Geophysical, geochemical and isotope analysis of the Figueira Branca Suite, Mato Grosso, Brazil

Abstract

The Figueira Branca Suite is a layered mafic-ultramafic complex in the Jauru Terrane, southwest Amazon Craton. New lithological, geochemical, gamma-ray and potential field data, integrated with geological, isotope and paleomagnetic data are used to characterize this pulse of Mesoproterozoic extension-related magmatism. The Figueira Branca Suite formed through juvenile magma emplacement into the crust at 1425 Ma, coeval with the later stages of the Santa Helena Orogen. In three papers, this suite was studied from microscopic to continental scales. First, the Figueira Branca suite was analysed through thin sections to determine the influence of inaccurate constraints in magnetic and gravity field modelling. Then, the extent of magmatism within the suite was delimited to four bodies to the north of Indiavaí city, MT - Brazil, with potential fields and gamma-ray data. Modelling gravity and magnetic field data indicated that the anomalous sources are close to the surface or outcropping. These intrusions trend northwest over 8 km, with significant remanent magnetization that is consistent with published direction obtained through paleomagnetic data. The increasing enrichment of LREE in the gabbroic bodies of the suite was interpreted as evidence of progressive fractionation of the magma. The emplacement, mineralogy and geochemical signature point towards a backarc extension tectonic framework in the later stages of the Santa Helena Orogen. The third part of the work consisted on evaluating reconstructions of the Paleo-Mesoproterozoic supercontinent Nuna with magnetic field data. The global magnetic anomaly map, EMAG2, allowed to observe continuity of magnetic lineaments and regimes in domains of similar ages in different cratons (Amazon, Baltica, West Africa and North China). These magnetic features indicated the theory which the magnetic field best supported, and suggested the regional environment where the Jauru Terrane was inserted by the time of the intrusion of the Figueira Branca Suite.