The Proterozoic intrusion and deformation of deep crustal 'sills' along the south coast of Natal.

C. J. Talbot, G. H. Grantham

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18 Citations (Scopus)

Abstract

Structural observations reveal that a vertical structural sequence of ortho- and paragneisses approx 1300 m thick is involved in the well-exposed 8-km coastal section from Port Edward to Palm Beach. The oldest rocks are metapelites (with thin interbedded calc-silicates) which were flowing subhorizontally in recumbent folds until the garnetiferous sill-like Glenmore granite was emplaced at the highest structural level exposed. At unknown intervals thereafter thin sill-like magmatic bodies of various compositions were emplaced at various structural levels. These bodies include in turn: Munster metabasites, the Palm Beach leucogranite, the Port Edward enderbite and the Portobello graphic granite. The relative age of Nicholson's Point granite is not clear but it postdates the metabasites and may predate the Port Edward enderbite. Both the metabasites and the Port Edward enderbite accumulated in pockets beneath the Glenmore granite before fracturing paths up through the Glenmore granite. The second regional strain involved gentle folding after the emplacement of the Palm Beach leucogranite at the lowest structural level exposed. After the emplacement of the Portobello graphic granite this deformation developed into a regional simple shear which imparted a planar foliation to the igneous rocks. The second regional foliation eventually became ubiquitous to all the orthogneisses. The paper concludes with speculation on how magmas with a wide range of composition could form deep crustal sill-like sheets and not rise to higher structural levels as large plutons. -A.W.H. Dept. of Geology, Uppsala Univ., Uppsala, Sweden.

Original languageEnglish
Pages (from-to)520-538
Number of pages19
JournalSouth African Journal of Geology
Volume90
Issue number4
Publication statusPublished - 1987

ASJC Scopus subject areas

  • Geology

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