Basalts from aseismic structures and guyots and their alteration are less studied than those from mid-ocean ridges. Aseismic ridges and plateaus represent giant structures on the ocean floor that are often linear and extend several thousand kilometers to form large igneous provinces (LIPs). These structures reveal the characteristic features of magma composition, extrusion environment (from shallow-water and subaerial to deepwater environments), thermal history, and circulation of both seawater and meteoric fluids (Kurnosov et al., 1995; Kurnosov and Murdmaa, 1996). Variation in tectonic setting during the formation of these volcanic structures leads to significant variation in chemical composition of lava flows and pillow units (Vallier et al., 1981).
The combination of these peculiarities for aseismic ridges and plateaus is somewhat specific in comparison to mid-ocean ridges. Therefore, alteration of basalts in these structures generates characteristic features that need further investigation. Study of basalt alteration requires analyses of thin sections, chemical composition of both altered rocks and their protoliths, densities, and alteration of secondary minerals. We used this approach during the study of basalts recovered from Holes 1136A, 1137A, 1138A, and 1140A (Leg 183) and from Hole 747C (Leg 120) from various parts of the Kerguelen Plateau.
In this article, we have determined