The extent and volcanic structures of the Quaternary Andahua Group, Andes, southern Peru

Abstract

The Quaternary Andahua volcanic group in southern Peru has been studied by present author since 2003. The Andahua Group stretches out at intervals within an area, which is 110 km long and 110 km wide. Seven regions bearing centres of volcanic eruptions have been distinguished: the Valley of the Volcanoes, Antapuna, Rio Molloco, Laguna Parihuana, Rio Colca Valley, Jaran, and Huambo. The Valley of the Volcanoes, where the Andahua Group was identified for the first time, contains the biggest variety of volcanic landforms. The valley is covered by a nearly 60 km long, continuous cover of lava flows. 165 individual eruption centres of the Andahua Group were distinguished including apparent pyroclastic cones, 50–300 m high, and usually smaller lava domes and fissure vents. Domes, eruptive vents and lava craters greatly outnumber pyroclastic cones. Most commonly, lava flows start from lava domes or craters. Small domes are often aligned along their feeding fissures. Lava domes and pyroclastic cones of the Andahua Group are aligned mainly along N–S and WNW–ESE trending fault systems. Projection points of the analysed Andahua lavas on the TAS diagram concentrate in the lower part of the trachyandesite field, entering also the basaltic trachyandesite or trachyte/trachydacite fields.