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Oceanic plateaus are formed by a large volume of basaltic rocks on top of the oceanic lithosphere. Alteration of these basalt lava piles leads to significant chemical element exchanges between mantle and oceans that can strongly influence chemical budget. Here we report boron (B), chlorine (Cl), and other element concentrations in basalt samples from the Shatsky Rise to define alteration processes and to estimate the significance of oceanic plateaus in storing these elements. Sampling includes 121 basaltic lavas and 92 fresh glasses collected at various depths from Holes U1346A, U1347A, U1349A, and U1350A during Integrated Ocean Drilling Program Expedition 324. Loss on ignition (LOI) results indicate that alteration affected basalts from the summit sites (U1346 and U1349) more deeply than those from the flank sites (U1347 and U1350). The positive correlations between B, K, and LOI observed in the basalts indicate that low-temperature seawater-derived alteration was the predominant process affecting Shatsky Rise basalts. This is confirmed by the elevated B/K and modest Cl/K ratios of these altered basalts relative to the fresh glasses. In addition, B concentrations in the summit basalts (~132 ppm) are significantly higher than those in normal altered oceanic crust and are likely related to the presence of illite. This suggests that the Shatsky Rise oceanic plateau may be an important sink for B in the Pacific oceanic crust.

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