STRAIN PARTITIONING AND FACTORIZATION IN A QUARTZ ARENITE

Most rocks deform by multiple grain-scale deformation mechanisms. In o rder to assess completely the contributions of each mechanism, the str ain associated with that mechanism must be known and compared to the f inite strain. This study describes the partitioning of strain between three mechanisms, pressure solution, dislocation creep, and microfract uring, in a quartz arenite deformed at low temperatures. Pressure solu tion, which occurred primarily during compaction, dominates the finite strain with an average of 24% shortening normal to bedding. Dislocati on creep, which occurred during layer-parallel shortening, accounts fo r about 2% shortening parallel to bedding dip. Microfractures, which o ccur in three orthogonal sets, resulted in 2-4% extension normal to be dding, parallel to bedding strike, and parallel to bedding dip. The va lidity of the mechanism strains was tested using strain factorization. Models were constructed using the mechanism strains in an order deter mined by their relative ages. Because porous, well-sorted quartz areni tes, such as the one studied; are likely to undergo some mechanical co mpaction in the early stages of diagenesis, variable amounts of mechan ical compaction were included in factorization models. Models using th e measured deformation mechanism strains with an initial 5-10% mechani cal compaction yield finite strains in close agreement with the measur ed finite strains. This suggests that the mechanisms identified, the s train associated with each mechanism, and the deformation sequence are plausible. (C) 1998 Elsevier Science Ltd. All rights reserved.