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Effects of decarbonation on elemental behaviors during subduction-zone metamorphism : evidence from a titanite-rich contact between eclogite-facies marble and omphacitite.

Xiao, Y.Y. and Niu, Y.L. and Zhang, H.F. and Wang, K.-L. and Iizuka, Y. and Lin, J.Y. and Tan, Y.L. and Xu, Y.J. (2017) 'Effects of decarbonation on elemental behaviors during subduction-zone metamorphism : evidence from a titanite-rich contact between eclogite-facies marble and omphacitite.', Journal of Asian earth sciences., 135 . pp. 338-346.

Abstract

In this paper, we show the effects of subducted carbonates on geochemical processes during subduction-zone metamorphism (SZM) through the study of an eclogite-facies marble coexisting with metabasite from the ultrahigh pressure metamorphic belt of the Chinese Western Tianshan orogen. Between the marble and metabasite is a titanite-rich contact resulting from fluid-facilitated metamorphic reactions between the two lithologies, and recording elemental changes of geodynamic significance. Because this titanite-rich contact is dominated by titanite (an important host for high field strength elements, HFSEs) without white micas (an important host for large ion lithophile elements, LILEs), HFSEs are largely conserved in titanite whereas LILEs are moved away. This observation emphasizes the potential significance of subducting carbonate in retaining HFSEs in the slab through the formation and stabilization of titanite, contributing to the characteristic “arc signature” unique to subduction-zone magmatism (i.e., high LILEs, low HFSEs). The implicit assumption in this interpretation is that the observed lithological assemblage represents residues of subducting oceanic crust that has undergone major episodes of dehydration. Subducted carbonates also have significant implications for the origin of mantle isotopic heterogeneity as revealed from oceanic basalts.

Item Type:Article
Full text:(AM) Accepted Manuscript
Available under License - Creative Commons Attribution Non-commercial No Derivatives.
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1016/j.jseaes.2017.01.006
Publisher statement:© 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/
Date accepted:11 January 2017
Date deposited:16 March 2017
Date of first online publication:12 January 2017
Date first made open access:12 January 2018

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