Young, olivine xenocryst-bearing alkali-basalt from the oceanward slope of the Japan Trench

Naoto Hirano, Junji Yamamoto, Hiroyuki Kagi, Teruaki Ishii

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44 Citations (Scopus)


Young (6 Ma) alkali-basalts were collected from the toe of the oceanward slope of the northern Japan Trench. Two types of olivine are present in these lavas, xenocrysts with reaction rims and magmatic. The forsterite (Fo) (no. 91-92) values and NiO contents (0.3-0.5 wt%) of the xenocrysts are similar in composition to those of the depleted mantle peridotite. The groundmass olivines have relatively lower Fo values (no. 81-88) and NiO contents (0.1-0.5 wt%). Reaction rims and the vicinity of the silicate inclusion in xenocrysts show the intermediate compositions between the xenocryst and magmatic olivines. Chromian spinel inclusions in the xenocrysts also show the depleted composition in the range of abyssal peridotite. CO2 fluid inclusions in the xenocryst records pressures before entrainment into the host magma up to 0.4 GPa, which corresponds to a depth of up to 14 km of lithospheric mantle. These data indicate that the xenocrysts originate from MORB-depleted mantle.

Original languageEnglish
Pages (from-to)47-54
Number of pages8
JournalContributions to Mineralogy and Petrology
Issue number1
Publication statusPublished - Sept 2004
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology


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