INVESTIGADORES
RAPELA Carlos Washington
artículos
Título:
The role of tectonism and fractional crystallization in the origin of Lower Paleozoic epidote-bearing granitoids, NW Argentina
Autor/es:
SAAVEDRA, J.; TOSELLI, A.J.; ROSSI DE TOSELLI, J.; RAPELA, C.W.
Revista:
GEOLOGY
Editorial:
GEOLOGICAL SOC AMER, INC
Referencias:
Lugar: Boulder; Año: 1987 vol. 15 p. 709 - 713
ISSN:
0091-7613
Resumen:
In the northern
Pampean Ranges a large group of peraluminous, two-mica Ordovician
granitoids commonly
contains epidote-bearing facies. This granitoid suite exhibits a wide
compositional range
within the calc-alkaline series, although the mineralogical and chemical
characteristics do
not fit the typical features of either I- or S-type granites. Many of these
plutons show
asymmetric compositional zoning, which is interpreted to be the product of
fractional
crystallization under tectonic stress. Tonalités occur only in the more
fractionated
plutons and are
interpreted as cumulates. Magmatic epidote in the granitoids suggests a
protracted
crystallization period. The pressure and temperature conditions at the
emplacement
level are inferred
to be moderate. Widespread tourmaline-bearing pegmatites indicate that the
later facies
crystallized from a water- and volatile-rich liquid. However, relict anhydrous
minerals and a
relatively low initial ^Sr/^Sr ratio (-0.705) suggest that the granitoids were
derived from a water-undersaturated parental magma of deep origin.