Structural analysis and implicit 3D modelling of high-grade host rocks to the Venetia kimberlite diatremes, Central Zone, Limpopo Belt, South Africa. (May 2016)

• Record Type: Journal Article
• Authors: Basson, I.J.; Creus, P.K.; Anthonissen, C.J.; Stoch, B.; Ekkerd, J.
• Is Part Of: Journal of structural geology. Volume 86(2016:May)
• Page Start: 47
• Page End: 61
• Publication Date: 2016-05
• Subjects: Venetia Mine -- Limpopo Belt -- Central Zone -- High grade -- Implicit -- 3D modelling; Geology, Structural -- Periodicals; Géomorphologie structurale -- Périodiques; Geology, Structural; Periodicals; 551.805
• DOI: 10.1016/j.jsg.2016.03.002
• Languages: English
• ISSNs: 0191-8141

Abstract

Abstract: The Beit Bridge Complex of the Central Zone (CZ) of the Limpopo Belt hosts the 519 ± 6 Ma Venetia kimberlite diatremes. Deformed shelf- or platform-type supracrustal sequences include the Mount Dowe, Malala Drift and Gumbu Groups, comprising quartzofeldspathic units, biotite-bearing gneiss, quartzite, metapelite, metacalcsilicate and ortho- and para-amphibolite. Previous studies define tectonometamorphic events at 3.3–3.1 Ga, 2.7–2.5 Ga and 2.04 Ga. Detailed structural mapping over 10 years highlights four deformation events at Venetia. Rules-based implicit 3D modelling in Leapfrog Geo™ provides an unprecedented insight into CZ ductile deformation and sheath folding. D1 juxtaposed gneisses against metasediments. D2 produced a pervasive axial planar foliation (S2 ) to isoclinal F2 folds. Sheared lithological contacts and S2 were refolded into regional, open, predominantly southward-verging, E–W trending F3 folds. Intrusion of a hornblendite protolith occurred at high angles to incipient S2 . Constrictional-prolate D4 shows moderately NE-plunging azimuths defined by elongated hornblendite lenses, andalusite crystals in metapelite, crenulations in fuchsitic quartzite and sheath folding. D4 overlaps with a: 1) 2.03–2.01 Ga regional M3 metamorphic overprint; b) transpressional deformation at 2.2–1.9 Ga and c) 2.03 Ga transpressional, dextral shearing and thrusting around the CZ and d) formation of the Avoca, Bellavue and Baklykraal sheath folds and parallel lineations. Highlights: The paper correlates deformational events at Venetia Mine with the surrounding Central Zone of the Limpopo Belt. A robust mapping dataset and downhole orientated drillcore provide rare insight into ductile deformation and sheath folding in the Central Zone. An implicit 3D model accurately reproduces the 3D geometry of upper-amphibolite to granulite facies, complexly deformed country rocks.