Tectonic history of the Barberton greenstone belt, South Africa: 490 million years of Archean crustal evolution

Abstract

Rocks of the 3570–3080 Ma Barberton greenstone belt record a geological history of at least 490 million years (m.y.), and were affected by regional thermal perturbations for over 1500 m.y. Small tectonic wedges of 3570–3511 Ma schistose tonalite are the oldest rocks yet recognized, but little is known about their tectonothermal history. The earliest, well‐recognized tectonothermal events (3490–3450 Ma) represent mid‐ocean ridge‐like processes. These were followed by two periods of arc‐related and trench‐related processes, separated by ∼160 m.y.; the first (3445–3416 Ma) recording an intraoceanic suprasubduction‐like environment and the second, (3260–3225 Ma) intra‐arc and interarc‐like processes, culminating in arc amalgamation. Accretion‐like convergent processes dominated between ∼3230 Ma and 3080 Ma, overlapping with the assembly of the Kaapvaal craton. At 3080 Ma the Barberton greenstone belt experienced a sudden shift from dominantly convergent to dominantly transtensional tectonism and was mineralized with mesothermal gold along a regional shear system. Soon afterward, transtension became distributed across the entire Kaapvaal craton, heralding the onset of formation of the Witwatersrand basin by ∼3070 Ma.

Determining accurate temperature–time paths from U–Pb thermochronology: An example from the Kaapvaal craton, southern Africa

“…A period of major convergent tectonism and inferred terrane accretion ca. 3.23 Ga imposed the dominant NE-SW structural trend of the belt (Jackson et al, 1987;de Ronde and de Wit, 1994;Heubeck and Lowe, 1994;Kamo and Davis, 1994;Lowe, 1999;de Ronde and Kamo, 2000), and may be responsible for the high-grade metamorphism in the plutonic complexes at the south of the belt (Dziggel et al, 2002;Stevens et al, 2002;Kisters et al, 2003;Diener et al, 2005). Following NW-SE convergent tectonism, there was a transition towards NE-SW strike-slip to transtensional faulting through at least the central belt (Jackson et al, 1987;de Ronde and de Wit, 1994;de Ronde and Kamo, 2000).…”

“…3.23 Ga orogenesis (Kisters et al, 2003) or $100 Myr later contemporaneous with ca. 3.11 Ga granitic intrusions (Jackson et al, 1987;de Ronde and de Wit, 1994;Kamo and Davis, 1994;Westraat et al, Fig. 2.…”

“…It is widely documented that following ca. 3.23 Ga convergence and thrust-faulting within the greenstone belt, the primary kinematics of the area switched to transtension and extension (Jackson et al, 1987;de Ronde and de Wit, 1994;de Ronde and Kamo, 2000). A proposed mechanism for this transition is extensional collapse of the ca.…”

“…A proposed mechanism for this transition is extensional collapse of the ca. 3.23 Ga orogen (Jackson et al, 1987;de Ronde and de Wit, 1994;Kamo and Davis, 1994;Kisters et al, 2003), though the timing is poorly constrained. De Ronde et al (1991) document movement on one such shear zone in the BGB near the Kaap Valley pluton to have occurred between 3126 ± 21 and 3084 ± 18 Ma by dating zircon and rutile from a syntectonic porphyry.…”

Evolution of the Earth: Plate Tectonics Through Time

“…It cuts syntectonic basins of the Moodies group (de Ronde and de Wit, 1994;Huebeck and Lowe, 1994). Like the San Andreas Fault, motion is parallel to the gross strike; piercing points are not recognized in spite of detailed mapping (de Ronde and de Wit, 1994;de Ronde and Kamo, 2000).…”