Banca de DEFESA: CLARISSA DE AGUIAR DALAN
Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.DISCENTE : CLARISSA DE AGUIAR DALAN
DATA : 03/09/2018
HORA: 09:00
LOCAL: Auditório do LGGP
TÍTULO:
GRANITES OF ALKALINE AFFINITY IN THE RIO PIRANHAS-SERIDÓ AND SÃO JOSÉ DO CAMPESTRE DOMAINS (BORBOREMA PROVINCE, NE OF BRAZIL): A COMPARATIVE STUDY AND REVALUATION OF CRISTALLIZATION CONDITIONS
PALAVRAS-CHAVES:
Province; type-A granitoids; geothermobarometry
PÁGINAS: 100
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Geociências
RESUMO:
The ediacaran granitic magmatism of alkaline affinity (A-type) within the São José do Campestre (SJC) and Rio Piranhas-Seridó (RPS) Domains, in northeastern part of the Borborema Province, is represented by the Japi, Caxexa, Serra do Boqueirão, Serra do Algodão, Olho D’Água and Serra Negra do Norte plutons, and by the Flores stock. This work presents an integrated and comparative petrographic and chemical (whole-rock and mineral chemistry) study among these plutons, with the main focus on the revaluation of the intensive crystallization parameters (P, T, ƒO2), in light of new geothermobarometric calibrations and crystallization modelling with the rhyolite-MELTS software. In order to provide a regional understanding of this magmatism, the results are compared with available data for chrono-correlated A-type granites within the Transversal Zone (TZ) Domain of the Borborema Province. Based on petrographic data, the plutons are divided in two groups: (1) plutons intrusive into the SJC Domain (Japi, Caxexa, Serra do Algodão, Serra do Boqueirão and Olho D’Água) that are made mainly of alkali-feldspar granites, syenites and syenogranites, with calcic amphibole and/or calcic and sodic-calcic clinopyroxene; (2) plutons that crop out in the RPS Domain (Serra Negra do Norte and Flores), comprising syeno- and monzogranites with biotite ± calcic amphibole and clinopyroxene (Serra Negra do Norte). Titanite, apatite, zircon and opaque minerals are the main accessories. Andradite is found in the Caxexa and Serra do Algodão plutons, and primary epidote in the Serra Negra do Norte. Overall, the studied rocks show well-defined alkaline to alkali-calcic affinities in lithochemical diagrams. They are iron-rich (ferroan) and have meta- to peraluminous character. The Serra Negra do Norte pluton differs by showing more magnesian compositions that approach those typical of calc-alkaline granites (cordilleran I-type). The mafic minerals follow the chemical signatures of their host-rocks. Clinopyroxenes vay from diopside and augite (Serra Negra do Norte and Japi) to hedenbergite and aegirine-augite (Caxexa, Serra do Algodão); amphiboles are mainly Mg-ferri-horblende, and the biotite is annite, with more magnesian compositions in the Serra Negra do Norte granites. The Caxexa, Serra do Algodão, Serra do Boqueirão and Olho D’Água plutons share petrographic and chemical similarities with peralkaline granites of the TZ Domain, whereas the Flores stock are akin to meta- to peraluminous A-type granites of the Alto Moxotó and Alto Pajeú terrains inside the ZT Domain. The Japi, and mainly the Serra Negra do Norte plutons are transitional, with chemical similarities sometimes with one group, sometimes with another. The revaluated thermobarometry reveals that the studied granites crystallized under pressures of 3.0–3.7 kbar (~11–14 km deep in the crust), except for those of the Japi pluton, with average pressures of 5.3 kbar (~20 km) that are akin to those found for the A-type granites in the Alto Moxotó and Alto Pajeú terrains. Crystallization modelling gave liquidus temperatures in the range 885–917 oC, and 818 oC for the Flores stock, and solidus between 660–700 o. When present, clinopyroxenes, amphiboles and biotite are formed between 813–822 oC, 728–751 oC, and 750–789 oC, respectively. Among the accessories, the geothermometer Zr-in-titanite yielded temperatures of about 780 oC (maximum of 830 oC). Crystallization took place under essentially oxidizing conditions for most of the plutons (+1.0 < ΔQFM < +2.1; +0.4 < ΔNNO < +1.5), except for the Flores stock formed under slightly more reduced conditions (ΔQFM ≈ 0.0; ΔQFM ≈ -0.6).
MEMBROS DA BANCA:
Interno - 080.368.454-15 - ANTONIO CARLOS GALINDO - UFRN
Presidente - 2042352 - FREDERICO CASTRO JOBIM VILALVA
Externo à Instituição - LUANA MOREIRA FLORISBAL - UFSC