Banca de DEFESA: MAYARA DIAS REIS

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : MAYARA DIAS REIS
DATE: 28/09/2026
TIME: 14:00
LOCAL: PPGMEG (via canal do Youtube)
TITLE:

Petrogenesis of the magmatic rocks within the pre-salt sedimentary sequence in well 1-BRSA-886-RJS, northern Santos Basin, SE Brasil.

KEY WORDS:

Santos Basin; Pre-salt; Alkaline magmatism; Cumulatic rocks; Campanian.

PAGES: 127
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUBÁREA: Geologia
SUMMARY:

The Santos Basin, located on the southeastern continental margin of Brazil and covering approximately 350,000 km2, records six magmatic events throughout its evolution. While the rift and post-rift megasequences are dominated by tholeiitic magmatism, the drift megasequence comprises three alkaline events: two in the Santonian–Campanian interval (85 75 Ma) and one in the Early Eocene (c. 50 Ma), occurring as both intrusive and extrusive rocks. This dissertation investigates a magmatic interval intersected in well 1-BRSA-886-RJS, in the northern portion of the Santos Basin, near the Cabo Frio High, between depths of 6,720.7 m and 6,521.5 m. The study aims to determine the intrusive or extrusive nature of this magmatism, its differentiation processes, its stratigraphic framework within the basin megasequences, and the mantle geodynamic mechanisms involved, through the analysis of 34 sidewall core samples. Petrography revealed a complex intercalation of igneous rocks, including gabbros, anorthosites, mesocumulatic olivine gabbros, mesocumulatic peridotites, and lamprophyres, interbedded with pelitic and carbonate rocks of the Barra Velha Formation. Lithogeochemistry characterizes the magmatism as alkaline to transitional, with compositions ranging from ultrabasic to intermediate. Most samples classify as gabbros, peridotitic gabbros, and monzogabbros, whereas two intermediate samples, a monzonite (with the highest incompatible element concentrations) and a syenite (richer in SiO2 and cumulatic in nature), represent the most evolved products. Geochemical modeling, applied exclusively to non-cumulatic samples, confirmed the cogenetic relationship and evolution by fractional crystallization among these rocks, while cumulates represent the complementary solid material accumulated in situ during the differentiation process. The physical intercalation of these lithotypes along the section reflects the synchronous operation of multiple differentiation mechanisms within the magma chamber, demonstrating that even relatively thin intrusions can record complex differentiation processes. 40Ar/39Ar dating obtained for three samples yielded ages of approximately 83 Ma, linking the studied magmatism to the Santonian–Campanian alkaline events of the Santos Basin. Isotopic data indicate two distinct and contemporaneous episodes of partial mantle melting: one generating the lamprophyric (monzogabbro) rocks and another producing the gabbroic suite. Binary mixing modeling reveals that the parental magmas derived from approximately 20% EMII-type mantle and 80% depleted mantle (DM), with monzogabbros exhibiting higher 87Sr/86Sr enrichment than gabbros. The results of partial melting modeling, combined with the obtained ages, indicate that a melting process in the garnet stability field was triggered during the Campanian in the Santos Basin. The proposed model assumes that lithospheric thinning combined with asthenospheric upwelling generated magmas that ascended and emplaced as a complex 300-meter-thick sill within the carbonates of the Barra Velha Formation.

COMMITTEE MEMBERS:
Externa à Instituição - BÁRBARA SANTOS QUEIROZ - UFRJ
Externo à Instituição - GABRIEL MEDEIROS MARINS - PETROBRAS
Interno - ***.345.068-** - JULIO CESAR LOPES DA SILVA - UFRJ
Presidente - 387109 - SERGIO DE CASTRO VALENTE