PALEOGENE AND NEOGENE VOLCANIC ARC EVOLUTION IN THE NEUQUÉN AND SOUTHERN MENDOZA ANDEAN SEGMENT, ARGENTINA

The Tertiary Andean uplift from southern Mendoza to Neuquén provinces in Argentina is related directly to the evolution of volcanic arc activity and its associated Tertiary continental deposits developed in the retroarc. The beginning of Tertiary uplift (Paleogene) took place in the southern segment and is characterized by a wide composition of volcanic rocks. The age of this activity is Paleogene and the diastrophism is associated with the Incaica phase. Toward the north a new and younger sequence of volcanic rocks developed over the anterior volcanic arc. This new activity is associated with continental sedimentary deposits and uplift of the main cordillera. Volcanic compositions are predominantly andesites and basalts. The age of this activity is Neogene and the diastrophism is associated with the Quechua phase. Due to pre-Neogene tectonic crustal thickening or as the result of the stagnation of the magmas, or a combination of both processes, the formation of mafic garnet granulites was promoted or favored to define the lower crust. During the Quechua phase, magma ascended from its mantle source and hit the lower crust, losing the capacity to ascend because of the lack of density contrast, spread melting, homogenization and ascent of the magmas when they were produced (in this case equilibrated with the lower crust). As a result of this process the characteristic Miocene-Pliocene volcanism ended with the Diaguita diastrophic phase.