JpGU-AGU Joint Meeting 2017

Presentation information

[EE] Poster

S (Solid Earth Sciences) » S-GC Geochemistry

[S-GC52] [EE] Volatile cycles in the Earth - from Surface to Deep Interior

Mon. May 22, 2017 3:30 PM - 5:00 PM Poster Hall (International Exhibition Hall HALL7)

convener:Takeshi Hanyu(Japan Agency for Marine-Earth Science and Technology, Department of Solid Earth Geochemistry), David R Hilton(University of California San Diego), Hirochika Sumino(Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo), Yuji Sano(Division of Ocean and Earth Systems, Atmosphere and Ocean Research Institute, University of Tokyo)

[SGC52-P06] Geochemistry of olivine melt inclusions in Pitcairn Island basalts: A multiple-instrument approach

*Takahiro Ozawa1, Takeshi Hanyu2, Hikaru Iwamori2,1, Morihisa Hamada2, Takayuki Ushikubo2, Kenji Shimizu2, Motoo Ito2, Jun-Ichi Kimura2, Qing Chang2, Tsuyoshi Ishikawa2 (1.Tokyo Institute of Technology, 2.Japan Agency for Marine-Earth Science and Technology)

Ocean island basalts (OIBs) provide essential information on evolution of the Earth’s mantle, because OIBs are sourced from plumes from the deep mantle that include recycling materials. OIBs at the Pitcairn Island show distinct geochemical characteristics from other OIBs with their enriched isotopic signatures, so called enriched mantle 1 (EM1) component. This particular feature could have been caused by the involvement of recycled materials including chemically differentiated oceanic plate slab or delaminated continental lithosphere and lower crust (e.g., Eisele et al., 2002). In order to understand behavior of volatile elements during mantle recycling, we analyzed H2O, CO2, F, S, and Cl in the olivine-hosted melt inclusions in the Pitcairn OIBs using a secondary ion mass spectrometry (SIMS). Major and trace elements, and Pb isotope compositions were also determined on the same melt inclusions with an electron probe micro analyzer (EPMA) and a laser ablation-inductively coupled plasma-mass spectrometer (LA-ICP-MS).
Most of the olivine-hosted melt inclusions contain microcrystals due to slow cooling after emplacement of the host lavas. In the preliminary study, we found that measured element concentrations were blurred by the microcrystals. Therefore, we homogenized the melt inclusions by a heating and quenching method. Homogenization experiment was performed in a CO2 + H2 atmosphere using an electric furnace. For the first step, liquidus temperature of the melt inclusions was explored by altering the furnace temperature at every 25 °C between 1100 °C and 1350 °C. We found that the liquidus temperature was between 1150 °C and 1175 °C. All the olivines were then heated just above the liquidus temperature at 1150 °C or 1175 °C for 10 minutes and quenched. Previous studies showed that H2O may be diffused out from a melt inclusion through host olivine during homogenization. In order to assess the effect on H2O diffusion, we also heated naturally homogeneous melt inclusions in a pyroclastic rock and compared H2O concentrations before and after heating. In this presentation, effects of homogenization on volatile compositions will be discussed. After corrections for the effects of post-entrapment crystallization, concentrations of the volatile elements together with the major and trace elements, and Pb isotopes in the melt inclusions are used to explore volatile contents in the source mantle of the Pitcairn OIBs.