Strain partitioning and factorization in a quartz arenite

• Published in: Journal of structural geology 1998-08, Vol.20 (8), p.1065-1074
• Main Authors: Onasch, Charles M., Shen-Tu, Bingming, Couzens-Schultz, Brent A.
• Format: Article
• Language: English
• ISSN: 0191-8141; 1873-1201
• DOI: 10.1016/S0191-8141(98)00037-6

Most rocks deform by multiple grain-scale deformation mechanisms. In order to assess completely the contributions of each mechanism, the strain associated with that mechanism must be known and compared to the finite strain. This study describes the partitioning of strain between three mechanisms, pressure solution, dislocation creep, and microfracturing, in a quartz arenite deformed at low temperatures. Pressure solution, which occurred primarily during compaction, dominates the finite strain with an average of 24% shortening normal to bedding. Dislocation creep, which occurred during layer-parallel shortening, accounts for about 2% shortening parallel to bedding dip. Microfractures, which occur in three orthogonal sets, resulted in 2–4% extension normal to bedding, parallel to bedding strike, and parallel to bedding dip. The validity of the mechanism strains was tested using strain factorization. Models were constructed using the mechanism strains in an order determined by their relative ages. Because porous, well-sorted quartz arenites, such as the one studied, are likely to undergo some mechanical compaction in the early stages of diagenesis, variable amounts of mechanical compaction were included in factorization models. Models using the measured deformation mechanism strains with an initial 5–10% mechanical compaction yield finite strains in close agreement with the measured finite strains. This suggests that the mechanisms identified, the strain associated with each mechanism, and the deformation sequence are plausible.