Geochronology of Massif-Type Anorthosites from the Ubendian Belt, Tanzania

Abstract

Massif-type anorthosites occur in East Africa at the margins of the Tanzania Craton in the Ubendian Belt. The massif assemblage constitutes of mafic-composition plutons (meta-anorthosite and meta-gabbro), ultramafic plutons, and titaniferous iron-ore. Silicic ortho-gneisses (tonalitic, dioritic, and granodioritic intrusives) also occur in the vicinity of the said massif-type anorthosites. This article presents ages of meta-anorthosites and meta-gabbros. The new U-Pb zircon age indicates that meta-gabbros and meta-anorthosites crystallized between 1915 ± 24 and 1905 ± 24 Ma concomitantly with the silicic magmatic bodies. Geochronological databases indicate that the period between 1920 and 1850 Ma HP-LT metamorphic interface was formed at subduction zone settings in the Ubendian Belt along with emplacement of arc related voluminous batholiths and volcanic rocks. The subduction tectonics was probably a driving engine for magmatism in the region. A Neoproterozoic metamorphic event dated at 547 ± 25 Ma reworked the Ubendian Belt massifs-type anorthosites.

Keywords: Ubendian Belt; massif-type Anorthosites; U-Pb zircon ages