Timing and mechanism of the rise of the Shillong Plateau in the Himalayan foreland

Govin, G. and Najman, Y. and Copley, A. C. and Millar, I. and van der Beek, P. and Huyghe, P. and Grujic, D. and Davenport, J. (2018) Timing and mechanism of the rise of the Shillong Plateau in the Himalayan foreland. Geology, 46 (3). pp. 279-282. ISSN 0091-7613 DOI https://doi.org/10.1130/G39864.1

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Official URL: https://doi.org/10.1130/G39864.1

Abstract

Island arcs provide insights into the origin and recycling of continental crust, but questions remain concerning source metasomatism, the depth of differentiation, the potential role of amphibole fractionation, and the time scales involved. Basaltic andesites on Batan Island (Philippines) contain ≥150 Ma peridotite fragments encased in hornblendite and gabbroic rinds produced via melt-rock reaction. The peridotites have some of the lightest δ7Li and δ57Fe values yet measured in mantle rocks. These values are too fractionated to have been created solely by equilibrium partial melting and thus require a combination of melt depletion and slab fluid addition and may be derived from diffusion-modified melt channel wall rocks. Stable isotope signals are easily modified by diffusive equilibration between peridotite and host magma, so the preservation of light δ7Li and δ57Fe here suggests magma ascent rates of ∼10 km yr−1. We show that melt–wall rock reactions at ∼25–30 km depth led to the crystallization of amphibole (± plagioclase) followed by gabbroic fractionation at ∼7 km depth. The former provides a location and mechanism for the “cryptic” amphibole fractionation observed in these and perhaps many other arc lavas and may obviate the requirement for delamination of cumulates.

Item Type: Article
Uncontrolled Keywords: 2018AREP; IA74
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
08 - Green Open Access
Journal or Publication Title: Geology
Volume: 46
Page Range: pp. 279-282
Identification Number: https://doi.org/10.1130/G39864.1
Depositing User: Sarah Humbert
Date Deposited: 01 Feb 2019 12:43
Last Modified: 01 Feb 2019 12:43
URI: http://eprints.esc.cam.ac.uk/id/eprint/4410

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