Abstract

Field relationships in the Sand River in the Central Zone of the Limpopo Belt show that the supracrustal rocks of the Beit Bridge Complex are intruded by granitoid phases of the Sand River Gneiss protoliths. This observation is confirmed by SHRIMP U-Pb zircon ages and a whole-rock Nd mean crustal residence age: a sample of Beit Bridge metapelite contains detrital zircons with zircon ages ranging from 3358 to 3709 Ga. Two grains have metamorphic overgrowths with a mean age of 2023+ or -12 Ma, identical to a zircon age of 2027+ or -4 Ma previously established for a peak of regional metamorphism in the Messina area of the Central Zone. The mean crustal residence age for this metapelite sample is 3580 Ma. Two samples of leucocratic and well-layered granitoid gneiss, termed Dorothy gneiss, contain concordant zircons with mean 207 Pb/ 206 Pb ages of 3239+ or -2 and 3240+ or -7 Ma, respectively. The former was collected in the Sand River on Verbaard farm where it cuts the foliation of the interlayered metapelites, and the latter occurs further downstream in the Sand River at the Causeway locality. These leucogneisses represent some of the oldest magmatic phases in the Central Zone of the Limpopo Belt dated so far.

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