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A 3.2 Ga magmatic arc preserving 50 Ma of crustal convergence in the Barberton terrain, South Africa

Abstract : The tectonic setting, sources and conditions of melting of Archean tonalite-trondhjemite-granodiorite (TTG) rocks, the main building blocks of all Archean continental kernels, are a matter of ongoing debate. In the 3.5- 3.1 Ga Barberton granitoid-greenstone terrain in South Africa, the main phase of terrane accretion in the greenstone belt (D2), associated shortlived, but voluminous TTG plutonism, and high-P low-T metamorphism in the southern TTG gneiss terrain of the Stolzburg domain are all recorded at 3.23 Ga. While terrane accretion and the deep-crustal burial of parts of the granitoid-greenstone terrane are interpreted to have occurred during subduction-driven processes in an arc-trench setting, the existence of a longlived magmatic arc, a tell-tale sign of crustal convergence preceding the final collisional events has, to date, not been identified. We document field and geochronological results from the hitherto poorly documented Badplaas domain, located to the immediate west of the high-grade Stolzburg domain south of the Barberton greenstone belt. The Badplaas domain is made up of a variety of compositionally and texturally distinct, variably gneissose trondhjemites. Multiple intrusive relationships between different phases are common and large parts of the Badplaas domain are developed as heterogeneous, intrusive breccias. The distinction of regional-scale lithotypes in this magmatic terrain has enabled us to constrain the relative timing of emplacement of the main TTGs. Geochronological work on the five main TTG phases reveals that the Badplaas domain was assembled over a period of ca. 50 Ma between ca. 3290 and 3240 Ma. We interpret the Badplaas domain to record 50Ma of convergence-related TTG plutonism, located above the NW-dipping subduction zone. The ages of this plutonism overlap with the sedimentation of 3260-3225 Ma fore- or back-arc deposits preserved in sediments of the Fig Tree Group in the greenstone belt. The results indicate that the different tectonostratigraphic domains of the Barberton granitoid-greenstone terrain may well preserve an almost complete inventory of a Mesoarchaean arc-trench system.
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Submitted on : Wednesday, July 25, 2007 - 10:57:07 AM
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  • HAL Id : insu-00165190, version 1

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A. Kisters, R. Belcher, Marc Poujol, G. Stevens, Jean-François Moyen. A 3.2 Ga magmatic arc preserving 50 Ma of crustal convergence in the Barberton terrain, South Africa. American Geophysical Union (AGU) Fall Meeting, Dec 2006, San Francisco, United States. ⟨insu-00165190⟩

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