The Saldanha Bay Volcanic Complex: Clarifying the Cambrian geology of the Postberg – Saldanha Area, West Coast, South Africa

Abstract

Re-examination of the field relations and thin-section petrography of the rocks presently known as the Saldanha quartz porphyry show that the entire sequence, on the northern side of Saldanha Bay on the West Coast of South Africa, is pyroclastic in character. Thus, the area around Saldanha Bay is a large, volcanic complex consisting of the Postberg and Saldanha eruption centres. We propose that this complex, of Cambrian age, should be named the Saldanha Bay Volcanic Complex. The low-Ti Saldanha Ignimbrite and the high-Ti Jacobs Bay Ignimbrite are confined mainly to the Saldanha centre (probably a volcanic cauldron) and represent two chemically distinct series. The Jacobs Bay Ignimbrite magmas were emplaced throughout the eruptive history of the Saldanha centre but overly the uppermost sections of the more felsic Saldanha Ignimbrite. Small amounts of the Jacobs Bay and Saldanha Ignimbrites are also present in the Postberg centre but the geochemical data suggest that this structure is mainly filled with the more felsic and chemically distinctive Plankiesbaai and Tsaarsbank Ignimbrites.