Publication Type:

Book Chapter

Authors:

Li, Chengcheng; Jiang, Dazhi

Source:

Flow of rocks; field analysis and modeling; in celebration of Paul F. Williams' contribution to mentoring, Elsevier, Oxford, International, Volume 33, p.203-219 (2011)

ISBN:

0191-8141

Keywords:

clasts, fabric, faults, geometry, kinetics, numerical analysis, Numerical models, plastic flow, preferred orientation, rigidity, shear zones, structural analysis, theoretical studies, transpression, vorticity

Abstract:

Estimating the kinematic vorticity numbers from rock fabrics presents many problems. In this paper we use numerical modeling to investigate the reliability of those widely-used vorticity analysis methods using rigid clasts. We use very simple flows (steady state, homogeneous, and having monoclinic symmetry) to represent plane-straining zones and transpressional zones and assume that the rotation of rigid clasts perfectly obeys the theory of Jeffery (1922, Proceedings of the Royal Society of London A102, 161-179). These are assumptions made in current vorticity analysis using rigid clasts. Even with these simple assumptions, our modeling shows that the current methods have intrinsic uncertainties so large that it is pointless to use the estimated vorticity numbers to constrain shear zone boundary conditions and kinematics. It is perfectly consistent with numerical modeling results if the currently reported vorticity numbers estimated from rigid clasts (in the range of 0.50-0.85) are all interpreted as being from natural shear zones with close-to-simple-shearing flows. The large uncertainties arise because the motion of rigid clasts is intrinsically a three dimensional problem. Abstract Copyright (2011) Elsevier, B.V.

Notes:

GeoRef, Copyright 2018, American Geological Institute.<br/>2011-064157<br/>vorticity analysis<br/>vorticity number