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

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.