206 Strain and Displacement: Patterns, Gradients, Partitioning, and Reconstructions

This session aims to bring together researchers from structure-related disciplines to facilitate discussions of approaches that inform our understanding of strain and displacement. We welcome contributions from observations, experiments, theory, and modeling that characterize deformation from micro to tectonic scales.

Tuesday, 21 October 2025
1:30 PM - 5:30 PM
HBGCC, 217C

Determining vorticity history through coupled U-Pb titanite dating and crystallographic vorticity analysis

Paper number: 206-2
Program: Technical Sessions
Time: 2:05 PM – 2:20 PM

Authors

Abstract

We couple petrochronology with crystallographic vorticity axes analysis to track vorticity history – a critical part of the strain history (or deformation path) - within a high-temperature shear zone. In Little Goose Creek orthogneiss of the western Idaho shear zone, USA, we can distinguish relict igneous, partially to fully recrystallized, and neoblastic titanite crystals. Trace element chemistry independently validates these titanite populations such that we can contextualize the relationship of the titanite grains within the macroscopic rock fabric to a high-precision isotope dilution U-Pb geochronological age. Thus, the onset of deformation and progressive strain accumulation is preserved in the trace element and U-Pb ages of these titanite crystals. Given this relationship, we assessed intra-grain crystallographic misorientation and crystallographic vorticity axes in the different titanite populations. The different populations of titanite yield different crystallographic vorticity axes in both the fabric and geographic reference frames, indicating that the vorticity axis changed through time. The shear zone initiates with vertical crystallographic vorticity axes, parallel to the stretching lineation but switched to predominantly horizontal crystallographic vorticity axes by ca. 84 Ma. We infer a transition lasting approximately 10 Ma from pure-shear dominated to wrench dominated dextral transpression within the western Idaho shear zone. Our integrated petrochronological and microstructural investigation documents that by combining titanite with crystallographic vorticity analysis, U-Pb ages, and trace element geochemistry, we can describe the vorticity path of a high-temperature shear zone through time. 

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-414530

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