Calderas associated to the Miocene Pire Mahuida Volcanic Field, Northern Patagonia, Argentina.

SALANI, F M,; CHERNICOFF, C.J.; REMESAL, M

Vulsini

Workshop; 4th International Workshop on Collapse Calderas; 2012

IAVCEI

In northern Patagonia (ca.42º S), in between the eastern end of the Andean arc and the beginning (68º 30´W) of the intraplate Somún Curá Plateau, it is exposed a volcanic field of 800 km2 and approximately 100 km3 of mainly acidic rocks, the most common facies being pyroclastic and lavic. Subordinate in volume, basaltic flows overlie the sequence of acidic rocks. This sequence makes the bulk of the sierra Pire Mahuida. A regional tectonic control is evidenced by the alignment of several Miocene bimodal volcanic complexes along a WNW-ESE trend, including the volcanic field studied herein. This field was built through several magmatic stages from 21 to 18 Ma, and it is mainly related to two volcanic structures and minor fissural vents, i.e. a- A series of rhyolite lava domes following a sub-circular pattern define most of the main caldera boundaries. Airborne magnetic and gamma-ray spectrometry surveys allow determining a sub-circular structure roughly at 42°05´48´´S/68°40´43´W, slightly displaced by a NE-SW fault. This feature would complete the eastern border of the elliptic shaped caldera whose major and minor axes are 16 and 10 km, respectively. b-The second and smaller caldera is located to the east of the previous one. It is circular, its diameter being approximately 7 km. Its center is occupied by a small pond referred to as Laguna de los Flamencos. There are compositional differences between the products of both centres that can express their different ages and evolutionary stages. Related to the bigger caldera, lava domes and ignimbrites constitute a calc-alkaline sequence that is relatively older than the one corresponding to the Laguna de los Flamencos Caldera. The emissions of the latter caldera are lava flows and subordinate pyroclastic flows, with more alkalic affinities.