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Sm-Nd dating of Fig Tree clay minerals of the Barberton Greenstone Belt, South Africa

Abstract:

Sm-Nd isotopic data from carbonate-derived clay minerals of the 3.22-3.25 Ga Fig Tree Group, Barberton greenstone belt, form a linear array corresponding to an age of 3102 ± 64 Ma, making these minerals the oldest dated clays on Earth. Nd model ages for the clays range from ~3.39 to 3.44 Ga and almost cover the age variation of the Barberton greenstone belt rocks, consistent with independent evidence that the clay minerals are derived from material of the belt. The combined isotopic and mineralogical data provide evidence for a cryptic thermal overprint in the sediments of the belt. However, the highest temperature reached by the samples since the time of clay-mineral formation was <300°C, lower than virtually any known early Archean supracrustal sequence. -from Authors