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Early-stage melt-rock reaction in a cooling crystal mush beneath a slow-spreading mid-ocean ridge (IODP Hole U1473A, Atlantis Bank, Southwest Indian Ridge)

Sanfilippo, Alessio, MacLeod, Christopher J., Tribuzio, Riccardo, Lissenberg, C. Johan and Zanetti, Alberto 2020. Early-stage melt-rock reaction in a cooling crystal mush beneath a slow-spreading mid-ocean ridge (IODP Hole U1473A, Atlantis Bank, Southwest Indian Ridge). Frontiers in Earth Science 8 , 579138. 10.3389/feart.2020.579138

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Abstract

Microtextural and chemical evidence from gabbros indicates that melts may react with the crystal framework as they migrate through crystal mushes beneath mid-ocean ridges; however, the importance of this process for the compositional evolution of minerals and melts remains a matter of debate. Here we provide new insights into the extent by which melt-rock reaction process can occur in oceanic gabbros by conducting a detailed study of cryptic reactive melt migration as preserved in an apparently unremarkable, homogeneous olivine gabbro from deep within a section of the plutonic footwall of the Atlantis Bank core complex on the Southwest Indian Ridge (International ocean discovery program Hole U1473A). High-resolution chemical maps reveal that mineral zoning increases toward and becomes extreme within a cm-wide band that is characterized by elevated incompatible trace element concentrations and generates extreme more/less incompatible element ratios. We demonstrate that neither crystallization of trapped melt nor diffusion can account for these observations. Instead, taking the novel approach of correcting mineral-melt partition coefficients for both temperature and composition, we show that these chemical variations can be generated by intergranular reactive porous flow of a melt as it migrated through the mush framework, and whose composition evolved by melt-rock reaction as it progressively localized into a cm-scale reactive channel. We propose that the case reported here may represent, in microcosm, a preserved snapshot of a generic mechanism by which melt can percolate through primitive mafic (olivine gabbro) crystal mushes, and be modified toward more evolved compositions via near-pervasive reactive transport.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Publisher: Frontiers Media
ISSN: 2296-6463
Date of First Compliant Deposit: 6 October 2020
Date of Acceptance: 23 September 2020
Last Modified: 26 Nov 2020 13:30
URI: http://orca.cardiff.ac.uk/id/eprint/135339

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