Retroarc volcanism in the Northern San Rafael block (34º-35º30´S)

ANDRÉS FOLGUERA A, JOSÉ A. NARANJO , YUJI ORIHASHI , HIROCHIKA SUMINO , KEISUKE NAGAO ,

JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH

ELSEVIER SCIENCE BV

Año: 2009 vol. 186 p. 169 - 185

0377-0273

One of the major retroarc volcanic provinces in the Southern Central Andes (34º and 37ºS) is developed in the Andean foothills of the San Rafael region between the orogenic front and foreland basement uplifts of Late Miocene age. The present data set is the first comprehensive geochronological study of the Pliocene-Holocene volcanism, previously dated mainly on stratigraphic bases. The new unspike K-Ar radiometric and two radiocarbon determinations encompass many volcanic centers, most of them monogenetic and of basaltic composition exposed between 34º and 35º30´S. The data constrained the basaltic volcanism between ~1.8 Ma and the Holocene. The distribution on time and space of the ages indicates that eruption in the retroarc was not a steady process but constituted a series of episodes with some distinct patterns. The orogenic front of the San Rafael Block is associated with 1-0.7 Ma volcanic eruptions, while the Malargüe fold and thrust belt front in the Andean foothills is related to much younger eruptions produced at 0.15-0.01 Ma. Both areas are associated with Late Cenozoic normal faults that dismembered an uplifted Late Miocene peneplain as indicated by normal relationships between Paleozoic rocks and Tertiary strata. This linkage indicates a major relationship between Pleistocene-Holocene retroarc eruptions of the basaltic centers, and extensional collapse of the foreland region, which show a migration of the last volcanic activity towards the hinterland.