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Abstract

Successive magma batches underplate, ascend, stall and erupt along spreading ridges, building the oceanic crust. It is therefore important to understand the processes and conditions under which magma differentiates at mid ocean ridges. Although fractional crystallization is considered to be the dominant mechanism for magma differentiation, open-system igneous complexes also experience Melting-Assimilation-Storage-Hybridization (MASH, Hildreth and Moorbath, 1988) processes. Here, we examine crystal-scale records of partial melting in lower crustal gabbroic cumulates from the slow-spreading Atlantic oceanic ridge (Kane Megamullion; collected with Jason ROV) and the fast-spreading East Pacific Rise (Hess Deep; IODP expedition 345). Clinopyroxene oikocrysts in these gabbros preserve marked intra-crystal geochemical variations that point to crystallization-dissolution episodes in the gabbro eutectic assemblage. Kane Megamullion and Hess Deep clinopyroxene core1 primocrysts and their plagioclase inclusions indicate crystallization from high temperature basalt (>1,160 and >1,200°C, respectively), close to clinopyroxene saturation temperature (in situ trapped melt. Intrusion of primitive hot reactive melt and percolation of interstitial differentiated melt are two distinct MASH processes in the lower oceanic crust. They are potentially fundamental mechanisms for generating the wide compositional variation observed in mid-ocean ridge basalts. We furthermore propose that such processes operate at both slow- and fast-spreading ocean ridges. Thermal numerical modeling shows that the degree of lower crustal partial melting at slow-spreading ridges can locally increase up to 50%, but the overall crustal melt volume is low (less than ca. 5% of total mantle-derived and crustal melts; ca. 20% in fast-spreading ridges).

Item Type:	Article
Authors/Creators:	Leuthold, J and Lissenberg, CJ and O'Driscoll, B and Karakas, O and Falloon, T and Klimentyeva, DN and Ulmer, P
Keywords:	hess deep ocean crust, gabbro, primocrysts, morb
Journal or Publication Title:	Frontiers in Earth Science
Publisher:	Frontiers Research Foundation
ISSN:	2296-6463
DOI / ID Number:	10.3389/feart.2018.00015
Copyright Information:	Copyright 2018 Leuthold, Lissenberg, O'Driscoll, Karakas, Falloon, Klimentyeva and Ulmer. Licensed under Creative Commons Attribution 4.0 International (CC BY 4.0) https://creativecommons.org/licenses/by/4.0/
Related URLs:	UTAS Profile: Falloon, T
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