Rare earth elements in olivine:determination, occurrence and behaviour
Citation:
STEAD, CLARE VICTORIA, Rare earth elements in olivine:determination, occurrence and behaviour, Trinity College Dublin.School of Natural Sciences.GEOLOGY, 2018Download Item:
Abstract:
Olivine is a widely occurring mineral that offers great potential for improving our
understanding of geological processes. Olivine is present across a range of
geologically significant settings, occurring in stony-iron meteorites, as inclusions
in diamonds and as a dominant phase in upper mantle peridotite. The utility of the
trace elements in olivine has been established through their application as
geothermobarometers and as a tool for discrimination of mantle lithologies. The
study of the rare earth elements (REE) in olivine has lagged behind that of the
trace elements due to their ultra-low abundances. However, the value of REE
studies has been proven through their application in minerals such as garnet, upon
which the field of mantle metasomatism, for example, has rapidly expanded, as
well as Ca perovskite, which has added much to our understanding of the
differentiation in the early earth. With the precedent set and rapidly advancing
analytical capabilities, the REE in olivine are in a prime position for geochemical
exploration.
This thesis presents a novel analytical technique for determination of the REE in
olivine using laser ablation quadrupole inductively coupled plasma mass
spectrometry (LA-QICP-MS) and demonstrates the application of this technique
for a global suite of olivine. Building upon this research, this thesis brings new
insights into olivine-melt and olivine-mineral REE partitioning behaviour. Key
findings from this aspect of the thesis are that: 1) the olivine Mg number (Mg#)
exerts a strong control over REE partitioning via its influence over lattice
elasticity; and 2) that the LREE in natural olivine may experience preferential
diffusion of the light REE (LREE) from neighbouring phases or grain boundary
fluids/melts. This work thus provides a framework within which the REE in
olivine can be interpreted. With this framework established the final aspect of this
thesis uses the study of the REE in olivine to assess the metasomatic model for
Archaean peridotite. Mass balance modelling of the REE in olivine,
orthopyroxene and garnet with a range of reasonable metasomatic agents has
shown that the conventional metasomatic model cannot replicate all three phases.
In doing so this work highlights the importance of analysing all the major phases
in such studies. Furthermore this thesis has revealed olivine to be an important
host of the REE in Archaean peridotite. This paves the way for future studies to
exploit the REE contents of olivine and bolster geochemical studies of the subcontinental
lithospheric mantle (SCLM).
Author's Homepage:
http://people.tcd.ie/steadcvDescription:
APPROVED
Author: STEAD, CLARE VICTORIA
Advisor:
Tomlinson, EmmaPublisher:
Trinity College Dublin. School of Natural Sciences. Discipline of GeologyType of material:
ThesisAvailability:
Full text availableKeywords:
Metasomatism, Mantle, Rare Earth Elements, Olivine, GeochemistryMetadata
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