Date of Award:

8-2024

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geosciences

Committee Chair(s)

Dennis L. Newell

Committee

Dennis L. Newell

Committee

Anthony R. Lowry

Committee

John W. Shervais

Abstract

Understanding flat-slab subduction is crucial as it involves the horizontal movement of an oceanic plate beneath a continental margin over a long distance. This tectonic process is widespread yet not fully understood, particularly regarding how it influences the chemical makeup of the continental plate and recycling in the hydrosphere. By analyzing isotopes, which are variations of certain elements found in minerals and water, we can gain insights into the sources of chemicals and geological processes at play. Our study area included six locations within the Navajo volcanic field (NVF), a region in the Colorado Plateau. We analyzed 23 lower crustal xenolith samples; xenoliths are fragments of rock brought up from deep within the interior of the by volcanic eruptions. Using a polarized microscope, we identified hydrous mineral phases that would give indications of past water-rock interactions. These minerals included hornblende, actinolite, biotite, muscovite, clinozoisite, epidote, and chlorite. By measuring the isotopic composition of hydrogen within these minerals, we can track the history of the rock’s interaction with water. Our findings revealed that during the Laramide orogeny, water from deep within the Earth’s crust, possibly originating from a tectonic plate called the Farallon slab, infiltrated the crustal rocks of the Colorado Plateau. This water caused changes in the mineralogy, leading to distinct isotopic signatures that we could measure. Interestingly, we found that isotopic composition of certain minerals from the Mules Ear and Moses Rock intrusions suggested a complex interaction between the rocks and the infiltrating water. This study explores how aqueous fluids moved from the flat slab to the continental plate above, ultimately impacting the mineralogical conditions of the lower crust and gives insights into complex interactions between fluids and rocks deep within the Earth’s crust.

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