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Goldschmidt2013 Conference Abstracts 551 Carbonation of olivine at CO2 Dissolved and particulate iron supercritical conditions: Reactivity concentrations and isotopic differences between synthetic and compositions in the South Atlantic natural olivines and Southern Ocean I. AABERG1, K. DIDERIKSEN1, C. ABADIE*1, F. LACAN1, A. RADIC1 J.D. RODRIGUEZ-BLANCO1, E. REGNARSSON1, AND F. POITRASSON2 1 2 2 J.OLSSON , H.T. JESPERSEN , K. SCHAUMBURG AND 1 LEGOS (CNRS/UPS/IRD/CNES), Observatoire Midi S.L.S. STIPP1 Pyrénées, F-31400, Toulouse, France 1Nano-Science Center, Dept. of Chemistry, University of (*correspondance : [email protected]) Copenhagen, Denmark ([email protected]) 2GET (CNRS/IRD/UPS), Observatoire Midi Pyrénées, F- 2The Department of Science, Systems and Models, Roskilde 31400, Toulouse, France University, Denmark Iron is an essential micronutrient for phytoplankton. It has The carbonation of ultramafic and mafic rocks has been been shown that in High Nutrient Low Chlorophyll areas proposed as a carbon capture and storage (CCS) method. This (HNLC), Fe is a limiting factor for phytoplankton growth. method is promising because CO2 would be captured in Therefore, Fe has an influence on the carbon cycle. Its sources carbonate minerals that are stable for geological time spans. to the ocean remain a matter of debate. It has been suggested The challenge, however, is that the reactions which lead to the that aerosol inputs and reductive dissolution within oxygen formation of carbonates are very slow. Learning more about it depleted sediments were the main sources of Fe to the water might offer the possibility of enhancing reaction kinetics. column, although recent studies highlighted that the non- Forsterite (Mg2SiO4) is an abundant mineral in mafic and reductive dissolution within oxic basins is another potential ultramafic rocks. The purpose of this study was to investigate source of Fe. the differences in reactivity between synthetic and natural We obtained new results on Fe concentrations and isotopic forsterite when exposed to pure deionised water and compositions in both the particulate and dissolved phases of supercritical CO2 (120 °C, 80 bars and 7 days of reaction). Fe (PFe and DFe) in seawater, in the oxic South Atlantic and Solids were characterised with scanning electron microscopy Southern Ocean, off the South African coast towards (SEM), transmission electron microscopy (TEM), energy Antarctica. During the Bonus GoodHope cruise in 2008, dispersive X-ray spectroscopy (EDXS), X-ray powder seawater samples have been taken from five stations, along a diffraction (XRD) and X-ray photoelectron spectroscopy section from 36.50°S 13.12°E to 57.55°S 0.04°E. Dissolved (XPS) and solution composition, with atomic absorption and particulate Fe concentrations range from 0.05 to 0.72 spectroscopy (AAS). nmol.L-1 and from 0.13 to 4.65 nmol.L-1, respectively. After reaction, synthetic forsterite had transformed partly Particulate Fe and Al concentrations are correlated for three to magnesite (MgCO3), with well defined crystals of up to 25 stations in the Northern part of the section suggesting µm in size and to spherical particles, consisting dominantly of lithogenic inputs of particulate iron originating from the SiO2. Aghulas Current. Unreacted natural forsterite (Fo91.1) had highly Iron isotopic compositions obtained so far range from - heterogeneous surface composition and morphology. Reaction 0.04‰ to 0.32‰ in !56Fe for PFe and from -0.71‰ to 0.27‰ produced very fine grained alteration products that were for DFe. With an average isotopic composition of 0.09‰ in difficult to identify unambiguously. Thus, only a few the Northern part of the section –close to that of the indications of carbonate mineral formation could be observed. continental crust, ~0.07‰ - the signature of the particles Our results show that natural and synthetic forsterite react very confirm their lithogenic origin. The lighter isotopic signatures differently. After reaction, etch pits are visible on the natural for both DFe and PFe in the Upper Circumpolar Deep Water samples and AAS shows Mg in solution, suggesting that the (UCDW) may be related to the remineralization of organic different behaviour could be caused by inhibited magnesite matter. nucleation and growth. This implies that the complex nature of Isotopically sligthly heavier DFe than PFe at the natural material should be taken into account when predicting northernmost station of the transect (~500 km away from the mineral carbonation. African margin) suggests a non-reductive release of DFe from the African margin sediments. This could be a major source of Fe in oxic basins, which are much more widespread than oxygen minimum zones in the global ocean. www.minersoc.org DOI:10.1180/minmag.2013.077.5.1 Downloaded from http://pubs.geoscienceworld.org/minmag/article-pdf/77/5/551/2920588/gsminmag.77.5.01-A.pdf by guest on 02 October 2021 552 Goldschmidt2013 Conference Abstracts Rare earth elements in marine Sr-Nd isotopic study of Papandayan sedimentary pore fluids area, West Java: Mapping the extent APRIL N ABBOTT1, BRIAN HALEY2, JAMES MCMANUS3 of Argoland beneath Java, Indonesia 3 AND CLARE REIMERS 1 1 M. ABDURRACHMAN * AND M. YAMAMOTO 1 CEOAS, Oregon State University, USA 1 Bandung Institute of Technology,Bandung 40132, Indonesia ([email protected]) (*correspondence: [email protected]) 2CEOAS, Oregon State University, USA 2Akita University, Akita-shi 010-8502, Japan ([email protected]) 3CEOAS, Oregon State University, USA Southern West and East Java have been suggested by ([email protected]) several researchers as the “home” of micro continent since 4CEOAS, Oregon State University, USA Late Cretaceous [1, 2, 3], uncertainty still remains as to ([email protected]) whether the two fragments are linked forming part of a larger micro-continent. For this reason, Sr-Nd isotopic ratios of The rare earth elements (REE) are powerful geochemical Papandayan and adjacent Cikuray volcanoes (Papandayan tracers with a number of geochemical applications. Here, we area) on the volcanic front in the Triangular Volcanic present REE concentrations from sediment pore fluids Complex (TVC) were employed to gain a better of tectonic extracted from cores taken from sites along the Oregon and development in Java. The eruptive product of Papandayan California margins. Our sites represent continental shelf-to- 87 86 volcano comprises medium-K series with high Sr/ Sr slope settings, which lie above, within, and below the oxygen (0.705243-0.705907) and low 143Nd/144Nd (0.512504- minimum zone of the Northeast Pacific. These sites are 0.512650) ratios. The Cikuray volcanic rocks are in contrast to characterized by varying degrees of net iron reduction; the 87 86 Papandayan, belong to low-K series, with low Sr/ Sr shelf sites are generally iron-rich (where near surface, pore (0.704172-0.704257) and high 143Nd/144Nd (0.512823- water Fe concentrations can exceed 100 !M), whereas slope 0.512858) ratios. Our study shows that the contrasting Sr-Nd sediments generally have less-pronounced iron reduction isotopic ratios in Papandayan area can be explained by the zones that penetrate deeper into the sediments. REE mixing of clear mantle wedge (I-MORB + AOC + Indian concentrations show a shallow (upper 2-10 cm) subsurface Sediments) with Australian Granites as the missing peak across all sites (up to two orders of magnitude higher “Argoland” which have separated from Western Australia in than sea water), and notably these peaks do not consistently the Late Jurassic and collided to SE Sundaland in the Late coincide with peaks in dissolved iron. Normalized patterns of Cretaceous [4]. We argue that the presence of “Argoland” fourteen REEs show distinct and large variation in the MREE beneath Southern West Java was responsible for Sr-Nd enrichments and HREE to LREE ratios with core depth. isotopic ratios diversity in Papandayan area as well as in TVC. These REE pore fluid enrichments highlight the potential Therefore, the suture zone should be laid between both importance of continental shelf and slope sediments as a volcanoes and Papandayan volcano probably is the only of source of REEs to the ocean’s water column. Quaternary volcanoes which is underlain by “Argoland”. If that so, the extension of East Java continental fragment can be continued to the West Java. [1] Abdurrachman (2011) Min Mag, 75 (3), 401. [2] Smyth et al (2007) Earth & Planetary Sci. Lett. 258, 269-282. [3] Clements & Hall (2007) IPA31st. Metcalfe (2011) Gondw. [4] Res, 106, 97-122. www.minersoc.org DOI:10.1180/minmag.2013.077.5.1 Downloaded from http://pubs.geoscienceworld.org/minmag/article-pdf/77/5/551/2920588/gsminmag.77.5.01-A.pdf by guest on 02 October 2021 Goldschmidt2013 Conference Abstracts 553 Multidisciplinary study on the Time-related changes in the Si oceanic plate: implications from the isotopic composition of Palaeo- to research on petitspot volcanoes Mesoarchaean granitoids N. ABE1 AND T. FUJIWARA2 K. ABRAHAM12, S.F. FOLEY3, A. HOFMANN4, 1 1 1 D. CARDINAL AND ANDRÉ L. IFREE, JAMSTEC, Japan ([email protected]) 2IFREE, JAMSTEC, Japan ([email protected]) 1Section of Mineralogy"Petrography"Geochemistry, Royal Museum for Central Africa, Leuvensesteenweg 13, Petitspot is a cluster of small volcanic knolls on the Tervuren, B 3080, Belgium oceanic lithosphere [1]. It is a kind of intraplate volcanism, 2Department of Earth Sciences,South Parks Road, Oxford similar to monogenetic volcanoes of alkaline basalts in OX1 3AN, UK continental plate, although there is no mantle upwelling 3ARC Centre for Core to Crust Fluid Systems, Macquarie beneath the eruption fields. Therefore, it is not related any University, North Ryde, 2109 NSW, Australia. OIB activities. The source region of the petitspot magma is 4Department of Geology, University of Johannesburg, South expected not at very deep, but just around the boundary Africa between the lithosphere and asthenosphere [2]. It is thought to be erupted through the small fracture on the oceanic Archaean TTG magmas are regarded to have formed by lithosphere [1].
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