The caldera of Payún Matrú volcano, southeastern Mendoza province, Argentina, a result of magma mixing

LLAMBÍAS, EDUARDO JORGE; HERNANDO, IRENE RAQUEL

Malargue, Mendoza

Simposio; ICES (International Center for Earth Sciences); 2005

CNEA

Payún Matrú is a Pleistocene volcano located in southeastern Mendoza province (36°25’S, 69°12’W). It is a typical volcanic dome crowned by a small caldera with a diameter of 8 km. At its base the diameter is 16 km and its summit rises 1.5 km above the ground level. With a mainly trachytic composition, it consists of (1) a large pre-caldera volcanic dome, (2) trachybasaltic to trachytic ignimbrites related to caldera collapse and (3) post-caldera lava flows in which trachyte dominates over trachybasalt. The volcano is surrounded by a large number of monogenic cones and lava flows, all of them of olvine basalt composition. Their occurrence, as both pre- and post-caldera eruptions, indicates that they were contemporaneous with the evolution of Payún Matrú volcano. Most of the cones are arranged along E-W La Carbonilla fault that cuts the volcano through its center (Figure 1). However, basaltic cones are absent within the area of the caldera, presumably because of the basaltic magma having been trapped into the trachytic magma chamber. In relation to this, the composition of both the caldera collapse ignimbrites and the first lava flows erupted through the ring fractures are intermediate between basalt and trachyte, which support the hypothesis of magma mixing.