The Caldas Novas dome, central Brazil: structural evolution and implications for the evolution of the Neoproterozoic Brası́lia belt

The Caldas Novas dome (Goiaás state, central Brazil) lies in the southern segment of the Neoproterozoic Brası́lia belt (center of the Tocantins Province) between the Goiás magmatic arc and the margin of the ancient São Francisco plate. The core of the dome comprises rocks of the Meso-Neoproterozoic Paranoá group (passive margin psamitic-pelitic sediments and subgreenschist facies) covered by a nappe of the Neoproterozoic Araxá group (backarc basin pelitic-psamitic sediments and volcanics of greenschist facies, bitotite zone). Hot underground waters that emerge along fractures in the Paranoá quartzite and wells in the Araxá schist have made the Caldas Novas dome an international tourist attraction. A recent detailed structural analysis demonstrates that the dome area was affected by a D1–D3 Brasiliano cycle progressive deformation in the ∼750–600 Ma interval (published U–Pb and Sm–Nd data). During event D1, a pervasive layer-parallel foliation developed coeval the regional metamorphism. Event D2 (intense F2 isoclinal folding) was responsible for the emplacement of the nappe. D1 and D2 record a regime of simple shear (top-to-SE relative regional movement) due to a WNW-ESE subhorizontal compression (σ1). Event D3 records a WSW-ENE compression, during which the dome rose as a large-scale F3 fold, possibly associated with a duplex structure at depth. During the domeʹs uplift, the layers slid back and down in all directions, giving way to gravity-slide folds and an extensional crenulation cleavage. A set of brittle fractures and quartz veins constitutes the record of a late-stage D4 event important for understanding the thermal water reservoir.