simulation of modern and middle cretaceous marine δ18o with an ocean atmosphere general circulation model 1 we have developed a coupled ocean atmosphere general circulation model the genesis mom model with the ability to transport and fractionate water isotopes in the ocean and atmosphere the model is used to predict modern and cretaceous precipitation and seawater 18o the model reproduces the large scale modern day isotopic distribution in the zonal mean the difference between simulated and observed seawater 18o is within 0 2 in the low and middle latitudes and within 1 at high latitudes in comparison to modern simulated cretaceous surface seawater 18o is systematically depleted by 0 3 at low and middle latitudes these differences are attributed to equilibrium fractionation during surface evaporation at low latitudes and an increased partitioning of 18o from the surface into the deep ocean due to intermediate and deep water formation in subtropical basins in the cretaceous we also find that regional seawater 18o is significantly influenced by the paleobathymetry and the resolution of oceanic gateways boundary conditions that are not well known for the past our simulation of cretaceous seawater 18o has major implications for oxygen isotope paleothermometry we conclude that conventional assumptions of past seawater 18o may lead to an overestimate of cretaceous sea surface temperatures especially at middle and high latitudes

shallow marine carbon and oxygen isotope and elemental records indicate icehouse greenhouse cycles during the early jurassic 1 for much of the mesozoic record there has been an inconclusive debate on the possible global significance of isotopic proxies for environmental change and of sequence stratigraphic depositional sequences we present a carbon and oxygen isotope and elemental record for part of the early jurassic based on marine benthic and nektobenthic molluscs and brachiopods from the shallow marine succession of the cleveland basin uk the invertebrate isotope record is supplemented with carbon isotope data from fossil wood which samples atmospheric carbon new data elucidate two major global carbon isotope events a negative excursion of 2 at the sinemurian pliensbachian boundary and a positive excursion of 2 in the late pliensbachian the sinemurian pliensbachian boundary event is similar to the slightly younger toarcian oceanic anoxic event and is characterized by deposition of relatively deepwater organic rich shale the late pliensbachian strata by contrast are characterized by shallow marine deposition oxygen isotope data imply cooling locally for both events however because deeper water conditions characterize the sinemurian pliensbachian boundary in the cleveland basin the temperature drop is likely of local significance in contrast a cool late pliensbachian shallow seafloor agrees with previous inference of partial icehouse conditions both the large scale long term and small scale short duration isotopic cycles occurred in concert with relative sea level changes documented previously from sequence stratigraphy isotope events and the sea level cycles are concluded to reflect processes of global significance supporting the idea of an early jurassic in which cyclic swings from icehouse to greenhouse and super greenhouse conditions occurred at timescales from 1 to 10 ma

geodynamic evolution of the sw europe variscides 1 the early evolution of sw europe variscides started by opening of the rheic ocean at 500 ma splitting avalonia from armorica iberia subduction on the se side of rheic generated the paleotethys back arc basin 430 390 ma splitting armorica from iberia with development of porto tomar ferreira do alentejo ptfa dextral transform defining the boundary between continental armorica and finisterra microplate to the w obduction of paleotethys was followed by armorica iberia collision and emplacement of nw iberian allochthonous units at 390 370 ma whereas toward the west of ptfa there was antithetic ophiolite obduction beja acebuches and rheic ophiolites plus finisterra continental slices on top of ossa morena zone with simultaneous development of eclogites and orogenic magmatism under a flake double wedge tectonic regime continued convergence 370 ma proceeded by intracontinental deformation with progressive tightening of the ibero armorican arc through dextral transpression on the cantabrian indentor from iberia to armorica the proposed model is discussed at the light of the driving mechanism of soft plate tectonics

generation and evolution of siliceous high magnesium basaltic magmas in the formation of the permian huangshandong intrusion xinjiang nw china abstract numerous permian orthopyroxene rich mafic ultramafic intrusions in the southern margin of the central asian orogenic belt caob have been emplaced in a post orogenic environment the huangshandong mafic ultramafic intrusion is the largest in the eastern tianshan orogenic belt of the caob and consists of a layered unit intruded by a massive unit the layered unit consists of lherzolite troctolite olivine gabbro hornblende gabbro gabbrodiorite and diorite whereas the massive unit is made of gabbronorite and olivine gabbronorite olivine from the layered unit has fo values of 75 to 84 and contains low nio and mno rocks from this unit have initial 87sr 86sr ratios 0 7031 0 7043 and end values 3 4 7 1 while plagioclase has initial 87sr 86sr ratios ranging from 0 70010 to 0 71569 olivine from the massive unit has relatively low fo values of 59 to 70 and high nio and mno rocks from this unit have relatively low and uniform initial 87sr 86sr ratios 0 7030 and high end values 6 0 7 5 and contain plagioclase with relatively low initial 87sr 86sr ratios 0 70042 to 0 70520 olivines from both units have low cao and cr2o3 both units formed from siliceous high magnesium basaltic magmas were derived from a hydrous depleted mantle source magma forming the layered unit experienced earlier removal of sulfides before emplacement with the earlier sulfide saturation caused by the addition of crustal material the magma that formed the massive unit has undergone fractional crystallization of olivine cr spinel siliceous high magnesium basaltic magmatism produced by melting of a hydrous depleted mantle source may be an important feature of orogenic belts

an alternative model for positive shifts in shallow marine carbonate 13c and 18o positive shifts in global seawater d 13 cdic are related to changes in the ratio of organic relative to inorganic carbon burial in oceanic basins whereas factors such as climatic cooling and the accumulation of polar ice are known to cause positive shifts in d 18 o here an alternative model is proposed for the formation of local positive isotope shifts in shallow marine settings the model involves geochemically altered platform top water masses and the effects of early meteoric diagenesis on carbonate isotopic composition both mechanisms are active on modern sub tropical carbonate platforms and result in low carbonate d 13 ca ndd 18 o relative to typical oceanic values during high amplitude transgressive events the impact of isotopically light meteoric fluids on the carbonate geochemistry is much reduced and 13 c depleted platform top water mixes with open oceanic water masses having higher isotope values both factors are recorded as a transient increase in carbonate 13 c and 18 o relative to low background values these processes must be taken into consideration when interpreting the geochemical record of ancient epeiric seas

how is strain localized in a meta granitoid mid crustal basement section spatial distribution of deformation in the central aar massif switzerland abstract this study investigates strain distribution in granitoid rocks formerly in the middle crust in the central aar massif switzerland and places the deformation behavior in the tectonic framework of the alpine orogeny strain is heterogeneously distributed in terms of strain partitioning forming several hundreds of closely spaced shear zones sz 80 sz km with sz thicknesses the majority of the steep shear zones preferentially accommodated upward motion by the southern block leading to an increase in peak metamorphic conditions from 250 c in the north to 450 c in the south of the aar massif the shear zones initiated at about 18 20 km depths during a stage of crustal thickening handegg phase subsequent deformation reactivated some shear zones with a gradual transition from reverse dip slip over oblique slip to strike slip shear zones under local transpressional conditions oberaar phase

is mid late paleozoic ocean water chemistry coupled with epeiric seawater isotope records isotopes of epeiric sea carbonates are used to construct seawater records for modeling global changes in paleozoic ocean chemistry climate and for intercontinental correlation we present for the first time geochemical results of paleozoic brachiopods biogenic low mg calcite blmc from open ocean permian carboniferous seamounts of japan situated in the tropical mid panthalassic ocean strontium isotope values of blmc from the panthalassic and paleotethys oceans are coupled with those of coeval specimens from epeiric seas of north america europe and russia p 0 393 but not with those of epeiric sea whole rocks matrix aragonite calcite mac p 0 029 and conodonts biogenic apatite ba p 0 031 oxygen isotope values of blmc from the panthalassic and paleotethys exhibit mixed results with studies of counterparts from epeiric seas p 0 596 reflecting overprinting of local environmental conditions on global trends carbon isotope values of blmc and mac from the panthalassic and paleotethys oceans are generally dissimilar to those of coeval material from epeiric seas of north america europe and russia p 0 001 and 0 002 respectively factors such as water mass stratification evaporation dilution depth temperature carbon burial and or oxidation variations and syndepositional diagenesis within the local environment probably influenced the chemistry of the fauna and accumulating sediments this decoupling of carbon and oxygen isotope values from the open ocean with those from epeiric seas makes questionable the use of isotope results from epeiric seas for international correlation constructing global seawater records determining fluxes in the global carbon cycle and for modeling climate changes and subsequently atmospheric carbon dioxide levels

threading the eye of the needle lessons from the search for another voisey s bay in labrador canada magmatic sulfide mineralization is present in three of the four compositional groupings in the mesoproterozoic nain plutonic suite and in compositionally similar paleoproterozoic rocks anorthosite hosted mineralization appears to be spatially linked to small gabbronorite bodies where sulfide liquids separated from silicate magmas to variable degrees depending on the wall rock conditions sulfide metal contents are low 0 2 1 0 ni and the ni cu ratio is variable although sulfide ni values remain fairly consistent within individual occurrences pyroxenite hosted mineralization is essentially restricted to minor intrusions and locally has higher sulfide metal contents up to 2 ni and less variable ni cu there are similarities between pyroxenite and anorthosite hosted mineralizations and they may form part of a broad continuum ferrodiorite hosted disseminated sulfide mineralization is associated with abundant iron oxides and typically has low amounts of ni in the sulfide 0 5 and ni cu 1 gabbro troctolite hosted mineralization contains the most variable and metal enriched sulfides containing from 1 to 7 percent ni and showing consistent ni cu 1 the best examples are associated with the voisey s bay intrusion dominantly troctolite and the pants lake intrusion dominantly olivine gabbro significantly these are the only nain plutonic suite mafic intrusions that were emplaced into or in close proximity to sulfide bearing paragneisses exploration of gabbroic and troctolitic rocks within archean orthogneisses has not yet revealed significant mineralization the pants lake intrusion has intriguing geologic similarities to the voisey s bay intrusion and supports some aspects of genetic models for the latter however it has lower sulfide ni contents around 2 and relatively elevated cu and co suggesting differences in the source magmas and or conditions of sulfide segregation the different styles of mineralization can be integrated with petrogenetic models for the nain plutonic suite and similar plutonic suites anorthosite hosted sulfide mineralization is interpreted to be derived from residual mafic magma that coalesced and migrated during ascent of semicrystalline anorthositic magmas and ferrodiorite hosted mineralization is interpreted to be derived from late fe enriched differentiates of deep seated mafic chambers in both cases the source magmas were fractionated which limits their potential for metals crustal sulfur from paragneisses may have played a role in sulfide saturation in both cases but does not appear to be a critical ingredient some pyroxenite hosted mineralization is akin to anorthosite hosted types but other examples may be linked to silicic contamination of more mafic magmas gabbro troctolite hosted mineralization is associated with mafic magmas that rose from deep crustal chambers prior to extensive fractionation these were richer in ni cu and co when they ascended into the upper crust sulfide bearing paragneisses apparently played a critical role in inducing sulfide saturation in the magmas the lessons from the search for nickel in labrador are mostly familiar from other areas the regional metallogeny of the nain plutonic suite underlines the critical roles of a relatively unevolved host magma and crustal contamination processes possibly involving addition of externally derived sulfur it emphasizes the importance of identifying and prioritizing these two key factors in the exploration of similar anorthosite dominated plutonic suites elsewhere in the world

the aguablanca cu ni ore deposit extremadura spain a case of synorogenic orthomagmatic mineralization age and isotope composition of magmas sr nd and ore s abstract the aguablanca cu ni orthomagmatic ore deposit is hosted by mafic and ultramafic rocks of the aguablanca stock which is part of the larger high k calc alkaline santa olalla plutonic complex this intrusive complex ca 338 ma in age is located in the ossa morena zone omz of the iberian variscan belt mineralization consists mainly of pyrrhotite pentlandite and chalcopyrite resulting from the crystallization of an immiscible sulphide rich liquid isotope work on the host igneous rocks sr nd and the ore s suggests that contamination with an upper crustal component took place at some depth before final emplacement of the plutons end338 6 to 7 5 sr 338 0 7082 to 0 7100 34s sulphides near 7 4 assimilation fractional crystallization afc processes are invoked to explain early cumulates and immiscible sulphide magma formation intrusion took place at the beginning of the type a oblique subduction of the south portuguese zone under the ossa morena zone and was probably driven by transpressive structures strike slip faults the mineralization is thus synorogenic aguablanca is probably the first case referred to in the literature of a magmatic cu ni ore deposit hosted by calc alkaline igneous rocks

cathodoluminescene at low fe and mn concentrations a sims study of zones in natural calcites abstract point analyses of natural calcite cements by sims confirm the earlier suggestions that 20 ppm mn is required to activate luminescence whereas fe concentrations in excess of 1400 ppm quench it partly independently of the mn content below this fe threshold luminescence is bright at mn concentrations in excess of 225 ppm in the range 20 225 mn all types of luminescence dull luminescent and nonluminescent can occur this undifferentiated domain is evident also from a compilation of literature data the type of luminescence is not a simple function of fe and mn concentrations other parameters influence cl sinc most diagenetic calcite cements have fe and mn concentrations that place them within the field of mixed cathodoluminescence these results force reassessment of models that equate the type of luminescence with the redox state of the diagenetic environment

depositional and diagenetic controls of source rock characteristics of the lower jurassic nordegg member western canada petrographic mineralogical and bulk geochemical xrd xrf and rock eval data indicate that depositional and early diagenetic processes were the principal controls on the organic and inorganic characteristics of the lower jurassic nordegg member source rock this unit comprises organic rich calcareous mudstones to marlstones and marly limestones that were deposited in a predominantly anoxic hypersaline silled marine basin during two transgressive regressive t r events sediments deposited during marine transgression have a higher content of carbonate calcite and dolomite and organic matter fe mainly as pyrite content varies inversely with carbonate content the basal nordegg member is phosphatic with stratiform apatite laminae and phosphatic nodules early diagenetic phosphatogenesis was probably mediated by bacteria under variably dysoxic conditions during the initial transgressive event regressive parts of t r cycles are expressed as an increase in abundance of silicate quartz illite kaolinite and minor k feldspar and lower organic carbon contents deposition of abundant marine organic matter fueled vigorous bacterial reduction of sulfate and almost total bacterial reworking of the sedimented organic matter resulting in significant production of reduced sulfur species and predominantly amorphous kerogen pyrite formation was ubiquitous but limited by the abundance of fe where fe contents fell below 3 wt excess sulfides were incorporated into the kerogen this process resulted in the early diagenetic formation of the sulfur rich kerogen type i ii s that typifies the nordegg thus fe availability in the depositional environment exerted an important control on the amount of s available for incorporation into the kerogen furthermore content of organic s increases with increasing hydrogen index indicating the importance of type and reactivity of organic matter on the extent of incorporation of sulfur into the kerogen during early diagenesis

chemical labelling of oyster shells used for time calibrated high resolution mg ca ratios a tool for estimation of past seasonal temperature variations abstract the geochemical compositions of biogenic carbonates are increasingly used for palaeoenvironmental reconstructions the skeletal 18o temperature relationship is dependent on water salinity so many recent studies have focused on the mg ca and sr ca ratios because those ratios in water do not change significantly on short time scales thus those elemental ratios are considered to be good palaeotemperature proxies in many biominerals although their use remains ambiguous in bivalve shells here we present the high resolution mg ca ratios of two modern species of juvenile and adult oyster shells crassostrea gigas and ostrea edulis these specimens were grown in controlled conditions for over one year in two different locations in situ monthly mn marking of the shells has been used for day calibration the daily mg ca ratios in the shell have been measured with an electron microprobe the high frequency mg ca variation of all specimens displays good synchronism with lunar cycles suggesting that tides strongly influence the incorporation of mg ca into the shells highly significant correlation coefficients 0 70

variscan ophiolite belts in the ossa morena zone southwest iberia geological characterization and geodynamic significance abstract the boundary between the iberian and south portuguese terranes in sw iberia is traced by a suture recording the closure of rheic and related oceans through nne directed subduction the western segment of the suture comprises imbrications of the iberian terrane relative autochthon neoproterozoic lower palaeozoic and allochthonous complexes the iberian terrane relative autochthon is overlain by lower middle devonian metasediments and an unconformable cover of lower carboniferous calc alkaline volcano sedimentary complexes both preserving evidence of very low grade metamorphism the allochthonous complexes include disrupted slivers of eclogite ca 370 ma klippen and slices of an internal ophiolite sequence iomzos a basal tectonic melange moura phyllonitic complex and an external ophiolite beja acebuches complex baoc a large layered gabbroic sequence lgs whereas part of the beja igneous complex intruded ca 350 340 ma the sw suture domains the iomzos represents obducted remnants of the rheic ocean for which available shrimp u pb data indicate an age of 479 5 ma this ocean which separated iberia from a promontory of gondwana and avalonia now represented by the south portuguese terrane opened near the cambrian ordovician boundary through a rift jump from an intra cratonic setting within the iberian terrane to oceanic rifting the baoc displays geochemical features compatible with derivation from a short lived back arc basin lower middle devonian t dm sm nd 380 440 ma the variscan ophiolite belts preserved along the sw variscides were emplaced by antithetic obduction in two stages both with shearing sense towards the nne the first stage which involved iomzos cold obduction exhumed hp rocks ca 370 ma and created a foreland bulge towards the iberian terrane s sw flank this mechanism controlled the development of the volcanic related carbonate shelves and the contemporaneous terena flysch trough to the ne the second stage corresponds to baoc hot obduction carrying the iomzos klippen in piggy back style and affecting the southern margin of the lgs at ca 350 340 ma

palaeoclimate reconstructions of the middle jurassic of kachchh western india an integrated approach based on palaeoecological oxygen isotopic and clay mineralogical data abstract the middle jurassic sedimentary succession of the kachchh basin shows significant changes in lithology faunal content and diversity across the bathonian callovian boundary the change in lithology from predominantly carbonates in the middle and late bathonian to siliciclastics in the callovian is accompanied by a drop in species diversity from high to moderate characteristic faunal elements of the bathonian corals sponges the bivalves eligmus and members of the opinae are absent or rare in the callovian in contrast callovian sediments contain comparatively high proportions of nuculid bivalves the clay mineral assemblage reveals prominent variations in the smectite vs kaolinite abundance especially during the bathonian to callovian transition from the bajocian to the middle bathonian smectite becomes the dominant clay mineral and is nearly exclusively present in the late bathonian towards the middle callovian its content gradually decreases and kaolinite becomes the dominant clay mineral illite generally is only a minor component throughout the middle jurassic based on these results the bajocian to middle bathonian time interval is interpreted to represent subtropical climatic conditions with seasonal droughts and a moderate supply of terrigenous clastics to the basin the late bathonian was a period with a semi arid climate hot seasonal droughts and a minor input of terrigenous clastics the increase in kaolinite contents in the callovian suggests a subtropical humid climate with less prominent seasonal droughts and a higher input of siliclastics into the basin accompanied by a higher nutrient influx oxygen isotope ratios measured on bathonian to early callovian brachiopod shells give palaeotemperatures of 19 24 c callovian to oxfordian paleotemperatures calculated from oxygen isotopes measured on belemnite rostra range from 11 to 21 c the lower palaeotemperatures estimated from the oxygen isotopic composition of belemnite calcite are explained by assuming that the belemnites spent most of their life span in colder regions of the malagassy gulf and migrated into the warmer subtropical waters of the kachchh basin combining these various lines of evidence the changes in lithology and faunal composition taking place in the kachchh basin during the middle jurassic appear to reflect largely a change towards increasing humidity rather than a distinct decrease in water temperature

palaeoecology of the marine reptiles of the redwater shale member of the sundance formation jurassic of central wyoming usa the redwater shale member oxfordian of the sundance formation was deposited in the foreland basin of the cordillera during the last and largest marine transgression of the jurassic in north america one ichthyosaur ophthalmosaurus natans two cryptocleidoid plesiosaurs tatenectes laramiensis pantosaurus striatus and one pliosauromorph megalneusaurus rex are known from the redwater shale member ichthyosaurs are much more abundant than plesiosaurs making up almost 60 of the fauna no actinopterygian fish have been found although four species have been identified from the lower sundance formation at least one hybodont shark and one neoselachian are known from rare isolated teeth the main food source for the marine reptiles was belemnoids as indicated by preserved gut contents for all four species in comparison the better known and slightly older peterborough member of the oxford clay formation of england has a much higher taxonomic and ecological diversity especially in the plesiosaurs marine crocodiles and fish the lower diversity in the redwater shale member probably reflects a much lower primary productivity in the sundance sea as well as restricted migration from the open ocean to the north

the partition of nickel between olivine magma and immiscible sulfide liquid abstract the ni contents of glasses in products of earlier experiments on the ni partition between olivine and immiscible sulfide liquid have been determined allowing the distribution coefficients for ni fe 2 exchange between sulfide and silicate k d 1 and olivine and silicate k d 2 to be calculated ni is relatively enriched in s bearing mg silicate liquids by complexing with dissolved s in consequence k d 1 and k d 2 are systematically dependent on both silicate liquid and sulfide liquid composition the present study re affirms the reliability of the existing ni partition data for coexisting olivine and sulfide and therefore supports the earlier conclusion that an immiscible sulfide liquid cannot be a normal product of upper mantle magmatic processes in s bearing systems k d 2 will be somewhat lower than the value for the corresponding s free system and this may account for the discrepancies between previously reported partition data

the ca 350 ma beja igneous complex a record of transcurrent slab break off in the southern iberia variscan belt abstract we report the results of an isotopic study of the large gabbro dioritic beja igneous complex bic in the boundary between the highly contrasting ossa morena om and south portuguese sp zones of the southern iberian variscan orogen this boundary is interpreted as a major suture zone materialized by discontinuous scattered strips of mafic ultramafic rocks the so called beja acebuches ophiolite complex baoc and by melange deposits of middle to late devonian age in the pulo do lobo accretionary prism plap the beja gabbro was interpreted either as part of the ophiolite like units or as a broadly arc related massif reflecting the northward subduction of oceanic lithosphere u pb zircon id tims dating of two diorites and a granodiorite points to igneous emplacement ages of 350 2 ma serpa 352 2 ma torrao and 353 4 ma sao pedro respectively whereas a felsic dyke yields a slightly younger age of 345 2 ma these results show that published ar ar dates do not represent igneous crystallization ages but merely reflect regional cooling below ca 500 c at least 10 ma after the major intrusive event probably as a result of uplift of the omz side of the suture zone relative to the subsiding spz 87sr 86sr350 and end350 display a large range of values from 0 7041 to 0 7093 and from 4 0 to 6 1 respectively which documents a rather complex petrogenetic history with an important role played by crustal contamination processes the more primitive sr and nd isotope signatures are measured in the mafic cumulates while radiogenic sr and unradiogenic nd isotope compositions occur in the more evolved rock types the broad trend of decreasing end350 with decreasing sm nd and increasing sio2 concentration is reminiscent of crustal assimilation combined with fractional assimilation afc end values of flasergabbros and associated cumulates ascribed to the ophiolite like unit in the guadiana valley are close to zero or even slightly negative irrespective of the age chosen for the correction for in situ radioactive decay of 147sm in the range 350 500 ma assumed to encompass the true geological age this observation conflicts with a truly oceanic derivation of these rocks which could rather represent early stage deformed and metamorphosed equivalents of the beja gabbro most metabasalts of the same area have positive albeit variable end consistent with mildly depleted mantle sources and or significant crustal assimilation only a few samples reach highly positive values end350 500 ca 8 similar to those typical for n morbs as do the acebuches amphibolites near aracena end350 500 ca 9 these data suggest that the baoc is not only disrupted but also composite since the gabbroic rocks are not cogenetic with the basalts based on the late devonian age of the collision between the omz and spz the emplacement of the beja gabbro cannot be related to an active subduction of oceanic lithosphere instead the generation in the mantle and emplacement in the overlying continental crust of copious volumes of mafic magmas with concomitant lp ht metamorphism is tentatively ascribed to a process of transcurrent slab break off that followed oblique subduction and collision

the timing of sulfide segregation in a variscan synorogenic gabbroic layered intrusion beja portugal implications for ni cu pge exploration in orogenic settings abstract a growing number of magmatic ni cu sulfide deposits discovered in orogenic environments has renewed the interest on this category and reinforced that most orogenic mafic magmas are pge depleted the beja layered gabbroic sequence lgs was emplaced during the same variscan tectono magmatic event as the aguablanca ni cu pge deposit in spain however no economic mineralization was yet found in lgs here we analyze three sulfide ore showings developed within different environments of lgs that provide a unique frame to assess sulfide segregation in orogenic mafic magmas the internal sulfides hosted at the core of the layered suite the marginal sulfides located at a complex domain where the lgs is intruded by late magmatic anorthosite tonalite trondhjemite att suite and the sulfide veins associated to late magmatic hydrothermal activity for this we performed detailed mineralogical electron probe micro analysis enabling to assess s2 t for sulfide equilibrium whole rock and isotopic sulfur and lead geochemistry for the sulfide occurrences which are further supported by a wide data set available for lgs and related mesocratic suites the internal sulfides developed under low sulfidation non dynamic magmatic conditions similar to those of the accessory sulfides in lgs gabbros they segregated from chalcophile depleted melts at the end of a crystal fractionation cycle without contribution from external sulfur the marginal sulfides have a pyrite bearing magmatic sulfide assemblage hosted in exceptionally coarse grained clinopyroxenites at the lgs sw border the metal poor sulfide veins occur within a metasomatic halo adjoining amphibole albite pegmatoid dykes the latter two sulfide types share geochemical affinities and represent late magmatic systems developed during uplift and intrusion by evolved lower crustal contaminated magmas the marginal sulfides are mafic precursors of the coeval magmatic hydrothermal system to which pegmatoid dykes and sulfide veins are related although estimated primary pge abundances for lgs magmas are within the range of morbs all sulfide types derived from pge ni depleted melts due to sulfide segregation during underplating the presence of deep crustal faults that prevent magma stalling and sulfide saturation at depth is paramount to generate orogenic magmatic sulfide deposits of economic value

magnetite free yellow lizardite serpentinization of olivine websterite canyon mountain complex n e oregon we document an example of serpentinization of olivine and orthopyroxene that produced virtually no magnetite but instead relatively fe rich yellow colored lizardite x fe 0 08 to 0 17 and the native fe ni co metals awaruite and wairauite lizardite s identity was confirmed by micro raman spectroscopy although peaks are broad electron microprobe analyses of the lizardite yield a continuous compositional trend of formula contents suggestive of the progressive uptake of fe 3 exclusively on m sites where it is charge balanced by vacancies although these observations are unusual this secondary mineral assemblage can be explained in terms of the likely intensive variables t f h 2 o f h 2 and a sio 2 attending the alteration the absence of magnetite in serpentinization does not signify a lack of oxidation by forming the hydrated phase component ferri lizardite instead of magnetite from the fayalite and ferrosilite components the yield of hydrogen is reduced by two thirds the usual inverse correlation of rock density with magnetic susceptibility is unlikely to be the case in this kind of serpentinization

mineral occurrence and its impact on fracture generation in selected qinshui basin coals an experimental perspective abstract the effect of mineral matter on the fracture evolution was investigated for lower permian and upper pennsylvanian coal samples from the qinshui basin of china optical microscopy scanning electron microscopy with energy dispersive x ray spectrometry sem eds and x ray computed tomography x ray ct were used to investigate the composition and modes of occurrence of minerals within the coals and to characterize the natural and induced fractures present within the samples the spatial distribution of mineral matter investigated by x ray ct demonstrates that the variation of mineralization within the cleats fractures occurred at fine scales and most of minerals were scattered in coal core samples the original fractures normally were present as two sets one set was almost parallel to the bedding plane and the other was almost perpendicular to the bedding plane for created fractures the difference in density between the matrix and mineral matter may weaken the cohesion of coals and it could explain why the created fractures propagate along the junction of minerals and organic coal matrix the internal fracture porosities varied from 0 06 to 20 69 which indicates a strong internal heterogeneity of the coals after a stress is applied the inclination of the main shear fractures ranges from 55 to 95 using energy analysis the fracture energy appears to represent nearly half of the total dissipated energy which can be correlated with the fracture density and orientation the formation and distribution of shear fractures is related to the spatial distribution of mineral matter and the overall mineral content these investigations serve to characterize hydro fracturing and pulverized coal generation during coalbed methane development

δ 18 o of carbonate quartz and phosphate from belemnite guards implications for the isotopic record of old fossils and the isotopic composition of ancient seawater belemnite guards of cretaceous and jurassic age were found to contain varying amounts of quartz deposited both on the external surface and inside the rostrum the oxygen isotopic composition of coexisting carbonate quartz and phosphate from the same rostrum was measured according to well established techniques none of these compounds showed isotopic values in equilibrium with one another assuming 18o values of the diagenetic water within the range of meteoric waters the 18o sio2 yield temperatures in agreement with the apparent secondary origin of this phase the 18o co32 range with a certain continuity between 10 8 and 0 97 pdb 1 with most of the intermediate values being within the range of the carbonate isotopic values of mesozoic fossils the most positive isotopic results obtained from phosphate are close to 23 24 v smow they can hardly be related to a secondary origin of the phosphate or to the presence of diagenetic effects since these results are among the most positive ever measured on phosphate as far as we know there is no widespread diagenetic process determining an 18o enrichment of phosphate the very low concentration of phosphate did not allow the determination of its mineralogical composition all the available 18o po43 values from belemnite and non belemnite fossils of marine origin of tertiary and mesozoic age are reported along with the newly measured belemnites the following conclusions may be drawn from the data reported 1 the pristine oxygen isotope composition of fossil marine organisms either carbonate or phosphate may easily undergo fairly large changes because of oxygen isotope exchange processes with diagenetic water this process is apparent even in the case of geologically recent fossils 2 the 18o po43 of belemnite rostra seems to be at least in the case of the most positive results in isotopic equilibrium with environmental water because of the similarity between the results from cretaceous belemnites and the results from cretaceous and lower tertiary pelecypods and fish teeth 3 if so the only feasible interpretation that can be suggested for the 18o enriched data is the possibility of a relatively large variation of the oxygen isotopic composition of ocean paleowater from jurassic to recent time

sulfide saturation and magma emplacement in the formation of the permian huangshandong ni cu sulfide deposit xinjiang northwestern china the eastern tianshan orogenic belt northwestern china hosts 120 mafic ultramafic intrusions and at least six of them host significant ni cu sulfide mineralization of which the permian huangshandong intrusion is the largest the mafic ultramafic rocks of the huangshandong intrusion comprise lherzolite gabbronorite gabbro and diorite individual orebodies are composed of pyrrhotite pentlandite and chalcopyrite as disseminated to net textured or massive to semimassive sulfide mineralization oxide bearing sulfide mineralization contains 1 to 5 magmatic magnetite that has ilmenite and spinel exsolution lamellae silicate rocks and sulfide mineralization have variable whole rock platinum group elements pge 0 38 362 ppb cu 42 97 000 ppm and ni 26 33 000 ppm concentrations the mineralization is broken out into two types termed oxide rich and oxide poor the oxide rich sulfide mineralization has high pge concentrations with low 187re 188os ratios 38 9 151 whereas oxide poor sulfide mineralization has low pge concentrations with high 187re 188os 159 781 both oxide rich and poor sulfide mineralization have highly variable os values 49 189 and 30 278 respectively oxide rich sulfide mineralization contains magnetite with variable amounts of mgo tio2 al2o3 feototal cr v zn and sn indicating that they crystallized from different stages during magma differentiation we propose that the host intrusion and associated sulfide mineralization were derived from high mg basaltic magmas from a mantle source that was previously modified by subducted oceanic slab oxide poor sulfide mineralization of the huangshandong intrusion formed from a magma that underwent 0 03 sulfide removal before emplacement and was thus pge depleted oxide rich sulfide mineralization formed from magma that had much lower amounts of sulfide 0 003 removed in the early stage before entering the huangshandong magma chamber an early sulfide saturation event was likely associated with fractionation of silicate minerals in a deep staging magma chamber the second sulfide saturation event that formed the sulfide mineralization was probably triggered by selective crustal contamination and fractionation in the high level chamber where mixing of magmas and accumulation of immiscible sulfide occurred

pb pb dating and pb isotope geochemistry of neoproterozoic carbonate rocks from the sao francisco basin brazil implications for the mobility of pb isotopes during tectonism and metamorphism abstract a u pb study was carried out on carbonate rocks from the neoproterozoic bambui group in the southern part of the sao francisco basin brazil pb isotopic compositions and u and pb concentrations were determined on more than 90 samples from different parts of the basin these samples were found to contain four distinct types of pb here called types i ii iii and iv type i pb was found in samples with low pb concentrations and relatively high u concentrations it represents in situ growth of radiogenic pb and has a large enough variation to define pb pb isochron ages type ii pb is present in samples with relatively high pb concentrations and low u concentrations it is nonradiogenic crustal pb that could either represent average crustal pb at the time of deposition or as interpreted here at the time of deformation of these rocks type iii pb is also found in samples with high pb concentrations and low u concentrations but it apparently is radiogenic crustal pb from the archean or paleoproterozoic basement that was incorporated into the carbonates during the 600 ma brasiliano orogeny type iv pb is intermediate in composition between type iii and type i pb it represents a mixture of these two types pb pb isochron ages obtained from mesoscopically undeformed carbonates containing type i pb range from 686 69 to 520 53 ma the older age is the minimum depositional age for carbonate rocks from the sete lagoas formation during the interval from 690 to 500 ma the pb isotope system of carbonates from the sao francisco basin was disturbed and in some areas it was totally reset type iii pb compositions define a straight line type ii pb falls on the lower end of this line which intercepts the stacey and kramers s k pb growth curve at about 520 and 2100 ma this line is interpreted as representing a stage of crustal pb evolution beginning about 2100 ma and ending about 550 to 500 ma when variably radiogenic pb from the basement was incorporated into these carbonates the ages determined in this study are in agreement with most published ages for brasiliano fold belts marginal to underlying sao francisco craton showing that isotopic systems of sao francisco basin rocks were largely affected by brasiliano tectonism

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

sr isotope stratigraphy of the upper jurassic of central portugal lusitanian basin based on oyster shells strontium isotope stratigraphy was performed on oyster shells from the late jurassic of the lusitanian basin central portugal this represents the first approach to obtain numerical ages for these strata the new chronostratigraphic data provide a more precise age determination of several units after a basin wide hiatus sedimentation in the late jurassic is proven in the cabo mondego and cabacos formations to resume as early as the middle oxfordian the alcobaca formation can be placed in the latest late oxfordian to late kimmeridgian while data from the upper part of the abadia formation indicate an early to late kimmeridgian age the farta pao formation ranges from the latest kimmeridgian to the latest tithonian the largely synchronous sobral arranho i and arranho ii members are overlain by the late early to late tithonian freixial member the brief local carbonate incursion of the arranho i member marks the kimmeridgian tithonian boundary oysters are shown once more to be suitable for strontium isotope studies their calcitic shells are often unaffected by diagenesis in particular for marginal marine jurassic and cretaceous strata where belemnites are usually absent oysters may serve as a valuable tool for isotope stratigraphy

shear failure mechanism in granite inferred from multi scale brittle structures the brittle structures of a hercynian granite la borne french massif central observed at several scales from regional to microscopic are presented and interpreted on mechanical terms emphasis is placed on strike slip faults joints and cracks related to incipient shear fracturing during horizontal compression three compressive tectonic phases have been identified according to their brittle structures and characterised by the burial depth at the time of their generation the two first phases h1 h2 are hercynian and occurred while the granite was deeply buried 5 to 3 km depth whereas the last phase p is pyrenean and occurred at very low depth the geometric organizations of cracks joints and faults are clearly similar at various scales from about 10 m to several m these field observations are strong arguments for the occurrence of shear structures at microscopic to macroscopic scales during tectonic events following this inference it is proposed that at least in the case of hercynian phases cracks joints and macroscopic strike slip faults have been generated by the same mechanical process under high overburden weight therefore incipient fractures seem to be generated as shearing structures and to evolve by coalescence with neighbouring ones with the same direction

stratification and paleocirculation of the late cretaceous western interior seaway of north america paleotemperature and salinity profiles for the western interior seaway are reconstructed by use of oxygen and carbon isotopic signatures of shell material data have been gathered on different groups of molluscs distributed in three distinct habitat types infaunal benthonic epifaunal benthonic and nektonic isotopic variations and inferred environmental tolerances of the organisms were used to determine upper and lower temperature boundaries for each habitat group and therefore water depth zones water density for each temperature salinity combination within a habitat range was calculated and used to develop a physically stable stratification model the results clearly show that the water column consisted of denser more saline warm bottom layers that were overlain by and decoupled from cooler less saline intermediate layers it is proposed that this profile originated due to a surface current transporting runoff water from the western highlands toward the eastern shallow border of the seaway where evaporation and heating of surface water in a warm humid atmosphere caused increased density and sinking followed by westward return flow of the warm saline bottom water this model is compatible with known climatic and oceanographic information for the cretaceous

origin damping and pattern of development of faults in granite observations of brittle fractures in the granite of the massif de la borne as well as in other rocks allow us to discuss the different hypotheses regarding the origin of faults it seems that all faults originate by shear along a preexisting plane which can be an important fracture joint former fault or a microflaw pore grain boundary the shear on the plane gives rise to an array of en echelon cracks that makes the rock less resistant and permits the lengthening of the fault we also found an arrangement of horsetail fractures damping the movements on the faults we then propose a pattern for the development of the faults they originate on preexisting plane and propagate by initiating en echelon cracks the movements are damped by horsetails which permit by faults connection in relays the creation of larger faults

facies and climate environmental changes recorded on a carbonate ramp a sedimentological and geochemical approach on middle jurassic carbonates paris basin france a detailed sedimentological geochemical and mineralogical study is carried out on the early bajocian to early callovian middle jurassic limestones of the paris basin objectives are to document and explain the facies changes in the context of the climate environmental evolution at the nw european scale deposits include 18 lithofacies which are stacked into 10 third order depositional sequences at a greater time scale 4 biosedimentary packages are distinguished by their allochems associations 1 an intracratonic carbonate environment with coral reefs and crinoid rich facies is typical of the early bajocian 2 a major facies change occurred at the early late bajocian transition with a shift from crinoid and coral rich facies to ooid rich facies during the late bajocian a southward dipping ooid ramp with successive progradational trends was emplaced 3 a large lagoon protected by ooid shoals developed during the bathonian in a muddy ramp setting 4 at the bathonian callovian boundary a second major change occurred with the lagoonal facies being superseded by an ooid bioclastic crinoids corals ramp associated with a waning of carbonate productivity retrogradational trend our geochemical study including a compilation of bibliographic data allows us to refine the existing sea surface palaeotemperature pattern a cooling from the latest early bajocian to the late bajocian and a subsequent warming from the earliest callovian to the early middle callovian transition are described using a proxy of sea surface temperatures together with 13c and mineralogical data our new 18o values suggest a palaeo climatic palaeo environmental control of facies in this shallow carbonate ramp environment

the permian huangshanxi cu ni deposit in western china intrusive extrusive association ore genesis and exploration implications the permian huangshanxi cu ni deposit is the second largest magmatic sulfide deposit discovered to date in a major ni cu province related to protracted basaltic magmatism in eastern xinjiang china it is hosted by a small mafic ultramafic intrusion comprised predominantly of lherzolites olivine websterites gabbronorites and gabbros the huangshanxi intrusion is coeval with permian basalts of tholeiitic and alkaline affinities in the tuha and tarim basins respectively to evaluate a possible genetic relationship between the huangshanxi intrusion and a specific type of coeval basalt in the region as well as ore genesis in the intrusion we have carried out an integrated mineralogical petrological and geochemical study our data reveal that the huangshanxi intrusive rocks are characterized by relatively flat chondrite normalized ree patterns depletion in nb and ta and elevated end values varying between 6 and 10 these features are similar to those of coeval tholeiitic basalts in the nearby tuha basin but are significantly different from those of coeval alkaline basalts in the relatively remote tarim basin the geochemical similarities and differences suggest that the huangshanxi intrusion is genetically related to the tholeiitic basalts in the tuha basin not to the alkaline basalts in the tarim basin as suggested previously by some researchers this implies that regional exploration for the huangshanxi type cu ni deposits should be centered in the tuha basin instead of the tarim basin more specifically the uplifted areas around the tuha basin where similar intrusions may have been brought close to the surface should be carefully examined for mineralization potential intrusive relations and mass balance constraints from incompatible trace elements and sulfide abundances suggest that the huangshanxi intrusion represents a dynamic magma conduit through which multiple pulses of magma ascended to higher levels or to the surface numerical simulation of magma evolution and mixing calculations using sr nd isotopes indicate that selective assimilation of s bearing crustal materials is important for sulfide saturation during the early stages of magma evolution when lherzolites formed fractional crystallization may have also played a role in the attainment of sulfide saturation during the later stages of magma evolution when olivine websterites and gabbronorites formed in both cases immiscible sulfide droplets were retained in the conduit to form disseminated sulfide lenses while the fractionated silicate liquids and buoyant phases such as plagioclase continued to ascend extremely low pge tenors in the sulfide ores of the huangshanxi deposit suggest that the parental magma was highly depleted in chalcophile elements possibly due to previous sulfide segregation at depth

plumbotectonic evolution of the ossa morena zone iberian peninsula tracing the influence of mantle crust interaction in ore forming processes the ossa morena zone in the variscan belt of the iberian peninsula is characterized by a complex geotec tonic evolution it hosts a neoproterozoic paleozoic sequence that records the existence of two orogenic events cadomian and variscan separated by rift and stable platform stages middle cambrian to late devonian volcanogenic and sediment hosted massive sulfides skarns magmatic ni cu deposits synmetamorphic and intragranitic and perigranitic veins and replacement bodies are related to different magmatic hydrothermal systems ranging in age from 650 ma to about 250 ma the lead isotope signatures from 26 different mineral deposits show variable ratios of 206pb 204pb 17 49 18 44 207pb 204pb 15 47 15 67 and 208pb 204pb 37 37 38 78 that have low average values 9 7 but high values 38 3 as a whole the lead isotope data define an irregular cluster that plots around the stacey and kramers 1975 growth curve but clearly marks the existence of two main ore forming events during cadomian and variscan times the most radiogenic samples are from some minor zn pb stratiform sedimentary exhalative mineralization they are interpreted as having a dominantly crustal derivation 10 1 in which most of the lead was leached from a pre cadomian continental basement with a long crustal history this basement has strong geochemical affinities with the oldest rocks of the iberian terrane however most of the ore samples investigated plot below the stacey and kramers 1975 reference curve indicating polyphase but variable mixing of lead from upper crustal and mantle lead reservoirs at the terrane scale clear mixing lines between the two end member reser voirs are evident only in the oldest volcanic rock and sedimentary rock hosted massive sulfide deposits related to the cadomian late neoproterozoic early cambrian magmatic arc in the other deposit types lead isotopes have more restricted values the crustal lead is interpreted as having been derived from ancient crust 2 1 2 5 ga and the derived shales montemolin formation that predated the cadomian orogeny the mantle derived lead may have been derived from three different sources neoproterozoic tholeiitic orthoamphibolite syn cadomian calc alkaline andesite or calc alkaline metaluminous plutonic rocks intruded during the variscan orogeny the first two sources probably controlled the lead isotope signatures of the cadomian massive sulfide deposits and the variscan synmetamorphic veins the input of primitive lead is especially significant during variscan times 350 300 ma and is interpreted as having been related to the existence of a large primitive reservoir that controlled the variscan magmatic metallogenic and hydrothermal evolution of the ossa morena zone this primitive lead is recognized in most of the magmatic hydrothermal deposits including the typically crust derived w and pb bearing perigranitic hydrothermal systems likewise associated plutonic rocks have more primitive lead isotope signatures than their counterparts in other iberian terranes the lead isotope evolution of the region is consistent with recent geophysical data that suggest that a deep large mafic sill was intruded below the ossa morena zone during variscan times this sill was a likely key factor in the different pb isotope evolution of the ossa morena zone compared with the nearby iberian terranes and the entire western mediterranean province which are char acterized by lengthy crustal histories with very little input of primitive lead the extensive mantle crust inter action probably explains the wide variety and the unusual metallogenic features of the ossa morena zone

emplacement in an extensional setting of the mont lozere borne granitic complex se france inferred from comprehensive ams structural and gravity studies the emplacement mode and setting of the late hercynian mont lozere borne granitic complex french massif central which consists of several plutons is investigated structural and anisotropy of magnetic susceptibility ams studies have been carried out to characterize the internal fabrics of the granitic plutons throughout the pont de montvert borne pluton an e w trending magnetic lineation is well developed in the host rock and the thermal aureole a conspicuous e w trending lineation is interpreted as an evidence of a late orogenic extensional event to the east of the pluton the ams fabric is characterized by values of anisotropy degree p around 4 5 with a prolate ellipsoid and subsolidus structures whereas to the west the p parameter is weaker with an oblate ellipsoid and purely magmatic microstructures a gravity investigation allows determination of the 3d shape of the pluton the western part of the granitic complex is thicker than the eastern one and is interpreted as the feeder zone this suggests an eastward spreading of the magma the consistency between regional stretching and directions of ams lineations in the pluton and the shape of the complex deduced from gravity strongly argues that the emplacement mode of the complex was influenced by the regional extensional tectonic setting during the collapse of the hercynian belt

two types of brittle fracture of silicate rocks under confining pressure and their implications in the earth s crust abstract four silicate rocks granite gabbro dunite and eclogite were triaxially compressed up to a confining pressure of 3 gpa at room temperature and were found to exhibit brittle fracture behaviour from the measurements of the compressive and frictional strengths and the activity of acoustic emission ae and the observations of the microstructure of fractured specimens the pattern of fracture was found to change when the compressive strength became equal to the frictional strength two types of fracture mechanism low pressure and high pressure types were inferred the low pressure type fracture exhibits features of brittle fracture equivalent to those recorded by previous workers the features of high pressure type fracture are similar to those observed between brittle fracture and ductile creep in high temperature triaxial experiments microcracks are not concentrated close to the main fault and the main fault is sharp and oriented at approximately 45 to the stress direction this suggests that the high pressure type fracture might correspond to the transitional fracture type between the brittle and ductile regimes at room temperature for granite and gabbro samples of a few centimeters size high pressure type fracturing begins at 0 8 gpa confining pressure while for dunite and eclogite it begins at 1 0 and 2 0 gpa respectively the size effect on compressive strength under confining pressure was estimated based on the suggestion that the uniaxial strength decreases with increasing specimen size and ceases to decrease for specimens 1 m this estimation suggests that the compressive strength for a granite specimen a few meters in size would become equal to the frictional strength at confining pressures as low as 60 mpa the significance of this is that it may be necessary to model earthquakes using the high pressure type fracturing because in the absence of pore pressure 60 mpa confining pressure corresponds to a depth of 3 km faulting processes in the crust including both the initial faulting and the movement of existing faults were inferred using the experimental results and the estimated size effect on strength

the oxfordian stable isotope record δ18o δ13c of belemnites brachiopods and oysters from the kachchh basin western india and its potential for palaeoecologic palaeoclimatic and palaeogeographic reconstructions abstract the study combines the results of stable isotope 13c 18o analyses of 187 belemnites brachiopods and oysters from the middle to upper jurassic upper callovian to kimmeridgian of the kachchh basin in western india generally belemnites show lower 13c and higher 18o ratios than the benthic fauna it is proposed that this discrepancy is caused by different life habitats of both groups with belemnites spending major parts of their life in deeper water outside the kachchh basin and entering shallow areas only occasionally e g during seasonal migrations to spawning grounds a mode of life as fast swimming nektonic predators similar to many modern squid species seems plausible the study emphasises that results of stable isotope analyses should be evaluated separately for each fossil group in addition to the influence of diagenetic alteration weathering salinity changes and sea level fluctuations the ecology of the analysed fossil taxa has to be considered temperatures calculated from 18o ratios point to relatively warm conditions around the middle to late jurassic transition with no evidence for a glacial phase which had been proposed for this boundary a distinct fall in temperatures is observed during the middle oxfordian reaching a minimum in the early late oxfordian it is tempting to connect this event with the break up of gondwana causing stronger upwelling in the northwestern tethys or alternatively the influx of polar water by the opening of the transgondwanan seaway however such connections cannot be verified without further data preferably from localities in the southern malagasy gulf e g madagascar and from younger horizons kimmeridgian tithonian

carbon isotope excursions in boreal jurassic cretaceous boundary sections and their correlation potential abstract the jurassic cretaceous j k boundary is one of the most problematic points on the geological timescale the boundary is not defined by a global stratotype section and point gssp because of the absence of well defined by significant faunal turnover widely correlatable biostratigraphic levels to fix the base of the berriasian a distinct earliest berriasian positive carbon isotope excursion is identified in the boreal marine carbonate belemnites carbon records from the maurynya river northern urals and the nordvik peninsula northern east siberia the excursion is found within the top part of the upper volgian craspedites taimyrensis ammonite zone slightly above the j k boundary which was established by palaeomagnetic data because a significant positive 13 c shift was also observed immediately above the j k boundary in the tethyan guppen heuberge pelagic carbonate section switzerland this positive carbon isotope event can be regarded as a useful marker for a panboreal and boreal tethyan correlation of j k boundary beds this 13 c excursion is interpreted as a record of increased rates of organic carbon burial the 13 c data obtained previously for the upper volgian and ryazanian in different boreal regions are also analysed in this paper other well documented carbon isotope excursions with less global significance allow the creation of a composite carbon isotope curve for boreal regions that characterises the upper volgian and ryazanian in detail

geochronology petrology and hf s isotope geochemistry of the newly discovered xiarihamu magmatic ni cu sulfide deposit in the qinghai tibet plateau western china this paper reports the first set of data for the newly discovered xiarihamu magmatic ni cu sulfide deposit in the eastern kunlun paleozoic arc terrane which is located in the northern part of the qinghai tibet plateau an on going drilling campaign reveals 100 million tons of sulfide mineralization with the average grade of 0 8 wt ni and 0 1 wt cu for the deposit this makes the xiarihamu deposit one of the 20 largest magmatic ni cu sulfide deposits in the world and the largest ever found in arc settings the deposit is hosted in a small ultramafic body intruding older gabbroic and metamorphic rocks new zircon u pb isotope age data reveal that the ultramafic body 411 6 2 4 ma is 20 ma younger than the host gabbroic intrusion 431 3 2 1 ma the ultramafic body is composed predominantly of lherzolite and olivine websterite with minor dunite websterite and orthopyroxenite mineralization mainly occurs as sub horizontal to gently dipping 30 disseminated sulfide zones that are generally concordant with the lithological structure of the ultramafic intrusion the lateral extension and thickness of individual mineralized zones are up to 200 m and 100 m respectively sulfide mineral assemblages are composed of pyrrhotite pentlandite and chalcopyrite the xiarihamu ultramafic rocks show light ree enrichments and pronounced negative nb anomalies plus significant ca depletion in olivine 700 ppm ca which are characteristic of many arc basalts in the world olivine crystals in the xiarihamu ultramafic rocks have relatively primitive compositions with fo contents up to 90 mol close to the mantle value the contrasting ni contents of olivine crystals with similar fo contents from different sulfide mineralized zones in a single drill core indicate that at least two pulses of sulfide laden magma with different ni compositions were involved in the development of the deposit estimated parental magma for the xiarihamu lherzolites contains 52 4 wt sio2 and 9 8 wt mgo which are within the ranges of boninites worldwide supporting the interpretation that the xiarihamu sulfide ore bearing ultramafic intrusion is the product of subduction related boninitic magmatism the ehf t values of zircon crystals from the xiarihamu ultramafic rocks vary from 1 to 5 indicating minor crustal contamination of the parent magma the involvement of external sulfur in the genesis of the xiarihamu magmatic sulfide deposit is evident from higher 34s values of sulfide ores 3 5 to 6 8 than typical mantle value 0 2 although the actual contaminants are yet to be identified

isotopic evidence for geochemical decoupling between ancient epeiric seas and bordering oceans implications for secular curves isotopic analysis of conodonts and their host limestones sampled between two regionally extensive altered volcanic ash layers in eastern laurentia shows that a 454 ma epeiric sea maintained large lateral differences in nd and c isotope compositions this is consistent with inferred temperature salinity defined epicontinental water masses and restricted circulation between epicontinental and oceanic environments because the majority of old marine fossils and sedimentary rocks are known from epeiric seas some isotope excursions in ancient marine strata may originate from expansion and contraction of geochemically distinct epicontinental water masses rather than global scale changes in the state of the earth ocean system

fractured micro granitoid enclaves a stress marker abstract systematic parallel and steeply dipping tensile fractures within rounded to sub rounded micro granitoid enclaves are analyzed to decipher the stress condition at chitradurga granite dharwar craton south india the study is performed in two steps 1 assessing the fracturing condition through thermo mechanical model as fractures in granite may be related to thermal stresses during its cooling or to tectonics stresses 2 performing the plane strain mechanical solution for circular rigid inclusions to fractured enclaves where rock mechanics concepts of fracturing are integrated with kinematic analysis we interpret that the parallel systematic fractures in the micro granitoid enclaves developed due to the stress amplification inside enclaves when the host pluton was at shallow depth of 2 4 km the derived paleostress orientation fits well with the orientation and sense of movement to the adjacent chitradurga shear zone the deduced paleostress conditions from fractured micro granitoid enclaves are also in a good agreement with the previously revealed regional tectonics we conclude that the fractured micro granitoid enclaves are reliable stress indicator

mg ca in fossil oyster shells as palaeotemperature proxy an example from the palaeogene of central asia fossil oyster shells are well suited to provide palaeotemperature proxies from geologic to seasonal timescales due to their ubiquitous occurrence from triassic to quaternary sediments the seasonal nature of their shell growth and their relative strong resistance to post mortem alteration however the common use to translate calcitic oxygen isotopes into palaeotemperatures is challenged by uncertainties in accounting for past seawater 18o especially in shallow coastal environment where oysters calcify in principle the mg ca ratio in oyster shells can provide an alternative palaeothermometer several studies provided temperature calibrations for this potential proxy based on modern species nevertheless their application to palaeo studies remains hitherto unexplored here we show that past temperature variability in seawater can be obtained from mg ca analyses from selected fossil oyster species and specimens high resolution mg ca profiles combined with 18o were obtained along 41 fossil oyster shells of seven different species from the palaeogene proto paratethys sea central asia found in similar as well as different depositional age and environments providing comparison suitable mg ca profiles defined by continuous cyclicity and reproducibility within one shell are found to be consistent for specimens of the same species but differ systematically between species implying a dominant species specific effect on the mg ca signal two species studied here ostrea turkostrea strictiplicata and sokolowia buhsii provide an excellent proxy for palaeoclimate reconstruction from china to europe in palaeogene marine sediments more generally the protocol developed here can be applied to identify other fossil oyster species suitable for palaeoclimate reconstructions

contrasting petrological and geochemical relationships in the voisey s bay and mushuau intrusions labrador canada implications for ore genesis new data on the voisey s bay and mushuau intrusions indicate that the two bodies which were formerly grouped as the reid brook complex differ markedly in age petrology geochemistry and the scale of known mineralization u pb dating of baddeleyite and zircon has revealed that the mushuau intrusion has an age of 1 313 ga which is 20 m y younger than the 1 333 ga voisey s bay intrusion the voisey s bay intrusion is host to the 124 million tons ni cu co sulfide deposit reserves resources mineralization occurs at the base of an upper subchamber the eastern deeps subchamber and in a conduit that connects the eastern deeps to a lower subchamber the reid brook subchamber the mineralization is associated with a basal breccia that contains abundant reacted inclusions of paragneiss within the eastern deeps the basal mineralization is overlain by a varied textured troctolite that contains variable amounts of disseminated sulfide and gneiss inclusions by comparison only minor amounts of sulfide mineralization have been observed within the mushuau intrusion the mushuau intrusion comprises a layered unit that has been intruded by a stellate textured troctolite along its contact with footwall orthogneiss the layered unit consists dominantly of melatroctolite at the margin with leucotroctolite toward the center and olivine gabbro at the core the cumulates of the mushuau intrusion are richer in olivine and thus have higher mgo contents than those of the voisey s bay intrusion notwithstanding this olivines in the melatroctolite inclusions of the voisey s bay intrusion which are thought to represent disrupted cumulus layers contain up to 81 mole percent forsterite whereas those in the melatroctolite of the mushuau intrusion contain no more than 70 mole percent forsterite nickel depletion in olivine is more pronounced in the voisey s bay intrusion than in the mushuau intrusion our data indicate that the parental magmas of both intrusions were broadly basaltic mgo 8 1 wt and that the magma of the mushuau intrusion was more evolved than that of the voisey s bay intrusion yet still capable of forming olivine rich cumulates the troctolites of the voisey s bay intrusion have ce yb 22 to 27 whereas most troctolites of the mushuau intrusion have ce yb 12 to 17 the rocks of the mushuau intrusion are simple mixtures of mantle derived magma and local orthogneiss whereas the rocks of the voisey s bay intrusion are formed by multiple stages of crustal contamination including an early stage of contamination at lower midcrustal level and a late stage of contamination by tasiuyak paragneiss at upper crustal level the assimilation of the sulfide bearing tasiuyak paragneiss by magma at voisey s bay may have promoted initial sulfide saturation and or increased sulfide oversaturation thus contributing to the segregation of large amounts of sulfide liquid from magma continuing flow of magma through a dynamic conduit system at voisey s bay has caused the local accumulation of sulfide of sufficient size and grade to constitute mineable reserves

the effect of trapped liquid crystallization on cumulus mineral compositions in layered intrusions a series of calculations have been carried out to evaluate the effect on cumulus mineral compositions of solidification of trapped intercumulus liquid in orthocumulates the calculation assumes local equilibrium between phases and that the system remains chemically closed during crystallization of the trapped liquid the latter assumption is held to be valid on a scale of tens to hundreds of centimeters it is not necessary to know the composition of the trapped liquid as the calculation only requires an estimate of feo content and trapping temperature the change in composition of a mineral from that of the initially precipitated cumulus crystals to the final composition after complete solidification is termed the trapped liquid shift its magnitude depends on the modal proportions of cumulus phases and the initial porosity and is only weakly dependent on initial phase compositions trapped liquid shifts are significant when compared with mineral composition changes occurring during fractional crystallization crystallization of 30 trapped liquid gives rise to shifts of up to 10 mol percent in mg number of olivine or pyroxene the size of the shift becomes greater when the initial cumulus assemblage has a lower total feo mgo content and vice versa as a result of the relationship between trapped liquid shift and cumulus mode mineral composition variations and trends may be generated in sequences of cumulates which originally had constant compositions of cumulus minerals for example in a cyclic unit grading from a pyroxenitic base to an anorthositic top crystallization of a uniform proportion of trapped liquid will result in an apparent iron enrichment trend from bottom to top of the cycle as has been observed in the upper critical zone of the bushveld complex

sulfide saturation in mafic magmas is external sulfur required for magmatic ni cu pge ore genesis the importance of externally derived sulfur in the genesis of sulfide rich magmatic ni cu platinum group element pge deposits remains a key yet unresolved issue calculations utilizing a variety of mafic magma types indicate that in general sulfide saturation by fractional crystallization occurs after ni has been depleted due to olivine crystallization cu and pge rich layers may form during relatively later stages of closed system crystallization but unless the collection of the cotectic proportion of immiscible sulfide is extremely efficient the mass of sulfide is too small to produce an economic deposit we show that there are numerous processes that may lead to early sulfide saturation in mafic ultramafic magmas contamination of mantle derived magmas by siliceous country rocks or their partial melts will lower the sulfur content needed to induce sulfide liquid saturation typically by amounts ranging from 200 to 700 ppm the mixing of magmas particularly if the result is to lower the liquidus temperature of the mixed magma may also lower the sulfur content needed to attain sulfide saturation by similar amounts an increase in magma fo2 related to the addition of volatiles such as h2o and co2 is less effective in decreasing the sulfur concentration needed to achieve sulfide liquid saturation contamination processes that lead to an increase in the activity of sio2 in the melt and hence may promote orthopyroxene rather than olivine crystallization aid in generating relative ni enrichment in remaining liquid as a result of the lower dni mineral melt value of orthopyroxene relative to olivine although contamination and magma mixing may produce early sulfide saturation without the addition of externally derived sulfur ni rich sulfide deposits can form in such cases only from large volume open systems where the efficiency of sulfide collection is high no matter what the liquidus minerals may be without the addition of country rock derived sulfur the mass of sulfide necessary to generate economic ni cu pge concentrations requires efficient sulfide collection from large but not necessarily unrealistic volumes of magma small deposits 4 30 mt of sulfide may form from the collection of cotectic proportions of sulfide from less than 50 km3 of magma larger deposits such as those at noril sk could involve more than 200 km3 of magma this volume of magma is not unreasonable particularly in rift plume related settings despite such possibilities sulfur isotope data clearly indicate that externally derived sulfur has been involved in the formation of many large deposits and that collection of mantle derived sulfide in sufficient quantities to produce orebodies is a rare process we propose that magmatic ni cu pge sulfide ore formation normally requires significant sulfide supersaturation and that the addition of sulfur derived from xenoliths is the most viable mechanism for producing sulfide well above the cotectic proportion in mafic ultramafic magmas

analysis of the internal structure of rocks and characterization of mechanical deformation by a non destructive method x ray tomodensitometry abstract tomodensitometry is a new non destructive method which reveals the internal structure of rocks through analysis of x ray images without any damage to the sample the scanner gives a radiological density which is a function of gravimetric density and mineralogy for limestones and sandstones an attempt is made to quantify the relation between radiological density and porosity spatial variations in the values of the radiological density measured on rock core specimens that are deformed and fractured in a triaxial cell are then related to the intensity of experimental volumetric deformation

microcracks in rocks a review abstract in the past decade the number of studies about microcracks in rocks has rapidly increased this review of recent work concentrates on microcracks in rock as separate entities emphasizing microcrack morphogenesis kinematics dynamics population statistics and observational techniques cracks are produced when the local stress exceeds the local strength the local stress may be augmented by twin lamellae interactions kink bands and deformation lamellae stress concentrations at grain boundary contacts and around intracrystalline cavities local strength may be reduced along cleavage planes along grain boundaries and along any internal surface as a result of corrosion by chemically active fluids dislocations appear not to be a significant factor for crack nucleation below about 500 c in silicates spatial and temporal changes in temperature can also induce microcracking as a result of differential thermal expansion between grains with different thermoelastic moduli and thermal conductivities the amount of quartz in the rock has a significant effect on thermally induced microcracks because of its large and variable thermal expansivity the application of hydrostatic pressure between 100 and 200 mpa effectively closes most cracks but the closure may not be uniform if crack wall asperities exist hydrostatic pressure appears to stabilize cracks and make crack growth more difficult the number and average size of mechanically induced microcracks is greater in rock deformed at higher pressures the application of a deviatoric stress field on the boundaries of a rock mass results on a microscopic scale in a very complex stress system which greatly affects nucleation and propagation paths the relative amount of intragranular and intergranular cracking appears to depend upon mineralogy rock type and stress state the vast majority of stress induced microcracks in rocks appear to be extensional statistically they are predominantly oriented within 30 of the macroscopic maximum stress direction crack densities increase as macroscopic deviatoric stress increases above a threshold level crack size distributions may be either lognormal or exponential fracture in rock under compressive boundary loads is a result of the coalescence of many microcracks not the growth of a single crack some crack configurations are more favorable for coalescence than others as deviatoric stress increases and rock failure is approached the microcrack population changes spatially from random to locally intense zones of cracking away from the fault the crack density dies off rapidly to the background level a few grains away under lesser deviatoric stresses slow subcritical microcrack growth can occur as a result of stress aided corrosion at the crack tip the rate governing mechanism may be either the chemical reaction rate or the rate at which water can get to the crack tip important details still remain to be worked out

climatic fluctuations and seasonality during the late jurassic oxfordian early kimmeridgian inferred from δ18o of paris basin oyster shells abstract oxygen isotope data from biostratigraphically well dated oyster shells from the late jurassic of the eastern paris basin are used to reconstruct the thermal evolution of western tethyan surface waters during the early oxfordian early kimmeridgian interval seventy eight oyster shells were carefully screened for potential diagenetic alteration using cathodoluminescence microscopy isotope analyses were performed on non luminescent parts of shells n 264 intra shell 18 o variability was estimated by microsampling along a transect perpendicular to the growth lines of the largest oyster shell the sinusoidal distribution of the 18 o values along this transect and the dependence of the amplitude of variations with bathymetry suggest that intra shell variability reflects seasonal variations of temperature and or salinity average amplitudes of about 5 c in shallow water environments and of about 2 3 c in deeper offshore environments are calculated these amplitudes reflect minimum seasonal temperature variation our new data allow to constrain existing paleotemperature trends established from fish tooth and belemnite 18 o data and are in better agreement with paleontological data more specifically a warming trend of about 3 c is reconstructed for oceanic surface waters during the early to middle oxfordian transition with maximum temperatures reaching 24 c in the transversarium zone late middle oxfordian from the transversarium zone to the bimmamatum zone a cooling of about 7 c is indicated whereas from the bimmamatum zone temperatures increased again by about 7 c to reach 24 c in average during the cymodoce zone early kimmeridgian

acadian synorogenic mafic intrusions in the maine appalachians two belts of syn acadian mafic intrusions the central maine belt is progressively more altered and metamorphosed toward the southwest at the northeast end the moxie pluton represents the least altered and most important example in the belt forsterite contents of the most primitive olivines are consistent with the derivation of the earliest magma from a largely unfractionated mantle melt the coastal maine belt is spatially associated with the siluro devonian coastal volcanics the age difference however between the volcanics and plutonics suggests that they may not be directly related the important pocomoonshine gabbro appears to represent the well layered roof zone of a major fractionated body mineral compositions are similar to those in the moxie pluton and suggest a similar primary magma intrusions in both belts have complex contacts pronounced contact aureoles and were all deformed by late acadian deformation modified journal abstract

comparison of carbonate c and o stable isotope records across the jurassic cretaceous boundary in the tethyan and boreal realms abstract carbon and oxygen stable isotope records were compared for jurassic cretaceous j k boundary sections located in the tethyan realm brodno western slovakia and puerto escano southern spain bulk limestones and the boreal realm nordvik peninsula northern siberia belemnites since a detailed biostratigraphic correlation of these tethyan and boreal sections is impossible due to different faunal assemblages correlation of the isotope records was based on paleomagnetic data this novel approach can improve our understanding of the synchroneity of individual isotope excursions in sections where detailed biostratigraphic correlation is impossible no significant excursions in either the carbon or oxygen isotope records to be used for future boreal tethyan correlations were found around the j k boundary the upper tithonian and lower berriasian magnetozones m20n to m18n in the studied sections at the nordvik section where a much longer section middle oxfordian basal boreal berriasian was documented the transition from the middle oxfordian to the kimmeridgian and further to the volgian is characterized by a decrease in belemnite 18 o values from 18 o values up to 1 6 vs v pdb in the oxfordian to values between 0 3 and 0 8 in the late volgian and earliest boreal berriasian this trend which has previously been reported from the russian platform and tethyan realm sections corresponds either to gradual warming or a decrease in seawater 18 o supposing that the oxygen isotope compositions of seawater in the arctic boreal and tethyan realms were similar then the differences between oxygen isotope datasets for these records indicate differences in temperature the boreal tethyan temperature difference of 7 9 c in the middle and late oxfordian decreases towards the j k boundary indicating a significant decrease in latitudinal climatic gradients during the late jurassic two positive carbon isotope excursions recorded for the middle oxfordian and upper kimmeridgian in the nordvik section can be correlated with a similar excursion described earlier for the russian platform minor influence of biofractionation at the carbon isotopes and the influence of migration of belemnites to deeper slightly cooler water at the oxygen isotopes cannot be excluded for the obtained belemnite data

reconstruction of late bajocian bathonian marine palaeoenvironments using carbon and oxygen isotope ratios of calcareous fossils from the polish jura chain central poland abstract oxygen and carbon isotope analyses were carried out on upper bajocian bathonian calcitic belemnite rostra and oyster shells as well as aragonitic ammonite nautiloid and trigoniid shells from the ore bearing czestochowa clay formation in south central poland all samples were studied by means of cathodoluminscence microscopy trace element x ray and scanning electron microscope sem analysis in order to select best preserved material sem studies allowed classifying some aragonitic ammonite and nautiloid shells 99 aragonite as diagenetically altered average 18o values of oysters belemnites and trigoniids translate into relatively low palaeotemperatures of 10 1 9 2 and 7 4 c respectively the comparable 18o values of bivalves and belemnites indicate that belemnites had a nectobenthic lifestyle and did not record surface water temperatures the ammonite fauna is interpreted to have been nektonic however palaeotemperatures derived from ammonite 18o around 18 6 c may be overestimated due to a lower than normal marine salinity of surface waters the reduced salinity is inferred as well from sedimentological observations and faunal composition the obtained 18o values indicate cool climatic conditions during the late bajocian bathonian in south central poland which may have been linked with the occurrence of a cold climatic episode despite the fact that all studied shells were not precipitated in carbon isotope equilibrium with ambient waters the 13c shell values enabled us to roughly estimate isotope composition of dissolved inorganic carbon dic in the late bajocian bathonian sea of south central poland water 13cdic values calculated from ammonite 13c are lower in comparison to 13cdic values calculated from oyster and belemnite carbon isotope ratios which in conjunction with ammonite 18o values indicates lower salinity of surface or shallow near coastal waters

integrating ams data with structural studies from granitoid rocks of the eastern dharwar craton south india implications on successive fabric development and regional tectonics abstract five successive deformation phases have been identified from structural analysis of granitoid and gneissic rocks of the study area the magnetic foliation data of the studied granitoids show two distinct nw and ne trending sets the nw trending magnetic foliation is found to be essentially parallel to the mesoscale planar structures of regional d1 d2 deformations and is thus correlated with the d1 d2 phases on the contrary the ne trending magnetic foliation appears to be kinematically compatible with the nw se compression direction deciphered from conjugate ductile shear zone patterns of the d3 event combining ams field and microstructural data the granitoid outcrop have been separated into older d1 d2 and younger d3 domains the published geochronological data from the area when compared with the established d1 d2 and d3 domains shows a good correlation pointing tentatively the timing of the d1 d2 deformation phase to be 2550 ma while the d3 phase to be 2524 ma hence the study highlights the importance of combining ams data with field and microstructural studies to constraint the timing of regional successive deformation imprints it also helps to identify the chronologically separated emplacement phases of the granitoid massif in question which would not have been possible otherwise

high northern palaeolatitude jurassic cretaceous palaeotemperature variation new data from kong karls land svalbard abstract the traditional view of warm equable global climates in the mesozoic with weakly developed latitudinal temperature gradients has been challenged by several recent studies however reliable high palaeolatitude palaeotemperature data is still rare in this study palaeotemperature data based on oxygen stable isotope palaeothermometry of well preserved mid jurassic to lower cretaceous belemnites from kong karls land svalbard are presented these data show cool high latitude marine isotopic palaeotemperatures for endemic species during the lower to mid valanginian 7 7 c which may be compatible with the formation of high latitude ice middle bathonian to kimmeridgian samples give warmer isotopic palaeotemperatures 9 4 c whilst samples from the aalenian to bajocian give isotopic palaeotemperatures which are warmer still 12 7 c comparison of the callovian temperatures with those from a mid latitude location shows them to be warmer than would be expected if previous latitudinal temperature gradients are correct this may be due to the ameliorating effect of oceanic heat transport pole wards from the panthalassa ocean via the south anyui ocean

strontium isotope profile of the early toarcian jurassic oceanic anoxic event the duration of ammonite biozones and belemnite palaeotemperatures we profile 87sr 86sr 13c 18o sr ca mg ca and na ca in belemnites through pliensbachian and toarcian strata on the yorkshire coast uk which include the early jurassic oceanic anoxic event the 87sr 86sr profile shows that the relative duration of ammonite subzones differ by a factor of up to 30 the lower jurassic exaratum subzone is 30 times longer than the clevelandicum subzone because the exaratum subzone in yorkshire which contains the anoxic event is condensed by a factor of between 6 5 and 12 2 times relative to adjacent strata using our 87sr 86sr profile the resolution in correlation and dating attainable in the interval is between 1 5 m and 15 m of section and better than 0 25 myr in parts of the sequence this stratigraphic resolution equals that attainable with ammonites a new age model is provided for late pliensbachian and early toarcian time that is based on the 87sr 86sr profile through the sequence the sr ca mg ca na ca and 18o of belemnite carbonate covary suggesting that elemental ratios may be useful for palaeotemperature measurement our 13cbelemnite data splits into three the previously reported positive isotope excursion to 6 5 in the early toarcian we speculate that the excursion s resulted from addition to surface waters of isotopically heavy co2 via ebullition of methanogenic co2 from the sediment during early burial of organic rich 10 toc sediments

confirmation of two types of fracture in granite deformed at temperatures to 300 c abstract shimada m 1992 confirmation of two types of fracture in granite deformed at temperatures to 300 c in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 259 268 dry granite samples were triaxially compressed at confining pressures of up to 2 gpa at temperatures to 300 c the existence of two types of fracture previously observed in room temperature experiments was confirmed the low pressure type occurs when the compressive strength is higher than the frictional strength and the high pressure type occurs when the compressive strength is equal to the frictional strength the rate of increase of strength with confining pressure in the high pressure type regime is lowered as temperature increases as if an ideal coulomb fracture criterion at a fracture angle of 45 might be applicable with increasing temperature near the boundary between the low and high pressure type regimes unusually high values of strength were measured the specimens after such runs gave the suggestion that both low and high pressure types of fracture coexist there are some discrepancies in the values of strength from room temperature and those performed previously which are considered to be due to the experimental variability however the present experimental results to 300 c confirmed that two types of brittle fracture exist and that the fracture type changes when the compressive strength becomes equal to the frictional strength this tends to confirm previous speculations that many crustal fractures are of the high pressure type if so the low pressure type of fracture in which precursory ae acoustic emission activity before final fracturing is observed would be anticipated only at very shallow depth at ordinary pore pressure conditions it would occur at the depth of seismogenic zones only in the case of very high pore pressure

isotopic evidence for partial geochemical decoupling between a jurassic epicontinental sea and the open ocean abstract we report stable isotope ratios 13c 18o minor and trace elements mn fe sr mg together with ca concentrations from bivalve shells and belemnites from the middle upper jurassic sundance seaway western united states we compare them with coeval open ocean tethyan data and reconstruct the palaeo circulation of seaway waters the sundance seaway was a 2000 km long epicontinental sea with a single entrance at mid latitudes 55 60 n which would have fostered substantial evolution of seawater chemistry relative to its open ocean source samples are distributed across the 13 million year marine history of the seaway and across a 540 km east west transect spanning wyoming delta13c values are in the same range as tethyan data and this suggests that they might record global changes in the carbon cycle with one exception in the oxfordian delta18o values from the seaway are in contrast highly depleted compared with tethyan data 2 to 6 and they indicate unrealistically high palaeotemperatures 20 40 c assuming an isotopic composition of seawater of 1 as generally used for the jurassic given more realistic temperature estimates from mg ca ratios of bivalve shells 10 25 c we explain such negative 18o values by the southward inflow of normal salinity isotopically depleted 3 4 arctic water into the seaway such water would become progressively more saline and denser as it flowed towards the southernmost portion of the seaway in the late jurassic characterised by wetter climate conditions less dense sundance waters may have instead exhibited a northward flow reducing the southward surface flow from the arctic the observed partial geochemical decoupling of sundance seaway water masses from the open ocean strongly recommends caution in interpreting the geochemical record of ancient shallow seas where local regional and global drivers of change all need to be considered

platinum group elements in svecokarelian nickel copper deposits finland platinum group elements and au have been analyzed from five finnish ni cu occurrences kotalahti vammala laukunkangas hitura and petolahti from a layered mafic intrusion in northern finland siika kaemae and from several weakly mineralized ultramafic bodies in lapland platinum group element values recalculated to 100 percent sulfide are slightly higher for rh pt and pd in the kotalahti deposit pd 72 ppb pd ir 22 6 than in laukunkangas pd 29 ppb pd ir 9 1 and in vammala pd 25 ppb pd ir 9 7 which exhibits the lowest platinum group element values of the ni cu occurrences analyzed the ultramafic hosted hitura deposit with a flat chondrite normalized distribution platinum group element pattern has a platinum group element concentration 20 to 40 times higher than those in laukunkangas and vammala the nickel deposit of petolahti pd 813 ppb in a postsvecokarelian diabase dike has platinum group element values close to those of hitura pd 750 ppb but the pd ir ratio of hitura 4 66 is much lower than that of petolahti 59 7 the slope of the platinum group element distribution pattern for siika kaemae is steep and the deposit has the highest concentrations analyzed in this study pt and pd being up to 656 and 1 790 ppm respectively recalculated to 100 percent sulfides the platinum group element values of the weakly mineralized ultramafic bodies of lapland are very low all well below the values reported from laukunkangas and vammala the hitura type ultramafic intrusion differs markedly from the other analyzed host rocks of the svecokarelian ni cu occurrences and its platinum group element distribution pattern corresponds to the komatiitic character observed also in major and trace elements of the rocks the fractionated platinum group element pattern of the kotalahti and laukunkangas deposits match well with the observations of rock sequences and geochemistry of the host rocks

crustal origin of hercynian peraluminous granitic batholiths of central spain petrological geochemical and isotopic sr nd constraints abstract in central spain it is possible to distinguish two main types of peraluminous late hercynian granites the pi types and the ps types the distinction between both types is made on the basis of differences in peraluminosity ps types are more peraluminous than pi types and also on the appearance of some characteristic mafic minerals ps types have biotite cordierite and monazite as the most typical accessory phase whereas pi types have biotite amphibole in the less evolved facies and allanite as the accessory mineral both granite types have similar trace element ratios and initial sr nd and pb isotopic signatures initial 87sr 86sr ratios of both types exhibit a large range from 0 7073 to 0 7193 whereas initial end varies in a restricted range from 5 4 to 6 6 the scarce associated basic rocks do not play a significant role in the chemical variability of these peraluminous granites which follow low pressure crystal fractionation trends from granodiorite monzogranite parental magmas mixing and afc modelling of sr and nd isotopic data reveal an unrealistically high mantle contribution based on major and trace element and isotopic data an orthogneissic protolith for both granitic series is proposed nevertheless none of the metamorphic country rocks of central spain has the appropriate sr isotopic composition to satisfy the origin of these granitic rocks and so it is argued that progressive isotopic re equilibration of crustal material during the granulization of the lower hercynian crust together with the possibility of isotopic disequilibrium during melting as has been demonstrated in migmatitic terranes in nearby areas may explain the isotopic differences between the granites and the high level metamorphic country rocks

oman diopsidites a new lithology diagnostic of very high temperature hydrothermal circulation in mantle peridotite below oceanic spreading centres abstract mafic ultramafic dykes scattered in the mantle section of ophiolites are generally crystallisation products from common silicate melts in the frame of a global survey of these melt migration relics in the oman mantle harzburgites we discovered a peculiar lithology made essentially of pure diopside 0 95 m g m g f e total 1 whose characteristics do not match a magmatic or mantle origin arguments against a magmatic or mantle origin for these diopsidites combine compositional and textural evidence in spite of their refractory composition they are strongly depleted in cr cr2o3 0 2 wt by the same way other minor elements al ti na and rare earth elements have peculiarly low abundances and plot away from magmatic differentiation trends in a few samples the paragenetic association includes pure anorthite an up to 0 99 minor amounts of forsterite fo 0 95 or traces of andradite when not deformed the diopsides are automorphic and their texture points to metamorphic growth in a matrix composed of antigorite and or carbonate diopsidites have textures reminiscent to that of skarns developing in contact metamorphic halos or that of rodingite frequently present in the serpentine bodies of the ophiolitic crust they frequently appear as dykes former cracks with a few mm to few tens of cm wide transitional zones which contain high amounts of hydrous minerals between the diopsidite facies and its host rock the diopsidites are not randomly distributed in the oman ophiolite being more abundant near former asthenospheric diapirs emplaced at shallow depth in the lithosphere we interpret the diopsidites as the footprint of very high temperature circulation of seawater and carbonated fluids 800 c which may have leached plagioclase rich lithologies before penetrating the mantle as shown by a well developed positive eu anomaly our data confirm the prediction of mccollom and shock t m mccollom e l shock fluid rock interactions in the lower oceanic crust thermodynamic models of hydrothermal alteration j geophys res 103 b1 1998 547 575 who proposed that common anhydrous minerals like pyroxene plagioclase and olivine may crystallise from high temperature fluids intermediate between silicate melts and supercritical water this confirms that there is no clear cut thermal and chemical boundary between the fields of magmatic and hydrothermal crystallisations

benthic foraminiferal mg ca paleothermometry a revised core top calibration core top samples from different ocean basins have been analyzed to refine our current understanding of the sensitivity of benthic foraminiferal calcite magnesium calcium mg ca to bottom water temperatures bwt benthic foraminifera collected from hawaii little bahama bank sea of okhotsk gulf of california ne atlantic ceara rise sierra leone rise the ontong java plateau and the southern ocean covering a temperature range of 0 8 to 18 c were used to revise the cibicidoides mg ca temperature calibration the mg ca bwt relationship of three common cibicidoides species is described by an exponential equation mg ca 0 867 0 049 exp 0 109 0 007 bwt stated errors are 95 ci the temperature sensitivity is very similar to a previously published calibration however the revised calibration has a significantly different preexponential constant resulting in different predicted absolute temperatures we attribute this difference in the preexponential constant to an analytical issue of accuracy some genera notably uvigerina show apparently lower temperature sensitivity than others suggesting that the use of constant offsets to account for vital effects in mg ca may not be appropriate downcore mg ca reproducibility as determined on replicate foraminiferal samples is typically better than 0 1 mmol mol 1 2 s e thus considering the errors associated with the cibicidoides calibration and the downcore reproducibility bwt may be estimated to within 1 c application of the revised core top mg ca bwt data to cenozoic foraminiferal mg ca suggests that seawater mg ca was not more than 35 lower than today in the ice free ocean at 50 ma

a review of the broad pattern of jurassic sea level changes and their possible causes in the light of current knowledge abstract an assessment is made of the current state of research into jurassic sea level changes based on new insights into depositional patterns in relation to these changes and new stratigraphic information from several widely separated regions across the world the bearing of this information on alternative models respectively involving sea level rise interrupted by stillstands or falls is then evaluated the gross pattern appears to be one of more or less gradual rise of sea level through the period interrupted by episodes of comparative stillstand rather than eustatic fall and several episodes of significant regression are shown to be the result of regional tectonics major episodes of eustatic rise took place in the early hettangian early sinemurian early pliensbachian early toarcian early and late bajocian middle callovian and late oxfordian to kimmeridgian a significant episode of rapid and very extensive regression possibly global took place at the end of the triassic but other regressive episodes in the late aalenian bathonian late oxfordian kimmeridgian and tithonian are clearly only regional in extent there is no evidence for glacioeustasy and most if not all of the regional or global changes recognised can readily be related to plate tectonics the events at the triassic jurassic boundary seem to be the result of mantle plume activity centred on the central atlantic region

hydrothermal nickel deposits secular variation and diversity abstract hydrothermal nickel systems are one of the most puzzling mineral systems that involve trace element mobility in the earth s crust nickel is an abundant element in the crust however the processes that are involved in its mobility and accumulation at ore scale are challenging a new empirical stochastic model is required to gain a deeper insight into these systems this special issue presents several studies on hydrothermal nickel accumulations world wide aiming to stimulate the debate on this intriguing deposit type

geochemistry of the j m howland reef of the stillwater complex minneapolis adit area i sulfide chemistry and sulfide olivine equilibrium platinum mineralization in the stillwater complex occurs within a complex sequence of olivine bearing plagioclase rich cumulates about 400 m above the base of the banded zone the reef consists of a 2 m thick layer of disseminated sulfides extending over the entire strike length of the complex in the area of this study the host rock to the reef sulfides shows a lateral transition over a strike length of 700 m from a heterogeneous olivine plagioclase cumulate mixed rock to a plagioclase olivine cumulate containing a high proportion of postcumulus bronzite with olivine preserved only as rare resorbed cores on bronzite grains platinum group elements within the reef correlate strongly with abundances of sulfides which show convincing textural evidence for having originated as immiscible sulfide liquid strong correlations are also observed between all six platinum group elements ni and cu despite the gradation in host rock mineralogy the sulfide fraction of the reef displays a constant bulk composition over 700 m of strike length containing 9 3 percent ni 6 9 percent cu and approximately 0 7 percent total platinum group elements principally pd these platinum group element concentrations are two to three orders of magnitude higher than those found in typical magmatic sulfide deposits and are attributed to equilibration of sulfide liquid with a very large volume of silicate melt olivines from the reef show a range of compositions from fo 71 to fo 85 and from 2 400 to 4 500 ppm ni a positive correlation is observed between nio and feo in olivines from sulfide bearing samples indicating ni fe exchange between olivine and sulfides on a local scale such that ni contents of olivines were buffered by that of the sulfide phase a value of 9 70 or 1 49 is obtained for the ni fe distribution coefficient between sulfide and olivine in agreement with values obtained at magmatic temperatures by boctor 1982 these observations may be interpreted in the framework of the plume model of campbell et al 1983 a pulse of replenishing magma enters the stillwater chamber as a buoyant plume and subsequently spreads to form a layer of hybrid melt sulfide liquation and olivine crystallization occur within the plume and the hybrid layer in response to mixing and subsequent cooling sulfide liquid attains high platinum group element concentrations during turbulent ascent and spreading of the plume crystallization of olivine from the hybrid layer gives rise to olivine sulfide boulders which settle to the floor of the chamber reaction between the boulders and the evolved liquid at the bottom of the chamber causes olivine to become more iron rich subsequent reequilibration between olivine and sulfide grains gives rise to the observed ni fe distribution

chemical and mineralogical heterogeneity in the basal zone of the partridge river intrusion implications for the origin of cu ni sulfide mineralization in the duluth complex midcontinent rift system copper nickel sulfide mineralization in the partridge river intrusion of the 1 1 ga duluth complex is restricted primarily to a 100 m thick zone near the base of the intrusion which is heterogeneous at meter scales in terms of both sulfide contents and rock types which include dunite melatroctolite troctolite leucotroctolite gabbro olivine gabbro gabbronorite and rare norite olivine rich troctolites and melatroctolites appear to have required mineral accumulation on a substrate whereas augite troctolite and gabbros are thought to have formed via in situ crystallization of magmas ranging in composition from high al olivine tholeiite to high ti tholeiite 18o values of orthopyroxene poor rocks in the partridge river intrusion range from 5 2 to 6 7 18o values of 6 7 are consistent with less than 20 contamination by high 18o metasedimentary country rock either via devolatilization or local partial melting rocks with greater than 15 orthopyroxene gabbronorites and norites are characterized by 18o values in excess of 6 9 and required the assimilation of larger amounts of siliceous country rocks sulfur isotopic values in leucotroctolitic rocks that contain less than 400 ppm s and that overlie the basal zone range between 1 5 and 2 values that are consistent with those of mantle derived sulfur in contrast 34s values in the basal zone range from 1 4 to 10 5 where the 34s enriched samples require an input of sulfur from metasedimentary country rocks 34s values of the rocks in the basal zone correlate with variations in olivine fo content but not with s abundance the wide range in 34s values of rocks in the basal zone strongly suggests that magmas interacted with layers in the sedimentary country rocks that were themselves characterized by variable sulfide contents and 34s values the s isotopic data suggest that the heterogeneity observed in the basal zone results from the emplacement of relatively thin sheets of compositionally distinct magma all rock types present in the basal zone can be produced as a result of variable degrees of fractionation of a parental high al olivine tholeiite followed by varying degrees of contamination of derivative liquids by country rocks the s contamination process was essential for the development of cu ni mineralization and was restricted to the earliest stages in the development of the duluth complex at a time when volatile species such as s and h2o and low t partial melts of country rocks were available to magmas

microfracturing damage and failure of brittle granites 1 the evolution of stress induced damage and the eventual brittle failure are experimentally analyzed for mount scott granite of oklahoma we quantify the damage intensity in two methods and directly compare model predictions and actual damage the 14 samples of the medium grain size granite were loaded triaxially at dry conditions room temperature and under 41 mpa confining pressure microfractures were mapped in five samples and the majority of them 80 belong to two groups tensile microfractures trending subparallel to the loading axis and shear microfractures trending 11 40 off the loading axis the tensile microfractures dominate the low stress stage and they remain intragranular with a stress increase the relative density of shear microfractures increases with increasing stresses and they formed elongated intergranular zones of coalescing microfractures we compared two independent values of damage intensity 1 the macroscopic experimentally measured reduction of the deformation modulus and 2 the expected reduction of this modulus calculated with several damage models for the density of the mapped microfractures our fracture density data best fit the model of noninteracting cracks of kachanov 1992

geochemistry of the kalatongke ni cu pge sulfide deposit nw china implications for the formation of magmatic sulfide mineralization in a postcollisional environment the kalatongke also spelt as karatungk ni cu platinum group element pge sulfide deposit containing 33 mt sulfide ore with a grade of 0 8 wt ni and 1 3 wt cu is located in the eastern junggar terrane northern xinjiang nw china the largest sulfide ore body which occupies more than 50 vol of the intrusion y1 is dominantly comprised of disseminated sulfide with a massive sulfide inner zone economic disseminated sulfides also occur at the base of the intrusions y2 and y3 the main host rock types are norite in the lower part and diorite in the upper part of each intrusion enrichment in large ion lithophile elements and depletion in heavy rare earth elements relative to mid ocean ridge basalt indicate that the mafic intrusions were produced from magmas derived from a metasomatized garnet lherzolite mantle the average grades of the disseminated ores are 0 6 wt ni and 1 1 wt cu whereas those of the massive ores are 2 wt ni and 8 wt cu the pge contents of the disseminated ores 14 69 ppb pt and 78 162 ppb pd are lower than those of the massive ores 120 505 ppb pt and 30 827 ppb pd however on the basis of 100 sulfide pge contents of the massive sulfides are lower than those of the disseminated sulfides very high cu pd ratios 4 5 104 indicate that the kalatongke sulfides segregated from pge depleted magma produced by prior sulfide saturation and separation a negative correlation between the cu pd ratio and the pd content in 100 sulfide indicates that the pge content of the sulfide is controlled by both the pge concentrations in the parental silicate magma and the ratio of the amount of silicate to sulfide magma the negative correlations between ir and pd indicate that the massive sulfides experienced fractionation

petrology of the st stephen intrusion and the genesis of related nickel copper sulfide deposits the st stephen intrusion is a tholeiitic mafic ultramafic intrusion of devonian age occurring in the gander terrane of the appalachian orogen the intrusion is dominated by olivine plagioclase cumulates olivine cumulates and plagioclase cumulates olivine ranges in composition from fo 61 to fo 85 and plagioclase from an 43 to an 89 variations in the compositions of clinopyroxene and orthopyroxene are within wo sub 42 47 en sub 37 50 fs sub 6 18 and wo sub 3 3 en sub 50 71 fs sub 26 47 respectively the cr cr al and mg mg fe super 2 ratios of chromites range from 0 25 to 0 75 and 0 01 to 0 65 respectively this appears to have resulted from the changes in the composition of the melt from which chromites were crystallized and reaction of the early formed cumulus chromites with the intercumulus melt the observed crystallization sequence olivine chromite olivine plagioclase olivine plagioclase clinopyroxene plagioclase clinopyroxene orthopyroxene olivine plagioclase orthopyroxene clinopyroxene plagioclase clinopyroxene appears to have resulted from simple fractional crystallization of a common tholeiitic parent magma the composition of the parent magma seems to have an affinity to the mid ocean ridge basalts the intrusion contains numerous zones of significant ni cu sulfide mineralization the principal sulfide minerals are those typical of magmatic assemblages pyrrhotite pentlandite and chalcopyrite ni and cu concentrations reach 2 40 and 3 90 percent respectively platinum group element concentrations are generally low with maximum abundances in massive sulfides for example not exceeding 62 ppb attainment of sulfur saturation in the st stephen magma during the early stages of the differentiation corresponds to the appearance of plagioclase on the liquidus following crystallization of about 10 percent of the olivine the nickel depleted nature of olivines at this interval can be explained by fractional crystallization of olivine and sulfide in the proportion of 50 1 an earlier segregation of sulfide from the parental magma seems to be responsible for the very low levels of platinum group elements in the interstitial sulfides associated with the olivine cumulates preferential assimilation of the sulfide rich portions of the country rock metasediments and attainment of sulfide silicate equilibrium on a local scale are believed to have played important roles in the formation of large pyrrhotite rich sulfide bodies

thermal barriers and the fate of perched faunas thermal barriers provide an explanation for the geologically sudden extinction of benthic faunas of epeiric seas when these seas disappeared by contracting to the open ocean biotic interactions could not have caused the sudden extinctions and neither could reduction of the regional area of seafloor because substantial areas of shallow seafloor remained along neighboring continental shelves when epeiric seas drained instead temperature contrasts must have been responsible epeiric seas had strongly seasonal climates and when some receded to continental margins many of their species would have encountered waters that failed to provide the maximum or minimum temperature required for reproduction when epeiric seas receded poleward equatorward or into coriolis driven currents many species faced lethal temperatures the history of the jurassic sundance sea provides a striking example of the fate of a warm adapted fauna driven westward into an area dominated by a cool coriolis driven current

fe ni exchange between olivine and sulphide liquid implications for oxygen barometry in sulphide saturated magmas abstract in order to better understand the behaviour of nickel in magmatic processes we have measured the apparent equilibrium constant k d for the exchange of fe and ni between coexisting olivine and sulphide liquid at controlled oxygen and sulphur fugacities f o 2 10 8 10 10 and f s 2 10 2 10 4 over the temperature range 1200 to 1400 c and with 5 to 50 wt nickel in the sulphide liquid measured values of k d are independent of temperature and sulphur fugacity but increase linearly with the nickel content of the sulphide liquid and follow a power law increase with oxygen fugacity behaviour that is consistent with previous measurements of k d under controlled conditions of f o 2 and f s 2 the variation of k d with melt nickel content and f o 2 is most likely the result of nonideal mixing in the sulphide liquid which results in a decrease in nis fes with melt metal sulphur ratio as a consequence of the systematic dependence of k d on f o 2 a new oxygen barometer is proposed for estimating oxygen fugacity in igneous rocks that were cosaturated in olivine and sulphide liquid application of the experimental results to natural samples shows that the relatively large variations that exist in k d values from different olivine sulphide saturated rock suites can be interpreted as arising from variations in f o 2 and or the nickel content of the sulphide liquid oxygen fugacities calculated for oceanic basalt samples using the proposed fe ni exchange oxybarometer are found to be relatively high 10 8 5 10 10 4 which is in accord with the range of values determined using glass ferric ferrous ratios moreover the very low f o 2 10 14 calculated for the mafic dike from disko island is consistent with the presence of native iron in these samples and is in quantitative agreement with indicators of f o 2 based on chromite and olivine melt partitioning of vanadium consideration of the f o 2 exhibited by olivine sulphide saturated intrusive suites reveals a range from relatively oxidized i e similar to oceanic basalts to values at or below that of disko island field petrographic and geochemical evidence suggests that the production of the low f o 2 suite of samples is probably the result of reduction accompanying the assimilation of carbonaceous country rock

geochronological and geochemical characterization of magmatic hydrothermal events within the southern variscan external domain cevennes area france geochronological mineralogical and geochemical analyses have been focussed on the mont lozere borne plutonic complex and surrounding rocks cevennes french massif central in which b w sn and as au sb mineralization is encountered two main results are highlighted 1 the existence of a 301 306 ma magmato hydrothermal event unrelated to the emplacement of the pont de montvert borne plutonic body at 316 ma 2 the magmatic and hydrothermal features are strongly associated both in time and in space thus demonstrating an intimate connection between mineralizing processes and magmatism in this part of the french massif central we also show that mineralization and associated hydrothermal occurrences do not correspond to a simple and single geochemical signature and that a contamination model must be invoked in order to account for the complexity of isotopic results this study demonstrates that the application of the o and h isotopic signatures as tracers of the source and nature of fluids in an orogenic context requires some specific care finally a model of the tectonic magmatic hydrothermal evolution of the study area is suggested in which we discuss two alternative scenarios the first one implies the existence of two different hydrothermal mineralizing events bo w sn and as au sb ones the second one suggests the same source for all hydrothermal and mineralized structures

stable isotopic constraints on fluid rock interaction and cu pge s redistribution in the sonju lake intrusion minnesota the sonju lake intrusion part of the 1 1 ga midcontinent rift related beaver bay complex is a 1 200 m thick strongly differentiated layered sequence of mafic cumulates located in northeastern minnesota basal melatroctolite and dunite layers are overlain by troctolite gabbro fe ti oxide rich gabbro apatite diorite and monzodiorite stratigraphic intervals rich in pt pd cu and s occur over 500 m in the fe ti oxide rich gabbro and apatite diorite units peak concentrations show offsets that are similar to those found in other tholeiitic layered intrusions concentrations of pd in excess of 100 ppb are confined to the lowermost 25 m of the interval copper shows a sharp increase to 630 ppm above the pd rich interval sulfur contents are low 375 ppm in the cu rich interval but they increase to values as high as 3 150 ppm above in the apatite diorite disseminated sulfides in the intrusion have 34s values that range from 2 2 to 3 per mil vienna canyon diablo troilite v cdt and suggest that contamination by country rock sulfur was not an important process in the formation of the metal rich interval 18o values of plagioclase from the intrusion range from 5 6 to 12 0 per mil v smow and indicate that a relatively low 18o fluid 18o 3 5 interacted with the rocks of the intrusion at temperatures less than 275 c clinopyroxene and fe ti oxides ilmenite with minor amounts of titanomagnetite show much more restricted ranges in 18o values 4 6 5 7 and 5 5 6 7 per mil respectively and attest to the kinetic control of the oxygen isotope exchange process the externally derived fluid that interacted with rocks now enriched in platinum group elements pge cu and fe sulfide minerals locally liberated sulfur and replaced chalcopyrite and pyrite with goethite in the cu rich zone goethite that replaces chalcopyrite may contain up to 8 5 weight percent cu it is evident that hydrothermal alteration resulted in a decoupling of copper and sulfur with sulfur being transferred out of the cu rich interval interaction between rocks in the pge cu s interval of the sonju lake intrusion and an externally derived fluid at low temperatures modified what appears to have been a primary stratigraphic metal sulfur zonation the effects of hydrothermal alteration on pge and base metal sulfide mobility and redistribution must be understood before models of primary zonation processes can be meaningfully applied

compositional variations of olivine and sulfur isotopes in the noril sk and talnakh intrusions siberia implications for ore forming processes in dynamic magma conduits olivine from the noril sk i main and northwestern talnakh ore bearing intrusions in the noril sk region occurs as inclusions discrete grains and poikilitic crystals the original compositions of olivine inclusions have been well preserved by their host oikocrysts from reaction with interstitial silicate and sulfide liquids in contrast the compositions of discrete and poikilitic olivine crystals have been variably modified by reequilibration with trapped silicate and sulfide liquids there are abrupt changes in the contents of nickel in olivine inclusions 500 1 500 ppm between different rock units in all three intrusions which indicates that the different rock units in these intrusions are not related to each other via in situ differentiation of a common parental magma but rather are consistent with separate pulses of magma with variable degrees of differentiation possibly involving olivine crystallization and assimilation of siliceous crustal material in a staging chamber the 34s values of the samples with high sulfur contents 800 ppm sulfur from all three ore bearing intrusions vary between 8 and 14 per mil two sulfur poor samples 600 ppm sulfur from the northwestern talnakh intrusion yield 34s values of 1 5 and 3 6 per mil these values are similar to the values of the sulfur poor rocks from the ore barren intrusions in the region and illustrate the fact that high sulfur contents couple with increasing 34s values such a relationship is consistent with the addition of crustally derived 34s enriched sulfur to the magma of the ore bearing intrusions in contrast to other models of sulfide segregation in closed systems we propose that sulfide segregation occurred in an open system and the magma involved was undersaturated in sulfur and undepleted in chalcophile elements we envision that the 34s enriched sulfur was introduced via circulating fluids that transported sulfur from evaporite in the underlying sedimentary sequence to the magma in a dynamic magma conduit the immiscible sulfide liquids that segregated during sulfur contamination settled down in the wider parts of the conduit as the magma continued to travel successive pulses of new magma entered the conduit reacted with the early sulfide and displaced much of the early magma in the conduit the ore bearing intrusions are thought to have crystallized within the wider parts of the conduits and their voluminous sulfide poor peripheral sills represent some if not all of the magma that flowed out of the conduits

meta igneous origin of hercynian peraluminous granites in n w french massif central implications for crustal history reconstructions seventy samples of hercynian peraluminous granites gueret millevaches and saint sylvestre massifs and metamorphic units of the limousin area were analysed for rb sr and sm nd the source rocks of the peraluminous granites can be found in the metamorphic rocks of limousin among them meta igneous rocks were largely predominent over meta sedimentary rocks in the source of the three granites millevaches and gueret granites were generated by the partial melting of rocks comprising meta volcanics and meta sediments whereas the saint sylvestre granite was produced exclusively by the melting of late precambrian granites this leads to confusing t dm nd values the confusion being amplified by the segregation of monazite during the petrogenetic evolution of the peraluminous granites which leads to dramatic fractionation in sm nd ratios the data of the present study tend to demonstrate that peraluminous granites do not give a good representation of isotopic mean crustal estimates late precambrian time seems however to have been a period of extensive crustal generation in western europe

detailed oxygen and carbon isotope stratigraphy of the oxfordian in central poland a collection of 73 belemnites and brachiopods from detailed stratigraphically documented sections in the polish jura chain of central poland representing almost the whole oxfordian stage was studied for oxygen and carbon isotopes the 18o and 13c v pdb values range from 3 6 to 0 5 and from 1 6 to 2 for belemnite rostra and from 2 5 to 0 4 and from 1 6 to 4 3 for brachiopod shells respectively the 13c temporal trends of belemnite rostra and brachiopod shells show a constant isotopic difference ca 2 5 3 which is interpreted as a vital effect of belemnites or as a result of different life environments 18o values are similar in both groups of fossils the 18o values in the lower and middle oxfordian oscillate around 0 and decrease in the upper oxfordian this decrease results mainly from diagenetic overprint as proved by the cathodoluminescence studies the lower and middle oxfordian 18o derived temperatures were constant in consequence of significant ocean depth for this reason there are no established links with distribution of ammonite faunas the 13c temporal trend displays a gentle slope through the oxfordian and reaches maximum values at the turn of the plicatilis transversarium zones of the middle oxfordian which is commonly considered as a global event it can be related to the sea level highstand and growth crisis of carbonate platforms the decrease in 13c values starting in the upper middle oxfordian is interpreted to be due to the acceleration of carbonate sedimentation rate during this time period

oxygen and carbon isotope composition of callovian lower oxfordian middle upper jurassic belemnite rostra from central poland a record of a late callovian global sea level rise abstract oxygen and carbon isotope data of well preserved and stratigraphically well dated belemnite rostra are presented from a callovian lower oxfordian succession of the polish jura chain south central poland that was deposited in a deep shelf environment palaeotemperatures calculated from belemnite 18 o values 9 to 14 c indicate relatively constant climatic conditions during studied callovian and early oxfordian intervals belemnite 13 c temporal trends which are interpreted to record primary variation in the isotope composition of dissolved inorganic carbon reservoir display a prominent positive carbon isotope shift up to around 1 7 vpdb in the upper callovian this excursion is preceded and followed by a drop in average 13 c values of belemnite rostra of around 1 the late callovian carbonate carbon isotope excursion is likely linked to the enhanced storage of organic carbon in shelf sediments during a global sea level rise the presented data are not compatible with the theory of prolonged global glaciation at the middle late jurassic transition

cenomanian palaeotemperatures derived from the oxygen isotopic composition of brachiopods and belemnites evaluation of cretaceous palaeotemperature proxies sixty low magnesium calcite samples from cenomanian articulate brachiopods belemnites and oysters from the epicontinental shelf sea of europe were geochemically and microscopically studied in order to evaluate their preservation and potential as carriers of palaeoenvironmental information the sampled localities in northern spain germany and southern england cover the transition between subtropical 25 30 n and temperate 33 38 n climates mean cenomanian salinity adjusted palaeotemperatures of diagenetically unaltered terebratulid and rhynchonellid brachiopods are 25 5 1 3 c in spain and 19 4 1 9 c in southern england the resulting low to mid latitude meridional temperature gradient of 0 7 c per degree latitude is similar to the gradient today and suggests modern heat transport values for cenomanian low latitudes oxygen isotopic composition of unaltered specimens of the upper cenomanian belemnite praeactinocamax plenus mean 0 2 is enriched in 18o by 1 in comparison to brachiopod shells correspondingly upper cenomanian palaeotemperatures derived from belemnite calcite 13 0 1 3 c underestimate modelled mid latitude sea surface temperatures by 6 c since p plenus occurs as boreal pulse fauna during a short interval in the late cenomanian its heavy oxygen isotopic composition can be attributed either to migration from a cooler and or deeper water mass or to unknown vital effects

nature and composition of the lower continental crust in central spain and the granulite granite linkage inferences from granulitic xenoliths xenolith bearing alkaline ultrabasic dykes were intruded into the of the hercynian basement of the spanish central system in early mesozoic times the suite of lower crustal xenoliths in the dykes divided into three groups felsic peraluminous granulites metapelitic granulites and charnockitic granulites the felsic granulites form 95 of the total volume of the xenoliths whereas the charnockitic and metapelitic granulites are much less abundant 0 01 5 respectively thermobarometric calculations based on mineral paragenesis indicate equilibration conditions around 850 950 c 7 11 kbar thus the xenoliths represent lower continental crustal material superimposed on this high t high p assemblage is a high t low p paragenesis represented mainly by kelyphitic coronas reflecting re equilibration during transport in the clearly restitic mineral assemblages with up to 50 garnet and 37 sillimanite major and trace element modelling supports the idea that the late hercynian peraluminous granites of central spain represent liquids in equilibrium with restitic material of similar composition to the studied lower crustal xenoliths 87sr 86sr and end of the felsic xenoliths calculated at an average hercynian age of 300 ma are in the range 0 706 0 712 and 1 4 to 8 2 respectively these values match the isotopic composition of the outcropping late hercynian granites the sr isotopic composition of the xenoliths is lower than that of the outcropping mid crustal lithologies orthogneisses pelites a major contribution from the lower crust to the source of hercynian granites greatly reduces the necessity of invoking a large mantle contribution in models of granite petrogenesis the felsic nature of the lower continental crust in central spain contrasts with the more mafic lower crustal composition estimated in other european hercynian areas suggesting a non underplated crust in this region of the hercynian orogenic belt

granulitic xenoliths from the french massif central petrology sr and nd isotope systematics and model age estimates the protoliths of granulitic xenoliths found in tertiary quaternary alkali volcanics from the french massif central are shown to have been principally immature sediments and calc alkaline intrusives the association may indicate formation of the crust in an island arc or continental margin environment pressure and temperature estimates indicate that they have undergone intermediate to high pressure granulite facies metamorphism 9 15 kbar followed by uplift to lower pressures 4 9 kbar rb sr and sm nd isotopic data and ree abundances are presented for both meta igneous and meta sedimentary suites esr present day values for the granulitic xenoliths range from 2 7 to 325 with end values between 0 2 and 12 0 there are no isochron relationships within the sr and nd data but possible mixing lines in the rb sr system may indicate sedimentation at 700 1000 myr t nd dm model ages indicate a proterozoic 800 2100 myr origin for the protoliths of the meta igneous samples and a similar provenance age for the meta sediments 1986 the geological society