Análisis de la zonación de plagioclasa en los filones tonalíticos de la quebrada del río Suquía, Sierra Chica de Córdoba

BALDO, EDGARDO; MURRA, JUAN A.; BELLO, FANNY C.; COLOMBO, FERNANDO

San Salvador de Jujuy

Congreso; 9º Congreso de Mineralogía y Metalogenia; 2008

Asociación Mineralógica Argentina

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 and minimal magmatic convection in the boundary melt layer. The sector with normal zoning most likely formed during the decompression and cooling that followed the intrusion of the magma in or near the final emplacement place.