eCite Digital Repository

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


Kamenetsky, VS and Eggins, SM and Crawford, AJ and Green, DH and Gasparon, M and Falloon, TJ, 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 Sciece Letters, 160 pp. 115-132. ISSN 0012-821X (1998) [Refereed Article]

DOI: doi:10.1016/S0012-821X(98)00090-9


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 Al 2O 3 (12.8-15.5 wt%), and form a linear array that ranges to extremely high CaO/Al 2O 3 values (0.8-1.2). These melt compositions are unusual for MORB, as is the observed phenocryst assemblage, which comprises primitive olivine (Fo 87-92 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 La n/Yb n 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.

Item Details

Item Type:Refereed Article
Research Division:Earth Sciences
Research Group:Geology
Research Field:Igneous and metamorphic petrology
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the earth sciences
UTAS Author:Kamenetsky, VS (Professor Vadim Kamenetsky)
UTAS Author:Crawford, AJ (Professor Anthony Crawford)
UTAS Author:Falloon, TJ (Dr Trevor Falloon)
ID Code:15405
Year Published:1998
Web of Science® Times Cited:109
Deposited By:Earth Sciences
Deposited On:1998-08-01
Last Modified:2010-08-25

Repository Staff Only: item control page