The birth, growth and ageing of the Kaapvaal subcratonic mantle

The birth, growth and ageing of the Kaapvaal subcratonic mantle The Kaapvaal craton and its underlying mantle is probably one of the best studied Archean entity in the world. Despite that, discussion is still vivid on important aspects. A major debate over the last few decades is the depth of melting that generated the mantle nuclei of cratons. Our new evaluation of melting parameters in peridotite residues shows that the Cr O /Al O ratio is the 2 3 2 3 most useful pressure sensitive melting barometer. It irrevocably constrains the pressure of melting (melt separation) to less than 2 GPa with olivine (ol), orthopyroxene (opx) and spinel (sp) as residual phases. Garnet (grt) grows at increasing pressure during lithosphere thickening and subduction via the reaction opx + sp → grt + ol. The time of partial melting is constrained by Re- depletion model ages (T ) mainly to the Archean (Pearson and Wittig 2008). However, only 3% of the ages are older than RD 3.1 Ga while crustal ages lie mainly between 3.1 to 2.8 Ga for the W- and 3.7 to 2.8 Ga for the E-block. Many T -ages are RD probably falsified by metasomatism and the main partial melting period was older than 3.1 Ga. Also, http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Mineralogy and Petrology Springer Journals

The birth, growth and ageing of the Kaapvaal subcratonic mantle

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Publisher
Springer Journals
Copyright
Copyright © 2018 by Springer-Verlag GmbH Austria, part of Springer Nature
Subject
Earth Sciences; Mineralogy; Inorganic Chemistry; Geochemistry
ISSN
0930-0708
eISSN
1438-1168
D.O.I.
10.1007/s00710-018-0577-8
Publisher site
See Article on Publisher Site

Abstract

The Kaapvaal craton and its underlying mantle is probably one of the best studied Archean entity in the world. Despite that, discussion is still vivid on important aspects. A major debate over the last few decades is the depth of melting that generated the mantle nuclei of cratons. Our new evaluation of melting parameters in peridotite residues shows that the Cr O /Al O ratio is the 2 3 2 3 most useful pressure sensitive melting barometer. It irrevocably constrains the pressure of melting (melt separation) to less than 2 GPa with olivine (ol), orthopyroxene (opx) and spinel (sp) as residual phases. Garnet (grt) grows at increasing pressure during lithosphere thickening and subduction via the reaction opx + sp → grt + ol. The time of partial melting is constrained by Re- depletion model ages (T ) mainly to the Archean (Pearson and Wittig 2008). However, only 3% of the ages are older than RD 3.1 Ga while crustal ages lie mainly between 3.1 to 2.8 Ga for the W- and 3.7 to 2.8 Ga for the E-block. Many T -ages are RD probably falsified by metasomatism and the main partial melting period was older than 3.1 Ga. Also,

Journal

Mineralogy and PetrologySpringer Journals

Published: Jun 1, 2018

References

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