Integrated heavy mineral study of Jurassic to Paleogene sandstones in the Mandawa Basin, Tanzania: Sediment provenance and source-to-sink relations

Abstract

This paper concerns the heavy mineral composition of Jurassic, Cretaceous and Paleogene sedimentary successions in the Mandawa Basin. The nature of the heavy mineral assemblages in 38 samples was investigated to assess changes in sediment provenance through time. Further, the geochemistry of detrital amphiboles and garnets and the detrital zircon populations were used to determine possible sediment source terranes. Based on the heavy mineral compositions the sandstones were grouped into four heavy mineral assemblages: garnet-dominated, amphibole-dominated, epidote-dominated and zircon-dominated. Garnet-dominated sandstones are abundant in most Middle Jurassic to Middle Eocene samples and represent the main sediment input into the Mandawa Basin. Amphibole-dominated sandstones occur in a few Lower Cretaceous samples deposited in close proximity to their sediment source in the Masasi Spur area. A change in provenance is observed in the epidote-dominated sandstones of Middle Eocene and Early Oligocene age. This change coincides with a climatic shift towards a wetter and cooler climate associated with an uplift phase in East Africa. The detrital zircon population in the investigated samples share the same age fractions and are indistinguishable within analytical error. Mineral chemistries and zircon ages imply that the sediments deposited in the Mandawa Basin were mainly derived from several high-grade sources within the Neoproterozoic Mozambique Belt to the west of the basin.