Evolution of the Mozambique Belt in Malawi constrained by granitoid U-Pb, Sm-Nd and Lu-Hf isotopic data

Abstract

U-Pb, Sm-Nd and Lu-Hf isotopic data for granitoid rocks from southern Malawi provide constraints on the timing and sources of magmatic activity within this segment of the Mozambique Belt and its role in the Rodinia and Gondwana supercontinent cycles. LA-ICP-MS single zircon U-Pb ages indicate a number of periods of magmatic activity: late Mesoproterozoic at ca. 1130 Ma, 1070 Ma, and 1050 to 1030 Ma; Neoproterozoic at ca. 960 Ma and 600 Ma; Cambrian at ca. 530 and 515 Ma, and Mesozoic at ca. 120 Ma. The oldest igneous activity, 1128 ± 30 Ma, corresponds with emplacement of a charnockitic granitoid in the southeast corner of Malawi (Mulanje area). This region subsequently experienced metamorphism dated at 515 ± 18 Ma. The youngest magmatism is alkaline in affinity and is associated with the East African Rift. Radiogenic isotope data indicate that the Mesoproterozoic samples have positive ɛNd and ɛHf values, signifying derivation from material with a suprachondritic signature, whereas the younger rocks have negative values suggestive of crustal material recycling and mixing for their source and origins. The data imply that in the Malawi region of the Mozambique Belt, addition of new crust occurred during Rodinia assembly whereas magmatic activity during Gondwana assembly was restricted to reworking and mixing.