Rapid magma ascent and formation of the Águas Belas-Canindé granitic batholith, NE Brazil: evidence of epidote dissolution and thermobarometry

Abstract

Mineral chemistry and intensive parameter estimates for the Major Isidoro (626 Ma) and Monteirópolis (627 Ma) magmatic epidote-bearing granitic plutons, emplaced along the Jacaré dos Homens transpressional shear zone (JHSZ), Borborema Province, are focused in this study. These plutons consist of medium-to-coarse grained equigranular to porphyritic tonalite to granite that show abundant dioritic enclaves. These granites contain biotite (Fe# 0.44 to 0.55), Fe-edenite (Major Isidoro), hastingsite (Monteirópolis), titanite, and epidote that often show allanite core as key mafic mineral phases. Pistacite molecular content in epidote is in the interval of 27 to 31 mol%, presenting TiO₂ < 0.30%, typical for magmatic epidote. Estimated intensive parameters reveal crystallization at 6.5 ± 1 (Major Isidoro) and 4.7 ± 0.6 kbar (Monteirópolis), temperatures from ~940°C (near-liquidus) to 675 ± 35°C (near-solidus) and oxidizing conditions. Partial corrosion of epidote took place during 15.6 to 32 (Major Isidoro) and 27-49 years (Monteirópolis), corresponding to rather high magma ascension rates of 365 to 750 and 395 to 635 m.years^-1, respectively. The JHSZ likely favored upward magma transport at the Sergipano and Pernambuco-Alagoas domains boundary, during the onset of the Brasiliano orogeny (650-620 Ma).

KEYWORDS:
Pernambuco-Alagoas Domain; calc-alkaline orogenic granites; crystallization conditions; magmatic epidote; high ascension rates