Geologia e geofísica de rochas ultramáficas e carbonatitos ediacaranos intrusivos no Complexo Senador Elói de Souza, Maciço São José do Campestre, Província Borborema - NE do Brasil

Abstract

Located in the São José do Campestre Massif, the Senador Elói de Souza Complex is a geological unit composed of 3.03 Ga granitic to tonalitic orthogneisses, mafic and ultramafic rocks characterized by metagabbros, metaclinopyroxenites and anorthosites with garnet and oligoclase, with the ultramafic bodies and carbonatites dated by the U-Pb method at 600 ± 03 Ma. These bodies have contact features evidenced through magmatic breccias with carbonate matrix and involving pyroxenite fragments. In addition, field data and 2D gravimetric modeling allowed interpreting carbonatites and pyroxenites as ellipsoidal bodies, the first one less expressive along the borders of the intrusion complex. The analysis of gravimetric data suggests they ate shallow bodies and appear to truncate the low angle structures of the basement gneiss rocks. Clinopyroxenites have a well-preserved igneous texture, a low fractional pattern of rare earth elements [(LaN / YbN) = 8.9-49.8] and negative Eu anomaly of (Eu/Eu* = 0.39-0.88). Carbonatites are calcite-rich, with diopside, phlogopite and olivine as main mafic phases, low concentration of rare earth elements, with parallel and slightly inclined patterns [(LaN /YbN) = 1.5-8.6], in addition to enrichment of rare earth elements lightweight compared to heavy rare earth elements. The distinct geochemical behavior between these lithologies in Harker-type diagrams, in addition to a magmatic gap, suggests partial mixture of magmas. Occurrences of symplectite between clinopyroxene and plagioclase and grossular partially consumed generating scapolite indicate retrogression processes in clinopyroxenite. Recrystallization of calcite, serpentinization of olivine and deformation of phlogopite in carbonatite indicate the action of metamorphic events and fluid-rich (CO2, H2O) metasomatism. The geological and geophysical data reported here may contribute to understand the Ediacaran mantelic events in the Archean domain of the São José do Campestre Massif.