Forward and Inverse Modeling of the Development of Quartz Crystallographic Preferred Orientation Textures in Shear Zones
Abstract
We describe numerical experiments that simulate the development of quartz crystallographic preferred orientation (CPO) textures in a deforming quartz-rich rock. Our forward model begins with a set of uniformly random quartz crystallographic orientations. Given an explicit shear zone deformation, where the strain magnitude, strain geometry (i.e., Flinn's k-value/Lodes ratio), and kinematic vorticity number (Wk) are all specified, the model simulates the rotation of each orientation according to the Taylor-Bishop-Hill theory (similar to the experiments developed by Lister et al. (1978)). Then it partitions the space of orientations into b boxes of equal volume and similar shape, for some large number b. By counting the post-deformation orientations in each box, it produces a 'histogram' of b integers, which quantifies aspects of the CPO. Our inverse model begins with a data set of orientations, assumes that they were initially uniform, and attempts to deduce the shear zone deformation that produced them. The inverse model minimizes the least-squares mismatch between histograms, by running the forward model repeatedly within a numerical optimizer. By working with synthetic data sets with realistic uncertainties, we explore the feasibility of this approach for naturally deformed quartz-rich rocks. We investigate the effects of sample size (number of data points), fineness of the partition (increasing b), aliasing (the discretization error arising from counting boxes individually), and model selection (e.g., monoclinic vs. triclinic shear zones).
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T43C0446D
- Keywords:
-
- 8011 Kinematics of crustal and mantle deformation;
- STRUCTURAL GEOLOGY;
- 8012 High strain deformation zones;
- STRUCTURAL GEOLOGY;
- 8030 Microstructures;
- STRUCTURAL GEOLOGY;
- 8031 Rheology: crust and lithosphere;
- STRUCTURAL GEOLOGY