Phone: +16048221697 Address: Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia 2020-2207 Main Mall, Vancouver, BC, V6T-1Z4, Canada
... ably deformed. Only the central part of the large Feda unit is rather homogeneous and poorly ... more ... 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 ...
the Late Cretaceous Caribbean large igneous province magmatism on land. It is composed by a ~2.5k... 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...
Introduction: Anthropogenic Pb remains the most important input of Pb in the troposphere today. I... 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.
The contemporary academic environment in Canada has undergone reorganization based on neoliberal ... 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 ...
Abstract: Baker et al.(2004) suggest that Pb isotope measurements by MC-ICP-MS using Tl to monito... 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 ...
Gabbros and diabases from Layer 3 of the oceanic lithosphere were recovered from the western wall... 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...
The Hidderskog massif is a charnockitic intrusion located in the Rogaland-Vest Agder segment of t... 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
Gabbros and diabases from Layer 3 of the oceanic lithosphere were recovered from the western wall... 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...
... ably deformed. Only the central part of the large Feda unit is rather homogeneous and poorly ... more ... 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 ...
... ably deformed. Only the central part of the large Feda unit is rather homogeneous and poorly ... more ... 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 ...
the Late Cretaceous Caribbean large igneous province magmatism on land. It is composed by a ~2.5k... 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...
Introduction: Anthropogenic Pb remains the most important input of Pb in the troposphere today. I... 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.
The contemporary academic environment in Canada has undergone reorganization based on neoliberal ... 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 ...
Abstract: Baker et al.(2004) suggest that Pb isotope measurements by MC-ICP-MS using Tl to monito... 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 ...
Gabbros and diabases from Layer 3 of the oceanic lithosphere were recovered from the western wall... 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...
The Hidderskog massif is a charnockitic intrusion located in the Rogaland-Vest Agder segment of t... 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
Gabbros and diabases from Layer 3 of the oceanic lithosphere were recovered from the western wall... 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...
... ably deformed. Only the central part of the large Feda unit is rather homogeneous and poorly ... more ... 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 ...
Non-spectral interferences in ICP-MS are caused by matrix elements effecting the ionisation and t... 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
ABSTRACT The Pacific Centre for Isotopic and Geochemical Research (PCIGR) at the University of Br... 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.
We have undertaken a high-precision geochemical and isotopic study of USGS reference materials by... 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
Data and observation from Drifting Program Leg 121 and plate-tectonic reconstructions indicate th... 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.
Secondary hotspot volcanism occurs on most oceanic island groups (Hawaii, Canary, Society) but it... 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
ABSTRACT The Hawaiian Ridge portion of the Hawaiian-Emperor Chain, the classic example of a mantl... more ABSTRACT The Hawaiian Ridge portion of the Hawaiian-Emperor Chain, the classic example of a mantle plume produced linear island chain, is 6000 km in length, active for 80 Myr, and tectonically simple. Despite its importance to our understanding of mantle plumes and Cenozoic plate motion, there are large data gaps for the age and geochemistry of lavas from volcanoes along the Hawaiian Ridge (HR) portion of the Chain. Ages: Only volcanoes near the Hawaiian-Emperor bend and in the Hawaiian Islands have modern Ar-Ar ages, leaving a gap of 2000 km where existing K-Ar ages suggest synchronous volcanism over a 1000 km section. Geochemistry: There is a 2900 km gap in high precision geochemical data for the HR. The Emperor Seamounts (&gt;45 Ma) have better regional coverage of recent isotopic data and show a correlation of Sr isotope composition with age of the underlying oceanic lithosphere (Regelous et al. 2003). The HR has an unexplained, exponential increase in magma flux over the last 30 Myr (Vidal &amp; Bonneville 2004). Potential explanations for the increase in magma flux include: changes in melting conditions (temperature and/or pressure), change in source fertility related to rock type (pyroxenite vs. peridotite) or previous melting history, and/or changes in plate stresses resulting from reconfigurations of plate motion. Our new multi-disciplinary project will: 1) Determine 40Ar/39Ar ages, and whole-rock major, trace element, and Pb, Sr, Nd and Hf isotopic geochemistry for lavas from 20 volcanoes spanning ~2150 km of the HR (NW of the Hawaiian Islands). 2) Use the geochemical data to determine the long-term evolution of the Hawaiian mantle plume source components and to evaluate whether there have been systematic variations in mantle potential temperature, melting pressure, and/or source lithology during the creation of the HR. If so, are they responsible for the 300% variation in melt production along the Ridge? Also, we will assess when the more fertile Loa source component appeared. 3) Reassess models for the origin of the HR using the new 40Ar/39Ar ages. 4) Recompute and compare the magma flux rate for the Hawaiian and Louisville Ridges using our new HR ages and IODP results for Louisville Ridge, and updated bathymetric data for both chains. 5) Utilize the new ages to revise Cenozoic Pacific plate motions and to compute differential motions as proxies for stress changes along the HR with time to evaluate the effects of plate motion on magma flux rate. These studies will have fundamental implications for mantle plume sources, plume dynamics, and plate kinematics. Vidal V, Bonneville A, 2004. J. Geophys. Res., 109, B03104, doi:10.1029/2003JB002559 Regelous M, Hofmann AW, Abouchami W, Galer SJG, 2003. Jour. Petrol. 44, 113-140
The Hawaiian Islands extend NW for 625 km from Lō‘ihi to Ka‘ula island. One anomalous feature cro... more The Hawaiian Islands extend NW for 625 km from Lō‘ihi to Ka‘ula island. One anomalous feature cross-cutting the Hawaiian Islands is the Kaua‘i Ridge, a 165 km-long bathymetric high with three well-defined gravity highs. These gravity highs are centered under or near the islands of Ka‘ula, Ni‘ihau and Kaua‘i, and represent the cores of three shield volcanoes whose volumes decrease dramatically with distance from the axis of the Hawaiian Chain (Kaua‘i, 58 x 103 km3, Ni‘ihau x 103 km, Ka‘ula 10 x 103 km; Robinson and Eakins 2006). Ka‘ula Volcano, on the SW end of the Kaua‘i Ridge, is centered 100 km off the axis of the Hawaiian mantle plume. The volcano is capped by a small island, which is a remnant of a nephelinitic tuff cone. The cone contains abundant accidental bombs of lava (tholeiite, phonolite and basanite), peridotite and pyroxenite, and unexploded ordnance from US military bombing. Two JASON dives on the flanks of Ka‘ula recovered only alkalic lavas. Three stage of Ka‘ula vol...
Mauna Loa's southwest rift zone (SWR) extends for 102 km from its summit caldera, at an eleva... more Mauna Loa's southwest rift zone (SWR) extends for 102 km from its summit caldera, at an elevation of 4,170 m above sea level, to submarine depths of over 4,500 m. About 65% of the rift zone is subaerial and 35% submarine. Recent sampling with the Jason II submersible of the `mile-high' (1800 m) Ka Lae submarine landslide scarp and the
Among Hawaiian shield volcanoes, Mauna Loa is distinct in having vents outside of its summit and ... 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
Improved analytical precision for radiogenic isotopes (down to ~100 ppm for Pb and to <50 ppm ... 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 ...
Kerguelen Archipelago flood basalts (29-24 Ma) were erupted onto the Northern Kerguelen Plateau w... 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
The PCIGR at the University of British Columbia has undertaken a systematic analysis of isotopic ... 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 ...
ABSTRACT Post-shield volcanism provides unique insight into the structure of mantle plumes and th... 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.
To date the majority of analytical procedures for δ18O analysis of silicates require relatively e... 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.
The long held notion that basaltic magmas are produced by decompressional melting of peridotite i... 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.
Submarine tholeiitic and transitional basaltic lavas from volcanic cones west of Ka‘ena Ridge bet... 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.
The number and origin of components involved in mantle plumes continues to be a subject of intens... 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).
We have measured O, He, Pb, Sr, and Nd isotope ratios in olivine separates and whole rock powders... 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.
The number and origin of components involved in mantle plumes continues to be a subject of intens... 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...
Geochemical studies of lavas from the accreted Wrangellia oceanic plateau forming a large part of... 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...
... a , Corresponding Author Contact Information , E-mail The Corresponding Author , James S. Sco... 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 ...
Investigation of an axial mid-ocean ridge fault to determine the character of focused hydrotherma... 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.
... Nevertheless, recent petrological, geochemical and isotopic studies (Mi-chot and Deutsch, 197... 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 ...
Spinel peridotite xenoliths in Late Cenozoic basalts from the Aldan-Stanovoi shield show effects ... 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.
We provide petrographic, major and trace element data for over 30 spinel peridotite xenoliths fro... 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
The post-collisional late Hercynian Tanncherfi intrusive complex (TIC) is part of a widespread in... 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 ...
... ably deformed. Only the central part of the large Feda unit is rather homogeneous and poorly ... more ... 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 ...
Variations in the δ7Li values of individual dikes of the Little Nahanni Pegmatite Group (LNPG) in... 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.
Spinel peridotite xenoliths in Late Cenozoic basalts from the Aldan-Stanovoi shield show effects ... 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.
The Stillwater Complex is a large mafic-ultramafic layered intrusion in the Beartooth Mountains o... 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,
Abstract Deposits of concentrated Fe–Ti oxide minerals are a characteristic component of many Pro... 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 ...
To investigate the differentiation and emplacement mechanisms of massif type anorthosites, we hav... 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.
ABSTRACT The goal of the present isotopic study is to characterize atmospheric Zn and Cu flux fro... 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.
Geochimica Et Cosmochimica Acta Acta Geochimica Et Cosmochimica Acta Acta Geochimica Et Cosmochimica Acta Acta Geochimica Et Cosmochimica Acta Acta, Feb 1, 2006
Many studies have argued for the contribution of at least three components, namely the mantle wed... 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).
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