FACILITATION OF THE STUDY OF MANTLE DYNAMICS THROUGH CALCIUM STABLE ISOTOPE MODELING AND SIMULANT GLASS SYNTHESIS

Author

Justin Hardin, University of Tennessee, KnoxvilleFollow

Orcid ID

https://orcid.org/0009-0000-1738-4221

Date of Award

8-2025

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Shichun Huang

Committee Members

Gregory A. Snyder, Nicholas J. Dygert, Daniel R. Dunlap

Abstract

I utilized new mineral-melt Ca isotope fractionation factors from Li et al. (2025) (the manuscript that this thesis is adapted from) to model the Ca isotope effects on both melts and residues during partial melting of spinel peridotite at 1-2 GPa, garnet peridotite at 3-7 GPa, and garnet pyroxenite / eclogite at 2.5-20.7 GPa. The model predicts that silicate melts only have δ^44/40Ca [delta calcium forty-four over calcium forty] up to 0.12 lower than their source value, consistent with previous estimates. Importantly, partial melts of spinel peridotite, garnet peridotite, and garnet pyroxenite / eclogite exhibit overlapping δ^44/40Ca [delta calcium forty-four over calcium forty] values, if their mantle sources have the same δ^44/40Ca [delta calcium forty-four over calcium forty]. In contrast to silicate melts, the model predicts that carbonatitic melts can have δ^44/40Ca [delta calcium forty-four over calcium forty] up to 0.24 lower than their mantle source, and the largest δ^44/40Ca [delta calcium forty-four over calcium forty] effect is found in carbonatitic melts produced under shallow mantle transition zone conditions. In both cases, partial melting alone cannot explain the full range of δ^44/40Ca [delta calcium forty-four over calcium forty] values observed in natural basalts and carbonatites, and at least part of this variation must reflect δ^44/40Ca [delta calcium forty-four over calcium forty] variations of their mantle sources.

The model calculations show that residues of partial melting always have δ^44/40Ca [delta calcium forty-four over calcium forty] higher than their mantle source, with the highest δ^44/40Ca [delta calcium forty-four over calcium forty] at 0.40 higher than the source value. This range is much smaller than that observed in natural ultramafic rocks that might represent residues of partial melting. In addition, the range and direction of intermineral Ca isotope fractionation factors predicted in the modeled residues for the mineral pairs orthopyroxene-clinopyroxene and garnet-clinopyroxene are much more restricted than those observed in natural ultramafic rocks, including peridotites, garnet pyroxenites, and eclogites. Therefore, most natural ultramafic rocks have likely experienced more complicated petrogeneses than partial melting.

In Chapter 2, the process of creating a simulant glass for the lower mantle mineral davemaoite is documented.

Recommended Citation

Hardin, Justin, "FACILITATION OF THE STUDY OF MANTLE DYNAMICS THROUGH CALCIUM STABLE ISOTOPE MODELING AND SIMULANT GLASS SYNTHESIS. " Master's Thesis, University of Tennessee, 2025.
https://trace.tennessee.edu/utk_gradthes/14497