CIG   05423
CENTRO DE INVESTIGACIONES GEOLOGICAS
Unidad Ejecutora - UE
artículos
Título:
Age and composition of granulite xenoliths from Paso de Indios, Chubut province, Argentina
Autor/es:
CASTRO, ANTONIO; ARAGON EUGENIO; DÍAZ-ALVARADO, JUAN; BLANCO, IDAEL; GARCIA-CASCO, ANTONIO; VOGT, KATHARINA; LIU, D-Y
Revista:
JOURNAL OF SOUTH AMERICAN EARTH SCIENCES
Editorial:
PERGAMON-ELSEVIER SCIENCE LTD
Referencias:
Lugar: Nueva York; Año: 2011
ISSN:
0895-9811
Resumen:
Granulite xenoliths enclosed in Paleogene alkali basalts from the locality of Paso de Indios in The Argentinean Patagonia, have been studied for petrology, geochemistry and U-Pb SHRIMP zircon geochronology. These are lower crust xenoliths composed of pyroxene and plagioclase dominantly. Symplectitic overgrowths with olivine and new pyroxene-plagioclase formation around the large pyroxene crystals are common. The study of phase equilibrium yields a decompression path from pressure 0.9 GPa at temperatures of about 1000 °C. The major element composition does not correspond with any known basaltic or andesitic magmas. They have SiO2<50 wt% and MgO=6 wt% and lower, very close in composition to the bulk lower continental crust composition. They are extremely depleted in incompatible elements with values as low as Rb=15.3 to 4.1 ppm; Y=6.2 to 2.5 ppm; Th=0.92 to 0.13 ppm; U=0.51 to 0.22 ppm; SREE=53 ppm. This depletion is attributed to a residual origin of the granulites. In situ age determination with SHRIMP yields a Concordia age of 175.9 ± 4.9 Ma with MSWD=1.4. This age represent the time of complex lithosphere evolution in relation with the formation of this residual crust.