Global variations in abyssal peridotite compositions

Warren, Jessica M.

Global variations in abyssal peridotite compositions

Author(s)	Warren, Jessica M.
Ordered Author	Jessica M.Warren
UD Author	Warren, Jessica M.	en_US
Date Accessioned	2016-11-22T14:59:44Z
Date Available	2016-11-22T14:59:44Z
Copyright Date	Copyright © 2016 The Author.	en_US
Publication Date	2016-01-09
Description	Publisher's PDF	en_US
Abstract	Abyssal peridotites are ultramafic rocks collected frommid-ocean ridges that are the residues of adiabatic decompression melting. Their compositions provide information on the degree of melting and melt–rock interaction involved in the formation of oceanic lithosphere, as well as providing constraints on pre-existing mantle heterogeneities. This review presents a compilation of abyssal peridotite geochemical data (modes, mineral major elements, and clinopyroxene trace elements) for N1200 samples from 53 localities on 6 major ridge systems. On the basis of composition and petrography, peridotites are classified into one of five lithological groups: (1) residual peridotite, (2) dunite, (3) gabbro-veined and/or plagioclase-bearing peridotite, (4) pyroxenite-veined peridotite, and (5) other types of melt-added peridotite. Almost a third of abyssal peridotites are veined, indicating that the oceanic lithospheric mantle is more fertile, on average, than estimates based on residual peridotites alone imply. All veins appear to have formed recently during melt transport beneath the ridge, though some pyroxenites may be derived from melting of recycled oceanic crust. A limited number of samples are available at intermediate and fast spreading rates, with samples from the East Pacific Rise indicating high degrees of melting. At slow and ultra-slow spreading rates, residual abyssal peridotites define a large (0–15% modal clinopyroxene and spinel Cr#=0.1–0.6) compositional range. These variations do not match the prediction for how degree of melting should vary as a function of spreading rate. Instead, the compositional ranges of residual peridotites are derived from a combination of melting, melt–rock interaction and pre-existing compositional variability, where melt–rock interaction is used here as a general term to refer to the wide range of processes that can occur during melt transport in the mantle. Globally, ~10% of abyssal peridotites are refractory (0% clinopyroxene, spinel Cr# N 0.5, bulk Al2O3 b 1wt.%) and someridge sections are dominated by harzburgiteswhile lacking a significant basaltic crust. Abyssal ultramafic samples thus indicate that the mantle ismulti-component, probably consisting of at least three components (lherzolite, harzburgite, and pyroxenite). Overall, the large compositional rangeamong residual andmelt-added peridotites implies that the oceanic lithospheric mantle is heterogeneous, which will lead to the generation of further heterogeneities upon subduction back into the mantle.	en_US
Department	University of Delaware. Department of Geological Sciences.	en_US
Citation	Warren, Jessica M. "Global variations in abyssal peridotite compositions." Lithos 248 (2016): 193-219.	en_US
DOI	doi:10.1016/j.lithos.2015.12.023	en_US
ISSN	0024-4937 ; e- 1872-6143	en_US
URL	http://udspace.udel.edu/handle/19716/19865
Language	en_US	en_US
Publisher	Elsevier	en_US
dc.rights	Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license 4.0	en_US
dc.source	Lithos	en_US
dc.source.uri	http://www.journals.elsevier.com/lithos	en_US
Title	Global variations in abyssal peridotite compositions	en_US
Type	Article	en_US