serpentinization of oceanic peridotites 2 kinetics and processes of san carlos olivine hydrothermal alteration 1 the kinetics of the reaction mg fe olivine h 2 o serpentine magnetite brucite h 2 were investigated at 500 bars in the 250 350 c range using natural olivine san carlos fo 91 with grain sizes between 1 and 150 mm and for run durations up to 514 d the amount of magnetite produced which directly relates to reaction progress was accurately monitored using up to 24 time resolved magnetic measurements per experiment eighty percent of serpentinization was achieved after 60 d for olivine grain sizes of 5 15 mm and after 500 d for grain sizes of 50 63 mm serpentinization kinetics were found to be inversely proportional to the geometrical surface area of the starting olivine grains they were one or two orders of magnitude slower than serpentinization kinetics commonly used for modeling serpentinization related processes the nature of the serpentine mineral product depended on the initial olivine grain size igs for igs in the 5 150 mm range lizardite formed and olivine dissolution was the rate limiting process at igs below 5 mm chrysotile crystallized instead of lizardite and the relationship between olivine surface area and reaction kinetics no longer held we infer that for such small olivine grain sizes dissolution is no longer the rate limiting process serpentinization in our experiments was associated with the creation of new reactive surface area according to two cooperative processes etch pits formation associated with dissolution and grain fracturing for igs above 20 mm interestingly fractures and etch pits with similar geometry and sizes were also observed for residual olivine with a typical grain size of 50 mm in serpentinized peridotite samples from the southwest indian ridge this suggests that the processes governing olivine serpentinization kinetics in our experiments are similar to those prevailing in natural systems we therefore suggest that the new kinetic data set that we present here which encompasses a range of olivine grain sizes and reaction temperatures is relevant to the serpentinization of olivine in the oceanic crust insofar as water is available

experimental study of the effects of solute transport on reaction paths during incipient serpentinization abstract this paper presents the results of 4 reactive percolation experiments set up for investigating the impact of flow rate on serpentinization reaction paths for conditions relevant of the oceanic peridotite sub seafloor during the initial stages of its hydrothermal alteration the experiments consisted in injecting artificial seawater into porous compressed olivine powder cores at constant flow rates q 0 24 0 48 1 14 and 5 21 ml h 1 the experiments were conducted at constant temperature 170 c and pressure 25 mpa and lasted 11 to 28 days at the end of the experiments the outlet fluids composition displayed similar compositions buffered by the formation of serpentine amg2 a h 2 9 7 10 asio2 3 9 to 5 2 ph in situ 6 1 these values were achieved in a few to up to 300 h for the high flow rate experiment suggesting that they corresponded to a steady state regime of mass transfer which depended on flow rate differences in the composition of fluid versus time and in the structure of reacted samples during and after the four reactive percolation experiments suggested also various incipient serpentinization reaction paths the low q experiments produced sio2 aq enriched outlet fluids and nodular aggregates were identified covering the reacted olivine surfaces during high q experiments fibrous filaments of proto serpentine were formed on the olivine surfaces and the fluids progressively achieved steady state compositions similar to the other experiments these results together with those of previously published reactive percolation experiments lead us to propose two end member reaction paths for incipient serpentinization of olivine dominated permeable rocks infiltrated by seawater derived hydrothermal fluids 1 a transport controlled reaction path occurring in diffusion dominated zones is characterized by transient brucite precipitation which produces mg trapping and si release in solution followed by serpentine precipitation and 2 a kinetics controlled reaction path occurring in advection dominated zones where transport conditions are favorable to mg leaching and where serpentine precipitates first the occurrence of these two end member reaction paths is determined locally by the composition of the fluid which varies along flow paths thus both reaction paths can coexist in the sample depending on the local pore geometry our study shows that the interplay between fluid transport and reaction kinetics controls the chemical fluxes between the mineral surface and the bulk solution and the incipient serpentinization reaction paths in natural systems the scale and distribution of these reaction domains will depend on the complex structure of the ultramafic basement our results suggest that the precipitation of serpentine and silica rich phases will be favored in fluid focusing zones such as faults and fractures whilst formation of brucite will preferentially occur as part of pervasive background serpentinization

incipient hydration of mantle lithosphere at ridges a reactive percolation experiment a reactive percolation experiment was conducted by injecting seawater into a permeable olivine aggregate at 190 c and 19 mpa to explore the relationships between hydration reactions and hydrodynamic properties during the onset of serpentinization in the ultramafic lithosphere exposed at mid ocean ridges the experiment was stopped after 23 days when the sample became impermeable the initial flow rate was 0 2 ml h and then was decreased down to 0 06 ml h after 8 days permeability decreased continuously throughout the experiment the analyses of fluid chemistry time series and of the mineralogy and structure of the reacted sample showed olivine dissolution and precipitation of proto serpentine brucite and fe oxides these reactions are controlled by coupled hydrodynamic and chemical processes interacting at different time and spatial scales their first characteristic is the production of silica rich outlet fluids in disequilibrium with the observed reacted mineral assemblages these compositions are interpreted as resulting from a suite of coupled dissolution precipitation reactions controlled at the pore scale by surface kinetic processes that rapidly reaches steady state constant fluid composition independent of fluid flux hence the effective rate of serpentinization was controlled to the first order by the transport of reactants during the experiment mass balance calculations show that the rate of olivine conversion was fast 0 2 0 5 wt day yet only 8 wt of the olivine sample reacted because the permeability drop limited fluid circulation porosity varied little during the experiment compared to permeability changes the decrease of permeability was explained by the structure of the newly formed serpentine favouring the clogging of fluid paths the rate at which permeability decreased was the fastest at low flux conditions this suggests that permeability changes were not controlled simply by the kinetics of the serpentinization reactions but mainly reflected the development of low peclet pore scale zones forming micro environments that control the serpentinization reaction paths these results outline the need to take into account the coupling of hydrodynamic and chemical processes when modelling the effects of reactive transport within the hydrating oceanic lithosphere

a review of the superior province of the canadian shield a product of archean accretion abstract the superior province consists of northern and southern high grade gneiss subprovinces and a central region of alternating granite greenstone and metasedimentary belts subprovinces are commonly fault bounded and display contrasting lithological assemblages metamorphic and structural styles geophysical characteristics and ages they are comparable to phanerozoic suspect terranes the middle and late archean rocks of the superior province are of mantle and juvenile crustal origin with little evidence of inheritance of components older than ca 3 1 ga high grade gneiss subprovinces are mainly deeper level equivalents of the supracrustal rich belts but one minnesota river valley is part of an older ca 3 6 ga terrane that was juxtaposed late in the tectonic history granite greenstone terranes are characterized by low grade volcano sedimentary sequences tholeiitic komatiitic submarine lava plain tholeiitic calc alkalic submarine to subaerial central complexes early platform type quartz arenite stromatolitic carbonate late timiskaming type shoshonitic alkalic volcanic fluvial sediment that range in age from ca 3 0 ga to 2 7 ga the volcanics represent oceanic island arc and continental arc volcanism the quartz arenite carbonate sequences deposition on relatively stable early formed ca 3 0 ga crust and the timiskaming type sequences deposition in pull apart basins developed along strike slip faults late archean ca 2 75 2 70 ga greenstone sequences occur throughout the superior province middle archean ca 3 0 2 8 ga sequences are common in northern and central superior province rare or absent in the south volcanism was accompanied by mafic to trondhjemitic plutonism the metasedimentary belts consist of variably metamorphosed volcanogenic turbidites with detrital zircons ranging in age from ca 3 0 ga to 2 7 ga the metasediments were deposited after major volcanism and probably represent accretionary prisms late archean orogenesis accompanied and followed by calc alkalic plutonism youngs southward from about 2 73 2 72 ga to 2 70 2 68 ga it involved large scale north south compression and dextral transpression and displays thin to thick skinned transitions the contemporaneity of events along the lengths of the belts and their southward younging coupled with the evidence of major compression are consistent with subduction driven oblique accretion of oceanic and continental volcanic arcs accretionary sedimentary wedges older microcontinental fragments etc in a convergent margin setting analogous to parts of the pacific rim differences eg abundance of komatiites and tonalitic plutonic suites are attributable to a hotter archean mantle

review of archean supracrustal assemblages of the southern abitibi greenstone belt in ontario canada products of microplate interaction within a large scale plate tectonic setting abstract previously formulated plate convergent models account for many aspects of the large scale regularity and parallelism between different subprovinces of the archean superior province such models do not however appear to adequately explain the within subprovince evolution of 2 75 2 68 ga supracrustal assemblages of the late archean southern abitibi greenstone belt principal supracrustal assemblage classes include l assemblages dominated by tholeiitic metabasalt and metakomatiite with varying amounts of tholeiitic intermediate to felsic metavolcanic rocks these assemblages probably formed in extensional settings the ratio of basalt to komatiite and the ratio of basalt komatiite to intermediate felsic metavolcanic rocks may be a function of mantle temperature and crustal thickness at the site of extension respectively 2 assemblages dominated by intermediate to felsic fragmental and or effusive rocks are generally of calcalkalic affinity and likely formed in island arc settings 3 assemblages containing a substantial component of iron formation may represent older supracrustal assemblages that form structural and or stratigraphic basement to some of the younger supracrustal assemblages 4 assemblages consisting almost wholly of turbidite facies metasedimentary rocks appear to postdate volcanic activity related to the previous assemblages deposition of these sediments broadly coincides with the onset of regional deformation these assemblages may represent distal deposits related to an emerging collisional orogen 5 assemblages consisting of alluvial fluvial metasedimentary rocks with or without spatially associated alkalic metavolcanic rocks are associated with crustal scale shear zones and are the youngest assemblages within the greenstone belt alluvial fluvial assemblages likely represent the final emergence of the consolidating orogen geochronological data and assemblage distribution suggest that the supracrustal assemblages of the southern abitibi greenstone belt may represent the amalgamation of products of diverse and intricate microplate tectonic settings repeated in time and space prior to the impingement of the large scale plate tectonic regime that dictated the final large scale configuration of the archean superior province

sequence stratigraphy and plate tectonic significance of the transvaal succession of southern africa and its equivalent in western australia the transvaal succession in the northeastern part of the kaapvaal province of southern africa is the erosional remnant of four 2 7 to 2 1 ga unconformity bounded stratigraphic units or sequences each of which is 102 to 103 m thick and spans 107 to 108 years three of these phanerozoic like cratonic sequences occur in the western part of the kaapvaal province and in the pilbara province of western australia thus the two provinces once were part of the same continent vaalbara the stratigraphically lowest sequence historically assigned to the transvaal succession is part of the ventersdorp supergroup in kaapvaal and the upper part of the fortesque group in pilbara it consists predominantly of arkosic sandstone and basaltic andesite it probably is 2687 2 ma the second sequence contains the quartz arenites dolomites and banded iron formations of the transvaal and griqualand west successions in the kaapvaal and the hamersley group in the pilbara the span of ages 2684 6 to 2432 31 ma lithologies and geographic extent of this sequence imply that the limpopo orogeny which welded the zimbabwe province to vaalbara is 2 47 ga not 2 67 0 05 ga the third sequence the pretoria and postmasburg groups in the kaapvaal and the lower part of the wyloo group in the pilbara probably is the clastic wedge generated by the limpopo orogeny the fourth sequence dominated by the felsites of the rooiberg group is restricted to northeastern kaapvaal sequence stratigraphy lithostratigraphy and lithofacies indicate that the pilbara rifted from the southern edge of western kaapvaal the penge iron formation in northeastern kaapvaal the asbesheuwels iron formation in southwestern kaapvaal and the brockman iron formation in the pilbara are the same formation in which cyclothemic units 0 6 to 15 0 m thick extended 1200 km

in situ carbonation of peridotite for co2 storage the rate of natural carbonation of tectonically exposed mantle peridotite during weathering and low temperature alteration can be enhanced to develop a significant sink for atmospheric co2 natural carbonation of peridotite in the samail ophiolite an uplifted slice of oceanic crust and upper mantle in the sultanate of oman is surprisingly rapid carbonate veins in mantle peridotite in oman have an average 14c age of 26 000 years and are not 30 95 million years old as previously believed these data and reconnaissance mapping show that 104 to 105 tons per year of atmospheric co2 are converted to solid carbonate minerals via peridotite weathering in oman peridotite carbonation can be accelerated via drilling hydraulic fracture input of purified co2 at elevated pressure and in particular increased temperature at depth after an initial heating step co2 pumped at 25 or 30 c can be heated by exothermic carbonation reactions that sustain high temperature and rapid reaction rates at depth with little expenditure of energy in situ carbonation of peridotite could consume 1 billion tons of co2 per year in oman alone affording a low cost safe and permanent method to capture and store atmospheric co2

archaean plate tectonics revisited 1 heat flow spreading rate and the age of subducting oceanic lithosphere and their effects on the origin and evolution of continents a simple model which relates the rate of seafloor creation and the age of the oceanic lithosphere at subduction to the rate of continental accretion can successfully explain the apparent differences between archaean and phanerozoic terrains in terms of plate tectonics the model has been derived using the following parameters 1 the spreading rate at mid ocean ridges 2 the age of the oceanic lithosphere at the time of subduction 3 the area age distribution of the seafloor 4 the continental surface area as a fraction of the total surface area of the earth and 5 the erosion rate of continents as a function of continental surface area and the total number of continental masses observations in phanerozoic terranes suggest that there are profound differences in the nature and volume of subduction zone igneous activity depending upon the age of the oceanic lithosphere being subducted and the nature of the overriding plate that is either continental or oceanic the subduction of young oceanic lithosphere less than 50 m y old which is thermally buoyant appears to result in a reduced volume of igneous activity most of the igneous activity caused by subduction of young oceanic lithosphere is either siliceous plutonism or bimodal tholeiitic rhyolitic volcanism when very young lithosphere is being subducted 50 m y old appears to result in greater volumes of igneous activity including the eruption of andesitic magmas thus andesites could only begin to be abundant in the rock record when older oceanic lithosphere began to be subducted our model predicts that as the earth aged and as heat flow from the interior of the earth diminished the proportion of old oceanic lithosphere being subducted increased fundamentally changing the nature of subduction zone igneous activity and the rate of continental accretion if the subduction of old oceanic lithosphere results in an 8 10 times greater volume of subduction zone magmatism our model predicts or explains all of the following observed features of earth history 1 archaean terranes appear to record two periods of rapid continental accretion between 3 8 and 3 5 b y ago and between 3 1 and 2 6 b y ago 2 there are very few differences and many marked similarities between rocks from archaean terranes and equivalent rocks from phanerozoic terranes 3 the total continental area appears to have remained essentially constant for the past 2 b y 4 archaean andesites are comparatively rare and the relative abundances of mafic and siliceous rocks appear to change during the archaean and the proterozoic with siliceous volcanics becoming proportionately more abundant in the geologic record with time 5 plutonic tonalites and trondhjemites appear to have been relatively much more abundant during the archaean plate tectonics is thus shown to have evolved over time due to a gradually decreasing rate of creation of oceanic lithosphere meaning that archaean tectonics and phanerozoic tectonics are but two points on an evolutionary continuum

overview of tectonic settings related to the rifting and opening of mesozoic ocean basins in the eastern tethys oman himalayas and eastern mediterranean regions

an olivine fabric database an overview of upper mantle fabrics and seismic anisotropy we present a unique database of 110 olivine petrofabrics and their calculated seismic properties the samples come from a variety of the upper mantle geodynamic environments ophiolites subduction zones and kimberlites with a wide range of micro structures a phenomenological relationship is established between p and s wave seismic anisotropy and the degree of crystal alignment fabric strength seismic anisotropy increases rapidly at low fabric strength before reaching a near saturation level of 15 to 20 for p waves and 10 to 15 for s waves despite a large variation in the symmetry of fabric patterns the average seismic properties of the different fabric micro structural and geodynamic settings have similar anisotropies in both magnitude and symmetry hence it would seem possible to determine some measure of fabric strength from seismic anisotropy if the dimensions of the anisotropic region are known but not geodynamic environment or details of the petrofabric pattern a simple pattern of seismic anisotropy characterises the average sample of the database which has the following features the polarisation plane of the fastest s wave is parallel or sub parallel to the foliation plane the maximum shear wave splitting is parallel to the y structural direction in foliation plane and normal to the lineation the maximum of the p wave velocity is parallel to the high concentration of 100 axes which is sub parallel to the lineation the 100 orientation distribution has the greatest influence on the p wave seismic anisotropy the 100 and 001 orientation distributions have the greatest influence on the symmetry of s wave anisotropy although the magnitude of anisotropy is influenced by the distribution of all three principal axes although the database only contains olivine petrofabrics this statistical study clearly shows that seismic anisotropy can be used to deduce the orientation of the structural frame in the upper mantle 1998 elsevier science b v all rights reserved

effect of water and stress on the lattice preferred orientation of olivine the influence of water and stress on the lattice preferred orientation lpo of olivine aggregates was investigated through large strain shear deformation experiments at high pressures and temperatures p 0 5 2 1 gpa t 1470 1570 k under both waterpoor and water rich conditions the specimens are hot pressed synthetic olivine aggregates or single crystals of olivine water was supplied to the sample by decomposition of a mixture of talc and brucite deformation experiments were conducted up to shear strain 6 using the griggs apparatus where water fugacity was up to 13 gpa at the pressure of 2 gpa the water content in olivine saturated with water increases with increasing pressure and the solubility of water in olivine at p 0 5 2 gpa was 400 1200 ppm h si several new types of lpo in olivine are found depending on water content and stress samples deformed in waterpoor conditions show a conventional lpo of olivine where the olivine 100 axis is subparallel to the shear direction the 010 plane subparallel to the shear plane type a however we identified three new types type b c and e of lpo of olivine depending on the water content and stress the type b lpo of olivine which was found at relatively high stress and or under moderate to high water content conditions is characterized by the olivine 001 axis subparallel to the shear direction the 010 plane subparallel to the shear plane the type c lpo which was found at low stress and under water rich conditions is characterized by the olivine 001 axis subparallel to the shear direction the 100 plane subparallel to the shear plane the type e lpo which was found under low stress and moderate water content is characterized by the olivine 100 axis subparallel to the shear direction the 001 plane subparallel to the shear plane observations by transmission electron microscopy tem and scanning electron microscopy sem show that the dislocations in water poor samples type a are curved and both b 100 and b 001 dislocations have a similar population numerous subgrains are seen in water poor samples in backscattered electron images in contrast water rich samples both type b and type c contain mostly b 001 dislocations and dislocations are straight and sub grain boundaries are rare compared to those in water poor samples these observations suggest that 1 dominant slip systems in olivine change with water fugacity and stress and 2 grain boundary migration is enhanced in the presence of water seismic anisotropy corresponding to the fabrics under water rich condition is significantly different from that under water poor condition consequently the relationship between seismic anisotropy and flow geometry in water rich regions is expected to be

archean magmatism and deformation were not products of plate tectonics abstract the granite and greenstone terrains that dominate upper crust formed from about 3 6 to about 2 6 ga and record magmatic and tectonic processes very different from those of a younger time they indicate heat loss by the archean earth primarily by voluminous magmatism from a mantle much hotter than that of the present plate tectonic processes were not then operating the distinctive array of petrologic structural and stratigraphic features that characterize phanerozoic convergent plate systems ophiolites magmatic arcs accretionary wedges fore arc basins etc have no viable analogues in archean terrains purported archean plate tectonic indicators consist merely of rock types that even superficially resemble actual phanerozoic indicators only when considered in isolation from their association and structure archean ultramafic and mafic volcanic rocks neither resemble ophiolitic rocks in petrology nor occur in ophiolite type successions they often depositionally overlie felsic basement rocks and often overlie and are intercalated with sedimentary and felsic volcanic rocks and they require a mantle about 200 c hotter than now archean graywackes are coherent strata derived from nearby volcanic rocks late in the histories of their regions and they lack the setting and disruption that characterize modern accretionary wedges the lithologic structural and stratigraphic assemblages that typify proterozoic and phanerozoic rifted and reassembled margins also lack archean analogues and no evidence has been found for archean rifting rotation and reassembly of continental plates conversely characteristic archean assemblages lack modern equivalents in any tectonic setting ultramafic lavas erupted at liquidus temperatures are voluminous granite and greenstone terrains have no modern analogues greenstone belts are typically anastomosing networks of upright synforms formed by crowding aside by and sinking between large rising diapiric elliptical composite batholiths the batholiths include both the products of new crustal melts and variably remobilized mid crustal gneisses the greenstone belts are defined by late deformation of regionally semiconcordant volcanic and sedimentary successions and are not relics of successively formed volcanic chains little deformation generally preceded the diapirism and metamorphism was primarily of contact type the regionally uniform areal density and accordant crustal level of the diapiric batholiths their contacts primarily against the oldest strata of the synforms their general age 10 20 million years younger than most of the flanking stratiform rocks and considerations of high archean radiogenic heat productivity all fit the explanation that the batholiths were mobilized by partial melting of hydrous lower crust by radiogenic heating diapirism was accompanied by modest regional orthogonal shortening and extension of the hot upper crust producing the orientations of the batholiths rise of the batholiths greatly increased the petrologic fractionation of the crust and the concentration of radionuclides high in it resulting in cooling of the deeper crust and subjacent mantle and thus cratonization the upper crust containing the granite and greenstone aggregates was decoupled from the gneissic middle crust which underwent flattening and extension subparallel to the elongation of the shallow batholiths this deep deformation may have been driven by flow of dense restites toward delamination loci from which they sank into the mantle the early earth was probably wholly molten the surface of the earth like that of the moon must have been wholly recycled by impacts before 3 9 ga and heavily modified by them until 3 8 ga zircons as old as 4 2 ga have been found as clastic grains in much younger archean quartzites and polycyclic migmatites last partly melted and reconstituted under hydrous conditions only after 3 6 ga contain relict zircons as old as 4 0 ga the lithologies of the early earth protoliths in which these zircons formed have not been established but impact melts and breccias must be represented and magma ocean fractionates may be the nature of the transition in tectonic style into the granite and greenstone mode is unknown plate tectonic rifting and convergence were operating by about 2 0 ga and were in an essentially modern mode by about 0 8 ga the nature of the transition from the granite and greenstone mode at about 2 6 ga to plate mode by about 2 0 ga has yet to be defined the change may have been facilitated by the increasing content of water and carbon dioxide in the mantle as dense but hydrated delaminated archean crust sank into it

unscrambling the stratigraphy of an archean greenstone belt a upb geochronological study of the favourable lake belt northwestern ontario canada abstract new zircon and baddeleyite u pb ages show that the major units of the archean favourable lake greenstone belt in the northern superior province were formed by episodic magmatism spanning more than 250 ma and demonstrate that the original stratigraphy is disrupted by thrusts that juxtaposed older supracrustal rocks on top of younger ones the oldest rocks of the area are a 2950 ma gneissic tonalite and a 3000 2960 ma granodiorite clast from a ca 2725 ma conglomerate five distinct volcanic and sedimentary groups formed during presumably short lived episodes at 2925 ma i 2870 ma ii 2858 ma iii 2734 ma iv and 2725 ma v the youngest group contains the thickest sedimentary unit a turbiditic and alluvial fluvial sequence compression caused thrusting that placed groups i and v on top of iv iii on v and ii on iii the thrust complex was subsequently isoclinally folded compression was accompanied by major plutonism that emplaced the bulk of the bounding batholiths between 2732 and 2711 ma ago the late tectonic mo mineralized setting net lake stock in the centre of the belt has an age of about 2708 ma and was overprinted by younger hydrothermal events that produced monazite 2706 ma titanite ca 2695 2690 ma and rutile the youngest rutile at 2657 ma similar late hydrothermal pulses are recorded by secondary titanite elsewhere in the belt and within the batholiths the protracted magmatic evolution of the belt is typical of that observed in a number of greenstone belts of the northern superior province but is uncommon farther to the south in contrast the structural complications and put of sequence stratigraphy appear to be a quite common tectonic characteristic of greenstone belts of the whole superior province

experimental evidence for chemo mechanical coupling during carbon mineralization in ultramafic rocks abstract storing carbon dioxide in the subsurface as carbonate minerals has the benefit of long term stability and immobility ultramafic rock formations have been suggested as a potential reservoir for this type of storage due to the availability of cations to react with dissolved carbon dioxide and the fast reaction rates associated with minerals common in ultramafic formations however the rapid reactions have the potential to couple with the mechanical and hydraulic behavior of the rocks and little is known about the extent and mechanisms of this coupling in this study we argue that the dissolution of primary minerals and the precipitation of secondary minerals along pre existing fractures in samples lead to reductions in both the apparent young s modulus and shear strength of aggregates accompanied by reduction in permeability hydrostatic and triaxial deformation experiments were run on dunite samples saturated with de ionized water and carbon dioxide rich solutions while stress strain permeability and pore fluid chemistry were monitored sample microstructures were examined after reaction and deformation using scanning electron microscopy sem the results show that channelized dissolution and carbonate mineral precipitation in the samples saturated with carbon dioxide rich solutions modify the structure of grain boundaries leading to the observed reductions in stiffness strength and permeability a geochemical model was run to help interpret fluid chemical data and we find that the apparent reaction rates in our experiments are faster than rates calculated from powder reactors suggesting mechanically enhanced reaction rates in conclusion we find that chemo mechanical coupling during carbon mineralization in dunites leads to substantial modification of mechanical and hydraulic behavior that needs to be accounted for in future modeling efforts of in situ carbon mineralization projects

surface specific measurements of olivine dissolution by phase shift interferometry natural olivine dissolution and replacement often occurs preferentially along specific crystallographic planes thus olivine reactivity at specific surfaces was examined in situ using phase shift interferometry which has a detection limit 10 5 nm s by dissolving two smoothed olivine crystal faces and a third sample corresponding to a surface that was generated by preferential dissolution along structural defects the experiments were conducted at 22 c and ambient pressure in 0 1 m nacl solutions that were acidified to phs between 1 and 4 using 0 1 m hcl these experiments show that olivine dissolution can vary from one surface to another as well as in different areas of the same surface that have similar characteristics the fastest vertical retreat occurred at the surfaces related to defects however only vertical advancement was observed at ph 1 on this surface consistent with the observation of isolated islands on the surface during atomic force microscopy investigations after the experiment raman analysis of the precipitated phase showed that it was not one of the thermodynamically stable phases expected from phreeqc modeling however the correlation between the siloxane ring peak of amorphous silica with a similar peak in the precipitate spectrum in conjunction with previous experimental and natural observations indicates that the precipitate was a si enriched amorphous phase therefore precipitation can facilitate the further dissolution of olivine on this surface as long as it does not completely armor the surface precipitate formation on surfaces associated with outcropping defects supports the natural observations of preferential dissolution and serpentinization along these defects implying that the fast dissolution of these surfaces will play a critical role during olivine replacement in addition comparison with flow through experiments indicates that outflow fluid chemistry may provide an incomplete picture of processes occurring during olivine dissolution

effect of surface orientation on dissolution rates and topography of caf2 this paper reports how during dissolution differences in surface chemistry affect the evolution of topography of caf2 pellets with a microstructure similar to uo2 spent nuclear fuel 3d confocal pr

geochronological constraints on the timing of magmatism deformation and gold mineralization in the red lake greenstone belt northwestern ontario the paper presents u pb ages on zircon baddeleyite titanite rutile and monazite from volcanic and plutonic rocks of the red lake greenstone belt in the northern superior province the purpose of the study was to refine a previously outlined time frame for the volcanic evolution of the belt define the time of major plutonism and deformation and constrain the age of formation of gold deposits volcanism spanned at least 270 ma between 3000 and 2730 ma new ages of 2989 3 and 2894 2 ma for units of a lower volcanic sequence and and 2744 1 ma for units of an upper volcanic sequence corroborate and refine the previously established relationships local gabbroic and felsic intrusions cutting through the lower sequence yield ages of 2870 15 and respectively volcanism was succeeded by major plutonism deformation alteration and metamorphism between about 2730 and 2700 ma these processes were interrelated and progressed as a relatively continuous sequence of events accentuated by major activity d

olivine dissolution and carbonation under conditions relevant for in situ carbon storage abstract in order to evaluate the chemistry and kinetics of mineral carbonation reactions under conditions relevant to subsurface injection and storage of co 2 olivine alteration was studied at 60 c and 100 bar co 2 pressure including olivine dissolution and the formation of carbonate minerals batch experiments were performed with olivine fo92 water co 2 and nacl inside gold cells contained within rocking autoclaves two reproducible experiments yielded an initial 1 h dissolution rate of 9 50 0 10 10 11 and a long term 10 70 days rate of 1 69 0 23 10 12 mol cm 2 s 1 the long term rate is consistent with previously published rate laws at 4 5 2 aq and sio 2 aq at 60 c a si rich surface layer forms on olivine grains within 2 days of reaction and appears to slow dissolution by passivating the surface the olivine dissolution rate decreases by 2 orders of magnitude over 4 days as the system approaches amorphous silica saturation but remains constant thereafter based on a linear increase in mg concentrations secondary phases consist of amorphous silica and magnesite with up to 7 mol olivine converted to mg carbonate over 94 days of reaction magnesite precipitation rates could not be precisely quantified due to experimental limitations however our minimum estimate of 1 40 10 13 mol cm 2 s 1 suggests that the precipitation rate is several orders of magnitude greater than predicted by previous studies finally the presence of 0 5 m nacl resulted in a decrease in olivine dissolution rate at reaction times of less than 4 days but a significant enhancement of the reaction rate at reaction times greater than 4 days relative to electrolyte free experiments our results suggest that geochemical models developed to predict the behavior of subsurface co 2 storage systems in mafic and ultramafic rocks should incorporate the effects of dissolved species including sio 2 and nacl

deformation and structural evolution of mantle peridotites during exhumation on transform faults a forced transition from ductile to brittle regime abstract the exhumation of peridotite rocks in oceanic transform zones passes by the rheological transition between the ductile and brittle deformation until the complete emplacement in the oceanic lithosphere the sao pedro and sao paulo archipelago spspa in the equatorial atlantic records the deformational products of ductile brittle and the rocks fluid interaction generating specific structures in each domain the deformational stages are related to the transpressional and transtensional geodynamics of sao paulo transform fault firstly during transpression exhumation occurs associated with the ductile domain causing intense mylonitization in temperatures between 700 and 800 c defined by olivine and orthopyroxene recrystallization the interaction with fluids initially originated from the mantle generates amphibole and oxide rich layers marking the passage to a semi brittle deformation the continuation of peridotite exhumation associated with an nw se shortening and transpressional led to a higher availability of hydrothermal fluids as a consequence four serpentinization episodes are recorded which are associated with semi brittle to brittle transition under temperatures between 300 and 400 c finally the complete exhumation and establishment of brittle mechanisms led to carbonatation phase near the surface with temperatures ranging from 300 to 150 c the active nw se tectonic stress generated e w strike slip faults that were filled by carbonates recording the final exhumation stage

dissolution of olivine during natural weathering abstract naturally weathered olivine occurring as phenocrysts in hawai ian volcanic rocks from several volcanic centers and regolith outcrop settings and as tectonized olivines from several metadunite bodies in the southern appalachian blue ridge are all similarly corroded by natural weathering conical funnel shaped etch pits occur as individual pits base to base pairs of cone shaped pits or en echelon arrays etch pit shapes and orientations in the smallest etch pit arrays visible in conventional scanning electron microscopy resemble even smaller features previously reported from transmission electron microscope investigations of olivine weathering etch pits occur in samples with chemical and or mineralogical evidence of weathering and or are associated with or proximal or directly connected to fractures or exposed outcrop surface and therefore are formed by weathering and not inherited from pre weathering aqueous alteration e g serpentinization iddingsitization of these parent rocks many etch pits are devoid of weathering products natural weathering of olivine is surface reaction limited similarity of corrosion forms from naturally weathered olivine from multiple igneous and metamorphic parent rock bodies suggests that olivine weathers in the same manner regardless of its specific crystallization recrystallization history eruption weathering exposure ages of the olivine s host rock and the local regolith history

autochthonous development of superior province greenstone belts abstract models for superior province greenstone belt development have changed over the last 30 years from ensimatic generally autochthonous models to suspect allochthonous terrane models based on the plate tectonic paradigm models intermediate between these end members such as autochthonous terrane models have not been prominent within the superior province there is a secular variation from early ca 3 ga platformal assemblages with overlying rift related komatiite tholeiite units representing breakup of ca 3 ga continental fragments to late ca 2 7 ga pull apart basins autochthonous terranes should demonstrate some sort of logical order such as that described above whereas allochthonous terranes will be largely oceanic in character and should be essentially random in their occurrence rather than exhibiting secular order in the face of this situation this paper reviews evidence from throughout the superior province that suggests many but not all greenstone assemblages developed autochthonously or parautochthonously the earliest greenstone assemblages in the superior province are generally quartzite and carbonate bearing platform sequences in the north caribou terrane and the marmion terrane deposited unconformably upon granitoid or greenstone basement the evidence for autochthonous parautochthonous development includes the presence of unconformities between keewatin type greenstone units such as 1 basal unconformities between ca 3 ga granitoid or volcanic basement and slightly younger platformal assemblages 2 between ca 2 9 ga platformal assemblages and younger platformal and andean arc assemblages stratigraphic patterns such as adjacent greenstone belt assemblages representing sharply differing geodynamic settings with some indication of palinspastic order or progression in the northern central and southern superior province are considered suggestive of orderly autochthonous progression from platforms through rifting of continental fragments and late assembly during the kenoran orogeny petrogenetic data indicating involvement of older granitoid crust in genesis of greenstone assemblages of a variety of ages throughout the superior province suggests the presence of older basement implying autochthonous or parautochthonous development of many assemblages younger greenstone assemblages in the abitibi wawa subprovince and the north caribou terrane contain xenocrystic zircons similar in age to stratigraphically underlying greenstone assemblages this pattern has been interpreted to represent autochthonous greenstone development the current above enumerated evidence for autochthonous development of greenstone assemblages is generally indirect few actual unconformities between keewatin type greenstone assemblages have been recognized in the superior province to aid in future recognition of unconformities in keewatin type greenstone assemblages examples of unconformities of varying degrees of subtlety in archean sequences are reviewed archean unconformities ranging from sharp angular discordances in the northern superior province to subtle stratigraphic patterns to weathering related geochemical mobilization along inter formational contacts are described these styles of unconformity in archean sequences suggest previously unrecognized major disconformities and unconformities may well exist between keewatin type assemblages in the superior province generally and the abitibi wawa subprovince specifically the most important disconformity suggested in the abitibi wawa subprovince is between the ca 2726 ma deloro and the ca 2708 ma tisdale assemblages the presence of unconformities and disconformities coupled with the indirect lines of evidence cited above suggest an autochthonous origin for many superior province greenstone belts this autochthonous origin involves either autochthonous or parautochthonous evolution of assemblages at least in part in place that is development of ca 3 ga platform sequences in selected locales followed by in place evolution of a succession of plume oceanic and arc assemblages culminating in late pull apart basin sequences implications of the autochthonous model for greenstone belts of the superior province particularly the abitibi wawa subprovince include the future ability to recognize unconformity bounded sequences potentially improving regional scale correlation

archaean plate tectonics revisited 2 paleo sea level changes continental area oceanic heat loss and the area age distribution of the ocean basins in a previous paper we derived plate tectonic models for continental accretion from the early archaean 3800 m y b p until the present the models are dependent upon the number of continental masses the seafloor creation rate and the continental surface area the models can be tested by examining their predictions for three key geological indicators sea level changes stable isotopic evolution e g continental surface area and oceanic heat loss models of paleo sea level changes produced by the accretion of the continents reproduce the following features of earth history 1 greater continental emergence lower sea level during the archaean than the proterozoic 2 maximum continental emergence about 3000 m y b p and 3 maximum continental submergence high sea level from 30 to 125 m y b p the high sea level stand between 380 525 m y b p is only weakly reproduced probably due to the simplified nature of the model changes in the number of continental masses can result in tectonic erosion or accretion of the continents with resulting changes in sea level the two major transgressions in the phanerozoic although still requiring some increase in the total terrestrial heat loss can be sucessfully explained by a combination of increases in continental surface area and in seafloor creation rate changes in the total heat loss of the ocean basins predicted by our plate tectonic models closely parallel the changes in terrestrial heat production predicted by wasserburg et al 1964 this result is consistent with thermal history models which assume whole mantle convection the history of changes in continental surface area predicted by our best continental accretion models lies within the ranges of estimated continental surface area derived from independent geochemical models of isotope evolution

b type olivine fabric induced by low temperature dissolution creep during serpentinization and deformation in mantle wedge the b type olivine fabric i e the 010 axes subnormal to foliation and the 001 axes subparallel to the lineation has been regarded as an important olivine fabric for interpreting global trench parallel s wave polarization in fore arc regions however strong serpentinization and cold temperature environment in the mantle wedge should inhibit development of the b type olivine fabric that requires high temperature to activate solid state plastic deformation here we report fabrics of olivine and antigorite generated at low temperatures 300 370 c during serpentinization in a fossil mantle wedge of the val malenco area central alps olivine in the serpentine matrix develops a pronounced b type fabric while antigorite in the same matrix displays a strong crystallographic preferred orientation cpo with the 001 planes and the 010 axes subparallel to foliation and lineation respectively the following evidence leads to the conclusion that the b type olivine fabric results from dissolution creep assisted by grain boundary sliding gbs and grain rotation rather than solid state plastic deformation 1 serpentinization took place at low temperatures and a fluid enriched environment ideal for dissolution precipitation creep 2 the voids and zigzag boundaries along the interface between antigorite and olivine suggest a fluid dissolution reaction 3 the primary coarse olivine develops a nearly random fabric indicating the b type fabrics in the fine grained olivine may not be inherited fabrics these results document for the first time the b type olivine cpo formed by dissolution creep at low temperatures during serpentinization and provide a mechanism to reconcile petrofabric observations with geophysical observations of trench parallel fast s wave seismic anisotropy in fore arc mantle wedge regions

co2 geological storage in olivine rich basaltic aquifers new insights from reactive percolation experiments to test the impact of fluid flow on the reactivity of porous ultra mafic rocks reactive percolation experiments were realized during which co2 enriched water was injected at two different injection rates q 0 1 and 1 ml h 1 through sintered analogues of olivine accumulation zones in basaltic flows at temperature and fluid composition conditions t 180 c nahco3 buffered solution favorable for co2 mineralization carbonation all experiments resulted in silicate dissolution carbonate precipitation upstream and proto serpentine formation downstream indicating a decrease in the fluid reactivity along flow paths the measured bulk carbonation rates ranged from 4 to 7 10 8 s 1 these values were significantly lower than previously published values of olivine carbonation rate obtained on powders in closed batch and flow through reactors our study show complex couplings at pore scale between fluid flow localization of reaction zones and chemical reaction kinetics which in turn control hydrodynamic properties carbonation rate and efficiency and fluid reactivity this results in carbonation rates being higher when injection rates are high and permeability ultimately controlling carbonation reactions by limiting fluid input during experiments notable changes in permeability occurred for only minor changes in porosity indicating a control by the geometry of the porous network heterogeneities in the distribution of flow paths favored the localization of precipitated minerals which in turn resulted in the closure of flow paths this mechanism was particularly efficient at low injection rates these results imply that controlling the injection rate could allow enhancing limiting the efficiency of in situ carbonation

u pb zircon ages in supracrustal and plutonic rocks north spirit lake area northwestern ontario the north spirit lake greenstone belt in the sachigo subprovince of the superior province comprises parts of three sequences of volcanic and sedimentary rocks the main youngest is separated from the older sequences by an unconformity to disconformity the belt is bounded by large granitoid batholiths and was metamorphosed under greenschist to locally hornblende cordierite facies u pb zircon dating was performed on volcanic sedimentary and plutonic rocks in order to establish an absolute chronology for the evolution of the area a tuff breccia in the lowermost supracrustal sequence is dated at 3023 2 ma zircons from a tuff in the middle sequence show complex u pb relationships although they do not allow a precise age determination the data suggest that the tuff formed sometime between 2950 and 2800 ma ago zircons from a quartz arenite also in the middle sequence yield a simple data pattern and define an age of suggesting derivation of the sediment from a uniform source of this age a zirco

lithospheric structure in the southern canadian cordillera from a network of seismic refraction lines lithospheric velocity structure and its relationship to regional tectonics and development of the southern canadian cordillera are derived from a synthesis of interpretations from nine in line seismic refraction wide angle reflection profiles and broadside data recorded during the lithoprobe southern cordillera refraction experiment score and other refraction experiments across southern british columbia and one profile in northwestern washington consistency of the score two dimensional models at their intersection positions is achieved through application of a simultaneous inversion of all relevant traveltime data the cross sectional and map presentations demonstrate the strong degree of three dimensional heterogeneity within the crust and upper mantle a first order characteristic is the continuous increase in crustal velocities westward from the foreland belt to the insular belt the variations do not correlate with the morphogeological belts they do correspond with large scale geological and or

serpentine mineral replacements of natural olivine and their seismic implications oceanic lizardite versus subduction related antigorite we report on microstructural data obtained by optical microscopy and transmission electron microscopy concerning the crystallographic relationships of serpentine minerals with their host olivine in two contrasting situations in the first case mesh textured lizardite liz is developed in a standard 60 serpentinized oceanic harzburgite from the oman ophiolite where olivine converts to columnar lizardite the joined columns are perpendicular to the basal plane 001 liz corresponding to the pseudofibres observed optically the plane 001 liz is locally parallel to the narrow boundary ol liz thus column orientations register the interface of serpentinization the ol liz relationships are not strictly topotactic but reflect preferred cracking orientations in olivine parallel to 010 ol in the second case antigorite atg develops in a rare sample of antigorite schist in a kimberlite from moses rock colorado plateau representative of a suprasubduction zone mantle wedge high resolution transmission electron microscopy hrtem images along 010 atg show domains of very regular modulation with a 43 center dot 5 a wavelength m 17 where m is the number of silicate tetrahedra along the wave with few defects indicative of hp ht antigorite and also heavily kinked regions as fingerprints of strong tectonic shear tem imaging and electron diffraction patterns reveal two topotactic relationships between antigorite and olivine 100 atg 010 ol and atg ol the planes in contact are 001 atg 100 ol and 001 atg 010 ol respectively the 010 atg 001 ol and antigorite lamellae are parallel to the forsterite b axis in both cases the topography of olivine serpentine interfaces is controlled by open fluid pathways along microcracks oriented according to the anisotropy of the olivine aggregate in the cases studied the serpentine aggregate exhibits a preferred orientation inherited from that of the peridotite these results have some relevance to the seismic anisotropy of serpentinized mantle anisotropy of propagation of seismic waves as a result of the olivine fabric is maintained and reinforced with the development of lizardite conversely the development of antigorite produces a trench parallel fast s wave polarization and an anisotropy that is lowered at low degrees of serpentinization and then increased with increasing serpentinization

the deleterious effect of secondary phases on olivine carbonation yield insight from time resolved aqueous fluid sampling and fib tem characterization geological storage of co2 in mafic and ultramafic rocks relies on the dissolution of their silicate components followed by the precipitation of carbonates the overall process being commonly referred to as carbonation to gain a better understanding of the rate and yield controlling factors of mineral carbonation three batch experiments were conducted in co2 saturated water at a 90 c b 120 c and c 170 c respectively with citrate ligands added to the 90 c experiment in a ti reactor at pco2 280 bar using san carlos olivine fo88 as a model mineral of ultra mafic environments those physicochemical conditions were purposely chosen so as to promote the dissolution rate of olivine a at 90 c 40 wt of olivine were dissolved within 3 weeks a result which suggests that the passivation barrier evidenced in previous studies carried out in citrate free media had been overcome however while saturation with respect to magnesite was overstepped in this experiment the carbonation yield remained below 1 wt which we attributed to the slow kinetics of magnesite precipitation b at 120 c the concentration of mg and si monitored by aqueous fluid sampling reached an apparent plateau for over 4 weeks at conditions close to saturation with respect to amorphous silica and with fe concentration being below the detection limit a resumption of the dissolution process was subsequently observed while the concentration of fe suddenly increased in solution the concentration plateau was attributed either to the formation of a protective si fe iii layer or to the occurrence of fe iii phases clogging the porosity of a secondary silica layer the resumption of olivine dissolution was ascribed to the increasingly reducing conditions that led to the breakdown of the protective phases this late resumption led to a carbonation yield slightly above 2 wt c at 170 c fe was incorporated into a presumably permeable fe rich phyllosilicate layer so that the dissolution process was likely less affected by such an interfacial layer nevertheless carbonate minerals still formed in low quantity 6 wt while other amorphous phases represented the main sink for mg cations overall this study emphasizes that achieving carbonation reactions in reducing environments and circum neutral aqueous solutions may represent a necessary requirement for making olivine carbonation a viable process in these temperature ranges it also insists on the importance of transitory phases which form both at the fluid silicate interface and from the bulk solution while they may not appear in overall carbonation equations or in thermodynamic databases arguably they can drive the global kinetics of olivine dissolution and its transformation towards magnesite

carbonate mineralization in percolated olivine aggregates linking effects of crystallographic orientation and fluid flow in situ mineralization of co 2 in ultramafic rock hosted aquifers is one of the promising solutions for decreasing co 2 concentrations in the atmosphere naturally altered ultramafic rocks suggest that carbonation processes are controlled by local heterogeneities in the structure of the rock and fluid transport at the water rock interfaces we studied the role of rock crystallographic anisotropy relative to the global fluid flow direction on the mineralization of co 2 by means of electron microscope analyses from the macro to the micrometer scale ebsd fib the sample used for the measurements was a hot pressed olivine core percolated by water enriched in co 2 pco 2 10 mpa at 180 c during the percolation experiment olivine was dissolved and two types of carbonates dolomite and magnesite were precipitated on olivine surfaces the results showed that the dissolution of olivine is controlled by its crystallographic properties as shown by the development of etch pits only on the 010 ol planes and with elongated shapes parallel to the 010 ol axes in contrast the precipitation of carbonates is governed by hydrodynamic properties carbonates are heterogeneously distributed in the percolated rock they are mainly located along the moderate for dolomite and the minor for magnesite flow paths both oriented parallel to the principal fluid flow direction which allow carbonates to be supplied with divalent cations e g ca 2 mg 2 and fe 2 in these flow paths carbonate growth is systematically oriented normal to the flow that facilitates the development of chemical gradients with cationic supersaturation conditions for carbonate precipitation near the walls in natural systems the 010 ol planes are parallel to the moho and the 100 ol planes are vertical our study suggests that flow of co 2 rich fluids will induce precipitation of carbonates localized along and preferentially clogging vertical flow paths while favoring olivine dissolution along horizontal fluid pathways this dual control of structure and fluid flow on carbonation mechanisms could be an important parameter allowing sustainable co 2 storage in peridotites while limiting the risks of leakage toward the surface

sequence stratigraphy of the archaean supracrustal belts of the pilbara block western australia abstract the stratigraphic succession of the 3580 2770 m y old granite greenstone terrain of the pilbara block is re assessed by the first and second order sequence stratigraphic techniques that are the standard for phanerozic terrains with the view to testing the conformity of stratigraphic cause and response a holistic tectonostratigraphic framework is presented that pairs the supracrustal and crustal rock records the resulting sequence scheme is tested against the cause of first order sequence cycles viz global sea level responses to supercontinent breakup and assembly three first order inter regional unconformities divide the stratigraphic succession of the supracrustal belts into four units of first order megasequence status in order of decreasing age these are named the warrawoona gorge creek roebourne and mount negri megasequences a total of 17 second order supersequences are also named although some may represent supersequence sets the megasequences and or their genetic crustal equivalents represent the preserved rock record of four megacycles of forearc arc and or back arc geotectonic evolution associated with the convergent margins of a pilbara continent individual supersequences are the rock record of separate second order basins or basin phases and reflect the different geotectonic components of each megasequence the four megacycles had respective longevities from oldest to youngest of 150 m y 230 m y 160 m y and 180 m y they are identical in their stratigraphic successions and predicted first order sea level cycles to phanerozoic first order tectono eustatic cycles and are interpreted as the same response to global tectonic change the warrawoona and gorge creek megacycles and the roebourne and mount negri megacycles are tectonogenetic pairs of the east pilbara and the west pilbara megacycle sets respectively the east pilbara megacycle set evolved over a period of 380 m y from 3490 ma to 3110 ma whereas the west pilbara megacycle set evolved over a period of 340 m y from 3110 ma to 2770 ma the two megacycle sets are identical in their longevity geotectonic components and predicted sea level cycles to convergent margin wilson and supercontinent cycles and are thereby interpreted individually as the oldest established records of the supercontinent cycle the implication of this interpretation is that a steady state global tectonic regime has been in operation from early in earth s history which has important consequences for theoretical modelling of the earth s early tectonic style and secular changes in its geochemical regime

evolution of the southern abitibi greenstone belt based on u pb geochronology autochthonous volcanic construction followed by plutonism regional deformation and sedimentation abstract new mapping and u pb zircon geochronological results in the southern abitibi greenstone belt sagb support an autochthonous regional stratigraphy comprised of nine supracrustal assemblages rather than the collage of allochthonous terranes proposed in recent publications based on lithological and geochronological criteria these supracrustal assemblages also encompass the swayze shining tree and montcalm greenstone belts indicating that despite separation by large granitic intrusions they are in fact part of one extensive greenstone belt in conjunction with the mapping the geochronological results support coherent upward facing stratigraphic sections with about 20 of the samples containing inherited zircons with ages similar to those found in underlying assemblages the seven oldest assemblages represent semi continuous volcanism from 2750 to 2697 ma the volcanism is compositionally diverse ranging from komatiite and tholeiitic basalt to calc alkaline mafic to felsic lavas intimate intermingling of the different magma clans occurs throughout much of the stratigraphic section regional fault control on the distribution of the volcanic assemblages provides evidence for early dip slip movement associated with volcanic extension dating back to at least 2725 ma the two youngest assemblages are dominantly sedimentary and were unconformably deposited on the volcanic assemblages in close proximity to regional faults the earlier sedimentary assemblage consists of turbidites and minor iron formation deposited from 2696 to 2692 ma and the youngest one of subaerial conglomerates fluvial sandstones and alkalic to shoshonitic volcanic rocks ranging in age from 2687 to 2675 ma the sedimentary assemblages are broadly contemporaneous with the emplacement of syntectonic granitic plutons regional folding and reactivated movement on the regional faults probably related to accretion of the abitibi to the superior province craton autochthonous repetition of different geodynamic environments over the 50 million years of volcanic activity with five dominantly tholeiitic komatiitic assemblages and two dominantly calc alkaline assemblages as well as the extensive intermingling of these different magma clans in a number of the assemblages appears to be unique to the archean it suggests complex large scale and long lived interaction between mantle plumes and subduction zone magmas the nd isotope data indicate a derivation of the diverse volcanic magmas from homogeneously depleted sources with end 2 5 0 5 demonstrating a lack of contamination by ancient enriched components

experimental study of carbonate formation in oceanic peridotite abstract interactions of co2 rich aqueous fluids with mantle peridotite have major implications for geochemical budgets and microbial life in the shallow oceanic lithosphere through the formation of carbonate minerals and reduced carbon species however the underlying mechanisms controlling the transformation of co2 to carbonates in ultramafic hosted hydrothermal systems remain incompletely understood a long term laboratory experiment was conducted at 300 c and 35 mpa to investigate serpentinization and carbonate formation pathways during hydrothermal alteration of peridotite powdered harzburgite was initially reacted with a ca rich aqueous fluid for 14 592 h 608 days and changes in fluid composition were monitored with time once the system reached a steady state a co2 aq rich fluid was injected and allowed to react with the system for 5907 h 246 days fluid speciation and mineral analyses suggest that serpentinization of harzburgite in the co2 poor system led to the precipitation of serpentine brucite magnetite and minor calcite in addition to other minor phases including chlorite and sulfur poor ni sulfides the addition of the co2 aq rich fluid caused dolomite ca rich dolomite and high mg calcite to form at the expense of olivine calcite and brucite while serpentine remained unreactive replacement textures and mineral assemblages mimic those documented in carbonate altered seafloor serpentinites particularly those from the mid atlantic ridge and the iberia margin in contrast to thermodynamic predictions magnesite did not form in the experiment because the dissolution of clinopyroxene in combination with the lack of serpentine reactivity maintained low mg ca ratios in solution clinopyroxene dissolution and unreactive serpentine may similarly maintain low mg ca ratios in submarine serpentinization systems and limit magnesite formation in subseafloor environments results of this study suggest that the formation of ca mg carbonates by mineral carbonation is favorable in subseafloor serpentinization systems and likely represents a significant but poorly quantified carbon sink in hydrothermally altered oceanic lithosphere at slow spreading mid ocean ridges

a serpentinite hosted ecosystem the lost city hydrothermal field the serpentinite hosted lost city hydrothermal field is a remarkable submarine ecosystem in which geological chemical and biological processes are intimately interlinked reactions between seawater and upper mantle peridotite produce methane and hydrogen rich fluids with temperatures ranging from 40 to 90 c at ph 9 to 11 and carbonate chimneys 30 to 60 meters tall a low diversity of microorganisms related to methane cycling archaea thrive in the warm porous interiors of the edifices macrofaunal communities show a degree of species diversity at least as high as that of black smoker vent sites along the mid atlantic ridge but they lack the high biomasses of chemosynthetic organisms that are typical of volcanically driven systems

linking nm scale measurements of the anisotropy of silicate surface reactivity to macroscopic dissolution rate laws new insights based on diopside linking nm scale measurements of the anisotropy of silicate surface reactivity to macroscopic dissolution rate laws new insights based on diopside damien daval a b roland hellmann c giuseppe d saldi a richard wirth d kevin g knauss a a earth sciences division lawrence berkeley national laboratory ms 90r 1116 1 cyclotron road berkeley ca 94720 usa laboratoire d hydrologie et de ge ochimie de strasbourg universite de strasbourg eost cnrs umr 7517 1 rue blessig 67084 strasbourg france c institute for earth sciences isterre universite de grenoble 1 cnrs observatoire des sciences de l univers a grenoble 38041 grenoble france d gfz german research centre for geosciences telegrafenberg 14473 potsdam germany b abstract the interfacial zone between a bulk uid and a mineral surface is where all exchange of matter and energy occurs during chemical weathering however our knowledge is still limited with respect to understanding where and how the rate determin ing dissolution reactions take place a complicating factor is the commonplace formation of amorphous si rich surface layers assls which may hinder contact between the uid and the mineral surface to address the role of assl we investigated the dissolution of a common silicate diopside and related the bulk dissolution rate with the nanoscale dissolution rate and surface chemistry of its individual prevalent faces while assl were evidenced on all of the investigated faces only those formed on 1 1 0 and 1 10 were passivating thereby controlling the reactivity of the underlying faces the 1 1 0 and 1 10 faces intersect the highest density of mg o si and fe o si bonds and this speciecity may explain the passivating behavior of the corresponding assl moreover we evidenced an inverse relation between aqueous silica concentration and the bulk dissolution rate of crushed diopside grains which suggest that the 1 1 0 and 1 10 faces are predominant in a powder by considering assl as a separate phase that can control silicate dissolution rates extrapolated laboratory based rates at conditions relevant to the eeld can be lowered by up to several orders of magnitude thereby decreasing the large gap between laboratory and natural rates this has important implications for more accurately modeling chemical weathering reactions so important today for the c cycle and co 2 sequestration and earth science processes whether it determines the rates of denudation and soil formation godderis et al 2010 co 2 uptake and its impact on climate change le hir et al 2008 beaulieu et al 2012 hydrothermal circu lation fritz et al 2010 durability of radioactive waste conenement glasses cailleteau et al 2008 frugier et al 2008 or geological sequestration of co 2 knauss et al 2005 the same strategy is commonly applied for determin ing the long term evolution of uid rock interactions this strategy relies on the experimental determination of the 1 introduction the chemical weathering of silicate materials plays a central role in many major engineering environmental corresponding author at laboratoire d hydrologie et de ge ochimie de strasbourg universite de strasbourg eost cnrs umr 7517 1 rue blessig 67084 strasbourg france tel 33 0 3 68 85 05 56 fax 33 0 3 68 85 04 02 e mail address ddaval unistra fr d daval

feedstocks study on co2 mineralization technology a tremendous amount of co2 has been released into the atmosphere over the past two centuries as a result of excessive use of fossil fuels a variety of methods to reduce co2 emissions into the atmosphere have been proposed but none of them so far has attained a concrete breakthrough developing new technologies using co2 and industrial alkaline wastes as alternatives to petroleum based feedstocks may offer attractive opportunities to reduce both the greenhouse gas emissions and the reliance on petroleum derivatives for production of important base chemical commodities recently a novel technique about harvesting electricity from co2 mineralization was proposed by our group based on the principle that chemical energy released from co2 mineralization process can be converted into electricity in addition to some high value chemical products of the reaction however this technology brings into question a number of issues including the chemical mechanisms taking place in the system the availability of adequate mineralizing feedstocks for harvesting electricity the quantity of co2 that can be sequestered and the quantity of electricity that can be generated by the co2 mineralization process a detailed investigation of the co2 mineralization was conducted including a study of the required raw materials herein classified as alkali and alkaline minerals industrial alkaline solid wastes and waste water the great significance of environmental implications estimates that approximately 10492 32 million tons and 150 35 million tons of co2 can be mineralized worldwide and in china respectively in other words annually 250 94 and 147 71 million tons of co2 can be sequestered worldwide and in china respectively accordingly the total amount of electricity produced will reach 2687 03 and 40 50 billion kwh worldwide and in china respectively i e 69 33 billion kwh worldwide and 39 94 billion kwh in china annually