Thrust exhumation of the Neoarchean ultrahigh-temperature Southern Marginal Zone, Limpopo Complex: Convergence of decompression-cooling paths in the hanging wall and prograde P-T paths in the footwall

Van Reenen D.D.; Smit C.A.; Perchuk L.L.; Roering C.; Boshoff R.

Thrust exhumation of the Neoarchean ultrahigh-temperature Southern Marginal Zone, Limpopo Complex: Convergence of decompression-cooling paths in the hanging wall and prograde P-T paths in the footwall

Date

2011

Authors

Van Reenen D.D.

Smit C.A.

Perchuk L.L.

Roering C.

Boshoff R.

Abstract

Integrated structural, metamorphic, and geochronological data indicate that the evolution of the Southern Marginal Zone (SMZ) of the Limpopo Complex of southern Africa was controlled by a single Neoarchean high-grade tectono-metamorphic event. The exhumation history refl ected by the high-grade rocks is determined by their location relative to the contact with the low-grade rocks of the Kaapvaal Craton. Exhumation of granulites far north from this contact is recorded by a decompressioncooling (DC) pressure-temperature (P-T) path linked to steep southward-verging thrusts related to the Hout River Shear Zone. This P-T path traverses from P ∼8 kbar, T ∼825 °C to P ∼5 kbar, T ∼550 °C and refl ects exhumation of the SMZ in the interval ca. 2.68-2.64 Ga. P-T paths for granulites close to this contact are characterized by a distinct infl ection at P ∼6 kbar, T ∼700 °C that exhibits near-isobaric cooling (IC) to T ∼580 °C. The IC stage is linked to low-angle, out-of-sequence, southward-verging thrusts that developed in the interval 2.63-2.6 Ga. The thrust-controlled exhumation of the SMZ furthermore is demonstrated by the convergence at P ∼6 kbar, T ∼700 °C of DC P-T paths in the hanging wall with prograde P-T loops in the footwall of the steeply southward-verging Hout River Shear Zone, and by the establishment of a retrograde isograd and zone of rehydrated granulites in the hanging wall derived from the dehydration of the low-grade rocks in the footwall. A composite deformation-pressure-temperature-time (D-P-T-t) diagram provides evidence in support of a tectonic model for the evolution of the Limpopo Complex that involves early crustal thickening and peak metamorphic conditions followed by doming and diapirism related to gravitational redistribution mechanisms. © 2011 The Geological Society of America.

Citation

Memoir of the Geological Society of America
207
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