New insights into the role of mantle hydration in the evolution of the Colorado plateau, U.S.A. and central Anatolia, Turkey

Riche, Alexis Taylor and Reid, Mary and Porter, Ryan (2023) New insights into the role of mantle hydration in the evolution of the Colorado plateau, U.S.A. and central Anatolia, Turkey. Doctoral thesis, Northern Arizona University.

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Abstract

Water has a significant impact on tectonic evolution. Hydration of the lithospheric mantle increases its susceptibility to melting and various forms of destabilization, which manifest at the surface as uplift and volcanism. However, how the shallow mantle lithosphere is hydrated and if water is preserved at geologic timescales remain poorly understood. In this dissertation, I investigate low-angle subduction as a mechanism for hydrating the shallow lithosphere in two regions: the Colorado Plateau in the southwestern United States of America (U.S.A.), and Central Anatolia, Turkey. The southwestern U.S.A. lithosphere may have been hydrated during Farallon flat slab subduction (~85-40 Ma), and Central Anatolia, Turkey, during Cyprean flat slab subduction (~40-20 Ma). We quantify water contents in near-primary post-orogenic basalts to provide insight into whether mantle sources remain hydrated after subduction ends. Water contents are compared to both newly obtained and previously reported major element, trace element, and isotopic compositions to evaluate whether hydration can be attributed to these flat slab events. Results show that the Colorado Plateau mantle lithosphere is variably but weakly hydrated. However, enrichment is attributed to silicate melt metasomatism that appears to predate Farallon slab subduction. We suggest that the presence of the Shatksy Rise Conjugate, a portion of the Farallon slab with overthickened crust, was drier than the rest of the slab and passed directly beneath the Colorado Plateau. Coupled with the effects of slab dehydration outboard of the Colorado Plateau, the Farallon slab was not carrying enough water to effectively hydrate the overlying mantle lithosphere. In contrast, water contents determined for subduction-modified Central Anatolian lithospheric mantle sources are significantly higher than those determined for the Colorado Plateau mantle lithosphere. Because no oceanic plateau subducted, the Cyprean slab was normally hydrated and could therefore transfer water into the overlying lithospheric mantle during subduction. However, mantle sources metasomatized by melts derived from the Cyprean slab and accompanying sediments have lower water contents than those of sources that represent the ambient upper mantle in this region. The ambient upper mantle may have been hydrated during a previous subduction event that occurred in the Late Cretaceous, and the mantle lithosphere retained water from both events. Unexpectedly low water contents in the Colorado Plateau mantle lithosphere can account for the resistance to deformation and limited volcanism in the plateau interior. Relatively higher water contents in the Central Anatolian mantle lithosphere could explain why Central Anatolia is characterized by more widespread volcanism and extensive lithospheric thinning than the Colorado Plateau. This dissertation also includes research that addresses the gender disparity in the field of geology, with a focus on female recruitment and retention at the undergraduate level. Much of the existing research on why women choose and remain in a geology major involves quantitative methods, but qualitative techniques are necessary to further explore the variables identified in quantitative studies. We therefore conducted interviews with several female students at a large public university in the U.S.A. Our analysis revealed that, while multiple factors such as personal interests and engagement in introductory courses influenced women to choose a geology major, relationships with faculty in the department were the most important in determining whether they would continue in the program through completion. We hope that geology departments globally may use these insights to reach gender parity.

Item Type:	Thesis (Doctoral)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	Geology; Central Anatolia, Turkey; Colorado Plateau; Farallon Slab; Cyprean Slab; Mantle hydration
Subjects:	Q Science > QE Geology
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > School of Earth Sciences and Environmental Sustainability
Date Deposited:	28 Jul 2026 17:43
Last Modified:	28 Jul 2026 17:43
URI:	https://openknowledge.nau.edu/id/eprint/6322

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