Continent stabilisation by lateral accretion of subduction zone-processed depleted mantle residues; insights from Zealandia

Scott, J.M., Liu, J., Pearson, D.G., Harris, G.A., Czertowicz, T.A., Woodland, S.J., Riches, A.J.V. and Luth, R.W. (2019) Continent stabilisation by lateral accretion of subduction zone-processed depleted mantle residues; insights from Zealandia. Earth and Planetary Science Letters, 507, pp. 175-186. (doi:10.1016/j.epsl.2018.11.039)

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Abstract

To examine how the mantle lithosphere stabilises continents, we present a synthesis of the mantle beneath Zealandia in the SW Pacific Ocean. Zealandia, Earth's “8th continent”, occurs over 4.9 M km2 and comprises a fore-arc, arc and back-arc fragment rifted from the Australia–Antarctica Gondwana margin 85 Myr ago. The oldest extant crust is ∼500 Ma and the majority is Permian–Jurassic. Peridotitic rocks from most known locations reveal the underpinning mantle to comprise regional domains varying from refractory (Al2O3 < 1 wt%, olivine Mg# > 92, spinel Cr# up to 80, Pt/Ir < 1) to moderately depleted (Al2O3 = 2–4 wt%, olivine Mg# ∼90.5, spinel Cr# < ∼60). There is no systematic distribution of these domains relative to the former arc configuration and some refractory domains underlie crust that is largely devoid of magmatic rocks. Re-depletion Os model ages have no correlation with depletion indices but do have a distribution that is very similar to global convecting mantle. Whole rock, mineral and isotopic data are interpreted to show that the Zealandia mantle lithosphere was constructed from isotopically heterogeneous convecting mantle fragments swept into the sub-arc environment, amalgamated, and variably re-melted under low-P hydrous conditions. The paucity of mafic melt volumes in most of the overlying crust that could relate to the depleted domains requires melting to have been followed by lateral accretion either during subduction or slab rollback. Recent Australia–Pacific convergence has thickened portions of the Zealandia mantle to >160 km. Zealandia shows that the generation of refractory and/or thick continental lithosphere is not restricted to the Archean. Since Archean cratons also commonly display crust–mantle age decoupling, contain spinel peridotites with extreme Cr# numbers that require low-P hydrous melting, and often have a paucity of mafic melts relative to the extreme depletion indicated by their peridotitic roots, they too may – in part – be compilations of peridotite shallowly melted and then laterally accreted at subduction margins.

Item Type:Articles
Additional Information:Sample collection and analysis was largely funded by a New Zealand Foundation for Research Science and Technology and University of Otago Research grants to JMS and a Canada Excellence Research Chairs program to DGP. Some Dun Mountain Ophiolite Belt fieldwork was supported by National Geographic Waitt Foundation grant 2841-3 to AJVR.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Riches, Dr Amy
Authors: Scott, J.M., Liu, J., Pearson, D.G., Harris, G.A., Czertowicz, T.A., Woodland, S.J., Riches, A.J.V., and Luth, R.W.
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
Journal Name:Earth and Planetary Science Letters
Publisher:Elsevier
ISSN:0012-821X
ISSN (Online):0012-821X
Published Online:18 December 2018
Copyright Holders:Copyright © 2018 Elsevier
First Published:First published in Earth and Planetary Science Letters 507:175-186
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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