Banca de DEFESA: DANIELA LEAL RODRIGUES

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE : DANIELA LEAL RODRIGUES
DATA : 13/04/2020
HORA: 14:00
LOCAL: IGEO/UFBA
TÍTULO:

GEOTERMOBAROMETRY OF SAFIRINE AND GARNET-ORTHOPYROXENE BEARING GRANULITES FROM PACIÊNCIA BEACH, SALVADOR, BAHIA

PALAVRAS-CHAVES:

CSEB. Sapphirine granulites. Garnet – Orthopyroxene granulites. UHT metamorphism.

PÁGINAS: 48
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Geociências
SUBÁREA: Geologia
ESPECIALIDADE: Petrologia
RESUMO:

The outcrop of the Paciência’s beach, in Salvador city, is located in the geotectonic setting of the São Francisco’s Craton, more specifically in the extreme south of the Salvador-Esplanada-Boquim Belt (CSEB). In this work, a study was realized in two of the metamorphic lithotypes present in the outcrop: garnet - orthopyroxene granulites and sapphirine granulites. The first consists of garnet and orthopyroxene porphyroblasts surrounded by a matrix formed by plagioclase + biotite ± K-feldspar ± quartz ± chlorite, in addition to zircon, apatite and sericite as traces. Simplectites between orthopyroxene + spinel + cordierite ± garnet occur at the rims of porphyroblasts or dispersed in the matrix. The sapphirine granulites are presented under three lithofacies: now formed by garnet porphyroblasts containing inclusions of sillimanite, sapphirine, mesoperthite and quartz, bordered by simplectites between orthopyroxene + spinel + cordierite and matrix formed by plagioclase + biotite ± K-feldspar ± quartz ± chlorite ± myrmekite; sometimes as simplectites between orthopyroxene + sapphirine + spinel + cordierite surrounded by a matrix of biotite + plagioclase + cordierite ± K-feldspar ± quartz ± chlorite; or as simplectites between orthopyroxene + sapphirine, where garnet can occur included in sapphirine and spinel in the center of the simplectites, this arrangement being surrounded by a matrix of biotite ± chlorite. Zircon, apatite and opaque can occur as traces in the three lithofacies. Mineral chemistry studies have indicated that, in garnet - orthopyroxene granulites, garnet is a solid solution dominated by the almandine - pyrope pair, with molar% content ranging between alm52-55 and prp40-43 in the core, and alm55-60 and prp28- 39 at the rims. XMg in garnet ranged from 0.45 to 0.37 and 0.64 - 0.69 in orthopyroxene. Al content in orthopyroxene ranged between 0.43 and 0.30 apfu in porphyroblasts, with values decreasing from the core towards the rims, while in simplectites between 0.35 and 0.26 apfu. Plagioclase porphyroblasts shows values of An43-19, and for the grains of the matrix between An40-31. In the sapphirine granulites, the garnet had contents of alm48-51 and prp44-45. XMg in garnet ranged between 0.46 - 0.48, in orthopyroxene 0.74 - 0.77 and sapphirine 0.82 - 0.87. Al content for orthopyroxene varied between 0.27 - 0.40 apfu. Thermobarometric studies on garnet - orthopyroxene granulites resulted in conditions of metamorphic peak of P ~ 1.04 GPa and T ~ 1016 °C, associated in this work with the Dn deformation phase of Salvador. It is suggested that the following steps of decompression and cooling Dn + 1, yielding the simplectites and reequilibrated the matrix, furthering the consumption of mineral phases by biotite ± chlorite during the late cooling phase. For this late phase, the calculated T break resulted in 616.5 - 770.7 ° C, by orthopyroxene - sapphirine thermometry. It is believed that the diffusion between Fe-Mg acted intensely during the late cooling stage in the safirina granulites sample, so that the results obtained for the pseudoseections showed up to be unreliable. However, reaction microstructures and petrogenetic grid suggest that these lithotypes crossed the P-T paths after a metamorphic peak of near-isothermal decompression.

MEMBROS DA BANCA:
Presidente - 2982944 - JAILMA SANTOS DE SOUZA DE OLIVEIRA
Interno - 1295799 - ANGELA BEATRIZ DE MENEZES LEAL
Externo ao Programa - 5196747 - CARLSON DE MATOS MAIA LEITE