Choiyoi Group

The group bears evidence of bimodal-style volcanism related to an ancient subduction zone that existed along the western margin of the supercontinent Gondwana.

[1][2] The Choiyoi Group has a large areal extent through western Argentina and parts of Chile, covering at least 200,000 square kilometres (77,000 sq mi), but probably around 500,000 square kilometres (190,000 sq mi).

During the Permian, the zone of arc magmatism moved 350 kilometres (220 mi) inland from the Chilean Coast Range, reaching San Rafael about 280 million years ago.

[2] In the Lower Choiyoi Group basaltic lava flows, andesites and breccias are common.

[2] Volcanic rocks of the Lower Choiyoi in La Pampa and westernmost Buenos Aires Province have shoshonitic and syenitic features.