Epidoto

Revista Brasileira de Geociências

Basílio E. Cruz Filho et al.

35(4 - Suplemento):83-92, dezembro 2005

QUÍMICA MINERAL E CONDIÇÕES DE COLOCAÇÃO DO BATÓLITO TRONDHJEMÍTICO NORDESTINA, NÚCLEO SERRINHA, BAHIA
BASÍLIO E. CRUZ FILHO1,2, HERBET CONCEIÇÃO1, 2, MARIADE LOURDES DASILVAROSA1,2,3, DÉBORACORREIA RIOS1,2,4, MOACYR MOURA MARINHO2,5

Abstract MINERAL CHEMISTRY AND EMPLACEMENT CONDITIONS OF THE NORDESTINA TRONDHJEMITIC BATHOLITH, SERRINHA NUCLEUS (BAHIA STATE) The Nordestina Trondhjemitic Batholith (NTB; 720 km2) is a ellipsoidal intrusion, exposed in the central part of Serrinha Nucleus, an Archaean-Paleoproterozoic segment of the São Francisco Craton at the eastern of the Bahia State. It intrudes the gneissic-migmatitic Archaean- Paleoproterozoic basement along its western margin and the Paleoproterozoic volcano-sedimentary sequences of the Rio Itapicuru Greenstone Belt along the southern and eastern contacts. Its north-south elongated shape, associated with concentric internal foliation, which becomes more intense toward the border, and crystallization age of 2.15 Ga, are interpreted as result of syn-tectonic emplacement during the compressional Transamazonic event and concomitant to the closure of the Rio Itapicuru Basin (2.2-2.1 Ga). The NTB is composed of zoned oligoclase (An17-An26), quartz, calcic amphibole (Fe-hornblende and Mg-hornblende), biotite (Fe-rich), microcline, epidote (pistacite Ps23 mole %), titanite, zircon and apatite. Iron oxides are rare to absent and the epidote occurs as euedral to subhedral magmatic grains included in biotite. Magnetic susceptibility, electron microprobe analyses of Al content in hornblende (aluminumin-hornblende barometry), coexisting hornblende-plagioclase (hornblende-plagioclase thermometry) and the presence of magmatic epidote were used to constrain the oxygen fugacity (f O2), P and T during the crystallization of the magma. The NTB crystallized from low f O2 magmas (between NNO and FMQ buffers), at ~