A review of the pressure–temperature–time evolution of the Limpopo Belt: Constraints for a tectonic model

Abstract

Published literature argues that the Limpopo Belt can be subdivided into three zones, each with a distinctive geological character and tectono-metamorphic fingerprint. There are currently two contrasting schools of thought regarding the tectono-metamorphic evolution of the CZ. One camp argues that geochronological, structural and prograde pressure-temperature (P-T) evidence collectively indicate that the CZ underwent tectono-metamorphism at ca. 2.0 Ga which followed a clockwise P-T evolution during a transpressive orogeny that was initiated by the collision of the Kaapvaal and Zimbabwe cratons. Deformation and metamorphism consistent with this scenario are observed in the southern part of the NMZ but are curiously absent from the whole of the SMZ. The opposing view argues that the peak metamorphism associated with the collision of the Kaapvaal and Zimbabwe cratons occurred at ca. 2.6 Ga and the later metamorphic event is an overprint associated with reactivation along Archean shear zones. Post-peakmetamorphic conditions, which at present cannot be convincingly related to either a ca. 2.6 or 2.0 Ga event in the CZ reveal contrasting retrograde paths implying either nearisothermal decompression and isobaric cooling associated with a 'pop-up' style of exhumation or steady decompression-cooling linked to exhumation controlled by erosion. Recent data argue that the prograde evolution of the ca. 2.0 Ga event is characterised by isobaric heating prior to decompression-cooling. Contrasting P-T paths indicate that either different units exist within the CZ that underwent different P-T evolutions or that some P-T work is erroneous due to the application of equilibrium thermobarometry to mineral assemblages that are not in equilibrium. The morphology of the P-T path(s) for the ca. 2.6-2.52 Ga event are also a matter of dispute. Some workers have postulated an anticlockwise P-T evolution during this period whilst others regard this metamorphic event as following a clockwise evolution. Granitoid magmatism is broadly contemporaneous in all three zones at ca. 2.7-2.5 suggesting a possible causal geodynamic link. P-T contrasts between and within the respective zones prevent, at present, the construction of a coherent and inter-related tectonic model that can account for all of the available evidence. Detailed and fully-integrated petrological and geochronological studies are required to produce reliable P-T-t paths that may resolve some of these pertinent issues.

Meso-Archaean and Palaeo-Proterozoic sedimentary sequence stratigraphy of the Kaapvaal Craton

“…Contemporaneously, or j ust prior to the deposition of the Transvaal Supergroup, the northernmost section of the Kaapvaal Craton was involved in an orogenic event, traditionally known as the 'Limpopo Orogeny' (see Rigby et al, 2008a and references therein). Rocks from the Southern Marginal Zone of the Limpopo Mobile Belt represent high-grade metamorphic equivalents of the adj acent granite-greenstone terranes that comprised the Kaapvaal Craton (e.g.…”

Conflicting P–T paths within the Central Zone of the Limpopo Belt: A consequence of different thermobarometric methods?

“…Musina) were affected by polymetamorphic evolution. However, pertinent contradictions in the morphology of the Neoproterozoic and Paleoproterozoic P-T paths, prevents at present, the construction of a coherent and inter-related tectonic model (Rigby et al, 2008a).…”

“…1) is an extensive high-grade terrane that can be subdivided into three zones, each with a distinctive geological character and tectono-metamorphic fingerprint (Rigby et al, 2008a). The Northern Marginal Zone (NMZ) is separated from the Zimbabwe Craton by a southwarddipping ductile shear zone known as the North Limpopo Thrust Zone (e.g.…”

“…Harris and Holland, 1984;Droop, 1989;Hisada and Miyano, 1996;Jaeckel et al, 1997;Holzer et al, 1998;Kröner et al, 1998Kröner et al, , 1999Smit et al, 2001;Van Reenen et al, 2004;Zeh et al, 2004;Zeh et al, 2005a,b;Hisada et al, 2005;Boshoff et al, 2006;Zeh et al, 2007;Rigby et al, 2008b;Gerdes and Zeh, 2009;Van Reenen et al, 2008;Perchuk et al 2008) who have defined different P-T paths. This has ultimately led to a great deal of controversy surrounding the tectonic evolution of the Limpopo Belt (Rigby et al, 2008a).…”

Comment on “Ultrahigh temperature granulites and magnesian charnockites: Evidence for the Neoarchean accretion along the northern margin of the Kaapvaal craton” by Rajesh et al.

“…Indeed, the general consensus about the evolution of this terrane is that it underwent a single tectono-metamorphic event at ∼2.7 Ga, ascribed to collision between the Kaapvaal and Zimbabwe Cratons (Barton et al, 2006;Eglington and Armstrong, 2004;Kröner et al, 2000;Kreissig et al, 2001;Roering et al, 1992;Rigby et al, 2008;Stevens and van Reenen, 1992a,b;Zeh et al, 2009). The study of the Limpopo belt, and in particular the SMZ, is therefore of primary interest to unravel the tectonic regimes that prevailed back in the late-Archean and their evolution throughout Earth history.…”