Trace-element zoning in garnets from sheared mantle xenoliths

Journal Article · Wed Feb 01 00:00:00 EST 1989 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(89)90407-9· OSTI ID:5023134

Griffin, W L; Cousens, D R; Ryan, C G; Sie, S H; Suter, G F ^[1]; Smith, D ^[2]; Boyd, F R ^[3]

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1. CSIRO, North Ryde (Australia)
2. Univ. of Texas, Austin (USA)
3. Carnegie Institution of Washington, DC (USA)

Proton-microprobe analyses of garnets from sheared high-temperature ultramafic xenoliths reveal marked zonation of trace elements, paralleling trends in major and minor elements. Garnet rims (600-1,000 {mu}m wide) are enriched in Fe, Ti, Zr, Y and Ga, and either enriched or depleted in Cr, relative to cores. Zoning profiles for Ti and Zr are S-shaped and extend further into the grains than the Cr and Ga gradients. The profiles are consistent with the formation of Ti, Zr, Y-enriched garnet overgrowths, followed by diffusive equilibration between rim and core over years to hundreds of years. This enrichment in Fe, Ca, Al and incompatible elements is ascribed to melt infiltration and consequent melt-crystal exchange and garnet growth, shortly before eruption. Zr/Y is 1 to 2 in garnet cores but 4 to 5 in rims, and so the infiltrating melt may have been relatively alkalic. Major and trace element concentrations in such high-temperature sheared xenoliths are not likely to resemble those of primitive mantle or of residual mantle depleted by melt extraction.

• OSTI ID: 5023134
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 53:2; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GARNETS
MINERALIZATION
PROTON MICROPROBE ANALYSIS
ZONING
ALUMINIUM
CALCIUM
CHEMICAL COMPOSITION
EARTH MANTLE
GALLIUM
GEOBAROMETRY
GEOCHEMISTRY
GEOTHERMOMETRY
IRON
MAGMA
MAGMATISM
PETROGENESIS
TITANIUM
TRACE AMOUNTS
YTTRIUM
ZIRCONIUM
ZONES
ALKALINE EARTH METALS
CHEMICAL ANALYSIS
CHEMISTRY
ELEMENTS
METALS
MICROANALYSIS
MINERALS
NONDESTRUCTIVE ANALYSIS
OXYGEN COMPOUNDS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENTS
580000* - Geosciences