Anisotropy of magnetic susceptibility of Serra da Caiçara pluton, Águas Belas-Canindé Batholith, Alagoas, Northeast Brazil

Abstract

The Anisotropy of Magnetic Susceptibility (AMS) technique was applied in the Serra da Caiçara pluton, which is part of the Águas Belas-Canindé batholith, Pernambuco-Alagoas Domain of Borborema Province, Northeastern Brazil. The pluton has high values of magnetic susceptibility (K) (90% of the values above 5 × 10^-3 SI), typical of granites of the magnetiteseries. The anisotropy degree (P) ranges from 1.025 to 1.320. The highest P values are associated with the margins of the body and have a positive correlation with K. The pluton presents a mixed, slightly more oblate, fabric, with T values between -0,822 and 0,823. In general, magnetic foliations and lineations are fairly uniform and have two preferred directions: NW-SE (dominant, usually plunging to SW) and NNE-SSW, with a more varied plunge (usually associated with high P values). The foliation and lineation of the hornblende quartz syenite facies have low to moderate dip and plunge, respectively, which agrees with the regional fabric. The lineations mostly have SE plunging, indicating the magmatic flow’s direction. The hornblende quartz alkali feldspar syenite facies (center of the body) has a discordant fabric, with flow from SW to NE and spreading to NW. The observed structural magnetic structure is consistent with the structural framework of the region, which has two main directions (NE-SW and NW-SE). Data suggest that the pluton intruded taking advantage of the regional foliation formed during the convergent phase of the Brasiliano orogenesis. During the final crystallization phase, the pluton was affected by the transcurrent phase of the Brasiliano event, mainly at the edges of the body, conditioning the NE-SW foliations and lineations.