Silica precipitation triggered by clastic sedimentation in the Archean: New petrographic evidence from cherts of the Kromberg type section, South Africa

The Kromberg Formation (ca. 3432Ma) in the Barberton Greenstone Belt, South Africa, contains well-preserved chert beds at the tops of turbidite deposits. At the interface, siltstone, which consist of K-feldspar, K-mica, microquartz with minor lithic fragments and heavy minerals, grades into chert, which consists of microquartz and minor K-mica (2 to the bulk composition, and (2) another phase that dominates the trace element composition. Here, K-mica and K-feldspar control the chemical signal and reflect a felsic source to the turbidites (i.e. Hooggenoeg dacites and volcaniclastics).