Clay minerals as alteration products in basaltic volcaniclastic deposits of La Palma (Canary Islands, Spain)

Phyllosilicates of the epiclastic units display wider compositional variations owing to wide variations in the mineralogical and chemical composition of the parent material. Most of the phyllosilicates (mica, corrensite, talc and chlorite) are inherited minerals derived from the erosion of the Basement Complex Unit, which had undergone hydrothermal alteration. Smectites of the epiclastic units are saponite and beidellite-montmorillonite derived from the hydrothermal Basement Complex Unit and from volcanic materials altered in the sedimentary environment. Conversely, clay minerals of unconformity-related paleosols are dominated by smectite composed of variable mixtures of saponite and beidellite, which were formed by pedogenetic processes with later hydrothermal influence. The mineralogical association in the pyroclastic unit is dominated by hydrothermally formed smectite (beidellite-montmorillonite), zeolites and calcite. This paper contributes to the differentiation between pyroclastic and epiclastic volcaniclastic rocks of several depositional settings in a basaltic volcanic complex by their clay minerals characterization.