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Evolution of the melt source during protracted crustal anatexis: An example from the Bhutan Himalaya

Hopkinson, Thomas; Harris, Nigel; Roberts, Nick M.W.; Warren, Clare J.; Hammond, Sam; Spencer, Christopher J. and Parrish, Randall R. (2019). Evolution of the melt source during protracted crustal anatexis: An example from the Bhutan Himalaya. Geology (Early Access).

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DOI (Digital Object Identifier) Link: https://doi.org/10.1130/g47078.1
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Abstract

The chemical compositions of magmatic zircon growth zones provide powerful insight into evolving magma compositions due to their ability to record both time and the local chemical environment. In situ U-Pb and Hf isotope analyses of zircon rims from Oligocene–Miocene leucogranites of the Bhutan Himalaya reveal, for the first time, an evolution in melt composition between 32 and 12 Ma. The data indicate a uniform melt source from 32 Ma to 17 Ma, and the progressive addition of an older source component to the melt from at least ca. 17 Ma. Age-corrected εHf ratios decrease from between –10 and –15 down to values as low as –23 by 12 Ma. Complementary whole-rock Nd isotope data corroborate the Hf data, with a progressive decrease in εNd(t) from ca. 18 to 12 Ma. Published zircon and whole-rock Nd data from different lithotectonic units in the Himalaya suggest a chemical distinction between the younger Greater Himalayan Series (GHS) and the older Lesser Himalayan Series (LHS). The time-dependent isotopic evolution shown in the leucogranites demonstrates a progressive increase in melt contribution from older lithologies, suggestive of increasing LHS involvement in Himalayan melting over time. The time-resolved data are consistent with LHS material being progressively accreted to the base of the GHS from ca. 17 Ma, facilitated by deformation along the Main Central thrust. From 17 Ma, decompression, which had triggered anatexis in the GHS since the Paleogene, enabled melting in older sources from the accreted LHS, now forming the lowermost hanging wall of the thrust.

Item Type: Journal Item
Copyright Holders: 2019 The Authors
ISSN: 1943-2682
Project Funding Details:
Funded Project NameProject IDFunding Body
OU-2012-DTG-Funding 3 Studentships (SE-12-050-MG)NE/K501074/1NERC (Natural Environment Research Council)
From Subduction to sand: Quantifying the balance between tectonic and surface processes during early continental collision and UHP rock exhumation. (SE-09-133-CW)NE/H016279/1NERC (Natural Environment Research Council)
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Environment, Earth and Ecosystem Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Item ID: 68349
SWORD Depositor: Jisc Publications-Router
Depositing User: Jisc Publications-Router
Date Deposited: 05 Dec 2019 09:52
Last Modified: 17 Dec 2019 05:59
URI: http://oro.open.ac.uk/id/eprint/68349
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