Date of Award

2018

Degree Type

Thesis

Degree Name

Master of Science in Biological and Environmental Sciences (MSBES)

Specialization

Environmental and Earth Sciences (EVES)

Department

Geosciences

First Advisor

Dawn Cardace

Abstract

Altered waters impacted by serpentinization of Coast Range Ophiolite (CRO) ultramafic units have been reacting with trapped Cretaceous seawaters, meteoric waters, and other surface derived waters since tectonic emplacement of this ophiolite. In 2011, groundwater monitoring wells of various depths were established near Lower Lake, CA, USA in the McLaughlin Natural Reserve, administered by the University of California-Davis, in order to understand ongoing low temperature alterations and biogeochemical interactions taking place. Wells were installed at two sites in the Reserve. There are three Quarry Valley area wells (QV1-1 [23m depth], QV1-2 [14.9m], QV1-3 [34.6m]) and five Core Shed area wells (CSW1-1 [19.5m], CSW1-2 [19.2m], CSW1-3 [23.2m], CSW1-4 [8.8m], CSW1-5 [27.4m]). Water samples were collected from all installed wells, as well as from an older well drilled near the historic core shed (Old Core Shed Well, or OCSW [82m]), and an upper (TC1) and lower (TC2) site sampling a nearby groundwater-fed alkaline seep, at Temptation Creek. Key environmental parameters (temperature, pH, conductivity, oxidation-reduction potential, and dissolved oxygen) were collected in the field using YSI-556 multiprobe meter, and total concentrations for major cations (Ca+2, Na+, Mg+2, K+) were analyzed using Thermo Scientific iCAP 7400 Inductively Coupled Plasma-Atomic Emission Spectrometry, and anions (F-, Cl-, SO4-2, NO3-) on Dionex Modular DX 500 Ion Chromatography.

Principal component analysis was conducted to determine key factors and processes controlling water chemistries at CRO. Geochemist’s Workbench software was used to model the low temperature alteration of a serpentinization-influenced model water volume passing through serpentinite over a period of 100 million years. Modeling provided insight into the changing pH, Eh, evolving water chemistries, stepwise mineral assemblages, appearance of marker minerals at geochemical transitions in the system, and supported evidence of pervasive impacts of low temperature, oxidative weathering of serpentinites. This work supports the case of incremental dilution and transformation of a deeply sourced Ca2+ -OH- Type II water in this environment, and constrains reaction status of present day CRO waters and those of similar sites, in terms of the progress of serpentinite weathering reactions. Further, the study informs our understanding of serpentinization-related geological environments present on other celestial bodies (e.g., Mars, Europa, Enceladus) in our Solar System and beyond.

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