GEOLOGIC EVOLUTION OF THE NEOPROTEROZOIC ZAMBEZI OROGENIC BELT IN ZAMBIA

Citation
Re. Hanson et al., GEOLOGIC EVOLUTION OF THE NEOPROTEROZOIC ZAMBEZI OROGENIC BELT IN ZAMBIA, Journal of African earth sciences, and the Middle East, 18(2), 1994, pp. 135-150
Citations number
NO
Categorie Soggetti
Geosciences, Interdisciplinary
ISSN journal
08995362
Volume
18
Issue
2
Year of publication
1994
Pages
135 - 150
Database
ISI
SICI code
0899-5362(1994)18:2<135:GEOTNZ>2.0.ZU;2-0
Abstract
The Neoproterozoic Zambezi belt links with the Mozambique belt Lufilia n are, and the inland branch of the Damara belt within the regional Pa n-African tectonic framework of southern Africa. The belt contains a t hick supracrustal sequence deposited on older sialic basement and pene tratively deformed with it during Neoproterozoic (Pan-African) orogene sis. In Zambia, where the entire width of the orogen is exposed, local bimodal Volcanic rocks at the base of the sequence are overlain by ps ammites and pelites, which in turn are succeeded by extensive carbonat e and calc-silicate rocks. Abundant scapolite in metamorphic assemblag es within the belt is taken as evidence for the original presence of e vaporites. The nature of the rock types and the inferred stratigraphic sequence are consistent with deposition in an intracontinental rift b asin invaded by marine waters. Available isotopic age brackets for the timing of supracrustal deposition show that the basin developed betwe en 880 and 820 Ma. Main-phase deformation in the belt involved both tr anscurrent shearing and south- to southwest-vergent thrusting and was associated with predominantly amphibolite-facies regional metamorphism . Mineral assemblages throughout much of the belt in Zambia, together with limited thermobarometric data, indicate typical Barrovian-type in termediate P/T conditions during metamorphism. Eclogites and other hig h-pressure metamorphic assemblages in parts of the belt, however, prov ide evidence that significant crustal. thickening occurred, presumably in relation to thrusting. Reworked basement and syntectonic granite w ere subjected to extensive mylonitization related to strike-slip and o blique, reverse-slip shearing. The major orogenic event is dated at c. 820 Ma, based on an igneous age for a sheet-like, syntectonic batholi th injected into a transcurrent shear zone within the central part of the belt. Pan-African orogenesis along the Zambezi-Lufilian-Damara tre nd was diachronous and records closure of intracratonic basins in the Zambezi belt and Lufilian are, with evidence for the involvement of oc eanic Lithosphere present only in the Damara belt.