The rheology of banded iron formation: constraints from axial compression experiments

• Autor(a) principal: Gonçalves,Cristiane Castro
• Data de Publicação: 2012
• Outros Autores: Hirth,Greg, Lagoeiro,Leonardo
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: REM. Revista Escola de Minas (Online)
• Texto Completo: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672012000400010
• topic: Banded iron formation; rheology; experimental deformation; axial compression

Samples of Banded Iron Formation (BIF) with different quartz and hematite contents were deformed in axial compression experiments in a Griggs-type apparatus, at T = 900ºC, P =1.5 GPa and strain rates of 10-5 and 10-6 s-1. The aim is to investigate the mineral phase that controls the rheology of multi-phase rocks and to determine the processes that control the observed rock strength. BIF samples from Quadrilátero Ferrífero region-Brazil were cored perpendicular to the foliation, which is defined by parallel bands of quartz and iron oxide. Sample strength decreases with increasing hematite content and decreasing strain rate. At a strain rate of 10-5 s-1, samples with well-developed compositional banding showed higher strength. At the slower strain rate of 10-6 s-1 no difference between samples with or without compositional banding is observed. For comparison, at 10-6 s-1, the highest quartz content sample is as weak as the highest hematite content sample at 10-5 s-1. Strain is localized in hematite-rich layers. One intriguing observation is that quartz grains within the more deformed hematite-rich bands show more evidence for crystal-plastic deformation than grains in quartz-rich bands.