- Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia
2020-2207 Main Mall, Vancouver, BC, V6T-1Z4, Canada - +16048221697
Research Interests: Geology and Geochemistry
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Research Interests: Earth Sciences, Geology, Geochemistry, Models, Lead, and 7 moreDrilling, Deformation, Trace Elements, Forage, Gabbro, Lithosphere, and Igneous Rocks
... ably deformed. Only the central part of the large Feda unit is rather homogeneous and poorly de-formed. There ... alkaline affinity. The average FeOto /MgO ratio for theFeda augen gneiss (Cpx zone) is 2.3 ± 1.0 (2o-). According ...
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the Late Cretaceous Caribbean large igneous province magmatism on land. It is composed by a ~2.5km-thick pile of massive and monotonous submarine flows of basalts, locally intruded by synvolcanic dikes and sills of dolerite. The... more
the Late Cretaceous Caribbean large igneous province magmatism on land. It is composed by a ~2.5km-thick pile of massive and monotonous submarine flows of basalts, locally intruded by synvolcanic dikes and sills of dolerite. The Pelona-Pico Duarte basalts Fm. was emplaced onto Turonian-Lower Campanian island-arc volcanic and sedimentary sequences, and is overlain by Maastrichtian platformal carbonates. Two 40Ar/39Ar plateau ages indicate both extrusive and intrusive magmatic activity at least during the 79-68Ma interval (Middle Campanian to Maastrichtian), so the magmas were in part coeval with the late phases of the Caribbean large igneous province. The basalts have a restricted major-and trace-element, and isotopic, compositional variation. For a range of 47.6-50.2wt. % SiO2, the Pelona-Pico Duarte basalts Fm. has relatively high contents in TiO2 (1.5-3.6wt.%) and Fe2O3T (10.7-13.1wt.%). On the basis of MgO contents, samples can be classified into tholeiitic basalts (<8wt.%) an...
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Introduction: Anthropogenic Pb remains the most important input of Pb in the troposphere today. It is now important to take sources other than automobile emissions (e.g., lead smelters, ferrous and non-ferrous metal manufacturing plants,... more
Introduction: Anthropogenic Pb remains the most important input of Pb in the troposphere today. It is now important to take sources other than automobile emissions (e.g., lead smelters, ferrous and non-ferrous metal manufacturing plants, fossil fuel combustion, waste incinerators, ...) into account in evaluating the lead content of atmospheric aerosols to discriminate the origins of pollution aerosols. The capability of lead isotopes to study the sources and transport of pollution aerosols [1] is demonstrated here above the Straits of Dover. We collected atmospheric aerosols above the Eastern Channel and the Southern Bight of the North Sea between March and November 1995. During the same period, to define more local contributions, we characterized the lead isotopic signatures of the main industrial sources on the French coast, near the Straits of Dover. Urban and automobile-derived aerosols were also collected.
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The contemporary academic environment in Canada has undergone reorganization based on neoliberal principles, and has increased attention focused on the importance of supporting interdisciplinary initiatives to address complex problems... more
The contemporary academic environment in Canada has undergone reorganization based on neoliberal principles, and has increased attention focused on the importance of supporting interdisciplinary initiatives to address complex problems affecting global society. The purpose of our study was to examine the experience of people participating in a specific university-funded interdisciplinary research initiative. As there is a strong emphasis within this program on reporting on the outcomes of the funding that supports interdisciplinary collaboration, our aim was to explore how participation may shape one’s intellectual quality of life (iQoL) and how one’s iQoL could be conceptualized and understood. Using a pragmatic constructivist case study, focus group and individual interviews were undertaken with 30 participants involved with university-funded interdisciplinary research teams. Findings illustrate that their iQoL was shaped by their capacity to engage in and achieve what they viewed ...
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Abstract: Baker et al.(2004) suggest that Pb isotope measurements by MC-ICP-MS using Tl to monitor mass fractionation produce results that are erroneous by up to 3300 ppm with respect to 'reference'double-or triple-spike... more
Abstract: Baker et al.(2004) suggest that Pb isotope measurements by MC-ICP-MS using Tl to monitor mass fractionation produce results that are erroneous by up to 3300 ppm with respect to 'reference'double-or triple-spike isotopic measurements by TIMS. We will show ...
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Gabbros and diabases from Layer 3 of the oceanic lithosphere were recovered from the western wall of the Mid-Atlantic Rift Valley near the Kane Fracture Zone (23.5°N, 45°W) during Ocean Drilling Program Leg 153. Thirty-five gabbroic... more
Gabbros and diabases from Layer 3 of the oceanic lithosphere were recovered from the western wall of the Mid-Atlantic Rift Valley near the Kane Fracture Zone (23.5°N, 45°W) during Ocean Drilling Program Leg 153. Thirty-five gabbroic samples from Sites 921 to 923 and three diabases from Sites 920 and 921 have been analyzed for major and trace elements. The gab- broic samples were chosen to be representative of range of composition and variation in degree of deformation. Sr-, Nd-, and Pb-isotope ratios were measured for 19 of the gabbros and a single diabase. Trace-element variations, in particular, reflect the nature of the samples, which varies from troctolite to gabbro (sensu stricto) to Fe-Ti-oxide-rich gabbro. Interpretation of the rare-earth element (REE) and Se characteristics of the gabbros leads to contrasting models for the origin of gabbros from Sites 921 and 923 as compared to those from Site 922. Site 921 and 923 troc- tolitic rocks and gabbros (sensu stricto) can be mode...
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The Hidderskog massif is a charnockitic intrusion located in the Rogaland-Vest Agder segment of the Sveconorwegian province of SW Norway. The U-Pb zircon age (1159 ± 5 Ma) and the Rb-Sr whole-rock isochron age (1153 ± 39 Ma) of this... more
The Hidderskog massif is a charnockitic intrusion located in the Rogaland-Vest Agder segment of the Sveconorwegian province of SW Norway. The U-Pb zircon age (1159 ± 5 Ma) and the Rb-Sr whole-rock isochron age (1153 ± 39 Ma) of this pluton are concordant. This age is interpreted as the magmatic emplacement age. The Hidderskog charnockitic intrusion is deformed and at
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Gabbros and diabases from Layer 3 of the oceanic lithosphere were recovered from the western wall of the Mid-Atlantic Rift Valley near the Kane Fracture Zone (23.5°N, 45°W) during Ocean Drilling Program Leg 153. Thirty-five gabbroic... more
Gabbros and diabases from Layer 3 of the oceanic lithosphere were recovered from the western wall of the Mid-Atlantic Rift Valley near the Kane Fracture Zone (23.5°N, 45°W) during Ocean Drilling Program Leg 153. Thirty-five gabbroic samples from Sites 921 to 923 and three diabases from Sites 920 and 921 have been analyzed for major and trace elements. The gab- broic samples were chosen to be representative of range of composition and variation in degree of deformation. Sr-, Nd-, and Pb-isotope ratios were measured for 19 of the gabbros and a single diabase. Trace-element variations, in particular, reflect the nature of the samples, which varies from troctolite to gabbro (sensu stricto) to Fe-Ti-oxide-rich gabbro. Interpretation of the rare-earth element (REE) and Se characteristics of the gabbros leads to contrasting models for the origin of gabbros from Sites 921 and 923 as compared to those from Site 922. Site 921 and 923 troc- tolitic rocks and gabbros (sensu stricto) can be mode...
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The primary isotopic characteristics of alkaline granites are often obscured by secondary processes enhanced by their unusual chemical compositions. This is true for radiogenic as well as for stable isotopes. For example, the 87Sr/ 86Sr... more
The primary isotopic characteristics of alkaline granites are often obscured by secondary processes enhanced by their unusual chemical compositions. This is true for radiogenic as well as for stable isotopes. For example, the 87Sr/ 86Sr ratios can vary drastically in closed systems because of very high Rb/Sr ratios and can also be easily modified by direct or indirect interaction with continental crust because of low Sr concentrations. Moreover, the frequent occurrence of the granitic massifs as hypovolcanic complexes increases the probability of interaction with meteoric waters which is a common source of important isotopic variability. The investigation of oxygen isotope systematics in alkaline acidic rocks from various environments shows the 18O content of their quartz to be highly invariable, and the δ 18O values to be close to the mantle range of values. This is due to the resistance of quartz to isotopic exchange, which makes it a good tracer of primary isotopic composition. If we eliminate the quartz δ 18O values for which interaction with meteoric water is well documented (five samples), the total range of variation (seventeen samples) is from 6.0 to 7.3‰ relative to SMOW. The values can easily be accounted for by, and correspond to, equilibrium with mantle-type material in a temperature range of 1200-800°C. If we consider possible effects of fractional crystallization, this temperature range can probably be reduced to its lower limit which is much more likely for rocks of acidic composition. The present oxygen isotope study strongly supports an origin for alkaline anorogenic granites from mantle-dominated sources.
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The mantle represents about 84 per cent of the Earth's volume, with the core representing around 15 per cent and the crust just 1 per cent. The mantle only rarely reaches the surface and as a result, it is mostly un-sampled, except... more
The mantle represents about 84 per cent of the Earth's volume, with the core representing around 15 per cent and the crust just 1 per cent. The mantle only rarely reaches the surface and as a result, it is mostly un-sampled, except for basalts or xenoliths (solid pieces of the mantle). In fact, there have been numerous attempts to directly sample and analyse the mantle, but they have been mostly unsuccessful. This leaves room for exciting work to be done, uncovering the composition of the largest part of the Earth. Your latest investigation focuses on the intraplate volcanism of the Hawaiian Islands. Can you explain why you study mantle plumes? Mantle plumes are hotter than the surrounding material and rise from deep in the mantle, all the way from the core-mantle boundary in some cases, a movement of around 2,890 km. When the plume head begins to melt near the surface, at a depth of about 100 km, it forms a large igneous province or oceanic plateau comprising huge volumes of ma...
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An analysis of marine and lacustrine cherts demonstrates that Rb-Sr and Sm-Nd systems may be used in elucidating the origin and evolution of cherts, and that the Rb-Sr system may be used for dating. All samples have high Rb/Sr ratios, and... more
An analysis of marine and lacustrine cherts demonstrates that Rb-Sr and Sm-Nd systems may be used in elucidating the origin and evolution of cherts, and that the Rb-Sr system may be used for dating. All samples have high Rb/Sr ratios, and though the site of these elements in cherts was not established, they appear to be correlated with Al content. Sm/Nd ratios were typical of continental sources, and the results show the Rb-Sr system in cherts to be isolated from the associated carbonate, with little Sr exchange. Data suggest that in many cases cherts are formed by dissolved SiO2 nucleating on clay-like material which preserves the isotropic characteristics of the detrital source, while in some cases it is possible that cherts were formed from silica-saturated waters from a nonmarine source.
Research Interests: Geology and Geochemistry
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Non-spectral interferences in ICP-MS are caused by matrix elements effecting the ionisation and transmission of analyte elements. They are difficult to identify in MC-ICP-MS isotopic data because affected analyses exhibit normal mass... more
Non-spectral interferences in ICP-MS are caused by matrix elements effecting the ionisation and transmission of analyte elements. They are difficult to identify in MC-ICP-MS isotopic data because affected analyses exhibit normal mass dependent isotope fractionation. We have therefore investigated a wide range of matrix elements for both stable and radiogenic isotope systems using a Nu Plasma MC-ICP-MS. Matrix elements commonly
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ABSTRACT The Pacific Centre for Isotopic and Geochemical Research (PCIGR) at the University of British Columbia has undertaken a systematic analysis of isotopic (Nd, Sr, Hf, Pb) composition and concentration of a broad compositional range... more
ABSTRACT The Pacific Centre for Isotopic and Geochemical Research (PCIGR) at the University of British Columbia has undertaken a systematic analysis of isotopic (Nd, Sr, Hf, Pb) composition and concentration of a broad compositional range of United States Geological Survey standards, including basalt (BCR-1, 2; BHVO-1, 2; BIR-1), dunite (DNC-1), andesite (AGV-1, 2), rhyolite (RGM-1, 2), syenite (STM-1, 2) and granite (G-2). USGS rock standards are geochemically well-characterized, but there is no systematic methodology nor database for radiogenic isotopic analyses, even for the widely used BCR-I. This investigation represents the first comprehensive, systematic analysis of the isotopic concentration and composition of USGS standards, and will provide an important database for the isotopic community. The wide range of equipment at PCIGR, including a Nu MC-ICPMS, a Triton TIMS, and an ElementII HR-ICPMS, permits a rigorous assessment and comparison of precision and accuracy in isotopic analyses. Our separation technique involves an HF/HNO3 dissolution in Teflon bombs, standard cation exchange elutriation for Sr and REE separation, and HDEHP Teflon columns for Nd separation. Samples are unspiked, and elemental concentration is determined by HR-ICPMS. Isotopic composition is determined by both thermal ionization mass spectrometry (Sr, Nd) and by multi-collector inductively coupled plasma mass spectrometry (Nd, Hf, Pb). Replicate runs of La Jolla Nd standard demonstrate excellent agreement between MC-ICPMS (143Nd/144Nd=0.511846+/-14 [n=100]) and TIMS (0.511850+/-16 [n=67]). Replicate analyses of strontium standard NBS987 yield 86Sr/87Sr values of 0.710256+/-15 [n=130]. Neodymium isotopic analyses (143Nd/144Nd values and Sm/Nd ratios) of previously characterized standards, such as BCR-1 (143Nd/144Nd=0.512623+/-2 [Nu; n=2]; 0.512627+/-8 [Triton; n=8]; Sm/Nd=0.1389) and BHVO-1 (0.512972+/-5 [Nu; n=2]; 0.512973+/-6 [Triton; n=14]; 0.1522-0.1532) are within error of published values. Replicate analyses of previously uncharacterized standards, such as AGV-1 (0.512776+/-4 [Nu; n=4]; 0.512781+/-7 [Triton; n=7]) and RGM-1 (0.512799+/-2 [Triton; n=2]), and second generation standards, such as BCR-2 (0.512639+/-6 [Triton; n=3]), BHVO-2 (0.512984+/-3 [Triton; n=3]), and AGV-2 (0.512792+/-1 [Triton; n=2]), provide the first reproducible data for these standards. Strontium analyses of BCR-1 (87Sr/86Sr= 0.705027+/-8 [Triton; n=4]) and BHVO-1 (0.703482+/-13 [Triton; n=6]) yield 86Sr/87Sr values that replicate known values. Replicate analyses of other standards, such as BCR-2 (0.705024+/-5 [Triton; n=3]), BHVO-2 (0.703487+/-9 [Triton; n=4]) and AGV-1 (0.703997+/-8 [Triton; n=7]) provide the first data for these standards. Hafnium and lead isotopic analyses on the same suite of samples are underway.
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We have undertaken a high-precision geochemical and isotopic study of USGS reference materials by HR-ICP-MS, TIMS and MC-ICP-MS, including basalt (BCR-1,2; BHVO-1,2), andesite (AGV-1,2), rhyolite (RGM-1), syenite (STM-1,2), granodiorite... more
We have undertaken a high-precision geochemical and isotopic study of USGS reference materials by HR-ICP-MS, TIMS and MC-ICP-MS, including basalt (BCR-1,2; BHVO-1,2), andesite (AGV-1,2), rhyolite (RGM-1), syenite (STM-1,2), granodiorite (GSP-2), and granite (G-2,3). Only a few 176Hf/177Hf results are published on these materials and with the increased use of MC-ICP-MS it is critical to build a solid reference database. Standard
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Research Interests: Geology and Geochemistry
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Research Interests: Geology and Geochemistry
The isotopic double-spike method allows for the determination of stable isotope ratios by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) with accuracy and precision in the range of ∼0.02 ‰ amu(-1), but its... more
The isotopic double-spike method allows for the determination of stable isotope ratios by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) with accuracy and precision in the range of ∼0.02 ‰ amu(-1), but its adoption has been hindered by the perceived difficulties in double-spike calibration and implementation. To facilitate the implementation of the double-spike approach, an explanation of the calibration and validation of a (97)Mo-(100)Mo double-spike protocol is given in more detail than has been presented elsewhere. The long-term external standard reproducibility is 0.05 ‰ on δ(98/95)Mo measurements of standards. δ(98/95)Mo values for seawater and U.S. Geological Survey (USGS) reference materials SDO-1 and BCR-2 measured in this study are 2.13 ± 0.04 ‰ (2 SD, n = 3), 0.79 ± 0.05 ‰ (2 SD, n = 11), and -0.04 ± 0.10 ‰ (2 SD, n = 3) relative to the NIST-SRM-3134. The double-spike method corrects for laboratory and instrumental fractionation which are not acco...
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Accuracy and precision achieved for Pb isotope ratio measurements by MC-ICP-MS are still significantly lower than those achieved for analysis of internally normalized elements (e.g. Hf). External normalization of the instrumental mass... more
Accuracy and precision achieved for Pb isotope ratio measurements by MC-ICP-MS are still significantly lower than those achieved for analysis of internally normalized elements (e.g. Hf). External normalization of the instrumental mass bias of Pb (f(Pb)) using f(Tl) requires that f(Pb) and f(Tl) respond identically in the presence of matrix, otherwise inaccuracies are introduced into the data. Addition of a common Mg matrix in an effort to matrix match samples and standards has been shown to improve the precision and accuracy of MC-ICP-MS Pb data (Barling & Weis, 2008). In order to better understand the effect of matrix on plasma conditions, we have measured Pb and Tl isotope ratios and intensities of Pb, Tl and Ar and matrix species over a range of sampling depths in the plasma. Paired matrix-free and matrix-bearing depth traverses were made for a number of matrix elements. For all traverses f(Pb) and f(Tl) decreased with increasing sampling depth. However, relative shifts between paired matrix-bearing and matrix-free traverses vary with element. For Mg, Cs and Sb trends are parallel to the matrix-free trends: for Mg (intermediate ionization potential -IP) and Cs (low IP) the matrix-bearing traverses have low f, whereas the Sb (high IP) trend has high f. By comparison with the matrix-free traverses, in the presence of Mg and Cs matrix, Pb and Tl show fractionation equivalent to a greater sampling depth in matrix-free plasma. This shift in fractionation may be related to enhanced electron-impact ionization due to extra electrons supplied by the matrix element. In contrast to Cs and Sb, Ba and Ce (two elements with low 2nd IP) form significant amounts of polyatomic species and doubly charged ions in the plasma. These matrices result in high f trends that are not parallel to matrix-free trends. For Ba the difference between matrix-bearing and matrix free trends decreases with increasing sampling depth while the reverse is true for Ce. This may relate to the formation of polyatomic species. For Ce these all initially increase in intensity (e.g. CeO) with sampling depth whereas for Ba they all decrease with increasing sampling depth. Of importance for the accuracy of mass bias correction are variations in f(Tl)/f(Pb). In general f(Tl)/f(Pb) increases with increasing sampling depth for all experiments except those with Ba-matrix. Mg, Ce and Sb matrix experiments generally had lower f(Tl)/f(Pb) than matrix-free experiments while the reverse was true for Cs. For Ba, f(Tl)/f(Pb) increases initially and then levels out. These trends in f(Tl)/f(Pb), f(Pb) and f(Tl) result in the under-correction of Pb isotope ratios by f(Tl) in the presence of all matrix elements except Ba. For Ba, Pb isotope ratios are under-corrected at shallow sampling depths but rapidly become over-corrected and level out as sampling depth increases. This behaviour mirrors the initial development of the Ba2+ signal in the plasma, suggesting that the changes in f(Pb) and f(Tl) associated with Ba matrix may relate to the contribution of extra electrons to the plasma due to the ionization of Ba+. Analogous behaviour can be expected for other analyte-external element pairs used in MC-ICP-MS anaylsis of non-traditional stable isotopes.
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Data and observation from Drifting Program Leg 121 and plate-tectonic reconstructions indicate that the Ninetyeast Ridge (Indian Ocean) was derived from the interaction of a deep-seated Dupal hotspot and a nearby spreading-ridge axis. The... more
Data and observation from Drifting Program Leg 121 and plate-tectonic reconstructions indicate that the Ninetyeast Ridge (Indian Ocean) was derived from the interaction of a deep-seated Dupal hotspot and a nearby spreading-ridge axis. The 5000-km-long ridge, from lat 34°S to Rat 10°N, was drilled at three sites during Leg 121. About 178 m of basalt, >38 to >80 Ma, were recovered from a total penetration of ˜310 m. Shipboard petrographic and geochemical studies showed that each site has distinctive characteristics. Most of the cored lavas have a tholeiitic basalt composition. Incompatible-element abundanes and ratios show systematic trends, consistent with an origin for the Ninetyeast Ridge lavas by mixing between a depleted component-Indian Ocean mid-ocean ridge basalt-and an enriched component-oceanic-island basalt similar to that observed in the youngest alkalic basalts from the Kerguelen archipelago. Preliminary shore-based trace element abundance and isotopic data are compatible with this hypothesis, although Pb isotopes indicate the involvement of another component. The long-lasting and more or less continuous activity of the Kerguelen-Heard plume (ca. 115 Ma), now located under Heard Island, south of the Southeast Indian Ridge, provides evidence that the source of the Dupal anomaly is deep seated.
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... Origin of Cretaceous continental tholeiites in southwestern Australia and eastern India: insights from Hf and ... mantle origins of these continental basalts and the nature and origin of any ... Second, the microcontinent that was... more
... Origin of Cretaceous continental tholeiites in southwestern Australia and eastern India: insights from Hf and ... mantle origins of these continental basalts and the nature and origin of any ... Second, the microcontinent that was incorporated into the early Kerguelen Plateau and now ...
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Découvertes en 1772 par Y. de Kerguelen, les îles Kerguelen furent l&amp;amp;amp;amp;amp;#x27;objet de plusieurs investigations scientifiques au cours des XVIIIème et XIXème siècles ainsi qu&amp;amp;amp;amp;amp;#x27;au début du... more
Découvertes en 1772 par Y. de Kerguelen, les îles Kerguelen furent l&amp;amp;amp;amp;amp;#x27;objet de plusieurs investigations scientifiques au cours des XVIIIème et XIXème siècles ainsi qu&amp;amp;amp;amp;amp;#x27;au début du XXème siècle. Ce n&amp;amp;amp;amp;amp;#x27;est pourtant qu&amp;amp;amp;amp;amp;#x27;avec Aubert de la Rue (1932) que leur connaissance ...
Leg 183 will penetrate igneous basement to depths of~ 200 m at several morphologically and tectonically diverse locations on the Kerguelen Plateau-Broken Ridge Large Igneous Province (LIP) in the Southeast Indian Ocean. This leg will... more
Leg 183 will penetrate igneous basement to depths of~ 200 m at several morphologically and tectonically diverse locations on the Kerguelen Plateau-Broken Ridge Large Igneous Province (LIP) in the Southeast Indian Ocean. This leg will build on results obtained by basement drilling at four Ocean Drilling Program (ODP) sites on the Central and Southern Kerguelen Plateau during Legs 119 and 120. LIPs are important to understand because the very large amounts of magma entering the crust in a relatively short time ...
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... Caution is clearly required when interpreting helium isotopic compositions of mantlederived samples ... Using uranium concentrations of 210 ppb, measured for the wholerock samples [10 ... consistent neon isotopic variations, largely... more
... Caution is clearly required when interpreting helium isotopic compositions of mantlederived samples ... Using uranium concentrations of 210 ppb, measured for the wholerock samples [10 ... consistent neon isotopic variations, largely consistent with helium isotopic ratios obtained by ...
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The number and origin of the source components that contributed to the long-term (~120 Ma) volcanism forming the Kerguelen Plateau, the Ninetyeast Ridge and Kerguelen Archipelago are still a matter of debate. Besides the overwhelming... more
The number and origin of the source components that contributed to the long-term (~120 Ma) volcanism forming the Kerguelen Plateau, the Ninetyeast Ridge and Kerguelen Archipelago are still a matter of debate. Besides the overwhelming contribution of Kerguelen plume there is compelling geochemical evidence for a continental component in basalt recovered by Ocean Drilling Program drilling at diverse locations on the Cretaceous Kerguelen Plateau. Mantle xenoliths found in Cenozoic basalt from the Kerguelen Archipelago also provide evidence for continental material at depth. Previous studies of the 30 - 24 Ma flood basalt forming the Kerguelen Archipelago we have emphasized roles of Kerguelen plume and MORB-related sources. Isotopic and geochemical data for an 860 m section of flood basalt at Mt. Capitole in the central part of the Kerguelen Archipelago show evidence of two stage mixing processes: a first stage, best shown by lavas forming the Northern Kerguelen Plateau, is between sour...
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Secondary hotspot volcanism occurs on most oceanic island groups (Hawaii, Canary, Society) but its origins remain enigmatic. A 28-day marine expedition used multibeam bathymetry and acoustic imagery to map the extent of submarine volcanic... more
Secondary hotspot volcanism occurs on most oceanic island groups (Hawaii, Canary, Society) but its origins remain enigmatic. A 28-day marine expedition used multibeam bathymetry and acoustic imagery to map the extent of submarine volcanic fields around the northern Hawaiian Islands (Kauai, Niihau and Kaula), and the JASON2 ROV to sample many volcanoes to characterize the petrology, geochemistry (major and trace
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Among Hawaiian shield volcanoes, Mauna Loa is distinct in having vents outside of its summit and rift zones. These radial vents are located on its northern and western flanks and account for approximately 10% of historic eruptions outside... more
Among Hawaiian shield volcanoes, Mauna Loa is distinct in having vents outside of its summit and rift zones. These radial vents are located on its northern and western flanks and account for approximately 10% of historic eruptions outside the summit region. Thirty-three subaerial and one submarine vent (active in 1877) were known prior to our work. During a recent Jason2
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We present high-precision isotopic ratios (MC-ICP-MS) and trace element concentrations (HR-ICP-MS) of post-shield lavas and submarine tholeiites from two paired sequences of Hawaiian volcanoes: Mauna Kea and Kohala on the Kea trend, and... more
We present high-precision isotopic ratios (MC-ICP-MS) and trace element concentrations (HR-ICP-MS) of post-shield lavas and submarine tholeiites from two paired sequences of Hawaiian volcanoes: Mauna Kea and Kohala on the Kea trend, and Hualalai and Mahukona on the Loa trend. Post-shield lavas from Hualalai have some of the least radiogenic Pb isotopic compositions of recent Hawaiian volcanoes (206Pb/204Pb = 17.888-18.011) and are significantly less radiogenic than shield stage lavas from Hualalai. Post-shield lavas from Mauna Kea (206Pb/204Pb = 18.341-18.421) lie on the lower extension of the HSDP-2 Kea field demonstrating a systematic shift as the volcano evolved from the shield to post-shield stage. In contrast, Kohala has become more radiogenic with respect to Pb during the waning stages of volcanism, with 206Pb/204Pb = ~18.28 for late-shield lavas and 206Pb/204Pb = ~18.44 for post- shield lavas. Importantly, the Loa-Kea bilateral asymmetry inferred for the < ~1.5 Myr Hawaiian plume is preserved. New Pb isotope results for samples from Penguin Bank (^{208}Pb^{*}/206Pb^{*} = 0.9437) provide further support that the Loa and Kea trends do not extend beyond the Molokai Fracture Zone. Post-shield lavas and tholeiites from the same volcano form linear arrays in Pb-Pb diagrams, with the Mahukona lavas extending the more radiogenic end of the Hualalai trend towards compositions comparable to Loihi. Post-shield lavas from Hualalai (and possibly Mauna Kea) lie on different mixing trends than most Hawaiian tholeiites, reflecting the contribution of another source component that is also observed in rejuvenated lavas from other Hawaiian volcanoes. Enriched trace element signatures of the post-shield lavas ((La/Yb)N = 6.0-16.3) contrast with their depleted isotopic characteristics and suggest that this component is not MORB. Our study demonstrates the importance of studying late-stage lavas formed by small degrees of melting to identify heterogeneities in the Hawaiian plume that are otherwise homogenized by higher degrees of melting during the shield stage.
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ABSTRACT High-precision Pb and Hf isotopic ratios by MC-ICP-MS and trace element concentrations by HR-ICP-MS of lavas forming Hawaiian volcanoes allow for new perspectives in the study of the source components associated with the Hawaiian... more
ABSTRACT High-precision Pb and Hf isotopic ratios by MC-ICP-MS and trace element concentrations by HR-ICP-MS of lavas forming Hawaiian volcanoes allow for new perspectives in the study of the source components associated with the Hawaiian mantle plume. In particular, late-stage lavas represent small-volume eruptions and small degrees of melting, and can provide better resolution of the geochemical heterogeneities in the plume. This study involves post-shield lavas from the Mauna Kea, Kohala, and Hualalai volcanoes on the island of Hawaii. Lavas from these specific volcanoes provide information about the region in which the plume is being deflected and sheared to the northwest by the movement of the Pacific plate. Pb isotopic compositions from Hualalai are the least radiogenic with 206Pb/204Pb = 17.888-18.028, compared to 18.343-18.408 for Mauna Kea and 18.286-18.439 for Kohala, which is consistent with each volcano belonging to their respective Loa-Kea Pb trends. Mauna Kea post-shield lavas are less radiogenic in Pb than the shield and post-shield Mauna Kea lavas from HSDP-2, showing a systematic decrease as the volcano evolved from the shield to post-shield stage. A similar trend is observed between the tholeiites and alkaline lavas of Hualalai, while the opposite trend is observed for Kohala. Hualalai and Kohala post-shield lavas form linear arrays in Pb-Pb space with their respective tholeiites, indicating an origin from the same source. However, the relative proportions of the components involved in the genesis of the post-shield lavas appear to be different. Mauna Kea post-shield lavas lie along the lower extension of the Kea-lo8 array of HSDP-2 (Eisele et al., 2003), distinct from older (350-550 kyr) Mauna Kea lavas and recent Kilauea lavas (Abouchami et al., 2005). The low 206Pb/204Pb ratios of Hualalai post-shield lavas are indicative of a unique component in that volcano. The Pb isotopic compositions of the post-shield lavas are thus sampling isotopically distinct compositional streaks at more peripheral parts of the Hawaiian plume that are not seen in the main tholeiitic stage.
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... The narrow-ness of the 3He signal suggests that it is confined to the central part of the melting region, which in turn is confined to the central part of the plume (Bryce et al. 2005). ... 1992) andDeccan (eg, Officer and Drake 1985)... more
... The narrow-ness of the 3He signal suggests that it is confined to the central part of the melting region, which in turn is confined to the central part of the plume (Bryce et al. 2005). ... 1992) andDeccan (eg, Officer and Drake 1985) flood ba-salts, respectively. ...
The results of the Hawaii Scientific Drilling Project have led to renewed interest in the existence of Kea and Loa trends defined by recent Hawaiian volcanoes, that is correlations between geochemical characteristics and volcano location... more
The results of the Hawaii Scientific Drilling Project have led to renewed interest in the existence of Kea and Loa trends defined by recent Hawaiian volcanoes, that is correlations between geochemical characteristics and volcano location along the recent hotspot track (Lassiter et al., 1996). Mauna Kea and Haleakala are well studied, relatively young but inactive Hawaiian volcanoes belonging to the Kea trend. East Molokai is an older Kea-trend volcano (shield and postshield volcanism from ˜1.5 to 1.75 Ma). We have analyzed major and trace element abundances and isotopic ratios of Sr, Nd and Pb in lavas from the 305 m Kalaupapa section that exposes lavas erupted at the end of shield building and during the transition to the alkalic postshield stage at East Molokai volcano (Beeson, 1976). In addition, our study includes older shield-stage lavas from below the Kalaupapa section and samples from the overlying rejuvenated-stage basalt, including submarine rejuvenated-stage lavas recovere...
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The new JASON2 ROV was used for 12 dives to explore and sample the submarine flanks of Mauna Loa, the world's largest active volcano. JASON2 collected 215 visually (using video and still camera) and spatially well-documented rock and... more
The new JASON2 ROV was used for 12 dives to explore and sample the submarine flanks of Mauna Loa, the world's largest active volcano. JASON2 collected 215 visually (using video and still camera) and spatially well-documented rock and sediment samples totaling 1130 kg from the volcano's southwest rift zone and western flank. The goals of the expedition were to investigate the nature and history of the Hawaiian mantle plume as revealed in a 1.6 km thick, submarine landslide scarp, to examine volcanic processes along the 37 km long, submarine portion of the southwest rift zone, which has 4.5 km of relief, and to sample the newly discovered submarine radial vents. In addition, detailed bathymetric data was collected for an area of 2000 km2 using an EM300 system, which has a pixel resolution of 30 m allowing for identification of small (horizontal) scale volcanic and tectonic features. These surveys provide the first detailed examination of the volcano's submarine rift zone and western flank. They revealed 11 new radial vents, many of which appear to be young based on examination by JASON2. Radial vents are uncommon on Hawaiian volcanoes and represent only 2 of the 39 historical Mauna Loa eruptions. Picritic basalts are remarkably abundant in the rift zone section, which may record 400,000 years of eruptive activity representing about one half of the volcano's total lifetime. This time period is comparable to that sampled by phase 2 of the Hawaiian Scientific Drilling Project. The initial bathymetric and geologic results from this cruise will be presented.
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Improved analytical precision for radiogenic isotopes (down to ~100 ppm for Pb and to <50 ppm for Sr, Nd and Hf), combined with statistical data treatment, allow for detailed investigations into the geochemical variations of basalts... more
Improved analytical precision for radiogenic isotopes (down to ~100 ppm for Pb and to <50 ppm for Sr, Nd and Hf), combined with statistical data treatment, allow for detailed investigations into the geochemical variations of basalts related to mantle plumes. For the main Hawaiian Islands, representing 4.5 myr of volcanism, we compiled high-precision Pb isotopic data (MC-ICP-MS or DS, TS TIMS) for 845 samples, integrated with Sr, Nd and Hf isotopic data on 500-600 samples for shield stage (67%), post-shield/late shield (22%) and rejuvenated lavas (10%). All data were normalized to the same standard values to avoid inter-laboratory biases and 30% of the analyses were determined at UBC. The Kea trend volcanoes have higher 206Pb/204Pb and 208Pb/204Pb, higher epsilon Nd, epsilon Hf, and lower 87Sr/86Sr than Loa trend volcanoes. This dichotomy does not stop at O`ahu as Loa characteristics are identified in the ~4.5 Ma Kaua`i lavas. Pb isotopes present the sharpest boundary between the ...
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Kerguelen Archipelago flood basalts (29-24 Ma) were erupted onto the Northern Kerguelen Plateau when the Southeast Indian Ridge was 200-400 km northeast of the Kerguelen hotspot. A depleted mantle component is evident in older (28-29 Ma)... more
Kerguelen Archipelago flood basalts (29-24 Ma) were erupted onto the Northern Kerguelen Plateau when the Southeast Indian Ridge was 200-400 km northeast of the Kerguelen hotspot. A depleted mantle component is evident in older (28-29 Ma) transitional-tholeiitic basalts on the archipelago, but is absent in younger (24-25 Ma) mildly alkalic lavas. This trend towards more alkalic volcanism primarily reflects decreasing
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The PCIGR at the University of British Columbia has undertaken a systematic analysis of isotopic (Nd, Sr, Hf, Pb) composition and concentration of a broad compositional range of United States Geological Survey standards, including basalt... more
The PCIGR at the University of British Columbia has undertaken a systematic analysis of isotopic (Nd, Sr, Hf, Pb) composition and concentration of a broad compositional range of United States Geological Survey standards, including basalt (BCR-1, 2; BHVO-1, 2; BIR-1), dunite ...
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ABSTRACT Post-shield volcanism provides unique insight into the structure of mantle plumes and the magmatic processes responsible for the evolution of ocean islands. Middle Bank is the closest seamount to the main Hawaiian archipelago,... more
ABSTRACT Post-shield volcanism provides unique insight into the structure of mantle plumes and the magmatic processes responsible for the evolution of ocean islands. Middle Bank is the closest seamount to the main Hawaiian archipelago, thus providing a perspective into the processes related to the dying phase of a Hawaiian volcano. We conducted a detailed survey of the volcano in 2007 using multibeam sonar coupled with Jason2 ROV imaging and sampling. According to plate tectonic models, Middle Bank volcano should be about 9.6 Ma, if it formed near the present location of Kilauea. Middle Bank is 100 km in diameter and rises nearly 5000 m from base level. Its morphology is dominated by three major rift zones that emanate to the east, west, and south from the beveled summit platform. The rifts are separated by talus fans, and the volcano is surrounded by dozens of satellite cones. Many of the satellite cones are covered by remarkably unsedimented lavas that were erupted in the submarine environment, which we interpret as a rejuvenated stage of volcanism. Most of the sampled rocks are strongly alkaline and range from basanite to hawaiite and trachyte. Samples from two sites are tholeiitic, which is consistent with them forming during the shield stage of volcanism. If so, then most of the late history of volcanism, from shield building to rejuvenated volcanism is preserved at Middle Bank. The alkaline basalts and basanites have La/Sm and La/Yb ratios that are higher than the tholeiites, and all of the rocks are strongly LREE enriched. Major and trace element compositions of hawaiites and trachytes are consistent with large amounts of crystal fractionation, which especially affected magmas erupted on the outer flanks of the volcano. The tholeiites have Sr/Nb and Zr/Nb that suggest that the Middle Bank shield is akin to the modern-day &quot;Kea&quot; trend geochemically. Thus, Middle Bank has preserved the archetypical tholeiitic-shield to alkaline-rejuvenated evolutionary stages that characterize the subaerial Hawaiian volcanoes.
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To date the majority of analytical procedures for δ18O analysis of silicates require relatively expensive apparatus involving the use of hazardous fluorine or halogen fluoride gases. Carbon reduction offers the potential to avoid the use... more
To date the majority of analytical procedures for δ18O analysis of silicates require relatively expensive apparatus involving the use of hazardous fluorine or halogen fluoride gases. Carbon reduction offers the potential to avoid the use of hazardous gases; however, it has been plagued by low yields and variable isotopic fractionation leading to significant differences in isotopic composition compared to conventional fluorination techniques (CFT). We adopt a carbon reduction method, which includes a fluorinated graphite polymer (F>60%) to help oxidize the silicate, thus increasing the percent yield as well as the precision of the analyses. Three silicate standards (NBS-28; UWG-2; GBW044190) were analyzed to compare this method against CFT. Silicate samples of 0.2mg are combined with 2mg of fluorinated graphite and sealed in a silver cup. The cups are then heated instantaneously to 1470°C in a high temperature conversion elemental analyzer (TC/EA). The evolved oxygen reacts with carbon in the furnace resulting in carbon monoxide which is transported via a helium carrier gas to a series of chemical and cold traps prior to introduction into the gas chromatograph. An Ascarite II and Mg(ClO4)2 chemical trap removes acids (e.g. HF) and water, followed by an LN2 cold trap to remove SiF4. The He carrier gas flow is kept low (0.7bar) to maximize reaction time, whereas He flow to the open split is increased (0.7bar) in order to reduce peak tailing in the IRMS. Using this method individual analysis can be completed in ~7 minutes. Oxygen yields range from 54-92%; however reproducibility better than 0.5‰ is normally achievable. Measured values are consistently enriched in 18O compared with accepted values; however, this offset is systematic and can be corrected for using a linear correction factor. Corrected values are: 9.11±0.3‰, 5.95±0.5‰, and -1.78±0.4‰ for NBS-28, UWG-2, and GBW044190 respectively. As the number of laboratories with CF-IRMS and TC/EA apparatus increases the development of this method has the potential to make δ18O analysis of silicates more widely available.
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The long held notion that basaltic magmas are produced by decompressional melting of peridotite is under challenge. Recent models for the Hawaiian and other plumes argue that they consist of a heterogeneous mix of peridotite and discrete... more
The long held notion that basaltic magmas are produced by decompressional melting of peridotite is under challenge. Recent models for the Hawaiian and other plumes argue that they consist of a heterogeneous mix of peridotite and discrete eclogite blobs, the latter derived from recycled subducted crust. Eclogite melting produces relatively siliceous magmas (dacite to andesite) which either mix with picritic melts from the peridotite, or, more plausibly, react with the peridotite to produce pyroxenite. Melting of varying proportions of the peridotite/pyroxenite mix is thought to produce the correlated compositional and isotopic characteristics of Hawaiian volcanoes. Magmas from Mauna Loa and Koolau volcanoes are thought to contain more of the recycled component; those from Loihi and Kilauea volcanoes contain less. A simple test of these mixed source models examines whether isotopic changes within the long magmatic history of a single volcano are accompanied by corresponding changes in major and trace element characteristics. Mauna Loa, where we have sampled around 400 - 500 ka of the volcano's eruptive history, provides an excellent opportunity for such a test. During this time, Mauna Loa will have traversed almost half the Hawaiian plume. According to the models, it should have erupted magmas produced from a range of pyroxenite/peridotite mixes with corresponding differences in both isotopic ratios and major and trace elements. Our data show that there is only minor isotopic (Sr, Pb, Nd, Hf) diversity in young lavas (<100 ka), but older lavas are highly diverse, ranging from modern values to those that are close to, and overlap with, those of Loihi volcano. If this isotopic diversity is a consequence of different proportions of pyroxenite and peridotite in the plume source, as the new models predict, we should expect to see correlated changes in bulk composition, particularly. in normalized SiO2, CaO/Al2O3, FeO/MgO and Ni - MgO relationships, as well as changes in Ni - Sc - V relationships. We do not. These parameters remain remarkably uniform over the 400 to 500 ka magmatic history of the volcano, with no correlated variation with isotopic ratios. We conclude that the isotopic heterogeneity within the Hawaiian plume is intrinsic to the peridotite plume source and not dependent on variable contributions from entrained, lithologically-discrete units.
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Submarine tholeiitic and transitional basaltic lavas from volcanic cones west of Ka‘ena Ridge between the Hawaiian Islands of Oah‘u and Kaua‘i were generated by the Hawaiian plume during a time of low magma productivity. Geochemical and... more
Submarine tholeiitic and transitional basaltic lavas from volcanic cones west of Ka‘ena Ridge between the Hawaiian Islands of Oah‘u and Kaua‘i were generated by the Hawaiian plume during a time of low magma productivity. Geochemical and Sr, Nd, Hf, and Pb isotopic compositions of West Ka‘ena lavas compared to basalts from Hawaiian shield volcanoes and volume calculations along axis of the Hawaiian Islands provide insights on the relationship between magmatic flux and source composition in the Hawaiian plume in the last 5 Myr. Ka‘ena Ridge is an elongate, relatively flat-topped submerged terrace 35-55 km wide that extends ~80 km from the western edge of Oah‘u The volcanic cones west of Ka‘ena Ridge were sampled by Jason II from R/V Kilo Moana in 2007. The flat-topped and conical cones are <400 m high and <2 km in diameter at water depths ranging between ~2700 to 4300 m, and consist predominantly of pillowed flows and mounds. Ar-Ar ages of eight lavas are between 4.9 and 3.6 Ma; three additional K-Ar ages range from 4.7 to 4.3 Ma. These ages overlap with shield volcanism on Kaua‘i (5.1-4.1 Ma) and Waianae volcano shield basalts (3.9-3.1 Ma) on Oah‘u. Half of the volcanic cones contain high-SiO2 basalts (51.0 to 53.5 wt% SiO_{2}). Isotopic compositions of West Ka‘ena lavas diverge from the main Ko‘olau-Kea mixing trend in binary isotope diagrams and extend to lower 206Pb/^{204}Pb and 208Pb/^{204}Pb ratios than any Hawaiian tholeiitic lava. Several West Ka‘ena samples are similar to SiO2-enriched, Loa-trend lavas of Ko‘olau Makapuu stage, Lanai, and Kahoolawe. However, compared to basalts from these volcanoes the lavas from West Ka‘ena have higher Hf and Nd and lower Sr isotope ratios and do not trend to high ^{208}Pb/$^{204}Pb. A correlation is apparent between magma productivity and isotopic compositions. Thus, west of Ka‘ena Ridge samples may have been generated from a source with a relatively high proportion of eclogite due to decreased plume flux, having formed further from the plume axis, and/or a different distribution of compositional heterogeneities.
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The number and origin of components involved in mantle plumes continues to be a subject of intense debate amongst geochemists. New analytical techniques are now allowing for a more refined analysis of individual oceanic islands. About 60... more
The number and origin of components involved in mantle plumes continues to be a subject of intense debate amongst geochemists. New analytical techniques are now allowing for a more refined analysis of individual oceanic islands. About 60 samples of Kerguelen Archipelago basalts (MgO > 2.3 wt.%) were re-analyzed for their Pb isotopic compositions by MC-ICP-MS (Nu Plasma 015). We carefully selected the samples on the basis of their Sr-Nd-Hf and Pb (TIMS) characteristics in order to cover the range of age, geographic and compositional variations observed on the archipelago. These new high-precision Pb isotopic compositions (2sigma: 100-150 ppm for 206Pb/204Pb and 207Pb/204Pb and 150 ppm for 208Pb/204Pb) reduce the total range of 207Pb/204Pb variations among Kerguelen basalts by a factor of 2. This provides an important new perspective on Kerguelen plume systematics and allows for the clear distinction of three groups: the 29-25 Ma tholeiitic-transitional basalts, the 25-24 Ma mildly alkalic basalts, and the <10 Ma more evolved, alkalic lavas and intrusions. This age and compositional evolution also corresponds to a geographic trend, where the older basalts are closest to the Southeast Indian Ridge (~300-400 km) while the mildly alkalic basalts are further away. The younger, more evolved alkalic rocks occur mainly in the same areas as the mildly alkalic basalts. These alkalic rocks result from lower degrees of melting and their distinctly lower 206Pb/204Pb (and 176Hf/177Hf) together with their significantly younger age indicate some interaction with the older Kerguelen Plateau. These important differences clearly reflect a Miocene change of regime of the Kerguelen plume (Mattielli et al., JP, 2002). Among the flood basalts that cover >80% of the Kerguelen Archipelago, the mildly alkalic basalts of the 24 Ma Crozier volcanic section stand out with distinctly higher 206Pb/204Pb. The isotopic compositions of the Crozier basalts are interpreted as representative of those of the Kerguelen plume. These basaltic magmas had little, if any, interaction with either the surrounding depleted mantle or the Kerguelen Plateau during ascent, either because their magma conduits became isolated or/and because by 24 Ma, the Southeast Indian Ridge was too far away. Our study confirms that the high-precision Pb isotope systematics of basaltic lavas represent an excellent tool to decipher components in major mantle plumes, as has also recently been shown in Hawaii (Eisele et al., G3, submitted; Blichert-Toft et al., G3, submitted).
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We have measured O, He, Pb, Sr, and Nd isotope ratios in olivine separates and whole rock powders from post-shield lavas of the island of Hawaii. These small-volume eruptions, which presumably correspond to small-volume source regions in... more
We have measured O, He, Pb, Sr, and Nd isotope ratios in olivine separates and whole rock powders from post-shield lavas of the island of Hawaii. These small-volume eruptions, which presumably correspond to small-volume source regions in the mantle, serve as high resolution probes of geochemical heterogeneity to complement data available from shield-stage tholeiites that originate in the primary melting region. He, Sr, and Nd ratios show small amplitude variations, well within the range of previously published data indicating little evidence for isotopically anomalous material in the melting region - either recycled sediments or oceanic crust. These data suggest that the plume does not contain large-amplitude isotopic variations at the scale of the source volume of post-shield lavas, which is likely to be about 100 times smaller than the volume averaged during main stage tholeiite production. However, the oxygen and lead isotope data indicate consistent, large amplitude differences between Hualalai and the other volcanoes. Samples from Hualalai have high delta18O (+5.5) and low 206Pb/204Pb (17.888-18.028). The only other volcanoes in the Hawaiian chain with such correlated extreme values are Koolau and Lanai, which have enriched radiogenic isotopic Sr and Nd compositions not seen in the data from Hualalai. Furthermore, correlated low helium values (8-10R/Ra)- high delta18O from Hualalai are consistent with a Koolau component in the source region for this volcano. The high delta18O contra-indicates a significant lithospheric interaction that would probably decrease delta18O rather than increase it to the values we measure. Samples from Mauna Kea and Kohala are consistently lower in delta18O (+4.8-5.12) than those from Hualalai, and fall within the range of previously measured values for late shield-stage lavas. The multiple isotope systems measured on the same post-shield samples indicate that simple models for Kea and Loa trends based on main stage tholeiitic lavas do not capture some of the most significant geochemical features. In particular, there are large temporal variations in the Loa trend, so that the difference between the Loa and Kea trends varies with time.
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Research Interests:
Research Interests: Geology and Geochemistry
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The number and origin of components involved in mantle plumes continues to be a subject of intense debate amongst geochemists. New analytical techniques are now allowing for a more refined analysis of individual oceanic islands. About 60... more
The number and origin of components involved in mantle plumes continues to be a subject of intense debate amongst geochemists. New analytical techniques are now allowing for a more refined analysis of individual oceanic islands. About 60 samples of Kerguelen Archipelago basalts (MgO > 2.3 wt.%) were re-analyzed for their Pb isotopic compositions by MC-ICP-MS (Nu Plasma 015). We carefully selected the samples on the basis of their Sr-Nd-Hf and Pb (TIMS) characteristics in order to cover the range of age, geographic and compositional variations observed on the archipelago. These new high-precision Pb isotopic compositions (2sigma: 100-150 ppm for 206Pb/204Pb and 207Pb/204Pb and 150 ppm for 208Pb/204Pb) reduce the total range of 207Pb/204Pb variations among Kerguelen basalts by a factor of 2. This provides an important new perspective on Kerguelen plume systematics and allows for the clear distinction of three groups: the 29-25 Ma tholeiitic-transitional basalts, the 25-24 Ma mildly...
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In geologic settings, Li isotopes are significantly influenced by both equilibrium and kinetic fractionation mechanisms. This has the potential to make delta7Li values valuable in identifying geological processes or tracing source rocks.... more
In geologic settings, Li isotopes are significantly influenced by both equilibrium and kinetic fractionation mechanisms. This has the potential to make delta7Li values valuable in identifying geological processes or tracing source rocks. Lithium isotopic analysis is becoming an increasingly popular geochemical tool, however, a better understanding of the mechanisms involved in Li isotopic fractionation is necessary if this method is to achieve its full potential. This study combined delta7Li values, trace element geochemistry, mineralogy and primary textural evidence from rock-forming minerals (quartz, albite, spodumene and mica) and whole rock samples taken from a coeval swarm of rare element pegmatite dikes, to look at the extent and mechanisms of Li isotopic fractionation during pegmatite formation. Pegmatite crystallization can be extremely rapid, potentially on a similar timescale to Li diffusion, as a result the influence of variable, non-equilibrium conditions during consolidation was assessed. Rock-forming minerals (given above) from the Little Nahanni Pegmatite Group (Northwest Territories, Canada) display delta7Li values that correlate with textural evidence supporting consolidation of the dikes under non-equilibrium conditions. Two examples of spodumene from different pegmatite samples have comparable delta7Li values of +3.5 and +3.70/00. In contrast, the delta7Li value of mineral separates from co-precipitated mineral assemblages varies from sample to sample. Very uniform delta7Li values for co-precipitated minerals from one sample (muscovite at +7.90/00, plagioclase at +7.90/00 and quartz at +8.70/00), contrast with very different delta7Li values for the same mineral assemblage from a different sample (muscovite at +2.20/00, plagioclase at +3.40/00 and quartz at +15.70/00). Whole rock samples from the same outcrops suggest strong Li isotope fractionation in peraluminous magma is associated with F build up in the late stages of magmatic differentiation. Pegmatites derived from the majority of the melt fraction (85%) are geochemically, relatively poorly evolved and display a restricted range of low delta7Li values (-0.94 to +2.90/00), similar to those of nearby granitoids (-0.4 to +2.20/00) and other examples of S-type magmatism (e.g., Lachlan Fold Belt, Bryant et al. 2004; -0.4 to +2.10/00). In contrast, consolidation of the final, flux component-rich, ~15% fraction of the melt resulted in pegmatite dikes with delta7Li values of up to +11.360/00. We propose that late stage build up of F in the melt is indicated by the Li isotopic signature of the whole rock, and that due to the variation in Li isotope diffusion rates isotopic signatures from minerals of these rapidly crystallised, peraluminous granitic rocks provide a qualitative assessment of the state of chemical equilibrium.
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We have measured O, He, Pb, Sr, and Nd isotope ratios in olivine separates and whole rock powders from post-shield lavas of the island of Hawaii. These small-volume eruptions, which presumably correspond to small-volume source regions in... more
We have measured O, He, Pb, Sr, and Nd isotope ratios in olivine separates and whole rock powders from post-shield lavas of the island of Hawaii. These small-volume eruptions, which presumably correspond to small-volume source regions in the mantle, serve as high resolution probes of geochemical heterogeneity to complement data available from shield-stage tholeiites that originate in the primary melting region. He, Sr, and Nd ratios show small amplitude variations, well within the range of previously published data indicating little evidence for isotopically anomalous material in the melting region - either recycled sediments or oceanic crust. These data suggest that the plume does not contain large-amplitude isotopic variations at the scale of the source volume of post-shield lavas, which is likely to be about 100 times smaller than the volume averaged during main stage tholeiite production. However, the oxygen and lead isotope data indicate consistent, large amplitude differences between Hualalai and the other volcanoes. Samples from Hualalai have high δ18O (+5.5) and low 206Pb/204Pb (17.888-18.028). The only other volcanoes in the Hawaiian chain with such correlated extreme values are Koolau and Lanai, which have enriched radiogenic isotopic Sr and Nd compositions not seen in the data from Hualalai. Furthermore, correlated low helium values (8-10R/Ra)- high δ18O from Hualalai are consistent with a Koolau component in the source region for this volcano. The high δ18O contra-indicates a significant lithospheric interaction that would probably decrease δ18O rather than increase it to the values we measure. Samples from Mauna Kea and Kohala are consistently lower in δ18O (+4.8-5.12) than those from Hualalai, and fall within the range of previously measured values for late shield-stage lavas. The multiple isotope systems measured on the same post-shield samples indicate that simple models for Kea and Loa trends based on main stage tholeiitic lavas do not capture some of the most significant geochemical features. In particular, there are large temporal variations in the Loa trend, so that the difference between the Loa and Kea trends varies with time.
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It is almost 50 years since the first documentation of mantle heterogeneity through the study of ocean island basalts (OIB) [1]. The origin, scale and source of these heterogeneities have been the subject of debate since then. One of the... more
It is almost 50 years since the first documentation of mantle heterogeneity through the study of ocean island basalts (OIB) [1]. The origin, scale and source of these heterogeneities have been the subject of debate since then. One of the most common approaches in the study of mantle heterogeneities is to analyze the geochemistry of oceanic basalts brought to the surface by mantle plumes. The composition of these ocean island basalts is usually different from those extruded at mid-ocean ridges (MORB), even if some of the post-shield/rejuvenated volcanism of some islands present depleted isotopic signatures. Improved analytical precision for radiogenic isotopes, combined with statistical data treatment, allow for more detailed investigations into the geochemical variations of basalts related to hotspots and mantle plumes and for modeling of the shallow and deep plume structure. Identification of two clear geochemical trends (Loa and Kea) among Hawaiian volcanoes [2, 3] in all isotope systems [4], together with the recurrence of similar isotopic signatures at >350 kyr intervals, have implications for the dynamics and internal structure of the Hawaiian mantle plume conduit [5]. In this lecture, I will present a compilation of recent isotopic data for samples from the shield, post-shield/late shield and rejuvenated stages on Hawaiian volcanoes, focusing specifically on high-precision Pb isotopic data (MC-ICP-MS or DS, TS TIMS) and integrated with Sr, Nd and Hf isotopes. The Hawaiian mantle plume represents >80 Myr of volcanic activity in a pure oceanic setting and corresponds to a high plume flux. All isotopic systems indicate source differences for Loa- and Kea-trend volcanoes that are maintained throughout the ~1 Myr activity of each volcano and that extend back in time on all the Hawaiian Islands (to ~5 Ma). The Loa-trend source is more heterogeneous in all isotopic systems by a factor of ~1.5 than the Kea-trend source. There are also different geochemical trends with time (such as an increase of Pb isotopic ratios). Hawaiian post-shield and rejuvenated lavas have more Kea-like geochemical characteristics than the underlying shield lavas with only two exceptions. Their isotopic compositions are much less variable and extend towards more depleted values that depart from the shield mixing trends and that do not intersect MORB-type compositions. Comparable observations have been made on other oceanic islands [6] and this implies that the depleted component in mantle plumes is distinct from the MORB source, and is most likely unique to each plume. These results from Hawaii will be compared to other hotspots in different tectonic settings, such as Kerguelen, Galapagos, and Iceland, and some implications for mantle geodynamics will be discussed. [1] Gast et al. (1964) Science 145, 1181-1185. [2] Tatsumoto (1978) Earth and Planetary Science Letters 38, 63-87. [3] Abouchami et al. (2005) Nature 434, 3401-3406. [4] Weis et al. (2009) Eos Trans. AGU, 90(52), Abstract V41F-03. [5] Farnetani and Hofmann (2009, 2010) Earth and Planetary Science Letters 282, 314-322; 295, 231-240. [6] White (2010) Annual Review of Earth and Planetary Sciences 38, 133-160.
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Geochemical studies of lavas from the accreted Wrangellia oceanic plateau forming a large part of Vancouver Island (~20,000 km2) in the Pacific Northwest of North America offer a view of the melting history of plume-derived magmas that... more
Geochemical studies of lavas from the accreted Wrangellia oceanic plateau forming a large part of Vancouver Island (~20,000 km2) in the Pacific Northwest of North America offer a view of the melting history of plume-derived magmas that does not involve continental lithosphere and where source heterogeneity does not play a major role. The Late Triassic Wrangellia flood basalts (~229-226 Ma) are predominantly homogeneous tholeiitic basalt. However, the lower submarine part of the 6 km-thick stratigraphy, on northern Vancouver Island, contains picritic pillow basalts. These high-MgO (9-20 wt%) lavas are depleted in LREE (La/YbCN= 0.5 ± 0.2), whereas the tholeiitic lavas (6-8 wt% MgO) are LREE-enriched (La/YbCN= 2.2 ± 0.3). Both lava groups have overlapping initial εHf (+10.3 ± 2.1) and εHf Nd (+7.7 ± 1.3), indicating a common, depleted (but not MORB) Pacific mantle source similar to the source of basalts from the Ontong Java and Caribbean Plateaus. The presence of picritic lavas indica...
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... a , Corresponding Author Contact Information , E-mail The Corresponding Author , James S. Scoates a , Dominique Weis a and Steve Israel b. ... is predominantly massive tholeiitic subaerial flows (~ 1000 m) with no intervening... more
... a , Corresponding Author Contact Information , E-mail The Corresponding Author , James S. Scoates a , Dominique Weis a and Steve Israel b. ... is predominantly massive tholeiitic subaerial flows (~ 1000 m) with no intervening sediments and a thin zone of pillow breccia along the ...
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Research Interests: Modeling, Igneous petrology, Multidisciplinary, Early Cretaceous, Heterogeneity, and 24 moreCretaceous, Age, Mesozoic, Isotopes, Cenomanian, Fusion, Volcanic Rocks, Basalts, Mantle, Magma, Phanerozoic, Trace Elements, Mantle melting, Isotope, Melting, Geophysical, Mantle plume, Picrite, Lava, Trace element, metamorphic Rocks, Igneous Rocks, Amphibole, and Plateau
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Research Interests: Earth Sciences, Models, Lead, Drilling, Deformation, and 5 moreTrace Elements, Forage, Gabbro, Lithosphere, and Igneous Rocks
Investigation of an axial mid-ocean ridge fault to determine the character of focused hydrothermal fluid flow. Tectonic escarpments at Pito Deep expose ocean crust formed at the super-fast spreading portion of the southern EPR (ca. 3 Ma).... more
Investigation of an axial mid-ocean ridge fault to determine the character of focused hydrothermal fluid flow. Tectonic escarpments at Pito Deep expose ocean crust formed at the super-fast spreading portion of the southern EPR (ca. 3 Ma). Ocean crust from Pito Deep is cut by high angle axial faults striking NE-SW parallel to the sheeted dykes. We focus on trace element and Sr isotopic compositional variations across an approximately 35 m fault zone within the sheeted dyke complex, ca. 100m below the lava-dyke transition, to explore the relationship between fluid flow, alteration and deformation. Samples from across this axial fault can be divided into 1) wall-rock basalts, 2) fault zone basalts and 3) fault zone breccias, ranging from simple cataclasites, veined cataclasites to quartz cataclasites. Breccias and basalts occur closely juxtaposed within the fault zone suggesting heterogeneous, highly localized deformation and fluid flow. Wall-rock basalts have been sampled a few to 30 m away from the fault zone and show extents of alteration typical of dykes away from fault zones with dominant replacement of primary phases by amphibole. The alteration in the fault zone basalts is also amphibole dominated with wider veins than the wall-rocks of quartz, chlorite ± amphibole. The fault zone breccias range in alteration mineralogy from chlorite to quartz dominated assemblages. Wall rock and fault zone basalts have similar trace element compositions to fresh crust. Breccias show large deviations in trace element compositions in comparison to adjacent altered basalts, with depletion of highly mobile elements such as K, Sr and both enrichment and depletion of Cu and Zn. 87Sr/86Sr of the dykes away from the fault zones are slightly elevated over fresh oceanic crust (0.7025- 0.7029) and fault zone samples have similar to higher 87Sr/86Sr. Quartz-epidote veins precipitated from fluids at Pito Deep have 87Sr/86Sr of approximately 0.7040. These new data provide insight into the chemical evolution of axial hydrothermal fluids during focused fluid flow.
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Research Interests: Gabbro and Igneous Rocks
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... Nevertheless, recent petrological, geochemical and isotopic studies (Mi-chot and Deutsch, 1977; Demaiffe et al., 1985) show the alkaline character of the Seychelles granites to ... I~:ocn es : B anch sseuseTr mpeuse Roch.Requin... more
... Nevertheless, recent petrological, geochemical and isotopic studies (Mi-chot and Deutsch, 1977; Demaiffe et al., 1985) show the alkaline character of the Seychelles granites to ... I~:ocn es : B anch sseuseTr mpeuse Roch.Requin &amp;quot; ~ANELLES $1LHOU ET TE ~&amp;quot;&amp;quot; Roches Brizards ...
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Spinel peridotite xenoliths in Late Cenozoic basalts from the Aldan-Stanovoi shield show effects of Meso-Cenozoic tectonic re-activation and magmatism on the ancient lithospheric mantle. Most of the xenoliths are harzburgites and cpx-poor... more
Spinel peridotite xenoliths in Late Cenozoic basalts from the Aldan-Stanovoi shield show effects of Meso-Cenozoic tectonic re-activation and magmatism on the ancient lithospheric mantle. Most of the xenoliths are harzburgites and cpx-poor lherzolites; less common are fertile lherzolites and olivine-rich cumulates. Petrographic and chemical data indicate profound metasomatic alteration of the refractory peridotites, possibly due to interaction with evolved magmatic liquids: precipitation of secondary clinopyroxene and gabbroic interstitial material, low Mg-numbers of olivine and whole-rocks in combination with high Cr in spinel; high whole-rock Ca/Al, enrichments in highly incompatible elements and/or inversely U-shaped REE patterns. Re abundances in all xenoliths are <0.06 ppb; Os abundances range from 0.1 to 4 ppb. Re and Os (0.9-3 ppb) in a subset of samples (including all cpx-rich lherzolites) that show no or limited metasomatism are positively correlated with modal clinopyroxene or whole-rock Al. 187/188Os in those xenoliths show linear correlations with Al or modal cpx consistent with a depletion age about 2 Ga and the formation of the lithosphere in the Precambrian. By contrast, the metasomatised refractory (2-7% cpx) xenoliths show a broad range in Os abundances and 187/188Os values (0.116-0.127), possibly due to disturbance of the Re-Os system during metasomatism. 176/177Hf is above the N-MORB average in one clinopyroxene separate and range between BSE and MORB values in the few other samples analysed. The 176/177Hf variations could be explained by mixing of ancient depleted mantle with an OIB-type metasomatic agent. We conclude that the xenoliths represent cratonic mantle strongly modified by metasomatism in hot-spot or subduction-related environments, possibly following removal of the cratonic keel and involving underplating of basaltic melts and their cumulates.
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We provide petrographic, major and trace element data for over 30 spinel peridotite xenoliths from the Tokinsky Stanovik (Tok) volcanic field on the Aldan shield to characterize the lithospheric mantle beneath the south-eastern margin of... more
We provide petrographic, major and trace element data for over 30 spinel peridotite xenoliths from the Tokinsky Stanovik (Tok) volcanic field on the Aldan shield to characterize the lithospheric mantle beneath the south-eastern margin of the Siberian craton, which formed in the Mesoproterozoic. High equilibration temperatures (870–1,010°C) of the xenoliths and the absence of garnet-bearing peridotites indicate a much thinner
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The post-collisional late Hercynian Tanncherfi intrusive complex (TIC) is part of a widespread intrusive episode in the Moroccan Meseta. The complex contains a wide range of rock types, from monzogabbros to monzogranites. Two distinct... more
The post-collisional late Hercynian Tanncherfi intrusive complex (TIC) is part of a widespread intrusive episode in the Moroccan Meseta. The complex contains a wide range of rock types, from monzogabbros to monzogranites. Two distinct magmatic series are ...
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Variations in the δ7Li values of individual dikes of the Little Nahanni Pegmatite Group (LNPG) in the Northwest Territories correlate with variations in the mineralogy and whole rock geochemistry suggesting compositional evolution of the... more
Variations in the δ7Li values of individual dikes of the Little Nahanni Pegmatite Group (LNPG) in the Northwest Territories correlate with variations in the mineralogy and whole rock geochemistry suggesting compositional evolution of the melt during emplacement of the pegmatites. A better understanding of the relationship between these aspects may help clarify some of the processes involved in pegmatite formation. Quartz, K-feldspar, plagioclase, spodumene and mica are the major rock-forming minerals of the majority of the > 200 LNPG pegmatites, with accessory phases including columbite-group minerals, cassiterite, tourmaline, beryl, lithiophilite and garnet. A minority of dikes contain no spodumene but significantly more mica than the others. Major element whole rock geochemistry of 23 samples show high abundance and variability in SiO2 (67.2 - 78.5 wt.%) and Al2O3 (12.7 - 19.6 wt.%), moderate abundance and variability in Na2O (2.5 - 5.4 wt.%) and K2O (2.1-4.4 wt.%) and extremely low abundance in FeO (or Fe2O3), CaO, MgO and MnO (< 1 wt.%). However, Harker diagrams show little correlation between the oxides. In contrast, trace element analyses provide a wealth of information with high (e.g. Li, Cs, Ta, Sn) or low (e.g. rare earth element (REE), Sr, Ba) abundances relative to continental crust, strong fractionation trends in Nb/Ta, Ce/Pb and Zr/Hf, and distinctive REE patterns. Less fractionated spodumene-bearing rocks exclusively correlate with `tetrad effect' REE patterns with strongly negative Eu anomalies. The more fractionated spodumene-free samples display LREE enriched, relatively straight or listric REE patterns. The pegmatites at LNPG are high in H2O, F, P, and Li, all of which are capable of postponing the onset of crystallisation by depolymerizing the cooling silicate melt, potentially to within the temperature range of Li isotope fractionation. Measurements by MC-ICP-MS of 6Li and 7Li in the LNPG whole rock samples range between δ7Li -0.73 and 11.36, with the least fractionated samples having among the lowest F, P, and δ7Li values. Higher δ7Li values for the more evolved pegmatite samples may be due to 7Li being preferentially retained in the fluid of the increasingly fractionated silicate melt. The data from LNPG record a range of mineralogical, geochemical and isotopic signatures indicating that the composition of the pegmatites evolved during crystallisation. Ongoing analysis is expected to shed more light on the mechanisms involved and their association with the δ7Li values of the pegmatites.
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Spinel peridotite xenoliths in Late Cenozoic basalts from the Aldan-Stanovoi shield show effects of Meso-Cenozoic tectonic re-activation and magmatism on the ancient lithospheric mantle. Most of the xenoliths are harzburgites and cpx-poor... more
Spinel peridotite xenoliths in Late Cenozoic basalts from the Aldan-Stanovoi shield show effects of Meso-Cenozoic tectonic re-activation and magmatism on the ancient lithospheric mantle. Most of the xenoliths are harzburgites and cpx-poor lherzolites; less common are fertile lherzolites and olivine-rich cumulates. Petrographic and chemical data indicate profound metasomatic alteration of the refractory peridotites, possibly due to interaction with evolved magmatic liquids: precipitation of secondary clinopyroxene and gabbroic interstitial material, low Mg-numbers of olivine and whole-rocks in combination with high Cr in spinel; high whole-rock Ca/Al, enrichments in highly incompatible elements and/or inversely U-shaped REE patterns. Re abundances in all xenoliths are <0.06 ppb; Os abundances range from 0.1 to 4 ppb. Re and Os (0.9-3 ppb) in a subset of samples (including all cpx-rich lherzolites) that show no or limited metasomatism are positively correlated with modal clinopyroxene or whole-rock Al. 187/188Os in those xenoliths show linear correlations with Al or modal cpx consistent with a depletion age about 2 Ga and the formation of the lithosphere in the Precambrian. By contrast, the metasomatised refractory (2-7% cpx) xenoliths show a broad range in Os abundances and 187/188Os values (0.116-0.127), possibly due to disturbance of the Re-Os system during metasomatism. 176/177Hf is above the N-MORB average in one clinopyroxene separate and range between BSE and MORB values in the few other samples analysed. The 176/177Hf variations could be explained by mixing of ancient depleted mantle with an OIB-type metasomatic agent. We conclude that the xenoliths represent cratonic mantle strongly modified by metasomatism in hot-spot or subduction-related environments, possibly following removal of the cratonic keel and involving underplating of basaltic melts and their cumulates.
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The Stillwater Complex is a large mafic-ultramafic layered intrusion in the Beartooth Mountains of Montana (USA) and host to the world-class J-M Reef platinum group element deposit. Despite low levels of incompatible elements, many... more
The Stillwater Complex is a large mafic-ultramafic layered intrusion in the Beartooth Mountains of Montana (USA) and host to the world-class J-M Reef platinum group element deposit. Despite low levels of incompatible elements, many cumulate samples contain both baddeleyite (ZrO2) and zircon (ZrSiO4). As part of a larger study on the age of the Stillwater Complex and duration of emplacement,
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Abstract Deposits of concentrated Fe–Ti oxide minerals are a characteristic component of many Proterozoic anorthosite massifs. Ferrian ilmenite (ilmenite with exsolution lamellae of hematite) is the principal ore mineral of titanium in... more
Abstract Deposits of concentrated Fe–Ti oxide minerals are a characteristic component of many Proterozoic anorthosite massifs. Ferrian ilmenite (ilmenite with exsolution lamellae of hematite) is the principal ore mineral of titanium in the largest deposits, Lac Tio–Lac Allard ...
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To investigate the differentiation and emplacement mechanisms of massif type anorthosites, we have undertaken a petrological study of three small elongated mafic intrusions (Loyning:1250×150m; Hogstad: 2000×200m; Koldal: 1250×500m)... more
To investigate the differentiation and emplacement mechanisms of massif type anorthosites, we have undertaken a petrological study of three small elongated mafic intrusions (Loyning:1250×150m; Hogstad: 2000×200m; Koldal: 1250×500m) occurring in the marginal zone of two massif-type anorthosites of the Rogaland Anorthositic Province (South Norway) (930 Ma). They are essentially made of norites, melanorites, leuconorites and locally mangerites (Koldal intrusion): these hypersthene-bearing lithologies are typical of Proterozoic AMCG (Anorthosite-Mangerite-Charnockite-Granite) suites. In Loyning, the rocks display a well-defined layering, thoroughly recrystallized and parrallel to the subvertical foliation in the enclosing anorthosite. Hogstad displays a less recrystallized vertical modal layering. In Koldal, the intrusion cuts across the foliation of the anorthosite. The least differentiated compositions of orthopyroxene and plagioclase (Loyning: Ens68-An52 - Hogstad: Ens64-An49 - Koldal: Ens66-An44) are close to those experimentally obtained on jotunites (hypersthene-bearing monzodiorites) suggesting that such liquids are possible parent magmas of these intrusions. Nevertheless, the orthopyroxene and plagioclase megacrysts of the enclosing anorthosites display slightly more primitive compositions (Ens74 to Ens75, An49 to An55), indicating that the parent magmas of the three mafic intrusions are residual after (some) anorthosite crystallization. This conclusion is supported by isotopic data as the 87Sr/86Sr (930Ma) and εNd(t) (Loyning: 87Sr/86Sr : 0.70406-0.70457, εNd : +7.6 to +3.4 - Hogstad: 87Sr/86Sr : 0.70537-0.70590, εNd : +2.59 to -0.23 - Koldal: 87Sr/86Sr : 0.70606-0.70805, εNd : +3.48 to -1.67) partly overlap the observed range in the enclosing anorthosites (87Sr/86Sr : 0.7033-0.7063, εNd : +5.9 to -1.8). Calculated densities of jotunites (at FMQ, 0%H_2O, 1150^oC) demonstrate that they are much denser (2.77) than the plagioclase of the surrounding anorthosite (2.625). We thus suggest that the limited spatial occurrence of these small intrusions in the marginal zone of the enclosing massif type anorthosites results from the crystallization of batches of dense liquids which were drained through the anorthositic crystal mush and crystallized in short-lived magma chambers at various stages of the evolution of the anorthosite diapir. A sloping floor is required for the draining of this dense liquid.
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Research Interests: Speciation, Metallurgy, Environmental Monitoring, Air pollution, Environmental Pollution, and 15 moreMultidisciplinary, Isotopic Analysis, Canada, Heavy metals, Isotopes, Heavy Metal, Lead, Zinc, Pb isotopes, Cadmium, Industrial Waste, Isotope fractionation, Trace element, Soil Pollutants, and Total Variation
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Research Interests: Water, Speciation, Scanning Electron Microscopy, France, Multidisciplinary, and 14 moreIsotopic Analysis, Cities, Steel, Iron, Chemical Analysis, Urban Environment, SEM-EDX, Particulate Matter, Industrial Waste, Isotope fractionation, Chemical Composition, Single Particle Analysis, Urban Area, and Troposphere
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ABSTRACT The goal of the present isotopic study is to characterize atmospheric Zn and Cu flux from industrial activities. Zn and Cu belong to traditional biolimiting elements. The geochemical cycle of these elements in the Earth... more
ABSTRACT The goal of the present isotopic study is to characterize atmospheric Zn and Cu flux from industrial activities. Zn and Cu belong to traditional biolimiting elements. The geochemical cycle of these elements in the Earth superficial envelopes influences the biological productivity in oceans or in soils and, in turn, the global environment (Maréchal et al., 2000; Pichat et al., 2003). Other than Zn and Cu arising from minor geogenic processes, all other sources of Zn and Cu are anthropogenic. Among world-wide anthropogenic sources of Cu and Zn aerosols, metallurgical processing for Cu and steel production, as well as coal production are among the major sources (Pacyna, 1998). Samples from two metallurgical plants, a Pb-Zn refinery and an integrated steel mill located in Northern France not far away from the southern bight of the North Sea, are investigated in the present study. Samples are ores and dusts directly collected on filtration devices mounted on the main exhaust systems of the plants. Dry deposi-tion plates were positioned near working units previously recognized as major aerosol emission sources (cf. Franssens et al., 2004): sintering plant and steel shop unit, and the main chimneystack.
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Many studies have argued for the contribution of at least three components, namely the mantle wedge, the subducted oceanic crust, and its sediment cover, to describe the geochemistry of island arc volcanics. However, isotope correlations... more
Many studies have argued for the contribution of at least three components, namely the mantle wedge, the subducted oceanic crust, and its sediment cover, to describe the geochemistry of island arc volcanics. However, isotope correlations reflecting a simple binary mixing can be observed at the scale of a single arc island or volcano. Here we investigate the possibility that these trends reflect pseudo-binary mixing relationships in a three-component system. We present a simplified, two-stage model for the systematic isotope modelling of a cogenetic suite of arc lavas. This includes metasomatism of portions of the mantle wedge by hydrous phases released from the down-going oceanic crust, and sediments, followed by progressive mixing and melting. A consequence of this model is that it leads to a two end-member mixing process from the mantle wedge, oceanic crust, and sediment components. To solve the model we reduce it to a step-by-step procedure combined with a Monte-Carlo simulation. The procedure consists of: (i) producing a large number of random values on each variable of the model; (ii) using the computed values to calculate the isotopic compositions of lavas; and (iii) comparing the obtained isotopic compositions with measured data. Applied to a new set of Sr, Nd, and Pb isotope data for volcanics (basalts, basaltic andesites, trachybasalts, and basaltic trachyandesites) from Merapi volcano (Java island, Sunda arc), the model successfully reproduces the binary mixing relationships previously documented for the medium-K and high-K lava series from this volcano, thus giving further support to the hypothesis that this distinction is inherited from the primary magmas and primarily reflects a property of the mantle source. The results allow identification of a set of numerical values for bulk partition coefficients (solid/hydrous fluid, and solid/H 2O-rich melt) and variables (e.g., the mass ratio between the metasomatizing phase and the mantle wedge), which can be used for quantitative arc-lava petrogenetic calculations. They also require a direct relationship between dehydration of the slab and melting of the metasomatized mantle wedge. Finally, our evaluation shows that for isotope modelling of the Merapi lavas, the two-stage procedure is controlled more by the considered source components (mantle wedge, oceanic crust, sediments, and their derivatives) than by the various processes involved (dehydration, melting, and mixing).