metasomatic replacement in the skaergaard intrusion east greenland preliminary observations abstract several unusual types of replacement structures in the layered series and marginal border series of the skaergaard intrusion indicate that metasomatic changes have altered the modal proportions and in places the mineral composition of the gabbro the geometrical forms and compositional patterns of these features indicate that they result from reactive fluids moving through the rocks at high temperatures shortly after the magma had reached an advanced stage of crystallization the principal effect of metasomatism has been to produce strongly contrasting mafic and felsic rocks

a unified approach to orbital solar and lunar forcing based on the earth s latitudinal insolation temperature gradient widespread empirical evidence suggests that extraterrestrial forcing influences the earth s climate but how this could occur remains unclear here we describe a new approach to this problem that unifies orbital solar and lunar forcing based on their common control of the earth s latitudinal insolation gradient lig the lig influences the climate system through differential solar heating between the tropics and the poles that gives rise to the latitudinal temperature gradient ltg which drives the earth s atmospheric and wind driven ocean circulation we use spectral analysis of recent changes in the earth s ltg to support earlier work on orbital timescales davis and brewer 2009 that suggests the climate system may be unusually sensitive to changes in the lig identification of lig forcing of the ltg is possible because the lig varies according to seasonally specific periodicities based on obliquity in summer 41 kyr orbital and 18 6 yr lunar cycle and precession 21 kyr orbital cycle and total solar irradiance 11 yr solar cycle in winter we analyse changes in the northern hemisphere ltg over the last 120 years and find significant 99 peaks in spectral frequencies corresponding to 11 years in winter and 18 6 years in summer consistent with lig forcing the cross seasonal and multi frequency nature of the lig signal and the diffuse effect of the ltg driver on the climate system may account for the complexity of the response to extraterrestrial forcing as seen throughout the climatic record this hypersensitivity of the ltg to the lig appears poorly reproduced in climate models but would be consistent with the controversial theory that the ltg is finely balanced to maximise entropy c 2011 elsevier ltd all rights reserved

geochemistry of cumulates from the bjerkreim sokndal layered intrusion s norway part ii ree and the trapped liquid fraction rare earth elements in bulk cumulates and in separated minerals plagioclase apatite ca poor and ca rich pyroxenes ilmenite and magnetite from the bjerkreim sokndal layered intrusion rogaland anorthosite province sw norway are investigated to better define the proportion of trapped liquid and its influence on bulk cumulate composition in leuconoritic rocks made up of plagioclase ca poor pyroxene ilmenite fmagnetite folivine where apatite is an intercumulus phase even a small fraction of trapped liquid significantly affects the ree pattern of the bulk cumulate together with cumulus minerals proportion and composition contrastingly in gabbronoritic cumulates characterized by the presence of cumulus ca rich pyroxene and apatite cumulus apatite buffers the ree content la sm and eu eu vs p2o5 variations in leuconorites display mixing trends between a pure adcumulate and the composition of the trapped liquid assumed to be similar to the parental magma assessment of the trapped liquid fraction in leuconorites ranges from 2 to 25 and is systematically higher in the north eastern part of the intrusion the likely reason for this wide range of tlf is different cooling rates in different parts of the intrusion depending on the distance to the gneissic margins the ree patterns of liquids in equilibrium with primitive cumulates are calculated with mass balance equations major elements modelling duchesne j c charlier b 2005 geochemistry of cumulates from the bjerkreim sokndal layered intrusion s norway part i constraints from major elements on the mechanism of cumulate formation and on the jotunite liquid line of descent lithos 83 299 254 permits calculation of the ree content of melt in equilibrium with gabbronorites partition coefficients for ree between cumulus minerals and a jotunitic liquid are then calculated calculated liquids from the most primitive cumulates are similar to a primitive jotunite representing the parental magma of the intrusion taking into account the trapped liquid fraction calculated from the p2o5 content consistent results demonstrate the reliability of liquid compositions calculated from bulk cumulates and confirm the hypothesis that the trapped liquid has crystallized as a closed system without subsequent mobility of ree in a migrating interstitial liquid d 2005 elsevier b v all rights reserved

the lower zone critical zone transition of the bushveld complex a quantitative textural study the lower zone critical zone boundary of the bushveld complex is an intrusion wide major stratigraphic transition from ultramafic harzburgite and pyroxenite in the lower zone to increasingly plagioclase richpyroxenitesandnoritesinthecriticalzone quantitative textural and compositional data for 29 samples through this transition show the following lower zone orthopyroxene grains are larger have higher aspect ratios are better foliated and have a lower trapped liquid component than those of the critical zone the larger grain size of the lower zone results in crystal size distribution plots that are rotated to lower slopes and intercepts relative to those in the critical zone although all rocks show differing amountsoffoliation mineral lineations are weak to absent these data are consistent with significant compaction driven recrystallization in the study section numerical modeling of concurrent compaction and crystallization provides a quantitative model of how the lower zone critical zone transition may have formed plagioclase is rare in the lower zone because compaction removes interstitial liquid before it reaches plagioclasesaturation however asthecrystalpilegrows plagioclase saturation is reached in the interstitial liquid before compaction is complete in more evolved pyroxenites producing more abundant but still modest amounts of plagioclase characteristic of the lower critical zone it is concluded that both the textures and the modal mineralogy are largely controlled by compaction and compactiondriven recrystallization primary magmatic textures are not preserved

bubble migration in a compacting crystal liquid mush recent theoretical models have suggested that bubbles are unlikely to undergo significant migration in a compaction crystal mush by capillary invasion while the system remains partly molten to test this experiments of bubble migration during compaction in a crystal liquid mush were modeled using deformable foam crystals in corn syrup in a volumetric burette compacted with rods of varying weights a bubble source was provided by sodium bicarbonate alka seltzer large bubbles several crystal sizes are pinched by the compacting matrix and become overpressured and deformed as the bubbles experience a load change from hydrostatic to lithostatic once they begin to move they move much faster than the compaction driven liquid bubbles that are about the same size as the crystals but larger than the narrower pore throats move by deformation or breaking into smaller bubbles as they are forced through pore restrictions bubbles that are less than the typical pore diameter generally move with the liquid the liquid bubble mixture behaves as a single phase with a lower density than the bubble free liquid and as a consequence it rises faster than bubble free liquid and allows for faster compaction the overpressure required to force a bubble through the matrix max grain size 5 mm is modest about 5 and it is estimated that for a grain size of 1 mm the required overpressure would be about 25 using apatite distribution in a stillwater olivine gabbro as an analog for bubble nucleation and growth it is suggested that relatively large bubbles initially nucleate and grow in liquid rich channels that develop late in the compaction history overpressure from compaction allows bubbles to rise higher into hotter parts of the crystal pile where they redissolve and increase the volatile content of the liquid over what it would have without the bubble migration leading to progressively earlier vapor saturation during crystallization of the interstitial liquid bubbles can also move rapidly by surfing on porosity waves that can develop in a compacting mush

occurrence and petrological significance of graphite in the upper critical zone western bushveld complex south africa abstract graphite occurs as a major rock forming constituent in pyroxenitic pegmatites near the platiniferous merensky reef in the western bushveld it is associated with amphibole biotite low k phyllosilicates chlorite sulphides and platinum group minerals rhass irass locally rocks with up to 80 graphite occur chlorine is a significant constituent in both hydrous silicates 0 1 0 3 cl and graphite 0 2 1 9 magnetite and quartz also occur with the above association this facilitates estimation oft 500 600 c andfo2 10 21 to 10 23 bar during graphite deposition which took place from c o h s fluids at an oxygen fugacity in the vicinity of qmf in equilibrium with maximum h2o mole fraction the latter accounts for the widespread association of graphite with hydrous silicates there is evidence for buffering offo2 of the melt by fluid phase this process may be more widespread than hitherto assumed c o h s fluids are considered instrumental not only in the formation of graphite rich pegmatites and associated mineralization but also in the genesis of pothole depressions and in the general development of stratiform pegmatites such as the merensky reef in layered igneous complexes

the influence of the thick banded series anorthosites on the crystallization of the surrounding rock of the stillwater complex montana the banded series of the archean aged stillwater complex contains three thick anorthosites overlain by olivine bearing rocks with apparently different crystallization sequence in that orthopyroxene appears late if at all as compared with that of the ultramafic and lower banded series where orthopyroxene appears before plagioclase conventional models suggest that the rocks above the anorthosites represent injection of a magma with a different liquid line of descent than the rest of the complex alternatively it has been suggested that the plagioclase pyroxene mush protolith above the anorthosites was hydrated by the degassing of the underlying thick anorthosite units to produce olivine rather than pyroxene by either expansion of the olivine phase field by addition of h2o incongruent melting of pyroxene and or silica loss to the vapor to test for hydration melting and a late silica loss electron microprobe core rim analyses were done on plagioclase grains from troctolite of olivine bearing zone v ob v approximately a dozen grains were analyzed for each of six thin sections in total 69 pairs were reversely zoned and 22 were normal or unzoned the most negative an difference was 8 25 the most positive was 4 32 but the majority of pairs were clustered from 5 to 1 the average was 2 1 core grains had an average an number of 77 8 typical for other plagioclase from the middle banded series a green na rich hornblende is commonly associated with plagioclase where the latter is enclosed in olivine the prevalence of reversely zoned grains is consistent with silica and sodium loss from pre existing plagioclase this evidence as well as the lack of plagioclase core compositions being reset to more primitive an rich compositions the amoeboidal poikilitic habit of the olivine and the presence of amphibole are all consistent with the troctolite and olivine gabbro of the middle banded series and lower parts of the upper banded series having formed as the result of a combination of processes including hydration incongruent melting and element leaching during degassing of the underlying anorthosites

investigations of the stillwater complex part v apatites as indicators of evolving fluid composition variations in the f cl and oh contents of apatite are not constrained by crystal chemical factors in contrast to micas and amphiboles and thus changes in the abundance of these components provide an indicator of halogen fugacity variations and insights into the degassing history of igneous rocks microprobe analysis of intercumulus apatites from the stillwater complex reveal that cl rich apatites typically containing 6 0 wt cl occur throughout the lower 1 3 of the complex excluding the basal series a change from cl rich to more f rich apatite occurs within olivine bearing zone i ob i of the banded series the host zone of the platiniferous j m reef although apatite compositions are somewhat variable above the j m reef more f rich apatites predominante and typically contain 1 2 wt f and 3 0 wt cl the most f rich apatites occur in the uppermost exposed cumulates pristine apatites from coeval sills and dikes from below the complex and from the basal series are similarly f rich in all apatites the cl and f contents are lower in rocks affected by later metamorphic fluids rare earth element ree concentrations in chlorapatites show a marked peak in the olivine rich rocks of the j m reef and contain up to 2 wt ce2o3 la2o3 the trend of first increasing then decreasing cl f ratios with stratigraphic height is modeled by a vapor driven zone refining process occurring within the cumulate pile causing cl enrichment in the interstitial melt accompanied by degassing at the top of the magma chamber causing overall loss of cl from the magma as crystallization proceeded the abrupt change from cl rich to more f rich apatites within ob i is interpreted as the result of a breakdown of the cl rich zone refining front and mixing with cl poor supernatant melt any high temperature fluids that exsolved and circulated through the lower 1 3 of the complex must have been enriched in cl and could have transported ree and trace metals

sill intrusion into pyroxenitic mush and the development of the lower upper critical zone boundary of the bushveld complex implications for the origin of stratiform anorthosites and chromitites in layered intrusions

a crystal size distribution study of the kiglapait layered mafic intrusion labrador canada evidence for textural coarsening crystal size distributions csd of plagioclase olivine and clinopyroxene from the kiglapait intrusion labrador were measured for a series of 13 samples spanning most of the exposed intrusion all csds lack small crystals and are slightly curved to the right concave up all csds of a mineral sweep out a fan as expected where there is relatively little variation in phase proportion csd dispersion can be replicated using the communicating neighbours model of textural coarsening ostwald ripening most of the textural variation in the intrusion is the result of variable degrees of coarsening it is proposed that coarsening occurred in the outer part of the crystallisation boundary layer where release of latent heat and changes in the intercumulus liquid composition resulted in a reduction in undercooling suppression of nucleation and coarsening particularly coarse grained areas reflect focusing of circulating magmatic fluids during coarsening the effects of crystal settling were not observed in the csds even within single well developed layers they were probably concealed by the pervasive textural coarsening csds do not suggest that mechanical compaction has played an important role in the formation of texture although it is very likely to have occurred however samples from the lower part of the intrusion show textural evidence of pressure solution compaction

discordant iron rich ultramafic pegmatites in the bushveld complex and their relationship to iron rich intercumulus and residual liquids the iron rich ultramafic pegmatites comprise a suite of coarse grained rocks that form discordant bodies within the layered sequence of the bushveld complex these pegmatites which are considerably more abundant than is generally realized provide evidence for the differentiation of iron rich residual melts the pegmatites are composed largely of iron rich olivine and clinopyroxene together with ti magnetite and ilmenite feldspar is characteristically absent but paradoxically the pegmatites preferentially replace anorthositic cumulates two subgroups are recognized olivine clinopyroxene pegmatite and fe ti oxide pegmatite with increased stratigraphic height the pegmatites become richer in fe ti oxides thus olivine clinopyroxene pegmatite is prevalent in the upper critical and lower main zones whereas fe ti oxide pegmatite is restricted to the upper main and upper zones zoned pegmatite with a core of fe ti oxide pegmatite is transitional between the two subgroups new whole rock and electron microprobe analyses of olivine clinopyroxene pegmatite from the upper critical and lower main zones provide convincing evidence that their composition is directly related to height cryptic compositional variations are analogous to those displayed by the layered cumulates but for a given height the pegmatites are always more evolved compositions of clinopyroxene in the pegmatites reflect a near linear relationship with height whereas cumulus pyroxenes display upward iron enrichment trends complicated by replenishment and reaction with trapped intercumulus liquid the olivine clinopyroxene pegmatite formed by magmatic replacement of earlier formed cumulates in response to infiltration of iron rich melts suitably differentiated melts comprised intercumulus and residual liquids derived from thick anorthosite layers the absence of feldspar although not fully understood is attributed to an immiscible relationship between dense iron rich melts and light silica alkali rich liquids the latter infiltrated upward to be reincorporated into the resident magma the iron rich melts however drained down into the crystallizing cumulate pile channelling along early formed fractures and joints was significant locally resulting in huge pipe like bodies of pegmatite the iron rich melts became increasingly differentiated with height partly in response to the fractional crystallization of more evolved cumulates the olivine clinopyroxene pegmatites are related to infiltration of fe ti oxide rich silicate melt whereas fe ti oxide pegmatite is ascribed to fe ti oxide liquid as originally argued by bateman 1951 the bushveld complex followed the fenner trend of almost uninterrupted iron enrichment evidence of pronounced iron enrichment is however manifested in the discordant iron rich ultramafic pegmatites several thousands of metres below the height at which iron rich cumulates are observed

halogen variations in the paleoproterozoic layered mafic ultramafic intrusions of east kimberley western australia implications for platinum group element mineralization a number of paleoproterozoic layered mafic ultramafic intrusions in the central part of the halls creek orogen of east kimberley western australia have been explored for platinum group elements chromium nickel copper cobalt and gold here we report on the halogen geochemistry of apatite and biotite in a number of these intrusions interstitial apatite is ubiquitous in these intrusions and in most samples tends to be relatively enriched in f and oh end members and relatively poor in cl 20 mole fluorapatite occurs in the more evolved igneous rocks and in samples from the margins of the intrusions that apparently have been contaminated by metamorphic country rock cl f ratios generally increase with bulk rock molar mg mg fe ratios as observed in other intrusions only a few samples show cl enrichment as high as that seen in the stillwater and bushveld complexes beneath the major stratabound platinum group element deposits the most cl rich compositions observed occur in the upper part of the springvale intrusion where it is associated with troctolite and in a single sample from the mcintosh intrusion for the former intrusion it is suggested that volatiles migrating out of the lower part of the mafic stratigraphy stabilized olivine at the expense of pyroxene associated biotite tends to contain little no more than 10 mole cl or f it is concluded that the east kimberley intrusions contained a low to moderate volatile component that during the combined processes of crystallization degassing and fractionation of interstitial halogen bearing minerals produced a late mobile interstitial silicate liquid or volatile rich fluid phase of variable cl f content that in turn caused most of the observed variations within any given intrusion the exceptions include the margins of the intrusions that appear to have been affected by country rocks either during emplacement assimilation or during later metamorphism apatite s generally low cl f ratio the lack of primary amphibole and the high background sulfur concentrations of the east kimberley intrusions suggest that these magmas were relatively volatile poor the development of high grade platinum group element enriched horizons by late stage hydrothermal processes that could have mobilized significant amounts of the platinum group elements and sulfur is considered to be unlikely

discordant bodies from olivine bearing zones iii and iv of the stillwater complex montana evidence for postcumulus fluid migration and reaction in layered intrusions mineralogically zoned and unzoned discordant bodies composed predominately of plagioclase with up to 35 olivine occur at three different levels in olivine bearing zones iii and iv of the middle banded series of the stillwater complex the discordant bodies are elongate perpendicular to the layering of the host cumulates with slender concordant apophyses although the host olivine gabbros are foliated with tabular plagioclase the discordant bodies lack a discernible fabric and have blocky plagioclase average olivine in the host rocks is slightly more magnesian than that of the discordant bodies mg 75 8 0 7 versus mg 74 6 0 3 respectively but plagioclase compositions are indistinguishable an77 6 2 0 versus an76 6 4 3 average host and discordant bodies respectively whole rock major and trace element compositions of the discordant bodies are generally indistinguishable from cumulates with similar modal abundance however bulk compositions of anorthositic cores from the discordant bodies are enriched in k na ba sr and p we conclude that the discordant bodies formed when cooler volatile fluids or fluid rich silicate liquids moved upward and encountered a hotter undersaturated solid plus liquid assemblage continued liquid fluid fluxing increased the permeability along the flow path and focused the flow allowing the original bulk compositions to be modified and leaving plagioclase rich troctolites and anorthosites the shapes of the discordant bodies suggest that the cumulus pile had anisotropic permeability during late stage liquid fluid flow chemical and mineralogical evidence from other parts of olivine bearing zones iii and iv suggests that the processes that formed the discordant bodies may have influenced other cumulates in fact it appears that the same processes that formed the discordant bodies operated within an anorthositic layer strongly modifying the chemistry of the rock but leaving no mineralogical or textural evidence

centrifuge modeling of end restraint effects in energy foundations abstractthis study presents the results from physical modeling experiments on centrifuge scale energy foundations in dry sand and unsaturated silt layers these experiments were performed to characterize end restraint effects on soil structure interaction for energy foundations in different soils and include tests on foundations with semifloating and end bearing toe boundary conditions and free expansion and restrained expansion head boundary conditions two scale model energy foundations having different lengths were constructed from reinforced concrete to simulate end bearing and semifloating conditions in soil layers having the same thickness the foundations include embedded thermocouples and strain gauges which were calibrated under applied mechanical loads and nonisothermal conditions before testing the variables measured during the experiments include axial strain and temperature distributions in the foundation temperature and volumetric water content measurements in the soil vertical displace

geologic section through the samail ophiolite and associated rocks along a muscat ibra transect southeastern oman mountains regional mapping at a 1 60 000 scale of a 30 km strip from the gulf of oman muscat across the oman mountains 130 km to the south provides the geologic setting for the 95 m y ibra section of the samail ophiolite where best preserved the ibra ophiolite section is an 8 km thick section of oceanic consisting of 0 5 km of pillow lavas 1 2 1 6 km of sheeted diabase dike complex 0 2 1 0 km of high level noncumulate gabbro and 3 0 5 0 km of cumulate gabbro that is underlain by tectonite peridotite 9 12 km thick the ibra section is found on the southward dipping limb of the sayah hatat antiform the tectonite peridotite represents uniformly depleted harzburgite and dunite that have been deformed by high temperature low stress asthenospheric flow discordant dunites within the tectonite peridotite appear to represent either flow crystallization products from primary picritic liquids or reaction products of these liquids with the harzburgite the structural base of the tectonite peridotite is overprinted by a high stress low temperature deformation that can be related to its oceanic detachment the layered gabbros are predominantly olivine clinopyroxene plagioclase cumulates and orthopyroxene does not occur as a cumulus phase occurrence of cumulate wehrlites and picrites at high stratigraphic levels within the layered gabbros is evidence that the gabbroic section crystallized predominantly from the bottom upward in a periodically replenished magma chamber high level gabbro represents remnants of crystallization at the roof of the magma chamber and intrudes most overlying diabase dikes both the diabase dike complex and pillow lavas are hydrothermally altered and alteration and metamorphism increase downward zeolite to epidote amphibolite facies in spite of pervasive alteration relict primary mineralogy and bulk chemistry suggest that the diabase dikes and pillow lavas are cogenetic with the underlying gabbros the present day samail thrust surface truncates ophiolite stratigraphy and puts the samail ophiolite on top of unmetamorphosed hawasina melange the last motion on this surface was probably no older than maestrichtian 70 65 m y garnet amphibolites exposed as remnants of earlier thrusting 90 m y record initial ophiolite detachment at a 14 20 km depth within the tethyan oceanic lithosphere the hawasina group which underlays the samail ophiolite is a block melange where exposed near muscat in the north and it grades into an imbricated broken formation at the southern limit of the map area the hawasina group is thrust over permian to late cretaceous shelf carbonates that represent autochthonous arabian continental shelf deposits recent post miocene collapse and dome structures such as the ibra dome have complicated ophiolite stratigraphy south of jabal dimh our geologic studies strongly indicate the samail ophiolite represents a large coherent slab of transported oceanic lithosphere formed at a late cretaceous spreading center in the tethyan sea

metal redistribution during fluid exsolution and migration in the middle banded series of the stillwater complex montana abstract olivine bearing zones iii and iv ob iii and iv of the stillwater complex mt preserve evidence of fluid migration particularly in the variation of apatite compositions this feature coupled with the lack of evidence of the addition of substantial amounts of primitive magma allows these zones to be used to test the importance of volatile fluids in redistributing metals the concentrations of cu au ag and as all show marked increases at and or below the levels inferred to represent the top of the fluid migration front in the crystal pile however no significant sulfide enrichment is associated with the maximum metal enrichments the au concentration peak is much sharper and offset stratigraphically above that of cu and corresponds with the maximum cl content of interstitial apatite these concentration profiles are modeled numerically assuming fluid transport and chromatographic concentration of the metals mass balance calculations indicate that cumulates significantly below the level of the inferred fluid saturation front lost cu while those at or immediately below gained cu we conclude that cl rich fluids redistributed the background metal concentrations although no dramatic enrichments are observed enrichment factors range from two to three the results demonstrate the potential importance of fluids in redistributing and concentrating metals in layered intrusions

the halogen geochemistry of the bushveld complex republic of south africa implications for chalcophile element distribution in the lower and critical zones solidification of the interstitial liquid the stratigraphic distribution halogen bearing minerals especially apatite are minor but ubiof s cu and the pge in the critical zone cannot readily be quitous phases throughout the bushveld complex interstitial apatite explained either by precipitation of sulfide as a cotectic phase or as is near end member chlorapatite below the merensky reef lower a function of trapped liquid abundance evidence from potholes and and critical zones and has increasingly fluorian compositions with the pge rich driekop pipe of the bushveld complex imply that increasing structural height above the reef main and upper zones migrating cl rich fluids mobilized the base and precious metal cl f variations in biotite are more limited owing to crystal chemical sulfides we suggest that the distribution of sulfide minerals and controls on halogen substitution but are also consistent with a the chalcophile elements in the lower and critical zones reflects a decrease in the cl f ratio with structural height in the complex general process of vapor refining and chromatographic separation of a detailed section of the upper lower zone to the critical zone is these elements during the evolution and migration of a metalliferous characterized by an upward decrease in sulfide mode from 0 01 cl rich fluid phase 0 1 to trace 0 001 cu tends to correlate with other incompatible elements in most samples whereas the platinum group elements pge can behave independently particularly in the critical zone the decrease in the cl f ratio of apatite in the

geochemistry and mineralogy of the platreef and critical zone of the northern lobe of the bushveld complex south africa implications for bushveld stratigraphy and the development of pge mineralisation the northern lobe of the bushveld complex is currently a highly active area for platinum group element pge exploration this lobe hosts the platreef a 10 300 m thick package of pge rich pyroxenites and gabbros that crops out along the base of the lobe to the north of mokopane formerly potgietersrus and is amenable to large scale open pit mining along some portions of its strike an early account of the geology of the deposit was produced by percy wagner where he suggested that the platreef was an equivalent pge rich layer to the merensky reef that had already been traced throughout the eastern and western lobes of the bushveld complex wagner s opinion remains widely held and is central to current orthodoxy on the stratigraphy of the northern lobe this correlates the platreef and an associated cumulate sequence that includes a chromitite layer known as the grasvally norite pyroxenite anorthosite gnpa member directly with the sequence between the ug2 chromitite and the merensky reef as it is developed in the upper critical zone of the eastern and western bushveld implicit in this view of the magmatic stratigraphy is that similar critical zone magma was present in all three lobes prior to the development of the merensky reef and the platreef however when this assumed correlation is examined in detail it is obvious that there are significant differences in lithologies mineral textures and chemistries mg of orthopyroxene and olivine and the geochemistry of both rare earth elements ree and pge between the two sequences this suggests that the prevailing interpretation of the stratigraphy of the northern lobe is not correct the critical zone of the northern lobe cannot be correlated with the critical zone in the rest of the complex and the simplest explanation is that the gnpa platreef sequence formed from a separate magma or mixture of magmas chilled margins of the gnpa member match the estimated initial composition of tholeiitic main zone type magma rather than a critical zone magma composition where the gnpa member is developed over the ultramafic lower zone hybrid rocks preserve evidence for mixing between new tholeiitic magma and existing ultramafic liquid this style of interaction and the resulting rock sequences are unique to the northern lobe the gnpa member contains at least seven sulphide rich horizons with elevated pge concentrations some of these are hosted by pyroxenites with similar mineralogy crystallisation sequences and pd rich pge signatures to the platreef chill zones are preserved in the lowest main zone rocks above the gnpa member and the platreef and this suggests that both units were terminated by a new influx of main zone magma this opens the possibility that the platreef and gnpa member merge laterally into one another and that both formed in a series of mixing quenching events involving tholeiitic and ultramafic magmas prior to the main influx of tholeiitic magma that formed the main zone

geochemistry of dendritic anorthosites and associated pegmatites in the skaergaard intrusion east greenland evidence for metasomatism by a chlorine rich fluid abstract in the upper zone uza of the skaergaard intrusion dendritic anorthosites and pegmatites are found in a zone of deformed gabbro along the flank of a trough banded structure apatite biotite some having over 2 wt c1 and amphibole have higher chlorine contents than those found in the surrounding rocks and indicate the presence of a high temperature aqueous fluid having a high hcl hf fugacity ratio the fluid must have been derived locally by exsolution of magmatic volatiles because hydrous minerals in nearby hydrothermal veins have low chlorine contents and the structures are far from the margin of the intrusion apatite and quartz in the pegmatites have abundant fluid inclusions containing cubic halide crystals giving evidence for a separate aqueous fluid coexisting with an evolved residual melt the pegmatites are also characterized by mafic and felsic clots with compositions similar to immiscible silicate liquids dendritic anorthosites have equal or higher abundances of zr hf ta and rare earth elements than the surrounding gabbros yet they contain little pyroxene or fe ti oxides the unusual trace element enrichment patterns and the associated rare assemblage of zirconolite zircon baddeleyite and allanite suggest that the chlorine rich fluid was enriched in trace elements derived from the residual melt and the reacted mafic minerals deformation of the magma at a crystallinity below the critical melt fraction resulted in localized exsolution and channeling of a magmatic aqueous fluid and an evolved residual melt dissolution of pyroxene olivine and fe ti oxides allowed for further deformation and expulsion of the mafic melt leaving a plagioclase rich residue these structures are the product of enhanced reaction locally of an aqueous fluid which may have moved upward as a nearly planar reactive front throughout the lower crystallization zone in addition to the transport of trace elements migration of a high temperature fluid through the zone of crystallization could aid in the compaction of igneous cumulates and the development of layering this study presents the first evidence for a high temperature chlorine rich aqueous fluid in the layered series of the skaergaard intrusion and illustrates the important effect of such fluids on the physical and chemical evolution of layered intrusions

the distribution and main geologic features of discordant bodies of iron rich ultramafic pegmatite in the bushveld complex transgressive bodies of iron rich ultramafic pegmatite composed predominantly of varying proportions of hortonolite clinopyroxene ilmenite and ti magnetite are abundantly distributed throughout the layered mafic sequence of the bushveld complex new information from field and underground studies together with interpretations of detailed magnetic surveys is presented along with an overview of the available literature some whole rock and mineralogical chemical data are also included within the bushveld complex a number of distinct but possibly genetically related groups of postcumulus ultramafic rock are recognized these include besides the main group of iron rich ultramafic pegmatite bodies of magnesian dunite and the well known platiniferous ultramafic or dunitic pipes transgressive often pipelike bodies composed almost entirely of fe ti oxides occur in the main and upper zones of the complex which although part of the iron rich ultramafic pegmatite suite are described separately composite bodies in which massive fe ti oxides occur as a core within a peripheral shell of silicate rich pegmatite are also recognized the major occurrences of iron rich ultramafic pegmatite are documented and depicted in a series of maps their distribution is subject to two major stratigraphic controls iron rich ultramafic pegmatite occurs largely above the ultramafic cumulates in the lower and lower critical zones it is abundant in the upper critical and main zones where plagioclase is a major cumulus phase but is rarely observed above the highest cumulus ti magnetite layer in the upper zone it is also evident that these rocks become increasingly iron rich toward the top of the layered sequence so that in the upper zone fe ti oxide pegmatite is the dominant variety many bodies particularly the large ones are structurally controlled and occur in disturbed areas characterized by faulting and post bushveld dikes stratigraphic magnetic anomalies in the complex may be related to anorthositic layers containing small specks of iron rich ferromagnesian silicates and fe ti oxides this iron rich material is considered to represent the accumulated and trapped late stage residual and intercumulus fluid resulting from fractional crystallization within a cyclic unit lateral migration and channeling of these pegmatitic fluids into areas of structural weakness resulted in the formation of large pipelike bodies of iron rich ultramafic pegmatite these bodies may have resulted from metasomatic replacement of preexisting cumulates or they may have crystallized directly from the pegmatitic fluids the authors believe that the pegmatitic fluids have been derived from within the crystallizing cumulate pile and it is concluded that the formation of iron rich ultramafic pegmatite is an integral feature of the layered sequence

the petrogenesis of a platiniferous dunite pipe in the bushveld complex infiltration metasomatism by a chloride solution the driekop dunite pipe crosscuts part of the noritic layered sequence of the upper critical zone in the eastern bushveld complex the central orebody of the pipe contains platinum group minerals base metal sulfides magnetite and iron rich olivine the country rock forms a collapse structure around the pipe with the layered sequence becoming almost vertical near the contact with the pipe it is proposed that a high temperature chloride solution flowed through irregular channel ways along a structural weakness near the axis of the pipe and reacted with the noritic host rocks leading ultimately to the formation of dunite reaction fronts advanced at different rates outward from the channelways and produced a sequence of metasomatic zones characteristics of infiltration metasomatism that are evident in the pipe include the movement of material over large distances in predominantly one direction the formation of a monomineralic rock the occurrence of a marginal zone that is enriched by displaced components and plateaus in the compositions of mineral solid solutions the reactions responsible for the major changes in the bulk composition of the host rocks were desilication of orthopyroxene to produce olivine and dissolution of plagioclase the 67 percent volume loss accompanying these reactions can account for the structural collapse of the critical zone around the pipe some olivine in the pipe is too fayalitic to have been produced by simple desilication of host rock orthopyroxene the enrichment of olivine in iron can take place bymg 2 sio 4 2fecl sub 2 sub aq fe 2 sio 4 2mgcl sub 2 sub aq forsterite fayalite aqueous chloride complexes are also believed to have played an important role in the transport and precipitation of the platinum group elements the base metals and other cations interdependent chemical reactions involving a chloride solution olivine magnetite and the platinum group elements can account for the preferential association of the ore with iron rich olivine infiltration metasomatism by a high temperature chloride solution may have an important bearing on the interpretation of other features of the bushveld complex

microstructures and late stage magmatic processes in layered mafic intrusions symplectites from the sept iles intrusion quebec canada replacive symplectites vermicular intergrowths of two or more minerals are an important feature of layered igneous intrusions recording evidence of late stage reactions between interstitial liquid and crystals they are common throughout the layered series of the 564 ma sept iles layered intrusion in quebec canada and fall into three types oxy symplectites type i symplectites and type ii symplectites oxy symplectites are comprised of magnetite and orthopyroxene nucleate on olivine primocrysts and form via the reaction olivine o2 orthopyroxene magnetite type i symplectites of which there are 3 distinct categories are comprised of anorthitic plagioclase with pyroxene amphibole or olivine vermicules grow from primocryst oxide grains and replace primary plagioclase and type ii symplectites of which there are 2 distinct categories are comprised of anorthitic plagioclase with orthopyroxene amphibole vermicules grow from primocryst olivine

shear zone controlled post magmatic ore formation in the huangshandong ni cu sulfide deposit nw china abstract the huangshandong ni cu sulfide deposit located in the kangguer jing erquan ductile shear zone belongs to the jueluotage island arc belt in eastern tianshan of the central asian orogenic belt the huangshandong mafic ultramafic pluton which has a fusiform shape is believed to have intruded strongly foliated late carboniferous volcanic rocks during the development of the regional ductile shear zone some orebodies in the deposit show intense ductile deformation among them the no 17 orebody is entirely controlled and hosted by the ductile shear zone host rocks and ores from this orebody show intense deformation and alteration and could be called ore mylonites furthermore numerous anastomosing veinlets can be observed in copper rich carbonate sulfide veins in the ductile shear zone geological field investigation and ore petrography studies indicate that sulfide ores at huangshandong are composed of three types undeformed magmatic ores deformed magmatic ores and hydrothermal overprinted ores magmatic ores with net fabrics remain unaltered and undeformed and sulfide minerals in them show only brittle fractures silicate and sulfide minerals in deformed magmatic ores are characterized by intense deformation fabrics examples for such fabrics are kink bands wavy extinction of uralite domino structure of phlogopite and elongated grains of pyrrhotite and pentlandite hydrothermal overprinted ores are characterized by strong deformation flattened grains and recrystallization of pyrrhotite moreover annealing of pyrrhotite is frequently observed pyrrhotite pentlandite and chalcopyrite in hydrothermal overprinted ores have high ni and co concentrations in pyrrhotite a higher ni concentration in pentlandite and high ag and cd concentrations respectively we attribute ni and co in fluid overprinted ores mainly to the alteration of olivine and the dissolution of primary chalcopyrite is the likely source of copper in chalcopyrite rich hydrothermal overprinted ores during the intruding and cooling of the huangshandong pluton intense regional ductile shearing caused the ductile deformation of sulfide ores in the deposit and subsequently ore mylonites were formed gangue minerals in the deformed orebodies were crushed to fine grained minerals and altered to serpentine chlorite and uralite during these processes fluid and ore elements were released and reacted with deformed rocks and ores forming anastomosing veinlets on hydrothermal overprinted ores

petrology and mineral compositions of the middle banded series of the stillwater complex montana the two olivine beating zones of the middle banded series of the stillwater complex are characterized by an increase in the number of cumulus minerals with height in each anorthosite and anorthositic troctolite dominate the lower part whereas olivine gabbro and gabbronorite form much of the upper portions electron microprobe analyses of cumulus minerals indicate little or no variation of average mineral compositions with height in addition no significant lateral variations in cumulus mineral compositions occur along 8 km of section plagioclase from throughout these zones shows the complex reverse and oscillatory zpnation patterns also seen in plagioclase from the thick 500 m anorthosites that sandwich the zones the data suggest that the entire middle banded series is genetically related and therefore requires models for the origin of the thick anorthosites to also explain the olivine bearing rocks between them however textural features such as discordant troctolites pegmatoids slump structures and variably developed mineral laminations and chemical features such as zpnation in clinopyroxene produced by intergranular exchange with orthopyroxene and large within sample variations in the mg number of olivine in lowolivine troctolites indicate that significant modification of these rocks by postcumulus processes has taken place thereby obscuring evidence of their genesis

effects of h2o on phase relations during crystallization of gabbros in the kap edvard holm complex east greenland in the kap edvard holm complex of east greenland layered monly results in the formation of discordant igneous bodies within crystallizing cumulus sequences in some olivine gabbros host numerous small discordant bodies of ultramafic cases partially molten cumulates appear to have reacted rock and magnetite gabbro that formed by late magmatic metasomatic with liquids or fluids that originated within the cumulus replacement of partially solidified gabbroic cumulates similar repile resulting in resorption of cumulus minerals crysplacive rocks are also present as large semi conformable sheet like tallization of intrusive or replacive bodies and rebodies within the layered gabbro sequence replacive bodies of all distribution of mass within the intrusion e g robins sizes are spatially associated with xenoliths of metabasaltic lava 1982 butcher 1985 butcher et al 1985 helz 1987 the small bodies cluster around xenoliths and the large bodies host irvine 1987 boudreau 1988 mcbirney sonnenthal swarms of xenoliths the replacive bodies are inferred to have formed 1990 larsen brooks 1994 scoon mitchell 1994 by reaction of gabbroic cumulates with pore liquids that were mathez 1995 meurer et al 1997 boudreau 1999 in enriched in h2o by degassing or dehydration melting of the other cases partially molten cumulates are inferred to metabasalts as these liquids migrated through the cumulus pile have reacted with externally derived magmas that inthey resorbed plagioclase and produced ultramafic bodies where the truded the cumulus pile resulting in the development liquids came to rest they reacted with gabbroic cumulates to produce of discordant replacive bodies via the reaction of the bodies of magnetite rich gabbro the most evolved pore liquids cumulates with intruding magmas e g morse et al 1987 segregated to form hornblende rich pegmatitic dikes of roughly dacitic bedard et al 1988 tegner wilson 1993 tegner composition suggesting that hydration and possibly oxidation of the robins 1996 because cumulus rocks preserve records magma shifted the liquid line of descent from a tholeiitic trend toward of magmatic fractionation and replenishment in large a calc alkaline trend these inferences imply that contamination of mafic intrusions recognizing and understanding postmagmas by dehydration of hydrothermally altered crustal rocks may cumulus processes such as these can provide insights significantly influence the evolution of mafic magma systems into the evolution of mafic magma chambers and the differentiation of basaltic magmas within the crust near the western margin of the kap edvard holm

on glacier retreat and drought cycles in the rocky mountains of montana and canada abstract the enigma of why mountain glacier started to retreat in the 1850s in the rocky mountains and elsewhere remains unresolved the most important factor affecting climate change presumably was a change in the mode of operation of the sun one or two decades earlier from irregular periodicity and low output to regular periods and greater brightness but the direct cause appears to have been the onset of drought in the 1830s interestingly there is no obvious solar information in the drought narrative in montana and southwestern canada the presence of tidal lines in the spectrum of the pacific decadal oscillation together with the presence of lines that could be interpreted as beat periods between solar and tidal forcing in the drought series suggests that the energy of solar variation is preempted for interference with tidal forcing within the system of oscillations informing precipitation patterns in the region the suggestion is supported by the presence of a strikingly dominant 12 5 year period in the drought series which is interpreted as a difference tone between the main sunspot cycle at 10 8 and a tidal period at 5 8 also this period is close to 2 3 of the nodal tide at 18 61

the lac des iles complex ontario petrology and platinum group elements mineralization in an archean mafic intrusion the lac des iles complex is a late archean mafic to ultramafic complex that is host to 20 4 106 t pt pd and au mineralization with an average grade of 6 34 g t platinum group elements pge the 30 km2 complex located in the wabigoon subprovince consists of several coalescing mafic to ultramafic intrusive centers the complex is emplaced into early gneissic tonalite and is contemporaneous with late granitoids the magmatic evolution of the complex reflects the emplacement of multiple pulses of previously fractionated magma some of which underwent subsequent in situ fractionation distinct magma sequences are recognized on the basis of intrusive relationships differences in the cumulus minerals crystallization order and trace element chemistry these sequences are 1 hornblende gabbro 2 gabbro and gabbronorite and 3 ultramafic where there is evidence of intrusive relations the most primitive sequences are emplaced late and occur toward the north end of the complex microprobe analyses in

recrystallization and the origin of layering in the bushveld complex abstract three rock types are distinguished in this study a the layered rocks b the reef pegmatites which are parallel to the layering and form prominent marker horizons and c the iron rich ultramafic irum pegmatites which are transgressive to the layered rocks reaction textures are observed in the layered rocks adjacent to reef pegmatites and are compared with similar reaction textures from alteration zones adjacent to and caused by the iron rich ultramafic irum pegmatites these include a clinopyroxene coronas around orthopyroxene b hornblende lamellae along 100 of orthopyroxene c orthopyroxene altered to olivine serpentine talc and or chlorite in the alteration zones adjacent to irum pegmatites the textures were generated by interaction between the pegmatite forming fluid and the wallrocks a similar origin is proposed for reaction textures in the layered rocks in the latter case they were formed by the fluid responsible for the formation of reef pegmatites in the layered rocks the reaction textures were modified to variable degrees during and after the emplacement of reef pegmatites these modifications include in leuconorites a clinopyroxene coronas overgrown by feldspar b orthopyroxene overgrown by feldspar and hornblende lamellae transforming to biotite and in olivine pyroxenites c olivine serpentine textures overgrown by a second generation of orthopyroxene the modifications suggest the subsolidus dissolution of orthopyroxene and precipitation of feldspar in leuconorites and the reverse process in pyroxenites the textures suggest considerable transfer of matter in the solid rock due to a fluid gradient orthopyroxene recrystallized in areas with a high ah2o plagioclase in regions of low ah2o this process is believed to be responsible for the stratification of the rock into pyroxene and plagioclase rich layers spherical mineral inclusions are relict textures in the three main minerals chromite orthopyroxene and plagioclase a number of similarities between the different inclusions suggest a similar origin the high content of hydrous minerals in all three suggests their formation during the emplacement of reef pegmatites these hydrous minerals were then trapped in the recrystallizing plagioclase orthopyroxene and chromite also spherical mineral inclusions witness the late crystallization of pyroxene in melanorite pyroxenite and the crystallization of plagioclase in leuconorite anorthosites after the emplacement of reef pegmatites

assimilation of peridotite in zoned calc alkaline plutonic complexes evidence from the big jim complex washington cascades the big jim complex is a concentrically zoned ultramafic to felsic plutonic complex which intruded the pelitic chiwaukum schist most of the major plutonic rock types from websterite through hornblendite gabbronorite hornblende gabbro and diorite to granodiorite enclose harzburgite and metaperidotite xenoliths similar to foliated metaperidotite lenses included in the chiwaukum schist the larger xenoliths preserve tectonite fabrics all have mg s mole fraction mgo mgo feo from 0 90 to 0 89 the same as those of chiwaukum metaperidotites and distinctly different from undeformed big jim dunite mg s 0 84 to 0 82 and websterite 0 82 to 0 78 contact relations indicate widespread stepwise replacement of harzburgite by pyroxenite hornblendite gabbro and diorite thermodynamic modelling using an expanded regular solution model for silicate liquids ghiorso 1985 ghiorso and carmichael 1985 predicts that reaction between olivine fo90 and a liquid with the composition of big jim diorite 1 5 wt h2o at 1 100 c and 3 kb would produce websterite mg s 0 75 to 0 81 and dunite 0 79 to 0 82 this process is exothermic and results in a negative change in volume since it increases total solid mass under conditions of decreasing temperature modelled crystal fractionation with assimilation of olivine reproduces important features of the chemical variation observed in the big jim complex where crystal fractionation alone fails the big jim complex has affinities with other ultramafic to felsic plutonic complexes such as the bear mountain complex snoke et al 1981 1982 and the emigrant gap complex james 1971 the latter have wehrlite and clinopyroxenite rather than websterite but both have concentric zoning with olivine bearing rock types surrounded by successively more felsic pyroxenite gabbro and diorite in general concentrically zoned complexes of this type may form where magma reacts with mantle derived wall rock or ultramafic cumulates assimilation of peridotite in fractionating magma may be important in subduction related magmatic arcs

origin of anorthosite by textural coarsening quantitative measurements of a natural sequence of textural development the textures of plagioclase crystals within large olivine oikocrysts preserve the sequence of the formation of anorthosite such textures have been quantified in a troctolite anorthosite from the proterozoic lac st jean anorthosite complex canada crystal size distributions csds indicate that initially plagioclase nucleated and grew in an introduction environment of linearly increasing undercooling producing a straight the textures of plutonic rocks are one of their most line csd during this phase latent heat of crystallization was striking aspects but they have been little used to elucidate largely removed by circulation of magma through the porous crystal petrological processes as compared with chemical and mush by about 25 solidification the crystallinity was such that isotopic methods where used discussion has tended it reduced but did not eliminate the circulation of magma resulting to be qualitative in contrast to quantitative chemical in the retention of more latent heat within the crystal pile the methods hence reducing the weight of this approach temperature rose until it was buvered by the solution of plagioclase indeed it is not possible to verify physical models if close to the liquidus temperature of plagioclase nucleation of quantitative data are not available quantitative textural plagioclase was inhibited and conditions were suitable for textural studies of volcanic rocks are becoming more common coarsening of both plagioclase and olivine to occur ostwald and these methods are applied here to the development ripening in this process small crystals were resorbed whereas of anorthosite larger crystals grew from both material recycled by the resorption of quantitative textural studies of plutonic rocks really crystals smaller than the critical size and new material brought in started with jackson s studies of the stillwater complex by the circulating magmatic fluid the results of this process resemble in 1961 jackson 1961 he measured crystal size disthose of high temperature metasomatism but there is no necessity for tributions but did not record the area that he measured a magmatic fluid with a diverent composition the shapes of the hence his data cannot be completely compared with plagioclase csds fit better the communicating neighbours equation of modern data his pioneering work was not really followed textural coarsening rather than the classic lifshitz slyozov wagner up and since then most studies have looked only at equation as do other examples drawn from the literature if olivine average or typical crystal sizes these data are much started to nucleate at a higher temperature than plagioclase then less revealing of petrological processes than crystal size during the textural coarsening phase olivine would have been more distributions partly because they only give one parameter undercooled than plagioclase and would have had a higher maximum for each sample the few existing studies of crystal size growth rate in these conditions olivine would coarsen more rapidly distributions in plutonic rocks have not treated than plagioclase and engulf it hence the order of crystallization plagioclase determined from the textures would be the reverse of the order of one problem especially pertinent to quantitative texfirst nucleation of the two phases from equilibrium phase diagrams tural studies is the way that many igneous petrologists maintenance of the temperature near the plagioclase liquidus may look at rocks they commonly try to reconstruct how a rock has formed by examining the final fully crystallized also inhibit the nucleation and growth of other phases

re os isotope and pd ru variations in chromitites from the critical zone bushveld complex south africa abstract rhenium osmium isotope measurements of selected chromitites from the critical zone of the bushveld igneous complex reveal that a significant component of radiogenic os was present in the magma when it formed 2 06 ga ago measured 187 os 188 os ratios increase with stratigraphic height and individual layers have similar values across the complex initial 187 os 188 os ratios for chromitites from the western bushveld decrease from 0 140 at the lg to 0 129 at the mg2 chromitite increasing to 0 153 at the ug2 chromitite the inflection at mg2 mg3 is the boundary between the lower and upper critical zone consistent with previous mineralogical and geochemical studies indicating a shift in magma composition at this point chromite separates have os values of 12 35 at 2 06 ga and are too radiogenic for a purely mantle derivation assimilation of 5 mafic granulitic lower crust in a tholeiitic parent magma can explain the radiogenic values pd ru ratios for the intergranular and chromite separate components of each layer differ by orders of magnitude but relative shifts from layer to layer are similar combined with the re os data the results suggest that pge were concentrated into chromitites by magmatic or early deuteric processes that were specific to each layer post layering upward mobilization of pge by hydrothermal processes probably did not play a significant role in pge enrichment

compositional convection in a reactive crystalline mush and melt differentiation fractional crystallization and partial melting involve relative motion of liquid and solid phases and chemical and thermal interactions between them to elucidate some physical principles of thermosolutal convection in a reactive porous medium we describe experiments on the directional solidification of aqueous ammonium chloride solutions the addition of small amounts of a polymerizing agent permits variation of the solution viscosity independently of thermal conditions the phase diagram and permeability solutions were cooled from below and crystallization developed at the base of the tank generating at first a field of thin plumes of light residual fluid released from the boundary layer at the top of the mush the interstitial fluid within the mush also became unstable eventually the onset of convection occurring when the porous medium rayleigh number of the mush reached a critical value this threshold value was found to be 25 at low initial superheat and to decrease with increasing superheat local thermodynamic equilibrium between crystals and liquid within the mush coupled the evolution of temperature composition and porosity convective motions locally caused dissolution and precipitation and hence fluctuations of porosity developed dissolution occurred preferentially in the central parts of upwellings and the upflow gradually focused being ultimately channelized into narrow chimneys devoid of crystals all else being equal the areal density of chimneys was greater the lower the viscosity chimney diameter increased with increasing solution viscosity in the liquid above the growing mush the convective plumes were very similar to salt fingers depending on solution viscosity and temperature gradient they exhibited a phenomenon of collective instability such that vertical motion was disrupted by wave instabilities the base plate temperature chosen was above the eutectic and hence the total amount of crystals at the end of experiments with the same initial composition and the same final temperature was a constant fixed by the phase diagram the spatial distribution of crystals and the final porosity of the mush were however determined by the strength of compositional convection as measured by the porous medium rayleigh number when no convection occurred mush thickness finally became equal to the initial layer thickness and the system was homogeneous when compositional convection occurred the overlying reservoir underwent chemical evolution and mush growth slowed dramatically in experiments with progressively lower solution viscosity and hence more vigorous convection final mush thickness was progressively less and final porosity lower final mush thickness was found to scale with solution viscosity to the power 0 33 during fractional crystallization of magma the effects of compositional convection can be recorded in the chemical and mineralogical features of cumulate rocks we speculate that fossil chimney structures can be found in the lower zone of the bushveld ultramafic complex in the form of iron rich platinum bearing dunite pipes this could explain the adcumulate nature of the lower zone rocks and the chemical and mineralogical similarities between the pipes and the overlying merensky reef the merensky reef would be interpreted as a hiatus in mush growth the results may also have applications to the flow structure in regions of partial melting and in the earth s core

an occurrence of igneous orthorhombic amphibole eriksberg gabbro southern sweden we document the first reported igneous occurrence of the orthoamphibole gedrite from a troctolitic cumulate in the eriksberg gabbro sweden the gedrite is sodic and coexists in textural equilibrium with plagioclase orthopyroxene ca amphibole and na rich phlogopite the gedrite crystallized from evolved interstitial liquid that was buffered by cumulus olivine geothermometry indicates that the assemblage equilibrated at around 900 c and 4 6 kbar gedrite shows a convex downward ree profile with a positive eu anomaly the rare earth element concentrations are 0 2 to 0 8 times chondritic abundances and much lower than in coexisting ca amphibole laser ablation icp ms analyses show that the gedrite has much lower concentrations of zr nb th and u and lower concentrations of sr ba rb and pb relative to co crystallizing ca amphibole however nickel and cobalt partition preferentially into gedrite comparison of zr and nb concentrations in early crystallized ca amphibole with gedrite and associated ca amphibole reveals that x m g of amphibole is not the best criteria to use for estimates of d a m p h l n b z r for cumulates where olivine is buffering the mg mg fe

comportement d un pieu bi fonction fondation et echangeur de chaleur the behaviour of a pile subjected to thermo mechanical loads was studied in situ with the aim of quantifying the thermal influence on the bearing capacity of heat exchanger piles to accomplish this a pile situated in a building under construction was equipped with a pipe system to inject heat into it using a special heat pump load cells deformation gauges and thermometers were installed to evaluate the behaviour of the pile during seven tests with coupled thermo mechanical loads the temperature variations applied to the pile were of the order of 15degreesc and the mechanical load reached 1300 kn the results permitted the quantification of three significant effects brought about by the temperature increase i pile uplift ii mobilization of skin friction due to the relative displacement of the pile with respect to the ground iii additional load generated in the pile by constrained dilation

compositions of pegmatoids beneath the j m reef of the stillwater complex montana u s a abstract pegmatoids sporadically occur in the cumulates of the ultramafic series and norite zone i and gabbronorite zone i the lower banded series below the level of the platiniferous j m reef of the stillwater complex but are less common in norite zone ii and gabbronorite zone ii above the reef the pegmatoids are composed of the same minerals plagioclase orthopyroxene and clinopyroxene as the host cumulates and in approximately the same proportions but with grains that may be in excess of several tens of centimeters in length whole rock compositions show the pegmatoids to be modestly enriched in lithophile incompatible major and trace elements relative to the host cumulates whereas average host cumulates of norite zone i and gabbronorite zone i have a whole rock molar mg mg fe ratio of 81 1 5 and a normative an content of 85 1 5 almost all pegmatoid samples have lower values with mg mg fe ratios as low as 71 and normative an content as low as 58 these results are confirmed by electron microprobe analyses ratios of soluble insoluble lithophile trace elements e g ba zr show inconsistent trends excess sulfide in some pegmatoids strongly affects chalcophile element abundance if it is accepted that the pegmatoids define pods where late stage volatile rich fluids were locally enriched or channel ways by which fluids migrated up through the cumulate sequence then it is clear that such fluids differ from the host assemblages only in that the fluids were in equilibrium with a slightly more evolved bulk rock compositions calculated fluid compositions are relatively rich in fe and na and poor in ca and mg and are consistent with the compositional features of the pegmatoids the lack of significant difference in the ratios of soluble insoluble lithophile trace elements between the pegmatoids and the host cumulates suggests that it could be difficult to detect geochemical signatures for the former presence of igneous fluid in nonpegmatoidal cumulate rocks using these elements alone

effects of hydrous alteration on the distribution of base metals and platinum group elements within the kevitsa magmatic nickel sulphide deposit abstract platinum and nickel are commonly assumed to be immobile in most conditions especially during low temperature hydrothermal alteration however only a small number of studies have rigorously tested this assumption the ni cu pge sulphide ore body hosted by the kevitsa intrusion northern finland provides a natural laboratory to study the behaviour of base metals and platinum group elements pge during low temperature alteration this ca 2060 ma mafic ultramafic intrusion located in the central lapland greenstone belt hosts disseminated ni cu pge sulphide mineralisation in the middle part of the main ultramafic body the mineralisation which contains a range of ni cu and pge grades is affected by three main alterations serpentinisation amphibolitisation and epidotisation and is cross cut by various types of veins the effect of the circulation of hydrothermal fluids on the distribution of base metals and pge was studied at two different scales interrogation of an extensive deposit wide assay database provided information on the deposit scale kilometre scale effect of these different alteration styles and a detailed study involving laboratory x ray fluorescence xrf portable xrf and micro xrf mapping of drill core samples containing cm scale cross cutting veins provided information on the small scale centimetre to decimetre scale remobilisation of base metals and pges results show that the hydration and carbonation of the kevitsa mineralised mafic ultramafic intrusion did not significantly affect the distribution of ni and pge at scales larger than a few mm and that cu and au are the only metals that are affected by small to large scale remobilisation from centimetre to kilometre scale

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

platinum group element geochemistry of continental tholeiites analysis of the long range dyke swarm newfoundland canada abstract the rift related late proterozoic long range continental dykes of western newfoundland have platinum group element pge pd pt rh ru and ir determined concentrations that correlate with indicators of magma evolution e g mg mg mg 0 9 fe tot and magma alkalinity la sm suggesting that metamorphism had a minimal effect on the pge the low melting point lmp pge pd pt and rh and cu behaved incompatibly as magma evolved indicating that sulphide fractionation did not occur and that the dykes hold little economic promise hypotheses that augite a major fractionating phase has an affinity for the pge are not supported primitive rocks tend to have lower ir than evolved rocks and all samples display a negative high melting point hmp pge ru and ir anomaly on mantle normalized diagrams olivine and early chromite fractionation may have decreased the concentrations of these elements the long range dykes confirm that pd ir ratios and absolute lmp pge concentrations tend to decrease with increasing hot spot magma alkalinity the lower pge concentrations in most morb compared with hot spot basalts imply that there are at least two mantle reservoirs for the pge lithosphere overlying mantle sources continental or oceanic has little effect on pge concentrations the apparently similar source region pge concentrations for hot spot basalts suggest that differences in pge concentrations between morb and hot spot basalts reflect incomplete segregation of the pge into the core during its formation and rise of the homogeneously dispersed elements to upper mantle depths in deep mantle plumes

using apatite to dispel the trapped liquid concept and to understand the loss of interstitial liquid by compaction in mafic cumulates an example from the stillwater complex montana the size paragenetic setting distribution and composition of apatite grains in 16 thin sections from one sample of an olivine gabbro from the stillwater complex montana were documented to determine whether they grew from trapped interstitial liquid or in an open system the grains show extreme variability in cross sectional area ranging from 300 000 m2 the apatite grains are not associated with quartz fe ti oxides or evolved overgrowths on cumulus grains as expected for the crystallization of a trapped liquid which suggests that they grew in an open system the grains are very irregularly distributed with a single cluster comprising almost 25 of the cumulative apatite cross sectional area from all 16 slides the spatial patterns of the apatite indicate that the interstitial liquid moved in tubular channels during the final stages of compaction the trace element composition of liquids calculated from apatite and silicate mineral compositions are similar indicating that the apatite crystallized from liquids that were not dramatically enriched in incompatible elements we conclude that the interstitial liquid never actually became trapped that liquid was lost in an open system to essentially zero porosity and that the model of cumulates as a combination of cumulus grains and trapped liquid should be discarded

compaction of igneous cumulates part ii compaction and the development of igneous foliations quantitative petrofabric analysis of 66 samples from olivine bearing zones iii and iv of the middle banded series of the stillwater complex montana was conducted to allow direct comparison among textural and chemical variations systematic variations in foliations with stratigraphic height are observed in both zones statistical analysis of the orientations of inequant grains was used to calculate an alignment factor af corresponding to the extent of the development of the foliation both petrofabric and petrographic evidence indicates that the foliation is best explained by compaction of the crystal pile comparison of afs with estimates of the amount of compaction based on whole rock compositions shows approximate agreement variations in mole fraction cl of interstitial apatite mimic the observed trends in the af indicating that local concentrations of fluids exsolved from interstitial liquid were important in the development of strong foliations we conclude that 1 differing amounts of co

the 190pt 186os decay system applied to dating platinum group element mineralization of the bushveld complex south africa abstract we evaluate the 190pt 186os decay system measured by laser ablation mc icpms as a useful geochronometric tool for direct dating of platinum group minerals pgm in large mafic ultra mafic intrusions by analysing mineralised rocks from the geochronologically well constrained bushveld complex s africa mixed pgm laurite cooperite laurite platarsite sperrylite and pt fe alloy from the merensky reef yield a pt os isochron age of 1995 50 ma 2 n 48 mswd 1 16 initial 186os 188os 0 119819 0 000006 while this is 59 myr younger than the u pb zircon age for the merensky reef scoates and friedman 2008 it is consistent with recent re os ages for the platreef considering the younger age recorded by both re os and pt os systems we propose that the pt os isochron age records a late low temperature hydrothermal event affecting pgm and sulphides in the platreef and merensky reef pt rich phases may also yield single grain 190pt 186os model ages since initial 186os 188os can be well constrained a pt os model age of 2024 ma 101 ma was calculated for a merensky cooperite a pt fe alloy from the onverwacht pipe and a tweefontein hill sperrylite give pt os model ages of 2113 106 ma and 2042 102 ma respectively a pt os isochron derived from all bushveld units gives an age of 2012 47 ma 2 186os 188osi 0 119818 0 000006 with an mswd of 1 19 hence pge mineralisation in different stratigraphic horizons of the complex cannot be distinguished temporally using the pt os chronometer nonetheless the potential for the pt os system in dating events in pge mineralised systems is evident and the agreement of single grain model ages in high pt os phases with the pt os and re os isochron ages indicates their usefulness in the geochronology of these systems

sr and pb isotopic disequilibrium between coexisting plagioclase and orthopyroxene in the bushveld complex south africa microdrilling and progressive leaching evidence for sub liquidus contamination within a crystal mush progressive leaching of plagioclase for sr iso topes and microdrilling for sr and pb isotopes from grains of plagioclase and orthopyroxene from the critical zone and the lower zone indicates that these minerals are not in isotopic equilibrium leaching suggests critical zone plagioclase either lost rb or had a more radiogenic sri rim relative to the core whereas plagioclase from an upper zone sample is isotopically homogeneous for sri microdrilling analyses of plagioclase from the lower and critical zones consistently have a higher initial 87 sr 86 sr sri and a less radiogenic modeled 238 u 204 pb composition l2 than coexisting ortho pyroxene the range of calculated sri for plagioclase and orthopyroxene is 0 70506 0 70662 34 and 0 70290 0 70654 36 respectively the average difference in sri between mineral pairs was 0 00095 the range of calculated l2 for plagioclase and orthopyroxene is 9 42 10 30 average 9 7 and 9 83 15 75 average 10 1 respectively the range of measured 208 pb 206 pb for plagioclase and orthopyroxene is 34 757 36 439 33 and 36 669 41 845 85 respectively one orthopyroxenite without evidence for more than one population of crystal size distribution nonetheless had sri 0 70654 36 with calculated l2 of 10 32 for larger grains as compared with sri 0 70290 32 and calculated l2 of 9 97 for smaller grain size fractions isotopic results from this study demonstrate that whole rock isotopic data may not provide the appropriate level of detail necessary to address some processes in the bushveld complex however systematic changes have the potential to elucidate the timing of contamination with regard to other processes crystal aging compaction driven recrystallization and mineral exsolution occurring within a slowly cooled crystal liquid vapor mush system

global surface temperatures over the past two millennia 1 we present reconstructions of northern and southern hemisphere mean surface temperature over the past two millennia based on high resolution proxy temperature data which retain millennial scale variability these reconstructions indicate that late 20th century warmth is unprecedented for at least roughly the past two millennia for the northern hemisphere conclusions for the southern hemisphere and global mean temperature are limited by the sparseness of available proxy data in the southern hemisphere at present

sulfide and platinum mineralization in the merensky reef evidence from hydrous silicates and fluid inclusions the base metal sulfides of the merensky reef are associated with hydrous silicates and intense deuteric hydrous alteration of cumulus and postcumulus silicates biotite and phlogopite crystallized in the vicinity of sulfides from a volatile enriched highly fractionated intercumulus melt amphibole chlorite and talc are later alteration phases of cumulus pyroxene and intercumulus plagioclase biotite is often accompanied by zircon rutile and quartz accessory quartz hosts a complex suite of h2o nacl cacl2 co2 ch4 fluid inclusions which have thus far not been described from the merensky reef the earliest fluid inclusion compositions are nacl h2o with less than 10 vol water co2 coexisting with a halite daughter crystal and brine and polyphase inclusions with up to six daughter and accidental phases and high contents of divalent cations the maximum trapping temperature is around 730 c at 4 to 5 kb pressure later inclusion generations are h2o nacl co2 h2o and pure co2 and ch4 the presence of cl rich fluids during the intercumulus stage of the crystallizing merensky reef is directly related to the mode of sulfide precipitation prior to sulfide unmixing in a hydrous magma sulfur is likely to be present as h2s sulfur saturation causes reaction of h2s with oxides of the silicate melt to form a sulfide melt plus water during reaction the magma is enriched in water until a separate fluid unmixes it carries all compounds with high fluid melt partition coefficients as well as metals capable of forming oh and cl complexes precious metals are assumed to have fractionated into the cl rich fluid as cl complexes rather than being dissolved in the sulfide melt during the cooling evolution of the fluid the precious elements precipitate around the periphery of sulfide melt droplets the model proposed explains the distribution pattern of platinum group minerals in the merensky reef better than any orthomagmatic mineralization concept offered so far

sulfides native metals and associated trace minerals of the skaergaard intrusion greenland evidence for late hydrothermal fluids sulfide assemblages precious metals transition metal alloys and associated accessory phases were characterized throughout the skaergaard intrusion to better constrain the sulfide saturation history of the intrusion and the role of late magmatic volatiles in modifying the skaergaard metal budget and distribution sulfides in and below the middle zone of the layered series of the intrusion are readily replaced by low ti magnetite the ratio low ti magnetite mode sulfide mode indicating oxidation of sulfides reaches maximum values in the lower zone of the layered series sulfide assemblages below the middle zone are typically accompanied by minor biotite apatite and rare calcite as well as trace compositionally distinctive clinopyroxene and orthopyroxene the occurrence of ag au pt cu and metal alloys outside of the middle zone is further evidence of the skaergaard intrusion parental magma being s poor native ag commonly accompanied by trace amounts of cl occurs both in and below the middle zone evidence of coexisting precious metal brine assemblages exists where native metals are accompanied by sylvite halite and ag is accompanied by ag halides ag occurrences in the middle zone are of irregular morphology with trace cl s calcite further evidence supportive of a metal brine assemblage is observed where ag quartz is found in an apparent open clinopyroxene hosted fluid inclusion consisting of na si cl ca k and s ag is used to model the behavior of precious and transition metals in the presence of an exsolving fluid phase numerical modeling suggests that in a sulfide bearing system residual ag concentrations and concentrations in the exsolved fluid are most affected at the point where sulfide is lost to a separating volatile fluid phase it is suggested that owing to the low s nature of the skaergaard system fractional crystallization and early fluid saturation produced enrichment of ag with other precious and transition metals in the interstitial silicate liquid much higher than normal due to delayed sulfide saturation as this interstitial liquid evolved ag was lost to an exsolved volatile phase of high salinity and migrated upward a similar process likely occurred for au and other elements with high affinities for cl

an evaluation of models of apatite compositional variability using apatite from the middle banded series of the stillwater complex montana apatite is a relatively common accessory mineral in the olivine bearing zones ob iii and ob iv of the middle banded series of the stillwater complex occurring interstitial to cumulus grains as monomineralic inclusions in cumulus grains and in polymineralic clusters which may or may not be included in the cumulus grains eighty nine of 185 samples examined were found to contain some apatite the f cl oh content of the apatite show distinct stratigraphic variations xclap mole fraction cl in apatite of interstitial apatite increases upsection in both ob iii and ob iv with average values ranging from 0 15 to 0 85 in ob iii and from 0 03 to 0 60 in ob iv xfap varies inversely with xclapwith average values ranging from 0 00 to 0 70 while xohap remains relatively constant near 0 40 or decreases slightly with height these variations are remarkable given that no appreciable stratigraphic variations in either the major or trace element compositions of any of the cumulus minerals are found in the 800 m of section that comprise ob iii and ob iv within sample variation of xclap for samples containing cl rich apatite is substantially larger up to 0 65 xclap than for samples with more f rich apatite xclap varies by approximately 0 15 although interstitial apatite is found throughout ob iii and ob iv apatite occurring as monomineralic inclusion in cumulus grains or in polymineralic clusters is almost exclusively found in samples with cl rich apatite the data are best explained by a model involving the degassing of a cl rich volatile phase from the crystallizing interstitial liquid the up section migration of this fluid resulted in the crystallization of f rich apatite in the lower portion and progressive cl enrichment in the apatite with height the presence of hornblende bearing dikes veins and pegmatoids at the level of maximum cl enrichment is consistent with a fluid migration model

solubility of pt in sulphide mattes implications for the genesis of pge rich horizons in layered intrusions the partitioning of pt in sulphide melt matte has been studied as a function of fs2 and fo2 at 1200 and 1300 c the results show that the solubility of pt in mattes increases strongly with increasing fs2 and decreases weakly with increasing fo2 the increase in pt solubility with increasing fs2 is attributed to pt dissolving in the melt as a sulphide species and the weak inverse dependence of pt solubility on fo2 to the diluting effect of increasing o in the melt at high fo2 these results coupled with measurements of pt solubility in silicate melts taken from the literature allow the calculation of pt matte silicate melt partition coefficients d pt matte sil for a range of conditions pertinent to the formation of pt rich horizons in layered intrusions the calculated values range between 107 and 1011 depending on fo2 and fs2 several orders of magnitude higher than previously published values our preferred value for d pt matte sil for conditions appropriate to the merensky reef is 107 and for the stillwater pt rich horizon 108 the new results are consistent with the magmatic hypothesis for pt rich horizons in layered intrusions

axial and radial thermal responses of energy pile under six storey residential building the axial and radial thermal responses of a cast in place energy pile 10 m long and 0 6 m in diameter installed in unsaturated sand under a six storey building are examined during a heating cooli

phenomenological solar signature in 400 years of reconstructed northern hemisphere temperature record 1 we study the solar impact on 400 years of a global surface temperature record since 1600 this period includes the pre industrial era roughly 1600 1800 or 1600 1900 when negligible amount of anthropogenic added climate forcing was present and the sun realistically was the only climate force affecting climate on a secular scale and the industrial era roughly since 1800 1900 when anthropogenic added climate forcing has been present in some degree we use a recent secular northern hemisphere temperature reconstruction moberg et al 2005 three alternative total solar irradiance tsi proxy reconstructions lean et al 1995 lean 2000 wang et al 2005 and a scale by scale transfer climate sensitivity model to solar changes scafetta and west 2005 2006 the phenomenological approach we propose is an alternative to the more traditional computer based climate model approach and yields results proven to be almost independent on the secular tsi proxy reconstruction used we find good correspondence between global temperature and solar induced temperature curves during the pre industrial period such as the cooling periods occurring during the maunder minimum 1645 1715 and the dalton minimum 1795 1825 the sun might have contributed approximately 50 of the observed global warming since 1900 scafetta and west 2006 we briefly discuss the global cooling that occurred from the medieval maximum 1000 1100 ad to the 17th century minimum