GEOLOGIC OBSERVATIONS ACROSS A TECTONO-METAMORPHIC BOUNDARY IN THE BABANGU AREA, GIYANI (SUTHERLAND) GREENSTONE-BELT, SOUTH-AFRICA

A narrow corridor across the tectono-metamorphic transition between "low-grade" and "high-grade" granite-greenstone terrains, respectively from the Giyani (also known as the Sutherland) Greenstone Belt into the hydrated granulites of the Southern Marginal Zone of the Limpopo Belt, has been mapped in detail. The two terrains are separated by a sharp tectonic (mylonitic) break. The "low-grade" greenstone terrain to the south of this break is part of a southward-dipping flattened antiformal thrust-stack, and is thus probably allochtonous. Regional variation of the dominant tectonic fabric is from shallow to steep; this is interpreted to be due to progressive deformation during northward-directed tectonic transport. The greenstone belt may lie on a flattish southward-dipping sole-thrust, "lubricated" by synkinematic granitoids in the foot and hanging walls. The northern margin of the greenstones is abruptly terminated by a late, steeply oriented shear zone, defined by mylonites. North of the shear zone, "high-grade" granite-greenstone terrain rocks (hydrated granulites) have been juxtaposed against and across the "low-grade" greenstone terrain. The tectonic break is either part of a transcurrent fault or a lateral ramp as part of a late southward-directed overthrust system. Although the rocks of the low-grade terrain have retained their early tectonic fabrics, their metamorphic character more reflects that of the "overriding" hydrated granulites.