Pirometamorphism in cretaceous carbonates from the Jandaíra Formation, Potiguar Basin, Northeastern Brazil

Abstract

This work focuses on the thermal effects caused by hypabyssal basic intrusions hosted in cretaceous carbonatic rocks of the Jandaíra Formation, onshore Potiguar Basin, Northeastern Brazil. For this purpose, we used data from field work, microscopic, X-ray diffraction, electron microprobe, and whole rock lithogeochemistry of carbonates. The preserved limestones, located nearby the studied area, have carbonates grains, matrices, cements, pores, and, mineralogically, they have calcite, ankerite, dolomite, minor amount of clays (montmorillonite), and traces of quartz, microcline, pyrite and limonite. Pyrometamorphosed limestones are coarser, the fossiliferous components disappear, and the porosity is irrelevant. The modal composition of carbonates suggests as protoliths calciferous to dolomitc carbonates. Lizardite and spinel minerals can be formed within recrystallized carbonates in little to moderate affected samples, and spinel, spurrite and forsterite in strongly affected samples. Considering the geological context, the mineralogical composition and petrological diagrams from the literature, maximum temperatures and pressures of 1050 to 1200ºC and 0.5 to 1.0 kbar, respectively, are suggested. Besides the petrological importance for the characterization of the pyrometamorphism, the conclusions of this research open the possibility of changing the petroliferous system of hydrocarbon reservoirs in the Potiguar Basin and other Brazilian sedimentary basins with associated magmatic rocks