(Fluorine geochemistry of volcanic rocks and petrogenetic application.)

Translated title of the contribution: Japanese with English abstract

K. I. Aoki, S. Kanisawa, K. I. Ishikawa

Research output: Contribution to journalArticlepeer-review

Abstract

The F contents in approx 500 samples of various types of basalts and related rocks from continental (southwestern USA, Zaire, Deccan and South Africa), island arc (Japan) and oceanic regions (Hawaii and Mid-Atlantic Ridge) were determined by a selective ion-electrode method. Of all of the major components in these basaltic rocks, F shows good correlation only with K2O. It increases regularly from low potassic tholeiite (island arc tholeiite) to perpotassic basalt (60-7600 ppm) on continents and island arcs, and from tholeiite to nephelinite (180-960 ppm) on Hawaii. In the F-K2O diagram all the basaltic rocks from continents, island arc and Hawaii plot between the origin of the coordinate axes and the field of phlogopite in upper mantle peridotite xenoliths in South African kimberlite. Accordingly, the major proportion of F, K2O and also H2O in these basaltic magmas are derived from phlogopite at the source regions in the mantle. On the other hand, F in abyssal tholeiites is relatively higher than that of the other tholeiites at equal K2O contents, and it is suggested that most of F, K2O and H2O are derived from pargasites. Japanese and Deccan tholeiitic series show remarkable F enrichment with increasing K2O due to separation of anhydrous and K-free minerals during fractionation. F in tholeiitic and alkali basalt magmas in Hawaii also increases regularly with K2O during progressive fractionation until the later stages, where rhyodacite and trachyte exhibit a relative decrease, owing to the effective subtraction of F-bearing amphibole and apatite, in addition to anhydrous minerals. However, when F contents of the Japanese Quaternary calc-alkaline series are plotted on the F-K2O and SiO2-F diagrams, they indicate no clear relations among F, K2O and SiO2. It seems likely that no simple interpretation can be applied to the calc-alkaline series based on these three components.-I.S.

Translated title of the contributionJapanese with English abstract
Original languageJapanese
Pages (from-to)207-213
Number of pages7
JournalJournal of the Japanese Association of Mineralogists, Petrologists & Economic Geologists
Issue numberSpecial Issue 3
Publication statusPublished - 1982 Jan 1

ASJC Scopus subject areas

  • Environmental Science(all)
  • Earth and Planetary Sciences(all)

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