modeling equilibrium dynamics of the benguela current system the regional ocean modeling system roms is used to systematically investigate equilibrium conditions and seasonal variations of the benguela system at a resolution of 9 km including both the large scale offshore flow regime and the economically and ecologically important coastal upwelling regime a shelf edge poleward flow exists in the northern benguela region i e north of 28 s and is driven primarily by the wind stress curl via the sverdrup relation as such it is strongly seasonal and is most intense during spring and summer when the wind stress curl is most negative the poleward flow deepens as it moves southward between 25 and 27 s much of it veers offshore because of the nature of the wind stress curl and its interaction with the northwestward path of the benguela current which is influenced by alongshore topographical variations the benguela current is driven by nonlinear interactions of passing agulhas rings and eddies and does not have a striking seasonal signal in the mean state it is characterized by two streams the more inshore stream is topographically controlled and follows the run of the shelf edge the meandering nature of the offshore stream is a result of the preferential path of agulhas rings the model simulates all seven of the major upwelling cells within its domain the three southernmost cells have the strongest seasonal signal and experience their greatest upwelling during spring and summer months whereas the two northernmost cells have less seasonal variability but nevertheless have increased upwelling from autumn to spring and least upwelling in summer and the central benguela upwelling cells experience year round upwelling the effect of topography on coastal upwelling was investigated by smoothing alongshore coastline and topography variations which showed that in all of the seven major upwelling cells upwelling is enhanced on the downstream side of capes

experimental study of subsolidus phase relations and mixing properties of pyroxene in the system cao al2o3 sio2 abstract subsolidus phase relations in the system cao al2o3 sio2 cas were experimentally determined with tight reversals of several univariant curves and with 14 equilibration experiments containing the assemblage pyroxene anorthite where pyroxene is a binary solid solution of ca tschermak cats caal2sio6 and ca eskola caes ca0 5alsi2o6 endmembers reversals were obtained on the following reactions bar c 3an gr 2ky q p 22t 700 3an cor gr 3ky p 21 8t 950 3cats gr 2cor p 55t 53900 and 6cats 1 x caesx 2 1 2x gr 4 1 2x cor 9xan observed slopes indicate 9 8 j mol k of al si disorder in ca tschermak pyroxene and 5 3 j mol k of al si disorder in anorthite at 1300 c it is suggested that al si disorder in anorthite increases by 1 9 j mol k from 700 c to 1300 c compositions of cats caes pyroxene in equilibrium with anorthite and pbo rich liquid were experimentally determined at 1400 1430 c and 22 7 30 8 kbar microprobe measurements gave compositions which are consistent with an ideal pyroxene solution and the following parameters for the reaction 3an 2cats 2caes j bar k 2rtln xcats xcaes 60200 86 4t 5 06 13 10 7p p 0 resulting in h0j 39 8 kj mol and s0 461 8 j mol k for the ca eskola endmember at 1300 c the obtained properties of the ca eskola component are necessary for thermobarometry based on pyroxene bearing assemblages containing plagioclase quartz or kyanite

ca eskola component in clinopyroxene experimental studies at high pressures and high temperatures in multianvil apparatus abstract in order to investigate the pressure implications of silica exsolution from clinopyroxene in ultrahigh pressure metamorphic rocks we have measured systematically the values of the calcium eskola ca esk component of clinopyroxenes over a considerable range of pressure and temperature a series of anhydrous experiments using powdered glass of composition wt sio2 59 29 al2o3 23 12 mgo 5 44 cao 10 37 and na2o 1 78 were conducted in a walker style multianvil apparatus in the p t range of 6 12 gpa and 900 1200 c we find that all clinopyroxenes synthesized in equilibrium with garnet kyanite and sio2 coesite or stishovite are cation deficient the highest value of the ca esk component 32 38 mol is reached at 6 gpa followed by slight decrease beginning at 8 gpa as the pyroxene progressively dissolves into garnet and more rapid decrease at 10 12 gpa when stishovite becomes stable in the assemblage comparison of our data with those available in the literature which all together covers a wider range of p and t shows that the ca esk activity depends strongly on bulk chemistry especially the silica content in general integrated analyses of published experiments on similar compositions show that the ca esk component rises rapidly to its highest values from 1 to 4 6 gpa then slightly decreases to 9 gpa followed by remarkable decrease to 15 gpa culminating in replacement of pyroxene by garnet in equilibrium with stishovite we conclude that the sio2 exsolution lamellae observed in clinopyroxenes from many ultrahigh pressure terranes can be explained by destabilization of the ca esk component during decompression however because silica solubility in clinopyroxene reaches its maximum at 6 8 gpa the practical upper pressure limit that can be inferred from this system is 200 250 km

observation of south atlantic subtropical mode waters with argo profiling float data south atlantic subtropical mode water sastmw is detected using temperature and salinity profiles obtained by argo floats marked by low potential vorticity within its extent mode waters are identified by homogeneous temperature and salinity values both horizontally and vertically their presence is evident in three regions the brazil current recirculation gyre on the western side of the basin the eastern side of the basin and along the southern edge of the gyre formation occurs between winter and mid spring in the regions of cumulative cooling of the ocean we showed that argo profilers do not preferentially sampled eddies yet from the profiles that found sastmw inside an eddy 80 are anticyclonic furthermore the mode water layer inside anticyclonic eddies is on average thicker than inside cyclonic eddies or anywhere else we investigate the correlation between the presence of mode water with the eddy kinetic energy eke the cross spectrum shows that the eke and the layer thickness are out of phase in the annual period band we addressed the role of negative surface heat fluxes during the sastmw period of formation nearly all profiles that indicated mode water formation occurred at the time and within the region where the cumulative heat flux was negative

geochemical and fluid dynamic modeling of compositional variations in archean komatiite hosted nickel sulfide ores in western australia stratigraphic volcanological petrological and fluid dynamic studies suggest that archean komatiite associated nickel sulfide deposits in western australia formed by thermal erosion of unconsolidated sulfidic sediments beneath channelized lava flows geochemical and nd isotope data for the type area at kambalda suggest that mineralized lava channels are less contaminated than barren flanking segments of the flow owing to high discharge rates and continuous replenishment within the channel this interpretation has several implications for the mode of emplacement of sulfides their degree of equilibration with the host komatiite and the compositions of sulfide ores 1 the solubility of sulfur in komatiite is relatively low so most of the sulfide in eroded sediments will be melted and remain as a dense layer at the base of the flow or be incorporated into the turbulently flowing komatiite as immiscible sulfide droplets 2 sulfide ores will not necessarily be in equilibrium with overlying komatiites but will record equilibration with variably contaminated lavas during initial stages of emplacement and crystallization and 3 ore compositions will vary from channel to channel shoot to shoot depending on i the composition of the hybridized komatiite ii the fluid dynamics of the system and the effective magma sulfide ratio r factor and iii the sulfide silicate partition coefficients under the prevailing conditions of temperature and f sub o 2 f sub s 2 the size of immiscible droplets and the interface between two immiscible layers are affected by inertial forces during turbulent flow turbulence causes coalescence of small droplets and breakup of large droplets leading to an equilibrium droplet size if the average size of the droplets is small and or the flowage rate is high they may be carried in suspension in the flowing komatiite droplets have a large surface area to volume ratio and will be effective in scavenging chalcophile elements since they are carried by the turbulent motion of the flowing komatiite if the average size of the droplets is large or if the flowage rate is low they will settle and collect at the base of the komatiite komatiite and sulfide liquids may continue to flow but the sulfide layer will have a low surface area to volume ratio and will be ineffective in extracting chalcophile elements from the overlying komatiite layer thus the initial stages of emplacement when sulfides are initially melted and are most likely to be in suspension if at all control the effective r factor and therefore the tenor of the sulfide ores numerical modeling of the observed variations in ore compositions constrained by known komatiite compositions and experimentally or empirically determined distribution constants indicates that the observed range of ore compositions in western australian komatiite associated nickel sulfide deposits can be accounted for primarily by variations in the effective sulfide silicate ratio 500 r 100 although required variations in the partition coefficient for ni 200 d ni 100 suggest that f sub o 2 f sub s 2 may also have varied systematically assimilation of h 2 o fes rich sediments should increase f sub o 2 f sub s 2 because of the relative abundances of the two components in the magma and unconsolidated sediments if low tenor ores represent equilibration at lower r and higher f sub o 2 f sub s 2 and high tenor ores represent equilibration at higher r and lower f sub o 2 f sub s 2 as suggested by the modeling then d ni appears to decrease with increasing f sub o 2 f sub s 2 as suggested by doyle and naldrett 1987 the range of calculated r values is relatively low suggesting that low tenor sulfides were not entrained into the komatiite lava but remained as a segregated layer at the base of the flow and that high tenor sulfides were not transported long distances in suspension but settled rapidly to the base of the flow magma compositions vary only slightly from an inferred parental komatiite low tenor ores appear to have equilibrated with only slightly more evolved contaminated and fractionated lavas

lagrangian circulation of antarctic intermediate water in the subtropical south atlantic this study combines float data from different projects collected between 1991 and 2003 in the south atlantic to describe the flow of antarctic intermediate water aaiw velocity space time averages are calculated for various grid resolutions and with cells deformed to match the bathymetry f h or f h with h being the water depth and h being the thickness of the aaiw layer when judged by the degree of alignment between respective isolines and the resulting average velocity fields the best grid is based on a nominal cell size of 3o latitude by 4o longitude with cell shapes deformed according to f h using this grid objectively estimated mean currents and their associated errors as well as meridional and zonal volume transports are estimated results show an anticyclonic subtropical gyre centred near 36os and spanning from 23o 1 s to 46 1os the south atlantic current meanders from 33os to 46os and shows a mean speed of 9 6 7 8 cm s 1 8 5 sv 3 5 sv 1 sv 1 106 m3 s 1 the northern branch of the subtropical gyre is located between 22os and 32os and flows westward with a mean speed of 4 7 3 3 cm s 1 9 3 sv 3 4 sv evidence of a cyclonic tropical gyre divided in two sub cells is visible on the stream function

weights of evidence and logistic regression modeling of magmatic nickel sulfide prospectivity in the yilgarn craton western australia abstract bayesian weight of evidence and logistic regression models are implemented in a gis environment for regional scale prospectivity modeling of greenstone belts in the yilgarn craton western australia for magmatic nickel sulfide deposits the input variables for the models consisted of derivative gis layers that were used as proxies for mappable exploration criteria for magmatic nickel sulfide deposits in the yilgarn about 70 of the 165 known deposits of the craton were used to train the models the remaining 30 was used to validate the models and therefore had to be treated as if they had not been discovered the weights of evidence and logistic regression models respectively classify 71 4 and 81 6 validation deposits in prospective zones that occupy about 9 of the total area occupied by the greenstone belts in the craton the superior performance of the logistic regression model is attributed to its capability to accommodate conditional dependencies amongst the input predictor maps and provide less biased estimates of prospectivity

ruthenium in chromite as indicator for magmatic sulfide liquid equilibration in mafic ultramafic systems abstract the platinum group element ruthenium ru is an important petrogenetic tracer of earth s accretion history core mantle interaction mantle evolution and the exploration for magmatic sulfide deposits however its geochemical behavior in mafic ultramafic systems is still not fully understood which limits its usefulness in the predictive modelling of geochemical systems to further develop the use of ru as a petrogenetic tracer we analyzed the ru contents of chromites from a global sample set of komatiites komatiitic basalts and ferropicrites by laser ablation icp ms and carius tube isotope dilution icp ms analysis the ru data are combined with full major and minor element microprobe analyses the data show that two groups of chromite can be distinguished on the basis of their ru contents this bimodal distribution occurs across komatiites komatiitic basalts and ferropicrites and corresponds to the sulfide saturation state of the magma during chromite crystallization chromites from sulfide undersaturated magmas contain between 150 and 600 ppb ru whereas chromites that crystallized from sulfide bearing magmas mostly contain less than 150 ppb ru the ru contents are independent of elements that typically document a modification of chromite suggesting that the determined ru concentrations reflect the primary magmatic chromite composition the ru contents are furthermore independent of magma type i e komatiites komatiitic basalts ferropicrites the magma source regions i e different cratons belt and localities the geochemical affinity i e munro type and karasjok type and age i e 2 7 ga and 2 0 ga and neither local fluctuations in fo2 nor emplacement styles i e intrusive vs extrusive can account for the bimodal ru distribution in chromite observed during this study as a consequence it is argued that the ru contents of chromites from mafic and ultramafic systems are indicative of the presence or absence of a sulfide liquid during chromite crystallization in sulfide saturated systems the chalcophile ru will dominantly partition into sulfides whereas in the absence of sulfides ru preferentially partitions into chromite over all other available phases because i high ru contents in chromites are exclusively associated with sulfide undersaturated systems and ii the ru contents of chromites can be measured via fast and cost effective laser ablation icp ms ru variability patterns in chromites allow the identification of magmas that have equilibrated with magmatic sulfide liquids prior to or during chromite crystallization and hence have potential to host metal sulfide orebodies

physical volcanology and geochemistry of a late archaean volcanic arc kurnalpi and gindalbie terranes eastern goldfields superterrane western australia abstract late archaean 2715 2704 ma calc alkaline volcanic complexes in the kurnalpi terrane are identical in facies and geochemistry to modern intra arc volcanic complexes preserved volcanic rocks and associated feldspathic sedimentary rocks represent proximal to medial submarine facies of submarine to locally emergent intra oceanic arc related volcanoes the least altered volcanic rocks are dominantly andesite but range from basalt and basaltic andesite to rare rhyolite and are the product of magmas similar in composition to those of modern arcs intermediate magmas were most likely derived from large ion lithophile element lile enriched mafic magmas by fractional crystallisation with or without assimilation processes the kurnalpi terrane thus provides an example of a late archaean volcanic arc in which hydrated mantle wedge melting was the main mechanism for magma genesis ttd suite volcanism derived from slab melting was either absent or played a subordinate role the adjacent gindalbie terrane contains younger 2692 2680 ma bimodal basalt rhyolite volcanic complexes with associated quartz rich sedimentary rocks and calc alkaline intermediate silicic volcanic complexes volcanosedimentary basement to the gindalbie volcanic sequences is deeply eroded equivalents of the calc alkaline volcanic complexes their associated sedimentary rocks and younger basaltic sequences found in the kurnalpi terrane gindalbie basalt rhyolite successions locally contain volcanic hosted massive cu zn mineral deposits rhyolites derived by low pressure fractional crystallisation or melting of andesites are more abundant than in the kurnalpi volcanic complexes facies associations and the local occurrence of distinctive incompatible element enriched mildly peralkaline a type rhyolites are consistent with rifting of a mature arc system the two terranes most likely represent volcanic evolution of the same late archaean volcanic arc but are different tectonic fragments that were welded together by 2660 ma

geochemistry and tectonic setting of two contrasting archaean felsic volcanic associations in the eastern goldfields western australia abstract archaean felsic volcanic rocks from two areas in the eastern yilgarn craton of western australia comprise dacite and rhyolite with subordinate basalt and andesite one suite from one of the areas black flag group is dominated by subaqueous dacite lava lobes and their reworked products the other suite from the other area melita and jeedamya volcanics consists of abundant rhyolitic and rhyodacitic pyroclastic deposits with less abundant dacitic lava flows both suites are intercalated with volumetrically subordinate basic and intermediate volcanic rocks black flag group dacites and rhyolites have steep ree patterns la yb cn about 40 and no eu anomaly high sr and al2o3 low nb and y hence high sr y melita and jeedamya dacites and rhyolites have flatter ree patterns la yb cn between 2 and 9 negative eu anomalies eu eu 0 4 0 6 and higher zr nb y and lower sr hence lower sr y on chemical grounds mafic rocks in both areas are genetically unrelated to felsic volcanic rocks black flag group andesites dacites and rhyolites are probably unrelated by fractional crystallization but resulted from 22 28 partial melting of amphibolite leaving a residual mineralogy of amphibole plagioclase garnet ilmenite clinopyroxene alternatively andesites may have been derived by partial melting of a metasomatised mantle source jeedamya rhyodacite could have been produced by 35 vapour absent melting of tonalite leaving a residual mineralogy of plagioclase orthopyroxene amphibole ilmenite the source would have had a slightly lree enriched pattern with a positive eu anomaly residual garnet in the source of black flag group rocks requires melting at depths greater than 35 km which is below the base of the present tectonically thinned crust the most likely source is subducted oceanic crust with black flag group rocks erupted in a back arc basin melita and jeedamya felsic volcanic rocks resulted from melting of thicker continental crust adjacent to the back arc

forsterite diopside spinel liquid equilibria in the system cao mgo al2o3 sio2 at 20 kbar and petrological applications liquidus phase relationships in the caalal sio6 mg2sio4 camgsi2o6 caalsi2o8 portion of the simplified basalt tetrahedron in the cao mgo sio2 al2o3 system have been experimentally determined at 20 kbar pressure the fo diss sp li univariant curve that pierces the fo di an join and meets the fo diss enss sp li invariant point in the basalt tetrahedron extends all the way to and pierces the di fo cats join the limit of the simplified basalt tetrahedron toward the silica undersaturated portion

southern ocean thermocline ventilation abstract an approximate mass volume budget in the surface layer of the southern ocean is used to investigate the intensity and regional variability of the ventilation process discussed here in terms of subduction and upwelling ventilation resulting from ekman pumping is estimated from satellite winds the geostrophic mean component is assessed from a climatology strengthened with argo data and the eddy induced advection is included via the parameterization of gent and mcwilliams together with eddy mixing estimates all three components contribute significantly to ventilation finally the seasonal cycle of the upper ocean is resolved using argo data the circumpolar averaged circulation shows an upwelling in the antarctic intermediate water aaiw density classes which is carried north into a zone of dense subantarctic mode water samw subduction although no consistent net production is found in the light samw density classes a large subduction of subtropical mode water stmw is observed the s

chromite in komatiites 3d morphologies with implications for crystallization mechanisms high resolution x ray computed tomography has been carried out on a suite of komatiite samples representing a range of volcanic facies chromite contents and degrees of alteration and metamorphism to reveal the wide range of sizes shapes and degrees of clustering that chromite grains display as a function of cooling history dendrites are spectacularly skeletal chromite grains formed during very rapid crystallization of supercooled melt in spinifex zones close to flow tops at slower cooling rates in the interiors of thick flows chromite forms predominantly euhedral grains large clusters up to a dozen of grains are characteristic of liquidus chromite whereas fine dustings of mostly individual 20 m grains form by in situ crystallization from trapped intercumulus liquid chromite in coarse grained olivine cumulates from komatiitic dunite bodies occurs in two forms as clusters or chains of euhedral crystals developing into chicken wire texture where chromite is present in supra cotectic proportions and as strongly dendritic semi poikilitic grains these dendritic grains are likely to have formed by rapid crescumulate growth from magma that was close to its liquidus temperature but supersaturated with chromite in some cases this process seems to have been favoured by nucleation of chromite on the margins of sulphide liquid blebs this texture is a good evidence for the predominantly cumulus origin of oikocrysts and in situ origin of heteradcumulate textures our 3d textural analysis confirms that the morphology of chromite crystals is a distinctive indicator of crystallization environment even in highly altered rocks

district to camp controls on the genesis of komatiite hosted nickel sulfide deposits agnew wiluna greenstone belt western australia insights from the multiple sulfur isotopes the agnew wiluna greenstone belt of western australia is the largest komatiite hosted nickel sulfide belt in the world and contains two world class ni cu pge deposits and a host of smaller deposits this study focuses on the broader scale geology of this greenstone belt in order to understand the key controls on the genesis of the komatiite hosted ni cu pge deposits with specific focus on camp to district controls we apply multiple sulfur isotopes to this geologic framework and conclude not only that the addition of crustal sulfur is a prerequisite for ore genesis in komatiite systems but above all that the sulfur required to generate world class deposits is most likely derived from barren volcanic massive sulfide lenses which are spatially and genetically associated with felsic volcanic and volcaniclastic sequences that were emplaced coevally with large komatiitic sills and channelized lava flows multiple sulfur isotope data can be utilized in exploration at the deposit to district scales at the deposit scale the spatial pattern of mass independent s isotope values 33 s provides crucial insight into the identification of proximal high grade and high tenor ores in mineralized systems in fact sulfur data reflect the assimilation process that occurred upon komatiite emplacement whereby hot turbulent magma thermomechanically eroded and assimilated exhalative sulfides spatially located close to vent with negative to near zero 33 s values whereas less turbulent flows interacted with distal sulfidic shales having 33 s values above 0 per mil accordingly the spatial variation of multiple sulfur isotope values in magmatic sulfides and associated host rocks may be utilized as a vector towards high grade ores of poorly known systems at the district scale rather than ascertaining what controls the distribution of komatiite hosted ni cu pge deposits the appropriate question to ask is what controls the distribution of country rock sulfides considering that exhalative sulfides may be crucial to ore genesis in komatiite systems we propose that felsic lava domes unambiguously mark their vents and can be directly mapped or inferred from gravity data this work provides the first step in identifying district scale control on komatiite hosted ni cu pge deposits this is the scale that has high impact on exploration for new komatiite hosted nickel sulfide belts globally

the nature of sulfidic metasediments at kambalda and their broad relationships with associated ultramafic rocks and nickel ores sedimentary horizons at kambalda occur at the base of and at interflow boundaries within the same lower one third of the ultramafic sequence as do the major ni cu orebodies although sediments occur on all the same stratigraphic horizons as the ores they are almost entirely absent from within the volume containing the ores being separated by zones free of both sediments and ni cu sulfides generally they are broadly lenticular are not very extensive in area and correlate poorly laterally mineralogically and chemically the sediments are very variable but much of this is attributable simply to a variable iron sulfide content geographic and stratigraphic location and lithology are other significant causes of these variations proximity to the ni cu ores has at best an exceedingly subtle control on chemistry or mineralogy the kambalda sediments are not compositionally very different from other archean sediments in broadly similar environments however their sulfur and chalcophile element levels are high and au is especially enriched sulfur isotopes have a narrow spread near zero range 1 5 5 and the s se is around 15 000 to 20 000 indicating a little modified magmatic source for the sulfur apart from transfer of sulfur due to pyrite breakdown at peak metamorphism to the ultramafics there was negligible chemical exchange across sediment ultramafic interfaces virtually no ni was extracted from the ultramafic silicates during this sulfurization and migration of ni into the sediments was negligible nickel sulfide ore formation by sulfurization or sedimentary replacement is rejected ores intimately involved with sediments make up only 3 to 5 percent of the total ni reserve there is a strong inverse relationship between the quality of ore environments and the amount of their ore which is in contact with sediments the four largest ore locations accounting for about 70 of the reserve each has considerably less than 1 percent of ore with sediments extensive ore sediment contact occurs locally and can result from either 1 physical injection of preexisting ni cu ore into previously barren sediments 2 a synsedimentary intermixing of ores and sediments or 3 a passive and largely coincidental relationship the volcanic exhalative model of lusk 1976 for the ni ores is rejected the sediments are interpreted to be a mixture of local mafic ultramafic and distant felsic granitic detritus s pb zn fe and cu from ultramafic exhalations s co ni and cu from local sea floor leaching of ultramafics a biological carbonaceous component and probably minor chemical silica sea floor alteration affecting na k and mn diagenesis and metasomatic k rb ba sr and co 2 introductions are evident

refining the planktic foraminiferal i ca proxy results from the southeast atlantic ocean abstract profound changes in upper ocean oxygenation have taken place in recent decades and are expected to continue in the future but the complexity of the processes driving these changes has yet to be fully unraveled planktic foraminiferal i ca is a promising tool to reconstruct the extent of past upper ocean oxygenation but a thorough assessment is necessary to evaluate both its potential and its limitations we used foraminifers from holocene core tops southeast atlantic ocean to document planktic i ca across a range of oceanographic conditions subsurface o2 concentrations may be the dominant control on planktic foraminiferal i ca and planktic i ca decreases rapidly at low o2 conditions o2

ocean climate of the south east atlantic observed from satellite data and wind models the near coastal south east atlantic ocean off africa is a unique and highly dynamic environment comprising the cool benguela current warm angola current and warm agulhas current strong coastal upwelling and the congo river strongly influence primary production much of the present knowledge of the south east atlantic has been derived from ship borne measurements and in situ sensors which cannot generally provide extensive spatial and temporal coverage similarly previous satellite studies of the region have often focused on small spatial areas and limited time periods this paper provides an improved understanding of seasonal and interannual variability in ocean dynamics along the south east atlantic coast of africa using time series of satellite and model derived data products eighteen years of satellite sea surface temperature data are complimented by 7 years of sea level data three years of chlorophyll a data illustrate the seasonal biological response but the time series is not of sufficient length for investigating interannual variability in chlorophyll biomass modelled wind fields are used to describe atmospheric forcing of the surface ocean this is the first synoptic scale description of the south east atlantic from a suite of large spatial coverage long time series products previous studies of seasonal and interannual variability in the region are reviewed and used to interpret key oceanographic features and processes identified in the satellite data key findings of this study are 1 descriptions of seasonal and interannual variability from these data show climate forcing of the south east atlantic coast of africa from both the northern and southern boundaries bimodal seasonal signals of equatorial origin propagate poleward along the angolan coast while the trade winds and events in the agulhas region dominate the agulhas bank and southern benguela the northern benguela is a mixed regime under the influence of forcing from both directions 2 the benguela nino years of 1984 and 1995 are clearly observed in sea surface temperature and sea level anomalies and correspond to anomalously weak southerly winds at the equator these conditions were also observed in 1999 suggesting this too may have been a benguela nino year 3 consideration of putative nino type events in the equatorial atlantic from this and other studies suggests that the frequency of these events is much higher than previously estimated and may be similar to the frequency of el nino southern oscillation enso events in the pacific ocean furthermore years of anomalously strong southerly winds at the equator occur during pacific enso years c 2003 elsevier ltd all rights reserved

experimentally determined stability of clinopyroxene garnet corundum in the system cao mgo al 2 o 3 sio 2

spatial characteristics of sediment trace metals in an eastern boundary upwelling retention area st helena bay south africa a hydrodynamic biological pump hypothesis st helena bay a retention zone located in the southern benguela upwelling system is an important fish nursery however it suffers from seasonal bottom water hypoxia causing major economic losses anoxic conditions are linked to sulfide fluxes from bottom sediments defined by a high sedimentation rate of organic matter it is proposed that trace metals may play an important role in alleviating part of the ecological stress by forming sulfide complexes in such systems a spatially intensive data set of sediment biogeochemical characteristics showed that poc and trace metals cr cu zn ni etc accumulated in the central zone of the bay furthermore trace metal concentrations were strongly correlated with both poc and al to explain the observed biogeochemical relationships in st helena bay we propose a hypothesis that links the upwelling retention hydrodynamics primary productivity and sediment trace metal distribution trace metals are incorporated into phytoplankton cells in the euphotic zone but rapidly sediment along with particulate organics on their senescence both the biological pump and the dispersion of particulates are primarily controlled by the hydrodynamics prevalent within st helena bay which also govern the retention zone in the shadow of one of the major upwelling cells the dynamics of entrainmentestratification drives the productivity while a residual cyclonic gyre concentrates the surface productivity within the bay bed shear stresses spatially constrain the accumulation of biogenic organic matter which governs the trace metal biogeochemistry of the sediments along a narrow terrigenous mud belt 2005 elsevier ltd all rights reserved

evidence of lateral thermomechanical erosion of basalt by fe ni cu sulfide melt at kambalda western australia the fe ni cu sulfide ores at kambalda western australia are interpreted to be the result of thermomechanical erosion of underlying rocks by the host komatiite lava flows however there is a long standing argument about the extent of the erosion process and the degree to which the linear embayments that host the ores were eroded by lava as opposed to formed by tectonic processes this controversy has fundamental implications for the origin of magmatic sulfide ore as well as for sinuous rilles on terrestrial planets the controversy at kambalda hinges on pinchout features where sulfide ore at the edges of embayments penetrates laterally into footwall rocks the most recently published studies of these features interpret them as forming by thrusting of basalts over sulfide komatiite contacts along the margins of tectonic embayments field evidence and x ray fluorescence element mapping on underground exposures in the moran deposit demonstrate that sulfide liquid melted its way both downward and laterally into basalt generating complex plumose melt layers melt emulsions and hybridized chromite decorated contacts these observations confirm an origin for the pinchouts by thermomechanical erosion driven by the high temperature high density and low viscosity of the sulfide melt they also provide some intriguing insights into the nature of interactions between sulfide melt and melting silicate rocks in magmatic ni cu platinum group element sulfide ore deposits in general

kinetic controls on the partitioning of trace elements between silicate and sulfide liquids mass transfer between sulfide and silicate liquids is often discussed elements pge has resulted from liquation immiscible by reference to a mass ratio between hypothetical liquid reservoirs liquid phase separation of sulfide liquid from mafic or at equilibrium defined as r in an open system not at equilibrium ultramafic silicate magma a central assumption of modthe mass of silicate melt from which a growing sulfide droplet els of magmatic sulfide deposit formation is that the base appears to have scavenged chalcophile elements will depend on metals and pge are strongly partitioned into the sulfide diffusivities di and dfes of the element and of the fes component melt previous discussions of the process by which sulfide in the silicate melt respectively on the degree of supersaturation of liquids become enriched in chalcophile metals have fothe melt with fes c o on the radius a of the droplet and on the cused almost exclusively on models in which coexisting velocity v with which the droplet is advected through the melt so bodies of sulfide and silicate melt are considered to be that in equilibrium at all times the intent of this paper is to demonstrate that natural sulfide deposits preserved in igneous rocks will in many r 1 c fes o di 1 2 adiv dfes 1 2 adfesv instances record metal distributions that never attained equilibrium as a result of the kinetic constraints on metal chalcophile elements are expected to show inter element variations partitioning between phases the consequences are that in d spanning several orders of magnitude in some melts leading different elements will seem to show evidence for equito large inter element variations in effective r in a given sulfide libration at different silicate sulfide mass ratios within body these variations in effective r will lead to spatial separations single sulfide bodies i describe the time dependent evolubetween zones of maximum enrichment of chalcophile elements tion of metal distributions in silicate sulfide melt systems produced during fractional segregation of sulfide in layered intrusions starting with analytical solutions for simple boundary whereas it has proven impossible to model the generation of spatially conditions and then adapting them to more complex offset stratiform horizons in the australian munni munni layered systems as numerical models intrusion using equilibrium partition coefficients the present kinetic model reproduces the observed patterns with great fidelity

the textures formation and dynamics of rare high mgo komatiite pillow lavas abstract pillow lavas are an abundant morphological lava type both on earth and on some extraterrestrial bodies we examine pillows from kambalda western australia komatiites that uniquely preserve pillow necks inter pillow cavities and internal crusts our study is the first description of true pillows from an archaean high mgo 31 komatiite their size ranges from 0 5 to 5 cm and most have equal vertical and horizontal axes due to very low melt viscosities 0 01 0 1 pa s these komatiite pillows are one to two orders of magnitude smaller than modern basaltic counterparts true high mgo komatiites such as those at kambalda require a low flow rate potentially found on distal flow edges such low flow rates are in conflict with the high flow velocities generally assumed for komatiites and hence explains the rarity of komatiite pillow lavas

enstatite jadeite join and its role in the earth s mantle phase relations on the enstatite jadeite join were experimentally determined at solidus temperatures and 90 152 kb and at 1400 2050 c 175 219 kb with a split sphere anvil apparatus ussa 2000 new findings include immiscibility in garnet and determination of the stability of naalsio4 calcium ferrite structure with stishovite a thermodynamic model for the enstatite jadeite join was developed to calculate a complete phase diagram for the join at 500 2500 c and 0 270 kb the results indicate that the two major discontinuities in the earth s mantle at 400 and 670 km depths could correspond respectively to the formation and the breakdown of garnet with a pyroxene composition a model for a chondritic upper mantle is proposed in which large scale chemical and mineral layering was produced by fractionation of liquidus phases in a magma ocean solidification was completed at 400 km depth by crystallization of sodium enriched residual melts which produced a pyroxene layer at 300 400 km depths

tectono stratigraphy of late archaean greenstone terranes in the southern eastern goldfields western australia abstract late archaean greenstone terranes in the southern part of the eastern goldfields are regionally extensive faultbounded entities defined on the basis of small but distinct differences in stratigraphy and structure the greenstones comprise volcano sedimentary successions that were all deposited at the same time c 2720 2675 ma on sialic crust hence the terranes are interpreted to represent contemporaneous probably adjacent basins these basins were affected by the same history of granite plutonism and regional deformation c 2675 2620 ma early subhorizontal deformation is poorly understood but includes at least locally significant thrust stacking d1 with a south to north movement direction this was followed by regional east west extension affecting all supracrustal successions above a province wide detachment now lying at depths between 4 and 7 km this detachment may have evolved from the greenstone basement contact but only after extensive reworking clastic basins developed along or above major extensional faults but no volcanism is associated with this extension subsequent east west d2 shortening resulted in regional scale thrusting folding and associated late stage transcurrent fault movements the d2 event is contemporaneous with a major thermal event represented by voluminous granite emplacement c 2660 ma and associated peak regional metamorphism in the greenstone succession predominantly monzo granite derived from older sialic crust was emplaced throughout the period of basin formation and deformation early synvolcanic granite c 2719 2710 ma is a minor component late synvolcanic granite c 2685 2675 ma is widespread and syn d2 granite c 2660 ma is abundant there are a few small late tectonic intrusions c 2640 ma to 2600 ma the lateral lithostratigraphic persistence of the contemporaneous basins the syn d2 low pressure regional metamorphism and the province wide monzo granite magmatism suggest that the greenstone basins possibly developed in a tectonic setting similar to that of failed rifts above aborted spreading centres the basins closed in response to far field compressional stresses

analytical numerical modeling of komatiite lava emplacement and thermal erosion at perseverance western australia abstract we have applied a thermal fluid dynamic geochemical model to investigate the emplacement and erosional potential of archean komatiite flows at perseverance western australia perseverance has been proposed as a site of large scale thermal erosion by large volume komatiite eruption s resulting in a 100 150 m deep lava channel containing one of the world s largest komatiite hosted fe ni cu pge sulfide deposits using constraints based on field theoretical and geochemical data we have modeled the emplacement of a range of flow thicknesses over felsic tuffaceous substrates with various degrees of consolidation and water contents thermo mechanical erosion becomes more effective for substrates that are increasingly unconsolidated and water rich for thermo mechanical erosion to be responsible for the formation of the 100 m deep concave perseverance embayment and the highly contaminated 10 20 perseverance komatiites the most likely scenarios require emplacement of thick e g 10 30 m turbulent channelized liquidus or superheated komatiite lavas over a welded or unconsolidated submarine tuff flow distances must have been long tens to hundreds of kilometers and flow volumes must have been very high hundreds to thousands of km 3 lava channels and tubes 110 km long have not been observed on earth but are consistent with those formed by low viscosity lavas on venus the moon mars and io flow volumes are consistent with those in continental flood basalt eruptions and oceanic plateau large igneous provinces and may represent the initial outpourings of komatiite lavas from archean mantle plume activity

the perseverance ultramafic complex western australia the product of a komatiite lava river the perseverance ultramafic complex is a body of olivine rich komatiitic rocks spatially associated with the agnew nickel deposit in the agnew wiluna greenstone belt of the archaean yilgarn block in western australia the complex consists of a central lenticular body up to 700 m thick of olivine adcumulates flanked by laterally extensive sheet like bodies of olivine orthocumulates and spinifextextured komatiite flows rocks progressively further away from the central lens have chemical compositions reflecting higher original proportions of komatiite liquid to cumulus olivine parent liquids had mgo contents between 25 and 32 mgo approximately chondritic al ti ratios and hree patterns and moderate depletion in lree olivines within the adcumulate lens show a progressive increase in forsterite content from fo93 at the bottom to fo94 5 at the top calculated original olivine compositions in ihe flanking rocks are similar to those at the base of the central lens original olivine nickel contents show a symmetrical variation from maximum values of 3500 ppm at the top of the central lens through minimum values of 1000 ppm at the base and margins of the central lens to intermediate values in the distal rocks the complex as a whole shows evidence for nickel depletion relative to other komatiite suites these observations are explained in terms of prolonged eruption and flow of komatiitic lava down a major flow channel or lava river adcumulates crystallized on the floor and sides of the central channel which was formed at an early stage by thermal erosion of floor rocks episodic overflow of the central channel produced distal flood plain rocks consisting of olivine orthocumulates and layered flows lavas became more magnesian and nickel rich with time giving rise to the observed spatial variation in primary olivine composition nickel depletion of the earliest lavas is attributed to pre eruption segregation of large volumes of immiscible fe ni sulfide which were concentrated to form the underlying agnew nickel deposit

seasonal climatologies of nutrients and hydrographic properties on quasi neutral surfaces for four coastal upwelling systems seasonal climatologies of upper ocean hydrographic properties and nutrients are presented for four different major coastal upwelling centers the california peru humboldt canary and benguela regions the climatologies are built from historical hydrographic data primarily to serve as a tool for comparative studies of productivity variations and nutrient fluxes in the near coastal zone care was taken to ensure that quantities were interpolated vertically to and averaged horizontally on approximately neutral surfaces to constrain averaging among only those water masses that would naturally mix easily rather than rely on potential density surfaces that are not coincident with neutral surfaces in regions with large vertical excursions of isopycnals the neutral surfaces were properly approximated through the use of specific volume anomaly surfaces and were spaced closely in the vertical approximately 0 1 unit apart horizontal averaging to a 1 6 spatial grid was accomplished via the application of bicubic splines under tension and provided sufficient spatial resolution for resolving upwelling patterns near the coastline seasonal mean nutrient to nutrient relationships also were constructed as another diagnostic tool for inter regional comparisons and are consistent with expected redfield ratios a consistent high resolution climatology is now publicly available as a tool for local and comparative studies of four different upwelling zones

terminology for layered intrusions the terminology of igneous cumulates was originally formulated on the concept that the rocks were concentrations of minerals accumulated by crystal settling it is now well established for several major intrusions that plagioclase that had been typed as cumulus should in fact have floated in its parental magmatic liquid nevertheless the terminology has been valuable in the classification of the rocks of these and other intrusions and it has been useful in certain aspects of their genetic interpretation the name cumulate is therefore redefined so that crystal settling is a possible but not essential process in the origins of the rocks to which it is applied the overall nomenclature of layered intrusions is then reviewed and definitions of names are refined and systematized to clarify their applications careful distinction is made between descriptive and genetic names a cumulate is defined as an igneous rock characterized by a framework of touching mineral crystals and grains that evidently were concentrated through fractional crystallization of their parental magmatic liquids a layer is a sheetlike unit of cumulate that is a distinctive entity in its compositional and or textural features a lamina is a thin 2 5 cm sharply defined layer igneous lamination is a general name for planar structure that is pervasive through cumulates on the scale of their grain size layering is the overall structure and fabric manifest through combinations of layers laminae and lamination the difference between layers and layering is essentially the difference between individuals and a population and the terms that describe one are not necessarily appropriate to the description of the other but the fundamental variants of all of layering lamination grading in layers and layer contacts can essentially be described by one or more of the four modifiers grain size modal textural and cryptic where the last refers to cumulus miner al compositions a system for subdividing layered intrusions is proposed in which distinction is made between general divisions ranked as series zones and subzones and prominent units that are called groups members rhythmic units and cyclic units applications to the skaergaard bushveld muskox stillwater and other intrusions are briefly described

a 3 d geological and structural synthesis of the leinster area of the agnew wiluna belt yilgarn craton western australia with special reference to the volcanological setting of komatiite associated nickel sulfide deposits the leinster area is situated toward the southern end of the agnew wiluna belt in the yilgarn craton of western australia and hosts the giant perseverance komatiite associated nickel sulfide deposit at in excess of 1 2 mt contained ni this is the biggest type 1 basal sulfide rich accumulation deposit in the world and it is associated with a number of smaller deposits that extend over a strike length of 20 km adjacent to the perseverance fault on the eastern margin of the belt in broad terms the greenstone sequence comprises an eastern rift proximal komatiite dacite sequence and a western and more marginal basalt dominated sequence with minor komatiite the komatiites display a wide range of compositions and textures from highly magnesian olivine meso to adcumulate rocks composed of olivine with forsterite contents of up to 94 5 to sequences of thin spinifex textured komatiite flow units this compositional range indicates considerable variation in volcanic facies from rift proximal to distal loci of focused flow termed pathways indicated by thickened cord like bodies of more olivine rich rock occur at all scales and are intimately associated with the ni sulfide mineralization the pathways are linked by thinner sequences of lower mgo rocks either layered olivine orthocumulate rocks or sequences of thin spinifex textured flow units some of the lower mgo komatiite sequences appear to emanate from the tops of pathways in the manner of breakout flows in tube fed basaltic terrains variably sulfidic black shales and cherts and barren exhalative iron sulfide horizons are intimately interlayered with the komatiitic rocks the overprinting effects of regional deformation and metamorphism spanning at least 80 m y are considerable at least eight local deformation events have been recognized by previous workers these have been used to constrain the 3 d model and can be linked to craton wide structural schemes some of the major faults are clearly accretionary and reflect reactivation of underlying basin forming structures early north over south thrusting was followed by e w directed basin closure and the development of nnw trending open regional folds extension accompanied batholithic granitoid intrusion and reactivated rift parallel nnw trending faults producing the major strike slip fault systems that divide the greenstone succession into a series of structural and stratigraphic domains the ensuing orogenic collapse resulted in overturning of the stratigraphy to the east subsequent brittle deformation events have produced fault sets in a variety of orientations that can be related to ongoing shortening with a variable principal stress orientation there is a complex interplay of structural and volcanological controls on the formation and subsequent deformation of the ni sulfide deposits in this ancient terrane three dimensional modeling has furthered a detailed understanding of the geologic and structural evolution of the belt allowed the identification of komatiite pathway positions and their plunges and provided quantitative data on the magnitude and direction of fault offsets of different generations the modeling exercise has shown that it is possible to strip away the effects of overprinting metamorphism and deformation to reveal some of the primary controls on komatiite volcanism and the location of ni sulfide deposits even in those portions of greenstone belts that are highly deformed and have undergone amphibolite facies metamorphism this is illustrated with case studies of the perseverance venus rocky s reward harmony and sir lancelot deposits three dimensional modeling has the capacity to integrate geologic geochemical and geophysical datasets in a way that fully utilizes the results of past exploration programs and produces a premium geologic product that can be used to guide further exploration the recent discovery of the venus deposit is in part a tribute to the power of this approach

exsolution of garnet within clinopyroxene of mantle eclogites major and trace element chemistry eclogite xenoliths from the mantle have experienced a wide variety of processes and p t conditions many of which are recorded in the mineral compositions and textures exsolution of garnet from clinopyroxene is one such texture occurring in a minority of mantle eclogites new analyses of clinopyroxene and garnet of eclogite xenoliths from kimberlites at bellsbank south africa and obnazhennaya yakutia russia are presented here and these are combined with data from the literature exsolution of garnet from clinopyroxene is generally lamellar although lens shaped garnets are also present major and trace element characteristics show a wide range of compositions and include eclogite groups a b and c rare earth element ree concentrations of garnet and pyroxene were determined by sims and the ree patterns are subtly different from those in ordinary eclogites differences include the absence of prominent eu anomalies in samples of this study and differences in the slopes of chondrite normalized ree patterns it is possible that these signatures are unique to exsolved eclogites a result of subsolidus elemental partitioning during exsolution some reconstructed whole rock compositions are aluminuous comparison with ordinary eclogites shows only minor differences implying a similar origin if the immediate precursor to the exsolved eclogites was a monomineralic pyroxenite the excess aluminium was tied up in tschermak s molecule although the occasional presence of kyanite exsolution lamellae is indicative of a ca eskola component reconstructed pyroxenes from kyanite and corundum rich samples contain unrealistic amounts of aluminium for mantle pyroxenes a protolith or parental pyroxene threshold of 24 al2o3 may exist above which as in a plagioclase cumulate the final assemblage is kyanite and or corundum bearing

thermomechanical erosion of ore hosting embayments beneath komatiite lava channels textural evidence from kambalda western australia abstract archean komatiite hosted nickel deposits at kambalda western australia are located in embayments within channelized lava flows the origin of these embayments is controversial the currently favoured model invokes pre existing topographic features filled in by the komatiite and sulfide melt and subsequently modified by thermomechanical erosion new evidence from sulfide deposits on the eastern limb of the kambalda dome includes well preserved magmatic textural relationships of the sulfides with the surrounding rocks suggesting the entire embayment was formed by thermomechanical erosion these textures are particularly well preserved within the moran deposit of the long victor complex which lacks the younger intense structural deformation that other kambalda deposits have undergone the vestiges of an older broad concave embayment are represented by sediment sulfide textures present on the flanks up to 150 m away from the younger steep sided embayment sediment sulfide contacts are marked here by a globular silicate sulfide intergrowth interpreted as emulsion and cumulate like mono sulfide solid solution mss grains surrounded by interstitial silicate melt textures preserved from the formation of a steep sided embayment are frozen into the basalt sulfide contact and include an undulating contact with sulfide filled microfractures and a ferrichromite layer basalt sulfide breccia and interpreted crystallized silicate sulfide liquid emulsions and basalt plumes rising into the sulfides textures from the last step of embayment formation are found in the pinchouts i e where the massive sulfide ore is bounded top and bottom by basalt they include the same textures that were formed during the excavation of the steep sided embayment but they also feature interpreted basalt sulfide emulsions on the upper contact cm scale silicate sulfide ferrichromite layering on the upper contact and a vesicular basalt scum layer floating on the sulfides beneath the solid older basalt all these textures represent frozen examples of different stages during the excavation and formation of the embayment and reflect physical processes responsible for thermomechanical erosion the initial disposition and orientation of ore hosting channels was controlled by paleo topography probably defined by syn volcanic faults but the textures we describe show that within the channel the geometry of the entire embayment was the product of erosion the sulfide melt itself played a major role in the process owing to its high density high heat content and very low viscosity but the hydrated nature of the underlying altered basalt was also critical fluids were released from the basalt due to the high temperature in the 1 2 cm immediately beneath the sulfide melt with instant flash boiling creating a network of microfractures pre existing fracture networks and breccia in the basalt allowed the sulfide melt to locally infiltrate the substrate to a greater depth increasing the hydraulic head at the tip of the fracture thus accelerating the erosion process once a critical sulfide melt thickness is reached partly aided by a growing pile of matrix net textured sulfides the pressure difference on the embayment floor compared to the basalt at the bottom edges of the embayment becomes high enough to allow the liquid sulfides to melt sideways to form a pinchout

origins and variability of the benguela current a subset of the benguela sources and transports best 1992 1993 data is analyzed to study the magnitude and variability of the large scale transports in the area the data consist of inverted echo sounder series and conductivity temperature depth stations the mean 16 month transport values for the upper 1000 m indicate that of the 13 sv northward transport within the benguela current 50 is derived from the central atlantic which from geometry may be chiefly south atlantic water 25 comes from the indian ocean which may be chiefly agulhas water and the remaining 25 may be a blend of agulhas and tropical atlantic water a simple schematic of the transport pattern with a somewhat restricted corridor for agulhas eddies translation is envisioned to the west of the eddy corridor flows the south atlantic source for the benguela current to the east is the agulhas indian ocean source the corridor is breached by south atlantic and indian water as the transient eddy field stirs these water masses

the physical volcanology of archaean komatiite sequences from forrestania southern cross province western australia abstract the archaean supracrustal sequence at forrestania contains at least five komatiitic belts which can be traced along strike for distances in excess of 30 km lithologies range from olivine cumulates which crystallised at the interface between substrate and flowing lava to spinifex textured rocks which underwent rapid crystallisation within ponded lava lobes characteristic associations of different rock types are interpreted in terms of variations in eruption rate which presumably reflect proximity to the vent or to a major lava river thick sequences of olivine adcumulate to mesocumulate crystallised in a dynamic environment where lava flow was continuous and eruptive velocities were high sheeted bodies of olivine cumulate formed from voluminous turbulent flow of lava over relatively refractory substrates such as basalt and oxide facies banded iron formation ribbon shaped olivine cumulate bodies formed in an equally dynamic environment within major lava channels where the substrate was less refractory and consisted of quartz rich sedimentary rocks which were susceptible to thermal erosion distributary lava channels in more distal settings are represented by thinner ribbon like accumulations of olivine mesocumulate to orthocumulate unusual poikilitic pyroxene bearing rocks are present at the base of some lava channels and appear to represent the crystallisation product of a komatiitic lava which has been contaminated by cherty sedimentary rocks pyroxene and plagioclase bearing cumulates are present at the top of other channel sequences and reflect late stage ponding and in situ differentiation of komatiitic lava within the channel the channel facies rocks are flanked by sequences comprising multiple thin spinifex textured flow units which formed from the episodic overflow of lava from the distributary channels similar rocks also occur stratigraphically above many of the thick olivine cumulate bodies and reflect episodic emplacement of thin cooling units during the waning stages of the eruptive cycle

roles of xenomelts xenoliths xenocrysts xenovolatiles residues and skarns in the genesis transport and localization of magmatic fe ni cu pge sulfides and chromite abstract most sulfide rich magmatic ni cu pge deposits form in dynamic magmatic systems by partial melting s bearing wall rocks with variable degrees of assimilation of miscible silicate and volatile components and generation of barren to weakly mineralized immiscible fe sulfide xenomelts into which ni cu co pge partition from the magma some exceptionally thick magmatic cr deposits may form by partial melting oxide bearing wall rocks with variable degrees of assimilation of the miscible silicate and volatile components and generation of barren fe ti oxide xenocrysts into which cr mg v ti partition from the magma the products of these processes are variably preserved as skarns residues xenoliths xenocrysts xenomelts and xenovolatiles which play important to critical roles in ore genesis transport localization and or modification incorporation of barren xenoliths autoliths may induce small amounts of sulfide chromite to segregate but incorporation of sulfide xenomelts or oxide xenocrysts with dynamic upgrading of metal tenors pge cu ni co and cr v ti respectively is required to make significant ore deposits silicate xenomelts are only rarely preserved but will be variably depleted in chalcophile and ferrous metals less dense felsic xenoliths may aid upward sulfide transport by increasing the effective viscosity and decreasing the bulk density of the magma denser mafic or metamorphosed xenoliths may also increase the effective viscosity of the magma but may aid downward sulfide transport by increasing the bulk density of the magma sulfide wets olivine so olivine xenocrysts may act as filter beds to collect advected finely dispersed sulfide droplets but other silicates and xenoliths may not be wetted by sulfides xenovolatiles may retard settling of or in some cases float dense sulfide droplets reactions of sulfide melts with felsic country rocks may generate fe rich skarns that may allow sulfide melts to fractionate to more extreme cu ni rich compositions xenoliths xenocrysts xenomelts and xenovolatiles are more likely to be preserved in cooler basaltic magmas than in hotter komatiitic magmas and are more likely to be preserved in less dynamic less turbulent systems domain phases than in more dynamic more turbulent systems domains phases massive to semi massive ni cu pge and cr mineralization and xenoliths are often localized within footwall embayments dilations jogs in dikes throats of magma conduits and the horizontal segments of dike chonolith and dike sill complexes which represent fluid dynamic traps for both ascending and descending sulfides oxides if skarns residues xenoliths xenocrysts xenomelts and or xenovolatiles are present they provide important constraints on ore genesis and they are valuable exploration indicators but they must be included in elemental and isotopic mass balance calculations

rapid mineralogical and geochemical characterisation of the fisher east nickel sulphide prospects western australia using hyperspectral and pxrf data abstract the use of shortwave infrared swir and thermal infrared tir hyperspectral data in mineral exploration has been well documented in many mineralisation types but is limited in komatiite hosted nickel sulphide deposits this project combines hyperspectral portable x ray fluorescence pxrf and whole rock geochemical data to assess different analytical techniques in the exploration of these deposits we use the fisher east nickel sulphide prospects western australia for our case study the fisher east prospects lie in an area of the eastern goldfields that has historically been underexplored and understudied the rocks have undergone intense deformation with primary igneous textures being destroyed along with strong alteration to talc carbonate assemblages combining different analytical tools allowed for differentiation of a and b zones of original komatiite flows and the reconstruction of original volcanological facies in a setting where whole rock chemistry as well as igneous textures have been substantially modified by metamorphism by using different lithogeochemical techniques including pxrf this study shows the fisher east prospects are hosted within channelised komatiite flows and have similar characteristics to kambalda style deposits

evolution of the archaean granite greenstone terranes of the eastern goldfields western australia shrimp upb zircon constraints abstract thirty five high precision shrimp u pb zircon dates with an average 95 confidence error of 6 ma have been obtained from the granite greenstone terranes in the southern part of the eastern goldfields of western australia these dates establish the timing of major deformation metamorphism and granite intrusion events and test inferred stratigraphic relationships within the greenstones these new data reveal that felsic volcanic rocks were erupted throughout the southern part of the eastern goldfields between c 2713 and c 2672 ma analytically indistinguishable dates of c 2705 ma were obtained for felsic volcanic rocks interbedded with komatiitic lavas at three sites dates on felsic volcanic rocks within tectonostratigraphic packages that include komatiites are also consistent with an inferred eruption age for these komatiites of c 2705 ma komatiitic lavas in the southern part of the eastern goldfields were probably emplaced during a single voluminous eruption that resulted in the flooding of a vast area of the late archaean landscape filling the topographic lows around older felsic volcanic vents the stratigraphic complexity within tectonostratigraphic domains is attributed to the existence of an undulating topography during the eruption of the mafic and ultramafic lavas and to the rapid and localized deposition of felsic volcanic rocks close to a number of isolated volcanic centres prior to and after the komatiite lava eruption event between c 2685 and c 2675 ma early pre d2 intrusive equivalents of the felsic volcanic rocks were emplaced as thick granite sheets into the base of the greenstone sequences regional east west compression between c 2675 and c 2657 ma reactivated early extensional structures and resulted in the stacking of the greenstones this was accompanied by further intrusion of granite within developing antiforms burial of greenstone slices by stacking and the effect of hydrothermal fluids emanating from both the granites and buried greenstones resulted in regional metamorphism to greenschist facies prior to c 2640 ma monzogranite and granodiorite emplaced near the western southern and eastern margins of the greenstones were deformed and metamorphosed to upper amphibolite facies and converted into gneisses during d2 and d3 compression events movement along large scale transcurrent d3 shear zones had ceased by c 2635 ma remnants of a c 2958 to c 2930 ma greenstone sequence preserved near norseman and ravensthorpe in the southeastern yilgarn craton and xenocryst zircons ranging in age from c 2910 2730 ma in the c 2713 2672 ma felsic volcanic rocks indicate that the exposed greenstone sequences were deposited on continental basement the eastern goldfields granite greenstone terranes were formed by the closure of a series of narrow back arc rift basins that developed along a continental margin and above an active subduction zone located to the east of the rift basins

late holocene dynamics of sea surface temperature and terrestrial hydrology in southwestern africa southwest africa is an important region for paleo climatic studies being influenced by both tropical and temperate climate systems and thus reflecting the interplay of variable controls the aim of this study was to unravel the interaction of sea surface temperature sst changes in the southernmost benguela upwelling system with precipitation changes in south africa s winter rainfall zone wrz during the late holocene therefore a marine sediment core from the southernmost benguela upwelling system was investigated to reconstruct climate changes in this region for the past 2000 years grain size and geochemical analyses were conducted to reconstruct changes in fluvial sediment discharge and weathering intensity while sst changes were estimated using alkenone paleo thermometry results show that the southernmost benguela behaves distinctly in comparison with the rest of the benguela system reflecting amplified sst changes decreasing ssts accompanied increasing river discharge during times of increas

partial melting and recrystallization of archeaan komatiites by residual heat from rapidly accumulated flows spinifex textured komatiites at honeymoon well western australia show evidence of partial melting and recrystallization of original igneous textures their textures and mineral compositions differ markedly from those typical of komatiites spinifex olivine plates are bent and broken while interstitial space between spinifex and cumulus olivine is occupied by polygonal aggregates of clinopyroxene orthopyroxene minor olivine and plagioclase similar granular pyroxene plagioclase aggregates occur as diffuse veins cutting spinifex zones and cumulate zones of the flows and in places form the matrix to a breccia containing corroded fragments of spinifex rock thermometry based on the two pyroxene assemblages yields temperatures of 1055 to 1141 c just below the low pressure komatiite solidus mineral compositions are different from those of typical komatiites clinopyroxenes are al poor and cr rich olivines are unusually iron rich and depleted in cr and ca and the low ca pyroxene is bronzite rather than the more typical pigeonite we interpret these observations as the results of thermal metamorphism partial remelting and subsequent slow crystallization of originally normal spinifex textured komatiite flows the rocks in question occupy a 40 70 m interval sandwiched between two olivine rich units an underlying 90 m thick olivine adcumulate layer forming part of the cumulate zone of a basal 160 m thick flow and an overlying 1 km thick extrusive body composed mostly of olivine mesocumulate and adcumulate and capped in turn by spinifex textured flows thermal modelling shows that a sinusoidal temperature profile of cool flow tops and hot flow centres would exist within this sequence shortly after eruption conductive thermal relaxation of this profile could reheat spinifex zones to the extent of inducing partial melting and textural reconstitution such reheating is largely dependent on the time interval between the emplacement of successive flows calculations suggest that at honeymoon well the emplacement interval must have been of the order of 10 years or less textural reconstitution may have contributed to the development of the thick orthocumulate sequences characteristic of komatiites in the agnew wiluna belt

comparison of archean dunites and komatiites associated with nickel mineralisation in western australia implications for dunite genesis the two important classes of archean fe ni cu sulphide deposits in western australia are those hosted by 1 coarse grained adcumulate dunites e g agnew mount keith and 2 komatiitic lavas e g kambalda close similarities in compositions of relict olivine pyroxene and chromite from dunitic and komatiitic host rocks and compositional and textural similarities between chilled margins of some dunites and some komatiites indicate origins from similar komatiitic liquids which contained 20 32 mgo as field relations suggest that the dunites are probably lateral stratigraphic equivalents of spinifextextured komatiites they are interpreted as the slowcooled end member of a continuum from spinifex textured komatiites former liquids through cumulate komatiites 40 90 olivine to adcumulate komatiitic dunite 90 olivine previous classification of these ni deposits as intrusive and volcanic related deposits now appears unwarranted and the terms komatiitic dunite hosted and komatiite hosted deposits are preferred

new analytical and numerical geospeedometers tested on garnet pyroxenites from braganca nappe complex ne portugal abstract two new geospeedometric approaches an analytical one phys earth planet inter 110 1999 95 and a numerical one am j sci 29 1998 30 are tested to evaluate cooling rate on upper mantle derived pyroxenites from the braganca massif ne portugal these estimations coupled with standard geobarometric techniques allow theoretically the determination of exhumation rates responsible for incorporation of these rocks within the lower crust in the present paper we discuss the most significant sources of uncertainties in geospeedometry whether numerical or analytical precision of temperature estimates and input diffusion data none of the available geospeedometrical tools when used independently is able to provide definitive results with less than a factor 10 in precision cross calibration is thus required in order to provide reliable cooling rate estimates we obtain for pyroxenites from the braganca massif a minimum cooling rate from 1000 to 750 c of the order of 250 c ma for a depth interval of 10 15 km

evidence of magmatic degassing in archean komatiites insights from the wannaway nickel sulfide deposit western australia abstract magmatic degassing from komatiite lava flows potentially influenced the geochemical evolution of the archean atmosphere and hydrosphere we argue that the escape of so2 rich volatiles from komatiites impacted on the mineralogical geochemical and isotopic composition of associated nickel sulfide mineralization leaving behind detectable and measurable footprints that can be best observed where the polarity of the magmatic sequence is clearly recognizable here we focus on the ore bearing sequence of the archean komatiite hosted n01 nickel sulfide orebody at wannaway yilgarn craton western australia this deposit displays a volcanic sequence with a well defined succession of stratigraphically correlated facies comprising a massive sulfide horizon at the base of the channelized komatiite flow overlain by matrix and disseminated sulfide mineralization pyrrhotite is the dominant sulfide phase in the lower part of the ore profile the amount of troilite gradually increases from the base of the matrix ore over several meters up sequence eventually becoming dominant at the expense of pyrrhotite in the upper portion of the mineralized sequence troilite is associated with accessory mn sulfide alabandite mns which is usually reported in reduced terrestrial and extra terrestrial environments such mineralogical and volcanological features are consistent with upwards decreasing in fs2 and fo2 away from the basal contact of the komatiite flow after evaluating the possible role of metamorphism the pyrrhotite troilite alabandite assemblage and the progressive up sequence decrease of the pyrrhotite troilite ratio across the upper part of the mineralized sequence are interpreted as magmatic and indicative of progressive loss of sulfur with concomitant establishment of reducing conditions within the sulfide melt ponding at the base of the komatiite lava in this context the investigation of spatially constrained sulfur isotopic signatures allows to isolate the multiple sulfur fractionation processes that impacted on sulfide mineralization and ultimately permits the identification of the isotopic shift associated with magmatic degassing following this approach we recognize two distinct sulfur isotope exchanges processes triggered by 1 assimilation of sulfidic shales during emplacement of the komatiite flow and 2 equilibration between the sulfide melt and the sulfur dissolved in the silicate melt we finally correlate the remaining 34 s depletion up stratigraphy with the loss of heavy sulfur isotopes through magmatic degassing of so2 rich volatiles from the ultramafic flow the emission of so2 upon emplacement and cooling of the magma flow would also explain the progressive reducing fo2 and f s 2 conditions indicated by variations in mineral assemblages from the base of the komatiite upwards

a two stage model for the formation of the granite greenstone terrains of the kalgoorlie norseman area western australia abstract accurate dating of granites and greenstones from the kalgoorlie norseman area shows that there is considerable overlap in time between the formation of granites and greenstones however within any given area the oldest granites are always younger than the oldest greenstones it is suggested that the long lived 100 ma thermal anomaly in the uppermost asthenosphere that gave rise to the greenstones is also responsible for regional metamorphism and widespread crustal melting leading to the production of granites the time lag between greenstone and granite formation reflects the time taken to conduct heat from the mantle to the lower crust anatexis of the lower crust produces a layer of light granitic magma that may temporarily stop the ascent of basaltic magma where this happens the basaltic magma ponds at the base of the crust supplying additional heat and accelerating the melting process eventually the granitic melt layer becomes unstable and rises within the crust areas intruded by granite become topographic highs with topographic lows forming above areas where light melt has been withdrawn from the lower crust when the topographic highs protrude above sea level they are eroded to shed sediments into the topographic lows which contain the basaltic greenstones thus the change from a basalt dominated lower greenstone succession to a sediment and felsic volcanic dominated upper whitestone sequence seen in many granite greenstone terrains results from the intrusion of granitic magma into the upper crust the crust of the kalgoorlie norseman area formed in two distinct stages separated by a time break of up to 700 ma the first stage involved the formation of primitive crust probably above subduction zones this primitive crust was characterized by low rb sr and high sm nd ratios the second stage resulted from a major change in mantle convection that produced thermal upwellings in the mantle below the continents this led to the eruption of basaltic magmas and to metamorphism and anatexis of the lower crust to produce granitic magmas melting reset the rb sr sm nd and u pb systems giving the impression that the second event which occurred at 2 7 ga was a major crust forming event it was in fact a crustal reworking process although some basalt was added to the crust at this time although the two stage history of the kalgoorlie norseman area is clearly seen in the lead isotopes and in zircons it is not readily discernible from the rb sr and sm nd systematics due to mantle like ratios of those elements in the primitive crust

komatiites and nickel sulphide orebodies of the black swan area yilgarn craton western australia 1 petrology and volcanology of host rocks the black swan succession is a bimodal association of dacitic and komatiitic volcanic rocks located about 50 km nne of kalgoorlie within the 2 7 ga eastern goldfields greenstone province of the yilgarn craton the komatiite stratigraphy comprises a steep dipping east facing package about 700 m in maximum thickness and about 2 5 km in strike length fig 1 which hosts a number of economically exploitable ni sulphide orebodies including the silver swan massive ore shoot approximately half a million tonnes at about 10 5 ni the sequence can be subdivided into a lower felsic unit comprising coherent and autobrecciated facies of multiple dacite lava flows an upper eastern and lower western ultramafic unit each showing marked lateral facies variation and an upper felsic unit coeval with the eastern ultramafic unit the komatiite sequence has been metamorphosed at sub greenschist facies in the presence of high proportions of co2 rich fluid giving rise to pervasive talc carbonate and talc carbonate quartz assemblages with extensive preservation of pseudomorphed igneous textures cores of lizardite serpentinite are present in the thickest parts of the ultramafic succession the degree of penetrative deformation is generally very low and original stratigraphic relationships are largely intact in much of the sequence the eastern ultramafic unit and western ultramafic unit are interpreted as components of a single large komatiite flow field representing overlapping stages in the emplacement of a series of distributory lava pathways and flanking sheet flows the western ultramafic unit which hosts the bulk of the high grade massive and disseminated ores is a sequence dominated by coarse grained olivine cumulates 2 km wide and up to 500 m thick with major magma pathways represented by thick homogenous olivine mesocumulate piles at its northern and southern ends respectively 400 and 200 m thick the sequence between the two major pathways consists of olivine orthocumulates ooc with minor spinifex textured intervals the unit is capped by a persistent spinifex textured crust less than 1 m thick and is locally vesicular the eastern ultramafic unit contains the black swan cumulate zone a 500 m thick sequence of very coarse grained hopper textured locally vesicular ooc containing disseminated sulphides in its lower 200 m the zone is flanked to the north and south by complexly interdigitated sequence of highly irregular spinifex capped olivine cumulate rich flow lobes between 1 and 100 m thick and dacitic lavas and tuffs the complexity of the 3 d spatial relationship of these units suggests a combination of simultaneous eruption of dacite and komatiite combined with thermal or thermomechanical erosion the eastern and western units are interpreted as the result of more or less continuous prolonged eruption of olivine charged komatiite lava which developed localised thermo mechanical erosion channels in the dacitic substrate komatiite and dacite eruption was synchronous giving rise to complex interdigitation and extensive contamination and hybridisation

dynamics of oxygen depletion in the nearshore of a coastal embayment of the southern benguela upwelling system acquisition of high resolution time series of water column and bottom dissolved oxygen do concentrations inform the dynamics of oxygen depletion in st helena bay in the southern benguela upwelling system at several scales of variability the bay is characterized by seasonally recurrent hypoxia 1 42 ml l 1 associated with a deep pool of oxygen depleted water and episodic anoxia 0 02 ml l 1 driven by the nearshore 20 m isobath decay of red tide coastal wind forcing influences do concentrations in the nearshore through its influence on bay productivity and the development of red tides through shoreward advection of the bottom pool of oxygen depleted water as determined by the upwelling downwelling cycle and through its control of water column stratification and mixing a seasonal decline in bottom do concentrations of 1 2 ml l 1 occurs with a concurrent expansion of the bottom pool of oxygen depleted water in st helena bay upwelling of this water into the nearshore causes severe drops in do concentration 0 2 ml l 1 particularly during end of season upwelling resulting in a significant narrowing of the habitable zone episodic anoxia through the entire water column is caused by localized degradation of red tides within the confines of the shallow nearshore environment oxygenation of the nearshore is achieved by ventilation of the water column particularly with the onset of winter mixing no notable changes are evident in comparing recent measures of bottom do concentrations in st helena bay to data collected in the late 1950s and early 1960s

rank statistical analysis of nickel sulphide resources of the norseman wiluna greenstone belt western australia estimating the undiscovered mineral resources of a terrane is a challenging yet essential task in mineral exploration we apply zipf s law rank statistical analysis to estimate the undiscovered nickel sulphide resources in the norseman wiluna greenstone belt western australia the analysis suggests that about 3 0 to 10 0 mt of nickel sulphide resources are yet to be discovered in this belt compared to the currently known total nickel sulphide endowment of 10 8 mt this undiscovered nickel sulphide endowment is likely to be hosted by incompletely delineated deposits and undiscovered deposits in less explored komatiites in the belt using the more detailed data subset of the kambalda domain this study manipulates zipf s law to estimate the sizes of undiscovered deposits in addition to the domain s total nickel sulphide endowment estimate importantly regression analysis shows that the gradient of the line of best fit through the logarithmic rank size plot for the detailed kambalda data subset is 1 this gradient which is the key zipf s law constant k has the value of 0 92 for the norseman wiluna greenstone belt which is collectively less mature than the kambalda domain this result corroborates the use of k 1 in zipf s law predictive analyses of mineral resources for deposit populations for which the value of k 1 has not yet been attained due to exploration immaturity

characteristics of the surface boundary layer important to the development of red tide on the southern namaqua shelf of the benguela upwelling system the southern namaqua shelf north of the cape columbine upwelling center is particularly prone to red tide two influences of the surface boundary layer on the development of red tide in this area were investigated the dynamics of the upper mixed layer in determining phytoplankton community composition and the role of mesoscale circulation in bloom concentration and transport two survey periods 18 february 11 march 2000 and 13 30 march 2001 are reported during which red tide dominated by the dinoflagellate gyrodinium zeta formed in the area a high degree of concordance between characteristics of stratification and groupings of phytoplankton demonstrated the importance of the upper mixed layer in determining species or life form selection and development ordination of across shelf phytoplankton samples revealed a consistent banded pattern created by a wind induced upwelling plume tending to isolate a nearshore zone from an offshore domain thereby creating an area of retention on the coastal side of the plume favoring development of dinoflagellate blooms the appearance of red tide was clearly associated with increasingly stratified conditions driven by alongshore flow from the north following periods of wind relaxation and consequent reversal of surface currents the southern benguela upwelling system forms part of one of four major eastern boundary current regions of the world ocean here a range of dinoflagellate species is responsible for toxic or otherwise harmful blooms pitcher and calder 2000 these blooms often referred to as red tides are common during the latter part of the upwelling season when the wind moderates and insolation is still strong causing seasonal stratification to increase their accumulation inshore and the formation of red tide is thought to be driven by synoptic weather patterns which dictate the across shelf and alongshore movement of blooms pitcher et al 1995 pitcher and boyd 1996 red tide has therefore been closely related to the prevailing winds of the region which govern most hydrodynamic processes on the continental shelf pitcher et al 1998 these observations are considered to reflect the consequences of two important influences of the surface boundary layer on the development of red tide the dynamics of the upper mixed layer in determining species selection and development and the role of mesoscale circulation in bloom retention and advection in the southern benguela three upwelling centers may be distinguished all of which coincide with a narrowing of the shelf the namaqua 30us cape columbine 33us and cape peninsula 34us upwelling centers fig 1 the region to the north of the cape columbine cell is particularly susceptible to red tide formation and its negative impacts and a historical perspective of faunal mortalities associated with red tides in this region is given by cockcroft et al 2000 here topographic and bathymetric features alter current patterns and mixing regimes features considered important in the development of red tide the shelf broadens to the north of columbine favoring stratification and stability of the water column airborne radiometer studies within this region have identified upwelling off cape columbine and along the coast north of dwarskersbos jury 1985 taunton clark 1985 under conditions of upwelling an equatorward coastal jet is formed off the columbine headland but wind stress shear promotes clockwise circulation within st helena bay jury 1985 thereby favoring retentive nearsurface circulation patterns within the region holden 1985 penven et al 2000 alongshore variability of flow considered to play a dominant role in driving the southward advection of phytoplankton blooms is thought to be associated with barotropic flow inshore generated by coastally trapped waves over the southern namaqua shelf with periods of 3 to 6 d lamberth and nelson 1987

garnet pyroxene equilibria in the system cao mgo al 2 o 3 sio 2 cmas prospects for simplified t independent lherzolite barometry and an eclogite barometer new experimental data on compositions of garnets in two pyroxene garnet assemblages in the system cao mgo al2o3 sio2 cmas are presented for conditions between 1 100 and 1 570 c and 30 to 50 kb garnets in these assemblages become less calcic with increasing pressure garnet orthopyroxene barometry al solubility barometry pertinent to geobarometry for garnet lherzolites has been evaluated with a set of experimental data covering the range 900 to 1 570 c and 15 to 100 kb various formulations of this barometer work well to 75 kb phase equilibria are not sufficient to positively verify the thermodynamic validity of any of such models empirical garnet orthopyroxene barometry at least in the system cmas can be formulated to obtain a pressure estimate without previous temperature estimation p kb 34 4 19 175 1n x al m1 17 702 1n x ca m2 the potential application of an analogous garnetclinopyroxene equilibrium is limited because the amount of ca tschermaks in natural clinopyroxenes is usually quite small in garnet lherzolites and many eclogites the ca mg exchange between garnet and clinopyroxene appears however sufficiently sensitive to pressure to allow calibration of a cmas barometer the reaction 3camgsi2o6 mg3al2si3o12 3mg2si2o6 ca3al2si3o12 has a v o of 3 5 cm3 the total pressure dependency of this reaction is however closer to a theoretical v o of about 5 cm3 when excess volume properties of the phases involved are taken into account we have calibrated such a barometer mean error of estimate 2 8 kb for assemblages with pyrope rich py 80 garnets and orthopyroxenes this may provide the basis for a geobarometer for eclogites from kimberlites

volcanological and structural controls on mineralization at the mount keith and cliffs komatiite associated nickel sulfide deposits agnew wiluna belt western australia implications for ore genesis and targeting the mount keith region of the agnew wiluna belt in western australia is perhaps best known for hosting the giant komatiite associated disseminated ni sulfide deposit known as mkd5 it also hosts the sizeable cliffs massive ni sulfide deposit which is the eighth largest in the archean yilgarn block a concerted program of regional scale three dimensional model construction has integrated a plethora of geological geochemical and geophysical data and led to a much better understanding of the tectonic and volcanic architecture of this ancient greenstone belt the disseminated mkd5 orebody occupies a curvilinear thickening in the olivine adcumulate core of the host mount keith ultramafic unit the orebody plunges shallowly to the south from surface over a distance of 3 5 km before bending sharply to plunge steeply to the north northwest at depth the thickest part of the orebody and the best ni grades are associated with the bend in the overall ore trend this also marks the approximate intersection point of two growth faults that appear to control the thickness variations in the adcumulate core and the plunge variations in the ore trend the olivine adcumulate core is mantled by olivine orthocumulate rocks which are best developed above and below the flanks of the orebody and a fractionated sequence of pyroxenitic and gabbroic rocks occurs at the top of the mount keith ultramafic unit above the inside of the bend in the ore trend these observations suggest a strong volcanological control on the position of the mkd5 orebody and the local curvilinear thickening in the adcumulate core is interpreted as a fluid pathway the locus of which was in turn controlled by the intersection of two broadly orthogonal growth faults the cliffs ultramafic unit consists of a lower olivine ortho to mesocumulate unit which varies in thickness along strike overlain by a sequence of thin spinifex textured komatiite flow units intercalated with variably sulfidic tuffaceous shales the cliffs massive ni sulfide deposit occurs at the base of a relative thickening to 100 m in the lower olivine ortho to mesocumulate unit the orebody is typically less than 6 m thick 500 m wide and plunges gently south from surface over a distance of 1 5 km terminating in a structurally complex zone across which there are marked differences in the internal stratigraphy and thickness of the cliffs ultramafic unit the orebody has relatively low tenor maximum 8 ni typically 5 ni and the tenor is strongly zoned with extremely low tenors 1 3 ni developed on the flanks a barren exhalative massive fe sulfide unit is typically present at the base of the cliffs ultramafic unit on the flanks of the orebody and probably acted as a source of sulfur the tenor zonation pattern suggests that the melting and entrainment of the underlying exhalative sulfide horizon occurred more vigorously in the center of the lava pathway the structurally complex zone at the southern end of the cliffs orebody is interpreted as a possible vent location this would explain the relatively low tenor of the orebody and the tenor zonation through limited mixing and entrainment of melted exhalative iron sulfide melt with the komatiite lava the poorly incised nature of the lava pathway and the abrupt change in internal komatiite stratigraphy across this zone there is good evidence that the southern terminations of both the mkd5 and the cliffs orebodies are marked by growth faults at a belt scale these points correspond roughly with the intersection of nne and nw trending lineaments these lineaments are on the order of 5 to 10 km in strike length and are visible in regional geophysical datasets both gravity and magnetics they are likely to mark the position of accretionary structures that were active at the time of volcanism and that probably controlled the volcanic architecture of the komatiite flow field and the location of ni sulfide accumulations within komatiite lava pathways repeated reactivation of these early crustal scale structures during subsequent orogenesis resulted in their upward propagation as sets of late brittle structures of broader significance to the understanding of the generation of komatiite associated nickel sulfide deposits is the conclusion that many such deposits may be developed proximal to vent rather than in a distal setting as has been proposed for the kambalda camp

emplacement and cooling of komatiite lavas we propose that komatiite lavas were emplaced as turbulent flows accompanied by vigorous forced convection with cooling rates often in excess of hundreds of c h 1 they melted and assimilated up to 10 of the ground over which they flowed forming deep channels nickel sulphide mineralization may have resulted from incorporation of sulphur rich sediment after emplacement high cooling rates persisted resulting in spinifex textures due to compositional convection

the volcanology of komatiites as deduced from field relationships in the norseman wiluna greenstone belt western australia abstract komatiites in the western part of the norseman wiluna greenstone belt in the yilgarn block of western australia display a wide variety of volcanic facies ranging from very thin differentiated munro township type flow units through to very thick olivine rich cumulate flow units containing high proportions of adcumulate dunite cumulate flow units have been mapped in detail in the agnew wiluna segment of the norseman wiluna greenstone belt in the yakabindie and mt keith areas thick lenticular bodies of olivine adcumulate are flanked and overlain by thinner sheet like sequences of finer grained olivine orthocumulates they show fine scale internal layering broad scale cryptic layering and upper fractionated sequences containing harrisites pyroxene bearing cumulates and in some cases gabbroic derivatives low grade disseminated sulphide mineralisation occurs within the dunite lenses in the stratigraphically equivalent kathleen east area adcumulate dunite grades laterally into olivine orthocumulates and spinifex textured flows a similar relationship is also seen further south where the perseverance ultramafic complex consists of a thick central dunite lens flanked on one side by thin fine grained orthocumulate sequences and on the other by intercalated orthocumulates and spinifex textured flows these field relationships indicate an extrusive origin for the adcumulate dunite bodies the walter williams formation in the west central part of the norseman wiluna belt is a very large cumulate flow unit 150 km long and 30 km wide in presently exposed extent it consists of a central sheet like body of adcumulate dunite underlain and overlain by olivine orthocumulates the adcumulate sheet is everywhere capped by a distinctive thin layer of olivine harrisite at its northernmost extent the flow unit consists of cyclically layered olivine and pyroxene bearing cumulates capped by gabbros dolerites and pyroxene spinifex textured material interpreted as a periodically replenished lava lake sequence both the lenticular dunite bodies of the agnew wiluna belt and the sheet like dunite body of the walter williams formation are interpreted as crystallisation products of very large submarine komatiite lava flows which erupted and flowed at very high rates the adcumulate dunites are interpreted as the products of in situ crystallisation at low degrees of supercooling at the top of upward and inward accreting crystal piles at the bases of the flows flanking and overlying olivine orthocumulates reflect higher rates of heat loss at the site of crystallisation due to lower lava flow rates field evidence from perseverance and the general geometry of the dunite lenses suggest that the lenses formed within large thermal erosion channels developed by turbulent lava rivers flowing over low melting felsic volcanic substrates the textural range exhibited by komatiites can be integrated into a comprehensive model for the geometry of large komatiite flow fields formed by rapid extrusion dunite sheets form close to the eruption sites and dunite lenses as a result of channellisation further away from the vent or close to the vent in the situation where the substrate is non refractory and thermal erosion can take place readily kambalda type volcanic facies develop in more distal environments where lava emplacement is channellised and episodic and munro type flow units represent small scale lava tubes formed at low flow rates on the distal flanks of major eruptions or close to the vent of very small ones waning eruption rates leads to proximal facies being overridden by distal ones a common observation in komatiite sequences the size of thermal erosion channels requires very rapid eruption rates comparable to those in phanerozoic flood basalt terrains

yakabindie revisited volcanological and structural controls on the komatiite hosted six mile well and goliath north deposits and implications for the architecture of the 2 7 ga rift event in the agnew wiluna belt yilgarn craton western australia the yakabindie area hosts significant deposits of disseminated fe ni cu sulfide in the six mile well 2 0 mt contained ni and goliath north 0 6 mt contained ni dunite lenses these dunite lenses form part of the same komatiitic ultramafic unit that hosts the giant mount keith mkd5 deposit 2 6 mt contained ni to the north but the morphology and internal stratigraphy of the host unit differs significantly three dimensional modeling of the yakabindie region reveals that each dunite lens is located at the intersection between steeply dipping nnw and nne trending synvolcanic faults which appear to have acted as conduits from which komatiitic lava vented onto the seafloor the igneous contacts dip more shallowly to the west and describe a w facing wedge of olivine cumulate rock probably less than 1 km in plunge extent and cored by adcumulate rock the mineralization at both six mile well and goliath north consists of multiple stacked lenses of disseminated fe ni cu sulfide associated with the olivine adcumulate core this core is interpreted as the pathway position that focused the flow of komatiite lava away from the vent rather than being linked by sheeted bodies of orthocumulate rocks as is typically the case along strike to the north the dunite lenses at yakabindie appear to be capped by a strike continuous sequence of thin komatiite flow units there is no evidence of the fractionated sequences of pyroxenite and dolerite which occur in pathway positions within the mount keith ultramafic unit to the north and which reflect late stage ponding and in situ fractionation of komatiite lava three sets of synvolcanic structures are recognized in the broader agnew wiluna belt and a model of oblique extension at ca 2 7 ga is proposed a nnw trending set of structures marks the overall rift orientation at ca 2 7 ga but is probably inherited from an earlier ca 2 81 ga phase of rifting a nw trending set is thought to represent ca 2 7 ga transfer faults but may also have much older roots these structures produce marked sinistral offsets in both the greenstone stratigraphy and the gravity response and can be used to divide the agnew wiluna belt into rift segments the third set of early structures trends nne subparallel with the volcanic grain of the greenstones as inferred from the orientation of komatiite lava pathways these are thought to have originated as extension orthogonal normal faults at ca 2 7 ga at the regional scale there is a strong spatial association between the larger fe ni cu sulfide deposits of the agnew wiluna belt and the locus of postulated nw trending transfer zones whereas at the deposit scale intersecting nw and nne trending synvolcanic faults exert a control on the location and best development in terms of thickness and or grade of fe ni cu sulfide mineralization in some deposits these spatial associations have major implications for exploration targeting at both regional and deposit scale

archean komatiite volcanism controlled by the evolution of early continents the generation and evolution of earth s continental crust has played a fundamental role in the development of the planet its formation modified the composition of the mantle contributed to the establishment of the atmosphere and led to the creation of ecological niches important for early life here we show that in the archean the formation and stabilization of continents also controlled the location geochemistry and volcanology of the hottest preserved lavas on earth komatiites these magmas typically represent 50 30 partial melting of the mantle and subsequently record important information on the thermal and chemical evolution of the archean proterozoic earth as a result it is vital to constrain and understand the processes that govern their localization and emplacement here we combined lu hf isotopes and u pb geochronology to map the four dimensional evolution of the yilgarn craton western australia and reveal the progressive development of an archean microcontinent our results show that in the early earth relatively small crustal blocks analogous to modern microplates progressively amalgamated to form larger continental masses and eventually the first cratons this cratonization process drove the hottest and most voluminous komatiite eruptions to the edge of established continental blocks the dynamic evolution of the early continents thus directly influenced the addition of deep mantle material to the archean crust oceans and atmosphere while also providing a fundamental control on the distribution of major magmatic ore deposits

komatiitic sills and multigenerational peperite at dundonald beach abitibi greenstone belt ontario volcanic architecture and nickel sulfide distribution the density and the tectonic stresses in the deep crust and the physical properties of komatiitic magmas determine the level to which they will rise but once in the near surface environment the density and rheology of the near surface rocks consolidated and dense lava flows and sedimentary rocks versus unconsolidated sedimentary or volcaniclastic deposits govern whether they will be emplaced as lava flows invasive flows or sills where near surface strata are competent i e flow dominated or consolidated sedimentary and or volcaniclastic successions komatiitic magma erupts as flows that form extensive lava shields e g kambalda however where near surface strata are not competent i e unconsolidated volcaniclastic and or sediment dominated successions komatiitic magmas typically are emplaced as high level sills that increase the bulk density of the volcano sedimentary pile and eventually allow the eruption of lava and the construction of complex sub volcanic volcanic lava shields e g dundonald and shaw dome abitibi belt raglan cape smith belt pechenga kola peninsula thompson ni belt manitoba the latter environment is illustrated in the volcano sedimentary succession in dundonald township which is only weakly metamorphosed and deformed and superbly exposed in glacially polished outcrops the volcano sedimentary succession in this area comprises from base to top 1 the mcintosh formation composed of a succession of pillowed and massive intermediate volcanic flows 2 the dundonald formation composed of a lower section of komatiite sills argillites and felsic volcaniclastic deposits and an upper section of komatiite flows komatiitic sills and pillowed intermediate volcanic flows and 3 the frederick house lake formation composed of massive and pillowed mafic flows the distribution and thickness of argillites and felsic volcaniclastic rocks define a synvolcanic graben in which the dundonald south and alexo ni cu pge deposits occur within the center and the margin respectively sills and peperites in the lower komatiitic succession at dundonald beach exhibit a multigenerational emplacement history recording progressive lithification and increases in the bulk density and rheological strength of the unconsolidated argillites which ultimately permitted the eruption of lavas at alexo importantly the nature of the near surface rocks also influences the localization of ni cu pge deposits in lava shields e g kambalda the initial eruptions are typically most voluminous and if erupted at sufficient flow rates form channelized flows conducive to thermomechanical erosion of sulfur rich footwall rocks in sub volcanic volcanic lava shields however channelized units may occur within the subvolcanic plumbing system and or within overlying lavas where only sills are channelized e g thompson mineralization will occur only within the subvolcanic environment where only the flows are channelized e g damba silwane zimbabwe mineralization will occur only within the volcanic environment where both sills and lava flows are channelized e g dundonald shaw dome raglan the distribution of the mineralization is more diverse and may occur as subsea or sea floor ni cu pge deposits

petrology of two diamondiferous eclogite xenoliths from the lahtojoki kimberlite pipe eastern finland abstract diamondiferous group a eclogites constitute a minor portion of the mantle derived xenoliths in the eastern finland kimberlites they have been derived from the depth interval 150 230 km where they are inferred to occur as thin layers or small pods within coarse grained garnet peridotites the chemical and isotopic composition of minerals suggest that they represent proterozoic mantle derived melts or cumulates rather than subducted oceanic lithosphere during magma ascent and emplacement of the kimberlites the eclogite xenoliths were mechanically and chemically rounded judging from the types of surface markings in addition those octahedral crystal faces of diamonds that were partially exposed from the rounded eclogite xenolith became covered by trigons and overlain by microlamination due to their reaction with the kimberlite magma the diamonds bear evidence of pervasive plastic deformation which is not however evident in the eclogite host this suggests that annealing at ambient lithospheric temperatures has effectively recrystallised the silicates while the diamond has retained its lattice imperfections and thus still has the potential to yield information about ancient mantle deformation one of our samples is estimated to contain approximately 90 000 ct ton diamond implying that some diamonds occur within very high grade pods or thin seams in the lithospheric mantle to our knowledge this is one of the most diamondiferous samples described

the role of early formed structures on the development of the world class st ives goldfield yilgarn wa a revised structural interpretation for the victory to kambalda area of the world class st ives goldfield in the archean yilgarn craton has mapped out the distribution of wnw trending faults within this area of the field these previously cryptic wnw trending structures had been identified in gravity data and also by isopach thickness variations the wnw trending faults acted as transfers syn gold mineralization although only discrete segments of these faults were active during the main stage of gold mineralization where mineralized the faults transferred strain from a complex combination of block on block movement associated with thrusting and strike slip movement on nw and n trending faults along some segments n trending mineralized faults terminate against the wnw trending faults many of the wnw trending faults correlate with major strike changes on regional and camp scale faults and they are domain boundaries for the critical n trending fault segments that host high grade gold within contractional jogs the wnw trending faults also show evidence for an older deformation history prior to main stage gold which may extend back to early basin development associated with ultramafic and mafic volcanism they are inferred to have been a series of early wnw trending normal faults and breached relay ramps associated with oblique rifting along an older nnw trending basement boundary

hydrographic variability in the st helena bay region of the southern benguela ecosystem cross shelf distributions of temperature salinity water masses and dissolved oxygen in st helena bay revealed substantial vertical and seasonal variations in the surface layers nearshore and offshore temperature and salinity patterns differed with bay scale variability linked to upwelling dynamics and coastal processes while the offshore region was influenced by solar insolation spectral analysis revealed that an annual signal prevailed at most stations and corroborated contrasting patterns between the offshore and nearshore regions with phase differences suggesting shoreward propagation of the offshore temperature signal the shelf was dominated by modified upwelled water muw and subantarctic mode water samw which comprised the primary source of upwelled water clear zonation of muw was evident across the shelf resulting from seasonal variations in locations of the oceanic and bifurcated shelf break fronts dynamics within st helena bay consistently differed from those further offshore due to the influences of the shelf break front cape columbine upwelling plume and cyclonic recirculation which appeared to be associated with an intraannual signal with a periodicity of 3 4 months persistent hypoxia in the bottom waters suggested the occurrence of a permanent reservoir of low oxygen water low seasonal shoreward and offshore expansion of low occurred throughout the upwelling season with maximum extent reached during summer and autumn due to the coupled effects of advection and local phytoplankton decay while wind mixing ventilated the water column at nearshore stations in winter and the onset of upwelling during spring introduced oxygen richer water from further offshore hypoxia persisted in the center of the bay

experimentally determined compositions of diopside jadeite pyroxene in equilibrium with albite and quartz at 1200 1350 c and 15 34 kbar abstract equilibrium compositions of diopside jadeite pyroxene coexisting with albite and quartz were experimentally determined at 25 different p t conditions using an electron microprobe for analysis the new data and the 600 c data of holland 1983 provided the following mixing properties of the diopside di jadeite jd solid solution j k g xs x jd x di 12600 9 45 t 12600 7 6 t x jd x di 21400 16 2 t x jd x di 2 the di jd solution is close to ideal above 1000 c but immiscible below 565 c the di jd solvus is slightly asymmetric with the crest at composition di 42 4 jd 57 6 excess enthalpy is positive but smaller than indicated by the enthalpy of solution measurements of wood et al 1980 disorder in the di jd solution is significantly smaller than complete disorder implied by the ionic two site model

dynamics of evolving magma chambers textural and chemical evolution of cumulates at the arrival of new liquidus phases abstract basaltic magma chambers are best exemplified by layered intrusions fossilized natural laboratories that historically constrain most fundamental principles of igneous petrology progressive fractional crystallization of basaltic melts in layered intrusions results in successive appearance of 5 10 liquidus minerals most minerals appear in the stratigraphy of layered intrusions via two distinct stages they first emerge as oikocrysts large irregularly shaped and interstitial crystals that form in a crystal liquid framework and then as primocrysts relatively small idiomorphic and cumulus crystals that crystallize from a main magma body the transition from oikocrysts to primocrysts is commonly marked by the following textural and chemical features a a similarity in chemical composition of the last forming oikocrysts and the first forming primocrysts b slow arrival modal overabundance and finer than normal size of the first primocrysts c a low abundance of trapped liquid in rocks with the first forming primocrysts d a step like increase in mineral dihedral angle in rocks slightly below the level of the primocryst arrival and e the rims on plagioclase primocrysts that are identical in composition to cores of plagioclase primocrysts at the first appearance of new liquidus phases higher up in the section the phase equilibria control on the cumulus stratigraphy of layered intrusions require large long lived and largely molten magma chambers and therefore their origin is not compatible with several recent concepts that deny the existence of such reservoirs in the earth s crust we therefore suggest that the systematic changes associated with the arrival of cumulus phases in layered intrusions are best explained by a traditional concept that considers layered intrusions as large initially crystal free melt bodies that gradually lose heat and crystallize from margins inwards through thin solidification fronts the entire magma body during its internal evolution is thought to be kinetically supercooled i e kept slightly below its liquidus temperature with respect to cumulus phases that crystallize at the margins each new cumulus phase arrives on the liquidus with some kinetic delay and nucleates heterogeneously against pre existing crystals at the floor roof and sidewalls of basaltic magma chambers this implies that internal differentiation of basaltic magma chambers mostly occurs through convective separation of evolved liquid from in situ growing crystals and its mixing with the main magma body

calculation and application of clinopyroxene garnet plagioclase quartz geobarometers recently published thermodynamic and experimental data in a variety of chemical systems have been evaluated to derive gibbs free energies for hedenbergite and pyrope these were used to calculate the geobarometric equilibria

excess silica in omphacite and the formation of free silica in eclogite silica lamellae in eclogitic clinopyroxene are widely interpreted as evidence of exsolution during decompression of eclogite however mechanisms other than exsolution might produce free silica and the possible mechanisms depend in part on the nature and definition of excess silica excess silica may occur in both stoichiometric and non stoichiometric pyroxene although the issue has been debated we show that all common definitions of excess silica in non stoichiometric clinopyroxene are internally consistent interchangeable and therefore equivalent the excess silica content of pyroxene is easily illustrated in a three component condensed composition space and may be plotted directly from a structural formula unit or recalculated end members in order to evaluate possible mechanisms for the formation of free silica in eclogite we examined the net transfer reactions in model eclogites using a thompson reaction space we show that there are at least three broad classes of reactions that release free silica in eclogite i vacancy consumption in non stoichiometric pyroxene ii dissolution of ti phases in pyroxene or garnet iii reactions between accessory phases and either pyroxene or garnet we suggest that reliable interpretation of the significance of silica lamellae in natural clinopyroxene will require the evaluation not only of silica solubility but also of titanium solubility and the possible roles of accessory phases and inclusions on the balance of free silica

komatiites of the wildara leonora belt yilgarn craton wa the missing link in the kalgoorlie terrane abstract the wildara leonora belt in the kalgoorlie terrane is located between the world class nickel provinces of the agnew wiluna belt to the north and the kambalda domain to the south it extends from the wildara station to the gold mining center of leonora and consists of a deformed package of mafic komatiitic and sedimentary rocks this package of rocks which hosts a number of small nickel sulfide occurrences has been explored extensively for komatiite hosted nickel deposits most recently within the sullivans unit in the south east of the wildara leonora belt lithostratigraphic similarities together with shared physical geochemical and textural properties support a common affiliation between the wildara leonora and the agnew wiluna belts on this evidence the wildara leonora belt represents the southern extension of the largest komatiite hosted nickel camp in the world the apparently lesser prospectivity for nickel sulfide deposits is interpreted as a consequence of contrasting volcanic facies assemblages komatiites in the wildara leonora belt present geochemical and volcanological characteristics consistent with turbulent lava flow emplacement however compared with the agnew wiluna belt the wildara leonora belt komatiites are not spatially associated with felsic volcanic units but rather overlie a thick sequence of pillowed basalts and sulfidic sediments the lower proportion of adcumulate greater degrees of fractionation and lower degrees of contamination are consistent with komatiites in the wildara leonora belt having been emplaced in a more distal position to the rift environment with lower magma flux and more tranquil emplacement than the agnew wiluna belt komatiites and consequently having lower potential for giant nickel sulfide deposits such as those at perseverance and mt keith

palynological evidence for holocene climatic and oceanographic changes off western south africa abstract atmospheric and oceanographic interactions between the atlantic and indian oceans influence upwelling in the southern benguela upwelling system in order to obtain a better knowledge of paleoceanographic and paleoenvironmental changes in the southern benguela region during the holocene 12 marine surface sediment samples and one gravity core geob8331 4 from the namaqualand mudbelt off the west coast of south africa have been studied for organic walled dinoflagellate cysts in high temporal resolution the results are compared with pollen and geochemical records from the same samples our study emphasizes significantly distinct histories in upwelling intensity as well as the influence of fluvial input during the holocene three main phases were identified for the holocene high percentages of cysts produced by autotrophic taxa like operculodinium centrocarpum and spiniferites spp indicate warmer and stratified conditions during the early holocene 9900 8400 cal yr bp suggesting reduced upwelling likely due to a northward shift of the southern westerlies in contrast the middle holocene 8400 3100 cal yr bp is characterized by a strong increase in heterotrophic taxa in particular lejeunecysta paratenella and echinidinium spp at the expense of autotrophic taxa this indicates cool and nutrient rich waters with active upwelling probably caused by a southward shift of the southern westerlies during the late holocene 3100 cal yr bp to modern brigantedinium spp and other abundant taxa interpreted to indicate fluvial nutrient input such as cyst of protoperidinium americanum and lejeunecysta oliva imply strong river discharge with high nutrient supply between 3100 and 640 cal yr bp

geochemistry of komatiites from forrestania southern cross province western australia evidence for crustal contamination the 2 9 ga old forrestania greenstone belt is intermediate in character between typical 3 0 ga and 2 7 ga belts in containing both al depleted and al undepleted komatiites the extensive nickel exploration database on the belt provides a unique opportunity to examine geochemical variations in the context of volcanological evolution within each of the six komatiitic units in the greenstone belt there is a transition from komatiites 18 28 wt mgo in the liquid to high and low magnesium komatiitic basalts 5 18 wt mgo with stratigraphic height and much of the chemical variance within the komatiitic suite can be explained in terms of the addition or fractionation of olivine there are however aspects of the incompatible element signatures which must be attributed to other factors the more primitive komatiites from the lower ultramafic units are al depleted al2o3 tio2 10 5 13 0 and depleted in both light and heavy ree lasmn 0 5 gdybn 1 5 komatiites from the uppermost ultramafic units are variably less depleted in al al2o3tio2 16 5 20 5 this is interpreted to reflect decreasing retention of garnet in the source region of the forrestania komatiites over time and possibly a decrease in the depth of melting within the al depleted suite there are also anomalous enrichments in sio2 feo tio2 and zr which correlate with regional variations in the composition of substrate metasedimentary rocks banded iron formation versus felsic tuff coupled with field evidence for trough structures at the base of lava channel sequences these chemical anomalies provide strong evidence for supracrustal thermal erosion by komatiite lavas the forrestania data indicate that 2 9 ga old komatiites were generated over a range of melting conditions spanning those typical of older and younger archaean sequences and that contamination by supracrustal thermal erosion can influence komatiite chemistry on a regional scale

subtropical mode waters in the south atlantic ocean this systematic study of the subtropical mode waters in the south atlantic is based on hydrological data the basin wide south atlantic ventilation experiment oceanus and ajax sections and the world ocean circulation experiment woce sections in the brazil malvinas confluence region the woce expendable bathythermograph data set and the atmospheric forcing produced by the national centers for environmental prediction reanalysis the main ventilation window of the subtropical gyre lies in the southwest and corresponds to the southern part of the recirculation region and to the overshoot of the brazil current bc some ventilation occurs along the southern branch of the gyre through deep mixed layers in harsh winters and in the east through the rings shed by the agulhas current however the ventilation from the eastern border concerns a small volume of water with highly variable characteristics three main types of subtropical mode water are observed the lightest around the 26 2 density surface and the second and third around the 26 5 and 26 7 density surfaces respectively the 26 2 subtropical mode water stmw1 corresponds to potential temperatures between 16 and 18 c and salinities between 35 9 and 36 2 the stmw1 thickness does not exceed 150 m the volume of the 26 5 mode water stmw2 is larger it is produced through the formation of deep mixed layers reaching 300 m or more in the active ventilation window over the bc overshoot its potential temperature ranges between 14 and 16 c and its salinity ranges between 35 5 and 35 9 its thickness can be above 300 m the last component observed around the 26 7 density surface stmw3 has a potential temperature between 12 and 14 c and a salinity of about 35 2 to 35 5 it is formed on the eastern flank of the bc overshoot and during harsh winters in the center of the southern branch of the gyre within the main ventilation window the stmws exhibit quite a significant variability in characteristics and volume there is a large interannual variability in the atmospheric forcing over the bc recirculation and bc extension and the observed variations of the subtropical mode waters are qualitatively correlated to the atmospheric forcing variations

contemporaneous ultramafic and felsic intrusive and extrusive magmatism in the archaean boorara domain eastern goldfields superterrane western australia and its implications abstract two komatiite emplacement styles are recognized in the boorara domain of the kalgoorlie terrane eastern goldfields superterrane yilgarn craton western australia 1 large volume dominantly cumulate textured komatiite bodies interpreted as high level intrusions based on the presence of symmetrical spinifex cumulate textural zonation together with apophysy injection and xenolith incorporation along the top and basal margins of the komatiite 2 extrusive komatiite lavas exhibit asymmetrical textural zonation with the top chilled flow margin preserving a fine grained fractured crust that coarsens downward into a supercooled former olivine spinifex zone and then into pseudomorphed olivine now serpentine orthocumulate texture above a thin basal chilled margin the intrusive komatiite unit is observed to be intercalated with quartz and feldspar phyric dacite the two lithologies exhibit primary irregular contacts against each other komatiite apophyses have been injected into the dacite and magma mingling has occurred these features are indicative of liquid liquid interaction between the two units and komatiite magmatism is interpreted to have been contemporaneous with dacitic magmatism the dacite was emplaced first and the komatiite intruded the dacite before it solidified the reconstructed stratigraphy of the boorara domain comprises a basal unit of quartzofeldspathic turbidite beds conformably overlain by high mg tholeiite basalt the intercalated dacite and komatiite units overlie the lower tholeiitic basalt with an unobserved contact an upper komatiitic basalt unit overlies the komatiite and at the stratigraphic top of the sequence are felsic volcaniclastic turbidite units with felsic porphyry intrusions these greenstone lithologies were emplaced within a deep submarine basin as indicated by carbonaceous metapelite units intercalated throughout the sequence the tectonic scale processes operating in and around the boorara domain depocentre include derivation of the komatiite unit from a likely mantle plume source the contemporaneous dacite magmatism is interpreted to be the result of melting of pre existing archaean crust during plume ascension although the exact composition of the primitive crust is yet to be determined

the benguela a laboratory for comparative modeling studies abstract equilibrium dynamics of the benguela system is investigated using the holistic nature of the spatially and temporally cohesive output of a numerical model the regional ocean modeling system roms is used to simulate the benguela system in its entirety it successfully simulates the cool coastal upwelling regime and its division into seven distinctly separate cells as well as the large scale offshore regime and the respective seasonal fluctuations it does however present a cool bias at the coast due to an underestimation of the coastal wind drop off as well as a warm bias offshore in the southern benguela due to the overestimation of agulhas current input the benguela can be divided into northern and southern regimes based on dynamic as well as topographic differences topographically the division between the northern and southern regimes coincides with an abrupt narrowing of the continental shelf toward the north at 28 s the large scale depth integrated flow to the north of this feature is weak but distinctly poleward while to the south the flow regime is governed by the meandering nature of the equatorward benguela current and is the pathway for eddies that originate at the agulhas retroflection the poleward flowing regime of the northern benguela is tied to the sverdrup relation which links meridional transport with wind stress curl the luderitz upwelling cell at 27 s experiences the most vigorous upwelling throughout the year and as a result offshore volume fluxes in this region are extremely large this upwelling cell divides the northern and southern benguela coastal upwelling systems into separate regimes based on the fact that their seasonal signals are out of phase the offshore gradient of eddy kinetic energy eke is generally strong in the benguela system and exceptionally so in the southern benguela due to vigorous mesoscale activity offshore of the shelf edge originating from the agulhas retroflection area the juxtaposition between the steep offshore eke gradients in the south and much weaker offshore gradients of eke in the northern benguela has different implications for cross shore exchanges

the association between ni cu pge sulfide and ni co lateritic ores and volcanic facies within the komatiites of the 2 7 ga east yilgarn craton large igneous province western australia abstract a critical factor in the generation of komatiite hosted ni cu pge sulfide deposits the addition of external sulfur via assimilation of s bearing substrate beneath channelised lava flows is a function of the komatiite flow field architecture this architecture is also critical in the development of magnesium rich bedrock lithologies that are prerequisites for the formation of komatiite hosted ni co laterite deposits to better understand the controls on the spatial distribution of both these deposit types a gis referenced map of komatiite flow regimes within the komatiitic component of the c 2 7 ga east yilgarn large igneous province and from parts of adjacent older greenstone belts in the yilgarn craton has been constructed using data from the field and the literature the regimes essentially divide komatiite sequences into those composed of thin 0 5 100 m laterally restricted 50 m 3 km cooling units and those composed dominantly of thick 100 m 1 km and laterally extensive 3 100 km cooling units the regimes are subdivided into six facies and five sub facies based on both stratigraphic and lateral variations in lithologies the facies define regional scale variations reflecting markedly different spatial and temporal crystallisation conditions within komatiite flow fields there is a marked spatial association between known magmatic nickel sulfides and particular komatiite facies facies favourable for hosting magmatic sulfides are those that contain early formed very magnesian cumulate sequences requiring high effusion rates of very hot turbulently flowing lava to form and thus have the potential to be contaminated by s bearing substrate rocks sulfide mineralised komatiites make up about 9 of the area of the current outcrop of the 2705 ma komatiite lip facies that have a low potential for nickel sulfide mineralisation are sheet like bodies in which basal rocks were emplaced under relatively quiescent conditions and where hot turbulently flowing lava and crystallisation of olivine rich cumulates developed only after the build up of a pile of high porosity olivine cumulates allowing no interaction with the substrate nickel cobalt laterite deposits are associated with thick originally laterally extensive high magnesian sequences some such sequences are also favourable for magmatic sulfide mineralisation but others occur in sheet like sequences

tissintite ca na alsi2o6 a highly defective shock induced high pressure clinopyroxene in the tissint martian meteorite tissintite is a new vacancy rich high pressure clinopyroxene with a composition essentially equivalent to plagioclase it was discovered in maskelynite shocked plagioclase and is commonly observed included within or in contact with shock melt pockets in the tissint meteorite a depleted olivine phyric shergottite fall from mars the simple composition of tissintite an58 69 and its precursor plagioclase an59 69 together with the limited occurrence both spatially only in maskelynite less than 25 m of a shock melt pocket and in terms of bulk composition make tissintite a goldilocks phase it formed during a shock event severe enough to allow nucleation and growth of vacancy rich clinopyroxene from a melt of not too calcic and not too sodic plagioclase composition that was neither too hot nor too cold with experimental calibration these limitations on occurrence can be used to place strong constraints on the thermal history of a shock event the kinetics for nucleation and growth of tissintite are probably slower for more sodic plagioclase precursors so tissintite is most likely to occur in depleted olivine phyric shergottites like tissint and other highly shocked meteorites and lunar and terrestrial rocks that consistently contained calcic plagioclase precursors in the appropriate compositional range for a shock of given intensity tissintite ca 0 45 na 0 31 0 24 al 0 97 fe 0 03 mg 0 01 si 1 80 al 0 20 o6 is a c2 c clinopyroxene containing 42 60 mol of the ca eskola component by far the highest known the cell parameters are 9 21 17 a b 9 09 4 a c 5 20 2 a 109 6 9 v 410 8 a 3 z 4z 4 the density is 3 32 g cm 3 and we estimate a cell volume for the ca eskola end member pyroxene of 411 13 a 3 which is consistent with a previous estimate and therefore supports the importance of this component in clinopyroxenes from ultra high pressure metamorphic rocks from the earth s upper mantle at least in c2 c clinopyroxenes as sodic as tissintite the a and b cell parameters as a function of vacancy concentration intersect at 0 3 vacancies pfu much lower than the ca eskola end member 0 5 an inversion of anisotropy suggesting an elastic instability that drives clinopyroxene toward a disordered trigonal structure closely related to that of wadeite it may mark the boundary beyond which the breakdown of vacancy rich clinopyroxene to a wadeite structured phase stishovite becomes stable although this was not observed in tissint