131-5 Detailed Fluid Records from the Whipple Mountains Core Complex.

Session: Going with the Shear - New Insights into Lithospheric Extensional and Strike-Slip Systems

Presenting Author:

Claudia Roig González

Authors:

Roig González, Claudia I. ¹, Bonamici, Chloë², Blum, Tyler³, Nachlas, William O.⁴

(1) Dipartimento di Scienze Biologiche, Geologiche e Ambientali–BiGeA, Alma Mater Studiorum Università di Bologna, Bologna, BO, Italy, (2) Department of Geoscience, University of Wisconsin-Madison, Madison, WI, USA, (3) Department of Geoscience, University of Wisconsin-Madison, Madison, WI, USA, (4) Department of Geoscience, University of Wisconsin-Madison, Madison, WI, USA,

Abstract:

Extensional detachment fault systems of metamorphic core complexes (MCC) have the potential to facilitate significant fluid movement between Earth’s surface and the ductile middle crust. Oxygen isotopes have long been recognized as potential tracers of surface-to-depth fluid flow in MCCs, and could provide a record of fault-controlled hydrothermal activity and fluid-assisted deformation. However, typical sampling methods and the competing effects between temperature and fluid composition have made oxygen isotope signatures of meteoric fluid infiltration difficult to detect and/or interpret in the MCC rock record. This study uses in situ secondary ion mass spectrometry (SIMS) δ¹⁸O analysis as a tool to investigate fluid-rock interactions in the Whipple Mountains MCC footwall mylonites at a new level of detail. Here we present two datasets: (1) the rock record of meteoric fluid interactions and temperature variation beneath the Whipple detachment fault (WDF) using SIMS δ¹⁸O measurements in quartz and epidote; (2) in situ SIMS δ¹⁸O measurements in feldspar porphyroclasts from quartzofeldspathic mylonites with multiple crosscutting brittle and ductile deformation microstructures to characterize intragrain oxygen isotope zoning, and relate δ¹⁸O signatures with deformation microstructures and fluids effects.   All of the phases investigated by SIMS – epidote, quartz, feldspars – record interactions with low- δ¹⁸O fluids during deformation-related recrystallization, though the relative timing and extent of interaction varies as a function of depth. Quartz and feldspars are modally and rheologically important phases in the Whipple Mountains detachment system, and the low-δ¹⁸O values preserved within plastically deformed domains of these minerals implicates fluid infiltration in fault weakening. Feldspars in particular preserve a rich history of alternating brittle and ductile deformation behavior that suggests initial meteoric fluid infiltration via pervasive microcracking and a subsequent switch to creep deformation mechanisms.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-4585

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