Volcanic facies of the debris avalanche deposit of Tata Sabaya Volcano, Central Andes.

Abstract

Debris avalanches

associated with partial sector collapse of volcanic edifices are common phenomena in the evolution of a volcano.

These flows are formed by edifice instability, which could be due to several factors such as the presence of hydrothermally

altered areas, climatic changes, earthquakes, shallow magma intrusions (cryptodomes and/or dykes) and/or fault

activity beneath or close to the volcano. The final product of this avalanche flow, known as debris avalanche deposit

(DAD) shows typical hummocky and closed drainage morphologies. More than 14 volcanic centers of the Central Andes

have volcanic DAD’s, being Tata Sabaya (Bolivia) one of them. The collapse that has originated the deposit could have

been generated by a combination of magmatic and seismic activity in the volcano. The deposit associated to the partial

collapse of Tata Sabaya volcano is distributed on its lower southern flank and partially fills the north-western part of

the Salar de Coipasa basin. The deposit covers a minimum area of 230 km2 and has an estimated minimum volume of

6±1 km3. The deposit is formed by 6 different types of hummocks, according to their compositions: lavic, pyroclastic,

sedimentary, mixed, pyroclastic breccia and basaltic-andesitic hummocks. Based on the predominant hummock type and

the spatial distribution, the deposit has been divided into 6 different facies (Toreva Block Facies, Volcanic Hummocks

Facies, Central Facies, Sedimentary Hummocks Facies, Mixed Facies and Pyroclastic Breccia Hummocks Facies).

Taking into account the facies distribution and their characteristics, we infer the pre-collapse structure of the volcano.