The Granite Boulders of St Helena Bay

Since a kid, I’ve always been fascinated by these big, warm, round, friendly boulders, often extending into the sea. They present almost an other-worldly, lunar feel to me. I decided to research what turned out to be The Cape Granite Suite.

St. Helena Bay's Geological Evolution:

St. Helena Bay, situated on South Africa's West Coast, showcases a rich geological history spanning billions of years. The Earth's formation, approximately 4650 million years ago, from cosmic dust following the Big Bang, set the stage for its dynamic evolution. Rapid cooling led to the emergence of continents around 4000 million years ago, marking the beginning of Earth's geological transformation.

The oldest known rocks, approximately 3800 million years old, provide insights into Earth's early geological processes. South Africa's geological story traces back to around 3500 million years ago, with the formation of the Kaapvaal Craton, the continent's foundational bedrock. Over time, subsequent geological activities, including the amalgamation of smaller continental blocks to form Gondwanaland, shaped South Africa's diverse geological landscape.

A typical granite outcrop.

Around 550 million years ago, during the collision between South America and South Africa, the Cape Granite Suite intruded the Malmesbury sediments, forming the Vredenburg Granite underlying St. Helena Bay. This intrusion occurred amidst continental drift, resulting in the melting of South American rocks beneath the South African continent. The molten rocks produced the granite that intruded the Malmesbury sediments, leaving behind xenoliths along the coast of St. Helena Bay as evidence of the assimilation process.

St. Helena Bay exhibits various stages of assimilation of the Malmesbury rocks, offering geological proof of the granites' molten origins. The region displays approximately five types of granite intrusions, identifiable through conspicuous intrusive contacts along the coast.

In addition to granite, St. Helena Bay boasts a diverse array of geological features, including limestones, coastal dunes, raised beaches, phosphates, and dolerite dykes. The area's mineral wealth has attracted mining activities targeting gypsum, phosphate, kaolin, building stone, and sand.

Beyond its shores, St. Helena Bay's geological wonders extend to neighbouring areas such as Vredenburg and Paternoster, offering a fascinating exploration of the region's geological heritage.

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