lithological and geochemical constraints on the magma conduit systems of the huangshan ni cu sulfide deposit nw china magmatic ni cu sulfide deposits in northern xinjiang china are associated with small mafic ultramafic complexes with the sulfide ores generally occurring in ultramafic rocks the huangshan deposit up to 65 mt of ore at 0 49 ni and 0 31 cu one of the largest magmatic ni cu deposits in northern xinjiang is composed of a layered sequence of lower websterite lower lherzolite websterite norite gabbro gabbro diorite and gabbronorite with sulfide mineralization mainly found in the lower lherzolite lower websterite and websterite systematic variations of the major oxides and trace elements suggest that the rocks of the huangshan deposit are fractionated from the same parental magma with the sharp contact and discontinuous trends of major oxide contents between different lithologies implying intrusion of four distinct stages of magma from a single deep seated staging chamber the reversals in olivine fo contents and major oxides in the lower lherzolite were the result of inhomogeneity in olivine within the lower chamber the se s ratios 63 1 150 10 6 and the negative correlation between se s and 34s 0 63 2 42 of the sulfide ores suggest that a large contribution of crustal s caused the sulfide segregation the sulfides in the lower lherzolite have lower cu contents 1386 2200 ppm and cu pd ratios 2 31 105 1 36 106 relative to those in the mineralized lower websterite cu 2300 to 18 700 ppm and cu pd 6 65 105 to 2 73 106 a positive correlation between pd ir and ni ir for the vein textured sulfides in the lower websterite likely reflects fractionated sulfides picked up by a new pulse of magma in contrast the restricted range of pd ir ratios indicates that the pge contents of the disseminated sulfides in the lower lherzolite resulted from reaction between the sulfides and new pulses of s undersaturated magma

variations in os isotope ratios of pyrrhotite as a result of water rock and magma rock interaction constraints from virginia formation duluth complex contact zones abstract os isotope ratios in pyrrhotite bearing pelitic rocks of the 1 85 ga virginia formation are variable with perturbations linked to the emplacement of the 1 1 ga duluth complex pyrrhotite in footwall rocks of the contact aureole show evidence for a mixing event at 1 1 ga involving a low 187 os 188 os fluid however because rocks with perturbed pyrrhotite os isotope ratios occur 1 km or more from the duluth complex the fluid is unlikely to have been of magmatic origin fluid inclusions in layer parallel quartz veins provide evidence of the involvement of a boiling fluid at temperatures between 300 and 400 c analyses of fluid inclusions via la icp ms show that the fluids contain up to 1 7 wt na 1 1 wt k 4330 ppm fe 2275 ppm zn and 415 ppm mg the veins also contain pyrite or pyrrhotite plus minor amounts of chalcopyrite bornite pentlandite and sphalerite the re os isotopic ratios of pyrite from the veins indicate that they crystallized from low 187 os 188 os fluids 18 o values of vein quartz range from 7 7 to 9 5 consistent with an origin involving fluid with a relatively low 18 o value between 2 and 5 meteoric water with such a low 18 o value could have interacted with the igneous rocks of the complex and would have acquired os with a low 187 os 188 os ratio strongly serpentinized olivine rich rocks of the complex are commonly characterized by such low 18 o values and we propose that the fluid involved in serpentinization was also responsible for the perturbation of the os isotopic system recorded by pyrrhotite in the virginia formation two important observations are that only pyrrhotite bearing assemblages in the contact aureole show isotopic perturbation and that intervals showing os exchange are spatially restricted and not uniformly distributed os exchange and mixing has occurred only where temperatures were sufficient to convert pyrite to pyrrhotite and where time integrated water rock ratios in the aureole were high enough to provide a supply of os troctolitic and gabbroic rocks of the partridge river intrusion duluth complex are characterized by os isotope ratios that are indicative of variable degrees of crustal contamination os values of 0 543 xenoliths of carbonaceous and sulfidic pelitic rocks of the virginia formation found in the igneous rocks provide evidence that os was released by organic matter and pyrite in the sedimentary rocks and assimilated by mantle derived magma however residual pyrrhotite produced as a result of pyrite breakdown in the xenoliths is characterized by 187 os 188 os ratios that are much lower than anticipated and similar to those of pyrrhotite in the contact aureole the os exchange and addition shown by pyrrhotite in the xenoliths highlight an unusual cycle of re os liberation during devolatilization kerogen maturation and pyrite to pyrrhotite conversion processes that contribute to magma contamination followed by os uptake by pyrrhotite during back reaction involving magma and or fluid characterized by a relatively low 187 os 188 os ratio the extreme os uptake recorded by pyrrhotite in the xenoliths as well as the lesser degree of uptake recorded by pyrrhotite in the contact aureole is in line with the high os diffusivity in pyrrhotite experimentally determined by brenan et al 2000 our data confirm that os isotope ratios in pyrrhotite bearing rocks may be readily perturbed for this reason caution should be exercised in the interpretation of os isotope ratios in rocks where pyrrhotite may be the primary host of os

controls on the disseminated ni cu pge sulfide mineralization at the tubane section northern molopo farms complex botswana implications for the formation of conduit style magmatic sulfide ores abstract the molopo farms complex mfc is located near the western margin of the archean kaapvaal craton in southern botswana the complex hosts low grade disseminated ni cu and platinum group elements pge mineralization restricted to the lower ultramafic cumulates notably in the feldspathic orthopyroxenites the mineralized feldspathic orthopyroxenites contain up to 0 47 ppm pt pd au manifested in the form of platinum group mineral pgm assemblages dominated by pge bismuthotellurides asernides and minor au and ag alloys the pgm encountered are froodite pdbi2 moncheite ptte2 michenerite pdbite sperrylite ptas2 largely associated with altered silicates and sulfide minerals the association of pgm with sulfides suggests that they were originally concentrated by sulfide melt while late stage reaction of sulfides with hydrothermal fluids resulted in the observed spatial proximity of pgm with altered silicates the cu pd ratios of most of the rocks fall within the primitive mantle range however the cu pd ratios of the feldspathic orthopyroxenites are more variable with few samples falling above and below the primitive mantle range suggesting the prior sulfide extraction from the magmas and the presence of cumulus sulfides this is supported by the cu zr ratios of these rocks which are also variable above and below unity trace element ratios on the th yb pm versus nb th pm plot indicate strong crustal contamination across all units including those not in proximity to the country rocks the 34s of the magmatic rocks are variable between 6 3 and 11 4 in contrast the 34s of dolomitic siltstones of the transvaal supergroup which constitute the immediate country rocks vary from 4 1 to 0 6 these data indicate that crustal contamination largely occurred prior to magma emplacement it is inferred that the most important contaminant and source of crustal s were the ramotswa and ditlhojana formations that include sulfidic shales at depth we consider that magnesian basaltic magmas of b1 bushveld magma composition underwent crustal contamination assimilation of crustal s and segregation of sulfide melt in the feeder conduit or staging chamber prior to final magma emplacement the feeder conduit or staging chamber was subsequently invaded by further b1 magma this magma entrained some of the sulfides lodged in the plumbing system and flushed them to the final mfc chamber studied here after the staging chamber had already partially solidified it was invaded by yet another influx of magma possibly even more primitive than the b1 bushveld magma being a crystal mush this magma assimilated and entrained some of the previously formed orthopyroxenites manifested by fragments of orthopyroxenite in the harzburgites of the final mfc chamber the presence of centimeter sized globular sulfides and fragments of orthopyroxenite within harzburgites suggests that the complex was emplaced as separate pulses of magmas therefore it is considered that sulfide accumulations may remain undiscovered in the feeder zones or the staging chamber

cu isotope variations between conduit and sheet style ni cu pge sulfide mineralization in the midcontinent rift system north america abstract disseminated ni cu pge sulfide mineralization in sheet like intrusions of the duluth complex are characterized by elevated bulk rock cu ni ratios typically in the range of 3 to 8 in order to evaluate whether the addition of crustal cu to parental magmas may have contributed to the high cu ni ratios cu isotope ratios were measured from sulfide minerals in the disseminated mineralization found within the sheet style partridge river and south kawishiwi intrusions of the duluth complex as well as sulfide mineralization in geometrically distinct conduit style deposits in the eagle intrusion and tamarack igneous complex these intrusions were emplaced during early stages of rift evolution 1110 1105 ma from picritic parental magmas with associated mineralization characterized by lower cu ni ratios in addition cu isotope ratios were determined from sulfidic and carbonaceous sedimentary country rocks to the intrusions 65cu values of disseminated sulfide mineralization in intrusions of the duluth complex range from 0 85 to 0 45 whereas values from the eagle intrusion and the tamarack igneous complex range from 0 69 to 1 84 65cu values of the sedimentary rocks range from 0 33 to 1 18 with two samples showing higher values of 2 65 and 3 12 the 65cu values of the duluth complex mineralization is consistent with the assimilation of significant amounts of sedimentary cu only if the 65cu value of the parental mantle derived magma was lower than 0 25 a value less than that proposed for the mantle based on analyses of terrestrial mafic igneous rocks the distinct difference in 65cu values between the sheet style and conduit style mineralization suggests that either mantle sources of the parental magmas in the rift differed or that cu isotope fractionation accompanied magmatic processes i e variable degrees of melting and sulfide retention sulfide liquid fractionation that were responsible for the relative enrichment of cu in the sheet style intrusions of the duluth complex

sulfur isotope exchange and metal enrichment in the formation of magmatic cu ni pge deposits sulfur isotope measurements provide a useful means of evaluating the source of sulfur in magmatic cu ni pge deposits although low sulfur pge rich deposits e g j m reef of the stillwater complex merensky reef of the bushveld complex show little or no isotopic evidence for the involvement of crustally derived sulfur several high sulfur deposits e g noril sk duluth complex show strong evidence for contamination of mafic magmas by sulfur of crustal origin processes such as magma degassing or redox changes accompanying crystallization are ineffective in significantly modifying sulfur isotope signatures of sulfides that crystallize from immiscible liquids that exsolve from the mafic magmas for this reason 34s values are primarily dependent on sulfur source characteristics and variations can often be treated using a two component mixing approach however deposits such as those at noril sk and voisey s bay that appear to have formed in magma conduit systems present another possibility for modification of sulfur isotope signatures these deposits are thought to have been upgraded in metal tenor by reaction with uncontaminated mantle derived melts that traversed the accumulated sulfide on their way to the surface our calculations illustrate the efficiency of reactions that involve the exchange of fe for cu ni or pge in producing increases in the metal tenor of the accumulated sulfide sulfur isotope exchange between the crustally contaminated sulfide ore accumulation and sulfur of mantle origin may accompany chalcophile element exchange and is capable of masking or limiting the degree of isotopic evidence for the initial stage of ore genesis that involved crustal sulfur sulfur isotope exchange is distinct from the addition of sulfur in the form of immiscible sulfide droplets from a sulfide saturated magma to the accumulated sulfide although both additive mixing and exchange can lead to similar isotopic effects stable isotopic exchange provides a mechanism in addition to additive mixing that may lead to decoupling of different isotopic systems

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

early palaeozoic palaeobiogeography of the variscan regions abstract the palaeobiogeographic method appears to be an attractive alternative for reconstruction of the palaeogeography of the variscan regions during the palaeozoic the evolution of faunal assemblages and climatic characteristics from the cambrian up to the end of the devonian demonstrates that baltica and north gondwana represent two major and independent palaeogeographic entities separated by a mid european rheic ocean which opened as early as the cambrian and closed progressively from the devonian the south armorican ocean whose closure generated the so called ligerian orogen is regarded as a branch of the rheic ocean both a tornquist s sea separating baltica from its western extension avalonia during the ordovician and a proto tethys ocean extending between southwestern europe and north africa during the devonian are excluded from our reconstructions

os nd o and s isotope constraints on country rock contamination in the conduit related eagle cu ni pge deposit midcontinent rift system upper michigan abstract the eagle cu ni pge deposit is hosted by mafic to ultramafic intrusive rocks associated with the marquette baraga dike swarm in northern michigan sulfide mineralization formed in a conduit system during early stages in the development of the 1 1 ga midcontinent rift system the conduit environment represents a prime location for melt rock interaction in order to better assess the extent of country rock contamination in the eagle system a combined trace element nd os o and s isotope study of country rocks sulfide bearing igneous rocks and massive sulfide was undertaken both the eagle and the weakly mineralized east eagle intrusion show trace element patterns that are similar to those of picritic basalts that formed during early stages of rift development the trace element os nd and o isotopic values of the igneous rocks are consistent with os 1100 and e nd 1100 values for the magmas are 34 and 2 18 o values of pyroxene in feldspathic pyroxenite range from 6 5 to 6 6 and provide the only indication that bulk contamination may locally have exceeded 20 sulfur isotopic values of disseminated and massive sulfide in the eagle intrusion range from 0 3 to 4 6 the 34 s values are much lower than those that characterize most of the country rocks but could still be indicative of a contribution of s from country rocks of up to 50 33 s values of the disseminated and massive sulfides range from 0 10 to 0 09 indicating a source in paleoproterozoic country rocks semi massive sulfide in the eagle deposit has 34 s values between 2 2 and 5 3 and 33 s values show a broad range between 0 86 and 0 86 indicating a major contribution from an archean source isotopic data from the eagle deposit strongly indicate that multiple sources of sulfur were involved in the generation of the ni cu pge mineralization and magmas which traversed variable paths through the mantle and crust were focused and utilized the same conduit at the level of the eagle deposit our results emphasize the fact that the sulfur isotopic values of immediate country rocks may not be appropriate as end member values for mixing calculations sulfur derivation from deeper in the conduit system may have involved rocks with very different sulfur isotope ratios in addition sulfur isotopic exchange reactions between passing magma and accumulated crystals or sulfide liquid in the conduit may have led to decreased sulfur isotope variability and 34 s values near those of mantle sulfur

the irish variscides a fold belt developed within a major surge zone an arcuate fold belt characterizes the irish variscides south of the dingle dungarvan line the folds are cross cut by numerous faults which tend to be sinistral in the west and dextral in the east clockwise transection of major fold axes by minor folds and by cleavage has been recorded in the east while anticlockwise transections are common in the west these and other features suggest that north south dextral and sinistral shearing occurred in the east and west respectively this is considered to be a consequence of the morphology of the munster basin which allowed the development of a surge zone in the centre of the fold belt the variscan sole thrust is believed to lie at the base of or within the old red sandstone however to the east thinning of the upper palaeozoic cover sequence forces the sole thrust to cut down laterally stratigraphic section into lower palaeozoic basement in the depocentre the sole thrust surged ahead by propagating along bedding surfaces or possibly a devonian carboniferous extensional detachment beneath the basin while to the east and offshore to the west its propagation was inhibited by the absence of easy decollement horizons within the basement consequently the tip line became strongly arcuate and the thrust developed into a surge zone the sole thrust propagated northwards by stick slip processes much of the deformation within the cover sequence occurred during sticking events particularly fold tightening and accommodation faulting

mechanisms and patterns of o and h isotopic exchange during hydrothermal alteration of the north shore volcanic group and related hypabyssal sills midcontinent rift system minnesota abstract hydrothermal flow systems developed in volcanic and interflow sedimentary rocks in response to the emplacement of 1 1ga mafic plutonic rocks during intracontinental rifting in the midcontinent region oxygen and hydrogen isotopic studies of the north shore volcanic group nsvg northeastern minnesota and related hypabyssal sills demonstrate the importance of both permeability and temperature in controlling isotopic exchange in the rift related hydrothermal system oxygen isotopic values of mineral separates and volcanic whole rocks range from 5 5 to 17 7 and show a strong correlation with whole rock water content and intensity of hydrothermal alteration in the shallow portion of the stratigraphic sequence elevated 18 o values and mineralogical alteration are confined principally to highly permeable amygdaloidal flow tops and bottoms massive flow interiors show little or no perturbation from 18 o values considered normal for fresh basaltic rocks with increased depth and temperature isotopic exchange becomes more pervasive 18 o values remain elevated and oxygen isotopic profiles show no difference between flow margins and interiors at depths where greenschist facies mineral assemblages are found flow margins show a reversal to 18 o values as low as 6 6 and d values decrease to 18 o and d values enhanced rates for hydrogen isotopic exchange relative to oxygen are suggested by whole rock d values that tend to be uniform throughout flows that are less than 7 m thick d profiles that parallel those of 18 o values are found in thicker flows the correlation between degree of hydrothermal alteration and 18 o values suggests that solution recrystallization was the primary mechanism of isotopic exchange in the hydrothermal system individual feldspar phenocrysts from a single lava flow may show a range of 18 o values from 10 5 to 17 7 and ranges in individual altered phenocrysts may be as large as 4 8 feldspar isotopic heterogeneity suggests that permeability varied on a grain to grain scale and that flow through microfractures was important in controlling isotopic variations coexisting plagioclase and pyroxene from hypabyssal sills show a very steep slope on a 18 o plagioclase 18 o pyroxene plot also suggestive of kinetically dominated exchange assuming a fluid buffered system in the permeable flow margins a duration of isotopic exchange on the order of 40 000 years is calculated this time period is short compared to the lifetime of the intrusive activity in the rift and suggests that fluid flow was either episodic in nature or confined to the late stages of magmatic evolution

mineral deposits of the mesoproterozoic midcontinent rift system in the lake superior region a space and time classification abstract the mesoproterozoic midcontinent rift system mrs of north america hosts a diverse suite of magmatic and hydrothermal mineral deposits in the lake superior region where rift rocks are exposed at or near the surface historically hydrothermal deposits such as michigan s native copper deposits and the white pine sediment hosted stratiform copper deposit were major mrs metal producers on going exploration for and potential development of copper nickel sulfide deposits hosted by the duluth complex of minnesota and the opening of the eagle nickel mine in michigan indicate an expanding interest in mrs magmatic deposits mrs hydrothermal and magmatic mineral deposits many of which are significant past present and likely future providers of critical minerals here are placed into a space and time metallogenic framework to construct this framework regional mrs mineral deposits extracted from the u s geological survey mineral resources data system mrds and the ontario ministry of energy northern development and mines mineral deposit inventory mdi were supplemented by other known and recently recognized mineral deposits described in the literature all mineral deposits were classified by deposit type host rock age and type and estimated timing of mineralization deposits were then put into a tectonic evolutionary framework stages for the mrs which shows that deposits formed within discrete spatial and temporal stages of rift evolution each stage of rift evolution is characterized by specific mineral deposit types that are largely confined both by their physical location in rift rocks and type and timing of mineralization examples include mrs nickel rich conduit type magmatic sulfide deposits which are restricted to an early magmatic stage mrs history when magma compositions were characterized by ni rich picrites and high mg basalts in contrast contact type magmatic sulfide deposits with cu ni were derived from more evolved al rich tholeiitic magmas that dominated a later time of voluminous magmatic activity hydrothermal sediment hosted stratiform chalcocite mineralization along the margins of western lake superior in michigan is economic only where fluid flow through red beds was concentrated by structures along the margins of a post volcanic mrs sedimentary basin widespread native cu and native ag mineralization occurred about 40 million years after formation of host basalt lava flows and interflow sedimentary rocks these descriptions of the diverse mineral deposits in the lake superior region cataloged within the space of the local and regional geology and over the more than 60 million year mineralizing history of the mrs are indicative of the complex and at times overlapping magmatic and hydrothermal mineral systems that operated within this major large igneous province

the meuse section across the condroz ardennes belgium based on a predeformational sediment wedge abstract from a critical review of published meuse cross sections it is concluded that the geometry of the predeformational sediment wedge never was discussed for the construction of these sections nevertheless in the ardennes case it represents a major constraint to produce a balanced cross section in order to determine this predeformational sediment wedge the thickness distribution of the several involved stratigraphic levels from lower devonian till lower carboniferous are derived using geostatistical techniques and also taking into account their necessary restoration to a predeformation geography the analysis shows that no synsedimentary faults are required in the predeformational wedge not even at the variscan front the depth and slope of the detachment plane are other constraints for the reconstruction of the predeformational wedge the detachment plane slope is determined using the classical balancing techniques in the yvoir unit in which also the predeformation sediment thickness and hence the detachment depth can be derived the extrapolation southwards is supported by the similar slope of seismic reflectors the stratigraphic levels cut by the detachment plane could be determined using the earlier derived sediment wedge adding to it the upper carboniferous thicknesses determined by maturity and illite crystallinity data the make up of the section is carried out consecutively in three units the namur unit the yvoir unit and the dinant unit in the latter unit the problem of a shale dominated multi layer was handled by considering the envelope of competent layers within the shale as representative for deeper structures a new profile is given taking these specific constraints for the ardennes into account

fabric development and metamorphic evolution of lower palaeozoic slaty rocks from the rocroi massif french belgian ardennes new constraints from magnetic fabrics phyllosilicate preferred orientation and illite crystallinity data abstract this paper presents new results of a petrofabric study from cambrian slates cropping out within the anchi epimetamorphic core of the rocroi massif ardennes variscan fold thrust belt of northern france and southern belgium this study includes measurements of the anisotropy of the isothermal remanent magnetisation airm and the phyllosilicate preferred orientation it completes the previous results of anisotropy of magnetic susceptibility ams and of magnetic mineralogy which were obtained in 47 sites situated in and around this massif these new data allow the characterisation of the different subfabrics carried by the ferromagnetic minerals metamorphic pyrrhotite and magnetite and the paramagnetic matrix fe rich phyllosilicates combined with some illite crystallinity data measured throughout the massif the petrofabric measurements evidence a polyphase tectonometamorphic evolution a major variscan compressional event is evidenced inducing the growth of highly anisotropic pyrrhotite coarse grained hematite and phyllosilicates by contrast the magnetite grains display a less well organised fabric due to the existence of an inherited orientation pattern in agreement with recent metamorphic studies it argues for an early diastathermal metamorphic event developed during a devonian crustal scale extension

stable isotopic studies of mafic sills and proterozoic metasedimentary rocks located beneath the duluth complex minnesota abstract thin 3 20 m picritic to noritic sills are found in the proterozoic metasedimentary footwall rocks of the duluth complex minnesota the sills were emplaced prior to the major intrusions that comprise the duluth complex and underwent contact metamorphism along with the country rocks oxygen hydrogen and sulfur isotopic compositions of the sills indicate a varied history of isotopic exchange between minerals melts and hydrothermal fluids in the high temperature environment below the major plutonic bodies of the midcontinent rift system the pre duluth complex sills exhibit a range in 18o values from 4 9 to 14 8 with values between 6 and 7 generally found in sill interiors high 18o values near sill contacts with high 18o metasedimentary rocks of the pelitic virginia formation or biwabik iron formation coupled with a smooth sigmoidal isotopic profile centered at the contact suggest that oxygen diffusion was an important exchange mechanism the elevated 18o values near the center of the thickest sills are thought to reflect the emplacement of isotopically contaminated basaltic magma dehydration reactions in the pelitic rocks of the contact aureole liberated high 18o fluids that enhanced subsolidus diffusive exchange advective displacement of the diffusion profiles toward the sill interior is less than 40 cm and suggests that layer parallel flow dominated in the dehydration of the contact aureole elevated but uniform 18o values 9 7 to 10 5 in thinner sills suggests that oxygen diffusivity was increased relative to country rocks due to enhanced porosity perhaps related to extensive development of microcracks although d values of the pelitic country rocks record a history of dehydration systematic variations of d 64 to 143 and h2o 0 15 to 5 40 wt content are not found in the sills 18o values of coexisting plagioclase and pyroxene from the sills indicate a close approach to isotopic equilibrium and are consistent with a diffusion dominant exchange process at temperatures near 500 c results of diffusion modelling suggest a duration of isotopic exchange that may have extended from tens of thousands of years to 1 4 ma depending on local controls of porosity and permeability as well as rates of fluid production in the contact aureole localized areas of 18o and d depletion in the sills values as low as 4 9 and 143 respectively denote exchange with meteoric water after interaction with the high 18o metamorphic fluids in the contact aureole although all of the elevated 18o samples in the contact environment may have suffered 18o depletion most exchange with meteoric water appears to be spatially localized and is thought to reflect highly channelized fracture controlled fluid flow sulfur isotopic values of the sills are variable 2 7 to 11 2 and indicative of an evolution involving pre emplacement contamination of basaltic magma and sub solidus exchange with an h2s bearing metamorphic fluid sulfur contents exceed 3 0 wt only within troctolitic to melatroctolitic sills and 34s values of 7 8 to 8 3 are strongly suggestive of pre emplacement contamination by sulfur derived from a proterozoic sedimentary unit high 18o and 34s rocks particularly at sill margins are consistent with either hydrothermal precipitation of fine grained sulfide minerals or isotopic exchange between magmatic sulfides and an h2s bearing metamorphic fluid

the possible role of fluids for the structuring of the continental crust abstract some well known seismic reflectivity patterns of continental crusts characterize specific tectonic terranes the role of fluids in enhancing or destroying such structures is studied seismicity is strongly dependent on the different pore pressure of fluids in intraplate settings in strike slip or extensional areas hydrostatic pore pressure seems to be approached in accordance with standard rheological models and standard seismicity depth distributions in suture zones or zones of developing loads possibly also along zones of near horizontal normal faults extremely high pore pressure develops which approaches lithostatic values they are accompanied by a number of weakening processes with enhanced shear and reduced viscosity these values correlate with low seismic velocities v p in accordance with an empirical v p relationship

tectonics and plate tectonics model for the variscan belt of europe abstract a plate tectonics model is presented to explain the tectonometamorphic characteristics of the european variscides after the closing of two oceanic domains by two sided subduction 500 420 ma and obduction 420 380 ma collision of the european and african continental plates occurred we propose that the subsequent complex intracontinental deformation 380 290 ma is the result of a double subduction of the continental lithosphere accompanied by crust mantle decollement this mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the variscan belt accounting for this model and for the relationships between the european variscides and the other paleozoic peri atlantic belts caledonides appalachian mauritanides and morocco we infer the relative positions of africa america and europe between the silurian and the permian

mechanism for postliquefaction water film generation in layered sand soil investigations at two sites demonstrate that layered structure or stratification in sand deposits is prevalent not only in reclaimed ground but also in natural alluvial ground one dimensional liquefaction tests in a lucite tube are then carried out for models of several types of layered sand indicating that water films will develop under most circumstances beneath or within less permeable sublayers a basic mechanism for the water film generation is discussed based on the measurements of soil settlement and excess pore pressure the development of the water film and the associated soil settlement are numerically simulated by a simple sedimentation analysis and a rational explanation of the test results is found thus a significant involvement of water films in liquefied sand deposits and their basic mechanism are clarified it is highly probable that water films are involved as a part of a sliding surface and play a significant role in a seismically induced flow failure in loose and layered sand deposits during liquefaction

mineralogic and oxygen isotopic studies of open system magmatie processes in the south kawishiwi intrusion spruce road area duluth complex minnesota the south kawishiwi intrusion located along the western margin of the duluth complex minnesota is one of several composite intrusions that are found in the complex the duluth complex is the principal exposed plutonic portion of the 1 1 ga midcontineni rift system in the spruce road area the south kawishiwi intrusion is divided into seven distinct units that are part of the broader south kawishiwi troctolite series defined by severson tech rep nrri tr 91 13a natural resources research institute university of minnesota duluth 1994 units may be characterized as follows unit i basal accumulation of heterogeneous gabbro troctolite and norite unit ii norite with abundant inverted pigeonite unit iii troctolite and olivine gabbro with local oxide rich layers unit iv melatroctolite troctolite olivine gabbro unit v increased plagioclase abundance in troctolites and leucocratic troctolites unit vi strongly altered troctolite unit vii similar to unit v troctolite and leucocratic troctolite country rocks in the spruce road area are granodiorite to quartz monzonite of the archean giants range batholith sutfide mineralization consisting of 1 5 vol of disseminated pyrrhotite cubanite chalcopyrite andpentlandite occurs in units i ii iii and vi oxygen isotopic analyses indicate that unit ii has experienced extensive crustal contamination 5o values of unit ii range from 69 to 7 l o and are 0 enriched compared with values of 5 1 6 8 o found in other units silica contamination is indicated based not only on 5 0 values but also by the predominance of orthopyroxene in the unit possible high 0 contaminant rocks include the giants range batholith and pelitic rocks of the lower proterozoic virginia formation or biwabik iron formation mass balance computations suggest that units in the spruce road area may be related through varying degrees offractionation of a high al olivine tholeiite magma modeling of trace element concentrations and variations in mineral chemistry suggest that discontinuities within the major units developed by in situ boundaryaayer equilibrium crystallization of solidification zones 20 50 m in thickness followed by recharge of fresh magma upward enrichment of incompatible elements olivine fa content and plagioclase ab content may be effectively explained by this process 5 0 values of uncontaminated rock types are strongly correlative with modal mineralogy and can also be modeled by boundary layer fractionation a parental magma 5 0 value of 6 3 o is calculated for unit vii based on olivine and plagioclase values and is similar to that of several other large layered mafic intrusives

geological interpretation of dekorp 2 s a deep seismic reflection profile across the saxothuringian and possible implications for the late variscan structural evolution of central europe abstract a 250 km long deep seismic section the first of its kind in west germany s dekorp project is interpreted in terms of late variscan collisional tectonics the structural model used is based on the intracontinental thrust tectonics concept of modern collision orogens the crustal profile across the saxothuringian zone seems to indicate north facing ramps antiformal stacks and culminations within the crystalline basement of the internal mid european variscides that have been only partially overprinted by permo mesozoic crustal stretching

mineralogy geochemistry and genesis of clays interlayered coal seams succession in the neogene lacustrine seyitomer coal deposit kutahya western turkey abstract the seyitomer coal deposit is an important source of energy in turkey this study aims to determine mineralogical geochemical characteristics and genesis of clays associated with coal seams in order to identify their precipitation environment the late miocene pliocene units comprise organic rich shale organic rich marl marl coal seam siltstone and sandstone deposited in a fluvial and lacustrine environment with associated tuff and tuffite in the seyitomer coal deposit serpentinite sandstone organic rich shale and tuffaceous host rocks of the coal deposit are partly to completely argillized and partially carbonate cemented having also stockwork type silica in fill fissures smectite illite and kaolinite are associated with quartz feldspar olivine gypsum and pyrite oriented flaky illite with irregular outlined kaolinite and smectite flakes edging and coating relict feldspar and volcanic glass grains developed by a dissolution precipitation mechanism in an alkaline micro environment during deposition and diagenetic process the occurrence of subrounded microorganisms on resorbed feldspar and the coexistence of smectite illite flakes with organic matter pyrite and siderite indicates that degradation of feldspar and devitrification of volcanic glass is biologically mediated the slight enrichment of heavy rare earth elements hree compared to light rare earth elements lree with a positive eu and ce anomalies reflects fractional crystallization of feldspar and amphibole alteration of feldspar biotite serpentine and volcanic glass resulted in the concentration of al fe mg and k in a stagnant environment and precipitation of beidellitic smectite and illite in an alkaline environment kaolinite precipitated in an acidic open hydrological system an increase in ni co and v v ni ratios in altered units also suggest anoxic and anoxic to dysoxic conditions occurrence of pityosporites microalatus pinus laevigatosporites haardti pityosporites spp polyvestibulopollenites verus alnus compositae and graminae in the seyitomer coal deposit suggest subtropical to warm temperature humid climate during late oligocene middle miocene period association of argillization and silicification with coal microorganisms pyrite and gypsum indicates a swampy environment and partial hydrothermal processes this interpretation is corroborated by the calculated formation temperatures from stable isotope analysis of 30 463 c for smectite and 140 156 c for illite the high 34s isotope values 16 8 33 3 indicate a mixed diagenetic and hydrothermal origin for the sulphide and sulfate minerals

the deep structure of the ardennes variscan thrust belt from structural and ecors seismic data abstract a new crustal tectonic model is proposed for the ardennes external variscides of northern france belgium on the basis of original microtectonic data further complemented by revised ecors deep seismic information this model is illustrated by both restored and balanced crustal sections that clearly emphasize the direct control exerted by pre existing extensional structures on the collision related processes of variscan deformation indeed the deep structure of the ardennes belt appears as a continental accretionary prism that thickens south towards the hinterland above a staircase type basal thrust innermost crustal shortening is here assigned to a deeply rooted foreland directed ramp thrust system soled at depth by a thick ductile decoupling shear zone actually imaged at about 20 km depth on the ecors section this thrust system is bounded upwards by a shallow infra devonian roof thrust to account for the present day high structural position of the rocroi cambrian inlier as well as for its internal superimposed ductile fabrics major uplift of a previously sheared crust is assumed to have occurred along a frontal ramp which nucleated on an early s dipping extensional fault the rocroi fault according to the ecors data the hanging wall of the rocroi fault has been translated about 40 km northwards along the dinant infra devonian shallow decollement this estimate is quite consistent with the 40 stratal shortening undergone at its front by the devonian detached cover whose thin skinned fold thrust structures also reflect the direct influence of early devonian normal faulting basin inversion tectonics are clearly expressed along the frontal thrust zone where the thin condroz basement sheet is now interpreted as resulting from slicing of the dinant decollement through the footwall of a major lower devonian extensional fault scarp that separated the namur shallow shelf from the dinant downthrowing basin the present thrust model also implies that the dinant decollement extends as a blind thrust beneath the slightly detached namur carboniferous coalfield and that the midi frontal ramp only represents a minor out of sequence thrust reactivating a rotated basement cover contact

hydrothermal flow systems in the midcontinent rift oxygen and hydrogen isotopic studies of the north shore volcanic group and related hypabyssal sills minnesota abstract rift related lavas of the north shore volcanic group nsvg are intruded by plutonic rocks of the duluth complex along the unconformity between the nsvg and the underlying proterozoic metasedimentary rocks animikie group and archean volcano sedimentary and plutonic rocks heat associated with the emplacement of the mafic intrusions generated fluid flow in the overlying plateau lavas 18o values for whole rocks from the nsvg and hypabyssal sills range from 5 5 to 17 7 and 5 3 to 11 5 respectively and most values are higher than those considered normal for basaltic rocks 5 4 to 6 0 in general there is a positive correlation between whole rock 18o and water content which suggests that elevated 18o values are related primarily to secondary mineral growth and isotopic exchange during hydrothermal alteration and metamorphism 18oh2o values computed from amygdule filling minerals such as smectite chlorite and epidote found in low to high temperature metamorphic zones range from 1 to 6 with an average value of 3 smectite in the lower grade zones gives computed dh2o values between 26 and 83 whereas epidote in the higher grade zones gives dh2o values of 15 to 6 fluid isotopic compositions computed from epidote and smectite values are suggestive of the involvement of at least two fluids during the early stages of amygdule filling fluid d and 18o values determined from epidote at the higher metamorphic grades indicate that seawater dominated the deeper portions of the system where greenschist facies assemblages and elevated 18o values were produced in flow interiors as well as margins smectite isotopic compositions suggest that meteoric water was predominant in the shallower portions of the system the increase in 18o values of massive flow interiors with depth is interpreted as a result of rock interaction with a fluid of constant oxygen isotopic composition with increasing temperature the stable isotopic data are supportive of previous suggestions that seawater was involved in the hydrothermal system associated with the midcontinent rift although the origin of the seawater remains problematic it appears that marine incursions may have occurred during the late stages of portage lake volcanism and periodically thereafter

accretion of a rifted passive margin the late paleozoic rhenohercynian fold and thrust belt middle european variscides in the western rhenish massif the rhenohercynian fold and thrust belt of the middle european varsicides exposes a telescoped complete devonian to early carboniferous passive margin this permits the analysis of geometry and kinematic processes of passive margin accretion to an erogenic wedge during variscan collision 330 300 ma the sedimentary cover of the passive margin was shortened by some 50 or 180 km crustal scale balancing and restoration reveals a wide symmetric rift with a central graben a marginal plateau separated this failed lower devonian rift from an emsian middle devonian oceanic basin in the south remnants of which are preserved in the southernmost imbricates and the giessen harz nappes the seismically well imaged aachen midi detachment faille du midi acted as the basal decollement of this thin to thick skinned orogenic wedge it shows a ramp and flat geometry from the blind tip down to middle crustal levels owing to its position below the base of the basin fill the thick synrift sequence and structure controlled structural evolution during contraction by localizing thrust branch lines and by inversion of rift structures synthetic to the subduction direction with formation of basement footwall shortcuts moreover the three dimensional detachment geometry shows large scale oblique ramp flat features which control the architecture of the belt and the distribution of metamorphic grade rocks and fabrics from the detachment show that the latter was located at the transition into the ductile field at the fossil 300 400 c isotherm in the restored section the detachment trajectory displays a saucershaped geometry rising to the surface at the rear and at the front this suggests that the basal detachment propagated into the passive margin by ductile failure during lithospheric flexure under the load of an advancing upper plate the regional pattern of synkinematic metamorphic grade shows varying modes of margin accretion basal underplating into the orogenic wedge by the shelf slope and marginal plateau with formation of duplex stacks and elongate thrust sheets and frontal accretion of the remaining thicker failed rift in the north into the propagating wedge with formation of several imbricate fans cyclical changes in accretion history and or critical taper are suggested by spaced domains of out of sequence thickening these are also related to internal domainal kinematic partitioning of the wedge controlled by oblique collision

accretionary history and crustal evolution of the variscan belt in western europe abstract the variscan belt of western europe is part of a large intra paleozoic belt extending on both sides of the atlantic from the ouachitas in the us and the mauritanides in west africa to the bohemian massif in czechoslovakia and poland the belt was constructed between 500 and 250 ma as a result of convergence and collision between two main continents laurentia baltica and africa after the closure of various oceanic basins iapetus rheic and galicia massif central now recorded as discrete in part cryptic sutures which form the roots of large crystalline nappes in which are found dismembered remnants of oceanic crust and mantle the accretionary history of the variscan belt in western europe is related to the progressive closure of probably two oceanic basins the rheic in the north and another the galicia massif central in the south by respectively southward and northward intraoceanic subduction followed by obduction and intracontinental lithospheric subduction the result is a broad 700 800 km fan like divergent belt which must be considered as a classical obduction collision orogen with a long intracontinental history of about 100 150 ma its arcuate shape is probably due to the northwestward impingement of a promontory of the african continent into laurentia baltica

segregation of magmatic fluids and their potential in the mobilization of platinum group elements in the south kawishiwi intrusion duluth complex minnesota evidence from petrography apatite geochemistry and coexisting fluid and melt inclusions abstract pegmatitic and other felsic rock pockets and dike like intrusions are abundant in the south kawishiwi intrusion of the duluth complex including the basal cu ni pge mineralized units these occurrences are found as pockets pods or as veins and contain abundant accessory apatite and quartz quartz hosts primary fluid inclusions as well as silicate melt inclusions combined microthermometry and raman spectroscopy helped to determine the bulk composition of primary fluid inclusions that are co 2 rich 95 mol and contain small amounts of h 2 o 4 5 mol ch 4 0 4 mol and trace n 2 respectively this combined technique also made it possible to measure total homogenization temperatures of the inclusions th tot 225 10 c otherwise not detectable during microthermometry silicate melt inclusions have been quenched to produce homogeneous glasses corresponding to the original melt composition of the entrapped melt is granitoid peraluminous and is very poor in mafic components we interpret the melt as a product of partial melting of the footwall rocks due to the contact effect of the south kawishiwi intrusion the presence of co 2 in the vapor bubbles of the quenched melt inclusions and petrographic evidence suggest that the fluid and melt inclusion assemblages are coeval the composition of the fluid and melt phase implies that the fluid originates from the mafic magma of the south kawishiwi intrusion and the fluid and melt phases coexisted as a heterogeneous melt fluid system until entrapment of the inclusions coexistence of primary fluid and melt inclusions makes it possible to calculate a minimum entrapment pressure 1 7 kbar and thus estimate formation depth 5 8 km for the inclusions chlorine is suggested to behave compatibly in the silicate melt phase in the fluid melt system represented by the inclusions indicated by the high up to 0 3 cl concentrations of the silicate melt and co 2 rich nature of the fluid apatite halogen contents provide further details on the behavior of cl apatite in pegmatitic pockets often has elevated cl concentrations compared to troctolitic rocks suggesting enrichment of cl with progressive crystallization systematic trends of cl loss at some differentiated melt pockets suggest that in some places cl exsolved into a fluid phase and migrated away from its source the segregation of cl from the melt is probably inhibited by the presence of co 2 rich fluids until the last stages of crystallization increasing the potential for the development of late stage saline brines platinum group minerals are often present in microcracks in silicate minerals in late stage differentiated sulfide veinlets and in association with chlorapatite indicating the potential role of cl bearing fluids in the final distribution of pges

l ecaille des gaux ardennes beiges un exemple d evolution tectono sedimentaire complexe lors du developpement d un pli de propagation the kinematics of internal structuration in the gaux thrust sheet charleroi coal basin belgium is explained with the help of a geometric model this model is controlled by the distribution of landelies red breccia outcrops that was syntectonically deposited probably during the namurian we suggest that the tectono sedimentary evolution was controlled by 1 the growth of a fault propagation fold 2 the formation of collapse structures and 3 localized interbed extension 1994 springer verlag

the variscan belt of northern france southern belgium geodynamic implications of new palaeomagnetic data abstract palaeomagnetic investigations were carried out in devonian early carboniferous rocks of the variscan foreland chain of northern france southern belgium in order to reveal the origin of its arcuate shape the brabant parautochthon was sampled in the boulonnais near calais and near tournai while the ardenne allochthon was sampled near maubeuge and in the givet area all the sampled localities yielded characteristic remanent magnetization as a result of stepwise demagnetization and component analysis fold or tilt tests were possible for three localities with negative results indicating pervasive remagnetization the tectonic position was sub horizontal at two localities while the tilt was monoclinal for the rest therefore the acquisition time of the magnetic signals was estimated by comparing the palaeolatitude computed from each magnetic component to the palaeolatitudes of variscan europe calculated after van der voo 1993 three components showing a a southern b a near equatorial and c a northern palaeolatitude are recognized from our data since a pre variscan age of component a observed only in boulonnais at 10 sites is not supported by data it is assigned to an early phase of deformation component b 16 sites was acquired during the peak of the variscan tectonics late westphalian while component c five sites originated during permian times regardless of the palaeolatitudes declinations fall between 190 and 210 thus being conformable with the declinations expected for variscan europe the declinations show no correlation with the arcuate shape of the belt neither are they different in the paraauthochthon and in the allochthon nor in the different components arc formation by moulding of the allochthon on the brabant parautochthon is therefore not supported by these data since this mechanism requires substantial opposed rotations on both wings of the arc the available palaeomagnetic data are conformable with a pre formed arc simply docking to the brabant obstacle of similar shape variable offsets along a main thrust make possible a third model which slightly unfolds the former passive arc

thin skinned tectonics in the northern rhenish massif germany a network of profiles in the hercynian mountain system geo traverse rhenoherzynikum is needed to determine details of the geological structure and find the reasons for tectonic movements outstanding features within the mountain system such as the large fault zone along the southern boundary of the hunsruck1 and the left flank of the rhinegraben have already been investigated by reflection seismology2 3 we describe here a new reflection refraction experiment carried out in 1978 in the most northern part of the rhenish massif across the stavelot venn massif near aachen fig 1 while layers in the lower crust dip to the nnw a strong upper reflector at 3 4 km depth shows a slight dip to the sse and indicates a prominent fault zone near aachen known in belgium as the faille du midi here a comparable and apparently identical reflector was found some 100 and 175 km to the west of our profile we interpreted this reflector as a prominent and well lubricated thrust fault along which a huge horizontal nappe displacement took place during the last stages of the variscan orogeny

sulfur and oxygen isotopic evidence of country rock contamination in the voisey s bay ni cu co deposit labrador canada abstract the emplacement of basaltic magma into sulfide bearing country rocks provides a favorable geologic environment for magmatic sulfide ore formation related either directly to assimilation of country rock sulfur or indirectly to a depression of sulfide solubility caused by assimilation induced changes in magma composition pelitic country rocks of the proterozoic tasiuyak gneiss in the area of the voisey s bay ni cu co deposit contain sulfidic layers that may have provided sulfur to basaltic magmas during emplacement of the voisey s bay intrusion sulfur isotopic compositions of the tasiuyak gneiss range from 0 9 to 17 0 values typical for sulfides produced via bacterial sulfate reduction in an open marine environment archean gneisses in the area contain low amounts of sulfide and are less likely to have served as a source of externally derived sulfur sulfur isotopic compositions of the sulfide minerals from the voisey s bay deposit show consistent variations both spatially and with rock types disseminated and massive sulfides show a decrease in 34 s to the west with values typically between 0 and 2 in the eastern deeps ovoid and discovery hill zone and between 2 and 4 in the reid brook zone 34 s values of the mushua intrusion to the north and the normal troctolite in the eastern deeps are more positive ranging between 0 5 and 1 8 this range is taken to represent the isotopic composition of primary mantle derived sulfur in the area because the mushua intrusion and normal troctolite show the least geochemical evidence for contamination by country rocks sulfur isotopic data from the reid brook zone are consistent with up to a 50 sulfur contribution from the tasiuyak gneiss correspondingly lower proportions are indicated for the eastern portion of the deposit where country rocks are predominantly low sulfide enderbitic and quartzofeldspathic gneisses oxygen isotopic values of gneiss fragments in the basal breccia sequence and feeder breccia suggest that the assimilation process involved a greater proportion of high 18 o contaminant to the west 18 o values of the tasiuyak gneiss 5 9 to 14 0 enderbitic gneiss 6 4 to 8 7 and archean quartzofeldspathic gneiss 9 5 to 9 7 are consistent with an increased proportion of tasiuyak gneiss contaminant to the west isotopic data strongly indicate that sulfur from the tasiuyak gneiss has been involved in ore deposition at the voisey s bay deposit however sulfur and oxygen isotopic data also strongly suggest that the addition of externally derived sulfur was not the sole process responsible for mineralization and that assimilation of both proterozoic and archean country rocks played a key role in depressing sulfide solubility prior to sulfide localization via dynamic physical mechanisms

selenium and sulfur concentrations in country rocks from the duluth complex minnesota usa implications for formation of the cu ni pge sulfides various studies suggest that the formation of a magmatic ni cu platinum group element pge sulfide deposit requires addition of s from the country rocks into the magma many sulfide deposits have s se ratios higher than primary magmas which is attributed to the preferential addition of s from the country rocks however this has not been clearly demonstrated because most studies do not determine se in the country rocks partly because although se concentration in igneous rocks can be assessed by most routine analytical techniques their detection limits are too low for measuring with precision the level of se in sedimentary rocks we have determined se abundances using thiol cotton fiber tcf combined with instrumental neutron activation analysis inaa s and delta super 34 s on the magmatic sulfides of the duluth complex and on the host rock sediments of the virginia formation our data show that the pelitic and metapelitic rocks of the virginia formation are characterized by low s se ratios approximately 3 000 close to the mantle values whereas the s rich layer known as the bedded pyrrhotite unit has high s se ratios approximately 20 000 consequently most of the virginia formation sediments and xenoliths are unsuitable as a source of s because they have s se ratios and delta super 34 s values lower than those of the mineralized rocks 10 000 only the bedded pyrrhotite unit which is present at the contact with the intrusion and as partly digested xenoliths within the intrusion has s se ratios and delta super 34 s values higher than those of the magmatic sulfides and could thus be the source of the s furthermore the presence of sulfides in the norites around the xenoliths suggests that the s was released from the xenolith during melting of the xenolith detailed sampling from the xenoliths into the norite shows that the s se ratio and delta super 34 s decrease with distance from the xenolith our results favor a mechanism of crustal s contamination by in situ assimilation of bedded pyrrhotite unit xenoliths

possible sources for ch4 rich fluid inclusions in olivine from troctolitic rocks of the bathtub intrusion duluth complex u s a abstract cumulus olivine from the babbitt deposit in the troctolitic bathtub intrusion duluth complex contains abundant ch4 rich fluid inclusions with common hydrous silicate and carbonate precipitates at their inclusion walls given the active rifting environment in which magma of the duluth complex 1 1 ga has intruded as repeated pulses fluid inclusions in olivine are traceable throughout an entire stratigraphic drill core section with comparable textural features that enable a classification of three generations 1 primary ch4 rich fluid inclusions oriented parallel to growth planes of olivine or arranged in clusters 2 intragranular fluid inclusion planes of ch4 rich fluid inclusions extending towards grain boundaries and 3 transgranular fluid inclusion planes of ch4 rich fluid inclusions closely associated with serpentinization the hydrous minerals and carbonates contained in fluid inclusions of generations 1 and 2 indicate that original constituents of the early homogenous magmatic fluid must have been h2o and co2 upon cooling below 700 c at fixed pfluid 2 kbar and fo2fluid at or below qfm conditions an increase of xch4 at the expense of co2 results in the ch4 rich chemistry of the fluid the formation of late secondary fluid inclusion planes of generation 3 is related to extensive magma country rock interaction these inclusions contain no solids and their composition reflects the reduction of co2 to ch4 during serpentinization in an upper stability limit of 620 c this study emphasizes fluid inclusions as powerful indicators in remodeling chemical changes of the magmatic fluid during crystallization of cumulus phases magma country rock interaction and subsequent alteration

sulfur and oxygen isotope studies of melt country rock interaction babbitt cu ni deposit duluth complex minnesota the babbitt cu ni deposit formerly known as minnamax occurs within troctolitic and gabbroic rocks of the precambrian duluth complex both massive and disseminated mineralizations are found in the deposit pyrrhotite cubanite chalcopyrite and minor pentlandite mineralization occurs near the basal contact with pelitic metasedimentary rocks of the virginia formation or higher in the igneous sequence associated with abundant country rock xenoliths cloud zones sulfur and oxygen isotope studies have been carried out to evaluate the importance of melt country rock interaction in localizing sulfide mineralization the delta 34 s values of pyrrhotite plus pyrite from the virginia formation located outside the contact aureole range from 5 6 to 13 7 per mil pyrrhotite from footwall virginia formation hornfels or inclusions in the basal zone exhibits delta 34 s values ranging from 1 5 to 6 2 per mil whereas delta 34 s values of pyrrhotite from xenoliths in cloud zones range from 2 6 to 21 4 per mil isotopic values of basal zone cu ni sulfides range from 6 0 to 13 0 per mil with a mode at 8 to 9 per mil two features highlight basal zone delta 34 s values first delta 34 s values of sulfide mineralization are higher than those of pyrrhotite in immediately adjacent virginia formation hornfels second higher grade ore areas 1 cu show 34 s enrichment with delta 34 s values in the range of 9 to 13 per mil sulfides in cloud zones show a wide range in delta 34 s values from 0 7 to 19 7 per mil sulfur isotope data suggest that most of the sulfur found in the deposit has been derived from sedimentary country rocks however an in situ process of sulfur derivation is not indicated sulfur in basal mineralized zones must have been derived at depth within an auxiliary magma chamber or during magma ascent and emplacement isotopic homogenization was not achieved during the sulfide forming process as evidenced by the spatial variability of delta 34 s values oxygen isotope values of both mildly metamorphosed virginia formation and footwall hornfels range from 8 2 to 14 0 per mil inclusions of virginia formation show pronounced isotopic effects due to interaction with melt xenolith margins may have values as low as 7 to 8 per mil and are depleted in 18 o with respect to xenolith interiors the delta 18 o values of igneous rocks from the babbitt deposit range from 3 9 to 12 2 per mil zones of 18 o depletion are rare and suggest that exchange with a low 18 o fluid phase was spatially restricted anomalous delta 18 o values in excess of 7 to 7 5 per mil are common throughout the deposit but are limited to within 3 m of virginia formation xenoliths a model of diffusion controlled 18 exchange between igneous material and xenoliths best describes the delta 18 o distribution devolatilization and desilicification of the xenoliths occurred early in their history when physical mixing in the host magma was possible addition of high 18 o material from these processes into a large volume of melt affected delta 18 o distributions only slightly continued exchange of oxygen after major cation transfer produced the observed delta 18 o profiles in the case of basal zone cu ni mineralization at babbitt isotopic evidence indicates that sulfide saturation was not caused by in situ addition of sulfur silica or oxygen sulfide saturation is thought to have been achieved at depth triggered by assimilation of large quantities of sulfide liberated through devolatilization reactions occurring in country rocks

hydrothermal alteration and cu ni pge mobilization in the charnockitic rocks of the footwall of the south kawishiwi intrusion duluth complex usa in the neoarchean 2 7 ga contact metamorphosed charnockitic footwall of the mesoproterosoic 1 1 ga south kawishiwi intrusion of the duluth complex the primary metamorphic mineral assemblage and cu ni pge sulfide mineralization is overprinted by an actinolite chlorite cummingtonite prehnite pumpellyite quartz calcite hydrothermal mineral assemblage along 2 3 cm thick veins in calcite hosted by the hydrothermal alteration zones and in a single recrystallized quartz porphyroblast four different fluid inclusion assemblages are documented the composition of these fluid inclusions provide p t conditions of the fluid flow and helps to define the origin of the fluids and evaluate their role in the remobilization and reprecipitation of the primary metamorphic sulfide assemblage pure co2 fluid inclusions were found as early inclusions in recrystallized quartz porphyroblast these inclusions may have been trapped during the recrystallization of the quartz during the contact metamorphism of the footwall charnockite in the footwall of the ski the estimated trapping pressure 1 6 2 0 kbar and temperature 810 920 c conditions correspond to estimates based on felsic veins in the basal zones of the south kawishiwi intrusion fluid inclusion assemblages with co2 h2o nacl and ch4 n2 h2o nacl compositions found in this study along healed microfractures in the recrystallized quartz porphyroblast establish the heterogeneous state of the fluids during entrapment the estimated trapping pressure and temperature conditions 240 650 bar and 120 150 c for co2 h2o nacl inclusions and 315 360 bar and 145 165 c for ch4 n2 h2o nacl inclusions are significantly lower than the p t conditions 700 c and 1 6 2 kbar during the contact metamorphism indicating that this fluid flow might not be related to the cooling of the duluth complex and its contact aureole the presence of chalcopyrite inclusions in these fluid inclusions and in the trails of these fluid inclusion assemblages confirms that at least on local scale these fluids played a role in base metal remobilization no evidences have been observed for pge remobilization and transport in the samples the source of the carbonic phase in the carbonic assemblages co2 ch4 could be the graphite present in the metasedimentary hornfelsed inclusions in the basal zones of the south kawishiwi intrusion the hydrothermal veins in the charnockite can be characterized by an actinolite cummingtonite chlorite prehnite pumpellyite calcite i ii quartz mineral assemblage chlorite thermometry yields temperatures around 276 308 c during the earliest phase of the fluid flow in the late calcite ii phase high salinity 21 6 28 8 nacl cacl2 equiv wt low temperature 90 160 c primary aqueous inclusions were found chalcopyrite sphalerite millerite replacing and intersecting the early hydrothermal phases are associated to the late calcite ii phase the composition of the formational fluids in the canadian shield is comparable with the composition of the studied fluid inclusions this suggests that the composition of the fluids did not change in the past 2 ga and base metal remobilization by formational fluids could have taken place any time after the formation of the south kawishiwi intrusion sulfur isotope studies carried out on the primary metamorphic 34s 7 4 8 9 and the hydrothermal sulfide mineral assemblage 34s 5 5 5 7 proves that during the hydrothermal fluid flow the primary metamorphic ores were remobilized

an application of two dimensional finite element modelling for studying the deformation of the variscan fold and thrust belt belgium abstract this paper presents 2d finite element simulations of fold and thrust belts with a focus on the variscan foreland thrust belt in belgium the numerical models are limited to the deformation of a 5 km thick sedimentary layer separated from a backstop by a deformable zone the sedimentary layer obeys an elastic plastic law and can include one detachment horizon with some ramps our study deals with the effects of rheological and geometrical parameters on the structural characteristics of the belt for regular basin geometries rectangular and wedge shapes results of numerical simulations show that deformation continuously propagates and decreases towards the foreland in agreement with sandbox experiments the basal friction appears to be a major parameter controlling the tectonic style of a fold and thrust belt our analysis has also shown that the strain propagation in time and space is strongly controlled by the presence of a weak intra detachment and of ramps which initiate shear bands for the rhenohercynian fold and thrust belt a major decollement is usually considered within the palaeozoic sediments and the existence of steps in the basin geometry is proven by numerous geological data showing the activity of pre orogenic normal faulting during the variscan orogeny this irregular detachment horizon influenced the regional tectonics simulation results show that ramps create strongly deformed anticlinioria separated by weakly deformed synclinoria which is the basic structure observed in the western and northern rhenohercynian belt

site investigations for involvement of water films in lateral flow in liquefied ground prior research indicates that if layered sand deposits are liquefied during earthquakes water films are likely to develop beneath less permeable sublayers and lead to the destabilization of sloping ground in niigata city japan large lateral flow displacements were reported in almost flat areas during the 1964 niigata earthquake in this paper involvement of water films in lateral flow failure during the earthquake is examined based on site investigation data soil profiles in the investigated areas estimated from many borehole logs indicate that continuous or partially continuous sublayers of fine soil that cap liquefiable loose sand exist elevation contours of 0 1 m increments are drawn based on an in situ leveling survey and local maps the ground slopes obtained are found to be closely related to flow displacements evaluated in earlier research indicating that a gentle slope of less than 1 results in displacement of several meters this strongly suggests that water films with literally no shear resistance formed beneath fine soil sublayers were highly responsible for the large lateral flow displacements in these areas during the niigata earthquake

oxygen isotope ratio of quartz veins from the auriferous ramagiri penakacherla schist belt and surrounding granitoids in the eastern dharwar craton a case for a possible link between gold mineralization and granite magmatism abstract in the eastern dharwar craton among the many shear zone hosted lode gold deposits those at ramagiri and penakacherla are located near the western margin of the craton mineralized quartz sulfide carbonate veins are hosted by the schistose metavolcanic and carbonaceous metasedimentary rocks in close spatial association with granitoids having quartz and quartzofeldspathic veins representing hydrothermal activities associated with them mineralized quartz veins from the ore zones in ramagiri and penakacherla regions and quartz or pegmatitic veins from the surrounding granitic terrane were chosen for 18 o analysis samples from the schistose and granitic domains show 18 o quartz values in the range of 10 4 14 9 and 9 3 10 9 respectively the ore zone fluids from the ramagiri and penakacherla regions give 18 o values of 7 9 1 5 and 5 1 0 8 calculated at pressure corrected temperatures obtained from fluid inclusion microthermometry the late magmatic fluid is relatively 18 o poor with 18 o values estimated at 4 5 0 7 and the value is closer to what is obtained for the ore zones based on the 18 o values reported and a possible magmatic contribution to ore fluid deciphered from fluid inclusion characteristics a genetic relationship between granitic magmatism and gold mineralization is surmised the observed increase in the 18 o 16 o ratio from the magmatic fluid to ore fluid in the shear zone is attributed to interaction of the magmatic fluid with host metasediments that agrees well with the variation in the co 2 ch 4 ratio of carbonic component in such fluids

ni cu au and platinum group element contents of sulphides associated with intraplate magmatism a synthesis the tectonic setting of intraplate magmas typically a plume intersecting a rift is ideal for the development of ni cu platinum group element bearing sulphides the plume transports metal rich magmas close to the mantle crust boundary the interaction of the rift and plume permits rapid transport of the magma into the crust thus ensuring that no sulphides are lost from the magma en route to the crust the rift may contain sediments which could provide the sulphur necessary to bring about sulphide saturation in the magmas the plume provides large volumes of mafic magma thus any sulphides that form can collect metals from a large volume of magma and consequently the sulphides will be metal rich the large volume of magma provides sufficient heat to release large quantities of s from the crust thus providing sufficient s to form a large sulphide deposit the composition of the sulphides varies on a number of scales i there is a variation between geographic areas in which sulphides from the noril

influence of heterogeneous lithostructural layering on orogenic deformation in the variscan front zone eastern belgium the ramp flat thrust model and other classical models based on rocky ountains or appalachians structures allow a better understanding of ault and fold interaction in a sequence dominated by competent rocks n which in most cases thrusts propagate forward in sequence this attern however fails to explain the deformation history of rock uccessions with low proportions of competent rocks in such ithologies out of sequence faults are more common features the ariscan front zone in eastern belgium serves as a case study for this on classical deformation model cross sections are well constrained by urface data covering a large area the devono carboniferous sequence esting unconformably on caledonian basement has shortened drastically nd the tectonic history can best be explained by a composite structural odel continuous and discontinuous deformations took place in uccessive steps a lame anticline developed first it evolved ubsequently into either break thrust or translated fault propagation olds out of sequence thrusting by the theux tunnel fault formed the esdre nappe the latter is the northern part of the ardenne allochthon he main discrepancies with the ramp flat thrust model are emphasized articularly the vesdre nappe which is the highest thrust sheet is ot the youngest event of deformation common elements of the variscan ront zone between northern france and western germany are discussed he theux tunnel fault has the same kinematics significance as the idi aachen fault the footwall of the vesdre nappe is the eastward rolongation of the brabant foreland the complex structure of the theux indow reflects imbrications under the allochthon and can be compared ith other wedges and thrust sheets c 1999 elsevier science b v all ights reserved

the variscan front and the midi fault between the channel and the meuse river abstract the ecors seismic profile allows a new insight into the deep geology of northern france various geological data such as ancient coal mines surface mapping and boreholes are used to interpret the seismic profile a new cross section directly superimposed on the ecors seismic profile cambrai dreux is compared with a previous one drawn along the meuse river through the ardenne massif the cylindrism and length balancing hypotheses are discussed by comparing the two cross sections the main geological results are a the emplacement of the dinant nappe is later than most of its internal deformation and b major folding and thrusting give an approximate 30 35 shortening without taking into account the internal deformation minor folding and cleavage and the unknown net translation vector of the dinant nappe 50 km at least possibly 150 km

laminated veins and hydrothermal breccia as markers of low angle faulting rhenish massif germany abstract the emplacement of bedding veins and vein breccia in a fold and thrust belt setting is discussed we relate vein types to thrusting regimes using the rhenish massif in germany as case example the rhenish massif is a slate belt in a hercynian fold and thrust system the slate belt cleavage generally dips to the southeast and locally has been rotated into low angle shear zones parts of these are parallel to bedding and marked by quartz carbonate veins both shear veins and extensional veins are distinguished on the basis of fibrous crack seal microstructures most shear veins grew by incremental pull apart between en echelon slip surfaces s0 the overlap of which produced a vein stack the stacks have a lineation l0 resulting from a combination of slip fibre growth and dissolution pressure solution slip the attitude of l0 relative to fold axes and the asymmetry of vein microstructures are consistent with vein emplacement during the hercynian thrusting early shear zone veins were thrusted mylonitized and finally boudinaged or folded depending on their setting the shear veins include coeval sheets of vein hosted breccia the breccia contains angular fragments of mylonitized veins and slate the orientation of s0 and s1 in the breccia varies randomly per fragment indicating random fragment rotation unencumbered spin of country rock debris implies rock expansion possibly by rapid pull apart events during the thrusting

petrogenesis of pelitic xenoliths at the babbitt cuni deposit duluth complex minnesota u s a abstract the babbitt deposit consists of disseminated cu fe ni sulfides found within mafic rocks of the duluth complex generally near contacts with underlying metasedimentary rock types host rocks for the deposit include troctolites olivine gabbros gabbronorites norites and occasionally country rock hornfels xenoliths of country rocks are abundant in the deposit and suggest a relationship between sulfide mineralization and country rock contamination country rocks in the babbitt area include those of the middle precambrian biwabik iron formation and both calcareous and non calcareous pelites of the virginia formation xenoliths contain the assemblage cordierite plagioclase biotite orthopyroxene and are thought to have been derived from virginia formation protoliths comparison of protoliths and xenoliths using composition volume element ratio and mass balance techniques suggests that xenoliths have been strongly depleted in volatiles alkalis and si footwall rocks show only a depletion in volatiles neither fluid phase transport nor diffusion through an intergranular fluid can account for the mass of material transferred extensive partial melting of xenoliths with residual enrichment of feo mgo and al2o3 is the most viable transfer process the lack of sio2 concentration gradients around xenoliths and anomalous igneous rock compositions suggest that desilicification occurred at a time when physical mixing of extracted partial melt and host magma was possible and prior to final emplacement sulfide saturation may have been initiated due to si assimilation with an auxiliary magma chamber however the composition of ores in the babbitt deposit is consistent with saturation being achieved by addition of sediment derived volatile sulfur independent of major element assimilation

highly siderophile and strongly chalcophile elements in magmatic ore deposits an ore deposit by definition must be economically viable that is to say it must contain sufficient material at high enough grade to make it possible to mine and process it at a profit bates and jackson 1987 this requires the elements to be collected and concentrated by some phase and for them to be deposited close to the surface of the earth at the oxygen fugacities found in the crust native fe is not normally stable and thus the highly siderophile elements defined as ru rh pd re os ir pt and au cannot behave as siderophile elements except in rare cases such as on disko island klock et al 1986 where the magma is sufficiently reduced for native fe to be present however if mafic magmas become saturated in a base metal sulfide liquid the highly siderophile elements behave as highly chalcophile elements table 1 thus these elements are generally found in association with base metal sulfide minerals which crystallized from a magmatic sulfide liquid namely pyrrhotite pentlandite chalcopyrite cubanite pyrite an exception to this is au although au is strongly chalcophile and is produced as a by product from many platinum group element pge deposits table 2 most primary au deposits consist of native au groves et al 1998 these will not be discussed in this chapter there are many pge deposits i e accumulations of pge minerals and base metal sulfides containing pge bates and jackson 1987 around the world but most of these do not constitute pge ore deposits because they are either too small or their grade is too low or other political or infrastructure factors prevent the economic exploitation of the deposit bates and jackson 1987 for the purpose of this work we have defined pge ore deposits as those which have significant production 2 of the annual world

emplacement of synkinematic plutons in the variscan odenwald germany controlled by transtensional tectonics in the odenwald area sw germany an intermediate level of variscan magmatic arc is exposed between 360 and 335 ma the neunkirchen intrusive complex intruded into an active ne sw trending zone of ductile divergent strike shear after the thermal peak of metamorphism but before the emplacement of the magmatic rocks shear zones developed in the wall rocks the microfabrics of these zones infer plastic deformation of feldspar hornblende and quartz and an increasing degree of postkinematic annealing towards the intrusive complex during emplacement and solidification the magmatic rocks experienced bulk strain the intrusive complex locally crosscut the shear zones of the wall rocks but show magmatic and also mylonitic foliations which parallel these zones a change from plastic to brittle behavior of feldspar and amphibole and a varying degree of postkinematic annealing of quartz suggest that in the intrusive complex strike shear continued during cooling in wall rocks and plutonic rocks kinematic indicators imply sinistral displacement in the wall rocks adjacent to the intrusive complex strike shear was combined with normal displacement this suggests that a component of horizontal extension which was associated with strike shear transtension facilitated ascend and emplacement of the magma transtension occurred at the same time when the schwarzwald vosges area in the south of the odenwald was subjected to nw se compression transtension was probably initiated by lateral escape of crustal fragments during overall convergent plate movements transtension is also supposed to be associated with significant uplift of metamorphic rocks

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

the origin of the basse normandie duplex boulonnais france abstract two hercynian duplexes are developed in visean limestones in the basse normandie quarry the lower duplex is completely exposed in a subvertical quarry wall the partially exposed upper duplex lies immediately above the lower duplex the duplexes are both located in the footwall of the hydrequent thrust which emplaced devonian clastic sediments above the visean limestones the lower duplex exposes all the internal thrusts a reference bed of chalky limestone the roof and floor thrusts and the duplex tip the duplex has been graphically restored to its pre deformation geometry by line length and area balancing and its resultant geometry is close to the model of boyer elliott the lower duplex shortened by two different mechanisms an initial phase of layer parallel shortening which produced no cleavage followed by thrust imbrication the average contraction of the front portion of the duplex was 49 natural strain of which 27 is layer parallel shortening and 22 is thrust imbrication however locally the bulk shortening increases from zero at the duplex tip to over 120 in a down dip direction the area balancing provides the most accurate estimates of bulk shortening line length balance calculations give minimum estimates only an area balance on the whole of the lower duplex gives a bulk shortening of 84 an area balance of the upper duplex yields an average contraction of 75 and the total contraction produced by both duplexes is 92

crustal viscosities and seismic velocities abstract based on a new correlation of seismic velocities and activation energy for creep of crustal rocks some tentative viscosity depth profiles are presented these profiles show certain correlations to velocity depth profiles and indicate possible zones of detachment from their low viscosity zones such zones are situated at the base of the upper granitic or gneissic crust and at the base of the gabbroic or granitic lower crust

traces of caledonian and proterozoic crustal features in deep seismic profiles recorded between france and the british isles abstract the area between france and the british isles has undergone three major orogenies since proterozoic times the cadomian monian late proterozoic caledonian late silurian early devonian and variscan devonian carboniferous this paper shows that crustal structures related to the first two orogenies can be recognized in deep seismic profiles in the english channel the celtic sea and the irish sea in the northernmost area remarkable north dipping reflections in the deep crust of the celtic and irish seas may be correlated with surface structures and interpreted as caledonian south verging thrusts parallel to the lapetus suture these features occur as far south as the cornubian ridge cornwall within the northern segment of the variscan north verging thrust belt the latter is characterized by south dipping reflections interpreted as variscan thrusts caledonian thrusts were probably re activated by the variscan compression evidence of caledonian thin skinned detachment cannot be recognized in the seismic profiles it is possible that either detachment structures were strongly deformed and obliterated by late caledonian thrusting or that detachment may never existed caledonian shortening was probably dominated by deep rooted crustal thrusts as a result of the overall obliquity of the collision caledonian thrusts are regarded as very late features formed when the crust between the colliding continents was already relatively thick they are distributed throughout the southern caledonides including the lapetus suture area deep south dipping reflections in the lower crust in the southern irish sea and the english channel may be related to the cadomian monian orogenic event the cadomian caledonian and variscan features have probably been re activated a number of times

re os sm nd and pb isotopic constraints on mantle and crustal contributions to magmatic sulfide mineralization in the duluth complex abstract previous petrologic and stable isotopic studies of sulfide mineralization in the duluth complex have led to the premise that sulfide genesis is strongly linked to the interaction between mantle derived magmas and sedimentary country rocks in a rift zone environment in order to more fully evaluate the nature of this interaction and to gain an insight into the possible importance of externally derived metals in the ore forming process pb sm nd and re os isotopic studies of the babbitt cu ni deposit were initiated rock types examined include low sulfide troctolite that show very little petrologic evidence for contamination disseminated sulfide bearing troctolitic to gabbroic rocks that occur close to the basal contact with country rocks and contain metasedimentary xenoliths and massive sulfide lead isotopic values of whole rocks plagioclase mineral separates and massive sulfides show only subtle differences and are compatible with 3 to 5 contamination of a mantle derived melt with a proterozoic crustal contaminant e nd 1 1 ga values of the troctolite and gabbro samples are chondritic and only the massive sulfides show strong evidence for contamination based on sm nd isotopic values massive sulfides tend to be more sensitive indicators of contamination in the sm nd system because of late stage incorporation of a light rare earth element rich fluid into a ca po 4 apatite component of the immiscible sulfide liquid os 1 1 ga values are also strongly anomalous and range from 500 to 1200 in disseminated sulfide bearing troctolites and massive sulfides these values are also consistent with from 1 to 3 contamination by c rich and strongly radiogenic proterozoic sedimentary rocks elemental and isotopic mass balance calculations suggest that up to 50 of the pb and at least 35 of the os in the sulfide mineralization have been derived from external sources a corollary is that other metals may also be in part derived from external sources which would aid in explaining the compositional diversity of the sulfide mineralization selective assimilation of country rocks by mantle derived magmas may occur in crustal staging chambers during ascent to shallower levels or in situ as a result of devolatilization reactions and partial melting

evidence for mid permian compressive tectonics in western europe supported by a comparison with the alleghanian geodynamic evolution abstract the final continental collision of gondwana with the appalachian variscan fold belt during mid permian times is evident from 1 the simultaneous deformation of the entire fold belt marked by a thin skin structural style in the appalachians and in parts of the variscan front midi fault 2 the disruption of the hercynian zones in western europe and 3 left lateral transcurrent displacement visible in features such as the leucogranite belt in france and associated with thrusting of the ales saint etienne and saar lorraine basins the line along which the main transcurrent movement occurs stretches through western europe from ales to ireland and it nearly coincides with the paris basin magnetic anomaly it is consistent with the movement along the biscay fault and with the existence of stable areas iberia aquitaine and armorica where local extension occurred there are symmetrical movements and deformations on both the american and european sides the alleghanian orogeny is interpreted as being the result of oblique dextral convergence and collision of gondwana with laurasia on the european side this collision resulted in sinistral displacement laterally associated with thrusting such a geometrical pattern can be achieved through a frontal intracontinental compression

effects of devolatilization on the hydrogen isotopic composition of pelitic rocks in the contact aureole of the duluth complex northeastern minnesota u s a abstract d values of unmetamorphosed chlorite plus muscovite bearing pelitic rocks of the virginia formation in northeastern minnesota range from 68 to 54 with h2o contents between 3 66 and 4 41 wt contact metamorphism by mafic magmas of the duluth complex has led to devolatilization and loss of 2 5 3 5 wt h2o accompanied by a decrease in whole rock d values minerals produced during metamorphism include cordierite biotite and locally orthopyroxene footwall hornfels at the dunka road cu 1bni deposit are characterized by d values between 91 and 59 with h2o contents between 2 52 and 1 10 wt xenoliths and footwall rocks at the babbitt cu 1bni deposit show a wide range in d 131 to 69 and h2o 0 50 2 63 values isotopic modelling of chlorite muscovite and biotite consuming reactions suggest that rayleigh fractionation during devolatilization may account for the trend of decreasing d and h2o content the computations indicate that the d and h2o data are consistent with the liberation of a fluid during contact metamorphism that contained up to 15 methane results are in excellent agreement with fluid compositions estimated from mineral equilibria and carbon isotopic data the average isotopic composition of the evolved fluid is 53 d values that are recorded in some xenoliths and footwall rocks at babbitt may be a result of retrograde hydration and isotopic exchange with a d depleted fluid of magmatic origin or may reflect variations in parent rock d value or chlorite muscovite ratio

evidence for as contamination and the partitioning of pd into pentlandite and co platinum group elements into pyrite in the fazenda mirabela intrusion brazil the fazenda mirabela intrusion in brazil hosts two zones of mineralization the santa rita ni cu sulfide ore zone occurring predominantly in an orthopyroxenite layer and an underlying basal platinum group element pge anomaly hosted in s poor dunite we show that in the northern and southern marginal zones of the intrusion pt pd ni cu fe bi te 2 minerals are accompanied by as bearing platinum group minerals pgm sperrylite ptas2 and irarsite rhirpt ass these as bearing pgm are extremely rare in the central zone of the intrusion suggesting that as has been introduced into the margins of the intrusion from the country rocks via crustal assimilation or synmagmatic hydrothermal processes other pgm and precious metal minerals pmm including hessite ag2te pd ag tellurides electrum and native au are observed in the santa rita ore zone and do not show any lateral variation in the semimetal and s poor dunite hosting the basal pge anomaly pge are predominantly retained in the base metal sulfides and only minor pge alloys are present in this s poor dunite pt au and semimetals partitioned into a fractionated cu rich liquid which formed during the crystallization of monosulfide solid solution mss and was largely removed by high temperature magmatic fluids palladium was not affected by this process and significant concentrations of pd are identified in pentlandite suggesting that pd preferentially partitioned into mss as it crystallized and subsequently pentlandite as it exsolved pyrite in the santa rita ore zone is co rich and contains higher concentrations of ipge os ir ru and rh than pyrrhotite and pentlandite suggesting that pyrite has not replaced and inherited the pge concentrations of these sulfides the pd poor nature of pyrite also indicates that it has not replaced pd rich pentlandite it is proposed that the ipge and co preferentially partitioned into pyrite as it exsolved from mss

reevaluation of the role of external sulfur addition in the genesis of ni cu pge deposits evidence from the nebo babel ni cu pge deposit west musgrave western australia the nebo babel ni cu pge sulfide deposit located in the west musgrave block western australia is hosted within a tube like concentrically zoned gabbronorite magma conduit emplaced at 1068 ma the nebo babel deposit is associated with the ca 1078 ma giles complex which is part of the warakurna large igneous province previous geologic and geochemical studies have shown that the nebo babel consists of chemically related but temporally distinct magma pulses the initial magma pulses which were the most primitive and the most contaminated formed the marginal units of the conduit the later pulses were emplaced into the core of the conduit the chilled margin rocks contain sulfide globules mineralization is confined to the early magma pulses and consists of massive sulfide breccias and stringers and disseminated gabbronorite hosted sulfides the ni tenor of the massive sulfides which have undergone sulfide liquid fractionation and the disseminated sulfides are almost the same indicating that both formed at similar r factors the whole rock massive and disseminated sulfides contain 650 ppb and 60 to 500 ppb total pge respectively all of the nebo babel rock units are slightly pge depleted with cu pd ratios higher than primitive mantle indicating early saturation and segregation of a sulfide and or pgm rocks with trace cumulus sulfides have the lowest cu zr and highest cu pd ratios and the most fractionated metal patterns indicating that these units have undergone the highest degrees of ni cu and pge depletion the average 34s value of all nebo babel disseminated and massive sulfides is 0 4 0 2 per mil which is consistent with the s originating in the mantle sulfur saturation did not occur in situ and is inferred to have been triggered by assimilation of felsic orthogneiss perhaps in the parental magma chamber this initial magma pulse with entrained sulfides formed marginal units of the nebo babel intrusion some of the entrained sulfides accumulated within physical traps on the way into the conduit and or at the exit from the chamber these sulfides were later emplaced along the footwall contact as massive and or marginal fragment laden sulfide liquid distribution of the disseminated sulfides was influenced by the conduit geometry and magma flow dynamics the final and volumetrically dominant barren magma pulse underwent crystal fractionation and oxide precipitation in the core of the nebo babel intrusion which in turn caused sulfide saturation and formed trace but pge depleted sulfides in these units the nebo babel deposit has a number of features in common with other ni cu pge deposits hosted in dynamic magma conduits e g voisey s bay such as multiple magma pulses and sulfide entrainment from depth rather than in situ sulfide segregation however si addition was the primary cause of sulfide saturation and external s addition did not play a role in the genesis of the nebo babel deposit

multiple sulfur and iron isotope composition of magmatic ni cu pge sulfide mineralization from eastern botswana we report here high precision multiple sulfur and iron isotope compositions for a series of mineralized samples from ni cu pge sulfide deposits in the archean tati greenstone belt and the phikwe complex of eastern botswana mineralized samples from the phoenix and selkirk ni cu pge deposits in the tati greenstone belt display slightly positive 34s isotope values ranging from 0 2 to 0 8 v cdt 33s values of sulfides at phoenix and selkirk are 0 01 to 0 08 v cdt suggesting either a dominantly mantle sulfur source or effective eradication of a crustal 33s anomaly through equilibration with large amounts of silicate melt in the selebi phikwe belt a granite gneiss terrane with abundant amphibolite lenses of either volcanic and or intrusive nature mineralized lower grade samples from the phikwe phokoje and dikoloti ni cu pge deposits have more variable 34s values ranging from 3 1 to 0 3 and display significant mass independent anomalies 33s values ranging from 0 89 to 0 27 suggesting that barren sulfides associated with distal or low temperature sea floor hydrothermal activity contributed sulfur to these deposits iron isotopes of sulfides from these deposits show a relatively small range of negative 56fe values 0 29 to 0 04 consistent with high temperature fractionations in magmatic systems with the exception of one sample from the dikoloti ni cu pge deposit of the selebi phikwe greenstone belt which shows a more negative 56fe value of 0 61 consistent with assimilation of sedimentary or hydrothermal sulfides rather than fractionations in high temperature magmatic systems data from this study highlight the complexity and variability that characterize ore forming processes in magmatic systems we suggest that the presence of sulfur bearing lithologic units in host rocks of mafic and ultramafic intrusions may not be essential toward the assessment of the prospectivity of a province to host orthomagmatic nickel sulfides geologic settings without any or little sulfur in the stratigraphy which have been traditionally neglected in terms of their prospectivity should thus be revisited and possibly reassessed considering the potential importance of external source of sulfur to generate ore deposits

deciphering magmatic and metasomatic processes recorded by fluid inclusions and apatite within the cu ni pge sulfide mineralized bathtub intrusion of the duluth complex ne minnesota usa

major crustal reflectors beneath sw england strong wide angle reflection events were detected during a crustal seismic experiment carried out in sw britain in 1979 three crustal reflectors have been identified referred to as rl r2 and r3 rl lies at a depth of about 8 km and appears to be restricted to the interior of the granite batholith underlying sw england the nature of this reflector is unknown r2 is a mid crustal reflector lying at a depth of 10 15 km and interpreted as rising gradually northwards it coincides locally with the base of the granite as predicted by gravity modeling but extends well beyond the northern limit of the granite body it is suggested that r2 may represent a major thrust of late variscan age r3 is the deepest reflector identified and lies at a depth of 27 30 km r3 is interpreted as the base of the crust and its computed depth is in close agreement with the local depth to the moho derived from an earlier seismic experiment in sw britain

up down or sideways emplacement of magmatic fe ni cu pge sulfide melts in large igneous provinces the preferential localization of fe ni cu pge sulfides within the horizontal components of dike sill lava flow complexes in large igneous provinces lips indicates that they were fluid dynamic tra

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

re os and o isotopic variations in magnetite from the contact zone of the duluth complex and the biwabik iron formation northeastern minnesota abstract osmium and oxygen isotopic analyses of magnetite from the south kawishiwi intrusion ski of the duluth complex and country rocks of the biwabik iron formation bif were undertaken to evaluate the potential importance of country rock assimilation in the genesis of pge enrichment in the intrusive rocks and to track the response of the re os isotopic system to contact metamorphism of the iron formation oxygen isotopic values of magnetite from contact metamorphosed biwabik iron formation and magnetite rich oxide assemblages from highly contaminated troctolitic rocks range from 7 0 to 13 7 distinctly higher than oxide minerals from less strongly contaminated troctolitic to melatroctolitic rocks of the ski that range from 2 3 to 6 9 187 re 188 os ratios of metamorphosed bif tend to be much lower than values from low grade weakly recrystallized bif only one sample of bif from the contact aureole shows the type of os isotope ratios expected as a result of mixing with a chondritic fluid at 1 1 ga the time of emplacement of the ski both low 18 o and high 18 o magnetite populations from the ski are characterized by 187 re 188 os values less than 7 2 and os isotopic ratios that plot above a 1 878 ga reference isochron for the low grade bif samples although elevated os values are consistent with the premise that the ski was contaminated by crustal material we suggest that the os isotopic compositions reflect a later lowering of re os ratios related to interaction with a fluid potentially that which was involved in the locally extensive serpentinization of the melatroctolitic rocks oxygen and h isotopic values of serpentine and serpentinized melatroctolites indicate that the fluids responsible for hydrothermal alteration t 300 c were low in 18 o and characterized by a large meteoric water component magnetite 18 o values record less than a 15 approach to equilibrium with the fluid involved in the serpentinization process suggesting that perturbations to the os isotopic system under hydrothermal conditions may occur in the absence of significant shifts in magnetite 18 o values

the influence of country rock assimilation and silicate to sulfide ratios r factor on the genesis of the dunka road cu ni platinum group element deposit duluth complex minnesota the dunka road deposit is one of several cu ni platinum group element pge sulfide occurrences found along the northwestern margin of the duluth complex where the host troctolitic rocks are in contact with metasedimentary rocks of the animikie group magma contamination through assimilation of sulfidic argillaceous country rocks is generally recognized as having played a key role in the genesis of the mineralization three main types of disseminated sulfide mineralization have been identified within the dunka road deposit i norite hosted sulfides ii troctolite hosted sulfides and iii pge rich sulfide horizons the norite hosted sulfides are found either adjacent to country rock xenoliths or near the basal contact the troctolite hosted sulfides form the bulk of the deposit and occur throughout the lower 250 m of the intrusion the pge rich sulfide horizons are typically localized directly beneath ultramafic layers the composition of the different types of sulfide occurrences is modelled using cuipd ratios it is shown that each type results from the interplay of two main parameters namely the degree of magma contamination and the silicate magma to sulfide melt ratio r factor the norite hosted sulfides formed at low r factors and high degrees of contamination as expressed by their pge depleted nature low seis ratios and elevated content in pyrrhotite and arsenide minerals the troctolite hosted sulfides formed at moderate r factors and small degrees of contamination as shown by their moderate pge content and mantle like seis ratios finally the pge rich sulfide horizons are modelled using elevated r factors from an uncontaminated parental magma which is substantiated by their elevated noble metal content and seis ratios and low pyrrhotite to precious metal sulfide ratio le gite de dunka road est un parmi plusieurs gites de sulfures de cu ni elements du groupe du platine egp trouves le long de la bordure nord ouest du complexe de duluth ou les roches hotes troctolitiques sont en contact avec les roches metasedimentaires du groupe d animikie il est generalement reconnu que la contamination du magma par l assimilation de roches argileuses sulfurees encaissantes a joue un role capital dans la genese de la mineralisation trois types principaux de mineralisation de sulfures dissemines ont ete identifies dans le gite de dunka road i sulfures dans la norite hote ii sulfures dans la troctolite hote et iii horizons de sulfures enrichis en egp les sulfures dans la norite hote apparaissent soit dans les zones adjacentes aux xenolites encaissants ou pres du contact basal les sulfures dans la troctolite hote forment le plus gros du gisement et ils apparaissent dans les 250m inferieurs de l intrusion la localisation typique des horizons de sulfures enrichis en egp se trouve directement sous les couches ultramafiques les rapports cu pd ont ete utilises pour elaborer un modele de la composition des differents types de mineralisation de sulfures il est demontre que chaque type resulte de l interaction de deux parametres dominants a savoir le degre de contamination du magma et le rapport du magma silicate au liquide sulfure facteur r les sulfures dans la norite hote ont ete formes sous des conditions de faibles facteurs r et de fortes contaminations comme en temoignent la teneur appauvrie en egp les faibles rapports se s et les concentrations elevees de la pyrrhotite et des mineraux arsenieux les sulfures dans la troctolite hote ont ete formes sous des conditions de facteurs r moderes et de faibles contaminations comme le revelent leur teneur modere en egp et les rapports se s analogues a ceux du manteau finalement les horizons de sulfures enrichis en egp sont modelises en utilisant des facteurs r eleves et un magma parental non contamine ce qui est appuye par leur forte teneur en elements nobles et les rapports se s eleves et par le rapport faible de la pyrrhotite sur les sulfures de metaux precieux

sulfur isotope and mineralogical studies of ni cu sulfide mineralization in the bovine igneous complex intrusion baraga basin northern michigan the bovine igneous complex referred to as the bic intrusion occurs within the marquette baraga dike swarm in the upper peninsula of michigan the intrusion is likely related to the 1 1 ga midcontinent rift system based on chemical similarities with the nearby eagle mine and other midcontinent rift related picrites the lack of deformation fabric and well developed hornfels that overprints penokean deformation fabrics however there is currently no age date for the bic intrusion to confirm that it is a rift related intrusion the bic is a relatively small layered intrusion with dimensions of 1 100 400 732 m thick units include feldspathic wehrlite olivine melagabbros feldspathic olivine clinopyroxenite and gabbro the little bic a satellite intrusion located 100 m from the main intrusion is primarily feldspathic wehrlite ni cu sulfide mineralization occurs in both intrusions with a higher relative proportion in the little bic intrusion sulfide assemblages are comprised predominantly of pyrrhotite chalcopyrite and pentlandite textural types vary from disseminated through globular to semimassive net textured and locally massive the 34s values of sulfide minerals in the bic intrusion range from 6 0 to 1 5 with 80 of the values between 0 and 1 5 the proterozoic michigamme formation country rocks show 34s values between 3 0 and 9 8 the 34s values of the semimassive sulfides in the little bic intrusion are similar to those in country rock 3 8 6 7 whereas the massive sulfide values are similar to those of the sulfide minerals in the bic intrusion although many values are near those of mantle derived sulfur the presence of strongly negative values in both intrusions indicates that crustally derived sulfur was involved in the mineralization process in addition the distinctly positive values of disseminated sulfides in the little bic intrusion indicate that a large fraction of the sulfur involved in the mineralization was of country rock origin and that at least two pulses of sulfide saturated liquids were involved in its genesis the 33s values for sulfide minerals in the bic and the little bic intrusions range from 0 33 to 0 35 indicating that a component of archean sulfur was also involved in the mineralization olivine fo and ni contents are consistent with rock types being related via fractional crystallization but this process cannot account for the wide range of sulfide zones found throughout both intrusions multiple pulses of magma several sulfide saturated and with distinct sulfur isotope compositions were involved in the formation of the bic and the little bic intrusions both sulfide concentration and isotopic composition suggest that sulfide saturation was promoted via the addition of country rock derived sulfur

a two stage exhumation in western french massif central new geochronological evidences of syn collisional extension abstract systematic 40ar 39ar dating of granitoids and surrounding metamorphic rocks has been performed in the limousin area w of french massif central in order to provide new constrains concerning its late orogenic thermal and tectonic evolution the same 40ar 39ar age of ca 335 338 ma is found on the present day outcrop surface for most of the limousin metamorphic rocks hence indicating that the entire massif was uniformly cooled down at this period these ages are very close to the 40ar 39ar ages proposed in the sioule and brevenne areas in the literature but also to the coupled tectonic and magmatic activity in the south limousin these results help to document the existence of two exhumation stages each one associated with an extensional stage a first exhumation stage has been active at ca 335 340 ma available data indicate that this extension and associated exhumation and cooling occurred over a distance of more than 200 km in the internal zones of the belt whereas compression was still active in the northern and southern parts of the belt a second exhumation stage may be related to the late orogenic extension and collapse of the belt at ca 310 305 ma and is characterized by the uplift of the st sylvestre complex by unroofing of the overlying metamorphic and granitoidic formations

cu ni pge mineralization in the south filson creek area south kawishiwi intrusion duluth complex mineralization styles and magmatic and hydrothermal processes the south filson creek mineralization occurs above the basal units of the south kawishiwi intrusion and represents an uncommon geologic setting of cu ni platinum group element pge mineralization within the duluth complex unlike other mineralization of economic interest in the basal heterogeneous troctolite units along the lower contact it is located at an approximate stratigraphic height of 1 000 m above the contact with the footwall granitoids in the usually unmineralized homogeneous troctolite unit magmatic sulfide mineralization forms disseminated fine grained patches and pockets in an area of approximately km2 of homogeneous troctolitic rocks in the northeastern part of the south kawishiwi intrusion pyrrhotite chalcopyrite pentlandite and cubanite are the main sulfide minerals with subordinate amounts of other copper bearing phases bornite covellite talnakhite cu pd ratios for unaltered mineralization indicate that sulfides were formed from multiple injections of magma that segregated sulfides with different r factors or having different initial compositions variation in the halogen contents of apatite from pegmatoids within troctolitic rocks revealed that a fluid has segregated from the crystallizing melt into which fluid cl and rare earth elements partitioned amphibole chlorite sericite prehnite pumpellyite and carbonate are associated with alteration along brittle structures and isolated patches in the area the hydrothermal fluid rock interaction has affected the composition of primary magmatic sulfide mineralization and is also responsible for mineralization in the anorthositic hanging wall of the south kawishiwi intrusion hydrothermal alteration resulted in a slight pd depletion in magmatic sulfide mineralization which might indicate remobilization of precious metals to an unknown location the hanging wall mineralization is characterized by relative cu enrichment in comparison to the magmatic sulfide mineralization with no pge enrichment partial remobilization of platinum group elements pge has also occurred as a result of a separate alteration event on the evidence that platinum group minerals pgm are also associated with serpentinization of olivine and ca enrichment of plagioclase along grain boundaries with sulfides this alteration was probably effective on a very local scale

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

water film in liquefied sand and its effect on lateral spread a one dimensional 1d saturated sand layer of 2 m in thickness in which a silt seam is sandwiched is liquefied by an instant shock it is found that a water film is easily formed beneath the silt seam with a thickness as thin as a few millimeters just after liquefaction in loose sand and that the film lasts longer than the postliquefaction settlement the effect of the water film on pore pressure distribution and sand settlement is intensively studied one gram shake table tests are then carried out for 2d models with or without seams of silt within a saturated sand layer in the former case water films formed beneath silt seams just after liquefaction enable the soil mass above them to glide because of an unbalanced force along the water films not only during but also after shaking in the latter case the soil deforms continuously mostly during shaking and stops afterward thus a significnat effect of water films formed beneath thin low permeability sublayers in a liquefied loose sand on the failure mode and timing in lateral spread is clearly demonstrated by these simple model tests

crustal structure of the rhenish massif results of deep seismic reflection lines dekorp 2 north and 2 north q the reflection seismic line dekorp 2 n reveals an almost complete cross section through the rhenohercynian zone the most external part of the variscan orogen in europe

solubility of copper in a sulfur free mafic melt the solubility of cu in s free mafic melts has been measured at a series of o2 values and temperatures of 1245 and 1300 c at constant temperature cu solubility increases from 0 04 wt at log o2 11 9 to 1 10 wt at log o2 7 4 copper solubilities were in excess of 8 wt in two runs controlled at very high o2 conditions of 10 1 4 and 10 22 partitioning of cu between metal and glass shows a strong o2 dependence with dcumetgl ranging from 90 at log o2 7 4 to 2190 at log o2 11 9 slopes of cu solubility and dcumet gl vs log o2 suggest that cu dissolves predominantly in the 1 valence state copper solubility decreases with increasing temperature at constant o2 similar to experimental results for ni co and mo dingwell et al 1994 holzheid et al 1994 the data are consistent with cu dissolution as an oxide represented by cuo0 5 and suggest that changes in o2 fe2 fe3 variations and cu1 complexation with fe3 may have large effects on the distribution of cu between silicate and sulfide magmas results also suggest that the extraction of oxide bonded cu in mafic magmas by externally derived s may be an important mechanism in the generation of cu rich sulfide ores

the basse normandie duplex boulonnais n france evidence for an out of sequence thrusting overprint abstract the thrust sheets outcropping in the basse normandie quarry near the hydrequent village boulonnais n france represents an exceptionally well exposed section of the nw european variscan thrust front these structures developed in the footwall of the main hydrequent thrust have been often described as a classic example of a duplex structure only the lower part of the structure satisfies however the geometric and kinematic criteria defining a duplex and more precisely an intraformational hinterland dipping duplex the upper thrust sheets of the imbricate stack exhibit a much more complex pattern of deformation than a simple piggy back duplication of the same rock sequence restoration of these thrust sheets based upon the definition of two marker beds as well as the analyses of fold thrust relationships and strain markers argues for a late ne verging thrust event that progressed within the thrust system from the tip of the upper thrust sheets towards the hydrequent thrust in a local break back style of thrust propagation this out of sequence thrusting event induced refolding and cross cutting of the forelimb of a hangingwall anticline developed previously above the footwall ramp of the nne verging basal thrust of the structure within the whole thrust system the lower duplex represents only a minor structure developed during the initial phase of thrusting in the foreland of the major anticline as a frontal second order duplex the structural data presented in this paper illustrate the tectonic processes acting within the deformed zones lying in the footwall of major thrusts and emphasize the out of sequence style of thrust migration that arises from the sequential blocking of thrust propagation towards the foreland

liquefaction and flow failure during earthquakes two aspects of seismically induced liquefaction are discussed which are of vital engineering significance the triggering condition and the consequences of liquefaction the triggering condition is examined with respect to liquefaction analysis note being taken of the onset condition which is governed by cyclic strength consequences of liquefaction are discussed with respect to post seismic stability analysis in which the residual strength plays a major role procedures used for liquefaction analysis based on the results of in situ sounding tests are introduced and the applicability of this method for estimating associated ground settlements is discussed the evaluation of residual strength requires a better understanding of undrained sand behaviour results of extensive laboratory rests on japanese standard sand are examined and new index parameters are proposed to quantify undrained sand behaviour better the results of laboratory tests on silty sands are examined in the same way ah the results are

metallogeny of the midcontinent rift system of north america abstract the 1 1 ga midcontinent rift system of north america is one of the world s major continental rifts and hosts a variety of mineral deposits the rocks and mineral deposits of this 2000 km long rift are exposed only in the lake superior region in the lake superior region the rift cuts across precambrian basement terranes ranging in age from 1850 ma to more than 3500 ma where exposed the rift consists of widespread tholeiitic basalt flows with local interlayered rhyolite and clastic sedimentary rocks beneath the center of lake superior the volcanic and sedimentary rocks are more than 30 km deep as shown by recent seismic reflection profiles this region hosts two major classes of mineral deposits magmatic and hydrothermal all important mineral production in this region has come from hydrothermal deposits rift related hydrothermal deposits include four main types 1 native copper deposits in basalts and interflow sediments 2 sediment hosted copper sulfide and native copper 3 copper sulfide veins and lodes hosted by rift related volcanic and sedimentary rocks and 4 polymetallic five element veins in the surrounding archean country rocks the scarcity of sulfur within the rift rocks resulted in the formation of very large deposits of native metals where hydrothermal sulfides occur i e shale hosted copper sulfides the source of sulfur was local sedimentary rocks magmatic deposits have locally supported exploration and minor production but most are subeconomic presently these deposits occur in intrusions exposed near the margins of the rift and include cu ni pge and ti fe v in the duluth complex u ree nb in small carbonatites and breccia pipes resulting from local hydrothermal activity around small felsic intrusions mineralization associated with some magmatic bodies resulted from the concentration of incompatible elements during fractional crystallization most of the sulfide deposits in intrusions however contain sulfur derived from country rocks the interaction between magma and country rocks was important in generation of the magmatic cu ni sulfide deposits a mantle plume origin has been proposed for the formation of the midcontinent rift more than 1 million km3 of mafic magma was erupted in the rift and a comparable volume of mafic intrusions are inferred beneath the rift providing a ready and structurally confined supply of mafic source rocks that were available for leaching of metals by basinal brines these brines were heated by a steep geothermal gradient that resulted from the melting and underplating of magma derived from the plume hydrothermal deposits were emplaced for at least 30 40 m y after rift magmatism and extension ceased this time lag may reflect either the time required to heat deeply buried rocks and fluids within the rift or may be due to the timing of post rift compression that may have provided the driving mechanism for expulsion of hydrothermal fluids from deep portions of the rift