Testing the Plagioclase Discriminator on the GEOROC Database to Identify Porphyry-Fertile Magmatic Systems in Japan

Benedict J. Williamson, Matthew Hodgkinson, Akira Imai, Ryohei Takahashi, Robin N. Armstrong, Richard J. Herrington

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Abstract

Despite showing favorable geology, there are no known porphyry-type deposits in Japan. This, therefore, provides an ideal porphyry-“barren” case area on which to test the recently developed plagioclase-based discriminator for porphyry-“fertile” calc-alkaline systems. The discriminator was applied to plagioclase data for Japan in the online GEOROC database for convergent margin settings. Of the 3933 data points available, and considered reliable, 91% fall in the “barren” field, which compares with 73% for equivalent data worldwide. “Fertile” signatures in certain parts of Kyushu and central Honshu should be further investigated, as well as areas where there are magnetite-series magmatic systems with elevated whole-rock Sr/Y but for which there are currently little or no plagioclase data (SW-, N-central-, and NE-Honshu). Why the Japanese arcs appear to show anomalously poor potential for porphyry deposits compared with other arcs worldwide, including Western Luzon, is as yet unclear but possibly relates to tectonic factors or the nature of the magmatic source or because melt PH2O in many of the magmatic systems was too low, as suggested from low average excess Al in plagioclase.

Original languageEnglish
Pages (from-to)138-143
Number of pages6
JournalResource Geology
Volume68
Issue number2
DOIs
Publication statusPublished - Apr 2018
Externally publishedYes

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All Science Journal Classification (ASJC) codes

  • Geology
  • Geochemistry and Petrology

Cite this

Williamson, B. J., Hodgkinson, M., Imai, A., Takahashi, R., Armstrong, R. N., & Herrington, R. J. (2018). Testing the Plagioclase Discriminator on the GEOROC Database to Identify Porphyry-Fertile Magmatic Systems in Japan. Resource Geology, 68(2), 138-143. https://doi.org/10.1111/rge.12162