The Geology and Stratigraphic Evolution of the North-Central Part of the Early Archean Barberton Greenstone Belt, South Africa.

Abstract

The north-central part of the 3.5 to 3.2 Ga Barberton greenstone belt, southwest of the town of Barberton, contains both the northern and southern facies of the Swaziland Supergroup including, from base to top, the Onverwacht, Fig Tree, and Moodies Groups. The facies are divided by the Inyoka Fault, a major thrust fault that was reactivated by dextral shearing. The two facies of Fig Tree and Moodies strata appear to be laterally gradational. The Moodies Group, a 2800+ m sequence of predominantly lithic arenite, sublitharenite, and arkosic arenite was studied in four large, structurally isolated blocks in the north-central part of greenstone belt: the Moodies Hills, Saddleback Syncline, Maid of the Mist Mountain Syncline, and Powerline Road Syncline. The northern facies was derived from two provenances: the underlying greenstone and a granitic/metamorphic terrane. The crystalline terrane may have been a part of the Ancient Gneiss Complex. South of the Inyoka Fault, strata are solely composed of material eroded from the greenstone belt. The upper part of the Moodies Group was probably derived from reworked, cannabalized, older Moodies strata. Petrographic and stratigraphic evidence suggests that the Moodies Group was deposited in a foreland basin formed by thrust faulting and uplift of the greenstone belt in the southeast. The depositional basin deepened to the north. Multiple stages of large-scale lateral tectonics affected the Barberton greenstone belt. Thrust faulting and nappe forming throughout the belt (D$\sb{\rm 1\ and\ 2}$) accompanied deposition of the Fig Tree Group. Further thrust faulting and folding (D$\sb3$) following deposition of the Moodies. After emplacement of the Kaap Valley pluton (D$\sb4$), the area was further disrupted by predominantly dextral folds and faults (D$\sb5$). The final stage of structural development resulted in approximately north-south striking, vertically dipping faults (D$\sb6$).