Journal
JOURNAL OF STRUCTURAL GEOLOGY
Volume 71, Issue -, Pages 41-57Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jsg.2014.10.005
Keywords
Metamorphic core complex; Detachment shear zone; Quartz microstructures; Hydrogen stable isotope; Oxygen stable isotope; Fluid-rock interaction
Categories
Funding
- Swiss Science Foundation [FNS-117694]
- US-NSF [EAR-0838541]
- NSF-EAR [0838058]
- DOE [93ER14389]
- LOEWE program of Hesse's Ministry of Higher Education, Research and the Arts
- Directorate For Geosciences
- Division Of Earth Sciences [1524336, 0838058] Funding Source: National Science Foundation
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Combined geochronological and stable isotope data of quartzite mylonite from the footwall of the Raft River detachment shear zone (NW Utah, USA) reveal that an important phase of ductile deformation and infiltration of meteoric water in the shear zone occurred in Miocene time. 40Ar/39Ar release spectra are complex, and plateau ages decrease systematically from 31.1 +/- 0.8 Ma at the top to 20.2 +/- 0.6 Ma at the bottom of the quartzite mylonite section, capturing a segment of the similar to 40-15 Ma geochronologic record that has been documented regionally and is likely related to partial to total overprinting of Eocene white mica 40Ar/39Ar ages in the Miocene. Hydrogen stable isotope values of syn-kinematic muscovite range from -123 parts per thousand to -88 parts per thousand and suggest that meteoric water infiltrated the detachment shear zone during mica (re)crystallization and mylonite development. Bulk stable isotope analyses from fluid inclusions in quartz support a meteoric origin for the fluid (low D/H and O-18/O-16 ratios). Quartz and muscovite oxygen isotope analyses show varying degrees of O-18 depletion, suggesting spatially variable time-integrated interaction of meteoric fluids with recrystallizing shear zone minerals. The overall pattern of D/H and O-18/O-16 ratios indicates that fluids were channelized along restricted layers or shear zones within the deforming detachment system. The variability in O-18/O-16 ratios of both quartz and muscovite and the fluid-rock isotopic exchange results can be explained by variations in the shear zone permeability (confined versus diffuse flow) along with strain variations along the transport direction (from flattening to constriction). Published by Elsevier Ltd.
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