Generation of the Mt Kinabalu granite by crustal contamination of intraplate magma modelled by Equilibrated Major Element Assimilation with Fractional Crystallisation (EME-AFC)

Burton-Johnson, A., Macpherson, C.G., Ottley, C.J., Nowell, G.M. and Boyce, A.J. (2019) Generation of the Mt Kinabalu granite by crustal contamination of intraplate magma modelled by Equilibrated Major Element Assimilation with Fractional Crystallisation (EME-AFC). Journal of Petrology, 60(7), pp. 1461-1487. (doi: 10.1093/petrology/egz036)

Abstract

New geochemical data are presented for the composite units of the Mount Kinabalu granitoid intrusion of Borneo and explore discrimination between crustal- and mantle-derived granitic magmas. The geochemical data demonstrate that the units making up this composite intrusion became more potassic through time. This was accompanied by an evolution of isotope ratios from a continental-affinity towards a slightly more mantle-affinity (87Sr/86Sri ∼0.7078; 143Nd/144Ndi ∼0.51245; 206Pb/204Pbi ∼18.756 for the oldest unit compared to 87Sr/86Sri ∼0.7065, 143Nd/144Ndi ∼0.51250 and 206Pb/204Pbi ∼18.721 for the younger units). Oxygen isotope ratios (calculated whole-rock δ18O of + 6.5–9.3‰) do not show a clear trend with time. The isotopic data indicate that the magma cannot result only from fractional crystallisation of a mantle-derived magma. Alkali metal compositions show that crustal anatexis is also an unsuitable process for genesis of the intrusion. The data indicate that the high-K units were generated by fractional crystallisation of a primary, mafic magma, followed by assimilation of the partially melted sedimentary overburden. We present a new, Equilibrated Major Element – Assimilation with Fractional Crystallisation (EME-AFC) approach for simultaneously modelling the major element, trace element, and radiogenic and oxygen isotope compositions during such magmatic differentiation; addressing the lack of current AFC modelling approaches for felsic, amphibole- or biotite-bearing systems. We propose that Mt Kinabalu was generated through low degree melting of upwelling fertile metasomatised mantle driven by regional crustal extension in the Late Miocene.

• Item Type: Articles
• Additional Information: Funding: NERC supported this study through a PhD studentship to AB-J and access to the Isotope Community Support Facility at SUERC.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Boyce, Professor Adrian
• Authors: Burton-Johnson, A., Macpherson, C.G., Ottley, C.J., Nowell, G.M., and Boyce, A.J.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Journal of Petrology
• Publisher: Oxford University Press
• ISSN: 0022-3530
• ISSN (Online): 1460-2415
• Published Online: 16 July 2019
• Copyright Holders: Copyright © 2019 The Authors
• First Published: First published in Journal of Petrology 60(7): 1461-1487
• Publisher Policy: Reproduced in accordance with the publisher copyright policy