Transport, survival and modification of xenoliths and xenocrysts from source to surface

Sasse, D. and Jones, T.J. and Russell, J.K. (2020) Transport, survival and modification of xenoliths and xenocrysts from source to surface. Earth Plan. Sci. Lett., 548. ISSN 0012-821X

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Abstract

A wide variety of magmas entrain, transport and erupt mantle material in the form of xenoliths and xenocrysts. The host magmas are often low viscosity in nature and range from basalt to more esoteric compositions such as kimberlite, nephelinite and basanite. Here we focus on kimberlite magmas which are particularly successful at transporting deep mantle cargo to the surface, including economically important quantities of diamond. Collections of mantle-derived xenoliths and xenocrysts are critical to our understanding of the structure, stability, composition, thermal state, age, and origin of the lithosphere. However, they also inform on magma transport conditions. Through a series of scaled analogue experiments, we document the relative mechanical stability of olivine, garnet, orthopyroxene, clinopyroxene and diamond xenocrysts during magma ascent. Our experiments fluidized these mantle minerals at a constant gas flux for variable amounts of time approximating transport in a high velocity, turbulent, fluid-rich (supercritical fluid or gas, depending on depth) magma. The evolution of mineral surface features, morphology and grain size distributions is analyzed as a function of residence time. We show that on timescales consistent with magma ascent, each mantle mineral is subject to mechanical modification resulting in mass loss and reshaping (rounding) by grain size reduction and surface pitting. We further discuss the chemical consequences of producing fine particle chips that are highly susceptible to dissolution. Lastly, we utilize an empirical model that relates textural observations (e.g. impact pit size) on xenocrysts to differential particle velocities. Our approach applied to natural kimberlitic olivine and garnet xenocrysts indicates differential velocities of ∼4ms −1 – the first direct estimate for velocity in an ascending kimberlite magma.

Item Type:
Journal Article
Journal or Publication Title:
Earth Plan. Sci. Lett.
Additional Information:
This is the author’s version of a work that was accepted for publication in Earth and Planetary Science Letters. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Earth and Planetary Science Letters, 548, 116499, 2020 DOI: 10.1016/j.epsl.2020.116499
Uncontrolled Keywords:
/dk/atira/pure/subjectarea/asjc/1900/1912
Subjects:
ID Code:
176265
Deposited By:
Deposited On:
06 Oct 2022 14:25
Refereed?:
Yes
Published?:
Published
Last Modified:
22 Nov 2022 11:50