Thermo-mechanical intrusion-wall rock interaction and granite emplacement mechanisms of the peninsula granite at the Sea Point contact, Cape Town, South Africa
Loading...
Date
2025
Journal Title
Journal ISSN
Volume Title
Publisher
Elsevier Ltd
Abstract
The Sea Point contact, Cape Town, South Africa exposes the intrusive contact between the ∼540 Ma S-type Peninsula Granite and the ∼560–555 Ma metasedimentary rocks of the Malmesbury Group of the Pan-African Saldania Belt. The western Saldania Belt was subjected to low-grade greenschist facies metamorphism and deformation during the ∼560–540 Ma Saldanian orogeny. The Peninsula Granite intruded as a series of numerous granite sheets which made use of the pre-existing country rock anisotropy in order to propagate. These are the steeply dipping S0 bedding due to folding during the Saldanian orogeny, and a steeply dipping axial planar S2 foliation to the F2 folds developed during the dominant D2 deformation. Magma overpressure relative to tensile stresses in the country rock and regional NE-SW-orientated compressional stresses allowed intrusion of variably crystal-laden magma along the anisotropies. The granitic sheets are commonly concentrated in the hinge zones of F2 folds, where structural traps facilitated magma “trapping.” Filter pressing at the tail of the magma-filled hydrofracture caused closing during magma through-flow resulting in the entrapping of magmatic crystals, most notably K-feldspar megacrysts, in the wall rock as well as xenoliths dislodged during magma infiltration and stoping, and possibly magma flow. Magma stresses have brought about the alignment of K-feldspar megacrysts as well as the long axes of xenoliths parallel to the orientation of granite sheets and wall rock septa in the complex lit-par-lit zone and adjacent to the contact.
Description
Keywords
Cape Granite Suite, Intrusion Along Country Rock Fabric, Late Syn-Tectonic Intrusion, Multiple Granite Sheet Propagation, S-Type Granite
Citation
Mhlanga, M., Bailie, R. and Reinhardt, J., 2025. Thermo-mechanical intrusion-wall rock interaction and granite emplacement mechanisms of the Peninsula granite at the Sea Point contact, Cape Town, South Africa. Journal of Structural Geology, p.105513.