the cr renazzo type carbonaceous chondrite group and its implications abstract a petrologic geochemical and oxygen isotopic study of eight meteorites identified as cr renazzo type chondrites reveals that they have a set of similar properties that distinguishes them from other chondrite groups and confirms cr as a carbonaceous chondrite group characteristics of the cr group include 1 1 abundant large multilayered fe ni metal rich type i chondrules 2 2 abundant matrix and dark inclusions di that contain microchondrules microfragments and magnetite framboids and platelets 3 3 unique assemblages of serpentine and chlorite rich phyllosilicates and ca carbonates 4 4 ca carbonate rims on chondrules 5 5 abundant fe ni metal with a positive ni vs co trend and a solar ni co ratio 6 6 low abundance of refractory rich inclusions 7 7 amoeboid olivine aggregates aoa with mn rich and mn poor forsterite and 8 8 oxygen isotopic compositions that form a unique mixing line the cr chondrites are breccias consisting of two major components the large layered chondrules and the matrix dark inclusions al rais is an anomalous member in having a higher abundance of the dark inclusion component 70 vol and this accounts for its having a higher volatile content than other members of the group the conditions that prevailed during aqueous alteration of the cr chondrites differed from those of other hydrated chondrite groups and may be the result of a higher temperature environment than that for the ci and cm chondrites the cr chondrite components chondrules matrix dark inclusions etc experienced aqueous alteration to differing degrees prior to assembly of the host chondrites and dark inclusions represent a lithology that was altered by water to a greater degree than the rest of the meteorite the overall degree of hydration in cr chondrites varies among meteorites with al rais being the most hydrated the oxygen isotopic variation of the whole rocks chondrules and matrices may be related to degree of hydration indicating that cr chondrites interacted with a water rich component having heavy oxygen and that was the same as ci and cm water

alkyldibenzofurans in terrestrial rocks influence of organic facies and maturation abstract dibenzofuran dbf dibenzothiophene dbt and phenanthrene phe have been determined along with their methyl derivatives mdbfs mdbts mps in coals carbonaceous shales and mudstones of lower cretaceous to upper carboniferous ages from the elmworth gas field canada and from the sakoa madagascar and ruhr coal germany basins the samples contained mainly terrestrial organic matter with thermal maturities in the 0 7 1 9 mean vitrinite reflectance rr range the pronounced predominance of mdbfs over mdbts in the sakoa samples is typical of plant debris deposited in lacustrine swamp environments onset of intense mdbf generation occurs at fairly low rank 0 77 rr as indicated by elevated concentrations of 50 120 g mdbfs g total organic carbon toc influences of lithology organic matter type and maturity on distributions of the target compounds were extracted from the molecular concentration data by multivariate statistical methods such as principal components analysis pca and fuzzy c means cluster analysis with nonlinear mapping nlm a specific source effect on 1 mdbt concentrations suggests that lichens contributed to the senescent coal forming forest in the sakoa coal basin alkyldibenzofurans hence are potential lichen biomarkers mdbfs can be used as maturity indicators only beyond 1 0 rr where ruhr coals displayed a distinct increase in the 1 4 mdbf ratio

a new hypothesis on parameters controlling the formation and size of porphyry copper deposits implications on thermal gradient of subducted oceanic slab depth of dehydration and partial melting along the kerman copper belt in iran abstract porphyry copper deposits in the tethyan metallogenic belt broadly occur in early mesozoic late mesozoic paleogene and neogene within a wide range of tectonic setting these deposits in iran often occur within the cenozoic urumieh dokhtar magmatic arc udma mostly in the kerman porphyry copper belt kpcb located in the southeast of this arc these deposits along the udma are mainly associated with the granitoids of miocene age 18 82 9 20 ma in this research geochemical characteristics pb and sr isotopes tectonic environment oxidizing conditions and source of magmas for the most important porphyry copper deposits of the udma have been compared and discussed on the basis of trace element discrimination diagrams the kerman belt granitoids formed in a volcanic arc type setting whereas the jebal barez granitoids seem to have formed in a different tectonic setting the eu eu of granitoids from the kerman belt are greater than 1 2 representing the oxidizing conditions for the crystallization of the granitoid magma whereas jebal barez granitoids were formed under reducing conditions the sr y ratio for kerman granitoids is greater than 60 indicating adakitic affinities and la yb n for these granitoid rocks is between 17 and 35 suggesting that their parental magma was generated from a deep garnet bearing source based on 87sr 86sr i values for kerman belt granitoids of 0 704 0 705 it is suggested that parental magmas originated from a subducted oceanic slab in the sarcheshmeh porphyry copper deposit the thermal gradient of the oceanic slab at depth was less than 9 c km warm cold slab the oceanic slab was highly hydrated and more than 80 of the water within the oceanic slab was released in the deep zone of the sub arc region at a depth of 110 130 km under saturated conditions the oceanic slab partially melted 20 25 a large volume of magma and magmatic water formed sarcheshmeh as a giant porphyry copper deposit in the iju deposit a small porphyry copper deposit the oceanic slab was slightly hydrated and minor water was released at the depth of 110 130 km a small volume of magma was formed due to water undersaturated melting conditions finally a new hypothesis is introduced regarding the roles of down dip thermal gradient of the oceanic slab water content depth of dehydration and degree of partial melting of oceanic slab which are important controls on the formation and size of the porphyry copper deposits within continental volcanic arcs

the isolation occurrence and origin of fluorenones in crude oils and rock extracts abstract a rapid method for the analysis of fluorenones in crude oils and reservoir core extracts based on solid phase extraction and gc ms is described a detailed reservoir study involving analysis of both fluids and core extracts was performed and variations in the distributions of fluorenones between reservoir phases are discussed concentrations of fluorenones in reservoir core extracts are often very high which may reflect sorption processes after fluorenone production but in general fluorenone abundance in flowed oils seems to be sporadic and may be related to sample age and storage history with recent production oils having lower fluorenone concentrations than corresponding older drill stem test oils while a geochemical origin for fluorenones cannot be eliminated in some settings we are concerned that these compounds may be frequently formed sporadically as a result of post sampling oxidation

noble gases in h chondrites and potential differences between antarctic and non antarctic meteorites abstract thirty one antarctic h chondrites from the allan hills have been analyzed for their noble gases seven of the specimens contain solar gases thirteen have a cosmic ray exposure age around 8 ma both fractions are as observed for h chondrites from the rest of the world scrutiny of the data for paired samples yields a minimum number of 17 independent falls with 6 falls required for the 8 ma peak of exposure age the distribution of exposure ages as well as that of radiogenic 4 he and 40 ar yield no evidence that h chondrites from the allan hills region represent a mixture of populations that is different from that brought to moderate latitudes of the earth in more recent times

stream sediment geochemical data analysis for district scale mineral exploration targeting measuring the performance of the spatial u statistic and c a fractal modeling abstract recognition of mineralization related geochemical footprints and modeling their multi element dispersion patterns are important aspects to consider when vectoring toward undiscovered ore deposits the collection analysis and interpretation of stream sediment geochemical data together make an exploration method that has proven to be successful at the district scale mineral exploration targeting identifying the possible sources of stream sediment geochemical anomalies and mapping evidence i e footprints of the underlying ore forming processes however are not trivial tasks this is because stream sediment samples represent transported material reflecting the entire geology upstream from the sample locations furthermore indicator element distribution patterns are commonly strongly affected by local factors such as regolith topographic gradient vegetation density and or climate therefore there is a need for finding a better geochemical anomaly separation method regarding the nature of geochemical data obtained from the area sampled the main objectives of this study were 1 evaluating and comparing the spatial u statistic and concentration area fractal modeling methods of anomaly identification both amenable to spatial analysis for recognizing geochemical footprints of porphyry copper mineralization and 2 measuring their performance in the context of district scale exploration targeting in an area located in southeast iran subsequently the methods were first evaluated on a dataset of element contents to decompose anomalous populations finally the geochemical model that proved more efficient with respect to predicting the known mineral deposits was integrated with additional evidence maps to delineate exploration targets our evaluation of the resulting geochemical targeting model demonstrated that the targets derived from this method are robust and worthy of follow up exploration

lead isotope compositions of late cretaceous and early tertiary igneous rocks and sulfide minerals in arizona implications for the sources of plutons and metals in porphyry copper deposits porphyry copper deposits in arizona are genetically associated with late cretaceous and early tertiary igneous complexes that consist of older intermediate volcanic rocks and younger intermediate to felsic intrusions the igneous complexes and their associated porphyry copper deposits were emplaced into an early proterozoic basement characterized by different rocks geologic histories and isotopic compositions lead isotope compositions of the proterozoic basement rocks define from northwest to southeast the mojave central arizona and southeastern arizona provinces porphyry copper deposits are present in each pb isotope province lead isotope compositions of late cretaceous and early tertiary plutons together with those of sulfide minerals in porphyry copper deposits and of proterozoic country rocks place important constraints on genesis of the magmatic suites and the porphyry copper deposits themselves the range of age corrected pb isotope compositions of plutons in 12 late cretaceous and early tertiary igneous complexes is 206 pb 204 pb 17 34 to 22 66 207 pb 204 pb 15 43 to 15 96 and 208 pb 204 pb 37 19 to 40 33 these pb isotope compositions and calculated model th u are similar to those of the proterozoic rocks in which the plutons were emplaced thereby indicating that pb in the younger rocks and ore deposits was inherited from the basement rocks and their sources no pb isotope differences distinguish late cretaceous and early tertiary igneous complexes that contain large economic porphyry copper deposits from less rich or smaller deposits that have not been considered economic for mining lead isotope compositions of late cretaceous and early tertiary plutons and sulfide minerals from 30 metallic mineral districts furthermore require that the southeastern arizona pb province be divided into two subprovinces the northern subprovince has generally lower 206 pb 204 pb and higher model th u and the southern subprovince has higher 206 pb 204 pb and lower model th u these pb isotope differences are inferred to result from differences in their respective post 1 7 ga magmatic histories throughout arizona pb isotope compositions of late cretaceous and early tertiary plutons and associated sulfide minerals are distinct from those of jurassic plutons and also middle tertiary igneous rocks and sulfide minerals these differences most likely reflect changes in tectonic setting and magmatic sources within late cretaceous and early tertiary igneous complexes that host economic porphyry copper deposits there is commonly a decrease in pb isotope composition from older to younger plutons this decrease in pb isotope values with time suggests an increasing involvement of crust with lower u pb than average crust in the source s of late cretaceous and early tertiary magmas lead isotope compositions of the youngest porphyries in the igneous complexes are similar to those in most sulfide minerals within the associated porphyry copper deposit this pb isotope similarity argues for a genetic link between them however not all pb in the sulfide minerals in porphyry copper deposits is magmatically derived some sulfide minerals particularly those that are late stage or distal to the main orebody or in proterozoic or paleozoic rocks have elevated pb isotope compositions displaced toward the gross average pb isotope composition of the local country rocks the more radiogenic isotopic compositions argue for a contribution of pb from those rocks at the site of ore deposition combining the pb isotope data with available geochemical isotopic and petrologic data suggests derivation of the young porphyry copper related plutons most of their pb and other metals from a hybridized lower continental crustal source because of the likely involvement of subduction related mantle derived basaltic magma in the hybridized lower crustal source an indiscernible mantle contribution is probable in the porphyry magmas clearly in addition pb was contributed from the local country rocks this is most evident in sulfide minerals in veins that are late stage hosted in proterozoic gneiss and or peripheral to the porphyry copper deposit

lead isotopic signatures of porphyry copper deposits in oceanic and continental settings colombian andes abstract three discrete sub belts of porphyry copper type mineralization are recognized in the colombian andes a western eocene sub belt an eastern jurassic to early cretaceous sub belt and between them a central miocene sub belt the western sub belt is part of an oceanic domain constituted by oceanic crust and overlying immature island arc rocks the eastern sub belt is within a continental domain underlain by the leading edge of the guayana shield and the central sub belt spans the faulted boundary between them the thicker continental crust includes important granulitic rocks which crop out locally as in the vicinity of the mocoa porphyry copper deposit pb isotopic ratios were determined for pyrite samples collected from 6 porphyry copper centers 3 in the western sub belt 2 in the eastern sub belt and one in the central sub belt ratios fall into 3 discrete populations the most radiogenic values represent the western sub belt the least radiogenic represent the eastern sub belt and an intermediate value corresponds to the central sub belt ratios therefore become progressively less radiogenic from the western oceanic domain to the eastern cratonic domain comparison of the pb isotopic ratios with those given in the literature for possible source materials for colombian porphyry copper leads enables the subcontinental mantle wedge subducted oceanic crust and subducted metalliferous sediments to be discounted as principal sources the relatively radiogenic signatures of 5 of the porphyry copper centers appear to be broadly compatible with either a subducted pelagic sediment source or an upper continental crust source whereas the sixth center mocoa is characterized by a distinctly less radiogenic 206 pb 204 pb ratio an admixture of a relatively small percentage of non radiogenic pb from granulitic material in the upper crust with the more radiogenic pb typical of the western sub belt centers could account for the mocoa data because much of the upper crustal section in the region of mocoa is thought to be dominated by granulitic material the radiogenic pb component could be best derived from subducted pelagic sediments if this is the case then a subducted pelagic sediment source could dominate the pb isotopic signatures of all colombian porphyry copper mineralization with some of the pb isotopic differences being produced by selective contamination with upper crustal leads of variable character if this conclusion is correct then the fundamental metal budgets of colombian porphyry copper systems are probably largely independent of upper crustal influences

acfer 182 and paired samples an iron rich carbonaceous chondrite similarities with alh85085 and relationship to cr chondrites three samples of a new fe rich chondrite were found in the sahara in 1990 and 1991 acfer 182 acfer 207 acfer 214 the samples are paired and the meteorite will be designated as acfer 182 the chondrite is chemically texturally and mineralogically similar to the allan hills meteorite alh85085 one important difference between the two meteorites is the smaller average chondrule size in alh85085 the major components of acfer 182 in decreasing abundance are 1 1 highly altered by terrestrial weathering matrix 2 2 mineral and polymineralic silicate fragments and aggregates 3 3 chondrule fragments 4 4 chondrules 5 5 metal 6 6 fine grained dark inclusions the abundance of chondrules is lower and the average chondrule size 90 m smaller than in most other chondrites chondrule fragments are often so large that they cannot be derived from the present chondrule population apparently size sorting has prevented accumulation of the larger parent chondrules several spectacular ca al rich inclusions were found rich in ca dialuminate hibonite or zr y sc bearing phases the chemical composition of acfer 182 and of alh85085 are almost indistinguishable major chemical signatures are 1 1 uniform enrichment of fe and other nonvolatile metals relative to ci chondrites by about 70 2 2 absence of enrichment in refractory lithophiles characteristic of most type 2 and 3 carbonaceous chondrites 3 3 strong depletion of volatile and moderately volatile elements based on the oxygen isotopic composition the chemical composition and the abundances of chondrules and matrix acfer 182 should be classified as a carbonaceous chondrite considering their affinity to carbonaceous chondrites and their high bulk iron content the two meteorites acfer 182 and alh85085 are designated as ch chondrites there are mineralogical and chemical similarities among acfer 182 alh85085 and cr chondrites which distinguish these meteorites from other types of carbonaceous chondrites 1 1 low feo contents of olivine and pyroxene and correspondingly high metal contents 2 2 high cr content in olivine 3 3 abundant fine grained dark inclusions 4 4 abundant ca dialuminate caal4o7 in cais 5 5 similarities in oxygen isotopic composition 6 6 low contents of moderately volatile elements 7 7 low refractory element contents 8 8 presence of a unique component of subsolar rare gases these observations suggest similar conditions of formation for the components of these meteorites a single common parent body is unlikely in view of the differences in chemical composition and in the size distribution of individual components

the effects of thermal maturity on distributions of dimethylnaphthalenes and trimethylnaphthalenes in some ancient sediments and petroleums abstract the distributions of di and trimethylnaphthalenes in two sedimentary sequences from western australia have been examined by capillary gas chromatography and combined gas chromatography mass spectrometry a general decrease was observed in the relative proportions of dimethylnaphthalenes and trimethylnaphthalenes with increasing thermal maturity similar trends were also observed for six crude oils which have very different ratios of ethylcholestane epimers indicating very different thermal histories these results suggest that changes in the relative abundances of certain methyl substituted naphthalenes may be useful indicators of thermal maturity of sedimentary organic matter and the use of a number of isomer ratios is illustrated

paired renazzo type cr carbonaceous chondrites from the sahara ten chondrites with chemical and mineralogical similarities to the carbonaceous chondrite renazzo were recovered at two locations of the sahara acfer 059 087 097 114 139 186 187 209 270 and el djouf 001 although the el djouf location is more than 500 km away from the acfer location all samples appear to result from a single fall based on chemical and petrographic similarities and supported by light element stable isotope geochemistry noble gas record and similar 26al contents the acfer el djouf meteorite is classified as a cr renazzo type carbonaceous chondrite this group presently comprises three non antarctic members al rais renazzo acfer el djouf and five antarctic meteorites the major lithological components of the acfer el djouf meteorite are large chondrules up to 1 cm in size mean diameter 1 0 0 6 mm chondrule and mineral fragments ca al rich inclusions feni metal about 8 10 vol and dark inclusions embedded in a fine grained fragment bearing groundmass mineral compositions of the ten acfer el djouf samples are similar to those of other cr chondrites most of the ca al rich inclusions are below 300 m in size and rich in melilite and spinel in some cais the rare phase caal4o7 is dominant fo rich cr bearing olivine fa0 4 and enstatite fs0 4 are the major phases of the chondrite the meteorite is mildly shocked with a shock stage of s2 indicating a peak shock pressure of 5 10 gpa for the bulk meteorite the oxygen isotopic compositions and carbon and nitrogen stable isotope geochemistry of the acfer el djouf samples are very similar to those of the other cr type chondrites the major element composition of the acfer el djouf meteorite is indistinguishable from cr chondrites when compared to renazzo the acfer el djouf samples however have systematically lower contents of the moderately volatile elements zn ga as au sb and se and the highly volatile elements br c and n this is thought to reflect primary differences between renazzo and the acfer el djouf meteorite

lead sources in mesozoic and cenozoic andean ore deposits north central chile 30 34 s mesozoic and cenozoic ore deposits in the chilean andes between la serena 30 s and santiago 34 s include polymetallic vein low and high sulfidation epithermal vein skarn porphyry copper molybdenum and porphyry copper gold these deposits are associated with volcanic and plutonic complexes emplaced in eastward migrating longitudinal arcs which formed during subduction along the continental margin of south america since the middle jurassic stratabound but epigenetic volcanic rock and sedimentary rock hosted manto deposits contain additional copper resources lead isotopic compositions in ore minerals from 29 deposits vary with age and geographic location and hence with basement and host rocks lead in most ore deposits is derived from temporally related igneous rocks except for the manto deposits whose lead is derived from host volcanic and sedimentary rock sequences lead in the ore deposits is dominated by two crustal sources low 207pb 204pb characterizes one source whereas high 207pb 204pb characterizes the second source lead isotopic compositions of jurassic and miocene ore minerals 206pb 204pb 18 50 207pb 204pb 15 61 lie along the average crustal growth curve by contrast most cretaceous deposits have ore minerals with lower 206pb 204pb 18 39 and 207pb 204pb 15 58 than jurassic ore minerals the shift in lead isotopic composition to lower lead isotopic values precludes derivation of lead from a source of similar composition to those in the jurassic or tertiary deposits for cretaceous deposits polymetallic and low sulfidation epithermal veins and a skarn have lower 206pb 204pb than a porphyry copper gold system and peripheral gold veins at andacollo 18 43 18 50 late cretaceous veins from the bellavista deposit have the lowest 206pb 204pb 18 33 of all deposits ore minerals in miocene and pliocene porphyry copper molybdenum deposits have higher 206pb 204pb 18 58 18 67 than cretaceous deposits consistent with their age being younger the miocene and pliocene ore minerals also have higher 207pb 204pb 15 58 15 66 than cretaceous ore minerals thereby requiring an additional input from the high 207pb 204pb source into the younger deposits miocene auriferous deposits in the north have similar 206pb 204pb values as the miocene and pliocene porphyry copper molybdenum deposits in the south but they are distinguished by higher and variable 207pb 204pb 15 61 15 66 and 208pb 204pb 38 54 39 01 which are arrayed along steep mixing trends these ore minerals have the largest input of high 207pb 204pb material in the deposits studied by contrast lead in the epigenetic manto deposits appears to be derived from the host volcanic or sedimentary rock dominated sequences and locally exhibits large scale isotopic heterogeneity within a deposit overall the lead isotopic compositions of ore minerals mimic the values and variations established in age equivalent rock sequences the low 207pb 204pb material in the deposits is derived from cretaceous igneous rocks or their sources as they evolved with time low 207pb 204pb characterizes these rocks by contrast high 207pb 204pb material is likely derived from carboniferous to triassic igneous rocks or their sources as this lead isotopic characteristic dominates these rocks

changes in hydraulic conductivity of laboratory sand clay mixtures caused by a seawater freshwater interface abstract the influence of small amounts of clay minerals on the hydraulic conductivity of sandy aquifer was investigated by laboratory experiments admixture of up to 1 5 by weight of clay minerals to sand did not cause any measurable decrease of hydraulic conductivity for seawater increasing the clay fraction from 1 5 to 10 decreased hydraulic conductivity by one order of magnitude montmorillonite caused the strongest decrease the effect of kaolinite and illite was only half as large when seawater was flushed by freshwater hydraulic conductivity of the montmorillonite sand mixture decreased drastically however flushing with freshwater did not measurably affect the hydraulic conductivity of an illite sand or kaolinite sand mixture the explanation for this behaviour is the capability of various types of clay to adsorb different quantities of water between their platelets which induces a gel droplet formation process this is governed by the chemical composition and the ionic strength of the solution

the preservation state of organic matter in meteorites from antarctica the recovery of large numbers of meteorites from antarctica has dramatically increased the amount of extraterrestrial material available for laboratory studies of solar system origin and evolution yet the great age of antarctic meteorites raises the concern that significant amounts of terrestrial weathering has corrupted their pre terrestrial record organic matter found in carbonaceous chondrites is one of the components most susceptible to alteration by terrestrial processes to assess the effects of antarctic weathering on both non antarctic and antarctic chondritic organic matter a number of cm chondrites have been analyzed mossbauer spectroscopy has been used to ascertain pre terrestrial and terrestrial oxidation levels while pyrolysis gas chromatography mass spectrometry was used to determine the constitution of any organic matter present increased oxidation levels for iron bearing minerals within the non antarctic chondrites are likely to be a response to increased amounts of parent body aqueous alteration parent body processing also appears to remove ether bonds from organic material and alkyl side chains from its constituent units the iron in antarctic chondrites is generally more oxidized than that in their non antarctic counterparts reflecting terrestrial weathering antarctic weathering of chondritic organic matter appears to proceed in a similar way to parent body aqueous alteration and simply enhances the organic responses observed in the non antarctic data set degradation of the record of preterrestrial processes in antarctic chondrites should be taken into account when interpreting data from these meteorites

aqueous alteration in cr chondrites meteorite parent body processes as analogue for long term corrosion processes relevant for nuclear waste disposal aqueous alteration of carbonaceous chondrites is one of the fundamental processes on accreting planetesimals that changes pristine materials from the formation of the solar system the study of mineralogical petrological and chemical changes resulting from this alteration provides insight into the physical and chemical setting of forming planetesimals cr chondrites provide samples for all stages of aqueous alteration from type 3 to 1 entirely hydrated and are thus suited to study the alteration of pristine materials in a coherent sequence vitrification is a common way to store and stabilize fission products and minor actinides resulting from the reprocessing of nuclear spent fuel in a nuclear boro silica glass in steel containers the waste material has to be stored safely for a period of at least 105 106 years in a clay rich geological repository laboratory experiments being too short to follow the long term evolution of these materials we analyzed the mineralogical petrological and chemical changes in a series of cr chondrites renazzo cr2 al rais cr2 and gro 95577 cr1 to serve as analogues rims of secondary materials around metal grains in contact to the fine grained matrix serve as analogue to the interface between steel containment and the surrounding clay rich geological layer while chondrule glassy mesostasis is used as a proxy of the nuclear glass with increasing degree of aqueous alteration in the sequence renazzo al rais gro 95577 the size of the rims increase fe rich alteration rims are 10 m in thickness around metal grains in the fine grained matrix in renazzo in al rais multi layered structures of interchanging fe s and p ca rich layers appear with a thickness of up to 30 m in the highly altered gro 95577 extensive inner and external rims of secondary phases reach up to 200 m into the surrounding matrix in chondrules metal in contact with the altered mesostasis shows similar trends but with thinner alteration rims altered mesostasis is similar to the surrounding fine grained matrix consisting of serpentine and smectite however the chemistry has not completely equilibrated as indicated by e g a remaining high al contents 2 2 wt fine grained matrix and altered mesostasis show a trend towards decreasing fe with progressing alteration matrix is also the main source of s in the alteration system most of the dissolved species stays close to the source the main source for fe ni p and also ti cr and mn is the altered metal these findings confirm the model for long term corrosion of nuclear disposal sites alteration rims of iron oxides form around the steel containments whereas dissolved species fe al and si diffuse into the surroundings

normal alkanes in meteorites molecular δ13c values indicate an origin by terrestrial contamination in the time period since 1961 n alkanes straight chain hydrocarbons have been detected in varying amounts in many meteorites proposed origins for these compounds have included extraterrestrial biotic extraterrestrial abiotic and terrestrial contamination processes to help establish the source of these compounds we determined the carbon isotopic compositions of individual n alkanes in meteorites of several different classes and terrestrial histories orgueil ci1 cold bokkeveld cm2 murchison cm2 vigarano cv3 allende cv3 ornans co3 and bishunpur ll3 the efficiency of supercritical fluid extraction sfe was exploited to provide extractable non polar organic matter from the meteorites the n alkanes in these extracts were then identified with gas chromatography mass spectrometry gc ms and the carbon isotopic composition of individual molecules was determined using isotope ratio monitoring gas chromatography mass spectrometry irm gc ms n alkanes were found in all but one of the meteorites analysed allende but carbon number distributions varied between samples pristane and phytane were also detected in five of the seven meteorites 13c values for the individual n alkanes occupied a range from 25 3 to 38 7 the 13c values for the meteoritic n alkanes have a similar range as those for n alkanes measured from petroleum in the literature therefore the n alkanes in meteorites appear to be terrestrial contaminants which may have originated from fossil hydrocarbons or petroleum products this type of contamination is analogous to that which will be threatening future meteorite falls and the samples returned from spaceflight missions over the next two decades and beyond for falls already contaminated irm gc ms appears useful in discriminating between indigenous compounds and those introduced by terrestrial contamination

differences between antarctic and non antarctic meteorites an assessment abstract the discovery of a statistically significant number of meteorites in antarctica over the past 20 years has posed many questions one of the most intriguing suggestions that came up during the study of the antarctic samples was that there might be a difference between the parent populations of antarctic and non antarctic meteorites this interpretation was put forward after the detection of a significant difference in the abundances of volatile and mobile trace elements in h l and c chondrites and achondrites other major differences include the occurrence of previously rare or unknown meteorites different meteorite type frequencies petrographic characteristics oxygen isotopic compositions and smaller average masses in addition antarctic meteorites have greater terrestrial residence ages and have collected on the ice shield over several 10 5 years the reality of numerous such differences has now been established beyond doubt however the main question regarding the cause of these differences remains it seems that they have a wide variety of origins ranging from pre terrestrial traits to collection recovery effects and terrestrial weathering studies of terrestrial weathering have shown that over the long time the meteorites spend in and on the ice even subtle processes can produce substantial effects for future investigations it will be important to pay more attention to the weathering status of samples and to develop a more reliable and quantitative weathering index e g based on infrared reflectance spectrometry or differential scanning calorimetry not all differences between the antarctic and non antarctic meteorite populations can be explained by weathering pairing or different collection procedures variable trace element abundances and distinct differences in the thermal history and thermoluminescence characteristics have to be interpreted as being pre terrestrial in origin such differences imply the existence of meteoroid streams whose existence poses problems in the framework of our current knowledge of celestial mechanics however several independent studies support the existence of such meteoroid streams thus being consistent with the suggestion of a time variable influx of extraterrestrial material to earth the generally smaller average size of antarctic meteorites may be the cause for the different meteorite type frequency and the higher abundance of rare samples because smaller meteorites may come from a slightly different parent population in this paper we summarize the contributions in this series and provide a review of the current state of the question for the reality and cause of differences between antarctic and non antarctic meteorites

mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites abstract the degree of compositional variation of fine grained minerals displayed by the members within any carbonaceous chondrite group i e ci cm cv cr is a direct reflection of the range of aqueous alteration assemblages present matrix and fine grained chondrule rims within any particular carbonaceous chondrite are mineralogically nearly identical to one another but not necessarily similar in bulk elemental composition even though they have subsequently experienced post accretional secondary processing aqueous alteration under identical conditions this may indicate preferential alteration of one component brecciation exchange of components between rims and matrix and or accretion of matrix and rims from mineralogically or compositionally distinct materials we propose that co chondrites experienced parent body conditions of low f o2 low water rock ratios and temperatures below 50 c cr chondrites experienced higher water rock ratios potentially higher temperatures 150 c and a wide range of f o2 the alteration mineralogy of cv chondrites indicates water rock ratios at the high end at least of the range for cr chondrites essebi and mac 87300 cm chondrites experienced temperatures below 50 c low f o2 and low water rock ratios except eet 83334 which probably experienced relatively higher f o2 and b 7904 and y 86720 which experienced postalteration temperatures in the range 500 700 c most ci chondrites experienced temperatures between 50 and 150 c relatively high water rock ratios and variable f o2 with a late stage increase in the latter due possibly to brecciation and consequent release of methane y 82162 witnessed post alteration heating possibly as high as 400 c

late cretaceous and early miocene andean type plutonic activity in northern makran and central iran two calc alkaline plutonic complexes bazman and natanz intruded through the south eastern active and south western ancient continental margins of central iran have been dated by the rb sr whole rock isochron method at 74 2 and 24 4 5 ma respectively detailed trace element studies together with low 87 sr 86 sr initial ratios 87 sr 86 sr ratios and the gabbros at least were intruded some 10 ma earlier

experimental investigation on irreversible changes of hydraulic conductivity on the seawater freshwater interface in coastal aquifers seawater and fresh groundwater were made to flow through columns filled with samples from a good aquifer that contained 5 or less clay minerals hydraulic conductivities decreased very sharply whenever seawater was flushed by fresh groundwater the extent of the decrease depended mainly on the percentage of clays and reached maximum values of 10 1 to 10 3 of the original hydraulic conductivity subsequent flushing with seawater restored hydraulic conductivity only in a slight measure if at all the mechanism of this process was investigated by using cacl2 and nacl solutions with the ionic strengths of seawater and fresh groundwater it appears that the decrease of hydraulic conductivity is caused by an incipient stage of gel formation the small water clay configurations that are formed during this stage behave as practically rigid particles and close the bottlenecks between adjacent pores the major implications of these findings for groundwater hydrology are as follows 1 in natural coastal aquifers the seawater freshwater interface is likely to undergo shifts on a semigeologic time scale if the aquifer contains even a small percentage of clays these shifts may create an almost impermeable boundary in the zone of the interface hitherto existing theories on movements of the interface regard permeability as constant 2 the attempt to repel a fresh water seawater interface by the injection of fresh water may create a practically impermeable boundary within a relatively short time and thus defeat its own purpose

petrogenesis of cretaceous adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china implications for geodynamics and cu au mineralization both adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china are associated with cretaceous cu au mineralization the shaxi quartz diorite porphyrites exhibit adakite like geochemical features such as light rare earth element lree enrichment heavy ree hree depletion high al2o3 mgo sr sr y and la yb values and low y and yb contents they have low end t values 3 46 to 6 28 and high 87sr 86sr i ratios 0 7051 0 7057 sensitive high resolution ion microprobe shrimp zircon analyses indicate a crystallization age of 136 3 ma for the adakitic rocks most volcanic rocks and the majority of monzonites and syenites in the luzong area are k rich or shoshonitic and were also produced during the cretaceous 140 125 ma they are enriched in lree and large ion lithophile elements and depleted in ti and nb and ba and exhibit relatively lower end t values ranging from 4 65 to 7 03 and relatively higher 87sr 86sr i ratios varying between 0 7057 and 0 7062 the shoshonitic and adakitic rocks in the luzong area have similar pb isotopic compositions 206pb 204pb 17 90 18 83 207pb 204pb 15 45 15 62 and 208pb 204pb 38 07 38 80 geological data from the luzong area suggest that the cretaceous igneous rocks are distributed along ne fault zones e g tanlu and yangtze river fault zones in eastern china and were likely formed in an extensional setting within the yangtze block the shaxi adakitic rocks were probably derived by the partial melting of delaminated lower crust at pressures equivalent to crustal thickness of 50 km i e 1 5 gpa possibly leaving rutile bearing eclogitic residue the shoshonitic magmas in contrast originated mainly from an enriched mantle metasomatized by subducted oceanic sediments they underwent early high pressure 1 5 gpa fractional crystallization at the boundary between thickened 50 km lower crust and lithospheric mantle and late low pressure 1 5 gpa fractional crystallization in the shallow 50 km crust the adakitic and shoshonitic rocks appear to be linked to an intra continental extensional setting where partial melting of enriched mantle and delaminated lower crust was probably controlled by lithospheric thinning and upwelling of hot asthenosphere along ne fault zones e g tanlu and yangtze river fault zones in eastern china both the shoshonitic and adakitic magmas were fertile with respect to cu au mineralization

geochemical investigations to explain iodine overabundances in antarctic meteorites abstract iodine bromine and chlorine concentrations were determined in different antarctic meteorite specimens eucrites high iron and low iron chondrites with isotope dilution mass spectrometry in all antarctic meteorites i overabundances have been analysed compared with the concentrations for non antarctic meteorites of the same class half of the antarctic specimens show especially high concentrations of more than 1 g a similarly high enrichment effect in antarctic meteorites was not found for br and cl but smaller cl excesses could be observed in some eucrites and high iron chondrites by analysing different types of antarctic rocks a significant decrease of the i concentration but not of the br and cl concentration was determined from the surfaces to the centers of the rocks this shows that atmospheric i compounds interact with the surfaces of antarctic rocks and therefore with those of antarctic meteorites as well analyses of atmospheric halogens show that the gaseous compound ch 3 i is probably responsible for the i overabundance in antarctic meteorites and rocks chloride and bromide are found in particles derived from sea spray in antarctic aerosols deposition of halogens in antarctic snow near the coast shows i cl ratios 10 190 higher than the average value for seawater the corresponding br cl ratios are in the same range as seawater on the basis of our results and of other reported data we construct a preliminary hypothesis for a geochemical i cycle in antarctica taking into consideration long distance and short distance transportation of different i compounds from the coast to inland antarctica

senonian basin inversion and rejuvenation of rifting in africa and arabia synthesis and implications to plate scale tectonics abstract the late paleozoic to tertiary stratigraphic record of much of the african plate reflects the effects of continental rifting and passive margin development several short lived but widespread and tectonically important compressional or wrench dominated events occurred however during the permian to recent evolution of africa we focus here on the best documented of these events which occurred during the late santonian at that time older sedimentary basins mostly ene wsw trending were folded and inverted including some basins along the tethyan margin from morocco to the syrian arc and the intraplate benue southern chad basins and the lugh mandera basin in oman ophiolites were obducted following the santonian tectonism an extensive phase of rifting occurred in central and north africa and northern arabia spanning from campanian to maastrichtian or paleocene times rejuvenation or acceleration of subsidence occurred in several basins located along the tethyan margin along the atlantic and indian ocean margins as well as within the intraplate domain rifting was sometimes accompanied by magmatic activity especially in offshore northern libya and along the indian ocean margin compressional deformations rejuvenated or developed by latest maastrichtian times along the tethyan margin and locally within the intraplate domain one of the most remarkable attributes of the santonian tectonic event which we consider representative of the major trans african stress field changes is the rapidity with which the change was reflected stratigraphically across north and central africa and its short duration the cause of the santonian compressional event is directly linked to the change in poles of rotation for the opening of the atlantic at 83 85 ma the end of the cretaceous normal magnetic quiet zone this was also synchronous with the obduction of ophiolites along the northeast margin of arabia oman the onset of separation between india and madagascar with formation of the mascarene oceanic basin and the development of the european alpine chain we interpret these phenomena as causally related aspects of a global tectonic event the santonian compressional event as well as the campanian maastrichtian rifting event and the end cretaceous compressional event illustrate the critical connection between intraplate tectonic histories and processes occurring at sometimes very distant plate boundaries

isotopic composition of lead in ore deposits of the cordillera oriental southeastern peru twenty five new lead isotope data are provided for 23 sulfide and 2 oxide minerals from 20 ore deposits embracing the wide variety of metallic mineralization present in the cordillera de carabaya southeastern peru segment of the central andean inner arc domain the deposits are subdivided into the following groups 1 cu or w or mo or sn veins hosted by permian and triassic metaluminous to peraluminous granitoid plutons 2 pb zn ag cu veins spatially related to small upper cretaceous stocks of granodioritic composition 3 major sn cu pb zn ag lodes associated with strongly peraluminous cordierite biotite monzogranite stocks of mid tertiary age 4 sn w cu pb zn ag and sb veins of undetermined but probably mid tertiary age and 5 fe or mn or ba manto deposits of poorly constrained age collectively the isotopic data indicate a dominantly crustal lead component in all suites with analyses plotting well above the 206 pb 204 pb 207 pb 204 pb orogen growth curve of zartman and doe 1981 for several mineralized centers permo triassic and a probable mid tertiary sb deposit the data overlap the upper crust curve although lead isotope data for cretaceous and mid tertiary group 3 ores exhibit tight clustering in all pb pb plots the data for permo triassic ores display a large spread and represent the most radiogenic compositions with 206 pb 204 pb values ranging from 18 819 to 25 18 isotopic analyses of acid leaches of sulfide ores from two mineralized centers of permo triassic age define regression lines in 206 pb 204 pb 207 pb 204 pb space and in at least one case indicate the presence of a 1 700 ma radiogenic lead component data for group 4 mineralization of probable mid tertiary age plot near group 3 data in all pb pb diagrams providing some corrobofating evidence for their inferred mid tertiary age the only exception is the sb mineralization which is relatively enriched in both 207 pb and 208 pb the isotopic compositions cannot be accommodated by a single reservoir model because 1 the implied age difference ca 100 125 ma between groups 2 and 3 in pb pb plots is greater than that for the host granites ca 55 ma and 2 group 1 mineralization the oldest analyzed contains the most radiogenic lead multiple source regions or complex mixing models are therefore predicated for the region as a whole a comparison of the southeastern peru ore lead data with those available for the metallo genically similar northwestern bolivian sn w ag province reveals broadly similar results for tertiary sn polymetallic ores but radically different compositions for permo triassic mineralization thus different source regions or processes are indicated for at least the older mineralization in addition whereas the mesozoic and cenozoic bolivian ore lead compositions could be accommodated by a common evolving source reservoir s tilton et al 1981 the peruvian data cannot the lead isotope compositions reported here overlap extensively with much of the pb isotope data available for central andean main arc mineralization although our results lie toward the more radiogenic ends of defined fields we therefore conclude that a model involving mixing of leads from a single source mantle with various crustal reservoirs can account for the observed data spread in pb pb plots this is consistent with the petrochemistry of the inner arc granitoid igneous suites which indicates involvement of mantle derived components in the anatectic granitoid rocks via magma mixing processes an important implication of this study is that multiple reservoirs have been involved in the metallogenic evolution of the central andean tin belt a conclusion arrived at earlier from petrologic studies of the associated igneous suites

lead isotope signatures of the igneous rocks and porphyry copper deposits from the kerman cenozoic magmatic arc se iran and their magmatic metallogenetic implications abstract copper deposits in the kerman cenozoic magmatic arc kcma of iran are genetically related to miocene porphyries the porphyries and their associated cu deposits were intruded and emplaced into eocene volcanic sedimentary successions lead isotope compositions of the eocene volcanic rocks exhibit homogeneous non radiogenic values 206 pb 204 pb 18 40 to 18 49 207 pb 204 pb 15 41 to 15 48 and 208 pb 204 pb 38 15 to 38 36 in contrast the miocene ore hosting porphyries and associated sulfide minerals also show a relatively radiogenic and homogenous pb isotopic values with orogen character 206 pb 204 pb 18 52 to18 60 207 pb 204 pb 15 58 to 15 64 and 208 pb 204 pb 38 57 to 38 80 the shift in the pb isotopic composition of igneous rocks with time towards higher pb isotopic values precludes derivation of the ore hosting porphyries from a reservoir of similar composition to those in the eocene volcanic rocks the non radiogenic pb isotope signature of the eocene volcanic rocks indicates an origin from subduction related mantle derived magmas whereas the higher pb isotopic values of the miocene ore hosting porphyries suggest an increasing involvement of crustal materials with lower u pb ratios than the upper crust in the source region of these rocks combining the pb isotope data with petrogenetic considerations suggests derivation of the middle miocene ore hosting porphyries from a mixed reservoir with slightly radiogenic pb values such as a hybridized lower continental crustal source this source probably formed because of the involvement of cretaceous oligocene subduction related mantle derived mafic magmas at the base of arc crust the contribution of the miocene collision related mantle derived mafic magma in melting of the hybridized lower continental crust caused generation of the middle miocene porphyries hosting large copper deposits with the least 206 pb 204 pb ratios among other porphyries the higher 206 pb 204 pb ratios of the late miocene pliocene porphyries hosting small copper deposits as well as barren porphyries may reflect a decreasing involvement of collision related mantle derived mafic magma in the source of the late miocene pliocene porphyries the overall similarity in pb isotope values between sulfide minerals and ore hosting porphyries suggests a magmatic source for most of the pb and possibly other metals the more radiogenic isotopic ratios of some late sulfide minerals suggest an insignificant metal contribution from an external source such as local country rocks during hydrothermal circulation

petrogenesis of adakitic porphyries in an extensional tectonic setting dexing south china implications for the genesis of porphyry copper mineralization the dexing adakitic porphyries quartz diorite granodiorite porphyries associated with giant porphyry cu deposits are located in the interior of a continent south china they exhibit relatively high mgo cr ni and sr contents high la yb and sr y ratios but low yb and y contents similar to adakites produced by slab melting associated with subduction however they are characterized by bulk earth like nd sr isotope compositions end t 1 14 to 1 80 and 87 sr 86 sr i 0 7044 0 7047 and high th 12 6 27 2ppm contents and th ce 0 19 0 94 ratios which are different from those of cenozoic slab derived adakites sensitive high resolution ion microprobe shrimp geochronology studies of zircons reveal that the dexing adakitic porphyries have a crystallization age of 171 3ma this age is contemporaneous with middle jurassic extension within the shi han rift zone and within plate magmatism elsewhere in south china indicating that the dexing adakitic porphyries were probably formed in an extensional tectonic regime in the interior of the continent rather than in an arc setting their high th contents and th ce ratios and middle jurassic age argue against an origin from a neoproterozoic 1000ma stalled slab in the mantle taking into account available data for the regional metamorphic magmatic rocks and the present day crustal thickness 31km in the area we suggest that the dexing adakitic porphyries were most probably generated by partial melting of delaminated lower crust which was possibly triggered by upwelling of the asthenospheric mantle due to the activity of the shi hang rift zone moreover the dexing adakitic magmas must have interacted with the surrounding mantle peridotite during their ascent which elevated not only their mgo cr and ni contents but also the oxygen fugacity fo2 of the mantle the high fo2 could have induced oxidation of metallic sulfides in the mantle and mobilization of chalcophile elements which are required to produce associated cu mineralization therefore the cu metallogenesis associated with the dexing adakitic porphyries is probably related to partial melting of delaminated lower crust similar to the metallogenesis accompanying slab melting

update on terrestrial ages of antarctic meteorites abstract cosmic ray produced 36 cl half life 3 01 10 5 years has been measured in 90 antarctic meteorites by accelerator mass spectrometry the terrestrial ages of the meteorites were calculated from the results after excluding possible paired objects 138 terrestrial ages from 18 different locations are available from 14 c 81 kr and 36 cl measurements for application to antarctic meteorite and glaciological studies the terrestrial ages of allan hills meteorites vary from 2000 years to 1 million years and are clearly longer than those of yamato meteorites and other antarctic meteorites the oldest allan hills meteorites were found close to the eastern edge and in the southeast of the main icefield among all antarctic meteorites measured to date only l and ll chondrites have terrestrial ages older than 370 000 years

risk quantification with combined use of lithological and grade simulations application to a porphyry copper deposit abstract the uncertainty in the recoverable tonnages and grades in a mineral deposit is a key factor in the decision making process of a mining project currently the most prevalent approach to model the uncertainty in the spatial distribution of mineral grades is to divide the deposit into domains based on geological interpretation and to predict the grades within each domain separately this approach defines just one interpretation of the geological domain layout and does not offer any measure of the uncertainty in the position of the domain boundaries and in the mineral grades this uncertainty can be evaluated by use of geostatistical simulation methods the aim of this study is to evaluate how the simulation of rock type domains and grades affects the resources model of sungun porphyry copper deposit northwestern iran specifically three main rock type domains porphyry skarn and late injected dykes that control the copper grade distribution are simulated over the region of interest using the plurigaussian model the copper grades are then simulated in cascade generating one grade realization for each rock type realization the simulated grades are finally compared to those obtained using traditional approaches against production data

antarctic and non antarctic meteorites form different populations compared with non antarctic falls antarctic meteorites include many of hitherto rare unique or unknown type1 such as lunar and putative martian samples2 4 attention has not previously been paid to the more common sorts of antarctic meteorites and here we focus on the most frequently encountered h5 chondrites we find that compositional differences between antarctic and non antarctic specimens of this class especially those involving thermally sensitive trace and ultra trace elements are so substantial that it seems extremely doubtful that the two sample populations are derived from the same parent population this implies that the contemporary falls less than 200 years old and the substantially older on average 300 000 years for victoria land antarctic meteorites either differ in genetic history or sample different extraterrestrial parent populations or both

origin of metallic fe ni in renazzo and related chondrites abstract the anomalous positive co ni correlation among metal grains from the renazzo and al rais chondrites reported in previous studies has two components 1 1 a chondrule trend that extends up to 120 145 mg g ni probably reflects the mixing of fe rich and fe poor nebular metal and 2 2 a weak extrachondrule trend that spans a ni range from 40 70 mg g reflects fe introduction during mild metamorphism to assess the formation of this metal we determined ni and co zoning profiles in metallic fe ni from different petrographic sites chondrule interiors chondrule margins chondrule rims and matrix in renazzo al rais and the related chondrite macalpine hills 87320 metal from chondrule interiors shows flat ni and co concentrations and profiles moderately large grain to grain compositional variations even within chondrules and generally high ni and co nickel concentrations extend above the kamacite stability limit etching such martensite shows high ni domains in some cases but observed ni concentrations do not exceed 190 mg g metal from chondrule margins adjacent to matrix shows convex inverted u shaped ni and co zoning profiles the highest ni and co concentrations are at grain centers although the mean central ni and co concentrations in margin grains are much lower than those in metal from chondrule interiors about half of the matrix metal shows flat co and ni profiles like those from chondrule interiors the remainder are convex the differences in mean co and ni contents between chondrules and extrachondrule materials may reflect differential sampling of nebular metal grains having compositions that varied with particle size we interpret the low co and ni contents at the edges of grains in chondrule margins to reflect dilution by fe produced by feo reduction the reduction seems not to have occurred in the nebula but rather during a brief period of parent body metamorphism reduction of fine grained feo produced metallic fe that plated onto nearby metal grains although diffusive exchange between pentlandite and metal could produce the observed ni gradient it is doubtful that it could produce the similar gradient of co metal from chondrule interiors was inaccessible during the reduction event and retained the flat profiles established during chondrule formation

lead isotope data from the sar cheshmeh porphyry copper deposit iran lead isotope compositions of nine sulfide concentrates from ore samples from the sar cheshmeh deposit are reported they range from virtually unaltered granodiorite through varying degrees of potassic alteration to ores showing strong phyllic alteration sericite veins the samples without strong phyllic alteration have fairly uniform lead isotope compositions around 206pb 204pb 18 6 207pb 204pb 15 6 and 208pb 204pb 38 7 two samples with sericite veins have markedly more radiogenic lead it is concluded that the fluid responsible for the potassic alteration and the associated mineralization was essentially magmatic whereas convecting meteoric water from the country rock acted as a mineralizing solution during phyllic alteration in the context of the plumbotectonics model the deposit has a typical orogen signature intermediate between primitive and mature island arc settings

the effect of biodegradation and water washing on the occurrence of alkylphenols in crude oils abstract biodegraded oils from california and nigeria were analysed to assess the impact of biodegradation upon alkylphenol occurrence in crude oils the extent of biodegradation in the 13 californian samples ranged from very mild full n alkane distribution present to moderate complete degradation of c 15 n alkanes and significant reduction of acyclic isoprenoids corresponding to a range of n alkanes and acyclic isoprenoids stage 5 the data from the naturally degraded sample suites were compared to the results of an in vitro aerobic biodegradation experiment conducted with a north sea oil biodegradation resulted in significant reduction in total alkylphenol abundance and preferential depletion of c 3 and c 2 alkylated compounds in the nigerian and laboratory degraded samples these effects were most pronounced in oils in which the methylated naphthalenes had been biodegraded biodegradation stage 4 or 5 there was no clear relationship between alkylphenol abundance or molecular distributions and the extent of biodegradation in the californian samples although alkylphenol distributions in the biodegraded samples were generally dominated by the c 3 compounds simple oil water partition calculations showed that these distributions were consistent with the effects of water washing

structural deformation of the leoville chondrite foliations defined by alignment of elongated chondrules have been noted previously in chondrites but none displays this effect so well as leoville cv3 the shapes of leoville chondrules were produced by deformation in situ as indicated by inclusions and clasts with similar shapes and preferred orientations to those of chondrules similarities in the aspect ratios of apparent strain ellipses measured for chondrules alone 1 9 and 2 0 by several methods and for the whole meteorite 2 0 indicate either that leoville deformed homogeneously or that it deformed as a framework of touching chondrules this amount of strain corresponds to approximately 33 uniaxial shortening assuming constant volume because the strain ellipse was measured in only one orientation this strain value is a minimum estimate for the meteorite lack of correlation between foliation and either shock or thermal effects argues that impact or metamorphism are unlikely to have produced this deformation compaction due to overburden from progressive accretion on the chondrite parent body is suggested to have been its cause estimates of maximum deviatoric stresses in the interiors of asteroid sized bodies and constraints on maximum temperatures for cv3 chondrites are consistent with diffusional flow as the deformation mechanism for olivine in these chondrules diffusional flow is also suggested by the scarcity of observed lattice dislocations deformation of leoville olivines by this mechanism at geologically reasonable strain rates appears to require higher temperatures than those believed to have been experienced by this meteorite 600 c however differences in olivine grain size the presence of water or a more complex deformation history might explain this discrepancy

geochemical study on a well in the western canada basin relation of the aromatic distribution pattern to maturity of organic matter abstract thirty one rock samples from a western canada basin well have been analysed for aromatics using glass capillary gas chromatography with simultaneous flame ionization and sulfur selective flame photometric detection a uniform aromatic distribution pattern with a marked predominance of di and tricyclic aromatic hydrocarbons was observed throughout a depth interval of 3000 meters comprising cretaceous and jurassic sediments the very high relative abundance of sulfur aromatics at two narrow intervals in the triassic and mississippian is attributed to a major change in facies gradual changes with increasing depth have been observed for a series of compound ratios which had been calculated from the isomers of methyl and dimethylphenanthrene and their parent compounds these changes reflect the increasing thermal maturation of the sedimentary organic matter a methylphenanthrene index mpi has been introduced which exhibited a very good correlation with vitrinite reflectance data the mpi is the first maturity parameter which is based on a series of aromatic hydrocarbons this hydrocarbon internal maturity parameter permits the recognition and definition of maturity levels in extracts which can be compared to the maturity e g vitrinite reflectance of source rocks

controls on cu mineralization in central part of the kerman porphyry copper belt se iran constraints from structural and spatial pattern analysis abstract the sarduiyeh area in the central part of the kerman porphyry copper belt kpcb se iran contains numerous cu deposits and prospects this area is bound by e w trending major faults which show the northern and southern borders of fault duplex minor faults first second or third orders were identified in three trends of nw n s and ne analysis of the fault kinematics data revealed an extensional fault duplex pattern for this area in this fault zone cu deposits are associated with faults that have a special trend this proposed kinematic model for evolution of sarduiyeh extensional fault duplex emphasizes that the main cu deposits in the sarduiyeh area are located within the dilatational zones related to nw se trending normal faults in this study the spatial pattern analysis conducted by fry fractal fracture density and buffer zones methods support the conceptual model of district scale mechanism of structural controls on final emplacement of cu deposits this investigation of sarduiyeh cu mineralization revealed that the nw se trending faults are effective in localization of cu mineralization in the central part of kpcb

chemical studies of h chondrites ii weathering effects in the victoria land antarctic population and comparison of two antarctic populations with non antarctic falls abstract we report rnaa data for 14 siderophile lithophile and chalcophile volatile mobile trace elements ag au bi cd co cs ga in sb se te tl u zn in interior portions of 45 different h4 6 chondrites 49 samples from victoria land antarctica and 5 h5 chondrites from the yamato mts antarctica relative to h5 chondrites of weathering types a and b all elements are depleted 10 at statistically significant levels in extensively weathered types b c and c samples probably by leaching on the ice sheet surface contents of 8 elements in extensively weathered samples may provide a qualitative ranking for terrestrial surface residence chondrites of weathering types a and b seem compositionally uncompromised and as useful as contemporary falls for trace element studies when data distributions for these 14 trace elements in non antarctic h chondrite falls and unpaired samples from victoria land and from the yamato mts queen maud land are compared statistically numerous significant differences are apparent concentrations of 8 elements differ significantly in the victoria land and non antarctic h5 chondrite populations essentially the same compositional differences and 53 mn content and shock history differences appear when h4 6 populations are compared contents of 8 elements differ when queen maud land and victoria land populations are compared and 5 for the queen maud land non antarctic comparison these and other differences give ample cause to doubt that the various sample populations derive from the same parent population the observed differences do not reflect weathering chance or other trivial causes a preterrestrial source must be responsible the least unlikely of these involves a temporal variation in the source regions from which meteoroids derive

constraints on arabian plate motion and extensional history of the red sea analysis of the geologic and geophysical data from the western and northern margin of the arabian plate combined with data from the red sea gulf of aden leads to an interpretation of arabian plate motion that supports an episodic extensional history in the red sea and gulf of aden phase 1 extension began in medial to late eocene and was caused by the nw propagation of the reoriented central indian ridge spreading center it stretched and thinned continental crust along numerous wrench and normal faults that reactivated preexisting structures first phase extension stopped when the arabian plate terminally sutured to eurasia in the medial miocene and halted northward movement of arabia relative to africa the combined african arabian plates moved north more slowly constricting and thickening continental crust in the bitlis zagros sutures while the red sea remained technically quiescent and accumulated salt by the early pliocene continued northward movement was accommodated by lateral extrusion of large continental wedges north of the bitlis zagros sutures this allowed arabia to move northward faster than africa and reopen the red sea where phase 2 extension was expressed by seafloor spreading extension within the red sea gulf of aden rift system has been controlled by the interactions and effects of two factors 1 convergent processes between the north margin of the arabian plate and the eurasian plate to the north and 2 northwest propagation of extension associated with the medial eocene reorganization of the central indian spreading center

convergence history across zagros iran constraints from collisional and earlier deformation the zagros orogen provides a unique opportunity within the alpine system to evaluate the interplay between a young tertiary collision and earlier subduction obduction processes within the crush zone and the sanandaj sirjan internal zone separating the zagros fold belt from central iran we document several major tectonic events taking place at the end of the cretaceous of the eocene and from the mio pliocene onwards ca 20 15 ma contrary to recent interpretations our data cross sections and description of the overall deformation style strongly suggest that the main zagros thrust mzt is deeply rooted possibly to moho depths and that the suture zone effectively runs along the mzt field observations show that the final resorption of the oceanic domain took place slightly after 35 ma and that collision must have started before ca 23 25 ma in northern zagros the shortening rate across the crush zone since the mid miocene 20 15 ma is estimated at a minimum 3 4 mm year shear movements in the crush zone during the eocene oligocene period and extensional strike slip movements in the internal zones during the late cretaceous point to an oblique setting early in the convergence history a geotectonic scenario for convergence from the time of obduction to the present is finally proposed

comparisons between antarctic and non antarctic meteorites based on carbon isotope geochemistry abstract the whole rock c isotopic composition of a suite of ordinary chondrites indicates that there is a difference between antarctic and non antarctic meteorites however this apparent distinction is not due to an inherent difference in the meteorite source populations but is rather a result of the presence of antarctic weathering products mainly bicarbonates which affect the overall 13 c of these meteorites when these weathering products are removed either by acid washing or combustion to 500 c the perceived division also disappears leading to the conclusion that ordinary chondrites both antarctic and non antarctic have similar 13 c values a similar effect is noted in data from three separate groups of achondrites the ureilites heds and sncs however here the weathering products do not influence total c data in the case of the ureilites this is readily understood since the indigenous c content is high the heds and sncs on the other hand with low indigenous c abundance contain relatively lower concentrations of weathering products compared to ordinary chondrites which can be removed by combustion to 200 c this suggests a different complement of weathering products in the achondritic and chondritic meteorites an effect which may be related to differences in chemistry or porosity the almost ubiquitous occurrence of weathering products with distinctive c isotopic composition highlights the importance of removing all terrestrial contaminants from meteorites with low indigenous c budgets before attempting any interpretation concerning their c abundance or isotopic composition the c chemistry of ci cm and cr chondrites is also subject to problematic interpretation whilst the indigenous c abundance is too high to be compromised by the addition of terrestrial weathering products the inhomogeneous distribution of an array of components with widely varying isotopic signatures leads to a random distribution of 13 c values analyses of individual components insoluble macromolecular material carbonates and silicon carbide reveal that there are no gross differences in c chemistry between antarctic and non antarctic chondrites the few distinctions that do exist might readily be explained by weathering or isotopic exchange in antarctic whilst not forming a separate population antarctic carbonaceous chondrites may extend the range of properties of non antarctic chondrites beyond the currently known limits

solid state cp mas 13 c nmr of the insoluble organic matter of the orgueil and murchison meteorites quantitative study solid state cp mas 13c nuclear magnetic resonance nmr study of the insoluble organic fraction isolated by hf hcl treatment under an inert atmosphere from the orgueil and murchison carbonaceous meteorites is reported based on these spectra eight different types of carbons aro and ali linked ch3 ch2 aliphatic c linked to heteroelements protonated and non protonated aromatic c carboxyls and carbonyls were identified their relative amounts were determined and theoretical nmr derived h c atomic ratios were calculated comparison of these h c ratios with those obtained from elemental analysis revealed that a large part of the carbons of the insoluble fraction of both meteorites are not detected by cp mas 13c nmr taking into account these undetected carbons the relative abundance of aromatic carbons as of the total carbons was calculated as between 69 and 78 in orgueil and 61 and 67 in murchison and thus shown to be much higher than previously thought in addition the nmr data allowed to calculate the ratio of non protonated and protonated aromatic carbons based on previous studies on chemical and thermal degradation the present nmr data were interpreted as reflecting the occurrence of highly substituted rather small aromatic moieties in these insoluble organic materials along with ftir data nmr results also pointed to a relatively high branching level in the aliphatic chains especially for murchison according to the above results the insoluble organic matter in these meteorites did not suffer a marked thermal maturation during the late hydrothermalism of the parent body its synthesis involved a statistical combination of all the possible bonds between ch3 ch2 and ch radicals producing both the aliphatic and the aromatic moieties this model explains not only the chemical features of the chondritic insoluble organic material but also the typical ftir signature of the interstellar medium therefore organic material found in the interstellar medium and that incorporated in the most primitive objects of the solar system seem to share a common organosynthesis

constraints on magma degassing beneath the far southeast porphyry cu au deposit philippines k silicate alteration in the far southeast fse porphyry cu au introduction deposit formed at 1 4 ma concentric to dikes of quartz diorite magmas become saturated with volatile components as porphyry at 2 km paleodepth the hydrothermal system consisted they ascend in the crust and either erupt or crystallize of magmatic hypersaline liquid and vapor at 550 c and 50 at depth saturated magmas that remain at depth exsolve mpa lithostatic pressure advanced argillic alteration formed at an aqueous fluid that forms a hydrothermal system on the same time over the deposit at 1 km paleodepth from acidic separation from the magma chamber burnham 1979 condensates of the vapor at 1 3 ma k silicate alteration was although part of the exsolved fluid a low density vapor overprinted by 350 c magmatic liquid 5 wt nacl equiv may discharge to the surface from passively degassing at hydrostatic pressure sericite alteration and much of the cu au volcanoes hedenquist 1995 part will remain at depth mineralization formed at this later stage evolution of the magmatic and this dense residual magmatic liquid may be asfluid composition was simulated with a magma chamber cryssociated with hydrothermal mineralization in the portallization model homogeneous crystallization during early stage phyry ore environment hedenquist lowenstern convection is assumed whereas at 50 vol crystals the chamber 1994 becomes stagnant and crystallizes from rim to core over a narrow in this paper we use evidence from a porphyry ore crystallization interval the model calculation based on a magma deposit in the philippines to determine the composition chamber with 2 km thickness at 6 km depth 150 mpa and of the fluid that exsolved from the deeper parent magma 800 c saturated melt composition at 30 vol crystals 5 the evolving composition of the magmatic fluid at the wt h2o 0 2 wt cl and dd of 40 can reproduce the depth of the ore body can then be used to place constraints chemical and isotopic compositions of the early and late magmatic on the nature of the evolved magma chamber far below fluids the most critical factor controlling the compositional evolution the porphyry ore body this approach differs from that of the model hydrothermal system is the transition from convective of other studies where a portion of the parent magma to stagnant magma chamber crystallization there is also a sharp chamber is available to study directly e g at yerington decrease in the rate of fluid exsolution associated with this transition nevada dilles 1987 which can account for the thermal collapse of the fse porphyry the far southeast fse porphyry cu au deposit system from k silicate to sericite alteration and overlying lepanto epithermal cu au ore body are

pb isotope bearing on the metallogenesis of sulfide ore deposits in central and southern peru twenty five pb isotope determinations are presented on galena chalcopyrite pyrite chalcocite and cerussite from 15 mineral deposits in the copper iron and polymetallic provinces of central and southern peru the results are evaluated in comparison with the pb isotope signatures of potential source materials which include plutonic rocks of the coastal batholith precambrian basement rocks of the arequipa massif as well as midocean ridge basalts morb of the nazca plate and pacific ocean pelagic metalliferous sediments subducted at the peru chile trench several types of mineral deposits are recognized in the copper province which roughly coincides areally with exposures of the early jurassic to paleogene coastal batholith amphibolitic cu fe skarns with the magnetite pyrite chalcopyrite mineral association define an array with a pb isochron age of 3 2 ga in the 207 pb 204 pb versus 206 pb 204 pb covariation diagram mineral deposits of the copper veins in granitoids association at the cata canete and cobre acari districts plot along the same array the isochron age of 3 2 ga is too old to have chronological significance the array of points is therefore interpreted as the product of mixing between two end members enriched subcontinental mantle produced by mixing in the subduction zone of pelagic and or metalliferous sediments and material from a morb like source and supracrustal sedimentary materials are the most likely end members the pb isotope compositions of disseminated porphyry cu mo deposits are virtually identical to those of the batholithic rocks with which they are genetically linked thus the el molino prospect has high pb ratios typical of plutons near the lima arequipa segment boundary in the coastal batholith mukasa 1986a the pb content of the plutons is chiefly from mixtures of a depleted morb like component and subducted pelagic metalliferous sediments the cerro verde deposit like its host rocks has low 206 pb 204 pb values most easily explained by mixing of materials derived from the precambrian basement with those from the subduction generated enriched subcontinental mantle keel deposits of the auriferous vein association and the unclassified unturos chacaya galena and pyrite deposit show a wide pb isotope scatter in the pacific ocean sediment field as well as both above and below it similarly galena and chalcopyrite from the polymetallic province show major pb isotope heterogeneities extensive metal scavenging from local supracrustal materials occurred demonstrably accordingly metal sulfides along andean type plate margins do not have a unique source

partial melting of thickened or delaminated lower crust in the middle of eastern china implications for cu au mineralization abstract field relations isotope systematics and plate tectonic reconstructions require that felsic adakites in the yangtze block and the dabie orogen eastern china were not derived from a subducting slab despite the signature of a mantle component in the contemporaneous mafic adakite hosts of cu au deposits in the same areas the apparently contradictory requirements are accounted for by a a deep crustal melting origin for barren adakites and b a crustal delamination origin followed by ascent through lithospheric mantle for adakites associated with mineralization the crustal delamination process associated with the prospective porphyries duplicates the metallogenically essential aspects of the subduction environment the importance of adakitic magmas in the genesis of porphyry style cu au deposits is affirmed by these findings but the range of prospective tectonic environments is extended to include an important intraplate postsubduction setting the porphyries of eastern china demonstrate

decrease of hydraulic conductivity in sand at the interface between seawater and dilute clay suspensions abstract the hydraulic conductivity of the seawater fresh groundwater interface zone in coastal aquifers may decrease due to 1 deflocculation and 2 dispersion of small amounts of arrangements of reactive clay minerals that exist in the rock this dispersed phase may influence to a large degree the connectivity between the conducting pores of a sediment a reduction of hydraulic conductivity by 2 3 orders of magnitude was observed in analytically pure sand as well as in shore sand packed in columns when an interface between seawater and a dilute suspension of montmorillonite was created the experiments were done by introducing suspensions of 5 15 30 and 60 mgl 1 of montmorillonite to columns in which a flow of seawater has previously been established an amount of clay as small as 5 10 3 was involved in the creation of low permeability the proposed model for the explanation of the observed reduction of hydraulic conductivity assumes that at a certain stage the fluid begins to behave as a non newtonian fluid since loose networks of clay particles trap 99 of water causing stoppage in the bottlenecks of the porous medium as a consequence the overall sediment behaves as a bingham system with a yield stress coating of sand grains with clay is also assumed to occur in the case of concentrated suspension

3d evolution of fold and thrust belts formed by oblique convergence abstract this paper presents the results of a series of scaled analogue models designed to simulate thrust belt development formed by orthogonal and oblique convergence the models were constructed to produce doubly vergent orogenic wedges with a pro wedge and a retro wedge separated by an uplifted orogenic core models were constructed from homogeneous layered sandpacks in a 3 m 1 3 m deformation rig the progressive evolution of the models was recorded using digital photography and the photographs were animated for analysis the experiments investigated convergence obliquities from orthogonal 90 to as low as 15 obliquity orthogonal models produced long linear critically tapered pro wedge fold and thrust belts parallel to the convergence margin together with a narrow uplifted core and a steep retro wedge thrust system the taper angle of the pro wedge was typically 11 12 whereas the retro wedge maintained a steeper taper of 38 42 models where the convergence vector was oblique at angles of 60 and 45 to the margin produced doubly vergent thrust wedges with thrust faults trending parallel to the margin there was little evidence of linked penetrative strike slip faulting but en echelon riedel like shear systems developed in the 45 oblique model subordinate oblique slip motion was observed on some thrust faults in contrast for 30 and 15 oblique convergence models strong deformation partitioning developed with steeply sloping pro wedges that did not have critical tapers through going linked strike slip faulting was developed that cut the uplifted axial zones of these models analysis of the models by animation of the digital photographs shows how the thrust systems initiated and propagated in particular it is clear that at any one time several thrusts were moving simultaneously serial cross sections through the moderately oblique convergence models 60 45 are almost indistinguishable from the orthogonal model cross sections the results of orthogonal convergence experiments compare well to the map patterns of faults and folds in the salt range pakistan 60 and 45 oblique convergence models compare well to the zagros where some strain partitioning on strike slip faults occurs the highly oblique models show very strong strain partitioning with penetrative margin parallel strike slip faulting similar to that found in ne venezuela

a remote sensing study of active folding and faulting in southern kerman province s e iran geomorphological observations reveal a major oblique fold and thrust belt in kerman province s e iran the active faults appear to link the sabzevaran right lateral strike slip fault in southeast iran to other strike slip faults within the interior of the country and may provide the means of distributing right lateral shear between the zagros and makran mountains over a wider region of central iran the rafsanjan fault is manifest at the earth s surface as right lateral strike slip fault scarps and folding in alluvial sediments height changes across the anticlines and widespread incision of rivers are likely to result from hanging wall uplift above thrust faults at depth scarps in recent alluvium along the northern margins of the folds suggest that the thrusts reach the surface and are active at the present day the observations from rafsanjan are used to identify similar late quaternary faulting elsewhere in kerman province near the towns of mahan and rayen no instrumentally recorded destructive earthquakes have occurred in the study region and only one historical earthquake lalehzar 1923 is recorded in addition gps studies show that present day rates of deformation are low however fault structures in southern kerman province do appear to be active in the late quaternary and may be capable of producing destructive earthquakes in the future this study shows how widely available remote sensing data can be used to provide information on the distribution of active faulting across large areas of deformation

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

recycling of orogenic arc crust triggers porphyry cu mineralization in kerman cenozoic arc rocks southeastern iran pre collisional eocene oligocene arc diorites quartzdiorites granodiorites and volcanic equivalents in the kerman arc segment in central iran lack porphyry cu mineralization and ore deposits whereas collisional middle late miocene adakite like porphyritic granodiorites without volcanic equivalents host some of the world s largest cu ore deposits petrological and structural constraints suggest a direct link between orogenic arc crust evolution and the presence of a fertile metallogenic environment ore hosting kuh panj porphyry intrusions exhibit high sr 400 ppm low y 20 no negative eu anomalies eu eu 1 and relatively non radiogenic sr isotope signatures 87sr 86sr 0 7042 0 7047 relative to eocene oligocene granitoids mainly sr 12 la yb 15 eu eu 1 87sr 86sr 0 7053 0 7068 trace element modeling indicates peridotite melting for the barren eocene oligocene intrusions and a hydrous garnet bearing amphibolite source for middle late miocene ore hosting intrusions the presence of garnet implies collisional arc crustal thickening by shortening and basaltic underplating from about 30 35 to 40 45 km or 12 kbar the changes in residual mineralogy in the source of eocene to miocene rocks in the kerman arc segment reflect probing of a thickening arc crust by recycling melting of the arc crustal keel underplating of cu and sulfur rich melts from fertile peridotite generated a fertile metallogenic reservoir at or near the crust mantle boundary and dehydration melting under oxidizing conditions produced syn and post collisional ore hosting intrusions while the lack of post collisional volcanism prevented the venting of volatiles to the atmosphere from sulfur rich and oxidized adakitic magmas

metal sources in mineral deposits and crustal rocks of ecuador 1 n 4 s a lead isotope synthesis ecuador consists of terranes having both continental chaucha tahuin loja terranes and oceanic macuchi alao salado terranes affinity which were accreted to the amazon craton from late jurassic to eocene four main magmatic arcs were formed by the subduction of the farallon nazca plate since the juras sic a jurassic continental arc on the western margin of the amazon craton a jurassic island arc alao terrane an early tertiary island arc macuchi terrane and a middle late tertiary continental arc encompassing the ter ranes of macuchi chaucha tahuin loja and alao after complete assembly of the ecuadorian crust mineral deposits formed during these magmatic arc activities include porphyry cu and gold skarn deposits in associa tion with the jurassic continental arc polymetallic volcanic hosted massive sulfide deposits vhms in associ ation with the jurassic island arc of alao au cu zn vhms deposits in association with the early tertiary is land arc of macuchi and porphyry cu and precious metal epithermal deposits in association with the middle late tertiary continental arc magmatism on the newly assembled crust of ecuador macuchi chaucha tahuin loja and alao terranes in this study we have compiled 148 new and 125 previously published lead isotope analyses on paleozoic to miocene metamorphic intrusive volcanic and volcanosedimentary rocks as well as on jurassic to miocene magmatic related ore deposits of ecuador lead isotope compositions of the magmatic rocks of the four main arc events derive from mixing of various sources including mantle variably enriched by pelagic sediments and or by a high 238u 204pb component and heterogeneous continental crust rocks lead isotope compositions of the ecuadorian ore deposits display a broad range of values 206pb 204pb 18 3 19 3 207pb 204pb 15 54 15 74 208pb 204pb 38 2 39 2 which is as large as the range previously re ported for all magmatic related ore deposits of the central andean provinces i and ii combined ore deposits formed before complete assembly of the ecuadorian crust through complete accretion of the several terranes i e pre eocene have lead isotope compositions overlapping those of the associated magmatic rocks sug gesting a largely magmatic origin for their lead in contrast post assembly ore deposits i e post eocene have lead isotope compositions that only partly overlap those of the coeval magmatic rocks of the continental arc in fact several ore deposits have lead isotope compositions shifted toward those of the basement rocks that host them suggesting that lead derives from a mixture of magmatic lead and basement rock lead leached by hy drothermal fluids most ecuadorian ores have high 207pb 204pb values 15 55 suggesting a dominant continental crust or pelagic sediment origin of the lead however we caution against concluding that chalcophile metals for ex ample cu and au also have a continental crust origin ore deposits of the different terranes of ecuador irrespective of their age plot in distinct isotopic fields which are internally homogeneous this suggests that lithologic factors had an important control on the lead isotope compositions ultimately lead isotope compositions of the ore deposits of ecuador mirror the isotopic compositions of the rocks of the host terranes and are consistent with the multiterrane nature of the ecuado rian crust

cretaceous tertiary convergence and continental collision sanandaj sirjan zone western iran abstract the sanandaj sirjan zone contains the metamorphic core of the zagros continental collision zone in western iran the zone has been subdivided into the following from southwest to northeast an outer belt of imbricate thrust slices radiolarite bisotun ophiolite and marginal sub zones which consist of mesozoic deep marine sediments shallow marine carbonates oceanic crust and volcanic arc respectively and an inner complexly deformed sub zone late palaeozoic mesozoic passive margin succession rifting and sea floor spreading of tethys occurred in the permian to triassic but in the sanandaj sirjan zone extension related successions are mainly of late triassic age subduction of tethyan sea floor in the late jurassic to cretaceous produced deformation metamorphism and unconformities in the marginal and complexly deformed sub zones deformation climaxed in the late cretaceous when a major southwest vergent fold belt formed associated with greenschist facies metamorphism and post dated by abundant palaeogene granitic plutons in the southwest of the zone a late cretaceous island arc passive margin collision occurred with ophiolite emplacement onto the northern arabian margin similar to that in oman final closure of tethys was not completed until the miocene when central iran collided with the northeast arabian margin

molecular and isotopic indicators of alteration in cr chondrites the cr group of carbonaceous chondrites may represent some of the most primitive extraterrestrial materials available for analysis however in contrast to other chondrite groups the cr organic fraction is poorly characterized the carbonaceous chondrite literature shows that relatively anhydrous thermal processing results in a condensed poorly alkylated o poor macromolecular material while for aqueous processing the converse is true such characteristics can be used to discern the alteration histories of the carbonaceous chondrites we have performed bulk elemental and isotopic analysis and flash pyrolysis on four cr chondrites renazzo al rais elephant moraine eet 87770 and yamato y 790112 to determine the nature of their organic component renazzo al rais and y 790112 release qualitatively similar pyrolysis products although there are some variations al rais macromolecular structure contains substantially higher relative abundances of alkylated and oxidized species and relatively lighter 15n suggesting that it has endured more extensive aqueous processing than the other cr chondrites renazzo appears relatively unprocessed with a low degree of alkylation a lack of detectable nitrogen bearing components and low methylnaphthalene ratio eet 87770 s low abundance of alkylated species suggests its macromolecular structure may be relatively condensed with condensation potentially assisted by a period of mild thermal alteration

investigating the variations in carbon and nitrogen isotopes in carbonaceous chondrites the carbonaceous chondrites contain significant amounts of carbon and nitrogen bearing components the most abundant of which is organic matter stepped combustion data of whole rock and hf hcl residues of carbonaceous chondrites reveal that the organic material can be subdivided operationally into three components 1 free organic matter fom which is readily extractable from whole rock meteorites and is enriched in 13c and 15n 2 labile organic matter lom which has a macromolecular structure but is liberated by hydrous pyrolysis lom is the parent structure for some fom and is also enriched in 13c and 15n and 3 refractory organic matter rom which is also macromolecular but is virtually unaffected by hydrous pyrolysis and is relatively depleted in 13c and 15n the macromolecular entities lom and rom are by far the most abundant organic components present and as such the relative abundances of the 13c and 15n enriched lom and the 13c and 15n depleted rom will have a major influence on the overall isotopic composition of the whole rock meteorite laboratory experiments designed to simulate the effects of parent body aqueous alteration indicate that this form of processing removes lom from the macromolecular material allowing rom to exert a stronger influence on the overall isotopic compositions hence aqueous alteration of macromolecular materials on the meteorite parent body may have a significant control on the stable isotopic compositions of whole rock carbonaceous chondrites the enstatite chondrites are also carbon rich but have been subjected to high levels of thermal metamorphism on their parent body stepped combustion data of hf hcl residues of enstatite chondrites indicate that if they and carbonaceous chondrites inherited a common organic progenitor metamorphism under reducing conditions appears to incorporate and preserve some of the 13c enrichments in lom during graphitisation however when metamorphism is at its most extreme the 15n enrichments in lom are lost

isotopic composition of carbonaceous chondrite kerogen evidence for an interstellar origin of organic matter in meteorites abstract stepwise combustion has revealed systematic patterns of isotopic heterogeneity for c h and n in the insoluble organic fraction m kerogen from the orgueil and murray carbonaceous chondrites those patterns are essentially identical for both meteorites indicating a common source of m kerogen the data cannot be reconciled with a single mass fractionation process acting upon a single precursor composition this indicates either a multi path history of mass dependent processing or a significant nucleogenetic contribution or both if mass fractionation were the dominant process the magnitude of the observed isotopic variability strongly suggests that ion molecule reactions at very low temperatures probably in interstellar clouds were responsible in any case an interstellar rather than solar nebular origin for at least some of the meteoritic organic matter is indicated this has interesting implications for the origin of prebiotic molecules temperatures in the early solar system and the isotopic compositions of volatiles accreted by the terrestrial planets

the origin of chondritic macromolecular organic matter a carbon and nitrogen isotope study the n and c abundances and isotopic compositions of acid insoluble carbonaceous material in thirteen primitive chondrites five unequilibrated ordinary chondrites three cm chondrites three enstatite chondrites a ci chondrite and a cr chondrite have been measured by stepped combustion while the range of c isotopic compositions observed is only delta 13c 30 the n isotopes range from delta 15n approximately 40 to 260 after correction for metamorphism presolar nanodiamonds appear to have made up a fairly constant 3 4 wt of the insoluble c in all the chondrites studied the apparently similar initial presolar nanodiamond to organic c ratios and the correlations of elemental and isotopic compositions with metamorphic indicators in the ordinary and enstatite chondrites suggest that the chondrites all accreted similar organic material this original material probably most closely resembles that now found in renazzo and semarkona these two meteorites have almost m shaped n isotope release profiles that can be explained most simply by the super position of two components one with a composition between delta 15n 20 and 40 and a narrow combustion interval the other having a broader release profile and a composition of delta 15n approximately 260 although isotopically more subdued the ci and the three cm chondrites all appear to show vestiges of this m shaped profile how and where the components in the acid insoluble organics formed remains poorly constrained the small variation in nanodiamond to organic c ratio between the chondrite groups limits the local synthesis of organic matter in the various chondrite formation regions to at most 30 the most 15n rich material probably formed in the interstellar medium and the fraction of organic n in renazzo in this material ranges from 40 to 70 the isotopically light component may have formed in the solar system but the limited range in nanodiamond to total organic c ratios in the chondrite groups is consistent with most of the organic material being presolar