cretaceous metamorphism and plutonism in the santa cruz mountains salinian block california and correlation with the southernmost sierra nevada new data on the ages of plutonism and metamorphism in the northern santa cruz mountains part of the enigmatic salinian block of california clarify the area9s geologic history uranium lead dates on zircon monazite sphene and apatite and initial pb and sr isotopic ratios provide a fingerprint for comparison to the rest of the salinian block and to other terranes the u pb zircon dates of plutonic rocks in the santa cruz mountains fall into three groups emplacement ages of the two younger undeformed groups are 91 ma and between 99 and 103 ma individual zircon analyses range from concordant to significantly discordant but have simple crystallization histories coupled with either inheritance of precambrian zircon or pb loss the older group of plutons includes recrystallized granite to well foliated orthogneisses that share the regional fabric analyses from the older group are slightly discordant and multistage histories that include inheritance pb loss and homogenization of pb complicate interpretation of their age emplacement ages for the older group are early cretaceous greater than about 103 ma and probably less than 130 ma foliated and unfoliated plutons from the older group appear to bracket the age of salinian deformation and metamorphism between about 103 and 130 ma lower intercept ages for detrital zircon from schist and quartzite further support a cretaceous metamorphic age the detrital zircon population contains a component at least 1 6 ga probably close to 1 7 ga uranium lead cooling ages measured on sphene and apatite are 96 to 93 and 93 to 88 ma respectively this cooling history appears to be a response to intrusion and rapid cooling of the youngest plutons common pb and sr initial isotopic ratios are radiogenic compared with ratios of oceanic rocks and the western parts of the cordilleran batholiths but they are the least radiogenic in the salinian block and fit the local geographic gradient of pb and sr initial ratios linear variation of pb isotope ratios between radiogenic wall rock and the least radiogenic rocks and correlation of inherited zircon with elevated pb isotope ratios suggest that plutons assimilated wall rock isotopic data and geologic histories of basement rocks in the northern santa cruz mountains fit the geographic patterns documented in the rest of the salinian block more intriguingly the santa cruz mountains plutons are strikingly similar to parts of the southern sierra nevada batholith ages of plutonism and metamorphism u pb zircon discordance systematics petrography and initial sr isotopes match closely between the santa cruz mountains crystalline rocks and units in the southernmost sierra nevada batholith these data reinforce the long standing view that the salinian block and sierra nevada batholiths were adjacent during their formation prior to right slip of about 310 km on the san andreas fault the probable westward continuation of the low angle rand fault system into the southern sierra nevada and the salinian block appears to have offset these two crystalline suites about 125 km

paleogeographic and tectonic setting of axial and western metamorphic framework rocks of the southern sierra nevada california this paper represents an update of our 1978 s e p m mesozoic paleogeography synthesis for the southern sierra nevada we originally postulated that much of the southern sierra nevada pre batholithic metamorphic framework consisted of lower mesozoic siliciclastic carbonate and pelitic strata with variable arc volcanic admixtures kings sequence recent syntheses however have attempted to minimize the importance of early mesozoic strata in the region and to extend coherent paleozoic terranes into the framework as the predominant protoliths neither lithologic correlations nor structural analysis can substantiate such a view however and the proposed configuration of the paleozoic terranes is in conflict with the petrochemical zonation pattern of the cretaceous batholith we present stratigraphic relations for the relatively well preserved lower mesozoic stratified rocks of the southern sierra which in general supports our 1978 synthesis as pointed out by more recent syntheses however we now recognize the likelihood of paleozoic basement rocks occurring in some or many of the kings sequence pendants such rocks are disparate fragments of a highly dismembered polygenetic basement composed of paleozoic ophiolitic shoo fly miogeoclinal and possibly antler belt rocks rather than coherent terranes or crustal blocks the lower stratal levels of the lower mesozoic kings sequence appears to have formed part of a regional post sonoman triassic marine overlap sequence above this basement complex dismemberment and accretion of the basement complex involved transform truncation of the southwest cordillera and foothills ophiolite belt emplacement prior to and coincident with sonoman thrust tectonics following the establishment of a carnian norian carbonate platform as part of the overlap sequence the region subsided and became part of a regional early jurassic forearc to intra arc extensional basin system with the deposition of kings sequence turbidites and olistostromes the basin system was destroyed by middle and late jurassic thrusting the assertion that much of the kings sequence is paleozoic in age is based on the discovery of probable eocambrian cambrian miogeoclinal strata in the snow lake pendant of the east central sierra nevada lahren and others 1991 these authors offer a reconstruction of the displacement of these strata as part of a large crustal block from the western mojave region through the axial sierra nevada along a now cryptic fault the bounds of the hypothetical crustal block however are at odds with batholithic petrochemical patterns we propose a more conservative offset history for the snow lake pendant rocks which considers a broader uncertainty in the bounds of the possible source area for the rocks and satisfies offsets of both batholithic petrochemical patterns and igneous metamorphic assemblages of the sierran batholithic complex

salinity stratification of the mediterranean sea during the messinian crisis a first model analysis abstract in the late miocene a thick and complex sequence of evaporites was deposited in the mediterranean sea during an interruption of normal marine sedimentation known as the messinian salinity crisis because the related deposits are mostly hidden from scrutiny in the deep basin correlation between onshore and offshore sediments is difficult hampering the development of a comprehensive stratigraphic model since the various facies correspond to different salinities of the basin waters it would help to have physics based understanding of the spatial distribution of salt concentration here we focus on modelling salinity as a function of depth i e on the stratification of the water column a box model is set up that includes a simple representation of a haline overturning circulation and of mixing it is forced by atlantic exchange and evaporative loss and is used to systematically explore the degree of stratification that results under a wide range of combinations of parameter values the model demonstrates counterintuitive behaviour close to the saturation of halite for parameter values that may well be realistic for the messinian we show that a significantly stratified mediterranean water column can be established in this case atlantic connectivity is limited but may be closer to modern magnitudes than previously thought in addition a slowing of mediterranean overturning and a larger deep water formation region both in comparison to the present day are required under these conditions we would expect a longer duration of halite deposition than currently considered in the msc stratigraphic consensus model

garnet geochemistry of tungsten mineralized xihuashan granites in south china abstract the xihuashan complex intrusion in south china which is emplaced at ca 154 ma mainly comprises medium grained porphyritic biotite granite medium grained biotite granite and fine grained two mica granite medium grained biotite and fine grained two mica granites are important tungsten bearing granites and contain an unusual amount of garnet garnets from this intrusion are dominated by almandine and spessartine which constitute 94 to 99 of the total molecular composition of the garnet these garnets display unusual compositional zoning the cores of these garnets are rich in heavy rare earth element hree y ca and contain abundant hree and y rich mineral inclusions their rims are free of mineral inclusions and have low of these elements two types of fluorite inclusions exist in garnet y fluorite and y poor fluorite garnet exhibits specific mn zoning with a relatively mn poor core but a relatively mn rich rim thus constituting a specific spessartine inverse bell shaped profile that belongs to typical magmatic garnets all analyzed garnets have high ree content and exhibit hree enriched and lree depleted patterns with strong negative eu anomalies the incorporation of ree into garnet is in part controlled by its crystal chemistry with ree3 following a coupled substitution of the type fe2 mn2 1viii ree3 1viii si4 1iv z3 1iv the texture and compositional zoning of garnet suggest that garnet growth is largely controlled by the pressure temperature composition condition of magmatic evolution internal crystal chemical parameters and kinetics during mineral growth the garnet core grows in near equilibrium with magmatic melt under a relatively high pressure temperature p t condition by contrast the garnet rim grows rapidly by the coexisting melt fluid phase and co2 rich volatile environment under a relatively low p t condition which is virtually unfavorable for the incorporation of ree into the magmatic garnet structure garnet fingerprints the magmatic hydrothermal transition during crystallization of these granites

metamorphism and deformation along the emplacement thrust of the samail ophiolite oman abstract the base of the samail ophiolite is a metamorphic shear zone that provides key information about ophiolite emplacement the classic exposure of this metamorphic sole at wadi tayin consists of a few meters of garnet clinopyroxene mafic gneiss and 80 m of upper amphibolite facies mafic and quartzose tectonite overlying 150 m of lower amphibolite facies mafic and sedimentary schist the sole is bounded by faults but is internally coherent peak metamorphic temperatures decrease exponentially from 825 c at the top of the sole to 500 c at its base as documented by changes in grain size hornblende composition the disappearance of chlorite and epidote garnet clinopyroxene element partitioning and garnet hornblende partitioning the inverted peak temperature gradient decreases from 4000 c km in the upper 50 m to 100 c km in the lower 150 m contrary to earlier reports greenschist facies tectonites are not present at wadi tayin although the entire sole underwent greenschist facies retrogression driven by the influx of fluids from the overlying peridotite or underlying carbonate calculations based on an amphibolite constitutive relation reveal that although the section represents a lithologic continuum the lower 200 m of the sole is a relatively undeformed block whereas the uppermost 25 m represent material initially separated by tens to a couple of hundreds of kilometers and now integrated into a single column

constraints from zircon u pb ages o and hf isotopic compositions on the origin of neoproterozoic peraluminous granitoids from the jiangnan fold belt south china zircon textures and micro chemical compositions precisely record the origin and petrogenesis of granitoids which are crucial for evaluating crustal growth and reworking thermal and geodynamic evolution zircons in peraluminous granitoids from the three largest 820 ma complexes guibei yueyang and jiuling in the jiangnan fold belt in south china are used to constrain their sources and petrogenetic processes zircons in the guibei granitoids have complex internal structures nearly all magmatic and inherited zircons have similar ehf 6 8 to 5 6 and 18o values 8 8 11 6 and dominantly lie between ehf evolution vectors for a crust created between 1 7 and 2 1 ga suggesting that the guibei granitoids were produced by partial melting of recycled heterogeneous supracrustal material however the yueyang granitoids contain zircons with high ehf 0 5 to 9 7 and relatively low 18o values 5 9 8 4 and two stage model ages of 1 1 1 8 ga and thus may have been formed by melting of mafic rocks from the lower crust the jiuling granitoids and their enclaves contain more complex zircons with more variable ehf 7 2 to 9 7 and 18o values 7 0 10 6 and lie along the mixing trend between the above proposed infracrustal and supracrustal granitoids therefore the neoproterozoic peraluminous granitoids in the jiangnan fold belt were produced by melting and mixing of continental crust compared with extremely low 4 and negative 18o values of neoproterozoic igneous zircons formed in its northern active continental margin the high 18o peraluminous granitoids in the southeastern yangtze block are considered to have been formed by melting of hydrothermally unaltered continental crust triggered by asthenosphere upwelling in the nanhua back arc basin

effects of cation substitutions in garnet and pyroxene on equilibrium oxygen isotope fractionations high grade metamorphic rocks were used to explore oxygen isotope fractionations between pyroxene and garnet and to investigate the effects on fractionation factors of the cation substitutions fe3 al 1 and ca fe mg 1 recrystallized granulite facies 725 c wollastonite ores from the northern adirondack highlands contain essentially only the minerals clinopyroxene a di hd solid solution garnet a grs adr solid solution wollastonite and exhibit a systematic dependence of measured fractionations on the fe3 content of calcic garnet cpx cagrt 0 14 0 12 0 78 0 20 xadr and wo cagrt 0 15 0 22 0 57 0 33 xadr in eclogites formed at t 650 c measured compositions of ca poor garnet and omphacite combined with experimental data indicate that ca poor fe rich garnet is enriched in 18o compared to both diopside and grossular extrapolating to 1000 k alm di c 0 2 and alm grs c 0 5 orthopyroxene and clinopyroxene from gore mountain new york show a constant fractionation that is independent of rock type as expected if they have the same closure temperature these data imply opx cpx c 0 7 at 1000 k measured fractionations among ca poor garnet orthopyroxene clinopyroxene and hornblende in the gore mountain rocks further indicate an 18o enrichment in ca poor garnet over grs c 0 5 at 1000 k the new measurements are indistinguishable from expected equilibrium values based on experiments for the minerals enstatite diopside grossular wollastonite and feldspar but consistently indicate a significant isotope effect for the simple octahedral cation substitutions fe3 al 1 grs vs adr and ca fe mg 1 ca poor garnet vs grs opx vs cpx neither cation substitution has been directly investigated for its effect on 18o 16o fractionation with experiments in silicates chemical characterization of minerals is required prior to petrological interpretation of oxygen isotope trends

the abad composite se spain a messinian reference section for the mediterranean and the apts a high resolution integrated stratigraphy is presented for the abad marls of the sorbas and nijar basins in se spain preevaporitic messinian of the western mediterranean detailed cyclostratigraphic and biostratigraphic analyses of partially overlapping subsections were needed to overcome stratigraphic problems in particular encountered at the complex transition from the lower to the upper abad the resulting abad composite section contains a continuous stratigraphic record from the tortonian messinian boundary up to the transition to the messinian evaporites of the yesares member all together 18 calcareous plankton events were recognized which were shown to be synchronous throughout the mediterranean by means of detailed bed to bed cyclostratigraphic correlations the magnetostratigraphy allowed the identification of the four magnetic reversals of chron c3an in the upper abad details in the sedimentary cycle patterns allowed the abad composite to be astronomically calibrated this calibration to the 658n summer insolation curve of solution la90 1 1 yielded astronomical ages for all sedimentary cycles calcareous plankton bioevents ash layers and paleomagnetic reversals up to now the abad composite is the only astronomically well calibrated section that provided a reliable cyclostratigraphy magnetostratigraphy and calcareous plankton biostratigraphy as such it will serve as a reference section both for the pre evaporite messinian in the mediterranean as well as for the messinian interval in the astronomical polarity time scale q 2001 elsevier science b v all rights reserved

sonic and gamma ray astrochronology cycle to cycle calibration of atlantic climatic records to mediterranean sapropels and astronomical oscillations a high resolution analysis of cyclical patterns in gamma ray and sonic logs of the lower pliocene sediments from the gulf of cadiz southern spain was carried out results suggest that these cycles can be successfully used for a bed to bed correlation with the global reference section for the astronomical time scale in capo rossello sicily cycle patterns were used to tune the logs to the astronomical solutions of j laskar the gamma ray and sonic cyclicity was interpreted in terms of precession induced oscillations of annual rainfall in southern spain that were in part responsible for the increasing input of freshwater into the mediterranean at times of sapropel formation we demonstrate that gamma ray and sonic astrochronology can be successfully used for interregional correlation and astronomical dating with errors not higher than 20 k y

do s type granites commonly sample infracrustal sources new results from an integrated o u pb and hf isotope study of zircon in contrast to i type granites which commonly comprise infracrustal and supracrustal sources s type granites typically incorporate predominantly supracrustal sources the initial aim of this study was to identify the sources of three scottish caledonian 460 ma s type granites kemnay cove and nigg bay by conducting oxygen u pb and hf isotope analyses in zircon in order to characterise one potential end member magma involved in the genesis of the voluminous late caledonian 430 400 ma i type granites field whole rock geochemical and isotopic data are consistent with the generation of the s type granites by melting their dalradian supergroup country rocks while hf isotope compositions of magmatic zircon u pb data of inherited zircons and high mean zircon 18o values of 9 0 2 7 2sd and 9 8 2 0 for the kemnay and cove granites support this model the nigg bay granite contains zircons with much lower 18o values 6 8 2 1 similar to those found in scottish i type granites this suggests that the nigg bay granite contains low 18o material representing either altered supracrustal material or more likely an infracrustal source component with mantle like 18o mixing trends in plots of 18o vs ehf for s type granite zircons indicate involvement of at least two sources in all three granites this pilot study of scottish caledonian s type granites demonstrates that while field and whole rock geochemical data are consistent with local melting of only supracrustal sources the oxygen isotopic record stored in zircon reveals a much more complex petrogenetic evolution involving two or more magma sources

deciphering the source and contamination history of peraluminous magmas using δ 18 o of accessory minerals examples from garnet bearing plutons of the sierra nevada batholith peraluminous granitoids provide critical insight as to the amount and kinds of supracrustal material recycled in the central sierra nevada batholith california major element concentrations indicate sierran peraluminous granitoids are high sio2 68 9 76 9 and slightly peraluminous average molar al2o3 cao na2o k2o 1 06 both major and trace element trends mimic those of other high silica sierran plutons garnet grt in the peraluminous plutons is almandine spessartine rich and of magmatic origin low grossular contents are consistent with shallow 4 kbar depths of garnet crystallization metasediments of the kings sequence commonly occur as wallrocks associated with the plutons including biotite schists that are highly peraluminous a cnk 2 25 and have high whole rock wr 18o values 9 6 21 8 average 14 5 2 9 n 26 ultramafic wallrocks of the kings kaweah ophiolite have lower average 18o 7 1 1 3 n 9 the 18o wr of the kings sequence is variable from west to east higher 18o values occur in the west where quartz in schists is derived from marine chert values decrease eastward as the proportion of quartz from igneous and metamorphic sources increases peraluminous plutons have high 18o wr values 9 5 13 consistent with supracrustal enrichment of their sources however relatively low initial 87sr 86sr values 0 705 0 708 indicate that the supracrustal component in the source of peraluminous magmas was dominantly altered ocean crust and or greywacke also plutons lack or have very low abundances 1 of grains of inherited zircon zrc cores average 18o zrc is 7 9 in peraluminous plutons a higher value than in coeval metaluminous plutons 6 7 diorites associated with peraluminous plutons also have high 18o zrc 7 4 8 3 which is consistent with the diorites being derived from a similar source magmatic garnet has variable 18o 6 6 10 5 avg 7 9 due to complex contamination and crystallization histories evidenced by multiple garnet populations in some rocks comparison of 18o zrc and 18o grt commonly reveals disequilibrium which documents evolving magma composition minor 5 7 contamination by high 18o wallrocks occurred in the middle and upper crust in some cases although low 18o wallrock may have been a contaminant in one case overall oxygen isotope analysis of minerals having slow oxygen diffusion and different times of crystallization e g zircon and garnet together with detailed textural analysis can be used to monitor assimilation in peraluminous magmas moreover oxygen isotope studies are a valuable way to identify magmatic versus xenocrystic minerals in igneous rocks

the upper tortonian lower messinian at monte dei corvi northern apennines italy completing a mediterranean reference section for the tortonian stage abstract a high resolution integrated stratigraphy including biostratigraphy magnetostratigraphy tephrostratigraphy and cyclostratigraphy is presented for the upper tortonian and lower messinian upper miocene at monte dei corvi numerical age control comes from a combination of magnetobiostratigrapic dating and astronomical tuning while radioisotope dating of ash layers produced less reliable ages the deep marine succession is characterized by large scale non repetitive stratigraphic changes allowing the discrimination between a lower brownish rossini and euxinic shale interval the sedimentary cycles which occur superimposed on these large scale changes are related to astronomical climate forcing astronomical tuning of the sedimentary cycles provides not only absolute ages for biostratigraphic events reversal boundaries and volcanic ash layers but also for the observed non cyclic changes these can be linked to environmental and geodynamic changes in the mediterranean region preceding the messinian salinity crisis the beginning of the brownish interval marked by tripartite cycles at 8 017 ma coincides with tectonic re arrangements in the mediterranean such as compression in the betics and opening of the rifian corridor at 7 616 ma the change to the calcareous rossini interval can be linked to tectonic uplift in the northern apennines and the deepening of the rifian corridor while the betic corridor became restricted coinciding with the end of evaporite deposition in the eastern betics the change to euxinic shales at 7 168 ma reflects basin wide restriction marked by diatomite and sapropel formation in the mediterranean basin related to the severely constricted betic and rifian corridors the occurrence of a tripartite construction of cycles in the euxinic shales at 6 719 ma coincides with diatomite formation in the eastern mediterranean uplift and shallowing in the northern apennines and further constriction of the atlantic gateways we conclude that late tortonian early messinian tectonic and environmental events occur remarkably synchronously in the mediterranean basin and most likely result from a combination of geodynamic processes and eccentricity controlled climatic changes in combination with the upper serravallian and lower tortonian interval which includes the formal tortonian global stratotype section and point gssp the monte dei corvi is the only complete section in the mediterranean covering the entire tortonian stage we therefore propose the monte dei corvi section as tortonian reference section particularly for the mediterranean region in addition it may serve as a unit stratotype for the tortonian

phase relations of peraluminous granitic rocks and their petrogenetic implications peraluminous granitic rocks are magmatic rocks that contain quartz po tassic feldspar and or sodic plagioclase and one or more aluminum rich minerals thus these rocks contain more aluminum than could be accom modated by feldspar in a cipw normative calculation and show normative corundum peraluminous granites are defined by their chemical nature but their recognition is often based on petrography this discrepancy thus may lead to inconsistency although peraluminous granitic rocks are com monly true granite streckeisen 1973 they range from tonalite to granite of special interest are strongly peraluminous as defi ned below granite granodiorite or in rare instances trondhjemite these rocks contain alumi nous minerals almandinic garnet cordierite tourmaline muscovite that are thought to be stable in silicate magmas only if these magmas are themselves peraluminous the origin of peraluminous granite and related intrusive rocks is of much current interest many of these form shallow level intrusions and they can reach enormous sizes examples are the batholiths in the lachlan fold belt in southeastern australia white chappell 1983 the cornub ian batholith in england exley stone 1966 the south mountain batholith in nova scotia mckenzie clarke 1975 the manaslu batho lith in the himalayas lefort 1981 much of the idaho batholith

chapter 12 geochemistry of the garnet bearing tharps peak granodiorite and its relation to other members of the lake kaweah intrusive suite southwestern sierra nevada california

gondwanan deglaciation and opening of neotethys the al khlata and saiwan formations of interior oman abstract new stratigraphic petrographic and paleontological data from the lower permian of southeastern arabia help to elucidate the still debated timing of neotethys rifting and the climatic evolution following the gondwanan glaciation the transition from the al khlata to the saiwan formation here described in detail is interpreted to record continental break up and onset of neotethyan spreading between northern gondwana and the cimmerian terranes at mid sakmarian times as constrained by brachiopod assemblages the eastern oman arm of the neotethyan rift system instead failed and sea floor spreading of the indo madagascar trough was delayed until final fragmentation of gondwana in the late jurassic petrographic composition of lower permian sandstones documents a distinct change from transitional to dissected rift shoulder provenance and widespread exposure of granitoid basement rocks at a late syn rift to early post rift stage very abundant pore filling celestite at the al khlata saiwan transition may have precipitated from circulating brines related to remobilization of proterozoic salt due to rift tectonics the sharp base of the saiwan formation records a major transgression related to the onset of neotethyan spreading final deglaciation and consequent global sea level rise as indicated by ravinement surfaces associated with lag deposits with tree trunks reworked ferruginous pedogenic concretions and phosphate and by paleoecological analyses the basal bed of the saiwan formation is characterized by the pioneer pachycyrtella paleocommunity with pachycyrtella omanensis 85 suspension feeding rapid rates of reproduction and growth r strategy early maturity high mortality rates in the juveniles the more mature secondary ecological succession developed higher in the saiwan formation records maximum flooding and significant climatic amelioration the saiwan formation at the beginning of the late sakmarian finally sutures the irregular rift related topography in the rim basin of interior oman and records a shift towards warmer temperate conditions after the end of the gondwanan glaciation

cretaceous sedimentary rocks on the masirah ophiolite sultanate of oman evidence for an unusual bathymetric history autochthonous sedimentary rocks on the masirah ophiolite preserve a record of vertical movements of their oceanic basement the masirah ophiolite was formed in the uppermost jurassic and subsequently underwent thermal subsidence for about 20 ma as documented by pelagic sediments submarine alkali basaltic volcanism in the lower barremian marks the onset of rapid basement uplift to or above sea level carbonate platforms grew in barremian mid aptian time on highs of oceanic basement the uplift is interpreted as the result of transpressive tectonism along a large oceanic fracture zone the platforms submerged in the mid aptian and reached the ccd in the albian ribbon cherts were deposited during the albian to santonian time the first influx of siliciclastic detritus shed from the arabian craton is recorded in coniacian sandstones ophiolitic conglomerates interfinger in the campanian to mid maastrichtian with continent derived sandstones reflecting regional compressive tectonism crystalline exotics deposited in the late maastrichtian are derived most likely from the precambrian basement of arabia whilst the origin of the sedimentary exotics dated triassic to cretaceous remains unclear the masirah ophiolite was overthrust at the cretaceous tertiary boundary by an upper ophiolite nappe and emplaced onto the margin of southeast oman

oxygen isotope geothermometers for metamorphic rocks the chicago mineral carbonate oxygen isotope fractionation curves have been combined with mineral water fractionation data for jadeite zoisite and rutile and new data for grossular water to provide a set of self consistent mineral pair calibrations the a coefficients in the equation 1000 in a 106t 2 of the new mineral pair fractionations are jadeite zoisite grossular rutile quartz 1 69 2 00 3 03 5 02 jadeite 0 31 1 34 3 33 zoisite 1 03 3 02 grossular 1 99 the isotopic fractionation properties of natural pyralspite garnet ca fe mg mn 3al2si3o12 can be approximated by those of the grossular end member appropriate substitutions also yield coefficients for the solid solution minerals sodic pyroxene and epidote e g aquartz sodic pyroxene 2 75 1 06xjd aquartz epidote 2 00 0 75xps where xjd and xps are the mole fractions of the jadeite and pistacite components respectively the new data set is particularly suitable for the geothermometry of metamorphic rocks 18o data from minerals of the high pressure metamorphic rocks of the sesia zone of italy and cyclades complex of greece yield well constrained mean temperatures of 572 and 478d c respectively type iii blueschist metabasalts of the franciscan formation of california give mean quartz garnet temperatures of 354d c

s type granites and their probable absence in southwestern north america criteria that have been and still are used to characterize s type granites of the lachlan fold belt lfb of southeastern australia are reviewed and comparisons are made with various peraluminous granites of southwestern north america some of which have been classified as s types on the basis of insufficient data virtually all of the vast volume of s type granites in the lfb are near surface batholithic granites that are commonly associated with s type volcanics and are not associated with regional metamorphic rocks and migmatites they are strongly peraluminous as shown by the presence of cordierite granites with primary muscovite are rare all are low in na ca and sr as a result of chemical weathering during formation of the sedimentary sources peraluminous granites of various ages in southwestern north america are distinctly different they rarely contain cordierite a mineral characteristic of lfb s types but some are highly evolved such that fe mn rich garnet has crystallized they are dominantly two mica granites indicating crystallization at higher water fugacities and greater depths than most peraluminous granites of the lfb cordierite bearing volcanics s types have not been reported sodium is generally high in the peraluminous granites of southwestern north america some of these rocks have trondhjemitic affinities the parent magmas seem more likely to have been produced by partial melting of altered basaltic rocks locally some peraluminous rocks marginal to metaluminous types may owe their compositions to high level contamination of i types these are not s type rocks no compelling evidence has been presented that any of the peraluminous granites of southwestern north america are s types

oxygen isotope trajectories of crystallizing melts insights from modeling and the plutonic record elevated oxygen isotope values in igneous rocks are often used to fingerprint supracrustal alteration or assimilation of material that once resided near the surface of the earth the 18 o value of a melt however can also increase through closed system fractional crystallization in order to quantify the change in melt 18 o due to crystallization we develop a detailed closed system fractional crystallization mass balance model and apply it to six experimentally and naturally determined liquid lines of descent llds which cover nearly complete crystallization intervals melt fractions of 1 to 0 1 the studied llds vary from anhydrous tholeiitic basalts to hydrous high k and calc alkaline basalts and are characterized by distinct melt temperature sio 2 trajectories as well as crystallizing phase relationships our model results demonstrate that melt fraction temperature sio 2 relationships of crystallizing melts which are strongly a function of magmatic water content will control the specific 18 o path of a crystallizing melt hydrous melts typical of subduction zones undergo larger increases in 18 o during early stages of crystallization due to their lower magmatic temperatures greater initial increases in sio 2 content and high temperature stability of low 18 o phases such as oxides amphibole and anorthitic plagioclase versus albite conversely relatively dry tholeiitic melts only experience significant increases in 18 o at degrees of crystallization greater than 80 total calculated increases in melt 18 o of 1 0 to 1 5 can be attributed to crystallization from 50 to 70 wt sio 2 for modeled closed system crystallizing melt compositions as an example application we compare our closed system model results to oxygen isotope mineral data from two natural plutonic sequences a relatively dry tholeiitic sequence from the upper and upper main zones uumz of the bushveld complex south africa and a high k hydrous sequence from the arc related dariv igneous complex mongolia these two sequences were chosen as their major and trace element compositions appear to have been predominantly controlled by closed system fractional crystallization and their llds have been modeled in detail we calculated equilibrium melt 18 o values using the measured mineral 18 o values and calculated mineral melt fractionation factors increases of 2 3 and 1 1 5 in the equilibrium melts are observed for the dariv igneous complex and the uumz of the bushveld complex respectively closed system fractional crystallization model results reproduce the 1 increase observed in the equilibrium melt 18 o for the bushveld uumz whereas for the dariv igneous complex assimilation of high 18 o material is necessary to account for the increase in melt 18 o values assimilation of evolved supracrustal material is also confirmed with sr and nd isotope analyses of clinopyroxene from the sequence beginning with a range of mantle derived basalt 18 o values of 5 7 pristine mantle to 7 0 heavily subduction influenced mantle our model results demonstrated that high silica melts i e granites with 18 o of up to 8 5 can be produced through fractional crystallization alone lastly we model the zircon melt 18 o fractionations of different llds emphasizing their dependence on the specific sio 2 t relationships of a given crystallizing melt wet relatively cool granitic melts will have larger zircon melt fractionations potentially by 1 5 compared to hot dry granites therefore it is critical to constrain zircon melt fractionations specific to a system of interest when using zircon 18 o values to calculate melt 18 o

the onset of the messinian salinity crisis in the eastern mediterranean pissouri basin cyprus the pissouri basin in cyprus contains one of the most suitable sedimentary successions with which to study the onset of the messinian salinity crisis in the eastern mediterranean exposures along the new paphos limassol motorway near pissouri exhibit distinct cyclic bedding which permits the construction of a chronology based on orbital tuning biostratigraphic results reveal 10 planktonic foraminifera events that have been astronomically dated in other mediterranean sections and as such provide an excellent first order age control magnetostratigraphic results are in good agreement with the biostratigraphic data and show that all magnetic chrons between c4n 1n and c3an 1n are present the pattern of sedimentary cycles generally fits well with the insolation curve astronomical tuning of the succession shows that the first gypsum bed at pissouri overlies a 40 60 kyr stromatolite bearing transitional interval and correlates with the amplitude increase in insolation at 5 96 ma as in the western mediterranean this indicates that the onset of evaporite precipitation was synchronous right across the entire mediterranean basin fl 2002 elsevier science b v all rights reserved

dynamic growth of garnet in granitic magmas in order to improve understanding of how accessory garnet crystallizes in igneous rocks and evaluate it as a mineral recorder of magma history we analyzed 18 o of garnets from the hallowell and togus plutons in south central maine united states by laser fluorination and in situ by ion microprobe two types of garnet are recognized magmatic and locally derived peritectic traverses of some single crystals show both gradual and abrupt changes of 18 o garnet commonly 1 while other garnet grains are isotopically homogeneous rimward increase of 18 o in many crystals indicates that garnet grew while high 18 o metamorphic wall rocks were assimilated peritectic grains have a complementary record of the transfer of high 18 o melts to the plutons in some rocks 18 o varies among neighboring grains evidence that crystals grew episodically or were juxtaposed from different sources during magma mixing garnet faithfully records changing magmatic 18 o and is a valuable tool to decipher magma petrogenesis

extremely thin oceanic crust in the proto indian ocean evidence from the masirah ophiolite sultanate of oman the masirah ophiolite is a good example of thin oceanic crust below pillow lavas and a sheeted dike complex with a relatively normal thickness of 1 1 5 km the gabbroic lower crust barely exceeds 500 m in thickness in spite of this reduced thickness the oceanic crust preserves all members of a model ophiolite in a coherent lithostratigraphic sequence the crust was formed during the uppermost jurassic circa 150 ma when the indian madagascar plate separated from the african arabian plate and is therefore related to the opening of the coeval somali basin geological relationships indicate that this portion of oceanic crust was formed at a ridge transform intersect the peculiarly reduced thickness of the gabbro layer is interpreted as the result of a weak magma supply at the edge of a ridge segment rather than the consequence of a tectonic thinning the cooling effect due to the vicinity of two large continental lithospheric blocks indian madagascar and african arabian plates during this initial stage of the oceanization might have been an additional factor contributing to the reduction of the crustal thickness

identifying late miocene episodes of connection and isolation in the mediterranean paratethyan realm using sr isotopes abstract after decades of research the timing and nature of late miocene connections between the mediterranean paratethys and the global ocean are still speculative the hydrologic flux implications of exchange or isolation are central to all hypotheses for generating the major lithological changes that represent the messinian salinity crisis moreover differences in the hydrologic fluxes envisaged are the primary distinction between models despite this these fluxes remain largely unconstrained this paper describes the basis for using sr isotope data innovatively combined with salinity data through hydrologic budget modelling to determine the timing and nature of mediterranean hydrologic connectivity we examine the hypotheses for three late miocene events to illustrate how this approach allows us to test implied hydrologic scenarios and exclude incompatible models 1 pre evaporite restriction of the mediterranean 2 the initiation of salt precipitation 3 connection between the sea of marmara and both paratethys and the mediterranean during the messinian this process suggests that the atlantic mediterranean exchange was significantly reduced up to three million years before evaporite precipitation it also indicates that end member hypotheses for initiating salt precipitation in the mediterranean desiccation and connected basin models are inconsistent with sr isotope data a contrasting model where evaporite formation was triggered by atlantic transgression into a strongly evaporation dominated mediterranean is shown to be more compatible with available datasets the application to sea of marmara samples indicates that salinity changes in the basin were not caused by changes to the amount of inflow from either paratethys or the mediterranean other possible as yet untested applications important for constraining different aspects of the messinian salinity crisis are highlighted

the messinian salinity crisis in the adriatic foredeep evolution of the largest evaporitic marginal basin in the mediterranean abstract the recent release of a large number of subsurface geological data by the italian minister of economic development including boreholes and seismic profiles provided the occasion for a new assessment of the deposits associated with the messinian salinity crisis msc in the adriatic foreland basin system and a new integration with the outcropping successions of the apennines in particular the study of the messinian evaporites allowed to reconstruct a new detailed palaeogeographic and palaeobathymetric framework for all the stages of the crisis we identified the largest evaporitic marginal basin ever described for the mediterranean hosting the precipitation of the primary shallow water gypsum deposits plg primary lower gypsum during the first stage of the crisis during the second and third stages of the crisis the plg basin underwent uplift and erosion and the evaporite accumulation moved to the deeper part of the basin and was characterized by the deposition of the resedimented lower gypsum unit including clastic evaporites recycling the plg ones primary halite and terrigenous deposits the distribution of the different evaporitic facies was the basis for an improved reconstruction of the upper miocene tectonic evolution of the apennines thrust belt our results show a clear separation between shallower depocenters located in the wedge top and in the adriatic foreland basins and characterized by msc stage 1 plg deposition and deeper water ones located in the adriatic foredeep and close to the calabrian arc where msc stage 2 terrigenous and gypsum bearing clastic deposits and primary halite accumulated

uranium lead isotopic ages from the sierra nevada batholith california this study provides new information on the timing and distribution of mesozoic magmatic events in the sierra nevada batholithic complex chiefly between 36 and 37 n latitude u pb ages have been determined for 133 zircon and 7 sphene separates from 82 samples of granitoid rocks granitoid rocks in this area range in age from 217 to 80 m y triassic intrusions are restricted to the east side of the batholith jurassic plutons occur south of the triassic plutons east of the sierra nevada as isolated masses within the cretaceous batholith and in the western foothills of the range cretaceous plutons form a continuous belt along the axis of the batholith and occur as isolated masses east of the sierra nevada no granitic intrusions were emplaced for 37 m y east of the sierra nevada following the end of jurassic plutonism however following emplacement of the eastern jurassic granitoids regional extension produced a fracture system at least 350 km long into which the dominantly mafic calc alkalic independence dike swarm was intruded 148 m y ago the dike fractures probably represents a period of regional crustal extension caused by a redistribution of the regional stress pattern accompanying the nevadan orogeny intrusion of cretaceous granitic plutons began in large volume about 120 m y ago in the western sierra nevada and migrated steadily eastward for 40 m y at a rate of 2 7 mm y this slow and constant migration indicates remarkably uniform conditions of subduction with perhaps downward migration of parent magma generation or a slight flattening of the subduction zone such steady conditions could be necessary for the production of large batholithic complexes such as the sierra nevada the abrupt termination of plutonism 80 m y ago may have resulted from an increased rate of convergence of the american and eastern pacific plates and dramatic flattening of the subduction zone u pb ages of the giant forest alaskite sequence in sequoia national park are all in the range 99 3 m y indicating a relatively short period of emplacement and cooling for this nested group of plutons u pb ages of a mafic inclusion and its host granodiorite indicate that both were derived from a common source or that the mafic inclusion was totally equilibrated with the granodioritic magma comparison of isotopic ages determined by different methods such as zircon u pb sphene u pb hornblende k ar and biotite k ar suggests that zircon u pb ages generally approximate the emplacement age of a pluton however some plutons probably contain inherited or entrained old zircons and the zircons of some samples are disturbed by younger thermal and metamorphic events the ages reported here are consistent with u pb age determinations previously made on granitic rocks to the north stern et al 1981 the age distribution of granitic belts determined here is in general agreement with those established by k ar dating evernden and kistler 1970 but does not differentiate the five epochs of plutonism determined in their study

regional variations in bulk chemistry mineralogy and the compositions of mafic and accessory minerals in the batholiths of california we define regional variations in mafic and accessory mineral assemblages and compositions and expand the current understanding of spatial variations in whole rock geochemistry in the batholiths of california in so doing we gain new insights into the nature of magmatic source rocks and mechanisms of magma generation in volcano plutonic arcs of active continental margins little studied metaluminous to strongly peraluminous granites containing fe rich biotite with log x mg x fe f oh and mn in biotite and amphibole increase on a regional scale from western i wc types to eastern i mc and i sc types parallel to eastward increases in incompatible elements and decreases in compatible elements in the plutons in contrast the belts of western i scr granites and eastern i wc quartz diorites and granodiorites disrupt the regional west to east systematics in both mineral and whole rock geochemistry spatial variations in the al content of amphibole are regional in scale and reflect pressures of pluton crystallization we conclude that significant previously unrecognized complexity exists in regional geochemical systematics in the california batholiths

sedimentological characteristics and morphology of the aeolian sand dunes in the eastern part of the uae a case study from ar rub al khali abstract the umm az zimul al wijan area is located in the southeastern part of the uae and covers about 1600 km 2 it is bounded to the east by the oman mountains and to the south and west by the extensive dune area of ar rub al khali field investigation revealed the common occurrence of parallel to sub parallel sand ridges with a general east west orientation also present but less frequent are barchan barchanoid and star dunes interdune areas are classified into four types that include dolomite mixed ancient sabkha and ophiolitic rock fragments mixed sand sheet and ophiolitic rock fragments and recent sabkha the textural characteristics of the sand forming the dunes are unimodal with a modal class in fine sand size moderately to very well sorted positively skewed and mesokurtic quartz grains are mainly subrounded to subangular the similarity in roundness properties in different dune types in the eastern province of the uae seems not to be influenced by dune form based on the heavy mineral suites and the angularity of quartz grains it is believed that the sand sediments are mostly derived from the ultrabasic rocks forming the ophiolitic sequence of the oman mountains acidic rocks of iran and from the coastal area

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

geochemical and petrographic investigation of triassic and late miocene organic rich intervals from onshore cyprus eastern mediterranean abstract in order to improve the understanding of potential petroleum systems in the still underexplored eastern mediterranean sea two field campaigns were performed to investigate potential source rocks onshore cyprus elemental data total organic toc and inorganic carbon tic total sulfur ts fe ni v rock eval pyrolysis biomarker and microscopic analysis organic petrography random vitrinite reflectance vrr palynofacies of the obtained mesozoic to cenozoic samples have proven the existence of organic matter om rich deposits within the following two geological formations 1 the triassic vlambouros formation fm of the mamonia complex comprises frequently occurring few centimeter thin clay layers interbedded between meter thick sandstone units the clay layers of this formation are characterized by toc contents of about 1 wt representing a type iii kerogen showing hydrogen index hi values of 48 mg hc g toc on average vrr values of 0 5 to 0 6 as well as several biomarker ratios indicate low thermal maturity the formation was deposited at the northern margin of gondwana and similar strata may be present in the basement of the levant basin and the eratosthenes seamount there thermal maturity would be higher and such rocks might contribute to thermogenic gas systems 2 in the miocene pakhna fm om bearing intervals are mainly present in the upper part of the formation in outcrops east of the troodos mountain while organic rich intervals are very scarce to absent in the south and southwest of the island the eastern outcrops show abundant fine grained marly mud to wackestones interbedded with coarser grained carbonates the fine grained intervals have toc contents of about 4 wt representing mainly type ii iii kerogen with hi values of 238 mg hc g toc on average the om is immature as indicated by vrr values between 0 3 and 0 5 ts toc 2 8 and several biomarker ratios indicate oxygen depleted even anoxic conditions during deposition a negative correlation between the toc and tic indicates that such conditions were reached during enhanced primary bioproductivity controlled by local and regional clastic derived nutrient input similar conditions may have been present along the southeastern margin of the eratosthenes seamount south of cyprus presence of abundant organic matter and high sedimentation rates during the miocene were favorable for microbial gas generation in the deeper parts of the basins

muscovite garnet granites in the mojave desert relation to crustal structure of the cretaceous arc a previously undocumented belt of upper cretaceous primary muscoviteand garnet bearing granites is exposed within the mesozoic batholith of the central and western mojave desert of california this granite belt occurs more than 140 km west of the better known cordilleran interior belt of primary muscovite bearing granitoids and the central and western mojave granites are derived from much different sources possibly pelona orocopia rand schists or similar rocks anatexis of pelona orocopia rand schists to produce these granites would require emplacement of the schists prior to the late cretaceous early tertiary the most widely accepted time of schist emplacement the granite belt may also correlate with similar rocks in the southernmost sierra nevada and eastern salinia the distinctive isotopic and petrologic character of the granite belt reflects differences in crustal structure between the mojave southern sierra nevada and the central sierra nevada portions of the cretaceous continental margin batholith possible correlation of this belt with rocks in eastern salinia also places further limits on the pre early tertiary position of salinia

evidence from the lamarck granodiorite for rapid late cretaceous crust formation in california strontium and neodymium isotopic data for rocks from the voluminous 90 million year old lamarck intrusive suite in the sierra nevada batholith california show little variation across a compositional range from gabbro to granite data for three different gabbro intrusions within the suite are identical within analytical error and are consistent with derivation from an enriched mantle source recognition of local involvement of enriched mantle during generation of the sierran batholith modifies estimates of crustal growth rates in the united states these data indicate that parts of the sierra nevada batholith may consist almost entirely of juvenile crust added during cretaceous magmatism

deformation at plate boundaries around the gulf of oman abstract seismic studies during charles darwin cruise 18 86 focused on three zones of deformation the makran accretionary prism the murray ridge owen fracture zone system and the continental margin of east oman a multichannel seismic reflection profile across the makran margin clearly imaged the imbricate thrust slices and their bounding faults a bottom simulating reflector bsr 500 800 m beneath the seabed marking the base of a gas hydrate stability zone may be traced across most of the profile the heat flow variation estimated from changes in the depth of this reflector shows evidence for localised fluid expulsion reflection profiles across the murray ridge show evidence for active extension along a series of major normal faults the rift structure is segmented with the fault polarity changing between segments a combined reflection and wide angle study of the east oman margin shows a deep offshore basin underlain by crust only 5 km thick and bounded by a basement ridge interpreted as a tilted fault block the wide angle data suggest a sleeply dipping moho beneath the margin the large lateral changes in crustal thickness may be explained by episodes of margin parallel shear

the late messinian lago mare event and the zanclean reflooding in the mediterranean sea new insights from the cuevas del almanzora section vera basin south eastern spain abstract the return to normal marine conditions in the mediterranean sea after the end of the messinian salinity crisis msc that led to the deposition of thick evaporitic succession followed by settlement of brackish to freshwater conditions of the lago mare is still subject to extensive debate between two opposite scenarios one scenario implies an abrupt reflooding through the gibraltar gateway of the mediterranean sea previously disconnected from the world ocean and partly desiccated the second scenario postulates that the mediterranean sea kept a high water level throughout the messinian salinity crisis and was connected continuously to the atlantic ocean and to the paratethys the stratigraphic record of the classical cuevas del almanzora section vera basin is of a crucial importance as the vera basin is located on the eastern margin of the alboran sea close to the gibraltar gateway where atlantic waters reflooded the mediterranean sea after the msc the present new study completes previous investigations pierre et al 2006 and is mostly focused on detailed sedimentological observations analysis of ostracod and foraminifer assemblages and on stable isotopes study of three species of planktonic foraminifers globigerina bulloides globigerinoides obliquus s l and sphaeroidinellopsis spp from the lower pliocene deposits biostratigraphical correlations with the reference deep sea section from odp site 975 balearic basin and the onshore succession of eraclea minoa sicily provide an accurate chronostratigraphy and paleoclimatic reconstruction during the zanclean during the late messinian the vera basin was characterized by very unstable lacustrine to brackish environments with significant water depth variations and the deposits display evidences of subaerial exposure the ostracod content is dominated by loxocorniculina djafarovi and cyprideis gr agrigentina associated to reworked planktonic foraminifera from older sediments the messinian zanclean contact is well marked by a clear erosional surface that grades laterally into a megabreccia with reworked gypsum blocks and to the large incision of the palomares canyon in the offshore domain the marine reflooding occurred abruptly with a sea level rise by more than 250 m an important value for a marginal basin in this western part of the mediterranean sea the marine invasion began with the onset of the lowermost biozone mpl 1 at the base of the zanclean the fluctuations of the planktonic foraminifer assemblages and of their stable isotopes allowed to identify five lithological cycles forced by milankovitch precession periodicity as well as paleoclimatic variations through the lower part of the zanclean thus these new data allow us to reaffirm that the messinian zanclean boundary corresponds to a major change characterized by an instantaneous restoration of marine conditions at the onset of the pliocene related to the abrupt re flooding of the mediterranean sea from the atlantic ocean

the messinian salinity crisis past and future of a great challenge for marine sciences forty years after the image of the mediterranean transformed into a giant salty lake was first conceived the fascinating history of the messinian salinity crisis msc still arouses great interest across a large and diverse scientific community early outcrop studies which identified severe palaeoenvironmental changes affecting the circum mediterranean at the end of the miocene were followed by investigations of the marine geology during the 1950s to 1970s these were fundamental to understanding the true scale and importance of the messinian event now after a long period of debate over several entrenched but largely untested hypotheses a unifying stratigraphic framework of msc events has been constructed this scenario is derived mainly from onshore data and observations but incorporates different perspectives for the offshore and provides hypotheses that can be tested by drilling the deep mediterranean basins the msc was an ecological crisis induced by a powerful combination of geodynamic and climatic drivers which had a great impact on the subsequent geological history of the mediterranean area and on the salinity of the global oceans these changed the mediterranean s connections with both the atlantic ocean and the freshwater paratethyan basins causing high amplitude fluctuations in the hydrology of the mediterranean the msc developed in three main stages each of them characterized by different palaeoenvironmental conditions during the first stage evaporites precipitated in shallow sub basins the msc peaked in the second stage when evaporite precipitation shifted to the deepest depocentres and the third stage was characterized by large scale environmental fluctuations in a mediterranean transformed into a brackish water lake the very high resolution timescale available for some late miocene intervals in the mediterranean makes it possible to consider environmental variability on extremely short time scales including in some places annual changes despite this fundamental questions remain some of which could be answered through new cores from the deepest mediterranean basins improvements in seismic imaging and drilling techniques over the last few decades make it possible to plan to core the entire basinal messinian succession for the first time the resulting data would allow us to decipher the causes of this extreme environmental change and its global scale consequences

deep basin evidence resolves a 50 year old debate and demonstrates synchronous onset of messinian evaporite deposition in a non desiccated mediterranean the messinian salinity crisis msc is perceived as an environmental crisis governed by climatic and tectonic controls affecting global oceans salinity and shaping the mediterranean sea s biochemical composition recently drilled offshore wells in the levant basin retrieved a sedimentary record of the deep basin mediterranean msc salt deposits and the underlying pre evaporite unit in this study we have concentrated on the pre evaporite interval and its transition into the overlying evaporites analysis of this data set changes the way these deposits have been perceived since the 1970s when they were first penetrated in their uppermost part during deep sea drilling project expeditions using sedimentology seismic interpretation biostratigraphy and astronomical tuning we show that messinian salt deposition in the eastern mediterranean began during stage 1 of the msc in contrast to the present paradigm salt was deposited synchronously with gypsum in the marginal and intermediate depth basins significantly before the 50 k y interval coined as the msc acme event 400 k y after the crisis began thus salt precipitation took place in a non desiccated deep basin having a restricted but often open connection with the atlantic ocean substantially altering our understanding of the mechanisms governing the deposition of salt giants a coeval onset of basinal halite and marginal gypsum precipitation calls for a revaluation of global scale climatic and oceanographic models of the msc taking into account a much older age for the beginning of halite deposition

the palaeoenvironmental significance of dune size hierarchies the size of a dune is a function of many factors one of which is the length of the period of consistent wind regime under which it grew ephemeral dunes are defined as those that are adjusted to diurnal wind regimes meso dunes to annual wind regimes and mega dunes to wind regimes that persist for longer periods these longer periods could be major climatic cycles but there seem to be no dunes whose size reaches that allowed by the length of some of these periods there may therefore be a maximum size beyond which mega dunes cannot grow dictated by sand supply aerodynamic processes such as speed up or by the scale of the atmospheric boundary layer these concepts are tested on dunes in the wahiba sands in oman analysed from a landsat image it is hypothesised that a large set of megadunes here formed in the lgm that a smaller set of mega dunes may be of younger dryas age and that there is a meso dune series of holocene age

chronology causes and progression of the messinian salinity crisis the messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years 1 3 earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated mediterranean basin that had been repeatedly isolated from the atlantic ocean1 2 but elucidation of the causes of the isolation whether driven largely by glacio eustatic or tectonic processes have been hampered by the absence of an accurate time frame here we present an astronomically calibrated chronology for the mediterranean messinian age based on an integrated high resolution stratigraphy and tuning of sedimentary cycle patterns to variations in the earth s orbital parameters we show that the onset of the messinian salinity crisis is synchronous over the entire mediterranean basin dated at 5 96 0 02 million years ago isolation from the atlantic ocean was established between 5 59 and 5 33 million years ago causing a large fall in mediterranean water level followed by erosion 5 59 5 50 million years ago and deposition 5 50 5 33 million years ago of non marine sediments in a large lago mare lake sea basin cyclic evaporite deposition is almost entirely related to circum mediterranean climate changes driven by changes in the earth s precession and not to obliquity induced glacio eustatic sea level changes we argue in favour of a dominantly tectonic origin for the messinian salinity crisis although its exact timing may well have been controlled by the 400 kyr component of the earth s eccentricity cycle

empirical calibration of oxygen isotope fractionation in zircon new empirical calibrations for the fractionation of oxygen isotopes among zircon almandine rich garnet titanite and quartz are combined with experimental values for quartz grossular the resulting a coefficients k2 are zrc alm grs ttn qtz 2 64 2 71 3 03 3 66 zrc 0 07 0 39 1 02 alm 0 32 0 95 grs 0 63 full size table table options view in workspace download as csv for the relation 1000 ln y x ay x 106 t2 the fractionation of oxygen isotopes between zircon and coexisting minerals can provide otherwise unavailable evidence of magmatic processes including crystallization remelting and assimilation fractional crystallization

peraluminous granites frequently with mantle like isotope compositions the continental type murzinka and dzhabyk batholiths of the eastern urals murzinka and dzhabyk are continental type batholiths of the middle and southern east uralian domain they comprise mainly undeformed peraluminous k rich granites whose elemental composition is similar to some late variscan granites of western europe but with much more primitive sr and nd isotope ratios murzinka 254 5 ma is composed of silica rich granites forming two different rock series with a 87sr 86srinit of 0 709 and 0 704 respectively both series have enormous variations in end255 11 9 to 0 1 and 8 9 to 4 1 that reveal derivation from heterogeneous sources dzhabyk 291 4 ma also comprises two coeval magmas which yielded voluminous granites and quartz monzonites respectively with smaller differences in 87sr 86srinit and end290 0 7043 0 8 to 1 6 and 0 7049 0 0 to 0 8 despite their isotope compositions both batholiths lack evidence of genetic involvement of a mantle derived parental magma moreover we suggest that dzhabyk granitoids were generated by polybaric partial melting of paleozoic island arc material whereas murzinka granitoids derived from an extremely heterogeneous source consisting mainly of paleozoic and proterozoic metagreywackes this implies a relative fast reworking of juvenile arc crust and burial of the protoliths during the orogenic evolution of the urals since there is neither evidence of significant extension nor a direct link with subduction we suggest that the main cause for late orogenic anatexis was elevated heat production and fertility in the protolith perhaps combined with some additional heat from unexposed mafic intrusions

2 7 ga plume associated vhms mineralization in the eastern goldfields superterrane yilgarn craton insights from the low temperature and shallow water ag zn au nimbus deposit economic volcanic hosted massive sulfide vhms deposits of the archaean yilgarn craton of western australia are restricted to zones of juvenile crust as revealed through regional nd pb and hf isotopic variations and the geochemistry of felsic volcanic rocks interpreted as archaean paleo rift zones one of these runs n s through the eastern goldfields superterrane broadly coincident with the kurnalpi terrane and is associated with the high grade ca 2690 ma teutonic bore jaguar and bentley deposits plus sub economic vhms mineralization further south to date only small historic cu occurrences e g anaconda and barren pyritic lenses have been recognized in the older 2 7 ga plume dominated lower stratigraphy of the eastern goldfields superterrane the nimbus ag zn au deposit 12 1 mt at 52 g t ag 0 9 zn and 0 2 g t au is located approximately 10 km east of kalgoorlie near the margin of the kurnalpi terrane its origin has been contentious for a number of years with previous models favouring seafloor sub seafloor vhms mineralization or a high sulfidation fault hosted system we present a detailed account of the deposit its host stratigraphy and associated hydrothermal alteration plus two new shrimp u pb zircon ages pb isotope galena and o isotope zircon constraints compared to other vhms occurrences in the yilgarn craton the nimbus deposit is unusual in terms of its tectono stratigraphic position the geochemistry of its host sequence i e fi affinity felsic volcanic rocks ocean plateau like low th basalts mineralogy e g abundance of ag sb pb as bearing sulfosalts high hg low cu and quartz carbonate sericite dominated alteration assemblages classification of nimbus as a shallow water and low temperature vhms deposit with epithermal characteristics i e a hybrid bimodal felsic deposit is consistent with its position near the margin of the kurnalpi paleo rift zone and radiogenic 238u 204pb values the recognition that the nimbus deposit is associated with c 2705 ma plume magmatism opens new areas for vhms exploration in the eastern goldfields superterrane over a strike length exceeding 500 km

messinian salinity crisis regulated by competing tectonics and erosion at the gibraltar arc the persistent shallow connection between the atlantic ocean and the mediterranean sea that caused the messinian salinity crisis may have been sustained by a balance between tectonic uplift and erosion due to inflow about six million years ago a series of geological factors drastically reduced the exchange of water between the atlantic ocean to the mediterranean sea through what is now the strait of gibraltar the resulting widespread salt precipitation in the mediterranean linked to a decrease in sea level of about 1 5 kilometres due to evaporation is known as the messinian salinity crisis the exact mechanism that caused the crisis remains uncertain here daniel garcia castellanos and antonio villasenor propose a competition between the obstruction of the gibraltar arc seaway by tectonic uplift and its erosional deepening by water inflow controlled by the resulting changes in sea level difference across the gibraltar arc as a possible mechanism for the crisis the messinian salinity crisis1 2 5 96 to 5 33 million years ago was caused by reduced water inflow from the atlantic ocean to the mediterranean sea resulting in widespread salt precipitation and a decrease in mediterranean sea level of about 1 5 kilometres due to evaporation3 the reduced connectivity between the atlantic and the mediterranean at the time of the salinity crisis is thought to have resulted from tectonic uplift of the gibraltar arc seaway and global sea level changes both of which control the inflow of water required to compensate for the hydrological deficit of the mediterranean1 4 however the different timescales on which tectonic uplift and changes in sea level occur are difficult to reconcile with the long duration of the shallow connection between the mediterranean and the atlantic5 needed to explain the large amount of salt precipitated here we use numerical modelling to show that seaway erosion caused by the atlantic inflow could sustain such a shallow connection between the atlantic and the mediterranean by counteracting tectonic uplift the erosion and uplift rates required are consistent with previous mountain erosion studies with the present altitude of marine sediments in the gibraltar arc6 7 and with geodynamic models suggesting a lithospheric slab tear underneath the region8 9 10 the moderate mediterranean sea level drawdown during the early stages of the messinian salinity crisis3 5 can be explained by an uplift of a few millimetres per year counteracted by similar rates of erosion due to atlantic inflow our findings suggest that the competition between uplift and erosion can result in harmonic coupling between erosion and the mediterranean sea level providing an alternative mechanism for the cyclicity observed in early salt precipitation deposits and calling into question previous ideas regarding the timing of the events that occurred during the messinian salinity crisis1

the deep structure of the east oman continental margin preliminary results and interpretation abstract we describe preliminary results of a coincident normal incidence and wide angle seismic experiment across the east oman continental margin just north of the masirah island ophiolite this margin is affected by tectonic deformation and may be the site of margin parallel shear in a zone parallel to the owen fracture zone the reflection profile is used to define upper crustal structure and shows a deep offshore basin dammed oceanwards by a ridge interpreted here as a rotated fault block wide angle data were collected using ten digital ocean bottom seismometers and 110 explosive shots preliminary raytracing of a crustal model based on the gravity model of whitmarsh 1979 shows rapid changes in crustal thickness across the margin a steep landward dipping reflector probably the moho lies beneath the continental slope the orientation of this reflector is exactly opposite to the direction of tectonic fabric predicted by a simple overthrust model of ophiolite emplacement from the ocean basin to the east

the rapid heating defocused beam technique a co2 laser based method for highly precise and accurate determination of δ18o values of quartz abstract we describe a laser fluorination technique specifically for quartz that allows both high accuracy and high precision determination of oxygen isotope ratios regardless of grain size the rapid heating defocused beam technique rhd utilizes a defocused 32 w co 2 laser at full power which delivers 17 w 20 w mm 2 to the sample to quickly react quartz in contrast other recent laser fluorination studies use a tightly focused laser beam and slow heating i e sharp and kirschner 1995 fouillac and girard 1996 kirschner and sharp 1997 and find laser analysis of fine grained quartz to be inaccurate three quartz standards nbs 28 qz bra and qz cwru were analyzed using the rhd technique at the university of wisconsin to test for grain size effects rhd analyses show no correlation between grain size and 18 o values and are in excellent agreement with 18 o values obtained using conventional fluorination techniques additional analyses of the same quartz standards performed at university of wisconsin using slow heating and a focused beam yield 18 o values that are both less precise and significantly up to 0 8 lower than the accepted values attempts to use the rhd technique with a 20 w co 2 laser which delivers 8 w 10 w mm 2 to the sample at brgm were unsuccessful probably due to insufficient power density of the defocused beam we conclude that the rhd technique yields excellent accuracy and precision but that power densities of 15 20 w mm 2 may be necessary across a large part of the sample surface we recommend the use of lasers with at least 30 w of power

the role of manganese in the paragenesis of magmatic garnet an example from the old woman piute range california a reply strongly peraluminous plutons of the old woman piute range southeastern california display the differentiation sequence muscovite biotite granite rightarrow muscovite garnet biotite granite rightarrow garnet muscovite granite rightarrow garnet muscovite aplite and pegmatite the garnets show no evidence of reaction but biotites in garnet bearing rocks are rimmed by muscovite metamorphic assemblages in the country rocks suggest pressures of emplacement less than 4 5 kb the plutons become relatively enriched in manganese with differentiation whole rock ratios of molar mn fe mg increase from 0 01 in least felsic garnet free rocks to 0 3 in most felsic garnet rich rocks mno concentrations show a corresponding rise in biotites 0 4 to 1 8 wt and less clearly in garnets 9 to 25 the differentiation sequence textural relations and mineral and whole rock compositions suggest that garnet paragenesis was controlled by the reaction biotite mn rich liquid rightarrow garnet

petrogenesis of sierra nevada plutons inferred from the sr nd and o isotopic signatures of mafic igneous complexes in yosemite valley california mafic complexes in the central sierra nevada batholith record valuable geochemical information regarding the role mafic magmas play in arc magmatism and the generation of continental crust in the intrusive suite of yosemite valley major and trace element compositions of the hornblende bearing gabbroic rocks from the rockslides mafic complex and of the mafic dikes in the north america wall are compositionally similar to high alumina basalt of these rocks two samples have higher ni and cr abundances as well as higher end values than previously recognized for the intrusive suite plagioclase crystals in rocks from the north america wall and the rockslides have prominent calcic cores and sharply defined sodic rims a texture commonly associated with mixing of mafic and felsic magmas in situ analyses of 87sr 86sr in plagioclase show no significant isotopic difference from the cores to the rims of these grains we propose that the high 87sr 86sr 0 7067 and low end 3 4 of bulk rocks the homogeneity of 87sr 86sr in plagioclase and the high 18o values of bulk rocks 6 6 7 3 and zircon lackey et al in j petrol 49 1397 1426 2008 demonstrate that continental crust was assimilated into the sublithospheric mantle derived basaltic precursors of the mafic rocks in yosemite valley contamination 20 40 likely occurred in the lower crust as the magma differentiated to high alumina basalt prior to plagioclase and zircon crystallization as a consequence the isotopic signatures recorded by whole rocks plagioclase and zircon do not represent the composition of the underlying lithospheric mantle we conclude that the mafic and associated felsic members of the intrusive suite of yosemite valley represent 60 80 new additions to the crust and include significant quantities of recycled ancient crust

petrography and mineral content of sea floor sediments of the tigris euphrates delta north west arabian gulf iraq abstract sea floor sediments of the iraqi territory of the arabian gulf have been studied in detail petrographically and mineralogically the carbonate fraction of these sediments comprises various allochems in order of abundance skeletal remains ooids peloids and composite grains on the other hand the insoluble residues of the sediments studied consist of quartz feldspars and mica the matrix is carbonate micrite containing various percentages of clays mineralogically the carbonate fraction consists of calcite mg calcite aragonite and dolomite mg calcite forming the radial cortex of the ooids is the most unexpected and significant of such components in addition the mg calcite micritic cement is the most commonly observed diagenetic product resulting in the formation of hardgrounds in some areas the clay minerals of the the fluvial loads of the shatt al arab i e tigris and euphrates rivers and karun rivers sand and dust from north westerly storm winds shamal are the main potential sources for the detrital sediments accumulating in the area of study the indigenous marine organisms and some inorganic precipitation as mg calcite are additional sources of the sediments and increase in percentage toward the open waters

evaluating the origin of garnet cordierite and biotite in granitic rocks a case study from the south mountain batholith nova scotia evaluating the origin of garnet cordierite and biotite in granites provides important insight into closed and open system magma evolution we present field textural major and trace element mineral chemical and sr nd whole rock isotopic data on garnet cordierite and biotite rich zones from the peraluminous south mountain batholith we infer that 1 garnet rich zones of decimeter to meter size with 30 vol large subhedral garnet with abundant inclusions of detrital country rock monazite represent partially assimilated metapelitic country rocks where garnet is the incongruent product of biotite dehydration melting 2 cordieriterich zones tens of meters to kilometers in dimension with 5v ol large subhedral to euhedral zoned cordierite formed by crystallization from relatively evolved magmas and subsequent crystal accumulation 3 biotite rich zones with large subhedral to euhedral biotite with abundant euhedral apatite inclusions making up 80 vol centimeter scale or 25 vol kilometer scale of the rocks formed dominantly by fractional crystallization throughout the chemical evolution of the batholith our results suggest that for garnet and cordierite a combination of textural and mineral chemical characterization is probably sufficient to determine their origin in granites however for biotite and other readily equilibrated minerals evaluating both mineral and rock textures and majorelement trace element and isotopic compositions is essential

the source magmatic contamination and alteration of the idaho batholith zircons from cretaceous and tertiary granitic rocks of the idaho batholith preserve the best record of magmatic oxygen isotope ratios the coupling of oxygen isotope data from refractory minerals such as zircon and garnet with that from less refractory minerals such as quartz reveals the complex evolution and alteration history of the idaho batholith values of 18o zircon throughout the batholith are relatively homogeneous at 6 9 0 9 1 sd n 21 rocks despite variations in age and chemistry samples from the bitterroot lobe have an average 18o zircon of 7 1 0 3 n 7 rocks and samples from the atlanta lobe have an average 18o zircon of 7 0 1 0 n 9 rocks four epizonal tertiary plutons have an average 18o zircon of 7 2 0 2 n 4 rocks these data indicate a similar magmatic source for all granitic rocks of the idaho batholith except the tertiary epizonal casto pluton which has a 18o zircon of 4 0 0 1 n 1 rock the zircon data show that the range of normal magmatic 18o is considerably more restricted than was previously inferred despite some samples containing two micas and or garnet or having a mildly peraluminous character quartz is more variable than zircon in 18o average 18o quartz for the entire batholith is 10 4 1 1 1 sd n 65 rocks with a range of 7 7 to 12 4 excluding the casto pluton the spread of quartz values is 2 7 larger and typically higher than that calculated relative to zircon quartz data from the bitterroot lobe and epizonal tertiary plutons suggest the alteration of primary 18o during metamorphic events quartz data from the atlanta lobe suggest closed system diffusional exchange during cooling igneous garnet 18o values are higher than and out of equilibrium with those of coexisting zircon by 0 1 0 9 assuming an average 18o for unaltered wall rock metasediments the incorporation of 10 metasediment into a magma after crystallization of zircon raises the 18o magma by 0 9 the largest measured garnet zircon these quartz and garnet 18o from the atlanta and bitterroot lobes suggest magmatic contamination with a high 18o rock after the crystallization of zircon and before that of garnet and quartz

chronology with a pinch of salt integrated stratigraphy of messinian evaporites in the deep eastern mediterranean reveals long lasting halite deposition during atlantic connectivity abstract the messinian salinity crisis msc 5 97 5 33 ma is considered an extreme environmental event driven by changes in climate and tectonics which affected global ocean salinity and shaped the biogeochemical composition of the mediterranean sea yet after more than 50 years of research msc stratigraphy remains controversial recent studies agree that the transition from the underlying pre evaporite sediments to thick halite deposits is conformal in the deep eastern mediterranean basin however the age of the base and the duration of halite deposition are still unclear also disputed is the nature of the intermediate and upper msc units which are characterized as periods of increased clastic deposition into the eastern mediterranean based on marginal outcrops and seismic data we provide a multidisciplinary study of sedimentary geochemical and geophysical data from industrial offshore wells in the levant basin which recovered a sedimentary record of deep basin mediterranean evaporites deposited during the msc in combination with previous observations of the msc throughout the mediterranean basin our results promote the need for a new chronological model remarkably the one kilometer thick lower part of the evaporitic unit is composed of essentially pure halite except for a thin transitional anhydrite layer at its base the halite is undisturbed and homogeneous lacking diverse features apparent in more proximal sections indicating a deep sea depositional environment we find that distinct meters thick non evaporitic intervals interbedded with the halite previously thought to be clastic layers are diatomites while xrd analysis confirms an increase in clastic components in these sediments they are composed primarily of well preserved marine and freshwater planktonic diatoms the occurrence of marine planktonic diatoms in these intervals indicates the input of atlantic waters into the mediterranean basin during the deposition of the massive halite unit seismic stratigraphy and well log cyclostratigraphy further support deep basin halite deposition which started about 300 kyr earlier than widely assumed 5 97 ma we propose that halite deposition in the deep mediterranean took place during stage 1 of the msc rather than being limited to the short 50 kyr msc acme when sea level was presumably at its lowest thus brine formation salt precipitation and faunal extinction occurred at least in part in a deep non desiccated basin with a restricted yet open mediterranean atlantic connection that allowed inflow of oceanic water we observe an increase in heavy minerals and reworked fauna within the clastic evaporitic interbedded evaporites of the basinal msc section and argue that these settings correspond in the deep basins with a significant sea level drawdown during stage 2 of the msc as observed in the marginal sections this correlation is corroborated by astrochronology and chemostratigraphic markers such as the distribution of n alkanes and biomarker based thermal maturity indices the levant deposits indicate that high sea level and partial connectivity with global oceans promoted the deposition of deep basin deep water halite while sea level drawdown promoted deposition of reworked and transported material from the margins into deep mediterranean basins this study modifies the current understanding of the mechanisms governing salt deposition throughout the msc with implications for other evaporitic events in the geologic record

late cretaceous early tertiary convergence between the indian and arabian plates recorded in ophiolites and related sediments abstract remnants of ocean floor forming the eastern ophiolite belt in oman and the western ophiolite belt in pakistan have a common plate tectonic history culminating in emplacement at the cretaceous tertiary boundary fragments of ocean floor in these two belts have ages between 150 and 65 ma and recorded tectonic events in the early indian ocean at 150 ma 130 120 ma 110 100 ma and 70 65 ma new radiometric and chronostratigraphic ages and paleomagnetic and sedimentary information are used to relocate these ophiolites in the frame of the evolving indian ocean which was characterised by the stepwise breakup of gondwana at 158 ma east and west gondwana 130 ma southern atlantic breakup of east gondwana 95 84 ma madagascar and india seychelles 65 ma india and seychelles and finally at 40 ma rifting between africa and arabia the 150 ma old oceanic rocks of masirah island in oman originally formed the extension of the basins now preserved along the eastern edge of the afro arabian plate masirah drifted together with india seychelles when a new ridge formed at approximately 130 ma separating microplates e g kabul block from the northern edge of greater india parts of this new ocean were later emplaced to form the western ophiolite belt in pakistan consumption of oceanic crust and emplacement of ophiolites during the closure of the neotethys occurred not only north of india seychelles but also along two or three subduction zones between the afro arabian plate and india seychelles documented by the formation of metamorphic soles beneath ophiolites relics of ocean floor formed approximately 65 70 ma ago now form the upper units in the western ophiolite belt of pakistan where they overlie an accretionary prism of pillow lavas of dominantly aptian albian age and sedimentary rocks the breakup of india and the seychelles at 65 ma was associated with the eruption of flood basalts deccan and seychelles and enhanced counter clockwise movement of india this breakup possibly caused the late jurassic early cretaceous fragments of ocean floor e g masirah to be thrust onto the eastern edge of oman the ophiolites which were emplaced onto the western edge of india drifted as part of this plate farther north where collision with eurasia and the accreted microplates occurred in the eocene 55 ma

cyclostratigraphy and astrochronology of the tripoli diatomite formation pre evaporite messinian sicily italy the ongoing debate about the messinian salinity crisis in the mediterranean is fuelled in part by the lach of an adequate time control the most accurate and at the same time detailed constrains are nowadays provided by the astronomical dating technique here we present an astronomical age model for the cyclically bedded tripoli diatomite formation on scily pre evaporite messinian italy based on an intergrated stratigraphic study of three key sections falconara gibliscemi and capodarso characteristic sedimentary cycle pattenrs allow i the sections to be cyclostratigraphically correlated the bed to bed correlations being confirmed by high resolution planktonic foraminiferal biostratigraphy and ii the tripoli cycles to thecalibrated to the astronomical record despite minor misfits the correctness of thetuning is evident from the match between precession obliquity interference in the astronomical target and its reflection in the sedimentary cycle record the tuning provides absolute astronomically dated at 7 005 ma indicating that the onset of diatomite formation is diachronous in the mediterranean since itstarted 300 000 years earlier on sicilt than on gavdos south of crete the top of the tripoli and thus the onset of the salinity crisis proper on sicily arrives at 5 98 ma

synchronous onset of the messinian evaporite precipitation first mediterranean offshore evidence the messinian salinity crisis msc was a major ecological crisis affecting shallow and deep water settings over the entire mediterranean basin however the evolution of the msc and its ecological impacts have mainly been explained on the basis of sediments from onshore outcrops lack of complete and physically connected records from onshore and offshore settings has inhibited comprehensive understanding of basin behaviour during the msc herein we present a continuous record from an intermediate depth basin on the balearic promontory that comprises late tortonian messinian marls and evaporitic beds from the first msc phase i e primary lower gypsum plg stage well log and biostratigraphic data allow us establishing a large scale calibration to the astronomical solutions and to correlate pre msc sediments with classical rhythmic successions outcropping onshore thickness and characteristic sedimentary patterns observed in the offshore evaporitic records resemble those from marginal plg sequences furthermore seismic reflectors from a bedded unit bu which corresponds to an evaporitic interval according to well to seismic ties are correlated with the onshore plg sequences this correlation constitutes the first attempt to link well known marginal sequences with intermediate depth offshore settings which have previously only been studied through seismic imaging our time calibration provides direct evidence supporting a synchronous onset of the plg phase between onshore and offshore settings along the southwestern balearic promontory margin those bu reflectors which were positively correlated to the plg were likely precipitated offshore the continental shelf at messinian times these results suggest that gypsum precipitation and or preservation was not always limited to 200 m water depths and could occur in non silled basins finally we only found a major erosion at the top of the plg sequences implying that the msc drawdown occurred after the precipitation of the onshore lower evaporites studied sequences provide new insights into the plg precipitation preservation settings as well as into the land sea correlations of msc units and thus could potentially help refine current msc models

magmatic arc asymmetry and distribution of anomalous plutonic belts in the batholiths of california effects of assimilation crustal thickness and depth of crystallization in order to better understand geologic fac tors controlling pronounced regional variations in whole rock chemistry mineralogy and mineral chemistry in the batholiths of california we calculate the magmatic intensive variables f hf f h 2 o f hf f hcl and f o 2 regional scale west to east increases in f oh in mafic silicates corresponding to the systematic i wc to i mc and i sc progression reflect orders of magnitude increase in f hf f h 2 o attending pluton crystallization low f hf f h 2 o of formation of western i wc types is consistent with their derivation from low fluorine source rocks in subducted oceanic slabs or the upper mantle in contrast higher f hf f h 2 o of crystallization of i mc and i sc types to the east implies the involvement of 1 progressively greater amounts of continental crustal source material such as biotite bearing metamorphic rocks their unweathered sedimentary derivatives retaining f rich mafic minerals or their fusion products and or 2 source materials which become more f rich toward the continental interior the regional distribution of i mc and i sc types suggests that the precambrian craton of western north america or derivative sediments may extend farther north in california and be morphologically more complex than previously thought from seemingly out of place occurrences of i wc plutons on the eastern slopes of the sierra nevada batholith we infer the existence of regions where precambrian basement was thin or absent in mesozoic time which prevented extensive cratonal contamination of subducted slab or upper mantle derived magmas new methods for estimating t f o 2 relations in the magmas demonstrate that i scr granites crystallize at oxygen fugacities as much as five orders of magnitude lower than those of i wc i mc and i sc types under conditions at or below the maximum stability limit of graphite in equilibrium with a c o h s gas phase the local scale formation of i scr granites in plutonic belts within specific wall rock terranes containing highly reducing sediments or metasediments may occur by contamination of i types with graphitic pelite or in some cases by the direct fusion of this reducing pelitic wall rock the spatial distribution of i scr granite provinces therefore is controlled simply by wall rock lithology amphibole geobarometry demonstrates a general west to east decrease in crystallization pressure across the sierra nevada batholith in contrast the peninsular ranges batholith displays a west to east crystallization pressure increase the bulk of the california batholiths crystallized at pressures less than 4 5 kb and depths less than about 15 19 km in the southern sierra nevada batholith the san gabriels and the eastern peninsular ranges however plutons crystallized at pressures exceeding 6 kb at deep crustal levels 23 km reconstruction of the pre erosion top of the batholith shows that in an east west cross section the central sierra nevada batholith was a horizontal tabular body with an aspect ratio of at least five to one

stable isotope systematics in mesozoic granites of central and northern california and southwestern oregon 18o d and h2o contents were measured for whole rock specimens of granitoid rocks from 131 localitics in california and southwestern oregon with 41 new determinations in the klamath mountains and sierra nevada initial strontium isotope ratios are known for 104 of these samples large variations in 18o 5 5 to 12 4 d 130 to 31 water contents 0 14 to 2 23 weight percent and initial strontium isotope ratios 0 7028 to 0 7095 suggest a variety of source materials and identify rocks modified by secondary processes regular patterns of variation in each isotopic ratio exist over large geographical regions but correlations between the ratios are generally absent except in restricted areas for example the regular decrease in d values from west to east in the sierra nevada batholith is not correlative with a quite complex pattern of 18o values implying that different processes were responsible for the isotopic variations in these two elements in marked contrast to a good correlation between 87sr 86sr o and 18o observed in the peninsular ranges batholith to the south such correlations are lacking except in a few areas d values on the other hand correlate well with rock types chemistry and 87sr 86sr o except in the coast ranges where few of the isotopic signatures are primary the uniformly low d values of samples from the mojave desert indicate that meteoric water contributed much of the hydrogen to the rocks in that area even so the 18o values and 18o fractionations between quartz and feldspar are normal in these same rocks

the origin of high δ18o zircons marbles megacrysts and metamorphism the oxygen isotope ratios 18o of most igneous zircons range from 5 to 8 with 99 of published values from 1345 rocks below 10 metamorphic zircons from quartzite metapelite metabasite and eclogite record 18o values from 5 to 17 with 99 below 15 however zircons with anomalously high 18o up to 23 have been reported in detrital suites source rocks for these unusual zircons have not been identified we report data for zircons from sri lanka and myanmar that constrain a metamorphic petrogenesis for anomalously high 18o in zircon a suite of 28 large detrital zircon megacrysts from mogok myanmar analyzed by laser fluorination yields 18o from 9 4 to 25 5 the u pb standard cz3 a large detrital zircon megacryst from sri lanka yields 18o 15 4 0 1 2 se by ion microprobe a euhedral unzoned zircon in a thin section of sri lanka granulite facies calcite marble yields 18o 19 4 by ion microprobe and confirms a metamorphic petrogenesis of zircon in marble small oxygen isotope fractionations between zircon and most minerals require a high 18o source for the high 18o zircons predicted equilibrium values of 18o calcite zircon 2 3 from 800 to 600 c show that metamorphic zircon crystallizing in a high 18o marble will have high 18o the high 18o zircons 15 from both sri lanka and mogok overlap the values of primary marine carbonates and marbles are known detrital gemstone sources in both localities the high 18o zircons are thus metamorphic the 15 25 zircon values are consistent with a marble origin in a rock dominated system i e low fluid external rock the lower 18o zircon values 9 15 are consistent with an origin in an external fluid dominated system such as skarn derived from marble although many non metasomatized marbles also fall in this range of 18o high 18o 15 and the absence of zoning can thus be used as a tracer to identify a marble source for high 18o detrital zircons this recognition can aid provenance studies in complex metamorphic terranes where age determinations alone may not allow discrimination of coeval source rocks metamorphic zircon megacrysts have not been reported previously and appear to be associated with high grade marble identification of high 18o zircons can also aid geochronology studies that seek to date high grade metamorphic events due to the ability to distinguish metamorphic from detrital zircons in marble

zircon oxygen isotopic constraint on the sources of late mesozoic a type granites in eastern china abstract a type granites are usually derived from partial melting of the lower crust and or the upper mantle within extensional settings but their exact sources for specific plutons are required to unravel a systematic laser fluorination analysis of oxygen isotopes was carried out for five well documented late mesozoic a type granites in eastern china zircon from 41 samples was separated and 109 aliquots of fresh zircon were analyzed along with whole rock powder and quartz from the same samples hydrothermally altered whole rock samples show scattered 18 o values of 2 3 to 7 4 with a total variation up to 9 7 in contrast zircon 18 o values vary only from 3 1 to 5 4 with a range of 2 3 most available zircon 18 o values of a type granites are lower than normal mantle zircon values of 5 3 0 6 2sd and high temperature equilibrium fractionations are well preserved between quartz and zircon in most cases the above lines of evidence suggest that the low 18 o zircons in a type granites were crystallized from low 18 o magmas because low 18 o magmas cannot be derived entirely from the mantle reworking and or recycling of crustal igneous rocks are involved for their petrogenesis the low 18 o zircons in this study thus offer evidence for a dominantly crustal origin of the late mesozoic a type granites in eastern china

age refinement of the messinian salinity crisis onset in the mediterranean we propose a revised age calibration of the messinian salinity crisis onset in the mediterranean at 5 971 ma based on the recognition of an extra gypsum cycle in the transitional interval of the perales section sorbas basin spain and the revision of the magnetostratigraphy of the monticino section vena del gesso basin italy this age re calibration allows to state more accurately that i the interval encompassing the msc onset is continuous thus ruling out any erosional feature or stratigraphic hiatus related to a major sea level fall affecting the mediterranean ii the first gypsum was deposited during the summer insolation peak at 5 969 ma associated with an eccentricity minimum and roughly coincident with glacial stage tg32 iii the msc onset was preconditioned by the tectonically driven reduction of the hydrological exchanges with the atlantic ocean and finally triggered by glacial conditions in the northern hemisphere and by arid conditions in northern africa

sumeini group oman evolution of a mesozoic carbonate slope on a south tethyan continental margin abstract deposition of the mostly mesozoic sumeini group occurred on the slope between the shallow marine arabian carbonate platform and the deep oceanic hawasina basin or south tethys sea these strata record the evolution of the northeast arabian continental margin from permian and triassic rifting to ocean basin closing with the late cretaceous obduction of the semail ophiolite platform margin type and its evolution can be inferred from exposures of these slope sediments at jebel sumeini in the western oman mountains in the lower permian base of the sequence bedded spicular limestones suggest deep marine conditions this is followed by an enigmatic thick sequence of bedded dolomite in the early to middle triassic small carbonate submarine fans formed along a distally steepened slope a subsequent interval of terrigenous clastic sedimentation was followed by development of a steep escarpment margin during ladinian to norian time with coralgal reefs at the shelf break and a debris apron at the base of the scarp the late triassic is marked by another influx of terrigenous sediment which accompanied widespread emergence of the platform in the jurassic a thick apron of thin bedded limestone formed on the slope this apron was cut by channelized gullies that now include blocks of older reefal material and oolitic sands a well documented submergence of the platform during the tithonian and early cretaceous led to the deposition of radiolarian cherts on the slope and basin upper lower cretaceous megabreccias up to 200 m thick suggest an interval of localized slope instability and or tectonism continued deposition of bedded limestone and marl with lesser calcirudite marks the top of stratigraphic sequence at jebel sumeini the early to middle triassic carbonate submarine fan deposits occur as discrete lenticular sequences of bedded calciturbidite modified grain flow and debris flow deposits which were derived from mostly slope sources the ladinian to norian base of slope debris apron deposits were derived from both slope and shallow marine sources including reefs and appear to form a laterally extensive but narrow belt of thick lenticular to sheet like beds of debris which accumulated over a long interval of time coarse limestones in the jurassic gullied slope deposits are distinct in that they occur randomly as individual channelized beds in a sequence dominated by thin bedded lime mudstones thick lower cretaceous megabreccias are distinguished by their great lateral distribution and general lack of matrix

applications of lead and strontium isotopic relationships to the petrogenesis of granitoid rocks central sierra nevada batholith california pb isotope data are given on 80 whole rock and or feldspar samples from 51 dated samples covering a traverse across the central sierra nevada batholith largely between latitudes 36 and 37 n in addition sr isotope data were measured on 30 whole rock samples no correlation is observed between age and isotope ratios in agreement with previously published data 87 sr 86 sr ratios are low 0 704 along the western margin and increase to high values 0 707 at the eastern margin 206 pb 204 pb ratios increase from 18 6 at the western margin to 19 5 in the middle of the batholith then decrease regularly to 18 5 toward the eastern margin 2o8 pb 204 pb ratios mirror the 206 pb 204 pb data but do not exhibit the decrease in values toward the eastern margin pb and sr isotopic data from the western margin plutons plot within or close to the field of primitive island arc magmas indicating predominantly mantle sources the high 206 pb 204 pb ratios in the central batholith suggest assimilation of sediments derived from precambrian basement rocks the decrease in 206 pb 204 pb ratios in the eastern segment of the batholith without corresponding reduction in 208 pb 204 pb ratios is attributed to assimilation of lower crustal granulitic amphibolitic rocks by mafic magmas initial pb ratios for samples with 87 sr 86 sr 0 706 from the central and eastern segments of the batholith indicate components from recycled crustal rocks with a mean 207 pb 206 pb age of ca 1 8 ga nd and o isotopic data from the literature are consistent with the pb sr model obtained in this study very similar isotope patterns to the present model are reported across the salinian block

petrogenesis of the mesozoic shuikoushan peraluminous i type granodioritic intrusion in hunan province south china middle lower crustal reworking in an extensional tectonic setting abstract the mesozoic shuikoushan granitoid intrusion in the jiangnan orogen between the yangtze and the cathaysia blocks in southern hunan province south china provides an opportunity to probe deep crustal composition and structure and to investigate the geodynamic evolution of south china the intrusion is composed of granodiorite with i type geochemical affinities and contains zircon with an u pb concordant age of 158 3 1 2 ma rocks from the intrusion have variable sio2 from 58 4 wt to 65 2 wt al2o3 from 15 0 wt to 17 2 wt tio2 from 0 57 wt to 0 76 wt and p2o5 from 0 27 wt to 0 52 wt they have a cnk from 0 97 to 1 23 1 04 on average and are dominantly peraluminous they are characterized by enrichment in lree la sm n 3 47 5 19 and lil e g k rb and depletion in hfse e g u th in primitive mantle normalized trace element diagrams these geochemical features indicate that the rocks are i type granodiorites and have undergone extensive fractional crystallization of hornblende biotite titanite and apatite all samples show negative ehf t 10 6 to 8 1 and end t 5 92 to 6 13 values with relatively high initial 87sr 86sr isr 0 7101 0 7102 and 18o ratios 8 4 9 7 these values significantly differ from mantle values suggesting that they are generated by the amphibole dehydration melting of a mafic source in the middle to lower crust beneath the jiangnan orogen the emplacement of the shuikoushan granitoid intrusion is contemporaneous with the late jurassic to early cretaceous extension within the shi hang rift zone indicating that it may have been formed under an extensional regime in response to both the pacific superplume activity and westward subduction of the pacific plate the extensional processes along with asthenosphere upwelling and basaltic underplating may have triggered the widespread late jurassic granitoid intrusion in southern hunan province and possibly in south china

oxygen isotope heterogeneities and diffusion profile in composite metamorphic magmatic garnets from the pyrenees unusually large 1 8 o heterogeneities 4 within single crystals are reported in garnets from dioritic migmatites in the pyrenees these heterogeneities together with contrasting ca and p zoning allow the identification of different growth zones garnet cores with high 1 8 o values 12 14 are relatively poor in ca 7 9 mol grs and rich in p 400 900 ppm p 2 o 5 in contrast garnet rims with lower 1 8 o values 7 12 o are richer in ca 12 14 grs and poorer in p 100 200 ppm these growth zones can be ascribed to a metamorphic event followed by crustal partial melting and contamination by magmas from the mantle high 1 8 o intra crystalline contrasts result from mineral growth in an open magmatic system involving the interaction of partial melts with distinct 1 8 o signatures at the garnet core rim interface compositional profiles in major divalent cations are consistent with the relaxation of an initial sharp step in ca fe and mg by ca fe mg interdiffusion at the same interface an o isotope profile is documented the analogy of ca and o isotope profiles suggests that the 1 8 o distribution may also result from a diffusion process in this particular case temperature garnet composition oxygen fugacity o diffusion appears to be of the same order of magnitude as ca fe mg interdiffusion considering a duration of 10 ma for the plutono metamorphic event in the pyrenees ca and o diffusivities in the range 10 2 2 m 2 s at 850 c are retrieved from the measured profiles like ca o diffusion in garnet at magmatic temperatures 850 900 c is both slow enough to preserve large 1 8 o heterogeneities and fast enough to generate relaxation profiles

from rifted margins to foreland basins investigating provenance and sediment dispersal across desert arabia oman u a e arid arabia where chemical weathering and anthropic modifications are negligible is a huge natural laboratory for the study of sediment provenance mafic and ultramafic detritus from ophiolite belts is found along the oman mountains and on masirah island obduction orogen provenance dominant cellular serpentinite grains from residual mantle harzburgites of the sama il ophiolite contrast with gabbroic diabase and basaltic grains from igneous crustal rocks of the masirah ophiolite detritus from autochthonous basement and cover rocks is found along the arabian sea margin rift shoulder provenance transition from carbonate dominated lithic sands undissected stage to hornblende rich plagioclase arkoses dissected stage is best documented at the northern edge of the gulf of aden along the older strike slip owen basin margin only locally are feldspars hornblende and garnet derived from small outcrops of pan african basement modern eolian sands from yemen to the arabian persian gulf display marked enrichment in quartz low plagioclase feldspar ratios and depleted dense mineral assemblages with rounded epidotes hornblende garnet and ultrastables pointing to extensive recycling also fostered by quaternary changes the rub al khali and wahibah sand seas have distinct quartz feldspar ratios reflecting largely separate transport pathways dune fields fed chiefly from rift highlands in the west and south mix with orogenic detritus in the northeast carbonate dominated sands in coastal uae are mostly derived from the zagros mountains blown by northerly shamal winds across the gulf during pleistocene lowstands to reach the backbulge depozone and the foreland beyond contributions from the oman mountains reach only 5 10 of bulk sediment along their southern apron and mostly indirectly through deflation of plio pleistocene fans the sama il ophiolite supplies enstatite and diopside to the eastern uae and wahibah sands the masirah ophiolite supplies amphiboles and clinopyroxenes locally along the batain coast the composition of desert sediments faithfully mirrors tectonic history of source terranes deformation style during orogeny and unroofing level during extension bulk petrography coupled with dense mineral analysis thus represents a powerful tool to investigate not only provenance and sediment transport but also crustal dynamics and geologic evolution at continental scale

a case of obduction related high pressure low temperature metamorphism in upper crustal nappes arabian continental margin oman p t paths and kinematic interpretation in the southeastern oman mountains the saih hatat tectonic window reveals arabian continental material beneath the oceanic sensu lato nappes i e the hawasina sedimentary units and the huge sumail ophiolite the northeastern internal half of the window suffered an intense deformation associated with a high pressure low temperature hp lt metamorphism approximately dated at 80 75 ma according to the available stratigraphie data after the deformation due to the absence of collision the obduction inherited structural and metamorphic pattern was virtually unmodified a metamorphic map is established based on mineral assemblages in metapelites and metabasites low grade assemblages occur in the highest units muscat nappes quryat unit characteristic minerals are femg carpholite lawsonite associated with kaolinite or pyrophyllite and locally sudoite in the metapelites while lawsonite and blue amphiboles are found in the metabasites high grade rocks outcrop in the deepest and easternmost units as sifah antiform and are typified by an epidote glaucophane bearing eclogite assemblage intermediate units hulw show assemblages of intermediate grade chloritoid schists and glaucophane bearing metabasites higher grade assemblages such as talc chloritoid were not found inverted gradients are observed locally in the muscat nappes pyrophyllitebearing units above kaolinite quartz bearing units and these are ascribed to late metamorphic thrust displacements which are demonstrated by microstructures a complex p t evolution is fairly well documented by the mineral assemblages prograde evolution in the subophiolitic continental rocks began with a rather hot gradient of about 30 35 c km with chloritoid growth in the higher units thereafter pressure increased with the temperature remaining constant or even decreasing chloritoid replaced by kaolinite oxides and carpholite growth in synkinematic conditions the peak p t conditions are close to 8 kbar 270 c for the muscat nappes and 11 kbar 400 c for the as sifah unit the corresponding surface related gradient is low 10 15 c km during the retrograde evolution pressure and temperature generally decreased concomitantly but in some of the upper units temperature remained constant or increased slightly for some time at which point sudoite growth from carpholite took place the metamorphic pattern and mineral evolution are interpreted in the framework of the late cretaceous obduction the already cold oceanic lithosphere was thrust upon a relatively hot thinned passive margin with coeval basaltic volcanism pressure progressively increased in the passive margin due to the wedge shape of the advancing ophiolite the maximum thickness of which was about 25 km in the as sifah area in this area the overburden was also attributable to the accumulation of continental material up to 5 km thick by means of a complex set of synmetamorphic often conjugated folds and thrusts the basal peridotites of the obducted slab were probably not hotter than 300 c during its thrusting upon the continental margin the temperature of the tectonic pile below the ophiolite remained low because it was thrust above more external and still colder continental areas late thrusting in the same southerly direction controlled the retrograde evolution together with erosional and gravity driven tectonic unloading

u pb zircon strontium and oxygen isotopic and geochronological study of the southernmost sierra nevada batholith california the southernmost sierra nevada offers a view into the deep levels of the mesozoic batholithic belt which constitutes much of the range to the north and represents one of the major tectonic features of western north america the main crystalline rocks of the study area are 1 the intrusive suite of bear valley a middle cretaceous tonalite batholith complex with coeval gabbroic intrusives and 2 the gneiss complex of the tehachapi mountains which consists of early cretaceous orthogneiss and subordinate paragneiss with local domains having granulite facies metamorphic assemblages the orthogneisses are dominantly tonalitic in composition with significant layers of granodioritic to granitic and lesser dioritic to gabbroic gneiss quartz rich and psammitic metasedimentary rocks with subordinate marble constitute the main framework assemblage into which the plutonic rocks were emplaced field relations demonstrate assimilation of metasedimentary material into the orthogneiss and tonalite batholith magmas and magma mixing between mafic tonalitic and granitic materials significant domains of both homogenization and inhomogenization are recognized isotopically within the mixed rocks u pb zircon studies have resolved two major igneous suites and a third suite of postdeformational intrusives all lying between 90 and 120 ma the first suite gneiss complex of the tehachapi mountains was emplaced at 115 ma and exhibits penetrative high temperature deformation developed at or near solidus conditions a number of discordance patterns along with the physical properties of the zircon suggest minor inheritance of proterozoic zircon and limited open system behavior in response to a major 100 ma plutonic event the 100 3 ma intrusive suite of bear valley crosscuts the older suite but also exhibits significant synplutonic deformation mainly concordant zircon ages indicate the igneous crystallization age but some discordances occur due to inheritance or entrainment of proterozoic zircon the high temperature deformation fabrics in these suites and within the metasedimentary framework rocks were crosscut by the granodiorite of claraville 90 ma and pegmatite dikes 95 ma the granodiorite of claraville shows strong inheritance of proterozoic zircon and high initial 87 sr 86 sr and 18 o zircon populations from paragneiss and quartzite samples are dominated by proterozoic detrital grains strontium and oxygen isotopic data on the zircon geochronology sample suite suggest simple twocomponent mixing of mantle derived gabbroic to tonalitic magmas with partial to complete melt products from the metasedimentary framework rocks sedimentary admixtures for some granitic rocks may be as high as 45 but for the tonalitic batholithic complex are no higher than about 15 modeled values of 10 20 metasediment are typical for the orthogneisses initial 87 sr 86 sr correlates directly with 18 o and generally correlates inversely with sr content some subtle complexities in the sr and o isotopic data suggest the involvement of a third cryptic component such a component could be early phanerozoic ensimatic accretionary terranes that were structurally beneath the observed metasedimentary sequence or altered oceanic crust and sediments introduced into the mantle magma source area by subduction one of the initial aims of this study was to seek out remnants of proterozoic sialic crystalline rocks within the gneiss complex of the tehachapi mountains no such remnants were found and our studies strongly suggest that sialic components within this link of the mesozoic batholithic belt were introduced into mantle derived magraatic systems by anatexis of continent derived sedimentary rocks

anatomy of garnets in a jurassic granite from the south eastern margin of the north china craton magma sources and tectonic implications abstract the late jurassic jingshan granite located at the south eastern margin of the north china craton contains abundant garnets which can be subdivided into three types based on texture and composition i euhedral garnet in mafic biotite and garnet rich enclave grt i ii coarse grained garnet grt ii in the host granite and iii small euhedral garnet in aplite grt iii in general grt i has higher feo cao and lower mno contents than grt ii grt iii has higher mn but lower ca contents than others grt i has lower mree and hree contents than grt ii grt iii has prominent and distinctly negative eu anomaly as well as higher mree composition compared to the others systematic variations in oxygen isotope compositions are observed among the three garnet types with 18 o values of 4 7 in grt iii some of the grt ii and grt iii display two distinct zonings with cores having similar major and trace element compositions to grt i cathodoluminescence cl images revealed that the zircons from different garnet bearing samples possess fine scale oscillatory zoned magmatic rims with inherited cores in situ zircon u pb dating and trace element analyses show that the dark luminescent magmatic rims all have jurassic concordia ages 160 ma and similar trace element patterns most of the inherited cores also display similar triassic ages of 210 236 ma which is similar to the ages of ultrahigh pressure uhp metamorphic rocks of the dabie sulu orogen 230 ma in addition jurassic concordia ages were also found in a zircon inclusion in grt i implying that the grt i was formed shortly before the main magmatic event the age data suggest that the three different garnet types may be genetically related and modified by cogenetic magmatic events based on the zircon u pb ages from different garnet bearing samples the major element trace element oxygen isotope and zoning textures of the three kinds of garnet we suggest that grt i may be peritectic garnet whereas grt ii and iii are probably the results of magmatic dissolution precipitation processes and re equilibration of garnets with changing magmatic conditions during melting differentiation crystallization and cooling within the granite we conclude from the oxygen isotopic character of the garnets and ages of the zircons that the source rocks for the jingshan granites are from dabie sulu orogen representing the south china craton

supracrustal input to magmas in the deep crust of sierra nevada batholith evidence from high δ 18 o zircon oxygen isotope ratios of zircon zc from intrusives exposed in the tehachapi mountains southern california reveal large inputs of high 18 o supracrustal contaminant into gabbroic and tonalitic magmas deep 30 km in the cretaceous sierra nevada batholith high 18 o zc values 7 8 0 7 predominate in the deep parts of the batholith but lower values 6 1 0 9 occur in shallower parts this indicates a larger gradient in 18 o with depth in the batholith than occurs from west to east across it oxygen sr and nd isotope data show that the supracrustal contaminant was likely young paleozoic or mesozoic hydrothermally altered upper oceanic crust or volcanic arc sediments such rocks were subducted or underthrust beneath the sierran arc during accretion of oceanic terranes onto north america this component yielded high 18 o magmas that were added to the base of the batholith on average gabbros in the southern sierra contain at least 18 of the subducted supracrustal component some tonalite and granodiorite magmas were additionally contaminated by kings sequence metasedimentary rocks as evidenced by 18 o zc and initial 87 sr 86 sr that trend toward values measured for the kings sequence besides high 18 o values in the southern sierra xenoliths in the central sierra also have elevated 18 o which confirms the widespread abundance of supracrustal material in the sub arc lithospheric mantle in contrast to 18 o zc whole rock 18 o values of many samples have undergone post magmatic alteration that obscures the magmatic contamination history of those rocks such alteration previously prevented confident determination of the mass of young hydrothermally altered mantle rocks that contributed to sierran granitoids

origin and nature of the rapid late tertiary filling of the levant basin the recent huge gas discovery in early miocene siliciclastics offshore israel highlighted a new world class gas province and has subsequently sparked great interest in the oligocene miocene deep water sediments of the levant basin based on a dense network of seismic data we present two fundamental observations first more than half of its sedimentary column accumulated within a mere 15 of the basin9s life span i e an 6 km thick section accumulated within 37 m y post middle eocene second this young section first accumulated in the deep basin and only then did large amounts of sediments amass along the eastern levant continental margin these fundamental observations allude to two feasible source to sink scenarios 1 the thick late tertiary section is composed of large amounts of terrigenous material that originated in arabia and was transported via the israeli margin and 2 the terrigenous material originated in africa and was transported northward via the region that eventually evolved into the nile river cone our data emphasize the difficulties of the first scenario and suggest that africa was the dominant sediment source this suggestion requires the submarine transport of sediments from offshore north africa to have been northeastward and thus raises new questions regarding ocean circulation at a time in which the neo tethys was closing and the marine connection to the mesopotamian basin gradually ceased

a cryptic record of magma mixing in diorites revealed by high precision sims oxygen isotope analysis of zircons high precision in situ ion microprobe sims oxygen isotope analysis of zircons from two diorite intrusions associated with the late caledonian lochnagar pluton in scotland has revealed large differences in the degree of heterogeneity in zircon 18o between the diorites zircon crystals from the cul nan gad diorite cng show a unimodal distribution of oxygen isotope values 18o 6 0 0 6 2 and no or only minor grain scale variation those from the allt darrarie diorite ad1 show a large range in 18o and an apparent bimodal distribution with modes of 6 6 0 4 and 7 3 0 4 variations of up to 1 2 occur between and within grains both an increase and decrease in 18o with zircon growth has been observed the 18o composition of growing zircon can only change if open system processes affect the magma composition i e if material of contrasting 18o composition is added to the magma the variability in ad1 is interpreted to represent a cryptic record of magma mixing a deep crustal hot zone is a likely site for generation of the dioritic magmas which developed by mixing of residual melts and crustal partial melts or by melting of mafic lower crustal rocks the overall small number of zircons with mantle like 18o values 5 3 0 6 2 in the lochnagar diorites is largely the product of crustal differentiation rather than crustal growth the 18o of quartz from the cng and ad1 diorites shows only minor variation cng 10 9 0 5 2 ad1 11 7 0 6 2 within single populations with no evidence of mixing quartz zircon isotopic disequilibrium is consistent with later crystallisation of quartz from late magmatic fluids and in case of the ad1 diorite after the inferred magma mixing from a homogenised higher 18o melt high precision sims oxygen isotope analysis of zircon provides a new approach to identifying and resolving previously undetected early stage magma mixing and constraining the compositions and origins of the component magmas a combination of zircon quartz and whole rock data has proven to be a powerful tool in reconstructing the petrogenetic evolution of diorite from early crystallisation to late alteration

oxygen isotope study of quartz al2sio5 pairs from the mica creek area british columbia implications for the recovery of peak metamorphic temperatures oxygen isotope analyses of quartz al2sio5 pairs have been made for samples from the mica creek area british columbia we have analysed quartz kyanite nodules and quartz kyanite and quartz sillimanite in multiphase pelitic rocks from the staurolite kyanite kyanite and sillimanite zones apparent temperatures calculated from oxygen isotopic fractionation range from 555 c staurolite kyanite zone to 695 c sillimanite zone temperatures from the quartz kyanite nodules range from 630 to 675 c some of the nodules show isotopic disequilibrium most of the results confirm predictions that bimineralic rocks will yield an estimate of peak metamorphic temperatures when the less abundant mineral an aluminium silicate is the slower oxygen diffuser using cooling rates of 10 100 c ma 1 for the multiphase rocks measured crystal sizes and modes the fast grain boundary diffusion model with wet diffusion data ph2o 1 0 kbar yields predicted apparent temperatures which are generally lower than the measured apparent temperatures the agreement is improved if slower diffusion coefficients are used this suggests that f h2o during cooling was lower than that of the hydrothermal experiments and thus that there was little interaction with aqueous fluids of internal or external origin to modify the isotopic compositions the measured apparent isotopic temperatures and apparent garnet biotite fe mg exchange temperatures show very poor agreement for the sillimanite zone samples with the garnet biotite fe mg exchange temperatures generally higher than the oxygen isotope temperatures compared with the other calibrations that we tested the measured apparent temperatures using the sharp calibration show the best agreeement with recently published p t grids although some variability in agreement is expected due to variable f h2o during cooling

temporal variations in the mantle source beneath the eastern tianshan nickel belt and implications for ni cu mineralization potential abstract many small mafic ultramafic intrusions are found in the eastern tianshan ni belt along the southern margin of the central asian orogenic belt caob the ni cu mineralized hulu intrusion is located in the eastern part of the jueluotage area of the eastern tianshan ni belt this mafic ultramafic intrusion comprises a shallow layered sequence and deeper dike like unit precise zircon u pb dating yielded ages of 381 0 1 3 and 377 0 3 0 ma for sulfide bearing samples from the layered unit and 388 6 2 7 ma for a mineralized gabbro from the dike like unit 176hf 177hf values of zircons from the layered unit range from 0 282846 to 0 283165 and correspond to ehf t values of 10 6 to 20 4 18o values for these zircons range from 4 8 to 5 5 similarly zircons from the sulfide bearing gabbro of the dike like unit have ehf t and 18o values from 13 0 to 18 2 and 5 0 to 5 6 respectively normalized sio2 al2o3 tio2 and na2o k2o contents increase with decreasing mgo content whereas the feototal content is positively correlated with mgo which indicates that the different lithologies resulted from the fractional crystallization of a common parental magma furthermore the mafic ultramafic intrusions and their calculated parental magmas in the jueluotage area have similar rare earth element ree patterns with slight enrichment of the light ree relative to heavy ree all of the rocks and estimated parental magmas exhibit depletions in high field strength elements hfse e g nb ta and zr and enrichments in large ion lithophile elements lile e g u the pronounced light ree and lile enrichments and hfse depletions of the mafic ultramafic intrusions and calculated parental magmas are indicative of a subduction modified mantle source clinopyroxenes in the hulu intrusion have variable al2o3 4 39 7 32 wt and low tio2 0 33 0 67 wt contents which are comparable to typical alaskan type complexes that were emplaced in subduction environments in a tio2 versus alz aliv 100 2 diagram data for the devonian mafic ultramafic intrusions in the jueluotage area fall within the fields of alaskan type complexes whereas data for most of the permian intrusions fall outside of these fields systematic in situ zircon o and hf isotope analyses from the devonian mafic ultramafic intrusions in the jueluotage area exhibit higher 18o and lower ehf t values than those of the permian intrusions which may be explained by a change from a devonian fluid to permian fluid and melt modified mantle source the mafic ultramafic intrusions that were emplaced in both subduction and post collisional extensional environments in the eastern tianshan ni belt were favorable hosts to magmatic ni cu deposits despite their different mantle sources

phase relationships of s type granite with h2o to 35 kbar muscovite granite from harney peak south dakota muscovite granite 13 8 muscovite 4 8 normative corundum was reacted with varying percentages of h 2o in cold seal vessels at 2 kbar and in piston cylinder apparatus between 10 and 35 kbar the diagrams illustrating melting crystallization relationships are p t sections with both excess h 2o and with no h 2o added 0 66 h 2o in rock t x h 2o sections at 15 kbar and 25 kbar showing h 2o undersaturated conditions the h 2o undersaturated surface for the crystallization of quartz coesite small amounts of aluminosilicate minerals persist to higher temperatures glass compositions measured by electron microprobe from samples with 5 h 2o at 15 kbar confirm that liquids are syenitic through at least 100 c above the solidus as predicted from the effect of pressure on the residua system results are explained successfully by phase relationships involving muscovite quartz and orthoclase in k 2o al 2o 3 sio 2 h 2o with reactions depicted in a p total p e h 2o t model with special reference to the divariant surfaces in the region p e h 2o p total with reduced p e h 2o or a h 2o produced either by small amounts of h 2o and h 2o undersaturation or by co 2 h 2o mixtures subsolidus dehydration reaction temperatures decrease vapor present solidus temperatures increase and muscovite stability in presence of liquid increases in general muscovite biotite and amphibole can be precipitated from magmas containing only a few tenths per cent h 2o although the h 2o undersaturated liquids coexisting with crystals may contain 3 or more dissolved h 2o this particular granite cannot be a primary magma from mantle or subducted oceanic crust it is a possible product of partial fusion of pelitic rocks between about 20 km and 40 km depth given sufficient h2o and xenocrystal muscovite or sillimanite from the source rocks the phase relationships are consistent with the idea of s type granites but not sufficient to prove the origin of this rock additional tests require phase relationships of other associated granitic rocks and details of geochemistry geophysics and field relationships

modern alluvial fan and deltaic sedimentation in a foreland tectonic setting the lower mesopotamian plain and the arabian gulf abstract the arabo persian gulf generally considered as a classical carbonate basin in fact also includes important terrigenous systems whose nature and geometry are related closely to the tectonic framework the gulf is bordered along its northeastern periphery by an active alpine system which constitutes a major source of both siliceous and calcareous detritus there are four types of terrigenous discharge which are classified according to their structural relationships numerous alluvial fans terminate ephemeral consequent streams draining the flanks of anticlines forming the external parts of the zagros mountain belt alluvial fan deltas studied in detail in southeastern iran terminate semi permanent streams which flow along major synclinal axis they are composed mainly of fine carbonate detritus part of which accumulates as spectacular marine mud banks two major types of delta occur relatively small marine deltas associated with permanent antecedent streams which cross the zagros fold system are scattered along the persian shoreline the other is the a major deltaic complex which is associated with the tigris euphrates rivers this system has prograded along the main axis of the gulf the resulting mesopotamian plain filling at least half of the original basin which in early quaternary times extended from hormuz to syria

neoarchean recycling of 18o enriched supracrustal materials into the lower crust zircon record from the north china craton abstract oxygen isotope analyses were carried out using sims technique cameca 1280 on zircons from well studied lower crust xenoliths xenocrysts from the north china craton ncc the results show that magmatic zircons with archean paleoproterozoic 207 pb 206 pb ages have an extremely large variation in 18 o values that range from less than normal mantle value 4 74 0 28 2 to 18 o enriched supracrustal value 8 88 0 40 2 and differ in localities of the ncc 18 o qindao from 5 27 0 45 to 8 88 0 40 18 o hannuoba from 6 78 0 23 to 7 69 0 41 18 o xiuyan from 4 74 0 28 to 6 57 0 39 such a variation demonstrates that the neoarchean lower crust beneath the ncc was highly heterogeneous in oxygen isotope compositions even in an individual region the fact that the predominant zircons have high 18 o values suggests that the recycling of 18 o enriched supracrustal materials into the neoarchean lower crust indeed happened during zircon crystallization some zircons with core rim texture have nearly identical 18 o both in core and its rim on the other hand others have a distinctive oxygen isotope ratio between the core and its rim possessing slightly higher 18 o in the rim than its core or vice versa such an oxygen isotope feature in zoned zircons suggests a complicated evolutional history of ancient lower crust in the ncc this study provides convincing evidence that a large amounts of the supracrustal materials have been recycled into the neoarchean lower crust beneath the ncc a process resulting in the highly heterogeneity in oxygen isotopes

lithology and characteristics of the messinian evaporite sequence of the deep levant basin eastern mediterranean abstract as the lithological composition of the messinian salt sequence of the levant basin is still controversial and unconstrained we reveal for the first time the lithology of the entire evaporite sequence from deep basin depth migrated seismic and borehole data the data presented here shows that the seismic transparent layers are composed of pure and uniform halite while the reflective layers are bundles of thin clay layers interbedded in the halite background the thin clay layers inside the deep basin evaporites have a cumulative thickness of 25 40 m high amplitude fan structures are observed on the deepest internal reflector which may suggest clay transportation among all the internal reflectors the upper units are more deformed while the deeper units are more coherent and flat two sets of folds faults are shown on the shallower intra units folds with nne ssw trending axes and thrust faults strike nw se on a regional scale the top salt reflector is generally horizontal while the other internal reflectors dip toward the nw the shallowest intra unit is the only one that has a wedge shape thickening to the nw while the other intra units generally have uniform thicknesses

modern sand from obducted ophiolite belts sultanate of oman and united arab emirates abstract oman and the united arab emirates host the largest ophiolites on earth and are characterized by arid tropical climate and desert conditions they thus provide an unexcelled natural laboratory in which to study sediments derived from allochthonous oceanic lithosphere and to define an actualistic petrogenetic model for obduction orogen provenance spectacularly exposed in se arabia are two distinct obducted ophiolite sequences sama il and masirah that contrast widely in formation setting spreading rate detachment level thermal state during emplacement and relief masirah beach sand chiefly consists of basaltic diabase to metadiabase plagioclase gabbroic and dunite grains from progressively deeper seated levels of the multilayered oceanic crust dense minerals include diopsidic clinopyroxene and hornblende from gabbros epidote and tremolite actinolite from altered dikes and augite from basaltic lavas in contrast sand from the sama il ophiolite includes cellular serpentinite grains and en