silicic acid dynamics in the glacial sub antarctic implications for the silicic acid leakage hypothesis 1 the silicic acid leakage hypothesis salh purports that changes in silicon and nitrogen depletion ratios in the glacial antarctic created a large pool of unused silicic acid that was transported to lower latitudes in subantarctic mode water samw where it enhanced diatom productivity lowering atmospheric pco2 however increased opal accumulation beneath the sub antarctic during glacial times implies significant consumption of silicic acid in subantarctic surface waters that may have significantly diminished or eliminated si leakage to test how nutrient dynamics in the sub antarctic affected the si oh 4 content of samw during the last glacial period we produced 30si opal records for cores from the subantarctic and subtropical zones of the indian ocean spanning the last 50 000 years comparison with diatom bound 15n records shows that subantarctic surface waters were enriched in si relative to n during the last glaciation consistent with the salh the record from the subtropics does not show this enrichment in si during the last glacial period suggesting that subantarctic surface waters were mainly incorporated into samw rather than being transported across the subtropical front isotope mass balance calculations were used to test for si leakage from the sub antarctic the results show that silicic acid concentration in samw would more than double during the last glaciation if upwelling and northward ekman drift in the antarctic were similar to the present day circulation calculations that assume increased stratification in the glacial antarctic eliminate si leakage but they do not produce the known increase in opal burial in the glacial sub antarctic reconciling the isotope data and opal burial records with a highly stratified antarctic requires the addition of a large local source of silicic acid in the glacial sub antarctic that is inconsistent with present day circulation and nutrient distributions including such a source in our calculations results in significant opal burial in the sub antarctic but it does not enhance si leakage over that occurring in the holocene resolving past changes in the circulation of the southern ocean is clearly vital to future tests of the salh

a corollary to the silicic acid leakage hypothesis 1 the silicic acid leakage hypothesis salh attempts to explain part of the large and regular atmospheric co2 changes over the last glacial interglacial cycles it calls for a reduction in the carbonate pump through a growth in diatoms at the expense of coccolithophorids in low latitude surface waters driven by a leakage of high si n waters from the southern ocean recent studies that present low opal accumulation rates from the glacial eastern equatorial pacific have challenged salh in a corollary to salh we argue that the key to salh is the dominance of diatoms over coccolithophorids and this does not depend on the magnitude of diatom production per se in support of our claim we show in a numerical model that atmospheric co2 can be lowered with even a reduced absolute flux of silicic acid leakage provided that si n in the leakage is elevated and that the excess si can be used by diatoms to shift the floral composition in their favor

post collisional tertiary quaternary mafic alkalic magmatism in the carpathian pannonian region a review mafic alkalic volcanism was widespread in the carpathian pannonian region cpr between 11 and 0 2 ma it followed the miocene continental collision of the alcapa and tisia blocks with the european plate as subduction related calc alkaline magmatism was waning several groups of mafic alkalic rocks from different regions within the cpr have been distinguished on the basis of ages and or trace element compositions their trace element and sr nd pb isotope systematics are consistent with derivation from complex mantle source regions which included both depleted asthenosphere and metasomatized lithosphere the mixing of dmm himu emii mantle components within asthenosphere derived magmas indicates variable contamination of the shallow asthenosphere and or thermal boundary layer of the lithosphere by a himu like component prior to and following the introduction of subduction components various mantle sources have been identified lower lithospheric mantle modified by several ancient asthenospheric enrichments source a young asthenospheric plumes with oib like trace element signatures that are either isotopically enriched source b or variably depleted source c old upper asthenosphere heterogeneously contaminated by dm himuemii emi components and slightly influenced by miocene subduction related enrichment source d old upper asthenosphere heterogeneously contaminated by dm himu emii components and significantly influenced by miocene subduction related enrichment source e melt generation was initiated either by i finger like young asthenospheric plumes rising to and heating up the base of the lithosphere below the alcapa block or ii decompressional melting of old asthenosphere upwelling to replace any lower lithosphere or heating and melting former subducted slabs the tisia block d 2004 published by elsevier b v

relevance of silicon isotopes to si nutrient utilization and si source assessment in antarctic waters 1 we analyzed 29si of dissolved silicate for eight water column profiles across the southern ocean south of australia in spring 2001 from the seasonal ice zone siz north to the subantarctic zone saz including the first isotopic compositions measured for si depleted seawaters all profiles display mixed layer enrichments in heavy si isotopes relative to deep water in accordance with preferential uptake of the light isotope by diatoms as silicate levels decrease from the siz northward across the polar front zone pfz to the saz surface and mesopelagic 29si signatures generally become progressively heavier but the most si depleted saz waters do not exhibit 29si values heavier than in the pfz this intricacy appears to derive from variations in the vertical and horizontal supply of silicate to surface waters and by applying a steady state open system model we estimate a fractionation factor 29 between diatoms and seawater of 0 45 0 17 independently of zones and phytoplankton community though encouraging these results are related to latitudinal changes in mesopelagic 29si values complexity in surface silicate 29si correlations and differences from previous studies which underline the need for caution in the use of silicon isotopes in paleoceanographic studies until systematic efforts have been undertaken to better understand modern variations

diatom bound 15n 14n new support for enhanced nutrient consumption in the ice age subantarctic 1 diatom bound 15n 14n was used to reconstruct the glacial nutrient status of the subantarctic zone in the southern ocean down core records from both the pacific and indian sectors show 15n of 5 to 6 during the last glacial maximum and a decrease coincident with the glacial termination to values as low as 2 the effect of either diatom assemblage or physiological change on the diatom bound 15n 14n is unknown and cannot yet be ruled out as a possible explanation for the observed change however the consistency between indian and pacific sector records and with other paleoceanographic data suggests that the glacial interglacial difference in diatom bound 15n 14n was driven by higher consumption of nitrate in the subantarctic surface during the last ice age such a change in nutrient consumption may have resulted from atmospheric iron fertilization and or decreased glacial mixed layer depths associated with sea ice melting enhanced nutrient consumption in the glacial subantarctic would have worked to lower the concentration of co2 in the ice age atmosphere it also would have reduced the preformed nutrient content of the low latitude thermocline leading to decreases in low latitude productivity suboxia and denitrification

southern ocean control of silicon stable isotope distribution in the deep atlantic ocean the fractionation of silicon si stable isotopes by biological activity in the surface ocean makes the stable isotope composition of silicon delta si 30 dissolved in seawater a sensitive tracer of the oceanic biogeochemical si cycle we present a high precision dataset that characterizes the delta si 30 distribution in the deep atlantic ocean from denmark strait to drake passage documenting strong meridional and smaller but resolvable vertical delta si 30 gradients we show that these gradients are related to the two sources of deep and bottom waters in the atlantic ocean waters of north atlantic and nordic origin carry a high delta 30 sisignature of 1 7 parts per thousand into the deep atlantic while antarctic bottom water transports si with a low delta si 30 value of around 1 2 parts per thousand the deep atlantic delta si 30 distribution is thus governed by the quasi conservative mixing of si from these two isotopically distinct sources this disparity in si isotope composition between the north atlantic and southern ocean is in marked contrast to the homogeneity of the stable nitrogen isotope composition of deep ocean nitrate delta n 15 no3 we infer that the meridional delta si 30 gradient derives from the transport of the high delta si 30 signature of southern ocean intermediate mode waters into the north atlantic by the upper return path of the meridional overturning circulation moc the basin scale deep atlantic delta si 30 gradient thus owes its existence to the interaction of the physical circulation with biological nutrient uptake at high southern latitudes which fractionates si isotopes between the abyssal and intermediate mode waters formed in the southern ocean

early cretaceous potassic volcanic rocks in the jiangnan orogenic belt east china crustal melting in response to subduction of the pacific izanagi ridge abstract eastern china is characterized by widespread mesozoic magmatism that was closely related to subduction of the paleo pacific plate but the genetic relationship between magmatism and subduction is not always clear the jiangnan orogenic belt job is a neoproterozoic collisional belt between the yangtze and cathaysian blocks early cretaceous felsic magmas from the tianmushan basin in the eastern job form a 3000 m thick volcanic sequence erupted within an extremely short period of time 132 130 ma these rocks are potassic k2o 3 86 6 05 and peraluminous a cnk 1 0 1 23 and are compositionally similar to experimental melts derived from predominantly clay poor and k rich metasediments or granodiorites at crustal conditions they are lile and lree enriched la yb cn 9 0 14 6 and display variable eu anomalies and nb ta depletion the weakly variable and negative whole rock end t 5 4 to 2 5 and heterogeneous zircon ehf t values 6 7 to 3 5 of these rocks are similar to those of basement rocks beneath the job suggesting a genetic relationship with basement no magmas with clear subduction related composition occurred at this time in the area and the compositions of the potassic rocks more closely resemble high temperature melts of extensively thinned crust in continental rift environments our data favors a model that the early cretaceous potassic magmas formed as subduction of the pacific izanagi ridge resulted in upwelling asthenosphere providing the high temperatures required to extensively melt the lower middle crust in the eastern job

northern timing of deglaciation in the eastern equatorial pacific from alkenone paleothermometry 1 the equatorial cold tongue ect of the eastern pacific is the most dynamic ocean region in the world s tropics and sets the tempo for global climate anomalies arising from el nino southern oscillation enso events this region s deglaciation history and relationship with north and south polar climates remains poorly understood impeding integration of tropical pacific ocean atmosphere dynamics and enso variability in our understanding of glacial cycles here we present alkenone reconstructions of sea surface temperature sst across the last glacial termination from five ect cores east of the galapagos islands a composite index of sst based on these demonstrates strong temporal affinity with the two step deglaciation of the northern hemisphere composed of two distinct warming steps at the beginning of the bolling and the end of the younger dryas intervals within dating uncertainty warming in the ect began in phase with the bolling excursion was followed by a 2 3 ka plateau and resumed with a second pulse at the end of the younger dryas on the basis of our reconstructions about two thirds of the warming materialized at or after the end of the younger dryas implying a marked delay in the region s response to deglaciation the results challenge the prevailing paradigm that ect deglacial history conforms to an antarctic timing commonly attributed to advection from the southern ocean through an interior oceanic link or to synchronous response of both regions to co2 forcing our results emphasize instead the role of dynamical adjustments linked to northern hemisphere processes most likely transmitted through the atmosphere

potassium rich magmatism in the western outer carpathians magmagenesis in the transitional zone between the european plate and carpathian pannonian region abstract miocene igneous rocks of the western outer carpathians in poland and moravia czech republic were emplaced in a tectonic setting transitional between the european foreland and the carpathian pannonian arc system they form medium to high k calc alkaline suites which are compositionally different to each other and to other calc alkaline sequences in the region geographically and compositionally the moravia rocks can be seen as transitional between the rift related alkaline magmatism of the foreland and the dominantly calc alkaline magmatism of the carpathian pannonian region certain moravia rocks are unusually enriched in incompatible trace elements e g nb 122 ppm and th 31 ppm the primary magmas of both suites were formed in metasomatised lithosphere mantle of the european plate but the enrichment mechanism differed in poland it was by ancient subduction related events whereas in moravia metasomatism was mainly by melts and or fluids from deeper mantle sources partial melting was promoted by impingement of rising asthenosphere on the base of the lithosphere possibly related to reactivation of trans lithospheric nw se trending fault zones

geometry and kinematics of adhesive wear in brittle strike slip fault zones abstract detailed outcrop surface mapping in late paleozoic cataclastic strike slip faults of coastal maine shows that asymmetric sidewall ripouts 0 1 200 m in length are a significant component of many mapped faults and an important wall rock deformation mechanism during faulting the geometry of these structures ranges from simple lenses to elongate slabs cut out of the sidewalls of strike slip faults by a lateral jump of the active zone of slip during adhesion along a section of the main fault the new irregular trace of the active fault after this jump creates an indenting asperity that is forced to plow through the adjoining wall rock during continued adhesion or be cut off by renewed motion along the main section of the fault ripout translation during adhesion sets up the structural asymmetry with trailing extensional and leading contractional ends to the ripout block the inactive section of the main fault trace at the trailing end can develop a sag or half graben type geometry due to block movement along the scallop shaped connecting ramp to the flanking ripout fault leading contractional ramps can develop thrust type imbrication and forces the humpback geometry to the ripout slab due to distortion of the inactive main fault surface by ripout translation similar asymmetric ripout geometries are recognized in many other major crustal scale strike slip fault zones worldwide ripout structures in the 5 500 km length range can be found on the atacama fault system of northern chile the qujiang and xiaojiang fault zones in western china the yalakom hozameen fault zone in british columbia and the san andreas fault system in southern california for active crustal scale faults the surface expression of ripout translation includes a coupled system of extensional trailing ramps as normal oblique slip faults with pull apart basin sedimentation and contractional leading ramps as oblique thrust or high angle reverse faults with associated uplift and erosion the sidewall ripout model as a mechanism for adhesive wear during fault zone deformation can be useful in studies of fault zone geometry kinematics and evolution from outcrop to crustal scales

geochemistry and tectonic development of cenozoic magmatism in the carpathian pannonian region this review considers the magmatic processes in the carpathian pannonian region cpr from early miocene to recent times as well as the contemporaneous magmatism at its southern boundary in the dinaride and balkans regions this geodynamic system was controlled by the cretaceous to neogene subduction and collision of africa with eurasia especially by adria that generated the alps to the north the dinaride hellenide belt to the east and caused extrusion collision and inversion tectonics in the cpr this long lived subduction system supplied the mantle lithosphere with various subduction components the cpr contains magmatic rocks of highly diverse compositions calc alkaline k alkalic ultrapotassic and na alkalic all generated in response to complex post collisional tectonic processes these processes formed extensional basins in response to an interplay of compression and extension within two microplates alcapa and tisza dacia competition between the different tectonic processes at both local and regional scales caused variations in the associated magmatism mainly as a result of extension and differences in the rheological properties and composition of the lithosphere extension led to disintegration of the microplates that finally developed into two basin systems the pannonian and transylvanian basins the southern border of the cpr is edged by the adria microplate via sava and vardar zones that acted as regional transcurrent tectonic areas during miocene recent times major trace element and isotopic data of post early miocene magmatic rocks from the cpr suggest that subduction components were preserved in the lithospheric mantle after the cretaceous miocene subduction and were reactivated especially by extensional tectonic processes that allowed uprise of the asthenosphere changes in the composition of the mantle through time support geodynamic scenarios of post collision and extension processes linked to the evolution of the main blocks and their boundary relations weak lithospheric blocks i e alcapa and western tisza generated the pannonian basin and the adjacent styrian transdanubian and z rand basins which show high rates of vertical movement accompanied by a range of magmatic compositions strong lithospheric blocks i e dacia were only marginally deformed where strike slip faulting was associated with magmatism and extension at the boundary of adria and tisza dacia strike slip tectonics and core complex extension were associated with small volume miocene magmatism in narrow extensional sedimentary basins or granitoids in core complex detachment systems along older suture zones sava and vardar accommodating the extension in the pannonian basin and afterward pliocene quaternary inversion magmas of various compositions appear to have acted as lubricants in a range of tectonic processes

flexural expression of european continental lithosphere under the western outer carpathians we present the results of an analysis of the flexural down bending of the european lithosphere under the western outer carpathians for a grid of five profiles with a lateral spacing of about 100 km crossing the carpathians and its foreland seismic sections including two deep seismic reflection lines and numerous wells allowed us to quantify the flexural curvature of the lithosphere in addition gravity data are used to obtain independent constraints two evolutionary scenarios involving subduction underthrusting of passive margin and a phase change in the lower crust are investigated in a context of relatively flat moho under the area furthermore recent uplift expressing itself in erosional features observed along the distal margin of the foredeep is quantified the generally modest bouguer gravity anomaly points to nonisostatic processes causing this uplift steeply dipping basement under the carpathians to about 10 km depth at the location of the pieniny klippen belt is explained by relatively weak lithosphere which is expressed in the predicted low values of effective elastic thickness of 16 km decreasing locally to 3 km the low strength of the european lithosphere in this region is probably caused by mechanical weakening controlled by partial yielding due to high flexural curvature the weakest parts of the lithosphere along the profiles corresponding to low effective elastic thicknesses are concentrated in the areas of maximum bending predicted flexural bending stresses as a function of bending moment and effective elastic thickness increase dramatically under the outer zone of the carpathian belt explaining reactivations of older basement structures in these regions

evidence of silicic acid leakage to the tropical atlantic via antarctic intermediate water during marine isotope stage 4 antarctic intermediate water aaiw and subantarctic mode water samw are the main conduits for the supply of dissolved silicon silicic acid from the deep southern ocean to the low latitude surface ocean and therefore have an important control on low latitude diatom productivity enhanced supply of silicic acid by aaiw and samw during glacial periods may have enabled tropical diatoms to outcompete carbonate producing phytoplankton decreasing the relative export of inorganic to organic carbon to the deep ocean and lowering atmospheric pco2 this mechanism is known as the silicic acid leakage hypothesis salh here we present records of neodymium and silicon isotopes from the western tropical atlantic that provide the first direct evidence of increased silicic acid leakage from the southern ocean to the tropical atlantic within aaiw during glacial marine isotope stage mis 4 60 70 ka this leakage was approximately coeval with enhanced diatom export in the nw atlantic and across the eastern equatorial atlantic and provides support for the salh as a contributor to co2 drawdown during full glacial development

diatom productivity in the equatorial pacific ocean from the last glacial period to the present a test of the silicic acid leakage hypothesis 1 the silicic acid leakage hypothesis salh suggests that during glacial periods unused silicic acid escaped the southern ocean into the equatorial oceans causing an ecological shift favoring diatoms relative to coccolithophorids and a drawdown of co2 the 230th normalized opal fluxes and 231pa 230th ratios were measured in eleven equatorial pacific cores to reconstruct diatom productivity over the past 30 kyr and to test the salh holocene spatial patterns of opal flux are strongly correlated with 231pa 230th ratios and with satellite estimates of primary productivity down core opal flux records do not support the salh but show holocene opal burial to exceed that of the late glacial period by 35 or 2 8 gt opal kyr across the equatorial pacific this suggests that the salh may not account for lower atmospheric co2 levels during the late glacial however the data do support results from previous studies that invoke increased el nino like conditions during this time

neogene quaternary magmatism and geodynamics in the carpathian pannonian region a synthesis in the carpathian pannonian region in neogene times westward dipping subduction in a land locked basin caused collision of two lithospheric blocks alcapa and tisia with the southeastern border of the european plate calc alkaline and alkaline magmatism was closely related to subduction rollback collision and extension from the spatial distribution of the magmatic activity four segments can be defined western segment magmatism occurring on the alcapa block central segment magmatism occurring on both alcapa and the tisia blocks south eastern segment and interior segment both on the tisia block most calc alkaline magmatism in the region resulted from melting of a heterogeneous asthenospheric mantle source modified by addition of fluids and sediment assimilation and fractionation processes at shallow crustal levels occurred in most of the segments strongly masking the deeper source processes long term subduction rollback and or delamination led to contamination of the asthenosphere beneath the western segment here large volume partial melts of the contaminated mantle caused underplating and crustal anatexis leading to mixing of mantle derived calc alkaline magmas with crustal melts in the central segment calc alkaline magmas were formed by subduction and rollback followed by back arc extension and slab breakoff avariable mantle source is indicated in the back arc setting and larger amount of fluid induced metasomatism source enrichment and assimilation nearer to the trench in the interior segment evolution from typical calc alkaline magmas to adakite like ones was related to extension due to fast rotations and transtensional tectonics here calc alkaline magmas formed by decompression melting of a heterogeneous crust mantle lithosphere while adakite like melts resulted from fliud dominated melting of the lithosphere along the south eastern segment slab breakoff was responsible for the generation of typical calcalkaline magmas but in the extreme south of the segment shallow level tearing of the slab followed breakoff strike slip tectonics allowed the rise of hot asthenosphere and generation of adakite like magmas via slab melting along the torn edge of the east european plate alkalic basaltic volcanism with an oib like asthenosphere source followed the calc alkaline stage

submillennial to millennial variability of diatom production off mauritania nw africa during the last glacial cycle 1 the low latitude upwelling regime off the mauritanian coast in the subtropical ne atlantic accounts for a significant part of global export production although productivity variations in coastal upwelling areas are usually attributed to changes in wind stress and upwelling intensity productivity dynamics off mauritania are less straightforward because of the complex atmospheric and hydrographic setting here we integrate micropaleontological diatoms and geochemical bulk biogenic sediment components x ray fluorescence and alkenones proxies to examine on submillennial to millennial changes in diatom production that occurred off mauritania nw africa for the last 25 ka during the last glacial maximum lgm 19 0 23 0 ka b p moderate silicate content of upwelled waters coupled with weakened ne trade winds determined moderate diatom productivity no significant cooling is observed during the lgm suggesting that our alkenone based sst reconstruction represents a local upwelling related signal rather than a global insolation related one extraordinary increases in diatom and opal concentrations during heinrich event 1 h1 15 5 18 0 ka b p and the younger dryas yd 13 5 11 5 ka b p are attributed to enhanced upwelling of silica rich waters and an enlarged upwelling filament due to more intense ne trade winds the synchronous increase of caco3 and k intensity and the decreased opal and diatoms values mark the occurrence of the bolling allerod ba 13 5 15 5 ka b p due to weakened eolian input and more humid conditions on land although the high export of diatoms is inextricably linked to upwelling intensity off mauritania variability in the nutrient content of the thermocline also plays a decisive role

natural variations of δ30si ratios during progressive basalt weathering hawaiian islands abstract silicon stable isotopes can be used to trace the biogeochemical pathways of si as it moves from its continental sources to its sink in ocean sediments along the way si is incorporated into clay minerals taken up by plants where it forms plant opal and leached into rivers the major land to ocean conduit compared to igneous rocks the waters that drain continents are enriched in heavy si isotopes but the mechanisms that control fractionation have not been elucidated we studied si isotope fractionation along a 4 million yr basaltic soil chronosequence on the hawaiian islands using the natural context of these samples in combination with laboratory experiments we demonstrate that the isotopic composition of dissolved si in weathering systems is determined by the combined effects of rock disintegration clay mineral neosynthesis and si biocycling weathering preferentially releases 28si into solution whereas secondary mineral formation preferentially removes 28si from solution in humid environments leached soils have lost large amounts of this soluble si thus creating a net loss of 30si from the entire soil system as soils develop and greater fractions of si reside in neoformed clay minerals 30sibulk soil values change progressively toward more negative values basalt 30si values are about 0 5 but older soils have 30si values up to 2 5 the difference between the solid and solution 30si values remains more or less constant with progressive weathering and therefore soil water from older soils has a more negative 30si composition in the upper horizons of the hawaiian soils this weathering driven 30si shift is modified by the addition of unweathered primary minerals via dust carrying 30si values of about 0 5 and by biocycling of si via plants producing negative 30si values in phytoliths and positive 30si values in soil solutions derived from upper horizons due to the high concentrations of dissolved si in these near surface layers rivers have more positive 30si values than predicted based on the weathering status of the lower horizons when combined with published 30si values from large rivers worldwide we find that the results from hawaii point to weathering control of si isotopes delivered to the oceans and thus to an important continent ocean linkage that warrants further investigation

opal sedimentation shifts in the world ocean over the last 15 myr biogenic silica opal accumulation records were used to trace mechanisms consequence and geographic pattern of shifts in the main locus of opal deposition of the world ocean over the last 15 myr over this time interval the main opal sink seems to have moved from the north atlantic to the pacific equatorial pacific eastern equatorial pacific eastern boundary current upwelling systems california namibia peru and finally to the southern ocean the interplay between opal deposition and a series of climatic tectonic oceanographic and biologic events has been analyzed and discussed these events include the cenozoic global cooling trend intensified glaciation in antarctica late miocene early pliocene biogenic bloom development of northern hemisphere glaciation nhg closing of the panama seaway transition of the climate system from a monopolarto a bipolar glaciated world mid pleistocene revolution mpr nutrient availability evolution of diatoms and c4 plants and changes in continental weathering rates while the observed shifts are mostly traceable to oceanic reorganizations and global climatic evolution conditions favorable to opal deposition involve the above mentioned complex mix of processes for this reason the interpretation of opal deposition records might not always be straightforward we however believe that it can still provide clear indications of large scale oceanographic reorganizations in the geological past d 2004 elsevier b v all rights reserved

thermo mechanical controls on the mode of continental collision in the se carpathians romania abstract the carpathians orogenic system with its along arc variations in topography developed in the aftermath of continental collision is associated with unusual foredeep basins large scale strain and seismicity concentration and high velocity mantle bodies the east carpathians continental collision was non cylindrical leading to large scale variations in thrust nappe kinematics orogenic uplift patterns and foredeep subsidence controlled by the mechanics and geometry of the lower plate thermo mechanical modelling demonstrates that in this low rate convergence regime the subducted lithosphere had enough time to interact with the mantle to advance towards a thermal resettlement this is favored by the low degree of metamorphism mechanical weakness of the lower plate and the lack of active surface processes at the contact with and in the upper plate in contrast low buoyant thick lower crust and active surface processes keep the continuity of the slab intact and promote the development of typical foredeep basins the model explains in a self consistent manner the unusual geometry of the vrancea seismogenic slab in the bend zone of the romanian carpathians the model is also consistent with the presence of two high velocity bodies inferred from seismic tomography studies and explains the depth zonation of seismicity in the vrancea area differences between the northern part of east carpathians and the southeastern bend of the carpathians arc are largely controlled by lateral variations in crustal structure topography emplacement and surface processes along the arc mechanical heterogeneity of the carpathians subduction leads to the development of two end member modes of collision allowing a study of these states and their transition lithospheric configuration and tectonic topography appear to be prime factors controlling variations in slab behavior in the se carpathians at the terminal phase of continental convergence slab delamination roll back and depocenter migration appear to play a more limited role at shallow and lithospheric levels

tertiary subduction and slab break off model of the carpathian pannonian region abstract this paper illustrates the application of multidisciplinary data analysis to the carpathian pannonian region and presents a new tertiary development model that incorporates all multidisciplinary parameters during the late cretaceous eocene the future carpathian orogen was part of the larger alpine carpathian orogen formed by the southeastward subduction 135 55 ma of the penninic ocean and the ultimate collision 55 40 ma of the european and adriatic continents the subduction in the alpine region ended by the slab break off of the subducting oceanic lithosphere from the continental one and by the related magmatism 43 24 ma while the eocene alps were under continental collision the eocene remnant carpathian flysch basin rcfb was still subducting the carpathians and eastern parts of the alps started to occupy the region of the present carpathians during the early miocene the oceanic plate underlying the rcfb subducted southwestwards later westwards while the northeastward and eastward migration velocity of the accreting plate boundary decreased through time the slower subduction rate caused a steeper dip of the subducting slab the beginning of the eggenburgian 22 19 ma and following duration of extension in the orogenic hinterland accompanied by the asthenosphere upwelling the onset of the crustally derived volcanism above the risen asthenosphere and the younger mantle derived volcanism progressively less contaminated by the crustal material all contemporaneous with a shortening in the carpathian accretionary wedge the subduction of the rcfb finally led at the end of the early miocene to a collision with the continental margin along the westernmost part of the present carpathian arc the subduction roll back of the subducting slab of the rcfb under the advancing inner carpathians the oblique closure of the basin the progressive change of the subduction to collision from the west to the east along the carpathian arc drove a scissors like break off of the subducting oceanic slab along the west carpathians the break off in the east carpathians was driven by the weight of a subducting oceanic slab and buoyancy of the attached continental slab the break off started in the west of the carpathian arc in the early miocene ran along the arc to its present position in the bend area between the east and south carpathians and separated the oceanic slab that subducted passively under its own weight from the european continental margin the lateral propagation rate of the slab tear decreased with time the break off related volcanism was synchronous with the final stages of the collision

silicic acid leakage from the southern ocean a possible explanation for glacial atmospheric pco2 1 using a simple box model we investigate the effects of a reduced si n uptake ratio by antarctic phytoplankton on the marine silica cycle and atmospheric pco2 recent incubation experiments demonstrate such a phenomenon in diatoms when iron is added hutchins and bruland 1998 takeda 1998 franck et al 2000 the southern ocean may have supported diatoms with reduced si n uptake ratios compared to today during the dustier glacial times petit et al 1999 a similar reduction in the uptake ratio may be realized with an increased production of nondiatom phytoplankton such as phaeocystis our model shows that reduced si n export ratios in the southern ocean create excess silicic acid which may then be leaked out to lower latitudes any significant consumption of the excess silicic acid by diatoms that leads to an enhancement in their growth at the expense of coccolithophorids diminishes caco3 production and therefore diminishes the carbonate pump in our box model the combination of a reduced carbonate pump and an open system carbonate compensation draw down steady state atmospheric co2 from the interglacial 277 to 230 242 ppm depending on where the excess silicic acid is consumed by comparison the atmospheric pco2 sensitivity of general circulation models to carbonate pump forcing is 3 5 fold greater which combined with carbonate compensation can account for peak glacial atmospheric pco2 we discuss the importance of the initial rain ratio of caco3 to organic carbon on atmospheric pco2 and relevant sedimentary records that support and constrain this silicic acid leakage scenario

deglacial variability of antarctic intermediate water penetration into the north atlantic from authigenic neodymium isotope ratios 1 understanding intermediate water circulation across the last deglacial is critical in assessing the role of oceanic heat transport associated with atlantic meridional overturning circulation variability across abrupt climate events however the links between intermediate water circulation and abrupt climate events such as the younger dryas yd and heinrich event 1 h1 are still poorly constrained here we reconstruct changes in antarctic intermediate water aaiw circulation in the subtropical north atlantic over the past 25 kyr by measuring authigenic neodymium isotope ratios in sediments from two sites in the florida straits our authigenic nd isotope records suggest that there was little to no penetration of aaiw into the subtropical north atlantic during the yd and h1 variations in the northward penetration of aaiw into the florida straits documented in our authigenic nd isotope record are synchronous with multiple climatic archives including the greenland ice core 18o record the cariaco basin atmosphere 14c reconstruction the bermuda rise sedimentary pa th record and nutrient and stable isotope data from the tropical north atlantic the synchroneity of our nd records with multiple climatic archives suggests a tight connection between aaiw variability and high latitude north atlantic climate change

filamentous microfossils in the early proterozoic transvaal supergroup their morphology significance and paleoenvironmental setting abstract well preserved filamentous microfossils siphonophycus transvaalensis n sp are described here from the carbonate campbellrand subgroup to iron formation kuruman iron formation transition of the transvaal supergroup south africa estimated to be 2 5 2 3 ga years old the microfossils occur in petrographic thin sections of a core sample of carbonate chert they are preserved by permineralization in both chert and in sparry ferroan dolomite stratigraphically the fossiliferous core sample occurs as part of an upward transition from a stromatolitic dolomite and limestone sequence campbellrand to the overlying iron rich sediments of the kuruman griquatown iron formations the average 13 c value of the kerogen in the sample is about 36 9 the microfossils are filamentous unbranched tubular to somewhat flattened 15 25 m in diameter and a few to many hundred microns in length they exhibit a coriaceous finely granular external surface texture resulting from the presence of adhering randomly distributed fine mineralic carbonate needles in salient morphological characteristics they are comparable to the tubular originally polysaccharide encompassing sheaths of extant oscillatoriacean cyanobacteria in comparison with previously described precambrian microfossils these fossil filaments are unusual because of their preservation in sparry carbonate in addition to chert their relatively large diameter and their coating by adhering precipitated carbonate needles they appear to be among the oldest assured microfossils now known from proterozoic age sediments the microfossils are interwoven occurring in subparallel aggregates that form a stromatolitic mat like fabric they are considered to be of an endogenetic in situ benthic origin occurring at the proximal margin of a deep shelf environment at the front distal margin of the campbellrand carbonate platform the water depth for this environment at the break in slope between deep shelf and euxinic basin is estimated to have been of the order of 40 45 m paleomagnetic data support our interpretation that the micro organisms inhabited a warm water marine environment probably at low latitudes

using silicon isotopes to understand the role of the southern ocean in modern and ancient biogeochemistry and climate abstract the growth of siliceous phytoplankton mainly diatoms in the southern ocean influences the preformed nutrient inventory in the ocean on a global scale silicic acid use by diatoms and deep circulation combine to trap dissolved si in the southern ocean resulting in high levels of silica production and expansive diatom oozes in southern ocean sediments the analysis of the silicon isotope composition of biogenic silica or opal and dissolved silicic acid provide insight into the operation of the global marine silicon cycle and the role played by the southern ocean in nutrient supply and carbon drawdown both in the modern and in the past silicon isotope studies of diatoms have provided insight into the history of silica production in surface waters while the analysis of spicules from deep sea sponges has defined both the spatial and the temporal variability of silicic acid concentrations in the water column together these and other proxies reveal variations in the northward flow of southern ocean intermediate and mode waters and how changes in southern ocean productivity altered their preformed nutrient content we present a new hypothesis the silicic acid ventilation hypothesis savh to explain the geographical variation of opal based proxy records in particular the contrasting patterns of opal burial change found in the low and high latitudes by understanding the silicon isotope systematics of opal and silicic acid in the modern we will be able to use opal based proxies to reconstruct past changes in the southern ocean and so investigate its role in global carbon cycling and climate

u pb zircon geochronology and anomalous sr nd hf isotope systematics of late orogenic andesites pieniny klippen belt western carpathians south poland abstract late orogenic andesites and basaltic andesites in the pieniny klippen belt pkb in the western carpathians display atypical isotope systematics strongly departing from those observed among other neogene quaternary calc alkaline rocks in the carpathian pannonian region low end values 10 6 to 5 2 and low ehf values 19 6 to 5 2 are accompanied by unusually low 87 sr 86 sr ratios 0 7052 to 0 7059 major trace element isotope and geochronological data presented in this study indicate two magma sources evolving with low rb sr ratio from which the pkb calc alkaline rocks originated basaltic andesites showing less enriched signature and wider range of isotope compositions end 7 7 to 5 2 ehf 11 3 to 5 2 and 87 sr 86 sr 0 7052 0 7059 are interpreted as having originated from the partial melts derived from an ancient metasomatized sub continental lithospheric mantle which during emplacement were contaminated by the upper crustal material andesites whose precise timing of emplacement was constrained by in situ la icp ms u pb zircon dating at 11 2 0 2 to 12 1 0 3 ma show more enriched signature and narrow range of nd and hf isotope compositions end 10 6 to 10 1 ehf 19 6 to 18 3 accompanied by low 87 sr 86 sr 0 70531 0 70541 u pb dating of the inherited domains in zircons revealed the presence of late paleozoic precambrian and archean age components which support crustal origin of the pkb andesites in situ hf isotope analyses of zircons suggest that andesites could have been derived from enriched initial ehf 13 to 10 permian igneous domains in the lower crust generation of the calc alkaline magmas in the upper lithospheric mantle and in the thickened crust was triggered by decompression or crustal delamination following middle miocene collision of the alcapa block with southern margin of the european platform the pkb fault zone and its splays acted as conduits which enabled ascent of small volumes of andesitic magmas into the upper crust of the western carpathians

radiocarbon and stable isotope constraints on last glacial maximum and younger dryas ventilation in the western north atlantic 1 foraminiferal abundance 14c ventilation ages and stable isotope ratios in cores from high deposition rate locations in the western subtropical north atlantic are used to infer changes in ocean and climate during the younger dryas yd and last glacial maximum lgm the 18o of the surface dwelling planktonic foram globigerinoides ruber records the present day decrease in surface temperature sst of 4 c from gulf stream waters to the northeastern bermuda rise if during the lgm the modern 18o salinity relationship was maintained this sst contrast was reduced to 2 c with lgm to interglacial 18o changes of at least 2 2 ssts in the western subtropical gyre may have been as much as 5 c colder above 2 3 km glacial 13c was higher than today consistent with nutrient depleted younger bottom waters as identified previously below that 13c decreased continually to 0 5 about equal to the lowest lgm 13c in the north pacific ocean seven pairs of benthic and planktonic foraminiferal 14c dates from cores 2 5 km deep differ by 1100 340 years with a maximum apparent ventilation age of 1500 years at 4250 m and at 4700 m apparent ventilation ages are presently unavailable for the lgm 2 5 km because of problems with reworking on the continental slope when sea level was low because lgm 13c is about the same in the deep north atlantic and the deep north pacific and because the oldest apparent ventilation ages in the lgm north atlantic are the same as the north pacific today it is possible that the same water mass probably of southern origin flowed deep within each basin during the lgm very early in the yd dated here at 11 25 0 25 n 10 conventional 14c kyr bp equal to 12 9 calendar kyr bp apparent ventilation ages 2 3 km water depth were about the same as north atlantic deep water today below 2 3 km four yd pairs average 1030 400 years the oldest apparent ventilation age for the yd is 1600 years at 4250 m this strong contrast in ventilation which indicates a front between water masses of very different origin is similar to glacial profiles of nutrient like proxies this suggests that the lgm and yd modes of ocean circulation were the same

magmagenesis in a subduction related post collisional volcanic arc segment the ukrainian carpathians abstract calc alkaline magmatism in the south west ukraine occurred between 13 8 and 9 1 ma and formed an integral part of the neogene subduction related post collisional carpathian volcanic arc eruptions occurred contemporaneously in two parallel arcs here termed outer arc and inner arc in the ukrainian part of the carpathians outer arc rocks mainly andesites are characterized by lile enrichment e g k and pb nb depletion low compatible trace element abundances high 87sr 86sr high 18o and low 143nd 144nd isotopic ratios 0 7085 0 7095 7 01 8 53 0 51230 0 51245 respectively inner arc rocks are mostly dacites and rhyolites with some basaltic and andesitic lavas they also show low compatible element abundances but have lower 87sr 86sr 18o and higher 143nd 144nd ratios 0 7060 0 7085 6 15 6 64 0 5125 0 5126 respectively than outer arc rocks both high nb and low nb lithologies are present in the inner arc based on the lile enrichment especially pb a higher fluid flux is suggested for the outer arc magmas compared with those of the inner arc combined trace element and sr nd o isotopic modelling suggests that the factors which controlled the generation and evolution of magmas were complex compositional differences between the inner and outer arcs were produced by introduction of variable proportions of slab derived sediments and fluids into a heterogeneous mantle wedge and by different extents of upper crustal contamination degrees of magmatic fractionation also differed between the two arcs the most primitive magmas belong to the inner arc isotopic modelling shows that they can be produced by adding 3 8 subducted terrigenous flysch sediments to the local mantle wedge source up to 5 upper crustal contamination has been modelled for fractionated products of the inner arc the geochemical features of outer arc rocks suggest that they were generated from mantle wedge melts similar to the inner arc primitive magmas but were strongly affected by both source enrichment and upper crustal contamination assimilation of 10 20 bulk upper crust is required in the afc modelling assuming an inner arc parental magma we suggest that magmagenesis is closely related to the complex geotectonic evolution of the carpathian area several tectonic and kinematic factors are significant 1 hydration of the asthenosphere during subduction and plate rollback directly related to collisional processes 2 thermal disturbance caused by ascent of hot asthenospheric mantle during the back arc opening of the pannonian basin 3 clockwise translational movements of the intracarpathian terranes which facilitated eruption of the magmas

quantifying the north pacific silica plume 1 new hydrostations plus a comprehensive compilation of existing data have allowed us to characterize the dissolved silica plume located at midwater depths in the north pacific the north pacific silica plume is a global scale anomaly extending from the north american continental margin in the east to beyond the hawaii emperor seamount chain in the west inventory of the plume between 2000 and 3000 m depth indicates that it contains 164 tmols 164 1012 mols of anomalous dissolved silica and is maintained by a horizontal flux of approximately 1 5 tmols yr from the east the source region of this plume has been previously suggested to be cascadia basin in the ne pacific biochemical and geothermal processes within this small region can produce approximately one third of the required flux but the majority of silica contained within the north pacific plume may originate in crustal fluid venting from the warm upper basement aquifer that underlies the easternmost pacific plate

exploring for hydrocarbons under thrust belts a challenging new frontier in the carpathians and elsewhere new significant reserves of hydrocarbons may occur in subthrust autochthonous and parautochthonous series buried below the frontal zones of thin skinned thrust belts the subthrust plays have been tested in several orogenic belts of the world the carpathians being one of the best examples the arcuate thin skinned carpathian orogenic belt which evolved during the mesozoic and cenozoic is thrust tens of kilometers over its neogene foredeeps and the underlying european plate various structural and stratigraphic settings and potential hydrocarbon plays have been recognized within the buried margins of the european plate including a late paleozoic hercynian compressional system mesozoic rifted margins of the tethys and a cenozoic synorogenic foreland type fault system possibly deeper parautochthonous structures documented on examples from the southern apennines may also be present below the thin skinned frontal zone of the carpathian thrust belt in addition to these structural settings large paleogene valleys submarine canyons have been found within the margins f the european plate these structural and morphologic features if combined with source rocks reservoirs and proper burial history represent potential hydrocarbon plays generation of hydrocarbons from sources within the subthrust plate was greatly enhanced by emplacement of the wedge shaped thrust belt which may also provide a regional seal therefore the combination of the long and complex geological history of the european plate with the impact of the alpine thrusting and foreland deformation created unique conditions for generation entrapment and preservation of hydrocarbons in subthrust settings

the western carpathians interaction of hercynian and alpine processes abstract the complicated structural and rheologic properties of western carpathian lithosphere reflect the complex geodynamic history of the carpathian orogen based on critical analysis of earlier models new interpolation of existing geophysical data and results of integrated modelling a new map of the lithosphere thickness for the carpathian pannonian region has been constructed the map allows for the distinction of a frontal orogen collision zone in the ne from increased lithosphere thickness as well as a zone of oblique collision with the bohemian massif in the west where lithosphere is not significantly thickened the moho discontinuity beneath the western carpathian hinterland danube and east slovak basins as defined by deep reflection seismic profiling is relatively shallow this probably reflects recent crustal extension related to oblique collision between the european plate and the alcapa block and an increase of the asthenospheric updoming from the middle miocene onward crustal thickness reflects the combined effects of deep seated orogenic processes and mantle thermal evolution beneath the pannonian basin system in this study we focus particularly the structures of 1 the late alpine collision and neogene back arc basin development including deep seated contacts between colliding plates a zone of slab detachment the compressional accretionary wedge of the outer western carpathian flysch belt and extensional structures produced by subduction rollback and asthenosphere upwelling 2 early alpine structures related to cretaceous thrust stacking including subhorizontal reflection packages interpreted as multi generational extensional structures the underplated intra penninic oravic continental ribbon and ophiolite traces of the meliatic oceanic suture and 3 north dipping reflectors interpreted as remnant hercynian lithotectonic fragments with opposed vergency to the subducted alpine units

sedimentary opal records in the eastern equatorial pacific it is not all about leakage 1 the clear predictions of the silicic acid leakage hypothesis salh resulted in a number of studies of downcore opal records from the tropical pacific the original salh predicts that unused silicic acid due to fe driven changes in si versus n limitation escaped from the glacial southern ocean to equatorial upwelling regimes where it enhanced diatom productivity thereby decreasing coccolith growth and lowering atmospheric co2 in contrast to salh predictions however sedimentary records from the eastern equatorial pacific eep do not show enhanced opal burial during the last glacial maximum lgm but higher rates of opal burial during the deglaciation and marine isotopic stage 3 mis3 the peak in opal productivity during the deglaciation has been attributed to increased supply of nutrient rich waters driven by stronger upwelling of deep water in the southern ocean at the end of last glacial period the large peak in opal burial observed in a number of eep cores during mis3 was interpreted as evidence for si leakage when southern ocean diatom productivity was limited by both low dust flux and extended sea ice on the other hand the paradoxical lgm decline in opal accumulation in the eep was explained by enhanced dust input that lowered the diatom si c uptake ratio here we use a combination of molecular fingerprints of algal productivity and radioisotope tracers of sedimentation to revisit opal burial in the eep in particular during the mis3 opal peak an increase in algal productivity is not supported by the sedimentary concentration of brassicasterol an organic molecule commonly found in diatoms or by the ratio of 231pa 230th xs 0 a proxy for opal export production we therefore conclude that the large peak in opal burial during mis3 reflects enhanced preservation of diatoms building on mechanisms invoked in previous studies we hypothesize that opal burial in the eep is controlled both by the physiological response of diatoms to low latitude fe inputs and by the high latitude processes leading to silicic acid leakage

plate tectonic evolution of the southern margin of eurasia in the mesozoic and cenozoic abstract thirteen time interval maps were constructed which depict the triassic to neogene plate tectonic configuration paleogeography and general lithofacies of the southern margin of eurasia the aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework the hercynian orogeny was completed by the collision of gondwana and laurussia whereas the tethys ocean formed the embayment between the eurasian and gondwanian branches of pangea during late triassic early jurassic times several microplates were sutured to the eurasian margin closing the paleotethys ocean a jurassic cretaceous north dipping subduction boundary was developed along this new continental margin south of the pontides transcaucasus and iranian plates the subduction zone trench pulling effect caused rifting creating the back arc basin of the greater caucasus proto south caspian sea which achieved its maximum width during the late cretaceous in the western tethys separation of eurasia from gondwana resulted in the formation of the ligurian penninic pieniny magura ocean alpine tethys as an extension of middle atlantic system and a part of the pangean breakup tectonic system during late jurassic early cretaceous times the outer carpathian rift developed the opening of the western black sea occurred by rifting and drifting of the western central pontides away from the moesian and scythian platforms of eurasia during the early cretaceous cenomanian the latest cretaceous paleogene was the time of the closure of the ligurian pieniny ocean adria alcapa terranes continued their northward movement during eocene early miocene times their oblique collision with the north european plate led to the development of the accretionary wedge of the outer carpathians and its foreland basin the formation of the west carpathian thrusts was completed by the miocene the thrust front was still propagating eastwards in the eastern carpathians during the late cretaceous the lesser caucasus sanandaj sirjan and makran plates were sutured to the iranian afghanistan plates in the caucasus caspian sea area a north dipping subduction zone jumped during paleogene to the scythian turan platform the shatski terrane moved northward closing the greater caucasus basin and opening the eastern black sea the south caspian underwent reorganization during oligocene neogene times the southwestern part of the south caspian basin was reopened while the northwestern part was gradually reduced in size the collision of india and the lut plate with eurasia caused the deformation of central asia and created a system of nw se wrench faults the remnants of jurassic cretaceous back arc systems oceanic and attenuated crust as well as tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems

transform faulting extension and subduction in the carpathian pannonian region the carpathian arc formed during the cretaceous to miocene continental collision of europe with a smaller continental fragment following southward and westward subduction of an oceanic terrane during and after the last stages of thrusting in the outer carpathians a set of discrete basins opened up inside the carpathian loop these basins are regions of local extension which appear to be associated with strike slip faults in general northeast and northwest trending sets of conjugate shears reflect east west extension of the intra carpathian region during the middle and late miocene palinspastic reconstruction of the basins indicates approximately 75 to 100 km of extension comparable to the magnitude of synchronous crustal shortening in the east carpathians extension may have occurred to accommodate continued westward a type subduction after plate convergence was prohibited by geometrical constraints and suggests that in this region miocene subduction is driven by forces acting on the downgoing plate

quantitative reconstruction of orogenic convergence in the northeast carpathians abstract the ne outer carpathians form a fold and thrust belt of large displacement this mainly consists of deformed cretaceous tertiary deep water clastics and can be divided into an imbricate stack of four major supracrustal nappes the magura dukla silesian and skole nappes an extensive reflection seismic surface geological and drillhole database is used to constrain the deformed geometry of the two uppermost and southernmost allochthonous units the magura and dukla nappes a retro deformable cross section shows that the cretaceous tertiary sediment piles are detached along a single large decollement at about 5 7 km depth the rear and frontal parts of the magura nappe show steep imbricate fan geometries while the central part has a duplex structure with long thrust horses to the ne the dukla nappe is a stack of imbricate slices and is separated from the subjacent silesian nappe by a large thrust flat reverse modelling of deformation reveals that the magura nappe was horizontally shortened by at least 80 km and the dukla nappe by about 20 km in the ne sw direction together with previously published estimates of shortening in the silesian and skole nappes the total orogenic contraction in the ne outer carpathians is at least 260 km shortening was accumulated between the middle oligocene and the middle miocene almost all of the shortening can be balanced against contemporaneous back arc extension and eastward extrusion of rock masses from the eastern alps

geochemical response of magmas to neogene quaternary continental collision in the carpathian pannonian region a review the carpathian pannonian region contains neogene to quaternary magmatic rocks of highly diverse composition calcalkaline shoshonitic and mafic alkalic that were generated in response to complex microplate tectonics including subduction followed by roll back collision subducted slab break off rotations and extension major element trace element and isotopic geochemical data of representative parental lavas and mantle xenoliths suggests that subduction components were preserved in the mantle following the cessation of subduction and were reactivated by asthenosphere uprise via subduction roll back slab detachment slab break off or slab tearing changes in the composition of the mantle through time are evident in the geochemistry supporting established geodynamic models magmatism occurred in a back arc setting in the western carpathians and pannonian basin western segment producing felsic volcaniclastic rocks between 21 to 18 ma ago followed by younger felsic and intermediate calc alkaline lavas 18 8 ma and finished with alkalic mafic basaltic volcanism 10 0 1 ma volcanic rocks become younger in this segment towards the north geochemical data for the felsic and calc alkaline rocks suggest a decrease in the subduction component through time and a change in source from a crustal one through a mixed crustal mantle source to a mantle source block rotation subducted roll back and continental collision triggered partial melting by either delamination and or asthenosphere upwelling that also generated the younger alkalic mafic magmatism in the westernmost east carpathians central segment calc alkaline volcanism was simultaneously spread across ca 100 km in several lineaments parallel or perpendicular to the plane of continental collision from 15 to 9 ma geochemical studies indicate a heterogeneous mantle toward the back arc with a larger degree of fluid induced metasomatism source enrichment and assimilation on moving north eastward toward the presumed trench subduction related roll back may have triggered melting although there may have been a role for back arc extension and asthenosphere uprise related to slab break off calc alkaline and adakite like magmas were erupted in the apuseni mountains volcanic area interior segment from15 9 ma without any apparent relationship with the coeval roll back processes in the front of the orogen magmatic activity ended with oiblike alkali basaltic 2 5 ma and shoshonitic magmatism 1 6 ma lithosphere breakup may have been an important process during extreme block rotations 608 between 14 and 12 ma leading to decompressional melting of the lithospheric and asthenospheric sources eruption of alkali basalts suggests decompressional melting of an oib source asthenosphere mixing of asthenospheric

paleoenvironmental conditions source and maturation of neogene organic matter from the siliciclastic deposits of the orava nowy targ basin abstract the orava nowy targ basin ontb is an intramontane depression filled with neogene and quaternary deposits located at the junction of the inner and outer carpathians the neogene infill of the basin consists mainly of siliciclastic rocks with very common lignite intercalations and is mostly of fluvial or lake origin the organic matter molecular analysis of seventeen neogene samples confirmed the terrigenous origin of organic matter with a predominance of higher plant input in most samples based on the distribution of n alkanes and steranes as well as the presence of tri and tetracyclic diterpenoids and triterpenoids representing oleanane ursane lupane chrysene and picene derivatives high concentrations of compounds originating from both angiosperms and gymnosperms suggest the presence of mixed forests additionally important input of mosses into the primary organic matter is indicated by the high concentration of n c 23 and presence of hop 17 21 enes in most samples a high average aromatic ring and conifer wood degradation index 0 7 indicate high activity of bacteria and wood degrading fungi in the sedimentary environment there was no evidence of weathering and scarce signs of biodegradation were identified all samples were subjected to water washing huminite reflectance and biomarker based parameters as well as the presence of unsaturated pentacyclic triterpenoids and steroids indicate an immature organic matter a trend of decreasing maturation of sediments from east to the west was observed as was a similarity of thermal maturity between the podhale synclinorium and the ontb although the latter seems to be coincidental a thermal gradient value of 35 c km was assumed for calculating the maximum thickness of eroded strata resulting in 1 1 6 km for the se area and a maximum temperature of the deepest buried samples equal to 45 65 c

lower export production during glacial periods in the equatorial pacific derived from 231pa 230th xs 0 measurements in deep sea sediments 1 the 231pa 230th xs 0 records obtained from two cores from the western md97 2138 1 25 s 146 24 e 1900 m and eastern ocean drilling program leg 138 site 849 0 11 59 n 110 31 18 w 3851 m equatorial pacific display similar variability over the last 85 000 years i e from isotopic stages 1 to 5a with systematically higher values during the holocene isotopic stage 3 and isotopic stage 5a and lower values approaching the production rate ratio of the two isotopes 0 093 during the colder periods corresponding to isotopic stages 2 and 4 we have also measured the 230th normalized biogenic preserved and terrigenous fluxes as well as major and trace elements concentrations in both cores the 231pa 230th xs 0 results combined with the changes in preserved carbonate and opal fluxes at the eastern site indicate lower productivity in the eastern equatorial pacific during glacial periods the 231pa 230th xs 0 variations in the western equatorial pacific also seem to be controlled by productivity carbonate and or opal the generally high 231pa 230th xs 0 ratios 0 093 of the profile could be due to opal and or mno2 in the sinking particles the profiles of 231pa 230th xs 0 and 230th normalized fluxes indicate a decrease in exported carbonate and possibly opal during isotopic stages 2 and 4 in md97 2138 using 230th normalized flux we also show that sediments from the two cores were strongly affected by sediment redistribution by bottom currents suggesting a control of mass accumulation rates by sediment focusing variability

silicic acid leakage from the southern ocean opposing effects of nutrient uptake and oceanic circulation 1 studies invoking the silicic acid leakage hypothesis to explain events of high biogenic opal deposition at low latitudes did not consider variations in formation rate of southern ocean intermediate waters comparison of 30si records from the southern ocean to records of biogenic opal accumulation from low latitude upwelling systems indicates a strong negative correlation between the silicic acid content of southern ocean surface waters and opal deposition at low latitudes during the last 80 kyr bp this implies that si leakage was somehow rendered ineffective when the silicic acid content of southern ocean waters was high comparison of opal accumulation records with records of intermediate water formation rates suggests that lower rates of intermediate water formation offset the higher silicic acid content of these water masses during glacial periods this indicates that physical processes that control intermediate water transport dominate over biological processes that set the silicic acid content of antarctic surface waters in determining the magnitude of silicic acid leakage from the southern ocean

principal characteristics of the upper silesian block and malopolska block border zone southern poland the upper silesian and malopolska blocks are situated near the southwestern boundary of the east european platform within the trans european suture zone the lower palaeozoic lithologies of the blocks reveal different stratigraphic and diastrophic development in the upper silesian block unmetamorphosed and gently folded lower cambrian to ordovician sedimentary rocks rest on a cadomian basement the lower cambrian is represented by an older sub holmia borzeta formation and a younger holmia goczalkowice formation the thickness of the cambrian lithologies increases from the southwest towards the lateral part of the block in the malopolska block palaeozoic and precambrian lithologies are represented by regionally metamorphosed and intensely folded lower cambrian vendian clastic rocks which are unconformably overlain by ordovician lower silurian carbonates and upper silurian clastic rocks the crystalline basement of the malopolska block has yet to be recognized the lower palaeozoic sediments of both blocks are overlain by devonian and carboniferous rocks the blocks are in direct contact along a narrow tectonic zone a part of the largely concealed hamburg krakow fault zone in which tectonic evolution has taken place spasmodically with strike slip movements predominating

magnetic fabric and petrology of miocene sub volcanic sills and dykes emplaced into the sw flysch belt of the west carpathians s moravia czech republic and their volcanological and tectonic implications abstract magnetic fabrics were investigated in the sub volcanic bodies occurring within the sw flysch belt of the western carpathians magnetite or low ti titanomagnetite is the principal carrier of the anisotropy of magnetic susceptibility ams in these rocks though various fe ti oxides were also identified in minor amounts the magnetic fabric in almost all sills and dykes is conformable to the shapes of the bodies and no doubt originated through more or less free magma flow that requires relatively open voids to be injected that likely originated in an extensive tectonic regime in an ankaramite sill where the rock creates typical hexagonal columns the magnetic fabric is related rather to the column axes than to the overall shape of the sill the magnetic fabric formation in this sill is controlled by the post emplacement process of the creation of the columns at some studied localities signs of post magmatic middle miocene tectonic deformation are observed in the field the youngest known in the flysch belt as the magnetic fabric is unrelated to those signs we conclude that these young tectonic movements did not penetrate ductilely in the volume of the volcanic body it seems that the strain was focused to thin zones along the faults since it did not change the preferred orientation of magnetic minerals in the rock volume substantially

revisiting nutrient utilization in the glacial antarctic evidence from a new method for diatom bound n isotopic analysis holocene in the indian sector is smaller than in previous measurements these data suggest no change in the degree of nitrate utilization in the atlantic sector and at most a 20 increase from 25 to 45 in the indian sector the new measurements suggest that during the last ice age in the atlantic sector of the antarctic the atmospheric source of biologically available iron was not so great as to become significant relative to the iron supply from below given the apparent spatial variability in the degree of nitrate drawdown more work is required to develop an adequate picture of the glacial antarctic nutrient field index terms 4806 oceanography biological and chemical carbon cycling 4845 oceanography biological and chemical nutrients and nutrient cycling 4894 oceanography biological and chemical instruments and techniques 9310 information related to geographic region antarctica

carbon isotope evidence for changes in antarctic intermediate water circulation and ocean ventilation in the southwest pacific during the last deglaciation 1 deep sea sediment core fr1 97 gc 12 is located 990 mbsl in the northern tasman sea southwest pacific where antarctic intermediate water aaiw presently impinges the continental slope of the southern great barrier reef analysis of carbon 13c and oxygen 18o isotope ratios on a suite of planktonic and benthic foraminifera reveals rapid changes in surface and intermediate water circulation over the last 30 kyr during the last glacial maximum there was a large 13c offset 1 1 between the surface dwelling planktonic foraminifera and benthic species living within the aaiw in contrast during the last deglaciation termination 1 the 13cplanktonic benthic offset reduced to 0 4 prior to an intermediate offset 0 7 during the holocene we suggest that variations in the dominance and direction of aaiw circulation in the tasman sea and increased oceanic ventilation can account for the rapid change in the water column 13cplanktonic benthic offset during the glacial interglacial transition our results support the hypothesis that intermediate water plays an important role in propagating climatic changes from the polar regions to the tropics in this case climatic variations in the southern hemisphere may have led to the rapid ventilation of deep water and aaiw during termination 1 which contributed to the postglacial rise in atmospheric co2

tertiary extension development and extension compression interplay in the west carpathian mountain belt abstract this paper describes palaeostresses calculated from fault striae data the inferred palaeostrain patterns and determines the inter relation of the compression and extension during the tertiary development of the west carpathians the calculated stress and inferred strain patterns for the palaeogene burdigalian indicate that the ancestral west carpathians formed a more or less straight orogenic belt this belt underwent contraction and uplift in its narrow frontal zone stretching along its strike during the paleocene chattian and regional contraction and uplift during the chattian burdigalian the strain stress pattern is similar to the collision related pattern known from the eastern alps for the paleocene burdigalian during the burdigalian tortonian the calculated and inferred west carpathian stress and strain patterns indicate narrow frontal contractional and lateral sinistral transpressional zones in the orogenic front and broad extensional and dextral transtensional zones in the orogenic interior the stress strain pattern is similar to the subduction related pattern known from areas such as the hellenic or sunda banda arcs

millennial variability and long term changes of the diatom production in the eastern equatorial pacific during the last glacial cycle 1 the modern eastern equatorial pacific eep is a major natural source for atmospheric carbon dioxide and is thought to be connected to high latitude ocean dynamics by oceanic teleconnections on glacial interglacial timescales a wealth of sedimentary records aiming at reconstructing last quaternary changes in primary productivity and nutrient utilization have been devoted to understanding those linkages between the eep and other distant oceanic areas most of these records are however clustered in the pelagic eep cold tongue with comparatively little attention devoted to coastal areas here we present downcore measurements of the composition and concentration of the diatom assemblage together with opal biogenic silica concentration at site md02 2529 recovered in the coastal panama basin piston core md02 2529 collected in an area affected by a multitude of processes provides evidence for strong variations in diatom production at the millennial timescale during the last glacial cycle the maxima in total diatom concentration occurred during the early marine isotopic stage mis 4 as well as during the mis 4 3 transition and mis 3 rapid changes in diatom concentrations during the mis 3 mimics bond cycles as independently recorded by the sea surface salinity estimation derived from planktonic foraminifera from the same core such patterns indicate a clear linkage between diatom production in the coastal eep and rapid climate changes in the high latitude north atlantic in parallel the long term succession of the diatom community from coastal diatoms predominantly thriving during mis 5 and 4 toward pelagic diatoms dominant during mis 3 and 2 points to a long term change in the surface hydrology during heinrich events diatoms strongly reduced their production probably because of enhanced stratification in the upper water column after the last glacial maximum diatom production and valve preservation strongly decreased in response to the advection of nutrient depleted h2sio4 warmer water masses our high resolution record highlights how regional climatic processes can modulate rapid changes in siliceous primary production as triggered by wind induced local upwelling indicating that millennial climatic variability can overtake other prominent hydrological processes such as those related to silicic acid leakage

biological fractionation of silicon isotopes in southern ocean surface waters 1 the fractionation of silicon isotopes by diatoms during silicification i e opaline cell wall formation provides a new tool for paleoceanographic studies of the silicon cycle here we examine the natural variations of the 30si 28si ratio in silicic acid si oh 4 and biogenic silica bsio2 in surface waters of the antarctic circumpolar current acc along 170 w the results provide direct evidence of biologically mediated fractionation of silicon isotopes with an enrichment factor of between 1 1 and 1 9 depending on the model employed comparison of the mass flux of bsio2 captured in sediment traps deployed in the study area with the silicon isotopic composition of that material establishes a direct linkage between diatom dynamics in surface waters and the isotopic signature of exported particles we calculated si oh 4 no3 utilization ratios from variations in silicon and nitrogen isotopic ratios in surface waters and sediment traps that agree well with direct observations of 4 1 in this region this work supports the use of variations in silicon isotopes in sedimentary opal as a proxy for relative si oh 4 utilization in surface waters

opal burial in the equatorial atlantic ocean over the last 30 ka implications for glacial interglacial changes in the ocean silicon cycle 1 the silicic acid leakage hypothesis salh suggests that during glacial periods excess silicic acid was transported from the southern ocean to lower latitudes which favored diatom production over coccolithophorid production and caused a drawdown of atmospheric co2 downcore records of 230th normalized opal fluxes and 231pa 230th ratios from seven equatorial atlantic cores were used to reconstruct diatom productivity over the past 30 ka where a is years and to test the salh downcore records of 231pa 230th ratios and opal fluxes are highly correlated suggesting that they constitute a production based record of opal flux opal flux records support the salh in that glacial opal burial exceeded holocene burial by 1 8 gt opal ka in the area 0 40 w and 5 n 5 s earlier results from the eastern equatorial pacific ocean showed the opposite trend with greater holocene than glacial opal burial but approximately the same magnitude of difference between glacial and interglacial opal burial we suggest four nonexclusive scenarios to explain the data from both basins 1 increased upwelling in the equatorial atlantic and el nino like conditions suppressing upwelling in the eastern equatorial pacific altered the overall nutrient supply to both basins 2 si leaked from the southern ocean because of fe fertilization but was prevented from upwelling in the equatorial pacific because of el nino like conditions during the lgm 3 si leaked from the southern ocean because diatom productivity was limited by increased sea ice extent and was again prevented from upwelling in the equatorial pacific or 4 changes in ocean circulation related to the decreased input of agulhas water to the glacial south atlantic provided excess dissolved si to the equatorial atlantic ocean a deglacial opal pulse is seen in both the atlantic and pacific oceans all four scenarios and the presence of the common deglacial opal pulse suggest a common driver in the southern ocean

changes in silicate utilisation and upwelling intensity off peru since the last glacial maximum insights from silicon and neodymium isotopes we combine the stable silicon isotope composition 30si of diatoms and the radiogenic neodymium isotope compositions end of past seawater extracted from the authigenic fraction of the sediments mn fe coatings of particles and benthic foraminifers as well as the radiogenic isotope compositions nd sr of the detrital material itself to reconstruct silicic acid utilisation water mass mixing and upwelling intensity from the same marine sediments in the peruvian upwelling region during the past 20 000 years additionally the sedimentary signals were compared to the water column isotope compositions along the peruvian shelf the dissolved end in the water column ranges from 5 7 to 0 6 the corresponding end signatures of the coatings and the benthic foraminifers of the surface sediments range from 4 5 to 1 8 and from 2 5 to 2 2 respectively the detrital end 87sr 86sr signatures range from 6 3 to 0 0 70508 0 71049 all phases show a trend from more radiogenic end values in the north towards less radiogenic values in the south broadly reflecting local weathering inputs and hinterland geology the end signatures of the coatings extracted from sediment core so147 106kl located in the present day centre of coastal upwelling near 12 s have been essentially constant 1 5 throughout the past 20 000 years while the detrital end 87sr 86sr varied between values of 0 7 0 70620 during the last glacial and 4 5 0 70849 during the late holocene reflecting changes in the origin of the sediment and current transport from a more northerly towards a more southerly source and from overall stronger to weaker upwelling the 30si signature of both total biogenic opal 30siopal and of hand picked diatoms 30sidiatom ranged from 0 3 last glacial to 1 4 late holocene confirming large variations in upwelling intensity driving silicic acid utilisation by diatoms our combined bsio2 mar 30siopal and detrital radiogenic isotope results demonstrate that the strongest el nino southern oscillation conditions off peru of the past 20 ka have prevailed during the past 5 ka

interplay of tectonics and neogene post collisional magmatism in the intracarpathian region abstract distribution of the neogene calc alkaline magmatism of the carpathian arc is directly related in space and time to the kinematics of the two major terranes of the intracarpathian area alcapa tisia getia along the south eastern border of the european plate in the west carpathians and adjacent areas the volcanic activity occurred between 20 11 ma with large volumes of both acidic and intermediate rocks generally distributed randomly sometimes transversally to the orogenic belt and as rare small occurrences along the flysch belt in the east carpathians the volcanic rocks are distributed along the northern margin of the zemplin block the north easternmost part of the alcapa and eastward along the front of the getic block at the contact with european plate between tokaj slanske vihorlat up to northern calimani mountains the magmatism occurred between 14 9 ma and along the calimani harghita chain between 9 0 2 ma the calc alkaline magmatic rocks of the apuseni mountains are located in the interior of the tisia block and occurred between 14 9 ma the generation of the calc alkaline magmatism is considered here as the result of complex interplay between plate roll back and lithospheric detachment tectonic processes and the break off of the subducted plate mostly in a post collisional setting 1 the magmatites of the western carpathians and the pannonian basin were generated in direct relation to subduction roll back processes over the downgoing slab during the period of lateral extrusion and back arc extension in this area characterized by maximum crustal shortening we can infer further delamination processes to explain the generation of magmas 2 the magmatic rocks from the northern sector of the east carpathians tokaj slanske vihorlat up to the northern calimani mountains resulted after subduction roll back processes and an almost simultaneous break off of the descending plate all along the arc segment during main clockwise rotation of the intracarpathian terranes 3 in the eastern sector of the east carpathians calimani up to harghita mountains the magmatic rocks were generated through partial melting of the subducted slab followed by gradual break off of the subducted plate along strike north to south 4 the apuseni mts magmatic activity resulted in transtensional tectonic regime by decompressional melting of lithospheric mantle during the translation and rotation of tisia getia block

paleo ocean chemistry records in marine opal implications for fluxes of trace elements cosmogenic nuclides 10be and 26al and biological productivity abstract here we provide evidence suggesting that marine diatom opal contains not only a high fidelity record of dissolved oceanic concentrations of cosmic ray produced radionuclides 10 be and 26 al but also a record of temporal variations in a large number of trace elements such as ti fe zn and mn this finding is derived from measurements in purified biogenic opal that can be separated from detrital materials using a newly developed technique based on surface charge characteristics initial results from a sediment core taken near the present day position of the antarctic polar front odp site 1093 show dramatic changes in the intrinsic concentrations of be al ti fe mn and zn in the opal assemblages during the past 140 kyr bp the results imply appreciable climatically controlled fluctuations in the level of bioreactive trace elements the time series of total be al ti fe and 10 be in the sediment core are all well correlated with each other and with dust records in the polar ice cores the observations suggest that a significant flux of these trace metals to oceans is contributed by the aeolian dust in this case presumably from the patagonia this observation also allows determination of fluxes of dust contributed 10 be to the antarctica ice sheets however our data show that the relationships among the various metals are not perfectly linear during periods of higher dissolved concentrations of trace elements indicated by fe and ti the relative concentrations of bioreactive elements be al mn and zn are decreased by contrast the fe zn and fe mn ratios decrease significantly during each transition from cold to warm periods the relative behavior could be consistent with any of the following processes i enhanced biological productivity due to greater supply of the bioreactive elements e g zn during cold periods ii increased biological and inorganic scavenging of particle active elements e g be and al during early interglacial periods iii differential uptake removal of the metals by the various diatom taxa whose relative productivity or growth rate changes with large scale climate in any case with one sedimentary phase and in single sedimentary sections we now have the potential to compare directly a proxy for aeolian input of micronutrients e g fe or ti with a proxy for production e g 26 al al ratios we expect that studies of the temporal records of trace elements and cosmogenic nuclides in contrasting regions of upwelling and productivity which exhibit different sensitivities to global climate fluctuations and micronutrient inputs would lead to a direct and comprehensive test of ideas such as the hypothesis of iron control of atmospheric carbon dioxide martin j h 1990 glacial interglacial co 2 change the iron hypothesis paleoceanography 5 1 13 our present data from a single site do not show that increases in dissolved fe concentrations per se were responsible for increased biological productivity however a much clearer picture of the effect of increased dust fluxes should emerge when we have data for trace elements and the cosmogenic nuclides 10 be and 26 al from various oceanic provinces

partial delamination of continental mantle lithosphere uplift related crust mantle decoupling volcanism and basin formation a new model for the pliocene quaternary evolution of the southern east carpathians romania abstract a geodynamic model is proposed for the mid miocene to quaternary evolution of the southern east carpathians in order to explain the relationships between shallow and deep geological phenomena that occurred synchronously during late collision tectonics in this area an active volcanic zone cross cuts since 2 my the suture between the overriding tisza dacia and subducting european continental plates mafic calc alkaline and alkaline magmas south harghita and persani volcanoes erupted contemporaneously these magmas were supplied by partial melting of the mantle lithosphere of the subducting and not of the overriding plate in an effort to decipher this geodynamically a typical setting of magma generation the spatial and temporal distribution of shallow and deep phenomena was successively examined in order to establish the degree of their interdependence our model indicates that intra mantle delamination of the subducting european plate is the principal cause of a succession of events it caused upwelling of the hot asthenosphere below a thinned continental lithosphere of the carpathians inducing the uplift of the lithosphere and its internal decoupling at the moho level by isostatic and mostly thermal effects during this uplift the crust deformed flexurally whilst the mantle deformed in a ductile way this triggered decompressional partial melting of the uppermost mantle lithosphere flexural deformation of the crust induced its fracturing allowing for the rapid ascent of magmas to the surface as well as reactivation of an older detachment horizon at the base of the carpathian nappe stack above which the brasov ciuc and gheorghieni hinterland basins formed by extension and gravity spreading the rapid subsidence of the focsani foreland basin is controlled by the load exerted on the lithosphere by the delaminated mantle slab that is still attached to it in this model crust mantle decoupling magma genesis and volcanism local near surface hinterland extension are consequences of uplift induced by asthenospheric upwelling triggered by intra mantle delamination this model enables to conceive that delamination induced decoupling began to be efficient 9 4 my ago at the northern end of the east carpathians when the mantle slab dipped westwards since then intra mantle delamination migrated laterally normal to the slab strike and follows the arcuate shape nw se sw of the carpathians nowadays whereas the mantle slab is still actively foundering below the vrancea seismic zone to the se of the most recent volcanic area south harghita persani a significant southwestward shift of the delamination process can be discerned

the elbe fault system in north central europe a basement controlled zone of crustal weakness abstract the elbe fault system efs is a wnw striking zone extending from the southeastern north sea to southwestern poland along the present southern margin of the north german basin and the northern margin of the sudetes mountains although details are still under debate geological and geophysical data reveal that upper crustal deformation along the elbe fault system has taken place repeatedly since late carboniferous times with changing kinematic activity in response to variation in the stress regime in late carboniferous to early permian times the elbe fault system was part of a post variscan wrench fault system and acted as the southern boundary fault during the formation of the permian basins along the trans european suture zone sensu geol mag 134 5 1997 585 the teisseyre tornquist zone ttz most probably provided the northern counterpart in a pull apart scenario at that time further strain localisation took place during late mesozoic transtension when local shear within the elbe fault system caused subsidence and basin formation along and parallel to the fault system the most intense deformation took place along the system during late cretaceous early cenozoic time when the elbe fault system responded to regional compression with up to 4 km of uplift and formation of internal flexural highs compressional deformation continued during early cenozoic time and actually may be ongoing the upper crust of the elbe fault system which itself reacted in a more or less ductile fashion is underlain by a lower crust characterised by low p wave velocities low densities and a weak rheology structural seismic and gravimetric data as well as rheology models support the assumption that a weak stress sensitive zone in the lower crust is the reason for the high mobility of the area and repeated strain localisation along the elbe fault system

modeling the modern marine δ30si distribution 1 the silicon isotopic composition of opal sediments can be used as a proxy for past si utilization and hence paleoproductivity for a fixed ocean circulation interpretation of this si utilization proxy is limited by our understanding of the present marine si isotope distribution observations show significant isotopic variations is silicic acid between deep water masses that are not captured by a previous global climate model gcm here simple box models of the global oceans for the si cycle are presented which can account for the observed 0 3 o difference between atlantic and pacific deep water 30 si values using typical opal export fluxes the 30 si gradient results from both a high 30 si of dissolved si overturning in the north atlantic and the dissolution of low 30 si of opal in the deep waters around the southern ocean that feed into the pacific

seismic crustal structure between the transylvanian basin and the black sea romania abstract in order to study the lithospheric structure in romania a 450 km long wnw ese trending seismic refraction project was carried out in august september 2001 it runs from the transylvanian basin across the east carpathian orogen and the vrancea seismic region to the foreland areas with the very deep neogene focsani basin and the north dobrogea orogen on the black sea a total of ten shots with charge sizes 300 1500 kg were recorded by over 700 geophones the data quality of the experiment was variable depending primarily on charge size but also on local geological conditions the data interpretation indicates a multi layered structure with variable thicknesses and velocities the sedimentary stack comprises up to 7 layers with seismic velocities of 2 0 5 9 km s it reaches a maximum thickness of about 22 km within the focsani basin area the sedimentary succession is composed of 1 the carpathian nappe pile 2 the post collisional neogene transylvanian basin which covers the local late cretaceous to paleogene tarnava basin 3 the neogene focsani basin in the foredeep area which covers autochthonous mesozoic and palaeozoic sedimentary rocks as well as a probably permo triassic graben structure of the moesian platform and 4 the palaeozoic and mesozoic rocks of the north dobrogea orogen the underlying crystalline crust shows considerable thickness variations in total as well as in its individual subdivisions which correlate well with the tisza dacia moesian and north dobrogea crustal blocks the lateral velocity structure of these blocks along the seismic line remains constant with about 6 0 km s along the basement top and 7 0 km s above the moho the tisza dacia block is about 33 to 37 km thick and shows low velocity zones in its uppermost 15 km which are presumably due to basement thrusts imbricated with sedimentary successions related to the carpathian orogen the crystalline crust of moesia does not exceed 25 km and is covered by up to 22 km of sedimentary rocks the north dobrogea crust reaches a thickness of about 44 km and is probably composed of thick eastern european crust overthrusted by a thin 1 2 km thick wedge of the north dobrogea orogen

anomalously deep mantle transition zone below central europe evidence of lithospheric instability 1 the depths of the 410 and 660 km phase transitions provide critical information on the thermal state of the mantle transition zone mtz and by implication on the circulation of the upper mantle we analyze converted seismic waves to produce a high resolution image of these discontinuities beneath the pannonian basin of central europe models to explain the extension of the basin in the middle miocene involve subduction roll back and gravitational instability of an over thickened lithosphere we find that cold dense material appears to have accumulated in the mtz consistent with the idea of supply from several subduction episodes or upper mantle overturn variation in depth of the 660 km discontinuity by as much as 40 km suggests that cold lithospheric mantle is ponding on top of this phase transition where the phase transition is deepest eventual transfer of this material into the lower mantle may be expected to develop