Kaapvaal Craton - Hooggenoeg Formation of The Barberton Greenstone Belt

Hooggenoeg Formation of The Barberton Greenstone Belt

Some controversy exists pertaining to the origin and emplacement of Archaean felsic suites. According to a dissertation by Louzada (2003): "The upper part of the Hooggenoeg Formation is characterized by ultramafic massive and pillow lavas, a trondhjemitic suite of silicified felsic intrusive and flow banded rocks, and sedimentary chert beds. Veins of felsic, chert and ultramafic material intrude the belt. The depositional environment is thought to be a shoaling shallow sea in which the Hooggenoeg Formation has been deposited in a west-block down, listric faulted, synsedimentary setting."

The Hooggenoeg Formation felsic rocks can be divided into two groups: an intrusive group of interlocking and shallow intrusive rocks, and a porphyritic group of rocks from the veins. Lavas from the upper part of the felsic unit are too altered to be assigned to one of these groups. The intrusive group is related to the tonalite-trondhjemite-granodiorite TTG-suite Stolzburg Pluton, which intruded along the southern margin of the Barberton greenstone belt. Melting of an amphibolite quartz eclogite has been suggested as a probable origin for these high-Al₂O₃ felsic magmas. Ultramafic rocks of the Hooggenoeg Formation were most likely not parental for the felsic rocks. Subduction processes may have played a role in the generation of the felsic rocks, but a tectonic setting for the ultramafic rocks remains uncertain. The felsic units of the Hooggenoeg Formation are very similar to those of the Panorama Formation of the Early Archaean Coppin Gap greenstone belt of Western Australia (See Yilgarn craton). Similarities in geological setting, petrography, and geochemical (trace element in particular) characteristics suggest a possible genetic relation between the two formations and support the theory that a combined continent Vaalbara existed ~3.45 Ga. (Louzada, 2003).