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doi:10.2204/iodp.proc.309312.201.2008 Data report: petrography and phase analyses in lavas and dikes from Hole 1256D (ODP Leg 206 and IODP Expedition 309, East Pacific Rise)1Wanja Dziony,2 Jürgen Koepke,2 and François Holtz2AbstractWe investigated 56 basalts drilled in Hole 1256D (equatorial East Pacific Rise) during Ocean Drilling Program Leg 206 and Integrated Ocean Drilling Program Expedition 309. Primary magmatic phases, pyroxenes, plagioclases, and Fe-Ti oxides were analyzed in 16 selected samples by electron microprobe analysis. Both clinopyroxene and plagioclase show strong zoning effects, especially in the outermost rims. Many clinopyroxenes show marked zoning, which is in part developed as sector zoning. Some clinopyroxenes bear cores of relict pigeonites, which show slightly higher Mg# (100 * molar MgO/[MgO + FeOtot], where FeOtot = total FeO) than the host crystals. Plagioclase shows a broad scattering in composition, often combined with zoning. We observed a slight trend toward more evolved compositions of mineral phases in the sheeted dikes. Only 1 of the 16 samples bears coexisting magnetite and ilmenite (from the uppermost volcanic unit, the lava pond). By applying the magnetite-ilmenite thermooxybarometer, we calculated an oxygen fugacity corresponding to ΔFMQ of –0.4 (0.4 log units below the oxygen fugacity of the fayalite-magnetite-quartz buffer). |
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