This paper presents alteration mineralogy of basalts from Sites U1346 and U1349 drilled during Integrated Ocean Drilling Program (IODP) Expedition 324 on Shatsky Rise oceanic plateau. These two sites are the more altered sites among the four basaltic sites drilled on the plateau and show the greatest variability in terms of alteration. X-ray diffraction (XRD) analyses were processed on nonoriented bulk rock powders and on oriented sections made after decarbonation of the <2 µm fraction of basalts, sampled at regular intervals from Holes U1346A and U1349A. These XRD analyses allow us to determine the nature and composition of clay minerals that predominantly replace primary mineralogy of the basalts and to evaluate the spatial variations in alteration conditions: lateral variations within the plateau and vertical variations within a single site. Alteration types differ between the two holes and include green alteration, brown alteration, and dark gray alteration in Hole U1346A, whereas Hole U1349A is characterized by red-brown alteration, a transition zone, and green alteration that differs significantly from that in Hole U1346A. Secondary mineral assemblages include smectites, calcite, kaolinite, illite, chlorite, zeolites, sulfides, Fe oxides (i.e., hematite), and Fe oxyhydroxides. These parageneses attest that basaltic rocks from the two sites were affected by low-to moderatetemperature alteration. Alteration at Shatsky Rise oceanic plateau is similar, although some differences occur, to that reported at oceanic plateaus (e.g., Ontong Java) and oceanic crust drilled during the Deep Sea Drilling Program and Ocean Drilling Program.
