Geochemistry of the Adwa – Yeha felsic plugs and domes, Tigray – Northern Ethiopia: Implications to their petrogenesis and tectonic setting

Abstract

The Adwa – Yeha felsic plugs and domes are chain of towering inverted cone-shaped isolated plugs and circular domes with wide basal diameters and steep-sided, narrow tops. They form contrasting prominent topography from the Trap basalt ridges of the Adwa – Axum - Tekeze volcanic ridge, located just west of the Northern Afar Depression. The felsic plugs and domes are concentrated in the Adwa – Yeha area, in a zone of about 20 km wide and 30 km long and generally aligned along NNE-SSW direction, parallel to the regional structural grain of the Precambrian basement and the Miocene - Pliocene rift margin faults. In this study, we investigated these felsic plugs and domes using petrological and major and trace element geochemical methods in order to constrain their petrogenetic evolution. Their possible tectonic link to the Western Afar Margin has also been investigated combining our geochemical data, with assessment of regional tectonic setting and geochronological data from previous studies. The results ascertain that the felsic plugs and domes are peralkaline trachytes and peralkaline to sub-alkaline rhyolites, formed by Assimilation Fractional Crystallization (AFC) of basaltic magma which involved removal of olivine, pyroxene, plagioclase, and Fe–Ti oxides, and moderate amount of crustal input. The eruption of the felsic plugs and domes occurred along reactivated Precambrian weakness zones during the formation of the western Afar boundary faults.