the indo pacific seaway and the development of a substantial western pacific warm pool along with the development of a strong equatorial undercurrent

radiolarian faunal turnover across the oligocene miocene boundary in the equatorial pacific ocean abstract the global warming trend of the latest oligocene was interrupted by several cooling events associated with antarctic glaciations these cooling events affected surface water productivity and plankton assemblages well preserved radiolarians were obtained from upper oligocene to lower miocene sediments at ocean drilling program odp leg 199 sites 1218 and 1219 in the equatorial pacific and 110 radiolarian species were identified four episodes of significant radiolarian faunal changes were identified middle late oligocene 27 5 to 27 3 ma latest oligocene 24 4 ma earliest miocene 23 3 ma and middle early miocene 21 6 ma these four episodes approximately coincide with increases and decreases of biogenic silica accumulation rates and increases in 18o values coded as oi and mi events these data indicate that antarctic glaciations were associated with change of siliceous sedimentation patterns and faunal changes in the equatorial pacific radiolarian fauna was divided into three assemblages based on variations in radiolarian productivity species richness and the composition of dominant species a late oligocene assemblage 27 6 to 24 4 ma a transitional assemblage 24 4 to 23 3 ma and an early miocene assemblage 23 3 to 21 2 ma the late oligocene assemblage is characterized by relatively high productivity low species richness and four dominant species of tholospyris anthophora stichocorys subligata lophocyrtis nomas and lithelius spp the transitional assemblage represents relatively low values of productivity and species richness and consists of three dominant species of t anthophora s subligata and l nomas the characteristics of the early miocene assemblage are relatively low productivity but high species richness the two dominant species present in this assemblage are t anthophora and cyrtocapsella tetrapera the most significant faunal turnover of radiolarians is marked at the boundary between the transitional early miocene assemblages we also reviewed changes in other microfossil assemblages in the low latitudes during the late oligocene through early miocene the microfossil assemblages of major groups show sequential changes near the oligocene miocene o m boundary 23 8 ma many extinction events and some first occurrences of calcareous nannofossils and many occurrences of radiolarians are found from about 24 8 to 23 3 ma and first occurrences of planktic foraminifers and diatoms followed from 23 2 through 22 ma hence the o m boundary is identified as a significant level for microfossil evolutions

orbitally paced climate oscillations across the oligocene miocene boundary the late oligocene and early miocene periods some 21 to 27 million years ago have generally been viewed as times of moderate global warmth and ice free conditions yet several lines of evidence suggest that this interval was punctuated by at least one and possibly several episodes of high latitude cooling and continental glaciation1 2 3 here we present stable isotope and per cent coarse fraction data from an equatorial western atlantic deep sea sediment core that provide high resolution records of the climate variability across the oligocene miocene transition 22 5 25 7 million years ago a strong 40 kyr periodicity in the oxygen isotope record is consistent with a high latitude orbital obliquity control on ice volume and temperature orbital influences are also apparent at precession and eccentricity frequencies including a series of 400 kyr oscillations that culminate in distinct maxima at the oligocene miocene boundary about 23 7 million years ago covariance between the carbon and oxygen isotope records suggests that the oceanic carbon cycle may have contributed to global cooling during the 400 kyr cycles particularly at the oligocene miocene boundary

multiple exhumation phases in the central pontides n turkey new temporal constraints on major geodynamic changes associated with the closure of the neo tethys ocean

petrology and 40ar 39ar dating of paragneisses from the devrekani massif central pontides northern turkey implications for the jurassic high t metamorphism in an extensional tectonic environment abstract the devrekani massif in the northern part of the central pontides northern turkey provides important clues to the regional tectonics and geodynamic processes associated with jurassic high grade metamorphic conditions this study reports new paragenetic assemblages mineral compositions whole rock geochemistry and 40ar 39ar geochronological data from the paragneisses in the massif and discusses the p t conditions and geodynamic implications of the jurassic metamorphism during continental extension in the central pontides upper amphibolite to lower granulite facies paragneisses form one of the main lithological units in the massif within these there are five different mineral parageneses with diagnostic mineral assemblages of quartz k feldspar an0 1ab4 26or73 96 plagioclase an18 35 biotite xphl 0 28 0 57 mg mg fe2 0 33 0 61 sillimanite cordierite mg mg fe2 0 48 0 71 and garnet alm43 80grs0 18prp5 23and0 4sps10 33 with minor hercynite based on na in crd thermometry and gasp barometry results the peak metamorphic conditions are 775 25 c and 6 1 kbar in the massif the field relations petrography and bulk chemical data suggest that the paragneisses derived from shale wackestone and pelitic sedimentary protoliths are typical rock lithologies of an active continental margin they display enrichments in lile over hfse coupled with negative nb and ti anomalies which are geochemical signatures of subduction related sources it is likely that the peak metamorphism took place during the middle upper jurassic period ca 174 156 ma suggesting that the metamorphic rocks cooled to 300 350 c at ca 156 ma the mineral assemblages reveal that the prograde history passed from sillimanite zone conditions up to the cordierite garnet k feldspar zone the petrological and geochronological data indicate that the protoliths are related to multiple sources such as volcano sedimentary successions we conclude that the devrekani massif represents the products of pre jurassic sedimentation and permo carboniferous continental arc magmatism overprinted by jurassic metamorphism

formation of recumbent folds during synorogenic crustal extension austroalpine nappes switzerland in sedimentary rocks of the austroalpine nappes in eastern switzerland several generations of alpine cretaceous tertiary folds can be distinguished by overprinting relations the second generation d 2 probably late cretaceous in age includes spectacular kilometre scale folds refolding the earlier formed nappe pile d 2 folds are interpreted here as resulting from east southeast directed crustal extension rather than as previously assumed from north south crustal shortening for the following reasons 1 d 2 folds are restricted to a predominantly ductile layer underlying the brittlely extended orogenic lid and 2 d 2 folds are associated with structures indicating extension in a direction parallel to the extension direction of the brittle layer before the east southeast extension started the layering of the rocks was already steeply inclined owing to earlier d 1 folding the deformation producing the second phase folds probably had a noncoaxial component with a top to the east southeast shear sense and a component of coaxial deformation leading to shortening in the vertical direction and stretching in an east southeast horizontal direction the folds developed with axes oblique to parallel to the direction of bulk stretching i suggest that folding of initially nonhorizontal layers by ductile crustal extension is an important deformation mechanism in the austroalpine and possibly also in other parts of the alps initially steep orientations of layers resulted from transpressive deformation in the obliquely convergent alpine belt and crustal extension parallel to the chain resulted from gravitational spreading i propose that this process can lead to the often encountered phenomenon of stretching parallel to the axes of folds

early and middle eocene radiolarian assemblages in the eastern equatorial pacific ocean iodp leg 320 site u1331 faunal changes and implications for paleoceanography abstract quantitative faunal analyses of radiolarians were used to reconstruct paleoceanographic conditions spanning the interval from zones rp8 early eocene to rp16 middle eocene in pelagic sequences recovered at integrated ocean drilling program iodp site u1331 in the eastern equatorial pacific ocean on the basis of relative abundance data from the low to high latitudes reported in the previous literature paleoceanographic indices were identified 1 species indicative of warmer conditions include stylosphaera coronata coronata phormocyrtis embolum dendrospyris didiceros phormocyrtis cf proxima and thyrsocyrtis triacantha 2 species indicative of cooler conditions include the lophocyrtis aspera group the lithocyclia ocellus group hexacontium sp a hexacontium sp b thecosphaerella glebulenta and lithelius sp a two warming and at least six cooling events in the early to middle eocene were identified from radiolarian assemblage variations the paleoclimatic trends can be summarized as follows warming in c23n 2n to c21r 51 5 49 0 ma and c18n 40 2 39 0 ma cooling in c21r 48 5 47 8 ma lower c20r 46 2 45 2 ma top c20r to c20n 44 0 43 0 ma top c20n to c19r 43 0 41 7 ma c19n to c18r 41 7 40 2 ma and c18n 1n 39 0 38 5 ma these cooling events corresponded to the eli and bli events which were identified in benthic foraminiferal 18 o of the southern ocean in general radiolarian and opal mass accumulation rates mars in the eastern equatorial pacific had higher values in cooling conditions during the middle eocene the changes in biological productivity in the eastern equatorial pacific were associated with cooling of tropical surface water the change in relative abundance of radiolarians and caco 3 content at site u1331 indicated that middle eocene carbonate events carbonate accumulation events caes lyle et al 2005 coincided with the cooling events of tropical surface water at least cae 2 and cae 3 were associated with high biological productivity as well as cooling

petrology and geochemistry of post collisional middle eocene volcanic units in north central turkey evidence for magma generation by slab breakoff following the closure of the northern neotethys ocean the eocene volcano sedimentary units of northern anatolia are confined into a narrow zone trending parallel to the intra pontide and izmir ankara erzincan sutures along which the northern branch of the neotethys ocean was closed during a period between late maastrichtian and paleocene the middle eocene formations overlie both the imbricated and highly deformed units of the suture zone which are paleocene or older in age as well as the formations of adjacent continental blocks with a regional disconformity therefore they can be regarded to be post collisional these units are composed of subaerial to shallow marine sedimentary beds i e the orencik formation at the base and a subaerial volcanic unit i e the hamamozu formation in the middle and at the top this sudden facies change from marine to subaerial environment in the middle eocene is a common phenomenon across northern turkey implying that a regional uplift event occurred possibly across the suture zone before the initiation of the volcanism during lutetian the middle eocene lavas span the whole compositional range from basalts to rhyolites and display a calc alkaline character except for alkaline to mildly alkaline lavas from the top of the sequence all lavas display a distinct subduction signature our geochemical data indicate that calc alkaline lavas were derived from a subduction modified source whereas alkaline to mildly alkaline lavas of the late stage were possibly sourced by an enriched mantle domain magmas evolved in magma chambers emplaced possibly at two different crustal levels magmas in deeper 13 km and possibly larger chambers fractionated hydrous mafic minerals e g amphibole and biotite two pyroxenes and plagioclase and assimilated a significant amount of crustal material intermediate to acid calc alkaline lavas and pyroclastics were derived from these chambers magmas in the shallower chambers on the other hand 12 km crystallized anhydrous mineral assemblages assimilated little or no crustal material and fed basic to intermediate lavas in the region both deep and shallow chambers were periodically replenished by mafic magmas we argue that a slab breakoff model explains better than any alternative model i why the volcanism during the middle eocene was confined into a rather narrow belt along the suture zone ii why it initiated almost contemporaneous with a regional uplift after the continental collision event iii why it postdated arc volcanism along the pontides in the north by 15 20 my iv why it assimilated significant amount of crustal material and v why alkalinity of lavas increased in time

burial and exhumation history of the daday unit central pontides turkey implications for the closure of the intra pontide oceanic basin in northern turkey the intra pontide suture zone represents one of the first order tectonic structures located between the istanbul zonguldak and the sakarya continental terranes it consists of an e w trending assemblage of deformed and variably metamorphosed tectonic units including sedimentary rocks and ophiolites derived from a neo tethyan oceanic basin known as the intra pontide oceanic basin one of these units is represented by the daday unit that consists of a block in matrix assemblage derived from supra subduction oceanic crust and related deep sea sedimentary cover of middle jurassic age this setting was acquired during late jurassic time by tectonic underplating at a depth of 35 42 km associated with blueschist facies metamorphism d1 phase the following d2 d3 and d4 phases produced the exhumation of the daday unit up to shallower structural levels in a time span running from the albian to late paleocene the high geothermal gradient detected during the d2 phase indicates that the daday unit was exhumed during a continent arc collisional setting the tectonic structures of the intra pontide suture zone resulting from the previously described tectonic history are unconformably sealed by the upper paleocene eocene deposits this tectonic setting was intensely reworked by the activity of the north anatolian fault zone producing the present day geometrical relationships of the intra pontide suture zone of the central pontides

blueschist facies metamorphism of peralkaline rhyolites from the tenda crystalline massif northern corsica evidence for involvement in the alpine subduction event the tenda crystalline massif northern corsica is a fragment of the western corsica basement involved in the alpine orogeny rhyolite dykes crosscutting the gabbroic complex of bocca di tenda southern sector of the tenda crystalline massif show an unusual metamorphic mineral assemblage defined by jadeite bearing up to 46 mol percentage aegirine riebeckite celadonite rich phengite si 3 50 3 65 apfu quartz albite and k feldspar jadeite bearing aegirine and riebeckite mostly occur as coronas around jadeite free aegirine and arfvedsonite respectively which both are relics of igneous origin this metamorphic assemblage reflects the peralkaline compositions which are characterised by anomalously high contents of sio2 and na2o and negligible cao and mgo the evolved rocks of the gabbroic sequence quartz diorites to tonalites and the surrounding granitoids are characterised by the development of riebeckite ferroglaucophane epidote celadonite rich phengite and albite thus pointing to a metamorphic crystallization in the epidote blueschist facies in all the studied rocks metamorphic reactions were controlled by fluid assisted mass transfer through grain boundaries and microfractures the different mineral assemblages allow the peak p t metamorphic conditions to be constrained to between 0 8 gpa 300 c and 1 1 gpa 500 c these estimates attest to a geothermal gradient dt dp of 10 13 c km 1 and indicate that the tenda crystalline massif was buried to a minimum depth of 27 km during the alpine orogeny the blueschist facies recrystallization in the tenda crystalline massif has been related to the cessation of an eastward dipping subduction event

paleoceanographic implications of miocene deep sea hiatuses miocene paleoceanographic evolution exhibits major changes resulting from the opening and closing of passages the subsequent changes in oceanic circulation and development of major antarctic glaciation the consequences and timing of these events can be observed in variations in the distribution of deep sea hiatuses sedimentation patterns and biogeographic distribution of planktic organisms the opening of the drake passage in the latest oligocene to early miocene 25 20 ma resulted in the establishment of the deep circumpolar current which led to thermal isolation of antarctica and increased global cooling this development was associated with a major turnover in planktic organisms resulting in the evolution of neogene assemblages and the eventual extinction of paleogene assemblages the erosive patterns of two widespread hiatuses ph 23 0 22 5 ma and nh 1 20 18 ma indicate that a deep circumequatorial circulation existed at this time characterized by a broad band of carbonate ooze deposition siliceous sedimentation was restricted to the north atlantic and a narrow band around antarctica a major reorganization in deep sea sedimentation and hiatus distribution patterns occurred near the early middle miocene boundary apparently resulting from changes in oceanic circulation beginning at this time deep sea erosion occurred throughout the caribbean hiatus nh 2 16 15 ma suggesting disruption of the deep circumequatorial circulation and northward deflection of deep currents and or intensification of the gulf stream sediment distribution patterns changed dramatically with the sudden appearance of siliceous ooze deposition in the marginal and east equatorial north pacific by 16 0 to 15 5 ma coincident with the decline of siliceous sedimentation in the north atlantic this silica switch may have been caused by the introduction of norwegian overflow water into the north atlantic acting as a barrier to outcropping of silica rich antarctic bottom water the main aspects of the present oceanic circulation system and sediment distribution pattern were established by 13 5 to 12 5 ma hiatus nh 3 coincident with the establishment of a major east antarctic ice cap antarctic glaciation resulted in a broadening belt of siliceous ooze deposition around antarctica increased siliceous sedimentation in the marginal and east equatorial north pacific and indian oceans and further northward restriction of siliceous sediments in the north atlantic periodic cool climatic events were accompanied by lower eustatic sea levels and widespread deep sea erosion at 12 to 11 ma nh 4 10 to 9 ma nh 5 7 5 to 6 2 ma nh 6 and 5 2 to 4 7 ma nh 7

late cretaceous infant intra oceanic arc volcanism the central pontides turkey petrogenetic and tectonic implications abstract a tectonic slice of an arc sequence consisting of low grade metavolcanic rocks and overlying metasedimentary succession is exposed in the central pontides north of the izmir ankara erzincan suture separating laurasia from gondwana derived terranes the metavolcanic rocks mainly consist of basaltic andesite andesite and mafic cognate xenolith bearing rhyolite with their pyroclastic equivalents which are interbedded with recrystallized pelagic limestone and chert the metasedimentary succession comprises recrystallized micritic limestone with rare volcanogenic metaclastic rocks and stratigraphically overlies the metavolcanic rocks the geochemistry of the metavolcanic rocks indicates an arc setting evidenced by depletion of hfse ti p and nb and enrichment of fluid mobile lile identical trace and rare earth elements compositions of basaltic andesites andesites and rhyolites suggest that they are cogenetic and derived from a common parental magma the arc sequence crops out between an albian turonian subduction accretionary complex representing the laurasian active margin and an ophiolitic melange absence of continent derived detritus in the arc sequence and its tectonic setting in a wide cretaceous accretionary complex suggest that the kosdag arc was intra oceanic zircons from two metarhyolite samples give late cretaceous 93 8 1 9 and 94 4 1 9 ma u pb ages these ages are the same as the age of the supra subduction ophiolites in western turkey which implies that that the kosdag arc may represent part of the incipient arc formed during the generation of the supra subduction ophiolites the low grade regional metamorphism in the kosdag arc is constrained to 69 9 0 4 ma by 40 ar 39 ar muscovite dating indicating that the arc sequence became part of a wide tethyan cretaceous accretionary complex by the latest cretaceous non collisional cessation of the arc volcanism is possibly associated with southward migration of the magmatism as in the izu bonin mariana arc system

kinematic reworking and exhumation within the convergent alpine orogen abstract kinematic data from the internal zones of the western alps indicate both top to se and top to nw shearing during synkinematic greenschist facies recrystallisation rb sr data from white micas from different kinematic domains record a range of ages that does not represent closure through a single thermal event but reflects the variable timing of synkinematic mica recrystallisation at temperatures between 300 and 450 c the data indicate an initial phase of accretion and foreland directed thrusting at ca 60 ma followed by almost complete reworking of thrust related deformation by se directed shearing this deformation is localised within oceanic units of the combin zone and the base of the overlying austroalpine basement and forms a regional scale shear zone that can be traced for almost 50 km perpendicular to strike the timing of deformation in this shear zone spans 9 ma from 45 to 36 ma the se directed shear leads to local structures that cut upwards in the transport direction with respect to tectonic stratigraphy and such structures have been interpreted in the past as backthrusts in response to ongoing alpine convergence however on a regional scale the top to se deformation is related to crustal extension not shortening and is coincident with exhumation of eclogites in its footwall during this extension phase deformation within the shear zone migrated both spatially and temporally giving rise to domains of older shear zone fabrics intercalated with zones of localised reworking top nw kinematics preserved within the combin zone show a range of ages the oldest 48 ma may reflect the final stages of emplacement of austroalpine units above piemonte oceanic rocks prior to the onset of extension however much of the top to nw deformation took place over the period of extension and may reflect either continuing or episodic convergence or tectonic thinning of the shear zone 40ar 39ar data from the region are complicated due to the widespread occurrence of excess 40ar in eclogite facies micas and partial ar loss during alpine heating reliable ages from both eclogite and greenschist facies micas indicate cooling ages in different tectonic units of between 32 and 40 ma these ages are slightly younger than rb sr deformation ages and suggest that cooling below ca 350 c occurred after juxtaposition of the units by se directed extensional deformation our data indicate a complex kinematic history involving both crustal shortening and extension within the internal zones of the alpine orogen to constrain the palaeogeographic and geodynamic evolution of the alps requires that these data be integrated with data from the more external zones of the orogen complexity such as that described is unlikely to be restricted to the western alps and spatially and temporally variable kinematic data are probably the norm in convergent orogens recognising such features is fundamental to the correct tectonic interpretation of both modern and ancient orogens

early mesozoic subduction in the eastern mediterranean evidence from triassic eclogite in northwest turkey an eclogite forms a 40 m long tectonic lens enveloped in serpentinite within a metabasite phyllite marble unit of permian triassic age in northwest turkey the eclogite consists mainly of garnet omphacite glaucophane and epidote it is associated with other lenses of serpentinite and metagabbro single grain laser probe 40ar 39ar dating of phengites from the eclogite gives ages of 203 to 208 ma corresponding to the triassic jurassic boundary regional geologic considerations also suggest a latest triassic to earliest jurassic metamorphic age for the eclogite and the enclosing metabasite marble phyllite unit the eclogite along with serpentinite and gabbro lenses were probably emplaced as diapirs into the metabasite phyllite marble unit during late triassic subduction the eclogite provides evidence for the often elusive triassic subduction history of the paleo tethys in the eastern mediterranean area

late jurassic amphibolite facies metamorphism in the intra pontide suture zone turkey an eastward extension of the vardar ocean from the balkans into anatolia the palaeogeography of neotethys during its closure is still a matter of debate this study provides new insights into the neotethys closure by the discovery in the intra pontide suture zone turkey of an accretionary complex that recorded a late jurassic c 163 ma amphibolite facies metamorphism results are discussed in the framework of the accretionary events that occurred at the southern margin of laurasia the resulting picture supports a new model in which the vardar suture zone in the balkans and the intra pontide suture zone in anatolia represent remnants of the same elongate oceanic basin supplementary material analytical procedures representative mineral compositions geothermobarometric estimates step heating and in situ 40 ar 39 ar data and backscattered electron photomicrographs showing the distribution of laser spot ages on rock chips are available at www geolsoc org uk sup18759

tectonic evolution of the intra pontide suture zone in the armutlu peninsula nw turkey abstract the armutlu peninsula and adjacent areas in nw turkey play a critical role in tectonic reconstructions of the southern margin of eurasia in nw turkey this region includes an inferred intra pontide oceanic basin that rifted from eurasia in early mesozoic time and closed by late cretaceous time the armutlu peninsula is divisible into two metamorphic units the first the armutlu metamorphics comprises a precambrian high grade metamorphic basement unconformably overlain by a palaeozoic low grade mixed siliciclastic carbonate volcanogenic succession including bimodal volcanics of inferred extensional origin with a possibly inherited subduction signature the second unit the low grade iznik metamorphics is interpreted as a triassic rift infilled with terrigenous calcareous and volcanogenic lithologies including basalts of within plate type the triassic rift was unconformably overlain by a subsiding jurassic late cretaceous cenomanian passive margin including siliciclastic carbonate turbidites radiolarian cherts and manganese deposits the margin later collapsed to form a flexural foredeep associated with the emplacement of ophiolitic rocks in turonian time geochemical evidence from meta basalt blocks within ophiolite derived melange suggests a supra subduction zone origin for the ophiolite the above major tectonic units of the armutlu peninsula were sealed by a maastrichtian unconformity comparative evidence comes from the separate almacik flake further east considering alternatives it is concluded that a mesozoic intra pontide oceanic basin separated eurasia from a sakarya microcontinent with a wider northern neotethys to the south lateral displacement of exotic terranes along the south eurasian continental margin probably also played a role e g during late cretaceous suturing in addition to overthrusting

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

thermal modeling of continental subduction and exhumation constrained by heat flow and seismicity in taiwan abstract the thermal evolution of crustal exhumation subsequent to the subduction of the continental margin is modeled through numerical solutions to the two dimensional heat conduction equation the boundary conditions used in the modeling are basically constrained by available geophysical and geological observations in the taiwan area temperature distributions are calculated at one million year intervals over a 5 ma duration although this study presents a tentative estimation based on some reasonable assumptions the preliminary results not only explain the sharp change in seismicity within the crust but also agree with the general heat flow pattern on the surface of taiwan more specifically both the high heat flow and the aseismic belt beneath the eastern central range which are probably attributed to higher temperatures within the crust are modeled by crustal exhumation after the subduction of the continental margin however the occurrence of deeper earthquakes east of the central range is a result of the lower thermal gradient which is due to the subduction of the cold continental crust into the uppermost mantle in summary preliminary thermal modeling supports the possibility of a tectonic model of active continental subduction and crustal exhumation for the taiwan orogen

whole rock geochemistry zircon u pb and hf isotope systematics of the cangaldag pluton evidences for middle jurassic continental arc magmatism in the central pontides turkey abstract the central pontides turkey includes several igneous complexes which are predominantly permo carboniferous and middle jurassic in age the cangaldag pluton is one of the largest igneous bodies located in the northern central pontides whose age and tectono magmatic evaluation is important to constrain the geological evolution of the northern neotethys the pluton tectonically overlies the cangaldag metamorphic complex which represents an arc back arc complex of middle jurassic age the cangaldag pluton consists mainly of non metamorphic gabbroic diorite dacite porphyry and lesser amount of granitic rocks geochemically the various rock types are akin to volcanic arc magmas displaying th nb and light rare earth element heavy rare earth element enrichments in situ u pb age results of zircons from dacite porphyry and granite samples yield ages of 161 5 ma and 170 2 ma respectively corresponding in situ average 176hf 177hf initial ratios are 0 28287 0 00004 and 0 28213 0 00002 for the dacite porphyry and granite samples respectively these results are consistent with derivation from a subduction modified mantle source based on hf isotope compositions tdm model ages vary between 624 and 1512 ma and suggest that the arc magmatism associated with the cangaldag pluton may have involved partial melting of neoproterozoic mesoproterozoic crustal rocks a common feature in gondwana derived terranes the geochemical hf isotope and geochronological data reported here confirm the presence of a continental arc system during the middle jurassic in the central pontides and suggests that the cangaldag pluton formed during northward subduction of the intra pontide branch of the northern neotethys

miocene evolution of atmospheric carbon dioxide changes in pco2 or ocean circulation are generally invoked to explain warm early miocene climates and a rapid east antarctic ice sheet eais expansion in the middle miocene this study reconstructs late oligocene to late miocene pco2 from ep values based on carbon isotopic analyses of diunsaturated alkenones and planktonic foraminifera from deep sea drilling project sites 588 and 608 and ocean drilling program site 730 our results indicate that highest pco2 occurred during the latest oligocene 350 ppmv but decreased rapidly at 25 ma the early and middle miocene was characterized by low pco2 260 190 ppmv lower intervals of pco2 correspond to inferred organic carbon burial events and glacial episodes with the lowest concentrations occurring during the middle miocene there is no evidence for either high pco2 during the late early miocene climatic optimum or a sharp pco2 decrease associated with eais growth paradoxically pco2 increased following eais growth and obtained preindustrial levels by 10 ma although we emphasize an oceanographic control on miocene climate low pco2 could have primed the climate system to respond sensitively to changes in heat and vapor transport

channel flow ductile extrusion and exhumation in continental collision zones this collection of 27 review and research papers provides an overview of the geodynamic concepts of channel flow and ductile extrusion in continental collision zones the focal point for this volume is the proposal that the middle or lower crust acts as a ductile partially molten channel flowing out from beneath areas of over thickened crust such as the tibetan plateau towards the topographic surface at plateau margins this controversial proposal explains many features related to the geodynamic evolution of the plateau and for example extrusion and exhumation of the crystalline core of the himalayan mountain chain to the south in this volume thermal mechanical models for channel flow extrusion and exhumation are presented and geological and geophysical evidence both for and against the applicability of such models to the himalayan tibetan plateau system as well as older continental collision zones such as the hellenides the appalachians and the canadian cordillera are discussed