evidence of isotopic equilibration between microgranitoid enclaves and host granodiorite warburton granodiorite lachlan fold belt australia abstract microgranitoid enclaves in the s type warburton granodiorite lachlan fold belt australia display a range in mineralogical and isotopic compositions many show obvious similarities to the host granodiorite they contain biotite as the sole ferromagnesian phase and have isotopic signatures similar to the host other enclaves contain cummingtonite actinolite and rare orthopyroxene mainly in the core of the enclaves these enclaves typically have higher nd i and lower sol 87 sr 86 sr i than the host rocks reversely zoned plagioclase megacrysts in some enclaves contain anhedral cores which are similar in composition to an poor plagioclase crystals in the host rock an45 these megacrysts are jacketed by an rich plagioclase an70 an80 the enclaves are interpreted to be globules of a more mafic magma which mingled with the host while it was still partially liquid megacrysts within the enclaves are thought to have been derived from the granodioritic magma the mafic enclave magma is likely to have been derived from a mantle source but equilibration between enclaves and host rock has changed the mineralogy and isotope geochemistry of all enclaves the equilibration process was incomplete for some enclaves resulting in mineralogical zoning and distinctions in isotopic signature between these enclaves and the host rock this equilibration process is likely to have been arrested as a result of rapid cooling of the pluton due to its small size and shallow emplacement level it is uncertain whether the compositions of the least equilibrated enclaves are truly representative of the original mafic enclave magma or whether their trace element signature has been affected by diffusional processes within a stratified magma chamber

residence of ree y th and u in granites and crustal protoliths implications for the chemistry of crustal melts a systematic study with laser ablation icp ms scanning electron microscopy and electron microprobe revealed that 70 95 wt of ree except eu y th and u in granite rocks and crustal protoliths reside within reeythu rich accessories whose nature composition and associations change with the rock aluminosity the accessory assemblage of peraluminous granites migmatites and high grade rocks is composed of monazite xenotime in low ca varieties apatite zircon thorthosilicate uraninite and betafite pyrochlore metaluminous granites have allanite sphene apatite zircon monazite and thorthosilicaie peralkaline granites have aeschinite fergusonite samarskite bastnaesite fluocerite allanite sphene zircon monazite xenotime and th orthosilicate granulite grade garnets are enriched in nd and sm by no less than one order of magnitude with respect to amphibolite grade garnets granulitegrade feldspars are also enriched in lree with respect to amphibolite grade feldspars accessories cause non henrian behaviour of ree y th and u during melt solid partitioning because elevated fractions of monazite xenotime and zircon in common migmatites are included within major minerals their behaviour during anatexis is controlled by that of their host settling curves calculated for a convecting magma show that accessories are too small to settle appreciably being separated from the melt as inclusions within larger minerals biotite has the greatest tendency to include accessories thereby indirectly controlling the geochemistry of ree y th and u we conclude that ree y th and u are unsuitable for petrogenetical modelling of granitoids through equilibrium based trace element fractionation equations

isotopic dating of pre alpidic rocks from the island of ios cyclades greece the lower tectonic unit of ios provides evidence of an at least four stage metamorphic and intrusive history which well might be generalized for large parts of the internal pelagonian

the trace element compositions of s type granites evidence for disequilibrium melting and accessory phase entrainment in the source within individual plutons the trace element concentrations in s type granites generally increase with maficity total iron and magnesium content and expressed as atomic fe mg in this study the degree of variability in trace element concentration also expands markedly with the same parameter the strongly peraluminous high level s type granites of the peninsular pluton cape granite suite south africa are the product of biotite incongruent melting of a metasedimentary source near the base of the crust leucogranites within the suite represent close to pure melts from the anatectic source and more mafic varieties represent mixtures of melt and peritectic garnet and ilmenite trace elements such as rb ba sr and eu that are concentrated in reactant minerals in the melting process show considerable scatter within the granites this is interpreted to reflect compositional variation in the source in contrast elements such as lree zr and hf which are concentrated within refractory accessory phases zircon and monazite show well defined negative correlations with increasing sio2 and increase linearly with increasing maficity this is interpreted to reflect coupled co entrainment of accessory minerals and peritectic phases to the melt leucocratic rocks cannot have evolved from the more mafic compositions in the suite by a process of fractional crystallisation because in this case they would have inherited the zircon saturated character of this hypothetical earlier magma trace element behaviour of granites from the peninsular pluton has been modelled via both equilibrium and disequilibrium trace element melting in the disequilibrium case melts are modelled as leaving the source with variable proportions of entrained peritectic phases and accessory minerals but before the melt has dis solved any accessory minerals thus the trace element signature of the melt is largely inherited from the reactants in the melting reaction with no contribution from zircon and monazite dissolution in the equilibrium case melt leaves the source with entrained crystals after reaching zircon and monazite saturation a significant proportion of the rocks of the peninsular pluton have trace element concentrations below those predicted by zircon and monazite saturation in the case of the most leucocratic rocks all compositions are zircon undersaturated whilst the majority of the most mafic compositions are zircon oversaturated however in both cases zircon is commonly xenocrystic thus the leucocratic rocks represent close to pure melts which escaped their sources rapidly enough that some very closely match the trace element disequilibrium melting model applied in this study zircon dissolution rates allow the residency time for the melt in the source to be conservatively estimated at less than 500 years

geochemistry and petrogenesis of late miocene granitoids cyclades southern aegean nature of source components abstract neogene igneous activity in the aegean region comprised both extrusive volcanism and intrusive granitoid plutonism granitoid plutonism in the cyclades was established in the mid miocene period and lasted until late miocene 18 to 9 ma the timing of granitoid intrusion was associated with the initiation of extensional tectonics in the aegean these intrusions form a broad belt about 200 km long running from the west lavrium and serifos to the eastern aegean both s type and i type granitoids are present the former generally being emplaced earlier than the i types 15 to 8 3 ma major and trace element variations reveal that three end member components are involved in the granitoids but the proportions of these vary in the different plutons initial isotopic compositions of all the granitoids are typical of crust derived magmas from heterogeneous metasedimentary sources i type 87 sr 86 sr 0 7091 0 712 e nd 6 4 to 10 4 s type 0 710 0715 e nd 7 5 to 10 1 three end member sources have been identified 1 one end member appears to be a metasedimentary biotite gneiss greywacke type such as that forming the metamorphic core complexes naxos and paros this is a dominant but not the only component in the s types 2a major trace element and sr nd isotopic composition correlations of the s type granitoids with basement gneiss require an extra source of sr and ca having lower initial 87 sr 86 sr indicating a more depleted metasedimentary source at depth due to possible interaction of metamorphic fluids with marbles and amphibolites and infiltration through the gneissic units at mid crustal levels 2b a possible second end member could be the marble component as indicated by the buffered values of the initial sr isotopic ratios major element variation of the mafic microgranular quartz diorites and tonalites enclaves are compatible with dehydration melting of a mafic source similar to the amphibolites island arc tholeiites at medium pressure 8 kb conditions 3 amphibolite is another end member which may contribute mostly to the source of the younger intrusions along the western flank of the arc

interactions between plutonism and detachments during metamorphic core complex formation serifos island cyclades greece in order to better understand the interactions between plutonic activity and strain localization during metamorphic core complexes formation the miocene granodioritic pluton of serifos cyclades greece is studied this pluton 11 6 9 5 ma intruded the cycladic blueschists during thinning of the aegean domain along a system of low angle normal faults belonging to the south dipping west cycladic detachment system wcds based on structural fieldwork together with microstructural observations and anisotropy of magnetic susceptibility ams we recognize a continuum of deformation from magmatic to brittle conditions within the magmatic body this succession of deformation events is kinematically compatible with the development of the wcds the architecture of the pluton shows a marked asymmetry resulting from its interaction with the detachments we propose a tectonic scenario for the emplacement of serifos pluton and its subsequent cooling during the aegean extension 1 a first stage corresponds to the metamorphic core complex initiation and associated southwestward shearing along the meghalo livadhi detachment 2 in a second stage the serifos pluton has intruded the dome at shallow crustal level piercing through the ductile brittle meghalo livadhi detachment southwest directed extensional deformation was contemporaneously transferred upward in the crust along the more localized kavos kiklopas detachment 3 a third stage was marked by syn magmatic extensional deformation and strain localization at the contact between the pluton and the host rocks resulting in narrow shear zones nucleation which 4 continued to develop after the pluton solidification

constraints on the kinematics of post orogenic extension imposed by stretching lineations in the aegean region abstract new kinematic data from shear zones of tertiary age in the metamorphosed basement of the aegean region in combination with published kinematic lithological and palaeomagnetic data have enabled us to determine a detailed kinematic evolution of the region during post orogenic extension in the aegean three distinct stages are recognised firstly extension of both the western and eastern aegean started in the late oligocene early miocene 36 25 ma ago initially in an 023 direction stage two started shortly after this with the division of the aegean crust into the west aegean block a coupled assemblage of small blocks bound on its northwestern and southeastern margins by the scutari pec line and mid cycladic lineament fracture zones respectively between 25 ma and 3 ma the west aegean block underwent 30 clockwise rotation whilst the eastern aegean underwent on average 19 anticlockwise rotation rotation of the west aegean block as a semi coherent block was aided by the relative coolness of the block compared to the warmer eastern aegean region as the crust thinned and rotated the nw se trending faults which characterise the west aegean block were cross cut by e w trending faults in the latest miocene pliocene the thermal front migrated westwards into the west aegean block and the mid cycladic lineament ceased activity the final kinematic stage marked the start of the subdivision of the west aegean block into two portions in the pliocene the southeastern portion nw cycladic area coupled with the sw cycladic area to form a central aegean block that started to translate southwest the northern and western portion rotated a further 10 15 clockwise whilst the southeastern rim rotated anticlockwise these data demonstrate that aegean post orogenic extension is not dominated by a single block rotation or radial spreading event but is characterised by the sequential formation and reformation of lithospheric scale blocks that have developed in response to large scale partitioning of rotational strain

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

oxygen isotope thermometry of quartz al 2 sio 5 veins in high grade metamorphic rocks on naxos island greece diffusion models predict that peak metamorphic temperatures are best recorded by the oxygen isotope fractionation between minerals in a bi mineralic rock in which a refractory accessory mineral with slow oxygen diffusion rate is modally minor to a mineral with a faster diffusion rate this premise is demonstrated for high grade metamorphism on the island of naxos greece where quartz kyanite oxygen isotope thermometry from veins in high grade metamorphic pelites gives temperatures of 635 690 c these temperatures are in excellent agreement with independent thermometry for the regional m2 peak metamorphic conditions and show that the vein minerals isotopically equilibrated at the peak of metamorphism quartz sillimanite fractionations in the same veins give similar temperatures 680 35 c and suggest that the veins grew near to the kyanite sillimanite boundary corresponding to pressures of 6 5 to 7 5 kbar for temperatures of 635 685 c by contrast quartz kyanite and quartz biotite pairs in the host rocks yield lower temperature estimates than the veins 590 600 and 350 550 c respectively these lower apparent temperatures are also predicted from calculations of diffusional resetting in the polyphase host rock system the data demonstrate that bimineralic vein assemblages can be used as accurate thermometers in high temperature rocks whereas retrograde exchange remains a major problem in many polymineralic rocks

zircon in amphibolites from naxos aegean sea greece origin significance and tectonic setting we report u pb zircon ages of c 700 550 ma 262 220 ma 47 38 ma and 15 14 ma from amphibolites on naxos island in the aegean extensional province of greece the zircon has complex internal structures based on cathodoluminescence response zoning and crosscutting relationships a minimum of four zircon growth stages are identified inherited core magmatic core inner metamorphic rim and an outer metamorphic rim trace element compositions of the amphibolites suggest igneous differentiation and crustal assimilation zircon solubility as a function of saturation temperatures zr content and melt composition indicates that the zircon did not originally crystallize in the mafic bodies but was inherited from felsic precursor rocks and subsequently assimilated into the mafic intrusives during emplacement zircon inheritance is corroborated by the complex xenocrystic nature of the zircon in one sample ages of c 700 550 ma and 262 220 ma are assigned to inherited zircon available geochemical data suggest that the 15 14 ma metamorphic rims grew in situ in the amphibolites corresponding to a high grade metamorphic event at this time however the geochemical data cannot conclusively establish if the c 40 ma zircon rims also grew in situ or whether they were inherited along with the xenocrystic cores two scenarios for emplacement of the mafic intrusives are discussed i intrusion during late triassic to jurassic ocean basin development of the aegean realm in which case the 40 ma zircon rims would have grown in situ and ii emplacement in the miocene as a result mafic underplating during large scale extension in this case only the 15 14 ma metamorphic outer rims would have formed in situ in the amphibolitic host rocks

southward extension of the bangonghu nujiang suture evidence from early cretaceous intermediate and felsic magmatism in the gaoligong orogen china abstract it remains debated as to whether the gaoligong orogen between the tengchong and baoshan blocks in yunnan china is the southward extension of the tibetan bangonghu nujiang suture bns here we present new geochronological and petrochemical data for early cretaceous magmatic rocks of the gaoligong orogen the la icp ms u pb dating of zircons from diorites granodiorites and granites yielded weighted mean 206pb 238u ages of 120 118 128 122 and 109 128 ma respectively for the diorites the ehf t values of zircons fall in a range of 1 2 to 5 4 with tdmc ages of 744 979 ma for the granodiorites they fall in a range of 9 8 to 2 9 with tdmc ages of 888 1564 ma and for the granites the range is 8 0 to 1 1 with tdmc ages of 1101 1488 ma they are magnsian calc alkaline enriched in liles and lrees and have strong negative nb ta p and ti anomalies and high values of mg all these features are indicative of continental arc affinities the data suggest that the dioritic and granitic magmas were produced by the mixing of variable proportions of mantle and crust derived magmas at an active continental margin the ages and tectonic settings of the diorites granodiorites and granites are similar to rocks found within the bns considering the ophiolitic melange belt the middle jurassic basaltic magmatism and the marine facies stratigraphic features of the gaoligong orogen are very similar to features in the bns we conclude that the gaoligong orogen represents the suture between the tengchong and baoshan blocks and is the southward extension of the bns

african provenance for the metasediments and metaigneous rocks of the cyclades aegean sea greece u pb geochronology on detrital and inherited zircons from metasediments as well as gneissic and metaigneous basement rocks of the cyclades aegean sea greece defines several periods of crustal growth prior to the carboniferous these ages are consistent with cycladic rocks being derived from the northern margin of gondwana there is a distinct mesoproterozoic age gap evident in zircons from the 25 samples considered this is characteristic of the west african craton and we suggest it will also prove characteristic of the aegean region this mesoproterozoic age gap may be used as a tool in terrane reconstruction to distinguish crustal material derived from different parts of gondwana

antiquity of the continental slope along the middle atlantic margin of the united states a detailed high resolution geophysical study of part of the continental slope along the mid atlantic margin of the united states indicates that it is an ancient relict landscape largely unmodified by modern slope processes the slope morphology is heavily influenced by bedrock outcrops including joints and bedding planes rather than by any single degradational process a pelagic drape averaging 3 to 5 meters in thickness blankets the slope carbon 14 dates from eight drop cores show that the drape was deposited in late pleistocene and holocene times the holocene part of the drape comprising the uppermost 1 meter was deposited at a continuous rate of 10 centimeters per 1000 years most features on the slope predate the drape cover

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

geochemistry of mafic enclaves and host granitoids from the chilliwack batholith washington chemical exchange processes between coexisting mafic and felsic magmas and implications for the interpretation of enclave chemical traits abstract mafic enclaves from three plutons in the chilliwack batholith have been compared with contemporaneous mafic stocks in order to determine 1 the processes by which mafic and felsic magmas hybridize in the plutonic environment and 2 whether analysis of early formed enclave minerals particularly apatite can provide a means of seeing through hybridization effects and deciphering the original trace element characteristics of enclave magmas whole rock and mineral chemistry data reveal a two stage history of enclave hybridization stage 1 a diffusive exchange of trace elements between coexisting liquids produced enclaves with distinctive concave upward rare earth element patterns that parallel those of the host granitoids but had minimal impact on the major elements whose transfer is rate limited by the slow diffusion of si this stage probably occurred at a mafic felsic interface in a stratified magmatic system stage 2 a partial reequilibration of enclave minerals with a differentiated and h

the late alpine evolution of an extensional shear zone naxos greece the mid miocene structural evolution of the metamorphic complex on naxos involved deformation in a kilometre scale low angle ductile shear zone the structures described are consistent with exhumation of the metamorphic complex during crustal extension after and possibly during localized high temperature barrovian style metamorphism non coaxial fabrics developed throughout the structural history indicate that upper levels were transported to the north during ductile extension this shear sense is opposite that inferred previously for the development cordilleran style metamophic core complexes in the cvclades ductile deformation was accompanied during its later stages by e w directed compression

generation of sodium rich magmas from newly underplated basaltic crust sodium rich rocks of trondhjemite tonalite dacite ttd or granodiorite ttg suites form much of precambrian continental crust1 they are thought to have formed by partial melting of subducted oceanic crust2 3 a process that would have been much more widespread early in earth history than at present owing to the higher thermal gradients prevailing at that time4 phanerozoic ttd suites do exist however and seem also to relate to subduction zones5 defant and drummond6 proposed that these suites form where young 25 myr hot oceanic lithosphere is subducted and melts thus locally simulating the conditions that led to widespread crustal growth in the archaean here we describe plutonic and volcanic rocks from the cordillera blanca complex in peru which have characteristics of the high al ttd suite but which were produced above a subduction zone containing a 60 myr old slab we present evidence that the complex formed by partial melting of newly underplated basaltic crust and argue that this mechanism should be considered more generally as an additional way of generating sodium rich arc magmas

ground truthing 6 5 khz side scan sonographs what are we really imaging a 1000 km2 area on the distal lobe of monterey fan shows a digitate pattern of juxtaposed high and low backscatter on gloria side scan sonographs this area was investigated using stereo photography high resolution seismic profiles and measurements of physical properties of cores to quantitatively evaluate the causes of backscatter from the 6 5 khz side scan sonar stereo photography and bottom video were used to determine that the sediment water interface typically has a bed roughness less than 10 cm over the entire ground truth area consequently bed roughness is not a significant contributor to the sonar backscatter vertical incidence 3 5 khz profiles reveal that high backscatter areas allow less penetration and have slightly more relief than low backscatter areas closely spaced measurements of p wave velocity density and grain size made on transponder navigated cores are used to investigate the geoacoustic properties of the sediment with the aid of a numerical model the model results demonstrate that the sediment water interface is in most cases acoustically transparent to the sonar energy and that most or all of the energy is refracted into the sediment to depths of at least a few meters rather than scattered from the surface the variability of the dominant lithofacies sands with minor silty clays or silty clay with minor sands accounts for a regional correlation with backscatter when viewed over hundreds to thousands of square kilometers but at the detailed scale of hundreds to a few square meters we have not yet been able to identify a correlation of backscatter intensity with the angle of incidence surface lithology measured acoustic impedance or attenuation however there is a qualitative but unexpected correlation with lithostratigraphic variability in this area thick up to 50 cm sand deposits with thin interbeds of silty clay correlate with lower backscatter than do silty clay deposits with thin interbeds of sand this suggests that volume inhomogeneities and complex constructive and destructive interferences caused by the subsurface volume inhomogeneities within the top few meters of the sediment ultimately modulate the intensity of backscatter the ground truthing effort was further complicated by trying to compare the very large sonar footprint of a pixel 70 000 m2 relative to the area of an individual core 0 006 m2 bottom photograph 5 m2 or seismic profile although 6 5 khz sonographs appear easy to interpret in a conventional and simplistic manner caution should be used when interpreting lithofacies from backscatter intensities

40ar 39ar dating of white micas from an alpine high pressure metamorphic belt on naxos greece the resetting of the argon isotopic system overprinting of white micas from high pressure low to medium temperature m1 metamorphic assemblages in pelitic schists on naxos during subsequent thermal dome m2 metamorphism ranges from minor in the southeast of the island to complete recrystallization in the amphibolite facies rocks near the migmatites in the centre of the dome the original m1 minerals are phengites si4 6 7 7 0 and the overprinting minerals are muscovites si4 6 0 6 45 40ar 39ar step heating analyses of white mica separates from rocks in the area where phengite and muscovite occur together yield complex age spectra characterized by low apparent ages in the first and the last stages of gas release and high apparent ages in between these upward convex age spectra are shown to be caused by mixing of two generations of micas each of which has a different age spectrum and argon release pattern seemingly good plateaus in some age spectra from white micas of the area must be interpreted as providing meaningless intermediate ages further the upward convex age spectra have been used to trace the isotopic signature of phengites toward increasing m2 metamorphic grade and suggest that as long as phengites can be observed in the rocks upward convex age spectra occur on naxos crystallization of muscovite at the expense of phengite appears to be the main mechanism of resetting argon isotopic ages in white micas however there is also good evidence for argon loss by volume diffusion from phengites simple diffusion calculations suggest that the m2 metamorphism was caused by a shortlived heat source

nb ta fractionation in peraluminous granites a marker of the magmatic hydrothermal transition in their late stages of evolution peraluminous granitic melts exsolve large amounts of fluidswhich can modify the chemical composition of granitic whole rock samples the niobium tantalum nb ta ratio is expected to decrease during the magmatic differentiation of graniticmelts but the behavior of both elements at the magmatic hydrothermal transition remainsunclear using a compilation of whole rock geochemical data available in the literature wedemonstrate that fractional crystallization alone is not sufficient to explain the distribution ofnb ta in most peraluminous granites however we notice that most of the granitic samplesdisplaying evidence of interactions with fluids have nb ta 5 we propose that the decreaseof the nb ta ratio in evolved melts is the consequence of both fractional crystallization andsub solidus hydrothermal alteration we suggest that the nb ta value of 5 fingerprints themagmatic hydrothermal transition in peraluminous granites furthermore a nb ta ratio of 5appears to be a good marker to discriminate mineralized from barren peraluminous granites

dehydration melting and water saturated melting of basaltic and andesitic greenstones and amphibolites at 1 3 and 6 9 kb

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

characteristics and genesis of the mnogovershinnoe gold silver deposit se russia abstract the mnogovershinnoe ore deposit is part of the bekchiul volcano plutonic complex located on the northern flank of the east sikhote alinsky belt in se russia the complex was developed in two stages during the senonian upper cretaceous and paleocene eocene the early stage is represented by a poorly differentiated andesite granodiorite association and the late stage is marked by subalkaline monzodiorite granite intrusions the vein metasomatic zones with au ag mineralization are associated with magmatic units of the early stage and are crosscut by large dikes of the late stage the deposit shows features of epithermal mineralization and a higher temperature overprint the total ca 1000 m zone of productive mineralization shows vertical zoning characterized by gold sulfosalt sulfide gold sulfide then gold telluride sulfide and telluride sulfide from bottom to top the hydrothermal system of the deposit shows evidence for mixing between fluids derived from the volcano plutonic units and meteoric water the mineralization is inferred to have formed from the mixing between these fluids and by the fluctuations of fluid pressure in the system

regional implications of geochemistry and style of emplacement of miocene i type diorite and granite delos cyclades greece abstract the miocene plutons of the cyclades were emplaced in a subduction setting during regional back arc extension of continental crust that led to flat lying mid crustal detachment faulting mapping of the island of delos shows that quartz diorite and tonalite were emplaced as dykes in country rock of schist and marble within shear zones parallel to the extension direction mafic magmas were followed by numerous small batches of felsic magma with magmatic and ductile deformation synchronous with magma emplacement late granite dykes occupy brittle fractures in the more deformed rocks mafic and intermediate rocks show a bimodal distribution of incompatible trace elements with one group of broadly tholeiitic character and the other with substantial enrichment in sr nb and hfse but low th and ba these differences appear to be inherited from two distinct mafic sources that are different from the mafic source for the plutons of the eastern cyclades voluminous granodiorite results from these mafic magmas fractionating and or mixing with felsic crustal material some of which was derived by anatexis of a sedimentary protolith indicated by high b and mn some late granites appear derived from partial melting of hercynian paragneiss regionally the shear zones appear to be feeders to more extensive granitic plutons located at space produced at ramps in detachment fault zones the shear zones parallel the mid cycladic lineament a broad zone of displacement between two crustal blocks rotating in opposing directions as rollback took place at the hellenic subduction zone distinctive geochemical features in miocene igneous rocks suggests that these two blocks had quite different geological histories the localisation of plutonism and core complexes near the mid cycladic lineament suggests that this crustal scale shear played a role in bringing subduction derived magmas to mid crustal levels the heat supplied by the mafic magmas promoted ductile deformation high in the crust where extension was concentrated leading to the formation of core complexes the regional extension resulted in progressive shallowing of the position of the granite solidus within the crust leading to welding of the mid cycladic lineament which is no longer seismically active

single grain argon laser probe dating of phengites from the blueschist to greenschist transition on sifnos cyclades greece measurements of 40ar 39ar age spectra on single white mica crystals of tertiary age is a new means of obtaining detailed geochronological information of alpine blueschists internal consistency of the data set as well as excellent agreement with previous conventional k ar results demonstrates that this new technique can be used with confidence to obtain information on the thermal evolution of young metamorphic belts

zr lree rich minerals in residual peraluminous granulites another factor in the origin of low zr lree granitic melts there is a significant enrichment in some trace elements in the major residual minerals of peraluminous granulite xenoliths from the lower crust those trace elements are released from the breakdown of accessory phases at high t granulite facies conditions n850 c around 10 35 of zr is hosted in granulite rutile and garnet whereas the entire lree eu budget is controlled by feldspar the zr and ree compatible behaviour of the major granulite phases combined with the scarcity of accessory phases which are mostly included in major granulite minerals leads to a disequilibrium in accessory dissolution in the peraluminous partial melts thus the melt extracts less zr and lree and consequently generates the false impression of having lower t when applying current accessory phase dissolution models

a model for monazite melt equilibrium and application to the generation of granitic magmas abstract in order to model the behaviour of zr hf ti p u th y and the rare earth elements ree in the continental crust the parameters which control the equilibria between accessory minerals and granitic melts must be determined this paper proposes equations for the equilibrium between monazite and ca poor felsic melts in a first step all the light ree are considered as a single component and an equation describing monazite solubility is deduced from the available experimental data in a second step the fractionation of ree by monazite is investigated on the basis of a natural example of coexisting monazite and obsidian from macusani peru the solubility of monazite can be used as a thermometer based on the total ree content of natural magmatic rocks application of ree thermometry to various peraluminous rock series suggests that it is a reliable tool for determining temperatures of magmatic processes the equation governing ree fractionation by monazite is used to discuss genetic relationships between a melt and a presumed parental rock using the composition of the monazite in the parental rocks and the ree pattern of the daughter rock this method has been applied successfully to high himalayan manaslu and tibetan slab granites it is suggested that detailed petrographical work on monazite including electron microprobe analyses and sem imaging of its internal structures combined with the model presented here can be a useful tool for deciphering the genesis and the differentiation of peraluminous granitic magmas in the continental crust

a review of the relationships between granitoid types their origins and their geodynamic environments abstract granitoids are divided into several types according to their mineral assemblages their field and petrographical features and their chemical and isotopic characteristics this typology complements most of the recent classifications because it is not based solely on chemical and isotopic criteria but also on the field petrographical and mineralogical criteria it thus has the advantage of distinguishing the various granitoid types in the field in most cases the proposed classification shares many similarities with the twenty most used genetic classifications of granitoids both types of peraluminous granitoids are of crustal origin the tholeiitic alkaline and peralkaline granitoids are of mantle origin and both types of calc alkaline granitoids are of mixed origin and involve both crustal and mantle materials each granitoid type is generated and emplaced in a very specific tectonic setting each stage of the wilson cycle is characterised by typical associations of granitoids well typed and precisely dated granitoids can then complement structural approaches and indicate on the geodynamic environment with reference to some case studies the use of granitoids as tracers of the geodynamic evolution is also proposed and discussed

increased continental margin slumping frequency during sea level lowstands above gas hydrate bearing sediments we present sup 14 c data on sediment samples from cores of the upper 7 m of the sediment column overlying a major continental rise gas hydrate field on the southern carolina rise and inner blake ridge offshore the southeastern united states the data show that glacial age sediments are underrepresented in the cores the observation is consistent with a previously predicted association between sea level lowstands and increased frequency of sea floor slumping on continental margins containing gas hydrates 26 refs 3 figs

hatteras transverse canyon hatteras outer ridge and environs of the u s atlantic margin a view from multibeam bathymetry and backscatter abstract previously unknown features in hatteras transverse canyon and environs were recently mapped during multibeam surveys of almost the entire eastern u s atlantic continental margin the newly identified features include 1 extensive landslide scarps on the walls of hatteras transverse and hatteras canyons 2 an area of multiple landslide deposits that block lower hatteras transverse canyon 3 a large depositional feature down canyon from the landslide deposits that rises 100 m above the uppermost hatteras fan and has buried the transition from the mouth of hatteras transverse canyon to uppermost hatteras fan 4 a zone of cyclic steps on upper hatteras fan that suggests supercritical turbidity currents performed a series of hydraulic jumps and formed large upstream migrating bedforms 5 several knickpoints in the channel thalwegs of both hatteras transverse canyon and hatteras canyon one 40 m high that suggest both canyon channels are out of equilibrium and are in the process of readjusting either to the channel blockage by the extensive landslide deposits or by a readjustments to increased sedimentation during the last eustatic lowstand 6 a large area of outcrop on the lower margin between pamlico and hatteras canyons that previously was interpreted as an area of slumps blocky slide debris and mud waves 7 headward erosion in the head region of hatteras transverse canyon where it has intercepted the lowest reaches of albemarle canyon channel as well as headward erosion in a small side channel that has eroded into hatteras outer ridge and 8 sections of bedforms on hatteras outer ridge that are partially buried by sediment from washington norfolk canyon channel as well as by sediment transported from hatteras abyssal plain the newly discovered features add a new level of detail to understand the recent processes that have profoundly affected hatteras transverse canyon hatteras canyon and to a lesser degree hatteras outer ridge

paleogene neogene depositional history of the middle u s atlantic continental rise mixed turbidite and contourite depositional systems abstract the construction of the middle u s atlantic continental rise from late paleogene to late pliocene time included downslope sediment gravity flows and alongslope contourite deposition some previous studies have suggested that contour following bottom currents were the dominant control on depositional patterns depositional relief from two large contourite drifts largely built in late miocene to late pliocene time continue to dominate present day lower rise morphology detailed seismic sequence mapping presented here suggests that significant turbidite fan systems also were active and are preserved in the stratigraphic section a single thick depositional sequence is mapped for oligocene to middle miocene sediments deposited when inferred fan systems off the norfolk washington canyons were reworked by bottom currents along the lower rise to form the proto hatteras outer ridge detailed mapping of three late miocene to late pliocene depositional sequences indicates that fan channel systems were active at the same time large contourite drifts were being constructed sediment delivered to the lower rise by these elongate turbidite systems undoubtedly was an important local source for construction of the hatteras outer ridge and through entrainment and resuspension was an important source for regional contourite deposition controlled by the deep western boundary undercurrent we suggest that submarine fans and current controlled sediment drifts may develop simultaneously as companion systems types of fan drift interaction include current only modification of fans transitional fan to drift and adjacent or overlapping submarine fan and sediment drift deposition

microgranitoid enclaves in granites globules of hybrid magma quenched in a plutonic environment microgranitoid enclaves autoliths cognate xenoliths mafic inclusions are common in high level granitoid plutons they have relatively fine grained igneous microgranitoid microstructures1 and many show evidence of having flowed in a magmatic condition2 these features counter interpretations that the enclaves represent transformed solid fragments of diverse wall rocks3 5 or restite6 11 an alternative interpretation is that the enclaves represent globules of mafic magma that have mingled commingled and quenched in the granitoid host magma12 16 a detailed review of the literature occurrence morphology and composition of micro granitoid enclaves strongly supports this view hut indicates that the enclave magmas range in composition from mafic to felsic and that magma mixing may be involved in their formation17 i summarize here the main features of microgranitoid enclaves and briefly outline the possible processes leading to their incorporation as magma globules in the host granitoid

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

synkinematic skarns and fluid drainage along detachments the west cycladic detachment system on serifos island cyclades greece and its related mineralization back arc extension in the aegean sea has been accommodated by several large scale detachments such as the west cycladic detachment system wcds in the oligocene and miocene the wcds especially crops out on serifos island cyclades with a synkinematic granodioritic intrusion as skarns represent metasomatic reactions near the contact between intrusions and the host rocks they sign the position of the main drains used by fluids while the mineralogy of the serifos skarns is well known geometrical and kinematic relations between the detachments and ore bodies remains poorly studied this study allows us to distinguish different types of skarn high temperature skarns correspond to 1 massive garnet endoskarns 2 ribbon and bubble garnet pyroxene endoskarns 3 garnet pyroxene cracks exoskarns whereas medium temperature pyroxene ilvaite bearing skarn breccias within the meghalo livadhi and kavos kiklopas detachments belonging to the wcds our observations show that skarn formation is associated with the activity of detachments and the syntectonic pluton emplacement endo and exoskarn deposits formed coeval with the ductile and brittle structures resulting from the activity of the wcds such as echelon veins veins with antithetic shear and boudinaged veins wrapped within sheath folds with a top to the ssw or sw shear senses compatible with the regional kinematics some skarn breccias formed within detachment planes far from the contact of the main granodioritic body attesting for the intense flow of magmatic fluids along these discontinuities these over pressurized fluids play a major role in the mechanical behaviour of the detachments and strain localization the two detachments acting as preferential crustal scale drains the pattern of magmatic fluid flows is not centred on the intrusion in this context iron rich skarns and associated primary magnetite deposits have been remobilized during late brittle increments of motion along the detachments together with surface derived fluids responsible for deposition of the economic fe ba mineralization

the hellenic subduction system high pressure metamorphism exhumation normal faulting and large scale extension the cenozoic history of the retreating hellenic subduction system in the eastern mediterranean involves subduction accretion arc magmatism exhumation normal faulting and large scale continental extension from 60 mya until the recent ages for high pressure metamorphism in the central aegean sea region range from 53 ma in the north the cyclades islands to 25 20 ma in the south crete younging of high pressure metamorphism reflects the southward retreat of the hellenic subduction zone the shape of pressure temperature time paths of high pressure rocks is remarkably similar across all tectonic units suggesting a steady state thermal profile of the subduction system and persistence of deformation and exhumation styles the high pressure metamorphic events were caused by the underthrusting of fragments of continental crust that were superimposed on slab retreat most of the exhumation of high pressure units occurred in extrusion wedges during ongoing lithospheric convergence at 23 19 mya large s

the relative importance of gravity induced versus current controlled sedimentation during the quaternary along the mideast u s outer continental margin revealed by 3 5 khz echo character abstract a detailed echo character map based on more than 50 000 km of 3 5 khz echograms reveals the relative importance of contour currents turbidity currents and mass wasting processes for the upper 50 100 m of sea floor sediments along the u s continental margin between southern georges bank and cape hatteras nineteen individual echo types are mapped and interpreted as deposits produced either by current controlled or gravity induced processes based on echo type distribution analysis of selected sediment core samples and the published results of other workers turbidity currents and mass wasting have apparently been the primary depositional agents throughout 60 of the region in contrast contour currents alone appear to have influenced only 10 of the region however combined processes i e non separable interaction between downslope and parallel to contour processes have influenced an estimated 25 of the margin the remaining 5 of the study area constitutes the outermost continental shelf echo types here reflect the influence of fluvial deltaic and shallow marine sedimentary processes changes in the relative distributions of various echo types with sea floor depth indicate that the dominant sedimentary processes change downslope and are significantly different within each physiographic province deposits formed by mass wasting dominate the continental slope where 50 of the sea floor is eroded and gullied by slides slumps and the heads of debris flows deposits developed under the influence of combined processes are most wide spread on the upper continental rise and cover 40 of the sea floor primarily in the form of deep sea channel levees modified by contour currents on the lower continental rise turbidites form more than 50 of the sea floor deposits the downslope deposits turbidity currents slumps debris flows etc were emplaced primarily during the pleistocene glacioeustatic sea level lowering moved beaches and rivers across the exposed continental shelf to the shelf edge where massive fluxes of terrigenous sediment could be delivered to the continental slope and rise by turbidity currents significant amounts of this sediment were transported through submarine canyons and leveed deep sea channels to the lower continental rise and formed the lower continental rise terrace a flat turbidite basin ponded behind the hatteras outer ridge southwest of the wilmington channel this glacially derived influx was diminished however depositional patterns indicate that downslope processes continued to be dominant at least as far south as cape hatteras where rapid deposition on the continental slope and uppermost continental rise created instabilities slope failure produced slumps slides and debris flows and provided an additional volumetrically important redistribution of sediment downslope the influence of contour currents is clearly observed only in those areas topographically shielded from the masking effects of downslope processes in particular along the seaward side of the buried chesapeake drift and the hatteras outer ridge

cryptic trace element variation as an indicator of reverse zoning in a granitic pluton the ricany granite czech republic cryptic variation recognized on the basis of trace element patterns shows the oieany granite in the northeastern part of the hercynian central bohemian pluton to be a reversely zoned high level intrusion unlike many other reversely zoned plutons there are no marked differences in modal composition between the margins and the centre of the intrusion the granite is generally peraluminous and geochemically evolved as demonstrated by its restricted and high sio 2 range and low k rb ratio coupled with a c two fold variation in ba and sr concentrations modelling shows that the geochemical variations can be most readily explained by k feldspar dominated fractionation in a magma chamber below the present level of exposure the reverse zoning is interpreted as the product of emplacement of an essentially single pulse of magma from a deeper level magma chamber in which fractionation has led to a vertical compositional gradient the least evolved magma was emplaced in the centre of the high level pluton with the more evolved magma around it recognition of cryptic reverse zoning in granites has major implications for granite petrogenesis in that the magmatic evolution of such bodies has to be established before assessing potential mechanisms of emplacement

giant magmatic water reservoirs at mid crustal depth inferred from electrical conductivity and the growth of the continental crust the formation of the continental crust at subduction zones involves the differentiation of hydrous mantle derived magmas through a combination of crystallization and crustal melting however understanding the mechanisms by which differentiation occurs at depth is hampered by the inaccessibility of the deep crust in active continental arcs here we report new high pressure electrical conductivity and petrological experiments on hydrated andesitic melt from uturuncu volcano on the bolivian altiplano by applying our results to regional magnetotelluric data we show that giant conductive anomalies at mid crustal levels in several arcs are characterized by relatively low amounts of intergranular andesitic partial melts with unusually high dissolved water contents 8 wt h2o below uturuncu the altiplano puna magma body apmb displays an electrical conductivity that requires high water content up to 10 wt dissolved in the melt based on crystal liquid equilibria and melt h2o solubility experiments such a super hydrous andesitic melt must constitute about 10 of the apmb the remaining 90 being a combination of magmatic cumulates and older crustal rocks the crustal ponding level of these andesites at around 6 kbar pressure implies that on ascent through the crust hydrous magmas reach their water saturation pressure in the mid crust resulting in decompression induced crystallization that increases magma viscosity and in turn leads to preferential stalling and differentiation similar high conductivity features are observed beneath the cascades volcanic arc and taupo volcanic zone this suggests that large amounts of water in super hydrous andesitic magmas could be a common feature of active continental arcs and may illustrate a key step in the structure and growth of the continental crust one sentence summary geophysical laboratory conductivity and petrological experiments reveal that deep electrical conductivity anomalies beneath the central andes cascades and taupo volcanic zone image the ponding of super hydrous andesitic melts which contributes to the growth of continental crust

geochemistry of the serifos calc alkaline granodiorite pluton greece constraining the crust and mantle contributions to i type granitoids the late miocene 11 6 9 5 ma granitoid intrusion on the island of serifos western cyclades aegean sea is composed of syn to post tectonic granodiorite with quartz monzodiorite enclaves cut by dacitic and aplitic dikes the granitoid a typical i type metaluminous calcic amphibole bearing calc alkaline pluton intruded the cycladic blueschists during thinning of the aegean plate combining field textural geochemical and new sr nd o isotope data presented in this paper we postulate that the serifos intrusion is a single zoned pluton the central facies has initial 87 sr 86 sr 0 70906 to 0 7106 e nd t 5 9 to 7 5 and 18 qtz 10 to 10 6 whereas the marginal zone or border facies has higher initial 87 sr 86 sr 0 711 to 0 7112 lower e nd t 7 3 to 8 3 and higher 18 qtz 10 6 to 11 9 the small range in initial sr and nd isotopic values throughout the pluton is paired with a remarkable uniformity in trace element patterns despite a large range in silica contents 58 8 to 72 wt sio 2 assimilation of a crustally derived partial melt into the mafic parental magma would progressively add incompatible trace elements and sio2 to the evolving mafic starting liquid but the opposite trend of trace element depletion during magma evolution is observed in the serifos granodiorites thermodynamic modeling of whole rock compositions during simple fractional crystallization fc or assimilation fractional crystallization afc processes of major rock forming minerals at a variety of pressure oxidation state and water activity conditions fails to reproduce simultaneously the major element and trace element variations among the serifos granitoids implying a critical role for minor phases in controlling trace element fractionation both saturation of accessory phases such as allanite and titanite at sio 2 71 wt to satisfy trace element constraints and assimilation of partial melts from a metasedimentary component to match isotopic data must have accompanied fractional crystallization of the major phases

an integrated zircon geochronological and geochemical investigation into the miocene plutonic evolution of the cyclades aegean sea greece part 1 geochronology we use 369 individual u pb zircon ages from 14 granitoid samples collected on five islands in the cyclades in the aegean sea greece for constraining the crystallisation history of i and s type plutons above the retreating hellenic subduction zone miocene magmatism in the cyclades extended over a time span from 17 to 11 ma the ages for s type granites are systematically 2 million years older than those for i type granites considering plutons individually the zircon data define age spectra ranging from simple and unimodal to complex and multimodal seven of the 14 investigated samples yield more than one distinct zircon crystallisation age with one i type granodiorite sample from mykonos island representing the most complex case with three resolvable age peaks two samples from s type granites on ikaria appear to have crystallised zircon over 2 3 million years whereas for the majority of individual samples with multiple zircon age populations the calculated ages deviate by 1 1 5 million years we interpret our age data to reflect a protracted history involving initial partial melting at deeper lithospheric levels followed by crystallisation and cooling at shallower crustal levels our study corroborates published research arguing that pluton construction is due to incremental emplacement of multiple magma pulses over a few million years assuming that multiple age peaks of our 14 samples can indeed serve to quantify time spans for magmatic emplacement our data suggest that aegean plutons were constructed over a few million years our tectonic interpretation of the u pb ages is that the s type granites resulted from partial melting and migmatisation of the lower crust possibly starting at 23 ma the i type granites and associated mafic melts are interpreted to reflect the magmatic arc stage in the cyclades starting at 15 ma

eocene tectonometamorphism on serifos western cyclades deduced from zircon depth profiling geochronology and mica thermochronology abstract phengite bearing metasedimentary sequences preserving relict glaucophane from serifos western aegean are indicative of high pressure conditions during cycladic blueschist metamorphism depth profiling and conventional sims u pb geochronology and o isotope analysis on zircon from highly strained orthogneisses at the base of the sequence reveal xenocrystic zircon with varying degrees of recrystallization one end member population has needle like or prismatic morphologies is internally oscillatory zoned with little to no rim material created during recrystallization these zircons yield triassic to carboniferous ages elevated th u and 18 o mostly ranging between 4 and 11 in marked contrast a separate zircon population has a spongy structure created by complete recrystallization of the pre existing crystal these zircons possess low th u and flat hree patterns and yield eocene ages with 18 o 7 chondrite normalized ree profiles are extremely depleted within this spectrum other zircons show variable states of recrystallization and mixed ages regression of u pb data from three mylonitic orthogneiss samples that exhibit near complete recrystallization and similar age depth profiles yields c 40 ma ages these new data are the first geochronological constraints that successfully demonstrate an eocene metamorphic event in the western cyclades and new 40 ar 39 ar phengitic mica ages of 38 32 ma presented here suggest the metamorphic wedge was exhumed into the shallow crust shortly thereafter

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

geochemistry and geochronology of hp melanges from tinos and andros cycladic blueschist belt greece abstract u pb zircon geochronology sr nd isotope and bulk rock geochemistry have been applied to meta igneous and meta sedimentary rocks from high pressure metamorphic melanges exposed on the cycladic islands of tinos syros and andros ion microprobe shrimp u pb zircon dating of 7 samples representing meta igneous blocks tinos a blackwall zone tinos and chlorite talc schists from block matrix contacts syros and tinos yielded cretaceous ages of c 80 ma many of the criteria commonly used to distinguish between magmatic or metamorphic zircon genesis internal structure th u ratio ree characteristics ti in zircon thermometry enclosed mineral phases do not provide unambiguous constraints for the mode of formation however a magmatic origin for cretaceous zircon of meta gabbros and eclogites is considered likely supporting evidence for a previously suggested metamorphic origin for c 80 ma zircon in eclogite has not been found zircon of the same age occurring in chlorite talc schists is presumably related to non magmatic processes well defined cretaceous age groups clustering at c 79 ma also occur in the detrital zircon populations of 2 quartz mica schists representing the melange matrix on tinos and suggest a much later time for sediment accumulation than previously assumed the importance of c 57 ma zircon ages remains unclear but may record either hp metamorphic processes or a post 57 ma depositional age the youngest age group in a third quartz mica schist from tinos collected outside the main melange occurrences clusters at c 226 238 ma in all clastic metasediments from tinos most data points plot along the concordia between c 300 and 900 ma single data points indicate concordant ages of c 2 5 ga 2 3 ga and 1 ga respectively the youngest 206 pb 238 u age group that has been recognized in a felsic paragneiss from andros indicates an age of 163 1 3 9 ma and mostly represents overgrowths around zircon with ages in the range from 272 to 289 ma single data points of other inherited cores provided 206 pb 238 u ages of c 630 and c 930 ma meta gabbros from tinos show a large compositional variability and were found at 4 locations each with distinct compositional characteristics suggesting different crystallization histories different sources and or significant post magmatic disturbance the geochemistry of melange blocks and the identical u pb zircon ages suggest that the block matrix associations on tinos and syros can be grouped together on a broader regional scale there seem to be similarities between some meta igneous rocks from tinos and evvia field relationships indicate that the melanges occurring in southern andros and northern tinos can be correlated but supporting geochemical and or geochronological evidence for this interpretation could not be established previously published jurassic ages for mafic and felsic melange blocks from andros suggest a genetic relationship to the ophiolite occurrences exposed in the larger balkan region a similar regional correlation is also considered likely for the cretaceous meta gabbros from tinos and syros but cannot be documented with certainty

apatite solubility in peraluminous liquids experimental data and an extension of the harrison watson model abstract new experimental data at 750 1000 c 2 5 kbar and for peraluminous melt compositions show a dramatic increase of apatite solubilities and phosphorus melt contents when compared to metaluminous or peralkaline compositions harrison and watson 1984 the formation of alumino phosphate units in peraluminous melts qualitatively explains our data a new apatite solubility model incorporating the data for the peraluminous region is presented application of this model to examples of peraluminous felsic suites is discussed

u pb geochronology of grossular andradite garnet abstract this study presents a new laser ablation inductively coupled plasma mass spectrometry la icpms based u pb geochronometric method for dating grossular andradite grandite garnet grandite is a primary skarn mineral therefore dating its growth directly dates hydrothermal activity as zircon u pb geochronometry provides a high resolution record of magmatic processes grandite u pb dating has the potential to provide a complementary record for hydrothermal systems this study characterizes four garnets of variable grossular andradite content and age as potential reference materials for la icpms u pb geochronology willsboro andradite 1020 ma adirondacks usa red and yellow mali grandite 200 ma southern mali and lake jaco grossular 35 ma coahuila mexico isotope dilution thermal ionization mass spectrometry id tims u pb analyses of willsboro andradite yield a mean 206pb 238u date of 1022 16 ma we use willsboro andradite as a primary reference material for la icpms u pb characterization of the two other garnets the non radiogenic pb pbc concentration in grandite is variable between specimens willsboro andradite and mali grandites contain almost purely radiogenic pb pb however lake jaco grossular has a higher pbc concentration comparatively and yields discordant u pb ratios for specimens with highly variable pb pbc linear regression is employed to derive a lower intercept age la icpms u pb dates for yellow mali grandite 202 2 ma 206pb 238u weighted mean and lake jaco grossular 35 2 ma lower intercept agree with independent id tims u pb 202 0 1 2 ma and u th he dates 35 5 ma derived for each specimen the precision of la icpms u pb dates varies between 1 10 2 for the analyzed garnets considering the short estimated lifespans of pluton related hydrothermal systems tens of thousands to a few million years neogene skarns present the best opportunity to test for and resolve separate episodes of garnet growth at these precision levels as a performance test for the method we present new u pb andradite data from a late miocene skarn system on serifos island greece this garnet yields a lower intercept age of 9 15 0 36 ma in agreement with biotite rb sr and zircon u pb dates from the causative pluton

sources and evolution of arc magmas inferred from coupled o and hf isotope systematics of plutonic zircons from the cretaceous separation point suite new zealand abstract coupled o and hf isotopic compositions of zircons from early cretaceous 113 124 ma granitoids of the separation point suite sps new zealand obtained by cathodoluminescence imaging guided micro beam methods sims la icpms are used as a record of evolving magma compositions in a prominent mesozoic arc system eight representative sps samples from individual plutons in the nelson and fiordland regions yield magmatic zircons with initial hf isotope ratios expressed in e hf ranging from 4 to 11 nelson and 5 to 12 fiordland respectively initial hf isotope ratios of zircons are extremely heterogeneous within individual samples with the vast majority of values distinctly less radiogenic than depleted mantle at 120 ma e hf 16 o isotope ratios are likewise variable with 18 o zircon smow values of 2 8 nelson and 0 7 fiordland the within rock variability in both zircon hf and o isotope ratios is testimony to open system processes that operated during magma evolution and zircon crystallisation average 18 o zircon for cores and rims allow constraints to be placed on the o isotopic composition of magmas from which zircon precipitated 18 o magma 4 8 elevated 18 o magma 6 5 require involvement of 18 o enriched supracrustal material weathered continental crust or low t seawater hydrothermally altered oceanic crust while 18 o magma 18 o depleted crustal component whole rock sr isotope nb ta and nd pb systematics are inconsistent with 18 o depleted slab melts 18 o 0 6 as a source component for sps magmas instead low 18 o values suggest incorporation of high t meteoric hydrothermally altered country rocks similar to those of the largs terrane presently exposed in northern fiordland in diagrams of sio 2 versus inferred 18 o magma the most primitive sps samples from the nelson and fiordland regions plot close to the expected composition for primitive arc magmas more evolved granitoids however show strongly divergent trends of o isotope composition as a function of sio 2 suggestive of assimilation coupled to fractional crystallisation afc in contrasting crustal environments emplacement level contamination by local crust is supported by age distributions of inherited zircons which indicate a predominance of palaeozoic and mesozoic zircons in nelson and fiordland granitoids respectively

deciphering subduction from exhumation in the segmented cycladic blueschist unit central aegean greece the cycladic blueschist unit cbu represents the northern passive margin of the adria continental block and ophiolites that are the remnants of the pindos ocean which were affected by high pressure low temperature metamorphism in the blueschist and eclogite facies during the eocene prior to the lutetian the ophiolitic and margin units were thrust towards the sw inside a ne dipping subduction zone two subsequent exhumation stages are characterized by top to the ne senses of shear i from mantle depths to lower crustal levels before 37 ma which was accommodated by an extensional inversion of the vardar suture zone and ii from deep crustal levels to the near surface between 30 and 20 ma which was accommodated by the north cycladic detachment it is during this late stage of ductile exhumation that the central cyclades core complex was exhumed segmentation of the cbu by normal faults started at 12 ma as recorded by the low temperature thermochronometers and was coeval with block rotation and folding with ns trending axes which were predominantly controlled by the myrthes ikaria strike slip fault in the centre of the cyclades a map restoration of the cbu geometry prior to segmentation has been carried out using available structural and paleomagnetic data the restoration shows that following the cbu exhumation from mantle depths to crustal levels a single core complex was exhumed along a single ne dipping detachment

partial melting of two amphibolites contrasting experimental results under fluid absent conditions a large portion of the lower continental crust may be amphibolitic in composition and without a free fluid phase as a consequence h2o undersaturated or fluid absent melting of amphibolites may be responsible for the formation of some granites and migmatites produced during major orogenic events in an attempt to determine the systematics of melting under fluid absent conditions a series of piston cylinder experiments was conducted on two natural amphibolites one a meta alkali basalt aba with a total water content of wt contained in hornblende and the other a meta island arc tholeiite iat which has 1 1 3 wt water contained in hornblende cummingtonite and biotite the experimentally determined melting ranges of the two amphibolites showed that the solidus temperatures and sta temperature interval over which amphibole was stable were controlled by the amphibolites different bulk compositions and their resulting metamorphic assemblages the volume of melt produced by melting of the two amphibolites were compared with estimated amounts based on burnham s 1979 water melt solubility model and the fluid absent melting model presented by clemens and vielzeuf 1987 the observed melt volumes were greater than estimated as the water content of melt largely detemines the volume of melt produced independent measurements of the water content of the glass formed during partial melting in the aba were made by thermogravimetric analyses the water content of the aba glass is 2 wt which is less than the assumed melt water content water content of the melt used in previous modeling of fluidabsent anatexis in mafic lithologies as a consequence more melt can be expected during fluid absent partial melting of mafic lower crust as is observed in the experiments a modification of the clemens and vielzeuf 1987 fluid absent melting model for mafic compositions has been made using the experimental data available on melting in basaltic systems and is presented here for pressures of 5 8 and 10 kbar tectonic scenarios in which the crust is thickened i e by collision then undergoes extension or where a previously thinned crust is later rethickened provide enough heat so that amphibolite melting under fluid absent conditions can become importan and hence responsible for some melts produced during post collisional magmatism the results may also have applications to melting in hydrated oceanic crust in subduction zones and in island arc terains

crystallization and resorption in plutonic plagioclase implications on the evolution of granodiorite magma gesiniec granodiorite strzelin crystalline massif sw poland abstract granodiorite from the gesiniec intrusion strzelin crystalline massif sw poland contains complexly zoned plagioclases five chemically and structurally distinct zones can be correlated among crystals cores 25 35 an inner mantles 40 45 an outer mantles 40 25 an resorption zones 35 50 an and rims 35 30 an good structural and chemical major and trace elements correlation of zones between crystals indicates that zonation was produced by changes in conditions of crystallization on a magma chamber scale plagioclase being the liquidus phase records a time span from the beginning of crystallization to emplacement and rapid cooling of granodiorite as thin dykes crystallization began with the formation of inner mantles the paucity and different sizes of inner mantles suggests slow crystallization in high temperature magma normally zoned inner mantles were formed under increasing undercooling compositional trends in mantles suggest closed system crystallization the major resorption zones were caused by injection of less evolved magma as indicated by the strontium increase in plagioclase the injection triggered a rapid rise of magma and plagioclase crystals facilitating mixing but also inducing fast kinetically controlled growth of complex multiple oscillatory zonation within resorption zones the ascent of magma caused decompression melting of plagioclase and produced melt inclusions within inner mantles the cores the decompression range is estimated at a minimum of 2 kbar emplacement of granodiorite as thin dykes allow rapid cooling and preservation of magmatic zonation in plagioclases melt inclusions crystallized completely during post magmatic cooling the zonation styles of plutonic plagioclase differ markedly from volcanic ones suggesting different magma evolution zones in plutonic plagioclase are well correlated indicating crystallization in quiescent magma where crystals accumulation and compositional magma stratification may occur crystals probably did not travel between different regimes resorption occurred but as single albeit complex episodes good correlation of zones in plutonic plagioclases allows a distinction between the main processes controlling zonation and superimposed kinetic effects

extensional faulting on tinos island aegean sea greece how many detachments zircon and apatite fission track zft and aft and u th he 40ar 39ar hornblende and u pb zircon ages from the granites of tinos island in the aegean sea greece suggest together with published zft data that there are three extensional detachments on tinos the tinos granites crosscut the tinos detachment cooling of the granites was controlled by the livadi detachment which occurs structurally above the tinos detachment our u pb zircon age is 14 6 0 2 ma and two 40ar 39ar hornblende ages are 14 4 0 4 and 13 7 0 4 ma zft and aft ages go from 14 4 1 2 to 12 2 1 0 ma and 12 8 2 4 to 11 9 2 0 ma u th he ages are from 10 4 0 2 to 9 9 0 2 ma zircon and 11 9 0 5 to 10 0 0 3 ma apatite all ages decrease northeastward in the direction of hanging wall transport on the livadi detachment and age distance relationships yield a slip rate of 2 6 3 3 1 0 km ma 1 this rate is smaller than a published slip rate of 6 5 km ma 1 for the vari detachment which is another detachment structurally above the tinos detachment because of the different rates and because published zft ages from the footwall of the vari detachment are 10 ma we propose that the vari detachment has to be distinguished from the older livadi detachment we discuss various models of how the extensional detachments may have evolved and prefer a scenario in which the vari detachment cut down into the footwall of the livadi detachment successively exhuming deeper structural units the thermochronologic ages demonstrate the importance of quantitative data for constraining localization processes during extensional deformation

collision vs subduction related magmatism two contrasting ways of granite formation and implications for crustal growth earth s continental crust is dominantly made of buoyant felsic igneous material granitoids that were ultimately extracted from the mantle as a result of earth s differentiation since felsic melts are not in chemical equilibrium with the mantle they can originate either from melting of older crustal lithologies or from differentiation of a primitive mantle melt only the latter case will contribute to crustal growth to understand the mechanisms of continental crust growth and differentiation through time it is therefore necessary to unravel the respective contribution of these two different mechanisms in the genesis of granitoid suites in modern earth granitoids are chiefly generated in convergent plate boundaries subduction and collision this paper examines the granitic suites in a late collision environment the variscan french massif central fmc and compares them with the suites found in an oceanic arc we therefore describe and compare two end members sites of granite generation in the fmc several main types of granites are described muscovite and cordierite bearing peraluminous granites resp mpg and cpg contain large amounts of inherited zircons and their chemistry demonstrates that their sources were older crustal material resp metasediments and metaigneous on the other hand potassic calc alkaline granites kcg associated to potassic diorites vaugnerites do not contain inherited zircons and ultimately derive from the vaugnerites the vaugnerites in turns form by partial melting of a mantle contaminated by the regional crust therefore although they are isotopically similar to the crust the kcg are net contributors to crustal growth thus we conclude that although late orogenic settings are dominated by crustal melting and recycling they may be sites of net crustal growth even though this is not visible from isotopes only in contrast arc granitoids are purely or almost purely mantle derived however the preservation potential of arcs is much smaller than the preservation of late orogenic domains such that at the scale of a whole orogenic belt late orogenic magmatism is probably as important as arc magmatism finally we speculate that the situation may have been similar in the archaean or even more skewed towards late orogenic sites or similar environments dominated by melting of a altered mafic protocrust owing to the hotter mantle and less stable subductions during that period

zircons from syros cyclades greece recrystallization and mobilization of zircon during high pressure metamorphism zircons were studied from high pressure low temperature metamorphosed meta igneous lithologies from syros these rocks carry several zircon generations related to each other by dissolution reprecipitation processes one generation is pristine zircon that shows growth zoning relatively elevated contents of trivalent cations and high th u ratios the other end member is a skeletal zircon generation with negligible trivalent cation contents and low th u ratios 0 1 texturally between these two there is a range of zircon crystals with complex inclusion populations of y hree th phases and fluid inclusions showing variable progress of replacement recrystallization both end members yield distinct sensitive high resolution ion microprobe shrimp u pb ages the pristine generation has an age of 80 2 1 6ma from a metagabbro and 76 4 2 1ma from a meta plagiogranite dyke the skeletal low th u zircon generation yields an age of 52 4 0 8ma the older late cretaceous zircons are interpreted to date emplacement of the magmatic protoliths in a small segment of oceanic crust the younger eocene age however dates a zircon recrystallization event which possibly coincides with high solubility and mobility of high field strength elements in a high pressure aqueous fluid phase intergrowth relations between zircon and peak metamorphic garnet and excellent agreement of the u pb ages with white mica ar ar ages for the same samples support the conclusion that eocene is the true age of high pressure metamorphism on syros

ree fractionation and nd isotope disequilibrium during crustal anatexis constraints from himalayan leucogranites abstract the processes controlling rare earth element ree behaviour during crustal anatexis have profound implications not only for ree abundances of crustally derived granites but also for their model nd ages for typical protoliths of anatectic granites such as are exposed in metapelites from the high himalayan crystalline series hhcs a high proportion 90 of bulk rock lree and mree are sited in the accessory phases apatite and monazite and of hree in garnet and apatite mass balance constraints indicate that observed ree abundances of himalayan leucogranites cannot be generated from ree deficient reactant phases in their metasedimentary protoliths muscovite biotite plagioclase and quartz but must result from the dissolution of accessory phases ree and th abundances in anatectic melts are modelled by combining empirical expressions for monazite apatite and zircon solubilities as a function of temperature melt composition and melt water content with analysed accessory phase ree abundances this approach which allows the contribution to the melt from each accessory phase to be identified successfully predicts himalayan leucogranite trace element abundances the lree and th concentrations of a metapelite derived melt are buffered by monazite stability although apatite dissolution contributes up to 10 of lree to the melt together with 50 of the mree and 90 of the hree zircon contributes a negligible proportion of ree to the melt during anatexis dissolution of monazite and apatite in the melt results in 1 increasing ree abundances and lree hree ratios with increasing temperature of melting 2 a negative eu anomaly in the melt 3 high sm nd ratios in the melt relative to its metasedimentary protolith and 4 nd isotope disequilibrium between the melt and its protolith all of these features are observed in the ree geochemistry of himalayan leucogranites the combined effects of sm nd fractionation and nd isotope disequilibrium during anatexis imply that model nd ages calculated for anatectic granites derived from apatite and monazite bearing protoliths should be treated with considerable caution

mid pleistocene lavas from the seguam volcanic center central aleutian arc closed system fractional crystallization of a basalt to rhyodacite eruptive suite in contrast to adjacent volcanic centers of the modern central aleutian arc seguam island developed on strongly extended arc crust k ar dates indicate that mid pleistocene late pleistocene and holocene eruptive phases constitute seguam this study focuses on the petrology of the mid pleistocene 1 07 07 ma turf point formation tpf which is dominated by an unusual suite of porphyritic basalt and basaltic andesite lavas with subordinate phenocryst poor andesite to rhyodacite lavas increasing whole rock feo mgo from basalt to dacite the anhydrous plag ol cpx opx mt phenocryst assemblage groundmass pigeonite and the reaction ol liq opx preserved in the mafic lavas indicate a tholeiitic affinity thermometry and comparison to published phase equilibria suggests that most tpf basalts crystallized plag ol cpx mt at 1160 c between about 3 5 kb 1 2 h2o andesites crystallized plag cpx opx mt at 1000 c between 3 4 kb with 3 5 h2o and dacites crystallized plag cpx opx mt at 1000 c between 1 2 kb with 2 3 h2o all lavas crystallized at f o 2 close to the nno buffer mineral compositions and textures indicate equilibrium crystallization of the evolved lavas petrographic evidence of open system mixing or assimilation is rare mgo cao al2o3 cr ni and sr abundances decrease and k2o na2o rb ba zr and pb increase with increasing sio2 50 71 lree enrichment ce yb n 1 7 0 2 characterizes most tpf lavas total ree contents increase and eu anomalies become more negative with increasing sio2 relative to other aleutian volcanic centers tpf basalts and basaltic andesites have lower k2o na2o tio2 rb ba sr zr y and lree abundances 87sr 86sr ratios 0 70361 0 70375 and ratios of 206pb 204pb 18 88 18 97 207pb 204pb 15 58 15 62 208pb 204pb 38 46 38 55 are the highest measured for any suite of lavas in the oceanic portion of the aleutian arc conversely end values 5 8 to 6 7 are among the lowest from the aleutians sr nd and pb ratios are virtually constant from basalt through rhyodacite whereas detectable isotopic heterogenity is observed at most other aleutian volcanic centers major and trace element ree and sr nd and pb isotopic compositions are consistent with the basaltic andesitic andesitic dacitic and rhyodacitic liquids evolving from tpf basaltic magma via closed system fractional crystallization alone fractionation models suggest that removal of 80 wt cumulate 61 plag 17 cpx 12 opx 7 ol and 3 mt can produce 20 wt rhyodacitic residual liquid per unit mass of parental basaltic liquid petrologic and physical constraints favor segregation of small batches of basalt from a larger mid crustal reservoir trapped below a low density upper crustal lid in these small magma batches the degree of cooling crystallization and fractionation are functions of the initial mass of basaltic magma segregated the thermal state of the upper crust and the magnitude of extension tholeiitic magmas erupted at seguam evolved by substantially different mechanisms than did calc alkaline lavas erupted at the adjacent volcanic centers of kanaga and adak on unextended arc crust these variable differentiation mechanisms and liquid lines of descent reflect contrasting thermal and mechanical conditions imposed by the different tectonic environments in which these centers grew at seguam intra arc extension promoted eruption of voluminous basalt and its differentiates unmodified by interaction with lower crustal or upper mantle wallrocks

physicochemical controls on bismuth mineralization an example from moutoulas serifos island cyclades greece the 11 6 to 9 5 ma serifos pluton intruded schists and marbles of the cycladic blueschist unit causing thermal metamorphism the development of magnetite ca exo and endo skarns and the formation of low temperature vein and carbonate replacement ores potentially the most important ores occur in the moutoulas prospect where the mineralization in retrograde skarn and quartz veins culminated with the deposition of native bismuth a combination of fluid inclusion microthermometry and isotope geothermometry suggests that the moutoulas mineralization formed at a hydrostatic pressure of 100 bars from moderate to low temperature 190 250 c and low salinity 1 3 5 6 wt nacl equivalent fluids the calculated 34 s h 2 s compositions are consistent with the ore fluids having been derived from the serifos pluton bismuth mineralization is interpreted to have occurred as a result of wall rock interaction and mixing of a bi bearing ore fluid with meteoric waters native bismuth and bismuthinite deposited at 200 c near neutral ph 6 5 low f s 2 f o 2

the geological signature of a slab tear below the aegean in this paper we explore the geology of the aegean region in the miocene to identify the geological signature of a first order slab tear observed in all tomographic models from 15 to 8 ma the tear is associated spatially and timely with a fast clockwise rotation of the external hellenides alkaline volcanism high temperature metamorphic domes with a predominance of north dipping detachments and south westward migration of granitoid intrusions these features suggest a warmer geodynamic environment during the rotation and the impact of a hot mantle flow associated with the tear the 8 ma duration between the first high temperature metamorphic domes in the centre of the archipelago and the beginning of the fast rotation may correspond to the time needed for the slab to bend stretch and finally tear

high grade metamorphism dehydration and crustal melting a reinvestigation based on new experiments in the silica saturated portion of the system kalo 2 mgo sio 2 h 2 o co 2 at p 1 5 gpa the system kalo2 mgo sio2 h2o co2 has long been used as a model for the processes of granulite facies metamorphism and the development of orthopyroxene bearing mineral assemblages through the breakdown of biotite bearing assemblages there has been considerable controversy regarding the role of carbon dioxide in metamorphism and partial melting we performed new experiments in this system at pressures of 342 to 1500 mpa with t between 710 and 1045 c and xflh2o between 0 05 and 1 00 accurately locating most of the dehydration and melting equilibria in p t xflh2o space the most important primary result is that the univariant reaction phl qtz fl en sa melt must be almost coincident with the fluid absent reaction phl qtz en sa melt in the co2 free subsystem in conjunction with the results of previous measurements of co2 solubility in silicate melts and phase equilibrium experiments our theoretical analysis and experiments suggest that co2 cannot act as a flux for partial melting crustal melting in the presence of h2o co2 mixed fluids will always occur at temperatures higher than with pure h2o fluid present magmas produced by such melting will be granitic s l in composition with relatively high sio2 and low mgo contents irrespective of the h2o co2 ratio in any coexisting fluid phase we find no evidence that lamprophyric magmas could be generated by partial fusion of quartz saturated crustal rocks the granitic melts formed will not contain appreciable dissolved co2 the channelled passage of hot co2 rich fluids can cause local dehydration of the rocks through which they pass in rock dominated as opposed to fluid dominated systems minor partial melting can also occur in veins initially filled with co2 rich fluid as dehydration and local disequilibrium drive the fluid towards h2o rich compositions however co2 is unlikely to be a significant agent in promoting regional granulite grade metamorphism melting magma generation metasomatism or long range silicate mass transfer in earth s crust the most viable model for the development of granulite facies rocks involves the processes of fluid absent partial melting and withdrawal of the melt phase to higher crustal levels

oxygen and hydrogen isotope geochemistry of s and i type granitoids the cape granite suite south africa abstract the late precambrian cape granite suite of the southwestern cape south africa can be subdivided into six major batholiths saldanha vredenburg darling malmesbury paarl wellington stellenbosch kuils river and peninsula individual plutons have been classified as a i and s type granites on the basis of petrography and chemical composition quartz and feldspar from the cape granites have 18o values which range from 8 6 to 13 4 and 5 0 to 13 6 respectively the 18o value of quartz is a very effective discriminator between s and i type granites and provides the best means to estimate the 18o value of the original magma the s type granites crystallized from magmas having 18o values between 9 5 and 11 4 mean 10 6 the a and i type granites crystallized from magmas having 18o values between 6 6 and 9 9 mean 7 8 there is almost no overlap of 18o values between the s and the i type granites with the boundary at 9 5 of the 31 quartz feldspar pairs analysed the vast majority have values of qtz fsp between 0 and 4 however only eight samples have values of qtz fsp between 0 7 and 1 55 which would be consistent with equilibrium under closed system conditions the remaining samples were affected by minor fluid rock interaction biotite d values range from 113 to 47 and show no correlation with estimated magma 18o value biotite water content or whole rock loss on ignition the variation in biotite d is probably caused by a combination of varying degree of magma degassing and minor low temperature alteration

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

local equilibrium of mafic enclaves and granitoids of the turtle pluton southeast california mineral chemical and isotopic evidence free to read on publisher s website major element and trace element compositions of whole rocks mineral compositions and rb sr isotopic compositions of enclaveand host granitoid pairs from the early cretaceous calc alkalineturtle pluton of southeasterncalifornia suggest that the local environment profoundly affects some enclave types in the turtle pluton where the source of fine grained mafic enclaves can be deduced to be magmatic by the presence of partially disaggregated basaltic dikes mineral chemistry suggests partial or complete local equilibrium among mineral species in the enclaveand its host granitoid because of local rb sr isotopic equilibration betweenfine grained enclaves and host granitoid one cannot use sr isotopes to distinguish an enclave source independent of its host rocks from an enclave sourcerelated to the enclosing pluton however preliminary nd isotopic data suggestan independent mantle source for enclaves

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

metamorphic core complexes of cordilleran type in the cyclades aegean sea greece the islands of ios and naxos in the cycladic archipelago greece contain elongate domes over which a pervasive north to north northeast stretching lineation is warped these islands may be metamorphic core complexes of cordilleran type involving middle crustal rocks drawn upward and outward from underneath the sedimentary basins now 100 km to the south from ca 25 ma onward during uplift the crystalline rocks now exposed on the islands were deformed noncoaxially in the deeper levels of a major shallow dipping ductile shear zone this shear zone may have connected with low angle normal faults in its upper levels because it is probable that its later history involved the metamorphic complexes being dragged out from under a stretching and fracturing upper plate composed mainly of unmetamorphosed sedimentary and ophiolite suite rocks this model can be extended to explain the exhumation of the high pressure low temperature metamorphic rocks on crete which with the cyclades forms a distended paired metamorphic belt separated by an active sedimentary basin