Calcic melt inclusions in primitive olivine at 43ºN MAR: evidence for melt–rock reaction=melting involving clinopyroxene-rich lithologies during MORB generation

Kamenetsky, Vadim S., Eggins, Stephen M., Crawford, Anthony J., Green, David H., Gasparon, Massimo and Falloon, Trevor J. (1998) Calcic melt inclusions in primitive olivine at 43ºN MAR: evidence for melt–rock reaction=melting involving clinopyroxene-rich lithologies during MORB generation. Earth and Planetary Science Letters, 160 1-2: 115-132. doi:10.1016/S0012-821X(98)00090-9


Author Kamenetsky, Vadim S.
Eggins, Stephen M.
Crawford, Anthony J.
Green, David H.
Gasparon, Massimo
Falloon, Trevor J.
Title Calcic melt inclusions in primitive olivine at 43ºN MAR: evidence for melt–rock reaction=melting involving clinopyroxene-rich lithologies during MORB generation
Formatted title
Calcic melt inclusions in primitive olivine at 43ºN MAR: evidence for melt–rock reaction=melting involving clinopyroxene-rich lithologies during MORB generation
Journal name Earth and Planetary Science Letters   Check publisher's open access policy
ISSN 0012-821X
1385-013X
Publication date 1998
Sub-type Article (original research)
DOI 10.1016/S0012-821X(98)00090-9
Open Access Status Not Open Access
Volume 160
Issue 1-2
Start page 115
End page 132
Total pages 18
Place of publication Amsterdam, Netherlands
Publisher Elsevier
Language eng
Formatted abstract
Olivine-hosted homogenized melt inclusions in a primitive basalt AII32-12-7 from 43°N Mid-Atlantic Ridge have magnesian basalt compositions (10-12 wt% MgO) with high CaO (13.2-15.2 wt%), relatively low Al2O3 (12.8-15.5 wt%), and form a linear array that ranges to extremely high CaO/Al2O3 values (0.8-1.2). These melt compositions are unusual for MORB, as is the observed phenocryst assemblage, which comprises primitive olivine (Fo87-92 with up to 0.45 wt% CaO), Cr-diopside (Mg 90-92), and Cr-rich spinel (Cr 50-70) and directly reflects these melt compositions. The melt compositional array extends from peridotite-saturated compositions formed near 1 GPa to lie well within the clinopyroxene phase volume, or possibly along a clinopyroxene + olivine phase boundary. We interpret the array as either the product of melt-wallrock reaction between a 1 GPa MORB melt and a clinopyroxene-rich lithology (wehrlte or clinopyroxenite), or of mixing between melt fractions derived separately from these distinct lithologies (ie peridotite and clinopyroxenite/wehrlite). Derivation of the melt array from a conventional mantle peridotite source, possibly involving fractional melting near or beyond the point of clinopyroxene exhaustion, is inconsistent with the melt compositions and the trend of the array. Trace element abundance patterns in the melt inclusions range from depleted to highly enriched (eg Lan/Ybn 0.6-7.0), and indicate the generation of compositionally diverse melt fractions via fractional melting processes and/or melting of geochemically distinct source heterogeneities. Most melt inclusions, and the pillow-rime glass, are enriched in the more incompatible trace elements, and have high Nb and Ta contents relative to other highly incompatible elements. These characteristics and the Pb isotopic composition of the pillow-rim glass (206Pb/204Pb=19.654) indicate that presence of a HIMU mantle source component that can be linked to lateral dispersion of a geochemical signal commonly attributed to the Azores mantle plume.
Keyword Mid-ocean ridge basalts
Inclusions
Petrology
Geochemistry
Heterogeneity
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Earth Sciences Publications
 
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Created: Tue, 02 Feb 2016, 16:12:05 EST by Associate Professor Massimo Gasparon on behalf of School of Earth Sciences