The Taita Hills-Galana River region is a key area to demonstrate the polycyclic nature of the Mozambique Belt in SE-Kenya. Based on petrological and tectonic data this area is composed of two different granulite-facies terranes, that are separated by the 20-30 km wide Galana Shear Zone. The Taita Hills and adjoining Sagala Hills exhibit a metamorphic overprint at 630-645 Ma, similar to areas in northeastern Tanzania. An emplacement age for the magmatic precursor rocks of 850-960 Ma was derived from zircon cores. Sm-Nd garnet-whole rock ages give 585 Ma, which are interpreted as cooling ages after 630-645 Ma metamorphism. Nd crustal residence ages are between 1000-1500 Ma. The 20-30 km wide Galana Shear Zone east of the Taita Hills contains strongly deformed tonalitic migmatites with inter-layered pegmatites that date a younger tectono-metamorphic event at 560-580 Ma. East of the shear zone a only young metamorphic age of 550 Ma was found. The Nd model ages are ~1500 Ma to ~2900 Ma. In a continental configuration prior to Gondwana break-up our study area was located close to Madagascar, where several large shear zones are observed. One of these shear zones (Ranotsara Shear Zone) may be a continuation of the Galana Shear Zone.

                        Geological scetch map of the investigated area.

                                    Summary of radiometric age data

2. Anorthosites in the Eastern Granulites of Tanzania – new SIMS zircon U-Pb age data, petrography and geochemistry (Tenczer et al. 2006, Precam. Res.)

Several occurrences of anorthosites are known in the Neoproterozoic Mozambique Belt in Tanzania. These are tectonically incorporated into a suite of enderbitic rocks and migmatitic orthogneisses of the Eastern Granulites. Two larger anorthosite bodies and associated rocks from the Pare Mountains and the Uluguru Mountains have been chosen for a comparative study regarding their formation age, age of subsequent metamorphic processes, mineral chemistry and rock chemistry. All the investigated magmatic bodies were overprinted by Neoproterozoic high pressure granulite facies metamorphism and deformation, documented by similar petrography and mineralogy, metamorphic textures and deformational characteristics. However, mineral chemistry, geochemistry and geochronology reveal major differences between the two occurrences. The Pare anorthosite contains igneous zircons that yield Archean formation ages of c. 2.64 Ga and a more calcic mineral and rock chemistry that is typical for Archean type anorthosites. Extremely narrow metamorphic rims around zircons could not be dated but may have grown during the Neoproterozoic metamorphic overprint. In contrast, the Uluguru anorthosite contains igneous zircon cores with U/Pb ages of 880-820 Ma. A broad metamorphic rim was be dated at c. 640-650 Ma. The adjacent migmatitic basement gneisses yield formation ages of c. 986 Ma followed by Pb-loss. Early Neoproterozoic events can also be inferred from both anorthosite suite and basement samples of the Mahenge Mountains. There U/Pb ages from zircon cores cluster around 730-800 Ma. Well developed metamorphic rims yield Neoproterozoic ages of 650 Ma. The basement gneisses are related to a destructive plate margin setting. The anorthosites may have formed when parts of central Madagascar rifted off East Africa at the time considered.