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

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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> 2 H values of synkinematic micas from nine transects through the &lt;6 to 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. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> 2 H values reveal a pervasive pattern of meteoric water infiltration into the frictional-viscous transition zone across the detachment. Gradients in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> 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 3-dimensional assessment of the footwall shear zone of the Cordillera Blanca Detachment indicates that fluid infiltration into the frictional-viscous transition zone is spatially heterogenous 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.