Banca de QUALIFICAÇÃO: CLARISSA DE AGUIAR DALAN

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
DISCENTE : CLARISSA DE AGUIAR DALAN
DATA : 19/12/2017
HORA: 14:00
LOCAL: Sala 1 - PPGG
TÍTULO:

LITOCHEMISTRY OF ALKALINE GRANITES IN THE RIO PIRANHAS-SERIDÓ AND SÃO JOSÉ DE CAMPESTRE DOMAIN, EXTREME NORTHEAST OF THE PROVINCE BORBOREMA: A COMPARATIVE STUDY

PALAVRAS-CHAVES:

Borborema Province, alkaline granites, lithochemistry.

PÁGINAS: 25
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Geociências
RESUMO:

The alkaline Neoproterozoic magmatism within the Rio Grande do Norte Domain, Borborema Province, is represented by seven bodies showing lithochemical and petrographical characteristics of A-type granites. This alkaline suite includes the Serra Negra do Norte and Flores plutons in the Rio Piranhas-Seridó Domain (RPSD), and Japi, Caxexa, Serra do Algodão, Serra do Boqueirão, and Olho D’Água Plutons, within the São José do Campestre Domain (SJCD). This work presents a petrographical and litochemical comparative study among these plutons, emphasizing their similarities and contrasts. In a broad view, the studied rocks are hololeucocratic, with magmatic layering and are, in some cases, intruded by dykes and sheets. They have fine to medium grained, equigranular, phaneritic textures. Petrographycally, these rocks define two distinct groups that correspond to the RPSD and SJCD domains. Plutons in the RPSD are alkali-feldspar granites and syenites, whereas in the SJCD they correspond mainly to syenogranites and quartz-monzonites. The chief mineralogy includes, besides quartz, plagioclase, and alkali feldspar, the mafics clinopyroxene, ±amphibole, and ±biotite. Acessory minerals are zircon, apatite, allanite, opaques, titanite, and ±andradite. Epidote is occasional (Serra Negra do Norte). Litochemically, these are rocks with alkaline to transitional (Serra Negra do Norte) affinities, peraluminous to metaluminous, with ferroan character. They show a relative enrichment of LREE over HREE, with the highest REE contents in the RPSD plutons. The latter also have negative to slightly positive Eu anomalies (0,24 < Eu/Eu* < 1,25), contrasting with the plutons from SJCD, where positive Eu anomalies are well-marked (1,49 < Eu/Eu* < 2,95). These positive anomalies can be explained by plagioclase fractionation in the source, or may represent more oxidizing crystallization conditions. In the geotectonic discriminant diagrams, the plutons from RPSD and SJCD show intraplate and syn-collisional signatures, respectively; the latter reflecting the influence of shear zones. Zr saturation temperatures vary between 567 and 899 ºC. The RPSD plutons show higher temperatures (709-899 ºC) when compared to those from the SJCD (567-821 ºC). The oxygen fugacity where calculated for the Caxexa Pluton based on the reaction hedenbergite + O2 ↔ andradite + magnetite + quartz, with values for log ƒO2 ranging between -15.4 and -15.7 (mean value of -15.5 ± 0.06). These values reinforce the oxidizing crystallization conditions for the SJCD plutons, slightly above the FQM (ΔFQM = +1.1), and TMQAI (ΔTMQAI = +0.8) buffers.

MEMBROS DA BANCA:
Presidente - 2042352 - FREDERICO CASTRO JOBIM VILALVA
Interno - 080.368.454-15 - ANTONIO CARLOS GALINDO - UFRN
Interno - 1513243 - MARCOS ANTONIO LEITE DO NASCIMENTO