a submarine hydrothermal manganese deposit from the south west pacific island arc hydrothermal deposits of a wide variety of types are being found with increasing frequency on or near actively spreading mid ocean ridges1 4 however they also have a potential to occur in other submarine volcanic settings including island arcs5 to follow up indications of mineralization associated with submarine hydrothermal activity in the south west pacific island arc6 a joint new zealand oceanographic institute imperial college research cruise was mounted in may 1981 aboard the rv tangaroa during this cruise over 130 sampling stations were occupied at one of which were dredged manganese deposits with strong hydrothermal affinities this is the first report of such deposits from an island arc setting

time scales of sedimentary transfer and weathering processes from u series nuclides clues from the himalayan rivers abstract in order to define time scales of erosion and sedimentary transfer in the himalaya 238 u 234 u 230 th disequilibria have been analysed in river bank sediments and in bedloads collected along the kali gandaki river one of the main nepalese rivers and in the ghaghara and gandak rivers two major plain tributaries of the ganges the th activity ratios and u th ratios in river sediments of the two ganges tributaries constantly decrease from upstream to downstream this is related to the maturation of sediments by weathering during their transfer to the plain the u series data allow to calculate a transfer time for the sediments in the alluvial gangetic plain from the chain front to the confluence with the ganges of about 100 kyr for both rivers the kali gandaki river sediment data highlight a decrease of both the th isotopic and u th ratios which is explained by a mixing between two sources with similar u th ratios but having suffered a different u th fractionation history interpretation of the u series data in the frame of this scenario gives long time scales of weathering of several 100 s kyr for the himalayan terranes the results imply that himalayan bedrocks are submitted to a long in situ stage of weathering before their erosion and transfer into the rivers in addition occurrence of similar u sr signatures in dissolved i e

experimental melting of biotite plagioclase quartz muscovite assemblages and implications for crustal melting abstract in order to understand the role of mica rich rocks as a source of granite magmas a series of melting experiments was performed on two different starting materials the first composition is a model biotite gneiss consisting of 30 wt biotite 30 wt plagioclase and 40 wt quartz the second composition is a model two mica pelites consisting of 15 wt biotite 15 wt muscovite 30 wt plagioclase and 40 wt quartz experiments were performed under vapor absent conditions at 1 0 gpa and between 750 o and 950oc with only biotite in the starting material the volume of melt is always less than 15 vol below 900oc and reaches 25 vol at 950oc in experiments that involve both biotite and muscovite in the starting material the melt proportion increases up to 28 vol at 825oc and reaches 60 vol at 950oc for the biotite plagioclase quartz bpq assemblage the solidus is located at 800oc at 1 0 gpa the melting reaction produces a metaluminous granitic liquid and leaves a residuum consisting of garnet biotite orthopyroxene plagioclase quartz in addition the experiments show that at 1 0 gpa biotite can be stable above 950oc with both micas in the starting material bpqm the solidus at 1 0 gpa is located at 750oc the melting reactions produce a peraluminous granitic liquid and leave a residuum of garnet sillimanite biotite quartz plagioclase kfeldspar in experiments below 900oc at 950oc the residuum consists of garnet orthopyroxene biotite plagioclase the melt fraction is determined by the proportions of the hydrous phases and of the amount of feldspar relative to quartz mineral modes of the source rocks particularly the amount of quartz are at least as important as the amount of available h20 in controlling the melt fraction generated during crustal anatexis

40ar 39ar and oxygen isotope studies of polymetamorphism from tinos island cycladic blueschist belt greece petrological oxygen isotope and 40ar 39ar studies were used to constrain the tertiary metamorphic evolution of the lower tectonic unit of the cyclades on tinos polyphase high pressure metamorphism reached pressures in excess of 15 kbar based on measurements of the si content in potassic white mica temperatures of 450 500 c at the thermal peak of high pressure metamorphism were estimated from critical metamorphic assemblages the validity of which is confirmed by a quartz magnetite oxygen isotope temperature of 470 c some 40ar 39ar spectra of white mica give plateau ages of 44 40 ma that are considered to represent dynamic recrystallization under peak or slightly post peak high pressure metamorphic conditions early stages in the prograde high pressure evolution may be documented by older apparent ages in the high temperature steps of some spectra eclogite to epidote blueschist facies mineralogies were partially or totally replaced by retrograde greenschist facies assemblages during exhumation oxygen isotope thermometry of four quartz magnetite pairs from greenschist samples gives temperatures of 440 470 c which cannot be distinguished from those deduced for the high pressure event the exhumation and overprint is documented by decreasing ages of 32 28 ma in some greenschists and late stage blueschist rocks and ages of 30 20 ma in the lower temperature steps of the ar release patterns of blueschist micas almost flat parts of ar ar release spectra of some greenschist micas gave ages of 23 21 ma which are assumed to represent incomplete resetting caused by a renewed prograde phase of greenschist metamorphism oxygen isotope compositions of blueschist and greenschist facies minerals show no evidence for the infiltration of a 18o enriched fluid rather the compositions indicate that fluid to rock ratios were very low the isotopic compositions being primarily controlled by those of the protolith rocks we assume that the fundamental control catalysing the transformation of blueschists into greenschists and the associated resetting of their isotopic systems was the selective infiltration of metamorphic fluid a quartz magnetite sample from a contact metamorphic skarn taken near the miocene monzogranite of tinos gave an oxygen isotope temperature of 555 c and calculated water composition of 9 1 the value of 18o obtained from this water is consistent with a primary magmatic fluid but is lower than that of fluids associated with the greenschist overprint which indicates that the latter event cannot be directly related to the monozogranite intrusion

metamorphic evolution of the attic cycladic metamorphic belt on naxos cyclades greece utilizing 40ar 39ar age spectrum measurements 40ar 39ar age spectrum analysis of phengite separates from naxos part of the attic cycladic metamorphic belt in greece indicates that cooling following high pressure low to medium temperature metamorphism m1 occurred about 50 ma ago phengite has 40ar gradients that suggest that part of the scatter observed in conventional k ar ages was caused by diffusion of radiogenic argon from the minerals during a younger metamorphism m2 in central naxos this metamorphism m2 has overprinted the original mineral assemblages completely and is associated with development of a thermal dome excellent 40ar 39ar plateaus at 15 0 0 1 ma 11 8 0 1 ma and 11 4 0 1 ma obtained on hornblende muscovite and biotite respectively from the migmatite zone indicate that relatively rapid cooling followed the m2 event and that no significant thermal overprinting occurred subsequent to m2 toward lower m2 metamorphic grade 40ar 39ar plateau ages of hornblendes increase to 19 8 0 1 ma concomitantly the proportion of excess 40ar in the spectra increases as well we propose that the peak of m2 metamorphism occurred beween 15 0 and 19 8 ma ago k ar ages of biotites from a granodiorite on the west coast are indistinguishable from those found in the metamorphic complex and hornblende k ar ages from the same samples are in the range 12 1 13 6 ma as the latter ages are somewhat younger than most ages obtained from the metamorphic complex intrusion of the granodiorite most likely followed the peak of the m2 metamorphism the metamorphic evolution of naxos is consistent with rapid crustal thickening during the cretaceous or early tertiary causing conditions at which supracrustal rocks experienced pressures in the range 900 1500 mpa transition to normal crustal thicknesses ended the m1 metamorphism about 50 ma ago the m2 metamorphism and granodiorite intrusion occurred during a period of heat input into the crust possibly related to the migration of the hellenic volcanic ar c in a southerly direction through the area

kinematic reconstructions and magmatic evolution illuminating crustal and mantle dynamics of the eastern mediterranean region since the late cretaceous the relationship between subduction dynamics and crustal deformation in the mediterranean region has been recently studied using three dimensional 3d numerical models such models require however a detailed information concerning the past geological evolution we use stratigraphic petrologic metamorphic structural paleomagnetic and magmatic data to build new kinematic reconstructions of the eastern mediterranean region since the late cretaceous using the principle of non rigid domains the motions of the 56 deforming domains defined in this work are calculated based on published paleomagnetic rotations the directions and amounts of displacement on crustal scale shear zones and the burial and exhumation histories of the main metamorphic units extracted from these reconstructions paleotectonic maps and lithospheric scale cross sections illustrate that the present day subduction zone has been continuously retreating southward since the late cretaceous and has accreted several small continental domains in the process we find evidence for two back arc related extensional events 1 slow extension along the balkans and the pontides in the late cretaceous while the trench was long and linear and 2 faster extension in the rhodope aegean west anatolian region since the eocene oligocene rapid rotation of the hellenides between 15 and 8 ma probably indicates a slab tearing event below western anatolia that could have further accelerated this extensional kinematics spatial distribution and the geochemical signature of magmatic centers integrated in these reconstructions allow us to trace mantle related processes revealing the deep dynamics that controls both the magma genesis and the crustal deformation

precise determination of the open ocean 234u 238u composition uranium has a long residence time in the open oceans and therefore its salinity normalized u concentration and 234u 238u activity ratio expressed herein as 234u the deviation from secular equilibrium are assumed to be uniform the marine 234u 238u activity ratio is currently in radioactive disequilibrium and shows a 15 excess of 234u with respect to the secular equilibrium value due to continuous input from riverine sources knowledge of the marine 234u and how it has evolved through the quaternary is important for validating age accuracy in the u series dating of marine carbonates which is increasingly relied upon for providing a chronological basis in paleoclimate research however accurate and precise measurements of 234u are technically difficult thus existing compilations of the open ocean 234u value vary by up to 10 and the assumed uniformity in the oceanic 234u remains to be confirmed using mc icpms techniques and a suite of multiple faraday cups instead of the typical configurations based on a combined faraday cup multiplier array a long term reproducibility of better than 0 3 2 is achieved for 234u measurements applying these very high precision techniques to open ocean seawater samples an average 234u of 146 8 0 1 2 m n 19 is obtained these high precision seawater measurements yield an external reproducibility of better than 0 4 2 and show that the open oceans have a uniform 234u on the sub level these new data constrain the vertical mixing time of the open oceans to less than 1000 years

thermochronology of the high pressure metamorphic rocks of crete greece implications for the speed of tectonic processes new fission track thermochronologic data from the high pressure p low temperature t rocks of crete greece combined with pressure temperature and stratigraphic constraints reveal that their subduction began between 36 and 29 ma metamorphism took place in western crete at peak conditions of 10 2 kbar and 400 50 c between 24 and 19 ma and rapid exhumation to 10 km and 300 c at a minimum rate of 4 km m y was completed before 19 ma constraints from the thermal history of the plate above the inferred extensional detachment reveal that tectonic unroofing contributed 85 to 90 of the overall exhumation of the high p low t rocks of crete we propose that the hellenic subduction zone has acted as a retreating plate boundary since at least the early oligocene and collision and extension during this time were driven by roll back associated with slab pull rather than by gravitational collapse as a consequence of crustal thickening the speed of subduction and exhumation of the high p low t rocks of crete within 10 m y has important implications for other orogenic belts showing that rocks can be subducted metamorphosed at high pressure and exhumed despite slow overall plate convergence within the uncertainties of many paleontologic and isotopic age data

differing controls over the cenozoic pb and nd isotope evolution of deepwater in the central north pacific ocean dissolved pb and nd isotope ratios of seawater as recorded by chemical marine precipitates such as hydrogenetic ferromanganese crusts have been used as paleoenvironmental proxy tracers for the north pacific however all ferromanganese crusts studied so far have either been subject to phosphatization or hydrothermal influence in their old part or only the young parts have been analyzed thus the pb and nd isotope compositions of north pacific deep waters prior to 20 ma are not well constrained we present new results for three ferromanganese crusts one of which cj01 shows no phosphatization and is located far away from the epr its age is inferred to be 75 ma and thus provides for the first time an opportunity to trace the nd and pb isotope evolution of central north pacific seawater back to the latest cretaceous the three crusts no matter whether phosphatized or not display very similar pb and nd isotope trends with age suggesting no modification of the pb and nd isotope distribution by post depositional phosphatization our data suggest that dissolved pb in deep waters of the central north pacific over the cenozoic and latest cretaceous has mainly been derived from eolian dust and only to a minor extent from weathering of island arcs for pb these trends broadly resemble the pb isotope evolution of the eolian silicate dust fraction of core ll44 gpc3 in the central north pacific we suggest that the isotope evolution of dissolved pb in central north pacific seawater has been mainly controlled by pb released from eolian dust from north america prior to 50 ma and after 40 ma from asia in contrast the nd isotope time series of the crusts are by no means similar to the nd isotope evolution of the silicate dust fraction in core gpc3 suggesting a decoupling from the pb and negligible contributions from dust to the dissolved nd in the central north pacific deep water the rise of nd isotope ratios of pacific seawater during the cenozoic has most likely been caused by the increasing volcanic activity and erosion of the volcanic arcs around the pacific

depth averaged drag coefficient for modeling flow through suspended canopies aquatic suspended canopies are porous obstacles that extend down from the free surface but have a gap between the canopy and bed examples of suspended canopies include those formed by aquaculture structures or floating vegetation the major difference between suspended canopies and the more common submerged canopies which are located on the bottom boundary is the influence of the bottom boundary layer beneath the suspended canopy data from laboratory experiments are presented which explore aspects of the flow through and beneath suspended canopies constructed from rigid cylinders the experiments using both acoustic doppler and two dimensional 2d particle tracking velocimetry give details of the flow structure that may be divided vertically into a bottom boundary layer a canopy shear layer and an internal canopy layer the experimental data show that the penetration of the shear layer into the canopy is limited by the distance between the canopy and bottom boundary layer peaks in velocity spectra indicate an interaction between the bottom boundary and canopy shear layer an analytical model is also developed that can be used to calculate a drag coefficient that includes the effect of both canopy drag and bed friction this drag coefficient is suitable for use in 2d depth averaged hydrodynamic modeling the model also allows the average velocity within and beneath the canopy to be calculated and is used to investigate the effect of canopy density and thickness on both total drag and bottom friction

the north cycladic detachment system and associated mineralization mykonos greece insights on the evolution of the aegean domain 1 in the aegean back arc domain some 30 35 ma ago an increase of the rate of slab retreat led to the initiation of post orogenic extension largely accommodated by large scale structures such as the north cycladic detachment system ncds although this extension is still active nowadays an e w compressional regime developed in the late miocene with the propagation of the north anatolian fault on mykonos island cyclades the ne sw back arc extension is particularly well expressed with the livada and mykonos detachments that belong to the ncds and that are associated with nw se barite veins emplaced during the synkinematic cooling of the mykonos intrusion this study shows that the formation of the mineralization occurred when the pluton crossed the ductile to brittle transition during its exhumation below the ncds at 11 10 ma in addition the kinematics of mineralized structures evolved with time 1 most of the displacement was accommodated by the top to the ne livada and mykonos detachments accompanied by the formation of mineralized normal faults that were 2 reworked in a strike slip regime with an e w direction of shortening and a persistent ne sw stretching and 3 a late post mineralization e w compressional stage with a minor reworking of shallow dipping faults locally including the detachments themselves we interpret this increase of the e w shortening component recorded during the mineral deposition as a consequence of the initiation of the westward motion of anatolia from 10 ma thus 4 ma before the propagation of the north anatolian fault in the dardanelles strait and the localization of the strain on the aegean sea margins

structure and kinematics of upper cenozoic extensional detachment on naxos and paros cyclades islands greece this paper presents a study of the ductile and brittle deformation on naxos and paros islands cyclades greece previous maps and studies of the two islands have shown that a major low angle fault zone separates surface rocks above the contact from an initially deep seated unit below showing a metamorphic evolution from high to low pressures structural analysis as well as available stratigraphical metamorphic and geochronological data taken together demonstrate that this fault zone is a major normal sense detachment zone dipping to the north rapid denudation of footwall rocks subsequent to high temperature metamorphism at an estimated rate of 1 8 9 5 mm yr attests for tectonic unroofing during regional scale top to the north ductile shearing the change from ductile to brittle behavior of the footwall rocks together with a progressive localization of high strain intensity deformations just below the hangingwall is explained by the progressive cooling of the uprisen footwall of the detachment mio pliocene clastic sediments in the hangingwall represent the infilling of half grabens opened in between major normal faults that are synthetic to the underlying ductile shear zone these sediments are as old as aquitanian 25 ma or younger than the earliest recognized evidence of ductile extension in the footwall this provides a minimum age for the onset of extension in the cyclades which appears significantly older than maximum ages reported up to now 13 5 ma structural data strongly suggest that the detachment fault was initially rather low dipping 35 an evolutionary model is proposed in which migmatite domes in the footwall correspond to the uprise of the lower ductile crust between two separating upper crustal blocks during a process of asymmetric boudinage of the crust this detachment model applies to a previously thickened continental lithosphere which then suffers thermal relaxation and weakening allowing extensional deformation to reach a climax during and subsequent to high temperature metamorphism in the cyclades crustal scale extension started after early cenozoic thrusting while the crust was still thick or less likely before late underthrusting below the present surface

post collisional plutonism with adakite like signatures the eocene saraycik granodiorite eastern pontides turkey the post collisional saraycik granodiorite intruded into a late paleocene to early eocene nappe pile that formed during collision of the pontides in the north and the anatolide tauride platform in the south leading to the formation of the izmir ankara erzincan suture a relatively shallow pluton intrusion depth 5 to 8 km was estimated from al in hornblende geobarometry and contact metamorphic assemblages the emplacement age is tightly constrained to 52 ma by two ar ar plateau and total fusion ages on biotite the main mass of the pluton consists of metaluminous to peraluminous biotite granodiorite and hornblende biotite granodiorite in addition up to 10 m thick dacitic and 25 cm thick aplitic dikes occur granodiorites and dacites show many close compositional similarities to high silica adakites from supra subduction zone settings but tend to be slightly more felsic and to have a higher aluminium saturation index chondrite normalized cn rare earth element patterns are characterized by high ratios of la yb cn concave upward shapes of the hree and a lack of significant eu anomalies in conjunction with relatively high abundances of ba and sr as well as low abundances of y hree and sc these patterns suggest a feldspar poor garnet amphibole rich fractionating mineral assemblage residue all samples have very similar nd sr isotopic characteristics regardless of rock type initial end values range from 0 3 to 1 2 and initial 87sr 86sr ratios from 0 70491 to 0 70529 it is suggested that the magmas formed by partial melting of mafic lower crust at elevated pressures 1 to 2 gpa

geology of the bozdag area central menderes massif sw turkey pan african basement and alpine deformation the menderes massif consists of a precambrian core series that preserves evidence for a polymetamorphic history and a paleozoic mesozoic cover series that experienced only the alpine tectonometamorphic evolution structural petrographic and geochronologic investigations in the central menderes massif demonstrate that a part of the metamorphic and structural evolution of the precambrian basement is older than the undeformed 551 1 4 ma old birgi metagranite and b inferred alpine fabrics overprinting the cover series largely have the same attitudes as the old structures in the much older core series the inferred alpine fabrics include both contractional and extensional structures contraction under greenschist to amphibolite facies conditions resulted in the imbrication of the core and cover series and generated an inverted metamorphic sequence by north directed thrusting during alpine extension most of the south dipping thrust faults were reactivated as extensional shear zones under decreasing greenschist facies conditions

nd sr isotopic and ree constraints on the genesis of hydrothermal manganese crusts in the galapagos manganese oxide crusts from the galapagos spreading centre interpreted to be of hydrothermal origin have nd isotopic compositions and rare earth element ree concentrations that approach seawater values as the age increases numerous authors1 2 have cited hydrothermal processes along the mid oceanic ridges to explain the composition of metalliferous sediments other authors believe that these sediments whether now located on a ridge axis or in some deep were derived from hydrothermal activity near ridges and were modified during removal from these ridges3 6 nd and sr isotopic compositions as well as concentrations of ree and cu ni and co in hydrothermal mn crusts of different ages from the galapagos spreading area were determined to provide new information regarding the problem of the alteration behaviour with time of oceanic sediments our data suggest that hydrothermal crusts react with seawater and ultimately acquire the trace element characteristics of hydrogeneous crusts

discriminating between different genetic types of marine ferro manganese crusts and nodules based on rare earth elements and yttrium marine ferro manganese fe mn crusts and nodules are metal rich chemical sediments that are archives of paleoceanographic proxies and potential metal resources and targets of deep sea mining traditionally crusts and nodules are subdivided into hydrogenetic diagenetic and hydrothermal types because these are characterized by different compositions and hence economic resource potential a useable genetic classification is not only a tool for geochemical studies but may also help to characterize potential exploration targets we propose two easy to use yet robust discrimination diagrams based on geochemical relationships controlling the rare earths and yttrium rey inventory of marine fe mn oxyhydr oxide deposits the rey are a set of trace elements that show coherent behavior are routinely determined in geochemical studies and for which the analytical quality can easily be evaluated graphs of ce anomaly vs nd concentration and ce anomaly vs y anomaly effectively discriminate between the different types of precipitates regardless of their diverse mineralogical composition both hydrogenetic crusts and nodules show positive ce anomalies negative y anomalies and high nd concentrations of 100 mg kg 1 although nodules tend to have slightly lower nd concentrations than crusts in marked contrast hydrothermal deposits generally yield negative ce anomalies positive y anomalies and low nd concentrations of 10 mg kg 1 in spite of their large geochemical mineralogical and sedimentological diversity diagenetic nodules show negative ce anomalies negative y anomalies and intermediate nd concentrations between 10 and 100 mg kg 1 we discuss the geochemical background of these diagrams the respective sources of rey in the different precipitates and address the processes that control their rey inventory besides the three end members we also use rey systematics to define mixed type diagenetic hydrogenetic nodules and classify well studied international reference standards

i type plutonism in a continental back arc setting miocene granitoids and monzonites from the central aegean sea greece miocene extension in the aegean sea was accompanied by the intrusion of granitoid and monzonitic magmas at upper crustal levels with increasing distance from the trench the metaluminous to slightly peraluminous i type intrusives show a systematic regional variation in their compositions medium to high k granodiorites in the wsw high k low silica granites in the central region and high k high silica granites monzonites monzogranites and composite lamprophyric monzonitic dikes in the ene the granodioritic and low silica granitic plutons comprise similar ranges of sio2 63 5 71 6 wt and initial nd sr and o isotopic values end i 7 0 to 9 8 87sr 86sr i 0 7092 0 7115 18o 9 7 11 5 but display significant differences in their chemical compositions compared with the granodiorites the low silica granites have higher abundances of large ion lithophile light rare earth and some high field strength elements initial isotopic signatures of the high silica granites in the ene end i 9 0 to 9 6 87sr 86sr i 0 7128 0 7144 18o 10 8 12 0 are slightly more crust like than those of the low silica granites in chemical variation diagrams samples from the high silica granites continue the trends defined by those from the low silica granites it is suggested that all granitoid magmas originated by dehydration melting of metaluminous older crustal sources most probably metagreywackes u pb systematics of zircon populations in conjunction with zr sio2 systematics and zircon saturation temperatures suggest a high proportion of restitic or assimilated crustal material in these magmas monzonitic to monzogranitic rocks show chemical and isotopic characteristics end i 0 8 to 3 6 87sr 86sr i 0 7059 0 7071 18o 9 4 10 6 that are significantly different from those of the granitoids a small portion of an older crustal component in these magmas is indicated by u pb systematics of zircon populations lamprophyric dikes display chemical and isotopic signatures end i 0 5 87sr 86sr i 0 7044 18o 8 9 that are compatible with an origin from either a mantle source previously enriched by slab derived hydrous fluids melts as suggested by negative nb ta anomalies or a new k rich basaltic underplate abundant composite dikes indicate the coexistence of and mingling mixing between lamprophyric melts and monzonitic magmas

sr z sbnd nd isotopic record of multi stage interactions between mantle derived magmas and crustal components in a collision context the ultramafic granitoid association from vivero hercynian belt nw spain late stage epizonal calc alkaline granitoids of the hercynian belt are often associated with coeval more basic rocks such granitoids have been the focus of special attention when studying the role of mantle derived magmas in granitoid genesis these studies conclude that basic magmas are involved in granitoid production but their contribution to the chemical composition of granitoids is often controversial the vivero massif nw spain includes calc alkaline granitoids and coeval ultramafic and mafic rocks but these granitoids are syntectonic and intruded into middle crustal levels during an early stage scattered major and trace element chemistry together with heterogeneous sr nd isotopic results preclude an origin of this ultramafic to granitoid association by any closed system fractionation process ultramafic rocks include peridotites pyroxenites and homblendites with endi from 3 5 to 1 3 and 87sr86sr i ratio from 0 7059 to 0 7080 they are interpreted as cumulates formed by in situ fractional crystallization from contaminated basaltic magmas particularly by interaction with 87sr enriched fluids mafic rocks comprise biotite amphibole diorites quartz diorites and tonalites with ndi from 3 8 to 0 0 and 87sr86sr i ratio from 0 7058 to 0 7073 they represent either cumulates or more evolved magmas of calc alkaline affinity these rocks display an inverse correlation between the degree of differentiation and the degree of contamination inferred from isotope data this points to wall rock assimilation by thermal erosion during ascent of basic magmas up to the middle crust and supports the participation of mantle sources with positive end and 87sr86sr i 0 7058 granitoids range from amphibole biotite tonalites through biotite granodiorites to monzonitic granites they show an isotopic trend which diverges from that of ultramafic and mafic rocks endi 6 0 to 1 9 decreases while 87sr86sr i ratio 0 7061 to 0 7082 increases from tonalites to monzonitic granites reflecting an increasing contribution of crustal components in more differentiated rocks assimilation and fractional crystallization mixing included account for such an evolution contamination of basic magmas by this process occurring at deeper crustal level produced hybrid tonalites and related mafic magmatic enclaves only monzonitic granites are interpreted as pure crustal melts their hree fractionated patterns gd yb 4 5 suggest equilibrium with a garnet rich residuum partial melting of moderate time integrated rb sr protolith such as greywackes and or meta igneous rocks of intermediate acid composition could account for the isotopic composition of these monozogranites this example shows that at least some calc alkaline granitoids of collisional setting are not produced by pure intra crustal melting they are formed through a complex multi stage hybridization process involving mantle derived magmas crustal components and several concomitant magmatic processes

granitoid rocks of the southern menderes massif southwestern turkey field evidence for tertiary magmatism in an extensional shear zone recent field campaign in the southern menderes massif in southwestern turkey revealed that the so called core of the massif comprises two distinct types of granitoid rocks an orthogneiss traditionally known as augen gneisses and leucocratic metagranite where the latter is intrusive into the former and the structurally overlying cover schists these differ from one another in intensity of deformation degree of metamorphism and kinematics the orthogneiss display penetrative top to the n nne fabrics formed under upper amphibolite facies conditions during the eocene main menderes metamorphism mmm whereas foliation and stretching lineation exists in the leucocratic metagranites but are not strongly developed the leucocratic metagranites show evidence of syn to post emplacement deformation in a series of weakly developed top to the s ssw fabrics formed under lower greenschist facies conditions leucocratic metagranite bodies occur all along the augen gneiss schist contact in the southern menderes massif they are emplaced as sheet like bodies into country rocks previously deformed and metamorphosed during a top to the n nne alpine orogeny along a ductile extensional shear zone located between orthogneisses and metasediments which was possibly active during emplacement the data presently available indicate that emplacement and associated ductile extensional deformation occurred during late oligocene early miocene time these results confirm previous contentions that there are tertiary granites in this part of the menderes massif

diffuse flow hydrothermal manganese mineralization along the active mariana and southern izu bonin arc system western pacific 1 abundant ferromanganese oxides were collected along 1200 km of the active izu bonin mariana arc system chemical compositions and mineralogy show that samples were collected from two deposit types fe mn crusts of mixed hydrogenetic hydrothermal origin and hydrothermal mn oxide deposits this paper addresses only the second type mn oxides cement volcaniclastic and biogenic sandstone and breccia layers mn sandstone and form discrete dense stratabound layers along bedding planes and within beds stratabound mn the mn oxide was deposited within coarse grained sediments from diffuse flow systems where precipitation occurred below the seafloor deposits were exposed at the seabed by faulting mass wasting and erosion scanning electron microscopy and microprobe analyses indicate the presence of both amorphous and crystalline 10 a and 7 a manganate minerals the fundamental chemical difference being high water contents in the amorphous mn oxides alternation of amorphous and crystalline laminae occurs in many samples which likely resulted from initial rapid precipitation of amorphous mn oxides from waxing pulses of hydrothermal fluids followed by precipitation of slow forming crystallites during waning stages the chemical composition is characteristic of a hydrothermal origin including strong fractionation between fe mean 0 9 wt and mn mean 48 wt for the stratabound mn generally low trace metal contents and very low rare earth element and platinum group element contents however mo cd zn cu ni and co occur in high concentrations in some samples and may be good indicator elements for proximity to the heat source or to massive sulfide deposits for the mn sandstones fe mean 8 4 and mn 12 4 are not significantly fractionated because of high fe contents in the volcaniclastic material however the proportion of hydrothermal fe nondetrital fe to total fe is remarkably constant 49 58 for all the sample groups regardless of the degree of mn mineralization factor analyses indicate various mixtures of two dominant components hydrothermal mn oxide for the stratabound mn and detrital aluminosilicate for the mn cemented sandstone and two minor components hydrothermal fe oxyhydroxide and biocarbonate biosilica our conceptual model shows that mn mineralization was produced by hydrothermal convection cells within arc volcanoes and sedimentary prisms that occur along the flanks and within calderas the main source of hydrothermal fluid was seawater that penetrated through fractures faults and permeable volcanic edifices the fluids were heated by magma enriched in metals by leaching of basement rocks and sediments and mixed with magmatic fluids and gases dikes and sills may have been another source of heat that drove small scale circulation within sedimentary prisms

numerical study of turbulence and wave damping induced by vegetation canopies article i nfo vegetation canopies control mean and turbulent flow structure as well as surface wave processes in coastal regions a non hydrostatic rans model based on nhwave ma et al 2012 is developed to study turbulent mixing surface wave attenuation and nearshore circulation induced by vegetation a nonlinear k e model accounting for vegetation induced turbulence production is implemented to study turbulent flow within the vegetation field the model is calibrated and validated using experimental data from vegetated open channel flow as well as nonbreaking and breaking random wave propagation in vegetation fields it is found that the drag related coefficients in the k e model cfk and cf can greatly affect turbulent flow structure but seldom change the wave attenuation rate the bulk drag coefficient cd is the major parameter controlling surface wave damping by vegetation canopies using the empirical formula of mendez and losada 2004 the present model provides accurate predictions of vegetation induced wave energy dissipation wave propagation through a finite patch of vegetation in the surf zone is investigated as well it isfound that the presenceof a finite patch of vegetation may generate strong pressure driven nearshore currents with an onshore mean flow in the unvegetated zone and an offshore return flow in the vegetated zone published by elsevier b v

geochemistry and u series dating of holocene and fossil marine hydrothermal manganese deposits from the izu ogasawara arc abstract this study investigated holocene and fossil hydrothermal manganese deposits in the izu ogasawara arc mineralogically these deposits comprise 10 a and 7 a manganate minerals and the fossil samples showed higher 10 a stabilities chemical compositions of the holocene samples are typical of other hydrothermal manganese deposits including low fe mn ratios low trace metals and low rare earth elements although the fossil samples generally have similar chemical characteristics they exhibit significant enrichment in ni cu zn cd ba ree tl and pb contents furthermore the chondrite normalized ree patterns showed more light ree enrichment trends these chemical characteristics suggest post depositional uptake of these metals from seawater u th dating of a holocene hydrothermal manganese deposit from the kaikata seamount indicated 8 8 0 94 ka for the uppermost layer and downward growth beneath the seafloor with a growth rate of ca 2 mm kyr this is approximately three orders of magnitude faster than that of hydrogenetic ferromanganese crusts u pb age of a fossil hydrothermal manganese deposit from the nishi jokyo seamount showed 4 4 1 6 ma which was contemporary with basaltic volcanism 5 8 0 3 ma hydrothermal manganese deposits contain high concentrations of high value mn but only small amounts of valuable minor metals their ages constrain the periods of past hydrothermal activity and provide a vector to explore for polymetallic sulfide deposits

low angle faults above and below a blueschist belt tinos island cyclades greece new observations from the island of tinos greece allow a better definition of the structural position of the alpine eocene blueschist belt exposed in the islands of the aegean sea these blueschists over a significant part of the aegean sea are delimited from below by a low angle thrust fault while from above they are delimited by a low angle normal type fault which omits a substantial crustal interval both underlying and overlying rocks were not affected by the high metamorphism the rapid uplift and exhumation of the high rocks was therefore mainly the result of fault movements rather than erosion and whole crust uplifting the low angle normal fault apparently had a major role in the uplift of the blueschists

u and th concentrations and isotope ratios in modern carbonates and waters from the bahamas the short residence times of th and pa in seawater make them very responsive to changes in the ocean environment we use a new multi ion counting technique to make th and pa isotope measurements in seawaters from a near shore environment in which oceanic chemical tracers are not overwhelmed by terrestrial inputs the bahamas an unusual feature of the bahamas setting is the shallow depth of water residing on the bank tops these waters have significantly lower 232th 230th 10 000 than those immediately adjacent to the banks 24 000 31 000 and a 231pa 230th near the production ratio 0 1 the change in 232th 230th and 231pa 230th on the bank tops is explained by almost quantitative removal of th and pa by scavenging and their replacement with a mixture of 230th and 231pa alpha recoiled from the underlying carbonates together with th from dust dissolution analysis of a water profile in the tongue of the ocean which separates the great and little bahama banks allows us to trace the movement of bank top water to depth a distinct minimum in both 232th 230th 13 000 and 231pa 230th 0 5 is observed at 430 m and is interpreted to reflect density cascading of bank top water with entrained carbonate sediment these results suggest that th and pa can be used as water mass tracers in near shore environments uranium concentration measurements on the same waters demonstrate that u is conservative across a range in salinity of 2 psu with a concentration of 3 33 ppb at a salinity of 35 the incorporation of u and th isotopes into marine carbonates has also been assessed by analyzing carbonate samples from the same location as these bahamas waters such incorporation is critical for u th geochronology u isotope analyses demonstrate that seawater 234u averages 146 6 and does not vary by more than 2 5 o and that carbonates capture this value additional high precision measurements 1 o on modern carbonates confirm that all oceans have identical 234u modern marine carbonates are shown to have 232th 230th ratios that reflect the local seawater in which they formed

tectonic setting petrology and geochronology of jadeite glaucophane and chloritoid glaucophane schists from north west turkey the north west turkish blueschists represent a subducted passive continental margin sequence dominated by metaclastic rocks and marble the depositional age of the blueschist protoliths are probably palaeozoic to mesozoic while the age of the high pressure low temperature metamorphism is late cretaceous blueschists are tectonically overlain by a volcanosedimentary sequence made up of accreted oceanic crustal material that locally shows incipient blueschist metamorphism and by spinel peridotite slices the metaclastic rocks with regional jadeite and glaucophane which comprise the lower part of the blueschist unit make up an over 1000 m thick coherent sequence in the kocasu region of north west turkey rare metabasic horizons in the upper parts of the metaclastic sequence with sodic amphibole iawsonite but no garnet indicate lawsonite blueschist facies metamorphism the blueschist metaclastics in the kocasu region are practically free of calcium and ferric iron and closely approximate the nfmash system in bulk composition two low variance mineral assemblages with quartz and phengite are jadeite glaucophane chlorite paragonite and chloritoid glaucophane paragonite the metaclastics comprise up to several metres thick layers of jadeite schist with quartz phengite and nearly 100 mol jadeite phase relations in the metaclastics show that the chloritoid glaucophane assemblage even in fe2 rich compositions is stable in the jadeite stability field in the nfash system the above assemblage without the accompanying garnet has a narrow thermal stability field mineral equilibria in the metaclastics involving chloritoid glaucophane jadeite paragonite and chlorite indicate metamorphic p t conditions of 20 2 kbar and 430 30 d c yielding geothermal gradients close to 5d c km 1 one of the lowest geotherms recorded blueschists in the kocasu region which have been buried to 70 km depth are tectonically overlain by the volcanosedimentary sequence and by peridotite buried not deeper than 30 km phengites from two jadeite schists were dated by ar ar laser probe they give an age of 88 5 0 5 ma interpreted as the age of metamorphism blueschists and the overlying peridotite bodies are intruded by 48 53 ma old granodiorite bodies that were emplaced at 10 km depth this suggests that the exhumation of blueschists by underplating of cold continental crust and normal faulting at the blueschist peridotite interface occurred during the late cretaceous to palaeocene 88 53 ma

the pb sr nd isotope geochemistry of some recent circum mediterranean granites pb sr and nd isotopic compositions have been analyzed in recent granites from northern africa northern italy and greece lead isotope compositions of k feldspars are rather homogeneous and cluster close to the modern lead of stacey and kramers 1975 but with slightly higher207pb 204pb and208pb 204pb ratios the cyclades samples however have higher206pb 204pb ratios addition of mantle derived lead was probably very limited which supports a quasi closed system evolution of this element in the continental crust the sr nd data fall in the enriched part of the143nd 144nd vs 87sr 86sr diagram and define a smooth hyperbolic mixing curve over a wide area straddling different orogens most granites may be accounted for by a binary mixture between a recycled crustal component and a depleted mantle like component no correlation is observed between either pb and sr or nd isotopic ratios or any isotopic ratio and major element contents quantitative modelling suggests that two cases fit the sr and nd characteristics of these granites they both require anatexis of the crust on a scale large enough to average the isotopic properties of heterogeneous terranes in the first case the mantle derived component may be represented by differentiated island arc type magmas and the granites result from mixing these magmas with anatectic melts in the second case mantle derived igneous rocks such as obducted ophiolites are part of the crustal source and their variable involvement in the anatectic process causes isotopic variations

geochemistry of hydrothermal manganese deposits from the pitcairn island hotspot southeastern pacific hydrothermal mn crusts from a submarine volcano in the pitcairn island region have been studied mineralogically radiometrically and by bulk and partition chemical techniques the crusts contain layers that comprise three morphological types a mechanism of formation by downward growth from a mn cemented surface sand hardpan is proposed age dating of the crusts suggests relatively recent and rapid formation mineralogically the crusts exhibit variable amounts of 10a and 7a manganite chemical data however indicate that the crusts do not show element associations characteristic of marine birnessite suggesting that the 7a manganite phase may have transformed from structurally unstable 10a manganite as a result of air drying trace element concentrations in massive finely laminated types 2 and 3 crust layers are significantly lower than those in similar crusts from island arc and back arc settings and in general are comparable with or lower than those of the most trace element poor crusts from mid oceanic ridge environments ree data suggest that these crusts are almost pure hydrothermal deposits with little or no hydrogenous component in the types 2 and 3 crusts only mo shows a significant enrichment that is likely to be hydrothermal in origin although it is enriched to lower levels than in hydrothermal crusts from most other geological settings friable mn cemented sand type 1 crusts contain elevated trace element concentrations in part as a result of incorporation of biogenic and volcaniclastic phases but also as a result of hydrogenous inputs consistent with their greater age and closer proximity to seawater in contrast to types 2 and 3 crusts which show no li enrichment type 1 crusts are enriched in li to levels above those that can be accounted for by hydrogenous input and a hydrothermal source for it is proposed the observed variability in the composition of hydrothermal mn crusts between midplate hotspot mid oceanic ridge island arc and back arc environments may be influenced by variability in basement composition and sea water rock ratio in the hydrothermal systems as both parameters are directly related to tectonic setting this may play an important role in controlling the chemistry of hydrothermal deposits

generation of metaluminous a type granites by low pressure melting of calc alkaline granitoids melting experiments on two calc alkaline rocks a tonalite and a granodiorite demonstrate that shallow dehydration melting of hornblende and biotite bearing granitoids generates metaluminous a type granitic melts profuse crystallization of calcic plagioclase orthopyroxene during low pressure p 4 kbar incongruent melting explains all of the major and trace element characteristics of a type granites e g their low al ca mg sr and eu contents and high ga al and k na ratios as well as their common association with anorthositic and mangeritic rocks the residual assemblage produced during melting of the same rocks in the deep crust p 8 kbar is dominated by clinopyroxene and as a consequence most of the chemical features diagnostic of a type granites are lost the high temperatures 900 c and low h 2 o contents 4 wt that are characteristic of a type magmas are adequately explained by the h 2 o poor nature of the granitoid source materials and require neither a granulitic nor a f rich source previous attempts to explain the origin of a type granites have focused on the nature of the source material these experiments show that pressure of melting is at least as important as source composition in engendering a type melts

highly fractionated late triassic i type granites and related molybdenum mineralization in the qinling orogenic belt geochemical and u pb hf and re os isotope constraints abstract we present new data on the highly fractionated late triassic i type liyuantang granite which is located in the middle segment of the south qinling subzone of central china and is associated with molybdenum mineralization zircon u pb dating indicates that the granite was emplaced at 210 1 1 9 ma with a single zircon containing an inherited core that yielded an age of 449 8 7 1 ma magmatic zircons from the granite have e hf t values of 4 0 to 1 5 whereas the inherited zircon core has a e hf t value of 5 3 calculated hf model ages of crust formation are indicative of substantial contributions from melting of proterozoic crust that ranges in age from 1501 to 1155 ma the granite contains high concentrations of si al na and k is enriched in rb th and u has elevated rb sr and ga al ratios and is depleted in ti fe mn mg ca and p with significantly negative eu anomalies eu 0 33 0 50 similar to other highly fractionated i type granites these data indicate that the magmas that formed the liyuantang pluton were produced during partial melting of proterozoic garnet absent quartz amphibolites the magmas then fractionated apatite feldspar ti bearing phases biotite and hornblende prior to emplacement re os isotope analysis of molybdenite from the study area yields a mineralization age of 200 9 6 2 ma suggesting that the liyuantang molybdenum deposit formed during a previously unrecognized mineralization event the present results together with previous data demonstrate that highly fractionated i type granites associated with the second pulse of magmatism in the south qinling subzone should be considered highly prospective for mineral exploration focusing on triassic early jurassic granitoids

contact metamorphism in pelitic rocks on the island of kos greece eastern aegean sea a test for the na in cordierite thermometer into cordierite by a coupled substitution involving tetrahedral and most of the applicable thermometers involving cordierite require octahedral sites whereas na may not be charge balanced by additional fe mg phases and knowledge of pressure and fluid phase lattice oxygen the results obtained suggest that the experimentally composition these conditions are not necessarily met with natural established relationship between na contents of cordierite and cordierite bearing metamorphic rocks a potential pressure intemperature is a useful thermometer for cordieriteand plagioclasedependent geothermometer for cordieriteand plagioclase bearing bearing metapelitic rocks the nature of na incorporation in cordierite rocks is the experimentally determined inverse linear relationship and its relation to fluid composition however must be constrained between temperature and na contents of mg cordierite coexisting by further experiments with naoh or albite and naoh in this paper the na incordierite thermometer is empirically tested on cordierite bearing metapelites from the island of kos contact metamorphosed by a quartz monzonite intrusion the variety of phase assemblages in the metapelites allows for tight constraints to be placed on temperatures

a comparison of geodetic and finite strain pattern in the aegean geodynamic implications abstract a comparison of the active strain pattern of the aegean constrained by global positioning system measurements and the oligo miocene finite strain field shows some striking similarities in terms of direction and rates of extension the geometry of extension at crustal scale is also very similar with north dipping normal faults connecting near the brittle ductile transition to shallow north dipping shear zones this pattern of extension is not significantly modified by the recent extrusion of the motion of anatolia and aegea the persistence over more than 25 myr of the same pattern of extension suggests that the cause for extension resides within the aegean lithosphere gravitational collapse allowed by extensional boundary conditions after 30 ma slab retreat is the primary cause for post orogenic extension in the aegean and western anatolia

middle triassic ultrapotassic rhyolites from the tanggula pass southern qiangtang china a previously unrecognized stage of silicic magmatism abstract there is a mid late mesozoic jurassic cretaceous arc magmatic belt in southern qiangtang subterrane associated with the north dipping subduction of the bangong nujiang tethyan ocean early mesozoic triassic magmatism tectonic evolution of the southern qiangtang subterrane and the mechanism of its crustal growth however remain unclear this paper reports zircon u pb age whole rock major trace elemental and sr nd hf isotopic components for the mesozoic tanggula pass rhyolites in southern qiangtang subterrane our new data reveal a significant previously unrecognized stage of magmatism in southern qiangtang subterrane the tanggula pass rhyolites are moderately strongly peraluminous a cnk 1 09 1 54 highly fractionated sio2 73 and ultrapotassic k2o na2o 44 zircon u pb dating by la icp ms yields a concordant age with a weighted mean 206pb 238u age of 235 9 0 86 ma n 18 mswd 0 25 the large variations of major and trace element concentrations are mainly attributed to fractional crystallization of plagioclase hornblende fe ti oxides and accessory minerals such as apatite allanite monazite and zircon in the shallow level k feldspar mainly occurs as cumulated mineral resulting in high k2o contents and k2o na2o ratios the rhyolites were derived by partial melting of mixed source rocks including older sedimentary rocks in the upper crust and juvenile materials triggered by north dipping subduction of the bangong nujiang tethyan oceanic lithosphere the eruption age of middle triassic suggests that the initiation of northward subduction of the bangong nujiang tethyan ocean took place earlier than is currently assumed whole rock nd ca 1 55 to 2 34 ga and zircon hf ca 1 77 to 2 33 ga data reflect the presence of the proterozoic basement in the southern qiangtang subterrane basaltic magma underplating and accretion of intra oceanic arc complexes and oceanic plateau contributed to vertical crustal growth and lateral crustal growth respectively

geochemistry of hydrothermal mn oxide deposits from the s w pacific island arc abstract hydrothermal mn oxide crusts have been removed from the tonga kermadec ridge the first such hydrothermal deposits to be reported in the s w pacific island arc in several respects the deposits are similar to hydrothermal mn crusts from oceanic spreading centre settings they are limited in areal extent comprise well crystalline birnessite and generally display extreme fractionation of mn from fe they are strongly depleted in many elements compared to hydrogenous mn deposits but are comparatively enriched in li zn mo and cd the group ia and group iia metals show strong intercorrelations and the behaviour of mg in the purest samples may indicate the extent to which normal seawater has influenced the composition of the deposits certain aspects of the deposits are not typical of hydrothermal mn deposits in particular at least some of the crusts have developed on a sediment or unconsolidated talus substrate some crusts or specific layers within some crusts display a chemical composition which suggests a significant input from normal seawater

amphibole out phase boundary in partially melted metabasalt its control over liquid fraction and composition and source permeability a number of experimental studies in recent years have demonstrated that partial melting of hydrated basalt at lower crustal to upper mantle pressures is capable of generating up to 40 high sio2 liquids closely comparable in many geochemical respects to tonalitic trondhjemitic granitoids ttg from these studies it is apparent that the initiation of melting coincides with the beginning of amphibole dehydration but that a broad reaction interval over which amphibole coexists with high sio2 liquids is defined by the wet basalt solidus on one side and the amphibole out phase boundary on the other the phase relations of an alkali rich tholeiitic metabasalt have been examined in the outer half of this region up to and beyond the amphibole out phase boundary results indicate that amphibole exerts a strong control over the amount and composition of coexisting liquid over this interval melt fraction increases slowly and gradually from 0 up to 20 30 between the wet basalt solidus and up to amphibole out but increases substantially from 30 to 50 across and immediately beyond it liquids are strongly to moderately peraluminous molar al2o3 cao na2o k2o a cnk 1 0 up to amphibole out neutral at the boundary a cnk 1 0 and increasingly metaluminous a cnk 1 0 beyond it up to amphibole out potassium is strongly partitioned into liquid relative to amphibole i e mineral melt kd 0 2 0 3 whereas titanium is strongly partitioned into liquid kd 2 0 6 0 physical and chemical criteria suggest that efficient melt segregation leading to ttg plutonism requires more than 20 30 batch melting of a garnet bearing basaltic protolith near or beyond the amphibole out phase boundary leaving dry residues of eclogite or garnet granulite and producing metaluminous liquids that are strongly depleted in heavy rare earth elements hrees and yttrium y lower degrees of melting may involve critical melting where melt is squeezed out of the residue by deformation of the crystalline matrix resulting in disequilibrium melt compositions

structural stability of marine 10 a manganates from the ogasawara bonin arc implication for low temperature hydrothermal activity abstract hydrothermal 10 a manganate deposits with distinct differences in structural stability when exposed to air were found on the kaikata seamount of the ogasawara arc western pacific the most stable 10 a manganates are concentrated near the center of the hydrothermal field while the unstable ones occur towards the field margins all manganates are characterized by very high mn fe ratios and extremely low contents of transition elements such as cu co and ni the variation in 10 a stability of the hydrothermal manganates is not regulated by mineral chemistry or aging but appears to be determined by other factors e g the hydrothermal fluid temperature at mineral deposition we propose a structural model for marine manganates showing two continuous series of increasingly stabilized 10 a manganates one series is of hydrothermal origin structurally similar to todorokite with a tunnel structure fixed at deposition and the other is a buserite like series of diagenetic origin comprising phyllomanganates all the marine 10 a manganates can be progressively stabilized in two different manners the todorokite like series by the establishment of smaller tunnels and the buserite like series by post depositional uptake of 10 a stabilizing interlayer cations both series are linked together with a common end member the most unstable 10 a manganate which appears to be formed at low temperature and easily transforms to a 7 a manganate in air

the timing of partial melting barrovian metamorphism and granite intrusion in the naxos metamorphic core complex cyclades aegean sea greece abstract the relationship between partial melting and granite intrusion in a classic barrovian metamorphic terrane has been assessed thirteen samples were dated by shrimp u pb zircon geochronology from the island of naxos greece one of the aegean metamorphic core complexes the effect of partial melting during peak barrovian metamorphism on naxos is recorded by fine

slab breakoff a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens we present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision slab breakoff allowing an explanation of syn to post collisional magmatism and metamorphism continental collisions are preceded by subduction of dense oceanic lithosphere and followed by attempted subduction of buoyant continental lithosphere this situation of opposing buoyancy forces leads to extensional deformation in the subducted slab a narrow rifting mode of deformation will result if there is strain localization slab breakoff results we have assessed the plausiblity of this process by quantitatively evaluating an upper bound for the strength of the lithosphere and have compared it with the change in buoyancy force during continental sbduction whether breakoff will occur and the depth at which it will occur is a strong function of temperature and hence the subduction velocity for a subduction velocity of 1 cm yr breakoff could occur at depths of between 50 and 120 km while at higher velocities it is still likely to occur but at deeper depths as a result of the rifting during breakoff the asthenosphere upwells into the narrow rift and following breakoff it impinges on the mechanical lithosphere of the overriding plate the resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere producing basaltic magmatism that leads to granitic magmatism in the crust dry asthenospheric mantle will melt only if breakoff occurs at a depth shallower than ca 50 km breakoff removes the force at the downdip side of the continental crust while the enhanced heating leads to a reduction of the strength of the underlying crust both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface leading to the rapid exhumation of eclogite facies continental crust the cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen we have tested the variety of predicted expressions of slab breakoff in the geological record of the alps the aegean islands and the dabie shan a comparison of the various belts highlights 1 that the magmatism and metamorphism are found near the suture and the centre of the orogen demonstrating the general steepening of suture during collision 2 that a vague inverse correlation exists between maximum depth of metamorphism and volume of syn orogenic magmatism and 3 that the melts can be emplaced in both compressive and extensional environments we suggest that slab breakoff is an important step in the evolution of many orogenic belts and it allows an explanation for the combined presence in collisional orogens of magmatism with a mantle parentage and ultra high pressure metamorphics

shallow submarine epithermal pb zn cu au ag te mineralization on western milos island aegean volcanic arc greece mineralogical geological and geochemical constraints abstract milos island contains several epithermal deposits e g profitis ilias chondro vouno pb zn ag au te cu triades galana agathia kondaros pb zn ag bi w mo cu au and katsimoutis kondaros vani pb zn ag mn of late pliocene to early pleistocene age these deposits are hosted in calc alkaline volcanic rocks emplaced as a result of three successive magma pulses in an emergent volcanic edifice submarine rhyolitic to rhyodacitic cryptodomes at ca 2 7 ma profitis ilias chondro vouno submarine to subaerial andesite to dacite domes at ca 2 2 to 1 5 ma triades galana kondaros katsimouti vani hydrothermal alteration of the volcanic rocks includes advanced argillic both hypogene and steam heated argillic phyllic adularia sericite and propylitic types in the northern sector triades galana agathia kondaros initial magma degassing derived from andesitic dacitic intrusives along ne sw to e w trending faults resulted in the development of pre ore hypogene advanced argillic alteration dickite alunite diaspore pyrophyllite halite and pyrite in a submarine environment mineralogical data indicate common features among the profitis ilias chondro vouno kondaros katsimoutis vani and triades galana mineralized centers all of which are characterized by the presence of galena fe poor sphalerite and chalcopyrite as well as abundant barite adularia sericite and to a lesser extent calcite which are typical of intermediate sulfidation epithermal type deposits locally at triades galana and kondaros agathia high sulfidation conditions prevailed as suggested by the presence of coexisting enargite and covellite the high silver and gold content of the western milos deposits is derived from ag bearing sulfosalts polybasite pearceite pyrargyrite freibergite and tellurides gold at profitis ilias both as native gold and silver gold tellurides is present in base metal precipitates within multicomponent blebs which recrystallized to form hessite petzite altaite coloradoite and native gold mineralogical evidence e g microchimney structures copper sulfides widespread occurrence of barite aragonite suggests that precious metal mineralization in western milos mineralization formed in a submarine setting we present information on the surface distribution of au ag cu pb zn as sb hg mo bi w and cd at western milos gold is enriched at profitis ilias chondro vouno deposits and to a lesser extent at triades galana arsenic is absent from the southern sector but shows elevated concentrations together with molybdenum bismuth and tungsten at the northern sector triades galana vani deposits the differences in precious and base metal abundances may be related to the depths at which the deposits are exposed and or different sources of magma the metal signatures of the triades galana and agathia kondaros katsimouti vani mo bi w as hg ag au occurrences compared to profitis ilias te au ag reflect different sources of magma dacite rhyodacite for profitis ilias andesite dacite for triades galana and dacite for kondaros katsimoutis the enrichment of te mo w and bi in the deposits is a strong indication of a direct magmatic contribution of these metals at western milos precious and base metal vein mineralization was deposited during episodic injection of magmatic volatiles and dilution of the hydrothermal fluids by seawater the mineralization represents seafloor sub seafloor precipitation of sulfides that formed in stockwork zones base and precious metal mineralization formed from intermediate to high sulfidation state fluids and mostly under boiling conditions as indicated by the widespread occurrence of adularia associated with metallic mineralization we speculate that the widespread occurrence of boiling and the shallow depth of the precious and base metal emplacement prevented the formation of seafloor massive sulfides

the tectono metamorphic evolution of a dismembered ophiolite tinos cyclades greece the six exposures of the upper tectonic unit of the cycladic massif occurring on the island of tinos are shown to comprise a metamorphosed dismembered ophiolite complex the common stratigraphic section consisting of tens of metres thick tectonic slices of mafic phyllites overlain by serpentinites and gabbros is considered to have been derived by a combination of thrusting during obduction and subsequent attenuation by low angle normal faults all rock types show evidence of a phase of regional greenschist facies metamorphism which in the case of the phyllites is accompanied by penetrative deformation the greenschist facies metamorphism in gabbros is preceded by high temperature sea floor amphibolite facies alteration whereas in the serpentinites the antigorite forsterite greenschist facies assemblage overprinted an earlier low temperature lizardite serpentinite trace element patterns of the mafic phyllites and a harzbur gitic origin of meta serpentinites suggest a supra subduction zone ssz affinity for the ophiolitic suite 5 o values of phyllites gabbros and serpentinites range from 6 to 15 o model calculations indicate that such values are consistent with low temperature 50 200 c alteration of parent rocks by sea water at varying water rock ratios this would agree with the early low temperature mineralogy of the serpentinites but the early high temperature alteration of the gabbros would require the presence of o enriched sea water the following overall history is suggested for tinos ophiolitic slices 1 oceanic crust was generated at a supra subduction zone spreading centre with high temperature alteration of gabbros 2 tectonic distur bance its early hot stages recorded in an amphibolitic shear zone at the base of serpentinites brought the already cooled ultramafics into direct contact with sea water and caused low 7 serpentinization 3 tectonism after cooling involved thrusting which caused repetition and inversion of the original order of the oceanic suite 4 regional metamorphism of all the ophiolite components at greenschist facies conditions 450 c overprinted the early alteration mineralogy it was probably induced by continued thrusting and piling up of nappes the tinos ophiolite dated as late cretaceous and genetically related to other low pres sure rock units of the same age in the aegean differs in age and degree of dismemberment and metamor phism from ophiolites in mainland greece

rb sr isotope studies on tinos island cyclades greece additional time constraints for metamorphism extent of infiltration controlled overprinting and deformational activity this study presents new rb sr age data concerning the metamorphic evolution of the attic cycladic crystalline belt which represents a complex polymetamorphic terrane within the alpidic orogenic belt of the hellenides two major groups of tectonic units can be distinguished metamorphism in parts of the upper units is commonly considered as a cretaceous event in contrast the group of lower units experi enced tertiary high pressure metamorphism which was followed by a medium pressure overprint we focus on the island of tinos where a representative spectrum of the rock units found in the cyclades is exposed in three tectonic units the upper unit the intermediate unit and the basal unit the complete range of tectono metamorphic and magmatic events affecting the attic cycladic crystalline belt is documented by numerous petrological and tectonic studies phyllites and phyllonites from the ophiolitic upper unit yielded rb sr apparent ages phengite whole rock between c 92 and 21 ma the older age differs from the cretaceous dates reported for upper unit rocks elsewhere in the cyclades it is suggested that the sequence studied belongs to the jurassic ophiolites of the hellenides rather than to cretaceous occurrences the spread to younger ages is related to non pervasive rejuvenation and resetting of the rb sr system during tectonic juxtaposition of the upper unit over the intermediate unit the youngest age obtained so far for a sample from the upper unit 21 ma is believed to approximate the timing of tectonic juxtaposition which probably occurred during a regional greenschist facies episode producing a pervasive overprint in the struc turally lower tectonic unit the major phyllite meta gabbro serpentinite sequence of the upper unit is inter preted as an emplacement related ductile shear zone which experienced reworking under brittle conditions in the intermediate unit a gradient in rb sr ages from top c 40 ma to the bottom c 22 ma was recog nized which is interpreted to represent greater effects of fluid infiltration and overprinting in the lower parts of this unit possibly controlled by variable intensity of deformation which might be related to tectonic jux taposition onto the basal unit we suggest that synmetamorphic stacking of all three tectonic units took place during an oligocene miocene greenschist event extensional deformation continued after tectonic stacking and after intrusion of the main granite as is indicated by a rb sr whole rock isochron 15 1 0 6 ma for a ductilely deformed garnet bearing leucogranite from the marginal parts of the main undeformed pluton application of the rb sr dating technique provided no unequivocal evidence that previously pub lished eocene k ar and 40 ar 39 ar dates for high pressure phengites from the lower units are significantly contaminated with excess argon

granite intrusion in a metamorphic core complex the example of the mykonos laccolith cyclades greece abstract the aegean domain is a well suited place to study the formation of metamorphic core complex mcc and to investigate the role of syn tectonic granites on their development in the northern cyclades the mykonos delos rhenia mcc is characterized by the intrusion of a kilometer scale late miocene pluton of i type granitoids within a migmatitic gneiss dome new combined ams anisotropy of magnetic susceptibility and microstructural studies on the mykonos granitoids together with recently published thermochronological data allow us to use the granitoids as strain markers the mykonos granitoids form a laccolith like intrusion with a n70 e long axis the laccolith is strongly asymmetric with an outlying root zone to the sw and a major body mainly developed to the ne the laccolith construction is due to successive pulses of more or less differentiated magma that intruded the cycladic blueschist unit the attitude of stretching markers suggests an important about 60 vertical axis local rotation phenomenon in the cycladic upper crust during the exhumation of the mykonos mcc structural data suggest a four stage evolution of the mykonos mcc i a first stage characterized by flat shearing toward the n ne and by the formation of a domal structure in migmatitic paragneisses with multi scale generation of folds with axes either perpendicular or parallel to the regional stretching as a result of the interplay between regional n20 e directed extension and ew shortening ii a second stage marked by the emplacement of the mykonos laccolith at 13 5 0 3 ma at the top of the migmatitic paragneisses iii the third stage corresponding to the development of protomylonitic foliations and lineations in the whole laccolith in high to medium temperature conditions and iv the late stage marked by an acceleration of the exhumation of the mykonos mcc this exhumation was accommodated by important rotations of upper crustal blocks during the end of the exhumation processes around 10 ma deformation localized at the top of the laccolith in semi ductile conditions and then in brittle conditions in the major detachment plane our study shows that the cycladic plutonism event had no role on the initiation of the mcc however the geometry of the mykonos intrusion supports that the magmas are sucked into the direction of regional extension and that the intrusion of magmas has caused an acceleration of the last stages of the mcc development this acceleration was marked by a very fast exhumation of the laccolith after its emplacement

transpression and transtension within different structural levels in the central aegean region in the central aegean region shortening structures within the miocene molasse arc known since long ago nevertheless recently most authors have recognized extensional structures within middle to upper miocene granitoids proposing a basin and range type model for the late cenozoic evolution of the area to resolve this problem structural mapping and mesoscopic analysis of 900 faults sampled from 12 islands have been carried out late orogenic uplift of the central aegean region is the result of a continuous convergence and indentation of the pelagonian plate by the apulian plate that took place throughout the miocene formation of core complexes can be associated with a large oblique upthrusts b steeply dipping strike slip faults and c low angle normal faults the latter are produced by low multidirectional extension which has affected small crustal regions as adjacent areas underwent transpression in the late stages of collision the overthickened crust began to collapse due to transtension which was replaced by extension caused by the roll back of the hellenic subduction zone in the lower pliocene time this extensional regime has lasted until the present day

continuous growth of hydrogenetic ferromanganese crusts since 17 myr ago on takuyo daigo seamount nw pacific at water depths of 800 5500 m ferromanganese crusts cover all outcrops on takuyo daigo seamount traversed during remotely operated underwater vehicle rov dives except in places covered by foraminifera sand takuyo daigo is a cretaceous seamount located in the northwest pacific ocean geological and bathymetric mapping provide the framework for this study chemical and mineralogical analyses of the hydrogenetic ferromanganese crusts show temporal and spatial variations typical of those found in previous studies outcrops from 800 to 5500 m water depths are covered with ferromanganese crusts up to 105 mm thick beryllium isotope dating shows that the crusts have apparently been growing continuously at all water depths even through the modern oxygen minimum zone omz contrary to some earlier models for deposition growth rates vary from 2 3 to 3 5 mm myr with fe or mn fluxes of 0 07 0 11 g cm2 myr since the early middle miocene co mn ratios decrease with water depth while fe mn and other metallic elements increase or show no change based on the analysis of the uppermost crust surface this is probably because co is the most abundant redox sensitive element derived from seawater that occurs in crusts

study of the crustal thickness and the subducting lithosphere in greece from gravity data the area of greece has experienced a complex tectonic history dominated by the subduction of the african plate beneath eurasia in this study the variations of the crustal thickness in the area of greece were obtained by means of the multiple source werner deconvolution mswd method applied to gravity data thicknesses of 40 49 km are estimated beneath the hellenides mountain belt to the west eastward thinning of the crust to thicknesses ranging from 25 km in the north to 30 km in the south is seen in the aegean region these results are in good agreement with recent seismological results demonstrating that the mswd method successfully treated the problem using the crustal model we derived we computed the gravity effect of the crust and extracted it from the bouguer anomaly we also extracted the gravity effect of the subducting lithosphere from the bouguer anomaly producing a residual map where most of the original gravity variation has been successfully removed the remaining anomalies appear related to near surface features and an area of low velocity mantle in the central aegean sea

226ra 238u and 228th 228ra disequilibrium as weathering indices in beach sand sediments associated with granitoids from cyclades greece abstract radioactive secular disequilibrium measured as the absolute difference from 1 of the 226ra 238u and 228ra 228th ratios have been used to determine weathering extent twenty eight samples from beach sands of cyclades islands all of them being the weathering products of the local granitic plutons are studied for their secular disequilibrium in both 238u and 232th series 226ra 238u and 228th 228ra respectively the results are compared to weathering indices already in use worldwide and suggest a significant linear correlation of u series disequilibrium with wip alkaline and alkaline earth element leaching and pwi silica leaching for the beach sands studied and significant non linear correlations with cia chemical index of alteration and pia plagioclase index of alteration considering only the heavy mineral enriched samples significant correlations exist between u series disequilibrium and cia ciw chemical index of weathering and pia therefore with an appropriate choice of the weathering index and samples both u series and weathering index can recover the extent of chemical weathering on the other hand the use of th series disequilibrium as a weathering index is limited due to 228th and 228ra geochemistry and especially due to their short radionuclide half lives u series disequilibrium can therefore be used as a relatively sensitive weathering index in sediments consistent with cia ciw and pia indices however the mineralogical composition must be considered more specifically the mineral content of the sediments should involve considerable amounts of sensitive to weathering minerals e g fe mg minerals as well as feldspars

submarine hydrothermal manganese deposits from the ogasawara bonin arc off the japan islands abstract numerous submarine hydrothermal sulfide and oxide deposits have been found in the mid ocean ridge systems but until now no activity has been found in an island arc system the geological survey of japan gsj has started a geological geophysical and geochemical investigation program in the bonin mariana arc since 1984 aiming at evaluation of submarine hydrothermal metal deposits and understanding of their geological background during the reconnaissance survey by r v hakurei maru in june 1984 thick hydrothermal manganese crusts were recovered from three seamounts of the bonin arc at a depth of ca 1000 m the chemical and mineralogical features and characteristic structure and occurrence of associated calcareous fossils and nontronite claystones suggest the quaternary low temperature hydrothermal activity forming well crystallized todorokite pyrolusite goethite and nontronite deposits thin hydrogenous ferromanganese encrustations on the hydrothermal crusts from a guyot of the northern arc indicate that the recent very active hydrothermal activities around this area may be declining or already finished whereas the fresh hydrothermal manganese crusts from the kaikata seamount suggest recent hydrothermal activity

vapour absent melting from 10 to 20 kbar of crustal rocks that contain multiple hydrous phases implications for anatexis in the deep to very deep continental crust and active continental margins

interplay between geochemistry and magma dynamics during magma interaction an example from the sithonia plutonic complex ne greece orogenic granitoids often display mineralogical and geochemical features suggesting that open system magmatic processes played a key role in their evolution this is testified by the presence of enclaves of more mafic magmas dispersed into the granitoid mass the occurrence of strong disequilibrium textures in mineralogical phases and or extreme geochemical and isotopic variability in this contribution intrusive rocks constituting the sithonia plutonic complex northern greece are studied on the basis of mineral chemistry whole rock major trace element geochemistry and sr and nd isotopic composition sithonia rocks can be divided into a basic group bearing macroscopic mafic enclaves microscopic disequilibrium textures geochemical and isotopic evidence of magma interaction and an acid group in which most geochemical and isotopic features are consistent with a magma mixing process but macroscopic and microscopic features are lacking a two step mixing plus fractional crystallization mfc process is considered responsible for the evolution of the basic group the firststepexplainsthechemicalvariationinthemaficenclavegroup abasicmagma representedbytheleastevolvedenclaves interacted

wave attenuation by flexible idealized salt marsh vegetation abstract wave attenuation by vegetation is a highly dynamic process and its quantification is important for understanding shore protection potential and modeling coastal hydrodynamics data documenting the interactions of spartina alterniflora represented by polyolefin tubing and single and double peaked irregular waves were collected in a large scale laboratory flume the laboratory provided a controlled environment to evaluate wave attenuation including the parameters of stem density submergence wave height and peak period wave attenuation appeared to be most dependent on stem density and the ratio of stem length to water depth wave attention increased slightly with wave height while no clear trend with respect to wave period was seen treating double peaked spectra as superimposed wave systems revealed a preferential dissipation of the higher frequency wave system relative to the lower frequency wave system under emergent conditions wave energy loss occurred at all frequencies of both spectral types with dissipation increasing with frequency above the spectral peak parameterizing the spectral equilibrium range as a function of frequency showed a steepening of the spectral tail compared to the 4 power law under emergent conditions an empirical relationship defining the bulk drag coefficient for s alterniflora as a function of the stem reynolds number is found to serve as a first estimate for engineering applications

non hydrostatic modeling of drag inertia and porous effects in wave propagation over dense vegetation fields a new wave vegetation model is implemented in an open source code swash simulating waves till shore the governing equations are the nonlinear shallow water equations including non hydrostatic pressure besides the commonly considered drag force induced by vertical vegetation cylinders drag force induced by horizontal vegetation cylinders in complex mangrove root systems as well as porosity and inertia effects are included in the vegetation model providing a logical supplement to the existing models the vegetation model is tested against lab measurements and existing models good model performance is found in simulating wave height distribution and maximum water level in vegetation fields the relevance of including the additional effects is demonstrated by illustrative model runs we show that the difference between vertical and horizontal vegetation cylinders in wave dissipation is larger when exposed to shorter waves because in these wave conditions the vertical component of orbital velocity is more prominent both porosity and inertia effects are more pronounced with higher vegetation density porosity effects can cause wave reflection and lead to reduced wave height in and behind vegetation fields while inertia force leads to negative energy dissipation that reduces the wave damping capacity of vegetation overall the inclusion of both effects leads to greater wave reduction compared to common modeling practice that ignores these effects but the maximum water level is increased due to porosity with good model performance and extended functions the new vegetation model in swash code is a solid advancement toward refined simulation of wave propagation over vegetation fields

numerical simulations of wave propagation over a vegetated platform abstract vegetated platforms have been constructed in recent years for the purpose of shore protection this paper addresses some fundamental questions concerning the vegetated platform 1 what is the difference in wave attenuation between a vegetated platform and a simple platform and how much can vegetation increase the efficiency of reducing wave transmission 2 are there any differences between the effects of stems and roots on wave attenuation 3 does vegetation always reduce wave transmission 4 is it possible to develop an empirical formula for estimating the wave transmission of a vegetated platform to answer the above questions a numerical model solving the navier stokes equations for wave propagation over a vegetated platform is established and validated by several existing laboratory experiments a total of 244 numerical experiments based on this model have been carried out the simulated results suggest that the platform plays a major role and the vegetation plays a supporting role in reducing wave transmission except for some special cases stems tend to have a larger influence than roots in reducing wave transmission with the same height the roots always help reduce wave transmission while the stems may increase wave transmission when the platform width is in the range of 37 5 62 5 of the incident wavelength based on our numerical experiments and existing laboratory data the paper proposes a simple formula for predicting the wave transmission coefficient of a vegetated platform for engineering applications

neodymium and strontium isotope content of microdiorite enclaves points to mantle input to granitoid production microdiorite enclaves are arguably the most poorly understood of the more prominent features of granitoids surprisingly they have been invoked as support for completely different models for the origin of chemical zonation in granitoids depending on whether they are interpreted as restites syn plutonic blobs of magma remobilized cumulate or basified country rock xenoliths here we present the first detailed neodymium and strontium isotope study of suites of such enclaves from two plutons in both cases we find relatively high nd values most readily explained if enclaves represent syn plutonic injections of mafic magma into the host granitoid magma as such they are the tangible remains of a very important process of mantle derived heat and mass transfer operating in the generation of granitic magmas

post collisional variscan lamprophyres black forest germany 40ar 39ar phlogopite dating nd pb sr isotope and trace element characteristics abstract subsequent to high pressure and temperature metamorphism of the axial zone of the variscan foldbelt in central europe at ca 340 to 330 ma formation of lamprophyre dikes during transtensional tectonics may be viewed as the beginning of the post collisional stage of the orogeny we report the results of 40 ar 39 ar mica dating major and trace element data and isotope compositions for lamprophyre and rhyodacite samples from the southern black forest the chemical compositions of these rocks shed light on the upper mantle and crust at the end of the variscan orogeny 40 ar 39 ar plateau ages for four phlogopite biotite separates from lamprophyres indicate emplacement at 332 to 314 ma this event coincides with melting of the crust as indicated by 40 ar 39 ar biotite plateau ages of ca 332 ma for rhyodacite dikes which are probably related to coeval undeformed granites incompatible trace element patterns of the lamprophyre samples reveal the characteristics of evolved continental crust and are interpreted as evidence for melting of sediment in a subduction modified mantle nd sr and pb isotope compositions indicate an enriched mantle source with end values of 1 5 to 6 8 which is similar to variscan crust significant contamination of the lamprophyric melts by variscan crust can be ruled out as mantle derived phlogopite phenocrysts have similar end values as in the whole rock samples we propose that the isotope compositions and incompatible trace element characteristics of the lamprophyres were predominantly inherited from melted sediment the isotope compositions of variscan lamprophyres from western europe suggest that enriched upper mantle was only partly delaminated when ascending hot mantle triggered melting of the lower crust as has been invoked for the origin of post collisional granites the isotope compositions of tertiary basalts and mantle xenoliths indicate a depleted upper mantle under western europe implying that the enriched variscan material was efficiently removed and mixed into the convecting mantle

a model for the formation of hydrothermal manganese crusts from the pitcairn island hotspot the distribution of elements in the hydrothermal mn crusts from the pitcairn island hotspot can be explained by considering processes occurring within the hotspot volcano these include the role of boiling of the ascending hydrothermal fluid which leads to sulphide deposition and seawater intrusion into the upper part of the volcano this in turn results in the development of an oxycline above which feooh can precipitate the high mn fe ratios and low contents of ni and zn in the massive crusts are thought to reflect the rapid incorporation of the ore elements into sulphide minerals such that only a small proportion of these elements are available for incorporation in the crusts the small positive eu anomaly in the crusts on a nasc normalized basis reflects the lower temperatures in the hydrothermal fluids at the pitcairn island hotspot 25dgc compared to those at mid ocean ridges c 350 c the oxyanions cro42 vo43 aso43 and po43 the rare earth elements ree and th are scavenged by feooh particles within the upper part of the seamount and can therefore be incorporated into the crusts associated with the fe rich phase molybdenum and uranium are scavenged in only negligible amounts by the feooh molybdenum is therefore most probably scavenged from seawater by manganese oxides during the actual formation of the mn crusts the alkali metals li rb and cs remain in solution in the hydrothermal fluids and are selectively incorporated into the buserite structure of the mn crusts in the absence of strong competition from the divalent transition metal ions the compositional characteristics of the hydrothermal mn crusts can therefore be explained in terms of a simple model of element scavenging and uptake occurring mainly within the seamount a laser ablation icpms profile in one of the hydrothermal crusts ds 63 4 revealed varying ree concentrations and patterns in the different layers of the crust these data indicate that the hydrothermal component was variable during the formation of the crust it was calculated to be almost 100 in the upper 18 0 mm of this crust apart from the samples at 6 0 8 0 mm and about 80 in the lower layers

hydrodynamics induced by wind waves in a vegetation field the wave induced kinematics and dynamics of a submerged or emerged vegetation field is analyzed using potential flow and an eigenfunction expansion the problem is solved considering regular as well as irregular incident waves the model takes into account the vegetation motion and solves for the complete wave system on the vegetation field and in its vicinity the model is validated against experimental laboratory data obtained by other authors showing a much better agreement than previous theoretical models in this paper the model is used to evaluate wave height evolution damping vegetation and fluid motion and forces and moments on the vegetation furthermore the inclusion of irregular waves provides force and moment distributions on the vegetation field depending on the wave climate statistics

cobalt in ferromanganese crusts as a monitor of hydrothermal discharge on the pacific sea floor ferromanganese oxide crusts which accumulate on unsedimented surfaces in the open ocean1 6 derive most of their metal content from dissolved and particulate matter in ambient bottom water7 8 in proportions modified by the variable scavenging efficiency of the oxide phase for susceptible ions9 they differ in this respect from abyssal nodules much of whose metals are remobilized from host sediments here we present maps of cobalt concentration and inferred accumulation rate of ferromanganese crusts from the pacific ocean we propose that depletion of cobalt in pacific crusts measures the location and intensity of submarine hydrothermal discharge use of the cobalt chronometer an algorithm inversely relating cobalt content and crust growth rate permits mapping of the accumulation rate of ferromanganese crusts with only indirect recourse to radioactivity based dating methods these maps show that crusts in hydrothermal areas grow from two to more than four orders of magnitude faster than in the central pacific ocean cobalt enriched crusts are found where water masses are most isolated from continental coastal and hydrothermal sources of metals now and in the past this relationship can resolve the problem of cobalt enrichment in crusts without recourse to hypotheses invoking special cobalt sources or enrichment mechanisms

o sr isotopic variations in miocene granitoids from the aegean evidence for an origin by combined assimilation and fractional crystallization sr o and d h isotopic compositions have been analyzed in miocene metaluminous to slightly peraluminous i type granitoids of the central aegean individual plutonic complexes display significant variations in their 18o and initial87sr 86sr compositions d and 18o compositions of minerals and whole rocks are mostly in the magmatic range some samples from naxos and mykonos delos show low d and 18o values characteristic of meteoric water hydrothermal interaction but as a whole the changes in 18o and sr isotopic compositions as a result of hydrothermal alteration were slight even in instances where marked alteration is petrographically observable consequently the bulk rock variations of 18o from 8 1 to 12 0 and of87sr 86sr from 0 70438 to 0 71450 may be regarded as primary and indicative of the conditions of their evolution heterogeneous isotopic compositions observed in the individual plutons of serifos ikaria samos and kos may be caused by the multiple intrusion of chemically and isotopically distinct magma pulses with high viscosities and relatively rapid consolidation in most cases preventing complete homogenization the granitoids of serifos ikaria and kos display weak correlations between the initial87sr 86sr and 18o and 1 sr the granitoid province shows a positive correlation between87sr 86sr and 18o and a non linear relationship between87sr 86sr and 1 sr whereby 1 sr increases more rapidly than the isotopic ratio as the degree of fractionation of the rocks increases it is argued that assimilation of older continental material by mantle derived arc magmas with combined fractionation afc is the most plausible model to explain the chemical and isotopic characteristics of the granitoids and the geological situation in which rock types trend from granodiorites in the south west near the inferred oligocene miocene suture to granites in the center and monzonites in the north east of the province

block rotations and continental extension in the central aegean sea palaeomagnetic and structural evidence from tinos and mykonos cyclades greece abstract the aegean sea floored by an attenuated continental crust is a mediterranean type back arc basin formed above the subducting african plate we investigated post 12 ma block rotation in relation to back arc extension in the area of the western cyclades central aegean sea on tinos island nw trending dacitic dikes and a miocene monzogranite penetrated an alpine metamorphic series k ar analyses of 6 dike samples yielded an average age of 11 5 0 4 ma the palaeomagnetic analyses of the dikes and the monzogranite reveal 23 vertical axis clockwise rotation we assume that the dacitic dikes intruded vertical as they are today and that no tilt correction is required this is supported by the fact that no inclination anomaly is revealed when the palaeomagnetic data is compared with a tilt corrected pole position from kimi evia the absence of tilting implies that post 12 ma crustal thinning in the area of tinos island was minor on mykonos a low angle normal fault dipping 30 to the ne juxtaposes a series of oligo miocene molasse sediments above a 10 12 ma granite published palaeomagnetic data revealed a considerable amount of inclination flattening and 22 clockwise rotation of the footwall granite we show that tilting predated vertical axis rotation and that the now low angle normal fault originated steeper dipping ca 54 planar rotational fault geometry indicates extension of ca 60 in spite of the significant variations in the magnitude of post 12 ma upper crustal extension across the tinos mykonos transect crustal thickness below the entire area changes only slightly this indicates that upper crustal levels were decoupled from the lower crust the widespread middle miocene granitic magmatism in the cyclades suggests that flow in the lower crust may have had a dominant role in maintaining the smooth moho assuming that the western cyclades constitute a set of nw striking crustal blocks it is estimated that vertical axis rotations increased the n s dimension of the area by ca 31 e g 25 km the exact timing of this clockwise rotation is not well constrained but it postdated the formation of low angle normal faults and tilting and may have taken place in the late miocene

submersible observations of hydrothermal manganese deposits on the kaikata seamount izu ogasawara bonin arc abstract during dive 408 of shinkai 2000 on the flank of the kaikata seamount located on the volcanic front of the izu ogasawara bonin arc possibly recent hydrothermal manganese deposits were observed on sandy volcanic sediments at water depths of between 800 and 1200 m the deposits cover almost the entire surface sediment across the manganese belt on the northwestern flank on the seamount on a scale of kilometers the occurrence of the deposits seafloor morphology and temperature of the sediments together with previous shipboard results lead to a possible model for the formation of the manganese deposits a low temperature hydrothermal solution ascends through fractures or faults in the volcanic substrate into permeable volcanic sands and precipitates manganate minerals which cement several centimeters of surface sand as hardpan more intense and probably intermittent discharge of hydrothermal solution follows and forms many typical ridge like vents and mounds on the seafloor subsequently pure dense manganate layers developed beneath the semi consolidated volcanic sandstone and act as a cap to the ascending fluids the proposed mechanism may be the dominant type of low temperature hydrothermal mineralization in submarine island arc volcanoes and rifts similar hydrothermal manganese deopsits most probably occur in other active areas of the modern seafloors and in inactive island arcs

back arc extension and denudation of mediterranean eclogites eclogite facies rocks exposed in mediterranean back arcs are delimited from above by low angle normal faults and detachments nevertheless our work demonstrates that these extensional structures associated with back arc extension played only a limited role in removing the overburden from above the eclogites extension in mediterranean back arcs began in the late oligocene or early miocene but the pressure temperature time p t t paths of eclogite facies rocks exposed in these areas indicate that a major part of the overburden several tens of kilometers has been removed from above these rocks prior to the oligo miocene we show that the time period bracketed between the peak of eclogite metamorphism eocene in the central aegean probably upper cretaceous in corsica and the betics and the onset of back arc extension in the oligo miocene was characterized by thrust faulting in the central aegean corsica and the betics eclogite bearing units were partly unroofed and then overthrusted lower pressure units we emphasize that with one exception tinos island greece the entire inventory of extensional contacts operated subsequently to the overthrusting of the eclogites above the lower grade sequences thus mediterranean back arc extension lags behind a major part of the denudation process and is superposed on orogenic wedges that contain eclogite facies rocks at relatively shallow structural levels we emphasize that the mode of occurrence of eclogites in mediterranean back arc regions involves a continuum of in situ crustal accretion below the eclogites widespread p t paths that show cooling or isothermal decompression and lower grade rocks at the bottom of the structural pile thus instead of reflecting whole crust back arc extension the tectonic style associated with the denudation of mediterranean eclogites better fits an active accretionary wedge setting this is similar to the mode of occurrence of eclogite facies rocks in mountain belts such as the western alps where decompression was synorogenic and back arc extension played no role

u pb zircon geochronology of unusual eclogite facies rocks from syros and tinos cyclades greece low temperature eclogite facies rocks from syros and tinos cyclades greece include meta igneous blocks of unclear origin meta olistostrome or tectonic melange with very high trace element concentrations e g zr up to 4850 ppm y up to 475 ppm the unusual geochemistry is considered to be the result of metasomatic alteration in a subduction zone environment locally metasomatic exchange with an ultramafic matrix further enhanced compositional anomalies a concordant u pb zircon age of 78 1 ma recorded for an omphacitite from syros is interpreted as the time of pre eocene high pressure metamorphism in the cyclades zircon dates of 61 and 63 ma for a jadeitite from tinos possibly indicate an additional discrete event deformation these results are a first geochronological indication that high pressure metamorphism in the cyclades commenced signif icantly earlier than indicated by previous white mica chronology which provided ages between c 50 and 40 ma

late miocene ductile extension and detachment faulting mykonos greece the geometry and style of structural relations at map to microscopic scale on mykonos cyclades aegean sea greece suggests ductile extension and detachment faulting during the late miocene this island is dominated by granitic rocks that have a well developed shallowly dipping mylonitic foliation and a northeast southwest trending mineral elongation lineation kinematic indicators in these rocks exhibit a top to the northeast down dip sense of shear textural relations suggest that conditions during mylonitic deformation were greenschist to amphibolite facies and published k ar geochronology suggests a late miocene age for this deformation event mylonitic rocks lie in the footwall of a low angle fault and fault striae parallel to the elongation lineation suggest kinematic coordination between mylonitic deformation and movement along the fault translation along the fault juxtaposes younger tilted sedimentary rocks of low metamorphic grade upon the once deeper mylonitic rocks the style and geometry of deformational fabrics and map relations on this island are strikingly similar to those observed in metamorphic core complexes of the western united states

uranium thorium chronometry of weathering rinds rock alteration rate and paleo isotopic record of weathering fluids abstract the potential of 238u 234u 230th chronometry for constraining the formation rate of weathering rinds developed on fresh rocks is assessed by analyzing a weathering rind on a basaltic clast from a 125 kyr old costa rican alluvial terrace eighteen subsamples were collected from one section of the clast by drilling cores 4 mm in diameter and 5 mm depth along two transects straddling the core rind boundary variations of major and trace element concentrations along the two transects point out a intense loss of alkaline and alkaline earth elements b conservative behaviour of elements such as zr hf and th and c external input of u into the rind without any evidence of u loss during basalt weathering in addition variations in u concentrations along the transects show that the main u th fractionation process associated with the weathering of the basaltic clast is an external input of u without addition nor loss of th in the basalt rind transition zone and that once deposited u is immobile in the weathering rind in the frame of this interpretation scheme a weathering rate of 0 5 0 2 mm kyr can be calculated for the studied clast which is consistent with geological and isotopic evidence constraining the depositional ages of the terraces in addition the variations in the 234u 238u ratio along the analysed transects as well as the increase in sr isotopic ratios within the weathering rind are best explained by temporal variation of the u activity ratios and sr isotope ratios of the soil solutions brought into the rind this work highlights how well detailed u th chronological studies of weathering rinds can 1 constrain the formation rates of weathering systems and 2 record the time variation of isotopic composition of weathering fluids

bivergent extension in orogenic belts the menderes massif southwestern turkey the central menderes massif is characterized by an overall dome shaped foliation pattern and a north northeast trending stretching lineation the asymmetry of shear bands and quartz c axis fabrics on either side of the structural dome demonstrate a top to thenorth northeastshearsenseinthenorthernpartandatoptothesouth southwestshear sense in the southern part of the submassif i e a bivergent downdip movement this suggests a symmetric collapse of the alpine menderes orogenic belt along two extensional shearzones conjugateshearbandsandsymmetricquartzc axisfabricsintheeast trendingtransitionzonedemonstrateacoaxialdeformationbetweenthetwoextensiondomains bivergent extension in the menderes massif is in contrast to asymmetric extension in the aegeansea here thestill activehellenicsubductionzoneevolvedfromanadvancingplate boundary associated with crustal thickening into a retreating plate boundary in oligocene miocene time southward rollback of the subducting plate during continuous northward subduction allowed asymmetric top to the north northeast extension in the back arc region during the exhumation of the cycladic core complexes in western turkey the arrival of the thick continental crust of the menderes massif halted subduction and probably caused the symmetric collapse of the massif because the high potential energy of the thickened crust was no longer supported by subduction