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Triple Oxygen Isotope Paleoaltimetry of the Kettle Metamorphic Core Complex (WA, USA)

The application of the triple oxygen isotope system (16O-17O-18O) provides a new tool for stable isotope paleoaltimetry. Here, we use triple oxygen isotope (Δ’17O) geochemistry to determine the past elevation of the Eocene Kettle Metamorphic Core Complex (MCC) (Washington, USA). We analyze quartz-muscovite pairs from mylonitic quartzites from the MCC-bounding shear zone. δ18O values range from 4.8 to 11.3‰ (muscovite) and 6.8 to 14.6‰ (quartz) and Δ’17O values (λref = 0.528) range from -0.054 to -0.077‰ (muscovite) and -0.052 to -0.071‰ (quartz). The calculated quartz-mica oxygen isotope equilibrium temperature averages 390°C ± 90°C, which in line with observed quartz microstructures. Compared to existing muscovite hydrogen isotope data (δD = -101 to -138‰), both approaches, δD-δ18O and δ’18O-Δ’17O, indicate oxygen and hydrogen isotopic exchange between syntectonically formed minerals and a meteoric-derived fluid within the Kettle shear zone. We find that the shear zone minerals are in isotopic equilibrium with a fluid having a δ18Owater value of ~-14‰, which likely reflects high-elevation inland precipitation. Combined with a low-elevation δ18Owater estimate (-6 to -8 ‰) from the Eocene near-coastal Chumstick Basin (WA, USA), the δ18Owater estimate translates into a paleoelevation of 3-4 km for the Eocene Kettle MCC. This is consistent with δD-based elevation estimates of 4.2 km and underscores the robustness and complementary nature of the two different isotopic approaches.

Details

Author
Katharina A. Methner1, Daniel E. Ibarra2, Andreas Mulch3, Page C. Chamberlain4
Institutionen
1University Leipzig, GER; 2Brown University, USA; 3Senckenberg Biodiversity and Climate Research Centre, GER; 4Stanford University, USA
Veranstaltung
GeoSaxonia 2024
Datum
2024
DOI
10.48380/yb0r-gf43