Emplacement and thermal effect of post-collisional Chewo Pluton (Arabian-Nubian Shield); implication for late East-African Orogeny

Abstract

The Chewo pluton built by pyroxene-amphibole to amphibole-biotite monzodiorite and quartz monzonite is a typical post-collisional intrusive body emplaced into a low-grade Neoproterozoic Tambien Group belonging to the Tokar-Barka Terrane in the southern Arabian–Nubian Shield. The pluton shows a high-K calc-alkaline and metaluminous composition with significant enrichment in both LREE and LILE due to hybridization and magma mixing between crustal and mantle-derived melts. Estimated P-T conditions of quartz monzonite magma solidification at T: 703 ± 23 °C and P: 0.32 ± 0.08 GPa and thermal overprint in the pluton aureole at T: ̴200–755 °C and P: 0.28 ± 0.06 GPa indicate that the Chewo pluton intruded at a depth of between ca. 10–13 km. The Chewo Pluton was emplaced diapirically, which was driven by a local extension in the hinge of the large-scale asymmetric syncline during the last increments of regional deformation – orogen-perpendicular WNW(NW)-ESE(SE) compression. It indicates that the regional WNW(NW)-ESE(SE) shortening is the main geodynamic event of the East African Orogen in the upper-crustal Tokar-Barka Terrane resulting in the assembly of the eastern and western Gondwana continents. In concordance, the zircon U/Pb age of the Chewo pluton (618.1 ± 1.5 Ma) provides the upper limit for the regional deformation.