Award Date

2009

Degree Type

Thesis

Degree Name

Master of Science in Geoscience

Department

Geoscience

Advisor 1

Adam Simon, Committee Chair

First Committee Member

Oliver Tschauner

Second Committee Member

Eugene Smith

Graduate Faculty Representative

Andrew Cornelius

Number of Pages

39

Abstract

Yttrium is used in geochemical investigations of arc volcanics and metamorphic geothermometers. The ability to use Y as a geochemical tool is predicated on an understanding of the mobility of Y during fluid-saturated conditions attending metamorphic and igneous processes. The goal of this work was to use the hydrothermal diamond anvil cell (HDAC) and synchrotron radiation X-ray fluorescence to quantify, in situ, the concentration of Y in aqueous fluids at 2-5 GPa and 650 - 800 °C; conditions likely at the oceanic lithosphere - mantle wedge interface in subduction zones. Previous studies have used modified diamond anvils which limits their maximum pressure to ~2 GPa. I used unmodified diamond anvils to extend this range to greater pressure, hence simulating greater depth (about 80-140 km), where significant dehydration of the subducting oceanic lithosphere is hypothesized to occur. With the detectors oriented 10° relative to forward scattering geometry, Rayleigh scattering of the diamond anvils was sufficiently reduced to observe Y fluorescence within the HDAC. However, I observed a non-linear relationship between concentration and fluorescence. The new technique offers great promise, and future work to increase sensitivity, perhaps by increasing counting times, is warranted.

Keywords

Arc volcanoes; Element mass transfer; Fluid phases; High pressure; Hydrothermal diamond anvil cells; In situ; Oceanic lithosphere; Solid phases; Sub-arc mantle wedge; Subduction zones; Synchrotron radiation X-ray fluorescence; Temperature-pressure conditions; Trace elements; Yttrium(Y)

Disciplines

Geochemistry | Geology | Tectonics and Structure | Volcanology

Language

English


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