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Cryptic crustal contamination of MORB primitive melts recorded in olivine-hosted glass and mineral inclusions

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Kamenetsky, VS and Gurenko, AA (2007) Cryptic crustal contamination of MORB primitive melts recorded in olivine-hosted glass and mineral inclusions. Contributions to Mineralogy and Petrology, 153 (4). pp. 465-481. ISSN 0010-7999

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Abstract

The origin of compositional heterogeneities among the magmas parental to mid-ocean ridge basalts (MORB) was investigated using a single rock piece of the olivine-phyric basalt from 43 degrees N, Mid-Atlantic Ridge (AII D11-177). The exceptional feature of this sample is presence of very primitive olivine crystals (90-91 mol% Fo) that are significantly variable in terms of CaO (0.15-0.35 wt%). A population of low-Ca olivine (0.15-0.25 wt% CaO) is also notably distinct from high-Ca olivine population in AII D11-177, and primitive MORB olivine in general, in having unusual assemblage of trapped mineral and glass inclusions. Mineral inclusions are represented by high-magnesian (Mg# 90.7-91.1 mol%) orthopyroxene and Cr-spinel, distinctly enriched in TiO2 (up to 5 wt%, c.f. < 1 wt% in common MORB spinel). Glass inclusions associated with orthopyroxene and high-Ti Cr-spinel have andesitic compositions (53-58 wt% SiO2). Compared to the pillow-rim glass and "normal" MORB inclusions, the Si-rich glass inclusions in low-Ca olivine have strongly reduced Ca and elevated concentrations of Ti, Na, K, P, Cl, and highly incompatible trace elements. Strong variability is recorded among glass inclusions within a single olivine phenocrysts. We argue that the observed compositional anomalies are mineralogically controlled, and thus may arise from the interaction between hot MORB magmas and crystal cumulates in the oceanic crust or magma chamber.

Item Type: Article
Keywords: morb, melt inclusions, olivine, orthopyroxene, spinel, felsic magmas, mantle, oceanic crust, assimilation, mid-atlantic ridge, east pacific rise, subduction-related magmas, midocean ridge, islands ophiolite, transform-fault, oceanic-crust, macquarie island, upper-mantle, basalts
Journal or Publication Title: Contributions to Mineralogy and Petrology
Page Range: pp. 465-481
ISSN: 0010-7999
Identification Number - DOI: 10.1007/s00410-006-0160-x
Additional Information:

The original publication is available at www.springerlink.com

Date Deposited: 06 Nov 2007 23:06
Last Modified: 18 Nov 2014 03:24
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