Pan-African deformation in se Kenya and ne Tanzania: geotectonic implications for the development of the north-central Mozambique belt.

Abstract

In the Taita Hills – Galana River area in SE Kenya, four tectonostratigraphic units can be distingui-shed. They differ in tectonic style, and in part in metamorphism, litho logy and age of peak metamor-phism as recently documented by U-Pb zircon dating. An older Pan-African granulite facies metamor-phism (~644-629 Ma) is found in domains showing S-SW directed low angle thrusting (Taita Hills) and NNW-SSE strike slip deformation (western Galana River). In an eastward direction, a late Pan-African granulite facies metamorphism (~550 Ma) occurs in a domain where structures indicate ~NE-SW shor-tening (eastern Galana River). The nearby granulites of the Pare-Usambara mountains as well as rocks of the Umba Steppe in NE Tanzania show similarities in age of high-grade metamorphism and structural appearance. Two tectonothermal events which were noticed in north- central Kenya could have affected both regions. The Samburuan-Sabachian event (starting at ~820 Ma), possibly associ-ated with island arc accretion and structurally documented as early recumbent and overturned folds, may have resulted in granulite facies metamorphism at ≥644-629 Ma. The vestiges of a related suture are likely to be in SE Kenya and are assumed to continue southwards across the NE granulites of Tanzania. Geochemical and recent geochronological (U-Pb zircon) data suggest that arc-related magmatism started in the early Neoproterozoic (>900 Ma). The Baragoian-Barsaloian event () 620 580 Ma ≤ ∼, as a tectonometamorphic overprint, presumably caused S-SW directed thrusting in the Taita Hills, cross folding and thrusting in NE Tanzania as well as a distinct scatter of lineations. This event could involve another collision and suturing of the Pan-African cycle and may be manifested in metamorphism and tectonic style of the Galana River area.