Microfabrics and zircon U-Pb (SHRIMP) chronology of mylonites from the Patos shear zone (Borborema Province, NE Brazil)

Autor(es)

Viegas, Luis Gustavo F. ^{[1, 2]} ; Archanjo, Carlos J. ^[1] ; Hollanda, Maria Helena B. M. ^[1] ; Vauchez, Alain ^[2]

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Inst Geociencias, BR-05508080 Sao Paulo - Brazil

^[2] Geosci Montpellier, F-34095 Montpellier 5 - France

• Tipo de documento: Artigo Científico
• Fonte: Precambrian Research; v. 243, p. 1-17, APR 2014.
• Citações Web of Science: 20

Resumo

Microstructures, U-Pb SHRIMP zircon ages and temperature estimates were used to constrain the fabric evolution and timing of mylonitisation in the Patos shear zone (NE Brazil). Melt-bearing HT-mylonitic orthogneiss displays solid-state fabrics with coarse quartz ribbons and sutured grain boundaries. K-feldspar is often fractured and shows peripheral myrmekite. The textures typically become magmatic at the contacts with the Espinho Branco anatexite. Zircon crystals from two samples of the leucosome show Paleoproterozoic (ca. 2.2 Ga) inherited cores that are enveloped by recrystallised Neoproterozoic rims. These zircon grains define a discordia with lower intercept ages of 558 and 562 Ma but with large analytical errors. A leucogranite with transitional contacts with host diatexites provides a well-constrained zircon mean age of 566 +/- 6 Ma (n = 15, 95% conf.), which is considered the best estimate for the peak metamorphic conditions. The transition from HT-mylonites to fine-grained mylonites and ultramylonites is marked by a progressive grain size reduction assisted by recrystallisation. Quartz crystallographic fabrics display {[}0 0 0 1] concentrations between Z and Y. K-feldspar and plagioclase fabrics record the activity of the (0 1 0){[}0 0 1] and (0 1 0){[}1 0 0] slip systems and, in the lower-temperature tectonites, the (1 0 0){[}0 1 0] slip system. These results suggest a diachronic evolution in which an initial HT northern domain was deformed by intracrystalline slip and melt-assisted granular flow, followed by medium- to low-temperature solid-state creep in the southern shear zone domain. The mylonites therefore record the rheological heterogeneities responsible for the formation of a late continental shear zone that nucleated under partially molten conditions and was later reactivated through melt-absent strain localization following exhumation. (C) 2014 Elsevier B.V. All rights reserved. (AU)

• Processo FAPESP: 10/50060-1 - Domos migmatiticos e milonitos do lineamento patos (provincia borborema, ne brasil): estudo estrutural e geocronologico dos eventos e alta temperatura.
• Beneficiário: Carlos José Archanjo
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 09/17537-1 - Mecanismos de deformação e cronologia de eventos na zona de cisalhamento Patos, Província Borborema (Nordeste do Brasil)
• Beneficiário: Luís Gustavo Ferreira Viegas
• Modalidade de apoio: Bolsas no Brasil - Doutorado