role of fluids in fe ti p mineralization of the proterozoic damiao anorthosite complex china insights from baddeleyite zircon relationships in ore and altered anorthosite abstract the damiao fe ti p deposit offers a rare opportunity for studying late stage fe ti ore forming processes in proterozoic anorthosites the orebodies are hosted in anorthosite and commonly show chlorite dominated alteration in the contact zone on both sides but the nature and origin of fluids in fe ti p mineralization remains contentious baddeleyite is a common accessory mineral in anorthosites and fe ti p orebodies and typically occurs as blebs and lamellae in primary ilmenite reflecting decreasing solubility of zr in ilmenite during slow cooling and consequent exsolution of zro2 two types of zircon are identified in the fe ti p orebodies and altered anorthosite at damiao and both are related to hydrothermal replacement of baddeleyite by si rich fluids the type i zircon shows subhedral to anhedral shapes with variable sizes 5 50 m in fe ti p orebodies and coexists with magnetite rutile symplectite formed by ilmenite breakdown in contrast the type ii zircon typically occurs as tiny aggregates in chlorite quartz titanite replacement fronts of altered anorthosite indicative of a hydrothermal origin the type i zircon yielded an age of 1739 16 ma similar to the age of baddeleyite previously reported for the orebodies formation of the type i zircon is related to the replacement of baddeleyite in the presence of si enriched hydrothermal fluids evolved from magma ti in zircon geothermometry indicates a fluid temperature of 700 c for the formation of the type i zircon however homogenization temperature of fluid inclusions in co precipitated apatite suggests that the type ii zircon in altered anorthosite may have formed by later hydrothermal fluids at temperature of 350 c our results indicate that the fe ti p mineralization of the damiao anorthosite complex involved hydrous melts and magmatic hydrothermal processes with the fe ti oxides being formed at the magmatic stage and apatite at the hydrothermal stage

u pb monazite ages in amphibolite to granulite facies orthogneiss reflect hydrous mineral breakdown reactions sveconorwegian province of sw norway in the rogaland vest agder terrain of the sveconorwegian province of sw norway two main sveconorwegian metamorphic phases are reported a phase of regional metamorphism linked to orogenic thickening m1 and a phase of low pressure thermal metamorphism associated with the intrusion of the 931 2 ma anorthosite charnockite rogaland igneous complex m2 phase m1 reached granulite facies to the west of the terrane and m2 culminated locally at 800 850 c with the formation of dry osumilite bearing mineral associations monazite and titanite u pb geochronology was conducted on 17 amphibolite to granulite facies orthogneiss samples mainly from a suite of 1050 2 8 ma calc alkaline augen gneisses the feda suite in these rocks prograde negatively discordant monazite crystallized during breakdown of allanite and titanite in upper amphibolite facies at 1012 1006 ma in the feda suite and other charnockitic gneisses concordant to slightly discordant monazite at 1024 997 ma probably reflects breakdown of biotite during granulite facies m1 metamorphism a spread of monazite ages down to 970 ma in biotite hornblende samples possibly corresponds to the waning stage of this first event in the feda suite a well defined monazite growth episode at 930 925 ma in the amphibolite facies domain corresponds to major clinopyroxene formation at the expense of hornblende during m2 growth or resetting of monazite was extremely limited during this phase in the granulite facies domain up to the direct vicinity of the anorthosite complex the m2 event was shortly followed by cooling through ca 610 c as indicated by tightly grouped u pb ages of accessory titanite and titanite relict inclusions at 918 2 ma over the entire region a last generation of u poor monazite formed during regional cooling below 610 c in hornblende rich samples at 912 904 ma this study suggests 1 that monazite formed during the prograde path of high grade metamorphism may be preserved 2 that monazite ages reflect primary or secondary growth of monazite linked to metamorphic reactions involving redistribution of rees and th and or fluid mobilisation 3 that the u pb system in monazite is not affected by thermal events up to 800 850 c provided that conditions were dry during metamorphism

calcite dolomite geothermometry in the system caco3 mgco3 feco3 an experimental study an experimental study of the system caco3 mgco3 feco3 was undertaken in order to calibrate the iron correction to the calcite dolomite geothermometer which is based on the solubility of magnesium in calcite in the assemblage calcite dolomite the experiments at 450 c and lower temperatures resulted in products with a very small grain size and incomplete equilibration however application of a carefully devised automatic data processing algorithm to analyses of the phases in experimental charges combined with a thermodynamic analysis results in geothermometer diagrams which should be preferred to previous theoretical predictions

liquidus phase relationships on the join anorthiteforsterite quartz at 20 kbar with applications to basalt petrogenesis and igneous sapphirine liquidus phase relationships determined on the join anorthite forsterite quartz at 20 kbar show primary phase fields for quartz q forsterite fo enstatite en spinel sp anorthite an sapphirine sa and corundum cor increasing pressure causes 1 thefo andan primary phase fields to contract 2 theen q andcor fields to expand 3 thefo en boundary line to move away from the q apex 4 theen q boundary line to move also away from the q apex but by a smaller amount and 5 a primary phase field forsa to appear at a pressure between 10 and 20 kbar seven liquidus piercing points at 20 kbar have been located as follows crystalline phases liquid composition wt temperature c sp sa cor an81fo17q2 1575 fo en sp an52fo39q9 1540 en sp sa an59fo31q10 1490 sa an cor an70fo15q15 1430 an q cor an66fo7q27 1410 sa an en an62fo18q20 1400 an en q an59fo15q26 1380 it is concluded that 1 the shift of thefo en boundary line away from the quartz apex with pressure confirms many other studies showing that melts generated from peridotite source rocks decrease in silica content as pressure increases 2 even though plagioclase is not a stable phase in peridotite source rocks at pressures above about 10 kbar it can crystallize from mafic magmas at pressures at least up to 20 kbar 3 sapphirine crystallizes from mafic magmas at high pressures and may be important in the construction of petrogenetic models based on trace element considerations

sveconorwegian massif type anorthosites and related granitoids result from post collisional melting of a continental arc root article i nfo two magmatic suites were emplaced during the post collisional evolution of the sveconorwegian orogeny an anorthosite mangerite charnockite suite amc suite and an hornblende and biotite bearing granitoids suite hbg suite the amc suite is exclusively located in the westernmost and warmest part of the orogen in granulite facies gneisses whereas the hbg suite intruded in the rest of the orogen but not in the granulite domain new u pb zircon geochronological data confirm previous age determinations 970 932 ma hbg suite and 933 916 ma amc suite the mafic facies of the two post collisional magmatic suites have similar geochemical compositions but the hbg differentiation trend displays higher cao sr u and th as well as lower k2o and feot mgo than the amc differentiation trend the hbg suite is hydrous and has a broadly higher fo2 whereas the amc suite is anhydrous the inferred parent magmas of both suites have overlapping initial sr nd and pb isotopic compositions with increasing differentiation the two trends point towards two different crustal contaminants together with the recent recognition of a major crustal shear zone located just east of the amc suite this difference suggests that the suites were emplaced in two different lithotectonic units using published experimental constraints and geochemical modeling we suggest that the mafic facies of both suites were produced by partial melting of lower crustal sources which were previously underplated probably during the evolution of a long lasting convergent margin later these lower crustal sources were modified by the regional granulite facies metamorphism 1 035 to 0 97 ga prevailing in the westernmost part of the orogen thus producing an anhydrous lower crustal source for the amc suite accordingly we conclude that the sveconorwegian massif type anorthosites result from partial melting of the continental arc root this process if accepted for other amcg anorthosite mangerite charnockite granite complexes was possible in the proterozoic because of a sufficiently high temperature but not in the archean because in subduction zones the main transfer to the crust was then felsic tonalites granodiorites and not basaltic we thus further suggest that the onset of massif type anorthosites at the beginning of the proterozoic may mark the time when plate tectonics began to operate in a similar way as today

emplacement of xenolith nodules in the kaupulehu lava flow hualalai volcano hawaii the basaltic kaupulehu 1800 1801 lava flow of hualalai volcano hawaii contains abundant ultramafix xenoliths many of these xenoliths occur as bedded layers of semi rounded nodules each thinly coated with a veneer typically 1 mm thick of lava the nodule beds are analogous to cobble deposits of fluvial sedimentary systems although several mechanisms have been proposed for the formation of the nodule beds it was found that at more than one locality the nodule beds are overbank levee deposits the geological occurrence of the nodules certain diagnostic aspects of the flow morphology and consideration of the inferred emplacement process indicate that the kaupulehu flow had an exceptionally low viscosity on eruption and that the flow of the lava stream was extremely rapid with flow velocities of at least 10 m s 1 more than 40 km h 1 this flow is the youngest on hualalai volcano and future eruptions of a similar type would pose considerable hazard to life as well as property

zircon coronas around fe ti oxides a physical reference frame for metamorphic and metasomatic reactions ilmenite in coronitic gabbros from the bamble and kongsberg sectors southern norway is surrounded by zircons ranging in diameters from a fraction of a micrometer to 10 m across the zircons are inert during subsequent metamorphism amphibolite to pumpellyite prehnite facies and metasomatism scapolitization and albitization and can be found as trails in silicates phlogopite talc chlorite amphibole albite and tourmaline in the altered rocks the trails link up to form polygons outlining the former oxide grain boundary this 3 dimensional framework of zircons is used to a recognize metasomatic origin of rocks b quantify the mobility of elements during mineral replacement c establish the growth direction of reaction fronts and to identify the reaction mechanism as dissolution reprecipitation zircon coronas on fe ti oxides have been described from a number of terrains and appear to be common in mafic rocks gabbros and granulites providing a tool for a better understanding of metasomatic and metamorphic reactions

quantitative modelling of the apparent decoupling of mg and ni in kimberlitic olivine margins a reply to the comment on cordier et al 2015 by a moore moore proposes in his comment moore 2017 that marginal zones in olivine grains in kimberlites fig 1a are produced by crystallization from kimberlite melt he suggests that the chemical zones observed in these marginal zones inner transition zones and outer margins illustrated in his fig 1 result from abrupt changes in distribution coefficients during crystallization he proposes that the transition zones characterized by variable fo at constant and high ni contents are produced by crystallization with high kdfe mg 0 45 and low dni 4 whereas the margins characterized by a sharp drop in ni content at nearly constant fo fig 1b are produced by crystallization with higher dni owing to a sudden change in physical conditions of crystallization p

ultramafic and mafic rocks from the garret transform fault near 13 30 s on the east pacific rise igneous petrology serpentinized peridotites metagabbros and fresh basaltic rocks were dredged from the garret transform fault near 13 s on the east pacific rise two dredge hauls taken on the northern wall from about 3100 3600 m consisted of aphyric and picritic basalts while peridotites gabbros and moderately phyric basalts were recovered in a single dredge located near the deepest part 4616 4820 m of the transform valley well preserved igneous textures and mineralogical assemblages enable us to differentiate between tectonites including harzburgites and clinopyroxene bearing harzburgites and cumulates consisting of plagioclase dunite troctolites olivine gabbros and ilmenite gabbros the harzburgites are likely to represent deep seated peridotites left after extraction of basaltic melt during upper mantle partial melting of a lherzolite the ultramafic cumulates underwent some deformation and show textural and mineralogical evidences which suggest formation at a minimum depth corresponding to the very lower crust it is also inferred that the composition of the coexisting liquid along with early cumulus crystals has a ratio mg mg fe2 of 0 7 high cao na2o ratios and a low ni content about 150 ppm when compared to similar rock types from atlantic fracture zones subsequent uplift during rifting of the oceanic lithosphere enhanced plastic deformation subsolidus recrystallization and retrogressive metamorphism of the gabbros and the ultramafics

magma chamber processes in the tellnes ilmenite deposit rogaland anorthosite province sw norway and the formation of fe ti ores in massif type anorthosites the origin of igneous fe ti oxide ores associated with massif type anorthosites is investigated through a detailed study of the world class tellnes ilmenite deposit part of the late proterozoic 930 920 ma amc series of the rogaland anorthosite province sw norway more than 100 samples from drill cores reveal significant petrographical and compositional variations within the ore body four zones are defined based on variations in modal proportions and cumulus mineral assemblages the lower and upper central zones and the lower and upper marginal zones plagioclase and whole rock compositions discriminate the zones and display patterns interpreted as a result of mixing of either plagioclase ilmenite or plagioclase ilmenite orthopyroxene olivine cumulates with a melt of ferrodioritic jotunitic composition with a content decreasing from 80 to 20 from the margins to the central part of the ore body phase diagrams for a jotunitic parental magma reproduce the crystallization sequence at 5 kb the orthopyroxene olivine liquidus boundary is a peritectic in the bjerkreim sokndal layered intrusion and a cotectic in tellnes and this explains the differences in the sequence of crystallization of the two intrusions the high concentration of ilmenite well above cotectic proportions resulted from gravity sorting in the tellnes ore body which represents the lower part of a larger magma chamber uniform sr isotope ratios do not support magma mixing the cryptic layering of the ore body precludes injection as a crystal mush but favours in situ crystallization from an evolving magma in a sill like magma chamber the present trough shape and mineral orientations result from deformation during gravity induced subsidence and by up doming of the anorthosite fractional crystallization of a tio2 rich magma with ilmenite as an early liquidus mineral and plagioclase buoyancy are the principal mechanisms responsible for the formation of fe ti deposits in proterozoic massif type anorthosites

experimental transport of si al and mg in hydrothermal solutions an application to vein mineralization during high pressure low temperature metamorphism in the french alps a study of hydrothermal vein mineralization in meta argillites subjected to high pressure low temperature metamorphism reveals that ferromagnesian e g chlorite and pure aluminosilicate e g pyrophyllite mineralization can be correlated with regimes of increasing and decreasing temperature respectively an experimental study of the transport of silica aluminum and magnesium in hydrothermal solutions has been undertaken to simulate variations in the physical conditions during metamorphism and the accompanying mass transport in a closed system thermodynamic and kinetic analysis of the experimental results indicates that local equilibrium among aqueous and mineral phases controls the distribution and composition of hydrothermal vein mineralization and that vein mineralogy can be used to infer the sense of variation of pressure and temperature during metamorphism

origin of ultramafic xenoliths containing exsolved pyroxenes from hualalai volcano hawaii hualalai volcano hawaii is best known for the abundant and varied xenoliths included in the historic 1800 kaupulehu alkalic basalt flow xenoliths which range in composition from dunite to anorthosite are concentrated at 915 m elevation in the flow rare cumulate ultramafic xenoliths which include websterite olivine websterite wehrlite and clinopyroxenite display complex pyroxene exsolution textures that indicate slow cooling websterite olivine websterite and one wehrlite are spinel bearing orthopyroxene olivine cumulates with intercumulus clinopyroxene plagioclase two wehrlite samples and clinopyroxenite are spinel bearing olivine cumulates with intercumulus clinopyroxene orthopyroxene plagioclase two pyroxene geothermometry calculations based on reconstructed pyroxene compositions indicate that crystallization temperatures range from 1225 to 1350 c migration or unmixing of clinopyroxene and orthopyroxene stopped between 1045 and 1090 c comparisons of the abundance of k2o in plagioclase and the abundances of tio2 and fe2o3in spinel of xenoliths and mid ocean ridge basalt and a single 87sr 86sr determination indicate that these hualalai xenoliths are unrelated to mid ocean ridge basalt similarity between the crystallization sequence of these xenoliths and the experimental crystallization sequence of a hawaiian olivine tholeiite suggest that the parental magma of the xenoliths is hualalai tholeiitic basalt xenoliths probably crystallized between about 4 5 and 9 kb the 155 230 c of cooling which took place over about 120 ka the age of the youngest hualalai tholeiitic basalt yield maximum cooling rates of 1 3 10 3 1 91 10 3 c yr hualalai ultramafic xenoliths with exsolved pyroxenes crystallized from hualalai tholeiitic basalt and accumulated in a magma reservoir located between 13 and 28 km below sealevel we suspect that this reservoir occurs just below the base of the oceanic crust at about 19 km below sealevel

investigation of three fe ti oxide deposits associated with grenvillian anorthosite massifs as potential source for lunar analogue ilmenite1 2 terrestrial ilmenite has been assessed for its suitability in the preparation of a simulant of lunar high ti mare regolith which is needed to test oxygen production on the lunar surface during fut

effect of grossular content in garnet on the partitioning of fe and mg between garnet and biotite in contrast to ferry 1980 x ca values in garnet even lower than 0 1 have a significant effect on the calculated equilibrium temperature using the experimental calibration of the fe and mg paritioning between garnet and biotite garnet compositions and mg fe distribution coefficients from samples of the eoalpine staurolite in zone in the southern otztal are related by the quadratic regression equation ink d 1 7500 0 0226 2 978 0 5317 x ca gt 5 906 2 359 x ca gt 2 temperatures derived by the ferry and spear 1978 calibration using chemistry corrected k d values are petrologically realistic analysis of our data supports non ideal mixing of grossular with almandine pyrope solid solution the derived excess mixing energies are quite small for the almandine pyrope solution w femg 133 cal mole and about 2775 cal mole for the difference between pyrope grossular and almandine grossular solutions w mgca w feca at metamorphic conditions of 570 c and 5 000 bar the mixing parameters proposed by ganguly and saxena 1984 are not confirmed by our data as they would result in significantly lower temperatures

metamorphic p t paths from pelitic schists and greenstones from the south west tauern window eastern alps petrological data from intercalated pelitic schists and greenstones are used to construct a pressure temperature path followed by the upper schieferhulle ush series during progressive metamorphism and uplift in the south west tauern window italy pseudomorphs of al epidote fe epidote albite oligoclase chlorite after lawsonite and data on amphibole crystal chemistry indicate early metamorphism in the lawsonite albite chlorite subfacies of the blueschist facies at p 7 8 kbar geothermometry and geobarometry yield conditions of final equilibration of the matrix assemblage of 475 25 c 5 6 kbar calculations with plagioclase and phengite inclusions in garnet indicate early garnet growth at pressures of 7 5 kbar garnet zoning patterns are complex and reversals in zoning can be correlated between samples thermodynamic modelling of these zoning profiles implies garnet growth in response to four distinct phases of tectonic activity fluid inclusion data from coexisting immiscible h2o co2 nacl fluids constrain the uplift path to have passed through temperatures of 380 30 c at 1 3 0 2 kbar there is no evidence for metamorphism of ush at pressures greater than 7 5 kbar in this area of the tauern window this is in contrast to pressures of 10 kbar recorded in the lower schieferhulle only 2 3 km across strike a history of differential uplift and thinning of the intervening section during metamorphism is necessary to reconcile the p t data obtained from these adjacent tectonic units

dissolution solution transfer diffusion versus fluid flow and volume loss during deformation metamorphism dissolution and solution transfer during deformation metamorphism are controlled by the partitioning of deformation into progressive shearing and shortening components progressive shearing is readily accommodated by slip on the planar crystal structure of phyllosilicates and graphite without accumulating dislocation density gradients across grain boundaries progressive shortening is accommodated by the cores of most other minerals including sulphides these minerals develop strain and hence dislocation density gradients on their rims due to progressive shearing along grain boundaries these gradients are particularly large when the mineral abuts phyllosilicate or graphite the resulting chemical potential gradients between the core and rim drive dissolution causing removal of the highly strained grain margins removal of dissolved material by solution transfer is aided by the geometry of shearing of phyllosilicates and graphite around other grains in an active anastomosing foliation interlayers and interfaces on boundaries lying at a low angle to the direction of shearing and oriented relative to the sense of shear such that they can open gape by small amounts water present in these interlayer spaces becomes destructured considerably enhancing diffusion rates along the foliation penetrative volume loss especially in deforming metamorphosing pelitic rocks is large at all metamorphic grades increasing and becoming more penetrative with depth to at least the transition into granulite and eclogite facies transference of material by fluid flow from deep to high levels in the earth s crust is precluded because thousands to tens of thousands of rock volumes of fluid are required necessitating continual recirculation of fluid from shallow to deep crustal levels in one large or several small sets of cells unless some extremely large scale form of fluid channelling is possible reassessment of diffusion mechanisms and hence rates during deformation and pervasive foliation generation in large volumes of rock where fluid channeling cannot provide enough fluid indicates that diffusion can proceed with sufficient rapidity that massive recirculation of fluid is no longer required the amount of fluid can be reduced sufficiently to allow large volume losses by a one way flow of fluid to the earth s surface in deforming metamorphosing environments where the fluid pressure equals or exceeds the hydrostatic pressure deformation partitioning controlled dissolution progressively changes the bulk chemistry of a rock containing phyllosilicates or graphite during deformation metamorphism because matrix minerals other than phyllosilicates and graphite are preferentially removed the large size of porphyroblasts if present tends to preserve them from dissolution hence the bulk chemistry operative during subsequent porphyroblast growth can have changed considerably from that operative when the first porphyroblasts grew in rocks in which bedding is still well preserved

crustal growth by magmatic overplating in the galapagos the isotopic compositions of xenoliths hosted in lavas from floreana island indicate that they formed from magmas unlike those at present day floreana instead the xenoliths are geochemically more similar to magmas now erupting from sierra negra and cerro azul volcanoes at the leading edge of the galapagos hotspot this is the first evidence for compositional evolution at a galapagos volcano and indicates increasing contributions from an iso topically enriched source with time as the volcano is carried away from the focus of the hot spot clinopyroxenes in many of the xenoliths exhibit positive anomalies of sr and eu which are attributed to the breakdown of plagioclase the growth of clinopyroxene at the expense of plagio clase results from compression as the crust cools compression is caused by growth mostly from above as shallow intrusions and lavas load the middle and upper oceanic crust

role of olivine cumulates in destabilizing the flanks of hawaiian volcanoes the south flank of kilauea volcano is unstable and has the structure of a huge landslide it is one of at least 17 enormous catastrophic landslides shed from the hawaiian islands mechanisms previously proposed for movement of the south flank invoke slip of the volcanic pile over seafloor sediments slip on a low friction decollement alone cannot explain why the thickest and widest sector of the flank moves more rapidly than the rest or why this section contains a 300 km3 aseismic volume above the seismically defined decollement it is proposed that this aseismic volume adjacent to the caldera in the direction of flank slip consists of olivine cumulates that creep outward pushing the south flank seawards average primary kilauea tholeiitic magma contains about 16 5 wt mgo compared with an average 10 wt mgo for erupted subaerial and submarine basalts this difference requires fractionation of 17 wt 14 vol olivine phenocrysts that accumulate near the base of the magma reservoir where they form cumulates submarine erupted kilauea lavas contain abundant deformed olivine xenocrysts derived from these cumulates deformed dunite formed during the tholeiitic shield stage is also erupted as xenoliths in subsequent alkalic lavas the deformation structures in olivine xenocrysts suggest that the cumulus olivine was densely packed probably with as little as 5 10 vol intercumulus liquid before entrainment of the xenocrysts the olivine cumulates were at magmatic temperatures 1100 c when the xenocrysts were entrained olivine at 1100 c has a rheology similar to ice and the olivine cumulates should flow down and away from the summit of the volcano flow of the olivine cumulates places constant pressure on the unbuttressed seaward flank leading to an extensional region that localizes deep intrusions behind the flank these intrusions add to the seaward push this mechanism ties the source of gravitational instability to the caldera complex and deep rift systems and therefore limits catastrophic sector failure of hawaiian volcanoes to their active growth phase when the core of olivine cumulates is still hot enough to flow

a recalibration of the chlorite biotite muscovite geobarometer massonne 1981 reported experiments on the composition of muscovite in the assemblage phlogopite muscovite k feldspar quart the experimental data have been used to recalculate the equilibrium conditions for the chlorite muscovite biotite quartz assemblage which has been proposed as a new geobarometer by powell and evans 1983 the recalculated equilibrium shows much steeperdp dt slopes than those calculated by powell and evans 1983 nevertheless with the necessary precautions it is suggested that the barometer may provide the critical user with valuable pressure estimates

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

ilmenite composition in the tellnes fe ti deposit sw norway fractional crystallization postcumulus evolution and ilmenite zircon relation major and trace element xrf and in situ la icp ms analyses of ilmenite in the tellnes ilmenite deposit rogaland anorthosite province sw norway constrains a two stage fractional crystallization model of a ferrodioritic fe ti p rich melt stage 1 is characterized by ilmenite plagioclase cumulates partly stored in the lower part of the ore body lower central zone lcz and stage 2 by ilmenite plagioclase orthopyroxene olivine cumulates upper central zone ucz the concentration of v and cr in ilmenite corrected for the trapped liquid effect 1 defines the cotectic proportion of ilmenite to be 17 5 wt during stage 1 and 2 implies an increase of dvilm during stage 2 most likely related to a shift in fo2 the proportion of 17 5 wt is lower than the modal proportion of ilmenite ca 50 wt in the ore body implying accumulation of ilmenite and flotation of plagioclase the fraction of residual liquid left after crystallization of tellnes cumulates is estimated at 0 6 and the flotation of plagioclase at 26 wt of the initial melt mass the increasing content of intercumulus magnetite with stratigraphic height from 0 to ca 3 wt results from differentiation of the trapped liquid towards magnetite saturation the mgo content of ilmenite 1 4 4 4 wt is much lower than the expected cumulus composition it shows extensive postcumulus re equilibration with trapped liquid and ferromagnesian silicates correlated with distance to the host anorthosite the zr content of ilmenite provided by in situ analyses is low 114 ppm and uncorrelated with stratigraphy or cr content the data demonstrate that zircon coronas observed around ilmenite formed by subsolidus exsolution of zro2 from ilmenite the u pb zircon age of 920 3 ma probably records this exsolution process

the crustal tongue melting model and the origin of massive anorthosites recent detailed field studies in several anorthosite complexes have shown that anorthosites are frequently associated with weakness zones in the crust which may have favoured their emplacement at mid crust levels recent experimental data have shown that the parent magma compositions of various anorthosite massifs lie on thermal highs in the relevant phase diagrams at 10 13 kbar indicating that these magmas cannot be derived by fractionation of peridotitic mantle melts but by melting of gabbronoritic sources in the lower crust at 40 50 km depths in the sveconorwegian province terne boundaries have been traced in deep seismic profiles to moho offsets or to tongues of lower crustal material underthrust to depths higher than 40 km in southern norway we suggest that a lithospheric scale weakness zone the feda transition zone has channelled the rogaland anorthosites through linear delamination asthenospheric uprise and melting of a mafic lower crustal tongue

molybdenite re os dating of biotite dehydration melting in the rogaland high temperature granulites s norway abstract the ability of the re os system in molybdenite to record and preserve the age of granulite facies metamorphism in polymetamorphic belts is tested using the orsdalen w mo district rogaland s norway a low pressure high temperature granulite facies domain displaying osumilite and pigeonite isograds is exposed around the 931 2 ma rogaland anorthosite complex available u pb monazite and zircon data show that a 0 93 ga contact metamorphism overprints a 1 03 0 97 ga regional sveconorwegian metamorphism in the gneiss basement molybdenite and scheelite in the orsdalen district occur in orthopyroxene bearing leucocratic veins parallel to the regional foliation the veins are interpreted as migmatic leucosomes formed by fluid absent incongruent melting of the biotite rich host rock above ca 800 c producing a granulite facies orthopyroxene garnet residual assemblage molybdenite is interpreted as a product of the melting reaction crystallized from trace amounts of mo released from biotite in the host rock during partial melting four re os analyses of molybdenite from three samples representing two mines yield an isochron age of 973 4 ma the isochroneity of the data indicates that the precipitation of molybdenite and the partial melting event are recorded on the district scale the re os system in molybdenite was not affected by subsequent 0 93 ga contact metamorphism corresponding to formation of garnet quartz coronitic textures around molybdenite and other minerals in the deposits the results indicate that granulite facies conditions prevailed at 973 4 ma near the end of a protracted event of regional metamorphism 1 03 0 97 ga biotite dehydration melting recorded in orsdalen took place at a pressure of ca 5 5 kbar orthopyroxene garnet plagioclase quartz thermobarometry possibly in association with regional decompression the study shows that granulite facies metamorphism 0 97 ga took place before intrusion of massif type anorthosites in rogaland 0 93 ga the study suggests that the high temperature osumilite bearing assemblage may be related to the 0 97 ga event and that massif type anorthosites may not be a cause for the high temperature thermal anomaly in the crust but a late expression of it

origin of rhythmic anorthositic pyroxenitic layering in the damiao anorthosite complex china implications for late stage fractional crystallization and genesis of fe ti oxide ores abstract the 1 7 ga damiao anorthosite complex dac in the north china craton contains abundant ti magnetite dominated ore deposits both the fe ti p rich silicate rocks and massive fe ti p ores occur as discordant late stage dikes cross cutting early stage anorthosites with irregular but sharp boundaries field and petrographic observations indicate that some late stage dikes are composed of unique oxide apatite gabbronorites oagns whereas others comprise well developed alternating late stage anorthosites and fe ti p rich pyroxenites defining rhythmic layers massive fe ti p ores are closely related to the fe ti p rich pyroxenites plagioclase and whole rock compositions of different rock types were analyzed to constrain the late stage magma evolution and genesis of the fe ti oxide ores the similar mineralogical assemblages ree and hfse patterns suggest that the different rock types formed by differentiation from a common parental magma early stage anorthosites are characterized by positive eu anomalies and low ree contents whereas the late stage dike like rocks display no significant eu anomalies and high ree contents plagioclase compositions in the late stage rocks show a decrease of an contents when compared to that of the early stage rocks based on field relations petrography and well defined linear compositional trends the sequence of crystallization is inferred as early stage anorthosites leuconorites norites oagns late stage anorthosites fe ti p rich pyroxenites massive fe ti p ores and massive fe ti p ores the oagns which underwent relatively rapid crystallization represent an early phase during the residual magma evolution after anorthosite separation whereas the rhythmic layers formed by slow but extensive fractional crystallization of interstitial melt high solubility of phosphorous played an important role in the formation of rhythmic layering massive fe ti p ores crystallized and segregated directly from the magma of fe ti p rich pyroxenites thus representing the most evolved products of the residual magma progressive and extensive fractional crystallization of residual ferrobasaltic magma is probably responsible for the formation of large scale massive fe ti p ores

an experimental study of the influence of oxygen fugacity on fe ti oxide stability phase relations and mineral melt equilibria in ferro basaltic systems

prograde metamorphic zircon formation in gabbroic rocks the tale of microtextures u pb zircon dates of metagabbroic rocks such as eclogite mafic granulite and garnet amphibolite are used to constrain the timing of tectonometamorphic evolution in orogens worldwide for such interpretation however it is imperative to define at which stage of the p t evolution that zircon crystallization took place the prograde peak or retrograde stage in order to accurately interpret metamorphic zircon ages it is necessary to assess how the zircon crystallized or recrystallized as zircon can dissolve or grow under different metamorphic conditions zircon is robust to retrograde isotopic resetting under most crustal conditions but equilibrium zr mass balance models have suggested that zircon is largely produced during retrograde metamorphism this study takes a textural approach and identifies and reviews zircon forming textures and reactions in gabbro and metagabbro at different metamorphic grades ranging from subgreenschist to upper amphibolite and eclogite facies and at different stages of metamorphic recrystallization the textural relationships demonstrate that in metagabbro metamorphic zircon grows during the early stage of metamorphic recrystallization independent of pressure and temperature the mode of zircon formation is remarkably similar throughout different stages of metamorphic recrystallization and the most significant source of zr is igneous baddeleyite hence in contrast to the equilibrium mass balance model most zircon in metagabbro forms by prograde metamorphic reactions that consume igneous phases and not by late retrograde reactions and the onset of zircon forming reactions is governed primarily by the introduction of a hydrous fluid commonly accompanied by ductile deformation less

the stillwater complex integrating zircon geochronological and geochemical constraints on the age emplacement history and crystallization of a large open system layered intrusion a reply to the comment by rais latypov on wall et al j petrology 59 153 190 2018

environments of crystallization and compositional diversity of mauna loa xenoliths two picrite flows from the sw rift zone of mauna loa contain introduction xenoliths of dunite harzburgite lherzolite plagioclase bearing xenoliths hosted in mauna loa s tholeiitic stage lavas lherzolite and harzburgite troctolite gabbro olivine gabbro and provide a rare opportunity to glimpse into the volcano s gabbronorite textures and olivine compositions preclude a mantle magma chambers and plumbing system in hawaii source for the xenoliths and rare earth element concentrations of xenoliths are much more abundant in alkalic lavas than xenoliths and clinopyroxene indicate that the xenolith source is in tholeiitic lavas as a result of reconfiguration of the not old oceanic crust but rather a hawaiian tholeiitic stage conduit and storage system as magma supply rate demagma pyroxene compositions phase assemblages and textural creases clague 1987 each xenolith records the chemrelationships in xenoliths indicate at least two different crys ical and physical environment in a small part of the tallization sequences calculations using the pmelts algorithm magma chamber at a particular time similarly the show that the two sequences result from crystallization of primitive individual crystals that compose xenoliths hosted in a mauna loa magmas at 6 kbar and 2 kbar independent single flow or series of flows may reflect the changes in calculations of olivine ni fo compositional variability in the magma composition over time textural and complagioclase bearing xenoliths over these crystallization sequences positional features of xenoliths preserve evidence for are consistent with observed olivine compositional variability variation in geochemical petrological and physical contwo parents of similar bulk composition but which vary in ni ditions within the magma system content are necessary to explain the olivine compositional compositions of mauna loa xenoliths range widely variability in the dunite and plagioclase free peridotitic xenoliths and include pyroxenite peridotite troctolite and dunite xenoliths probably crystallized in a small magma storage area as well as gabbroic lithologies many exhibit distinctive beneath the rift zone rather than the large sub caldera magma cumulate or laminated textures previous studies of reservoir primitive picritic magmas are introduced to isolated mauna loa xenoliths are few white 1966 jackson et rift zone storage areas during periods of high magma flux al 1982 so the initial objective of this study is to subsequent eruptions reoccupy these areas and entrain and characterize the petrography and geochemistry of a reptransport xenoliths to the surface resentative collection of samples the second objective is to analyze textures mineral assemblages phase relationships and compositions to identify genetic relationships among the xenoliths as well as with the host to construct a crystallization history of the magmas that are parental to the xenoliths and ultimately to model the

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

variations of trace element concentration of magnetite and ilmenite from the taihe layered intrusion emeishan large igneous province sw china implications for magmatic fractionation and origin of fe ti v oxide ore deposits abstract in situ la icp ms trace elemental analysis has been applied to magnetite and ilmenite of the taihe layered intrusion emeishan large igneous province sw china in order to understand better fractionation processes of magma and origin of fe ti v oxide ore deposits the periodic reversals in mg ti mn in magnetite and mg sc in ilmenite are found in the middle zone of the intrusion and agree with fractionation trends as recorded by olivine fo plagioclase an and clinopyroxene mg compositions these suggest the taihe intrusion formed from open magma chamber processes in a magma conduit with multiple replenishments of more primitive magmas the v and cr of magnetite are well correlated with v and cr of clinopyroxene indicating that they became liquidus phases almost simultaneously at an early stage of magma evolution ilmenite from the middle and upper zones shows variable cr ni v mg nb ta and sc contents indicating that ilmenite at some stratigraphic levels crystallized slightly earlier than magnetite and clinopyroxene the early crystallization of magnetite and ilmenite is the result of the high feot and tio2 contents in the parental magma the ilmenite crystallization before magnetite in the middle and upper zones can be attributed to higher tio2 content of the magma due to the remelting of pre existing ilmenite in a middle level magma chamber compared to the coeval high ti basalts the relatively low zr hf nb and ta contents in both magnetite and ilmenite throughout the taihe intrusion indicate that they crystallized from fe ti p rich silicate magmas positive correlations of ti with mg mn sc and zr of magnetite and zr with sc hf and nb of ilmenite also suggest that magnetite and ilmenite crystallized continuously from the homogeneous silicate magma rather than an immiscible fe rich melt therefore frequent replenishments of fe ti p rich silicate magma and gravitational sorting and settling are crucial for the formation the massive and apatite rich disseminated ores in the lower and middle zones of the taihe intrusion

internally consistent geothermometry and h 2 o barometry in metamorphic rocks the example garnet chlorite quartz temperature and h2o activity can be determined with high precision using metamorphic mineral assemblages that define both a dehydration equilibrium and a temperature sensitive cation exchange equilibrium such determinations are obtained by applying the gibbs method and then integrating two resulting differential equations as illustrated here for the assemblage garnet chlorite quartz the first equation a geothermometer that monitors temperature based upon fe mg exchange between garnet and chlorite was calibrated using rocks at pecos baldy new mexico 0 0 05 p bars 19 02 t k 4607 ln kd 24 156 with errors of 8 c based upon analytical precision the second equation monitors differences in the activity of water between specimens 1 and 2 0 0 1 xmg chl 1 2 05 p2 p1 33 02 5 96 ln xfe chl 1 xalm 1 t2 t1 2 67 rt1ln a h2o 2 a h2o 1 5 96 t1ln xfe chl 2xalm 1 xfe chl 1xalm 2

imaging downward granitic magma transport in the rogaland igneous complex sw norway combining geological mapping and petrological structural and geophysical gravity and seismic data already available for the late proterozoic rogaland igneous complex of norway allows the 3d shape of the bjerkreim sokndal layered intrusion to be modelled as a thick cumulate series capped by massive granitic rocks using the latter data along with the spectacular convergent linear flow pattern that covers both the cumulates and the felsic rocks of this chamber evidence is presented to show that the granitic material was downdragged through the sinking of its high density mafic floor into lower density anorthosites and granulitic gneisses this example illustrates that downward gravity driven flows of rocks were active in addition to upward flows in the building of the early crust up to late proterozoic times helping to explain the geochemical and structural complexities of the old crust

metamorphic zircon formation at the transition from gabbro to eclogite in trollheimen surnadalen norwegian caledonides a transition from gabbro to eclogite has been investigated at vinddoldalen in south central norway with the aim to link reaction textures to metamorphic zircon growth and to obtain a direct u pb zircon age of the metamorphic process in the different rocks of the transition zone zircon occurs as i igneous prismatic grains ii metamorphic polycrystalline rims and pseudomorphs after baddeleyite and iii as tiny 10 mu m bead like zircon grains textural relations suggest that type ii zircon formed by breakdown of baddeleyite in the presence of silica whereas fe ti oxides were the main zr source for the type iii zircon subsolidus liberation of zr and formation of bead zircon took place by oxyexsolution of titanomagnetite during fluid assisted metamorphism and by resorption of fe ti oxide in rock domains that were completely recrystallized to eclogite sims secondary ion mass spectrometry and tims thermal ionization mass spectrometry dating provides comparable u pb ages of magmatic zircon and baddeleyite baddeleyite tims yielded an age of 1457 11 ma for the gabbro emplacement bead type metamorphic zircon from eclogite gave 425 10 ma tims dating the metamorphic transition from gabbro to eclogite in the upper basement of the lower allochthon in the south central scandinavian caledonides less

fluid flow and diffusion in the waterville limestone south central maine constraints from strontium oxygen and carbon isotope profiles oxygen carbon and strontium isotopic profiles across the margin of the waterville limestone member are used to investigate advective and diffusive transport during metamorphism of the waterville formation in south central maine usa rb sr isotopic systematics were homogenized on the 10 cm hand specimen scale at ages that are within error of the 366 6 ma rb sr whole rock age of the syn metamorphic hallowell pluton this is consistent with a plutonic heat source for this low pressure andalusite and sillimanite grade acadian metamorphic terrane advective displacements of all three isotope profiles at the garnet grade blue rock quarry indicate fluid flow to the east into the limestone and the oxygen isotope profile implies a time integrated fluid flux of 3 2 1 5 m 3 m 2 2 error this cross layer flux is insufficient to cause the observed reaction progress of the muscovite ankerite quartz to biotite anorthite in plagioclase calcite reaction in the 100 m thick waterville limestone member and much of the fluid flow responsible may have been layer parallel the isotope profiles indicate advective diffusive homogenization over distances of 1 5 m 13 c to 6 m 18 o and such homogenization distances are difficult to reconcile with observations of order of magnitude variations in reaction progression the centimetre scale or less it is possible that infiltration occurred during events short lived compared with diffusion that the reactions started at different temperatures dependent on bulk composition or that diffusion of water from layers with less reactants to layers with more reactants was important in driving the biotite producing reaction however variations of fluid composition inferred from the mineral assemblages are apparently inconsistent with diffusion driving reactions progress and models of precursor assemblages do not indicate significant compositional control of the temperature of the first appearance of biotite in the rocks irrespective of the details of flow and diffusive exchange on the centimetre scale the average reaction progress in the waterville limestone member requires significant layer parallel fluid fluxes

crystallization sequence and magma chamber processes in the ferrobasaltic sept iles layered intrusion canada the sept iles layered intrusion quebec canada 564 ma is a large plutonic body with a diameter of 80 km and a thickness of 6 km made up from its base to top of a layered series with troctolite and gabbro and an upper border series with anorthosite capped by cupolas of a type granite chilled margin compositions suggest a ferrobasaltic parental magma close to that of the skaergaard intrusion but much richer in iron and titanium samples from drill cores and surface sampling of the 4 7 km thick layered series reveal a succession of massive troctolites and layered gabbros that contain 24 fe ti oxide layers cm to m thick and many anorthositic autolithic blocks the sequence of crystallization in the layered series is plagioclase an72 34 and olivine fo75 21 followed by magnetite and ilmenite then ca rich pyroxene and finally apatite an olivine gap is observed between fo66 and fo59 the saturation of fe ti oxides before ca rich pyroxene is interpreted to be the result of the high feot and tio2 contents and the low cao content of the parental magma contamination by old continental crust has occurred during crystallization of the layered series as indicated by sr isotopic compositions 87sr 86sr564 0 70360 0 70497 the differentiation trend of the intrusion is interrupted by two large and many small reversals to more primitive compositions of cumulus phases cr content of magnetite and lower sr isotope ratios these reversals and the intermittent disappearance of some phases are interpreted as resulting from magma chamber replenishments by undifferentiated primitive basaltic magma and mixing with the resident magma the author 2010 published by oxford university press all rights reserved for permissions please e mail journals permissions oxfordjournals org

experimental study of liquid evolution in an fe rich layered mafic intrusion constraints of fe ti oxide precipitation on the t f o 2 and t ϱ paths of tholeiitic magmas the newark island layered intrusion a composite intrusion displaying a similar fractionation sequence to the skaergaard has both dikes which preserved liquids fed into the intrusion and chilled pillows of liquids resident in the chamber this study reports experimentally determined one atmosphere liquid lines of descent of these compositions as a function of oxygen fugacity which varies from qfm quartz fayalite magnetite to 0 5 log10 units above iw iron wustite these experiments reveal a strong oxygen fugacity dependence on the order of appearance and relative abundances of the fe ti oxide minerals titanomagnetite saturates prior to ilmenite at qfm but the order is reversed at lower oxygen fugacities in the layered series of the newark island intrusion ilmenite arrives shortly before titanomagnetite and the titanomagnetite ilmenite ratio decreases monotonically after the cumulus appearance of titanomagnetite comparison of the crystallization sequence in the intrusion with that of the experiments requires that the oxygen fugacity in the intrusion increased relative to qfm before titanomagnetite saturation and decreased afterward but always remained between the qfm and iw buffers similar trends in the modes of the fe ti oxides ilmenite and titanomagnetite in the skaergaard kiglapait and somerset dam intrusions along with fe2o3 feo ratios in morbs suggest that such a temperature oxygen fugacity path may be typical of tholeiitic magma differentiation calculations of the temperature density paths of the experimental liquids indicate that at all possible oxygen fugacities the density must have decreased abruptly after fe ti oxide saturation accordingly liquids replenishing the intrusion after fe ti oxide saturation should pond at the bottom of the chamber quenching against older cumulates field observation at the newark island intrusion confirm this prediction the similarities in the fractionation paths of several other layered intrusions to that of the newark island intrusion suggest that the density of the liquids in these intrusions also decreased after fe ti oxide saturation experiments on a suggested initial skaergaard liquid are consistent with this model

cosmic ray exposure dating with in situ produced cosmogenic 3he results from young hawaiian lava flows in an effort to determine the in situ production rate of spallation produced cosmogenic 3 he and evaluate its use as a surface exposure chronometer we have measured cosmogenic helium contents in a suite of hawaiian radiocarbon dated lava flows the lava flows ranging in age from 600 to 13 000 years were collected from hualalai and mauna loa volcanoes on the island of hawaii because cosmic ray surface exposure dating requires the complete absence of erosion or soil cover these lava flows were selected specifically for this purpose the 3 he production rate measured within olivine phenocrysts was found to vary significantly ranging from 47 to 150 atoms g 1 yr 1 normalized to sea level although there is considerable scatter in the data the samples younger than 10 000 years are well preserved and exposed and the production rate variations are therefore not related to erosion or soil cover data averaged over the past 2000 years indicate a sea level 3 he production rate of 125 30atoms g 1 yr 1 which agrees well with previous estimates the longer record suggests a minimum in sea level normalized 3 he production rate between 2000 and 7000 years 55 15atoms g 1 yr 1 as compared to samples younger than 2000 years 125 30 atoms g 1 yr 1 and those between 7000 and 10 000 years 127 19atoms g 1 yr 1 the minimum in production rate is similar in age to that which would be produced by variations in geomagnetic field strength as indicated by archeomagnetic data however the production rate variations a factor of 2 3 0 8 are poorly determined due to the large uncertainties in the youngest samples and questions of surface preservation for the older samples calculations using the atmospheric production model of o brien 1979 35 and the method of lal and peters 1967 11 predict smaller production rate variations for similar variation in dipole moment a factor of 1 15 1 65 because the production rate variations archeomagnetic data and theoretical estimates are not well determined at present the relationship between dipole moment and production rate will require further study precise determination of the production rate is an important uncertainty in the surface exposure technique but the data demonstrate that it is feasible to date samples as young as 600 years of age providing that there has been no erosion or soil cover therefore the technique will have important applications for volcanology glacial geology geomorphology and archaeology

time calibration of a pt path from the western tauern window eastern alps the problem of closure temperatures new hornblende k ar and 39ar 40ar and mica rb sr and k ar ages are used to place specific timemarks on a well constrained pressure temperature path for the late alpine metamorphism in the western tauern window after identification of excess 40ar the closure behavior of ar in hornblende is compared with that of sr and ar in phengite and biotite samples were collected in three locations whose maximum temperatures were 570 c zemmgrund 550 c pfitscher joch and 500 540 c landshuter hutte

the effect of pressure on dsr plag melt and dcr opx melt implications for anorthosite petrogenesis the crystal liquid partition coefficients for sr and cr dsr and dcr have been determined from electron microprobe analyses of plagioclase liquid and orthopyroxene liquid pairs produced in melting experiments run at pressures from 1 bar to 27 kbar on two compositions relevant to anorthosite petrogenesis one is a primitive jotunite hypersthene monzodiorite tj the other is a sample of an anorthositic dyke 500b results indicate that dsr plag liq remains nearly constant with increasing pressure tj 1 7 to 2 6 500b 0 9 to 1 4 this modest variation apparently results from the combined and opposing effects of crystal chemistry and pressure dsr increases with the albite content of plagioclase which itself increases with pressure along a composition s liquidus so pressure must have an intrinsic negative effect the two models for dsr j blundy b wood geochim cosmochim acta 55 1991 193 209 i bindeman a davis m drake geochim cosmochim acta 62 1998 1175 1193 that take into account the strong correlation between dsr and plagioclase composition overestimate dsr at high pressure whereas the two models that ignore plagioclase composition s morse geochim cosmochim acta 56 1992 1735 1738 r nielsen comput geosci 18 1992 773 788 underestimate it moreover since none of these models takes into account any pressure effect the discrepancies between predicted and observed dsr increase with pressure for all models the new results also show that dcr opx liq increases significantly with pressure dcr 2 at 1 atm and 14 2 at 10 kbar these new data confirm earlier less precise determinations of dcr that were used to infer a high pressure origin for al and cr rich orthopyroxene megacrysts the calculated sr and cr concentrations of liquids in equilibrium at 10 kbar with plagioclase and orthopyroxene megacrysts from anorthosite massifs sr 370 to 610 ppm and cr 20 to 130 ppm are in the range of what is observed in high al gabbros and primitive jotunites the inferred parent magmas of massive anorthosites fl 2000 published by elsevier science b v all rights reserved

rare earth element geochemistry of garnet lherzolite and megacrystalline nodules from minette of the colorado plateau province abstract mineral and whole rock ree abundances in garnet lherzolite and megacrystalline nodules from the thumb display broad correlations with major element compositions lherzolites with 12 modal clinopyroxene plus garnet high ca al lherzolites have relatively flat chondrite normalized whole rock ree patterns lherzolites poor in clinopyroxene and garnet low ca al lherzolites have lower hree in clinopyroxenes and garnets and higher whole rock lree hree it is concluded that the low ca al lherzolites may have undergone lree metasomatism after depletion of the major element compositions by partial melting and that much of the garnet now present was originally dissolved in aluminous orthopyroxene the high ca al lherzolites may be interpreted either as primordial mantle samples or as products of equilibration with very lree enriched liquids the megacrystalline nodules are medium to ultracoarse grained intergrowths and megacrysts with mineral compositions similar to discrete nodule suites in kimberlites the ree abundances of the megacrystalline minerals are consistent with an origin as cumulates from magma with extremely fractionated ree similar to minette or kimberlite the patterns of correlation of ree and major elements in this inclusion suite are similar to the patterns observed in the garnet lherzolite and discrete nodule suites of southern african kimberlites both of the subcontinental mantle provinces represented by these suites contain three distinct petrogenetic components refractory garnet lherzolite enriched in lree and depleted in hree fertile garnet lherzolite with generally chondritic ree abundances and a suite of ultracoarse minerals precipitated from magma with extremely fractionated ree generally similar to the host magmas

p t evolution of metasediments from the eclogite zone south central tauern window austria abstract petrologic data on the paragenesis of i kyanite zoisite marbles and ii garnet chloritoid quartz mica schists are presented with the goal of providing constraints on the pressure temperature evolution of the eclogite zone tauern window austria the peak metamorphic assemblages in the two rock types are i kyanite zoisite dolomite quartz zoisite muscovite dolomite calcite quartz and ii garnet chloritoid kyanite muscovite quartz epidote dolomite zn staurolite the estimated peak metamorphic conditions are 19 2 kbar 590 20 c secondary alteration of the kyanite zoisite marbles was accomplished in two stages the early stage resulted in the production of margarite paragonite secondary muscovite and chlorite and the later stage resulted in the formation of sudoite a di trioctahedral mg al layer silicate and kaolinite the early alteration is bracketed at conditions between 3 and 10 kbar 450 550 c and the later alteration between 200 and 350 c p 3 kbar the p t path is characterized by maximum burial to approximately 19 kbar 60 70 km at 590 c followed by nearly isothermal decompression to approximately 10 kbar 30 km and then more gradual decompression with cooling to approximately 3 kbar 10 km alteration was apparently accomplished by the influx of h 2 o rich fluids with the composition of the fluid locally buffered by the mineral assemblage

the open system geochemical evolution of alkalic cap lavas from haleakala crater hawaii usa lavas ranging from alkalic basalt to mugearite are exposed in a continuous stratigraphic section in haleakala crater on the island of maui these lavas define a series of discrete magma batches separated by sharp compositional breaks characterized by upsection increases in incompatible element e g k2o nb ree th ba rb contents al2o3 cao ratios and la sm ratios and complementary decreases in compatible element e g mgo ni cr v sc contents within magma batches there are systematic upsection decreases in incompatible element contents al2o3 cao ratios and la sm ratios and systematic increases in compatible element contents the observed compositional cyclicity can be explained as the result of alternating periods of low and high magma chamber recharge rates the upsection interbatch compositional breaks represent periods of low or negligible magma chamber recharge during which eruption is suppressed and the geochemical effects of crystal fractionation dominate those imposed by magma mixing at the initiation of recharge the influx of mafic magma into the magma chamber produces an eruption resulting in partial evacuation of the magma chamber following eruption recharge magma mixes with magma remaining in the magma chamber continued recharge and mixing during these eruptive periods cause the compositions of lavas to become more mafic with time thus during a recharge period the bulk composition of the magma chamber approaches that of the recharge magmas the most mafic lavas i e the youngest lavas within each magma batch typically are relatively evolved mg 48 mgo 7 wt and therefore cannot represent primary magmas evidence for polybaric fractionation suggests that these lavas represent recharge magmas that have undergone crystal fractionation in a deeper level reservoir prior to injection into the shallow level haleakala magma chamber the observed fine scale geochemical cyclicity is superimposed over the larger scale systematic changes in isotope ratios and highly incompatible trace element ratios that are attributed to time dependent changes in the proportions of distinct mantle components in the source of these lavas these contrasting scales of temporal geochemical variability illustrate how shallow level magma chamber processes have imposed short time period 2000 years compositional controls on magmas whose compositions were also changing over relatively long time periods 800 000 years due to source related effects the decrease in magma supply rates during the alkalic cap phase of hawaiian volcanism probably results in increased magma chamber residence times thus creating the greater magmatic diversity observed the specifics of the petrologic and geochemical evolution of individual hawaiian volcanoes during this period differ at least in part because of differences in magma supply rates

mineralogical evidence for fluid rock interaction accompanying prograde contact metamorphism of siliceous dolomites alta stock aureole utah usa contact metamorphism of siliceous dolomite in the southern part of agrees well with the q m tiff 3 4 10 7 mol m 2 determined by the metamorphic aureole of the alta stock utah usa produced numerical simulation of the temperature and 18 o depletion profiles the prograde isograd sequence talc tc tremolite tr forsterite preserved in the southern aureole the estimates of q m tiff for the fo and periclase per calcite cc dolomite do ge forsterite and tremolite zones have much greater uncertainty but othermometry and phase equilibria define a general prograde t may indicate that fluid flux was considerably lower in these zones x co2 path of decreasing x co2 with rising temperature for than in the periclase zone given the outward down temperature the dolomite high variance assemblages typify the aureole per subhorizontal flow geometry indicated by a variety of petrologic cc and fo cc do characterize the inner aureole per and geochemical and geothermometry evidence presented here and elsefo zones and tr do cc and tc do cc are where this decrease implies that fluid has leaked from the flow widespread in the outer aureole tr and tc zones low variance system between the periclase and tremolite zones assemblages are rare and the thickness of reaction zones coexisting reactant and product minerals at the isogradic reaction fronts are narrow tens of metres or less the mineral assemblages calculated progress of isograd reactions and the prograde t x co2 path all key words alta fluid flow infiltration marble mineralogical indicate that massive dolomite was infiltrated by significant fluxes of water rich fluids during prograde metamorphism and that the fluid flow was down temperature and laterally away from the igneous contact fluid infiltration continued through at least the initial retrograde cooling of the periclase zone down t fluid flow introduction is also consistent with the results of cc do geothermometry and both mineral assemblages and stable isotopes have been patterns of 18 o depletion in this area the close spatial association

genesis of intermediate igneous rocks at the end of the sveconorwegian grenvillian orogeny s norway and their contribution to intracrustal differentiation abundant ferroan metaluminous granitoids 970 950 ma emplaced at the end of the sveconorwegian collisional orogeny 1130 900 ma are dominated by intermediate to silicic compositions with rare mafic facies both 73 fractional crystallization of an amphibole bearing gabbroic cumulate substracted from the parent mafic composition and 30 non modal batch melting of an amphibolitic source equivalent in composition to the mafic facies produce a monzodioritic liquid with appropriate trace element composition a better fit is obtained for the partial melting process both processes could have occurred simultaneously to produce mafic cumulates and restites as there is no evidence for large volumes of dense mafic rocks in the sveconorwegian upper crust these dense mafic rocks were probably produced in the lower crust formation of these granitoids thus contributed to the vertical stratification of the proterozoic continental crust and also to the transfer of water from the lower crust to the surface

temperature and age constraints on the metamorphism of the tethyan himalaya in central nepal a multidisciplinary approach abstract metasediments of devonian to triassic age of the tethyan himalaya th from several areas in central and western nepal between western dolpo and marsyandi valley were sampled for thermo metamorphic studies illite and chlorite crystallinity vitrinite reflectance calcite dolomite and chlorite chloritoid geothermometers k ar dating on illite rich fractions and zircon fission track thermochronology this paper reports for the first time the occurrence of chloritoid in the th out of the range of granite contact aureoles it also presents the first zircon fission track dating performed on th metasediments the peak temperatures of metamorphism have been around 250 300 c 320 350 c 330 370 c and 400 450 c in the western dolpo hidden valley manang and marpha areas respectively in the manang and hidden valley areas illite k ar data are interpreted as ages of recrystallized k white micas newly formed during metamorphism at around 25 30 ma in the marpha area illite k ar and zircon fission track ages 12 15 ma are consistent representing cooling ages after metamorphic overprinting of higher grade than in the other areas the joint investigation of the organic maturation and zircon ft chronology yields insight on the thermal calibration of zircon reset the rmax of 5 7 to 8 0 indicates a temperature range of ca 315 325 c which is in the partial annealing zone of the zircon ft thermochronometer our results might be explained by the presence of a thick thrust sheet once existing above the study area

titanium aluminum and interlayer cation substitutions in biotite from high grade gneisses west greenland detailed electron microprobe study pelitic to mafic metamorphic rocks from two localities higher ti k k na and possible k na similar al iv and lower al vi in granulite vs amphibolite grade samples modified journal abstract

geochemical constraints on the genesis of the tellnes ilmenite deposit southwest norway the ilmenite norite of the tellnes fe ti deposit in the aana sira massif type anorthosite is connected to a main dike which varies in composition from monzonorite to quartz mangerite fine grained satellite dikes also occur in the vicinity of the main dike a number of rock samples have been analyzed for 36 major and trace elements an rb sr whole rock isochron 12 samples gives an age of 930 ma initial sr isotope compositions of the ilmenite noritc the main dike and the satellite dikes are 0 7050 0 7069 and 0 7100 respectively thus precluding a comagmatic origin without invoking contamination the evolution of the main dike can be accounted for by a closed system fractional crystallization of a monzonoritic magma that is without progressive contamination which gave rise to a series of liquids prior to intrusion mass balance calculation permits a two stage process in which noritic cumulates were subtracted trace element behavior is also consistent with such a model the satellite dikes represent undifferentiated monzonorites with trace elements and isotopic ratios implying a source material quite different from that of the main dike monzonorite the orebody is made up of ilmenite norite and small amounts of more plagioclase rich rocks which plot on linear trends in variation diagrams it is interpreted as a noritic cumulate which was enriched in dense oxide rich magma before being emplaced as a crystal mush the parental magma was noritic in composition unsaturated in apatite and probably derived from the crystallization of the enclosing massif anorthosite it is not precluded either that it could have given rise to the main dike monzonoritic liquid after being contaminated by lower crustal material nevertheless as an alternative it is not possible to reject two distinct parental magmas for the orebody and the main dike they would have evolved in two separated magma chambers before the tapping of these chambers and simultaneous injection of their contents in the dike the main dike illustrates the process by which a quartz mangerite can derive from a monzonoritic magma and gives support to a comagmatic origin of charnockitic and monzonoritic rocks

the plagioclase magma density paradox re examined and the crystallization of proterozoic anorthosites intermediate composition plagioclase an40 60 is typically less dense than the relatively evolved basaltic magmas from which it crystallizes and the crystallization of plagioclase produces a dens residual liquid thus plagioclase should have a tendency to float in these magmatic systems there is however little direct evidence for plagioclase flotation cumulates either in layered intrusions or in proterozoic anorthosite complexes the layered series of the poe mountain anorthosite southeast wyoming contains numerous anorthosite leucogabbro blocks that constrain density relations during differentiation all blocks are more mafic than their hosting anorthositic cumulates their plagioclase compositions are more calcic and each block is in strong sr isotopic disequilibrium with its host cumulate associated structures disrupted and deformed layering indicate that 1 a floor was present during crystallization and that plagioclase was accumulating and or crystallizing on the floor 2 compositional layering and plagioclase lamination formed directly at the magma crystal pile interface and 3 the upper portions of the crystal pile contained significant amounts of interstitial melt liquid densities are calculated for proposed high al olivine gabbroic parental magmas and fe enriched ferrodioritic and monzodioritic residual magmas of the anorthosites taking into account pressure oxygen fugacity p2o5 estimated volatile contents and variable temperatures of crystallization for all reasonable conditions calculated block densities are greater than those of the associated melt the liquid densities however are greater than those for an40 60 plagioclase which cannot have settled to the floor plagioclase must either have been carried to the floor in relatively dense packets of cooled liquid plus crystals or have crystallized in situ a sloping floor possibly produced by diapiric ascent of relatively light plagioclase rich cumulates is required to allow for draining and removal of the dense interstitial liquid produced in the crystal pile and may be a characteristic feature during the crystallization of many proterozoic anorthosites and layered intrusions

molybdenite re os dating constrains gravitational collapse of the sveconorwegian orogen sw scandinavia abstract re os dating of molybdenite from small deposits is used to define crustal domains exhibiting ductile versus brittle behaviour during gravitational collapse of the sveconorwegian orogen in sw scandinavia a 1019 3 ma planar quartz vein defines a minimum age for brittle behaviour in central telemark in rogaland vest agder molybdenite associated with deformed quartz and pegmatite veins formed between 982 3 and 947 3 ma in the amphibolite facies domain three deposits and between 953 3 and 931 3 ma west of the clinopyroxene in isograd two deposits in the vicinity of the 0 93 0 92 ga rogaland anorthosite complex the data constrain the last increment of ductile deformation to be younger than 0 95 and 0 93 ga in these two metamorphic zones respectively molybdenite is the product of an equilibrium between biotite oxide and sulfide minerals and a fluid or hydrated melt phase after the peak of 1 03 0 97 ga regional metamorphism molybdenite precipitation is locally episodic a model for gravitational collapse of the sveconorwegian orogen controlled by lithospheric extension after 0 97 ga is proposed in the west of the orogen the rogaland vest agder sector is interpreted as a large shallow gneiss dome formed slowly in two stages in a warm and structurally weak crust the first stage at 0 96 0 93 ga was associated with intrusion of the post collisional hornblende biotite granite suite the second stage at 0 93 0 92 ga restricted to the southwesternmost area was associated with intrusion of the anorthosite mangerite charnockite suite most of the central part of the orogen was already situated in the brittle upper crust well before 0 97 ga and did not undergo significant exhumation during collapse in the east of the orogen situated against the colder cratonic foreland exhumation of high grade rocks of the eastern segment occurred between 0 97 and 0 95 ga and included preservation of high pressure rocks but no plutonism

zircon growth during progressive recrystallization of gabbro to garnet amphibolite eastern segment sveconorwegian orogen the interpretation of whether a dated metamorphic zircon generation grew during the prograde peak or retrograde stage of a metamorphic cycle is critical to geological interpretation this study documents a case at herrestad in the eastern part of the 1 0 ga sveconorwegian province involving progressive metamorphic recrystallization of gabbro to garnet amphibolite and associated behaviour of zr bearing minerals in this case textures show that baddeleyite is by far the main source of zr for metamorphic zircon growth the amount of metamorphic zircon formed was primarily controlled by the degree of metamorphic recrystallization which in turn was controlled by deformation and the presence of a fluid as a transport medium zircon in the herrestad rocks shows a range of morphologies and internal textures at different degrees of metamorphic recrystallization igneous zircon occurs together with baddeleyite in coarse grained olivine free facies of the gabbro metamorphic polycrystalline zircon rims on baddeleyite and minute 5 m bead like zircon grains at fe ti oxide boundaries characterize the transition to coronitic metagabbro with increasing metamorphic recrystallization polycrystalline zircon rims grow at the expense of baddeleyite and the amount of minute bead like zircon increases forming strings of zircon beads with increasing distance from fe ti oxide grains the progressive breakdown of baddeleyite results in polycrystalline zircon aggregates that become denser and finally form single grains in completely recrystallized garnet amphibolite late magmatic zircon crystallized at 156765 ma whereas metamorphic zircon dates amphibolite facies metamorphic recrystallization at 97067 ma the herrestad case illustrates a general rule that the bulk zr budget in originally baddeleyite bearing rocks will rapidly become locked into metamorphic zircon during the first event of metamorphic recrystallization when silica and zr are released from the igneous minerals incomplete metamorphic recrystallization and partial preservation of baddeleyite however also allows later stages of zircon formation thus in incompletely reacted rocks the final result may be highly complex with microscale zircon of several age generations less

crystallization of titaniferous chromite magnesian ilmenite and armalcolite in tholeiitic suites in the karoo igneous province titaniferous chromite up to 8 wt tio2 and magnesian ilmenite up to 10 wt mgo coexist at the base of the differentiated tholeiitic mount ayliff intrusion in the karoo province of southern africa suggesting that the original magma was tio2 rich picritic lavas with 3 tio2 from the lebombo monocline of the karoo province also contain microphenocrysts of magnesian ilmenite up to 6 wt mgo and armalcolite up to 7 wt mgo these oxide mineral associations and compositions are atypical of tholeiitic magmas in which chromite usually has less than 1 wt tio2 ilmenite less than 3 wt mgo and armalcolite is rarely a primary mineral experiments have been conducted at one atmosphere pressure on a range of compositions to determine the effect of tio2 on the crystallization and composition of chromite ilmenite and armalcolite the results indicate that increasing the tio2 content of picritic magmas increases the tio2 content of the spinel mainly at the expense of al2o3 whereas cr2o3 is not affected spinel compositions in the mount ayliff intrusion with over 45 wt cr2o3 less than 10 wt al2o3 and 8 wt tio2 were duplicated in experiments on a picrite at temperatures of about 1 200 c at the ni nio buffer increasing fo2 from fayalite magnetite quartz to ni nio buffer is shown to increase the crystallization temperature of armalcolite and to decrease that of ilmenite the total feo content of the liquid has little influence on the crystallization temperature of these phases the tio2 content of the liquid when either ilmenite or armalcolite crystallizes varies inversely with sio2 content the mgo content of the liquid at which ilmenite or armalcolite crystallizes depends upon the tio2 content of the starting composition with naturally occurring and experimetally determined saturation being demonstrated for liquids with 5 wt mgo and 5 5 wt tio2 the partition coefficent for mgo between armalcolite or ilmenite and liquid is about 1 5 observed magnesian armalcolite and ilmenite compositions in picrite lavas both minerals and in the mount ayliff intrusion ilmenite only are consistent with crystallization from a tio2 rich magma with approximately 5 wt mgo the fe23 tio5 component of armalcolite in the picrite lavas matches those formed experimentally at temperatures of 1 150 1 110 c and fo2 of the ni nio to ni nio 1 log unit similarities also exist between the compositions of chromite ilmenite and armalcolite and liquid fraction ation trends of some hawaiian high tio2 lavas and the experimental studies presented here

cumulate origin and polybaric crystallization of fe ti oxide ores in the suwalki anorthosite northeastern poland fe ti oxide ores in the proterozoic suwalki massif type anorthosite northeastern poland have been recognized through geophysical exploration and extensive drilling down to 2 600 m depth the fe ti oxide rich rocks from suwalki consist of vanadium poor ti magnetite in lenses varying from the centimeter to the kilometer scale fe ti rich rocks are commonly layered and have gradational contacts with the host anorthosite they do not represent well defined intrusions such as the major tellnes and lac tio deposits based on petrography modal proportions whole rock analyses and liquidus phase compositions of fe ti oxide ores the sequence of crystallization is as follows plagioclase ti magnetite ilmenite followed by orthopyroxene then clinopyroxene and finally apatite the comparatively low v content 0 20 0 67 wt v in ti magnetite results from relatively oxidized crystallization conditions the diapiric emplacement of the anorthositic pluton influenced the crystallization of the fe ti ores and is responsible for the crystal sorting controlled by the density contrast of liquidus phases polybaric crystallization of fe ti oxide ores is evidenced by variable al2o3 ca 1 5 wt content of the associated orthopyroxene polybarism is responsible for the appearance of fe ti oxides before orthopyroxene due to the decreasing stability field of orthopyroxene with pressure

fe ti v p ore deposits associated with proterozoic massif type anorthosites and related rocks abstract magmatic rocks containing economic concentrations of iron titanium vanadium and phosphorous are commonly associated with massif type anorthosites and related rocks this rock association is part of the anorthosite mangerite charnockite rapakivi granite suites that are restricted to the proterozoic understanding the geochemistry and emplacement mechanisms of ilmenite magnetite and apatite ore deposits is crucial for exploration efficient mining operations and ore processing this review discusses the controlling factors on the grade of an ore its mineralogy and its major and trace element distribution we present petrogenetic models of currently mined deposits lac tio tellnes damiao and discuss the characteristics of minor ore bodies from anorthosite provinces worldwide grenville north china craton east european craton rogaland laramie models of formation of anorthosite and related rocks are presented as well as the nature of the possible parental magmas of the suite a mineralogical classification of fe ti ores is proposed 1 gabbro noritic ilmenite ore apatite magnetite 2 ti magnetite dominated ore 3 nelsonite fe ti oxides apatite and 4 rutile ilmenite ore the stability of ilmenite and magnetite is then critically reviewed and the influence of various factors particularly oxygen fugacity and crystallization pressure is examined we discuss liquidus compositions of fe ti oxides and the behavior of important trace elements such as cr and v both of which are sensitive to fo2 variations post cumulus evolution of both oxides can occur due to re equilibration with trapped liquid re equilibration with ferromagnesian silicates exsolution oxidation reaction between ilmenite and magnetite and metamorphic overprinting these various processes are described and their effects on the oxide geochemistry are emphasized several potential ore forming processes have been invoked and can explain the formation of huge concentration of ilmenite magnetite apatite fractional crystallization can be combined with crystal sorting and plagioclase buoyancy to produce relative enrichment of dense ore minerals silicate liquid immiscibility can segregate conjugate si rich and fe rich melts the latter being enriched in fe ti p magma mixing can produce hybrid magmas located in a single phase field of the phase diagram and precipitate a pure ilmenite cumulate alternative processes are also described such as ejection of fe ti enriched residual melts by filter pressing and compaction solid state remobilization of ilmenite in veins and hydrothermal transport of fe and ti from the host anorthosite followed by concentration in veins and lenticular ore bodies the magnetic properties of fe ti ore deposits present contrasting signatures depending on whether the natural remanent magnetization is dominated by hemo ilmenite or multi domain magnetite micro and macro scale deformation features of ore rocks are intimately correlated with magma emplacement and with ballooning of the anorthosite diapir associated with gravitational sagging of dense ore bodies exploration perspectives show that oxide apatite gabbronorites are interesting targets because ilmenite in these rocks is poorer in cr and mg and because the ti resource may be combined with apatite and vanadiferous magnetite

marginal mafic intrusions as indicators of downslope draining of dense residual melts in anorthositic diapirs abstract geochemical and isotopic investigation of three small mafic intrusions loyning 1250 150 m hogstad 2000 200 m koldal 1250 500 m in the marginal zones of the egersund ogna loyning koldal and ana sira massif type anorthosites hogstad rogaland anorthositic province south norway 930 ma provides new insights into the late evolution of anorthositic diapirs these layered mafic intrusions are essentially of norite gabbronorite as well as leuconorite and display conspicuous evidence of subsolidus recrystallization in loyning and hogstad the modal layering is parallel to the subvertical foliation in the enclosing anorthosite the northern part of the koldal intrusion cuts across the foliation of the anorthosite whereas in its southern part the subvertical layering is parallel to the anorthosite s foliation the regularity of the layered structures suggests that the layering was initially acquired horizontally and later tilted during the final movements of the diapirs the least differentiated compositions of plagioclase and orthopyroxene in the three intrusions an 59 en 68 in loyning an 49 en 64 in hogstad and an 44 en 61 in koldal and the ree contents in apatite hogstad indicate that their parent magmas were progressively more differentiated in the sequence loyning hogstad koldal isotopic data loyning 87 sr 86 sr 0 70376 0 70457 e ndt 6 8 to 2 7 hogstad 87 sr 86 sr 0 70537 0 70588 e ndt 2 1 to 0 5 koldal 87 sr 86 sr 0 70659 0 70911 e ndt 3 5 to 1 6 also indicate that in this sequence parent magmas were characterized by a progressively more enriched sr and nd isotopic signature in loyning the parent magma was slightly more magnesian and anorthitic than a primitive jotunite in hogstad it is a primitive jotunite and in koldal an evolved jotunite given that plagioclase and orthopyroxene of the three intrusions display more differentiated compositions than the orthopyroxene and plagioclase megacryts of the enclosing anorthosites it is suggested that the parent magmas of the small intrusions are residual melts after anorthosite formation which were entrained in the anorthositic diapir during its rise from lower crustal chambers calculated densities of primitive jotunites 2 73 2 74 at fmq 0 15 h 2 o 200 ppm co 2 435 ppm f 1150 c 3 kb and evolved jotunites 2 75 2 76 at fmq 0 30 h 2 o 400 ppm co 2 870 ppm f 1135 c 3 kb demonstrate that they are much denser than the plagioclase of the surrounding anorthositic crystal mush 2 61 2 65 efficient migration and draining of dense residual melts through the anorthositic crystal mush could have taken place along sloping floors zones of lesser permeability in the mush which occur along the margins of the rising anorthositic diapirs this process takes into account the restricted occurrence of the mafic intrusions in the margins of the massif anorthosites in a later stage when the anorthosite was nearly consolidated the residual melts were more differentiated evolved jotunites and could have been extracted into extensional fractures in the cooling and contracting anorthositic body in a similar way as aplitic dikes are emplaced in granitic plutons as in the rogaland anorthositic province these dikes are much more abundant than the small mafic intrusions collection and transport along dikes was probably more efficient than draining through the crystal mush

alpine metamorphism in the south east tauern window austria 1 p t variations in space and time the pennine rocks exposed in the south east tauern window austria contain mineral assemblages which crystallized in the mid tertiary late alpine regional metamorphism the pressure and temperature conditions at the thermal peak of this event have been estimated for rocks at four different structural levels using a variety of published and thermochemically derived geobarometers and geothermometers the results are a in the garnet chlorite zone 2 5 km structurally above the staurolite biotite isograd t 490 50 c p 7 1 kbar b within 0 5 km of the staurolite biotite isograd t 560 300c p 7 1 kbar c in the staurolite biotite zone c 2 5 km structurally below the staurolite biotite isograd t 610 30 c p 7 6 1 2 kbar d in the staurolite biotite zone 3 4 km structurally below the staurolite biotite isograd t 630 40 c p 6 6 1 2 kbar the pressure estimates imply that the total thickness of overburden above the basement cover interface in the mid tertiary was c 26 4 km this overburden can only be accounted for by the austro alpine units currently exposed in the vicinity of the tauern window if the altkristallin the middle austro alpine nappe was itself buried beneath an upper austro alpine nappe or nappe pile which was 7 4 km thick at that time the occurrence of epidote margarite quartz pseudomorphs after lawsonite in garnet indicates that part of the mesozoic pennine cover sequence in the south east tauern experienced blueschist facies conditions t 450 c p 12 kbar in early alpine times evidence from the central tauern is used to argue that the blueschist facies imprint post dated the main phase of tectonic thickening d1a and was thus a direct consequence of continental collision combined oxygen isotope and fluid inclusion studies on late stage veins thought to have been at lithostatic pressure and in thermal equilibrium with their host rocks during formation suggest that they crystallized from aqueous fluids at 1 1 0 4 kbar and 420 20 c early alpine late alpine and vein formation p t constraints have been used to construct a p t path for the base of the mesozoic cover sequence in the south east tauern window the prograde part of the p t path between early and late alpine metamorphic imprints is unlikely to have been a smooth curve and may well have had a low dp dt overall the decompression presumably due to erosion which occurred immediately before the thermal peak and possibly also earlier in the tertiary was probably partly or completely cancelled by the effects of early to mid tertiary d2a tectonic thickening the thermal peak of metamorphism was followed by a phase of almost isothermal decompression which implies a period of rapid uplift in the middle tertiary the peak metamorphic p t estimates are compared with the solutions of england s 1978 one dimensional conductive thermal model of the eastern alps and are shown to be consistent with the idea that the late alpine metamorphism was caused by tectonic burial of the pennine zone beneath the austro alpine nappes in the absence of extraneous heat sources such as large intrusions at depth

the isotope systematics of a juvenile intraplate volcano pb nd and sr isotope ratios of basalts from loihi seamount hawaii abstract sr nd and pb isotope ratios for a representative suite of 15 basanites alkali basalts transitional basalts and tholeiites from loihi seamount hawaii display unusually large variations for a single volcano but lie within known ranges for hawaiian basalts nd isotope ratios in alkali basalts show the largest relative variation 0 51291 0 51305 and include the nearly constant tholeiite value 0 51297 pb isotope ratios show similarly large ranges for tholeiites and alkali basalts and continue tatsumoto s 31 loa trend towards higher 206pb 204pb ratios resulting in a substantial overlap with the kea trend 206pb 204pb ratios for loihi and other volcanoes along the loa and kea trends 31 are observed to correlate with the age of the underlying lithosphere suggesting lithosphere involvement in the formation of hawaiian tholeiites loihi lavas display no correlation of nd sr or pb isotope ratios with major element compositions or eruptive age in contrast with observations of some other hawaiian volcanoes 38 isotope data for loihi as well as average values for hawaiian volcanoes are not adequately explained by previously proposed two end member models new models for the origin and the development of hawaiian volcanoes must include mixing of at least three geochemically distinct source regions and allow for the involvement of heterogeneous oceanic lithosphere

geothermobarometry in metasediments of the southern grossvenediger area tauern window austria metasediments in the southern grossvenediger area tauern window austria were studied along a cross section through rocks of increasing metamorphic grade from the margin of the tauern window in the south to the base of the upper schieferhulle including the eclogite zone in the north in the southern part of the cross section there is no evidence for a pre late alpine metamorphic history in the form of high pressure relics or pseudomorphs mineral assemblages are characterized by the stability of tremolite calcite biotite calcite and biotite chlorite calcite in the northern part a more complete alpine metamorphic evolution is preserved primary high pressure assemblages are dolomite quartz tremolite zoisite zoisite dolomite quartz phengite i and probably tremolite dolomite phengite i secondary post kinematic assemblages tremolite calcite talc calcite phengite ii chlorite calcite quartz biotite chlorite calcite biotite zoisite calcite formed as a result of the dominant late alpine metamorphic overprint the occurrence of biotite zoisite calcite is confined to the northernmost area and defines a biotite zoisite calcite isograd p t estimates based on standard thermobarometric techniques and on stability relationships of tremolite calcite dolomite quartz and zoisite give consistent results p t conditions of the main tertiary metamorphic overprint were 525 c p 7 5 1 kbar in the northern part of the cross section the southern part was metamorphosed at lower temperatures of 430 470 c the si content of phengites from this area is almost as high as that of phengites from the eclogite zone simax 3 4 pfu pressures 10 kbar at 420 c are suggested by phengite barometry according to massone schreyer 1987 in the absence of high pressure relics or pseudomorphs these phengites which lack late alpine re equilibration are the only record that rocks of the southern part probably also experienced an early non eclogitic high pressure metamorphism

petrogenesis of ultramafic xenoliths from the 1800 kaupulehu flow hualalai volcano hawaii the 1800 kaupulehu flow on hualalai volcano hawaii contains abundant xenoliths of dunite wehrlite and olivine clinopyroxenite with minor gabbro troctolite anorthosite and websterite the petrography and mineral compositions of 41 dunite wehrlite and olivine clinopytoxenite xenoliths have been studied and clinopyroxene separates from eight of these have been analyzed for ba k rb sr rare earth elements 87sr 6sr and 143nd 14 nd temperatures of equilibration obtained by olivine spinel and pyroxene geothermometry range from 1000 to 1200 c mineralogical data combined with published fluid inclusion data indicate depths of origin in the range of 8 30 km the rarity of orthopyroxene the presence of fe rich olivine fog 89 and clinopyroxene fs3 2x and the occurrence of high tio2 in spinel 0 9 2 8 wt and clinopyroxene 0 35 1 33 wt all indicate that the xenoliths are cumulates not residues from partial fusion the separated clinopyroxenes have 87sr 6sr 0 70348 0 70367 and nd nd o 51293 o 51299 values that are different from sr and nd isotope ratios of pacific abyssal basalts 0 5130 respectively also clinopyroxenes and spinels in the xenoliths have generally higher tio2 contents o 35 and 0 91 wt respectively than their counterparts in abyssal cumulates 0 40 and 0 70wt respectively these differences indicate that the xenoliths are not a normal component of oceanic crust because the xenoliths and alkalic to transitional hualalai lavas have similar values for cr cr al

esmeralda bank geochemistry of an active submarine volcano in the mariana island arc esmeralda bank is the southernmost active volcano in the izu volcano mariana arc this submarine volcano is one of the most active vents in the western pacific it has a total volume of about 27 km3 rising to within 30 m of sea level two dredge hauls from esmeralda recovered fresh nearly aphyric vesicular basalts and basaltic andesites and minor basaltic vitrophyre these samples reflect uniform yet unusual major and trace element chemistries mean abundances of tio2 1 3 and feo 12 6 are higher and cao 9 2 and al2o3 15 1 are lower than rocks of similar silica content from other active mariana arc volcanoes mean incompatible element ratios k rb 488 and k ba 29 of esmeralda rocks are indistinguishable from those of other mariana arc volcanoes on a ti zr plot esmeralda samples plot in the field of oceanic basalts while other mariana arc volcanic rocks plot in the field for island arcs

igneous and shock processes affecting chassignite amphibole evaluated using chlorine water partitioning and hydrogen isotopes amphibole in chassignite melt inclusions provides valuable information about the volatile content of the original interstitial magma but also shock and postshock processes we have analyzed amphibole and other phases from nwa 2737 melt inclusions and we evaluate these data along with published values to constrain the crystallization cl and h2o content of phases in chassignite melt inclusions and the effects of shock on these amphibole grains using a model for the cl oh exchange between amphibole and melt we estimate primary crystallization oh contents of chassignite amphiboles sims analysis shows that amphibole from nwa 2737 currently has 0 15 wt h2o it has lost 0 6 wt h2o from an initial 0 7 0 8 wt h2o due to intense shock chassigny amphibole had on average 0 3 0 4 wt h2o and suffered little net loss of h2o due to shock nwa 2737 amphibole has d 3700 it absorbed martian atmosphere derived heavy h in the aftermath of shock chassigny amphibole with d 1900 incorporated less heavy h low h2o cl ratios are inferred for the primitive chassignite magma which had significant effects on melting and crystallization volatiles released by the degassing of martian magma were more cl rich than on earth resulting in the high cl content of martian surface materials

variation in trace element content of magnetite crystallized from a fractionating sulfide liquid sudbury canada implications for provenance discrimination abstract laser ablation icp ms analysis has been applied to many accessory minerals in order to understand better the process by which the rock formed and for provenance discrimination we have determined trace element concentrations of fe oxides in massive sulfides that form ni cu pge deposits at the base of the sudbury igneous complex in canada the samples represent the crystallization products of fractionating sulfide liquids and consist of early forming fe rich monosulfide solution mss cumulates and residual cu rich intermediate solid solution iss this study shows that fe oxide geochemistry is a sensitive petrogenetic indicator for the degree of fractionation of the sulfide liquid and provides an insight into the partitioning of elements between sulfide and fe oxide phases in addition it is useful in determining the provenance of detrital fe oxide in a sulfide melt all lithophile elements cr ti v al mn sc nb ga ge ta hf w and zr are compatible into fe oxide the concentrations of these elements are highest in the early forming fe oxide titanomagnetite which crystallized with fe rich mss upon the continual crystallization of fe oxide from the sulfide liquid the lithophile elements gradually decrease so that late forming fe oxide magnetite which crystallized from the residual cu rich liquid is depleted in these elements this behavior is in contrast with fe oxides that crystallized from a fractionating silicate melt whereby the concentration of incompatible elements such as ti increases rather than decreases the behavior of the chalcophile elements in magnetite is largely controlled by the crystallization of the sulfide minerals with only ni co zn mo sn and pb present above detection limit in magnetite nickel mo and co are compatible in fe rich mss and thus the co crystallizing fe oxide is depleted in these elements in contrast magnetite that crystallized later from the fractionated liquid with cu rich iss is enriched in ni mo and co because fe rich mss is absent the concentrations of sn and pb which are incompatible with fe rich mss are highest in magnetite that formed from the fractionated cu rich liquid at subsolidus temperatures ilmenite exsolved from titanomagnetite whereas al spinel exsolved from the cores of some magnetite locally redistributing the trace elements however during laser ablation icp ms analysis of these fe oxides both the magnetite and its exsolution products are ablated so that the analysis represents the original magmatic composition of the fe oxide that crystallized from the sulfide melt

magma influx and mixing in the bjerkreim sokndal layered intrusion south norway evidence from the boundary between two megacyclic units at storeknuten abstract the bjerkreim sokndal layered intrusion belongs to the proterozoic anorthositic province in the rogaland area of southern norway the northwestern part of the intrusion comprises a ca 6 km thick layered series made up of megacyclic units mcu arranged in a syncline each megacyclic unit reflects the influx of fresh magma into the chamber the boundary between megacyclic units iii and iv has been studied in detail at storeknuten on the southern flank of the syncline the megacyclic units can be subdivided into a series of cumulate stratigraphic zones the interval from the top of zone iiie to the base of zone ivd is exposed in the storeknuten area modally layered plagioclase hypersthene ilmenite magnetite augite apatite cumulates belonging to zone iiie are overlain by 30 m of massive plagioclase rich rocks commonly containing ilmenite and or hypersthene constituting zone iva the entry of cumulus olivine defines the base of zone ivb dominantly plagioclase olivine ilmenite cumulates which is about 100 m thick many of the olivines are partly or completely replaced by ca poor pyroxene fe ti oxide symplectites this massive leucotroctolitic zone is overlain by modally layered laminated plagioclase hypersthene ilmenite cumulates of zone ivc the successive entry of magnetite apatite accompanied by ca rich pyroxene and inverted pigeonite defines zones ivd e and f respectively the entry of k feldspar accompanied by fe rich olivine defines the base of a jotunitic transition zone which passes upwards into mangerites and quartz mangerites there is a compositional regression through zone iva the upper part of zone iiie has ca poor pyroxene with about en68 plagioclase with an44 48 and a sr isotope ratio of about 0 7062 while the base of zone ivb has olivine with fo75 together with en78 an53 and 0 7050 respectively similar reversals are shown by the minor element compositions of plagioclase and fe ti oxides sr isotope ratios increase systematically up through zone ivb reaching 0 7058 in zone ivd while an and sr in plagioclase and ni and cr in fe ti oxides decrease olivine compositions vary unsystematically and are believed to have changed their fe mg ratios as a result of trapped liquid shift the magma residing in the chamber when the influx at the base of megacyclic unit iv took place was compositionally zoned and assimilation of gneissic country rock at the roof had resulted in the sr isotope ratio increasing up through the magma column the new magma had a sr isotope ratio of about 0 7050 while the resident magma had a ratio of 0 7062 at the floor increasing upwards the new magma mixed with the basal layer s of the compositionally zoned resident magma and crystallization of this hybrid magma during influx and mixing produced the compositional regression in zone iva when magma influx ceased olivine bearing rocks began to crystallize at the base of zone ivb the leucotroctolites at the base of this zone are the most primitive rocks in the entire intrusion the systematic increase in sr isotope ratios up through zone ivb resulted from progressive mixing between new and resident magma this mixing either took place during magma influx or by the progressive mixing of overlying resident magma layers during crystallization calculations based on geochemical modelling the thickness of cumulate stratigraphy repeated and sr isotope ratios indicate that the new magma influx had a thickness of 350 500 m in the storeknuten section and that the leucotroctolites of zone ivb represent about 20 30 crystallization of this influx

hawaiian xenolith populations magma supply rates and development of magma chambers hawaiian volcanoes pass through a sequence of four eruptive stages characterized by distinct lava types magma supply rates and xenolith populations magma supply rates are low in the earliest and two latest alkalic stages and high in the tholeiitic second stage magma storage reservoirs develop at shallow and intermediate depths as the magma supply rate increases during the earliest stage magma in these reservoirs solidifies as the supply rate declines during the alkalic third stage these magma storage reservoirs function as hydraulic filters and remove dense xenoliths that the ascending magma has entrained during the earliest and latest stages no magma storage zone exists and mantle xenoliths of lherzolite are carried to the surface in primitive alkalic lava during the tholeiitic second stage magma storage reservoirs develop and persist both at the base of the ocean crust and 3 7 km below the caldera only xenoliths of shallow origin are carried to the surface by differentiated lava during the alkalic third stage magma in the shallow subcaldera reservoir solidifies and crustal xenoliths including oceanic crustal rocks are carried to the surface in lava that fractionates in an intermediate depth reservoir worldwide xenolith populations in tholeiitic and alkalic lava may reflect the presence or absence of subvolcanic magma storage reservoirs

the grader layered intrusion havre saint pierre anorthosite quebec and genesis of nelsonite and other fe ti p ores abstract the grader layered intrusion is part of the havre saint pierre anorthosite in the grenville province quebec canada this intrusion has a basin like morphology and contains significant resources of fe ti p in ilmenite and apatite outcropping lithologies are massive oxide alternating with anorthosite layers banded ilmenite apatite plagioclase rocks and layered oxide apatite gabbro norites drill cores provide evidence for stratigraphic variations of mineral and whole rock compositions controlled by fractional crystallization with the successive appearance of liquidus phases plagioclase and ilmenite followed by apatite then orthopyroxene together with magnetite and finally clinopyroxene this atypical sequence of crystallization resulted in the formation of plagioclase ilmenite apatite cumulates or nelsonites in plagioclase free layers fine grained ferrodiorites that cross cut the cumulates are shown to be in equilibrium with the noritic rocks the high tio 2 and p 2 o 5 contents of these assumed liquids explains the early saturation of ilmenite and apatite before fe mg silicates thus the nelsonites represent cumulates rather than crystallized fe ti p rich immiscible melts the location of the most evolved mineral and whole rock compositions several tens of meters below the top of the intrusion forming a sandwich horizon is consistent with crystallization both from the base and top of the intrusion the concentrations of v and cr in ilmenite display a single fractionation path for the different cumulus assemblages and define the cotectic proportion of ilmenite to 21 wt this corresponds to bulk cotectic cumulates with ca 8 wt tio 2 which is significantly lower than what is commonly observed in the explored portion of the grader intrusion the proposed mechanism of ilmenite enrichment is the lateral removal of plagioclase due to its relative buoyancy in the dense ferrodiorite melt this plagioclase has probably accumulated in other portions of the intrusion or has not been distinguished from the host anorthosite

alpine metamorphism in the south east tauern window austria 2 rates of heating cooling and uplift existing geochronological data are reviewed and new rb sr k ar and 39ar 40ar ages are presented including a suite of 33 mica ages from a 20 km north south tunnel section these data are discussed in relation to the thermal history from the overthrusting of the autroalpine nappes c 65 myr ago to the present the earliest phase of metamorphism involving lawsonite crystallization is associated with emplacement of these nappes subsequently temperatures in the rocks beneath rose at a mean rate of 3 6 c myr until the climax of metamorphism at high structural levels published data indicate an age 35 myr for the metamorphic climax in contrast a new 39ar 40ar step heating age of 23 8 0 8 myr on amphibole from near the base of peripheral schieferhulle closely approximates the age of metamorphism and provides the first clear indication that the climax of metamorphism occurred later at deeper structure levels following the climax near isothermal uplift and erosion reduced pressure to c 1 kbar before white mica closure at 19 myr this implies uplift at 3 mm yr along the tunnel section white mica k ar ages vary systematically from 24 myr to 16 5 myr with position relative to a late 4 km amplitude dome whereas biotite rb sr ages are uniform at 16 5 myr across the whole profile doming is thus dated at 16 5 myr with transient uplift rates 5 mm yr at other times uplift rates were 1 mm yr

the relative permeabilities of quartzites and schists during active metamorphism at mid crustal levels the hot spot near bristol new hampshire was an area of high fluid flow during metamorphism in order to determine the mechanisms of fluid flow through the area we made a detailed study of the 18o values of quartz from an outcrop of interlayered quartzites and schists results indicate that the permeability of the quartzite was very low in comparison to that of the schist the 18qtz values from schist layers are remarkably homogenous 15 5 15 8 in contrast to the 18qtz values of schist units outside of the hot spot which vary widely quartz veins that cut the quartzites and pinch out in the schists have the same 18o values 15 7 as quartz from the schists in the quartzites 18qtz values immediately adjacent to the veins and schists are similar to those in the veins and schists but decrease by 1 permil in the centers of the layer we interpret these results to indicate that fluid flow in the hot spot was mainly through the schists and fractures in the quartzites the oxygen isotope exchange fronts in the quartzites prove that there was some flow from the the schists and the fractures into the quartzites comparisons of the shapes of these exchange fronts with exchange fronts predicted by two different models of fluid flow in rocks indicate that fluid transport in the quartzite was predominantly by advection and that the kinetic rates of isotope exchange were fast relative to the advective velocity of the fluid infiltrating the system considering the slow rate of oxygen isotope exchange between quartz and a fluid this implies that fluid flow from the schist and vein fracture into the quartzite was extremely limited

a new geobarometer for the assemblage biotite muscovite chlorite quartz the equilibrium thermodynamics of the reaction 4kmga1si40 o oh mg5a1 si30 o oh muscovlte chlorite muscovite biotite ka13si 0 oh 3kmg3aisi 0 0 oh 7si0 4h o quartz fluid can be formulated as a geobarometer thermo dynamic data for the mg a1 celadonite end member of muscovite is derived from the reversed mineral equilibria experiments of velde i 965 using the calculation method of powell 1978 giving afh 1298 5823 5 kj s 1298 0 3060kjk v 1298 13 8kjkbar

internal control of fluid compositions in amphibolite facies scapolitic calc silicates mary kathleen australia unaltered metasediments of the mary kathleen fold belt are composed predominantly of layered amphibolite facies scapolitic calc silicate rocks in which minimal infiltration of externally derived fluids occurred during regional metamorphism there were substantial differences in volatile activities between different layers in the layered sequences in particular a co2 a h 2 o inferred from reaction progress estimates and analysis of biotite clinopyroxene fluid phase relations a nacl a h 2 o inferred from scapolite compositions and a hcl a h 2 o inferred from biotite compositions in one outcrop in which a clinopyroxene producing reaction dominated differences in approximate x co 2of up to 0 25 occurred between several samples collected over 50 metres variations in a h 2 o a hcl of up to one order of magnitude are inferred at 1 to 50 m scales from biotite cl contents and variations in nacl contents of scapolite from 0 0 to up to 0 6 cl atoms in the cl co3 so4 site reflect a large variation of a nacl in the coexisting fluid at similar scales most calcsilicate layers internally buffered fluid compositions in the h2o co2 nacl hcl system local occurrences of nacl rich scapolite suggest that some layers may have been in equilibrium with halite during early prograde metamorphism at peak metamorphic temperatures disolution of halite was complete but layers containing high nacl scapolite continued to buffer fluid at high values of a nacl fluid immiscibility does not appear to have affected the progress of the devolatilization reactions although fluid was predominantly internally buffered moderate quantities of fluid were released by prograde mineral reactions in many layers up to 30 cm3 fluid per 100 cm3 rock numerous episodes of fluid escape were required probably via microfractures such that the released fluid did not obviously influence reaction progress in the layers through which it passed the anomaly of beautifully preserved internal buffering signatures and the requirement for produced fluid locally to pass across layers in a deforming rock sequence suggest that the escaping fluid did not leave any readily observable tracks this is explained by rapid rates of fracture propogation and fluid migration therein this internally buffered system contrasts strongly with adjacent calc silicate rocks that show evidence for infiltration of externally derived fluids at high fluid rock ratios and highlights the broad range of fluid behaviour that can be expected in deforming heterogeneous rock sequences

he diffusion in olivine helium diffusion in olivine dunite xenolith has been measured in the temperature range 1180 1460 c a linear arrhenius function was obtained with an activation energy of 120 27 32 kcal mole and a pre exponential factor d0 2 2 108 cm2 s diffusion mechanisms are not a viable means of degassing he from the mantle olivine phenocrysts can be expected to retain previously trapped he during cooling in extrusive basalts provided the flow units are thinner than 50 m xenoliths will retain mantle he signatures only if magma transport times are less than 50 years or if the he fugacity in the magma is high enough to prevent xenolith degassing the lower oceanic crust is probably substantially degassed of he trapped he will be qualitatively retained in quenched submarine basalt glass only if the cooling rate is faster than 5 1014 c m y glass at several centimeters depth in a basalt flow near the spherulite zone will have cooling rates lower than this so he loss may be significant in many basalt glass samples

major and trace element variation in ilmenite in the skaergaard intrusion petrologic implications abstract ilmenite separates from the floor ls roof ubs and wall mbs sequences of the skaergaard intrusion were analyzed for major and trace elements using dcp aes and icp ms techniques in all three sequences feo progressively increases and mgo and al 2 o 3 progressively decrease with differentiation although trace element abundances are in general higher in ubs ilmenite than in mbs and ls ilmenite all three sequences have similar trends for trace element abundance vs crystallization ba cs rb sr th u y and the rees are excluded elements in ilmenite and remained at low abundances during differentiation cr ni sc and v are included elements in ilmenite and other mafic phases and decreased during differentiation v contents in ilmenite however do not decrease significantly until the upper part of the middle zone suggesting that magnetite did not begin to affect the magma differentiation trend until much later than when it first appears in the intrusion hf nb ta and zr which are strongly excluded elements in silicates are included elements in ilmenite the element ratios zr hf y ho nb ta and u th are relatively constant in skaergaard ilmenite from different parts of the intrusion suggesting that fluid transport did not significantly effect these elements during differentiation or post solidification cooling calculated partition coefficients for ilmenite in the skaergaard intrusion are similar to those reported from previous studies of lunar and terrestrial basalts and kimberlites and for most elements are significantly lower than those reported for ilmenite in rhyolitic magma similar d i s for zr hf nb and ta suggest that ilmenite crystallization did not significantly affect zr nb or hf ta in the skaergaard magma but the ratios of zr hf nb or ta to other high field strength elements such as th u y or the rees may have been altered by ilmenite fractionation

origin of the giant allard lake ilmenite ore deposit canada by fractional crystallization multiple magma pulses and mixing abstract the late proterozoic allard lake ilmenite deposit is located in the havre saint pierre anorthosite complex part of the allochtonous polycyclic belt of the grenville province presently the world s largest fe ti oxide deposit it had a pre mining amount in excess of 200 mt at grades over 60 wt hemo ilmenite the main ore body is a funnel shaped intrusion measuring 1 03 1 10 km and 100 300 m thick two smaller bodies are separated by faults and anorthosite the ore is an ilmenite rich norite or ilmenitite made up of hemo ilmenite hem22 6 29 4 66 2 wt on average andesine plagioclase an45 50 aluminous spinel and locally orthopyroxene whole rock chemical compositions are controlled by the proportions of ilmenite and plagioclase orthopyroxene which supports the cumulate origin of the deposit ore forming processes are further constrained by normal and reverse fractionation trends of cr concentration in cumulus ilmenite that reveal multiple magma emplacements and alternating periods of fractional crystallization and magma mixing mixing of magmas produced hybrids located in the stability field of ilmenite resulted in periodic crystallization of ilmenite alone the unsystematic differentiation trends in the allard lake deposit arising from a succession of magma pulses hybridisation and the fractionation of hemo ilmenite alone or together with plagioclase suggest that the deposit formed within a magma conduit this dynamic emplacement mechanism associated with continuous gravity driven accumulation of fe ti oxides and possibly plagioclase buoyancy in a fractionating ferrobasalt explains the huge concentration of hemo ilmenite the occurrence of sapphirine associated with aluminous spinel and high alumina orthopyroxene 7 6 9 1 wt al2o3 lacking exsolved plagioclase supports the involvement of a metamorphic overprint during the synchronous ottawan orogeny which is also responsible for strong textural equilibration and external granule of exsolved aluminous spinel due to slow cooling

leucocratic and gabbroic xenoliths from hualalai volcano hawai i a diverse range of crustal xenoliths is hosted in young alkali basalt lavas and scoria deposits erupted 3 5 ka at the summit of hual alai leucocratic xenoliths including monzodiorites diorites and syenogabbros are distinctive among hawaiian plutonic rocks in having alkali feldspar apatite zircon and biotite and evolved mineral compositions e g albitic feldspar clinopyroxene mgnumber 67 78 fine grained diorites and monzodiorites are plutonic equivalents of mugearite lavas which are unknown at hual alai these xenoliths appear to represent melt compositions falling along a liquid line of descent leading to trachyte a magma type which erupted from hual alai as a prodigious lava flow and scoria cone at 114 ka inferred fractionating assemblages melts modeling pyroxene geobarometry and whole rock norms all point to formation of the parent rocks of the leucocratic xenoliths at 3 7 kbar pressure this depth constraint on xenolith formation coupled with a demonstrated affinity to hypersthenenormative basalt and petrologic links between the xenoliths and the trachyte suggests that the shift from shield to post shield magmatism at hual alai was accompanied by significant deepening of the active magma reservoir and a gradual transition from tholeiitic to alkalic magmas subsequent differentiation of transitional basalts by fractional crystallization was apparently both extreme culminating in 5 5 km of trachyte and rapid at 2 75 10 m magma crystallized year

application of zr in rutile thermometry a case study from ultrahigh temperature granulites of the khondalite belt north china craton zr in rutile thermometry was applied to ultrahigh temperature uht granulites from three localities dongpo tuguishan and dajing tuguiwula of the khondalite belt north china craton zr concentrations of analyzed rutiles were detected by la icp ms and emp which display a mutative composition zoning a large inter grain variation a bimodal distribution at around 1 500 and 6 000 ppm and no relationship with the textural setting matrix vs inclusion these characteristics were likely caused by post peak diffusional resetting associated with slow cooling rates and the presence of a co2 rich fluid the grains with lower zr concentrations 500 to 3 000 ppm and temperature estimates 650 to 850 c occur close to or in contact with zircon which was easily affected by post peak processes for example diffusion dissolution reprecipitation the lowest temperatures 650 to 700 c we obtained represent the closure temperature of zr in rutile rutiles with higher zr concentrations 3 000 to 8 000 ppm and calculated temperatures 850 to 1 000 c were least affected by late resetting giving near peak metamorphic temperatures these temperature results higher than 900 c even in excess of 1 000 c from the three localities reconfirm the presence of uht metamorphism our results also suggest that zr in rutile thermometry is valid for ultrahigh temperature estimates in addition there are positive correlations between concentrations of zr and hf nb and ta of the investigated rutiles but the correlations weaken as the concentrations increase especially for nb and ta implying fractionation of nb and ta