San Antonio beach
The chaos of a subduction channel
This beach, located on the north-east edge of the town of O Porto de Espasante, is like a natural laboratory: the Somozas Mélange exposes a matrix of serpentinites that includes a large tectonic block of crystalline marble, which may contain microfossils. The serpentinites represent a mantle subduction channel, formed on a plate that was sinking towards the mantle in a peri-Gondwanan oceanic domain. Fragments of the descending plate were torn away to form a gigantic breach between the serpentinites, a tectonic mélange that mixes materials of very diverse origins. The tectonic blocks detached in the active subduction channel are subject to an upward flow dynamic. The sight of crystalline marbles embedded in the matrix of serpentinites amazes and fascinates both geology experts and laymen alike. This outcrop is unique in the Iberian Peninsula and probably in the whole of Europe. It is visited by geology students every year.
The tides reveal this geological puzzle at every low tide, inviting visitors to touch the rocks that once stood at the boundary between plates. Although their beauty is immediately apparent, a visit to this site is one of those that really requires the services of a geological guide, who will help us to understand and enjoy the history of the formation of this amazing natural treasure.
Photo: Creative Commons
