El Rojo Sur is a monogenetic volcano in the Andes, in the form of a cone.
It is similar to El Rojo Norte 260 kilometres (160 mi) farther north. A mafic andesite lava flow was erupted from the 100 metres (330 ft) high cone that also features red scoria. Ages obtained by potassium-argon dating are 2.93±0.13, 3.4±0.4 and 3.23±0.12 mya.
Rojo Sur erupted undifferentiated mafic magmas. Its lead isotope composition is different from the composition of that segment of the Andes, being non-radiogenic. This isotope signature may be the effect of assimilation of deeper basement rocks during magma formation. In addition, the magmas are rich in incompatible elements.
References
El Rojo Sur Wikipedia(Text) CC BY-SA