The eclogites of the Lato hills, south Togo, West Africa: Relics from the early tectonometamorphic evolution of the Pan-African orogeny

Abstract

The eclogites of the Lato hills outcrop within the Pan-African orogenic belt of south Togoland (Dahomeyides) are located within the western border of the Bénin plain structural unit (ex Dahomeyen). They are closely associated with epi- to mesozonal metasediments, which are similar to the Pan-African cover formations of the Atacora unit. Two groups of eclogites have been distinguished according to field relations and to the nature of the country rocks; but they display a similar metamorphic history. The mineralogical and textural transformations of eclogites indicate: (1) a progressive increase of the P— T regime; (2) a mylonitization event close to the culmination of eclogitic metamorphism; and (3) a retrograde evolution towards amphibolite-facies conditions. Likewise, quartzites, closely associated with eclogites, exhibit high- P parageneses compatible with that of the eclogite formation. These observations allow us to consider the eclogitisation processes as a crustal transformation of mafic igneous rocks, and to assign a Pan-African age to these recrystallizations. Therefore, the Mount Lato eclogites represent rare witnesses from the early tectonometamorphic evolution of the Dahomeyides range.