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Ilhabela

Geological Origin

Brazil Tours / Geology – The geological setting is one of the highlights of any tour on Ilhabela. The archipelago of São Sebastião, including the Ilhabela island, is emplaced into the central part of the Ribeira Belt (Northern Mantiqueira Province).

Similar to Itatiaia in the north, the archipélago is composed of intrusive bodies which were formed 80 million years ago, during the Upper Cretaceous by alkaline magmatism, probably caused by the deflected melts of the Trindade Mantle Plume. In that time, molten alkaline rock (magma) intruded into the Earth's crust, where it slowly cooled and crystallized, forming ingeous rocks.

As this happened below the surface these rocks are called intrusive or plutonic rocks. Over time, the surrounding, softer sedimentary rock eroded away making these plutonic rocks visible for us. Ilhabela is composed of four of these plutons (stocks), named Canas, Serraria, São Sebastião and Mirante. They are mainly formed by syenitic rock which is principally composed of alkali feldspar a rock - forming silicate (tectosilicate) mineral which makes up as much as 60% of the Earth's crust – Geotravel & tours / Brazil.

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