Journal of the Geological Society , London, Vol. 164, 2007, pp. 189–201. Printed in Great Britain. 189 SHRIMP U–Pb zircon and Sm–Nd garnet ages from the granulite-facies basement of SE Kenya: evidence for Neoproterozoic polycyclic assembly of the Mozambique Belt CHRISTOPH A. HAUZENBERGER 1 , HOLGER SOMMER 2 , HARALD FRITZ 1 , ANDREAS BAUERNHOFER 1 , ALFRED KRO ¨ NER 2 , GEORG HOINKES 1 , ECKART WALLBRECHER 1 & MARTIN THO ¨ NI 3 1 Institut fu ¨r Erdwissenschaften, Universita ¨t Graz, Universita ¨tsplatz 2, Graz 8010, Austria (e-mail: christoph.hauzenberger@uni-graz.at) 2 Institut fu ¨r Geowissenschaften, Universita ¨t Mainz, Becherweg 21, Mainz 55099, Germany 3 Instititut fu ¨r Geologische Wissenschaften, Universita ¨t Wien, Althanstraße 14, Wien 1090, Austria Abstract: The Taita Hills–Galana River region is a key area to demonstrate the polycyclic nature of the Mozambique Belt in SE Kenya. On the basis of petrological and tectonic data, this area is composed of two different granulite-facies terranes, which 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 Tanzania. An emplacement age for the magmatic precursor rocks of 850–960 Ma was derived from zircon cores. Sm– Nd garnet–whole-rock analyses give an age of 585 Ma, interpreted as the cooling age after 630–645 Ma metamorphism. Nd crustal residence ages are between 1000 and 1500 Ma. The Galana Shear Zone east of the Taita Hills contains strongly deformed tonalitic migmatites with interlayered pegmatites that date a younger tectonometamorphic event at 560–580 Ma. East of the shear zone only a young metamorphic age of 550 Ma was found. The Nd model ages are c. 1500 Ma to c. 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. The late Neoproterozoic Mozambique Belt of East Africa (Holmes 1951) extends from Mozambique to Ethiopia through Madagascar, Malawi, Tanzania and Kenya (Fig. 1), and is composed of deformed high-grade rocks of different ages. The high-grade terranes of the Mozambique Belt in East Africa and the lower-grade terranes of NE Africa and Arabia (Arabian– Nubian shield) together make up the East African Orogen (Stern 1994). Most current models suggest that the East African Orogen resulted from late Neoproterozoic ‘Himalayan-type’ continent– continent collision between Neoproterozoic India and the Con- go–Tanzania–Bangweulu continent (Dewey & Burke 1972; McWilliams 1981; Key et al. 1989; Meert 2003; Boger & Miller 2004; Collins & Pisarevsky 2005) following closure of the ‘Mozambique Ocean‘ (Hoffman 1991; Stern 1994; Shackleton 1996). The peak of regional granulite-facies metamorphism in the Mozambique Belt of Tanzania was dated between 620 and 640 Ma on the basis of sensitive high-resolution ion microp- robe (SHRIMP) and secondary ion mass spectrometry (SIMS) analysis on metamorphic zircons and monazite (Coolen et al. 1982; Mo ¨ller et al. 2000; Muhongo et al. 2001; Kro ¨ner et al. 2003; Sommer et al. 2003, 2005; Tenczer et al. 2006). In northern Mozambique metamorphic zircons grew at c. 615 Ma (Costa et al. 1994; Kro ¨ner et al. 1997), in southern Malawi at c. 550–580 Ma (Kro ¨ner et al. 2001), and in Madagascar at 520–630 Ma (Ashwal et al. 1999; Tucker et al. 1999; Kro ¨ner et al. 2000; De Wit et al. 2001; Collins et al. 2003c; Cox et al. 2004). Stern (1994) argued that the East African Orogen evolved through the c. 900 Ma break-up of the supercontinent Rodinia and subsequent amalgamation of Gondwana. He proposed two episodes of metamorphism, the first occurring at c. 700 Ma during continent–continent collision; the second at c. 500 Ma during crustal thickening, which either was associated with a second, younger con- tinent–continent collision or was the product of eastward crustal thickening progression across the c. 700 Ma collision. Meert (2003) suggested that two major tectonometamorphic events occurred between 750 and 530 Ma, but he provided no structural or petrological data to support his claim. In his view, ages extending from 750 to 620 Ma reflect the East African Orogen, whereas younger ages between 570 and 530 Ma are attributed to a second major episode, referred to as the Kuunga Orogeny. Collins & Pisarevsky (2005) named the younger event the Malagasy Orogeny in Madagascar and Eastern Africa. They argued that the Kuungwa Orogeny is restricted to the orogeny formed by the collision of India with East Antarctica–Australia and the coeval Malagasy Orogeny is related to the collision of India with an assembled Congo–Azania–Bangweulu continent. The strongly deformed granulite-facies metamorphic rocks found throughout the Mozambique Belt make it difficult to reconstruct the original evolutionary history of the belt. It is difficult to recognize individual tectonic domains that experi- enced similar deformation and metamorphic histories. Further- more, the exhumation and cooling history of these high-grade terranes are not well understood. The aims of this paper are: (1) to report single zircon and garnet–whole-rock ages from the Taita Hills and parts of the Tsavo East National Park (Galana River) (Fig. 2); (2) to compare domains of different ages in the Taita Hills and Tsavo East National Park area, by means of