Focusing Fluids in Faults: Evidence From Stable Isotopic Studies of Dated Clay‐Rich Fault Gouge of the Alberta Rockies

Isotopic studies of Canadian Rocky Mountain thrust faults preserve the timing and identity orogenic fluids their fault zone pathways. Using previously dated samples, we measure O- H-isotopic compositions gouge. These nearly 100% neomineralized gouges associated damage zones act as primary fluid As such, they provide a specific local look into nature Late Jurassic to Early Eocene plumbing system in Alberta Rockies. Considering clay polytype stability regional temperature conditions, obtain range geofluid isotopic during Jurassic-Eocene faulting: δ18Ofluid ranged from ∼−3.3 9.2 ± 3.2‰; δDfluid −119 −46 13‰ VSMOW. The reflects mixing sources, including pervasive presence surface-sourced (up ∼90%). interpreted prevalence surface source rocks is agreement with trends observed undated veins fractured host rock. Our results confirm that Mountains acted major fluid-focusing conduits activity. We further show these incorporated both deeply sourced enhanced dynamic permeability, heterogeneously distributing along planes across fold-thrust belt, promoting growth fault-zone weakening minerals.