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Title: Deformation partitioning during folding and transposition of quartz layers.
Authors: Lagoeiro, Leonardo Evangelista
Hippertt, João
Lana, Cristiano de Carvalho
Keywords: Deformation partitioning
Dissolution-precipitation creep
Foliation transposition
Issue Date: 2003
Citation: LAGOEIRO, L. E.; HIPPERTT, J.; LANA, C. de C. Deformation partitioning during folding and transposition of quartz layers. Tectonophysics, v. 361, p. 171-186, 2003. Disponível em: <>. Acesso em: 30 set. 2014.
Abstract: Banded iron formation (BIF) from the Quadrilátero Ferrífero (southeastern Brazil) shows a compositional layering with alternating iron-rich and quartz-rich layers. This layering was intensively folded and transposed at a centimeter/millimeter scale through a component of bedding-parallel shear related to flexural slip at middle to high greenschist facies conditions (400–450 jC). The microstructure and c-axis fabrics of normal limbs, inverted limb and hinge zones of a selected isoclinal fold were analyzed combining optical and scanning electron microscopy (SEM) and digital image analysis. In the normal limbs, recrystallized quartz grains show undulose extinction, relatively dry grain boundaries, c-axes at high angle to foliation and a pervasive grain shape fabric (GSF) indicating operation of crystal-plastic processes. In the inverted limb, quartz grains show more serrated and porous (‘‘wet’’) grain boundaries; the GSF is similar to that of the normal limb, but c-axes are oriented at 90j to those of the normal limb. We interpreted these characteristics as reflecting operation of solution-precipitation deformation in inverted limbs, as a consequence of grains having been rotated to an orientation that was hard to basal hai glide, but easy to dissolution-precipitation creep. This deformation partitioning between crystal-plasticity and solution-transfer during folding/ transposition of quartz may explain the common occurrence of layered quartz rocks, where individual layers show alternating caxis fabrics with opposite asymmetries but a consistent GSF orientation. Such characteristics may reflect an earlier event of pervasive folding/transposition of a preexisting layering.
ISSN: 0040-1951
metadata.dc.rights.license: O periódico Tectonophysics concede permissão para depósito deste artigo no Repositório Institucional da UFOP. Número da licença: 3480320613550.
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