Geology of Ecuador

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Geology in Ecuador is built from very old rocks plus many pieces of crust that joined together over millions of years, creating the Andes and other rocky features.

Most of the country sits on ancient Precambrian basement rocks. The Piedras Group in El Oro Province on the western slope contains greenschist and amphibolite, with quartz-sericite schist and quartzite. These rocks are about 743 million years old and show signs of multiple metamorphic events.

In the north-central region, the Peltetec-Portovelo fault marks the boundary between the old South American craton and the Amotape-Chaucha terrane. This area partly subducted beneath a Mesozoic volcanic arc, helping thread together different pieces of crust.

The El Oro metamorphic complex includes Triassic mafic and granitoid rocks, and the Raspas metamorphic complex contains higher-grade rocks like eclogite, blueschist, and amphibolite. This section was once pushed back into the mantle but later emerged with tectonic activity.

During the breakup of the supercontinent Gondwana in the Triassic, Ecuador saw S-type granite plutons form, followed by calc-alkaline batholiths in the Jurassic. Later, Jurassic and Cretaceous oceanic basalts were accreted to the continental edge as a separate terrane around 130 million years ago, creating a belt of basalt, diabase, tuff, and metasedimentary rocks that runs north–south through the country.

In the Cenozoic, the Andes rose extensively. Volcanic rocks differ between the eastern and western ranges: the east mainly has rhyolite andesite and andesite-dacite, while the west is richer in andesite and plagioclase-rich rocks. This variety is linked to the melting of garnet-bearing amphibolites under hydrous conditions.

Most of Ecuador’s mineable deposits are epithermal gold or porphyry copper, hosted in Paleogene rocks from the Eocene to the Miocene. These deposits may have originated from enriched mid-ocean ridge basalt (MORB). Compared with neighboring countries, copper deposits are relatively small. Explanations include compression that limited magma chambers about nine million years ago or limited surface exposure of deposits.