Granites were shown to be excellent geochronological, structural and geodynamic markers. Among several generations of granites described in the Neoproterozoic of Ethiopia, we studied the post-tectonic Konso pluton to characterise the post-Pan-African evolution of the Mozambique Belt (MB) of southern Ethiopia. The Konso pluton is a composite intrusion of slightly peraluminous and ferro-potassic, bt (biotite)-leucogranites, bt-hbl (hornblende)-granites and subordinate coeval metaluminous monzodiorites, intruded into high-grade gneiss-migmatite associations of the MB. The whole suite displays chemical features of A-type granites. It is LIL- and HFS-elements enriched with Y/Nb and Yb/Ta≥1.2. The granites and leucogranites show non-fractionated to fractionated REE patterns [(La/Y-b)N=0.3-9.4] with strong negative Eu anomalies. The monzodiorites show fractionated REE patterns [(La/Yb N=5.5-7.4] with negligible negative Eu anomaly. The low initial (87Sr/86Sr)450 ratios (0.70113-0.70441) and positive εNd(450) values (+1.8 to +3.3) suggest an isotopically primitive source. The Konso granites are likely to be derived from a basaltic parent, with minor contamination by crustal material with high Y/Nb and low Sr initial isotopic ratios. Age of pluton emplacement is constrained by a Rb-Sr isochron and zircon U-Pb data at 449±2 Ma. The Konso pluton is, therefore, the witness of an Ordovician A-type magmatic event, which marks a change from convergence, related to the Pan-African collision, to extension in the Mozambique Belt of southern Ethiopia.
All Science Journal Classification (ASJC) codes
- Earth and Planetary Sciences(all)