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

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 ol...

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Bibliographic Details
Published in:Contributions to Mineralogy and Petrology
Main Authors: Kamenetsky, VS, Gurenko, AA
Format: Article in Journal/Newspaper
Language:English
Published: 2007
Subjects:
260101 Mineralogy and Crystallography
260102 Igneous and Metamorphic Petrology
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
Mid-Atlantic Ridge
Pacific
Macquarie Island
Online Access:https://eprints.utas.edu.au/2392/
https://eprints.utas.edu.au/2392/1/CMP-43oN-MORB.pdf
https://doi.org/10.1007/s00410-006-0160-x
Description
Summary: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.

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