deep penetration of sedimentary fluids in basement rocks from southern norway evidence from hydrocarbon and brine inclusions in quartz veins abstract this paper presents evidence for fluid flow and fluid rock interaction at upper crustal levels within the crystalline basement of southern norway in the high grade modum complex postmetamorphic veins of quartz occur in association with albitisation of metagabbros and metasediments pressure temperature conditions for the formation of these veins are in the range 250 300 c and ca 1 2 kbar primary and pseudosecondary fluid inclusions in the quartz veins show two fluids 1 hydrocarbon c0 2 inclusions and 2 aqueous inclusions with variable salinities dark carbonaceous solid inclusions are also present the hydrocarbon inclusions are methane dominated ca 80 100 mot and the presence of higher complex hydrocarbons is demonstrated the aqueous inclusions in the metagabbro hosted veins show more saline compositions than the metasediment hosted veins a salinity range of ca 23 0 wt nacl eq is found some of the aqueous inclusions may contain nahco 3 crush leach analyses of inclusion fluids show na ca k ci dominated compositions with na ca k hydrocarbon poor concentrates yield br cl ratios close to seawater while hydrocarbon rich concentrates show higher values the types and chemistry of the hydrocarbons in these veins indicate a biogenic origin of the hydrocarbon fluids the inclusion fluids are interpreted as derived from an overlying sedimentary basin in late precambrian or permian times the veining is interpreted as the deep expression of the percolation of basinal fluids into the metamorphic basement during crustal extension

stable isotope geochemistry and phase equilibria of coesite bearing whiteschists dora maira massif western alps peak metamorphic temperatures for the coesite pyrope bearing whiteschists from the dora maira massif western alps were determined with oxygen isotope thermometry the 18o smow values of the quartz after coesite 18o 8 1 to 8 6 n 6 phengite 6 2 to 6 4 n 3 kyanite 6 1 n 2 garnet 5 5 to 5 8 n 9 ellenbergerite 6 3 n 1 and rutile 3 3 to 3 6 n 3 reflect isotopic equilibrium temperature estimates based on quartz garnet rutile fractionation are 700 750 c minimum pressures are 31 32 kb based on the pressure sensitive reaction pyrope coesite kyanite enstatite in order to stabilize pyrope and coesite by the temperature sensitive dehydration reaction talc kyanite pyrope coesite h2o the a h2o must be reduced to 0 4 0 75 at 700 750 c the reduced a h2o cannot be due to dilution by co2 as pyrope is not stable at x co2 0 02 t 750 c p 30 kb in the absence of a more exotic fluid diluent e g ch4 or n2 a melt phase is required granite solidus temperatures are 680 c 30 kb at a h2o 1 0 and are calculated to be 70 c higher at a h2o 0 7 consistent with this hypothesis kyanite jadeite quartz bands may represent a relict melt phase peak p t f h2o estimates for the whiteschist are 34 2 kb 700 750 c and 0 4 0 75 the oxygen isotope fractionation between quartz 18o 11 6 and garnet 18o 8 7 in the surrounding orthognesiss is identical to that in the coesitebearing unit suggesting that the two units shared a common final metamorphic history hydrogen isotope measurements were made on primary talc and phengite d smow 27 to 32 on secondary talc and chlorite rite after pyrope d 39 to 44 and on the surrounding biotite d 64 and phengite d 44 gneiss all phases appear to be in nearequilibrium the very high d values for the primary hydrous phases is consistent with an initial oceanicderived connate fluid source the fluid source for the retrograde talc chlorite after pyrope may be fluids evolved locally during retrograde melt crystallization the similar d but dissimilar 18o values of the coesite bearing whiteschists and hosting orthogneiss suggest that the two were in hydrogen isotope equilibrium but not oxygen isotope equilibrium the unusual hydrogen and oxygen isotope compositions of the coesite bearing unit can be explained as the result of metasomatism from slab derived fluids at depth

ichnofabric characterization of a deep marine clastic system a subsurface study of the middle eocene ainsa system spanish pyrenees this paper documents a subsurface trace fossil and ichnofabric study of the proximal parts of a structurally confined and channelized sand rich lower slope and proximal basin floor deep marine system in the middle eocene ainsa basin spanish pyrenees five depositional environments are recognized based on sedimentary facies associations depositional architecture and stratigraphic context channel axis channel off axis channel margin levee overbank and interfan as well as a channel abandonment phase each environment is characterized by distinct and recurring ichnofabrics ichnological measurements and observations were recorded from six cores recovered from six wells drilled at a spacing of between 400 m and 500 m at outcrop and totalling 1213 m in length from channel axis to levee overbank environments there is a trend of increasing bioturbation intensity and ichnodiversity ichnofabrics in channel axis and channel off axis environments are characterized by low bioturbation intensity and low ichnodiversity thalassinoides dominated firmground ichnofabrics associated with erosive sediment gravity flows are common in these environments in contrast channel margin and levee overbank environments are characterized by ichnofabrics associated with high bioturbation intensity and ichnodiversity sediments of the interfan are characterized by the highest bioturbation intensity associated with burrow mottling and an absence of primary sedimentary structures this paper demonstrates that in core based studies ichnofabric analysis is an important and valuable tool in discriminating between different environments in channelized deep marine siliciclastic systems the results of this study should find wide applicability in reservoir characterization studies in the petroleum industry in field based analogue ichnofabric studies and other core based studies in deep water siliciclastic systems worldwide such as the integrated ocean drilling program

sedimentology and reservoir modelling of the ormen lange field mid norway abstract reservoir in the ormen lange field offshore norway is provided by upper cretaceous and lower paleocene turbidite sandstones deposited in a sand rich submarine fan systematic vertical and down fan changes in facies and section properties thickness percentage sand and percentage amalgamation are documented bulk sediment accumulation rates are very low suggesting that the system was not directly delta fed paucity of mud in the supply mix prevented the development of channel overbank systems with strong segregation of sands in channel fills and muds in overbank areas the resultant architecture is externally tabular with internally varying degrees of erosional amalgamation between beds a novel approach to 3d quantitative reservoir modelling has been taken at a regional scale 475 180 3 km 3 3d models integrate all well and structural information and provide a context for field scale models nested within the regional models high resolution hierarchical reservoir models of the field have been generated models combine detailed sedimentological observations in core with petrophysical pressure seismic amplitude and structural data modelling rules are derived from partial analogues and a forward geometric model that addresses the nature of distal and lateral sandstone body terminations

anisotropic zonation in the lithosphere of central north america influence of a strong cratonic lithosphere on the mid continent rift we present shear wave splitting analyses of sks and skks waves recorded at sixteen superior province rifting earthscope experiment spree seismic stations on the north shore of lake superior as well as fifteen selected earthscope transportable array instruments south of the lake these instruments bracket the mid continent rift mcr and sample the superior penokean yavapai and mazatzal tectonic provinces the data set can be explained by a single layer of anisotropic fabric which we interpret to be dominated by a lithospheric contribution the fast s polarization directions are consistently ene wsw but the split time varies greatly across the study area showing strong anisotropy up to 1 48 s in the western superior moderate anisotropy in the eastern superior and moderate to low anisotropy in the terranes south of lake superior we locate two localized zones of very low split time 0 6 s adjacent to the mcr one in the nipigon embayment an mcr related magmatic feature immediately north of lake superior and the other adjacent to the eastern end of the lake at the southern end of the kapuskasing structural zone ksz both low splitting zones are adjacent to sharp bends in the mcr axis we interpret these two zones along with a low velocity linear feature imaged by a previous tomographic study beneath minnesota and the dakotas as failed lithospheric branches of the mcr given that all three of these branches failed to propagate into the superior province lithosphere we propose that the sharp bend of the mcr through lake superior is a consequence of the high mechanical strength of the superior lithosphere ca 1 1 ga

modelling facies belt distribution in fan deltas coupling sequence stratigraphy and geostatistics the eocene sant llorenc del munt example ebro foreland basin ne spain abstract the eocene sant llorenc del munt fan delta complex developed in the ebro foreland basin the stratigraphy of this succession about 1000 m thick has been described as made up of several transgressive regressive composite sequences each composed of a stack of fundamental sequences in turn made up of a transgressive systems tract and an overlying regressive systems tract systems tracts are composed of several facies belts proximal alluvial fan distal alluvial fan fan delta front carbonate platform and fan delta slope and prodelta a 3d facies model of a 130 m thick stratigraphic succession was built using outcrop data from one of the composite sequences the modelling followed a hierarchical approach a deterministic method was used to reconstruct the surfaces bounding fundamental sequences and their constituent systems tracts data input was outcrop traces digitized on photorealistic terrain models the stacking trend and interfingering of adjacent facies belts within each systems tract was added by means of a geostatistical algorithm and was conditioned to measured stratigraphic logs the analysis of the resultant 3d facies distributions allows revising the architectural interpretation of the studied interval leading to the conclusion that the observed arrangements are accommodation not supply driven furthermore the 3d models were flow simulated in two injector producer scenarios up depositional and down depositional dip waterflooding flow simulation results show that the depositional architecture of the studied succession controls potential recovery efficiencies in that a considerable proportion of moveable oil is trapped at the dead ends in depositional pinch outs of the main potential reservoir fan delta front deposits also that up dip waterflooding predicts better recovery efficiencies than down dip the dataset methods and results herein make the sant llorenc del munt complex a ready for application analogue for marine transitional reservoirs

cracking the lid sill fed dikes are the likely feeders of flood basalt eruptions although subparallel swarms of dikes are thought to be the primary feeders to voluminous volcanic eruptions increasing recognition of volumetrically significant sill complexes suggests that they too play an important role in magma ascent through the shallow crust however the extent to which sills and interconnected sill fed dikes actually transport magma to the earth s surface in many large igneous provinces lip is presently unclear by analyzing field relationships and dimensions of intrusions of the ferrar lip in south victoria land antarctica we show that sill fed dikes were the likely feeders for voluminous flood basalt eruptions these intrusions are small but numerous with cumulative dimensions equivalent to a feeder network 308 000 km long and 1 8 m wide due to the tremendous aerial extent of this intrusive network each individual dike feeder segment would only be required to actively feed magma for 2 to 3 days on average to erupt the 70 000 km3 of flood lavas represented by the kirkpatrick basalts the ferrar intrusions form a broadly distributed array of small moderately dipping dikes 2 km long 1 8 m wide 56 mean dip exhibiting almost any orientation this sill fed dike network contrasts with dike swarms conventionally depicted to feed flood basalt provinces and has the appearance of a variably cracked lid atop a sill complex the cracked lid model may apply to a range of shallow feeder systems 4 km depth intruding sedimentary basins where the effects of far field tectonic stresses are negligible and sill intrusions exert the dominant control on dike orientations we conclude that sill inflation and resulting deformation of surrounding host rock plays a critical role in the ascent of magma in shallow volcanic systems that span the full spectrum of eruptive volumes

formation of quartz veins by local dissolution and transport of silica a simple model is proposed for the often thick quartz veins observed in the modum complex in southern norway the formation of these veins cannot easily be explained by silica imported by hot ascending fluids the proposed model has dissolution in the host rock adjacent to the veins as the source for silica the suggested process for vein formation is represented by a reaction diffusion equation and the process is studied in terms of a damkohler number estimates for the growth rate of quartz cement are derived the estimates for the growth rate can be used to constrain poorly known parameters of the vein formation process like for instance the degree of supersaturation in the host rock

transport mechanisms of sand in deep marine environments insights based on laboratory experiments reply first of all we would like to thank dr shanmugam for his interest in our study of transport mechanisms of sand in deep marine environments breien et al 2010 in order to answer the remarks of shanmugam we here provide some more details around the experiments and we specify the intention of the study the main objective of the experiments presented in our paper was to study transportation and depositional processes in sand rich slurries run in water and how these mechanisms respond to changing sand clay ratios we find some of the comments of shanmugam 2011 to be more concentrated on the bouma sequence and the properties of its divisions ta te than on the mechanism of sediment transport itself we do not claim to have produced a complete bouma sequence cf bouma 1962 walker 1965 middleton and hampton 1973 however we rather see that our experiments indicate that similar graded bed deposits may be produced by different transport mechanisms we show that dense laminar flows may transport sand through fluidization and incrementally produce sand deposits resembling deposits produced by turbulent turbidity currents thus we regard the process observed in the laboratory as only one out of several mechanisms to transport and deposit clean sand in submarine basins as part of a ph d program breien 2009 47 debris flow experiments were performed prepared with five different compositions of varying sand clay ratio 5 10 15 20 and 25 clay by weight content of water and coal

formation of sapphirine and corundum in scapolitised and mg metasomatised gabbro terra nova 22 166 171 2010 abstract sapphirine mg3 41fe0 11al4 45 al4 55si1 45 o20 and corundum are found as inclusions 0 2 mm in cl rich scapolite me24 25 and plagioclase an20 24 in the metasomatised parts of the odegarden gabbro bamble sector south norway microtextural relationships suggest that the overall reaction plagioclase mg cl sapphirine corundum scapolite ca fe took place in two stages possibly related to infiltration of two metasomatic fronts gresen analyses support that the scapolitisation was combined with a strong mg metasomatism and removal of fe and ca on a whole rock scale the ferromagnesian minerals associated with sapphirine in the scapolite metagabbro have especially high mg ratios orthopyroxene mg 0 96 phlogopite mg 0 95 amphibole mg 0 81 0 87 clinopyroxene mg 0 95 this is much higher than in biotite mg 0 60 and clinopyroxene mg 0 78 0 81 in the unscapolitised parts of the gabbro and comparable with that found in sapphirine bearing orthoamphibole cordierite schists in the region suggesting that they also formed by metasomatism a metasomatic origin for the sapphirine has consequences for models of crustal growth and metamorphic history

building a training image with digital outcrop models summary current standard geostatistical approaches to characterizing subsurface heterogeneity may not capture realistic facies geometries and fluid flow paths multiple point statistics mps has shown promise in portraying complex geometries realistically however realizations are limited by the reliability of the model of heterogeneity upon which mps relies that is the training image ti attempting to increase realism captured in tis a quantitative outcrop analog based approach utilizing terrestrial lidar and high resolution calibrated digital photography is combined with lithofacies analysis to produce tis terrestrial lidar scans and high resolution digital imagery were acquired of a westwater canyon member morrison formation outcrop in ojito wilderness new mexico usa the resulting point cloud was used to develop a cm scale mesh digital images of the outcrop were processed through a combination of photogrammetric techniques and manual digitizing to delineate different facies and sedimentary structures the classified images were projected onto the high resolution mesh creating a physically plausible digital outcrop model dom portions of which were used to build mps tis the resulting mps realization appears to capture realistic geometries of the deposit and empirically honors facies distributions

introduction to special issue of canadian journal of earth sciences the lake nipigon region geoscience initiative the lake nipigon region geoscience initiative lnrgi was a 3 year collaborative geoscience data acquisition and compilation project that focussed on lake nipigon in ontario and involved partnerships between mineral industry university and provincial and federal government geoscientists a major objective of the initiative was to collect new geoscience information to better understand the geological history of the nipigon region to inform land use planning identify areas of high mineral potential and attract mineral exploration the special issue on the lnrgi highlights the scientific successes of the initiative in the fields of geology petrology geochemistry geochronology stratigraphy and basin analysis mineral deposits and surficial geology and geochemistry

the igneous petrology and magmatic evolution of the midcontinent rift system klewin k w and shirey s b 1992 the igneous petrology and magmatic evolution of the midcontinent rift system in p a ziegler editor geodynamics of rifting volume ii case history studies on rifts north and south america and africa tectonophysics 213 33 40 the 1100 ma midcontinent rift system of north america is one of the world s great igneous provinces containing over one million km3 of mafic volcanic and plutonic rocks volcanic rocks range from picrite to rhyolite although tholeiitic basalt predominates plutonic rocks range from peridotite to granite with plagioclase rich gabbros and troctolites being most abundant the igneous history of the rift can be divided into early and late stages flows of the early stage form a trend having low alumina high magnesia picrite as the primitive endmember whereas flows from the late stage form a trend having high alumina olivine tholeiite as the primitive endmember the early basalts have enriched nd isotopic compositions and were derived largely from old heterogeneous subcontinental lithosphere the late basalts have chondritic to depleted nd isotopic compositions and were derived from large degree partial melts of a mantle plume that had mixed with isotopically depleted asthenospheric mantle apparently melting began initially in the subcontinental lithosphere as it was stretched subsequently a lower mantle plume which had entrained asthenospheric mantle during its ascent rose beneath the rift and melted at large degrees to yield the voluminous later basalts

geochemistry and geodynamic implications of the mesoproterozoic english bay granite rhyolite complex northwestern ontario the mesoproterozoic english bay complex consists of a granite rhyolite assemblage outcropping on the shores of lake nipigon in western superior province canada it intrudes neoarchean rocks and is disconformably overlain by a rift infracratonic basin sedimentary succession recording subsidence following a heating event the granites and rhyolites are characterized by light rare earth element lree enrichment la smn 2 8 5 1 and only weakly fractionated heavy ree hree gd ybn 1 1 1 6 the felsic igneous rocks are high k enriched in zr nb y and ree satisfying all the criteria for an a type suite trace element geochemistry particularly the absence of any negative nb anomalies indicates this melt did not originate in a suprasubduction zone setting unlike the st francois mountain complex to the south the english bay complex may record the northern portion of a mesoproterozoic plume track a plume that possibly led to earlier igneous activity and infracratonic basin formation to the north and would later interact with a suprasubduction zone margin to the south

seismic modelling of outcrop carbonate systems an application to the cretaceous platform to basin system of the maiella mountain central apennines italy

high fo2 metasomatism during whiteschist metamorphism zambezi belt northern zimbabwe the kadunguri whiteschists are a group of talcand kyanitethe kalahari craton it includes the damara belt of namibia the lufilian arc of zambia and the democratic bearing lithologies that occur in the chewore inliers from the zambezi belt of northern zimbabwe they crop out on the southern republic of congo and the zambezi belt of southern zambia and northern zimbabwe it interacts complexly margin of the chewore ophiolite terrane a mesoproterozoic ophiolite and island arc as a 5 km 1 5 km southeasterly dipping semiat its eastern margin with the north south trending east african orogen of northern mozambique and east continuous block and contain the second known natural occurrence of yoderite major element analyses define the whiteschists within africa the zambezi belt is a complex polyorogen recording the relatively simple mfash system major and trace element analyses indicate that the whiteschists originate from the metasomatic major tectonothermal events at 890 880 ma and 520 550 ma both of which predominantly rework older alteration of alkalic ocean island type metabasalts similar to those in the underlying ophiolite terrane synmetamorphic or metasomatic crustal components mesoproterozoic to archaean with the addition of minor juvenile material hanson et al mineral parageneses indicate peak p t conditions of between 13 and 15 kbar at 550 600 c and the highly oxidizing nature of 1988 1993 1994 wilson et al 1993 armstrong et al 1999 within this belt and within basement inliers of all reactions indicates the presence of a high fo2 metasomatic fluid the peak p t conditions require that this synmetamorphic exotic the lufilian arc are a string 150 km long 50 100 km metasomatic fluid was available at depths near 55 km the age of wide of high pressure kyanite bearing meta gabbroic high pressure metamorphism is constrained within the pan african eclogites and whiteschist fragments fig 1 vrana tectonothermal cycle at 550 520 ma tectonometamorphism in barr 1972 vrana et al 1975 cosi et al 1992 johnson the zambezi belt is related to a period of extensive crustal thickening oliver 1998 dirks sithole 1999 john et al 1999 possibly related to amalgamation of gondwanaland 2000 until recently these high pressure moderate temperature fragments have been poorly studied but some are now the focus of detailed investigations e g johnson oliver 1998 oliver et al 1998 dirks sithole 1999

40ar 39ar phlogopite and u pb perovskite dating of lamprophyre dykes from the eastern lake superior region evidence for a 1 14 ga magmatic precursor to midcontinent rift volcanism thin lamprophyre dykes are abundant in the vicinity of the ca 1 1 ga midcontinent rift system and the late archean early proterozoic kapuskasing uplift in the canadian shield northeast of lake superior however the relationship between these dykes and spatially associated alkalic carbonatite complexes has been unclear to ascertain the temporal relationship between the two we have determined by 40ar 39ar and u pb dating precise emplacement ages for six lamprophyre dykes from the region the ma u pb date for perovskite from the western marathon and wawa areas is indistinguishable from the 1144 7 ma 40ar 39ar date for phlogopite from the eastern kapuskasing uplift and it is concluded that these dykes are part of a regional 1 14 ga swarm that extends over 300 km these dykes were therefore emplaced some 35 ma prior to the 1109 ma commencement of midcontinent rift volcanism and coeval alkaline complex activity but essentially simultaneously with emplacement of the 1141 2 ma abitibi diabase dyke

sedimentary architecture of a canyon style fairway feeding a deep water clastic system the miocene cingoz formation southern turkey significance for reservoir characterisation and modelling abstract the sedimentary architecture of a submarine canyon fill supplying sediment to a deep water fan system in the adana basin southern turkey is described and quantified the canyon is at least 9 km long 3 4 km wide asymmetric in cross section and has an exposed fill 360 m thick consisting of sands and gravels deposited in sheets across the entire width of the canyon normal graded and nongraded pebbly sandstones reflecting deposition from both waning and waxing high density turbidity currents dominate these deposits facies are identified and correlated between closely spaced sedimentary logs a hierarchy of bedding scales is recognised ranging from individual beds and their sedimentary structures through 3 21 m thick packages of beds to 100 m thick major units this hierarchy provides the framework for computer generated 3d models where sandstone bodies and facies are stochastically modelled to provide a better understanding of the internal sedimentary architecture within similar types of canyons in subsurface or in areas of poor exposure

cordierite formation during the experimental reaction of plagioclase with mg rich aqueous solutions the reaction between plagioclase labradorite and oligoclase and mg rich aqueous solutions was studied experimentally at hydrothermal conditions 600 700 c 2 kbar during the experiments plagioclase grains were readily converted to cordierite and quartz within 4 days the cordierite crystals had well developed polyhedral shapes but showed skeletal internal morphologies suggesting that the initial growth occurred fast under high driving force conditions in pure mgcl2 solutions 0 5 5 m plagioclase dissolution and cordierite precipitation were spatially uncoupled indicating that al was to some extent mobile in the fluid cordierite crystals formed at 700 c showed orthorhombic symmetry whereas those formed at 600 c dominantly persisted in the metastable hexagonal form suggesting a strong increase in al si ordering speed between 600 and 700 c the thermodynamic evolution of the fluid solid system ultimately resulted in stabilization of ca rich plagioclase as demonstrated by partial anorthitization of unreacted plagioclase grains cordierite was also observed to form when mg was added to a potentially albitizing na silicate bearing solution in that case cordierite precipitation appeared to be more closely coupled to plagioclase dissolution and secondary alteration of remnant plagioclase grains did not occur most likely due to armoring of the plagioclase by the cordierite overgrowth the fast reaction rates observed in our experimental study have potential implications for mg metasomatism as a rock forming process

boron isotopes in tourmaline as a tracer of metasomatic processes in the bamble sector of southern norway the bamble sector of southern norway comprises metagabbros and metasediments that were metasomatically altered to various extents during a late stage of the sveconorwegian orogeny 1 06 ga the infiltration of highly saline brines along veins led to penetrative scapolitization and albitization on a regional scale and the local deposition of fe ti oxides typical secondary mineral assemblages include either scapolite apatite amphibole phlogopite tourmaline or albite epidote calcite chlorite white mica indicating that the fluids introduced large amounts of na cl mg ca k p and b to the system metasomatic tourmalines associated with different alteration stages as identified by variations in major element composition and initial 87sr 86sr were analyzed for b isotopic compositions to constrain possible sources and the evolution of the hydrothermal fluid s measured 11b values range from 5 to 27 relative to srm 951 suggesting marine evaporites interlayered with various amounts of continental detritus and pelagic clay as a possible b source reservoir the influence of a seawater derived component is clearly indicated by the heavy b isotope signature of tourmaline related to al mg rich metapelites in contrast negative 11b values can be explained by the influence of pneumatolytic fluids associated with granitic pegmatites on a regional scale i e several km 11b values in tourmaline vary widely whereas variations within a single outcrop tens of m are typically small and can be ascribed to different generations of tourmaline related to several fluid pulses

closing of the midcontinent rift a far field effect of grenvillian compression the midcontinent rift formed in the laurentian supercontinent between 1109 and 1094 ma soon after rifting stresses changed from extensional to compressional and the central graben of the rift was partly inverted by thrusting on original extensional faults thrusting culminated at about 1060 ma but may have begun as early as 1080 ma on the southwest trending arm of the rift the crust was shortened about 30 km on the southeast trending arm strike slip motion was dominant the rift developed adjacent to the tectonically active grenville province and its rapid evolution from an extensional to a compressional feature at ca 1080 ma was coincident with renewal of northwest directed thrusting in the grenvllle probably caused by continent continent collision a zone of weak lithosphere created by rifting became the locus for deformation within the otherwise strong continental lithosphere stresses transmitted from the grenville province utilized this weak zone to close and invert the rift

complex reservoir geometries in a deep water clastic sequence gryphon field ukcs injection structures geological modelling and reservoir simulation abstract the balder formation sandstone reservoir of the gryphon field was deposited during the late paleocene early eocene while the background sedimentation comprised pelagic shales and tuffs sediment gravity flows transported sands from the shelf area in the west the crawford ridge acted as a barrier to sediment transport in the east causing the sands to be deposited predominantly as massive sand bodies as flow velocities decreased during burial sand remobilisation and injection occurred possibly localised around faults cored intervals show a range of injection structures from thin cm scale dykes to more massive metre scale chaotic intrusive features the cross cutting nature of the injection structures as observed in core and in seismic sections accounts for the high degree of reservoir connectivity observed in the field a study was undertaken with the objective of constructing a 3d geological model for dynamic reservoir simulation in order to evaluate future development activities in the field as previous purely deterministic models had proven unsuitable the complex depositional and post depositional history of the gryphon field reservoir has resulted in a system for which there is no published analogue to aid in 3d reservoir modelling preliminary stochastic models based on analogues chosen to reflect the reservoir sand body geometries did not match the field production history the fact that both the deterministic and fully stochastic models were unsuitable suggested that a novel approach was required to model this field subsequent models constructed using a combination of stochastic and deterministic models have proven successful in matching the production history of the field and evaluating infill opportunities

trace element characteristics and pb isotopic evolution of metasediments and associated proterozoic rocks from the amphibolite to granulite facies bamble sector southern norway abstract a study of trace element distribution and rb sr sm nd and pb isotopic compositions has been performed on amphibolite and granulite facies metasediments mafic granulites dioritic gneiss intrusive enderbitic veins and calc alkaline tonalitic gneisses from the proterozoic bamble sector southern norway the lile content of the granulite facies metapelites is similar to the average of the upper crust and post archaean average shales the k rb ratios of the amphibolite and granulite facies semipelites and impure quartzites are similar and the k rb ratios of the metapelites show overall similarities to the ratios of undepleted metapelites sr isotopic system and a poor correlation in the sm nd system the calculated t dm model ages for the metasediments can represent crustal residence times of 1 67 to 2 05 ga the present day lead isotopic data can be reproduced by a three stage model of pb evolution in which t 0 4 57 ga t 1 1 9 or 1 5 ga t2 1 1 ga 1 238 u 204 pb 7 9 1 232 th 238 u 2 5 2 4 15 where t 1 and t 2 are related to separation from the mantle and the sveconorwegian orogeny respectively the protolith of the metasediments the dioritic gneiss and the mafic granulites evolved in high u pb environments prior to sveconorwegian times 2 16 32 19 and18 45 respectively most of these rock units experienced conditions of 2 3 and 2 3 suggesting a large scale fractionation in the u th pb system connected to u mobility during the medium to high grade metamorphism there are no unambiguous differences in the pb isotopic composition between the amphibolite and granulite facies rocks but the mafic granulites from the classical depleted granulite area of tromoy island evolved in overall lower 2 238 u 204 pb environments than similar rocks from the neighbouring hisoy island this suggests that the similar u content of these rocks largely can be due to local pre sveconorwegian 238 u 204 pb variations sveconorwegian intrusive enderbitic dykes and veins crystallized with low lile and nb concentrations at granulite facies p t aco 2 conditions pre sveconorwegian granulite facies tonalitic gneisses show a less depleted trace element pattern and low nb concentrations and the hornblende free tonalitic gneisses have significantly lower u content than their hornblende bearing counterparts the investigated metasediments have very low contents of the less mobile elements nb sr cu and p 2 o 5 which probably represent characteristics of the pre sedimentary protolith

architecture of the tectonically influenced sobrarbe deltaic complex in the ainsa basin northern spain abstract the syn tectonic sobrarbe deltaic complex eocene of the ainsa basin spanish pyrenees is confined by lateral thrust ramps and influenced by intra basinal growth anticlines six facies associations have been distinguished within the deltaic complex i slope marls and turbidite sandstones ii distal delta front silty and bioturbated sandstones iii proximal delta front and delta plain deposits tidal inlet tidal flat mouth bar bay distributary channel and floodplain environments iv biogenic deposits at flooding surfaces v collapse zone sediments and vi nummulite dominated shallow marine carbonates the deltaic complex comprises four composite sequences which each contain a number of minor sequences of the genetic maximum flooding surface bounded type regressive unconformities and their correlative surfaces separate the composite sequences cs and each cs can be divided into lowstand transgressive and highstand components at the base the comaron cs is a wnw prograding deltaic complex containing six minor sequences characterized by basinward stepping sandstone wedges separated by transgressive mudstones double regressive unconformities are often associated with these sandstone wedges proximally in the basin growth of the intra basinal arcusa anticline caused gentle folding of the comaron cs and syn growth strata at the base of the overlying las gorgas cs contain a prominent forced regressive sandstone wedge the las gorgas sandbody and display thinning of bedsets onto the crest of the anticline moreover it can be demonstrated that relative sea level rise took place in the growth synclines at the same time as a fall in relative sea level occurred on the growth anticlines the tectonic deformation caused a shift in the direction of deltaic progradation towards the north northwest as demonstrated by the well developed clinoforms in the highstand sequence set of the las gorgas cs a second phase of tectonic activity this time triggering large scale collapse of the delta front occurred at the transition between the las gorgas and barranco el solano cs tilting of the basin floor led to the development of coeval transgressive and regressive strata separated by a fulcrum line of zero net vertical movement of the shoreline in the post tilt phase reduced sediment supply and accelerated subsidence led to widespread transgression and a change from clastic to carbonate dominated sedimentation this phase was terminated by a gradual increase in sediment supply causing progradation of a mixed clastic carbonate system dominated by large nummulite banks and bioturbated shoreface marls and sandstones finally a pronounced fall in relative sea level associated with the transition to the buil cs triggered slope instabilities and eventually established fluvial conditions all over the study area with the exception of the anticline crests the relatively high rate of tectonic subsidence in the study area suppressed relative sea level falls resulting in development of discontinuous lowstand strata and bounding surfaces the segmented nature of many regressive unconformities may be related to incremental growth of thrust related structures and each segment is separated from neighbouring segments by gaps of limited vertical and lateral displacement precursors of progressive unconformities are seen in the upper proximal part of the comaron cs by downdip fanning and updip convergence of minor sequences these differentially tilted stratal units provide reliable indicators of syn sedimentary tectonism

combining geologic process models and geostatistics for conditional simulation of 3 d subsurface heterogeneity 1 the goal of simulation of aquifer heterogeneity is to produce a spatial model of the subsurface that represents a system such that it can be used to understand or predict flow and transport processes spatial simulation requires incorporation of data and geologic knowledge as well as representation of uncertainty classical geostatistical techniques allow for the conditioning of data and uncertainty assessment but models often lack geologic realism simulation of physical geologic processes of sedimentary deposition and erosion process based modeling produces detailed geologically realistic models but conditioning to local data is limited at best we present an aquifer modeling methodology that combines geologic process models with object based multiple point and variogram based geostatistics to produce geologically realistic realizations that incorporate geostatistical uncertainty and can be conditioned to data first the geologic features of grain size or facies distributions simulated by a process based model are analyzed and the statistics of feature geometry are extracted second the statistics are used to generate multiple realizations of reduced dimensional features using an object based technique third these realizations are used as multiple alternative training images in multiple point geostatistical simulation a step that can incorporate local data last a variogram based geostatistical technique is used to produce conditioned maps of depositional thickness and erosion successive realizations of individual strata are generated in depositional order each dependent on previously simulated geometry and stacked to produce a fully conditioned three dimensional facies model that mimics the architecture of the process based model we demonstrate the approach for a typical subsea depositional complex

petrology of cordierite gedrite bearing sodic granulite from the grenvillian long range inlier newfoundland sodium rich potassium poor granulite in the long range inlier contains ab qtz crd bt opx ilm and either gedrite or garnet but rarely both the distribution of garnet in the sodic gneiss was influenced by bulk compositional controls e g higher al2o3 sio2 textural evidence indicates that gedrite was metastable with respect to crd opx during granulite grade metamorphism peak metamorphic conditions are estimated to have been 700 c at 600 mpa the metamorphic fluid was co2 rich the preservation of pelitic sil crd bt grt qtz mc and layers in which k2o na2o suggests a sedimentary precursor for the sodic gneiss but the granulites are more sodic and less magnesian than primary sediments recently identified as possible precursors to cordierite orthoamphibole rocks e g ultramafic derived greywackes evaporitic mudstones leucosomes tend to be more sodic mean na2o k2o 23 5 than mesosomes mean na2o k2o 17 8 m garnet free gneiss and 1 4 m garnetiferous gneiss so unl

crustal contamination identified in keweenawan osler group tholeiites ontario a trace element perspective in the lake superior area voluminous middle proterozoic tholeiitic basalt with minor rhyolite and interflow sediments occupy the midcontinent rift and overlie archean and older proterozoic basement the 3000 m thick section of gently dipping 10 sse basalts on the black bay peninsula is divided into three suites based on the relationship between stratigraphy petrography and geochemical variations e g mg number a1 2 o 3 la sm and gd yb the lower suite consists of augite olivine porphyritic lavas with high mg number sio 2 tio 2 and gd yb but low la sm the overlying central suite flows are either aphyric or plagioclase porphyritic and have lower mg number sio 2 la sm and gd yb decline upward through the central suite the upper suite lavas are either aphyric or plagioclase porphyritic and element ratios plot on slightly different trends compared to the central suite the lower suite has a narrow compositional range the average of the four most primitive lavas is used

geologic and geochemical evidence for the nature and development of the middle proterozoic keweenawan midcontinent rift of north america abstract general models of active continental rifting must take into account the large plateau basalt provinces many of which have been precursors of or associated with continental breakup the keweenawan middle proterozoic midcontinent rift mcr of north america 2300 km long is one such major continental rift but it aborted before significant crustal separation was achieved these plateau basalt rifts including the mcr differ from the east african type in being dominated by broad subsidence rather than rift valleys tholeiitic flood basalts rather than alkalic central volcanoes and large positive gravity anomalies geologic and geophysical evidence is reviewed which contradicts some recent models which have been proposed for the development of the mcr the basic causes of the pre rift subsidence the u shaped nature of the structure and the abrupt termination of its activity are obscure a triple junction in the usual sense does not appear to have been formed

age and lead isotope systematics of uranium enriched cobalt mineralization in the modum complex south norway abstract in the modum complex in the precambrian kongsberg sector of south norway cobalt sulphides and arsenides chalcopyrite and pyrite occur in stratiform bands and lenses the cobalt ore minerals are intimately associated with thorian uraninite both on a regional and on a microscopic scale due to the presence of coeval inclusions and intergrowths of uraninite in the cobalt minerals hand picked separates of ore minerals show a large range of u pb ratios this has led to a very large range of present day lead isotopic composition 206 pb 204 pb 18 1 to 277 207 pb 204 pb 15 6 to 36 208 pb 204 pb 37 to 57 two groups of samples can be discerned group 1 defines an imperfectly fitted pb pb lead isochron with an age of 1434 29 ma group 2 defines a pb pb correlation line with an age of 1146 66 ma these results indicate that the uranium bearing cobalt ore was deposited during the orogenic interlude commonly thought to separate the gothian kongsbergian ca 1 5 ga and sveconorwegian 1 2 0 9 ga orogenies in the baltic shield multi stage lead modelling indicates that the initial isotopic composition of the lead in the ores is indistinguishable from that of lead in the country rock metasediments suggesting that it was extracted from such a source the group 2 leads were affected by a strongly localized hydrothermal reworking process during the sveconorwegian orogeny which led to small scale partial pb isotopic homogenization and to strong fractionation of uranium thorium and lead the 1 43 ga age for primary mineralization defines a definite lower age limit for the onset of clastic sedimentation in the kongsberg sector the crustal precursor of the sediments must have retained a high lile upper continental crust character for several hundred million years prior to sedimentation

u pb geochronologic constraints on the crustal evolution of the long range inlier newfoundland the long range mountains of newfoundland expose the northeastern most basement inlier of the appalachian orogen u pb results for two samples of basement gneiss reveal crustal formation ages of 1466 10 ma western brook pond charnockite and 1530 8 ma cat arm road gneiss indicating an affinity with pinwarian magmatism 1510 1450 ma in labrador a third sample of basement gneiss from the cat arm road dam site yielded a minimum formation age of 1631 ma these basement gneisses were intruded by granite plutons during two periods of grenvillian magmatism group i at 1032 1022 ma and group ii at 993 985 ma group i intrusions include the 1032 0 1 5 ma lomond river granite and the 1022 0 2 0 ma lake michel igneous suite group ii intrusions include the 999 4 ma potato hill charnockite 993 7 ma horse chops granite 984 9 1 6 ma cloud river granite and may include the apsy granite the metamorphic history of the long range inlier is complex and three discrete proterozoic metamorphic events can

proterozoic and archean geology of the nipigon embayment implications for emplacement of the mesoproterozoic nipigon diabase sills and mafic to ultramafic intrusions the nipigon embayment is underlain by archean rocks of the english river wabigoon and quetico subprovinces and intruded along the west side by late to post tectonic mafic to ultramafic intrusions the early mesoproterozoic ultramafic to felsic badwater intrusion and felsic english bay complex are located in the northwest corner of the nipigon embayment three mafic to ultramafic intrusions the disraeli seagull and hele intrusions are located south of lake nipigon and the kitto intrusion is located east of the lake a number of mafic to ultramafic bodies jackfish island shillabeer kama hill nipigon bay have only limited outcrops the gabbroic nipigon diabase sills intrude all other rocks in the nipigon embayment and generally have a consistent mineralogy and geochemistry except for the inspiration sill s and the mcintyre sill geological and geophysical data suggest emplacement of the ultramafic intrusions by mechanisms similar to those controlling emplacement of the saucer shaped diabase sills these mechanisms are partially dependent on a series of pre existing north northwest and northeast trending faults formed prior to keweenawan magmatism the presence of sills rather than dykes indicates that the nipigon embayment was not extensional during the keweenawan midcontinent rift suggesting that the nipigon embayment is not a classic failed arm

the age of the gunflint formation ontario canada single zircon u pb age determinations from reworked volcanic ash the gunflint formation a paleoproterozoic chemical clastic sedimentary assemblage outcropping to the immediate northwest of lake superior became famous in 1954 as containing the oldest fossil assemblage known at that time older microfossils have since been discovered but the gunflint procaryotes remain one of the most diverse precambrian fossil communities the finding of possible multicellular organisms in correlative lithic units in michigan has recently added to the need for an exact age of the formation zircons were extracted from rainout and storm reworked volcanoclastic beds in the upper portion of the gunflint formation a euhedral zircon population has yielded a 1878 3 1 3 million years bp u pb age believed to be nearly synchronous with the depositional age this not only provides a precise age for the community of organisms but also strongly supports a back arc extensional setting for the animikie basin rather than a foreland trough resume la formation de gunflint un assemblage sedimentaire chimique et clastique datant du paleoproterozoique affleurant immediatement au nord ouest du lac superieur est devenue celebre en 1954 car elle contenait les plus an ciens assemblages fossiliferes connus a cette epoque de plus anciens microfossiles ont ete decouverts depuis mais les procaryotes de gunflint demeurent l une des communautes fossiles precambriennes les plus diversifiees la decouverte

synchronous extension and contraction in frontal thrust sheets of the spanish pyrenees the ainsa marine foreland basin of the southern pyrenees contains eocene deltaic and turbidite sequences that were deformed synchronously by both thrusting and extensional faulting during sedimentation two basin scale extensional truncation surfaces developed within a prograding imbricate thrust wedge in the footwall of the cotiella thrust sheet detailed mapping and analysis have shown that these features are major extensional detachment faults that produced complex sedimentological and stratal relations

petrology and geothermobarometry of granulite facies metapelites from the hisoy torungen area south norway new data on the sveconorvegian p t t path of the bamble sector the high grade rocks metapelite quartzite metagabbro of the hisoy torungen area represent the south westernmost exposures of granulites in the proterozoic bamble sector south norway the area is isoclinally folded and a metamorphic p t t path through four successive stages m1 m4 is recognized petrological evidence for a prograde metamorphic event m1 is obtained from relict staurolite chlorite albite staurolite hercynite ilmenite cordierite sillimanite fine grained felsic material quartz and hercynite biotite sillimanite within metapelitic garnet the phase relations are consistent with a pressure of 3 6 0 5 kbar and temperatures up to 750 850 c m1 is connected to the thermal effect of the gabbroic intrusions prior to the main m2 sveconorwegian granulite facies metamorphism the main m2 granulite facies mineral assemblages quartz plagioclase k feldspar garnet biotite sillimanite are best preserved in the several metre wide al rich metapelites which represent conditions of 5 9 9 1 kbar and 790 884 c these p t conditions are consistent with a temperature increase of 80 100 c relative to the adjacent amphibolite facies terranes no accompanying pressure variations are recorded up to 1 mm wide fine grained felsic veinlets appear in several units and represent remnants of a former melt formed by the reaction bt sil qtzgrt lq this dehydration reaction together with the absence of large scale migmatites in the area suggests a very reduced water activity in the rocks and xh2o 0 25 in the c o h fluid system was calculated for a metapelitic unit a low but variable water activity can best explain the presence or absence of fine grained felsic material representing a former melt in the different granulitic metapelites the strongly peraluminous composition of the felsic veinlets is due to the reaction grt former melt silcrd bt qtz h2o which has given poorly crystalline cordierite aggregates intergrown with well crystalline biotite the cordierite and biotite producing reaction constrains a steep first stage retrograde relative to m2 uplift path decimetre to metre wide strongly banded metapelites quartz plagioclase biotite garnet sillimanite inter layered with quartzites are retrograded to m3 amphibolite facies assemblages a p t estimate of 1 7 5 6 kbar 516 581 c is obtained from geothermobarometry based on rim rim analyses of garnet biotite plagioclase sillimanite quartz assemblages and can be related to the isoclinal folding of the rocks m4 greenschist facies conditions are most extensively developed in millimetre wide chlorite rich calcite bearing veins cutting the foliation

geochemistry of the mesoproterozoic intrusive rocks of the nipigon embayment northwestern ontario evaluating the earliest phases of rift development the intrusive rocks of the nipigon embayment comprise a series of four mafic to ultramafic intrusions and a number of laterally extensive diabase sills that are among the oldest expression of the

petrologic evolution of a nipigon diabase sill ontario canada insights from compositional and textural profiles petrographic and geochemical profiles collected through a 250 m thick nipigon diabase sill near black sturgeon lake ontario constrain the complex emplacement and differentiation processes that controlled the magmatic evolution of these rocks several nested reinjections of phenocryst bearing magma compactiondriven redistribution of mildly evolved interstitial liquids in the central portion of the sill and segregation of highly evolved interstitial liquids into micropegmatitic veins near the upper contact these processes impact not only the silicate mineralogy of the rocks but also distribution of sulfide phases both petrographic and geochemical data demonstrate that the sill was gradually inflated via several discrete injections of olivine bearing magma plagioclase crystal size trends exhibit several reversals that are correlated with increases in olivine abundance and bulk rock mgo content these textural and compositional reversals are attributed to reinjections of olivine bearing magma into partially solidified magma from earlier injections mixing between evolved resident magma and reinjections of less evolved magma is commonly proposed as a mechanism for triggering sulfide mineralization in this sill which contains no significant mineralization localized minor enrichments and depletions in copper content are associated with the margins of a well constrained reinjection horizon chemical differentiation of the magma was controlled by three distinct processes flow differentiation crystal mush compaction and solidification front instability although the mineralogy of the sill is dominated by plagioclase and clinopyroxene major oxide compositional variations are largely controlled by the mechanical concentration of olivine via flow differentiation or phenocryst redistribution within the individual reinjection pulses this redistribution of phenocryst phases is the primary factor controlling the major element composition of the rocks in most of the sill in the central portion of the sill the abundances of incompatible trace elements are influenced by the compaction of partially crystalline mush and the expulsion of incompatible rich interstitial liquid this is recognized by a negative correlation between the alignment of plagioclase crystals and concentrations of incompatible trace elements such as zr finally there is a 2 5 m thick silicic segregation approximately 32 m below the upper contact whose composition is consistent with residual liquid after 65 to 85 fractional crystallization of magma with a composition equivalent to that of the marginal rocks similar veins and patches are common throughout the upper 50 m of the sill indicating that this segregation process was common and widespread during the cooling and crystallization of the sill the complexity of intrusion and differentiation in this sill despite its generally unremarkable texture and composition suggests that many diabase sills may have experienced a range of processes that have previously been recognized to impact the petrologic evolution of larger igneous systems and that these processes can be identified in minor intrusions such as sills and dikes using simple and robust analytical techniques

three dimensional reconstruction of geological surfaces an example of growth strata and turbidite systems from the ainsa basin pyrenees spain the external and internal geometry of four turbidite systems outcropping around the buil syncline ainsa basin spanish pyrenees has been reconstructed with reservoir scale resolution in three dimensions 3 d the irregular geometry of the syncline and the resolution required for the reconstruction cannot be resolved with cross sections therefore reconstruction has been carried out with a new methodology that applies a 3 d dip domain geometrical model and 3 d restoration techniques to achieve reservoir scale resolution in kilometric scale reconstructions this methodology is aimed at resolving 3 d geometries in folded areas and regions with variable thickness stratigraphy the 3 d reconstruction of the buil syncline reveals the synsedimentary growth of an intrabasinal anticline and the foreland lithospheric flexure associated with tectonic loading north of the ainsa basin

tectonic setting of the midcontinent rift system abstract the continental lithosphere which hosts the midcontinent rift mcr system comprises a crustal assemblage ranging in age from 3 6 to 1 5 ga the most voluminous igneous activity along the mcr occurred within late archean 2 7 ga crust presumably due to magmatism associated with a rising mantle plume two major arms of the rift extend to the southeast and the southwest where rifting magmatism and sedimentation were confined to a 2000 km long rift that cuts through the various crustal provinces ranging in age from 3 6 to 1 5 ga tensional reactivation of pre existing crustal discontinuities may have influenced the location of parts of the mcr however direct cause and effect are difficult to distinguish for want of sufficient exposures the most active phases of magmatism and rifting occurred between 1109 and 1087 ma a u pb age of 1097 ma for the southern end of the mcr shows that magmatic activity was synchronous throughout its length there is evidence of rifting and magmatism prior to 1109 ma but there is little evidence of magmatism after 1087 ma rifting may have effectively ceased by that time rifting may have ceased as a result of compressional forces being exerted on the foreland during the grenville collisional event spanning 1030 970 ma and compressional reactivation of normal faults may have resulted in partial inversion of the mcr chemical data and u pb and sm nd isotopic data for igneous rocks along the rift are similar to those for mcr rocks in the lake superior area which are best explained in terms of a mantle plume model however since the distal arms of the mcr were developed in proterozoic lithosphere and did not involve nearly as much magmatism as in the lake superior area mantle plume sources may not have been as important in formation of the distal magmas data from the buried arms are also consistent with the mafic magmas being derived by decompression melting of proterozoic lithosphere during rifting

p t conditions for the arendal granulites southern norway implications for the roles of p t and co2in deep crustal lile depletion the orthopyroxene clinopyroxene garnet orthopyroxene and garnet clinopyroxene geothermometers and the garnet orthopyroxene plagioclase garnet clinopyroxene plagioclase and anorthite ferrosilite grossular almandine quartz geobarometers are applied to metabasites and the garnetplagioclase sillimanite quartz geobarometer is applied to a metapelite from the proterozoic arendal granulite terrain bamble sector norway p t conditions of metamorphism were 7 3 0 5 kbar and 800 60 c this terrain shows a regional gradation from the amphibolite facies into normal lile content granulite facies rocks and finally strongly lile deficient granulite facies gneisses neither p nor t vary significantly across the entire transition zone the change in grade parallels the increasing dominance of co2 over h2o in the fluid phase lile depletion is not a pre condition of granulite facies metamorphism granulites may have either depleted or normal chemistries the results presented herein show that lile deficiency in granulite facies orthogneisses is not necessarily related to variations in either p or t the important mechanisms in the arendal terrain were a direct synmetamorphic crystallization from magma with primary lile poor mineralogies imposed by the prevailing fluid regime and b metamorphic depletion involving scavenging of liles during flushing by mantle derived co2 rich fluids the latter process is constrained by u pb and rb sr isotopic work to have occurred no later than 50 ma after intrusion of the acid intermediate gneisses and was probably associated with contemporary basic magmatism in a tectonic environment similar to a present day cordilleran continental margin

retrograde fluid infiltration in the high grade modum complex south norway evidence for age source and ree mobility the high grade metamorphic basement of the modum complex south norway exhibits retrogradation and alteration due to late stage fluid infiltration extensive alteration zones of albite and calcite rich veining occur especiallywithin and around numerous metagabbros the gabbros intruded at 1224 15ma are now partly altered to amphibolites due to the subsequent high grade metamorphism two generations of albite rich rocks have been recognized 1 a fine grained foliated type 2 a coarse grained crosscutting type both types show a typical greenschist facies mineralassemblage albite actinolite chlorite talc the calcite veins dykesrepresent a younger generation of veins than both albite rich types u pb data for spheneof type 1 yielded an age of 1080 3 ma determining a point on the retrogradep t t path of the modum complex increasing albitisation of themetagabbros leads to a decrease in 143nd 144nd oand an increase in 87sr 86 o albite and calcite rich samples show negative nd and positive sr suggesting that fluids which interacted with the metagabbros originated from a crustal reservoir the nd and sr isotopic data show disequilibrium at the microscale as well as at the macroscale negative sm nd model ages of the albite rich rocks demonstrate that rare earth elements rees were mobile and fractionated during albitisation

post keweenawan compressional faults in the eastern lake superior region and their tectonic significance glimpce aeromagnetic data in eastern lake superior are characterized by a series of strong easterly and northeasterly oriented gradients that relate to mapped post keweenawan faults occurring along the eastern shore the reversed nature of three of the faults is established through field observations and potential field modelling middle keweenawan volcanic rocks at mamainse point are in fault contact on their south side with upper keweenawan sandstone of bayfield jacobsville type gravity modelling suggests that the fault is a low angle thrust dipping to the north field observations and high resolution aeromagnetic data show that it extends inland along the southern margin of the batchawana greenstone belt for at least 17 km to the west the mamainse point fault may extend across eastern lake superior to the keweenaw peninsula linking several offsets in the seismic data that are consistent with the same attitude and sense of displacement along the south side of batchawana bay at havilland sandstones of bayfield jacobsville type are isoclinally folded against a package of upthrust older rocks that include drag folded middle keweenawan volcanics at grindstone point north of cape gargantua a reverse fault separating isoclinally folded upper keweenawan sandstones from archean basement may on aeromagnetic evidence be an eastward extension of the michipicoten island fault these faults mark a significant change in the style of late compressional tectonism observed within the midcontinent rift all cut keweenawan rocks across strike the inference is that broad north south or northwest southeast compression consistent in timing and orientation with the grenville orogeny led to a reversal of movement along the major graben faults in western lake superior and was taken up in the eastern region by reverse faults oriented normal to the extensional axis of the rift

phase relations in the mgo p2o5 h2o system and the stability of phosphoellenbergerite petrological implications the polymorphic relations for mg3 po4 2 and mg2po4oh have been determined by reversed experiments in the temperature pressure t p range 500 1100 c 2 30 kbar the phase transition between the low pressure phase farringtonite and mg3 po4 2 ii the mg analogue of sarcopside is very pressure dependent and was tightly bracketed between 625 c 7 kbar and 850 c 9 kbar the high temperature high pressure polymorph mg3 po4 2 iii is stable above 1050 c at 10 kbar and above 900 c at 30 kbar the low pressure stability of farringtonite is in keeping with its occurrence in meteorites the presence of iron stabilizes the sarcopside type phase towards lower p from the five mg2po4oh polymorphs only althausite holtedahlite mg2po4oh the hydroxyl analogue of wagnerite and mg2po4oh were encountered relatively speaking holtedahlite is the low temperature phase 600 c mg2po4oh the high temperature low pressure phase and mg2po4oh the high temperature high pressure phase with an intervening stability field for althausite which extends from about 3 kbar at 500 c to about 12 kbar at 800 c althausite and holtedahlite are to be expected in f free natural systems under most geological conditions however wagnerite is the most common mg phosphate mineral implying that fluorine has a major effect in stabilizing the wagnerite structure coexisting althausite and holtedahlite from modum s norway show that minor fluorine is strongly partitioned into althausite kdf oh 4 and that holtedahlite may incorporate up to 4 wt sio2 synthetic phosphoellenbergerite has a composition close to mg0 9 0 1 2mg12p8o38h8 4 it is a high pressure phase which breaks down to mg2po4oh mg3 po4 2 h2o below 8 5 kbar at 650 c 22 5 kbar at 900 c and 30 kbar at 975 c the stability field of the phosphate end member of the ellenbergerite series extends therefore to much lower p and higher t than that of the silicate end members stable above 27 kbar and below ca 725 c thus the si p ratio of intermediate members of the series has a great barometric potential especially in the si buffering assemblage with clinochlore talc kyanite rutile h2o application to zoned ellenbergerite crystals included in the dora maira pyrope megablasts western alps reveals that growth zoning is preserved at t as high as 700 725 c however the record of attainment of the highest t and or of decreasing p through p rich rims 1 to 2 si pfu is only possible in the presence of an additional phosphate phase oh bearing or even oh dominant wagnerite in these rocks otherwise the trace amounts of p in the system remain sequestered in the core of si rich crystals 5 to 8 si pfu and can no longer react

geological modeling for simulation studies reservoir heterogeneity is hierarchical in nature and different levels of reservoir heterogeneity need to be quantified by the reservoir geologist for numerical simulation studies at the largest scale field scale sand body continuity and interconnectedness are the most important parameters at the scale of a reservoir or a genetic sand body areal permeability trends presence and distribution of permeability baffles vertical profiles of permeability and presence of directional permeability within a sand body are the most critical parameters at a smaller scale the influence of cross bedding on displacement processes is shown to be significant and in fact should be assessed to obtain more meaningful results from larger scale simulation models the examples given show some of the effects of the different scales of heterogeneity on fluid flow patterns these examples indicate the degree of detail that must be considered at different scales if simulations are to give meaningful results

capturing and modelling metre scale spatial facies heterogeneity in a jurassic ramp setting central high atlas morocco each simulation algorithm including truncated gaussian simulation sequential indicator simulation and indicator kriging is characterized by different operating modes which variably influence the facies proportion distribution and association of digital outcrop models as shown in clastic sediments a detailed study of carbonate heterogeneity is then crucial to understanding these differences and providing rules for carbonate modelling through a continuous exposure of bajocian carbonate strata a study window 320 m long 190 m wide and 30 m thick was investigated and metre scale lithofacies heterogeneity was captured and modelled using closely spaced sections ten lithofacies deposited in a shallow water carbonate dominated ramp were recognized and their dimensions and associations were documented field data including height sections were georeferenced and input into the model four models were built in the present study model a used all sections and truncated gaussian simulation during the stochastic simulation for the three other models model b was generated using truncated gaussian simulation as for model a model c was generated using sequential indicator simulation and model d was generated using indicator kriging these three additional models were built by removing two out of eight sections from data input the removal of sections allows direct insights on geological uncertainties at inter well spacings by comparing modelled and described sections other quantitative and qualitative comparisons were carried out between models to understand the advantages disadvantages of each algorithm model a is used as the base case indicator kriging model d simplifies the facies distribution by assigning continuous geological bodies of the most abundant lithofacies to each zone sequential indicator simulation model c is confident to conserve facies proportion when geological heterogeneity is complex the use of trend with truncated gaussian simulation is a powerful tool for modelling well defined spatial facies relationships however in shallow water carbonate facies can coexist and their association can change through time and space the present study shows that the scale of modelling depositional environment or lithofacies involves specific simulation constraints on shallow water carbonate modelling methods

outcrop analog for an oolitic carbonate ramp reservoir a scale dependent geologic modeling approach based on stratigraphic hierarchy considerable effort has been devoted to the development of simulation algorithms for facies modeling whereas a discussion of how to combine those techniques has not existed the integration of multiple geologic data into a three dimensional model which requires the combination of simulation techniques is yet a current challenge for reservoir modeling this article presents a thought process that guides the acquisition and modeling of geologic data at various scales our work is based on outcrop data collected from a jurassic carbonate ramp located in the high atlas mountain range of morocco the study window is 1 km 0 6 mi wide and 100 m 328 1 ft thick we describe and model the spatial and hierarchical arrangement of carbonate bodies spanning from largest to smallest 1 stacking pattern of high frequency depositional sequences 2 facies association and 3 lithofacies five sequence boundaries were modeled using differential global position system mapping and light detection and ranging data the surface based model shows a low angle profile with modest paleotopographic relief at the inner to middle ramp transition facies associations were populated using truncated gaussian simulation to preserve ordered trends between the inner middle and outer ramps at the lithofacies scale field observations and statistical analysis show a mosaiclike distribution that was simulated using a fully stochastic approach with sequential indicator simulation this study observes that the use of one single simulation technique is unlikely to correctly model the natural patterns and variability of carbonate rocks the selection and implementation of different techniques customized for each level of the stratigraphic hierarchy will provide the essential computing flexibility to model carbonate settings this study demonstrates that a scale dependent modeling approach should be a common procedure when building subsurface and outcrop models

paleomagnetism and geochemistry of 1144 ma lamprophyre dikes northwestern ontario implications for the north american polar wander and plate velocities

sapphirine kornenipine bearing rocks and crustal uplift history of the limpopo belt southern africa sapphirine kornerupine bearing rocks occur within the anorthosites of the messina layered intrusion in the limpopo mobile belt of zimbabwe the xmg range of the major minerals is as follows cordierite 0 98 0 93 enstatite 0 97 0 86 chlorite 0 98 0 92 phlogopite 0 98 0 90 sapphirine 0 98 0 86 kornerupine 0 94 0 88 gedrite 0 96 0 85 spinel 0 92 0 78 there are four rock types the constituent minerals of which have different x m g values which decrease in the above mineral order other minerals are corundum sillimanite and relict kyanite we recognise twenty reactions without phlogopite and nine reactions involving phlogopite the textural relations and the plots of the microprobe data of coexisting minerals in the mgo al2o3 sio2 h2o system are consistent with the following sequence of main reactions 1 enstatite corundum cordierite sapphirine 4 sapphirine sillimanite cordierite corundum 8 kornerupine corundum cordierite sapphirine 13 kornerupine cordierite sapphirine enstatite 15 enstatite spinel chlorite sapphirine 18 cordierite sapphirine chlorite corundum 20 sapphirine chlorite corundum spinel the early reactions are shown by coarse grained reaction intergrowths kornerupine and gedrite breakdown is shown by finer grained symplectites and the latest reactions by very fine grained products in micro fractures these selected reactions illustrate a remarkably steep trajectory from thept peak close to 10 kbar and 800 c to the minimum observable at 3 5 4 5 kbar and 700 c as indicated by the pure mash system very rapid uplift took place under nearly isothermal conditions the protolith of this material was possibly sedimentary derived from altered volcanic rocks the bulk composition is close to the composition of kornerupine or to a mixture of alunite chlorite and pyrophyllite these texturally and mineralogically complex rocks contain a wealth of relevant data for documenting crustal uplift history

metagabbros in the modum complex southern norway an important heat source for sveconorwegian metamorphism abstract the precambrian modum complex in southern norway is characterized by supracrustal rocks penetrated by numerous gabbro intrusions occurring as elongated bodies subparallel with the regional foliation these gabbroic bodies show a partial alteration to amphibolites the best preserved parts of the metagabbros show a subophitic texture with olivine and plagioclase as the major cumulus phases and clinopyroxene orthopyroxene and ilmenite as the major intercumulus phases subsequent alteration of these igneous phases has led to formation of coronas around olivine in contact with plagioclase and recrystallization of clinopyroxene the igneous phases indicate intrusion temperatures in the range of 1100 1000 c and pressures below 5 8 kbar formation of coronas and recrystallization of clinopyroxene occurred in the pressure temperature range of 7 10 kbar and 800 600 c a 1224 15 ma sm nd mineral isochron obtained from igneous phases indicates emplacement at the start of the sveconorwegian metamorphism a complex evolution is suggested for the sveconorwegian metamorphic event involving both magmatism and high grade metamorphism

geochemical stratigraphy of the keweenawan midcontinent rift volcanic rocks with regional implications for the genesis of associated ni cu co and platinum group element sulfide mineralization the development of the north american midcontinent rift can be understood in the context of a tectonic and magmatic event in which the far field effects of continental drift influenced magmatism produced by a mantle plume we report and interpret new data for samples collected from stratigraphically controlled sequences of basaltic rocks in the osler volcanic group and the mamainse point volcanic group in ontario canada we confirm that the earliest phase of rift development involved primitive melts that produced basalts in the lower formation of the osler volcanic group with fo74 80 olivine 1 490 2 280 ppm ni the earliest basalts are primitive in both the mamainse point volcanic group and osler volcanic group sections with elevated mgo cr and ni these rocks also have high tio2 and high gd yb which are features that indicate low degrees of melting of a garnet bearing lherzolite mantle the central formation a and b basalts of the osler volcanic group that overlie the lower formation lavas record an upward increase and then decrease in the degree of contamination of basaltic rocks with normal ni and platinum group element pge abundance levels that require no sulfide saturation event to accompany contamination the upper formation of the osler volcanic group is characterized by a limited number of pge depleted flows although these basalts are highly fractionated and typically develop textures with stellate to laminated plagioclase feldspar they are usually not significantly contaminated the lower and upper formations of the mamainse point volcanic group show a diversity in geochemistry consistent with contributions from different mantle sources but contamination is restricted to a small number of flows with normal ni and pge abundance levels there is no indication of a regional metal depletion signature on the scale of the nadezhdinsky formation at noril sk but there is evidence that local s saturation events were triggered in the unexposed conduits feeding some of the upper sequence flows in response to fractionation of the magma massive to heavy disseminated ni cu pge sulfide mineralization in the midcontinent rift is hosted by small primitive intrusions that were formed early in the evolution of the rift and are typically associated with transtensional structures in the cratonic blocks adjacent to the main rift examples include the eagle deposit in michigan the tamarack mineralization in minnesota and the current lake complex in ontario the american examples are associated with splays of the great lakes tectonic zone and the canadian example is associated with the quetico fault zone the intrusions share the geochemical fingerprints of the more primitive lowermost volcanic rocks of the midcontinent rift and they are broadly contemporaneous with the development of the lower stratigraphy of the osler volcanic group and mamainse point volcanic group although the low grade but large tonnage cu ni pge deposits of the duluth were formed significantly later than the small primitive intrusions their host rocks share the same lithophile trace element signature as these early intrusions the parental magmas that produced all of these intrusions were derived from deeper mantle depths where garnet was a stable phase than the magmas that produced the central formation basalts and some of the upper formation basalts investigated in this study

keweenaw hot spot geophysical evidence for a 1 1 ga mantle plume beneath the midcontinent rift system the proterozoic midcontinent rift system of north america is remarkably similar to phanerozoic rifted continental margins and flood basalt provinces like the younger analogues the volcanism within this older rift can be explained by decompression melting and rapid extrusion of igneous material during lithospheric extension above a broad asthenospheric thermal anomaly which the authors call the keweenaw hot spot great lakes international multidisciplinary program on crustal evolution seismic reflection profiles constrain end member models of melt thickness and stretching factors which yield an inferred mantle potential temperature of 1 500 1 570c during rifting combined gravity modeling and subsidence calculations are consistent with stretching factors that reached 3 or 4 before rifting ceased and much of the lower crust beneath the rift consists of relatively high density intruded or underplated synrift igneous material the isotopic signature of keweenawan volcanic rocks presented in a companion paper by nicholson and shirey this issue is consistent with the model of passive rifting above an asthenospheric mantle plume

connectivity estimation between turbiditic channels and overbank deposits from the modelling of an outcrop analogue pab formation maastrichtian pakistan conceptual models showing the sedimentary architecture of the turbidite depositional systems and their evolution trough time such as those published by e mutti and his school were first established in the outcrop at the reservoir scale the field development of turbidite reservoirs now requires detailed reservoir models finely describing the distribution of the heterogeneity which may influence the reservoir dynamic behaviour during production information derived from quantified outcrop models can then be used to better constrain the reservoir models in the subsurface outcrops models first focused on the heterogeneity distribution within the channel conduits emphasizing the diversity of the channel architecture regarding to the complexity of the depositional processes the facies architecture of turbiditic overbank deposits laterally to the channels are even less understood than within the channels if the general geometry of levees can be easily seen on seismic their facies and the sand shale ratio close to the channel border are poorly known as overflow deposits are rarely drilled in the subsurface and crevasse lobes are below seismic resolution the conceptual models of the overbank distribution at the reservoir scale must then rely on outcrops models the questions on which we would like to focus are the followings 1 what kind of facies model can we expect in the overbank deposits laterally to the channel conduits 2 do these facies constitute reservoir bodies with a significant volume 3 is there any heterogeneity between the channel conduits and the levees which may reduce their connectivity 4 can overbank deposits such as crevasses or spill over lobes insure connectivity between two channel conduits and homogenise the pressure regime during the reservoir production the relationship between channels and overbank are well exposed in the pab mountain range outcrops in pakistan in this paper we propose to characterize the relationships between the channel conduits and their overbank deposits from a sedimentological seismic and dynamic point of view using a geocellar model compiled in the pab outcrops the consequences on the reservoir development in the subsurface will be emphasized

best practice stochastic facies modeling from a channel fill turbidite sandstone analog the quarry outcrop eocene ainsa basin northeast spain using data from an outcrop characterization of a sandstone rich turbidite channel fill the so called quarry outcrop in the ainsa basin several stochastic facies models were constructed at bed scale resolution cells 2 5 m 8 ft wide and 0 05 m 2 in thick several industry standard reservoir modeling algorithms were employed truncated gaussian simulation sequential indicator simulation multiple point geostatistics and object based methods with varying degrees of complexity the degree of similarity i e realism between realizations and the outcrop characterization was quantified through the use of several responses 1 static connectivity 2 effective permeability and 3 recovery efficiency from waterflood simulations differences in the responses measured from the outcrop and facies models were observed these are mostly algorithm related instead of caused by soft data or different stochastic realizations differences increase greatly when the permeability of the heterolithic packages and mudstone beds ht m decreases and reflect the methods ability to model the inclined and undulating ht m packages and beds that occur in the outcrop these packages and beds can drape scours and sandstone beds with depositional topography and pinch outs producing sandstone thinning and dead ends object based methods capable of introducing highly undulating ht m beds provided the most realistic models variogram based and simple object based methods failed to capture and reproduce the whole length of undulating beds multiple point geostatistics provided realizations with responses intermediate between variogram based and simple object based methods and the more successful advanced object based methods the conditioning to hard data capabilities of multiple point geostatistics are higher than those of the object based methods which give them an added advantage

turbidite systems part 2 subseismic scale reservoir characteristics part i of this two part paper tle april 1999 outlined the general types of turbidite systems gravel rich sand rich mixed sand mud and mud rich and their seismic stratigraphic and wireline log characteristics in this paper we summarize reservoir properties their measurement and identification and their value in predicting reservoir performance approximately 75 of the world s giant turbidite fields have a stratigraphic component to their trapping mechanism pettingill 1998 so we focus here only on stratigraphic and related properties

the radiogenic isotope characteristics of dikes and sills associated with the mesoproterozoic midcontinent rift near thunder bay ontario canada abstract new radiogenic isotope data are presented for intrusive rocks of the mesoproterozoic midcontinent rift from the north shore of lake superior these mafic rocks are amongst the older portions of the rift sequence and offer insights into the early development and evolution of the rift two sill suites are recognized within the study area an earlier spatially restricted ultramafic unit termed the riverdale sill and the predominant logan sills as well as three dike sets the north east trending pigeon river swarm the north west trending cloud river dikes and the mt mollie dike in addition an enigmatic extrusive unit termed the devon basalts is also present the logan sills are characterized by 87sr 86sri values of 0 7048 0 7119 with 143nd 144nd values from 0 512012 to 0 512187 whereas the riverdale sill is characterized by 87sr 86sri values ranging from 0 7037 to 0 7078 and 143nd 144nd of 0 511938 0 511984 both the cloud river and pigeon river dikes show a range of isotope data with the cloud river dikes having 87sr 86sri values ranging from 0 7042 to 0 7064 and 143nd 144nd values from 0 512222 to 0 512379 whereas the pigeon river dikes have 87sr 86sri values from 0 7041 to 0 7243 and 143nd 144nd from 0 511640 to 0 512383 the mt mollie dike is characterized by 87sr 86sri of 0 7041 0 7074 and 143nd 144nd values range from 0 512014 to 0 512371 the majority of samples are characterized by negative ndt which are interpreted to be the result of contamination of a plume related mantle source by older crustal material the lack of correlation with other indices of fractionation e g sio2 for the majority of samples implies interaction with subcontinental lithospheric mantle either through assimilation or melting of the mantle rather than contamination during emplacement however a small number of samples appear to have assimilated material during emplacement resulting in strongly negative ndt values the radiogenic isotope data are consistent with a suite of rocks that have undergone complex contamination histories requiring variable crustal residence times and assimilation of material both at depth in large magma chambers and during emplacement

discovery of distal ejecta from the 1850 ma sudbury impact event a 25 70 cm thick laterally correlative layer near the contact between the paleoproterozoic sedimentary gunflint iron formation and overlying rove formation and between the biwabik iron formation and overlying virginia formation western lake superior region contains shocked quartz and feldspar grains found within accretionary lapilli accreted grain clusters and spherule masses demonstrating that the layer contains hypervelocity impact ejecta zircon geochronologic data from tuffaceous horizons bracketing the layer reveal that it formed between ca 1878 ma and 1836 ma the sudbury impact event which occurred 650 875 km to the east at 1850 1 ma is therefore the likely ejecta source making these the oldest ejecta linked to a specific impact shock features particularly planar deformation features are remarkably well preserved in localized zones within the ejecta whereas in other zones mineral replacement primarily carbonate has significantly altered or destroyed ejecta features

early history of the midcontinent rift inferred from geochemistry and sedimentology of the mesoproterozoic osler group northwestern ontario the mesoproterozoic 1108 1105 ma osler group a3k m thick succession of basaltic flows and sedimentary units on the north shore of lake superior is among the oldest expressions of the midcontinent rift basal sediments of the simpson island formation new name deposited by braided fluvial systems record westward transport of debris eroded from local archean and proterozoic rock units strata deposited by this fluvial system are intercalated with and overlain by ocean island basalt oib like basalts which become increasingly contaminated up section end 1100ma 0 3 to 5 3 the light rare earth element lree enriched la smn 1 5 3 9 and heavy ree hree fractionated gd ybn 1 5 3 7 subaerial flows are divisible into two units that correlate with other sections of the osler group to the east but simple correlations with more distant sequences are difficult the volcanic rock dominated portion of the succession is overlain by a thin 25 m thick conglomerate sandstone assemblage representing southeast progradation of an alluvial fan in a semi arid climatic setting clast lithologies and geochemistry indicate no extra rift detritus was delivered from the hinterland of the fan various lines of evidence in both volcanic and sedimentary rocks support a scenario where early pre 1108 ma subsidence along a north south axis from the western arm of the rift to the nipigon embayment was replaced by subsidence along the east west rift axis between 1108 and 1105 ma resume le groupe d osler mesoproterozoique 1108 1105 ma une succession de coulees basaltiques et d unites sedimentaires d une epaisseur de 3 km sur la rive nord du lac superieur est l une des plus anciennes expressions du rift mi continental les sediments a la base de la formation simpson island nouveau nom deposes par un systeme fluvial anastomose enregistrent le transport vers l ouest de debris erodes des unites rocheuses locales archeennes et proterozoiques des basaltes de points chauds recouvrent et sont intercales avec les strates deposees par ce systeme fluvial ces basaltes sont de plus en plus contamines en remontant la section end 1100ma 0 3 to 5 3 les ecoule ments sub aeriens de terres rares legeres enrichies la smn 1 5 3 9 et de terres rares lourdes enrichies fractionnees gd ybn 1 5 3 7 peuvent etre divises en deux unites qui correspondent a d autres sections du groupe d osler vers lst mais de simples correlations avec des sequences plus eloignees sont difficiles la portion de la succession dominee par des roches volcaniques est recouverte d un mince 25 m assemblage conglomerat gres qui represente la prograda tion vers le sud est d un delta alluvionnaire dans un environnement climatique semi aride la lithologie des clastes et la geochimie indiquent qu aucun detritus hors du rift ne provient de l arriere pays du delta diverses preuves a la fois dans les roches sedimentaires et les roches volcaniques soutiennent un scenario selon lequel une subsidence precoce avant 1108 ma le long d un axe nord sud a partir du bras ouest du rift vers la baie nipigon a ete remplacee par de la subsidence le long de l axe est ouest du rift entre 1108 et 1105 ma

the sudbury huronian heat flow anomaly ontario canada abstract new measurements of the surface heat flux and radiogenic heat production in deep boreholes at 8 different sites are added to 10 older data to determine the heat flow field around the sudbury basin ontario canada this structure straddles the boundary between the archean superior province to the north and the paleoproterozoic southern province to the south which terminates against the grenville front the structure that includes the sudbury igneous complex sic was created by a meteorite impact ca 1 85 ga the mean value of the heat flux 50 mw m 2 is higher than that for the superior province 40 mw m 2 heat flow values are hardly perturbed by the presence of the sic and require a regional enhancement of heat production in the upper crust with respect to the average superior due mostly to the enriched huronian metasediments of the southern province the average radiogenic heat production of sic lithologies 1 2 w m 3 is higher than that of the local archean basement indicating that the impact melt sheet was partly derived from huronian sediments local variations in heat flux can be related to heat production differences between the abitibi upper crust and the huronian metasediments as well as thrusting and tectonic thickening in the southern province the higher than average values of heat flux and crustal heat production in the southern province imply elevated crustal temperatures and a weak rheology in the lower crust at the time of the meteorite impact and of the contemporaneous penokean orogeny large variations of crustal thermal structure at the edge of the superior province may have led to along strike differences in the style and extent of thrusting during the grenville orogeny

speculations on the origin of the north american midcontinent rift cannon w f and hinze w j 1992 speculations on the origin of the north american midcontinent rift in p a ziegler editor geodynamics of rifting volume ii case history studies on rifts north and south america and africa tectonophysics 213 49 55 the midcontinent rift is an example of lithospheric extension and flood basalt volcanism induced when a new mantle plume arrived near the base of the lithosphere very large volumes of basaltic magma were generated and partly erupted before substantial lithospheric extension began volcanism continued along with extension and deep rift subsidence for the ensuing 15 m y much of the basaltic magma including some of the earliest flows was formed by partial melting of isotopically primitive asthenosphere contained in the plume head the intense but relatively short duration of rifting and magmatism is a result of the dissipation of thermal and mechanical energy in the plume head as the plume head spread beneath the lithosphere it stretched the overlying lithosphere radially away from the lake superior region the triple junction of the rift system and partially melted to form the great volume of basalt and related intrusive rocks of the region the plume arrived beneath a continent that was under compression as a result of the ongoing grenville orogeny that affected a large region east of the rift that compression prevented full continental separation and eventually returned the region to compressional tectonics as the energy of the plume head waned

the geochemistry geochronology and paleomagnetism of dikes and sills associated with the mesoproterozoic midcontinent rift near thunder bay ontario canada abstract the midcontinent rift mcr of north america comprises a series of basaltic sheets flows and intrusive rocks emplaced in the lake superior region during the mesoproterozoic the mafic rocks preserved on the northern flank of lake superior represent the older portions of the rift sequence and offer insights into the early development of the rift new geochronological geochemical and paleomagnetic data are presented for the dikes and sills located in and south of thunder bay ontario three sill suites are recognized within the study area an earlier spatially restricted ultramafic unit termed the riverdale sill the predominant logan sills and nipigon sills in the north of the study area in addition three dike sets are recognized the north east trending pigeon river swarm the north west trending cloud river dikes and the mt mollie dike the geochemical data demonstrate that the majority of sills south of thunder bay are of logan affinity and distinct from those of broadly similar age in the nipigon embayment to the north the pigeon river dikes that intrude the sills are geochemically coherent but distinct from the logan sills and could not be feeders to the sills the new age of 1109 2 4 2 ma for the cloud river dike and its r polarity are consistent with published magnetostratigraphy the mt mollie dike age 1109 3 6 3 ma indicates that it is not coeval with the spatially associated crystal lake gabbro as previously thought the complexity of the dike and sill suites on the northern flank of suggests that the early phases of rifting occurred in distinct and changing stress fields prior to the main extensional rifting preserved in younger rocks to the south the geochemistry and geochronology of the intrusions suggest a long lived and complex magmatic history for the midcontinent rift

rift wide correlation of 1 1 ga midcontinent rift system basalts implications for multiple mantle sources during rift development magmatism that accompanied the 1 1 ga midcontinent rift system mrs is attributed to the upwelling and decompression melting of a mantle plume beneath north america five distinctive flood basalt compositions are recognized in the rift related basalt succession along the south shore of western lake superior based on stratigraphically correlated major element trace element and nd isotopic analyses these distinctive compositions can be correlated with equivalent basalt types in comparable stratigraphic positions in other mrs localities around western lake superior four of these compositions are also recognized at mamainse point more than 200 km away in eastern lake superior these regionally correlative basalt compositions provide the basis for determining the sequential contribution of various mantle sources to flood basalt magmatism during rift development extending a model originally developed for eastern lake superior in this refined model the earliest basalts were derived from small degrees of partial melting at great depth of an enriched ocean island type plume mantle source e value of about 0 followed by magmas representing melts from this plume source and interaction with another mantle source most likely continental lithospheric mantle e 0 the

hierarchical geocellular facies modelling of a turbidite reservoir analogue from the eocene of the ainsa basin ne spain geocellular models of outcrop analogues can provide useful insights into modelling strategies for the subsurface reservoirs a model of the outcropping ainsa slope turbidite system was built to test the effects of different scales of heterogeneity on production in deep water systems the modelling began with a structural reconstruction based primarily upon the outcrop data to remove the post depositional structural relief of the reservoir analogue the facies modelling workflow consisted of three nested stages each corresponding to a different scale a the first scale addressed the deterministic reconstruction of surfaces that bound sedimentary bodies b the second scale related to the modelling of the interfingering at the gradational boundaries of the sedimentary bodies c the third scale reproduced the internal heterogeneity within the sandstone dominated sedimentary bodies flow simulation was used as a dynamic test of the differences in recovery efficiency for the different scales at which the geological heterogeneity was modelled

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

radiogenic isotope characteristics of the mesoproterozoic intrusive rocks of the nipigon embayment northwestern ontario the ca 1110 1120 ma diabase sills of the nipigon embayment represent the oldest phase of the midcontinent rift recognized to date the sills can be subdivided into five geochemically distinct suites nipigon mcintyre inspiration shillabeer and jackfish sm nd rb sr and pb pb isotope data for the sills can be used to evaluate the source regions and emplacement histories of these sills the endt values for all the sill suites are consis tently negative 0 5 to 6 6 but show coherent variations both within and between suites the negative endt values can be interpreted as the result of contamination of a plume related mantle source by older crustal material the initial strontium sri values 0 7032 0 7068 for the sills indicate that at least two distinct contaminants are required 1 a source with strongly negative endt and lower sri likely archean metasediment or granite and 2 one with elevated sri likely sedimentary rocks of the proterozoic sibley group the pb data for the nipigon and inspiration sills form distinct linear arrays consistent with variable contamination of a source comparable to that of other igneous suites of the midcontinent rift the radiogenic isotopes preserve a complex contamination history best interpreted as the result of 5 contamination by a variety of archean and proterozoic sources the ultramafic jackfish sill shows the least ev idence of contamination and is interpreted to have been emplaced along a crustal scale fault with little interaction with crustal material in contrast the other sill suites have undergone complex contamination histories requiring variable crustal residence times and assimilation of material both at depth in large magma chambers and during emplacement

the paleoproterozoic marathon large igneous province new evidence for a 2 1 ga long lived mantle plume event along the southern margin of the north american superior province abstract three paleoproterozoic diabase dyke swarms the marathon kapuskasing and fort frances which outcrop around the northern margin of lake superior radiate from a focal region south of the lake u pb dating shows that the marathon and kapuskasing swarms range in age between 2126 and 2101 ma and the fort frances between 2076 and 2067 ma the convergence of the dyke swarms to a common focal area and the lack of apparent polar wander during the time interval 2125 2067 ma suggest that a single periodically active plume was responsible this 60 m y period of magmatism manifest over an area of at least 400 000 km2 is designated as the marathon large igneous province only a single magnetic field reversal has been recognized throughout the 60 m y of plume activity this observation together with u pb geochronology has helped to place dykes within each swarm in a chronological order based on their magnetic polarity for the dyke population as a whole older dykes tend to show more enriched and more fractionated incompatible trace element patterns compared to younger ones a result which suggests that the marathon kapuskasing and fort frances swarms are genetically related and underwent a secular reduction both in the degree of crustal contamination and or depth of mantle melting over the course of plume activity a similar geochemical relationship has also been found for the 2171 2166 ma biscotasing swarm but determining whether it is a common feature of plume development must await further study

further refinement to the timing of mesoproterozoic magmatism lake nipigon region ontario the midcontinent rift in the lake superior region of north america is one of the best preserved examples of an aborted precambrian intercontinental rift one that hosts a diverse suite of rock types in addition to the well studied and voluminous rift fill flood basalts although there is a growing database of high precision age information for the main volcanic packages and the largest mafic intrusions there is relatively little information available on the absolute timing of mafic ultramafic intrusions dyke swarms and alkaline complexes especially in the ontario portion of the rift we report new high precision u pb ages for 29 samples primarily collected in the lake nipigon area ontario from these new age results it is now possible to expand the known distribution of geon 15 magmatism in the region confirm an early stage of midcontinent rift mafic magmatism between 1150 and 1130 ma provide evidence that significant mafic ultramafic magmatism occurred in the lake nipigon region slightly earlier

statistical modelling and validation of correlation in turbidites an example from the tertiary piedmont basin castagnola fm northern italy abstract a reservoir scale analysis which integrated outcrop and geostatistical studies was applied to a turbidite sandbody late oligocene miocene cropping out in the eastern part of the tertiary piedmont basin nw italy the geometry stratigraphic relationships facies distribution and palaeocurrent directions all indicate that the sandbody was deposited in a confined basin principally controlled by synsedimentary tectonic activity this geological model forms a template for subsequent geostatistical simulations that provide equi probable representations of small scale geological heterogeneities the method used to obtain the conditional simulation of facies heresim methodology is based on a truncated gaussian random function the application of such a methodology includes five main steps i database compilation ii geometrical reconstruction of the external surfaces iii statistical analysis of facies distribution iv variogram computation and v lithofacies simulation conditional simulations lead to a better characterization of the depositional environment in terms of facies variation that are consistent with the observed sedimentological framework in addition to their qualitative interest the geostatistical simulations enabled the quantification of geological parameters the testing of different geological hypotheses and to appreciate the uncertainties of the results when less geological information is available to constrain the model the integration of outcrop data and geostatistical analysis allows a quantitative sedimentological model to be constructed which helps to improve the efficiency of outcrop observation as a predictive tool for estimating facies heterogeneity in subsurface reservoirs

whiteschists and orthoamphibole cordierite rocks and the p t t path of the modum complex south norway abstract this paper describes the second known occurrence of whiteschist from norway whiteschists and orthoamphibole cordierite rocks which can both be described in the m f ash system are found in the modum complex together with albitites in contact zones between metagabbros and supracrustals they are formed due to extensive hydrothermal activity bulk rock and mineral chemistry define a bimodal fe mg distribution talc kyanite schists and fe poor orthoamphibole cordierite rocks form a leucocratic group and fe rich orthoamphibole cordierite rocks a melanocratic group the break down of an early orthoamphibole cordierite paragenesis to a later talc kyanite paragenesis indicates a cooling path at isobaric conditions or under increasing pressure the temperature pressure regime is of the order of 600 750 c and 6 8 kb reaction textures with talc albite kyanite forming pseudomorphs after gedrite indicate excess albite these nonisochemical reactions indicate the presence of an active na bearing fluid at deep levels in the crust

kornerupine parageneses in whiteschists and other magnesian rocks is kornerupine talc a high pressure assemblage equivalent to tourmaline orthoamphibole kornerupine fe mg mg fe al 9 si al b 5 o oh f 22 has been reported with talc in rocks from six localities worldwide but only at chilapila hill in the lufilian arc zambia do textural relationships imply that kornerupine krn equilibrated with talc tlc during a prograde metamorphic event at t 640 c p 13 kbar a prograde krn tlc assemblage has also been reported from mautia hill tanzania p 13 kbar in order to estimate possible constraints on the stability range for the kornerupine talc paragenesis in nature we constructed a p t diagram in the model system mgo al2o3 sio2 h2o mash for seven phases quartz qtz b free kornerupine sensu stricto anthophyllite ath chlorite chl cordierite crd kyanite ky and talc the minimum pressure for krn tlc ky stability in mash is close to that for ky tlc stability i e 6 8 kbar at t 780 c however in the natural system b2o3 and na2o are major constituents in krn and orthoamphibole oam respectively and dravitic tourmaline tur is widespread the critical assemblage alternative to krn tlc in nature is tur oam the upper pressure limit of tur ath is determined by the upper pressure for anthophyllite 7 7 10 5 kbar at 682 794 c in the mgo sio2 h2o system chernosky et al 1985 am mineral 70 223 236 and is undoubtedly higher in the presence of na2o cao and al2o3 at three of the six localities talc is a retrograde phase nonetheless it possibly equilibrated with kornerupine on the retrograde path or during a later metamorphic event at p t conditions appropriate for ky tlc at the sixth locality mulvoj southwestern pamir mountains tajikistan krn is found in the same thin section as talc and kyanite and all three minerals formed during a prograde metamorphic event at t 650 c p near 7 kbar however krn is restricted to a lens 4 to 6 mm thick of phlogopite anthophyllite tur and it does not touch either talc or kyanite a reaction relating the mulvoj and chilapila hill krn tlc ky qtz tur parageneses is calculated from compositions in the mulvoj rock to be 0 40tur 2 55ath 1 33h2o 0 27f krn 2 16tlc 0 36b2o3 0 02rutile 0 19na2o 0 17cao given the difference in metamorphic pressures estimated for mulvoj and chilapila hill krn tlc is inferred to be favored by increasing pressure as well as by low na2o and cao contents some feo f fe2o3 and beo are present in measurable amounts in at least one of the phases in the mulvoj and chilapila hill whiteschists e g krn contains 0 24 0 67 wt beo but the effect of these constituents is subordinate to that of na2o cao and b2o3 the krn tlc could be a more important assemblage in b bearing whiteschists than has been reported to date particularly at pressures where orthoamphibole is no longer stable

p wave teleseismic traveltime tomography of the north american midcontinent the remains of the 1 1 ga midcontinent rift mcr lie in the middle of the tectonically stable portion of north america previous and ongoing studies have imaged strong heterogeneity associated with the mcr in the crust but have not imaged such within the mantle it is unclear whether this is due to the absence of rift related mantle structures or these studies had insufficient resolution to image them to address this issue we measured 46 374 teleseismic p wave delay times from seismograms recorded by the usarray transportable array superior province rifting earthscope experiment and surrounding permanent stations we included these and 54 866 delay times from prior studies in our tomographic inversion we find that high velocity anomalies are widespread in our study area but there are also prominent low velocity anomalies two of these are coincident with high bouguer gravity anomalies associated with the mcr in iowa and the minnesota wisconsin border at 50 to 150 km depth extensive resolution testing shows that these anomalies could be the result of downward vertical smearing of relatively low velocities from rift related material that underplated the crust although we cannot exclude that the subcrustal mantle lithosphere beneath the mcr is anomalously enriched hydrated or warm other anomalies occur at syntaxes of the penokean orogen one with the superior province and marshfield terrane in southern minnesota and another with the yavapai and mazatzal terranes both at 100 to 250 km depth in the midmantle we image two linear high velocity anomalies interpreted as subducted fragments of the farallon and kula plates