18°28′S 69°12′W / 18.467°S 69.200°W[1] El Rojo Norte is a cinder cone in the Andes,[2] constructed on top of volcano debris in the Lauca basin.[1]
The cone is 150 metres (490 ft) high[3] and 300 metres (980 ft) wide at its foot. Its profile has been reduced by erosion;[1] the cone sits on an andesitic mound.[4] A lava flow containing mafic andesite is associated with the cone.[3] Phreatomagmatic deposits are also found.[4]
The cone is formed by reddish scoria.[1] Its rocks are basaltic andesite. It was erupted 3.1 ± 0.2 million years ago on the basis of potassium-argon dating.[2] Other dates are 3.05 ± 0.22, 3.35 ± 0.16 and 2.34 ± 0.16 mya. Which age is correct is unclear, but the cone is partly buried by the 2.72 mya old Lauca-Pérez ignimbrite indicating that it's older than this ignimbrite.[3]
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