Geochemistry of altered smectites

During the first stage, the Mg-smectites are the most abundant; they are occasionally associated with Al-smectites. Afterwards, they are gradually replaced by iron-rich smectites.

The REE distribution follows the same trend as the mineralogical changes. During the f'trst stage of alteration, REE distribution in clay minerals is the same as in the fresh glasses but, when the iron-rich smectites increase, the Ce has a specific behaviour. The Ce shows a positive anomaly in iron-rich smectites formed early in palagonitized glasses, and a negative one in authigenic smectites formed later from solutions in equilibrium with seawater.