Gravimetric, radiometric, and magnetic susceptibility study of the Paleoproterozoic Redenc ¸a ˜o and Bannach plutons, eastern Amazonian Craton, Brazil: Implications for architecture and zoning of A-type granites Davis Carvalho de Oliveira a,c , Roberto Dall’Agnol a, * , Joa ˜o Batista Corre ˆa da Silva b , Jose ´ Arimate ´ia Costa de Almeida a a Group of Research on Granite Petrology, Instituto de Geocie ˆncias, Universidade Federal do Para ´ , Caixa Postal 8608, 66075-100 Bele ´m, PA, Brazil b Geophysics Graduate Program, Instituto de Geocie ˆncias, Universidade Federal do Para ´ , Caixa Postal 8608, 66075-100 Bele ´m, PA, Brazil c Geology Undergraduate Course, Campus de Maraba ´ , Universidade Federal do Para ´ , Brazil Received 1 May 2006; accepted 1 May 2007 Abstract The 1.88 Ga, anorogenic, A-type Redenc ¸a ˜o and Bannach granites, representative of the Jamon suite and associated dikes, are intru- sive in Archean granitoids of the Rio Maria Granite–Greenstone Terrane in the eastern Amazonian Craton in northern Brazil. Petro- graphic and geochemical aspects associated with magnetic susceptibility and gamma-ray spectrometry data show that the Redenc ¸a ˜o and the northern part of Bannach plutons are normally zoned. They were formed by two magmatic pulses: (1) a first magma pulse was frac- tionated in situ after emplacement at shallow crustal level, generating a series of coarse, even-grained monzogranites with variable modal proportions of biotite and hornblende; and (2) a second, slightly younger magma pulse, located to the center of the plutons, was com- posed of a more evolved liquid from which even-grained leucogranites derived. Gravity modeling indicates that the Redenc ¸a ˜ o and Bann- ach plutons are sheeted-like composite intrusions, approximately 6 and 2 km thick, respectively. These plutons follow the general power law for laccolith dimension and are similar in this respect to classical rapakivi granite plutons. Gravity data suggest that the growth of the northern part of the Bannach pluton resulted from the amalgamation of smaller sheeted-like plutons that intruded in sequence from northwest to southeast. The Jamon suite plutons were emplaced in an extensional tectonic setting, and the stress was oriented approx- imately NNE–SSW to ENE–WSW, as indicated by the occurrence of diabase and granite porphyry dyke swarms, orientated WNW–ESE to NNW–SSE and coeval with the Jamon suite. The 1.88 Ga A-type granite plutons and stocks of Caraja ´s are disposed along a belt that follows the general trend defined by the dikes. The inferred tabular geometry of the studied plutons and the high contrast of viscosity between the granites and their Archean country rocks can be explained by magma transport via dikes. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Gravity; Magmatic zoning; Laccolith; Anorogenic; Amazonian Craton 1. Introduction During the past two decades, Proterozoic, A-type gran- ites, dominantly rapakivi, have been described from many Precambrian shield areas, such as North America (Anderson and Bender, 1989; Emslie, 1991; Barnes et al., 2002; Ander- son and Morrison, 2005), Fennoscandia (Haapala and Ra ¨mo ¨, 1990; Ra ¨mo ¨ and Haapala, 1995; Kosunen, 2004), and the Amazonian Craton (Bettencourt et al., 1999; Dal- l’Agnol et al., 1999a, 2005). In the Amazonian Craton, felsic volcanic rocks and mafic and charnockitic plutonic rocks are also associated with rapakivi granites (Bettencourt et al., 1999; Dall’Agnol et al., 1999a; Fraga, 2002). 0895-9811/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jsames.2007.10.003 * Corresponding author. Tel.: +55 91 3201 7123; fax: +55 91 3201 7537. E-mail address: robdal@ufpa.br (R. Dall’Agnol). www.elsevier.com/locate/jsames Journal of South American Earth Sciences 25 (2008) 100–115