The Sea Point contact, Cape Town, South Africa: a geological site made famous by Charles Darwin's visit

Abstract

Abstract The Sea Point intrusive contact on the Atlantic coast, South Africa, is a site of historical significance that continues to be useful for studying the details of granite–wall rock relationships, some of which have not been properly evaluated yet. At a time when the origin of granites was still controversial, and the concept of contact metamorphism not yet properly developed, Charles Darwin visited the Sea Point contact to make some geologically important observations. He concluded that the granite originated as a magma deep in the Earth, intruded a country rock of sedimentary origin and changed this country rock's appearance owing to the thermal action of the hot granite magma. He also contemplated the long periods of time required to expose the rocks by erosion. Besides its historic value, the Sea Point heritage site exposes unique features giving rare insights into the physical and chemical interaction between intruding granitic magma and a regionally low-grade metamorphosed sedimentary sequence. Questions regarding mechanisms of magmatic emplacement may be answered from this outcrop, including emplacement dynamics and interrelationships of various granitic phases, pre- versus syn-intrusive deformation and metamorphism, assimilation of country rock by a granitic magma and the origin of feldspar phenocrysts seemingly ‘stranded’ in the country rock.