INVESTIGADORES
RAPELA Carlos Washington
artículos
Título:
Evolución magmática y geotectónica de la "Serie Andesítica" andina en la Cordillera Norpatagónica
Autor/es:
RAPELA, C.W.; SPALLETTI, L.A.; MERODIO J.C.
Revista:
Revista Asociacion Geologica Argentina
Editorial:
Asociación Geológica Argentina
Referencias:
Lugar: Buenos Aires; Año: 1983 vol. 38 p. 469 - 484
ISSN:
0004-4822
Resumen:
The Patagonian Andesitic Series is a polyciclic
volcanic volcanoclastic complex (Rapela et al., 1982) evolved along subparallel
belts in the western continental margin of the South American plate. Geological,
geochemical and tectonic characteristics of the westernmost belt of the Andesitic
Series, known as the Andean Andesitie Series (AAS) and better recognized between
40º 00 and 43º 30 SL,
are described.
The volcanic rocks of the AAS are calc-alkaline and high K calc-alkaline series
ranging in composition from basalt to rhyolite; but andesites are dominant.
Lava flows of basalts and basic andesites besides pulsatory pyroclastic-lava
flow facies are widely distributed, while high silica ignimbritic and explosive
plinian facies are restricted to Bariloche, Pilcaniyeu and Sierra de Cuyín
Manzano areas. The volume ratio of basic to intermediate and acidic members of
the AAS increases with time while the sequences show progressive iron
enrichment. In some sequences there are also local variations from
acid-to-basic composition.
New K-Ar ages corroborate that the volcanic activity of the AAS started (at
least) in the Middle Paleocene and lasted a protracted period of 15 m.y.
Paleosubduction geometries inferred from K-h relationships suggest that the
probable depths of magma origin during the Paleocene-Eocene could be located
around 140-200 km deep. Compositional variations of Oligocene and
Pliocene-Recent volcanics of the same latitude also suggest a variable dip-variable-depth
subduction regime with flattening of the subducting slab during the Oligocene.
The magmatic evolution of the AAS seems to have ocurred during a progressively
extensional environment that ended with block faulting of the arc and
development of the basins filled with thick volcanoclastic deposits in the
Oligocene (Ñirihuau Formation). As an indirect consequence of the subduction
process, the regime developed alkaline lava series in the back-arc area
(Middle Eocene to Recent).