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1 School of Geological Sciences, Kingston University, Kingston-upon-Thames, Surrey KT1 2EE, UK
2 Department of Geology, University of Zimbabwe, PO Box MP167, Mount Pleasant, Harare, Zimbabwe
Recent models of the structural evolution of the Zimbabwe Archaean craton have stressed the role of WSW-trending sinistral strike-slip shears in accommodating the WSW-directed extrusion of crust thickened in response to NNW-SSE compression and shortening. This relationship between crustal thickening and crustal extrusion is analogous to the structural response of Tibetan crust to the Tertiary collision of India and Asia. We have re-examined many of the structures of the Zimbabwe craton and find the extrusion model largely untenable. Instead, a conjugate set of ESE-striking dextral shears and NNE-striking sinistral shears have been identified, on both regional and outcrop scale, which apparently reflect part of the structural response of the Zimbabwe crust to NNW-SSE shortening resultant from collision of the craton with the Central zone of the Limpopo belt to the south. This collision, at about 2.58 Ga, post-dated the 2.68 Ga aged collision between the Central zone and the Kaapvaal craton which represents the Limpopo orogeny sensu stricto. The suture between the Zimbabwe craton and the Central Zone was re-activated at c. 2.0 a as a major intracontinental dextral strike-slip shear zone. Partial melting of the lower crust at c. 2.58 Ga accompanied thickening of the Zimbabwe Archaean crust following collision with the Central zone. The conjugate shears deform fabrics that date from that collision, are synchronous with, or post-date, granite emplacement and may have acted as conduits for transport of the Chilimanzi monzogranitic magmas from the lower to the upper crust. Contacts between greenstone belts and granites are commonly sheared. These marginal shear zones are often parallel to the regional conjugate shears, although local variations in stress trajectories imposed by pluton emplacement may result in them being non-parallel to the major shears.
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