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

causes of recent himalayan uplift deduced from deposited patterns in the ganges basin the hypothesis1 that late cenozoic uplift of many of the world s mountain ranges was a response to climate change rather than to tectonic processes is based on the premise that enhanced erosion in an altered climate led to a reduction in both the total mass of a mountain range and its mean elevation this reduction was coeval with increased regional relief and with passive isostatic uplift of the remaining summits the hypothesis is difficult to evaluate because both climate and tectonic forces affect uplift in many active ranges in the absence of sufficient denudational and uplift data from the mountains themselves depositional patterns in adjacent basins may sometimes be used to distinguish between uplift arising from erosional or from tectonic processes in foreland basins uplift of the proximal basin and a reduction or absence of asymmetric subsidence are predicted responses to erosionally driven uplift2 here i show that patterns of sediment accumulation and the position of major rivers in the neogene gangetic foreland basin seem to have changed markedly in plio pleistocene times these changes lend support to the hypothesis that the importance of erosional unloading has increased in the himalayas during the past 4 myr

the record of sea water 187os 186os variation through the cenozoic the variation of sea water 187os 186os during the cenozoic has been determined by analyzing the hydrogenous os released by acidic hydrogen peroxide leaching of layers in an abyssal north pacific pelagic clay core overall sea water 187os 186os has increased from 3 2 at 58 ma to the present day value of 8 6 this pattern is similar to the well known 87sr 86sr evolution of sea water the increase in the proportion of continental os 187os 186os 10 could be due to enhanced weathering rates of black shales associated with the uplift of the himalayas other elements associated with black shale weathering such as u and p should show effects in the sedimentary record

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

the xigaze forearc basin evolution and facies architecture cretaceous tibet abstract the mid cretaceous to eocene flysch deposits of the xigaze forearc basin in southern tibet were investigated in a 120 km segment along the indus yarlung suture zone the basin evolved south of the magmatic arc gangdise belt of the lhasa block on top of trapped oceanic or transitional crust remnants of shelf carbonates are preserved along the northern edge of the basin the mapped segment was shortened by about 65 metamorphism reached low grade conditions along the northern margin of the basin the flysch sequence reaches a thickness of at least 5 km and consists to a large degree of volcaniclastic andesitic to dacitic material shed from the magmatic arc gangdise belt particularly in the western part of the study area plutonic and sedimentary rocks from deep erosion levels and or more distal sources contributed to the basin fill rivers from the lhasa block acted as point sources and fed five major deep sea channel systems turbidity currents in the channels were directed towards the growing accretionary wedge of the subduction zone thus indicating that the basin was continuously filled up to outer ridge level and gradually shallowing the forearc flysch is subdivided into at least three megasequences which begin with wide up to several km incised 10 to 50 m coarse grained channel fills and their associated fan deposits the upper parts of the megasequences contain hemipelagic dark shales and marls deposited above the calcite compensation depth lateral channel migration channel lobe switching but also volcanic pulses generated a predominantly fining upward high frequency cyclicity after continental collision the marine sedimentation in the forearc basin was replaced by fluvial deposits of the eocene oligocene qiuwu formation which is time equivalent to the kailas and indus molasses farther west and rich in coarse gravel derived from the gangdise belt both forearc flysch and qiuwu formation were deformed simultaneously during the miocene we assume that the molasse type qiuwu formation represents the final continental facies of the forearc basin filling

mesozoic tertiary tectonic evolution of albania in its regional eastern mediterranean context abstract research carried out since the opening of albania to the western geological community in the 1990s allows the geology and tectonics of this small balkan country to be integrated into an overall interpretation of neotethys in the eastern mediterranean region specifically greece and the former yugoslavia region albanian geology is most famous for the occurrence of contrasting ophiolites of jurassic age the country is sub divided into three main geotectonic units those in the west i e sazani ionian kruja krasta cukali and the albanian alps relate to the western margin of apulia effectively part of north africa from early mesozoic time onwards in the east is the korabi zone interpreted as a microcontinent located further northeast within neotethys between the two is the mirdita zone dominated by two contrasting jurassic ophiolites the western type ophiolite and the eastern type ophiolite taking account of evidence from greece and former yugoslavia the following tectonic evolution is proposed from early mesozoic time onwards neotethys in albania existed as a northward continuation of the pindos oceanic basin in greece pindos mirdita ocean a korabi microcontinent was rifted off apulia in the early mid triassic followed by passive margin subsidence until late middle jurassic time a rifted slow spreading mor type ophiolite formed within the western pindos mirdita oceanic basin in late triassic early late jurassic time using present co ordinates the shkoder peje scutari pec lineament in the north of albania is interpreted as an important transform fault zone that influenced the regional tectonic evolution during the entire mesozoic early tertiary rift drift emplacement history of the pindos mirdita ocean taking account of evidence from the greek and former yugoslavia ophiolites the easterly albanian ophiolites formed within the pindos mirdita ocean above a westward dipping intra oceanic subduction zone in the early late jurassic metamorphic soles were formed during initial intra oceanic displacement ca 162 174 m y and underlying melanges originated as subduction accretion complexes the mor western type ophiolite evolved into the iat boninitic eastern type ophiolite after subduction began during tithonian berriasian time trench margin collision emplaced the ophiolites eastwards over the korabi margin coupled with redeposition of ophiolitic and continental margin material as exotic blocks debris flow deposits and turbidites these were emplaced onto the upper surface of the ophiolitic thrust sheet during the latest stages of emplacement onto the korabi microcontinent following collision in the east oceanic crust remained within a small remnant pindos mirdita oceanic basin passive conditions were restored in the mid late cretaceous with shallow water carbonate deposition on microcontinental units and both pelagic and redeposited carbonates in basinal settings from the maastrichtian onwards africa eurasia convergence resulted in large scale westward thrusting deforming the apulian foreland in oligo miocene time the suture zone was re activated in oligo miocene time as the albanie thassalie piggy back type basin in central and southern albania albania as a whole was rotated 45 clockwise as part of the western aegean arc in post eocene time coastal and offshore albania experienced strong subsidence after early miocene time forming the periadriatic basin including the tirana depression interpreted as a foredeep related to continuing regional convergence southern albania experienced extensional tectonics in plio quaternary time related to southward roll back of the aegean active margin

plate tectonics and island arcs the plate tectonic concepts that developed rapidly in the late l960s made possible the understanding of island arcs before that time mobilistic concepts evolved slowly hindered particularly in the united states by an obstructionist geoscience establishment the volcanic belts of island arcs form about 100 km above subducting plates convergent plate boundaries evolve complexly with time and at any one time vary greatly along their lengths seismicity defines positions but not trajectories of descending slabs which sink more steeply than they dip and are overridden by advancing upper plates subduction occurs beneath only one side at a time of an internally rigid plate and the common regime in an overriding plate behind a surficial accretionary wedge is extensional except where a collision is underway back arc basin lithosphere is built behind or by migrating island arcs which lengthen and increase their curvatures a collision can involve two active arcs in which case intervening lithosphere sinks beneath both of them or an active margin and a passive one either type of collision generally is followed by the breaking through of new subduction beneath the composite mass of light crust from a new trench on the outside of the aggregate conversely a new subduction system commonly is a by product of collision a strip of back arc basin crust is in many cases left attached to the aggregate in front of the new trench and becomes the basement for a fore arc basin the leading edge of which is raised as melange is stuffed under it sedimentation in trenches is predominantly longitudinal and can be from distant sources accretionary wedges are dynamic being thickened at both toes and bottoms by tectonic accretion and thinned by gravitational forward flow melange is largely a product of tectonic imbrication and flowage driven by these conflicting processes not of submarine sliding high pressure metamorphic rocks form beneath overriding plates not within wedges in front of them arc magmas incorporate much material from the lithosphere through which they rise and vary correspondingly with the evolving composition of that lithosphere arc crust is inflated into geanticlines by intrusive rocks and thermal expansion submarine island arc volcanic rocks are widely spilitized with na enrichment and ca depletion by hydrothermal reaction with sea water the lower crust of mature island arcs consists of granulite facies rocks of mafic intermediate and felsic intermediate compositions the mohorovicic discontinuity may be primarily a constructional boundary representing the shallow limit off crystallization of voluminous rocks of ultramafic composition or plagioclase free mineralogy

comparison of evolution and tectonic significance of the pindos and vourinos ophiolite suites northern greece abstract the pindos ophiolite located on the western edge of the sub pelagonian othris zone comprises a complex series of westward verging thrust sheets dominantly composed of peridotite tectonite phaneritic mafic and leucocratic rocks and pillow lavas harzburgite tectonites from part of the east central thrust sheet dramala complex show three well developed foliations the oldest compositional layering s 0 has been isoclinally folded and preferred orientations of elongate grains and aggregates of olivine and orthopyroxene parallel to the axial surfaces of the isoclines define the second foliation s 1 spinel lineations parallel fold axes of the isoclinal folds thermometric calculations from mineral compositions and grain sizes of olivines and pyroxenes associated with the oldest preserved foliations compositional layering s 0 s 1 indicate that rocks of the tectonite suite equilibrated at depths of between 45 and 60 km at temperatures between 1210 c and 925 c and at differential stresses from 5 to 10 mpa in general rocks indicative of higher temperatures of equilibration formed at lower values of differential stress the third and youngest foliation is defined by bands of fine grained olivine and pyroxene mylonite that cut across older structural elements mylonites equilibrated at temperatures between 650 c and 710 c presumably indicative of shallower depths 30 20 km than the older foliations accompanied by differential stresses ranging from 200 to 300 mpa and probably formed during obduction of the complex the sense and orientation of shear determined from kinematic indicators within the mylonitic zones indicate an updip displacement vector inclined at an angle of 20 to 40 toward 016 suggesting obduction to the east northeast relative to the present position of the pindos ophiolite there is no direct evidence for the amount of rotation about a vertical axis that may have occurred during obduction or later tectonic transport the composition internal structure environments of equilibration stress history and inferred direction of obduction of the pindos ultramafites are strikingly similar to those of the vourinos complex located 40 km to the northeast on the eastern margin of the sub pelagonian zone it is probable that the two ophiolites shared a common origin and an identical early obduction history during late jurassic times the vourinos and its metamorphic sole were thrust over a thick sequence of shelf carbonates and a thin diamictitic melange both units being metamorphosed to lower greenschist facies comparable units beneath the pindos thrust sheet the loumnitsa unit and the avdella melange are thicker somewhat more lithologically diverse and comprise amphibolite greenschist radiolarite pillow lava garnetite exotic marble flysch and poorly metamorphosed fossiliferous limestone typically occurring in tightly folded thin thrust slices differences in the timing and direction of post emplacement thrust transport of the two complexes are marked and may have begun late in the obduction phase

stratigraphic evidence for an early collision between northwest india and asia the collision of india with asia1 had a profound influence on late cretaceous and cenozoic oceanography2 climate3 fauna extinctions4 and the motion of at least some of the earth s litho spheric plates5 as the collision ended a period of rapid indo asian convergence6 a precise knowledge of its timing when the crust of the neo tethys ocean was completely subducted7 at some point along the plate boundary is important for understanding its wider consequences but current estimates of the collision age range from 65 to 38 myr before present6 8 11 here we report the results of extensive biostratigraphic analyses from waziristan and kurram in northwest pakistan which show that accretionary prism and trench strata were first thrust onto the northwest indian passive margin after 66 myr but before 55 5 myr after this time volcanic arc fragments the accretionary prism trench material and imbricates of the north indian slope were raised to shallow water depths and overlapped by upper palaeocene shallow water carbonates and shales12 14 indicative of post collision thrusting in this region finally both the suture and the indian craton were overlapped by continuous unconformable upper lower eocene shallow marine strata demonstrating that suturing was complete by 49 myr

kinematics of the central hellenides structural analysis along 24 cross sections crosscutting several windows in the central hellenides provides the sense of nappe movements as well as the location of destroyed oceans lying between the apulian and eurasian continents from the mesozoic orogeny took place in two phases the first phase the eo hellenic phase was initiated by convergence of the apulian and pelagonian plates with west directed subduction and closure of the pindos ocean late jurassic obduction of oceanic lithosphere over the western margin of the pelagonian plate was followed by footwall imbrication mylonites and sheath folds during the late cretaceous uplift was associated with ductile normal faulting at depth and tectonic unroofing at shallow crustal levels the second phase the meso hellenic phase comprised the closure of the ambelakia ocean at the eastern margin of the pelagonian plate and continental subduction along the eastern margin of the apulian plate west directed subduction of the ambelakia ocean was associated with eastward directed ductile thrusting folding and blueschist metamorphism blueschist formed within a simple duplex structure at depth and was subsequently overthrusted in the late eocene onto the olympos microcontinent which acted as a major obstacle to the eastward directed nappe movements up to 150 m thick cataclasites kink folds and a spaced cleavage were formed during the late stage of the continental collision a subduction along the eastern margin of the apulian plate caused kink folding and reimbrication of the western parts of the pelagonian basement since the oligocene the overthickened crust collapsed by means of low angle normal faults

the himalayas organic carbon burial and climate in the miocene cooling ages of rock in the himalayas imply that rapid exhumation between the main central thrust system and the south tibetan detachment system occurred between 21 and 17 ma the generation of relief and enhanced weathering which followed this event may have resulted in a pronounced increase in the delivery of dissolved strontium carbon phosphorus and other chemical weathering products to the ocean richter et al 1992 the increased supply of nutrients stimulated productivity in oceanic upwelling zones and expansion of the oxygen minimum zone leading to enhanced burial and preservation of organic matter in the monterey formation and other deposits from this interval a downdraw of atmospheric co2 associated with enhanced chemical weathering rates and organic matter burial may have led to global cooling and the expansion of the antarctic ice sheet by 15 ma the above scenario differs from the monterey hypothesis of vincent and berger in that co2 downdraw is primarily via silicate weathering rather than organic carbon burial and that organic carbon burial is driven by increased delivery of nutrients to the ocean rather than by stronger upwelling a carbon mass balance calculation which assumes that river fluxes have been increasing over the last 40 ma predicts that absolute organic carbon burial increased over this interval while at the same time the fraction of carbon buried as organic matter versus carbonate decreased this implies that the organic carbon cycle has acted as a net source of co2 to the atmosphere over the late cenozoic

himalayan tectonics weathering processes and the strontium isotope record in marine limestones the time evolution of the isotopic composition of seawater strontium the ratio of strontium 87 to strontium 86 over the last 500 million years has the form of an asymmetric trough the values are highest in the cambrian and recent 0 7091 and lowest in the jurassic 0 7067 superimposed on this trend are a number of smaller oscillations consideration of the geochemical cycle of strontium and the dynamics of weathering shows that only himalayan style continental collisions can influence the isotope ratio on the scale observed the contemporary himalayan orogeny is by far the largest since the late precambrian pan african event that produced the high in the cambrian

post 125 ma carbon storage associated with continent continent collision tectonic fragments subjected to high pressure metamorphism in the alps contain up to 1 vol each of dolomite and graphite indicating that significant amounts of carbon bearing sediment were transported to depths greater than 50 km during the alpine orogeny the absence of a cretaceous tertiary volcanic arc on the overriding plate suggests that much of the subducted carbon remains at depth today averaged over the length of the alpine chain and the estimated amount of subduction that occurred in the past 125 m y 10 16 kg of carbon was buried because of collision in the alpine region additional consideration of the himalayan chain suggests that more than 10 17 kg of carbon has been buried since 125 ma by continent continent collision transfer of this amount of carbon from atmospheric and sedimentary reservoirs into a deep seated metamorphic reservoir may help explain the significant decrease in global surface temperature that occurred from 125 ma to the present

multicyclic history of the northern india continental margin northwestern himalaya 1 the geologic evolution of northern india is best recorded in the stratigraphic succession of the zanskar range northwestern himalaya which represents the most complete transect through this ancient continental margin sedimentary history began in the late proterozoic and recorded a late pan african orogenic event around the cambrian ordovician boundary when the gondwana supercontinent was eventually assembled the following long period of epicontinental deposition in shallow seas linked to palaeo tethys lasted until the early permian when a neo tethyan rift began to open between paleo india and the cimmerian microcontinents neo tethyan history can be subdivided into two sedimentary megasequences both recording a major tectonic and magmatic event in the lower part the first one began with breakup in the late permian and lasted until the end of the jurassic the second one started in the early cretaceous with the final detachment of india from gondwana and the opening of the indian ocean and ended with the india eurasia collision in the early eocene the two megasequences can be in turn subdivided into six transgressive regressive supersequences bounded by tectonically enhanced unconformities basal sandstone units of early permian late permian norian callovian early cretaceous and paleocene age are invariably associated with oolitic ironstones or reworked glauco phosphorites and mark the transgre sive part of each supersequence next condensed nodular carbonates or shales with pelagic fauna are typically overlain by thick shallowing upward marly units capped by regressive platformal carbonates the six tectono eustatic supercycles reflect successive rifting episodes which punctuated the progressive separation of india from the rest of gondwana and document the combination of plate microplate reorganizations and eustatic climatic and oceanographic changes in the tethyan domain after the onset of collision between india and asia close to the paleocene eocene boundary obduction of the remnants of the neo tethys ocean floor onto the indian margin began and the latter underwent multiphase deformation with fold thrust shortening followed by heating and extension after the main metamorphic event ophiolitic nappes were re thrusted and finally emplaced with their sedimentary sole on top of the passive margin succession

organic carbon exhumation and global warming during the early himalayan collision organic carbon eroded and oxidized from marine sediments on the passive and active neo tethyan margins during the early indian asian collision may have been sufficient to shift the carbon isotopic ratios of late paleocene early eocene marine carbonates toward lighter values and may have contributed to coeval global warming via the greenhouse effect new limits on the timing of collision and the organic carbon content of himalayan sedimentary sources and sinks allow us to estimate the net paleogene flux our calculations suggest that continental collisions play a fundamental role in the global carbon cycle and climate through the exhumation as well as burial of organic carbon

intracontinental wedging and post orogenic collapse in the mesohellenic trough the mesohellenic trough is a 130 km long and about 30 km wide subsiding area which contains a thick sequence of well exposed late cenozoic post orogenic sediments this intermontane basin located at the contact between the apulian and pelagonian collided margins provides a good example of the characteristics needed to study the chronology of late orogenic intracontinental structures

tectono stratigraphy and evolution of the mesozoic pindos ophiolite and related units northwestern greece the northwest pindos mountains expose mesozoic and tertiary thrust sheets which include the jurassic pindos ophiolite composed of ultramafic and mafic oceanic crustal rocks the tectono stratigraphy of these units is i mainly ultramafic ophiolitic thrust sheet and basal metamorphic sole dramala complex and loumnitsa unit ii late cretaceous platformal limestones orliakas group iii dismembered intrusive and extrusive ophiolitic rocks aspropotamos complex iv tectonic melange and olistostromes dominated by triassic jurassic volcanic and sedimtntary rocks avdella melange v coherent thrust sheets of late jurassic late cretaceous deep water sediments dio dendra group vi early tertiary flysch pindos flysch immobile trace element studies indicate that triassic and jurassic extrusives of the volcanic sedimentary melange formed mainly at within plate and or mid ocean ridge settings by contrast structurally overlying ophiolitic extrusives include boninitic volcanics and island arc tholeiites of supra subduction zone origin initial ophiolite displacement c 165 ma is recorded in metamorphic sole formation including basal peridotite mylonite amphibolites and greenschists the sole rocks have morb and wpb chemical affinities in our favoured model the pindos ophiolite formed above a mid jurassic westerly dipping intra oceanic subduction zone accompanied by accretion to form melange followed by collision and emplacement with the pelagonian margin final suturing of the pindos ocean however did not take place until early tertiary times

the himalayan passive margin from precambrian to cretaceous times abstract the himalaya passive margin should be separated into the indian himalaya and the pakistan himalaya divided by the nanga parbat haramosh basement uplift in the northwestern syntaxes the indian passive margin shows a complex history involving splitting of microcontinents off the northern gondwana margin from early paleozoic times until the jurassic in contrast the pakistan himalaya formed part of the stable indian shelf until separation from africa started in the jurassic each margin has a distinct stratigraphic history until the mid mesozoic after which they show similar histories until the tertiary the himalaya mountains in india consist of three distinct tectonic units juxtaposed during the neogene by southward thrusting of the northern indian precambrian to mesozoic passive margin the lesser himalaya on the south forms a late precambrian passive margin usually directly overlain by late cretaceous to tertiary clastics its stratigraphy is closest to that of the indian shield in contrast the high himalaya has a thin ordovician to carboniferous shelf sequence deposited after early ordovician deformation and granite intrusion above this thick permian and mesozoic shelf sequences mark the separation of continental blocks off the northern indian margin and the opening of the neotethys ocean the north himalaya formed the slope and basin of this ocean and consists of reactivated paleozoic gneiss domes overlain by thick mesozoic sediments which pass in the northeastern himalaya into an enormously thick sedimentary sequence resting on oceanic crust paleomagnetic and structural evidence indicates at least 500 km of southward thrusting along the main central thrust between the lesser and high himalaya this thrusting together with a further 250 km of erosion at the front of the nappes has removed the entire inner shelf of the himalaya passive margin and can explain the startling contrast between the high and lesser himalaya stratigraphic sequences but there are still discrepancies particularly in the eastern himalaya where precambrian basement is juxtaposed with the north himalaya mesozoic slope these discrepancies can be partly resolved by strike slip movements roughly parallel to the himalaya which have removed parts of the northern indian passive margin such faults of the requisite orientation displacement and age occur in southeast asia where their cumulative displacements can add up to several thousand kilometres similar faults of undoubted pre tertiary age occur in the pakistan himalaya here the passive margin shows a much simpler history of jurassic to miocene subsidence

natural controls of fluvial denudation rates in major world drainage basins we present a new compilation of estimates of modern rates of mechanical and chemical denudation for externally drained basins exceeding 5 105 km2 in area these estimates are based on sediment and solute load data selected in order to represent natural rates as far as possible chemical denudation rates have been calculated by deducting the nondenudational component of solute load mechanical denudation rates range from 1 mm kyr 1 for the st lawrence and dnepr basins to 670 mm kyr 1 for the brahmaputra basin chemical denudation rates vary from 1 mm kyr 1 kolyma niger nile and rio grande basins to 27 mm kyr 1 chiang jiang basin the kolyma basin has the lowest 4 mm kyr 1 and the brahmaputra basin the highest overall rate of denudation 688 mm kyr 1 relationships between denudation rates and a range of morphometric hydrologic and climatic variables are investigated through correlation and regression analysis morphometric variables such as mean local relief are accurately calculated for large basins for the first time by using the national geophysical data center 10 minute topographic database variables expressing basin relief characteristics and runoff are found to be most strongly associated with both mechanical and chemical denudation rates with more than 60 of the variance in total denudation being accounted for by basin relief ratio and runoff basin area runoff variability and mean temperature however are only weakly associated with rates of denudation although direct comparisons cannot be made it appears that rates of basin denudation derived from present day mass flux estimates are not overall significantly different from estimates of long term rates based on sediment volume and thermochronologic data it therefore appears that the key factors identified as controlling denudation rates here are also applicable to the geological time spans relevant to the interaction between tectonic and denudational processes

tectonics and structural zonation of southern tibet china the yarlung zangbo suture zone is composed of several thrust sheets with distinct stratigraphies states of deformation and metamorphic grades successive deformations have been produced by persistent north south shortening since obduction of the ophiolites by late cretaceous palaeocene times a possible decoupling of the crust may be associated with the intracontinental thrust system which has formed in the subducted indian plate this article emphasizes the role of shear deformations in the building of a collision belt

mid ocean ridge and supra subduction affinities in the pindos ophiolites greece implications for magma genesis in a forearc setting abstract the pindos ophiolitic massif is considered an important key area within the albanide hellenide ophiolitic belt and is represented by two tectonically distinct ophiolitic units 1 a lower unit including an intrusive and a volcanic section and 2 an upper ophiolitic unit mainly including mantle harzburgites both units share similar metamorphic soles and tectono sedimentary melanges at their bases the intrusive section of the lower unit is composed by an alternation of troctolites with various ultramafic rock types including dunites lherzolites olivine websterites olivine gabbros anorthositic gabbros gabbros and rare gabbronorites the volcanic and subvolcanic sequence of the lower unit can geochemically be subdivided into three groups of rocks 1 basalts and basaltic andesites of the lower pillow section showing a clear high ti affinity 2 basaltic andesites of the upper pillow section with high ti affinity but showing many geochemical differences with respect to the first group 3 very low ti boninitic basaltic and basaltic andesitic lava flows separating the lower and upper pillow sections and dykes widespread throughout the pindos ophiolites these different magmatic groups originated from fractional crystallization from different primary magmas which were generated in turn from partial melting of mantle sources progressively depleted by previous melt extractions group 1 volcanics may have derived from partial melting ca 20 of an undepleted lherzolitic source while group 2 basaltic rocks may have derived from partial melting ca 10 of a mantle that had previously experienced mid ocean ridge basalt morb extraction finally the group 3 boninites may have derived from partial melting ca 12 17 of a mantle peridotite previously depleted by primary melt extraction of groups 1 and 2 primary melts in order to explain the coexistence of these geochemically different magma groups two petrogenetic models formerly proposed for the albanian ophiolites are discussed

paleoatmospheric consequences of co2 released during early cenozoic regional metamorphism in the tethyan orogen the eocene was the warmest epoch of the cenozoic with published estimates of eocene atmospheric co2 content ranging from two to six times the current value calculations of co2 consumption by silicate weathering show that co2 fluxes to the atmosphere of ca 1018 myr could account for inferred paleocene eocene atmospheric co2 contents and the resulting greenhouse effect would have contributed to eocene warmth extensive portions of the tethyan orogen underwent regional metamorphism culminating in the eocene prograde metamorphism may have been contemporaneous with the late paleocene global warming we calculated the amount of metamorphic co2 produced at depth in the himalayan orogen with data on the timing of the india asia collison duration of prograde regional metamorphism and proportions and bulk compositions of metamorphic co2 source rocks if co2 was generated at a constant rate over a 10 myr period of prograde metamorphism in the himalayan orogen we estimate that ca 1018 1019 moles myr of metamorphic co2 were produced at depth significant expulsion of metamorphic co2 to the atmosphere may have occurred by focused fluid flow along shear zones such as the extensive main central thrust in the himalayan orogen an additional ca 1018 myr could have been contributed by eocene regional metamorphism in the mediterranean tethys i e from the alps to turkey the extensive metamorphism associated with the india asia collision and the closing of tethys may have contributed to co2 greenhouse warming in the early to mid cenozoic

microcracks in ultrabasic rocks under uniaxial compressive stress the initiation and propagation of microcracks under stress are highly dependent upon the mineralogical and textural characteristics of the various lithotypes detailed observation and quantification of microcracks before and after uniaxial compression test were conducted a fresh olivine rich harzburgite and a serpentinized dunite were analyzed collected from the pindos and vourinos ophiolites northern greece respectively in order to compare their microcrack patterns quantitative analysis indicated that during uniaxial compression the intragranular microcracks which are the dominating crack type are gradually transformed or organized into transgranular cracks some of the newly formed transgranular cracks may also be a result of the growth of existing grain boundary cracks the new intragranular microcracks in the olivine rich harzburgite are oriented predominantly parallel to the compressive stress direction while those in the serpentinized dunite show a scattered orientation presumably due to the mesh texture of this rock type the new transgranular cracks of both peridotites tend to be subparallel to the compressive stress direction however many of them show a random orientation due to the fact that they have been formed as a result of the propagation of grain boundary cracks the occurrence of the soft serpentine along fracture surfaces of olivine when it is in assemblage with orthopyroxene tends to absorb the applied stress hampering the development of microcracks in olivine on the other hand in serpentinized peridotites the microcracks are enhanced in olivine because it is surrounded by large amounts of the much softer and flexible serpentine microcracks are usually formed along the cleavage planes of orthopyroxene porphyroclasts indicating that such crystallographic preferred orientations act as planes of weakness controlling the direction of the crack paths cr spinel grains likely comprise locations of initiation of microcracks due to their very hard nature and different mechanical behaviour relative to the surrounding silicate phases knowledge of the mineralogical and textural characteristics may assist in the prediction of potential development of failure surfaces of an ultrabasic rock in service