carbonates in fractures of martian meteorite allan hills 84001 petrologic evidence for impact origin carbonates in martian meteorite allan hills 84001 occur as grains on pyroxene grain boundaries in crushed zones and as disks veins and irregularly shaped grains in healed pyroxene fractures some carbonate disks have tapered mg rich edges and are accompanied by smaller thinner and relatively homogeneous magnesite microdisks except for the microdisks all types of carbonate grains show the same unique chemical zoning pattern on mgco3 feco3 caco3 plots this chemical characteristic and the close spatial association of diverse carbonate types show that all carbonates formed by a similar process the heterogeneous distribution of carbonates in fractures tapered shapes of some disks and the localized occurrence of mg rich microdisks appear to be incompatible with growth from an externally derived co2 rich fluid that changed in composition over time these features suggest instead that the fractures were closed as carbonates grew from an internally derived fluid and that the microdisks formed from a residual mg rich fluid that was squeezed along fractures carbonate in pyroxene fractures is most abundant near grains of plagioclase glass that are located on pyroxene grain boundaries and commonly contain major or minor amounts of carbonate we infer that carbonates in fractures formed from grain boundary carbonates associated with plagiociase that were melted by impact and dispersed into the surrounding fractured pyroxene carbonates in fractures which include those studied by mckay et al 1996 could not have formed at low temperatures and preserved mineralogical evidence for martian organisms

the fine grained matrix of the semarkona ll3 0 ordinary chondrite an induced thermoluminescence study to investigate the nature origin and history of the fine grained matrix in semarkona and develop techniques suitable for small samples we have measured the induced thermoluminescence properties of six matrix samples 10 m to 400 m in size the samples had tl sensitivities comparable with 4 mg of bulk samples of type 3 2 3 4 ordinary chondrites which is very high relative to bulk semarkona the other induced tl properties of these samples tl peak temperatures and tl peak widths distinguish them from other ordinary chondrite samples where the tl is caused by feldspar cathodoluminescence images and other data suggest that the cause of the luminescence in the semarkona fine grained matrix is forsterite in some respects the matrix tl data resemble that of semarkona chondrules in which the phosphor is forsterite and terrestrial forsterites from a variety of igneous and metamorphic environments however differences in the tl peak temperature versus tl peak width relationship between the matrix samples and the other forsterites suggest a fundamentally different formation mechanism we also note that forsterite appears to be a major component in many primitive materials such as nebulae cometary dust and stardust particles

aragonite breunnerite calcite and dolomite in the cm carbonaceous chondrites high fidelity recorders of progressive parent body aqueous alteration abstract carbonate minerals in cm carbonaceous chondrite meteorites along with the silicates and sulphides with which they are intergrown provide a detailed record of the nature and evolution of parent body porosity and permeability and the chemical composition temperature and longevity of aqueous solutions fourteen meteorites were studied that range in petrologic subtype from mildly aqueously altered cm2 5 to completely hydrated cm2 0 all of them contain calcite whereas aragonite occurs only in the cm2 5 cm2 2 meteorites and dolomite in the cm2 2 cm2 0 all of the aragonite crystals and most of the calcite and dolomite grains formed during early stages of parent body aqueous alteration by cementation of pores produced by the melting of tens of micrometre size particles of h2o rich ice aragonite was the first carbonate to precipitate in the cm2 5 to cm2 2 meteorites and grew from magnesium rich solutions in the least altered of these meteorites the aragonite crystals formed in clusters owing to physical restriction of aqueous fluids within the low permeability matrix the strong correlation between the petrologic subtype of a meteorite the abundance of its aragonite crystals and the proportion of them that have preserved crystal faces is because aragonite was dissolved in the more altered meteorites on account of their higher permeability and or greater longevity of the aqueous solutions dolomite and breunnerite formed instead of aragonite in some of the cm2 1 and cm2 2 meteorites owing to higher parent body temperatures the pore spaces that remained after precipitation of aragonite dolomite and breunnerite cements were occluded by calcite following completion of cementation the carbonates were partially replaced by phyllosilicates and sulphides calcite in the cm2 5 cm2 2 meteorites was replaced by fe rich serpentine and tochilinite followed by mg rich serpentine in the cm2 1 and cm2 0 meteorites dolomite breunnerite and calcite were replaced by fe rich serpentine and fe ni sulphide again followed by mg rich serpentine the difference between meteorites in the mineralogy of their replacive sulphides may again reflect greater temperatures in the parent body regions from where the more highly altered cms were derived this transition from fe rich to mg rich carbonate replacement products mirrors the chemical evolution of parent body solutions in response to consumption of fe rich primary minerals followed by the more resistant mg rich anhydrous silicates almost all of the cms examined contain a second generation of calcite that formed after the sulphides and phyllosilicates and by replacement of remaining anhydrous silicates and dolomite dedolomitization the ca and co2 required for this replacive calcite is likely to have been sourced by dissolution of earlier formed carbonates and ions may have been transported over metre plus distances through high permeability conduits that were created by impact fracturing

a compositional classification scheme for meteoritic chondrules a taxonomic scheme is proposed for the main component of the primitive chondrite meteorites the chondrules the scheme provides insight into the variety of chondrules originally produced in the primordial solar nebula and the effects on them of secondary processes on meteorite parent bodies it may also contribute to understanding the origin of compositional diversity in the chondrites

origin of chondrule rims and interchondrule matrices in unequilibrated ordinary chondrites optical microscopy electron probe microanalysis scanning electron microscopy and analytical transmission electron microscopy were used to study the interchondrule matrix and opaque chondrule rims in bishunpur krymka semarkona chainpur all ll3 tieschitz and sharps both h3 the size distribution of grains in matrix in bishunpur obeys a power law rims around chondrules tend to be finer grained than matrix and may be layered all rims and matrices studied contain clasts of forsteritic olivine and low ca pyroxene in bishunpur the clasts may be cemented by amorphous glue rich in normative albite and partly altered to smectite rims in krymka sharps chainpur and tieschitz have a densely packed olivine groundmass with a grain size of about 0 1 m in krymka groundmass olivine is fo20 30 and forms interlocking dendrites various fe oxides are present in rims and matrices grain size distribution and chemical data indicate that clastic olivines and pyroxenes are derived from chondrules from analyses matrices rims in the ll group apparently are enriched in a feldspathic component tieschitz rims are slightly enriched but here the feldspathic component is present as white matrix sharps rims are not enriched in a feldspathic component opaque interchondrule matrices and chondrule rims probably formed from the products of fragmentation of chondrules partly induced by contraction of protopyroxene on inversion to clinopyroxene fragmented silica rich chondrule mesostases reacted with fe oxides and na to form the groundmass of fayalitic olivine and feldspathic glue a low temperature nebular or pre solar component is limited to 3 vol of each meteorite so equilibrium condensate was not the carrier of volatiles such as tl and bi

chemical and physical studies of type 3 chondrites ix thermoluminescence and hydrothermal annealing experiments and their relationship to metamorphism and aqueous alteration in type 3 3 ordinary chondrites samples of four type 3 chondrites have been annealed at 400 850 c and 0 77 1 kbar for 10 500 h in the presence of various amounts of water 0 10 wt and sodium disilicate 0 2 molal and their thermoluminescence properties measured after annealing for 20 h at temperatures 600 c the tl sensitivity of the samples increased by factors of up to 40 after annealing at 800 c when both high and low forms were present originally the low form was destroyed preferentially we suggest that these data are consistent with the tl metamorphism trends observed in type 3 2 chondrites being due to the formation of feldspar with structural details being dependent on formation temperature by the devitrification of chondrule glass during metamorphism for types 3 2 the tl data are equally consistent with these types experiencing lower levels of metamorphism than the higher types or with type 3 0 being produced from higher types by aqueous alteration the presence of water with non terrestrial d h ratios and petrographic evidence for aqueous alteration in semarkona lead us to favour the aqueous alteration hypothesis

geochronology of unconformity related uranium deposits in the athabasca basin saskatchewan canada and their integration in the evolution of the basin the importance of geochronology in the study of mineral deposits in general and of unconformity type uranium deposits in particular resides in the possibility to situate the critical ore related processes in the context of the evolution of the physical and chemical conditions in the studied area the present paper gives the results of laser step heating 40ar 39ar dating of metamorphic host rock minerals pre ore and syn ore alteration clay minerals and laser ablation inductively coupled plasma mass spectrometer la icp ms u pb dating of uraninite from a number of basement and sediment hosted unconformity related deposits in the athabasca basin canada post peak metamorphic cooling during the trans hudson orogen of rocks from the basement occurred at ca 1 750 ma and gives a maximum age for the formation of the overlying athabasca basin pre ore alteration occurred simultaneously in both basement and sandstone hosted mineralizations at ca 1 675 ma as indicated by the 40ar 39ar dating of pre ore alteration illite and chlorite the uranium mineralization age is ca 1 590 ma given by la icp ms u pb dating of uraninite and 40ar 39ar dating of syn ore illite and is the same throughout the basin and in both basement and sandstone hosted deposits the mineralization event older than previously proposed as well as several fluid circulation events that subsequently affected all minerals studied probably correspond to far field continent wide tectonic events such as the metamorphic events in wyoming and the mazatzal orogeny ca 1 6 to 1 5 ga the berthoud orogeny ca 1 4 ga the emplacement of the mckenzie mafic dyke swarms ca 1 27 ga the grenville orogeny ca 1 15 to 1 ga and the assemblage and break up of rodinia ca 1 to 0 85 ga the results of the present work underline the importance of basin evolution between ca 1 75 ga basin formation and ca 1 59 ga ore deposition for understanding the conditions necessary for the formation of unconformity type uranium deposits

detection of carbonates in dust shells around evolved stars carbonates on large solar system bodies like earth and mars1 2 the latter represented by the meteorite alh84001 form through the weathering of silicates in a watery co3 2 solution the presence of carbonates in interplanetary dust particles and asteroids again represented by meteorites is not completely understood but has been attributed to aqueous alteration on a large parent body which was subsequently shattered into smaller pieces despite efforts3 4 5 the presence of carbonates outside the solar system has hitherto not been established6 7 here we report the discovery of the carbonates calcite and dolomite in the dust shells of evolved stars where the conditions are too primitive for the formation of large parent bodies with liquid water these carbonates therefore are not formed by aqueous alteration but perhaps through processes on the surfaces of dust or ice grains or gas phase condensation the presence of carbonates which did not form by aqueous alteration suggests that some of the carbonates found in solar system bodies no longer provide direct evidence that liquid water was present on large parent bodies early in the history of the solar system8

characterization of antarctic micrometeorites by thermoluminescence in order to explore the nature and history of micrometeorites we have measured the thermoluminescence tl properties of four micrometeorites three cosmic spherules and one irregular scoriaceous particle that we found in a survey of 17 micrometeorites these micrometeorites have tl sensitivities ranging from 0 017 0 002 to 0 087 0 009 on a scale normalized to 4 mg of the h3 9 chondrite dhajala the four micrometeorites have very similar tl peak temperatures and tl peak widths and these distinguish them from ci most cm cv co and ordinary chondrites however the tl properties of these micrometeorites closely resemble those of the unusual cm chondrite macalpine hills mac 87300 and terrestrial forsterites heating experiments on submillimeter chips of a cm chondrite and a h5 chondrite suggest that these tl properties are have not been significantly affected by atmospheric passage thus we suggest that there is no simple linkage between these micrometeorites and the established meteorite classes and that forsterite is an important component of these micrometeorites as it is in many primitive solar system materials

numerical simulation of strain localization and its relationship to formation of the sue unconformity related uranium deposits eastern athabasca basin canada abstract unconformity related uranium deposits in the athabasca basin canada are spatially associated with reactivated basement faults that cut the unconformity surface between archean to paleoproterozoic basement and paleoproterozoic to mesoproterozoic sedimentary rocks of the athabasca group the sue deposits sue a b c d and e are located in the eastern athabasca basin along a 2 km long north northeast trending structural corridor and have both sandstone hosted sue a and sue b to the north and basement hosted sue c sue d and sue e to the south orebodies all the deposits are structurally controlled by north northeast trending basement faults that demonstrate different degrees of reverse displacements of the unconformity surface however it is not clear why the mineralization is distributed in such a pattern along the corridor in this study both 2 dimensional 2d and 3 dimensional 3d numerical modeling of deformation were conducted to examine the relationship between the distribution of strain and uranium mineralization the modeling shows that dilation positive volumetric strain thought to correlate with the development of extensional fracture systems and dilational jogs that represent potential mineralization sites is primarily controlled by the rheological contrasts in basement rocks and the degree of deformation the presence of faulted graphitic pelitic gneiss associated with the sandstone hosted sue a and sue b deposits favours dilation localized within the sandstone at low degrees of deformation mainly due to the overlying competent hangingwall granitic gneiss in contrast the basement hosted sue c sue d and sue e deposits are associated with dilation zones localized along the contact between the faulted graphitic pelitic gneiss and competent footwall silicified gneiss at higher degrees of deformation the modeling results highlight the importance of both graphitic basement structures and strong rheological contrasts between basement rocks in uranium exploration in the athabasca basin

matrix material in type 3 chondrites occurrence heterogeneity and relationship with chondrules abstract matrix material in type 3 chondrites forms rims on chondrules metal sulfide aggregates ca al rich inclusions and chondritic clasts it also forms lumps up to a millimeter in size which may contain coarser silicates chondrules of all types were found with internal matrix lumps that appear to have entered the chondrules before the latter had crystallized mean concentrations of mg na al and ca in matrix occurrences show up to fivefold variations in a single chondrite variations between mean matrix compositions of individual type 3 ordinary chondrites are almost as large and partly reflect systematic differences between h l and ll matrices such variations are probably a result of nebular separation of feldspathic material and ferromagnesian silicates compositions of chondrules and their matrix rims are normally unrelated although rim compositions are correlated with those of matrix lumps inside chondrules a single chondrule was found with a composition nearly identical to that of its internal matrix lump suggesting that some chondrules may have formed from matrix material matrix lumps are as heterogeneous as chondrules but mean chondrule and matrix compositions differ even allowing for possible loss of metallic fe ni during chondrule formation since bulk compositions of matrix lumps and rims have probably not changed significantly since their formation except for fe mg exchange our matrix samples cannot represent typical chondrule precursor materials

volcanological and tectonic control of stratigraphy and structure in the western deccan traps many of the world s flood basalt provinces form elevated plateaux at the margins of continents although in most cases their present large elevation is not the result of mountain building processes several explanations have recently been put forward to explain such occurrences of epeirogeny the deccan trap basalt province forms one such elevated plateau and results are presented here showing how the epeirogenic uplift in this region combined with crustal subsidence probably associated with the rifting of the indian continental margin has affected the structure of the basalt sequence trace element analytical data are used for samples from numerous vertical sections through the deccan traps lava series along and around the western ghats ridge in india the results reinforce the previously defined stratigraphy of the mahabaleshwar area and extend it over a region covering some 36 000 km2 reaching as far south as belgaum and the trap basement contact these results show that the lava pile is not flat lying but forms a very low amplitude anticlinal fold structure plunging southwards by up to 0 3 over most of the area although in the south there is evidence of a reversal of this plunge the fold is interpreted as being the result of two tilting processes 1 westward tilting near the coast due to the foundering of the passive continental margin and 2 epeirogenic uplift along the whole west coast of india producing the observed topography and the peninsula wide drainage patterns and also the easterly component of dip variations in the magnitude of the latter effect along the western continental margin may also be important in generating the plunge of the fold although the possibility of some component of depositional dip may also be important this latter possibility can be modelled using a simple computer program the results of this modelling show that a migrating linear volcanic edifice fits the observations best

clay minerals and sr nd isotopes of the sediments along the western margin of india and their implication for sediment provenance mineralogy and sr nd isotopic composition of the 2 m fraction of the holocene and late pleistocene sediments from 12 gravity cores collected along the western margin of india were used to delineate the provenance and understand the response of isotopes with respect to the source rock composition holocene sediments show distinct clay mineral associations representing three major sources illite chlorite rich sediments from the indus smectite dominated sediments from the deccan traps and kaolinite and smectite enriched sediments from gneissic rocks the mixing of indus derived sediment with the deccan traps derived sediment or the deccan traps derived sediment with gneissic rock derived sediment occurs in the deeper water cores sr isotopes are very sensitive to weathering and laterization weathering does not influence nd isotopes the 87sr 86sr ratios of the holocene sediments in shallow water cores are higher and fluctuated widely than those in deeper water cores nd correlates well with the clay mineral associations indicating source rock composition or mixing of source sediments kaolinite enriched sediments coupled with high sr ratios and low nd on the sw margin of india suggest intense chemical weathering in the hinterland the influence of the sediment from the ganges brahmaputra transported by the bay of bengal waters during the ne monsoon surface current or sw monsoon underwater current on the composition of the sediments of the sw indian margin is insignificant the late pleistocene sediments reflect a decrease of hydrolytic processes resulting in decrease of smectite and sr isotopic ratio clay minerals and nd values suggest that the provenance and transport pathways of the late pleistocene sediments are the same as those of the holocene for each region

metal rich fluid inclusions provide new insights into unconformity related u deposits athabasca basin and basement canada the paleoproterozoic athabasca basin canada hosts numerous giant unconformity related uranium deposits the scope of this study is to establish the pressure temperature and composition p t x conditions of the brines that circulated at the base of the athabasca basin and in its crystalline basement before during and after uo2 deposition these brines are commonly sampled as fluid inclusions in quartz and dolomite cementing veins and breccias associated with alteration and u mineralization microthermometry and laser ablation inductively coupled plasma mass spectrometry la icp ms data from five deposits rabbit lake p patch eagle point millennium and shea creek complement previously published data for the mcarthur river deposit in all of the deposits investigated fluid inclusion salinity is between 25 and 40 wt nacl equiv with compositions displaying a continuum between a nacl rich brine end member cl na ca mg k and a cacl2 rich brine end member cl ca mg na k the cacl2 rich brine has the highest salinity and shows evidence for halite saturation at the time of trapping the continuum of compositions between the nacl rich brine and the cacl2 rich brine end members combined with p t reconstructions suggest anisothermal mixing of the two brines nacl rich brine 180 30 c and 800 400 bars cacl2 rich brine 120 30 c and 600 300 bars that occurred under fluctuating pressure conditions hydrostatic to supra hydrostatic however because the two brines were u bearing and therefore oxidized brine mixing was probably not the driving force for uo2 deposition several scenarios are put forward to account for the cl na ca mg k composition of the brines involving combinations of seawater evaporation halite dissolution mixing with a halite dissolution brine mg ca exchange by dolomitization na ca exchange by albitization of plagioclase na k exchange by albitization of k feldspar and mg loss by mg rich alteration finally the metal concentrations in the nacl rich and cacl2 rich brines are among the highest recorded compared to present day sedimentary formation waters and fluid inclusions from basin hosted base metal deposits up to 600 ppm u 3000 ppm mn 4000 ppm zn 6000 ppm cu 8000 ppm pb and 10 000 ppm fe the cacl2 rich brine carries up to one order of magnitude more metal than the nacl rich brine though the exact origin of major cations and metals of the two brines remains uncertain their contrasting compositions indicate that the two brines had distinct flow paths and fluid rock interactions large scale circulation of the brines in the athabasca basin and basement was therefore a key parameter for metal mobility including u and formation of unconformity related u deposits

soils and climatic geomorphology on the karnataka plateau peninsular india abstract as a result of extensive field reconnaissance in southern india a geographical traverse across the planation surface of the karnataka uplands which lie in the rainshadow of the western ghats was selected to assess the consequences of a steep rainfall gradient on soil and landform patterns the study of the traverse described in detail reveals a characteristic progression of soil type and wash divide form from the high rainfall to the semi arid end of the continuum and invites a critical reappraisal of classical notions in climatic geomorphology and the soil sciences the assumption that alternations of wet and dry climates are necessary to achieve planation is given special consideration and the often held belief that kaolinite minerals are diagnostic of humid palaeoclimates when found in a semi arid climate is challenged the findings for the indian traverse are set against the better known data for west africa where the rainfall range between the gulf of guinea and the sahel is comparable with that observed in the south western deccan differences outweighing similarities attention is drawn to the possibility that tectonic regime which also controls the degree of landscape stripping is a major key to understanding the climatic geography of soils the tread of planation surfaces and the shape of hillslopes from one region of the tropics to another

identification of relict forsterite grains in forsterite rich chondrules from the mokoia cv3 carbonaceous chondrite magnesium rich forsterite grains fo 98 in feo poor chondrules show variations in cathodoluminescence cl intensity that are associated closely with variations in al 2 o 3 and tio 2 contents cl thus can be used to map the distribution of al and ti in individual grains we describe several categories of cl distribution including grains that are homogeneous grains that are zoned continuously grains that show oscillatory zoning and grains that show a heterogeneous distribution of cl intensity heterogeneous cl intensity is interpreted as the result of disequilibrium growth from the chondrule melt cl surveys of individual chondrules help to identify forsterite grains that are potentially relics in their host chondrules i e grains that did not crystallize in situ from the chondrule melt several of these grains show minor element variations that differ from the majority of melt grown grains in their host chondrules this observation supports the inference that they are relics little evidence exists for growth of individual grains in multiple brief heating episodes identification of the abundance of relict grains is important for determining the thermal histories of chondrules as well as the nature of the precursor assemblages from which they formed

crustal evolution and age of thermotectonic reworking in the western hinterland of the trans hudson orogen northern saskatchewan abstract the hearne province in northern saskatchewan forms the western hinterland of the trans hudson orogen it is a fault bounded terrane lying structurally and geographically between the rae province to its west and the wathaman batholith and orogenic internides to its east the hearne province is comprised primarily of high grade metamorphic archean rocks structurally overlain by archean or proterozoic metasedimentary rocks and intruded by paleoproterozoic granites whereas the rae terrane on its west boundary is comprised primarily of still higher grade archean rocks the calc alkaline wathaman batholith was intruded at ca 1 855 ga and the orogenic internides to the east of it include mostly high grade mafic and intermediate volcanic rocks crystallized between 1 92 and 1 86 ga terminal collision and orogenesis in the internides have been constrained to be later than 1 82 ga and earlier than 1 78 ga mineral u pb data presented here unequivocally demonstrate that high grade metamorphism and large volume anatexis across the southern hearne province were approximately synchronous with terminal collision and high grade metamorphism across the trans hudson orogen zircon data for most samples form complex arrays in concordia space but demonstrate a high grade metamorphic overprint at 1810 1800 ma zircons typically have inherited components of archean age suggesting the presence of extremely old material in the hearne and a potential archean connection with the rae province sm nd data indicating ca 3500 ma model ages for similar parageneses in both terranes further support the proposed archean connection between hearne and rae province and the great antiquity of hearne crust sm nd data also elucidate the similarity of the ca 1 80 ga anatectic granites of the hearne to the 1 82 ga junction granite which intruded the virgin river shear zone and constrains the timing of final motion on that structure monazite 207 pb 206 pb ages are not older than 1812 ma or younger than 1769 ma and rutile 207 pb 206 pb ages and u pb ages are tightly constrained at about 1750 ma these data in combination with results of standard thermobarometric analysis permit determination of post orogenic cooling and denudation rates high cooling 7 c ma and denudation 240 m ma rates suggest fault accomodated uplift during post orogenic collapse

accretionary dust mantles in cm chondrites evidence for solar nebula processes abstract the texture and modal composition of fourteen carbonaceous chondrites of the cm group were studied in detail to unravel the origin of their various components and the evolution of their parent body ies the analysis and mapping of complete thin sections by scanning electron and optical microscopy revealed textural units in most samples in which all coarse grained primordial chondritic components chondrules chondrule fragments refractory inclusions particles rich in hydrous silicates pcp and various mineral fragments are coated by fine grained serpentine and tochilinite rich dust the dust mantled particles have spheroidal shapes and form a special lithology in which they are densely aggregated and compacted without any interstitial clastic material the dust mantles termed accretionary dust mantles and their host lithology called primary accretionary rock are interpreted as products of accretion processes in the solar nebula an origin by processes on the parent body is excluded for textural and mineralogical reasons most cm chondrites are affected by secondary impact induced brecciation of variable intensity except for yamato 791198 which is composed entirely of a primary accretionary rock obviously unaltered by secondary parent body processes such as aqueous alteration or brecciation the cm chondrites y74662 haripura cold bokkeveld kivesvaara mighei pollen nogoya y793321 alh 83100 murray and murchison consist of clasts of primary accretionary rock embedded in a fine grained clastic matrix derived from primary rock material the volume percentage of the clastic matrix ranges from 5 y74662 to 76 murchison bells and essebi are brecciated and affected by aqueous alteration to an extent that fragments of primary rock are not preserved the evaluation of literature data indicates that solar wind implanted noble gases are absent in the primary accretionary rock component of cm chondrites they are only present in brecciated samples it must be concluded from the relation between the content of trapped solar wind and degree of brecciation that 1 the solar noble gases are residing exclusively in the clastic matrix and 2 some cm chondrites are regolith breccias and others are fragmental or monomict breccias both types were formed on the parent body although the latter were never exposed to the solar wind based on the results of textural chemical and mineralogical investigations we conclude that a major portion of the water bearing phases in cm chondrites were produced by the hydration of refractory phases prior to the formation of dust mantles and prior to the formation of the recent cm parent body this process requires special physicochemical conditions which allow the crystallization of oh bearing silicates e g higher density of the nebula gas or special precursor planetesimals of the cm chondrite parent body

the geomorphological and geological importance of palaeosurfaces this special publication is a collection of papers which identifies describes and interprets the occurrence of palaeosurfaces in the geological record the concept of a palaeo surface is one which is generally understood across the geomorphological and geological sciences but according to discipline and application often differs in the emphasis and detail of its interpretation in order to encompass the widest range of contributions and views upon the subject of palaeosurfaces a broad remit was deliberately adopted during the preparation of this volume cations of ancient palaeosurfaces the research areas represented are geographically widespread and include examples from australia africa south america india and europe

geochemical isotopic and geochronlologic constraints on the formation of the eagle point basement hosted uranium deposit athabasca basin saskatchewan canada and recent remobilization of primary uraninite in secondary structures the athabasca basin hosts many world class unconformity related uranium deposits recently uranium reserves for the eagle point basement hosted deposit have increased with the discovery of new mineralized zones within secondary structures a paragenetic study of eagle point reveals the presence of three temporally distinct alteration stages a pre athabasca alteration a main alteration and mineralization comprised of three substages and a post main alteration and mineralization stage that culminated in remobilization of uraninite from primary to secondary structures the pre athabasca alteration stage consists of minor amounts of clinochlore followed by dolomite and calcite alteration in the hanging wall of major fault zones and kaolinitization of plagioclase and k feldspar caused by surface weathering the main alteration and uranium mineralization stage is related to three temporally distinct substages all of which were produced by isotopically similar fluids a major early alteration substage characterized by muscovite alteration and by precipitation ca sr lree rich aluminum phosphate sulfate minerals both from basinal fluids at temperatures around 240 c prior to 1 600 ma the mineralization substage involved uraninite and hematite precipitated in primary structures the late alteration substage consists of dravite uranophane beta veins calcite veins and sudoite alteration from mg ca rich chemically modified basinal fluids with temperatures around 180 c the post main alteration and mineralization stage is characterized by remobilization of main stage uraninite from primary to secondary structures at a minimum age of ca 535 ma u pb resetting events recorded on primary and remobilized uraninites are coincident with fluid flow induced by distal orogenies remobilizing radiogenic pb to a distance of at least 225 m above the mineralized zones

partitioning of ca and al between forsterite and silicate melt in dynamic systems with implications for the origin of ca al rich forsterites in primitive meteorites we report the results of dynamic crystallization experiments that were specifically designed to study the dependence of ca and al partitioning between forsterite and melt in rapidly cooling ca and al rich melts the partitioning of ca between olivine and silicate melt is found to be independent of the cooling rate within the range of 1 5 to 1000 c hr and at cao contents of up to 25 wt within analytical uncertainty our data plot on the equilibrium partitioning curve obtained by libourel 1999 the partitioning behavior of al at high cooling rates is more complex aluminum is much more heterogenously distributed in the olivine and the co existing melt than ca but no systematic trend of al partition coefficient with cooling rate is observed we apply the results of the experiments to the formation of meteoritic forsterites with relatively high contents of ca and al although these forsterites are found frequently inside chondrules the ca contents of their host chondrules are far too low to crystallize these high ca forsterites this is also true for very rapid cooling of chondrule melts the parental melt of these forsterites requires cao contents above 20 wt

topographic features of the sub athabasca group unconformity surface in the southeastern athabasca basin and their relationship to uranium ore deposits topographic features of the sub athabasca unconformity surface such as paleovalleys topographic highs and fault scarps have been documented locally in the eastern athabasca basin and available data indicate that they are spatially associated with mineralization however the mechanisms by which such topographic features were generated their size and distribution at the regional scale as well as their relationship to mineralization are still not completely understood a 100 by 60 square kilometre area of the southeastern athabasca basin encompassing the mcarthur river phoenix and key lake deposits was selected to study the relationship between these topographic features and u mineralization in this region three dominant sets of sub vertical faults were identified on the basis of aeromagnetic data northeast trending north northwest trending and northwest trending a detailed three dimensional 3 d model of this part of the basin was constructed using data from more than 1200 drill holes th

fluid p t x characteristics and evidence for boiling in the formation of the phoenix uranium deposit athabasca basin canada implications for unconformity related uranium mineralization mechanisms abstract the phoenix uranium deposit in the southeastern athabasca basin canada is a typical unconformity contact hosted uranium deposit characterized by an association with reactivated basement faults graphite rich rocks in the underlying basement and a pervasive clay alteration halo surrounding the mineralized zones petrographic results suggest that the mineralizing hydrothermal system was characterized by alternating desilicification and silicification events uraninite and clay size minerals tourmaline kaolinite illite and minor chlorite mainly precipitated in the desilicification periods whereas hydrothermal quartz mainly drusy quartz formed during the silicification periods primary fluid inclusions in the hydrothermal quartz are inferred to represent the ore forming fluids even though quartz did not co precipitate with uraninite the coexistence of multiple types of fluid inclusions liquid dominated biphase vapor dominated biphase vapor only and halite bearing triphase within individual fluid inclusion assemblages is interpreted to indicate fluid boiling and heterogeneous trapping bulk fluid inclusion volatile analysis by mass spectrometry indicates h2o as the dominant species with less than 1 mol non aqueous volatiles that show a compositional trend typical of fluid boiling microthermometric and cryogenic raman spectroscopic analyses indicate that the mineralizing fluids are of h2o nacl cacl2 mgcl2 composition with salinities ranging mainly from 23 4 to 31 1 wt the liquid dominated biphase inclusions excluding those interpreted to have resulted from heterogeneous trapping have homogenization temperatures from 90 to 157 c these data are generally consistent with the classical diagenetic hydrothermal model in which basinal brines that extracted uranium from the basin or the basement were channeled along reactivated basement faults and precipitated uraninite near the unconformity through reaction with reducing agents however the relatively low fluid inclusion homogenization temperatures documented in this paper together with fluid boiling inferred from fluid inclusion assemblages suggest that the deposit may have formed in a shallower environment 2 5 km than assumed in the conventional diagenetic hydrothermal model 5 km abrupt fluid pressure drops during episodic faulting may have resulted in fluid boiling flash vaporization changing the fluid ph and promoting uraninite precipitation with the alternating liquid vapor conjugates of the boiling system resulting in alternating precipitation of quartz and uraninite respectively

oxygen isotopic constraints on the origin of mg rich olivines from chondritic meteorites chondrules are the major high temperature components of chondritic meteorites which accreted a few millions years after the oldest solids of the solar system the calcium aluminum rich inclusions were condensed from the nebula gas chondrules formed during brief heating events by incomplete melting of solid dust precursors in the protoplanetary disk petrographic compositional and isotopic arguments allowed the identification of metal bearing mg rich olivine aggregates among the precursors of magnesian type i chondrules two very different settings can be considered for the formation of these mg rich olivines either a nebular setting corresponding mostly to condensation evaporation processes in the nebular gas or a planetary setting corresponding mostly to differentiation processes in a planetesimal an ion microprobe survey of mg rich olivines of a set of type i chondrules and isolated olivines from unequilibrated ordinary chondrites and carbonaceous chondrites revealed the existence of several modes in the distribution of the 17o values and the presence of a large range of mass fractionation several within each mode the chemistry and the oxygen isotopic compositions indicate that mg rich olivines are unlikely to be of nebular origin i e solar nebula condensates but are more likely debris of broken differentiated planetesimals each of them being characterized by a given 17o mg rich olivines could have crystallized from magma ocean like environments on partially molten planetesimals undergoing metal silicate differentiation processes considering the very old age of chondrules mg rich olivine grains or aggregates might be considered as millimeter sized fragments from disrupted first generation differentiated planetesimals finally the finding of only a small number of discrete 17o modes for mg rich olivines grains or aggregates in a given chondrite suggests that these shattered fragments have not been efficiently mixed in the disk and or that chondrite formation occurred in the first vicinity of the breakup of these planetary bodies

precambrian continental crust of india and its evolution the indian precambrian continental crust exhibits a variety of geological features fashioned at different times by different geotectonic processes the bulk of this crust was formed prior to 2600 m y ago and remobilized at least twice between 2600 2000 m y ago early proterozoic mobile belt epmb and 2000 1500 m y ago middle proterozoic mobile belt mpmb three early precambrian nucleii karnataka kn jeypore bastar jbn and singhbhum sn appear to have survived in the craton and are characterized by low grade supracrustals and tonalitic trondhjemite gneisses formed 3800 2600 m y ago the epmb event involved sedimentation amphibolite granulite facies metamorphism and co 2 k metasomatism and produced amphibolite facies rocks and k granites in the north and charnockite and other granulite facies rocks in the south gold sporadically distributed in the supracrustal rocks of the craton was remobilized during the epmb event k granites form a garland around the central dharwar craton sugg

origin of chondritic forsterite grains abstract iron poor and refractory lithophile element rle rich forsterite grains occur in all major types of unequilibrated chondrites in our laser ablation inductively coupled mass spectrometry la icpms minor and trace element study we show that refractory forsterites rf from carbonaceous cc unequilibrated ordinary uoc and a rumuruti chondrite rc have similar chemical compositions with high rle concentrations and low concentrations of mn fe co and ni fractionation of rles and rare earth elements rees is in agreement with formation by crystallization from a rle rich silicate melt low concentrations and the fractionation of moderately siderophile elements fe co ni in rfs suggests formation at low oxygen fugacity possibly in equilibrium with primitive fe ni metal condensates in a gas of solar composition anomalously high ti in the parental melt can be explained by ti3 ti4 1 5 supporting formation of rf in highly reducing conditions low mn concentrations indicate formation at high temperatures 1160 k the model of formation of rfs and the accompanying physico chemical conditions during their formation as well as their relation to non refractory olivine are discussed

thermoluminescence of forsterite and fused quartz as a candidate for the extended red emission thermoluminescence of silicates interesting in interstellar and circumstellar medium after irradiation of gamma ray and fast neutron is investigated in detail the silicates are forsterite orthoenstatite olivine quartz and crystalline silicon the irradiated enstatite shows weak and broad peaks at 545 and 760 nm on the contrary irradiated bulk and powder samples of forsterite show strong and broad peak at 640 660 nm although thermoluminescence of bulk forsterite is very similar to ere of red rectangle iradiated powdered forsterite did not reveal any sharp emission features over broad band further possibility of thermoluminescence of crystalline silicon is investigated which luminescence scarcely appears it is emphasized that the prominent carrier of ere is forsterite and fused quartz

brine rock interaction in the athabasca basement mcarthur river u deposit canada consequences for fluid chemistry and uranium uptake terra nova 22 303 308 2010 abstract the nature of uranium source rocks transport conditions and deposition processes are still highly controversial for world class unconformity related u deposits this article presents the first detailed chemistry of brines associated with the giant mcarthur river u deposit canada la icp ms analysis of individual fluid inclusions suggests mixing between a na ca mg k sr ba brine and a ca mg na k sr ba brine the brines share a common origin evaporated seawater and show evidence for contrasting interaction with basement rocks the na rich brine lost mg and k in alteration haloes around u ores while the ca rich brine results from na ca exchange and sr ba gain u concentrations 0 3 530 g g 1 are anomalously high compared with usual basinal fluids this indicating that u uptake occurred within basement rocks the two brine end members have mixed within the main u deposit area which could be one of the major driving forces for u deposition

matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 origins and evidence for diverse primitive nebular dust components abstract the mineralogical and chemical characteristics of dark matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 have been investigated in detail by scanning electron microscopy electron microprobe analysis and transmission electron microscopy matrix and fine grained rims on chondrules and other objects are compositionally homogeneous on the scale of 10 m and there are no compositional differences between matrix and rims mineralogically both the matrix and rims are extremely diverse and consist of a highly unequilibrated assemblage of si and fe rich amorphous material olivine pyroxene fe ni metal magnetite pentlandite pyrrhotite anhydrite and mixed layer phyllosilicate phases several distinct components can be recognized within the matrix and rims based on their textural and compositional characteristics which appear to represent basic fine grained units of nebular dust the microstructures of these different components show that they have experienced significantly different thermal histories unlike the ordinary chondrites an origin for any significant component of the matrix or rims in alha77307 from chondrules is improbable based on compositional and microstructural evidence the matrix and rim components in alha77307 formed by disequilibrium condensation processes as fine grained amorphous dust that is represented by the abundant amorphous component in the matrix such condensation could have occurred under a variety of conditions at different times and locations within the solar nebula or possibly earlier in a circumstellar environment subsequent thermal processing of this primitive condensate material in a variety of environments in the nebula resulted in partial or complete recrystallization of the fine grained dust the intimate association of fine grained components with disparate compositions and thermal histories shows that mixing of fine grained dust within the nebula must have been extremely thorough

new insights from 2 and 3 d numerical modelling on fluid flow mechanisms and geological factors responsible for the formation of the world class cigar lake uranium deposit eastern athabasca basin canada the cigar lake uranium deposit in the athabasca basin is the world s second largest high grade unconformity related uranium deposit its distinct geological architecture includes heterogeneous basement lithologies a local basement high and sub vertical faults the sub vertical faults are classified further into two sub types faults that are restricted to the basement termed basement faults and faults that are distinctly related to post athabasca fault reactivation in that they extend upward into the sandstone termed extended basement faults this study aims to evaluate the effects of the aforementioned geological factors on the fluid flow patterns under two different driving forces buoyancy due to variation of fluid density or thermal convection and deformation or a combination of them and to determine the most probable fluid flow scenarios for the formation of the deposit the numerical results show that fluid flow is strongly affected by the two types of faults while the basement faults represent fluid paths with complex fluid flow patterns depending on the driving forces providing favourable physical conditions for different chemical processes such as fluid fluid and fluid rock interactions the extended basement faults enhance the permeability of an e w corridor within the sandstone and significantly strengthen the overall upwelling flow above the basement faults promoting sandstone hosted mineralization the numerical results also suggest that the main deposit likely formed via fluid convection during tectonically quiet periods although faulting played a critical role in increasing permeability in turn enhancing thermal convection

petrographic and oxygen isotopic study of refractory forsterites from r chondrite dar al gani 013 r3 5 6 unequilibrated ordinary and carbonaceous chondrites we have conducted petrographic chemical and in situ oxygen isotopic studies of refractory forsterites from unequilibrated ordinary and carbonaceous chondrites as well as an unequilibrated r chondrite refractory forsterites occur in all types of unequilibrated chondrites and all have very similar chemical composition with low feo and high refractory lithophile element rle contents refractory forsterites are typically enriched in 16o relative to normal olivine independent of the bulk o isotope ratios of the parent meteorites analyses of refractory forsterites spread along a 17o mixing line with 17o ranging from 2 to 10 due to similarities in oxygen isotopes and chemical compositions we conclude that refractory forsterites of various types of chondrites come from a single common reservoir implications of this hypothesis for the chemical and o isotope evolution of silicates in the early solar nebular are discussed

the microstructure of semarkona and bishunpur abstract the ordinary chondrites semarkona and bishunpur appear to have experienced in situ hydrous alteration here we report the results of the first detailed tem examination of them which supports this conclusion in semarkona all but the most magnesian mafic minerals have been destroyed and primary sulphides most likely troilite have been partially altered to phyllosilicates and ni rich pyrrhotite in bishunpur alteration is confined to the production of smectite from an amorphous feldspathic material in the chondrule rims and interchondrule matrix during hydrous alteration of both meteorites the temperature probably did not exceed 260 c the equilibrium composition of the gas present during the alteration of semarkona was not solar but was dominated by h2o the formation of smectite does not require the presence of liquid water however evidence for the redistribution of elements such as ca zn and si over tens of microns or more implies that there was at least some transient grain boundary fluid present the alteration in semarkona and bishunpur is far from complete thermodynamic modelling suggests that more altered ordinary chondrites would be mineralogically similar to the cm and ci carbonaceous chondrites superficially the mineralogy mineral chemistry and bulk chemistry of semarkona matrix rims resemble those of some chondritic interplanetary dust particles cidps the ordinary chondrite parent bodies may therefore be a source of some cidps

shoulder uplift of the western ghats passive margin india a denudational model the paper presents a denudational rift flank uplift model of the western ghats of karnataka india the cenozoic denudation of the deccan plateau was constrained by relative dating of regional planation surface levels in combination with preliminary apatite fission track results the denudational history of the western ghats escarpment coastal foreland was constrained both by onshore fission track and offshore sediment data methods are briefly described results were used as reference data to elaborate a computer simulation model of both flexural rift flank upwarp and escarpment retreat from the k t boundary to the present depending on the assumptions concerning the attributes of the thin elastic lithospheric sheet infinite or semi infinite the shape and elevation of the initial deccan topography flat lying or affected by lithospheric updoming due to the reunion mantle plume and the position of the continental divide upon rifting the flexural response to denudational unloading is shown to yield either a concave up flexure of the dharwar craton or a convex monoclinal downwarp of the margin the relative merits of each model are discussed in the light of auxiliary field evidence particularly from the neighbouring deccan traps however the diverse assumptions on boundary conditions fail to entirely avoid geomorphological equifinality 1998 john wiley sons ltd

compositions and textures of relic forsterite in carbonaceous and unequilibrated ordinary chondrites several percent of the olivine in the c2 c3 and unequilibrated ordinary chondrites uoc can be distinguished by blue cathodoluminescence cl and an unusual composition for forsterite this olivine has the following textural features 1 1 forms cores in single olivine grains 2 2 shows subhedral to euhedral boundaries against rim olivine 3 3 rarely contains inclusions 4 4 has embayments containing olivine like that of the rim 5 5 occurs within chondrules especially in uoc meteorites the blue olivine is always fe poor 0 25 feo 1 0 and shows the following average and maximum values al2o3 0 25 0 5 tio2 0 05 0 09 cao 0 5 0 8 cr2o3 0 15 0 5 and mno 0 02 0 15 vanadium is present within a single olivine and within all blue olivines al ca and ti are strongly positively correlated as are mn fe and cr in olivine surrounding the blue the blue cores are not zoned but each element shows a marked change at the boundary of the blue with al showing the most rapid change these are interpreted as diffusion profiles between rim and core olivine textures suggest initial free growth probably from a gas and later addition of olivine by liquid crystallization to form single crystals or chondrules the unusual olivine composition indicates high temperature growth from a refractory rich reservoir with al entering olivine in tetrahedral coordination vapor growth is suggested as the process allowing the high minor element levels the occurrence of blue olivine in all primitive meteorites indicates that it is relic material which was widespread prior to chondrule and hence meteorite formation similarities in composition exist between this relic olivine and olivine of cosmic dust and deep sea particles pointing to this olivine being a common component in all primitive extraterrestrial material

u redox fronts and kaolinisation in basement hosted unconformity related u ores of the athabasca basin canada late u remobilisation by meteoric fluids proterozoic basement hosted unconformity related uranium deposits of the athabasca basin saskatchewan canada were affected by significant uranium redistribution along oxidation reduction redox fronts related to cold and late meteoric fluid infiltration these redox fronts exhibit the same mineralogical and geochemical features as the well studied uranium roll front deposits in siliclastic rocks the primary hydrothermal uranium mineralisation 1 6 1 3 ga of basement hosted deposits is strongly reworked to new disseminated ores comprising three distinctly coloured zones a white green zone corresponding to the previous clay rich alteration halo contemporaneous with hydrothermal ores a uranium front corresponding to the uranium deposition zone of the redox front brownish zone rich in goethite and a hematite rich red zone marking the front progression the three zones directly reflect the mineralogical zonation related to uranium oxides pitchblende sulphides iron minerals hematite and goethite and alumino phosphate sulphate aps minerals the zoning can be explained by processes of dissolution precipitation along a redox interface and was produced by the infiltration of cold 50 c meteoric fluids to the hydrothermally altered areas u fe ca pb s ree v y w mo and se were the main mobile elements in this process and their distribution within the three zones was for most of them directly dependent on their redox potential the elements concentrated in the redox fronts were sourced by the alteration of previously crystallised hydrothermal minerals such as uranium oxides and light rare earth element lree rich aps the uranium oxides from the redox front are characterised by lree enriched patterns which differ from those of unconformity related ores and clearly demonstrate their distinct conditions of formation uranium redox front formation is thought to be linked to fluid circulation episodes initiated during the 400 300 ma period during uplift and erosion of the athabasca basin when it was near the equator and to have been still active during the last million years a major kaolinisation event was caused by changes in the fluid circulation regime reworking the primary uranium redox fronts and causing the redistribution of elements originally concentrated in the uranium enriched meteoric related redox fronts

chemical and physical studies of type 3 chondrites iv annealing studies of a type 3 4 ordinary chondrite and the metamorphic history of meteorites abstract samples of a type 3 4 chondrite have been annealed at 400 1000 c for 1 200 hours their thermoluminescence properties determined and analyzed for k na mn sc and ca by instrumental neutron activation analysis after annealing at 900 c the samples showed a 50 decrease in tl sensitivity while after annealing at 1000 c it fell to 0 1 0 01 times its unannealed value and loss of na and k occurred the tl and compositional changes resemble those observed for the equilibrated kernouve chondrite after similar annealing treatments except that the sharp tl decrease and element loss occurred at 1100 c this difference is presumably due to petrographic differences in the feldspar of the two meteorites the temperature and the width of the tl peak showed a discontinuous increase after annealing at 800 c peak temperature jumped from 130 to 200 c and peak width increased from 90 to 150 c the activation energies for these tl changes are 7 10 kcal mole similar increases in the tl peak temperature have been reported in tl studies of amelia va albite where they were associated with the low to high temperature transformation however the activation energy for the transformation is 80 kcal mole these changes in tl emission characteristics resemble trends observed in type 3 ordinary chondrites and it is suggested that type 3 3 3 5 chondrites have a low feldspar as tl phosphor and 3 5 have high feldspar as the phosphor thermoluminescence therefore provides a means of palaeothermometry for type 3 ordinary chondrites

the deccan traps an interpretation in terms of progressive lithospheric flexure in response to a migrating load abstract structural and geochemical data from the western ghats india have been used to construct an accurate north south section of the volcanic stratigraphy of the southwest part of the deccan province the characteristic style of the section is one of southerly dip reversing in the extreme south southward overstep of higher units onto pre deccan rocks and down dip thinning of individual formations in contrast an east west section shows continuity of essentially horizontal stratigraphic units without overstepping relationships previous authors have interpreted these data in terms of the progressive southward migration of the volcanic source as india drifted northwards over a hot spot now centered beneath reunion we have compared the observed stratigraphy to the predictions of a geophysical model based on the flexural response of the continental lithosphere to a migrating volcanic load the best fit to the observed section is for the structurally lowest part of the modelled sections with an elastic thickness of the lithosphere of 100 km this value explains the present day width of the traps in peninsula india but requires that up to 5 5 km of the upper part of the flank section has been removed by erosion the origin of the erosion is not clear but it may be related to flexural rebound following removal of the cone loads that formed along the trace of the plume the model cannot explain the subsidence of the traps beneath the shelf off bombay or the rim uplift of the traps in the western ghats we attribute these modifications of the stratigraphy to vertical movements uplift and subsidence that followed rifting of india from the mascarene plateau during the eocene

the millennium uranium deposit athabasca basin saskatchewan canada an atypical basement hosted unconformity related uranium deposit the millennium uranium basement hosted unconformity related deposit is one of the most recent discoveries of basement hosted deposits and may hold as much as 46 8 million pounds 18 000 metric tonnes u at an average grade of 4 53 percent u3o8 the alteration zone associated with the deposit is atypical as it consists predominantly of muscovite rather than the chlorite and muscovite commonly found in the other basement hosted deposits of the athabasca basin the preore stage consists of early minor clinochlore alteration at temperatures of about 275 c interpreted to result from retrograde metamorphism of the basement rocks prior to the deposition of the athabasca basin this clinochlore event is followed by an extensive 1mc muscovite alteration of the basement rocks by na k fe rich basinal brines at temperatures of about 250 c creating up to 25 percent void space in the basement rocks subsequently a weak chamoisite alteration resulted from fe mg ca rich fluids with temperatures of about 300 c that evolved from reactions between the basinal brines and the basement rocks ore stage uraninite has an extrapolated chemical age of 1590 ma and is contemporaneous with synore 1mc muscovite and iron oxide deposited at temperatures near 250 c from fluids with similar 18o but lower d values to preore basinal fluids the low d values indicate postdepositional exchange of h isotopes with cenozoic fluids postore alteration consists of dravite and sudoite precipitated from mg ca rich fluids from the same evolved basinal brines that precipitated preore chamoisite at temperatures of about 185 c filling voids created during the preore stage our results indicate that the pre and synore minerals were formed dominantly by basinal fluids with no contribution from basement fluids which differ from some other basement hosted deposits in the athabasca basin where basement derived fluid influx was more significant several u pb and ar ar resetting events recorded on preore muscovite and on uraninite are coincident with fluid flow induced by distal orogenies remobilizing radiogenic pb from the deposit the radiogenic pb remobilization events were not widespread as the presence of radiogenic pb is restricted to basement rocks proximal to the deposit and along the unconformity

structural constraints and localization of gold mineralization in leather jacket lodes ballarat victoria australia gold mineralization at the ballarat east deposit central victoria australia is hosted in lodes that are historically known as leather jackets these are quartz dominant vein arrays related to low displacement w dipping faults 45 that transect the core and or eastern limb of tight asymmetric n s trending anticlines the leather jacket lodes typically have dip extents from 5 to 65 m widths of 20 m and strike lengths up to hundreds of meters but their along strike continuity is disrupted by oblique low displacement listric faults known as cross courses the gold lodes are characterized by distinct phases of sulfide paragenesis with minor gold arsenopyrite pyrite defining the early sulfide stage late stage coarse gold was precipitated with galena sphalerite pyrrhotite chalcopyrite late pyrite also occurs the gold mineralization events are linked to low strain mineralized fracture networks which are closely related to the final deformation stages and the amplification of the major folds enclosing the lodes this amplification produced domal fold culminations with plunges 30 and localized minor parasitic folds with shallower plunges 10 a network of dilation sites on the w dipping faults preferentially developed in the cores of anticlines particularly in zones where there are changes in strike of bedding or fault bifurcation and refraction through contrasting sandstone and interbedded packages of sandstone and shale numerical three dimensional simulations were undertaken to test our geologic observations and replicate conditions controlling the emplacement of the leather jacket lodes two different scenarios were investigated first to determine how changes in the local stress field orientation influences dilation and fluid infiltration secondly to test variations in fault geometry during the last stages of deformation that is within the final 2 of shortening when most of the mineralized sites were created results show that strain and fluid flow localized along refracted sections of faults and around changes in dip specifically on the shallower dipping sections within subvertical sandstone units this is consistent with the observation that high grade gold bearing quartz is associated with localized changes in fault dip in thicker sandstone and sandstone shale packages there was also a component of strike slip motion and near field nw to se or n to s stress fields which can be attributed to the development of a component of out of plane motion during the development of fold culminations the preferred model for the distribution of the high grade auriferous vein arrays defining the leather jacket lodes is one of fold amplification and extension parallel to the fold axes which produced an increasing out of plane relaxation the main fluid conduits responsible for the leather jacket style of mineralization involve infiltration along steep bedding parallel faults and veins that link up with the arrays of low displacement w dipping faults

matrices of type 3 ordinary chondrites primitive nebular records petrologic studies were made on the fine grained matrices of type 3 ordinary chondrites of the lowest petrologic subtype the matrix minerals in order of abundance are olivine fo99 to fo9 enstatite or bronzite augite or subcalcic augite albite fe ni metal troilite magnetite spinel mgal2o4 chromite and calcite fe and mg rich fluffy particles and albite like particles are also major constituents the chemical compositions of olivine and pyroxenes vary within and among the chondrites and are in gross disequilibrium showing that the matrix materials were hardly heated after their formation textural relationships indicate that magnesian olivine was formed after ca pyroxene followed by intermediate to iron rich olivine intermediate olivine was formed from enstatite and metallic iron under relatively oxidizing conditions the observations indicate that matrices of chondrites are neither the fragments of chondrules nor the precursors of chondrules they were mostly the products of condensation and reaction among solids and or between solids and the ambient gas mostly at low temperatures and thus they contain records of primitive processes in the nebula in order to explain the presence of olivines more iron rich than fo50 the presence of free sio2 or a high activity of sio2 in the gas is necessary which was not shown in previous thermochemical calculations mineral assemblages of matrix minerals of chondrites of different chemical groups differ systematically according to oxidation state of the parental meteorites indicating that they were formed at different oxygen fugacities the rims of chondrules and surrounding matrix materials must have accreted onto chondrules during turbulent movements of the nebula

enhancement of radiative transfer in the upper mantle by oh in minerals abstract diffusion of heat by radiation in the mantle has previously been associated with absorption of light by fe 2 the near ir absorptions of structurally incorporated oh provide another mechanism to convert the energy of photons into lattice vibrations the effective diffusive radiative thermal conductivity due to protonation k rdf wet may be important within the mantle because low absorption strengths as expected for trace to minor oh contents allow light to travel long distances in the medium available calibrations of band strength with oh content are used to develop a formula for k rdf wet as a function of temperature grain size and hydroxyl concentration that is generally applicable to mantle phases these results are compared to new data on the phonon contribution for olivine and to calculations of fe 2 radiative transfer as t increases k rdf wet increases as oh content increases k rdf wet initially increases reaches a maximum near 100 1000 ppm hydroxyl content as h 2 o and then decreases at higher concentrations a similar dependence on grain size exists with the maximum k rdf wet near d 1 cm grain sizes and oh contents of hydrous upper mantle samples foster radiative transport via protonation for example at 1500 k sub cm grain sizes with 10 100 ppm h 2 o provide k rdf wet that is 1 4 of k rdf arising from the combined effect of overtones and fe 2 transitions and 1 8 of the lattice contribution to k of olivine given that oh concentrations vary among mantle minerals the above results suggest that mantle heat flow is heterogeneous and anisotropic the dependence of both k rdf and viscosity on grain size and hydration suggests that the dynamical behavior in or near subducting slabs will be complex

a geological map of the southern deccan traps india and its structural implications a geological map of an area of over 125 000 km 2 within the southern deccan traps india is presented which is based upon variations in the basalt geochemistry it represents a synthesis of new data and earlier work the use of large data sets has allowed stratigraphic boundaries to be established with greater accuracy over a much larger area than before the geochemical sections demonstrate that the southward overstepping stratigraphic style encountered along the ghats ridge has an essentially north to south polarity and that there appears to be detectable overstep in an east to west sense however the stratigraphy defines a pronounced coastward dipping monoclinal flexure across the western ghats ridge between 16 n and 18 n the data are consistent with two models of eruption the first considers the deccan eruptive focus to have been fixed throughout the volcanic episode producing an essentially annular flow pattern the second considers the flow pattern to have been generated from a southerly migrating eruptive centre resulting from the northerly drift of india over a fixed hotspot both hypotheses are consistent with recent quantitative models which suggest that rapid and voluminous flood basalt eruptions are the result of continental rifting events associated with plume generated thermal 9highs9 until a causal link between established plume hotspot trails and impact sites can be satisfactorily demonstrated we find it unnecessary to invoke a cataclysmic impact event as an explanation for the deccan eruptions

minor element signature of relic olivine grains in deep sea particles a match with forsterites from c2 meteorites deep sea particles dsp extracted magnetically from oceanic sediments are the products of aerodynamic heating and cooling of extraterrestrial materials1 most dsp have bulk compositions and elemental ratios similar to ci and cm c2 carbonaceous meteorites2 and some contain relic grains3 of mg rich olivine forsterite here we describe the results of high precision electron microprobe analyses on relic forsterites 26 spots in 13 different dsp comparing their minor element mn cr ca ti al signatures with those of olivines found in several types of meteorites our studies show that the dsp olivines do not match those from terrestrial and lunar rocks and achondritic meteorites4 match poorly those of the carbonaceous allende cv3 and orgeuil ci meteorites5 but are well matched with olivines from c2 meteorites5 6 including the unusual belgica 7904 meteorite7 we believe this demonstrates the power of the minor element signature to fingerprint olivines an idea we have introduced in the accompanying paper5

mixing of sodic and calcic brines and uranium deposition at mcarthur river saskatchewan canada a raman and laser induced breakdown spectroscopic study of fluid inclusions the richest u deposit in saskatchewan canada occurs in the mcarthur river area in the vicinity of the unconformity between the athabasaca sandstones and an archean to lower proterozoic basement paleofluids related to the silicification of the sandstones and the formation of pre and postore cements in breccias were studied using microthermometry raman microspectroscopy and laser induced breakdown spectroscopy libs on individual fluid inclusions a detailed reconstruction of the fluid composition in the system na ca mg cl shows that two types of brines are responsible for the main quartz cements an nacl rich brine 25 wt nacl up to 14 wt cacl 2 and up to 1 wt mgcl 2 which is interpreted as a primary formation water that was expelled from bedded evaporites and a cacl 2 rich brine 5 8 wt nacl 20 wt cacl 2 and up to 11 wt mgcl 2 which is considered to have formed during the interaction between the nacl rich brine and ca rich minerals in the basement and was introduced into the fault system and mixed with the nacl rich brine during the critical stage of u deposition the pressure temperature conditions of formation of the quartz cements are estimated to be 1 200 to1 400 bars and 190 to 235 c for the silicification events during the preore stage and 500 to 900 bars after a pressure decrease from lithostatic conditions and slightly lower temperatures due to the mixing of the nacl rich brine with the cooler approx 140 c cacl 2 rich brine during the main stage of breccia sealing temperature and pressure drops combined with the effects of brine mixing appear to be key factors for the main stages of quartz cementation and u deposition at the mcarthur deposit

late archean manganese mineralization and younger supergene manganese ores in the anmod bisgod region western dharwar craton southern india geological characterization palaeoenvironmental history and geomorphological setting abstract the field setting mineralogical geochemical genetic and depositional features of late archean metasedimentary manganese as well as cenozoic supergene manganese and ferromanganese ores along the 75 km long linear tract of the anmod bisgod region in the western dharwar craton southern india are described the 2700 ma metasedimentary manganiferous formation is underlain by stromatolitic limestone dolomite and quartzite arenite and also occurs within the former the older quartzite arenite which contains redox sensitive detrital pyrite and uraninite as well as thucolite indicates sedimentation under anoxic to oxic transitional palaeoenvironmental condition whereas the younger stromatolitic limestone dolomite indicates development of oxygen in the depositional environment the manganese ore types have been classified into three categories one of which is a mn rich duricrust once capping the late archean manganiferous formation it formed during a cenozoic lateritic weathering event and was eroded in response to crustal uplift perhaps uniquely clastic deposits of the eroded mn duricrust occur in mineable quantities in the form of fluvial palaeochannel fills these cryptomelane rich supergene ores are also suitable for radiometric dating knowing their age would help to constrain the timing of mn duricrust formation and indirectly the regional weathering event responsible for the extensive laterite occurrences of southern india

synchronous egress and ingress fluid flow related to compressional reactivation of basement faults the phoenix and gryphon uranium deposits southeastern athabasca basin saskatchewan canada previous studies on unconformity related uranium deposits in the athabasca basin canada suggest that egress flow and ingress flow can develop along single fault systems at different stages of compressional deformation this research aims to examine whether or not both ingress and egress flow can develop at the same time within an area under a common compressional stress field as suggested by the reverse displacement of the unconformity surface by the basement faults the study considers the phoenix and gryphon uranium deposits in the wheeler river area in the southeastern part of the athabasca basin two dimensional numerical modeling of fluid flow coupled with compressional deformation and thermal effects was carried out to examine the fluid flow pattern the results show that local variations in the basement geology under a common compressional stress field can result in both egress and ingress flow at the same time the fault zone at phoenix underwent a relatively low degree of deformation as reflected by minor reverse displacement of the unconformity and egress flow developed whereas the fault zone at gryphon experienced a relatively high degree of deformation as demonstrated by significant reverse displacement of the unconformity and ingress flow was dominant the correlation between strain development and location of uranium mineralization as exemplified by gryphon and phoenix uranium deposits suggests that the localization of dilation predicted by numerical modeling may represent favourable sites for uranium mineralization in the athabasca basin

paleogeographic maps of the continents bordering the indian ocean since the early jurassic paleomagnetic data from the african plate from the early jurassic onward are critically re evaluated and updated resulting in a set of 30 paleopoles from which an apparent polar wander path is derived using 20 ma intervals this path is then used in conjunction with kinematic models of the indian and atlantic oceans to place other continents bordering the indian ocean eurasia india islands and plateaus madagascar seychelles mascarene and blocks involved in the collision of india with eurasia south tibet indochina in an absolute paleogeographic frame fixed with respect to africa paleogeographic maps are presented for the early jurassic pre breakup the jurassic cretaceous boundary anomaly ml5 the early cretaceous m2 the late cretaceous a 34 the cretaceous tertiary boundary a 29 the early eocene a 24 the middle eocene a 21 and the oligocene miocene boundary a 6 observed and predicted paleomagnetic directions for landmasses other than africa i e for western europe china korea india and australia which are not used in deriving the maps are found to be in very satisfactory agreement the quality of reconstructions as measured by rms discrepancies between observed and predicted paleolatitudes is of the order of 5 the main features of the paleogeographic maps are discussed with the aim of relating oceanic and on land geodynamic events the constraints provided by tibetan data on the india asia collision and the 20 ma reorganization of geology and plate boundaries in a band extending from the south china sea through tibet to the red sea system are discussed in more detail we emphasize the episodic nature of the breakup of gondwanaland and formation of the indian ocean and subsequent interaction with eurasia in which six major discrete events are identified separated by 30 ma phases of rather uniform plate motion

contrasting patterns of alteration at the wheeler river area athabasca basin saskatchewan canada insights into the apparently uranium barren zone k alteration system previous studies on athabasca basin unconformity related uranium deposits have focused on major deposits and have not investigated sites with barren alteration systems that could clarify some of the critical factors controlling mineralization processes a paragenetic study of the wheeler river area reveals the presence of minerals that formed during the diagenetic the main hydrothermal which is subdivided into early mid and late hydrothermal substages and the late alteration stages the diagenetic stage consists of early quartz overgrowths siderite rutile hematite and abundant dickite in the pore spaces of the manitou falls formation the early hydrothermal alteration substage is characterized by pervasive 1mc muscovite alteration and minor goyazite clusters which formed from oxidizing basinal fluids at temperatures around 240 c prior to 1550 ma based on ar ar dates the mid hydrothermal alteration substage comprises dravite and sudoite in the basal 200 m of the manitou falls formation which are interpreted to have formed at temperatures around 175 c from fluids chemically distinct but isotopically similar to the basinal fluids involved during the early hydrothermal alteration substage the late hydrothermal substage was observed only at zone k of the wheeler river area and is characterized by the precipitation of clinochlore copper sulfides and florencite from reducing basement fluids emerging into the manitou falls formation at temperatures around 230 c creating a 250 m high by 250 m wide reducing halo oxidized uranium bearing basinal fluids interacted with the manitou falls formation during the early hydrothermal substage prior to the arrival of the reducing fluids during the mid and late hydrothermal substages and this precluded uranium precipitation the post hydrothermal alteration stage is characterized by formation of kaolinite after late hydrothermal clinochlore near fractures by meteoric waters a minimal amount of leachable radiogenic pb with a pb pb model age of 1907 ma that is older age than both the athabasca basin and the main mineralization event of 1590 ma was encountered at zone k indicating low probability of this area to host uranium mineralization however areas of possible unconformity related uranium deposits were identified outside zone k wherein significant amounts leachable radiogenic pb were observed

structural controls on fluid flow during compressional reactivation of basement faults insights from numerical modeling for the formation of unconformity related uranium deposits in the athabasca basin canada the unconformity related uranium deposits in the athabasca basin canada are generally associated with reactivated basement faults crosscutting the basin basement unconformity two dimensional 2 d numerical modeling of coupled compression and fluid flow in a reverse fault system was carried out with varying dip angles preexisting offsets and degrees of deformation the results indicate that the fluid flow pattern associated with structural reactivation is sensitive to the degree of bulk shortening at a low bulk shortening stage fluid is driven up along the fault zone into the sandstone in the basin whereas at a relatively high bulk shortening stage fluid tends to flow down into the fault zone and the basement this is interpreted to indicate that the fluid pressure within the fault zone increases at the early stage of deformation due to pore volume decreases in relation to shortening whereas the fluid pressure within the fault zone decreases at later stages of deformation due to dilation in relation to fracturing and reverse displacement variation of the dip angles and preexisting offsets of the faults shows little effect on the strain distribution and fluid flow patterns the simulation results demonstrate that both unconformity contact and basement hosted orebodies may be generated at different stages of deformation within the same fault system under a unified compressional stress regime

the age of unconformity related uranium mineralization in the athabasca basin northern saskatchewan age data are presented for major athabasca basin uranium deposits at cigar lake cluff lake collins bay dawn lake eagle point mcarthur river midwest and rabbit lake as well as for several minor or undeveloped deposits including hughes lake and nisto the best constrained data indicate that almost all the deposits formed in a restricted time interval between about 1330 and 1380 ma this range of ages is believed to be real and not the result of uncertainties in the calculation of ages based on discordant data the one major exception is the recently discovered nias free deposit at mcarthur river for which a well determined age of 1514 18 ma 2 has been obtained even this deposit yields an age in the1330 1380 ma range for some material periods of reworking redeposition occurred at 1280 1000 575 and 225 ma these may be basin wide affecting to some degree all the deposits that we have studied other times of redeposition are less well determined but may be present as well no ages tha

formation of u rich mineralizing fluids through basinal brine migration within basement hosted shear zones a large scale study of the fluid chemistry around the unconformity related cigar lake u deposit saskatchewan canada abstract the evolution of basinal brines through percolation into basement rocks is studied in the paleo to mesoproterozoic athabasca basin and its underlying basement this specific geological context includes the evolution of a nacl rich basinal brine to a u mineralizing cacl2 rich brine that is of particular importance for the understanding of the formation of giant u deposits the objective of this study is to determine the physico chemical parameters p t x of the basinal brines and their changes both within the athabasca group sandstones and the underlying basement lithologies on the scale of several km around the world class unconformity related cigar lake u deposit particularly this study focuses on the basement hosted fault systems that are considered to be the main fluid flow pathways a comprehensive study including microthermometry raman spectroscopy and la icp ms analyses was carried out on fluid inclusions as was a semi quantitative estimation of the microfracture paleoporosity based on the surface density of fluid inclusion planes initial nacl rich brines were trapped during early diagenesis c a 1 7 1 65 ga in dickite rich sandstones under a three to seven kilometers thick sedimentary cover at around 90 to 150 c under hydrostatic pressure or at 120 210 c assuming lithostatic conditions at the time of u deposits formation ca 1 46 1 29 ga these brines percolated through the entire basement but preferentially within the damage zones of some graphite rich faults formed during the ca 1 8 ga trans hudson orogeny and active during the subsequent retrograde metamorphism and exhumation ca 1 8 1 72 ga the circulation of the basinal brines into these structures was enhanced and structurally controlled by the microfracture network inherited from earlier brittle reactivation during basement uplift the resulting high microfracture paleoporosity in the vicinity of some but not all of these structures favored intense interaction between the brines and basement rocks that induced the formation of illite sudoite alteration haloes in the basement the percolating brines scavenged mn k ba sr and especially u and evolved from the original nacl dominant composition toward a higher salinity cacl2 rich composition the resulting u bearing brine mixed with the unmodified diagenetic nacl rich brine in above and all along the reactivated faults either during thermal convection in isobaric settings and higher temperatures 110 200 c or through episodic tectonic reactivation in isothermal settings through episodic pressure fluctuation in direct vicinity of the u deposits the interactions between the brines and the basement rocks were the strongest which is marked by the highest intensity of alteration of the host rocks thus the formation of ore forming fluids resulted from the interaction between nacl rich basinal brines and highly microfractured basement rocks this study reinforces the hypothesis that interaction with basement rocks enhanced by strong fluid flow in cataclastic zones can significantly modify the physico chemical characteristics of basin derived brines leading to the formation of mineralizing fluids and the genesis of giant ore deposits such as the unconformity related u deposits

thermal profiles inferred from fluid inclusion and illite geothermometry from sandstones of the athabasca basin implications for fluid flow and unconformity related uranium mineralization abstract the proterozoic athabasca basin and underlying basement host numerous unconformity related uranium deposits that were formed from extensive fluid circulation near the basement cover interface although it is generally agreed that the mineralizing fluids were basinal brines it is still unclear what driving forces were responsible for the circulation of the basinal fluids because different fluid flow driving forces are associated with different thermal profiles knowing the basin scale distribution of paleo fluid temperatures can help constrain the fluid flow mechanism this study uses fluid inclusions entrapped in quartz overgrowths and authigenic illite in sandstones from three drill cores wc 79 1 bl 08 01 and dv10 001 in the central part of the athabasca basin as thermal indicators of paleo fluids in the basin a total of 342 fluid inclusions in quartz overgrowths were studied for microthermometry the homogenization temperatures t h range from 50 to 235 c recording the minimum temperatures in various diagenetic stages temperatures estimated from illite geothermometry 121 points range from 212 to 298 c which are systematically higher than partly overlapping the t h values suggesting that illite was precipitated in hotter fluids following the formation of quartz overgrowths neither the fluid inclusion t h values nor the illite temperatures show systematic increase with depth in individual drill cores this together with the high illite temperatures that cannot be explained by burial at a normal geothermal gradient 35 c km is interpreted to indicate that basin scale fluid convection took place during the diagenetic history of the basin prolonged fluid convection is inferred to be responsible for delivering uranium extracted from the basin or the upper part of the basement to the unconformity where uranium mineralization took place due to redox reactions associated with fluid rock interaction or structurally controlled fluid mixing

modelling of deformation around magmatic intrusions with application to gold related structures in the yilgarn craton western australia abstract this study simulates rock deformation around high temperature granite intrusions and explores how gold bearing shear zones near intrusions were developed in the yilgarn using a new continuum damage mechanics algorithm that considers the temperature and time dependent elastic visco plastic constitutive behaviour of crustal materials the results demonstrate that strain rates have the most significant effects on structural patterns for both extensional and compressional cases smaller strain rates promote the formation of narrow high strain shear zones and strong strain localisation along the flank or shoulder areas of the intrusion and cold granite dome wider diffuse shear zones are developed under higher strain rates due to strain hardening the cooling of the intrusion to background temperatures occurred over a much shorter time interval when compared to the duration of deformation and shear zones development strong strain localisation near the intrusion and shear zone development in the crust occurred under both extensional and compressional conditions there is always clear strain localisation around the shoulders of the intrusion and the flanks of the cold granitic dome in early deformation stages in the models containing a pre existing fault strain localisation near the intrusion became asymmetric with much stronger localisation and the development of a damage zone at the shoulder adjacent to the reactivated fault at higher deformation stages the models produced a range of structural patterns including graben and half graben basin extension pop up wedge structures compression tilted fault blocks and switch of shear movement from reverse to normal on shear zones the model explains in part why a number of gold deposits e g wallaby and paddington deposits in the yilgarn were formed near the flank of granite cored domes and deep tapping faults and shows that the new modelling approach is capable of realistically simulating high strain localisation and shear zone development

tertiary palaeosurfaces of the sw deccan western india implications for passive margin uplift two genetically distinct lateritized palaeosurfaces of different ages are recognized in the southwest deccan traps region of western india using a combination of geochemical topographical and satellite image data the deccan traps were erupted at the cretaceous tertiary boundary c 65 ma and comprise a huge area of originally near horizontal basalt lavas covering much of northwest peninsular india and topographically forming the coast parallel western ghats escarpment and elevated maharashtra plateau to the east remnants of the older palaeosurface currently exist as a series of isolated laterite capped plateaux forming the highest elevations along the western ghats 15 30 18 15 n this surface is of late cretaceous early tertiary age and originally developed upon flows which lay at or near to the top of the lava sequence this lateritization phase was terminated by a period of uplift and extensive erosion in lower to mid tertiary times during which the low lying low relief coastal konkan plain developed through the eastward recession of the ghats scarpline a second phase of lateritisation occurred upon this coastal pediplain during mid to late tertiary times since the earlier uplift had gently deformed the lava pile prior to the development of the pedimented surface the low level konkian laterite lies with marked angular unconformity upon the lava stratigraphy both surfaces have been subject to further large scale distortion resulting from continuing uplift effects development and evolution of these deccan palaeosurfaces is important since together they provide a record of uplift effects in western india moreover they offer a datum against which the uplift erosional history may be further constrained and demonstrate that uplift effects have acted upon the indian margin throughout the tertiary since such longevity of uplift is difficult to reconcile with the commonly cited thermal and dynamic post rift mechanisms known to act upon passive margins the morphological and structural evolution of the rifted deccan margin is better described in terms of denudational isostasy

mechanical controls on fluid flow during regional metamorphism some numerical models the control of fluid flow by plastic deformation during metamorphism is critical to our understanding of metamorphic processes various geological observations and field studies demonstrate the consequences of fluid flow control by deformation so that the concept appears to be accepted at least for small scale public for example faults and vein public however the concept appears to be less well recognized at regional scales considered here are examples of simple conceptual models based on fully coupled mechanical fluid flow concepts they include deformation of a section of fluid saturated crust containing a block or a layer of material of different properties from its surrounds in particular rheological and permeability contrasts between rock types during deformation associated with regional metamorphism are sufficient to control the form of fluid flow over the range of a few kilometres low contrasts and small strains allow pervasive fluid flow whereas greater contrasts and increasing strains cause focusing of the flow such focusing is generally associated with localization of the deformation especially for a strongly dilatant elastic plastic material however a rate of fluid flow much greater than the rate of deformation may result in pervasive flow although for most models pervasive flow is difficult to attain over regional distances furthermore lateral and downward fluid flow may occur demonstrated here by simple models for folding and for deformation of regions containing plutons therefore such modelling may be used as a means of testing the various hypotheses concerning the volumes of fluid predicted to have passed through some rock volumes numerical models of the future will become increasingly complex and powerful allowing greater coupling of thermal mechanical chemical and fluid flow effects and based more on the physical processes involved combined field and laboratory studies will provide correspondingly greater understanding and will permit the determination of the timing of fluid flow and structural controls on fluid flow patterns

fluid flow in extensional environments numerical modelling with an application to hamersley iron ores the mechanical feasibility of focusing both surface and basinal derived fluids towards sites of iron ore genesis during proterozoic deformation in the hamersley province is tested here by computer simulation finite difference modelling of porous media flow during extensional deformation of a mountain range shows that surface fluids are drawn towards areas of failure and focus into the centre of the mountain the addition of permeable structures such as a normal fault provides focused fluid pathways in which mechanical and geological conditions are particularly conducive to both upward and downward flow upward flow from the base of the fault within the model overall is favoured by low permeability basement materials and supra hydrostatic pore pressures downward migration of fluids becomes more prominent as extension progresses and upward fluid flow from the base diminishes the introduction of sedimentary layering into the models allows lateral fluid flow such that sites of potential fluid mixing may then occur within permeable iron formation units close to the fault zone allowing parts of the stratigraphy to become more permeable as a function of high fluid flux simulates permeability enhancement by silica dissolution as a mechanism for iron ore genesis the involvement of both basinal and surficial fluids in the genesis of the ore deposits is supported by the mechanical models and in addition provides an explanation for a progression from relatively reduced to oxidised conditions at the mt tom price deposit and possibly other large deposits with time

the oxygen isotope composition of chondrules and isolated forsterite and olivine grains from the tagish lake carbonaceous chondrite abstract the oxygen isotope compositions obtained by laser fluorination of hand picked separates of isolated forsterite isolated olivine and chondrules from the tagish lake carbonaceous chondrite describe a line 17o 0 95 18o 3 24 r2 0 99 similar to the trend known for chondrules from other carbonaceous chondrites the isolated forsterite grains fo99 6 99 8 18o 7 2 to 5 5 17o 9 6 to 8 2 are more 16o rich than the isolated olivine grains fo39 6 86 8 18o 3 1 to 5 1 17o 0 3 to 2 2 and have chemical and isotopic characteristics typical of refractory forsterite chondrules contain olivine fo97 2 99 8 with oxygen isotope compositions 18o 5 2 to 5 9 17o 8 1 to 1 2 that overlap those of isolated forsterite and isolated olivine an inverse relationship exists between the 17o values and fo contents of tagish lake isolated forsterite and chondrules the chondrules likely underwent greater exchange with 16o poor nebular gases than the forsterite the oxygen isotope compositions of the isolated olivine grains describe a trend with a steeper slope 1 1 0 1 r2 0 94 than the carbonaceous chondrite anhydrous mineral line ccamslope 0 95 the isolated olivine may have crystallized from an evolving melt that exchanged with 16o poor gases of somewhat different composition than those which affected the chondrules and isolated forsterite the primordial components of the tagish lake meteorite formed under conditions similar to other carbonaceous chondrite meteorite groups especially cms its alteration history has its closest affinities to ci carbonaceous chondrites

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

petrographic constraints on the diversity of chondrule reservoirs in the protoplanetary disk abstract chondrules from different chondrite groups show characteristic properties including abundances of different chondrule textural types chondrule sizes oxygen isotope compositions chondrule bulk compositions and petrographic properties of type i and type ii chondrules including abundances of relict grains overall it can be argued that each chondrite group sampled a unique chondrule reservoir and that chondrite groups may represent fractions of larger reservoirs that are represented by chondrite classes these observations provide constraints for models of the early solar system in which it is necessary to establish multiple separate chondrule reservoirs and maintain them over extended time periods models for accretion of chondrite parent bodies must be able to account for localized accretion of chondrules that were formed in spatially or temporally separated reservoirs