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

Rem: Revista Escola de Minas

Cristiane Castro Gonçalves²  Greg Hirth¹  Leonardo Lagoeiro¹ 

[1] ,DEGEO-EM-UFOP

关键词: Banded iron formation;    rheology;    experimental deformation;    axial compression;    Formação ferrífera bandada;    reologia;    deformação experimental;    compressão axial;   

DOI  :  10.1590/S0370-44672012000400010

来源: SciELO

【 摘 要 】

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.

【 授权许可】

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