Banca de DEFESA: Joilma Prazeres Santos

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : Joilma Prazeres Santos
DATE: 03/10/2022
TIME: 08:30
LOCAL: Sala de videconferência do IGD
TITLE:

PETROGENESIS OF THE CERAÍMA AND ESTREITO MASSIFS AND COMPARISON BETWEEN THE POTASSIC/ULTRAPOTASSIC MAGMATISM OF THE SOUTHWEST AND EASTERN OF THE STATE OF BAHIA, BRAZIL.

KEY WORDS:

São Francisco Craton, shoshonite, potassic, ultrapotassic post-collisional

PAGES: 115
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUMMARY:

The Ceraíma and Estreito massifs are representatives of the alkaline potassic to ultrapotassic magmatic domain located in the western portion of the Bahia State, occupying a total area of 6,000 km2, and recording the geological history of a magmatic event that took place at the end of the Paleoproterozoic during the Rhyacian-Orosirian orogeny within the São Francisco Craton. This work aims to understand this magmatic scenario and how it affected the craton, expanding the horizons for the understanding of the magmatic processes and the tectonic/crustal significance of the Ceraíma and Estreito massifs, , and establishing a correlation with other magmatic units between 2.05 and 2.1 Ga in age, both in the Bahia State and Brazil. In this study, mapping procedures aimed to identify and single out the different magmatic facies based on petrographic features along with mineral chemistry and lithogeochemical data. The rocks of both massifs are approximately 2.05 Ga in age, and are intrusive in migmatized gneissic rocks and migmatites of the Santa Isabel Complex, of Archean age. Intrusion was controlled by fault systems in the preferred N-S and NNE-SSW directions. The lithological distribution in both massifs consists of facies with compositions varying from syenite to monzonite and, locally, monzo- to syenogranite. The Ceraíma massif consists of five facies whereas the Estreito massif displays three distinct faciologies. The rocks preserve textural features indicative of magmatic flow, marked by the presence of aligned feldspar phenocrysts. Near the edges of the Estreito massif, feldspar phenocrysts appear rotated under the influence of shear zones, which imprints a mylonitic fabric to the rocks of syenitic and monzonitic facies. Petrographic observations indicate that the massifs exhibit a mineralogical diversity, which starts in sequence with the early formation of apatite, zircon and magnetite, followed by the crystallization of pyroxene (diopside/augite) and microcline, and a late generation of amphibole (edenite and magnesio-hornblende), biotite and plagioclase (albite and andesine). Chlorite, actinolite and muscovite were identified as a result of late- to post-magmatic processes. The geochemical behavior of the massifs is characterized by an alkaline potassic signature with some ultrapotassic representatives of shoshonitic, metaluminous to weakly peraluminous nature. Similar geochemical signatures are found in other alkaline magmatic rocks in Bahia, such as the Guanambi Facies to the west, and the Santanápolis massif to the east. The compositions in geochemical diagrams show rectilinear trends of both major and trace elements, with enrichment in LREE and LILE in relation to HREE and HSFE. REE patterns are strongly fractionated and display weak to moderate negative to positive europium anomalies. These characteristics suggest that the facies of both massifs are cogenetic with each other, as well as with the Guanambi facies. The geochemical patterns indicate a genetic relationship between the parent magmas of the western massifs and the Santanápolis massif, originated by at least two magmatic pulses, which formed the syenites and the monzonites. The geochemical data suggest a post-collisional setting for the magmatism, as highlighted by the negative anomalies of some trace elements (Ta, Nb and Ti) and by the time gap between the age of intrusion (2.05 Ga.) and the age of peak regional metamorphism (2.09 to 2.1 Ga.).

BANKING MEMBERS:
Externa à Instituição - MARIA DE LOURDES DA SILVA ROSA - UFS
Externo à Instituição - ANTÔNIO MISSON GODOY - UNESP
Interna - 1555904 - CATARINA LABOURE BEMFICA TOLEDO
Interno - 1336460 - FEDERICO ALBERTO CUADROS JIMENEZ
Presidente - 6404885 - NILSON FRANCISQUINI BOTELHO