Twelfth International Congress of the Brazilian Geophysical Society Integrated Airborne Magnetic and Gamma-Ray Data Applied for Structural Analysis on a section of the Transbrasiliano Lineament – Central Brazil Aureliano Augusto Vieira da Nóbrega 1 ; Reinhardt Adolfo Fuck 2 ; Roberta Mary Vidotti 2 ; Elton Luiz Dantas 2 (1) Programa de Pós-Graduação em Geologia - IG /UnB (aurelianoaugusto@gmail.com ); (2) Instituto de Geociências, Universidade de Brasilia (UnB) Copyright 2011, SBGf - Sociedade Brasileira de Geofísica This paper was prepared for presentation during the 12 th International Congress of the Brazilian Geophysical Society held in Rio de Janeiro, Brazil, August 15-18, 2011. Contents of this paper were reviewed by the Technical Committee of the 12 th International Congress of the Brazilian Geophysical Society and do not necessarily represent any position of the SBGf, its officers or members. Electronic reproduction or storage of any part of this paper for commercial purposes without the written consent of the Brazilian Geophysical Society is prohibited. ____________________________________________________________________ Abstract Southern Tocantins features a very complex geological scenario concerning the lithological units and structural context. The main structural feature of the region is the Transbrasiliano Lineament (TLB) a continental scale discontinuity that resulted from the collision of continental blocks at the end of the Neoproterozoic. The opportunity to cover a large area in a small time with high resolution data has turned the geophysical airborne techniques as the most frequently used tools for geological mapping. In the study area, geophysical images provide useful information of deep crustal structures as well as of shallow geological units and soils. In this work, an integrated study of airborne magnetic and gamma-ray geophysical data was carried out to highlight the arrangement of crustal blocks, their relations and boundaries. Introduction The Transbrasiliano Lineament (TBL) (Schobbenhaus et al. 1975) is a continental wide discontinuity between the Amazonian Craton and the eastern South American Platform, representing a mega- structure that was active during Gondwana supercontinent amalgamation, from Late Neoproterozoic to Early Paleozoic (Cordani and Sato 1999, Cordani et al. 2000, Almeida et al. 2000). The origin and evolution of this structure have been widely discussed by many authors in the last decades, including Costa and Hasui (1988), Hasui et al. (1994), Cordani and Sato (1999), Almeida et al. (2000) and Dantas et al. (2007). However, recent studies conducted in the region of Porto Nacional-Natividade (Chiarini, 2007) reinforce the idea that the TBL is related to late (post-collisional) stages of the Brasiliano Orogeny. Field techniques have proven effective for decades in detailed mapping, for the recognition of lithologic and structural features. However, at regional scale, it is sometimes difficult to cover the entire area in situ, due to the high costs of this kind of survey. With this purpose geophysical techniques have been widely used for the study of suture zones of continental scale as a tool for defining units and carrying out structural studies (Grauch et al. 2001; Dantas et al. 2006; Chiarini, 2007; Stewart et al., 2009). High-resolution airborne geophysical methods have been an important tool in large-scale geological mapping in central Brazil (e.g. Blum, 1999; Chiarini, 2007). This paper comprises an integrated study of airbone magnetic and gamma-ray data in order to carry out a structural analysis and contribute to the understanding of the structural context and arrangement of crustal blocks in southern Tocantins affected by the Transbrasiliano Lineament. It represents the first step of a work whose goal is to understand the origin of this structure and its role in the development of the Brazilian continental crust. Geological Setting The influence region of the TBL in the work area fits into the context of the Tocantins Province. This province, described by Almeida et al. (1981) as one of the major structural units that comprise the Brazilian geological framework is defined as a set of orogens resulting from the collision of three continental blocks: Amazonian, São Francisco and Paranapanema cratons. The province is subdivided into the Brasília, Araguaia and Paraguay belts. In turn the Brasília Belt, at the western border of the São Francisco Craton, comprises a thrust and fold belt, metamorphic core, Goiás Massif, and the Goiás Magmatic Arc (Fuck et al. 2006). Hasui et al. (1994) described the work area as the amalgamation of various continental blocks related to a Precambrian collisional process. Other authors such as Dantas et al. (2006) relate this process to the end of the Neoproterozoic, as the culminating event of convergence and collision of crustal blocks, including generation of supracrustal rocks at their boundaries, post-tectonic events and thermal reactivation at the end of the Brasiliano Orogeny. These subsequent reactivations in the region are closely linked to the context of the TBL, featuring the Serra Azul and Serra Grande transcurrent systems (SATS and SGTS, Hasui et al. 1994, Dantas et al. 2006, Chiarini, 2007). These large scale shear zones define the limit of large crustal blocks in the region, affecting mainly the transition zone between the Araguaia and Brasília belts (Figure 1).