Showing papers by "Gezahegn Yirgu published in 1997"

Timing of the Ethiopian flood basalt event and implications for plume birth and global change

Abstract: Continental flood basalts are often considered as fossil evidence of mantle plume heads impinging on the lithosphere1,2 and have been related to continental breakup3,4,5. Many of these flood basalts erupted within a short time span—of the order of 1 Myr—and were apparently synchronous with crises in global climate and with mass extinctions6. Here we present geochronological (40Ar/39Ar) and magnetostratigraphic results for the Ethiopian traps, one of the last remaining flood basalts for which few such data were available. The bulk of the traps, which have been inferred to mark the appearance of the Ethiopian-Afar plume head at the Earth's surface, erupted approximately 30 Myr ago, over a period of 1 Myr or less. This was about the time of a change to a colder and drier global climate, a major continental ice-sheet advance in Antarctica, the largest Tertiary sea-level drop and significant extinctions.

Rifting actif ou passif en Éthiopie ? éléments de réponse apportés par l'étude des xénolites péridotitiques de la région du lac Tana

Abstract: The comparative study of peridotitic xenoliths from Oligocene and Quaternary volcanic formations of north-western Ethiopia shows that the textural, mineralogical, thermal and geochemical characteristics of the lithospheric mantle of this region were acquired in Oligocene times. These data suggest that the impinging of the Afar plume beneath the Ethiopian lithosphere occurred prior to the traps emplacement and the Plio-Quaternary rifting. This favours a model of active rifting for the Afar triple junction.