the origin and age of the metamorphic sole from the rogozna mts western vardar belt new evidence for the one ocean model for the balkan ophiolites abstract this study brings new geochronological and petrochemical data from the metamorphic sole beneath the rogozna mts western vardar ophiolite belt the rogozna metamorphic sole is located at the base of a serpentinite nappe and consists of amphibolites and talc chlorite schists the rogozna amphibolites are medium to fine grained rocks with nematoblastic texture and pronounced foliation they consist of green amphibole 70 vol with variable silica contents 6 4 to 7 8 si apfu as well as mg molmg mg fe tot 0 53 to 0 77 and variably albitized plagioclase 30 vol ab 24 ab 98 amphibolites are overprinted by a retrograde assemblage containing actinolite epidote clinoclore sericite chlorite and magnetite the amphibolites formed due to metamorphism of two basaltic suites subalkaline tholeiitic and alkaline subalkaline tholeiitic amphibolites possess low zr nb y th hf tio 2 and p 2 o 5 values and a lree depleted pattern typical for the n morb normal mid ocean ridge basalt to bab back arc basalt origin alkaline amphibolites show elevated concentrations of zr nb y th hf tio 2 and p 2 o 5 with a lree enriched pattern typically displayed by oib ocean island basalt amphibolites were crystallized during intra oceanic thrusting at temperatures between 685 c and 765 c and at a depth of 12 17 km 40 ar 39 ar cooling ages of amphibole ranging from 165 to 170 ma slightly postdate the sole formation talc chlorite schists are related to retrograde greenschist facies metamorphism they consist of fe rich talc and cr rich chlorite peninite diabantite pseudomorphs after amphibole and morb type cr al spinel surrounded by al and mg poor ferrit chromite the occurrence of ferrit chromite is related to earlier amphibolite facies metamorphism chlorite pseudomorphs after amphibole were formed at 300 410 c this study suggests that there is no essential difference in the emplacement age of the dinaric and west vardar ophiolite belts supporting the interpretation involving a single mesozoic ocean in the balkan sector

mid to late holocene hydrological and sea level change reconstructions from la mancha coastal lagoon veracruz mexico abstract we studied a 13 meter sediment core collected from la mancha coastal lagoon veracruz mexico to determine paleoenvironmental variations linked to the mid to late holocene sea level rise we examined modern and fossil benthic foraminiferal assemblages isotopic values in tests of ammonia tepida 18o foram and 13c foram 13c in organic matter 13c org and sediment elemental ratios fe ca ca ti and k rb to reconstruct salinity variations coastal processes and the morphologic evolution of a partially closed coastal lagoon we identified four main periods of environmental change 1 from 7800 to 6500 cal yr bp the core site was an open lagoon with higher oceanic influence than today through the presence of a southern mouth as evidenced by the euryhaline assemblage ammonia quinqueloculina bolivina nonionella low 18o foram and high 13c values on foraminifera shells indicate greater inputs of seawater and 13c org values reflect a lagoon environment elemental ratios of lower fe ca moderate ca ti and higher k rb suggest increased coastal weathering and reduced detrital deposits than today 2 from 6500 to 4600 cal yr bp the lagoon experienced the progressive closure of the southern mouth to the point that sedimentation restricted seawater entrance as evidenced by variable 13c org values a lowering trend in 18o foram and 13c foram values low fe ca higher ca ti but moderate k rb values at this time benthic foraminifera were dominated by the opportunistic ammonia elphidium polyhaline assemblage 3 from 4600 to 1400 cal yr bp the northern mouth was the only source of seawater to the lagoon establishing the optimal environment for calcareous foraminifera of the polyhaline assemblage ammonia elphidium lowest 13c org values indicate greater organic input by terrestrial plants 4 at 1400 cal yr bp modern conditions of a partially closed lagoon were established while increased terrigenous inputs and freshwater runoff favored the growth of agglutinated foraminifera species at millennial time scales in addition to the sea level rise effects the lagoon evolution fits in the paleoclimatic context that links insolation the latitudinal change of itcz ocean currents longshore drift and moisture transport as driving factors of morphological change in the western coast of the gulf of mexico

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

new radiolarian biostratigraphic age constraints on middle triassic basalts and radiolarites from the inner hellenides northern pindos and othris mountains northern greece and their implications for the geodynamic evolution of the early mesozoic neotethys the avdella melange in the northern pindos mountains and its equivalent formation the loggitsion unit in the othris mountains expose early mesozoic mid late triassic oceanic fragments beneath the western greek ophiolite belt of the inner hellenides northern greece the melange consists of locally interfingering blocks and slices of ribbon radiolarite radiolarian chert and pillow basalt and is usually overthrust by jurassic ophiolites new middle and upper triassic radiolarian biostratigraphic data are presented from radiolarites and basalt radiolarite sequences within melange blocks pillow basalts associated with the radiolarites provide clues to the opening of the neotethyan ocean basin the radiolarians indicate a middle triassic age latest anisian probably early illyrian which is documented for the first time in the northern pindos mountains the new radiolarian biostratigraphic data suggest that rift type basalt volcanism already began in pre ladinian time late scythian anisian these basalts were then overlain by upper anisian to carnian norian radiolarites

tectonostratigraphic models of the alpine terranes and subduction history of the hellenides abstract the tectonostratigraphy of the hellenic terranes is related to their paleogeodynamic and paleogeographic evolution which comprises three major stages i continental rifting in the northern margin of gondwana characterised by volcanosedimentary complexes of late paleozoic triassic ii continental drifting and contemporaneous oceanic opening of tethyan basins in between the continental terranes during triassic paleogene with shallow water carbonate platforms on the continental terranes and ophiolite suites interlayered with pelagic sediments within the tethyan basins iii accretion of the tectonostratigraphic terranes with docking along the active european margin characterised by flysch melange sedimentation along the trenches from early jurassic to neogene two tectonostratigraphic models can be distinguished one for the continental terranes carbonate platforms and another for the oceanic basins the duration of each geodynamic stage for each terrane is obtained from the chronology of the tectonostratigraphic facies change the general trend is younger ages observed in the southern terranes and older ages towards the northern terranes the two alternative tectonostratigraphic models are applied in the two groups of terranes and the chronology of the geodynamic paleogeographic stages is estimated the hellenic subducted slab as shown in the seismic tomographic images is correlated to the terrane paleogeography using the estimated widths and the average subduction rates the upper 1700 km of the slab correspond to the three southern more external terranes whereas the remainingpart of the slab may represent the other more internal terranes a palinspastic model of the hellenides is presented taking into account the chronology of each stage for every terrane obduction of ophiolites over the southern platforms is observed in all four oceanic basins blueschist exhumation formation of core complexes and tectonic windows through extensional detachments occur after micro collision of continental terranes platforms and their isostatic uplift within the upper plate after their detachment from the subducting slab

flow structure and transport in the yucatan channel 1 the direct ocean current observations across the yucatan channel collected during the canek program allow the best description to date of the exchange between the caribbean sea and the gulf of mexico a net transport of 23 8 1 sv 1 sv 106m3s 1 95 confidence interval flowed through the yucatan channel from the caribbean sea into the gulf of mexico during the period between september 1999 and june 2000 this is about 20 percent less than the 30 sv accepted as the nominal transport of the florida current and less also than the 28 sv assumed for yucatan in closing the transport budgets for caribbean passages the discrepancy may be an imbalance due to fluctuations in the transports through other passages of the system especially the old bahama and northwest providence channels which remain poorly known our data corroborate the principal features of the flow through the yucatan channel the northerly surface yucatan current and its southerly under current off mexico and the southerly surface cuban counter current near cuba but previously unobserved mean currents are found to exist at depth especially on the eastern side of the channel fluctuations seen in the deep flows are related to volume anomalies over the gulf of mexico a transport through the yucatan channel smaller than previously thought has significant implications for the dynamics of the gulf of mexico and its modeling since this transport is the principal forcing of its circulation the circulation budgets in the western subtropical atlantic should be revised considering these new results

geochronology geochemistry and isotope tracing of the oligocene magmatism of the buchim damjan borov dol ore district implications for timing duration and source of the magmatism abstract timing source and magmatic evolution of the intrusions in the buchim damjan borov dol ore district of the former yugoslav republic of macedonia f y r o m have been studied they intrude the circum rhodope unit close to the contact with the vardar zone and are a part of the late eocene oligocene macedonian rhodope north aegean belt the magmatism at buchim damjan borov dol occurred between 24 04 0 77 and 24 51 0 89 ma as indicated by chemical annealing ca la icp ms zircon dating major element trace and rare earth element analyses have been performed on the various intrusive rocks all ore bearing magmas were classified as trachyandesitic except the youngest intrusion which is not associated with mineralization the black hill locality 24 04 0 77 ma shows a trachytic composition the distribution of the trace elements enrichment of large ion lithophile elements lile and depletion in high field strength elements hfse indicates subduction related magmatism most of the magmas follow a calc alkaline fractionation trend with shoshonitic affinities additionally sr y 10 to 90 and la yb values show some similarities to adakite like magmas sr and nd isotope ratios sr i 0 70658 to 0 70740 and nd i 0 512425 0 512497 show that the magmatic products were slightly contaminated by continental crust material e g the variscan cadomian basement in the late eocene oligocene belt the magmatism between 29 and 35 ma is dominated by crustal melting with an increase in the mantle contribution between 20 and 27 ma we suggest the following scenario for the magmatic history of the buchim damjan borov dol ore district a slab rollback of an oceanic slab located further to the sw which led to extensional and compressional features in upper levels of the continental crust in the middle to upper crust three consecutive crystallization stages occurred at variable depths as indicated by amphibole zonation mixing of newly formed crust with mantle like affinities and continental crust material in variable degrees during the ascent of the magma can explain all geochemical characteristics the magma crystallized as dykes or stocks near the earth s surface 1 km after its final emplacement and contemporaneous hydrothermal activity led to different mineralization styles depending on the lithology of the host rocks

petrology and evolution of the hercynian pieria granitoid complex thessaly greece paleogeographic and geodynamic implications abstract the upper carboniferous pieria granitoid complex pgc and associated pelagonian basement units are remnants of a hercynian orogenic belt incorporated into the alpine nappe systems of the central hellenides the granitoid rocks range from tonalite to granite and are mildly peraluminous the lack of significant negative eu and sr anomalies suggests insignificant high level crystal fractionation involving plagioclase meta diorite sheets that cut and are deformed with the granitoids are characterized by metamorphic fabrics their trace element signatures are similar to enriched morb and the high ba la is typical of subduction related mafic rocks they are interpreted as representing predominantly asthenosphere derived melts intruded into the granitoids the bimodal mafic felsic association observed in the pgc is also found in other plutonic complexes throughout the flambouron unit of the pelagonian terrane geochemically and isotopically these plutons resemble hercynian plutons of western europe interpreted to result from melting of lower crustal orthogneisses the flambouron unit plutons were situated paleogeographically on the northern margin of gondwana mantle enrichment resulted from short lived subduction during devonian to early carboniferous collision of gondwana and laurasia whereas plutonism occurred during regional extension as gondwana rotated clockwise with respect to laurasia in the late carboniferous

geochemistry of mylonitic gneisses from the cycladic basement unit paros and serifos aegean sea implications for protoliths of the high grade gneisses the nature of the protolith s of high grade gneisses from the aegean cycladic basement unit of the islands of paros and serifos is investigated using whole rock geochemistry and sr nd o isotopes in order to better understand their origin and to compare with possible equivalents from the southern aegean region on paros the basement unit consists of heterogeneous mylonitized upper amphibolite grade paragneisses and associated migmatitic rocks whereas on serifos it consists of a mylonitized felsic gneiss intercalated with layers and lenses of s type leucogranites and minor mafic metavolcanics new nd sr and o isotope data suggest a predominantly crustal derived source in the gneiss protolith from both islands high initial 87sr 86sr ratios 7052 to 0 711 calculated at 300 ma negative initial end 2 8 to 7 7 values for bulk rock gneiss samples and high 18o values of quartz separates 10 to 12 7 major and trace element variations corroborate that chemical differentiation within the nw paros gneiss subunit results from progressive migmatitization peraluminous gneisses from eastern paros share clear similarities with metapelitic gneisses from the naxos gneiss dome in terms of their trace element patterns end 300 and o isotope characteristics the mineral assemblage the fine grain size due to intense mylonitization and the metaluminous affinity of the south serifos grey quartzofeldpathic gneiss do not allow for an unambiguous interpretation for these undated rocks however a combination of geochemical parameters and tectonic discrimination diagrams indicates an immature siliciclastic greywacke protolith from a continental island arc setting sr nd isotopic systematics indicates an increasing lower crustal component in gneisses from nw paros which is closer to the migmatitic core of the paros dome the overall isotopic trend of the gneissic cycladic basement unit on paros is spatially correlated with that of the naxos gneiss dome

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

zircon u pb o and hf isotopic constraints on mesozoic magmatism in the cyclades aegean sea greece compared to the well documented cenozoic magmatic and metamorphic rocks of the cyclades aegean sea greece the geodynamic context of older meta igneous rocks occurring in the marble schist sequences and melanges of the cycladic blueschist unit is as yet not fully understood here we report o hf isotopic compositions of zircons ranging in age from ca 320 ma to ca 80 ma from metamorphic rocks exposed on the islands of andros ios sifnos and syros with special emphasis on triassic source rocks ion microprobe shrimp ii single spot oxygen isotope analysis of pre cretaceous zircons from various felsic gneisses and meta gabbros representing both the marble schist sequences and the melanges of the study area yielded a large range in 18o values varying from 2 7 to 10 1 vsmow with one outlier at 0 4 initial ehf values 12 5 to 15 7 suggest diverse sources for melts formed between late carboniferous to late cretaceous time that record derivation from mantle and reworked older continental crust in particular variable 18o and ehf t values for triassic igneous zircons suggest that magmatism of this age is more likely rift than subduction related the significant crustal component in 160 ma meta gabbros from andros implies that some jurassic gabbroic rocks of the hellenides are not part of ssz type supra subduction zone ophiolites that are common elsewhere along the margin of the pelagonian zone

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

disentangling abrupt deglacial hydrological changes in northern south america insolation versus oceanic forcing paleoenvironmental studies and climate models demonstrate that fl uvial runoff and moisture availability in the caribbean hinterland react very sensitively to climatic variations late pleistocene and holocene climate records document pronounced dry and wet periods over tropical south america mainly caused by shifts of the intertropical convergence zone itcz however forcing mechanisms for changes in the itcz position remain controversial here we present high resolution foraminiferal ba ca and 18oseawater records from a core located within the orinoco river outfl ow documenting abrupt hydrological changes in the orinoco catchment area during the deglacial and holocene our data obtained from the surface dwelling foraminifera globigerinoides ruber pink show an abrupt increase in ba ca ratios in the early holocene starting 600 yr after the end of the younger dryas yd cold interval at ca 10 8 ka and suggesting a massive reorganization of moisture sources in northern south america in contrast the salinity dependent 18oseawater from the same samples shows a gradual decrease starting at the end of the yd the offset of our ba ca peak excludes meltwater release in conjunction with the northern andean glacier retreat well before the end of the yd as a forcing mechanism we suggest that the ba ca record documents an abrupt increase in ba rich waters of a northern andean source caused by the insolation driven shift of the itcz and or enhanced monsoon activity

therma volvi gomati complex of the serbo macedonian massif northern greece a middle triassic continental margin ophiolite of neotethyan origin we present field chemical and u pb age data for metamafic ultramafic bodies of the triassic rift related therma volvi gomati tvg complex of the serbo macedonian massif smm in the northern aegean region the tvg rocks record igneous textures overprinted by alpine metamorphism and deformation the high ti volvi body was transformed into amphibolites which also rim the low ti gomati and nea roda bodies the compositions are compatible with normal n and enriched e mid ocean ridge basalt morb and weak ocean island basalt oib signatures of the high ti rocks whereas the low ti rocks are depleted with respect to morb suggesting melt extraction from a mantle source u pb geochronology reveals triassic crystallization of the volvi body at 240 ma ordovician to carboniferous xenocrystic zircons were found in the stratoni body of the tvg complex which were sampled from the smm basement the triassic arnea rift related metagranite intrudes the volvi body comparison of the compositions of the volvi body and the arnea metagranite of the smm with triassic metagranite of the rhodope massif rm supports the presence of a regional bimodal rift suite the location of the tvg complex at the smm rm margin of eurasia confirms its origin as a middle triassic rift suite and its nature as a continental margin ophiolite representing an ocean continent transition of the propagating neotethys supplementary material whole rock chemical analyses and u pb geochronology analytical results data tables are available at https doi org 10 6084 m9 figshare c 4087022 thematic collection this article is part of the tethyan ophiolites and tethyan seaways collection9 available at https www lyellcollection org cc tethyan ophiolites and tethyan seaways

triassic mid ocean ridge basalts from the argolis peninsula greece new constraints for the early oceanization phases of the neo tethyan pindos basin

upper water mass variability in the anegada jungfern passage ne caribbean during the last 11 100 cal yr using qualitative and quantitative analyses of planktonic foraminifera assemblages 18o measurements mg ca temperature relationship globigerinoides ruber pink sensu stricto data and sea surface temperatures ssts derived from artificial neural network ann transfer functions a reconstruction was made of upper water mass variability in the anegada jungfern passage ajp northeastern caribbean sea over the last c 11 100 years our record is based on the study of two marine sediment cores and reveals three main circulation stages during the holocene in the early holocene 11 100 6300 cal yr bp ann based sst estimations indicate moderately cooler than present winter condition in the ne caribbean with ssts of 25 5 c these conditions presumably reflect advection of well mixed upper water masses from the guyana upwelling area associated with a strong atlantic meridional overturning circulation amoc and enhanced trade wind activity linked to a more northerly location of the inter tropical convergence zone itcz between 6300 and 3700 cal yr bp a relative warming of winter ssts 26 5 c was probably related to a weaker circulation and upper water mass mixing because of less intense trade wind activity as the itcz moved southwards from 3700 cal yr bp to the present the region was characterised by small seasonal sst variations and generally stable winter and summer ssts the data suggest a minor shift in the sub surface inflow pattern during the last 2000 years possibly related to changes in northern hemisphere large scale atmospheric circulation also observed at higher latitude the ann based temperature pattern is supported by fluctuations in the mg ca derived temperature record although temperature maxima derived from the mg ca ratio appear anomalously high on a holocene timescale we conclude that the northeastern caribbean sst and circulation regime have been mainly dependent on the position of the itcz which in turn is controlled by changes in hemispheric solar insolation

overview of tectonic settings related to the rifting and opening of mesozoic ocean basins in the eastern tethys oman himalayas and eastern mediterranean regions

first u pb shrimp zircon and 40ar 39ar ages of metarhyolites from the afyon bolkardag zone sw turkey implications for the rifting and closure of the neo tethys abstract the afyon bolkardag zone abz is one of the most important metamorphic zones in turkey this zone consists of metasedimentary and metavolcanic rocks which have undergone regional greenschist facies metamorphism the metavolcanic rocks are dominated by rhyolite dacite and trachyandesite in the ilgin konya area the low grade metavolcanics were originally rhyolitic lavas and tuffs we present new precise sensitive high resolution ion microprobe shrimp 206 pb 238 u age analyses of zircons and 40 ar 39 ar age data of phengite from metarhyolites that enable a more precise reconstruction of the abz shrimp analyses of euhedral or sub euhedral magmatic zircons from two metarhyolite samples yield weighted means 230 2 ma and 229 2 ma these ages are interpreted as formation age of rhyolitic volcanics implying they were formed in the late triassic time carnian we suggest that these upper triassic magmatic rocks were formed in an extensional tectonic setting on the northern active margin of gondwana which led to the development of the northern branch of the neo tethys 40 ar 39 ar dating of two phengite samples from metarhyolites gave plateau ages of between 63 7 0 1 ma and 62 6 0 1 ma these dates are interpreted as the metamorphic age of these volcanic rocks and as the age of metamorphism that affected the abz consequently these earliest tertiary ages also constrain the timing of the closure of the neo tethys

evidence of variscan and alpine tectonics in the structural and thermochronological record of the central serbo macedonian massif south eastern serbia the serbo macedonian massif smm represents a composite crystalline belt within the eastern european alpine orogen outcropping from the pannonian basin in the north to the aegean sea in the south the central parts of this massif south eastern serbia consist of the medium to high grade lower complex and the low grade vlasina unit outcrop and micro scale ductile structures in this area document three major stages of ductile deformation the earliest stage d1 is related to isoclinal folding commonly preserved as up to decimetre scale quartz feldspar rootless fold hinges d2 is associated with general south eastward tectonic transport and refolding of earlier structures into recumbent metre to kilometre scale tight to isoclinal folds stages d1 and d2 could not be temporally separated and probably took place in close sequence the age of these two ductile deformation stages was constrained to the variscan orogeny based on indirect geological evidence i e ca 408 ca 328 during this period the smm was involved in a transpressional amalgamation of the western and eastern parts of the galatian super terrane and subsequent collision with laurussia outcrop scale evidence of the final stage d3 is limited to spaced and crenulation cleavage which are probably related to formation of large scale open upright folds as reported previously 40ar 39ar thermochronology was applied on hornblende muscovite and biotite samples in order to constrain the age of tectonothermal events and activity along major shear zones these 40ar 39ar data reveal three major cooling episodes affecting the central smm cooling below greenschist facies conditions in the western part of the vlasina unit took place in a post orogenic setting extensional or transtensional in the early permian 284 1 ma the age of activity along the top to the west shear zone formed within the orthogneiss in the bo ica area of the vlasina unit was constrained to middle triassic 246 1 ma this age coincides with widespread extension related to the opening of the mesozoic tethys the greenschist facies retrogression in the lower complex probably occurred in the early jurassic 195 1 ma and it was related to the thermal processes in the overriding plate above the subducting slab of the mesozoic tethys ocean

evolution of boninites and island arc tholeiites in the pindos ophiolite greece whole rock geochemical and sm nd isotope data are presented for a representative suite of crustal rocks from the pindos ophiolite in order to resolve the origin of the geochemical signature of the boninites comparison is made with triassic morb from the avdella melange and with other ophiolitic rocks of northwestern greece hydrothermal alteration results in large scatter in sr and k and some variability in ba th and u the pindos boninites contain high zr and hf with respect to ree characteristic of many boninites pb la sm and nb decrease with decreasing tio 2 from morb to iat but then increase in the boninites nd isotopic values expressed as e nd decrease systematically with decreasing tio 2 from 7 8 in iat to 0 6 3 0 in boninites as mantle wedge harzburgite became increasingly depleted another magma source contributed significant amounts of pb ree and probably nb the pb and other large ion lithophile elements may have been transported in aqueous solutions from the subducting slab but the ree and nb imply an ocean island basalt oib type source within the mantle wedge this oib source is a consequence of mantle plume activity during late triassic rifting

ultramafic lavas and high mg basaltic dykes from the othris ophiolite complex greece we evaluate the petrography and geochemistry of an unusual suite of subduction related phanerozoic high mgo rocks from the othris ophiolite complex in greece some of which have previously been described as komatiitic lavas in particular we study ultramafic olivine phyric lavas from the agrilia area and high mg basaltic dykes from the pournari area we seek to define primary magmatic mgo contents and initial liquidus temperatures as well as the differentiation sequence and cooling rates experienced by the lavas and dykes one of our goals is to relate the othris case to known komatiite and boninite occurrences and to address whether othris documents an important new constraint on the temporal evolution of ambient mantle temperature plume related magmatism and subduction of oceanic lithosphere we conclude that despite whole rock mgo contents of 31 33 wt the olivine phyric lavas at agrilia had an upper limit liquid mgo content of 17 wt and are therefore picrites not komatiites the agrilia lavas contain the unusual ti rich pyroxenoid rhonite we discuss the significance of this occurrence in the case of the pournari high mg dykes the distinctive dendritic or plumose clinopyroxene texture though it resembles in some ways the classic spinifex texture of komatiites is simply evidence of rapid cooling at the dyke margin and not evidence of extraordinarily high liquidus temperatures we correlate the dendritic texture with disequilibrium mineral chemistry in clinopyroxene to constrain the cooling rate of the dyke margins

climatic solar oceanic and geomagnetic influences on late glacial and holocene atmospheric 14c 12c change late glacial and holocene 14c12c ratios of atmospheric co2 vary in magnitude from a few per mil for annual decadal pertubations to more than 10 for events lasting millennia a data set illuminating 10 to 104 yr variability refines our understanding of oceanic climatic versus geomagnetic or solar forcing of atmospheric 14c12c ratios most of the variance in the holocene atmospheric 14c12c record can be attributed to the geomagnetic millennia time scale and solar century time scale influence on the flux of primary cosmic rays entering the atmosphere attributing the observed atmospheric 14c12c changes to climate alone leads to ocean circulation and or global wind speed changes incompatible with proxy records climate ocean related 14c redistribution between carbon reservoirs while evidently playing a minor role during the holocene may have perturbed atmospheric 14c12c ratios measurably during the late glacial younger dryas event first order corrections to the radiocarbon time scale 12 000 30 000 14c yr b p are calculated from adjusted lake sediment and tree ring records and from geomagnetically defined model 14c histories paleosunspot numbers 100 9700 cal yr b p are derived from the relationship of model 14c production rates to sunspot observations the spectral interpretation of the 14c12c atmospheric record favors higher than average solar activity levels for the next century minimal evidence was found for a sun weather relationship

thermochronometric constraints on the tectonic evolution of the serifos detachment aegean sea greece we constrain the timing and kinematics of the serifos detachment in the southwestern cyclades greece using low temperature thermochronometry fission track dating shows that the serifos detachment was active between 13 and 6 ma and that the serifos granodiorite in its footwall intruded at or before 12 11 ma into the extensional shear zone and initially cooled very rapidly at rates 180 c per million year the mylonite zone at the top of the granodiorite and mylonitic structures in its country rocks record a consistent top ssw shear sense in the ductile crust in the brittle regime top nne shear sense indicators occur as well conjugate top ssw and top nne high angle normal faults are the youngest deformational features and cut across the detachment age distance relationships for the fission track data display a relatively flat pattern we discuss a model advocating initial top ssw movement on the serifos detachment before and during emplacement of the granodiorite updoming of the detachment during exhumation and cooling caused subsequent bivergent extension in the brittle crust

petrogenesis and time progressive evolution of the cenozoic continental volcanism in the biga peninsula nw anatolia turkey abstract the post collisional cenozoic magmatic activity in the biga peninsula nw anatolia started in the middle eocene 45 3 0 9 ma and lasted continuously until the late miocene 8 32 0 19 ma with minor punctuations producing widespread volcanoplutonic complexes these magmatic suites are characterized by calc alkaline high k calc alkaline shoshonitic mildly alkaline and alkaline series the middle eocene to middle miocene lavas have high lile lree lile hfse and 87sr 86sr i 0 7046 0 7087 and low nd i 1 2 to 6 4 values by contrast the late miocene lavas have the lowest 87sr 86sr i 0 7030 0 7033 and the highest nd i 2 6 to 6 7 values geochemical features of these rocks indicate two episodes of enrichment processes during the evolution of the eocene early miocene volcanism in the biga peninsula the first stage source enrichment metasomatism occurred within the continental lithospheric mantle as a result of the previous subduction event s and produced a heterogeneously enriched source the second stage crustal contamination resulted from interaction between the metasomatized mantle derived melts and those magmas derived from the sakarya crustal basement during their ascent to the surface slab breakoff induced asthenospheric upwelling caused the melting of metasomatized mantle lithosphere beneath the sakarya continent and produced the middle eocene calc alkaline lavas geochemical isotopic and age relationships suggest increasing amounts of crustal contamination and a decreasing subduction signature during the evolution of magmas from the eocene through the early miocene crustal input was peaked during the early miocene volcanism coinciding with the exhumation and rapid uplift of the kazdag metamorphic massif asthenospheric upwelling beneath the kazdag core complex contributed to the generation of hybrid magmas formed from mixing of mantle and crustal melts during this stage the middle miocene 15 2 ma mildly alkaline rocks show less pronounced enrichment in lile and lree and display intermediate major and trace element compositions between the early miocene and late miocene lavas the cenozoic volcanism in biga peninsula waned briefly during 15 11 ma and was subsequently rejuvenated late miocene 11 0 0 4 8 32 0 19 ma producing mainly oib type alkaline lavas advanced extensional tectonics throughout nw anatolia in the late miocene led to upwelling of the asthenospheric mantle and its decompressional melting that collectively resulted in the eruption of short lived episodes of mainly oib type alkaline lavas this tectonomagmatic evolution of the cenozoic continental volcanism in western anatolia presents a well documented case study of an idealized post collisional magmatism in most orogenic belts around the world

from obduction to continental collision new data from central greece the aim of this paper is to contribute to deciphering the evolutionary history of the hellenides by the study of a large sector of the chain located between the front of the ophiolitic units and the external zones classically attributed to the continental margin of adria in particular the tectonic units located in boeotia a key area located in central greece at the boundary between the internal and external hellenides were studied from structural stratigraphic and biostratigraphic points of view addressing the main debated aspects concerning the origin of the ophiolite nappe s the tectonic evolution of the hellenic orogen was revised with a particular emphasis on the period between obduction and continental collision new findings were compared with consolidated data concerning the main metamorphic events recorded in the more internal hellenides geochemistry and age of the ophiolites and main stratigraphic constraints obtained in other sectors of the belt finally a new reconstruction of the tectonic evolution of this area was introduced and in the context of the dispute concerning the origin of the ophiolitic belts as a possible record of multiple oceanic basins we put forward for consideration a single ocean tectonic model spanning from triassic up to tertiary times and valid for the whole hellenic albanian sector

the nature of triassic extension related magmatism in greece evidence from nd and pb isotope geochemistry the widespread triassic volcanic rocks of greece dismembered during the hellenide orogeny are used to interpret the nature of triassic rifting four assemblages of volcanic rocks are distinguished on geochemical criteria 1 a predominant subalkaline basalt andesite dacite series with a high proportion of pyroclastic rocks 2 minor shoshonites 3 alkali basalt and 4 morb the stratigraphic and palaeogeographic distribution of these rock types is synthesized new pb and nd isotopic data are used to discriminate between hypotheses suggesting that either subduction or extension was responsible for the triassic volcanism in the subalkaline basalt assemblage e nd is negative with depleted mantle model ages 1 5 ga pb isotopic compositions are mostly close to the very distinctive compositional field of cenozoic extensional rocks of the aegean area with very high 207 pb 204 pb for relatively low 206 pb 204 pb ratios these isotopic data confirm interpretations based on trace elements that subalkaline basalts were predominantly derived from melt depleted peridotite in the sub continental lithospheric mantle as a result of extension small areas of enriched hydrous mantle partially melted to yield shoshonitic magmas nd and pb isotopic compositions of the alkali basalts are quite different from those in other rock types and suggest a himu mantle source component derived from a small plume which also influenced morb compositions distribution of these various rock types is used to constrain palaeogeographic reconstruction of triassic micro continental blocks

century scale movement of the atlantic intertropical convergence zone linked to solar variability 1 the abundance of the planktic foraminifer globigerinoides sacculifer in gulf of mexico gom sediments is a proxy for the influx of caribbean surface waters the loop current into the gom penetration of the loop current into the gom is related to the position of the intertropical convergence zone itcz northward migration of the itcz results in increased incursion of the loop current into the gom southward migration of the itcz results in decreased penetration of the loop current into the gom abundance variations of g sacculifer in a sediment core from the pigmy basin in the gom show distinct century scale cyclicity over the last 5 000 years the periodicity of these abundance variations is similar to the century scale periodicity observed in proxy records of solar variability which suggests that the average position of the itcz and thus holocene century scale variability in the caribbean gom region is linked to solar variability

regional similarities in lead isotopes and trace elements in galena of the cyclades mineral district greece with implications for the underlying basement abstract polymetallic ore deposits of the aegean sea greece are temporally and spatially associated with the emplacement of miocene granitoids and pliocene to quaternary volcanic units along the active volcanic arc and occur adjacent to the crustal scale detachment systems a variety of mineral deposits e g carbonate replacement skarn porphyry vein type and low to high sulfidation epithermal deposits formed during different stages of back arc evolution and can be found in the footwall and hanging wall of the major detachment systems and all tectono stratigraphic units new galena pb isotope data collected by laser ablation inductively coupled plasma mass spectrometry la icp ms analysis exhibit a range of isotopic ratios 206pb 204pb 18 68 18 91 207pb 204pb 15 67 15 75 and 208pb 204pb 38 83 39 18 with a resolvable geographic pattern together with compiled pb isotope data of cycladic galena large scale regional similarities in the pb isotope signatures are recognized suggesting distinct sources of lead in the underlying basement base metal rich deposits in the west cyclades have a common lead source with a more radiogenic signature whereas lead in the deposits in the north central cyclades was derived from a less radiogenic source similarities between the pb isotopic signature of galena and regional host rocks suggest that the pre alpine cycladic basement was the main source of lead for the deposits in the north and central and the metamorphosed volcano sedimentary lower cycladic blueschist nappe was the source of lead for the deposits in the west moreover there is a close spatial relationship of the 206pb 204pb 18 84 line and trace of the proposed trans cycladic thrust regional trends were also observed in the new la icp ms trace element analysis in galena galena in carbonate replacement and skarn deposits in the west is enriched in base metals and silver whereas galena in vein type deposits in the north and low to high sulfidation epithermal deposits along the active volcanic arc is enriched in gold tellurides and selenium combined trace element and isotopic data of galena indicate distinct metal sources in the cyclades heterogenous rock assemblages of mixed provenance and age account for the differences in lead isotopes whereas the base metals and silver are ultimately sourced from the basement the precious metals might be derived from the metasomatized lithospheric mantle

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

geodynamic evolution of ophiolites from albania and greece dinaric hellenic belt one two or more oceanic basins all the geological constraints for an exhaustive reconstruction of the triassic to tertiary tectonic history of the southern dinaric hellenic belt can be found in albania and greece this article aims to schematically reconstruct this long tectonic evolution primarily based on a detailed analysis of the tectonic setting the stratigraphy the geochemistry and the age of the ophiolites in contrast to what was previously reported in the literature we propose a new subdivision on a regional scale of the ophiolite complexes cropping out in albania and greece this new subdivision includes six types of ophiolite occurrences each corresponding to different tectonic units derived from a single obducted sheet these units are represented by 1 sub ophiolite melange 2 triassic ocean floor ophiolites 3 metamorphic soles 4 jurassic fore arc ophiolites 5 jurassic intra oceanic arc ophiolites and 6 jurassic back arc basin ophiolites the overall features of these ophiolites are coherent with the existence of a single though composite oceanic basin located east of the adria pelagonian continental margin this oceanic basin was originated during the middle triassic and was subsequently early jurassic affected by an east dipping intra oceanic subduction this subduction was responsible for the birth of intra oceanic arc and back arc oceanic basins separated by a continental volcanic arc during the early to middle jurassic from the uppermost middle jurassic to the early cretaceous an obduction developed during which the ophiolites were thrust westwards firstly onto the neighboring oceanic lithosphere and then onto the adria margin

i and s type plutonism on serifos w cyclades greece abstract tertiary i and s type plutonism is widespread in the aegean region and frequently associated with extensional tectonic structures this investigation presents the first evidence of protracted magmatism on the island of serifos in the western cyclades and at least two discrete generations of plutonism and coeval dyke generations can be distinguished 1 an older granitoid with s type characteristics intruded the attic cycladic crystalline rocks the granitoid and its host rocks were mylonitized by an earlier phase of deformation at temperature conditions 450 c and wsw directed shear this crustal scale ductile shear zone has been reactivated during the initial stage of a metamorphic core complex formation recording top ssw sense of shear rb sr muscovite data from the orthogneiss yield cooling respectively deformation ages of 15 11 3 ma 2 an i type hornblende biotite granodiorite pluton with dacitic to andesitic dyke generations intruded syn to post kinematically during ongoing extensional deformation at shallow crustal levels single grain zircon tims u pb ages of the main granodiorite body and its associated dykes are 11 6 9 5 ma cooling ages of these samples scatter between 8 5 and 7 7 ma rb sr on biotite

development of concepts concerning the genesis and emplacement of tethyan ophiolites in the eastern mediterranean and oman regions this article uses evidence mainly from the eastern mediterranean and oman to help understand the origin and emplacement of ophiolites field studies in these regions emphasize the diversity of ophiolite related sedimentary and tectonic processes topics to be discussed here include the sedimentary covers of ophiolites their metamorphic soles related melanges and emplaced continental margin slope rise units modes of ophiolite emplacement will also be considered and tectonic reconstructions that have a direct bearing on the origin and emplacement of ophiolites the writer argues that there is compelling evidence that many ophiolites formed by spreading above intraoceanic subduction zones evidence from their intact sedimentary covers however indicates that such subduction was only incipient in most cases as directly associated volcanic arcs or back arc basins are rare metamorphic soles record fragments of oceanic lithosphere derived from settings ranging from open ocean to continental slope rise settings underlying melanges record the subduction of most of the ocean lithosphere formed at spreading ridges continental margin units beneath ophiolites demonstrate that these ophiolites were formed in ocean basins that were mainly initiated by continental rifting in the eastern mediterranean and oman regions ophiolite emplacement was commonly achieved by trench margin collision although strike slip transpression and large scale accretion along subducting margins played a role in some cases taking account of the mesozoic palaeotectonic setting of the eastern mediterranean region it is widely believed that ophiolites of two main ages mid jurassic and late cretaceous were formed in several small oceanic basins separated by rifted microcontinents the history of tethys in pre mesozoic time remains more open to question lastly giant subduction related ophiolites as in oman cyprus or the balkans may not be forming anywhere in the world ocean today but may instead relate to rare events in earth history when regional to global plate boundaries were drastically reorganised

overview of ophiolites and related units in the late palaeozoic early cenozoic magmatic and tectonic development of tethys in the northern part of the balkan region abstract the northern balkan peninsula including serbia montenegro bosnia croatia and the former yugoslavian republic of macedonia represents an excellent region for the study of tectonic processes related to mesozoic tethyan ophiolite genesis and emplacement we first summarise the main tectonic units of the northern balkan peninsula and then use this information to discuss tectonic processes including rifting sea floor spreading ophiolite genesis and emplacement melange accretion ocean basin closure and collision we then discuss alternative models of ophiolite genesis and emplacement for the region and suggest that multi ocean basin interpretations fit the data better than single ocean basin interpretations rifting of adria gondwana during the triassic created a rift in the south budva zone and opened a triassic oceanic basin further north dinaride ocean occurrences of inferred sub continental mantle lithosphere in the dinaride ophiolite belt e g zlatibor may record extensional exhumation within an ocean continent transition zone bordering the adria dinaride continent this was followed by emplacement together with ophiolites and melange during upper jurassic early cretaceous time upper triassic radiolarites and mid ocean ridge type basalts formed at a spreading ridge after continental break up the oceanic lithosphere of the dinaride ophiolite belt was partly generated above a subduction zone the metamorphic soles of the dinaride ophiolites formed during mid late jurassic mainly based on k ar dating widespread melange that is associated with the ophiolites represents a subduction complex controlled by tectonic accretion and sedimentary reworking in trench and fore arc basin settings a possible cause of jurassic dinaride ophiolite emplacement was collision of a subduction trench with a continental margin further north mesozoic oceanic lithosphere subducted northeastwards present coordinates opening a late jurassic marginal basin in the main vardar zone the dinaride ocean in the south closed during late jurassic early cretaceous time tithonian berriasian deformed oceanic crust melange and magmatic arc rocks further north main vardar zone were transgressed by mainly clastic sediments during the early cretaceous however part of the vardar ocean vardar zone western belt or sava zone remained partially open until latest cretaceous time generally northward subduction within this remnant ocean triggered further supra subduction zone ophiolite genesis during the late cretaceous the ocean closed by the maastrichtian followed by early cenozoic regional scale southward thrusting that locally intercalated older and younger mesozoic ophiolites and melanges future progress particularly depends on determining the crystallisation ages of the ophiolites obtaining better structural data on the direction of initial ophiolite emplacement and unravelling the palaeozoic tectonic development of the eurasian continental margin

synthesis of the tectonic sedimentary evolution of the mesozoic early cenozoic pindos ocean evidence from the nw peloponnese greece

coherent high and low latitude climate variability during the holocene warm period a faunal record of sea surface temperature sst variations off west africa documents a series of abrupt millennial scale cooling events which punctuated the holocene warm period these events evidently resulted from increased southward advection of cooler temperate or subpolar waters to this subtropical location or from enhanced regional upwelling the most recent of these events was the little ice age which occurred between 1300 to 1850 a d when subtropical ssts were reduced by 3 to 4 c these events were synchronous with holocene changes in subpolar north atlantic ssts documenting a strong in phase link between millennial scale variations in high and low latitude climate during the holocene

neotethyan evolution of eastern greece pagondas melange evia island inferred from radiolarian biostratigraphy and the geochemistry of associated extrusive rocks this paper presents new radiolarian biostratigraphic and igneous metamorphic geochemical data for a mesozoic volcanic sedimentary melange on the island of evia euboea or evvoia eastern greece this melange includes dismembered thrust sheets and blocks of radiolarian chert and basalt biostratigraphic age data show that radiolarites interbedded with basalt derived coarse clastic sediments near the base of a coherent succession were deposited in middle and late triassic time late ladinian carnian norian geochemical evidence shows that associated extrusive rocks of inferred triassic age range from enriched alkaline basalts to transitional basalts and more depleted mid ocean ridge type basalts amphibolite facies meta basalts from the metamorphic sole of the over riding evia ophiolite exhibit similar chemical compositions both the basalts and the meta basalts commonly show an apparent subduction related influence e g relative nb depletion that may have been inherited from a previous subduction event in the region the basalts are interpreted to have erupted during middle late triassic time late ladinian carnian related to initial opening of a neotethyan ocean basin adjacent to a rifted continental margin radiolarites located stratigraphically higher in the coherent succession studied are dated as middle jurassic late bathonian early callovian similar aged radiolarites are depositionally associated with ophiolitic rocks including boninites in some other areas of greece and albania during initial ocean basin closure bajocian bathonian the adjacent shallow water carbonate platform pelagonian zone disintegrated to form basins in which siliceous sediments were deposited and highs on which shallow water carbonates continued to accumulate this facies differentiation is seen as a response to crustal flexure as the neotethyan ocean began to close the over riding pagondas melange and other similar units in the region are interpreted as accretionary prisms related to subduction of neotethyan oceanic crust in middle late jurassic time these melanges were emplaced probably diachronously during oxfordian kimmeridgian time when the passive margin collapsed creating a foredeep ahead of advancing thrust sheets of melange and ophiolites

prediction of critical strains and critical support pressures for circular tunnel excavated in strain softening rock mass abstract the critical strain is a strain level at the tunnel periphery beyond which the instability and squeezing problems are likely to occur thereby it provides helpful guide to assess the tunnel stability among the current studies for predicting the critical strain the influence factors such as the required support pressure the strain softening behaviour of the rock mass and the in situ stress condition have not been comprehensively considered this paper aims to overcome the limitation by proposing an improved tunnel critical strain classification which consists of five typical critical strains and critical support pressures specifically two critical levels correspond to the occurrences of the plastic softening and residual zones of the strain softening rock mass at the tunnel periphery three tunnel strains of 2 5 5 and 10 represent the squeezing potentials of the rock mass the correlations between the input geological parameters and the geological strength index gsi are proposed on the basis of the existing empirical equations a numerical procedure is presented to solve the five critical strains and critical support pressures according to a large amount of the calculation result the response surfaces for the critical support pressures in relation to the gsi and in situ stress are obtained by the nonlinear regression method the obtained critical strains are compared with the critical strain levels and measured tunnel strains by the current studies the results indicate that the reason for the unexpected secure condition with the large deformation in the rock mass can be attributed to the non existence of the plastic residual zone as the rock mass strength improves the critical strain level reveals an unexpected growth which is correlative to the considerations of the in situ stress condition and the strain softening behaviour of the rock mass

serbo macedonian revisited a silurian basement terrane from northern gondwana in the internal hellenides greece abstract new geochronological and geochemical data on basement orthogneisses from the vertiskos unit of the serbo macedonian massif smm internal hellenides northern greece are used in order to constrain the pre alpine tectonic history of the basement units in the metamorphic hinterland of the hellenides the prevailing rock types in the vertiskos crystalline basement are coarse grained biotite augengneisses with subordinate leucocratic muscovite gneisses and two mica gneisses zircon pb pb and u pb ages on 20 samples range from 425 9 4 2 ma to 443 4 5 5 ma with a mean of 432 2 3 2 ma and are interpreted as primary crystallisation ages of the basement granites on the basis of the magmatic internal structure of the zircon grains trace element and isotope geochemistry of the gneisses show that they originated in a magmatic arc setting but also contain material from pre existing continental crust the rocks are slightly peraluminous and some leucocratic gneisses are strongly depleted in incompatible trace elements the zircon ages document an early silurian magmatic phase in the internal hellenides the association of lithologies and ages is distinctly different from that of the adjacent basement massifs this difference in basement provenance and the fact that the vertiskos unit is bordered by ophiolitic material both to the west and to the east leads to the conclusion that this part of the smm is an exotic terrane of northern gondwanan origin which was finally accreted to its present position during the alpine orogeny the vertiskos terrane may have been part of the hun superterrane which evolved at the northern active continental margin of gondwana in the early palaeozoic and rifted away from it during the opening of the rheic ocean in the cambrian to silurian parts of this superterrane such as the vertiskos terrane are present throughout the variscan and alpine orogens

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

millennial to century scale variability in gulf of mexico holocene climate records of the intertropical convergence zone itcz related to orbital forcing the d 18 o of the surface dwelling planktic foraminifer globigerinoides ruber show negative excursions between 14 and 10 2 ka radiocarbon years that reflect influx of meltwater into the western gom during melting of the laurentide ice sheet the relative abundance of the planktic foraminifer globigerinoides sacculifer is related to transport of caribbean water into the gom maximum transport of caribbean surface waters and moisture into the gom associated with a northward migration of the average position of the itcz occurs between about 6 5 and 4 5 ka in addition abundance variations of g sacculifer show century scale variability throughout most of the holocene the gom record is consistent with records from other areas suggesting that century scale variability is a pervasive feature of holocene climate the frequency of several cycles in the climate records is similar to cycles identified in proxy records of solar variability indicating that at least some of the century scale climate variability during the holocene is due to external solar forcing index terms 4267 oceanography general paleoceanography 9604 information related to geologic time cenozoic 3030 marine geology and geophysics micropaleontology

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

hydrological changes and paleoproductivity in the gulf of california during middle and late holocene and their relationship with itcz and north american monsoon variability abstract this study investigates changes in precipitation patterns and variations in paleoproductivity in the tropical pacific region associated with the north american monsoon intertropical convergence zone itcz latitudinal migration and changes in insolation during the middle and late holocene major and trace element records al ba c k si and ti and zr al and ba al ratios in a core from alfonso basin southern gulf of california are used as proxies of terrigenous input and bio productivity records reveal an increase in precipitation and low bio productivity ca 6200 to 2400 cal yr bp associated with the strengthening of monsoonal precipitation and northward shift of the itcz mean position in the eastern tropical pacific a multi centennial drought from ca 2400 to 1900 cal yr bp and a dry and cold interval ca 700 and 500 cal yr bp are characterized by strong aeolian input and enhanced productivity associated with diminution of the summer monsoonal precipitation and reduced insolation in the northern hemisphere and more southerly itcz position correlation of alfonso basin records with other records in the gulf of california and the pigmy and cariaco basins in the gulf of mexico and central atlantic provides constraints on nam itcz migration and insolation driven changes

high resolution tropical climate record for the last 6 000 years 1200 800 cal yrs b p the initial d 18 oi ncrease centered at 5 500 years ago is coincident with the development of arid conditions in the caribbean region and the end of the african humid period indicating a global drying of the northern tropics at this time synchronous with the aridification of the caribbean region are the onset of wetter conditions in the south american altiplano and the reoccupation of this region by humans this combination of contrasting climate conditions is attributed to a southward displacement of the intertropical convergence zone itcz that would have resulted in decreased precipitation and increased trade wind intensity in the caribbean region and increased rainfall over the altiplano index terms 4267 oceanography general paleoceanography 4231 oceanography general equatorial oceanography 4870 oceanography biological and chemical stable isotopes 4802 oceanography biological and chemical anoxic environments citation tedesco k and r thunell high resolution tropical climate record for the last 6 000 years geophys res lett 30 17 1891 doi 10 1029 2003gl017959 2003

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

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

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

a global event with a regional character the early toarcian oceanic anoxic event in the pindos ocean northern peloponnese greece the early toarcian early jurassic c 183 ma was characterized by an oceanic anoxic event t oae primarily identified by the presence of globally distributed approximately coeval black organic rich shales this event corresponded with relatively high marine temperatures mass extinction and both positive and negative carbon isotope excursions because most studies of the t oae have taken place in northern european and tethyan palaeogeographic domains there is considerable controversy as to the regional or global character of this event here we present the first high resolution integrated chemostratigraphic carbonate organic carbon delta 13 c carb delta 13 c org and biostratigraphic calcareous nannofossil records from the kastelli pelites cropping out in the pindos zone western greece during the mesozoic the pindos zone was a deep sea ocean margin basin which formed in mid triassic times along the northeast passive margin of apulia in two sections through the kastelli pelites the chemostratigraphic and biostratigraphic nannofossil signatures of the most organic rich facies are identified as correlative with the lower toarcian tenuicostatum polymorphum falciferum serpentinum levisoni ammonite zones indicating that these sediments record the t oae both sections also display the characteristic negative carbon isotope excursion in organic matter and carbonate this occurrence reinforces the global significance of the early toarcian oceanic anoxic event

the maliac ocean the origin of the tethyan hellenic ophiolites the hellenides part of the alpine orogeny in greece are rich in ophiolitic units these ophiolites and associated units emplaced during jurassic obduction testify for the existence of one or several tethyan oceanic realms the paleogeography of these oceanic areas has not been precisely described however all the authors now agree on the presence of a main triassic jurassic ocean on the eastern side of the pelagonian zone vardar domain we consider that this maliac ocean is the most important ocean in greece and albania here we limit the detailed description of the maliac ocean to the pre convergence period of approximately 70 ma between the middle triassic rifting to the middle jurassic convergence period a quick overview on the destiny of the different parts of the maliac ocean during the convergence period is also proposed the studied exposures allow to reconstruct 1 the middle to late triassic maliac oceanic lithosphere corresponding to the early spreading activity at a mid oceanic ridge 2 the western maliac margin widely exposed in the othris and argolis areas 3 the eastern maliac margin in the eastern vardar domain peonias and paikon zones we established the following main characteristics of the maliac ocean 1 the middle triassic rifting marked by a rapid subsidence and volcanism seems to be short lived few my 2 the maliac lithosphere is only represented by middle to late triassic units especially the fourka unit composed of wpb oib and morb pillow lavas locally covered by a pelagic middle triassic to middle jurassic sedimentary cover 3 the western margin is the most complete and our data allow to distinguish a proximal and a deeper distal margin 4 the evolution of the eastern margin peonias and paikon series is similar to that of the w margin except for its jurassic terrigenous sediments while the proximal w margin was dominated by calcarenites 5 we show that the w and e margins are not volcanic passive margins and 6 during the middle jurassic convergence period the eastern margin became an active margin and both margins were affected by obduction processes

paleolatitudes of late triassic radiolarian cherts from argolis greece insights on the paleogeography of the western tethys the hellenides fold and thrust range comprises two subparallel ophiolite belts of triassic to jurassic age the external ophiolite belt e g mirdita pindos argolis in the west and the internal ophiolite belt in the east broadly separated by the continental crust units of the korabi pelagonian zone it is still a matter of debate whether these ophiolites derived from a single ocean meliata maliac vardar or mark the suture of two distinct oceanic seaways pindos and meliata maliac vardar we contribute to the resolution of this controversy by studying the migdalitsa ophiolitic complex in argolis greece which contains triassic oceanic basalts and pertains to the external western ophiolite belt three key areas were mapped and several sites were targeted for structural biostratigraphic and paleomagnetic analyses radiolarian cherts in primary or tectonic contact with oceanic basalts were dated to the late triassic carnian norian using radiolarians and provided paleomagnetic directions of primary origin carried by magnetite and hematite the derived mean direction was corrected for sedimentary inclination shallowing and yielded a paleolatitude of 22 n that was placed in a broader paleogeographic context by reconstructing pangea at 225 5 ma using a recent apparent polar wander path corrected for sedimentary inclination shallowing the late triassic paleogeography of the tethys ocean was constrained using additional paleolatitude estimates from the literature which we checked and corrected when possible for sedimentary inclination shallowing according to our reconstruction the meliata maliac vardar ocean between adria the promontory of africa and europe represents the locus of origin of the late triassic argolis ophiolitic rocks of the external ophiolite belt presently resting in tectonic contact on the pindos subpelagonian zones which represent a deep water trough with no substantial evidence of in situ oceanization in the triassic

a high resolution late quaternary upwelling record from the anoxic cariaco basin venezuela results are presented of a high resolution study of the planktonic foraminiferal faunas from two piston cores recovered from the cariaco basin in the southern caribbean sea the cariaco basin is a small anoxic marine basin on the northern continental margin of venezuela in an area today characterized by both seasonal trade wind induced upwelling and pronounced dry and wet seasons our data indicate that large changes in the intensity of upwelling and hence trade wind strength occurred in this region during the last glacial interglacial transition and throughout the holocene during the last glacial lowstand of sea level the cariaco basin was effectively isolated from the open caribbean along its northern margin by the then largely emergent tortuga bank oxic conditions existed in the deep cariaco basin at this time and surface productivity was low about 12 600 years ago the abrupt initiation of strong upwelling over the basin and the onset of permanent anoxia in the deep waters are coincident with the rapid rise of sea level that accompanied the peak interval of meltwater discharge from the laurentide ice sheet into the gulf of mexico strong upwelling between 12 600 and about 10 000 years ago may be related to intensified trade winds resulting in part from cooler sea surface temperatures in the caribbean and gulf of mexico after about 10 000 years ago upwelling intensity was reduced though highly variable a preliminary frequency domain analysis of the holocene portion of the cariaco basin time series suggests that solar forcing may explain a significant component of the century scale variability observed in the record of upwelling and trade wind strength