Abstract
The Serido Formation of northeastern Brazil consists predominantly of mica schists. Mineral assemblages include biotite, quartz, plagioclase, and garnet, and may also include cordierite, sillimanite, andalusite, tourmaline, muscovite, ilmenite, zircon, and apatite. Pressure and temperature estimates using garnet-plagioclase and garnet-biotite exchange reactions indicate a metamorphic field gradient of 30–45°C/km for Brasiliano metamorphism. Minimum P-T conditions at the staurolite-out isograd were 550°C, 2.5 kbar; at the andalusite = sillimanite phase transition, 580°C, 3 kbar; and at the breakdown of cordierite, 600°C, 4 kbar. The metamorphic grade in general increases from west to east, reaching a maximum in the central part of the region.
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