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doi:10.2204/iodp.proc.324.203.2013

Introduction

Basaltic lavas of Shatsky Rise oceanic plateau, recovered during Integrated Ocean Drilling Program (IODP) Expedition 324, erupted during the Late Jurassic and Early Cretaceous (~145 Ma; Mahoney et al., 2005) close to the triple junction of the Pacific-Farallon-Izanagui lithospheric plates. Since their emplacement on the ocean floor, the basaltic rocks have undergone fluid-rock interactions, whose conditions vary laterally from one site to another and vertically within a single site. Actually, the two Sites U1347 and U1350, located at the flanks of Tamu and Ori Massifs, respectively, are only slightly altered, whereas Sites U1346 and U1349, located on the summits of Shirshov and Ori Massifs, respectively, show the highest degrees of alteration with significant variations in alteration types with depth (see the “Expedition 324 summary” chapter [Expedition 324 Scientists, 2010a]). In order to precisely characterize types and conditions (temperature, redox, and water-rock ratios) of alteration of the two most altered sites, secondary mineralogy and especially the nature and characteristics of clay minerals were specifically identified by X-ray diffraction (XRD) on nonoriented bulk rock powder and on oriented sections of the decarbonated <2 µm fractions. These data complete preliminary secondary mineral characterizations made onboard by the Expedition 324 Scientific Party (Expedition 324 Scientists, 2010a).

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