U‐Pb sensitive high‐resolution ion microprobe (SHRIMP) zircon geochronology of granitoid rocks in eastern Zambia: Terrane subdivision of the Mesoproterozoic Southern Irumide Belt

Abstract

The Southern Irumide Belt (SIB) is a structurally and metamorphically complex region of mainly Mesoproterozoic igneous rocks in southern and eastern Zambia, northern Mozambique and northern Malawi that was strongly overprinted in the Neoproterozoic to Cambrian Damara‐Lufilian‐Zambezi (DLZ) orogeny. Because of the scarcity of geological data from this region, little is known about the timing of tectonomagmatic events; however, this belt has traditionally been considered to be a southerly continuation of the adjacent Irumide Belt (IB). Here we provide 27 new U‐Pb sensitive high‐resolution ion microprobe (SHRIMP) zircon ages that constrain the Paleoproterozoic to Cambrian tectonomagmatic history of this belt and which, for the first time, allow for direct comparison with the adjoining IB. The SIB is floored by a predominantly late Paleoproterozoic basement, which was intruded by voluminous continental margin arc‐related magmas between 1.09 and 1.04 Ga and accompanied by high‐temperature/low‐pressure metamorphism. In contrast, the IB is floored by a late Paleoproterozoic basement that is generally older than 2.0 Ga, contains significant mid‐Mesoproterozoic plutonic rocks that are not present within the SIB, and underwent moderate‐pressure/moderate‐temperature compressional metamorphism and S‐type granitoid magmatism at circa 1.02 Ga. These data indicate that the crust underlying the SIB is not a continuation of that underlying the IB but represents an allocthonous continental margin arc terrane juxtaposed against the Congo‐Tanzania‐Bangweulu Craton during the late Mesoproterozoic Irumide orogeny. Reworking and shearing of the SIB occurred during the DLZ orogen, resulting in the present‐day architecture as a series of stacked terranes which have been exploited by voluminous posttectonic granitoid batholiths.