The Precambrian Rio Paraiba do Sul Shear Belt comprises a 200-km-wide anastomosing network of NE-SW trending ductile shear zones extending over 1000 km of the southeastern coast of Brazil. Granulitic, gneissic-migmatitic, and granitoid terrains as well as low-to medium-grade metavolcanosedimentary sequences are included within it. These rocks were affected by strong contractional, tangential tectonics, due to west-northwestward oblique convergence of continental blocks. Subsequent transpressional tectonics accomodated large dextral, orogen-parallel movements and shortening. The plutonic Socorro Complex is one of many deformed granites with a foliation subparallel to that of the shear belt and exposes crosscutting relationships between its tectonic, magmatic, and metamorphic structures. These relationships point to a continuous magmatic evolution related to regional thrusts and strike slip, ductile shear zones. The tectonic and magmatic structural features of the Serra do Lopo Granite provide a model of emplacement by sheeting along shear zones during coeval strike-slip and cross shortening of country rocks. Geochronological data indicate that the main igneous activity of Socorro Complex spanned at least 55 million years, from the late stage of the northwestward ductile thrusting (650 Ma), through right-lateral strike slip (595 Ma) deformation. The country rocks yield discordant age data, which reflect a strong imprint of the Transamazonian tectono-metamorphic event (1.9 to 2.0 Ma). We propose a model for the origin of calcalkaline granites of the Ribeira Belt by partial melting of the lower crust with small contributions of the lithospheric mantle during transpressional thickening of plate margins, which were bounded by deep shear zones. The transpressional regime also seems to have tbcused granite migration from deeper into higher Crustal levels along these shear zones. M A.S. Basel, Nb and Pb Isotope studies bearing on the crustal evolution of southeastern Brazil, Rev. , Approximation of terrestrial lead isotope evolution by two-stage model, Earth Planet. Sci. Lett., 26, 207-221, 1975. Steiger, R.H., and E. Jager, Subcommission on geochronology: Convention on the use of decay constant in geo-and costoo-chronology, Earth Planet. Sci. Lett., 36, 359-362, 1977. Tommasi, A, A Vauchez, L.A.D. Fernandes, and C C. Potschef, Magma-assisted strain localization in an orogen-parallel transcurrent shear zone in southern Brazil, Tectonics, 13, 421-437, 1994. UIbrich, H H G.J, S.R F. Vlach, V.A. Janasi, and A R. Alineida, Ascens•1o e coloca$,no de granit6ides proteroz6icos em ,'ireas do embasamento do Estado de S•1o Paulo, Brasil Meridional: paradoxos da amtlise geom•trica, Bol. lnstituto de Geoci•ncias-Universidade de Sc•o Paulo, Publ. Esp., 12, 143-144, 1992. Vlach, S.R.F., V.A. Janasi, and C.A.C.B. Vasconc•los, The Itu-belt: associated calcalkaline a•'d aluminous A-type late Brasiliano granitoids 2n the states of S•Io Paulo and Paramt SE-B•'azil, paper presented at the 36. Congresso Bra,zileiro de Geologia, Sociedade Br...

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Comparativo study of six granitoid complexes associated with transcurrent faults in the State of São Paulo, Brazil, concerning their architecture and magmatic cycles is presented. Three of these complexes are calc-alkaline (Itaqui, São Roque, Cantareira) and the other three are rapakivi ones (São Francisco, Sorocaba, Itu). The architecture of the complexes is the result of the coalition of severa! magmatic phases with the following temporal emplacement sequence: 1. Early Phase; 2. Main Phase; 3. Early Lateral Accretionary Phase; 4. Phase of Stocks and Circular Intrusions; 5. Final Lateral Accretionary Phase. Also the magmatic units whiçh built up the complexes belong to at least two magmatic cycles with or without an intra-cycle mafic dike phase. The recurrence of the architecture style and the presence of successive magmatic cycles in ali complexes independently of their serial character is discussed in terms of magma emplacement mechanisms, the presence of collecting magma chambers successively tapped and recharged and the reactivation-phases of the transcurrent faults to which the complexes are associated.