Provenance study on the Karoo sedimentary rocks of the Chicôa-Mecúcoè sub-basin of the Zambezi Basin, Tete Provence, Mozambique: implications for basin development, sedimentary processes and tectonic controls

Abstract

The Chicôa-Mecúcoè sub-basin of the Zambezi Basin in northern Mozambique hosts Karoo Supergroup rocks of the Vúzi, “Transitional,” Moatize and Matinde formations, deposited from the Late Carboniferous to the Early Jurassic. The strata record periods of changing depositional environments resulting in cyclic sedimentary sequences and coal measures. This project focuses on the Vúzi Formation, a conglomeratic unit of glacial outwash gravel, the “Transitional” formation, a deltaic coarsening upward clastic sequence, and the Matinde formation, a sequence of fluviatile/lacustrine clastic sediments and coal measures. A single borehole intersection drilled from surface into basement rock provided a continuous intersection of Karoo Supergroup rocks for analysis and interpretation. The borehole was drilled in 2011 by Eurasian Natural Resources Corporation (“ENRC”) and made available for research in 2015 and forms the basis for the deglaciation and provenance study. Detrital zircon age population data obtained from Laser Ablation Inductively Coupled Plasma Mass Spectrometry (“LA-ICP-MS”) analysis was compared to published aged data for the surrounding area. The age data in northern Mozambique is not well documented and often based on a limited number of analysis. Predominant Mesoproterozoic age data from 1000 - 1100 Ma suggest Kibaran and Irumide Orogen Monte Capirimpica granitoids and the Cassacatiza suite as primary source areas, confirming a westward and south westward directed paleoflow during Karoo sedimentation with zircon morphology suggesting a relatively short transport history. The Cambrian to Neoproteroic aged data from 500 - 999 Ma suggests a secondary south easterly directed palaeoflow from localised elevated areas associated with late Pan African Matunda, Monte Inchinga and Atchiza suites. Zircon data from samples taken from the Vúzi Formation show a relatively stable supply, indicating that the glaciers were possibly fault bounded, while deepening existing valleys. A detailed lithological log of 11MTD001 identified a ~120 m thick intersection of Vúzi Formation stratigraphy which assisted in the identification of cycles associated with advancing and retreating glaciers and confirm a glacial origin for the Vúzi Formation in the Chicôa-Mecúcoè sub-basin. The four cycles identified were compared to similar deglaciation cycles in South Africa, Botswana, Zimbabwe and Tanzania. Clast composition and percentages indicates that maximum glacial advance was achieved in the first cycle and progressively becoming less prominent with each successive cycle, with the period between glacial advance and retreat increasing.