SHRIMP ZIRCON U-PB GEOCHRONOLOGY AND GEOCHEMISTRY OF THE CHOMA – KALOMO BLOCK GRANITOIDS (ZAMBIA): GEOLOGICAL IMPLICATIONS

The Choma–Kalomo Block is a Mesoproterozoic terrane exposed in southern Zambia, south of the Pan-African Zambezi Belt. It includes a large plutonic complex in the central part, surrounded by supracrustal metasedimentary assemblages. The plutonic complex represents a set of intrusive bodies that yielded TIMS U-Pb zircon dates between c. 1345 and 1200Ma (Hanson et al., 1988). Two deformation events were recorded in this terrane: D1 is presumably coeval with the emplacement of the c. 1345 Ma granitoids (converted into orthogneisses) and D2 coeval with emplacement of c. 1200 Ma granitoids. Because of its location between the Mesoproterozoic Irumide Belt of Zambia and the Ngamiland province of Botswana, the Choma-Kalomo Block is a critical terrane in the reconstruction of the late-Mesoproterozoic (Kibaran) orogenic system of central and southern Africa. To better understand the evolution of the Choma-Kalomo Block, zircons extracted from five granitoid samples were investigated using the U-Pb SHRIMP technique and yielded the following results: CK4: medium-grained two mica granite: 1174±27 Ma; CK10: foliated medium- to coarse-grained biotite granite: 1188±11 Ma; CK12: gneiss containing mica-rich restites: 1177±70 Ma; CK25: foliated, medium- to coarse-grained biotite granite: 1181±9 Ma; CK13: augen (ortho) gneiss: 1368±10 Ma