177 Chronology of Orogenesis: Unlocking the Timelines of Mountain Building

The focus of this session is the use of geochronological methods (including but not limited to U-Pb, Ar/Ar, FT, (U/Th)-He) to establish the timing of key events in mountain building, including different orogenic phases, exhumation, and uplift rates.

Tuesday, 21 October 2025
8:00 AM - 12:00 PM
HBGCC, 304C

Zircon and Titanite U-Pb Petrochronology Records Strain Localization Facilitated by Magmatism: An Example from the Western Idaho Shear Zone

Paper number: 177-2
Program: Technical Sessions
Time: 8:07 AM – 8:27 AM

Authors

Abstract

In convergent margin settings, granitoid-hosted shear zones record deformation related to the construction and modification of continental magmatic arcs. In sheared granites, we can leverage tandem zircon and titanite U-Pb geochronology to decipher the spatial-temporal patterns of magmatism and solid-state deformation. Moreover, titanite ages can be characterized with trace element geochemistry and thermometry, thereby distinguishing titanite populations that correspond to magmatic intrusion versus those related to subsequent high-temperature deformation. 

 

The western Idaho shear zone (WISZ) is a Cretaceous, lithospheric-scale structure at the boundary between accreted terranes and Laurentia. Across a 20 km transect, we document 25 million years of magmatism (115-90 Ma) and 30 million years of deformation (105-75 Ma). This deformation duration is longer than previous estimates of WISZ shearing. In general, titanite records strain progressing inward towards the continent, mimicking the progression of pluton emplacement ages as determined by zircon geochronology. We document areas of distributed strain and strain localization that are correlated with nearby magmatic intrusions. In the WISZ, the spatial-temporal patterns of magmatism appear to exert a first-order control on the spatial-temporal patterns of deformation. Our results suggest that arc magmatism manifests in western Idaho as km-scale intrusions that weaken the crust and prompt strain localization related to the collision of the Insular superterrane. These zones remain weak and deform for a protracted period coincident with the translation of terranes along the Cordilleran margin.

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

doi: 10.1130/abs/2025AM-412358

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