Análisis de la zonación de plagioclasa en los filones tonalíticos de la quebrada del Río Suquía, sierra Chica de Córdoba

BALDO, E.; MURRA, J.; BELLO, C.; COLOMBO, F.

Jujuy

Congreso; 9º Congreso de Mineralogía y Metalogenia; 2008

Asociación Geológica Argentina - Asociación Mineralógica Argentina

Analysis of plagioclase zoning in the tonalitic dykes of the Quebrada del río Suquía, Sierra Chica de Córdoba. Tonalitic dykes are common in the area of the Suquía River valley (Sierra Chica de Córdoba). The studied sample comes from the La Gallinita quarry (31° 21´ 25.7´´ S – 64° 20´ 57.0´´ W); it lacks ductile deformation and has a porphyritic texture, with 2-mm long plagioclase phenocrysts set in a groundmass of  ~0.5 mm. The rock is composed mainly of quartz, plagioclase and biotite [Fe/(Fe+Mg) @ 0.5), with lesser amounts of microcline and calcic clinoamphibole (ferroedenite to ferropargasite, Fe2+/(Fe2++Mg) @ 0.6) . Accessory phases are epidote, allanite, apatite-(CaF), zircon, pyrite, ilmenite (with up to 10.42% MnO) and titanite; chlorite, epidote (another generation) and muscovite are secondary minerals. Plagioclase phenocrysts display two contrasting zoning patterns: a core with oscillatory zoning (An53 to An48) and a rim with normal zoning, with sharply decreasing Ca content (from An50 to An14). The oscillatory zoning probably formed in almost static conditions, with a low undercooling degree and minimal magmatic convection in the boundary melt layer. The sector with normal zoning most likely formed during an event of strong undercooling, probably in or near the final emplacement place.    Keywords: plagioclase zoning – Sierra Chica de Córdoba – tonalite – magmatic crystallization