Idades U-Pb por LA-ICP-MS em veios de carbonatos de calcários da Formação Jandaíra, região sudoeste da Bacia Potiguar, NE do Brasil

Abstract

Lately, minerals that fill brittle structures and veins are on the spotlight for academic and industry studies due to their potential as a geochronometer for deformation. These minerals can be used in different geosciences studies, such as tectonics, hydrocarbons, metallogeny, seismology, and environmental and hydrogeological assessments. Several geochronological methods have been applied to date brittle deformations, and the U-Pb dating of carbonates precipitated in fault planes or veins is one of them. Carbonate minerals such as calcite, aragonite, and dolomite form in diverse geological environments, these minerals can accumulate U during their formation, making them useful for U-Pb geochronology. However, the implementation of a routine in the laboratory using these minerals isn't trivial, due to several factors, such as the low uranium content in carbonates, difficulties in the development of carbonate standards, and laboratory procedures (equipment, software). The purpose of this work is the implementation of the U-Pb method in carbonates in the Multilab UERJ routine and the application on samples from the Potiguar Basin. In northeastern Brazil, intracontinental basins related to the opening of the South Atlantic developed over the Precambrian basement of the Borborema Province. The Potiguar Basin and other intracontinental rift basins in this region (eg Araripe, Rio do Peixe, Jatobá, etc.) are key segments for the comprehension and evolution of Equatorial and South Atlantic margins, due to their relationship with two branches of Atlantic rif system, along with stratigraphic record and structures related to aborted rift systems developed during the Neocomian. These basins are controlled by brittle faults from reactivations of Neoproterozoic shear zones, providing direct evidence that the Precambrian tectonic heritage of the Borborema Province played an important role in the development of the Atlantic rift. The study area of this work is located in the southwest portion of the Potiguar Basin, in a karst valley formed by the Apodi-Mossoró River. It is composed of the Jandaíra Formation limestones that were deposited during the Eoturionian-Eocampanian (Upper Cretaceous), related to the post-rift and drift stage of the Potiguar Basin evolution. The outcrops in the study area are intensively fractured, and some of these fractures are filled with carbonates, their formation is related to the post-rift stress field that affected not only Jandaíra limestones, but also other units of this basin, and reactivated regional fault systems. This work reports the first U-Pb ages of carbonate veins filling brittle structures in the Potiguar Basin. The ages were obtained during the implementation of the U-Pb method in carbonate at the Multilab UERJ, carried out by this work. The ages found for the N-S direction veins provide the minimum ages of formation of these structures between 45 and 30 Ma. The ages obtained are associated with extensional tectonics of the continental crust in the region during the opening of the Atlantic Ocean and related to the drift of the South American plate after the breakup of Pangea, in addition, these ages can also be related to magmatism events in the Potiguar Basin and the Andean Orogeny.