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The solubilities of the most common grain -growth inhibitors (GGIs) Cr, V, Ta, Mo, Nb, Zr and certain combinations there of in the binder phase of WC-Co hardmetals as well as hardmetals of the type WCTiC-TiN-TaC-NbC-Co containing an fcc MC carbide (or carbonitride) phase "MC"("WC-MC-Co" hardmetals) were analysed by means of WDS-EPMA. The carbon potential of the binder phase was fixed at its highest and lowest maxima by the presence of either graphite or eta (M6C) phases. In case of low-carbon hardmetals the composition of M6C, and in the MC-containing hardmetals the composition of the MC phase, was analysed. Two types of solubilities were determined. The first type was measured after controlled cool-down from liquid-phase sintering temperature and represented the binder phase state of an industrially prepared hardmetal. The second type representing the equilibrium solubility was measured in alloys annealed at 1000 degrees C for 168 h after liquid -phase sintering. The measured solubilities were subsequently used to prepare hardmetals with an optimised GGI concentration. The samples were analysed with respect to hardness, toughness, magnetic properties, transverse rupture strength and Weibull parameter. A complex doping with Cr, V and Ta with optimised concentrations near the solubility limit of these metals in the binder phase turned out to yield best combination of mechanical properties and reliability. This was successfully adopted in industrial production.

The solubilities of the most common grain -growth inhibitors (GGIs) Cr, V, Ta, Mo, Nb, Zr and certain combinations there of in the binder phase of WC-Co hardmetals as well as hardmetals of the type WCTiC-TiN-TaC-NbC-Co containing an fcc MC carbide (or carbonitride) phase "MC"("WC-MC-Co" hardmetals) were analysed by means of WDS-EPMA. The carbon potential of the binder phase was fixed at its highest and lowest maxima by the presence of either graphite or eta (M6C) phases. In case of low-carbon hardmetals the composition of M6C, and in the MC-containing hardmetals the composition of the MC phase, was analysed. Two types of solubilities were determined. The first type was measured after controlled cool-down from liquid-phase sintering temperature and represented the binder phase state of an industrially prepared hardmetal. The second type representing the equilibrium solubility was measured in alloys annealed at 1000 degrees C for 168 h after liquid -phase sintering. The measured solubilities were subsequently used to prepare hardmetals with an optimised GGI concentration. The samples were analysed with respect to hardness, toughness, magnetic properties, transverse rupture strength and Weibull parameter. A complex doping with Cr, V and Ta with optimised concentrations near the solubility limit of these metals in the binder phase turned out to yield best combination of mechanical properties and reliability. This was successfully adopted in industrial production.

The solubilities of the most common grain -growth inhibitors (GGIs) Cr, V, Ta, Mo, Nb, Zr and certain combinations there of in the binder phase of WC-Co hardmetals as well as hardmetals of the type WCTiC-TiN-TaC-NbC-Co containing an fcc MC carbide (or carbonitride) phase "MC"("WC-MC-Co" hardmetals) were analysed by means of WDS-EPMA. The carbon potential of the binder phase was fixed at its highest and lowest maxima by the presence of either graphite or eta (M6C) phases. In case of low-carbon hardmetals the composition of M6C, and in the MC-containing hardmetals the composition of the MC phase, was analysed. Two types of solubilities were determined. The first type was measured after controlled cool-down from liquid-phase sintering temperature and represented the binder phase state of an industrially prepared hardmetal. The second type representing the equilibrium solubility was measured in alloys annealed at 1000 degrees C for 168 h after liquid -phase sintering. The measured solubilities were subsequently used to prepare hardmetals with an optimised GGI concentration. The samples were analysed with respect to hardness, toughness, magnetic properties, transverse rupture strength and Weibull parameter. A complex doping with Cr, V and Ta with optimised concentrations near the solubility limit of these metals in the binder phase turned out to yield best combination of mechanical properties and reliability. This was successfully adopted in industrial production.

The solidification paths for UFeB4, UFe3B2 and UFe4B, ternary compounds, situated along the U:(Fe,B) = 1:5 line in the B-Fe-U phase diagram, are proposed based on x-ray powder diffraction measurements, differential thermal analysis, heating curves and scanning electron microscopy observations complemented with energy and wavelength dispersive x-ray spectroscopies. The compounds melt incongruently and are formed by peritectic reactions. The present work demonstrates the existence of a cascade of peritectic reactions along the U:(Fe,B) = 1:5 composition line, establishes peritectic temperatures and proposes an isopleth diagram along this line.

The solidification paths for UFeB4, UFe3B2 and UFe4B, ternary compounds, situated along the U:(Fe,B) = 1:5 line in the B-Fe-U phase diagram, are proposed based on x-ray powder diffraction measurements, differential thermal analysis, heating curves and scanning electron microscopy observations complemented with energy and wavelength dispersive x-ray spectroscopies. The compounds melt incongruently and are formed by peritectic reactions. The present work demonstrates the existence of a cascade of peritectic reactions along the U:(Fe,B) = 1:5 composition line, establishes peritectic temperatures and proposes an isopleth diagram along this line.

The solidification paths for UFeB4, UFe3B2 and UFe4B, ternary compounds, situated along the U:(Fe,B) = 1:5 line in the B-Fe-U phase diagram, are proposed based on x-ray powder diffraction measurements, differential thermal analysis, heating curves and scanning electron microscopy observations complemented with energy and wavelength dispersive x-ray spectroscopies. The compounds melt incongruently and are formed by peritectic reactions. The present work demonstrates the existence of a cascade of peritectic reactions along the U:(Fe,B) = 1:5 composition line, establishes peritectic temperatures and proposes an isopleth diagram along this line.

On continental margins, oxidation of methane-rich fluids from the sediment often leads to formation of authigenic carbonate pavements on the seafloor. The biogeochemical processes involved during this carbonate precipitation are increasingly understood, but little is known about the duration or mode of carbonate crust formation. Here, we report uranium and thorium concentrations and isotope compositions for a set of 14 samples drilled across an authigenic carbonate pavement, which provide the first stratigraphy for a cold-seep carbonate crust. The 5.5-cm thick crust (NL7-CC2) was collected by Submersible on the Nile deep-sea fan in an area of active fluid venting. U-Th analyses must be corrected for initial Th and measurement of co-existing sediments indicates the presence of both scavenged and detrital initial Th-230, which must be considered during this correction. The calculated Th-230/U age-depth profile for NL7-CC2 provides evidence for continuous downward carbonate precipitation at the studied location over the last similar to 5000 years. Three distinct phases can be distinguished from top to bottom with average growth rates of similar to 0.4, 5 and 0.8 cm/kyr, respectively, corresponding to carbonate precipitation rates ranging from similar to 7 to 92 mu mol m(2) h(-1) (rates consistent with previous estimates), High-resolution delta C-13 profiles [Gontharet, S., Pierre, C., Blanc-Valleron, M.-M., Rouchy,J.M., Fouquet, Y., Bayon, G., Foucher,J.P., Woodside,J., Mascle,J., The Nautinil Scientific Party, 2007. Nature and origin of diagenetic carbonate crusts and concretions from mud volcanoes and pockmarks of the Nile deep-sea fan (eastern Mediterranean Sea). Deep Sea Res. 1154,1292-1311] and major elements across NL7-CC2 show that the variations in carbonate precipitation rates were also accompanied by changes in carbonate mineralogy and fluid composition. We suggest that these changes primarily reflect modification of the diagenetic environment, i.e. a progres

On continental margins, oxidation of methane-rich fluids from the sediment often leads to formation of authigenic carbonate pavements on the seafloor. The biogeochemical processes involved during this carbonate precipitation are increasingly understood, but little is known about the duration or mode of carbonate crust formation. Here, we report uranium and thorium concentrations and isotope compositions for a set of 14 samples drilled across an authigenic carbonate pavement, which provide the first stratigraphy for a cold-seep carbonate crust. The 5.5-cm thick crust (NL7-CC2) was collected by Submersible on the Nile deep-sea fan in an area of active fluid venting. U-Th analyses must be corrected for initial Th and measurement of co-existing sediments indicates the presence of both scavenged and detrital initial Th-230, which must be considered during this correction. The calculated Th-230/U age-depth profile for NL7-CC2 provides evidence for continuous downward carbonate precipitation at the studied location over the last similar to 5000 years. Three distinct phases can be distinguished from top to bottom with average growth rates of similar to 0.4, 5 and 0.8 cm/kyr, respectively, corresponding to carbonate precipitation rates ranging from similar to 7 to 92 mu mol m(2) h(-1) (rates consistent with previous estimates), High-resolution delta C-13 profiles [Gontharet, S., Pierre, C., Blanc-Valleron, M.-M., Rouchy,J.M., Fouquet, Y., Bayon, G., Foucher,J.P., Woodside,J., Mascle,J., The Nautinil Scientific Party, 2007. Nature and origin of diagenetic carbonate crusts and concretions from mud volcanoes and pockmarks of the Nile deep-sea fan (eastern Mediterranean Sea). Deep Sea Res. 1154,1292-1311] and major elements across NL7-CC2 show that the variations in carbonate precipitation rates were also accompanied by changes in carbonate mineralogy and fluid composition. We suggest that these changes primarily reflect modification of the diagenetic environment, i.e. a progres

On continental margins, oxidation of methane-rich fluids from the sediment often leads to formation of authigenic carbonate pavements on the seafloor. The biogeochemical processes involved during this carbonate precipitation are increasingly understood, but little is known about the duration or mode of carbonate crust formation. Here, we report uranium and thorium concentrations and isotope compositions for a set of 14 samples drilled across an authigenic carbonate pavement, which provide the first stratigraphy for a cold-seep carbonate crust. The 5.5-cm thick crust (NL7-CC2) was collected by Submersible on the Nile deep-sea fan in an area of active fluid venting. U-Th analyses must be corrected for initial Th and measurement of co-existing sediments indicates the presence of both scavenged and detrital initial Th-230, which must be considered during this correction. The calculated Th-230/U age-depth profile for NL7-CC2 provides evidence for continuous downward carbonate precipitation at the studied location over the last similar to 5000 years. Three distinct phases can be distinguished from top to bottom with average growth rates of similar to 0.4, 5 and 0.8 cm/kyr, respectively, corresponding to carbonate precipitation rates ranging from similar to 7 to 92 mu mol m(2) h(-1) (rates consistent with previous estimates), High-resolution delta C-13 profiles [Gontharet, S., Pierre, C., Blanc-Valleron, M.-M., Rouchy,J.M., Fouquet, Y., Bayon, G., Foucher,J.P., Woodside,J., Mascle,J., The Nautinil Scientific Party, 2007. Nature and origin of diagenetic carbonate crusts and concretions from mud volcanoes and pockmarks of the Nile deep-sea fan (eastern Mediterranean Sea). Deep Sea Res. 1154,1292-1311] and major elements across NL7-CC2 show that the variations in carbonate precipitation rates were also accompanied by changes in carbonate mineralogy and fluid composition. We suggest that these changes primarily reflect modification of the diagenetic environment, i.e. a progres

The transformation of pyroxene to its high-pressure polymorph akimotoite (MgSiO3 ilmenite type structure) is documented in the shock-induced melt veins of the L6 Tenham chondrite. Four textural relationships between pyroxene and akimotoite are observed in former pyroxene grains entrained in the shear melt vein and in pyroxene grains attached to the wall of the melt vein. In one of the entrained enstatite grains the transformation to akimotoite is partial. One third of the grain is transformed to a polycrystalline aggregate of akimotoite with a scalloped interface with enstatite. Akimotoite (Fe0.4Mg1.24Ca0.07Na0.12Al0.14)(Si1.963Al0.037)O-6 is slightly enriched in Ca (CaO = 1.74%), Al and Na with respect to enstatite (CaO = 0.71%). Narrow bands of polycrystalline akimotoite with three crystallographic orientations and a chemical composition similar to the Surrounding enstatite intersect the other part of the grain. In a second grain entrained in the shear melt vein, tablets of akimotoite are interwoven with a pyroxene glass with a lower Na and Fe content and a higher Mg content compared to the adjacent akimotoite. This pyroxene glass is probably the product of (Mg,Fe)SiO3-perovskite amorphization. Polycrystalline akimotoite is also formed at the expense of enstatite at the vein wall of the shear melt vein. In that case akimotoite is also enriched in Ca (CaO = 2.85%) Na (NaO = 1.72%) and Al (Al2O3=4.14%). All these observations suggest that akimotoite is mainly formed by solid-state transformation of former pyroxenes with subsequent diffusion of calcium, aluminum and sodium from the chondritic melt of the shear melt vein. Finally, the first complete X-ray diffraction pattern of natural akimotoite is presented. (c) 2008 Elsevier B.V. All rights reserved.

The transformation of pyroxene to its high-pressure polymorph akimotoite (MgSiO3 ilmenite type structure) is documented in the shock-induced melt veins of the L6 Tenham chondrite. Four textural relationships between pyroxene and akimotoite are observed in former pyroxene grains entrained in the shear melt vein and in pyroxene grains attached to the wall of the melt vein. In one of the entrained enstatite grains the transformation to akimotoite is partial. One third of the grain is transformed to a polycrystalline aggregate of akimotoite with a scalloped interface with enstatite. Akimotoite (Fe0.4Mg1.24Ca0.07Na0.12Al0.14)(Si1.963Al0.037)O-6 is slightly enriched in Ca (CaO = 1.74%), Al and Na with respect to enstatite (CaO = 0.71%). Narrow bands of polycrystalline akimotoite with three crystallographic orientations and a chemical composition similar to the Surrounding enstatite intersect the other part of the grain. In a second grain entrained in the shear melt vein, tablets of akimotoite are interwoven with a pyroxene glass with a lower Na and Fe content and a higher Mg content compared to the adjacent akimotoite. This pyroxene glass is probably the product of (Mg,Fe)SiO3-perovskite amorphization. Polycrystalline akimotoite is also formed at the expense of enstatite at the vein wall of the shear melt vein. In that case akimotoite is also enriched in Ca (CaO = 2.85%) Na (NaO = 1.72%) and Al (Al2O3=4.14%). All these observations suggest that akimotoite is mainly formed by solid-state transformation of former pyroxenes with subsequent diffusion of calcium, aluminum and sodium from the chondritic melt of the shear melt vein. Finally, the first complete X-ray diffraction pattern of natural akimotoite is presented. (c) 2008 Elsevier B.V. All rights reserved.

The transformation of pyroxene to its high-pressure polymorph akimotoite (MgSiO3 ilmenite type structure) is documented in the shock-induced melt veins of the L6 Tenham chondrite. Four textural relationships between pyroxene and akimotoite are observed in former pyroxene grains entrained in the shear melt vein and in pyroxene grains attached to the wall of the melt vein. In one of the entrained enstatite grains the transformation to akimotoite is partial. One third of the grain is transformed to a polycrystalline aggregate of akimotoite with a scalloped interface with enstatite. Akimotoite (Fe0.4Mg1.24Ca0.07Na0.12Al0.14)(Si1.963Al0.037)O-6 is slightly enriched in Ca (CaO = 1.74%), Al and Na with respect to enstatite (CaO = 0.71%). Narrow bands of polycrystalline akimotoite with three crystallographic orientations and a chemical composition similar to the Surrounding enstatite intersect the other part of the grain. In a second grain entrained in the shear melt vein, tablets of akimotoite are interwoven with a pyroxene glass with a lower Na and Fe content and a higher Mg content compared to the adjacent akimotoite. This pyroxene glass is probably the product of (Mg,Fe)SiO3-perovskite amorphization. Polycrystalline akimotoite is also formed at the expense of enstatite at the vein wall of the shear melt vein. In that case akimotoite is also enriched in Ca (CaO = 2.85%) Na (NaO = 1.72%) and Al (Al2O3=4.14%). All these observations suggest that akimotoite is mainly formed by solid-state transformation of former pyroxenes with subsequent diffusion of calcium, aluminum and sodium from the chondritic melt of the shear melt vein. Finally, the first complete X-ray diffraction pattern of natural akimotoite is presented. (c) 2008 Elsevier B.V. All rights reserved.

This paper reports new field observations and new petrological, textural and geochemical data on two gabbroic intrusions and one pegmatoid dyke from the French Polynesian islands Maupiti and Bora Bora, respectively. Olivine crystals from the Faataufi and Barque de Hiro gabbros (Maupiti) include High Temperature Iddingsite (HTI), exhibiting three distinct morphological facies. Chemical and crystallographical data performed by electron microprobe, scanning microscope, X-ray diffractometry and Near InfraRed spectroscopy show that HTI results from modifications of olivine structure through intense hydroxylation and Fe-oxidation. The HTI-free 120 m-wide Cloche de Hiro dyke (Bora Bora) exhibits a textural zonation from heterogranular/intergranular gabbro (peripheral part) to typical pegmatoid (inner area). We propose a textural tetrahedral classificatory diagram which can be used to clearly distinguish the textural characteristics of the pegmatoids from those of the other coarse-grained samples. Through comparison with a lava flow containing vesicle-rich segregation sheets, we suggest that the Cloche de Hiro dyke may correspond to a huge segregation structure derived from a Maupiti-type HTI-bearing gabbro through a vapor-differentiation process. Both intrusions might be considered as representative of two superposed levels in a vertically arranged magmatic complex. In this view, the Maupiti gabbroic bodies would represent the lower part of the postulated system. Under high oxygen fugacity, olivine crystals would have undergone important modifications of their structure, leading to HTI. The huge Bora Bora pegmatoid dyke would be the upper part of the complex. After expulsion from the HTI-bearing gabbroic solidification zone by build-up of gas pressure, vesicle-rich residual melt would have gathered into a shallow level and crystallized there as a pegmatoid body. (C) 2006 Elsevier B.V All rights reserved.

This paper reports new field observations and new petrological, textural and geochemical data on two gabbroic intrusions and one pegmatoid dyke from the French Polynesian islands Maupiti and Bora Bora, respectively. Olivine crystals from the Faataufi and Barque de Hiro gabbros (Maupiti) include High Temperature Iddingsite (HTI), exhibiting three distinct morphological facies. Chemical and crystallographical data performed by electron microprobe, scanning microscope, X-ray diffractometry and Near InfraRed spectroscopy show that HTI results from modifications of olivine structure through intense hydroxylation and Fe-oxidation. The HTI-free 120 m-wide Cloche de Hiro dyke (Bora Bora) exhibits a textural zonation from heterogranular/intergranular gabbro (peripheral part) to typical pegmatoid (inner area). We propose a textural tetrahedral classificatory diagram which can be used to clearly distinguish the textural characteristics of the pegmatoids from those of the other coarse-grained samples. Through comparison with a lava flow containing vesicle-rich segregation sheets, we suggest that the Cloche de Hiro dyke may correspond to a huge segregation structure derived from a Maupiti-type HTI-bearing gabbro through a vapor-differentiation process. Both intrusions might be considered as representative of two superposed levels in a vertically arranged magmatic complex. In this view, the Maupiti gabbroic bodies would represent the lower part of the postulated system. Under high oxygen fugacity, olivine crystals would have undergone important modifications of their structure, leading to HTI. The huge Bora Bora pegmatoid dyke would be the upper part of the complex. After expulsion from the HTI-bearing gabbroic solidification zone by build-up of gas pressure, vesicle-rich residual melt would have gathered into a shallow level and crystallized there as a pegmatoid body. (C) 2006 Elsevier B.V All rights reserved.

This paper reports new field observations and new petrological, textural and geochemical data on two gabbroic intrusions and one pegmatoid dyke from the French Polynesian islands Maupiti and Bora Bora, respectively. Olivine crystals from the Faataufi and Barque de Hiro gabbros (Maupiti) include High Temperature Iddingsite (HTI), exhibiting three distinct morphological facies. Chemical and crystallographical data performed by electron microprobe, scanning microscope, X-ray diffractometry and Near InfraRed spectroscopy show that HTI results from modifications of olivine structure through intense hydroxylation and Fe-oxidation. The HTI-free 120 m-wide Cloche de Hiro dyke (Bora Bora) exhibits a textural zonation from heterogranular/intergranular gabbro (peripheral part) to typical pegmatoid (inner area). We propose a textural tetrahedral classificatory diagram which can be used to clearly distinguish the textural characteristics of the pegmatoids from those of the other coarse-grained samples. Through comparison with a lava flow containing vesicle-rich segregation sheets, we suggest that the Cloche de Hiro dyke may correspond to a huge segregation structure derived from a Maupiti-type HTI-bearing gabbro through a vapor-differentiation process. Both intrusions might be considered as representative of two superposed levels in a vertically arranged magmatic complex. In this view, the Maupiti gabbroic bodies would represent the lower part of the postulated system. Under high oxygen fugacity, olivine crystals would have undergone important modifications of their structure, leading to HTI. The huge Bora Bora pegmatoid dyke would be the upper part of the complex. After expulsion from the HTI-bearing gabbroic solidification zone by build-up of gas pressure, vesicle-rich residual melt would have gathered into a shallow level and crystallized there as a pegmatoid body. (C) 2006 Elsevier B.V All rights reserved.

Temporal variations in Fe isotope compositions at three locations in the Pacific Ocean over the last 10 Ma are inferred from high-resolution analyses of three hydrogenetic ferromanganese crusts. Iron pathways to the central deep Pacific Ocean appear to have remained constant over the past 10 Ma, reflected by a remarkably constant Fe isotope composition, despite large changes in the Fe delivery rates to the surface ocean via dust. These results suggest that the Fe cycle in the deep ocean is decoupled from that in surface waters. By contrast, one ferromanganese crust from the Izu-Bonin (IB) back-arc/marginal basin of the W. Pacific exhibits large delta Fe-56 variations. In that crust, decreases in delta Fe-56 values correlate with increases in Mn, Mg, Ni, Cu, Zn, Me, and V contents, and consistent with periods of intense hydrothermal input and increased growth rates. A second crust located within 100 km of the first IB sample does not record any of these periods of enhanced hydrothermal input. This probably reflects the isolated pathways by which hydrothermally sourced Fe may have migrated in the back arc, highlighting the high degree of provinciality that Fe isotopes may have in the modem (oxic) oceans. Our results demonstrate that despite efficient removal at the source, hydrothermal Fe injected into the deep ocean could account for a significant fraction of the dissolved Fe pool in the deep ocean, and that hydrothermally sourced Fe fluxes to the open ocean may have lower delta(56) Fe values than those measured so far in situ at hydrothermal vents. Correlation between 656 Fe values and elements enriched in hydrothermal fluids may provide a means for distinguishing hydrothermal Fe from other low-delta Fe-56 sources to the oceans such as dissolved riverine Fe or porewaters in continental shelf sediments. (c) 2006 Elsevier B.V. All rights reserved.

Hydroschorlomite, a Ti-, Ca-, Fe-rich andraditic garnet present in the deepest cores of basalts (661-749 mbsf) drilled in Hole 1256D during Ocean Drilling Program (ODP) Leg 206 (equatorial east Pacific), is reported here for the first time in oceanic crust. Detailed petrological and mineralogical studies by optical microscope, electron microprobe, scanning and transmission electron microscope, and micro-Raman spectroscopy are used to characterize this hydrogarnet and its relationships with other minerals. Hydroschorlomite occurs in Hole 1256D as small (5-50 mu m) anhedral or euhedral crystals associated either with celadonite in black halos adjacent to celadonite veins or with brown saponitic phyllosilicate in brown alteration halos adjacent to veins of saponite and iron oxyhydroxides. Both types of halos are formed at low temperature (less than about 100 degrees C). Textural observations suggest that hydroschorlomite formation is contemporaneous with the phyllosilicates. Hydroschorlomite is rich in CaO (22.5-26.5 wt%), TiO2 (22.0-28.6 wt%), and FeOt (6.2-12.9 wt%) and contains significant F (up to 0.85 wt%) and Zr2O3 (up to 0.34 wt%). The presence of OH suggested by the low total percentages of oxides (95.2-97.3 wt%) is confirmed by the OH vibration at 3557 cm(-1) in the micro-Raman spectrum. Chemical mapping indicates that hydroschorlomite is not zoned and is always associated with either celadonitic or saponitic phyllosilicates. Some hydroschorlomite crystals partly include tiny(<10 mu m) skeletal titanomagnetite. The occurrence of hydroschorlomite in Hole 1256D basalts coincides with a general downward increase in temperatures and overall intensity of alteration manifest by the alteration of plagioclase and the occurrence of small amounts of mixed-layer chlorite-smectite. The titanium necessary to form hydroschorlomite is provided by the breakdown of primary tiny (<10 mu m) titanomagnetite, while calcium is provided by the replacement of plagioclase by albite. H

Ion-microprobe was used to measure Li abundances and isotopic compositions in pyroxenes from three Martian meteorites belonging to the nakhlite family. The profiles performed across augite crystals from Northwest Africa 817 show a large isotopic zoning from crystal cores (delta Li-7 similar to 0 parts per thousand) to rims (delta Li-7 similar to +20 parts per thousand) while Li abundances are almost constant (similar to 9.2 mu g/g). Unlike NWA 817, the pyroxene studied in the Miller Range 03346 nakhlite shows a zoning in Li abundance, with concentrations increasing from similar to 2.5 mu g/g in the core to similar to 9 mu g/ g in the rim. The augite rim (delta Li-7 = +7 parts per thousand) is slightly enriched in Li-7 with regard to the core (delta Li-7 = +4 parts per thousand), but most of the isotopic variations observed occur at an intermediate position along the profile, where 67 Li falls down to similar to-11 parts per thousand. In the case of Nakhla, Li concentrations in augite increase from cores (similar to 3.5 mu g/g) to rims (similar to 6.5 mu g/g), while the delta Li-7 variation is restricted (i.e., between delta Li-7 = +6.0 and +12.6 parts per thousand). For the three meteorites the Li abundances were also measured in the groundmass, which was found to be enriched in lithium (similar to 10 mu g/g). Conventional magmatic and post-magmatic processes such as alteration and fractional crystallization, fail to explain the dataset obtained on nakhlites. Degassing processes, which were previously proposed to explain the Li distribution in shergottite crystals, cannot result in the strong decoupling between Li abundances and isotopic composition observed in nakhlites. We suggest that the original magmatic Li distributions (concentrations and isotopic compositions) in nakhtites have been modified by diffusion of Li from the Li-rich groundmass towards the pyroxene crystals during sub-solidus cooling. Diffusion appears to have been efficient for NWA 817 and MIL 033

Temporal variations in Fe isotope compositions at three locations in the Pacific Ocean over the last 10 Ma are inferred from high-resolution analyses of three hydrogenetic ferromanganese crusts. Iron pathways to the central deep Pacific Ocean appear to have remained constant over the past 10 Ma, reflected by a remarkably constant Fe isotope composition, despite large changes in the Fe delivery rates to the surface ocean via dust. These results suggest that the Fe cycle in the deep ocean is decoupled from that in surface waters. By contrast, one ferromanganese crust from the Izu-Bonin (IB) back-arc/marginal basin of the W. Pacific exhibits large delta Fe-56 variations. In that crust, decreases in delta Fe-56 values correlate with increases in Mn, Mg, Ni, Cu, Zn, Me, and V contents, and consistent with periods of intense hydrothermal input and increased growth rates. A second crust located within 100 km of the first IB sample does not record any of these periods of enhanced hydrothermal input. This probably reflects the isolated pathways by which hydrothermally sourced Fe may have migrated in the back arc, highlighting the high degree of provinciality that Fe isotopes may have in the modem (oxic) oceans. Our results demonstrate that despite efficient removal at the source, hydrothermal Fe injected into the deep ocean could account for a significant fraction of the dissolved Fe pool in the deep ocean, and that hydrothermally sourced Fe fluxes to the open ocean may have lower delta(56) Fe values than those measured so far in situ at hydrothermal vents. Correlation between 656 Fe values and elements enriched in hydrothermal fluids may provide a means for distinguishing hydrothermal Fe from other low-delta Fe-56 sources to the oceans such as dissolved riverine Fe or porewaters in continental shelf sediments. (c) 2006 Elsevier B.V. All rights reserved.

Hydroschorlomite, a Ti-, Ca-, Fe-rich andraditic garnet present in the deepest cores of basalts (661-749 mbsf) drilled in Hole 1256D during Ocean Drilling Program (ODP) Leg 206 (equatorial east Pacific), is reported here for the first time in oceanic crust. Detailed petrological and mineralogical studies by optical microscope, electron microprobe, scanning and transmission electron microscope, and micro-Raman spectroscopy are used to characterize this hydrogarnet and its relationships with other minerals. Hydroschorlomite occurs in Hole 1256D as small (5-50 mu m) anhedral or euhedral crystals associated either with celadonite in black halos adjacent to celadonite veins or with brown saponitic phyllosilicate in brown alteration halos adjacent to veins of saponite and iron oxyhydroxides. Both types of halos are formed at low temperature (less than about 100 degrees C). Textural observations suggest that hydroschorlomite formation is contemporaneous with the phyllosilicates. Hydroschorlomite is rich in CaO (22.5-26.5 wt%), TiO2 (22.0-28.6 wt%), and FeOt (6.2-12.9 wt%) and contains significant F (up to 0.85 wt%) and Zr2O3 (up to 0.34 wt%). The presence of OH suggested by the low total percentages of oxides (95.2-97.3 wt%) is confirmed by the OH vibration at 3557 cm(-1) in the micro-Raman spectrum. Chemical mapping indicates that hydroschorlomite is not zoned and is always associated with either celadonitic or saponitic phyllosilicates. Some hydroschorlomite crystals partly include tiny(<10 mu m) skeletal titanomagnetite. The occurrence of hydroschorlomite in Hole 1256D basalts coincides with a general downward increase in temperatures and overall intensity of alteration manifest by the alteration of plagioclase and the occurrence of small amounts of mixed-layer chlorite-smectite. The titanium necessary to form hydroschorlomite is provided by the breakdown of primary tiny (<10 mu m) titanomagnetite, while calcium is provided by the replacement of plagioclase by albite. H

Ion-microprobe was used to measure Li abundances and isotopic compositions in pyroxenes from three Martian meteorites belonging to the nakhlite family. The profiles performed across augite crystals from Northwest Africa 817 show a large isotopic zoning from crystal cores (delta Li-7 similar to 0 parts per thousand) to rims (delta Li-7 similar to +20 parts per thousand) while Li abundances are almost constant (similar to 9.2 mu g/g). Unlike NWA 817, the pyroxene studied in the Miller Range 03346 nakhlite shows a zoning in Li abundance, with concentrations increasing from similar to 2.5 mu g/g in the core to similar to 9 mu g/ g in the rim. The augite rim (delta Li-7 = +7 parts per thousand) is slightly enriched in Li-7 with regard to the core (delta Li-7 = +4 parts per thousand), but most of the isotopic variations observed occur at an intermediate position along the profile, where 67 Li falls down to similar to-11 parts per thousand. In the case of Nakhla, Li concentrations in augite increase from cores (similar to 3.5 mu g/g) to rims (similar to 6.5 mu g/g), while the delta Li-7 variation is restricted (i.e., between delta Li-7 = +6.0 and +12.6 parts per thousand). For the three meteorites the Li abundances were also measured in the groundmass, which was found to be enriched in lithium (similar to 10 mu g/g). Conventional magmatic and post-magmatic processes such as alteration and fractional crystallization, fail to explain the dataset obtained on nakhlites. Degassing processes, which were previously proposed to explain the Li distribution in shergottite crystals, cannot result in the strong decoupling between Li abundances and isotopic composition observed in nakhlites. We suggest that the original magmatic Li distributions (concentrations and isotopic compositions) in nakhtites have been modified by diffusion of Li from the Li-rich groundmass towards the pyroxene crystals during sub-solidus cooling. Diffusion appears to have been efficient for NWA 817 and MIL 033

Temporal variations in Fe isotope compositions at three locations in the Pacific Ocean over the last 10 Ma are inferred from high-resolution analyses of three hydrogenetic ferromanganese crusts. Iron pathways to the central deep Pacific Ocean appear to have remained constant over the past 10 Ma, reflected by a remarkably constant Fe isotope composition, despite large changes in the Fe delivery rates to the surface ocean via dust. These results suggest that the Fe cycle in the deep ocean is decoupled from that in surface waters. By contrast, one ferromanganese crust from the Izu-Bonin (IB) back-arc/marginal basin of the W. Pacific exhibits large delta Fe-56 variations. In that crust, decreases in delta Fe-56 values correlate with increases in Mn, Mg, Ni, Cu, Zn, Me, and V contents, and consistent with periods of intense hydrothermal input and increased growth rates. A second crust located within 100 km of the first IB sample does not record any of these periods of enhanced hydrothermal input. This probably reflects the isolated pathways by which hydrothermally sourced Fe may have migrated in the back arc, highlighting the high degree of provinciality that Fe isotopes may have in the modem (oxic) oceans. Our results demonstrate that despite efficient removal at the source, hydrothermal Fe injected into the deep ocean could account for a significant fraction of the dissolved Fe pool in the deep ocean, and that hydrothermally sourced Fe fluxes to the open ocean may have lower delta(56) Fe values than those measured so far in situ at hydrothermal vents. Correlation between 656 Fe values and elements enriched in hydrothermal fluids may provide a means for distinguishing hydrothermal Fe from other low-delta Fe-56 sources to the oceans such as dissolved riverine Fe or porewaters in continental shelf sediments. (c) 2006 Elsevier B.V. All rights reserved.

Hydroschorlomite, a Ti-, Ca-, Fe-rich andraditic garnet present in the deepest cores of basalts (661-749 mbsf) drilled in Hole 1256D during Ocean Drilling Program (ODP) Leg 206 (equatorial east Pacific), is reported here for the first time in oceanic crust. Detailed petrological and mineralogical studies by optical microscope, electron microprobe, scanning and transmission electron microscope, and micro-Raman spectroscopy are used to characterize this hydrogarnet and its relationships with other minerals. Hydroschorlomite occurs in Hole 1256D as small (5-50 mu m) anhedral or euhedral crystals associated either with celadonite in black halos adjacent to celadonite veins or with brown saponitic phyllosilicate in brown alteration halos adjacent to veins of saponite and iron oxyhydroxides. Both types of halos are formed at low temperature (less than about 100 degrees C). Textural observations suggest that hydroschorlomite formation is contemporaneous with the phyllosilicates. Hydroschorlomite is rich in CaO (22.5-26.5 wt%), TiO2 (22.0-28.6 wt%), and FeOt (6.2-12.9 wt%) and contains significant F (up to 0.85 wt%) and Zr2O3 (up to 0.34 wt%). The presence of OH suggested by the low total percentages of oxides (95.2-97.3 wt%) is confirmed by the OH vibration at 3557 cm(-1) in the micro-Raman spectrum. Chemical mapping indicates that hydroschorlomite is not zoned and is always associated with either celadonitic or saponitic phyllosilicates. Some hydroschorlomite crystals partly include tiny(<10 mu m) skeletal titanomagnetite. The occurrence of hydroschorlomite in Hole 1256D basalts coincides with a general downward increase in temperatures and overall intensity of alteration manifest by the alteration of plagioclase and the occurrence of small amounts of mixed-layer chlorite-smectite. The titanium necessary to form hydroschorlomite is provided by the breakdown of primary tiny (<10 mu m) titanomagnetite, while calcium is provided by the replacement of plagioclase by albite. H

Ion-microprobe was used to measure Li abundances and isotopic compositions in pyroxenes from three Martian meteorites belonging to the nakhlite family. The profiles performed across augite crystals from Northwest Africa 817 show a large isotopic zoning from crystal cores (delta Li-7 similar to 0 parts per thousand) to rims (delta Li-7 similar to +20 parts per thousand) while Li abundances are almost constant (similar to 9.2 mu g/g). Unlike NWA 817, the pyroxene studied in the Miller Range 03346 nakhlite shows a zoning in Li abundance, with concentrations increasing from similar to 2.5 mu g/g in the core to similar to 9 mu g/ g in the rim. The augite rim (delta Li-7 = +7 parts per thousand) is slightly enriched in Li-7 with regard to the core (delta Li-7 = +4 parts per thousand), but most of the isotopic variations observed occur at an intermediate position along the profile, where 67 Li falls down to similar to-11 parts per thousand. In the case of Nakhla, Li concentrations in augite increase from cores (similar to 3.5 mu g/g) to rims (similar to 6.5 mu g/g), while the delta Li-7 variation is restricted (i.e., between delta Li-7 = +6.0 and +12.6 parts per thousand). For the three meteorites the Li abundances were also measured in the groundmass, which was found to be enriched in lithium (similar to 10 mu g/g). Conventional magmatic and post-magmatic processes such as alteration and fractional crystallization, fail to explain the dataset obtained on nakhlites. Degassing processes, which were previously proposed to explain the Li distribution in shergottite crystals, cannot result in the strong decoupling between Li abundances and isotopic composition observed in nakhlites. We suggest that the original magmatic Li distributions (concentrations and isotopic compositions) in nakhtites have been modified by diffusion of Li from the Li-rich groundmass towards the pyroxene crystals during sub-solidus cooling. Diffusion appears to have been efficient for NWA 817 and MIL 033

Northwest Africa (NWA) 1950 is a new member of the lherzolitic shergottite clan of the Martian meteorites recently found in the Atlas Mountains. The petrological, mineralogical, and geochemical data are very close to those of the other known lherzolitic shergottites. The meteorite has a cumulate gabbroic texture and its mineralogy consists of olivine (FO66 to FO75), low and high-Ca pyroxenes (En(78)Fs(19)Wo(2)-En(60)FS(26)W(14); En(53)Fs(16)Wo(31)-En(45)Fs(14)Wo(41)), and plagioclase (An(57)Ab(41)Or(1) to An(40)Ab(57)Or(3); entirely converted into maskelynite during intense shock metamorphism). Accessory minerals include phosphates (merrillite), chromite and spinels, sulfides, and a glass rich in potassium. The oxygen isotopic values lie on the fractional line defined by the other SNC meteorites (Delta(17)O = 0.312 parts per thousand). The composition of NWA 1950 is very similar to the other lherzolitic shergottites and Suggests an origin from the same magmatic system, or at least crystallization from a close parental melt. Cosmogenic ages indicate an ejection age similar to those of the other lherzolitic shergottites. The intensity of the shock is similar to that observed in other shergottites, as shown by the occurrence of small melt pockets containing glass interwoven with stishovite.

After a laser gas nitriding treatment of the Ti-7.5Al (atom %) titanium-based alloy, we used a combination of electron backscattered diffraction (EBSD) in scanning electron microscope and electron probe microanalysis (EPMA) techniques in order to efficiently characterize the different phases in the resolidified layer. Representative measurements of chemical composition and reliable determination of crystal structure were possible for each phase of the complex microstructure. The reaction zone is formed by a mixture of isostructural TiN phases with dendritic and/or 'coarse' needles morphology, fixed into a alpha'-Ti matrix (martensite) with a thin needle aspect. The nitrogen solubility was found to remain very low in the alpha'-Ti matrix (up to 2-3 atom %), while in the TiN phase, an aluminum solubility as high as 4 atom % was measured, reducing drastically the nitrogen content into a Ti79N17Al4 chemical composition. Copyright (C) 2005 John Wiley and Sons, Ltd.

Northwest Africa (NWA) 1950 is a new member of the lherzolitic shergottite clan of the Martian meteorites recently found in the Atlas Mountains. The petrological, mineralogical, and geochemical data are very close to those of the other known lherzolitic shergottites. The meteorite has a cumulate gabbroic texture and its mineralogy consists of olivine (FO66 to FO75), low and high-Ca pyroxenes (En(78)Fs(19)Wo(2)-En(60)FS(26)W(14); En(53)Fs(16)Wo(31)-En(45)Fs(14)Wo(41)), and plagioclase (An(57)Ab(41)Or(1) to An(40)Ab(57)Or(3); entirely converted into maskelynite during intense shock metamorphism). Accessory minerals include phosphates (merrillite), chromite and spinels, sulfides, and a glass rich in potassium. The oxygen isotopic values lie on the fractional line defined by the other SNC meteorites (Delta(17)O = 0.312 parts per thousand). The composition of NWA 1950 is very similar to the other lherzolitic shergottites and Suggests an origin from the same magmatic system, or at least crystallization from a close parental melt. Cosmogenic ages indicate an ejection age similar to those of the other lherzolitic shergottites. The intensity of the shock is similar to that observed in other shergottites, as shown by the occurrence of small melt pockets containing glass interwoven with stishovite.

After a laser gas nitriding treatment of the Ti-7.5Al (atom %) titanium-based alloy, we used a combination of electron backscattered diffraction (EBSD) in scanning electron microscope and electron probe microanalysis (EPMA) techniques in order to efficiently characterize the different phases in the resolidified layer. Representative measurements of chemical composition and reliable determination of crystal structure were possible for each phase of the complex microstructure. The reaction zone is formed by a mixture of isostructural TiN phases with dendritic and/or 'coarse' needles morphology, fixed into a alpha'-Ti matrix (martensite) with a thin needle aspect. The nitrogen solubility was found to remain very low in the alpha'-Ti matrix (up to 2-3 atom %), while in the TiN phase, an aluminum solubility as high as 4 atom % was measured, reducing drastically the nitrogen content into a Ti79N17Al4 chemical composition. Copyright (C) 2005 John Wiley and Sons, Ltd.

Northwest Africa (NWA) 1950 is a new member of the lherzolitic shergottite clan of the Martian meteorites recently found in the Atlas Mountains. The petrological, mineralogical, and geochemical data are very close to those of the other known lherzolitic shergottites. The meteorite has a cumulate gabbroic texture and its mineralogy consists of olivine (FO66 to FO75), low and high-Ca pyroxenes (En(78)Fs(19)Wo(2)-En(60)FS(26)W(14); En(53)Fs(16)Wo(31)-En(45)Fs(14)Wo(41)), and plagioclase (An(57)Ab(41)Or(1) to An(40)Ab(57)Or(3); entirely converted into maskelynite during intense shock metamorphism). Accessory minerals include phosphates (merrillite), chromite and spinels, sulfides, and a glass rich in potassium. The oxygen isotopic values lie on the fractional line defined by the other SNC meteorites (Delta(17)O = 0.312 parts per thousand). The composition of NWA 1950 is very similar to the other lherzolitic shergottites and Suggests an origin from the same magmatic system, or at least crystallization from a close parental melt. Cosmogenic ages indicate an ejection age similar to those of the other lherzolitic shergottites. The intensity of the shock is similar to that observed in other shergottites, as shown by the occurrence of small melt pockets containing glass interwoven with stishovite.

After a laser gas nitriding treatment of the Ti-7.5Al (atom %) titanium-based alloy, we used a combination of electron backscattered diffraction (EBSD) in scanning electron microscope and electron probe microanalysis (EPMA) techniques in order to efficiently characterize the different phases in the resolidified layer. Representative measurements of chemical composition and reliable determination of crystal structure were possible for each phase of the complex microstructure. The reaction zone is formed by a mixture of isostructural TiN phases with dendritic and/or 'coarse' needles morphology, fixed into a alpha'-Ti matrix (martensite) with a thin needle aspect. The nitrogen solubility was found to remain very low in the alpha'-Ti matrix (up to 2-3 atom %), while in the TiN phase, an aluminum solubility as high as 4 atom % was measured, reducing drastically the nitrogen content into a Ti79N17Al4 chemical composition. Copyright (C) 2005 John Wiley and Sons, Ltd.

Northwest Africa (NWA) 1950 is a new member of the lherzolitic shergottite clan of the Martian meteorites recently found in the Atlas Mountains. The petrological, mineralogical, and geochemical data are very close to those of the other known lherzolitic shergottites. The meteorite has a cumulate gabbroic texture and its mineralogy consists of olivine (FO66 to FO75), low and high-Ca pyroxenes (En(78)Fs(19)Wo(2)-En(60)FS(26)W(14); En(53)Fs(16)Wo(31)-En(45)Fs(14)Wo(41)), and plagioclase (An(57)Ab(41)Or(1) to An(40)Ab(57)Or(3); entirely converted into maskelynite during intense shock metamorphism). Accessory minerals include phosphates (merrillite), chromite and spinels, sulfides, and a glass rich in potassium. The oxygen isotopic values lie on the fractional line defined by the other SNC meteorites (Delta(17)O = 0.312 parts per thousand). The composition of NWA 1950 is very similar to the other lherzolitic shergottites and Suggests an origin from the same magmatic system, or at least crystallization from a close parental melt. Cosmogenic ages indicate an ejection age similar to those of the other lherzolitic shergottites. The intensity of the shock is similar to that observed in other shergottites, as shown by the occurrence of small melt pockets containing glass interwoven with stishovite.

Lithium abundances and isotopic compositions were measured by ion microprobe in individual grains of pyroxene, and in a few maskelynites and Ca-phosphates grains, from the Martian meteorite Northwest Africa 480 (NWA 480). In pyroxenes Li abundances are nearly constant from core to rim with concentrations ranging between 3 and 4 mug/g. In contrast, a significant isotopic zoning is observed with delta(7)Li values increasing within single crystals from similar to -17parts per thousand in the core to similar to +10parts per thousand in the rim, most of the variability being observed in the core. Plagioclase (now maskelynite) and phosphate crystals, which co-crystallized with the pyroxene rims, display similar delta(7) Li values. Because of the incompatible behavior of Li, the present constancy of Li concentrations within zoned pyroxenes rules out any simple crystallization model in a closed system for Li. The large Li isotopic variations observed within pyroxenes support this conclusion. There is no evidence in support of secondary alteration of NWA 480 to explain the Li isotopic variations, which thus most likely reflect magmatic processes on Mars. Degassing might explain the Li systematics observed in NWA 480 pyroxenes. Because Li has a strong affinity with water-rich fluids, a significant loss of Li from NWA 480 parental melt can happen upon melt emplacement and cooling. Such a Li loss could compensate the effect of crystal fractionation and thus help to maintain constant the Li content of the melt. Li isotopic fractionation is anticipated to accompany this process, Li-7 being depleted relative to Li-6 in the volatile phase. The magnitude of the isotopic change of the fractionating melts is difficult to predict because it depends on the value of the Li isotopic fractionation and on the amount of Li loss, but at first glance it seems consistent with the increase of delta(7)Li values observed in NWA 480 pyroxenes with increasing fractionation. The present data suggest

Lithium abundances and isotopic compositions were measured by ion microprobe in individual grains of pyroxene, and in a few maskelynites and Ca-phosphates grains, from the Martian meteorite Northwest Africa 480 (NWA 480). In pyroxenes Li abundances are nearly constant from core to rim with concentrations ranging between 3 and 4 mug/g. In contrast, a significant isotopic zoning is observed with delta(7)Li values increasing within single crystals from similar to -17parts per thousand in the core to similar to +10parts per thousand in the rim, most of the variability being observed in the core. Plagioclase (now maskelynite) and phosphate crystals, which co-crystallized with the pyroxene rims, display similar delta(7) Li values. Because of the incompatible behavior of Li, the present constancy of Li concentrations within zoned pyroxenes rules out any simple crystallization model in a closed system for Li. The large Li isotopic variations observed within pyroxenes support this conclusion. There is no evidence in support of secondary alteration of NWA 480 to explain the Li isotopic variations, which thus most likely reflect magmatic processes on Mars. Degassing might explain the Li systematics observed in NWA 480 pyroxenes. Because Li has a strong affinity with water-rich fluids, a significant loss of Li from NWA 480 parental melt can happen upon melt emplacement and cooling. Such a Li loss could compensate the effect of crystal fractionation and thus help to maintain constant the Li content of the melt. Li isotopic fractionation is anticipated to accompany this process, Li-7 being depleted relative to Li-6 in the volatile phase. The magnitude of the isotopic change of the fractionating melts is difficult to predict because it depends on the value of the Li isotopic fractionation and on the amount of Li loss, but at first glance it seems consistent with the increase of delta(7)Li values observed in NWA 480 pyroxenes with increasing fractionation. The present data suggest

Lithium abundances and isotopic compositions were measured by ion microprobe in individual grains of pyroxene, and in a few maskelynites and Ca-phosphates grains, from the Martian meteorite Northwest Africa 480 (NWA 480). In pyroxenes Li abundances are nearly constant from core to rim with concentrations ranging between 3 and 4 mug/g. In contrast, a significant isotopic zoning is observed with delta(7)Li values increasing within single crystals from similar to -17parts per thousand in the core to similar to +10parts per thousand in the rim, most of the variability being observed in the core. Plagioclase (now maskelynite) and phosphate crystals, which co-crystallized with the pyroxene rims, display similar delta(7) Li values. Because of the incompatible behavior of Li, the present constancy of Li concentrations within zoned pyroxenes rules out any simple crystallization model in a closed system for Li. The large Li isotopic variations observed within pyroxenes support this conclusion. There is no evidence in support of secondary alteration of NWA 480 to explain the Li isotopic variations, which thus most likely reflect magmatic processes on Mars. Degassing might explain the Li systematics observed in NWA 480 pyroxenes. Because Li has a strong affinity with water-rich fluids, a significant loss of Li from NWA 480 parental melt can happen upon melt emplacement and cooling. Such a Li loss could compensate the effect of crystal fractionation and thus help to maintain constant the Li content of the melt. Li isotopic fractionation is anticipated to accompany this process, Li-7 being depleted relative to Li-6 in the volatile phase. The magnitude of the isotopic change of the fractionating melts is difficult to predict because it depends on the value of the Li isotopic fractionation and on the amount of Li loss, but at first glance it seems consistent with the increase of delta(7)Li values observed in NWA 480 pyroxenes with increasing fractionation. The present data suggest

Axial bathymetry, major/trace elements, and isotopes suggest:that the Pacific-Antarctic Ridge (PAR) between 56 degrees S and 66 degrees S is devoid of any hotspot influence. PAR (56-66 degrees 5) samples have in-average lower Sr-87/Sr-86 and Nd-143/Nd-144 and higher Pb-206/(204)pb than northern Pacific midocean ridge basalts (MORB), and also than MORE from the other oceans. The high variability of Pb isotopic ratios (compared to Sr and Nd) can be due to either a;general high mu (HIMU) (high U/Pb) affinity of the southern Pacific upper mantle or to a mantle event first recorded in time by Pb isotopes. Compiling the results of this study with those from the PAR between 53 degrees S and 57 degrees S gives a continuous view of mantle characteristics from south Pitman Fracture Zone (FZ) to Vacquier FZ, representing about 3000 km of spreading axis. The latitude of Udintsev FZ (56 degrees S) is a limit between, to the north, a domain with large geochemical Variations and, to the south, one with small Variations. The spreading rate has intermediate values (54 mm/yr at 66 degrees S to 74 mm/yr at 56 degrees S) which increase along the PAR, while the axial morphology: changes from valley to dome. The morphological transition is not recorded by the chemical properties of the ridge basalts nor by the inferred mantle temperature which displays few variations (30-40 degrees C) along the PAR. Contrary to what is observed along the South-East Indian Ridge, PAR morphology appears to be controlled more by spreading rate rather than by mantle temperature. Much of the major and trace element variability results from segmentation control on the shallowest thermal structure of the mantle. The cold edge of a fracture zone seems to be more efficient when occurring in an axial dome context.:It is expressed as an increase of the magnitude of the Transform Fault Effect along the valley-dome transition, resulting in a clear increase of trace element ratio variability (such as Nb/Zr). There is

A range of X-ray analytical techniques contributes particularly well to the mineralogical and geochemical characterisations of cobalt-rich iron and manganese oxides crusts. X-ray diffraction is used to identify the weak crystallinity of the material. Bulk geochemical characterisation of the crusts is done by X-ray fluorescence for the precise determination of ca. thirty major and trace elements. Fine scale analysis is carried out by electron microprobe to quantitatively map the distribution of elements in oxide phases within the crusts. Microprobe work is essential to obtain the chemical composition of the embedded metallic micro-meteorites.

Axial bathymetry, major/trace elements, and isotopes suggest:that the Pacific-Antarctic Ridge (PAR) between 56 degrees S and 66 degrees S is devoid of any hotspot influence. PAR (56-66 degrees 5) samples have in-average lower Sr-87/Sr-86 and Nd-143/Nd-144 and higher Pb-206/(204)pb than northern Pacific midocean ridge basalts (MORB), and also than MORE from the other oceans. The high variability of Pb isotopic ratios (compared to Sr and Nd) can be due to either a;general high mu (HIMU) (high U/Pb) affinity of the southern Pacific upper mantle or to a mantle event first recorded in time by Pb isotopes. Compiling the results of this study with those from the PAR between 53 degrees S and 57 degrees S gives a continuous view of mantle characteristics from south Pitman Fracture Zone (FZ) to Vacquier FZ, representing about 3000 km of spreading axis. The latitude of Udintsev FZ (56 degrees S) is a limit between, to the north, a domain with large geochemical Variations and, to the south, one with small Variations. The spreading rate has intermediate values (54 mm/yr at 66 degrees S to 74 mm/yr at 56 degrees S) which increase along the PAR, while the axial morphology: changes from valley to dome. The morphological transition is not recorded by the chemical properties of the ridge basalts nor by the inferred mantle temperature which displays few variations (30-40 degrees C) along the PAR. Contrary to what is observed along the South-East Indian Ridge, PAR morphology appears to be controlled more by spreading rate rather than by mantle temperature. Much of the major and trace element variability results from segmentation control on the shallowest thermal structure of the mantle. The cold edge of a fracture zone seems to be more efficient when occurring in an axial dome context.:It is expressed as an increase of the magnitude of the Transform Fault Effect along the valley-dome transition, resulting in a clear increase of trace element ratio variability (such as Nb/Zr). There is

A range of X-ray analytical techniques contributes particularly well to the mineralogical and geochemical characterisations of cobalt-rich iron and manganese oxides crusts. X-ray diffraction is used to identify the weak crystallinity of the material. Bulk geochemical characterisation of the crusts is done by X-ray fluorescence for the precise determination of ca. thirty major and trace elements. Fine scale analysis is carried out by electron microprobe to quantitatively map the distribution of elements in oxide phases within the crusts. Microprobe work is essential to obtain the chemical composition of the embedded metallic micro-meteorites.

Axial bathymetry, major/trace elements, and isotopes suggest:that the Pacific-Antarctic Ridge (PAR) between 56 degrees S and 66 degrees S is devoid of any hotspot influence. PAR (56-66 degrees 5) samples have in-average lower Sr-87/Sr-86 and Nd-143/Nd-144 and higher Pb-206/(204)pb than northern Pacific midocean ridge basalts (MORB), and also than MORE from the other oceans. The high variability of Pb isotopic ratios (compared to Sr and Nd) can be due to either a;general high mu (HIMU) (high U/Pb) affinity of the southern Pacific upper mantle or to a mantle event first recorded in time by Pb isotopes. Compiling the results of this study with those from the PAR between 53 degrees S and 57 degrees S gives a continuous view of mantle characteristics from south Pitman Fracture Zone (FZ) to Vacquier FZ, representing about 3000 km of spreading axis. The latitude of Udintsev FZ (56 degrees S) is a limit between, to the north, a domain with large geochemical Variations and, to the south, one with small Variations. The spreading rate has intermediate values (54 mm/yr at 66 degrees S to 74 mm/yr at 56 degrees S) which increase along the PAR, while the axial morphology: changes from valley to dome. The morphological transition is not recorded by the chemical properties of the ridge basalts nor by the inferred mantle temperature which displays few variations (30-40 degrees C) along the PAR. Contrary to what is observed along the South-East Indian Ridge, PAR morphology appears to be controlled more by spreading rate rather than by mantle temperature. Much of the major and trace element variability results from segmentation control on the shallowest thermal structure of the mantle. The cold edge of a fracture zone seems to be more efficient when occurring in an axial dome context.:It is expressed as an increase of the magnitude of the Transform Fault Effect along the valley-dome transition, resulting in a clear increase of trace element ratio variability (such as Nb/Zr). There is

A range of X-ray analytical techniques contributes particularly well to the mineralogical and geochemical characterisations of cobalt-rich iron and manganese oxides crusts. X-ray diffraction is used to identify the weak crystallinity of the material. Bulk geochemical characterisation of the crusts is done by X-ray fluorescence for the precise determination of ca. thirty major and trace elements. Fine scale analysis is carried out by electron microprobe to quantitatively map the distribution of elements in oxide phases within the crusts. Microprobe work is essential to obtain the chemical composition of the embedded metallic micro-meteorites.

Axial bathymetry, major/trace elements, and isotopes suggest:that the Pacific-Antarctic Ridge (PAR) between 56 degrees S and 66 degrees S is devoid of any hotspot influence. PAR (56-66 degrees 5) samples have in-average lower Sr-87/Sr-86 and Nd-143/Nd-144 and higher Pb-206/(204)pb than northern Pacific midocean ridge basalts (MORB), and also than MORE from the other oceans. The high variability of Pb isotopic ratios (compared to Sr and Nd) can be due to either a;general high mu (HIMU) (high U/Pb) affinity of the southern Pacific upper mantle or to a mantle event first recorded in time by Pb isotopes. Compiling the results of this study with those from the PAR between 53 degrees S and 57 degrees S gives a continuous view of mantle characteristics from south Pitman Fracture Zone (FZ) to Vacquier FZ, representing about 3000 km of spreading axis. The latitude of Udintsev FZ (56 degrees S) is a limit between, to the north, a domain with large geochemical Variations and, to the south, one with small Variations. The spreading rate has intermediate values (54 mm/yr at 66 degrees S to 74 mm/yr at 56 degrees S) which increase along the PAR, while the axial morphology: changes from valley to dome. The morphological transition is not recorded by the chemical properties of the ridge basalts nor by the inferred mantle temperature which displays few variations (30-40 degrees C) along the PAR. Contrary to what is observed along the South-East Indian Ridge, PAR morphology appears to be controlled more by spreading rate rather than by mantle temperature. Much of the major and trace element variability results from segmentation control on the shallowest thermal structure of the mantle. The cold edge of a fracture zone seems to be more efficient when occurring in an axial dome context.:It is expressed as an increase of the magnitude of the Transform Fault Effect along the valley-dome transition, resulting in a clear increase of trace element ratio variability (such as Nb/Zr). There is

The howardite-eucrite-diogenite (HED) achondrites are a group of meteorites that probably originate from the asteroid Vesta. Howardites are complex polymict breccias that sometimes contain, in addition to various rock debris, impact melt glasses which show an impressive range of compositions. In this paper we report on the geochemistry and O isotopes of a series of 6 Saharan polymict breccias (4 howardites and 2 polymict eucrites), and on the trace element abundances of high-K impact spherules found in two of them, Northwest Africa (NWA) 1664 and 1769, which are likely paired. The high-K impact spherules found in the howardites NWA 1664 and NWA 1769 display remarkable trace element patterns. Compared to eucrites or howardites, they all show prominent enrichments in Cs, Rb, K, Li and Ba, strong depletion in Na, while the REE and other refractory elements are unfractionated. These features could not have been generated during impact melting of their host howardites, nor other normal HED target materials. The involvement of Na-poor rocks, and possibly rocks of granitic composition, appears likely. Although these lithologies cannot be well constrained at present, our results demonstrate that the surface of Vesta is certainly more diverse than previously thought. Indeed, despite the large number of available HED meteorites (about 1000 different meteorites), the latter are probably not sufficient to describe the whole surface of their parent body.

The howardite-eucrite-diogenite (HED) achondrites are a group of meteorites that probably originate from the asteroid Vesta. Howardites are complex polymict breccias that sometimes contain, in addition to various rock debris, impact melt glasses which show an impressive range of compositions. In this paper we report on the geochemistry and O isotopes of a series of 6 Saharan polymict breccias (4 howardites and 2 polymict eucrites), and on the trace element abundances of high-K impact spherules found in two of them, Northwest Africa (NWA) 1664 and 1769, which are likely paired. The high-K impact spherules found in the howardites NWA 1664 and NWA 1769 display remarkable trace element patterns. Compared to eucrites or howardites, they all show prominent enrichments in Cs, Rb, K, Li and Ba, strong depletion in Na, while the REE and other refractory elements are unfractionated. These features could not have been generated during impact melting of their host howardites, nor other normal HED target materials. The involvement of Na-poor rocks, and possibly rocks of granitic composition, appears likely. Although these lithologies cannot be well constrained at present, our results demonstrate that the surface of Vesta is certainly more diverse than previously thought. Indeed, despite the large number of available HED meteorites (about 1000 different meteorites), the latter are probably not sufficient to describe the whole surface of their parent body.