The volcanic outcrop of Cerro del Hoyazo is a pretty special place, looking rather like a lunar crater. But despite it being caled Crater del Hoyazo by many sources, this isn't a volcanic crater, or a meteorite crater - instead the cliffs forming the rim of the bowl are 10 million year old coral reefs. At the time, many of the young Betic basins were below sea level, with sub-marine volcanic eruptions around the Cabo da Gata and Carboneras regions. The dacite which erupted here was highly viscous, forming a squat dome whicjh would have sat a few tens of metres above the sea floor, proviging a light and stable base for the corals to grow. But that isn't why El Hoyazo is so special - the magma was sourced from the lower crust (over 30 km deep) where high-pressure minerals are stable. In addition to xenoliths of garnet and sillimanite gneiss there are primary garnet phenocrysts which grew from the magma. A great place to collect gem-quality garnets and other semi-precious stones as well as to understand the dynamics of a complex corner of the Betic mountain chain.
6 сен 2024
