Portal de Periódicos da CAPES

O GRANITO PEDRA DO SAL E SUAS FEIÇÕES DE CISALHAMENTO

1988; Sociedade Brasileira de Geologia; Volume: 18; Issue: 4 Linguagem: Inglês

10.25249/0375-7536.1988424432

2177-4382

THEODOMIRO GAMA, Paulo Sérgio de Sousa Gorayeb, Francisco de Assis Matos de Abreu,

Clay minerals and soil interactions

Detailled petrostructural investigation of the Pedra do Sal Granite revealed the existence of narrow and discontinuous mylonitic zones. They correspond to NE-SW and NW-SE dextral and sinistral shear zones, respectively. The low angle stretching lineation is parallel to the shear zones. It can be identified protomylonite, mylonite, ultramylonite, and pseudotachylite from the undeformed granite to the centre of the shear zones. The analysis of the microstructures permitted the recognition of five petrographic-structural domaines, in which it can be observed the progressive textural and mineralogical transformations. The six principal mineral phases behaved differently under deformation. Quartz is recrystalized and shows essentially ductile deformation. Plagioclase and microcline by their turn show a brittle-ductile behavior and have been recrystalized only at advanced stages of deformation. Finally, amphibole and titanite are esencially brittle. Besides the mylonitic foliation, other identified microstructures are microfactures, kinkbands, pressure shadows, microboudinage, bending and stretched minerals followed' by comminution and dynamic recristalization. These features suggest a progressive brittle-ductile shearing process related to a major strike-slip motion under metamorphic condictions varying from low amphibolite to high greenschist facies.