Volcanic and tectonic history of the El Tatio area (22°.16 to 22°.30 S, central Andes, northern Chile): explanatory notes to the 1:50.000 scale geological map.

The geological map at 1:50.000 scale of the El Tatio volcanic area (central Andes, northern Chile) is presented. The map is performed on the basis of i) geological field survey, ii) satellite-aerial imagery analysis, iii) petrochemical investigation and iiii) literature radiometric ages. Using reconstructed unconformity-bounded stratigraphy, together with more descriptive lithostratigraphic units and lithosomes, the Miocene Quaternary geological history of the study area is described in terms of the interaction between volcanic activity of local and external provenance, and regional fault systems. Local andesitic to dacitic lava cones, stratovolcanoes and monogenic lava domes are emplaced mostly during the Pleistocene (and subordinately during the Miocene) under control of NE-SW to N-S alignments. Local volcanic products are interbedded with regional ignimbrite sheets originated in the Altiplano Puna Volcanic Complex from Miocene to Pleistocene. Periods of volcanic inactivity during the Pleistocene are characterized by extensional tectonic phases developing along NW-SE-aligned normal faults. The youngest tectonic event during middle-late Pleistocene is demonstrated by a series of roughly NNE-SSW trending, west-verging thrust faults, which, in addition to a local NW-SE-oriented strike-slip lineament, indicate contractional deformation processes in a NW-SE direction. The easternmost thrust fault is proposed to have driven magma ascent leading to the emplacement of the 34-ka-old Co. La Torta rhyolitic lava dome, which is the youngest recorded phase of activity in the study area. Field evidence of glacial advance during the Last Glacial Maximum (and, subordinately, during middle-late Pleistocene major glaciations) is recorded in the entire study area providing a relative age assignment of most of volcanic products and tectonic features. At present, the study area is characterized by intense fluid discharge in the El Tatio geothermal field, which is apparently conditioned by the westermost portion of the demonstrated thrust fault system.