Banca de QUALIFICAÇÃO: JOSÉ ALEXANDRE PAIXÃO DA CUNHA

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
DISCENTE : JOSÉ ALEXANDRE PAIXÃO DA CUNHA
DATA : 28/06/2017
HORA: 15:00
LOCAL: Sala 1 - PPGG
TÍTULO:

Emplacement mechanism and thermal aureole provoked by the Catingueira pluton, Ediacaran of the Transversal Zone, Borborema Province, NE Brazil

PALAVRAS-CHAVES:

Transversal Zone; Catingueira Granite; Thermal Aureole; Ediacaran.

PÁGINAS: 21
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Geociências
RESUMO:

To the South of the Patos Shear Zona (PSZ), within the Piancó – Alto Brígida Terrane on the Transversal Zona, is situated the Catingueira pluton (grCat with an area of exposition of approximately 12 km² and U/Pb zircon of 573±14 Ma. The grCat is a classic peralkaline granite in the region, that intrudes and provoke contact metamorphism over metapelitic rocks of the Santana dos Garrotes Formation. This study characterizes the thermal evolution of the grCat by using informations from field work, petrography, whole rock and mineral chemistries, structural geology and petrophysical properties (thermal conductivity, specific heat, thermal diffusivity, and density). Petrogenetic grids indicate metamorphism of high temperature and low pressure to distance <2.5 km from the contact, with the assemblage staurolite ± garnet ± cordierite, coexistence of chlorite + muscovite, rare sillimanite, and absence of migmatization. These characteristics suggest temperature between 640 and 540^oC and pressure <3 kbar near the contact with the pluton. The geothermometer of Zr for peralkaline rocks was used to define the initial temperature of the magma, calculated as 771^oC, whereas the application of the saturation of Ti in biotite from the micaschist with staurolite indicated an average value of 538ºC. The first result would be a proxy for the liquidus temperature of the magma, considering zircon an earlier formed phase together with apatite. The presence of perthitic textures indicates that the final cooling occurred under temperature below the solvus, there is T<650^oC. Microprobe analyses of staurolite show X_Mg≤0.2, suggesting that this mineral crystallized under P<3.0 kbar and T=520^oC. In this way, an interval of temperature of 771-650^oC and P~3.0 kbar is estimated for the emplacement of the peralkaline magma. Numerical modelling of the thermal regime was done by software Heat 3D. The simulations were calculated from two geometric shapes, one vertical cylinder and a horizontal parallelepiped, using geothermal gradients varying from 30^oC/km to 70^oC/km. To achieve the thermal equilibrium under the conditions described above, cooling times of 194, 300, 408, 720 e 880 thousand years were calculated. The gradient with the best adjustment was 70^oC/km, with a cooling time of 880 thousand years. The results obtained here in terms of dimension, shape, depth, and metamorphic assemblages are comparable to other examples of plutonic bodies described in the Seridó Belt, to the north of the PSZ and in other continents. 

MEMBROS DA BANCA:
Externo ao Programa - 346302 - JAZIEL MARTINS SA
Externo ao Programa - 346468 - JOSE ANTONIO DE MORAIS MOREIRA
Presidente - 350630 - ZORANO SERGIO DE SOUZA