Kasahara, J., Stephen, R.A., Acton, G.D., and Frey, F.A. (Eds.) Proceedings of the Ocean Drilling Program, Scientific Results Volume 200 3. COMPOSITION, PETROGRAPHY , AND MINERAL CHEMISTRY OF ODP SITE 1224 EOCENE FERROBASALTS (LEG 200; NORTH PACIFIC OCEAN) 1 Michele Lustrino 2, 3 ABSTRACT The ~46-m.y.-old igneous basement cored during Leg 200 in the North Pacific represents one of the few cross sections of Pacific oceanic crust with a total penetration into basalt of >100 m. The rocks, em- placed during the Eocene at a fast-spreading rate (~14 cm/yr; full rate) are strongly differentiated tholeiitic basalts (ferrobasalts) with 7–4.5 wt% MgO, relatively high TiO 2 (2–3.5 wt%), and total iron as Fe 2 O 3 (9.1–16.8 wt%). The differentiated character of these lavas is related to unusually large amounts of crystallization differentiation of plagioclase, clinopyroxene, and olivine. The lithostratigraphy of the basement (cored to ~170 meters below seafloor) is divided into three units. The deepest unit (lithologic Unit 3), is a succession of lava flows of no more that a few meters thickness each. The intermediate unit (lithologic Unit 2) is represented by inter- mixed thin flows and pillows, whereas the shallowest unit (lithologic Unit 1), comprises two massive flows. The rocks range from aphyric to sparsely clinopyroxene-plagioclase-phyric (phenocryst content = <3 vol%) and from holocrystalline to hypohyaline. Chilled margins of pil- low fragments show holohyaline to sparsely vitrophyric textures. Site 1224 oxide minerals present a type of alteration not previously seen, where titanomagnetite is only partially destroyed and the pure magnetite component is partially removed from the mineral, leaving, in the most extreme case, a nearly pure ulvöspinel residuum. As a result of this dissolution, iron, mainly in the oxidized state, is added to the 1 Lustrino, M., 2006. Composition, petrography, and mineral chemistry of ODP Site 1224 Eocene ferrobasalts (Leg 200; North Pacific Ocean). In Kasahara, J., Stephen, R.A., Acton, G.D., and Frey, F.A. (Eds.), Proc. ODP, Sci. Results, 200, 1–36 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/ publications/200_SR/VOLUME/ CHAPTERS/008.PDF>. [Cited YYYY- MM-DD] 2 Dipartimento di Scienze della Terra, Università degli Studi di Roma La Sapienza, Piazzale Aldo Moro 5, 00185 Rome, Italy. michele.lustrino@uniroma1.it 3 Istituto di Geologia Ambientale e Geoingegneria, CNR, Piazzale Aldo Moro 5, 00185 Rome, Italy. Initial receipt: 22 May 2005 Acceptance: 11 April 2006 Web publication: 7 July 2006 Ms 200SR-008