INSUGEO   12554
INSTITUTO SUPERIOR DE CORRELACION GEOLOGICA
Unidad Ejecutora - UE
artículos
Título:
Lower Carboniferous post-orogenic granites in central-eastern Sierra de Velasco, Sierras Pampeanas, Argentina: U-Pb monazite geochronology, geochemistry and Sr-Nd isotopes.
Autor/es:
GROSSE, P.; SÖLLNER, F.; BÁEZ, M. A.; TOSELLI, A. J.; ROSSI, J.N.; DE LA ROSA, D.
Revista:
International Journal of Earth Sci (Geol Rundsch)
Editorial:
Springer
Referencias:
Lugar: Berlin; Año: 2008 vol. 97 p. 1 - 25
ISSN:
1437-3262
Resumen:
Abstract: The central-eastern part of the Sierra de Velasco
(Sierras Pampeanas, NW Argentina) is formed by the large
Huaco (40 9 30 km) and Sanagasta (25 9 15 km) granite
massifs and the small La Chinchilla stock (2 9 2 km). The
larger granites intrude into Ordovician metagranitoids and
crosscut Devonian (?) mylonitic shear zones, whereas the
small stock sharply intrudes into the Huaco granite. The two
voluminous granites are biotitic-muscovitic and biotitic
porphyritic syeno- to monzogranites. They contain small
and rounded tonalitic and quartz-dioritic mafic microgranular
enclaves. The small stock is an equigranular,
zinnwaldite- and fluorite-bearing monzogranite. The studied
granites are silica-rich (SiO2 [70%), potassium-rich
(K2O[4%), ferroan, alkali-calcic to slightly calk-alkalic,
and moderately to weakly peraluminous (A/CNK: 1.06
1.18 Huaco granite, 1.011.09 Sanagasta granite, 1.05
1.06 La Chinchilla stock). They have moderate to strong
enrichments in several LIL (Li, Rb, Cs) and HFS (Nb, Ta,
Y, Th, U) elements, and low Sr, Ba and Eu contents. UPb
monazite age determinations indicate Lower Carboniferous
crystallization ages: 350358 Ma for the Huaco granite,
352.7 ± 1.4 Ma for the Sanagasta granite and 344.5 ±
1.4 Ma for the La Chinchilla stock. The larger granites have
similar eNd values between -2.1 and -4.3, whereas the
younger stock has higher eNd of -0.6 to -1.4, roughly
comparable to the values obtained for the Carboniferous
San Blas granite (-1.4 to -1.7), located in the north of the
sierra. The Huaco and Sanagasta granites have a mainly
crustal source, but with some participation of a more
primitive, possibly mantle-derived, component. The main
crustal component can be attributed to Ordovician peraluminous
metagranitoids. The La Chinchilla stock derives
from a more primitive source, suggesting an increase with
time in the participation of the primitive component during
magma genesis. The studied granites were generated during
a post-orogenic period in a within-plate setting, possibly as
a response to the collapse of the previous Famatinian orogen,
extension of the crust and mantle upwelling. They are
part of the group of Middle DevonianLower Carboniferous
granites of the Sierras Pampeanas. The distribution and
UPb ages of these granites suggests a northward arc-parallel
migration of this mainly post-orogenic magmatism
with time.