Evidence for southward subduction of the Mongol-Okhotsk oceanic plate: implications from Mesozoic adakitic lavas from Mongolia

Sheldrick, T., Barry, T. L., Millar, I. L., Barfod, D. N. , Halton, A. M. and Smith, D. J. (2020) Evidence for southward subduction of the Mongol-Okhotsk oceanic plate: implications from Mesozoic adakitic lavas from Mongolia. Gondwana Research, 79, pp. 140-156. (doi: 10.1016/j.gr.2019.09.007)

Abstract

A combination of new 40Ar/39Ar dating results, major- and trace-element data, plus Sr-Nd-Pb-Hf isotope data, are used to investigate the petrogenesis of Triassic high-Si adakite (HSA), Cretaceous low-Si adakite-like (LSA) lavas, and Cretaceous high-K and shoshonitic trachyandesite lavas, from eastern and south-central Mongolia. All samples are light rare-earth element and large-ion lithophile element enriched but depleted in some high-field strength elements (notably Nb, Ta and Ti). Two alternative models are proposed to explain the petrogenesis of the HSA samples. (1) A southward-subducting Mongol-Okhotsk slab underwent partial melting in the Triassic during the closure of the Mongol-Okhotsk Ocean, with the resultant melts assimilating mantle and crustal material. Alternatively (2), a basaltic underplate of thickened (>50 km; >1.5 GPa), eclogitic lower crust foundered into the underlying mantle, and underwent partial melting with minor contamination from mantle material and some shallow-level crustal contamination. The LSA samples are interpreted as melts derived from a lithospheric mantle wedge that was previously metasomatised by slab melts. Similarly, the trachyandesite lavas are interpreted as melts deriving from a subduction-enriched subcontinental lithospheric mantle. The spatial distribution of these samples implies that metasomatism likely occurred due to a southward-subducting Mongol-Okhotsk slab associated with the closure of the Mongol-Okhotsk Ocean. When this interpretation is combined with previous evidence for a northward-subducting Mongol-Okhotsk slab it advocates that the Mongol-Okhotsk Ocean closed with double-sided subduction.

• Item Type: Articles
• Additional Information: The analyses were supported by NERC grant IP-1610-0516.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Barfod, Dr Dan
• Authors: Sheldrick, T., Barry, T. L., Millar, I. L., Barfod, D. N., Halton, A. M., and Smith, D. J.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Gondwana Research
• Publisher: Elsevier
• ISSN: 1342-937X
• ISSN (Online): 1878-0571
• Published Online: 09 October 2019
• Copyright Holders: Copyright © 2019 The Authors
• First Published: First published in Gondwana Research 79:140-156
• Publisher Policy: Reproduced under a Creative Commons license