Dominios ricos en aluminio en granulitas con granate-cordierita de la Sierra de Córdoba: mineralogía, geoquímica y génesis.

VERDECCHIA, SEBASTIÁN O.; COLOMBO, FERNANDO; CASQUET, CÉSAR; BALDO, EDGARDO; VERDECCHIA, SEBASTIÁN O.; COLOMBO, FERNANDO; CASQUET, CÉSAR; BALDO, EDGARDO

Cordoba

Congreso; XIII Congreso de Mineralogía, Petrología Ígnea y Metamórfica, y Metalogénesis; 2019

Asociación Mineralógica Argentina y Asociación Geológica Argentina

Migmatites of the early Cambrian Pampean Orogeny occur over wide areas of the Sierras de Córdoba (review in Casquet et al. 2018). They include small elongated bodies of garnet- and cordierite-rich granulites (kinzigites after Gordillo 1979; granulites after Otamendi et al. 1999). One body near the Santa Rosa river (northern Sierra de Comenchingones; 32°2´32"S; 64°43´38"W) is enclosed within sillimanite and garnet metatexites that include lenses of amphibolites and metagabbros (Otamendi y Patiño Douce 2001 and refs. therein). Granulites show a complex mineral assemblage of Qz-Pl-Grt-Crd with lesser Ath-Cum-Bt-Ky-Sil-Sp(Her)-St-Usp-Ilm-Mag-Zrn-Mnz(Ce)-Ap, and late Ms-Chl-REE Ep (abbreviation after Whitney and Evans, 2010). Moreover, mm- to cm-size domains contain cordierite (52% modal on the whole; XMg 0.87-0.90), anorthite (10%; An88-93), staurolite (18%, XMg 0.31-0.36), gedrite and tschermakite (4%), Hc-rich spinel + högbomite (3%), ilmenite (4%), magnetite + ulvoespinel (5%), corundum (3%), biotite (1%) and minor garnet (Alm55-58-Py33-35-Grs5.2-5.6), chlorite and sillimanite. Calculated rock composition is: 34% Al2O3, 38% SiO2 and 21.7 % FeO+MgO (#Mg=0.495). Similar rocks elsewhere were interpreted as either the product of metasomatism, partial melt residuums or alteration prior to metamorphism (Schneiderman y Tracy 1991). Whole rock chemistry and the evidence of relic garnet replaced by cordierite suggest that these complex domains evolved from an earlier ferromagnesian Grt- and plagioclase (An48-50)-rich anatectic residuum. In fact, sillimanite and spinel are often found as inclusions in garnet, which implies that the garnet grew Al-saturated conditions. Work is in progress to precise the meaning and evolution of these granulites.