CHAPTER 7.2 The Evolution and Tectonic Setting of the Luis Alves Microplate of Southeastern Brazil: An Exotic Terrane during the Assembly of Western Gondwana $ Miguel A.S. Basei 1 , Allen Nutman 2,3 , Oswaldo SigaJu ´nior 1 , Cla ´udia R. Passarelli 1 and Cesar O. Drukas 1 Contents 7.2.1. Introduction 273 7.2.2. Regional Geological Divisions 275 7.2.3. Basement Rocks of the Luı ´s Alves Microplate 275 7.2.4. Neoproterozoic Units of the Luı ´s Alves Microplate 276 7.2.4.1. The Campo Alegre Basin 276 7.2.4.2. The Serra do Mar Suite: anorogenic alkaline2peralkaline granitoids 278 7.2.4.3. The Itajaı ´ Basin 279 7.2.5. The Age of the Luı ´s Alves Microplate Basement 280 7.2.6. Interpretation and Discussion of Radiometric Results 283 7.2.7. Tectonic Implications 283 7.2.8. Conclusion 286 Acknowledgements 287 Appendix 1 287 7.2.1. Introduction The structural framework of southeastern Brazil (central portion of the Mantiqueira Province) resulted from the juxtaposition of several crustal blocks, which were variably affected by Neoproterozoic subduction and collision events. The resulting assembly of continental masses led to the formation of western Gondwana (Brito Neves et al., 1999; Basei et al., 2000, 2008; Campos Neto, 2000; Cordani et al., 2000, 2003). Part of this crustal segment is the older domain to the west represented by the Rı ´o de La Plata and Paranapanema cratons (see Part 4 and Chapter 7.1), which are now extensively covered by the Palaeozoic sediments of the Parana ´ Basin. The eastern, accreted domain is formed by the Neoproterozoic Ribeira (to the north) and Dom Feliciano (to the south) fold belts, separated by migmatitic 2 granitic 2 gneissic terrains that constitute the basement of the Curitiba Microplate (to the north) and Luı ´s Alves Microplate (LAM; to the south) (Figure 7.2.1). Further east is the Paranagua ´ Batholith, which is an accreted arc consisting of calc-alkaline granitoids. This compartmentalisation can be seen in Figure 7.2.1A and the spatial relationships between the main geotectonic units are sketched in the hypothetical section of Figure 7.2.1B. $ Basei, M.A.S., Nutman, A., SigaJu ´nior, O., Passarelli, C.R., Drukas, C.O. 2009. The evolution and tectonic setting of the Luis Alves Microplate of Southeastern Brazil: an exotic terrane during the assembly of Western Gondwana. In: Gaucher, C., Sial, A.N., Halverson, G.P., Frimmel, H.E. (Eds): Neoproterozoic-Cambrian Tectonics, Global Change and Evolution: a focus on southwestern Gondwana. Developments in Precambrian Geology, 16, Elsevier, pp. 2732291. 1 Centro de Pesquisas Geocronolo ´gicas, Instituto de Geocie ˆncias, Universidade de Sa ˜o Paulo, Rua do Lago 562, CEP 05508-080 Sa ˜o Paulo, SP, Brazil. 2 Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia. 3 Beijing SHRIMP Centre, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing 100037, China. Developments in Precambrian Geology, Volume 16 r 2010 Elsevier B.V. ISSN 0166-2635, DOI 10.1016/S0166-2635(09)01620-X All rights reserved. 273