Heterogeneity and depletion of the mantle assessed from abyssal peridotite geochemistry
Abstract/Contents
- Abstract
- Mid-ocean ridges are the surface expressions of plate tectonics and mantle convection, where decompression melting of the upper mantle produces the basaltic crust. Despite the information provided by basalts on mantle composition, they are mixtures of melts sourced from large regions. In contrast, abyssal peridotites are the residues of melting and they can be used to directly study the Earth's mantle in locations where they are emplaced on the seafloor. In this dissertation, I use abyssal peridotites to constrain mantle composition, including evidence for long-term heterogeneity and an exploration of the behavior of the element lead (Pb) -- a key geochemical tracer -- during melting. In Chapter 1, I use peridotites from the ultraslow spreading Gakkel Ridge in the Arctic Ocean to assesses the spatial variation in chemical compositions of peridotite and to explore the long-term effects of ocean ridge melting and refertilization on mantle composition. In chapter 1, the spatial length-scale of compositional variability observed among Gakkel peridotites indicates the existence of a heterogeneous mantle, including refractory mantle produced by ancient melt depletion unrelated to the current ridge setting. Chapters 2 and 3 explore the distribution and partitioning of Pb in the mantle, using peridotites from the Gakkel and Southwest Indian Ridges. Despite the importance of Pb for isotopic models of Earth's geochemical evolution, the mineralogical host of Pb in the mantle is poorly constrained. Sulfide has been suggested to contain the majority of mantle Pb, even though it occurs at modal abundances < 0.1% in peridotite. In Chapter 2, I develop a method for the in situ measurement of Pb and other trace element abundances in sulfides. Sulfides have an average Pb concentration of 2 ppm, which I incorporate into a model of sulfide petrogenesis to suggest that current estimates for source mantle composition contain too little Pb. Finally, Chapter 3 presents a comprehensive mass balance for Pb, by using Pb concentrations in the silicate phases, in addition to the sulfides, to reconstruct whole rock compositions and compare these to the measured whole rock. The results of this calculation show that Pb is hosted in a combination of silicate and sulfide phases, which is key for understanding the transport and long-term storage and abundance of mantle Pb.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2016 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | D'Errico, Megan Emily Willi |
|---|---|
| Associated with | Stanford University, Department of Geological and Environmental Sciences. |
| Primary advisor | Grove, Marty, 1958- |
| Primary advisor | Warren, Jessica |
| Thesis advisor | Grove, Marty, 1958- |
| Thesis advisor | Warren, Jessica |
| Thesis advisor | Ernst, W. G. (Wallace Gary), 1931- |
| Advisor | Ernst, W. G. (Wallace Gary), 1931- |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Megan Emily Willi D'Errico. |
|---|---|
| Note | Submitted to the Department of Geological and Environmental Sciences. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2016. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2016 by Megan E D'Errico
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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