Jadeite, albite and nepheline as inclusions in spinel of chromitite from Hess Deep, equatorial Pacific: their genesis and implications for serpentinite diapir formation

Article Abstract:

Polymineralic inclusions made of a few grains of diopside, enstatite, jadeite, nepheline, albite, pargasite, phlogopites and olivine were found in chromian spinel in a chromitite pod and in troctolite from Hess Deep, equatorial Pacific. The modes of occurrence and mineral chemistry of the inclusions were regulated by magmatic precipitation and subsequently applied more primary melt. At the off-ridge conditions, the rocks were cooled and serpentinized by circulation of sea water at the mantle depth to produce jadeite in chromitite.

Pacific Ocean, Silicate minerals, Spinel

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P-T history of a mantle diapir: the Horoman peridotite complex, Hokkaido, northern Japan

Article Abstract:

Mineralogic and petrographic differences between an upper zone and lower zone of the Horoman peridotite complex in Hokkaido, Japan, indicate that the complex preserves evidence of temperature variations from its formation as an upwelling upper mantle diapir. Aluminum and calcium concentrations in orthopyroxine indicate a higher temperature path of decompression path for the upper zones, 1100-1150 degrees C at about 20 kbar, than the lower zone, 900-950 degrees C at about 20 kbar.

Research, Origin, Hokkaido, Petrogenesis, Diapirs

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The influence of water on melting of mantle peridotite

Article Abstract:

A study was conducted to evaluate the effects of varying concentrations of dissolved water on the compositions of peridotite partial melts. The hydrous and anhydrous partial melts of similar silicate bulk composition were compared. The comparison of compositions of both melts may be useful in understanding the compositions of subduction-related lavas but it cannot explain the thermodynamic controls on the compositions of the water-bearing peridotite partial melts.

Silicates, Lava

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