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The genesis of kimberlites and some low-SiO_2, high-alkali magmas

Wyllie, P. J. (1989) The genesis of kimberlites and some low-SiO_2, high-alkali magmas. In: Kimberlites and related rocks. Special publication (Geological Society of Australia). Vol.1. No.14. Blackwell Scientific , Cambridge, MA, pp. 603-615. ISBN 0867930330.

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There are four levels within the upper mantle where critical changes occur in the physical processes that control the chemistry and migration of these magmas. The first two (2) and (3), are the depths where the solidus for peridotite-C-H-O is intersected by the geotherm, limiting the depth interval within which the magmas can be generated. The third critical level, (1), is the depth of the asthenosphere-lithosphere boundary, where the mantle flow regime changes from convective (ductile) to static (brinle). The fourth critical level, (4), is the narrow depth interval within which the solidus for peridotite-CO_2-H_2O changes slope, and becomes subhorizontal, with low dP/dT. The depth of level (4) differs according to different experimental investigators. Levels (2), (3) and (4) are different for lherzolites and harzburgites. The depths of levels (2), (3) and (1) vary as a function of geotherm and local thermal history, and levels (2) and (3) vary as a function of oxygen fugacity. Consider a mantle plume diverging laterally at the base of the lithosphere. Sparse volatile components (C-H-O-S-K) entrained in the plume will generate melt at level (2), near 275 km. As the plume diverges laterally below depth (1), 200 km, the melt becomes concentrated in the lithosphere. This is followed by thinning of the lithosphere. The evolution of vapour from lateral magma chambers promotes the propagation of cracks through the lithosphere, and the eruption of kimberlite magmas. Magmas in the heated lithosphere above the plume may percolate upwards or promote the uprise of diapirs, and intersect the solidus at level (4) in the range of 100-75 km. Vapours will be evolved causing metasomatism in the overlying mantle, and causing intermittent crack propagation releasing magmas through the lithosphere. A variety of alkalic magma compositions may be generated at level (4), depending sensitively upon conditions.

Item Type:Book Section
Alternate Title:The genesis of kimberlites and some low-SiO2, high-alkali magmas
Additional Information:© 1989 by Geological Society of Australia Inc. Published by Blackwell Scientific Publications. This research was supported by the Earth Sciences section of the U.S. National Science Foundation, grant EAR84-16583.
Funding AgencyGrant Number
Subject Keywords:carbonatite, craton, kimberlite, lithosphere thinning, metasomatism, nephelinite, oxygen fugacity, peridotite-CO_2-H_2O , rift valley
Series Name:Special publication (Geological Society of Australia)
Issue or Number:14
Record Number:CaltechAUTHORS:20160224-110304848
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:64734
Deposited By: Tony Diaz
Deposited On:24 Feb 2016 19:30
Last Modified:03 Oct 2019 09:40

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