Semester of Graduation

Summer 2026

Degree

Master of Science (MS)

Department

Geology and Geophysics

Document Type

Thesis

Abstract

Abyssal peridotites provide a direct record of mantle melting and melt transport beneath mid-ocean ridges. However, the pervasive presence of plagioclase-bearing domains suggests that many peridotites have been chemically modified by melt-rock interaction during upwelling. This study investigates the mineral chemical systematics and small-scale spatial variation within a suite of 18 exceptionally fresh peridotite samples recovered from a single dredge site (PS59-235) on the ultraslow-spreading Gakkel Ridge. Using Electron Probe Microanalysis (EPMA), three distinct petrographic groups were characterized: plagioclase-free (PFP), plagioclase-impregnated (PIP), and plagioclase-bearing (PBP) peridotites. The PFP group represents a relatively fertile baseline (Cr# 0.07 – 0.20), corresponding to low degrees of partial melting (F ≈ 1 – 5%). In contrast, the PIP and PBP groups define a transverse geochemical trajectory, with spinel Cr# reaching 0.61 (F ≈ 15%) and Mg# dropping as low as 0.53. This major element shift is coupled with a significant enrichment in incompatible minor elements, including TiO2 (up to 0.49 wt.%) and MnO (up to 0.23 wt.%). These results demonstrate that the PS59-235 sample suite is not a simple homogenized residue of mid-ocean ridge melting, but a complex mantle mosaic that reveals a multi-stage cooling and evolutionary history. The coupled Fe – Ti enrichment and the presence of modal clinopyroxene (up to 8%) in the depleted samples provides definitive evidence for reactive porous flow and subsolidus re-equilibration within a conductively cooling lithosphere. Resolving these extreme small-scale variations highlights the impact of channelized melt transport on mantle composition and confirms that global averages are insufficient for capturing the complex structural and chemical evolution of ultraslow-spreading ridge systems.

Date

4-27-2026

Committee Chair

Loocke, Matthew

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

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