Date of Award
8-2025
Department
Geological and Environmental Sciences
First Advisor
David Zakharov, Ph.D.
Second Advisor
Stephen Kaczmarek, Ph.D.
Third Advisor
Christopher Mattinson, Ph.D.
Keywords
Ophiolite, triple-o isotopes
Access Setting
Masters Thesis-Open Access
Abstract
The Ingalls Ophiolite Complex is an ophiolite of Jurassic age in central WA, USA. Much of the complex formed in a supra-subduction zone setting in a back-arc ocean basin during subduction of the Farallon plate beginning 192 Ma. Between formation and obduction, mafic and ultramafic lithologies experienced alteration in the presence of water, which previous studies inferred to be seawater. Previously published δ¹⁸O and δD data from the Ingalls indicates isotopic depletion possibly caused by interaction with meteoric water at current latitude (~47.5 °N). The current study reports new δD, δ¹⁸O, and Δ ′¹⁷O measurements from mafic and ultramafic lithologies in the Ingalls complex to untangle different fluid-induced alteration episodes caused by water-rock interactions in various tectonic settings. Variably serpentinized ultramafics have δD values which range between -160‰ to -60‰ VSMOW, and δ18O ranges between 0-7‰ VSMOW. Low δD values and some of the low δ¹⁸O values are best explained by recent serpentinization by meteoric waters similar in composition to those falling over central Washington today. One calculated equilibrium fluid has composition δD = -112.8‰ VSMOW and δ¹⁸O = -4.0‰ VSMOW at W/R(water-to-rock ratio) =1, which corresponds to a shifted meteoric water of original composition δD = -96.2‰ VSMOW; δ¹⁸O = -9.0‰ VSMOW, if serpentinization occurred at 100 °C. Based on petrographic analyses, field relationships, and stable isotope data, these data suggest that mafic and ultramafic lithologies record an intricate alteration history. The proposed model includes original seawater-derived fluids recorded in serpentinites and meteoric waters involved in serpentinization along faults.
Recommended Citation
Stevens, Zachary Russell, "Understanding the fluid source during alteration of former oceanic lithosphere in the polygenetic Ingalls Ophiolite Complex, Washington, USA" (2025). Masters Theses. 5474.
https://scholarworks.wmich.edu/masters_theses/5474