Heterogeneous meteoric fluid infiltration within a young detachment-related shear zone

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Syn-orogenic detachment faults exhuming extensional shear zones are ever-present features in orogenic settings on Earth. Kinematic and fluid-flow models for brittle detachment faults paired with crystal–plastic shear zones continue to evolve alongside new data and techniques. Evidence for meteoric water infiltrating the frictional–viscous transition zone in detachment-related shear zones has survived revisions of these models, but the extent and influence of meteoric–hydrothermal circulation is not fully understood. Kinematic analysis and δ 2 H values of syn-kinematic micas from nine transects through the <6–0 Ma footwall shear zone of the Cordillera Blanca Detachment in the Peruvian Andes explore patterns of fluid flow during shear zone initiation and evolution at a previously unattained resolution. δ 2 H values reveal a pervasive pattern of meteoric water infiltration into the frictional–viscous transition zone across the detachment. Gradients in δ 2 H values reveal that fluid infiltration follows patterns of anataxial magmatism and the distribution of syn-kinematic fractures within and across the shear zone. Cumulatively, a three-dimensional assessment of the footwall shear zone of the Cordillera Blanca Detachment indicates that fluid infiltration into the frictional–viscous transition zone is spatially heterogeneous and correlated with the style of shear zone initiation and strain localization. Observed variability of fluid–rock interaction across the Cordillera Blanca Detachment highlights the importance of assessing for spatial heterogeneity when quantifying or qualifying fluid activity in meteoric–hydrothermally modified detachment faults.