Miocene to Holocene geological evolution of the Lazufre segment in the Andean volcanic arc

[摘要] The Lazufre bulging zone, in the area of the Pleistocene–Holocene Azufre, Cordón del Azufre, Bayo, and Lastarria volcanic complexes, has been a major focus of study over the past few decades. Since 1998, interferometric synthetic aperture radar (InSar) analysis has shown structural deformation, likely a result of an active magmatic and hydrothermal system. Our new mapping provides clues about the causes and possible consequences of this deformation, based on the reinterpretation of important structures or regional lineaments. The bulge is located upon the hanging wall of the east-vergent, Pedernales-Arizaro NE-SW–trending Middle Miocene major thrust fault. The footwall of this fault was previously affected by a major explosive activity producing the Los Colorados caldera at ca. 9.4–9.8 Ma, the source of the homonymous 115–185 km 3 ignimbrite. Conjugated at ∼30° to the Pedernales-Arizaro thrust, the Imilac-Salina del Fraile oblique, slightly dextral strike-slip fault constitutes a major structure in the area, which favored the opening of transtensive spaces, parallel to the Los Colorados caldera–Lazufre bulge alignment. Notably, since the Late Pliocene, volcanism has been concentrated in the Lazufre intumescence, including extrusion of ∼120 km 3 total lava volume. The lava accumulation rate estimated since Late Pliocene to the present at Lazufre bulging zone area is approximately one-third of the rate estimated for the generation of the Los Colorados caldera. The migration of volcanic activity from this Miocene caldera area to the northwestern Lazufre bulging zone could be the consequence of local strain field variations that opened tectonic space and favored magmatic ascent and storage.

[学科分类] 地质学