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Generation of the Mt Kinabalu granite by crustal contamination of intraplate magma modelled by equilibrated major element assimilation with fractional crystallization (EME-AFC).

Burton-Johnson, A and Macpherson, C G and Ottley, C J and 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 crystallization (EME-AFC).', Journal of petrology., 60 (7). pp. 1461-1487.

Abstract

New geochemical data are presented for the composite units of the Mount Kinabalu granitoid intrusion of Borneo and utilised to explore the 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 crystallization 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 crystallization of a primary, mafic magma, followed by assimilation of the partially melted sedimentary overburden. We present a new, Equilibrated Major Element -Assimilation with Fractional Crystallization (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 metasomatized mantle driven by regional crustal extension in the Late Miocene.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1093/petrology/egz036
Publisher statement:This is a pre-copyedited, author-produced PDF of an article accepted for publication in Journal of Petrology following peer review. The version of record Burton-Johnson, A, Macpherson, C G, Ottley, C J, Nowell, G M & Boyce, A J (2019). Generation of the Mt Kinabalu Granite by Crustal Contamination of Intraplate Magma Modelled by Equilibrated Major Element Assimilation with Fractional Crystallization (EME-AFC). Journal of Petrology 60(7): 1461-1487 is available online at: https://doi.org/10.1093/petrology/egz036
Date accepted:11 July 2019
Date deposited:02 September 2019
Date of first online publication:16 July 2019
Date first made open access:16 July 2020

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