Twinning Strains in Synfolding Calcite, Proterozoic Sinian System, China

Geosciences

John P. Craddock¹  Junlai Liu²  Yuanyuan Zheng² 

[1] Geology Department, Macalester College, St. Paul, MN 55105, USA;State Key Laboratory of Geological Processes and Mineral Resources and Key Laboratory of Lithosphere Tectonics, China University of Geosciences, 29 Xueyuan Rd., Beijing 100083, China;

关键词: structural geology;    folding dynamics;    strain analysis;   

DOI  :  10.3390/geosciences8040131

来源: DOAJ

【 摘 要 】

Synfolding calcite was precipitated between layers of Neoproterozoic sandy dolomite and striated parallel to the fold axis of an open anticline with a shallow plunge during folding. The fold had limb dips of 45° and plunged 20° to the south. The synfolding calcite had sub-horizontal grooves that trended parallel to the fold. Limb-hinge-limb calcite samples (3 samples; n = 100 grains) preserved a layer-parallel shortening strain that trended at an acute (45°) angle to the trend of the fold axis and fold lineations. Extension axes were vertical and there was no strain overprint (low NEVs). Shortening strain magnitudes were −2.9% and the differential stress responsible for twinning was −38 MPa. The commonly observed structures were layer-parallel slip striations normal to the fold axis: sub-horizontal interlayer slip surfaces parallel to a fold axis (parallel to bedding strike) were unreported; as was a sub-horizontal shortening strain at an acute angle to the axis of a plunging fold.

【 授权许可】

Unknown